MULTI-MODE TRANSMISSION

The present disclosure relates to a transmission unit. Wheeled vehicles comprise various means for transmitting power generated by a motor to wheels of the vehicle. Gear and clutch mechanisms are commonly used to achieve this. It is also known to combine variable ratio drives ("variators") and an epicyclic gear set to give an Infinitely Variable Transmission (IVT), which provides a smooth spread of input : output ratio from forward to reverse.

A variator is a mechanical transmission device configured to provide stepless ratio change within a defined range. Such an arrangement is shown in figure 1 . An input drive disc 10 is coupled to a first input shaft 12. An output drive disc 14 is coupled to a second output shaft 16. A pair of rollers 18 comprising a first roller 20 and a second roller 22 is mounted in a carriage 24 between the discs 10,14. The carriage 24 is fixed to ground, that is to say non rotatable, as indicated in the figure by a link 26 to ground 28. The input and output drive discs rotate in the same direction, providing a positive value of speed ratio. Power is transferred between the rollers and discs through a combination of fluid shear, the necessary shear force being generated through a combination of high contact pressure, high resulting local fluid viscosity and relative slip velocity.

An epicyclic gear set coupled to the variator performs a summing function of input and output speeds of the variator. When this sum equals zero, the output speed of the transmission is zero, even though the input is rotating and supplying power. This condition is therefore termed "geared neutral". Thus IVTs provide a means for launching a vehicle from rest. The supplied power is "recirculated" and dissipated as heat in the transmission whilst in the geared neutral position. Transmission efficiency can be compromised by degrees of recirculating power at other vehicle speeds. With such IVTs, either ratio range or transmission efficiency is compromised whilst optimising the other. Multiple modes are used such that sufficient overall ratio spread is provided with good efficiency. Hence a device which provides the same functionality of a conventional IVT but without the associated efficiency losses arising from recirculated power, and without the need for extra gearing would be high desirable.

Summary

According to the present invention there is provided an apparatus as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Accordingly there may be provided a variable transmission unit comprising: a first drive disc and a second drive disc centred on a common axis; a planet carrier assembly rotatably mounted about the common axis and comprising a first rolling element in rotatable engagement with a second rolling element; wherein the planet carrier assembly comprises an actuation system configured to : maintain rotatable

engagement between and the first rolling element and first drive disc over a first engagement region; maintain rotatable engagement between and the second rolling element and second drive disc over a second engagement region; and vary the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis. The actuation system may be further configured to : vary the distance between the first engagement region and the common axis; and vary the distance between the second engagement region and the common axis.

The first drive disc may be fixed to ground; the planet carrier assembly may be coupled to a transmission input; and the second drive disc is coupled to a transmission output. At least one of the first and second drive discs may be provided with a part toroidal contact surface for engagement with one of the rolling elements.

The first drive disc, second drive disc and planet carrier may be configured such that when the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis is 1 , the second shaft has zero angular velocity.

There may also be provided a variable transmission unit comprising : a first drive disc and a second drive disc centred on a common axis; a planetary drive assembly rotatably mounted about the common axis; the planetary drive assembly comprising : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting configured to bring the first roller and second roller into rotatable engagement with the first drive disc and second drive disc respectively. The carriage may be configured to vary the angle of the first roller and second roller relative to the first drive disc and second drive disc respectively to thereby control the relative rotational speed and relative direction of rotation of the second drive disc and carrier. The carrier may be coupled to a first shaft and the second drive disc is coupled to a second shaft. The variable transmission unit may be configured to transfer power in both directions between the first shaft and second shaft.

The variable transmission unit may be configured for a first operational condition in which the carrier is rotated about the common axis, which causes rotation of the first roller due to engagement between the first roller and the first disc, and consequently causes rotation of the second roller, thereby driving the second drive disc about the common axis. The variable transmission unit may be configured for a second operational condition in which the second drive disc is rotated about the common axis which causes rotation of the second roller due to contact between the second roller and the second disc, and consequently causes rotation of the first roller, thereby driving the carrier about the common axis.

There may also be provided a variable transmission unit comprising : a non-rotatable disc spaced apart from a rotatable drive output disc, and a rotatable input planetary drive transmission assembly; the rotatable drive output disc and input planetary drive transmission assembly being rotatable about a common axis; opposing surfaces of the discs defining a toroidal cavity centred about the common axis; the input planetary drive assembly comprising : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting between the discs; the first roller being mounted in rotatable engagement with the non-rotatable disc; and the second roller being mounted in rotatable engagement with the drive output disc; wherein, in use, the output disc is driven about the common axis by rotation of the carrier, which causes rotation of the first roller due to contact between the first roller and the non-rotatable disc, and consequently causes rotation of the second roller, thereby causing rotation of the output disc. There may also be provided a multi-mode variable transmission unit comprising: a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier assembly; each of the branches being rotatably mounted about a common axis; the planet carrier assembly comprising: a first rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the first drive disc; a second rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the second drive disc; the variator comprising an actuation system configured to vary the relative speed of the first and second drive discs. There may be provided means to selectively engage at least two branches with two of either the first shaft, the second shaft and/or ground; wherein in a first mode of operation one branch is fixed to ground by constraining means, a second branch is connected to the first shaft and a third branch is connected to the second shaft; and in a second mode of operation, a different combination of branch connections is provided to ground, the first shaft and the second shaft, thereby providing a different range of transmission ratios between the first shaft and second shaft to the first mode. There may also be provided a multi-mode variable transmission unit comprising: a first shaft and a second shaft; a variator configured as a planetary device having a first branch comprising a first drive disc selectively engageable with the first shaft; a second branch comprising a second drive disc selectively engageable with the second shaft; a third branch comprising a planet carrier assembly selectively engageable to ground; each of the branches being rotatably mounted about a common axis; the planet carrier assembly comprising: a first rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the first drive disc; a second rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the second drive disc; the variator comprising an actuation system configured to vary the relative speed of the first and second drive discs.

In a first mode of operation the first branch may be disengaged from the first shaft and engaged to ground; the third branch may be engaged with the first shaft and

disengaged with ground; and the second branch may be free to rotate in reaction against the rotation of the third branch relative to the first branch.

In a second mode of operation : the first branch may be engaged with the first shaft and disengaged with ground; the third branch may be disengaged from the first shaft and engaged to ground; and the second branch may be free to rotate in reaction against the rotation of the first branch relative to the third branch.

The planet carrier assembly may comprise an actuation system configured to : maintain rotatable engagement between and the first rolling element and first drive disc over a first engagement region; maintain rotatable engagement between and the second rolling element and second drive disc over a second engagement region; vary the distance between the first engagement region and the common axis; vary the distance between the second engagement region and the common axis; and thereby vary the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis. The first drive disc, second drive disc and planet carrier may be configured such that : when the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis is 1 , the second shaft has zero angular velocity.

At least one of the first and second drive discs may be provided with a part toroidal contact surface for engagement with one of the rolling elements.

There may also be provided a multi-mode variable transmission unit comprising : a first drive disc selectively engageable with a first shaft; a planetary drive assembly selectively engageable with the first shaft; a second drive disc freely rotatable relative to the first shaft; the first drive disc, second drive disc and planetary drive assembly centred on a common axis, the planetary drive assembly being in rotatable engagement with the first drive disc and second drive disc; the transmission unit further comprising a clutch mechanism and a brake mechanism configured such that : in a first mode of operation the first drive disc is prevented from rotating by the brake mechanism and the planetary drive assembly is engaged with the first shaft via the clutch mechanism, such that rotation of the first shaft causes rotation of the planetary drive assembly which, in turn, drives the second disc about the common axis; and in a second mode of operation the planetary drive assembly is prevented from rotating by the brake mechanism and the first drive disc is engaged with the first shaft via the clutch mechanism, such that rotation of the first shaft causes rotation of the first drive disc which, via the planetary drive assembly, drives the second disc about the common axis. The first drive disc may be spaced apart from the second drive disc; whereby opposing surfaces of the discs define a toroidal cavity centred about the common axis.

The planetary drive assembly may comprise : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting between the drive discs; the first roller being mounted in rotatable engagement with the first drive disc; and the second roller being mounted in rotatable engagement with the second drive disc; whereby, in both modes of operation, rotation of the first roller due to contact between the first roller and the first drive disc causes rotation of the second roller, thereby causing rotation of the second disc.

The planetary drive assembly may comprise : a first substantially spherical roller; the first roller being rotatably mounted to a carriage about a first rotational axis ; the first roller being mounted in rotatable engagement with the first drive disc and the second drive disc.

The two branches of the planetary variator may coupled to an epicyclic gear unit, or an alternative differential mechanism.

Brakes may be employed instead of clutches. There may be provided only one brake or clutch per mode of operation. Brakes or clutches may be provided on each branch coupling of the variator and epicyclic assembly. The assembly may be configured such that, in one mode of operation, closing one of the brakes or clutches will simultaneously ground one branch of the epicyclic and one branch of the variator. The assembly may also be configured such that in another mode of operation, the first brake or clutch is opened and the second brake or clutch is closed, to thus provide a different ratio spread.

The assembly may also be configured such one brake or clutch may be engaged in a first mode (open in the second mode) and the other brake or clutch may be engaged in a second mode (open in the first mode).

The carrier of the variator may be connected to the carrier of the epicyclic, the first disc of the variator may be coupled to the sun of the epicyclic, a first shaft (e.g. transmission input) may be connected to the annulus of the epicyclic and a second shaft (e.g.

transmission output) may be connected to the second disc of the variator. The epicyclic gear set may be configured to provide the required ratios, and the base ratio can be chosen to reverse carrier direction in the first mode.

The devices of the present disclosure may be configured such that first mode described in the preceding five paragraphs provides Infinitely Variable Transmission (IVT), that is geared neutral with forwards and/or reverse.

The devices of the present disclosure may be configured such that in the first mode of operation described in the preceding six paragraphs the carrier is caused to rotate in an opposite direction to that of the first disc in the second mode of operation.

There may be provided a planetary variator with more than three branches. Such an arrangement can provide additional modes of operation. One branch may be braked to ground. There may be provided only one clutch/brake for each mode of operation. There may also be provided a multi-mode transmission comprising : a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier assembly; each of the branches being rotatably mounted about a common axis; a two-degrees-of-freedom differential device comprising three coaxial branches; configured such that a first branch of the variator is connected to a first branch of a differential, a second branch of the variator is connected to a second branch of the differential, a third branch of the differential is connected to the first shaft, a third branch of the variator is connected to the second shaft; a first clutch and a second clutch, configured such that when any one clutch is closed, the system only has one degree of freedom, defining a transmission ratio between the first and second shaft; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio. In at least one mode, the overall transmission ratio between the first and second shafts may depend on the variator base ratio. One side of at least one of the first or second clutches may be fixed to ground such that it is braked. At least one of the first or second clutches, when closed, may connects two branches of the variator via a fixed gear ratio.

The planet carrier assembly may comprise : a first rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the first drive disc; a second rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the second drive disc; the variator comprising an actuation system configured to vary the relative speed of the first and second drive discs.

There may also be provided a multi-mode transmission comprising a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier drive assembly; each of the branches being rotatably mounted about a common axis; the first and second drive discs being in rotatable engagement with the planet carrier drive assembly;a first differential device comprising three coaxial branches and possessing two degrees-of- freedom, such that the speeds of two branches must be known to determine the speed of a remaining branch; configured such that a first branch of the variator is coupled to a first branch of the first differential, a second branch of the variator is coupled to a second branch of the first differential, a third branch of the first differential is coupled to the first shaft, a third branch of the variator is coupled to the second shaft; a first clutch and a second clutch, configured such that when one clutch is closed, the system only has one degree-of-freedom, defining a transmission ratio between the first and second shafts; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio.

There may also be provided a multi-mode transmission comprising a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier drive assembly; each of the branches being rotatably mounted about a common axis; the first and second drive discs being in rotatable engagement with the planet carrier drive assembly; a first differential device and a second differential device, each comprising three coaxial branches and possessing two degrees-of-freedom, such that the speeds of two branches must be known to determine the speed of a remaining branch; configured such that a first branch and a second branch of the first differential are coupled to two branches of the variator, and two branches of the second differential are coupled to two branches of the variator, a third branch of the first differential is coupled to the first shaft, a third branch of the second differential is coupled to the second shaft; a first clutch and a second clutch, configured such that when one clutch is closed, the system only has one degree-of-freedom, defining a transmission ratio between the first and second shaft; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio.

In at least one mode, the overall transmission ratio between the first and second shafts may depends on the variator base ratio, that is, the ratio of the relative speed of the second disc to the planet carrier drive assembly and the relative speed of the first drive disc to the planet carrier drive assembly.

One side of at least one of the first or second clutches may be fixed to ground, such that the clutch is in fact a brake.

The brake, when closed, may simultaneously ground one branch of the variator and one branch of the first differential. The brake may be coupled to a fourth branch of the variator. At least one of the first or second clutches, when closed, may be connected to two branches of the variator via a fixed gear ratio.

At least one of the first or second clutches, when closed, may connect two branches of the differential via a fixed gear ratio.

At least one of the first or second clutches, when closed, may connect two branches of one of the first or second differentials via a fixed gear ratio. A clutch may be provided between one branch of the variator and at least one branch of either the first or second differentials, such that when the clutch is opened, and at least one other clutch is closed, a direct drive bypassing the variator is provided.

In all modes, the relative speed between the first and second drive discs may have the same sign (positive or negative).

At least one of the first or second drive discs may be toroidal in geometry.

The planet carrier drive assembly of the variator may comprise a first roller in rotatable engagement with a second roller, the first roller being in rotatable engagement with the first drive disc, and the second roller being in rotatable engagement with the second drive disc.

The planet carrier drive assembly may be further configured to minimise contact losses arising from spin (differential velocity).

Since the device of the present disclosure inherently provides a planetary transmission arrangement with positive planetary ratio, and able to provide a value of +1 , it may operate as an IVT without the need of an epicyclic gear set. This avoids the efficiency penalty associated with recirculating power and also beneficially reduces system complexity, and hence manufacture and cost. The IVTs of the present disclosure may provide a wide ratio range simultaneously with high efficiency, in fewer modes than a conventional IVT.

The apparatus of the present disclosure may further be defined as set out in the following paragraphs.

There may be provided a variable transmission unit comprising: a first drive disc and a second drive disc centred on a common axis; a planet carrier assembly rotatably mounted about the common axis and comprising a first rolling element in rotatable engagement with a second rolling element; wherein the planet carrier assembly comprises an actuation system configured to : maintain rotatable engagement between the first rolling element and first drive disc over a first engagement region; maintain rotatable engagement between and the second rolling element and second drive disc over a second engagement region; and vary the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis.

The actuation system may be further configured to : vary the distance between the first engagement region and the common axis; andvary the distance between the second engagement region and the common axis.

Optionally the first drive disc is fixed to ground; the planet carrier assembly is coupled to a transmission input; and the second drive disc is coupled to a transmission output. At least one of the first and second drive discs may be provided with a part toroidal contact surface for engagement with one of the rolling elements.

The first drive disc, second drive disc and planet carrier may be configured such that when the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis is 1 , the second shaft has zero angular velocity. The variable transmission unit as may be configured such that in all modes of operation the angular speed of the drive discs is greater than the angular speed of the planet carrier. The geometry of the rollers may be chosen such that spin losses are minimised at a condition where the variator ratio is 1 :1 .

There may also be provided a variable transmission unit comprising : a first drive disc and a second drive disc centred on a common axis; a planetary drive assembly rotatably mounted about the common axis; the planetary drive assembly comprising : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting configured to bring the first roller and second roller into rotatable engagement with the first drive disc and second drive disc respectively.

The carriage may be configured to vary the angle of the first roller and second roller relative to the first drive disc and second drive disc respectively to thereby control the relative rotational speed and relative direction of rotation of the second drive disc and carrier.

The carrier may be coupled to a first shaft and the second drive disc is coupled to a second shaft. The variable transmission unit may be configured to transfer power in both directions between the first shaft and second shaft.

The may also be provided a variable transmission unit comprising : a non-rotatable disc spaced apart from a rotatable drive output disc, and a rotatable input planetary drive transmission assembly; the rotatable drive output disc and input planetary drive transmission assembly being rotatable about a common axis; opposing surfaces of the discs defining a toroidal cavity centred about the common axis; the input planetary drive assembly comprising : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting between the discs; the first roller being mounted in rotatable engagement with the non-rotatable disc; and the second roller being mounted in rotatable engagement with the drive output disc; wherein, in use, the output disc is driven about the common axis by rotation of the carrier, which causes rotation of the first roller due to contact between the first roller and the non-rotatable disc, and consequently causes rotation of the second roller, thereby causing rotation of the output disc.

There may also be provided a multi-mode variable transmission unit comprising: a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier assembly; each of the branches being rotatably mounted about a common axis; the planet carrier assembly comprising: a first rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the first drive disc; a second rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the second drive disc; the variator comprising an actuation system configured to vary the relative speed of the first and second drive discs.

The multi-mode variable transmission unit may further comprise : means to selectively engage at least two branches with two of either the first shaft, the second shaft and/or ground; wherein in a first mode of operation one branch is fixed to ground by

constraining means, a second branch is connected to the first shaft and a third branch is connected to the second shaft; and in a second mode of operation, a different combination of branch connections is provided to ground, the first shaft and the second shaft, thereby providing a different range of transmission ratios between the first shaft and second shaft to the first mode.

Optionally the first branch is disengaged from the first shaft and engaged to ground; the third branch is engaged with the first shaft and disengaged with ground; and the second branch is free to rotate in reaction against the rotation of the third branch relative to the first branch.

Optionally, in a second mode of operation : the first branch is engaged with the first shaft and disengaged with ground; the third branch is disengaged from the first shaft and engaged to ground; and the second branch is free to rotate in reaction against the rotation of the first branch relative to the third branch.

Optionally the planet carrier assembly comprises an actuation system configured to : maintain rotatable engagement between and the first rolling element and first drive disc over a first engagement region; maintain rotatable engagement between and the second rolling element and second drive disc over a second engagement region; vary the distance between the first engagement region and the common axis; vary the distance between the second engagement region and the common axis; and thereby vary the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis.

The first drive disc, second drive disc and planet carrier may be configured such that : when the ratio of the distance between the first engagement region and the common axis and the distance between the second engagement region and the common axis is 1 , the second shaft has zero angular velocity.

At least one of the first and second drive discs amy provided with a part toroidal contact surface for engagement with one of the rolling elements.

There may also be provided a multi-mode variable transmission unit comprising : a first drive disc selectively engageable with a first shaft; a planetary drive assembly selectively engageable with the first shaft; a second drive disc freely rotatable relative to the first shaft; the first drive disc, second drive disc and planetary drive assembly centred on a common axis; the planetary drive assembly being in rotatable engagement with the first drive disc and second drive disc; the transmission unit further comprising a clutch mechanism and a brake mechanism configured such that : in a first mode of operation the first drive disc is prevented from rotating by the brake mechanism and the planetary drive assembly is engaged with the first shaft via the clutch mechanism, such that rotation of the first shaft causes rotation of the planetary drive assembly which, in turn, drives the second disc about the common axis; and in a second mode of operation the planetary drive assembly is prevented from rotating by the brake mechanism and the first drive disc is engaged with the first shaft via the clutch mechanism, such that rotation of the first shaft causes rotation of the first drive disc which, via the planetary drive assembly, drives the second disc about the common axis. The first drive disc may be spaced apart from the second drive disc; whereby opposing surfaces of the discs define a toroidal cavity centred about the common axis.

The planetary drive assembly may comprise : a first roller in rotatable engagement with a second roller; the first roller and second roller being rotatably mounted to a carriage about a first rotational axis and second rotational axis respectively; the carriage being supported on a pivotable mounting between the drive discs; the first roller being mounted in rotatable engagement with the first drive disc; and the second roller being mounted in rotatable engagement with the second drive disc; whereby, in both modes of operation, rotation of the first roller due to contact between the first roller and the first drive disc causes rotation of the second roller, thereby causing rotation of the second disc.

The planetary drive assembly may comprise : a first substantially spherical roller; the first roller being rotatably mounted to a carriage about a first rotational axis ; the first roller being mounted in rotatable engagement with the first drive disc and the second drive disc.

There may also be provided a multi-mode transmission comprising : a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier assembly; each of the branches being rotatably mounted about a common axis; a two-degrees-of-freedom differential device comprising three coaxial branches; configured such that a first branch of the variator is connected to a first branch of a differential, a second branch of the variator is connected to a second branch of the differential, a third branch of the differential is connected to the first shaft, a third branch of the variator is connected to the second shaft; a first clutch and a second clutch, configured such that when any one clutch is closed, the system only has one degree of freedom, defining a transmission ratio between the first and second shaft; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio.

In at least one mode, the overall transmission ratio between the first and second shafts depends on the variator base ratio.

One side of at least one of the first or second clutches may be fixed to ground such that it is braked.

At least one of the first or second clutches, when closed, may connect two branches of the variator via a fixed gear ratio.

The planet carrier assembly may comprise : a first rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the first drive disc; a second rolling element rotatably mounted within the planet carrier assembly and in rotatable engagement with the second drive disc; the variator comprising an actuation system configured to vary the relative speed of the first and second drive discs.

There may also be provided a multi-mode transmission comprising a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier drive assembly; each of the branches being rotatably mounted about a common axis; the first and second drive discs being in rotatable engagement with the planet carrier drive assembly; a first differential device comprising three coaxial branches and possessing two degrees-of- freedom, such that the speeds of two branches must be known to determine the speed of a remaining branch; configured such that a first branch of the variator is coupled to a first branch of the first differential, a second branch of the variator is coupled to a second branch of the first differential, a third branch of the first differential is coupled to the first shaft, a third branch of the variator is coupled to the second shaft; a first clutch and a second clutch, configured such that when one clutch is closed, the system only has one degree-of-freedom, defining a transmission ratio between the first and second shafts; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio. There may also be provided a multi-mode transmission comprising a first shaft and a second shaft; a variator configured as a planetary device having three branches, namely a first drive disc, second drive disc and a planet carrier drive assembly; each of the branches being rotatably mounted about a common axis; the first and second drive discs being in rotatable engagement with the planet carrier drive assembly; a first differential device and a second differential device, each comprising three coaxial branches and possessing two degrees-of-freedom, such that the speeds of two branches must be known to determine the speed of a remaining branch; configured such that a first branch and a second branch of the first differential are coupled to two branches of the variator, and two branches of the second differential are coupled to two branches of the variator, a third branch of the first differential is coupled to the first shaft, a third branch of the second differential is coupled to the second shaft; a first clutch and a second clutch, configured such that when one clutch is closed, the system only has one degree-of-freedom, defining a transmission ratio between the first and second shaft; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, defining a first transmission ratio between the first and second shafts, and in a second mode of operation, the second clutch is closed and the first clutch is open, defining a second transmission ratio between the first and second shafts; the second transmission ratio being different from the first transmission ratio.

In at least one mode, the overall transmission ratio between the first and second shafts may depend on the variator base ratio, that is, the ratio of the relative speed of the second disc to the planet carrier drive assembly and the relative speed of the first drive disc to the planet carrier drive assembly.

One side of at least one of the first or second clutches may be fixed to ground, such that the clutch is in fact a brake.

The brake, when closed, may simultaneously ground one branch of the variator and one branch of the first differential. The brake may coupled to a fourth branch of the variator.

At least one of the first or second clutches, when closed, may connect two branches of the variator via a fixed gear ratio. At least one of the first or second clutches, when closed, may connects two branches of the differential via a fixed gear ratio.

At least one of the first or second clutches, when closed, may connect two branches of one of the first or second differentials via a fixed gear ratio.

A clutch may be provided between one branch of the variator and at least one branch of either the first or second differentials, such that when the clutch is opened, and at least one other clutch is closed, a direct drive bypassing the variator is provided. The multi-mode may be configured such that in all modes, the relative speed between the first and second drive discs has the same sign (positive or negative). At least one of the first or second drive discs may be toroidal in geometry.

The planet carrier drive assembly of the variator may comprise a first roller in rotatable engagement with a second roller, the first roller being in rotatable engagement with the first drive disc, and the second roller being in rotatable engagement with the second drive disc.

The planet carrier drive assembly may be further configured to minimise contact losses arising from spin (differential velocity).

In all modes of operation, the sign of the relative angular velocity of either of the drive discs with respect to the planet carrier assembly may remain the same.

Accordingly there may be provided a variator comprising : a first race (32) and a second race (34) rotatably mounted about a variator axis (38), such that the races (32,34) define a cavity (46) between them; a carriage (52) mounted within the cavity (46), and configured to rotate about a precession axis (53) that is perpendicular to and offset from the variator axis (38) such that precession about the precession axis (53) corresponds to a change in variator ratio; each carriage (52) comprising : a first rolling element (48) and a second rolling element (50), each being urged into driving engagement with the other rolling element and one, but not the same, race (32,34) at contact regions (88,89), the contact regions (88,89) defining a contact axis; wherein the position and orientation of at least one of the rolling elements is controlled by contact with its respective race and the other rolling element; a steering means input for the rolling element; and an additional positional constraint.

It is preferable in some variators with rolling elements to constrain the elements with three points, as this is sufficient to define the element's position and orientation. The said three contacts may comprise a contact with a race, a second contact with a rotary element (for example a race or another roller) and a spherical joint that affords the rolling element sufficient articulation, for example for ratio change and axial movement. In variators with two rollers per carriage it may be advantageous to better support the rolling elements within the carriage such that the carriage structure does not suffer a potential buckling mode.

The carriage (52) may be configured to rotate about a precession axis (53) passing through the central plane of the cavity (46), wherein the cavity central plane is

perpendicular to the variator axis (38), and equidistant between the surface of races (32,34).

The cavity (46) may be toroidal.

The cavity (46) may be full toroidal.

The variator may be configured such that the additional positional constraint is operable to define at least one of the rolling elements (48,50) position in a radial direction with respect to the variator axis (38), and the rolling element position in a circumferential direction about the variator axis (38).

The additional positional constraint may be operable to permit movement of one or both rolling elements (48,50) for the transmission of clamp load between the races (32,34) and rolling elements (48,50), and between the rolling elements (48,50).

The axes of rotation of the rolling elements (48,50) may be inclined to one another.

The axis of at least one rolling element and the axis of the race with which it is in contact may intersect a plane tangential to the said contact (between said rolling element and said race) at substantially the same point, at at least one variator ratio.

A plurality of carriages (52) may be provided in the cavity (46).

The steering input to each carriage may be configured such that the precession angl of all carriages (52) are adjusted simultaneously to substantially the same angle. The lever may be configured to tilt both rolling elements in the carriage or carriages such that the first rolling element is tilted in a sense counter to that of the second element. The steering inputs of each carriage (52) may be engaged with each other for simultaneous and timed motion.

Each carriage may be engaged with the other carriages such that they precess substantially in concert.

The additional positional constraint may be provided by a carriage support (51 ) forming part of the carriage (52)

The carriage support (51 ) may comprises an internal cylindrical surface whose axis is substantially coaxial with the contact axis.

The said carriage support (51 ) may permit precession of the carriage about the precession axis (53). The carriage may further comprise : a tilt member (55) rotatably (that is to say, tiltably) mounted within the carriage support (51 ), and each rolling element (48,50) is rotatably mounted within the tilt member (55).

The tilt member may be adapted to receive a steering input from a lever (83).

The steering input for the rolling element or elements may be provided as a lever (83) extending from the carriage support (51 ).

The distal end of the lever may be offset from one or both of the contact axis and the carriage precession axis (53).

Each carriage may be meshed with another carriage. The variator may comprise an actuation member (80) in engagement with the lever (83). The actuation member (80) may be a ring shaped member (82) is concentric with the variator axis (38) and may be coupled to the tilt member (55).

The ring shaped member may be radially outward of the cavity (46) and/or rolling elements.

The ring shaped member may be radially inward of the cavity (46) and/or rolling elements.

The actuation member (80) may be configured to translate in the direction parallel to the variator axis (38) and is thus operable to urge the rolling elements (48,50) to simultaneously tilt about their contact axes, thereby resulting in the precession of the rolling element (48,50) respective carriage.

At least one carriage (52) may be mounted on a carrier (36); and the carrier (36) is rotatable about the variator axis (38).

The carrier (36) may be located radially (with respect to the variator axis (38) within the cavity (46) at least in part by contact between rolling elements and the races (32,34). The carrier (36) may be located within the cavity (46) by at least one bearing mounted that is concentric with the variator axis (38).

The carrier may be adapted for movement in the direction of the variator axis (38). There may also be provided a variator comprising : a first race (32) and a second race (34) rotatably mounted about a variator axis (38), such that the races (32,34) define a cavity (46) between them; a carriage (52) mounted within the cavity (46), and configured to rotate about a precession axis (53) that is perpendicular to and offset from the variator axis (38) such that precession about the precession axis (53) corresponds to a change in variator ratio; each carriage (52) comprising : a first rolling element (48) and a second rolling element (50), each being urged into driving engagement with the other rolling element and one, but not the same, race (32,34); at least one carriage (52) is mounted on a carrier (36); and the carrier (36) is rotatable about the variator axis (38).

The carrier (36) may be located radially (with respect to the variator axis 38) within the cavity (46) at least in part by contact between rolling elements and the races (32,34).

The carrier (36) may be located within the cavity (46) by at least one bearing mounted that is concentric with the variator axis (38). The variator may further comprise an actuator operable to induce a force on the carriage (52) to cause the carriage or carriages to rotate about the precession axis and thereby adjust the position of the rolling element relative to its respective race.

The carrier may be adapted for movement in the direction of the variator axis (38).

The axis of at least one rolling element and the axis of the race with which it is in contact intersect may be a plane tangential to the said contact (between said rolling element and said race) at substantially the same point, at at least one variator ratio. The carriage may be adapted such that clamp load may be transmitted between rolling elements (48,50), and between each rolling element and each race.

There may also be provided a multi-mode transmission comprising : a first shaft and a second shaft; a variator configured as a planetary device comprising three branches, each branch being one of a first drive disc, a second drive disc and a planet carrier drive assembly; the planet carrier drive assembly being rotatably mounted about a variator main axis; a first differential device comprising three branches configured such that a first branch of the variator is coupled to a first branch of the first differential, a second branch of the variator is coupled to a second branch of the first differential, a third branch of the first differential is coupled to at least one of the first shaft and a first clutch, a third branch of the variator is coupled to at least one of the second shaft and a second clutch; wherein in a first mode of operation, the first clutch is closed and the second clutch is open, and in a second mode of operation, the second clutch is closed and the first clutch is open.

The multi-mode transmission may also comprise a second differential device having a first branch and second branch coupled to respective branches of the variator, and a third branch coupled to the second shaft, such that in at least one mode of operation, the variator may be coupled to the second shaft via the second differential device.

In at least one mode of operation, the overall transmission ratio between the first and second shafts may be dependent upon on the variator base ratio, the variator base ratio being the operable angular speed ratio of the second drive disc and first drive disc in the frame of reference of the planet carrier drive assembly.

In at least one mode of operation in which at least one clutch is closed, the overall transmission ratio between the first and second shafts may be independent of the variator base ratio, the variator base ratio being the operable angular speed ratio of the second drive disc and first drive disc in the frame of reference of the planet carrier drive assembly. At least one of the clutches may be a brake. The brake, when closed, may ground a branch of the differential. The the brake, when closed, may ground a branch of the variator. The brake, when closed, may ground a branch of the variator and a branch of the differential. At least one of the clutches, when closed may connects two branches of the variator via a gear ratio. At least one of the clutches, when closed, may connects two branches of a differential via a gear ratio. The variator may comprise a fourth branch coupled to a third clutch, the third clutch being a brake. The differential may comprise a fourth branch coupled to a third clutch, the third clutch being a brake.

A clutch may be provided between one branch of the variator and at least one branch of either the first or second differentials, such that when the clutch is opened and at least one other clutch is closed, a direct drive bypassing the variator is provided. Substantially zero differential speed across a clutch may be obtained immediately prior to engagement.

There may be provided a multi-mode transmission according wherein in all modes of operation, the sign of the angular velocity of either of the drive discs relative to the planet carrier drive assembly does not change.

The variator may comprise an actuation system such that only a proportion of the power required to change variator base ratio is provided by the actuation system. The first and second drive discs of the variator may rotate in the same direction when viewed from the frame of reference of the planet carrier drive assembly.

The variator may be is a tilting ball variator. The variator may be a toroidal device. The planet carrier drive assembly may comprise a first rolling element drivingly engaged with the first drive disc via a first traction surface, a second rolling element drivingly engaged with the second drive disc via a second traction surface, the first and second rolling elements being in driving engagement via a third traction surface, such that torque can be transferred between the first and second drive discs via the first, third and second traction surfaces in series. There may also be provided a variable transmission unit comprising a first drive disc, second drive disc and planet carrier assembly centred on a main variator axis; the planet carrier assembly rotatably mounted about said main variator axis; the planet carrier assembly further comprising a first rolling element drivingly engaged with the first drive disc via a first traction contact, a second rolling element drivingly engaged with the second drive disc via a second traction contact, the first and second rolling elements being in driving engagement with eachother via a third traction contact, such that torque can be transferred between the first and second drive discs via the first, third and second traction contacts in series.

The first and second rolling elements may rotate about respective rotational axes, the respective axes inclined in such a manner to reduce spin losses in at least one of the first, second and third traction contacts. The variator may comprise two cavities.

Brief Description of the Drawings

Examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a variator, as previously described;

Figure 2 shows a diagrammatic representation of a single mode infinitely variable transmission drive according to the present disclosure;

Figure 3 shows an actuation system of a variator of the present disclosure;

Figure 4 shows a view of a variator and actuation system of the present disclosure; Figure 5 shows an exploded view of a carriage of a variator of the present disclosure;

Figure 6 shows a view of a carrier of a variator of the present disclosure; and

Figures 7 to 46 show various example variator and epicyclic arrangements of the present disclosure.

Detailed Description

Figures 2 to 6 shows a single mode Infinitely Variable Transmission Unit 30 according to the present disclosure. The variable transmission unit 30 comprises a drive disc 32 spaced apart from a rotatable drive output disc 34, and a rotatable input planetary drive transmission assembly (also referred to as a planet carrier assembly) shown generally as 36. In figure 2 the drive disc 32 is non-rotatable. The rotatable drive output disc 34 and input planetary drive transmission assembly 36 are rotatable about a common axis 38. Opposing surfaces of the discs 32,34 define a toroidal cavity, shown generally as 46, centred about the common axis 38. The input planetary drive assembly 36 comprises a first roller 48 in rotatable engagement with a second roller 50. The first roller 48 and second roller 50 are rotatably mounted to a carriage 52 about a first rotational axis 54 and second rotational axis 56 respectively. The carriage 52 is supported on a pivotable mounting 58 between the discs 48, 50. The first roller 48 is mounted in rotatable engagement with the non-rotatable disc 32, and the second roller 50 is mounted in rotatable engagement with the drive output disc 34. The rotational axes of the rolling elements may be configured such that they are aligned such that they intersect the main variator axis at a position coincident with the intersection of the contact tangent plane and the main variator axis. This arrangement greatly reduces spin losses in variators, providing a notable increase in transmission efficiency.

The carriage 52 is configured to vary the angle of the first roller 48 and second roller 50 relative to the first drive disc 32 and second drive disc 34 respectively to thereby control the relative rotational speed and relative direction of rotation of the second drive disc 34 and carrier 36. The carriage 52 is coupled to a first shaft 60 and the second drive disc 34 is coupled to a second shaft 62. The first and second shafts are centred on the common axis 38. In one example the first shaft 60 is an input shaft, and the second shaft 62 is an output shaft. That is to say that the first shaft is directly or indirectly engaged with a motor or drive transmission means, and the second shaft 62 is a power take-off from the transmission drive leading to, for example, the wheels of a vehicle.

The present disclosure also relates to control mechanism (or system) for a non- planetary variator and a planetary variator, both of which are described below.

By way of an example, and using common reference numerals to that previously described with reference to Figures 3 to 6, a non-planetary toroidal variator comprises a first race 32 and a second race 34 mounted for rotation about a variator axis 38. The races 32,34 define a cavity 46 between them. A carriage 52 is mounted within the cavity 46 for power transmission, and each carriage 52 is rotatable about a precession axis 53 which may, in some examples, pass through the cavity 46 central plane and be perpendicular to and offset from the variator axis 38 such that precession about said axis corresponds with a change in variator ratio. Each carriage 52 comprises a first rolling element 48 and a second rolling element 50 which may be located by a carriage support 51 , each rolling element 48,50 mounted for rotation about an axis and each urged into driving engagement with the adjacent rolling element and the races 32,34 at contact areas 84,86, which comprises specific contact regions 88,89, or points, which the rolling elements and races come into contact at each instant of operation. The contact regions 88,89 define a contact axis which preferably passes also through the contact region between the two rolling elements (as shown in figure 3) whereby at least one rolling element 48,50 is tiltable about said axis in order to effect precession of the carriage 52. The position and orientation of the rolling element 48,50 in space is defined by a first contact with a race, a second contact with an adjacent rolling element, a steering input point and a further positional constraint. This additional positional constraint improves stability of the carriage 52 structure as compared with a three point constraint system of the related art (as shown in Figure 1 ) particularly when axial load is applied to the rolling element pairs. The provision of a fourth constraint ensures that the position of the rolling elements 48,50 is defined under all conditions.

The rolling elements 48,50 are preferably rollers. Twin rolling elements provide a positive speed ratio in the variator, with associated benefits of reduced thrust bearing losses when used in conjunction with a mainshaft positioned on the variator axis 38 in a single cavity 46 configuration. The rolling element 48,50 axes may optionally be inclined to one another such that the spin effect is generally reduced or eliminated as previously described. In one such embodiment, the axis of a rolling element and the axis of the race with which it is in contact intersect the contact tangent plane at substantially the same point, thus providing minimal or nominally zero spin at one or more operating ratio of the variator. One or both rolling elements 48,50 in the carriage 52 may be configured in this way. The rolling element positional constraint may act to define one or both of the roller position in a radial direction with respect to the variator axis 38, and the roller position in a circumferential direction about the variator axis 38.

The additional positional constraint may be provided by the carriage support 51 which permits tilt of at least one rolling element 48,50 about its contact axis. The carriage support 51 may optionally allow for motion of the rolling element or elements generally in the direction of the variator axis 38, said movement facilitating the transmission of clamp load between the rolling elements 48,50 and from the first race 32 to the second race 34. Within the support 51 , which may be cylindrical in character (that is, with cylindrical axis parallel with the contact axis), at least one rolling element rotates on an axle within a tilt member 55, said member 55 being tiltable within the carriage support 51 . Within the carriage support 51 , the tilt member 55 or members may further be afforded a degree of freedom in the general direction of the variator axis 38, and more specifically in the direction of the carriage support (51 ) cylindrical axis. The carriage support 51 circumferential internal surface and tilt member 55 external circumferential surface are preferably coaxial. The carriage support 51 , if cylindrical, may encircle one or both rolling elements. It may be advantageous to mount the tilt member 55 or members on low friction bearings which may be bushes, plain journal bearings or rolling element bearings such that, as the carriage support 51 bears the loads from the rolling elements 48,50, effort to tilt the rolling elements and hence actuation power is reduced thus reducing actuator size, cost and weight.

The variator cavity 46 comprises at least one carriage 52, but preferably comprises two, three or more carriages 52.

The variator may comprise one cavity 46 only, but may alternatively comprise two cavities 46', 46", as shown in Figure 7, defined by outer discs 32, 34 and an inner disc 35, where, preferably, the outer discs 32,34 may be coupled for synchronous rotation, for example by a mainshaft, so that variator clamp load is reacted by the end races 32,34 that run at the same rotational speed. In contrast with a single cavity 46 variator, there is no need for a thrust bearing to accommodate a difference in race speeds whilst reacting clamp load, and therefore power losses are advantageously reduced.

The rolling element steering input point may be offset from one or both of the contact axis and the carriage 52 precession axis 53. Steering input or inputs may effect tilt of one or both tilt members 55 in the carriage 52. Where both rolling elements are tilted, the first element must be tilted in a sense counter to that of the second element in order that the precession angle of the carriage 52 is steered effectively. It is preferable that all carriages 52 steer to the same nominal precession angle simultaneously. This may be achieved in a number of ways. In each of the following embodiments, carriage 52 precession, and therefore ratio change, may be effected by an actuation member that move rotationally about the variator axis 38, or a translationally whereby the translational input is preferably in the direction of the variator axis 38. Where multiple or all rolling elements 48,50 or carriages 52 are simultaneously actuated by the actuation member, the said member 82 may encircle the cavity 46. This member 82 may be a ring which effects inputs on the rolling elements or carriages by virtue of its translation or rotation, preferably by translation in the direction of the variator axis 38. Preferably said ring 82 may be radially inward of the rolling elements 48,50 in which case it may preferably moveable in a direction parallel to the variator axis 38 beneath a race 32,34 and may protrude in an axial direction such that it may be access by an actuator. This may provide advantages of reduced package size and reduced actuator friction. Preferably the ring may be coaxial with the variator axis 38. Where a single carriage 52, rolling element or pair of rolling elements 48,50 are actuated then a translational linear actuation member may apply the input that effects the carriage 52 precession.

Furthermore, the ratio change is effected by an actuator, preferably the actuator acts on an actution member that is preferably a ring and the actuator is either an electric motor, stepper motor or a hydraulic piston.

In a preferred embodiment the first 48 and optionally second rolling element 50 steering inputs 83 on all carriages 52 are timed for simultaneous movement such that all actuated rolling elements steer, and as a consequence all carriages 52 adjust their precession angles, in concert. Such an input may comprise an actuator member such as the ring shaped actuator 80 that may be directly coupled to each carriage lever, or steering input 83 such that all actuated rolling elements steer, and as a consequence all carriages precess, in concert. The ring 82 may comprise an inner profiled surface that is coupled to one or more tilt members 55, preferably via the steering input 83. The lever 83 is located in a groove in the ring 82 such that it may freely pivot relative to the ring. In this example, the actuation member actuates all steering inputs individually, but simultaneously, as shown in Figures 3 to 5.

In an alternative embodiment, a rolling element or elements in one carriage 52 within the cavity 46 may receive a steering input, with the precession of other carriages 52 being timed directly such that all carriages 52 adjust their precession angles in concert. Timing may preferably be achieved by gearing means (as shown in figure 6, which shows the non-limiting example whereby adjacent carriages are meshed with one another) but may be achieved by other means such as toothed belts. A linear translational actuation member may be coupled to the lever 83 for tilting of the rolling elements 48,50 about their contact axis, with related options and features as previously described. In a further embodiment a ring shaped actuator 80 may be directly coupled to each carriage assembly 52 separately, effecting equal changes to the precession angle on all carriages 52 simultaneously. That is to say, the actuation member directly and forceably precesses all carriages 52 individually, but simultaneously about their respective precessional axes 53. The input to the variator may be applied by a ring member 82 that is coupled to each carriage 52 and translates in the direction of the variator axis 38, with related options and features as previously described. In this example, the rolling elements 48,50 are preferably not tiltable within the carriage 52.

Alternatively in this forced precession mode of operation, one carriage may be forceably precessed by a linear translational actuation member (adapted for movement in a direction parallel to the variator axis 38) that may be coupled to the carriage 52 for forced precession about its precession axis 53. Other carriages 52 may be timed for simultaneous and equal precession, with related options and features as previously described. Timing may be achieved by gearing means (similar to that shown in figure 6, which shows the non-limiting example whereby adjacent carriages are meshed with one another) but may be achieved by other means such as toothed belts. In this example the rollers (48, 50) are preferably not tiltable within the carriage.

In embodiments with three or four carriages 51 per cavity 46, the gears may be of the bevel gear type such that the angular spacing between the carriages 52 is accommodated effectively, as shown in figure 6.

Some or all aspects of the non-planetary embodiments previously described may be applied to a similar variator adapted for planetary operation. However, the essential difference is that a planetary variator comprises at least one carriage 52 mounted on a carrier 36, as shown in Figure 6, for rotation about the variator axis 38. In this example, the carrier 36 carries three pairs of rollers, although the figure only shows one roller from each pair of rollers. The carrier 36 may comprise two or more carriages 52. The carrier 36 may at least in part be located radially with respect to the variator axis 38 within in the cavity 46. It further, or alternatively, be mounted for rotation about the variator axis 38 on at least one bearing centred on the variator axis 38. The carrier may be further adapted for movement in the direction of the variator axis (38).

The planetary variator may include any or all of the actuation features described for the non-planetary variator. For example, the planetary variator may preferably comprise the actuation system 80 as shown in Figures 3 to 5. This may comprise an actuation ring 82 coupled to the carrier 36 via a lever, or steering input, 83. The lever 83 is located in a groove in the ring 82 such that it may freely pivot relative to the ring. The ring 82 is configured to move axially, that is to say parallel to the axis 38.

The planetary device may feature one or two cavities or any of the other features disclosed with reference to the non-planetary example herein described.

For the avoidance of doubt, the word "precession" is taken to mean the (relatively) slow rotation of a spinning body around an axis. In this example, precession of the carriages 52 causes a change to the contact radii on the input and output discs. As the ring 82 is moved, it tilts the carriage 52 within the carrier 36 such that the carriage 52 tilts about its precession axis, and hence rotates the rollers 48,50 such that their region of contact with the drive discs 32,34 changes. That is to say, as the ring 82 is moved, it tilts the carriage 52 and pivots the rollers 48,50 such that the position of their engagement regions 88,89 on the drive discs 32,34 changes.

In a first operational condition in which the carrier 36 is rotated about the variator axis 38, rotation of the carrier 36 causes rotation of the first roller 48 due to engagement between the first roller 48 and the first disc 32, and consequently causes rotation of the second roller 50, thereby driving the second drive disc 34 about the common axis, and hence driving the second/output shaft 62. The first operational condition relates to a scenario in which the carrier is the transmission input, and the second shaft 62 is the transmission output, for example during ordinary driving of a vehicle. In a second operational condition in which the second drive disc 34 is rotated about the common axis 38, rotation of the second drive disc 34 causes rotation of the second roller 50 due to contact between the second roller 50 and the second disc 34, and this causes rotation of the first roller 48 due to engagement between the first roller and the first disc 32, and consequently causes rotation of the carrier 36, thereby driving the carrier 36 about the common axis 38, and hence driving the first shaft 60. The second operational condition relates to a scenario in which the second shaft 62 is the transmission input and the carrier 36 is the transmission output, for example, when engine "launch" is taking place.

As described above, the actuation system is configured to vary the distance between the first engagement region on a contact region 88 and the common axis 38. That is to say, vary the distance between the region which the first roller 48 is engaged with the first disc 32 and the common axis 38. The actuation system 80 is also configured to vary the distance between the second engagement region on a contact region 89 and the common axis 38. That is to say, vary the distance between the region which the second roller 50 is engaged with the second disc 34 and the common axis 38. In doing so the actuation system 80 varies the ratio of the distance between the first

engagement region 88 and the common axis 38 and the distance between the second engagement region 89 and the common axis 38. The first drive disc 32, second drive disc 34 and carrier 36 are configured such that when the ratio of the distance between the first engagement region 84 and the common axis 38 and the distance between the second engagement region 89 and the common axis 38 is "1 ", the second shaft 62 will have zero angular velocity. In the context of a motor vehicle, this means that the drive to the wheels of the vehicle would be in geared neutral having zero output speed.

Moving to a variator ratio either side of the geared neutral condition will provide either forward or reverse output speed, depending on which way the ratio is changed.

It should be noted that it is the ratio of the distances between the first engagement region 88 and the common axis 38 and the distance between the second engagement region 89 and the common axis 38 that is important, rather than the distances themselves. The device of the present disclosure comprises a planetary twin-roller toroidal device, wherein the carrier is configured to rotate and is able to provide a change in variator ratio, thereby providing a geared-neutral condition when the ratio equals 1 .

In other examples, the variator ratio may be altered by different means than that described above. For example, if only one of the said distances changes whilst the other remains constant, the ratio will still change. Thus a device according to the present disclosure could achieve the same functionality (albeit with narrower ratio range) by changing only one of the said distances. This could be achieved by having only one of the drive discs provided with a toroidal surface, the other having an alternative profile, for example planar. Hence as the distance between the engagement region and the common axis on the toroidal disc varies, the distance between the engagement region and the common axis on the other disc remains constant. This may be achieved by pivoting the carriage 52 about the contact region on the non- toroidal disc.

The actuation system 80 is configured to maintain rotatable engagement between the first rolling element 48 and the first drive disc 32 over a range, or "spread", of first engagement regions to define a contact region 84 on the first drive disc 32. Likewise, the actuation system 80 is also configured to maintain rotatable engagement between the second rolling element 50 and the second drive disc 34 over a range, or "spread", of second engagement regions to define a contact region 86 on the second drive disc 34. In this context, the term first/second engagement region is intended to mean the region at which the rolling elements 48,50 contact their respective drive discs 32,34 at any given moment.

Figure 6 shows a side section of the variable transmission units described above . The carrier 36 carries three pairs of rollers, although the figure only shows one roller from each pair of rollers. Figure 7 shows a further example of a multi-mode planetary variator transmission 500, comprising a variator 502, and epicyclic gear unit 504, a first clutch (or brake) (C1 ) 506 and a second clutch (or brake) (C2) 508. The two branches of the planetary variator 502 are coupled to two respective branches of an epicyclic (differential mechanism) and two brakes 506,508 are provided, one for each branch coupling.

Differentials (i.e. differential mechanisms) possess three or more coaxial branches and are two degrees-of-freedom systems, meaning that the angular velocities of two branches must be known in order to determine the angular velocity of a third branch. Epicyclic gearboxes are an example of such a differential mechanism. Thus, in the drawings, "EPI" is used, but the scope of the invention is not limited to a specific kind of differential. The underlying physical equations are common for any differential.

The following speed equation describes all planetary/differential (i.e. 2 degrees of freedom) systems : l3 = (W ₃ /Wi )w2=0 = (W ₃ - W ₂ )/(W1 - W ₂ ) that is:

where R is a ratio (i.e. R13 is the speed ratio of branch 3 relative to branch 1 when bran h 2 is fixed to ground) and w (or ω) is shaft angular velocity.

A planetary variator is a differential with variable base ratio. A base ratio may be defined as the speed ratio of two branches when a third branch is fixed to ground. Thus a base ratio for the variator may be defined as the ratio between the second and first drive discs when the planet carrier drive assembly is fixed to ground: R ^ disci

ω disci J

In other words, this is the speed ratio between the first and second drive discs in the frame of reference of the planet carrier drive assembly.

The epicyclic gear unit 504 is coupled to first shaft 510, which is an input shaft, and the variator is coupled to a second shaft 512, which is an output shaft. This arrangement is advantageous as only one clutch/brake per mode of operation is required. That is to say, two clutches/brakes are required for a two-mode system

In one mode of operation, closing one of the clutches/brakes 506, 508 will

simultaneously ground one respective branch of the epicyclic 504 and one respective branch of the variator 502. Hence in one mode of operation, as shown in Figure 8, the first brake (C1 ) 506 is opened and the second brake (C2) 508 is closed such that variator disc 1 (d1 ) is grounded, to provide a first ratio spread, the epicyclic 504 providing gear ratio R ₁₃ . In another mode of operation, as shown in Figure 9, the first brake (C1 ) 506 is closed such that the variator carrier (c) is grounded, and the second brake (C2) 508 is opened provide a second ratio spread different to the first ratio spread, the epicyclic 504 providing gear ratio R _u . That is to say, and as shown in Figure 8 and Figure 9, one clutch/brake is engaged/closed in a first mode of operation (open in the second mode) and the other clutch/brake is engaged/closed in a second mode of operation (open in the first mode).

Figure 10 shows a more detailed representation of the multi mode transmission system 500 presented functionally/schematically in Figures 7 to 9. In the Figure 10 example the planetary variator 502 is a twin-roller toroidal device having a first disc 520, a second disc 522 in rotatable engagement with a twin roller arrangement 524 having a carrier 526, for example as previously described, where the rollers 524 may be configured for minimising contact spin. The variator 502 is coupled with a "simple" epicyclic 504. The term "simple" epicyclicFigure 10 is taken to mean an epicyclic arrangement having a sun gear (s)(branch 2) in engagement with one or more planet gears held in a carrier (c)(branch 3), which are in turn in engagement with an annulus gear (a) (branch 1 ), the planet gears being radially outward of the sun gear, and the annulus gear being radially outward of the planet gears. Hence in this example, the epicyclic 504 comprises a sun gear 530, a planet carrier 532 which carries plant gears, and an annulus gear 534. The carrier 526 of the variator 502 is connected to the planet carrier 532 of the epicyclic 504, the first disc 520 of the variator is coupled to the sun 530 of the epicyclic 504, the first shaft (e.g. transmission input) 510 is connected to the annulus 534 of the epicyclic 504, and the second shaft (e.g. transmission output) 512 is connected to the second disc 522 of the variator 502. This arrangement is such that, , in the first mode of operation, the carrier is caused to rotate in an opposite direction to the rotation of the first disc 520 in the second mode of operation. Thus values of base ratio can be provided by a "simple" epicyclic.

If different values of base ratio are required (for example for different variator ratio spread, ratio position at which mode change is desired, or no reversal of carrier direction) then this may be achieved by use of an alternative differential. The alternative differential may be architecturally different (e.g. an "idler" epicyclic rather than a "simple" epicyclic) or may be an alternative combination of connections (i.e. in which respective branches of the differential are connected to respective branches of the variator etc). The choice of differential may be based on the base ratios required. Some examples may exist where there is more than one type of differential that will satisfy the requirements and the choice will depend on practicality and other factors.

Since

R,

R 12

R, where and

If R ₁₃ < 1 (i.e. -ve or +ve and < 1 ) then R _u has an opposite sign to R ₁₃ , and hence there is a reversal of direction.

If R ₁₃ > 1 then R _n has the same sign as R ₁₃ , and hence the branches have the same direction of rotation.

The desired R ₁₃ and R _u is achieved by selecting an appropriate differential gear set.

Such an arrangement (R ₁₃ <1 ) allows the carrier to rotate in opposite direction (in mode

1 ) to the discs in mode 2, which is highly desirable, to keep the direction of roller rotation the same in all modes. It also provides freedom to a designer to choose bias of overall spread of the transmission to forwards, or increase reverse range.

A further alternative example is shown in Figure 1 1 , which shows an alternative example of the system presented functionally/schematically in Figures 7 to 9 and provides the same, or similar, functionality. Common features have the same integer numbers as described in relation to Figure 10. The example in Figure 12 is a "Kopp" type alternative to the example of Figure 10, which (as discussed above) differs at least in that it has spherical rollers 527 rather a twin roller arrangement 526, and the spherical rollers 527 are constrained by a radially outward ring 529 against radially inner drive discs 520,524 A further alternative example is shown in Figure 12, which shows an alternative example of the system presented functionally/schematically in Figures 7 to 9 and provides the same, or similar, functionality. Common features have the same integer numbers as described in relation to Figure 10. The example in Figure 12 is a "tilting ball" type alternative to the example of Figure 10, which (as discussed above) differs at least in that it has spherical rollers 540 rather a twin roller arrangement 526. Further planetary devices may also be used as an alternative to the tilting ball type arrangement.

In the twin roller toroidal or tilting ball examples shown in Figure 10 and Figure 12, the first mode provides an Infinitely Variable Transmission (IVT), that is, provides geared neutral, forwards and/or reverse, if the variator can achieve ratio. If instead a planetary variator was used which could not provide a ratio, there will be no geared neutral state, but a wider range of transmission ratios may still be beneficially provided. The arrangement 600 in Figure 13 is a variation of the example of Figure 7, and common features carry common reference numerals. However, in this example, a gear ratio mechanism 602 and brake/clutch (C3) 604 are provided between the branches. Further a gear ratio mechanisms and brake/clutches 606 may be provided between the branches. These configurations provide additional modes of operation, for example provide gear ratios between branches. Beneficially, only one clutch/brake per mode is required to be provided, as is the case with conventional IVTs.

The arrangement 700 in Figure 14 is a variation of the example of Figure 7. and common features carry common reference numerals. Figure 14 shows a planetary variator 700 with more than 3 branches. That is to say, it has two branches in common with the previous examples, but also an additional branch 702, with a brake/clutch 704 (C3). Such an arrangement can provide additional modes of operation. A remaining branch may be braked to ground. Only one clutch/brake needed for each mode. The examples of Figures 7 to 14 are advantageous as the number of clutch/brake devices required is reduced from four to two. Additionally, brakes are easier to design and cheaper than clutches, since one side is irrotational. Also regime change is easier to control - control of two clutches/brakes simultaneously is known in automatic transmissions, where shift quality/comfort is very high. Further the gear set is used to provide the required ratios, and the base ratio can be chosen to reverse carrier direction in first mode if desired, which is elegantly achieved with minimal number of components. Additionally the arrangements are essentially coaxial, which facilitates packaging a transmission into a vehicle. However, the transmissions disclosed herein are suitable for use in other applications beyond vehicles, which may also benefit from the coaxial nature of these power transmissions with wide ratio range. Figures 15 and 16 show other clutch position arrangements that may achieve a similar functionality of the previous examples.

Figure 15 shows a multi-mode planetary variator transmission 800, comprising a variator 802, and epicyclic gear unit 804, a first clutch (or brake) (C1 ) 806

engageable/disengageable to ground 807 and a second clutch (or brake) (C2) 810 in series with a gear ratio mechanism (R2) 812 between the branches of the transmission unit 800. The epicyclic gear unit 804 is coupled to a first shaft 810, which is an input shaft, and the variator is coupled to a second shaft 812, which is an output shaft. Figure 16 shows a further example of a multi-mode planetary variator transmission 900, comprising a variator 902, and epicyclic gear unit 904, a first clutch (or brake) (C1 ) 906 in series with a gear ratio mechanism (R1 ) 908 and a second clutch (or brake) (C2) 910 in series with a gear ratio mechanism (R2) 912 in between the branches of the transmission unit 900. The epicyclic gear unit 904 is coupled to a first shaft 914, which is an input shaft, and the variator 902 is coupled to a second shaft 916, which is an output shaft.

In the examples of Figures 15 and 16, it is possible for recirculating power to be present, and the gear ratios and differential may be selected to avoid power

recirculation in at least one mode.

It should also be noted that a planetary variator may have one or more planets within the carrier. A device with one planet will still provide the planetary functionality and thus can be used in the present disclosure.

Figures 17 to 46 show further examples according to the present disclosure. The features represented in figures 17 to 46 are consistent with the convention of the preceding examples. Common to all examples is a first shaft, indicated as "S1 ", which is an input shaft, a second shaft, indicated as "S2", which is an output shaft, and a variator, indicated as "VAR" Differential mechanism are also indicated using "EPI" , but, as previously described the scope of the invention is not limited to an epicydic gearbox. Clutches/brakes are indicated by C1 , C2, C3 etc.

Figure 17 shows a multi-mode planetary variator transmission where clutches (when closed) connect two branches of a variator via a fixed gear ratio, where the different clutches each connect respective branches of the transmission via a different ratio.

Figure 18 shows another further alternative example of a multi-mode planetary variator transmission where clutches (when closed) connect two branches of a differential via a fixed gear ratio, where the different clutches each connect respective branches by a different ratio.

Figures 19 to 30 show examples of multi-mode transmissions comprising two

differential mechanisms in combination with a planetary variator. The transmissions of Figure 19 and Figure 20 differ from conventional IVT shunts arrangements (which may comprise a variator with one input and one output coupled with one or more

differentials) by being arranged such that the epicydic is configured to be continuously variable and the usual variable ratio is configured to be a fixed ratio. A plurality of clutches are shown, which (when one is closed) remove a degree of rotational freedom from the system and thus make the transmission ratio between any two shafts fully determinate (one degree-of-freedom). The clutches shown in the figures, when closed, each remove a degree-of-freedom from the system in a different manner. The

examples shown are illustrative of only a few of the configurations possible, without departing from the spirit of the present invention, to achieve various ratio spreads in each mode. Once a clutch is closed to make the system possess only one degree-of-freedom, all shafts speeds are determinate, hence a speed ratio between any two shafts in the system is defined, not just the first and second shafts. Clutches that, when closed, define a fixed gear ratio between two branches may be added in parallel, each having a different ratio. The branches of the variator are shown generally as, "a", "b" and "c" (rather than "disci ", "disc2" and "carrier"), since the principle of operation remains the same. Gear ratio mechanisms may be provided at various locations, shown as circles with an "R" in Figure 19 and figure 20, and as previously presented in the figures and description.

Figures 21 to 23 illustrate specific modes of the example of Figure 19. Figure 21 represents a mode in which clutch Ca is closed and all other clutches are open, one branch of each of the planetary variator, the first and second differentials are all simultaneously braked to ground. This provides a fixed gear ratio through the first differential, a potential spread of ratio through the planetary variator and a further fixed ratio through the second differential. This defines an overall ratio or ratio spread between the first and second shafts. This defines a configuration in which the variator ratio may be defined as :

Figure 22 represents a mode in which clutch Cb is closed, branch "3" of the first differential and branch "b" of the variator are simultaneously braked to ground, but all three branches of the second differential remain rotational. This provides a fixed ratio via the first differential, and also a conventional input-coupled shunt arrangement via the planetary variator and the second differential, where the overall speed ratio depends on the base ratio of the variator. This defines a configuration in which the variator ratio may be defined as :

Figure 23 represents a mode in which clutch Cc is closed, a similar result is achieved to when clutch Cb is closed, but an output-coupled shunt is provided by the first differential and the planetary variator, and a fixed ratio is provided by the second differential. This defines a configuration in which the variator ratio may be defined

Figures 24 to 29 show alternative examples of multi-mode transmissions having two differential mechanisms in combination with a planetary variator. That is to say, they show further ways of creating multi-mode transmissions with a planetary variator with more than three (i.e. four or more) branches. Again, clutches are used to remove a degree of freedom from the system. These systems comprise one or two fixed-ratio differentials, coupled in a similar manner to the examples of Figures 7 to 18 (by coupling two branches of the variator to two branches of a differential), allowing the number of clutches required to be minimised (in general, only one clutch required per mode).

Figure 24 shows an example similar to that of the example of Figure 19, except that an extra mode is provided by grounding a further (fourth) branch of the variator. This extra mode is achieved by closing clutch C2 (whilst the others remain open), and creates a kind of "double shunt" arrangement, where three branches of the variator are carrying rotational power. This potentially allows a given size of variator to be transferring more power, for the same traction forces in the contacts. Whether this power is truly split or recirculated depends on the base ratio of the variator, the base ratios of the differentials and also on which branches are connected to each other.

Figure 25 shows a multi-mode transmission where the clutches provided are actually brakes which (when closed individually) each ground a different member of the variator and a respective branch of a differential. This means no recirculating power can exist in that respective loop, but there may be recirculating power in the other loop, depending on the base ratios of the variator and differentials. Figure 26 shows an example similar to that of the example of Figure 25, but (in similar fashion to the example of Figure 24) an extra mode is provided by grounding a further (fifth) branch of the variator by closing clutch C5. Figure 27 shows a multi-mode transmission where each clutch (when closed) couples two respective branches of the variator via a respective fixed gear ratio. Clutches C3 and C4 also simultaneously define a fixed ratio between two respective branches of a respective differential. Figure 28 shows a multi-mode transmission where each clutch (when closed) couples to respective branches of a differential via a respective fixed gear ratio.

Figure 29 shows a multi-mode transmission where each clutch (when closed) defines a fixed gear ratio between two branches of the variator, whilst the ratios between the branch of the differentials are variable, in accordance with the variator base ratio.

Figure 29 also shows that some of the power in the transmission in both modes does not pass through the variator, but instead may bypass the variator, being transferred directly between the first differential (namely branch 2) and the second differential (namely branch 4).

Figures 30 and 31 show two examples where a lockout mode can be provided, in which power flow through the transmission bypasses the variator. This may be desirable in situations such as motorway cruising. In both examples, this mode is achieved when clutches Cb and Cc are closed and clutch CL is open. In Figure 30, during the lockout mode, the variator is completely disconnected, and is made dormant or inactive (two branches are simultaneously grounded, therefore all branches are grounded). This means changing to another mode must allow time for the variator to start-up again. However, in Figure 31 , during the lockout mode, the variator remains rotational, and the response time will be faster when changing to another mode, but cumulative fatigue damage to the variator in the lockout mode may reduce the fatigue life of the variator relative to Figure 31 . When not in the lockout mode, the transmissions depicted in Figures 30 and 31 will behave like the system shown in Figure 22 when clutch Cb is closed, and behave like the system shown in Figure 23 when clutch Cc is closed, producing input and output coupled shunts respectively.

A differential coupled to two or more branches of a planetary variator may also possess more than three branches, for example, a Ravigneaux gear set may be used. This allows more ratios to be obtained in a compact arrangement. Figures 32 to 46 show alternative embodiments with specific differentials and connections to the planetary variator chosen to provide advantages in the mechanical detailed design. In these figures, various planetary variators are shown, to demonstrate that the functionality of the whole multi-mode transmission will be similar for any planetary variator with positive base ratio between the first and second discs, capable of achieving +1 base ratio. A tilting ball variator or the like, for example may be used as an example. Thus the scope of the present invention should not be seen as limited to the devices shown, but these are shown rather by way of example. If a variator is used that meets these criteria, then in the following embodiments, an IVT is created in mode 1 (when a first clutch/brake C1 is closed) with forward, reverse and geared neutral, and a CVT is created in mode 2. Furthermore, the differentials and coupling arrangements chosen in the embodiments illustrated in Figures 32 to 36 are such that in mode 1 the carrier of the variator rotates in an opposite direction to that of the first disc of the variator in mode 2. This means that the direction of variator planet rotation relative to the frame of reference of the carrier is the same in all modes. This is equivalent to saying that the angular velocity of a given drive disc relative to the angular velocity of the carrier always has the same sign in all modes. This allows the use of a variator control mechanism that could require relatively low power and/or be torque-controlled.

Figure 32 shows an alternative arrangement to Figures 10 and 1 1 . The differential used is still a "simple" epicyclic, but a different coupling arrangement to the first shaft S1 and planetary variator akin to a tilting ball type is provided. In this embodiment, a first shaft S1 is coupled to the sun 530 of an epicyclic 504, a carrier (c) of the planetary variator VAR is coupled to a carrier 532 of the epicyclic, the first disc d1 of the planetary variator is coupled to an annulus 534 of the epicyclic and a second disc d2 of the planetary variator is coupled to the second shaft S1 . A first brake C1 , when closed (the first mode), simultaneously grounds the first disc of the variator and the annulus of the epicyclic. A second brake, when closed (the second mode), simultaneously grounds the carrier of the epicyclic and the carrier of the variator. This coupling arrangement can provide a greater overlap of overall ratio between the first and second mode than the embodiments shown in Figures 10 and 1 1 , which can be beneficial. A further benefit provided by the embodiment shown in Figure 32 is that a drum may be provided that is coupled to the first disc of the variator and encloses the second disc and carrier of the variator. A clamping mechanism to generate the required normal loads in the traction contacts of the variator is provided axially between the drum and the second disc, on the opposite side of the second disc to the first disc. A thrust bearing is provided between the drum and second disc, so that it only runs at the difference of speeds between the first and second discs, which is zero when both discs rotate at the same speed (base ratio is +1 ), resulting in zero power loss in this bearing in this condition. Preferably, the clamping mechanism may be placed between the drum and the thrust bearing, so that the clamping mechanism does not rotate in the first mode, when the first clutch is closed and the first disc of the variator is grounded. Alternatively, the clamping mechanism may be placed between the thrust bearing and the second disc, so that it rotates with the same velocity as the second disc. The second shaft may be hollow, to allow access to the carrier to actuate a mechanism capable of varying the base ratio of the variator. Figure 33 shows an arrangement similar to that of Figure 32, except a "Kopp" type variator is included as part of the arrangement instead of the "tilting ball" type. Hence the spherical rollers 527 of the example of Figure 33 are constrained by a radially outward ring 529 against radially inner drive discs d1 ,d2. This embodiment also illustrates the possibility of having the first and second shaft concentric and on the same side of the transmission, such as may be beneficial for a front-wheel-drive transmission. Figure 34 provides an arrangement in which the differential coupled to the planetary variator is a so-called "idler" epicydic, where the carrier supports two sets of planet gears in series between the sun and annulus. This arrangement is illustrative of a combination of choosing a suitable differential and branch connections that facilitate the use of a twin cavity variator, to double the torque capacity of the variator for the same cavity size and eliminate the losses associated with a thrust bearing required to react the axial load in the variator due to clamping in a single-cavity arrangement. This arrangement also provides that the carrier may be accessed from a radially outward position from the main axis of the variator in one cavity, in order to actuate a

mechanism capable of varying the base ratio of the variator in both cavities. In this embodiment, the sun 530 of the epicydic is coupled to the first shaft S1 , the carrier 532 of the epicydic is coupled to the first disc d1 of the variator, the annulus 534 of the epicydic is coupled to the carrier (c) of the variator, the second disc d1 of the variator is coupled to the second shaft S2. The variator also comprises a third disc d3 in which rollers are held by the carrier c. A first brake C1 , when closed (the first mode), simultaneously grounds the first disc d1 of the variator and the carrier 532 of the epicydic. A second brake, when closed (the second mode), simultaneously grounds the annulus 534 of the epicydic and the carrier c of the variator. A third shaft S3 coupled to the first disc d1 of the variator passes through the centre of the second disc S2 to connect to the third disc d3.

Figure 35 shows a further alternative embodiment, similar to that shown Figure 32, but here a so-called planetary differential is used to provide a suitable base ratio. This kind of differential does not possess an annulus, but rather the planet gears have a double mesh, axially spaced apart, which each mesh with a respective sun gear. Thus the three branches of this differential are a larger sun gear, a smaller sun gear and a planet carrier. Since there is no annulus, this kind of differential can beneficially be cheaper to manufacture since all the meshes to be machined are external. This is achieved possibly at the expense of axial length, but this depends on the detailed design.

Another advantage of this kind of differential is that it can afford the designer more freedom in the choice of base ratio available, since values of base ratio can be achieved with this kind of differential that cannot be achieved with either a simple or idler epicyclic. In this embodiment, the first shaft S1 is coupled to the small sun, the carrier of the variator is coupled to the large sun and the first drive disc is coupled to the carrier. 4except that Figure 36 shows an example of a multi-mode transmission using a tilting ball planetary variator possessing two cavities, resulting in a doubling of the power/torque which can be transferred for the same cavity size46 and the elimination of losses associated with a thrust bearing.tilting ball In the embodiment shown in Figure 36, a third disc d1 is provided on the opposite side of the second disc d2 to the first disc d1 , and facing the first disc d1 . The second disc d2 has a similar contact face on both axial sides, or alternatively may be formed from separate components coupled together. In terms of the branches of the planetary variator, the third disc d3 is the same as the first disc d1 , and so they shall be referred to collectively as the "first disc". The carrier (c)is extended into the second cavity 46"in drivable engagement with the second d2 and third d3 (first d1 ) discs. The carrier forms a branch of the planetary variator. In this example the second shaft S2 is in driveable engagement with the second disc d2, to provide a transmission output to a layshaft rather than a true coaxial arrangement, such as that previously described in Fig.36' Figure 37 shows a way of coupling a final drive differential 608 to a second shaft S2, particularly useful if the present invention is to be applied to a vehicle with a transverse mounted engine. The use of a chain and idler gear pair 620 allows ease of selection of a desired final drive ratio, so as to match the overall transmission ratio to the

requirements of a particular vehicle. Alternatively, the chain may be replaced by a gear mesh, to provide an opposite sign of final drive ratio.

It is also worth noting that other differentials (such as a so-called "planetary" differential, where two suns and a carrier are used, where the planets have two separate co- rotating meshes, one for each sun) can also be used successfully as the differential in embodiments of the present invention. "Simple" and "idler" epicyclics are shown by way of example only. The "planetary" differential benefits from being able to create base ratios that are not possible with either "simple" or "idler" epicyclics, and also because they do not possess an annulus gear, they can be much cheaper to manufacture.

Subtle methods of actuation of variators have been previously proposed which require low power and/or offer the potential for torque control. Low power is defined as being less than the total power required to change ratio directly; thus some of the power required to change ratio will be provided by the transmission itself (from an inertia or power source) as the variator rolling elements steer themselves to a new ratio. Stability of such a self-steering mechanism may be achieved by providing means for self- restoring, wherein the variator ratio will tend to an instantaneous equilibrium ratio position; the steering action of the rollers tends to zero as this position is reached.

Self-restoring means may be provided by a geometrical feature, such as an angle or offset present in the constraints of the system. For some self-restoring, self-steering systems, for a given direction of rotation of the device, this angle/offset provides stability for one direction or sign of the angle/offset and instability in the opposite direction or sign of the angle. This is equivalent to saying that for a given direction or sign of this angle/offset, then one direction of rotation of the device will be stable and function correctly (self-restore), whereas the opposite direction of rotation of the device will be unstable.

In the present disclosure, the variator may be configurable as a planetary device, which is taken to mean that the carrier member which supports at least one rolling element (planet/roller) is itself rotatable about the main variator axis, and thus rotation of this carrier member causes the planet to orbit the main axis. In the case of a planetary variator, stability of an actuation system comprising self-restoring geometry is dependent on the sign of angular velocity of one of the discs relative to the carrier (i.e. the direction of rotation of the disc in the frame of reference of the carrier). This is also equivalent to saying that one direction of planet rotation is stable with respect to the variator control mechanism, and the opposite direction is unstable. Thus a designer has a few options to ensure that a preferable actuation system will function in a stable manner in a multi-mode transmission according to the present disclosure. For example, it may be advantageous to have an actuation system with reversible self-restoring geometry, and this will need to be controlled by the control system. It may be more preferable to choose suitable ratios in the transmission such that the direction of rotation of the discs from the carrier assembly's frame of reference does not change, such that a low-power or torque-controlled actuation system can be used without the need for reversible geometry. This will always be stable without any need for a specific control system input, avoiding the potential for the variator to be damaged if there is a control/actuation system failure in this regard.

For the example shown in Figure 7, this would be achieved by selecting a value of R_13 (the ratio of speed between branch three and branch 1 when branch two has zero speed) which is less than one (i.e. positive and less than one, or negative)

When the sign of the relative speed of (either) drive disc with respect to the planet carrier drive assembly is opposite in mode 2 to mode 1 , then the variator control mechanism is unstable in one mode, unless reversing of geometrical feature is created.

This means when the clutch C1 (506) is closed, the carrier would spin in an opposite direction to the first disc when clutch C2 (508 is closed).

This creates a reduction into the variator.

Figures 39 and40 show systems, similar to that shown in Figure 7, except they are provided with one or more gear ratios Rto counter the reduction in the variator.

However The example of Figure 38 would experience an extra transmission loss in both modes, whereas the examples of Figures 39 and 40 would only experience the extra loss when the respective branch on which the ratio is placed is rotating. An equivalent ratio R_13" or R_13"' needs to be selected, and can be easily calculated as a function of R_13 (which will preferably be <1 ) and the value of R1 . Figures 41 to 44 show yet further embodiments of the present invention, which use two of the modes shown in Figure 19 (those when Ca and Cb are closed, shown in Figures 21 and 22). These transmissions differ from that shown in Fig.7 because they have the property that in the second mode only a proportion of the transmitted power passes through the variator (in the aforementioned embodiments, all of the power passes through the variator in the second mode). This can provide increased transmission efficiency and also has advantages in terms of increased variator durability and/or reduced variator size. Thus a first mode beneficially provides an IVT without power recirculation and the second mode is an input-coupled shunt which can have higher efficiency than the variator itself. Here a value of R_13 which is negative may be selected, which (because this value is mathematically less than +1 ) still ensures that the sign of the angular velocity of a given drive disc relative to the carrier is the same in all modes, thus enabling the use of a relatively low power or torque controlled variator actuation system to be employed. Advantageously, the magnitude of R_13 can at the same time be greater than one (so R_13 is mathematically less than minus 1 ) which provides a step up of speed into the variator in the first mode. This potentially allows the variator to be made smaller and can also beneficially provide a net reduction of the centripetal loads on the at least one roller in the planet carrier drive assembly. Figures 41 to 44 can easily be modified to accommodate a double cavity variator.

Figure 42 and Figure 43 have the characteristic that the overall ratio spread of the transmission can be configured to be shared almost equally between forwards and reverse, and that in the second mode a relatively small factor of the power being transmitted is recirculated backwards through the variator, this factor reaching a minimum at maximum overall ratio in the second mode, which provides a good overdrive condition in terms of efficiency (which is higher than the variator efficiency) and durability for the variator (it can be made smaller). In the embodiment of Figure 42, the first differential is a simple epicyclic, comprising a sun coupled to the carrier c of the planetary variator, a carrier coupled to the first disc d1 of the planetary variator and an annulus coupled to the first shaft S1 . The second differential is also a simple epicyclic comprising a sun coupled to the second disc d2 of the variator, a carrier coupled to the first disc d1 of the variator and an annulus coupled to the second shaft S2. A first clutch Ca when closed simultaneously grounds the first disc d1 of the variator, the carrier of the first differential and the carrier of the second differential. A second clutch Cb when closed simultaneously grounds the sun of the first differential and the carrier c of the planetary variator.

In the embodiment of Figure 43, the first differential is an idler epicyclic, comprising a sun coupled to the carrier c of the planetary variator, a carrier coupled to the first shaft S1 and an annulus coupled to the first disc d1 of the planetary variator. The second differential is a simple epicyclic comprising a sun coupled to the second disc d2 of the variator, a carrier coupled to the first disc d1 of the variator and an annulus coupled to the second shaft S2. A first clutch Ca when closed simultaneously grounds the first disc d1 of the variator, the annulus of the first differential and the carrier of the second differential. A second clutch Cb when closed simultaneously grounds the sun of the first differential and the carrier of the planetary variator.

The embodiment shown in Figure 44 is slightly different in that it has the characteristic that the ratio spread in the first mode (which is an IVT with forwards and reverse) is biased towards the forwards direction, and the second mode is a true power-split mode providing further forwards ratio spread at higher efficiency than the variator efficiency. In this embodiment the first differential is a simple epicyclic, comprising a sun coupled to the carrier c of the planetary variator, a carrier coupled to the first disc d1 of the planetary variator and an annulus coupled to first shaft S1 . The second differential is also a simple epicyclic comprising a sun coupled to the second disc d2 of the variator, an annulus coupled to the first disc d1 of the variator and a carrier coupled to the second shaft S2.

Figure 45 shows another embodiment of the present invention. This is like Figure 7, but rotated 90 degrees on the page, so that the first and second shafts (510,512) have swapped places with the first and second clutches (C1 ,C2). The connections of the variator have also been swapped around so that the first disc of the variator can be grounded by the first clutch, the carrier of the variator may be coupled to the first shaft and the second disc of the variator may be coupled to the second shaft. It is understood that in another embodiment, the three branches of the variator may be coupled differently. The differential may have a fourth branch which can be selectively grounded via a third clutch. The differential then may be a ravigneaux type, or alternatively may be formed of two differentials coupled together to achieve the same result of a four- branch two-degrees of freedom unit (two branches of the two differentials coupled to eachother, the two sets of coupled branches providing the first two branches of the four-branch unit, and the third and fourth branches are provided by the one remaining branch of each of the differentials).

Thus closing the second clutch creates a fixed transmission ratio of:

Likewise, closing the third clutch creates a fixed transmission ratio of: Preferably, the value of "R14,2" or "R14,3" be selected such that they lie either at an extreme of the ratio range provided by the first mode when clutch C1 is closed, or somewhere within the ratio range. If this is the case, then the transmission can shift from a variable mode to a fixed ratio mode with a synchronous shift (no differential speed across a clutching device). If "R14,2" and "R14,3" are selected to be at opposite extremes (or almost extremes) of the ratio range of the first mode (when C1 is closed), then this may be useful for a vehicle that frequently shuttles backwards and forwards and then usually travels at a more or less constant speed, such as a forklift truck, as a non-limiting example. If only one fixed ratio mode is desired, the ravigneaux-type (or four-branch) differential may be replaced with a more conventional 3-branch differential and one of the second or third clutches C2,C3 could be removed. The embodiments shown in Figure 45 and Figure 46 are illustrative of a multi-mode transmission using a planetary variator [where in at least one mode, the carrier of the variator is rotating] where there can be fully synchronous shifts between modes. Furthermore, it is illustrative of a multi-mode transmission, where one side of the clutch is grounded (i.e. it is a brake), which has significant advantages in reducing driveline drag by eliminating rotating seals for supplying hydraulic fluid to actuate a friction clutch. Furthermore, the designer may use dog clutches which require no power to keep them engaged.

In Figure 45, the first shaft S1 is coupled to a first branch of the planetary variator, which may be the carrier c, and also to a first branch of the differential. The second shaft S2 is coupled to a second branch of the planetary variator, which may be a second drive disc d2, and to a second branch of the differential. A first clutch C1 , when closed, grounds a third branch of the variator, which may be a drive disc d1 . A second clutch C2, when closed, grounds a third branch of the differential. Optionally, a third clutch C3, when closed, grounds a fourth branch of the differential.

Figure 46 shows the transmission of Figure 45 but with a fourth clutch C4 coupling the third branch of the variator to the first shaft S1 . There may be a ratio provided between the first shaft and the third branch of the variator. There may be a ratio provided between the first branch of the variator and the first shaft S1 . The first clutch C1 may be closed and torque transmitted between the first and second shafts S1 ,S2 via the planetary variator. The variator base ratio may move to one extreme and a change of regime may be desired. One of either the second or third clutches C2,C3 may be closed and the first clutch may be opened. Torque may be transferred between the first and second shafts S1 ,S2 via the differential. The variator base ratio may then be swept to the opposite extreme. The ratios of the system may be selected such that when the variator base ratio is at this opposite extreme there is substantially zero or very low differential speed across the fourth clutch C4, which may then be closed. There is then provided an input-coupled shunt mode between the first and second shafts S1 ,S2, when clutch C4 is closed and all other clutches remain open, where the planetary variator behaves as the differential. Advantageously, higher efficiency than the efficiency of the variator can be achieved in this mode.

Advantageously, this arrangement provides an example of achieving a synchronous regime change in a multi-mode variable transmission after a resweep of variator base ratio, and no torque interruption between the first and second shafts S1 ,S2 during the regime change. Torque may be transmitted between the first and second shafts S1 ,S2 via the fixed ratio provided by either closing the second clutch C2 or the third clutch C3. The variator may be disconnected from the torque path by opening the first clutch C1 . Torque transfer between the first and second shafts without interruption during the regime change is achieved by virtue of having a parallel mechanical path with a fixed ratio. This fixed ratio mechanical path may also provide a variable ratio if the second or third clutches are slipped. It is also appreciated that other embodiments of the present invention may include a dog clutch or brake in parallel with a friction clutch or brake, whose two sides are connected to the same two sides of the friction clutch, such that the friction clutch may be employed during the shift process or in a slipping state to aid launching of the vehicle from rest, but once this has been achieved, the dog clutch can be closed and the friction clutch de-energised, thus requiring no power to maintain engagement of the clutch. When release of the clutch arrangement is required, the friction clutch can be energised and then the dog clutch can be released, allow another phase of variable engagement if required. Alternatively, another friction clutch (corresponding to another mode of the transmission) can be engaged and the dog simply released.

It is also appreciated that there may be an input clutch or torque converter provided between the first shaft and a source of motive power.

Although not shown in all the Figures, one skilled in the art would understand that when the present invention is applied to wheeled vehicles, there may be provided a differential as known in the art to share torque between two axles, coupled to the second shaft. As a non-limiting example, the second shaft in the present disclosure may be a vehicle propshaft.

The devices of the present disclosure share some similarities with a conventional automatic gearbox, comprising compounded/multiple geared planetary (epicyclic) gear sets, wherein the different discrete gear ratios are achieved by using clutches or brakes to connect/release different branches to/from ground or to/from other branches. Using a planetary variator of the present disclosure provides multiple ranges of continuously variable ratio, rather than just multiple discrete ratios in automatic transmissions. This allows engine speed to be optimised for fuel efficiency. Furthermore, this provides a transmission with a wide range of ratios (potentially including forward, geared neutral and reverse, depending on the planetary variator and configuration used) matching or superior to automatic transmissions in terms of ratio range, whilst potentially requiring no additional gearing and less clutches than current automatic transmissions. This clearly has the potential for savings in cost, weight and transmission packaging space.

For any of the transmissions of disclosed herein, the base ratio of the variator may be manipulated during the change between modes to assist the shift process and reduce the energy dissipated in the clutches/brakes.

Furthermore, the coaxial nature of planetary devices can be very beneficial to packaging and mechanical design considerations. The design requirements for the clutch components are similar to those used in automatic gearboxes (where there exists decades of design and durability experience) and therefore the mass-production tooling and facilities already exist.

Additionally, and as discussed above in relation to Figure 3, a twin-roller arrangement in toroidal devices can advantageously reduce spin losses. The positive ratio created by having two rollers in series can offer certain advantages for transmission architectures. For instance, a geared neutral condition can be created by driving a carrier supporting the rolling elements (as opposed to having a carrier which is rotationally constrained), fixing one of the discs to ground, and the second disc being driven. When the rolling elements are in a position that corresponds to a base ratio of +1 (speed ratio of the two discs when the carrier is fixed to ground), the second disc has zero output velocity, thus providing geared neutral. This is achieved without recirculating power. It will also be understood by one skilled in the art that whilst traction drives have been discussed, the present invention may be applied to a friction drive configured as a planetary variator. Thus the planetary variator may be either a traction or a friction drive, or indeed a traction drive device that sometimes operates in part as a friction drive, particularly when low rolling velocities are present in the device.

Furthermore, one skilled in the art will understand that a variety of features must be present in either a traction or friction drive for the device to function. This includes a clamping mechanism to create contact normal loads to enable torque to be transferred. It is known in the art that the at least one rolling element mounted in the variator carrier (whether the carrier is rotating or not) must have suitable constraints such that the clamp load can be transferred from one drive disc to another via the at least one rolling element as they are urged together. This usually means that some means for the at least one roller to float in a direction parallel to the main axis must be provided. It is appreciated that clamping mechanisms known in the art may be employed in the present invention. Non-limiting examples include a roller and ramp arrangement (sometimes referred to as a cam arrangement), hydraulic arrangement and a spring. There is usually the need for a minimum load to be generated to start the device, which may be provided by a spring. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.