INTRODUCTION TO THE INVENTION

This invention relates to a drive unit for a vehicle, such as an automobile. More particularly, but not exclusively, this invention relates to a drive system which is configured so that drive can be transferred between two or more drive sources and a drive shaft of a vehicle.

BACKGROUND TO THE INVENTION

Of recent, global legislative restrictions related to carbon emissions and fuel consumption, coupled with dwindling natural resources, have been key driving forces behind a continued search for improved efficiency in the drive systems of vehicles.

While electrical and other complete replacements for fossil fuel drive systems are being developed to achieve commercial viability, other avenues which can reduce carbon emissions of current fossil fuel drive systems are being investigated. In this regard, some well-known alternative systems relate to energy harvesting by means of regenerative braking, engine optimisation as well as continuously variable transmissions.

In particular, engine optimisation systems relate to the concept of utilising electronic engine management systems to regulate engine operation to achieve higher efficiencies. Engines are managed to operate closer to their most efficient lines for improved fuel saving, sometimes even at a cost of performance.

Regenerative braking refers to the concept of converting kinetic energy associated with the momentum of a travelling vehicle into stored potential energy for later use, while the vehicle is being slowed down or stopped. In other words, when a travelling vehicle has to be slowed down by means of its brakes, a regenerative braking system is configured to rather harvest and store energy instead of dissipating it in the form of heat, as in conventional braking systems.

A further alternative to reduce fuel consumption and carbon emissions is to increase the number of gears of a transmission to allow the engine to vary the revolutions per minute of the engine at a certain road speed. One such transmission through which the number of gears is increased is a Lepelletier transmission which is used for example in some automatic transmissions and in itself represents a further development of the so-called Ravigneaux set, “a double planetary gear set”. The Lepelletier set is produced in that a Ravigneaux set is preceded by a further single planetary gear set and is connected by various configurations of clutches and brakes that result in several selectable gears, typically between 6 to 10 with present configurations. For a 6-speed transmission which is based on the Lepelletier set a sun gear of the single planetary gear set is typically permanently connected to a casing of the gear set to restrict rotation of the planetary gear set. For a 7-speed transmission and above, the sun gear is typically free to rotate via an additional clutch. Therefore, in current configurations based on the Lepelletier gear set the sun gear is either locked to the casing of the gear set or is configured to rotate freely.

It is well known to prevent an engine of a drive system from stalling it must run above predetermined rotations per minute. The typical solution is to use a coupling, such as a clutch, torque converter, fluid coupling, or another known device so that the engine can still idle while the vehicle is standing still or at low speeds that would normally stall the engine. The input of the coupling is typically connected to an output of the engine with the output of the coupling typically the input to the first planet stage of the Lepelletier set.

The power output in the Lepelletier set usually occurs via the ring gear of the Ravigneaux set. The power output is further connected via the differential gear to the drive wheels. It is disadvantageous that several clutches and brakes as well as separate acceleration devices such as the hydrodynamic torque converters are required. A further disadvantage is that during travel, especially in conditions of either low speed and low load, and high speed with low load, the engine finds it difficult to operate closer to the optimum point for power from the given fuel consumption. In response to a demand for a slight acceleration, the injection of fuel is increased for a change in the throttle setting. At the time of braking, the inertial energy of the vehicle is usually converted by the vehicle’s brakes to thermal energy which is dissipated in the form of heat. Thus, further demand for improved mileage and cleaner exhaust gases is not sufficiently satisfied.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide a drive unit with which the applicant believes the aforementioned limitations and disadvantages may at least partially be alleviated, and/or which would provide a useful alternative for known drive units.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a drive unit for a vehicle, the drive unit comprising:

- a gear assembly having a first gear element, which is connected to a drive shaft of a vehicle for operatively transferring drive from the drive shaft to wheels of the vehicle, a second gear element, and a third gear element;

- a drive means coupled to the second gear element of the gear assembly so that drive can be transferred from the drive means to the gear assembly;

- an electrical/hydraulic mechanism coupled to the third gear element of the gear assembly so that drive can be transferred between the electrical/hydraulic mechanism and the gear assembly; wherein the drive unit can selectively be configured in one of i) a first configuration wherein the drive means transfers drive to either or both the electrical/hydraulic mechanism and the drive shaft; and ii) a second configuration wherein drive is transferred from the drive means and the electrical/hydraulic mechanism to the drive shaft and subsequently the wheels via the gear assembly. In the first configuration, the drive means may drive the electrical/hydraulic mechanism and the drive shaft in a drive-splitting configuration. In the drive-splitting configuration, the drive produced by the drive means is directed to the drive shaft, to drive the wheels of the vehicle, and to the electrical/hydraulic mechanism where the drive is converted into potential energy for storage. In the first configuration, the electrical/hydraulic mechanism is configured to subtract drive, received from the first drive means, from the gear assembly. In the first configuration, the drive means may be operated at a peak efficiency which produces excess drive than what is required at the drive shaft. The excess drive may be subtracted and converted by the electrical/hydraulic mechanism to potential energy and subsequently stored.

In the second configuration, the drive means and the electrical/hydraulic mechanism may drive the drive shaft in a drive-summing configuration. In the second configuration, the drive means may be operated at peak efficiency which produces a drive shortfall at the drive shaft. The electrical/hydraulic mechanism may transfer drive to the drive shaft in order to provide the drive shortfall to the drive shaft. In the second configuration, the electrical/hydraulic mechanism is configured to add drive to the gear assembly to supplement drive from the drive means.

The drive unit may further be selectively configured in a third configuration. In the third configuration, the gear elements of the gear assembly may be coupled together allowing the drive means, electric/hydraulic mechanism, and drive shaft to be locked together. In the third configuration, the drive means, electrical/hydraulic mechanism, and the drive shaft may be in a torque-summing configuration.

The drive unit may further be selectively configured in a fourth configuration. In the fourth configuration, drive from the drive shaft and subsequently the kinetic energy of the vehicle may operatively be reduced by transferring drive from the wheels and drive shaft to the electrical/hydraulic mechanism. In the fourth configuration, the drive shaft may drive the electrical/hydraulic mechanism in a regenerative braking configuration with the electrical/hydraulic mechanism configured to convert the drive into potential energy for storage. In the fourth configuration, the drive from the drive means may also be transferred to the electrical/hydraulic mechanism. The gear assembly may include a first gear arrangement and a second gear arrangement which is selectively coupled to allow drive to be transferred between the first and second gear arrangements. The first gear arrangement may include the first gear element. The second gear arrangement may include the second and third gear elements.

The first gear arrangement may be in the form of a double planetary gear set, also known as a Ravigneaux gear set. The first gear arrangement may comprise a plurality of gear elements. The plurality of gear elements may include a first sun gear, a second sun gear, a ring gear, a set of first planetary gears, a set of second planetary gears, and a planetary carrier. The set of first planetary gears may mesh with the ring gear and the second sun gear. The set of second planetary gears may mesh with the first sun gear and the set of first planetary gears. The sets of first and second planetary gears may be connected to a planetary carrier. The first gear element may be defined by the ring gear of the first gear arrangement and may be connected to the drive shaft in any known manner.

The second gear arrangement may be in the form of a single planetary gear set. The second gear arrangement may include a plurality of gear elements. The plurality of gear elements may include a sun gear, a ring gear, and a set of planetary gears which mesh with the sun gear and the ring gear. The second gear element of the gear assembly may be defined by the planetary carrier or the ring gear of the second gear arrangement. The third gear element of the gear assembly may be defined by the sun gear of the second gear arrangement.

The gear assembly may include a plurality of drive transmission mechanisms defined by a plurality of clutches which is configured to selectively connect/disconnect the gear elements of the first and second gear arrangements to one another. The drive transmission mechanisms may further be defined by a plurality of brakes for connecting/disconnecting the gear elements of the first and second gear arrangements to a fixed member, such as a casing of the gear assembly, to restrict rotation. The drive transmission mechanisms may be actuated via a controller allowing the controller to change the configuration of the drive unit as well as a gear ratio of the first and/or second gear arrangements.

The gear assembly may define a Lepelletier gear assembly.

The drive means may be in the form of an internal combustion engine, an electrical motor, a flywheel, and the like. The drive means may include an input shaft which is connected to the second gear element of the gear assembly. One end of the input shaft and the second gear element may have corresponding engagement formations allowing the drive means and the second gear element of the gear assembly to be coupled together and drive to be transferred.

In a first example embodiment, the electrical/hydraulic mechanism may be in the form of an electrical machine configurable as one of an electrical motor/alternator and electrical generator. In a second example embodiment, the electrical/ hydraulic mechanism may be in the form of a hydraulic mechanism configurable as one of a hydraulic motor and pump. The electrical/hydraulic mechanism may include a shaft which is connected to the third gear element of the gear assembly. More specifically, the electrical/hydraulic mechanism may be connected to the third gear element via a gear train or co-axially connected to the third gear element.

The drive unit may further include an energy storage means associated with the electrical/hydraulic mechanism. With the electrical/hydraulic mechanism in the form of an electrical machine, the energy storage means may be in the form of a battery, a capacitor, a fuel cell, or the like. The electrical machine may be in electrical communication with the energy storage means. With the electrical/hydraulic mechanism in the form of a hydraulic mechanism, the energy storage means may be in the form of a hydraulic accumulator. The hydraulic mechanism may be in fluid flow communication with the energy storage means.

In the first and fourth configurations with the electrical/hydraulic mechanism in the form of the electrical machine, the electrical machine may act as an electrical generator/alternator to convert kinetic energy from the third gear element into electrical potential energy to be stored by the energy storage means. In the first configuration, excess drive from the drive means which is not required at the drive shaft may therefore be stored as electrical potential energy. In the fourth configuration drive from the drive shaft and the vehicle’s wheels may be stored as electrical potential energy while reducing the drive of the drive shaft and subsequently the speed of the vehicle. In the second and third configurations, the electrical machine may act as a motor to convert the electrical potential energy from the energy storage means into kinetic energy. Drive from the drive means may therefore be supplemented by drive from the electrical machine.

Similarly, in the first and fourth configurations with the electrical/hydraulic mechanism in the form of the hydraulic mechanism may act as a pump to utilise kinetic energy from the gear assembly to provide pressurised hydraulic fluid to the energy storage means, thereby storing potential energy in energy storage means. In the first configuration, excess drive from the drive means which is not required at the drive shaft may be stored as hydraulic potential energy. In the fourth configuration drive from the drive shaft may be stored as hydraulic potential energy while reducing the drive of the drive shaft and subsequently the speed of the vehicle. In the second and third configurations, the hydraulic mechanism may act as a hydraulic motor to convert stored potential energy from the energy storage means into kinetic energy. Drive from the drive means may therefore be supplemented by drive from the hydraulic mechanism. Alternatively, the hydraulic mechanism may comprise an open-loop, overcentre, variable displacement hydraulic mechanism, in the form of a plurality of axially reciprocating pistons and an associated manipulatable swash-plate arrangement which is controllable to move over-centre.

The drive means may be permanently connected to the second gear element of the gear assembly without the need for a torque converter. When the vehicle is stationary and the drive means is idling at the required speed not to stall, the drive produced by the drive means while idling is transferred to the electrical/hydraulic mechanism which is configured to convert the drive to potential energy and store it in the energy storage means. When a user wishes to accelerate, drive from the drive means may be directed to the drive shaft with some of the drive diverted to the electric/hydraulic mechanism. As the vehicle’s speed is increased less drive from the drive means may be diverted to the electric/hydraulic mechanism until a certain speed where drive from the electric/hydraulic mechanism supplements the drive from the drive means.

The drive unit further provides a wider speed range for each gear ratio due to the electrical/hydraulic mechanism’s ability to increase the drive delivered to the drive shaft while the drive from the drive means remains constant. More specifically, the drive unit may be configured to adjust the speed of the third gear element thereby providing a wider speed range for each gear.

The drive unit may furthermore comprise a control system to control interactions, configurations, and gear rations of different components of the drive unit.

The third gear element of the gear assembly in known drive units is either locked to a case of the gear assembly, whereby the third gear element remains stationary, or to another gear element, whereby the third gear element rotates with the other gear element. The drive unit may be configured to allow drive, in the form of speed and/or torque, of the third gear element to be controlled by the electrical/hydraulic mechanism.

According to a second aspect of the invention, there is provided a method of operating a drive unit, the method comprising one of i) driving a drive shaft by at least one of a drive means and an electrical/hydraulic mechanism selectively configured as a motor via a first and second gear arrangement; and ii) configuring the electrical/hydraulic mechanism as a generator/pump and driving the electrical/hydraulic mechanism via at least one of the drive means and the drive shaft.

The method may include storing potential energy in an energy storage means associated with the electrical/hydraulic mechanism configured as a generator/pump, by driving the electrical/hydraulic mechanism via the drive means and/or the output drive.

These and other features of the invention are described in more detail below. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The invention will now be described by way of example only with reference to the accompanying drawings wherein:

Figure 1 is a simplified cross-sectional view of a known drive unit;

Figure 2 is a cross-sectional view from the side of a drive unit in accordance with the invention; and

Figure 3 is a schematic diagram of the drive unit of Figure 2.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT OF THE INVENTION

In Figure 1 a known drive unit 100 having a first and second gear arrangement is shown. The first and second gear arrangements may collectively define a Lepelletier gear arrangement 102. The Lepelletier gear arrangement 102 is produced in that a Ravigneaux gear set 104 is preceded by a single planetary gear set 106 with the gear sets connected by various configurations of clutches 108 and brakes (not shown) that result in several selectable gears, typically from 6 to 10 selectable gears are obtained with present configuration. A sun gear 1 12 of the single planetary gear set 106 is typically permanently connected to a casing of the gear set and does not rotate or is free to rotate via an additional clutch. Therefore, in the current configuration based on the Lepelletier gear set the planetary carrier 1 10 or sun gear is either locked to the casing of the gear set or is configured to rotate freely. A planetary carrier 1 10 is connected to an internal combustion engine (not shown) through a fluid coupling 116. The fluid coupling 1 16 is in the form of a torque converter 1 16 which comprises a pump impeller (not shown), which is connected to an output shaft 1 14 of an internal combustion engine (not shown), and a turbine (not shown) which is connected to the planetary carrier 1 10 of the single planetary gear set 106 via an input shaft 1 18. In use, the impeller (not shown) is rotated by the internal combustion engine (not shown) which causes the turbine (not shown) to drive the planetary carrier 1 10 of the single planetary gear set 106.

The drive output of the drive unit 100 occurs via the ring gear 120 of the Ravigneaux gear set 104 and is connected via a differential 122 to drive wheels (not shown) of a vehicle (not shown).

Referring to figures 2 to 3, in which like features are indicated by like numerals, an example embodiment of a drive unit in accordance with the invention is generally designated by reference numeral 10.

The drive unit 10 comprises a gear assembly which includes a first gear arrangement 12 and a second gear arrangement 16 which is selectively couplable to the first gear arrangement to allow drive to be transferred between the first 12 and second 16 gear arrangements. The first gear arrangement 12 includes a first gear element, which in this example embodiment is defined by the ring gear 22, which is connected to a drive shaft 14 for operatively transferring drive between the gear assembly and a differential of a vehicle (not shown).

In this example embodiment of the invention, the gear assembly is in the form of a Lepelletier gear set with the first gear arrangement 12 in the form of a double planetary gear set, also called a Ravigneaux gear set. The first gear arrangement includes a plurality of gear elements which include a first sun gear 18, a second sun gear 20, the ring gear 22, a set of first planetary gears 24, and a set of second planetary gears 26. The set of first planetary gears 24 meshes with the ring gear 22 and the first sun gear 18. The set of second planetary gears 26 meshes with the second sun gear 20 and the set of first planetary gears 24. The sets of first and second planetary gears 24,26 are connected to a planetary carrier 28.

The second gear arrangement 16 is in the form of a single planetary gear set which is located upstream from the first gear arrangement 12. The second gear arrangement 16 includes a plurality of gear elements which are selectively couplable to the gear elements of the first gear arrangement 12 to adjust the gear ratio between the first 12 and second 16 gear arrangements. The plurality of gear elements of the second gear arrangement includes a sun gear 30, a ring gear 32, and a set of third planetary gears 34 which is connected to a planetary carrier 36. The set of third planetary gears 34 meshes with the sun gear 30 and the ring gear 32.

The drive unit 10 further comprises a drive means 38 which is coupled to a second gear element of the second gear arrangement. In this example embodiment, the second gear element is defined by the ring gear 32 of the second gear arrangement 16 so that drive can be transferred from the drive means 38 to the second gear arrangement 16 and subsequently the drive shaft 14.

The drive means 38 is in the form of an internal combustion engine having an input shaft 40 which is connected to the ring gear 32 of the second gear arrangement 16. One end of the input shaft 40 is coupled to the internal combustion engine 32 with an opposed end of the input shaft coupled to the ring gear 32. The opposed end of the input shaft 40 and the ring gear 32 includes corresponding engagement formations (not shown) so that the internal combustion engine 38 and the ring gear 32 are coupled and drive can be transferred from the internal combustion engine 38 to the ring gear 32.

The drive unit 10 also comprises an electrical and/or hydraulic mechanism 42 coupled to a third gear element of the gear arrangement. In this example embodiment, the third gear element is defined by the sun gear 30 of the second gear arrangement 16 so that drive can be transferred between the electrical/hydraulic mechanism 42 and the second gear arrangement 16 and subsequently the drive shaft 14. The electrical/hydraulic mechanism 42 is connected to the sun gear 32 of the second gear arrangement 16 via a gear train 44 which is coupled to a shaft 46 secured to the sun gear 30. Alternatively, the electrical/hydraulic mechanism 42 may be co-axially connected to the sun gear 46.

The drive unit 10 may be selectively configured in a first configuration wherein the drive means 38 transfers drive to either or both the electrical/hydraulic mechanism 42 and the drive shaft 14, and a second configuration wherein drive is transferred from the drive means 38 and the electrical/hydraulic mechanism 42 to the drive shaft 14.

In a first example embodiment, the electrical/hydraulic mechanism 42 is in the form of an electrical machine configurable as one of an electrical motor and generator. In a second example embodiment the electrical/hydraulic mechanism 42 is in the form of a hydraulic mechanism configurable as one of a hydraulic motor and pump.

The drive unit 10 may further include an energy storage means (not shown) associated with the electrical/hydraulic mechanism 42. With the electrical/hydraulic mechanism 42 in the form of an electrical machine the energy storage means (not shown) is in the form of a battery, a capacitor, or the like. The electrical machine 42 is in electrical communication with the energy storage means (not shown).

With the electrical/hydraulic mechanism 42 in the form of a hydraulic mechanism, the energy storage means (not shown) is in the form of a hydraulic accumulator. The hydraulic mechanism is in fluid flow communication with the energy storage means (not shown).

In the first configuration with the electrical/hydraulic mechanism 42 in the form of the electrical machine, the electrical machine 42 acts as an electrical generator or alternator to convert kinetic energy from the sun gear 30 of the second gear arrangement 16 into electrical potential energy. The electrical potential energy is then stored in the energy storage means (not shown). Excess drive produced by the drive means 38 which is not required at the output shaft 14 is therefore diverted to the electrical machine 42 and stored as electrical potential energy in the energy storage means (not shown).

In the second configuration the electrical machine 42 acts as an electrical motor to convert the electrical potential energy from the energy storage means (not shown) into kinetic energy. The drive produced by the drive means 38 is therefore supplemented with drive from the electrical motor 42. Similarly, in the first configuration with the electrical/hydraulic mechanism 42 in the form of the hydraulic mechanism, the hydraulic mechanism 42 acts as a pump to utilise kinetic energy from the sun gear 30 of the second gear arrangement 16 to provide pressurised hydraulic fluid to the energy storage means (not shown), thereby storing potential energy in the energy storage means (not shown). Excess drive produced by the drive means 38 which is not required at the output shaft 14 is therefore diverted to the hydraulic mechanism 42 and stored as hydraulic potential energy in the energy storage means (not shown).

In the second configuration, the hydraulic mechanism 42 acts as a hydraulic motor to convert the stored potential energy from the energy storage means (not shown) into kinetic energy. The drive produced by the drive means 38 may therefore be supplemented with drive from the hydraulic motor 42.

In the first configuration the drive means 38 drives the electrical/hydraulic mechanism 42 and the drive shaft 14 in a drive-splitting configuration. In this drive-splitting configuration, the drive means 38 is operated at optimal fuel efficiency which may cause the drive means to produce excess drive than what is required at the drive shaft. At optimal fuel efficiency the drive means 38 may produce an excess amount of drive which is not required at the output shaft 14 due to the current speed of the vehicle. The excess drive is then diverted to the electrical/hydraulic mechanism 42, with the electrical/hydraulic mechanism configured to convert the excess drive into potential energy for storage in the energy storage means (not shown).

In the second configuration the drive means 38 and the electrical/hydraulic mechanism 42 drives the drive shaft 14 in a drive-summing configuration. In the second configuration, the drive means 38 while operated at optimal efficiency does not produce sufficient drive to match the drive required at the drive shaft 14. The electrical/hydraulic mechanism 42 is then configured to transfer drive to the drive shaft to supplement the drive produced by the drive means 38.

The drive unit 10 may further be selectively configured in a third configuration. In the third configuration the gear elements of the gear assembly 12,16 are coupled together allowing the drive means 38, electrical/hydraulic mechanism 42 and drive shaft 14 to be locked together. In the third configuration the drive means 38 and the electrical/hydraulic mechanism 42 is in a torque-summing configuration.

The drive unit 10 may further be selectively configured in a fourth configuration. In the fourth configuration drive from the output shaft 14 is reduced by transferring drive from the output shaft 14 to the electrical/hydraulic mechanism 42. In the fourth configuration the drive shaft 14 drives the electrical/hydraulic mechanism in a regenerative braking configuration with the electrical/hydraulic mechanism configured to convert the drive into potential energy for storage.

The drive means 38 may be permanently connected to the sun gear 30 without the need for a torque converter. When the vehicle is stationary and the drive means 38 is idling at the required speed not to stall, the drive of the drive means 38 is transferred to the electrical/hydraulic mechanism 42 with the electrical/hydraulic mechanism 42 configured to convert the drive to potential energy and store it in the energy storage means (not shown). When a user wishes to accelerate, drive from the drive means 38 is directed to the drive shaft 14 with some of the drive diverted to the electric/hydraulic mechanism 42. As the vehicle’s speed is increased less drive from the drive means 38 is diverted to the electric/hydraulic mechanism 42 until a certain speed where drive from the electric/hydraulic mechanism 42 supplements the drive from the drive means 38.

The first 12 and second 16 gear arrangements further include a plurality of drive transmission mechanisms (not shown) defined by a plurality of clutches which are configured to selectively connect and disconnect the gear elements of the first 12 and second 16 gear arrangement to one another. The drive transmission mechanism may further be defined by a plurality of brakes for connecting and disconnecting the gear elements of the first and second gear arrangements to a fixed member to stop rotation. The drive transmission mechanism (not shown) may be actuated via a controller (not shown) allowing the controller to change the configuration of the drive unit 10 as well as a gear ratio of the first and/or second gear arrangements. The drive unit 10, therefore, provides a wider speed range for each gear step as opposed to known drive units due to the electrical/hydraulic mechanism’s 42 ability to increase the drive and subsequently speed delivered to the drive shaft 14 within the selected gear. More specifically, the drive unit is configured to adjust the speed of the third gear element thereby providing a wider speed range for each gear. The drive unit 10, therefore, provides continuously variable adjustment of the speed-gear ratio.

In known drive units, the third gear element of the gear assembly is either locked to a case of the gear assembly, whereby the third gear element remains stationary, or to another gear element, whereby the third gear element rotates with the other gear element. The drive unit of the current invention is however configured to allow drive, in the form of speed and/or torque, of the third gear element to be controlled by the electrical/hydraulic mechanism.

It will be appreciated that the invention teaches a drive unit 10 that optimise the drive efficiency and performance of a hybrid drive system.

It will be appreciated by those skilled in the art, that the invention is not limited to the precise details as herein described and that many different configurations are possible without departing from the scope and spirit of the invention. For example, the electrical/hydraulic mechanism may be connected to any of the gear elements of either the first or second gear arrangements. Also, the electrical/hydraulic mechanism could be replaced by any device which can add and/or subtract drive/speed from the first or second gear arrangements to allow the drive means to operate at optimal efficiency.

The description is presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention.