TECHNICAL FIELD

The present invention relates to a differential gear arrangement. In particular, the invention relates to differential gear arrangements for the drive shafts of a vehicle. However, although the invention will mainly be described in relation to differential gear on the drive shaft of a vehicle, the invention is also applicable for differential gear arrangements used in other applications, such as for central differentials or non-driven differentials.

BACKGROUND

Vehicles, and in particular road going vehicles with more than two wheels, have issues with traction in curves as the outer and inner wheels on an axle will rotates at different speeds, which may e.g. cause slip. One technical solution to this may be a differential gear. An example of a differential gear for a driving axle works by distributing torque from a drive shaft via a pinion to a ring gear or crown gear arranged on one of two half axle shafts. Each of the two half axle shafts may be arranged to drive a wheel of the vehicle. The rotation of the crown gear is transferred to two or more differential pinions that are in meshed connection with each of a differential side gear, which are, respectively, arranged rotationally fixed on the respective half axle shaft.

The differential gear may distribute torque evenly when the vehicle is driven straight ahead on a surface with homogenous friction, while in a curve the torque and rotation may be distributed so that the wheels are allowed to rotate at different speeds. However, as the torque may be distributed in favor of the half axle with the least resistance, there is a risk that reduced traction in corners or in conditions with varying friction will occur.

Several devices and systems exist that are arranged to mitigate or prevent traction losses, such as differential locks, limited slip differentials or systems that may redistribute the torque from the differential by for example inducing resistance in one of the axles with controlled braking. Such solutions are often reactive rather than proactive and/or may result in energy losses and increased wear on, for examples, the brakes of the vehicle. Typically, these systems are engaged and affect the powertrain even when driving on a straight road, i.e. in a straight line. There is hence a need to further improve the controllability of the differential gear while maintaining or minimizing the energy losses. SUMMARY

It is an object of the present invention to provide a differential gear arrangement which is controllable in relation to an intended path of a vehicle, while maintaining energy loss levels compared to more common differential gears. This object is at least partly achieved by an arrangement according to claim 1

According to a first aspect of the invention there is provided a differential gear arrangement for a vehicle, the differential gear arrangement comprising a first planetary gear set. The first planetary gear set comprising a first sun gear arrangement, a first plurality of planetary gears in meshed connection with the first sun gear arrangement and in connection with a first planet carrier, and a first ring gear in meshed connection with the first plurality of planetary gears. The differential gear arrangement further comprises a second planetary gear set, comprising a second sun gear arrangement, a second plurality of planetary gears in meshed connection with the second sun gear arrangement and in connection with a second planet carrier, and a second ring gear in meshed connection with the second plurality of planetary gears. The differential gear arrangement further comprises a rotational control means connected to each one of the first and the second ring gears, for controlling a relative difference in rotational speed between the first planet carrier and the second planet carrier. The first and second planetary gear sets may be formed as common planetary gear sets which are arranged sufficiently adjacent to each other to allow the rotational control means to connect to each one of the first and the second ring gears. The wording "rotational control means" should in the following and throughout the entire description be interpreted as an

arrangement which may provide a rotational output torque which is

transferred to each one of the first and the second ring gears. The rotational output of the rotational control means may be controlled in relation to both a rotational direction and a rotational speed, and the connection to the first and the second ring gears is such that the rotational direction of the first ring gear will be reversed compared to the rotational direction of the second ring gear. Furthermore, the connection between the rotational control means and the first and second ring gears may be provided by means of gears in meshed connection, further described below. However, other alternatives are of course conceivable, such as connection by means of friction, belt, chain etc.

Furthermore, it should readily be understood that a rotational speed of the first planet carrier and the second planet carrier relates to a rotation which may be induced by kinetic energy of the vehicle or by the vehicle drive train, wherein the first planet carrier and the second planet carrier may be connected to a wheel of the vehicle, respectively. The wording "controlling a relative difference in rotational speed between the first planet carrier and the second planet carrier" should be understood as the reaction on rotation of planet carriers in planet gear sets when the ring gears are rotated, wherein two ring gears may be controlled in counter rotation to each other, which may cause a relative difference in rotational speed for the planet carriers.

The present invention is based on the insight that by providing a first and second planetary gear sets with a rotational control means implemented as a differential gear arrangement it is possible to control the rotational speed difference by controlling the rotational speed and direction of the rotational control means. An increase in speed of the rotational control means increases the difference, while a decrease in speed decreases the difference.

Furthermore, the present invention allows for proactive control of the different speed of the wheels of the vehicle. A measurable curve input or a steering angle input may be used to control the rotational control means. The present invention allows for control of rotation output, without increased wear on for example brakes. Hence, the energy losses may be less than that of a torque vectoring system which brakes with individual brakes. Additionally, while driving in a straight driving direction, without frictional differences on the road surface, the rotational control means can be stationary, causing no additional energy losses compared to for example an automatic gear box in the driveline. If the control system were to malfunction so that the rotational control means locks, a differential gear arrangement according to the invention would still work as an ordinary differential gear. According to an example embodiment of the present invention the rotational control means may be in meshed connection with each one of the first and the second ring gears. Hereby, the wear and the energy losses may be kept minimal compared to for example a friction connection. Also, a relatively secure connection between the rotational control means and the first and second ring gears is provided.

According to an example embodiment of the present invention, the rotational control means may comprise a pinion arranged between the first and second ring gears and in meshed connection with each one of the first and the second ring gears. The first and the second ring gear may be provided with external bevel gears to mesh with the pinion. The external gears may be integrated with the ring gears, however, they may also be attached to the ring gears by suitable fastening means. Alternatively, according to another example embodiment of the present invention, the rotational control means may comprise a first and a second rotational control shaft, respectively in meshed connection with circumferentially arranged gears of the first and the second ring gears, wherein the first rotational control shaft is in meshed connection with the second rotational control shaft.

Hereby, robust connections between the ring gears and the rotational control means are provided, wherein one rotational input controls both ring gears. According to an example embodiment of the present invention the rotational control means may be connected to a variable transmission arrangement connected to a drive train of the vehicle. The connection to the drive train allows the rotational control means to control the rotational speed difference between the first planet carrier and the second planet carrier as a function of the drive train's rotational speed.

A "variable transmission" should be understood as a transmission arrangement which provides a rotational output, wherein transmission ratio may be controlled. The variable transmission may be a continuously variable transmission, whereby the transmission ratio is continuously variable between a minimum and a maximum transmission ratio.

According to an example embodiment of the present invention the variable transmission arrangement may comprise an elevation controlled disc, the elevation controlled disc is arranged perpendicularly to a drive train disc connected to the drive train, such that a circumferential surface of the elevation controlled disc is connected to the drive train disc by means of friction. The friction connection may also be a fluid connection, meaning that the drive train disc causes a fluid to have a rotational flow which is transferred to the elevation controlled disc being in contact with the fluid. The drive train disc may for example be connected to the vehicle transmission, possibly with a high transmission ratio to give the drive train disc a higher rotational speed than the vehicle drive shaft. The higher rotational speed may be

advantageous for transferring rotational motion in fluid connections.

According to an example embodiment of the present invention the elevation controlled disc may be displaceable along a diameter of the drive train disc, such that a transmission ratio of the variable transmission arrangement correlates to the radial distance of a friction connection point to the centre of the drive train disc. The wording "diameter" should be

understood as a line from one circumferential point on the disc to the opposite circumferential point, the line crossing the centre of the disc. Furthermore, the wording "friction connection point" should be understood as the point on the drive train disc's surface where the circumferential area of the elevation control disc is connected by friction. Consequently when the elevation controlled disc has a frictional connection to the centre of the drive train disc no rotation will be transferred to the elevation controlled disc. The "radial distance", which is the distance from the centre of the drive train disc to the friction connection point, decides the rotational speed transferred to the elevation controlled disc from the drive train disc. An "elevation controlled disc" should be understood as a disc which is displaceable along its axis of rotation. Furthermore, the elevation controlled disc is connected to the rotational output of the variable transmission. For example, the elevation controlled disc may be arranged on an output shaft of the variable transmission arrangement, along which it is displaceable.

Alternatively, the shaft may be displaceable while the elevation controlled disc is rotational ly fixed on the shaft.

According to an example embodiment of the present invention the elevation controlled disc may be displaceable along a diameter of the drive train disc, such that a rotational direction of an output of the variable transmission arrangement correlates to a radial direction of a friction connection point. An advantage with such an arrangement is that the transmission ratio may vary from zero to the maximal transmission ratio in both directions as the elevation controlled disc may be displaced from the centre of the drive train disc in both directions. According to an example embodiment of the present invention the displacement of the elevation controlled disc is controlled by a steering arrangement of the vehicle such that a displacement of said elevation controlled disc is controlled by the steering arrangement of said vehicle.. A "steering arrangement" should be understood as for example the steering rack of a vehicle. However, this may also be understood as part of a hydraulic steering or electric steering. The steering arrangement may be connected in such a way as to control the elevation of the elevation controlled disc, such that its displacement correlates to the steering input of a driver. The elevation controlled disc may be located at the centre of the drive train disc when the steering input indicates a driver's intention to drive straight ahead. An advantage of this example embodiment is that variable transmission provides an output torque proportional to both drive train rotational speed and to the steering input's magnitude and direction. Hereby, the relative difference in rotational speed between the first planet carrier and the second planet carrier may be controlled by the steering and may be correlated to the vehicle speed.

According to an example embodiment of the present invention the displacement of the elevation controlled disc may be controlled by a lateral acceleration sensing arrangement of the vehicle. A "lateral acceleration sensing arrangement" should be understood as an arrangement displacing the elevation controlled disc in relation to lateral acceleration of the vehicle, for example a resiliently suspended weight displaceable parallel with the elevation controlled disc. Alternatively, the elevation controlled disc may be controlled by an axial actuator connected to a vehicle sensor or to an electronic control unit (ECU) connected to a vehicle data network, whereby data from one or more vehicle sensors may be aggregated to an actuator control signal indicative of vehicle dynamics such as lateral acceleration. According to an example embodiment of the present invention the rotational control means may comprise a motor arranged to control a rotational speed and a rotational direction of the rotational control means. The motor may for example be an electric motor. An electric motor may be compact and requires only a wiring harness. Additionally an electric motor may have a small need for maintenance. According to one example embodiment of the present invention the electric motor may be controlled by means of a signal indicative of a lateral movement of the vehicle. The electric motor may be connected to one or more vehicle sensors such as an acceleration sensor, steering angle sensor, drive train rotation sensor, etc. or to an ECU connected to a vehicle data network, whereby data from one or more vehicle sensors may be aggregated to an actuator control signal indicative of vehicle dynamics such as lateral acceleration.

An "ECU" should be understood as an Electronic Control Unit and a "vehicle data network" may for example be a CAN network of a vehicle.

An advantage of this example embodiment is the flexibility of controlling the electric motor with a wide variety of signals, as well as the possibility to combine several signals.

According to one example embodiment of the present invention a drive shaft of the vehicle may be arranged to drive each of the first and second sun gear arrangement. The present invention may advantageously be used in the differential gear for a drive axle of a vehicle.

According to one example embodiment of the present invention, a drive gear may be arranged in a rotationally fixed connection with each of the first and second sun gear arrangements and arranged in meshed connection with the drive shaft of the vehicle. A "drive gear" should be understood as a gear which is driven by the drive shaft. The drive gear may be arranged between the first and the second planetary gear sets, as this may allow a balanced weight distribution and a central placement of the drive shaft. However, the drive gear may also be eccentric and/or arranged on either side of the first or the second planetary gear sets. "Rotationally fixed" should be understood as having the same rotational speed. According to one example embodiment of the present invention the first and second sun gear arrangements are each arranged on a sun gear shaft. The sun gear arrangements may comprise gears attached or formed on the sun gear shaft. According to one example embodiment of the present invention the drive gear is connected by splines on the sun gear shaft. However, the drive gear may also be press fitted, forged, cast on the sun gear shaft, forming an integral part or fixedly attached part of the sun gear shaft. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. For example, the various meshed connections described above can be external gears, internal gears, bevel gears, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:

Fig. 1 is a perspective view illustrating a vehicle provided with an example embodiment of a differential gear arrangement, the vehicle travelling in a curved path; Fig. 2 is a perspective view of an example embodiment of a differential gear arrangement;

Fig. 3 is a partly exploded perspective view of another example embodiment of a differential gear arrangement; and

Fig. 4 is perspective cutaway view of another example embodiment of a differential gear arrangement. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description. In the following, the present invention is described with reference to a car equipped with a differential gear arrangement adapted to distribute torque to the driven wheels. The vehicle is preferably equipped with a driveline comprising a motor and a transmission, the output of which is connected to the differential gear arrangement. Furthermore, the vehicle is also preferably arranged with a steering wheel adapted to provide control of the steering of the vehicle and to provide an input to the differential gear arrangement which is proportional to a steering wheel angle.

Fig. 1 shows an exploded view of an exemplary vehicle, here illustrated as a passenger car, in which a differential gear arrangement according to the present invention may be incorporated. The car is provided with a driveline, illustrated by a box, connected to a differential gear arrangement 1 . The differential gear arrangement 1 is connected to the driven wheels via shafts. In this illustrated example the car is front wheel drive, and only the front axle is provided with a differential gear arrangement. The car is illustrated as driving in a curve and if the front wheels would have been fixed on a shaft the wheels would have rotated with the same rotational speed. That is, with reference to the radius of the curve, either the inner wheel would have rotated more than required for the distance of the inner curve or the outer wheel would have rotated less than required for the distance of the outer curve. Both results in reduced grip, so that the vehicle deviates from the course set by the steering wheel through the turned angle of the two steerable front wheels. Fig. 1 illustrates with a small arrow adjacent to the inner wheel that the differential gear arrangement distributes the torque to rotate the outer wheel more, which is illustrated with a larger arrow adjacent to the outer wheel. Fig. 2 shows an illustration of the differential gear arrangement 1 in perspective view. In this example embodiment the differential gear

arrangement 1 comprises a first planetary gear set 2. The first planetary gear set 2 has a cogged sun gear 4 in meshed connection with three planetary gearwheels 5. The planetary gearwheels 5, also referred to as planetary gears 5 are evenly distributed around the sun gear 4. Each planetary gear 5 is rotatably arranged to a planetary gear carrier 6 which is arranged on one side of the planetary gear set 2 and arranged to rotate coaxially with the sun gear 4. The planetary gear carrier 6 is arranged with a wheel shaft 24 aligned with the rotational axis of the planetary gear carrier 6 and extending away from the first planetary gear set 2. A ring gear 7 is arranged around the planetary gears 5. The ring gear 7 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears 5, so that the planetary gears 5 may rotate along the inner circumference of the ring gear 7. The ring gear 7 is further formed to have an outer circumference arranged with beveled cogs 13a. The beveled outer cogs 13a are inclined so that the ring gear 7 has a larger diameter to the side of the first planetary gear set 2 where the planetary gear carrier 6 is arranged compared to the diameter on the side opposite the planetary gear carrier 6.

The differential gear arrangement 1 further comprises a second planetary gear set 3 arranged coaxially with the first planetary gear set 2. The second planetary gear set 3 is arranged on the opposite side of the first planetary gear set 2 from the planetary gear carrier 6. The second planetary gear set 3 has a sun gear (not shown) with cogs. This sun gear (not shown) is in meshed connection with three planetary gears (not shown). The planetary gears (not shown), are evenly distributed around the sun gear (not shown). Each planetary gear (not shown) is individually rotatably arranged to a planetary gear carrier (not shown) which is arranged on the side of the second planetary gear set 3 opposite to the first planetary gear set 2 and arranged to rotate coaxially with the sun gear (not shown). The planetary gear carrier (not shown) is arranged with a wheel shaft 25 aligned with the rotational axis of the planetary gear carrier (not shown) and extending away from the second planetary gear set 3. A ring gear 8 is arranged around the planetary gears (not shown). The ring gear 8 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears (not shown), so that the planetary gears (not shown) may rotate along the inner circumference of the ring gear 8. The ring gear 8 is further formed to have an outer circumference arranged with beveled cogs 13b. The beveled outer cogs 13b are inclined so that the ring gear 8 has a larger diameter to the side of the second planetary gear set 3 where the planetary gear carrier (not shown) is arranged compared to the diameter proximal to the first planetary gear set 2.

The second planetary gear set 3 is bilaterally symmetric to the first planetary gear set 2 in its composition and size. While components are mirrored in form they may move independently of the mirrored components in the other planetary gear set, as will be further explained. The sun gear 4 of the first planetary gear set 2 and the sun gear (not shown) of the second planetary gear set 3 are comprised in a sun gear arrangement (not shown) so that the respective sun gear is rotationally fixed with respect to its mirror component. The sun gear arrangement, with both sun gears, is rotatable around the rotational axis of the first 2 and second 3 planetary gear set. With reference to the first planetary gear set 2 the planetary gears 5 rotate as the sun gear arrangement, and consequently the sun gear 4, rotates. The rotation of the planetary gears 5 is reversed to the sun gear arrangement. As the planetary gears 5 rotate, they also move rotationally around the sun gear 4, transferring the rotational movement to the planetary gear carrier 6. The rotational movements are mirrored by the second planetary gear set 3 as long as both ring gears 7, 8 are fixed. Again returning to referencing the first planetary gear set 2, the ring gear 7 may influence the rotational movement of the planetary gears 5 and consequently that of the planetary gear carrier 6. While moving rotationally around the sun gear 4 the planetary gears 5 may move faster if the ring gear 7 rotates in the opposite direction to the sun gear 4, or the planetary gears 5 may move slower around the sun gear 4 if the ring gear 7 rotates in the same direction as the sun gear 4. Hence, the rotational direction of the ring gear 7, 8 controls if the sun gear driven rotation of the planetary gear carrier 6, (not shown) is faster or slower than the ratio defined by the size of the wheels. Furthermore, the rotational speed of the ring gear 7, 8 controls how much faster or slower.

The differential gear arrangement 1 illustrated in Fig. 2 further comprises a rotational control means 9 connected to the first 2 and second 3 planetary gear sets with a pinion 10 in meshed connection with the ring gears 7, 8 via their respective beveled outer cogs 13a, 13b. The pinion 10 is arranged transversely to the rotational axis of the first 2 and second 3 planetary gear sets. Rotation of the pinion 10 will cause the ring gears 7, 8 to rotate in opposite directions. The rotational control means 9 drives the pinion 10 via a shaft, for example the rotational control means 9 may comprise an electric motor 18 to drive the pinion. Fig. 3 shows a perspective partly exploded view of another differential gear arrangement 1 according to an embodiment of the invention. In this example embodiment the differential gear arrangement 1 comprises a first planetary gear set 2. The first planetary gear set 2 has a cogged sun gear 4 in meshed connection with three planetary gearwheels 5. The planetary gears 5, are evenly distributed around the sun gear 4. Each planetary gear 5 is individually rotatably arranged to a planetary gear carrier 6 which is arranged on one side of the planetary gear set 2 and to rotate coaxially with the sun gear 4. The planetary gear carrier 6 is arranged with a wheel shaft 24 aligned with the rotational axis of the planetary gear carrier 6 and extending away from the first planetary gear set 2. A ring gear 7 is arranged around the planetary gears 5. The ring gear 7 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears 5, so that the planetary gears 5 may rotate along the inner circumference of the ring gear 7. The ring gear 7 is further formed to have an outer circumference arranged with cogs 13c.

The differential gear arrangement 1 further comprises a second planetary gear set 3 arranged coaxially with the first planetary gear set 2. The second planetary gear set 3 is arranged on the opposite side of the first planetary gear set 2 from the planetary gear carrier 6. The second planetary gear set 3 has a sun gear 20 with cogs. This sun gear 20 is in meshed connection with three planetary gears 23. The planetary gears 23 are evenly distributed around the sun gear 20. Each planetary gear 23 is individually rotatably arranged to a planetary gear carrier (not shown) which is arranged on the side of the second planetary gear set 3 opposite to the first planetary gear set 2 and arranged to rotate coaxially with the sun gear 20. The planetary gear carrier (not shown) is arranged with a wheel shaft 25 aligned with the rotational axis of the planetary gear carrier (not shown) and

extending away from the second planetary gear set 3. A ring gear 8 is arranged around the planetary gears 23. The ring gear 8 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears 23, so that the planetary gears 23 may rotate along the inner circumference of the ring gear 8. The ring gear 8 is further formed to have an outer circumference arranged with cogs 13d. The rotational movement of the components in the differential gear arrangement 1 illustrated in Fig. 3 is similar to the movement of the components in the differential gear

arrangement 1 illustrated in Fig. 2. Furthermore, Fig. 3 shows an example of how the sun gear arrangement (not shown) may be driven. A driveshaft 17 connected to a driveline, such as the driveline illustrated in Fig. 1 , is further connected to a pulley 26. The pulley 26 further connects to a sun gear pulley 28 via a belt 27. The sun gear pulley 28 is in turn rotationally fixed to the sun gear arrangement, or preferably comprised on the sun gear arrangement. Hence, the driveline drives the sun gear arrangement via a belt drive, which illustrates one of several possible drive means such as chain drives, belt drives gear drives, etc.

The differential gear arrangement 1 illustrated in Fig. 3 further comprises a rotational control means 9 connected to the first 2 and second 3 planetary gear sets with a first 1 1 and second 12 rotational control shaft, respectively, in meshed connection with the ring gears 7, 8 via their respective circumferential outer cogs 13c, 13d. The first rotational control shaft 1 1 is in this exemplary embodiment arranged at the circumferential outer edge of the second planetary gear set 3, the control shaft 1 1 is parallel to the rotational axis of the first 2 and second 3 planetary gear sets. The first rotational control shaft 1 1 is provided with splines that engage with the outer cogs 13d of the ring gear 8. Furthermore, the first rotational control shaft 1 1 extends towards the first planetary gear set 2 and is provided with splines that engage with splines on the second rotational control shaft 12. The second rotational control shaft 12 is located at the same radial distance from the rotational axis of the first 2 and second 3 planetary gear sets as the first rotational control shaft 1 1 . The second rotational control shaft 12 extends further towards the first planetary gear set 2 and is provided with splines that engage with the outer cogs 13c of the ring gear 7. Rotation of the first rotational control shaft 1 1 will cause the second rotational control shaft 12 to rotate in the opposite direction, and consequently the rotation of the first rotational control shaft 1 1 will cause the ring gears 7, 8 to rotate in opposite directions. The rotational control means 9 drives the first rotational control shaft 1 1 , the rotational control means 9 may for example comprise an electric motor 18 to drive the first rotational control shaft 1 1 . The splines may run along the entire lengths of the first 1 1 and the second 12 rotational control shafts or they may be provided on the respective portions adjacent to the ring gears 7, 8 and the respective portions between the planetary gear sets 2, 3 where the rotational control shafts 1 1 , 12 overlap.

Fig. 4 shows a cutaway of another differential gear arrangement 1 according to an embodiment of the invention. In this example embodiment the differential gear arrangement 1 comprises a first planetary gear set 2. The first planetary gear set 2 has a cogged sun gear 4 in meshed connection with three planetary gearwheels 5. The planetary gearwheels 5, also referred to as planetary gears 5 are evenly distributed around the sun gear 4. Each planetary gear 5 is individually rotatably arranged to a planetary gear carrier 6 which is arranged on one side of the planetary gear set 2 and arranged to rotate coaxially with the sun gear 4. As illustrated in Fig. 4 the planetary gears 5 are each provided with central holes through which a pivot 29 or shaft extends from the planetary gear carrier 6. The pivots 29 or shafts transfers the rotational movement of the planetary gears 5 to rotation of the planetary gear carrier 6. The planetary gear carrier 6 is arranged with a wheel shaft 24 aligned with the rotational axis of the planetary gear carrier 6 and extending away from the first planetary gear set 2. A ring gear 7 is arranged around the planetary gears 5. The ring gear 7 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears 5, so that the planetary gears 5 may rotate along the inner circumference of the ring gear 7. The ring gear 7 is further formed to have an outer circumference arranged with beveled cogs (not shown). The beveled outer cogs (not shown) are inclined so that the ring gear 7 has a larger diameter to the side of the first planetary gear set 2 where the planetary gear carrier 6 is arranged compared to the diameter on the side opposite the planetary gear carrier 6.

The differential gear arrangement 1 further comprises a second planetary gear set 3 arranged coaxially with the first planetary gear set 2. The second planetary gear set 3 is arranged on the opposite side of the first planetary gear set 2 from the planetary gear carrier 6. The second planetary gear set 3 has a sun gear 20 with cogs. This sun gear 20 is in meshed connection with three planetary gears 23. The planetary gears 23, are evenly distributed around the sun gear 20. Each planetary gear 23 is individually rotatably arranged to a planetary gear carrier 30 which is arranged on the side of the second planetary gear set 3 opposite to the first planetary gear set 2 and arranged to rotate coaxially with the sun gear 20. The planetary gear carrier 30 is arranged with a wheel shaft 25 aligned with the rotational axis of the planetary gear carrier 30 and extending away from the second planetary gear set 3. A ring gear 8 is arranged around the planetary gears 23. The ring gear 8 has an inner circumference arranged with cogs which are in meshed connection with the planetary gears 23, so that the planetary gears 23 may rotate along the inner circumference of the ring gear 8. The ring gear 8 is further formed to have an outer circumference arranged with beveled cogs 13b. The beveled outer cogs 13b are inclined so that the ring gear 8 has a larger diameter to the side of the second planetary gear set 3 where the planetary gear carrier 30 is arranged compared to the diameter proximal to the first planetary gear set 2.

The second planetary gear set 3 is bilaterally symmetric to the first planetary gear set 2 in its composition and size. While components are mirrored in form they may move independently of the mirrored components in the other planetary gear set, as will be further explained. As shown in Fig. 4 the sun gear 4 of the first planetary gear set 2 and the sun gear 20 of the second planetary gear set 3 are comprised in a sun gear arrangement 22 so that the respective sun gear 4, 20 is rotationally fixed with respect to its mirror component. The sun gear arrangement 22, together with both sun gears 4, 20 is rotatable around the rotational axis of the first 2 and second 3 planetary gear set. The sun gear arrangement 22 may be formed in one piece with both sun gears 4, 20, or the sun gear arrangement 22 may comprise a shaft on which both sun gears 4, 20 are attached so that they are rotationally fixed relative to the shaft and each other. With reference to the first planetary gear set 2 the planetary gears 5 rotate as the sun gear arrangement rotates. The rotation of the planetary gears 5 is reversed to the sun gear arrangement. As the planetary gears 5 rotate, they also move rotationally around the sun gear 4, transferring the rotational movement to the planetary gear carrier 6. The rotational movements are mirrored by the second planetary gear set 3 as long as both ring gears 7, 8 are fixed. Again returning to referencing the first planetary gear set 2, the ring gear 7 may influence the rotational movement of the planetary gears 5 and consequently that of the planetary gear carrier 6. While moving rotationally around the sun gear 4 the planetary gears 5 may move faster if the ring gear 7 rotates in the opposite direction to the sun gear 4, or the planetary gears 5 may move slower around the sun gear 4 if the ring gear 7 rotates in the same direction as the sun gear 4. Hence, the rotational direction of the ring gear 7, 8 controls if the sun gear driven rotation of the planetary gear carrier 6, 30 is faster or slower than the ratio defined by the size of the wheels. Furthermore, the rotational speed of the ring gear 7, 8 controls how much faster or slower.

Furthermore, Fig. 4 shows an example of how the sun gear

arrangement 22 may be driven. A driveshaft 17 connected to a driveline, such as the driveline illustrated in Fig. 1 , is further connected to a gear 19. The gear 19 and the driveshaft 17 are arranged parallel to the rotational axis of the first 2 and second 3 planetary gear sets, and the gear 19 is arranged along the rotational axis so that it is located between the first 2 and second 3 planetary gear sets. The gear 19 is in meshed connection with a drive gear 21 comprised on the sun gear arrangement 22. The drive gear 21 is rotationally fixed to the both sun gears 4, 20. The sun gear arrangement 22 may be formed in one piece with drive gear 21 , or the sun gear arrangement 22 may comprise a shaft on which the drive gear 21 is attached so that it is

rotationally fixed relative to the shaft. Hence, the driveline drives the sun gear arrangement via a gear drive, which illustrates one further of several possible drive means.

The differential gear arrangement 1 illustrated in Fig. 4 further comprises a rotational control means 9 connected to the first 2 and second 3 planetary gear sets with a pinion 10 in meshed connection with the ring gears 7, 8 via their respective beveled outer cogs (not shown), 13b. The pinion 10 is arranged transversely to the rotational axis of the first 2 and second 3 planetary gear sets. Rotation of the pinion 10 will cause the ring gears 7, 8 to rotate in opposite directions. The rotational control means 9 drives the pinion 10 via a shaft, linkage and a transmission 14 connected to the driveline. There are several possible embodiments of a variable transmission 14. Fig. 4 shows a transmission comprising an elevation controlled disc 15, arranged perpendicularly to a drive train disc 16. The drive train disc 16 is connected to the drive train via the gear 19 and the drive shaft 17. The drive train disc 16 is preferably connected to the drive shaft with gears providing a high

transmission ratio so that the rotational speed of the drive train disc 16 is higher than the rotational speed of the drive train. The elevation controlled disc 15 is connected to the steering, either by mechanical linkage or via sensors and electrically controlled actuators, so that the elevation controlled disc 15 is displaceable along a diameter of the drive train disc 16. The elevation controlled disc 15 is connected to the drive train disc 16 at a point along its circumference so that the rotational speed of the drive train disc 16 is transferred to the elevation controlled disc 15 by friction. As the elevation controlled disc 15 is displaceable along the diameter of the drive train disc 16 the ratio of the rotational speed depends on the distance from the centre of the drive train disc 16. Furthermore, the rotational direction depends on which direction from the centre of the drive train disc 16 the elevation controlled disc 15 was displaced. When positioned at the centre of the drive train disc 16, no rotational movement is transferred to the elevation controlled disc 15. This central position may for example correspond to a steering angle indicating the driver's desire to travel along a straight path. The rotational movement of the elevation controlled disc 15 is transferred via linkage, illustrated by arrows in Fig. 4, to the pinion 10. By this arrangement the rotational control means 9 drive the ring gears 7, 8 in a direction controlled by the steering wheel and proportionate to the steering angle and to the rotational speed of the drive train. The following table indicates 27 exemplary scenarios. "Drive train output" indicates the output on the drive shaft and may indicate the speed of the vehicle. "Ay" indicates the curvature of the path or the speed at which the curve was taken. If for example positive indicates left, this means that a higher Ay represents a tighter left hand corner when the the speed is constant. Alternatively this may indicate a higher speed through a corner with a constant radius. "Steer" indicates the steering angle or the desired steering input of the driver. "Action on rotational control means" indicates the rotation it has to have for the car to be neutral in a corner. In this context neutral should be understood as steering without understeer or oversteer.

■ΪΞϊϊί llillBiiBlB ■ΙϊΙΙΙΙϊΙίΙΙΙ

1 increase + + +

2 increase + 0 0

3 increase + - -

4 increase 0 + +

5 increase 0 0 0

6 increase 0 - -

7 increase - + +

8 increase - 0 0

9 increase - - -

10 constant + + +

11 constant + 0 0

12 constant + - -

13 constant 0 + + 14 constant 0 0 0

15 constant 0 - -

16 constant - + +

17 constant - 0 0

18 constant - - -

19 decrease + + +

20 decrease + 0 0

21 decrease + - -

22 decrease 0 + +

23 decrease 0 0 0

24 decrease 0 - -

25 decrease - + +

26 decrease - 0 0

27 decrease - - -

When the rotational control means comprises an electrically controlled motor 18 the linkage and the variable transmission may be substituted by sensors that provide inputs that indicate the steering angle and the rotational speed of the drive train. Further signals may be used to improve distribution of the rotational movement. A lateral acceleration sensor may for example indicate reduced traction, a yaw rate sensor may indicate oversteer or understeer. Wheel speed sensors may indicate traction and speed.

Accelerator pedal sensor and gear selector sensor may indicate speed, improve indication on traction and indicate level of desired activity from the driver. Ambient sensors such as temperature and rain sensors may indicate traction. Weight sensors may indicate weight of vehicle and improve estimation of traction, as may tire pressure sensors. Cameras adapted to detect for example road lanes may indicate road curvature. All these signals may improve the use of the differential gear arrangement by increasing or decreasing the rotational speed of the rotational control means in combination with the inputs based on the steering input and the drive train input. Some signals could even replace the steering input and the drive train input, such as for example a road curvature input from a camera or a gps signal in combination with map data replacing the steering input. With reference to Fig. 1 the wheel shafts 24, 25 illustrated in Figs. 2-4 are connected to the front wheels. However, a differential gear arrangement 1 is also suitable for rear wheel drive cars when the differential gear is connected to the two rear wheels or all wheel drive cars when there are two differential gear arrangements. Furthermore, a differential gear arrangement 1 may be used as a central differential gear, for example on a four wheel drive vehicle, distributing torque to a rear and a front axle rotating at different speeds, having different turning radiuses in a curve. As with open differential gears there are several possible applications, in particular when there is a need to actively control the relative speed of the output shafts.

While there are three planetary gears 5, 23 in each planetary gear set of the illustrated exemplary embodiments of the invention, the number of planetary gears as well as the number of cogs on each gear, the cut of the cogs, etc. may be adapted to provide a desired gear ratio, robustness, reduction of noise and play. This and variations to arrange pinions to drive either sun wheel arrangements or a ring wheel are known to a person skilled in the art, and therefore such variations will not be further described in this application.

The electric motor 18 in the rotational control means 9 may be connected directly to the pinion 10, but it is also possible to use a

transmission between the pinion 10 and the electric motor 18 to achieve a transmission ratio.

It may even be possible to lock the sun gear arrangement and drive the planetary gear carriers in opposite rotational directions by driving the ring gears with the rotational control means. On a vehicle such as an agricultural tractor, having a differential gear arrangement connected to a rear driven axle, this would allow rotation of the tractor when the planetary gear carriers rotate in different rotational directions transferring the rotation to the two rear wheels via the wheel shafts. Other possible mechanical solutions to control the rotational control means is to arrange an axial piston pump or hydrostatic transmission connected to the drive train, wherein the displacement of the pistons is connected to a steering input. For example the swashplate of the pump may be connected to the steering input, so that an inclination of the swashplate is controlled. Alternatively the swashplate may be connected to a weight so that lateral movement of the vehicle causes the swashplate to move by the inertia of the vehicle. The hydraulic fluid typically drives a hydraulic motor, substituting the electric motor 18.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Furthermore, in the claims, the word "comprising" does not exclude other elements and the indefinite article "a" or "an" does not exclude a plurality.