A DIFFERENTIAL

Abstract

Some embodiments are directed to a differential including: a left-side planetary gear set having a sun gear configured to receive rotational drive input from a drive source, a ring gear in a torque connection with an electric motor and a carrier gear configured to be operatively coupled with a left-side vehicle drive member in a torque connection; a right-side planetary gear set having a sun gear configured to receive rotational drive input from the drive source, a ring gear in a torque connection with the electric motor and a carrier gear configured to be operatively coupled with a right-side vehicle drive member in a torque connection; wherein the sun gears of the left and right side planetary gear sets are rotationally fixed relative to each other and, in use, the amount of power transferred between the drive source and each of the respective drive members can be selectively controlled.

Claims

1. A differential, comprising: a left-side planetary gear set having a sun gear configured to receive rotational drive input from a drive source, a ring gear in a torque connection with an electric motor, and a carrier gear configured to be operatively coupled with a left-side vehicle drive member in a torque connection; a right-side planetary gear set having a sun gear configured to receive rotational drive input from the drive source, a ring gear in a torque connection with the electric motor, and a carrier gear configured to be operatively coupled with a right-side vehicle drive member in a torque connection; wherein the sun gears of the left and right side planetary gear sets are rotationally fixed relative to each other; and wherein the torque connection of the respective ring gears to the electric motor only permits rotation of the ring gears relative to one another in an equal and opposite sense, which rotation may be free or selectively powered by the electric motor.

2. The differential according to claim 1, wherein the respective ring gears are in an torque connection with the electric motor via a common bevel gear, rotation of which causes equal and opposite rotation of the respective ring gears.

3. A vehicle, comprising: the differential according to claim 1.

4. The vehicle of claim 3, wherein the vehicle drive members are wheels.

5. The vehicle of claim 3, wherein the vehicle drive members are sprockets for driving tracks on opposite sides of the vehicle.

6. A differential, comprising: a left-side planetary gear set having a sun gear configured to receive rotational drive input from a drive source, a ring gear in a torque connection with an electric motor, and a carrier gear configured to be operatively coupled with a left-side vehicle drive member in a torque connection; a right-side planetary gear set having a sun gear configured to receive rotational drive input from the drive source, a ring gear in a torque connection with the electric motor and, a carrier gear configured to be operatively coupled with a right-side vehicle drive member in a torque connection; and wherein the sun gears of the left and right side planetary gear sets are rotationally fixed relative to each other and, in use, the amount of power transferred between the drive source and each of the respective drive members can be selectively controlled by operating the electric motor to drive or apply torque to the ring gears in opposite directions.

7. (canceled)

8. A vehicle, comprising: the differential according to claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Some embodiments will now be described by way of non-limiting example with reference to the accompanying drawings, in which:

[0035] FIG. 1 is a schematic drawing of a related art differential;

[0036] FIG. 2 is a schematic drawing of a differential according to an embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0037] Some aspects and embodiments of the presently disclosed subject matter concern a type of limited slip differential which includes an electric motor to control the torque output to each of the left and right sides.

[0038] An electric motor assisted differential system is illustrated in FIG. 2, which represents a rear wheel drive vehicle with engine at the front (bottom of page) and differential 10 at the back between the two rear wheels 30.sub.L, 30.sub.R. Limited Ackerman steering may be achieved by the front two wheels (not shown).

[0039] The differential 10 has two planetary gear sets 12.sub.L, 12.sub.R arranged back-to-back. The left and right outputs of the differential 10 are the left and right carriers 14.sub.L, 14.sub.R with a common sun 16.sub.L, 16.sub.R as the drive input. Moreover, the sun gears 16.sub.L, 16.sub.R of the two planetary gear sets 12.sub.L, 12.sub.R are connected by a cross shaft 18, which is operatively coupled to a drive source 20 (i.e. features up stream in the vehicle powertrain such as a combustion engine, electric motor/generator and transmission etc.) through a bevel gear arrangement 23. The left and right ring gears 22.sub.L, 22.sub.R mesh with an additional bevel gear 24 that is operatively connected to an electric motor 26 of the differential 10. FIG. 2 shows that the bevel gear 24 is operatively connected to the (traction assisting) electric motor 26 via an additional gear reduction stage 28 (another planetary gear set) but this is not essential.

[0040] During straight-line driving with the electric motor 26 de-energised, the left and right carriers 14.sub.L, 14.sub.R output the same speed and torque. As such the torques exerted on the respective rings gears 22.sub.L, 22.sub.R are similar, providing that respective torques exerted thereby on the bevel gear 24 are equal and opposite so that both it and the ring gears 22.sub.L, 22.sub.R themselves do not turn.

[0041] During a turn to the right however with the electric motor de-energised, the left carrier 14.sub.L attached to the outside wheel will turn faster than the right carrier 14.sub.R attached to the inside wheel. With the bevel gear arrangement 23 driving the cross-shaft 18, the unit will behave as a normal differential. The torque will equally be applied to sun gears 16.sub.L, 16.sub.R and the torques exerted on the bevel gear 24 by the ring gears 22.sub.L, 22.sub.R will be equal and opposite and the bevel gear 24 will be free to rotate at the resultant speed. With the electric motor 26 de-energised its rotor will turn with the bevel gear 24 and the torque on the left and right sides of the differential 10 will balance such that it behaves as a typical differential.

[0042] If one of the wheels loses traction during straight-line driving, then in a typical differential the side that lost traction will begin to spin excessively. The present embodiment can address this by energising the electric motor 26 to provide a holding torque to balance the torque on the side that lost traction. Therefore, in such a situation, all the drive torque can be delivered to the side with traction to maintain all possible traction. By controlling the output torque from the electric motor 26, the torque output from the engine and transmission 20 to cross-shaft 18 (and sun gears 16.sub.L and 16.sub.R) can be directed to either output carrier 14.sub.L or output carrier 14.sub.R or both.

[0043] If one of the wheels loses traction during a clock-wise turn with the electric motor 26 energised the carrier 14.sub.L attached to the outside wheel will turn faster than the carrier 14.sub.R attached to the inside wheel. The ring gears 22.sub.L, 22.sub.R can be caused to turn in opposite directions at equal speeds upon energising the motor 26. The electric motor 26 will turn with the bevel gear 24 and can thus deliver torque as required to direct the power flow to the wheels. An anti-clockwise turn will operate in the opposite sense.

[0044] The differential 10 can also be used for skid-steering if desired.

[0045] A skid steered wheeled or tracked vehicle can be steered by forcing wheels or tracks on one side of the vehicle to run at different speeds to the wheels/tracks on the other side of the vehicle. For example, for tracked vehicles to steer, large driving force differences are required between tracks on opposite sides of the vehicle i.e. large braking torques on the inner tracks and high driving torques on the outer tracks. In the currently disclosed subject matter, differential gears and cross-shafts are used to control the relative speeds of the tracks and transfer the braking power from the inner track to the outer track to sustain the turn. Steering powers can be 3 to 4 times higher than powers for straight-line driving.

[0046] The control of the electric motor 26 will allow the mechanical transfer of the large regenerative torque and power (i.e. braking torque and power) from the inside wheel (or sprocket) to the outside wheel (or sprocket) through the differential. Therefore, the large skid-steering powers required for turning can be obtained from a compact (steer) motor 26 and differential coupled to a much smaller engine and transmission propulsion system 20.

[0047] The differential 10 can be used to control the relative speeds of opposing wheels and transfer the braking power from the inner wheel to the outer wheel to sustain the turn.

[0048] A vehicle traversing in a straight-line on a side-slope will require more torque on the wheel on the downward side and less torque in the wheel on the upward side. The traction assisting motor can be controlled to impart an equal and opposite holding torque which allows more torque to be added to the engine drive torque to the downward side wheel and allows torque to be subtracted from the engine drive torque to the upward side wheel while keeping the vehicle in a straight line.

[0049] Also, with the vehicle stopped (i.e. shaft 18 stationary), the traction assisting motor can impart equal and opposite torques and speeds at the wheels (or sprockets) causing the vehicle to pivot about its neutral axis (i.e. skid steer). A clockwise rotation of the vehicle is achieved by rotating the electric motor in one direction and an anti-clockwise rotation of the vehicle is achieved by rotating the electric motor in the opposite direction.

[0050] A similar arrangement to that described could be used for a skid steered tracked vehicle, whereby the wheels illustrated in FIG. 2 are replaced with sprockets for driving opposing tracks.

[0051] Power to drive the electric motor 26 could come from a larger generator attached to the engine 20.

[0052] It will be appreciated that whilst various aspects and embodiments of the presently disclosed subject matter have heretofore been described, the scope of the presently disclosed subject matter is not limited to the embodiments set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the spirit and scope of the appended claims. In particular, whilst bevel gears are shown here for illustration, a spur gear differential could also be used to cause equal and opposite rotation of the ring gears.