GB2348253A

GB2348253A - Differential assembly with yaw control motor

Info

Publication number: GB2348253A
Application number: GB9906911A
Authority: GB
Inventors: John Spooner
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1999-03-26
Filing date: 1999-03-26
Publication date: 2000-09-27
Anticipated expiration: 2019-03-26
Also published as: GB9906911D0; GB2348253B

Abstract

A differential assembly, for an electric or series hybrid vehicle, includes a differential mechanism 35 driven through a two speed epicyclic reduction unit 23 by an electric traction motor 21. The torque difference on differential output shafts 36, 37 is controlled by an electric yaw control motor 38 acting through epicyclic gear trains 39, 41. A carrier 44 of the first epicyclic 39 is held stationary by a housing member 34 so that when both output shafts 36, 37 rotate at the same speed the yaw control motor 38 is also stationary. Torque fro the yaw control motor 38 in one direction produces a torque in the same direction on the adjacent output shaft 37. The yaw control motor may also be used as a brake and the differential 35 may be driven by a conventional mechanical transmission (see figs 3 and 4). Hydraulic yaw control or traction motors may be used.

Description

Transmission Differential Assemblv The invention relates to differential assemblies for motor vehicle transmissions and to motor vehicle transmissions incorporating such assembles.

Differentials which control the relative rotation of a wheel on one side of a vehicle with a wheel on the other side of the vehicle are well known. Generally such differentials impart some form of braking effect on the relative rotation and thus rely on friction for their action. Additionally or alternatively a brake acting on one of the wheels may be applied in a controlled manner so as to enhance the traction available at the other wheel. Whilst both of these methods are generally satisfactory for short term use, they are inherently wasteful of energy due to their reliance on friction and may have overheating problems if used continuously on extended split 4 road surfaces. The present invention aims to avoid such problems.

According to one aspect of the invention there is provided a differential assembly for a motor vehicle transmission including a differential input member, a first differential output member for connection to a wheel on one side of the vehicle, a second differential output member for connection to a wheel on the other side of the vehicle and a yaw control motor acting between two of said differential members.

Preferably, said two differential members and the yaw control motor are interconnected by gear means such that a torque applied by the yaw control motor in one direction imparts a torque in one differential output member in one direction and a torque on the other differential output member in the other direction and vice versa.

Conveniently, said gear means is arranged such that when said two differential members rotate at the same speed, the yaw control motor does not rotate whereas when one of said two differential members rotates faster than the other of said two differential members the yaw control motor rotates in one direction and when the other of said two differential members rotates faster than said one of said two differential members the yaw control motor rotates in the other direction. This arrangement avoids unnecessary wear and tear on the yaw control motor.

Said gear means may comprise first and second gear trains, the first gear train including a first element connected to one of said two differential members, a second element which is fixed and a third element and the second gear train including a first element connected to the other of said two differential members, a second element which is connected to the yaw control motor and a third element which is connected to the third element of the first gear train. Said first and second gear trains may be epicyclic, the first element of each gear train comprising a respective sun gear, the second element comprising a respective planet carrier and the third element comprising a respective annulus gear, the planet carriers each carrying a respective set of planet gears which each mesh with the respective sun gear and annulus gear. The annulus gear may be common to both gear trains.

The yaw control motor may be electric or hydraulic.

The invention also provides a novel motor vehicle transmission. Hence, according to another aspect of the invention there is provided a motor vehicle transmission incorporating a differential assembly according to said one aspect of the invention. In such a transmission, the differential input member may be driven by a traction motor which may drive the differential input member through change-speed gearing. Conveniently, the change-speed gearing comprises an epicyclic reduction gear train. The traction motor may be electric or hydraulic.

The invention will now be described by way of example and with reference to the accompanying drawings, of which: Fig. 1 is a diagrammatic plan view of a motor vehicle incorporating a differential assembly and a transmission according to the invention; Fig. 2 is a diagrammatic sectional view of a drive motor and differential assembly shown in Fig. 1 ; Fig. 3 is a view similar to Fig. 1 showing an alternative transmission; and Fig. 4 is a view similar to Fig. 2 showing a differential assembly shown in Fig. 3.

Referring to Figs. 1 and 2, a motor vehicle includes an engine 11 driving an electrical generator 12 which supplies power through a controller 13 to a traction motor/differential assembly 14 which is mechanically connected to rear wheels 15, 16 through drive shafts 17,18. Such an arrangement is frequently referred to a series hybrid and would normally include a battery 65.

The traction motor/differential assembly 14 includes an electric traction motor 21 connected to the sun gear 22 of an epicyclic reduction gear train 23. This provides change-speed gearing between the traction motor and a differential input member 24 of a differential assembly 25 which transmits the drive from the traction motor to the rear road wheels 15 and 16. The sun gear 22 meshes with planet gears 26 which also mesh with an annulus gear 27. The planet gears 26 are rotatable on pins 28 on a carrier 29 fixed to the differential input member 24.

A selector sleeve 31 has external splines 32 which engage the gear teeth on the annulus gear 27 and internal splines 33 which, in one direction of axial movement of the selector sleeve 31, engage corresponding splines on the carrier 29 (as seen in the upper part of Fig. 2) and, in the other direction of axial movement, engage corresponding splines on a fixed housing part 34 (as seen in the lower part of Fig. 2). When the selector sleeve 31 is locked to the carrier 29, the sun gear 22, the annulus gear 27 and the carrier 29 are locked together and provide a direct drive from the traction motor 21 to the differential input member 24. When the selector sleeve 31 is engaged with the fixed housing member 34, this locks the annulus gear 27 to the fixed housing member 34 and the differential input member 24 rotates at a reduced speed to that of the rotor 21.

The differential assembly 25 includes a conventional bevel gear differential mechanism 35, a first differential output member in the form of an output shaft 36 connected to the left hand drive shaft 17 and a second differential output member in the form of another output shaft 37 connected to the right hand drive shaft 18.

Differential control means is provided between the differential input member 24 and the right hand output shaft 37 and this includes a yaw control motor in the form of an electric motor 38 which acts through gear means comprising a first epicyclic gear train 39 and a second epicyclic gear train 41.

The first epicyclic gear train 39 has a first element in the form of a sun gear 42 connected to the differential input member 24, a second element in the form of a carrier 43 which is fixed to the fixed housing member 34 and a third element in the form of an annulus gear 44. The second gear train 41 has a first element in the form of a sun gear 45 fast with the right hand output shaft 37, a second element in the form of a carrier 46 connected to the yaw control motor 38 and a third element in the form of an annulus gear 47 which is formed integrally with the annulus gear 44 of the first gear train therefore connected to it to form a common annulus gear 50. Planet gears 48 are carried by pins 49 on the carrier 43 of the first gear train and planet gears 51 are carried on pins 52 on the carrier 46.

The common annulus gear 50 is free to rotate, being carried on suitable bearings (not shown). The pitch circle diameters of the sun gears 42 and 45 are the same, as are the pitch circle diameters of the planet gears 48 and 51. This means that, in use, when the differential input member 24 and the output shafts 36 and 37 are all rotating at the same speed, then the carrier 46 of the second gear train 41 is stationary and there is no rotation of the yaw control motor 38.

The arrangement of the first and second epicyclic gear trains 39 and 41 is such that a torque applied by the yaw control motor 38 in one direction imparts a torque on one output shaft 36 in one direction and a torque on the other output shaft 37 in the other direction and vice versa. Furthermore, if, for example, the right hand output shaft 37 rotates faster than the left hand output shaft 36 then the yaw control motor 38 will rotate in the same direction. Conversely if the left hand output shaft 36 rotates faster than the right hand output shaft 37 then the yaw control motor 38 will rotate in the opposite direction. This means that if the yaw control motor 38 is used to apply a torque in one direction then a torque in the same direction is applied to the right hand output shaft 37 and a torque in the opposite direction is applied to the left hand output shaft 36 and vice versa. Thus the yaw control motor 38 can be used to apply more torque to one rear wheel 15 or 16 than the other rear wheel 16 or 15 to control yaw of the vehicle or slippage of the wheels 15, 16. Such control may be performed by the controller 13 using signals from wheel speed sensors 55,56 and/or a yaw sensor 57.

The traction motor/differential assembly 14 may also be used in a vehicle powered solely by a battery or by a fuel cell.

In the alternative arrangement shown in Figs. 3 and 4 parts which are identical to or similar to the corresponding parts in Figs. l and 2 carry the same reference numeral but with the addition of 100. An engine 111 drives a change speed transmission 161 which in turn drives a differential assembly 114 through a propshaft 162 which drives the differential input member 124 through a conventional bevel pinion 163 and crown wheel 164.

The yaw control motor 138 controls the differential assembly 125 through gear trains 139 and 141 in a similar manner to that described above for Figs. 1 and 2. The yaw control motor 138 is controlled by a controller 113 which draws power from a starter/generator 112 which is driven directly by the engine. Power is also available from a battery 165 and, if required, the load on the generator 112 can be varied by the controller 113 to dump power to the battery 165 or a resistive load and thereby vary the torque applied to the propshaft 162 to optimise traction.

By using an electric motor 38,138 to control the action of the differential assembly 25,125 there are no unnecessary friction losses. If required, the yaw control motor 38 or 138 can act as a retarder or brake to control the action of the differential assembly 25,125.

Although the gear trains 39,139 and 41, 141 act between the input member and an output member of the differential mechanism 35,135, it will be appreciated that such gear trains may be arranged to act between the two output members.

Instead of an electric yaw control motor 38 or 138, an hydraulic, e. g. hydrostatic, motor could be used. Similarly, the electric traction motor 21 could be replaced by an hydraulic motor.

Claims

CLAIMS 1. A differential assembly for a motor vehicle transmission including a differential input member, a first differential output member for connection to a wheel on one side of the vehicle, a second differential output member for connection to a wheel on the other side of the vehicle and a yaw control motor acting between two of said differential members.
2. A differential assembly according to claim 1 wherein said two differential members and the yaw control motor are interconnected by gear means such 'that a torque applied by the yaw control motor in one direction imparts a torque in one differential output member in one direction and a torque on the other differential output member in the other direction and vice versa.
3. A differential assembly according to claim 2 wherein said gear means is arranged such that when said two differential members rotate at the same speed, the yaw control motor does not rotate whereas when one of said two differential members rotates faster than the other of said two differential members the yaw control motor rotates in one direction and when the other of said two differential members rotates faster than said one of said two differential members the yaw control motor rotates in the other direction.

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4. A differential assembly according to claim 3 wherein said gear means comprises first and second gear trains, the first gear train including a first element connected to one of said two differential members, a second element which is fixed and a third element and the second gear train including a first element connected to the other of said two differential members, a second element which is connected to the yaw control motor and a third element which is connected to the third element of the first gear train.
5. A differential assembly according to claim 4 wherein said first and second gear trains are epicyclic, the first element of each gear train comprising a respective sun gear, the second element comprising a respective planet carrier and the third element comprising a respective annulus gear, the planet carriers each carrying a respective set of planet gears which each mesh with the respective sun gear and annulus gear.
6. A differential assembly according to claim 5 wherein the annulus gear is common to both gear trains.
7. A differential assembly according to any preceding claim wherein the yaw control motor is an electric motor.
8. A differential assembly according to any of claims 1 to 6 wherein the yaw control motor is an hydraulic motor.
9. A motor vehicle transmission incorporating a differential assembly according to any preceding claim.
10. A transmission according to claim 9 wherein the differential input member is driven by a traction motor.
11. A transmission according to claim 10 wherein the traction motor is an electric motor.
12. A transmission according to claim 10 wherein the traction motor is an hydraulic motor.
13. A transmission according to any of claims 10 to 12 wherein the traction motor drives the differential input member through change-speed gearing.
14. A transmission according to claim 13 wherein the change-speed gearing comprises an epicyclic reduction gear train.
15. A differential assembly substantially as described herein with reference to Figs. l and 2 or Figs. 3 and 4 of the accompanying drawings.
16. A motor vehicle transmission substantially as described herein with reference to Figs. l and 2 or Figs. 3 and 4 of the accompanying drawings.