GB2341585A

GB2341585A - Vehicle traction control

Info

Publication number: GB2341585A
Application number: GB9920102A
Authority: GB
Inventors: Carl Charles Bourne; Andrew Julian Burrows
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-09-05
Filing date: 1999-08-26
Publication date: 2000-03-22
Anticipated expiration: 2019-08-26
Also published as: GB9920102D0; GB2341585B; GB9819328D0

Abstract

A vehicle drive train includes four propeller shafts (22) each of which extends substantially longitudinally of the vehicle and is coupled to a respective drive shaft (24) which extends substantially transversely to the vehicle and has one end connected to a wheel (26). Couplings (28) between the drive shafts (24) and the propeller shafts (22) are arranged such that driving torque applied to each propeller shaft (22) in a direction to drive the vehicle forwards will tend to apply a torque to the drive shaft (24) about an axis substantially perpendicular to the axis of the drive shaft (24) so as to tend to move the wheel (26) vertically downwards relative to the vehicle. The torque supplied to each of the wheels (26) is controlled in such a manner as to provide the most desirable distribution of contact forces between the wheels (26) under various circumstances.

Description

Vehicle Traction Control The present invention relates to the improvement

of traction in vehicles and in particular, but not exclusively, to traction control in electric or socalled hybrid vehicles.

Generally, a typical vehicle drive train includes a single propeller shaft extending longitudinally of the vehicle. This propeller shaft is coupled to a drive shaft extending laterally of the vehicle with one end connected to a wheel of the vehicle. Thus, any driving torque, or braking torque, in the propeller shaft will tend to apply a torque to the drive shaft about an axis longitudinal to the vehicle. This tends to cause the end of the drive shaft connected to the wheel to be raised or lowered relative to the vehicle body. It will be understood that the drive shaft must be free or suspended to move in this manner in order to accommodate normal vertical movement of the vehicle wheels as a result of normal operational motion.

Clearly, with a single propeller shaft coupled to respective drive shafts for each wheel, the torque effect is consistent across an axle and so tends to lift or lower the whole rear or front of a vehicle. Thus, previously such torque induced reactions have tended to be consider as generally undesirable and potential dangerous as they can lead to vehicle instability.

It will be understood that vehicle traction control is an important factor in vehicle operation. Thus, it would be advantageous to make use of this torque induced effect in a controlled manner to improve the handling of the vehicle.

Accordingly the present invention provides a vehicle having a suspended part between at least two opposed wheels on opposite sides thereof and a drive train comprising two propeller shafts coupled through a respective coupling to a respective drive shaft, wherein each drive shaft extends substantially transversely to the vehicle and has one end connected to one of said wheels, and torque input means for applying a driving torque to each of said propeller shafts, wherein the respective couplings between the drive shafts and propeller shafts are arranged such that driving torque applied to each propeller shaft will tend to apply a torque to its respective drive shaft with a substantial torque component presented in an axis substantially perpendicular to the respective drive shaft so as to tend to move the wheel relative to the suspended part of the vehicle in order to alter the weight distribution between the opposed wheels, the system further comprising control means arranged to control the driving torques applied to each propeller shaft so as to produce controlled variation in the weight distribution between the opposed wheels and so the load presented at each of said opposed wheels.

Preferably the vehicle further comprising a driver operated control member, such as an accelerator, movable by the driver to control the torque applied to the wheels, and the control means is arranged to vary said torques at least partially independently of the operation of the control 5 member thereby to control said loads upon at least one of said wheels.

The control means may be arranged to vary the ratio of the torques applied to the two propeller shafts, or to produce pulsed changes in the torques applied to the two propeller shafts.

Preferably the vehicle also includes two further opposed wheels on opposite sides and the power train comprises two further propeller shafts coupled by respective further couplings to a respective one of two further drive shafts which extend substantially transversely to the vehicle and has one end connected to one of said two further opposed wheels, the torque input means being arranged to apply a driving torque to each of said four propeller shafts, and the further couplings between the further drive shafts and further propeller shafts being arranged such that driving torque applied to each further propeller shafts will tend to apply a torque to its respective further drive shaft with a substantial torque component presented in an axis substantially perpendicular to the respective further drive shaft so as to tend to move the respective wheel relative to said suspended part in order to alter the weight distribution between the opposed wheels of the vehicle.

The control means may be arranged to provide an increase in torque to one diagonally opposed pair of said wheels Whilst providing a decrease in torque to another diagonally opposed pair of said wheels.

Preferably the total torque applied to all of said wheels is controlled so as to remain at a value or level which is either substantially constant or controllable by the driver, typically through the control member.

Preferably the couplings are arranged such that if the driving torque applied to the propeller shaft is in a direction to drive the vehicle forwards, the torque applied to the drive shaft is in a direction so as to tend to move the wheel vertically downwards relative to a sprung or suspended part of the vehicle.

Indeed the present invention further provides a vehicle having two wheels on opposite sides thereof and a drive train comprising two propeller shafts each of which extends substantially longitudinally of the vehicle and is coupled to a respective drive shaft, wherein each drive shaft extends substantially transversely to the vehicle and has one end connected to one of said wheels, torque input means for applying a driving torque to each of said propeller shafts, wherein the couplings between the drive shafts and propeller shafts are arranged such that driving torque applied to the propeller shaft in a direction to drive the vehicle forwards will tend to apply a torque to the drive shaft about an axis substantially perpendicular to the axis of the drive shaft so as to tend to move the wheel vertically downwards relative to a sprung part of the vehicle.

Preferably, the vehicle further comprises means for detecting cornering of the vehicle, and the control means is arranged to increase the fraction of total drive torque applied to a wheel which is detected as being on the outside of a corner.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in 10 which:

Figure 1 is a schematic representation of a vehicle according to a first embodiment of the invention; Figures 2 and 3 are schematic end views of part of the vehicle of Figure 1; - Figure 4 is a schematic end view similar to Figure 3 in a vehicle according to a second embodiment of the invention; Figures 5a and 5b are schematic plan views of the embodiment of Figure 4; Figures 6 and 7 show one axle of the vehicle of Figure 4 under dillerent conditions; and Figure 8 is a cross section through the vehicle of Figure 4 during cornering.

Referring to Figure 1, a hybrid vehicle comprises an internal combustion engine 10, an electrical generator 12 driven by that engine 10 and a storage battery 14 for storing electrical energy produced by the generator 12. The hybrid vehicle also includes four electric motors 16a, 16b, 16c, 16d which are each driveable independently, using energy from the battery 14. The motors 16a, 16b, 16c 16d are under the control of a control unit 18 to produce respective driving torque for each of four wheels 20a, 20b, 20c, 20d.

Each of the motors 16 drives a respective propeller shaft 22a, 22b, 22c, 22d which extends longitudinally of the vehicle. Each propeller shaft 22a, 22b, 22c, 22d is connected to a drive shaft 24a, 24b, 24c, 24d which extends, in the embodiment depicted, at right angles to that propeller shaft 22a, 22b, 22c, 22d and transversely of the vehicle. Each drive shaft 24a, 24b, 24c, 24d drives a respective one of the two rear wheels 26a, 26b and two front wheels 26c, 26d. The propeller shafts 22 are coupled to the drive shafts 24 by means of bevel gear box couplings 28 which are arranged to rotate with the drive shafts 24 relative to the sprung or suspended parts of the vehicle during vertical wheel travel.

The bevel gear box couplings 28 are each arranged to provide a driving torque in a respective propeller shaft 22. Thus, as described in relation to only one coupling 28 for clarity, when the driving torque is in the direction which will drive the wheel 26 in a forward direction then the shaft 22 applies a torque to the drive shaft 24 through a bevel gear box coupling 28 about the longitudinal axis of the propeller shaft 22. In such circumstances, there is a reaction force to the driving torque in a direction which tends to lower the outboard end of the drive shaft 24. Thus, the wheel 26 is urged downwards relative to the sprung or suspended parts of the vehicle whilst that driving torque persists.

As can be seen in Figure 2, the downward reaction force F on the wheel 26 is equal to the torque T transmitted into the drive shaft 24 divided by the lateral distance d between the bevel gear box coupling 28 and the contact patch of the wheel 26.

Referring to Figure 3, the illustrated embodiment has an independent suspension system which means that the respective drive torque to each of the wheels 26 can be used to control each respective contact force F at each of the wheels 26 independently of the wheels 26, subject to obvious physical and dimensional constraints.

The contact force F cannot be increased to or at all of the wheels 26 for long periods or at the same time. The contact force F to each wheel 26 can be increased briefly, to provide an upward acceleration or movement of the vehicle body relative to the ground i.e. wheel contact patch. However, this upward movement will then decrease as the limit of vertical travel is reached.

The distribution of the total drive torque T can be varied to alter the vehicle weight distribution presented as load between the four wheels. Thus, an altered weight distribution can be sustained over longer periods in the steady state as the total contact force F can be kept constant. i. e. equal to the weight of the vehicle. In such circumstances, there are various ways in which the torque supply to the respective vehicle wheels can be controlled to improve the traction of the wheels. Typically, the controlled variations in torque for weight distribution are superimposed on top of the mean torque T to each wheel 26 which is controlled by the driver using the accelerator pedal in the usual manner for vehicle motion and acceleration.

In a first mode of operation, the control unit 18 alternates the torque supplied to all four wheels 26. As mentioned above, this will result in an oscillation of the contact force F for all of the wheels 26 about its mean value as the vehicle body moves up and down.

It is well known that, under some circumstances, if a vehicle is stuck in an area of soft ground where traction is not good, it is helpful to "bounce" the vehicle up and down to improve traction. In this invention, the same effect can be achieved by alternating the torque to all, four wheels simultaneously at a frequency approximately equal to the natural frequency of the vehicle in bounce, which is generally of the order of 1 or 2 Hz. This not only produces the desired vertical bouncing of the vehicle, but also ensures that, when the vehicle is travelling forwards, the maximum torque is provided to the wheels at the time when the contact force is greatest thereby Maximising traction.

In another mode of operation the invention can be used to improve traction in a situation where the wheels of the vehicle are on surfaces of different coefficient of friction. It is well known to control the torque applied to the wheels of a vehicle so that greater torque is applied to the wheel or wheels which are on a surface with higher coefficient of friction. This can be done passively using a mechanical differential, or actively by measuring the coefficient of friction at each wheel.

In the vehicle of Figure 1 the control unit 18 is arranged to monitor the coefficients of friction at each of the wheels 26. The control unit 18 can modify the torque distribution between the wheels 26 so as to provide a higher torque to wheels on surfaces with a higher coefficient of friction. It is due to such modified torque distribution that that wheel or those wheels in contact with higher friction surface will tend to be moved downwards most and will therefore take a higher proportion of the total weight of the vehicle than other wheels. Thus, the maximum tractive force available is higher than if the weight remained more evenly distributed between the wheels.

Alternatively, this traction effect can be achieved if the control means operates not by actually measuring the coefficient of friction at each of the wheels 26, but.by limiting the difference in speeds between the vehicle wheels 26. Thus, the control unit 18 will increase the torque to slower moving wheels and decrease the torque to faster moving wheels. This is the electrical equivalent of a mechanical differential.

In a vehicle with beam axles the invention can still be made to work, although the ways in which it can be controlled and utilised are more limited. Referring to Figure 4, in a second embodiment of the invention a vehicle has the same drive train layout as shown in Figure 1. However, the suspension is different in that the rear wheels 40a, 40b are mounted on opposite ends of a rigid beam 42, and the drive shafts 44a, 44b driving them are rigidly mounted in the beam 42.

The beam 42 is free to move relative to the sprung or suspended parts of the vehicle to allow vertical wheel travel. If the torques Ti and T2 applied to the two rear wheels 40a, 40b are the same then the resultant torque on the beam 42 will be zero. However, if one of the torques T1 or T2 is greater than the other, a resultant net torque will be produced in the beam 42 which will tend to raise one of the wheels 40a, 40b and lower the other relative to the sprung or suspended part of the vehicle.

As with the fully independent type suspension illustrated in figures 1-3 this effect of torque induced movement can be utilised in various ways. Firstly, if the torque distribution is oscillated from side to side at both the front and rear axles simultaneously at frequencies of the order of the roll frequency of the vehicle, i.e. typically of the order of 0. 5to 2Hz. This 15 'rocking motion will then be set up the vehicle so that the contact load force L on the two sides of the vehicle will oscillate in an out-of-phase manner. Provided the vehicle is in a forward gear the side with the greatest contact force L will be the side where the greatest driving torque is applied at any one time.

As an alternative the torques supplied to the two axles could be arranged to oscillate from side to side in an out of phase manner, as illustrated in Figure 5. This will increase the contact force at first in one diagonally opposite pair of wheels 40a, 40d and then in the other pair of wheels 40b, 40c in turn. While the contact force of one such pair is increased that of the other such pair will be decreased, and vice versa. Therefore the overall resultant movement of the suspended or sprung part of the vehicle will be substantially zero. With this embodiment the use of torque distribution control when the wheels are on surfaces of unequal coefficient of friction can be used in the same way as the first embodiment.

Referring to Figure 6, if one of the wheels 40a is on a surface with a lower coefficient of friction il than that coefficient 92 of the other three wheels then the torque supplied across an axle can be redistributed so as to reduce the driving torque Ti to that one wheel 40a and increase the driving torque T2 to the other wheel on the same axle. This will transfer the weight of the vehicle away from the wheel 40a having the least traction and therefore increase the effective total traction from all of the wheels. In order to prevent body roll, the torque and distribution across the other axle could be controlled in the opposite direction by the same amount.

In other circumstances it is important to keep the tractive torques at the wheels equal, rather than achieving the maximum total tractive force.

In such circumstances, for each axle, the torque to the wheel on the surface of lower coefficient of friction needs to be increased compared to that to the wheel on the surface of higher coefficient of friction, until the maximum tractive force, i.e. force in the forward direction is equal on the two wheels.

This would be particularly useful in a two-wheel drive application where the resulting change in load distribution at the other axle would not affect the total tractive torque.

Referring to Figure 7, the drive train layout of the invention can also be utilised to overcome grounding in some circumstances. If one wheel 40b is lifted off the ground due to grounding of the vehicle body there will be no wheel 40b ground contact and so no available traction from that wheel 40b. In order to simultaneously increase the available traction and transfer weight off the grounded part of the vehicle, the driving torque T1 to the ground contacting wheel 40a can be increased above that torque T2applied to the non-ground contacting wheel 40b. This torque differential will urge the ground contacting wheel 40a downwards with a force Fi and the nonground contacting wheel 40b upwards with a force F2. This will tend to transfer weight from the grounded part of the vehicle into the groundcontacting wheel 40a, and therefore help with freeing the vehicle.

The downward force on the ground-contacting wheel 40a is related to the difference between the driving torques Ti and T2of the two wheels 40a, 40b. Thus, it is possible to enhance this effect by applying a backward driving torque through the drive train to a braked or non-ground contacting wheel 40b and an increased forward driving torque to the ground contacting wheel 40a. This would preferably require braking of the non-ground contacting wheel 40b. Such braking could be achieved by co-ordinated control of the vehicle brakes which is known in conventional traction control systems.

It will also be understood from above that rather than only brake wheels 40 when there is ground clearance that deliberate selective braking of wheels whilst in motion could be used to amplify vehicle weight distributions by altering body movements. Thus, whilst the vehicle is in motion, individual wheels could be marginally braked against the torque applied in order to emphasis the torque differential across a wheel pair for relative body ie. suspended part lift or drop. Clearly, heavy braking to stop, or near stop, would be unusual but transient short term braking of individual wheels will provide the weight re-distributions desired for traction control, at least transiently.

It will be understood that there is an inherent hysteresis with most vehicle suspension arrangements. Thus, although only transient, weight redistributions as a result of torque differentials may affect traction control 15- for longer periods of time as the natural damping of the suspension arrangement oscillates about and returns to its steady state position.

As indicated above deliberate selective and deliberate wheel braking may be used to 'lift ' a vehicle in order to amplify down force in a driven wheel. Similarly, a vehicle may be "bounced" in order to find which wheels have better traction and then the vehicle 'set' in terms of the relative torque distribution between the wheels and vehicle weight distribution through body lift etc. for best or desired traction control. In such circumstances, it will be understood that a vehicle suspension arrangement will be used that can vary in terms of hardness and damping in order to retain the vehicle 'set' created by torque distribution. In any event, it will be understood that, for example upon vehicle take-off from a standing start additional traction can be provided to those wheels best suited to such acceleration by retention of an appropriate vehicle body orientation produced by differential torque -15 and sustained by the suspension arrangement or otherwise. The vehicle weight would then be re-aligned for more even distribution for normal driving.

It will be understood that each side of the vehicle could be lifted one after the other. Thus, one side would be braked preferably against a torque whilst the other is subject to an opposite torque to provide vehicle lift or 16- lowering. This lift or lowering will be sustained and the roles reversed to lift or lower the other side.

A further use of the present invention is with regard to straight or substantially straight line vehicle motion. It will be understood that a vehicle driven in a straight may be subjected to significant jostle due to striking pot-holes and ruts, cross winds and road camber etc. In such circumstances, it will be understood that such jostle may be ameliorated by torque differential and weight distribution in accordance with the traction control mechanism described above. The effect of altering torque across the wheels will adjust for the variations in friction coefficients of ground contact. Normally, the torque differentials will be pulsed for trim correction rather than sustained vehicle torque distribution or suspended part body orientation.

Referring to Figure 8, a further application of the invention is in the control of body roll in a vehicle, for example during cornering. By applying a greater driving torque T2 to the wheels 40b on the outside of the corner, than that the torque T1 applied to the wheels 40a on the inside of the corner, the vehicle body 42 is urged to roll towards the inside of the corner, thereby counteracting the normal tendency to roll towards the outside of the corner under centrifugal forces. This controlled re-distribution of driving torque can be made in response to detection of vehicle cornering, for example by means of lateral accelerometers, or by means of sensors of vehicle speed and steering angle. The fraction of the total driving torque applied to the outside wheels 40b is increased with increasing lateral acceleration during cornering so that the resistance to roll increases as 5 required to keep the vehicle body as level as possible.

As illustrated it is normal for the drive shafts to each wheel to be substantially perpendicular to its propeller shaft in order to maximise the torque ellect upon its respective wheel and so across a wheel pair. However, it will be understood by those skilled in the art that it is the perpendicular component of the torque which provides the effect in accordance with the present invention. Thus, the drive shafts could be arranged relative to their respective wheel and propeller shaft at an angle diflerent to perpendicular provided there is a significant perpendicular torque component applied to the wheel for reaction effect in accordance with the present invention.

Normally, an angle greater than 45 will be required for such a perpendicular torque component.

Claims

- isCLAIMS

1. A vehicle having a suspended part between at least two opposed wheels on opposite sides thereof and a drive train comprising two propeller shafts coupled through a respective coupling to a respective drive shaft, wherein each drive shaft extends substantially transversely to the vehicle and has one end connected to one of said wheels, and torque input means for applying a driving torque to each of said propeller shafts, wherein the respective couplings between the drive shafts and propeller shafts are arranged such that driving torque applied to each propeller shaft will tend to apply a torque to its respective drive shaft with a substantial torque component presented in an axis substantially perpendicular to the respective drive shaft so as to tend to move the wheel relative to the suspended part of the vehicle in order to alter the weight distribution between the opposed wheels, the system further comprising control means arranged to control the driving torques applied to each propeller shaft so as to produce controlled variation in the weight distribution between the opposed wheels and so the load presented at each of said opposed wheels.

2. A vehicle according to claim 1 further comprising a driver operated control member movable by the driver to control the torque applied to the opposed wheels, wherein the control means is arranged to vary said torques at least partially independently of the operation of the driver operated control member thereby to control said loads presented at each of said opposed wheels.

3. A vehicle according to claim 1 wherein the control means is arranged to vary the ratio of the respective torques applied between the two propeller shafts.

4. A vehicle according to claim 1 or claim 2 wherein the control means is arranged to produce pulsed changes in the respective torques applied to the two propeller shafts.

5. A vehicle according to any foregoing claim wherein there is provided two further opposed wheels on opposite sides of the vehicle and the power train comprises two further propeller shafts coupled by respective further couplings to a respective one of two further drive shafts which extend substantially transversely to the vehicle and has one end connected to one of said two further opposed wheels, the torque input means being arranged to apply a driving torque to each of said four propeller shafts, and the further couplings between the further drive shafts and further propeller shafts being arranged such that driving torque applied to each further propeller shafts will tend to apply a torque to its respective further drive shaft with a substantial torque component presented in an axis substantially perpendicular to its respective further drive shaft so as to tend to move the respective opposed wheel relative to said suspended part in order to alter the weight distribution between the opposed wheels of the vehicle.

6. A vehicle according to claim 5 wherein the control means is arranged to consider the opposed wheels as two diagonally opposed pairs and so provide an increase in torque across one diagonally opposed pair of said opposed wheels whilst providing a decrease in torque across the other diagonally opposed pair of said opposed wheels.

1

7. A vehicle according to claim 6 wherein the total torque applied to all of said opposed wheels is controlled so as to remain at a value which is either substantially constant or variably controlled by the driver through the control member.

8. A vehicle according to any foregoing claim wherein the couplings are arranged such that if the driving torque applied to each propeller shaft is in a direction to drive the vehicle forwards, the torque applied to the respective drive shaft is in a direction so as to tend to move the wheel vertically downwards relative to the suspended part of the vehicle.

9. A vehicle as claimed in any preceding claim wherein the respective propeller shafts are substantially arranged longitudinally within the vehicle.

10. A vehicle as claimed in any preceding claim wherein each drive shaft is arranged to be substantially perpendicular to its propeller shaft.

11. A vehicle having two wheels on opposite sides thereof and a drive train comprising two propeller shafts each of which extends substantially longitudinally of the vehicle and is coupled to a respective drive shaft, wherein each drive shaft extends substantially transversely to the vehicle and has one end connected to one of said wheels, torque input means for applying a driving torque to each of said propeller shafts, wherein the couplings between the drive shafts and propeller shafts are arranged such that driving torque applied to the propeller shaft in a direction to drive the vehicle forwards will tend to apply a torque to the drive shaft about an axis substantially perpendicular to the axis of the drive shaft so as to tend to move the wheel vertically downwards relative to a sprung part of the vehicle.

12. A vehicle according to claim 11 further comprising control means arranged to control the distribution of driving torque between the wheels.

13. A vehicle according to claim 11 or claim 12 further comprising means for detecting cornering of the vehicle, wherein the control means is arranged to increase the fraction of total drive torque applied to a wheel which is detected as being on the outside of a corner.

14. A vehicle substantially as hereinbefore described with reference to the accompanying drawings.