GB2345895A

GB2345895A - Vehicle steering by differentially driving steerable wheels

Info

Publication number: GB2345895A
Application number: GB9901296A
Authority: GB
Inventors: Carl Charles Bourne; Martin Ranson
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1999-01-22
Filing date: 1999-01-22
Publication date: 2000-07-26
Anticipated expiration: 2019-01-22
Also published as: GB2345895B; GB9901296D0

Abstract

A vehicle having steerable wheels 24, 26 driven by individual motors 16, 18 has the motors controlled to create a torque imbalance in response to the steering angle to reduce the turning circle. The torque imbalance may be triggered by the approach of the steering to the full lock position. The vehicle may have a hybrid drive system with all wheels driven by electric motors.

Description

A Vehicle This invention relates to vehicles and in particular to a vehicle which has a hybrid powertrain.

It is known to provide a vehicle with at least one steerable pair of wheels.

When the wheels are at the greatest angle to which they can be steered from the centreline of the vehicle, the steering is said to be at full-lock. When the vehicle is at full-lock, it will describe the circle having the shortest radius which can be achieved by that vehicle. This circle is known in the art as the turning-circle and is a limiting factor in the manoeuvrability of many wheeled vehicles.

It is an object of this invention to provide an improved vehicle.

Accordingly, the invention provides a vehicle comprising at least a first pair of wheels which are steerable, each wheel of said first pair being provided with an independent driving means under the control of a controller, the controller being arranged in use to control said driving means so as to apply selectively a torque imbalance between said first pair of wheels in order to assist in a steering manoeuvre of the vehicle.

Said torque imbalance may be applied in response to a steering signal from a steering transducer. Said steering signal may be indicative of a substantially fulllock position of a steering means which is arranged in use to steer said first pair of wheels.

The torque imbalance may be arranged to reduce the turning circle of the vehicle. The turning circle may be reduced by increasing the rotational speed of an outside wheel of said first pair in relation to the rotational speed of an inside wheel thereof, which may be achieved by applying a forward torque to the driving means associated with the outside wheel and/or applying a braking torque to the inside wheel and/or by applying a reversing torque to the inside wheel.

The vehicle may further comprise at least one further pair of wheels, the control means being arranged also to apply a torque imbalance across said further pair of wheels so as to further assist in a steering manoeuvre. The torque imbalance across the further pair of wheels may be applied only after substantially all the torque imbalance available across the first pair of wheels has been applied thereacross. The torque imbalance across the further pair of wheels may be implemented by applying a braking torque imbalance thereacross Said driving means may comprise a motor and said vehicle may comprise a hybrid powertrain.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a vehicle according to the invention; Figure 2 is a schematic diagram of a first embodiment of a steering transducer of the vehicle of Figure 1; Figure 3 is a graphical representation of the effects of user demand on tractive torque at each wheel of the vehicle of Figure 1; Figure 4 is a graphical representation of the effects of user demand on brake bias at each wheel of the vehicle of Figure 1; Figure 5 is a schematic diagram of a second embodiment of a steering transducer which is suitable for use in place of the steering sensor of Figure 2; and Figure 6 is a schematic diagram of a third embodiment of a steering transducer which is suitable for use in place of the steering transducer of Figure 2.

Referring now to Figures 1 to 4, a vehicle comprises a series hybrid vehicle 10 having an engine 12 which is arranged in use to drive a generator 14. The generator 14 supplies electrical power to individual electrical machines in the form of traction motors 16,18,20,22 which are associated one each with a respective wheel 24,26,28,30.

The rotational force supplied to the wheels 24,26,28,30 is controlled by a controller 32, which regulates the magnitude and the polarity of the torque T1, T2, T3, T4 supplied to the motors 16,18,20,22. The magnitude and polarity of the torque T1, T2, T3, T4 supplied to each motor 16,18,20,22 is controlled independently by the controller 32 for each wheel 16,18,20,22.

The front pair of wheels 16,18 are steerable using a steering mechanism 34, which includes a steering angle transducer 36A. The transducer 36A comprises a target wheel 38 which is driven by the steering mechanism 34 and which includes a series of targets 40, using which a sensor 42 supplies to the controller 32 a steered angle and steering demand signal which is indicative of the angle to which the front wheels 16,18 have been steered.

As the steering mechanism 34 approaches full-lock, the controller 32 detects the approach of the limit of possible steered angle and the demanded steering angle by means of the steered angle and steering demand signal. The targets 40 are arranged such that the controller 32 can detect the absolute limit of steering lock and at this point the controller 32 varies the torque distribution to the wheels 24,26,28,30 so as to increase the turning moment of the vehicle 10 and thereby reduce the turning circle.

Such a torque imbalance is shown with particular reference to Figures 3 and 4 and is first applied to only the steerable wheels 24,26. As driver demand increases, e. g. by keeping the steering mechanism 34 at full lock, the controller 32 also biases the torque across the rear wheels 28,30 so as to further increase the turning moment.

The torque imbalance across a pair of wheels 24,26 or 28,30 is initiated by increasing the forward torque T1, T3 to the outer wheel 24,28 (as shown with particular reference to Figure 3). The torque imbalance and hence turning moment can then be further increased by applying a reverse torque T2, T4 to the inner wheel 26,30 (as shown with particular reference to Figure 4).

Referring now to Figure 5, a second embodiment of the steering transducer 36B comprises a threaded collar 44 which translates rotary motion of the steering mechanism 34 into linear motion L which displaces a pair of linear potentiometers 46,48 so as to produce the steered angle and steering demand signal in the form of a differential voltage V across the potentiometers 46,48.

Referring now to Figure 6, a third embodiment of the steering transducer 36C comprises a proximity sensor 50 which produces the steered angle and steering demand signal in proportion to the approach towards a fixed sensor mounting 52 of a steering stop 54 on a steered hub 56.

Claims

CLAIMS 1. A vehicle comprising at least a first pair of wheels which are steerable, each wheel of said first pair being provided with an independent driving means under the control of a controller, the controller being arranged in use to control said driving means so as to apply selectively a torque imbalance between said first pair of wheels in order to assist in a steering manoeuvre of the vehicle.
2. A vehicle according to Claim 1, wherein said torque imbalance is applied in response to a steering signal from a steering transducer.
3. A vehicle according to Claim 2, wherein said steering signal is indicative of a substantially full-lock position of a steering means which is arranged in use to steer said first pair of wheels.
4. A vehicle according to any preceding claim, wherein the torque imbalance is arranged to reduce the turning circle of the vehicle.
5. A vehicle according to Claim 4, wherein the turning circle is reduced by increasing the rotational speed of an outside wheel of said first pair with respect to the rotational speed of an inside wheel thereof.
6. A vehicle according to Claim 5, wherein the relative speed of the outside wheel is increased by applying a forward torque to the driving means associated therewith.
7. A vehicle according to Claim 5 or Claim 6, wherein the relative speed of the outside wheel is increased by applying a braking torque to the inside wheel.
8. A vehicle according to any one of Claims 5 to 7, wherein the relative speed of the outside wheel is increased by applying a reversing torque to the inside wheel.
9. A vehicle according to any preceding claim, further comprising at least one further pair of wheels, the control means being arranged also to apply a torque imbalance across said further pair of wheels so as to further assist in a steering manoeuvre.
10. A vehicle according to Claim 9, wherein the torque imbalance across the further pair of wheels is applied only after substantially all the torque imbalance available across the first pair of wheels has been applied thereacross.
11. A vehicle according to Claim 9 or Claim 10, wherein the torque imbalance across the further pair of wheels is implemented by applying a braking torque imbalance thereacross.
12. A vehicle according to any preceding claim, said driving means comprising a motor.
13. A vehicle according to any preceding claim, comprising a hybrid powertrain.
14. A vehicle substantially as described herein with reference to the accompanying drawings.