Method of Braking a Vehicle

Abstract

A method of braking a vehicle which includes ground engaging wheels, and a braking system with ABS capability and including an operator actuated brake control, the ABS becoming operative in response to the operator actuating the brake control, and upon the braking system sensing the slippage or impending slippage of at least one of the ground wheels relative to the ground, to vary the braking force applied to the at least one of the wheels between, in alternative periods, an applied state in which the braking force is applied, and a released state in which the braking force is released, and characterised in that the method includes applying torque to assist acceleration of the wheel 16-19 at least during periods in which the braking force is released by the ABS.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a graph plotting a perceived vehicle speed determined by an ABS against actual vehicle speed;

FIG. 2 is a diagrammatic illustration of a vehicle to which the present invention may be applied;

FIG. 3 is a diagrammatic illustration of the control system of the vehicle of FIG. 2;

FIG. 4 is a graph showing the vehicle deceleration expected by the ABS, the actual wheel speed and engine speed without the method of the present invention being performed;

FIG. 5 is a graph similar to FIG. 4, when the method of the invention is performed.

Claims

1. A method of braking a vehicle which includes ground engaging wheels, and a braking system with ABS capability and including an operator actuated brake control, the ABS becoming operative in response to the operator actuating the brake control, and upon the braking system sensing the slippage or impending slippage of at least one of the ground wheels relative to the ground, to vary the braking force applied to the at least one of the wheels between, in alternative periods, an applied state in which the braking force is applied, and a released state in which the braking force is released, and characterised in that the method includes applying torque to assist acceleration of the at least one wheel at least during periods in which the braking force is released by the ABS.

2. A method according to claim 1 wherein the torque which is applied is derived from a prime mover.

3. A method according to claim 2 wherein the prime mover is an engine which in normal use acts to drive the wheels to provide the vehicle with forward or reverse motion.

4. A method according to claim 3 wherein the method includes, at least during those periods when the braking force is released and torque is applied to the at least one wheel to accelerate the wheel, maintaining a minimum engine speed.

5. A method according to claim 4 wherein the method includes providing a signal to an engine controller during braking, at least when the ABS is operated and it is desired to provide torque to the wheel, to maintain the engine speed at a minimum speed.

6. A method according to claim 5 wherein the engine controller responds to the signal by accelerating the engine speed up to a minimum speed if the engine speed is below the minimum speed.

7. A method according to claim 3 wherein the vehicle has a CVT to transmit power from the prime mover, to drive wheels of the vehicle.

8. A method according to claim 7 wherein during the periods in which the braking force is released by the ABS and torque is applied to accelerate the at least one wheel, a signal is sent to a CVT controller, to require the CVT to select a transmission ratio appropriate for applying the required torque to the at least one wheel.

9. A method according to claim 7 wherein the CVT is controllable to reduce the transmission ratio to or towards zero during the periods while the braking force is applied.

10. A method according to claim 9 wherein the transmission includes a variater which is a hydraulic motor and the transmission ratio is varied during the periods while the braking force is applied by increasing hydrostatic pressure.

11. A method according to claim 7 wherein the transmission isolates the prime mover from the wheel by disengagement of a clutch during the periods while the braking force is applied.

12. A method according to claim 1 wherein the method includes determining any discrepancy between sensed wheel angular velocity and the vehicle speed determined by the ABS, and applying torque to the wheel at least during periods in which the braking force is released, where any discrepancies is determined to be sufficiently great to indicate that the at least one wheel is not accelerating to bring its angular velocity sufficiently towards the actual vehicle speed during those periods.

13. A method according to claim 12 wherein such error is determined by a torque controller which analyses the actual wheel speed sensed, and compares it to a reference signal provided by the ABS which is indicative of vehicle deceleration determined by the ABS.

14. A method according to claim 13 wherein an auxiliary sensor provides an input to the torque controller indicative of vehicle speed relative to the ground, independent of any wheel speed sensor, to enable the torque controller more accurately to determine any error between the vehicle speed determined by the ABS and actual vehicle speed relative to the ground.

15. A method according to claim 14 wherein the sensor is an accelerometer.

16. A vehicle which includes ground engaging wheels, and a braking system with ABS capability and including an operator actuated brake control, the ABS being operative upon the braking system sensing the slippage or impending slippage of at least one of the ground wheels relative to the ground, to vary the braking force applied to the at least one of the wheels between, in alternative periods, an applied state in which the braking force is applied, and a released state in which the braking force is released, and characterised in that the vehicle includes a torque controller which is operative to apply torque to assist acceleration of the at least one wheel at least during periods in which the braking force is released by the ABS.