Kelsey-hayes Company

Thomas M Atkins

Peter Every

Edward Nelson Fuller

Leonard T Tribe

Brian C Tuck

Roger L Miller

The duration and average deceleration of a vehicle wheel are measured during a wheel speed departure and compared to duration and deceleration thresholds to determined if a wheel sneakdown condition exists for the wheel.

Algorithm for preventing wheel speed sneakdown on a low mu surface

Reapply pulses for increasing the brake fluid pressure applied to controlled wheel brakes in an anti-lock brake system are generated as a function of vehicle speed. A reapply pulse is generated when the vehicle speed decreases by a predetermined amount.

Algorithm for scheduling extra reapply pulses in a rear wheel anti-lock brake system

Upon detection of a potential transition from a low mu road surface to a high mu road surface, a rear wheel anti-lock brake system generates one dump pulse to increase the braking effort of the controller rear wheel as a test of the road surface. If the wheel accelerates following the test pulse, the transition is false and the anti-lock brake system continues as before. If the wheel does not accelerate following the test pulse, the transition is true and the anti-lock brake system proceeds to increase the braking effort of the controlled wheel brake.

Algorithm for testing road surface with a small pressure release in an anti-lock brake system

During wheel speed sneakdown conditions, a deceleration threshold in an anti-lock brake system control algorithm is incrementally increased to enhance the anti-lock braking system effort.

Incremental brake pressure increases for speed sensitive surfaces

The speed of a controlled wheel in a rear wheel anti-lock brake system is monitored during a spin-and-brake condition. Acceleration of the rear wheel following a string of dump pulses is an indication that the spin-and brake condition ended before the vehicle brakes were applied. A lack of acceleration of the rear wheel following a string of dump pulses is an indication that the spin-and-brake condition is present.

Wheel spin-and-brake algorithm for a rear wheel anti-lock brake system

The present invention concerns a vehicle anti-lock brake control system which does not require the use of an auxiliary hydraulic pump and, in the preferred embodiment, is adapted to control only the rear brakes of a four-wheel vehicle. The control system includes a normally open solenoid actuated isolation valve connected between the master cylinder and the rear wheel brakes, and a normally closed solenoid actuated dump valve connected between the rear wheel brakes and a fluid accumulator. A computer control is connected to monitor the rear wheel speed and deceleration and, during braking of the vehicle, functions to control the application of hydraulic pressure to the rear brakes via the isolation and dump valves in order to correct wheel speed departures and prevent lock-up of the brakes. The computer control is adapted to detect a low to high mu road surface change which occurs during a wheel speed departure, and thereafter applies additional pressure to the rear brakes by selectively opening the isolation valve. Further, the control is adapted to detect when one of the rear wheels remains locked after anti-lock measures have been taken. In these instances, the standard operating parameters which control the reapplication of additional pressure are modified.

Vehicle anti-lock brake system

A vehicle braking system such as an anti-lock brake system and/or a traction control utilizes a separate solenoid-actuated, two position, three-way valve in each controlled channel of the brake system for controlling the application of pressure to the respective wheel brake circuit. The valve includes a first port connected to the controlled wheel brake(s), a second port connected to an outlet of a hydraulic pump, and a third port connected to the inlet of the hydraulic pump. The valve is only moveable between a first position wherein the outlet of the pump is connected to the wheel brake to increase pressure to the wheel brake, and a second position wherein the wheel brake is connected to the inlet of the pump to decrease pressure to the wheel brake. An electronic control is provided for operating the valve to control the application of pressure to the selected wheel brakes. The control cyclically moves the valve between the first and second positions during a predetermined time period to alternately increase and decrease pressure to the wheel brake. More specifically, the control generates a pulse-width-modulated signal to modulate the time periods during which the valve is maintained in either the first or second positions to control the effective pressure to the wheel brake to obtain a net increase, decrease, or constant pressure to the wheel brake during the predetermined time period.

The present invention concerns a vehicle anti-lock brake control system which does not require the use of an auxiliary hydraulic pump and, in the preferred embodiment, is adapted to control only the rear brakes of a four-wheel vehicle. The control system includes a normally open solenoid actuated isolation valve connected between the master cylinder and the rear wheel brakes, and a normally closed solenoid actuated dump valve connected between the rear wheel brakes and a fluid accumulator. A computer control is connected to monitor the rear wheel speed and deceleration and, during breaking of the vehicle, functions to control the application of hydraulic pressure to the rear brakes via the isolation and dump valves in order to prevent lock-up of the brakes. In the event excessive rear wheel deceleration is detected during a vehicle stop, the computer control closes the isolation valve to hold pressure to the rear brakes at a relatively constant level. If, after the isolation valve has been closed, the difference between the actual rear wheel speed and a calculated theoretical speed ramp valve exceeds a predetermined slip threshold, the dump valve is selectively opened to reduce pressure to the rear brakes and correct the wheel slip condition. The computer control is adapted to monitor several operating parameters while the system is in the anti-lock mode in order to determine whether additional pressure should be applied to the rear brakes by selectively opening the isolation valve.

In accordance with the present invention, a normally open isolation valve is connected between a master cylinder and the selected wheel brakes, and a normally closed dump valve is connected between the selected wheel brakes and a fluid accumulator. A computer control module is connected to operate the isolation valve and the dump valve. In operation, when a slip condition of the controlled wheels is detected, the computer control module closes the isolation valve to hold fluid pressure to the controlled brakes at a relatively constant level. If the deceleration of the controlled wheels exceeds a predetermined amount, the computer control module will selectively open the dump valve to enable fluid to flow into the accumulator, thereby reducing the deceleration of the associated wheels. After the isolation valve has been closed and the slip condition is corrected, the computer control module can detect when the vehicle travels from a low friction surface such as wet asphalt to a high friction surface such as a dry concrete, because the braked wheels of the vehicle which are not controlled by the skid control system will cause an increase in deceleration of the vehicle. Under these conditions, pressure to the controlled wheel brakes can generally be increased without causing a lock-up condition. The control module is responsive to an increase in wheel deceleration above a predetermined rate to selectively open the isolation valve after the valve has been closed to gradually increase pressure to the controlled wheel brakes.

Vehicle skid control system

A hydraulically operated automotive skid control system. The system includes a regulator that regulates pump pressure that operates on the modulator in response to variations in braking system pressure. A combined bypass and isolation valve is incorporated for providing a direct source of actuating fluid in the event of failure of the pump to maintain adequate pressure.

Skid control system embodying fail safe bypass

A skid control system utilizing a skid detector which is responsive to wheel deceleration, a skid recovery detector which is responsive to wheel acceleration, a holding circuit including a capacitor for modifying the response of the system in accordance with the level of charge on the capacitor, and charging and discharging circuits for charging and discharging the capacitor in accordance with various skid condition related signals.

Skid control system

A vehicular skid control system for relieving the brake pressure when an incipient skid condition is sensed. The system includes a combined check and bleed valve between the master cylinder and rear wheel brakes, a modulator assembly actuable by a ancillary source of fluid pressure, a fal safe bypass valve for communicating unmodulated master cylinder pressure directly to the rear brakes upon failure of the ancillary pressure source, and a regulator provided in the circuit connecting the source of ancillary fluid with the expansion chamber for maintaining at least a predetermind pressure in the circuit. Certain of the elements of the system may be automatically cycled each time the vehicle engine is started and stopped.

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Ann Arbor, MI, United States of America

Thomas M Atkins