ABS
ABS
What is claimed is:
1. In a wheeled vehicle having means for supplying pressurized brake fluid to actuate the associated wheel brakes of the vehicle, a brake control system for controlling the application of pressurized brake fluid to at least one selected wheel brake to control the braking of the associated wheel, said control system comprising:
a normally open isolation valve means connected between the supply means and the selected wheel brake;
a normally closed dump valve means connected between the selected wheel brake and a fluid reservoir; and
control means connected to operate said isolation valve means and said dump valve means, said control means including means for detecting wheel speed departures of the associated wheel relative to the actual speed of the vehicle, said control means operable to close said isolation valve means to hold the fluid pressure to the selected wheel brake at a relatively constant level after a first wheel speed departure of the associated wheel is detected, said control means operable to selectively open said dump valve means after said isolation valve means has been closed to enable fluid to flow into said fluid reservoir to selectively reduce fluid pressure to the selected wheel brake to a first predetermined pressure and correct said first wheel speed departure, said control means further operable to selectively open said isolation valve to selectively increase pressure to the wheel brake to cause a second wheel speed departure after said first wheel speed departure has been corrected, said control means operable to selectively open said dump valve means after said second wheel speed departure has been detected to selectively reduced pressure to the selected wheel brake to a second predetermined pressure greater than said first predetermined pressure.
2. The control system according to claim 1 wherein said control means includes means for sensing deceleration of the vehicle, said control means being operable to selectively open said isolation valve means to selectively increase pressure to the wheel brake to cause a third wheel speed departure after said second wheel speed departure has been corrected and the increase in deceleration of the vehicle has exceeded a predetermined amount, said control means operable to selectively open said dump valve means after said third wheel speed departure has been detected to selectively reduce pressure to the selected wheel brake to a third predetermined pressure.
3. The control system according to claim 2 wherein said third predetermined pressure is greater than said second predetermined pressure.
4. The control system according to claim 1 wherein said control means includes means for determining when the vehicle has approached an end-of-stop condition and for automatically operating said isolation valve means to apply and maintain additional pressure to the selected wheel brake when the vehicle is in said end-of-stop condition.
5. The control system according to claim 1 wherein said control means includes means for sensing the acceleration of the associated wheel during spin-up portions of said wheel speed departures, said control means being operable to selectively open said isolation valve means to selectively increase pressure to the selected wheel brake to cause a further wheel speed departure after a previous wheel speed departure has been corrected and the acceleration of the associated wheel during a spin-up portion of said previous wheel speed departure exceeds a predetermined rate.
6. The control system according to claim 5 wherein said previous wheel speed departure is said second wheel speed departure and said further wheel speed departure is a third wheel speed departure.
7. The control system according to claim 5 wherein said control means is operable to selectively open said dump valve means after said further wheel departure has been detected to selectively reduce pressure to the selected wheel brake to a third predetermined pressure.
8. The control system according to claim 7 wherein said third predetermined pressure is greater than said second predetermined pressure.
9. The control system according to claim 1 wherein said control means includes means for monitoring the time said dump valve means has been open after said first wheel speed departure has been detected and prior to correction of said first wheel speed departure, said control means operable to selectively open said isolation valve means to increase pressure to the selected wheel brake after said dump valve means has been open during said first wheel speed departure for a predetermined time period.