B - Operations – Transporting – 60 – T
Patent
B - Operations, Transporting
60
T
303/18
B60T 8/34 (2006.01) B60T 8/17 (2006.01) B60T 13/66 (2006.01)
Patent
CA 2038807
An air brake system for a truck includes a treadle valve, a pilot control isolation valve, an exhaust valve, a relay valve, an air pressure transducer, a wheel speed sensor, an electronic control unit (ECU) and an air brake chamber associated with a brake actuator. In heavy braking operations, the pilot system pressure rise rate is monitored and restricted by modulation of the pilot control isolation valve. During heavy braking operations, if braking of the vehicle wheel results in a wheel velocity change which exceeds a predetermined deceleration threshold, the pressure rise rate is further restricted in attempt to "creep" up on the brake system pressure at which the lock condition is expected to occur. At another predetermined deceleration threshold, the brake system pressure is vented. The brake system pressure decreases resulting in a reduction in the applied brake force thereby permitting the vehicle wheel to roll back up to speed. The roll up rate is a function of the coefficient of friction of the road surface, the loading of the respective vehicle wheel and residual brake force remaining in the system. Empirical testing has revealed that a close approximation of the friction force available for stopping the vehicle may be made by use of the pilot system pressure when the vehicle wheel reaches minimum velocity and the time required to reach a certain wheel velocity greater than the minimum velocity. The friction force may be used to control parameters of operation of the antilock brake system during subsequent antilock cycles. For example, subsequent cycle brake system pressure rise rate is restricted by values determined from the friction force noted from previous cycles. Also, the deceleration condition at which the brake system pressure is exhausted and the pressure to which the system is exhausted are determined from the calculation of the friction force available during previous cycles.
Murphy Bryan R.
Peck David E.
Pascal & Associates
Rockwell International Corporation
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