Method and system for controlling brake pressure under 'low Mu braking surface' (surface with a low coefficient of friction) conditions in a vehicular ABS

摘要

Method and system for reducing the brake pressure rise rate under low Mu braking surface conditions by utilizing a vehicle reference speed and a fixed bleed rate to determine if the wheels are being over-braked. When over-braking occurs, the pressure rise rate is restricted by not allowing an ABS valve (10) to go into an Apply state (approximately 100 psi/sec.), regardless of wheel acceleration levels. A Ramp state is used in place of the Apply state and the pressure rise is therefore limited to approximately 30 psi/sec. to improve wheel control. The Ramp duty cycle is also modified to provide the smallest pressure steps possible with the current valve hardware.