Current control method for a solenoid operated fluid control valve of an

Abstract

The solenoid control valves of a solenoid-operated automotive antilock braking system are cyclically controlled to enable the valves to operate in a stable, partially open position that provides a desired fluid flow while minimizing noise associated with acceleration and deceleration of the controlled fluid. After an incipient lock-up condition is detected and the solenoid valve has been energized to hold and/or permit a partial release of the brake pressure, the solenoid is initially de-energized for a defined interval designed to reduce the current to a scheduled value. In this interval, the solenoid current is re-circulated through a free-wheeling diode for a smooth decay, allowing the valve to slowly open in a smooth and stable fashion. Then the solenoid is pulse-width modulated (PWM) at a frequency and duty cycle designed to maintain the solenoid current at the scheduled value. The interval of PWM is relatively brief to avoid any instability associated with the current pulsation. At this point, the solenoid is re-energized just long enough to reach its steady state value, thereby returning the valve to a closed or nearly closed position, and completing the current control cycle. The solenoid is then de-energized and the cycle is repeated, allowing the controller to smoothly return the brake pressure to the system pressure while minimizing any attendant hydro-mechanical noise.