| 摘要 |
<p>Pulse frequency modulation is used to control brakes and clutches 10 which are operated by fluid pressure actuators 22 controlled by electrically actuated solenoid valves 28. Short pulse periods for all duty cycles are generated by feedback from the solenoid valve 28 or from the actuator 22. In one circuit an electrical control 30 triggers a flip-flop 38 which starts solenoid current. Solenoid movement results in back-emf and its effects on the solenoid flux field or current is detected and used as a feedback signal to reset the flip-flop 38 to thereby turn off the current as soon as the valve 28 is operated. In another circuit, a computer control 30' emits a command for a certain pulse period. Actuator pressure or position is monitored to produce a feedback signal to the computer. If the signal is not received, the pulse period is increased for the next pulse command so that a sufficient pulse period will be found. If the magnitude of the actuator response exceeds a threshold, the pulse period is decreased for the next pulse command. Pulse width modulation may also be improved by the same technique for minimizing the pulse period at the lowest duty cycles and yet assuring actuation. <IMAGE></p> |
