Frequency modulated valve control

摘要

Valve apparatus 1, eg for operating a motor vehicle fluid actuated clutch or transmission, comprises a main valving element 5, an auxiliary valve 10 and a proportional valve 20 controlled by an electronic unit 30 which, via a plurality of sensors 131a, 131b, receives input signals 31a, 31b denoting parameters such as pilot control pressure, fluid temperature, pump flow etc. These parameters determine an output control signal 32 from the electronic unit 30. In order to minimize hysteresis of plunger 22, the output control signal 32 is a composite of two component control signals, a first modulated at a relatively high chopper frequency (eg between 220 to 600 hertz) the other modulated at a lower frequency (eg between 1/3 and 1/5 of the first frequency), generated and superimposed upon each other by the electronic unit 30. The lower modulated frequency is regulated so that the valve element 5 and the plunger 21 oscillate but the plunger 21 does not impact or chatter against seat 22.