I've been researching available hydraulic valves for a transmission control application. The need is for proportional (PWM) control of pressure in a clutch slave cylinder. It's not a standard clutch, instead the springs keep the plates apart and hydraulic pressure clamps the clutch. This is so drive disconnects for a failure of hydraulic pressure.

What kind of hydraulic circuit &(Butterfly Valves) valve type is normally used to control clutches for torque converter lockup or in twin-clutch gearboxes like DSG?

I'm thinking this type of hardware could be adapted for our application.

You didn't say if this was for off-road, but my first thought is to use the same type of brake circuit used in many off-road brakes that are spring applied, hydraulically released. This is for safety reasons - you break a line and brakes come one, just like air brakes but without the compressor. When you apply the brakes you meter the hydraulic pressure off. Mico is one supplier, but I'm sure there are others. Just google SAHR (spring applied, hydraulically released).

From very old memories, the old auto stick shifts like on some European cars in the 60s or thereabouts used a centrifugal clutch with a servo over ride that was actuated by pressure on the change lever. If you accidentaly touched the lever, the clutch slipped.

I think from memory, the VW version used a torque converter plus a servo operated clutch and pressure plate system.

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