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Hydraulic valves for transmission control

Hydraulic valves for transmission control

Hydraulic valves for transmission control

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 & 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.

Thanks, Ian

RE: Hydraulic valves for transmission control

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).


RE: Hydraulic valves for transmission control

The hydraulic valves in every transmission that I know of use all proprietary components. Probably this won't be an option in your case.

You can buy servohydraulic valves from the common industrial hydraulic component suppliers (Bosch-Rexroth, Parker, etc) but they will be overkill for your application and REALLY expensive. A normal hydraulic directional solenoid valve isn't designed for use with PWM.

Any problem like this is solvable with money. How much do you have?

RE: Hydraulic valves for transmission control

Torque converter can use PWM type solenoids that control a signal pressure to the actuating valve.  The valves and solenoids are integrated into the valve body or front pump.  Most service manuals have hydraulic schematics that can be studied.

DSG solenoids are of the VFS type which operate at a higher electrical frequency, but directly control the clutch pressure.  VFS are also typically used to control line pressure in a planetary automatic, but without the flow demand of the clutch control solenoid.

Solenoids are designed for specific leakages, pressures, flow rates.  Hardware could be adapted, but the electronic control will be the bigger challenge.

RE: Hydraulic valves for transmission control

Thanks for the info.

Does anyone know if the clutch control on the current auto-shift manual gearboxes is done as a closed loop slip control, or a closed loop pressure / position control?

Thanks, Ian

RE: Hydraulic valves for transmission control

You mean DSG-type transmissions? It would make a lot more sense to vary the duty cycle (i.e. clutch engagement pressure) according to engine speed during the conditions that it wants to be slipping the clutch. Nobody knows for sure but the original system programmers, and they're probably not hanging around here, and if they were, they're probably not going to talk.

Keep in mind that an old fashioned centrifugal clutch varies its engagement pressure according to input speed. But, you can't disengage those during gear changes.

RE: Hydraulic valves for transmission control

Auto-shift manual gearboxes would include DSG, yes, but there are automated conventional shift manuals available too (with automated clutch).

I guess I'm asking if anyone knows the control feedback mechanism(s) in use for that type of clutch during vehicle launch. But as you say, maybe those that do know aren't here or can't tell.

Regards, Ian

RE: Hydraulic valves for transmission control

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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