Proportional Directional Valves
The two proportional directional valves have three positions: pressure reduction, pressure holding, and pressure increase. See Fig 1 . The proportional directional valves are set in the pressure reduction position when there is no gear shifting or clutch operation in progress. In this condition the two cylinders (clutch cylinder and selector angle cylinder) are connected to the expansion tank. During clutch operation or main selector shaft rotation the valve is placed in the pressure increase position. In this position the valve connects the cylinder to the hydraulic pressure accumulator. At this stage the solenoid will consume approximately 1.1-2.0 amps. The valve is fully open up to 2 amps. When the clutch is to be disengaged or the main selector shaft is to remain in the activated position, the valve switches to the pressure holding position. With the valve in this position the flow of hydraulic oil to the cylinder is interrupted and the piston of the activated cylinder remains in a pressurized mode.