Hydraulic-pneumatic shift (HPS), function

B26.18-0021-06

1 Gearbox shift group cylinder (GV)

2 Shift gate valve

3 Gearbox GP cylinder

4 Compressed air reservoir

A3 Vehicle/engine control unit (module FR)

B2 Clutch course sensor

P2 INS Module (tool panel

S3 Gearbox shift group switch (GV)

S8 Gearbox GV pilot lamp switch

Y29 Gearbox GV electromagnetic valve

Y30 Gearbox GV electromagnetic valve

Operation

The air of the reservoir (4) supplies the GV activating valves (Y29, Y30) and the GP activating valve located in the shift gate (2).

When the GV activating switch (S3) is put on the engaged position, the control mechanism drive module (A3) sends a signal to the electromagnetic valve (Y29) which releases air to the GV cylinder (1), which pushes the piston and activates the GV. When the GV activating switch (S3) is put on the disengaged position, the module (A3) sends a signal to the electromagnetic valve (Y30), which releases air to the chamber opposite to the GV cylinder (1). This air pushes the piston back and deactivates the GV. The engagement or disengagement of the GV change group is only «possible when the clutch pedal is applied in 70% of its course. This verification is done by the clutch shift sensor (B2). If the course of the clutch pedal is not enough, the module (A3) doesn't send the signals to the GV activating valve (Y29) or the GV deactivation valve (Y30).

To activate the GP cylinder (3) there is a valve in the shift gate (2) that, according to the gearshift lever position, moves the cylinder piston, activating or deactivating the GP. With the gearshift lever in the 1st H position, the valve releases compressed air to activate the GP and, with the lever in the 2nd H, the valve releases compressed air to deactivate the GP.