Gear selection, function

W26.60-1073-05

Shift control unit, side view

5 Shift control unit

6 Gear shift cylinder

B88 Shift force assist pressure sensor 1
(odd gears)

B89 Shift force assist pressure sensor 2
(even gears)

Selection directions

A Even gears (2nd, 4th, etc.)

C Odd gears (R, 1st, 3rd, etc.)

N Neutral position

W26.60-1214-12

5 Shift control unit

6 Gear shift cylinder

6.1 Hydraulic cylinder

6.2 Pneumatic cylinder

A3 Drive control (FR) control unit

A52 Shift force assistance control unit

B88 Shift force assist pressure sensor 1 (odd gears)

B89 Shift force assist pressure sensor 2 (even gears)

Y68 Shift force assist solenoid valve 1 (odd gears)

Y69 Shift force assist solenoid valve 2 (even gears)

X Compressed-air supply

According to the movement of the gearshift lever (driver's specification), a hydraulic circuit transmits the hydraulic pressure and fluid stream from the shift control unit (5) to the hydraulic cylinder (6.1) in the gear shift cylinder (6).

This hydraulic pressure is also detected by the shift force assistance pressure sensor 1 (B88) or the shift force assistance pressure
sensor 2 (B89) on the shift control unit (5) and passed on to the shift force assistance control unit (A52). The electronics in the shift force assistance control unit (A52) evaluates the information and uses the pressure characteristic to calculate the valve opening time required at shift force assistance solenoid valve 1 (Y68) and shift force assistance solenoid valve 2 (Y69).

The two 3/2-way solenoid valves are actuated by the shift force assistance control unit (A52) and release appropriate pneumatic pressure for the pneumatic cylinder (6.2) in the gear shift cylinder (6), which ensures sufficient shift force assistance.

The pneumatic pressure (compressed-air supply) for the two
3/2-way solenoid valves is taken from the auxiliary consumer circuit of the compressed-air system.

At a certain transmission input speed the shift force assistance is no longer required and is therefore shut down. The shift force assist is similarly inactive for as long as the transmission is in neutral.

 If the pressure sensors or the 3/2-way solenoid valves fail, shift force assistance is switched off. The vehicle can still be shifted hydraulically, although with greater effort.