Gear selection, function

W26.60-1073-05

Illustration: Pick-up unit viewed from the side

5 Pick-up 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

W26.60-1074-12

5 Pick-up unit

6 Gear shift cylinder

6.1 Hydraulic cylinder

6.2 Pneumatic cylinder

A52 Shift force assist control module

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 pick-up unit (5) to the hydraulic cylinder (6.1) in the combination gear shift cylinder (6).

In addition this hydraulic pressure is sensed by the shift force assist pressure sensors (B88 or B89) on the pick-up unit (5) and relayed to the shift force assist control module (A52). The electronics in the shift force assist control module (A52) evaluates the information and uses the pressure characteristic to calculate the valve opening time required at the shift force assist 3/2-way solenoid valve unit (Y68/Y69).

The two shift force assist 3/2-way solenoid valves (Y68/Y69) are actuated by the shift force assist control module (A52) and enable a corresponding pneumatic pressure for the pneumatic cylinder (6.2) in the combination shift cylinder (6), which ensures sufficient shift force assistance.

The pneumatic pressure (compressed-air supply) for the two shift force assist 3/2-way solenoid valves (Y68/Y69) 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.

 In the event of failure of the shift force assist pressure sensors (B88/B89) or the shift force assist 3/2-way solenoid valves (Y68/Y69), shift force assistance is shut down. The vehicle can still be shifted hydraulically, although with greater effort.