Engage gear range, function - GF27.60-P-3009AHO

TRANSMISSION 724.2 in MODEL 212 

Function requirements for Engage gear range, general 

• Circuit 87 (connected circuit 15) ON
• Internal combustion engine running and/or electric machine (A79/1) ON

Engage gear range, general 

Each gear change is triggered by the fully integrated transmission control system. In the process one component group is assigned to each shift operation.

One component group consists of the respective control solenoid valve, the regulating valve involved, the responsible shift valve and the required multidisk brake or required multidisk clutch.

The pressure in the multidisk brake or multidisk clutch to be engaged is increased constantly while at the same time the pressure in the multidisk brake or multidisk clutch to be disengaged is reduced. The transition here is a smooth one, but nevertheless the components involved are actuated directly and as a result enable downshifting through several gears.

Gear range engagement, function sequence 

The function sequence is subdivided into the following steps:

• Gear range change, function sequence 
• Shifting "N" to "D" (1st gear), function sequence 

Gear range change, function sequence 

Changing between gear ranges is triggered by the fully integrated transmission control unit (Y3/8n4) through actuation of the D/R switchover valve (Y3/8y10) or the park pawl switchover valve (Y3/8y11).

The feed line to multidisk brake B2 or multidisk brake BR is opened via the D/R switchover valve and multidisk brake B2 (gear range "D") or BR (gear range "R") is filled with oil.

The feed line to the hydraulic cylinder of the electrohydraulic park pawl actuation system is opened via the park pawl switchover valve. The park pawl switchover valve actuates the park pawl shift valve, which passes on or blocks off the working pressure applied in accordance with the actuation.

Oil pressure switches D/R 1 and 2 (Y3/8b3, Y3/8b4) (redundant design) record the position of the D/R shift valve via the valve supply pressure applied (as per the position of the D/R shift valve).

Gear ranges "P" or "Emergency P" are recorded by the park pawl position sensor (Y3/8s4).

Oil pressure switches D/R 1 and 2 as well as the park pawl position sensor are integrated in the fully integrated transmission controller unit (Y3/8).

Shifting "N" to "D" (1st gear), function sequence 

In position "N" of the DIRECT SELECT lever (S16/13), multidisk brake B3 and multidisk clutch K3 are engaged. When the transmission is shifted from position "N" to position "D" by the fully integrated transmission control unit, multidisk brake B2 control solenoid valve (Y3/8y6) is actuated, the feed line to the multidisk brake B2 is opened and multidisk brake B2 is filled with oil.

The fully integrated transmission control unit uses the rpm difference (actual slip) between the crankshaft speed and transmission input speed to detect whether multidisk brake B2 is full. Multidisk brake control solenoid valve B2 actuates regulating valve B2 or BR, which converts the applied working pressure into shift pressure and passes it on to the multidisk brake B2

In the fully integrated transmission control unit, the required slip (specified slip) is stored for the respective gear. The control pressure on regulating valve B2 or BR is changed via multidisk brake control solenoid valve B2 depending on this. The shift pressure produced by the regulating valve B2/BR depends on the geometry of the regulating valve B2/BR. The pressure in multidisk brake B2 is changed until the specified slip stored in the fully integrated transmission control unit is reached.