GF27.60-P-4014GA Shifting N to D (1st Gear), Function

GF27.60-P-4014GA Shifting N to D (1st gear), function
- TRANSMISSION 722.6





Engine started





Activation sequence active





Initial situation:
^ Selector lever in position "N" or "P"
^ Engine off
^ No pressure in hydraulic system
^ All valves in the shift plate in neutral position

Aim
To engage 1st gear with program "S" selected Shifting 2nd gear with program selection "W" or "C" (depending on the production period)

Function

Start engine
The working pressure (p-A) is formed, reaches via the holding pressure 2-3 shift valve, the command valve 2-3 and ball valve (33a) to the rear multi-disk clutch (K3) and via the command valve 3-4 (31c) to the end face of the shift pressure 3-4 (29c) shift valve. The 3-4 shift pressure shift valve (29c) is moved against the force of the spring towards the right. At the same time the 3-4 solenoid valve (Y3/6y4) is energized.

As a result shift valve pressure (p-SV) reaches the spring chamber of the shift valve B2 (26) and the end face of the command valve 3-4 (31c).

The shift valve B2 (26) is held in the upper position and the 3-4 command valve (31c) switches towards the right. The working pressure (p-A) is replaced by the shift valve pressure (p-SV) at the end face of the shift pressure 3-4 shift valve. (See diagram "Engine started")

Move selector lever from "N" to "D"
The selector valve (52) opens the shift pressure (p-S) feed connection from the ball valve (33b) with the shift valve B2 (26). In the upper position of the shift valve B2 (26) shift pressure (p-S) reaches behind (p-S) the piston of the multi-disk brake (B2a) and simultaneously to the opposed surface of the rear multi-disk brake piston (B2b). The rear multi-disk brake begins to close. (See diagram "Activation sequence active").

The pressure on the opposed surface of the piston of the rear multi-disk brake (B2b) causes a gentle engagement of the rear multi-disk brake.

The ETC control unit (N15/3) monitors the engagement process via the reduced speed of the drive shaft as the frictional connection of the rear multi-disk brake increases. When the speed drops to the specified level, the ETC control module (N15/3) shuts off the power to the 3-4 shift solenoid valve (Y3/6y4). The spring chamber of the shift valve B2 (26) is depressurized and switches downwards. As a result the line to the opposed surface of the rear multi-disk brake piston (B2b) is connected to the pressure maintaining valve (32). The pressure on the opposed surface of the rear multi-disk brake piston (B2b) reduces to a residual pressure.

The 3-4 command valve (31c) moves to the left. The working pressure (p-A) reaches via the holding pressure shift valve 3-4 (28c) and the command valve 3-4 (31c) to the piston of the rear multi-disk brake (B2a).

The activation sequence is complete; 1st gear is engaged. (See diagram "1st gear engaged")

Move selector lever from "N" to "R"
The selector valve (52) opens the connection of the feed of shift pressure (p-S) with the center multi-disk brake (B3). The further sequence of the switch-on process is as when engaging the rear multi-disk brake.

No mating surface on the piston of the center multi-disk brake (B3).

Residual pressure
To avoid air getting into the hydraulic system, which causes a deterioration in shift quality, the line system remains filled with oil in steady-state operation of the automatic transmission.