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

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

Component Identification:

Circuit 61 ON

Component Identification:

Starting situation:
^ DIRECT SELECT gear selector switch (S16/13) in position "N" or "P"
^ Circuit 61 OFF
^ No pressure in hydraulic system
^ All valves in the shift plate in neutral position

Aim
To engage 1st gear with program "S" selected

Engage 2nd gear with program "C" selected

Function

Start engine
The working pressure is generated, forwarded via the 2-3 holding pressure shift valve, 2-3 command valve and ball valve (33a) to the multi-disk clutch K3 and over the 3-4 command valve to the end face of the 3-4 shift pressure shift valve. The 3-4 shift pressure shift valve is switched against the force of the spring towards the right. At the same time the 3-4 shift solenoid valve is energized.

With this the shift valve pressure enters the spring chamber of the shift valve B2 and acts on the end face of the 3-4 command valve. The shift valve B2 is held in the upper position and the 3-4 command valve switches towards the right.

At the end face of the 3-4 shift pressure shift valve the working pressure is replaced by shift valve pressure. (See picture "circuit 61 ON".)

Shift DIRECT SELECT gear selector switch from "N" to "D"
The selector valve opens the shift pressure feed connection from the ball valve (33b) with the shift valve B2. In the upper position of the shift valve B2 the shift pressure is applied behind the piston of the multi-disk brake B2 and simultaneously to the mating surface of the piston of the multi-disk brake B2. The multi-disk brake B2 then starts to close.

(See "Activation sequence active" picture)
The pressure applied to the mating surface of the piston of the multi-disk brake B2 induces smooth engagement of the multi-disk brake B2.

The ETC control unit (N15/3) monitors the engagement process via the reduced speed of the input shaft as the frictional connection of the B2 multi-disk brake increases. When the speed drops to the specified level, the ETC control unit shuts off the power to the 3-4 shift solenoid valve. The spring chamber of shift valve B2 is depressurized and shifts downwards. In doing so the line to the mating surface of the piston of the multi-disk brake B2 is connected to the pressure holding valve. The pressure on the mating surface of the piston of the multi-disk brake B2 drops to a residual pressure.

The 3-4 command valve shifts to the left. Working pressure is routed over the 3-4 holding pressure shift valve and 3-4 command valve to the piston of the multi-disk brake B2.

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

Shift DIRECT SELECT gear selector switch from "N" to "R"
The selector valve opens the shift pressure feed connection with the multi-disk brake B3. The remaining switch-on procedure sequence corresponds to the sequence when activating the multidisk brake B2.

No mating surface on piston of multi-disk brake B3.

Residual pressure
To prevent air getting into the hydraulic system and causing a reduction in shift quality, the line system remains filled with oil when the automatic transmission is stationary.