GF27.60-P-3009ACW Engage Gear Range, Function

GF27.60-P-3009ACW Engage gear range, function
- TRANSMISSION 722.618/640/646/695/699

Function requirements for gear range engagement general
^ Circuit 87 ON
^ Circuit 61 OFF
^ Electronic selector lever module control unit (N15/5) in position "N" or "P"
^ No pressure in hydraulic system
^ All valves in the shift plate in neutral position
^ To engage 1st gear with transmission mode "S" selected
^ To engage 2nd gear with transmission mode "C" selected

Gear range engagement general
Each gear change is triggered by the electronic transmission control system. Each shift sequence is assigned a control block. In each case this includes an overlap regulating valve, a holding pressure shift valve, a shift pressure shift valve, a command valve as well as an electromagnetically operated switchover valve (gearshift solenoid valve 3-4 (Y3/6y4)).

Actuation of the solenoid valve switches over from stationary mode to the shift phase.

When the gear change is complete the solenoid valves are no longer actuated as the different gears are subject to a self-hold function in stationary mode.

Gear range engagement function sequence
The function sequence is subdivided into the following steps:
^ Start engine (circuit 61 ON)
^ Shift from "N" to "D" (engagement process active)
^ Shift from "N" to "R"

Start engine (circuit 61 ON)
The working pressure (p-A) is routed via ball valve (33a) to the multidisk clutch K3 (26) and via the command valve 3 - 4 (31c) to the end face of the shift pressure shift valve 3 - 4 (29c). The 3 - 4 shift pressure shift valve (29c) is moved against the force of the spring towards the right. The 3-4 gearshift solenoid valve is energized simultaneously.

This allows shift valve pressure (p-SV) to enter the spring chamber of the shift valve B2 (62) and to reach the end face of the 3 - 4 command valve (31c).

The shift valve B2 (62) is held in the upper position and the 3 - 4 command valve (31c) switches to the right.

At the end face of the 3 - 4 shift pressure shift valve (29c) the working pressure (p-A) is replaced by shift valve pressure (p-SV).





Shift from "N" to "D" (engagement process active)
The selector valve (52) opens the shift pressure (p-S) feed connection from the ball valve (33b) with the shift valve B2 (62). In the upper position of the shift valve B2 (62) shift pressure (p-S) is applied.

(p-S) downstream of the piston of the multidisk brake B2 (22a) and simultaneously to the mating surface of the multidisk brake piston B2 (22b). The multidisk brake B2 starts to close.

The pressure applied to the opposed surface of the piston of multi-disk brake B2 (22b) ensures soft engagement of the multi-disk brake B2.

The electronic transmission-control control unit (N15/3) monitors the engagement process via the reduced speed of the input shaft as the frictional connection of the rear multiple-disc brake B2 increases. With a corresponding rpm drop the electronic transmission-control control unit switches off the current to the 3-4 gearshift solenoid valve.

The spring chamber of the shift valve B2 (62) is depressurized and switches downwards. This causes the line to the opposed surface of the piston of multi-disk brake B2 (22b) to connect to the pressure holding valve (32). The pressure on the opposed surface of the piston of multi-disk brake B2 (22b) drops to a residual pressure. The 3-4 command valve (31c) moves to the left. Working pressure (p-A) is applied to the piston of multi-disk brake B2 (22a) via the 3 - 4 holding pressure shift valve (28c) and the 3 - 4 command valve (31c).

The activation sequence is complete; 1st gear is engaged.





Shift from "N" to "R"
The selector valve (52) opens the shift pressure (p-S) feed connection to the multi-disk brake B3 (23). There is no opposed surface at the piston of multi-disk brake B3 (23). The engagement process is then identical to that for engaging the multi-disk brake B2.

Residual pressure
When the transmission is in stationary mode the line system remains filled with oil. As a result no air can enter the hydraulic system and reduce the shift quality.