GF27.60-P-3009ACM Engage Gear Range, Function
GF27.60-P-3009ACM Engage gear range, function
- TRANSMISSION 722.643/649
- refinement package
- as of model year 09
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
^ Shifting of 1st gear on transmission mode "S"
^ Shifting of 2nd gear on transmission mode "C"
Gear range engagement, general
Each gear change is triggered by the electronic transmission control. Each shift sequence is assigned a control block.
In each case these include 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 (shift solenoid valve).
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 N to D (engagement process active)
^ Shift N to R
Start engine (circuit 61 ON)
The working pressure reaches the multidisk clutch K3 via the ball valve and the end face of the 3-4 shift pressure shift valve via the 3-4 command 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.
As a result shift valve pressure reaches into the spring chamber of the shift valve B2 and onto 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 shifts to the right.
The working pressure is replaced by the shift valve pressure on the end face of the 3-4 shift pressure shift valve.
Shift N to D (engagement process active)
The selector valve opens the connection of the feed for shift pressure from the ball valve with the shift valve B2. In the upper position of the shift valve B2 shift pressure reaches behind the piston of the multidisk brake B2 and simultaneously reaches the mating surface of the piston of the multidisk brake B2. The multidisk brake B2 begins to close.
The compression on the opposite surface of the piston of the multidisk brake B2 causes multidisk brake to be connected gently 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. With a corresponding speed reduction the electronic transmission control control unit switches off the current to the 3-4 shift solenoid valve.
The spring chamber of the shift valve B2 is unpressurized and switches downwards. As a result the line to the opposite surface of the piston of the multidisk brake B2 is connected to the pressure holding valve. The pressure on the opposite surface of the multidisk brake B2 drops to a residual pressure.
The 3-4 command valve switches to the left. Working pressure reaches the piston of the multidisk brake via the 34 holding pressure shift valve and 34 command valve B2. The activation sequence is complete; 1st gear is engaged.
Shift N to R
The selector valve opens the connection of the feed for shift pressure with the multidisk brake B3. There is no mating surface on the piston of the multidisk brake B3. The continued sequence of the engagement process corresponds to the sequence when engaging the multidisk brake B2.
Residual pressures
The line system remains filled with oil in the steady-state mode of the transmission. As a result no air can enter the hydraulic system and reduce the shift quality.
