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

TRANSMISSION 722.649 in MODEL 216.3 as of Model Year 09 /YoM 08

TRANSMISSION 722.649 in MODEL 221.1 as of Model Year 09 /YoM 08

Function requirements for gear range engagement, general

Circuit 87 ON
Circuit 61 OFF
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. Each shift sequence is assigned a control block.

For this purpose 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), function sequence
Shift from "N" to "D" (engagement process active), function sequence
Shift from "N" to "R", function sequence

Start engine (circuit 61 ON), function sequence

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. At the same time the 3-4 shift solenoid valve (Y3/6y4) is energized.

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).

Fig 1: Identifying Gear Range Engagement Function Diagram

Courtesy of MERCEDES-BENZ USA

Shown here, applied position at circuit

Shift from "N" to "D" (engagement process active), function sequence

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 multidisk brake B2 (22b) ensures soft engagement of the multidisk 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. With a corresponding rpm drop the ETC control unit switches off the current to the 3-4 shift 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 multidisk brake B2 (22b) to connect to the pressure holding valve (32). The pressure on the opposed surface of the piston of multidisk 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.

Fig 2: Identifying Gear Range Engagement Function Diagram (Shift From N To D)

Courtesy of MERCEDES-BENZ USA

Shown here, applied position when shifting "N" to "D"

Shift from "N" to "R", function sequence

The selector valve (52) opens the shift pressure (p-S) feed connection to the multidisk brake B3 (23). There is no opposed surface at the piston of multidisk 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.

Fig 3: Identifying Gear Range Engagement Function Diagram (Shift From N To R)

Courtesy of MERCEDES-BENZ USA

Shown here, applied position when shifting "N" to "R"

Electronic transmission control unit, component description

N15/3

GF27.60-P-5164ACS