Mercedes-Benz ML320. Service manual — part 173

Fig. 89: Holding Pressure Shift Valve, Function
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Operation - The holding pressure shift valve (28) is engaged by pressure in the shift elements acting on the
front face and spring. It assigns the working pressure (p-A) to the shift element with the higher pressure (taking
into account the spring force and the effective area). See Fig. 89.

The other element of the shift group is then unpressurized. The valve switches over only during the shift phase
and only at a certain pressure ratio between the overlap pressure (p-U) and the shift pressure (p-S).

Shift Pressure Shift Valve, Location/Task/Function

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

Fig. 90: Shift Pressure Shift Valve, Location/Task/Function
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Shift Pressure Shift Valve, Location

Each shift group possesses one shift pressure shift valve. The 1-2/4-5 shift pressure shift valves (29a) and
2-3 shift pressure shift valve (29b) are installed in the valve housing of the shift plate (2b), the 3-4 shift
pressure shift valve (29c) is installed in the valve housing of the shift plate (2a). See Fig. 90.

Shift Pressure Shift Valve, Task

To assign shift pressure to the engaging shift actuator and to assign the overlap pressure, controlled by the
overlap regulating valve, to the disengaging shift actuator.

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

Shift Pressure Shift Valve, Function

See SHIFT PRESSURE SHIFT VALVE, FUNCTION.

Shift Pressure Shift Valve, Function

Fig. 91: Shift Pressure Shift Valve, Function
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Operation - When the multiple-disc brake (B) is engaged, the working pressure (p-A) is applied to the end face
of the shift valve (29) via the command valve (31). See Fig. 91. Its shift condition is retained in the shift phase,

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me

whilst the shift element pressure acting on the end face and which is variable during the shift phase is replaced
by a corresponding, constant pressure.

When the multiple-disc clutch (K) is engaged (K) the end face of the shift pressure shift valve (29) is
depressurized during the stationary and shift phases, here the shift condition is also retained during the shift
phase.

Shift Pressure Regulating Valve, Location/Task/Function Also Float, Location/Function

2001 Mercedes-Benz ML320

1998-03 AUTOMATIC TRANSMISSIONS Complete Transmissions - ML 320 - 722.662

me