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

Transmission 725.0 in model 463 

Function requirements, general 

• Terminal 15 ON
• Engine running

Engage gear range, general 

Each gear change is triggered by the fully integrated transmission control system. In the process one component group is assigned to each shift operation. A component group consists of the respective solenoid, the regulating valve involved, the responsible shift valve and the required multidisk brake or multidisk clutch. The pressure in the multidisk brake or multidisk clutch to be engaged is increased constantly while at the same time the pressure in the multidisk brake or multidisk clutch to be disengaged is reduced. The process is a smooth transition and the components affected are actuated directly. This makes it possible to downshift, even through several gears.

The engage drive range function is subdivided into the following points:

• Gear range change 
• Shift "N" to "D1" (described using 1st gear) 
• "No power" in gear range "D" 
• "No power" in gear range "D" at vehicle standstill 
• "No power" in gear range "D" when driving 

Gear range change 

Changing between gear ranges is triggered by activating the D/R switchover valve (Y3/8y10) and/or the park pawl switchover valve (Y3/8y11) by the fully integrated transmission control unit (Y3/8n4). The feed to multidisk brake B2 or multidisk brake BR is released over the D/R switchover valve and multidisk brake B2 (gear range "D") or multidisk brake BR (gear range "R") is filled with oil. The feed line to the hydraulic cylinder of the electrohydraulic park pawl actuation system is opened via the park pawl switchover valve. The park pawl switchover valve actuates the park pawl shift valve, which passes on or blocks off the working pressure applied in accordance with the actuation.

Oil pressure switch D/R 1 (Y3/8b3) and oil pressure switch D/R 2 (Y3/8b4) (redundant design) record the position of the D/R shift valve via the supply pressure applied (corresponding to the position of the D/R shift valve). Gear ranges "P" or "Not P" are recorded by the park pawl position sensor (Y3/8s4). Oil pressure switches D/R 1 and D/R 2 as well as the park pawl position sensor are integrated into the controller unit for the fully integrated transmission control (Y3/8).

Shift "N" to "D1" (described using 1st gear) 

In position "N" of the DIRECT SELECT lever (S16/13), multidisk brake B06 and multidisk clutch B05 are engaged. When shifting from the "N" position into the "D1" position using the fully integrated transmission control unit, the clutch control solenoid K38(Y3/8y14) is actuated, the feed to the multiplate clutch K38 released and the multiplate clutch K38 is filled with oil. The fully integrated transmission control unit uses the RPM difference (actual slip) between the crankshaft speed and transmission input speed to detect whether multidisk clutch K38 is full. The K38 clutch control solenoid actuates the K38 multidisk clutch regulating valve, which converts the available working pressure into the shift pressure and forwards it to the K38 multidisk clutch. The fully integrated transmission control unit stores the specified value for the desired timing of the RPM difference for the respective gear. Dependent on this, the multidisk clutch control solenoid K38 is used to modify the control pressure to the multidisk clutch regulating valve K38. The shift pressure generated by the K38 multidisk clutch regulating valve depends on the geometry of the K38. multidisk clutch regulating valve. The pressure in the K38 multidisk clutch is changed until the specified value for the RPM difference stored in the fully integrated transmission control unit is reached.

Function requirements for "no power" in gear range "D" 

• After engaging selector lever position "D" a vehicle speed of at least approx. 15 km/h must be exceeded once

"No power" in gear range "D" 

Function sequence of "no power" in gear range "D" is activated when one of the following conditions is met:

• Stall protection (dependent on geographical altitude and at low outside temperatures) activated by the fully integrated transmission control (VGS)
• VGS initiates braked or unbraked coast down shifting from 2nd gear to 1st gear when driving

The "no power" function sequence in drive range "D" is activated each time the vehicle is at a standstill in selector lever position "D", if the following conditions are met:

• Transmission oil temperature 10 to 110 °C
• Coolant temperature 0 to 120 °C
• Accelerator not operated
• Engine speed lower 1000 RPM
• Braking torque is at least 250 Nm
• Value for transmission-internal calculation of uphill gradient is 3 to 6 %
• Drive program "C" (Comfort) selected
• 1 st gear engaged by VGS

Vehicle standstill can be reached through one of the following conditions:

• Driver brakes the vehicle
• HOLD function (Hill Start Assist) is active
• Vehicle is automatically braked with active DISTRONIC (with code EZ9 (Distance Pilot DISTRONIC) or code EM4 (Driver Assistance Plus Package))

"No power" in gear range "D" at vehicle standstill 

Engine speed above 1000 RPM

The VGS de-energizes the K38 clutch control solenoid so that the shift pressure is reduced via the K38 multidisk clutch regulating valve and the B05 multidisk brake is unpressurized. This reduces the transmission output torque with the vehicle stationary and reduces consumption.

The function sequence of "no power" in gear range "D" at vehicle standstill is deactivated if the following conditions are met:

• Vehicle speed above 0 km/h
• Transmission oil temperature above 110 °C
• Coolant temperature above 120 °C
• Accelerator operated
• Braking torque lower than 250 Nm or brake pedal not operated
• Value of transmission-internal calculation of uphill gradient is above 25 %
• When the vehicle is stopped after a transmission mode change
• A touch shift is detected or the DIRECT SELECT lever is moved from selector lever position "D" to "N", "R" or "P"
• A fully integrated transmission control system error is recognized
• No driver assistance system for longitudinal control is active

"No power" in gear range "D" when driving 

The function sequence of "no power" in gear range "D" when driving is activated if the following conditions are met:

• Accelerator pedal and brake not operated
• Low accelerator pedal gradient (slow accelerator release)
• Speed in "Intercity range" between 60 km/h and 170 km/h
• Gradient of road surface sufficiently level and no tight corners
• The short-term M mode is not active
• Selector lever position "D" and selected transmission mode "C"
• Transmission oil temperature 10 to 110 °C
• Coolant temperature 0 to 120 °C

The VGS de-energizes the solenoid corresponding to the engaged gear so that the shift pressure is reduced and the multidisk brake corresponding to the engaged gear is unpressurized. This results in a reduction in the transmission output torque and a reduction in consumption.

The function sequence of "no power" in gear range "D" when driving is deactivated if the following conditions are met:

• Transmission leaves mode "E"
• Accelerator operated
• Braking torque above 1500 Nm
• Braking integral above 150 kJ
• Speed below 50 or above 170 km/h
• Uphill gradient above 7 %
• Downhill gradient above 7 %
• Converter temperature above 10 °C or below 110 °C
• Multidisk temperature above 120 °C
• Manual intervention by driver through the DIRECT SELECT lever or the steering wheel gearshift buttons
• The driver longitudinal control system activates the cruise control or DTR (with code EZ9 (Distance Pilot DISTRONIC) or code EM4 (Driver Assistance Plus Package))

Overview of system components for automatic transmission (AT)

GF27.10-P-9992ANE