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

Transmission 725.0 in model 253 

Function requirements for Engage gear range, general 

• Circuit 15 ON
• Internal combustion 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.

Function sequence for engage gear range Shift "N" to "D1" (described using 1st gear) 

If the gear range "N" is selected via the DIRECT SELECT lever (S16/13), the B06 multidisk brake and the B05 multidisk brake are engaged. When shifted from position "N" to position "D1" by the fully integrated transmission control unit (Y3/8n4), the K38 clutch control solenoid (Y3/8y14) is actuated, the supply to the K38 multidisk clutch is enabled and the K38 multidisk clutch is filled with oil.

From the rpm difference (actual slip) of engine speed to turbine wheel speed, the fully integrated transmission control unit detects whether the K38 multidisk clutch is filled.

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. Depending on this, the K38 clutch control solenoid is used to modify the control pressure to the K38 multidisk clutch regulating valve. 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.

"No power" in gear range "D" 

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

• After selector lever position "D" is engaged, a vehicle speed of v = approx. 15 km/h must be exceeded once.
• Function sequence of "no power" in gear range "D" is activated when one of the following conditions is met:

• Stall protection activated by the VGS (depending on geographical altitude and at low outside temperatures)
• The VGS initiates braked or unbraked coast down shifting from 2nd gear to 1st gear when driving.
• The function sequence of "no power" in gear range "D" is activated each time the vehicle stops in selector lever position "D" if the following conditions are met:
• Transmission oil temperature 10°C ≥ T ≤ 110°C
• Coolant temperature 0°C ≥ T ≤ 120°C
• Accelerator not operated
• Engine rpm n < 1000 rpm
• Braking torque at least 250 Nm.
• Transmission's internal calculation of incline is 3 to 6 %
• Transmission mode "E" (Economy) selected
• 1st gear engaged by VGS
• Fully operational fully integrated transmission control.

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

• Driver brakes the vehicle.
• "HOLD function" (Hill Start Assist) is active.
• Vehicle is automatically braked by active Distronic (adaptive cruise control) (DTR), on vehicles with code 233 (DISTRONIC PLUS).

Function sequence for "no power" in gear range "D" at vehicle standstill 

The VGS deenergizes 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 v > 0 km/h
• Transmission oil temperature T > 110°C
• Coolant temperature T > 120°C
• Accelerator operated
• Engine speed n > 1000 rpm
• Braking torque < 250 Nm or brake pedal not operated
• Transmission's internal calculation of incline is > 25 %.
• When the vehicle is stopped after a transmission mode change
• A touch shift has been detected or the DIRECT SELECT selector lever has been shifted out of selector lever position "D" into "N", "R" or "P".
• A VGS system error is detected.
• No driver assistance system for longitudinal control is active.

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

The function requirements must be fulfilled simultaneously when the accelerator pedal is released within a wake-up period (1 s).

Function sequence for "no power" in gear range "D" when driving 

• 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
• Short-term M program not activated
• Selector lever position "D" and selected transmission mode "E"
• Transmission oil temperature 10°C ≥ T ≤ 110°C
• Coolant temperature 0°C ≥ T ≤ 120°C
• Fully operational fully integrated transmission control.

The VGS deenergizes 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 > approx. 1500 Nm
• Braking integral > approx. 150 kJ
• Speed < 50 or > 170 km/h
• Uphill gradient > 7 %
• Downhill gradient > 7 %
• Torque converter temperature T > 10°C or < 110°C Disk temperature T > 120°C
• Manual intervention by driver through the DIRECT SELECT lever or the steering wheel gearshift buttons
• Longitudinal control system, driver activates cruise control or DTR+.