Engage Gear Range, Function - GF27.60-D-3009TSA

Transmission 725.0 in model 907 

Function requirements for Engage gear range, general 

• Circuit 15ON
• Internal combustion engine running.

Engage gear range, function 

The function sequence is described in the following steps:

• Engage gear range, general
• Shift "N" to "D1"
• "No power" in gear range "D"

Engage gear range, general 

Every gear change is triggered by the fully integrated transmission control unit (N15/15n4). In the process one component group is assigned to each shift operation.

A component group consists of the respective solenoids, the regulating valve involved, the responsible shift valve and the required multidisk brake or multiplate 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.

Shift "N" to "D1" 

The process is described here on the 1st gear.

If gear range "N" is selected using the DIRECT SELECT selector lever (S16/13), multidisk brake B06 and multidisk brake B05 are engaged.

When shifting from the "N" position o the "D1" position using the fully integrated transmission control unit, clutch control solenoid K38 (N15/15y14) is actuated, the feed to the multiplate clutch K38 is released and the multiplate clutch K38 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, clutch control solenoids K38 is used to modify the control pressure to multiplate 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 - no power in drive range "D" 

• After engaging selector lever position "D", 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 (depending on geographical altitude and at low outside temperatures) is activated by fully integrated transmission control.
  • The fully integrated transmission control 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 °C < T > 110 °C
  • Coolant temperature 0 °C < T > 120 °C
  • Accelerator not operated
  • Engine speed n > 1000 rpm
  • Braking torque is at least 250 Nm.
  • Value for transmission-internal calculation of uphill gradient is 3 to 6%.
  • Transmission mode "E" (Economy) selected
  • 1st gear of fully integrated transmission control engaged
  • The fully integrated transmission control is operating correctly.

"No power" in gear range "D" 

The function sequence is described in the following steps:

• "No power" in gear range "D" at vehicle standstill
• "No power" in gear range "D" when driving

Additional function requirements - no power in drive range "D" at vehicle stillstand 

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

• Driver brakes the vehicle.
• The "HOLD function" (Hill-Start Assist) is active.
• The vehicle is automatically braked with Active Brake Assist (vehicles with code BA3 (Active Brake Assist)).

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

The fully integrated transmission control deenergizes clutch control solenoids K38 so that the shift pressure is reduced via multiplate clutch regulating valve K38 and multidisk brake B05 is unpressuriz This reduces the transmission output torque with the vehicle station 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
• Value of transmission's internal calculation of incline is > 25 %.
• When the vehicle is stopped after a transmission mode change
• A Touchshift has been detected or the DIRECT SELECT lever has been shifted from selector lever position "D" to "N", "R" or "P".
• A system error in the fully integrated transmission control has been detected.
• No driver assistance system for longitudinal control is active.

Additional function requirements - no power in drive range "D"  in operating status

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

• 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 mode or manual shift mode is not activated.
• Selector lever position "D" and selected drive program "E"
• Transmission oil temperature 10 °C < T > 110 °C
• Coolant temperature 0 °C < T > 120 °C
• The fully integrated transmission control is operating correctly.

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

The fully integrated transmission control deenergizes the solenoids for 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 drive range "D" when driving is deactivated if the following conditions are met:

• Leaving drive program "E"
• Accelerator operated
• Braking torque < approx. 1500 Nm
• Speed > 50 or < 170 km/h
• Uphill gradient of road surface > 7 %
• Downhill gradient of road surface > 7 %
• Torque converter temperature T > 10 °C or < 110 °C
• Disk temperature T > 120 °C
• Manual intervention by driver using DIRECT SELECT lever or by using steering wheel gearshift buttons
• Driver activates cruise control or DISTRONIC.

Overview of system components of automatic transmission (AT)

GF27.10-D-9992TSA