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Gear Shift, Function - GF27.60-P-2000ANE

Transmission 725.0 in model 463 

Function requirements, general 

Shift operation, general 

Use of the fully integrated transmission control means that an additional mechanical or electronic gear range adjustment system is no longer necessary. The fully integrated transmission control initiates all shift operations and gear range changes by means of electrohydraulic actuation. The DIRECT SELECT lever (S16/13) located at the right on the steering column tube module is used to select drive ranges "P", "R", "N" and "D". The shift positions of the DIRECT SELECT lever are read in by the steering column tube module control unit (N80) and sent via chassis FlexRay (Flex E), powertrain control unit (N127) and drivetrain CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

IMPORTANTMessages and displays in instrument cluster (A1) 

Information on the selected gear, the engaged gear range and the transmission mode is sent by the fully integrated transmission control unit via the drivetrain CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit (N73) and user interface CAN (CAN HMI) to the instrument cluster. This then actuates the relevant display. The CDI control unit (N3/9) or the ME-SFI control unit (N3/10) sends the status of the engine management, the signal for "operational drivetrain" and the signal for "engine running" via the drivetrain CAN to the fully integrated transmission control unit.

The fully integrated transmission control unit processes the signals for the following components:

The following component parts are actuated by the fully integrated transmission control unit:

The following data is exchanged between the fully integrated transmission control unit and the CDI control unit or ME-SFI [ME] control unit via the drivetrain CAN:

The gearshift system is subdivided into the following points:

Data transfer during shift operations 

Compared to the Sport "S" transmission mode, the Comfort "C" transmission mode has a shorter shift range (shifting at low RPM of the combustion engine or the electric machine) and therefore a lower drive torque is available when starting off forwards and starting off in reverse. Reverse gear, park position and neutral can only be shifted via the DIRECT SELECT lever.

The basic shifting program can be influenced by the driver via the DYNAMIC SELECT switch (N72/4s1), which is located in the area of the center console in the left lower control panel (N72/4). The left lower control panel sends the signal over the LCP-LIN (LIN A3), Audio/COMAND control panel (A40/9), telematics CAN (CAN A), head unit (A26/17), user interface CAN, electronic ignition lock control unit and the suspension FlexRay to the Electronic Stability Program control unit (N30/4). The Electronic Stability Program control unit sends information about the selected drive program over the suspension FlexRay, powertrain control unit and the drive CAN to the fully integrated transmission control unit.

In the Sport PLUS ("S+") and Sport "S" transmission modes, the driver can also select the following function by operating the steering wheel downshift button (S110/1) and the steering wheel upshift button (S111/1):

Activate gear limitation 

Pressing the steering wheel downshift button once activates the gear limitation function (if the speed of the internal combustion engine permits, a downshift is made to the gear immediately below the currently selected one).

Shift to optimum gear 

The function "Shift into optimum gear" is selected by pressing and holding the downshift steering wheel gearshift button. The gear that allows optimum vehicle acceleration is selected.

Increase gearshift limitation 

Pressing the steering wheel upshift button once with gear limitation selected increases gearshift limitation by one gear (e.g. from 3 to 4).

Cancel gear limitation 

Pressing and holding down the upshift steering wheel gearshift button cancels the gear limitation function completely (gearshift to "D").

The steering wheel electronics (N135) read in the signals directly from the steering wheel gearshift buttons and sends them over the steering wheel CAN (CAN LR), steering column tube module control unit, suspension FlexRay, powertrain control unit and the drive CAN to the fully integrated transmission control unit. This control unit converts the request into hydraulic signals which are executed by the respective regulating valve.

Shifting (described shifting from 1st Into 2nd gear) 

Multidisk brake B05, multidisk brake B06 and multidisk clutch K38 are engaged in 1st gear. When shifting from 1st gear to 2nd gear, multidisk brake B05 is disengaged and multidisk clutch K81 is engaged. The shift operation can be started by the fully integrated transmission control unit. Here, the multidisk brake B08 is filled and the pressure in multidisk brake B08 is increased continuously. Simultaneously the pressure in multidisk brake B06 is reduced. This involves a flowing transition. When the 2nd gear torque is reached, the speed of the internal combustion engine must be adapted to the 2nd gear level (elevation phase). This speed adjustment is achieved by increasing the pressure in the multidisk brake B08 and, if necessary, reducing the engine torque through the CDI control unit or ME-SFI [ME] control unit.

IMPORTANT A forced downshift occurs at excessively low RPM and a forced upshift occurs at an excessively high RPM. If the vehicle is stationary, 1st gear is automatically selected. It is possible to start off both in 1st or 2nd gear.

IMPORTANTShort-term M program 

The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons are operated. When one of the steering wheel gearshift buttons is operated, the transmission control switches up or down a gear, if it is allowed. If not, the current gear is maintained. After a specified time window, the short-term M mode is deactivated. The time window can be extended by undershooting a minimum speed (e.g. stopping), upon recognition of a lateral acceleration or if the vehicle is in overrun mode. After this time window has elapsed, a switch is made back to the initial shift program. The driver can prematurely end the short-term M program through specific actions, e.g. if he presses and holds the steering wheel upshift button, changes the drive range or changes the drive program. In this case, a switch is made to the initial shift program.

IMPORTANTPermanent M-program setting 

The M-program is activated when the manual shifting mode button (N72/4s12) is operated. Upon pressing the steering wheel gearshift buttons, the transmission control upshifts or downshifts if this is allowed. If not, the current gear is maintained.

If the permanent setting is activated, the automatic transmission does not automatically perform an upshift even when the engine's maximum governed RPM is reached.

  Electrical function schematic for shift operation   PE27.19-P-2057-97ZGC 
  Overview of system components for automatic transmission (AT)   GF27.10-P-9992ANE 
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