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Transmission Control, Function - GF27.60-P-2002ANE

Transmission 725.0 in model 463 

Function requirements in general 

Transmission control, general 

The function of the fully integrated transmission control unit (Y3/8n4) consists of the evaluation of various input signals (relevant for the transmission function). Depending on these, the electromechanical hydraulic valves (solenoids) are actuated which in turn determine the transmission ratio of the automatic transmission (gear selection), the gear ranges ("P", "N" "R", and "D") and the working pressure. The solenoids are positioned on the fully integrated transmission control controller unit (Y3/8) and they ensure the hydraulic usability is given. The fully integrated transmission control unit and the CDI control unit (N3/9) (diesel engine) or ME-SFI [ME] control unit (N3/10) (gasoline engine) read in the status of circuit 15 to check the function requirements. The status of circuit 15 is sent by the electronic ignition lock control unit (N73) over the chassis FlexRay (Flex E), powertrain control unit (N127) and the drivetrain CAN (CAN C1).

Gear ranges "P", "R", "N" and "D" are selected using the DIRECT SELECT lever (S16/13) which is located on the right of the steering column tube module control unit (N80). The steering column tube module control unit reads in the DIRECT SELECT lever signals directly and sends them over the chassis FlexRay, powertrain control unit and the drivetrain CAN to the fully integrated transmission control unit. The fully integrated transmission control unit processes the signals for the following components:

The fully integrated transmission control unit actuates the following assembly parts directly:

The fully integrated transmission control unit also receives and sends the following signals:

IMPORTANTMessages and displays in instrument cluster (A1) 

Messages are sent by the fully integrated transmission control unit over the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and the user interface CAN (CAN HMI) to the instrument cluster.

The transmission control is subdivided into the following points:

Basic shift program 

The basic shift program includes upshift and downshift characteristics for all nine gears, designed for:

The shift programs are adapted by offsetting the characteristics, depending on:

IMPORTANT The trailer recognition control unit (N28/1) sends the status of the trailer recognition over the interior CAN (CAN B), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and the drive CAN to the fully integrated transmission control unit.

The fully integrated transmission control unit monitors and shifts (gear) depending on:

The Electronic Stability Program control unit (N30/4) receives the signals from the left front axle RPM sensor (L6/1), right front axle RPM sensor (L6/2), left rear axle RPM sensor (L6/3), right rear axle RPM sensor (L6/4) and routes the vehicle speed over the suspension FlexRay, powertrain control unit and the drive CAN to the fully integrated transmission control unit and the CDI control unit or the ME-SFI [ME] control unit.

The powertrain control unit reads in the signals from the accelerator pedal sensor (B37) directly and sends them via the drivetrain CAN to the fully integrated transmission control unit.

Slow accelerator release:

Rapid accelerator release:

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 status via 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, chassis FlexRay, powertrain control unit and drivetrain CAN to the fully integrated transmission control unit.

Electronic and hydraulic transmission control 

While the electronic transmission control is responsible for gear selection and adaptation of pressures to the torque to be transmitted, power supply control for the automatic transmission is performed by the hydraulic elements of the fully integrated transmission control controller unit. The oil supply for the hydraulic elements (hydrodynamic torque converter, shift elements, hydraulic transmission control) is provided through an oil pump (primary pump) connected to the drive shaft or through the electric transmission oil pump. The transmission control system makes possible a precise adaptation of pressures to the respective operating states and to the engine output during the gearshift phase, resulting in a significant improvement in shift quality. It is possible to reach the engine RPM limit in the individual gears using full throttle and kickdown. The transmission control system prevents impermissible high engine speeds with a downshift lockout function. Furthermore, the transmission control system offers the advantage of a flexible adaptation to various vehicle and engine versions.

IMPORTANT The electric transmission oil pump ensures a continued supply of oil to the hydraulic system when the combustion engine is switched off. It also supports the primary pump in the combustion engine's lower speed range. The CDI control unit (diesel engine) or the ME-SFI [ME] control unit (gasoline engine) sends the "Electric transmission oil pump ON" request over the drive CAN to the fully integrated transmission control unit. The fully integrated transmission control unit actuates the electric transmission oil pump directly and sends the status over the drive CAN to the CDI control unit or the ME-SFI [ME] control unit.

Kickdown 

The driver's wish for maximum acceleration is met by the kickdown function. The kickdown function is activated as from a pedal travel of more than 90 %. The "kick-down" signal from the accelerator pedal sensor is read in by the powertrain control unit. The powertrain control unit sends the signals from the accelerator pedal sensor over the drive CAN to the fully integrated transmission control unit. Based on this information the fully integrated transmission control unit actuates the solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.

Limp-home mode 

In the event of a defective solenoid, the corresponding gear is then locked. This gear can no longer be selected. The driver can engage the desired gear ranges "P", "R", "N" or "D" using the DIRECT SELECT lever. The driver can choose been forward and reverse travel, engage the park pawl or, when in neutral, interrupt the power flow between torque converter and automatic transmission.

  Electrical function schematic, fully integrated transmission control   PE27.19-P-2061-97ZGB 
  Overview of system components for automatic transmission (AT)   GF27.10-P-9992ANE 
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