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

TRANSMISSION 724.204 in MODEL 166 

Function requirements for transmission control, general 

Transmission control, general 

The transmission control activates the actuators (control solenoid valves, switchover valves) electronically. The control solenoid valves are located in the hydraulic valve body assembly. This implements the hydraulic functions. The function of the fully integrated transmission control unit basically consists of the evaluation of various input signals relevant to the transmission function. Depending on these, ten electromechanical control solenoid valves are actuated which in turn determine the transmission ratio of the transmission (gear selection), the gear ranges ("P" or "Not P", "R" and "D"), the working pressure and control of the wet clutch.

The fully integrated transmission control unit and the ME-SFI [ME] control unit (N3/10) read in the status of Circuit 15 ON to check the function requirements. The status of "Circuit 15 ON" from the electronic ignition lock control unit (N73) (transmitter key (A8/1) inserted) over the chassis CAN 1 (CAN E1) to the powertrain control unit (N127). The powertrain control unit sends the status via the drive train CAN (CAN C) to the fully integrated transmission control unit and via the engine CAN (CAN C1) to the ME-SFI [ME] control unit.

Gear ranges "P", "R", "N", "D" are selected using the DIRECT SELECT lever (S16/13) located on the right of the steering column tube module control unit (N80). The selector lever positions "P", "R", "N", "D" are transmitted from the DIRECT SELECT lever through the steering column tube module control unit on the chassis CAN 1 to the powertrain control unit. This relays the information via the drive train CAN to the fully integrated transmission control unit.

The ME-SFI [ME] control unit receives the status of the electric machine (A79/1) from the power electronics control unit (N129/1) over the engine CAN (CAN C), powertrain control unit, and the hybrid CAN (CAN L).

IMPORTANT The enable signal from the drive authorization system is sent from the electronic ignition lock control unit via the chassis CAN 1 to the powertrain control unit. The powertrain control unit sends the enable via the drive train CAN to the fully integrated transmission control unit and via the engine CAN to the ME-SFI [ME] control unit. The following control solenoid valves are actuated by the fully integrated transmission control unit:

The following components are switched on by the fully integrated transmission control unit:

The following signals are read in by the fully integrated transmission control unit:

The following data is exchanged via the drive train CAN, powertrain control unit, and engine CAN between the fully integrated transmission control unit and ME-SFI [ME] control unit:

IMPORTANT Messages and displays in instrument cluster

Messages and requests are sent by the fully integrated transmission control unit to the drive train CAN. The powertrain control unit receives and forwards these over the chassis CAN1, electronic ignition lock control unit and chassis CAN 2 (CAN E2) to the instrument cluster. This then actuates the multifunction display (A1p13) or the engine diagnosis indicator lamp (A1 e58). The information is also sent via the drive train CAN, powertrain control unit, and engine CAN to the ME-SFI [ME] control unit.

Transmission control function sequence 

The function sequence is subdivided into the following steps:

Function sequence for basic shift program 

The basic shift program includes upshift and downshift characteristics for all 7 gears, designed for:

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

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

The Electronic Stability Program control unit (N30/4) receives the sensor signal 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 the signal from the pedal angle sensor (B37/1) and sends the vehicle speed and the service brake status to the powertrain control unit over the chassis CAN 1. This routes the status over the drive train CAN to the fully integrated transmission control unit and over the engine CAN to the ME-SFI [ME] control unit.

Slow accelerator release:

Rapid accelerator release:

The basic shift program can be influenced by the driver via the transmission mode control (N72/4s1). The controller status is sent via the transmission mode control panel (N72/4), center console switch LIN (LIN B12), SAM control unit (N10), and interior CAN (CAN B) to the electronic ignition lock control unit and via the chassis CAN 1, powertrain control unit, and drive train CAN to the fully integrated transmission control unit.

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control is responsible for gear selection and the adaptation of pressures to the torque to be transferred, the automatic transmission's power supply is controlled through the hydraulic elements of the fully integrated transmission controller unit (Y3/8). The oil to the hydraulic elements (wet clutch, shift elements, hydraulic transmission control) is supplied through an oil pump (primary pump) connected to the transmission input shaft or through the electric transmission oil pump. The transmission control system allows for precise adaptation of pressures to the respective operating conditions and to the engine output or output of the electric machine during the shift phase, which results in a significant increase 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 Using the two switchover valves (D/R switchover valve and park pawl switchover valve) installed on the fully integrated transmission controller unit, gear range selection is carried out electrohydraulically and there is no need for an intelligent servo module.

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function. The kickdown function is activated as of a pedal travel > 90%. The "kick-down" signal from the accelerator pedal sensor (B37) is read in by the ME-SFI [ME] control unit.

Function sequence for limp-home mode 

If the signals are implausible, the transmission control system is only partially operational and switches to the programmed emergency performance map. The fault is stored with the assigned fault code in the fault memory. Due to integration of the DIRECT SELECT shift components (D/R switchover valve and park pawl switchover valve) in the fully integrated transmission control controller unit, the hydraulic limp-home function no longer functions if the fully integrated transmission control unit malfunctions. If the hydraulic control system fails, e.g. due to interruption of the power supply of the fully integrated transmission control unit, the park pawl is engaged through actuation of the park pawl lift solenoid by the electronic ignition lock control unit via the AUX power supply line. It is only possible to release the park pawl hydraulically via the park pawl switchover valve.

IMPORTANT Up to 16 faults can be stored simultaneously in the fault memory. These can be read out using Xentry diagnostics. The status of the transmission control diagnosis is sent to the diagnostic connector (X11/4) by the fully integrated transmission control unit over the drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit, and the diagnostic CAN (CAN D).

IMPORTANTIntroduction of short-term M program 

The gear limitation is replaced by the function "Short-term M mode". The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons are operated. Pressing in the positive (+) direction triggers an upshift and pressing in the negative (-) direction triggers a downshift, insofar as this is permissible. If not, the current gear is maintained. After a specified time window, this function deactivates again automatically. The activated time can be extended by undershooting a minimum speed (e.g. stopping), upon recognition of a lateral acceleration or if the vehicle is in a deceleration phase. If none of the stated criteria are active anymore, the short-term M mode remains active for a prescribed remaining time. After this remaining time has elapsed, a switch is made back to the initial shift program. In addition, the driver is shown a recommended shift operation in the instrument cluster. This is part of the gearshift recommendation that is also integrated. The driver can prematurely cancel the short-term M mode through specific actions, e.g. if he/she presses and holds the steering wheel upshift button in the "positive" direction (+), if the gear range changes or if he/she changes the transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

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