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

GF27.60-P-2002LEH Transmission control, function
- TRANSMISSION 722.950

Function requirements for transmission control, general
^ Circuit 87 (connected circuit 15) ON
^ Function check performed on fully integrated transmission control unit (VGS) (Y3/8n4)

Transmission control, general
The transmission control system electronically actuates the actuators (control solenoid valves). The valves are located in the hydraulic valve body assembly. This contains the hydraulic functions.

The function of the electric controller unit (VGS) (Y3/8) is primarily to evaluate various input signals that are relevant to transmission operation. Based on this, eight electromechanical hydraulic valves are actuated which determine the gear ratio of the transmission (gear selection), the working pressure and the torque converter lockup.

Transmission control function sequence
The function sequence is described i : n the following steps:

^ Basic shift program function sequence
^ Electronic and hydraulic transmission control function sequence
^ Kick-down function sequence
^ Limp-home mode function sequence

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

- Empty vehicle
- Operating temperature
- Level road
- Sea level

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

- Vehicle load
- Change in driving resistance
- Accelerator pedal movement

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

- Vehicle speed
- Selector lever position
- Accelerator pedal position
- Transmission mode selection
- Selected gear in transmission mode Manual "M" (except code (494) USA version)
- Signals on the drive train CAN (CAN C)

Slow accelerator release:

- Undesired downshifts in the upper vehicle speed range are prevented

Rapid accelerator release:

- Upshifting to the next gear up is prevented and only permitted again when the vehicle accelerates more slowly

Electronic and hydraulic transmission control function sequence
Whilst the electronic transmission control takes over the gear selection and adaptation of pressures to the torque to be transmitted, the power supply of the transmission is controlled via the hydraulic elements of the electric controller unit (VGS). The oil supply to the hydraulic elements, such as the hydrodynamic torque converter, the shift elements and the hydraulic transmission control, is provided by way of an oil pump connected to the torque converter. The electric transmission oil pump (M42) safeguards the hydraulic system's oil supply when the internal combustion engine is switched off. It also supports the primary pump during coast down shifting in hot idling. This is actuated through the gear oil auxiliary pump control unit (N89).

The transmission control system makes possible a precise adaptation of pressures to the respective operating conditions 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 impermissibly high engine speeds with a downshift lockout device. Furthermore, the transmission control system offers the advantage of a flexible adaptation to various vehicle and engine versions.

Kick-down function sequence
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 "kickdown" signal is sent from the accelerator pedal sensor (B37) to the ME-SFI [ME] control unit (N3/10), and forwarded over the drive train CAN to the fully integrated transmission control unit (VGS).

Based on this information the fully integrated transmission control (VGS) control unit actuates the control solenoid valves so that the upshifts and downshifts take place at higher engine speeds in order to achieve maximum performance.

Limp-home mode function sequence
If the signals are implausible, the transmission control system is only partially operational and switches to the programmed emergency performance map.

The malfunction is filed along with the assigned fault code in the fault memory and the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) is actuated by the central gateway control unit (N93) via the central CAN (CAN F).

The malfunction is also notified to the ME-SFI [ME] control unit over the drive train CAN.