GF27.60-P-2002AHZ Transmission Control, Function
GF27.60-P-2002AHZ Transmission control, function
- Transmission 722.902/903/904/906/907 [model 164.1]
- Transmission 722.902/903/904 [model 164.8]
- Transmission 722.902/904/906/999 [model 251.1]
Function requirements for transmission control, general
^ Circuit 87 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 positioned on the electric controller unit (VGS). This implements the hydraulic functions. The function of the electric controller unit (VGS) 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 subdivided into 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 basic shift program can be influenced by the driver through the transmission mode switch (N72/1s32).
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 (VGS) control unit (Y3/8n4) 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 engine compartment 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 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 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 kick down.
The transmission control system prevents impermissibly high engine speeds with a downshift lock-out 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 kick down function.
The kick down function is activated as of a pedal travel greater than 90 %. The "Kick-down" signal is transferred to the fully integrated transmission control unit (VGS) by the CDI control unit (N3/9) or ME-SFI [ME] control unit (N3/10) via the engine compartment CAN. 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 driver can engage the desired gear ranges "P, R, N, D" with the DIRECT SELECT gear selector switch (S16/13).
The driver can choose been forward and reverse travel, engage the park pawl or interrupt the power flow between torque converter and transmission in the neutral position.
