GF27.60-P-2002AHI Transmission Control, Function
GF27.60-P-2002AHI Transmission control, function
- TRANSMISSION 722.930
Function requirements for transmission control, general
^ Circuit 87 ON
^ Function test of electric controller unit (VGS) (Y3/8) performed
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 then realizes the hydraulic functionality.
The function of the electric controller unit (VGS) is 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 starting clutch.
Transmission control function sequence
The function sequence is subdivided into the following steps:
^ Basic shift program
^ Electronic and hydraulic transmission control
^ Kickdown
^ Emergency running
Basic shift program
The basic shift program includes upshift and downshift characteristics for all 7 gears, designed for:
- Empty vehicle
- Warm operating condition
- Level road
- Sea level
The basic shift program can be influenced by the driver using the drive unit transmission mode adjustment rotary switch (S192).
The shift programs are adapted by offsetting the characteristics, depending on:
- Vehicle load
- Change in driving resistance
- 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, for Manual "M" transmission mode
- 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
While the electronic transmission control is responsible for gear selection and for matching the pressures to the torque to be transmitted, the transmission's power supply control occurs via hydraulic elements in the electric controller unit (VGS). The oil supply to the hydraulic elements, such as the starting clutch, shift elements and the hydraulic transmission control, is provided by way of an oil pump connected with the starting clutch. 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 shift range can be changed while driving in the forward gears. 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.
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 is transferred to the fully integrated transmission-control control unit (VGS) by the 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.
The forced downshift into the next lower gear is performed when transmission temperatures are too high and lower Vehicle speed.
Emergency running
If the signals are implausible, the transmission control system is only partially operational and switches to the programmed emergency performance map. The driver can use the selector lever to select the desired gear ranges "P, R, N, and D".
The driver can choose been forward and reverse travel, engage the park pawl or interrupt the power flow between the starting clutch and the transmission when in neutral.
