GF27.60-P-2002ACL Transmission Control, Function
GF27.60-P-2002ACL Transmission control, function
- Transmission 722.618/646/694/696
Function requirements
^ Circuit 87 ON
^ Function test of electronic transmission-control control unit (N15/3) performed
General
The transmission control actuates the following actuators (solenoid valves and control solenoid valves) electronically:
- Modulating pressure control solenoid valve (Y3/6y1)
- Shift pressure control solenoid valve (Y3/6y2)
- 1-2 and 4-5 gearshift solenoid valve (Y3/6y3)
- 3-4 gearshift solenoid valve (Y3/6y4)
- 2-3 gearshift solenoid valve (Y3/6y5)
- Torque converter lockup clutch control solenoid valve (Y3/6y6)
The valves are located in the hydraulic valve body assembly. This implements the hydraulic functions.
The function of the automatic transmission electric controller unit (Y3/6) is primarily to evaluate various input signals that are relevant to transmission operation. Depending on the latter, 8 electromechanical hydraulic valves are actuated which for their part determine the gear ratio of the transmission (gear selection) and torque converter lockup.
Function sequence
The function sequence is described in 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 5 gears, designed for:
- Empty vehicle
- Operating temperature
- Level road
- Sea level
The basic shift program can be influenced by the driver through the automatic transmission's transmission mode button (S16/12)
The shift programs are adapted by offsetting the characteristics, depending on:
- Vehicle load
- Change in driving resistance
- Accelerator pedal movement
The electronic transmission-control control unit monitors and shifts depending on:
- Vehicle speed
- Selector lever position
- Accelerator pedal position
- Transmission mode selection
- 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 slowly
Electronic and hydraulic transmission control function sequence
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 automatic transmission's electrical transmission control unit.
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 led from the CDI control unit (N3/9) (with diesel engine) or ME-SFI control unit (N3/10) (with gasoline engine) to the electronic transmission control control unit via the drive train CAN. Based on this information the electronic transmission control 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
In the case of implausible signals the transmission control is only operational to a limited extent and shifts into the programmed limp-home mode characteristic map. The driver can engage the required gear ranges "P", "R", "N" and "D" using the selector lever. 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.
