GF27.60-P-2002AHC Transmission Control, Function
GF27.60-P-2002AHC Transmission control, function
- Transmission 722.902/904/906/908
Function requirements
^ Circuit 87 ON
^ Function test of fully integrated transmission control unit (Y3/8n4) carried out
General
The transmission control actuates the following actuators electronically:
- Working pressure control solenoid valve (Y3/8y1)
- Clutch control solenoid valve K1 (Y3/8y2)
- Clutch control solenoid valve K2 (Y3/8y3)
- Clutch control solenoid valve K3 (Y3/8y4)
- Multidisk brake control solenoid valve B1 (Y3/8y5)
- Multidisk brake control solenoid valve B2 (Y3/8y6)
- Multidisk brake control solenoid valve B3 (Y3/8y7)
- Torque converter lockup clutch control solenoid valve (Y3/8y8)
The valves are located in the hydraulic valve body assembly. This implements the hydraulic functions.
The function of the fully integrated transmission control controller unit (Y3/8) basically consists of the evaluation of various input signals relevant to the function. Depending on the latter, 8 electromechanical hydraulic valves are actuated which for their part determine the gear ratio of the transmission (gear selection), the working pressure 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 7 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 fully integrated transmission control unit 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 slowly
Electronic and hydraulic transmission control function sequence
While the electronic transmission control takes over the gear selection and adaptation of pressures to the torque to be transmitted, the power supply control of the transmission via the hydraulic elements of the fully integrated transmission controller 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 engines) or ME-SFI control unit (N3/10) (with gasoline engines) to the fully integrated transmission control unit via the drive train CAN.
Based on this information the fully integrated transmission control unit actuates the control solenoid valves so that upshifts and downshifts take place at an increased engine speed 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 fault is stored in the fault memory with the assigned fault code and the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) is actuated.
The driver can engage the required gear ranges "P", "R", "N" and "D" with 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.
