GF27.60-P-2002AHL Transmission Control, Function
GF27.60-P-2002AHL Transmission Control, Function
- TRANSMISSION 722.9 (except 722.930 /931) in MODEL 212
Function requirements for transmission control, general
^ Circuit 87 ON
^ Function test of fully integrated transmission control unit (Y3/8n4) carried out
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 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. 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 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
Production breakpoint for ECO start/stop function
- Model 212.0/2 with engine 271.8 as of 1.3.2011
- Model 212.0/2 with engine 276.9 and 278.9 as of 1.6.2011
- Model 212.0/2 with engine 651.9 as of 1.6.2011
- Model 212.0/2 with engine 642.8 as of 1.12.2011
Depending on the model, the production breakpoint for the ECO start/stop function may be at a later time.
Basic shift program function sequence
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 via the automatic transmission mode button (S16/12) on the lower control panel control unit (N72).
The shift programs are adapted by offsetting the characteristics, depending on:
- Load condition of vehicle
- Change in driving resistance
- Pedal movement
The fully integrated transmission 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 the drive train CAN (CAN C)
Slow accelerator release
- Undesired downshifts in the upper vehicle speed range are 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 for the hydraulic elements such as hydrodynamic torque converter, actuators and hydraulic transmission control is provided through an oil pump (primary pump) connected to the torque converter or through the electric transmission oil pump (M42) (with code (B03) ECO start/stop function). 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.
For code (B03) ECO Start-stop function
The electric transmission oil pump provides the hydraulic system's oil supply when the internal combustion engine is switched off. It also supports the primary pump when the combustion engine is operating in the low speed range. This is actuated through the gear oil auxiliary pump control unit (N89).
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 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
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.
The forced downshift into the next lower gear is performed when transmission temperatures are too high and lower Vehicle speed.
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.
Using the DIRECT SELECT lever (S16/13) the driver can engage the desired gear ranges "P, R, N, D"
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.
