Automatic Program
ADAPTIVE SHIFT CURVE ADAPTATIONThe transmission control unit uses the following signals to determine the optimum shift curve:
Measuring parameter Type of measurement
Throttle position Potentiometer resistance
Throttle positioning speed Time for change of resistance at potentiometer
Engine speed Frequency measurement (from DME)
Vehicle speed No. of pulses of transmission shaft rotor
Vehicle transverse accel Signal of transverse acceleration sensor on center console
Vehicle axial accel/decel Change of number of pulses within clock time (time-dependent change of speed)
The above signals and measurement parameters are determined within time intervals of 30...100 milliseconds and are processed in the control unit.
When these measurements are compared with the stored programs, factors are generated that can be used to enter or shift into one of the five shift maps.
The change from SC1 (very comfortable and economical shifting) to SC5 (very sporting shifting) can be accomplished within a minimum of 60 seconds.
Adaptive shift curve adaptation remains active all the time (including the manual program).
NOTE: In addition to five shift maps that are determined automatically by the control unit in accordance with the style of driving, the electronic transmission control can also be activated briefly by the driver (short-term input).
ACTIVE GEAR SHIFT (SKIP INTO SPORTING SHIFT MAP SC5)
If the accelerator is depressed suddenly and abruptly, the system shifts immediately from the current shift map into the shift map offering maximum output (SC5). When the acceleration process is completed, the previously used shift map is selected again.
UPSHIFT PREVENTION
Prevents thrust upshifts ahead of bends
When the accelerator is released rapidly ahead of curves (throttle control speed), the control unit detects this driving situation and prevents shifting.
STAYING IN GEAR DURING CORNERING
The transverse acceleration sensor sends a signal to the control unit as soon as vehicle exceeds the transverse acceleration thresholds at which no shifts should be made. The engaged gear then remains selected regardless of any accelerator movement.
SLIP MONITORING
The engine braking effect during coasting, especially in the lower gears and on slippery surfaces, may cause the driven wheels to slip or even to lock. This status, i.e. the wheel speed difference between front and rear wheels, is detected by the transmission control unit (Using input from the ABS control unit, this unit constantly compares the speed of the driven wheels to the speed of the right- hand front wheel). To increase vehicle stability, the next higher gear is then selected immediately and the torque converter lockup clutch is opened.
WARM-UP MAP
To ensure that the catalytic converter reaches its operating temperature as fast as possible, the transmission selects a shift map with higher shift speeds within the automatic program during the engine warm-up phase.
When moving off for the first time and while the engine is cold, the vehicle moves off in 1St gear. The control signal is computed in the DME control unit and is sent to the transmission control unit.
TRANSMISSION PROTECTION AT HIGH ATF TEMPERATURES
To avoid excessive loads on transmission components due to overheating, the transmission control unit selects a shift map with minimum power loss within a specified temperature range and closes the torque converter lockup clutch.
As an additional protective measure, the transmission shifts down at higher engine speeds.
ELECTRONIC KICKDOWN LATCHING
The kickdown latching function allows the kickdown shift points (= max. rpm) to be used even at smaller throttle angles. The function is started when the kickdown switch is actuated and the accelerator is released rapidly (e.g. interrupted kickdown overtaking).
This condition is detected and processed by the transmission control unit. The kickdown shift speeds remain active until the accelerator is released to 50% of the full-throttle position.
DOWNSHIFTING DURING BRAKING (AHEAD OF BENDS)
Depending on actuation of the brakes, brake deceleration, transverse acceleration and vehicle speed, downshifts are executed during braking at higher speeds than during normal vehicle deceleration. In the braking phase, downshifts into the next lower gear are made ahead of the curve. This allows the braking effect of the engine to be used and load on the service brakes to be reduced.