Adaptive transmission control
In the same way as the automatic transmissions used to date, this 6-speed-automatic transmission also offers a choice between a comfort program and sport program.
The adaptive transmission control (component of the electronic transmission control) adapts the shift characteristics of the comfort program and sport program to the driver's demand and the driving situation.
In each of the two programs, the adaptive transmission control switches on request from a basic characteristic map into a performance-oriented characteristic map:
- Comfort program at selector-lever position "D"
The comfort program is based on various characteristic maps: e.g. the characteristic map "XE" (extreme economy) and the characteristic map "E" (economy). The EGS control module normally chooses the economical characteristic map "XE" (= basic characteristic map). With special requirements (e.g. load requirement), a switch is made to the performance-oriented characteristic map "E". If the input signals change towards "more moderate driving style", there is a switch back to the economical characteristic map "XE".
- Sport program at selector-lever position "M/S"
The Sport program implements dynamic sports shift characteristics. In the sport program, there are various characteristic maps, e.g. the basic characteristic map "S" (sport) and the performance-oriented characteristic map "XS" (extreme sport). With a very dynamic driving style, there is a switch from the basic characteristic map "S" to the performance-oriented characteristic map "XS".
The adaptive transmission control takes account of the following requirements:
Adaptation to the driver type
The adaptation to the driver type runs via the following values:
- Kick fast
When the accelerator pedal is pressed down quickly, the shift program is changed accordingly. Here, the determined accelerator-pedal value is compared with threshold values in the EGS control module. The result of this comparison is that one of the two possible programs is proposed (e.g. with comfort program "XE" or "E", with sport program "S" or "XS").
- Cornering detection
The cornering detection reacts to the lateral acceleration of the vehicle with an indirect adaptation to the driver type.
The lateral acceleration is regarded as an indirect statement on the preferred dynamism and does not lead to an immediate gearshift reaction (gearshifts in bends can negatively influence driving stability).
The lateral acceleration is calculated from the signals of the wheel-speed sensors as well as the yaw rate and driving speed.
- Brake assessment
The brake assessment is similar to the process for assessment of "kick fast".
The braking deceleration is determined and compared with threshold values in the EGS control module. The result of this comparison is that one of the two possible programs is proposed (e.g. with comfort program "XE" or "E", with sport program "S" or "XS").
The adaptation to the driver type is restarted every time the vehicle drives off from a standstill.
Hill ascent and operation with trailer
This function is based on a comparison of the actual car acceleration with a nominal value. Taking account of the current operating condition of the engine, the acceleration on a trip with normal load on a float road is estimated. If the actual acceleration is significantly below the theoretical value, the function "Hill ascent and operation with trailer" becomes active.
The configuration of the corresponding shift characteristic maps permit a driving style with high revolutions. Unwanted upshifts and frequently upshifts and downshifts are excluded or severely limited.
Hill descent
When the EGS control module detects a hill descent, it shifts to the next-lowest gear if the driving speed increases. This reinforces the brake effect of the engine. A downshift only takes place if the engine speed lies below the maximum number of revolutions of the next-lowest gear.
The EGS control module detects the hill descent by the signals from the throttle valve potentiometer (load), from the wheel-speed sensors (driving speed) and from the brake-light switch (brake operation).
Braking deceleration and automatic upshift
To brake the vehicle, the driver takes his or her foot from the accelerator pedal and operates the brake if required. According to the characteristic curve, closure of the throttle would trigger an upshift. These gear changes make no sense in conjunction with braking, as they prevent use of the engine braking effect.
The braking intention can frequently be recognized by a very rapid return of the driving pedal to the zero position. When such an action is detected, an upshift is suppressed until the accelerator pedal is in the zero position and the vehicle is coasting.
Winter program (only in selector-lever position "D")
If the drive wheels slip even at low acceleration, the winter program is activated automatically. The winter program ensures better traction by eliminating 1st gear. Early upshifts reduce the reaction on load change. If the wheels do not slip with high input torque for a number of seconds, the winter program is deactivated again.