Intelligent regulation systems prevent the vehicle from swerving when accelerating on a loose surface and thus ensure that directional stability is reliably maintained.
Your benefits :
Function in detail :
As ASC+T prevents the drive wheels from spinning, it is a logical extension of the Anti-lock Brake System (ABS).
To ensure optimum driving stability with enhanced traction under all driving conditions, ASC+T acts on three factors as a function of the specific driving situation :
1) Drive power control :
Whenever there is a substantial power surplus with slip on the drive wheels, engine torque is cut back by changing the position of the throttle butterfly or the parameter responsible for the power provided. If this is not sufficient to quickly reduce wheel spin, drive power is cut back briefly by changing the ignition angle and cancelling out the ignition.
2) Brake force control :
A further function serves to automatically apply the brakes on a drive wheel about to spin. Since each drive wheel can be braked individually, this system has the same effect as a limited-slip differential. The result is optimum traction comparable with the efficiency of a limited-slip differential with locking action up to almost 100%. This limited slip-effect is generated only at speeds up to 40 km/h. At speeds of more than 80 km/h (new 3 Series) and 100 km/h (5 Series), there is no further intervention in the brakes. Instead, control action is limited to a modification of the throttle butterfly position in accordance with the driving situation by means of Digital Motor Electronics (DME)/Digital Diesel Electronics (DDE).
3) Engine drag torque control (MSR) :
The MSR modification is performed by ASC, as when the engine begins to brake the car (transition from drive to coasting), the drag torque is so large that the driven wheels could lock at low road-surface friction coefficients.
This vehicle reaction may particularly arise at high engine speeds in low gears and when the road-surface friction coefficient is low (e.g. ice, snow, and loose gravel).
If the driven wheel speed is too small compared with the non-driven wheels, the command to increase engine torque is issued to the engine management control unit by the ASC control unit.
The engine management control unit then inhibits the coasting function and, at the same time, energises the idlespeed charger actuator, which is opened as a result. This measure converts drag torque into a positive engine torque. The engine management control unit informs the ASC control unit that the engine torque has been increased.
During MSR control, neither cylinder fade-out nor ignition timing is modified.
MSR control is possible only at speeds greater than 20 km/h. This is to prevent it from beginning its control routine when a car negotiates a narrow bend at a low speed, thus producing an undesirable coasting effect.
An applied handbrake is identified by a logic system stored in the ASC control unit. The handbrake-light warning switch is not used for identification purposes.
An applied handbrake is identified if a wheel spin is less than 5 km/h for longer than 200 ms and engine speed greater than 1 200 rpm.
In the event of ASC+T being activated, the driver is notified by means of a flashing control lamp in the instrument cluster.
Under specific driving conditions or when road conditions require, ASC can be deactivated by a switch in the centre console (in which case the ASC telltale comes on permanently). This may be desirable in situations where the car is subject to above-average wheel spin, e.g. on loose sand or snow, when using the emergency wheel or with an extremely sporty style of motoring.