Dynamic Stability Control (DSC)
Dynamic Stability Control (DSC) is a further development of the Anti-lock Brake System (ABS) and Automatic Stability Control and Traction (ASC+T) slip control systems.
While the latter takes the longitudinal forces occurring in straight-ahead running into account, DSC additionally registers and analyses lateral dynamic forces to ensure directional stability.
This means that also - and particularly - in cornering at high speeds, unstable vehicle states such as oversteering or understeering are effectively countered and vehicle stability and road safety are enhanced.
Not only when starting, driving in a straight path or braking does the vehicle remain entirely stable - this feature particularly provides maximum stability when taking bends.
The steering wheel movement, vehicle speed, transverse acceleration and yaw are used by DSC to register imminent instability when taking a bend at speed.
DSC then intervenes via the engine management system, reducing drive torque, activating wheel brakes when necessary and thus keeping the vehicle stable.
All this happens within milliseconds - more quickly and precisely than a driver could ever react.
Your benefits :
With DSC there is a significant reduction in the risk of skidding during sudden swerve manoeuvres or on slippery bends, on cobblestones or similar road situations.
In combination with the basic functions of ABS and ASC+T, there is optimum use of road surface friction (wheel grip).
Function in detail :
Whilst ABS and ASC+T take account of longitudinal forces when the vehicle is travelling in a straight path, DSC also monitors and regulates the lateral forces.
The DSC computer constantly calculates an ideal driving condition that is compared with the current status. If the vehicle oversteers or understeers, the calculated ideal deviates from the measured status. DSC then intervenes within a few milliseconds via the engine management system by influencing the engine torque and activating brakes on individual wheels where necessary.
The system thus counteracts unstable vehicle behaviour in normal driving situations, e.g. when accelerating, braking, rolling or under sudden load changes (when changing gear, swerving or suddenly releasing the throttle).
These reactions translate into so-called "oversteer" (rear of car brakes into a slide towards the outside of the curve) and "understeer" (front of car pushes towards the outside of the curve).
In the case of oversteer, DSC would brake the "outer" rear (and, if needed, also the "outer" front) wheel in order to correct the vehicle's stance by generating a counter-momentum to neutralise the oversteer. In the new 3 Series, the braking effect is applied at both "outer" wheels.
Similarly, in the case of understeer DSC would act upon the "inner" rear (and, if needed, front) wheel to regain vehicle stability. In the new 3 Series, the braking effect is applied at both "inner" wheels.
These regulatory interventions are effected by the DSC electronic and hydraulic systems more rapidly and precisely than a driver's reactions, and, moreover, they are hardly felt by the vehicle's occupants.
Components :
DSC makes use of the ABS wheel-speed sensors, and also of the following additional components :
steering angle sensor to detect the driver's chosen path
lateral-acceleration sensor to define the lateral forces which must be transmitted to the road by the tyres
rate-of-turn sensor to define the vehicle's degree of rotary movement
brake-pressure sensor to define the longitudinal forces acting between tyres and road surface under braking
Automatic Stability Control combined with Traction Control
Intelligent regulation systems prevent the vehicle from swerving when accelerating on a loose surface and thus ensure that directional stability is reliably maintained.
If a wheel threatens to spin, the wheel brake is applied or else the system intervenes to regulate the engine management accordingly. Only so much throttle is accepted for acceleration so as not to impair lateral stability, even if the accelerator is fully depressed.
A similarly integrated engine drag torque regulation system stops the drive wheels from blocking if the driver suddenly removes his/her foot from the accelerator.
The system can be switched off if, for example, oversteering in bends is required for a sporty driving style.
Your benefits :
Optimum safety on slippery road surfaces such as ice, snow, loose gravel etc.
Even sudden patches of slippery road surface are immediately registered and the system reacts accordingly.
No blocking of wheels even when the accelerator is suddenly released on a slippery surface ( or there is a change down to a lower gear ).
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.
Note :
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.