DSC & ASC de-mystified

You’ve had some questions regarding Dynamic Stability Control (DSC) & Automatic Stability Control (ASC).
We here at Mini Mania would like to present the following information for your consideration.

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ASC/DSC EXPLAINED

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for the MINI, integrated by BMW

FUNCTION:
ASC & DSC work with the ABS system to provide enhanced vehicle stability.

ASC – Automatic Stability Control
ASC uses speed sensors at each wheel and throttle position to improve traction by applying the rear brakes if the rear wheels spin faster than the front. It can also shut off individual fuel injectors and close the throttle valve to help maximize traction. ASC also acts as a virtual limited slip differential by detecting a spinning wheel and applying braking force to just that wheel until traction is regained. AWD models (the BMW xi) use ASC-X which monitors all 4 wheels to provide limited slip differential effect. The ASC system also provides traction control by modulating throttle, ignition timing and braking force to maintain traction.

DSC – Dynamic Stability Control
DSC builds on the features of the ASC system. While ASC functions only during acceleration and braking, DSC functions during all driving conditions such as cornering and emergency maneuvers. Additional sensors are added to acheive this level of stability such as lateral, yaw, brake pedal, and steering angle sensors. In DSC, each of the three subsystems: ABS, ASC, and DSC have jobs to do, and these are:

ABS: Cornering Brake Control, Electronic Brake Proportioning
ASC: Brake Intervention (or ABD-Automatic Braking Differential), Drag/Drive Torque Reduction
DSC: Dynamic Brake Control, Maximum Brake Control

Let’s dig deeper, shall we?

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Dynamic Stability Control (DSC) is a suspension control system which goes beyond the single components of Anti-lock Brake System (ABS), Cornering Brake Control (CBC) and Automatic Stability Control + Traction (ASC + T).

The steering wheel movement, vehicle speed, transverse acceleration and yaw are all used by DSC to register imminent instability when cornering. DSC then intervenes via the engine management system, reducing drive torque and activating wheel brakes when necessary to keep the vehicle stable. These events occur within milliseconds.

DSC is, in fact, a further development of the ABS and ASC+T slip control systems.

While ASC + T analyzes the longitudinal forces occurring in straight-ahead operation, DSC additionally registers and analyses lateral dynamic forces.
When cornering at high speeds, DSC counters unstable vehicle states such as oversteering (rear of car brakes into a slide towards the outside of the curve) or understeering (front of car pushes towards the outside of the curve).
The DSC feature can provide maximum stability when cornering.
With DSC there is a significant reduction in the risk of skidding.
BMW’s Dynamic Stability Control system has been available on a variety of BMW models over the last three years.

Here’s how it works:

DSC constantly compares vehicle speed, wheel speed, steering angle, and yaw rate with a benchmark of plausible and optimum driving conditions’ data. In a fraction of a second, DSC recognizes a threatening instability and a danger of skidding. The DSC system can correct an unstable driving condition by applying precise braking action to the individual wheels. As with ASC, DSC will if necessary also cut back the engine speed to automatically stabilize the vehicle.

The ASC + T system will reduce engine output until the vehicle can move or or until acceleration can occur without the wheels spinning. If this reduction is insufficient, each drive wheel is braked individually until both wheels have optimum traction.

This makes it possible to drive on snow, wet roads or other slippery grounds without the wheels spinning. Even if the back wheels suddenly lose traction in a bend during acceleration, ASC + T intervenes so quickly that the vehicle is stabilized before it can oversteer and swing out of the bend. The instrument console informs the driver of any control intervention and the relevant situation.

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, and DSC will intervene within a few milliseconds via the engine management system by reducing the engine torque and applying the brakes on individual wheels where necessary.

DSC makes use of the ABS wheel-speed sensors and 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 tires.
rate-of-turn sensor to define the vehicle’s degree of rotary movement.
brake-pressure sensor to define the longitudinal forces acting between tires and road surface under braking.

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ASC/DSC CONTROL BUTTON
The control button on the center console is used to deactivate the ASC/DSC systems.

NOTE: On all systems, ABS IS ACTIVE AT ALL TIMES.

A indicator lamp between the tachometer and speedometer is used to show ASC/DSC status.
A flashing indicator lamp indicates the system has activated.
A steady indicator lamp indicates the system is turned off or inoperative.

On the ASC system:
Press the ASC button to disable ACS while leaving ABD active.

On rear-wheel drive DSC systems:
Press the DSC button to disable DSC while leaving ABD active.
Press and hold the DSC button for 3+ seconds and the “BRAKE” instrument panel lamp will light yellow and disable all stability/traction systems.

On all-wheel drive (xi) DSC systems:
Press the DSC button to disable DSC while leaving ADB active in maximum output mode.

On ALL systems:
Pressing the ASC/DSC button again will reactive the system. If the indicator lamp does not go out or if it should come on and stay on during driving, a component has failed and should be serviced.

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WARNING:

If the ABS, ASC/DSC, and BRAKE lamp should all come on during driving, DO NOT drive the car and have it serviced immediately.

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These different systems all work in unison to provide a very safe and stable vehicle under almost all circumstances. Remember, physics does still apply and even our MINI’s have their limits. On numerous occasions, however, I have felt the DSC system kick in on slippery surfaces and jerk the car back straight without any input from me. It is quite impressive to say the least. While some may feel that ASC/DSC limits their MINI’s performance, the payoff in safety on the road is too great to gamble with. At the track… well, that’s a different story…