System function

Fig 1: DSA System Overview

Courtesy of VOLVO CARS OF NORTH AMERICA.

The DSA system must take account of any deviations caused by the steering wheel. It is therefore important that no incorrect data is introduced by the system itself and that it goes through a number of stages before the torque reduction is activated.

• When the DSA control module detects wheelspin it first determines the extent of the spin.
• The average spin of the two front wheels is calculated. Differences in wheel speed because of cornering is compensated using sensors on the rear wheels.
• Information about the engine speed and load comes from the engine control module (ECM). The torque required from the engine is calculated from this.
• The selected gear can be derived by comparing wheel speed with engine speed. From this the friction coefficient between the tire and road surface can be deduced.
• Acceptable spin can be deduced from the accelerator pedal (AP) position and the friction coefficient.
• The engine control module (ECM) decreases torque by disengaging the injectors, so preventing wheel spin.

The DSA control module only sends information to the engine control module (ECM). It is this that close the fuel injection. The engine control module (ECM) can control the injection by closing the injectors, so that one or more injectors can be closed every 4th cylinder compression. It reduces torque in 16 stages.

• Partial closure of the injectors occurs randomly to ensure that the heat is evenly distributed.
• If the torque reduction is very small, a safety program is activated. After a given period the DSA shuts off several injectors (greater torque reduction) to ensure that the combustion chambers are correctly ventilated.
• The DSA system functions up to maximum. It is also active while reversing.
• The DSA system aligns itself so that it is does not identify different wheel diameter as wheelspin, in cases of variable tire pressure for example. DSA is not engaged if there is a slow puncture in one of the tires.
• Switch off the DSA system when driving on a "special spare tire". If not the system aligns itself to the diameter of the tire on the wheel. To assist this the car should be driven slowly, then accelerated hard for approximately 4 seconds. The accelerator pedal (AP) should be released quickly so that the engine brakes the car for approximately 4 seconds. Repeat this one more time. This procedure should be repeated when the special spare tire is replaced by a normal tire.