• Stability and Traction Control (STC) can be described as a combination of two existing Volvo systems, the low-speed, brake-activating TRACS system in the S70/V70/C70 models and the speed-independent, torque-limiting DSA system in the S40 and V40.
• STC is designed to prevent the driving wheels from spinning when starting and accelerating, as well as counteracting wheel spin if the driving wheels hit slippery patches when driving.
• The system improves tire grip on slippery surfaces and provides the optimum combination of traction and side stability, which in turn enhances the high level of active safety.
• The traction function works at lower speeds, up to 25 mph, by transferring the engine power to the wheel with the best grip from the one with the least grip. This is done using the ABS sensors and the brake system.
• The stability function reduces engine torque, by cutting down on the fuel supply, if one of the driving wheels starts to lose its grip on the road, both during acceleration and when driving on a slippery road. This minimizes wheel spin and helps bring the car back to full stability.
• The system reacts and is activated within milliseconds and driving characteristics are never affected. An indicator lamp on the dashboard flashes if and when STC is engaged.
• STC is a standard feature on the Volvo S80.
• Dynamic Stability and Traction Control (DSTC) is an even more sophisticated stability system to improve active safety by also intervening and counteracting any tendency to skid.
• If the car makes a sudden movement and loses its directional line, or enters a corner too fast and the rear end starts to turn the car around, DSTC gently returns it to the right line. Applying the brakes on one or more wheels does this.
• DSTC works through the ABS system, which has been further developed.
• A number of yaw angle sensors monitor the rotational speed of all four wheels, the steering wheel angle and the directional behavior of the car.
• The DSTC processor receives the signals and compares the actual behavior of the car with the desired behavior. Any deviation from the norm, such as the rear wheels starting to break away, and the system intervenes and makes corrections, activating the brakes on the wheel that will bring the car back in line. If necessary, the system also reduces engine torque, like STC.
• In a way, it would be true to say that DSTC is able to partially compensate for the driver's mistakes up to a certain point, as it counteracts and prevents skidding when the driver has already started to lose control.
• The system is particularly effective if the driver has to brake hard and steer away at the same time. The system counteracts any tendencies to skid and returns the car to its original course.
• DSTC works through the ABS system, which has been further, developed to incorporate this system. In addition to more relief valves and a more powerful microprocessor, a brake reinforcement unit with electronic activation, sensors for side acceleration, yaw rate and steering wheel angle has been added.
• The DSTC optional system will be available for order in early 1999.
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