Traction control (another name – traction control ) is designed to prevent slipping of the drive wheels.
Depending on the manufacturer, the traction control system has the following trade names:
- ASR (Automatic Slip Regulation, Acceleration Slip Regulation) on Mercedes, Volkswagen, Audi and others;
- ASC (Anti-Slip Control) on BMW cars;
- A-TRAC (Active Traction Control) on Toyota cars;
- DSA (Dynamic Safety) on Opel cars;
- DTC (Dynamic Traction Control) on BMW cars;
- ETC (Electronic Traction Control) on Range Rover vehicles;
- ETS ( Electronic Traction System) on Mercedes cars;
- STC (System Traction Control) on Volv o vehicles ;
- TCS (Traction Control System) on Honda cars;
- TRC (Traking Control) on Toyota cars.
Despite the variety of names, the design and principle of operation of these traction control systems are very similar in many respects; therefore, they are considered using one of the most common systems as ASR systems.
The traction control system is built on the constructive basis of the anti-lock brake system. The ASR system has two functions: electronic differential lock and engine torque control.
To implement anti-slip functions, the system uses a return pump and additional solenoid valves (switching and high-pressure valves) to each of the drive wheels in the ABS hydraulic unit.
The ASR system is controlled by the appropriate software included in the ABS control unit. In its operation, the ABS / ASR control unit interacts with the control unit of the engine control system.
The principle of operation of the traction control system
The ASR system prevents wheel slippage over the entire range of vehicle speeds:
- at low speeds (from 0 to 80 km / h), the system provides torque transmission due to the braking of the drive wheels;
- at speeds above 80 km / h, the forces are regulated by reducing the torque transmitted from the engine.
Based on the signals from the wheel speed sensors, the ABS / ASR control unit determines the following characteristics:
- angular acceleration of driving wheels;
- vehicle speed ( based on the angular speed of the non-driving wheels );
- the nature of the car’s movement – straight or curved ( based on a comparison of the angular speeds of the non-driving wheels );
- the amount of slippage of the driving wheels ( based on the difference in the angular speeds of the driving and non-driving wheels ).
Depending on the current value of the operating characteristics, brake pressure control or engine torque control is performed.
The brake pressure is controlled cyclically. The duty cycle has three phases – pressure increase, pressure retention and pressure relief. The increase in brake fluid pressure in the circuit provides braking of the drive wheel. It is done by turning on the return pump, closing the changeover valve and opening the high-pressure valve. Pressure retention is achieved by shutting off the return pump. Pressure relief is performed at the end of slipping with the intake and switching valves open. If necessary, the work cycle is repeated.
The engine torque is controlled in conjunction with the engine management system. Based on the information on the slip of the drive wheels received from the wheel speed sensors and the actual value of the torque received from the engine control unit, the traction control unit calculates the amount of required torque. This information is transmitted to the engine control system control unit and is implemented using various actions:
- throttle position changes;
- skipping fuel injections in the injection system ;
- skipping ignition pulses or changing the ignition timing in the ignition system ;
- gear shift cancellation in cars with automatic transmission.
When the traction control is activated, the control lamp on the instrument panel lights up. The system has the ability to shut down.
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