Antilock Brakes / Traction Control Systems: Description and Operation
SYSTEM COMPONENT
The Anti-Lock Brake System (ABS) controls the hydraulic brake pressure of all four gear wheels during sudden braking and braking on hazardous road surfaces, preventing the wheels from locking. This ABS provides the following benefits.
(1) Enables steering around obstacles with a greater degree of certainty even during panic braking.
(2) Enables stopping during panic braking while allowing stability and steerability to a minimum, even on curves.
In case a malfunction occurs, a diagnosis function and fail-safe system have been included for serviceability.
The traction control is a variable system designed to enhance traction during acceleration and cornering. It does so by determining the optimum amount of wheel spin for any given driving situation, then suppressing surplus engine power accordingly.
The integrated control unit (HECU) gets signals about the vehicle's speed, direction and road conditions from sensors at the wheels and the steering column. Based on these signals, the control unit will determine the optimum amount of wheel spin. Because the system is variable, the control unit may determine, depending on the driving conditions, that some wheel spin is beneficial (thus enhancing straight-line acceleration), or that no wheel spin is beneficial (thus enhancing cornering). For any given driving situation, the control unit will determine the amount of wheel spin best suited to the driver's needs. The system is automatically ready whenever the engine is started, but can be manually canceled with the TCS switch.
However, once actuated, the system cannot be canceled until it is once again in the ready state.
SYSTEM DIAGRAM
HECU
EBD (Electronic Brake-force Distribution)
The EBD is additionally applied instead of the proportioning valve to make the ideal distribution of a fluid pressure to the front and rear brake to prevent the brakes from skidding in the event of rearwheel lock and to obtain a higher brake efficiency within the range of service brake application.
ADVANTAGES
Function improvement of base-brake system
- Compensation of different friction coefficients
- Elimination of proportioning valve
- Failure recognition by warning lamp
COMPARISON BETWEEN WITH P-VALVE AND WITH EBD
TCS FUNCTION
1. Driving control
When the drive wheel speed exceeds the vehicle speed by a given amount, the HECU judges that the drive wheels are slipping, and it outputs the traction control signal to reduce engine power.
2. Rough road control
Based on signals from the wheel sensors, the control unit detects a rough road based on frequency of wheel rotational vibration. The control unit then signals the TCS control valve actuator and ECM to relax engine power, thus improving acceleration efficiency.
3. Grip control
Based on signals about wheel speed, the control unit determines the efficiency of the grip of the tires on the road and signals the TCS control valve actuator and ECM relax engine power if necessary, thus improving grip.