Antilock Brakes / Traction Control Systems: Description and Operation

COMPONENTS





DESCRIPTION
This specification applies to Hydraulic and Electronic Control Unit (HECU) of the Anti lock Braking System(ABS) and Traction Control System(TCS).
This HECU has the functions as follows:
- Input of signal from the wheel speed sensors attached to each wheel.
- Control of braking force and traction force.
- Fail-safe function.
- Self diagnosis function.
- Interface with the external diagnosis tester.

OPERATION
The HECU shall be put into operation by switching on the operating voltage (IGN).
On completion of the initialization phase, the HECU shall be ready for operation.
In the operating condition, the HECU shall be ready, within the specified limits (voltage and temperature), to process the signals offered by the various sensors and switches in accordance with the control algorithm defined by the software and to control the hydraulic and electrical actuators.
The HECU shall receive wheel speed signal from the four inductive wheel sensors.
The wheel signals are converted to square wave by the signal conditioning circuit and given as input to the mu- processor.
The sensor connections shall be monitored for short-circuit and interruption and then in the event of 2 sensor failures, the HECU shall shut down the system.
When one side of the valve coil is connected to the positive voltage that is provided through the valve relay and the other side is connected to the ground by the MOSFET, the solenoid valve goes into operation.
The electrical function of the valves is always monitored by the valve test pulse under normal operation conditions.
When overvoltage is detected(above 16V), the HECU switches off the valve relay and shuts down the system. When voltage is returned to operating range, the system goes back to the normal condition after the initialization phase.
In the event of undervoltage(below 10V), ABS control shall be inhibited and the warning lamp shall be turned on.When voltage is returned to operating range, the warning lamp is switched off and the HECU returns to normal operating mode.
The pump motor operates when the ABS is functioning.
The HECU performs a pump motor test at a speed of 20km/h once after turned the Ignition switch on. You may hear the motor operation at this time, but it is normal.
Malfunctions or failures detected by the HECU are encoded on the HECU, stored in a EEPROM and read out by diagnostic equipment (hi-scan pro) when the ignition switch is turned on.


TCS(TRACTION CONTROL SYSTEM) CONTROL





TRACTION CONTROL SYSTEM (TCS) FUNCTION
1. Main performance
A. Traction: Lower vibration and higher launchability, acceleration and climbability by slip control.
B. Cornering and passing: Stable cornering and passing.
C. Steering stability: Control traction force traverse vector prior to provide easy turning when turning the steering wheel.
2. General TCS features
A. Improved drivability. Minor operation of acceleration is not necessary in launching and acceleration on slippery road.
B. More stable cornering by stable acceleration on normal road condition.
C. TCS system will compare vehicle speed received from rear wheel speed sensor and driving wheel speed from front wheel speed sensor on slippery road condition, and provide optimum slipping rate of driving wheels.

FULL TRACTION CONTROL SYSTEM (FTCS)
1. The TCS control module (HECU) controls TCS control. It includes ABS control module.
2. HECU will compare signals from front (driving) and rear wheel speed sensors to detect driving wheels slip.
3. Upon detecting driving wheels slip, HECU will perform TCS control. The TCS control will include brake TCS (BTCS) control.
4. HECU will transmit engine torque reduction request, fuel cut cylinder number, and TCS control request signals in accordance with slip level to engine ECM and TCM through BUS line which will provide CAN communication for TCS control.
5. Engine ECM will perform fuel cut as requested by HECU and retard ignition timing as per engine torque reduction request signal.
6. TCM will hold shift position by TCS control time according to TCS operation signal. Then enhanced acceleration by kick-down will not occur.





BRAKE TRACTION CONTROL SYSTEM (BTCS)
1. On TCS control, only brake control will be performed. (engine and TCM control will not happen)
2. Controlled by motor pump output pressure.

SYSTEM FUNCTION
ABS OPERATION
1. NORMAL BRAKING














2. DUMP MODE














3. HOLD MODE














4. INCREASE MODE
















TRACTION CONTROL SYSTEM (TCS) OPERATION

1. NORMAL MODE










2. PRESSURE INCREASE MODE










3. PRESSURE DUMP MODE










4. PRESSURE HOLD MODE