ESC (Electronic Stability Control) System

Description of ESC

Optimum driving safety now has a name: ESC, the Electronic Stability Control.

ESC recognizes critical driving conditions, such as panic reactions in dangerous situations, and stabilizes the vehicle by wheel-individual braking and engine control intervention.

ESC adds a further function known as Active Yaw Control (AYC) to the ABS, TCS, EBD and EDC functions. Whereas the ABS/TCS function controls wheel slip during braking and acceleration and, thus, mainly intervenes in the longitudinal dynamics of the vehicle, active yaw control stabilizes the vehicle about its vertical axis.

This is achieved by wheel individual brake intervention and adaptation of the momentary engine torque with no need for any action to be taken by the driver.

ESC essentially consists of three assemblies: the sensors, the electronic control unit and the actuators.

The stability control feature works under all driving and operating conditions. Under certain driving conditions, the ABS/TCS function can be activated simultaneously with the ESC function in response to a command by the driver.

In the event of a failure of the stability control function, the basic safety function, ABS, is still maintained.





Description of ESC Control
ESC system includes ABS/EBD, TCS and AYC function.

ABS/EBD function The ECU changes the active sensor signal (current shift) coming from the four wheel sensors to the square wave.
By using the input of above signals, the ECU calculates the vehicle speed and the acceleration & deceleration of the four wheels.
And, the ECU judges whether the ABS/EBD should be actuated or not.

TCS function prevents the wheel slip of drive direction by adding the brake pressure and engine torque reduction via CAN communication.
TCS function uses the wheel speed sensor signal to determine the wheel slip as far as ABS function.

AYC function prevents unstable maneuver of the vehicle. To determine the vehicle maneuver, AYC function uses the maneuver sensor signals(Yaw Rate Sensor, Lateral Acceleration Sensor, Steering Wheel Angle Sensor).
If vehicle maneuver is unstable (Over Steer or Under Steer), AYC function applies the brake pressure on certain wheel, and send engine torque reduction signal by CAN.
After the key-on, the ECU continually diagnoses the system failure. (Self-diagnosis)
If the system failure is detected, the ECU informs driver of the system failure through the BRAKE/ABS/ESC warning lamp. (fail-safe warning)





Input and Output Diagram






ESC Operation Mode

ESC Hydraulic System Diagram




1. ESC Non-operation : Normal braking.





Operation
In this position, the inlet valve and the TCS valve are open, the electrically operated shuttle valve and the outlet valve are closed.
* ESV: Electric reversing valve.




2. ESC operation





Operation
The on/off booster builds up a pressure of approx. 10 bar in order to enable the ESC pump to suck brake fluid at low temperatures. In this position, the inlet valve is driven in a pulsed cycle. The TCS valve is closed. The outlet valve remains closed. The electrically operated shuttle valve is opened. The hydraulic pressure is led to the wheel brakes which are to be applied for a brief period of time.





ABS Operation Mode
1. Normal Braking





When braking, the hydraulic pressure in the TMC is increased. The pressure reaches the wheel brake via the current less open inlet valve IV. The current less closed outlet valve OV is closed. For the sake of simplicity the diagram is limited to only the solenoid valve pair of one brake circuit. The wheel speed is reduced as the brake pressure increases, in the extreme case until the wheel locks.




2. Dump Mode





If the wheel speed decreases, there is still a tendency to lock; the brake pressure on the corresponding wheel must be reduced accordingly. For this, the outlet valve OV is opened, the inlet valve IV remains closed.
The brake pressure to the low-pressure accumulator is reduced. The wheel in danger of locking gains speed again.




3. Hold Mode





When a wheel (or several) tends to lock the inlet valve IV is first closed to avoid a further increase in brake pressure. The outlet valve OV remains closed: the brake pressure is kept constant.




4. Increase Mode





For optimum brake from the certain wheel acceleration a brake pressure increase is necessary. For this, the inlet valve IV is opened and the outlet valve OV is closed. The pump of the unit starts to run and aspirates the necessary quantity of fluid from the Low-pressure accumulator, in order to produce the necessary brake pressure for the pressure increase phase in seconds.
With an increase in the brake pressure the wheel speed is reduced. These control phases are repeated until the ABS control unit no longer detects any tendency of the wheels to lock.

NOTE:
During ABS control function, the brake pedal only moves in accordance with the volume requirement of the wheels. Because of a sudden change in friction coefficient this pedal movement may increase slightly.






ABS Warning Lamp Module





ABS Warning Lamp Module
The active ABS warning lamp module indicates the self test and failure status of the ABS.
The ABS warning lamp shall be on:
- During the initialization phase after IGN ON.
(Continuously 3 seconds).
- In the event of inhibition of ABS functions by failure.
- During diagnostic mode.
- When the ECU Connector is separated from ECU.

EBD/Parking Brake Warning Lamp Module
The active EBD warning lamp module indicates the self test and failure status of the EBD. However, in case the Parking Brake Switch is turned on, the EBD warning lamp is always turned on regardless of EBD functions.
The EBD warning lamp shall be on:
- During the initialization phase after IGN ON.
(Continuously 3 seconds).
- When the Parking Brake Switch is ON or brake fluid level is low.
- When the EBD function is out of order.
- During diagnostic mode.
- When the ECU Connector is separated from ECU.

ESC Warning Lamp (ESC System)
The ESC warning lamp indicates the self test and failure status of the ESC.
The ESC warning lamp is turned on under the following conditions:
- During the initialization phase after IGN ON.
(Continuously 3 seconds).
- In the event of inhibition of ESC functions by failure.
- During diagnostic mode.

ESC Function Lamp (ESC System)
The ESC function lamp indicates the self-test and operating status of the ESC.
The ESC Function lamp operates under the following conditions:
- During the initialization phase after IGN ON.
(Continuously 3 seconds).
- When the ESC control is operating. (Blinking - 2Hz)

ESC ON/OFF Switch (ESC System)
The ESC On/Off Switch shall be used to toggle the ESC function between On/Off states based upon driver input.
The On/Off switch shall be a normally open, momentary contact switch. Closed contacts switch the circuit to ignition.
Initial status of the ESC function is on and switch toggle the state.

AUTO HOLD Function Lamp (EPB System)
The AUTO HOLD function lamp indicates the operating status of the ESP.
The ESP Function lamp operates under the following conditions:
- the initialization phase after IGN ON.
(Continuously 3 seconds).
- The lamp is turned on when a driver put the AUTO HOLD switch.

EPB Warning Lamp (EPB System)
The EPB warning lamp indicates the self-test and failure status of the EPB.
The EPB warning lamp shall be on:
- During the initialization phase after IGN ON.
(Continuously 3 seconds).
- In the event of inhibition of EPB functions by failure.