Electronic Stability Control (ESC) Operation
ESP OPERATION MODE1. 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 approximately 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.
COMPONENT INSPECTION
ACTIVE WHEEL SPEED SENSOR
The wheel speed sensor assembly consists of a permanent magnet attached to a sensor element (IC), which is molded into plastic. The sensor element is connected to the sensor cable. The sensor cable ensures an electric connection of the sensor element to the electronic control unit (ECU).
A toothed rotor is fixed to the rotating member of the wheel, the sensor to the static member of the suspension. As the wheel rotates the toothed rotor causes magnetic flux changes in the magnetic field of the permanent magnet. The sensor element senses these changes. Depending on the flux changes the sensor sends a signal out to the ECU. The change in magnet flux thus the sensor signal is directly correlated to the wheel speed.
The controller monitors the sensor signal, compares the four wheel-speed signals and initiates action as required.
STEERING WHEEL ANGLE SENSOR
Steering wheel angle sensor detects the operating speed of handle and is composed of the three photo transistor. Steering wheel angle sensor is located in the multifunction switch of steering wheel. The specifications of sensor are as following.
1. Specification
2. Neutral position detect
1) It should remain the satisfied condition as followed more than 2 seconds in order to detect neutral position.
2) The vehicle speed should be above 10 km/h.
3) The brake switch should be in position "OFF"
4) It should be lasted more than two seconds after turning ignition "OFF".
5) The neutral signal (STN) valve should be "O"
3. Output characteristic
YAW-RATE & LATERAL ACCELERATION SENSOR (SENSOR CLUSTER)
Sensor cluster consists of yaw-rate sensor, lateral acceleration sensor and micro controller in aluminum case and is installed in the lower floor of center crash pad.
YAW-RATE SENSOR
Application
Detect the yawing motion of the vehicle, triggering an ESC control intervention if the yaw velocity reaches round about 4°/s (=full circle in 90 s)
Design and function
The yaw-rate sensor relies on the action of microscopic tuning forks.
The plane in which these forks vibrate shifts when the car turns about its vertical axis. This shift is evaluated electronically.
Failsafe
^ A faulty yaw rate sensor produces an output signal of 0V.
Installation position
^ Tuning forks vertical.
^ Required accuracy of position : max. 30° tolerance to maintain full comfort.
^ Failure to maintain the specified installation position will result in asymmetrical control.
1. Specification
2. Output voltage
3. Circuit Diagram
LATERAL ACCELERATION SENSOR
Application
Sense the lateral acceleration of the vehicle
Design
In the interior of the sensor, a small mass element is attached to a movable lever arm which is deflected by lateral acceleration.
Function
^ Between two electrically charged stationary plates having the same polarity, an electrically charged silicon element having the opposite polarity is attached to the end of a cantilever arm.
^ Between these three plates, two electric fields are generated by the capacitances C1 and C2.
^ The capacitances C1 and C2 change in response to lateral acceleration. This change can be used to calculate the direction and amount of lateral acceleration acting on the vehicle.
^ The same sensor can also be used as longitudinal acceleration sensor if it is installed in the direction of travel (e.g. VW 4 motion with Haldex clutch).
^ For 0 g lateral acceleration, the sensor produces an output signal with a voltage of 2.5 V
Other
^ The signal of the lateral acceleration sensor alone cannot trigger an ESC intervention. The sensor is mainly used for estimating the coefficient of friction.
^ The installation location of the lateral acceleration sensor is more critical than that of the yaw-rate sensor (lever arm).
^ The installation location may not be changed after repairs.
1. Specification
2. Output voltage
3. Circuit Diagram
PRESSURE SENSORS
Application
^ Sense the driver's braking intentions (braking while an ESC intervention is in progress)
^ Control the precharging pressure
Design
The sensor consists of two ceramic disks, one of which is stationary and the other movable. The distance between these disks changes when pressure is applied.
Function
^ The pressure sensors operate on the principle of changing capacitance (a).
^ The distance (s) between the disks and, thus, the capacitance changes when pressure is applied to the movable disk by a braking intervention.
^ The fluid displacement of the sensor is negligible.
^ Max. measurable pressure : 170 bar
Guaranteed by redundant installation
Installation location
The sensors are mounted on the TMC (primary and secondary circuits).
1. Specification
2. Output voltage
3. Circuit Diagram
ESC OFF (TCS OFF) SWITCH
1. ESC OFF (TCS OFF) switch is installed on crash pad switch plate of driver's side.
2. A driver can choose at driver's option.
3. When forbidding the ESC (TCS) control, the driver can operate the ESP OFF (TCS OFF) switch.
4. When choosing, ESC OFF (TCS OFF) function lamp is turned on.
5. Circuit Diagram
BRAKE LAMP SWITCH
1. The brake lamp switch determines to judge if ESC and ABS should be controlled by transmitting whether braking should be tried to HECU.
2. The brake lamp switch uses as the basic signal of ABS & ESC braking control.
3. Circuit diagram.
