Lateral Accelerometer: Description and Operation

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.





Block diagram





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. 3° 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
Failsafe
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.