Rotation Rate (Yaw) Sensor

GENERAL





This new sensor is a major contributor of the expanded capabilities of DSC III.

The sensor is located under the driver's seat and mounted to the floor by 3 mounting nuts. The sensor is connected to the system by a 5 pin plug.





To access the sensor the seat must be removed, the door jamb interior trim pulled out of the way and the carpet rolled back. A sound insulating foam shell covers the sensor, this too must be pulled upward off the sensor prior to removal.

SENSOR OPERATION





The sensor is a sealed, self contained microprocessor that monitors the vehicle's rate of rotational acceleration on its vertical axis (yaw angle).

The sensor contains an internal oscillating cylinder which is excited by various piezo elements to an oscillation frequency of 14 KHz. This puts the cylinder in a free floating neutral state (zero point).

When driving, the cylinder is deflected (rotated) by the effect of the forces from the vehicle cornering - this produces a torsional "twist" on the cylinder.

The sensor counteracts the "twist" of the cylinder by increasing the pulse frequency of the piezo elements to deflect the cylinder back to it's zero point.

The pulse frequency increase is measured and represents the real time vehicle rotation rate. Based on the measurement, the sensor produces a linear DC voltage signal that the DSC III control module uses to determine vehicle yaw angle.

ROTATION RATE SENSOR SIGNALS





The Dynamic Stability Control (DSC) III control module provides the Rotation Rate Sensor 12 volts operating power and ground. In return, the sensor provides:

^ a standing 2.5 volt reference voltage signal (pin 4 of sensor)
^ a linear voltage signal ranging from 0.7 to 4.3 volts (pin 3 of sensor)

The linear signal voltage equates to a range of -500 (.7v) to +500 (4.3v) vehicle rotation rate change per second. The DSC III control module monitors the signal voltage every 20ms.
In conjunction with the steering angle, front wheel speeds and lateral forces, the rotation rate signal provides confirmation of a vehicle pushing the limits of acceptable yaw. The DSC III control module then regulates the torque output of the vehicle and manipulates the brake system hydraulics as needed to correct the under/oversteer condition.
For continual plausibility testing, the DSC control module sends a predetermined test voltage signal to the rotation rate sensor (pin 5 of sensor). The sensor calculates the voltage value and sends feedback to the DSC III control module over the signal line (pin 2) every other 20ms signal cycle. If the feedback is out of plausible range the DSC III sets a fault.
The DSC III control module also checks the actual signal for plausibility by comparing it to combined signals from the front wheel speed sensors, lateral acceleration sensor and the steering angle signal from the CAN Bus.

SENSOR REPLACEMENT
If the rotation rate sensor is replaced, the new sensor must be calibrated with the DSC III control module through the DIS Service Functions.