Acura 3.5 RL Manual page 1298

Yaw Rate Sensor
The yaw rate sensor (located in the navigation unit) detects the direction change (angular speed) of the vehicle. The sen-
sor is an oscillation gyro built into the navigation unit.
Sensor Element Structure
The sensor element is shaped like a tuning fork, and it consists of the piezoelectric parts, the metal block, and the support
pin. There are four piezoelectric parts: one to drive the oscillators, one to monitor and maintain the oscillation at a regular
frequency, and two to detect angular velocity. The two oscillators, which have a 90-degree twist in the center, are connect-
ed at the bottom by the metal block and supported by the support pin. A detection piezoelectric part is attached to the top
of each oscillator. The driving piezoelectric part is attached to the bottom of one oscillator, and the monitoring piezoelec-
tric part is attached to the bottom of the other oscillator.
Oscillation Gyro Principles
The piezoelectric parts have "electric/mechanical transfer characteristics." They bend vertically when voltage is applied to
both sides of the parts, and voltage is generated between both sides of the piezoelectric parts when they are bent by an
external force. The oscillation gyro functions by utilizing this characteristic of the piezoelectric parts and "Coriolis force."
(Coriolis force deflects moving objects as a result of the earth's rotation.) In the oscillation gyro, this force moves the sen-
sor element when angular velocity is applied.
Operation
1. The driving piezoelectric part oscillates the oscillator by repeatedly bending and returning when an AC voltage of 6 kHz
is applied to the part, The monitoring-side oscillator resonates because it is connected to the driving-side oscillator by
the metal block.
2. The monitoring piezoelectric part bends in proportion to the oscillation and outputs voltage (the monitor signal). The
navigation unit control circuit controls the drive signal to stabilize the monitor signal.
3. When the vehicle is stopped, the detecting piezoelectric parts oscillate right and left with the oscillators, but no signal is
output because the parts are not bent (no angular force).
4. When the vehicle turns to the right, the sensor element moves in a circular motion with the right oscillator bending for-
ward and the left oscillator bending rearward. The amount of forward/rearward bend varies according to the angular
velocity of the vehicle.
5. The detecting piezoelectric parts output voltage (the yaw rate signal) according to the amount of bend. The amount of
vehicle direction change is determined by measuring this voltage.