Honda 2004 Odyssey Service Manual page 2038

Yaw Rate Sensor
The yaw rate sensor detects the direction change (angular speed) of the vehicle. The sensor 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 connected 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 piezoelectric 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 piezoelectoric parts when they
are bent by an external force. The oscillation gyro fuctions 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 sensor element when angular velocity is applied.
Operation
1. The driving piezoelectric part oscillates the oscillator by repeatedly bending and returning when an AC voltage at
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 bend 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 forward 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.
Enlarged view of sensor element
SUPPORT PIN
DRIVING
PIEZOELECTRIC
PART
METAL BLOCK
DETECTING PIEZOELECTRIC
PARTS
OSCILLATORS
Oscillation
Coriolis force
Bend
MONITORING PIEZOELECTRIC
PART
Sensor element top view
Turn to
right
Coriolis force
Oscillation
(cont'd)
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