Honda ACCORD HYBRID 2005 Service Manual page 2052

Navigation System
S y s t e m D e s c r i p t i o n ( c o n t ' d )
Y a w Rate Sensor
The y a w rate sensor (located in the navigation unit) 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 t u n i n g 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 t w o to detect angular velocity. The t w o oscillators, w h i c h have a 90-degree t w i s t in the
center, are connected at the b o t t o m 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 b o t t o m of one oscillator, and
the m o n i t o r i n g piezoelectric part is attached to the b o t t o m of the other oscillator.
Oscillation Gyro Principles
The piezoelectric parts have "electric/mechanical transfer characteristics." They bend vertically w h e n voltage is
applied to both sides of the parts, and voltage is generated between both sides of the piezoelectoric parts w h e n they
are bent by an external force. The oscillation gyro functions by utilizing this characteristic of the piezoelectric parts and
"Coriolis f o r c e . " (Coriolis force deflects m o v i n g objects as a result of the earth's rotation.) In the oscillation gyro, this
force moves the sensor element w h e n angular velocity is applied.
Operation
1. The driving piezoelectric part oscillates the oscillator by repeatedly bending and returning w h e n 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. W h e n the vehicle is stopped, the detecting piezoelectric parts oscillate right and left w i t h the oscillators, but no
signal is output because the parts are not bent (no angular force).
4. W h e n the vehicle turns to the right, the sensor element moves in a circular m o t i o n w i t h the right oscillator
bending f o r w a r d and the left oscillator bending rearward. The a m o u n t of f o r w a r d / r e a r w a r d bend varies according
to the angular velocity of the vehicle.
5. The detecting piezoelectric parts output voltage (the y a w rate signal) according to the a m o u n t of bend. The
a m o u n t of vehicle direction change is determined by measuring this voltage.
23-86