VSA

Wheel Sensor





The wheel sensors are the magnetic contact less type. As the gear pulser teeth rotate past the wheel sensor's magnetic coil, AC current is generated. The AC frequency changes in accordance with the wheel speed. The VSA control unit detects the wheel sensor signal frequency and thereby detects the wheel speed.

Wheel Speed and Modulator Control (ABS)





When the wheel speed drops sharply below the vehicle speed, the inlet valve closes and the outlet valve opens momentarily to reduce the caliper fluid pressure. The pump motor starts at this time. As the wheel speed is restored, the inlet valve re-opens momentarily to increase the caliper fluid pressure.

Steering Angle Sensor





The steering angle sensor detects the steering wheel turning angle. A disk with evenly spaced slits is positioned between the facing parts of a Light Emitting Diode (LED), and a light receiving part (photo transistor). As the disk rotates, it interrupts the light from the LED. The light which passes through a slit is converted into electric current by the photo transistor, and the waveform of this electric current is converted by the comparator into a square wave output of the disk's rotation.
The analysis performance of the system is improved by providing the fixed slit in front of the LED, and thereby identifying the brightness and darkness of the light which is received at the photo transistor.
The output signal is a 2-phase output (A-phase and B-phase), and the steering wheel turning angle and the turning direction are calculated by the VSA control unit.

Lateral Acceleration Sensor





The lateral acceleration sensor detects crisscross direction acceleration against the fixed electrode and movable electrode. The sensor is a static electricity capacity type, and the sensor detects static electricity between the fixed electrode and the movable electrode which is changed by lateral acceleration.

Yaw Rate Sensor
The yaw rate sensor detects the direction change (angular speed) of the vehicle. The sensor is an oscillation gyro.

Sensor Element Structure
The sensor element is shaped like a tuning fork, and it consists of piezoelectric parts, a metal block, and a support pin.
There are four piezoelectric parts: one to drive the oscillators, one for monitoring that maintains the oscillation at a regular frequency, and two to detect angular velocity. The two oscillators have a 90 degree twist in the center, are connected at the bottom by the metal block, and supported by the support pin. A detecting 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 "electro/mechanical transfer characteristics." The piezoelectric parts bend vertically when voltage is applied to both sides of the parts, and voltage is generated between both sides of the piezoelectric parts when then 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 sensor element when the 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 parts bends in proportion to the oscillation and outputs voltage (the monitor signal). The VSA control 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.

VSA-TCS Control Valve Assembly





The VSA-TCS control valve assembly consists of the VSA-TCS control valve actuator (DC motor), VSA-TCS control valve sensor, VSA-TCS control valve, return spring, and three gears. When the TCS is activated, the VSA control unit signals the VSA-TCS control valve actuator and the PCM. The actuator is linked to the VSA-TCS control valve which is normally returned to the fully open position by the return spring. Although the throttle valve is still within the driver's control, the engine output is reduced by the VSA-TCS control valve and the PCM to achieve optimum traction.