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An accurate assessment of the acceleration or deceleration of a vehicle for active and passive safety or navigation systems is just as important as the vestibular apparatus for humans. These forces have several directions, therefore, sensors of various designs are used.
Spin-Turn
The rotation of the car around a vertical axis is usually measured by gyro sensors. Now the most common type of vibration sensors. Compared to conventional rotary gyroscopes, they are simpler and cheaper, but their accuracy is comparable.
In stability control and navigation systems, sensors based on the piezoelectric effect are used. Piezocrystals can be deformed under the influence of electric voltage (fuel piezo injectors) and, conversely, create stress during deformation (detonation sensors). In gyro sensors both of these properties are used.
Triangular Gyro Sensor Rack
The navigation gyro sensor consists of a triangular rack and piezosensors located on each face: one exciting and two receiving ones. When voltage is applied to the excitation sensor, it makes the entire rack vibrate. Receiving sensors convert this vibration to output voltage. Initial vibration is needed to calibrate and reduce signal distortion, while still providing a constant output from the gyro sensor. Under the influence of forces when turning the car, the receiving sides of the rack are deformed. Two receiving piezoelectric sensors convert the deformation into electrical signals to determine the angle of rotation.
The Electronic Stability Program (ESP) uses a tuning fork type gyro sensor, which also uses the piezoelectric effect. The double tuning fork is made of a piezocrystal and consists of three parts (Fig. A): middle, exciting and measuring. The middle part is fixed inside the sensor. An excitation tuning fork creates an initial vibration when voltage is applied (Fig. B). Measuring tuning fork under the influence of forces during rotation is deformed. Its twisting changes the charge distribution, and this is fixed by the sensor electronics (Fig. C) to determine the moment of rotation of the car around the vertical axis.
Tuning tuning fork gyro sensor
IN PROFILE AND ANFACE
The longitudinal and lateral acceleration sensors are used for directional stability and passive safety systems. They are arranged according to one principle: depending on the installation method, the same sensor is capable of measuring accelerations in different directions.
The acceleration or deceleration is determined by the movement of the movably fixed mass inside the sensor. In piezoelectric sensors, an elastic piezoelectric plate is bent, and in mechanical sensors an additional element (Hall sensor) monitors the movement of a spring loaded load. Another type was an analogue in which the mechanical part is made of silicon. All these sensors have an internal measurement circuitry and transmit an already processed signal.
A simple capacitive acceleration sensor is arranged. It consists of two plates of the same charge and a plate with an opposite charge movably fixed between them, which moves when the car accelerates / decelerates. The operation of the sensor is based on the dependence of the capacitance of the capacitor on the distance between the plates. This distance at the same time
corresponds to the potential difference between the plates: the closer the plates are to each other, the greater the voltage. By changing it, the movement of the moving part of the sensor is determined.
Capacitive Acceleration Sensor Circuit
RESTORATION IS NOT SUBJECT
In the event of a sensor failure, an indication of a malfunction of the associated security system will light up. The error code and description can only be retrieved using computer diagnostics. Without need, it is better not to touch the sensors and do not replace them yourself. They require careful installation and a controlled tightening torque of the fasteners, otherwise the accuracy of the measurements will suffer. After replacement, some sensors require initialization using a computer. For all their complexity, they are very reliable, and they are usually changed due to mechanical damage. Repair is not provided, and they can even suffer from falling to the floor.