Function of wheel speed sensor: Function
The function of wheel speed sensor is to measure the wheel speed of automobile.
Description: The wheel speed sensor is used to measure the wheel speed of an automobile. Commonly used wheel speed sensors generally include magnetoelectric wheel speed sensor and Hall wheel speed sensor. For modern cars, wheel speed information is very important. Vehicle dynamic control system (VDC), vehicle electronic stability program (ESP), anti-lock braking system (ABS) and automatic transmission control system basically need wheel speed information. Therefore, the wheel speed sensor is one of the most critical sensors in modern automobiles.
Principle: Magnetoelectric wheel speed sensor consists of permanent magnet core and coil. The magnetic field lines come out from one pole of the magnetic core, pass through the gear ring and the air body, and return to the other pole of the magnetic core. Because the coil of the sensor is wound on the magnetic core, these magnetic lines will also pass through the coil. When the wheel rotates, the gear ring (rotor) synchronized with the wheel rotates correspondingly, and the teeth and gaps on the gear ring pass through the magnetic field of the sensor quickly in turn. In this way, when the reluctance of the magnetic circuit changes, it will affect the change of the induced potential in the coil and produce potential pulses with necessary amplitude and frequency. The frequency of pulses, that is, the number of pulses per second, reflects the speed of wheel rotation.
Function of wheel speed sensor: classification and characteristics
In most cases, all speed sensors can basically be used as wheel speed sensors, but considering the actual factors such as the working environment of the wheel and the size of the empty space, the commonly used wheel speed sensors generally include magnetoelectric wheel speed sensors and Hall wheel speed sensors.
Magnetoelectric wheel speed sensor
Magnetoelectric wheel speed sensor is designed with the help of electromagnetic induction principle, and its key components are shown in the following figure.
It has the characteristics of simple structure, low cost and no fear of mud, and is widely used in ABS anti-lock braking system of modern cars.
However, the magnetoelectric wheel speed sensor also has a disadvantage:
(1) frequency response is not high. When the vehicle speed is too high, the frequency response of the sensor can't keep up and it is easy to produce false signals.
(2) The ability to resist electromagnetic interference is poor, especially when the output signal amplitude is small.
Hall wheel speed sensor
The Hall wheel speed sensor is made by using the Hall effect principle, as shown in the following figure. Hall wheel speed sensor is also widely used in automobiles.
The Hall wheel speed sensor has the following characteristics:
(1) The voltage amplitude of the output signal is independent of the speed;
(2) High frequency response;
(3) Strong anti-electromagnetic interference ability.
Function of wheel speed sensor: structural principle
Magnetoelectric wheel speed sensor
(1) structure
Most magnetoelectric wheel speed sensors consist of a magnetic induction sensor head and a gear ring. The sensing head consists of a permanent magnet, a polar axis and an induction coil. The gear ring is a moving part, most of which is installed on the hub or axle and rotates with the wheel. The wheel speed sensor head is a fixed part, and there is a necessary gap between the magnetic pole of the sensor head and the end face of the gear ring. As shown in the figure below.
The vehicle wheel speed sensor is usually installed on the wheel, but in some models, it is installed in the main reducer or gearbox.
According to the different shapes of poles, there are three types: chiseled, cylindrical and drilled, as shown in the following figure. Different sensor heads with different shapes are not necessarily installed in the same way as the gear ring. Most diamond shaft speed sensor heads are installed radially perpendicular to the gear ring; The rotating speed sensor head of the chisel shaft is installed on the axial tangent of the gear ring; The polar axis speed sensor head is vertically installed on the axis of the gear ring. Installation should be firm. In order to prevent the influence of water and dust on the operation of the sensor, grease the sensor before installation.
(2) principle
Magnetoelectric wheel speed sensor is composed of permanent magnet core and coil. The magnetic field lines come out from one pole of the magnetic core, pass through the gear ring and the air body, and return to the other pole of the magnetic core. Because the coil of the sensor is wound on the magnetic core, these magnetic lines will also pass through the coil. When the wheel rotates, the gear ring (rotor) synchronized with the wheel rotates correspondingly, and the teeth and gaps on the gear ring pass through the magnetic field of the sensor quickly in turn. In this way, when the reluctance of the magnetic circuit changes, it will affect the change of the induced potential in the coil and produce potential pulses with necessary amplitude and frequency. Pulse frequency, that is, the number of pulses per second, reflects the speed of wheel rotation, as shown in the following figure.
Hall wheel speed sensor
(1) structure
Hall wheel speed sensor consists of sensor head and gear ring. The sensor head consists of a permanent magnet, a Hall element and an electronic circuit. As shown in the figure below.
(2) principle
The Hall wheel speed sensor is based on the Hall effect principle, that is, applying an adjusting current at both ends of the semiconductor chip and a magnetic field with a magnetic field strength of B in the vertical direction of the chip will generate a potential at the other end of the chip whose size is proportional to the product of the adjusting current and the magnetic induction strength B, which is called Hall potential.
When Hall element is used as the wheel speed sensor of automobile, the magnetic induction intensity B is often used as the input signal, and the magnetic induction intensity B generates Hall potential pulse with the change of wheel speed. The pulse sequence is output to the outside world after amplification, shaping and power amplification in Hall IC, and its air ratio changes with the angular velocity of the turntable. The rotation of the disk alternately changes the magnetic resistance, which leads to the change of magnetic induction intensity, so that the Hall potential pulse output by the sensor can be measured.
As shown in the figure below, the magnetic field lines of the permanent magnet reach the gear through the Hall element, which is equivalent to a magnetic collector.
① When the gear is in the position shown in Figure A), the magnetic lines passing through the Hall element are scattered and the magnetic field is weak.
② When the gear is in the position shown in Figure b), the magnetic field is concentrated by the Hall element, and the magnetic field becomes stronger year-on-year.
③ When the gear is running, the density of magnetic lines passing through the Hall element changes, resulting in the change of Hall voltage. Hall element will output a millivolt quasi-sine wave voltage, which will be converted into a standard pulse voltage by electronic circuit. Pulse frequency, that is, the number of pulses per second, reflects the speed of wheel rotation, and the speed of wheel can be known by pulse frequency.
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