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1. Structure and Principle of the Electromagnetic Induction Wheel Speed Sensor

The electromagnetic induction wheel speed sensor mainly consists of a sensor head and a magnetic gear ring. The sensor head comprises a permanent magnetic core and an induction coil group. The sensor head is installed on the non-rotating parts of the wheel, such as the steering knuckle, suspension support, half shaft housing, and brake bottom plate. The magnetic gear ring is made of ferromagnetic material and mounted on the parts rotating with the wheel, such as the hub, brake disc, and half shaft. The gap between the sensor head and the magnetic gear ring is very small, usually only 0.5-1.0 mm, and is generally not adjustable.

When the magnetic gear ring rotates, the tooth top and tooth gap alternately pass through the magnetic center of the sensor head. When the tooth top is aligned with the sensor head, the gap between the magnetic center and the gear ring is minimum, and the magnetic flux generated by the permanent magnetic center can easily pass through the gear ring, resulting in a strong magnetic field around the induction coil. When the tooth gap is aligned with the sensor head, the gap between the magnetic center and the gear ring is maximum, and the magnetic flux is not easy to pass through the gear ring, resulting in a weak magnetic field around the induction coil. This rapid change in magnetic field strength induces an alternating voltage in the induction coil, and the frequency of the alternating voltage is directly proportional to the wheel speed. The electronic control device can process the pulse voltage signal to obtain the wheel speed and other parameters.

2. Detection of the Electromagnetic Induction Wheel Speed Sensor

(1) Inspection of the Output Voltage of the Wheel Speed Sensor
1) Lift the wheel off the ground and release the parking brake to allow the wheel to rotate freely.
2) Use a multimeter to measure the AC voltage between the sensor output terminals. When the wheel is rotating, you should be able to measure an AC voltage signal, and the voltage amplitude and frequency should vary with the wheel speed.
3) If there is no output signal, the sensor itself or the wiring may be faulty, and further inspection of the sensor and wiring is required.

The electromagnetic induction wheel speed sensor has a simple structure and low cost, so it has a wide range of applications. However, because the frequency and amplitude of the output signal are greatly affected by the speed, the anti-electromagnetic interference ability is poor, and it is easy to produce false signals, it is only suitable for speeds of 15-160 km/h. In the future, as the required speed range expands to 8-260 km/h or even higher, the electromagnetic induction wheel speed sensor will be difficult to adapt. Therefore, Hall effect wheel speed sensors are gradually replacing electromagnetic induction sensors and are becoming more widely used in ABS systems.