The multi-pole magnetic ring used in wheel speed sensors [core function principle main material]

The multi-pole magnetic ring for wheel speed sensors is one of the core components in modern automotive active safety systems such as ABS, ESP, and TCS. It is typically installed on the wheel hub bearing or half-shaft. By generating periodic magnetic pole signals that interact with Hall effect sensors, it provides precise speed output, enabling dynamic stability control during braking and acceleration. This article will introduce the core functions, working principles, and main material types of such multi-pole magnetic rings.

The multi-pole magnetic ring for wheel speed sensors is a multi-pole magnetized circular magnet installed on the wheel bearing or half-shaft of a vehicle. It works in conjunction with Hall effect sensors or magnetoresistive sensors to detect wheel rotation speed and vehicle speed in real time. Common pole numbers include 48, 60, 96, and 120 poles. The higher the pole number, the higher the signal resolution and the more precise the speed detection.

Core Function and Working Principle of the Multi-pole Magnetic Ring for Wheel Speed Sensors

The multi-pole magnetic ring for wheel speed sensors serves as the "eyes" of modern automotive active safety systems. Its core function is to accurately detect wheel rotation speed and vehicle speed in real time. This ring-shaped magnet, installed on the wheel bearing or half-shaft, has 48 to 192 alternating N/S magnetic poles along its circumference. As the wheel rotates, these poles pass quickly over a fixed Hall effect sensor or magnetoresistive sensor, generating a continuous pulse signal. The ECU calculates the instantaneous speed of each wheel by measuring the pulse frequency. This data forms the basis for the ABS anti-lock braking system (preventing brake lockup and slipping), the ESP vehicle stability system (correcting loss of steering control), and the TCS traction control system (preventing drive wheel spin). It also provides data for the speedometer display, cruise control, and mileage calculation. The higher the pole number of the magnetic ring, the higher the detection resolution. It plays a crucial role in vehicle safety by collecting key data for driving protection. Every time the brakes are applied, it responds in milliseconds to safeguard the occupants.

For example, a 96-pole magnetic ring generates 48 pulses per rotation (48 pairs of magnetic poles). If the ECU detects a pulse frequency of 800 Hz, it can calculate the wheel speed to be 1000 rpm.

In terms of materials, the main choices are injection-molded ferrite and injection-molded neodymium iron boron. Injection-molded ferrite is the mainstream choice, accounting for about 75% of the market. Its core advantages include low cost, excellent high-temperature resistance (it can operate stably in environments ranging from -40°C to +150°C), natural corrosion resistance without the need for additional protective treatment, and the ability to integrate installation structures such as clips and positioning bosses directly through the injection molding process. Injection-molded neodymium iron boron has much higher magnetic performance than ferrite, resulting in stronger signal output and is suitable for high-precision wheel speed detection. It is used in high-performance, sports, or vehicles with extremely high low-speed precision requirements.

This is an overview of the functions, working principles, and materials related to the multi-pole magnetic ring used in wheel speed (vehicle speed) sensors.