ABS Magnetic Ring

The Anti-lock Braking System (ABS) is a crucial cornerstone of active safety in modern vehicles. One of the key components ensuring the precise operation of this system is a seemingly inconspicuous yet indispensable part—the ABS magnetic encoder ring, also known as a tone wheel. It acts as the “eyes” of the system, working in conjunction with a Hall effect sensor to continuously provide the ABS control unit with accurate information about wheel speed.

Table of content
  • Material Property
  • Key Parameters
  • Process Introduction
  • Typical Applications

Material Property

I. Composition Materials

The core function of the ABS magnetic ring is to generate magnetic field variations detectable by the sensor. Therefore, its material selection directly affects signal stability and durability.

  1. Magnetic Material:

    • Ferrite Permanent Magnet Material: This is the most commonly used and economical material. It is a ceramic material made by mixing and sintering iron oxides (e.g., Fe₂O₃) with other metal oxides (e.g., SrO or BaO). Its advantages are high hardness, corrosion resistance, and low cost, but its magnetic properties are relatively weak, and performance may slightly decrease in extremely low temperatures.

  2. Matrix Material:
    The magnetic ring is typically formed by combining magnetic powder (ferrite) with rubber (such as NBR Nitrile Butadiene Rubber) or plastic (such as PA66 Nylon, PPS Polyphenylene Sulfide) through injection molding or die-casting processes.

    • Rubber Magnetic Ring: The majority of magnetic rings on the market are rubber magnetic rings. They offer good toughness and resistance to thermal shock, can adapt to some deformation, and are easy to install. The following product parameters and process descriptions are based on rubber magnetic rings.

    • Plastic Magnetic Ring: Offers higher dimensional accuracy and mechanical strength, better high-temperature resistance, and oil resistance.

  3. Support Material:
    To facilitate installation, magnetic rings often use stainless steel as a skeleton. This allows the magnetic ring to be easily fixed via an interference fit between metal parts.

Key Parameters

Key technical parameters for evaluating the performance of an ABS magnetic ring include:

  • Number of Magnetic Poles: The quantity of North and South magnetic poles arranged alternately around the circumference of the ring. Common numbers are 30, 60,58 etc. A higher number of poles provides more pulse signals per unit time for the sensor, allowing the system to calculate speed more accurately, especially at very low speeds.

  • Pole Accuracy: The tolerance for the angle or spacing between each pole must be extremely precise. Any deviation can cause uneven pulse signals, leading to false fault reports by the ABS system.

  • Magnetic Flux Density: A physical quantity measuring the strength of the magnetic field, units are Gauss (Gs) or Tesla (T). Sufficient magnetic field strength is essential to ensure the sensor can reliably detect the signal.

  • Operating Temperature Range: Typically required to operate stably in environments from -40°C to +150°C to withstand heat generated during braking and harsh winter conditions.

  • Corrosion Resistance: Must be able to resist corrosion from salt spray, water, and brake fluid.

Process Introduction

The manufacturing of ABS magnetic rings is a precision process, with main steps as follows:

  1. Magnetic Powder Preparation and Mixing: Precisely mixing ferrite or neodymium magnet powder with a binder (rubber or plastic pellets), plasticizer, stabilizer, etc., according to exact proportions.

  2. Molding:

    • Compression Molding: Placing pre-formed compound and metal parts into a mold, where they are vulcanized and bonded together under high temperature and pressure using a rubber compression molding machine.

  3. Magnetization: This is the most critical step. The formed ring itself is non-magnetic (isotropic). It needs to be placed into a multi-pole magnetizing machine, where an instant ultra-strong pulse current generates a huge magnetic field, magnetizing the magnetic material inside the ring according to the preset number of poles and polarity, thus forming a regular N-S alternating magnetic field.

  4. Testing & Quality Control (QC): 100% testing for magnetic field strength and pole accuracy (single pole deviation and total deviation).                                                                                                                                                            

Typical Product Applications

ABS magnetic rings are used in almost all modern passenger cars and commercial vehicles.

  • Passenger Car Hub Bearing Units: This is currently the most mainstream application. The magnetic ring is directly injection molded onto the seal of the wheel hub bearing, integrating with the bearing into a single unit. This design is compact, offers good sealing, is simple to assemble, and provides high signal accuracy. For example, the vast majority of models from brands like Volkswagen, Toyota, and GM use this design.

  • Transmission Output Shaft: Used not only for wheel speed monitoring but also for monitoring transmission output speed, providing data for the vehicle control system.

  • Engine Crankshaft and Camshaft Speed: Due to their flexible arrangement, magnetic rings can sometimes be used for speed and position measurement of the engine crankshaft and camshaft.

OTE has years of experience in rubber magnetic materials and magnetization processes. We offer a rich selection of product models and also support custom requirements from clients.

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