June 30, 2008
Development of “High Magnetic Force Rubber Encoder
for Wheel Rotation Sensors”
[Achieving world's highest level of performance with rubber encoder,
New Product Contributing to Advanced Safety Driving Control
with Enhanced Reliability and Stability]
NTN Corporation has developed a “High Magnetic Force Rubber Encoder for Wheel Rotation Sensors” for ABS*1 sensors mounted on hub unit bearings that has a 25% increase in magnetic force.
Wheel rotation sensors, called ABS sensors, are mounted on many automobile wheel bearings. It is a magnetic detection sensor and works in conjunction with a magnetic encoder, which is in the shape of a ring. The magnetic encoder is built into the wheel bearing and rotates with the wheel and the sensor detects the resulting variation of the magnetic poles on the encoder, thus determining the wheel speed. Widely used conventional magnetic encoders are made with rubber materials and are hot-formed after mixing ferrite powder and the rubber materials. The magnitude of the magnetic force of the ferrite particles depends on their orientation, which makes it necessary for the particles to be orientated in the same direction. However, as the material flows during the forming process the alignment of the particles is disturbed, which can result in insufficient magnetic force for the encoder. This has been the problem with conventional encoders.
The new “High Magnetic Force Rubber Encoder for Wheel Rotation Sensor” product has made the magnetic force of the encoder strong by optimally aligning the ferrite particles in the rubber material. In addition, a new rubber forming process was developed where in the hot forming the orientation of the ferrite powder is aligned in the same direction by applying a magnetic force to the entire body of the mold before rubber solidification. Also, by optimizing the composition of the rubber ingredients more amount of ferrite powder can be added to attain a 25% increase in magnetic force compared to the conventional type encoder. Through these innovations it becomes possible to reduce the positioning accuracy needed at the sensor mounting location, but still able to generate the equivalent output of a conventional encoder.
Moreover, by using a rubber material that has been proven in the market as having superior flexibility and resistance to damage such as chipping and cracking resulting from various shocks to the during encoder assembly to the bearing, or from environmental temperature, severe variations during vehicle driving can be avoided.
NTN will globally market the “High Magnetic Force Rubber Encoder for Vehicle Rotation Sensors”.
*1 Antilock braking system
[ Features ]
| 1. | Magnetic force: Increased by 25% (vs. conventional encoder) |
| 2. |
Improved durability at severe environmental temperature conditions (thermal shock) Glass transition temperature of the rubber material (the temperature when impact resistance decreases sharply): Decreased by 3 to 10 °C. |
[ Photo ]
