Multi-Pole Magnetic Encoders for Active Speed-Measurement Systems

Paper #:
  • 1999-01-3402

Published:
  • 1999-10-10
Citation:
Nachtigal, D. and Bergmann, G., "Multi-Pole Magnetic Encoders for Active Speed-Measurement Systems," SAE Technical Paper 1999-01-3402, 1999, https://doi.org/10.4271/1999-01-3402.
Pages:
8
Abstract:
Automotive wheel speed sensors have generally been based on principles of magnetic field sensing. “Active” sensors, as Hall and Magneto-Resistive, overcome some drawbacks of the previous systems. However, recent conceptual advancements, focusing on the tone-wheel, have proved significant for system performance. The tone-wheel is replaced in fully active systems by a precise ring of steel, bonded to magnetized rubber, where multiple poles are produced in the circumference. The ring serves as an encoder for magnetic sensors, eliminating the need for a large, strong permanent magnet on the sensor - thus significantly reducing size. Active sensor and encoder allow detectable speeds down to zero, improved accuracy, and significantly larger air-gaps and allowable tolerances. These properties, in turn, provide major advantages in manufacture and assembly costs. Usage of elastomeric compounds provides excellent mechanical, dynamic and environmental behavior. Furthermore, many speed-sensing systems are integrated at shaft-ends or in the vicinity of bearings, where seals are required. Elastomeric encoder technology allows combination of multiple functions, as sealing, into a single component - thereby reducing the number of parts.
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