Variable-reluctance sensor with offset magnets having improved magnetic flux members

摘要

A means is provided for improving the magnetic permeability of a magnetic circuit within a variable-reluctance sensor having off-set, permanent magnets (25,26) by appropriately annealing a magnetic flux member (30) of the sensor. The annealing process includes heating the machined magnetic flux member (30) in a vacuum to a temperature and for a duration sufficient to convert the magnetic steel into austenite so that complete carbide solution is obtained, for example at about 704°C (1300°F) to about 843°C (1550°F) for a duration of about 15 to 30 minutes. The magnetic flux member (30) is then appropriately cooled in the vacuum so as to prevent the formation of martensite. The magnetic circuit, incorporating the annealed magnetic flux member (30), exhibited improved magnetic permeability, and the sensor signal was increased by as much as about 60 percent during operation. The method of this invention enhances the overall effectiveness of the sensor, particularly when sensing low rotational speeds such as when employed within automotive anti-lock braking or traction control systems.