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As the social aaareness of the need for greater automobile safety has risen, autonolive parts manufacturers have focused a lot of new research and development to aulomotive brake systems. Aith the much rapid advances and steady cost reductions in microelectronics technology, highly reliable, electronically controlled lour-thee1 antilock brake systems (ABS) are beginning to gain broad acceptance. Horever, wide acceptance of ABS depends upon the system and having superior performance, and high reliability at an affordable price. The toothed wheels (sensor rings) used for measuring the wheel velocity in the ABS require high precision in the pitch error of the teeth and specific magnetic properties in order to accurately detect wheel velocity, which is the first signal for brake control. Moreover, as these sensor rings are located close to the wheel, they require increased corrosion resistance ability higher than any other automotive parts.

The sensor ring for Antilock Brake Systems was developed by the Powder metallurgy(P/M) process. The P/M process provides the following merits;better dimensional tolerance, flexibility of tooth design, versatility of the materials, and better economics. Residual porosity introduced by the P/M process decreases the output voltage of the sensor. A representative porosity of 10% was confirmed to be allowable. By developing a new surface treatment suited to P/M parts which contain the residual porosity, we succeeded in developing the P/M sensor ring which can endure a 500 Hr. salt spray test.