BENDIX BW1662 manual Description, Operation

®

SD-13-4754

Bendix® WS-20™AntiLock Wheel Speed Sensor

DEUTSCH 2 PIN	PACKARD 2 PIN
CONNECTOR	CONNECTOR

STRAIGHT WS-20™SENSOR 90° WS-20™SENSOR

FIGURE 1 - WS-20™ANTILOCK WHEEL SPEED SENSORS

DESCRIPTION

The WS-20™wheel speed sensor is an electromagnetic device used to obtain vehicle speed information for an antilock controller. When the wheel rotates, the sensor and an exciter (e.g. rotor or tone wheel) generate a simple AC signal. This signal is sent to the controller, which analyzes the data and commands the antilock system accordingly.

Specifically, the speed sensor consists of a coil, pole piece, and magnet. The exciter is a steel ring or gear-like device that has regularly spaced high and low spots called "teeth." The sensor is mounted in a fixed position, while the exciter is installed on a rotating member so that its "teeth" move, in close proximity, past the tip of the sensor.

The WS-20™wheel speed sensor is available in both straight and right angle versions, to accommodate axle/wheel space limitations. (See Figure 1.)

OPERATION

The sensor's magnet and pole piece form a magnetic field. As an exciter tooth passes by the sensor, the magnetic field is altered, which generates AC voltage in the sensor

coil. Each time an exciter tooth and its adjacent space move past the tip of the sensor, an AC voltage "cycle" is generated.

The number ofAC cycles per revolution of the vehicle's wheel depends on the number of teeth in the exciter, which is programmed into the antilock controller. Using the programmed data, the controller can calculate "vehicle speed" by analyzing the frequency of AC cycles sent by the speed sensor. (The frequency of AC cycles is directly proportional to wheel speed.)

AC voltage is also proportional to speed, but voltage is not used to determine speed. It is only an indication of AC signal strength. The amount of AC voltage generated by a specific speed sensor depends on the distance, or "gap," between the tip of the sensor and the surface of the exciter. Voltage increases as the sensor gap decreases.

The WS-20™wheel speed sensor is installed in a mounting block that is affixed to the axle housing. (See Figure 2.) A spring loaded retainer bushing provides a friction fit between the mounting block bore and the WS-20™sensor. The friction fit allows the WS-20™sensor to "slide" back and forth under force but to retain its position when force is removed. This

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