Wheel Speed Sensor: Description and Operation

GF42.45-P-5134RT Wheel rpm sensor, component description

Component Identification:

Task
The rpm sensors supply the current wheel speeds to the ESP control unit (N47-5). The ESP evaluates these signals corresponding to the direction of rotation, the wheel speed and fault detection.





Design
The rpm sensors are active sensors, consisting of a housing and a sensor element which is based on the magneto-resistive measuring principle.

The diagram shows the current curve through an active rpm sensor during an acceleration phase.

Function of the active wheel speed sensor
The strength and direction of an external magnetic field causes a change in the internal resistance inside the sensor. Via an electronic analysis system housed in the sensor a square wave signal is generated, the frequency of which depends on the rotational speed. The amplitude height remains constant.

This signal is read in and processed by the ESP control unit. The external magnetic field is produced by a multipole ring. This consists of an elastomer plastic containing metallic particles. The metal particles are aligned via a special magnetizing process so that magnets arise the polarity of which at the circumference change from north to south.