Wheel RPM sensor, component description - GF42.45-P-5134TM

MODEL 211.0/2, 219.3 as of 1.6.06

except CODE (494) USA version

except CODE (498) Japan version

MODEL 211.0/2, 219.3 as of 1.7.06

with CODE (494) USA version

with CODE (498) Japan version

Illustrated on model 219.3

Fig 1: Locating Wheel RPM Sensors

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 2: Current Path Of Active Wheel Speed Sensor On Acceleration Phase

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Location

The left front RPM sensor and right front RPM sensor are mounted on the front axle steering knuckle.

The left rear RPM sensor and right rear RPM sensor are mounted on the rear axle wheel carrier.

Design

Active sensor consisting of a housing with integrated evaluation circuit and a sensor element which is based on the Hall principle.

Task

Generates a square wave signal from which the ESP control unit (N47-5) determines the current wheel speeds.

The presentation shows the current curve through the active RPM sensor during an acceleration phase.

Function

Due to the strength and direction of an external magnetic field, a change of internal resistance is caused inside the RPM sensor. An electronic analysis system in the RPM sensor (supplied with voltage by the ESP control unit) generates a square wave signal the frequency of which depends on the RPM, and the amplitude of which is constant. The direction of travel is detected by a different signal representation when the wheel is running to the left or right. This signal is read in by the ESP control unit and placed on the Controller Area Network bus class C (engine compartment) (CAN-C).

The external magnetic field is produced by a multipole ring.

This consists of an elastomer plastic into which metal particles have been incorporated. These are aligned by a special magnetization method so as to produce various magnets whose polarity at the circumference alternates from north to south.

Advantages compared with a passive (inductive) RPM sensor:

Sensing of low RPMs down to v = 0 km/h
Improvement in signal quality (digital signal).
Signal largely insensitive to vibrations and temperature differences
Lower weight and smaller design than induction-type pulse generator.

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