SAFARI

ANTI-LOCK BRAKES

ABS

Wheel Speed Sensor

Electromagnetic pulse pick up with toothed wheels

mounted directly to the rotating components of the

drive train or wheel hubs. These devices provide a

digital signal whose frequency is proportional to

wheel rotational velocity.

The ECU derives the wheel speeds from the signal

sent by the wheel speed sensor. Inductive wheel

speed sensor (DF6) has a stator pole with coil

windings and installed directly above the Toner

Wheel. The Toner Wheel is generally fitted on to the

wheel hub. The stator pole is linked to a permanent

magnet, thus inducing a magnetic field into the toner

wheel. The alternating teeth and gap that

accompanies the wheel rotation induces

corresponding fluctuation in the magnetic field

through the stator pole.

This variation in magnetic field induces an alternating

current at the end of the winding. The frequency of

the current is proportional to the speed of the wheel.

The voltage is zero when the vehicle is stationary.

The minimum detectable rotation rate is decided by

Fig. 11

factors like tooth geometry, gap, voltage rise rate and

the ECU sensitivity to incoming signals. The sensor

has to be installed on a stable mount to prevent

oscillation pattern from the brakes resulting in distorting

sensor signals. The wheel speed sensor also has a

coating of grease to prevent it from dirt and water

spray.

Fig. 10

Front wheel speed

sensor