RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Wheel Speed Sensor: Description and Operation
FRONT WHEEL SPEED SENSOR
DESCRIPTION
The ABS brake system uses 3 wheel speed sensors. A sensor is mounted to each front hub/bearings. The third sensor is mounted on top of the rear
axle differential housing.
OPERATION
The Wheel Speed Sensor consists of a magnet surrounded by windings from a single strand of wire. The sensor sends a small AC signal to the CAB.
This signal is generated by magnetic induction. The magnetic induction is created when a toothed sensor ring (exciter ring or tone wheel) passes the
stationary magnetic WSS.
When the ring gear is rotated, the exciter ring passes the tip of the WSS. As the exciter ring tooth approaches the tip of the WSS, the magnetic lines of
force expand, causing the magnetic field to cut across the sensor's windings. This, in turn causes current to flow through the WSS circuit in one
direction. When the exciter ring tooth moves away from the sensor tip, the magnetic lines of force collapse cutting the winding in the opposite
direction. This causes the current to flow in the opposite direction. Every time a tooth of the exciter ring passes the tip of the WSS, an AC signal is
generated. Each AC signal (positive to negative signal or sinewave) is interpreted by the CAB. It then compares the frequency of the sinewave to a
time value to calculate vehicle speed. The CAB continues to monitor the frequency to determine a deceleration rate that would indicate a possible
wheel-locking tendency.
The signal strength of any magnetic induction sensor is directly affected by:
-
Magnetic field strength; the stronger the magnetic field, the stronger the signal
-
Number of windings in the sensor; more windings provide a stronger signal
-
Exciter ring speed; the faster the exciter ring/ tone wheel rotates, the stronger the signal will be
-
Distance between the exciter ring teeth and WSS; the closer the WSS is to the exciter ring/tone wheel, the stronger the signal will be.
The rear WSS is not adjustable. A clearance specification has been established for manufacturing tolerances. If the clearance is not within these
specifications, then either the WSS or other components may be damaged. The clearance between the WSS and the exciter ring is 0.005 - 0.050
inch.
