Dodge Durango (HB). Manual - part 124
SENSOR-WHEEL SPEED-ABS-FRONT
OPERATION
The Wheel Speed Sensor consists of a magnet (1)
surrounded by windings from a single strand of wire
(5). The sensor sends a small AC signal to the ABM.
This signal is generated by magnetic induction. The
magnetic induction is created when a toothed sensor
ring (exciter ring or tone wheel) (4) passes the station-
ary magnetic WSS.
When the ring gear is rotated, the exciter ring (4)
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 (5). 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 wind-
ing 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 sig-
nal is generated current. Each AC signal (positive to
negative signal or squarewave) is interpreted by the
ABM. It then compares the frequency of the sinewave
to a time value to calculate vehicle speed. The ABM
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 (3) “air gap” 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 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 clear-
ance between the WSS and the exciter ring is 0.005 – 0.050 in.
The assembly plant performs a “Rolls Test” on every vehicle that leaves the assembly plant. One of the test per-
formed is a test of the WSS. To properly test the sensor, the assembly plant connects test equipment to the Data
Link Connector (DLC). This connector is located to the right of the steering column and attached to the lower portion
of the instrument panel. The rolls test terminal is spliced to the WSS circuit. The vehicle is then driven on a set of
rollers and the WSS output is monitored for proper operation.
HB
BRAKES - ABS SERVICE INFORMATION
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