Bendix WS-20 WHEEL SPEED SENSOR User Manual

®

Bendix® WS-20™ AntiLock Wheel Speed Sensor

SD-13-4754

DEUTSCH 2 PIN

CONNECTOR

STRAIGHT WS-20™ SENSOR

FIGURE 1 - WS-20™ ANTILOCK WHEEL SPEED SENSORS

DESCRIPTION

The WS-20™ wheel speed sensor is an electromagnetic
device used to obtain vehicle speed information for an antilock
controller. When the wheel rotates, the sensor and an exciter
(e.g. rotor or tone wheel) generate a simple AC signal. This
signal is sent to the controller, which analyzes the dat a and
commands the antilock system accordingly .

Specifically , the speed sensor consists of a coil, pole piece,
and magnet. The exciter is a steel ring or gear-like device
that has regularly spaced high and low spots called "teeth."
The sensor is mounted in a fixed position, while the exciter
is installed on a rotating member so that its "teeth" move, in
close proximity , p ast the tip of the sensor.

The WS-20™ wheel speed sensor is available in both straight
and right angle versions, to accommodate axle/wheel space
limitations. (See Figure 1.)

OPERATION

The sensor's magnet and pole piece form a magnetic field.
As an exciter tooth passes by the sensor, the magnetic
field is altered, which generates AC voltage in the sensor

PACKARD 2 PIN

CONNECTOR

™

90° WS-20

SENSOR

coil. Each time an exciter tooth and its adjacent space move
past the tip of the sensor , an AC voltage "cycle" is generated.

The number of AC cycles per revolution of the vehicle's wheel
depends on the number of teeth in the exciter, which is
programmed into the antilock controller. Using the
programmed data, the controller can calculate "vehicle
speed" by analyzing the frequency of AC cycles sent by the
speed sensor. (The frequency of AC cycles is directly
proportional to wheel speed.)

AC voltage is also proportional to speed, but voltage is not
used to determine speed. It is only an indication of AC signal
strength. The amount of AC voltage generated by a specific
speed sensor depends on the distance, or "gap," between
the tip of the sensor and the surface of the exciter. V olt age
increases as the sensor gap decreases.

The WS-20™ wheel speed sensor is installed in a mounting
block that is affixed to the axle housing. (See Figure 2.) A
spring loaded retainer bushing provides a friction fit between
the mounting block bore and the WS-20™ sensor. The friction
fit allows the WS-20™ sensor to "slide" back and forth under
force but to retain its position when force is removed. This

1

feature allows the WS-20™ sensor to "self adjust" after it
has been installed in the mounting block and the wheel is
installed.

When the WS-20™ sensor is inserted all the way into the
mounting block and the wheel is installed on the axle, the
hub exciter contacts the sensor, which pushes the sensor
back. Also, normal bearing play will "bump" the sensor away
from the exciter. The combination of these two actions will
establish a running clearance or air gap between the sensor
and exciter.

TECHNICAL INFORMATION

Electrical Connector- 2 Pin.
Output Volt age- With a 3,000 Ohm resistor across

the two sensor leads, output voltage
measured on a VOM = .800 VAC
Minimum at 42 Hz, or

approximately 5 mph.
Sensor Gap- 0 to .015 inch.
Sensor Body- Formulated Epoxy; .628" Diameter.
Normal Resistance

Range at Room T emp- 2000-2500 ohms

PEAK TO PEAK

LOW SPEED

PEAK TO PEAK

HIGH SPEED

FIGURE 2 - SPEED SENSOR VOLTAGE CYCLE OUTPUT

ANTILOCK CONTROLLER

& RELAY

WS-20™ SPEED SENSORS

EXCITERS

FRONT WHEEL

REAR WHEELS

FIGURE 3 - TYPICAL ANTILOCK SYSTEM

2

PREVENTIVE MAINTENANCE

1. Every 3 months; 25,000 miles; 900 operating hours; or

during the vehicle chassis lubrication interval, make the
visual inspections noted in "SERVICE CHECKS"
below.

2. Every 12 months; 100,000 miles; or 3600 operating hours,

perform the OPERA TIONAL TEST in this manual.

SERVICE CHECKS

Check all wiring and connectors. Make sure connections
are free from visible damage.

Examine the sensor. Make sure the sensor, mounting
bracket, and foundation brake components are not damaged.
Repair/replace as necessary .

WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the

parking brakes, and always block the wheels.
Always wear safety glasses.

2. Stop the engine and remove ignition key when

working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.

3. Do not attempt to install, remove, disassemble or

assemble a component until you have read and
thoroughly understand the recommended
procedures. Use only the proper tools and observe
all precautions pertaining to use of those tools.

4. If the work is being performed on the vehicle’s air

brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure from