1. Sensors used in ABS (Anti-Lock Braking System)
Dr. Shahin H. Berisha
GateWay Community College
Phoenix, Arizona, USA

2. What is ABS? ABS provides safety Prevent the wheels from locking
Maintain directional stability
ABS controls each front brake separately and the rear brakes as a pair
ABS helps to stop a car in shortest possible distance without locking the wheel and maintaining directional control (Fig. on page 119)

3. Basic Operation of ABS
Four wheel ABS use a speed sensor at each wheel, (slide)
Signal voltage from these sensors is connected to ECU,
In rapid braking each sensor detect change in speed and send signal to ABS ECU,
Based on this information the ABS ECU calculates necessary parameters and then provides optimum braking pressure on each wheel.

4. Components of ABS System
Speed Sensors monitor wheel speed,
G - Sensor monitors rate of acceleration,
ABS Actuators control brake system pressure,
Control Relay controls Actuator Pump Motor and Solenoids,
ABS ECU monitors sensor inputs and controls the Actuator,
ABS Warning Lamp alerts driver to system conditions. (Fig. On page 125)

5. Wheel Speed Sensors Basic Operation
This sensor is an electromagnet in which a ac voltage is induced into the coil (Figure on page 127),
As the sensor rotor rotates it induces the voltage in the coil of electromagnet,
As the rotation of the sensor rotor increases, the magnitude and the frequency of induced voltage increases,
The induced voltage is information feed into ABS ECU.

6. Deceleration Sensor
This sensor measures the car’s rate of deceleration to improve braking performance,
Deceleration sensor is used on all full-time 4WD
The deceleration sensor senses the vehicle’s rate of deceleration and sends signal to the ABS ECU.
The ECU compares the rate of deceleration and vehicle speed to determine the precise road surface condition and takes appropriate control measures.

7. Deceleration Sensor Basic Operation
The LED’s are On when the ignition switch is ON
When the vehicle’s rate of deceleration changes, the split plate swings in the vehicle’s rear-to-front direction.
The slits in the slit plate act to expose the light from the LEDs to the phototransistors.
This movement of slit plate switches the phototransistors ON and OFF. (Figure on page 128)

8. Semi-Conductor Deceleration Sensor
Introduced in 1996 Toyota RAV4
Consist of two semiconductor sensors
Each semiconductor is provided with a mass which exerts pressure based on the deceleration force applied on the vehicle
The sensor converts the force into electric signal