Sensors used in ABS (Anti-Lock Braking System)

Dr. Shahin H. BerishaGateWay Community CollegePhoenix, Arizona, USA

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)

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.

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)

Wheel Speed SensorsBasic 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.

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.

Deceleration SensorBasic 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)

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