Sensors used in ABS (Anti-Lock Braking System)

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Sensors used in ABS (Anti-Lock Braking System)

• Dr. Shahin H. Berisha
• GateWay Community College
• Phoenix, Arizona, USA

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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)

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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.

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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)

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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.

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Deceleration Sensor

• This sensor measures the cars rate of
  deceleration to improve braking performance,
• Deceleration sensor is used on all full-time 4WD
• The deceleration sensor senses the vehicles 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.

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Deceleration SensorBasic Operation

• The LEDs are On when the ignition switch is ON
• When the vehicles rate of deceleration changes,
  the split plate swings in the vehicles
  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)

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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