Motor Vehicle Level 3 Electronics and Electronic Components Resource 1

Motor Vehicle Level 3

Electronics and Electronic Components

Resource 1

Motor Vehicle LevelResource 1

Aims


To recognize the role of electronics within an ABS system

Objectives

By the end of the session you will be able to:

1. Identify Electronic ABS components2. Recognize the inputs and outputs of an ABS system3. Describe the operation of ABS electrical components.

Motor Vehicle Level 3Resource 1


ABS ECU Block Diagram



Location of Components (Electrical)



Electronic ABS Components

An ABS system will include the following electronic components•Wheel Speed Sensors•Wiring•Relays•ABS •ECU•Actuators



Location of ABS Electronic Components



Wheel Speed Sensors

•A wheel speed sensor mounted on each wheel is utilised within an ABS system in order to determine the rotational speed of the vehicles wheels (to determine if a wheel is skidding or de-accelerating), this is then sent to the ABS ECU. •Front wheel speed sensors are mounted onto the steering knuckle.•Rear wheel speed sensors can be mounted to the rear axle carrier or mounted to the suspension arm depending on set up.



Wheel Speed Sensors



Wheel Speed Sensor Operation

•As the teeth of the sensor rotor pass the iron core, the magnetic lines of force cut through the coil windings•This causes a voltage to be induced into the coil•When the tooth is centered on the iron core the magnetic field does not move and 0v is produced.•As the tooth moves away from the iron core the magnetic field expands causing a negative voltage•The faster the rotor increases the signal increases indicating a high wheel speed which is then sent to the ECU.



Wheel Speed Sensor Operation

•Voltage is induced to the coil when the magnetic field is altered each time the sensor passes the iron core



ABS relays

Supplies power to the solenoids in order to prevent wheel lock up but only when the following conditions are met:-•The IGN is on•The self diagnostic check performed by the vehicle on start up was completed OK•If any of these conditions are not met, the ECU will switch the solenoids off.



Circuit Diagram showing ABS relays



Relays

•The motor relay will switch the voltage to the pump motor•The solenoid relay switches the voltage to the actuator solenoids



Actuators

•The actuators on an ABS system will control the amount of brake pressure that the wheel is subjected to, depending on information received from wheel speed sensors etc. •It controls this via three solenoids:-

•Pressure holding •Pressure increase•Pressure Reduction

•These solenoids will be discussed further in the next session.



Actuators



ABS ECU

•The ECU (Electronic control unit) is the vehicles on board computer that will ensure that all systems are performing correctly. •The ECU will collect data from sensors, battery and brake light switch in order to determine how the ABS system is performing. •If a wheel speed sensor is measuring as de-accelerating (lock up) the ECU will react by sending a signal to the actuators to reduce that pressure at the offending wheel.



Block Diagram ABS ECU



Circuit Diagram ECU



Summary

Aim: •To recognize the role of electronics within an ABS system

Objectives: At the end of the session, students should be able to:•Identify Electronic ABS components•Recognize the inputs and outputs of an ABS system•Describe the operation of ABS electrical components.



Documents

Motor Vehicle Level 3 Electronics and Electronic Components Resource 1