Motor Vehicle Level 3

ABS Sensors Their Operation and Waveform Produced

Resource 4

Motor Vehicle Level 3Resource 4

Aims

ABS Sensors Their Operation and Waveform Produced

To recognize various sensors used within ABS systems and their role within the system

Objectives

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

•Identify various sensors including hall, and be able to describe passive and inductive sensors and their operation •Recognize the role of the speed sensor and it's location•Recognize and comment on the waveforms produced.•Comment briefly on how to maintain the sensor, and identify possible faults.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Types of sensor : Active Sensor

•Example:-Magnetised pick up (crankshaft sensor, ABS sensor)•Voltage signal produced is sent to the input of the ECU for analysation.•The ECU will covert this Analogue signal to Digital signal which the ECU can read. •The ECU will now react (alter the brake pressure depending on this voltage signal.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Types of sensor : Passive Sensor (three wire)

•Three wire device •Supply voltage for the sensor is supplied via the ECU •The internal resistance alters with a change in environment these are usually used to sense movement (i.e. throttle position)•This is measured by the ECU and the ECU will alter accordingly

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Types of sensor : Passive Sensor (two wire device)

•Similar to a three wire device, the sensors internal resistance will alter with a change in environment rather than change in movement (i.e. engine coolant)•ECU Supplies voltage to the sensor,•The ECU will measure the change in internal resistance and react accordingly.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

ABS Sensors

•Of course, ABS will use an active sensor •Why do you think that is?•Could it use a passive sensor?

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

ABS Wheel Speed Sensor

•Wheel Speed Sensors are mounted at each wheel and sends a rotation signal to the ECU•Wheel speed sensors can be mounted to the steering knuckle or to the axle carrier

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

ABS Wheel Speed Sensor

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

ABS Wheel Speed Sensor

•As the teeth of the sensor rotor pass the iron core, magnetism will cut through the coil windings Inducing a voltage•When the tooth is centered to the iron core 0v is produced•As the tooth moves away from the iron core, the magnetic field expands producing a negative voltage •As the wheel rotates faster the voltage and frequency increase (indicating to the ECU that the vehicle is travelling faster)

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

•In order to diagnose a fault within an ABS system waveforms are useful in order to determine system performance, and will also give hints as to the problem.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

•The following images where taking using a diagnostic tool called a Picoscope•These show two wheel speed sensors being monitored, one has a fault...is it the red trace or the blue trace?

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

•this small capture taken from the waveform produced indicates a fault compared with the blue trace•The fact the we have a waveform at all indicates that the sensor is producing a signal.•Therefore, we can diagnose that the rotor wheel has failed.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

•This vehicle measures rear wheel speed via a driveshaft, upon inspection, we can see that the teeth have been damaged, furthermore, we can see this corresponds to our waveform produced. •Another factor that could have produced a similar waveform could have been distance from the sensor to the rotor or contamination of the sensor.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Waveform produced

•In order to check the voltage is correct to the sensor •Ensure that your multimeter is correct and on the correct function (direct v)•Measure between the terminals as shown (always refer to manufactures guidelines)•The voltage should be between 10v-14v

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Probing a Sensor

•Continuity check•Is done to check that there is no faults in the wiring harness between the ECU, the Actuator and the ABS relays and possibly to the sensors.•Refer to manufactures guidelines•From the signal contact in the terminal blocks check the resistance between each components. •The resistance should be around 4-6Ώ

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced

Summary

Have We:-•Identified various sensors including hall, and be able to describe passive and inductive sensors and their operation •Recognized the role of the speed sensor and it's location•Recognized and commented on the waveforms produced.•Commented briefly on how to maintain the sensor, and identify possible faults.

Motor Vehicle Level 3Resource 4

ABS Sensors Their Operation and Waveform Produced