The very first ABS systems featured the use of what are known as passive wheel sensors. Working on the basis of the principle of induction , they supply an analogue signal in the form of an alternating voltage to the electronic control unit.
How does an ABS wheel speed sensor work?
The sensors work with the toothed tone wheels to monitor and provide the anti-lock brake module (ABM) with wheel speed information. ... The result is an alternating current (AC) voltage that is generated in the speed sensor coil by magnetic lines of force fluctuating as the tone wheel passes by the magnetic sensor.
What type of electrical signal is supplied to the ABS ECU by wheel speed sensors?
The frequencies and amplitudes of the alternating voltage are related to the wheel speed. The sensor creates a AC signal that changes frequency as the wheel changes speed. The ABS control unit converts the AC signal to a digital signal for interpretation.
Does ABS use wheel speed sensor?
An ABS wheel speed sensor converts the pulses created by the magnet , and the sensor ring rotates. The voltage fluctuations are sent to the ABS control unit, which uses this data to determine wheel speed and evaluate whether the ABS works properly.
Does a wheel speed sensor use magnetism?
Magneto Resistive (Active Wheel Speed Sensors)
A magneto resistive sensor has a sensing element that contains an output module that is mounted on a substrate and magnetic material . These magnetic rings are often located on the seal of the bearing.
What are wheel speed sensors used for?
Active wheel-speed sensors are an integral part of brake control systems. They detect the rotational wheel speed of vehicles using a non-contacting measurement principle.
What sensors are used in ABS?
An ABS consists of wheel speed sensors provided for individual wheels, an ECU that obtains the slip ratio and calculates the signals that will adjust the slip ratio to an adequate value, and an actuator that sets the brake pressure based on the signals from the ECU, as shown in Figure 6.
What type of signal does a wheel speed sensor produce?
An active wheel speed sensor creates a digital signal . This type of digital wheel speed sensor uses a hall effect or a variable reluctance signal with a square wave pattern. The sensor may have two or three wires.
How many wires does a wheel speed sensor have?
Active wheel speed sensors have two wires . One wire provides 12 volts to power the sensor. The other wire is the signal wire. The signal wire changes the frequency of the waves as the magnets of the tone ring pass by.
How is ABS controlled by the ECU?
ABS is based on several main components. The car's ECU (Electronic Control Unit, or computer “brain”) is connected to four speed sensors, one attached to each wheel. ... As the wheel speed returns to a similar level to the others, braking force is then electronically increased again.
What reference voltage supply voltage is used with digital wheel speed sensors?
Active sensors often have three wires: a voltage reference input ( 5 to 12 volts ), a signal output and ground. But some active sensors have only two wires (reference voltage and signal return).
What does a magnetic pulse type wheel speed sensor produce?
A vehicle speed sensor generates a magnetic pulse in the form of a wave , proportional to the speed of the vehicle.
What is the resistance of a wheel speed sensor?
A wheel speed sensor and circuit will usually have a resistance of 800 to 1400 ohms . Measure the resistance across the sensor itself if it has too much resistance.
What is an AC system wheel speed sensor?
The passive speed sensor creates its own AC signal that changes frequency with wheel speed . This signal is only present while the wheel is turning at a rate fast enough to create the AC signal. Vehicles equipped with passive wheel speed sensors do not read at or below 2 mph coming from a dead stop.
How do speed sensors work?
How does the speed sensor work? The vehicle speed sensor measures the rotational speed of the gears in your transmission system . Then, it converts this measurement into an analog signal or a low voltage square wave signal and relays it to electronic control units (ECUs) inside your car.
Is wheel speed sensor important?
Car wheel speed sensors are an important safety feature . It helps the ABS system work when you need to make an emergency stop.
Where are the wheel speed sensors?
A wheel speed sensor, also called an “ABS sensor,” is part of the Anti-lock Brake System (ABS). It is located on the tires (near the brake rotors for the front tires and in the rear end housing for the rear tires).
Which speed sensor controls the speedometer?
The output speed sensor measures how fast a vehicle moves and sends that information to other vehicle systems. The transmission control unit uses the speed to determine when to change gears, adjust the torque converter and display the vehicle's speed in the speedometer.
What is a ABS control module?
The ABS control module is a microprocessor that runs diagnostic checks of a vehicle's antilock braking system and processes information from wheel-speed sensors and the hydraulic brake system to determine when to release braking pressure at a wheel that's about to lock up and start skidding.
How does a two wire speed sensor work?
First off is testing the 2 wire speed sensor. These sensors are self powered, meaning the revolutions inside the case generate the signal needed to create movement in the speedometer. ... Using the drill to operate the sensor shows that as the RPM's of the drill increases, the voltage output of the sensor increases.
Which sensor modifies the reference voltage signal?
An engine coolant temperature sensor or ECT sensor is a variable resistor that uses resistance to change a 5-volt reference signal from the PCM. The sensor's signal changes according to the engine's coolant temperature.
Where is ABS control module located?
ABS Control Module Location
The ABS control module is found in the engine compartment of most vehicles . However, it can also be found on the driver's side frame rail in a few models. You may need to lift the vehicle to find the ABS control module. It could also be located under plastic panels or covers.
What are the wires used for on a 2 wire magneto resistive WSS?
Magneto Resistive WSS may have 2 or 3 wires (normally 2). ... If it has 3 wires (most don't) one wire will be voltage in, one wire will be ground, and the third wire will be a signal or trigger wire. As the tone ring turns and triggers the WSS, the signal wire puts out a square wave signal of 2 distinct voltages.
