Home  Sensors

Dec 27 2017

What is a Wheel Speed Sensor?

I Introduction

The wheel speed sensor, also known as the vehicle speed sensor (VSS), is a SENSOR used to measure the steering of the car wheels. Commonly used wheel speed sensors are: magnetoelectric wheel speed sensors and Hall effect wheel speed sensors.

For modern vehicles, wheel speed information is essential. Vehicle dynamic control system (VDC), automotive electronic stabilization program (ESP), anti-lock braking system (ABS), automatic transmission control system, etc., all require wheel speed information. So wheel speed sensor is one of the most important sensors in modern automobile.

Wheel Speed Sensor Operation & Testing

Catalog

I Introduction

II How Does The Wheel Speed Sensor Work?

III Types of Wheel Speed Sensor

 3.1 Classification of Wheel Speed Sensor

 3.2 Magnetoelectric Wheel Speed Sensor

 3.3 Hall Effect Wheel Speed Sensor

IV The Location of Wheel Speed Sensor

V What Does The Wheel Speed Sensor Do?

VI Symptoms of a Faulty Wheel Speed Sensor

VII Why is The Wheel Speed Sensor Broken?

VIII Detection Method of Wheel Speed Sensor

IX Wheel Speed Sensor Failure Case Analysis

 9.1 Fault Phenomenon

 9.2 Inspection and Analysis

 9.3 Troubleshooting

X One Question Related to the Wheel Speed Sensor

II How Does The Wheel Speed Sensor Work?

The function of the wheel speed sensor is to transmit the wheel speed signal to the ABS electronic control unit. The MK20-Ⅰ ABS system has four wheel speed sensors, the ring gear (43 teeth) of the front wheel is installed on the transmission shaft, and the speed sensor is installed on the steering knuckle, as shown in the following figure. The ring gear (43 teeth) of the rear wheel is installed on the rear wheel hub, and the speed sensor is installed on the fixed bracket.

Front wheel speed sensor installation location

Figure1. Front wheel speed sensor (G45 / G47) installation location

1-Ring gear 2-Front wheel speed sensor

Installation position of rear wheel speed sensor

Figure2. Installation position of rear wheel speed sensor (G44 / G46)

1-Ring gear 2-Rear wheel speed sensor

The sensor is composed of electromagnetic induction sensor head and magnetic ring gear. The sensor head is composed of a permanent magnetic core and an induction coil, and the ring gear is made of ferromagnetic material.

When the ring gear rotates, the tooth tip and backlash alternately face the magnetic core. When the ring gear turns to the tooth tip and faces the sensor head magnetic core, the gap between the sensor head core and the ring gear is the smallest. The magnetic force lines generated by the magnetic core can easily pass through the ring gear, and the magnetic field around the induction coil is strong, as shown in figure a below; and when the ring gear rotates to the backlash and the sensor core, the sensor head core and the ring gear The gap between them is the largest, the magnetic field lines generated by the permanent magnetic core cannot easily pass through the ring gear, and the magnetic field around the induction coil is weak, as shown in (b).

At this time, the magnetic flux changes rapidly and alternately, an alternating voltage is generated in the induction coil, and the frequency of the alternating voltage will change in direct proportion to the wheel speed. The electronic control unit can process the voltage pulse frequency input by the rotation speed sensor to determine the rotation speed of the wheel, the reference speed of the car, and the like.

Working principle of wheel speed sensor

Figure3. Working principle of wheel speed sensor

(a) When the ring gear tooth tip is opposite to the sensor core

(b) When the ring gear tooth gap is opposite to the sensor core

1-Ring gear 2-Core end tooth 3-Induction coil terminal 4-Induction coil 5-Core sleeve 6-Magnetic force line 7-Magnetic field 8-Core 9-Tooth top

III Types of Wheel Speed Sensor

Generally speaking, all speed sensors can be used as wheel speed sensors, but considering practical factors such as the working environment of the wheels and the size of the space, commonly used wheel speed sensors are mainly: magnetoelectric wheel speed sensors, Hall type wheel speed sensors .

3.1 Classification of Wheel Speed Sensor

(1) According to the principle of signal generation, it can be divided into two types: magnetoelectric and Hall. The wheel speed sensors used by different models of the same brand may be different. In the Shanghai GM Buick car series, the models that use magnetoelectric wheel speed sensors are Regal, Excelle, LaCrosse and Rongyu. Models include Boulevard, New Regal and New LaCrosse.

(2) Divided by structure, there are split type and integrated type. The split type means that the sensor and the signal gear ring or magnetic coding ring matched with it are not integrated in one assembly, such as Sail, Excelle (front wheel), New Regal, etc. Integrated means that the sensor and the signal gear ring or magnetic coding ring cooperated with it are integrated in an assembly, usually with the bearing as an assembly, such as Regal, LaCrosse and Excelle (rear wheel), etc. Wheel bearing assembly.

Different Types of Wheel Speed Sensor

Figure4. Different Types of Wheel Speed Sensor

3.2 Magnetoelectric Wheel Speed Sensor

(1) Structure

Magnetoelectric speed sensors are one of the most commonly used sensor types in automobiles. The magnetoelectric wheel speed sensor is generally composed of a magnetic induction sensor head and a ring gear. The sensor head is composed of a permanent magnet, a polar shaft, an induction coil, and the like. The ring gear is a moving part, which is generally installed on the wheel hub or axle to rotate with the wheel. The wheel speed sensor head is a stationary part, and there is a certain gap between the magnetic pole of the sensor head and the end surface of the ring gear.

Magnetoelectricity

Figure5. Magnetoelectricity

The polar axis is divided into three types: chisel type, column type and diamond shape according to different shapes. The mounting methods of the sensor heads with different shapes with respect to the ring gear are also different. The diamond-shaped polar shaft speed sensor head is generally installed radially perpendicular to the ring gear; the chisel-shaped polar shaft speed sensor head is installed tangentially to the ring gear; the cylindrical polar shaft speed sensor head is installed perpendicular to the ring gear. The installation should be firm. In order to avoid the influence of water and dust on the sensor, the sensor must be filled with grease before installation.

(2) Principle

The magnetoelectric wheel speed sensor is composed of a permanent magnetic core and a coil. The lines of magnetic force emerge from one pole of the core, pass through the ring gear and air, and return to the other pole of the core.

Since the coil of the sensor is wound on the magnetic core, these lines of magnetic force will also pass through the coil. When the wheel rotates, the ring gear (rotor) synchronized with the wheel rotates, and the teeth and gaps on the ring gear quickly pass the magnetic field of the sensor in turn. The result is that the magnetic resistance of the magnetic circuit is changed, resulting in the induction potential in the coil. Changes, generates a potential pulse of a certain amplitude and frequency. The frequency of the pulse, that is, the number of pulses generated per second, reflects the speed of the wheel rotation,

Magnetoelectric Speed Sensor Signal Processing Circuit

Figure6. Magnetoelectric Speed Sensor Signal Processing Circuit

(3) Advantages and disadvantages

It has the characteristics of simple structure, low cost, and is not afraid of mud, etc. It is widely used in the ABS anti-lock brake system of modern cars.

But the magnetoelectric wheel speed sensor also has some disadvantages:

① The frequency response is not high. When the vehicle speed is too high, the frequency response of the sensor can not keep up, which is easy to produce false signals;

② Poor resistance to electromagnetic interference, especially when the amplitude of the output signal is small.

3.3 Hall Effect Wheel Speed Sensor

(1) Structure

The Hall effect wheel speed sensor is composed of a sensing head and a ring gear. The sensor head is composed of permanent magnet, Hall element and electronic circuit.

Hall Effect Sensor

Figure7. Hall Effect Sensor

(2) Principle

Hall effect wheel speed sensor USES the hall effect principle, that is, the two ends of the semiconductor wafer pass to control the current, in the vertical direction of the wafer to apply the magnetic field intensity B magnetic field, the other two ends of the wafer will produce a size and control current, magnetic induction intensity B product is proportional to the potential. This is the hall potential.

Hall Effect Wheel Speed Sensor

Figure8. Hall Effect Wheel Speed Sensor

When the hall element is used as the wheel speed sensor of automobile, the magnetic induction intensity B is used as the input signal. The magnetic induction intensity B changes with the wheel speed to generate hall potential pulse. After amplifying, shaping and amplifying power amplifier in hall IC, pulse train is output to the outside, and its duty ratio changes with the angular velocity of the turntable. The rotation of the tooth disk alternately changes the reluctance, causing the change of magnetic induction intensity, and the hall potential pulse output by the sensor can be measured.

Related Post: Hall Effect Pressure Sensor

(3) Features

① The amplitude of the output signal voltage is not affected by the speed;

② High frequency response;

③ Strong anti-electromagnetic interference ability.

④ Compared with the magnetoelectric wheel speed sensor, the Hall effect wheel speed sensor has the advantages of wide measuring range, high accuracy, and simultaneous detection of vehicle forward and reverse.

IV The Location of Wheel Speed Sensor

The wheel speed sensor is usually located at the front wheel brake disc and mounted on the hub of each wheel, but some cars are different. Some rear-wheel-driven vehicles have only an electromagnetic induction speed sensor in the main reducer or gearbox. The sensor is mounted on the main reducer housing or transmission housing, and the gear ring is mounted on the main reducer input shaft or transmission output shaft. It provides a signal to the ABS system that controls the braking force.

The Location of WSS

Figure9. The Location of WSS

V What Does The Wheel Speed Sensor Do?

(1) The wheel speed sensor is mainly used to detect the frequency signal of each wheel rotation (in fact, it can also be said as a speed signal), and then transmit this signal to the ABS computer.

For example, when the vehicle speed reaches 40KM / h (in fact, the wheel speed sensor detects the wheel speed frequency is also 40KM / h), you brake the emergency brake, and the ABS system starts working. When the ABS computer controls the wheel to loosen for a moment, the wheel speed sensor sends the distance signal that detects the rotation of the tire from the brake to the rotation to the ABS computer, so that the ABS controls the brake to achieve the best braking distance.

(2) Monitor the rotation speed of each wheel, automatically adjust the pressure of the brake pump, avoid individual wheels from locking, and improve the safety of the car.

Wheel Speed Sensor

Figure10. Wheel Speed Sensor

VI Symptoms of a Faulty Wheel Speed Sensor

(1) Engine instability at idle speed;

(2) When the vehicle starts or decelerates to stop while driving, a momentary pause or flameout occurs;

(3) Engine acceleration performance is reduced;

(4) There is a deviation in the speed display on the meter;

(5) The engine fault light is on.

VII Why is The Wheel Speed Sensor Broken?

In fact, the wheel speed sensor is not a very complicated part. For the Hall-type wheel speed sensor, it is composed of a sensor head and a ring gear. The sensor head is composed of a permanent magnet, a Hall element, and an electronic circuit. These things Packaging is also a very solid thing, normally it is not easy to damage. Why is the wheel speed sensor broken? In addition to quality and natural damage, more lies in the following two aspects:

Signs of a Faulty WSS

Figure11. Signs of a Faulty WSS

(1)“Fake damage

Dirty sensor head and contamination by magnetic substances may cause the wheel speed sensor to fail. If you find that the wheel speed sensor often occurs after walking through waterways, muddy roads, sand roads, etc., it is probably dirty It's just dirty, you can clean it up and take a look.

(2) External force torn off the wheel speed sensor wiring harness

For models earlier than 2011, there was no reserved length for the wheel speed sensor wiring harness, which caused the wire harness to be broken when the wheel was often killed. If you meet a good master, you will modify the wheel speed sensor bracket from the reserved length of the wire harness, then it will not be damaged after replacement; if you meet a general master, you will replace it, and the next time you hit the dead direction again The wheel speed sensor alarmed.

VIII How to Test a Faulty Wheel Speed Sensor?

When the wheel speed sensor fails, the ABS module cannot receive the correct signal from the wheel speed sensor. At this time, a trouble code will be generated and the indicator will indicate the trouble light. When we suspect that a sensor is malfunctioning, we can make the following measurements to determine whether the sensor malfunctions and cannot output the correct signal to the ABS module.

How to Test a Faulty Wheel Speed Sensor

Figure12. How to Test a Faulty Wheel Speed Sensor

Step 1: Measure the voltage on the plug of the wheel speed sensor. Hall-type sensors have Hall elements, voltage regulator circuits, and operational amplifiers. These electronic components need power and ironing. This step can directly determine whether the module has a voltage output. , Is there any problem with the power supply of the module, whether there is a short circuit and other faults.

Step 2: To further determine whether the sensor is a two-wire Hall-type wheel speed sensor, the resistance of the sensor can be directly measured with a multimeter resistance 2K file. The two-wire Hall wheel speed sensor cannot measure the resistance. It is in an infinite state and is measured with a diode There should be a tube voltage drop of 0.3V-0.7V. If the resistance can be measured with a multimeter resistance 2K, the range is about 1K-1.6K. This sensor is a magnetoelectric sensor.

Step 3: Measure the sensor signal. The Hall-type wheel speed sensor outputs a square wave pulse signal. This signal is strong against interference. Generally, the signal wire of the oscilloscope probe is used to clamp the signal wire, and the black clip is used to clamp the body to hit the iron. Turning the signal plate normally can see the square wave signal waveform of 0.5V-1.5V.

Note: Some cars are designed with power lines for signal output, and most cars are designed with iron wire for signal output.

Step 4: Sensor data flow comparison method, enter the ABS module to read the sensor data flow, and start the road test to observe the sensor data flow comparison with the other three wheel speed sensors. This method can apply occasional sensor failure detection.

How to Diagnose the Wheel Speed Sensor with a multimeter?

Some repair shops do not have an oscilloscope, but only a multimeter measurement method as shown in the figure below: the black test lead strikes iron, the red test lead connects to the signal line, and the signal dial is rotated by hand. The voltage of the multimeter display will fluctuate from 0.5V to 1.5V as normal. If there is no signal output, you should check: signal disk (whether the signal is dirty), sensor gap, sensor itself, etc.

How to test the Wheel Speed Sensor with a multimeter

Figure13. How to test the Wheel Speed Sensor with a multimeter

Related Post: How to test a capacitor with a multimeter?

IX Wheel Speed Sensor Failure Case Analysis

9.1 Fault Phenomenon

In a 2006 Excelle car, users reported that the car's ABS fault light was on.

9.2 Inspection and Analysis

(1) The maintenance personnel did not find the fault phenomenon reflected by the user during the test drive. The fault diagnostic instrument was used to detect it, and a historical fault code C0040-the front right wheel speed sensor circuit performance fault was found.

(2) Maintenance personnel inspected the axle shaft ring gear and found no damage, and the appearance and clearance of the wheel speed sensor were normal.

(3) Disconnect the wheel speed sensor connector and measure the resistance of the wheel speed sensor. The resistance value is 1 700 Ω (normal).

(4) Turn the right front wheel and measure its AC voltage at the same time, the voltage is 120 ~ 200 mV (normal), disconnect the ABS control unit connector and connector C111, the measurement line is free of grounding and short circuit. At this time, when the wheel speed sensor connector is shaken, the resistance displayed on the multimeter changes slightly. After tightening the connector and testing the vehicle, the ABS fault lamp is lit again, and the fault code remains.

(5) The maintenance personnel checked the ABS data. When the vehicle speed is lower than 10 km / h, the right front wheel speed sensor shows 0 km / h. When the vehicle speed is higher than 10 km / h, the right front wheel speed sensor shows normal.

(6) Re-measure the resistance of the wheel speed sensor line and find that when the bent part of the wire harness is shaken, the line is broken (see the figure below).

The broken line

Figure14. The broken line

9.3 Troubleshooting

Because the sensor harness and the sensor body are inseparable, the right front wheel speed sensor is replaced and the test failure disappears.

Question:

Wheel speed sensors should be checked for which of the following with a DVOM?

  1. Open
  2. Ground
  3. High resistance
  4. All of the above

Answer:

D

Feedback:

A WSS can be tested electrically for each of the above, with a DVOM.

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