Application of CAN bus in the design of automobile wheel speed sensor

At present, network technology is a new technology developed in the field of automotive electronics. It is not only a technology to solve the problems of complex circuits and increased wiring harnesses in automotive electronics, but also its communication and resource sharing capabilities have become a basis for the application of new electronic and computer technologies in vehicles and a support for vehicle information and control systems.

According to their functions, automotive electronic networks can be divided into control-oriented networks (CON) and information transmission-oriented networks (ION). According to the speed of network information transmission, the Society of Automotive Engineers (SAE) of the United States divides networks into three categories: A, B, and C. Category A is a low-speed network with a baud rate below 9600bps, and the baud rate below 125kbps is a medium-speed network category B, and the baud rate above 125kbps is a high-speed network category C. The wheel speed (i.e., the linear speed of the wheel rotating around the wheel axle) sensor (referred to as the wheel speed sensor) signal can be shared by the engine control module, the anti-lock braking system (ABS) control module, and the instrument control module, so that during the braking process of the vehicle, the anti-lock braking control module and the engine control module can be jointly controlled to achieve the best braking performance. Although the ABS system has been widely used in developed countries, the method of processing wheel speed signals is protected by special circuits and chips in the form of hardware and software as part of the electronic controller (ECU) of the ABS system. Most of the domestic processing of wheel speed signals has the problem that the threshold value of wheel speed recognition is too high (when the vehicle speed, i.e., the speed of the vehicle body, is lower than 10km/h, the wheel speed cannot be correctly measured).

The author uses the developed drum wheel speed sensor test bench to conduct experiments. According to the signal characteristics of the wheel speed sensor, the author designs a CAN bus-based automobile wheel speed sensor signal processing circuit, and uses a single-chip microcomputer to collect and quantify the signal. The results show that the designed wheel speed sensor system has the advantages of low wheel speed measurement threshold (vehicle speed up to 3km/h), reliable operation, strong anti-interference ability, etc. At the same time, it can be used as a measurement point of the CAN bus local area network to realize the digitalization and network transmission of sensor signals.

Wheel speed sensor

Since magnetoelectric sensors work stably and reliably and are hardly affected by environmental factors such as temperature and dust, variable reluctance electromagnetic sensors are widely used in wheel speed sensors currently used in automobiles. Variable reluctance wheel speed sensors consist of a stator and a rotor. The stator includes an induction coil and a magnetic head (a magnetic pole composed of a permanent magnet). The rotor can be in the form of a ring gear or a gear. The gear-shaped rotor is shown in Figure 1 (a). The magnetic head is fixed on the magnetic pole bracket, the bracket is fixed on the long shaft, the ring gear is connected to the wheel hub and the brake hub, and the long shaft passes through the wheel and cooperates with the internal bearing, as shown in Figure 1 (b).

The speed of the rotor is proportional to the angular velocity of the wheel. The drum drives the wheel to rotate, and the tooth tops and gaps between the teeth of the sensor rotor alternately approach and leave the magnetic poles, causing the magnetic field in the stator induction coil to change periodically, inducing an AC sine wave signal in the coil. The control test bench makes the wheel run under various working conditions and measures the sensor output signal. The experimental results show that the signal generated by the variable reluctance wheel speed sensor has the following characteristics:

(1) The signal generated by the sensor is a sinusoidal signal close to zero mean;

(2) The amplitude of the sine wave signal is affected by the air gap (the air gap between the magnetic head and the gear ring, generally about 1.0mm is the most ideal) and the wheel speed. The smaller the air gap, the higher the wheel speed, and the greater the amplitude of the sine wave signal;

(3) The frequency of the sine wave signal is affected by the number of teeth on the gear ring and the wheel speed. It is the number of teeth passing through the magnetic head coil per second, which is equal to the number of teeth on the gear ring multiplied by the wheel speed per second. The signal generated by the variable reluctance wheel speed sensor is shown in Figure 2.

The test simulates the front wheel of the BJ212 model, and the drum speed is used to simulate the vehicle speed. When the drum speed is controlled to 3km/h, the amplitude of the sine wave signal generated by the 88-tooth sensor is about 1V, and its frequency is 31Hz; when the drum speed is controlled to 100km/h, the amplitude of the sine wave signal generated by the sensor is about 7V, and its frequency is 1037Hz. Due to the burrs generated by gear processing and other environmental factors, the actual signal is a certain frequency component interference signal superimposed on the above signal, as shown in Figure 2 (b).

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Application of CAN bus in the design of automobile wheel speed sensor

http://ee.ofweek.com/2011-01/ART-8300-2809-28436740.html

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Automobile wheel speed sensor CAN bus anti-interference

(Editor: Kevin)

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At present, network technology is a new technology developed in the field of automotive electronics. It is not only a technology to solve the problems of complex circuits and increased wiring harnesses in automotive electronics, but also its communication and resource sharing capabilities have become a basis for the application of new electronic and computer technologies in vehicles and a support for vehicle information and control systems.

According to their functions, automotive electronic networks can be divided into control-oriented networks (CON) and information transmission-oriented networks (ION). According to the speed of network information transmission, the Society of Automotive Engineers (SAE) of the United States divides networks into three categories: A, B, and C. Category A is a low-speed network with a baud rate below 9600bps, and the baud rate below 125kbps is a medium-speed network category B, and the baud rate above 125kbps is a high-speed network category C. The wheel speed (i.e., the linear speed of the wheel rotating around the wheel axle) sensor (referred to as the wheel speed sensor) signal can be shared by the engine control module, the anti-lock braking system (ABS) control module, and the instrument control module, so that during the braking process of the vehicle, the anti-lock braking control module and the engine control module can be jointly controlled to achieve the best braking performance. Although the ABS system has been widely used in developed countries, the method of processing wheel speed signals is protected by special circuits and chips in the form of hardware and software as part of the electronic controller (ECU) of the ABS system. Most of the domestic processing of wheel speed signals has the problem that the threshold value of wheel speed recognition is too high (when the vehicle speed, i.e., the speed of the vehicle body, is lower than 10km/h, the wheel speed cannot be correctly measured).

The author uses the developed drum wheel speed sensor test bench to conduct experiments. According to the signal characteristics of the wheel speed sensor, the author designs a CAN bus-based automobile wheel speed sensor signal processing circuit, and uses a single-chip microcomputer to collect and quantify the signal. The results show that the designed wheel speed sensor system has the advantages of low wheel speed measurement threshold (vehicle speed up to 3km/h), reliable operation, strong anti-interference ability, etc. At the same time, it can be used as a measurement point of the CAN bus local area network to realize the digitalization and network transmission of sensor signals.

Wheel speed sensor

Since magnetoelectric sensors work stably and reliably and are hardly affected by environmental factors such as temperature and dust, variable reluctance electromagnetic sensors are widely used in wheel speed sensors currently used in automobiles. Variable reluctance wheel speed sensors consist of a stator and a rotor. The stator includes an induction coil and a magnetic head (a magnetic pole composed of a permanent magnet). The rotor can be in the form of a ring gear or a gear. The gear-shaped rotor is shown in Figure 1 (a). The magnetic head is fixed on the magnetic pole bracket, the bracket is fixed on the long shaft, the ring gear is connected to the wheel hub and the brake hub, and the long shaft passes through the wheel and cooperates with the internal bearing, as shown in Figure 1 (b).

The speed of the rotor is proportional to the angular velocity of the wheel. The drum drives the wheel to rotate, and the tooth tops and gaps between the teeth of the sensor rotor alternately approach and leave the magnetic poles, causing the magnetic field in the stator induction coil to change periodically, inducing an AC sine wave signal in the coil. The control test bench makes the wheel run under various working conditions and measures the sensor output signal. The experimental results show that the signal generated by the variable reluctance wheel speed sensor has the following characteristics:

(1) The signal generated by the sensor is a sinusoidal signal close to zero mean;

(2) The amplitude of the sine wave signal is affected by the air gap (the air gap between the magnetic head and the gear ring, generally about 1.0mm is the most ideal) and the wheel speed. The smaller the air gap, the higher the wheel speed, and the greater the amplitude of the sine wave signal;

(3) The frequency of the sine wave signal is affected by the number of teeth on the gear ring and the wheel speed. It is the number of teeth passing through the magnetic head coil per second, which is equal to the number of teeth on the gear ring multiplied by the wheel speed per second. The signal generated by the variable reluctance wheel speed sensor is shown in Figure 2.

The test simulates the front wheel of the BJ212 model, and the drum speed is used to simulate the vehicle speed. When the drum speed is controlled to 3km/h, the amplitude of the sine wave signal generated by the 88-tooth sensor is about 1V, and its frequency is 31Hz; when the drum speed is controlled to 100km/h, the amplitude of the sine wave signal generated by the sensor is about 7V, and its frequency is 1037Hz. Due to the burrs generated by gear processing and other environmental factors, the actual signal is a certain frequency component interference signal superimposed on the above signal, as shown in Figure 2 (b).