introduction
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With the advancement and development of science and technology, the requirements for vehicle driving performance and safety and comfort are greatly improved, and the number of electronic control units on the vehicle is gradually increased. 
However, the connection of the electronic control unit (such as various switches, actuators, sensors, etc.) on the vehicle is still realized by the conventional wiring harness, which causes the wiring harness in the vehicle to be excessive and the wiring to be complicated, thereby causing serious electromagnetic interference. Lead to reduced system reliability In high-class cars, electronic components and their systems account for more than 20% of the price of the entire car, and there is an increasing trend In this case, the electronic control circuit in the car will be more complicated. How to make the devices in the car network and reduce the number of wiring harnesses becomes a key research direction for improving the interior system.
In the network and communication system of vehicles, local network methods are becoming more and more abundant. Among them, network technologies such as CAN, Profibus, LON, ASI, EIB and eBus have been developed quite maturely, and the standardization of various network technologies has also been introduced. And, these mature network technologies have already completed the integration work. The CAN bus shows strong advantages in automotive applications in terms of stability, immediacy and cost performance. It is highly competitive as a LAN technology in distributed control. At present, many cars use the CAN bus to connect the entire vehicle control system for unified management, realize data sharing and work together with each other, make the wiring harness in the car convenient and reliable, improve the overall safety and cost performance of the car, and enhance its competition. force
The premise of implementing networked control of vehicle systems is the intelligent design of network contacts, including the intelligence of sensors, controllers and actuators. In this paper, the linear control electronic throttle is taken as the research object, and the CAN bus intelligent contact of the pedal position sensor, the throttle position sensor and the throttle position control actuator is designed. Based on this, the CAN bus control network is composed and the section is completed. Precise control of valve position
1 Vehicle CAN bus and distributed control system structure
The control area network (CAN) belongs to the industrial field bus. It is a communication protocol developed by Bosch in Germany in the early 1980s as a data exchange between many control and test instruments in modern automobiles. In November 1993, ISO officially promulgated the international standard for high-speed communication CAN (ISO 11898) The acquisition of field data in the CAN bus system is done by sensors. At present, there are not many types of sensors with CAN bus interface, and the price is relatively expensive.
There are a large number of sensors, electronic control units, actuators, etc. in the vehicle control system. Usually, multiple controllers share the same sensor information, and the requirements for real-time and rapidity are high. How to connect them to form a distributed control network system Is an important development direction of modern control systems Fieldbus control system (FCS) is one of the typical control network architecture implementations. CAN belongs to the field bus field. It is a multi-master serial bus that effectively supports distributed control or real-time control. It is interconnected by field devices with its short message frame and excellent CSMA/BA bit-wise arbitration protocol. Favor
The vehicle distributed control network system based on CAN bus is shown in Figure 1. It uses a field distributed control system (FDCS) structure, which consists of sensors, actuators, controller intelligent nodes and CAN field control network. Multiple intelligent nodes independently complete data acquisition, system setting, operation control, etc., and exchange various data and management control information between intelligent nodes through CAN field bus.
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2 Principle and structure of the line-controlled electronic throttle system
Electronic throttle control technology first appeared in the early 1980s, initially used only in high-end cars With the development of electronic technology, the increasingly prominent energy and environmental issues, and the improvement of automotive performance requirements, electronic throttle has become the most important control device on all-electric control engines, and has begun to be widely applied to various vehicles. The advantage is that the throttle can be quickly and accurately controlled to the optimum opening according to the driver's wishes, emissions, fuel consumption and safety requirements, and various control functions can be set to improve driving safety and comfort. At present, BMW, BOSCH, Toyota and other companies are studying this technology, and manufacturers such as BMW, GM, Toyota, AUDI have successfully applied in some models.
As shown in Fig. 2, the system consists of an accelerator pedal position sensor and an electronic throttle body. The throttle body includes an actuator, a throttle valve and a throttle position sensor. They are packaged as one. The actuator consists of a DC motor and associated drive components The accelerator pedal is a high-precision linear potentiometer. As a sensor device for the driver's desired throttle opening, the output is an analog voltage signal proportional to the pedal stroke; the throttle body is forward and reverse 2 As a control throttle opening feedback signal, the position sensor obtains a corresponding voltage feedback value at the current opening degree through a pair of high-precision potentiometers inside the throttle body, and the feedback value changes linearly with the throttle opening angle.
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3 Intelligent sensor CAN bus interface design
The design of the smart sensor contacts is based on Microchip's PIC16F877A microcontroller and the standalone CAN bus controller MCP2510 and CAN transceiver PCA82C250.
PIC16F877A uses RISC command system's high performance 8 microprocessor, Harvard bus structure, low power consumption, high speed Integrated ADC, serial peripheral interface (SPI) and Flash program memory, with PWM output and other functions PIC16F877A can achieve seamless connection with CAN controller MCP2510 through SPI interface
The hardware schematic diagram of the CAN smart sensor node based on PIC16F877A is shown in Figure 3.
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The communication module of the intelligent sensor CAN node is composed of independent CAN controller MCP2510 and CAN transceiver PCA82C250. MCP2510 can complete all functions of physical layer and data link layer of CAN bus, support high-speed SPI interface (maximum data transmission rate can reach 5MB/s), support CAN2.0A/CAN2.0B protocol The CAN transceiver PCA82C250 is the interface between the CAN controller and the physical bus. It provides differential transmission capability to the physical bus and differential reception capability for the CAN controller. At the same time, it can increase the communication distance and improve the embedded CAN intelligent node. Anti-interference ability
The PIC16F877A is connected to the CAN controller MCP2510 via SPI. Its serial data input (SDI) pin is connected to the SO pin of the MCP2510. Its serial data output (SDO) pin is connected to the SI pin of the MCP2510. Its serial clock (SCK) pin Connected to the SCK pin of the MCP2510 The reset signal and chip select signal of MCP2510 are provided by the microcontroller.
The SPI interface is operated in active mode by setting the SPI interface status register and control register of the PIC16F877A. The timing when the PIC16F877A communicates with the MCP2510 is very important. When sending data, first send a write command, then send the register address, and finally send the data. When the MCP2510 receives the data from the bus, it will generate an interrupt. The MCU responds to the interrupt. When the data is read, the read command is sent first, then the register address is sent, and the data is automatically written into the buffer of the SPI interface of the microcontroller.
Since the MCU itself has a 10-bit A/D converter, the analog signals output from the foot pedal position sensor and the throttle position sensor are directly connected to the MCU for digital-to-analog conversion without adding a new A/D conversion device. In Figure 3, the sensor is input via RA0/AN0. In order to filter out high frequency noise, an RC filter circuit is connected to the analog input. At the same time, in the control of the DC motor of the electronic throttle device actuator, the PIC16F877A has a PWM port, and the DC motor can be driven by connecting the drive circuit. The device driver uses L298.
The whole CAN bus control network is composed of a foot pedal intelligent position sensor node, a throttle body position sensor and an actuator node, and a controller node, wherein the foot pedal intelligent position sensor node, the throttle body position sensor and the actuator node are composed of a single chip microcomputer. The CAN bus mechanism is completed, and its main function is to transmit the pedal position and the feedback signal throttle position signal to the controller, and at the same time, receive the driving command signal sent by the controller to the actuator. The controller adopts the microcomputer to realize CAN bus communication and corresponding control algorithm through Advantech PCL-841 card to complete the control of the wire-controlled electronic throttle
4 system control principle and experimental results
The system control process is shown in Figure 4.
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The control system is a closed-loop control process. The foot pedal position sensor is used as the input of the system. After A/D conversion, it is sent to the controller through the CAN bus. Similarly, the throttle position sensor is used as a feedback signal. After A/D conversion, it is sent to the controller through the CAN bus. The two signals are compared in the controller, and the controller uses the corresponding control algorithm (such as PID) to make decisions and make decisions. The result is sent by the CAN bus to the throttle body position sensor and the actuator node, which generates a corresponding PWM signal to drive the actuator through the drive.
In order to verify the performance of the control system, the experimental platform and the real vehicle experiment were carried out using the adaptive PID control algorithm. The experimental results are shown in Fig. 5. Among them, PPS indicates the position of the pedal, TPS1 indicates the experimental result of the throttle position under the experimental platform, and TPS2 indicates the experimental result of the throttle position in the case of the actual vehicle. From the control results, it can meet the real-time and accuracy requirements of electronic throttle control. At the same time, the system has certain anti-noise ability after testing in real vehicle environment.
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5 Conclusion
As a reliable automotive computer network bus, CAN bus has been applied in many advanced vehicles. The CAN bus is applied to smart sensors, so that the signals obtained by the sensors can be transmitted in real time, reliably, high speed and accurately through the bus. It enables each automotive computer control unit to share all information and resources through the CAN bus, simplifying wiring, reducing the number of sensors, avoiding duplication of control functions, improving system reliability, reducing costs, and better matching and coordinating various control systems. At the same time, since the entire intelligent sensor network adopts all-digital communication, the bus also has good anti-interference ability, which is the development trend of intelligent sensors and intelligent control networks in the future.
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