The CAN (Controller Area Network) bus is a serial communication network that effectively supports distributed control and real-time control. At present, it has been widely used in the electrical network of foreign automobiles. In order to meet the urgent needs of the domestic car body control bus, we designed a hardware solution for the vehicle management system based on CAN bus. The program focuses on the overall structure of the system, the node setting of the CAN bus of the body control system, the node and the central control and the interface circuit of the CAN bus.
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With the development of automotive electronics technology and the continuous improvement of automotive performance, there are more and more electronic devices on the car. Traditional electrical systems mostly use point-to-point single communication methods, and there is little connection between them, which inevitably results in a huge wiring system. At present, many foreign vehicle manufacturers and automobile electrical appliance manufacturers adopt network technologies such as CAN and LIN, SAEJ1850, etc. in the vehicle management system. Among them, CAN is widely used. The CAN bus was proposed by the German company BOSCH in the early 1980s. It replaces the plastic industrial network with only two simple cable wires for the wiring of various signals on the car. Various electronic devices on the car are hung through the CAN controller. On these two cables, cables are used for data communication and data sharing between devices, which greatly reduces the wiring harness on the car. The CAN bus has a unique structure and reliable performance and is recognized as one of the most promising field control buses.
Due to the limitation of objective conditions, at present, China's vehicle manufacturing plants and automotive electronics and electrical plants have hardly involved in the field of automotive electrical network design. However, with the development of China's automobile industry and electronics industry, the research and development of networked automotive electrical appliances has become an important issue.
1. Overall structure design of vehicle management system The sensitivity of various electrical appliances on the vehicle to the delay of network information transmission is very different. The coordination relationship between engine controller, automatic transmission controller, ABS controller, airbag controller, etc. The required real-time performance is very strong, and the simple events such as the switch of the front and rear lights, door opening and closing, seat adjustment and so on are much more relaxed on the information transmission delay (transmission delay is allowed to be 10ms-100ms), if these functions are simple nodes Hanging on the high-speed bus will inevitably increase the technical requirements and cost of the node, so it is necessary to design a multi-channel bus. Considering the consistency with international standards, two CAN buses are used here.
High-speed CAN is used in the car drive system, and the information transmission speed is 500K-1M bps. The main connection objects are: engine, automatic transmission, ABS/ASR, airbag, active suspension, cruise system, electric steering system and combination instrument signal. Acquisition system, etc. The control objects of the drive system CAN are all system industrial automation networks directly related to the vehicle travel control. The transmission requirements of the signals are highly real-time. There is more information exchange between them, and many of them are continuous and high speed.
Low-speed CAN is adopted in the body system, and the information transmission rate is 100Kpbs. The main connection objects are: front and rear light control switch, electric seat control switch, central door lock and anti-theft control switch, electric rear view mirror control switch, electric window lift switch , climate (air conditioning) control switch, fault diagnosis system, combination switch and driver control signal acquisition system, instrument display, etc. The control objects of the body system CAN are mainly low-speed motors, solenoid valves and switching devices. They have low requirements for real-time information transmission, but the number is large. Separating these electronic control units from the vehicle drive system is beneficial to ensure the real-time operation of the drive system. The use of low-speed CAN bus can also increase the transmission distance of the bus, improve the anti-interference ability and reduce the hardware cost.
The two CAN buses are independent of each other, and data exchange and resource sharing are performed through the gateway server. The central controller is the control core of the vehicle management system and the basis of the integrated control of the whole vehicle. The main function is to analyze and process various information and issue instructions to coordinate the work of the vehicle control units and electrical equipment. At the same time MMSonline.com.cn, the central controller is also a gateway server for high-speed CAN bus and low-speed CAN bus.
2, node setting This design focuses on the low-speed CAN bus-based body control system, in order to convert all kinds of original signals on the car into digital signals that can be transmitted on the CAN bus, and also to improve system reliability. , the node is set on the low speed bus. The function of the node is: receiving the analog signal, digital signal or switch signal output by the sensor, processing by the ECU, converting into a data message format that can be communicated on the CAN bus, and transmitting it to the CAN bus through the CAN controller in the ECU, At the same time, the data information received from the CAN bus is converted into an analog signal or a digital signal capable of driving an actuator or an illumination lamp. The setting principle of the node only considers the physical position of each electrical component on the vehicle.
Node 1: Mainly controls the front lights and car horns, located at the front of the cab.
Node 2: Acquires the combination switch and other signals located near the dashboard, located near the dashboard.
Node 3: Processes the content that needs to be displayed on the meter, outputs it, and displays it inside the dashboard.
Node 4: Collect status signals of switches such as air conditioners, central door locks, and cab flips, and control air conditioners, anti-theft and remote door locks, wipers, etc., located near the glove box in the cab.
Node 5: The driver's door control node collects the metal processing network of each switch signal to control the action of the door lock, the window and the electric mirror on the driver's side, and is located on the driver's door.
Node 6: Passenger side door control node, located on the passenger side door.
Node 7: Collect meter display signals and driver control signals, including fuel quantity, coolant temperature, oil pressure, power supply voltage, neutral switch, reverse switch, etc., located near the instrument panel.
Node 8: The central controller of the vehicle management system coordinates and manages the work of each vehicle system and acts as a gateway to connect the high-speed and low-speed buses, located near the dashboard.
Node 9: Acquire the signals related to the display of the instrument in the drive system, such as the speed of the vehicle, the engine speed, the temperature of the coolant, etc., located near the glove box in the cab.
Node 10: The electric seat node collects the seat switch signal and controls the seat action, located on the driver's seat.
Node 11: Controls the rear lights of the car, the reverse horn and the anti-collision radar monitor nc.qoos.ipi, located at the rear of the car.
3. Interface design of node and CAN bus The vehicle management system is a local area network composed of many nodes connected by CAN bus. Therefore, the design of CAN bus is extremely important. Among them, the selection of CAN controller, CAN transceiver and anti-interference measures will become the key to the design.
(1) Selection of CAN controller In order to meet the needs of system functions and further expansion, the CAN controller adopts MICROCHIP's internal microcontroller (microcontroller) PIC18F248 with CAN engine, which has five 10-bit A/D converters on chip. 8bit, two 16bit timer/counter, 1-4 PWM output controller and 22 I/O ports. In addition to analog and digital acquisition and control, it can also be pulse width modulated (PWM). Control the speed of various actuator motors.
(2) Selection of CAN transceiver
The CAN transceiver uses MCCH2551 from MICROCHIP, which is an interface chip between the widely used CAN controller and the physical bus, which can differentially transmit and receive information on the bus. It can increase communication distance, improve the system's instantaneous anti-interference ability, protect the bus, reduce radio frequency interference and so on.
(3) Electromagnetic interference on the photoelectric isolation vehicle is more severe, and the anti-interference ability of the system is relatively high. In order to further improve the anti-interference ability of the system, an increase is made between the CAN controller (single-chip microcomputer) and the CAN transceiver MCP2551 of the drive bus. The opto-isolated circuit consists of a high-speed isolation device 6N137, and the power supply is also isolated by a micro DC/DC module.
4. Interface design of central controller (gateway server) and CAN bus
The central controller selects:
A digital signal processing (DSP) chip with two CAN controllers and supporting CAN2.0B communication protocol is selected as the node control core. This can increase the control speed of the system, enhance the flexibility of system control and improve the reliability of the system. Here we use MICROCHIP's dsPIC30F series of 16-bit fixed-point DSP chips: dsPIC30F6010, which has a maximum processing capacity of 30MIPS, an operating temperature range of (-40--+125), and a 16-channel 10bit high-speed A/D. Converter, five 16-bit timer/counters, eight universal PMW controllers and eight dedicated motor-controlled PWM controllers. In addition, the chip also has MCU + DSP dual CPU core and up to 68 I / O ports.
Because the dsPIC30F6010 has a dual CAN engine inside, it can function as a gateway between the high-speed CAN channel and the low-speed CAN channel. At the same time, its DSP processing speed and rich peripheral interface resources make it enough for the car electronic control unit. Constantly upgrading the demand.
5. Conclusion The vehicle management system is designed for domestic cars, off-road vehicles and light trucks. The overall structure of the vehicle management system based on CAN bus, the body control system, the node arrangement of the CAN bus, the interface between the node and the CAN bus, and the interface circuit between the central controller and the CAN bus are designed. Applying the system to the vehicle control system can significantly reduce the wiring harness on the car, better control and coordinate the various systems of the car, to reduce the dependence on the quality of the driver, and make the domestic car keep up with the international technology trend in the future. The market competition is more competitive.
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