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With more and more electronic control devices on the car, the body wiring is becoming more and more complicated, which makes the operation reliability lower and the difficulty of repairing the fault. In order to improve the utilization of signals, a large amount of data information can be shared among different electronic control units, and a large number of control signals in the integrated control system of the vehicle can also be exchanged in real time. However, the traditional automotive electronic system adopts the method of serial communication, such as the implementation of the standard such as SAE1587, the communication speed is slow, the amount of data transmitted is small, and the demand for high-speed communication is far from being met. In recent years, CAN bus has developed into the mainstream bus of automotive electronic systems, and has been produced based on the CAN bus communication protocol vehicle application layer communication standard SAEJ1939 [1~4].
The communication network of the pure electric vehicle (EV) electronic control system developed by CAN bus has the characteristics of high communication speed, accuracy and high reliability, which is easy to connect and manage the vehicle control network, and is the calculation information of the sensor signal and each control unit. It provides a basic platform for sharing with the operating state and troubleshooting with on-board or off-board, and it is also possible to develop an online calibration and real-time monitoring system for controllers based on the communication network.
In this paper, based on CAN2.0B SAEJ1939 communication protocol, MC68376 is taken as an example to design and develop a CAN bus communication system for EV electronic control system.
1 EV electronic control system CAN communication design
1.1EV control system CAN bus communication principle
In the EV control system, the controller includes: a brake controller (ABS/ASR), a powertrain controller PTCM (Powertrain Control Module), a power battery manager BPCM (Battery Pack Control Module), a drive motor controller DMCM ( Driver Motor Control Module), power steering controller and instrument controller IPCM (Instrument Pack Control Module). Data is exchanged between the controllers through the CAN communication network, data sharing is achieved and the respective control performance is improved. Figure 1 is a schematic diagram of CAN communication between EV controllers.
Figure 1 CAN communication network topology diagram of pure electric vehicle control system
1.2 Design of CAN communication in EV electronic control system
According to the CAN communication principle, the hardware is mainly composed of a CAN controller and a CAN driver. The power control assembly PTCM and the battery management control module BPCM adopt the CAN controller integrated on the 32-bit high-performance microprocessor MC68376; the instrument controller IPCM module adopts the CAN controller integrated on the FUJ 32-bit high-performance microprocessor; motor control The DMCM module, power steering control module and brake control module use the SJA1000 controller. The CAN drivers are all PCA82C250.
2 is a connection diagram of the EV's in-vehicle CAN communication network node, and each bus terminal is connected with a load resistance for suppressing reflection indicated by RL. The load resistor is connected between CAN-H and CAN-L. For ECUs without integrated termination resistors (usually used), this resistor is 60Ω; for ECUs with integrated termination resistors, this resistor is 120Ω. The termination load resistor is preferably placed at the end of the bus to cancel the load resistance RL inside the ECU, because if one of the ECUs is disconnected from the bus, the bus will lose the terminal.
Figure 2 Pure electric vehicle CAN communication network node connection diagram
The following is a 32-bit high-intelligent microprocessor MC68376 as an example to introduce the design of CAN communication in EV electronic control system.
1.3 Design of CAN communication based on MC68376 EV electronic control system [6~7]
1.3.1 Basic Features of TouCAN Embedded in MC68376
The TouCAN module is a CAN controller embedded in the MC68376 that implements the CAN communication protocol. Its maximum transmission speed is up to 1Mbit/s, which can support both standard (11-bit) and extended (29-bit) ID message modes in the CAN protocol. The TouCAN module contains 16 message buffers with transmit and receive functions. In addition, it also has a message filtering function for comparing the received message ID code with a preset receiving buffer ID code to determine whether the received message is valid.
Figure 3 is a block diagram of TouCAN, where CANTX and CANRX are transmit and receive pins, respectively.
Figure 3 TOUCAN block diagram
1.3.2 Design of MC68376 CAN Communication Hardware Interface
Figure 4 is a schematic diagram of the CAN node hardware interface circuit, in which CAN+5V is a dedicated power supply for the CAN bus interface circuit, which realizes the isolation of the CAN bus power supply from the CPU power supply, so that the voltage fluctuation of the CAN system does not affect the normal working voltage of the CPU. 6N137 is a photoelectric coupling chip that can electrically isolate electrical signals.
The PCA82C250 is used to provide differential transmit capability to the bus and differential receive capability to the CAN controller, fully compatible with the ISO11898 standard. In a mobile environment, the PCA82C250 is resistant to transients, radio frequency and electromagnetic interference. The internal current-limiting circuit protects the transmit output stage when the circuit is shorted.
Figure 4 CAN node hardware interface circuit schematic
1.3.3 Design of MC68376 CAN Communication Software
Each controller sends data (vehicle speed, battery voltage, current, temperature, etc.) to the bus in the specified format and cycle, and also receives information from other controllers. The other controllers on the bus take the required messages as needed. For receiving data, the system is implemented by means of interrupts. Once an interrupt occurs, the data to be received is automatically loaded into the corresponding message register. At this time, the mask filtering method can also be adopted, and the mask filter register is used to selectively compare the identifier of the received message with the identifier set in advance when the receiving buffer is initialized, and only the identifier matching message can enter. Receive buffers, those that do not meet the requirements will be masked outside the receive buffer, thereby reducing the burden on the CPU to process the message. And different data is placed in different message registers, so it is easy to determine which received message is caused by the interrupt in the receiving interrupt service routine.
Figure 5 is a flow chart of the CAN communication program based on MC68376.
Figure 5 program flow diagram
2 CAN communication in the development of EV electronic control system
The CAN communication of the EV electronic control system establishes a communication network between the controllers, and realizes information exchange between the controllers and the dashboard. Through the development of the online calibration system and monitoring system, the parameters of each controller can be monitored in real time on the PC. 6 and 7 are charge and discharge characteristics curves obtained by a nickel-hydrogen battery real-time monitoring system designed by CAN communication. The CAN communication data transmission rate is 500 kbit/s, and the system reflects the charging and discharging characteristics of the nickel-hydrogen battery in real time.
As a reliable automotive computer network bus, CAN bus has begun to be applied in advanced vehicles, enabling each computer control unit to share all information and resources through the CAN bus, simplifying wiring, reducing the number of sensors, and avoiding duplication of control functions. Improve system reliability and maintainability, reduce costs, and better match and coordinate the purpose of each control system. This makes the car's power, operational stability, and safety all rise to new heights. With the development of automotive electronics technology, CAN bus communication protocol with high flexibility, simple scalability, excellent anti-interference and processing error will be more widely used in automotive electronic control systems.
references
1 SAE Standard. Recommended Practice for a Serial Control and Communication Vehi-cle Network
J1939 Issued 2000
2 SAE Specification. Implementation of CAN for Heavy Duty truck and Bus Market-Specification
J1939 Issued 1995
3 SAE Standard. Vehicle Application La
Yer SAE J1939/73 Issued 1994
4 SAE Standard. Vehicle Application Layer Diagnostics SAE J1939/73 Issued, 1996
5 Cheng Jun. Implementation Method of CAN Bus Communication for Vehicle Control System. Automotive Engineering, 2001(5)
6 MC68300 Family MC68336/376 User's Manual.MOTOROLA INC, 1996
7邬Kuanming. CAN bus principle and application system design. Beijing: Beijing University of Aeronautics and Astronautics Press, 1996
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