CAN bus based on EV electric control system design and development of communication

With the car more and more electronic control devices, vehicle routing and more and more complex, making lower reliability, fault repairs more difficult. In order to improve the utilization of signals require a large number of data in a variety of electronic control unit share, while in the vehicle integrated control system is also a large number of control signals can be exchanged in real time. However, the traditional automotive electronic system uses serial communication methods, such as with SAE1587 and other standards to implement, slow communication, transmission of data is less, can not meet the demand for high-speed communications. CAN bus in recent years has developed into the mainstream of automotive electronic systems, bus, and a CAN bus communication protocol based on the vehicle application layer communication standard SAEJ1939 [1 ~ 4] produce.

Use of CAN bus development pure electric vehicles (EV) electronic control system communication network has a communication rate is high, accurate, high reliability, easy-to-vehicle control network connectivity and management of the sensor signal, the calculation of each control unit information and operation of state or from the car sharing and attendant fault diagnosis provides a base platform, while developing the communication network controller based on-line calibration and real-time monitoring system is also possible.

In this paper, the SAEJ1939 communication protocol based on CAN2.0B to MC68376, for example, designed and developed electronic control system used in EV CAN bus communication system.

1EV electric control system design of CAN communication

1.1EV CAN bus communication control system theory

In the EV control system, the controller including: brake control (ABS / ASR), powertrain controller PTCM (PowertrainControlModule), Power Battery Manager BPCM (BatteryPackControlModule), drive motor controller DMCM (DriverMotorControlModule), power steering controller and instrument controller IPCM (InstrumentPackControlModule) and so on. Between the various controllers exchange data via CAN communication networks, data sharing and to control their own performance are improved. Figure 1 EV CAN communication between the controller schematic.

CAN bus based on EV electric control system design and development of communication

Figure 1 electric vehicle control system CAN communication network topology

1.2EV electric control system design of CAN communication

According to CAN communication theory, hardware, mainly by the CAN controller and CAN drive component. Power control assembly PTCM and battery management control module BPCM 32-bit high performance microprocessor MC68376 integrates the CAN controller; instrument controller IPCM modules FUJ32 bit high-performance microprocessor integrated CAN controller; motor control DMCM module, power steering control module and brake control module SJA1000 controller. CAN drive all use PCA82C250.

Figure 2 is a EV-vehicle CAN communication network node connection graph, each bus terminal with access to useful to express the inhibitory reflex RL load resistance. Load resistor connected to the CAN-H and CAN-L between the termination resistors for the non-integrated (usually used) ECU, the resistance of 60Ω; with integrated termination resistors for the ECU, the resistance is 120Ω. Best placed in the bus terminal end of the load resistance, abolition of the internal load resistance ECU RL, because if one of the ECU disconnected from the bus, the bus terminal will be lost.

CAN bus based on EV electric control system design and development of communication

Figure 2 electric vehicles CAN communication network node connection graph

Following a 32-bit microprocessor MC68376 intelligent example to explain EV electric control system design of CAN communication.

1.3 based on the MC68376's EV electric control system design of CAN communication [6 7]

1.3.1MC68376 embedded the basic characteristics of TouCAN

MC68376 TouCAN module is the realization of embedded communication protocol CAN CAN controller. The maximum transfer rate up to 1Mbit / s, can support both the standard CAN protocol (11) and extended (29) ID model of two messages. 16 TouCAN module contains functions that send and receive message buffer. In addition, it has packet filtering for the received message ID code and pre-set receive buffer ID codes are compared to determine the received packet is valid.

Figure 3 is a block diagram of TouCAN which CANTX and CANRX send and receive pins, respectively.

CAN bus based on EV electric control system design and development of communication

Block diagram of Figure 3 TOUCAN

1.3.2MC68376CAN communication hardware interface design

Figure 4 is a CAN node hardware interface circuit diagram, which CAN 5V CAN bus interface circuit is a dedicated power supply, to achieve power and CPU power CAN bus isolation, so that CAN system CPU voltage fluctuation does not affect the normal operating voltage. 6N137 for the optical coupler chip, can achieve electrical isolation between signals.

PCA82C250 used to provide differential transmit capability to the bus and differential receive capability to CAN controller, fully compliant with the ISO11898 standard. In the campaign environment, PCA82C250 with anti-transient, the performance of radio frequency and electromagnetic interference, internal current limiting circuit with short circuit protection on the transfer function of the output stage.

CAN bus based on EV electric control system design and development of communication

Figure 4 CAN node hardware interface circuit diagram

1.3.3MC68376CAN Communication Software

The controller sends the required format and cycle data (speed, battery voltage, current and temperature, etc.) to the bus, while also receiving other controllers. Other controllers on the bus take what the message as needed. For receiving data, the system achieved by way of interruption, when an interrupt occurs, will automatically load the received data packet to the corresponding register. At this point can also be shielded filter, using filter mask register identifier of the received packet and pre-set when the receive buffer identifier initialized selectively by-bit comparison, only packets that match the identifier to entry into the receiving buffer, which do not meet the requirements of message buffer will be screened at the reception outside, so as to reduce the burden on CPU processing messages. And different data packets into a different register, so the receiver can interrupt service program is easy to determine which interrupt is caused to receive messages.

Figure 5 MC68376 CAN-based communication program flow chart.

CAN bus based on EV electric control system design and development of communication

Program flow diagram of Figure 5

2CAN EV electronic control system of communication in development application

CAN communication EV electronic control system established communication network between the controller realized between the controller and the exchange of information with the instrument panel. Through the development of the online calibration system and monitoring system, PC, real-time monitoring of the controller parameters. Figure 6 and Figure 7 for the use of CAN communication Ni-MH battery designed to obtain real-time monitoring system for the charge and discharge curve. CAN communication data transfer rate of 500kbit / s, the system reflects the real-time Ni-MH battery charging and discharging characteristics.

CAN bus as a reliable network bus has Kaishi Automotive Computers in the advanced car on the applied, Shi Dege car computer Kongzhi unit Nenggou through the CAN bus Gongxiangsuoyou information and 资源, to simplify wiring and reduce the number of sensors to avoid the control Gongnengzhongfu and improve system reliability and maintainability, lower costs, better matching and coordination of the various control purposes. This makes the car power, operational stability, security are rising to new heights. With the development of automotive electronic technology, highly flexible, simple scalability, excellent noise immunity and Subjective Error handling of the CAN bus communication protocol in the automotive electronic control system will be used more widely.