Research On CAN Communication Of Driving Force Electronic Control System For Light-duty Vehicle

The driving force electronic control system composed of electronic control engine, automatic transmission and Traction Control System(TCS), can achieve the active adjustments of driving force, make good use of surface adhesion, and enhance the vehicle's power performance, passing ability and handling stability on the low adhesion road. As one of the in-vehicle networks, Controller Area Network(CAN) could not only avoid redundancy of wiring harness and sensors, cut down the system's cost, reduce the signals'mutual interference, but also achieve the high-speed, accurate and real-time communication among the controllers in the driving force electronic control system. CAN bus technology abroad has beening mature, and is widely applied in the automobile, while there is a certain gap in this aspect at home.Works in this thesis are based on a certain major scientific project. Taking a certain light-duty vehicle as the development object in this thesis, CAN communication network of the driving force electronic control system, which is composed of electronic control diesel engine, automated mechanical transmission(AMT) and TCS, is constructed according to the research status and development trend of in-vehicle network as well as CAN bus protocol at home and abroad. Through the deep study, a communication protocol is made for the network. By the usage of CANoe which is a development tool for CAN bus, the off-line simulation, semi-physical simulation and integration testing for the network are accomplished. This thesis puts forward a feasible development process for the CAN communication of driving force electronic control system, and provides an important reference to the research and development of CAN communication for electronic control systems. 1. CAN Communication Protocol DesignFirst, message transmission and communication mechanism in CAN2.0 technical specification are introduced. Additionally, the detailed analysis of layered structure and contents in SAE J1939 protocol is also present. These will help to lay a theoretical foundation of designing CAN communication protocol for driving force electronic control system. Then, according to the actual situation of target vehicle, SAE J1939 protocol is chosed. Besides, two CAN communication schemes for driving force electronic control system are put forward based on the functional requirements of the system. Scheme One is realization of direct communication among electronic control engine, AMT and TCS. The network architecture of this scheme is simple, and it caters to tendency of automobile technology. While Scheme Two is that AMT and TCS control the engine indrectly by means of adding electronic throttle. Although the network architecture of Scheme Two is more complicated, it can achieve the functional requirements of driving force electronic control system in the case that external messages could not control the engine directly. At last, the physical layer protocols, data link layer protocols and application layer protocols of the two schemes are established in detail on the basis of CAN2.0B technical specification and SAE J1939 protocol.2. CAN Communication Protocol Off-line SimulationAfter the two sets of communication protocols are established, their rationalities and feasibilities need to be verified through off-line simulation. Based on the definitions of network nodes, messages, signals as well as the receiving and transmitting of messages in protocols, the systems'databases are built separately by the use of CANdb++ which is an operation tool for database, the network node models of communication systems are generated in CANoe, the communication functions of nodes are realized by CAPL language programming, the virtual operating dashboards used for control and display during the simulation are founded by using panel editor. Then, baud rate setting is done, sequentially the off-line simulations of two protocols are carried out in CANoe. The results of simulations show that the network communication performances of two schemes are good, the busload and real-time property meet the design requirements, the working flow of every node is perfect, and functional requirements are accomplished well. Therefore, two sets of network communication protocols are both reasonable and feasible.3. CAN Communication Network Node DesignSince the rationalities and feasibilities of the communication protocols have been verified through off-line simulations, then every node in the network system can be developed concurrently and separately by different developer. In this thesis, the software and hardware design for the electronic throttle node in the communication system of Scheme Two are performed according to the requirements for communication protocol, node functions and adaptation of working environment. In hardware design, the chip of MC9S12DP512MPVE, which has a CAN block as the CAN controller, is applied here. PCA82C250 is applied as a high speed transceiver. The electric circuits for MCU, A/D module, D/A module, CAN bus interface module are completed. In software design, the softwares for each module's initialization, signal acquisition and filtering of accelerator pedal, CAN messages receiving and transmitting, control of throttle analog signal output are also completed.4. CAN Communication Semi-physical Simulation and Integration TestingFirst, considering that there is a possibility that external messages could not control the engine of target vehicle directly, the feasibility of Scheme One needs to be validated through semi-physical simulation on the real vehicle. In simulation model, break the connection between simulation engine node and simulation bus, connect the simulation bus to engine ECU on the real vehicle, and carry out semi-physical simulation. Multiple tests indicate that as for the target vehicle, external messages could not control the engine directly, so Scheme One is not feasible. Then, the control effect and communication performances of electronic throttle which has been designed need to be proved by semi-physical simulation. Disconnect the simulation node of electronic throttle in models, connect the real electronic throttle node to the remaining simulation bus system and carry out semi-physical simulation. The tests including following test, response test and communication test prove that electronic throttle can receive the control messages reliably, and export desired analog value, moreover, the control effect can satisfy with functional requirements. Because Scheme One is not feasible, so the design of system nodes follows the communication protocol of Scheme Two. At last, when all nodes'design is completed, integration testing needs to be performed to test communication performances. The results of integration testing on the real vehicle demonstrate that communication is well and functional requirements are accomplished in this system. Till then, the design and development of CAN communication for driving force electronic control system are finished.