Study and Design of CAN / LIN Hybrid Network of Automotive Body. Peng Huang

Transcription

1 Advanced Materials Research Online: ISSN: , Vol. 940, pp doi: / Trans Tech Publications, Switzerland Study and Design of CAN / LIN Hybrid Network of Automotive Body Peng Huang Hunan Communication Polytechnic, Changsha, Hunan Province, China, cshuangpeng@163.com Keyword: CAN Bus; LIN Bus; Bus network technology; CAN/LIN hybrid network Abstract: Due to the extensive application of automobile electronic control technologies, the demand of automotive network is growing. Automotive operation data sharing has become a feature of the automotive network. CAN network is most widely applied in the automobiles. LIN network is a supplement for CAN network in practical application. The hybrid network of CAN/LIN can improve the stability of the system, and also reduce network cost without influencing the performance of the network. In this paper, through the study of CAN/LIN hybrid network technologies of automotive body, a system scheme of the automotive body network with CAN/LIN dedicated gateway is proposed. Introduction The application of bus technology of automotive network can share a large amount of data in the control unit, and realize real-time transmission and exchange of a large number of control signals in the typical automotive electronic system to improve the safety and reliability of the automobile. Automotive body network technology has become an important component of the automotive network technology, and it is mainly used in the intellectualization and comfort of the automobile. Via the bus, control nodes are connected to form an intelligent automotive body network. The automotive body network realizes all the functions by intelligent sensors and actuators, and corresponding control strategies. On the basis of regular application scheme of automotive body CAN/LIN hybrid network, CAN/LIN dedicated gateway is added and the design of the hardware system of CAN/LIN gateway is completed. CAN Bus Network CAN Bus Network Structure CAN Bus is a kind of computer network with various network topologies. They can freely combine with each other to form different topologies, that is, the hybrid network. According to the protocol, CAN bus can be of any topology, but in general, there are 4 kinds of common topologies. (1) Bus topology: this is the most basic CAN bus topology. Bus topology is formed by a single cable connected to all the nodes in the network. The bus is a single cable and the bus bandwidth can be shared by all the nodes. In the bus network, when data is sent from one node to the target node, it can be intercepted by all the nodes. Only when the data is received and disposed by the target node, will it be ignored by the other nodes. (2) Ring topology: each node is connected to two closest nodes, and the whole network is connected to form a ring. Data is sent in one direction of the ring. The relay node that sends or forwards data signals of the ring can obtain the signals transmitted in the ring and forward it to the next node. (3) Star topology: all the nodes in the network are connected together via a central node, such as the hub. All the data between the nodes in the network is transmitted through the central node. (4) Mesh topology: each node is connected together to form a mesh. The reliability is high, but the cost is also very high. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-11/05/16,05:36:50)

2 470 Machinery, Materials Science and Engineering Applications 2014 Network Form of CAN Bus CAN bus is a part of the control network and it is a serial communication network, which can support distributed control and real-time control. CAN is a multimaster sending network structure. It is a peer-to-peer network. Any node can send data to other nodes at any time. When a conflict occurs, there is priority arbitration function to deal with the conflict. However, in some specific applications, the principal and slave nodes are distinguished in consideration of the reliability and integrity of the system. The general structure of CAN bus control system is shown in Figure 1. Figure 1 The general structure of CAN bus control system Minimum control system is a simple closed-loop control system, i.e. a single-loop control system consisting of a single sensor, a single controller and a single actuator. Some mutually independent control systems can form network control system based on CAN bus. However, they must share a control network - CAN bus. According to the concept of fieldbus control system, the intelligent node can be the sensor node or the actuator node of integrated controller. Bus nodes of the automobile are mostly intelligent nodes, and the sensor, actuator and controller are integrated to form a real distributed bus control system. LIN Bus Network LIN Bus: automotive bottom network protocol is a low-speed network achieved through low-cost serial communication, which has stable performance and is a supplement for existing automotive CAN bus. LIN falls into the class A network of automobile, with the communication rate lower than 20kbps. In case of low bus bandwidth and no need for multi-function, such as the communication between the intelligent actuator and air-conditioning control system, the application of LIN bus can obviously reduce the cost. Compared with CAN bus, the cost reduction of LIN bus can be attributed to the following reasons. (1) The communication between LIN nodes only needs one signal cable of 12V. (2) The cost of LIN nodes is lower than that of CAN nodes. Each LIN node only needs one transceiver. The communication protocol is relatively simple, and can be realized in the software without extra controllers. Microcontrollers generally have LIN interfaces based on UART/SCI serial interfaces, even if not, it can be achieved through the simulation of common I/O software. (3) Slave nodes of Lin don t need a crystal oscillator or ceramic oscillator to achieve self-synchronization and thus save the hardware cost of slave units. Network Structure of LIN Bus The principal node and several slave nodes of LIN constitute the LIN bus network. Limited by the physical characteristics of the network, the number of nodes in a LIN network is generally less than 12. Each LIN node consists of microprocessor, sensor/actuator and transceiver. The network structure of LIN is shown in Figure 2.

3 Advanced Materials Research Vol Figure 2 LIN network structure Network Form of LIN Bus When LIN bus is used in the automotive body control, the nodes are mainly in the four door-control modules and the body control module (BCM). Single LIN network, multiple LIN network and CAN/LIN hybrid network are the three LIN network forms that can be used by the automobiles. Solely relying on LIN cannot overcome all the limitations. Thus, how LIN is applied to the automotive? LIN is a complement for CAN, but doesn t entirely replace CAN. LIN-layered CAN is shown in Figure 3. Figure 3 LIN-layered CAN Generally, BCM is connected with four doors via CAN network, with each door as a single LIN network. CAN/LIN hybrid network is the typical solution employed by the current manufacturers. Although this solution may increase the number of microcontrollers, a distributed system with stronger functions and more flexibility can be obtained if microcontrollers and LIN state machines are chosen properly. With LIN structure, smaller microcontrollers can be chosen to achieve the door function. Besides supplying the CAN interface needed by BCM communication, there are enough resources to control the single LIN network. In this case, the microcontroller of the driver door is the CAN interface of BCM, and also the primary node of LIN network, which is used to control the manipulation of the rear mirrors, the keyboard, the door locks and the window lifters. Gateway Model of Automotive CAN/LIN Hybrid Network The cost of each LIN node is generally 1/3 or 1/2 of the cost of each CAN node, suggesting it has a great cost advantage. Because there are a large number of nodes used to control the automotive body, the total cost saved is very large. The communication within the LIN subnets can obviously relieve the burden of the communication of CAN backbone network and relieve the data jam of the backbone network, which is of great importance for the real-time control system. Therefore, automobile manufacturers always use CAN/ LIN hybrid network as solution. CAN and LIN are two different types of network protocol, which have different transmission rates. Gateway is used to accomplish the data exchange between them. Automotive gateway is an interface device to connect different types of networks, and can explain and interpret different protocols of both sides on the physical layer, data link layer and application layer of OSI reference model. The gateway mainly processes the information by three steps: read the information received from the first network, translate the information and transmit processed information to the second network. If necessary, the process should be reversible, that is, bidirectional communication. The gateway model of CAN / LIN is shown in Figure 4.

4 472 Machinery, Materials Science and Engineering Applications 2014 Figure 4 CAN/LIN gateway model Implementation Scheme Design of Automotive Body CAN/LIN Hybrid Network System Regular Application Scheme of Automotive Body CAN/LIN Hybrid Network Regular application scheme of automotive body CAN/LIN hybrid network is shown in Figure 5. In this scheme, four light controllers are used as CAN/LIN gateway. CAN network control system consists of four light controller nodes, air-conditioning control unit, instrument control unit, seat control unit, luggage compartment control unit, sunroof control unit and central control unit. The subsystem of each door is realized via LIN protocol. Each door module uses a controller, i.e. the rear mirrors, door locks and window lifters are controlled via a controller. Figure 5 Regular application scheme of automotive body CAN/LIN hybrid network In view of feasibility and cost, the door control system is placed in the LIN network, and four light controllers are used as gateways, which necessarily increases the workload for designing the software program of the whole network. However, in this scheme, the processing programs of the four nodes as gateways are almost the same, and the connection approach of LIN network is also the same. Thus, the development difficulty is reduced in some degree.

5 Advanced Materials Research Vol Optimization Design of Automotive CAN/LIN Hybrid Network Microcontroller is becoming increasingly powerful. In order to reduce the complexity of light control unit and improve the stability of network system, on the basis of traditional application scheme, a special CAN/LIN gateway module is designed to connect CAN to LIN, which makes the design hierarchy of the whole automotive body network system clearer and the structure simpler. The gateway microcontroller and its corresponding CAN and LIN interface devices can realize the conversion of the network protocol. Thus, it is highly cost-effective. When dedicated CAN/LIN gateway is employed, the data transmission between LIN nodes is more convenient and the structure becomes simpler. Its anti-interference ability is strong enough to improve the system stability. This scheme facilitates the expansion of subsequent functions and the development of subsequent programs. The optimization design scheme of the automotive body network is shown in Figure 6. Dedicated gateway is established to form CAN network and LIN network. CAN network control system consists of four light control modules, instrument control module, seat memory control module (driver), luggage compartment control module, air-conditioning control module, and comfort system central control module (CAN/LIN dedicated gateway). The LIN network controlled by CAN/LIN dedicated gateway consists of four door-control units. Figure 6 Optimization design of the automotive body network Dedicated CAN/LIN gateway is established between CAN and LIN to connect them. In this way, CAN/LIN gateway becomes the control center of the whole network. It can communicate with four light control units via CAN, and can also forward control signal to LIN network via CAN/LIN gateway to indirectly control the door system. CAN/LIN gateway is in charge of the bus hibernation and the control of conversion and transmission between various control signals. Conclusion In this paper, the network form of CAN bus and LIN bus are analyzed respectively. Both bus network technologies are studied. The difference between the structures is compared. The gateway model of CAN/LIN hybrid network is proposed. Based on the study of regular application scheme of automotive body network, an automotive body hybrid network system scheme with CAN/LIN dedicated gateway is optimized and designed. The scheme features simple structure, low cost and

6 474 Machinery, Materials Science and Engineering Applications 2014 high stability, which facilitates the expansion of subsequent functions and the development of subsequent programs. This paper is one of the research results of General Program of Scientific Research Project of Colleges and Universities in Hunan Province: Study and Design of Intelligent Automotive Body Network System Based on CAN/LIN (Project # 12C1071). References [1] Gong Jinfeng, Wu Zheng. CAN/LIN hybrid network in the car door control system in the application of [J]. automotive engineering, [2] Rao Yuntao. Principle and application of CAN field bus technology [M]. Beijing: Beihang University press, [3] Guo Chuansheng, Pan Ming et al. The vehicle interior network embedded CAN bridge design based on [J]. instrument technique and sensor, [4] What Jingneng, Cheng Anyu et al. The MC68HC908GZ32 design of CAN-LIN gateway based on [J]. microcontroller and embedded system application, [5] Qin Guihe, Ge Anlin. The automobile network technology ( J ). Automotive engineering, [6] Wang Fenghua. Research and application of automobile CAN/LIN hybrid networking technology. Master Thesis of Jiangsu University, 2006 [7] Jiang Shuxia, Han Zhigang. CAN /LIN bus network optimization design and CAN communication ( J ) based on. Instrument technique and sensor, [8] Javier Diaz, Elias Rodriguez, Luis Hurtado, Hugo Cacique. CAN Bus Embedded System for Lighting Network Applications,IEEE,2002 [9] LIN Consortium.LIN Specification Package Revision2.0.Sep23,2003 [10] Ma Jimin, Chen Hui. Intelligent light control system based on CAN/LIN bus.process Automation Instrumentation, 2009, 30(9)

7 Machinery, Materials Science and Engineering Applications / Study and Design of CAN/LIN Hybrid Network of Automotive Body /