Abstract : Combining the advantages and disadvantages of CAN bus and LIN bus, a hierarchical door control system based on CAN/LIN bus was designed and implemented. First, the implementation and characteristics of centralized control system structure and distributed control system structure are described, and the reasons for choosing the distributed structure are discussed. Then, the implementation of the door distributed system and related technologies are detailed.
Keywords : Bus CAN LIN Door Control
introduction
With the emergence of various sensors and the rapid development of chip technology, the safety and intelligence of automobiles are increasing day by day. The functions of automotive electronic control units (ECUs) and the information interaction between ECUs are increasing day by day. Automobile manufacturers have developed a variety of bus technologies to provide reliable and low-cost connections and realize corresponding network structures according to different requirements of safety and intelligence [1] to meet the data exchange requirements between units. For the control of the door area, there are many functions to be realized, including window lifting, rearview mirror position adjustment, door lock switch, and detection of switch quantity. For different target customer groups, there are also many intelligent functions that can be implemented, including window anti-pinch, rearview mirror folding and heating, etc. The author used low-speed CAN bus and LIN bus to realize the door distributed control system, selectively realizing some intelligence. The system can also be quickly modified and upgraded without much design change. This article describes the determination of the system structure and the specific implementation of distributed control.
Determining the system structure
The door control system adopts a bus-based topology. The bus typically uses a low-speed CAN bus or a LIN bus. Different bus protocols and topologies can provide different levels of intelligence. The first approach is to use a centralized control CAN node for each door, with the BSI and the four doors connected through a CAN network, as shown in Figure 1.
The second approach uses a distributed LIN network structure for each door, making each function a separate node: a separate rearview mirror control node, a window control node, a door lock control node, and a switch input control node. This switch input control node can also serve as the LIN master node. Each door's master node is also a CAN-LIN gateway node. The BSI and the four doors are connected via a CAN network, as shown in Figure 2.
Option 1 is a typical solution currently adopted by many manufacturers. This centralized control method integrates window lifting and anti-pinch, rearview mirror position adjustment, door lock, and switch input detection into one ECU. It has a low cost, uses a low-speed CAN bus connection, has a simple topology structure, simple and real-time communication, and a relatively simple protocol. In addition, CAN adopts a multi-master dual-line fault-tolerant mechanism, so the security is high. The diagnostics based on the CAN bus also makes fault finding and repair relatively convenient.
With the development of technology and consumers’ pursuit of automotive intelligence, the improvement of automotive intelligence and rapid upgrading are key factors to ensure the competitiveness of car manufacturers. The disadvantages of centralized control using a single CAN bus have also begun to be exposed. Since the high-performance MCU in the door node directly controls the windows and mirrors, when the intelligence requirements of the ECU are getting higher and higher, and functions or intelligence need to be added, the MCU functions of each centralized control node can only be enhanced, resulting in an increase in MCU specifications; and centralized control is complicated to install, with more connectors and connecting cables. When intelligence is added, the number of interconnections increases, lacking flexibility. Product upgrades require a lot of costs, ultimately leading to reduced efficiency [2].
Layered networks are an effective solution for the rapid and cost-effective upgrading of automotive products. LIN bus, as an effective supplement to CAN bus, is a key factor in the feature upgrade and function enhancement of layered automotive networks [3]. Using the CAN-LIN layered network structure shown in Scheme 2, the advantages of CAN/LIN bus are fully utilized, some functions are transplanted to smaller and more reliable nodes, the complexity of each ECU is reduced, and each LIN node in the four doors can be universal, with better interchangeability and compatibility. A node can be added or removed at any time according to the configuration requirements of the door function without affecting the entire network. Thus, rapid upgrading can be achieved without incurring greater cost consumption.
The emergence of single-chip sensors and actuators has provided a low-cost solution for distributed nodes, making it possible to reduce costs by adopting distributed technologies. With the continuous maturation of LIN bus technology, appropriate selection of MCUs and LIN state machines can yield more powerful and flexible distributed systems.
Implementation of Distributed Control
In the distributed control implementation of the car door system, each car door is a LIN network. The front door includes window nodes, rearview mirror nodes, and door lock nodes, while the rear door does not include rearview mirror nodes. The following discussion focuses on the implementation of the distributed control system for car doors from two aspects: the implementation of distributed nodes and the implementation of the gateway.
The rearview mirror node solution is shown in the figure below. It realizes the position adjustment of the rearview mirror in both vertical and forward/backward directions, and implements folding and heating functions. It is implemented using Freescale's intelligent distributed control single chip MM908E625. The MM908E625 is a highly integrated single-package solution that integrates an HC08 core and a SmartMOS analog control IC in an SOIC54 package. The analog control IC includes a LIN physical layer transceiver, a voltage regulator, four half-H bridges and a high-side switch. The half-H bridges are used to drive the rearview mirror motor to realize position adjustment and folding, and the high-side switch is used to realize the rearview mirror heating.
The window node solution is shown in the figure below. To achieve window lifting and anti-pinch functionality, a smart power drive chip with current feedback is used. A small algorithm based on current feedback is designed to implement the anti-pinch function. After the window motor starts, it can operate smoothly within a few hundred milliseconds. During this startup time, the current feedback value of the drive chip is sampled. This sampled value is then compared with a threshold value by the ADC in the MCU on the window ECU. If an obstacle is encountered, the operating current of the window motor increases, and the ADC sampled value exceeds the set threshold. At this point, it is considered that an obstacle has been encountered, and the MCU controls the drive chip to stop driving the window motor, thus achieving anti-pinch.
The gateway's master node in the LIN network for each vehicle door detects the open/closed status of that door area, controls all communication on that LIN network, designs a reasonable schedule to control the transmission of each information frame, and effectively controls the maximum transmission delay of critical signals. This node also serves as a CAN-LIN gateway node, handling data buffering and information exchange between the CAN and LIN networks.
Conclusion
This paper comprehensively considers the advantages and disadvantages of different system structures and the requirements of intelligentization and upgrading of automotive products, and designs and implements a distributed door control system based on CAN/LIN bus. The system operates well and has certain practical value.
References :
1. Liu Xiaoming, Gao Qingchun, Xiong Dong, Design of Automotive Communication Network Based on CAN/LIN Bus, Microcomputer Development, 2005.08
2. Zheng Rongliang and Yuan Pengping, Application of LIN Bus in Local Area Networks in Vehicles, Journal of Jiangsu University, 2004.02
3. Hou Shumei, Zhang Yunlong, Su Jian, A Novel Low-End Communication Bus LIN for Automobile Bodies, Automotive Technology, 2003, Issue 11.
