Working principle and interface standard CAN bus supports message-based working mode. Messages can be broadcast to any node at any time on the network. Messages appear in the form of message packets, including four types: data message packets, RTR message packets, error message packets, and overload message packets.
The system design complies with the following basic principles in the structure and function design of the system: (1) Modular integration: Each signal unit should not only be convenient for centralized detection and control, but also independent of each other. Its physical structure is manifested as modular integration, and the system integration is manifested as a virtual instrument structure.
(2) Project expansion: Due to the continuous enrichment of automotive instrument functions, the test and inspection items and their requirements are constantly changing, which requires the design to consider the scalability of the system and improve the cost-effectiveness of the system. The scalability of the system is manifested in the flexible connection of system software and hardware and the simulated physical interface and semi-physical interface.
(3) Programmable items: The programmable principle is expressed as the program grouping of options such as test items, action timing, signal type, amplitude, and inspection accuracy. For various test purposes, users can flexibly set and program programs according to the requirements of the test content.
(4) The test operation interface is required to be vivid, simple and convenient.
System working requirements (1) Durability: The performance of the system meets the requirements of the durability test, continuous and reliable operation for 72 hours, with reliable anti-interference ability and self-healing ability. (2) Compatibility: The system has strong compatibility, can be matched with other automobile test equipment, and can be further comprehensively tested. (3) Working environment: The ambient working temperature of the system is 0～70℃, the external working voltage is AC 220V, and the working current is 5A.
The overall system structure is based on the system requirements, and the overall system structure is as follows. System function and configuration System configuration and development environment hardware configuration: The system operation console is a PC (PII, display 20′); a set of camera monitoring system (interface card, camera); the local area network system includes the bus control device 82C200, 82C250 and other interface adaptation devices. System overall structure development environment: operating system above WINDOWS98, DELPHI5.0 and assembly development tools.
Main functions and interface design Through the analysis and summary of the automobile test, the main functions of the following system are determined: (1) The simulation speed, vehicle speed, mileage, etc. are detected by pulse, and the oil pressure, oil volume, water temperature, voltage and indoor are detected by simulation. Signals such as outside temperature. It can simulate left and right steering, reversing, car lights and more than 20 kinds of switch signals. (2) With program setting function, it can automatically control the magnitude and timing of various signals. (3) Query and analyze the input signal data, and generate test reports.
According to the system function requirements, design the system interface such as, the specific main functions are described as follows: System maintenance: password, system parameter setting, file management, etc. User management: test project registration, user and car registration. Test plan: The full set of plans, program combinations and corresponding databases of this test project can be set arbitrarily, including test technical indicators and requirements. Test procedure: Carry out the test according to the test plan, which can be tested automatically under the guidance of the wizard. Including the principles and methods of automobile testing. The test procedure is automatically controlled and flexible.
System simulation: simulate the entire test process according to the test plan. Data query: The test data can be categorized and inquired. Analysis report: According to the test principle and method, the test data is analyzed in various forms such as graphs, and the test report is generated. Instrument monitoring: real-time monitoring of the working status of the instrument through the camera on the combined instrument. User help: provide services such as system introduction, installation guide and instructions for use.
Conclusion The automobile combination instrument simulation and performance experiment system has realized the high reliability of automobile experiment and the low cost of system development due to the design of distributed control system and the adoption of CAN bus technology. In addition, the high efficiency of the DELPHI development environment <3> provides a solid foundation for system integration. As the problem of distributed control system is solved well, the application level of the system has reached a new level.
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