PIC16F877A of CAN-based design of intelligent sensor
With the scientific and technological progress and development of the vehicles safe and comfortable driving performance and a significant increase of the requirements, making the vehicle's electronic control unit on the number of a gradual increase, but the vehicles electronic control unit (for example, a variety of switches, the implementation of , sensors, etc.) still connected with the traditional wiring harness to achieve, making the car and the wiring harness too complex, resulting in a severe electromagnetic interference, resulting in decreased reliability of the system. In the limousine, the electronic components and systems accounted for more than 20% of vehicle price, and the increasing trend. In this case, the vehicle electronic control circuit will be more complex, how to make the devices inside the network, and reduce the number of wiring harness with the vehicle system to improve the focus of a research direction.
In the vehicle networks and communication systems, local networks become increasingly rich, which, CAN, Profibus, LON, ASI, EIB and eBus-to-peer network technology has reached a mature state of development, the standardization of the various network technologies have also introduced and that such a mature network technology integration work has been completed. CAN bus in stability, such as real-time and cost-effective applications in the car show a strong advantage, as a distributed control LAN technology is relatively competitive. At present, a lot of vehicles will be used throughout the automotive CAN bus control system linked to the unified management, data sharing and coordination between the work of wiring harness to make the car reliable and user-friendly, improve the overall vehicle safety and cost-effective, enhance the competitiveness of their own.
The realization of the network traffic control system on the premise that contact of the Intelligent Design network, including sensors, controllers and intelligent actuators. In this paper, by-wire electronic throttle for the study was designed pedal position sensor, throttle position sensor and throttle position control actuator intelligent contact the CAN bus as a basis for the composition of CAN bus control network, the completion of throttle position for precise control.
1 vehicle CAN bus architecture with distributed control
Controller Area Network (controller area network, CAN) are industrial fieldbus, is the German company Bosch in the early 20th century, 80 as a solution to many of Hyundai Motor control and testing equipment for data exchange between the development of a communication protocol. In November 1993, ISO formally promulgated CAN high-speed communications of international standard (ISO 11898). CAN bus system in the field data collection completed by the sensor, at present, with a CAN bus interface is not the type of sensors and more expensive prices.
Vehicle control system of the existence of a large number of sensors, electronic control unit, such as executing agency, usually, multi-sensor controller share the same information, and real-time, higher speed requirements, how they connect together to form distributed control network system of modern control systems an important direction of development. Fieldbus control system (field control system, FCS) is one of the control of a typical realization of the network structure. CAN field bus belonging to the scope of support it is an effective control or real-time control of distributed multi-master serial bus, with its short message frame and outstanding CSMA / BA-by-bit arbitration agreement was subject to each field device even of all ages.
Vehicles based on the CAN bus network distributed control system as shown in Figure 1, the use of fieldbus-style distribution system (field distributed control system, FDCS) structure, from sensors, actuators, controllers and CAN-site intelligent control node network group into. A number of smart nodes to complete their own independent data collection, system configuration, operational control and so on, through the CAN field bus, the smart nodes to exchange data between the control and management information.
2-by-wire electronic throttle system, the principle and structure
Electronic throttle control technology first appeared in the 20th century, the early'80s, was initially used only on high-end cars. With the increasing development of electronic technology, energy issues and environmental issues have become increasingly prominent, as well as the improvement of vehicle performance, electronic throttle control engine power become the most important control device, and has been widely applied to various types of vehicles, the The advantage is that according to the wishes of the driver, emissions, fuel consumption and safety requirements to enable fast and precise throttle control in the best opening, and set up a variety of control functions to improve driving safety and comfort. At present, research on this technology are BMW, BOSCH, Toyota and other companies, but also, BMW, General Motors, Toyota, AUDI and other manufacturers have been part of its successful application of models.
As shown in Figure 2, the system from the accelerator pedal position sensor and electronic throttle body composition, including the actuators throttle body, throttle valve and throttle position sensor 3, which are packaged into one. Actuator by a DC motor drive and related components. Accelerator pedal is a high-precision linear potentiometers, as drivers look forward to opening the throttle sensor device, the output of which is a pedal stroke is directly proportional to the analog voltage signal; throttle body from the forward and reverse 2 only as a position sensor in the throttle opening control feedback signal, through the throttle body inside a pair of high-precision potentiometers to obtain under the current aperture value of the corresponding voltage feedback, the feedback value and the throttle opening angle of a linear change .
3 Intelligent Sensor CAN Bus Interface Design
Contact smart sensor design is based on Microchip's PIC16F877A mcu and independent CAN bus controller and CAN transceiver MCP2510 to complete the PCA82C250.
PIC16F877A instruction using high-performance RISC microprocessor 8, the Harvard bus architecture, low power, high speed. Internal integration of the ADC, Serial Peripheral Interface (SPI) and the flash program memory, with multiple functions such as PWM output. PIC16F877A through the SPI interface can be achieved with the CAN controller MCP2510 seamlessly.
PIC16F877A of CAN-based smart sensor node hardware schematic diagram shown in figure 3.
Smart Sensor CAN Node independent CAN communication module and the CAN controller MCP2510 transceiver components PCA82C250. MCP2510 can complete CAN bus physical layer and data link layer of all the features to support high-speed SPI interface (maximum data transfer rate can reach 5MB / s), support CAN2.0A/CAN2.0B agreement. CAN transceiver PCA82C250 is CAN bus controller and the physical interface between the physical differential bus to provide the ability to send the CAN controller provides differential receive capability, at the same time, it can increase the communication distance, improve the Embedded CAN Intelligent anti-interference ability of the node.
PIC16F877A through CAN controller MCP2510 with SPI connectivity, its serial data input (SDI) pin and the SO pin MCP2510 connected, the serial data output (SDO) and the MCP2510 pin connected to the SI pin, the serial clock (SCK) pin SCK pin and connected to the MCP2510. MCP2510 reset signal, chip select signal provided by a single chip.
PIC16F877A by setting the SPI interface status register and control register SPI interface so that a proactive approach to work. PIC16F877A when communication with the MCP2510 timing is very important. Sending data, first send written instructions, and then send register address, and finally send data. When the MCP2510 received came from the data bus will be interrupted, single-chip microcomputer in response to interruption, read data before sending read commands, and then send register address, data is automatically written into the single-chip SPI interface of the buffer .
Itself as a result of a single-chip 10-bit A / D converter, therefore, pedal position sensor and throttle position sensor output analog signals for direct access to single-chip digital-to-analog conversion, do not need to add a new A / D conversion devices, in Figure 3, the sensor input by RA0/AN0, in order to filter out high frequency noise in the analog-to-digital input then an RC filter circuit. At the same time, electronic throttle actuator device control of DC motor, PIC16F877A I have the PWM, through drive circuit connected to the DC motor can be driven, the device driver using L298.
CAN bus control the entire network is intelligent pedal position sensor nodes, throttle body position sensor and actuator nodes and controller nodes, in which intelligent pedal position sensor nodes, throttle body position sensor and actuator nodes by a single machine CAN bus organizations, and its main function is to transfer to the controller pedal position and throttle position feedback signal, at the same time, the receiving controller to the actuator command signal issued by the driver. Controller through the use of computer Advantech PCL-841 card CAN bus communication and the corresponding control algorithm to complete the by-wire electronic throttle control.
4, system control theory and experimental results
System control process shown in Figure 4.
Control system is a closed-loop control process, as the pedal position sensor input, A / D conversion through the CAN bus is sent to the controller. Similarly, the throttle position sensor as a feedback signal, A / D conversion through the CAN bus is sent to the controller, the two signals compared in the controller by the controller using the corresponding control algorithm (such as PID, etc.) decision-making, decision-making results from the CAN bus is sent to the throttle body position sensor and the actuator node, the node processor to produce the PWM signal by the driver drives the operation of the executing agency.
In order to verify the performance of control systems, adaptive PID control algorithm using a real vehicle test platform and experimental results in Figure 5. Which, PPS said pedal position, TPS1 experimental platform that results under the throttle position, TPS2 real vehicle that case the experimental results throttle position. Results from the control to meet the electronic throttle control and accuracy of real-time requirements, at the same time, the real vehicle test environment, the system has a certain anti-noise ability.
CAN Bus vehicle as a reliable computer network bus has been a number of advanced automotive applications, the CAN bus used in the smart sensor to sensor signals received through the bus in real time, reliable, high-speed and accurate to carry out transmission, making the computer control unit of the vehicle through the CAN bus can share all information and resources to simplify the wiring, sensors to reduce the number of control functions to avoid duplication, improve system reliability and lower costs, better matching and coordination The purpose of the various control systems. At the same time, the entire smart sensor network-wide digital communications, the bus also has a very good anti-interference ability, the future of intelligent sensors and intelligent control of the development trend of the network.
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