Qian WANG, Hui-zhong YANG, Zhao-bo QING

College of Mechanical Engineering, China Jiliang University, Hangzhou 310018, China

Intelligent automobile pedal controller based on CAN bus

Qian WANG?, Hui-zhong YANG, Zhao-bo QING

CollegeofMechanicalEngineering,ChinaJiliangUniversity,Hangzhou310018,China

This paper is mainly about automobile door pedal used in the production. It carried out the research of CAN bus (controller area network-bus), analyzed its working principle, hierarchical structure and protocol. Combined with the analysis of the door pedal operating principle, this paper designed a distributed CAN bus control system. The system consists of a master CPU and four distributed control units, adopting CAN transceiver PCA82C250 to connect with each other. The method of software implementation of the CAN communication system was carried out, and comparatively the algorithm of the anti-pinch and anti-collision function was analyzed. Finally it verifies the running effect of the controller with LabVIEW.

CAN bus, Intelligent car pedal controller, Anti-pinch function, Anti-collision function, PCA82C250 transceiver

1.Introduction

Abroad automatic telescopic pedal is already in application on many public transport equipments, such as public bus, luxury bus, city light rail. While auto intelligent pedal system used on the cars and limos is just appeared recently, such as that of Range rover, but the installation cost is too high. The largest domestic company focusing on automobile intelligent adjustable pedal system is T-Max, whose imitation is more, the cost is high. That requires research and development of new smart car pedal controller. Figure 1 is one kind of producing car door pedal for SUVs. This paper introduces Microchip Company's single-chip microcomputer PIC18F25K80 with internal CAN module as the core, as well as the design process of CAN bus intelligent car pedal controller hardware and software program.

2.CAN bus technology

CAN (controller area network) is a multiple hosts local network system exploited by Bosch company for automotive application. Bus adopts differential signal serial communication to work, whose anti-jamming capability is strong, which has non-destructive arbitration function based on priority, can realize multiple address message transmission. In addition to automotive electronics, CAN bus has been widely used in areas, such as industrial automation and control equipment, medical instrument and environment detection. CAN bus users have become accustomed to the traditional independent CAN controller. With the development of the various application requirements and technology, more and more CAN modules of controllers appear in the form of inside and outside the chip. CAN bus communication system based on embedded microcontroller controller (MCU) has some advantages such as simple interface circuit, flexible operation, powerful features[1].

The topology[2] of the CAN bus is a typical serial bus structure. CAN bus protocol resolves bus conflict by a way of non-destructive arbitration. CAN bus is a protocol based on message rather than site address. CAN protocol is based on the ISO/OSI model, but only takes the physical layer of the OSI bottom, data link layer and application layer of the OSI top, whose transmission medium is the twisted-pair cable. Communication rate is up to 1 Mbps/40 m. Direct transmission distance is as far as 10 km/5 kbps. Articulated devices number can reach 110. Signal transmission of CAN adopts the short frame structure, whose effective number of bytes per frame is eight, transmission time is short, and the probability of interference is low. When nodes have serious mistakes, it has automatic shutdown function, to cut off the node with the bus connection, which strong anti-interference ability.

Figure 1. Pedal out

In CAN system design, the most used microcontroller is external independent CAN controller, such as Philips company PCA82C200, SJA1000 and Intel's 82526, 82527[3] and other chips. Using such chip is harmful for system integration. This paper selected microcontroller PIC18F25K80 which embedded CAN controller as the CPU.

3.The Composition of Car Pedal Controller Communication Network

Electric pedal control system communication network with a total of four CAN node electronic controllers, which are left front doors controller, right front doors controller, the left rear doors controller, and right rear doors controller. The CAN bus communication technology can realize the communication between the four door controllers, as shown in Figure 2.

The way that controller realizes the function is shown as follows: function of CAN bus to send and receive data, read analog on-board network signal in the door, battery voltage signal. The basic function of normal telescopic pedal is when the pedal stretches out and meets the collision objects, it stops and reversely recovers; when the pedal takes back and meets the collision objects, it stops back, back out. Pedal has collision and clamping material information completely from the feedback signal to the motor current of the controller. For different obstacles, the motor current curve is different.

Figure 2. Communication network structure

4.Controller hardware design

Car pedal controller is mainly composed of single chip microcomputer minimum system, power supply module, motor driver module, motor current sampling module, CAN bus network interface circuit.

Among them, the power supply module is to convert the 12 V supply of the car to give standard voltage of 5 V for controller, as shown in Figure 3. Considering the cost and function need, motor driver module used the H bridge driving mode, which saves the cost, also can achieve the required functionality, as shown in Figure 4. Motor current sampling module adopts the amplifier for resistance voltage, to represent the motor current feedback value. CAN bus network interface module adopts PCA82C250 transceiver (TTL signals of single chip microcomputer is converted to differential signal of CAN bus). Current is limited by resistor to protect the transceiver from the impact of the flow. Small capacitance can rise to filter out high frequency interference and electromagnetic radiation on the bus, as shown in Figure 5.

Figure 3. Power supply module

Figure 4. Motor driver module

Figure 5. CAN bus interface module

5.Sensorless control clip anti-collision fun- ction implementation

Sensorless implementation of anti-pinch and anti-collision function relies mainly on the recognition of motor current waveform figure, as shown in Figure 6. There are three ways for the motor current waveform recognition: the slope method and amplitude method and integral method[4].

Figure 6. Motor current waveform figure

This design tests area of motor current in three cases stopped in traffic, normal, and edges of curve respectively. In these three cases, the area while the pedal stopped in traffic is much larger than that of the other two cases.

6.The pedal control unit software design and implementation

The software design of the system is very important. Tools used in the design are: software MPLAB IDE, the emulator ICD2.5. In order to improve the reliability and understandability, the paper adopts modularization program design idea, and the whole program is divided into five parts: ① the main program, including system initialization program and monitoring program; ② the CAN communication program, including message program, message receiving and sending CAN error management procedures, etc; ③ the clip collision prevention program, using integral algorithm, discrimination encountered obstacles, and make the right response; ④ the peripheral interface program, mainly includes the current signal acquisition program, switch signal recognition, received message analysis program and display; ⑤ interrupt program.

The Program ②, ③mentioned above are the keys of the design. Figure 7 is the CAN communication program (the left figure is the initial subprogram, the intermediate one is node data sending program, the right one is the node data reception procedures). Figure 8 is the clip collision prevention program.

The initialization program of the CAN interface design is important. If the design is not good, the system will not work properly.

PIC18F25K80 MCU CAN interface initialization should set the first control registers, status register in configuration mode, the baud rate registers, I/O control register, receiving and filtering the mask registers set according to requirements of the system, to ensure the smooth of CAN bus.

Figure 7. CAN communication program

Data is sent to subroutine. Data is sent automatically by the CAN controller based on CAN bus protocol. Data is sent by data query, that is, to send the information frame to sending buffer, and set up request identifier in the command register, then start the sending button.

Receiving and sending the data are similar, which are done automatically by the CAN controller. The receiving application program only receives the data read from the receiving buffer, then follows the corresponding processing. Receiving data adopts interrupt mode, that is, when receiving a message, the information will go through the filter of the acceptance, that produce a receiving interrupt, then the data received from receiving register is transferred to the specified storage area and save up, finally the interrupt returns.

Figure 8. Clip collision prevention program

Clip collision prevention program adopts integral algorithm, that is, to calculate integral value of motor current curve, then compare the integral value with the threshold, then make the corresponding action.

Master CPU (as shown in Figure 9) is responsible for collecting gating signals, battery voltage, determining the doors' open and close status, and sending commands to the subunit, thereafter receiving the subunit feedback information, monitoring subunit, which has the effect of the eye and brain.

Figure 9. Car stepping control the main unit

In order to guarantee the stability of the controller, it needs to monitor several key parts of the controller circuit, so dedicated test bed for signal acquisition is set up with PC software LabVIEW and USB acquisition card. PC monitor screen is shown in Figure 10. Figure in the collection of information has a motor current waveform diagram, PIC18F25K80 control motor output pin status, control relay status, etc. So it is beneficial for finding interference problems in the circuit and optimizing the controller.

Figure 10. PC monitor screen

7.Conclusion

Intelligent vehicle pedal based on CAN bus will become the development trend of limo and SUV, which has a broad application prospect. This design adopts the single chip microcomputer PIC18F25K80 embedded CAN controller, CAN transceiver PCA82C250, whose circuit is simple and reliable, which monitors state of the door through CAN bus communication, then accordingly reacts quickly and accurately.CAN bus communication network in the design makes the pedal controller to integrate on-board network one step further.

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基于CAN總線的智能車踏控制器

王 謙?，楊惠忠，卿兆波

中國計量學院 機電工程學院，杭州 310018

以某款用于生產(chǎn)的汽車門踏板為例，展開了對CAN總線的研究。分析了CAN總線的工作原理、分層結(jié)構(gòu)以及協(xié)議，又結(jié)合對門踏板工作原理的分析，設計了一種分布式CAN總線控制系統(tǒng)。系統(tǒng)硬件包括一個主控CPU和4個分布式控制單元，采用CAN收發(fā)器PCA82C250進行互聯(lián)。系統(tǒng)軟件提出了CAN通信的實現(xiàn)方法，對比分析了車踏防夾防撞算法。最后運用LabVIEW軟件對控制器的運行效果進行了驗證。

CAN總線；智能車踏控制；防夾功能；防撞功能；PCA82C250收發(fā)器

U270.1+4

2014-01-20

10.3969/j.issn.1001-3881.2014.12.020

? Qian WANG, E-mail: 1013177030@qq.com