Developing PC-Based Automobile Diagnostic System

Based on OBD System

Authors ：Hu Jie, Yan Fuwu, Tian Jing, Wang Pan, Cao Kai

School of Automotive Engineer Wuhan University of Technology

Speaker ：陳明睿 M98G0105

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Outline

• Introduction• Architecture of diagnostic system• Hardware of system• Software of system

– Curing software designing– Diagnostic software designing

• Experiments and result analysis• Conclusion

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Introduction

• The widely application of electronic control technology makes the structure of automotive electronic control system more and more complicated.

• It is more difficult to find the cause and position of fault.

• Data in vehicle technical supports shows that the time for finding fault is 70%, while the time for troubleshooting and maintenance accounts for 30%.

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Introduction

• The widely used diagnostic equipments in the current market mostly are the second-generation hand-held diagnostic devices, which just have some extensions based on code reader.

• They mainly have several problems:– hardware system is relatively unchangeable,

– difficult to upgrade or expansion modules

– The slow running speed of devices

– less function can not fully meet the vehicle real-time diagnostics maintenance requirement;

– limited memory of the handheld devices

– Due to the lacking of network connection

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Introduction

• The author proposes a general pc-based automobile fault diagnostics system based on OBD system design, which combines with network technology and modern fault diagnosis technology.

• This system can not only solve the problems in hand-held diagnostic devices, but also caters to the new trend of the automobile fault diagnosis technology.

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Introduction of OBD system

• OBD system was originally designed for vehicle exhaust emission controlling.

• Initially, there was no uniform standard for the OBD systems made by different car manufacturers.

• In 1996, the U.S. Society of Automotive Engineers SAE, EPA, California Air Resources Board (CARB) coordinates the submission of standards of the OBDII (the Second-generation on board diagnostic system)

• OBD II provides unified detection method for different automobile manufacturers, and also lays the foundation for developing general automotive fault diagnosis system.

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Introduction of OBD system

• The physical layers and link layers of J1850, ISO9141, KWP2000, and CAN protocol are various, while the protocol of their application layers are uniform.

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Architecture of diagnostic system

• In view of layering of OBD system diagnostic protocol– physical layer

– link layers

– uniqueness in application layer

• The system can be divided to PC diagnostic software

VCI system (Vehicle Communication Interface)

Vehicle network

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Architecture of diagnostic system

• PC diagnostic software– Human-computer interaction interface .

– Achieves the application layer of the protocol .

– Single maintenance station connect the automobile manufacturers by internet.

• Thus, a diagnostic network is formed and the function of resource sharing and remote diagnostics can be achieved.

PC diagnostic software Automobile manufactures after service center

Internet

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Architecture of diagnostic system

• VCI system (Vehicle Communication Interface)

– bridge which connects the vehicle diagnostic system and host computer diagnosis system

• According to data flow, divided into three sub-functional modules– Protocol conversion function module

– Host microcontroller module

– USB bridge module

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Architecture of diagnostic system

• Protocol conversion function module

– Achieves connection of physical layers of the entire communication.

• Host microcontroller module

– analyze the on-board network data, and sent message to host computer diagnostic system

– It will achieve controlling of parts of the man-machine interface, and the corresponding data storage

• USB bridge module

– transfer the serial data streams to USB data stream

– communication link between the host computer diagnostic system and the host microcontroller system.

VCI system (Vehicle Communication Interface)

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Architecture of diagnostic system

• Vehicle networks consist– ECU, sensors, fault indicators, diagnostics connection, and the

bus.

• ECU constantly monitors the input information of sensors and actuators by CAN

• When diagnosing faults– communicate with ECUn and storage fault codes and fault

information

Vehicle Network

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Hardware of system

• Use different diagnostic protocols of different vehicles.

• It is necessary to design various protocols transfer circuits in order to meet different diagnostic requirements of different models

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Hardware of system

• The hardware system consists– Human-computer interaction module.

– Serial ports switch to USB module.

– Information indicator modules.

– Protocol conversion module.

– Microcontroller module

– Data storage module

– Power conversion modules

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Software of system

• Take K-line diagnosis for example.

Curing Software Designing Diagnostic Software Designing15

Software of system

• Curing Software Designing– communication management and

diagnostic service management.

– Communication management includes the initialization of communication parameters, selection of protocols and initialization of diagnostic protocols as well as the starting and stopping of communication

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Software of system

• Diagnostic Software Designing– Host computer diagnostic software is developed with

Visual Basic 6.0, while its database is designed by Access2000. Diagnostic software interface

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Software of system

• Diagnostic Software Designing– The overall function principle of the host computer

diagnostic software

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Experiments and result analysis

• Vehicle diagnostic interface is connected to PC diagnostic system and parts of the vehicle real-time parameters is monitoring.

• The parameters include throttle position, intake manifold pressure, ignition advance angle, engine speed and vehicle speed.

• The road testing under various working conditions– Stopping module

– Starting module

– Idle speed

– Accelerating module

– Decelerating module

– Cruising module.

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Experiments and result analysis

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When the vehicle stops, the intake manifold pressure is 0.1Mpa close to the atmospheric pressure.

When the engine run at idle speed model and the engine speed is keeping at 750r/min, the intake manifold pressure is around 0.028Mpa, indicating that engine works smoothly under the idle speed condition.

Experiments and result analysis

• If the throttle valve is released after acceleration, the intake manifold pressure drops sharply and the ignition advance angle is affected significantly.

• So the ignition advance angle becomes negative.

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Experiments and result analysis

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Conclusion

• According the vehicle testing, the entire hardware system is reliable and stable.

• The diagnostic software is easy and intelligent and the entire system can run smoothly and diagnose accurately.

• Compared to hand-held diagnostic devices– More powerful repairing help and guidance– Upgraded more conveniently and able to achieve remote

diagnostic extension.23

Thank You

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