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
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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:
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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 Secondgeneration 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.
Internet
PC diagnostic software
Automobile manufactures after service center
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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
VCI system (Vehicle Communication Interface)
• 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.
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Architecture of diagnostic system
Vehicle Network
• 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
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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
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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.
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Curing Software Designing
Diagnostic Software Designing
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
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Stopping module
Starting module
Idle speed
Accelerating module
Decelerating module
Cruising module.
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Experiments and result analysis
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.
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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.
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T h a n k
Y o u
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