1 Introduction
All cars and light trucks manufactured and sold in the United States must be equipped with an on-board automatic diagnostic system (OBD-II) as of January 1, 1996. However, OBD-II is mainly used for the diagnosis of emission systems, and various other subsystems of the vehicle can be diagnosed by OBD-II relatively less. Although these diagnostic codes are very useful for diagnosing some faults, the information is not enough to effectively distinguish specific fault parts. The fault code can be obtained through the scanning tool connected to the OBD-II interface, but the standards for the communication between the handheld scanning tools provided by various manufacturers and OBD-II are not uniform. Europe and most Asian countries use the ISO9141 standard to communicate with OBD-II GM's cars and light trucks use the SAE j1850 vpwm standard, and Ford uses the SAE j1850pwm standard.
This leads to the following shortcomings of traditional car fault diagnosis: diagnostic technology is not formed between different car manufacturers, which will undoubtedly lead to a significant increase in the cost of vehicle diagnosis; fault diagnosis requires driving the vehicle to a specific repair location, which leads to driving It is inconvenient for the user, and it is impossible to regularly carry out regular diagnosis and maintenance; a comprehensive diagnosis requires specific equipment and skilled technicians, which will make the diagnosis cost high; the information provided by the fault code is usually not accurate enough Point out the source of the fault; as the automotive electronic control system becomes more and more complex, it is more and more difficult to diagnose the fault of each part.
The number of various electronic control units in automobiles is increasing, and the connecting wires are significantly increasing. Therefore, improving the communication reliability between control units and reducing the cost of wires has become an urgent problem to be solved. To this end, the German Bosch company, known for its R & D and production of automotive electronic products, developed the CAN bus protocol and made it an international standard (ISO11898). One of the biggest features of the CAN protocol is to abolish the traditional station address coding and instead encode the communication data block. Using this method can make the number of nodes in the network theoretically unlimited, and can also make different nodes simultaneously Receive the same data.
With the advancement of remote communication, bus technology, model-based diagnosis, electronics and embedded technology, vehicle fault diagnosis and monitoring technology has been greatly developed, enabling remote diagnosis and monitoring during vehicle driving. The availability of these technologies and the increasing interest of car owners have led the automotive industry to invest more and more energy to achieve remote diagnosis and monitoring.
2 System structure design
2.1 System principle
Vehicle remote fault diagnosis is a multi-disciplinary complex system, including on-board fault diagnosis unit, remote vehicle information technology service center and wireless communication network system. Many related patents and articles have appeared recently.
Figure 1 is the working principle diagram of the vehicle's remote fault diagnosis system. The on-board fault diagnosis unit and the service center realize remote diagnosis through wireless communication: the remote service center obtains the status information sent by the on-board fault diagnosis unit through the wireless network, and then analyzes the vehicle's Operating parameters and fault codes, the remote information technology service center informs the owner of the severity of the fault, provides necessary support services, and arranges necessary maintenance or recommended repairs to resolve the fault.
2.2 Functional design
(1) The vehicle can intelligently provide fault codes, key sensor values ​​and other relevant operating parameters to the remote service center, and has the ability to obtain downloads or system software upgrades.
(2) Both the vehicle and the remote service center have advanced real-time diagnostic and monitoring modules with appropriate human-machine interfaces.
(3) The vehicle's remote fault diagnosis service center has authoritative experts responsible for complex diagnosis and monitoring and communication with the driver.
(4) Ensure the data communication between the remote fault diagnosis service center and the corresponding vehicle and the wireless network for talking with the driver.
From the analysis of the system schematic diagram (Figure 1), it can be concluded that the diagnosed vehicle maintains communication with the vehicle information technology service center (telmaTIcs service providers, tsp) through the wireless network. The vehicle information technology service center can not only provide Internet services like traditional ISPs, but also provide security, GPS, customer relationship management and other services. Moreover, the vehicle information technology service center can also provide professional fault diagnosis experts to provide diagnosis services for vehicle owners. Diagnostic experts analyze the vehicle's fault level in real time through the fault code transmitted from the on-board electronic system. Owners can also browse the more specific fault code descriptions provided by the vehicle information technology service center through mobile computer wireless Internet access or mobile phones through wap, as well as other navigation services. At the same time, our vehicle information technology service center should also have the following resources, such as vehicle manufacturer data center, road rescue vehicle and vehicle repair, maintenance store, etc.
3 Software design
The software design of the system is mainly divided into two parts: the expert system design located in the vehicle information technology service center and the vehicle-mounted fault diagnosis unit design located in the vehicle.
3.1 Expert system design
This part is an application located in the vehicle information technology service center. In addition to ordinary web services, GPS services, tracking services, etc., the most important thing is to provide expert diagnosis of failures. This part of the function is assisted by the expert system and completed by on-site experts. Through the expert system, feedback the fault diagnosis information to the vehicle owner as soon as possible, and put forward the expert suggestions for solving.
To develop an expert system, first of all, a large amount of actual maintenance experience of experts in the field of automobile maintenance needs to be summarized and refined into a knowledge base, which constitutes the core part of the expert system; then an inference engine can be established, which can be based on the data sent by the on-board fault diagnosis unit , Use the knowledge in the knowledge base, infer according to a certain strategy, and get the diagnosis result. The structure of the expert system is shown in Figure 2:
The establishment of the knowledge base is directly related to the service quality of the vehicle information technology service center, and it also affects whether car owners use this system in large numbers. Therefore, the work of collecting and collating expert knowledge is particularly important. The difficulty lies in the collection and expression of expert knowledge. Because there are so many car manufacturers now, there are more specific car series. Although most vehicles now provide the OBD-II interface, the information of the fault codes read from the interface is very limited; the communication protocols between the handheld devices used by major auto manufacturers to detect faults and OBD-II are also inconsistent, and the The fault code contains a lot of information is interpreted by the experience of maintenance workers. Therefore, the accumulation and organization of expert knowledge is very important.
There are many factors to consider when summarizing knowledge. In order to make full use of the symbolic reasoning ability of the expert system, all knowledge that can be described by mathematical formulas are implemented as a specific solver method, and the rest are stored as rules in the knowledge base.
The expression of rule knowledge is:
Rule number if (premise) then (conclusion)
The premise is a condition or the "and" form of several conditions. In the latter case, the conclusion will be accepted only if several conditions are established. Each condition can be in the form of an "or" of several items.
The following is a specific rule:
rule5:
if
(1) Received fault code: p0201
(2) Received fault code: p0202
(3) Received fault code: p0203
(4) Received fault code: p0204
(5) Number of engine cylinders: 8
then
The fuel injector of the engine is faulty and needs to be repaired immediately.
When the inference engine is designed, the system uses a two-level es inference control strategy. Combining domain knowledge, the overall fault analysis and solution task is decomposed into different subtasks, such as engine fault analysis subtask and tire fault diagnosis subtask. Each subtask has its own target solution variable, subject to different solution methods, and is independent and interrelated. Solve its target variable through forward reasoning, and display the result to the owner.
There is a certain dependence between the sub-tasks of automobile fault diagnosis, and the solution of each sub-task has certain prerequisites. For example, the solution of the sub-task of the cylinder injector must be solved under the premise that the line voltage of the nozzle is known. To proceed, therefore, activation conditions are set in each solver. Only when these conditions are met, the solver can be activated to solve the target variable. The meta-level inference engine uses this set of related object information to activate related solvers in a certain order for re-inference.
The explanation mechanism uses the data output from the inference engine to answer questions such as how, why, what, why, etc.
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