A mixed fault diagnosis method for CAN bus intermittent open circuit and intermittent short circuit

Abstract

The present invention discloses a method for diagnosing a mixed fault of intermittent open circuit (IOC) and intermittent short circuit (ISC) of a CAN bus, comprising the following steps: step S1: collecting data link layer and physical layer double-layer network signals when a communication error occurs; step S2: defining an IOC alarm and an ISC alarm based on the double-layer network signals; step S3: deriving the IOC evidence status and the ISC evidence status of a transmission path based on the IOC alarm and the ISC alarm; step S4: solving a mapping relationship from a transmission path to a cable link based on network topology information; step S5: calculating the IOC suspicion and the ISC suspicion of the cable link based on the mapping relationship and the two types of evidence status; step S6: completing the diagnosis of an IOC and ISC mixed fault in the network based on an evidence status-guided suspicion priority fault diagnosis algorithm; the present invention can accurately identify the type and location of an IOC and ISC mixed fault in various mixed scenarios.

Description

Technical Field

[0001] The present invention relates to the field of fault diagnosis methods, in particular to a method for diagnosing a mixed type fault of intermittent open circuit and intermittent short circuit of a CAN bus. Background Art

[0002] CAN bus networks play a vital role in networked industrial systems, and their reliability therefore determines system performance and even operational safety. Intermittent connection failures are random, recurring, and short-duration connection issues that can degrade network reliability and, in severe cases, even lead to system failure. However, there is currently no diagnostic method for mixed intermittent connection failures, which involve both intermittent open circuits (IOCs) and intermittent short circuits (ISCs). This paper proposes a hybrid IOC and ISC fault diagnosis method for CAN bus networks. This method utilizes both data link layer and physical layer network signals when intermittent connection failures induce errors, analyzes error patterns, identifies mixed fault conditions, and locates the corresponding faults. First, by analyzing the error patterns of network communication, different fault types are defined, and the evidence status of the transmission path is derived by detecting the statistical significance of the alarms. Then, to specify the fault condition at the cable link level, an undirected graph-based transmission path-cable link mapping algorithm is developed using network topology information. The fault suspicion of each cable link in the network is evaluated based on the mapping relationship. Finally, an evidence-state-guided suspicion-prioritized fault diagnosis algorithm is developed to locate IOC and ISC faults separately. Case studies conducted on the constructed testbed demonstrate that the proposed method can accurately identify the type and location of mixed IOC and ISC faults in various mixed scenarios. Summary of the Invention

[0003] To solve the problems existing in the prior art, the present invention provides a mixed fault diagnosis method for CAN bus intermittent open circuit and intermittent short circuit. The present invention can accurately identify the type and location of IOC faults and ISC faults in mixed scenarios of various intermittent connection faults.

[0004] The specific technical solutions provided by the present invention are as follows:

[0005] The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method includes the following steps:

[0006] Step S1: collecting data link layer and physical layer double-layer network signals when communication errors occur;

[0007] Step S2: defining IOC alarms and ISC alarms based on the dual-layer network signals;

[0008] Step S3: deriving the IOC evidence status and ISC evidence status of the transmission path according to the IOC alarm and the ISC alarm;

[0009] Step S4: solving the mapping relationship between transmission paths and cable links based on the network topology information;

[0010] Step S5: Calculate the IOC suspicion and ISC suspicion of the cable link based on the mapping relationship and the two types of evidence status;

[0011] Step S6: Complete the diagnosis of mixed IOC and ISC faults in the network according to the evidence-state-oriented suspicion-priority fault diagnosis algorithm.

[0012] Preferably, step S1 includes the following sub-steps:

[0013] Sub-step S11: placing two FPGA-based sensors at two ends of the bus respectively;

[0014] Sub-step S12: Once each FPGA sensor detects an error frame, it collects the data link layer logic signal and physical layer analog signal of the interrupted frame.

[0015] Sub-step S13: extract the signal between the start of the frame and the last bit before the error flag of the interrupted frame, and define it as test data.

[0016] Sub-step S14: During normal network communication, the normal data frames sent by all nodes are recorded and defined as reference data.

[0017] Sub-step S15: extracting the source address of the interrupted frame from the address segment of the interrupted frame.

[0018] Preferably, step S2 is specifically:

[0019] For an interrupted frame collected by a sensor, determine whether the comparison result of the logic signal of the test data is consistent with the reference data with the same source address; if so, it means that the interrupted frame is only interrupted by the error frame, but is not damaged by any type of mixed fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of mixed fault, and the inconsistent bit is defined as an error bit, and the analog signal of the error bit is analyzed to generate corresponding alarms for different types of mixed faults;

[0020] Alarms include IOC alarms and ISC alarms;

[0021] An IOC alarm is an analog signal for the error bits of the test data collected by a sensor. If the differential voltage of the error bits is 0V, it means that the interrupted frame has been damaged by an IOC fault, and the IOC fault has occurred in the transmission path between the source node of the interrupted frame and the sensor. In this case, the sensor generates an IOC alarm.

[0022] The ISC alarm is an analog signal for the error bit of the test data collected by a sensor. If the differential voltage of the error bit is non-0V, it means that the interrupted frame has been damaged by the ISC fault. As for the ISC fault occurring in the transmission path between the source node of the interrupted frame and which sensor, it is necessary to determine by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors. If the ISC fault occurs in the transmission path between the source node of the interrupted frame and the sensor with the smaller error bit differential voltage, then the sensor with the smaller error bit differential voltage will generate an ISC alarm.

[0023] Preferably, step S3 specifically includes: deriving the evidentiary status of the transmission path pointed to by the alarm by evaluating the statistical significance of the alarms collected over a period of time, and using the IOC alarms and ISC alarms to derive the IOC evidentiary status and ISC evidentiary status of each transmission path respectively, and the derivation method is as follows:

[0024] If an IOC alarm is statistically significant, it indicates that the alarm is caused by an IOC, and the IOC evidence status of the transmission path pointed by the alarm is IOC positive. Conversely, if an IOC alarm is statistically insignificant, it indicates that the alarm is not caused by an IOC, but a false alarm caused by environmental factors, and the IOC evidence status of the transmission path pointed by the alarm is IOC negative.

[0025] The ISC evidence status is: if an ISC alarm is statistically significant, it means that the alarm is caused by ISC, and the ISC evidence status of the transmission path pointed to by the alarm is ISC positive; conversely, if an ISC alarm is statistically insignificant, it means that the alarm is not caused by ISC, but is a false alarm caused by environmental factors, and the ISC evidence status of the transmission path pointed to by the alarm is ISC negative.

[0026] Preferably, step S4 includes the following sub-steps:

[0027] Sub-step S41: using an undirected graph to describe the equivalent topology of the CAN network. In order to describe the connection relationship between network ports, an adjacency matrix of the undirected graph is defined.

[0028] Sub-step S42: establishing a transmission path-cable link mapping algorithm based on the undirected graph, wherein the mapping algorithm is established by finding a minimum set of edges between two vertices in the undirected graph, and the input of the algorithm includes a starting vertex associated with a starting network port of the path and an ending vertex associated with an ending network port of the path;

[0029] Sub-step S43: The output is a set of all cable links constituting the solved transmission path.

[0030] Preferably, step S5 is specifically:

[0031] For each cable link, the fault suspicion of the cable link is calculated by evaluating the overall degree of match between the cable link and the evidence status of all transmission paths containing the cable link. The transmission paths containing the cable link are provided by the mapping relationship between transmission paths and cable links provided by the undirected graph-based transmission path-cable link mapping algorithm. The IOC evidence status and ISC evidence status are used to calculate the IOC suspicion and ISC suspicion of each cable link, respectively. The calculation method is as follows:

[0032] For all transmission paths containing the cable link, a transmission path with an IOC positive evidence status increases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault matches the IOC positive evidence status; a transmission path with an IOC negative evidence status decreases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault does not match the IOC negative evidence status;

[0033] For all transmission paths containing the cable link, a transmission path with an ISC positive evidence status increases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault matches the ISC positive evidence status; a transmission path with an ISC negative evidence status decreases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault does not match the ISC negative evidence status.

[0034] Step S6 selects cable links in order of their suspicion to match the evidence status of the transmission path. The higher the suspicion of a cable link, the greater the likelihood of a fault and the higher the diagnostic priority. Diagnosis is complete when the selected fault location meets the following two conditions: (1) covering all positive evidence states and (2) avoiding any negative evidence states.

[0035] The technical effects of the CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method of the present invention are as follows:

[0036] 1. This paper proposes a diagnostic method for mixed intermittent open circuit and short circuit faults in CAN networks. This method uses the integrated information of the physical layer and data link layer during errors, analyzes the different error modes caused by IOC faults and ISC faults, and defines IOC alarms and ISC alarms.

[0037] 2. The present invention derives the IOC evidence status and ISC evidence status of each transmission path based on the statistical significance of the corresponding alarms.

[0038] 3. The present invention develops an undirected graph-based transmission path-cable link mapping algorithm to represent the transmission path according to the cable link set, so that the corresponding fault suspicion of each cable link can be calculated according to the corresponding evidence status of the transmission path.

[0039] 4. The evidence-state-oriented suspicion-priority fault diagnosis algorithm of the present invention is used to locate mixed IOC and ISC faults.

[0040] 5. The present invention can be implemented in various mixed scenarios of IOC and ISC, including single IOC fault mixed with single ISC fault mixed, single IOC fault mixed with multiple ISC faults, multiple IOC faults mixed with single ISC fault, and multiple IOC faults mixed with multiple ISC faults, to achieve diagnosis of IOC and ISC faults in the CAN network. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a diagram illustrating a mixed fault scenario of IOC and ISC in a CAN network of the present invention.

[0042] Figure 2 This is the overall flow chart of the IOC and ISC hybrid fault diagnosis framework of the present invention. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0044] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0045] The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method includes the following steps:

[0046] Step S1: collecting data link layer and physical layer double-layer network signals when communication errors occur;

[0047] Step S2: defining IOC alarms and ISC alarms based on the dual-layer network signals;

[0048] Step S3: deriving the IOC evidence status and ISC evidence status of the transmission path according to the IOC alarm and the ISC alarm;

[0049] Step S4: solving the mapping relationship between transmission paths and cable links based on the network topology information;

[0050] Step S5: Calculate the IOC suspicion and ISC suspicion of the cable link based on the mapping relationship and the two types of evidence status;

[0051] Step S6: Complete the diagnosis of mixed IOC and ISC faults in the network according to the evidence-state-oriented suspicion-priority fault diagnosis algorithm.

[0052] Step S1 of this embodiment includes the following sub-steps:

[0053] Sub-step S11: placing two FPGA-based sensors at two ends of the bus respectively;

[0054] Sub-step S12: Once each FPGA sensor detects an error frame (6 consecutive dominant bits), it collects the data link layer logic signal and physical layer analog signal of the interrupted frame.

[0055] Sub-step S13: extract the signal between the start of frame (SOF) and the last bit before the error flag of the interrupted frame, and define it as test data.

[0056] Sub-step S14: During normal network communication, the normal data frames sent by all nodes are recorded and defined as reference data.

[0057] Sub-step S15: extracting the source address of the interrupted frame from the address segment of the interrupted frame.

[0058] Step S2 of this embodiment is specifically as follows:

[0059] For an interrupted frame collected by a sensor, determine whether the comparison result of the logic signal of the test data is consistent with the reference data with the same source address; if so, it means that the interrupted frame is only interrupted by the error frame, but is not damaged by any type of mixed fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of mixed fault, and the inconsistent bit is defined as an error bit, and the analog signal of the error bit is analyzed to generate corresponding alarms for different types of mixed faults;

[0060] Alarms include IOC alarms and ISC alarms;

[0061] An IOC alarm is an analog signal for the error bits of the test data collected by a sensor. If the differential voltage of the error bits is 0V, it means that the interrupted frame has been damaged by an IOC fault, and the IOC fault has occurred in the transmission path between the source node of the interrupted frame and the sensor. In this case, the sensor generates an IOC alarm.

[0062] The ISC alarm is an analog signal for the error bit of the test data collected by a sensor. If the differential voltage of the error bit is non-0V, it means that the interrupted frame has been damaged by the ISC fault. As for the ISC fault occurring in the transmission path between the source node of the interrupted frame and which sensor, it is necessary to determine by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors. If the ISC fault occurs in the transmission path between the source node of the interrupted frame and the sensor with the smaller error bit differential voltage, then the sensor with the smaller error bit differential voltage will generate an ISC alarm.

[0063] Step S3 of this embodiment is specifically: by evaluating the statistical significance of alarms collected over a period of time, the evidentiary status of the transmission path pointed to by the alarms is derived. The IOC evidentiary status and ISC evidentiary status of each transmission path are derived using IOC alarms and ISC alarms respectively. The calculation method is as follows:

[0064] If an IOC alarm is statistically significant, it indicates that the alarm is caused by an IOC, and the IOC evidence status of the transmission path pointed by the alarm is IOC positive. Conversely, if an IOC alarm is statistically insignificant, it indicates that the alarm is not caused by an IOC, but a false alarm caused by environmental factors, and the IOC evidence status of the transmission path pointed by the alarm is IOC negative.

[0065] The ISC evidence status is: if an ISC alarm is statistically significant, it means that the alarm is caused by ISC, and the ISC evidence status of the transmission path pointed to by the alarm is ISC positive; conversely, if an ISC alarm is statistically insignificant, it means that the alarm is not caused by ISC, but is a false alarm caused by environmental factors, and the ISC evidence status of the transmission path pointed to by the alarm is ISC negative.

[0066] Step S4 of this embodiment includes the following sub-steps:

[0067] Sub-step S41: using an undirected graph to describe the equivalent topology of the CAN network. In order to describe the connection relationship between network ports, an adjacency matrix of the undirected graph is defined.

[0068] Sub-step S42: establishing a transmission path-cable link mapping algorithm based on the undirected graph, wherein the mapping algorithm is established by finding a minimum set of edges between two vertices in the undirected graph, and the input of the algorithm includes a starting vertex associated with a starting network port of the path and an ending vertex associated with an ending network port of the path;

[0069] Sub-step S43: The output is a set of all cable links constituting the solved transmission path.

[0070] Step S5 of this embodiment is specifically as follows:

[0071] For each cable link, the fault suspicion of the cable link is calculated by evaluating the overall degree of match between the cable link and the evidence status of all transmission paths containing the cable link. The transmission paths containing the cable link are provided by the mapping relationship between transmission paths and cable links provided by the undirected graph-based transmission path-cable link mapping algorithm. The IOC evidence status and ISC evidence status are used to calculate the IOC suspicion and ISC suspicion of each cable link, respectively. The calculation method is as follows:

[0072] For all transmission paths containing the cable link, a transmission path with an IOC positive evidence status increases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault matches the IOC positive evidence status; a transmission path with an IOC negative evidence status decreases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault does not match the IOC negative evidence status;

[0073] For all transmission paths containing the cable link, a transmission path with an ISC positive evidence status increases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault matches the ISC positive evidence status; a transmission path with an ISC negative evidence status decreases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault does not match the ISC negative evidence status.

[0074] Step S6 selects cable links in order of their suspicion to match the evidence status of the transmission path. The higher the suspicion of a cable link, the greater the likelihood of a fault and the higher the diagnostic priority. Diagnosis is complete when the selected fault location meets the following two conditions: (1) covering all positive evidence states and (2) avoiding any negative evidence states.

[0075] When this implementation plan is implemented,

[0076] CAN error handling mechanism: The CAN bus has two logical states: dominant and recessive. A differential voltage greater than 0.9V is considered dominant, while a differential voltage less than 0.5V is considered recessive. Any node in the network that detects a logic error transmits an error frame, interrupting the current data transmission. The error frame consists of six consecutive dominant bits. At this point, other nodes are aware of the error and transmit their own error frames. The resulting composite error frame is a superposition of error frames from different nodes, containing six to twelve consecutive dominant bits.

[0077] Mixed intermittent open circuit and intermittent short circuit faults: Based on the type of incorrect connection, they are divided into intermittent open circuit (IOC) and intermittent short circuit (ISC). Both types of faults will pull down the differential voltage of the bus, causing the bus logic state to change from dominant to recessive.

[0078] The main tasks of CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis are to identify and characterize the IOC fault and ISC fault types; for a certain type of fault, how to calculate the probability of the fault occurring on each cable line from the data with the corresponding error pattern; and when the two types of faults coexist, how to accurately locate the position of each type of fault based on the probability information.

[0079] The basic idea of ​​the method of the present invention is to analyze the destructive behavior of IOC faults and ISC faults on the signals within the CAN bus, obtain the characteristics of each fault type, and then diagnose each type of fault separately by integrating network topology information and the statistical significance of the corresponding fault characteristics.

[0080] The overall process for diagnosing mixed intermittent open and short circuit faults is as follows: First, sensors deployed at both ends of the bus collect data link and physical layer network signals during communication errors. The error data is examined for corruption patterns and the source address is analyzed to generate separate alarms corresponding to IOC and ISC faults, respectively. Second, the evidence status of the transmission path is derived based on the statistical significance of the corresponding alarms. Then, based on network topology information, an undirected graph-based transmission path-to-cable link mapping algorithm is applied to refine the transmission path down to the cable link level. Using this mapping relationship, the fault suspicion of each cable link is calculated based on the evidence status of the transmission path. Finally, a search-based algorithm is designed to locate IOC and ISC faults, using the evidence status of the transmission path as a guide for the diagnostic scope and the fault suspicion of the cable link as the basis for the diagnostic order. Each component is described in detail below.

[0081] (1) Collecting data link layer and physical layer network signals during communication errors: Two FPGA-based sensors are placed at the two ends of the bus (i.e., the two terminal resistors). Once each sensor detects an error frame (six consecutive dominant bits, the minimum length of an error flag defined by the CAN protocol), it collects the data link layer logic signal and physical layer analog signal of the interrupted frame. To facilitate subsequent analysis, the following assumptions are made.

[0082] The signal between the start of frame (SOF) and the last bit before the error flag of the interrupted frame is defined as test data.

[0083] Normal frames of all nodes are recorded during normal communication in the network and are defined as reference data.

[0084] The source address of the interrupted frame can be obtained through the address segment.

[0085] (2) Definition of alarms for mixed faults of intermittent open circuit and intermittent short circuit: For an interrupted frame collected by a sensor, if the comparison result of the logic signal of the test data and the reference data with the same source address is consistent, it means that the interrupted frame is only interrupted by an error frame, but is not damaged by any type of mixed fault, and no alarm is generated. For an interrupted frame collected by a sensor, if the comparison result of the logic signal of the test data and the reference data with the same address is inconsistent, it means that the interrupted frame is damaged by a certain type of mixed fault, and the inconsistent bit is defined as an error bit, and the analog signal of the error bit is analyzed as follows to generate corresponding alarms for different types of mixed faults.

[0086] IOC alarm: For the analog signal of the erroneous bit of the test data collected by a sensor, if the differential voltage of the erroneous bit is 0V, it means that the interrupted frame is damaged by the IOC fault, and the IOC fault occurs in the transmission path between the source node of the interrupted frame and the sensor, then the sensor generates an IOC alarm.

[0087] ISC alarm: For the analog signal of the error bit of the test data collected by a sensor, if the differential voltage of the error bit is non-0V, it means that the interrupted frame has been damaged by the ISC fault. As for the ISC fault occurring in the transmission path between the source node of the interrupted frame and which sensor, it is necessary to determine it by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors. If the ISC fault occurs in the transmission path between the source node of the interrupted frame and the sensor with the smaller error bit differential voltage, then the sensor with the smaller error bit differential voltage will generate an ISC alarm.

[0088] Subsequently, the IOC alarm and the ISC alarm are used to locate the IOC fault and the ISC fault respectively. That is, a series of analyses are performed on the IOC alarm to ultimately locate the IOC fault, and a series of analyses are performed on the ISC alarm to ultimately locate the ISC fault.

[0089] (3) Derivation of the Evidence Status of a Transmission Path: The evidence status of a transmission path is used to describe whether a certain mixed-type fault has occurred on the transmission path. Because environmental factors such as electromagnetic interference (EMI) may cause a small number of false alarms, the evidence status of the transmission path to which the alarm refers is derived by evaluating the statistical significance of alarms collected over a period of time. The IOC and ISC evidence status of each transmission path are derived using IOC and ISC alarms, respectively. The derivation details are as follows.

[0090] IOC Evidence Status: If an IOC alert is statistically significant, indicating that the alert is caused by an IOC, the IOC evidence status for the transmission path pointed to by the alert is IOC Positive. Conversely, if an IOC alert is statistically insignificant, indicating that the alert is not caused by an IOC but is a false alarm caused by environmental factors, the IOC evidence status for the transmission path pointed to by the alert is IOC Negative.

[0091] ISC Evidence Status: The derivation logic is the same as above, except that ISC alerts are used instead of IOC alerts.

[0092] (4) Mapping transmission paths to cable links: In order to locate the fault on a specific cable link, the transmission path needs to be further refined to the cable link level, so the mapping relationship between the transmission path and the cable link needs to be given. First, an undirected graph is used to describe the equivalent topology of the CAN network. In order to describe the connection relationship between network ports, the adjacency matrix of the undirected graph is defined. Then, based on the transmission path-cable link mapping algorithm of the undirected graph, the mapping algorithm is established by finding the minimum edge set between two vertices in the undirected graph. The input of the algorithm includes the starting vertex related to the starting network port of the path and the ending vertex related to the ending network port of the path; the output is a set of all cable links that constitute the transmission path to be solved.

[0093] (5) Calculating the cable link's fault suspicion: The cable link's fault suspicion is used to describe the likelihood of a mixed-type fault occurring on the cable link. For each cable link, the cable link's fault suspicion is calculated by evaluating the overall degree of match between the cable link and the evidence status of all transmission paths containing the cable link. The transmission paths containing the cable link are provided by a mapping relationship between transmission paths and cable links using an undirected graph-based transmission path-cable link mapping algorithm. The IOC and ISC evidence statuses are used to calculate the IOC and ISC suspicions of each cable link, respectively. The calculation details are as follows.

[0094] IOC suspicion: For all transmission paths containing the cable link, a transmission path with an IOC positive evidence status increases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault matches the IOC positive evidence status; a transmission path with an IOC negative evidence status decreases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault does not match the IOC negative evidence status.

[0095] ISC Suspicion: The calculation logic is the same as above, except that the ISC evidence status is used instead of the IOC evidence status.

[0096] (6) Evidence-state-guided suspicion-prioritized fault diagnosis algorithm: The locations of all faults in the network should simultaneously match all evidence states. That is, two conditions must be met simultaneously: first, all positive evidence states must be covered, and second, any negative evidence states must be avoided. Furthermore, the higher the suspicion of a cable link, the greater the likelihood of a fault, and the higher the diagnostic priority should be. Therefore, the logic of hybrid IC fault diagnosis is to select cable links in order of their suspicion until all evidence states are fully matched.

[0097] 3. Conclusion and Effect

[0098] The present invention proposes a method for diagnosing mixed faults of intermittent open circuit and intermittent short circuit of CAN bus, which utilizes the integrated information of physical layer and data link layer at the time of error. Different error modes caused by IOC fault and ISC fault are analyzed, and corresponding alarms are defined. The evidence status of each transmission path is derived according to the statistical significance of the corresponding alarm. An undirected graph-based transmission path-cable link mapping algorithm is developed to represent the transmission path according to the cable link set, so that the fault suspicion of each link can be calculated according to the evidence status of the path. The evidence status-oriented suspicion priority fault diagnosis algorithm is used to locate IOC fault and ISC fault. It can be implemented in various mixed scenarios, including a single IOC fault mixed with a single ISC fault, a single IOC fault mixed with multiple ISC faults, multiple IOC faults mixed with a single ISC error, and a mixture of multiple IOC faults and multiple ISC errors, to diagnose IOC and ISC faults in CAN network.

Claims

1. A mixed fault diagnosis method for intermittent open circuit and intermittent short circuit of CAN bus, characterized in that: The following steps are involved: Step S1: collecting data link layer and physical layer double-layer network signals when communication errors occur; Step S2: defining IOC alarms and ISC alarms based on the dual-layer network signals; Step S3: deriving the IOC evidence status and ISC evidence status of the transmission path according to the IOC alarm and the ISC alarm; Step S4: solving the mapping relationship between transmission paths and cable links based on the network topology information; Step S5: Calculate the IOC suspicion and ISC suspicion of the cable link based on the mapping relationship and the two types of evidence status; Step S6: Complete the diagnosis of mixed IOC and ISC faults in the network according to the evidence-state-oriented suspicion-priority fault diagnosis algorithm.

2. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: The step S1 includes the following sub-steps: Sub-step S11: placing two FPGA-based sensors at two ends of the bus respectively; Sub-step S12: Once each FPGA sensor detects an error frame, it collects the data link layer logic signal and physical layer analog signal of the interrupted frame; Sub-step S13: extracting the signal between the start of the frame and the last bit before the error flag of the interrupted frame, and defining it as test data; Sub-step S14: recording normal data frames sent by all nodes during normal network communication and defining them as reference data; Sub-step S15: extracting the source address of the interrupted frame from the address segment of the interrupted frame.

3. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: The step S2 is specifically as follows: For an interrupted frame collected by a sensor, determine whether the comparison result of the logic signal of the test data is consistent with the reference data with the same source address; if so, it means that the interrupted frame is only interrupted by the error frame, but is not damaged by any type of mixed fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of mixed fault, and the inconsistent bit is defined as an error bit, and the analog signal of the error bit is analyzed to generate corresponding alarms for different types of mixed faults; The alarms include IOC alarms and ISC alarms; The IOC alarm is an analog signal for the error bit of the test data collected by a sensor. If the differential voltage of the error bit is 0V, it means that the interrupted frame has been damaged by the IOC fault, and the IOC fault has occurred in the transmission path between the source node of the interrupted frame and the sensor, then the sensor generates an IOC alarm. The ISC alarm is an analog signal for the error bit of the test data collected by a sensor. If the differential voltage of the error bit is non-0V, it means that the interrupted frame has been damaged by the ISC fault. As for the ISC fault occurring on the transmission path between the source node of the interrupted frame and which sensor, it is necessary to determine by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors. If the ISC fault occurs on the transmission path between the source node of the interrupted frame and the sensor with the smaller error bit differential voltage, then the sensor with the smaller error bit differential voltage will generate an ISC alarm.

4. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: Step S3 specifically includes: evaluating the statistical significance of alarms collected over a period of time to derive the evidentiary status of the transmission path pointed to by the alarms, using IOC alarms and ISC alarms to derive the IOC evidentiary status and ISC evidentiary status of each transmission path, respectively. The calculation method is as follows: The IOC evidence status is: if an IOC alarm is statistically significant, indicating that the alarm is caused by IOC, then the IOC evidence status of the transmission path pointed to by the alarm is IOC positive; On the other hand, if an IOC alarm is statistically insignificant, it means that the alarm is not caused by IOC but is a false alarm caused by environmental factors. In this case, the IOC evidence status of the transmission path pointed to by the alarm is IOC negative. The ISC evidence status is: if an ISC alarm is statistically significant, indicating that the alarm is caused by ISC, then the ISC evidence status of the transmission path pointed to by the alarm is ISC positive; On the contrary, if an ISC alarm is statistically insignificant, it means that the alarm is not caused by ISC but is a false alarm caused by environmental factors. In this case, the ISC evidence status of the transmission path pointed to by the alarm is ISC negative.

5. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: The step S4 includes the following sub-steps: Sub-step S41: using an undirected graph to describe the equivalent topology of the CAN network. In order to describe the connection relationship between network ports, an adjacency matrix of the undirected graph is defined. Sub-step S42: establishing a transmission path-cable link mapping algorithm based on the undirected graph, wherein the mapping algorithm is established by finding a minimum set of edges between two vertices in the undirected graph, and the input of the algorithm includes a starting vertex associated with a starting network port of the path and an ending vertex associated with an ending network port of the path; Sub-step S43: The output is a set of all cable links constituting the solved transmission path.

6. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: The step S5 is specifically as follows: For each cable link, the fault suspicion of the cable link is calculated by evaluating the overall degree of match between the cable link and the evidence status of all transmission paths containing the cable link. The transmission paths containing the cable link are provided by the mapping relationship between transmission paths and cable links provided by the undirected graph-based transmission path-cable link mapping algorithm. The IOC evidence status and ISC evidence status are used to calculate the IOC suspicion and ISC suspicion of each cable link, respectively. The calculation method is as follows: For all transmission paths containing the cable link, a transmission path with an IOC positive evidence status increases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault matches the IOC positive evidence status; a transmission path with an IOC negative evidence status decreases the IOC suspicion of the cable link by 1, because the situation where the cable link has an IOC fault does not match the IOC negative evidence status; For all transmission paths containing the cable link, a transmission path with an ISC positive evidence status increases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault matches the ISC positive evidence status; a transmission path with an ISC negative evidence status decreases the ISC suspicion of the cable link by 1, because the situation where the cable link has an ISC fault does not match the ISC negative evidence status.

7. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1 is characterized in that: Step S6 selects cable links in order of their suspicion to match the evidence status of the transmission path; the higher the suspicion of the cable link, the greater the possibility of a fault and the higher the priority of the diagnosis; the diagnosis is completed when the selected fault location meets the following two conditions at the same time: one is to cover all positive evidence states; the other is to avoid any negative evidence states.

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