Hybrid fault diagnosis method for intermittent open circuit and intermittent short circuit of CAN bus

Abstract

The invention discloses a hybrid fault diagnosis method for an intermittent open circuit (IOC) and an intermittent short circuit (ISC) of a CAN (Controller Area Network) bus. The hybrid fault diagnosis method comprises the following steps of S1, acquiring double-layer network signals of a data link layer and a physical layer when a communication error occurs; s2, defining an IOC alarm and an ISC alarm according to the double-layer network signal; s3, deriving an IOC evidence state and an ISC evidence state of the transmission path according to the IOC alarm and the ISC alarm; s4, solving a mapping relation from a transmission path to a cable link according to the network topology information; s5, calculating the IOC suspicion degree and the ISC suspicion degree of the cable link according to the mapping relation and the two types of evidence states; s6, completing the diagnosis of IOC and ISC hybrid faults in the network according to a suspicion degree priority fault diagnosis algorithm guided by an evidence state; according to the invention, the type and the position of the IOC and ISC hybrid fault can be accurately identified in various hybrid scenes.

Description

Technical Field

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

[0002] CAN bus network plays an important role in networked industrial systems, so the reliability of CAN bus network determines the system performance and even the operational safety. Intermittent connection failure is a random, recurring, short-duration connection problem, which may reduce the reliability of the network and even cause the whole system to fail in severe cases. However, there is no diagnostic method for mixed intermittent connection failure with both intermittent open circuit (IOC) and intermittent short circuit (ISC) problems. This paper proposes a CAN bus IOC and ISC mixed fault diagnosis method, which uses the data link layer and physical layer double-layer network signals when intermittent connection failure induces errors, analyzes the error mode, identifies the mixed fault situation, and locates the corresponding fault. First, the alarms of different fault types are defined by analyzing the error mode of network communication, and the evidence status of the transmission path is derived by detecting the statistical significance of the alarm. Then, in order to concretize the fault situation to the cable link level, an undirected graph-based transmission path-cable link mapping algorithm is developed using network topology information, and 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 respectively. Case study results conducted on the constructed testbed show that the proposed method can accurately identify the types and locations of IOC and ISC mixed faults in various mixed scenarios. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a mixed fault diagnosis method for intermittent open circuit and intermittent short circuit of CAN bus, which can accurately identify the type and location of IOC fault and ISC fault 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 alarm and ISC alarm according to the double-layer network signal;

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

[0009] Step S4: solving the mapping relationship between the transmission path and the cable link according to the network topology information;

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

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

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

[0013] Sub-step S11: arranging 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 frame start 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, 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 specifically includes:

[0019] For an interrupted frame collected by a sensor, it is determined whether the comparison result of the logic signal of the test data is consistent with the reference data having 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 the mixed type fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of the mixed type 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 the mixed type faults;

[0020] Alarms include IOC alarms and ISC alarms;

[0021] 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 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;

[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 not 0V, it means that the interrupted frame is 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 respectively. If the ISC fault occurs on the transmission path between the source node of the interrupted frame and the sensor with a smaller differential voltage of the error bit, then the sensor with a smaller differential voltage of the error bit generates an ISC alarm.

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

[0024] The IOC evidence status is: if an IOC alarm is statistically significant, it means that the alarm is caused by IOC, and the IOC evidence status of the transmission path pointed by the alarm is IOC positive; on the contrary, if an IOC alarm is statistically insignificant, it means that the alarm is not caused by 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 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 topological structure of the CAN network, and defining an adjacency matrix of the undirected graph to describe the connection relationship between network ports;

[0028] Sub-step S42: establishing a transmission path-cable link mapping algorithm based on an undirected graph, wherein the mapping algorithm is established by finding a minimum edge set 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 quantity 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 matching degree between the cable link and the evidence status of all transmission paths including the cable link, wherein the transmission path including the cable link is provided by the mapping relationship between the transmission path and the cable link provided by the transmission path-cable link mapping algorithm based on an undirected graph. The IOC evidence status and the ISC evidence status are used to calculate the IOC suspicion and the ISC suspicion of each cable link, respectively, and the calculation method is as follows:

[0032] For all transmission paths including 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 that 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 that the cable link has an IOC fault does not match the IOC negative evidence status;

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

[0034] Step S6 selects cable links in order of suspicion to match the evidence status of the transmission path. The higher the suspicion of the cable link, the greater the possibility of failure and the higher the priority of diagnosis. The diagnosis is completed when the selected fault location meets the following two conditions: one is to cover all positive evidence status; the other is to avoid any negative evidence status.

[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. The present invention proposes a diagnosis method for mixed intermittent open circuit and intermittent short circuit faults in CAN network. The method uses the integrated information of physical layer and data link layer at the time of error, analyzes the different error modes caused by IOC fault and ISC fault, and defines IOC alarm and ISC alarm.

[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 a 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, 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 The figure illustrates the mixed fault scenario of IOC and ISC in the CAN network of the present invention.

[0042] Figure 2 It is an 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 implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept 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 alarm and ISC alarm according to the double-layer network signal;

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

[0049] Step S4: solving the mapping relationship between the transmission path and the cable link according to the network topology information;

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

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

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

[0053] Sub-step S11: arranging 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) of the interrupted frame and the last bit before the error flag, and define it as test data.

[0056] Sub-step S14: During normal network communication, 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, it is determined whether the comparison result of the logic signal of the test data is consistent with the reference data having 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 the mixed type fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of the mixed type 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 the mixed type faults;

[0060] Alarms include IOC alarms and ISC alarms;

[0061] 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 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;

[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 not 0V, it means that the interrupted frame is 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 respectively. If the ISC fault occurs on the transmission path between the source node of the interrupted frame and the sensor with a smaller differential voltage of the error bit, then the sensor with a smaller differential voltage of the error bit generates an ISC alarm.

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

[0064] The IOC evidence status is: if an IOC alarm is statistically significant, it means that the alarm is caused by IOC, and the IOC evidence status of the transmission path pointed by the alarm is IOC positive; on the contrary, if an IOC alarm is statistically insignificant, it means that the alarm is not caused by 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 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 topological structure of the CAN network, and defining an adjacency matrix of the undirected graph to describe the connection relationship between network ports;

[0068] Sub-step S42: establishing a transmission path-cable link mapping algorithm based on an undirected graph, wherein the mapping algorithm is established by finding a minimum edge set 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 quantity 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 matching degree between the cable link and the evidence status of all transmission paths including the cable link, wherein the transmission path including the cable link is provided by the mapping relationship between the transmission path and the cable link provided by the transmission path-cable link mapping algorithm based on an undirected graph. The IOC evidence status and the ISC evidence status are used to calculate the IOC suspicion and the ISC suspicion of each cable link, respectively, and the calculation method is as follows:

[0072] For all transmission paths including 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 that 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 that the cable link has an IOC fault does not match the IOC negative evidence status;

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

[0074] Step S6 selects cable links in order of suspicion to match the evidence status of the transmission path. The higher the suspicion of the cable link, the greater the possibility of failure and the higher the priority of diagnosis. The diagnosis is completed when the selected fault location meets the following two conditions: one is to cover all positive evidence status; the other is to avoid any negative evidence status.

[0075] When this implementation plan is implemented,

[0076] CAN error handling mechanism: The CAN bus is divided into two logical states: dominant and recessive. The differential voltage is greater than 0.9V for dominant state, and the differential voltage is less than 0.5V for recessive state. Any node in the network that detects a logic error will send an error frame to interrupt the current data transmission. The error frame contains 6 consecutive dominant bits. At this time, other nodes can know the error and send their own error frames. The final synthesized error frame is the superposition of error frames from different nodes, which contains 6 to 12 consecutive dominant bits.

[0077] Mixed intermittent open circuit and intermittent short circuit faults: According to 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 and change the logic state of the bus 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; 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 in the CAN bus, obtain the characteristics of each fault type, and then diagnose each type of fault separately by integrating the network topology information and the statistical significance of the corresponding fault characteristics.

[0080] The overall process of mixed fault diagnosis of intermittent open circuit and intermittent short circuit is as follows: First, the sensors deployed at both ends of the bus collect the data link layer and physical layer double-layer network signals when the communication error occurs, and check the damage mode of the error data. At the same time, the source address is analyzed to generate different alarms corresponding to IOC faults and ISC faults. Secondly, the evidence status of the transmission path is derived according to the statistical significance of the corresponding alarms. Then, based on the network topology information, the transmission path-cable link mapping algorithm based on the undirected graph is applied to refine the transmission path to the cable link level. With the help of the mapping relationship, the fault suspicion of each cable link is calculated from the evidence status of the transmission path. Finally, with the evidence status of the transmission path as the guide for the diagnosis range and the fault suspicion of the cable link as the basis for the diagnosis order, a search algorithm is designed to locate the IOC fault and ISC fault. Each part is introduced in detail as follows.

[0081] (1) Collecting data link layer and physical layer double-layer network signals when communication errors occur: Two FPGA-based sensors are placed at the two ends of the bus (i.e., two terminal resistors). Once each sensor detects an error frame (6 consecutive dominant bits, i.e., the minimum length of the 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) of the interrupted frame and the last bit before the error flag is defined as the test data.

[0083] The 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 intermittent open circuit and intermittent short circuit mixed faults: 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 the 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 an analog signal of an erroneous bit of 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 an analog signal of an error bit in test data collected by a sensor, if the differential voltage of the error bit is not 0V, it means that the interrupted frame is damaged by the ISC fault. As for the transmission path between the source node of the interrupted frame and which sensor the ISC fault occurs on, it is necessary to judge by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors respectively. If the ISC fault occurs on the transmission path between the source node of the interrupted frame and the sensor with a smaller differential voltage of the error bit, then the sensor with a smaller differential voltage of the error bit generates 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 eventually locate the IOC fault, and a series of analyses are performed on the ISC alarm to eventually locate the ISC fault.

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

[0090] IOC evidence status: If an IOC alarm is statistically significant, it means that the alarm is caused by IOC, and the IOC evidence status of the transmission path pointed to by the alarm is IOC positive. On the contrary, if an IOC alarm is statistically insignificant, it means that the alarm is not caused by IOC, but a false alarm caused by environmental factors, and the IOC evidence status of the transmission path pointed to by the alarm 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 path to cable link: 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 it is necessary to give a mapping relationship between the transmission path and the cable link. First, an undirected graph is used to describe the equivalent topological structure 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, a 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 fault suspicion of the cable link: The fault suspicion of the cable link is used to describe the possibility of a certain mixed type of fault occurring on the cable link. For each cable link, the fault suspicion of the cable link is calculated by evaluating the overall matching degree between the evidence status of the cable link and all transmission paths containing the cable link, wherein the transmission path containing the cable link is provided by the mapping relationship between the transmission path and the cable link provided by the transmission path-cable link mapping algorithm based on an undirected graph. The IOC suspicion and ISC suspicion of each cable link are calculated using the IOC evidence status and the ISC evidence status, respectively. The calculation details are as follows.

[0094] IOC suspicion: For all transmission paths including 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 that 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 that 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-oriented suspicion-priority fault diagnosis algorithm: The locations of all faults in the network should match all evidence states at the same time, that is, two conditions should be met at the same time: one is to cover all positive evidence states, and the other is to avoid any negative evidence states. In addition, the higher the suspicion of the cable link, the greater the possibility of failure, and the higher the priority of diagnosis should be. Therefore, the logic of hybrid IC fault diagnosis is to select cable links in the order of the suspicion of the cable link until all evidence states are fully matched.

[0097] 3. Conclusion and Effect

[0098] The present invention proposes a diagnosis method for a mixed type fault of intermittent open circuit and intermittent short circuit of a CAN bus, which utilizes the integrated information of the physical layer and the data link layer at the time of error. Different error modes caused by IOC faults and ISC faults are analyzed, and corresponding alarms are defined. The evidence status of each transmission path is derived according to the statistical significance of the corresponding alarms. 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 faults and ISC faults. The diagnosis of IOC and ISC faults in a CAN network 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 multiple IOC faults mixed with multiple ISC errors.

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 alarm and ISC alarm according to the double-layer network signal; Step S3: deriving the IOC evidence status and the ISC evidence status of the transmission path according to the IOC alarm and the ISC alarm; Step S4: solving the mapping relationship between the transmission path and the cable link according to the network topology information; Step S5: Calculate the IOC suspicion and ISC suspicion of the cable link according to the mapping relationship and the two types of evidence status; Step S6: According to the evidence-state-oriented suspicion-priority fault diagnosis algorithm, the diagnosis of mixed IOC and ISC faults in the network is completed.

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 comprises the following sub-steps: Sub-step S11: arranging 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: extract the signal between the frame start and the last bit before the error flag of the interrupted frame, and define it as test data. Sub-step S14: During normal network communication, normal data frames sent by all nodes are recorded and defined 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, characterized in that: The step S2 is specifically as follows: For an interrupted frame collected by a sensor, it is determined whether the comparison result of the logic signal of the test data is consistent with the reference data having 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 the mixed type fault, and no alarm is generated; if not, it means that the interrupted frame is damaged by a certain type of the mixed type 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 the mixed type faults; The alarms include IOC alarms and ISC alarms; The IOC alarm is an analog signal of an 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 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; The ISC alarm is an analog signal of an error bit of test data collected by a sensor. If the differential voltage of the error bit is not 0V, it means that the interrupted frame is damaged by the ISC fault. As for the transmission path between the source node of the interrupted frame and which sensor the ISC fault occurs on, it is necessary to judge by comparing the differential voltages of the error bits of the interrupted frame collected by the two sensors respectively. If the ISC fault occurs on the transmission path between the source node of the interrupted frame and the sensor with a smaller differential voltage of the error bit, then the sensor with a smaller differential voltage of the error bit generates an ISC alarm.

4. The CAN bus intermittent open circuit and intermittent short circuit mixed fault diagnosis method according to claim 1, characterized in that: The step S3 is specifically: deriving the evidence status of the transmission path pointed to by the alarm by evaluating the statistical significance of the alarms collected within a period of time, and using the IOC alarm and the ISC alarm to derive the IOC evidence status and the ISC evidence status of each transmission path respectively, and the calculation method is as follows: The IOC evidence status is that 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 contrary, if an IOC alarm is statistically insignificant, it means that the alarm is not caused by IOC, but 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, characterized in that: The step S4 comprises the following sub-steps: Sub-step S41: using an undirected graph to describe the equivalent topological structure of the CAN network, and defining an adjacency matrix of the undirected graph to describe the connection relationship between network ports; Sub-step S42: establishing a transmission path-cable link mapping algorithm based on an undirected graph, wherein the mapping algorithm is established by finding a minimum edge set 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 quantity 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, 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 matching degree between the cable link and the evidence status of all transmission paths including the cable link, wherein the transmission path including the cable link is provided by the mapping relationship between the transmission path and the cable link provided by the transmission path-cable link mapping algorithm based on an undirected graph. The IOC evidence status and the ISC evidence status are used to calculate the IOC suspicion and the ISC suspicion of each cable link, respectively, and the calculation method is as follows: For all transmission paths including 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 that 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 that the cable link has an IOC fault does not match the IOC negative evidence status; For all transmission paths including the cable link, a transmission path with an evidence status of ISC positive increases the ISC suspicion of the cable link by 1, because the situation that the cable link has an ISC fault matches the ISC positive evidence status; a transmission path with an evidence status of ISC negative decreases the ISC suspicion of the cable link by 1, because the situation that 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, characterized in that: The step S6 selects the cable links in order of the suspicion of the cable links to match the evidence status of the transmission path. The higher the suspicion of the cable link, the greater the possibility of failure and the higher the priority of diagnosis. The diagnosis is completed when the selected fault location meets the following two conditions at the same time: first, all positive evidence status is covered; second, any negative evidence status is avoided.

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