Patent Publication Number: US-10316812-B2

Title: Hierarchical fault diagnosis and prognosis of a system

Description:
INTRODUCTION 
     Internal combustion engines are often used as torque-generating devices in vehicles, power plants, and a wide range of other systems. In general, a starter motor may be energized during an engine starting operation to crank the engine to a threshold starting speed sufficient for drawing a mixture of fuel and air into the engine&#39;s cylinders. As part of the starter circuit, a starter solenoid may be activated in response to motion of an ignition key or depression of a start button. Rotation of the ignition key or depression of the start button requests closing of the starter circuit and delivery of an electrical current from an auxiliary battery to the starter solenoid. The energized starter solenoid closes a switch to allow the battery current to energize the starter motor and commence cranking of the engine. 
     When the starter motor is fully energized, a pinion gear of the starter translates into meshed engagement with an engine flywheel, with output torque from the starter motor rotating the flywheel to the threshold starting speed. The solenoid then disengages the pinion gear from the flywheel when the engine has successfully started. A fuel delivery system thereafter feeds fuel into the engine&#39;s cylinders to sustain engine rotation via regulation of the internal combustion process. 
     Control of an engine starting system and other systems involves the complex interaction of multiple different subsystems, as well as communication with associated electronic control units, communications links, electrical switches, and relays. For instance, the engine starting function described above involves control of various subsystems such as the auxiliary battery and a connected power distribution system, starter solenoid, starter motor, and fuel delivery system. Engine parameters are also closely monitored and controlled to ensure proper operation. Degradation of a given interconnected subsystem or subsystem-level electronic control unit may affect the performance of one or more interconnected subsystems, possibly resulting in a reported fault mode, e.g., a “no-start” or “no-crank” fault in the example engine starting function noted above. While various approaches exist for detecting a fault mode in a given subsystem, there remains a need for holistic consideration of the system and its constituent subsystems when isolating a root cause of a given failure mode. 
     SUMMARY 
     A method is disclosed herein for diagnosing the state of health of a system having multiple subsystems or components, e.g., an engine starting system as described herein, and for identifying a “root cause subsystem” as a likely root cause of an impending or present system fault mode. Different fault modes may occur in different systems. Due to the nature of the various subsystems constituting a given system, degradation of one or more subsystems may adversely affect the performance of other subsystems or a state of health of the system as a whole. Hence, new types of fault modes may emerge over time as a result of complex interaction of the subsystems. For example, a faulty auxiliary battery may result in an extended engine crank time, which in turn may impair the performance or structural integrity of the starter motor. 
     The present approach is intended to improve upon existing methodologies that are limited to diagnosing the performance of a subsystem, such as by using individual subsystem-specific controllers to compare measured parameters to calibrated values. For instance, individual algorithms may be used to separately diagnose the auxiliary battery, starter motor, or fuel delivery system. The method disclosed herein may compliment such subsystem-focused techniques. Specifically, the method operates by assigning a hierarchical priority level to multiple possible fault modes. The root cause of a particular failure mode may be identified using the assigned priority level and a fault report matrix. Thereafter, an appropriate control action may be executed in response to the identified root cause. Thus, states of health of the individual subsystems are determined and thereafter evaluated according to an assigned hierarchical order of precedence, with the least healthy of the subsystems identified and acted upon as the most likely root cause of the fault mode. 
     An example method for diagnosing a fault mode in a system having multiple subsystems includes recording, in memory of a controller, a hierarchical precedence rule that assigns a relative priority level to a plurality of fault modes of the system. The method also includes recording, in a fault report matrix, one or more fault reports indicative of a corresponding one or more of the fault modes, and then using the hierarchical precedence rule to determine the assigned relative priority level for the fault reports. 
     Furthermore, the method may include identifying a root cause subsystem of the system, i.e., a subsystem having the highest of the assigned priority levels, and then executing a control action with respect to the system via the controller responsive to the identified root cause subsystem. The control action may include recording a diagnostic code and/or transmitting a message indicative of the identified root cause subsystem. Thus, the present holistic method is intended as an improvement to the operation and function of existing diagnostic machines and processes, making the overall diagnostic and prognosis of the system more efficient and useful relative to subsystem-focused methodologies. 
     Recording the fault reports may include recording one or more fault reports for corresponding subsystems, with the reports provided from electronic control units corresponding to such subsystems, and/or recording a subsystem fault report identifying a detected fault mode or state of health of one or more of the subsystems. 
     The predetermined event in an example engine starting application may be an ignition cycle or a key cycle initiating operation of the system. The subsystems in such an engine starting application may include an auxiliary battery, a starter motor, a starter solenoid, an alternator, and a fuel delivery system. 
     A system is also disclosed that includes a plurality of subsystems, at least one of which includes an electronic control unit operable, when active, for outputting an embedded fault report indicative of a fault mode of the corresponding subsystem. When the electronic control unit is not operable, this may be indicated by an absence of such an embedded fault report. The system also includes a controller in communication with the various subsystems. The controller is programmed with a hierarchical precedence rule that assigns a relative priority level to a plurality of system fault modes, and is configured to diagnose a fault mode of the system by executing the method noted above. 
     Also disclosed herein is a computer-readable medium on which is recorded a hierarchical precedence rule that assigns a relative priority level to a plurality of fault modes of a system and diagnostic instructions, the execution of which by a controller causes the controller to execute the method noted above. 
     The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiments and best modes for carrying out the disclosure when taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic illustration of a vehicle and a controller programmed to execute a method for diagnosing and evaluating an example engine starting system. 
         FIG. 2  is a representative fault report matrix that may be populated and used as part of the present method. 
         FIG. 3  is a sample graphical illustration of an application of hierarchical precedence within the fault report matrix of  FIG. 2 . 
         FIG. 4  is a flow chart describing an embodiment of a method for diagnosing and evaluating the engine starting system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components, a vehicle  10  is depicted in  FIG. 1  as a non-limiting example embodiment of a top-level system having multiple interrelated subsystems. The vehicle  10  is used hereinafter to illustrate a non-limiting type of system that lends itself to the beneficial use of a hierarchical and holistic diagnostic method  100 , an example of which is depicted in  FIG. 4  and explained below. The method  100  may also be readily applied to non-vehicular systems and subsystems other than those described herein. For illustrative clarity and consistency, the vehicle  10  of  FIG. 1  will be described hereinafter in the context of an engine starting system  28  without limiting applications of the method  100  to systems in the form of the vehicle  10  or the engine starting system  28 . 
     The vehicle  10  includes an internal combustion engine (E)  12  that is coupled to a transmission (T)  14 , with the latter having internal gear sets, rotating and/or braking clutches, and interconnecting members (not shown). The engine  12  may include an input member  13  and an output member  15 . The output member  15  may be coupled to an input member  17  of the transmission  14  via a clutch device C 1 , e.g., a hydrodynamic torque converter assembly or a friction clutch. Engine torque (arrow T E ) is transferred via operation of the clutch device C 1  from the output member  15  of the engine  12  to the input member  17  of the transmission  14 . In turn, input torque (arrow T I ) is transferred from the input member  17 , through the transmission  14 , and to an output member  19  of the transmission  14 , with output torque (arrow T O ) from the transmission  14  ultimately powering drive wheels  22  of the vehicle  10  via one or more drive axles  21 . 
     The engine  12  is selectively cranked and started via the engine starting system  28 , which is used herein for illustrative purposes as an example system to which the method  100  is applied. Specifically, the engine starting system  28  may include an auxiliary battery (B)  18  that, in a simplified illustrative embodiment, is electrically connected to a starter solenoid (S)  24  via a starter switch (SS), e.g., a key-operated or button-activated switch. The starter solenoid  24 , when energized by the auxiliary battery  18  when the starter switch (SS) is closed, engages a starter motor (M S )  25 . The energized starter motor  25  in turn translates a pinion gear  23  into direct meshed engagement with an engine flywheel  16 , the resultant rotation of which delivers a cranking torque (arrow T C ) to the input member  13  of the engine  12 . 
     A fuel delivery system  30 , which may be considered as a part of the engine starting system  28  in certain embodiments, may include a fuel pump (P F )  32  and a fuel injector rail  34 . When the input member  13  is cranked to a threshold rotational speed, combustible fuel (arrow F) is fed via the fuel pump  32  to the fuel injector rail  34 . The engine starting function is discontinued when the threshold speed is attained, with the internal combustion process of the engine  12  thereafter sustaining rotation. Additionally, the rotating engine  12  may power an alternator (A)  11  to generate and deliver electricity to the battery  18 . As is known in the art, such an alternator  11  includes a belt (not shown) or other drive element that rotates in conjunction with rotation of the engine  12  to generate electricity. 
     As part of the vehicle  10 , a controller (C)  50  may be equipped with requisite memory (M) and a processor (P), as well as associated hardware and software such as an oscillator, input/output circuitry, etc. The memory (M) may include a computer-readable medium or media, including sufficient amount of read only memory, for instance magnetic or optical memory, on which is recorded computer-readable diagnostic instructions embodying executable portions of the method  100  described below. In some embodiments, a hierarchical precedence rule  60  assigning a relative priority level to fault modes of a given system, e.g., the engine starting system  28 , is recorded in memory (M), with execution by the processor (P) of the diagnostic instructions embodying the method  100  causing the controller  50  to perform the various aspects of the method  100  as set forth below in  FIG. 4 . 
     Additionally as part of the method  100 , the controller  50  receives input signals (arrow CC I ) from multiple components, subsystems, and/or electronic control units of the vehicle  10 . After executing the method  100  using a fault report matrix  40  and a hierarchical precedence rule  60 , the controller  50  transmits output signals (arrow CC O ) to an output device  33 , e.g., a display screen, a cell phone, or an external/web-based server, such as a vehicle telematics system. 
     Examples of the fault report matrix  40  and the hierarchical precedence rule  60  are depicted in  FIGS. 2 and 3 , respectively. As part of the method  100 , a particular system is first divided into constituent subsystems within the fault report matrix  40  of  FIG. 2 . Using the engine starting system  28  of  FIG. 1  as an example, embedded systems (column ES) provide various embedded fault reports. As used herein, “embedded fault report” refers to a fault report that is automatically generated by a corresponding electronic control unit (ECU) for and/or logic of a given subsystem. “Subsystem fault report” refers to a report generated by a health management module, a body control module, engine control module, etc., which may include the controller  50  or other control devices in different embodiments, and which may involve sensor-based fault detection or ongoing subsystem-level state of health determination. For instance, in the vehicle  10  shown in  FIG. 1 , embedded fault reports and/or subsystem fault reports may pertain to functional diagnosis and prognosis of the starting system, including the battery  18 , the starter solenoid  24 , the starter motor  25 , the alternator  11 , and/or a critical component of the fuel delivery system  30  such as the fuel pump  32 . 
     Embedded fault reports provide information on the status of the engine starting process. In the example of  FIG. 2 , the embedded system (ES) reports may include a first set of embedded faults (F 1 ), such as “no crank request”, “no fault report”, or “ECU short to ground”. A second set of embedded faults (F 2 ) may describe a “starter disabled” condition, which may be further divided into “no engine rotation” (F 2A ), “long injection delay” (F 2B ), and “maximum cranking time expired” (Fac). A third set of embedded faults (F 3 ) may include “start and stall/engine shutdown during starting”. 
     In addition to the embedded system fault reports, the fault report matrix  40  delineates possible root cause subsystems. In the example engine starting system  28 , this may include the starter system  28  with the battery (B)  18 , a charging system (CS) such as the alternator  11  and associated electrical sensors and connections, driver behavior (DB), multiple crank events (MCE) by numeric count, the fuel delivery system  30 , and the engine (E)  12 . 
     For each of the possible root cause systems, the fault report matrix  40  may identify specific fault modes. The battery  18  may exhibit a low state of charge (SOC L ), a low state of health (SOH L ), or parasitic loads and/or battery sensor faults (F PL,B ). The engine starting system  28  may have a low state of health (SOH L ) for the starter motor  25  or the starter solenoid  24 . The charging system (CS) may exhibit a charging system fault (F CS ) in the form of a low state of health for the alternator  11 , belt slip of the alternator  11 , a broken electrical connection between the battery  18  and the alternator  11 , or another charging system fault (F CS ). Regarding driver behavior (DB), this column may refer to a calibrated number of short trips or extended parking times, as compared to a calibrated time (t c ), or multiple crank events (MCE) by numeric count. The fuel delivery system  30  may have a low state of health, or the fuel pump  32  may be blocked, leak, or exhibit a sensor fault or other fault (F 30 ). One these faults may be a root cause of a reported fault condition. 
     While the particular manner in which such states of health or other status conditions are determined may vary within the intended scope of the disclosure, an example of such an approach may be found in U.S. Ser. No. 15/399,947, which is hereby incorporated by reference in its entirety. For the auxiliary battery  18  or other DC power source, for instance, such existing methods may include determining when the state of charge is low and then evaluating potential root causes associated with the low state of charge. A fault probability may be determined for each of candidate root cause, with a root cause having the highest fault probability being selected as the root cause for that particular subsystem. 
     Similarly, such subsystem-level approaches may define a state of health as an available electric power capacity of a fully-charged battery  18 , e.g., as a ratio of the original electric power capacity of the battery  18 . Such a state of health may be determined by periodically monitoring voltage, current, and temperature states of the battery  18  during operation and subjecting such measurements to a predefined empirical or physical model that may include differential equations and/or equivalent circuits that are reduced to executable algorithms and calibrations that reside in the battery controller (not shown). In one embodiment, the voltage, current and temperature states and the predefined empirical or physical model may be employed to determine an open-circuit voltage and/or an internal charging resistance of the battery  18 , which may be analyzed to determine the state of health. Similar approaches may be used for other subsystems within the vehicle  10 . 
     The fault report matrix  40  is then populated with a code or other information indicative of whether or not a fault report was generated, e.g., with “X” denoting the existence of such a fault report and “*” denoting the absence thereof. Additionally, within the fault report matrix  40 , each of the embedded system faults F 1 , F 2A , F 2B , F 2C , and F 3  and each root cause subsystem is assigned a corresponding hierarchical priority, shown nominally as one of three relative priorities (1), (2), or (3) in  FIG. 2 . More priority levels may be used in other embodiments. In a row R 1  having just one recorded fault, i.e., a low state of health of the auxiliary battery  18  with no other faults, the method  100  need not resort to the assigned hierarchy for fault reporting. However, in a row R 2  having multiple possible fault modes, e.g., a “no-crank request fault” in which a low state of health of the auxiliary battery  18  is detected, along with battery sensor faults, a charging system fault, and a threshold number of short trips, the controller  50  of  FIG. 1  may resort to a hierarchical precedence strategy to determine an appropriate control action, including outputting one or more fundamental root causes. 
     Hierarchical treatment of multiple possible fault modes may be described with particular reference to  FIG. 3 . In a simplified version, the hierarchical precedence rule  60  has three priority levels L1, L2, and L3, which correspond in the fault report matrix  40  of  FIG. 2  to the priorities (1), (2), and (3). At the lowest level (L3) lies the fundamental effect of a detected failure, e.g., an ECU short-to-ground condition (F STG ). Level L2 is likewise a fundamental effect of a detected failure, albeit at a higher priority level in the hierarchy than level L3. For instance, a low state of charge of the battery  18  (SOC B =L) and multiple cranking events (MCE) may represent the second level L2 of the hierarchy. At the highest level, L1, are the fundamental root causes for a given fault, e.g., a “no-start” fault of the vehicle  10  of  FIG. 1 . Such root causes may include driver behavior (DB), charging system (CS), and parasitic loads (PL), as well as low battery state of health (SOH B =L), low starter state of health (SOH M =L), low fuel delivery system state of health (SOH 30 =L), and low engine state of health (SOH E =L). Thus, the hierarchical precedence rule  60  is used to set forth the root causes and the effects in a descending order of priority. 
       FIG. 4  describes an example embodiment of the method  100  noted above, in the illustrative context of diagnosis of an engine starting process that is diagnosed using the approach set forth above, i.e., using the fault report matrix  40  and the assigned hierarchical precedence rule  60 . While an onboard embodiment is described with reference to  FIG. 4 , as will be appreciated by one having ordinary skill in the art in view of this disclosure, the method  100  may reside as instructions on a service tool and/or remotely/accessed via the cloud rather than residing aboard the vehicle  10 . For instance, the vehicle  10  may remotely communicate with a service station via a telematics unit as a possible embodiment of output device  33  of  FIG. 1 , with the method  100  executed offboard. Thus, while the controller  50  is described below for illustrative simplicity, the scope of the disclosure is intended to apply to onboard or offboard implementations in different embodiments. 
     Beginning with step S 102 , the controller  50  of  FIG. 1  receives, as an example of a “predetermined condition” as used herein, a crank request indicative of a requested starting of the engine  12 . Such a request may be generated by a body control module (BCM) in certain vehicular embodiments, with the BCM being part of the controller  50  or a separate device in different configurations. The controller  50  reads available fault reports of the particular subsystems that are being evaluated. For instance, step S 102  may include reading one or more fault reports describing a state of the battery  18  and/or the starter motor  25 , as well as any associated diagnostic codes indicative of a failure mode. The method then proceeds to step S 104 . 
     Step S 104  includes determining if an embedded fault report is available for the present ignition cycle, i.e., the ignition cycle that is active and ongoing. The method  100  proceeds to step S 106  if an embedded fault report is available for the present ignition cycle. The method  100  otherwise proceeds to step S 108 . 
     At step S 106 , the controller  50  determines if a subsystem fault report is available for the present ignition cycle. If so, the method  100  proceeds to step S 112 . The method  100  otherwise proceeds to step S 109 . 
     Step S 108  may entail determining whether a subsystem fault report is available for a calibrated number of prior ignition cycles. The method  100  proceeds to step S 110  if such reports are available, and to step S 109  in the alternative if no prior subsystem fault reports are available. 
     Step S 109  includes evaluating and examining the fault probabilities of the individual subsystems under evaluation. As part of step S 109 , the controller  50  determines that the least healthy subsystem is the likely root cause of the present fault mode, and in response to such a determination, the controller  50  executes a corresponding control action. For instance, the controller  50  may record a diagnostic code identifying the root cause/identified subsystem, or may transmit a text message to an operator of the vehicle  10  or a repair facility. The method  100  is then complete, a status that is indicated by “**” in  FIG. 4 . 
     Step S 110  may include computing probabilistic weighted subsystem fault reports from the prior ignition cycles, e.g., by applying predetermined weights to the various faults so as to apply a greater weight to faults that are more critical and a lesser weight to faults that are deemed less critical. The method  100  then proceeds to step S 112 . 
     At step S 112 , the controller  50  next references the fault report matrix  40  and identifies the root cause of the present fault mode before proceeding to step S 114 . 
     At step S 114 , the controller  50  determines whether there are multiple root cause outputs from the fault report matrix  40 , and then proceeds to step S 116  when this is not the case. 
     Step S 116  is executed for single root cause events. In this instance, the root cause for the engine no-start condition is identified and communicated in a suitable manner, such as via text message, registration of a corresponding diagnostic code, or the like. The method  100  is then complete, as indicated by “*” in  FIG. 4 . 
     Step S 118  include referring to the hierarchical precedence rule  60  to select and identify the root cause. The method  100  then proceeds to step S 120 . 
     At step S 120 , the controller  50  outputs the root cause for the vehicle no-start event. The method  100  is then complete, as indicated by “**” in  FIG. 4 . 
     Thus, the method  100  may be recorded as instructions on the computer-readable medium of memory (M), as noted above. Such instructions, when executed by the processor (P), cause the controller  50  to record, in the fault report matrix  40 , one or more fault reports indicative of one or more of the fault modes, and to use the hierarchical precedence rule  60  to determine the assigned relative priority level for such fault reports. This is done in response to a predetermined condition, such as a detected requested engine starting or ignition event. Execution of the instructions also causes the controller to identify a root cause subsystem as a particular subsystem having the highest of the assigned priority levels, and to execute a control action with respect to the system responsive to the identified root cause subsystem. Such a control action may include recording a diagnostic code and/or transmitting a message indicative of the identified root cause subsystem, or other suitable control actions within the scope of the disclosure. 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the inventive scope is defined solely by the claims. While some of the best modes and other embodiments for carrying out the disclosure have been described in detail herein, various alternative designs and embodiments exist within the intended scope of this disclosure. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.