JP2012052498A - Method and device for diagnosing internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for diagnosing an internal combustion engine, that suppress ill influence to an ignition plug or an exhaust gas purifying filter when diagnosing presence or absence of a cylinder whose air fuel ratio is abnormal.SOLUTION: According to this method and device 14 for diagnosing the internal combustion engine, any one of a plurality of cylinders 32 whose air fuel ratio is abnormal is identified during the engine 16 being in operation. The engine diagnosing device 14 has an abnormal cylinder identifying part 84 to identify the abnormal cylinder from the relation between the air fuel ratio changed in steps and the frequency of misfire occurrence of each of the plurality of cylinders 32, and a protection part 84 to protect the ignition plug 36 or the exhaust gas purifying filter 18 by interrupting the step-by-step changes of the air fuel ratio in case the frequency of misfire occurrence of any cylinder 32 or the sum total of them has exceeded a prescribed level during the air fuel ratio being changed in steps.

Description

  The present invention relates to an internal combustion engine diagnostic apparatus and an internal combustion engine diagnostic method for identifying an abnormal cylinder having an abnormal air-fuel ratio among a plurality of cylinders during operation of the internal combustion engine.

  When an internal combustion engine in an automobile or the like is operated, an air-fuel ratio sensor is provided from the viewpoint of exhaust gas purification, and the fuel supply amount is controlled to maintain the air-fuel ratio in a good state by air-fuel ratio feedback control.

  Even if the exhaust gas itself is maintained in a good state, if the air-fuel ratio varies between the cylinders, the purification rate of the catalyst that purifies the exhaust gas may be reduced. Monitoring is also performed (see Patent Document 1 and Patent Document 2).

  In Patent Document 1, for example, a cycle in which combustion of all the cylinders makes a round is regarded as one cycle, and the fluctuation of the air-fuel ratio within the one cycle is measured.

  In Patent Document 2, when misfire is detected, ignition control for each cylinder is stopped individually and sequentially, the output average value and output fluctuation value of the air-fuel ratio sensor at this time are taken in, and values before stopping the ignition control are obtained. The misfire cylinder is specified by comparison (refer to claim 1). Here, one or more air-fuel ratio sensors can be provided (page 4, lower left column, lines 6 to 10).

JP 2009-270543 A Japanese Patent Laid-Open No. 3-189371

  By the way, in the case where the above-described failure occurs, if misfire frequently occurs by reproducing the failure event for failure repair work, the temperature in the combustion chamber of the cylinder is lowered and the spark plug is likely to burn (燻Tends to accumulate). As a result, there is a high possibility that misfire occurs due to the soot, and it is assumed that the number of misfire occurrences caused by the change in the air-fuel ratio cannot be accurately determined. In addition, soot that accumulates in the spark plug may adversely affect the durability of the spark plug. In addition, when misfire occurs, unburned gas that has not been burned in the combustion chamber may be discharged from the internal combustion engine and ignited in the catalyst by the heat of the exhaust gas purification filter (catalyst). This phenomenon occurs frequently. Then, the catalyst becomes too hot, which may adversely affect the durability of the filter (catalyst).

  The present invention has been made in consideration of such a problem, and is capable of suppressing an adverse effect on a spark plug or an exhaust gas purification filter when diagnosing the presence or absence of a cylinder having an abnormal air-fuel ratio. An object of the present invention is to provide an engine diagnostic device and an internal combustion engine diagnostic method.

  An internal combustion engine diagnostic apparatus according to the present invention is for identifying an abnormal cylinder having an abnormal air-fuel ratio among a plurality of cylinders during operation of the internal combustion engine, and controlling a fuel injection amount for each of the plurality of cylinders. The air-fuel ratio is changed stepwise by the step, the abnormal cylinder specifying unit for specifying the abnormal cylinder from the relationship between the air-fuel ratio changed stepwise and the number of misfire occurrences of each of the plurality of cylinders, and the air-fuel ratio stepped When the number of misfire occurrences or the sum of any one of the plurality of cylinders exceeds a predetermined value during the change, the ignition plug or the exhaust gas purification filter is stopped by stopping the stepwise change in the air-fuel ratio. And a protection part for protecting the device.

  According to the present invention, when the air-fuel ratio is changed stepwise, if the number of misfire occurrences or the total of any of the plurality of cylinders exceeds a predetermined value, the step-wise change of the air-fuel ratio is stopped. This protects the spark plug or the exhaust gas purifying filter. For this reason, according to the predetermined value, for example, it is possible to suppress an adverse effect on the spark plug or the exhaust gas purification filter.

  That is, as described above, if misfire frequently occurs, the temperature in the combustion chamber of the cylinder is lowered, and the spark plug is likely to burn (soot tends to accumulate). As a result, there is a high possibility that misfire occurs due to the soot, and it is assumed that the number of misfire occurrences caused by the change in the air-fuel ratio cannot be accurately determined. In addition, soot that accumulates in the spark plug may adversely affect the durability of the spark plug. In addition, when misfire occurs, unburned gas that has not been burned in the combustion chamber may be discharged from the internal combustion engine and ignited in the catalyst by the heat of the exhaust gas purification filter (catalyst). This phenomenon occurs frequently. Then, the catalyst may become too hot and adversely affect the durability of the catalyst. According to the present invention, when the air-fuel ratio is changed stepwise, if the number of misfire occurrences or the total of any of the plurality of cylinders exceeds a predetermined value, the step-wise change of the air-fuel ratio is stopped. This protects the spark plug or the exhaust gas purifying filter. Therefore, for example, by setting a value that does not cause the catalyst temperature to rise excessively from the data value of the possibility of combustion in the catalyst as a result of frequent misfires, It is possible to avoid the adverse effects of. Further, by setting a value smaller than the number of misfire occurrences at which soot easily accumulates in the spark plug as the predetermined value, it is possible to avoid adverse effects on the spark plug.

  The abnormal cylinder specifying unit may increase or decrease the air-fuel ratio stepwise by controlling the fuel injection amount sequentially for the plurality of cylinders one by one in a state where the internal combustion engine is not loaded. . As a result, it is possible to check the abnormality of the cylinders one by one, so that it is possible to determine the abnormal cylinder more accurately.

  An example of the state where no load is applied to the internal combustion engine is an idle operation state.

  The abnormal cylinder specifying unit may decrease the fuel injection amount in a stepwise manner starting from a set value for realizing the theoretical air-fuel ratio. As a result, the stoichiometric air-fuel ratio at which the number of misfire occurrences is substantially zero is changed to the lean side where the number of misfire occurrences increases, so that an abnormal cylinder can be accurately determined and an ignition plug or It is possible to suppress adverse effects on the catalyst as much as possible.

  That is, as described above, if misfires occur frequently, it is assumed that the number of misfires caused by changes in the air-fuel ratio cannot be accurately determined, and the durability of the spark plug and the filter may be adversely affected. There is. According to the present invention, since the temperature drop in the combustion chamber can be minimized, the generation of soot that accumulates in the spark plug can be suppressed. Therefore, it is possible to prevent the above problems.

  The abnormal cylinder specifying unit may count the number of misfire occurrences or the total of any of the plurality of cylinders for each measurement cycle in which the air-fuel ratio is changed. As a result, it is possible to determine the number of misfire occurrences in any of the plurality of cylinders or the sum of the abnormalities for each air-fuel ratio value, and to suitably detect misfire abnormalities at the time of specifying the abnormal cylinders. Become.

  An internal combustion engine diagnosis method according to the present invention specifies an abnormal cylinder having an abnormal air-fuel ratio among a plurality of cylinders during operation of the internal combustion engine, and controls a fuel injection amount for each of the plurality of cylinders. The step of changing the air-fuel ratio step by step, an abnormal cylinder specifying step for specifying the abnormal cylinder from the relationship between the air-fuel ratio changed stepwise and the number of misfire occurrences of each of the plurality of cylinders, and stepping the air-fuel ratio When the number of misfire occurrences or the sum of any one of the plurality of cylinders exceeds a predetermined value during the change, the ignition plug or the exhaust gas purification filter is stopped by stopping the stepwise change in the air-fuel ratio. And a protection step for protecting.

  In the abnormal cylinder specifying step, the air-fuel ratio may be increased or decreased stepwise by controlling the fuel injection amount in order for each of the plurality of cylinders one by one in a state where no load is applied to the internal combustion engine. .

  In the abnormal cylinder specifying step, the fuel injection amount may be decreased stepwise starting from a set value for realizing a theoretical air-fuel ratio.

  In the abnormal cylinder specifying step, the number of misfire occurrences or a total of any of the plurality of cylinders may be counted for each measurement cycle in which the air-fuel ratio is changed.

  According to the present invention, when the air-fuel ratio is changed stepwise, if the number of misfire occurrences or the total of any of the plurality of cylinders exceeds a predetermined value, the step-wise change of the air-fuel ratio is stopped. This protects the spark plug or the exhaust gas purifying filter. For this reason, according to the predetermined value, for example, it is possible to suppress an adverse effect on the spark plug or the exhaust gas purification filter.

1 is a block diagram showing a schematic configuration of an internal combustion engine diagnostic system having an internal combustion engine diagnostic apparatus according to an embodiment of the present invention. It is a figure which shows the schematic structure inside an engine. It is a flowchart which shows the outline | summary of the abnormality diagnosis of each cylinder. It is a time chart which shows an example of the relationship of the various signals at the time of performing the process shown in FIG. 3, a numerical value, and a process. It is a time chart which shows a part of FIG. 4 in detail. It is a flowchart of a warm-up process. It is a flowchart of an engine speed stabilization process. It is a figure which shows an example of the cumulative value of the frequency | count of misfire occurrence of each cylinder after an engine start. It is a flowchart of a 1st diagnostic process. It is a 1st flowchart of a 2nd diagnostic process. It is a 2nd flowchart of the 2nd diagnostic processing. It is a figure which shows an example of the cumulative value of the misfire occurrence frequency for every measurement period. In a 2nd diagnostic process, it is a flowchart for specifying the presence or absence of each cylinder, and the kind when the failure has occurred. In a 2nd diagnostic process, it is explanatory drawing of the method of specifying the presence or absence of each cylinder, and the type when the failure has occurred. It is a figure which shows the 1st example of the data table of the cumulative value of the frequency | count of misfire occurrence which an internal combustion engine diagnostic apparatus acquires, the graph based on a data table, and the screen displayed on the display part of an internal combustion engine diagnostic apparatus. It is a figure which shows the 2nd example of the screen displayed on the data table of the cumulative value of the frequency | count of misfire occurrence which an internal combustion engine diagnostic apparatus acquires, the graph based on a data table, and the display part of an internal combustion engine diagnostic apparatus. It is a figure which shows the 3rd example of the screen displayed on the data table of the cumulative value of the misfire occurrence frequency which an internal combustion engine diagnostic device acquires, the graph based on a data table, and the display part of an internal combustion engine diagnostic device. It is a figure which shows the 4th example of the screen displayed on the data table of the cumulative value of the frequency | count of misfire occurrence which an internal combustion engine diagnostic apparatus acquires, the graph based on a data table, and the display part of an internal combustion engine diagnostic apparatus. It is a figure which shows an example of the air fuel ratio of each cylinder at the time of using only fuel-injection basic control. It is a figure which shows an example of the air fuel ratio of each cylinder at the time of using fuel injection basic control and air fuel ratio feedback control. It is a figure which shows the 1st modification of switching of the correction amount of the ratio of the target injection quantity with respect to the reference | standard injection quantity in a 2nd diagnostic process. It is a figure which shows the 2nd modification of the switching of the said correction amount in a 2nd diagnostic process.

A. Embodiment 1 FIG. Configuration (1) Overall Configuration FIG. 1 is also referred to as an internal combustion engine diagnosis system 10 (hereinafter also referred to as “system 10”) having an internal combustion engine diagnosis device 14 (hereinafter also referred to as “diagnosis device 14”) according to an embodiment of the present invention. Is a block diagram showing a schematic configuration of. The system 10 includes a vehicle 12 equipped with an engine 16 as a diagnosis target, and a diagnosis device 14 that diagnoses the engine 16.

(2) Vehicle 12
(A) Overall Configuration In addition to the engine 16, the vehicle 12 includes an exhaust gas filter 18 that purifies exhaust gas from the engine 16 (hereinafter also referred to as “filter 18”), and an engine electronic control unit 20 that controls the output of the engine 16 ( Hereinafter referred to as “engine ECU 20”), a temperature sensor 22 for detecting the temperature Tw [° C.] of the cooling water of the engine 16, and an ignition switch 24 (hereinafter referred to as “IGSW 24”).

(B) Engine 16
FIG. 2 shows a schematic configuration inside the engine 16. The engine 16 is a so-called in-line four-cylinder engine, an intake air amount sensor 28, a throttle valve 30, an opening degree sensor 31, and first to fourth cylinders 32a to 32d (hereinafter collectively referred to as “cylinder 32”). The fuel injection valve 34 for each cylinder 32, the spark plug 36 for each cylinder 32, the air-fuel ratio sensor 38, the crankshaft 40, the crank angle sensor 41, and the top dead center sensor 42 for each cylinder 32.

  The intake air amount sensor 28 detects the amount of air sucked into the engine 16 (hereinafter referred to as “intake air amount Qaf”) according to the opening θth [°] of the throttle valve 30 and outputs it to the engine ECU 20. The throttle valve 30 is disposed in the intake manifold 44. The opening sensor 31 detects the opening θth of the throttle valve 30 and outputs it to the engine ECU 20. The fuel injection valve 34 and the spark plug 36 are disposed facing the combustion chamber 46 of each cylinder 32. The air-fuel ratio sensor 38 includes an oxygen sensor (not shown), and is disposed in the exhaust manifold 48. The air-fuel ratio sensor 38 detects the air-fuel ratio of the entire engine 16 (hereinafter referred to as “total air-fuel ratio Raf_total”) and outputs it to the engine ECU 20. The crank angle sensor 41 detects the rotation angle (hereinafter referred to as “crank angle Ac”) [°] of the crankshaft 40 and outputs it to the engine ECU 20. The top dead center sensor 42 detects the top dead center of the piston 49 and outputs it to the engine ECU 20.

(C) Exhaust gas filter 18
The exhaust gas filter 18 is disposed on the downstream side (exhaust side) of the exhaust manifold 48 and purifies and discharges exhaust gas from the engine 16. The filter 18 in the present embodiment includes a three-way catalyst for exhaust gas purification.

(D) Engine ECU 20
The engine ECU 20 controls the operation of the engine 16 and includes an input / output unit 50, a calculation unit 52, and a storage unit 54 as shown in FIG.

  The engine ECU 20 in the present embodiment executes, for example, an engine speed calculation function, a misfire occurrence count function, a throttle valve control function, a fuel injection valve control function, and a spark plug control function.

  The engine rotation speed calculation function is a function for calculating the rotation speed (engine rotation speed Ne) [rpm] of the engine 16 based on the output from each top dead center sensor 42. In the present embodiment, each top dead center sensor 42 is combined with the engine speed sensor. Instead, an engine speed sensor independent of the engine ECU 20 may be provided, and the output thereof may be transmitted to the engine ECU 20.

  The misfire occurrence count function determines whether or not misfire has occurred in each cylinder 32 based on the output from the crank angle sensor 41, and counts the number of misfire occurrences in each cylinder 32 when it is determined that misfire has occurred. In this embodiment, a misfire counter is configured by combining with the crank angle sensor 41. The determination of whether or not misfire has occurred is, for example, by detecting the combustion pressure at a predetermined crank angle and determining that a misfire has occurred when the combustion pressure is less than or equal to a predetermined value, or A known means such as determining that misfire has occurred when the angular velocity is equal to or less than a predetermined value can be used.

  The throttle valve control function is a function of controlling the output of the engine 16 by controlling the opening degree θth of the throttle valve 30 based on an operation amount of an accelerator pedal (not shown).

  The fuel injection valve control function is a function of controlling the output of the engine 16 by controlling the fuel injection amount Qfi (target value) from the fuel injection valve 34 based on an operation amount of an accelerator pedal (not shown).

  The spark plug control function is a function for controlling the output of the engine 16 by controlling the ignition timing of each spark plug 36 based on the operation amount of an accelerator pedal (not shown).

(3) Diagnostic device 14
The diagnosis device 14 diagnoses the presence or absence of an abnormality in the air-fuel ratio in each cylinder 32, and includes a repeater 60 and a main body 62 as shown in FIG.

  The repeater 60 relays communication between the main body 62 and the engine ECU 20, and includes a cable 70 for connecting to the engine ECU 20, an input / output unit 72 to which the cable 70 is connected, and wireless communication with the main body 62. A communication unit 74 that performs control, a calculation unit 76 that controls each unit, and a storage unit 78 that stores various programs and data such as a control program used in the calculation unit 76.

  The main body 62 includes an input / output unit 80 including a keyboard and a touch pad (not shown), a communication unit 82 that performs wireless communication with the repeater 60, a calculation unit 84 that controls each unit and determines abnormality of each cylinder 32, and a calculation. It has the memory | storage part 86 which memorize | stores various programs and data, such as a control program used in the part 84, and an abnormality diagnosis program, and the display part 88 which performs various displays. As a hardware configuration of the main body 62, for example, a commercially available notebook personal computer can be used. Hereinafter, the abnormality determination function of each cylinder 32 executed by the calculation unit 84 is referred to as “abnormal cylinder determination function”.

  When an abnormality diagnosis of each cylinder 32 is performed using the diagnostic device 14, the cable 70 of the repeater 60 is provided on an instrument panel (not shown) of the vehicle 12 with one end of the cable 70 connected to the input / output unit 72 of the repeater 60. The other end of the cable 70 is connected to a connector (data link connector) not shown. Thereafter, the main body 62 performs an abnormality diagnosis of each cylinder 32 in accordance with an operation from the user with respect to the input / output unit 80 of the main body 62. At that time, the main body 62 operates the engine 16 via the engine ECU 20. Details of the abnormality diagnosis of each cylinder 32 performed by the main body 62 will be described later.

2. Abnormality Diagnosis of Cylinder 32 FIG. 3 is a flowchart showing an outline of abnormality diagnosis of each cylinder 32. FIG. 4 is a time chart showing an example of the relationship between various signals, numerical values, and processing when the processing shown in FIG. 3 is performed. FIG. 5 is a time chart showing a part of FIG. 4 in detail.

  As described above, before starting the abnormality diagnosis, the cable 70 of the relay device 60 is connected to the engine ECU 20 of the vehicle 12 so that the main body 62 of the diagnostic device 14 and the engine ECU 20 can communicate with each other via the relay device 60. And

  When receiving a diagnosis start command from the user via the input / output unit 80 of the main body 62, the diagnostic device 14 performs a warm-up process that causes the engine ECU 20 to perform a warm-up operation in step S1.

  FIG. 6 shows a flowchart of the warm-up process (details of S1 in FIG. 3). In step S11, the calculation unit 84 of the diagnostic device 14 displays a message for requesting the start of the engine 16 by the operation of the IGSW 24 on the display unit 88 and inquires of the engine ECU 20 whether the engine 16 has started.

  If the engine 16 has not yet been started, that is, if the engine ECU 20 has not been notified of the start of the engine 16 (S12: NO), the process returns to step S11. When the engine 16 is started, that is, when the start of the engine 16 is notified from the engine ECU 20 (S12: YES) (time t1 in FIG. 4), in step S13, the calculation unit 84 warms up the engine ECU 20. The engine ECU 20 that requests the start of the operation and starts the warm-up operation of the engine 16 receives the request. The warm-up operation here refers to, for example, increasing the engine speed Ne to a predetermined value for warm-up (for example, 3000 rpm).

  Further, during the warm-up operation, the engine ECU 20 uses normal air-fuel ratio control that is generally used when the engine 16 is operated. The normal air-fuel ratio control is a control used in the fuel injection valve control function of the engine ECU 20, and is a combination of fuel injection basic control and air-fuel ratio feedback control (hereinafter referred to as “air-fuel ratio FB control”).

  The basic fuel injection control in the present embodiment is a ratio of fuel (here, gasoline) to air (hereinafter referred to as “cylinder air-fuel ratio Raf_1 to Raf_4” in the air-fuel mixture supplied to each cylinder 32, or these are collectively referred to as “cylinder empty”. In this control, the air-fuel ratio Raf_n or the air-fuel ratio Raf_n is set to the stoichiometric air-fuel ratio (fuel: air = 1: 14.7).

  More specifically, in the fuel injection basic control, the relationship between the intake amount Qaf detected by the intake amount sensor 28 and the target value of the fuel injection amount Qfi of the fuel injection valve 34 is mapped and set in advance and detected. The fuel injection valve 34 is controlled according to the target value of the fuel injection amount Qfi corresponding to the intake air amount Qaf.

  However, the air-fuel ratio Raf_n of each cylinder 32 and the engine 16 are not necessarily due to various factors such as variations in operation timing (tuppet clearance) of intake / exhaust valves (not shown) of each cylinder 32 and aging of the fuel injection valve 34. The overall air-fuel ratio Raf_total is not equal to the theoretical air-fuel ratio.

  The air-fuel ratio FB control in the present embodiment is control that feeds back so that the total air-fuel ratio Raf_total becomes equal to the stoichiometric air-fuel ratio. Specifically, when the detected value of the air-fuel ratio sensor 38 is not the stoichiometric air-fuel ratio, the stoichiometric air-fuel ratio is increased or decreased so that the detected value becomes the stoichiometric air-fuel ratio. Realize the fuel ratio. At this time, the fuel injection amount Qfi is corrected using the correction value Pc. The correction value Pc is a correction value of a fuel injection rate Rfi_n [%] (target value) of each cylinder 32 to be described later, but other values (for example, a fuel injection amount Qfi (target value) or an overall air-fuel ratio) Raf_total).

  In the present embodiment, since one air-fuel ratio sensor 38 is only provided on the downstream side of the exhaust manifold 48, the air-fuel ratio Raf_n of each cylinder 32 is not detected. Therefore, in the fuel injection basic control, the overall air-fuel ratio Raf_total of the engine 16 can be converged to the stoichiometric air-fuel ratio, but the air-fuel ratio Raf_n of each cylinder 32 cannot be converged to the stoichiometric air-fuel ratio.

  In step S <b> 14, the calculation unit 84 of the diagnostic device 14 determines whether the engine 16 has been warmed up. Specifically, the calculation unit 84 requests the engine ECU 20 for the temperature Tw of the coolant for the engine 16, and the engine ECU 20 that has received the request detects the temperature detected by the temperature sensor 22 from the calculation unit 84. Send Tw. And the calculating part 84 determines whether temperature Tw is more than threshold value TH_Tw [degreeC]. The threshold value TH_Tw is a threshold value for determining the end of warm-up.

  If the warm-up has not ended (S14: NO), step S14 is repeated. When the warm-up is completed (S14: YES) (time t2 in FIG. 4), the process proceeds to step S15.

  In step S <b> 15, the calculation unit 84 requests the engine ECU 20 to end warm-up and displays a message for requesting the IGSW 24 to be turned off on the display unit 88. If the IGSW 24 remains on (S16: NO), the process returns to step S15. If the IGSW 24 is turned off (S16: YES) (time t3 in FIG. 4), the warm-up process is terminated.

  Returning to FIG. 3, in step S <b> 2, the diagnostic device 14 performs an engine speed stabilization process for stabilizing the engine speed Ne.

  FIG. 7 shows a flowchart of the engine speed stabilization process (details of S2 in FIG. 3). In step S <b> 21, the calculation unit 84 displays a message for requesting restart of the engine 16 on the display unit 88 in order to start abnormality diagnosis. If the engine 16 has not been restarted (S22: NO), the process returns to step S21. When the engine 16 is restarted (S22: YES) (time t4 in FIG. 4), the process proceeds to step S23.

  In the subsequent step S23, the engine ECU 20 starts counting the cumulative value Tmf_total_n [times] of the number of misfire occurrences after starting the engine 16 for each cylinder 32. Note that the initial value of each cumulative value Tmf_total_n (the value when the engine 16 is started) is zero. In addition, “n” in “Tmf_total_n” indicates the number of each cylinder 32. For example, the cumulative value Tmf_total_1 indicates the cumulative value of the first cylinder 32a.

  As described above, misfire detection is performed by combining the output from the crank angle sensor 41 and the determination in the engine ECU 20. Further, as shown in FIG. 8, the count of the cumulative value Tmf_total_n is continued without reset until a request for resetting the cumulative value Tmf_total_n is received from the diagnostic device 14 after the engine 16 is started.

  In subsequent step S24, the calculation unit 84 determines whether or not the engine speed Ne is stable. This determination is made based on whether or not a predetermined time (for example, 30 seconds) has elapsed since the engine 16 was restarted.

  When the predetermined time has elapsed (S24: YES) (time t5 in FIG. 4), preparation for abnormality diagnosis is completed. Note that after the predetermined time has elapsed, the calculation unit 84 requests the engine ECU 20 to cause the engine 16 to idle, and the engine ECU 20 that has received the request causes the engine 16 to idle. At this time, the engine ECU 20 uses both the fuel injection basic control and the air-fuel ratio FB control.

  Returning to FIG. 3, in step S <b> 3, the diagnostic device 14 executes a first diagnostic process. The first diagnosis process is a diagnosis process associated with stopping the air-fuel ratio FB control.

  FIG. 9 is a flowchart of the first diagnosis process. When the advance preparation is completed as described above (time t5 in FIG. 4), in step S31, the calculation unit 84 of the diagnostic device 14 requests the engine ECU 20 to transmit the correction value Pc, and the engine that has received the request. The ECU 20 transmits the correction value Pc currently used in the air-fuel ratio FB control to the diagnostic device 14. Thereby, the calculating part 84 acquires the correction value Pc.

  The correction value Pc is a correction value for changing the overall air-fuel ratio Raf_total of the engine 16. That is, the correction value Pc is set as a value of a fuel injection rate Rfi_n (described later) corresponding to the difference ΔRaf between the theoretical air fuel ratio and the overall air fuel ratio Raf_total.

  In step S <b> 32, the calculation unit 84 of the diagnostic device 14 determines whether there is a cylinder 32 that has misfired (hereinafter referred to as “misfire cylinder”). Specifically, the calculation unit 84 requests the engine ECU 20 for a cumulative value Tmf_total_n [times] of the number of misfire occurrences of each cylinder 32 after the engine 16 is started. The cumulative value Tmf_total_n is notified to the unit 84. Then, the calculation unit 84 individually determines whether or not the accumulated value Tmf_total_n of each cylinder 32 exceeds a threshold TH_total1 (for example, TH_total1 = 0) for determining the occurrence of misfire. If the accumulated value Tmf_total_n exceeds the threshold TH_total1, it is determined that misfire has occurred in the cylinder 32 (that is, there is a misfire cylinder).

  If no misfire has occurred in any of the cylinders 32 (S32: NO), the process proceeds to step S44. If a misfire has occurred in any of the cylinders 32 (S32: YES), in step S33, the calculation unit 84 of the diagnostic device 14 requests the engine ECU 20 to stop the air-fuel ratio FB control. Upon receiving the request, the engine ECU 20 stops the air-fuel ratio FB control and executes only the fuel injection basic control.

  In step S34, the calculation unit 84 of the diagnostic device 14 determines whether or not misfire has stopped in the state of only the fuel injection basic control. Specifically, the calculation unit 84 determines whether or not the cumulative value Tmf_total2_n of the number of misfire occurrences of each cylinder 32 after a predetermined time has elapsed since shifting to the state of only fuel injection basic control is equal to or less than the threshold value TH_total1. judge. If the accumulated value Tmf_total2_n of each cylinder 32 is less than or equal to the threshold value TH_total1, it is determined that misfire has stopped.

  If misfire has stopped as a result of stopping the air-fuel ratio FB control (S34: YES), it can be said that all the cylinders 32 are normal although the misfire has occurred due to the air-fuel ratio FB control. In this case, the process proceeds to step S44. If misfire occurs in any of the cylinders 32 and misfire does not stop (S34: NO), the process proceeds to step S35.

  In step S35, the calculation unit 84 of the diagnostic device 14 determines whether or not the correction value Pc acquired in step S31 is greater than or equal to a threshold value TH_Pc1. The threshold value TH_Pc1 is for determining whether or not the fuel is excessively rich by the correction by the correction value Pc (whether or not the fuel is excessively lean when there is no air-fuel ratio FB control). + 8%.

  When the correction value Pc is equal to or greater than the threshold value TH_Pc1 (S35: YES), in step S36, the diagnosis device 14 determines whether or not the misfire cylinder is moving (changed) by stopping the air-fuel ratio FB control. . If the misfire cylinder is moving (S36: YES), in step S37, the calculation unit 84 of the diagnostic device 14 determines that a lean failure has occurred in the moved misfire cylinder. Here, the lean failure means that the target value of the cylinder air-fuel ratio Raf_n in the engine ECU 20 is set to the stoichiometric air-fuel ratio (that is, the fuel injection amount Qfi (target value) corresponds to the stoichiometric air-fuel ratio. The actual air-fuel ratio Raf_n of the misfiring cylinder has changed excessively to the lean side, in other words, the fuel supply is insufficient for some reason. Say.

  On the other hand, when the misfire cylinder has not moved (changed) (S36: NO), in step S38, the calculation unit 84 of the diagnostic device 14 determines that a lean failure has occurred in the misfire cylinder.

  Returning to step S35, when the correction value Pc is not equal to or greater than the threshold value TH_Pc1 (S35: NO), in step S39, the calculation unit 84 determines whether or not the correction value Pc acquired in step S31 is equal to or less than the threshold value TH_Pc2. The threshold value TH_Pc2 is for determining whether or not the fuel is excessively thinned by the correction by the correction value Pc (whether or not the fuel is excessively rich when there is no air-fuel ratio FB control). It can be -8%.

  When the correction value Pc is not less than or equal to the threshold value TH_Pc2 (S39: NO), the process proceeds to step S44. When the correction value Pc is equal to or less than the threshold value TH_Pc2 (S39: YES), in step S40, the calculation unit 84 of the diagnosis device 14 determines whether or not the misfire cylinder has moved (changed) because the air-fuel ratio FB control is stopped. Determine whether. When the misfire cylinder is moving (S40: YES), in step S41, the calculation unit 84 determines that a rich failure has occurred in the moved misfire cylinder. The rich failure here means that the target value of the cylinder air-fuel ratio Raf_n in the engine ECU 20 is set to the stoichiometric air-fuel ratio (that is, the fuel injection amount Qfi (target value) corresponds to the stoichiometric air-fuel ratio. In spite of being set to a value), the air-fuel ratio Raf_n of the misfire cylinder is in a state where it has changed excessively to the rich side, in other words, a state where the fuel supply is excessive for some reason.

  On the other hand, if the misfire cylinder has not moved (changed) (S40: NO), in step S42, the calculation unit 84 of the diagnostic device 14 determines that a rich failure has occurred in the misfire cylinder.

  After steps S37, S38, S41, and S42, in step S43, the calculation unit 84 of the diagnostic device 14 displays the content of the failure on the display unit 88 (displays an error).

  When there is no misfire cylinder in step S32 (S32: NO), when misfire is stopped in step S34 (S34: YES), or when the correction value Pc is not less than or equal to the threshold TH_Pc2 in step S39 (S39: NO), each cylinder 32 Cannot detect the failure. In this case, in step S44, as in step S33, the air-fuel ratio FB control is stopped, and the current first diagnosis process is terminated (time t6 in FIG. 4).

  Returning to FIG. 3, in step S <b> 4, the calculation unit 84 of the diagnostic device 14 determines whether or not the identification of the abnormal cylinder has ended. The case where the identification of the abnormal cylinder is completed is a case where one of steps S37, S38, S41, and S42 in FIG. 9 is passed. When the identification of the abnormal cylinder is finished (S4: YES), the current diagnosis is finished. If the identification of the abnormal cylinder is not completed (S4: NO), the process proceeds to step S5.

  In step S5, the diagnostic device 14 executes the second diagnostic process (time t6 in FIG. 4). The second diagnostic process is a diagnostic process involving switching (change) of the air-fuel ratio Raf_n for each cylinder 32. More specifically, in the second diagnosis process, a correction value (hereinafter referred to as “cylinder correction value Cfi_n” or “correction value Cfi_n”) [%] for changing the air-fuel ratio Raf_n for each cylinder 32 is switched (changed). ) With diagnostic processing.

  The correction value Cfi_n is a target value of the fuel injection amount Qfi with respect to the fuel injection amount Qfi (“cylinder reference injection amount”) for setting the cylinder air-fuel ratio Raf_n to the theoretical air-fuel ratio in relation to the intake air amount Qaf in the basic fuel injection control. (Hereinafter referred to as “cylinder fuel injection rate Rfi_n” or “fuel injection rate Rfi_n”). The fuel injection rate Rfi_n is obtained by adding the correction value Cfi_n to 100% (corresponding to the cylinder reference injection amount) (Rfi_n = 100 + Cfi_n).

  “N” in each of “Cfi_n” and “Rfi_n” indicates the number of each cylinder 32. For example, the cylinder correction value Cfi_1 indicates the correction amount Cfi_n of the first cylinder 32a, and the fuel injection rate Rfi_1 indicates the first cylinder. A fuel injection rate Rfi_n of 32a is shown.

  Note that when the first diagnosis process is completed, the air-fuel ratio FB control is stopped (see S33 and S44 in FIG. 9). Accordingly, only the fuel injection basic control is executed when the second diagnosis process is started.

  10 and 11 are flowcharts of the second diagnosis process. Note that by executing the flowcharts of FIGS. 10 and 11, for example, waveform data as shown in FIG. 5 can be acquired.

  In steps S51 and S52, the calculation unit 84 of the diagnostic device 14 performs initial setting. Specifically, in step S51, the calculation unit 84 sets 1 to a variable n indicating a cylinder 32 (hereinafter referred to as “target cylinder”) for switching the cylinder correction value Cfi_n. n = 1 indicates the first cylinder 32a, n = 2 indicates the second cylinder 32b, n = 3 indicates the third cylinder 32c, and n = 4 indicates the fourth cylinder 32d. Therefore, by setting 1 to the variable n in step S51, the process from now on indicates that the first cylinder 32a is the target cylinder. In step S52, the calculation unit 84 sets 0% for the correction amount Cfi_1 of the first cylinder 32a (Cfi_1 ← 0%). In other words, the fuel injection rate Rfi_1 of the first cylinder 32a is set to 100% for realizing the theoretical air-fuel ratio (Rfi_1 ← 100%).

  In subsequent steps S53 and S54, the calculation unit 84 of the diagnostic device 14 determines whether or not the exhaust gas filter 18 is in an overheated state. Specifically, in step S53, the calculation unit 84 determines whether or not each cumulative value Tmf_total_n of the number of misfire occurrences of the target cylinder after the engine 16 is started is equal to or greater than a threshold value TH_total2 [times]. The threshold value TH_total2 is a threshold value for determining that the filter 18 is in an overheated state. Further, as described above, since the accumulated value Tmf_total_n is counted by the engine ECU 20 from the start of the engine 16, the calculation unit 84 acquires each accumulated value Tmf_total_n from the engine ECU 20.

  When the cumulative value Tmf_total_n of the target cylinder is less than the threshold value TH_total2 (S53: NO), in step S54, the calculation unit 84 sets the cumulative value Tmf_cyl_n [times] of the number of misfire occurrences of the target cylinder in the measurement cycle Pm [sec]. It is determined whether or not TH_cyl [times] or more. The measurement period Pm is a period for switching the correction amount Cfi_n (that is, a period for switching the fuel injection rate Rfi_n and the cylinder air-fuel ratio Raf_n) (see FIGS. 5 and 12). Therefore, the cumulative value Tmf_cyl_n is a cumulative value of the number of misfire occurrences of the target cylinder every time the correction amount Cfi_n is switched. The threshold value TH_cyl is a threshold value for determining that the filter 18 is in an overheated state.

  The accumulated value Tmf_cyl_n is counted by the calculation unit 84 of the diagnostic device 14. Specifically, in response to a command from the diagnostic device 14, the engine ECU 20 notifies the diagnostic device 14 of the number of the cylinder 32 and the occurrence of misfire every time a misfire occurs. The diagnostic device 14 that has received the notification counts the number of misfire occurrences for each measurement period Pm, as shown in FIGS.

  When the accumulated value Tmf_cyl_n is less than the threshold value TH_cyl (S54: NO), the process proceeds to step S56. When the accumulated value Tmf_total_n is greater than or equal to the threshold value TH_total2 (S53: YES) or when the accumulated value Tmf_cyl_n is greater than or equal to the threshold value TH_cyl (S54: YES), the calculation unit 84 displays an error on the display unit 88 in step S55. That is, since the number of misfire occurrences is large, the calculation unit 84 displays on the display unit 88 that the diagnosis should be temporarily stopped for cooling the filter 18 and stops the second diagnosis process. According to the error display, the user temporarily stops the second diagnosis process and reduces the temperature of the filter 18, whereby the second diagnosis process can be resumed. When the diagnosis (the process of FIG. 3) is resumed, each accumulated value Tmf_total_n is reset based on a user operation on the input / output unit 80.

  In step S56, the calculation unit 84 stops the determination of the emission (E / M) deterioration misfire level. The E / M worsening misfire level means the degree of misfire occurrence caused by the accumulation of soot in the spark plug 36. In the present embodiment, priority is given to the misfire determination for protecting the filter 18 (S53, S54 in FIG. 10) by stopping the determination of the E / M worsening misfire level. However, it is possible to continue the determination of the E / M worsening misfire level during the second diagnosis process.

  Through steps S57 to S67, the calculation unit 84 identifies an abnormal cylinder. That is, as shown in FIG. 5, in the present embodiment, the four cylinders 32 are selected in order as diagnosis targets. As already described, the cylinder 32 to be diagnosed is referred to as “target cylinder”. Then, while performing basic fuel injection control with the correction value Cfi_n being set to 0% for three of the four cylinders 32 other than the target cylinder, the correction value Cfi_n for the target cylinder is changed stepwise. At this time, the correction value Cfi_n is switched in the order of ± 0%, −10%, −20%, −30%, and −40%. In other words, the cylinder air-fuel ratio Raf_n is changed by decreasing the fuel injection rate Rfi_n in the order of 100% (theoretical air-fuel ratio), 90%, 80%, 70%, and 60%.

  In order to perform the process as described above, in step S57, the calculation unit 84 notifies the engine ECU 20 of the variable n and the correction value Cfi_n of the target cylinder indicated by the variable n for each one or a plurality of explosion processes. Receiving the notification, the engine ECU 20 executes the explosion process a predetermined number of times with the correction value Cfi_n in the target cylinder. In the present embodiment, the explosion process is repeated 50 times for each correction value Cfi_n (that is, for each fuel injection rate Rfi_n or cylinder air-fuel ratio Raf_n) by repeating step S57.

  While the engine ECU 20 is executing the explosion process, in step S58, the calculation unit 84 counts the cumulative value Tmf_total_n and the cumulative value Tmf_cyl_n. More specifically, the engine ECU 20 notifies the calculation unit 84 every time a misfire is detected. In response to the notification, the calculation unit 84 counts the cumulative value Tmf_total_n and the cumulative value Tmf_cyl_n.

  In steps S62 and S66, which will be described later, the accumulated value Tmf_cyl_n is reset every time the cylinder air-fuel ratio Raf_n changes. Therefore, the accumulated value Tmf_cyl_n is accumulated for each cylinder correction value Cfi_n (that is, for each measurement period Pm), as shown in FIGS.

  In step S59, the calculation unit 84 determines whether or not the measurement in the current measurement cycle Pm is completed (whether or not the explosion process has been performed 50 times with the cylinder correction value Cfi_n in the target cylinder). The determination can be performed, for example, by receiving the output of the crank angle sensor 41 via the engine ECU 20 and detecting the rotation speed of the crankshaft 40 using the output. When the measurement in the current measurement cycle Pm is not completed (S59: NO), the process returns to step S53. When the measurement in the current measurement period Pm is completed (S59: YES), the process proceeds to step S60 in FIG.

  In step S60 of FIG. 11, the calculation unit 84 determines whether or not the correction value Cfi_n can be changed in the same target cylinder (in other words, whether or not an unmeasured correction value Cfi_n remains in the same target cylinder). Determine. That is, as described above, in this embodiment, the correction value Cfi_n is changed in the order of ± 0%, −10%, −20%, −30%, and −40%. If not%, the correction value Cfi_n can be changed.

  When the correction value Cfi_n can be changed (S60: YES), after storing the cumulative value Tmf_cyl_n according to the cylinder 32 and the fuel injection rate Rfi_n (see FIGS. 15 to 18), in step S61, the calculation unit 84 The correction value Cfi_n is changed for the same target cylinder. Specifically, if the current correction value Cfi_n of the target cylinder is ± 0%, it is -10%, if the correction value Cfi_n is -10%, it is -20%, and if the correction value Cfi_n is -20%. If the correction value Cfi_n is −30%, it is changed to −40%. In subsequent step S62, the calculation unit 84 resets the accumulated value Tmf_cyl_n, and returns to step S53 in FIG.

  When the correction value Cfi_n is not changeable (S60: NO), that is, when the current correction value Cfi_n of the target cylinder is −40%, the correction value Cfi_n is reset, and according to the cylinder 32 and the fuel injection rate Rfi_n. The accumulated value Tmf_cyl_n is stored (see FIGS. 15 to 18). Thereafter, in step S63, the calculation unit 84 determines whether or not the diagnosis has been completed for all the cylinders 32. When the diagnosis has not been completed for some of the cylinders 32 (S63: NO), in step S64, the calculation unit 84 adds 1 to the current value of the variable n that identifies the target cylinder to obtain a new variable n. (N ← n + 1). As a result, the target cylinder is switched (time points t11, t12, t13 in FIG. 5).

  In subsequent step S65, the calculation unit 84 substitutes 0% for the correction value Cfi_n of the new target cylinder. Thereby, the operation of the new target cylinder is started from the theoretical air-fuel ratio (± 0%). In subsequent step S66, operation unit 84 resets accumulated value Tmf_cyl_n, and returns to step S53.

  Returning to step S63, when the diagnosis is completed for all the cylinders 32 (S63: YES) (time t7 in FIG. 5), in step S67, the calculation unit 84 determines the number of misfire occurrences of each cylinder 32 acquired in each step. On the basis of the accumulated value Tmf_cyl_n, the presence / absence of a failure in each cylinder 32 and the type of the failure are specified.

  FIG. 13 is a flowchart (details of S67 in FIG. 11) for specifying whether or not each cylinder 32 has failed in the second diagnosis process, and the type of the failure, if any. The process of FIG. 13 is performed for each cylinder 32. FIG. 14 is an explanatory diagram of a method for identifying the presence / absence of a failure in each cylinder 32 and a type of the failure in the second diagnosis process.

  In step S71 of FIG. 13, the calculation unit 84 of the diagnosis device 14 determines whether or not the cumulative value Tmf_cyl_n of the number of misfire occurrences when the fuel injection rate Rfi_n is 70% (correction value Cfi_n is −30%) is zero. judge. When the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 70% is zero (S71: YES), in step S72, the calculation unit 84 determines that the cylinder 32 has a rich failure. As described above, the rich failure refers to a state where the fuel supply is excessive for some reason. When the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 70% is not zero (S71: NO), the process proceeds to step S73.

  In step S73, the calculation unit 84 determines whether or not the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 90% (correction value Cfi_n is −10%) is equal to or greater than the threshold value TH_lean [times]. The threshold value TH_lean is a threshold value for determining a lean failure, and is 25 times in the present embodiment. When the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 90% is greater than or equal to the threshold value TH_lean (S73: YES), in step S74, the calculation unit 84 determines that the cylinder 32 has a lean failure. As described above, the lean failure refers to a state where the fuel supply is insufficient for some reason. When the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 90% is not equal to or greater than the threshold value TH_lean (S73: NO), in step S75, the calculation unit 84 determines that the cylinder 32 is normal.

  By performing the determination process as described above, as shown in FIG. 14, it is possible to determine whether each cylinder 32 is normal, rich failure, or lean failure. The result of the determination process is filed in a predetermined format (from time t7 to time t8 in FIG. 4) and displayed on the display unit 88 (from time t8 to time t9 in FIG. 4).

  In the determination of FIG. 13, values when the fuel injection rate Rfi_n is 100%, 80%, and 60% (correction value Cfi_n is ± 0%, −20%, −40%) are not used. The data on the fuel injection rate Rfi_n is used when the user analyzes the data after the calculation unit 84 determines a failure.

  Returning to FIG. 11, in step S <b> 68, the calculation unit 84 of the diagnostic device 14 outputs the determination result of step S <b> 67 to the display unit 88.

  15 to 18 are graphs based on the data tables 100, 110, 120, and 130 of the cumulative value Tmf_cyl_n of the number of misfire occurrences acquired by the diagnostic device 14 and the data tables 100, 110, 120, and 130 in the present embodiment. 102, 112, 122, 132, and screens 104, 114, 124, 134 displayed on the display unit 88.

  FIG. 15 shows a data table 100, a graph 102, and a screen 104 when each cylinder 32 is normal. FIG. 16 shows a data table 110, a graph 112, and a screen 114 when each cylinder 32 has a rich failure. FIG. 17 shows a data table 120, a graph 122, and a screen 124 when each cylinder 32 has a lean failure. FIG. 18 shows a data table 130, a graph 132, and a screen 134 when the first cylinder 32a and the third cylinder 32c are normal, the second cylinder 32b is rich, and the fourth cylinder 32d is lean. It is shown.

  Note that the graphs 122 and 132 in FIGS. 17 and 18 include data in a portion where the fuel injection rate Rfi_n exceeds 100%, for convenience of explanation.

3. Effects of the Present Embodiment As described above, according to the present embodiment, it is possible to identify an abnormal cylinder (rich failure and lean failure) with an abnormal cylinder air-fuel ratio Raf_n with high accuracy and simplicity.

  That is, generally, in the normal cylinder 32, the actual cylinder air-fuel ratio Raf_n that changes according to the fuel injection amount Qfi is substantially the same as the target value of the cylinder air-fuel ratio Raf_n that corresponds to the correction value Cfi. The relationship between the air-fuel ratio Raf_n of the cylinder 32 and the occurrence of misfire is determined to some extent according to the configuration of the engine 16. For example, when the actual cylinder air-fuel ratio Raf_n is equal to the stoichiometric air-fuel ratio, the occurrence of misfire is substantially zero, but the misfire occurrence rate increases as the actual cylinder air-fuel ratio Raf_n moves toward the lean side or the rich side. In the present embodiment, the cylinder air-fuel ratio Raf_n (the fuel injection rate Rfi_n and the correction value Cfi_n) is changed stepwise, and the cumulative value Tmf_cyl_n of the number of misfire occurrences is counted to obtain the combustible fuel injection range. Abnormality of the fuel ratio Raf_n is detected. Therefore, it is easy to detect an abnormality in the cylinder air-fuel ratio Raf_n, and it is possible to identify the abnormal cylinder with high accuracy.

  The control of the cylinder air-fuel ratio Raf_n is generally performed for the engine 16, and the cumulative value Tmf_cyl_n of the number of misfire occurrences is counted by, for example, the crank angle sensor 41 and the engine ECU 20. It becomes possible. Accordingly, the control of the cylinder air-fuel ratio Raf_n and the counting of the cumulative value Tmf_cyl_n of the number of misfires can be performed using the existing configuration related to the engine 16. According to the present embodiment, the abnormal cylinder is identified from the relationship between the cylinder air-fuel ratio Raf_n (fuel injection rate Rfi_n) changed in stages and the cumulative value Tmf_cyl_n of the number of misfire occurrences of the plurality of cylinders 32. Therefore, it is possible to easily identify an abnormal cylinder by using the cylinder air-fuel ratio Raf_n (fuel injection rate Rfi_n) that can be controlled or determined using the existing configuration related to the engine 16 and the cumulative value Tmf_cyl_n of the number of misfire occurrences. It becomes possible.

  The calculation unit 84 of the diagnosis device 14 controls the cylinder air-fuel ratio Raf_n by controlling the fuel injection amount Qfi (correction value Cfi_n) sequentially for each of the plurality of cylinders 32 one by one in an idle state where the engine 16 is not loaded. (See FIG. 5). Thereby, since abnormality of the cylinder 32 can be confirmed one by one, it becomes possible to determine an abnormal cylinder more accurately.

  The calculation unit 84 of the diagnostic device 14 starts the fuel injection rate Rfi_n from 100% and decreases it step by step by decreasing the correction value Cfi_n starting from 0% (see FIG. 5).

  As a result, the stoichiometric air-fuel ratio at which the cumulative value Tmf_cyl_n of the number of misfire occurrences is substantially zero is changed to the lean side where the cumulative value Tmf_cyl_n of the number of misfire occurrences increases, so that the abnormal cylinder can be accurately determined. Thus, it is possible to suppress the adverse effect on the spark plug 36 or the filter 18 due to the occurrence of misfire as much as possible.

  That is, if misfire frequently occurs, the temperature in the combustion chamber 46 of the cylinder 32 is lowered, and the spark plug 36 is likely to be burned (soot tends to accumulate). As a result, there is a high possibility that misfire occurs due to the soot, and it is assumed that the cumulative value Tmf_cyl_n of the number of misfire occurrences caused by the change in the cylinder air-fuel ratio Raf_n (correction value Cfi_n) cannot be accurately determined. . In addition, the soot that accumulates in the spark plug 36 may adversely affect the durability of the spark plug 36. Further, when misfire occurs, unburned gas that has not been combusted in the combustion chamber 46 may be discharged from the engine 16 and ignited in the filter 18 due to the heat of the filter 18. 18 durability may be adversely affected. According to the present embodiment, the temperature is gradually changed from a normal combustion operation state to a state in which misfire is likely to occur, so that a temperature drop in the combustion chamber 46 can be minimized. Therefore, it is possible to prevent the above problems.

  In the present embodiment, when the fuel injection rate Rfi_n is 70% (when the correction value Cfi_ is −30%), if there is a cylinder 32 whose accumulated misfire occurrence value Tmf_cyl_n is zero, the calculation of the diagnostic device 14 is performed. The unit 84 determines that the rich failure in which the fuel is excessively supplied has occurred in the cylinder 32. Thereby, it is possible to easily determine a rich failure.

  In the present embodiment, when the fuel injection rate Rfi_n is 90% (when the correction value Cfi_ is −10%), when there is a cylinder 32 in which the cumulative value Tmf_cyl_n of the number of misfire occurrences is 25 times or more, the diagnostic device 14 The calculation unit 84 determines that a lean failure with insufficient fuel supply has occurred in the cylinder 32. This makes it possible to easily determine a lean failure.

  According to the present embodiment, when the correction value Cfi_n (that is, the fuel injection rate Rfi_n or the cylinder air-fuel ratio Raf_n) is changed stepwise, the cumulative value Tmf_total_n of the number of misfire occurrences exceeds the threshold value TH_total2, or the misfire When the cumulative value Tmf_cyl_n of the number of occurrences exceeds the threshold value TH_cyl, the stepwise change of the correction value Cfi_n is stopped. For this reason, it becomes possible to suppress the bad influence to the spark plug 36 or the filter 18 according to these threshold values, for example. In order to suppress an adverse effect on the spark plug 36, when the second diagnostic process is resumed, an operation for performing both the fuel injection basic control and the air-fuel ratio FB control is performed before the stepwise change of the correction value Cfi_n. Thus, the soot and the like accumulated in the spark plug 36 can be burned off.

  In the present embodiment, the calculation unit 84 of the diagnostic device 14 counts the cumulative value Tmf_cyl_n of the number of misfire occurrences of the target cylinder every measurement period Pm. As a result, it is possible to determine an abnormality of the accumulated value Tmf_cyl_n for each correction value Cfi_n (that is, the fuel injection rate Rfi_n or the cylinder air-fuel ratio Raf_n). It becomes possible.

  According to the present embodiment, even when there is no problem in the control of the overall air-fuel ratio Raf_total of the engine 16, it is possible to detect a malfunction in the control of the air-fuel ratio Raf_n that has occurred in each cylinder 32.

  That is, during normal operation of the engine 16, the fuel injection basic control and the air-fuel ratio FB control are used in combination. The engine 16 includes four cylinders 32, one of which (the first cylinder 32a) is supplied with fuel. When an insufficient lean failure occurs, the air-fuel ratio Raf_n of the other three cylinders 32 (second to fourth cylinders 32b to 32d) is adjusted by the air-fuel ratio FB control so as to increase the fuel supply, By adjusting the air-fuel ratio Raf_n of the first cylinder 32a so as to reduce the fuel supply, the target air-fuel ratio can be realized as the overall air-fuel ratio Raf_total of the engine 16. In this case, as can be seen from FIGS. 19 and 20, it is not possible to detect the lean failure of the first cylinder 32a.

  According to the present embodiment, when the engine 16 is diagnosed, the air-fuel ratio FB control is stopped and only the fuel injection basic control is executed. Therefore, the abnormal cylinder can be identified with high accuracy and easily. Therefore, even when only the entire air-fuel ratio sensor 38 is provided in the engine 16 to be inspected, the abnormal cylinder can be identified with high accuracy and easily.

  In the present embodiment, the target air-fuel ratio is the stoichiometric air-fuel ratio, and in the fuel injection basic control, the fuel injection rates Rfi_n (air-fuel ratios) of the plurality of cylinders 32 so that the air-fuel ratios Raf_n of the cylinders 32 become the stoichiometric air-fuel ratio. The fuel ratio Raf_n) is controlled. Further, in the air-fuel ratio FB control, the same correction value Pc is applied to each of the plurality of cylinders 32 when the overall air-fuel ratio Raf_total of the engine 16 deviates from the theoretical air-fuel ratio in an idle state where the engine 16 is not loaded. Thus, the overall air-fuel ratio Raf_total is controlled to be equal to the theoretical air-fuel ratio. As a result, since the theoretical air-fuel ratio is used as a reference during both normal operation and diagnosis of the engine 16, it is easy to determine an abnormal cylinder.

B. Modifications It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted based on the contents described in this specification. For example, the following configuration can be adopted.

  In the above embodiment, the diagnosis device 14 is used for diagnosis of the engine 16 of the vehicle 12, but is not limited thereto, and can be used for other devices having an internal combustion engine (for example, a moving body such as a ship). In the above embodiment, the diagnostic device 14 communicates with the engine ECU 20 from the outside of the vehicle 12, but may be mounted inside the vehicle 12. In other words, the engine ECU 20 can have the function of the diagnostic device 14.

  In the above embodiment, the engine 16 is an in-line four-cylinder engine, but the arrangement and number of the cylinders 32 are not limited to this. For example, the engine 16 may be a V type 6 cylinder engine.

  In the above embodiment, one air-fuel ratio sensor 38 is provided for the entire engine 16, but the present invention is not limited to this, and the air-fuel ratio sensor 38 may be provided for each of the plurality of cylinders 32.

  In the above embodiment, the calculation unit 84 of the diagnostic device 14 switches the cylinder air-fuel ratio Raf_n (fuel injection rate Rfi_n and correction value Cfi_n) via the engine ECU 20. The cylinder air-fuel ratio Raf_n (fuel injection rate Rfi_n and correction value Cfi_n) may be switched by directly controlling the injection valve 34. Alternatively, by providing the engine ECU 20 with the function of the diagnostic device 14, the engine ECU 20 (diagnostic device 14) directly controls the fuel injection valve 34 to switch the cylinder air-fuel ratio Raf_n (fuel injection rate Rfi_n and correction value Cfi_n). It can also be done.

  In the above embodiment, the cumulative value Tmf_total_n of the number of misfire occurrences after the engine 16 is started is obtained for each cylinder 32. However, the present invention is not limited to this. It can also be used in search of.

  In the above embodiment, the cumulative value Tmf_total_n is the cumulative value of the number of misfire occurrences after the engine 16 is started. However, the present invention is not limited to this. For example, the cumulative value Tmf_total_n is, for example, from another time point (for example, after a predetermined time has elapsed since the engine 16 was started). It can also be a cumulative value of the number of misfire occurrences.

  In the above-described embodiment, the fuel injection basic control and the air-fuel ratio FB control are simultaneously used before stopping the air-fuel ratio FB control in steps S33 and S44. After that, only the air-fuel ratio FB control can be executed. In this case, when the air-fuel ratio FB control is stopped in steps S33 and S44, the fuel injection basic control is resumed. Alternatively, before stopping the air-fuel ratio FB control in steps S33 and S44, first, the fuel injection basic control and the air-fuel ratio FB control are started simultaneously, and then the fuel injection basic control is stopped and only the air-fuel ratio FB control is performed. May be continued. Also in this case, the fuel injection basic control may be restarted when the air-fuel ratio FB control is stopped in steps S33 and S44.

  In the second diagnosis process of the above embodiment, the air-fuel ratio Raf_n of each cylinder 32 is decreased from the stoichiometric air-fuel ratio to the lean side by decreasing the correction value Cfi_n. However, the present invention is not limited to this. For example, as shown in FIG. 21, the cylinder air-fuel ratio Raf_n can be gradually switched from the rich side to the lean side by switching the correction value Cfi_n stepwise from positive to negative. Alternatively, as shown in FIG. 22, the cylinder air-fuel ratio Raf_n can be gradually switched from the lean side to the rich side by gradually switching the correction value Cfi_n from negative to positive. In these cases, the correction value Cfi_n is not only a combination of ± 0%, −10%, −20%, −30%, and −40%, but can be changed as appropriate.

  In the second diagnosis process of the above embodiment, the air-fuel ratio Raf_n (correction value Cfi_n) is gradually changed for the target cylinder while performing the fuel injection basic control for the cylinders 32 other than the target cylinder. Not limited to this, for the cylinders 32 other than the target cylinder, the fuel injection basic control can be stopped and the fuel injection and ignition can be stopped.

  In the second diagnosis process of the above embodiment, the failure is identified using the flowchart of FIG. 13, but the failure identification method is not limited to this. For example, in step S71, it is determined whether or not a rich failure has occurred based on the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 70% (when the correction value Cfi_n is −30%). However, for the determination of the rich failure, for example, if the fuel injection rate Rfi_n is lower than the lean-side fuel limit value (critical value at which misfire does not occur) determined by the characteristics of the engine 16, another value (see FIG. 14). It may be. In addition, the threshold value (first threshold value) of the accumulated value Tmf_cyl_n at that time may be a positive value other than zero.

  Furthermore, in step S73, it is determined whether or not there is a lean failure based on the cumulative value Tmf_cyl_n when the fuel injection rate Rfi_n is 90% (when the correction value Cfi_n is −10%). However, regarding the determination of the lean failure, for example, if the combustion injection rate Rfi_n is 100% or a value within the fuel possible range value (range where no misfire occurs) determined by the characteristics of the engine 16, another value ( (See FIG. 14). In addition, the threshold value TH_lean (second threshold value) at that time can be set as appropriate.

  Further, when the cylinders 32 other than the target cylinder are out of order, another step can be added to the flowchart of FIG. For example, before it is determined in step S74 in FIG. 13 that the target cylinder has a lean failure, the range (see FIG. 14) in which the cumulative value Tmf_cyl_n of the number of misfire occurrences should change is determined (see FIG. 14). A change amount of the cumulative value Tmf_cyl_n when Raf_n changes (for example, a difference between the cumulative value Tmf_cyl_n when the air-fuel ratio Raf_n of the target cylinder is 90% and 100%) is calculated. And when the said variation | change_quantity is more than predetermined value, it can also determine with an object cylinder having a lean failure.

DESCRIPTION OF SYMBOLS 12 ... Vehicle 14 ... Engine diagnostic apparatus 16 ... Engine 20 ... Engine ECU (misfire counter)
32, 32a to 32d ... cylinder 84 ... calculation unit (abnormal cylinder specifying unit, catalyst protection unit)

Claims (8)

An internal combustion engine diagnostic device for identifying an abnormal cylinder having an abnormal air-fuel ratio among a plurality of cylinders during operation of the internal combustion engine,
By controlling the fuel injection amount for each of the plurality of cylinders, the air-fuel ratio is changed stepwise, and the abnormal cylinder is determined from the relationship between the step-changed air-fuel ratio and the number of misfire occurrences of each of the plurality of cylinders. An abnormal cylinder identification part to be identified;
When changing the air-fuel ratio stepwise, if the number of misfire occurrences or the sum of any of the plurality of cylinders exceeds a predetermined value, the ignition plug is stopped by stopping the step-wise change of the air-fuel ratio Or an internal combustion engine diagnostic apparatus, comprising: a protection unit that protects the exhaust gas purification filter. The internal combustion engine diagnostic apparatus according to claim 1,
The abnormal cylinder specifying unit controls the fuel injection amount for each of the plurality of cylinders one by one in order to increase or decrease the air-fuel ratio stepwise in a state where no load is applied to the internal combustion engine. An internal combustion engine diagnostic device. The internal combustion engine diagnostic apparatus according to claim 1 or 2,
The internal combustion engine diagnostic apparatus, wherein the abnormal cylinder specifying unit starts to decrease the fuel injection amount in a stepwise manner starting from a set value for realizing a theoretical air-fuel ratio. The internal combustion engine diagnostic apparatus according to any one of claims 1 to 3,
The internal combustion engine diagnostic apparatus, wherein the abnormal cylinder specifying unit counts the number of misfire occurrences or the total of any of the plurality of cylinders for each measurement cycle in which the air-fuel ratio is changed. An internal combustion engine diagnosis method for identifying an abnormal cylinder having an abnormal air-fuel ratio among a plurality of cylinders during operation of the internal combustion engine,
By controlling the fuel injection amount for each of the plurality of cylinders, the air-fuel ratio is changed stepwise, and the abnormal cylinder is determined from the relationship between the step-changed air-fuel ratio and the number of misfire occurrences of each of the plurality of cylinders. An abnormal cylinder identification step to identify;
When changing the air-fuel ratio stepwise, if the number of misfire occurrences or the sum of any of the plurality of cylinders exceeds a predetermined value, the ignition plug is stopped by stopping the step-wise change of the air-fuel ratio Or a protection step for protecting the exhaust gas purification filter. The internal combustion engine diagnosis method according to claim 5, wherein
In the abnormal cylinder specifying step, the fuel injection amount is controlled sequentially for each of the plurality of cylinders one by one in order to increase or decrease the air-fuel ratio in a state where no load is applied to the internal combustion engine. An internal combustion engine diagnostic method. The internal combustion engine diagnosis method according to claim 5 or 6,
In the abnormal cylinder specifying step, the fuel injection amount is gradually decreased starting from a set value for realizing a theoretical air-fuel ratio. The internal combustion engine diagnostic method according to any one of claims 5 to 7,
The internal combustion engine diagnosis method, wherein the abnormal cylinder specifying step counts the number of misfire occurrences or the total of any of the plurality of cylinders for each measurement cycle in which the air-fuel ratio is changed.

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