JP6276096B2 - Air-fuel ratio imbalance diagnosis device and air-fuel ratio imbalance diagnosis method - Google Patents

Description

  The present invention relates to an air-fuel ratio imbalance diagnosis apparatus and an air-fuel ratio imbalance diagnosis method for diagnosing variation in air-fuel ratio among cylinders in an internal combustion engine having a plurality of cylinders.

  Conventionally, in an air-fuel ratio control of an internal combustion engine having a plurality of cylinders mounted on a vehicle, the air-fuel ratio detected downstream of the joining point of an exhaust passage connected to each cylinder of the internal combustion engine becomes a target value. As described above, feedback control of the fuel injection amount and the intake air amount is performed. This air-fuel ratio indicates the average air-fuel ratio of all cylinders and is detected using an air-fuel ratio sensor.

  Here, in an internal combustion engine having a plurality of cylinders, air-fuel ratios may vary among cylinders due to differences in intake characteristics among the cylinders or differences in injection characteristics due to clogging of fuel injection valves provided in each cylinder. is there. If this variation in air-fuel ratio becomes large, exhaust emission may be worsened. Therefore, a self-diagnosis (hereinafter referred to as “air-fuel ratio imbalance diagnosis”) that diagnoses the variation in air-fuel ratio using the sensor value of the air-fuel ratio sensor. .) Is executed (see, for example, Patent Document 1).

JP 2011-89443 A

  However, the conventional air-fuel ratio imbalance diagnosis described in Patent Document 1 assumes that the air-fuel ratio sensor is normal. For this reason, when the responsiveness of the air-fuel ratio sensor is lowered, there is a possibility that the abnormality cannot be detected despite the variation in the air-fuel ratio. Specifically, the air-fuel ratio amplitude increases as the air-fuel ratio variation increases, but if the air-fuel ratio sensor response decreases, the sensor value amplitude becomes smaller than the actual air-fuel ratio fluctuation amount. As a result, there may be cases where variations in the air-fuel ratio cannot be found. In particular, in an air-fuel ratio sensor, an abnormality in which the responsiveness of the air-fuel ratio sensor decreases only when the air-fuel ratio changes in either the lean direction or the rich direction (hereinafter, such abnormality is referred to as “one-side response delay”). May occur). When this one-side response delay has occurred, the amplitude of the sensor value of the air-fuel ratio sensor is smaller than the actual air-fuel ratio amplitude, so that there is a possibility that variation in the air-fuel ratio between cylinders cannot be detected.

  On the other hand, since the decrease in the responsiveness of the air-fuel ratio sensor affects the air-fuel ratio control, a self-diagnosis (hereinafter referred to as “responsiveness diagnosis”) that diagnoses the responsiveness of the air-fuel ratio sensor is also executed. It is like that. If the air-fuel ratio variation has occurred, even if the air-fuel ratio imbalance diagnosis does not determine that the air-fuel ratio is abnormal, if the air-fuel ratio sensor response is determined to be abnormal, the air-fuel ratio control is executed normally. It is possible to grasp the state that is not done. However, in the responsiveness diagnosis of the air-fuel ratio sensor, there is a case where the abnormality is set so as not to be determined to be abnormal if the responsiveness is low but it is a slight abnormality that is absorbed by feedback control or the like.

  FIG. 12 shows an abnormality detection situation based on air-fuel ratio sensor responsiveness diagnosis, an abnormality detection situation based on air-fuel ratio imbalance diagnosis, and a warning lamp (MIL) lighting state in a state where variations in air-fuel ratio occur. In region A, the response of the air-fuel ratio sensor is within the standard, and an abnormality is detected by the air-fuel ratio imbalance diagnosis, so the warning lamp is lit. Further, in region C, the response of the air-fuel ratio sensor is reduced, and no abnormality is detected by the air-fuel ratio imbalance diagnosis, but the response of the air-fuel ratio sensor is significantly reduced, and the abnormality is detected by the response diagnosis. Therefore, the warning lamp lights up. On the other hand, in region B, no abnormality is detected in the air-fuel ratio imbalance diagnosis, and no abnormality is detected in the response diagnosis of the air-fuel ratio sensor, so even if the air-fuel ratio varies, the warning lamp does not light up. . Therefore, in the region B, even if the air-fuel ratio varies between the cylinders, the air-fuel ratio control is executed without detecting any abnormality.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to vary the variation in air-fuel ratio between cylinders even when there is a one-side response delay of the air-fuel ratio sensor. It is an object of the present invention to provide a new and improved air-fuel ratio imbalance diagnosis apparatus and air-fuel ratio imbalance diagnosis method that can be detected.

In order to solve the above-described problem, according to an aspect of the present invention, in an air-fuel ratio imbalance diagnosis apparatus for diagnosing variation in air-fuel ratio between cylinders of an internal combustion engine, a fluctuation amount of a sensor value of an air-fuel ratio sensor A first time from the rich side peak to the lean side peak and a second time from the lean side peak to the rich side peak in the fluctuation of the sensor value of the air / fuel ratio sensor. An air-fuel ratio imbalance diagnosis apparatus comprising: a correction unit that corrects the fluctuation amount based on a ratio to the time of the first time; and an imbalance determination unit that determines variation in the air-fuel ratio based on the fluctuation amount after the correction. Provided.

  Further, the correction unit may correct the fluctuation amount by a correction coefficient corresponding to a ratio between the first time and the second time.

  In addition, the correction unit may calculate the first time and the second time in a state where a fluctuation cycle of the sensor value is synchronized with a rotation cycle of the internal combustion engine.

  The correction unit may correct the variation when the ratio between the first time and the second time is within a predetermined range.

  Further, the predetermined range may include a range of a ratio indicated by a state in which the responsiveness of the air-fuel ratio sensor is lowered, but is not determined to be abnormal by a separately executed responsiveness diagnosis.

In order to solve the above-described problem, according to another aspect of the present invention, in an air-fuel ratio imbalance diagnosis method for diagnosing variation in air-fuel ratio between cylinders of an internal combustion engine, a sensor value of an air-fuel ratio sensor And a first time from the rich side peak to the lean side peak and a second time from the lean side peak to the rich side peak in the fluctuation of the sensor value of the air-fuel ratio sensor and correcting the variation amount based on the ratio of the air-fuel ratio imbalance diagnostic method characterized by and a determining variation of the air-fuel ratio based on the amount of variation of the corrected are provided The

  According to the present invention, it is possible to detect variations in air-fuel ratio among cylinders even when a one-side response delay of the air-fuel ratio sensor occurs.

It is a mimetic diagram showing the whole internal combustion engine composition concerning an embodiment of the invention. It is a block diagram which shows the structure of the air fuel ratio imbalance diagnostic apparatus which concerns on the same embodiment. It is a figure which shows the output of an air fuel ratio sensor. It is a figure which shows the output of the air fuel ratio sensor which has produced the one-side response delay. It is a figure which shows the ratio and bias | inclination index | exponent of 1st time and 2nd time. It is explanatory drawing which shows the setting method of a correction parameter. It is a flowchart which shows the air fuel ratio imbalance diagnosis process which concerns on the same embodiment. It is a flowchart which shows the air-fuel ratio fluctuation amount calculation process which concerns on the same embodiment. It is a flowchart which shows the correction parameter calculation process which concerns on the embodiment. It is a flowchart which shows the air fuel ratio imbalance diagnosis process which concerns on the same embodiment. It is a figure which shows the diagnosis condition by the embodiment. It is a figure which shows the conventional diagnostic condition.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

1. Overall Configuration of Internal Combustion Engine First, an example of the overall configuration of an internal combustion engine 10 provided with an air-fuel ratio imbalance diagnosis apparatus 100 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing an overall configuration of an internal combustion engine 10 provided with an air-fuel ratio imbalance diagnosis apparatus 100.

  The internal combustion engine 10 is, for example, a horizontally opposed four-cylinder gasoline engine. In the internal combustion engine 10, the air sucked through the air cleaner 16 is throttled by a throttle valve 13 provided in the intake pipe 15, and is sucked into each cylinder of the internal combustion engine 10 through the intake manifold 11. The amount of air taken in through the air cleaner 16 is detected by an air flow meter 14 provided between the air cleaner 16 and the throttle valve 13. Further, the intake manifold 11 is provided with a vacuum sensor 30 for detecting the pressure of intake air. Further, the throttle valve 13 is provided with a throttle opening sensor 31 that detects the opening of the throttle valve 13.

  The intake port 22 that branches from the intake manifold 11 and communicates with each cylinder is provided with a fuel injection valve 12 that injects fuel for each cylinder. The fuel injection valve 12 injects the fuel sucked and sent from the fuel tank 23 by the feed pump 24 into the intake port 22. The cylinder head of each cylinder is provided with a spark plug 17 that ignites a mixture of fuel and air. In each cylinder of the internal combustion engine 10, an air-fuel mixture in which the sucked air and the fuel injected by the fuel injection valve 12 are mixed is ignited by the spark plug 17 and burned. Exhaust gas after combustion is exhausted through an exhaust pipe 18.

  The exhaust pipe 18 is provided with an air-fuel ratio sensor 19 that outputs a signal corresponding to the oxygen concentration in the exhaust. The air-fuel ratio sensor 19 is provided on the downstream side of the merge point 26 or the merge point 26 of the exhaust port communicating with each cylinder. As the air-fuel ratio sensor 19, a sensor capable of linearly detecting the exhaust air-fuel ratio is used.

An exhaust purification catalyst 20 is provided downstream of the air-fuel ratio sensor 19. The exhaust purification catalyst 20 is a three-way catalyst, for example, which simultaneously performs oxidation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust and reduction of nitrogen oxides (NO _x ), thereby causing harmful gases in the exhaust. The components are purified to harmless carbon dioxide (CO ₂ ), water vapor (H ₂ O), and nitrogen (N ₂ ).

  The internal combustion engine 10 is provided with a crank angle sensor (not shown) that detects the position of the crankshaft. Along with the crank angle sensor, sensor signals of the air flow meter 14, the vacuum sensor 30, the throttle opening sensor 31, and the air-fuel ratio sensor 19 described above are transmitted to an electronic control unit (hereinafter referred to as “ECU”) 100. Further, the ECU 100 receives sensor signals from various sensors (not shown) such as an accelerator opening sensor that detects the amount of depression of the accelerator pedal, that is, an accelerator pedal opening, and a vehicle speed sensor that detects the vehicle speed.

  The ECU 100 is mainly configured with a known microcomputer. The ECU 100 includes a storage unit such as a ROM or a RAM. The ROM stores, for example, a program for causing the microcomputer to execute each process. The RAM stores various data such as calculation results. In addition, the ECU 100 includes a drive circuit that drives the fuel injection valve 12, a drive circuit that drives the spark plug 17, a drive circuit that drives the electric motor 25 that opens and closes the throttle valve 13, and the like. In the present embodiment, the ECU 100 has a function as an air-fuel ratio imbalance diagnosis device.

[2. Configuration example of air-fuel ratio imbalance diagnosis device (ECU)]
FIG. 2 is a functional block diagram showing a part related to the air-fuel ratio imbalance diagnosis in the configuration of the ECU 100. The ECU 100 includes an air-fuel ratio detection unit 110, an air-fuel ratio fluctuation amount calculation unit 120, a correction unit 140, and an imbalance determination unit 130. Specifically, each of these units is realized by executing a program by a microcomputer.

  The air-fuel ratio detection unit 110 reads the sensor value Saf of the air-fuel ratio sensor 19 at a predetermined cycle. The reading period of the sensor value Saf varies depending on the performance of the air-fuel ratio sensor 19 or the ECU 100, but can be set to 1 msec, for example.

  The air-fuel ratio fluctuation amount calculation unit 120 calculates the fluctuation amount P of the read sensor value Saf. The fluctuation amount P of the sensor value Saf can be, for example, an average value of the difference ΔS1 between the maximum value Saf_max and the minimum value Saf_min for each rotation cycle of the internal combustion engine 10. The fluctuation amount P of the sensor value Saf of the air-fuel ratio sensor 19 obtained by the air-fuel ratio fluctuation amount calculation unit 120 is a value used when executing the air-fuel ratio imbalance diagnosis.

  FIG. 3 is a diagram schematically showing the sensor value Saf when the responsiveness of the air-fuel ratio sensor 19 is within an appropriate range. In the drawing, the solid line indicates the sensor value Saf when there is a variation in the air-fuel ratio among the cylinders, and the dotted line indicates the sensor value Saf when there is no variation in the air-fuel ratio between the cylinders. The alternate long and short dash line indicates the target air-fuel ratio Af_tgt.

  As shown in FIG. 3, the sensor value Saf of the air-fuel ratio sensor 19 repeats the amplitude around the target air-fuel ratio Af_tgt in accordance with the rotation cycle of the internal combustion engine 10. This amplitude increases as the variation in the air-fuel ratio among the cylinders increases. For example, the air-fuel ratio fluctuation amount calculation unit 120 obtains a difference ΔS1 between the maximum value Saf_max and the minimum value Saf_min of the sensor value Saf of the air-fuel ratio sensor 19 for each rotation cycle of the internal combustion engine 10, and averages the accumulated difference ΔS1. Let the value be the fluctuation amount P. At this time, the air-fuel ratio fluctuation amount calculation unit 120 can obtain the fluctuation amount P by using the difference ΔS1 accumulated by the sensor value Saf in a predetermined time period Ti_A0 or more. Thereby, the influence of the fluctuation of the air-fuel ratio that appears instantaneously can be reduced. The predetermined time Ti_A0 can be set to 10 seconds, for example.

  FIG. 4 is a diagram schematically showing sensor values Saf in the case where there is a one-side response delay of the air-fuel ratio sensor 19 and in the case where there is a variation in air-fuel ratio among cylinders. A solid line A shows the air-fuel ratio sensor 19 in a state where only the response when the air-fuel ratio changes from the rich side to the lean side is lowered (hereinafter, this state is referred to as “lean direction one-side response delay”). The sensor value Saf1 is shown. The solid line B shows the air-fuel ratio in a state where only the response when the air-fuel ratio changes from the lean side to the rich side is lowered (hereinafter, this state is referred to as “rich direction one-side response delay”). The sensor value Saf2 of the sensor 19 is shown. A dotted line C indicates the sensor value Saf3 of the air-fuel ratio sensor 19 in which the responsiveness is in an appropriate range, and the transition of the sensor value Saf3 can be regarded as corresponding to the actual fluctuation of the air-fuel ratio.

  For example, the sensor value Saf1 of the air-fuel ratio sensor 19 in the lean one-side response delay state indicated by the solid line A has a rising speed slower than the actual air-fuel ratio change speed, as shown in FIG. On the other hand, the air-fuel ratio sensor 19 responds appropriately when the air-fuel ratio changes from the lean side to the rich side. Therefore, when the air-fuel ratio changes to the rich side, the lean side, and the rich side, the sensor value Saf1 is a lower peak value (hereinafter referred to as “rich-side peak”) at a speed slower than the actual air-fuel ratio change speed. )) In the lean direction. Thereafter, the sensor value Saf1 decreases from a point in time coincident with the actual air-fuel ratio value that changes to the rich side before increasing to the upper peak value of the actual air-fuel ratio. As a result, the fluctuation amount of the sensor value Saf1 becomes smaller than the actual fluctuation amount of the air-fuel ratio. At this time, as the degree of the one-sided delay in the lean direction increases, the rising time of the sensor value Saf becomes longer, while the falling time becomes shorter.

  Further, the sensor value Saf2 of the air-fuel ratio sensor 19 in the rich-side one-side response delay state indicated by the solid line B has a lowering speed than the actual air-fuel ratio changing speed. On the other hand, the air-fuel ratio sensor 19 responds appropriately when the air-fuel ratio changes from the rich side to the lean side. Therefore, when the air-fuel ratio changes to the lean side, the rich side, and the lean side, the sensor value Saf2 is referred to as an upper peak value (hereinafter referred to as a “lean side peak”) at a speed slower than the actual air-fuel ratio change speed. ) In the rich direction. Thereafter, the sensor value Saf2 rises from a point in time coincident with the actual air-fuel ratio value that changes to the lean side before it falls to the lower peak value of the actual air-fuel ratio. As a result, the fluctuation amount of the sensor value Saf2 becomes smaller than the actual fluctuation amount of the air-fuel ratio. At this time, the greater the degree of one-side delay in the rich direction, the longer the falling time of the sensor value Saf2, while the shorter the rising time.

  The correction unit 140 calculates a correction parameter α when performing the air-fuel ratio imbalance diagnosis using the fluctuation amount P of the sensor value Saf of the air-fuel ratio sensor 19. This correction parameter α is used to approximate the fluctuation amount P of the sensor value Saf that is smaller than the actual fluctuation amount of the air-fuel ratio due to the one-side response delay of the air-fuel ratio sensor 19 to the original fluctuation amount. It is done. Specifically, for each rotation cycle of the internal combustion engine 10, the correction unit 140 performs the first time Per1 until the sensor value Saf of the air-fuel ratio sensor 19 reaches from the rich peak to the lean peak, and the rich from the lean peak. The second time Per2 until reaching the side peak is calculated.

  Further, the correction unit 140 calculates the bias index R based on the calculated first time Per1 and second time Per2, and sets the average value of the accumulated bias index R as the average bias index Ra. In the present embodiment, the ratio of the first time Per1 to the total time of the first time Per1 and the second time Per2 is defined as a bias index R. The ratio of the second time Per2 to the total time may be the bias index R. At this time, the correction unit 140 can obtain the average bias index Ra by using the bias index R accumulated by the sensor value Saf in a period equal to or longer than a predetermined time Ti_B0 set in advance. Thereby, the influence of the fluctuation of the air-fuel ratio that appears instantaneously can be reduced. The predetermined time Ti_B0 can be set to 10 seconds, for example.

  FIG. 5 shows an example of the bias index R in the sensor values of the air-fuel ratio sensor in which the responsiveness is in an appropriate range, the air-fuel ratio sensor in the lean direction one-side response delay state, and the air-fuel ratio sensor in the rich direction one-side delay state. ing. When the responsiveness of the air-fuel ratio sensor 19 is within an appropriate range, the first time Per1 and the second time Per2 are substantially equal, and the bias index R is 0.5. On the other hand, in the lean direction one-side response delay state, the ratio of the first time Per1 and the second time Per2 is 8: 2, and the bias index R is 0.8. In the rich direction one-side response delay state, the ratio of the first time Per1 and the second time Per2 is 2: 8, and the bias index R is 0.2.

  As shown in FIG. 5, when the responsiveness of the air-fuel ratio sensor 19 is within an appropriate range, the first time Per1 and the second time Per2 are set regardless of whether the air-fuel ratio varies among the cylinders. Are almost equal. The air-fuel ratio imbalance diagnosis according to the present embodiment is based on this knowledge.

  When determining the average deviation index Ra, the correction unit 140 calculates a correction parameter α corresponding to the average deviation index Ra. The correction parameter α is an optimal value in advance by simulation using an actual machine so that the fluctuation amount P of the sensor value Saf when the one-side response delay occurs can be approximated to the fluctuation amount of the actual air-fuel ratio. Set to

  FIG. 6 is an explanatory diagram showing a method for setting the correction parameter α. The horizontal axis indicates the bias index R, and the vertical axis indicates the variation amount of the air-fuel ratio. In FIG. 6, the data indicated by triangles △ is data obtained with no air-fuel ratio variation between cylinders, and the data indicated with circles ○ is obtained with air-fuel ratio variations between cylinders. Data. In FIG. 6, it is assumed that it is determined that the variation of the air-fuel ratio has occurred when the variation amount of the air-fuel ratio exceeds the threshold value Pd0.

  Since the data indicated by circles is data when there is a variation in the air-fuel ratio, an abnormality can be detected if it is equal to or greater than the threshold value Pd0. Here, the data belonging to the area A3 is appropriately detected as abnormal because it exceeds the threshold value Pd0. Such a region A3 shows a state in which the bias index R is near 0.5 and the first time Per1 and the second time Per2 are substantially equal, that is, the air-fuel ratio sensor has no one-side response delay. On the other hand, the data belonging to the areas A1, A2, A4, and A5 indicates data in a one-side response delay state in which the ratio between the first time Per1 and the second time Per2 is biased. In the data belonging to the regions A1, A2, A4, and A5, the variation amount of the air-fuel ratio is less than the threshold value Pd0 due to the one-side response delay, and no abnormality is detected. Therefore, the correction parameter α is set so that the corrected variation value exceeds the threshold value Pd0 so that an abnormality is detected in these data.

  However, in the data belonging to the regions A1 and A2, the bias index R is R1 or less, or R2 or more, and an abnormality can be detected by the responsiveness diagnosis of the air-fuel ratio sensor 19 executed separately. Therefore, in particular, the correction parameter α may be set so that data belonging to the regions A4 and A5 is determined to be abnormal by the air-fuel ratio imbalance diagnosis. Specifically, the correction parameter α is set according to the bias index R so that the data belonging to the regions A4 and A5 become the data of the circles ◯ shown by the broken lines exceeding the threshold value Pd0. At this time, the correction parameter α is set so that data having no variation in the air-fuel ratio indicated by the triangle Δ does not exceed the threshold value Pd0. For example, the correction parameter α when the bias index R is R1, R2 may be 3, and the correction parameter α may be linearly changed so that the correction parameter α becomes zero when the bias index R is 0.5. Further, the correction parameter α may be changed stepwise instead of linearly.

  When calculating the correction parameter α as described above, the correction unit 140 calculates the first time Per1 and the second time Per2 when the sensor value Saf of the air-fuel ratio sensor 19 fluctuates in a specific cycle. You may make it calculate. For example, the first time Per1 and the second time Per2 may be calculated when the sensor value Saf varies in synchronization with the rotation cycle of the internal combustion engine 10. As a result, the influence of the change in the air-fuel ratio due to the accelerator operation of the driver can be eliminated, and the presence and extent of the one-side response delay can be accurately reflected.

  The imbalance determination unit 130 corrects the fluctuation amount P obtained by the air-fuel ratio fluctuation amount calculation unit 120 with the correction parameter α obtained by the correction unit 140, and then determines whether or not the air-fuel ratio varies between cylinders. . For example, the imbalance determining unit 130 obtains the diagnostic fluctuation amount Pd by multiplying the fluctuation amount P by the correction parameter α, and when the diagnostic fluctuation amount Pd exceeds a preset threshold value Pd0, variation in the air-fuel ratio occurs. It is determined that The threshold value Pd0 to be used can be set to an appropriate value in advance by simulation or the like using an actual machine.

[3. Example of air-fuel ratio imbalance diagnosis process]
Next, an example of the air-fuel ratio imbalance diagnosis process executed by the air-fuel ratio imbalance diagnosis apparatus (ECU) 100 according to the present embodiment will be described based on the flowcharts of FIGS. The air-fuel ratio imbalance diagnosis process described below can be executed at least once during the period from when the ignition switch of the internal combustion engine 10 is turned on to when it is turned off.

  First, in step S100 in FIG. 7, the ECU 100 determines whether or not the operating state of the internal combustion engine 10 is a state in which the air-fuel ratio fluctuation amount P can be calculated. For example, the determination can be made based on whether the required torque of the internal combustion engine 10 is stable. If the operation state is not such that the air-fuel ratio fluctuation amount P can be calculated (S100: No), the process proceeds to step S400 without executing the process of calculating the air-fuel ratio fluctuation amount P. On the other hand, when the operation state is such that the variation amount P of the air-fuel ratio can be calculated (S100: Yes), the process proceeds to step S200.

  In step S200, the ECU 100 determines whether or not a time Ti_A spent for calculating the accumulated air-fuel ratio fluctuation amount P is less than a predetermined time Ti_A0 set in advance. If the calculation time Ti_A of the air-fuel ratio fluctuation amount P has already reached the predetermined time Ti_A0 (S200: No), the process proceeds to step S400 without executing the process of calculating the air-fuel ratio fluctuation amount P. On the other hand, when the calculation time Ti_A of the air-fuel ratio fluctuation amount P is less than the predetermined time Ti_A0 (S200: Yes), the process proceeds to step S300, and the ECU 100 executes the calculation process of the air-fuel ratio fluctuation amount P.

  FIG. 8 is a flowchart illustrating an example of a calculation process of the air-fuel ratio fluctuation amount P. In the air-fuel ratio fluctuation amount calculation process, first, in step S310, the ECU 100 continuously reads the sensor value Saf of the air-fuel ratio sensor 19. Next, in step S320, the ECU 100 calculates a difference ΔS1 of the sensor value Saf for each rotation cycle of the internal combustion engine 10. Specifically, the maximum value Saf_max and the minimum value Saf_min of the sensor value Saf are specified for each rotation cycle of the internal combustion engine 10, and the difference ΔS1 is calculated.

  Next, in step S330, the ECU 100 calculates the average value of the accumulated difference ΔS1 as the fluctuation amount P. Next, in step S340, the ECU 100 determines whether or not the operating state in which the air-fuel ratio fluctuation amount P can be calculated continues. For example, the determination can be made based on whether or not the required injection amount of the internal combustion engine 10 has changed greatly. When the said driving | running state is continuing (S340: Yes), it returns to step S310 and repeats step S310-step S330 along the procedure mentioned above. On the other hand, when the operation state in which the variation amount P of the air-fuel ratio can be calculated is lost (S340: No), the calculation processing of the variation amount P of the air-fuel ratio is terminated. At this time, the time spent to calculate the fluctuation amount P of the air-fuel ratio this time is added to the accumulated time so far and recorded as the total calculation time Ti_A.

  Returning to FIG. 7, in step S400, the ECU 100 determines whether or not the operation state of the internal combustion engine 10 is a state in which the correction parameter α can be calculated. For example, the determination can be made based on whether the required torque of the internal combustion engine 10 is stable. Alternatively, the determination can be made based on whether or not the fluctuation cycle of the sensor value Saf of the air-fuel ratio sensor 19 is synchronized with the rotation cycle of the internal combustion engine 10. If the operation state is not such that the correction parameter α can be calculated (S400: No), the process proceeds to step S700 without executing the process of calculating the correction parameter α. On the other hand, when the operation state is such that the correction parameter α can be calculated (S400: Yes), the process proceeds to step S500.

  In step S500, the ECU 100 determines whether or not a time Ti_B spent for calculating the correction parameter α that has already been accumulated is less than a predetermined time Ti_B0 set in advance. When the calculation time Ti_B of the correction parameter α has already reached the predetermined time Ti_B0 (S500: No), the process proceeds to step S700 without executing the process of calculating the correction parameter α. On the other hand, when the calculation time Ti_B of the correction parameter α is less than the predetermined time Ti_B0 (S500: Yes), the process proceeds to step S600, and the ECU 100 executes the calculation process of the correction parameter α.

  FIG. 9 is a flowchart illustrating an example of a calculation process of the correction parameter α. In the correction parameter calculation process, first, in step S610, the ECU 100 continuously reads the sensor value Saf of the air-fuel ratio sensor 19. Next, in step S620, the ECU 100 performs the first time Per1 from the rich-side peak to the lean-side peak and the second time from the lean-side peak to the rich-side peak every air-fuel ratio fluctuation period. Per2 is calculated. Specifically, the rich-side peak and the lean-side peak of the sensor value Saf of the air-fuel ratio sensor 19 are specified for each fluctuation period of the air-fuel ratio, and the first time Per1 is obtained using the rich-side peak as a starting point. A second time Per2 from the side peak to the rich side peak of the next cycle is obtained.

  Next, in step S630, the ECU 100 calculates the ratio of the first time Per1 to the total time of the first time Per1 and the second time Per2 as the bias index R for each air-fuel ratio fluctuation period. Next, in step S640, the ECU 100 calculates an average value of the accumulated bias index R and sets it as the average bias index Ra. Next, in step S650, the ECU 100 calculates a correction parameter α corresponding to the average bias index Ra by referring to a map stored in advance. At this time, the greater the degree of one-side response delay of the air-fuel ratio sensor 19, the greater the required correction parameter α.

  Next, in step S660, it is determined whether or not the operation state in which the correction parameter α can be calculated continues. For example, the determination can be made based on whether or not the required torque of the internal combustion engine 10 has changed greatly. When the said driving | running state is continuing (S660: Yes), it returns to step S610 and repeats step S610-step S650 along the procedure mentioned above. On the other hand, if the operation state in which the correction parameter α can be calculated is lost (S660: No), the process proceeds to step S670, the control for repeatedly changing the fuel rich state and the fuel lean state of the air-fuel ratio is terminated, and the correction parameter α is completed. The calculation process is terminated. At this time, the time spent for calculating the correction parameter α this time is added to the accumulated time so far and recorded as the total calculation time Ti_B.

  Returning to FIG. 7, in step S700, the ECU 100 determines whether the calculation time Ti_A of the air-fuel ratio fluctuation amount P has already reached the predetermined time Ti_A0 and the calculation time Ti_B of the correction parameter α has already reached the predetermined time Ti_B0. Determine whether or not. When at least one of the calculation times Ti_A and Ti_B has not reached the predetermined time Ti_A0 and Ti_B0 (S700: No), the process returns to step S100, and steps S100 to S600 are repeated according to the above-described procedure. On the other hand, if both the calculation times Ti_A and Ti_B have reached the predetermined times Ti_A0 and Ti_B0 (S700: Yes), the process proceeds to step S800, and the ECU 100 executes air-fuel ratio imbalance diagnosis.

  FIG. 10 is a flowchart showing an example of the air-fuel ratio imbalance diagnosis process. In the air-fuel ratio imbalance diagnosis process, first, in step S810, the ECU 100 calculates the diagnostic fluctuation amount Pd by multiplying the air-fuel ratio fluctuation amount P by the correction parameter α. Next, in step S820, the ECU 100 determines whether or not the diagnostic fluctuation amount Pd exceeds a preset threshold value Pd0. When the diagnostic variation amount Pd exceeds the threshold value Pd0 (S820: Yes), the process proceeds to step S830, and the ECU 100 determines that the air-fuel ratio varies among the cylinders. Along with this, measures such as turning on a warning lamp (MIL) are performed. On the other hand, when the diagnostic fluctuation amount P is equal to or less than the threshold value Pd0 (S820: No), the process proceeds to step S840, and the ECU 100 determines that there is no variation in air-fuel ratio among the cylinders.

  As described above, the value of the correction parameter α used in the air-fuel ratio imbalance diagnosis according to the present embodiment increases as the one-side response delay of the air-fuel ratio sensor 19 increases. Accordingly, by correcting the air-fuel ratio fluctuation amount P obtained during operation of the internal combustion engine 10 with the correction parameter α, the diagnostic fluctuation amount Pd in a state where the influence of the one-side response delay of the air-fuel ratio sensor 19 is reduced is obtained. be able to. By executing the air-fuel ratio imbalance diagnosis using the diagnostic fluctuation amount Pd, a diagnosis result in which the influence of the one-side response delay of the air-fuel ratio sensor 19 is reduced can be obtained.

  FIG. 11 shows an abnormality detection situation based on the responsiveness diagnosis of the air-fuel ratio sensor 19, an abnormality detection situation based on the air-fuel ratio imbalance diagnosis according to the present embodiment, and a warning lamp (MIL) being lit. Indicates the situation. In the region A and the region C, as in the case shown in FIG. 12, the responsiveness abnormality or the air-fuel ratio imbalance abnormality is detected, and the warning lamp is turned on. Further, according to the air-fuel ratio imbalance diagnosis apparatus 100 according to the present embodiment, the air-fuel ratio imbalance diagnosis is performed even in the region B where the one-side response delay of the air-fuel ratio sensor 19 has occurred to such an extent that no abnormality is detected in the response diagnosis. It becomes possible to detect an abnormality. Therefore, it is possible to prevent the air-fuel ratio control from being executed without detecting any abnormality even if the air-fuel ratio varies between the cylinders.

  As described above, the air-fuel ratio imbalance diagnosis apparatus 100 according to the present embodiment uses the diagnostic fluctuation amount Pd obtained by multiplying the fluctuation amount P of the sensor value Saf of the air-fuel ratio sensor 19 by the correction parameter α. Perform balance diagnosis. Therefore, the air-fuel ratio imbalance diagnosis can be executed after reducing the influence of the one-side response delay of the air-fuel ratio sensor 19. Thereby, even when the one-side response delay of the air-fuel ratio sensor 19 occurs, it is possible to detect the variation in the air-fuel ratio between the cylinders. As a result, it is possible to prevent the air-fuel ratio control from continuing without turning on the warning lamp or the like.

  In particular, in the present embodiment, when calculating the correction parameter α, the sensor value Saf detected in a state where the fluctuation cycle of the sensor value Saf of the air-fuel ratio sensor 19 is synchronized with the rotation cycle of the internal combustion engine 10 is calculated. Thus, the correction parameter α is obtained. Therefore, it is possible to obtain the correction parameter α in which the variation in the air-fuel ratio due to the driver's accelerator operation or the like is eliminated and the one-side response delay is reflected. Therefore, it is possible to obtain an appropriate correction parameter α according to the degree of one-side response delay of the air-fuel ratio sensor 19. As a result, variation in the air-fuel ratio between cylinders can be detected with high accuracy.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can make various modifications or application examples within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above embodiment, when the calculation time Ti_A of the air-fuel ratio fluctuation amount P and the calculation time Ti_B of the correction parameter α are equal to or longer than the predetermined times Ti_A0 and Ti_B0, respectively, the air-fuel ratio imbalance determination is started. However, it is not limited to this example. The air-fuel ratio imbalance determination may be started when the difference ΔS1 between the maximum value Saf_max and the minimum value Saf_min of the air-fuel ratio or the number of times the bias index R is calculated exceeds a predetermined number.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Fuel injection valve 18 Exhaust pipe 19 Air fuel ratio sensor 100 Air fuel ratio imbalance diagnostic apparatus (ECU)
110 Air-fuel ratio detection unit 120 Air-fuel ratio fluctuation amount calculation unit 130 Imbalance determination unit 140 Correction unit

Claims (6)

In an air-fuel ratio imbalance diagnostic apparatus for diagnosing variation in air-fuel ratio between cylinders of an internal combustion engine,
An air-fuel ratio fluctuation amount calculating unit for calculating the fluctuation amount of the sensor value of the air-fuel ratio sensor;
The fluctuation amount based on the ratio of the first time from the rich side peak to the lean side peak and the second time from the lean side peak to the rich side peak in the fluctuation of the sensor value of the air-fuel ratio sensor. A correction unit for correcting
An imbalance determination unit for determining a variation in the air-fuel ratio based on the corrected variation amount;
An air-fuel ratio imbalance diagnosis device comprising:   2. The air-fuel ratio imbalance diagnosis apparatus according to claim 1, wherein the correction unit corrects the fluctuation amount by a correction coefficient corresponding to a ratio between the first time and the second time.   The air-fuel ratio according to claim 1 or 2, wherein the correction unit calculates the first time and the second time in a state where a fluctuation cycle of the sensor value is synchronized with a rotation cycle of the internal combustion engine. Imbalance diagnostic device.   The air-fuel ratio imbalance diagnosis according to any one of claims 1 to 3, wherein the correction unit corrects the fluctuation amount when a ratio between the first time and the second time is within a predetermined range. apparatus.   5. The air-fuel ratio input according to claim 4, wherein the predetermined range includes a range of a ratio indicated by a state in which the response of the air-fuel ratio sensor is reduced but is not determined to be abnormal by a separately executed response diagnosis. Balance diagnostic device. In an air-fuel ratio imbalance diagnosis method for diagnosing variation in air-fuel ratio between cylinders of an internal combustion engine,
Calculating the fluctuation amount of the sensor value of the air-fuel ratio sensor;
The fluctuation amount based on the ratio of the first time from the rich side peak to the lean side peak and the second time from the lean side peak to the rich side peak in the fluctuation of the sensor value of the air-fuel ratio sensor. A step of correcting
Determining a variation in the air-fuel ratio based on the corrected variation amount;
An air-fuel ratio imbalance diagnosis method comprising:

Images