JP2006138280A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately diagnose the presence of abnormality of each cylinder without being affected by an abnormal cylinder during air-fuel ratio control according to cylinders. <P>SOLUTION: The air-fuel ratio control according to the cylinders is performed by estimating the air-fuel ratio of each cylinder based on a detection value of an air-fuel ratio sensor 37, and controlling the air-fuel ratio of each cylinder to reduce air-fuel ratio dispersion among the cylinders based on the estimated air-fuel ratio of each cylinder. During this air-fuel ratio control according to the cylinders, the estimated air-fuel ratios of the i-th cylinder (i=1, 2, ...) and the average value of the remaining estimated air-fuel ratios excluding the minimum value and the maximum value out of the estimated air-fuel ratios of the cylinders other than the i-th cylinder, are compared for every cylinder to determine whether the i-th cylinder is abnormal. Consequently, even if the abnormal cylinder exists among the cylinders other than the i-th cylinder, whether the i-th cylinder is abnormal is accurately diagnosed by comparing the estimated air-fuel ratio of the i-th cylinder with the average value of the remaining estimated air-fuel ratio excluding the estimated air-fuel ratio of the abnormal cylinder from the estimated air-fuel ratios of the cylinders other than the i-th cylinder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine having a function of diagnosing the presence or absence of abnormality for each cylinder of the internal combustion engine.

  In recent years, in order to reduce the air-fuel ratio variation between cylinders of an internal combustion engine and improve the air-fuel ratio control accuracy, each of the cylinders is based on the output of an air-fuel ratio sensor installed in an exhaust gas collecting portion where the exhaust gas of each cylinder collects and flows. Estimate the air-fuel ratio of each cylinder, and set the air-fuel ratio correction amount (for example, fuel injection correction amount) for each cylinder so that the variation in air-fuel ratio among the cylinders is reduced based on the estimated air-fuel ratio for each cylinder. There is one that performs “cylinder-by-cylinder air-fuel ratio control” for controlling the cylinder.

  In such a system that performs cylinder-by-cylinder air-fuel ratio control, for example, as described in Patent Document 1 (Japanese Utility Model Publication No. 6-45644), the air-fuel ratio correction amount of any one of the cylinders is set to other values. In some cases, the presence or absence of abnormality of the cylinder is diagnosed by comparing with the average value of the air-fuel ratio correction amount of the cylinder.

Further, as described in Japanese Patent No. 2684011, it is determined for each cylinder whether or not the air-fuel ratio correction amount of each cylinder is within a predetermined range, and the presence or absence of abnormality in each cylinder is diagnosed. Some of them are
Japanese Utility Model Publication No. 6-45644 (page 3, etc.) Japanese Patent No. 2684011 (first page, etc.)

  However, in the abnormality diagnosis of Patent Document 1, when comparing the air-fuel ratio correction amount of a predetermined cylinder with the average value of the air-fuel ratio correction amounts of cylinders other than the predetermined cylinder, there is an abnormality in the cylinders other than the predetermined cylinder. If there is a certain cylinder (for example, a cylinder in which the air-fuel ratio is rich or greatly deviated in the lean direction), the information on the abnormal cylinder is included in the average value of the air-fuel ratio correction amounts of the cylinders other than the predetermined cylinder. The accuracy of abnormality diagnosis using the average value is lowered, and in the worst case, a normal cylinder may be erroneously diagnosed as having an abnormality.

  In general, in the cylinder-by-cylinder air-fuel ratio control, when the deviation of the air-fuel ratio of a certain cylinder is large, control is performed so as to correct the air-fuel ratio of other cylinders so as to eliminate it. However, in the abnormality diagnosis of Patent Document 2, the air-fuel ratio correction amount of one cylinder is simply set to a predetermined value without comparing the air-fuel ratio correction amount of the cylinder to be diagnosed with the air-fuel ratio correction amount of other cylinders. In order to diagnose the presence or absence of abnormality of the cylinder only by whether or not it is within the range, when the air-fuel ratio correction amount of the normal cylinder greatly changes due to the influence of the deviation of the air-fuel ratio of the other abnormal cylinder, There is a possibility that a normal cylinder is erroneously diagnosed as abnormal.

  The present invention has been made in consideration of these circumstances, and therefore the object of the present invention is an internal combustion engine that can accurately diagnose the presence or absence of abnormality in each cylinder without being affected by the abnormal cylinder. It is to provide a control device.

  In order to achieve the above object, an internal combustion engine control apparatus according to claim 1 of the present invention detects an air-fuel ratio of each cylinder of an internal combustion engine by a cylinder-by-cylinder air-fuel ratio detection means, and the cylinder-by-cylinder air-fuel ratio control means. In a system that performs cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio for each cylinder based on the detected air-fuel ratio of each cylinder, during cylinder-by-cylinder air-fuel ratio control, the cylinder-by-cylinder abnormality diagnosis means detects the detected air-fuel ratio of a predetermined cylinder or correlates with it. Information (hereinafter referred to as “detected air-fuel ratio information”) is compared with the average value of the remaining detected air-fuel ratio information excluding the maximum value and the minimum value of the detected air-fuel ratio information of the other cylinders. It is intended to diagnose the presence or absence of.

  When an abnormality diagnosis of a predetermined cylinder is performed, if there is an abnormal cylinder (for example, a cylinder in which the air-fuel ratio is rich or greatly deviated in the lean direction) among the other cylinders, detected air-fuel ratio information (for example, a detected air-fuel ratio) of the abnormal cylinder is present. The fuel ratio, the air-fuel ratio correction amount, etc.) are the maximum value or the minimum value among the other cylinders. Focusing on this point, as in claim 1, the detected air-fuel ratio information of the predetermined cylinder is the detected air-fuel ratio information of the remaining cylinders excluding the maximum value and the minimum value of the detected air-fuel ratio information of the other cylinders. Compared with the average value, even if an abnormal cylinder exists among the other cylinders, the detected air-fuel ratio information of the predetermined cylinder is obtained, and the detected air-fuel ratio information of the abnormal cylinder is obtained from the detected air-fuel ratio information of the other cylinders. It can be compared with the average value of the detected air-fuel ratio information of the remaining cylinders excluded, and the presence / absence of abnormality of the predetermined cylinder can be diagnosed with high accuracy. In this way, if abnormality diagnosis is performed for each cylinder, the presence or absence of abnormality in each cylinder can be accurately diagnosed without being affected by the detected air-fuel ratio information of the abnormal cylinder.

  Further, as in claim 2, during the air-fuel ratio control for each cylinder, the detected air-fuel ratio information of the predetermined cylinder is compared with the median (median value) of the detected air-fuel ratio information of the other cylinders, and the abnormality of the predetermined cylinder is detected. The presence or absence may be diagnosed. In this way, even if there is an abnormal cylinder among the other cylinders, the detected air-fuel ratio information of the predetermined cylinder is used as the detected air-fuel ratio information (maximum value) of the abnormal cylinder among the detected air-fuel ratio information of the other cylinders. Or the detected air-fuel ratio information (median) other than the minimum value), it is possible to accurately diagnose the presence / absence of abnormality of the predetermined cylinder, without being affected by the detected air-fuel ratio information of the abnormal cylinder, The presence or absence of abnormality in each cylinder can be diagnosed with high accuracy.

  By the way, if a misfire occurs during air-fuel ratio control for each cylinder, the detection accuracy of the detected air-fuel ratio of each cylinder decreases, so the diagnosis accuracy of abnormality diagnosis using the detected air-fuel ratio information decreases, and the presence or absence of an abnormality is erroneously detected. There is a possibility of diagnosis.

  Therefore, as described in claim 3, it is preferable to prohibit the abnormality diagnosis by the cylinder-specific abnormality diagnosis means at the time of misfire of the internal combustion engine and until a predetermined period thereafter. In this way, during the period when the detection accuracy of the detected air-fuel ratio of each cylinder decreases due to the effect of misfire, the abnormality diagnosis using the detected air-fuel ratio information is prohibited to prevent the erroneous diagnosis of the presence or absence of abnormality. be able to.

  Also, if misfire occurs during cylinder-by-cylinder air-fuel ratio control, the detection accuracy of the detected air-fuel ratio of each cylinder decreases, so that the control accuracy of cylinder-by-cylinder air-fuel ratio control using the detected air-fuel ratio information decreases, so that There is a possibility that the air-fuel ratio variation of the engine will deteriorate.

  Therefore, as described in claim 4, the cylinder-by-cylinder air-fuel ratio control may be prohibited when a misfire occurs in the internal combustion engine and until a predetermined period thereafter. In this way, the cylinder-by-cylinder air-fuel ratio control using the detected air-fuel ratio information is prohibited during the period when the detection accuracy of the detected air-fuel ratio of each cylinder is lowered due to the effect of misfire, and the cylinder-by-cylinder air-fuel ratio control accuracy is reduced. It is possible to prevent deterioration in air-fuel ratio variation between cylinders.

  By the way, an air-fuel ratio sensor may be installed in each exhaust manifold of each cylinder so that the air-fuel ratio of the exhaust gas of each cylinder is directly detected by the air-fuel ratio sensor of each cylinder. The same number of air-fuel ratio sensors are required, causing a problem of increasing costs.

  Therefore, as described in claim 5, it is preferable to estimate the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor installed in the exhaust collecting portion where the exhaust gas of each cylinder collects and flows. In this way, the air-fuel ratio of all the cylinders can be estimated with one air-fuel ratio sensor, and the demand for cost reduction can be satisfied.

  Hereinafter, the best mode for carrying out the present invention will be described using two Examples 1 and 2.

  A first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An in-line six-cylinder engine 11 that is an internal combustion engine, for example, has six cylinders, a first cylinder # 1 to a sixth cylinder # 6, and an air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11. An air flow meter 14 for detecting the intake air amount is provided on the downstream side of the air cleaner 13. On the downstream side of the air flow meter 14, a throttle valve 15 whose opening is adjusted by a motor or the like and a throttle opening sensor 16 for detecting the throttle opening are provided.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. During engine operation, the fuel in the fuel tank 21 is sent to the delivery pipe 23 by the fuel pump 22 and fuel is injected from the fuel injection valve 20 of each cylinder at each injection timing of each cylinder. A fuel pressure sensor 24 that detects fuel pressure (fuel pressure) is attached to the delivery pipe 23.

  Further, the engine 11 is provided with variable valve timing mechanisms 27 and 28 for changing the opening and closing timings of the intake valve 25 and the exhaust valve 26, respectively. Further, the engine 11 is provided with an intake cam angle sensor 31 and an exhaust cam angle sensor 32 that output a cam angle signal in synchronization with the rotation of the intake cam shaft 29 and the exhaust cam shaft 30, and the rotation of the crank shaft of the engine 11. Is provided with a crank angle sensor 33 for outputting a pulse of a crank angle signal at every predetermined crank angle (for example, every 30 ° C. A).

  On the other hand, an air-fuel ratio sensor 37 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust collecting portion 36 where the exhaust manifold 35 of each cylinder of the engine 11 gathers. A catalyst 38 such as a three-way catalyst for purifying CO, HC, NOx and the like is provided.

  Outputs of various sensors such as the air-fuel ratio sensor 37 are input to an engine control circuit (hereinafter referred to as “ECU”) 40. The ECU 40 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount of the fuel injection valve 20 can be changed according to the engine operating state. Control ignition timing.

  The ECU 40 executes a cylinder-by-cylinder air-fuel ratio control program shown in FIG. 2 to be described later. First, for example, using a cylinder-by-cylinder air-fuel ratio estimation model, the detected value of the air-fuel ratio sensor 37 (exhaust gas flowing through the exhaust collecting unit 36). The actual air / fuel ratio) is estimated based on the air / fuel ratio α (#i) of each cylinder. Here, (#i) is a cylinder number and means any one of (# 1) to (# 6). Then, the average value of the estimated air-fuel ratios α (# 1) to α (# 6) of all cylinders is set as the reference air-fuel ratio, and the estimated air-fuel ratio α (#i) and the reference air-fuel ratio are set for each cylinder. The air-fuel ratio correction amount (fuel injection correction amount) is calculated so that the deviation becomes small, and the fuel injection amount of each cylinder is corrected based on the air-fuel ratio correction amount of each cylinder, so that the air-fuel mixture supplied to each cylinder “Cylinder-by-cylinder air-fuel ratio control” is performed in which the air-fuel ratio is corrected for each cylinder so as to reduce the variation in air-fuel ratio among the cylinders.

  Further, the ECU 40 executes an abnormality diagnosis program for each cylinder shown in FIGS. 3 and 4 to be described later, so that the estimated air-fuel ratio of the cylinders other than the i-th cylinder #i is determined for each cylinder during the cylinder-by-cylinder air-fuel ratio control. Find the minimum value αmin (#i) and the maximum value αmax (#i) and exclude the minimum value αmin (#i) and the maximum value αmax (#i) from the estimated air-fuel ratio of cylinders other than the i-th cylinder #i The average value αave (#i) of the remaining estimated air-fuel ratio is calculated (i = 1, 2,..., 6). For each cylinder, the minimum value αmin (#i) and the maximum value αmax (#max) of the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the estimated air-fuel ratios of cylinders other than the i-th cylinder #i. Based on the deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio excluding i), the presence or absence of abnormality in the i-th cylinder #i is determined.

In the abnormality diagnosis of the i-th cylinder #i, if there is an abnormal cylinder (for example, a cylinder in which the air-fuel ratio is rich or lean in the lean direction) among the cylinders other than the i-th cylinder #i, the abnormal cylinder The estimated air-fuel ratio becomes the maximum value or the minimum value among the cylinders other than the i-th cylinder #i. Therefore, as in the first embodiment, the minimum value αmin (#i) and the maximum value among the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the estimated air-fuel ratio of cylinders other than the i-th cylinder #i. If the presence or absence of abnormality in the i-th cylinder #i is diagnosed based on the deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio excluding αmax (#i), the i-th Even if an abnormal cylinder exists in cylinders other than cylinder #i, the abnormal cylinder is determined from the estimated air-fuel ratio α (#i) of i-th cylinder #i and the estimated air-fuel ratio of cylinders other than i-th cylinder #i. Based on the deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio excluding the estimated air-fuel ratio, it is possible to accurately diagnose whether or not the i-th cylinder #i is abnormal.
Hereinafter, the processing content of each program of FIG. 2 thru | or FIG. 4 which ECU40 performs is demonstrated.

[Air-fuel ratio control by cylinder]
The cylinder-by-cylinder air-fuel ratio control program shown in FIG. 2 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. As a role. When this program is started, first, in step 101, it is determined whether or not the execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied. As execution conditions for the cylinder-by-cylinder air-fuel ratio control, for example, there are the following conditions (1) to (4).

(1) The air-fuel ratio sensor 37 is in an active state
(2) The air-fuel ratio sensor 37 is not determined to be abnormal (failure)
(3) The engine 11 is in a warm-up state (for example, the cooling water temperature is equal to or higher than a predetermined temperature).
(4) The engine operating range (for example, engine speed and intake pipe pressure) is an operating range that can ensure the air-fuel ratio estimation accuracy. When all of these four conditions (1) to (4) are satisfied, the air-fuel ratio for each cylinder If the control execution condition is satisfied and any one of the conditions is not satisfied, the execution condition is not satisfied. If the execution condition is not satisfied, the program is terminated without performing the subsequent processing.

  On the other hand, if the execution condition is satisfied, the process proceeds to step 102, the output of the air-fuel ratio sensor 37 (air-fuel ratio detection value) is read, and in the next step 103, for example, this time using a cylinder-by-cylinder air-fuel ratio estimation model. The air-fuel ratio α (#i) of the cylinder that is the target of the air-fuel ratio is estimated based on the detected value of the air-fuel ratio sensor 37. The processing in step 103 serves as cylinder-by-cylinder air-fuel ratio detection means in the claims.

Thereafter, the routine proceeds to step 104, where the average value of the estimated air-fuel ratios α (# 1) to α (# 6) of all cylinders is calculated, and the average value is set as the reference air-fuel ratio.
Thereafter, the routine proceeds to step 105, where the deviation between the estimated air-fuel ratio α (#i) of each cylinder and the reference air-fuel ratio is calculated, and the air-fuel ratio correction amount (fuel injection correction amount) of each cylinder is reduced so that the deviation becomes smaller. ) Is calculated, the process proceeds to step 106, and the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder by correcting the fuel injection amount of each cylinder based on the air-fuel ratio correction amount of each cylinder. Thus, control is performed so as to reduce variations in the air-fuel ratio between the cylinders.

[Abnormal diagnosis by cylinder]
The cylinder-specific abnormality diagnosis program shown in FIG. 3 and FIG. 4 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33, and the cylinder-specific abnormality diagnosis referred to in the claims. Acts as a means. When this program is started, first, in step 201, it is determined whether or not an execution condition for abnormality diagnosis for each cylinder is satisfied. For example, the following conditions (1) to (3) are conditions for executing the cylinder-by-cylinder abnormality diagnosis.

(1) Air-fuel ratio control for each cylinder is in progress
(2) Not determined to have misfire
(3) A predetermined period of time has elapsed after the misfire has occurred. When all of these three conditions (1) to (3) are satisfied, the condition for executing the abnormality diagnosis for each cylinder is satisfied, and any one of the conditions is not satisfied. If there is, the execution condition is not satisfied. If the execution condition of the cylinder-by-cylinder abnormality diagnosis is not satisfied, the program is terminated without performing the process related to the cylinder-by-cylinder abnormality diagnosis from step 202 onward.

  If misfire occurs during the air-fuel ratio control for each cylinder, the estimation accuracy of the estimated air-fuel ratio α (#i) of each cylinder decreases, so the diagnosis accuracy of the abnormality diagnosis for each cylinder based on the estimated air-fuel ratio α (#i) There is a possibility that it may be mistakenly diagnosed for abnormality. Therefore, by setting the conditions (2) and (3) above as conditions for executing the cylinder-by-cylinder abnormality diagnosis, the estimated accuracy of the estimated air-fuel ratio of each cylinder is reduced when a misfire occurs and for a predetermined period thereafter (because of misfire). The cylinder-by-cylinder abnormality diagnosis is prohibited until a period of time elapses. In this case, the process of step 201 serves as a cylinder-specific abnormality diagnosis prohibiting means as defined in the claims.

  On the other hand, when it is determined in step 201 that the execution condition for the cylinder-by-cylinder abnormality diagnosis is satisfied, the processing relating to the cylinder-by-cylinder abnormality diagnosis from step 202 is executed as follows. First, in step 202, the estimated air-fuel ratio α (#i) of each cylinder is read.

Thereafter, the process proceeds to step 203, and the minimum value αmin (#i) of the estimated air-fuel ratios of the cylinders other than the i-th cylinder #i is obtained for each of the cylinders # 1 to # 6.
αmin (# 1) = min {α (# 2), α (# 3), α (# 4), α (# 5), α (# 6)}
αmin (# 2) = min {α (# 1), α (# 3), α (# 4), α (# 5), α (# 6)}
αmin (# 3) = min {α (# 1), α (# 2), α (# 4), α (# 5), α (# 6)}
αmin (# 4) = min {α (# 1), α (# 2), α (# 3), α (# 5), α (# 6)}
αmin (# 5) = min {α (# 1), α (# 2), α (# 3), α (# 4), α (# 6)}
αmin (# 6) = min {α (# 1), α (# 2), α (# 3), α (# 4), α (# 5)}

Thereafter, the routine proceeds to step 204, where the maximum value αmax (#i) of the estimated air-fuel ratios of the cylinders other than the i-th cylinder #i is obtained for each of the cylinders # 1 to # 6.
αmax (# 1) = max {α (# 2), α (# 3), α (# 4), α (# 5), α (# 6)}
αmax (# 2) = max {α (# 1), α (# 3), α (# 4), α (# 5), α (# 6)}
αmax (# 3) = max {α (# 1), α (# 2), α (# 4), α (# 5), α (# 6)}
αmax (# 4) = max {α (# 1), α (# 2), α (# 3), α (# 5), α (# 6)}
αmax (# 5) = max {α (# 1), α (# 2), α (# 3), α (# 4), α (# 6)}
αmax (# 6) = max {α (# 1), α (# 2), α (# 3), α (# 4), α (# 5)}

  Thereafter, the process proceeds to step 205, and the remaining values excluding the minimum value αmin (#i) and the maximum value αmax (#i) among the estimated air-fuel ratios of the cylinders other than the i-th cylinder #i for each of the cylinders # 1 to # 6. The average value αave (#i) of the estimated air-fuel ratio is obtained.

αave (# 1) = [{α (# 2) + α (# 3) + α (# 4) + α (# 5) + α (# 6)}
− {Αmin (# 1) + αmax (# 1)}] / 3
αave (# 2) = [{α (# 1) + α (# 3) + α (# 4) + α (# 5) + α (# 6)}
− {Αmin (# 2) + αmax (# 2)}] / 3
αave (# 3) = [{α (# 1) + α (# 2) + α (# 4) + α (# 5) + α (# 6)}
− {Αmin (# 3) + αmax (# 3)}] / 3
αave (# 4) = [{α (# 1) + α (# 2) + α (# 3) + α (# 5) + α (# 6)}
− {Αmin (# 4) + αmax (# 4)}] / 3
αave (# 5) = [{α (# 1) + α (# 2) + α (# 3) + α (# 4) + α (# 6)}
− {Αmin (# 5) + αmax (# 5)}] / 3
αave (# 6) = [{α (# 1) + α (# 2) + α (# 3) + α (# 4) + α (# 5)}
− {Αmin (# 6) + αmax (# 6)}] / 3

Thereafter, the process proceeds to step 206 in FIG. 4, and for each cylinder # 1 to # 6, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the estimated air-fuel ratio of the cylinders other than the i-th cylinder #i A deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio excluding the minimum value αmin (#i) and the maximum value αmax (#i) is obtained.
Δα (#i) = α (#i) −αave (#i)

  Thereafter, the process proceeds to step 207, where it is determined whether or not the deviation Δα (#i) is equal to or greater than the lean determination value for each cylinder # 1 to # 6, and the deviation Δα (#i) is equal to or greater than the lean determination value. When it is determined that the lean abnormality counter is incremented (step 208), and when it is determined that the deviation Δα (#i) is smaller than the lean determination value, the lean normal counter is incremented (step 208). 209).

  Thereafter, the routine proceeds to step 210, where it is determined whether or not the deviation Δα (#i) is equal to or less than the rich determination value for each of the cylinders # 1 to # 6, and the deviation Δα (#i) is equal to or less than the rich determination value. Is determined (step 211), and when it is determined that the deviation Δα (#i) is larger than the rich determination value, the rich normal counter is counted up (step 211). 212).

  Thereafter, the process proceeds to step 213, where it is determined whether or not the count value of the lean abnormality counter exceeds the lean abnormality determination value for each cylinder # 1 to # 6, and the count value of the lean abnormality counter of any cylinder is lean. When the abnormality determination value is exceeded, the routine proceeds to step 214, where it is determined that there is a lean abnormality for the cylinder whose count value of the lean abnormality counter exceeds the lean abnormality determination value.

  Thereafter, the process proceeds to step 215, and for each cylinder # 1 to # 6, it is determined whether or not the count value of the rich abnormality counter has exceeded the rich abnormality determination value, and the count value of the rich abnormality counter of any cylinder is rich. When the abnormality determination value is exceeded, the routine proceeds to step 216, where it is determined that there is a rich abnormality for the cylinder whose count value of the rich abnormality counter exceeds the rich abnormality determination value.

  The abnormality diagnosis result of this program is stored in a rewritable nonvolatile memory such as a backup RAM (not shown) of the ECU 40.

  In the first embodiment described above, for each cylinder, the estimated value αmin (#i) of the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the estimated air-fuel ratio of cylinders other than the i-th cylinder #i. ) And the deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio excluding the maximum value αmax (#i), the presence / absence of abnormality in the i-th cylinder #i is diagnosed. Therefore, even if there is an abnormal cylinder other than the i-th cylinder #i, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the cylinders other than the i-th cylinder #i Existence of abnormality in the i-th cylinder #i is accurately diagnosed on the basis of the deviation Δα (#i) from the average value αave (#i) of the remaining estimated air-fuel ratio obtained by excluding the estimated air-fuel ratio of the abnormal cylinder from the estimated air-fuel ratio can do. As a result, it is possible to accurately diagnose whether there is an abnormality in each cylinder without being affected by the estimated air-fuel ratio of the abnormal cylinder.

  Further, in the first embodiment, the cylinder-by-cylinder abnormality diagnosis is prohibited at the time of misfire and until a predetermined period thereafter, so that the estimated accuracy of the estimated air-fuel ratio α (#i) of each cylinder is affected by the misfire. During the period of decrease, cylinder-by-cylinder abnormality diagnosis based on the estimated air-fuel ratio α (#i) can be prohibited to prevent erroneous diagnosis of the presence or absence of abnormality.

  Further, in the first embodiment, since the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor 37 installed in the exhaust collecting portion 36, one air-fuel ratio sensor 37 is used for all the cylinders. The air-fuel ratio can be estimated, and the demand for cost reduction can be satisfied.

Next, Embodiment 2 of the present invention will be described with reference to FIGS.
In the second embodiment, by executing the cylinder-specific abnormality diagnosis program of FIG. 5 and FIG. 6, for each cylinder, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the i-th cylinder #i The presence or absence of abnormality in the i-th cylinder #i is determined based on the deviation Δα (#i) from the median αmed (#i) of the estimated air-fuel ratio of this cylinder. As a result, even if an abnormal cylinder exists among the cylinders other than the i-th cylinder #i, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the cylinders other than the i-th cylinder #i Based on the deviation Δα (#i) from the median αmed (#i), which is an estimated air-fuel ratio other than the estimated air-fuel ratio (maximum value or minimum value) of the abnormal cylinder among the estimated air-fuel ratios, The presence or absence can be accurately diagnosed.

  In the cylinder-by-cylinder abnormality diagnosis program shown in FIGS. 5 and 6, first, at step 301, it is determined whether or not the execution condition of the cylinder-by-cylinder abnormality diagnosis is satisfied, and it is determined that the execution condition is satisfied. In step 302, the estimated air-fuel ratio α (#i) of each cylinder is read.

Thereafter, the process proceeds to step 303, and the median αmed (#i) of the estimated air-fuel ratio of the cylinders other than the i-th cylinder #i is obtained for each of the cylinders # 1 to # 6.
αmed (# 1) = med {α (# 2), α (# 3), α (# 4), α (# 5), α (# 6)}
αmed (# 2) = med {α (# 1), α (# 3), α (# 4), α (# 5), α (# 6)}
αmed (# 3) = med {α (# 1), α (# 2), α (# 4), α (# 5), α (# 6)}
αmed (# 4) = med {α (# 1), α (# 2), α (# 3), α (# 5), α (# 6)}
αmed (# 5) = med {α (# 1), α (# 2), α (# 3), α (# 4), α (# 6)}
αmed (# 6) = med {α (# 1), α (# 2), α (# 3), α (# 4), α (# 5)}

Thereafter, the process proceeds to step 304 in FIG. 6, and for each cylinder # 1 to # 6, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the median of the estimated air-fuel ratio of cylinders other than the i-th cylinder #i. Find the deviation Δα (#i) from αmed (#i).
Δα (#i) = α (#i) −αmed (#i)

  Thereafter, the process proceeds to step 305, where it is determined whether or not the deviation Δα (#i) is greater than or equal to the lean determination value for each cylinder # 1 to # 6, and the deviation Δα (#i) is greater than or equal to the lean determination value. When it is determined that the lean abnormality counter is counted up (step 306), when it is determined that the deviation Δα (#i) is smaller than the lean determination value, the lean normal counter is counted up (step 306). 307).

  Thereafter, the process proceeds to step 308, where it is determined whether or not the deviation Δα (#i) is less than or equal to the rich determination value for each cylinder # 1 to # 6, and the deviation Δα (#i) is less than or equal to the rich determination value. Is determined (step 309), and when it is determined that the deviation Δα (#i) is larger than the rich determination value, the rich normal counter is counted up (step 309). 310).

  Thereafter, the process proceeds to step 311 to determine whether or not the count value of the lean abnormality counter has exceeded the lean abnormality determination value for each of the cylinders # 1 to # 6, and the count value of the lean abnormality counter of any cylinder is lean. If the abnormality determination value has been exceeded, the routine proceeds to step 312, where it is determined that there is a lean abnormality for the cylinder whose count value of the lean abnormality counter has exceeded the lean abnormality determination value.

  Thereafter, the process proceeds to step 313, and for each cylinder # 1 to # 6, it is determined whether or not the count value of the rich abnormality counter exceeds the rich abnormality determination value, and the count value of the rich abnormality counter of any cylinder is rich. If the abnormality determination value has been exceeded, the routine proceeds to step 314, where it is determined that there is a rich abnormality for the cylinder whose count value of the rich abnormality counter has exceeded the rich abnormality determination value.

  In the second embodiment described above, the estimated air-fuel ratio α (#i) of the i-th cylinder #i and the estimated air-fuel ratio median αmed (#i) of cylinders other than the i-th cylinder #i are determined for each cylinder. Since the presence or absence of abnormality of the i-th cylinder #i is diagnosed based on the deviation Δα (#i) of the engine, even if there is an abnormal cylinder among cylinders other than the i-th cylinder #i, The median that is the estimated air-fuel ratio other than the estimated air-fuel ratio (maximum value or minimum value) of the abnormal cylinder among the estimated air-fuel ratio α (#i) of i-cylinder #i and the estimated air-fuel ratio of cylinders other than i-th cylinder #i Based on the deviation Δα (#i) from αmed (#i), it is possible to accurately diagnose whether or not the i-th cylinder #i is abnormal, and without being affected by the estimated air-fuel ratio of the abnormal cylinder, The presence or absence of abnormality can be diagnosed with high accuracy.

  In the first and second embodiments, the cylinder air-fuel ratio control is performed based on the output of the air-fuel ratio sensor 37 installed in the exhaust collecting portion 36 where the exhaust manifold 35 of each cylinder of the engine 11 gathers. Although the present invention is applied, an exhaust system is configured for each cylinder group as in, for example, a V-type engine, and a cylinder is provided for each cylinder group based on an output of an air-fuel ratio sensor installed in an exhaust collection portion of each exhaust system. When the present invention is applied to a system that performs separate air-fuel ratio control, instead of performing cylinder-by-cylinder abnormality diagnosis based on the estimated air-fuel ratio of each cylinder for each cylinder group, the engine as a whole system is used. An abnormality diagnosis for each cylinder may be performed based on the estimated air-fuel ratio of each cylinder. In this way, it is possible to more accurately eliminate the influence of abnormal cylinders and perform the cylinder-specific abnormality diagnosis with higher accuracy.

  Further, when performing the cylinder-specific abnormality diagnosis according to the present invention, as a parameter to be compared with the estimated air-fuel ratio of the predetermined cylinder, the remaining estimated air-fuel ratio excluding the minimum value and the maximum value among the estimated air-fuel ratios of cylinders other than the predetermined cylinder Any one of a method using the average value (the method described in the first embodiment) and a method using the median of the estimated air-fuel ratio of cylinders other than the predetermined cylinder (the method described in the second embodiment) is adopted. It can be selected as follows according to the number of cylinders of the engine to which the present invention is applied.

(1) In the case of a four-cylinder engine, a method using a median is adopted.
(2) In the case of a 5-cylinder engine, either a method using an average value or a method using a median may be adopted. In this case, since the number of cylinders other than the predetermined cylinder is four, the average value of the remaining estimated air-fuel ratios excluding the minimum and maximum values of the estimated air-fuel ratio of the cylinders other than the predetermined cylinder, and the cylinders other than the predetermined cylinder The estimated median of the air / fuel ratio becomes the same value.
(3) In the case of a 6-cylinder engine, either a method using an average value or a method using a median may be adopted.
(4) In the case of an 8-cylinder engine, either a method using an average value or a method using a median may be adopted.
(5) In the case of a 12-cylinder engine, either a method using an average value or a method using a median may be adopted.

  In the case of (3) to (5), that is, in the case of an engine having 6 or more cylinders, the minimum value, the next smaller value, the maximum value, and the next largest value of the estimated air-fuel ratios of the cylinders other than the predetermined cylinder. An average value or median of the remaining estimated air-fuel ratios excluding a total of four values may be used.

  Further, in each of the first and second embodiments, the cylinder-by-cylinder abnormality diagnosis is prohibited at the time of misfiring and until a predetermined period thereafter. However, the cylinder-by-cylinder air-fuel ratio control at the time of misfiring and after the predetermined period elapses. May be prohibited. In this way, the cylinder-by-cylinder air-fuel ratio control based on the estimated air-fuel ratio is prohibited during the period when the estimated accuracy of the estimated air-fuel ratio of each cylinder is lowered due to the misfire, and It is possible to prevent the deterioration of the air-fuel ratio variation in the meantime.

  Further, in each of the first and second embodiments, the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor 37 installed in the exhaust collecting portion 36 where the exhaust gas of each cylinder collects and flows. However, an air-fuel ratio sensor may be installed in each cylinder's exhaust manifold, and the air-fuel ratio of the exhaust gas in each cylinder may be directly detected by the air-fuel ratio sensor in each cylinder. Further, the air-fuel ratio correction amount of each cylinder may be used as substitute information for the detected air-fuel ratio or the estimated air-fuel ratio of each cylinder.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. It is a flowchart which shows the flow of a process of the air-fuel ratio control program classified by cylinder. It is a flowchart (the 1) which shows the flow of a process of the abnormality diagnosis program classified by cylinder of Example 1. 6 is a flowchart (part 2) illustrating a flow of processing of the cylinder-by-cylinder abnormality diagnosis program according to the first embodiment. It is a flowchart (the 1) which shows the flow of a process of the abnormality diagnosis program classified by cylinder of Example 2. It is a flowchart (the 2) which shows the flow of a process of the abnormality diagnosis program classified by cylinder of Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 35 ... Exhaust manifold, 36 ... Exhaust collecting part, 37 ... Air-fuel ratio sensor, 40 ... ECU (air-fuel ratio detection for each cylinder) Means, cylinder-specific air-fuel ratio control means, cylinder-specific abnormality diagnosis means, cylinder-specific abnormality diagnosis prohibition means, cylinder-specific air-fuel ratio control prohibition means)

Claims (5)

Cylinder air-fuel ratio detection means for detecting the air-fuel ratio of each cylinder of the internal combustion engine, and cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio for each cylinder based on the detected air-fuel ratio of each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means In a control device for an internal combustion engine comprising a cylinder-by-cylinder air-fuel ratio control means for performing
During the air-fuel ratio control for each cylinder, the detected air-fuel ratio of a predetermined cylinder or information related thereto (hereinafter referred to as “detected air-fuel ratio information”) is excluded from the detected air-fuel ratio information of other cylinders. A control apparatus for an internal combustion engine, comprising: a cylinder-by-cylinder abnormality diagnosis means for diagnosing the presence / absence of an abnormality of the predetermined cylinder in comparison with an average value of the remaining detected air-fuel ratio information. Cylinder air-fuel ratio detection means for detecting the air-fuel ratio of each cylinder of the internal combustion engine, and cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio for each cylinder based on the detected air-fuel ratio of each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection means In a control device for an internal combustion engine comprising a cylinder-by-cylinder air-fuel ratio control means for performing
During the cylinder-by-cylinder air-fuel ratio control, the detected air-fuel ratio of the predetermined cylinder or information correlated therewith (hereinafter referred to as “detected air-fuel ratio information”) is compared with the median of the detected air-fuel ratio information of the other cylinders. A control device for an internal combustion engine, characterized by comprising cylinder-specific abnormality diagnosis means for diagnosing the presence or absence of the abnormality.   3. The internal combustion engine according to claim 1, further comprising a cylinder-specific abnormality diagnosis prohibiting unit that prohibits abnormality diagnosis by the cylinder-specific abnormality diagnosis unit when a misfire occurs in the internal combustion engine and until a predetermined period thereafter. Engine control device.   4. A cylinder-by-cylinder air-fuel ratio control prohibiting unit that prohibits the cylinder-by-cylinder air-fuel ratio control when a misfire occurs in an internal combustion engine and until a predetermined period thereafter elapses. Control device for internal combustion engine.   The cylinder-by-cylinder air-fuel ratio detecting means estimates the air-fuel ratio of each cylinder based on a detection value of an air-fuel ratio sensor installed in an exhaust gas collecting portion where exhaust gas of each cylinder collects and flows. The control apparatus for an internal combustion engine according to any one of 1 to 4.

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