JP2011226363A - Abnormality diagnosis apparatus of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the diagnosis precision of an inter-cylinder imbalance abnormality diagnosis of the engine.SOLUTION: When an inter-cylinder imbalance abnormality diagnosis is performed during an operation of an EGR device 35, a part influenced by an EGR gas is calculated by a map or the like on the basis of a degree of opening or the like of an EGR control valve 34, an abnormality decision threshold is corrected in accordance with a part influenced by the EGR gas, and thereby, such erroneous decision as to assume that there is no inter-cylinder imbalance abnormality (normality) caused by an influence of the EGR gas is prevented. Furthermore, when the inter-cylinder imbalance abnormality diagnosis is performed during the operation of the EGR device 35 and such decision as to assume that there is an inter-cylinder imbalance abnormality is performed such a possibility of erroneous decision as to assume that there is an inter-cylinder imbalance abnormality caused by an influence of the EGR gas is determined and, when it is decided that the remaining amount of the EGR gas in an intake system reaches a prescribed value or smaller in such a state as to inhibit or limit an operation of an EGR device 32, the inter-cylinder imbalance abnormality diagnosis is again performed, and thereby, the presence or absence of the inter-cylinder imbalance abnormality is precisely decided without being affected by the ECR gas.

Description

  The present invention relates to an abnormality diagnosis device for an internal combustion engine having a function of performing an inter-cylinder imbalance abnormality diagnosis for determining whether or not there is an imbalance between cylinders in the internal combustion engine.

  When the variation among cylinders such as the fuel injection amount and the intake air amount of the internal combustion engine becomes large, the variation in the air-fuel ratio between the cylinders may increase, and the exhaust emission may deteriorate. Therefore, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2009-156216), an air-fuel ratio sensor is arranged for each cylinder of the internal combustion engine, and each cylinder detected by these air-fuel ratio sensors is arranged. There is an apparatus that performs an inter-cylinder imbalance abnormality diagnosis for determining the presence or absence of an inter-cylinder imbalance abnormality (air-fuel ratio imbalance between cylinders) based on the air-fuel ratio. Furthermore, in the technique of Patent Document 1, when it is determined that there is an imbalance abnormality between cylinders when an abnormality diagnosis between cylinders is performed during the operation of the EGR device (exhaust gas recirculation device), the operation of the EGR device is performed. And when it is determined that there is no inter-cylinder imbalance abnormality when the inter-cylinder imbalance abnormality diagnosis is executed again during this stop period, it is determined that the EGR device is abnormal.

JP 2009-156216 A

  By the way, in a system equipped with an EGR device, when EGR gas (exhaust gas recirculated to the intake system) is distributed to each cylinder and sucked, variation in the amount of EGR gas distributed to each cylinder occurs. In some cases, the degree of variation in air-fuel ratio between cylinders changes due to such variation in EGR gas amount between cylinders.

  However, in the technique of the above-mentioned Patent Document 1, when the abnormality diagnosis between cylinders is executed during the operation of the EGR device, the influence of EGR gas is not considered at all. Inter-cylinder imbalance is a state in which the degree of variation in air-fuel ratio between cylinders is reduced due to the effect of EGR gas, despite the occurrence of an imbalance among cylinders due to variations in cylinders such as injection amount and intake air amount) There is a possibility that it is erroneously determined that there is no abnormality (normal), and there is a problem that the detectability of the imbalance abnormality between cylinders is lowered.

  Therefore, the problem to be solved by the present invention is to diagnose the abnormality of the internal combustion engine that can improve the detectability of the imbalance abnormality between the cylinders when the abnormality diagnosis between the cylinders is performed during the operation of the exhaust gas recirculation device. To provide an apparatus.

  In order to solve the above-mentioned problem, the invention according to claim 1 compares information for evaluating the degree of imbalance between cylinders of an internal combustion engine (hereinafter referred to as “degree of imbalance between cylinders”) with a predetermined abnormality determination threshold value. An internal combustion engine comprising abnormality diagnosis means for diagnosing an imbalance abnormality between cylinders for determining whether there is an imbalance abnormality between cylinders in the internal combustion engine, and an exhaust gas recirculation device for recirculating a part of the exhaust gas of the internal combustion engine to the intake system In this abnormality diagnosis device, the abnormality diagnosis means includes a change in the degree of imbalance between cylinders (hereinafter referred to as “EGR gas influence component”) due to the influence of exhaust gas (hereinafter referred to as “EGR gas”) recirculated to the intake system by the exhaust gas recirculation device. When calculating an imbalance abnormality between cylinders during the operation of the exhaust gas recirculation device, the abnormality determination threshold value is corrected according to the EGR gas influence component. In which was formed.

  In this configuration, considering that the degree of variation in air-fuel ratio between cylinders changes due to the variation in EGR gas amount between cylinders, and the degree of imbalance among cylinders (information for evaluating the degree of imbalance between cylinders) changes. When the amount of EGR gas influence (change in the degree of imbalance between cylinders due to the effect of EGR gas) is calculated and an abnormality diagnosis between cylinders imbalance is made during the operation of the exhaust gas recirculation device, the amount of influence on the EGR gas is Thus, the abnormality determination threshold value can be corrected in a direction in which the abnormality detectability is increased (a direction in which abnormality is easily detected). As a result, an abnormality in the internal combustion engine (an inter-cylinder variation such as fuel injection amount or intake air amount) causes an imbalance among cylinders (for example, an abnormality in which the variation in air-fuel ratio exceeds an allowable level). In spite of this, it is possible to prevent the state in which the degree of variation in air-fuel ratio between cylinders from being reduced due to the effect of EGR gas from being erroneously determined that there is no abnormality (normal) between cylinders, and exhaust gas. It is possible to improve the detectability of the cylinder imbalance abnormality when the cylinder imbalance abnormality diagnosis is executed during the operation of the reflux device.

  In this case, as in claim 2, the opening degree of the EGR control valve for adjusting the EGR gas amount, the engine rotational speed, the intake air amount, the intake pressure, the intake air temperature, and the amount of fuel evaporative gas purged to the intake system are adjusted. The EGR gas influence may be calculated based on at least one of the opening degrees of the purge control valve. The amount of EGR gas distributed to each cylinder changes according to the opening degree of the EGR control valve, the engine speed, the intake air amount, the intake pressure, the intake air temperature, the opening degree of the purge control valve, etc. Since the change in the degree of imbalance between cylinders due to the influence of EGR gas changes, the opening degree of the EGR control valve, the engine speed, the intake air amount, the intake pressure, the intake air temperature, the opening degree of the purge control valve, etc. are used. Thus, by calculating the EGR gas influence by a map or a mathematical formula, the EGR gas influence can be obtained with high accuracy.

  By the way, when performing an inter-cylinder imbalance abnormality diagnosis during the operation of the exhaust gas recirculation device, a state in which the degree of variation in the air-fuel ratio between the cylinders due to the effect of EGR gas is erroneously determined to be an inter-cylinder imbalance abnormality. There is a possibility.

  Therefore, as described in claim 3, when it is determined that there is an inter-cylinder imbalance abnormality when the inter-cylinder imbalance abnormality diagnosis is performed during the operation of the exhaust gas recirculation apparatus, the operation of the exhaust gas recirculation apparatus is prohibited or In this state, when it is determined that the remaining amount of EGR gas in the intake system (for example, in the surge tank) has become equal to or less than a predetermined value (for example, the remaining amount of EGR gas in which the effect of EGR gas is almost 0), It is advisable to execute an interim imbalance abnormality diagnosis.

  That is, when it is determined that there is an imbalance abnormality between cylinders when an abnormality diagnosis between cylinders is performed while the exhaust gas recirculation device is operating, the degree of variation in the air-fuel ratio between cylinders has increased due to the effect of EGR gas. When it is determined that there is a possibility that the imbalance abnormality between cylinders is erroneously determined and the operation of the exhaust gas recirculation device is prohibited or restricted, the remaining amount of EGR gas in the intake system has become a predetermined value or less. When the determination is made, the inter-cylinder imbalance abnormality diagnosis is performed again, so that it is possible to accurately determine whether there is an inter-cylinder imbalance abnormality without being affected by the EGR gas. Accuracy can be improved.

  In this case, as in claim 4, the remaining amount of EGR gas in the intake system (for example, in the surge tank) is less than a predetermined value based on at least one of the output of the air-fuel ratio sensor, the intake air amount, and the intake pressure. It is better to determine whether or not. Since the output of the air-fuel ratio sensor, the intake air amount, the intake pressure, etc. are all correlated with the remaining amount of EGR gas in the intake system, if the output of the air-fuel ratio sensor, the intake air amount, the intake pressure, etc. are used, the intake air It is possible to accurately determine whether or not the remaining amount of EGR gas in the system has become a predetermined value or less.

FIG. 1 is a diagram showing a schematic configuration of an engine control system in one embodiment of the present invention. FIG. 2 is a diagram for explaining a state when an imbalance between cylinders is abnormal. FIG. 3 is a time chart for explaining the output waveform of the air-fuel ratio sensor when the cylinder imbalance is abnormal. FIG. 4 is a diagram for explaining a problem in the case of performing an inter-cylinder imbalance abnormality diagnosis while the EGR device is operating. FIG. 5 is a flowchart (part 1) for explaining the flow of processing of the inter-cylinder imbalance abnormality diagnosis routine. FIG. 6 is a flowchart (part 2) for explaining the flow of processing of the inter-cylinder imbalance abnormality diagnosis routine.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 that introduces air into each cylinder of the engine 11, and a fuel injection valve that injects fuel toward the intake port in the vicinity of the intake port of the intake manifold 20 of each cylinder. 21 is attached. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of the ignition plug 22 of each cylinder.

  On the other hand, an air-fuel ratio for detecting the air-fuel ratio of the exhaust gas is provided in an exhaust collecting portion 32 (portion where exhaust gases of the respective cylinders merge and flow) of the exhaust pipe 23 of the engine 11 where the exhaust manifolds 31 of the respective cylinders gather. A sensor 24 is provided, and a catalyst 25 such as a three-way catalyst for purifying exhaust gas is provided downstream of the air-fuel ratio sensor 24.

  Between the downstream side of the air-fuel ratio sensor 24 in the exhaust pipe 23 and the downstream side of the throttle valve 16 in the intake pipe 12, there is an EGR pipe 33 for returning a part of the exhaust gas to the intake system. An EGR control valve 34 that adjusts the amount of EGR gas (the amount of exhaust gas recirculated to the intake system) is provided in the middle of the EGR pipe 33. An EGR device 35 (exhaust gas recirculation device) is constituted by the EGR pipe 33, the EGR control valve 34, and the like.

  A cooling water temperature sensor 26 that detects the cooling water temperature and a knock sensor 27 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 29 that outputs a pulse signal every time the crankshaft 28 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 28, and the crank angle and the engine are determined based on the output signal of the crank angle sensor 29. The rotation speed is detected.

  Outputs of these various sensors are input to an electronic control circuit (hereinafter referred to as “ECU”) 30. The ECU 30 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 and the ignition timing are determined according to the engine operating state. In addition to controlling the throttle opening (intake air amount) and the like, the opening of the EGR control valve 34 is controlled to control the EGR gas amount.

  At this time, the ECU 30 determines that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the output of the air-fuel ratio sensor 24 when a predetermined air-fuel ratio feedback control execution condition is satisfied. Air-fuel ratio feedback control is performed to calculate the fuel-fuel ratio feedback correction amount and correct the fuel injection amount of the fuel injection valve 21 using the air-fuel ratio feedback correction amount.

  By the way, when the variation among the cylinders such as the fuel injection amount and the intake air amount of the engine 11 becomes large, the variation of the air-fuel ratio between the cylinders becomes large, and the exhaust emission may be deteriorated. For example, as shown in FIG. 2, when an abnormality occurs in which the fuel injection amount of one cylinder varies to the increase side and the air-fuel ratio of the abnormal cylinder becomes rich, the air-fuel ratio detected by the air-fuel ratio sensor 24 (each cylinder) Therefore, the fuel injection amount of each cylinder is adjusted so that the air-fuel ratio (average air-fuel ratio of each cylinder) detected by the air-fuel ratio sensor 24 by the air-fuel ratio feedback control becomes the target air-fuel ratio. It is corrected in the lean direction. In this case, the air-fuel ratio is controlled to be rich in the abnormal cylinder, and the air-fuel ratio is controlled to be lean in the other cylinders. Therefore, the abnormal air-fuel ratio is abnormal compared to the normal time when all the cylinders are controlled to the stoichiometric air-fuel ratio (stoichiometric). A lot of rich components (HC, etc.) are discharged from the cylinders, and a lot of lean components (NOx, etc.) are discharged from the other cylinders.

  When such an inter-cylinder imbalance abnormality (for example, an abnormality in which variation in air-fuel ratio between cylinders exceeds an allowable level) occurs, for example, as shown in FIG. It will vibrate at.

  Therefore, the ECU 30 executes an inter-cylinder imbalance abnormality diagnosis routine of FIGS. 5 and 6 to be described later, thereby evaluating the degree of imbalance between cylinders (the degree of imbalance between cylinders) based on the output of the air-fuel ratio sensor 24. Information) is calculated, and the degree of imbalance among cylinders is compared with a predetermined abnormality determination threshold value to execute an inter-cylinder imbalance abnormality diagnosis for determining whether or not there is an abnormality in the cylinder imbalance. In this embodiment, the amplitude of the output waveform of the air-fuel ratio sensor 24 (difference between the maximum value and the minimum value in a predetermined period) is calculated as the degree of imbalance between cylinders, and the degree of imbalance between cylinders exceeds the abnormality determination threshold value. If there is, it is determined that there is an abnormality in the imbalance between cylinders.

  By the way, in the system provided with the EGR device 35, when EGR gas (exhaust gas recirculated to the intake system) is distributed to each cylinder and sucked, the amount of EGR gas distributed to each cylinder varies between cylinders. The degree of variation in the air-fuel ratio between the cylinders varies depending on the variation in the EGR gas amount between the cylinders.

  Here, as shown in FIG. 4, the air-fuel ratio of the second cylinder # 2 becomes abnormally rich due to the inter-cylinder variation of the air-fuel ratio due to engine abnormality (for example, variation between cylinders such as fuel injection amount and intake air amount). Two cases where the variation in air-fuel ratio between cylinders due to the variation in the EGR gas amount between the cylinders in the state where the imbalance abnormality between the cylinders has occurred will be described as an example.

  As shown in (a), when the air-fuel ratio of the second cylinder # 2 changes in the rich direction due to the air-fuel ratio variation between cylinders due to the EGR gas amount variation among cylinders, the air-fuel ratio of the second cylinder # 2 The degree of richness increases further. In this case, since the degree of variation in the final air-fuel ratio between the cylinders further increases and the degree of imbalance among cylinders further increases, the degree of imbalance between cylinders is surely larger than the abnormality determination threshold, and It is determined that there is an imbalance abnormality.

  On the other hand, as shown in (b), when the air-fuel ratio of the second cylinder # 2 changes in the lean direction due to the air-fuel ratio variation between the cylinders due to the EGR gas amount variation among the cylinders, the second cylinder The richness of the air / fuel ratio of # 2 decreases. In this case, since the degree of variation in the final air-fuel ratio between the cylinders is reduced and the degree of imbalance among cylinders is reduced, the degree of imbalance between cylinders may be smaller than the abnormality determination threshold value. For this reason, when an inter-cylinder imbalance abnormality diagnosis is performed without considering the influence of EGR gas during the operation of the EGR device 35, an engine abnormality (for example, a variation between cylinders such as a fuel injection amount or an intake air amount) is actually detected. ), The state in which the degree of variation in the air-fuel ratio between the cylinders is reduced due to the effect of the EGR gas is erroneously determined as no abnormality (normal) between the cylinders. There is a possibility that the detectability of an imbalance among cylinders is lowered.

  As a countermeasure, in the present embodiment, the degree of opening of the EGR control valve 34 is considered in consideration that the degree of variation in air-fuel ratio between cylinders changes due to the variation in EGR gas amount between cylinders and the degree of imbalance among cylinders changes. When the EGR gas influence amount (change in the degree of imbalance between cylinders due to the influence of EGR gas) is calculated based on the above, etc. using a map or a mathematical formula, etc., and when the EGR device 35 is operating, the cylinder imbalance abnormality diagnosis is performed. The abnormality determination threshold value is corrected in a direction in which abnormality detectability is increased (a direction in which abnormality is easily detected) in accordance with the EGR gas influence.

  By the way, when performing an inter-cylinder imbalance abnormality diagnosis during the operation of the EGR device 35, it is possible to erroneously determine that there is an inter-cylinder imbalance abnormality when the degree of variation in the air-fuel ratio between the cylinders is increased due to the effect of EGR gas. There is also sex.

  Therefore, in this embodiment, when it is determined that there is an inter-cylinder imbalance abnormality when the inter-cylinder imbalance abnormality diagnosis is performed during the operation of the EGR device 35, the air-fuel ratio variation between the cylinders is affected by the EGR gas. It is determined that there is a possibility that the degree of increase is erroneously determined as an imbalance between cylinders, and the operation of the EGR device 32 is prohibited or restricted, and in that state, the intake system (for example, the surge tank 18) When it is determined that the remaining amount of EGR gas has become equal to or less than a predetermined value (for example, the remaining amount of EGR gas in which the effect of EGR gas is substantially zero), the inter-cylinder imbalance abnormality diagnosis is executed again.

  The above-described cylinder imbalance abnormality diagnosis is executed by the ECU 30 in accordance with the cylinder imbalance abnormality diagnosis routine shown in FIGS. The processing contents of this routine will be described below.

  The inter-cylinder imbalance abnormality diagnosis routine shown in FIGS. 5 and 6 is repeatedly executed at a predetermined cycle while the ECU 30 is turned on, and serves as abnormality diagnosis means in the claims. When this routine is started, first, in step 101, it is determined whether or not an execution condition for the inter-cylinder imbalance abnormality diagnosis is satisfied. Here, the execution condition of the inter-cylinder imbalance abnormality diagnosis is, for example, satisfying all the following conditions (1) to (3).

(1) The air-fuel ratio sensor 24 is activated
(2) The engine 11 is in a steady operation state
(3) The engine operating state is a high load region or a low rotation region.

  Here, the high load region is an operation region in which the amount of exhaust gas of each cylinder increases and the influence of the imbalance abnormality between the cylinders is likely to appear in the output waveform of the air-fuel ratio sensor 24, and the low rotation region is a region of each cylinder. Since the exhaust gas discharge interval is widened and the influence of the cylinder imbalance abnormality is likely to appear in the output waveform of the air-fuel ratio sensor 24, the condition (3) is the condition for executing the cylinder imbalance abnormality diagnosis. It is set as one. The condition (3) may be changed as appropriate, for example, “the engine operating state is in a high load region”. Alternatively, “the engine operating state is in a low rotation range” may be used. Further, “the engine operating state is a high load region and a low rotation region” may be used.

  If all of the above conditions (1) to (3) are satisfied, the execution condition of the inter-cylinder imbalance abnormality diagnosis is established, but there is a condition that does not satisfy any one of the above conditions (1) to (3). If so, the condition for executing the abnormality diagnosis between cylinders is not satisfied. Note that the execution condition of the inter-cylinder imbalance abnormality diagnosis is not limited to the above conditions (1) to (3), and may be changed as appropriate.

If it is determined in step 101 that the execution condition of the inter-cylinder imbalance abnormality diagnosis is not satisfied, this routine is terminated without executing the processing from step 102 onward.
On the other hand, if it is determined in step 101 that the execution condition for the inter-cylinder imbalance abnormality diagnosis is satisfied, the processing after step 102 is executed as follows.

  First, in step 102, whether or not the EGR device 35 is operating (exhaust gas is recirculated to the intake system), for example, whether or not the opening degree of the EGR control valve 34 is greater than or equal to a predetermined value, etc. Determine by.

  If it is determined in this step 102 that the EGR device 35 is in operation, the routine proceeds to step 103, where the degree of imbalance between cylinders (the degree of imbalance between cylinders is evaluated based on the output of the air-fuel ratio sensor 24). Information). In this embodiment, the amplitude of the output waveform of the air-fuel ratio sensor 24 (see FIG. 3) is calculated as the degree of imbalance between cylinders. Specifically, by calculating the difference between the maximum value and the minimum value of the output waveform of the air-fuel ratio sensor 24 in a predetermined period (for example, 1 cycle = 720 CA), the amplitude of the output waveform of the air-fuel ratio sensor 24 (inter-cylinder input) is calculated. Find the degree of balance.

  Thereafter, the process proceeds to step 104, and referring to the map of EGR gas influence (change in the degree of imbalance among cylinders due to the effect of EGR gas), the opening degree of the EGR control valve 34, the engine speed, the intake air amount, An EGR gas influence is calculated according to one or more parameters of the intake pressure (intake pipe pressure), intake air temperature, and opening of the purge control valve (not shown). Alternatively, the EGR gas is expressed by a mathematical formula or the like using one or more parameters of the opening degree of the EGR control valve 34, the engine speed, the intake air amount, the intake pressure, the intake air temperature, and the opening degree of the purge control valve. The influence amount may be calculated. The map or mathematical expression for the EGR gas influence is created in advance based on test data, design data, etc., and stored in the ROM of the ECU 30.

  The method for calculating the EGR gas influence may be changed as appropriate. For example, the base value of the EGR gas influence corresponding to the opening degree of the EGR control valve 34 is calculated by a map or a mathematical formula, and the EGR gas influence is calculated. The final EGR gas is corrected by correcting the base value of the minute according to one or more parameters of the engine speed, the intake air amount, the intake pressure, the intake air temperature, and the opening degree of the purge control valve. You may make it obtain | require an influence part.

  The amount of EGR gas distributed to each cylinder varies depending on the opening degree of the EGR control valve 34, the engine speed, the intake air amount, the intake pressure, the intake air temperature, the opening degree of the purge control valve, etc. Minute (change in the degree of imbalance between cylinders due to the effect of EGR gas) changes, so that the opening degree of the EGR control valve 34, the engine rotation speed, the intake air amount, the intake pressure, the intake air temperature, the opening degree of the purge control valve, etc. By calculating the EGR gas influence component by using a map or a mathematical formula or the like, the EGR gas influence component can be accurately obtained.

  Thereafter, the process proceeds to step 105, and the normal abnormality determination threshold value is corrected to decrease by the amount affected by the EGR gas, thereby correcting the abnormality determination threshold value in a direction in which the abnormality detectability is increased (a direction in which the abnormality is easily detected). In this case, the normal abnormality determination threshold value (abnormality determination threshold value before correction) may be a fixed value set in advance, or may be changed according to the engine operating state or the like.

  Thereafter, the process proceeds to step 106, in which it is determined whether or not the degree of imbalance between cylinders exceeds the corrected abnormality determination threshold value. As a result, when it is determined that the degree of imbalance between cylinders is equal to or less than the corrected abnormality determination threshold, the routine proceeds to step 107, where it is determined that there is no abnormality (normal) between cylinders and the abnormality flag is kept OFF. Then, this routine is finished.

  On the other hand, if it is determined in step 106 that the degree of imbalance between cylinders exceeds the corrected abnormality determination threshold, the routine proceeds to step 108, where it is temporarily determined that there is an abnormality in the cylinder imbalance ( Temporarily, it is determined that there is an imbalance between cylinders). In this case, it is determined that there is a possibility that the state in which the degree of variation in the air-fuel ratio among the cylinders due to the EGR gas has increased is erroneously determined that there is an abnormality in the cylinder imbalance, and the processing after step 109 in FIG. Run like this.

  First, in step 109, the operation of the EGR device 35 is prohibited (the EGR control valve 34 is maintained in a closed state). Alternatively, the operation of the EGR device 35 is limited (the opening degree of the EGR control valve 34 is limited to a predetermined value or less).

  Thereafter, the routine proceeds to step 110, where the remaining EGR gas in the intake system (for example, in the surge tank 18) is determined based on one or more of the output of the air-fuel ratio sensor 24, the intake air amount, and the intake pressure. calculate. Since the output of the air-fuel ratio sensor 24, the intake air amount, the intake pressure, etc. are all correlated with the EGR gas remaining amount in the intake system, if the output of the air-fuel ratio sensor 24, the intake air amount, the intake pressure, etc. are used, It is possible to accurately calculate the remaining amount of EGR gas in the intake system and accurately determine whether or not the remaining amount of EGR gas in the intake system has become a predetermined value or less.

  Thereafter, the routine proceeds to step 111, where it is determined whether or not the remaining amount of EGR gas in the intake system has become a predetermined value or less. Here, the predetermined value is set to, for example, an EGR gas remaining amount at which the EGR gas influence is almost zero.

  When it is determined in this step 111 that the remaining amount of EGR gas in the intake system has become a predetermined value or less, it is determined that the EGR gas influence has become almost zero, and the process proceeds to step 112 where the air-fuel ratio sensor 24 Based on the output, the degree of imbalance between cylinders (in this embodiment, the amplitude of the output waveform of the air-fuel ratio sensor 24) is calculated.

  Thereafter, the process proceeds to step 113, where it is determined whether or not the degree of imbalance between cylinders exceeds a normal abnormality determination threshold value (abnormality determination threshold value before correction). As a result, when it is determined that the degree of imbalance between cylinders is equal to or less than the normal abnormality determination threshold value, the routine proceeds to step 114, where it is determined that there is no abnormality between cylinders (normal) and the abnormality flag is kept OFF. To end this routine.

  On the other hand, if it is determined in step 113 that the degree of imbalance between cylinders exceeds the normal abnormality determination threshold value, the process proceeds to step 115 and finally it is determined that there is abnormality between cylinders. The abnormality flag is set to ON and a warning lamp (not shown) provided on the instrument panel of the driver's seat is turned on, or a warning display section (not shown) of the instrument panel of the driver's seat is turned on. A warning is displayed to warn the driver, and the abnormality information (abnormality code, etc.) is rewritable non-volatile memory such as a backup RAM (not shown) of the ECU 30 (rewritable data stored even when the ECU 30 is powered off). Memory).

  Thereafter, the process proceeds to step 116 and shifts to the retreat travel mode. In the retreat travel mode, for example, the engine 11 is operated in a state where the throttle opening (intake air amount), the fuel injection amount, and the like are limited to a predetermined value or less.

  On the other hand, if it is determined in step 102 in FIG. 5 that the EGR device 35 is not operating (exhaust gas is not recirculated to the intake system), the process proceeds to step 112 in FIG. After calculating the degree of imbalance between cylinders based on the output, it is determined whether or not the degree of imbalance between cylinders exceeds a normal abnormality determination threshold, and the degree of imbalance between cylinders is below the normal abnormality determination threshold. If determined, it is determined that there is no inter-cylinder imbalance abnormality (normal), and if it is determined that the degree of imbalance between cylinders exceeds the normal abnormality determination threshold, it is determined that there is an inter-cylinder imbalance abnormality. Determination is made (steps 112 to 115).

  In the present embodiment described above, the cylinders during the operation of the EGR device 35 are taken into consideration that the degree of variation in the air-fuel ratio between the cylinders changes due to the variation in the amount of EGR gas among the cylinders and the degree of imbalance among the cylinders changes. When performing an inter-imbalance abnormality diagnosis, the amount of EGR gas influence (the amount of change in the degree of imbalance between cylinders due to the effect of EGR gas) is calculated based on the opening degree of the EGR control valve 34, etc., using a map or a mathematical formula, Since the abnormality determination threshold value is corrected in a direction in which abnormality detectability is increased (a direction in which abnormality is easily detected) according to the EGR gas influence, in reality, engine abnormality (such as fuel injection amount and intake air amount) is corrected. Although the cylinder-to-cylinder imbalance abnormality has occurred due to the cylinder-to-cylinder variation), the degree of variation in the air-fuel ratio between cylinders has been reduced due to the effect of EGR gas. It is possible to prevent erroneous determination that there is no malfunction (normal) in the engine, and to improve the detectability of the imbalance abnormality between cylinders when the diagnosis of the imbalance abnormality between cylinders is performed while the EGR device 35 is operating. Can do.

  Furthermore, in this embodiment, when it is determined that there is an inter-cylinder imbalance abnormality when the inter-cylinder imbalance abnormality diagnosis is performed during the operation of the EGR device 35, the air-fuel ratio variation between the cylinders is affected by the EGR gas. It is determined that there is a possibility that the degree of increase is erroneously determined as an imbalance between cylinders, and the operation of the EGR device 32 is prohibited or restricted, and in that state, the intake system (for example, the surge tank 18) When it is determined that the remaining amount of EGR gas is equal to or less than a predetermined value (for example, the remaining amount of EGR gas at which the effect of EGR gas is substantially 0), the inter-cylinder imbalance abnormality diagnosis is executed again. Therefore, it is possible to accurately determine the presence / absence of an imbalance between cylinders without being influenced by the above, and to improve the diagnosis accuracy of the abnormality diagnosis between cylinders.

  Further, in the present embodiment, the degree of imbalance between cylinders is calculated based on the output of one air-fuel ratio sensor 24 arranged in the exhaust collecting portion 32, and the degree of imbalance between cylinders is compared with an abnormality determination threshold value. Since it is determined whether or not there is an imbalance abnormality, it is not necessary to estimate the air-fuel ratio of each cylinder for each cylinder, and it is possible to easily perform an inter-cylinder imbalance abnormality diagnosis, and an air-fuel ratio sensor is provided for each cylinder. There is no need to provide it, and it is possible to meet the demand for cost reduction, which is an important technical issue in recent years.

  In the above embodiment, the amplitude of the output waveform of the air-fuel ratio sensor 24 is used as the degree of imbalance between cylinders (information for evaluating the degree of imbalance between cylinders). As the degree of imbalance, for example, the area of the output waveform of the air-fuel ratio sensor 24 (area surrounded by the output waveform in a predetermined period and the output waveform in the normal period), the slope of the output waveform of the air-fuel ratio sensor 24 (output waveform in the predetermined period) Or the ratio of change), the length of the output waveform of the air-fuel ratio sensor 24 (the trajectory length in a predetermined period), the frequency of the output waveform of the air-fuel ratio sensor 24, or the like may be used. When the cylinder imbalance increases and the variation in air-fuel ratio between cylinders increases, the output fluctuation of the air-fuel ratio sensor 24 increases, and the output amplitude, area, inclination, length, frequency, etc. of the air-fuel ratio sensor 24 increase. Therefore, all of these parameters are information that accurately reflects the degree of imbalance between cylinders.

  Further, the degree of imbalance between cylinders is obtained from, for example, torque pulsation (engine rotation fluctuation) obtained from the output of the crank angle sensor or the output of an exhaust gas sensor (air-fuel ratio sensor or oxygen sensor) arranged on the downstream side of the catalyst. The air-fuel ratio learning value (for example, the learning value of the sub-feedback correction amount) or the like may be used, and any parameter that changes in accordance with the degree of imbalance among cylinders (for example, the degree of variation in the air-fuel ratio between cylinders). It can be used as the degree of imbalance between cylinders.

  In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 18 ... Surge tank, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe, 24 ... Air-fuel ratio sensor, 25 ... Catalyst, 30 ... ECU (abnormality diagnosis means), 33 ... EGR piping, 34 ... EGR control valve, 35 ... EGR device (exhaust gas recirculation device)

Claims (4)

Information for evaluating the degree of imbalance between cylinders of the internal combustion engine (hereinafter referred to as “inter-cylinder imbalance degree”) is compared with a predetermined abnormality determination threshold value to determine whether there is an abnormality in the inter-cylinder imbalance of the internal combustion engine. In an abnormality diagnosis device for an internal combustion engine comprising abnormality diagnosis means for performing a balance abnormality diagnosis, and an exhaust gas recirculation device that recirculates part of the exhaust gas of the internal combustion engine to the intake system,
The abnormality diagnosing means is a change in the degree of imbalance between cylinders (hereinafter referred to as “EGR gas influence”) due to an influence of exhaust gas (hereinafter referred to as “EGR gas”) recirculated to the intake system by the exhaust gas recirculation device. An internal combustion engine characterized in that the abnormality determination threshold value is corrected according to the EGR gas influence when the inter-cylinder imbalance abnormality diagnosis is performed during operation of the exhaust gas recirculation device. Engine abnormality diagnosis device.   The abnormality diagnosis means includes a purge control valve for adjusting the opening degree of the EGR control valve for adjusting the EGR gas amount, the engine rotational speed, the intake air amount, the intake pressure, the intake air temperature, and the amount of fuel evaporative gas purged to the intake system. The abnormality diagnosis apparatus for an internal combustion engine according to claim 1, wherein the EGR gas influence is calculated based on at least one of the opening degrees.   The abnormality diagnosis means prohibits the operation of the exhaust gas recirculation device when it is determined that there is an imbalance abnormality between the cylinders when the interim cylinder imbalance abnormality diagnosis is performed during the operation of the exhaust gas recirculation device. 3. The inter-cylinder imbalance abnormality diagnosis is executed again when it is determined that the remaining amount of EGR gas in the intake system has become a predetermined value or less in that state. An abnormality diagnosis device for an internal combustion engine.   The abnormality diagnosis means determines whether or not the remaining amount of EGR gas in the intake system has become a predetermined value or less based on at least one of the output of the air-fuel ratio sensor, the intake air amount, and the intake pressure. The abnormality diagnosis apparatus for an internal combustion engine according to claim 3,

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