JP5461373B2 - Cylinder air-fuel ratio variation abnormality detection device - Google Patents

Description

  The present invention relates to an apparatus for detecting an abnormal variation in the air-fuel ratio between cylinders of a multi-cylinder internal combustion engine, and more particularly to an apparatus for detecting that the air-fuel ratio between cylinders in a multi-cylinder internal combustion engine is relatively large. .

  In general, in an internal combustion engine equipped with an exhaust gas purification system using a catalyst, a mixture ratio of air and fuel in an air-fuel mixture burned in the internal combustion engine, that is, an air-fuel ratio, is used to efficiently remove harmful components in exhaust gas with a catalyst. Control is essential. In order to perform such air-fuel ratio control, an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine, and feedback control is performed so that the air-fuel ratio detected thereby coincides with a predetermined target air-fuel ratio.

  On the other hand, in a multi-cylinder internal combustion engine, air-fuel ratio control is normally performed using the same control amount for all cylinders. Therefore, even if air-fuel ratio control is executed, the actual air-fuel ratio may vary between cylinders. If the degree of variation is small at this time, it can be absorbed by air-fuel ratio feedback control, and harmful components in the exhaust gas can be purified by the catalyst, so that exhaust emissions are not affected and there is no particular problem.

  However, for example, if the fuel injection system of some cylinders breaks down and the air-fuel ratio between the cylinders varies greatly, exhaust emission deteriorates, causing a problem. It is desirable to detect such a large air-fuel ratio variation that deteriorates the exhaust emission as an abnormality. In particular, in the case of an internal combustion engine for automobiles, in order to prevent the traveling of a vehicle whose exhaust emission has deteriorated, it is required to detect an abnormal variation in air-fuel ratio between cylinders in an on-board state. There is also a movement to regulate the law.

  For example, Patent Document 1 discloses a technique for diagnosing an EGR distribution deterioration state (deterioration state of EGR gas distribution to each cylinder) in a multi-cylinder internal combustion engine and further dealing with it.

JP 2010-156295 A

  By the way, when the air-fuel ratio variation abnormality occurs, the fluctuation of the air-fuel ratio sensor output increases. Therefore, it is possible to detect an abnormality in the air-fuel ratio variation by monitoring the degree of variation.

  However, in an internal combustion engine having a turbocharger, an air-fuel ratio sensor is generally provided on the downstream side of the turbocharger. In this case, since the exhaust gas is agitated inside the turbocharger, the air-fuel ratio is averaged, and there is a problem that it is difficult to obtain an output fluctuation according to the air-fuel ratio variation degree by the air-fuel ratio sensor on the downstream side of the turbocharger.

  To cope with this, it is conceivable to install an air-fuel ratio sensor upstream of the turbocharger. However, since the pressure is high on the upstream side of the turbocharger, an air-fuel ratio sensor that can withstand high pressure is necessary, which increases costs. Connected.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an inter-cylinder air-fuel ratio variation abnormality detecting device suitable for an internal combustion engine having a turbocharger.

According to one aspect of the invention,
A twin entry turbocharger installed in a multi-cylinder internal combustion engine;
EGR means for executing EGR for extracting exhaust gas from one of the two introduction passages for introducing the exhaust gas into the turbocharger and circulating it to the intake passage;
An air-fuel ratio sensor installed downstream of the turbocharger;
Air-fuel ratio control means for feedback-controlling the air-fuel ratio to the target air-fuel ratio based on the output of the air-fuel ratio sensor;
Changing means for changing the basic ignition timing according to the presence or absence of the EGR;
Knock detecting means for detecting knocking of the internal combustion engine;
Knock control means for executing knock control for correcting an actual ignition timing with respect to the basic ignition timing according to a detection result of the knock detection means;
When the air-fuel ratio feedback control is being executed and the knock control is being executed, when the state is changed from the state without EGR to the state with the EGR, the air-fuel ratio of the EGR gas is estimated based on the actual ignition timing before and after the change. An abnormality that corrects the fuel injection amount of the cylinder connected to the one introduction passage so as to bring the estimated air-fuel ratio closer to the target air-fuel ratio, and detects an abnormality in the inter-cylinder air-fuel ratio variation based on the correction amount of the fuel injection amount Detection means;
An inter-cylinder air / fuel ratio variation abnormality detecting device is provided.

  Preferably, the abnormality detection means determines that the variation abnormality is present when the absolute value of the correction amount is equal to or greater than a predetermined value.

  Preferably, when the fuel injection amount is corrected, the abnormality detection unit also corrects the fuel injection amount of the cylinder connected to the other introduction passage so that the air-fuel ratio of the total gas approaches the target air-fuel ratio.

  Preferably, when correcting the fuel injection amount, the abnormality detection unit corrects the fuel injection amount so that the actual ignition timing approaches the basic ignition timing.

  Preferably, the abnormality detecting unit updates the correction amount at every predetermined update period when correcting the fuel injection amount.

  Preferably, when the air-fuel ratio of the EGR gas is estimated, the abnormality detection unit is configured to detect the deviation amount of the actual ignition timing with respect to the basic ignition timing in a state without EGR and the basic ignition timing in a state with EGR. The air-fuel ratio of the EGR gas is estimated based on the difference from the actual ignition timing deviation.

  Preferably, the target air-fuel ratio is stoichiometric.

  According to the present invention, an excellent effect that an inter-cylinder air-fuel ratio variation abnormality detecting device suitable for an internal combustion engine having a turbocharger can be provided is exhibited.

1 is a schematic view of an internal combustion engine according to an embodiment of the present invention. An EGR control map is shown. It is a time chart which shows the air-fuel ratio sensor output fluctuation | variation according to the air-fuel ratio variation degree between cylinders. It is a graph which shows the mode of a change of ignition timing. The air-fuel ratio of each cylinder when there is no EGR is shown. The air-fuel ratio of each cylinder with EGR and before correction of the fuel injection amount is shown. The air-fuel ratio of each cylinder with EGR and after fuel injection amount correction is shown. It is a time chart which shows transition of each value in the process of fuel injection amount correction. It is a flowchart which shows a variation abnormality detection routine.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic view of an internal combustion engine according to the present embodiment. The internal combustion engine (engine) 1 of the present embodiment is a multi-cylinder internal combustion engine for automobiles, more specifically, an in-line 4-cylinder spark ignition internal combustion engine, that is, a gasoline engine. However, the number of cylinders, usage, type, etc. of the engine are arbitrary.

  The engine 1 includes # 1 to # 4 cylinders, and each cylinder includes an injector (fuel injection valve) 2 for injecting fuel into an intake passage, particularly an intake port, and an ignition plug 3 for igniting an in-cylinder mixture. Prepare. The firing order is, for example, the order of # 1, # 3, # 4, and # 2.

  The engine 1 includes a turbocharger 4. The turbocharger 4 of this embodiment is a twin entry turbocharger, and introduces exhaust gas from the two introduction passages 5A and 5B. The first introduction passage 5A is connected to the # 2 and # 3 cylinders forming the first cylinder group, and introduces the exhaust gas of the # 2 and # 3 cylinders to the turbine 6 of the turbocharger 4. The second introduction passage 5B is connected to the # 1 and # 4 cylinders forming the second cylinder group, and introduces the exhaust gas of the # 1 and # 4 cylinders to the turbine 6 of the turbocharger 4. These introduction passages 5A and 5B constitute a part of the exhaust passage 7 and are usually defined by individual exhaust manifolds.

  Although not shown, as is well known, two scrolls are defined in the turbine housing of the turbocharger 4, and these scrolls are individually connected to the first introduction passage 5A and the second introduction passage 5B, respectively. Yes. It suppresses exhaust interference between cylinders and improves output.

  The turbocharger 4 has a compressor 8 that is coaxially connected to a turbine 6. The turbocharger 4 has a bypass device (not shown) that selectively bypasses the exhaust gas to the turbine 6 in order to prevent supercharging.

  The compressor 8 is installed in the middle of the intake passage 30. An air flow meter 9 is provided on the upstream side of the compressor 8. The air flow meter 9 is for detecting the amount of air taken into the engine 1 per unit time, that is, the amount of intake air. An intercooler 10 and a throttle valve 11 are provided on the downstream side of the compressor 8. The throttle valve 11 is an electronically controlled type. A surge tank 12 is provided downstream of the throttle valve 11, and intake air stored in the surge tank 12 is distributed to each cylinder via an intake manifold 13.

  On the downstream side of the turbine 6, an air-fuel ratio sensor 14 for detecting the air-fuel ratio of the exhaust gas and a catalyst 15 made of a three-way catalyst are provided in this order from the upstream side. Hereinafter, the air-fuel ratio sensor is also referred to as a pre-catalyst sensor. The pre-catalyst sensor 14 is installed immediately before the catalyst 15 and detects the air-fuel ratio based on the oxygen concentration in the exhaust gas. A three-way catalyst may be additionally provided on the downstream side of the catalyst 15.

  In the present embodiment, the pre-catalyst sensor 14 is a so-called wide-area A / F sensor that outputs a voltage signal having a magnitude proportional to the exhaust air-fuel ratio (having linear characteristics). However, the present invention is not limited to this, and the pre-catalyst sensor 14 may be a so-called O2 sensor in which the output voltage changes abruptly (has Z characteristics) at the stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.6).

  The engine 1 is provided with an EGR device 16. The EGR device 16 performs EGR (external EGR) in which exhaust gas is extracted from only one of the two introduction passages 5A and 5B (first introduction passage 5A in the present embodiment) and recirculated to the intake passage 7. belongs to. The EGR device 16 includes an EGR passage 17 that connects the first introduction passage 5A and the surge tank 12, and an EGR catalyst 18, an EGR cooler 19, and an EGR valve 20 that are provided in the EGR passage 17 in order from the upstream side. The EGR cooler 19 cools the extracted exhaust gas, that is, EGR gas. The EGR catalyst 18 is for burning and removing foreign matters such as deposits contained in the EGR gas, and is composed of, for example, a three-way catalyst.

  Each cylinder of the engine 1 is provided with an in-cylinder pressure sensor 21 for detecting the in-cylinder pressure. The cylinder pressure sensor 21 outputs a signal having a magnitude proportional to the cylinder pressure (cylinder pressure).

  The engine 1 is provided with an electronic control unit (ECU) 100. The ECU 100 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The ECU 100 inputs signals from the crank angle sensor 22, the accelerator opening sensor 23, and the water temperature sensor 24 in addition to the air flow meter 9, the pre-catalyst sensor 14, and the in-cylinder pressure sensor 21 described above.

  The ECU 100 detects the crank angle itself based on the crank pulse signal from the crank angle sensor 18, performs cylinder discrimination, and calculates the rotation speed of the engine 1. Here, “the number of rotations” means the number of rotations per unit time and is synonymous with the rotation speed. In the present embodiment, it means rpm per minute.

  The ECU 100 detects the opening degree of the accelerator pedal operated by the driver, that is, the accelerator opening degree based on the signal from the accelerator opening degree sensor 23, and detects the cooling water temperature of the engine 1 based on the signal from the water temperature sensor 24. To do.

  The ECU 100 controls the injector 2, the spark plug 3, the throttle valve 11 and the EGR valve 20 based on these detected values, and sets the fuel injection amount, fuel injection timing, ignition timing, throttle opening and EGR amount (or EGR rate). Control.

  The fuel injection amount control is performed by the following method. First, the ECU 100 determines a basic injection amount according to a map (a function, which may be a function) that predetermines the relationship between a parameter (referred to as an engine parameter; for example, engine speed and load) and a basic injection amount representing an engine operating state. This basic injection amount is a value that makes the air-fuel ratio of the in-cylinder mixture substantially stoichiometric, which is the target air-fuel ratio.

  Then, the ECU 100 executes air-fuel ratio feedback control (stoichiometric control) so that the air-fuel ratio of the exhaust gas actually flowing into the catalyst 15 approaches the stoichiometric. Specifically, the ECU 100 calculates an injection correction amount (specifically, a correction coefficient) according to the difference between the actual air-fuel ratio or the detected air-fuel ratio detected by the pre-catalyst sensor 14 and the stoichiometric ratio, and this injection The basic injection amount is corrected by the correction amount. Then, fuel equal to the corrected injection amount is injected from the injector 2. As a result, the fuel injection amount and thus the air-fuel ratio are feedback-controlled so that the actual air-fuel ratio is close to the stoichiometric range, and the purification rate of the catalyst 15 can be maintained to the maximum.

  Similarly, regarding the fuel injection timing, the ECU 100 determines a basic injection timing according to a map (a function may be used, and the same applies hereinafter) in which the relationship between the engine parameter and the basic injection timing is determined in advance, and appropriately corrects the basic injection timing. Fuel is injected from the injector 2 at the corrected injection timing.

  On the other hand, the ignition timing control is performed by the following method. First, the ECU 100 determines the basic ignition timing according to a map in which the relationship between the engine parameters and the basic ignition timing is determined in advance. This basic ignition timing is a timing (maximum of the so-called MBT) that has been advanced to the maximum so that the maximum torque can be obtained.

  ECU 100 detects the presence or absence of knocking based on a signal from in-cylinder pressure sensor 21 and executes knock control for correcting the actual ignition timing with respect to the basic ignition timing in accordance with the detection result. When knocking occurs, the knock frequency component is superimposed on the output waveform of the in-cylinder pressure sensor. Therefore, knocking can be detected by detecting the presence of the knock frequency component by various signal processing.

  When there is no knocking, the ECU 100 advances the actual ignition timing by a predetermined angle with respect to the basic ignition timing every calculation cycle. When knocking is detected, ECU 100 retards the actual ignition timing by a predetermined angle from the current value for each calculation cycle. The amount of retardation per calculation cycle is larger than the amount of advancement per calculation cycle. In other words, the control is repeated such that the angle is gradually advanced when knocking is not performed, and the angle is greatly retarded when knocking is detected.

  Control of the fuel injection amount and fuel injection timing is performed uniformly for all cylinders, that is, using the same control amount for all cylinders. On the other hand, the ignition timing is controlled for each cylinder.

  According to such ignition timing control, it is possible to bring the actual ignition timing closer to the MBT for each cylinder that varies depending on the product and the variation between cylinders.

  On the other hand, EGR control is performed by the following method. First, the ECU 100 determines whether or not EGR can be executed with reference to a map as shown in FIG. 2 based on the detected actual engine parameters. In the figure, Ne is the engine speed and KL is the engine load. When the actual engine parameter is in the EGR execution region I, the ECU 100 determines that EGR should be executed, and opens the EGR valve 20. On the other hand, when the actual engine parameter is in the EGR non-execution region II, the ECU 100 determines that EGR should not be executed, and fully closes the EGR valve 20.

  When it is determined that EGR should be executed, ECU 100 determines a target EGR rate according to a map in which the relationship between the engine parameter and the target EGR rate is determined in advance. Then, the opening degree of the EGR valve 20 is controlled so that the determined target EGR rate is actually realized.

  The map for determining the basic injection amount, basic injection timing, and basic ignition timing is switched according to the presence or absence of EGR, and each value for the same engine parameter is between the value without EGR and the value with EGR. Will be changed.

  In particular, when changing from the state without EGR to the state with presence, the basic ignition timing is advanced relatively large from the value A when there is no EGR to the value B when there is EGR.

  As a result of the execution of the knock control, the actual ignition timing when EGR is present is slightly deviated from the basic ignition timing when EGR is present.

  Now, for example, it is assumed that the injectors 2 of some cylinders out of all the cylinders have failed and air-fuel ratio variations (imbalance) occur between the cylinders. For example, the # 1 cylinder has a larger fuel injection amount than the other # 2, # 3, and # 4 cylinders, and its air-fuel ratio is greatly shifted to the rich side. Even at this time, if a relatively large correction amount is given by the aforementioned air-fuel ratio feedback control, the air-fuel ratio of the total gas supplied to the pre-catalyst sensor 14 may sometimes be stoichiometrically controlled. However, looking at each cylinder, # 1 cylinder is larger and richer than stoichiometric, and # 2, # 3 and # 4 cylinders are leaner than stoichiometric. Is clear. In view of this, the present embodiment is equipped with a device that detects such a variation in air-fuel ratio between cylinders.

  FIG. 3 shows an example of a typical in-line four-cylinder engine different from that of the present embodiment. The detected air-fuel ratio A / F of the pre-catalyst sensor tends to periodically vary with one engine cycle (= 720 ° CA) as one cycle. When the variation in the air-fuel ratio between cylinders occurs, the fluctuation within one engine cycle increases. The air-fuel ratio diagrams a, b, and c in (B) show the case where there is no variation and only one cylinder has a rich shift at an imbalance ratio of 20%, and only one cylinder has a rich shift at an imbalance ratio of 50%. As can be seen, the greater the degree of variation, the greater the amplitude of the air-fuel ratio fluctuation.

  Here, the imbalance ratio (%) is a parameter representing the degree of variation in the air-fuel ratio between cylinders. In other words, the imbalance ratio is the amount of fuel injection in a cylinder (imbalance cylinder) causing the fuel injection amount deviation when only one of the cylinders has caused the fuel injection amount deviation. The ratio is a value indicating whether the fuel injection amount is not deviated from the fuel injection amount of the cylinder (balance cylinder) that has not caused the fuel injection amount deviation, that is, the reference injection amount. When the imbalance ratio is IB, the fuel injection amount of the imbalance cylinder is Qib, and the fuel injection amount of the balance cylinder, that is, the reference injection amount is Qs, IB = (Qib−Qs) / Qs. The greater the imbalance ratio IB, the greater the fuel injection amount deviation between the imbalance cylinder and the balance cylinder, and the greater the air-fuel ratio variation.

  As can be understood from the above description, when the air-fuel ratio variation abnormality occurs, the output fluctuation of the air-fuel ratio sensor increases. Therefore, it is possible to detect an abnormality in the air-fuel ratio variation by monitoring the degree of variation.

  However, as described above, in the engine having the turbocharger as in the present embodiment, the exhaust gas is agitated inside the turbine, and the air-fuel ratio of the exhaust gas is averaged. Therefore, there is a problem that it is difficult to obtain output fluctuations according to the degree of air-fuel ratio variation with the air-fuel ratio sensor downstream of the turbocharger.

  To cope with this, it is conceivable to install an air-fuel ratio sensor upstream of the turbocharger. However, since the pressure is high on the upstream side of the turbocharger, an air-fuel ratio sensor that can withstand high pressure is necessary, which increases costs. Connected.

  In particular, in the engine 1 having the twin entry turbocharger 4 as in the present embodiment, since there are two introduction passages 5A and 5B on the upstream side of the turbine 6, two air-fuel ratio sensors are necessary, which further increases the cost. It leads to.

  Therefore, in the present embodiment, in order to overcome such a problem, the air-fuel ratio variation abnormality is detected by the following method without using the output fluctuation of the air-fuel ratio sensor.

  As already described, and as shown in FIG. 4, when the EGR is changed from the non-existing state to the existing state, the basic ignition timing determining map is switched. As a result, the basic ignition timing is referred to as A when there is no EGR. The value is relatively advanced to a value B when EGR is present. As a result of the execution of the knock control, the actual ignition timing B 'when EGR is present becomes a value slightly deviated from the basic ignition timing B due to a manufacturing error or the like.

  This is based on the premise that the EGR gas has a stoichiometric air-fuel ratio, specifically, stoichiometric control is being performed. That is, the basic ignition timing B when EGR is present is a value that is adapted on the assumption that the EGR gas has a stoichiometric air-fuel ratio, and is a value corresponding to the stoichiometric air-fuel ratio EGR gas. In this respect, the basic ignition timing of A when there is no EGR is the same.

  On the other hand, according to the research results of the present inventors, when the air-fuel ratio of EGR gas deviates from stoichiometry, the actual ignition timing B ′ of each cylinder is relatively large from the basic ignition timing B even during the stoichiometric control. It turned out that it shifted.

  Specifically, as shown in the figure, if the air-fuel ratio of the in-cylinder gas of a specific cylinder shifts from the stoichiometric to the rich side as a result of the shift of the air-fuel ratio of the EGR gas from the stoichiometric to the rich side, The ignition timing B ′ is shifted from the basic ignition timing B toward the advance side.

  Further, when the air-fuel ratio of the in-cylinder gas of a certain cylinder shifts from the stoichiometric to the lean side as a result of the deviation of the air-fuel ratio of the EGR gas from the stoichiometric side, the actual ignition timing B ′ of the specific cylinder becomes the basic ignition timing. Shift from B to the retarded angle side.

  If there is no abnormal variation in air-fuel ratio between cylinders during the execution of stoichiometric control (that is, if it is normal), the air-fuel ratio of EGR gas is basically at or near stoichiometric. However, if the variation in the air-fuel ratio between cylinders occurs, even if the stoichiometric control is being performed, the air-fuel ratio of the in-cylinder gas of each cylinder deviates from the stoichiometric, and the actual ignition timing B ′ of each cylinder becomes different from the basic ignition timing B. Shift.

  Therefore, in the present embodiment, the ECU 100 performs variation abnormality detection using this phenomenon. The outline of the variation abnormality detection of this embodiment will be described below.

  FIG. 5 shows the air-fuel ratio of each cylinder during the stoichiometric control execution, the knocking control execution, and no EGR. In the illustrated example, the lean shift abnormality occurs in the # 1 cylinder, and the air-fuel ratio of the # 1 cylinder shifts to the lean side corresponding to -30% in an imbalance ratio with respect to the stoichiometry. In the other # 2, # 3, and # 4 cylinders, the air-fuel ratio is shifted to the rich side corresponding to + 10% as an imbalance ratio with respect to the stoichiometric ratio. By stoichiometric control, the air-fuel ratio of the total gas (a gas formed by collecting exhaust gases of all cylinders) is balanced with stoichiometry.

  Due to such an air-fuel ratio shift, the actual ignition timing is retarded by −30% with respect to the basic ignition timing in the # 1 cylinder, and the actual ignition timing with respect to the basic ignition timing in the other # 2, # 3, and # 4 cylinders. + 10% equivalent advance.

  However, at this time, it is difficult to determine whether the actual ignition timing is shifted as a result of the knock control or whether the actual ignition timing is shifted as a result of the variation abnormality. Therefore, the actual ignition timing with EGR is compared with the actual ignition timing without EGR as a reference.

  FIG. 6 shows the air-fuel ratios of the respective cylinders during the stoichiometric control, during the knock control, and immediately after the EGR is changed from the non-existing state to the existing state. In this case, the exhaust gas equivalent to + 10% of the # 2 and # 3 cylinders shown in FIG. 5 is distributed to each cylinder as EGR gas, so that the air-fuel ratio of each cylinder shifts to the rich side corresponding to α% (however, α > 0). Corresponding to this air-fuel ratio rich shift, the actual ignition timing of each cylinder also shifts to the advance side.

  Then, the ECU 100 estimates the air-fuel ratio of EGR gas based on the actual ignition timing before and after the change from the state without EGR to the state with the EGR.

  Specifically, as shown in FIG. 5, a deviation amount of the actual ignition timing with respect to the basic ignition timing immediately before the start of EGR is obtained. This is, for example, ΔBa for the # 2 cylinder. Next, as shown in FIG. 6, a deviation amount of the actual ignition timing with respect to the basic ignition timing immediately after the start of EGR is obtained. For example, this is ΔBb in the # 2 cylinder. Then, a difference ΔB = ΔBb−ΔBa between both deviation amounts is obtained, and based on this difference ΔB, the air-fuel ratio of the EGR gas is estimated using a predetermined map. It will be understood that this difference ΔB corresponds to the air-fuel ratio deviation amount α and is a value reflecting the air-fuel ratio of the EGR gas.

  5 and 6, the air-fuel ratio deviation amount α is on the rich side, and the estimated air-fuel ratio of the EGR gas, that is, the estimated air-fuel ratio is richer than the stoichiometric value.

  If the actual ignition timing is only shifted as a result of the knock control, the air-fuel ratio of EGR gas should basically be stoichiometric, so such an α-fuel ratio shift does not occur. The air-fuel ratio shift of α occurs because the actual ignition timing is shifted as a result of the variation abnormality. Therefore, for the first time at this point, it is tentatively determined that a variation abnormality has occurred. That is, if the difference ΔB is zero, there is no variation abnormality, and if the difference ΔB is not zero, it is temporarily determined that there is a variation abnormality. As a result, it is possible to discriminate or distinguish between a difference in ignition timing due to knock control and a difference in ignition timing due to abnormal variations.

  After tentatively determining that a variation abnormality has occurred, the ECU 100 corrects the fuel injection amount so that the estimated air-fuel ratio approaches the stoichiometric ratio.

  FIG. 7 shows the air-fuel ratios of the respective cylinders in a state in which the stoichiometric control is being performed, the knock control is being performed, EGR is being performed, and the fuel injection amount correction has been completed. As shown in the figure, for the # 2 and # 3 cylinders that extract exhaust gas, the fuel injection amount is corrected to decrease so that the actual ignition timing approaches the basic ignition timing, that is, the air-fuel ratio approaches the stoichiometry.

  When it is determined that the variation abnormality has occurred, the difference ΔBb between the actual ignition timing and the basic ignition timing of the # 2 and # 3 cylinders in the state without EGR and before correction shown in FIG. 6 is the difference between the estimated air-fuel ratio and the stoichiometry. Is a value that reflects Therefore, the fuel injection amount is corrected to decrease for the # 2 and # 3 cylinders so as to eliminate this difference, that is, to eliminate the difference ΔBb between the actual ignition timing and the basic ignition timing.

  On the other hand, from the viewpoint of emissions, the air-fuel ratio of the total gas needs to be kept stoichiometric. Accordingly, the fuel injection amount is increased and corrected for the # 1 and # 4 cylinders so as to balance the reduction correction for the # 2 and # 3 cylinders (to bring the air-fuel ratio of the total gas closer to the stoichiometric ratio).

  As a result, the air-fuel ratio of the # 2 and # 3 cylinders, and thus the air-fuel ratio of the EGR gas, is stoichiometric, and the imbalance ratio is 0%. On the other hand, as a result of the increase correction corresponding to β%, the air-fuel ratio of the # 1 cylinder shifts from the stoichiometric to the lean side by -30 + α + β%, and the air-fuel ratio of the # 4 cylinder shifts from the stoichiometric to the rich side by + 10 + α + β%.

  In this way, feedback control is performed here to make the EGR gas stoichiometric. If EGR gas that is not stoichiometric is recirculated to the intake side, EGR gas that contains a relatively large amount of foreign matter such as deposits will be recirculated, and the EGR valve 20 and the throttle will be exhausted if the EGR catalyst 18 cannot fully process the exhaust gas. There is a risk of the valve 11 being blocked. In addition, if EGR gas that is not stoichiometric is circulated against a system that is originally intended to circulate EGR gas that is close to stoichiometric, an unexpected problem may occur.

  According to the present embodiment, since the EGR gas can be stoichiometric, these problems can be solved.

  In this correction, when the increase correction is performed for the # 2 and # 3 cylinders, the decrease correction is performed for the # 1 and # 4 cylinders so as to balance with this. This correction is performed for each cylinder in cooperation with the stoichiometric control.

  By the way, when this correction is performed, the correction amount of the fuel injection amount of each cylinder increases. Particularly in the # 2 and # 3 cylinders, the correction amount becomes large in order to eliminate the air-fuel ratio deviation from the stoichiometry. Therefore, a feature of the present embodiment is that a variation abnormality is detected based on the correction amounts of the # 2 and # 3 cylinders.

  FIG. 8 shows the transition of each value in the correction process. (A) is the ignition timing of the # 2 and # 3 cylinders, and (B) is the fuel injection amount correction amount. The correction is performed every predetermined update period T. The update period T is a period much longer than the above-described calculation period (for example, 4 ms). In (A), the air-fuel ratio corresponding to the ignition timing is shown in parentheses.

  Prior to time t1, the actual ignition timing B 'is advanced from the basic ignition timing B corresponding to the rich air-fuel ratio. Therefore, at time t1, which is the update time, the correction amount on the decrease side is increased and the fuel injection amount is further decreased so that the actual ignition timing B 'becomes the basic ignition timing B. The increase amount of the correction amount at this time can be determined from a map or the like based on the difference between the actual ignition timing B 'and the basic ignition timing B.

  However, even if such correction is performed, since the variation abnormality has occurred, the actual ignition timing B 'is shifted again from the basic ignition timing B to the advance side due to some cause (time t2).

  Then, at the time t3 after the elapse of the update cycle T from the time t1, the correction amount on the reduction side is increased so that the actual ignition timing B ′ becomes the basic ignition timing B again. At this point, since the absolute value of the correction amount is equal to or greater than a predetermined threshold value, it is determined that a variation abnormality has occurred.

  As described above, the fuel injection amounts of the # 2 and # 3 cylinders are feedback-corrected every update cycle T based on the difference between the actual ignition timing B 'and the basic ignition timing B. When such fuel injection amount correction is executed, the correction amount is gradually updated toward a value corresponding to the degree of air-fuel ratio deviation. Therefore, it is determined that a variation abnormality has occurred when the absolute value of the correction amount becomes equal to or greater than a predetermined threshold.

  In this example, the rich deviation occurs in the # 2 and # 3 cylinders, but it will be understood that the variation abnormality can be detected in the same manner when the lean deviation abnormality occurs in the reverse pattern. . That is, in this case, when the correction amount on the fuel injection amount increase side is increased and the absolute value of this correction amount is equal to or greater than a predetermined value, it is determined that a variation abnormality has occurred. The correction amount here is an addition term and is a value added to the basic injection amount after correction by air-fuel ratio feedback control. When one of the # 2 and # 3 cylinders is rich and the other is lean, the fuel injection amount is individually corrected so as to eliminate the deviation. Then, it is determined that a variation abnormality has occurred when the absolute value of any of the correction amounts becomes equal to or greater than a predetermined threshold value.

  Thus, according to the present embodiment, it is possible to provide an inter-cylinder air-fuel ratio variation abnormality detection device suitable for an engine having a turbocharger. In particular, since it is not necessary to provide two air-fuel ratio sensors that can withstand high pressure, the cost does not increase, which is extremely suitable for an engine having a twin entry turbocharger as in this embodiment.

  Next, the abnormality detection routine will be described with reference to FIG. This routine is repeatedly executed by the ECU 100, for example, every predetermined calculation cycle.

  First, in step S101, it is determined whether EGR is being executed. If the EGR is not being executed, the current process is terminated. If the EGR is being executed, the process proceeds to step S102.

  In step S102, it is determined whether air-fuel ratio feedback control is being executed. If it is not being executed, the current process is terminated, and if it is being executed, the process proceeds to step S103.

  In step S103, it is determined whether knock control is being executed. If it is not being executed, the current process is terminated. If it is being executed, the process proceeds to step S104.

  In step S104, it is determined whether the current time is immediately after the start of EGR. If it is immediately after the start of EGR, the process proceeds to step S105, and if not immediately after the start of EGR, steps S105 and S106 are skipped and the process proceeds to step S107.

  In step S105, as shown in FIG. 6, the difference ΔB in the amount of deviation of the actual ignition timing from the basic ignition timing of the specific cylinder (here, # 2 cylinder) immediately before and after the start of EGR is obtained. Then, the absolute value of the difference ΔB is compared with a predetermined value X. The predetermined value X is set to a positive value close to zero so as to allow some errors.

  If the difference ΔB is less than the predetermined value X, the air-fuel ratio of the EGR gas can be regarded as almost stoichiometric, so the routine proceeds to step S110 where it is determined that there is no variation abnormality, that is, normal.

  On the other hand, if the difference ΔB is greater than or equal to the predetermined value X, the air-fuel ratio of EGR gas is estimated in step S106 using a predetermined map based on the difference ΔB.

  In step S107, the correction of the fuel injection amount as described above is executed for all the cylinders including the specific cylinder so that the estimated air-fuel ratio approaches the stoichiometric ratio. That is, the fuel injection amount is increased or decreased so that the actual ignition timing B ′ of the # 2 and # 3 cylinders from which the EGR gas is extracted is brought close to the basic ignition timing B, and the remaining # 1, Perform the reverse correction for # 4 cylinder.

  Next, in step S108, the absolute value of the correction amount ΔQ for the specific cylinder is compared with a predetermined threshold Y. If the absolute value of the correction amount ΔQ is less than the threshold value Y, the current process is terminated. On the other hand, if the absolute value of the correction amount ΔQ is equal to or greater than the threshold Y, it is determined in step S109 that there is a variation abnormality.

  Note that it is preferable to activate a warning device such as a check lamp to notify the user of the fact of abnormality simultaneously with the abnormality determination in step S109. The fuel injection amount correction amount may be a multiplication term instead of an addition term.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable.

  For example, instead of the in-cylinder pressure sensor 21, knocking may be detected using a more general knock sensor 25 (see FIG. 1). In this case, one knock sensor 25 is provided in common for all the cylinders, and the ignition timing of all the cylinders is uniformly corrected according to the detection result of the knock sensor 25. In the example of FIG. 5, the actual ignition timing of all cylinders is retarded equally from the basic ignition timing in response to the air-fuel ratio shift of the # 1 cylinder because knocking is likely to occur in a cylinder leaner than stoichiometric. That is, in the example of FIG. 5, the actual ignition timing is equivalent to -30% for all cylinders. Thereafter, the EGR gas air-fuel ratio estimation, fuel injection amount correction, and variation abnormality detection are executed in the same manner.

  In the above embodiment, the target air-fuel ratio is stoichiometric and each process is performed based on stoichiometry. However, for example, when performing lean control, the target air-fuel ratio may be other than stoichiometric, and each process may be performed based on the air-fuel ratio other than stoichiometric.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
2 Injector 3 Spark plug 4 Turbocharger 5A First introduction passage 5B Second introduction passage 7 Exhaust passage 14 Air-fuel ratio sensor (pre-catalyst sensor)
15 Catalyst 16 EGR device 21 In-cylinder pressure sensor 25 Knock sensor 30 Intake passage 100 Electronic control unit (ECU)

Claims (7)

A twin entry turbocharger installed in a multi-cylinder internal combustion engine;
EGR means for executing EGR for extracting exhaust gas from one of the two introduction passages for introducing the exhaust gas into the turbocharger and circulating it to the intake passage;
An air-fuel ratio sensor installed downstream of the turbocharger;
Air-fuel ratio control means for feedback-controlling the air-fuel ratio to the target air-fuel ratio based on the output of the air-fuel ratio sensor;
Changing means for changing the basic ignition timing according to the presence or absence of the EGR;
Knock detecting means for detecting knocking of the internal combustion engine;
Knock control means for executing knock control for correcting an actual ignition timing with respect to the basic ignition timing according to a detection result of the knock detection means;
When the air-fuel ratio feedback control is being executed and the knock control is being executed, when the state is changed from the state without EGR to the state with the EGR, the air-fuel ratio of the EGR gas is estimated based on the actual ignition timing before and after the change. An abnormality that corrects the fuel injection amount of the cylinder connected to the one introduction passage so as to bring the estimated air-fuel ratio closer to the target air-fuel ratio, and detects an abnormality in the inter-cylinder air-fuel ratio variation based on the correction amount of the fuel injection amount Detection means;
An inter-cylinder air-fuel ratio variation abnormality detection device comprising: 2. The inter-cylinder air-fuel ratio variation abnormality detecting device according to claim 1, wherein the abnormality detecting unit determines that the variation abnormality is present when an absolute value of the correction amount exceeds a predetermined value. When the fuel injection amount is corrected, the abnormality detection means also corrects the fuel injection amount of the cylinder connected to the other introduction passage so that the air-fuel ratio of the total gas approaches the target air-fuel ratio. The inter-cylinder air-fuel ratio variation abnormality detection device according to claim 1 or 2. 4. The fuel injection amount according to claim 1, wherein when the fuel injection amount is corrected, the abnormality detection unit corrects the fuel injection amount so that the actual ignition timing approaches the basic ignition timing. 5. The inter-cylinder air-fuel ratio variation abnormality detection device described. The inter-cylinder air-fuel ratio variation according to any one of claims 1 to 4, wherein when the fuel injection amount is corrected, the abnormality detection unit updates the correction amount every predetermined update period. Anomaly detection device. The anomaly detection means, when estimating the air-fuel ratio of the EGR gas, the deviation amount of the actual ignition timing with respect to the basic ignition timing in a state without EGR, and the actual ignition timing with respect to the basic ignition timing in a state with EGR. The inter-cylinder air-fuel ratio variation abnormality detection device according to any one of claims 1 to 5, wherein the air-fuel ratio of the EGR gas is estimated based on a difference from an ignition timing deviation amount. The target air-fuel ratio is stoichiometric. The inter-cylinder air-fuel ratio variation abnormality detection device according to any one of claims 1 to 6, wherein the target air-fuel ratio is stoichiometric.

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