JP5919836B2 - Cylinder air-fuel ratio variation abnormality detection device - Google Patents

Description

  The present invention relates to an apparatus for detecting an abnormal variation in air-fuel ratio between cylinders in an internal combustion engine having a plurality of cylinders.

  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. Such a large air-fuel ratio variation is desirably detected as abnormal.

  For example, in the apparatus described in Patent Document 1, a value corresponding to the change rate of the detected air-fuel ratio is obtained based on the output value of the air-fuel ratio sensor, and the air-fuel ratio cylinder is calculated based on the comparison result between this value and the determination threshold value. It is determined whether or not an imbalance state has occurred.

JP 2011-47332 A

  By the way, in general, in an internal combustion engine, one air-fuel ratio sensor is provided for detecting an air-fuel ratio of exhaust from a plurality of cylinders at an exhaust merge portion of the exhaust passage or downstream thereof. The flow of exhaust gas reaching the air-fuel ratio sensor may vary among cylinders. For example, when the exhaust from the first cylinder is relatively easy to reach the detection unit of the air-fuel ratio sensor and the exhaust from the second cylinder different from the first cylinder is relatively difficult to reach the detection unit of the air-fuel ratio sensor, There may be variations between cylinders in terms of gas hitting the sensor. Therefore, since the rate of change of the detected air-fuel ratio can change between the case where the cylinder having the air-fuel ratio abnormality is the first cylinder and the case where it is the second cylinder, the abnormality in the air-fuel ratio variation between cylinders can be detected more appropriately. For this purpose, it is desired to further examine the gas flow from each cylinder to the air-fuel ratio sensor, that is, per gas.

  Accordingly, the present invention has been created in view of the above circumstances, and an object of the present invention is to provide an internal combustion engine having a plurality of cylinders even when there is a variation in how the gas hits the air-fuel ratio sensor among the cylinders. An object of the present invention is to provide an apparatus for appropriately detecting the presence or absence of an abnormality in air-fuel ratio variation between cylinders based on the output of a fuel ratio sensor.

  According to one aspect of the present invention, an inter-cylinder air-fuel ratio variation abnormality detecting device for an internal combustion engine having a plurality of cylinders, the obtaining means operating to obtain an output of an air-fuel ratio sensor provided in an exhaust passage. The ignition timing retarding control for executing the ignition timing retarding control for retarding the ignition timing of the specific cylinder by a predetermined retardation amount for a predetermined period, and the ignition timing retarding control is not executed by the retard controlling means. Non-retarded time value calculating means for calculating a value representing a change in the air-fuel ratio based on the output value of the air-fuel ratio sensor acquired by the acquiring means at times, and the ignition timing retarded control by the retarded control means A delay time value calculating means for calculating a value representing a change in the air / fuel ratio based on the output value of the air / fuel ratio sensor acquired by the acquiring means when Based on the calculated value And a threshold value calculation means for calculating a determination threshold value for abnormality in variation in air-fuel ratio between cylinders, a value calculated by the non-retarded time value calculation means so as to determine the presence or absence of abnormality in air-fuel ratio variation between cylinders, and An inter-cylinder air-fuel ratio variation abnormality detection device is provided that includes comparison means that compares the threshold value calculated by the threshold value calculation means.

  Preferably, the retard angle control means sets each of the cylinders of the internal combustion engine to specific cylinders one by one in order, executes the ignition timing retard control for each specific cylinder, and the retard angle value calculation means A value representing a change in the air-fuel ratio as a value related to each specific cylinder based on the output value of the air-fuel ratio sensor acquired by the acquisition means when the ignition timing retarding control is executed in each specific cylinder The threshold value calculation means calculates a value set for the cylinder having the largest value calculated by the retard angle value calculation means among all the cylinders of the internal combustion engine as the determination threshold value.

  Preferably, the retard angle control means calculates an ignition delay amount based on the value calculated by the non-retard time value calculating means, and sets the calculated ignition delay amount to the predetermined delay amount. And a retard amount setting means. The retard amount setting means may set the smaller ignition retard amount as the predetermined retard amount as the value calculated by the non-retard time value calculating means is larger. Preferably, the retard control means executes the ignition timing retard control for a shorter period as the ignition retard amount set by the retard amount setting means is larger, and the retard time value calculating means is the retard time value calculating means. A value representing a change in the air-fuel ratio may be calculated based on an output value of the air-fuel ratio sensor acquired by the acquisition unit corresponding to an execution period of the ignition timing retardation control by the angle control unit.

  Alternatively, preferably, the retard control unit includes a retard amount setting unit that variably sets an ignition retard amount based on a load of the internal combustion engine, and the retard time value calculating unit includes the retard angle value calculating unit. The output of the air-fuel ratio sensor acquired by the acquisition unit when the ignition timing retardation control is being executed by the retardation control unit according to the average value of the ignition retardation amount set by the amount setting unit Correction means for correcting a value representing a change in the air-fuel ratio calculated based on the value is provided.

  Further preferably, preferably, the retard angle control means executes an ignition timing retard control for retarding an ignition timing of a specific cylinder including two or more cylinders by a predetermined delay amount for a predetermined period at the same time. The retard angle value calculating means changes the air-fuel ratio based on the output value of the air-fuel ratio sensor acquired by the acquiring means when the ignition timing retard control is being executed by the retard control means. The threshold value calculating means uses the value calculated by the non-retarded angle value calculating means and the value calculated by the retarded angle value calculating means to determine the threshold value for determination. calculate.

1 is a schematic view of an internal combustion engine according to a first embodiment of the present invention. It is a graph which shows the output characteristic of a pre-catalyst sensor and a post-catalyst sensor. It is a graph which shows the fluctuation | variation of the exhaust air fuel ratio according to the air-fuel ratio variation degree between cylinders. FIG. 4 is an enlarged view corresponding to a U portion in FIG. 3. It is a graph which shows the relationship between an imbalance ratio and an output variation | change_quantity. It is a graph which shows the relationship between an output variation | change_quantity and the threshold value for determination. 3 is a flowchart of an inter-cylinder air ratio variation abnormality detection control routine according to the first embodiment. It is a flowchart of the output variation calculation control routine of the first embodiment. It is a flowchart of the threshold value calculation control routine of 1st Embodiment. It is a graph which shows the change of the cylinder pressure by retarding the ignition timing. It is a graph which shows the relationship between the output variation | change_quantity and ignition retard amount when not performing ignition timing retard control of 2nd Embodiment. It is a graph regarding the third embodiment, and is a graph showing a tendency of the output change amount when the ignition timing retarding control is executed with the # 1 cylinder as an abnormal cylinder, the other cylinders as normal cylinders, and each cylinder as a specific cylinder. is there. It is a graph regarding 3rd Embodiment, and is a graph which shows the relationship between dispersion | variation, the frequency | count of averaging, and ignition retard amount. It is a graph regarding 4th Embodiment, and is a graph which shows the relationship between an engine load, an ignition retard amount, and an output variation | change_quantity. It is a graph which shows the relationship between the output variation | change_quantity and a cylinder of 5th Embodiment. It is a flowchart of the output variation | change_quantity calculation control routine of 5th Embodiment. It is a flowchart of the threshold value calculation control routine of 5th Embodiment.

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

  FIG. 1 is a schematic view of an internal combustion engine according to the first embodiment. As shown in the figure, an internal combustion engine (engine) 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston. The engine 1 of the present embodiment is an internal combustion engine that is mounted on an automobile and has a plurality of cylinders, that is, a multi-cylinder internal combustion engine, more specifically, an in-line four-cylinder spark ignition internal combustion engine. The engine 1 includes # 1 to # 4 cylinders. However, the present invention does not particularly limit the number of cylinders, the application, the type, and the like of the engine.

  Although not shown, the cylinder head of the engine 1 has an intake valve for opening and closing the intake port and an exhaust valve for opening and closing the exhaust port for each cylinder. Each intake valve and each exhaust valve are opened and closed by a camshaft. Be made. A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 8 which is an intake air collecting chamber via a branch pipe 4 for each cylinder. An intake pipe 13 is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. The intake port, the branch pipe 4, the surge tank 8 and the intake pipe 13 each define a part of the intake passage.

  An injector (fuel injection valve) 12 for injecting fuel into an intake passage, particularly an intake port, is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve is opened, compressed by the piston, and ignited and burned by the spark plug 7.

  On the other hand, the exhaust port of each cylinder is connected to the exhaust manifold 14. The exhaust manifold 14 includes a branch pipe 14a for each cylinder forming an upstream portion thereof and an exhaust collecting portion 14b forming a downstream portion thereof. An exhaust pipe 6 is connected to the downstream side of the exhaust collecting portion 14b. The exhaust port, the exhaust manifold 14 and the exhaust pipe 6 each define a part of the exhaust passage.

  An upstream catalytic converter 11 and a downstream catalytic converter 19 each having an exhaust purification catalyst composed of a three-way catalyst are attached in series to the upstream side and the downstream side of the exhaust pipe 6. These catalytic converters 11 and 19 have an oxygen storage capacity (O2 storage capacity). That is, the catalytic converters 11 and 19 store excess oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is larger (lean) than stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.6), and store NOx. Reduce. Further, the catalytic converters 11 and 19 release stored oxygen and oxidize HC and CO when the air-fuel ratio of the exhaust gas is smaller (rich) than the stoichiometric ratio.

  First and second air-fuel ratio sensors, that is, a pre-catalyst sensor 17 and a post-catalyst sensor 18 for detecting the air-fuel ratio of the exhaust gas in the upstream catalytic converter 11, that is, the exhaust passages upstream and downstream of the catalyst there, respectively. is set up. The pre-catalyst sensor 17 and the post-catalyst sensor 18 are installed at positions immediately before and immediately after the upstream catalytic converter 11, and can detect the air-fuel ratio based on the oxygen concentration in the exhaust gas. Thus, the single pre-catalyst sensor 17 is installed in the exhaust gas merging portion on the upstream side of the upstream catalytic converter 11.

  The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as a control means or a control device. The ECU 20 includes a CPU (not shown), a storage device including a ROM and a RAM, an input / output port, and the like. In addition to the air flow meter 5, the pre-catalyst sensor 17, and the post-catalyst sensor 18, the ECU 20 includes a crank angle sensor 16 that detects the crank angle of the engine 1 and an accelerator opening that detects the accelerator opening, as shown in the figure. The degree sensor 15 and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc. Thus, the ECU 20 substantially takes on the functions of ignition (timing) control means, fuel injection control means, intake air amount control means, and air-fuel ratio control means.

  The throttle valve 10 is provided with a throttle opening sensor (not shown), and a signal from the throttle opening sensor is sent to the ECU 20. The ECU 20 normally feedback-controls the opening of the throttle valve 10 (throttle opening) to a target throttle opening determined according to the accelerator opening.

  The ECU 20 detects the amount of intake air per unit time, that is, the amount of intake air based on the signal from the air flow meter 5. The ECU 20 detects the load of the engine 1 based on at least one of the detected accelerator opening, throttle opening, and intake air amount.

  The ECU 20 detects the crank angle itself and the rotational speed of the engine 1 based on the crank pulse signal from the crank angle sensor 16. 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.

  Further, the ECU 20 performs ignition timing correction control with respect to a reference ignition timing determined based on the engine operating state, for example, the engine rotation speed and the engine load. The ECU 20 operates the spark plug 7 based on an output from a knock sensor (not shown) so that the ignition timing approaches the ignition timing (MBT) at which the engine 1 generates the maximum torque and avoids the occurrence of knocking. Control. That is, the engine 1 is provided with a knock control system (KCS) so as to control the ignition timing near the knock limit. The ignition timing is corrected and controlled to retard the ignition when it is determined that there is a knock based on the output from the knock sensor, and to advance the ignition when it is determined that there is no knock. The ignition order is the order of # 1 cylinder, # 3 cylinder, # 4 cylinder, # 2 cylinder.

  The pre-catalyst sensor 17 as the first air-fuel ratio detection means is a so-called wide-range air-fuel ratio sensor, and can continuously detect the air-fuel ratio over a relatively wide range. FIG. 2 shows the output characteristics of the pre-catalyst sensor 17. As shown in the figure, the pre-catalyst sensor 17 outputs a voltage signal Vf having a magnitude proportional to the exhaust air-fuel ratio. The output voltage when the exhaust air-fuel ratio is stoichiometric is Vreff (for example, about 3.3 V).

  On the other hand, the post-catalyst sensor 18 as the second air-fuel ratio detection means is a so-called O2 sensor, and has a characteristic that the output value changes suddenly at the stoichiometric boundary. That is, the post-catalyst sensor 18 has an output characteristic that the output fluctuation is larger than the output characteristic of the pre-catalyst sensor 17 with respect to the air-fuel ratio change in the predetermined air-fuel ratio region. FIG. 2 shows the output characteristics of the post-catalyst sensor 18. As shown in the figure, the output voltage when the exhaust air-fuel ratio is stoichiometric, that is, the stoichiometric equivalent value is Vrefr (for example, 0.45 V). The output voltage of the post-catalyst sensor 18 changes within a predetermined range (for example, 0 to 1 V). When the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage of the post-catalyst sensor becomes lower than the stoichiometric equivalent value Vrefr. When the exhaust air-fuel ratio is richer than stoichiometric, the output voltage of the post-catalyst sensor becomes higher than the stoichiometric equivalent value Vrefr.

  The upstream catalytic converter 11 and the downstream catalytic converter 19 simultaneously purify NOx, HC and CO, which are harmful components in the exhaust gas, when the air-fuel ratio A / F of the exhaust gas flowing into each of them is close to the stoichiometric. The air-fuel ratio width (window) that can simultaneously purify these three with high efficiency is relatively narrow.

  Therefore, during normal operation of the engine 1, the air-fuel ratio control of the ECU 20, here specifically the part responsible for the air-fuel ratio feedback control, is such that the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 11 is controlled in the vicinity of stoichiometry. Then, air-fuel ratio feedback control (stoichiometric control) is executed. This air-fuel ratio feedback control is detected using the main air-fuel ratio feedback control and the post-catalyst sensor 18 so that the exhaust air-fuel ratio detected using the pre-catalyst sensor 17 coincides with the predetermined target air-fuel ratio. The auxiliary air-fuel ratio feedback control is performed so that the exhaust air-fuel ratio matches the stoichiometric value. Specifically, in the main air-fuel ratio feedback control, in order to make the current exhaust air-fuel ratio detected based on the output of the pre-catalyst sensor 17 follow a predetermined target air-fuel ratio, a first correction coefficient is calculated, Control is performed to adjust the fuel injection amount from the injector 12 based on the first correction coefficient. Further, in the auxiliary air-fuel ratio feedback control, control is performed such that the second correction coefficient is calculated based on the output of the post-catalyst sensor 18 and the first correction coefficient obtained in the main air-fuel ratio feedback control is corrected. Is done.

  Now, for example, some abnormality (particularly one cylinder) of all cylinders may cause an abnormality, and variations in air-fuel ratio (imbalance) may occur between the cylinders. For example, if the # 1 cylinder injector 12 fails and the fuel injection amount of the # 1 cylinder becomes relatively large, the air / fuel ratio of the # 1 cylinder is larger than the air / fuel ratios of the other # 2, # 3 and # 4 cylinders. This is the case when shifting to the rich side. Even at this time, if a relatively large correction amount is given by the aforementioned main air-fuel ratio feedback control, the air-fuel ratio of the total gas supplied to the pre-catalyst sensor 17 may be able to approach the stoichiometric condition. However, looking at each cylinder, # 1 cylinder is larger and richer than stoichiometric, and # 2, # 3 and # 4 cylinders are slightly leaner than stoichiometric. It is clear. Therefore, the engine 1 is provided with a cylinder-to-cylinder air ratio variation abnormality detecting device 22 that detects such an abnormality when the cylinder-to-cylinder air-fuel ratio variation occurs.

  Here, an outline of detection of the variation in air-fuel ratio between cylinders in this embodiment will be described.

  As shown in FIG. 3, when the variation in the air-fuel ratio between cylinders occurs, the variation in the exhaust air-fuel ratio during one engine cycle (= 720 ° CA) increases. The air-fuel ratio diagrams a, b, and c in (B) are not varied, and the pre-catalyst in the case of a rich shift with an imbalance rate of 20% for only one cylinder and a rich shift with an imbalance rate of 50% for only one cylinder. An air-fuel ratio A / F detected by the sensor 17 is shown. As can be seen, the greater the degree of variation, the greater the amplitude of the air-fuel ratio fluctuation.

  Here, the imbalance rate (%) is one parameter representing the degree of variation in the air-fuel ratio between cylinders. In other words, the imbalance rate is the amount of fuel injection in a cylinder (imbalance cylinder) in which the fuel injection amount deviation occurs when only one of the cylinders has a fuel injection amount deviation. It is a value that indicates whether the fuel injection amount is 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 rate 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 × 100. The larger the absolute value of the imbalance rate IB, the greater the difference in fuel injection amount between the imbalance cylinder and the balance cylinder, and the greater the variation in air-fuel ratio.

  As understood from FIG. 3, the output fluctuation of the pre-catalyst sensor 17 increases as the imbalance ratio increases, that is, as the degree of variation in the cylinder air-fuel ratio increases. That is, the greater the imbalance rate, the greater the change in the air-fuel ratio in the exhaust passage.

  Therefore, paying attention to this characteristic, detection of abnormality in variation in air-fuel ratio between cylinders is performed. In other words, as will be described below, the cylinder-to-cylinder air ratio variation abnormality detection device 22 mounted on the engine 1 changes (or fluctuates) the air-fuel ratio based on the output of the pre-catalyst sensor 17, that is, the output value. A value to be expressed (hereinafter referred to as an output change amount) is calculated, and detection of abnormality in variation in air-fuel ratio between cylinders is executed based on this value. The output value of the pre-catalyst sensor 17 corresponds to the detection value detected using the pre-catalyst sensor 17, and the value representing the change in the air-fuel ratio corresponds to a value corresponding to the change rate of the detected air-fuel ratio.

  Hereinafter, calculation for deriving a value representing the change in the air-fuel ratio, that is, an output change amount in the present embodiment will be described. FIG. 4 is an enlarged schematic view corresponding to the U portion of FIG. 3, and particularly shows a change in the output value of the pre-catalyst sensor 17 within one engine cycle. As the output value of the pre-catalyst sensor, a value obtained by converting the output voltage Vf of the pre-catalyst sensor 17 into an air-fuel ratio A / F is used here. However, it is also possible to directly use the output voltage Vf of the pre-catalyst sensor 17 as an output value.

As shown in FIG. 4B, the ECU 20 acquires the output value A / F of the pre-catalyst sensor at a predetermined time interval, that is, at a predetermined period τ (unit time, for example, 4 ms) within one engine cycle. Operate. Then, the difference ΔA / Fn between the value A / Fn acquired at the current timing (latest timing) (second timing) and the value A / Fn−1 acquired at the previous timing (first timing) is expressed as ( 1) Obtained by the equation. This difference ΔA / Fn can be rephrased as a differential value or inclination at the current timing.
ΔA / Fn = A / Fn−A / Fn−1 (1)

  Most simply, this difference ΔA / Fn, preferably its absolute value, represents a value representing a change in the air-fuel ratio, that is, an output change amount. This is because the gradient of the air-fuel ratio diagram increases as the degree of fluctuation increases, and the absolute value of the difference ΔA / Fn increases. Therefore, the difference ΔA / Fn at a predetermined timing or the absolute value thereof can be used as the output change amount.

  However, in this embodiment, in order to improve accuracy, a value related to the average value of the plurality of differences ΔA / F is set as the output change amount. In particular, in the present embodiment, as will be apparent from the following description, an average value of the difference ΔA / F is obtained for each of the case where the difference ΔA / F is positive and the case where it is negative, thereby obtaining the output change amount. It is done. In short, since the output value A / F related to the pre-catalyst sensor 17 may increase or decrease, the difference ΔA / F and the average value thereof are obtained for each of these cases, and the absolute values of these differences are output variations. Can be used as

  Note that whether the difference ΔA / F is positive or negative may be ignored. For example, the difference ΔA / F can be obtained regardless of whether it is positive or negative, and the average value of the absolute values can be used as the output change amount.

  FIG. 5 shows an example of the relationship between the imbalance rate IB (%) and the output change amount X. As shown in the figure, there is a strong correlation between the imbalance rate IB and the output change amount X, and the absolute value of the output change amount X tends to increase as the absolute value of the imbalance rate IB increases. .

  Therefore, it is possible to detect an abnormality in the air-fuel ratio variation between cylinders based on the output change amount X. That is, if the output change amount X, which is an absolute value, is greater than or equal to a predetermined determination threshold value, it is determined that there is a variation abnormality, and if the output change amount X, which is an absolute value, is less than the predetermined determination threshold value, there is no variation abnormality. It can be determined as normal.

  Incidentally, as described above, the ECU 20 can detect an abnormality in variation in the air-fuel ratio between cylinders based on a comparison between the output change amount X and the determination threshold value. However, the detection value of the pre-catalyst sensor 17 varies among cylinders due to the difference in the flow of exhaust gas from each cylinder to the pre-catalyst sensor 17 that is an air-fuel ratio sensor. Therefore, regardless of which cylinder is abnormal, if the same determination threshold value is used, there is a possibility that an abnormality in variation in the air-fuel ratio between cylinders cannot be detected properly (reliably).

  Here, consider an internal combustion engine with a remarkable variation in how exhaust from each cylinder hits the air-fuel ratio sensor. In FIG. 6 (a), when there is no air-fuel ratio abnormality in each cylinder, the output change amount, that is, the inclination of each cylinder calculated based on the above equation (1) is shown on the right side in the figure, and the air-fuel ratio abnormality is present in the cylinder. The same change amount of each cylinder when there is is shown on the left side in the figure. Further, FIG. 6A shows an example of a determination threshold value for abnormality in variation in air-fuel ratio between cylinders. Here, the same threshold value is shown for all cylinders. In this case, if there is such an abnormality in the # 1 or # 2 cylinder, the output change amount of those cylinders exceeds the threshold value, so that the abnormality can be detected, but there is such an abnormality in the # 3 or # 4 cylinder. However, since the output change amount of those cylinders does not exceed the threshold value, there is a possibility that the abnormality cannot be detected. Conversely, if the threshold value is lowered, there is a possibility that it is determined that there is an abnormality when there is a variation in the air-fuel ratio between the cylinders that is not abnormal.

  Therefore, in consideration of how the exhaust from each cylinder hits the air-fuel ratio sensor, a specific determination threshold value for each cylinder is determined in advance, preferably determined by experiment, and a cylinder that seems to have a high degree of variation in air-fuel ratio (that is, Cylinders that may be abnormal) are specified, and the determination threshold related to the specified cylinder is compared with the value obtained as described above, thereby detecting the abnormality in the air-fuel ratio variation between cylinders. For example, as shown in FIG. 6B, the threshold values for the strong # 1 and # 2 cylinders per gas to the sensor are set higher than the threshold values for the weak # 3 and # 4 cylinders per gas to the sensor.

  FIG. 6 shows an example of an output change amount in each cylinder in an internal combustion engine having a variation in gas per sensor to each cylinder. The threshold value in FIG. It is expressed without considering the output change amount of the exhaust gas from On the other hand, in the detection control of the air-to-cylinder air ratio variation abnormality described below according to the embodiment, the determination threshold value for each cylinder is not only per gas to the sensor in each cylinder but also for all cylinders. It is determined in consideration of the output change amount of the exhaust gas from the engine.

  Hereinafter, detection control of such an abnormality in air-fuel ratio variation between cylinders in the first embodiment will be described with reference to the flowcharts of FIGS. Note that the routine of FIG. 7 can be repeatedly executed by the ECU 20 at predetermined intervals.

  However, the control of the inter-cylinder air ratio variation abnormality detecting device described in detail below is substantially executed by the ECU 20 as will be apparent from the following description. The ECU 20 functions as an acquisition unit, a retard control unit, a non-retard time value calculation unit, a retard time value calculation unit, a threshold value calculation unit, and a comparison unit of the inter-cylinder air ratio variation abnormality detection device 22. It has several parts and these parts are related to each other.

  First, in step S701 in FIG. 7, it is determined whether or not a predetermined precondition is satisfied. For example, the predetermined precondition may include that the air-fuel ratio feedback control is executed so that the exhaust air-fuel ratio follows the predetermined air-fuel ratio. In this case, the predetermined air-fuel ratio is preferably the stoichiometric air-fuel ratio, that is, stoichiometry. The fact that the predetermined precondition is satisfied is preferably satisfied at least when the calculation of FIG. 8 is performed, particularly when the output of the pre-catalyst sensor is acquired. However, the present invention can allow such a precondition to be omitted from the detection control of the abnormal variation in the air-fuel ratio between cylinders.

More specifically, in step S701 of the first embodiment, for example, when all of the following (condition a) to (condition e) are satisfied, it is determined that a predetermined precondition is satisfied.
(Condition a) Engine warm-up has been completed. The ECU 20 determines that the warm-up is finished when the water temperature detected using a water temperature sensor (not shown) exceeds a predetermined value (for example, 75 ° C.). Further, an oil temperature sensor for detecting the temperature of the engine oil may be provided, and it may be determined that the warm-up has been completed when the detected oil temperature exceeds a predetermined value.
(Condition b) The pre-catalyst sensor 17 and the post-catalyst sensor 18 are activated. The ECU 20 determines that both sensors are activated when the impedance of both sensors is a value corresponding to a predetermined activation temperature.
(Condition c) The catalysts of the upstream catalytic converter 11 and the downstream catalytic converter 19 are activated. The ECU 20 determines that both catalysts have been activated when the temperature of the catalyst of the upstream catalytic converter 11 and the temperature of the catalyst of the downstream catalytic converter 19 estimated based on the engine operating state are values corresponding to predetermined activation temperatures, respectively. To do.
(Condition d) The engine is in steady operation. The ECU 20 determines that the engine is in steady operation when the fluctuation range of the engine rotation speed and the load within a predetermined time is within a predetermined value.
(Condition e) The normal air-fuel ratio feedback control is being executed. Here, the normal air-fuel ratio feedback control is executed when the air-fuel ratio feedback control is executed so that the air-fuel ratio of the exhaust gas is controlled in the vicinity of the stoichiometry.

  Since the predetermined precondition is satisfied in step S701, if an affirmative determination is made, in step S703, the output change amount X is calculated by output change amount calculation control based on FIG. As can be understood from the above description, the output change amount X is a value representing a change in the output of the pre-catalyst sensor 17 during a predetermined time. In step S705, a threshold value for determination is calculated by threshold value calculation control based on FIGS. 8 and 9 described later.

  In step S707, the output change amount X calculated in step S703 is compared with the determination threshold value calculated in step S705. If the output change amount is less than the threshold value, a negative determination is made in step S707, and the routine ends. This means that since the output change amount is small, an abnormality in variation in air-fuel ratio between cylinders was not detected, that is, it was determined to be normal.

  On the other hand, if the determination in step S707 is affirmative because the amount of change in output is greater than or equal to the threshold value, the abnormality flag is turned on so that an abnormality is determined in step S709. As a result, in this embodiment, a warning lamp (not shown) that can be provided on the front panel of the driver's seat is turned on. As a result, the driver or the like is urged to check or repair the engine 1. Note that the abnormality flag is OFF in the initial state.

  Now, the calculation of the output change amount based on the output value of the pre-catalyst sensor 17 will be described based on the flowchart of FIG.

  The ECU 20 is constructed so that the output of the pre-catalyst sensor 17 is acquired at predetermined time intervals, that is, every time the predetermined time elapses. The predetermined time interval for acquiring the sensor output is set to 4 ms, for example. However, the predetermined time may be other than 4 ms, and is set to an arbitrary time between 4 ms and 10 ms, for example. More specifically, the ECU 20 operates so as to acquire the output of the sensor 17 in association with the crank angle. The acquired output value A / F of the pre-catalyst sensor 17 is stored in association with the crank angle.

  In step S801, the difference ΔA / Fn between the current (latest) output value A / Fn and the previous output value A / Fn−1 acquired and stored so far is expressed by the above equation (1). Calculated based on

  Then, whether or not the difference ΔA / F calculated in step S801 is positive is calculated in step S803. In step S803, since ΔA / F is positive, if an affirmative determination is made, ΔA / F is added to the total psum of positive differences ΔA / F in step S805. In step S807, the integration counter value pcount for the positive difference ΔA / F is increased by one. Note that the total psum of positive differences and the integrated counter value pcount are each set to zero in the initial state.

  On the other hand, if ΔA / F after correction is not positive (roughly negative) in step S803, a negative determination is made in step S809, in which the absolute value of ΔA / F calculated in step S801 is a negative difference ΔA. It is added to the total nsum of / F. In step S811, the integrated counter value ncount for the negative difference ΔA / F is incremented by one. Note that the total negative sum nsum and the integrated counter value ncount are each set to zero in the initial state.

  In step S813, it is determined whether or not the crank angle CA is 0 ° (that is, 720 °). Note that the crank angle in step S813 is the crank angle of a predetermined cylinder, for example, the crank angle of the # 1 cylinder. The determination in step S813 can be included in determining whether a predetermined period has elapsed.

  If the determination in step S813 is affirmative, the next step S815 is executed. If the determination in step S813 is negative, the routine ends, and as a result, the process returns to step S801 and the above calculation is repeated. Therefore, the above steps S801 to S813 are repeatedly executed until the crank angle of a predetermined cylinder advances by 720 °, and the values psum, nsum, pcount, and ncount are obtained, respectively.

  If an affirmative determination is made in step S813, 1 is added to the counter value C that is set to zero in the initial state in the next step S815. Then, in the next step S817, the latest average value of positive differences (psum / pcount) is added to the integrated value paves of the average value of the positive difference ΔA / F so far, and the average value of the positive difference is calculated. The integrated value paves is updated. Similarly, in step S817, the average value of the latest negative difference (nsum / ncount) is added to the integrated value nave of the average value of the negative difference ΔA / F so far, and the average value of the negative difference is added. The integrated value “nave” is updated. In the initial state, the integrated value paves of the average value of positive differences and the integrated value naves of the average value of negative differences are each set to zero.

  In the next step S819, the values psum, nsum, pcount, and ncount are reset to zero. In step S821, it is determined whether or not the counter value C exceeds a predetermined number N. The predetermined number N is a constant here, but may be 0 or any positive integer. This step S821 is also included in the determination of whether or not a predetermined period has elapsed. Note that the number N of times of step S821 can be set according to step S813. If a negative determination is made in step S821, the routine ends, and as a result, steps S801 to S821 are repeated.

  If an affirmative determination is made in step S821, in step S823, the positive difference average value (= paves / C) calculated by dividing the positive difference average integrated value paves by the counter value C is negative. Is compared with the average value of negative differences (= naves / C) calculated by dividing the integrated value nave of the average value of the difference by the counter value C, and the larger of these is the output change amount Set to X. Note that the output change amount calculated here can be expressed as a normal (non-retarded) output change amount Xn in the following description, and is compared with a determination threshold value in step S707.

  In step S825, the counter value C, the positive value average integrated value paves, and the negative difference average integrated value saves are each reset to zero.

  Next, the calculation of the determination threshold value in step S705 will be described based on the flowchart of FIG.

  In step S901, it is determined whether the calculation completion flag is ON. The calculation completion flag is a flag for determining whether or not the output change amount has been calculated as described above with the ignition timing of the specific cylinder retarded by a predetermined amount, and is set to OFF in the initial state.

  Since the calculation completion flag is OFF, if a negative determination is made in step S901, the ignition retard flag that is set to OFF in the initial state is turned ON in step S903. When the ignition retard flag is turned ON, the ignition timing retard control is executed so that the cylinder corresponding to the cylinder counter cyl is a specific cylinder and the ignition timing in that cylinder is retarded by a predetermined retard amount. However, here, the predetermined retardation amount is a constant and is determined in advance by experiments based on the inventive concept described later. The reference ignition timing is a normal ignition timing by the ignition timing control means.

  Then, in step S905, the output change amount is calculated in the same manner as described based on the flowchart of FIG. 8 in a state where the ignition timing retarding control is executed for the cylinder of the cylinder counter cyl. In the initial state, the cylinder counter cyl is set to zero. When the cylinder counter cyl is zero, the # 1 cylinder becomes a specific cylinder, and the ignition timing of the # 1 cylinder is retarded by a predetermined amount with respect to the ignition timing that is normally set. When the cylinder counter cyl is 1, the # 2 cylinder is a specific cylinder, and the ignition timing of the # 2 cylinder is retarded by a predetermined amount with respect to the normally set ignition timing. Further, when the cylinder counter cyl is 2, the # 3 cylinder becomes a specific cylinder, and the ignition timing of the # 3 cylinder is retarded by a predetermined amount with respect to the ignition timing that is normally set. Similarly, when the cylinder counter cyl is 3, the # 4 cylinder is a specific cylinder, and the ignition timing of the # 4 cylinder is retarded by a predetermined amount with respect to the ignition timing that is normally set.

  For example, when the cylinder counter is zero, the ignition timing retarding control is executed for the # 1 cylinder in step S903 and only the normal ignition timing control is performed for the # 2 to # 4 cylinders. In step S905, the output change amount (# 1 cylinder retarded output change amount) X1 is calculated as described above.

  In step S907, 1 is added to the cylinder counter cyl, and the cylinder counter cyl becomes 1. In step S909, it is determined whether or not the cylinder counter cyl is equal to or greater than the total number of cylinders Acyl, that is, 4 or more. Here, since the cylinder counter cyl is 1, the determination is negative and the routine ends.

  In the next routine, the result in Step S901 is negative, and in Step S903, the cylinder counter cyl is 1, so that the ignition delay control is executed for the # 2 cylinder, and for the # 1, # 3, and # 4 cylinders. In a state where only normal ignition timing control is performed, the output change amount (# 2 cylinder retarded time output change amount) X2 is calculated in step S905 as described above. In this way, by repeatedly performing the ignition retard control and the calculation, # 1 cylinder retarded output change amount X1, # 2 cylinder retarded output change amount X2, # 3, each of which is a retarded value. An output change amount X3 at the time of cylinder delay and an output change amount X4 at the time of # 4 cylinder delay are calculated.

  Then, in step S907 after the output change amount X4 at the time of retarding # 4 cylinder is calculated, the cylinder counter cyl is set to 4, and since the cylinder counter cyl is 4 or more in step S909, an affirmative determination is made. As a result, the cylinder counter cyl is reset to zero in step S911, the ignition retard flag is turned off in step S913, the calculation completion flag is turned on in step S915, and the routine ends. Since the ignition delay flag is turned off, the ignition delay control is not executed.

  In step S901 of the next routine, since the calculation completion flag is ON, an affirmative determination is made, and the maximum output change amount Xmax is calculated in step S917. The maximum output change amount Xmax is the maximum value among the output changes X1 to X4 at the time of retarding the # 1 to # 4 cylinders, and is obtained by comparison calculation. The maximum output change amount Xmax is an output change amount at the time of ignition delay in the cylinder having the largest difference between the normal change amount at retard and the normal output change amount Xn.

  In step S919, the cylinder corresponding to the maximum output change amount Xmax, that is, the cylinder corresponding number, is set to the threshold setting cylinder corresponding number imbcyl. In the next step S921, the threshold value is calculated by searching the data that defines the relationship between the cylinder set in advance based on the experiment and the determination threshold value using the threshold setting cylinder correspondence number imbcyl. For example, when the cylinder corresponding to the maximum output change amount Xmax is the # 3 cylinder, the threshold setting cylinder correspondence number ibcyl is 2, and the threshold value corresponding to the cylinder correspondence number is calculated. In step S923, the calculation completion flag is turned off, and the routine ends.

  As described above, the ignition timing retarding control is executed for a specific cylinder as a specific cylinder, and the determination threshold is set according to the specific cylinder having a large absolute value of the output change amount, that is, the inclination at that time. . The reason for this setting will be described with reference to FIG.

  In FIG. 10, the horizontal axis represents the crank angle or time, and the change in the in-cylinder pressure is represented. T1 in FIG. 10 is an ignition timing in normal ignition timing control, and t2 in FIG. 10 is an ignition timing retarded by turning on the ignition retard flag. When ignited at the normal ignition timing, the in-cylinder pressure changes as indicated by line A. On the other hand, when the ignition timing is retarded, the in-cylinder pressure changes as represented by line B. As can be understood from FIG. 10, the cylinder pressure when the exhaust port is opened is higher when the ignition is retarded than when normal ignition, and the flow velocity of the gas flowing out from the combustion chamber to the exhaust passage is faster.

  Therefore, when the specific cylinder on which the ignition timing retarding control is executed is an abnormal cylinder, that is, an imbalance cylinder, the exhaust flow velocity from the cylinder increases, so the exhaust near the pre-catalyst sensor 17 is exhausted from the exhaust of other normal cylinders. Increases the speed of switching to abnormal cylinder exhaust. As a result, in this case, the output change amount required as described above becomes large.

  On the other hand, when the specific cylinder for which the ignition timing retarding control is executed is a normal cylinder, the exhaust flow velocity from the cylinder increases, but the exhaust flow velocity of the abnormal cylinder does not change, and the exhaust near the catalyst front sensor 17 is not. The speed at which the exhaust from the normal cylinder is switched to the exhaust from the abnormal cylinder does not change. As a result, in this case, the output change amount obtained as described above does not change greatly.

  From these, it can be specified that the cylinder having the maximum output change amount when the ignition timing retarding control is executed is the cylinder most suspected of being an abnormal cylinder. Therefore, by setting the value related to the cylinder as the determination threshold value, it is possible to appropriately detect an abnormality in variation in the air-fuel ratio between cylinders.

  Next, a second embodiment of the present invention will be described. Since the configuration of the engine of the second embodiment is substantially the same as the configuration of the engine 1 of the first embodiment, the configuration of the engine of the second embodiment is similarly used here by using the same reference numerals used in the above description. The description of is omitted.

  The inter-cylinder air ratio variation abnormality detecting device applied to the engine of the second embodiment relates to the inter-cylinder air ratio variation abnormality detecting device of the first embodiment with respect to ignition timing retardation control for a specific cylinder. With different points. Below, only the characteristic part is demonstrated and the other overlapping description is abbreviate | omitted. Note that the cylinder-to-cylinder air ratio variation abnormality detection control according to the second embodiment is substantially the same as the control based on FIGS. 7 to 9 described above.

  Also in the inter-cylinder air-fuel ratio variation abnormality detection device of the second embodiment, as described above, detection control of inter-cylinder air-fuel ratio variation abnormality is executed based on FIGS. 7 to 9. However, in the ignition timing retard control for the specific cylinder, the ignition retard amount is calculated based on the normal (non-retard) output change amount Xn calculated in step S823 in FIG.

  In the second embodiment, the mapped data shown in FIG. 11 is searched based on the normal (non-retarded) output change amount Xn calculated in step S823 in FIG. A retard amount is calculated. Then, when this ignition delay amount is set as a predetermined retard amount, and the ignition delay flag is turned ON in step S903, the ignition for retarding the ignition timing of the specific cylinder by this predetermined delay amount in step S905. Timing retard control is executed. Note that the data in FIG. 11 is constructed so that the smaller the ignition output amount Xn (the magnitude) during normal times, the smaller the ignition delay amount, so the calculation is based on this relationship. The ignition retard amount is set as the predetermined retard amount. Note that the data in FIG. 11 can be determined in advance by experiments. Such setting of the ignition retard amount is executed by a portion that functions as a retard amount setting means of the ECU 20.

  The reason for setting the ignition retardation amount based on the normal output change amount Xn is that there is a high possibility that the air-fuel ratio variation abnormality is high when the normal output change amount is large. When there is an abnormality in the air-fuel ratio variation, there may be a case where the amount of fuel injected from the injector is large and a large amount of unburned components are discharged into the exhaust passage. In this case, combustion of unburned components may occur in the catalytic converter, that is, the catalyst, and further, overheating of the catalyst may occur due to ignition timing retardation control. Therefore, for example, when the normal output change amount is large, a relatively small ignition retardation amount is set so as to prevent thermal deterioration of the catalyst.

  Next, a third embodiment of the present invention will be described. Since the configuration of the engine of the third embodiment is substantially the same as the configuration of the engine 1 of the first embodiment, here, the configuration of the engine of the third embodiment is similarly used by using the same reference numerals used in the above description. The description of is omitted.

  The inter-cylinder air ratio variation abnormality detecting device applied to the engine of the third embodiment relates to the ignition timing retardation control for the specific cylinder and the calculation of the output change amount when it is performed. This is different from the cylinder air-fuel ratio variation abnormality detecting device. Below, only the characteristic part is demonstrated and the other overlapping description is abbreviate | omitted. Note that the cylinder-to-cylinder air ratio variation abnormality detection control of the third embodiment is substantially the same as the control based on FIGS. 7 to 9 described above.

  Also in the third embodiment, as described in the second embodiment, ignition timing retard control is executed by calculating the ignition retard amount based on the normal output change amount Xn and using it as a predetermined retard amount. Is done. The number of times N in step S821 related to step S905 in FIG. 9 is variable with respect to the ignition retardation amount calculated and set in this way. That is, the number of differences ΔA / F used to obtain the retarded output change amount, that is, the execution time or execution period of the ignition timing retard control for obtaining the retarded output change amount is the ignition retard. It is variable according to the amount.

  FIG. 12 schematically shows the amount of change in output when the ignition timing retardation control is executed with the # 1 cylinder as an abnormal cylinder, the other cylinders as normal cylinders, and each cylinder as a specific cylinder. FIG. 12A schematically shows the amount of change in retard output when the ignition retard amount is relatively large, and FIG. 12B shows the retard output when the ignition retard amount is relatively small. The amount of change is schematically shown. In both cases of FIGS. 12A and 12B, the number of times N in step S821 is the same.

  As shown in FIG. 12A, by increasing the ignition delay amount to some extent, the abnormal cylinder # 1 is designated as the specific cylinder even when the range of variation in the calculated value (or detection value) is taken into consideration. The amount of change in output at the time of retard can be clearly differentiated from the amount of change in output at the time of retard when the normal cylinder is the specific cylinder. On the other hand, when the ignition retardation amount is small to some extent, depending on the degree of variation in the calculated value, the output change amount at the time of retardation when the abnormal cylinder # 1 cylinder is the specific cylinder, the normal cylinder is the specific cylinder There is a case where it is not possible to clearly differentiate from the output change amount at the time of delay when the angle is set (see FIG. 12B).

  On the other hand, as schematically shown in FIG. 13A, the range of variation in the calculated value of the output change amount is narrowed by increasing the number of differences ΔA / F used in the above calculation, that is, the averaging count N. obtain. Therefore, in the present embodiment, using the mapped data as shown in FIG. 13B, the larger the ignition retard amount, the smaller the number of times of averaging N in step S821, in other words, the ignition delay. The smaller the angular amount, the larger the averaging count N in step S821. Therefore, by doing in this way, as shown in FIG. 12 (c), even when the ignition retardation amount is relatively small, the number of times of averaging N is made larger than in the case of FIG. 12 (b). As a result, the range of variation can be narrowed. Therefore, when the # 1 cylinder, which is an abnormal cylinder, is the specific cylinder, the output change amount at the time of retard when the normal cylinder is the specific cylinder, and when the normal cylinder is the specific cylinder Can be clearly differentiated.

  Note that the setting of the number of times of averaging N in step S821 related to step S905 of FIG. 9 may be performed together with the setting of the ignition retard amount. However, the number N of times in step S821 in the calculation control of the normal (non-retarded) output change amount Xn is a constant as described in the first embodiment.

  Note that the larger the ignition retard amount, the smaller the averaging number N in step S821 related to step S905, the smaller the ignition retard amount, the shorter the time or period, the more the ignition timing retarded for a specific cylinder. Means to control. Then, the retarded output change amount is calculated based on the output value of the air-fuel ratio sensor 17 corresponding to the execution time or period of the ignition timing retarding control. Therefore, even when the ignition retard amount is small, the cylinder discrimination accuracy for setting the determination threshold value is ensured, and when the ignition retard amount is large, the cylinder discrimination can be completed quickly.

  Next, a fourth embodiment of the present invention will be described. Since the configuration of the engine of the fourth embodiment is substantially the same as the configuration of the engine 1 of the first embodiment, the configuration of the engine of the fourth embodiment is similarly used here by using the same reference numerals used in the above description. The description of is omitted.

  The cylinder-to-cylinder air-ratio variation abnormality detecting device applied to the engine of the fourth embodiment relates to the ignition timing retardation control for a specific cylinder and the calculation of the output change amount when it is performed. This is different from the cylinder air-fuel ratio variation abnormality detecting device. Below, only the characteristic part is demonstrated and the other overlapping description is abbreviate | omitted. Note that the cylinder-to-cylinder air ratio variation abnormality detection control of the fourth embodiment is substantially the same as the control based on FIGS. 7 to 9 described above.

  In the fourth embodiment, the ignition retard amount in the ignition timing retard control for calculating the retard output change amount based on the load of the engine 1 (for example, the accelerator opening and / or the intake air amount) is variable. Is done. This is because when the engine is operated in a high load operation region, the exhaust temperature is likely to rise. In such a case, if the ignition delay is performed in the same manner as in the operation in the low load operation region, a catalytic converter, that is, a catalyst is used. This is because there is a possibility of overheating. Therefore, in order to prevent thermal degradation of the catalyst, for example, here, depending on the engine operating state, here particularly the engine load, based on the mapped data as shown in FIG. An ignition retardation amount is calculated and set as a predetermined retardation amount. That is, in the ignition timing retard control for calculating the retarded output change amount, the ignition retard amount is made variable according to the engine operating state at that time. Such setting of the ignition retard amount is executed by a portion that functions as a retard amount setting means of the ECU 20.

  Here, if the ignition retard amount is made variable according to the load, the ignition timing retard control is performed by shifting the specific cylinders one by one in order, so that the ignition retard amount varies among the specific cylinders. Due to variations in the ignition retard amount, there is a possibility that the retarded output change amount when the abnormal cylinder is the specific cylinder is smaller than the retard output change amount when the normal cylinder is the specific cylinder.

  Here, reference is made to FIG. 14B showing an example of the relationship between the ignition retard amount and the output change amount. In FIG. 14B, a change example of the output change amount when the abnormal cylinder is the specific cylinder is represented by a line L1, and a change example of the output change amount when the normal cylinder is the specific cylinder is represented by a line L2. Has been. In general, the output change amount when the abnormal cylinder is the specific cylinder tends to be larger than the output change amount when the normal cylinder is the specific cylinder. However, for example, when the abnormal cylinder is the specific cylinder and the ignition delay amount is D1, the output change amount is when the normal cylinder is the specific cylinder and the ignition delay amount is D2. The output change amount is smaller than that, and such a relationship is reversed. Therefore, here, an average value of the ignition retard amount for calculating the retarded output change amount is obtained, and the retarded output change amount is corrected according to the average value. Note that such correction of the output change amount is executed by a portion that functions as a correction unit of the ECU 20.

  For example, a case will be described in which the ignition timing retardation control is executed with the # 1 cylinder as a specific cylinder and the # 1 cylinder retardation output change amount X1 is calculated based on the output of the air-fuel ratio sensor 17 at that time. In this case, since the ignition delay amount in the ignition timing retardation control changes in a plurality of cycles until the determination in step S821 is affirmative with respect to step S905 in FIG. 9, the average value (average retardation amount) of these ignition retardation amounts changes. ) Is required. In order to evaluate the average retardation amount and determine the correction coefficient, the reference retardation amount is used here. The reference retardation amount is set in advance, and the ignition retardation amount that is variable as described above is set so as to change based on the reference retardation amount. Therefore, here, the reciprocal of the ratio of the average retardation amount to the reference retardation amount (reference retardation amount / average retardation amount) is calculated, and this inverse number is used as the correction coefficient. Then, the correction coefficient is multiplied by the # 1 cylinder retardation output change amount X1 obtained as described above (X1 × correction coefficient), and the corrected # 1 cylinder retardation output change amount X1 is calculated. In step S917, the corrected value is compared with the corrected retarded output change amount obtained in the same manner for the other cylinders.

  Here, reference is made to FIG. 14C showing an example of the relationship between the ignition retard amount and the output change amount. FIG. 14C shows a case where the average retardation amount is smaller than the reference retardation amount. In this case, a value larger than 1 is calculated as the correction coefficient, and the retardation output change amount before correction is set as the retardation output change amount after correction (correction value in FIG. 14C). It should be noted that the retardation output change amount after correction can be regarded as the output change amount when the average retardation amount is shifted to the reference retardation amount.

  As described above, since the ignition retard amount is made variable based on the engine load and the output change amount is corrected as described above, it is possible to improve the accuracy of determining an abnormal cylinder while appropriately suppressing catalyst deterioration. .

  Next, a fifth embodiment of the present invention will be described. Since the configuration of the engine of the fifth embodiment is substantially the same as the configuration of the engine 1 of the first embodiment, the configuration of the engine of the fifth embodiment is similarly used here by using the same reference numerals used in the above description. The description of is omitted.

  The inter-cylinder air-ratio variation abnormality detection device applied to the engine of the fifth embodiment relates to the ignition timing retardation control, the calculation of the output change amount, and the calculation of the determination threshold for the specific cylinder. This is different from the cylinder air-fuel ratio variation abnormality detecting device. Below, only the characteristic part is demonstrated and the other overlapping description is abbreviate | omitted. Note that FIG. 7 described above is used in the following description of the air cylinder ratio variation abnormality detection control of the fifth embodiment.

  As described with reference to FIG. 10, by performing the ignition retard, the cylinder pressure in the ignition retard execution cylinder when the exhaust port is opened increases, and the exhaust flow velocity from the cylinder increases. As described above, the difference ΔA / F may change due to such an increase in the exhaust flow velocity. This is because the cylinder for which the ignition timing retarding control is performed is an abnormal cylinder, or The air-fuel ratio shift is due to the effect of lean shift or rich shift.

  Here, a case where the air-fuel ratio of a certain cylinder is shifted to rich will be described. In this case, if the ignition timing retarding control is executed simultaneously for the # 1 cylinder and the # 2 cylinder, the following tendencies (trend 1R) to (trend 4R) are recognized.

(Trend 1R)
A case where the # 1 cylinder is richly deviated will be described. Since the ignition timing retarding control is executed in the # 1 cylinder and the exhaust flow velocity from there is increased, the air / fuel ratio detected by the pre-catalyst sensor 17 is changed from the air / fuel ratio (lean) by the exhaust of the # 2 cylinder to the # 1 cylinder air Since the sensor output quickly changes to the fuel ratio (rich), the sensor output changes in a smaller direction (see FIG. 2), so the negative difference ΔA / F, that is, the magnitude of the negative slope increases. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 1 cylinder to the exhaust air-fuel ratio of the # 3 cylinder is difficult to increase because the ignition timing retarding control is not executed in the # 3 cylinder. The difference ΔA / F, that is, the positive slope does not substantially increase.

(Trend 2R)
A case where the # 2 cylinder is richly deviated will be described. Since the ignition timing retarding control is executed in the # 2 cylinder and the exhaust flow velocity from there is increased, the air-fuel ratio detected by the pre-catalyst sensor 17 is changed from the air-fuel ratio (lean) by the exhaust of the # 4 cylinder to the # 2 cylinder air Since the fuel ratio is quickly switched to the fuel ratio (rich), the negative difference ΔA / F, that is, the magnitude of the negative slope increases. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 2 cylinder to the exhaust air-fuel ratio of the # 1 cylinder increases because the ignition timing retarding control is executed in the # 1 cylinder, so a positive difference ΔA / F, that is, the positive slope increases.

(Trend 3R)
The case where the # 3 cylinder is richly deviated will be described. Since the ignition timing retarding control is not executed in the # 3 cylinder, the air / fuel ratio detected by the pre-catalyst sensor 17 is switched from the exhaust air / fuel ratio (lean) of the # 1 cylinder to the exhaust air / fuel ratio (rich) of the # 3 cylinder. The speed is not large, and the negative difference ΔA / F, that is, the magnitude of the negative slope does not substantially increase. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 3 cylinder to the exhaust air-fuel ratio of the # 4 cylinder is also difficult to increase because the ignition timing retarding control is not executed in the # 4 cylinder. ΔA / F, that is, the positive slope does not substantially increase.

(Trend 4R)
The case where the # 4 cylinder is richly deviated will be described. Since the ignition timing retarding control is not executed in the # 4 cylinder, the air / fuel ratio detected by the air / fuel ratio sensor 17 is switched from the exhaust air / fuel ratio (lean) of the # 3 cylinder to the exhaust air / fuel ratio (rich) of the # 4 cylinder. The speed of the time does not increase, and the negative difference ΔA / F, that is, the magnitude of the negative slope does not substantially increase. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 4 cylinder to the exhaust air-fuel ratio of the # 2 cylinder increases because the ignition timing retarding control is executed in the # 2 cylinder, and therefore, a positive difference ΔA / F, that is, the positive slope increases.

  On the contrary, when the air-fuel ratio of a certain cylinder deviates leanly, the following tendencies (trend 1L) to (trend 4L) occur when the ignition timing retarding control is executed simultaneously in the # 1 cylinder and the # 2 cylinder. Is recognized.

(Trend 1L)
The case where the # 1 cylinder is deviated lean will be described. Since the ignition timing retarding control is executed in the # 1 cylinder and the exhaust flow velocity from there is increased, the detected air-fuel ratio in the pre-catalyst sensor 17 is changed from the exhaust air-fuel ratio (rich) of the # 2 cylinder to the exhaust air of the # 1 cylinder. Since the sensor output is rapidly changed to the fuel ratio (lean) (see FIG. 2), the positive difference ΔA / F, that is, the positive slope is increased. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 1 cylinder to the exhaust air-fuel ratio of the # 3 cylinder is difficult to increase because the ignition timing retarding control is not executed in the # 3 cylinder, and therefore negative. The difference ΔA / F, that is, the magnitude of the negative slope does not substantially increase.

(Trend 2L)
The case where the # 2 cylinder is lean is described. Since the ignition timing retarding control is executed in the # 2 cylinder and the exhaust flow velocity from there is increased, the detected air-fuel ratio in the pre-catalyst sensor 17 is changed from the exhaust air-fuel ratio (rich) of the # 4 cylinder to the exhaust air of the # 2 cylinder. Since the fuel cell is quickly switched to the fuel ratio (lean), the positive difference ΔA / F, that is, the positive slope increases. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 2 cylinder to the exhaust air-fuel ratio of the # 1 cylinder increases because the ignition timing retarding control is executed in the # 1 cylinder, so a negative difference ΔA / F, that is, the magnitude of the negative slope also increases.

(Trend 3L)
The case where the # 3 cylinder is lean is described. Since the ignition timing retarding control is not executed in the # 3 cylinder, the air / fuel ratio detected by the pre-catalyst sensor 17 is switched from the exhaust air / fuel ratio (rich) of the # 1 cylinder to the exhaust air / fuel ratio (lean) of the # 3 cylinder. The speed at that time is not large, and the positive difference ΔA / F, that is, the positive slope does not substantially increase. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 3 cylinder to the exhaust air-fuel ratio of the # 4 cylinder is also difficult to increase because the ignition timing retarding control is not executed in the # 4 cylinder, and therefore a negative difference ΔA / F, that is, the magnitude of the negative slope does not substantially increase.

(Trend 4L)
The case where the # 4 cylinder is lean is described. Since the ignition timing retarding control is not executed in the # 4 cylinder, the air / fuel ratio detected by the air / fuel ratio sensor 17 is switched from the exhaust air / fuel ratio (rich) of the # 3 cylinder to the exhaust air / fuel ratio (lean) of the # 4 cylinder. The speed at that time does not increase, and the positive difference ΔA / F, that is, the positive slope does not increase substantially. On the other hand, the speed at which the detected air-fuel ratio switches from the exhaust air-fuel ratio of the # 4 cylinder to the exhaust air-fuel ratio of the # 2 cylinder increases because the ignition timing retarding control is executed in the # 2 cylinder, and thus the negative difference ΔA / F, that is, the magnitude of the negative slope increases.

  The above tendencies (trend 1R) to (trend 4L) are summarized as shown in FIG. In FIG. 15, in each region, a cylinder number that is highly likely to have a rich shift is written on the left side, and a cylinder number that is likely to be a lean shift is written to the right side. Further, it is possible to determine whether the rich abnormality or the lean abnormality is based on the output change amount when the ignition timing retardation control is not performed, that is, the magnitude of the inclination. Therefore, the ignition timing retard control is executed simultaneously with the # 1 cylinder and the # 2 cylinder, and the positive non-retarded and retarded output change amount and the negative non-retarded and retarded output change amount. And comparing them, it is possible to appropriately determine a cylinder that is highly likely to be abnormal.

  Note that the rich abnormality or the lean abnormality can be determined by the output change amount when the ignition timing retarding control is not performed, that is, the magnitude of the inclination, and will be supplementarily described here. For example, particularly when only one cylinder has a rich shift, the pre-catalyst sensor output rapidly changes to the rich side (that is, rapidly decreases) when the pre-catalyst sensor 17 receives exhaust gas corresponding to the one cylinder. It is possible to use a value only on the decrease side for detecting a rich shift. The reverse is also possible. Therefore, rich based on a comparison between the average value of the absolute value of the difference ΔA / F only when the pre-catalyst sensor output decreases and the average value of the absolute value of the difference ΔA / F only when the pre-catalyst sensor output increases. It is possible to determine whether there is a deviation or a lean deviation.

  Therefore, in the fifth embodiment, a cylinder having a high possibility of abnormality is specified based on such a relationship, specifically, the relationship or data shown in FIG. 15, and a threshold setting cylinder correspondence number mbcyl is determined. It is done.

  The cylinder-to-cylinder air ratio variation abnormality detection control in the fifth embodiment will be described with reference to FIGS.

  In step S701 in FIG. 7, it is determined whether or not the predetermined precondition is satisfied. Since a predetermined precondition is satisfied in step S701, if an affirmative determination is made, in step S703, the positive output change amount Pave and the negative output change are controlled by output change amount calculation control based on FIG. The quantity Nave is calculated. In step S705, a threshold value for determination is calculated by threshold value calculation control based on FIGS. 16 and 17 described later.

  In step S707, the larger one of the positive output change amount Pave and the negative output change amount Nave calculated in step S703 is set as the normal output change amount Xn, and is calculated in step S705. It is compared with the threshold value for determination. If the output change amount is less than the threshold value, a negative determination is made in step S707, and the routine ends. On the other hand, if the determination in step S707 is affirmative because the amount of change in output is greater than or equal to the threshold value, the abnormality flag is turned on so that an abnormality is determined in step S709.

  Now, the calculation of the positive output change amount Pave and the negative output change amount Nave based on the output value of the pre-catalyst sensor 17 will be described based on the flowchart of FIG.

  In step S1601, the difference ΔA / Fn between the current (latest) output value A / Fn and the previous output value A / Fn−1 acquired and stored so far is expressed by the above equation (1). Calculated based on Then, whether or not the difference ΔA / F calculated in step S1601 is positive is calculated in step S1603. If ΔA / F is positive in step S1603 and a positive determination is made, ΔA / F is added to the total psum of positive differences ΔA / F in step S1605. In step S1607, the integration counter value pcount for the positive difference ΔA / F is incremented by one.

  On the other hand, if ΔA / F after correction is not positive (roughly negative) in step S1603, a negative determination is made. In step S1609, the absolute value of ΔA / F calculated in step S1601 is a negative difference ΔA. It is added to the total nsum of / F. In step S1611, the integrated counter value ncount related to the negative difference ΔA / F is incremented by one.

  In step S1613, it is determined whether or not the crank angle CA is 0 ° (that is, 720 °). If an affirmative determination is made in step S1613, the next step S1615 is executed. If a negative determination is made in step S1613, the routine ends, and as a result, the process returns to step S1601, and the above calculation is repeated. Accordingly, the above steps S1601 to S1613 are repeatedly executed until the crank angle of a predetermined cylinder advances by 720 °, and the values psum, nsum, pcount, and ncount are obtained, respectively.

  If an affirmative determination is made in step S1613, 1 is added to the counter value C set to zero in the initial state in the next step S1615. In the next step S1617, the average value (psum / pcount) of the latest positive difference is added to the integrated value paves of the average value of the positive difference ΔA / F so far (initially set to zero). Are added, and the integrated value paves of the average value of positive differences is updated. Similarly, in step S1617, the average value of the latest negative difference (nsum / ncount) is further added to the integrated value “naves” of the average value of the negative difference ΔA / F so far (initially set to zero). ) Is added, and the integrated value nave of the average value of the negative differences is updated.

  In the next step S1619, the values psum, nsum, pcount, and ncount are each reset to zero. In step S1621, it is determined whether or not the counter C has exceeded a predetermined number N. If a negative determination is made in step S1621, the routine ends, and as a result, steps S1601 to S1621 are repeated.

  If an affirmative determination is made in step S1621, the average value of positive differences (= paves / C) calculated by dividing the integrated value paves of the average value of positive differences by the counter value C is positive in step S1623. The output change amount is Pave. Further, the negative difference average value (= naves / C) calculated by dividing the integrated value nave of the negative difference average value by the counter value C is set as the negative output change amount Nave. The positive output change amount calculated based on the sensor output when the ignition timing retard control is not performed at normal time is referred to as a positive non-retarded output change amount Paven. The negative output change amount calculated based on the sensor output when the timing retard control is not performed can be referred to as negative non-retard angle output change amount Naven.

  In step S1625, the counter value C, the positive value average integrated value paves, and the negative difference average integrated value nave are reset to zero.

  Thus, steps S1601 to S1621 and S1625 in FIG. 16 correspond to steps S801 to S821 and S825 in FIG. 8, respectively. Therefore, detailed description of these steps is omitted above.

  Next, the calculation of the determination threshold value in step S705 will be described based on the flowchart of FIG.

  In step S1701, it is determined whether the calculation completion flag set to OFF in the initial state is ON. Since the calculation completion flag is OFF, if a negative determination is made in step S1701, the ignition delay flag that is set to OFF in the initial state is turned ON in step S1703. When the ignition retard flag is turned on, as described above, the ignition timing retard control is executed in the cylinders at the same time with the # 1 cylinder and the # 2 cylinder as specific cylinders.

  Then, in the state in which the ignition timing retarding control is being executed in the # 1 cylinder and the # 2 cylinder in step S1705, the positive retarded output change amount Paved is explained in the same manner as described based on the flowchart of FIG. And a negative retardation output variation amount Naveed are calculated.

  In step S1707, the ignition delay flag is turned off, in step S1709, the calculation completion flag is turned on, and the routine ends. Since the ignition delay flag is turned off, the ignition delay control is not executed.

  In step S1701 of the next routine, since the calculation completion flag is ON, an affirmative determination is made, and in step S1711, a positive output change amount difference Δpave (positive retarded output change amount Paved−positive non-retarded time output). The difference Δnave between the change amount Paven) and the negative output variable (negative delay output change amount Nave−negative non-retard output change amount Naven) is calculated.

  In step S1713, it is determined whether or not the difference Δpave between the positive output change amounts calculated in step S1711 is less than a predetermined value α (see FIG. 15). If an affirmative determination is made in step S1713, it is determined in step S1715 whether or not the negative output change amount difference Δnave calculated in step S1711 is less than a predetermined value β (see FIG. 15). If an affirmative determination is made in step S1715, the threshold setting cylinder correspondence number imbcyl is set to 2 in step S1717 (see the lower left region in FIG. 15), and the threshold value corresponding to the threshold setting cylinder correspondence number imbcyl is next step S1719. Is calculated. Since the threshold setting cylinder correspondence number mbcyl is “2”, the threshold corresponding to the # 3 cylinder is calculated as described in the first embodiment. In step S1721, the calculation completion flag is turned off, and the routine ends.

  On the other hand, if a negative determination is made in step S1715, it is determined in step S1723 whether the negative non-retarded output change amount Naven is larger than the positive non-retarded output change amount Paven. If this relationship is satisfied, there is a possibility that a rich shift has occurred as described above. Therefore, if an affirmative determination is made in step S1723, as described on the left side of the upper left area in FIG. 15, the threshold setting cylinder correspondence number imbcyl is set to 0 in step S1725 (corresponding to # 1 cylinder). Conversely, if a negative determination is made in step S1723, as described on the right side of the upper left area in FIG. 15, the threshold setting cylinder correspondence number imbcyl is set to 3 in step S1727 (corresponding to # 4 cylinder).

  If a negative determination is made in step S1713, it is determined in step S1729 whether the negative output change amount difference Δnave calculated in step S1711 is less than a predetermined value β (see FIG. 15) in the same manner as in step S1715. Determined. If a negative determination is made in step S1729, the threshold setting cylinder correspondence number imbcyl is set to 1 in step S1731 (corresponding to # 2 cylinder) as described in the upper right region of FIG.

  If an affirmative determination is made in step S1729, it is determined in step S1733 whether the negative non-retarded output change amount Naven is larger than the positive non-retarded output change amount Paven, as in step S1723. Is done. If an affirmative determination is made in step S1733, the threshold setting cylinder correspondence number imbcyl is set to 3 (corresponding to # 4 cylinder) in step S1735, as described on the left side of the lower right region of FIG. On the other hand, if a negative determination is made in step S1733, the threshold setting cylinder correspondence number imbcyl is set to 0 (corresponding to the # 1 cylinder) in step S1737 as described on the right side of the lower right region of FIG.

  Then, in step S1719 as described above, a threshold value corresponding to the threshold value setting cylinder correspondence number imbcyl set in this way is calculated.

  As described above, in the fifth embodiment, the ignition timing retarding control is executed at the same time for a plurality of cylinders and the determination threshold value is calculated. Therefore, it is possible to detect an abnormality in variation in the air-fuel ratio between cylinders in a shorter time.

  The five embodiments have been described with respect to the four-cylinder engine. However, since the variation per cylinder in the sensor per cylinder is more remarkable, for example, in an 8-cylinder engine, the present invention is more effective in an internal combustion engine having a larger number of cylinders.

  Embodiments of the present invention are not limited to the above-described embodiments, and the present invention allows embodiments in which these embodiments are combined with each other within a consistent range. All modifications, applications, and equivalents included in the spirit of the present invention defined by the claims are included in the present invention. 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
7 Spark plug 11 Upstream catalytic converter 12 Injector 17 Pre-catalyst sensor (air-fuel ratio sensor)
20 Electronic control unit (ECU)
22 Cylinder air ratio variation abnormality detection device

Claims (7)

An inter-cylinder air-fuel ratio variation abnormality detecting device for an internal combustion engine having a plurality of cylinders,
Acquisition means that operates to acquire the output of an air-fuel ratio sensor provided in the exhaust passage;
Retard control means for executing ignition timing retard control for retarding the ignition timing of a specific cylinder by a predetermined retard amount for a predetermined period;
Non-retarding time for calculating a value representing a change in the air-fuel ratio based on the output value of the air-fuel ratio sensor acquired by the acquiring means when the ignition timing retarding control is not executed by the retarding control means A value calculating means;
A retard time value for calculating a value representing a change in the air fuel ratio based on the output value of the air fuel ratio sensor acquired by the acquiring means when the ignition timing retard control is being executed by the retard control means. A calculation means;
Threshold calculation means for calculating a threshold for determining an abnormality in the air-fuel ratio variation between cylinders based on the value calculated by the retardation time value calculation means, and based on the value calculated by the retardation time value calculation means Threshold value calculating means for specifying a cylinder that is considered to have a high degree of variation in air-fuel ratio and calculating a value set for the specified cylinder as the determination threshold value ;
A cylinder provided with a comparing means for comparing the value calculated by the non-retarded angle value calculating means with the threshold value calculated by the threshold value calculating means so as to determine whether there is an abnormality in the air-fuel ratio variation between cylinders; Inter-air-fuel ratio variation abnormality detection device. The retard angle control means sets all the cylinders of the internal combustion engine to specific cylinders one by one in order, and executes the ignition timing retard angle control for each specific cylinder,
The retard angle value calculating means is a value relating to each specific cylinder based on the output value of the air-fuel ratio sensor acquired by the acquiring means when the ignition timing retard control is being executed in each specific cylinder. , Calculate a value representing the change in the air-fuel ratio,
The threshold value calculation means calculates a value set for the cylinder having the largest value calculated by the retard angle value calculation means among all the cylinders of the internal combustion engine as a determination threshold value.
The inter-cylinder air ratio variation abnormality detection device according to claim 1.   The retard control means calculates an ignition delay amount based on the value calculated by the non-retard time value calculation means, and sets the calculated ignition delay amount to the predetermined retard amount. The inter-cylinder air ratio variation abnormality detection device according to claim 1, further comprising an amount setting unit.   The inter-cylinder engine according to claim 3, wherein the retard amount setting means sets a smaller ignition retard amount as a predetermined retard amount as the magnitude of the value calculated by the non-retard time value calculating means increases. Sky ratio variation abnormality detection device. The retard control means executes the ignition timing retard control for a shorter period as the ignition retard amount set by the retard amount setting means is larger,
The retard angle value calculating means is configured to change the air-fuel ratio based on the output value of the air-fuel ratio sensor acquired by the acquiring means corresponding to the execution period of the ignition timing retard control by the retard control means. Calculate a value representing
The inter-cylinder air / fuel ratio variation abnormality detection device according to claim 4. The retard control means includes a retard amount setting means for variably setting an ignition retard amount based on a load of the internal combustion engine,
The retard time value calculating means is configured to execute the ignition timing retard control when the retard timing control means is executing the ignition timing retard control according to the average value of the ignition retard amount set by the retard amount setting means. Correction means for correcting a value representing a change in the air-fuel ratio calculated based on the output value of the air-fuel ratio sensor acquired by the acquisition means;
The inter-cylinder air ratio variation abnormality detection device according to claim 1 or 2. The retard control means executes ignition timing retard control for retarding the ignition timing of a specific cylinder composed of two or more cylinders by a predetermined retard amount for a predetermined period at the same time,
The retard time value calculating means calculates an air-fuel ratio change based on the output value of the air-fuel ratio sensor acquired by the acquiring means when the ignition timing retard control is being executed by the retard control means. Calculate the value to represent,
The threshold value calculation means calculates the threshold value for determination using the value calculated by the non-retarded time value calculating means and the value calculated by the retarded time value calculating means.
The inter-cylinder air-fuel ratio variation abnormality detection device according to claim 1.

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