JP2012246813A - Inter-cylinder air-fuel ratio variation failure detection device for multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly detect inter-cylinder air-fuel ratio variation failure in a multi-cylinder internal combustion engine.SOLUTION: This inter-cylinder air-fuel ratio variation failure detection device for a multi-cylinder internal combustion engine 1 comprises: a primary determination execution means for executing primary determination including the determination whether there is the possibility of inter-cylinder air-fuel ratio variation failure; a fuel injection amount change control means for executing fuel injection amount change control for forcibly changing the fuel injection amount of a predetermined target cylinder by a predetermined amount when the primary determination execution means determines that there is such possibility; and a secondary determination execution means for determining whether there is inter-cylinder air-fuel ratio variation failure on the basis of output variation when the fuel injection amount change control is executed.

Description

  The present invention relates to an apparatus for detecting a variation abnormality in an air-fuel ratio between cylinders of a multi-cylinder internal combustion engine.

  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 follows a predetermined target air-fuel ratio.

  On the other hand, in a multi-cylinder internal combustion engine, since air-fuel ratio control is normally performed using the same control amount for all cylinders, 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 air-fuel ratio between the cylinders varies greatly due to failure of the fuel injection system of some cylinders or the valve mechanism of the intake valve, exhaust emissions become worse, which becomes a problem. It is desirable to detect such a large air-fuel ratio variation that deteriorates the exhaust emission as an abnormality.

For example, in the internal combustion engine disclosed in Patent Document 1, it is first determined that the air-fuel ratio between the cylinders of the internal combustion engine is in an imbalance state based on the calculated value of the air-fuel ratio feedback control. In the internal combustion engine, main air-fuel ratio feedback control is executed based on the detection result of the A / F sensor provided on the upstream side of the purification catalyst in the exhaust passage, and the O ₂ sensor provided on the downstream side of the purification catalyst. Sub air-fuel ratio feedback control is executed based on the detection result. When the average value of the calculated values of the sub air / fuel ratio feedback control exceeds the normal value, it is determined that the air / fuel ratio between the cylinders is in an imbalance state. Further, in the internal combustion engine of Patent Document 1, when it is determined that there is an air-fuel ratio abnormality between the cylinders, a process of reducing the fuel injection time of the injectors of each cylinder by a predetermined time is executed, thereby causing misfire. It is identified that the cylinder in which the air-fuel ratio has occurred is the cylinder in which the air-fuel ratio imbalance has occurred.

JP 2010-112244 A

  By the way, in a multi-cylinder internal combustion engine, fuel injection amount change control for forcibly changing the fuel injection amount to each cylinder is executed. It is possible to detect that the fuel ratio is in an imbalance state. However, since such fuel injection amount change control actively changes the fuel injection amount, it is desired that the number of executions is small from the viewpoint of exhaust emission and the like.

  Accordingly, the present invention has been made in view of the above circumstances, and the object thereof is to suitably suppress an abnormality in the air-fuel ratio between cylinders in a multi-cylinder internal combustion engine while suppressing execution of fuel injection amount change control for forcibly changing the fuel injection amount. There is to detect.

  According to one aspect of the present invention, primary determination execution means for performing a primary determination based on an output fluctuation of an internal combustion engine, wherein the primary determination may be an abnormal variation in the air-fuel ratio between cylinders. And determining whether or not there is a possibility that there is an abnormality in the air-fuel ratio variation between the cylinders by the primary determination executing means and the primary determination executing means. The fuel injection amount change control means for executing the fuel injection amount change control for forcibly changing the fuel injection amount and the secondary determination based on the output fluctuation of the internal combustion engine when the fuel injection amount change control is executed A secondary determination execution means comprising secondary determination execution means for determining whether or not there is an abnormality in the air-fuel ratio variation between cylinders as the secondary determination. A detection device is provided.

  Preferably, the primary determination execution means includes a first output fluctuation value calculation means for calculating a value representing an output fluctuation of the internal combustion engine, and a value calculated by the first output fluctuation value calculation means is a predetermined first region. If the calculated value is in the predetermined second region that does not overlap the predetermined first region, there is no abnormality in the air-fuel ratio variation between cylinders. First determination means for determining and determining that there is an abnormality in the air-fuel ratio variation between cylinders when the calculated value is in a predetermined third region that does not overlap the predetermined first region and the predetermined second region.

1 is a schematic view of an internal combustion engine according to an 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 time chart for demonstrating the value showing rotation fluctuation. It is a time chart for demonstrating another value showing rotation fluctuation. It is a graph which shows the change of rotation fluctuation when fuel injection quantity is increased or decreased. It is a figure which shows the mode of the increase in fuel injection quantity, and the change of the rotation fluctuation | variation before and behind the increase. It is a flowchart of the primary determination in embodiment. It is a flowchart relevant to the flowchart of FIG.

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

  FIG. 1 schematically shows an internal combustion engine according to this embodiment. An illustrated internal combustion engine (engine) 1 is a V-type 8-cylinder spark ignition internal combustion engine (gasoline engine) mounted on an automobile. The engine 1 has a first bank B1 and a second bank B2, and the first bank B1 is provided with odd-numbered cylinders, that is, # 1, # 3, # 5, and # 7 cylinders. B2 is provided with even-numbered cylinders, that is, # 2, # 4, # 6, and # 8 cylinders. The # 1, # 3, # 5, and # 7 cylinders form the first cylinder group, and the # 2, # 4, # 6, and # 8 cylinders form the second cylinder group.

  Each cylinder is provided with an injector (fuel injection valve) 2. The injector 2 injects fuel into the intake passage of the corresponding cylinder, particularly into an intake port (not shown). Each cylinder is provided with a spark plug 13 for igniting the air-fuel mixture in the cylinder. The ignition order in the engine 1 is the order of # 1, # 8, # 7, # 3, # 6, # 5, # 4, and # 2 cylinder.

  The intake passage 7 for introducing the intake air includes a surge tank 8 as a collective portion, a plurality of intake manifolds 9 connecting the intake ports of each cylinder and the surge tank 8, and the upstream side of the surge tank 8. Are formed by the intake pipe 10 and the like. The intake pipe 10 is provided with an air flow meter 11 and an electronically controlled throttle valve 12 in order from the upstream side. The air flow meter 11 outputs a signal having a magnitude corresponding to the intake flow rate.

  A first exhaust passage 14A is provided for the first bank B1, and a second exhaust passage 14B is provided for the second bank B2. The first and second exhaust passages 14 </ b> A and 14 </ b> B are joined upstream of the downstream catalytic converter 19. Since the structure of the exhaust system upstream of the merge position is the same in both banks, only the first bank B1 side will be described here, and the second bank B2 side will be given the same reference numeral in the drawing and description thereof will be omitted. To do.

  The first exhaust passage 14A includes exhaust ports (not shown) of the cylinders # 1, # 3, # 5, and # 7, an exhaust manifold 16 that collects exhaust gases of these exhaust ports, and an exhaust manifold 16 A compartment is formed by an exhaust pipe 17 or the like installed on the downstream side. The exhaust pipe 17 is provided with an upstream catalytic converter 18. A pre-catalyst sensor 20 and a post-catalyst sensor 21 that are air-fuel ratio sensors for detecting the air-fuel ratio of the exhaust gas are installed on the upstream side and the downstream side (immediately and immediately after) of the upstream catalytic converter 18, respectively. Thus, one upstream catalytic converter 18, one before catalyst 20, and one after catalyst 21 are provided for a plurality of cylinders (or cylinder groups) belonging to one bank.

  It is also possible to separately provide the downstream catalytic converter 19 without joining the first and second exhaust passages 14A and 14B.

  The engine 1 is provided with an electronic control unit (hereinafter referred to as an ECU) 100 that performs various functions as various control means (control device) and various detection means (detection unit). The ECU 100 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 11, the pre-catalyst sensor 20 and the post-catalyst sensor 21, the ECU 100 includes a crank angle sensor 22 for detecting the crank angle of the engine 1 and an accelerator opening sensor 23 for detecting the accelerator opening. The water temperature sensor 24 for detecting the temperature of the engine cooling water and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 100 controls the injector 2, spark plug 13, throttle valve 12, etc. so as to obtain a desired output based on detection values of various sensors and the like, and controls the fuel injection amount, fuel injection timing, ignition timing, throttle opening degree. Control etc.

  As described above, the ECU 100 functions as a fuel injection control unit, an ignition control unit, an intake air amount control unit, an air-fuel ratio control unit, and the like. As will be described in detail later, the engine 1 is equipped with an inter-cylinder air-fuel ratio variation abnormality detection device, and the ECU 100 includes fuel injection amount change control means, primary determination execution means, and secondary determination execution means. It is essentially responsible for the function. The primary determination execution means includes a first output fluctuation value calculation means and a first determination means for making a determination to be described later based on a value calculated by the first output fluctuation value calculation means. The secondary determination execution means includes second output fluctuation value calculation means and second determination means for making a determination to be described later based on a value calculated by the second output fluctuation value calculation means.

  The throttle valve 12 is provided with a throttle opening sensor (not shown), and a signal from the throttle opening sensor is sent to the ECU 100. The ECU 100 normally feedback-controls the opening of the throttle valve 12 (throttle opening) to an opening determined according to the accelerator opening.

  Further, the ECU 100 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 11. The ECU 100 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 100 detects the crank angle itself and the rotational speed of the engine 1 based on the crank pulse signal from the crank angle sensor 22. 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. Note that a portion that substantially functions as a detection unit that detects an abnormality in variation in the air-fuel ratio between cylinders of the ECU 100 calculates a value representing output fluctuation based on the output of the crank angle sensor 22 serving as an output detection unit.

  Then, ECU 100 normally sets the fuel injection amount (or fuel injection time) using data or the like previously stored in the storage device based on the intake air amount and the engine rotation speed, that is, the engine operating state. Based on the fuel injection amount, fuel injection from the injector 2 is controlled. In addition, the fuel injection amount by such normal fuel injection control is referred to herein as a normal fuel injection amount.

  By the way, the pre-catalyst sensor 20 is a so-called wide-range air-fuel ratio sensor, and can continuously detect an air-fuel ratio over a relatively wide range. FIG. 2 shows the output characteristics of the pre-catalyst sensor 20. As shown in the figure, the pre-catalyst sensor 20 outputs a voltage signal Vf having a magnitude proportional to the detected exhaust air-fuel ratio (pre-catalyst air-fuel ratio A / Ff). The output voltage when the exhaust air-fuel ratio is stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.5) is Vreff (for example, about 3.3 V).

On the other hand, the post-catalyst sensor 21 is a so-called O ₂ sensor and has a characteristic that the output value changes suddenly at the stoichiometric boundary. FIG. 2 shows the output characteristics of the post-catalyst sensor 21. As shown in the figure, the output voltage when the exhaust air-fuel ratio (post-catalyst air-fuel ratio A / Fr) is stoichiometric, that is, the stoichiometric equivalent value is Vrefr (for example, 0.45 V). The output voltage of the post-catalyst sensor 21 changes within a predetermined range (for example, 0 to 1 V). Generally, when the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage Vr of the post-catalyst sensor is lower than the stoichiometric equivalent value Vrefr, and when the exhaust air-fuel ratio is richer than the stoichiometric, the output voltage Vr of the post-catalyst sensor is higher than the stoichiometric equivalent value Vrefr. Get higher.

  The upstream catalytic converter 18 and the downstream catalytic converter 19 are made of a three-way catalyst, and simultaneously purify NOx, HC and CO, which are harmful components in the exhaust, when the air-fuel ratio A / F of the exhaust gas flowing into each of them is near 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 ECU 100 executes air-fuel ratio control (stoichiometric control) for controlling the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 18 in the vicinity of the stoichiometric. In this air-fuel ratio control, the air-fuel ratio of the air-fuel mixture (specifically, the fuel injection amount) is feedback-controlled so that the exhaust air-fuel ratio detected by the pre-catalyst sensor 20 becomes a stoichiometric value that is a predetermined target air-fuel ratio. Fuel ratio control (main air-fuel ratio feedback control) and auxiliary air-fuel ratio control that feedback-controls the air-fuel ratio (specifically, fuel injection amount) of the air-fuel mixture so that the exhaust air-fuel ratio detected by the post-catalyst sensor 21 becomes stoichiometric. (Auxiliary air-fuel ratio feedback control). 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 20 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 2 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 21 and the first correction coefficient obtained in the main air-fuel ratio feedback control is corrected. Is done. However, in the present embodiment, the predetermined target air-fuel ratio, that is, the reference value (target value) of the air-fuel ratio is stoichiometric, and the fuel injection amount corresponding to this stoichiometric (referred to as stoichiometric equivalent amount) is the fuel injection amount reference value ( Target value). However, the reference values for the air-fuel ratio and the fuel injection amount may be other values.

  The air-fuel ratio control is performed on a bank basis or on a bank basis. For example, the detection values of the pre-catalyst sensor 20 and the post-catalyst sensor 21 on the first bank B1 side are used only for air-fuel ratio feedback control of the # 1, # 3, # 5, and # 7 cylinders belonging to the first bank B1. This is not used for the air-fuel ratio feedback control of the # 2, # 4, # 6, and # 8 cylinders belonging to the second bank B2. The reverse is also true. Air-fuel ratio control is executed as if there were two independent in-line four-cylinder engines. In the air-fuel ratio control, the same control amount is uniformly used for each cylinder belonging to the same bank.

  For example, in some cylinders (particularly one cylinder) of all the cylinders, a failure of the injector 2 or the like may occur, and variations in air-fuel ratio (imbalance) may occur between the cylinders. For example, for the first bank B1, the fuel injection amount of the # 1 cylinder becomes larger than the fuel injection amounts of the other # 3, # 5, and # 7 cylinders due to poor closing of the injector 2, and the air-fuel ratio of the # 1 cylinder is This is a case where the air-fuel ratio of the other # 3, # 5, and # 7 cylinders is greatly shifted to the rich side.

  Even at this time, if a relatively large correction amount is given by the above-described air-fuel ratio feedback control, the air-fuel ratio of the total gas (exhaust gas after joining) supplied to the pre-catalyst sensor 20 may sometimes be stoichiometrically controlled. However, looking at each cylinder, # 1 cylinder is larger and richer than stoichiometric, and # 3, # 5, and # 7 cylinders are leaner than stoichiometric. Is clear. In view of this, the present embodiment is equipped with a device that detects such a variation in air-fuel ratio between cylinders.

  Here, a value that is an imbalance rate is used as an index value that represents the degree of variation in the air-fuel ratio between cylinders. The imbalance rate is the ratio of the fuel injection amount of the cylinder (imbalance cylinder) causing the fuel injection amount deviation when only one cylinder among the plurality of cylinders causes the fuel injection amount deviation. Thus, it is a value indicating whether or not there is a deviation from the fuel injection amount of the cylinder (balance cylinder) that does not cause the fuel injection amount deviation, that is, the reference injection amount (corresponding to the normal fuel 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 greater the imbalance rate IB, whether positive or negative, the greater the fuel injection amount deviation between the imbalance cylinder and the balance cylinder, and the greater the air-fuel ratio variation.

  On the other hand, in the present embodiment, when the fuel injection amount of a predetermined target cylinder is actively or forcibly increased or decreased and changed in this way, that is, due to the rotational fluctuation of the target cylinder at least after the increase or decrease. Based on this, a variation abnormality is detected.

  First, rotational fluctuation will be described. The rotational fluctuation is included in the output fluctuation of the engine 1 and means a change in the engine rotational speed or the crankshaft rotational speed. In this specification, a value representing rotational fluctuation, that is, a value representing the degree of rotational fluctuation is referred to as a rotational fluctuation amount. For example, a value (amount) obtained by measuring a time required for the crankshaft to rotate by a predetermined angle and calculating the measured value can be used as the rotation fluctuation amount. It will be understood that various values can be used as the rotational fluctuation amount in the following description using FIG. 3 and FIG. 4.

  FIG. 3 shows a time chart for explaining the rotation fluctuation. The illustrated example is an example of an in-line four-cylinder engine, but it will be understood that the present invention can also be applied to a V-type eight-cylinder engine as in this embodiment. The ignition order in the in-line four-cylinder engine of FIG. 3 is the order of # 1, # 3, # 4, and # 2 cylinders.

  In FIG. 3, (A) shows the crank angle (° CA) of the engine. One engine cycle is 720 (° CA), and the crank angle for a plurality of cycles detected sequentially is shown in a sawtooth shape in the figure.

  FIG. 3B shows the time required for the crankshaft to rotate by a predetermined angle, that is, the rotation time T (s). Here, the predetermined angle is 30 (° CA), but may be another value (for example, 10 (° CA)). The longer the rotation time T, the slower the engine rotation speed. Conversely, the shorter the rotation time T, the faster the engine rotation speed. The rotation time T is detected by the ECU 100 based on the output of the crank angle sensor 22.

  FIG. 3C shows a rotation time difference ΔT described later. In the drawing, “normal” indicates a normal case in which no air-fuel ratio shift occurs in any cylinder, and “lean shift abnormality” indicates an imbalance rate IB = −30 (%) for only the # 1 cylinder. This shows an abnormal case where the lean deviation of is occurring. The lean deviation abnormality can be caused by, for example, clogging of an injector nozzle hole or a poor valve opening.

  First, the rotation time T at the same timing of each cylinder is detected by the ECU. Here, the rotation time T at the timing of compression top dead center (TDC) of each cylinder is detected. The timing at which the rotation time T is detected is referred to as detection timing.

  Next, at each detection timing, the ECU calculates a difference (T2−T1) between the rotation time T2 at the detection timing and the rotation time T1 at the immediately preceding detection timing. This difference is a rotation time difference ΔT shown in (C), and ΔT = T2−T1.

  Usually, in the combustion stroke after the crank angle exceeds TDC, the rotational speed increases, so the rotational time T decreases. In the subsequent compression stroke, the rotational speed decreases, and the rotational time T increases.

  However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The rotation time T is increased. Therefore, the rotation time difference ΔT in the # 3 cylinder TDC is a large positive value as shown in (C). The rotational time and rotational time difference in the # 3 cylinder TDC are defined as the rotational time and rotational time difference of the # 1 cylinder, respectively, and are represented by T1 and ΔT1, respectively. The same applies to the other cylinders.

  Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the rotation time T is only slightly reduced compared to that of the # 3 cylinder TDC. Therefore, the rotation time difference ΔT3 of the # 3 cylinder detected in the # 4 cylinder TDC is a small negative value as shown in (C). Thus, the rotation time difference ΔT of a certain cylinder is detected for each ignition cylinder TDC.

  In the subsequent # 2 cylinder TDC and # 1 cylinder TDC, the same tendency as in the case of the # 4 cylinder TDC is observed, and both the rotation time difference ΔT4 of the # 4 cylinder and the rotation time difference ΔT2 of the # 2 cylinder detected at both timings are both. It is a small negative value. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the rotation time difference ΔT of each cylinder is a value representing the rotation fluctuation of each cylinder, and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the rotation time difference ΔT of each cylinder can be used as an index value of the rotation fluctuation of each cylinder, that is, the rotation fluctuation value or the rotation fluctuation amount. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases and the rotation time difference ΔT of each cylinder increases.

  On the other hand, as shown in FIG. 3C, in the normal case, the rotation time difference ΔT is always near zero.

  In the example of FIG. 3, the case of the lean deviation abnormality is shown. However, the reverse tendency of the rich deviation, that is, the case where a large rich deviation occurs in only one cylinder has the same tendency. This is because when a large rich shift occurs, combustion is insufficient due to excessive fuel even when ignited, and sufficient torque cannot be obtained, resulting in large rotational fluctuations.

  Next, with reference to FIG. 4, an example of another value representing the rotation fluctuation, that is, another rotation fluctuation amount will be described. FIG. 4 (A) shows the crank angle (° CA) of the engine as in FIG. 3 (A).

  FIG. 4B shows an angular velocity ω (rad / s) which is the reciprocal of the rotation time T. ω = 1 / T. As a matter of course, the larger the angular velocity ω, the faster the engine rotational speed, and the smaller the angular velocity ω, the slower the engine rotational speed. The waveform of the angular velocity ω has a shape obtained by vertically inverting the waveform of the rotation time T.

  FIG. 4C shows an angular velocity difference Δω, which is a difference in angular velocity ω, similarly to the rotation time difference ΔT. The waveform of the angular velocity difference Δω also has a shape obtained by vertically inverting the waveform of the rotation time difference ΔT. “Normal” and “lean deviation abnormality” in the figure are the same as those in FIG.

  First, the angular velocity ω at the same timing of each cylinder is detected by the ECU. Again, the angular velocity ω at the timing of compression top dead center (TDC) of each cylinder is detected. The angular velocity ω is calculated by dividing 1 by the rotation time T.

  Next, at each detection timing, the ECU calculates a difference (ω2−ω1) between the angular velocity ω2 at the detection timing and the angular velocity ω1 at the immediately preceding detection timing. This difference is the angular velocity difference Δω shown in (C), and Δω = ω2−ω1.

  Normally, the rotational speed increases in the combustion stroke after the crank angle exceeds TDC, so the angular speed ω increases. In the subsequent compression stroke, the rotational speed decreases, and the angular speed ω decreases.

  However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The angular velocity ω at is small. Therefore, the angular velocity difference Δω in the # 3 cylinder TDC is a large negative value as shown in (C). The angular velocity and the angular velocity difference in the # 3 cylinder TDC are the angular velocity and the angular velocity difference of the # 1 cylinder, respectively, and are represented by ω1 and Δω1, respectively. The same applies to the other cylinders.

  Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the angular velocity ω is only slightly increased compared to that of the # 3 cylinder TDC. Therefore, the angular velocity difference Δω3 of the # 3 cylinder detected in the # 4 cylinder TDC is a small positive value as shown in (C). Thus, the angular velocity difference Δω of a certain cylinder is detected for each ignition cylinder TDC.

  In the subsequent # 2 cylinder TDC and # 1 cylinder TDC, the same tendency as in the case of the # 4 cylinder TDC is observed, and both the angular velocity difference Δω4 of the # 4 cylinder and the angular velocity difference Δω2 of the # 2 cylinder detected at both timings are both. It is a small positive value. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the angular velocity difference Δω of each cylinder is a value representing the rotational fluctuation of each cylinder and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the angular velocity difference Δω of each cylinder can be used as an index value of the rotation fluctuation of each cylinder. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases, and the angular velocity difference Δω of each cylinder decreases (increases in the minus direction).

  On the other hand, as shown in FIG. 4C, in the normal case, the angular velocity difference Δω is always near zero.

  As described above, there is a similar tendency in the case of reverse rich shift abnormality.

  Next, changes in rotational fluctuation when the fuel injection amount of a certain cylinder is actively increased, that is, forcibly increased or decreased to change the air-fuel ratio in the cylinder will be described with reference to FIG. However, in this case, when the fuel injection amount is actively increased or decreased, the operation of the throttle valve 12 and the like is controlled so that the intake air amount does not change.

  In FIG. 5, the horizontal axis represents the imbalance rate IB, and the vertical axis represents the angular velocity difference Δω as an index value of rotation fluctuation, that is, the amount of rotation fluctuation. Here, the imbalance rate IB of only one cylinder among all eight cylinders is changed, and the relationship between the imbalance rate IB of the one cylinder and the angular velocity difference Δω of the one cylinder at this time is indicated by a line a. The one cylinder is referred to as an active target cylinder. All the other cylinders are balance cylinders, and the stoichiometric equivalent amount is injected as the reference injection amount Qs.

  In the horizontal axis of FIG. 5, IB = 0 (%) means a normal case where the imbalance ratio IB of the active target cylinder is 0 (%) and the active target cylinder is injecting a stoichiometric amount. The data at this time is indicated by plot b on line a. When moving from the state of IB = 0 (%) to the left side in the figure, the imbalance rate IB increases in the positive direction, and the fuel injection amount becomes excessive, that is, a rich state. On the contrary, when moving from IB = 0 (%) to the right side in the figure, the imbalance rate IB increases in the minus direction, and the fuel injection amount becomes too small, that is, a lean state.

  As can be seen from the characteristic line a, even if the imbalance ratio IB of the active target cylinder increases in the positive direction from 0 (%) or increases in the negative direction, the rotation fluctuation of the active target cylinder increases, and the active target cylinder increases. The angular velocity difference Δω tends to increase in the minus direction from near zero. As the imbalance rate IB increases from 0 (%), the slope of the characteristic line a becomes steeper, and the change in the angular velocity difference Δω with respect to the change in the imbalance rate IB tends to increase.

  Here, as indicated by an arrow c, it is assumed that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder from the stoichiometric equivalent amount (IB = 0 (%)) by a predetermined amount Δf1 is executed. . In the illustrated example, the imbalance rate is increased by approximately 40 (%). At this time, since the slope of the characteristic line “a” is gentle in the vicinity of IB = 0 (%), the angular velocity difference Δω does not change significantly after the increase, and the difference between the angular velocity differences Δω before and after the increase is extremely small. .

  On the other hand, as shown by plot d, consider a case where a rich shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large positive value. In the illustrated example, a rich shift of about 50 (%) occurs in the imbalance rate. As indicated by an arrow e from this state, assuming that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by the same amount Δf1, the slope of the characteristic line a is steep in this region. Therefore, the angular velocity difference Δω after the increase is greatly changed to the minus side before the increase, and the difference between the angular velocity differences Δω before and after the increase is increased. In other words, the rotational fluctuation of the active target cylinder increases as the fuel injection amount increases.

  Therefore, it is possible to detect a variation abnormality based on at least the angular velocity difference Δω of the active target cylinder after the increase when the fuel injection amount of the active target cylinder is forcibly increased by a predetermined amount.

  That is, when the angular velocity difference Δω after the increase is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the increase is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the increase. In this case, if the angular velocity difference before the increase is Δω1 and the angular velocity difference after the increase is Δω2, the difference dΔω can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β1 (dΔω> β1), it can be determined that there is a variation abnormality, and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β1 (dΔω ≦ β1), at least the active target cylinder can be determined to be normal.

  The same can be said when forced reduction is performed in a region where the imbalance rate is negative, that is, when fuel injection amount reduction control is executed. As indicated by an arrow f, it is assumed that fuel injection amount reduction control is executed to forcibly reduce the fuel injection amount of the active target cylinder from the stoichiometric equivalent amount (IB = 0 (%)) by a predetermined amount Δf2. In the illustrated example, the imbalance rate is reduced by about 10%. The reason why the amount of reduction is smaller than the amount of increase is that if too much weight reduction is performed on the lean deviation abnormal cylinder, a misfire will occur. However, the present invention does not exclude detecting a variation abnormality based on output fluctuation at that time by causing a misfire by reducing (or increasing) the fuel injection amount. At this time, since the slope of the characteristic line a is relatively gradual, the angular velocity difference Δω after the decrease is only slightly smaller than before the decrease, and the difference between the angular velocity differences Δω before and after the increase is small.

  On the other hand, as shown by the plot g, let us consider a case where a lean shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large negative value. In the illustrated example, a lean shift of about −20 (%) occurs in the imbalance rate. As indicated by an arrow h from this state, assuming that the fuel injection amount reduction control for forcibly reducing the fuel injection amount of the active target cylinder is performed by the same amount Δf2, the slope of the characteristic line a is relatively steep in this region. Therefore, the angular velocity difference Δω after the weight reduction is greatly changed to the minus side before the weight reduction, and the difference between the angular velocity differences Δω before and after the weight reduction becomes large. That is, the rotational fluctuation of the active target cylinder increases due to the decrease in the fuel injection amount.

  Therefore, it is possible to detect an abnormal variation in the air-fuel ratio between cylinders based on at least the angular velocity difference Δω of the active target cylinder after the reduction when the fuel injection amount of the active target cylinder is forcibly reduced by a predetermined amount.

  That is, if the angular velocity difference Δω after the reduction is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the reduction is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the weight reduction. Also in this case, the difference dΔω between them can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β2 (dΔω> β2), it can be determined that there is a variation abnormality and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β2 (dΔω ≦ β2), at least the active target cylinder can be determined to be normal.

  Here, since the increase amount is significantly larger than the decrease amount, the abnormality determination value β1 at the time of increase is made larger than the abnormality determination value β2 at the time of decrease. However, both abnormality determination values can be arbitrarily determined in consideration of the characteristics of the characteristic line a and the balance between the increase amount and the decrease amount. Both abnormality determination values can be set to the same value.

  It will be understood that the abnormality detection and the abnormal cylinder identification can be performed by the same method even when the rotation time difference ΔT is used as the index value of the rotation fluctuation of each cylinder, that is, the rotation fluctuation amount. Further, other values than those described above can be used as the index value of the rotational fluctuation of each cylinder.

  FIG. 6 shows the increase in the fuel injection amount for all eight cylinders and the change in rotational fluctuation before and after the increase. The upper row is before the increase, and the lower row is after the increase. As shown in the left end column in the left-right direction, as a method of increasing, all cylinders are increased uniformly and simultaneously by the same amount. That is, here, the predetermined target cylinders are all cylinders. Before the increase, a valve opening command is issued to inject the stoichiometric amount of fuel to the injectors 2 of all the cylinders, and after the increase, a predetermined amount of fuel is injected into the injectors 2 of all the cylinders by a predetermined amount more than the stoichiometric amount. A valve opening command is issued.

  In addition to the method of increasing all the cylinders at the same time, there is a method of increasing the number of cylinders in order and alternately in an arbitrary number of cylinders. For example, there is a method of increasing the amount by one cylinder, increasing the amount by two cylinders, or increasing the amount by four cylinders. The number of cylinders to be increased and the cylinder number can be arbitrarily set.

  As the number of target cylinders increases, there is a merit that the total increase time can be shortened, and there is a demerit that exhaust emission deteriorates. Conversely, the smaller the number of target cylinders, there is a merit that deterioration of exhaust emission can be suppressed, but there is a demerit that the total increase time becomes longer.

  Similar to FIG. 5, the angular velocity difference Δω is used as an index value of the rotation fluctuation of each cylinder.

  For example, in the normal state shown in the center column in the left-right direction, that is, when there is no air-fuel ratio deviation abnormality in any cylinder, the angular velocity difference Δω of all the cylinders is almost equal to 0 before the increase, There is little rotation fluctuation of the cylinder. Further, even after the increase, the angular velocity difference Δω of all the cylinders is almost equal and slightly increases in the minus direction, and the rotational fluctuations of all the cylinders do not increase that much. Therefore, the difference dΔω in the angular velocity difference before and after the increase is small.

  However, when the abnormality is shown in the right end column in the left-right direction, the behavior is different from that in the normal state. At the time of this abnormality, a rich shift abnormality corresponding to an imbalance rate of 50% occurs only in the # 8 cylinder, and only the # 8 cylinder is an abnormal cylinder. In this case, the angular velocity difference Δω of the remaining cylinders other than the # 8 cylinder is approximately equal to 0 before the increase, but the angular velocity difference Δω of the # 8 cylinder is slightly larger in the minus direction than the angular velocity difference Δω of the remaining cylinder.

  Nevertheless, there is not much difference between the angular velocity difference Δω of the # 8 cylinder and the angular velocity difference Δω of the remaining cylinders. Therefore, depending on the angular velocity difference Δω before the increase, abnormality detection and abnormal cylinder identification cannot be performed with sufficient accuracy.

  On the other hand, after the increase, the angular velocity difference Δω of the remaining cylinders is almost equal and slightly changes in the minus direction compared to before the increase, but the angular velocity difference Δω of the # 8 cylinder greatly changes in the minus direction. Therefore, the difference dΔω in angular velocity difference before and after the increase in the # 8 cylinder is significantly larger than that in the remaining cylinders. Therefore, using this difference, abnormality detection and abnormal cylinder identification can be performed with sufficient accuracy.

  In this case, only the difference dΔω between the # 8 cylinders becomes larger than the abnormality determination value β1, so that it is possible to detect that there is a rich shift abnormality in the # 8 cylinder.

  It will be understood that the same method can be adopted when the fuel injection amount is forcibly reduced to detect a lean deviation abnormality of any cylinder.

  As described above, in order to detect an abnormality in the air-fuel ratio variation between cylinders, as described above, the control for forcibly changing the fuel injection amount or changing the fuel injection amount, that is, the fuel injection amount change control is performed to change the rotational fluctuation amount. It is effective to increase. However, since execution of such fuel injection amount change control actively changes the fuel injection amount as described above, the number of executions is small from the viewpoint of exhaust emission, fuel consumption, drivability, etc. Is desired.

  Therefore, as will be described in detail below, when the fuel injection amount change control is executed in order to detect an abnormal variation in the air-fuel ratio between cylinders, it is limited here only when there is a possibility of an abnormal variation in the air-fuel ratio between cylinders. Is done. As a result, an abnormality in the variation in the air-fuel ratio between cylinders in the multi-cylinder internal combustion engine is suitably detected while refraining from executing the fuel injection amount change control for forcibly changing the fuel injection amount.

  Hereinafter, control for detecting an abnormality in variation in air-fuel ratio between cylinders in this embodiment, that is, air-fuel ratio diagnosis control in this embodiment will be described with reference to both flowcharts of FIGS.

  First, according to the flowchart shown in FIG. 7, the primary determination is executed by the part that functions as the primary determination execution means of the ECU 100. Here, the primary determination includes determining whether or not there is a possibility that there is an abnormality in the air-fuel ratio variation between cylinders, and further here, whether there is no abnormality in the air-fuel ratio variation between cylinders, that is, whether or not it is normal. In addition, it also includes a determination as to whether or not there is an abnormal variation in the air-fuel ratio between cylinders.

  When the engine 1 is started, it is determined in step S701 whether or not the engine is in a predetermined first operating state. The predetermined first operating state can be arbitrarily determined. For example, the predetermined first operating state is set to be an idle state, a steady running state, or a predetermined operating state after engine warm-up. Preferably, an operating state in which the output fluctuation of the engine 1 increases when there is an imbalance cylinder as described above is set as the predetermined first operating state. When the engine 1 is in the predetermined first operating state, the engine 1 is performing normal fuel injection control. For example, in the steady running state, the fuel of the reference injection amount, that is, the normal fuel injection amount is injected from each injector 2, and in addition, the air-fuel ratio feedback control is executed so that the exhaust air-fuel ratio follows the stoichiometry.

  If an affirmative determination is made in step S701, in step S703, data at that time, particularly data based on the output of the crank angle sensor 22 as the output detection means, is recorded for a predetermined period. Note that the predetermined period may be arbitrarily determined, and may be equal to or longer than a period in which only one combustion stroke is executed in each of at least all cylinders, for example, at least one cycle.

  In the next step S705, the rotation fluctuation amount is calculated as a value representing the output fluctuation of the engine 1, that is, the output fluctuation amount. In particular, the rotational fluctuation amount of each cylinder is calculated here as such an output fluctuation amount. Here, as described above, the angular velocity difference Δω is calculated as the rotational fluctuation amount of each cylinder.

  In step S707, it is determined whether or not the angular velocity difference Δω calculated in step S705 is equal to or smaller than a first predetermined value. This is executed for each calculated angular velocity difference Δω, and when at least one angular velocity difference Δω is equal to or smaller than the first predetermined value, an affirmative determination is made in step S707. The first predetermined value is determined according to a predetermined first operating state.

  If an affirmative determination is made in step S707 that the angular velocity difference Δω is less than or equal to the first predetermined value, it is determined in step S709 whether or not the angular velocity difference Δω is greater than or equal to a second predetermined value. The second predetermined value is smaller than the first predetermined value in step S707, that is, a value larger on the minus side. This determination is performed for each angular velocity difference Δω calculated in step S705 or only for the angular velocity difference Δω determined to be equal to or smaller than the first predetermined value in step S707, and at least one angular velocity difference Δω less than the second predetermined value is determined. If there is, a negative determination is made in step S709. The second predetermined value is determined according to a predetermined first operating state.

  Then, if an affirmative determination is made in step S709 that the angular velocity difference Δω is greater than or equal to the second predetermined value, this corresponds to the determination in step S711 that there is a possibility that the air-fuel ratio variation between cylinders may be abnormal. The possibility flag is turned ON, and the flow ends. Note that the possibility flag is OFF in the initial state. Thus, when an affirmative determination is made in both steps S707 and S709, the angular velocity difference Δω as the rotational fluctuation amount is in the predetermined first region.

  On the other hand, if a negative determination is made in step S707, the flow ends. This means that a normal determination is made that there is no abnormality in variation in the air-fuel ratio between cylinders. Note that the negative result in step S707 is when the angular velocity difference Δω as the rotational fluctuation amount is in the predetermined second region.

  If a negative determination is made in step S709, the abnormality flag is turned ON to correspond to the determination that there is an abnormality in the air-fuel ratio variation between cylinders in step S713, and the flow ends. Note that the abnormality flag is OFF in the initial state. As a result, in this embodiment, a warning lamp (not shown) is turned on, and the driver or the like is informed that there is a variation in the air-fuel ratio between cylinders. Note that the negative result in step S709 is when the angular velocity difference Δω as the rotational fluctuation amount is in the predetermined third region.

  As described above, it is determined whether or not there is a possibility of abnormality in the air-fuel ratio variation between the cylinders based on the rotation fluctuation amount as the output fluctuation of the engine 1 when the fuel injection amount change control is not performed. However, the predetermined third region is determined based on the experimental results obtained by examining experimentally the output fluctuation of the engine 1 that may occur when a sufficient amount of fuel is not injected from the injector 2 in any of the cylinders. be able to. Therefore, the predetermined third region is a region where the output fluctuation is large, and is a region where the output fluctuation amount (absolute value) is relatively larger than the predetermined first region and the predetermined second region. Further, the predetermined second region may be determined based on an experimental result obtained by examining an output fluctuation of the engine 1 that may occur when a desired amount of fuel is appropriately injected in all the cylinders. it can. Therefore, the predetermined second area is an area where the output fluctuation is small, and the output fluctuation amount (absolute value) is relatively smaller than the predetermined third area and the predetermined first area. A predetermined first area can be defined as an area between the predetermined second area and the predetermined third area. These three predetermined first, second, and third regions are continuous without overlapping each other, and the output fluctuation amount of the engine 1 calculated in step S705 is included in any one of these regions.

  By the way, if there is a possibility that the air-fuel ratio variation between cylinders is abnormal in step S711 in FIG. 7, if the possibility flag is turned ON, an affirmative determination is made in step S801 in FIG. In step S801, it is determined whether or not there is a possibility of abnormality in the air-fuel ratio variation between cylinders, and the determination is executed based on the possibility flag.

  If an affirmative determination is made in step S801, it is then determined in a next step S803 whether or not the vehicle is in a predetermined second operating state. The predetermined second operating state can be arbitrarily determined. The predetermined second operating state may be the same as or different from the predetermined first operating state. The predetermined second operating state is a predetermined operating state after the engine is started, and can be variously determined. Here, the load is within a predetermined range (for example, the intake air amount is within a predetermined intake air amount range (for example, 15 to 50 g / s)), and the engine rotation speed is within a predetermined engine rotation speed range (for example, 1500 rpm to 2000 rpm). The state satisfying both of the conditions is set as the predetermined second operation state.

  In such a predetermined second operation state, normally, air-fuel ratio feedback control is executed so that the exhaust air-fuel ratio follows the stoichiometric condition in order to perform exhaust gas purification with the catalytic converter 18 as described above. Has been. Therefore, in the present embodiment, the determination in step S803 corresponds to the determination as to whether or not the air-fuel ratio control is being performed so that the exhaust air-fuel ratio follows the predetermined target air-fuel ratio. The fuel ratio is stoichiometric. However, the predetermined target air-fuel ratio can be other than stoichiometric.

  If an affirmative determination is made in step S803, the routine proceeds to step S805, where fuel injection amount change control is executed for a predetermined period of time, and data associated therewith, in particular, data based on the output of the crank angle sensor 22 serving as output detection means is recorded. The As described above, the fuel injection amount change control can be executed according to various settings. In the present embodiment, the fuel injection amount change control is executed at the same time for all eight cylinders as shown in FIG. In the fuel injection amount change control here, before or after the fuel injection amount increase control is executed, the fuel injection amount decrease control is executed, and data for determining whether or not both the rich abnormality and the lean abnormality are present. To be acquired.

  Note that the target cylinders for which the fuel injection amount change control is executed in step S805 need not be all cylinders. For example, the target cylinder on which the fuel injection amount change control is executed is determined by the primary determination that the rotational fluctuation amount is in the predetermined first region (positive determination in step S707 and step S709), and only one or more cylinders Can be taken.

  In the next step S807, the rotation fluctuation amount is calculated as a value representing the engine output fluctuation. In particular, here, the rotation fluctuation amount of each cylinder of the target cylinder is calculated as a value representing the output fluctuation of the target cylinder on which the fuel injection amount change control is executed. Here, the angular velocity difference Δω is calculated as the rotational fluctuation amount of each cylinder.

  In step S809, it is determined whether the angular velocity difference Δω calculated in step S807 is less than a third predetermined value. This is executed for each calculated angular velocity difference Δω, and if at least one angular velocity difference Δω is less than the third predetermined value, an affirmative determination is made in step S809. The third predetermined value is determined according to a predetermined second operating state. This third predetermined value will be a value that is at least negatively greater than the first predetermined value.

  If a negative determination is made in step S809, the flow ends. This means that a normal determination is made that there is no abnormality in variation in the air-fuel ratio between cylinders. On the other hand, if an affirmative determination is made in step S809, the abnormality flag is turned ON to correspond to the determination that there is an abnormality in the air-fuel ratio variation between cylinders in step S811, and the flow ends. As a result, as described above, a warning lamp (not shown) is turned on, and the driver or the like is informed that there is a variation in the air-fuel ratio between cylinders.

  As described above, the primary determination is first performed based on the output fluctuation of the engine 1 when only the normal fuel injection control is executed without executing the fuel injection amount change control. The fuel injection amount change control is executed only when it is determined in the primary determination that there is a possibility that the air-fuel ratio variation between cylinders is abnormal. Then, the secondary determination (for detecting the abnormality) is performed based on the output fluctuation when the fuel injection amount change control is performed to determine whether there is an abnormality in the air-fuel ratio variation between cylinders. In the above embodiment, the fuel injection amount change control is not executed when it is determined that the primary determination is normal or abnormal. Therefore, it is possible to appropriately detect an abnormality in variation in the air-fuel ratio between cylinders while reducing the number of executions of the fuel injection amount change control.

  Here, after the engine 1 is started and before it is stopped, the detection control of the air-to-cylinder air ratio variation abnormality described according to FIGS. 7 and 8 is executed only once. However, this control may be executed at an appropriate time. For example, the control can be executed when the operating time of the engine 10 or the travel distance of the vehicle equipped with the engine 10 reaches a predetermined value.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, in the above embodiment, the angular velocity difference Δω is adopted as the rotation fluctuation amount, but various values including the above-described values such as the rotation time difference ΔT may be used as the rotation fluctuation amount. For example, the rotational fluctuation amount calculated in step S705 and the rotational fluctuation amount calculated in step S807 may be different types, for example, the rotational fluctuation amount calculated in any of these steps. May be a rotation time difference ΔT. The value calculated in step S705 and / or step S807 is not limited to the rotation fluctuation amount, and may be a value representing (reflecting) the output fluctuation of the engine. For example, an in-cylinder pressure sensor as in-cylinder pressure detection means It may be a value based on the in-cylinder pressure detected based on the output from. Alternatively, the value calculated in at least one of these steps may not be a value for each cylinder. For example, the difference between the maximum value and the minimum value of the engine rotation speed or the crankshaft rotation time T in one or a plurality of cycles may be calculated as a value representing engine output fluctuation. Note that the calculation of the value in step S705 is executed by the part serving as the first output fluctuation value calculation means of the ECU 100, and the calculation of the value in step S807 functions as the second output fluctuation value calculation means of the ECU 100. Although executed by the responsible portion, these output fluctuation value calculation means may be a single means.

  Further, the present invention can be applied to a multi-cylinder engine having two or more cylinders of various types, and not only a port injection type engine but also an in-cylinder injection type engine, an engine using gas as fuel, and the like. Can be applied.

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

1 Internal combustion engine
2 Injector 11 Air flow meter 12 Throttle valve 13 Spark plug 18 Upstream catalytic converter 20 Pre-catalyst sensor 22 Crank angle sensor 23 Accelerator opening sensor 100 Electronic control unit (ECU)

Claims (2)

Primary determination execution means for performing a primary determination based on an output fluctuation of the internal combustion engine, wherein the primary determination includes determining whether or not there is a possibility of an abnormality in the air-fuel ratio variation between cylinders; Primary determination execution means;
A fuel that executes fuel injection amount change control for forcibly changing the fuel injection amount of a predetermined target cylinder when the primary determination execution means determines that there is a possibility of an abnormal variation in the air-fuel ratio between cylinders. Injection amount change control means;
Is secondary determination execution means for performing a secondary determination based on output fluctuation of the internal combustion engine when the fuel injection amount change control is executed, and whether there is an abnormality in the air-fuel ratio variation between cylinders as the secondary determination? An apparatus for detecting an abnormality in the air-fuel ratio variation between cylinders of a multi-cylinder internal combustion engine, comprising: secondary determination execution means for determining whether or not. The primary determination execution means includes:
First output fluctuation value calculating means for calculating a value representing output fluctuation of the internal combustion engine;
When the value calculated by the first output fluctuation value calculating means is in the predetermined first area, it is determined that there is a possibility that the air-fuel ratio variation between cylinders is abnormal, and the calculated value overlaps with the predetermined first area. It is determined that there is no abnormality in the air-fuel ratio variation between cylinders when in the predetermined second region that does not become, and when the calculated value is in the predetermined third region that does not overlap the predetermined first region and the predetermined second region The inter-cylinder air-fuel ratio variation abnormality detection device for a multi-cylinder internal combustion engine according to claim 1, further comprising first determination means for determining that there is an air-fuel ratio variation abnormality.

Images