JP5541237B2 - Cylinder air-fuel ratio variation abnormality detecting device for multi-cylinder internal combustion engine - Google Patents

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

  When detecting an abnormal variation in the air-fuel ratio between cylinders, in addition to identifying the cylinder having the abnormality, in addition to performing control suitable for the abnormal air-fuel ratio variation between the cylinders, for example, an abnormal cylinder Therefore, it is desired to specify whether more fuel is injected than other normal cylinders or whether less fuel is injected, that is, the type of abnormality. However, for that purpose, referring to the description in Patent Document 1, after performing the detection process of the air-to-cylinder air ratio variation abnormality and the process for identifying the cylinder having the abnormality in a stepwise manner, It will be necessary to perform an abnormality type specific process not described in Patent Document 1. Since this requires a plurality of stepwise processes, there is room for improvement in terms of the transition time to control suitable for an abnormality in the air-fuel ratio variation between cylinders.

  Accordingly, the present invention was created in view of the above circumstances, and an object of the present invention is to quickly identify a cylinder having an abnormal air-fuel ratio in a multi-cylinder internal combustion engine, and to determine which side of the air-fuel ratio is that cylinder. It is to identify whether it is off.

  According to one aspect of the present invention, the fuel injection amount change control means for executing the fuel injection amount change control for forcibly changing the fuel injection amount of the predetermined target cylinder by a predetermined amount, and the output fluctuation relating to the predetermined target cylinder. A value deriving means for deriving a value representing the value, a value at the time of non-execution of the fuel injection amount change control derived by the value deriving means, and an execution time of the fuel injection amount change control derived by the value deriving means Provided is an air-fuel ratio variation abnormality detecting device for a cylinder of a multi-cylinder internal combustion engine, comprising a detecting means for detecting an abnormality in the air-fuel ratio related to the predetermined target cylinder and a type of the abnormality based on a comparison result with the value of Is done.

  Preferably, the value at the time of non-execution is a value representing an output fluctuation related to the predetermined target cylinder immediately before or after execution of the fuel injection amount change control.

  Preferably, the fuel injection amount change control means executes fuel injection amount increase control for forcibly changing the fuel injection amount of the predetermined target cylinder by a predetermined amount as the fuel injection amount change control, and the detection means Is the air-fuel ratio for the predetermined target cylinder when the execution value differs from the non-execution value by an amount exceeding the predetermined amount for rich abnormality determination in a direction in which the output fluctuation related to the predetermined target cylinder increases. It is determined that the abnormality is a rich abnormality, and on the other hand, the value at the time of execution leans so that the output fluctuation related to the predetermined target cylinder becomes smaller than the value at the time of non-execution. When the amount exceeds the predetermined amount for abnormality determination, the determination unit includes a determination unit that determines that the predetermined target cylinder has an abnormality in the air-fuel ratio and the abnormality is a lean abnormality. In this case, air-fuel ratio feedback control means for executing air-fuel ratio feedback control so as to cause the exhaust air-fuel ratio to follow a predetermined target air-fuel ratio is further provided, and the fuel injection amount change control means executes the air-fuel ratio feedback control. When the fuel injection amount is changed, the fuel injection amount increase control is executed as the fuel injection amount change control, and the determination unit of the detection means performs the predetermined value with respect to the non-execution value. When the output fluctuation related to the target cylinder is different by an amount exceeding the first predetermined amount in the direction in which the output fluctuation increases, the air / fuel ratio abnormality is related to the predetermined target cylinder, and the abnormality is the air / fuel ratio related to the predetermined target cylinder It is determined that there is an abnormality that deviates from the fuel ratio to the rich side, and in contrast thereto, the output value related to the predetermined target cylinder varies with respect to the non-execution value. When the amount exceeds the second predetermined amount in an increasing direction, there is an abnormality in the air / fuel ratio with respect to the predetermined target cylinder, and the abnormality is caused by the deviation of the air / fuel ratio with respect to the predetermined target cylinder from the predetermined target air / fuel ratio to the lean side. It is good to determine that it is abnormal.

  Alternatively, the fuel injection amount change control means performs fuel injection amount reduction control for forcibly changing the fuel injection amount of the predetermined target cylinder by a predetermined amount as the fuel injection amount change control, and the detection means When the value at the time of execution differs from the value at the time of non-execution by an amount exceeding the predetermined amount for rich abnormality determination in a direction in which the output fluctuation related to the predetermined target cylinder decreases, the air-fuel ratio of the predetermined target cylinder is It is determined that there is an abnormality and the abnormality is a rich abnormality, and on the other hand, the lean value is such that the output value related to the predetermined target cylinder increases with respect to the execution value with respect to the non-execution value. It is preferable to include a determination unit that determines that the abnormality is a lean abnormality when there is an abnormality in the air-fuel ratio with respect to the predetermined target cylinder when the amount exceeds the predetermined amount for determination. In this case, air-fuel ratio feedback control means for executing air-fuel ratio feedback control so as to cause the exhaust air-fuel ratio to follow a predetermined target air-fuel ratio is further provided, and the fuel injection amount change control means executes the air-fuel ratio feedback control. When the fuel injection amount change control is performed, the fuel injection amount decrease control is executed, and the determination unit of the detecting means performs the predetermined value with respect to the non-execution value. When the output variation related to the target cylinder is different by an amount exceeding the third predetermined amount, the air-fuel ratio abnormality is related to the predetermined target cylinder, and the abnormality is the air-fuel ratio related to the predetermined target cylinder It is determined that there is an abnormality that deviates from the fuel ratio to the rich side, and in contrast thereto, the output value related to the predetermined target cylinder varies with respect to the non-execution value. When the difference exceeds the fourth predetermined amount in the direction to become sharp, there is an abnormality in the air / fuel ratio for the predetermined target cylinder, and the abnormality is caused by the deviation of the air / fuel ratio for the predetermined target cylinder from the predetermined target air / fuel ratio to the lean side. It is good to determine that it is abnormal.

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 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 as an example for demonstrating the change of rotation fluctuation when increasing fuel injection quantity. It is a conceptual graph for demonstrating how the rotation fluctuation | variation changes by the increase in the amount of fuel injection. FIG. 7 is a diagram related to FIG. 6, and is a conceptual diagram showing a relationship between an imbalance rate of a predetermined target cylinder and a change in a value representing a rotational fluctuation accompanying an increase in the fuel injection amount in the cylinder. It is a flowchart in 1st Embodiment of this invention. It is a flowchart in 2nd Embodiment of this invention.

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

  FIG. 1 schematically shows an internal combustion engine according to the first 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 the 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.

  Such an 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 derives a value representing the output variation of the fuel injection amount change control means and a predetermined target cylinder. Each function of the value deriving means and the detecting means for detecting the abnormality of the air-fuel ratio related to the predetermined target cylinder and the type of the abnormality is substantially assumed.

  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. In the present embodiment, the portion that substantially functions as the value deriving unit of the ECU 100 calculates (derives) a value representing output fluctuation based on an output from the crank angle sensor 22 serving as an output detecting unit, that is, a signal. .

  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 may be referred to as a normal fuel injection amount herein.

  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 each composed of a three-way catalyst and 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 ratio. To do. 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, the fuel injection amount of the predetermined target cylinder is actively or forcibly increased, and when this change is made, that is, based on the rotational fluctuation of the predetermined target cylinder at least after the increase, Detect variation anomalies.

  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 signal 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, a change in rotational fluctuation when the fuel injection amount of a certain cylinder is actively increased, that is, forcibly increased 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 or forcibly increased, 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. Here, 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 right 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. Conversely, when moving from IB = 0 (%) to the left 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, for example, about 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, if the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by the same amount Δf1 is executed, 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 the variation in the air-fuel ratio between cylinders 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. For example, if the angular velocity difference Δω after the increase is smaller than a predetermined negative value α as shown in the figure (Δω <α), that is, if the rotational fluctuation amount exceeds a predetermined amount, it is determined that there is a variation abnormality, and The active target cylinder can be identified as an abnormal cylinder. Conversely, if the angular velocity difference Δω after the increase is not smaller than the value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  These can be expressed by the difference dΔω between the angular velocity differences Δω before and after the increase. If the angular velocity difference before the increase is Δω1 and the angular velocity difference after the increase is Δω2, the difference dΔω between them can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive value β1 (dΔω> β1), it is determined that there is a variation abnormality, and the active target cylinder can be identified as an abnormal cylinder. Conversely, if the difference dΔω does not exceed the value β1 (dΔω ≦ β1), at least the active target cylinder can be determined to be normal. As described above, when the active target cylinder has already caused a rich shift that causes a problem, if the fuel injection amount of the cylinder is changed by a predetermined amount, the rotational fluctuation after the increase becomes larger than the rotational fluctuation before the increase. The amount of change (absolute value) exceeds a predetermined amount (absolute value).

  On the other hand, when the forced increase of the fuel injection amount is similarly performed in a region where the imbalance rate is negative, the opposite is true. Although not shown, 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. Similarly, if the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder is executed from this state, the angular velocity difference Δω2 after the increase is smaller than the angular velocity difference Δω1 before the increase, and changes to the plus side. The difference in angular velocity difference Δω before and after the increase is increased. That is, the rotation fluctuation of the active target cylinder is reduced by increasing the fuel injection amount. Therefore, it is possible to detect the variation in the air-fuel ratio between cylinders 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. In short, if there is a lean shift that is already a problem in the active target cylinder, if the fuel injection amount of the cylinder is changed by a predetermined amount, the rotational fluctuation after the increase will be smaller than the rotational fluctuation before the increase. The amount of change (absolute value) exceeds a predetermined amount (absolute value).

  These relationships will be further described with reference to FIG. For example, consider a case where the state of the active target cylinder is on the line m, that is, a case where a relatively large lean shift has already occurred in the active target cylinder. Assume that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by a predetermined amount is executed from this state as indicated by an arrow m1. In this case, the angular velocity difference Δωm2 after the increase of the same cylinder changes in a direction in which the rotation variation becomes smaller than the angular velocity difference Δωm1 as the rotation variation of the active target cylinder before the increase, and the difference between the angular velocity differences before and after the increase increases. The magnitude of the difference dΔωm (Δωm1−Δωm2) exceeds a predetermined amount. Further, for example, consider a case where the state of the active target cylinder is on the line n, that is, a case where a relatively large rich shift has already occurred in the active target cylinder. Assume that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by a predetermined amount is executed from this state as indicated by an arrow n1. In this case, the angular speed difference Δωn2 as the rotational fluctuation amount after the increase of the same cylinder changes in the direction in which the rotational fluctuation becomes larger than the angular speed difference Δωn1 as the rotational fluctuation amount of the active target cylinder before the increase. The magnitude of the difference dΔωn (Δωn1−Δωn2) of these angular velocity differences exceeds a predetermined amount. In contrast, for example, consider a normal case where the active target cylinder is injecting a stoichiometric amount. Assume that the fuel injection amount increase control for forcibly increasing the fuel injection amount of the active target cylinder by a predetermined amount is executed from this state as indicated by an arrow p1. In this case, the change in the angular velocity difference as the rotational fluctuation amount before and after the increase is small. Therefore, based on the sign and magnitude of the difference between the rotational fluctuation amounts before and after the increase, whether or not an air-fuel ratio abnormality has occurred with respect to a predetermined target cylinder, and if there is such an abnormality, the abnormality is It is possible to identify the abnormality.

  This relationship is represented in FIG. In FIG. 7, the horizontal axis indicates the imbalance rate IB when the fuel injection amount increase control for a predetermined target cylinder is not executed, and the vertical axis indicates the difference dΔω in angular velocity difference as the difference in rotational fluctuation before and after the increase. However, here, the difference dΔω is a value obtained by subtracting the angular velocity difference Δω <b> 2 after the increase in the same cylinder, that is, when the increase is made, from the angular velocity difference Δω <b> 1 before the increase in the predetermined target cylinder. An angular velocity difference Δω1 before the increase of the predetermined target cylinder is obtained, and an angular velocity difference Δω2 after the increase (medium) of the predetermined target cylinder is obtained, and the difference dΔω (Δω1-Δω2) is obtained. When the difference dΔω is larger than the first predetermined value γ, there is an abnormality in the air / fuel ratio with respect to the predetermined target cylinder, and the abnormality is shifted to the rich side from the predetermined target air / fuel ratio. That is, for example, it can be understood that the fuel injection amount of the predetermined target cylinder is excessive. On the other hand, when the obtained difference dΔω is smaller than the second predetermined value δ, there is an abnormality in the air-fuel ratio with respect to the predetermined target cylinder, and the abnormality deviates from the predetermined target air-fuel ratio to the lean side That is, for example, it can be understood that the fuel injection amount of the predetermined target cylinder is too small. Note that the magnitude (absolute value) of the first predetermined value γ, that is, the first predetermined amount, and the magnitude (absolute value) of the second predetermined value δ, that is, the second predetermined amount may be the same or different. .

  Hereinafter, the control for detecting an abnormality in the air-fuel ratio variation between cylinders in the first embodiment, that is, the air-fuel ratio diagnosis control in the first embodiment according to the above inventive concept will be described with reference to the flowchart of FIG.

  First, when the engine 1 is started, the cylinder counter C is set to zero in step S801. In the next step S803, it is determined whether or not the vehicle is in a predetermined operating state. This determination is performed by the ECU 100 and is performed based on the engine rotation speed and the engine load detected as described above. For example, when the engine is in a predetermined operating state after the engine is started, an affirmative determination is made in step S803. Specifically, the engine coolant temperature is equal to or higher than a predetermined temperature (for example, 70 ° C.), the load is within a predetermined range (for example, the intake air amount is in a predetermined intake air amount range (for example, 15 to 50 g / s)). In the operation state that satisfies all the conditions that the engine rotation speed is in a predetermined engine rotation speed range (for example, 1500 rpm to 2000 rpm), an affirmative determination is made in step S803.

  In such an operating state, normally, air-fuel ratio feedback control is executed so that the exhaust air-fuel ratio follows the stoichiometric condition in order to more suitably perform exhaust purification by the catalytic converter 18 as described above. Therefore, the determination in step S803 corresponds to a determination as to whether or not air-fuel ratio feedback control is being performed so that the exhaust air-fuel ratio follows the predetermined target air-fuel ratio. In particular, the predetermined target air-fuel ratio is stoichiometric. is there. However, the predetermined target air-fuel ratio can be other than stoichiometric. In the present invention, the fact that such air-fuel ratio control is performed can be included in the condition for executing the abnormality detection of the inter-cylinder air-fuel ratio variation, but it may not be included.

  If an affirmative determination is made in step S803 because the engine 1 is in the predetermined operating state, one cylinder corresponding to the cylinder counter C is not executed in step S805 without executing the fuel injection amount change control including the fuel injection amount increase control. In particular, data based on the output signal of the crank angle sensor 22 serving as output detection means is recorded. When the cylinder counter C is zero, the corresponding cylinder is the # 1 cylinder. As the cylinder counter C increases by 1, the cylinders corresponding to the cylinder counter C change in the order of # 1, # 8, # 7, # 3, # 6, # 5, # 4, and # 2. The order of the cylinders may be other than this, and can be arbitrarily set.

  In the next step S807, the fuel injection amount increase control for increasing the fuel injection amount by a predetermined amount is executed for the cylinder corresponding to the cylinder counter C as a predetermined target cylinder, and the data, particularly the output associated therewith is executed. Data based on the output signal of the crank angle sensor 22 as detection means is recorded. Note that the amount of fuel increased by the fuel injection amount increase control is, for example, an amount equivalent to about 40 (%) in terms of an imbalance rate.

  Then, in the next step S809, the value representing the output fluctuation when the fuel injection amount increase control is not executed, that is, the output fluctuation amount, and the fuel injection amount increase control for the cylinder corresponding to the cylinder counter C, that is, the # 1 cylinder here. The output fluctuation amount at the time of execution is calculated. Here, the rotation fluctuation amount of the cylinder is calculated as such an output fluctuation amount. Here, as described above, the angular velocity difference Δω is calculated as the rotation fluctuation amount. However, the angular velocity difference Δω1 when the fuel injection amount increase control is not executed is calculated (derived) based on the data acquired at step S805, and the angular velocity difference Δω2 when the fuel injection amount increase control is executed is acquired at step S807. Is calculated (derived) based on the obtained data. In this embodiment, the angular velocity difference Δω1 of the predetermined target cylinder when the fuel injection amount increase control is not executed is a value immediately before the execution of the fuel injection amount increase control for the same cylinder. The value may be a value immediately after the execution of the amount increase control, that is, immediately after the influence of the fuel injection amount increase control is eliminated, or may be a value at any time when the fuel injection amount increase control of the same cylinder is not executed. . However, the operating state when step S805 and step S807 are executed is preferably substantially equal.

  In the next step S811, for the cylinder corresponding to the cylinder counter C, that is, the # 1 cylinder, the angular velocity difference Δω2 calculated in step S809 is subtracted from the angular velocity difference Δω2 calculated in step S809, thereby calculating the difference dΔω between these angular velocity differences. . In the following, the difference dΔω in the angular velocity difference for the # 1 cylinder is represented by the symbol dΔω1.

  In step S813, it is determined whether or not the difference dΔω1 related to the # 1 cylinder calculated in step S811 is equal to or smaller than a first predetermined value γ (see FIG. 7). If the difference dΔω1 exceeds the first predetermined value γ in step S813, a negative determination is made. In step S815, the # 1 cylinder has an air-fuel ratio abnormality, and the abnormality is a rich abnormality, that is, a predetermined target air-fuel ratio. The abnormality data of the # 1 cylinder is recorded so as to determine that the abnormality is shifted to the rich side.

  On the other hand, if the difference dΔω1 related to the # 1 cylinder is equal to or smaller than the first predetermined value γ in step S813, an affirmative determination is made. In step S817, the difference dΔω1 related to the cylinder corresponding to the cylinder counter C, here the # 1 cylinder, is determined. Is greater than or equal to a second predetermined value δ (see FIG. 7). If the difference dΔω1 relating to the # 1 cylinder is less than the second predetermined value δ in step S817, a negative determination is made, and in step S819, there is an air-fuel ratio abnormality in the # 1 cylinder, and the abnormality is a lean abnormality, that is, a predetermined value. The abnormality data of the # 1 cylinder is recorded so as to determine that the abnormality is shifted to the lean side from the target air-fuel ratio. As described above, the first predetermined value in step S813 (absolute value), that is, the first predetermined amount as the rich abnormality determination predetermined amount, and the second predetermined value in step S817 (absolute) Value), that is, the second predetermined amount as the predetermined amount for lean abnormality determination may be the same or different.

  On the other hand, if the difference dΔω1 related to the cylinder # 1 corresponding to the cylinder counter C is greater than or equal to the second predetermined value δ in step S817, if an affirmative determination is made, the cylinder # 1 is not determined to be abnormal. On the other hand (while it is determined that the # 1 cylinder is normal), the cylinder counter C is incremented by 1 in step S821. Note that the cylinder counter C is incremented by 1 in step S821 also after step S815 or S819. In step S823, it is determined whether the cylinder counter C is 8. This is because the engine 1 has eight cylinders.

  Note that, in steps S813 to S819, the determinations of steps S813 and S817 are executed by the part that functions as the determination unit of the detection means in the ECU 100.

  If the cylinder counter C is not 8 in step S823, the determination returns to step S803. Next, steps S803 to S819 are executed for the # 8 cylinder, which is the cylinder corresponding to the cylinder counter C (= 1). The

  Then, if the cylinder counter C is 8 in step S823, the flow ends when an affirmative determination is made.

  As described above, in each cylinder, based on the comparison result of the output fluctuation amount when the fuel injection amount increase control is not executed and the output fluctuation amount when the fuel injection amount increase control is executed, particularly based on the difference between them, In addition, it is possible to simultaneously determine whether or not there is an air-fuel ratio abnormality and what the abnormality is (what kind of abnormality is). Therefore, according to the present embodiment, it is possible to quickly identify an abnormal cylinder and to which side the air-fuel ratio in the cylinder is shifted.

  Here, after the engine 1 is started and before it is stopped, the detection control of the inter-cylinder air ratio variation abnormality described according to FIG. 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 1 or the travel distance of the vehicle on which the engine 1 is mounted becomes a predetermined value.

  When abnormality data is recorded for at least one of the cylinders, ECU 100 can be configured to perform control suitable for such abnormality in engine 1 based on the abnormality data. For example, when a rich abnormality is detected for the # 1 cylinder, the fuel injection amount of the # 1 cylinder can be controlled so as to reduce the fuel injection amount of the # 1 cylinder by a predetermined amount. Further, when abnormal data is recorded, an abnormality flag that is normally turned off may be turned on, and a warning lamp (not shown) that may be provided on the front panel of the driver's seat or the like may be turned on. As a result, it is possible to urge the driver or mechanic to maintain or repair the engine 1.

  In the above embodiment, the fuel injection amount increase control per cycle is applied to only one of the cylinders. However, for example, fuel injection amount increase control may be applied to any two, three, four, or eight cylinders per cycle at the same time. As a result, it is possible to shorten the time for detecting an abnormality in the air-fuel ratio variation between cylinders.

  Further, for example, in the above-described 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. The value calculated in step S809 is not limited to the rotational fluctuation amount, and may be a value representing (reflecting) the output fluctuation of the engine. For example, the output signal from the in-cylinder pressure sensor serving as the in-cylinder pressure detecting means It may be a value based on the in-cylinder pressure detected based on it. In this case, data based on the output signal from the in-cylinder pressure sensor is recorded in steps S805 and S807.

  In the above embodiment, the difference dΔω is calculated by subtracting the angular velocity difference Δω2 from the angular velocity difference Δω1 in step S811. However, the difference dΔω may be calculated by subtracting the angular velocity difference Δω1 from the angular velocity difference Δω2. In this case, the sign of the difference dΔω is reversed. For example, in step S813, it can be determined whether the difference dΔω is equal to or greater than a first predetermined value, and in step S817, it can be determined whether the difference dΔω is equal to or smaller than a second predetermined value. .

  By the way, in the said embodiment, the fuel injection amount increase control which changes the fuel injection amount of a predetermined | prescribed object cylinder by a predetermined amount increase was performed as fuel injection amount change control. However, as the fuel injection amount change control, fuel injection amount reduction control for changing the fuel injection amount of a predetermined target cylinder by a predetermined amount may be executed. However, in this case, the fuel amount to be reduced will be smaller than the fuel amount to be increased in the above embodiment. This is because if the lean deviation has already occurred in the predetermined target cylinder and the fuel injection amount is greatly reduced in the cylinder, the possibility of misfire increases in the cylinder. However, the present invention does not exclude the case where a misfire occurs in a predetermined target cylinder when the fuel injection amount is reduced.

  Here, a second embodiment will be described in which, unlike the first embodiment, the fuel injection amount of a predetermined target cylinder is changed by a predetermined amount in order to detect an abnormality in variation in air-fuel ratio between cylinders. However, when the fuel injection amount reduction control for changing the fuel injection amount of the predetermined target cylinder by a predetermined amount is not executed, the output fluctuation amount (for example, the rotation fluctuation amount) is executed, and the fuel injection amount reduction control is executed for the cylinder. Since the interrelationship between the output fluctuation amount at this time, the difference between the output fluctuation amounts, and the imbalance rate or air-fuel ratio of the predetermined target cylinder is clear from the above description based on FIGS. These descriptions are omitted. However, the various modifications described with respect to the first embodiment can be applied to the second embodiment.

  Hereinafter, control for detecting an abnormality in variation in air-fuel ratio between cylinders in the second embodiment will be described based on the flowchart of FIG. However, Steps S901 to S905, S909 to S911, S915, and S919 to S923 substantially correspond to Steps S801 to S805, S809 to S811, S815, and S819 to S823, respectively. Omitted except.

  When the non-execution data of the fuel injection amount reduction control is recorded in step S905, the cylinder corresponding to the cylinder counter C is set as a predetermined target cylinder in the next step S907, and the fuel injection amount is reduced by a predetermined amount. The fuel injection amount reduction control is executed, and data accompanying this, particularly data based on the output signal of the crank angle sensor 22 is recorded. Note that the amount of fuel reduced by the fuel injection amount reduction control is, for example, an amount equivalent to about 10 (%) in terms of an imbalance rate.

  In step S909, the angular velocity difference Δω1 when the fuel injection amount reduction control is not executed and the angular velocity difference Δω2 when the fuel injection amount reduction control is executed are calculated for the cylinder corresponding to the cylinder counter C. In the next step S911, with respect to the cylinder corresponding to the cylinder counter C, the angular velocity difference Δω2 is subtracted from the angular velocity difference Δω1, thereby calculating the difference dΔω of these angular velocity differences.

  However, if a considerable degree of rich deviation has already occurred in a predetermined target cylinder that is a cylinder corresponding to the cylinder counter C, the angular velocity difference is subject to rotational fluctuation due to execution of the fuel injection amount reduction control in the predetermined target cylinder. The difference dΔω becomes a negative value. On the other hand, when a considerable lean deviation has already occurred in a predetermined target cylinder that is a cylinder corresponding to the cylinder counter C, the angular velocity difference is rotationally fluctuated by executing the fuel injection amount reduction control in the predetermined target cylinder. Changes in an increasing direction, and the difference dΔω becomes a positive value.

  In step S913, it is determined whether or not the difference dΔω relating to the cylinder corresponding to the cylinder counter C calculated in step S911 is equal to or greater than a third predetermined value. If the determination in step S913 is negative because the difference dΔω is less than the third predetermined value, in step S915, the cylinder has an air-fuel ratio abnormality, and the abnormality is a rich abnormality, that is, a rich side from a predetermined target air-fuel ratio. The abnormality data of the cylinder is recorded so as to determine that the abnormality is deviated.

  In contrast, if the difference dΔω related to the cylinder corresponding to the cylinder counter C is greater than or equal to the third predetermined value in step S913, an affirmative determination is made. In step S917, the difference dΔω related to the cylinder corresponding to the cylinder counter C is the fourth predetermined value. It is determined whether it is less than or equal to the value. It should be noted that the magnitude (absolute value) of the third predetermined value in step S913, that is, the third predetermined quantity as the predetermined quantity for rich abnormality determination, and the magnitude (absolute value) of the fourth predetermined value in step S917, that is, the lean abnormality. The fourth predetermined amount as the predetermined amount for determination may be the same or different. If a negative determination is made in step S917 because the difference dΔω regarding the cylinder exceeds the fourth predetermined value, in step S919, the cylinder has an air-fuel ratio abnormality, and the abnormality is a lean abnormality, that is, a predetermined target sky. The abnormality data of the cylinder is recorded so as to determine that the abnormality is deviating from the fuel ratio to the lean side.

  As described above, according to the second embodiment, the output fluctuation related to the predetermined target cylinder varies with respect to the value when the fuel injection amount reduction control for reducing the fuel injection amount of the predetermined target cylinder is not executed. When the amount exceeds the third predetermined amount in the direction of decreasing, there is an abnormality in the air-fuel ratio with respect to the predetermined target cylinder, and the abnormality is an abnormality in which the air-fuel ratio with respect to the predetermined target cylinder deviates from the predetermined target air-fuel ratio to the rich side It is determined that On the other hand, when the fuel injection amount reduction control execution value differs from the non-execution value by an amount exceeding the fourth predetermined amount in a direction in which the output fluctuation related to the predetermined target cylinder increases, the predetermined target cylinder It is determined that there is an abnormality in the air-fuel ratio, and the abnormality is an abnormality in which the air-fuel ratio related to the predetermined target cylinder deviates from the predetermined target air-fuel ratio to the lean side.

  In the above two embodiments, when the air-fuel ratio feedback control is being performed, the control (including the fuel injection amount change control) for detecting the abnormal variation in the air-fuel ratio between the cylinders is executed as described above. However, the present invention may be applied in a predetermined operating state other than when air-fuel ratio feedback control is being executed, or may be applied to an internal combustion engine that does not perform air-fuel ratio feedback control. Specifically, the present invention may be applied when fuel injection control that is open loop control is being executed. For example, when fuel injection control is executed (or predetermined operation) in which a fuel amount is determined based on a predetermined air-fuel ratio and intake air amount set in advance, and this predetermined amount of fuel is simply injected from an injector. In the state), the control for detecting the abnormality in variation in the air-fuel ratio between the cylinders as described above in the present invention may be executed. In this case, the reference of the rich abnormality or the lean abnormality described above may be such a predetermined air-fuel ratio.

  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.

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 (5)

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;
Value deriving means for deriving a value representing an output fluctuation with respect to the predetermined target cylinder;
Based on the comparison result between the non-execution value of the fuel injection amount change control derived by the value derivation unit and the execution time value of the fuel injection amount change control derived by the value derivation unit, Detecting means for detecting an abnormality in the air-fuel ratio related to a predetermined target cylinder and the type of the abnormality ,
The fuel injection amount change control means executes fuel injection amount increase control for forcibly changing the fuel injection amount of the predetermined target cylinder by a predetermined amount as the fuel injection amount change control,
When the value at the time of execution differs from the value at the time of non-execution by an amount exceeding a predetermined amount for rich abnormality determination in a direction in which output fluctuation related to the predetermined target cylinder increases, the predetermined target cylinder It is determined that there is an abnormality in the air-fuel ratio and the abnormality is a rich abnormality. On the other hand, the value at the time of execution is smaller in output fluctuation with respect to the predetermined target cylinder than the value at the time of non-execution. Including a determination unit that determines that the abnormality is a lean abnormality when the direction is different from the predetermined amount for lean abnormality determination by an abnormality in the air-fuel ratio with respect to the predetermined target cylinder.
A cylinder-to-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine.   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;
  Value deriving means for deriving a value representing an output fluctuation with respect to the predetermined target cylinder;
  Based on the comparison result between the non-execution value of the fuel injection amount change control derived by the value derivation unit and the execution time value of the fuel injection amount change control derived by the value derivation unit, Detecting means for detecting an abnormality of the air-fuel ratio related to a predetermined target cylinder and the type of the abnormality;
With
  The fuel injection amount change control means executes fuel injection amount reduction control for forcibly changing the fuel injection amount of the predetermined target cylinder by a predetermined amount as the fuel injection amount change control,
  When the value at the time of execution differs from the value at the time of non-execution by an amount exceeding a predetermined amount for rich abnormality determination in a direction in which output fluctuation related to the predetermined target cylinder becomes smaller, the predetermined target cylinder It is determined that there is an abnormality in the air-fuel ratio and the abnormality is a rich abnormality. Including a determination unit that determines that the abnormality is a lean abnormality when the direction is different from the predetermined amount for lean abnormality determination by an abnormality in the air-fuel ratio with respect to the predetermined target cylinder.
A cylinder-to-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine. Air-fuel ratio feedback control means for executing air-fuel ratio feedback control so as to cause the exhaust air-fuel ratio to follow a predetermined target air-fuel ratio;
The fuel injection amount change control means executes the fuel injection amount increase control as the fuel injection amount change control when the air-fuel ratio feedback control is being executed,
The determination unit of the detection means, when the value at the time of execution differs from the value at the time of non-execution by an amount exceeding a first predetermined amount in a direction in which output fluctuation related to the predetermined target cylinder increases. It is determined that there is an abnormality in the air-fuel ratio with respect to the target cylinder, and the abnormality is an abnormality in which the air-fuel ratio with respect to the predetermined target cylinder is shifted to the rich side from the predetermined target air-fuel ratio. Is different from the non-execution value by an amount exceeding the second predetermined amount in a direction in which the output fluctuation related to the predetermined target cylinder becomes smaller, the air / fuel ratio abnormality is related to the predetermined target cylinder. it is determined to be abnormal air-fuel ratio about the predetermined target cylinder is shifted to the lean side from the predetermined target air-fuel ratio, the air-fuel ratio variation abnormality detection device among the cylinders of multi-cylinder internal combustion engine according to claim 1. Air-fuel ratio feedback control means for executing air-fuel ratio feedback control so as to cause the exhaust air-fuel ratio to follow a predetermined target air-fuel ratio;
The fuel injection amount change control means executes the fuel injection amount decrease control as the fuel injection amount change control when the air-fuel ratio feedback control is being executed,
The determination unit of the detection means determines the predetermined value when the value at the time of execution differs from the value at the time of non-execution by an amount exceeding a third predetermined amount in a direction in which an output fluctuation related to the predetermined target cylinder decreases. It is determined that there is an abnormality in the air-fuel ratio with respect to the target cylinder, and the abnormality is an abnormality in which the air-fuel ratio with respect to the predetermined target cylinder is shifted to the rich side from the predetermined target air-fuel ratio. Is different from the non-executed value by an amount exceeding the fourth predetermined amount in a direction in which the output fluctuation related to the predetermined target cylinder increases, the air / fuel ratio abnormality is related to the predetermined target cylinder. 3. The inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine according to claim 2 , wherein the air-fuel ratio relating to the predetermined target cylinder is determined to be abnormal in which the air-fuel ratio is shifted to the lean side from the predetermined target air-fuel ratio.   The multi-cylinder according to any one of claims 1 to 4, wherein the non-execution value is a value representing an output fluctuation related to the predetermined target cylinder immediately before or after execution of the fuel injection amount change control. An inter-cylinder air-fuel ratio variation abnormality detection device for an internal combustion engine.

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