JP4936140B2 - Abnormality diagnosis device for internal combustion engine - Google Patents

Description

  The present invention relates to an abnormality diagnosis device for an internal combustion engine.

  2. Description of the Related Art In recent years, in an internal combustion engine mounted on a vehicle or the like, an intake valve variable that continuously variably controls the operation angle (crank angle from opening to closing) of each cylinder according to the load of the internal combustion engine, etc. Some are equipped with a control device. In such an internal combustion engine, the amount of air taken into the combustion chamber can be changed over the entire operating range by changing the operating angle of the intake valve. Therefore, the throttle opening can be opened or omitted more than usual, thereby reducing the pumping loss, the same output can be obtained with a smaller amount of air and fuel, and fuel efficiency can be improved.

  On the other hand, in an internal combustion engine mounted on a vehicle or the like, the air-fuel ratio (cylinder-by-cylinder) of each cylinder is estimated based on the output of an air-fuel ratio sensor installed in an exhaust collection portion where the exhaust gas of each cylinder collects. There is. In an internal combustion engine that can execute the intake valve operating angle control and the cylinder-by-cylinder air-fuel ratio estimation at the same time, even if it can detect that the air-fuel ratio of a certain cylinder is abnormal, it is common to identify the cause or the abnormal part. It is difficult to. The reason is that the air-fuel ratio abnormality can be mainly caused by both the fuel system abnormality (injector abnormality, etc.) and the air system abnormality (intake valve variable control apparatus abnormality, etc.).

  In the apparatus described in Patent Document 1, the air-fuel ratio of each cylinder is estimated, and whether there is an abnormality in the variable valve lift device is diagnosed based on the estimated air-fuel ratio value of each cylinder and the control state of the variable valve lift device. ing. By evaluating the air-fuel ratio estimated value of each cylinder and the control state of the variable valve lift device, the abnormality of the variable valve lift device can be diagnosed separately from other fuel system abnormalities.

Japanese Patent Laid-Open No. 2005-214073

  However, the apparatus described in Patent Document 1 can diagnose the abnormality of the variable valve lift device based on the estimated air-fuel ratio value of each cylinder, but cannot diagnose the abnormality of the fuel system. Further, it is impossible to make a distinction between a fuel system abnormality and an air system abnormality.

  Accordingly, an object of the present invention is to enable diagnosis of an abnormality in the fuel system based on the estimated air-fuel ratio value of each cylinder, and another object of the present invention is based on the estimated air-fuel ratio value of each cylinder. Thus, it is possible to make a diagnosis by distinguishing between a fuel system abnormality and an air system abnormality.

According to an aspect of the present invention, in the internal combustion engine abnormality diagnosis device including the intake valve variable control device that variably controls the operating angle of the intake valve of each cylinder according to the load of the internal combustion engine,
Cylinder-specific air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder;
When the load of the internal combustion engine is larger than a predetermined value, the abnormality of the fuel system of each cylinder is determined based on the amount of deviation from the predetermined reference value of the air-fuel ratio estimated value of each cylinder obtained by the cylinder-by-cylinder air-fuel ratio estimating means. An abnormality diagnosing device for an internal combustion engine is provided.

  According to this, abnormality of the fuel system of each cylinder can be diagnosed based on the deviation amount from the predetermined reference value of the air-fuel ratio estimated value of each cylinder, particularly the air-fuel ratio estimated value of each cylinder. When the load of the internal combustion engine is greater than a predetermined value, preferably when the load is high, the absolute amount of the intake air amount increases, so that the influence of an abnormality in the air system on the intake air amount is reduced. Therefore, paying attention to this point, when the load of the internal combustion engine is larger than a predetermined value, the presence or absence of abnormality in the fuel system of each cylinder is diagnosed. As a result, the influence of the air system abnormality can be eliminated, and the fuel system abnormality can be distinguished from the air system abnormality and reliably diagnosed.

  Preferably, the abnormality diagnosing means diagnoses the presence or absence of an abnormality in the fuel system of each cylinder based on a difference or ratio between the air-fuel ratio estimated value and the reference value. The difference or ratio is suitable as an index value representing the amount of deviation from the reference value of the estimated air-fuel ratio value of each cylinder.

  Preferably, the abnormality diagnosis means diagnoses whether there is an abnormality in the fuel system of each cylinder when the load of the internal combustion engine is greater than a predetermined value and the operating angle is greater than a predetermined value. By adding the condition that the operating angle is larger than the predetermined value, it is possible to further ensure the condition that the influence of the air system abnormality is reduced.

  Preferably, the abnormality diagnosis device includes a correction unit that corrects the fuel injection amount so that the air-fuel ratio estimated value approaches the reference value for a cylinder whose fuel system is not diagnosed as normal by the abnormality diagnosis unit, The abnormality diagnosing means, after diagnosing that the fuel system of all cylinders is normal or after being corrected by the correcting means, when the load of the internal combustion engine is smaller than a predetermined value, the reference of the air-fuel ratio estimated value The presence or absence of an abnormality in the air system of each cylinder is diagnosed based on the amount of deviation from the value.

  According to this, after eliminating the influence of the fuel system abnormality, the air system abnormality is diagnosed under a condition where the influence of the air system abnormality is large, and the air system abnormality is distinguished from the fuel system abnormality and reliably diagnosed. it can. In this way, it is possible to make a diagnosis by distinguishing between a fuel system abnormality and an air system abnormality based on the estimated air-fuel ratio of each cylinder.

  Preferably, the abnormality diagnosing means diagnoses the presence or absence of an abnormality in the air system of each cylinder based on a difference or ratio between the air-fuel ratio estimated value and the reference value.

  Preferably, the abnormality diagnosis means diagnoses whether there is an abnormality in the air system of each cylinder when the load of the internal combustion engine is smaller than a predetermined value and the working angle is smaller than the predetermined value. By adding a condition that the operating angle is smaller than a predetermined value, it is possible to further ensure the condition that the influence of the air system abnormality becomes large.

  Preferably, the intake valve variable control device corrects and controls a working angle for a predetermined time so that the air-fuel ratio estimated value approaches the reference value for a cylinder whose air system is not diagnosed as normal by the abnormality diagnosis unit, The abnormality diagnosing means diagnoses that the intake valve variable control apparatus is abnormal when the estimated air-fuel ratio does not approach the reference value within a predetermined value after the correction control.

  Preferably, for the cylinder, when the estimated air-fuel ratio approaches the reference value within a predetermined value after the correction control, the intake valve variable control device maintains the correction state of the working angle.

  According to the present invention, a fuel system abnormality can be diagnosed based on the estimated air-fuel ratio value of each cylinder, and a fuel system abnormality and an air system abnormality can be determined based on the estimated air-fuel ratio value of each cylinder. An excellent effect that both can be diagnosed can be demonstrated.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, an in-cylinder spark ignition internal combustion engine (gasoline engine) 11 is mounted on the vehicle as an internal combustion engine. The engine 11 has a plurality of cylinders 12 in which pistons 13 are accommodated so as to be able to reciprocate. Each piston 13 is connected to a crankshaft 16 that is an output shaft of the engine 11 via a connecting rod 15. The reciprocating motion of each piston 13 is converted into a rotational motion by the connecting rod 15 and then transmitted to the crankshaft 16.

  An intake passage 22 having a throttle valve 18, a surge tank 19, an intake manifold 21, etc. is connected to the combustion chamber 17 for each cylinder 12. Air outside the engine 11 passes through each part of the intake passage 22 and is taken into the combustion chamber 17. The throttle valve 18 is rotatably provided in the intake passage 22 and is drivingly connected to an actuator 23 made of an electric motor or the like. The actuator 23 operates in response to a depression operation of the accelerator pedal 24 by the driver, and rotates the throttle valve 18. The amount of air flowing through the intake passage 22 (intake air amount) varies according to the rotation angle (throttle opening) of the throttle valve 18.

  Further, an exhaust passage 26 having an exhaust manifold 25, a catalyst 60, and the like is connected to the combustion chamber 17. Exhaust gas generated in the combustion chamber 17 passes through each part of the exhaust passage 26 and is discharged to the outside of the engine 11. Note that another catalyst is also provided on the downstream side of the illustrated catalyst 60.

  The engine 11 is provided with an intake valve 27 for opening and closing a connection portion of the intake passage 22 with the combustion chamber 17 and an exhaust valve 28 for opening and closing a connection portion of the exhaust passage 26 with the combustion chamber 17 for each cylinder 12. Yes. These intake / exhaust valves 27, 28 are always in a direction (valve closing direction, substantially upward in FIG. 1) in which communication between the intake / exhaust passages 22, 26 and the combustion chamber 17 is blocked by a valve spring (not shown). It is energized. An intake camshaft 31 having an intake cam 31A is provided substantially above the intake valve 27, and an exhaust camshaft 32 having an exhaust cam 32A is provided substantially above the exhaust valve 28. These intake / exhaust camshafts 31 and 32 rotate when the rotation of the crankshaft 16 is transmitted. With this rotation, the intake / exhaust camshafts 31, 32 push down the intake / exhaust valves 27, 28 against the valve spring. By this depression, the intake / exhaust passages 22 and 26 are in communication with the combustion chamber 17 (opened state). In this manner, the intake / exhaust valves 27, 28 are periodically opened and closed as the intake / exhaust camshafts 31, 32 rotate.

  An electromagnetic injector (fuel injection valve) 33 is attached to the engine 11 for each cylinder 12. Each injector 33 is controlled to open and close, thereby directly injecting and supplying high-pressure fuel to the corresponding combustion chamber 17. The fuel injected from the injector 33 is mixed with the air in the combustion chamber 17 and becomes an air-fuel mixture.

  A spark plug 34 is attached to the engine 11 for each cylinder 12. Each spark plug 34 operates based on an ignition signal from the igniter 35. A high voltage output from the ignition coil 36 is applied to the spark plug 34. The air-fuel mixture is ignited by the spark discharge of the spark plug 34 and burned. The piston 13 is reciprocated by the high-temperature and high-pressure combustion gas generated at this time, the crankshaft 16 is rotated, and the driving force (output torque) of the engine 11 is obtained.

  This driving force is adjusted according to the depression operation of the accelerator pedal 24 by the driver. That is, according to the depression operation of the accelerator pedal 24, the throttle valve 18 is driven by the actuator 23 to adjust the throttle opening, and the intake air amount into the combustion chamber 17 changes. In response to this change, the amount of fuel injected from the injector 33 is controlled, and the amount of air-fuel mixture charged in the combustion chamber 17 changes to adjust the output of the engine 11.

  By the way, the engine 11 has a series of four strokes (cycles) of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the crankshaft 16 rotates twice (720 ° CA rotation) and the piston 13 reciprocates twice. This is a so-called four-cycle engine. The intake stroke and the expansion stroke are performed when the piston 13 is lowered, and the compression stroke and the exhaust stroke are performed when the piston 13 is raised. By these strokes, the state in each cylinder 12 changes roughly as follows.

  In the intake stroke, the exhaust valve 28 is closed and the intake valve 27 is opened, and air is sucked into the combustion chamber 17 due to a decrease in pressure in the combustion chamber 17 as the piston 13 descends. In the compression stroke, the intake valve 27 is closed in addition to the exhaust valve 28. For this reason, the pressure in the combustion chamber 17 increases as the piston 13 rises. In the expansion stroke, ignition is performed by the spark plug 34 in a state where both the intake and exhaust valves 27 and 28 are closed, and the air-fuel mixture of the intake air and the fuel injected from the injector 33 is ignited and burned. The downward force accompanying the combustion pushes down the piston 13, and a rotational force is applied to the crankshaft 16 through the connecting rod 15. In the exhaust stroke, the exhaust valve 28 is opened. For this reason, the exhaust gas generated in the combustion chamber 17 is discharged to the exhaust passage 26 as the piston 13 rises.

  The engine 11 is provided with a variable valve timing mechanism 41 and a variable operating angle mechanism 42 as variable valve mechanisms that change the valve characteristics of the intake valve 27. The variable valve timing mechanism 41 changes the relative rotation phase of the intake camshaft 31 with respect to the crankshaft 16 to thereby change the operating angle of the intake valve 27 (from opening to closing as indicated by a solid line and a two-dot chain line in FIG. 2). This is a mechanism for advancing or retarding both the valve opening timing and the valve closing timing of the intake valve 27 in a state where the valve opening period is kept constant.

  Further, the working angle varying mechanism 42 is a mechanism that continuously varies the working angle of the intake valve 27 as shown in FIG. In the present embodiment, the maximum lift amount of the intake valve 27 is also continuously changed by the operating angle variable mechanism 42. The operating angle and the maximum lift amount are changed in synchronization with each other by the operating angle variable mechanism 42, and the maximum lift amount decreases as the operating angle decreases, and the maximum lift amount increases as the operating angle increases.

  As the working angle variable mechanism 42, for example, as shown in FIG. 1, an intermediate drive mechanism 43 provided for each cylinder 12 and a control shaft 44 and an actuator 46 common to the intermediate drive mechanisms 43 of all cylinders are provided. (See JP 2001-263015 A). The actuator 46 includes, for example, an electric motor and a power transmission mechanism that converts the rotation of the electric motor into a linear motion and transmits the linear motion to the control shaft 44. And if an electric motor rotates by electricity supply, a power transmission mechanism will act | operate in connection with it and the control shaft 44 will be displaced to an axial direction.

  Each intermediate drive mechanism 43 is provided between the intake camshaft 31 and the intake valve 27 and includes an input arm 47 and an output arm 48. A power transmission slider 49 is interposed between the control shaft 44 and the input / output arms 47 and 48 so as to be rotatable and movable in the axial direction. The slider 49 and the input / output arms 47 and 48 are meshed with each other by a helical spline.

  When the intake camshaft 31 rotates, the input cam 47 swings up and down around the control shaft 44 by the intake cam 31A. This swing is transmitted to the output arm 48 via the slider 49, and the output arm 48 swings up and down. The swinging output arm 48 drives the intake valve 27 to open and close.

  Further, when the control shaft 44 is moved in the axial direction by the actuator 46, the slider 49 rotates while being displaced in the same direction, and the input arm 47 and the output arm 48 in the swinging direction of the input / output arms 47, 48. And the relative phase difference is changed. With this change, the valve characteristics (working angle and maximum lift amount) of each intake valve 27 change continuously and uniformly. When the relative phase difference is small, both the operating angle and the maximum lift amount are small, and the intake air amount per cylinder 12 is small. As the relative phase difference increases, both the operating angle and the maximum lift amount increase and the intake air amount increases.

  Further, various sensors for detecting the state of each part are attached to the vehicle. As these sensors, for example, a crank angle sensor 51, a rotation angle sensor 52, an air flow meter 53, a throttle opening sensor 54, an accelerator opening sensor 55, and the like are used.

  The crank angle sensor 51 generates a pulse signal every time the crankshaft 16 rotates by a certain angle. This signal is used for calculation of a crank angle that is a rotation angle of the crankshaft 16 and an engine rotation speed that is a rotation speed of the crankshaft 16 per unit time. The rotation angle sensor 52 detects the rotation angle of the electric motor in the actuator 46 in order to detect the valve characteristics (working angle and maximum lift amount) of the intake valve 27. The air flow meter 53 detects the amount of air flowing through the intake passage 22 (intake air amount), the throttle opening sensor 54 detects the throttle opening, and the accelerator opening sensor 55 depresses the accelerator pedal 24 by the driver. The amount, that is, the accelerator opening is detected.

An air-fuel ratio sensor for detecting the exhaust air-fuel ratio based on the oxygen concentration in the exhaust, that is, a pre-catalyst air-fuel ratio sensor 61 and a post-catalyst air-fuel ratio sensor 62 are attached to the upstream side and downstream side of the catalyst 60, respectively. The pre-catalyst air-fuel ratio sensor 61 is attached to an exhaust collecting portion after the exhaust manifolds 25 of the cylinders of the engine 11 are gathered. The pre-catalyst air-fuel ratio sensor 61 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide range, and outputs a signal having a value proportional to the exhaust air-fuel ratio. On the other hand, the post-catalyst air-fuel ratio sensor 62 is a so-called O ₂ sensor, and has a characteristic that the output value changes abruptly at the stoichiometric air-fuel ratio (stoichiometric, for example, A / F = 14.6).

  The vehicle is provided with an electronic control unit (hereinafter referred to as ECU) 100 that controls each part such as the engine 11 based on the various signals. The ECU 100 is configured around a microcomputer, and a central processing unit (CPU) performs arithmetic processing according to a control program, initial data, a control map, and the like stored in a read-only memory (ROM). Various controls are executed based on this. The calculation result by the CPU is temporarily stored in a random access memory (RAM). Examples of the control performed by the ECU 100 include fuel injection control of the engine 11, ignition timing control, throttle opening control, working angle control of the intake valve 27, and the like.

  The catalyst 60 purifies NOx, HC and CO simultaneously with high efficiency when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 60 is close to the stoichiometric air-fuel ratio. Accordingly, in response to this, the ECU 100 controls the air-fuel ratio or the fuel injection amount of the air-fuel mixture so that the air-fuel ratio of the exhaust gas flowing into the catalyst 60 matches the stoichiometric air-fuel ratio. Specifically, the ECU 100 determines the basic injection amount so that the air-fuel ratio of the air-fuel mixture becomes a predetermined air-fuel ratio target value (specifically, the stoichiometric air-fuel ratio) based on the operating state of the engine 11 such as the engine speed and load. Is calculated from a map (which may be a function, and so on). Then, the air-fuel ratio feedback correction amount is calculated based on the deviation between the actual air-fuel ratio detected by the pre-catalyst air-fuel ratio sensor 61 and the air-fuel ratio target value, and the deviation is calculated based on the basic injection amount and the air-fuel ratio feedback correction amount. The air-fuel ratio of the air-fuel mixture or the fuel injection amount is feedback controlled so as to be zero. Such air-fuel ratio control is called main air-fuel ratio control.

  Further, the ECU 100 controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing out from the catalyst 11, that is, the air-fuel ratio detected by the post-catalyst air-fuel ratio sensor 62 matches the air-fuel ratio target value. Such air-fuel ratio control is called sub air-fuel ratio control. Even if the main air-fuel ratio control is being executed, the actual center air-fuel ratio may deviate from the stoichiometric air-fuel ratio due to product variations or deterioration of the pre-catalyst air-fuel ratio sensor 61. Control is performed simultaneously. The main air-fuel ratio control is executed with a very short time period, whereas the sub air-fuel ratio control is executed with a relatively long time period.

  The air-fuel ratio control can also be performed by setting the air-fuel ratio target value to a value other than the stoichiometric air-fuel ratio. For example, to improve fuel efficiency, air-fuel ratio control (so-called lean burn control) can be performed by setting the air-fuel ratio target value to a value leaner than the theoretical air-fuel ratio. In any case, the air-fuel ratio target value becomes the reference value of the air-fuel ratio when controlling the air-fuel ratio.

  In throttle opening control, the throttle valve 18 is opened more as the accelerator opening representing the load of the engine 11 (requested load from the driver), that is, the accelerator opening detected by the accelerator opening sensor 55 is larger. As described above, the actuator 23 is driven and controlled by the ECU 100.

  On the other hand, in the operating angle control of the intake valve 27, the target operating angle is calculated based on parameters relating to the operating state of the engine 11, particularly the engine speed and load. Based on the rotation angle detected by the rotation angle sensor 52, the actual operating angle of the intake valve 27 corresponding to the rotation angle is calculated. Energization of the actuator 46 is controlled by the ECU 100 so that the actual operating angle becomes the target operating angle. In particular, the working angle of the intake valve 27 is increased to increase the intake air amount of the engine 11 as the engine load increases, and the operating angle of the intake valve 27 is decreased to decrease the intake air amount of the engine 11 as the engine load decreases. It is made smaller. Although the throttle opening and the intake valve operating angle are coordinately controlled, the intake air amount can be increased or decreased by increasing or decreasing the intake valve operating angle. Is controlled to open. For this reason, pumping loss can be reduced and fuel consumption can be increased.

  As can be understood from this description, the variable operating angle mechanism 42, the rotation angle sensor 52, and the ECU 100 variably control the operating angle of the intake valve 27 of each cylinder in accordance with the load of the engine 11. Configure. If such an intake valve variable control device is provided, it is possible to control the entire intake air amount only by controlling the intake valve working angle, so that the throttle valve 18 can be omitted. The intake valve variable control device of the present embodiment also includes a valve timing variable mechanism 41. In addition to the one in this embodiment, the intake valve variable control device, for example, one that individually controls the intake valve of each cylinder using an electromagnetically driven valve, the one that makes the operating angle variable while keeping the maximum lift constant, etc. Any thing can be adopted.

  In the present embodiment, the above-described air-fuel ratio control (main air-fuel ratio control and sub air-fuel ratio control) is uniformly performed for all cylinders. That is, for each engine cycle (720 ° CA), the basic injection amount and the air-fuel ratio feedback correction amount common to all the cylinders are calculated, and the fuel injection amount calculated based on these is injected from each cylinder.

  In this way, the air-fuel ratio of each cylinder varies somewhat with respect to the air-fuel ratio target value as the reference value, but in this embodiment, the ECU 100 individually estimates the air-fuel ratio of each cylinder (air-fuel ratio for each cylinder). I have to. The cylinder-by-cylinder air-fuel ratio is estimated based on the detection value of the pre-catalyst air-fuel ratio sensor 61, and is performed using a cylinder-by-cylinder air-fuel ratio estimation model as disclosed in Patent Document 1.

  Paying attention to the gas exchange in the exhaust gas collection portion where the pre-catalyst air-fuel ratio sensor 61 is installed, the detection value of the pre-catalyst air-fuel ratio sensor 61 is used as the history of the air-fuel ratio of each cylinder in the exhaust gas collection portion and the detection value of the air-fuel ratio sensor 61. And the history is multiplied and multiplied by a predetermined weight, and the air-fuel ratio of each cylinder is estimated using the model. A Kalman filter is used as the observer.

  A model of gas exchange in the exhaust collecting part is approximated by the following equation (1).

Here, y is a detected value of the pre-catalyst air-fuel ratio sensor 61, u is an air-fuel ratio of the gas flowing into the exhaust gas collecting portion, and k1 to k4 are predetermined constants. In the exhaust system, there are a first-order lag element for gas inflow and mixing in the exhaust collecting portion and a first-order lag element due to a response delay of the air-fuel ratio sensor 61. Therefore, in the above equation (1), the history for the past two times is referred to in consideration of these first order lag elements.

  When the above equation (1) is converted into a state space model, the following equations (2a) and (2b) are derived.

Here, A, B, C, and D are model parameters, Y is a detected value of the air-fuel ratio sensor 61, X is a cylinder-by-cylinder air-fuel ratio as a state variable, and W is noise.

  Further, when the Kalman filter is designed by the above equations (2a) and (2b), the following equation (3) is obtained.

Here, the term on the left side (referred to as “X hat (k + 1 | k)” for convenience) is the estimated value of the air-fuel ratio of each cylinder, and K is the Kalman gain. The meaning of the term on the left side indicates that the estimated value of time (k + 1) is obtained from the estimated value of time (k).

  As described above, by configuring the cylinder-by-cylinder air-fuel ratio estimation model with the Kalman filter type observer, it is possible to sequentially estimate the air-fuel ratio for each combustion cycle of each cylinder.

  When the cylinder-by-cylinder air-fuel ratio can be estimated as in this embodiment, the air-fuel ratio is uniformly controlled even though the air-fuel ratio of each cylinder is uniformly controlled to a predetermined air-fuel ratio target value (for example, the theoretical air-fuel ratio). If there is a cylinder that shows an abnormal air-fuel ratio estimated value far from the target value, it can be seen that there is a possibility that at least one of a fuel system abnormality and an air system abnormality has occurred in the cylinder. It is inevitable that the air-fuel ratio of each cylinder varies somewhat due to variations in each cylinder due to manufacturing reasons, for example, variations in the injector 33 of each cylinder and the mediation drive mechanism 43 of the variable operating angle mechanism 42. If there is a cylinder-by-cylinder air-fuel ratio that is too far from the target value, it can be considered that a fuel system or air system abnormality has occurred in the cylinder. Here, the abnormality in the fuel system refers to an abnormality in which the amount of fuel supplied to the target cylinder is excessive or insufficient from the predetermined amount. In addition to the abnormality of the injector 33 such as clogging, valve opening or valve closing failure, the abnormality of the fuel supply device , Including poor distribution of blow-by gas and fuel vapor. The abnormality in the air system refers to an abnormality in which the amount of intake air with respect to the target cylinder is more or less than the predetermined amount. In addition to the abnormality in the intake valve variable control device such as the opening / closing timing of the intake valve 27 and the deviation of the operating angle. Including abnormalities in tappet clearance, abnormalities due to deposits, etc.

  However, it is generally difficult to identify whether a fuel system abnormality or an air system abnormality has occurred in the cylinder. Therefore, in the present embodiment, first, the presence or absence of abnormality in the fuel system of each cylinder is diagnosed by the following method, and then a state in which there is no abnormality in the fuel system for all cylinders (that is, a state where the fuel system is normal) is guaranteed. In the above, the presence or absence of an abnormality in the air system is diagnosed, and a diagnosis is made by distinguishing between an abnormality in the fuel system and an abnormality in the air system.

  In the case of an engine having a variable intake valve operating angle as in the present embodiment, an abnormality in the air system is largely due to an operating angle shift in which the actual operating angle deviates from the target value, and in turn, an abnormality in the operating angle variable mechanism 42. Since the mediation drive mechanism 43 is provided for each cylinder, an air system abnormality may occur for each cylinder. However, the effect of this operating angle deviation on the actual intake air amount decreases as the operating angle increases, that is, as the engine load increases.

  FIG. 4 is a graph showing how much the actual intake air amount deviates from the target value as the engine load changes when there is a certain amount of operating angle deviation. The positive diagram a shows a case where the actual operating angle of a certain cylinder is larger by a certain amount (for example, 5 ° CA) than the target value corresponding to the engine load, and the minus diagram b is constant on the contrary. The case where the amount is small is shown. For example, with respect to the diagram a, when the engine load is low, that is, when the operating angle is small, the actual intake air amount is greatly deviated to the positive side with respect to the target value corresponding to the engine load. As the value increases, the amount of deviation decreases, and when the engine load is high, that is, when the operating angle is large, the amount of deviation becomes extremely small. The same can be said for diagram b, although the opposite is true, and when the engine load is low, that is, when the operating angle is small, the actual intake air amount is greatly deviated from the target value, but the engine load is high. When the operating angle is large, the amount of deviation is extremely small.

  FIG. 5 is a diagram for explaining the reason for this tendency. The area inside the illustrated valve lift diagram is a value that correlates with the actual intake air amount. For example, in the case of a high load and a large working angle, even if the working angle is deviated by a certain amount Δα with respect to the target value (solid line) αt, the effect of this deviation on the area, that is, the actual intake air amount is small. This is because the original area, that is, the intake air amount is large. On the other hand, in the case of a low load and small working angle, if the working angle deviates by a certain amount Δα with respect to the target value (solid line) αt, this deviation has a large effect on the area, that is, the actual intake air amount. This is because the original area, that is, the intake air amount is small. It will be understood that the deviation of the tappet clearance and the deviation of the air amount due to deposit adhesion are also smaller for the high load and large working angle than for the low load and small working angle.

  Therefore, in the present embodiment, focusing on the characteristic that the working angle deviation has a small effect on the actual intake air amount at high load and large working angle, the fuel system of each cylinder at high load and large working angle. Diagnose the presence or absence of abnormalities. In other words, even when there is an air system abnormality such as an operating angle shift at a high load and a large operating angle, the effect is small. Therefore, if there is a cylinder in which the estimated air-fuel ratio deviates greatly from the air-fuel ratio target value at this time, it can be specified that the fuel system of the cylinder is abnormal. After the diagnosis of the fuel system abnormality is completed, the normal state of the fuel system is guaranteed and the presence or absence of the air system abnormality is diagnosed at a low load and a small operating angle. This is because if the normal state of the fuel system is guaranteed, the deviation of the air-fuel ratio estimated value that appears at a low load and a small operating angle can be considered to be caused by an air system abnormality.

  Hereinafter, specific examples of abnormality diagnosis processing will be described with reference to FIGS.

  First, the first example shown in FIG. 6 will be described. Such diagnosis processing is repeatedly executed by the ECU 100 at predetermined intervals (for example, 16 msec). In this first example, the presence or absence of abnormality in the fuel system is finally diagnosed for each cylinder.

  First, in step S101, the actually detected values of the engine speed NE and the load KL are acquired by the ECU 100. Next, in step S102, it is determined whether or not the acquired engine load KL is greater than a predetermined value X. The predetermined value X is set to a value that forms a boundary between a medium load or a high load (preferably a high load) and a lower load.

  If the engine load KL is less than or equal to the predetermined value X, the routine is terminated. On the other hand, if the engine load KL is greater than the predetermined value X, that is, if the engine load KL is a medium load or a high load, the estimated air-fuel ratio value of each cylinder based on the detected value of the pre-catalyst air-fuel ratio sensor 61 in step S103. Is calculated. The air / fuel ratio estimated value of #i cylinder (i represents a cylinder number, for example, i = 1, 2, 3, 4 in the case of a 4-cylinder engine) is represented by A / Fe (i).

  Next, in step S104, the value of the air-fuel ratio target value A / Ft is acquired from a map stored in advance in the ECU 100 based on the values of the engine speed NE and the load KL. In this embodiment, the air-fuel ratio target value A / Ft (that is, the air-fuel ratio reference value) of all cylinders is equal, for example, the theoretical air-fuel ratio, but even if the air-fuel ratio target value A / Ft is different for each cylinder. Good.

  Thereafter, in step S105, for each cylinder, the cylinder-specific air-fuel ratio difference ΔA / F (i) = A / Fe (i), which is the difference between the air-fuel ratio estimated value A / Fe (i) and the air-fuel ratio target value A / Ft. -A / Ft is calculated. This cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is an index value representing the amount of deviation of the air-fuel ratio estimated value A / Fe (i) from the air-fuel ratio target value A / Ft. A ratio may be used instead of the difference between the two.

  Next, in step S106, the air-fuel ratio difference ΔA / F (i) for each cylinder is compared with a predetermined abnormality determination value A. The abnormality determination value A is a positive value, and is a relatively large value sufficient to regard the deviation amount of the air-fuel ratio estimated value A / Fe (i) as abnormal.

  If there is a cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is greater than or equal to the abnormality determination value A, in step S107, there is an abnormality in the fuel system for that cylinder, and in particular, the fuel is insufficient. It is determined that an abnormality has occurred and the routine is terminated.

  On the other hand, if it is determined in step S106 that there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or greater than the abnormality determination value A, the process proceeds to step S108, and the cylinder-by-cylinder air-fuel ratio difference ΔA. / F (i) is compared with the minus abnormality determination value -A. Here, the positive abnormality determination value A and the negative abnormality determination value −A are symmetrical with respect to zero and have the same absolute value, but may be asymmetric and different absolute values.

  In the case where there is a cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or less than the abnormality determination value −A, in step S109, the fuel system abnormality, particularly the fuel in which the cylinder-by-cylinder air-fuel ratio greatly shifts to the rich side It is determined that an excessive abnormality has occurred, and the routine is terminated.

  On the other hand, if it is determined in step S108 that there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or less than the abnormality determination value −A, the process proceeds to step S110, and the fuel systems of all cylinders are normal. The routine is terminated.

  As described above, since the presence or absence of abnormality in the fuel system is diagnosed under the condition that the engine load KL is medium load or high load (preferably high load) greater than the predetermined value X, the influence of the air system abnormality is small. Abnormalities in the fuel system can be diagnosed, and abnormalities in the fuel system can be reliably diagnosed separately from the air system abnormality.

  Next, a second example of the abnormality diagnosis process will be described with reference to FIG. This second example is substantially the same as the first example shown in FIG. 6 and diagnoses a fuel system abnormality, but differs mainly in the following points.

  First, in first step S201A, it is determined whether or not the intake valve operating angle α is larger than a predetermined value C. The predetermined value C is set as a minimum value among relatively large values that can reduce the influence of the air system abnormality. Due to the characteristics of the working angle control, a large working angle is obtained if the load is high, and if the high load is ensured, the condition of a large working angle can be secured naturally. However, in this second example, the working angle α Whether it is large or not is determined separately. The value of the working angle used here may be a target working angle value determined based on the rotational speed and load of the engine, or an actual working angle value based on a detection value of the rotational angle sensor 52.

  When the operating angle α is equal to or smaller than the predetermined value C, the routine is terminated. On the other hand, when the operating angle α is larger than the predetermined value C, the values of the engine speed NE and the load KL are acquired in step S201 as in step S101.

  Thereafter, steps S202 to S209 are the same as steps S102 to S109. By step S202, the condition that the engine load KL is larger than the predetermined value X, that is, the condition that the load is medium load or high load is secured.

  When it is determined in step S208 that there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or less than the abnormality determination value −A, in step S210, the cylinder-by-cylinder air-fuel ratio difference ΔA / F. (I) is compared with a predetermined normal judgment value B. The normal determination value B is a positive value and smaller than the abnormality determination value A, and is set as a value corresponding to the maximum allowable value of the deviation amount of the cylinder-by-cylinder air-fuel ratio.

  If there is a cylinder having a cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) larger than the normal determination value B, the normal determination of the fuel system of all cylinders is suspended in step S211. That is, in this case, although the cylinder is not so large as to be regarded as abnormal, a lean deviation of the cylinder-by-cylinder air-fuel ratio that is too large to be regarded as normal has occurred. As a result, the fuel system is not determined to be normal or abnormal.

  On the other hand, if there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is larger than the normal determination value B, the process proceeds to step S212, and the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is normal on the negative side. It is compared with the judgment value -B. Similar to the above, the positive normal determination value B and the negative normal determination value -B are symmetric with respect to zero and have the same absolute value, but may be asymmetric and different absolute values. .

  If there is a cylinder having a cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) that is less than the negative-side normal determination value −B, the routine proceeds to step S211, and fuel system normal determination for all cylinders is suspended. On the other hand, if there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is less than the negative normal determination value −B, the routine proceeds to step S213, where it is determined that the fuel system of all cylinders is normal, and the routine Is terminated.

  Next, a third example of the abnormality diagnosis process will be described with reference to FIG. This third example is processing that is substantially performed after the fuel system abnormality diagnosis is completed according to the first example shown in FIG. 6 or the second example shown in FIG. This process is also repeatedly executed by the ECU 100 at predetermined intervals (for example, 16 msec). In this third example, the presence or absence of an abnormality in the air system is finally diagnosed for each cylinder.

  First, in step S301, it is determined whether or not normal determination has been made for the fuel systems of all cylinders according to the first or second example. If normality is determined, the process proceeds to step S303.

  On the other hand, when the normality determination is not made, that is, when either the fuel shortage abnormality determination or the fuel excessive abnormality determination is made for a certain cylinder, or when the fuel system normality determination for all cylinders is suspended, step S302. In the former case, correction of the fuel injection amount is performed for the cylinder in which the abnormality is determined (abnormal cylinder), and in the latter case, the cylinder in which the abnormality is not determined to be normal (semi-abnormal cylinder). It is then determined whether or not this correction has been completed.

  This correction is performed when the engine load KL is a medium load or a high load greater than the predetermined value X. In this correction, the fuel injection amount is corrected so that the air-fuel ratio estimated value A / Fe (i) approaches or equals the air-fuel ratio target value A / Ft only in the abnormal cylinder or the semi-abnormal cylinder. As a result, the abnormal state or semi-abnormal state of the fuel system in the abnormal cylinder or semi-abnormal cylinder is eliminated, and the fuel system is in a normal state of all cylinders.

  However, if the correction cannot be performed because the injector is completely broken or the like, the correction is not completed and the routine is terminated. On the other hand, if the correction is possible and the correction is completed, the process proceeds to step S303.

  In step S303, it is determined whether or not the intake valve operating angle α is smaller than a predetermined value D. The predetermined value D is set as the maximum value among relatively small values that can sufficiently increase the influence of the air system abnormality. This is because the abnormality of the air system is diagnosed under the condition of a low load and a small working angle where the influence of the air system abnormality is likely to occur. Although the condition that the engine load is low is also determined in a later step, here, for safety, whether or not the operating angle α is small is separately determined. The value of the operating angle may be a target operating angle value or an actual operating angle value. Note that the predetermined value D in step S303 and the predetermined value C in step S201A may be the same value or different values. When making it different, it is preferable to make the former smaller than the latter.

  When the operating angle α is equal to or greater than the predetermined value D, the routine is terminated. On the other hand, if the operating angle α is smaller than the predetermined value D, the values of the engine speed NE and the load KL are acquired in step S304 as in step S101.

  In the next step S305, it is determined whether or not the acquired engine load KL is smaller than a predetermined value Y. The predetermined value Y is set to a value that forms a boundary between a low load and a higher load. The predetermined value Y in step S305 and the predetermined value X in step S102 may be the same value or different values. When making it different, it is preferable to make the former smaller than the latter.

  If the engine load KL is greater than or equal to the predetermined value Y, the routine is terminated. On the other hand, when the engine load KL is smaller than the predetermined value Y, that is, when the engine load KL is low, in step S306, the air-fuel ratio of each cylinder is determined based on the detected value of the pre-catalyst air-fuel ratio sensor 61 in step S103. The estimated fuel ratio A / Fe (i) is calculated.

  Next, in step S307, the value of the air-fuel ratio target value A / Ft is acquired as in step S104. In step S308, the air-fuel ratio difference ΔA / F (i) for each cylinder of each cylinder is calculated as in step S105. .

  Next, in step S309, the air-fuel ratio difference ΔA / F (i) for each cylinder is compared with a predetermined abnormality determination value A ′. The abnormality determination value A ′ is a positive value, and is a relatively large value sufficient to regard the deviation amount of the air-fuel ratio estimated value A / Fe (i) as abnormal.

  Here, the abnormality determination value A ′ related to the air system, the normal determination value B ′, which will be described later, and the negative abnormality determination value −A ′ and the normal determination value −B ′ are the characteristics shown in FIG. Is determined in accordance with the engine load KL.

  If there is a cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or greater than the abnormality determination value A ′, in step S310, the air system abnormality of the cylinder, in particular, the air in which the cylinder-by-cylinder air-fuel ratio greatly deviates to the lean side. It is determined that an excessive abnormality has occurred, and the routine is terminated.

  On the other hand, if it is determined in step S309 that there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or greater than the abnormality determination value A ′, the process proceeds to step S311 to determine the cylinder-by-cylinder air-fuel ratio difference. ΔA / F (i) is compared with the abnormality determination value −A ′ on the negative side. Here, the positive abnormality determination value A ′ and the negative abnormality determination value −A ′ are symmetrical with respect to zero and have the same absolute value, but may be asymmetric and different absolute values. .

  If there is a cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or less than the negative abnormality determination value −A ′, in step S312, an abnormality in the air system, particularly the cylinder-by-cylinder air-fuel ratio is rich. It is determined that there is an air shortage abnormality that greatly deviates, and the routine is terminated.

  On the other hand, if it is determined in step S311 that there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is equal to or less than the abnormality determination value −A ′, the process proceeds to step S313 to determine the cylinder-by-cylinder air-fuel ratio. The difference ΔA / F (i) is compared with a predetermined normal judgment value B ′. The normality determination value B ′ is a positive value and smaller than the abnormality determination value A ′, and is set to the maximum allowable value of the deviation amount of the air-fuel ratio estimation value A / Fe (i).

  If there is a cylinder having a cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) larger than the normal determination value B ′, the normal determination of the air system of all cylinders is suspended in step S314. That is, in this case, the cylinder (semi-abnormal cylinder) is not so large that it can be regarded as abnormal, but there is a lean deviation of the cylinder-by-cylinder air-fuel ratio A / F (i) that is too large to be regarded as normal. Air system normality judgment is suspended. As a result, the air system is not determined to be normal or abnormal.

  On the other hand, if there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is greater than the normal determination value B ′, the process proceeds to step S315, and the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is negative. It is compared with the normal judgment value −B ′. As described above, the positive normal determination value B ′ and the negative normal determination value −B ′ are values having the same absolute value that are symmetric with respect to zero, but are asymmetric and values having different absolute values. Also good.

  If there is a cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is less than the normal determination value −B ′ on the negative side, the process proceeds to step S314, and the normal determination of the air system for all the cylinders is suspended. On the other hand, if there is no cylinder in which the cylinder-by-cylinder air-fuel ratio difference ΔA / F (i) is less than the negative normal determination value −B ′, the process proceeds to step S316, where it is determined that the air system of all cylinders is normal, The routine is terminated.

  As described above, since the presence or absence of an abnormality in the air system is diagnosed under the condition that the fuel system is in a normal state and the engine load KL is a low load smaller than the predetermined value Y, the possibility of the abnormality in the fuel system is eliminated. Thus, the air system abnormality can be diagnosed under a condition where the influence of the air system abnormality is great, and the air system abnormality can be reliably diagnosed separately from the fuel system abnormality.

  Next, a modification of the third example of the abnormality diagnosis process will be described with reference to FIG.

  This modification is premised on an intake valve variable control device capable of controlling the operating angle of the intake valve of each cylinder for each cylinder. For example, the present invention can be applied to the variable working angle mechanism 42 that can control the intermediary drive mechanism 43 of each cylinder for each cylinder, or that can control the intake valve of each cylinder for each cylinder by an electromagnetic drive valve. Here, similarly to the above, the maximum lift amount is also changed in synchronization with the operating angle.

  Steps S401 to S416 are the same as steps S301 to S316 of the third example, respectively. The intake valve operating angle is uniform for all cylinders, including the first or second example, until the air system abnormality, semi-abnormality (normal determination pending) or normal is determined in steps S410, S412, S414, and S414. Be controlled.

  When the air system abnormality is determined in step S410 or S412, or when the air system semi-abnormality is determined in step S414 (that is, when the air system normality determination is not made), the process proceeds to step S417. In this step S417, the air-fuel ratio estimated value A / Fe (ix) is made equal to the air-fuel ratio target value A / Ft (that is, the cylinder-by-cylinder air-fuel ratio difference) for the cylinder ix in which the air system is determined to be abnormal or semi-abnormal. The working angle is corrected and controlled for a predetermined time so that ΔA / F (ix) becomes zero. As a result, an attempt is made to correct the air amount in the cylinder ix so that the air-fuel ratio estimated value A / Fe (ix) matches the air-fuel ratio target value A / Ft. Note that such working angle correction control is not performed in cylinders other than the cylinder ix.

  If the correction control for the predetermined time is completed, the process proceeds to step S418, and whether the actual air-fuel ratio estimated value A / Fe (ix) is sufficiently close to the air-fuel ratio target value A / Ft within the predetermined value. Specifically, it is determined whether or not the absolute value of the cylinder specific air-fuel ratio difference ΔA / F (ix) is equal to or less than a predetermined value E (> 0).

  When the absolute value of the cylinder-by-cylinder air-fuel ratio difference ΔA / F (ix) is equal to or smaller than the predetermined value E, the air amount deviation can be eliminated by correcting the operating angle. In step S419, the final operating angle of the cylinder ix The correction state is maintained. Thereby, in the subsequent air-fuel ratio control or the like, the air amount deviation of the cylinder ix does not occur, and normal control can be performed.

  On the other hand, if the absolute value of the cylinder-by-cylinder air-fuel ratio difference ΔA / F (ix) does not become equal to or smaller than the predetermined value E, the air amount deviation cannot be eliminated even if the operating angle is corrected. It is determined that the control device is abnormal. This abnormality of the intake valve variable control device typically includes an abnormality of a portion related to the cylinder ix of the intake valve variable control device (particularly, the operating angle variable mechanism 42). In the case of an abnormality other than the intake valve variable control device, that is, a tappet clearance abnormality, deposit adhesion abnormality, or the like, the deviation of the air amount is not so large and is likely to be eliminated by correcting the operating angle. However, if the deviation of the air amount cannot be resolved even if the operating angle is corrected, there is a high possibility that it is a more serious abnormality, that is, an abnormality in the intake valve variable control device. Therefore, in this case, if the air-fuel ratio deviation cannot be eliminated even after correcting the operating angle for the cylinder ix, it is determined that the intake valve variable control device is abnormal (particularly, the abnormality related to the cylinder ix), and the abnormal part is determined. It is going to be specified in more detail. Thereby, a more accurate and precise abnormality diagnosis becomes possible.

  Although the embodiment of the present invention has been described in detail above, various other embodiments of the present invention are conceivable. For example, the use and type of the internal combustion engine are arbitrary, and may be other than for vehicles, for example, a compression ignition internal combustion engine (diesel engine), a port direct injection type, or the like. The number of cylinders is arbitrary as long as it is multi-cylinder. In the above embodiment, the reference value of the deviation amount of the cylinder-by-cylinder air-fuel ratio is set to a uniform air-fuel ratio target value for all cylinders, for example, the theoretical air-fuel ratio, but is not limited to this, for example, the average value of the cylinder-by-cylinder air-fuel ratio May be set as the reference value. Also, when the normal determination of the fuel system is suspended in the second example of FIG. 7 (step S211) and when the normal determination of the air system is suspended in the third example of FIG. 8 (step S314), both abnormalities are normal. Normal determination may be suspended only for cylinders that cannot be considered, and normal determination may be performed for other cylinders.

  The present invention includes all modifications, applications, and equivalents included in the spirit 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.

It is the schematic of the engine which concerns on one Embodiment of this invention. It is a diagram which shows the variable timing characteristic of an intake valve. It is a diagram which shows the variable action angle characteristic of an intake valve. It is a graph which shows the relationship between an engine load in case there exists working angle deviation, and the amount of intake air deviation. It is a figure for demonstrating the reason that the amount of intake air deviations changes according to engine load. It is a flowchart which concerns on the 1st example of abnormality diagnosis processing. It is a flowchart which concerns on the 2nd example of abnormality diagnosis processing. It is a flowchart which concerns on the 3rd example of abnormality diagnosis processing. It is a map for calculating the air system abnormality determination value and the normality determination value. It is a flowchart which concerns on the modification of the 3rd example of abnormality diagnosis processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Internal combustion engine 27 Intake valve 42 Operating angle variable mechanism 43 Intermediary drive mechanism 52 Rotation angle sensor 55 Accelerator opening sensor 61 Pre-catalyst air-fuel ratio sensor 100 Electronic control unit (ECU)
KL Load α Working angle A / Fe (i) Air-fuel ratio estimated value A / Ft for each cylinder Target air-fuel ratio ΔA / F (i) Air-fuel ratio difference for each cylinder

Claims (5)

In the internal combustion engine abnormality diagnosis device comprising an intake valve variable control device that variably controls the operating angle of the intake valve of at least each cylinder according to the load of the internal combustion engine,
Cylinder-specific air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder;
When the load of the internal combustion engine is larger than a predetermined value, the abnormality of the fuel system of each cylinder is determined based on the amount of deviation from the predetermined reference value of the air-fuel ratio estimated value of each cylinder obtained by the cylinder-by-cylinder air-fuel ratio estimating means. Abnormality diagnosis means for diagnosing the presence or absence of ,
Correction means for correcting the fuel injection amount so that the estimated air-fuel ratio approaches the reference value for a cylinder whose fuel system is not diagnosed as normal by the abnormality diagnosis means;
With
The abnormality diagnosing means, after diagnosing that the fuel system of all cylinders is normal or after being corrected by the correcting means, when the load of the internal combustion engine is smaller than a predetermined value, the reference of the air-fuel ratio estimated value Based on the amount of deviation from the value, diagnose whether there is an abnormality in the air system of each cylinder,
The intake valve variable control device corrects and controls a working angle for a predetermined time so that the air-fuel ratio estimated value approaches the reference value for a cylinder whose air system has not been diagnosed as normal by the abnormality diagnosing means,
The abnormality diagnosing means diagnoses an abnormality of the intake valve variable control device when the estimated air-fuel ratio does not approach the reference value within a predetermined value after the correction control for the cylinder,
For the cylinder, when the estimated air-fuel ratio approaches the reference value within a predetermined value after the correction control, the intake valve variable control device maintains the correction state of the working angle.
An abnormality diagnosis apparatus for an internal combustion engine characterized by the above. 2. The abnormality of the internal combustion engine according to claim 1, wherein the abnormality diagnosis unit diagnoses whether there is an abnormality in a fuel system of each cylinder based on a difference or ratio between the estimated value of the air-fuel ratio and the reference value. Diagnostic device. The abnormality diagnosis means diagnoses whether or not there is an abnormality in the fuel system of each cylinder when the load of the internal combustion engine is larger than a predetermined value and the working angle is larger than a predetermined value. The abnormality diagnosis apparatus for an internal combustion engine according to 1 or 2.   The abnormality diagnosis means diagnoses the presence or absence of abnormality in the air system of each cylinder based on the difference or ratio between the estimated air-fuel ratio value and the reference value.
  The abnormality diagnosis apparatus for an internal combustion engine according to any one of claims 1 to 3.   The abnormality diagnosis means diagnoses whether there is an abnormality in the air system of each cylinder when the load of the internal combustion engine is smaller than a predetermined value and the working angle is smaller than the predetermined value.
  The abnormality diagnosis apparatus for an internal combustion engine according to claim 4.

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