JP2015121112A - Air-fuel ratio controller abnormality diagnosis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of an apparatus for diagnosing abnormality of an air-fuel ratio control apparatus.
An abnormality diagnosis device includes an air-fuel ratio detection unit for detecting an air-fuel ratio of an internal combustion engine, and an air-fuel ratio control unit configured to bring the air-fuel ratio closer to a theoretical air-fuel ratio based on an output of the air-fuel ratio detection unit. Based on the operation amount determination unit 43 that corrects the operation amount, the correction value associated with the correction amount for the operation amount, and the comparison value that is set regardless of the correction by the operation amount determination unit 43, the air-fuel ratio control device And a diagnosis unit 44 for diagnosing abnormality.
[Selection] Figure 2

Description

  The present invention relates to an apparatus for diagnosing an abnormality in an air-fuel ratio control apparatus for an internal combustion engine.

  A controller mounted on a vehicle may be configured to perform self-diagnosis of the vehicle system or device. For example, Patent Document 1 discloses an abnormality diagnosis device for an air-fuel ratio feedback control system. The air-fuel ratio feedback control system sets an air-fuel ratio correction coefficient according to the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio, and corrects the fuel supply amount so that the air-fuel ratio becomes the target air-fuel ratio. . The abnormality diagnosis device uses a deviation between the current value of the air-fuel ratio correction coefficient and the average value of the correction coefficient as an abnormality determination element, and compares the abnormality determination element with a threshold value to diagnose an abnormality in the air-fuel ratio feedback control system. .

Japanese Patent Laid-Open No. 10-2245

  However, since the influence is included in the average value when there is an initial failure, the initial failure cannot be detected. In addition, when the deviation between the current value and the average value is used as an abnormality determination element, it is difficult to accurately detect anomalies that are recognized due to the gradual progress of deterioration.

  Therefore, an object of the present invention is to provide a more reliable abnormality diagnosis apparatus.

  An abnormality diagnosis apparatus for an air-fuel ratio control apparatus according to the present invention is an apparatus for diagnosing an abnormality in an air-fuel ratio control apparatus for controlling an air-fuel ratio of an internal combustion engine, and an air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine; An operation amount determination unit that corrects the operation amount of the air-fuel ratio control device so as to bring the air-fuel ratio closer to the theoretical air-fuel ratio based on the output of the air-fuel ratio detection means, and a correction value associated with the correction amount for the operation amount And a diagnosis unit for diagnosing an abnormality of the air-fuel ratio control device based on a comparison value set regardless of the correction by the operation amount determination unit.

  According to the above configuration, since the comparison value that does not depend on the correction amount is used for abnormality diagnosis, even if an initial failure exists in the air-fuel ratio control device, the comparison value does not include the initial failure. For this reason, the diagnostic unit can detect an initial failure. Further, even when it is recognized that the deterioration has gradually progressed and the air-fuel ratio control apparatus has become abnormal, it becomes easy to detect this. Therefore, the reliability of the abnormality diagnosis device is increased.

  The air-fuel ratio detection means further includes a storage unit that stores a correspondence relationship that defines a correction amount necessary for the air-fuel ratio to become the stoichiometric air-fuel ratio corresponding to the operating state of the internal combustion engine, The O2 sensor reverses the output characteristics when straddling the vicinity of the air-fuel ratio, and the operation amount determination unit corrects the operation amount according to the correspondence relationship, and then brings the O2 sensor closer to the stoichiometric air-fuel ratio. The manipulated variable may be corrected stepwise as time elapses based on the output.

  According to the above configuration, when the air-fuel ratio control apparatus is not abnormal, it is possible to shorten the time until the air-fuel ratio approaches the stoichiometric air-fuel ratio. As a result, even when the air-fuel ratio control apparatus is abnormal, it is possible to shorten the time until this is detected.

  The correction value may be set based on a correction amount that is required to bring the air-fuel ratio closer to the stoichiometric air-fuel ratio after correcting the operation amount according to the correspondence relationship.

  In the above configuration, if the air-fuel ratio control device is in an ideal state without individual differences, deterioration, or abnormality, the operation amount should be corrected according to the corresponding relationship, so that the air-fuel ratio should reach the stoichiometric air-fuel ratio. A further correction amount after the correction is necessary when the air-fuel ratio is different from the stoichiometric air-fuel ratio because the air-fuel ratio control device is not, and compensates for this air-fuel ratio error. Since the correction value is set based on such a correction amount, the diagnosis unit discriminates whether it is out of the ideal state due to individual differences or deterioration, not abnormalities, or abnormal. It becomes easy. Therefore, it is easy to improve the reliability of the abnormality diagnosis apparatus. In addition, since the comparison value does not have to be changed greatly depending on the operating state, the comparison value can be easily set.

  When the state where the correction value exceeds the comparison value continues for a predetermined time, the diagnosis unit may diagnose that the air-fuel ratio control device is abnormal.

  According to the said structure, even if it is a case where a correction value instantaneously exceeds a comparison value by the influence of noise etc., the diagnostic precision of a diagnostic part improves.

  The correction value may be a value associated with an average of correction amounts acquired within a predetermined period.

  According to the above configuration, the diagnostic accuracy of the diagnostic unit is improved even when the current value of the correction amount instantaneously exceeds the comparison value due to the influence of noise or the like.

  The diagnosis unit determines whether or not a diagnosis permission condition is satisfied including a condition that the operating state of the internal combustion engine is stably changing, or a condition that the correction amount is stably changing, The abnormality diagnosis of the air-fuel ratio control device may not be performed if the diagnosis permission condition is not satisfied, and the abnormality diagnosis of the air-fuel ratio control device may be performed if the diagnosis permission condition is satisfied.

  According to the above configuration, since the abnormality diagnosis is performed when the driving state and the correction amount are stable, the diagnosis accuracy of the diagnosis unit is improved.

  If the air-fuel ratio control device is diagnosed as abnormal, an alarm device may be further provided to notify the driver accordingly.

  According to the above configuration, the driver can be notified of an abnormality in the air-fuel ratio control device, and the driver can be encouraged to take appropriate measures.

  According to the present invention, a highly reliable abnormality diagnosis apparatus can be provided.

It is a conceptual diagram which shows the structure of the air fuel ratio control apparatus which concerns on 1st Embodiment. It is a block diagram which shows the structure of the air fuel ratio control apparatus shown in FIG. 1, and its abnormality diagnosis apparatus. It is a figure which shows an example of a 1st correspondence. It is a figure which shows an example of a 2nd correspondence. (A) is a figure which shows an example of a valve opening period and an air fuel ratio in the case where the air fuel ratio control apparatus shown in FIG. 2 is in an ideal state with no individual difference, deterioration and abnormality. (B) And (c) is a figure which shows an example of a valve opening period and an air fuel ratio in case an individual difference or deterioration exists in the air fuel ratio control apparatus shown in FIG. It is a graph which shows an example of the setting method of a fluctuation | variation correction coefficient. 3 is a flowchart showing an example of air-fuel ratio control and abnormality diagnosis executed by the air-fuel ratio control apparatus and the abnormality diagnosis apparatus shown in FIG. It is a flowchart which shows an example of the abnormality diagnosis process shown in FIG. (A)-(c) is a graph which shows an example of diagnosis permission conditions. (A) And (b) is a graph which shows an example of abnormal condition. It is explanatory drawing of the abnormal condition illustrated to Fig.10 (a). It is a block diagram which shows the structure of the air fuel ratio control apparatus which concerns on 2nd Embodiment, and its abnormality diagnosis apparatus. It is a graph which shows an example of the setting method of a closed loop correction coefficient and a learning correction coefficient. It is a figure which shows an example of a valve opening period and an air fuel ratio in case an individual difference or deterioration exists in the air fuel ratio control apparatus shown in FIG. It is a flowchart which shows an example of the air fuel ratio control performed by the air fuel ratio control apparatus shown in FIG. 12, and its abnormality diagnosis apparatus, and abnormality diagnosis. It is a block diagram which shows the structure of the air fuel ratio control apparatus which concerns on 3rd Embodiment, and its abnormality diagnosis apparatus. It is a graph which shows an example of the setting method of a real-time learning coefficient and a long-term learning coefficient. (A) is a figure showing an example of the 3rd correspondence. (B) is a figure showing an example of the 4th correspondence. It is a block diagram which shows the structure of the air fuel ratio control apparatus which concerns on 4th Embodiment, and its abnormality diagnosis apparatus. It is a figure which shows an example of the determination method of the combustion state by a 1st determination part. It is a figure which shows an example of the determination method of the combustion state by a 2nd determination part. It is a graph which shows an example of the setting method of an idle correction coefficient. FIG. 20 is a flowchart showing an example of air-fuel ratio control and abnormality diagnosis executed by the air-fuel ratio control apparatus and the abnormality diagnosis apparatus shown in FIG. 19. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same code | symbol through all the figures, and the overlapping description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a conceptual diagram showing the configuration of the air-fuel ratio control apparatus according to the first embodiment. The air-fuel ratio control device is mounted on a vehicle (for example, a motorcycle, an uneven terrain vehicle, a four-wheel vehicle, or a small planing boat) that uses the internal combustion engine 1 as a drive source. The internal combustion engine 1 is connected to a piston 5 through a main body 2 that forms a cylinder 3 and a combustion chamber 4, a piston 5 that reciprocates in the cylinder 3, and a connecting rod 6, and a crankshaft (not shown) that is driven to rotate by the piston 5. A). The downstream end of the intake passage 7 opens into the combustion chamber 4 and is opened and closed by an intake valve 8. The upstream end of the exhaust passage 9 opens into the combustion chamber 4 and is opened and closed by an exhaust valve 10.

  The intake passage 7 includes an inner space of the air cleaner 11, an inner space of the throttle device 12, and an intake port 13 of the main body 2 in order from the upstream side of the intake flow. Outside air flows into the air cleaner 11 and is purified, and the purified outside air passes through the throttle device 12 and is taken into the intake port 13.

  The driver can operate the throttle valve 15 built in the body of the throttle device 12 by operating the accelerator operation member 14 such as a throttle grip or an accelerator pedal according to his / her acceleration, constant speed or deceleration request. is there. The intake air amount is adjusted according to the opening of the throttle valve 15 (hereinafter referred to as “throttle opening”). The throttle valve 15 includes an electric throttle valve 15 a that is driven by a valve motor 16. The valve motor 16 is controlled by an electronic control unit (hereinafter referred to as “ECU”) 40, and the valve motor 16 operates in accordance with the amount of operation of the accelerator operation member 14 (hereinafter referred to as “accelerator operation amount”). It depends on the amount of operation. The throttle valve 15 may include a manual throttle valve 15b that is mechanically driven according to the operation of the accelerator operation member 14, and in this case, the two valves 15a and 15b are arranged in the intake flow direction in the intake passage 7. .

  The fuel system includes a fuel tank 17 that stores fuel (for example, gasoline), an injector 18 that injects fuel, a fuel pipe 19 that connects the fuel tank 17 to a fuel inlet of the injector 18, and fuel in the fuel tank 17 that is fuel pipe 19. As a result, it includes a fuel pump 20 that pumps the fuel to the fuel inlet. In this embodiment, the fuel is injected into the intake passage 7, but may be injected into the combustion chamber 4. The injector 18 is controlled by the ECU 40 and injects fuel every engine cycle. The internal combustion engine 1 is, for example, a four-stroke engine, and one engine cycle is configured by, for example, four strokes of intake, compression, expansion, and exhaust.

  In the intake stroke, the intake valve 8 opens the intake passage 7, and intake air and fuel are supplied to the combustion chamber 4. The air-fuel mixture in the combustion chamber 4 is compressed in the compression stroke and ignited and burned by the spark plug 21. In the exhaust stroke, the exhaust valve 10 opens the exhaust passage 9 and the combustion exhaust gas is discharged from the combustion chamber 4 to the exhaust passage 9.

  The exhaust passage 9 includes an exhaust port 22 in the main body 2, an internal space of the exhaust manifold 23, an internal space of the three-way catalyst pipe 24, and an internal space of the exhaust muffler 25 in order from the upstream of the exhaust flow. The combustion exhaust gas is discharged to the outside air through the exhaust passage 9. While passing through the three-way catalyst tube 24, hydrocarbons, carbon monoxide and nitrogen oxides are removed from the combustion exhaust gas.

  Although not shown in detail, the internal combustion engine 1 is a multi-cylinder type having a plurality of cylinders 3. The combustion chamber 4, the piston 5 and the connecting rod 6 individually correspond to the cylinders 3, and the crankshaft is common to all the cylinders 3. The air cleaner 11 is common to all the cylinders 3, and the intake valve 8 and the intake port 13 individually correspond to the cylinders 3. As an example, the throttle valves 15 individually correspond to the cylinders 3 but operate all at once so that the throttle openings are the same in all the cylinders 3. The fuel tank 17 and the fuel pump 20 are common to all the cylinders 3, and the injectors 18 individually correspond to the cylinders 3. The fuel pipes 19 are gathered in the upstream portion and branch in correspondence with the injector 18 in the downstream portion. The exhaust valve 10 and the exhaust port 22 individually correspond to the cylinder 3, and the three-way catalyst pipe 24 and the exhaust muffler 25 are common to all the cylinders 3. The exhaust manifold 23 branches in correspondence with the exhaust port 22 in the upstream portion, and gathers in the downstream portion.

  FIG. 2 is a block diagram showing the configuration of the air-fuel ratio control device and the abnormality diagnosis device shown in FIG. The air-fuel ratio control device includes the ECU 40, the electric throttle valve 15a, and the injector 18 described above. In addition, the air-fuel ratio control device includes an operation state detection unit that detects an operation state of the internal combustion engine 1 (see FIG. 1) and an air-fuel ratio detection unit that detects the air-fuel ratio of the internal combustion engine 1.

  The operating state detection means includes, for example, a crank angle sensor 31, a throttle opening sensor 32, and an accelerator operation amount sensor 33. The crank angle sensor 31 detects the rotational position of the crankshaft (hereinafter referred to as “crank angle”). The ECU 40 can detect the engine speed based on the output of the crank angle sensor 31. The throttle opening sensor 32 detects the throttle opening. The accelerator operation amount sensor 33 detects the accelerator operation amount.

  When the air-fuel ratio of the internal combustion engine 1 (see FIG. 1) straddles the vicinity of the theoretical air-fuel ratio (that is, when the air-fuel ratio shifts from rich to lean or vice versa) The O2 sensor 38 reverses the output characteristics. The O2 sensor 38 is common to all the cylinders 3 (see FIG. 1). For example, the O2 sensor 38 is attached to the downstream portion of the exhaust manifold 23 (see FIG. 1), and has a high voltage or low voltage depending on the oxygen concentration of the combustion exhaust gas in the exhaust manifold 23. Outputs a voltage signal. When the oxygen concentration of the combustion exhaust gas in the exhaust manifold 23 rises or falls across the exhaust gas oxygen concentration value assumed to be obtained when the stoichiometric air-fuel ratio mixture is burned, the O2 sensor 38 outputs characteristics. Is reversed. The ECU 40 can determine whether the air-fuel ratio of the internal combustion engine 1 is in a rich state or a lean state based on the output of the O2 sensor 38. The ECU 40 can determine that the air-fuel ratio is near the stoichiometric air-fuel ratio based on the output characteristics of the O2 sensor 38 being inverted.

  The ECU 40 controls the valve motor 16 and the injector 18 as control objects according to the operating state, thereby controlling the air-fuel ratio as a control amount. The ECU 40 performs feedback control for correcting the operation amount of the air-fuel ratio control device so that the air-fuel ratio approaches the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means. The operation amount that affects the air-fuel ratio includes the position of the valve motor 16, the throttle opening, and the valve opening period of the injector 18. In the present embodiment, the valve opening period of the injector 18 is subject to correction when the feedback control is performed.

  The injector 18 is an electromagnetic on-off valve that normally closes its injection port. The ECU 40 determines the valve opening period of the injector 18 for each engine cycle according to the operating state. The injector 18 receives a valve opening command from the ECU 40 until the determined valve opening period elapses from an appropriate time. During the valve opening period, the injection port is opened, and the pumped fuel is injected from the injection port. The amount of fuel injected from the injector 18 is determined according to the design values (for example, the injection port diameter) of the parts constituting the fuel system, the fuel properties (for example, viscosity), the fuel pressure, and the valve opening period of the injector 18. The design values and fuel properties are substantially constant, and the fuel pressure is also substantially as long as there are no abnormalities in the components constituting the fuel system such as the fuel pump 17 (see FIG. 1), the injector 18 or the fuel pipe 19 (see FIG. 1). Kept constant. Therefore, by treating the valve opening period of the injector 18 as the operation amount, fuel injection control and air-fuel ratio control with the fuel amount and air-fuel ratio as control amounts can be implemented.

  If the target air-fuel ratio cannot be obtained no matter how much the valve opening period is corrected, it can be considered that there is an abnormality in the components constituting the fuel system. Alternatively, it can be considered that there is an abnormality in a part constituting the intake system such as the air cleaner 11 (see FIG. 1) or the throttle valve 15 (see FIG. 1). Alternatively, it can be considered that there is an abnormality in the components constituting the detection system such as the operating state detection means or the air-fuel ratio detection means. When the target air-fuel ratio can be obtained without greatly correcting the valve opening period, the correction amount is an individual difference between components constituting the internal combustion engine 1 (see FIG. 1), the intake system, the fuel system, and the detection system, or It can be considered that the correction amount is necessary to compensate for an allowable error caused by deterioration of these components.

  The ECU 40 diagnoses an abnormality of the air-fuel ratio control device based on the correction value associated with the correction amount and the comparison value set regardless of the correction amount. The ECU 40 constitutes an air-fuel ratio control device and also constitutes an abnormality diagnosis device.

  The abnormality diagnosis device includes an alarm device 39 that notifies the driver when the air-fuel ratio control device is diagnosed as having an abnormality. The alarm device 39 is controlled by the ECU 40. The alarm device 39 may be a display device that notifies the driver's vision and notifies the abnormality by performing a warning display. The display device may be arranged on an instrument panel of a vehicle, and a lamp or a liquid crystal panel can be adopted as the display device. The alarm device 39 may be a speaker device that informs the driver's hearing and notifies the abnormality by emitting a warning sound.

  The ECU 40 includes a storage unit 41, a mode determination unit 42, an operation amount determination unit 43, and a diagnosis unit 44 as functional modules that realize the above air-fuel ratio control and abnormality diagnosis. The storage unit 41 is realized by a hardware element of the ECU 40 such as a memory. The mode determination unit 42, the operation amount determination unit 43, and the diagnosis unit 44 are realized by a software element of the ECU 40 such as a program stored in a memory and a hardware element of the ECU 40 such as a CPU that executes the program.

  The mode determination unit 42 determines whether or not a condition for performing feedback control (hereinafter, “feedback execution condition”) is satisfied based on the operation state. If the feedback execution condition is satisfied, the mode determination unit 42 sets the “feedback mode” as the control mode, and corrects the operation amount so that the air-fuel ratio is close to the theoretical air-fuel ratio based on the output of the air-fuel ratio detection means. Implement feedback control. If the feedback execution condition is not satisfied, the mode determination unit 42 sets “non-feedback mode” as the control mode, and the ECU 40 performs non-feedback control that determines the operation amount regardless of the output of the air-fuel ratio detection means. For example, at the time of high load and sudden acceleration, the feedback execution condition is not satisfied.

  The operation amount determination unit 43 includes a throttle opening determination unit 51 and an injector valve opening period determination unit 52. The throttle opening determination unit 51 determines a position command value of the valve motor 16 according to the operating state according to an opening map (not shown) stored in the storage unit 41. The ECU 40 drives the valve motor 16 according to the determined position command value, whereby the throttle opening is controlled according to the operating state. For example, the throttle opening is controlled to be proportional to the accelerator operation amount, and the output of the internal combustion engine 1 (see FIG. 1) and the propulsive force and speed of the vehicle are adjusted according to the driver's request.

  The injector valve opening period determining unit 52 determines the valve opening period of the injector 18 according to the operating state, and the ECU 40 monitors the output of the crank angle sensor 31 and opens the valve only from the appropriate timing for the valve opening period. A valve opening command is given to the injector 18. The valve opening period TAU is determined using, for example, the following equation (1A).

TAU = TBASE × FFB (1A)
TBASE is a standard value of the valve opening period, and FFB is a feedback correction coefficient. When using the equation (1A), the valve opening period TAU is obtained by multiplying and correcting the standard value TBASE by a correction coefficient. However, this is only an example, and the valve opening period TAU may be obtained by adding / subtracting a correction amount to / from the standard value TBASE.

  The feedback correction coefficient FFB corrects the valve opening period TAU from the standard value TBASE so that the air-fuel ratio approaches the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means during the feedback control. During the execution of the non-feedback control, the feedback correction coefficient FFB is set to the reference value, so that the valve opening period TAU is not corrected by the feedback correction coefficient FFB. When using the formula (1A), the reference value of the feedback correction coefficient FFB is 1. As derived from the equation (1A), the correction amount TFB of the valve opening period TAU by the feedback correction coefficient FFB is a value obtained by subtracting the standard value TBASE from the product of the standard value TBASE and the feedback correction coefficient FFB (TFB = TBASE). * FFB-TBASE = TBASE (FFB-1)).

  The standard value TBASE is a valve opening period corresponding to the operation state. In this embodiment, during the non-feedback correction, the valve opening period TAU is set to the standard value TBASE (see the second embodiment for cases where this is not the case). The standard value TBASE satisfies various demands on the output characteristics of the internal combustion engine 1 (see FIG. 1) and the characteristics of combustion exhaust gas (for example, contained components) when the valve opening period TAU is set to the standard value TBASE. It is set according to the driving state so as to be an assumed standard value ABASE suitable for the driving region in consideration. The assumed standard value ABASE of the air-fuel ratio is assumed initially (that is, at the design stage of the vehicle, the internal combustion engine 1 and the air-fuel ratio control device), similarly to the standard value TBASE during the valve opening period. The assumed standard value ABASE of the air-fuel ratio is not necessarily the stoichiometric air-fuel ratio. For example, in a high-powered motorcycle, the assumed standard value ABASE of the air-fuel ratio is a rich value over almost the entire driving state as a result of taking the above requirements into consideration.

  For example, the storage unit 41 stores in advance a first correspondence 61 that defines a standard value TBASE corresponding to the operating state. The first correspondence relationship 61 defines a plurality of operation regions by throttle opening and engine speed, and associates the plurality of operation regions with a plurality of standard values TBASE on a one-to-one basis (see FIG. 3). In this case, the injector valve opening period determination unit 52 can determine the standard value TBASE corresponding to the operating state according to the first correspondence 61. However, the first correspondence 61 is not limited to a table or map form, and may be an arithmetic expression. The standard value TBASE may be determined according to the operating state other than the throttle opening and the engine speed according to the first correspondence 61.

  The feedback correction coefficient FFB according to the present embodiment is an air excess ratio correction coefficient (hereinafter referred to as “λ correction coefficient”) FO2RAM set based on the operating state and the air / fuel ratio to the stoichiometric air / fuel ratio based on the output of the air / fuel ratio detection means. And a fluctuation correction coefficient VFFB variably set so as to be close to each other. Considering this point, the expression (1A) can be transformed into the following expression (2A).

TAU = TBASE × FO2RAM × (1 + FVFB) (2A)
In the equation (2A), the feedback correction coefficient FFB is the product of the λ correction coefficient FO2RAM and the value obtained by adding 1 to the fluctuation correction coefficient VFFB, the reference value of the λ correction coefficient FO2RAM is 1, and the reference value of the fluctuation correction coefficient FVFB Is zero. However, this is an example, and the feedback correction coefficient FFB may be a product of two coefficients FO2RAM and VFFB (FFB = FO2RAM × FFFB). In this case, both reference values are 1. During the execution of non-feedback control, the two coefficients FO2RAM and VFFB are set to reference values.

  The λ correction coefficient FO2RAM is a correction coefficient that is multiplied by the standard value TBASE in order to change the air-fuel ratio from the assumed standard value ABASE to the theoretical air-fuel ratio AST. In other words, the λ correction coefficient FO2RAM is an excess air ratio obtained by dividing the assumed standard value ABASE corresponding to the standard value TBASE by the theoretical air-fuel ratio AST (FO2RAM = ABASE / AST). Hereinafter, a value obtained by multiplying and correcting the standard value TBASE by the corresponding λ correction coefficient FO2RAM is referred to as “theoretical value TST” (TST = TBASE × FO2RAM).

  For example, the storage unit 41 stores in advance a second correspondence 62 that defines a λ correction coefficient FO2RAM corresponding to the operating state. The second correspondence relationship 62 defines a plurality of operation regions exactly the same as the first correspondence relationship 61, and associates the plurality of operation regions with the plurality of λ correction coefficients FO2RAM on a one-to-one basis (see FIG. 4). That is, the λ correction coefficient FO2RAM is associated with the standard value TBASE on a one-to-one basis for each operating region defined by the correspondences 61 and 62 via the first and second correspondences 61 and 62. In this case, during the feedback control, the injector valve opening period determination unit 52 determines the standard value TBASE according to the operating state according to the first correspondence 61 and λ correction according to the same operating state according to the second correspondence 62. The coefficient FO2RAM is determined, and the standard value TBASE is multiplied and corrected by the λ correction coefficient FO2RAM.

  The standard value TBASE is initially determined. If the standard value TBASE is determined, the corresponding λ correction coefficient FO2RAM is uniquely determined, and the theoretical value TST is also determined. Therefore, in the second correspondence relationship, a plurality of operation regions may be associated with a plurality of theoretical values TST on a one-to-one basis. In this case, during the feedback control, the injector valve opening period determination unit 52 does not use the first correspondence 61 but directly determines the theoretical value TST according to the operating state according to the second correspondence according to this modification. To do.

  FIG. 5A is a diagram illustrating an example of the valve opening period and the air-fuel ratio when the air-fuel ratio control apparatus is in an ideal state without individual differences, deterioration, or abnormality. In this case, as shown in FIG. 5A, when the valve opening period TAU is set to the standard value TBASE during the non-feedback control, the actual air-fuel ratio ABASE (A) at that time is assumed to be the assumed standard value ABASE. (See bar a-1). When the feedback control is started and the valve opening period TAU is set to the theoretical value TST, the actual air-fuel ratio AST (A) at that time becomes equal to the theoretical air-fuel ratio AST (see bar a-2). As derived from the equation (2A), the correction amount TO2RAM of the valve opening period TAU by the λ correction coefficient FO2RAM is a value obtained by subtracting the standard value TBASE from the product of the standard value TBASE and the λ correction coefficient FO2RAM, that is, the theoretical value TST. It is a value obtained by subtracting the standard value TBASE from (TO2RAM = TBASE × FO2RAM−TBASE = TST−TBASE).

  When the operating state changes during the feedback control and the standard value TBASE is changed, the λ correction coefficient FO2RAM is also changed at the same time. For this reason, the valve opening period TAU is set to the theoretical value TST corresponding to the operating state after the change, and the air-fuel ratio is maintained at the theoretical air-fuel ratio AST.

  FIGS. 5B and 5C are diagrams showing examples of the valve opening period and the air-fuel ratio when there are individual differences or deterioration in the air-fuel ratio control apparatus. As shown in FIG. 5B, even if the valve opening period TAU is set to the standard value TBASE during the non-feedback control, the actual air-fuel ratio ABASE (A) at that time may be lower than the assumed standard value ABASE. (See bar b-1). That is, the actual fuel amount becomes larger than the initially assumed fuel amount corresponding to the standard value TBASE, or the actual intake amount is larger than the initially assumed intake amount corresponding to the operation state associated with the standard value TBASE. May be less. In this case, even if the feedback control is started and the valve opening period TAU is set to the theoretical value TST, the actual air-fuel ratio AST (A) at that time may be lower than the theoretical air-fuel ratio AST (bar b-2). reference).

  As shown in FIG. 5C, even if the valve opening period TAU is set to the standard value TBASE during the non-feedback control, the actual air-fuel ratio ABASE (A) at that time can exceed the assumed standard value ABASE. (See bar c-1). That is, the actual fuel amount is smaller than the initially assumed fuel amount corresponding to the standard value TBASE, or the actual intake amount is more than the initially assumed intake amount corresponding to the operation state associated with the standard value TBASE. May also increase. In this case, even if the feedback control is started and the valve opening period TAU is set to the theoretical value TST, the actual air-fuel ratio AST (A) at that time may exceed the theoretical air-fuel ratio AST (bar c-2). reference).

  In this embodiment, since the air-fuel ratio detection means is composed of the O2 sensor 38, how far the actual air-fuel ratio ABASE (A) is from the assumed standard value ABASE, and the actual air-fuel ratio AST (A) is theoretically. It is impossible to accurately detect how far away from the air-fuel ratio AST. On the other hand, the fluctuation correction coefficient FVFB changes based on the output of the O2 sensor 38 during the feedback control, and corrects the valve opening period TAU step by step with time. The valve opening period TAU is first corrected from the standard value TBASE to the theoretical value TST using the λ correction coefficient F02RAM, and then secondarily corrected from the theoretical value TST using the fluctuation correction coefficient FVFB. The fluctuation correction coefficient FFB can compensate for an air-fuel ratio error (AST (A) -AST) caused by individual differences or deterioration, and thereby the air-fuel ratio is brought closer to the stoichiometric air-fuel ratio AST (bar b- 3 and c-3).

  As derived from the equation (2A), the correction amount TVFB of the valve opening period TAU based on the fluctuation correction coefficient FVFB is obtained by multiplying the standard value TBASE by the product of the standard value TBASE, the λ correction coefficient F02RAM, and the value obtained by adding 1 to the fluctuation correction coefficient FVFB. A value obtained by subtracting the product of the λ correction coefficient FO2RAM, that is, the product of the theoretical value TST and the fluctuation correction coefficient VFFB (TFFB = TBASE × FO2RAM × (1 + FVFB) −TBASE × FO2RAM = TST × FVFB).

  When the operating state changes during the feedback control and the standard value TBASE is changed, the λ correction coefficient FO2RAM is also changed at the same time, and the theoretical value TST is changed to a value corresponding to the changed operating state. Since the correction amount TFFB by the fluctuation correction coefficient VFFB is a product of the theoretical value TST and the fluctuation correction coefficient VFFB, it is automatically changed depending on the changed theoretical value TST. Therefore, even if the operating state changes and the intake air amount changes, the air-fuel ratio error can be continuously compensated without greatly changing the value of the fluctuation correction coefficient VFFB.

  FIG. 6 is a graph showing an example of a method for setting the fluctuation correction coefficient VFFB. The left side of FIG. 6 shows an example of the fluctuation correction coefficient VFFB in the case shown in FIG. 5B, and the right side of FIG. 6 shows an example of the fluctuation correction coefficient VFFB in the case shown in FIG. Yes. As shown in FIG. 6, when feedback control is started, the fluctuation correction coefficient VFFB is first set to a reference value. On the other hand, although not shown in detail in FIG. 6, when feedback control is started, the λ correction coefficient FO2RAM is set to a value corresponding to the operating state, and the valve opening period TAU is set to the theoretical value TST.

  As shown on the left side of FIG. 6, in the case shown in FIG. 5B, immediately after the valve opening period TAU is set to the theoretical value TST, the output characteristic of the O2 sensor 38 shows a rich state. The fluctuation correction coefficient FVFB changes based on the output of the O2 sensor 38 so that the air-fuel ratio approaches the stoichiometric air-fuel ratio. That is, the fluctuation correction coefficient FVFB gradually decreases so that the air-fuel ratio approaches the stoichiometric air-fuel ratio from the rich state. When the output characteristic of the O2 sensor 38 is inverted, the fluctuation correction coefficient VFFB is inverted in increase / decrease. When the output characteristics and the increase / decrease tendency are reversed, the fluctuation correction coefficient VFFB may be changed with the increase / decrease reversed from the value at the time of inversion after skipping to the inversion side by a predetermined skip value. Here, since the fluctuation correction coefficient VFFB gradually decreases, the fluctuation correction coefficient VFFB is skipped so as to increase by a predetermined skip value from the value at the time of inversion, and then gradually increases. Thereafter, every time the output characteristic of the O2 sensor 38 is inverted, the fluctuation correction coefficient VFFB is skipped and the increase / decrease is inverted. The greater the air / fuel ratio error, the greater the amount of change from the reference value of the fluctuation correction coefficient VFFB.

  As shown on the right side of FIG. 6, the same applies to the case shown in FIG. Immediately after the valve opening period TAU is set to the theoretical value TST, the output characteristic of the O2 sensor 38 shows a lean state. The fluctuation correction coefficient FVFB changes based on the output of the O2 sensor 38 so that the air-fuel ratio approaches the stoichiometric air-fuel ratio. In this case, the fluctuation correction coefficient FVFB first increases gradually.

  FIG. 7 is a flowchart showing an example of air-fuel ratio control and abnormality diagnosis executed by the air-fuel ratio control apparatus and its abnormality diagnosis apparatus. This flow is repeatedly executed every other engine cycle while the ECU 40 and the internal combustion engine 1 are in operation. As shown in FIG. 7, the throttle opening determining unit 51 determines the target position of the valve motor 16 and thus the target throttle opening according to the accelerator operation amount (S1). The injector valve opening period determining unit 52 determines the standard value TBASE of the valve opening period according to the operating state (for example, the operating range defined by the engine speed and the throttle opening) according to the first correspondence 61 (S2). ).

  The mode determination unit 42 determines whether the feedback execution condition is successful (S3). If the feedback execution condition is not satisfied (S3: NO), the ECU 40 performs non-feedback control. As part of this, the injector valve opening period determination unit 52 sets the feedback correction coefficient FFB to a reference value (S11). That is, the λ correction coefficient FO2RAM is set to the reference value (1), and the fluctuation correction coefficient VFFB is set to the reference value (zero).

  Next, the injector valve opening period determination unit 52 determines the valve opening period TAU (S30). In the present embodiment, the valve opening period TAU is set to the standard value TBASE during the non-feedback control. The injector valve opening period determination unit 52 monitors the output of the crank angle sensor 31, and gives an opening command to the injector 18 during the valve opening period TAU determined in step S30 from that time when the output becomes appropriate. If the air-fuel ratio control apparatus is in an ideal state as shown in FIG. 5A, the air-fuel ratio becomes the assumed standard value ABASE. Therefore, as initially intended, the output characteristics of the internal combustion engine 1 and the properties of the combustion exhaust gas are suitable for the operating state. If individual differences or deterioration occurs as shown in FIGS. 5B and 5C, an error occurs between the actual air-fuel ratio ABASE (A) and the assumed standard value ABASE. Due to this error, the output characteristics of the internal combustion engine 1 and the properties of the combustion exhaust gas may deviate from the initial aims.

  If the feedback execution condition is satisfied (S3: YES), the ECU 40 performs feedback control. As part of this, the injector valve opening period determination unit 52 determines the λ correction coefficient FO2RAM according to the operating state according to the second correspondence 62, and determines the fluctuation correction coefficient VFFB based on the output of the O2 sensor 38 (S14). . The method for setting the fluctuation correction coefficient FVFB is as described above. Next, abnormality diagnosis processing of the air-fuel ratio control device is executed (S20).

  FIG. 8 is a flowchart showing the procedure of the abnormality diagnosis process S20 of the air-fuel ratio control apparatus. As shown in FIG. 8, in the abnormality diagnosis process S20, the diagnosis unit 44 determines whether or not a condition for performing diagnosis (hereinafter referred to as “diagnosis permission condition”) is successful (S21). If the diagnosis permission condition is not satisfied (S21: NO), the abnormality diagnosis process S20 is terminated, and the process proceeds to step S30 (see FIG. 7). If the diagnosis permission condition is satisfied (S21: YES), the diagnosis unit 44 diagnoses an abnormality of the air-fuel ratio control device (S22). If it is diagnosed that there is no abnormality (S22: NO), the abnormality diagnosis processing S20 is terminated, and the process proceeds to step S30. If it is diagnosed as abnormal (S22: YES), the alarm device is activated (S23), and the process proceeds to step S30. In the abnormality diagnosis process S20, one of the three routes is followed to proceed to step S30. In step S30, the standard value TBASE determined in step S2 and the two coefficients FO2RAM and VFFB determined in step S14 are used. Thus, the valve opening period TAU is determined.

  FIGS. 9A to 9C are graphs showing examples of diagnosis permission conditions. The diagnosis permission condition includes a first diagnosis permission condition (see FIG. 9A) that the driving state is stably changing, and a second diagnosis permission condition that the fluctuation correction coefficient VFFB is stably changing. (See FIGS. 9B and 9C). The diagnosis permission condition may be satisfied when both the first diagnosis permission condition and the second diagnosis permission condition are satisfied, or may be satisfied when one of the conditions is satisfied.

  As shown in FIG. 9A, for example, the first diagnosis permission condition is defined by a lower limit threshold and an upper limit threshold during a first predetermined period P1 until the throttle opening reaches the condition determination time point (current time). It is a condition that the change is within an allowable range. A solid line a1 indicates a case where the condition is satisfied. When staying for the first predetermined period P1 within the region above the upper threshold or below the lower threshold (see broken lines a2 and a3), or when accelerating or decelerating to cross either threshold ( The conditions are not satisfied at the broken lines a4 and a5). The first diagnosis permission condition has a similar condition regarding the engine speed. The first diagnosis permission condition may be satisfied when both the condition related to the throttle opening and the condition related to the engine speed are satisfied, or may be satisfied when one is satisfied.

  As shown in FIG. 9B, for example, the second diagnosis permission condition is the maximum value VFFBmax among the plurality of variation correction coefficients VFFB acquired within the second predetermined period P2 up to the condition determination time point (current time). This is a condition that the difference dVFFBmm from the minimum value VFFBmin is less than a predetermined value. As shown in FIG. 9C, for example, the second diagnosis permission condition is that the change rate dFVFBav of the average value VFFBav of the fluctuation correction coefficient VFFB is during the third predetermined period P3 until the condition determination time point (current time). It is a condition that the transition is within a predetermined range defined by the upper limit threshold and the lower limit threshold. The average value VFFBav is an average of a plurality of variation correction coefficients VFFB acquired within the fourth predetermined period P4 (see FIG. 9B) until the calculation time point, and the average is an arithmetic average or a weighted average. In the case of a weighted average, the weighting coefficient may be higher as the correction amount is closer to the time of calculation. The second diagnosis permission condition may be satisfied when both of the condition regarding the difference dFVFBmm and the condition regarding the change rate dFVFBav are satisfied, or may be satisfied when one of the conditions is satisfied. The first to fourth predetermined periods P1 to P4 may have the same length or different lengths.

  In step S22, the diagnosis unit 44 detects an abnormality in the air-fuel ratio control device based on the correction value associated with the correction amount for the valve opening period TAU as an example of the operation amount and the comparison value set regardless of the correction. Diagnose. The “correction amount” that is the basis of the correction value used for diagnosis includes the correction amount TFB of the valve opening period during the execution of feedback control. The correction amount TFB includes a correction amount TO2RAM based on the λ correction coefficient FO2RAM and a correction amount TFFB based on the variation correction coefficient VFFB. These correction amounts TFB, TO2RAM, TFFB are determined by the coefficients FFB, FO2RAM, FVFB. In this document, the “correction amount” that is the basis of the correction value used for diagnosis includes not only the correction amounts TFB, TO2RAM, TFFB itself for the valve opening period TAU, but also the coefficients FFB, F02RAM, FVFB that determine them.

  The “correction amount” is updated every engine cycle. The “correction value” associated with the correction amount may be the current value of the correction amount set to determine the valve opening period TAU in the current engine cycle. Further, the “correction value” may be an average value of correction amounts acquired within a predetermined period. The predetermined period is, for example, the current engine cycle and one or more engine cycles in the past.

  The correction value according to the present embodiment is a correction amount that is secondarily required from when the standard value TBASE is temporarily corrected to the theoretical value TST until the air-fuel ratio reaches the vicinity of the theoretical air-fuel ratio, that is, The correction amount TFFB and the fluctuation correction coefficient VFFB that determines the correction amount TFFB are set. For example, the correction value is the current value of the fluctuation correction coefficient VFFB and the average value of the fluctuation correction coefficient VFFB.

  On the other hand, the “comparison value” used for diagnosis is set regardless of the correction amount. For example, the comparison value is stored in advance in the storage unit 41. At this time, the comparison value may be a constant value regardless of the operating state. A plurality of comparison values may be associated with each of the plurality of operation regions defined by the first and second correspondences 61 and 62 on a one-to-one basis. The comparison value may be obtained by a function that does not include the valve opening period TAU and its correction value.

  The “comparison value” includes an upper limit comparison value and a lower limit comparison value, and these two comparison values define an allowable range of the correction value. Based on the comparison between the correction value and the comparison value (upper limit comparison value and lower limit comparison value), the diagnosis unit 44 sets a condition (hereinafter, referred to as “abnormal condition”) that gives a diagnosis result that the air-fuel ratio control device is abnormal. Determine success or failure.

  FIGS. 10A and 10B are graphs showing examples of abnormal conditions. As shown in FIG. 10A, the abnormal condition is that the current value of the fluctuation correction coefficient VFFB exceeds the upper limit comparison value U1 and the lower limit comparison value L1 and is outside the allowable range R1 for a predetermined period P11. Including conditions. As shown in FIG. 10B, the abnormal condition is such that the average value FVFBav of the fluctuation correction coefficient FVFB exceeds the upper limit comparison value U2 and the lower limit comparison value L2 and is outside the allowable range R2 for a predetermined period P12. Including conditions. The two periods P11 and P12 may have the same length or different lengths.

  FIG. 11 is an explanatory diagram of the abnormal condition illustrated in FIG. As described above, the correction amount TVFB for the valve opening period TAU based on the fluctuation correction coefficient FVFB is the product of the theoretical value TST and the fluctuation correction coefficient FVFB. Therefore, in FIG. 11, the fluctuation correction coefficient VFFB, the upper limit comparison value U1, and the lower limit comparison value L1 are converted into products with the theoretical value TST and represented on the valve opening period axis. As shown in FIG. 11, during the feedback control, correction by the fluctuation correction coefficient VFFB is performed, and if the current value of the fluctuation correction coefficient VFFB is within the allowable range R1, the air-fuel ratio control apparatus is diagnosed as not abnormal. (See bar 3). The ECU 40 diagnoses that the air-fuel ratio control device is not abnormal even when the current value of the fluctuation correction coefficient VFFB goes out of the allowable range R1 and returns to the allowable range R1 within the predetermined period P11 (see FIG. 10A). To do. In these cases, the ECU 40 continues to perform control to compensate for an error in the air-fuel ratio, if allowed. When the fluctuation correction coefficient VFFB goes out of the allowable range R1 and the predetermined period P11 has elapsed, the ECU 40 determines that the air-fuel ratio error cannot be corrected appropriately even by correction using the fluctuation correction coefficient VFFB. Is diagnosed (see bar 4).

  The case where the correction value falls below the lower limit comparison value occurs when the output characteristic of the O2 sensor 38 continues to show a rich state and the fluctuation correction coefficient VFFB and its average value VFFBav continue to decrease. That is, it occurs when the output characteristic of the O2 sensor 38 continues to indicate a rich state even if the valve opening period TAU is shortened to reduce the fuel amount. As an abnormality of the air-fuel ratio control device assumed in such a case, the valve closing of the injector 18 due to foreign matter biting in the injection port of the injector 18, the filter of the air cleaner 11 is clogged, the throttle valve on the throttle opening closing side 15 stacks, poor detection of the O2 sensor 38 (underestimation of oxygen concentration), disconnection of the O2 sensor 38, and the like.

  The case where the correction value exceeds the upper limit comparison value occurs when the output characteristic of the O2 sensor 38 continues to indicate a lean state and the fluctuation correction coefficient VFFB and its average value VFFBav continue to increase. That is, it occurs when the output characteristic of the O2 sensor 38 continues to indicate a lean state even if the valve opening period TAU is increased to increase the amount of fuel. As an abnormality of the air-fuel ratio control device assumed in such a case, the fuel pump 17 discharge failure, the injector 18 valve opening failure, the fuel pipe 19 seal failure, the throttle valve 15 stack on the throttle opening opening side, The detection failure of the O2 sensor 38 (overestimation of oxygen concentration), the disconnection of the O2 sensor 38, etc. are conceivable.

  In the abnormality diagnosis device according to the present embodiment, the injector valve opening period determination unit 52 of the ECU 40 is an example of the operation amount of the air-fuel ratio control device so that the air-fuel ratio approaches the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means. The valve opening period TAU is corrected. Based on the correction value associated with the correction amount for the valve opening period TAU and the comparison value set regardless of the correction in the injector valve opening period determination unit 52, the diagnosis unit 44 of the ECU 40 determines the abnormality of the air-fuel ratio control device. Diagnose. Thus, since the comparison value that does not depend on the correction amount is used for the abnormality diagnosis, even if an initial failure exists in the air-fuel ratio control device, the comparison value does not include the influence. For this reason, the diagnosis unit 44 of the ECU 40 can detect an initial failure. Further, even when it is recognized that the deterioration has gradually progressed and the air-fuel ratio control apparatus has become abnormal, it becomes easy to detect this. Therefore, the reliability of the abnormality diagnosis device is increased. In particular, since the correction value is based on the current value or the average value rather than the change rate of the correction amount (difference between the current value and the past value or the average value), it is easy to detect an abnormality accompanying the gradual progress of deterioration.

  The mode determination unit 42 of the ECU 40 performs a feedback control in which the air-fuel ratio is brought close to the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means, and non-feedback for determining the operation amount without being based on the output of the air-fuel ratio detection means The control mode is switched between the non-feedback mode in which the control is performed. When the feedback control is started, the injector valve opening period determination unit 52 corrects the valve opening period TAU from the standard value TBASE according to the second correspondence relation 62, and then the valve opening period TAU is secondarily stepwise with time. The air-fuel ratio is made closer to the theoretical air-fuel ratio AST by correcting to. For this reason, when the air-fuel ratio control apparatus is not abnormal, it is possible to shorten the time required for the air-fuel ratio to approach the stoichiometric air-fuel ratio AST. As a result, when the air-fuel ratio control device is abnormal, it is possible to shorten the time until it is detected.

  The correction value is based on a secondary fluctuation correction coefficient VFFB from when the valve opening period TAU is corrected to the theoretical value TST according to the second correspondence 62 until the air-fuel ratio reaches the theoretical air-fuel ratio AST. Is set. If the valve opening period TAU is set primarily according to the second correspondence 62, the air-fuel ratio should reach the stoichiometric air-fuel ratio AST if the air-fuel ratio control device is in an ideal state with no individual differences, deterioration, or abnormality. It is. The fluctuation correction coefficient FVFB is used to compensate for an error in the air-fuel ratio that occurs because the air-fuel ratio control device does not. Conversely, if the air-fuel ratio control apparatus is in an ideal state, the fluctuation correction coefficient VFFB hardly fluctuates from the reference value (although there may be fluctuation for the skip value). Since the correction value used for abnormality diagnosis is set based on such a correction amount, it is easy to distinguish whether the error is allowable due to individual differences or deterioration, or whether an abnormality has occurred. Therefore, the reliability of the abnormality diagnosis device is increased.

  The total correction amount TFB from the standard value TBASE of the valve opening period TAU necessary for the air-fuel ratio to become the stoichiometric air-fuel ratio AST varies depending on the operating state. This is because the intake air amount is different, and the assumed standard value ABASE of the air-fuel ratio is different depending on the operation state. However, if the valve opening period TAU is temporarily corrected to the theoretical value TST in accordance with the second correspondence relationship 62, the correction amount TFFB required thereafter does not change greatly due to changes in the operating state. In addition, in the present embodiment, the correction amount TFFB is a value obtained by multiplying the theoretical value TST by the fluctuation correction coefficient VFFB, and the fluctuation correction coefficient VFFB does not have to be changed sensitively according to changes in the operating state. Therefore, the comparison value does not need to be greatly changed according to the operating state, and the comparison value can be easily set.

  The diagnosis unit 44 diagnoses that the air-fuel ratio control apparatus is abnormal when the state where the correction value exceeds the comparison value continues for a predetermined time. For this reason, even when the correction value instantaneously exceeds the comparison value due to the influence of noise or the like, the diagnosis accuracy of the diagnosis unit 44 is improved. Further, the average value of the correction amount is also adopted as the correction value. For this reason, even if the current value momentarily exceeds the comparison value due to the influence of noise or the like, the diagnosis accuracy of the diagnosis unit 44 is improved.

  The diagnosis unit 44 performs abnormality diagnosis of the air-fuel ratio control device when the diagnosis permission condition is satisfied, and does not perform abnormality diagnosis of the air-fuel ratio control device if the diagnosis permission condition is not satisfied. The diagnosis permission condition includes a first diagnosis permission condition that the driving state is stably changing and a second diagnosis permission condition that the fluctuation correction coefficient VFFB is stably changing. Since the abnormality diagnosis is performed when the operation state and the fluctuation correction coefficient VFFB are stable, the diagnosis accuracy of the diagnosis unit 44 is improved.

  When the air-fuel ratio control device is diagnosed as abnormal, the ECU 40 activates the alarm device 39. As a result, the driver can be notified of the abnormality of the air-fuel ratio control device, and the driver can be encouraged to take appropriate measures.

(Second Embodiment)
FIG. 12 is a block diagram showing the configuration of the air-fuel ratio control device and its abnormality diagnosis device according to the second embodiment. In the present embodiment, the fluctuation correction coefficient FVFB is mainly divided into a closed loop correction coefficient FAF and a learning correction coefficient FLAF, and the valve opening period TAU is corrected using the deterioration correction coefficient FDLAF during the non-feedback control. , And that the abnormal condition includes conditions based on these coefficients FAF, FLAF, and FDLAF. Hereinafter, the second embodiment will be described focusing on this difference.

  The ECU 240 according to the present embodiment includes an operation amount determination unit 243, and the injector valve opening period determination unit 252 determines the valve opening period TAU using the equation (1B).

TAU = TBASE × FFB × (1 + FDLAF) (1B)
FDLAF is a deterioration correction coefficient. During the feedback control, the deterioration correction coefficient FDLAF is set to the reference value, and the valve opening period TAU is not corrected by the deterioration correction coefficient FDLAF. When Expression (1B) is used, the reference value of the deterioration correction coefficient FDLAF is zero.

  The feedback correction coefficient FVFB includes a λ correction coefficient F02RAM and a fluctuation correction coefficient FVFB, and the fluctuation correction coefficient FVFB includes a closed loop correction coefficient FAF and a learning correction coefficient FLAF. Considering this point, the expression (1B) can be transformed into the following expression (2B).

TAU = TBASE × FO2RAM × (1 + FAF + FLAF) × (1 + FDLAF) (2B)
As shown in Expression (2B) and Expression (2A) according to the first embodiment, the sum of the closed loop correction coefficient FAF and the learning correction coefficient FLAF corresponds to the fluctuation correction coefficient VFFB according to the first embodiment. When using the equation (2B), the reference values of the coefficients FAF and FLAF are zero. During the non-feedback control, the coefficients FO2RAM, FAF, and FLAF are all set to reference values. The correction amount TAF by the closed loop correction coefficient FAF is the product of the theoretical value TST and the closed loop correction coefficient FAF (TAF = TST × FAF), and the correction amount TLAF by the learning correction coefficient FLAF is the product of the theoretical value TST and the learning correction coefficient FLAF. (TLAF = TST × FLAF).

  FIG. 13 is a graph showing an example of a method for setting the closed loop correction coefficient FAF and the learning correction coefficient FLAF. Here, it is assumed that the output characteristic of the O2 sensor 38 shows a rich state even when the feedback control is started and the valve opening period TAU is set to the theoretical value TST. In this case, the closed loop correction coefficient FAF and the learning correction coefficient FLAF are gradually decreased based on the output of the O2 sensor 38 so as to bring the air-fuel ratio closer to the theoretical air-fuel ratio AST.

  When the output characteristic of the O2 sensor 38 is reversed, the closed loop correction coefficient FAF increases by a predetermined skip value and then gradually increases so that the air-fuel ratio approaches the stoichiometric air-fuel ratio. Next, when the output characteristic of the O2 sensor 38 is inverted, the closed loop correction coefficient FAF is decreased by a predetermined skip value, and then gradually decreased so that the air-fuel ratio approaches the stoichiometric air-fuel ratio. Thereafter, the variation of the closed loop correction coefficient FAF is repeated until the feedback control is completed.

  The learning correction coefficient FLAF continues to decrease until the closed loop correction coefficient FAF crosses a predetermined learning stop value FAFstop when the closed loop correction coefficient FAF is skipped. Note that the learning stop value FAFstop may be a reference value, or the two learning stop values FAFstop may be set so as to sandwich the reference value of the closed loop correction coefficient FAF. When the closed loop correction coefficient FAF crosses the learning stop value FAFstop, the learning correction coefficient FLAF is fixed at the value at that time until the feedback control is finished thereafter.

  When the closed loop correction coefficient FAF decreases, the decrease in the learning correction coefficient FLAF is taken into account, and the time until the output characteristic of the O2 sensor 38 is reversed is shortened. When the closed-loop correction coefficient FAF increases, the air-fuel ratio is brought closer to the stoichiometric air-fuel ratio against the decrease of the learning correction coefficient FLAF, so that the time until the output characteristic of the O2 sensor 38 is reversed becomes longer. Therefore, the closed loop correction coefficient FAF approaches the reference value while inverting the increase / decrease. In order to realize this, the change rate of the learning correction coefficient FLAF is smaller than the change rate of the closed loop correction coefficient FAF.

  As described above, when the two coefficients FAF and FLAF both decrease after the feedback control is started and the air-fuel ratio error is compensated once (the output characteristic of the O2 sensor 38 is reversed), the learning correction coefficient FLAF becomes the closed loop correction coefficient FAF. While the initial decrease (error compensation) continues to decrease, the closed loop correction coefficient FAF returns to the reference value while repeatedly increasing and decreasing. The coefficient value is transferred while monitoring the output of the O2 sensor 38. Therefore, this delivery is performed while maintaining the air-fuel ratio in the vicinity of the theoretical air-fuel ratio.

  That is, the learning correction coefficient FLAF is removed from the fluctuation correction coefficient FVFB according to the first embodiment by removing or increasing or skipping elements based on the output of the O2 sensor 38, and the valve opening period TAU is set to the theoretical value TST. This is a correction coefficient obtained by extracting an element that compensates for an error of the air / fuel ratio that occurs from the theoretical air / fuel ratio. The learning correction coefficient FLAF is updated and stored in the storage unit 241 every time feedback control is completed. Although detailed illustration is omitted, when the next feedback control is started, the learning correction coefficient FLAF is first set to a value stored in the storage unit 241. Therefore, the period from when the feedback control is started until the output characteristic of the O2 sensor 38 is once reversed is shortened.

  FIG. 14 is a diagram showing an example of the valve opening period and the air-fuel ratio when there is an individual difference or deterioration in the air-fuel ratio control apparatus shown in FIG. As shown in FIG. 14, even when the feedback control is started and the valve opening period TAU is set to the theoretical value TST, the actual air-fuel ratio AST (A) at that time may be different from the theoretical air-fuel ratio AST. Yes (see bar 2). During the feedback control, the air-fuel ratio error is compensated once by correction with the closed loop correction coefficient FAF and the learning correction coefficient FLAF (see bar 3), and then the learning correction coefficient FLAF gradually increases the error compensation of the closed loop correction coefficient FAF. Take care (see stick 4).

  When this feedback control is completed and non-feedback control is started, the valve opening period TAU is set to a value obtained by correcting the standard value TBASE with the deterioration correction coefficient FDLAF. The deterioration correction coefficient FDLAF compensates for the error when the actual air-fuel ratio ABASE (A) does not become the assumed standard value ABASE even if the valve opening period TAU is set to the standard value TBASE during non-feedback control. The valve opening period TAU is corrected from the standard value TBASE (see bar 5). Since FO2RAM = 1 and FAF, FLAF = 0 during non-feedback control, the correction amount TDLAF of the valve opening period TAU based on the deterioration correction coefficient FDLAF is derived from the standard value TBASE and deterioration correction, as derived from the equation (2B). The value obtained by subtracting TBASE from the product of the value obtained by adding 1 to the coefficient FDLAF, that is, the product of the standard value TBASE and the coefficient FDLAF (TDLAF = TBASE × (1 + FDLAF) −TBASE = TBASE × FDLAF).

  The deterioration correction coefficient FDLAF is set based on the learning correction coefficient FLAF. In the present embodiment, the deterioration correction coefficient FDLAF is set to the same value as the learning correction coefficient FLAF updated and stored in the storage unit 241 at the end of the immediately preceding feedback control (see the third embodiment for other cases). Thereby, when the actual air-fuel ratio ABASE (A) does not become the assumed standard value ABASE, the error can be compensated by the deterioration correction coefficient FDLAF. Therefore, the air-fuel ratio can be brought close to the assumed standard value ABASE, and the output characteristics of the internal combustion engine and the properties of the combustion exhaust gas can be kept good regardless of individual differences and the presence of deterioration.

  FIG. 15 is a flowchart showing an example of air-fuel ratio control and abnormality diagnosis executed by the air-fuel ratio control apparatus and abnormality diagnosis apparatus shown in FIG. As shown in FIG. 15, the target position of the valve motor 16 and thus the target throttle opening is determined (S201). The standard value TBASE is determined according to the first correspondence 61 (S202), and the success or failure of the feedback execution condition is determined (S203). If the feedback execution condition is not satisfied (S203: NO), non-feedback control is executed. As part of this, the feedback correction coefficient FFB is set as a reference value (S211), and the deterioration correction coefficient FDLAF is determined based on the learning correction coefficient FLAF (S212). If the feedback execution condition is satisfied (S203: YES), feedback control is performed. As part of this, the deterioration correction coefficient FDLAF is determined as a reference value (S213), and the feedback correction coefficient FFB is determined (S214). That is, the λ correction coefficient FO2RAM is determined according to the second correspondence 62, and the closed loop correction coefficient FAF and the learning correction coefficient FLAF are determined based on the output of the air-fuel ratio detection means.

  Next, abnormality diagnosis processing of the air-fuel ratio control device is executed (S220), and the valve opening period TAU is determined (S230). In the present embodiment, the abnormality diagnosis process S220 is executed even during the non-feedback control. The procedure itself of the abnormality diagnosis process S220 is the same as that of the first embodiment (see FIG. 8), and the diagnosis permission condition is also the same as that of the first embodiment.

  Regarding the abnormality diagnosis in step S22 (see FIG. 8), the “correction amount” that is the basis of the correction value used for the diagnosis is the correction amount TFB during the valve opening period during the feedback control and the opening amount during the non-feedback control. It includes a valve period correction amount TDLAF and a coefficient that determines these correction amounts. The correction amount TFB includes the correction amount TO2RAM based on the λ correction coefficient FO2RAM, the correction amount TAF based on the closed loop correction coefficient FAF, the correction amount TLAF based on the learning correction coefficient FLAF, and the fluctuation correction coefficient FVFB (the closed loop correction coefficient FAF and the learning correction coefficient FLAF). Sum)) and the correction amount TVFB. The correction amounts TFB, TO2RAM, TAF, TLAF, TFFB, and TDLAF are determined by the coefficients FFB, FO2RAM, FAF, FLAF, FVFB, and FDLAF.

  The correction value according to the present embodiment is based on a correction amount that is secondarily required after the standard value TBASE is temporarily corrected to the theoretical value TST until the air-fuel ratio reaches the vicinity of the theoretical air-fuel ratio. Is set. The correction value includes the current value of the closed loop correction coefficient FAF, the average value of the closed loop correction coefficient FAF, the current value of the learning correction coefficient FLAF, and the current value of the fluctuation correction coefficient FVFB (the sum of the closed loop correction coefficient FAF and the learning correction coefficient FLAF). . The correction value includes the current value of the deterioration correction coefficient FDLAF. The deterioration correction coefficient FDLAF is set based on the learning correction coefficient FLAF, which is the correction amount that is secondarily required, and thus the current value of the deterioration correction coefficient FDLAF is also a value set based on the correction amount. is there. The comparison value is set corresponding to these correction values.

  While the feedback control is being performed, the abnormal condition is that the current value of the closed loop correction coefficient FAF exceeds the upper limit comparison value and the lower limit comparison value and is outside the allowable range, and the closed loop correction The condition that the average value of the coefficient FAF exceeds the upper limit comparison value and the lower limit comparison value and is outside the allowable range continues for a predetermined period, and the current value of the learning correction coefficient FLAF is the upper limit comparison value and the lower limit comparison value. The condition that the state of exceeding the allowable range is continued for a predetermined period, and the state that the current value of the fluctuation correction coefficient VFFB exceeds the upper limit comparison value and the lower limit comparison value is determined to be out of the allowable range Including the condition that the period continues. The diagnosis unit 244 may determine that the abnormal condition is satisfied when all of these conditions are satisfied, or may determine that the abnormal condition is satisfied when at least one of the conditions is satisfied.

  During the implementation of non-feedback control, the abnormal condition includes a condition that the current value of the degradation correction coefficient FDLAF exceeds the upper limit comparison value and the lower limit comparison value and is outside the allowable range for a predetermined period. .

  Also in this embodiment, during the feedback control, a reliable abnormality diagnosis can be performed in the same manner as in the above embodiment. In the present embodiment, the injector valve opening period determination unit 252 corrects the valve opening period TAU based on the correction amount set during the execution of the feedback control in the past during the execution of the non-feedback control. Therefore, the diagnosis unit 244 diagnoses the abnormality of the air-fuel ratio control device based on the correction value associated with the correction amount and the comparison value set regardless of the correction amount even during the non-feedback control. Can do.

  According to the above configuration, the fluctuation correction coefficient responsible for compensating for the air-fuel ratio error due to individual differences, deterioration or abnormality is learned as the learning correction coefficient, and the stored learning correction coefficient is changed from the start of the next O2 feedback control. To be taken into account. For this reason, the time from the start of feedback control to the completion of error compensation is shortened. Therefore, the output of the internal combustion engine 1 and the properties of the combustion exhaust gas are quickly changed to required ones.

  When an abnormality is diagnosed using the learning correction coefficient FLAF, even if the abnormality occurs before the feedback control is performed, the abnormality can be detected immediately after the feedback control is performed. Further, when an abnormality is diagnosed using the sum of the learning correction coefficient FLAF and the closed loop correction coefficient FAF, it becomes easy to detect even if the abnormality is recognized due to the gradual progress of deterioration.

(Third embodiment)
FIG. 16 is a block diagram illustrating a configuration of an air-fuel ratio control device and an abnormality diagnosis device thereof according to the third embodiment. In the present embodiment, the learning correction coefficient FLAF is mainly divided into the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF, the learning correction coefficient FLAF is stored corresponding to the driving state, and the deterioration correction coefficient FDLAF is long-term. This is different from the above embodiment in that it is set based on the learning coefficient FLLAF. Hereinafter, the third embodiment will be described focusing on this difference.

  The ECU 340 according to the present embodiment includes an operation amount determination unit 343, and the injector valve opening period determination unit 352 determines the valve opening period TAU using the above-described equation (1B). The feedback correction coefficient FVFB includes a λ correction coefficient F02RAM and a fluctuation correction coefficient FVFB. The fluctuation correction coefficient FVFB includes a closed loop correction coefficient FAF and a learning correction coefficient FLAF. The learning correction coefficient FLAF includes the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF. including. Considering this point, the expression (1B) can be transformed into the following expression (2C).

TAU = TBASE × FO2RAM × (1 + FAF + FRLAF + FLLAF)
× (1 + FDLAF)… (2C)
As shown in Expression (2C) and Expression (2B) according to the second embodiment, the sum of the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF corresponds to the learning correction coefficient FLAF according to the second embodiment. When Expression (2C) is used, the reference values of the two coefficients FLLAF and FRLAF are zero, and the coefficients FO2RAM, FAF, FRLAF, and FLLAF are all set to the reference values during the non-feedback control. The correction amount TRLAF based on the real-time learning coefficient FRLAF is the product of the theoretical value TST and the real-time learning coefficient FRLAF (TRLAF = TST × FRLAF). (TLLAF = TST × FLLAF).

  FIG. 17 is a graph showing an example of a method for setting the real-time learning coefficient FRLAF and the long-term learning coefficient FLLAF. As shown in FIG. 17, when feedback control is started, the learning correction coefficient FLAF (the sum of the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF) is set so that the closed-loop correction coefficient FAF has a learning stop value as described in the second embodiment. It changes gradually until it crosses. The long-term learning coefficient FLLAF does not change and only the real-time learning coefficient FLLAF changes. When the real-time learning coefficient FRLAF reaches the predetermined transition threshold values FTH1 and FTH2, the real-time learning coefficient FRLAF is subtracted by a predetermined transition value ΔF, while the long-term learning coefficient FLLAF is added by the transition value ΔF. Thus, the value is transferred from the real-time learning coefficient FRLAF to the long-term learning coefficient FLLAF while maintaining the sum of both coefficients FLLAF and FLLAF. If the closed-loop correction coefficient FAF has not yet crossed the learning stop value at this time, the long-term learning value does not change as the value after addition, and the real-time learning coefficient FRLAF continues to change gradually from the value after subtraction. The real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF are updated and stored in the storage unit 341.

  For example, the storage unit 341 stores a third correspondence 363 that associates the real-time learning coefficient FRLAF with the driving state, and a fourth correspondence 364 that associates the long-term learning coefficient FLLAF with the driving state. The third correspondence relationship 363 defines a plurality of operation regions by throttle opening and engine speed, and associates the plurality of operation regions with a plurality of real-time learning coefficients FRLAF on a one-to-one basis (see FIG. 18A). The fourth correspondence relationship 364 defines a plurality of operation regions by throttle opening and engine speed, and associates the plurality of operation regions with a plurality of real-time learning coefficients FRLAF on a one-to-one basis (see FIG. 18B). When the feedback control is finished, the actual learning coefficient FLLAF and the long-term learning coefficient FLLAF at that time are updated and stored in association with the operation region at that time. When the driving state changes during the feedback control, the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF at the time of change may be updated and stored in association with the driving region at that time. Although detailed illustration is omitted, when the next feedback control starts, the real-time learning coefficient FRLAF according to the driving state is read according to the third correspondence 363, and long-term learning according to the driving state according to the fourth correspondence 364. The coefficient FLLAF is read and the coefficients FLLAF and FLLAF are set to the read values.

  The deterioration correction coefficient FDLAF is set based on the long-term learning coefficient FLLAF stored in the fourth correspondence relationship 364 stored in the storage unit 341. For example, the deterioration learning coefficient FDLAF is a weighted average value of a plurality of long-term learning coefficients FLLAF associated with each of a plurality of driving regions. At this time, the weighting coefficient may be set to a larger value as the engine speed is smaller, and may be set to a larger value as the throttle opening is smaller. As a result, the sensitivity of fuel correction increases as the amount of intake air decreases, and correction for dealing with deterioration can be performed more accurately.

  The diagnosis unit 344 diagnoses an abnormality of the air-fuel ratio control device during the non-feedback control based on the comparison between the current value of the deterioration learning coefficient FDLAF set in this way and the corresponding comparison value. Also good.

(Fourth embodiment)
In FIG. 1, a configuration according to the fourth embodiment is also shown by a two-dot chain line. The present embodiment mainly includes a system in which the vehicle supplies secondary air to the exhaust port 22, and performs control for stabilizing the combustion state based on the output of the air-fuel ratio detection means using the system during idling. The control is different from the above-described embodiment in that the operation amount of the control target of the air-fuel ratio control device (for example, the valve opening period of the injector 18) is corrected, and the abnormal condition includes a condition based on this correction. Hereinafter, the fourth embodiment will be described focusing on this difference.

  As shown by a two-dot chain line in FIG. 1, in this embodiment, the clean side of the air cleaner 11 is connected to the exhaust port 22 via the secondary air supply pipe 426. The secondary air supply pipe 426 is opened and closed by a secondary air supply valve 427. When the secondary air supply valve 427 opens the secondary air supply pipe 426, the purified outside air bypasses the throttle device 12 and the combustion chamber 4 and is sent from the air cleaner 11 to the exhaust port 22. By supplying this secondary air to the exhaust port 22, the combustion exhaust gas can be reburned, and hydrocarbons and carbon monoxide in the combustion exhaust gas can be reduced. Secondary air supply valve 427 is controlled by ECU 440. Note that the backflow of the combustion exhaust gas is prevented by a check valve 428 arranged on the secondary air supply pipe 426 downstream of the secondary air supply valve 427.

  FIG. 19 is a block diagram illustrating a configuration of an air-fuel ratio control device and an abnormality diagnosis device thereof according to the fourth embodiment. If the internal combustion engine 1 (see FIG. 1) is in an idling state, the mode determination unit 442 sets “idle mode” as the control mode, and the air-fuel ratio including the secondary air is rich based on the output of the air-fuel ratio detection means. Idle deterioration correction control is performed to correct the operation amount so as not to occur. If the internal combustion engine 1 is not in the idling state, the mode determination unit 442 determines whether or not the feedback execution condition is satisfied based on the operating state. Similarly to the above embodiment, if the feedback execution condition is satisfied, the feedback mode is set and the feedback control is performed. If the feedback execution condition is not satisfied, the non-feedback mode is set and the non-feedback control is performed.

  The operation amount determination unit 443 includes an injector valve opening period determination unit 452 and a secondary air supply determination unit 453 in addition to the throttle opening determination unit 51 similar to that in the above embodiment. The injector valve opening period determining unit 452 determines the valve opening period TAU using, for example, the equation (1D).

TAU = TBASE x FFB x (1 + FDLAF) x FILAF (1D)
FILAF is an idle correction coefficient and is individually set for each injector 18 (for each cylinder 3 (see FIG. 1)). During the feedback control and the non-feedback control, the idle correction coefficient FILAF is set to the reference value. When Expression (1D) is used, the reference value of the idle correction coefficient FILAF is 1. On the contrary, during the execution of the idle deterioration correction control, the coefficients FFB and FDLAF are set to the reference values. Note that, similarly to the modification from the expression (1B) to the expression (2C) in the third embodiment, the expression (1D) can be transformed into the following expression (2D3).

TAU = TBASE × FO2RAM × (1 + FAF + FRLAF + FLLAF)
× (1 + FDLAF) × FILAF (2D3)
The storage unit 441 stores third and fourth correspondences 363 and 364 similar to those in the third embodiment. The degradation correction coefficient FDLAF is set based on the long-term learning coefficient FLLAF, as in the third embodiment.

  The secondary air supply determination unit 453 gives an open command to the secondary air supply valve 427 when the idle deterioration correction control is performed. In addition, the secondary air supply determination unit 453 gives an open command to the secondary air supply valve 427 when the feedback execution condition is not satisfied and the operation state is in a specific operation region. By providing the opening command, the secondary air supply valve 427 opens the secondary air supply passage 426. The secondary air supply determination unit 453 does not perform idle deterioration correction control, and does not give an open command to the secondary air supply valve 427 if the operation state is not in a specific operation region when the feedback execution condition is not satisfied. . Thereby, the secondary air supply valve 427 closes the secondary air supply passage 426.

  The ECU 440 includes a combustion state determination unit 445 that determines the combustion state when the idle deterioration correction control is performed. The combustion state determination unit 445 includes a first determination unit 456 and a second determination unit 457. The combustion state determination unit 445 is realized by a software element of the ECU 440 such as a program stored in a memory and a hardware element of the ECU 440 such as a CPU that executes the program.

  FIG. 20 is a diagram illustrating an example of a method for determining the combustion state by the first determination unit 456. The first determination unit 456 extracts the minimum value and the maximum value from the detected values of the plurality of engine speeds detected within the predetermined period Δt1 during the execution of the idle deterioration correction control, and the deviation Δω between the maximum value and the minimum value. Through the calculation, it is determined whether or not the deviation Δω is greater than or equal to a threshold value. The predetermined period Δt1 is set to a sufficiently long time that allows one or more engine cycles to elapse when the internal combustion engine 1 is idling. That is, it is set to a sufficiently long time to macroscopically monitor the combustion state. If deviation (DELTA) omega is less than a threshold value, the 1st determination part 456 will determine with the combustion state being stable. If deviation (DELTA) omega is more than a threshold value, the 1st determination part 456 will determine with a combustion state being unstable.

  FIGS. 21A and 21B are diagrams illustrating an example of a combustion state determination method by the second determination unit 457. FIG. 21A shows a typical example when the combustion state is stable, and FIG. 21B shows a typical example when the combustion state is unstable. The second determination unit 457 uses the first rotation speed ωA acquired near the start of the expansion stroke of each cylinder 3 (for example, crank angle: 15 [degCA]), and near the end of the expansion stroke (for example, the crank angle). : 135 [degCA]), and a difference value from the second rotational speed ωB acquired at 135 [degCA]) is calculated. The difference value is obtained by subtracting the first rotation speed ωA from the second rotation speed ωB. The difference value is calculated for each engine cycle until a predetermined number of engine cycles elapses. A deviation change coefficient is calculated by extracting a maximum value and a minimum value from a predetermined number of difference values and performing a blunting process of dividing a deviation between the maximum value and the minimum value by a filter coefficient.

  If normal combustion is performed, the engine speed changes in a convex upward trend from the start of the expansion stroke to the vicinity of the end (see FIG. 21A). For this reason, the difference value takes a relatively large positive value. If such combustion continues, the deviation change coefficient becomes a relatively large positive value. On the other hand, when a low fire or misfire occurs, the engine speed does not show a significant increase from the start of the expansion stroke to the end of the expansion stroke. In extreme cases, the engine speed decreases as shown in the figure. It changes with a tendency (refer FIG.21 (b)). In this case, even if the difference value is a positive value, it is a value close to zero, and in an extreme case a negative value. If such combustion continues, the deviation change coefficient takes a positive value near zero or a value less than or equal to zero.

  The second determination unit 457 determines whether or not the deviation change coefficient is greater than or equal to the threshold for each cylinder 3. Here, the threshold value is set to a positive value. If the deviation change coefficient is equal to or greater than the threshold value, the second determination unit 457 determines that the combustion state of the cylinder 3 is stable. If the deviation change coefficient is less than the threshold value, the second determination unit 457 determines that the combustion state of the cylinder 3 is unstable.

  FIG. 22 is a graph showing an example of a method for setting the idle correction coefficient FILAF. As shown in FIG. 22, when the internal combustion engine 1 is in an idling state, the secondary air supply determination unit 453 gives an open command to the secondary air supply valve 427, and the first and second determination units 456 and 457 enter the combustion state. judge. The injector valve opening period determining unit 452 determines the standard value TBASE according to the first correspondence 61 and determines the idle correction coefficient FILAF. The initial value of the idle correction coefficient FILAF is the reference value (1).

  Then, it is monitored whether or not the output characteristic of the O2 sensor 38 changes from the rich state to the lean state. In the idle deterioration correction control, the secondary air supply valve 427 is open. For this reason, the O2 sensor 38 is not the combustion exhaust gas itself of the air-fuel mixture supplied to the combustion chamber 4 but secondary air is added to this, and in some cases, after recombustion, to the downstream portion of the exhaust manifold 23 A high voltage or low voltage signal is output according to the reached oxygen concentration of the flue gas.

  It is determined whether or not a predetermined time has elapsed since the start of the idle deterioration correction control, and when the output characteristic of the O2 sensor 38 changes to indicate a lean state before the predetermined time elapses, the idle correction coefficient FILAF is corrected. The idle deterioration correction control is continued without doing so. If the output characteristic of the O2 sensor is reversed from the one indicating the lean state to the one indicating the rich state during the execution of the idle deterioration correction control, the output characteristic of the O2 sensor 38 is lean until the predetermined time elapses from the inversion time. Monitor whether it is reversed again to indicate status.

  If the output characteristic of the O2 sensor 38 does not change to indicate a lean state within a predetermined time, the injector valve opening period determination unit 452 corrects the idle correction coefficient FILAF by a predetermined decrease from the value at that time. To do. Then, it is monitored whether or not the output characteristic of the O2 sensor 38 changes to one showing a lean state before a predetermined time elapses from this correction time point. Until the output characteristic of the O2 sensor 38 changes to indicate a lean state, the reduction correction is continued by the above-mentioned reduction amount every predetermined time. By this correction, even when the internal combustion engine 1 is in the idling state, it is possible to satisfactorily suppress the air-fuel ratio including the secondary air from becoming excessively rich due to deterioration. The decrease correction of the idle correction coefficient FILAF based on the output of the O2 sensor 38 is performed only for the cylinder 3 for which it is determined that the combustion state is stable.

  The decrease correction based on the output of the O2 sensor 38 may cause weakening or misfire. Therefore, when it is determined that the combustion state is unstable, the idle correction coefficient FILAF is increased by a predetermined increment every time the predetermined time Δt3 elapses until it is determined that the combustion state is stable from that point. . Thereby, the reduction correction amount based on the O2 sensor 38 is gradually reduced.

  Since the first determination unit 456 macroscopically determines the combustion state, when the first determination unit 456 determines that the combustion state is unstable, the idle correction coefficient FILAF of all the cylinders 3 is uniformly increased. Since the second determination unit 457 determines the combustion state for each cylinder 3, when the second determination unit 457 determines that the combustion state is unstable, the idle correction coefficient FILAF of the cylinder 3 determined as such. Only increase. By performing such correction, it is possible to prevent overcorrection of the idle correction coefficient FILAF based on the O2 sensor. The correction based on the determination result of the combustion state may be made so that the value of the idle coefficient FILAF is not further increased after the idle correction coefficient FILAF reaches the reference value. Thereby, it can suppress that the air-fuel ratio containing secondary air becomes rich.

  FIG. 23 is a flowchart showing an example of air-fuel ratio control and abnormality diagnosis executed by the air-fuel ratio control apparatus and abnormality diagnosis apparatus shown in FIG. As shown in FIG. 23, the target position of the valve motor 16 and thus the target throttle opening is determined (S401). A standard value TBASE is determined (S402), and it is determined whether the internal combustion engine 1 is idling (S404). If it is not in the idling state (S404: NO), whether or not the feedback execution condition is satisfied is determined (S403). If the feedback execution condition is not satisfied (S403: NO), non-feedback control is executed. As part of this, the feedback correction coefficient FFB and the idle correction coefficient FILAF are set as reference values (S411), and the deterioration correction coefficient FDLAF is determined (S412). If the feedback execution condition is satisfied (S403: YES), feedback control is performed. As part of this, the deterioration correction coefficient FDLAF and the idle correction coefficient FILAF are determined as reference values (S413). A feedback correction coefficient FFB is determined (S414). That is, the λ correction coefficient FO2RAM is determined according to the second correspondence 62, the closed loop correction coefficient FAF is determined based on the output of the air-fuel ratio detection means, and the real-time learning coefficient FLLAF and the long-term learning coefficient FLLAF correspond to the third and fourth correspondences. It is determined based on the operating state according to the relations 363 and 364 and based on the output of the air-fuel ratio detecting means. Next, abnormality diagnosis processing of the air-fuel ratio control device is executed (S420), and the valve opening period TAU is determined (S430).

  If the internal combustion engine 1 is idling (S404: YES), idle deterioration correction control is performed. As part of this, the feedback correction coefficient FFB and the deterioration correction coefficient FDLAF are set as reference values (S415), and the idle correction coefficient FILAF is determined (S416). The method for setting the idle correction coefficient FILAF is as described above. Next, after proceeding to the abnormality diagnosis process S420, the valve opening period TAU is determined (S430). Thus, in the present embodiment, the abnormality diagnosis process S420 is executed even during the execution of the idle deterioration correction control. The procedure itself of the abnormality diagnosis process S420 is the same as that of the first embodiment (see FIG. 8), and the diagnosis permission condition is also the same as that of the first embodiment.

  Regarding the abnormality diagnosis in step S22 (see FIG. 8), the correction amount that is the source of the correction amount used for the diagnosis includes the correction amount TILAF by the idle correction coefficient FILAF and the idle correction coefficient FILAF that determines the correction amount. The correction value includes the current value of the idle correction coefficient FILAF of each cylinder 3. The comparison value is set corresponding to the current value of the idle correction coefficient FILAF.

  While the idle deterioration correction control is being performed, the abnormal condition is that the current value of the idle correction coefficient FILAF exceeds the lower limit comparison value and is outside the allowable range for a predetermined time. Since the idle correction coefficient FILAF itself has a limit on the upper limit, the upper limit of the allowable range is an upper limit value (for example, a reference value) of the idle correction coefficient FILAF. The abnormal condition during the non-feedback control and the abnormal condition during the feedback control are the same as those in the above embodiment. In the present embodiment, the diagnosis unit 444 operates the abnormality of the air-fuel ratio control device based on the correction value associated with the correction amount and the comparison value set regardless of the correction amount even during the execution of the idle deterioration correction control. Can be diagnosed.

(Example of change)
The fourth embodiment may be modified so that the second embodiment is applied to the method of setting the deterioration learning coefficient FDLAF. In that case, the equation (1D) can be transformed into the following equation (2D2). The fourth embodiment may be modified so that the deterioration correction coefficient FDLAF is not taken into account when determining the valve opening period TAU. In that case, the expression (1D) can be changed to the following expression (1E). Any one of the first, second and third embodiments may be applied to the method of setting the feedback correction coefficient FFB, and the expression (1E) can be transformed into the following expression (2E1), (2E2) or (2E3). is there.

TAU = TBASE × FO2RAM × (1 + FAF + FLAF)
× (1 + FDLAF) × FILAF (2D2)
TAU = TBASE × FFB × FILAF (1E)
TAU = TBASE x FO2RAM x (1 + FVFB) x FILAF (2E1)
TAU = TBASE × FO2RAM × (1 + FAF + FLAF) × FILAF (2E2)
TAU = TBASE × FO2RAM × (1 + FAF + FRLAF + FLLAF) × FILAF (2E3)
When the equation for determining the valve opening period TAU is changed as described above, the abnormal condition is changed accordingly.

  The valve opening period TAU may be corrected according to the traveling environment. As a result, the fluctuation correction coefficient does not have to compensate for an air-fuel ratio error due to a change in the traveling environment. For this reason, the accuracy of diagnosing an abnormality in the air-fuel ratio control apparatus using the correction value set based on the fluctuation correction coefficient is further improved. In this case, when the correction is applied to the first embodiment, the equation (2A) may be changed to the following equation (3A). The same applies to other embodiments and the above modification.

TAU = TBASE x FO2RAM x (1 + FKI + VFFB) (3A)
FKI is an environmental correction coefficient. The environmental correction coefficient FKI is variably set according to the cooling water temperature and the intake pressure of the internal combustion engine.

  At the time of transition from non-feedback control to feedback control, the valve opening period changes from the standard value to the theoretical value, but the λ correction coefficient may gradually change from the reference value to a value corresponding to the operating state. Thereby, it is possible to suppress a sudden change in the output of the internal combustion engine due to a sudden change in the fuel amount at the time of mode transition.

  During the execution of the non-feedback control, the deterioration correction coefficient FDLAF may be corrected according to the combustion state, similarly to the idle deterioration correction control. In this case, the deterioration correction coefficient FDLAF is a representative set in common to all cylinders based on the learning correction coefficient FLAF (or the long-term learning coefficient FLLAF) based on the learning correction coefficient FLAF as in the second or third embodiment. A correction coefficient and a combustion state correction coefficient that is individually set in the cylinder to correct the representative correction coefficient when it is determined that the combustion state is unstable may be included.

  In the above embodiment, the standard value TBASE is obtained from the throttle opening and the engine speed. However, the first related value that changes according to the throttle opening, the second related value that changes according to the engine speed, The standard value TBASE may be obtained based on the above. For example, the intake pressure that is the pressure in the supply passage may be used as the first related value, or the intake pressure and the throttle opening may be used in combination. As the second related value, the vehicle speed and the gear ratio of the transmission may be used, or the value of the cam angle sensor may be used. In addition, the standard value TBASE may be obtained using another calculation method or a map. For example, the standard value TBASE may be corrected according to other operating conditions.

  In the above embodiment, the air-fuel ratio control device corrects the valve opening period of the injector to control the air-fuel ratio, and the abnormality of the air-fuel ratio control device is diagnosed based on the correction amount. As a result, the throttle opening may be corrected. In that case, the abnormality diagnosis device can diagnose an abnormality in the air-fuel ratio control device based on a comparison between a correction value associated with the correction amount of the valve motor position or the throttle opening and a corresponding comparison value. Good.

  The air-fuel ratio control device only needs to be able to control the air-fuel ratio. Although the throttle opening can be treated as an operation amount for that purpose, the throttle valve 15 does not necessarily include the electric throttle valve 15a as long as the air-fuel ratio control can be realized by correcting the valve opening period of the injector. .

  In the above embodiment, the internal combustion engine is a 4-stroke type, but the internal combustion engine may be a 2-stroke type. The fuel for the internal combustion engine may be a fuel other than gasoline (for example, ethanol, ethanol-mixed gasoline, light oil). In the above embodiment, the internal combustion engine is a multi-cylinder type, but the arrangement of the cylinders in that case is not particularly limited, and may be, for example, a parallel type or a V type. The internal combustion engine may be a single cylinder type. The present invention can be suitably used for a vehicle having an internal combustion engine as a drive source, and can be applied to all devices including the internal combustion engine.

  The present invention can be used for all devices including an internal combustion engine, and in particular, can be used as an OBD (On-Board Diagnostics) device for a vehicle equipped with an air-fuel ratio control device.

1 Internal combustion engine 18 Injector 38 O2 sensor 40, 240, 340, 440 ECU
41, 241, 341, 441 Storage unit 43, 243, 343, 443 Operation amount determination unit 44, 244, 344, 444 Diagnosis unit 52, 252, 352, 452 Injector valve opening period determination unit 61 First correspondence 62 Correspondence

Claims (7)

An apparatus for diagnosing an abnormality in an air-fuel ratio control device that controls an air-fuel ratio of an internal combustion engine,
Air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine;
An operation amount determination unit that corrects the operation amount of the air-fuel ratio control device so that the air-fuel ratio approaches the stoichiometric air-fuel ratio based on the output of the air-fuel ratio detection means;
A diagnosis unit that diagnoses an abnormality of the air-fuel ratio control device based on a correction value associated with a correction amount for the operation amount and a comparison value set regardless of the correction by the operation amount determination unit. An abnormality diagnosis device for an air-fuel ratio control device. Corresponding to the operation state of the internal combustion engine, further comprising a storage unit for storing a correspondence relationship that defines a correction amount necessary for the air-fuel ratio to become the stoichiometric air-fuel ratio,
The air-fuel ratio detecting means is an O2 sensor that reverses the output characteristics when the air-fuel ratio crosses the vicinity of the theoretical air-fuel ratio,
The manipulated variable determination unit corrects the manipulated variable in stages with time based on the output of the O2 sensor so as to bring the air-fuel ratio closer to the theoretical air-fuel ratio after correcting the manipulated variable according to the correspondence relationship. The abnormality diagnosis device for an air-fuel ratio control device according to claim 1.   The air-fuel ratio control apparatus according to claim 2, wherein the correction value is set based on a correction amount that is necessary to bring the air-fuel ratio closer to the stoichiometric air-fuel ratio after correcting the operation amount according to the correspondence relationship. Abnormality diagnosis device.   The air-fuel ratio control according to any one of claims 1 to 3, wherein when the state where the correction value exceeds the comparison value continues for a predetermined time, the diagnosis unit diagnoses that the air-fuel ratio control device is abnormal. Device abnormality diagnosis device.   The abnormality diagnosis device for an air-fuel ratio control device according to any one of claims 1 to 4, wherein the correction value is a value associated with an average of correction amounts acquired within a predetermined period. The diagnosis unit determines whether or not a diagnosis permission condition is satisfied including a condition that the operating state of the internal combustion engine is stably changing, or a condition that the correction amount is stably changing,
The abnormality diagnosis of the air-fuel ratio control device is not performed if the diagnosis permission condition is not satisfied, and the abnormality diagnosis of the air-fuel ratio control device is performed if the diagnosis permission condition is satisfied. The abnormality diagnosis device for an air-fuel ratio control device according to claim 1.   The abnormality diagnosis device for an air-fuel ratio control device according to any one of claims 1 to 6, further comprising an alarm device for notifying a driver when the air-fuel ratio control device is diagnosed as abnormal.

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