JP5041294B2 - Air-fuel ratio sensor abnormality diagnosis device - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor abnormality diagnosis device, and more particularly to an air-fuel ratio sensor abnormality diagnosis device arranged in an exhaust passage of an internal combustion engine.

  In an internal combustion engine equipped with an exhaust gas purification system using a catalyst, in order to effectively remove harmful components of exhaust gas by the catalyst, the mixture ratio of air and fuel in the air-fuel mixture burned in the internal combustion engine, that is, the air-fuel ratio is reduced. Control is essential. In order to perform such control of the air-fuel ratio, an air-fuel ratio sensor for detecting the air-fuel ratio is provided in the exhaust passage of the internal combustion engine based on the concentration of a specific component of the exhaust gas, and the detected air-fuel ratio is set to a predetermined target air-fuel ratio. Feedback control is carried out so that it can approach.

  By the way, if an abnormality such as deterioration or failure occurs in the air-fuel ratio sensor, accurate air-fuel ratio feedback control cannot be performed, and exhaust gas emission deteriorates. Therefore, it has been conventionally performed to diagnose abnormality of the air-fuel ratio sensor. In particular, in the case of an engine mounted on an automobile, it is requested by the laws and regulations of each country to detect an abnormality in the air-fuel ratio sensor in an on-board state (onboard) in order to prevent traveling in a state where exhaust gas has deteriorated. ing.

  For example, Patent Document 1 discloses an apparatus that detects an abnormality of an air-fuel ratio sensor based on a trajectory length of an air-fuel ratio sensor output when the fuel injection amount is periodically increased or decreased.

JP 2005-30358 A

  However, although the technique described in Patent Document 1 can determine whether the air-fuel ratio sensor itself is normal or abnormal, it cannot determine which of the characteristics of the air-fuel ratio sensor is normal or abnormal. That is, the air-fuel ratio sensor includes a plurality of characteristics, but with the technique described in Patent Document 1, it is impossible to determine which of these characteristics is abnormal.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide an abnormality diagnosis device for an air-fuel ratio sensor that can preferably diagnose abnormality of individual characteristics included in the air-fuel ratio sensor. There is.

According to one aspect of the invention,
An abnormality diagnosis apparatus for an air-fuel ratio sensor disposed in an exhaust passage of an internal combustion engine,
Active control means for performing active control for periodically switching the fuel injection amount from the fuel injection valve to alternately switch the air-fuel ratio as an input to a rich side and a lean side with respect to a predetermined center air-fuel ratio;
During active control, parameters in the first-order lag element are identified based on the input to a model obtained by modeling the system from the fuel injection valve to the air-fuel ratio sensor with a first-order lag element and the output of the air-fuel ratio sensor. An identification means;
An abnormality determining means for determining an abnormality of a predetermined characteristic of the air-fuel ratio sensor based on the parameter identified by the identifying means;
The active control means calculates a fuel injection amount (center injection amount) corresponding to the central air-fuel ratio based on a predetermined learning value, and calculates a fuel injection amount during active control based on the central injection amount. Injecting from the fuel injection valve,
The learning value is learned for each operation region of the internal combustion engine divided into a plurality of parts,
When the operation state of the internal combustion engine shifts between the learning completion region and the learning incomplete region during execution of the active control and identification, the identification is temporarily stopped immediately after the transition, or the active control is performed simultaneously with the transition. And an abnormality diagnosis device for an air-fuel ratio sensor, further comprising a transition prohibiting means for canceling the identification.

  According to this aspect of the present invention, the abnormality of the predetermined characteristic of the air-fuel ratio sensor is determined instead of simply determining the abnormality of the air-fuel ratio sensor. Therefore, it can be determined which of the plurality of characteristics of the air-fuel ratio sensor is abnormal, and the abnormality diagnosis of the air-fuel ratio sensor can be executed more precisely and in detail. In particular, a learning value is learned for each operating region of the internal combustion engine, a central injection amount is calculated based on the learning value, and a fuel injection amount (active injection amount) during active control is calculated based on the central injection amount. The At this time, if the operating state of the internal combustion engine shifts between a learning value learning completion region and a learning incomplete region during execution of active control and identification, the center injection amount may not be accurately calculated. Therefore, in one embodiment of the present invention, the identification is temporarily stopped immediately after the transition, or the active control and the identification are stopped simultaneously with the transition. In this way, in the former case, a waiting time immediately after the transition is provided, so that an incorrect active injection amount calculation based on an inaccurate center injection amount during that time, and thus an identification by an incorrect input can be prevented. it can. On the other hand, in the latter case, the active control and the identification are stopped simultaneously with the transition, so that the identification by the incorrect input can be similarly prevented. In this way, it is possible to improve the parameter identification accuracy and thus the diagnosis accuracy.

  Preferably, the transition prohibition means temporarily stops identification immediately after the transition, and stops the identification from the transition to the end of the predetermined period of the active control. is there.

  Preferably, the learning value includes an air-fuel ratio learning value and a purge concentration learning value.

According to another aspect of the invention,
An abnormality diagnosis apparatus for an air-fuel ratio sensor disposed in an exhaust passage of an internal combustion engine,
Active control means for performing active control for periodically switching the fuel injection amount from the fuel injection valve to alternately switch the air-fuel ratio as an input to a rich side and a lean side with respect to a predetermined center air-fuel ratio;
During active control, parameters in the first-order lag element are identified based on the input to a model obtained by modeling the system from the fuel injection valve to the air-fuel ratio sensor with a first-order lag element and the output of the air-fuel ratio sensor. An identification means;
An abnormality determining means for determining an abnormality of a predetermined characteristic of the air-fuel ratio sensor based on the parameter identified by the identifying means;
The internal combustion engine includes a canister that adsorbs the evaporated fuel generated in a fuel tank, and a purge unit that performs a purge for sucking the purge gas containing the evaporated fuel from the canister into the intake passage,
The active control means calculates a fuel injection amount (center injection amount) corresponding to the central air-fuel ratio based on a learning value including an air-fuel ratio learning value and a purge concentration learning value during execution of the purge and active control. In addition, the fuel amount (purge fuel amount) contained in the purge gas sucked into the intake passage is estimated based on the purge concentration learning value, and active control is being performed based on the central injection amount and the estimated purge fuel amount. An abnormality diagnosis device for an air-fuel ratio sensor, characterized in that a fuel injection amount is calculated and injected from the fuel injection valve is provided.

  According to the other embodiment of the present invention, the abnormality of the air-fuel ratio sensor is not simply determined, but the abnormality of a predetermined characteristic of the air-fuel ratio sensor is determined. Can be executed. In particular, during execution of the purge and active control, the actual purge fuel amount is estimated based on the purge concentration learning value, and the active injection amount is calculated based on the estimated purge fuel amount. Therefore, the effect of the increase / decrease in the actual purge fuel amount can be reflected in the active injection amount, and the calculation accuracy of the active injection amount is improved regardless of the actual purge fuel amount, thereby improving the input accuracy. It becomes possible to improve identification accuracy and diagnostic accuracy.

  Preferably, the parameter in the first-order lag element includes at least a gain and a time constant, and the predetermined characteristic of the air-fuel ratio sensor includes at least an output corresponding to the gain and responsiveness corresponding to the time constant.

  As a result, the output and responsiveness, which are typical characteristics of the air-fuel ratio sensor, can be diagnosed individually and simultaneously, and a more detailed and detailed abnormality diagnosis can be executed.

  According to the present invention, an excellent effect that an abnormality of each characteristic included in the air-fuel ratio sensor can be suitably diagnosed is exhibited.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic view of an internal combustion engine according to the present embodiment. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 of the present embodiment is a vehicular multi-cylinder engine (for example, a four-cylinder engine, only one cylinder is shown), and is a spark ignition internal combustion engine, more specifically a gasoline engine. However, the type, type, application, etc. of the internal combustion engine are not particularly limited.

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

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

  An injector (fuel injection valve) 12 that injects fuel into the intake passage, particularly into the intake port, is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve Vi is opened, compressed by the piston 4, and ignited and burned by the spark plug 7. It is done.

On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder. An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. Catalysts 11 and 19 made of a three-way catalyst are attached to the exhaust pipe 6 on the upstream side and the downstream side. Air-fuel ratio sensors 17 and 18 for detecting the air-fuel ratio of the exhaust gas, that is, pre-catalyst sensors and post-catalyst sensors 17 and 18 are installed at positions before and after the upstream catalyst 11, respectively. These pre-catalyst sensors and post-catalyst sensors 17 and 18 detect the air-fuel ratio based on the oxygen concentration in the exhaust gas. The pre-catalyst sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide area, and outputs a current signal proportional to the air-fuel ratio. On the other hand, the post-catalyst sensor 18 is a so-called O ₂ sensor, and has a characteristic that the output voltage changes suddenly at the theoretical air-fuel ratio.

  The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5, the pre-catalyst sensor 17, and the post-catalyst sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1 and an accelerator that detects the accelerator opening, as shown in the figure. The opening sensor 15 and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc. The throttle opening is normally controlled to an opening corresponding to the accelerator opening.

  The catalysts 11 and 19 simultaneously purify NOx, HC and CO when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 11 and 19 is the stoichiometric air-fuel ratio (stoichiometric, for example, A / F = 14.6). In response to this, the ECU 20 controls the air-fuel ratio so that the air-fuel ratio A / F of the exhaust gas flowing into the catalysts 11 and 19 becomes equal to the stoichiometric air-fuel ratio during normal operation of the internal combustion engine (so-called stoichiometric). control). Specifically, the ECU 20 sets a target air-fuel ratio A / Ft that is equal to the stoichiometric air-fuel ratio, and makes the basic injection amount such that the air-fuel ratio of the air-fuel mixture flowing into the combustion chamber 3 matches the target air-fuel ratio A / Ft. Is calculated. Then, the basic injection amount is feedback-corrected according to the difference between the actual air-fuel ratio detected by the pre-catalyst sensor 17 and the target air-fuel ratio A / Ft, and the injector 12 is operated for the energization time corresponding to the corrected injection amount. Energize (turn on). As a result, the air-fuel ratio of the exhaust gas supplied to the catalysts 11 and 19 is maintained near the stoichiometric air-fuel ratio, and the maximum purification performance is exhibited in the catalysts 11 and 19. Thus, the ECU 20 feedback-controls the air-fuel ratio or the fuel injection amount so that the actual air-fuel ratio detected by the pre-catalyst sensor 17 approaches the target air-fuel ratio A / Ft. The post-catalyst sensor 18 is provided to correct the deviation of the center air-fuel ratio in such air-fuel ratio feedback control.

  In addition, the internal combustion engine 1 is provided with a canister 31 that adsorbs the evaporated fuel generated in the fuel tank 30 and a purge unit that performs a purge for sucking the purge gas containing the evaporated fuel from the canister 31 into the intake passage. ing. The canister 31 is provided with activated carbon inside thereof, and the evaporated fuel in the fuel tank 30 is introduced and adsorbed through the inlet 31A. The canister 31 according to the present embodiment is disposed inside the fuel tank 30, but may be disposed outside. The canister 31 includes an air introduction port 31 </ b> B and sends purge gas to the intake passage of the internal combustion engine 1 through the purge passage 32. The purge passage 32 communicates with the intake pipe 13 between the throttle valve 10 and the surge tank 8. The purge passage 32 is provided with a purge control valve 33 for controlling the flow rate of the purge gas flowing through the purge passage 32. The opening degree of the purge control valve 33 is controlled by the ECU 20 being duty controlled. Thus, the ECU 20, the purge control valve 33 and the purge passage 32 constitute a purge means.

  A fuel pump 34, a fuel filter 35, and a pressure regulator 36 are provided in the fuel tank 30, and the fuel sucked by the fuel pump 34 is regulated by the pressure regulator 36 after passing through the fuel filter 35, and passes through the fuel passage 37. To the delivery pipe 38. The fuel stored in the delivery pipe 38 is injected from the injector 12.

[Basic contents of air-fuel ratio sensor abnormality diagnosis]
Next, abnormality diagnosis of the air-fuel ratio sensor in the present embodiment will be described. The object of diagnosis in this embodiment is an air-fuel ratio sensor installed on the upstream side of the upstream catalyst 11, that is, a pre-catalyst sensor 17.

  In the abnormality diagnosis, the system from the injector 12 to the pre-catalyst sensor 17 is modeled by a first-order lag element, and the parameters of the first-order lag element are identified based on the input to this model and the output of the pre-catalyst sensor 17 ( Presumed. Then, based on the identified parameter, an abnormality of a predetermined characteristic of the pre-catalyst sensor 17 is determined.

  As an input, a ratio Ga / Q between the fuel injection amount Q calculated based on the energization time of the injector 12 and the intake air amount Ga calculated based on the output of the air flow meter 5, that is, the input air-fuel ratio is used. Hereinafter, the input or the input air-fuel ratio is represented by u (t) (u (t) = Ga / Q). On the other hand, as the output of the pre-catalyst sensor 17, the output air-fuel ratio, that is, the pre-catalyst air-fuel ratio A / Ff converted from the output voltage Vf of the pre-catalyst sensor 17 is used. Hereinafter, the output or the output air-fuel ratio is represented by y (t) (y (t) = A / Ff). A parameter in the first-order lag element is identified from how the output air-fuel ratio y (t) is given when the input air-fuel ratio u (t) is given to the model, and predetermined characteristics of the pre-catalyst sensor 17 are determined based on the identified parameter. Is determined to be abnormal.

  As shown in FIG. 2, in the present embodiment, in parameter identification, the fuel injection amount is periodically increased or decreased so that the input air-fuel ratio is rich and lean with respect to a predetermined center air-fuel ratio A / Fc. Active control (identification active control) that switches alternately is executed. In this active control, the fuel injection amount Q is set at a constant cycle so that the target air-fuel ratio A / Ft and thus the input air-fuel ratio u (t) are swung with the same amplitude on the lean side and the rich side with respect to the center air-fuel ratio A / Fc. Vibrated. The amplitude of vibration is larger than that in normal air-fuel ratio control, and in this embodiment, the air-fuel ratio is set to 0.5. The center air-fuel ratio A / Fc is made equal to the stoichiometric air-fuel ratio.

  The reason for executing this active control is that the active control is executed during the steady operation of the engine, so that each control amount and each detected value are stabilized, and diagnostic accuracy is improved. This is also because when the input air-fuel ratio u (t) is deliberately changed, the quality (especially output and responsiveness) of each sensor can be suitably diagnosed.

  As shown in the figure, the input air-fuel ratio u (t) has a substantially stepped waveform, whereas the output air-fuel ratio y (t) has a waveform with a first-order lag. In the figure, L is a dead time based on a transport delay from the input air-fuel ratio u (t) to the output air-fuel ratio y (t). This dead time L corresponds to the time difference from the time of fuel injection in the injector 12 until the exhaust gas resulting from the fuel injection reaches the pre-catalyst sensor 17.

  Assuming that the dead time L is zero for simplification, the first-order lag element is represented by G (s) = k / (1 + Ts). Here, k is the gain of the pre-catalyst sensor 17, and T represents the time constant of the pre-catalyst sensor 17. The gain k is a value related to output among the characteristics of the pre-catalyst sensor 17, while the time constant T is a value related to responsiveness among the characteristics of the pre-catalyst sensor 17. In FIG. 2, a solid line representing the output air-fuel ratio y (t) indicates a case where the pre-catalyst sensor 17 is normal. On the other hand, when an abnormality occurs in the output characteristics of the pre-catalyst sensor 17, the gain k becomes larger than normal, and the sensor output increases (expands) as indicated by a, or the gain k becomes smaller than normal. As shown by b, the sensor output decreases (reduces). Therefore, an increase abnormality or a decrease abnormality of the sensor output can be specified by comparing the identified gain k with a predetermined value. On the other hand, if an abnormality occurs in the responsiveness of the pre-catalyst sensor 17, in most cases, the time constant T becomes larger than normal, and the sensor output comes out with a delay as shown by c. Therefore, the responsiveness abnormality of the sensor can be specified by comparing the identified time constant T with a predetermined value.

  Next, a method for identifying the gain k and time constant T executed by the ECU 20 will be described.

Equation (20) is a function of values at the current sample time t and the previous sample time t−1, and this equation means that b ₁ and b ₂ are based on the current value and the previous value, That is, T and k are updated every time. Thus, the time constant T and the gain k are sequentially identified by the sequential least square method. In this sequential identification method, a large number of sample data is acquired and temporarily stored, and the calculation load can be reduced as compared with the method of performing identification, and the capacity of the buffer for temporarily storing data can be reduced. It is suitable for mounting on an ECU (particularly an automotive ECU).

  The sensor characteristic abnormality determination method executed by the ECU 20 is as follows. First, when the identified time constant T is larger than a predetermined time constant abnormality determination value Ts, a response delay occurs, and it is determined that the pre-catalyst sensor 17 is responsive abnormality. On the other hand, when the identified time constant T is equal to or less than the time constant abnormality determination value Ts, the pre-catalyst sensor 17 is determined to be normal with respect to responsiveness.

  If the identified gain k is greater than the predetermined gain increase abnormality determination value ks1, the pre-catalyst sensor 17 is determined to have an output increase abnormality, and the identified gain k is the gain reduction abnormality determination value ks2 (<ks1). If it is smaller, it is determined that the pre-catalyst sensor 17 has an output decrease abnormality. When the identified gain k is not less than the gain reduction abnormality determination value ks2 and not more than the gain increase abnormality determination value ks1, it is determined that the pre-catalyst sensor 17 is normal with respect to the output.

  As described above, according to the abnormality diagnosis according to the present invention, the abnormality of the predetermined characteristic of the air-fuel ratio sensor is determined instead of simply determining the abnormality of the air-fuel ratio sensor itself. Based on the two identification parameters T and k, abnormalities in the two sensor characteristics of responsiveness and output are determined particularly simultaneously and individually. Therefore, it is possible to realize a very precise and preferable one for abnormality diagnosis of the air-fuel ratio sensor.

  3 and 4 show the results of sequentially identifying the time constant T and the gain k by the sequential least square method in the case of the normal pre-catalyst sensor 17 and in the case of the abnormal pre-catalyst sensor 17. 3 shows the case of the normal pre-catalyst sensor 17, and FIG. 4 shows the case of the abnormal pre-catalyst sensor 17. FIGS. 3A and 4A show how the input air-fuel ratio (broken line) and the output air-fuel ratio (solid line) vibrate.

  FIGS. 3B and 4B show transitions of the time constant T (broken line) and the gain k (solid line) from the start of active control. The time constant T and the gain k are updated every sampling time and gradually converge to a constant value. The time constant T and the gain k are acquired at a time point (determination time) t1 after a predetermined time (for example, 5 seconds) has elapsed from when the active control starts (at the start of identification) t0, and the values almost converge. The obtained time constant T and gain k are compared with the abnormality determination values Ts1, ks1, and ks2, and abnormality determination of responsiveness and output is made.

  When a test was performed using an abnormal pre-catalyst sensor 17 having a response almost equal to that of the normal pre-catalyst sensor 17 and an output of ½, the time constant T at the determination time t1 is It was almost the same as 0.18 for the normal sensor and 0.17 for the abnormal sensor. On the other hand, the gain k at the determination time t1 is 1 for the normal sensor and 0.5 for the abnormal sensor. As a result, it was confirmed that the same result as the actual sensor could be obtained.

  By the way, an actual engine has various disturbances such as load fluctuations, and the identification accuracy and robustness cannot be improved unless these are properly considered. For this reason, in the abnormality diagnosis according to the present embodiment, various corrections are performed on the following input / output data.

  FIG. 5 is a block diagram of the entire system for identifying model parameters. Such a system is built in the ECU 20. In order to identify the parameters T and k as described above in the identification unit (identification unit) 50, an input calculation unit 52, a bias correction unit 54, and a dead time correction unit (dead time correction unit) 56 are provided. Note that an active control flag output unit 58 is also provided because abnormality diagnosis is performed during active control.

  The input calculation unit 52 calculates the input air-fuel ratio u (t). In the above example, the input air-fuel ratio u (t) is a ratio Ga / Q between the fuel injection amount Q calculated based on the energization time of the injector 12 and the intake air amount Ga calculated based on the output of the air flow meter 5. Met. However, here, the fuel injection amount Q calculated based on the injector energization time is corrected based on the fuel wall adhesion amount and the evaporation amount, and the corrected fuel injection amount Q ′ is used to input the air / fuel ratio u (t ) Is calculated. u (t) = Ga / Q ', and as a result, the input air-fuel ratio u (t) is corrected based on the amount of fuel adhering to the wall and the amount of evaporation.

  When fuel is injected from the injector 12, most of the fuel is sucked into the in-cylinder combustion chamber 3, but the remaining portion adheres to the inner wall surface of the intake port and does not enter the combustion chamber 3. Therefore, if the fuel amount injected from the injector 12 is fi, and the fuel adhesion rate for all cylinders is R (<1), the amount of the injected fuel amount fi that adheres to the wall surface of the intake port is R · fi, The amount entering the combustion chamber 3 is represented by (1-R) · fi.

  On the other hand, some of the fuel adhering to the wall surface of the intake port evaporates and enters the combustion chamber 3 in the next intake stroke, but the rest remains and remains attached. Therefore, if the fuel amount adhering to the wall surface of the intake port is fw and the fuel residual ratio for all cylinders is P (<1), the amount of fuel adhering to the wall surface of the wall surface adhering fuel amount fw is P · fw, The amount that enters the combustion chamber 3 is represented by (1-P) · fw.

  The intake, compression, expansion, and exhaust strokes of the four-cycle engine are completed once to make one cycle (that is, one cycle = 720 ° crank angle), the current cycle is ks, and the next cycle is ks + 1. Further, when the fuel amount entering the in-cylinder combustion chamber 3 is fc, the following relationship is established.

  The expression (21) means that the wall-attached fuel amount fw (ks + 1) of the next cycle is the residual amount P · fw (ks) of the wall-attached fuel amount fw (ks) of the current cycle and the injected fuel of the current cycle. That is, it is expressed as the sum of the amount fi (ks) and the wall surface adhesion R · fi (ks). In addition, the expression (22) means that the inflow fuel amount fc (ks) flowing into the combustion chamber 3 in the current cycle is an evaporation amount (1-) of the wall surface attached fuel amount fw (ks) in the current cycle. P) · fw (ks) and the sum (1-R) · fi (ks) of the injected fuel amount fi (ks) of this cycle that flows directly into the combustion chamber 3 without adhering to the wall surface. That is.

  Thus, when calculating the input air-fuel ratio u (t), the value of the inflow fuel amount fc is used as the value of the fuel injection amount Q ′. This inflow fuel amount fc is nothing but a correction of the fuel injection amount calculated based on the energization time of the injector 12 based on the amount of fuel adhering to the wall and the evaporation amount. Therefore, by using the value of the inflow fuel amount fc for calculating the input air-fuel ratio u (t), the value of the input air-fuel ratio can be made a more accurate value close to the actual situation, and the parameter identification accuracy can be improved. Is possible.

  Note that the higher the engine temperature and the intake air temperature, the more the fuel vaporization is promoted, so the fuel adhesion amount decreases and the fuel evaporation amount increases. Therefore, the fuel residual rate P and the fuel adhesion rate R are preferably functions of at least one of the engine temperature (or water temperature) and the intake air temperature. The correction based on the fuel wall adhesion amount and the evaporation amount as described herein is referred to as “fuel dynamics correction”.

  FIG. 6 shows test results obtained by examining the difference in the input air-fuel ratio u (t) during active control when there is no fuel dynamics correction (broken line) and when there is a solid line (solid line). As shown in the circle in the figure, the waveform of the input air-fuel ratio u (t) is slightly rounded immediately after the input air-fuel ratio u (t) is reversed, compared with the case where there is no fuel dynamics correction. It is in.

  Next, bias correction performed by the bias correction unit 54 will be described. In the bias correction unit 54, both the input air-fuel ratio u (t) and the output air-fuel ratio y (t) are removed so as to remove the bias between the input air-fuel ratio u (t) and the output air-fuel ratio y (t). Is shifted.

  The input air-fuel ratio u (t) and the output air-fuel ratio y (t) are biased to the lean side or the rich side with respect to one, due to factors such as load fluctuation, learning deviation, and sensor value deviation (deviation). There is a case. FIG. 7 is a test result showing the state of the bias. In the figure, u (t) c and y (t) c respectively represent values obtained by passing the input air-fuel ratio u (t) and the output air-fuel ratio y (t) through a low-pass filter, or their moving averages. Since the air-fuel ratio detected by the pre-catalyst sensor 17 is controlled to be close to the theoretical air-fuel ratio (A / F = 14.6), the output air-fuel ratio y (t), which is the detected value of the pre-catalyst sensor 17, is controlled. Fluctuates around the stoichiometric air-fuel ratio, and the value passed through the low-pass filter or the moving average y (t) c is also kept near the stoichiometric air-fuel ratio. On the other hand, the input air-fuel ratio u (t) is biased to the lean side in the illustrated example for the reason described above.

  Since it is not preferable to perform identification in such a bias state, a correction that removes the bias is performed. Specifically, as shown in FIG. 8, the data of the input air-fuel ratio u (t) and the output air-fuel ratio y (t) are passed through a low-pass filter, or the moving average is calculated, and the bias value u (t) c and y (t) c are calculated sequentially. Then, sequentially, the difference Δu (t) (= u (t) −u (t) c) between the input air-fuel ratio u (t) and its bias value u (t) c and the output air-fuel ratio y (t) And a difference Δy (t) (= y (t) −y (t) c) between the bias value y (t) c and the bias value y (t) c, and the differences Δu (t) and Δy (t) are set to zero reference values. Replaced. These differences Δu (t) and Δy (t) are collectively displayed as ΔA / F (the same applies to FIGS. 3A and 4A).

  In this way, the bias is removed, and the input / output air-fuel ratio values Δu (t) and Δy (t) after the bias removal are changed to zero reference values as shown in FIG. That is, the center of both fluctuations is set to zero, and influences such as load fluctuations and learning deviation can be eliminated. As a result, robustness against load fluctuation, learning deviation, and the like can be improved.

  In this example, the method of correcting both the input / output air-fuel ratio and removing the bias by adjusting the fluctuation center of the input-output air-fuel ratio to zero is adopted, but other methods can also be adopted. For example, it is possible to correct only the input air-fuel ratio and align the fluctuation center with the fluctuation center of the output air-fuel ratio, or vice versa. The correction target may be at least one of the input and output air-fuel ratios.

  Next, the dead time correction unit 56 will be described. As described above, there is a dead time L due to transport delay between the input air-fuel ratio u (t) and the output air-fuel ratio y (t). However, in order to accurately identify the model parameter, it is preferable to perform correction so as to remove this dead time L. Therefore, such a correction is performed by the dead time correction unit 56. Specifically, the dead time L is calculated by a method described later, and at least one of the input air-fuel ratio u (t) and the output air-fuel ratio y (t) is corrected based on the calculated dead time L. Particularly in this embodiment, the input air-fuel ratio u (t) is delayed so as to approach the output air-fuel ratio y (t) by the calculated dead time L.

  FIG. 10 shows the input air-fuel ratio (dashed line) before the dead time correction, the input air-fuel ratio (solid line) and the output air-fuel ratio (one-dot chain line) after the dead time correction. Note that values after bias correction are used as the input air-fuel ratio and the output air-fuel ratio. When the input air-fuel ratio is delayed by the dead time L, the oscillation of the input air-fuel ratio and the oscillation of the output air-fuel ratio come to synchronize without time difference, thereby improving the accuracy of model parameter identification.

  Hereinafter, a method for calculating the dead time will be described. First, the dispersion value σ of the input air-fuel ratio and the output air-fuel ratio during active control is sequentially obtained by the following equation (23).

η means the input air-fuel ratio or output air-fuel ratio, and η _avg is the M-time moving average of the input air-fuel ratio or output air-fuel ratio at this time (t), that is, (M−1) times before (t) this time (t -(M-1)) is an average value of data. For example, M is 5 or the like. The dispersion value increases as the change in the input air-fuel ratio or the output air-fuel ratio increases.

  FIG. 11 shows a test result regarding the dead time correction, and shows a case of a normal sensor. The upper graph shows a: the input air-fuel ratio before the dead time correction, b: the input air-fuel ratio after the dead time correction, and c: the output air-fuel ratio. Note that the input air-fuel ratios indicated by a and b are values after the fuel dynamics correction and the bias correction are performed, and the output air-fuel ratios indicated by c are values after the bias correction is performed. The middle graph shows the dispersion value of the input air-fuel ratio before the dead time correction indicated by d: a and the dispersion value of the output air-fuel ratio indicated by e: c. In the lower graph, the sawtooth waveform f is the dead time counter value, the horizontal line g at the high position is the dead time calculated as described later, and the horizontal line h at the lower position is the dead time g ¼. Each of the values is shown.

  FIG. 12 shows only a, c, d, and e in FIG. 11 in a simplified manner. As can be seen from FIG. 12, the dispersion values d and e of the input air-fuel ratio and the output air-fuel ratio rise instantaneously according to the timing at which the input air-fuel ratio a and the output air-fuel ratio c start to reverse. Therefore, the dead time calculation start timing is set, for example, as the timing when the dispersion value peak dp of the input air-fuel ratio a appears, and the dead time calculation end timing is set as the output air-fuel ratio dispersion value e exceeds a predetermined threshold value eps. The time difference between these timings is calculated as a dead time g. Referring to FIG. 11, when the dispersion value peak dp of the input air-fuel ratio occurs, the dead time counter f starts counting time from the time of occurrence. Then, when the dispersion value e of the output air-fuel ratio exceeds the threshold value eps, the count is stopped and the count value is held as a dead time g. The dead time g is updated every time the input air-fuel ratio is reversed, and the dead time h after the annealing is calculated for each inversion. The reason for calculating the dead time h after annealing is to remove the influence of noise. The value of the dead time h after annealing will eventually converge to a certain value. Therefore, the dead time h after the annealing is acquired at the time after the predetermined time when the dead time h after the annealing converges to a substantially constant value from the start of the active control, and the obtained value Is determined as the final dead time L.

  By the way, although the above calculation method demonstrated with FIG.11 and FIG.12 is a case of a normal sensor, when it is the case of the sensor deteriorated to some extent, it may be difficult to employ | adopt the same method. That is, as shown in FIGS. 13 and 14, for example, in the case of a sensor having a response delay, a sufficiently large value exceeding the threshold value eps can be obtained as the dispersion value e of the output air-fuel ratio b. Therefore, the dead time cannot be calculated.

  Therefore, the dispersion value of the output air-fuel ratio e is compared with a predetermined threshold value eps, and when the dispersion value e exceeds the threshold value eps, as shown in FIGS. The dead time g is defined as the time difference between the time when the difference is exceeded and the time when the dispersion value peak dp of the input air-fuel ratio appears. On the other hand, as shown in FIGS. 13 and 14, when the dispersion value e of the output air-fuel ratio does not exceed the threshold value eps, the time difference between the extreme values ap and cp of the input and output air-fuel ratios a and c itself (cp− ap) is the dead time g. As a result, even in the case of a deteriorated sensor, the dead time can be calculated accurately.

  In this dead time correction, the input air-fuel ratio is delayed by the dead time to make the timing coincide with the output air-fuel ratio. However, other methods can be adopted. For example, if you do not perform sequential identification, for example, if you acquire a lot of sample data and store it temporarily, then perform identification, the output air-fuel ratio may be advanced by the dead time to match the timing with the input air-fuel ratio. The input air-fuel ratio can be delayed and the output air-fuel ratio can be advanced to make the timings coincide. The correction target may be at least one of the input and output air-fuel ratios.

  Further, the start timing of the dead time calculation is not limited to the timing when the dispersion value peak dp of the input air-fuel ratio a appears as described above. In the first place, since the ECU itself switches or reverses the input air-fuel ratio a (specifically, the target air-fuel ratio A / Ft), the ECU itself knows the timing. Further, the time lag from switching of the target air-fuel ratio A / Ft to switching of the actual fuel injection amount is negligible. Therefore, the time when the ECU 20 switches the input air-fuel ratio a, specifically, the time when the target air-fuel ratio A / Ft is switched or the time when the fuel injection amount is switched can be set as the start timing of the dead time calculation. Incidentally, the timing at which the dispersion value peak dp of the input air-fuel ratio a appears coincides with the timing at which the fuel injection amount is switched.

  Next, an air-fuel ratio sensor abnormality diagnosis procedure including all the above-described corrections will be described with reference to FIG. First, in step S101, active control for forcibly oscillating the air-fuel ratio is executed. In step S102, the value of the input air-fuel ratio u (t) after the fuel dynamics correction is calculated. In step S103, the input / output is calculated. The values of the input air-fuel ratio u (t) and the output air-fuel ratio y (t) are shift-corrected so that there is no bias between the air-fuel ratios.

  In the subsequent step S104, the dead time L is calculated, and the value of the input air-fuel ratio u (t) after bias correction is shift-corrected by the dead time L so that the dead time L is eliminated in step S105. In the next step S106, model parameters are derived from the relationship between the input air-fuel ratio u (t) after the dead time correction obtained in step S105 and the output air-fuel ratio y (t) after the bias correction obtained in step S103. A time constant T and a gain k are identified. In step S107, the identified parameters T and k are compared with each abnormality determination value (time constant abnormality determination value Ts, gain increase abnormality determination value ks1 and gain reduction abnormality determination value ks2), and an air-fuel ratio sensor (catalyst) The response of the front sensor 17) and the normality / abnormality of the output are determined.

Various modifications can be considered for the above-described abnormality diagnosis. For example, in the case of a direct injection engine that directly injects fuel into the combustion chamber 3, it is not necessary to consider fuel adhesion to the wall surface of the intake passage, so that fuel dynamics correction is omitted. Although the above diagnosis is an application example to a so-called wide-range air-fuel ratio sensor, an application example to a so-called O ₂ sensor such as the post-catalyst sensor 18 is also possible. A sensor for detecting the air-fuel ratio of exhaust gas including such an O ₂ sensor is referred to as an air-fuel ratio sensor according to the present invention. In the above diagnosis, the two parameters k and T of the first-order lag element G (s) = k / (1 + Ts) are identified, and abnormality of two characteristics (output and responsiveness) corresponding to each is diagnosed. Alternatively, three or more parameters may be identified and an abnormality may be diagnosed for one or more characteristics. For example, including a dead time as a first-order lag element, that is,

, Three parameters k, T, and L may be simultaneously identified, and abnormality in three characteristics (output, responsiveness, and dead time) corresponding to each may be diagnosed simultaneously. The identification of each parameter may be performed with a time difference, and the abnormality determination of each characteristic may be performed with a time difference.

  By the way, in order to improve identification accuracy and diagnostic accuracy, it is appropriate to accurately calculate and control the input air-fuel ratio. Therefore, a method for that purpose will be described below.

[Basic mode of input air-fuel ratio calculation]
As described above, the input air-fuel ratio u (t) is the ratio Ga between the fuel injection amount Q calculated based on the energization time of the injector 12 and the intake air amount Ga calculated based on the output of the air flow meter 5. / Q. The fuel injection amount Q here is calculated as follows.

  First, a fuel injection amount (basic injection amount Qb) at which a central air-fuel ratio A / Fc, that is, a theoretical air-fuel ratio = 14.6 is obtained for a certain intake air amount Ga is calculated by the following equation (24). . This basic injection amount Qb forms the central injection amount referred to in the present invention.

Here, Qm is a map injection amount obtained from a predetermined map based on the detected value of the intake air amount Ga, and this map injection amount Qm is such that the stoichiometric air-fuel ratio can be obtained in a standard state such as when the engine is adapted. It is previously defined as a correct value. Kf is an increase / decrease correction coefficient, and is a value used for increase / decrease correction accompanying acceleration / deceleration or the like. Kg is a learning value, the content of which will be described later. Qfb is an air-fuel ratio feedback correction term, which is a value based on the difference between the actual air-fuel ratio detected by the pre-catalyst sensor 17 and the stoichiometric air-fuel ratio, and for bringing the actual air-fuel ratio closer to the stoichiometric air-fuel ratio. Value. For example, when the actual air-fuel ratio is leaner than the stoichiometric air-fuel ratio, it becomes a large value (positive value) to increase the basic injection amount Qb, and conversely, when the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio, It becomes a small value (negative value) to decrease the basic injection amount Qb. Qw is a wet correction term and is a value that takes into account the fuel wall surface adhesion, and is obtained from a predetermined map based on a cooling water temperature detected by a water temperature sensor (not shown) before completion of engine warm-up.

  The learning value Kg is expressed by the following equation (25).

  Kfb is an air-fuel ratio learning value, which is a learning value that is updated as needed based on the air-fuel ratio feedback correction term Qfb. Specifically, when the difference between the actual air-fuel ratio and the stoichiometric air-fuel ratio is large, an air-fuel ratio feedback correction term Qfb having a large absolute value is obtained sequentially (at each sampling time). As the air-fuel ratio learning value Kfb is gradually reflected in the longer predetermined period, the absolute value of the air-fuel ratio feedback correction term Qfb becomes smaller. In short, the air-fuel ratio learning value Kfb corresponds to a value obtained by changing the air-fuel ratio feedback correction term Qfb that changes at each sampling time. If the air-fuel ratio learning value Kfb reaches a value that matches the actual condition, the air-fuel ratio feedback correction amount is small. This air-fuel ratio learning value Kfb is used for the purpose of absorbing air-fuel ratio individual variations for each internal combustion engine.

  Kp is a purge concentration learning value, which is a learning value corresponding to the amount of fuel (purge fuel amount) contained in the purge gas at the time of purge execution. When purging, the fuel contained in the purge gas is drawn into the combustion chamber 3 in addition to the fuel injected from the injector 12. Therefore, unless the fuel injection amount from the injector 12 is determined in consideration of the purge fuel amount, a fuel amount capable of realizing a desired air-fuel ratio (theoretical air-fuel ratio) cannot be supplied into the combustion chamber 3. Therefore, the purge concentration learning value Kp is used when calculating the basic injection amount Qb. The purge concentration learning value Kp is updated based on the difference between the actual air-fuel ratio feedback correction term Qfb at the time of purge execution and the reference value (0 in this embodiment) of the air-fuel ratio feedback correction term Qfb. That is, when the purge fuel is large, the output of the pre-catalyst sensor 17 swings to the rich side, and accordingly, the air-fuel ratio feedback correction term Qfb becomes small so as to reduce the fuel injection amount from the injector 12. Conversely, when the purged fuel is low, the output of the pre-catalyst sensor 17 swings to the lean side, and accordingly, the air-fuel ratio feedback correction term Qfb increases so as to increase the fuel injection amount from the injector 12. Since the amount of purge fuel is thus reflected in the air-fuel ratio feedback correction term Qfb, the purge concentration learning value Kp is learned at any time by the difference between the actual air-fuel ratio feedback correction term Qfb and the reference value at the time of purge execution. Thus, the average purge fuel amount at the time of purge execution can be reflected in the fuel injection amount from the injector 12. The purge is performed after the internal combustion engine has been warmed up. When purging, a target purge rate is calculated, and a drive signal having a duty ratio corresponding to the target purge rate is sent to the purge control valve 33. The purge rate is a value representing the ratio of the purge gas flow rate to the intake air amount Ga in percent.

  The basic injection amount Qb thus determined is a fuel injection amount from the injector 12 such that the air-fuel ratio in the combustion chamber 3 is the stoichiometric air-fuel ratio with respect to the actual intake air amount Ga. Therefore, the basic injection amount Qb is injected from the injector 12 during the stoichiometric control. However, during active control, it is necessary to set the air-fuel ratio in the combustion chamber 3 to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio or a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio. Therefore, the basic injection amount Qb is multiplied by the active coefficient Ka to calculate the fuel injection amount (active injection amount) Qa injected from the injector 12 during active control (Qa = Ka × Qb).

  The active coefficient Ka is substantially equal to a value obtained by dividing the theoretical air-fuel ratio by the air-fuel ratio (lean air-fuel ratio or rich air-fuel ratio) during active control. In the present embodiment, the lean air-fuel ratio = 15.1, the rich air-fuel ratio = 14.1, the active coefficient Kar at the lean air-fuel ratio is 0.965, and the active coefficient Kar at the rich air-fuel ratio is 1. 035. That is, the fuel injection amount is decreased by 0.035Qb when the air-fuel ratio is lean, and the fuel injection amount is increased by 0.035Qb when the air-fuel ratio is rich. The fuel injection amount for this decrease or increase is collectively referred to as the active increase / decrease injection amount, the fuel injection amount for the decrease is referred to as the active decrease injection amount, and the fuel injection amount for the increase is referred to as the active increase injection amount. The active injection amount Qa thus determined forms the fuel injection amount Q when calculating the input air-fuel ratio u (t), and the injector 12 is energized for a time corresponding to the active injection amount Qa, and the active injection amount An amount of fuel equal to Qa is injected from the injector 12.

  Note that the meaning of the air-fuel ratio feedback correction term Qfb differs between the stoichiometric control and the active control. The air-fuel ratio feedback correction term Qfb during stoichiometric control is simply a value based on the difference between the air-fuel ratio detected by the pre-catalyst sensor 17 and the stoichiometric air-fuel ratio, but the air-fuel ratio feedback correction term Qfb during active control is The value based on the difference between the value obtained by the air-fuel ratio detected by the pre-catalyst sensor 17 and the stoichiometric air-fuel ratio. Accordingly, while the fuel injection amount is feedback controlled during the stoichiometric control, the fuel injection amount is controlled by a method almost similar to the open control during the active control.

  In the above calculation method, the calculation is performed in the unit of the fuel injection amount. However, since the fuel injection amount and the energization time of the injector 12 are in a proportional relationship, the calculation may be performed in the unit of the energization time. The case where the calculation is performed in units of the energization time is also included in the present invention.

[First aspect: Consideration of operating state of internal combustion engine]
By the way, the condition for executing the active control and the parameter identification is when one of the following conditions (1) and (2) is satisfied.
(1) There is a learning completion history of the learning value Kg in the operating region where the current operating state of the internal combustion engine is located.
(2) The feedback (F / B) correction rate obtained from the current air-fuel ratio feedback correction term Qfb is within a predetermined range.

  The condition (1) will be described. As shown in FIG. 16, the entire operation region of the internal combustion engine is divided or divided into a plurality of regions L1 to L5 in advance according to the load (more specifically, the intake air amount Ga). ing. In order to satisfy the condition (1), it is necessary that learning of the learning value Kg is completed at least once at any time in the past. For example, immediately after the shipment of a new car or immediately after battery replacement, no value is input as the learning value Kg for all the regions L1 to L5, and learning has not yet been completed for all the regions L1 to L5. Then, as the vehicle travels thereafter, learning for each region is completed in sequence. In the illustrated example, learning is completed (with learning completion history) in regions L1 to L3, but learning is not completed (no learning completion history) in regions L4 to L5. Therefore, if the current operating state of the internal combustion engine is located in the learning completion region (any one of L1 to L3) as indicated by a black circle in the figure, the condition (1) is satisfied. On the contrary, if the current operating state of the internal combustion engine is located in the learning incomplete region (any of L4 to L5) as indicated by white circles in the figure, the condition (1) is not satisfied.

  Note that the method of dividing the operation region of the internal combustion engine is not limited to the division based only on the load as described herein. In addition to the load or instead of the load, it may be classified according to the engine speed, or may be classified according to other operating state parameters. The number of divisions is not limited to five as shown above.

  Next, the condition (2) will be described. The F / B correction rate is represented by the ratio between the basic injection amount Qb and the air-fuel ratio feedback correction term Qfb, and specifically is represented by Qfb / Qb. Condition (2) is, for example, that the F / B correction rate is within ± 2%.

  The reason why the condition (1) is required is that if the current operating state of the internal combustion engine is located in an operating region having a learning completion history, the air-fuel ratio deviation based on the individual difference of the internal combustion engine has already been learned, and the basic injection This is because the accuracy of the amount Qb is guaranteed and the active injection amount Qa can also be accurately calculated. The reason for the requirement (2) is that if the F / B correction rate is within a predetermined range, the actual air-fuel ratio deviation is small, the accuracy of the basic injection amount Qb is guaranteed, and the active injection amount Qa is also accurate. This is because it can be calculated as follows.

  Incidentally, the execution condition of the active control is that either of the conditions (1) and (2) is satisfied. Therefore, even if the condition (1) is not satisfied (that is, even if the operating state of the internal combustion engine is not located in the learning completion region), if the condition (2) is satisfied (that is, the F / B correction factor is predetermined). If so, active control can be performed.

  However, after the start of the active control, the meaning of the air-fuel ratio feedback correction term Qfb is different from that before the start, and even if the F / B correction rate is within the predetermined range, the operating state of the internal combustion engine is in the learning completion region. The calculation accuracy of the basic injection amount Qb, which is equivalent to when it is positioned, cannot be guaranteed. For this reason, there is a possibility that the basic injection amount Qb cannot be accurately calculated when the learning completion area is shifted to the learning incomplete area as shown by the arrow in FIG. 16 during active control. A similar problem can also occur when the learning incomplete area is shifted to the learning completed area during active control.

Therefore, in the first aspect, when the operation state of the internal combustion engine shifts between the learning completion region and the learning incomplete region during execution of active control and identification, any of the following measures (A) and (B) Apply.
(A) The identification is temporarily stopped immediately after the transition.
(B) The active control and identification are stopped simultaneously with the transition.
In this way, in the case of the measure (A), a waiting time immediately after the transition is provided, and the incorrect active injection amount Qa is calculated based on the inaccurate basic injection amount Qb during that time, and thus the inaccurate input empty Identification by the fuel ratio u (t) can be prevented. On the other hand, when such a waiting time elapses, each value settles to a value corresponding to the area after the transition. By restarting the identification after this elapse, the accurate active injection amount Qa based on the accurate basic injection amount Qb can be obtained. It is possible to realize calculation and high-precision identification based on the accurate input air-fuel ratio u (t). On the other hand, in the case of the measure (B), the active control and the identification are stopped simultaneously with the transition, so that the identification by the inaccurate input air-fuel ratio u (t) can be similarly prevented.

  Hereinafter, specific examples of these countermeasures (A) and (B) will be described in order. FIG. 17 shows a procedure of active control and parameter identification executed by the ECU 20 so as to realize the countermeasure (A).

  First, in step S201, whether or not there is a learning completion history of the learning value Kg in the operating region (current region) where the current operating state of the internal combustion engine is located (that is, whether or not the condition (1) is satisfied). ) Is judged. If the determination result is yes, the process proceeds to step S203 and active control is executed or started. In step S204, data (input / output data) of the input air-fuel ratio u (t) and the output air-fuel ratio y (t) are acquired. Identification is performed with the acquired data.

  On the other hand, if the determination result in step S201 is no, the process proceeds to step S202, and whether or not the current F / B correction rate is within a predetermined range (that is, whether or not the condition (2) is satisfied). Is judged. If the determination result is yes, the process proceeds to steps S203 and S204, where active control and identification are executed. On the other hand, if the determination result is no, the determination result of either step S201 or step S202 is yes. It will be in a standby state.

  After step S204, the process proceeds to step S205, where it is determined whether or not the operating state of the internal combustion engine has shifted between a learning completion region and a learning incomplete region. If there is no transition, the process returns to step S203 to continue the active control and identification, but if there is a transition, the identification is temporarily stopped (paused) in steps S206 to S211. That is, the active control is continued during the temporary stop period, but the input / output data is discarded, and the identification is also stopped. Here, “with transition” includes not only the case where the learning completion area is transferred to the learning incomplete area but also the case where the learning completion area is shifted to the learning completion area. In the former case, the determination result in step S201 is yes and the active control is started from the learning completion region. In the latter case, the determination result in step S201 is no but the determination result in step S202 is yes and the learning is not performed. This can happen when active control is started from the completion area.

  First, in step S206, the value N of the mask counter is set to a predetermined initial value. The initial value of this embodiment is 5. In step S207, it is determined whether or not the value N of the mask counter is equal to or greater than a predetermined mask release threshold value Ns. The mask release threshold value Ns in this embodiment is 1. If the determination result is yes, in step S208, a stop flag for stopping the identification is turned on. In step S209, the input / output data captured by the ECU 20 is discarded, and the identification using the input / output data is performed. Stopped. As a result, the update of the gain k and the time constant T, which are identification parameters, is temporarily stopped. Next, in step S210, it is determined whether one cycle of active control has ended. One cycle of the active control refers to a period from when the input air-fuel ratio u (t) is switched from one of the rich air-fuel ratio and the lean air-fuel ratio to the next when it is switched in the same direction. If one cycle has not ended, the standby state is entered, and the input / output data discard and identification stop in step S209 are continued. On the other hand, when one cycle is completed, the process proceeds to step S211 where the value N of the mask counter is subtracted by 1 (N = N-1), and the process returns to step S207.

  Thus, when there is a transition between the learning completed and incomplete areas, immediately after that, until N ≧ Ns does not hold, in this embodiment, the input / output data continues to be discarded for five cycles of active control, and identification is performed. Will continue to be stopped.

  On the other hand, if N ≧ Ns is not established in step S207, the process proceeds to step S212, the stop flag is turned off, the pause is released, and acquisition and identification of input / output data are resumed in step S213. As a result, the gain k and the time constant T, which are identification parameters, are updated again from the values immediately before the start of the temporary stop.

  Next, countermeasure (B) will be described. FIG. 18 shows a procedure of active control and parameter identification executed by the ECU 20 so as to realize the measure (B). The flowchart shown in FIG. 18 differs from the flowchart shown in FIG. 17 in that the entire process is repeatedly executed every predetermined sampling period.

  In steps S301 and S302, as in steps S201 and S202, whether or not there is a learning completion history of the learned value Kg in the operating region where the current operating state of the internal combustion engine is located (that is, the condition (1) is satisfied). And whether or not the current F / B correction factor is within a predetermined range (that is, whether or not the condition (2) is satisfied).

  If any determination result is NO, the process proceeds to step S308 where the active control is prohibited, and then the input / output data taken into the ECU 20 is discarded in step S309, and the identification is prohibited.

  On the other hand, if any one of the determination results is YES, the process proceeds to step S303, and it is determined whether or not the transition flag is OFF. This transition flag is a flag that is turned on when the operating state of the internal combustion engine transitions between the learning completion region and the learning incomplete region during active control, and the initial state is off. When the transition flag is not off (on), active control is prohibited in steps S308 and S309, input / output data is discarded, and identification is prohibited.

  On the other hand, when the transition flag is off, the process proceeds to step S304, where active control is executed or started, input / output data is acquired in step S305, and identification is executed based on the acquired data. Thereafter, the process proceeds to step S306, and it is determined whether or not there has been a shift in the operating state of the internal combustion engine between the learning completed / uncompleted regions. If there is no transition, the process is terminated. If there is a transition, the transition flag is turned on in step S307, and the process is terminated.

  According to this, first, active control is started when either of the conditions (1) and (2) is satisfied (Yes in either S301 or S302), and input / output data acquisition and identification are executed (S304, S302). S305). At this stage, the transition flag is still off (Yes in S303). Then, when there is a transition between the learning completed and incomplete areas (Yes in S306), the transition flag is turned on (S307). When the next routine is executed, the transition flag is on (No in S303), so that active control is prohibited, input / output data is discarded, and identification is prohibited (S308, S309). In this way, active control and identification are stopped simultaneously with the transition.

[Second Embodiment: Improvement of Active Injection Amount Calculation Method]
As described above, in the basic mode, the active injection amount Qa is calculated by multiplying the basic injection amount Qb calculated by the following equation (24) by the active coefficient Ka.

However, Qm is a map injection amount, Kf is an increase / decrease correction coefficient, Kg is a learning value, Qfb is an air-fuel ratio feedback correction term, and Qw is a wet correction term.

  The learning value Kg is represented by the following equation (25).

However, Kfb is an air-fuel ratio learning value, and Kp is a purge concentration learning value. Since the learning value Kg includes the purge concentration learning value Kp, the basic injection amount Qb includes an influence of an average or approximate purge fuel amount based on the past circumstances.

  However, during purge execution and active control, the actual or current purge fuel amount is not necessarily equal to the fuel amount corresponding to the purge concentration learning value Kp. For this reason, when the actual purge fuel amount is larger than the fuel amount corresponding to the purge concentration learning value, for example, the basic injection amount Qb becomes smaller than the stoichiometric amount, and the active injection amount Qa also becomes smaller than the target air-fuel ratio. As a result, the air-fuel ratio becomes leaner than the target air-fuel ratio. In other words, when the actual purge fuel amount is larger than the fuel amount corresponding to the purge concentration learning value, the output of the pre-catalyst sensor 17 fluctuates to the rich side with respect to the target air-fuel ratio, and negative air-fuel ratio feedback is performed so as to eliminate this rich error. A correction term Qfb is calculated. Then, the calculated basic injection amount Qb becomes smaller than the stoichiometric amount. Since the active injection amount Qa is a product of the basic injection amount Qb and a constant active coefficient Ka, the calculated active injection amount Qa is also equivalent to the target air-fuel ratio when the basic injection amount Qb is smaller than the stoichiometric equivalent amount. Less than the injection amount. As a result, the actual injection amount becomes smaller than the injection amount corresponding to the target air-fuel ratio, and the air-fuel ratio (input air-fuel ratio u (t)) of the exhaust gas supplied to the pre-catalyst sensor 17 becomes leaner than the target air-fuel ratio. . When the actual purge fuel amount is smaller than the fuel amount corresponding to the purge concentration learning value, the active injection amount Qa is larger than the injection amount corresponding to the target air-fuel ratio by the reverse principle, and as a result, the air-fuel ratio becomes the target air-fuel ratio. Become richer.

  Thus, when active control is performed during purge execution, there is a problem that the input air-fuel ratio u (t) causes an error with respect to the target air-fuel ratio in accordance with the actual purge fuel amount.

  In order to solve this problem, the calculation method used when the ECU 20 calculates the active injection amount Qa is changed as follows. First, the basic injection amount Qb is calculated by the previous equation (24), and then the purge fuel amount Qp as an estimated value is calculated by the following equation (26).

The purge fuel amount Qp is an estimated value of the fuel amount contained in the actual purge gas. The reason why Kp is divided by 100 is that Kp is a value having a unit of percent. Thus, the actual purge fuel amount Qp is estimated as a value independent of the basic injection amount Qb.

  Next, based on the basic injection amount Qb and the estimated purge fuel amount Qp, an active increase / decrease injection amount ΔQ that is increased or decreased with respect to the basic injection amount Qb is calculated by the following equation (27).

However, the active coefficient Ka at the time of increasing (during rich air-fuel ratio control) is 1.035, and the active coefficient Ka at the time of decreasing (during lean air-fuel ratio control) is 0.965.

  Finally, the active injection amount Qa is calculated by the following equation (28) based on the basic injection amount Qb and the active increase / decrease injection amount ΔQ. The injector 12 is energized only for a time corresponding to the active injection amount Qa thus calculated, and an amount of fuel equal to the active injection amount Qa is injected from the injector 12.

  According to this calculation method, the estimated purge fuel amount Qp is calculated separately from the basic injection amount Qb, and the sum of the basic injection amount Qb and the estimated purge fuel amount Qp is multiplied by (Ka-1) to increase or decrease the amount. The active increase / decrease injection amount ΔQ is calculated, and the active increase / decrease injection amount ΔQ is added to the basic injection amount Qb to obtain the active injection amount Qa. In particular, since the estimated purge fuel amount Qp is calculated separately from the basic injection amount Qb, the effect of the actual increase or decrease in the purge fuel amount can be reflected in the active injection amount Qa. Specifically, the estimated purge fuel amount Qp is multiplied by (Ka-1) to obtain an increase or decrease for the estimated purge fuel amount Qp alone (Equation (27)), and this is added to the basic injection amount Qb. Thus, the active injection amount Qa is obtained (formula (28)). As a result, regardless of the actual amount of purge fuel, it is possible to improve the calculation accuracy of the active injection amount Qa, improve the accuracy of the input air-fuel ratio u (t), and increase the identification accuracy and diagnosis accuracy. .

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, the sequential least square method is used as the identification method in the first-order lag model in the above embodiment, but various other identification methods can be employed, such as the Kalman filter method.

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

1 is a schematic view of an internal combustion engine according to an embodiment of the present invention. It is a figure which shows roughly the mode of the change of the input air fuel ratio at the time of active control, and an output air fuel ratio. It is a graph which shows the result of having identified a gain and a time constant, and is a case of a normal sensor. It is a graph which shows the result of having identified a gain and a time constant, and is a case of an abnormal sensor. It is a block diagram of an abnormality diagnosis system. It is a test result comparing the input air-fuel ratio with and without fuel dynamics correction. It is a test result which shows the mode of a change with an input air fuel ratio and an output air fuel ratio, and is the state before bias correction. It is the schematic for demonstrating the method of bias correction. It is a test result which shows the mode of a change with an input air fuel ratio and an output air fuel ratio, and is the state after bias correction | amendment. It is a test result which shows the input air fuel ratio before and behind dead time correction. It is a test result for demonstrating a dead time calculation method, and is a case of a normal sensor. It is the schematic corresponding to FIG. 11 for demonstrating a dead time calculation method. It is a test result for explaining a dead time calculation method, and is a case of an abnormal sensor. It is the schematic corresponding to FIG. 13 for demonstrating a dead time calculation method. It is a flowchart which shows the procedure of an air fuel ratio sensor abnormality diagnosis roughly. It is a figure which shows the division | segmentation of the driving | running | working area | region of an internal combustion engine, the learning completion / uncompleted area | region, and the transition of the driving | running state in the meantime. It is a flowchart which concerns on a 1st aspect. It is another flowchart which concerns on a 1st aspect.

Explanation of symbols

1 Internal combustion engine 3 Combustion chamber 6 Exhaust pipe 11 Upstream catalyst 12 Injector 14 Exhaust manifold 17 Pre-catalyst sensor 20 Electronic control unit (ECU)
30 Fuel tank 31 Canister 32 Purge passage 33 Purge control valve A / Fc Central air-fuel ratio u (t) Input air-fuel ratio y (t) Output air-fuel ratio Qb Basic injection amount Kg Learning value Kfb Air-fuel ratio learning value Kp Purge concentration learning value Qa Active injection amount Qp Purge fuel amount k Gain T Time constant

Claims (4)

An abnormality diagnosis apparatus for an air-fuel ratio sensor disposed in an exhaust passage of an internal combustion engine,
Active control means for performing active control for periodically switching the fuel injection amount from the fuel injection valve to alternately switch the air-fuel ratio as an input to a rich side and a lean side with respect to a predetermined center air-fuel ratio;
During active control, parameters in the first-order lag element are identified based on the input to a model obtained by modeling the system from the fuel injection valve to the air-fuel ratio sensor with a first-order lag element and the output of the air-fuel ratio sensor. An identification means;
An abnormality determining means for determining an abnormality of a predetermined characteristic of the air-fuel ratio sensor based on the parameter identified by the identifying means;
The active control means calculates a fuel injection amount (center injection amount) corresponding to the central air-fuel ratio based on a predetermined learning value, and calculates a fuel injection amount during active control based on the central injection amount. Injecting from the fuel injection valve,
The learning value is learned for each operation region of the internal combustion engine divided into a plurality of parts,
When the operation state of the internal combustion engine shifts between the learning completion region and the learning incomplete region during execution of the active control and identification, the identification is temporarily stopped immediately after the transition, or the active control is performed simultaneously with the transition. And an abnormality diagnosing device for an air-fuel ratio sensor, further comprising a transition prohibiting means for canceling the identification. The transition prohibition means temporarily stops identification immediately after transition, and stops identification from the transition to the end of the predetermined period of the active control. The abnormality diagnosis device for an air-fuel ratio sensor according to claim 1. The abnormality diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the learning value includes an air-fuel ratio learning value and a purge concentration learning value.   The parameter in the first-order lag element includes at least a gain and a time constant, and the predetermined characteristic of the air-fuel ratio sensor includes at least an output corresponding to the gain and a responsiveness corresponding to the time constant.
  The abnormality diagnosis apparatus for an air-fuel ratio sensor according to any one of claims 1 to 3.

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