JP4985357B2 - Abnormality diagnosis apparatus and abnormality diagnosis method for air-fuel ratio sensor - Google Patents

Description

  The present invention relates to an apparatus and a method for diagnosing abnormality of an air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas 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.

  Patent Document 1 discloses an abnormality of an air-fuel ratio sensor that detects an abnormality of the air-fuel ratio sensor based on a trajectory length or area of an air-fuel ratio sensor output that periodically increases and decreases by open-loop control. A detection device is disclosed. Patent Document 2 discloses an air-fuel ratio control apparatus that sequentially identifies a plant model that represents the detection delay characteristic of an air-fuel ratio sensor and sets a control gain in air-fuel ratio feedback control using parameters of the identified plant model. Has been. In this case, the identification is sequentially stopped when the response deterioration diagnosis of the air-fuel ratio sensor is performed during the feedback control.

JP 2005-30358 A JP 2004-68602 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. However, with the technique described in Patent Document 1, it is impossible to determine which of these characteristics is abnormal.

  Moreover, in the technique described in Patent Document 2, only the deterioration of responsiveness is diagnosed among the characteristics of the air-fuel ratio sensor. However, the air-fuel ratio sensor includes other characteristics, and it is impossible to determine abnormality of the other characteristics. In the first place, the technique described in Patent Document 2 is related to air-fuel ratio control, and is not specialized for abnormality diagnosis of an air-fuel ratio sensor. Therefore, the parameters of the plant model identified sequentially are used to set the control gain of the air-fuel ratio feedback control, and the sequential identification is stopped at the time of response delay diagnosis of the air-fuel ratio sensor.

  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 and abnormality diagnosis method for an air-fuel ratio sensor that can preferably diagnose abnormality of individual characteristics included in the air-fuel ratio sensor. Is to provide.

According to the first aspect of the present invention,
An air-fuel ratio sensor abnormality diagnosis device for detecting an air-fuel ratio of exhaust gas of an internal combustion engine,
The system from the fuel injection valve to the air-fuel ratio sensor is modeled by a first-order lag element, and parameters in the first-order lag element are identified based on the input air-fuel ratio given to the air-fuel ratio sensor and the output air-fuel ratio output from the air-fuel ratio sensor. An identification means;
There is provided an abnormality diagnosis device for an air-fuel ratio sensor, comprising abnormality determination means for determining an abnormality of a predetermined characteristic of the air-fuel ratio sensor based on the parameter identified by the identification means.

  According to the first embodiment, the abnormality of the air-fuel ratio sensor is not simply determined, but the abnormality of the predetermined characteristic of the air-fuel ratio sensor is determined. 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.

According to a second aspect of the present invention, in the first aspect,
The abnormality determination means determines at least two abnormalities among the characteristics of the air-fuel ratio sensor based on at least two parameters identified by the identification means.

  According to the second embodiment, since at least two abnormalities of the characteristics of the air-fuel ratio sensor are determined, the abnormalities of the at least two characteristics can be determined simultaneously and individually as an abnormality diagnosis of the air-fuel ratio sensor. It can be very suitable.

According to a third aspect of the present invention, in the second aspect,
The at least two parameters are at least a time constant and a gain, and at least two of the characteristics of the air-fuel ratio sensor are at least responsiveness and output.

  Among the characteristics of the air-fuel ratio sensor, responsiveness and output are important characteristics that affect the performance of the sensor. According to the third embodiment, at least the abnormality of these two important characteristics can be diagnosed, so that it is extremely suitable as an abnormality diagnosis of the air-fuel ratio sensor.

According to a fourth aspect of the present invention, in any one of the first to third aspects,
A dead time correction unit that calculates a dead time between the input air-fuel ratio and the output air-fuel ratio, and shift-corrects at least one of the input air-fuel ratio and the output air-fuel ratio by the dead time. And

  As a result, the influence of transport delay can be eliminated, and the parameter identification accuracy can be improved.

According to a fifth aspect of the present invention, in the fourth aspect,
The dead time correction means calculates the dead time according to a predetermined map or function based on at least one parameter relating to the operating state of the internal combustion engine.

According to a sixth aspect of the present invention, in the fourth aspect,
The dead time correcting means calculates a dispersion value between the input air-fuel ratio and the output air-fuel ratio, and when the dispersion value peak of the output air-fuel ratio is larger than a predetermined value, the dispersion value peak of the input air-fuel ratio and the output The dead time is calculated based on a time difference from the dispersion value peak of the air-fuel ratio.

According to a seventh aspect of the present invention, in the sixth aspect,
The dead time correction means calculates the dead time based on a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio when a dispersion value peak of the output air-fuel ratio is equal to or less than the predetermined value. And

According to an eighth aspect of the present invention, in the fourth aspect,
The dead time correction means calculates a first dead time according to a predetermined map on the basis of at least one parameter relating to the operating state of the internal combustion engine, and also distributes a dispersion value peak between the input air-fuel ratio and the output air-fuel ratio. Or a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio, a second dead time is calculated, and a deviation amount of the second dead time with respect to the first dead time is greater than a predetermined value. When it is larger, the second dead time is determined as a final dead time, and the map data is updated by the second dead time.

According to a ninth aspect of the present invention, in any one of the first to eighth aspects,
Bias correction means is provided for shifting and correcting at least one of the input air-fuel ratio and the output air-fuel ratio so as to remove a bias between the input air-fuel ratio and the output air-fuel ratio.

  As a result, robustness against load fluctuation, learning deviation, and the like can be improved.

According to a tenth aspect of the present invention, in any one of the first to ninth aspects,
Fuel correction means is provided for correcting the input air-fuel ratio based on the amount of fuel adhering to the wall and the amount of evaporation.

  This makes it possible to improve parameter identification accuracy.

According to an eleventh aspect of the present invention, in any one of the first to tenth aspects,
The identification means sequentially identifies the parameter by a sequential least square method.

  As a result, the calculation load and the memory capacity for identification are reduced, and the practicality is improved.

According to a twelfth aspect of the present invention,
An air-fuel ratio sensor abnormality diagnosis method for detecting an air-fuel ratio of exhaust gas of an internal combustion engine,
The system from the fuel injection valve to the air-fuel ratio sensor is modeled by a first-order lag element, and parameters in the first-order lag element are identified based on the input air-fuel ratio given to the air-fuel ratio sensor and the output air-fuel ratio output from the air-fuel ratio sensor. Steps,
And determining an abnormality of the air-fuel ratio sensor based on the identified parameter.

In a thirteenth aspect of the present invention, in the twelfth aspect,
The abnormality determining step is characterized in that at least two abnormalities among the characteristics of the air-fuel ratio sensor are determined based on the identified at least two parameters.

According to a fourteenth aspect of the present invention, in the thirteenth aspect,
The at least two parameters are at least a time constant and a gain, and at least two of the characteristics of the air-fuel ratio sensor are at least responsiveness and output.

According to a fifteenth aspect of the present invention, in any one of the twelfth to fourteenth aspects,
The method includes a step of calculating a dead time between the input air-fuel ratio and the output air-fuel ratio and shift-correcting at least one of the input air-fuel ratio and the output air-fuel ratio by the dead time.

According to a sixteenth aspect of the present invention, in the fifteenth aspect,
The dead time correction step includes calculating the dead time according to a predetermined map or function based on at least one parameter relating to an operating state of the internal combustion engine.

According to a seventeenth aspect of the present invention, in the fifteenth aspect,
The dead time correction step calculates a dispersion value between the input air-fuel ratio and the output air-fuel ratio, and when the dispersion value peak of the output air-fuel ratio is larger than a predetermined value, the dispersion value peak of the input air-fuel ratio and the output The abnormality diagnosis method for an air-fuel ratio sensor according to claim 15, further comprising calculating the dead time based on a time difference from a dispersion value peak of the air-fuel ratio.

According to an eighteenth aspect of the present invention, in the seventeenth aspect,
The dead time correction step includes calculating the dead time based on a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio when a dispersion value peak of the output air-fuel ratio is equal to or less than the predetermined value. It is characterized by that.

According to a nineteenth aspect of the present invention, in the fifteenth aspect,
The dead time correction step calculates a first dead time according to a predetermined map on the basis of at least one parameter relating to the operating state of the internal combustion engine, and also distributes a dispersion value peak between the input air-fuel ratio and the output air-fuel ratio. Or a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio, a second dead time is calculated, and a deviation amount of the second dead time with respect to the first dead time is greater than a predetermined value. When the time is larger, the second dead time is determined as a final dead time, and the map data is updated with the second dead time.

According to a twentieth aspect of the present invention, in any one of the twelfth to nineteenth aspects,
And a step of shift correcting at least one of the input air-fuel ratio and the output air-fuel ratio so as to remove a bias between the input air-fuel ratio and the output air-fuel ratio.

According to a twenty-first aspect of the present invention, in any one of the twelfth to twentieth aspects,
The method includes a step of correcting the input air-fuel ratio based on a fuel wall adhesion amount and an evaporation amount.

According to a twenty-second aspect of the present invention, in any one of the twelfth to twenty-first aspects,
In the identifying step, the parameters are sequentially identified by a sequential least square method.

  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.

  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 A / Ffr detected by the pre-catalyst sensor 17 and the target air-fuel ratio A / Ft, and only the energization time according to the corrected injection amount is obtained. The injector 12 is energized (turned 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 (fuel injection amount) so that the actual air-fuel ratio A / Ffr detected by the pre-catalyst sensor 17 approaches the target air-fuel ratio A / Ft.

  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 input air-fuel ratio supplied to the pre-catalyst sensor 17 and the output air-fuel ratio output from the pre-catalyst sensor 17 are Based on this, the parameters in the first-order lag element are identified (estimated). Then, based on the identified parameter, an abnormality of a predetermined characteristic of the pre-catalyst sensor 17 is determined.

  As the input air-fuel ratio, 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 is used. Hereinafter, the input air-fuel ratio is represented by u (t) (u (t) = Ga / Q). On the other hand, the output air-fuel ratio is the pre-catalyst air-fuel ratio A / Ffr calculated based on the output of the pre-catalyst sensor 17. Hereinafter, the output air-fuel ratio is represented by y (t) (y (t) = A / Ffr). Based on how the output air-fuel ratio y (t) is output when such an input air-fuel ratio u (t) is applied to the pre-catalyst sensor 17, a parameter in the first-order lag element is identified, and based on the identified parameter, the pre-catalyst An abnormality in a predetermined characteristic of the sensor 17 is determined.

  As shown in FIG. 2, in the present embodiment, active control for forcibly oscillating the air-fuel ratio is executed at the time of abnormality diagnosis of the air-fuel ratio sensor. In this active control, the air-fuel ratio A / Ffr (that is, the output air-fuel ratio y (t)) detected by the pre-catalyst sensor 17 is the same amplitude on the lean side and the rich side with a predetermined center air-fuel ratio A / Fc as a boundary. The target air-fuel ratio A / Ft (that is, the input air-fuel ratio u (t)) is oscillated at a constant period so as to swing. The amplitude of the vibration is larger than that in the normal air-fuel ratio control, for example, 0.5 at the air-fuel ratio. The center air-fuel ratio A / Fc is made equal to the stoichiometric air-fuel ratio.

  The reason why the active control is executed at the time of abnormality diagnosis is that the active control is executed at the time of steady operation of the engine, so that each control amount and each detected value are stabilized, and diagnostic accuracy is improved. However, abnormality diagnosis may be executed during normal air-fuel ratio control.

  As shown in the figure, the input air-fuel ratio u (t) has a step-like waveform, while 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). That is, the dead time L corresponds to a 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 suitable abnormality diagnosis for 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 (bias correction unit) 54, and a dead time correction unit (dead time correction unit) 56 are provided. It is done. 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.
fw (ks + 1) = P · fw (ks) + R · fi (ks) (21)
fc (ks) = (1-P) .fw (ks) + (1-R) .fi (ks) (22)

  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, 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 shift-corrected.

  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 the input air-fuel ratio u (t) is delayed so as to approach the output air-fuel ratio y (t) by this 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.

  As a first aspect of the dead time calculation, there is a method of calculating the dead time according to a predetermined map or function based on at least one parameter relating to the engine operating state. FIG. 11 shows an example of such a dead time calculation map. In this map, the dead time L is calculated based on the detected value of the engine speed Ne.

  There is the following as a second mode of dead time calculation. First, the dispersion values of the input air-fuel ratio and the output air-fuel ratio during active control are sequentially obtained by the following equations.

η is a value of the input air-fuel ratio or the output air-fuel ratio, and η _avg is a moving average of M times, that is, an average value of data from (t) to (M−1) times before (t− (M−1)). It is. 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. 12 shows the test results regarding the dead time correction, and shows the 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. 13 shows only a, c, d, and e in FIG. 12 in a simplified manner. As can be seen from FIG. 13, the dispersion value d of the input air-fuel ratio and the dispersion value e of the output air-fuel ratio have the peaks dp and ep of the dispersion values d and e at the timing when the input air-fuel ratio a and the output air-fuel ratio c are reversed. Arise. Therefore, the time difference (ep−dp) between these peaks is calculated as the dead time g. Returning to FIG. 12, when the dispersion value peak dp of the input air-fuel ratio occurs, the dead time counter f starts counting time from the time when the dispersion value peak dp occurs. Then, when the dispersion value peak ep of the output air-fuel ratio occurs, 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 by FIG.12 and FIG.13 is a case of a normal sensor, when it is the case of an abnormal sensor, it is not necessarily appropriate to employ | adopt the same method. That is, as shown in FIGS. 14 and 15, for example, in the case of an abnormal sensor with a response delay, a sufficiently large value cannot be obtained as the dispersion value e of the output air-fuel ratio b, and its peak ep appears. The error also increases with respect to timing.

  Therefore, the dispersion value peak ep of the output air-fuel ratio is compared with a predetermined threshold value eps, and when the dispersion value peak ep is larger than the threshold value eps as shown in FIGS. 12 and 13, as described above. A time difference g between the dispersion value peaks dp and ep of the input / output air-fuel ratio (ep−dp) is defined as a dead time g. On the other hand, as shown in FIGS. 14 and 15, when the output air-fuel ratio dispersion value peak ep is equal to or less than 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. Thereby, even in the case of an abnormal sensor, the dead time can be calculated accurately.

  Now, it is possible to calculate the dead time using only one of these first and second modes and correct the dead time of the input air-fuel ratio. In the third mode below, The dead time is calculated using both the embodiment and the second embodiment. In the third aspect, the first dead time calculated from the map according to the first aspect is compared with the second dead time calculated from the dispersion value or the extreme value according to the second aspect, and both are approaching. If so, the first dead time calculated from the map is used. On the other hand, if the two are separated, the second dead time calculated from the dispersion value or the extreme value is used, and the map data is updated using the second dead time. Originally, the optimum time delay value does not deviate greatly from the map value, but the optimum time delay value may deviate greatly from the map value for some reason. On the other hand, the second dead time calculated from the variance value or the extreme value can be said to be an actual value reflecting the current situation. Therefore, by performing such a map update, it becomes possible to cope with unforeseen situations, and it is possible to always maintain the map data at an optimum value in accordance with the current situation.

  FIG. 16 schematically shows the procedure of the third aspect. First, in step S101, according to the first mode, a first dead time L1 is calculated from a map as shown in FIG. Next, in step S102, the second dead time L2 is calculated from the dispersion value or extreme value of the input / output air-fuel ratio according to the second mode. Thereafter, in step S103, a dead time deviation amount L12 which is an absolute value of the difference between the first and second dead times L1 and L2 is calculated, and the dead time deviation amount L12 is compared with a predetermined value L12s. If the dead time deviation amount L12 is equal to or smaller than the predetermined value L12s, the first dead time L1 calculated from the map is determined as the final dead time L in step S104, assuming that the deviation between the two is small.

  On the other hand, if the dead time deviation amount L12 is larger than the predetermined value L12s, the second dead time L2 calculated from the dispersion value or extreme value of the input / output air-fuel ratio is determined as the final value in step S105, assuming that the deviation between the two is large. The dead time L is determined. In step S106, the first dead time L1 in the map corresponding to the second dead time L2 is replaced with the second dead time L2, and the map data is updated.

  In the above-described 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 employed. 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.

  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 S201, active control for forcibly oscillating the air-fuel ratio is executed. In step S202, the value of the input air-fuel ratio u (t) after the fuel dynamics correction is calculated. In step S203, FIG. As shown in FIG. 9, 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 input and output air-fuel ratios.

  In subsequent step S204, 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 S205. In the next step S206, model parameters are derived from the relationship between the input air-fuel ratio u (t) after the dead time correction obtained in step S205 and the output air-fuel ratio y (t) after the bias correction obtained in step S203. A time constant T and a gain k are identified. In step S207, 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.

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 above-mentioned internal combustion engine is an intake port (intake passage) injection type, but the present invention can also be applied to a direct injection type engine. However, in this case, it is not necessary to consider fuel adhesion to the wall surface of the intake passage, so that fuel dynamics correction is omitted. In the above embodiment, an example of application to a so-called wide-range air-fuel ratio sensor has been described. However, the present invention can also be applied to a so-called O ₂ sensor such as the post-catalyst sensor 18. A wide range of sensors for detecting the air-fuel ratio of exhaust gas including such an O ₂ sensor shall be referred to as an air-fuel ratio sensor according to the present invention. In the above-described embodiment, abnormality of two characteristics of response characteristics and output among the characteristics of the air-fuel ratio sensor is diagnosed. However, the invention is not limited to this, and abnormality of one or more characteristics may be diagnosed. . Similarly, only one of the time constant T and the gain k may be used as a parameter in the primary delay element, or another parameter may be used in addition to the time constant T and the gain k. In the above embodiment, the two parameters T and k in the first-order lag element are identified at the same time, and the abnormality of the two characteristics of the air-fuel ratio sensor is judged at the same time. However, the present invention is not limited to this, and at least two parameters are identified with a time difference. Alternatively, the abnormality determination of at least two characteristics may be performed with a time difference.

  In the above-described embodiment, the ECU 20 constitutes an identification unit, an abnormality determination unit, a dead time correction unit, a bias correction unit, and a fuel correction unit.

  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.

It is the schematic of the internal combustion engine which concerns on this embodiment. It is a graph which shows the mode of a change with an input air fuel ratio and an output air fuel ratio. This is a test result showing a change in time constant and gain with respect to a change in input air-fuel ratio and output air-fuel ratio, and is a case of a normal sensor. This is a test result showing a change in time constant and gain with respect to a change in input air-fuel ratio and output air-fuel ratio, and is a case of an abnormal sensor. It is a block diagram of the whole system for identifying a parameter. 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 dead time calculation map. It is a test result for demonstrating the 2nd aspect of dead time calculation, and is a case of a normal sensor. It is the schematic corresponding to FIG. 12 for demonstrating a dead time calculation method. It is a test result for demonstrating the 2nd aspect of dead time calculation, and is a case of an abnormal sensor. It is the schematic corresponding to FIG. 14 for demonstrating a dead time calculation method. It is a flowchart which concerns on the 3rd aspect of dead time calculation. It is a flowchart which shows roughly the procedure of the abnormality diagnosis of the air fuel ratio sensor of this embodiment.

Explanation of symbols

1 Internal combustion engine 3 Combustion chamber 5 Air flow meter 6 Exhaust pipe 7 Spark plug 11 Catalyst 12 Injector 14 Crank angle sensor 15 Accelerator opening sensor 17 Pre-catalyst sensor 18 Post-catalyst sensor 19 Catalyst 20 Electronic control unit (ECU)
A / F Air-fuel ratio u (t) Input air-fuel ratio y (t) Output air-fuel ratio T Time constant k Gain L Dead time L1 First dead time L2 Second dead time

Claims (16)

An air-fuel ratio sensor abnormality diagnosis device for detecting an air-fuel ratio of exhaust gas of an internal combustion engine,
The system from the fuel injection valve to the air-fuel ratio sensor is modeled by a first-order lag element, and parameters in the first-order lag element are identified based on the input air-fuel ratio given to the air-fuel ratio sensor and the output air-fuel ratio output from the air-fuel ratio sensor. An identification means;
An abnormality determination means for determining an abnormality of a predetermined characteristic of the air-fuel ratio sensor based on the parameter identified by the identification means ;
A dead time correcting means for calculating a dead time between the input air-fuel ratio and the output air-fuel ratio and shift-correcting at least one of the input air-fuel ratio and the output air-fuel ratio by the dead time;
With
The dead time correcting means calculates a dispersion value between the input air-fuel ratio and the output air-fuel ratio, and when the dispersion value peak of the output air-fuel ratio is larger than a predetermined value, the dispersion value peak of the input air-fuel ratio and the output An abnormality diagnosis apparatus for an air-fuel ratio sensor , wherein the dead time is calculated based on a time difference from a dispersion value peak of the air-fuel ratio.   2. The air-fuel ratio sensor according to claim 1, wherein the abnormality determination unit determines at least two of the characteristics of the air-fuel ratio sensor based on at least two parameters identified by the identification unit. Abnormality diagnosis device.   3. The abnormality diagnosis apparatus for an air-fuel ratio sensor according to claim 2, wherein the at least two parameters are at least a time constant and a gain, and at least two of the characteristics of the air-fuel ratio sensor are at least responsiveness and output. .   The dead time correction means calculates the dead time based on a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio when a dispersion value peak of the output air-fuel ratio is equal to or less than the predetermined value. The abnormality diagnosis device for an air-fuel ratio sensor according to any one of claims 1 to 3.   The dead time correction means calculates a first dead time according to a predetermined map on the basis of at least one parameter relating to the operating state of the internal combustion engine, and also distributes a dispersion value peak between the input air-fuel ratio and the output air-fuel ratio. Or a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio, a second dead time is calculated, and a deviation amount of the second dead time with respect to the first dead time is greater than a predetermined value. 5. The abnormality diagnosis of an air-fuel ratio sensor according to claim 4, wherein when the time is larger, the second dead time is determined as a final dead time and the map data is updated by the second dead time. apparatus.   2. A bias correction unit that shift-corrects at least one of the input air-fuel ratio and the output air-fuel ratio so as to remove a bias between the input air-fuel ratio and the output air-fuel ratio. 5. The abnormality diagnosis device for an air-fuel ratio sensor according to any one of 5 above.   7. The abnormality diagnosis apparatus for an air-fuel ratio sensor according to claim 1, further comprising fuel correction means for correcting the input air-fuel ratio based on the amount of fuel adhering to the wall and the amount of evaporation.   The abnormality diagnosis device for an air-fuel ratio sensor according to any one of claims 1 to 7, wherein the identification unit sequentially identifies the parameter by a sequential least square method.   An air-fuel ratio sensor abnormality diagnosis method for detecting an air-fuel ratio of exhaust gas of an internal combustion engine,
  The system from the fuel injection valve to the air-fuel ratio sensor is modeled by a first-order lag element, and parameters in the first-order lag element are identified based on the input air-fuel ratio given to the air-fuel ratio sensor and the output air-fuel ratio output from the air-fuel ratio sensor. Steps,
  Determining an abnormality of the air-fuel ratio sensor based on the identified parameters;
  Calculating a dead time between the input air-fuel ratio and the output air-fuel ratio, and shift-correcting at least one of the input air-fuel ratio and the output air-fuel ratio by the dead time;
  With
  The dead time correction step calculates a dispersion value between the input air-fuel ratio and the output air-fuel ratio, and when the dispersion value peak of the output air-fuel ratio is larger than a predetermined value, the dispersion value peak of the input air-fuel ratio and the output Calculating the dead time based on a time difference from the dispersion value peak of the air-fuel ratio.
  An abnormality diagnosis method for an air-fuel ratio sensor.   10. The air-fuel ratio sensor abnormality diagnosis method according to claim 9, wherein the abnormality determination step determines at least two abnormalities of the characteristics of the air-fuel ratio sensor based on the identified at least two parameters. .   11. The air-fuel ratio sensor abnormality diagnosis method according to claim 10, wherein the at least two parameters are at least a time constant and a gain, and at least two of the characteristics of the air-fuel ratio sensor are at least responsiveness and output. .   The dead time correction step includes calculating the dead time based on a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio when a dispersion value peak of the output air-fuel ratio is equal to or less than the predetermined value. The abnormality diagnosis method for an air-fuel ratio sensor according to any one of claims 9 to 11.   The dead time correction step calculates a first dead time according to a predetermined map on the basis of at least one parameter relating to the operating state of the internal combustion engine, and also distributes a dispersion value peak between the input air-fuel ratio and the output air-fuel ratio. Or a time difference between extreme values of the input air-fuel ratio and the output air-fuel ratio, a second dead time is calculated, and a deviation amount of the second dead time with respect to the first dead time is greater than a predetermined value. 13. The air-fuel ratio sensor according to claim 12, further comprising: determining the second dead time as a final dead time when the time is larger, and updating data of the map with the second dead time. Abnormality diagnosis method.   14. The method according to claim 9, further comprising a step of performing shift correction on at least one of the input air-fuel ratio and the output air-fuel ratio so as to remove a bias between the input air-fuel ratio and the output air-fuel ratio. An abnormality diagnosis method for an air-fuel ratio sensor according to claim 1.   15. The method for diagnosing abnormality of an air-fuel ratio sensor according to claim 9, further comprising a step of correcting the input air-fuel ratio based on the amount of fuel adhering to the wall and the amount of evaporation.   16. The abnormality diagnosis method for an air-fuel ratio sensor according to claim 9, wherein the identifying step sequentially identifies the parameter by a sequential least square method.

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