JP2008128005A - Catalyst abnormality diagnosis device for internal combustion engine - Google Patents

Abstract

When a primary abnormality that causes a secondary abnormality of a catalyst occurs, a potential secondary abnormality of the catalyst is quickly detected thereafter.
Means for measuring a deterioration index value of a catalyst disposed in an exhaust passage of an internal combustion engine, detecting deterioration of the catalyst based on the deterioration index value, means for detecting the primary abnormality (S101), Means (S104) for determining the presence or absence of catalyst deterioration progress based on the deterioration index values measured before and after the detection of a primary abnormality, and determining that the catalyst is abnormal when it is determined that the catalyst has progressed. Means (S105). Even if the catalyst is at a stage before complete deterioration or failure, it can be determined that there is progress of deterioration, and a potential secondary abnormality of the catalyst can be detected.
[Selection] Figure 4

Description

  The present invention relates to a catalyst abnormality diagnosis device that diagnoses abnormality of a catalyst disposed in an exhaust passage of an internal combustion engine.

Generally, in an internal combustion engine, a catalyst is disposed in an exhaust passage in order to purify exhaust gas. Such a catalyst, for example, a three-way catalyst, adsorbs and holds excess oxygen present in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio, that is, when the air-fuel ratio becomes lean. When the air-fuel ratio of the gas becomes smaller than the stoichiometric air-fuel ratio, that is, when the air-fuel ratio becomes rich, it has an O ₂ storage function for releasing the adsorbed oxygen. Accordingly, during the normal operation of the internal combustion engine, even if the air-fuel mixture by the operating conditions around the stoichiometric air-fuel ratio is gone swing to the rich side or the lean side, the catalyst surface is kept to the stoichiometric air-fuel ratio, O ₂ having a three-way catalyst Due to the storage function, when the air-fuel mixture becomes lean, excess oxygen is adsorbed and held by the catalyst, so NOx is reduced. When the air-fuel mixture becomes rich, oxygen adsorbed and held by the catalyst is released. HC and CO are oxidized, so that NOx, HC and CO can be simultaneously purified.

  Therefore, an air-fuel ratio sensor for detecting the exhaust air-fuel ratio is disposed in the exhaust passage upstream of the catalyst, and when the exhaust air-fuel ratio becomes lean, the fuel supply amount is increased, and when the exhaust air-fuel ratio becomes rich By reducing the fuel supply amount, the air-fuel ratio is controlled around the stoichiometric air-fuel ratio, so that even if the fuel is alternately swung to the rich side or the lean side, NOx, HC and CO can be reduced simultaneously. It has become.

By the way, when the three-way catalyst deteriorates, the exhaust gas purification rate decreases. There is a correlation between the degree of deterioration of the three-way catalyst and the degree of reduction of the O ₂ storage function because they are reactions through noble metals. Therefore, it is possible to detect that the catalyst has deteriorated by detecting that the O ₂ storage function has deteriorated.

  As an apparatus for detecting catalyst deterioration based on such a principle, for example, there is one disclosed in Patent Document 1. In this device, active air-fuel ratio control is performed to forcibly switch the air-fuel ratio from lean to rich or vice versa with respect to the stoichiometric air-fuel ratio, and the three-way catalyst can be occluded during the execution of this active air-fuel ratio control. The amount of oxygen, that is, the oxygen storage capacity is calculated. The calculated oxygen storage capacity is compared with a predetermined deterioration determination value. If the oxygen storage capacity exceeds the deterioration determination value, it is determined that the catalyst is normal, and if the oxygen storage capacity is equal to or less than the deterioration determination value, it is determined that the catalyst is deteriorated.

  On the other hand, in an electronic control system for an internal combustion engine for in-vehicle use or the like, an abnormality diagnosis device is provided for the purpose of detecting abnormalities in various components and systems. In this type of abnormality diagnosis device, an abnormality diagnosis is generally executed at predetermined time intervals or at predetermined crank angle intervals.

  In Patent Document 2, when any of various factors that increase the frequency of occurrence of an abnormality occurs, the processing interval is shortened for abnormality diagnosis corresponding to the factor in order to suppress an increase in the processing load of the microcomputer. A technique for increasing the processing interval for abnormal diagnosis is disclosed.

  As another conventional technique, for example, Patent Document 3 discloses an apparatus that determines that a system is abnormal only when the abnormality diagnosis of the system is executed a plurality of times and the number of times of abnormality detection reaches a predetermined value. ing. In this case, when the engine is started and stopped, that is, when the trip is short, the engine may be stopped before one abnormality is detected, and such a short trip is repeated. There is a problem that the number of times of abnormality detection does not readily reach the predetermined value, and the final abnormality determination cannot be performed or the determination is delayed. Patent Document 4 monitors the frequency of execution of abnormality diagnosis and changes the abnormality diagnosis condition (execution condition, diagnosis method, determination condition) to increase the execution frequency when it is determined that the execution frequency is insufficient. Is disclosed.

JP-A-5-133264 JP 2002-61535 A JP 2001-349239 A JP 2003-193900 A

  Incidentally, the above-described abnormality diagnosis apparatus has the following problems. For example, when a specific component fails in an internal combustion engine mounted on a vehicle and an abnormality occurs in an ignition system or a fuel supply system, the abnormality is detected by an abnormality diagnosis device, particularly an electronic control unit (hereinafter referred to as an ECU). For example, a check lamp is lit to warn the user. When this happens, the user carries the vehicle into the maintenance shop, and the maintenance shop replaces the failed part in accordance with the diagnostic code and the repair document stored in the ECU to eliminate the abnormal state.

  However, if the abnormality is a primary abnormality (hereinafter referred to as a primary abnormality) that causes a secondary abnormality of the catalyst (hereinafter referred to as a secondary abnormality), there are the following problems. That is, if the primary abnormality, such as engine misfire or air-fuel ratio abnormality, is a primary abnormality that damages the catalyst and promotes catalyst deterioration or causes catalyst failure later, the primary abnormality Even if the part that caused the problem is replaced and the vehicle is returned to the user, then an unacceptable deterioration (complete deterioration) or failure of the catalyst occurs, which is detected by the abnormality diagnosis device and the check lamp lights up Then, there may occur a situation where the user has to bring the vehicle into the maintenance shop again and replace the catalyst. This is time consuming for the user and is not preferable. If a secondary abnormality (complete deterioration or failure) of the catalyst occurs immediately after the occurrence of the primary abnormality, the secondary abnormality of the catalyst is detected by the abnormality diagnosis device, and the catalyst can be replaced simultaneously. However, this is not a case of such an immediate secondary abnormality, which is a problem in the case of a potential secondary abnormality that occurs in the future after a certain period of time such as several weeks or months. In addition, there is a possibility that the vehicle will be driven in a state where exhaust emission has deteriorated from the occurrence of the primary abnormality to the replacement of the catalyst.

  To solve this problem, it is appropriate to detect the potential secondary abnormality of the catalyst immediately after the occurrence of the primary abnormality and to replace the catalyst at the same time as the replacement of the component that caused the primary abnormality. It is.

  On the other hand, this problem cannot be solved by the technique disclosed in the patent document. For example, in the technique disclosed in Patent Document 2, although the processing interval for the abnormality diagnosis of the catalyst can be shortened after the occurrence of the primary abnormality, the catalyst is completely deteriorated immediately or is out of order. Therefore, it is impossible to detect a potential secondary abnormality of the catalyst in the previous stage.

  Therefore, the present invention has been made in view of such a situation, and the purpose thereof is to promptly detect the potential secondary of the catalyst immediately after the occurrence of the primary abnormality that causes the secondary abnormality of the catalyst. An object of the present invention is to provide a catalyst abnormality diagnosis device for an internal combustion engine that can detect the next abnormality.

In order to achieve the above object, a catalyst abnormality diagnosis device for an internal combustion engine according to a first invention comprises:
A catalyst deterioration detecting means for measuring a deterioration index value of the catalyst disposed in the exhaust passage of the internal combustion engine and detecting the deterioration of the catalyst based on the deterioration index value;
Primary abnormality detection means for detecting a primary abnormality that causes a secondary abnormality of the catalyst;
When the primary abnormality is detected by the primary abnormality detection means, a deterioration progress determination for determining whether or not the catalyst has progressed based on the deterioration index value measured by the catalyst deterioration detection means before and after detecting the primary abnormality. Means,
And a catalyst abnormality determining unit that determines that the catalyst is abnormal when the deterioration determining unit determines that the catalyst has progressed.

  According to the catalyst abnormality diagnosis apparatus for an internal combustion engine according to the first aspect of the present invention, when a primary abnormality that causes a secondary abnormality of the catalyst is detected, the deterioration index value is detected by the catalyst deterioration detecting means after the detection. It is measured. Based on the deterioration index value measured after the primary abnormality is detected and the deterioration index value measured before the primary abnormality is detected, whether the catalyst has progressed or not is determined. It is determined.

  Thus, when a primary abnormality is detected, the presence or absence of catalyst deterioration is immediately determined thereafter, and the abnormality of the catalyst is detected based on the determination result. Therefore, in addition to detecting secondary anomalies actually occurring in the catalyst, it can be determined that there is progress in deterioration even if the catalyst is in the stage of complete deterioration or failure. Secondary abnormalities can also be detected effectively.

The second invention is the first invention, wherein
After the primary abnormality is detected by the primary abnormality detection means, the catalyst deterioration detection means measures the deterioration index value within the same trip, and the deterioration progress determination means uses the measured deterioration index value to It is characterized by determining whether or not the deterioration of the catalyst has progressed, and the catalyst abnormality determining means determines the abnormality of the catalyst according to the determination result.

  Thereby, after the primary abnormality is detected, the catalyst abnormality can be detected immediately within the same trip as that at the time of detection.

The third invention is the first or second invention, wherein
When the primary abnormality is detected by the primary abnormality detection means, a normal determination invalidation means for invalidating the catalyst normality determination made by the catalyst deterioration detection means before the primary abnormality detection within the same trip is further provided. It is characterized by that.

  When the determination of whether the catalyst is normal or deteriorated by the catalyst deterioration detection means is executed once per trip, when the normality determination is performed before the primary abnormality detection in the same trip as the primary abnormality detection Thereafter, the deterioration is not detected within the same trip, and the deterioration index value is not measured. However, according to the third aspect of the invention, the normality determination made in the same trip before the primary abnormality is detected is invalidated. As a result, the measurement of the deterioration index value by the catalyst deterioration detecting means can be executed again.

Further, a fourth invention is any one of the first to third inventions,
Precondition establishment determination means for determining whether or not a predetermined precondition for performing catalyst deterioration detection by the catalyst deterioration detection means is satisfied;
And a precondition relaxation means for relaxing the precondition when the primary abnormality is detected by the primary abnormality detection means.

  As a result, when a primary abnormality is detected, more opportunities for detecting catalyst deterioration, that is, opportunities for measuring the deterioration index value can be secured, and it is possible to easily detect abnormality of the catalyst.

  According to the present invention, when a primary abnormality that causes a secondary abnormality of the catalyst occurs, an excellent effect is exhibited that a potential secondary abnormality of the catalyst can be detected immediately thereafter. Is done.

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

  FIG. 1 is a schematic diagram showing the configuration of 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 is a vehicular multi-cylinder engine (only one cylinder is shown), and is a spark ignition type 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. Further, an injector (fuel injection valve) 12 is disposed in the cylinder head for each cylinder so that fuel is directly injected into the combustion chamber 3. The piston 4 is configured as a so-called deep dish top surface type, and a concave portion 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel is directly injected from the injector 12 toward the concave portion 4 a of the piston 4 in a state where air is sucked into the combustion chamber 3. As a result, a layer of a mixture of fuel and air is formed (stratified) in the vicinity of the spark plug 7 and separated from the surrounding air layer, and stable stratified combustion is executed.

  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 surge tank 8 and the intake pipe 13.

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, and a catalyst 11 made of a three-way catalyst having an O ₂ storage function is connected to the exhaust pipe 6. It is attached. An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. Pre-catalyst sensors and post-catalyst sensors 17 and 18 for detecting the exhaust air-fuel ratio are installed on the upstream side and the downstream side of the catalyst 11, respectively. 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 ECU 20 also functions as an abnormality diagnosis device that detects abnormalities in various components of the internal combustion engine system. The ECU 20 performs an abnormality diagnosis of the above-mentioned and other components (including sensors, actuators, harnesses, etc.) in accordance with various programs stored in the ROM, and according to the type and location of the abnormality when detecting the abnormality. The diagnostic code is stored in the RAM, and a warning device (for example, a check lamp) is activated to notify the user of the occurrence of an abnormality. At a later repair stage, the diagnostic code is read and used as appropriate for repairing or replacing parts.

  The catalyst 11 simultaneously purifies NOx, HC and CO when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 11 is a stoichiometric air-fuel ratio (stoichiometric) A / Fs (for example, 14.6). In response to this, the ECU 20 changes the air-fuel ratio of the exhaust gas upstream of the catalyst flowing into the catalyst during normal operation of the internal combustion engine (hereinafter referred to as pre-catalyst air-fuel ratio A / Ffr) to the stoichiometric air-fuel ratio A / Fs. The air-fuel ratio is controlled so that Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the theoretical air-fuel ratio A / Fs, and the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst sensor 17 matches the target air-fuel ratio A / Ft. Thus, the fuel injection amount injected from the injector 12 is controlled. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

The ECU 20 detects the deterioration of the catalyst 11 as one of abnormality diagnosis. Various methods can be adopted as a method for detecting the deterioration of the catalyst. In this embodiment, focusing on the characteristic that the oxygen storage capacity decreases with catalyst deterioration, the oxygen storage capacity (OSC; O ₂ Storage Capacity) of the catalyst is used. The unit detects or measures g), and detects deterioration based on the value. The oxygen storage capacity is the maximum amount of oxygen that can be stored by the current catalyst, and this deterioration detection method is called the Cmax method. The detected value of the oxygen storage capacity is a deterioration index value representing the degree of deterioration of the catalyst. In detecting the deterioration, active air-fuel ratio control is executed in which the pre-catalyst air-fuel ratio A / Ffr is forcibly switched from one of the predetermined rich air-fuel ratio A / Fr and lean air-fuel ratio A / Fl to the other at a predetermined timing. Is done. Hereinafter, the catalyst deterioration detection method of this embodiment will be described in detail.

  First, the deterioration detection of the catalyst 11 is started when a predetermined precondition is satisfied. This precondition is satisfied when, for example, any of 1) the internal combustion engine is in a steady operation state and 2) the catalyst is in the active temperature range is satisfied. With regard to 1), whether or not the internal combustion engine is in a steady operation state can be determined, for example, based on whether or not the value of the intake air amount GA detected by the air flow meter 5 is within a predetermined range. Regarding 2), the temperature of the catalyst 11 may be directly detected using a temperature sensor, but in the present embodiment, it is estimated from the operating state of the internal combustion engine. The ECU 20 calculates the engine load KL calculated based on the intake air amount GA detected by the air flow meter 5, the engine rotational speed NE calculated based on the output of the crank angle sensor 14, and the detected value of the throttle opening sensor 19. Based on at least one of the above, the temperature of the catalyst 11 is estimated using a map or function set in advance through experiments or the like. When the temperature of the catalyst 11 thus detected or estimated is equal to or higher than a predetermined lower limit temperature Tc1 and equal to or lower than the upper limit temperature Tc2 corresponding to the active temperature range of the catalyst 11, the condition 2) is satisfied. The preconditions are not limited to those described here, and other conditions may be added as appropriate.

  In the present embodiment, the deterioration detection of the catalyst 11 is executed once per trip of the internal combustion engine, and the final deterioration determination is made when it is determined that the catalyst 11 has deteriorated continuously at least twice (two trips). A warning device such as a check lamp is activated. One trip means a period from the start to the stop of the engine once.

  Next, the active air-fuel ratio control and the catalyst deterioration determination made in accordance with the execution will be described. 2A and 2B, the outputs of the pre-catalyst sensor 17 and the post-catalyst sensor 18 when the active air-fuel ratio control is executed are indicated by solid lines, respectively. In FIG. 2A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The outputs of the pre-catalyst sensor 17 and the post-catalyst sensor 18 represent the pre-catalyst air / fuel ratio A / Ffr and the post-catalyst air / fuel ratio A / Frr, respectively.

  As shown in FIG. 2A, the target air-fuel ratio A / Ft is centered on the theoretical air-fuel ratio A / Fs as the center air-fuel ratio, and then has a predetermined amplitude (rich amplitude Ar, Ar> 0) on the rich side. ) Separated by an air-fuel ratio (rich air-fuel ratio A / Fr) and an air-fuel ratio (lean air-fuel ratio A / Fl) separated from the air-fuel ratio by a predetermined amplitude (lean amplitude Al, Al> 0) on the lean side. And alternately. Then, the pre-catalyst air-fuel ratio A / Ffr as an actual value is switched with a slight time delay with respect to the target air-fuel ratio A / Ft so as to follow the switching or vibration of the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ffr are equivalent except that there is a time delay.

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, theoretical air fuel ratio A / Fs = 14.6, rich air fuel ratio A / Fr = 14.1, lean air fuel ratio A / Fl = 15.1, rich amplitude Ar = lean amplitude Al = 0.5. Compared with the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  By the way, the timing at which the target air-fuel ratio A / Ft is switched is the timing at which the output of the post-catalyst sensor 18 is switched from rich to lean, or from lean to rich. As shown in the figure, the output voltage of the post-catalyst sensor 18 changes suddenly at the theoretical air-fuel ratio A / Fs, and the post-catalyst air-fuel ratio A / Frr is the rich air-fuel ratio smaller than the theoretical air-fuel ratio A / Fs. When the output voltage becomes equal to or higher than the rich determination value VR, and when the post-catalyst air-fuel ratio A / Frr is the lean air-fuel ratio greater than the theoretical air-fuel ratio A / Fs, the output voltage becomes lower than the lean determination value VL. Here, VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V).

  As shown in FIGS. 2A and 2B, when the output voltage of the post-catalyst sensor 18 changes from the rich value to the lean value and becomes equal to the lean determination value VL (time t1), the target sky The fuel ratio A / Ft is switched from the lean air-fuel ratio A / Fl to the rich air-fuel ratio A / Fr. Thereafter, when the output voltage of the post-catalyst sensor 18 changes from the lean value to the rich side and becomes equal to the rich determination value VR (time t2), the target air-fuel ratio A / Ft becomes lean from the rich air-fuel ratio A / Fr. The air-fuel ratio is switched to A / Fl.

  While performing the active air-fuel ratio control that performs such an air-fuel ratio change, the oxygen storage capacity OSC of the catalyst 11 is calculated as follows, and the deterioration of the catalyst 11 is determined.

  Referring to FIG. 2, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl before time t1, and the lean gas flows into the catalyst 11. At this time, the catalyst 11 continues to absorb oxygen, but when it fully absorbs oxygen, it can no longer absorb oxygen, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the lean side, and when the output voltage of the post-catalyst sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. Or reversed. In this way, the target air-fuel ratio A / Ft is reversed using the output of the post-catalyst sensor 18 as a trigger.

  This time, rich gas flows into the catalyst 11. At this time, the oxygen stored in the catalyst 11 continues to be released from the catalyst 11. Therefore, the exhaust gas of the theoretical air-fuel ratio A / Fs flows out to the downstream side of the catalyst 11 and the post-catalyst air-fuel ratio A / Frr does not become rich, so the output of the post-catalyst sensor 18 is not reversed. When oxygen is continuously released from the catalyst 11, all of the stored oxygen is eventually released from the catalyst 11, and at that time, no more oxygen can be released, and the rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the rich side, and when the output voltage of the post-catalyst sensor 18 reaches the rich determination value VR (t2), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl. Can be switched to.

  The larger the oxygen storage capacity OSC, the longer the time during which oxygen can be absorbed or released. That is, when the catalyst is not deteriorated, the inversion cycle of the target air-fuel ratio A / Ft (for example, the time from t1 to t2) becomes longer, and the inversion cycle of the target air-fuel ratio A / Ft becomes shorter as the deterioration of the catalyst proceeds. .

  Therefore, using this fact, the oxygen storage capacity OSC is calculated as follows. As shown in FIG. 3, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ffr as the actual value is slightly delayed with a rich air-fuel ratio A / Fr. Switch to Fr. Then, from the time t11 when the pre-catalyst air-fuel ratio A / Ffr reaches the stoichiometric air-fuel ratio A / Fs to the time t2 when the target air-fuel ratio A / Ft next reverses, the oxygen storage capacity for every minute time is given by the following equation (1). dC is calculated, and the oxygen storage capacity dC for each minute time is integrated from time t11 to time t2. In this way, the oxygen storage capacity OSC1, that is, the amount of released oxygen in this oxygen release cycle is calculated.

  Here, Q is the fuel injection amount, and the excess air amount can be calculated by multiplying the air-fuel ratio difference ΔA / F by the fuel injection amount Q. K is the proportion of oxygen contained in the air (about 0.23).

  Basically, the oxygen storage capacity OSC1 calculated at this time is compared with a predetermined deterioration determination value. If the oxygen storage capacity OSC1 exceeds the deterioration determination value, the oxygen storage capacity OSC1 is normal, and the oxygen storage capacity OSC1 is less than the deterioration determination value. Then, deterioration of the catalyst can be determined such as deterioration. However, in the deterioration determination of the present embodiment, in order to improve accuracy, the oxygen storage capacity (in this case, the oxygen absorption amount) is calculated on the lean side as well. That is, the oxygen storage capacity is calculated at least once on the rich side and on the lean side, and the average value is compared with the deterioration determination value to make a final deterioration determination.

  On the lean side, as shown in FIG. 3, after the target air-fuel ratio A / Ft is switched to the lean air-fuel ratio A / Fl at time t2, the oxygen storage capacity dC for each minute time is calculated by the previous equation (1). And the oxygen storage capacity dC for each minute time from the time t21 when the pre-catalyst air-fuel ratio A / Ffr reaches the stoichiometric air-fuel ratio A / Fs, and then when the target air-fuel ratio A / Ft reverses to the rich side Integration is performed until t3. Thus, the oxygen storage capacity OSC2, that is, the amount of absorbed oxygen in this oxygen absorption cycle is calculated. The oxygen storage capacity OSC1 of the previous cycle and the oxygen storage capacity OSC2 of the current cycle should be approximately equal.

  In this way, a plurality of oxygen storage capacities OSC1, OSC2,... OSCn (n is an integer of 2 or more) are repeatedly calculated, and the average value OSCav is compared with a predetermined deterioration determination value OSCs. If the oxygen storage capacity average value OSCav exceeds the deterioration determination value OSCs, the catalyst 11 is determined to be normal, and if the oxygen storage capacity average value OSCav is equal to or less than the deterioration determination value OSCs, the catalyst 11 is determined to be deteriorated. As can be seen from this, the oxygen storage capacity average value OSCav becomes a deterioration index value indicating the degree of deterioration of the catalyst.

  Note that a method other than the Cmax method as described herein can be adopted as a method for detecting the deterioration of the catalyst. For example, when the pre-catalyst air-fuel ratio A / Ffr is oscillated with the theoretical air-fuel ratio A / Fs as the boundary, the post-catalyst air-fuel ratio A / Frr follows the pre-catalyst air-fuel ratio A / Ffr as the degree of catalyst deterioration increases. It is known to tend to vibrate. Therefore, the pre-catalyst air-fuel ratio A / Ffr is forcibly vibrated, the ratio of the output trajectory lengths of the pre-catalyst sensor 17 and the post-catalyst sensor 18 at this time is calculated, and this ratio is compared with a predetermined deterioration judgment value. There is a method for detecting deterioration of the catalyst. This is called a deterioration detection method based on the trajectory length ratio. Here, the output trajectory length is a value obtained by integrating a change amount of the sensor output value per minute time for a predetermined period. According to this method, when defined as (output trajectory length ratio) = (post-catalyst sensor output trajectory length) / (pre-catalyst sensor output trajectory length), the higher the catalyst deterioration degree, the larger the output trajectory length ratio. In this case, the output trajectory length ratio becomes a deterioration index value.

  Alternatively, the pre-catalyst air-fuel ratio A / Ffr is forcibly oscillated for a predetermined time in a predetermined manner, and the output trajectory length of the post-catalyst sensor 18 at this time is compared with a predetermined deterioration judgment value to cause deterioration of the catalyst. There is a way to detect. This is called a deterioration detection method based on the trajectory length. According to this method, the higher the degree of catalyst deterioration, the longer the output trajectory length. In this case, the output trajectory length becomes a deterioration index value.

  Alternatively, an exhaust gas sensor for detecting the concentration of a specific exhaust gas component (HC, NOx, etc.) is provided on the downstream side of the catalyst 11, the component concentration is detected by this exhaust gas sensor, and this is compared with a predetermined deterioration judgment value. There is a method for detecting deterioration of the catalyst. This is called a deterioration detection method based on exhaust gas components. This method is based on the idea that the higher the degree of catalyst deterioration, the lower the purification rate and the higher the component concentration. In this case, the component concentration forms a deterioration index value.

  As described above, primary abnormalities that cause secondary abnormalities in the catalyst, such as engine misfires due to ignition system failures and air-fuel ratio abnormalities due to fuel supply system failures, etc. Even if the cause of the primary abnormality is removed, a secondary abnormality such as complete deterioration or failure of the catalyst will occur after a certain period of time. There is a problem that the vehicle is driven by emission. To solve this problem, immediately detect whether there is a possibility that the catalyst may have a secondary abnormality after the occurrence of the primary abnormality, and replace the catalyst at the same time as replacing the part that caused the primary abnormality. It is appropriate.

  Therefore, in order to achieve this, in the present embodiment, the following catalyst abnormality diagnosis is executed.

  FIG. 4 shows a flowchart of a routine according to the first form of catalyst abnormality diagnosis. First, in step S101, the ECU 20 determines whether or not a primary abnormality has been detected by the abnormality diagnosis function of the ECU 20 as described in detail above. For example, the determination is YES when engine misfire is detected or when it is detected that the pre-catalyst air-fuel ratio A / Ffr is an abnormal value. If no primary abnormality is detected, this routine is terminated, and if it is detected, the process proceeds to step S102.

  In step S102, it is determined whether the catalyst deterioration detection preconditions (for example, the conditions 1) and 2)) as described above are satisfied. If not established, this routine is terminated. If established, the process proceeds to step S103.

  In step S103, detection of catalyst deterioration by the aforementioned Cmax method is executed. By executing the catalyst deterioration detection, an oxygen storage capacity average value OSCav as a deterioration index value is measured. However, the catalyst deterioration detection here only measures the oxygen storage capacity average value OSCav. The comparison between the measured oxygen storage capacity average value OSCav and the deterioration judgment value, and deterioration based on this comparison. Judgment is not performed.

  In the next step S104, it is determined whether or not catalyst deterioration has progressed. That is, in normal catalyst deterioration detection, the measured oxygen storage capacity average value OSCav is compared with a predetermined deterioration determination value to determine deterioration of the catalyst. However, when a primary abnormality is detected as in this case, such a normal deterioration determination is not performed, and instead, whether or not the deterioration of the catalyst has progressed due to the occurrence of the primary abnormality. More specifically, it is determined whether or not the deterioration progress rate of the catalyst is higher than usual. Specifically, the previous oxygen storage capacity average value OSCav calculated in the previous trip stored in the ECU 20 is acquired, and the current oxygen storage capacity average value OSCav is subtracted from the previous oxygen storage capacity average value OSCav. . If the difference is equal to or greater than the predetermined value, that is, if the current value of the oxygen storage capacity average value OSCav is substantially lower than the previous value, it is determined that the catalyst has been deteriorated, and the process proceeds to step S105. Conversely, if the difference is less than the predetermined value, that is, if the current value of the oxygen storage capacity average value OSCav has not substantially decreased from the previous value, it is determined that the catalyst has not deteriorated, and this routine is terminated. .

  The greater the deterioration of the catalyst caused by the occurrence of the primary abnormality, the lower the current value of the oxygen storage capacity average value OSCav than the previous value. The threshold value of the difference between the current value and the previous value for determining whether the catalyst has progressed or not is the secondary abnormality actually occurring in the catalyst (that is, the catalyst actually falls into complete deterioration or failure). As well as potential secondary anomalies that the catalyst will reach in the future (ie, the catalyst is in the stage before full degradation or failure). ing.

  If it is determined in step S104 that the deterioration has progressed, the cause of the deterioration is the primary abnormality that has already occurred, and the secondary abnormality of the catalyst has actually occurred, or a potential secondary abnormality has occurred. Is considered to be. In any case, it is determined in step S105 that the catalyst is abnormal (secondary abnormality), and a diagnostic code corresponding to the catalyst abnormality is stored in the ECU 20. Then, a warning device such as a check lamp is activated.

  In this case, the diagnostic code corresponding to the primary abnormality and the diagnostic code corresponding to the catalyst abnormality are stored in the ECU 20 and the user is prompted to carry the vehicle to the maintenance shop. Once the vehicle is transported to the maintenance shop, the parts causing the primary abnormality and the catalyst are exchanged according to the diagnostic codes. Therefore, it is possible to prevent the user from taking time and effort twice. Since it is assumed that the user conveys the vehicle immediately after the warning, the vehicle traveling time in a state where the exhaust emission is deteriorated is minimized.

  As described above, when a primary abnormality that causes a secondary abnormality of the catalyst occurs, an actual secondary abnormality of the catalyst and a potential secondary abnormality can be detected immediately thereafter. In particular, even if the catalyst is in the stage before complete deterioration or failure, it is detected by the progress of deterioration, so it is possible to effectively detect potential secondary abnormalities of the catalyst. It is.

  Further, in normal catalyst deterioration detection, multiple trips are required for final deterioration detection. On the other hand, in the above-described catalyst abnormality detection, abnormality detection can be executed within the same trip as that at the time of detection after detecting the primary abnormality, so that the catalyst abnormality can be detected earlier than the normal catalyst deterioration detection. Further, even when the vehicle is transported to the maintenance shop within the same trip as when the primary abnormality is detected, the catalyst abnormality is already detected, so that the catalyst can be replaced simultaneously.

  Next, a second form of catalyst abnormality diagnosis will be described. FIG. 5 shows a flowchart of a routine according to the second embodiment. First, in step S201, when a primary abnormality is detected as in step S101, it is determined in next step S202 whether or not catalyst normality determination has already been made. If such normality determination is made, the normality determination is invalidated (cleared) in step S203, and the process proceeds to step S204. On the other hand, when such a normal determination is not made, step S203 is skipped and the process proceeds to step S204.

  As described above, in the normal detection of catalyst deterioration, the determination of whether the catalyst is normal or deteriorated is executed once per trip. Therefore, when the normality determination has already been performed, deterioration detection is not performed within the same trip. However, here, when a primary abnormality is detected, the normality determination made in the same trip before the detection of the primary abnormality is invalidated. As a result, the catalyst deterioration detection can be performed again, and the oxygen storage capacity average value OSCav can be measured again.

  In step S204, preconditions for performing catalyst deterioration detection are relaxed. As described above, this precondition is satisfied when any of 1) the internal combustion engine is in a steady operation state and 2) the catalyst is in the active temperature range is satisfied. However, in step S204, for example, the allowable range of the intake air amount according to the condition 1) is expanded, or the allowable range of the catalyst temperature according to the condition 2) is expanded, so that the precondition is relaxed. As a result, more opportunities for detecting catalyst deterioration, that is, more opportunities for measuring the oxygen storage capacity average value OSCav can be ensured, and secondary abnormality of the catalyst can be easily detected.

  It should be noted that the deterioration index value after detecting the primary abnormality may be changed from the oxygen storage capacity average value OSCav to one oxygen storage capacity OSC, whereby the measurement condition of the deterioration index value is relaxed, and the secondary abnormality of the catalyst is detected. Can be detected more easily.

  Next, in step S205, it is determined whether or not a precondition after relaxation for execution of catalyst deterioration detection is satisfied. If not established, this routine is terminated, and if established, the process proceeds to step S206. In step S206, detection of catalyst deterioration is executed in the same manner as in step S103. Thereafter, in step S207, as in step S104, it is determined whether or not catalyst deterioration has progressed more than the previous trip. Then, if there is no progress of deterioration, this routine is terminated, and if there is progress of deterioration, the process proceeds to step S208. In step S208, it is determined that the catalyst is abnormal as in step S105. A diagnostic code corresponding to the catalyst abnormality is stored in the ECU 20, a warning device such as a check lamp is actuated, and this routine is terminated.

  As described above, in the second embodiment, when the normal determination is made in the same trip before the primary abnormality is detected, it is invalidated. As a result, it is possible to detect the catalyst deterioration again and detect the abnormality of the catalyst. In addition, since the preconditions for detecting catalyst deterioration are relaxed, it is possible to promote early detection of secondary abnormality of the catalyst.

  In the above-described embodiment, the ECU 20 refers to the catalyst deterioration detecting means, the primary abnormality detecting means, the deterioration progress determining means, the catalyst abnormality determining means, the normal determination invalidating means, the precondition establishment determining means, and the precondition relaxation according to the present invention. Configure the means.

Various other embodiments of the present invention are conceivable. For example, although the above-described internal combustion engine is a direct injection type, the present invention is also applicable to an intake port (intake passage) injection type or a dual injection type internal combustion engine having both injection types. In the above embodiment, a so-called O ₂ sensor is used as the post-catalyst sensor 18, but an air-fuel ratio sensor similar to the pre-catalyst sensor 17 can also be used. Similarly, in the embodiment, a so-called air-fuel ratio sensor is used as the pre-catalyst sensor 17, but an O ₂ sensor similar to the post-catalyst sensor 18 may be used.

  In the embodiment, the presence / absence of catalyst deterioration progress is determined based on the difference between the current value of the oxygen storage capacity average value OSCav and the previous value. However, other methods may be used, for example, the current value and the previous value. Whether or not the catalyst deterioration has progressed may be determined on the basis of the ratio. In the embodiment, the average value OSCav of the plurality of oxygen storage capacities OSC is used as the deterioration detection value. However, for example, one oxygen storage capacity OSC may be used instead of such an average value. In the above embodiment, the catalyst abnormality determination is performed within the same trip when a primary abnormality is detected. However, it is not always necessary to determine the catalyst abnormality within the same trip. Furthermore, the catalyst to which the present invention is applied is not necessarily limited to the three-way catalyst, and may be another catalyst.

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

It is the schematic which shows the structure of embodiment of this invention. It is a time chart for demonstrating active air fuel ratio control. FIG. 3 is a time chart similar to FIG. 2 for illustrating a method for calculating an oxygen storage capacity. It is a flowchart of the routine which concerns on the 1st form of a catalyst abnormality diagnosis. It is a flowchart of the routine which concerns on the 2nd form of a catalyst abnormality diagnosis.

Explanation of symbols

1 Internal combustion engine 6 Exhaust pipe 11 Catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
OSC Oxygen storage capacity OSCave Oxygen storage capacity average value OSCs Degradation judgment value

Claims (4)

A catalyst deterioration detecting means for measuring a deterioration index value of the catalyst disposed in the exhaust passage of the internal combustion engine and detecting the deterioration of the catalyst based on the deterioration index value;
Primary abnormality detection means for detecting a primary abnormality that causes a secondary abnormality of the catalyst;
When the primary abnormality is detected by the primary abnormality detection means, a deterioration progress determination for determining whether or not the catalyst has progressed based on the deterioration index value measured by the catalyst deterioration detection means before and after detecting the primary abnormality. Means,
A catalyst abnormality diagnosis device for an internal combustion engine, comprising: a catalyst abnormality determination unit that determines that the catalyst is abnormal when the deterioration determination unit determines that the catalyst has progressed.   After the primary abnormality is detected by the primary abnormality detection means, the catalyst deterioration detection means measures the deterioration index value within the same trip, and the deterioration progress determination means uses the measured deterioration index value to The catalyst abnormality diagnosis device for an internal combustion engine according to claim 1, wherein the presence or absence of deterioration of the catalyst is determined, and the catalyst abnormality determination means determines abnormality of the catalyst according to the determination result.   When the primary abnormality is detected by the primary abnormality detection means, a normal determination invalidation means for invalidating the catalyst normality determination made by the catalyst deterioration detection means before the primary abnormality detection within the same trip is further provided. The catalyst abnormality diagnosis apparatus for an internal combustion engine according to claim 1 or 2, Precondition establishment determination means for determining whether or not a predetermined precondition for performing catalyst deterioration detection by the catalyst deterioration detection means is satisfied;
4. The catalyst abnormality of the internal combustion engine according to claim 1, further comprising: precondition relaxation means for relaxing the precondition when the primary abnormality is detected by the primary abnormality detection means. 5. Diagnostic device.

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