JP2008121465A - Catalyst deterioration detection device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the execution of deterioration detection in a state that a rich component adheres to a catalyst and a sensor in a certain period after starting an internal combustion engine. <P>SOLUTION: When the deterioration detection of a catalyst is executed within a predetermined period (S102: YES) after starting an internal combustion engine, the deterioration detection is executed (S104) by using, as a condition, the presence of a predetermined operation state (for instance, fuel cut F/C) where an exhaust air-fuel ratio on the upstream side of the catalyst is set remarkably lean (S103: YES) before its execution. After a remarkably lean gas is supplied to the sensor before executing the deterioration detection to cause a rich component adhering to the sensor to disappear, the deterioration detection can be executed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a catalyst deterioration detection device that detects deterioration 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. Therefore, during normal operation of the internal combustion engine, if the air-fuel mixture is alternately swung to the rich side or the lean side centering on the stoichiometric air-fuel ratio, when the air-fuel mixture becomes lean due to the O ₂ storage function of the three-way catalyst, excess NOx is reduced because oxygen is adsorbed and held by the catalyst, and when the air-fuel mixture becomes rich, oxygen adsorbed and held by the catalyst is released, so that HC and CO are oxidized, whereby NOx, HC and CO can be purified at the same time.

  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 alternately shifted to the rich side or the lean side around the theoretical air-fuel ratio, thereby NOx, HC and CO are simultaneously reduced.

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 deterioration of the O ₂ storage function. 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. This apparatus determines an abnormality of the downstream catalyst among the upstream catalyst and the downstream catalyst arranged in series in the exhaust passage of the internal combustion engine. An inter-catalyst sensor that detects an inter-catalyst air-fuel ratio between the upstream catalyst and the downstream catalyst, and a post-catalyst sensor that detects a post-catalyst air-fuel ratio downstream of the downstream catalyst are provided. Active air-fuel ratio control is performed in which the pre-catalyst air-fuel ratio upstream of the upstream catalyst is switched from lean to rich or vice versa in response to switching of the output of the inter-catalyst sensor from rich to lean or vice versa. An abnormality of the downstream catalyst is determined based on the sensor output emitted from the post-catalyst sensor during the execution of the active air-fuel ratio control.

As another conventional technique, for example, Patent Document 2 discloses a technique for reducing the amount of oxygen during restart in order to suppress high-temperature deterioration of the catalyst after engine restart. Further, in Patent Document 3, the oxygen storage amount of the catalyst is saturated by the air-fuel ratio control immediately before the internal combustion engine is automatically stopped, and sufficient oxygen is consumed by the catalyst by the air-fuel ratio control at the restart after the automatic stop. A technique for injecting fuel so that the equivalent ratio, which is the reciprocal of the air-fuel ratio, is on the rich side is disclosed. In Patent Document 4, when an unburned component adhering to the detection electrode reaches a predetermined amount in an oxygen concentration detection device having a detection electrode and a reference electrode, an electrode processing voltage is applied between both electrodes. Thus, a technique is disclosed in which oxygen is pumped from a reference electrode to a detection electrode to burn and remove unburned components adhering to the detection electrode. Patent Document 5 discloses that the target air-fuel ratio is switched to rich immediately after the fuel cut ends in order to calculate the O ₂ storage amount of the catalyst without deteriorating the exhaust emission.

JP 2004-176615 A JP-A-2005-299400 JP 2003-148200 A Japanese Patent Laid-Open No. 11-326273 JP 2001-115879 A

  By the way, when executing the active air-fuel ratio control, the output value of the post-catalyst sensor provided on the downstream side of the catalyst is reversed to the rich side or the lean side, and at the same time, the target air-fuel ratio is reversed and supplied to the catalyst following this. The air-fuel ratio of exhaust gas may be reversed. In this case, the target air-fuel ratio is reversed at the timing when the output value of the post-catalyst sensor is reversed.

  However, within a certain period after the internal combustion engine is started, rich components such as HC and CO in the exhaust gas due to the rich air-fuel ratio of the air-fuel mixture to be burned and the exhaust gas temperature being low. (Or unburned components) tend to adhere to the catalyst itself and the air-fuel ratio detection sensor installed on the upstream and downstream sides of the catalyst. In particular, on the downstream side of the catalyst, since the heat of the exhaust gas has already been taken away by the upstream exhaust pipe and the catalyst, the exhaust temperature is low, and therefore the rich component adheres to the sensor downstream of the catalyst. As described above, when a rich component adheres to the upstream and downstream sensors of the catalyst, particularly the downstream sensor, the output from the sensor becomes unstable, and normal output cannot be performed from the sensor. Further, if the deterioration of the catalyst is detected based on the sensor output, there is a possibility of erroneous detection.

  Therefore, the present invention has been made in view of such circumstances, and its purpose is to prevent detection of deterioration in a state where rich components adhere to the catalyst and the sensor within a certain period after the internal combustion engine is started. An object of the present invention is to provide a catalyst deterioration detecting device for an internal combustion engine.

In order to achieve the above object, the first invention provides:
An apparatus for detecting deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
When performing the deterioration detection of the catalyst within a predetermined period after the internal combustion engine is started, the deterioration detection is executed on the condition that there is a predetermined operation state in which the exhaust air-fuel ratio on the upstream side of the catalyst is lean before the execution. It is characterized by doing.

  According to the first aspect of the invention, when detecting the deterioration of the catalyst within a predetermined period after the internal combustion engine is started, the lean gas is supplied to the sensor before the detection of the deterioration, and the rich component adhering to the sensor disappears. Can be made. Therefore, it is possible to prevent the deterioration detection from being performed while the rich component is attached to the sensor, stabilize the output of the sensor to prevent erroneous detection, and improve the accuracy of the catalyst deterioration detection.

  Here, “to make the exhaust air / fuel ratio upstream of the catalyst lean” preferably means “to make the exhaust air / fuel ratio upstream of the catalyst significantly lean”. “To make the exhaust air / fuel ratio on the upstream side of the catalyst remarkably lean” means that the exhaust air / fuel ratio on the upstream side of the catalyst is made an air / fuel ratio on the lean side further than the lean air / fuel ratio at the time of normal air / fuel ratio control.

The second invention is the first invention, wherein
The predetermined operation state is fuel cut.

  When the fuel cut for stopping the fuel injection is executed, air having an infinite air-fuel ratio is caused to flow through the exhaust passage. As a result, a remarkable lean state is realized, and the same effect as the first invention is exhibited.

The third invention is the first invention, wherein
The predetermined operation state is a lean spike.

  Even when a lean spike is executed in which the exhaust air-fuel ratio on the upstream side of the catalyst is temporarily significantly lean, a remarkably lean gas flows in the exhaust passage. Therefore, the same effect as the first invention is exhibited.

Moreover, 4th invention is set in 3rd invention,
The lean spike is executed when a predetermined lean spike permission condition is satisfied.

  Since the lean spike temporarily makes the air-fuel ratio of the combustion mixture lean significantly, there is a concern about the deterioration of emission and drivability due to its execution. Therefore, it is preferable to execute the lean spike when a predetermined lean spike permission condition that prevents such deterioration is satisfied.

The fifth invention is the fourth invention, wherein
The lean spike permission condition is satisfied when at least one of the following conditions A to C is satisfied.
A. There is no acceleration request for the internal combustion engine.
B. The internal combustion engine is not in a predetermined operating range where the amount of NOx emission increases.
C. The temperature of the downstream catalyst located on the downstream side of the catalyst is in a predetermined activation temperature range.

  When the condition A is satisfied, the lean spike permission condition is satisfied to prevent the deterioration of drivability, and when the conditions B and C are satisfied, the lean spike permission condition is satisfied to prevent the emission deterioration. The

Also, a sixth invention is any one of the first to fifth inventions,
A post-catalyst sensor for detecting an exhaust air / fuel ratio downstream of the catalyst is provided, and the predetermined period is a period before the post-catalyst sensor reaches a predetermined active temperature range.

  According to the sixth aspect of the invention, even after the start of the internal combustion engine and before the post-catalyst sensor reaches the predetermined activation temperature range, the deterioration detection is suitably performed without the influence of the rich component adhering to the post-catalyst sensor. Can be executed. Further, even within such a short period after the start of the internal combustion engine, the deterioration detection can be suitably performed, the execution frequency of the deterioration detection can be increased, and the execution start timing of the deterioration detection can be advanced.

  According to the present invention, an excellent effect is exhibited that it is possible to prevent deterioration detection from being performed in a state in which rich components adhere to the catalyst and the sensor within a certain period after the internal combustion engine is started.

  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. An opening sensor 15, a throttle opening sensor 19 for detecting the opening of the throttle valve 10, 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 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). Correspondingly, during normal operation of the internal combustion engine, the ECU 20 controls the air / fuel ratio so that the exhaust air / fuel ratio upstream of the catalyst, that is, the pre-catalyst air / fuel ratio A / Ffr becomes the stoichiometric air / fuel ratio A / Fs. 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.

Here, the catalyst 11 will be described in more detail. As shown in FIG. 2, in the catalyst 11, a coating material 31 is coated on the surface of a carrier base material (not shown), and the coating material 31 is held in a state in which a large number of particulate catalyst components 32 are dispersedly arranged. The catalyst 11 is exposed inside. The catalyst component 32 is mainly composed of a noble metal such as Pt or Pd, and serves as an active point for reacting exhaust gas components such as NOx, HC and CO. On the other hand, the coating material 31 plays the role of a promoter that promotes the reaction at the interface between the exhaust gas and the catalyst component 32 and includes an oxygen storage component capable of absorbing and releasing oxygen according to the air-fuel ratio of the atmospheric gas. Oxygen storage component, for example made of cerium dioxide CeO _2. For example, when the atmosphere gas of the catalyst component 32 and the coating material 31 is richer than the theoretical air-fuel ratio A / Fs, oxygen stored in the oxygen storage component existing around the catalyst component 32 is released, and as a result, release Unburned components such as HC and CO are oxidized and purified by the released oxygen. Conversely, if the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the theoretical air-fuel ratio A / Fs, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmosphere gas, and as a result, NOx is reduced. Reduced and purified.

  Even if the pre-catalyst air-fuel ratio A / Ffr slightly varies from the stoichiometric air-fuel ratio A / Fs during the normal air-fuel ratio control, the three exhaust gas components such as NOx, HC, and CO can be obtained. Can be purified simultaneously. Therefore, in normal air-fuel ratio control, it is also possible to purify exhaust gas by causing the pre-catalyst air-fuel ratio A / Ffr to oscillate slightly around the stoichiometric air-fuel ratio A / Fs and to repeatedly absorb and release oxygen.

  By the way, in the catalyst 11 in the new state, as described above, a large number of fine particulate catalyst components 32 are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is kept high. However, when the catalyst 11 deteriorates, some of the catalyst components 32 are lost, and some of the catalyst components 32 are baked and solidified by exhaust heat (see broken lines in the figure). In this case, the contact probability between the exhaust gas and the catalyst component 32 is lowered, and the purification rate is lowered. In addition to this, the amount of the coating material 31 existing around the catalyst component 32, that is, the amount of the oxygen storage component decreases, and the oxygen storage capacity itself decreases.

Thus, the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11 are in a correlation. Therefore, in this embodiment, the degree of deterioration of the catalyst 11 is detected or determined by detecting the oxygen storage capacity of the catalyst 11. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of an oxygen storage capacity (OSC; O ₂ Storage Capacity, unit: g), which is the amount of oxygen that the catalyst 11 can store.

Hereinafter, detection of deterioration of the catalyst in the present embodiment will be described.
In the present embodiment, active air-fuel ratio control by the ECU 20 is executed when the deterioration of the catalyst 11 is detected. Here, the active air-fuel ratio control means that the pre-catalyst air-fuel ratio A / Ffr that is the exhaust air-fuel ratio upstream of the catalyst is changed from one of the predetermined rich air-fuel ratio A / Fr and lean air-fuel ratio A / Fl to a predetermined value. This control is forcibly switched (or reversed) at the timing.

  Here, the deterioration detection of the catalyst 11 is executed when the internal combustion engine 1 is in a steady operation and when the catalyst 11 is in a predetermined activation temperature range. The temperature of the catalyst 11 may be detected directly, but in the present embodiment, it is estimated using a predetermined map or function based on the engine operating state. The detection of the deterioration of the catalyst 11 is executed once for every operation of the engine, and at least twice in succession, when it is determined that the catalyst 11 is in a deteriorated state, the final deterioration of the catalyst 11 is detected, and the warning device Operated.

  3A and 3B, 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. Further, in FIG. 3A, the target air-fuel ratio A / Ft that is an internal value of 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. 3A, 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. Accordingly, the pre-catalyst air-fuel ratio A / Ffr is also forcibly and alternately switched between the rich air-fuel ratio A / Fr and the lean air-fuel ratio A / Fl in the same manner as 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. 3A and 3B, 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.

  In this way, the output value of the post-catalyst sensor 18 is inverted and reaches the rich determination value VR or the lean determination value VL. At the same time, the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl or the rich air-fuel ratio A / Fr. It is forcibly switched.

  While performing this active air-fuel ratio control, 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. 3, 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. 4, 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 the 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 once is used and compared with a predetermined threshold value (catalyst deterioration determination threshold value). If the oxygen storage capacity OSC1 exceeds the threshold value, For example, the deterioration of the catalyst can be determined such that the deterioration is normal and the oxygen storage capacity OSC1 is lower than the threshold value. However, in this embodiment, in order to improve the accuracy, the oxygen storage capacity (oxygen absorption amount in this case) is calculated on the lean side as well, and the calculation is repeated a plurality of times on the rich side and the lean side as necessary. The final deterioration judgment is performed by comparing the value with a threshold value.

  Specifically, as shown in FIG. 4, 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 every 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. Thus, a plurality of oxygen storage capacities OSC1, OSC2,... OSCn (for example, n is 5 or more) are repeatedly calculated, and the average value OCCSav is compared with a predetermined threshold value OSCs. If the average value OCCSav exceeds the threshold value OSCs, the catalyst 11 is determined to be normal, and if the average value OCCSav is equal to or less than the threshold value OSCs, the catalyst 11 is determined to be deteriorated.

  Note that the calculation number n of the oxygen storage capacity OSC may be changed in accordance with a value that correlates with the degree of catalyst deterioration, such as the travel distance of the vehicle. For example, if it is assumed that the travel distance is relatively small and the deterioration is not significantly advanced, the value of n is set to a small value. If the travel distance is relatively large and the deterioration may be advanced to a considerable degree, the value of n is increased. And

  In the active air-fuel ratio control described above, the output voltage of the post-catalyst sensor 18 is reversed to the lean side and reaches the lean determination value VL (t1 in FIG. 3). At the same time, the target air-fuel ratio A / Ft is rich. At the same time that the output voltage of the post-catalyst sensor 18 is reversed to the rich side and reaches the rich determination value VR (t2 in FIG. 3), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl. Can be switched. That is, the target air-fuel ratio A / Ft is reversed at the timing when the output of the post-catalyst sensor 18 is reversed.

  On the other hand, within a certain period after the internal combustion engine is started, rich components such as HC and CO in the exhaust gas due to the rich air-fuel ratio of the air-fuel mixture to be burned and the low exhaust gas temperature. (Or unburned components) tend to adhere to the catalyst 11 itself and the sensors 17 and 18 before and after the catalyst. In particular, on the downstream side of the catalyst 11, since the heat of the exhaust gas has already been taken away by the upstream exhaust pipe and the catalyst 11, the exhaust temperature is low and the post-catalyst sensor 18 rather than the pre-catalyst sensor 17. However, the activity tends to be delayed, and adhesion of rich components is remarkable. Thus, if rich components adhere to the sensors 17 and 18 before and after the catalyst, particularly the post-catalyst sensor 18, the sensor output becomes unstable and normal output from the sensor cannot be performed. Further, if the deterioration of the catalyst is detected based on the sensor output, there is a possibility of erroneous detection. For example, the reversal timing of the target air-fuel ratio A / Ft may be affected by the rich component adhering to the post-catalyst sensor 18, and the calculated oxygen storage capacity value may become an incorrect value.

  Therefore, in order to avoid such a problem, in the present embodiment, when detecting the deterioration of the catalyst within a predetermined period after the start of the internal combustion engine, the exhaust air-fuel ratio (the pre-catalyst air before the catalyst) is detected before the detection. Deterioration detection is executed on the condition that there is a predetermined operation state in which the fuel ratio (A / Ffr) is markedly lean. In other words, the present embodiment relates to a precondition when performing catalyst deterioration detection within a predetermined period after the internal combustion engine is started.

  Hereinafter, a first embodiment of the catalyst deterioration detection control of the present embodiment will be described with reference to FIG. The execution routine of the catalyst deterioration detection control shown in the figure is repeatedly executed by the ECU 20 every predetermined minute time (for example, 16 msec).

  First, in step S101, it is determined whether or not basic execution conditions for catalyst deterioration detection control are satisfied. The basic execution conditions are, for example, 1) that the internal combustion engine 1 is in a steady operation state, and 2) that the temperature of the catalyst 11 is in a predetermined activation temperature range. If the basic execution condition is not satisfied, this routine is terminated. If the basic execution condition is satisfied, the process proceeds to step S102.

  In step S102, a post-start period, which is a period from the start of the internal combustion engine to the present time, is compared with a predetermined period. Here, the post-start period is measured by a timer or the like equipped in the ECU 20, while the predetermined period is set in advance as a period (for example, a value of several minutes) such that the post-catalyst sensor 18 reaches a predetermined active temperature range. Are input to the ECU 20.

  When the post-start period is not less than the predetermined period, that is, when the post-start period is greater than or equal to the predetermined period, it is considered that the post-catalyst sensor 18 has reached the predetermined active temperature range, and the process proceeds to step S104 and the catalyst deterioration detection as described above is executed. Is done. That is, normal / deterioration of the catalyst is determined through the steps of executing active air-fuel ratio control, calculating the oxygen storage capacity OSC of the catalyst, and comparing the calculated oxygen storage capacity OSC with the catalyst deterioration determination threshold value. . After execution of step S104, this routine is terminated.

  On the other hand, when the post-start period is less than the predetermined period, it is considered that the post-catalyst sensor 18 has not reached the predetermined active temperature range, the process proceeds to step S103, and during the period from the start of the internal combustion engine to the present time, It is determined whether or not there is a history of fuel cut (F / C) that stops fuel injection. Since the pre-catalyst air-fuel ratio A / Ffr becomes a substantially infinite value due to the fuel cut, the fuel cut is brought into a predetermined operation state that makes the pre-catalyst air-fuel ratio A / Ffr remarkably lean as described above. Equivalent to. Here, “to make the pre-catalyst air / fuel ratio A / Ffr remarkably lean” means that the pre-catalyst air / fuel ratio A / Ffr is slightly leaner than the stoichiometric air / fuel ratio during normal air / fuel ratio control. The air-fuel ratio on the lean side further than the air-fuel ratio shifted to the side). For example, in the fuel cut, 1) the accelerator opening detected by the accelerator opening sensor 15 is substantially fully closed, and 2) the engine speed calculated based on the output of the crank angle sensor 14 is slightly higher than the idle speed. It is executed when the two conditions of exceeding a predetermined speed are satisfied.

  If there is a fuel cut history, the process proceeds to step S104, and the catalyst deterioration detection is executed as described above. On the other hand, when there is no fuel cut history, the routine proceeds to step S105, where the routine is terminated without detecting the catalyst deterioration.

  According to the first form of the catalyst deterioration detection control, when the post-start period is less than the predetermined period, that is, when the post-catalyst sensor 18 does not reach the predetermined active temperature range and after a short period after engine start ( Even if it is (step S102: YES), if there is a previous fuel cut history (step S103: YES), catalyst deterioration detection is executed.

  In general, the catalyst deterioration detection is not performed for a short period after the engine is started so that the post-catalyst sensor 18 does not reach the predetermined activation temperature range. In order to secure opportunities as much as possible, if the catalyst temperature enters the activation temperature range and the basic execution condition is satisfied (step S101: YES), the catalyst deterioration detection is basically executable. However, during such a short period, the air-fuel ratio is often rich to stabilize combustion, and the exhaust gas temperature is also low, so the exhaust gas contains a lot of rich components (HC, CO). In addition, this rich component adheres to the post-catalyst sensor 18 and makes the output of the post-catalyst sensor 18 unstable.

  However, even in this case, since the catalyst deterioration detection is executed on the condition that there is a fuel cut history, such a problem is solved. In other words, air or fresh air flows through the exhaust passage due to the fuel cut, and this air is chemically reacted with the rich component adhering to the post-catalyst sensor 18 (particularly the combustion reaction), thereby eliminating the rich component. it can. Further, the rich component adhering to the post-catalyst sensor 18 by air can be physically blown away. As a result, the rich component can be purged and the post-catalyst sensor 18 can be refreshed, the influence of the rich component is eliminated, the output of the post-catalyst sensor 18 is stabilized, and the rich component adheres to the post-catalyst sensor 18 and deteriorates. It is possible to prevent detection. Further, it is possible to prevent erroneous detection due to such rich component adhesion and to improve the accuracy of catalyst deterioration detection.

  In addition, the rich component adhering to the pre-catalyst sensor 17 can be chemically and physically lost by the fresh air circulation by the fuel cut. As a result, the pre-catalyst sensor 17 can obtain the same benefits as the post-catalyst sensor 18.

  Next, a second embodiment of the catalyst deterioration detection control of this embodiment will be described based on FIG. The execution routine of the catalyst deterioration detection control shown in the figure is also repeatedly executed by the ECU 20 every predetermined minute time (for example, 16 msec).

  First, in step S201, as in step S101, it is determined whether or not basic execution conditions for catalyst deterioration detection control are satisfied. In the next step S202, the post-start period is compared with a predetermined period, as in step S102.

  When the period after the start is not less than the predetermined period (that is, when it is equal to or longer than the predetermined period), it is considered that the post-catalyst sensor 18 has reached a predetermined activation temperature range, and the process proceeds to step S204 and the catalyst is the same as in step S104. Deterioration detection is executed, and this routine is terminated.

  On the other hand, when the post-start period is less than the predetermined period, it is considered that the post-catalyst sensor 18 has not reached the predetermined active temperature range, the process proceeds to step S203, and from the start of the internal combustion engine to the present time, as in step S103. It is determined whether or not there is a fuel cut history between.

  If there is a fuel cut history, the routine proceeds to step S204, where catalyst deterioration detection is performed as described above. On the other hand, if there is no fuel cut history, the routine proceeds to step S205, where it is determined whether the lean spike permission condition is satisfied, and if the lean spike permission condition is satisfied, the lean spike is executed in step S206. Then, the process proceeds to step S204, where catalyst deterioration detection is executed. On the other hand, when the lean spike permission condition is not satisfied, the routine proceeds to step S207, where the routine is terminated without detecting the catalyst deterioration.

  In the second embodiment, the catalyst deterioration detection is not immediately performed when there is no fuel cut history as in the first embodiment, but when the lean spike permission condition is satisfied even when there is no fuel cut history. Forcibly executes a lean spike and then detects catalyst deterioration.

  Lean spike is the air-fuel ratio of the air-fuel mixture in the combustion chamber, that is, the pre-catalyst air-fuel ratio A / Ffr, which is temporarily or instantaneously further on the lean side than the lean air-fuel ratio during normal air-fuel ratio control (ie, significantly This is a control for making the air / fuel ratio lean. For example, fuel injection is performed with the target air-fuel ratio A / Ft set to a value of about 15 to 15.5, and the actual air-fuel ratio detected by the pre-catalyst sensor 17 reaches a value equal to the target air-fuel ratio A / Ft. Then, the control is terminated. As a result, the pre-catalyst air-fuel ratio A / Ffr temporarily becomes significantly lean, and the post-catalyst sensor 18 can be refreshed as in the case of the fuel cut. That is, the rich component adhering to the post-catalyst sensor 18 can be chemically and physically lost by the remarkable lean gas based on the lean spike, and the output of the post-catalyst sensor 18 can be stabilized without the influence of the rich component. And the misdetection resulting from such rich component adhesion can be prevented, and the precision of catalyst degradation detection can be improved. The rich component adhering to the pre-catalyst sensor 17 can also be eliminated by the lean spike as described above.

  In this way, even when there is no fuel cut history, the lean spike can be executed and the catalyst deterioration can be detected, so that more opportunities for detecting the catalyst deterioration can be secured.

  Here, since the lean spike is a control that temporarily makes the air-fuel ratio of the air-fuel mixture to be burned significantly lean, there is a concern that the emission and the drivability may deteriorate due to the execution. Although the value of the air-fuel ratio at the time of lean spike execution is set so as not to adversely affect the emission and drivability as much as possible, it is desirable to minimize the influence on these.

Therefore, in the present embodiment, it is determined whether or not a condition for permitting the execution of the lean spike is satisfied (step S205). The lean spike permission condition is satisfied when at least one, preferably all of the following conditions A to C are satisfied.
A. There is no acceleration request for the internal combustion engine.
B. The internal combustion engine is not in a predetermined operating range where the amount of NOx emission increases.
C. The temperature of the downstream catalyst located on the downstream side of the catalyst 11 is in a predetermined activation temperature range.

  Condition A is based on a drivability viewpoint. For example, in an internal combustion engine for a vehicle, if the driver depresses the accelerator and tries to accelerate, if the air-fuel ratio is temporarily made lean, the sense of acceleration will be lost momentarily during the acceleration, resulting in a sense of incongruity. Therefore, to avoid this, the lean spike is not executed when there is an acceleration request to the internal combustion engine, and conversely, the lean spike is executed when there is no acceleration request to the internal combustion engine.

  The determination of the condition A can be performed as follows, for example. That is, when the value of the accelerator opening detected by the accelerator opening sensor 15 is larger than a predetermined value or when the change speed of the accelerator opening is larger than a predetermined value, it is determined that there is a request for acceleration. When the value of is not more than a predetermined value or the change rate of the accelerator opening is not more than a predetermined value, it is determined that no acceleration is requested.

  Condition B is based on an emission viewpoint. For example, there may be an operation region where NOx is easily discharged, such as a region where lean burn operation (lean burn operation) for improving fuel efficiency is performed, and the air-fuel ratio is temporarily set in this operation region. If it becomes a remarkable lean, NOx will get worse. Therefore, in order to avoid this, when the internal combustion engine is in an operation region where the NOx emission amount increases, the lean spike is not executed, and conversely, the operation region where the internal combustion engine increases the NOx emission amount. If not, perform lean spike.

  As a determination method of the condition B, for example, a lean spike execution region map is created in advance in association with parameters (for example, rotation speed and load) representing the engine operating state, and is input to the ECU 20, and the detected values of these parameters and the lean Comparison with the spike execution area map is made to determine whether condition B is satisfied or not.

  Condition C is also based on an emission viewpoint. For example, in order to improve emissions, an additional catalyst may be provided in the exhaust passage on the downstream side of the catalyst 11. This added catalyst is referred to as a downstream catalyst. The downstream catalyst is usually installed on the downstream side of the post-catalyst sensor 18. In this case, even if NOx is discharged by the execution of lean spike and passes through the upstream catalyst 11, if the downstream catalyst is in the active temperature range, the NOx can be removed by the downstream catalyst. Therefore, the lean spike is not executed when the downstream catalyst is not in the active temperature range, and conversely, the lean spike is executed when the downstream catalyst is in the active temperature range.

  As a determination method of the condition C, for example, the temperature of the downstream catalyst is estimated, and when the estimated temperature is equal to or higher than the predetermined temperature, the condition C is satisfied, and when the estimated temperature is lower than the predetermined temperature, the condition C is not satisfied.

  As described above, since whether or not the execution permission condition is satisfied is determined before the execution of the lean spike, it is possible to prevent the emission and the drivability from being deteriorated due to the lean spike.

  Next, a third form of the catalyst deterioration detection control of this embodiment will be described with reference to FIG. The execution routine of the catalyst deterioration detection control shown in the figure is also repeatedly executed by the ECU 20 every predetermined minute time (for example, 16 msec).

  The execution routine of the third form is substantially the same as the execution routine of the first form. In the third mode, steps S301, S302, S304, and S305 are the same as steps S101, S102, S104, and S105 in the first mode, and only step S303 is different from step S103 in the first mode.

  In step S103 of the first embodiment, it is determined whether or not there is a history of fuel cut execution from the start of the internal combustion engine to the present time. On the other hand, in step S303 of the third embodiment, it is determined whether there is a history of execution of lean spikes from the start of the internal combustion engine to the present time. By executing this lean spike, the sensors 17 and 18 (particularly the post-catalyst sensor 18) before and after the catalyst can be refreshed similarly to the fuel cut. Therefore, the fuel cut history of the first embodiment is replaced with the lean spike history. Can exhibit the same effects as those of the first embodiment.

  Note that the case where the lean spike is executed between the start of the internal combustion engine and the present time refers to the case where the lean spike is executed based on other conditions that are related to or unrelated to the detection of catalyst deterioration, for example.

  As described above, according to the present embodiment, the deterioration of the catalyst is detected on the condition that there is a predetermined operation state in which the pre-catalyst air-fuel ratio A / Ffr is remarkably lean within a certain period after the internal combustion engine is started. Execute. As a result, the catalyst deterioration can be detected after the rich component adhering to the sensor is purged in advance. Therefore, when performing catalyst deterioration detection, it is possible to prevent deterioration detection with rich components attached to the sensor, stabilize the sensor output to prevent false detection, and improve the accuracy of catalyst deterioration detection. it can.

  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, 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. There is no particular limitation on the type and application of the internal combustion engine. The post-catalyst sensor 18 can be replaced with a global air-fuel ratio sensor similar to the pre-catalyst sensor 17.

  In the embodiment, as a catalyst deterioration detection method, a method (so-called Cmax method) is adopted in which the oxygen storage capacity of the catalyst is calculated and compared with a catalyst deterioration determination threshold value to determine deterioration. However, other catalyst deterioration detection methods can be employed. For example, a method of detecting catalyst deterioration based on the ratio of sensor output trajectory lengths before and after the catalyst as disclosed in Patent Document 1, a method of detecting catalyst deterioration based on the output trajectory length of the post-catalyst sensor more simply, etc. Can be adopted.

  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 which shows the structure of this embodiment. It is a schematic sectional drawing which shows the structure of a catalyst. 3 is a time chart for explaining the basics of active air-fuel ratio control. FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for calculating the oxygen storage capacity. It is a flowchart of the 1st form of catalyst deterioration detection control. It is a flowchart of the 2nd form of catalyst deterioration detection control. It is a flowchart of the 3rd form of catalyst deterioration detection control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 3 Combustion chamber 5 Air flow meter 6 Exhaust pipe 7 Spark plug 10 Throttle valve 11 Catalyst 12 Injector 15 Accelerator opening sensor 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
A / F Air-fuel ratio A / Ffr Pre-catalyst air-fuel ratio A / Frr Post-catalyst air-fuel ratio A / Ft Target air-fuel ratio A / Fs Theoretical air-fuel ratio OSC Catalyst oxygen storage capacity VR Rich judgment value VL Lean judgment value

Claims (6)

An apparatus for detecting deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
When performing the deterioration detection of the catalyst within a predetermined period after the internal combustion engine is started, the deterioration detection is executed on the condition that there is a predetermined operation state in which the exhaust air-fuel ratio on the upstream side of the catalyst is lean before the execution. An apparatus for detecting catalyst deterioration in an internal combustion engine.   2. The catalyst deterioration detection device for an internal combustion engine according to claim 1, wherein the predetermined operation state is fuel cut.   2. The catalyst deterioration detection apparatus for an internal combustion engine according to claim 1, wherein the predetermined operation state is a lean spike.   4. The catalyst deterioration detection device for an internal combustion engine according to claim 3, wherein the lean spike is executed when a predetermined lean spike permission condition is satisfied. The catalyst deterioration detection device for an internal combustion engine according to claim 4, wherein the lean spike permission condition is satisfied when at least one of the following conditions A to C is satisfied.
A. There is no acceleration request for the internal combustion engine.
B. The internal combustion engine is not in a predetermined operating range where the amount of NOx emission increases.
C. The temperature of the downstream catalyst located on the downstream side of the catalyst is in a predetermined activation temperature range.   The post-catalyst sensor for detecting an exhaust air-fuel ratio downstream of the catalyst is provided, and the predetermined period is a period before the post-catalyst sensor reaches a predetermined active temperature range. The catalyst deterioration detection device for an internal combustion engine according to any one of claims 5 to 5.

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