JP2008045427A - Catalyst deterioration detecting device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent erroneous detection caused by operation of a variable valve gear. <P>SOLUTION: This internal combustion engine has the variable valve gear in an intake-exhaust system. The device detects the deterioration in a catalyst arranged in its exhaust passage, and has a means for performing active air-fuel ratio control for forcibly switching the exhaust air-fuel ratio on the catalyst upstream side to the other from one of the rich air-fuel ratio and the lean air-fuel ratio, a means (S102) determining whether or not the operation timing of an intake valve and an exhaust valve falls within a predetermined mask area, and a means (S103) prohibiting the active air-fuel ratio control when determining that the operation timing falls within the mask area. The erroneous detection based on an unstable oxygen storage capacity calculating value can be prevented. <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. 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. 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 post-catalyst sensor from rich to lean or vice versa. During the execution of this active air-fuel ratio control, the oxygen storage capacity of the downstream catalyst is calculated, and abnormality of the downstream catalyst is determined based on this calculated value.

  As another prior art, for example, Patent Document 2 discloses that the deterioration detection of the catalyst means is prohibited when the engine load fluctuates greatly. Patent Document 3 discloses that the deterioration detection of the catalyst means is prohibited when the valve timing switching mechanism is abnormal. Further, Patent Document 4 discloses that catalyst deterioration detection is prohibited when an abnormality of the valve timing adjusting device is detected. Further, in Patent Document 5, in the control device for an internal combustion engine that variably controls at least one of the maximum lift amount and the operating angle of the intake valve, the maximum value of the intake valve is determined when the deterioration of the exhaust purification catalyst is judged as compared to when it is not. A technique for increasing at least one of a lift amount and a working angle is disclosed.

JP 2004-176615 A JP-A-9-41952 JP-A-6-42338 JP 11-190234 A JP 2006-37841 A

  By the way, in an internal combustion engine, there may be provided a variable valve operating device that can change the operation timing and lift of the intake valve (or exhaust valve). In this case, as a result of changing the operation timing and lift of the intake valve by the variable valve operating apparatus, the composition of the exhaust gas changes, and this composition change may affect the calculated value of the oxygen storage capacity. The calculated value of oxygen storage capacity varies in an unstable manner, which may cause erroneous determination and erroneous detection.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a catalyst deterioration detection device for an internal combustion engine that can prevent erroneous detection due to the operation of a variable valve device. is there.

In order to achieve the above object, the first invention provides:
An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
Determining means for determining whether at least one of an operation timing and a lift of at least one of an intake valve and an exhaust valve related to the variable valve operating device is within a predetermined range;
When the determination means determines that at least one of the operation timing and the lift is within a predetermined range, the active air-fuel ratio control is stopped or interrupted during execution, or before the active air-fuel ratio control is executed. And an active air-fuel ratio control stopping means for prohibiting.

In addition, the second invention,
An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
A storage capacity calculating means for calculating an oxygen storage capacity of the catalyst during execution of the active air-fuel ratio control;
Determining means for determining whether at least one of an operation timing and a lift of at least one of an intake valve and an exhaust valve related to the variable valve operating device is within a predetermined range;
When the determination means determines that at least one of the operation timing and the lift is within a predetermined range during the calculation of the oxygen storage capacity by the storage capacity calculation means, the calculated oxygen storage capacity value is invalidated. And an invalidating means for converting to the above.

The third invention is the first or second invention, wherein
The predetermined range is a predetermined range in which the operation timing of the intake valve is relatively advanced, or a predetermined range in which the operation timing of the exhaust valve is relatively retarded.

In addition, the fourth invention is
An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
Transient determination means for determining whether or not the change speed of at least one of the operation timing and the lift of at least one of the intake valve and the exhaust valve related to the variable valve operating system exceeds a predetermined value;
When it is determined by the transient determination means that the change speed of at least one of the operation timing and the lift exceeds a predetermined value, the active air-fuel ratio control is stopped or interrupted during execution, or the active air-fuel ratio control is performed. And a transient active air-fuel ratio control stop means for prohibiting before execution.

In addition, the fifth invention,
An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
A storage capacity calculating means for calculating an oxygen storage capacity of the catalyst during execution of the active air-fuel ratio control;
Transient determination means for determining whether or not the change speed of at least one of the operation timing and the lift of at least one of the intake valve and the exhaust valve related to the variable valve operating system exceeds a predetermined value;
During the calculation of the oxygen storage capacity by the storage capacity calculation means, when the transition determination means determines that the change speed of at least one of the operation timing and the lift exceeds a predetermined value, the calculated oxygen storage capacity And a transient invalidating means for invalidating the value of.

  According to the present invention, an excellent effect is exhibited that it is possible to prevent erroneous detection caused by the operation of the variable valve operating apparatus.

  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). Here, as the variable valve operating device, each of the intake valve Vi and the exhaust valve Ve has a variable valve timing mechanism (hereinafter referred to as “VVT”, the intake side VVT is referred to as “VVTi”, and the exhaust side VVT is referred to as “VVTe”) 21, 22 is attached, and the operation timing of the intake valve Vi and the exhaust valve Ve is variable. 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 above-described spark plug 7, throttle valve 10, injector 12, VVTi21, VVTe22, and the like 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, an intake pressure sensor 16 for detecting the intake pressure, 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 (not shown). Has been. The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, the VVTi 21, the VVTe 22, and the like 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 The timing, throttle opening, intake valve Vi opening / closing timing, exhaust valve Ve opening / closing timing, and the like are controlled. The throttle opening is normally controlled to an opening corresponding to the accelerator opening.

  VVTi21 and VVTe22 have the same configuration, and only VVTi21 on the intake side will be described as a representative here. The VVTi 21 advances or retards the angle of the intake camshaft relative to the crank angle (cam angle), thereby simultaneously opening and closing the operation angles of the intake valves Vi of all the cylinders. In addition, the angle is advanced or retarded by the same amount. The lift of the intake valve Vi (maximum lift amount per lift) does not change. The detailed configuration of the VVTi 21 is the same as that disclosed in, for example, Japanese Patent Laid-Open No. 8-218823. The VVTi 21 is provided with a cam angle sensor that detects the cam angle, and the output of the cam angle sensor is sent to the ECU 20. The ECU 20 sets a target value of the cam angle based on the engine operating state (for example, the rotational speed NE and the load factor KL), and controls the VVTi 21 so that the actual cam angle detected by the cam angle sensor matches the target value. To do. The ECU 20 can calculate the operation timing of the intake valve Vi corresponding to each cam angle, that is, the opening / closing timing.

  The opening / closing timing of the intake valve Vi can be changed as shown in FIG. 6, for example. That is, when the relative position of the cam angle with respect to the crank angle is referred to as a VVTi position ivt, the opening timing of the intake valve Vi is VVTi from θo1 when the VVTi position ivt is at the most retarded reference position (ivt = 0). It can be changed up to θo2 when the position ivt is at the maximum advance angle position (ivt = ivt0) on the most advance side. The closing timing can be changed from θc1 to θc2 in accordance with the change of the opening timing. However, the operating angle Δθ, which is an angle between the opening timing and the closing timing, and the maximum lift amount per lift are constant. The VVTi position ivt is calculated from the detection values of the crank angle sensor 14 and the cam angle sensor.

  Although not shown in the figure, the exhaust valve Ve has the reference timing on the most advanced side, contrary to the intake valve Vi. That is, the opening timing of the exhaust valve Ve is from the timing when the VVTe position evt is at the most advanced reference position (evt = 0) to the maximum retarded position (evt = evt0) at which the VVTe position evt is most retarded. ) Can be changed up to the timing when

  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 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 performed once for each operation of the engine, and the warning device is activated when it is determined that the catalyst 11 is in a deteriorated state at least twice.

  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 cycles of oxygen storage capacity OSCm (m = 1, 2,..., N, n is an integer of 2 or more) are repeatedly calculated, and the average value OSCav is compared with a predetermined threshold value OSCs. If the average value OSCav exceeds the threshold value OSCs, the catalyst 11 is determined to be normal, and if the average value OSCav 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

  Here, the relationship between the oxygen storage capacity OSC and the catalyst temperature is shown in FIG. As can be seen, the oxygen storage capacity OSC tends to increase as the catalyst temperature increases. The oxygen storage capacity OSC is the maximum for a new catalyst, and decreases as the catalyst deteriorates. When the oxygen storage capacity OSC becomes equal to or less than the threshold value OSCs, the catalyst 11 is determined to be deteriorated.

  Now, in this embodiment, VVTi21 and VVTe22 are provided as variable valve operating devices, but the opening and closing timings of the intake valve Vi and the exhaust valve Ve are changed by the operation of the VVTi21 and VVTe22, and as a result, the composition of the exhaust gas The composition change may affect the calculated value of the oxygen storage capacity OSC. Then, the calculated oxygen storage capacity becomes unstable, which may cause erroneous detection.

  Specifically, the composition components in the exhaust gas are roughly classified into HC and CO as unburned components and NOx as an oxidizing component. The ratio of these HC, CO and NOx is the intake valve Vi and It changes depending on the opening / closing timing of the exhaust valve Ve. When the opening / closing timing of the intake valve Vi and the exhaust valve Ve is in a specific region, the calculated value of the oxygen storage capacity OSC becomes unstable due to the change in the composition ratio in the exhaust gas. May deviate significantly. It is not appropriate to perform deterioration determination by comparing such a value with the deterioration determination threshold value OSCs, and may lead to erroneous determination and erroneous detection.

  According to the results of a test study by the present inventor, if the opening / closing timing of the intake valve Vi is advanced, the combustion temperature tends to decrease and NOx tends to decrease, and even if the opening / closing timing of the exhaust valve Ve is retarded. A similar trend was found. Even if the pre-catalyst air-fuel ratio A / Ffr is controlled to the same value by the active air-fuel ratio control, the exhaust gas components differ depending on the opening / closing timing of the intake valve Vi and the exhaust valve Ve, and the exhaust gas sensed by the post-catalyst sensor 18 differs. Thus, the same oxygen storage capacity calculation value cannot be obtained, and as a result, a value that deviates relatively from the true value may be calculated.

  FIG. 7 shows changes in the outputs of the pre-catalyst sensor 17 and the post-catalyst sensor 18 when the intake valve Vi and the exhaust valve Ve are opened and closed in a region where the calculated oxygen storage capacity becomes unstable. The illustrated example particularly shows the case where the NOx ratio in the exhaust gas is small (that is, the ratio of HC and CO is large) and the post-catalyst sensor 18 is an exhaust gas component that makes it difficult to detect richness. At this time, the post-catalyst sensor 18 does not rapidly reverse from lean to rich as in a normal case (see FIG. 3), but gently reverses. Accordingly, the inversion timing of the target air-fuel ratio A / Ft, and hence the oxygen storage capacity calculation value, also varies. In order to accurately calculate the oxygen storage capacity OSC, the output of the post-catalyst sensor 18 is required to be clearly inverted. However, in such a state, it is difficult to accurately calculate the oxygen storage capacity OSC.

  Therefore, in order to prevent erroneous detection due to the operation of VVTi21 and VVTe22, in the present embodiment, the ECU 20 executes at least one of the following first to fourth processes.

  FIG. 8 shows a routine relating to the first processing. This routine is repeatedly executed by the ECU 20 every minute time. First, in step S101, it is determined whether an execution condition for active air-fuel ratio control is satisfied. For example, this condition is satisfied when the internal combustion engine 1 is first in a steady operation state after the engine is started and the estimated temperature of the catalyst 11 enters a predetermined activation temperature range. If the execution condition of the active air-fuel ratio control is not satisfied, the process proceeds to step S103 and the active air-fuel ratio control is prohibited. As a result, the active air-fuel ratio control is not executed. On the other hand, if the execution condition of the active air-fuel ratio control is established, the process proceeds to step S102.

  In step S102, it is determined whether or not the operation timing of the intake valve Vi and the exhaust valve Ve is within a predetermined mask region. The mask region is an operation timing region of the intake / exhaust valve where the oxygen storage capacity calculation value becomes unstable, and is a hatching region as indicated by M in FIG. Here, FIG. 9 is a map showing the relationship between the VVTi position ivt and VVTe position evt and the mask region M, which is created in advance through experiments or the like and stored in the ECU 20.

  As described with reference to FIG. 6, the VVTi position ivt advances as it increases from the most retarded reference position 0, and the opening timing of the intake valve Vi gradually advances from the reference timing θo1 accordingly. (Becomes faster). The VVTe position evt is retarded as it increases from the reference position 0 on the most advanced angle side, and the opening timing of the exhaust valve Ve is gradually delayed (delayed) from the reference timing.

  For reference, FIG. 9 shows the relationship between the opening timing of the intake and exhaust valves and the ratio of the NOx amount to the total amount of HC, CO and NOx in the exhaust gas (NOx ratio) N1, N2, N3, N4 and N5. . However, N1> N2> N3> N4> N5. As can be seen, the NOx ratio decreases as the intake valve Vi opens earlier, and the NOx ratio decreases as the exhaust valve Ve opens later. In this map, a mask region M is an intake / exhaust valve opening timing region showing a low NOx ratio N4, N5 that makes it impossible to stably calculate the oxygen storage capacity OSC. The mask region M is preferably at least a region where the opening timing of the intake valve Vi is within a predetermined range on the relatively advanced side, or the opening timing of the exhaust valve Ve is within a predetermined range on the relatively retarding side. .

  Now, returning to FIG. 8, in step S <b> 102, it is determined whether or not the operation timing of the intake valve Vi and the exhaust valve Ve is in the mask region M. Specifically, it is determined whether or not the actual VVTi position ivt and VVTe position evt calculated based on the detection values of the crank angle sensor 14 and the cam angle sensor are within the mask region M in the map of FIG. The If it is determined that it is not in the mask region M, active air-fuel ratio control is executed in step S104. On the other hand, if it is determined that it is in the mask region M, active air-fuel ratio control is prohibited in step S103. Therefore, when it is determined that the current position is within the mask region, the active air-fuel ratio control is prohibited before the execution even though the execution condition of the active air-fuel ratio control is satisfied.

  During execution of the active air-fuel ratio control, when either the VVTi position ivt or the VVTe position evt is changed and the operation timing of the intake valve Vi and the exhaust valve Ve enters the mask region M, the active air-fuel ratio control is performed. It may be interrupted or canceled during execution. Here, the interruption means that the active air-fuel ratio control is resumed when the operation timing of the intake valve Vi and the exhaust valve Ve subsequently leaves the mask region M. Also, the term “stop” means that the active air-fuel ratio control is not resumed even when the active air-fuel ratio control is completely terminated at that time and the operation timing of the intake valve Vi and the exhaust valve Ve subsequently leaves the mask region M. . In the case of interruption, only the oxygen storage capacity calculation value of the cycle at the time of the interruption is discarded or invalidated, and the oxygen storage capacity calculation values of the other cycles are used for the calculation of the final oxygen storage capacity OSCav. In the case of cancellation, the oxygen storage capacity calculation value before the cancellation is discarded or invalidated, and the final oxygen storage capacity OSCav is not calculated.

  Thus, when the operation timing of the intake valve Vi and the exhaust valve Ve is within a predetermined range, the active air-fuel ratio control is stopped, that is, the active air-fuel ratio control is prohibited before execution or during execution. Suspended or canceled. Therefore, the calculation of the oxygen storage capacity OSC and the catalyst deterioration determination when the exhaust gas composition component is such that the oxygen storage capacity OSC cannot be calculated stably can be avoided, and the erroneous determination or erroneous detection of the catalyst deterioration can be prevented. Can do.

  Next, FIG. 10 shows a routine related to the second process. This routine is also repeatedly executed by the ECU 20 every minute time. First, in step S201, as in step S101, it is determined whether an execution condition for active air-fuel ratio control is satisfied. If the execution condition for the active air-fuel ratio control is not satisfied, the present process is terminated. If the execution condition for the active air-fuel ratio control is satisfied, the process proceeds to step S202.

  In step S202, active air-fuel ratio control is executed, and the oxygen storage capacity OSCm of each cycle is sequentially calculated during execution of this active air-fuel ratio control.

  In the next step S203, it is determined whether or not the operation timings of the intake valve Vi and the exhaust valve Ve are within a predetermined mask region, as in step S103. If it is determined that it is not within the mask region, this process is terminated, and the active air-fuel ratio control and the calculation of the oxygen storage capacity are continued. On the other hand, if it is determined that it is within the mask region, in step S204, the oxygen storage capacity calculation value OSCm of the current cycle is discarded or invalidated.

  In the second process, when the operation timing of the intake valve Vi and the exhaust valve Ve enters the mask region during the calculation of the oxygen storage capacity OSCm of a certain cycle, the active air-fuel ratio control and the oxygen storage capacity calculation are not stopped. While continuing, only the oxygen storage capacity calculation value of the cycle entering the mask region is invalidated. This is different from the interruption of the first process in that the active air-fuel ratio control is continued. Since the active air-fuel ratio control and the oxygen storage capacity calculation are continued and the catalyst deterioration detection can be performed using the oxygen storage capacity calculation value of the cycle that is not in the mask region, it is possible to secure as many opportunities for detecting the catalyst deterioration as possible. The same effect as that of the first process can be exhibited by the second process.

  Next, FIG. 11 shows a routine according to the third process. This routine is also repeatedly executed by the ECU 20 every minute time. First, in step S301, it is determined whether active air-fuel ratio control is being executed. If the active air-fuel ratio control is not being executed, this process is terminated. If the active air-fuel ratio control is being executed, the process proceeds to step S302.

  In step S302, it is determined whether or not at least one of the change timing Wi of the operation timing of the intake valve Vi and the change speed We of the operation timing of the exhaust valve Ve has exceeded a predetermined threshold value Ws. That is, when the VVTi21 or VVTe22 is actuated rapidly and the opening / closing timing of the intake valve Vi or the exhaust valve Ve is rapidly changed, for example, when the engine operating state temporarily becomes a transient state, the air-fuel ratio, the engine load factor This may affect at least one of the intake air amount and the detected value after the catalyst, and the oxygen storage capacity calculation value may become unstable, leading to erroneous determination and erroneous detection. Therefore, in the third process, erroneous determination and erroneous detection due to such a rapid change in valve timing are prevented.

  Specifically, in this step S302, based on the detection values of the cam angle sensors of VVTi21 and VVTe22, the changing speeds of VVTi position ivt and VVTe position evt are calculated, and this changing speed is compared with a predetermined threshold value. . Since these two calculation comparison methods are the same, only the intake side will be described as a representative. As shown in FIG. 12, the difference between the current time t2 and the VVTi positions ivt1 and ivt2 at time t1 that is a minute before that is shown in FIG. Δivt = ivt2−ivt1 is calculated, and the absolute value of the difference Δivt is set as the change speed of the VVTi position ivt. The change speed of the VVTi position ivt is equal to the intake valve operation timing change speed Wi. Then, it is determined whether or not the absolute value of the difference Δivt exceeds a predetermined threshold value Δivts. This threshold value Δivts is a value equal to the threshold value Ws of the intake valve operation timing change speed.

  Thus, when it is determined that neither the intake valve operation timing change speed Wi and the exhaust valve operation timing change speed We exceed the threshold value Ws, the present process is terminated, and the active air-fuel ratio control and the oxygen storage capacity associated therewith are terminated. Calculation continues. On the other hand, if it is determined that at least one of the intake valve operation timing change speed Wi and the exhaust valve operation timing change speed We exceeds the threshold value Ws, the active air-fuel ratio control is interrupted in step S303. Thereby, erroneous determination and erroneous detection based on an unstable oxygen storage capacity calculation value can be prevented in advance.

  The term “interruption” used here has the same meaning as described in the first process. In addition to this interruption, the active air-fuel ratio control may be stopped as described in the first process, and further, the active air-fuel ratio control may be prohibited before the execution of the active air-fuel ratio control.

  Next, FIG. 13 shows a routine for the fourth process. This routine is also repeatedly executed by the ECU 20 every minute time. First, in step S401, as in step S301, it is determined whether or not active air-fuel ratio control is being executed. If the active air-fuel ratio control is not being executed, this process is terminated. If the active air-fuel ratio control is being executed, the process proceeds to step S402.

  In step S402, as in step S302, it is determined whether or not at least one of the change timing Wi of the operation timing of the intake valve Vi and the change speed We of the operation timing of the exhaust valve Ve has exceeded a predetermined threshold value Ws. Is done.

  When it is determined that neither the intake valve operation timing change speed Wi nor the exhaust valve operation timing change speed We exceeds the threshold value Ws, this processing is terminated, and the active air-fuel ratio control and the oxygen storage capacity calculation associated therewith are calculated. To continue. On the other hand, when it is determined that at least one of the intake valve operation timing change speed Wi and the exhaust valve operation timing change speed We exceeds the threshold value Ws, in step S403, as in step S204, The oxygen storage capacity calculation value OSCm is discarded or invalidated. This also prevents erroneous determination and erroneous detection based on the unstable oxygen storage capacity calculation value.

  In the fourth process, as in the second process, during the calculation of the oxygen storage capacity OSCm in a certain cycle, at least one of the intake valve operation timing change speed Wi and the exhaust valve operation timing change speed We has a threshold value Ws. Is exceeded, the active air-fuel ratio control and the oxygen storage capacity calculation continue without stopping, and only the oxygen storage capacity calculated value OSCm of the cycle including the time point when the threshold value Ws is exceeded is invalidated. . This is different from the interruption of the third process in that the active air-fuel ratio control is continued. Since the active air-fuel ratio control and the oxygen storage capacity calculation are continued and the catalyst deterioration detection can be performed using the oxygen storage capacity calculation values of cycles other than the invalid cycle, there is an advantage that as many opportunities for detecting the catalyst deterioration as possible can be secured. This fourth process can also exhibit the same effects as the third process.

  In the above-described embodiment, the ECU 20 and the injector 12 constitute active air-fuel ratio control means, and the ECU 20 comprises determination means, active air-fuel ratio control stop means, storage capacity calculation means, invalidation means, transient determination means, transient time Active air-fuel ratio control stop means and transient invalidation means are configured.

  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.

  In the above-described embodiment, the variable valve gears (VVTi21 and VVTe22) are provided on both the intake side and the exhaust side. However, it is also possible to provide the variable valve gear on only one (for example, the intake side). In the above embodiment, only the operation timing of the intake valve Vi and the exhaust valve Ve is variable. However, both the operation timing and the lift may be variable, or only the lift may be variable. Furthermore, the working angle may be variable. These valve parameters can be arbitrarily combined with intake / exhaust and variable / fixed. Also, each valve parameter can be compared with the mask area, or the change speed of each valve parameter can be compared with the threshold value. Is optional.

  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 graph which shows the relationship between oxygen storage capacity and catalyst temperature, and is a figure for demonstrating the catalyst degradation determination method. FIG. 5 is a timing diagram for explaining the operation of the intake side variable valve timing mechanism (VVTi) and the state of changing the opening / closing timing of the intake valve. It is a time chart which shows the mode of the output change of the pre-catalyst sensor and the post-catalyst sensor when there is an intake / exhaust valve operation timing in a region where the oxygen storage capacity calculation value becomes unstable. It is a flowchart of a 1st process. It is a map which shows a mask area | region. It is a flowchart of a 2nd process. It is a flowchart of a 3rd process. It is a figure for demonstrating the calculation method of intake / exhaust valve operation timing change speed, and the comparison of the calculated change speed and a threshold value. It is a flowchart of a 4th process.

Explanation of symbols

1 Internal combustion engine 3 Combustion chamber 6 Exhaust pipe 11 Catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
21 Intake side variable valve timing mechanism (VVTi)
22 Exhaust variable valve timing mechanism (VVTe)
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 A / Fr Rich air-fuel ratio A / Fl Lean air-fuel ratio OSC Catalyst oxygen storage capacity OSCs Degradation determination threshold M Mask area ivt VVTi position evt VVTe position Wi Intake valve operation timing change speed We Exhaust valve operation timing change speed Ws Threshold

Claims (5)

An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
Determining means for determining whether at least one of an operation timing and a lift of at least one of an intake valve and an exhaust valve related to the variable valve operating device is within a predetermined range;
When the determination means determines that at least one of the operation timing and the lift is within a predetermined range, the active air-fuel ratio control is stopped or interrupted during execution, or before the active air-fuel ratio control is executed. An active air-fuel ratio control stop means for prohibiting is provided. A catalyst deterioration detection apparatus for an internal combustion engine, comprising: An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
A storage capacity calculating means for calculating an oxygen storage capacity of the catalyst during execution of the active air-fuel ratio control;
Determining means for determining whether at least one of an operation timing and a lift of at least one of an intake valve and an exhaust valve related to the variable valve operating device is within a predetermined range;
When the determination means determines that at least one of the operation timing and the lift is within a predetermined range during the calculation of the oxygen storage capacity by the storage capacity calculation means, the calculated oxygen storage capacity value is invalidated. A catalyst deterioration detection device for an internal combustion engine, comprising:   The predetermined range is a predetermined range in which the operation timing of the intake valve is relatively advanced, or a predetermined range in which the operation timing of the exhaust valve is relatively retarded. Item 3. A catalyst deterioration detection device for an internal combustion engine according to Item 1 or 2. An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
Transient determination means for determining whether or not the change speed of at least one of the operation timing and the lift of at least one of the intake valve and the exhaust valve related to the variable valve operating system exceeds a predetermined value;
When it is determined by the transient determination means that the change speed of at least one of the operation timing and the lift exceeds a predetermined value, the active air-fuel ratio control is stopped or interrupted during execution, or the active air-fuel ratio control is performed. An apparatus for detecting catalyst deterioration in an internal combustion engine, comprising: an active air-fuel ratio control stop means during transition that is prohibited before execution. An internal combustion engine provided with a variable valve device in at least one of the intake and exhaust systems, and a device for detecting deterioration of a catalyst disposed in the exhaust passage,
Active air-fuel ratio control means for forcibly switching the exhaust air-fuel ratio upstream of the catalyst from one of a predetermined rich air-fuel ratio and a predetermined lean air-fuel ratio to the other at a predetermined timing;
A storage capacity calculating means for calculating an oxygen storage capacity of the catalyst during execution of the active air-fuel ratio control;
Transient determination means for determining whether or not the change speed of at least one of the operation timing and the lift of at least one of the intake valve and the exhaust valve related to the variable valve operating system exceeds a predetermined value;
During the calculation of the oxygen storage capacity by the storage capacity calculation means, when the transition determination means determines that the change speed of at least one of the operation timing and the lift exceeds a predetermined value, the calculated oxygen storage capacity A catalyst deterioration detecting device for an internal combustion engine, comprising: a transient invalidating means for invalidating a value of the internal combustion engine.

Images