JP4586678B2 - Catalyst deterioration detection device for internal combustion engine - Google Patents

Description

  The present invention relates to a catalyst deterioration detection device for an internal combustion engine, and more particularly, to a catalyst deterioration detection device for detecting deterioration of a catalyst that purifies exhaust gas from an internal combustion engine.

  Conventionally, for example, in Patent Document 1, an oxygen storage capacity (OSC (Oxygen Storage Capacity) capacity) of a catalyst provided in an exhaust passage of an internal combustion engine is calculated, and deterioration of the catalyst is detected based on the calculated OSC capacity. A catalyst deterioration detection device is disclosed. More specifically, in this apparatus, the air-fuel ratio upstream of the upstream catalyst (hereinafter referred to as “target air-fuel ratio”) is changed from the rich side (or lean side) to the lean side (or rich side). The OSC ability of the catalyst is calculated by calculating the amount of oxygen stored in the upstream catalyst (or the amount of oxygen released) until the output of the oxygen sensor downstream of the catalyst is reversed. Then, catalyst deterioration is detected based on the value of the OSC ability (hereinafter referred to as “catalyst deterioration detection control”).

FIG. 6 is a timing chart for explaining the operation when the catalyst deterioration detection control is executed. In FIG. 6, a waveform indicated by a solid line indicates a case where the output of the oxygen sensor (sub O ₂ sensor) downstream of the catalyst is normal, and a waveform indicated by a broken line indicates a case where the output of the oxygen sensor is abnormal. . When the catalyst deterioration detection control described above is executed, the target air-fuel ratio is alternately changed between lean and rich, as shown in FIG. When the target air-fuel ratio is controlled to be lean, the value of the stored oxygen counter osarise for counting the amount of oxygen stored in the upstream catalyst increases as shown in FIG. 6 (B). Then, when the output oxs of the oxygen sensor is reversed, the target air-fuel ratio is changed to rich. When the target air-fuel ratio is changed to rich, the value of the stored oxygen counter osarise is reset, and instead, the value of the released oxygen counter osafall that counts the amount of oxygen released from the upstream side catalyst increases. Then, when the output oxs of the oxygen sensor is reversed, the target air-fuel ratio is changed to lean again. Such processing is repeated while the catalyst deterioration detection control is being executed.

JP 2003-97334 A Japanese Patent Publication No. 7-33788 Japanese Patent Laid-Open No. 11-200853 JP 2001-152913 A Japanese Patent Laid-Open No. 8-121216

  During the execution of the above-described catalyst deterioration detection control, at the timing immediately before the output oxs of the oxygen sensor behind the catalyst is reversed, that is, at the timing when the oxygen storage amount of the catalyst is saturated or disappears, the purification performance of the catalyst starts to decrease. In particular, when the target air-fuel ratio is rich, before the oxygen stored in the catalyst disappears, the amount of methane that is difficult to be purified by the catalyst increases as the HC purification capacity decreases. The oxygen sensor is sensitive to methane. For this reason, when a gas with a high methane concentration flows, the oxygen sensor may emit an output that is higher (rich) than the actual air-fuel ratio. A waveform indicated by a broken line in FIG. 6D shows a waveform when the oxygen sensor emits such an output. When the oxygen sensor emits such an abnormal output, the output of the oxygen sensor is reversed at an earlier timing than the normal waveform indicated by the solid line in FIG.

  As a result, there is a possibility that it may be erroneously determined that the catalyst has deteriorated even though there is still a surplus in the oxygen storage amount. Further, when the oxygen sensor emits the above abnormal output, it is switched from release to occlusion while oxygen is being released from the catalyst. Further, as shown in FIG. The storable amount during oxygen storage is also reduced. As described above, when the oxygen sensor exhibits an abnormal output as described above, the behavior of the output reversal of the oxygen sensor becomes unstable during the catalyst deterioration detection control, and the detected OSC ability varies. there is a possibility.

  The present invention has been made to solve the above-described problems, and stabilizes the behavior of the exhaust gas sensor disposed behind the catalyst when the output fluctuates, thereby improving the catalyst deterioration detection accuracy. An object of the present invention is to provide a catalyst deterioration detection device capable of performing the above.

In order to achieve the above object, the first invention is provided downstream of the catalyst provided in the exhaust passage of the internal combustion engine, and the air-fuel ratio of the exhaust gas is on the fuel rich side with respect to the stoichiometric air-fuel ratio or the fuel lean. An exhaust gas sensor for detecting whether
Base air-fuel ratio control that alternately varies the target air-fuel ratio upstream of the catalyst between a rich base target air-fuel ratio that is richer than the stoichiometric air-fuel ratio and a lean base target air-fuel ratio that is leaner than the stoichiometric air-fuel ratio Means,
In the process from when the target air-fuel ratio is switched to the rich side or the lean side by the base air-fuel ratio control means until the target air-fuel ratio is switched to the lean side or the rich side, the amount of oxygen released or stored by the catalyst is Oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the catalyst;
A catalyst deterioration detection device for an internal combustion engine comprising: catalyst deterioration detection means for detecting deterioration of the catalyst based on the oxygen storage capacity;
The target air-fuel ratio is changed with a short period and a small amplitude in comparison with the rich base target air-fuel ratio and / or the lean base target air-fuel ratio along the rich base target air-fuel ratio and / or the lean base target air-fuel ratio. A second air-fuel ratio control means is provided.

  The second invention is characterized in that, in the first invention, the short period and / or the small amplitude are determined based on an oxygen storage capacity acquired at the time of detecting the previous catalyst deterioration.

  According to a third aspect, in the first or second aspect, the short period and / or the small amplitude are determined based on an intake air amount.

  According to a fourth invention, in any one of the first to third inventions, the short period is based on the rich base target air-fuel ratio and / or the excess oxygen amount and the deficient oxygen amount with respect to the lean base target air-fuel ratio. It further comprises short cycle control means for controlling.

  In a fifth aspect based on the fourth aspect, the short cycle control means matches the excess oxygen amount and the deficient oxygen amount in one cycle of short cycle fluctuations by the second air-fuel ratio control means. It is characterized by being set to.

  In a sixth aspect based on any one of the first to fifth aspects, the second air-fuel ratio control means is configured such that the base air-fuel ratio control means includes the rich base target air-fuel ratio and the lean base target air-fuel ratio. When the target air-fuel ratio is switched between, the target air-fuel ratio is changed from the side closer to the theoretical air-fuel ratio with respect to the rich base target air-fuel ratio or the lean base target air-fuel ratio.

  According to the first aspect of the invention, along the rich base target air-fuel ratio and / or lean base target air-fuel ratio, in the upstream of the catalyst with a short period and a small amplitude compared to the rich base target air-fuel ratio and / or lean base target air-fuel ratio. By changing the target air-fuel ratio, the purification performance of the catalyst can be improved. For this reason, according to the present invention, it is possible to stabilize the behavior of the exhaust gas sensor when the output fluctuates, thereby improving the catalyst deterioration detection accuracy.

  According to the second aspect of the present invention, when the target air-fuel ratio is subjected to short-period fluctuation, it is possible to avoid giving an excessive target air-fuel ratio fluctuation to the current oxygen storage capacity. It is possible to prevent the emission characteristics of the exhaust gas from being deteriorated due to the target air-fuel ratio fluctuation being given.

  According to the third aspect of the present invention, when the target air-fuel ratio is subjected to short period fluctuations, it is possible to avoid the oxygen storage capacity from failing due to a large amount of intake air.

  According to the fourth aspect of the invention, the short cycle is controlled by the parameter based on the weight of the rich base target air-fuel ratio and the excess oxygen amount and the insufficient oxygen amount with respect to the lean base target air-fuel ratio, so that the air-fuel ratio fluctuation is reproduced. It can be controlled well.

  According to the fifth aspect, when the target air-fuel ratio after the short cycle fluctuation is viewed as an average value, the target air-fuel ratio is maintained at the rich base target air-fuel ratio or the lean base target air-fuel ratio before the short-cycle fluctuation is given. Can be controlled. For this reason, according to the present invention, it is possible to prevent an unintended shift in the target air-fuel ratio from occurring on the rich side or the lean side due to the short period fluctuation.

  According to the sixth aspect, when the target air-fuel ratio varies alternately between the rich base target air-fuel ratio and the lean base target air-fuel ratio, the change in the target air-fuel ratio can be minimized, Torque fluctuations of the internal combustion engine can be suppressed, and deterioration of the exhaust gas emission characteristics can be suppressed.

Embodiment 1 FIG.
[Configuration of Device of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of a catalyst deterioration detection device for an internal combustion engine according to Embodiment 1 of the present invention. As shown in FIG. 1, the apparatus of this embodiment includes an upstream catalyst (S / C) 12 and a downstream catalyst (U / F) 14 disposed in an exhaust passage 10 of the internal combustion engine. The upstream catalyst 12 and the downstream catalyst 14 are all three-way catalysts that can simultaneously purify CO, HC, and NOx.

A main air-fuel ratio sensor 16 and a sub O ₂ sensor (oxygen sensor) 18 are disposed upstream and downstream of the upstream catalyst 12, respectively. The main air-fuel ratio sensor 16 is a sensor that emits a substantially linear output with respect to the air-fuel ratio A / F of the exhaust gas flowing into the upstream catalyst 12. On the other hand, the sub O ₂ sensor 18 generates a rich output (for example, 0.8 V) when the exhaust gas flowing out from the upstream catalyst 12 is rich with respect to the stoichiometric air-fuel ratio, and the exhaust gas is lean. In this case, the sensor generates a lean output (for example, 0.2 V).

The output of the main air-fuel ratio sensor 16 and the output of the sub O ₂ sensor 18 are respectively supplied to an ECU (Electronic Control Unit) 20. The ECU 20 is further connected to an air flow meter 22, a rotation speed sensor 24, a fuel injection valve 26, and the like. The air flow meter 22 is a sensor that detects an intake air amount Ga of the internal combustion engine. The rotational speed sensor 24 is a sensor that generates an output corresponding to the engine rotational speed Ne. The fuel injection valve 26 is an electromagnetic valve for injecting fuel into the intake port of the internal combustion engine.

[Features of Embodiment 1]
FIG. 2 is a timing chart for explaining the characteristics of the catalyst deterioration detection control of the present embodiment. More specifically, FIG. 2A shows that the target air-fuel ratio upstream of the upstream catalyst 12 in the exhaust passage 10 changes in a rectangular manner with the lean target air-fuel ratio aflfl and the rich target air-fuel ratio afrref alternately. The waveform is shown. FIG. 2B shows a waveform representing a change in the stored oxygen counter osarise that counts the amount of oxygen stored in the upstream catalyst 12 when the target air-fuel ratio is controlled to be lean. FIG. 2C shows a waveform representing a change in the excess oxygen amount counter loss which counts the excess oxygen amount excessively supplied to the upstream catalyst 12 when the lean target air-fuel ratio aflfl is used as a reference. (D) shows waveforms representing changes in the deficient oxygen amount counter losafall for counting the deficient amount of oxygen supplied to the upstream catalyst 12 when the lean target air-fuel ratio aflfl is used as a reference. FIG. 2E shows a waveform representing a change in the released oxygen counter osafall that counts the amount of oxygen released from the upstream catalyst 12 when the target air-fuel ratio is controlled to be rich. FIG. 2G shows waveforms each representing changes in the excess oxygen amount counter rosarise and the deficient oxygen amount counter rosafall with respect to the rich target air-fuel ratio afrref. Further, FIG. 2H shows a waveform representing a change in the output oxs of the sub O ₂ sensor 18 downstream of the upstream catalyst 12.

Also in the catalyst deterioration detection control in the present embodiment, the OSC ability is calculated based on the respective counter values of the stored oxygen counter osarise and the released oxygen counter osafall, and the calculated OSC ability is smaller than a predetermined determination reference value. The catalyst is judged to have deteriorated. For this purpose, as shown in FIG. 2A, the target air-fuel ratio is alternately changed in a rectangular manner between the lean target air-fuel ratio aflfl and the rich target air-fuel ratio afrref. Here, the waveform in which the target air-fuel ratio is alternately changed in a rectangular manner between the lean target air-fuel ratio afrefl and the rich target air-fuel ratio afrefr is referred to as the “target air-fuel ratio base waveform” or simply “ This is referred to as a “base waveform”. In the present embodiment, in order to stabilize the behavior at the time of inversion of the sub O ₂ sensor output oxs, it follows the base waveform, and particularly in the case of FIG. It is characterized by providing a short period A / F fluctuation with a short period and amplitude compared to the fluctuation of the waveform.

Specifically, the short period A / F fluctuation is given to the target air-fuel ratio by the following method. Here, the description will proceed by taking as an example a case where the target air-fuel ratio is controlled to the rich target air-fuel ratio afrref.
As shown in FIG. 2A, the rich side amplitude afamprefr, which is the amplitude in the short cycle A / F fluctuation, is given with the base waveform of the target air-fuel ratio as the fluctuation center. In the present embodiment, the rich side amplitude afamprefr is determined based on the OSC ability (maximum oxygen storage amount Cmax value) calculated during the previous catalyst deterioration detection control and the intake air amount Ga.

  In the present embodiment, the excess oxygen amount counter rosarise and the deficient oxygen amount counter rosafall are set in order to determine the rich side cycle afsycrefr in the short cycle A / F fluctuation. As described above, these counters are counters that count the amount of excess oxygen or the amount of deficient oxygen with respect to the rich target air-fuel ratio afrefr as time passes, and when these counter values reach the respective target values rosarisetg and rosafalltg. In short cycle A / F fluctuations, the target air-fuel ratio is set so as to be inverted by a value half that of the rich-side amplitude afamprefr with respect to the rich target air-fuel ratio. In other words, the rich-side cycle afsycrefr can be changed by changing their target values rosarisetg and rosafalltg.

  The rich side period afsycrefr is determined based on the previously calculated OSC ability and intake air amount Ga, similarly to the rich side amplitude afamprefr. More specifically, the above target values rosarisetg and rosafalltg are determined based on the previously calculated OSC ability and intake air amount Ga, and these excess oxygen amount target value rosarisetg and insufficient oxygen amount target value rosafalltg By adjusting the value of, the rich side cycle afsycrefr is controlled to be an ideal cycle (for example, 0.5 to 3 Hz). Further, in this embodiment, by giving the short cycle A / F fluctuation, the short period A / F fluctuation is excessive in one cycle so that the target air-fuel ratio when viewed as an average value does not deviate from the base waveform. The amount of oxygen and the amount of deficient oxygen are controlled to match.

  Further, in the present embodiment, the target air-fuel ratio in the base waveform is set to the lean target air-fuel ratio afrefl and the rich target in order to suppress the torque fluctuation accompanying the air-fuel ratio fluctuation and the deterioration of the exhaust gas emission characteristics during the execution of the catalyst deterioration detection control. When switching between the air-fuel ratio afrefr, as shown in FIG. 2A, the target air-fuel ratio is set to start short-cycle A / F fluctuations from the side close to the stoichiometry.

[Specific Processing in Embodiment 1]
Next, specific processing executed by the ECU 20 in the present embodiment in order to realize the above-described function will be described with reference to FIGS. 3 and 4. 3 and 4 show a series of completed processes, that is, a routine for catalyst deterioration detection control of this embodiment.

  In this routine, first, in FIG. 3, it is determined whether or not the internal combustion engine and the upstream catalyst 12 have been warmed up (step 100). As a result, when it is determined that the warm-up is completed, it is determined whether or not the catalyst deterioration detection control can be executed, specifically, whether or not the internal combustion engine is in a stable operating state. (Step 102). If it is determined in step 100 that the warm-up has not been completed, and if it is determined in step 102 that the catalyst deterioration detection control cannot be executed, the processing of this routine is terminated. In this case, it is determined that the deterioration determination control of the upstream catalyst 12 cannot be performed with high accuracy.

  If it is determined in step 102 that the catalyst deterioration detection control can be executed, the catalyst deterioration detection control is started (step 104). Specifically, first, the rich side amplitude afamprefr, the excess oxygen target value rosarisetg of the excess oxygen amount counter rosarise with respect to the rich target air-fuel ratio afrefr, and the deficient oxygen target value rosafalltg of the deficient oxygen amount counter rosafall with respect to the rich target air-fuel ratio afrefr Is calculated (step 106).

  The process of step 106 will be described in more detail. In step 106, first, the OSC ability of the upstream catalyst 12 and the current intake air amount Ga calculated during the previous catalyst deterioration detection control are acquired. The rich side amplitude afamprefr is determined based on the previous OSC ability and the intake air amount Ga. More specifically, the rich-side amplitude afamprefr is set so as to increase as the previous OSC performance increases, and is set to decrease as the intake air amount Ga increases. Furthermore, the OSC ability of the catalyst has the property that it increases as the catalyst temperature increases. Therefore, the rich side amplitude afamprefr may be set to increase as the current temperature of the upstream catalyst 12 increases.

  As described above, the rich-side cycle afsycrefr is preferably set to a value of about 0.5 to 3 Hz, for example. Therefore, in step 106, the excess oxygen target value rosarisetg and the deficient oxygen target value rosafalltg are set so that the rich-side cycle afsycrefr becomes the above-mentioned target value while considering the previous OSC ability and the intake air amount Ga. The Specifically, the excess oxygen target value rosarisetg and the deficient oxygen target value rosafalltg are set so that the rich side cycle afsycrefr becomes longer as the previous OSC capability is larger. Further, the excess oxygen target value rosarisetg and the deficient oxygen target value rosafalltg are set so that the rich side period afsycrefr becomes shorter as the intake air amount Ga is larger. Further, the excess oxygen target value rosarisetg and the deficient oxygen target value rosafalltg are set to values such that the excess oxygen amount and the deficient oxygen amount in one cycle of the short-cycle A / F fluctuation match.

  In FIG. 3, next, the target air-fuel ratio is set to a value obtained by adding the rich target air-fuel ratio afrefr and a half value of the rich-side amplitude afamprefr (step 108). Next, it is determined whether or not the output oxs of the oxygen sensor 18 is larger than the rich inversion reference value oxsR (step 110). As a result, when the determination of oxs> oxsR is established, the process proceeds to * 1 shown in FIG. 4. On the other hand, when the determination of oxs> oxsR is not established, can the catalyst deterioration detection control be continued? It is determined whether or not (step 112).

  If the catalyst deterioration detection control can be continued in step 112, that is, if it can be determined that the internal combustion engine is continuously in a stable operating state, the value of the excess oxygen amount counter rosarise with respect to the rich target air-fuel ratio afrefr is excessive. It is determined whether or not it is larger than the oxygen target value rosarisetg (step 114). As a result, while the value of the excess oxygen amount counter rosarise does not reach the excess oxygen target value rosarisetg, the current target air-fuel ratio is continuously used. Here, the current target air-fuel ratio is continuously used. However, the present invention is not limited to this, and the value of the intake air amount Ga is updated as needed, and the rich side amplitude is determined based on the updated value of the intake air amount Ga. The target air-fuel ratio may be updated by updating afamprefr.

  On the other hand, if it is determined in step 114 that the value of the excess oxygen counter rosarise has reached the excess oxygen target value rosarisetg, the target air-fuel ratio is reduced from the rich target air-fuel ratio afrefr to 1/2 the rich-side amplitude afamprefr. (Step 116). The target air-fuel ratio set in step 116 is until the value of the deficient oxygen amount counter rosafall with respect to the rich target air-fuel ratio afrref is determined to be larger than the deficient oxygen target value rosafalltg (step 122). Unless the output oxs is inverted or the catalyst deterioration detection control cannot be continued (steps 118 and 120), the output oxs is continuously used.

  On the other hand, if the oxygen sensor output oxs exceeds the rich inversion reference value oxsR while the target air-fuel ratio is alternately changing between the value of step 108 and the value of step 116, then, A series of processes after * 1 shown in FIG. 4 are executed. Specifically, first, the current value of the released oxygen counter osafall is cleared after being stored in the memory of the ECU 20 (step 200). Next, when the catalyst deterioration detection control can be continued (step 202), the lean side amplitude afamprefl, the excess oxygen target value losarisetg of the excess oxygen amount counter losarise with respect to the lean target air fuel ratio aflfl, and the lean target air fuel ratio aflfl The deficient oxygen target value losafalltg of the deficient oxygen amount counter losafall is calculated (step 204). Since these values are set in the same manner as the setting on the rich side in step 106, detailed description thereof is omitted here.

  Next, the target air-fuel ratio is set to a value obtained by adding the lean target air-fuel ratio afrefl and a half value of the lean side amplitude afamprefl (step 206). The target air-fuel ratio set in step 206 is until the value of the excess oxygen amount counter “losarise” with respect to the lean target air-fuel ratio “afrefl” is determined to be larger than the excess oxygen target value “losarisetg” (step 214). Unless the output oxs is inverted or the catalyst deterioration detection control cannot be continued (steps 210 and 212), the output is continuously used.

  On the other hand, if it is determined in step 214 that the value of the excess oxygen amount counter “losarise” has reached the excess oxygen target value “losarisetg”, the target air-fuel ratio is reduced from the lean target air-fuel ratio afrefl to ½ of the lean side amplitude afamprefl. (Step 216). The target air-fuel ratio set in step 216 is until the value of the deficient oxygen amount counter losafall with respect to the lean target air-fuel ratio aflfl is determined to be larger than the deficient oxygen target value losafalltg (step 222). Unless the output oxs is reversed or the catalyst deterioration detection control cannot be continued (steps 218 and 220), the output is continuously used.

  While it is determined in step 210 or 218 that the oxygen sensor output oxs is smaller than the lean inversion reference value oxsL while the processes in steps 206 to 222 are being performed, the value of the stored oxygen counter osarise is then used. Is cleared in the memory of the ECU 20 (step 224).

  Next, it is determined whether or not a series of detection processes in the current catalyst deterioration detection control is completed (step 226). Specifically, it is determined whether or not the values of the stored oxygen counter osarise and the released oxygen counter osafall can each be stored twice or more, and whether or not the stored data is stable data. The As a result, when it is determined that such data has not yet been stored, it is determined whether or not the catalyst deterioration detection control can be continued (step 228). A series of processes after 2 are executed.

  On the other hand, if it is determined in step 226 that a series of detection processes in the catalyst deterioration detection control has been completed, then the OSC ability (maximum oxygen storage amount Cmax value) of the catalyst 12 is Cmax = (osarise + osafall) / It is calculated according to the relationship 2 (step 230). Next, it is determined whether or not the maximum oxygen storage amount Cmax calculated in step 230 is smaller than a determination reference value Cmaxs for determining whether the catalyst 12 has deteriorated (step 232). As a result, when it is determined that the relationship of Cmax <Cmaxs is not established, it is determined that the catalyst 12 has not deteriorated, and the current catalyst deterioration detection control is terminated. On the other hand, when it is determined that the relationship of Cmax <Cmaxs is established, it is determined that the upstream catalyst 12 has deteriorated, and an abnormality lamp for warning the driver of the abnormality of the catalyst 12 is turned on (step 234). ).

  FIG. 5 is a timing chart for explaining the effects obtained by the processing of the routines shown in FIGS. More specifically, FIG. 5 is a diagram showing a comparison between the case where the short-period A / F fluctuation of the present embodiment described above is given to the target air-fuel ratio and the case where it is not given. FIG. 5C and FIG. 5D show the CO and THC emissions downstream of the upstream catalyst 12. According to FIG. 5C and FIG. 5D, when the short cycle A / F variation is given to the target air-fuel ratio as in this embodiment, such a short cycle A / F variation is not given. In comparison, it can be seen that the increase in CO and THC over time is suppressed. That is, it can be seen that when the short-period A / F fluctuation is given to the target air-fuel ratio, the purification performance of the catalyst 12 at the time of output reversal of the oxygen sensor 18 is improved.

For this reason, when the target air-fuel ratio is controlled to the rich side, the HC emission immediately before the oxygen stored in the catalyst 12 disappears is suppressed, and the methane emission that adversely affects the output of the oxygen sensor 18 is reduced. To do. As a result, as shown in FIG. 5B, when the short-period A / F fluctuation is given to the target air-fuel ratio, the output change amount of the sub O ₂ sensor 12 is larger than that when it is not given. growing. That is, a more normal output change characteristic is exhibited. As described above, according to the control of the present embodiment, the behavior of the oxygen sensor 18 when the output is reversed can be stabilized, thereby improving the accuracy of detecting the deterioration of the catalyst 12.

  If a catalyst whose OSC capacity is decreasing due to the start of deterioration, if the target air-fuel ratio changes excessively with respect to the current OSC capacity, the catalyst cannot absorb such changes in the air-fuel ratio. Further, the emission characteristics of exhaust gas during catalyst deterioration detection control are deteriorated. In the above routine, the amplitude afamprefr and afamprefl in the short cycle A / F fluctuation are set based on the previous OSC, more specifically, the larger the previous OSC capability, the larger the setting, so that Deterioration of exhaust emissions can be suppressed.

  Even if the target air-fuel ratio is varied by the same amount, if the intake air amount Ga is different, the amount of oxygen released or stored during lean or rich control will also be different. In the above routine, the amplitudes afamprefr and afamprefl in the short cycle A / F fluctuation are set based on the intake air amount Ga, and more specifically, set so as to decrease as the intake air amount Ga increases. When the cycle A / F fluctuation is performed, it is possible to avoid the oxygen storage capacity from immediately breaking down.

  In the above routine, the cycle afsycrefr and afsycrefl in the short cycle A / F fluctuation are adjusted based on the oxygen excess / deficiency amount (excess oxygen amount counter rorise, etc.) with respect to the rich target air-fuel ratio afrref and the lean target air-fuel ratio aflfl. It is said. According to such a method, it is not a method of adjusting based on a ratio such as an air-fuel ratio, but a parameter based on the weight of oxygen amount (obtained from the intake air amount Ga), and in a short cycle A / F fluctuation Since the periods afsycrefr and afsycrefl can be adjusted, the air-fuel ratio fluctuation can be controlled with good reproducibility.

  In the above routine, the excess oxygen amount in one cycle of the short-cycle A / F fluctuation is set to coincide with the deficient oxygen amount using an excess oxygen amount counter rose or the like. According to such a setting, even when the short-period A / F fluctuation is given to the target air-fuel ratio, the target air-fuel ratio becomes smaller when the target air-fuel ratio after the short-cycle A / F fluctuation is viewed as an average value. Thus, it is possible to perform control so as to maintain the rich target air-fuel ratio afrefr and the lean target air-fuel ratio afrefl, which are references before giving the short-cycle A / F fluctuation. For this reason, it is possible to prevent an unintended shift of the target air-fuel ratio from occurring on the rich side or the lean side due to the short cycle A / F fluctuation.

  In the above routine, when the target air-fuel ratio is changed on the rich side for a short period A / F, the above step 108 is executed first instead of the above step 116. This is the same when the target air-fuel ratio is changed on the lean side by a short period A / F, and step 206 is executed first instead of step 216. That is, in these processes, when the catalyst deterioration detection control is executed, when the target air-fuel ratio alternately changes rectangularly between the rich target air-fuel ratio afrefr and the lean target air-fuel ratio afrefl, the air-fuel ratio close to the stoichiometry is always obtained. The short period A / F fluctuation is started from the side. According to these processes, the change of the target air-fuel ratio when the target air-fuel ratio is changed due to the output reversal of the oxygen sensor 18 can be minimized, the torque fluctuation of the internal combustion engine is suppressed, and the exhaust gas emission characteristics are deteriorated. Can be suppressed.

  By the way, in Embodiment 1 described above, the air-fuel ratio downstream of the upstream catalyst 12 is detected by the oxygen sensor 18, but the present invention is not limited to this, and the air downstream of the upstream catalyst 12 is empty. The fuel ratio may be detected by an air-fuel ratio sensor.

In the first embodiment described above, the sub O ₂ sensor (oxygen sensor) 18 is the “exhaust gas sensor” in the first invention, and the rich target air-fuel ratio arefr is the “rich base target air” in the first invention. The lean target air-fuel ratio afrfl corresponds to the “lean base target air-fuel ratio” in the first aspect of the invention.
Further, when the ECU 20 executes the processing of steps 108 and 110, 116 and 118, 206 and 208, and 214 and 216, the “base air-fuel ratio control means” in the first aspect of the invention becomes the step 200, By executing the processes 222 and 228, the “oxygen storage capacity acquisition means” in the first invention is executed, and the “catalyst deterioration detection means” in the first invention is executed by executing the process in step 230. By executing the processes of steps 104 to 122 and 204 to 220, the “second air-fuel ratio control means” in the first aspect of the present invention is realized.
Further, the “short cycle control means” in the fourth aspect of the present invention is realized by the ECU 20 executing the processing of steps 106, 114, 122, 204, 212, and 220.

It is a figure for demonstrating the structure of the catalyst deterioration detection apparatus of the internal combustion engine in Embodiment 1 of this invention. It is a timing chart for demonstrating the characteristic of the catalyst deterioration detection control of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. FIG. 5 is a timing chart for explaining an effect obtained by the processing of the routine shown in FIGS. 3 and 4. FIG. It is a timing chart for demonstrating operation | movement at the time of the conventional catalyst deterioration detection control execution.

Explanation of symbols

10 Exhaust passage 12 Upstream catalyst 16 Main air-fuel ratio sensor 18 Sub O ₂ sensor (oxygen sensor)
20 ECU (Electronic Control Unit)
afamprefl Lean side amplitude
afamprefr Rich side amplitude
afrefl Lean target air-fuel ratio
afrefr Rich target air-fuel ratio
afsycrefr Rich cycle
losafall deficient oxygen counter
losafalltg deficient oxygen target value
losarise excess oxygen counter
losarisetg Excess oxygen target value
osafall release oxygen counter
osarise occlusion oxygen counter
oxs oxygen sensor output
rosafall deficient oxygen counter
rosafalltg deficient oxygen target value
rosaries excess oxygen counter
rosarisetg Excess oxygen target value

Claims (6)

An exhaust gas sensor provided downstream of the catalyst provided in the exhaust passage of the internal combustion engine, and detecting whether the air-fuel ratio of the exhaust gas is a fuel rich side or a fuel lean side of the stoichiometric air fuel ratio;
Base air-fuel ratio control that alternately varies the target air-fuel ratio upstream of the catalyst between a rich base target air-fuel ratio that is richer than the stoichiometric air-fuel ratio and a lean base target air-fuel ratio that is leaner than the stoichiometric air-fuel ratio Means,
In the process from when the target air-fuel ratio is switched to the rich side or the lean side by the base air-fuel ratio control means until the target air-fuel ratio is switched to the lean side or the rich side, the amount of oxygen released or stored by the catalyst is Oxygen storage capacity acquisition means for acquiring the oxygen storage capacity of the catalyst;
A catalyst deterioration detection device for an internal combustion engine comprising: catalyst deterioration detection means for detecting deterioration of the catalyst based on the oxygen storage capacity;
The target air-fuel ratio is changed with a short period and a small amplitude in comparison with the rich base target air-fuel ratio and / or the lean base target air-fuel ratio along the rich base target air-fuel ratio and / or the lean base target air-fuel ratio. An internal combustion engine catalyst deterioration detection device comprising a second air-fuel ratio control means.   2. The catalyst deterioration detection device for an internal combustion engine according to claim 1, wherein the short period and / or the small amplitude are determined based on an oxygen storage capacity acquired at the time of the previous detection of catalyst deterioration.   3. The catalyst deterioration detection apparatus for an internal combustion engine according to claim 1, wherein the short period and / or the small amplitude is determined based on an intake air amount.   4. The short cycle control means for controlling the short cycle based on the rich base target air-fuel ratio and / or an excess oxygen amount and a deficient oxygen amount with respect to the lean base target air-fuel ratio. The catalyst deterioration detection device for an internal combustion engine according to any one of the preceding claims.   5. The short cycle control means is set to match the excess oxygen amount and the deficient oxygen amount in one cycle of short cycle fluctuations by the second air-fuel ratio control means. The catalyst deterioration detection apparatus of the internal combustion engine. The second air-fuel ratio control means is configured to switch the rich base target air-fuel ratio or the rich base target air-fuel ratio when the base air-fuel ratio control means switches the target air-fuel ratio between the rich base target air-fuel ratio and the lean base target air-fuel ratio. 6. The catalyst deterioration detection device for an internal combustion engine according to claim 1, wherein the target air-fuel ratio is changed from the side closer to the stoichiometric air-fuel ratio with respect to the lean base target air-fuel ratio.

Images