JP2010223075A - Catalyst deterioration detection device for internal combustion engine - Google Patents

Abstract

The present invention relates to a catalyst deterioration detection device for an internal combustion engine, and an object thereof is to accurately detect the degree of deterioration of an EGR catalyst.
An internal combustion engine catalyst deterioration detection apparatus of the present invention measures an oxygen storage capacity of an EGR catalyst based on an output of an exhaust gas sensor after an EGR catalyst that detects an air-fuel ratio of exhaust gas emitted from the EGR catalyst. At that time, active air-fuel ratio control is performed in which the air-fuel ratio of the internal combustion engine is forcibly switched alternately between the rich side and the lean side with the theoretical air-fuel ratio interposed therebetween. When the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst after the air-fuel ratio of the internal combustion engine is switched by active air-fuel ratio control is earlier than the timing at which the air-fuel ratio of the exhaust gas flowing out from the EGR catalyst is switched, Execution of active air-fuel ratio control is prohibited.
[Selection] Figure 2

Description

  The present invention relates to a catalyst deterioration detection device for an internal combustion engine.

  2. Description of the Related Art Devices that perform EGR (Exhaust Gas Recirculation) for recirculating a part of exhaust gas of an internal combustion engine to an intake passage are widely used. When EGR is performed, deposits are likely to accumulate on the EGR pipe, EGR cooler, intake port, intake valve, and the like. One cause of the deposit is that the exhaust gas that recirculates (EGR gas) contains unburned HC, particulate matter, and the like. As a technique for suppressing deposit accumulation, a technique is known in which an EGR catalyst for purifying (removing) unburned HC and particulate matter in EGR gas is provided in the EGR passage.

  Japanese Patent Laying-Open No. 2005-264821 discloses a technique that uses an EGR catalyst for the purpose of suppressing deterioration of exhaust emission when the internal combustion engine is cold.

JP 2005-264821 A JP 2008-157133 A JP 2006-161718 A

  Similar to the exhaust purification catalyst provided in the exhaust system, the EGR catalyst also deteriorates over time. For this reason, in order to sufficiently fulfill the purpose of suppressing deposit accumulation and exhaust emission, it is necessary to accurately detect the degree of deterioration of the EGR catalyst. However, conventionally, an appropriate method for detecting the degree of deterioration of the EGR catalyst has not been proposed.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a catalyst deterioration detection device for an internal combustion engine that can accurately detect the degree of deterioration of an EGR catalyst.

In order to achieve the above object, a first invention is a catalyst deterioration detection device for an internal combustion engine,
An EGR passage that branches off from the exhaust passage of the internal combustion engine and recirculates part of the exhaust gas to the intake passage;
An EGR catalyst provided in the middle of the EGR passage;
An exhaust gas sensor after the EGR catalyst for detecting an air-fuel ratio of the exhaust gas emitted from the EGR catalyst;
EGR catalyst oxygen storage capacity measuring means for measuring the oxygen storage capacity of the EGR catalyst based on the output of the exhaust gas sensor after the EGR catalyst;
It is characterized by providing.

The second invention is the first invention, wherein
An active air-fuel ratio control for forcibly switching the air-fuel ratio of the internal combustion engine alternately between the rich side and the lean side across the theoretical air-fuel ratio when measuring the oxygen storage capacity of the EGR catalyst Control means;
An exhaust purification catalyst provided in the exhaust passage downstream of the location where the EGR passage branches;
The timing at which the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst after the air-fuel ratio of the internal combustion engine is switched by the active air-fuel ratio control is earlier than the timing at which the air-fuel ratio of the exhaust gas flowing out from the EGR catalyst is switched. In the case, active air-fuel ratio control prohibiting means for prohibiting execution of the active air-fuel ratio control,
It is characterized by providing.

The third invention is the first invention, wherein
An active air-fuel ratio control for forcibly switching the air-fuel ratio of the internal combustion engine alternately between the rich side and the lean side across the theoretical air-fuel ratio when measuring the oxygen storage capacity of the EGR catalyst Control means;
An exhaust purification catalyst provided in the exhaust passage downstream of the location where the EGR passage branches;
Capacity value storage means for storing the value of the oxygen storage capacity of the EGR catalyst and the value of the oxygen storage capacity of the exhaust purification catalyst;
A gas amount ratio acquisition means for acquiring, as a gas amount ratio, a ratio of an exhaust gas flow rate passing through the EGR catalyst to an exhaust gas flow rate passing through the exhaust purification catalyst;
A value obtained by multiplying the oxygen storage capacity value of the exhaust purification catalyst stored in the capacity value storage means by the gas amount ratio is a value of the oxygen storage capacity of the EGR catalyst stored in the capacity value storage means. When smaller, active air-fuel ratio control prohibiting means for prohibiting execution of the active air-fuel ratio control;
It is characterized by providing.

According to a fourth invention, in any one of the first to third inventions,
A turbocharger having a turbine disposed in the middle of the exhaust passage and a compressor disposed in the middle of the intake passage;
The EGR passage is branched from an exhaust passage on the upstream side of the turbine.

According to a fifth invention, in any one of the first to fourth inventions,
A turbocharger having a turbine disposed in the middle of the exhaust passage and a compressor disposed in the middle of the intake passage;
The EGR passage is branched from an exhaust passage on the downstream side of the turbine.

  According to the first aspect of the present invention, the post-EGR catalyst exhaust gas sensor that detects the air-fuel ratio of the exhaust gas exiting the EGR catalyst is provided, and the oxygen storage capacity of the EGR catalyst is measured based on the output of the post-EGR catalyst exhaust gas sensor. it can. Thereby, the deterioration degree of the EGR catalyst can be detected with high accuracy.

  According to the second invention, when measuring the oxygen storage capacity of the EGR catalyst, the active air-fuel ratio control for forcibly switching the air-fuel ratio of the internal combustion engine alternately between the rich side and the lean side across the theoretical air-fuel ratio is performed. Can be executed. Thereby, the oxygen storage capacity of the EGR catalyst can be measured more accurately. Further, according to the second aspect of the invention, the timing at which the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst after the air-fuel ratio of the internal combustion engine is switched by active air-fuel ratio control is the timing of the exhaust gas flowing out from the EGR catalyst. If it is earlier than the timing at which the fuel ratio is switched, the execution of the active air-fuel ratio control can be prohibited. Thereby, when measuring the oxygen storage capacity of the EGR catalyst, it is possible to reliably prevent the unpurified component from flowing out to the downstream side of the exhaust purification catalyst. Therefore, it is possible to reliably avoid the deterioration of emission.

  According to the third aspect of the invention, when measuring the oxygen storage capacity of the EGR catalyst, the air-fuel ratio of the internal combustion engine is forcibly switched alternately between the rich side and the lean side with the theoretical air-fuel ratio interposed therebetween. Can be executed. Thereby, the oxygen storage capacity of the EGR catalyst can be measured more accurately. According to the third invention, the ratio of the exhaust gas flow rate passing through the EGR catalyst to the exhaust gas flow rate passing through the exhaust purification catalyst is obtained as a gas amount ratio, and the gas amount ratio is obtained as the oxygen amount of the exhaust purification catalyst. When the value obtained by multiplying the value of the storage capacity is smaller than the value of the oxygen storage capacity of the EGR catalyst, execution of the active air-fuel ratio control can be prohibited. Thereby, when measuring the oxygen storage capacity of the EGR catalyst, it is possible to reliably prevent the unpurified component from flowing out to the downstream side of the exhaust purification catalyst. Therefore, it is possible to reliably avoid the deterioration of emission.

  According to the fourth invention, it is possible to accurately detect the degree of deterioration of the EGR catalyst provided in the EGR passage branched from the exhaust passage upstream of the turbine of the turbocharger.

  According to the fifth aspect of the present invention, it is possible to accurately detect the degree of deterioration of the EGR catalyst provided in the EGR passage branched from the exhaust passage on the downstream side of the turbine of the turbocharger.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the fluctuation | variation of the control target air fuel ratio of an internal combustion engine, the output of an after-catalyst O2 sensor, and the output of an O2 sensor after a high pressure EGR catalyst during execution of active air-fuel ratio control in 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. It is a figure which shows the fluctuation | variation of the control target air fuel ratio of an internal combustion engine, the output of a post-start catalyst O2 sensor, and the output of a low pressure EGR catalyst post-O2 sensor during execution of active air-fuel ratio control in the second embodiment of the present invention. It is a figure for demonstrating the method to measure the oxygen storage capacity of a high pressure EGR catalyst in Embodiment 3 of this invention. It is a flowchart of the routine performed in Embodiment 4 of this invention. It is the map showing the tendency of the emission reduction effect cost by a high pressure EGR catalyst. It is a map showing the trend of tailpipe emissions.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a spark ignition type internal combustion engine 10. The internal combustion engine 10 is used as a power source for a vehicle or the like. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, the number of cylinders and the cylinder arrangement of the internal combustion engine in the present invention are not limited to this.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injector 12 that injects fuel directly into the cylinder. The present invention is not limited to such an in-cylinder injection type internal combustion engine, but can be similarly applied to a port injection type internal combustion engine that injects fuel into an intake port.

  The exhaust gas discharged from each cylinder of the internal combustion engine 10 is collected by the exhaust manifold 20 and flows into the exhaust passage 18. The internal combustion engine 10 of the present embodiment includes a turbocharger 24 that performs supercharging with the energy of exhaust gas. The turbocharger 24 includes a turbine 241 that is rotated by the energy of exhaust gas, and a compressor 242 that is driven by the turbine 241 to rotate. The turbine 241 is disposed in the middle of the exhaust passage 18, and the compressor 242 is disposed in the middle of the intake passage 28.

  A start catalyst 26 and an underfloor catalyst 27 for purifying harmful components in the exhaust gas are installed in the exhaust passage 18 on the downstream side of the turbine 241. A post-start catalyst O 2 sensor 25 for detecting the air-fuel ratio of the exhaust gas flowing out from the start catalyst 26 is installed on the downstream side of the start catalyst 26.

  An air cleaner 30 is provided near the inlet of the intake passage 28 of the internal combustion engine 10. Further, an air flow meter 38 for detecting the intake air amount is installed in the vicinity of the downstream side of the air cleaner 30.

  An intercooler 32 is installed in the intake passage 28 on the downstream side of the compressor 242. The air sucked through the air cleaner 30 is compressed by the compressor 242 of the turbocharger 24 and then cooled by the intercooler 32. The air that has passed through the intercooler 32 passes through the intake manifold 34 and flows into each cylinder. A throttle valve 36 is installed in the intake passage 28 between the intercooler 32 and the intake manifold 34.

  The internal combustion engine 10 is provided with an EGR device for performing EGR (Exhaust Gas Recirculation) for recirculating a part of the exhaust gas to the intake passage 28. The EGR device in the present embodiment includes two EGR paths, a path for performing high pressure EGR and a path for performing low pressure EGR.

  The high pressure EGR passage 40 for performing the high pressure EGR includes an exhaust passage upstream of the turbine 241 (exhaust manifold 20 in the configuration of FIG. 1) and an intake passage 28 downstream of the compressor 242 (in the configuration of FIG. 1, the throttle valve 36). And the intake manifold 34). In the middle of the high-pressure EGR passage 40, a high-pressure EGR catalyst 41 that purifies harmful components in the recirculated exhaust gas, a high-pressure EGR cooler 43 that cools the recirculated exhaust gas, and the amount of recirculated exhaust gas (EGR amount). A high-pressure EGR valve 44 for adjustment is provided in this order from the upstream side.

  Further, on the downstream side of the high pressure EGR catalyst 41, a post-high pressure EGR catalyst O2 sensor 39 for detecting the air-fuel ratio of the exhaust gas flowing out from the high pressure EGR catalyst 41 is installed. The high-pressure EGR post-catalyst O2 sensor 39 includes a heater for raising the temperature of the sensor element to the activation temperature. The post-high pressure EGR catalyst post-O 2 sensor 39 may be installed on the downstream side of the high pressure EGR cooler 43, but in this embodiment, the post-high pressure EGR catalyst post-O 2 sensor 39 is interposed between the high pressure EGR catalyst 41 and the high pressure EGR cooler 43. Is installed. Accordingly, the high-temperature exhaust gas before being cooled by the high-pressure EGR cooler 43 can be applied to the post-high-pressure EGR catalyst post-O 2 sensor 39 to warm the post-high-pressure EGR catalyst post-O 2 sensor 39. For this reason, since the energization amount to a heater may be small, power consumption can be reduced.

  The low pressure EGR passage 42 for performing the low pressure EGR includes an exhaust passage 18 downstream of the turbine 241 (between the start catalyst 26 and the underfloor catalyst 27 in the configuration of FIG. 1) and an intake passage 28 upstream of the compressor 242. And connected. In the middle of the low-pressure EGR passage 42, a low-pressure EGR catalyst 45 that purifies harmful components in the recirculated exhaust gas, a low-pressure EGR cooler 46 that cools the recirculated exhaust gas, and an amount of the recirculated exhaust gas are adjusted. A low pressure EGR valve 47 is provided in this order from the upstream side.

  Further, on the downstream side of the low pressure EGR catalyst 45, a low pressure EGR post-catalyst O2 sensor 48 for detecting the air-fuel ratio of the exhaust gas flowing out from the low pressure EGR catalyst 45 is installed. The low-pressure EGR post-catalyst O2 sensor 48 includes a heater for raising the temperature of the sensor element to the activation temperature. The low-pressure EGR post-catalyst O2 sensor 48 may be installed on the downstream side of the low-pressure EGR cooler 46, but in this embodiment, the low-pressure EGR post-catalyst O2 sensor 48 is interposed between the low-pressure EGR catalyst 45 and the low-pressure EGR cooler 46. Is installed. Thus, the high-temperature exhaust gas before being cooled by the low-pressure EGR cooler 46 can be applied to the post-low-pressure EGR catalyst post-O 2 sensor 48 to warm the post-low-pressure EGR catalyst post-O 2 sensor 48. For this reason, since the energization amount to a heater may be small, power consumption can be reduced.

  The application target of the present invention is not limited to an internal combustion engine having a plurality of EGR paths as described above. The present invention is also applicable to an internal combustion engine having a single EGR path.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50. In addition to the various sensors and actuators described above, ECU 50 is provided with a crank angle sensor 52 that detects the rotation angle of the crankshaft (output shaft) of internal combustion engine 10 and a driver's seat of a vehicle on which internal combustion engine 10 is mounted. An accelerator opening sensor 54 that detects the position of the accelerator pedal (accelerator opening) is electrically connected. The ECU 50 controls the operating state of the internal combustion engine 10 by operating each actuator according to a predetermined program based on the output of each sensor.

  The post-start catalyst O2 sensor 25, the high-pressure EGR catalyst post-O2 sensor 39, and the low-pressure EGR post-catalyst O2 sensor 48 in the present embodiment are oxygen sensors having characteristics in which the output changes suddenly with the theoretical air-fuel ratio as a boundary. However, in the present invention, a wide-range air-fuel ratio sensor may be used instead of the post-start catalyst O2 sensor 25, the high-pressure EGR catalyst O2 sensor 39, and the low-pressure EGR catalyst post-O2 sensor 48. A wide-range air-fuel ratio sensor is a sensor that emits an output that changes linearly with respect to a change in air-fuel ratio and can continuously detect an air-fuel ratio over a relatively wide range.

  The start catalyst 26, the underfloor catalyst 27, the high pressure EGR catalyst 41, and the low pressure EGR catalyst 45 simultaneously purify the three components HC, CO, and NOx when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio. This is a catalytic converter having a function as a three-way catalyst. These catalytic converters contain noble metals (active points) such as Pt and Pd and oxygen storage components capable of absorbing and releasing oxygen as catalyst components. When the air-fuel ratio of the exhaust gas flowing into these catalytic converters is richer than the stoichiometric air-fuel ratio, oxygen is released from the oxygen storage component, and the released oxygen oxidizes unburned components such as HC and CO. And can be purified. Conversely, when the air-fuel ratio of the exhaust gas flowing into these catalytic converters is leaner than the stoichiometric air-fuel ratio, the oxygen storage component absorbs excess oxygen in the exhaust gas, thereby reducing and purifying NOx. Can do. In this way, even if the oxygen storage component absorbs and releases oxygen, even if the air-fuel ratio of the exhaust gas flowing into the catalytic converter varies somewhat from the stoichiometric air-fuel ratio, the three components of HC, CO, and NOx are reduced. It can be purified well.

  The high-pressure EGR catalyst 41 and the low-pressure EGR catalyst 45 also have a function of burning (oxidizing) particulate matter (Particulate Matter) in exhaust gas such as soot and SOF (Soluble Organic Fraction). By burning and removing particulate matter (hereinafter referred to as “PM”) by the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45, the high pressure EGR passage 40, the low pressure EGR passage 42, the high pressure EGR cooler 43, the low pressure EGR cooler 46, Accumulation of deposits on the intake port, intake valve, and the like of the internal combustion engine 10 can be sufficiently suppressed.

  The purification performance of catalytic converters deteriorates over time. It is known that the degree of deterioration of a catalytic converter is related to an oxygen storage capacity (OSC) which is the maximum amount of oxygen that can be stored by the catalytic converter. That is, it can be determined that the deterioration of the catalytic converter progresses as the oxygen storage capacity decreases. Therefore, the deterioration of the catalytic converter can be detected by measuring the oxygen storage capacity of each catalytic converter.

  Hereinafter, in the present embodiment, control when measuring the oxygen storage capacities of the start catalyst 26 and the high-pressure EGR catalyst 41 will be described. In this embodiment, the oxygen storage capacities of the start catalyst 26 and the high pressure EGR catalyst 41 are simultaneously measured by executing active air-fuel ratio control. The active air-fuel ratio control is a control for forcibly switching the air-fuel ratio of the internal combustion engine 10 alternately between the rich side and the lean side with the theoretical air-fuel ratio interposed therebetween.

FIG. 2 is a diagram showing fluctuations in the control target air-fuel ratio of the internal combustion engine 10, the output of the post-start catalyst O2 sensor 25, and the output of the post-high pressure EGR catalyst O2 sensor 39 during execution of the active air-fuel ratio control of the present embodiment. is there. As shown in FIG. 2, during the execution of the active air-fuel ratio control, the ECU 50 sets the control target air-fuel ratio of the internal combustion engine 10 to an air-fuel ratio (hereinafter referred to as “the air-fuel ratio” separated from the theoretical air-fuel ratio to the rich side by a predetermined amplitude ΔA / F _R Forcibly and alternately switch between the “rich air / fuel ratio” and the air / fuel ratio (hereinafter referred to as “lean air / fuel ratio”) separated from the theoretical air / fuel ratio by a predetermined amplitude ΔA / F _L on the lean side. .

  In FIG. 2, before the time t1, the control target air-fuel ratio is set to a lean air-fuel ratio, so the internal combustion engine 10 is operated at an air-excess lean air-fuel ratio. For this reason, a lean air-fuel ratio exhaust gas containing surplus oxygen flows into the start catalyst 26. As the surplus oxygen is absorbed by the start catalyst 26, the downstream of the start catalyst 26 becomes almost the stoichiometric air-fuel ratio. However, when the start catalyst 26 cannot absorb oxygen any more (oxygen is full), excess oxygen begins to flow downstream of the start catalyst 26. As a result, the output of the O2 sensor 25 after the start catalyst changes (reverses) from rich to lean (time t1). As a trigger, the control target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio.

  When the control target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio, the internal combustion engine 10 is operated at a rich air-fuel ratio with excess fuel. For this reason, after the time t1, the start catalyst 26 runs out of oxygen and a rich air-fuel ratio exhaust gas containing surplus unburned components flows. The start catalyst 26 purifies excess unburned components by releasing the stored oxygen. As a result, the downstream of the start catalyst 26 becomes almost the stoichiometric air-fuel ratio. However, when the oxygen stored in the start catalyst 26 reaches the bottom, excess unburned components begin to flow out downstream of the start catalyst 26. As a result, the output of the O2 sensor 25 after the start catalyst changes (reverses) from lean to rich (time t3). As a trigger, the control target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio.

  Similarly, the control target air-fuel ratio is alternately switched between the rich air-fuel ratio and the lean air-fuel ratio, triggered by the reversal of the output of the O2 sensor 25 after the start catalyst. That is, when the output of the post-start catalyst O2 sensor 25 is reversed from rich to lean, the control target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio (time t5, t9 in FIG. 2). When the output of the sensor 25 is reversed from lean to rich, the control target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio (time t7).

At time t1, the oxygen in the start catalyst 26 is full, and at time t3, the oxygen in the start catalyst 26 is empty. Therefore, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 is equal to the amount of oxygen released from the start catalyst 26 between time t1 and time t3. Between time t1 and time t3, the rich air-fuel ratio exhaust gas in which oxygen is insufficient flows into the start catalyst 26. Oxygen is released from the start catalyst 26 so as to compensate for the oxygen deficiency.

Therefore, the amount of oxygen released from the start catalyst 26 per unit period is equal to the oxygen shortage per unit period in the start catalyst 26. The oxygen deficiency per unit period in the start catalyst 26 corresponds to the oxygen deficiency per unit period of the internal combustion engine 10. Oxygen-deficient amount per unit period of the internal combustion engine 10 can be calculated based on the rich side amplitude .DELTA.A / F _R, the fuel injection quantity, the value of such oxygen mass fraction of air (about 0.23). A value obtained by integrating the calculated oxygen shortage per unit period from time t1 to time t3 corresponds to the value of the oxygen storage capacity OSC _{s / c} of the start catalyst 26. By performing the same calculation, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 can be calculated between time t5 and time t7.

The oxygen storage capacity OSC _{s / c} of the start catalyst 26 can also be calculated as follows. At time t3, the oxygen in the start catalyst 26 is empty, and at time t5, the oxygen in the start catalyst 26 is full. Accordingly, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 is equal to the amount of oxygen absorbed by the start catalyst 26 from time t3 to time t5. During the period from time t3 to time t5, the lean air-fuel ratio exhaust gas containing surplus oxygen flows into the start catalyst 26, and the surplus oxygen is absorbed by the start catalyst 26.

Therefore, the amount of oxygen absorbed in the start catalyst 26 per unit period is equal to the excess oxygen amount per unit period in the start catalyst 26. The oxygen surplus amount per unit period in the start catalyst 26 corresponds to the oxygen surplus amount per unit period of the internal combustion engine 10. The oxygen surplus amount per unit period of the internal combustion engine 10 can be calculated based on values such as the lean side amplitude ΔA / F _L , the fuel injection amount, and the oxygen mass ratio in the air. A value obtained by integrating the calculated oxygen surplus amount per unit period from time t3 to time t5 corresponds to the value of the oxygen storage capacity OSC _{s / c} of the start catalyst 26. By performing the same calculation, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 can be calculated between time t7 and time t9.

The “start catalyst OSC calculation counter” shown in FIG. 2 represents a change in the integrated value of the oxygen release amount (or oxygen absorption amount) ΔOSC _{s / c} of the start catalyst 26 per unit period described above. In FIG. 2, the integrated values of ΔOSC _{s / c} at times t3, t5, t7, and t9 correspond to the value of the oxygen storage capacity OSC _{s / c} of the start catalyst 26, respectively. Thus, by calculating the integrated value of ΔOSC _{s / c} during execution of the active air-fuel ratio control, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 can be repeatedly measured. Then, by obtaining the average value of these measured values, the oxygen storage capacity OSC _{s / c} of the start catalyst 26 can be accurately calculated.

  On the other hand, the oxygen storage capacity OSC of the high-pressure EGR catalyst 41 can be calculated as follows. At time t0 in FIG. 2, the output of the post-high pressure EGR catalyst O2 sensor 39 changes from rich to lean. That is, at the time t0, the oxygen in the high pressure EGR catalyst 41 is full. However, the control target air-fuel ratio is maintained at the lean air-fuel ratio even after time t0. Then, the control target air-fuel ratio is switched to the rich air-fuel ratio after waiting for the output of the O2 sensor 25 to reverse after the start catalyst (time t1). Therefore, the rich air-fuel ratio exhaust gas starts to flow into the high-pressure EGR catalyst 41 after time t1.

Thereafter, at time t2, the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed from lean to rich. That is, at the time t2, the oxygen in the high pressure EGR catalyst 41 becomes empty. Therefore, the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 is equal to the amount of oxygen released from the high-pressure EGR catalyst 41 between time t1 and time t2. During this time, the rich air-fuel ratio exhaust gas lacking oxygen flows into the high pressure EGR catalyst 41, and oxygen is released from the high pressure EGR catalyst 41 so as to compensate for the oxygen shortage. Therefore, the oxygen release amount ΔOSC _HEGR per unit period in the high pressure EGR catalyst 41 is equal to the oxygen shortage amount per unit period in the high pressure EGR catalyst 41. The oxygen deficiency per unit period in the high pressure EGR catalyst 41 includes the oxygen deficiency ΔOSC _{s / c} per unit period in the start catalyst 26 and the high pressure EGR rate (of the exhaust gas discharged from the internal combustion engine 10, the high pressure And the ratio of the exhaust gas flowing into the EGR passage 40). A value obtained by integrating the oxygen shortage per unit period in the high pressure EGR catalyst 41 from time t1 to time t2 calculated in this way corresponds to the value of the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41. By performing the same calculation, the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 can be calculated between time t5 and time t6.

  Further, the oxygen storage capacity OSC of the high pressure EGR catalyst 41 can be calculated as follows. At time t2 in FIG. 2, the output of the post-high pressure EGR catalyst O2 sensor 39 changes from lean to rich. That is, at the time t2, the oxygen in the high pressure EGR catalyst 41 is empty. However, the control target air-fuel ratio is maintained at the rich air-fuel ratio even after time t2. Then, the control target air-fuel ratio is switched to the lean air-fuel ratio after waiting for the output of the O2 sensor 25 to reverse after the start catalyst (time t3). Therefore, the lean air-fuel ratio exhaust gas starts to flow into the high-pressure EGR catalyst 41 after time t3.

Thereafter, at time t4, the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed from rich to lean. That is, at time t4, the oxygen in the high pressure EGR catalyst 41 is full. Therefore, the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41 is equal to the amount of oxygen absorbed by the high pressure EGR catalyst 41 from time t3 to time t4. During this time, the lean air-fuel ratio exhaust gas containing surplus oxygen flows into the high pressure EGR catalyst 41, and the surplus oxygen is absorbed by the high pressure EGR catalyst 41. Therefore, the oxygen absorption amount per unit period in the high-pressure EGR catalyst 41 is equal to the oxygen surplus amount per unit period in the high-pressure EGR catalyst 41. The excess oxygen amount per unit period in the high-pressure EGR catalyst 41 can be calculated based on the excess oxygen amount ΔOSC _{s / c} per unit period in the start catalyst 26 and the high-pressure EGR rate. A value obtained by integrating the excess oxygen amount per unit period in the high pressure EGR catalyst 41 from time t3 to time t4 calculated in this way corresponds to the value of the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41. By performing the same calculation, the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 can be calculated between time t7 and time t8.

The “high-pressure EGR catalyst OSC calculation counter” shown in FIG. 2 represents a change in the integrated value of the oxygen release amount (or oxygen absorption amount) ΔOSC _HEGR of the high-pressure EGR catalyst 41 per unit period described above. In Figure 2, the integrated value of ΔOSC _HEGR at time t2, t4, t6, t8, respectively, corresponds to the value of the oxygen storage capacity OSC _HEGR pressure EGR catalyst 41. Thus, by calculating the integrated value of ΔOSC _HEGR during execution of the active air-fuel ratio control, the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 can be repeatedly measured. And the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 can be calculated with high accuracy by _obtaining the average value of these measured values.

  FIG. 3 is a flowchart of a routine executed by the ECU 50 when the deterioration detection (measurement of oxygen storage capacity) of the start catalyst 26 and the high-pressure EGR catalyst 41 is executed according to the above-described method. According to the routine shown in FIG. 3, first, a process of switching the control target air-fuel ratio of the internal combustion engine 10 from the rich air-fuel ratio to the lean air-fuel ratio or from the lean air-fuel ratio to the rich air-fuel ratio is executed (step 100). Next, it is determined whether or not the output of the post-EGR catalyst O2 sensor 39 has been reversed (step 102).

  If the output of the post-EGR-catalyst O2 sensor 39 is not yet reversed in step 102, the process waits until the output of the post-EGR-catalyst O2 sensor 39 is reversed. If it is recognized that the output of the post-EGR catalyst O2 sensor 39 has been reversed, it is next determined whether or not the output of the post-start catalyst O2 sensor 25 has been reversed (step 104). If the output of the post-start catalyst O2 sensor 25 has not yet been reversed in step 104, the process waits until the output of the post-start catalyst O2 sensor 25 is reversed.

If it is determined in the above step 104 that the output of the O2 sensor 25 after the start catalyst is reversed, then the oxygen storage capacity OSC _{s / c of the} start catalyst 26 and the oxygen storage capacity OSC of the high pressure EGR catalyst 41 are next. _HEGR is calculated (step 106). Specifically, the integrated value of ΔOSC _{s / c} at the time when the output of the O 2 sensor 25 after the start catalyst is inverted is read as the current measured value of the oxygen storage capacity OSC _{s / c} of the start catalyst 26, and this time The average value of the measured value and the previous measured value is stored as the value of the oxygen storage capacity OSC _{s / c} of the start catalyst 26. Also, the integrated value of ΔOSC _HEGR at the time when the output of the O2 sensor 39 after the high pressure EGR catalyst is inverted is read as the current measured value of the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41, and this measured value and the previous time The average value with the measured values up to is stored as the value of the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41.

Following the processing of step 106, it is determined whether or not the elapsed time after the start of detection of deterioration of the start catalyst 26 and the high pressure EGR catalyst 41 has reached a predetermined time (step 108). This predetermined time is a time that _allows the number of measurements of the oxygen storage capacities OSC _{s / c} and OSC _HEGR (that is, the number of inversions of both the O2 sensors 25 and 39) to reach the required number of times to ensure sufficient measurement accuracy Are set in advance.

If it is determined in step 108 that the elapsed time has not reached the predetermined time, it can be determined that the number of measurements of the oxygen storage capacity OSC _{s / c} and OSC _HEGR has not reached the required number. In this case, since it is necessary to continue the measurement of the oxygen storage capacity, the processing after step 100 is executed again. Note that the processing of steps 106 and 108 is instantaneously ended in practice. For this reason, when returning from step 108 to step 100, the internal combustion engine 10 is detected in step 100 immediately after it is recognized in step 104 that the output of the O2 sensor 25 after the start catalyst is reversed. The control target air-fuel ratio is switched.

On the other hand, if it is determined in step 108 that the elapsed time has reached the predetermined time, it can be determined that the number of measurements of the oxygen storage capacity OSC _{s / c} and OSC _HEGR has reached the required number. In this case, the execution of the deterioration detection using the active air-fuel ratio control by this routine is ended.

In the present embodiment, as shown in FIG. 2 described above, when active air-fuel ratio control is executed, the timing (time t0, t2, t4, t6, t8) at which the output of the O2 sensor 39 after the high pressure EGR catalyst is inverted is reversed. The oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41 is measured in a situation where the output of the O2 sensor 25 after the start catalyst is earlier than the timing at which the output of the O2 sensor 25 is reversed (time t1, t3, t5, t7, t9). It is characterized by that.

  On the other hand, if the output of the O2 sensor 25 after the start catalyst is reversed when the active air-fuel ratio control is executed, if the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed, There is a problem like this.

In order to accurately measure the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41, it is necessary to maintain the control target air-fuel ratio at a lean air-fuel ratio or a rich air-fuel ratio until the oxygen of the high-pressure EGR catalyst 41 is full or empty. is necessary. Therefore, when the output of the O2 sensor 25 after the start catalyst is reversed before the output of the O2 sensor 39 after the high pressure EGR catalyst, the control target air-fuel ratio is maintained until the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed thereafter. It is necessary to postpone switching. For this reason, exhaust gas containing a large amount of unpurified components flows out downstream of the start catalyst 26.

  That is, if the output of the O2 sensor 25 is reversed from rich to lean after the start catalyst, the oxygen in the start catalyst 26 is full at that time. Thereafter, the control target air-fuel ratio is maintained at the lean air-fuel ratio until the output of the O2 sensor 39 after the high-pressure EGR catalyst reverses from rich to lean. That is, the lean air-fuel ratio exhaust gas containing surplus oxygen continues to flow into the start catalyst 26. Therefore, during this time, the air-fuel ratio in the start catalyst 26 is lean, so that NOx cannot be sufficiently purified, and NOx flows out downstream of the start catalyst 26.

  On the other hand, if the output of the O2 sensor 25 after the start catalyst is reversed from lean to rich, the oxygen in the start catalyst 26 is empty at that time. Thereafter, the control target air-fuel ratio is maintained at the rich air-fuel ratio until the output of the O2 sensor 39 after the high-pressure EGR catalyst reverses from lean to rich. That is, rich air-fuel ratio exhaust gas containing excess unburned components continues to flow into the start catalyst 26. Accordingly, during this time, the air-fuel ratio in the start catalyst 26 is richly biased, so that excess unburned components (HC, CO) cannot be sufficiently purified, and HC and CO flow out downstream of the start catalyst 26.

  Unpurified components that have flowed out downstream of the start catalyst 26 are purified by the underfloor catalyst 27. However, since the purification rate is not necessarily 100%, some unpurified components also flow out downstream of the underfloor catalyst 27. Therefore, it is desirable that the amount of unpurified components flowing out downstream of the start catalyst 26 is as small as possible.

  As described above, when active air-fuel ratio control is executed to measure the oxygen storage capacity of the high-pressure EGR catalyst 41, the timing at which the output of the O2 sensor 25 after the start catalyst is reversed is the O2 sensor 39 after the high-pressure EGR catalyst. As a result, the unpurified component is discharged to the downstream side of the start catalyst 26.

  In contrast, in the present embodiment, when active air-fuel ratio control is executed, the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed before the output of the O2 sensor 25 after the start catalyst is reversed. In addition, the execution of the active air-fuel ratio control is permitted, and the oxygen storage capacity of the high-pressure EGR catalyst 41 is measured. For this reason, it is possible to reliably suppress the unpurified component from flowing out to the downstream side of the start catalyst 26.

As the oxygen storage capacity OSC _{s / c of the} start catalyst 26 increases, the timing at which the output of the O 2 sensor 25 after the start catalyst is reversed is delayed. On the other hand, as the exhaust gas flow rate FR _{s / c} passing through the start catalyst 26 increases, the timing at which the output of the O 2 sensor 25 after the start catalyst is reversed becomes earlier. Further, as the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41 increases, the timing at which the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed is delayed. On the other hand, as the exhaust gas flow rate FR _HEGR passing through the high pressure EGR catalyst 41 increases, the timing at which the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed is _advanced .

Therefore, in the case of executing the active air-fuel ratio control, in order to output the high-pressure EGR catalyst after O2 sensor 39 is inverted before the output of the start catalyst after O2 sensor 25 is inverted, the oxygen storage capacity OSC _s of the start catalyst 26 _/ a _c, and the exhaust gas flow rate FR _{s / c} to pass through the start catalyst 26, the oxygen storage capacity OSC _HEGR pressure EGR catalyst 41, between the exhaust gas flow rate FR _HEGR passing through a high-pressure EGR catalyst 41, the following equation It is sufficient to satisfy the following conditions.
OSC _{s / c} / FR _{s / c} ≧ OSC _HEGR / FR _HEGR (1)

The above equation (1) can be modified as the following equation.
OSC _{s / c} × FR _HEGR / FR _{s / c} ≧ OSC _HEGR (2)

When the above equation (2) is satisfied, when active air-fuel ratio control is executed, the output of the high pressure EGR post-catalyst O2 sensor 39 is inverted before the output of the post-start catalyst O2 sensor 25 is inverted. Therefore, in this case, it is _possible to measure the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 by executing active air-fuel ratio control while reliably preventing discharge of _unpurified components into the atmosphere.

On the other hand, when the above equation (2) is not established, that is, when the following equation (3) is established, the timing at which the output of the O2 sensor 25 after the start catalyst is inverted when the active air-fuel ratio control is executed. However, it is earlier than the timing at which the output of the O2 sensor 39 after the high pressure EGR catalyst is reversed. Therefore, if active air-fuel ratio control is executed to measure the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41, it can be predicted that _unpurified components will flow out downstream of the start catalyst 26.
OSC _{s / c} x FR _HEGR / FR _{s / c} <OSC _HEGR (3)

  Therefore, in the present embodiment, when the above equation (3) is established, execution of the active air-fuel ratio control is prohibited. FIG. 4 is a flowchart of a routine executed by the ECU 50 to realize this function. According to this routine, first, the success or failure of the above equation (3) is determined (step 110).

In step 110, the value of FR _HEGR / FR _{s / c} (hereinafter referred to as “gas amount ratio”) in the above equation (3) can be obtained as follows. The gas amount ratio FR _HEGR / FR _{s / c} is a value representing the ratio of the exhaust gas flow rate passing through the high pressure EGR catalyst 41 to the exhaust gas flow rate passing through the start catalyst 26. The gas amount ratio FR _HEGR / FR _{s / c} varies depending on the operating state of the internal combustion engine 10 (opening of the high pressure EGR valve 44, engine speed, intake air amount, etc.). Therefore, the relationship between the operating state parameter and the gas amount ratio FR _HEGR / FR _{s / c} is examined in advance and stored in the ECU 50 as a map, whereby the gas amount ratio FR _HEGR in the current operating state is _stored. / FR _{s / c} can be calculated.

Further, in step 110, the value of the oxygen storage capacity OSC _HEGR the oxygen storage capacity OSC s / _c and the high-pressure EGR catalyst 41 of the start catalyst 26, is calculated by the processing of the routine shown in FIG. 3 in the previous deterioration detection A value stored in the ECU 50 can be used. Since the deterioration of the start catalyst 26 and the high pressure EGR catalyst 41 does not proceed so rapidly, the values of the current oxygen storage capacity OSC _{s / c} and OSC _HEGR are the oxygen storage capacity OSC _s calculated when the previous deterioration was detected. It can be considered to be approximately equal to the values of _{/ c} and OSC _HEGR . Accordingly, in step 110, the value of the calculated oxygen storage capacity OSC s / _c and OSC _HEGR in the previous deterioration detection can be substituted for the current value of the oxygen storage capacity OSC s / _c and OSC _HEGR .

In step 110, the success or failure of equation (3) is determined using the values of FR _HEGR / FR _{s / c} , OSC _{s / c} , and OSC _HEGR obtained as described above. As a result, when the equation (3) is determined to be satisfied, and if you execute a active air-fuel ratio control in order to measure the oxygen storage capacity OSC _HEGR pressure EGR catalyst 41, the start catalyst 26 It can be predicted that unpurified components will flow downstream. Therefore, in this case, execution of active air-fuel ratio control for measuring the oxygen storage capacity OSC _HEGR of the EGR catalyst 41 is prohibited (step 112).

On the other hand, if it is determined in step 110 that the expression (3) is not established, even if active air-fuel ratio control is executed to measure the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41, the start is started. It can be predicted that there is no risk of unpurified components flowing out downstream of the catalyst 26. Therefore, in this case, execution of active air-fuel ratio control for measuring the oxygen storage capacity OSC _HEGR of the EGR catalyst 41 is permitted (step 114).

By the way, in Embodiment 1 described above, the oxygen storage capacity OSC _HEGR of the high pressure EGR catalyst 41 and the oxygen storage capacity OSC _{s / c of the} start catalyst 26 are measured simultaneously. You may make it measure separately.

  Further, in the above-described first embodiment, whether or not the timing at which the output of the O2 sensor 25 after the start catalyst is inverted is earlier than the timing at which the output of the O2 sensor 39 after the high pressure EGR catalyst is inverted is determined by the process of step 110 described above. The prediction is made in advance, but the present invention is not limited to this. For example, in the present invention, the active air-fuel ratio control is started without performing the prior prediction as in step 110, and the output of the post-start catalyst O2 sensor 25 is changed before the output of the post-high pressure EGR catalyst O2 sensor 39 is reversed. When it is actually detected that the rotation has been reversed, the execution of the active air-fuel ratio control may be prohibited.

  In the first embodiment described above, the post-high pressure EGR catalyst O2 sensor 39 is the “post-EGR catalyst exhaust gas sensor” in the first invention, and the high pressure EGR catalyst 41 is the “EGR” in the first to third inventions. The high pressure EGR passage 40 corresponds to the “catalyst”, the “EGR passage” in the first and fourth inventions, and the start catalyst 26 corresponds to the “exhaust purification catalyst” in the second and third inventions. Further, when the ECU 50 executes the routine shown in FIG. 3, the “EGR catalyst oxygen storage capacity measuring means” in the first invention and the “active air-fuel ratio control means” in the second and third inventions are provided. By executing the processing of step 110, the “gas amount ratio acquisition means” in the third aspect of the invention executes the processing of steps 110 and 112, and the “active sky” in the second and third aspects of the invention. "Fuel ratio control prohibiting means" is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 5. The description will focus on the differences from the first embodiment described above, and the same matters will be simplified or described. Omitted. The hardware configuration of this embodiment is the same as that of the first embodiment shown in FIG.

  In this embodiment, the oxygen storage capacity of the low pressure EGR catalyst 45 is measured by executing active air-fuel ratio control. FIG. 5 is a diagram showing fluctuations in the control target air-fuel ratio of the internal combustion engine 10, the output of the start post-catalyst O2 sensor 25, and the output of the low-pressure EGR post-catalyst O2 sensor 48 during execution of the active air-fuel ratio control of the present embodiment. is there.

  At time t1 in FIG. 5, the oxygen of the low pressure EGR catalyst 45 is full, and the output of the O2 sensor 48 after the low pressure EGR catalyst is reversed from rich to lean. As a trigger, the control target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio. Thereby, after time t1, the rich air-fuel ratio exhaust gas containing surplus unburned components flows into the start catalyst 26. The start catalyst 26 purifies the excess unburned components by releasing the stored oxygen. Therefore, the stoichiometric air-fuel ratio exhaust gas without oxygen excess or deficiency flows into the low pressure EGR catalyst 45.

  Thereafter, at time t2, the output of the O2 sensor 25 after the start catalyst is reversed from lean to rich. This indicates that the oxygen stored in the start catalyst 26 has bottomed out, and excess unburned components have started to flow out downstream of the start catalyst 26. Accordingly, after time t2, the rich air-fuel ratio exhaust gas containing excess unburned components starts to flow into the low-pressure EGR catalyst 45. The low pressure EGR catalyst 45 purifies surplus unburned components by releasing the stored oxygen. Thereafter, at time t3, the output of the O2 sensor 48 after the low pressure EGR catalyst is inverted from lean to rich. This indicates that oxygen stored in the low pressure EGR catalyst 45 has bottomed out, and excess unburned components have started to flow out downstream of the low pressure EGR catalyst 45.

  The control target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio triggered by the reversal of the output of the O2 sensor 48 after the low-pressure EGR catalyst at time t3. Thus, after time t3, the exhaust gas having a lean air-fuel ratio containing excess oxygen flows into the start catalyst 26. The excess oxygen is absorbed by the start catalyst 26. When the oxygen in the start catalyst 26 becomes full, surplus oxygen begins to flow out downstream of the start catalyst 26. As a result, the output of the O2 sensor 25 after the start catalyst is reversed from rich to lean (time t4). After this time t4, the lean air-fuel ratio exhaust gas containing surplus oxygen flows into the low pressure EGR catalyst 45, and the surplus oxygen is absorbed by the low pressure EGR catalyst 45. When the oxygen in the low pressure EGR catalyst 45 becomes full, excess oxygen begins to flow out downstream of the low pressure EGR catalyst 45. As a result, the output of the O2 sensor 48 after the low pressure EGR catalyst is reversed from rich to lean (time t5). As a trigger, the control target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio.

  Thus, in the present embodiment, the control target air-fuel ratio is alternately switched between the rich air-fuel ratio and the lean air-fuel ratio in response to the inversion of the output of the post-low-pressure EGR catalyst O2 sensor 48.

The oxygen storage capacity OSC of the low pressure EGR catalyst 45 can be calculated as follows. At time t2, the oxygen in the low pressure EGR catalyst 45 is full, and at time t3, the oxygen in the low pressure EGR catalyst 45 is empty. Therefore, the oxygen storage capacity OSC _LEGR of the low-pressure EGR catalyst 45 is equal to the amount of oxygen released from the low-pressure EGR catalyst 45 from time t2 to time t3. The oxygen release amount per unit period (that is, the oxygen shortage amount) ΔOSC _LEGR in the low pressure EGR catalyst 45 is the rich side amplitude ΔA / F _R , the fuel injection amount, the oxygen mass ratio in the air, the low pressure EGR rate (from the internal combustion engine 10). It can be calculated based on a value such as a ratio of the exhaust gas flowing into the low pressure EGR passage 42 among the exhaust gas discharged. A value obtained by integrating the calculated oxygen release amount per unit period from time t2 to time t3 corresponds to the value of the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45. By performing the same calculation, the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45 can be calculated between time t6 and time t7.

Further, the oxygen storage capacity OSC of the low-pressure EGR catalyst 45 can be calculated as follows. At time t4, the oxygen in the low pressure EGR catalyst 45 is empty, and at time t5, the oxygen in the low pressure EGR catalyst 45 is full. Therefore, the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45 is equal to the amount of oxygen absorbed by the low pressure EGR catalyst 45 from time t4 to time t5. The oxygen absorption amount (that is, the oxygen surplus amount) ΔOSC _LEGR per unit period in the low pressure EGR catalyst 45 is calculated based on the lean side amplitude ΔA / F _L , the fuel injection amount, the oxygen mass ratio in the air, and the low pressure EGR rate. be able to. A value obtained by integrating the calculated oxygen absorption amount ΔOSC _LEGR per unit period from time t4 to time t5 corresponds to the value of the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45. By performing the same calculation, the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45 can be calculated between time t8 and time t9.

As described above, in order to measure the oxygen storage capacity OSC _LEGR of the low-pressure EGR catalyst 45, it is necessary to allow the exhaust gas having a rich air-fuel ratio or a lean air-fuel ratio to flow into the low-pressure EGR catalyst 45. That is, it is necessary to discharge exhaust gas containing unpurified components downstream of the start catalyst 26. For this reason, it is important to reliably purify the unpurified components that have flowed out downstream of the start catalyst 26 with the underfloor catalyst 27. For this purpose, it is necessary to prevent the oxygen in the underfloor catalyst 27 from becoming empty or full.

  In order to avoid the oxygen in the underfloor catalyst 27 being empty or full, it is preferable that the period during which the rich air-fuel ratio or lean air-fuel ratio exhaust gas flows downstream of the start catalyst 26 is as short as possible. In order to shorten the period during which the rich air-fuel ratio or lean air-fuel ratio flows in the downstream side of the start catalyst 26, it is necessary to advance the timing at which the output of the O2 sensor 48 after the low pressure EGR catalyst is reversed. As the flow rate of exhaust gas passing through the low pressure EGR catalyst 45 increases, the timing at which the output of the O2 sensor 48 after the low pressure EGR catalyst is reversed is earlier.

As described above, in the present embodiment, it is desirable to execute the measurement of the oxygen storage capacity OSC _LEGR of the low pressure EGR catalyst 45 only in an operation state in which the amount of EGR by the low pressure EGR passage 42 is relatively large.

  In the second embodiment described above, the low-pressure EGR post-catalyst O2 sensor 48 is the “EGR post-catalyst exhaust gas sensor” in the first invention, and the low-pressure EGR catalyst 45 is the “EGR catalyst” in the first invention. The EGR passage 42 corresponds to the “EGR passage” in the first and fifth inventions, respectively.

Embodiment 3 FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 6. The description will focus on the differences from the first embodiment described above, and the same matters will be simplified or described. Omitted. The hardware configuration of this embodiment is the same as that of the first embodiment shown in FIG.

  In the present embodiment, the oxygen storage capacity of the high pressure EGR catalyst 41 is measured without executing active air-fuel ratio control. FIG. 6 is a diagram for explaining a method of measuring the oxygen storage capacity of the high-pressure EGR catalyst 41 in the present embodiment. At time t1 in FIG. 6, the output of the O2 sensor 39 after the high pressure EGR catalyst is lean. At this time t1, the EGR control execution flag is turned ON, and the high pressure EGR is started. That is, the exhaust gas starts to flow into the high pressure EGR catalyst 41 from time t1. Here, it is assumed that the internal combustion engine 10 is operated with a rich air-fuel ratio after fuel increase. Therefore, it is assumed that the exhaust gas flowing into the high pressure EGR catalyst 41 is richer than the stoichiometric air-fuel ratio and lacks oxygen. Oxygen is released from the high-pressure EGR catalyst 41 so as to compensate for this oxygen deficiency. At time t2, the oxygen of the high pressure EGR catalyst 41 becomes empty, and the output of the O 2 sensor 39 after the high pressure EGR catalyst is inverted from lean to rich.

Between time t1 and time t2, the amount of oxygen ΔOSC _HEGR released from the high pressure EGR catalyst 41 per unit period can be calculated in the same manner as in the first embodiment. By integrating this ΔOSC _HEGR from time t1 to time t2, that determine the amount of oxygen released from the high-pressure EGR catalyst 41 during the period from time t1 to time t2 (hereinafter referred to as "oxygen total release") it can.

At time t1, the oxygen in the high-pressure EGR catalyst 41 is not always full. For this reason, the total oxygen release amount described above is not necessarily equal to the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41. However, the oxygen storage capacity OSC _HEGR pressure EGR catalyst 41, at least, can be said to be above oxygen total release more values.

  6 will be further described. At time t3, the fuel cut flag is turned ON, and the fuel cut of the internal combustion engine 10 is started. Therefore, after time t3, air containing no fuel flows into the high-pressure EGR catalyst 41. This inflowing oxygen in the air is absorbed by the high-pressure EGR catalyst 41. At time t4, the EGR control execution flag is turned OFF, and the high pressure EGR is stopped. That is, the flow of gas (air) into the high pressure EGR catalyst 41 is stopped at time t4. At the time t4, the output of the post-high pressure EGR catalyst O 2 sensor 39 has not yet reversed from rich to lean.

  The flow rate of air passing through the high-pressure EGR catalyst 41 during the fuel cut can be calculated based on the intake air amount, the high-pressure EGR valve 44 opening degree, the engine speed, and the like. Then, by integrating the value obtained by multiplying the air flow rate passing through the high pressure EGR catalyst 41 by the oxygen mass ratio in the air from time t3 to time t4, it is absorbed by the high pressure EGR catalyst 41 from time t3 to time t4. The amount of oxygen (hereinafter referred to as “total oxygen absorption”) can be determined.

In the example shown in FIG. 6, at time t4, the output of the post-high pressure EGR catalyst post-O2 sensor 39 has not yet reversed from rich to lean. That is, at time t4, the oxygen in the high pressure EGR catalyst 41 is not always full. Therefore, the total oxygen absorption amount described above is not necessarily equal to the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41. However, it can be said that the oxygen storage capacity OSC _HEGR of the high-pressure EGR catalyst 41 is at least a value equal to or greater than the total oxygen absorption amount described above.

In this embodiment, as described above, the total oxygen release amount is measured when the fuel increase is executed, and the total oxygen absorption amount is measured when the fuel cut is executed. As described above, the oxygen storage capacity OSC _HEGR is at least a value equal to or greater than the total oxygen release amount or the total oxygen absorption amount. Therefore, in this embodiment, the maximum value (hereinafter referred to as “maximum measurement value”) of the total oxygen release amount or the total oxygen absorption amount measured so far is used as the value of the oxygen storage capacity OSC _HEGR. It was. In other words, when the total oxygen release or total oxygen absorption is newly measured, the new measured value is compared with the previous maximum measured value, and the new measured value exceeds the previous maximum measured value. If so, update the maximum measurement. Then, by treating this maximum measured value as the value of the oxygen storage capacity OSC _HEGR , it is possible to determine the catalyst deterioration.

Embodiment 4 FIG.
Next, the fourth embodiment of the present invention will be described with reference to FIG. 7 to FIG. 9. The difference from the above-described embodiment will be mainly described, and the description of the same matters will be simplified. Or omit. The hardware configuration of the present embodiment is the same as that of the first embodiment shown in FIG. 1, but in this embodiment, the deterioration detection of the high-pressure EGR catalyst 41 and the deterioration detection of the low-pressure EGR catalyst 45 are performed. It can be applied to both. Therefore, in the following description, the high pressure EGR and the low pressure EGR are not distinguished from each other, and are simply referred to as “EGR catalyst”, “EGR post-catalyst O 2 sensor”, or the like.

  Depending on the EGR catalyst, components such as manganese in the exhaust gas may adhere and accumulate over time. In particular, components such as manganese are likely to adhere to a portion where the exhaust gas collides near the inlet of the EGR catalyst. If this deposit accumulates, the ventilation resistance of the EGR catalyst increases and the EGR gas may not flow easily. For this reason, in some cases, it is necessary to correct the contents of the engine control or warn the driver to urge repair.

  As described above, the post-EGR catalyst O2 sensor includes a heater for raising the temperature of the sensor element to the activation temperature. When the temperature of the sensor element is lower than the activation temperature, the ECU 50 feedback-controls energization to the heater so that the temperature of the sensor element rises to the activation temperature.

  When the fuel cut is executed in the internal combustion engine 10, air flows into the EGR catalyst, and the O2 sensor is cooled after the EGR catalyst, so that the heater is energized to control the sensor element to be warmed. At this time, the greater the airflow resistance of the EGR catalyst, the smaller the air flow rate passing therethrough, so that the O2 sensor after the EGR catalyst is less likely to be cooled. As a result, the total energization amount to the heater (hereinafter referred to as “heater control amount”) required to raise the temperature of the sensor element to the activation temperature is reduced. Therefore, in this embodiment, the ventilation resistance of the EGR catalyst is determined based on the heater control amount during the fuel cut.

  FIG. 7 is a flowchart of a routine executed by the ECU 50 in order to realize the above function. The routine shown in FIG. 7 is executed when the fuel cut of the internal combustion engine 10 is performed. According to this routine, first, it is determined whether or not it is necessary to perform OBD (On-Board Diagnostic) of the EGR catalyst (step 120). If it is necessary to perform OBD, it is next determined whether the heater control of the O2 sensor after EGR catalyst is performed (step 122). In step 122, the heater control amount of the post-EGR catalyst O2 sensor is acquired.

  Following the processing of step 122, the state of fuel cut execution is determined (step 124). In this step 124, the EGR valve opening, the intake air amount, the engine speed, etc. during the fuel cut are acquired.

  Following the process of step 124, the ventilation resistance of the EGR catalyst is determined (step 126). As the flow rate of air passing through the EGR catalyst increases, the O2 sensor after the EGR catalyst is cooled, so that the heater control amount increases. The ECU 50 stores a map created by examining the relationship between the air flow rate passing through the EGR catalyst and the heater control amount in advance. In step 126, first, an estimated value of the air flow rate passing through the EGR catalyst is calculated based on the EGR valve opening, the intake air amount, the engine speed, etc. acquired in step 124. Next, based on the estimated air flow rate and the map, the heater control amount is calculated backward from the estimated air flow rate. Then, the actual heater control amount acquired in step 122 is compared with the heater control amount calculated backward from the estimated air flow rate. When the actual heater control amount is smaller than the heater control amount calculated backward from the estimated air flow rate, it can be determined that the actual air flow rate is smaller than the estimated air flow rate. The fact that the actual air flow rate is smaller than the estimated air flow rate means that the ventilation resistance of the EGR catalyst is increased. Therefore, it can be determined that the greater the difference between the heater control amount calculated backward from the estimated air flow rate and the actual heater control amount, the greater the airflow resistance of the EGR catalyst and the greater the amount of deposits such as manganese.

  By the way, the exhaust gas path from the internal combustion engine 10 to the high pressure EGR catalyst 41 is shorter than the exhaust gas path from the internal combustion engine 10 to the start catalyst 26. Therefore, if the high pressure EGR is performed when the internal combustion engine 10 is cold, the high pressure EGR catalyst 41 can be warmed up earlier than the start catalyst 26. Therefore, it is possible to reduce tail pipe emissions (emissions released into the atmosphere) by performing high pressure EGR in the cold and purifying the exhaust gas with the high pressure EGR catalyst 41.

  In the exhaust purification apparatus that performs the control as described above, the amount of EGR decreases as the ventilation resistance of the high pressure EGR catalyst 41 increases, so the emission reduction effect cost by the high pressure EGR catalyst 41 decreases. Of course, as the degree of deterioration of the high-pressure EGR catalyst 41 increases, the emission reduction effect cost by the high-pressure EGR catalyst 41 decreases. That is, as the oxygen storage capacity of the high pressure EGR catalyst 41 becomes smaller, the emission reduction effect margin by the high pressure EGR catalyst 41 decreases. FIG. 8 is a map showing the above-described tendency of the emission reduction effect cost due to the high pressure EGR catalyst 41. According to this map, the emission reduction effect margin by the high pressure EGR catalyst 41 can be calculated based on the ventilation resistance of the high pressure EGR catalyst 41 and the oxygen storage capacity of the high pressure EGR catalyst 41. As the emission reduction effect due to the high-pressure EGR catalyst 41 calculated in this way becomes smaller, the tailpipe emission becomes worse.

  Further, the tailpipe emission becomes worse as the degree of deterioration of the start catalyst 26 increases, that is, as the oxygen storage capacity of the start catalyst 26 decreases. FIG. 9 is a map showing the above-described tendency of tailpipe emissions. According to this map, it is possible to determine the degree of deterioration of tail pipe emission due to aging deterioration based on the above-mentioned emission reduction effect cost by the high pressure EGR catalyst 41 and the oxygen storage capacity of the start catalyst 26. As a result, when it is determined that the degree of deterioration of the tail pipe emission exceeds a predetermined threshold value, an abnormality can be notified to the driver by turning on a MIL (Malfunction Indicator Lamp).

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Fuel injector 18 Exhaust passage 20 Exhaust manifold 24 Turbocharger 241 Turbine 242 Compressor 25 O2 sensor 26 after start catalyst 26 Start catalyst 27 Underfloor catalyst 28 Intake passage 34 Intake manifold 36 Throttle valve 38 Air flow meter 39 O2 after high pressure EGR catalyst Sensor 40 High pressure EGR passage 41 High pressure EGR catalyst 42 Low pressure EGR passage 43 High pressure EGR cooler 44 High pressure EGR valve 45 Low pressure EGR catalyst 46 Low pressure EGR cooler 47 Low pressure EGR valve 48 Low pressure EGR catalyst post O2 sensor 50 ECU

Claims (5)

An EGR passage that branches off from the exhaust passage of the internal combustion engine and recirculates part of the exhaust gas to the intake passage;
An EGR catalyst provided in the middle of the EGR passage;
An exhaust gas sensor after the EGR catalyst for detecting an air-fuel ratio of the exhaust gas emitted from the EGR catalyst;
EGR catalyst oxygen storage capacity measuring means for measuring the oxygen storage capacity of the EGR catalyst based on the output of the exhaust gas sensor after the EGR catalyst;
A catalyst deterioration detection device for an internal combustion engine, comprising: An active air-fuel ratio control for forcibly switching the air-fuel ratio of the internal combustion engine alternately between the rich side and the lean side across the theoretical air-fuel ratio when measuring the oxygen storage capacity of the EGR catalyst Control means;
An exhaust purification catalyst provided in the exhaust passage downstream of the location where the EGR passage branches;
The timing at which the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst after the air-fuel ratio of the internal combustion engine is switched by the active air-fuel ratio control is earlier than the timing at which the air-fuel ratio of the exhaust gas flowing out from the EGR catalyst is switched. In the case, active air-fuel ratio control prohibiting means for prohibiting execution of the active air-fuel ratio control,
The catalyst deterioration detection device for an internal combustion engine according to claim 1, comprising: An active air-fuel ratio control for forcibly switching the air-fuel ratio of the internal combustion engine alternately between the rich side and the lean side across the theoretical air-fuel ratio when measuring the oxygen storage capacity of the EGR catalyst Control means;
An exhaust purification catalyst provided in the exhaust passage downstream of the location where the EGR passage branches;
Capacity value storage means for storing the value of the oxygen storage capacity of the EGR catalyst and the value of the oxygen storage capacity of the exhaust purification catalyst;
A gas amount ratio acquisition means for acquiring, as a gas amount ratio, a ratio of an exhaust gas flow rate passing through the EGR catalyst to an exhaust gas flow rate passing through the exhaust purification catalyst;
A value obtained by multiplying the oxygen storage capacity value of the exhaust purification catalyst stored in the capacity value storage means by the gas amount ratio is a value of the oxygen storage capacity of the EGR catalyst stored in the capacity value storage means. When smaller, active air-fuel ratio control prohibiting means for prohibiting execution of the active air-fuel ratio control;
The catalyst deterioration detection device for an internal combustion engine according to claim 1, comprising: A turbocharger having a turbine disposed in the middle of the exhaust passage and a compressor disposed in the middle of the intake passage;
4. The catalyst deterioration detection device for an internal combustion engine according to claim 1, wherein the EGR passage is branched from an exhaust passage on the upstream side of the turbine. A turbocharger having a turbine disposed in the middle of the exhaust passage and a compressor disposed in the middle of the intake passage;
The catalyst deterioration detection device for an internal combustion engine according to any one of claims 1 to 4, wherein the EGR passage is branched from an exhaust passage on the downstream side of the turbine.

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