JP2010112313A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently reduce emission immediately after the start of an internal combustion engine without causing a substantial cost increase in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: The exhaust emission control device of the internal combustion engine comprises an exhaust emission control catalyst which is included in an exhaust system, an EGR passage which connects the exhaust system to an intake system, an EGR valve which adjusts an amount of exhaust gas passing through the EGR passage, an EGR gas purifier which is disposed at some midpoint in the EGR passage and which has a function of adsorbing a harmful component, and an adsorption control means which forces a harmful component to be adsorbed to the EGR gas purifier by opening the EGR valve to circulate exhaust gas in the EGR passage when the exhaust emission control catalyst is determined to be inactive. The adsorption control means continues adsorption by opening the EGR valve until the temperature of the EGR gas purifier reaches a prescribed desorption temperature and completes the adsorption by closing the EGR valve when the temperature of the EGR gas purifier exceeds the desorption temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Immediately after the cold start of the internal combustion engine, the temperature of the engine itself is low, so that the injected fuel is difficult to vaporize. In order to compensate for the insufficient vaporization of the fuel, control is performed so that the air-fuel ratio is higher than the stoichiometric air-fuel ratio. Further, the fuel that could not be vaporized adheres to the inner wall of the intake port in the case of a port injection engine, and adheres to the wall surface in the cylinder in the case of a cylinder injection engine. This wall-attached fuel is vaporized with a delay to further enrich the air-fuel ratio. For this reason, immediately after the start of the engine, the inside of the cylinder is likely to be in excess of fuel (oxygen shortage) compared to after the warm-up is completed. As a result, the amount of HC (hydrocarbon) that is an unburned fuel component tends to be extremely large in the exhaust gas.

  Further, immediately after the engine is started, the temperature of the exhaust purification catalyst is low and the catalyst is not activated. Thus, immediately after the engine is started, the amount of HC discharged from the engine is large and the catalyst cannot sufficiently purify the HC. For this reason, there is a problem that a large amount of HC is easily discharged into the atmosphere immediately after the engine is started.

  Japanese Patent Application Laid-Open No. 2005-264821 discloses a system in which an EGR catalyst is provided in the middle of an EGR passage, and exhaust gas is purified by the EGR catalyst by performing EGR when the internal combustion engine is cold-started.

  However, in the system described in the above publication, HC cannot be sufficiently purified during the period until the temperature of the EGR catalyst rises above the activation temperature. For this reason, this system cannot sufficiently suppress the discharge of HC into the atmosphere immediately after the engine is started.

JP 2005-264821 A

  In order to prevent a large amount of HC from the engine immediately after starting from being discharged into the atmosphere, an adsorbent capable of temporarily adsorbing HC is provided in the exhaust system, and the temperature of the exhaust purification catalyst sufficiently increases. Until now, a technique for capturing HC in the exhaust gas with the adsorbent has been proposed. However, this technique has the following problems.

  As exhaust gas flows through the adsorbent, the temperature of the adsorbent gradually increases. When the temperature of the adsorbent becomes equal to or higher than a predetermined desorption temperature (for example, about 100 ° C.), the adsorbed HC is easily desorbed. On the other hand, the activation temperature of the exhaust purification catalyst is, for example, about 350 ° C., which is greatly different from the desorption temperature of the adsorbent. Therefore, when the temperature of the adsorbent reaches the desorption temperature, the temperature of the exhaust purification catalyst is still considerably lower than the activation temperature. If HC is desorbed from the adsorbent at this point, the HC is discharged into the atmosphere without being purified by the exhaust purification catalyst. Therefore, it is essential to switch the route of the exhaust gas so that the exhaust gas does not flow to the adsorbent before the temperature of the adsorbent reaches the desorption temperature. For this purpose, it is necessary to provide the exhaust system with a bypass passage for allowing the exhaust gas to flow through the adsorbent and a flow path switching valve for switching the flow path of the exhaust gas. For this reason, a significant cost increase is inevitable.

  The present invention has been made in order to solve the above-described problems. The exhaust of an internal combustion engine that can sufficiently reduce the emission immediately after the start of the internal combustion engine and does not significantly increase the cost. An object is to provide a purification device.

In order to achieve the above object, a first invention is an exhaust purification device for an internal combustion engine,
An exhaust purification catalyst provided in the exhaust system of the internal combustion engine;
An EGR passage connecting an exhaust system and an intake system of the internal combustion engine;
An EGR valve that adjusts the amount of exhaust gas passing through the EGR passage;
An EGR gas purifier provided in the middle of the EGR passage and having a function of adsorbing harmful components;
An adsorption control means for adsorbing harmful components to the EGR gas purifier by opening the EGR valve and allowing the exhaust gas to flow through the EGR passage when it is determined that the exhaust purification catalyst is not activated;
It is characterized by providing.

The second invention is the first invention, wherein
The EGR gas purifier is an EGR catalyst having both a function of adsorbing harmful components and a function of purifying the harmful components.

The third invention is the first or second invention, wherein
EGR gas purifier temperature acquisition means for acquiring the temperature of the EGR gas purifier,
The adsorption control means continues the adsorption by opening the EGR valve until the temperature of the EGR gas purifier reaches a predetermined desorption temperature at which harmful components easily desorb, and the temperature of the EGR gas purifier When the temperature exceeds the desorption temperature, the adsorption is terminated by closing the EGR valve.

According to a fourth invention, in any one of the first to third inventions,
EGR gas purifier temperature acquisition means for acquiring the temperature of the EGR gas purifier,
Blow-through determination means for determining whether blow-in of the intake gas to the exhaust passage occurs when the valve overlap of the intake valve and the exhaust valve of the internal combustion engine is open,
When it is determined that the blow-in of intake gas is generated by the blow-off determination means and the temperature of the EGR gas purifier is lower than a predetermined desorption temperature at which harmful components are easily desorbed, the EGR valve is opened to exhaust the exhaust gas. Blow-through gas adsorbing means for adsorbing harmful components to the EGR gas purifier by flowing gas through the EGR passage;
It is characterized by providing.

According to a fifth invention, in any one of the first to fourth inventions,
The adsorption control means causes the EGR gas purifier to adsorb harmful components during idling after the internal combustion engine is started.

According to a sixth invention, in any one of the first to fourth inventions,
The adsorption control means causes the EGR gas purifier to adsorb harmful components during the first acceleration after the internal combustion engine is started.

According to a seventh invention, in any one of the first to sixth inventions,
A second EGR passage connecting the exhaust system and the intake system of the internal combustion engine;
A second EGR valve for adjusting the amount of exhaust gas passing through the second EGR passage;
A second EGR gas purifier provided in the middle of the second EGR passage and having a function of adsorbing harmful components;
When it is determined that the exhaust purification catalyst is not activated, the second EGR valve is opened to allow exhaust gas to flow through the second EGR passage, thereby removing harmful components from the second EGR gas purification. Second adsorption control means for adsorbing the container;
With
The adsorption control unit and the second adsorption control unit execute adsorption at different times.

  According to the first invention, when it is determined that the exhaust gas purification catalyst of the internal combustion engine is not activated, the EGR valve is opened and the exhaust gas is circulated through the EGR passage, whereby harmful components are supplied to the EGR gas purifier. Can be adsorbed. Thereby, when the temperature of the exhaust purification catalyst is not sufficiently increased (such as immediately after the cold start), it is possible to reliably reduce the discharge amount of harmful components to the atmosphere. Further, according to the first invention, the start and stop of the adsorption can be switched using the existing EGR passage and the EGR valve. For this reason, in the first invention, unlike the case where harmful components are adsorbed by the adsorbent provided in the exhaust system, there is no need to newly install a bypass passage or a flow path switching valve in the exhaust system. Therefore, it is possible to suppress an increase in manufacturing cost, and it is possible to prevent the system from becoming complicated and large.

  According to the second invention, an EGR catalyst having both a function of adsorbing harmful components and a function of purifying and reacting harmful components can be used as an EGR gas purifier. As a result, deposit accumulation in the EGR passage can be prevented and soot in the exhaust gas can be reduced.

  According to the third invention, the adsorption is continued by opening the EGR valve until the temperature of the EGR gas purifier reaches the desorption temperature, and when the temperature of the EGR gas purifier exceeds the desorption temperature, the EGR is Adsorption can be terminated by closing the valve. Thereby, it can prevent more reliably that the harmful component once adsorbed to the EGR gas purifier is desorbed. For this reason, the discharge | emission amount of the harmful | toxic component to air | atmosphere can further be reduced.

  According to the fourth invention, when it is determined that the blow-in of the intake gas occurs and the temperature of the EGR gas purifier is lower than the desorption temperature, the exhaust gas is circulated through the EGR passage by opening the EGR valve. , Harmful components can be adsorbed to the EGR gas purifier. Thereby, when the valve overlap is lengthened during high load operation, harmful components flowing into the exhaust port by riding in the intake gas can be adsorbed to the EGR gas purifier. For this reason, the discharge | emission amount of the harmful | toxic component to air | atmosphere can further be reduced.

  According to the fifth aspect of the present invention, it is possible to sufficiently reduce the amount of harmful components discharged into the atmosphere during idling after the internal combustion engine is started.

  According to the sixth aspect of the invention, it is possible to sufficiently reduce the amount of harmful component discharged into the atmosphere during the first acceleration after the internal combustion engine is started.

  According to the seventh invention, in a system including two EGR passages, harmful components can be adsorbed to two EGR gas purifiers at different times. Thereby, the harmful component discharge | release amount to air | atmosphere can be fully reduced in the both periods. For this reason, the harmful component discharge | release amount to air | atmosphere as the whole can be reduced more reliably.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

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 an internal combustion engine 10. The internal combustion engine 10 is mounted on a vehicle or the like and used as a power source. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  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.

  An exhaust purification catalyst 26 that purifies harmful components in the exhaust gas is installed in the exhaust passage 18 on the downstream side of the turbine 241.

  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 fresh air that has passed through the intercooler 32 passes through the intake manifold 34 and flows into each cylinder. A throttle valve 36 is provided between the intercooler 32 and the intake manifold 34.

  The internal combustion engine 10 includes an apparatus for performing EGR (Exhaust Gas Recirculation) for recirculating a part of the exhaust gas to the intake passage 28. In particular, the internal combustion engine 10 of this embodiment includes two EGR devices. That is, the internal combustion engine 10 of the present embodiment includes a high pressure EGR passage 40 for performing high pressure EGR and a low pressure EGR passage 42 for performing low pressure EGR.

  The high-pressure EGR passage 40 connects the exhaust system upstream of the turbine 241 (the exhaust manifold 20 in the configuration of FIG. 1) and the intake passage 28 downstream of the intercooler 32. In the middle of the high pressure EGR passage 40, a high pressure EGR catalyst 41, a high pressure EGR cooler 43, and a high pressure EGR valve 44 are provided in this order from the exhaust manifold 20 side.

  The low pressure EGR passage 42 connects the exhaust passage 18 downstream of the exhaust purification catalyst 26 and the intake passage 28 upstream of the compressor 242. In the middle of the low pressure EGR passage 42, a low pressure EGR catalyst 45, a low pressure EGR cooler 46, and a low pressure EGR valve 47 are provided in this order from the exhaust passage 18 side.

  Both the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 have a function of adsorbing harmful components (especially HC) in addition to a function of purifying harmful components in the recirculated exhaust gas (hereinafter also referred to as “EGR gas”). Have. As such a high pressure EGR catalyst 41 and a low pressure EGR catalyst 45, for example, an adsorbent layer containing zeolite or the like and a catalyst layer containing a noble metal can be laminated on the surface of the carrier.

  FIG. 2 is a view showing a cross section of one cylinder of the internal combustion engine 10 shown in FIG. Hereinafter, the internal combustion engine 10 will be further described. As shown in FIG. 2, a crank angle sensor 62 that detects a rotation angle (crank angle) of the crankshaft 60 is attached in the vicinity of the crankshaft 60 of the internal combustion engine 10.

  Further, the internal combustion engine 10 has an intake variable valve operating device 54 that makes at least the closing timing variable among the valve opening characteristics of the intake valve 52, and an exhaust that makes at least the opening timing variable among the valve opening characteristics of the exhaust valve 56. And a variable valve operating device 58. Specific configurations of the intake variable valve operating device 54 and the exhaust variable valve operating device 58 are not particularly limited, and can be realized by various known mechanisms.

  In the present embodiment, the intake variable valve operating device 54 and the exhaust variable valve operating device 58 may be omitted. That is, in this embodiment, the valve opening characteristics of the intake valve 52 and the exhaust valve 56 may be fixed.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50. In addition to the various sensors and actuators described above, the ECU 50 includes an accelerator opening sensor 48 that detects the position of the accelerator pedal (accelerator opening) provided in the driver's seat of the vehicle, and a vehicle speed sensor 49 that detects the vehicle speed. 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.

  In the system of the present embodiment, when executing EGR, the high pressure EGR and the low pressure EGR are switched according to the operation state (load, engine speed, etc.) of the internal combustion engine 10. As a general rule, high-pressure EGR is performed in the operation region on the low load side. In the operating region on the low load side where the fuel injection amount is small, the in-cylinder temperature tends to be low, so HC in the exhaust gas tends to increase. In this case, if high pressure EGR is executed, HC can be reduced. That is, in the high pressure EGR, the high-temperature exhaust gas upstream of the turbine 241 returns to the intake system as EGR gas. As a result, the in-cylinder temperature can be sufficiently increased, so that HC in the exhaust gas can be reduced.

  On the other hand, in the operating region on the high load side, as a rule, low pressure EGR is executed. In the operating region on the high load side where the fuel injection amount is large, the in-cylinder temperature (combustion temperature) tends to be high, and therefore NOx in the exhaust gas tends to increase. In this case, the combustion temperature can be sufficiently lowered by executing the low pressure EGR, so that NOx can be reduced.

  Further, in the medium load region, both high pressure EGR and low pressure EGR may be executed.

  When the temperature of the high-pressure EGR catalyst 41 and the low-pressure EGR catalyst 45 is higher than the activation temperature, harmful components such as HC in the EGR gas can be purified. For this reason, in the present embodiment, deposits can be prevented from being accumulated in the EGR passage, and soot in the exhaust gas can be reduced.

  Further, the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 can adsorb HC when the temperature is low. However, when the temperature exceeds the desorption temperature (for example, about 100 ° C.), the adsorbed HC is desorbed.

  Immediately after the cold start of the internal combustion engine 10, the amount of HC discharged from the internal combustion engine 10 is larger than after the warm-up is completed, and the exhaust purification catalyst 26 is not yet activated. For this reason, there is a problem that the amount of HC emission to the atmosphere tends to increase. In order to solve this problem, in the present embodiment, when the exhaust purification catalyst 26 has not reached the activation temperature, the high pressure EGR or the low pressure EGR is executed by opening the high pressure EGR valve 44 or the low pressure EGR valve 47. . When the high pressure EGR or the low pressure EGR is executed, HC in the exhaust gas can be adsorbed by the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45. Therefore, the amount of HC discharged into the atmosphere can be reduced.

  As described above, when the temperature of the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 exceeds the desorption temperature, the adsorbed HC is desorbed. When the temperatures of the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 exceed the desorption temperature, the temperature of the exhaust purification catalyst 26 has not yet risen to the activation temperature. For this reason, if HC is desorbed at this time, HC will be discharged into the atmosphere. Therefore, in the present embodiment, when adsorption of HC to the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45 is executed, the high pressure EGR valve 44 or the low pressure EGR valve 47 is closed when the temperature reaches the desorption temperature. To end the adsorption. Thereby, it is possible to reliably prevent the temperature of the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45 from rising beyond the desorption temperature when performing adsorption. For this reason, it is possible to more reliably prevent the once adsorbed HC from being desorbed.

  FIG. 3 is a graph showing the vehicle speed of a vehicle equipped with the internal combustion engine 10 and the amount of HC emission into the atmosphere. The time on the horizontal axis indicates the elapsed time from the cold start of the internal combustion engine 10. In FIG. 3, the graph of the HC emission amount indicated by a solid line shows the case of the comparative example. As shown in this figure, generally speaking, the amount of HC emission to the atmosphere tends to increase when the internal combustion engine 10 is idling after starting and when the internal combustion engine 10 is started to start the vehicle. Is when the first acceleration is performed. According to the present embodiment, the amount of HC discharged into the atmosphere can be greatly reduced by adsorbing HC to the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45 at these times. In addition, the graph of HC discharge | emission amount shown with a broken line in FIG. 3 shows the case of this embodiment.

  In the present embodiment, HC is adsorbed by the high pressure EGR catalyst 41 during idling, and HC is adsorbed by the low pressure EGR catalyst 45 during the first acceleration. As described above, when the temperature of the EGR catalyst reaches the desorption temperature, it is necessary to end the adsorption. For this reason, it is difficult to adsorb both HC at the time of idling and at the time of the first acceleration to one EGR catalyst. On the other hand, in the present embodiment, the HC at the time of idling and the HC at the time of the first acceleration can be adsorbed by using two EGR catalysts of the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45, respectively. For this reason, the amount of HC emissions into the atmosphere can be further reduced.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to the routine shown in FIG. 4, it is first determined whether or not the temperature of the exhaust purification catalyst 26 is lower than the activation temperature (step 100). The ECU 50 can calculate the estimated temperature of the exhaust purification catalyst 26 based on the history of the engine speed, the fuel injection amount, the exhaust gas flow rate and the like since the start of the internal combustion engine 10. In step 100, the calculated estimated temperature is compared with a predetermined activation temperature (for example, 350 ° C.). The exhaust gas flow rate can be calculated based on the intake air amount detected by the air flow meter 38.

  In the present invention, the method for obtaining the temperature of the exhaust purification catalyst 26 is not limited to the above method. For example, a temperature sensor that detects the exhaust gas temperature at the inlet or outlet of the exhaust purification catalyst 26 may be provided, and the temperature of the exhaust purification catalyst 26 may be calculated based on the output of the temperature sensor. Further, a temperature sensor for detecting the bed temperature of the exhaust purification catalyst 26 may be provided to directly detect the temperature of the exhaust purification catalyst 26.

  If it is determined in step 100 that the temperature of the exhaust purification catalyst 26 is equal to or higher than the activation temperature, it can be determined that the exhaust purification catalyst 26 can sufficiently remove harmful components such as HC. In this case, it is not necessary to adsorb HC to the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45. Therefore, in this case, normal EGR control is executed (step 102). That is, the opening degree of the high pressure EGR valve 44 and the low pressure EGR valve 47 is controlled according to the engine speed and the engine load according to a predetermined EGR map.

  On the other hand, if it is determined in step 100 that the temperature of the exhaust purification catalyst 26 is lower than the activation temperature, the exhaust purification catalyst 26 cannot sufficiently purify harmful components such as HC, so that HC adsorption is executed. It can be judged that it is necessary. In this case, it is next determined whether or not the internal combustion engine 10 is in an idle state based on the engine speed or the vehicle speed (step 104).

  As described above, in the present embodiment, HC is adsorbed by the high-pressure EGR catalyst 41 when the internal combustion engine 10 is idle. Therefore, if it is determined in step 104 that the internal combustion engine 10 is in an idle state, it is next determined whether or not the temperature of the high pressure EGR catalyst 41 is lower than a predetermined desorption temperature (for example, 100 ° C.). (Step 106). The ECU 50 can calculate the estimated temperature of the high pressure EGR catalyst 41 based on the history of the engine speed, the fuel injection amount, the opening degree of the high pressure EGR valve 44, the exhaust gas flow rate, etc. from the start of the high pressure EGR. In step 106, the calculated estimated temperature is compared with the desorption temperature. In the present invention, the method for acquiring the temperature of the high-pressure EGR catalyst 41 is not limited to the above method. For example, a temperature sensor for detecting the EGR gas temperature at the inlet or outlet of the high pressure EGR catalyst 41 may be provided, and the temperature of the high pressure EGR catalyst 41 may be calculated based on the output of the temperature sensor. Further, a temperature sensor that detects the bed temperature of the high-pressure EGR catalyst 41 may be provided, and the temperature of the high-pressure EGR catalyst 41 may be directly detected.

  If it is determined in step 106 that the temperature of the high pressure EGR catalyst 41 is lower than the desorption temperature, it can be determined that HC can be adsorbed by the high pressure EGR catalyst 41. Therefore, in this case, a process for adsorbing HC to the high-pressure EGR catalyst 41 is performed by opening the high-pressure EGR valve 44 and allowing the exhaust gas to flow through the high-pressure EGR passage 40 (step 108). In this step 108, the opening degree of the high pressure EGR valve 44 is calculated based on a predetermined map so that the opening degree is the maximum within a range where the required engine speed or engine torque can be exhibited.

  According to the processing of step 108, as shown by the broken line in the HC emission amount graph of FIG. 3, the HC emission amount to the atmosphere during idling after the internal combustion engine 10 is started can be greatly reduced. it can.

  When the high pressure EGR is started in step 108, the temperature of the high pressure EGR catalyst 41 increases. If it is determined in step 106 that the temperature of the high pressure EGR catalyst 41 has reached the desorption temperature, it can be determined that HC will desorb from the high pressure EGR catalyst 41 if the high pressure EGR is continued further. Therefore, in this case, the adsorption of HC to the high pressure EGR catalyst 41 is stopped by closing the high pressure EGR valve 44.

  On the other hand, if it is determined in step 104 that the internal combustion engine 10 is not in the idle state, then whether or not the internal combustion engine 10 is in the first acceleration state after the start is determined based on the engine speed or the vehicle speed. A determination is made based on this (step 112).

  As described above, in this embodiment, HC is adsorbed by the low pressure EGR catalyst 45 during the first acceleration of the internal combustion engine 10. Therefore, if it is determined in step 112 that the internal combustion engine 10 is in the first acceleration state, then whether or not the temperature of the low pressure EGR catalyst 45 is lower than a predetermined desorption temperature (for example, 100 ° C.). Is determined (step 114). The ECU 50 can calculate the estimated temperature of the low pressure EGR catalyst 45 based on the history of the engine speed, the fuel injection amount, the opening of the low pressure EGR valve 47, the exhaust gas flow rate, and the like from the start of the low pressure EGR. In step 114, the calculated estimated temperature is compared with the desorption temperature. In the present invention, the method for obtaining the temperature of the low pressure EGR catalyst 45 is not limited to the above method. For example, a temperature sensor that detects the EGR gas temperature at the inlet or outlet of the low pressure EGR catalyst 45 may be provided, and the temperature of the low pressure EGR catalyst 45 may be calculated based on the output of the temperature sensor. Further, a temperature sensor for detecting the bed temperature of the low pressure EGR catalyst 45 may be provided, and the temperature of the low pressure EGR catalyst 45 may be directly detected.

  If it is determined in step 114 that the temperature of the low pressure EGR catalyst 45 is lower than the desorption temperature, it can be determined that HC can be adsorbed by the low pressure EGR catalyst 45. Therefore, in this case, a process for adsorbing HC to the low pressure EGR catalyst 45 is performed by opening the low pressure EGR valve 47 and allowing the exhaust gas to flow through the low pressure EGR passage 42 (step 116). In this step 116, the opening degree of the low pressure EGR valve 47 is calculated based on a predetermined map so as to be the maximum opening degree within a range where the required engine speed or engine torque can be exhibited.

  According to the processing in step 116, as shown by the broken line in the HC emission amount graph of FIG. 3, the HC emission amount to the atmosphere during the first acceleration after the start of the internal combustion engine 10 is significantly reduced. be able to.

  When the low pressure EGR is started by the process of step 116, the temperature of the low pressure EGR catalyst 45 rises. If it is determined in step 114 that the temperature of the low pressure EGR catalyst 45 has reached the desorption temperature, it can be determined that HC will desorb from the low pressure EGR catalyst 45 if the low pressure EGR is continued further. Therefore, in this case, the adsorption of HC to the low pressure EGR catalyst 45 is stopped by closing the low pressure EGR valve 47.

  After the adsorption of HC to the high-pressure EGR catalyst 41 and the low-pressure EGR catalyst 45 is finished, when the vehicle continues to travel, the temperature of the exhaust purification catalyst 26 rises and eventually becomes higher than the activation temperature. When the temperature of the exhaust purification catalyst 26 becomes equal to or higher than the activation temperature, normal EGR control is started by the processing in step 102 described above. In this normal EGR control, when high pressure EGR or low pressure EGR is executed, the temperature of the high pressure EGR catalyst 41 or the low pressure EGR catalyst 45 rises above the desorption temperature. For this reason, HC adsorbed by the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 is desorbed. Therefore, at the next start, HC can be adsorbed again by the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45. The HC desorbed from the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 is recirculated into the cylinder of the internal combustion engine 10 and burned. For this reason, since the desorbed HC becomes a part of the output of the internal combustion engine 10, an effect of improving fuel consumption can be obtained.

  According to the routine processing shown in FIG. 4 described above, the amount of HC emissions into the atmosphere immediately after the internal combustion engine 10 is started can be sufficiently reduced. In particular, in the present embodiment, the HC during idling after start-up is adsorbed by the high-pressure EGR catalyst 41, and the HC during the first acceleration is adsorbed by the low-pressure EGR catalyst 45. Both the HC emission amount during the first acceleration can be sufficiently reduced. In contrast to the present embodiment, the HC during idling after start-up may be adsorbed by the low-pressure EGR catalyst 45 and the HC during the first acceleration may be adsorbed by the high-pressure EGR catalyst 41.

  As described above, in the present embodiment, the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 are adsorbed at different times. However, in the present invention, the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 are simultaneously You may make it perform adsorption | suction.

  According to the present invention, the HC adsorption start and adsorption stop can be switched using the existing EGR passage and EGR valve. Therefore, in the present invention, unlike the case where HC is adsorbed by the adsorbent provided in the exhaust system, it is not necessary to newly install a bypass passage and a flow path switching valve in the exhaust system. Therefore, it is possible to prevent an increase in manufacturing cost and complexity / enlargement of the system.

  In the first embodiment described above, the high pressure EGR passage 40 is provided in the “EGR passage” in the first invention, the high pressure EGR valve 44 is provided in the “EGR valve” in the first invention, and the high pressure EGR catalyst 41 is provided in the first invention. In the “EGR gas purifier” in the first invention, the low pressure EGR passage 42 is in the “second EGR passage” in the seventh invention, and the low pressure EGR valve 47 is in the “second EGR passage” in the seventh invention. The low-pressure EGR catalyst 45 corresponds to the “second EGR gas purifier” in the seventh aspect of the invention. Further, when the ECU 50 executes the processing of the steps 100 to 110, the “adsorption control means” in the first invention executes the processing of the step 106, whereby the “EGR gas purification” in the third invention is executed. The “second temperature control means” in the seventh aspect of the present invention is realized by executing the processing of the above steps 112 to 118 by the “temperature acquisition means”.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit. The hardware configuration of this embodiment is the same as that of the first embodiment described above. This embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG.

  In the internal combustion engine 10 of this embodiment, the intake valve 52 is opened by delaying the closing timing of the intake valve 52 by the intake variable valve operating device 54 and by opening the exhaust valve 56 by the exhaust variable valve operating device 58 earlier. An overlap between the valve period and the valve opening period of the exhaust valve 56 can be provided. This overlap is called valve overlap. That is, during the valve overlap period, both the intake valve 52 and the exhaust valve 56 are open. The ECU 50 controls the intake variable valve operating device 54 and the exhaust variable valve operating device 58 so that the valve overlap becomes longer during high load operation. Thereby, volumetric efficiency can be improved.

  However, when the valve overlap is lengthened during high load operation, there are the following problems. Since the internal combustion engine 10 of the present embodiment includes the turbocharger 24, the intake pressure (supercharging pressure) may be higher than the exhaust pressure. For this reason, in the valve overlap state, the intake gas flowing into the cylinder from the intake port is likely to blow through to the exhaust port as it is (hereinafter simply referred to as “blow-through”). When blow-through occurs, unburned HC generated by volatilization of the fuel adhering to the inner wall surface of the cylinder (in the case of a port injection engine, the intake port) rides on the blow-through and goes directly to the exhaust port. It will be discharged. If it does so, there exists a possibility that the exhaust purification catalyst 26 may not fully purify HC, and HC will be discharged | emitted in air | atmosphere.

  In the present embodiment, in order to prevent the discharge of HC accompanying the blow-through, the HC is adsorbed on the EGR catalyst when the temperature of the EGR catalyst is lower than the desorption temperature under the operating conditions in which the blow-through occurs. In this case, in this embodiment, HC may be adsorbed by the high pressure EGR catalyst 41, HC may be adsorbed by the low pressure EGR catalyst 45, or both of the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 have HC. May be adsorbed. Therefore, in the following description, the high pressure EGR catalyst 41 and the low pressure EGR catalyst 45 are collectively referred to as an EGR catalyst, and the high pressure EGR valve 44 and the low pressure EGR valve 47 are collectively referred to as an EGR valve.

[Specific Processing in Second Embodiment]
FIG. 5 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. According to the routine shown in FIG. 5, it is first determined whether or not the operating condition is that a blow-through occurs (step 130). In this step 130, for example, the length of the valve overlap is calculated by detecting the current state of the variable intake valve device 54 and the variable exhaust valve device 58, and the length of the valve overlap is larger than a predetermined value. In the case, it is determined that a blow-through occurs.

  If it is determined in step 130 that no blow-through occurs, it is not necessary to adsorb HC on the EGR catalyst. Therefore, in this case, normal EGR control is executed (step 132). On the other hand, if it is determined in step 130 that blow-through occurs, it is next determined whether or not the temperature of the EGR catalyst is lower than the desorption temperature (step 134). If it is determined in step 134 that the temperature of the EGR catalyst is equal to or higher than the desorption temperature, HC cannot be adsorbed on the EGR catalyst. Therefore, in this case, normal EGR control is executed (step 132).

  On the other hand, if it is determined in step 134 that the temperature of the EGR catalyst is lower than the desorption temperature, HC can be adsorbed on the EGR catalyst. Therefore, in this case, a process for adsorbing HC on the EGR catalyst is performed by opening the EGR valve and allowing the exhaust gas to flow through the EGR catalyst (step 136). In this step 136, the opening degree of the EGR valve is calculated based on a predetermined map so as to be the maximum opening degree within a range where the required engine speed or engine torque can be exhibited.

  According to the processing of the routine shown in FIG. 5 described above, when blow-through occurs due to valve overlap during high-load operation, unburned HC that has flowed into the exhaust system through this blow-through is adsorbed to the EGR catalyst. Can do. For this reason, it can suppress reliably that HC is discharged | emitted in air | atmosphere at the time of high load driving | operation.

  In this embodiment, after the HC is adsorbed on the EGR catalyst, the EGR valve may be controlled to be closed (that is, EGR is prohibited) until the operation under the condition that the blow-through occurs is completed. FIG. 6 is a flowchart of a routine that the ECU 50 executes when performing such control. In FIG. 6, the same steps as those shown in FIG. 5 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 6, step 138 is added compared to the routine shown in FIG. When exhaust gas is circulated through the EGR catalyst to adsorb HC, the temperature of the EGR catalyst rises. For this reason, the temperature of the EGR catalyst eventually reaches the desorption temperature. According to the routine shown in FIG. 6, when it is determined in step 134 that the temperature of the EGR catalyst has reached the desorption temperature, a process for stopping EGR by closing the EGR valve is executed (step 138). ). This prevents the temperature of the EGR catalyst from rising above the desorption temperature, thereby avoiding HC desorption from the EGR catalyst. Thereafter, according to the routine shown in FIG. 6, when it is determined in step 130 that the operation under the condition that the blow-through occurs is completed, normal EGR control is started (step 132). In this normal EGR control, the exhaust gas flows through the EGR catalyst that has previously adsorbed HC, so that the temperature of the EGR catalyst rises above the desorption temperature. As a result, HC is desorbed from the EGR catalyst, and the desorbed HC is refluxed into the cylinder. At this time, the operation of the internal combustion engine 10 has been completed under conditions where blow-by occurs. For this reason, it is possible to reliably prevent HC desorbed from the EGR catalyst and refluxed into the cylinder from being blown again into the exhaust port.

  In the second embodiment described above, the ECU 50 executes the process of step 130, so that the “blow-through determination means” in the fourth aspect of the invention executes the processes of steps 134 and 136. Each of the “blow-by gas adsorbing means” in the present invention is realized.

  As mentioned above, although each embodiment of this invention was described, this invention is not limited to each embodiment mentioned above. In the above-described embodiment, the internal combustion engine having two EGR paths of high pressure EGR and low pressure EGR has been described as an example. However, the present invention is an internal combustion engine having only one of high pressure EGR and low pressure EGR. It is also applicable to. The present invention is also applicable to an internal combustion engine that does not include a turbocharger.

  In the above-described embodiment, the EGR catalyst having the function of adsorbing the harmful component and the function of purifying the harmful component in the EGR passage has been described as an example. The adsorbent that adsorbs and the catalyst that purifies and reacts harmful components may be installed separately in the EGR passage. In the present invention, only the adsorbent may be installed in the EGR passage as an EGR gas purifier. That is, in the present invention, the catalyst may not be provided in the EGR passage.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the internal combustion engine shown in FIG. It is a graph which shows the vehicle speed of the vehicle carrying an internal combustion engine, and HC discharge | emission amount to air | atmosphere. 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 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Fuel injector 18 Exhaust passage 20 Exhaust manifold 24 Turbocharger 241 Turbine 242 Compressor 26 Exhaust purification catalyst 28 Intake passage 34 Intake manifold 36 First intake throttle valve 38 Air flow meter 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 50 ECU
52 Intake valve 54 Intake variable valve operating device 56 Exhaust valve 58 Exhaust variable valve operating device 62 Crank angle sensor 64 Piston

Claims (7)

An exhaust purification catalyst provided in the exhaust system of the internal combustion engine;
An EGR passage connecting an exhaust system and an intake system of the internal combustion engine;
An EGR valve that adjusts the amount of exhaust gas passing through the EGR passage;
An EGR gas purifier provided in the middle of the EGR passage and having a function of adsorbing harmful components;
An adsorption control means for adsorbing harmful components to the EGR gas purifier by opening the EGR valve and allowing the exhaust gas to flow through the EGR passage when it is determined that the exhaust purification catalyst is not activated;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the EGR gas purifier is an EGR catalyst having a function of adsorbing harmful components and a function of purifying and reacting harmful components. EGR gas purifier temperature acquisition means for acquiring the temperature of the EGR gas purifier,
The adsorption control means continues the adsorption by opening the EGR valve until the temperature of the EGR gas purifier reaches a predetermined desorption temperature at which harmful components easily desorb, and the temperature of the EGR gas purifier The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein when the temperature exceeds the desorption temperature, the adsorption is terminated by closing the EGR valve. EGR gas purifier temperature acquisition means for acquiring the temperature of the EGR gas purifier,
Blow-through determination means for determining whether blow-in of the intake gas to the exhaust passage occurs when the valve overlap of the intake valve and the exhaust valve of the internal combustion engine is open,
When it is determined that the blow-in of intake gas is generated by the blow-off determination means and the temperature of the EGR gas purifier is lower than a predetermined desorption temperature at which harmful components are easily desorbed, the EGR valve is opened to exhaust the exhaust gas. Blow-through gas adsorbing means for adsorbing harmful components to the EGR gas purifier by flowing gas through the EGR passage;
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, further comprising:   The exhaust purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the adsorption control means adsorbs harmful components to the EGR gas purifier during idling after the internal combustion engine is started. .   The internal combustion engine according to any one of claims 1 to 4, wherein the adsorption control means adsorbs harmful components to the EGR gas purifier during the first acceleration after the internal combustion engine is started. Exhaust purification equipment. A second EGR passage connecting the exhaust system and the intake system of the internal combustion engine;
A second EGR valve for adjusting the amount of exhaust gas passing through the second EGR passage;
A second EGR gas purifier provided in the middle of the second EGR passage and having a function of adsorbing harmful components;
When it is determined that the exhaust purification catalyst is not activated, the second EGR valve is opened to allow exhaust gas to flow through the second EGR passage, thereby removing harmful components from the second EGR gas purification. Second adsorption control means for adsorbing the container;
With
The exhaust purification device for an internal combustion engine according to any one of claims 1 to 6, wherein the adsorption control means and the second adsorption control means execute adsorption at different times.

Images