JP2008008206A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of completing warming up for an exhaust emission control catalyst for a shorter period of time. <P>SOLUTION: This exhaust gas recirculation device is provided with an oxidation catalyst 12 arranged in an exhaust pipe 4 on the downstream side of the turbine of a turbocharger 5, an exhaust gas throttle valve 19 provided in an exhaust pipe 4 arranged further downstream from the oxidation catalyst 12, a low pressure EGR (exhaust gas recirculation) passage 31 connecting the exhaust pipe 4 arranged further downstream from the exhaust gas throttle valve 19 and an intake pipe 3 on the upstream side of the compressor of the turbocharger 5, a low pressure EGR valve 32 arranged in the low pressure EGR passage 31, catalyst temperature detection means (18, 20, S104) detecting the temperature of the oxidation catalyst 12, and catalyst warming up means (20, S105, S106, S107) comparing the detected temperature with a case that the detected temperature is not lower than a predetermined temperature when temperature detected by the catalyst temperature detection means is lower than the predetermined temperature, controlling the exhaust gas throttle valve 19 in a valve closing direction, and controlling the low pressure EGR valve 32 in a valve opening direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  As a technique for reducing the amount of NOx contained in the exhaust gas from the internal combustion engine, an EGR passage that connects the exhaust manifold and the intake manifold of the internal combustion engine is provided, and a part of the exhaust gas from the internal combustion engine is subjected to the internal combustion through the EGR passage. A technique for recirculation to a combustion chamber of an engine is known (see, for example, Patent Document 1).

In addition, an exhaust purification catalyst such as an oxidation catalyst that oxidizes unburned fuel such as hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas to change it into water, carbon dioxide, etc. is disposed in the middle of the exhaust passage. Thus, a technology for purifying exhaust gas discharged into the atmosphere is known.
JP 2004-150319 A JP 2003-269202 A JP 2003-343287 A Japanese Utility Model Publication No. 5-61444

  By the way, when the temperature of the exhaust purification catalyst is low, the exhaust purification catalyst is in an inactive state, and the exhaust purification action cannot be suitably exhibited. In such a case, unburned fuel or the like flowing into the exhaust purification catalyst passes through the exhaust purification catalyst as it is without being oxidized by the exhaust purification catalyst, and is discharged into the atmosphere as white smoke. In particular, when the temperature of the exhaust purification catalyst is low, such as when the internal combustion engine is cold started, the exhaust purification catalyst is warmed up and activated as soon as possible in order to suppress the deterioration of exhaust emission. It is necessary to make it into a state.

  An object of the present invention is to provide a technique that makes it possible to complete the warm-up of the catalyst in a shorter time.

In order to achieve the above object, an exhaust gas recirculation device for an internal combustion engine of the present invention comprises:
A turbocharger having a turbine in the exhaust passage of the internal combustion engine and a compressor in the intake passage;
An exhaust purification catalyst provided in an exhaust passage downstream from the turbine;
An exhaust throttle valve that is provided in an exhaust passage downstream from the exhaust purification catalyst and changes a flow passage cross-sectional area of the exhaust passage;
A low pressure EGR passage connecting an exhaust passage downstream from the exhaust purification catalyst and an intake passage upstream from the compressor;
A low pressure EGR valve that is provided in the low pressure EGR passage and changes a cross-sectional area of the low pressure EGR passage;
Catalyst temperature detecting means for detecting the temperature of the exhaust purification catalyst;
When the temperature detected by the catalyst temperature detecting means is lower than a predetermined temperature, the exhaust throttle valve is closed in a valve closing direction as compared with the case where the detected temperature is not lower than the predetermined temperature. And a catalyst warm-up means for controlling the low-pressure EGR valve in the valve opening direction.
It is characterized by providing.

Here, the predetermined temperature is a temperature at which the exhaust purification catalyst is sufficiently activated to exhibit an exhaust purification action, and is determined in advance. The catalyst temperature detecting means may be a sensor that directly measures the temperature of the exhaust purification catalyst, or the exhaust temperature, the temperature and flow rate of the intake air, and the exhaust gas that is recirculated to the intake passage through the low pressure EGR passage. The temperature of the exhaust purification catalyst may be estimated based on the operation state of the internal combustion engine such as the flow rate or the operation history of the internal combustion engine.

  According to the above configuration, when the temperature of the exhaust purification catalyst is low and the exhaust purification catalyst is not activated, the exhaust throttle valve is controlled in the valve closing direction and lower pressure EGR than when the exhaust purification catalyst is activated. The valve is controlled in the valve opening direction. By controlling the exhaust throttle valve in the valve closing direction, the back pressure in the exhaust passage upstream from the exhaust throttle valve increases. As a result, the load on the internal combustion engine increases and the fuel injection amount increases, so the temperature of the exhaust from the internal combustion engine rises. Further, the back pressure in the exhaust passage upstream of the exhaust throttle valve increases, so that the amount of exhaust remaining in the cylinder in the exhaust stroke increases. Therefore, the intake air mixed with the high-temperature burned gas is used for combustion, and the temperature of the exhaust gas from the internal combustion engine rises. Further, by controlling the low pressure EGR valve in the valve opening direction, a part of the exhaust gas from the internal combustion engine recirculates in the intake passage through the low pressure EGR passage. As a result, the temperature of the intake air rises and the temperature of the exhaust gas from the internal combustion engine rises. In this way, the temperature of the exhaust purification catalyst is raised by the exhaust gas that has become high in temperature, so that the exhaust purification catalyst can be rapidly activated.

  In the present invention, the exhaust gas recirculated to the intake passage through the low pressure EGR passage (hereinafter referred to as the low pressure EGR gas) is the exhaust after passing through the exhaust purification catalyst, and therefore, unburned fuel and particulates contained in the exhaust, There is little quantity of inactive ingredients such as soot. Therefore, an EGR passage that connects an exhaust passage (for example, an exhaust manifold) upstream from the turbine and an intake passage (for example, an intake manifold) downstream from the compressor (hereinafter referred to as a high-pressure EGR passage to distinguish it from the low-pressure EGR passage of the present invention). The temperature of the exhaust gas from the internal combustion engine can be more reliably increased as compared with the conventional exhaust gas recirculation device in which the exhaust gas is recirculated through the exhaust gas, and more efficient and reliable catalyst warm-up is performed. Can do.

  In the present invention, the low pressure EGR passage may be a passage connecting the exhaust passage downstream of the exhaust throttle valve and the intake passage upstream of the compressor. In this case, when the opening of the exhaust throttle valve is reduced, the pressure of the exhaust passage upstream of the exhaust throttle valve increases, but the pressure of the exhaust gas in the low pressure EGR passage connected to the exhaust passage downstream of the exhaust throttle valve increases. It becomes difficult to do. Therefore, even when the opening degree of the exhaust throttle valve is further reduced to further increase the catalyst warm-up efficiency, it is possible to suppress a decrease in accuracy when the amount of exhaust gas flowing through the low pressure EGR passage is metered by the low pressure EGR valve. it can. Therefore, it is possible to favorably perform exhaust gas recirculation via the low pressure EGR passage. As a result, the temperature of the exhaust gas from the internal combustion engine can be increased more reliably, and the catalyst warm-up can be completed in a shorter time.

  The exhaust purification catalyst has an adsorption capacity to adsorb unburned fuel that flows in when the temperature of the exhaust purification catalyst is low, and to desorb the unburned fuel that has been adsorbed as the temperature of the exhaust purification catalyst increases. There is. On the other hand, the exhaust purification action of the exhaust purification catalyst is not suitably exhibited until the temperature of the exhaust purification catalyst becomes higher than the predetermined temperature and the exhaust purification catalyst is sufficiently activated. For this reason, depending on the temperature of the exhaust purification catalyst, unburned fuel or the like may be desorbed even though the exhaust purification action is not activated. In that case, there is a possibility that unburned fuel or the like desorbed from the exhaust purification catalyst becomes white smoke and is discharged into the atmosphere.

  On the other hand, according to the present invention, since the catalyst warm-up can be completed rapidly as described above, the catalyst warm-up can be completed in a shorter time than in the case of the conventional exhaust gas recirculation device. . Accordingly, it is possible to suppress the unburned fuel and the like desorbed from the exhaust purification catalyst from being discharged as white smoke without being purified.

  The present invention makes it possible to complete catalyst warm-up in as short a time as possible.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas recirculation apparatus for an internal combustion engine according to this embodiment is applied, and its intake system and exhaust system. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  An intake pipe 3 and an exhaust pipe 4 are connected to the internal combustion engine 1. A second intake throttle valve 9 that adjusts the flow rate of intake air flowing through the intake pipe 3 is provided in the middle of the intake pipe 3. The second intake throttle valve 9 is opened and closed by an electric actuator. The intake pipe 3 upstream of the second intake throttle valve 9 is provided with an intercooler 8 that exchanges heat between intake air and outside air. The intake pipe 3 upstream of the intercooler 8 is provided with a compressor housing 5a of a turbocharger 5 that operates using exhaust energy as a drive source. The intake pipe 3 upstream of the compressor housing 5 a is provided with a first intake throttle valve 6 that adjusts the flow rate of intake air flowing through the intake pipe 3. The first intake throttle valve 6 is opened and closed by an electric actuator. The intake pipe 3 upstream of the first intake throttle valve 6 is provided with an air flow meter 7 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake pipe 3. The intake air amount of the internal combustion engine 1 is measured by the air flow meter 7.

  On the other hand, a turbine housing 5 b of the turbocharger 5 is provided in the middle of the exhaust pipe 4. An exhaust gas purification device 10 is provided in the exhaust pipe 4 downstream from the turbine housing 5b. The exhaust emission control device 10 includes an oxidation catalyst 12 and a particulate filter (hereinafter referred to as a filter) 13 at the subsequent stage of the oxidation catalyst 12. The filter 13 carries an NOx storage reduction catalyst (hereinafter referred to as NOx catalyst). The filter 13 collects particulate matter (hereinafter referred to as PM) in the exhaust. Further, the NOx catalyst occludes nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high, and occludes when the oxygen concentration of the exhaust flowing into the NOx catalyst decreases. Release the NOx that had been stored. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, NOx released from the NOx catalyst is reduced. A temperature sensor 18 that measures the temperature of the exhaust gas flowing out from the exhaust purification device 10 is provided in the exhaust pipe 4 immediately downstream of the exhaust purification device 10. The temperature of the oxidation catalyst 12 or the filter 13 can be estimated from the temperature of the exhaust gas measured by the temperature sensor 18. The exhaust pipe 4 downstream of the exhaust purification device 10 is provided with an exhaust throttle valve 19 that adjusts the flow rate of the exhaust gas flowing through the exhaust pipe 4. The exhaust throttle valve 19 is opened and closed by an electric actuator.

  The internal combustion engine 1 is provided with a low pressure EGR device 30 that recirculates a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a low pressure. The low pressure EGR device 30 includes a low pressure EGR passage 31, a low pressure EGR valve 32, and a low pressure EGR cooler 33.

The low pressure EGR passage 31 connects the exhaust pipe 4 downstream of the exhaust throttle valve 19 and the intake pipe 3 upstream of the compressor housing 5a and downstream of the first intake throttle valve 6. Exhaust gas is recirculated through the low pressure EGR passage 31 at a low pressure. In this embodiment, the exhaust gas recirculated through the low-pressure EGR passage 31 is referred to as low-pressure EGR gas. The low pressure EGR valve 32 is a low pressure EG
By changing the cross-sectional area of the R passage 31, the amount of low-pressure EGR gas flowing through the low-pressure EGR passage 31 is adjusted. The low pressure EGR cooler 33 exchanges heat between the low pressure EGR gas passing through the low pressure EGR cooler 33 and the cooling water of the internal combustion engine 1 to reduce the temperature of the low pressure EGR gas.

  Further, the internal combustion engine 1 is provided with a high pressure EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a high pressure. The high pressure EGR device 40 includes a high pressure EGR passage 41, a high pressure EGR valve 42, and a high pressure EGR cooler 43.

  The high pressure EGR passage 41 connects the exhaust pipe 4 upstream of the turbine housing 5 b and the intake pipe 3 downstream of the second intake throttle valve 9. Exhaust gas is recirculated at high pressure through the high pressure EGR passage 41. In the present embodiment, the exhaust gas recirculated through the high pressure EGR passage 41 is referred to as high pressure EGR gas. The high pressure EGR valve 42 adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage 41 by changing the flow path cross-sectional area of the high pressure EGR passage 41. The high pressure EGR cooler 43 performs heat exchange between the high pressure EGR gas passing through the high pressure EGR cooler 43 and the cooling water of the internal combustion engine 1 to reduce the temperature of the high pressure EGR gas.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 is a computer that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. In addition to the temperature sensor 18, the ECU 20 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 14 by the driver to detect the engine load, and a crank position for detecting the engine speed. Sensors 16 are connected via electrical wiring, and output signals from these various sensors are input to the ECU 20. The ECU 20 is connected to the first intake throttle valve 6, the second intake throttle valve 9, the exhaust throttle valve 19, the low pressure EGR valve 32, and the high pressure EGR valve 42 through electric wiring. The device is controlled.

  Here, the exhaust gas recirculation performed using the low pressure EGR device 30 and the high pressure EGR device 40 in this embodiment will be described. The exhaust gas recirculation performed by the low pressure EGR device 30 and the exhaust gas recirculation performed by using the high pressure EGR device 40 are based on the operating conditions of the internal combustion engine capable of suitably performing exhaust gas recirculation in advance. It is sought experimentally. In the present embodiment, the exhaust gas is recirculated by switching the low pressure EGR device 30 and the high pressure EGR device 40 according to the operating state of the internal combustion engine or using them together.

  FIG. 2 is a diagram showing switching patterns of the low pressure EGR device 30 and the high pressure EGR device 40 that are determined for each region of the operating state of the internal combustion engine 1. The horizontal axis in FIG. 2 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the fuel injection amount of the internal combustion engine 1. The fuel injection amount is a parameter that represents the engine load of the internal combustion engine 1.

  In FIG. 2, a region HPL is a region where the operating state of the internal combustion engine 1 is a low load and low rotation, and here, exhaust gas is recirculated by the high pressure EGR device 40. A region MIX in FIG. 2 is a region in which the operation state of the internal combustion engine 1 is a medium load / medium speed rotation. Here, the high pressure EGR device 40 and the low pressure EGR device 30 are used together to perform exhaust gas recirculation. A region LPL in FIG. 2 is a region where the operating state of the internal combustion engine 1 is a high-load high-speed rotation, and here, exhaust gas is recirculated by the low-pressure EGR device 30.

  As described above, the exhaust gas is recirculated by switching the high pressure EGR device 40 and the low pressure EGR device 30 according to the operating state of the internal combustion engine 1 or using them together to perform exhaust gas recirculation in a wide operating range. This makes it possible to reduce NOx emissions.

Further, in this embodiment, when the EGR rate does not reach the target EGR rate even when the opening of the low pressure EGR valve 32 is fully opened, the low pressure EGR passage 31 is controlled by controlling the first intake throttle valve 6 in the valve closing direction. The differential pressure between the upstream side and the downstream side is increased, thereby increasing the amount of low-pressure EGR gas. Since the first intake throttle valve 6 operates in a low temperature environment, it is possible to control the opening degree with high accuracy.

  The oxidation catalyst 12 adsorbs hydrocarbons (HC) in exhaust gas and removes it from the exhaust gas, and exhaust purification that oxidizes unburned fuel such as HC and converts it into water or carbon dioxide by catalytic action. And having a function.

  The oxidation catalyst 12 has the property of adsorbing HC when the catalyst bed temperature is low, and releasing adsorbed HC by decreasing the adsorption capacity as the catalyst bed temperature increases. Further, the oxidation catalyst 12 hardly exhibits the exhaust purification action when the catalyst bed temperature is low, and when the catalyst bed temperature becomes higher than a certain level, the exhaust purification action of the oxidation catalyst 12 is suitably exerted so that the unburned fuel in the exhaust is Oxidized.

  FIG. 3A is a graph showing a trend of correlation between the catalyst bed temperature of the oxidation catalyst 12 and the HC adsorption amount. FIG. 3B is a graph showing a correlation trend between the catalyst bed temperature of the oxidation catalyst 12 and the catalyst activity. As shown in FIG. 3, the catalyst bed temperature region where the HC adsorption amount of the oxidation catalyst 12 begins to decrease may be close to the catalyst bed temperature region where the catalytic activity of the oxidation catalyst 12 begins to increase. In this case, in the temperature range D of the catalyst bed temperature, HC adsorbed on the oxidation catalyst 12 starts to be desorbed, whereas the oxidation catalyst 12 has not yet been sufficiently activated, so that the HC desorbed from the oxidation catalyst 12 May pass through the oxidation catalyst 12 without being oxidized. In this case, HC is discharged into the atmosphere as white smoke.

  Such white smoke is particularly likely to occur during a cold start of the internal combustion engine 1 in which the oxidation catalyst 12 is used in a state where the catalyst bed temperature is low. This is because, when warming up the oxidation catalyst 12 from a state where the catalyst temperature rise is low, it takes a long time for the catalyst to warm up, so that the time during which the catalyst bed temperature belongs to a temperature region where white smoke may be generated becomes long. This is because there is a tendency. FIG. 4A is a graph showing the change over time of the catalyst bed temperature when the catalyst of the oxidation catalyst is warmed up in the conventional exhaust gas recirculation apparatus. The horizontal axis of FIG. 4A represents the elapsed time after the start of catalyst warm-up, and the vertical axis represents the catalyst bed temperature of the oxidation catalyst 12. As shown in FIG. 4A, when the time required for warming up the catalyst is long, the time ΔTa belonging to the temperature region D in which the catalyst bed temperature may cause white smoke is long, so that the unburned fuel is white. There is a possibility of being discharged into the atmosphere as smoke.

  On the other hand, in this embodiment, the catalyst warm-up is completed in as short a time as possible so that the time during which the catalyst bed temperature belongs to a temperature region where white smoke may be generated is shortened. Specifically, when the catalyst is warmed up, the exhaust throttle valve 19 is controlled in the valve closing direction and the low pressure EGR valve 32 is controlled in the valve opening direction. As a result, the pressure in the exhaust pipe 4 upstream from the exhaust throttle valve 19 increases, the pump loss increases, and the load on the internal combustion engine 1 increases. Therefore, the fuel injection amount in the internal combustion engine 1 increases, and the temperature of the exhaust gas from the internal combustion engine 1 rises. Thereby, since high temperature exhaust gas flows into the oxidation catalyst 12, the oxidation catalyst 12 can be heated.

Further, exhaust gas is recirculated by the low pressure EGR device 30. In the present embodiment, even if the opening of the exhaust throttle valve 19 is throttled to a very small opening, the low pressure EGR passage 31 is connected to the exhaust pipe 4 downstream from the exhaust throttle valve 19, so that the low pressure There is no possibility that the pressure in the EGR passage 31 will rise excessively. Therefore, even when the exhaust throttle valve 19 is throttled to increase the load on the internal combustion engine 1 as described above, the metering accuracy of the low pressure EGR valve 32 is not easily lost, and the exhaust gas is preferably recirculated by the low pressure EGR device 30. Can be done. By performing exhaust gas recirculation by the low pressure EGR device 30, the catalyst warm-up can be performed while the clean exhaust gas that has passed through the exhaust gas purification device 10 is recirculated to the intake pipe 3 of the internal combustion engine 1. As compared with the case of the conventional exhaust gas recirculation device that assists the catalyst warm-up by recirculating the exhaust gas using only the exhaust gas, it is possible to perform the catalyst warm-up more efficiently and more reliably. . Further, since there is no possibility that the low pressure EGR passage 31 is in a high pressure state, the opening of the exhaust throttle valve 19 can be made smaller than that of the conventional exhaust gas recirculation device. As a result, the temperature of the exhaust gas from the internal combustion engine 1 can be increased more reliably, and the catalyst bed temperature of the oxidation catalyst 12 can be increased in a short time.

  FIG. 4B is a graph showing the change over time of the catalyst bed temperature when the above-described catalyst warm-up of the oxidation catalyst 12 is performed in the exhaust gas recirculation apparatus of the present embodiment. The horizontal axis in FIG. 4B represents the elapsed time after the start of catalyst warm-up, and the vertical axis represents the catalyst bed temperature of the oxidation catalyst 12. As shown in FIG. 4B, according to this embodiment, since the catalyst warm-up can be completed in a short time, the time when the catalyst bed temperature belongs to the temperature region D in which white smoke may be generated. ΔTb is shortened. Thereby, even when the catalyst is warmed up from a state where the catalyst bed temperature of the oxidation catalyst 12 is low, such as when the internal combustion engine 1 is cold started, generation of white smoke can be suppressed.

  Here, the catalyst warm-up control of this embodiment described above will be described based on the flowchart of FIG. The flowchart of FIG. 5 is a flowchart showing a routine for performing catalyst warm-up control of this embodiment. This routine is repeatedly executed every predetermined period.

  First, in step S101, the ECU 20 detects the operating state of the internal combustion engine 1. Specifically, the engine load of the internal combustion engine 1 is detected based on the detection value of the accelerator opening sensor 15, and the engine speed of the internal combustion engine 1 is read based on the detection value of the crank position sensor 16.

  Next, in step S102, the ECU 20 obtains a target high pressure EGR valve opening and a target low pressure EGR valve opening corresponding to the operating state of the internal combustion engine 1 detected in step S101. The target high pressure EGR valve opening and the target low pressure EGR valve opening are obtained in advance by experiments as functions or maps determined according to the engine load and engine speed of the internal combustion engine 1, respectively.

  Next, in step S103, the ECU 20 controls the high pressure EGR valve 42 so that the opening degree of the high pressure EGR valve 42 becomes the target high pressure EGR valve opening degree obtained in step S102, and the opening degree of the low pressure EGR valve 32. The low pressure EGR valve 32 is controlled so that the target low pressure EGR valve opening degree obtained in step S102 is obtained.

  Next, in step S <b> 104, the ECU 20 obtains the catalyst bed temperature T of the oxidation catalyst 12. Specifically, the catalyst bed temperature T is estimated based on the temperature of the exhaust gas immediately downstream of the exhaust gas purification device 10 detected by the temperature sensor 18.

  Next, in step S105, the ECU 20 determines whether or not the oxidation catalyst 12 is activated. Specifically, it is determined whether or not the catalyst bed temperature T detected in step S104 is lower than a predetermined temperature T0. Here, the predetermined temperature T0 is a catalyst bed temperature at which it can be determined that the oxidation catalyst 12 is sufficiently activated, and is obtained in advance by experiments.

  If an affirmative determination is made in step S105, the ECU 20 proceeds to step S106 in order to warm up the oxidation catalyst 12. On the other hand, if a negative determination is made in step S105, the ECU 20 determines that the oxidation catalyst 12 is sufficiently activated and proceeds to step S108.

  In step S106, the ECU 20 controls the exhaust throttle valve 19 in the valve closing direction. As a result, the load on the internal combustion engine 1 increases and the temperature of the exhaust gas from the internal combustion engine 1 rises.

  In subsequent step S107, the ECU 20 controls the low pressure EGR valve 32 in the valve opening direction. As a result, the exhaust gas is recirculated by the low pressure EGR device 30 and the temperature of the exhaust gas from the internal combustion engine 1 rises. After executing Step S107, the ECU 20 returns to Step S105, and again determines the active state of the oxidation catalyst 12.

  If it is determined in step S105 that the oxidation catalyst 12 is sufficiently activated, the process proceeds to step S108, the exhaust throttle valve 19 is opened, and the opening of the low pressure EGR valve 32 is returned to the opening by the normal control in step S109. .

  The embodiment described above is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, a downstream oxidation catalyst may be further provided in the exhaust pipe 4 downstream of the exhaust purification device 10. As a result, the unburned fuel that has passed through the exhaust purification device 10 even when the catalyst warm-up of the present embodiment described above is performed can be purified by the subsequent oxidation catalyst, and the exhaust emission can be further improved. Further, in the above embodiment, the catalyst bed temperature of the oxidation catalyst 12 is estimated based on the temperature of the exhaust immediately downstream of the exhaust purification device 10, but is estimated based on the operation state, operation history, etc. of the internal combustion engine 1. Alternatively, a sensor for measuring the catalyst bed temperature of the oxidation catalyst 12 may be provided to directly detect the catalyst bed temperature. In the above embodiment, the exhaust gas is recirculated using the low pressure EGR device 30 during the catalyst warm-up, but at the same time, the exhaust gas may be recirculated by the high pressure EGR device 40, or vice versa. In addition, the high pressure EGR valve 42 may be closed to stop the exhaust gas recirculation by the high pressure EGR device 40.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas recirculation device for an internal combustion engine according to a first embodiment is applied, and an intake system and an exhaust system thereof. It is a figure which shows the switching map of the low voltage | pressure EGR apparatus and high voltage | pressure EGR apparatus in Example 1. FIG. 2 is a graph showing the correlation between the catalyst bed temperature of the oxidation catalyst and the HC adsorption amount in Example 1, and the graph showing the correlation between the catalyst bed temperature of the oxidation catalyst and catalyst activity in Example 1. FIG. The graph which shows the time change of the catalyst bed temperature after the catalyst warm-up start when the catalyst warm-up in the conventional exhaust gas recirculation apparatus is performed, and the catalyst warm-up after the catalyst warm-up in Example 1 is performed It is a graph which shows the time change of a catalyst bed temperature. 3 is a flowchart illustrating a routine for performing catalyst warm-up control in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake pipe 4 Exhaust pipe 5 Turbocharger 5a Compressor housing 5b Turbine housing 6 First intake throttle valve 7 Air flow meter 8 Intercooler 9 Second intake throttle valve 10 Exhaust purification device 12 Oxidation catalyst 13 Filter 14 Accelerator pedal 15 Accelerator opening sensor 16 Crank position sensor 18 Temperature sensor 19 Exhaust throttle valve 20 ECU
30 Low pressure EGR device 31 Low pressure EGR passage 32 Low pressure EGR valve 33 Low pressure EGR cooler 40 High pressure EGR device 41 High pressure EGR passage 42 High pressure EGR valve 43 High pressure EGR cooler

Claims (2)

A turbocharger having a turbine in the exhaust passage of the internal combustion engine and a compressor in the intake passage;
An exhaust purification catalyst provided in an exhaust passage downstream from the turbine;
An exhaust throttle valve that is provided in an exhaust passage downstream from the exhaust purification catalyst and changes a flow passage cross-sectional area of the exhaust passage;
A low pressure EGR passage connecting an exhaust passage downstream from the exhaust purification catalyst and an intake passage upstream from the compressor;
A low pressure EGR valve that is provided in the low pressure EGR passage and changes a cross-sectional area of the low pressure EGR passage;
Catalyst temperature detecting means for detecting the temperature of the exhaust purification catalyst;
When the temperature detected by the catalyst temperature detecting means is lower than a predetermined temperature, the exhaust throttle valve is closed in a valve closing direction as compared with the case where the detected temperature is not lower than the predetermined temperature. And a catalyst warm-up means for controlling the low-pressure EGR valve in the valve opening direction.
An exhaust gas recirculation device for an internal combustion engine, comprising: In claim 1,
The exhaust gas recirculation apparatus for an internal combustion engine, wherein the low pressure EGR passage is a passage connecting an exhaust passage downstream of the exhaust throttle valve and an intake passage upstream of the compressor.

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