JP4957343B2 - EGR system for internal combustion engine - Google Patents

Description

  The present invention relates to an EGR system for an internal combustion engine.

  As a technique for reducing the amount of NOx emitted from an internal combustion engine, EGR is known in which a part of exhaust gas flows into an intake system and is returned to the combustion chamber of the internal combustion engine. Further, in an internal combustion engine equipped with a turbocharger, HPL means for returning a part of the exhaust gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream of the turbine of the turbocharger and an intake passage downstream of the compressor of the turbocharger. And an LPL means for returning a part of the exhaust gas to the internal combustion engine via an LPL passage connecting the exhaust passage downstream from the turbine and the intake passage upstream from the compressor, and HPL means according to the operating state of the internal combustion engine There is also known a technique for performing EGR by using or switching between LPL and LPL means (see, for example, Patent Document 1).

  There is also known a technique in which an exhaust purification catalyst having an oxidizing ability and an ability to collect PM in exhaust gas is provided in the middle of an exhaust passage, and PM discharged from an internal combustion engine is collected by the exhaust purification catalyst. With regard to this technology, when a PM accumulation amount in the exhaust purification catalyst exceeds a predetermined allowable amount, a reducing agent such as a fuel is supplied into the exhaust, and the exhaust gas is exhausted by reaction heat when the reducing agent undergoes an oxidation reaction in the exhaust purification catalyst. There is also known a technique for maintaining the PM collection ability of the exhaust purification catalyst by executing a process of oxidizing and removing PM deposited on the purification catalyst (hereinafter referred to as PM regeneration process).

  By the way, if the intake passage or LPL passage is scavenged by low-temperature air during fuel cut operation during deceleration, etc., and the low-temperature air remains in the intake passage or LPL passage, the fuel cut operation is changed to normal operation due to reacceleration or the like. When returning, the remaining low-temperature air is first sucked into the internal combustion engine. For this reason, immediately after returning from the fuel cut operation, the intake air temperature may be excessively lowered than expected, leading to problems such as poor combustion and increased HC emissions.

  On the other hand, during the fuel cut operation, the throttle valve that adjusts the amount of air flowing into the intake passage is closed, and the LPL valve that adjusts the amount of EGR gas that flows through the LPL passage is opened. Proposed technology to confine EGR gas in the operating state immediately before shifting to the cut operation in a loop including an exhaust passage upstream of the LPL passage, an LPL passage, and an intake passage downstream of the LPL passage (hereinafter referred to as an EGR circulation route). Has been.

According to this technology, the intake passage and the LPL passage are suppressed from being scavenged by the low-temperature air during the fuel cut operation, and immediately after returning from the fuel cut operation, the high-temperature EGR gas confined in the EGR circulation path is Since it is inhaled by the engine, it is possible to avoid poor combustion such as misfire. In addition, since various characteristics such as the oxygen concentration and carbon dioxide concentration of the EGR gas confined can be estimated based on the operation state immediately before shifting to the fuel cut operation, a known concentration immediately after returning from the fuel cut operation. The EGR gas can be supplied to the internal combustion engine, and the emission immediately after returning from the fuel cut operation can be accurately controlled. In this technique, the control of the throttle valve and the LPL valve performed at the time of fuel cut is hereinafter referred to as EGR gas circulation control.
Japanese Patent Laying-Open No. 2005-076456

By the way, in the EGR system capable of performing the EGR gas circulation control, when the internal combustion engine is in a fuel cut operation state when the PM regeneration process is being performed, and the EGR gas circulation control is performed, the exhaust during the PM regeneration process is performed. High-temperature gas discharged from the purification catalyst circulates in the EGR circulation path. At this time, as long as oxygen is present in the gas in the EGR circulation path, the oxidation reaction of the reducing agent and PM proceeds in the exhaust purification catalyst, so the temperature of the gas circulating in the EGR circulation path further increases. As a result, the exhaust purification catalyst may become excessively hot and cause problems such as thermal deterioration, or when returning from fuel cut operation, the intake air temperature may become excessively high and exhaust characteristics such as smoke and NOx may deteriorate. It was.

  At this time, if the oxygen in the gas in the EGR circulation path is exhausted by the PM regeneration process, the oxidation reaction of PM does not proceed any more. Therefore, the PM deposited on the exhaust purification catalyst by the PM regeneration process is reduced. There is a possibility that it cannot be removed sufficiently and the PM trapping ability of the exhaust purification catalyst cannot be suitably maintained. Further, since the oxidation reaction of the reducing agent does not proceed any more, there is a problem that the supplied reducing agent adheres to the exhaust purification catalyst without being reacted. Furthermore, since the gas having a very low oxygen concentration is sucked into the internal combustion engine after returning from the fuel cut operation, there is a risk of causing a combustion failure such as misfire.

  The present invention has been made in view of such problems, and in an EGR system capable of executing EGR gas circulation control, even when a condition for executing EGR gas circulation control is satisfied during execution of PM regeneration processing. It is an object of the present invention to provide a technique that makes it possible to suitably perform exhaust purification.

  In order to achieve the above object, the present invention provides an exhaust purification device provided in an exhaust passage of an internal combustion engine and having an oxidation capability and a capability of collecting PM in the exhaust, and the exhaust gas by supplying a reducing agent into the exhaust. A part of the exhaust gas is EGRed through a PM regeneration unit that performs a PM regeneration process that oxidizes PM accumulated in the purification device, and an EGR passage that connects an exhaust passage downstream of the exhaust purification device and an intake passage of the internal combustion engine. EGR means for returning to the combustion chamber of the internal combustion engine as gas, an EGR valve provided in the EGR passage for adjusting the amount of EGR gas flowing through the EGR passage, and provided upstream of the connection portion of the EGR passage in the intake passage. A throttle valve for adjusting the amount of intake air flowing into the intake passage; and closing the throttle valve when the internal combustion engine is in a fuel cut operation state; By opening the R valve, EGR gas is circulated in an EGR gas circulation path including an exhaust passage upstream of the EGR passage, the EGR passage, and an intake passage downstream of the EGR passage during fuel cut operation. An EGR system for an internal combustion engine provided with EGR gas circulation control means for performing gas circulation control is assumed.

  In this EGR system, low-temperature air is prevented from flowing into the intake passage and the EGR passage during the fuel cut operation of the internal combustion engine. As a result, it is possible to avoid the intake air temperature from being excessively lowered due to the low-temperature intake air existing in the intake passage or the EGR passage being taken into the internal combustion engine when returning from the fuel cut operation. Therefore, it is possible to suppress the occurrence of poor combustion such as misfire when returning from the fuel cut operation. In this EGR system, the gas in the EGR gas circulation path is sucked into the internal combustion engine when returning from the fuel cut operation, and various characteristics such as oxygen concentration and carbon dioxide concentration of this gas shift to the fuel cut operation. Since it can be estimated based on the operation state of the immediately preceding internal combustion engine, it is possible to accurately control emissions such as NOx at the time of return from the fuel cut operation.

  Now, in an EGR system capable of executing such EGR gas circulation control, the present invention relates to a reducing agent that is used when the PM regeneration means performs the EGR gas circulation control during execution of the PM regeneration processing. The supply is stopped.

According to this configuration, when the internal combustion engine is in the fuel cut operation state when the PM regeneration process is being performed and the EGR gas circulation control is performed by the EGR gas circulation control means, the PM regeneration process is being performed. However, the supply of the reducing agent is stopped. As a result, during the execution of the EGR gas circulation control, the reducing agent oxidation reaction is not performed in the exhaust purification device. Accordingly, the temperature of the gas circulating in the EGR gas circulation path is not increased by the oxidation reaction heat of the reducing agent, and therefore, the temperature of the gas circulating in the EGR gas circulation path is suppressed from becoming excessively high. Therefore, it is possible to suppress the exhaust gas purification device from being thermally deteriorated and the exhaust characteristics such as smoke and NOx from being deteriorated when returning from the fuel cut operation.

  Further, according to the present invention, when the EGR gas circulation control means is in a fuel cut operation state during execution of the PM regeneration process, the throttle valve is opened at a predetermined opening degree from the fully closed state. It can also be set as the structure.

  Here, the “predetermined opening degree” is an opening degree of a throttle valve that can supply at least an amount of oxygen necessary for the oxidation reaction of PM in the exhaust gas purifier to the gas circulating in the EGR gas circulation path. The “predetermined opening” is an opening at which the intake passage, the EGR passage, etc. are not scavenged by the air passing through the throttle valve and flowing into the intake passage when the throttle valve is set to the predetermined opening. A smaller opening is set. The “predetermined opening” may be an opening mapped in advance by experiments or the like, or feedback control based on a measured value by a sensor (for example, an air flow meter) that acquires some physical quantity related to the intake oxygen concentration The opening degree determined by

  According to this configuration, even when the EGR gas circulation control is being executed, an amount of oxygen necessary for the oxidation reaction of PM is supplied to the gas circulating in the EGR gas circulation path. Therefore, it is possible to avoid a situation in which the oxidation reaction of PM can no longer proceed because oxygen in the gas in the EGR gas circulation path is exhausted by the PM regeneration process. Thereby, even if it is performing EGR gas circulation control, oxidation of PM can be accelerated | stimulated and the PM collection capability of an exhaust gas purification apparatus can be maintained suitably.

  Even if the opening of the throttle valve is opened from the fully closed position, the opening is such that the intake passage and the EGR passage are not scavenged by the air passing through the throttle valve and flowing into the intake passage. Further, scavenging of high-temperature EGR gas in the EGR gas circulation path by low-temperature air can be suppressed.

  In the case of the above configuration, the supply of the reducing agent into the exhaust during the EGR gas circulation control may be continued. Even in this case, oxygen continues to be supplied to the EGR gas circulation system, so that the oxidation reaction of the reducing agent in the exhaust purification device can also continue to proceed. Therefore, it is possible to avoid a situation in which the reducing agent that has become unable to undergo the oxidation reaction adheres to the exhaust purification device without being reacted.

  In each of the above configurations, the amount of EGR gas returned to the internal combustion engine by the EGR means immediately after the internal combustion engine returns from the fuel cut operation state is set to the execution time of the EGR gas circulation control in the fuel cut operation state immediately before the return. It is preferable to control accordingly.

  When the PM regeneration process is executed during the EGR gas circulation control, oxygen is consumed and carbon dioxide is generated by the oxidation reaction of PM, and the oxygen concentration in the gas circulating in the EGR gas circulation path is reduced and the carbon dioxide is reduced. The carbon concentration increases. That is, the carbon dioxide concentration (or oxygen concentration) in the gas circulating through the EGR gas circulation path varies depending on the execution time of the EGR gas circulation control. Therefore, the EGR gas having a different concentration is supplied to the internal combustion engine immediately after returning from the fuel cut operation depending on the execution time of the EGR gas circulation control.

  Therefore, if the EGR gas amount immediately after returning from the fuel cut operation is uniformly set to a prescribed amount that is determined according to the operating state of the internal combustion engine after the return, for example, the shorter the execution time of EGR gas circulation control is, the shorter the execution time is. More oxygen than expected is supplied to the internal combustion engine, and there is a possibility that the amount of NOx generated will be larger than expected. On the other hand, as the execution time of the EGR gas circulation control is longer, less oxygen than expected is supplied to the internal combustion engine, which may cause a combustion failure such as misfire.

  On the other hand, according to the above configuration, the amount of EGR gas immediately after the return from the fuel cut operation is controlled according to the execution time of the EGR gas circulation control. Therefore, the EGR gas at the time when the EGR gas circulation control is terminated. An appropriate amount of EGR gas reflecting the carbon dioxide concentration (or oxygen concentration) of the gas in the circulation path can be supplied to the internal combustion engine. Therefore, it is possible to suppress an excess or deficiency in the amount of oxygen supplied to the internal combustion engine, and to avoid an increase in the amount of NOx generated and combustion instability immediately after the return from the fuel cut operation.

  In the above configuration, as the execution time of the EGR gas circulation control is longer, it is preferable to reduce the amount of EGR gas returned to the internal combustion engine by the EGR means immediately after returning from the fuel cut operation state.

  As described above, when the EGR gas circulation control is executed during the PM regeneration process, the oxygen concentration in the EGR gas supplied to the internal combustion engine immediately after returning from the fuel cut operation (immediately after the end of the EGR gas circulation control) is There is a tendency that the longer the execution time of EGR gas circulation control is, the lower the carbon dioxide concentration is (the longer the execution time of EGR gas circulation control is, the higher the execution time is). Therefore, according to the above configuration, it is possible to suppress the oxygen concentration in the EGR gas supplied to the internal combustion engine immediately after returning from the fuel cut operation from becoming excessively low or excessively high. Therefore, an increase in the amount of NOx generated and combustion instability immediately after returning from the fuel cut operation can be avoided.

  As described above, when the EGR gas circulation control is executed during the PM regeneration process, the configuration adopted by the EGR system of the present invention in order to suitably execute both the PM regeneration process and the EGR gas circulation control has been described. When the condition for executing the EGR gas circulation control is established during the regeneration process, that is, when the internal combustion engine shifts to the fuel cut operation state, the EGR gas circulation control can be omitted.

  In this case, there are problems such as thermal deterioration of the exhaust purification device due to high-temperature exhaust gas circulated in the EGR gas circulation path due to the execution of the PM regeneration process, and smoke and NOx increase immediately after returning from the fuel cut operation. Can be avoided.

  As described above, as an EGR system, a system has been developed in which an LPL unit and an HPL unit are provided together, and EGR is performed by using or switching both in accordance with the operating state of the internal combustion engine. In such an EGR system, the response to changes in the operating state of the internal combustion engine of various characteristics (temperature, oxygen concentration, etc.) of the exhaust gas (LPL gas) returned to the internal combustion engine by the LPL means tends to be slower than that by the HPL means. There is. Therefore, when the LPL passage is scavenged by low-temperature air during the fuel cut operation, the low-temperature air remaining in the LPL passage after scavenging the LPL passage is discharged from the internal combustion engine after returning from the fuel cut operation. It takes a relatively long time to be replaced by hot exhaust gas. Therefore, the EGR system that performs EGR gas circulation control during the fuel cut operation that is the premise of the present invention is preferably applied to the LPL means.

  According to the present invention, in an EGR system capable of executing EGR gas circulation control, it is possible to perform exhaust gas purification even when a condition for executing EGR gas circulation control is satisfied during execution of PM regeneration processing.

  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 only to those unless otherwise specified.

  FIG. 1 is a diagram schematically showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  The intake ports (not shown) of the respective cylinders 2 gather in the intake manifold 17 and communicate with the intake passage 3. An HPL passage 41, which will be described later, is connected in the vicinity of the connection portion between the intake manifold 17 and the intake passage 3. A second throttle valve 9 that adjusts the amount of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream from the connection location of the HPL passage 41. An intercooler 8 for cooling the intake air is disposed in the intake passage 3 upstream of the second throttle valve 9. A compressor 11 of a turbocharger 13 is disposed in the intake passage 3 upstream from the intercooler 8. An LPL passage 31 described later is connected to the intake passage 3 upstream of the compressor 11. A first throttle valve 6 that adjusts the amount of fresh air flowing into the intake passage 3 is disposed in the intake pipe 3 upstream of the connection point of the LPL passage 31. An air flow meter 7 that measures the amount of fresh air flowing into the intake passage 3 is provided in the intake passage 3 upstream of the first throttle valve 6. An air cleaner (not shown) is connected to the intake passage 3 further upstream. Hereinafter, the intake passage 3, the intake manifold 17, the intercooler 8, the compressor 11, and the like arranged in these may be collectively referred to as “intake system”.

  In the intake system configured as described above, the air from which dust or dust has been removed through the air cleaner flows into the intake passage 3. The air flowing into the intake passage 3 is pressurized after passing through the compressor 11 and then cooled through the intercooler 8 and is also introduced into the intake passage 3 by the LPL device 30 and the HPL device 40 described later. The gas flows into the intake manifold 17 while being mixed with gas, and is distributed to the intake port of each cylinder 2 through each branch pipe of the intake manifold 17. The intake air distributed to the intake port is drawn into the combustion chamber of each cylinder 2 when an intake valve (not shown) is opened.

The exhaust ports (not shown) of the respective cylinders 2 are gathered in the exhaust manifold 18 and communicate with the exhaust passage 4. The exhaust manifold 18 is provided with a fuel addition valve 21 for adding fuel as a reducing agent to the exhaust. An HPL passage 41 is connected in the vicinity of the connection portion between the exhaust manifold 18 and the exhaust passage 4. A turbine 12 of the turbocharger 13 is disposed in the exhaust passage 4 downstream from the connection location of the HPL passage 41. The turbocharger 13 is a variable capacity turbocharger including a nozzle vane 5 that makes the flow area of exhaust gas passing through the turbine 12 variable. An exhaust purification device 10 is disposed in the exhaust passage 4 downstream from the turbine 12. The exhaust purification device 10 is configured to include an oxidation catalyst and a particulate filter (hereinafter referred to as a filter) that is disposed downstream of the oxidation catalyst and collects PM in the exhaust and deposits it inside. The configuration of the exhaust purification device 10 is not limited to this example, and for example, an NOx storage reduction catalyst may be further provided. An exhaust throttle valve 19 that adjusts the amount of exhaust gas flowing through the exhaust passage 4 is disposed in the exhaust passage 4 downstream of the exhaust purification device 10. An LPL passage 31 is connected to the exhaust passage 4 downstream from the exhaust throttle valve 19. A configuration in which the exhaust throttle valve 19 is disposed in the exhaust passage 4 downstream from the connection point of the LPL passage 31 can also be employed. Hereinafter, the exhaust passage 4, the exhaust manifold 18, and the turbine 12, the exhaust purification device 10, and the like arranged in these may be collectively referred to as “exhaust system”.

  In the exhaust system configured as described above, the burned gas burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 through the exhaust port and flows into the exhaust passage 4. Exhaust gas flowing into the exhaust passage 4 is driven to rotate the turbine 13 to remove harmful substances such as PM contained in the exhaust gas purification device 10, and a part thereof is converted into EGR gas by the LPL device 30 and the HPL device 40 described later. It is guided to the intake passage 3. After being purified by the exhaust purification device 10, the exhaust is released into the atmosphere.

  The internal combustion engine 1 includes an HPL device 40 that guides a part of the exhaust gas flowing through the exhaust passage 4 upstream from the turbine 12 to the intake passage 3 downstream from the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. Yes. The HPL device 40 includes an HPL passage 41 that connects the exhaust passage 4 upstream of the turbine 12 and the intake passage 3 downstream of the second throttle valve 9, and intakes a part of the exhaust through the HPL passage 41. It flows into the passage 3. The exhaust gas returned to the combustion chamber by the HPL device 40 is hereinafter referred to as “HPL gas”.

  An HPL valve 42 that changes the flow area of the HPL passage 41 is disposed in the HPL passage 41. The amount of HPL gas flowing through the HPL passage 41 is adjusted by adjusting the opening degree of the HPL valve 42. As means for adjusting the amount of HPL gas, means for adjusting the back pressure by adjusting the opening of the second throttle valve 9 or adjusting the opening of the nozzle vane 5 may be employed.

  The internal combustion engine 1 is provided with an LPL device 30 that guides a part of the exhaust gas flowing through the exhaust passage 4 downstream from the turbine 12 to the intake passage 3 upstream from the compressor 11 and returns the exhaust gas to the combustion chamber of the internal combustion engine 1. Yes. The LPL device 30 has an LPL passage 31 that connects the exhaust passage 4 downstream from the exhaust throttle valve 19 and the intake passage 3 upstream from the compressor 11, and a part of the exhaust is taken into the intake passage via the LPL passage 31. 3 is allowed to flow. The exhaust returned to the combustion chamber by the LPL device 30 is hereinafter referred to as “LPL gas”.

  An LPL cooler 33 for cooling the LPL gas is disposed in the middle of the LPL passage 31. An LPL valve 32 that changes the flow area of the LPL passage 31 is disposed in the LPL passage 31 on the downstream side (the intake passage 3 side) of the LPL cooler 33. By adjusting the opening degree of the LPL valve 32, the amount of LPL gas flowing through the LPL passage 31 is adjusted. As means for adjusting the amount of LPL gas, means for adjusting the differential pressure between the upstream and downstream of the LPL passage 31 by adjusting the opening of the first throttle valve 6 may be employed.

  When EGR is performed by the HPL device 40 and the LPL device 30 configured as described above, incombustible and endothermic inert gas components such as water and carbon dioxide are mixed in the intake air. As a result, the NOx generation amount decreases.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the internal combustion engine 1. The ECU 20 is a microcomputer provided with a CPU, a ROM, a RAM, an input / output port, and the like. In addition to the air flow meter 7 described above, the ECU 20 outputs a water temperature sensor 14 that outputs an electric signal corresponding to the temperature of the cooling water circulating in the water jacket of the internal combustion engine 1, and an electric signal corresponding to the operation amount of the accelerator pedal. A sensor such as an accelerator opening sensor 15 and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are electrically connected. Input to the ECU 20. The ECU 20 is electrically connected to the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, the exhaust throttle valve 19, the LPL valve 32, the HPL valve 42, and the fuel addition valve 21, and is output from the ECU 20. These devices are controlled by the control signal.

  ECU20 acquires the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the signal input from each said sensor. For example, the ECU 20 calculates the engine speed based on the signal input from the crank position sensor 16 and calculates the requested engine load based on the signal input from the accelerator opening sensor 15. Then, fuel injection control and EGR control are performed by controlling each of the above devices according to the calculated engine load and engine speed.

  Here, the EGR control performed in the EGR system of the present embodiment will be described.

  As shown in FIG. 2, in the EGR system of the present embodiment, EGR is performed by using or switching the HPL device 40 and the LPL device 30 in accordance with the operating state of the internal combustion engine 1. In FIG. 2, the horizontal axis represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1. As shown in FIG. 2, in the EGR control of this embodiment, when the operating state of the internal combustion engine 1 is low load and low rotation, EGR is performed mainly by the HPL device 40, and the HPL device increases as the engine load or the engine speed increases. The EGR amount (HPL gas amount) performed by the engine 40 is decreased and the EGR amount (LPL gas amount) performed by the LPL device 30 is increased. When the operating state of the internal combustion engine 1 is at a high load or high rotation side, the LPL is mainly performed. EGR is performed by the device 30.

  In FIG. 2, an area indicated by “HPL” represents an operating state area where EGR is mainly performed by the HPL device 40. This region is hereinafter referred to as an HPL region. An area indicated by “LPL” represents an operating state area where EGR is performed mainly by the LPL device 30. This region is hereinafter referred to as an LPL region. A medium load or medium rotation region represented by “MIX” between the HPL region and the LPL region represents a region where EGR is performed by using the HPL device 40 and the LPL device 30 together. This area is hereinafter referred to as a MIX area. As described above, in the MIX region, the control is performed to decrease the amount of HPL gas and increase the amount of LPL gas as the operation state becomes higher or higher. In other words, the higher the load or the higher rotation side, the lower the ratio of HPL gas in the total EGR gas and the higher the ratio of LPL gas.

  The control target values of the HPL gas amount and the LPL gas amount corresponding to each operation state are the NOx generation amount, smoke generation amount, HC generation amount, fuel consumption rate, etc. when the internal combustion engine 1 is in steady operation in the operation state. Various characteristics relating to the engine performance and the exhaust performance are determined in advance by an adaptation operation so as to achieve a predetermined regulation value and a desired target value, and are stored in the ROM of the ECU 20. Based on the acquired engine operating state, the ECU 20 reads the control target value of the HPL gas amount and the LPL gas amount corresponding to the operating state from the ROM, and the amount of exhaust gas returned to the combustion chamber by the HPL device 40 and the LPL device 30 is determined. The opening degree of the HPL valve 42, the LPL valve 32, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 19, the nozzle vane 5, etc. is controlled so that the respective control target values are obtained.

  When the ECU 20 determines that the amount of PM accumulated on the filter exceeds a predetermined allowable value, the ECU 20 causes the fuel addition valve 21 to add fuel into the exhaust gas. When fuel is added to the exhaust gas from the fuel addition valve 21, the added fuel undergoes an oxidation reaction in the oxidation catalyst in the upstream stage of the filter, and the oxidation reaction of PM deposited on the downstream filter is promoted by the reaction heat at that time, PM accumulated on the filter is removed. In this way, the PM collecting ability of the filter is maintained by appropriately removing the PM deposited on the filter by oxidation. In this manner, the process of adding fuel into the exhaust gas from the fuel addition valve 21 and oxidizing and removing the PM deposited on the filter is hereinafter referred to as PM regeneration process. In this embodiment, the ECU 20 that performs PM regeneration processing corresponds to the PM regeneration means in the present invention.

As a method for estimating the amount of PM deposited on the filter, a known PM accumulation amount estimation method can be employed. For example, it can be estimated on the basis of the intake air amount and fuel consumption since the previous PM regeneration process, the travel distance of the vehicle, the differential pressure across the filter, and the like. In addition, the “predetermined allowable amount” is an upper limit value of the PM accumulation amount such that the pressure loss in the filter does not hinder normal operation of the internal combustion engine, or a predetermined margin is expected for the upper limit value. It is a fixed amount.

  When the internal combustion engine 1 is performing a fuel cut operation during deceleration or the like, the intake passage 3, the LPL passage 31, the HPL passage 41, and the like are scavenged by low-temperature air (fresh air), and the low-temperature air is removed from the intake passage 3 and the LPL. When remaining in the passage 31, when the internal combustion engine 1 returns from the fuel cut operation to the normal operation due to reacceleration or the like, the remaining low-temperature air is first sucked into the internal combustion engine 1 and then returned from the fuel cut. The high-temperature exhaust gas discharged from the internal combustion engine 1 scavenges the low-temperature air from the LPL passage 31, and the exhaust gas from the internal combustion engine 1 after being restored is taken into the internal combustion engine 1 as EGR gas. Therefore, immediately after returning from the fuel cut operation, the intake air temperature may be excessively lowered than expected, leading to problems such as poor combustion and increased HC emissions.

  In contrast, in the EGR system of the present embodiment, the LPL gas in the operating state immediately before the shift to the fuel cut operation is performed by closing the first throttle valve 6 and opening the LPL valve 32 during the fuel cut operation. Is confined in a loop (hereinafter referred to as an EGR circulation path) including the exhaust passage 4 upstream of the LPL passage 31, the LPL passage 31, and the intake passage 3 downstream of the LPL passage 31.

  As a result, the intake passage 3 and the LPL passage 31 are prevented from being scavenged by the low temperature air during the fuel cut operation, and the high temperature LPL gas confined in the EGR circulation path immediately after returning from the fuel cut operation is Therefore, a combustion failure such as misfire can be avoided. Further, since various characteristics such as the oxygen concentration and carbon dioxide concentration of the LPL gas confined can be estimated based on the operation state immediately before shifting to the fuel cut operation, a known concentration immediately after returning from the fuel cut operation. The EGR gas can be supplied to the internal combustion engine 1, and the emission immediately after returning from the fuel cut operation can be accurately controlled. In the present embodiment, the control for circulating the EGR gas in the EGR circulation path by controlling the opening and closing of the first throttle valve 6 and the LPL valve 32 as described above at the time of the fuel cut is called EGR circulation control.

  By the way, when the internal combustion engine 1 is in the fuel cut operation state during the PM regeneration process and the EGR gas circulation control is performed, the high-temperature gas discharged from the filter during the PM regeneration process circulates in the EGR circulation path. Will do. At this time, as long as oxygen is present in the gas in the EGR circulation path, the oxidation reaction of the reducing agent and PM proceeds in the oxidation catalyst and the filter. Therefore, the gas heated by the reaction heat of the oxidation reaction becomes EGR. The circulation path continues to circulate and the temperature of the gas in the EGR circulation path becomes very high. As a result, the exhaust purification device 10 becomes excessively hot and causes problems such as thermal deterioration in the oxidation catalyst and filter, or the intake air temperature becomes excessively high when returning from fuel cut operation, and exhaust characteristics such as smoke and NOx are reduced. There was a risk of worsening.

Further, at this time, if the oxygen in the gas in the EGR circulation path is exhausted by the PM regeneration process, the oxidation reaction of PM does not proceed any more in the exhaust purification device 10 even during the PM regeneration process. The PM accumulated on the filter cannot be sufficiently removed, and there is a possibility that the PM collecting ability of the filter cannot be suitably maintained even if the PM regeneration process is performed. Further, since the oxidation reaction of the fuel no longer proceeds in the oxidation catalyst, there is a problem that the added fuel adheres to the oxidation catalyst and the filter without being reacted. Furthermore, since the gas having a very low oxygen concentration is sucked into the internal combustion engine 1 after returning from the fuel cut operation, there is a risk of causing a combustion failure such as misfire.

  On the other hand, in the EGR system of the present embodiment, when the EGR gas circulation control is performed during the execution of the PM regeneration process, the fuel addition from the fuel addition valve 21 is stopped. Thereby, the oxidation reaction of the fuel in the oxidation catalyst is not performed during the execution of the EGR gas circulation control. Accordingly, the temperature of the gas circulating through the EGR gas circulation path is not increased by the reaction heat accompanying the oxidation reaction of the fuel, and therefore, the temperature of the gas circulating through the EGR gas circulation path is suppressed from becoming excessively high. Therefore, it is possible to prevent the oxidation catalyst and the filter from being thermally deteriorated and the exhaust characteristics such as smoke and NOx from being deteriorated when returning from the fuel cut operation.

  Hereinafter, the EGR gas circulation control performed by the ECU 20 during the above-described PM regeneration process will be described with reference to FIG. FIG. 3 is a flowchart showing a routine for performing EGR gas circulation control during PM regeneration processing. This routine is repeatedly executed by the ECU 20 every predetermined time during the operation of the internal combustion engine 1.

  First, in step S101, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the engine speed is calculated based on a signal input from the crank position sensor 16, and the requested engine load is calculated based on a signal input from the accelerator opening sensor 15.

  In step S102, the ECU 20 determines whether or not the internal combustion engine 1 is in an operation state in which the fuel cut operation should be performed based on the operation state acquired in step S101. For example, the ECU 20 determines that the fuel cut operation is to be performed during the deceleration operation. If an affirmative determination is made in step S102, the ECU 20 proceeds to step S103. If a negative determination is made in step S102, the ECU 20 once ends the execution of this routine.

  In step S103, the ECU 20 determines whether the PM regeneration process is being executed. If an affirmative determination is made in step S103, the ECU 20 proceeds to step S104. If a negative determination is made in step S103, the ECU 20 proceeds to step S105.

  In step S <b> 104, the ECU 20 stops fuel addition into the exhaust by the fuel addition valve 21.

  In step S105, the ECU 20 executes EGR gas circulation control. Specifically, the first throttle valve 6 is fully closed and the LPL valve 32 is fully opened.

  Next, a second embodiment of the present invention will be described. The schematic configuration of the internal combustion engine to which the EGR system according to the second embodiment is applied and its intake system and exhaust system are the same as those of the first embodiment. Below, description is abbreviate | omitted about the component same or equivalent to Example 1, and the code | symbol and name which were used in Example 1 are used.

In the EGR system of the present embodiment, when the condition for performing the EGR gas circulation control is satisfied during the execution of the PM regeneration process, that is, when the internal combustion engine 1 enters the fuel cut operation state, the first throttle valve 6 The EGR gas circulation control is performed by controlling the opening degree to a predetermined opening degree on the opening side from the fully closed state. That is, when the PM regeneration process is not being executed, the EGR gas circulation control is performed by fully closing the first throttle valve and fully opening the LPL valve 32, whereas when the PM regeneration process is being executed. The EGR gas circulation control is performed by opening the first throttle valve to a predetermined opening on the opening side from the fully closed state and fully opening the LPL valve 32.

  Here, the “predetermined opening” is the opening of the first throttle valve 6 that can supply at least an amount of oxygen necessary for the oxidation reaction of PM in the filter into the gas circulating in the EGR gas circulation path. Further, the “predetermined opening” means that when the first throttle valve 6 is set to the predetermined opening, a large amount of low-temperature air passes through the first throttle valve 6 and flows into the intake passage 3. Therefore, the opening is smaller than the opening at which the intake passage 3 and the LPL passage 31 are not scavenged.

  Here, the amount of oxygen necessary for the oxidation reaction of PM in the filter is determined based on, for example, the temperature of the filter. That is, when the temperature of the filter is determined, the amount of PM that can be oxidized per unit time is determined. Based on this amount, the amount of oxygen necessary to convert all the carbon contained in the oxidizable PM to carbon dioxide can be determined. The “predetermined opening degree” can be determined as the opening degree of the first throttle valve 6 that can supply the oxygen amount thus calculated at least into the gas in the EGR circulation path.

  The “predetermined opening” may be determined in advance by experiments or the like as a map according to the temperature of the filter, the operating state of the internal combustion engine 1, or the first throttle valve 6 may be determined based on the measured value by the air flow meter 7. The opening degree may be feedback controlled.

  As a result, even during the execution of the EGR gas circulation control, an amount of oxygen necessary for the oxidation reaction of PM deposited on the filter is supplied to the gas circulating in the EGR gas circulation path. Therefore, it is possible to avoid a situation in which oxygen in the gas in the EGR gas circulation path is exhausted by the PM regeneration process and the oxidation reaction of PM deposited on the filter can no longer proceed. Thereby, even if it is performing EGR gas circulation control, PM regeneration processing can be performed suitably and the PM collection ability of a filter can be maintained suitably.

  Even if the first throttle valve 6 is opened from the fully closed position, the intake passage 3 and the LPL passage 31 are scavenged by the air passing through the first throttle valve 6 and flowing into the intake passage 3. Since the opening is controlled to be smaller than the opening, it is possible to suppress scavenging of the high temperature EGR gas in the EGR gas circulation path by the low temperature air.

  In the case of the present embodiment, unlike the case of Embodiment 1, the addition of fuel into the exhaust during the EGR gas circulation control can be continued. That is, according to the present embodiment, oxygen continues to be supplied to the EGR gas circulation system, so that the oxidation reaction of the reducing agent in the catalyst can also proceed. Therefore, it is possible to avoid a situation in which the reducing agent that has become unable to undergo the oxidation reaction adheres to the oxidation catalyst and the filter without being reacted.

  Hereinafter, the EGR gas circulation control performed by the ECU 20 during the above-described PM regeneration process will be described with reference to FIG. FIG. 4 is a flowchart showing a routine for performing EGR gas circulation control during PM regeneration processing. This routine is repeatedly executed by the ECU 20 every predetermined time during the operation of the internal combustion engine 1.

  First, in step S201, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the engine speed is calculated based on a signal input from the crank position sensor 16, and the requested engine load is calculated based on a signal input from the accelerator opening sensor 15.

In step S202, the ECU 20 determines whether or not the internal combustion engine 1 is in an operating state in which the fuel cut operation should be performed based on the operating state acquired in step S201. For example, the ECU 20 determines that the fuel cut operation is to be performed during the deceleration operation. If an affirmative determination is made in step S202, the ECU 20 proceeds to step S203. If a negative determination is made in step S202, the ECU 20 once ends the execution of this routine.

  In step S203, the ECU 20 determines whether the PM regeneration process is being executed. If an affirmative determination is made in step S203, the ECU 20 proceeds to step S204. If a negative determination is made in step S203, the ECU 20 proceeds to step S205.

  In step S204, the ECU 20 controls the opening of the first throttle valve 6 to a predetermined opening on the opening side from the fully closed state, and opens the LPL valve 32 fully.

  In step S205, the ECU 20 fully closes the opening of the first throttle valve 6 and fully opens the LPL valve 32.

  Next, Embodiment 3 of the present invention will be described. The schematic configuration of the internal combustion engine to which the EGR system according to the third embodiment is applied and its intake system and exhaust system are the same as those of the first embodiment. Below, description is abbreviate | omitted about the component same or equivalent to Example 1, and the code | symbol and name which were used in Example 1 are used.

  In the EGR system of the present embodiment, when the EGR gas circulation control is executed during the PM regeneration process, the LPL valve 32 immediately after the internal combustion engine 1 returns from the fuel cut operation and the EGR gas circulation control ends. The opening degree is controlled according to the execution time of EGR gas circulation control during the fuel cut operation. Specifically, as the execution time of the EGR gas circulation control is longer, the opening degree of the LPL valve 32 immediately after the return from the fuel cut operation is controlled to the closing side opening degree.

  When the PM regeneration process is executed during the EGR gas circulation control, oxygen is consumed and carbon dioxide is generated by the oxidation reaction of PM, and the oxygen concentration in the gas circulating in the EGR gas circulation path is reduced and the carbon dioxide is reduced. The carbon concentration increases. That is, the carbon dioxide concentration in the gas circulating through the EGR gas circulation path becomes higher as the execution time of the EGR gas circulation control is longer, and conversely, the oxygen concentration in the gas circulating through the EGR gas circulation path is higher than the EGR gas circulation path. The control execution time tends to be lower as the execution time is shorter.

  Therefore, if the opening degree of the LPL valve 32 immediately after the return from the fuel cut operation is uniformly set to a prescribed opening degree determined according to the operating state of the internal combustion engine after the return, for example, the EGR gas circulation control is executed. When the time is short, more oxygen than expected is supplied to the internal combustion engine 1, and there is a possibility that the amount of NOx generated is larger than expected. On the other hand, when the execution time of the EGR gas circulation control is long, less oxygen than expected is supplied to the internal combustion engine 1, which may cause a combustion failure such as misfire.

On the other hand, according to the present embodiment, the opening degree of the LPL valve 32 immediately after returning from the fuel cut operation is controlled to the closing side opening degree as the execution time of the EGR gas circulation control is longer. That is, the execution time of the EGR gas circulation control is longer, and therefore, the higher the carbon dioxide concentration in the gas in the EGR gas circulation path, the smaller the opening of the LPL valve 32 immediately after returning from the fuel cut operation. Thereby, it is possible to suppress an excessive amount of inactive components from being supplied to the internal combustion engine 1 immediately after the return from the fuel cut operation, and to suppress a combustion failure such as misfire. On the contrary, the opening time of the LPL valve 32 immediately after the return from the fuel cut operation is increased as the execution time of the EGR gas circulation control is shorter and therefore the oxygen concentration in the gas in the EGR gas circulation path is higher. Thereby, it is possible to suppress an amount of oxygen larger than expected from being supplied to the internal combustion engine 1 immediately after returning from the fuel cut operation, and it is possible to suppress an increase in the amount of NOx generated.

  Hereinafter, the EGR gas circulation control during the PM regeneration process performed by the ECU 20 will be described with reference to FIG. FIG. 5 is a flowchart showing a routine for performing EGR gas circulation control during PM regeneration processing. This routine is repeatedly executed by the ECU 20 every predetermined time during the operation of the internal combustion engine 1.

  First, in step S301, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the engine speed is calculated based on a signal input from the crank position sensor 16, and the requested engine load is calculated based on a signal input from the accelerator opening sensor 15.

  In step S302, the ECU 20 determines whether or not the internal combustion engine 1 is in an operation state in which the fuel cut operation should be performed based on the operation state acquired in step S301. For example, the ECU 20 determines that the fuel cut operation is to be performed during the deceleration operation. If an affirmative determination is made in step S302, the ECU 20 proceeds to step S303. If a negative determination is made in step S302, the ECU 20 proceeds to step S304.

  In step S303, the ECU 20 executes EGR gas circulation control. That is, the first throttle valve 6 is closed and the LPL valve 32 is fully opened. At this time, if the PM regeneration process is being executed, the fuel addition is stopped or the opening of the first throttle valve 6 is set to a predetermined value on the opening side from the fully closed state, as described in the above embodiments. You may control to the opening degree of. After executing Step S303, the ECU 20 returns to Step S302.

  In step S304, the ECU 20 ends the execution of the EGR gas circulation control. That is, the opening degree of the first throttle valve 6 is controlled to a specified opening degree corresponding to the operating state of the internal combustion engine 1. The opening degree of the LPL valve 32 is determined in steps after step S305.

  In step S305, the ECU 20 determines whether or not the EGR gas circulation control executed in step S303 is performed during the PM regeneration process. If an affirmative determination is made in step S305, the ECU 20 proceeds to step S306. On the other hand, if a negative determination is made in step S304, the ECU 20 proceeds to step S307.

  In step S306, the ECU 20 controls the opening of the LPL valve 32 to an opening corresponding to the execution time of the EGR gas circulation control. Specifically, as described above, the longer the execution time of the EGR gas circulation control, the closer the opening is controlled, and the shorter the execution time of the EGR gas circulation control, the more the opening is controlled. The relationship between the execution time of the EGR gas circulation control and the opening degree of the LPL valve 32 is obtained by, for example, experiments in advance and mapped.

  In step S307, the ECU 20 controls the opening degree of the LPL valve 32 to a specified opening degree. The specified opening may be, for example, an opening determined in advance according to the operating state of the internal combustion engine 1, or is estimated based on the operating state of the internal combustion engine 1 immediately before shifting to the fuel cut operation. The opening degree determined based on the oxygen concentration and the carbon dioxide concentration in the gas in the EGR gas circulation path to be performed may be used.

  Next, a fourth embodiment of the present invention will be described. The general configuration of the internal combustion engine to which the EGR system according to the fourth embodiment is applied and the intake system and exhaust system thereof are the same as those of the first embodiment. Below, description is abbreviate | omitted about the component same or equivalent to Example 1, and the code | symbol and name which were used in Example 1 are used.

  In the EGR system of the present embodiment, when the condition for performing the EGR gas circulation control is satisfied during the execution of the PM regeneration process, that is, when the internal combustion engine 1 enters the fuel cut operation state, the EGR gas circulation control is performed. Do not execute. That is, in the normal time when the PM regeneration process is not executed, the EGR gas circulation control is executed when the internal combustion engine 1 is in the fuel cut operation state, but when the PM regeneration process is being executed. Even when the internal combustion engine 1 is in the fuel cut operation state, the EGR gas circulation control is not executed.

  According to the present embodiment, high-temperature exhaust discharged from the exhaust purification device 10 during the execution of the PM regeneration process does not circulate in the EGR gas circulation path, so that the oxidation catalyst and the filter are in an excessively high temperature state. Thus, it is possible to suppress the deterioration of the smoke and NOx exhaust performance immediately after the return from the fuel cut operation due to the heat deterioration and the intake air temperature immediately after the return from the fuel cut operation state becomes excessively high.

  Hereinafter, the above-described EGR control performed by the ECU 20 will be described with reference to FIG. FIG. 6 is a flowchart showing a routine for performing the above-described EGR control. This routine is repeatedly executed by the ECU 20 every predetermined time during the operation of the internal combustion engine 1.

  First, in step S401, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the engine speed is calculated based on a signal input from the crank position sensor 16, and the requested engine load is calculated based on a signal input from the accelerator opening sensor 15.

  In step S402, the ECU 20 determines whether or not the internal combustion engine 1 is in an operating state in which the fuel cut operation should be performed based on the operating state acquired in step S401. For example, the ECU 20 determines that the fuel cut operation is to be performed during the deceleration operation. If an affirmative determination is made in step S402, the ECU 20 proceeds to step S403. If a negative determination is made in step S402, the ECU 20 once ends the execution of this routine.

  In step S403, the ECU 20 determines whether the PM regeneration process is being executed. If an affirmative determination is made in step S403, the ECU 20 once ends the execution of this routine. That is, the execution of this routine is terminated without executing the EGR gas circulation control. On the other hand, if a negative determination is made in step S403, the ECU 20 proceeds to step S404.

  In step S404, the ECU 20 executes EGR gas circulation control. That is, the first throttle valve 6 is closed and the LPL valve 32 is fully opened. After executing step S404, the ECU 20 once ends the execution of this routine.

  Each of the embodiments described above is an example for explaining the present invention, and the above-described embodiments may be modified or combined with each other without departing from the spirit of the present invention. Can be implemented.

It is a figure which shows schematic structure of the internal combustion engine to which the EGR system in an Example is applied, its intake system, and an exhaust system. It is a figure which shows the EGR control map in an Example. 3 is a flowchart showing an EGR gas circulation control routine during execution of PM regeneration processing in Embodiment 1. 7 is a flowchart showing an EGR gas circulation control routine during execution of PM regeneration processing in Embodiment 2. 12 is a flowchart showing an EGR gas circulation control routine during execution of PM regeneration processing in Embodiment 3. 10 is a flowchart illustrating an EGR control routine according to a fourth embodiment.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Nozzle vane 6 First throttle valve 7 Air flow meter 8 Intercooler 9 Second throttle valve 10 Exhaust purification device 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank Position sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
21 Fuel addition valve 30 LPL device 31 LPL passage 32 LPL valve 33 LPL cooler 40 HPL device 41 HPL passage 42 HPL valve

Claims (8)

An exhaust purification device provided in an exhaust passage of an internal combustion engine and having an oxidation capability and a capability of collecting PM in exhaust;
PM regeneration means for performing PM regeneration processing for oxidizing PM deposited in the exhaust purification device by supplying a reducing agent into the exhaust;
EGR means for returning a part of the exhaust gas as EGR gas to the combustion chamber of the internal combustion engine via an EGR passage connecting an exhaust passage downstream of the exhaust purification device and an intake passage of the internal combustion engine;
An EGR valve that is provided in the EGR passage and adjusts an amount of EGR gas flowing through the EGR passage;
A throttle valve that is provided upstream of the connection portion of the EGR passage in the intake passage and adjusts the amount of intake air flowing into the intake passage;
By closing the throttle valve and opening the EGR valve when the internal combustion engine is in the fuel cut operation state, the exhaust passage upstream of the EGR passage, the EGR passage, and the EGR passage are opened during the fuel cut operation. In an EGR system for an internal combustion engine, comprising: EGR gas circulation control means for performing EGR gas circulation control for circulating EGR gas in an EGR gas circulation path including a downstream intake passage.
The EGR system for an internal combustion engine, wherein the PM regeneration means stops the supply of the reducing agent when the EGR gas circulation control is performed during the execution of the PM regeneration process. An exhaust purification device provided in an exhaust passage of an internal combustion engine and having an oxidation capability and a capability of collecting PM in exhaust;
PM regeneration means for performing PM regeneration processing for oxidizing PM deposited in the exhaust purification device by supplying a reducing agent into the exhaust;
EGR means for returning a part of the exhaust gas as EGR gas to the combustion chamber of the internal combustion engine via an EGR passage connecting an exhaust passage downstream of the exhaust purification device and an intake passage of the internal combustion engine;
An EGR valve that is provided in the EGR passage and adjusts an amount of EGR gas flowing through the EGR passage;
A throttle valve that is provided upstream of the connection portion of the EGR passage in the intake passage and adjusts the amount of intake air flowing into the intake passage;
By closing the throttle valve and opening the EGR valve when the internal combustion engine is in the fuel cut operation state, the exhaust passage upstream of the EGR passage, the EGR passage, and the EGR passage are opened during the fuel cut operation. In an EGR system for an internal combustion engine, comprising: EGR gas circulation control means for performing EGR gas circulation control for circulating EGR gas in an EGR gas circulation path including a downstream intake passage.
The EGR gas circulation control means sets the throttle valve to a predetermined opening on the opening side from the fully closed state when the internal combustion engine is in a fuel cut operation state during the execution of the PM regeneration process. EGR system for internal combustion engines. In claim 1 or 2,
The amount of EGR gas returned to the internal combustion engine by the EGR means immediately after the internal combustion engine returns from the fuel cut operation state is controlled according to the execution time of the EGR gas circulation control in the fuel cut operation state immediately before the return. An EGR system for an internal combustion engine. In claim 3,
An EGR system for an internal combustion engine, wherein the longer the execution time of the EGR gas circulation control is, the smaller the amount of EGR gas returned to the internal combustion engine by the EGR means immediately after returning from the fuel cut operation state. An exhaust purification device provided in an exhaust passage of an internal combustion engine and having an oxidation capability and a capability of collecting PM in exhaust;
PM regeneration means for performing PM regeneration processing for oxidizing PM deposited in the exhaust purification device by supplying a reducing agent into the exhaust;
EGR means for returning a part of the exhaust gas as EGR gas to the combustion chamber of the internal combustion engine via an EGR passage connecting an exhaust passage downstream of the exhaust purification device and an intake passage of the internal combustion engine;
An EGR valve that is provided in the EGR passage and adjusts an amount of EGR gas flowing through the EGR passage;
A throttle valve that is provided upstream of the connection portion of the EGR passage in the intake passage and adjusts the amount of intake air flowing into the intake passage;
By closing the throttle valve and opening the EGR valve when the internal combustion engine is in the fuel cut operation state, the exhaust passage upstream of the EGR passage, the EGR passage, and the EGR passage are opened during the fuel cut operation. In an EGR system for an internal combustion engine, comprising: EGR gas circulation control means for performing EGR gas circulation control for circulating EGR gas in an EGR gas circulation path including a downstream intake passage.
The EGR gas circulation control means does not perform the EGR gas circulation control when the internal combustion engine is in a fuel cut operation state during execution of the PM regeneration process. In any one of Claims 1-5,
A turbocharger further comprising a compressor provided in the intake passage and a turbine provided upstream of the exhaust purification device in the exhaust passage;
The EGR system for an internal combustion engine, wherein the EGR passage is a passage connecting an exhaust passage downstream of the exhaust purification device and an intake passage upstream of the compressor. In claim 2,
The predetermined opening is an opening smaller than the opening at which the intake passage and the EGR passage are not scavenged by the air flowing through the throttle valve and flowing into the intake passage when the throttle valve is set to the predetermined opening. An EGR system for an internal combustion engine. In claim 2 or 7,
The EGR system for an internal combustion engine, wherein the PM regeneration means continues to supply the reducing agent into the exhaust when the EGR gas circulation control means sets the throttle valve to the predetermined opening.

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