JP4792997B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  As a technique for reducing the amount of nitrogen oxide (hereinafter referred to as “NOx”) discharged from an internal combustion engine, an exhaust gas recirculation (hereinafter referred to as “EGR”) device is known. This is a technique for reducing the amount of NOx generated by reflowing the gas discharged from the internal combustion engine into the combustion chamber (see, for example, Patent Document 1).

In recent years, a low-pressure EGR device has also been developed as a technique for increasing the amount of exhaust gas (hereinafter referred to as “EGR gas”) recirculated to an internal combustion engine. This is an EGR device that recirculates a part of the exhaust flowing in the exhaust passage downstream of the turbocharger turbine to the intake passage upstream of the turbocharger compressor.
JP-A-10-281016 JP 2000-130270 A JP 2004-116402 A

  By the way, when the amount of EGR gas is increased, the amount of NOx produced tends to decrease while the amount of unburned fuel such as hydrocarbons (hereinafter referred to as “HC”) tends to increase. Further, when the high-temperature exhaust gas is cooled in the low-pressure EGR device, moisture in the exhaust gas may be condensed. Therefore, when a large amount of EGR gas is recirculated using the low pressure EGR device, the amount of unburned fuel flowing into the low pressure EGR device and the amount of condensed water generated also increase. These unburned fuel and condensed water adhere to the EGR passage, the EGR cooler, and the like, and cause soot in the EGR gas to accumulate. Therefore, when a large amount of unburned fuel flows into the low pressure EGR device, the amount of unburned fuel, soot and the like attached and accumulated increases, which may increase the pressure loss of the EGR passage and decrease the performance of the EGR cooler.

  The present invention has been made in view of such problems, and an object of the present invention is to suitably use unburned fuel and condensed water staying in the low pressure EGR device in an exhaust gas purification system for an internal combustion engine equipped with the low pressure EGR device. And a technique for suppressing the occurrence of problems such as an increase in pressure loss and a decrease in performance of the low-pressure EGR device.

In order to achieve the above object, the present invention employs the following means. That is, the exhaust gas purification system for an internal combustion engine according to claim 1 is:
A supercharging device for supplying pressurized intake air to the internal combustion engine;
An EGR passage that recirculates part of the exhaust gas flowing through the exhaust passage of the internal combustion engine to the upstream side of the supercharging device of the intake passage of the internal combustion engine;
An EGR flow rate adjusting device for adjusting an amount of exhaust gas recirculated to the intake passage via the EGR passage;
A bypass passage for allowing a portion of the intake air pressurized by the supercharging device to flow into the EGR passage;
When the internal combustion engine is in a predetermined operating state, the intake air is guided to the EGR passage through the bypass passage, and the EGR flow rate control device is controlled to reversely flow the intake air from the downstream side to the upstream side of the EGR passage. Scavenging means
It is characterized by having.

  In the exhaust gas purification system for an internal combustion engine configured as described above, the exhaust gas recirculated from the exhaust passage to the intake passage via the EGR passage is pressurized together with fresh air by the supercharging device and is supercharged to the internal combustion engine. Become. Therefore, a large amount of exhaust gas can be recirculated to the internal combustion engine, and the amount of NOx generated in the internal combustion engine can be greatly reduced.

  Further, when the internal combustion engine is in a predetermined operation state by the scavenging means, a part of the high-pressure intake air pressurized by the supercharging device is introduced into the EGR passage through the bypass passage. At this time, the EGR flow rate control device is controlled so that the high-pressure intake air flowing into the EGR passage flows backward from the downstream side to the upstream side of the EGR passage. That is, considering the exhaust pressure in the exhaust passage, the intake pressure upstream of the supercharger, the pressure loss in the EGR passage and the EGR flow control device, etc., the intake air flowing into the EGR passage is closer to the exhaust passage from the intake passage closer to the EGR passage. The EGR flow control device is controlled so as to flow in the direction toward the front.

  Here, “downstream” and “upstream” of the EGR passage are concepts based on the direction of the exhaust gas flow in the EGR passage when the exhaust gas is recirculated. Further, as the EGR flow rate adjusting device, an EGR valve provided in the EGR passage, a device for controlling the differential pressure upstream and downstream of the EGR passage by adjusting the opening degree of the exhaust throttle valve and / or the intake throttle valve, etc. It can be illustrated.

  The high-pressure intake air guided to the EGR passage flows back through the EGR passage and blows into the exhaust passage while blowing off unburned fuel and condensed water existing in the EGR passage. At this time, the unburned fuel and condensed water blown off are also carried to the exhaust passage by the flow of the intake air. Therefore, even when the amount of unburned fuel flowing into the EGR passage and the amount of condensed water in the EGR passage increase with the implementation of a large amount of EGR, these can be removed from the EGR passage.

  Thereby, it is suppressed that unburned fuel and condensed water remain in an EGR passage, and it can control that soot in exhaust gas accumulates inside an EGR passage. As a result, it is possible to suppress the occurrence of problems such as an increase in pressure loss in the EGR passage and a decrease in performance.

  Here, the predetermined operating state of the internal combustion engine is an operating state of the internal combustion engine that can appropriately perform scavenging of the EGR passage by the scavenging means as described above.

  In the exhaust gas purification system for an internal combustion engine, the EGR flow control device is an EGR valve provided in the EGR passage, and an EGR cooler for cooling the exhaust gas flowing in the EGR passage is provided in the EGR passage upstream of the EGR valve. If so, a bypass passage may be provided so that the EGR passage upstream of the EGR valve and downstream of the EGR cooler communicates with the intake passage downstream of the supercharger.

  In this case, a bypass opening / closing valve that opens and closes the bypass passage is provided in the bypass passage, and when the scavenging means performs scavenging of the EGR passage, the bypass opening / closing valve is opened and the EGR valve is closed. .

  In this way, when the internal combustion engine is in a predetermined operating state, a part of the high-pressure intake air flows into the EGR passage via the bypass passage, flows back through the EGR passage via the EGR cooler, and exhaust passage To flow into.

In the exhaust purification system having such a configuration, the moisture in the exhaust gas is condensed in the EGR cooler, and condensate is likely to be generated particularly in the EGR cooler and its downstream, but high-pressure intake air flows from the downstream of the EGR cooler into the EGR passage. Even when condensed water is generated, the condensed water is blown off by intake air and removed from the EGR passage.

  Further, since the EGR valve is closed when scavenging is performed, all of the high-pressure intake air introduced to the EGR passage flows back through the EGR passage and flows into the exhaust passage. Therefore, scavenging of the EGR passage can be performed more reliably.

  In the above-described exhaust gas purification system for an internal combustion engine, “the internal combustion engine is in a predetermined operation state” in which scavenging of the EGR passage is performed can be exemplified by an operation state in which exhaust gas is not recirculated through the EGR passage.

  That is, in an exhaust gas purification system for an internal combustion engine having an EGR control means for recirculating exhaust gas from the exhaust passage to the intake passage upstream of the supercharger by opening the EGR valve, the exhaust by the EGR control means Is not operated (hereinafter referred to as “EGR”).

  The “operating state in which EGR is not performed” is an operating state in which it is not necessary to perform EGR or an operating state in which it is preferable not to perform EGR, and examples thereof include a high-load operating state and a deceleration operating state.

  This is because when EGR is performed when the internal combustion engine is in a high load state, the amount of smoke generated tends to increase. Therefore, the effect of reducing NOx emissions and the effect of increasing smoke emissions associated with the implementation of EGR This is because, when both are considered, the total exhaust emission may be improved when the EGR is stopped.

  Further, when the internal combustion engine is in a decelerating operation state when the engine speed is high, the internal combustion engine may be controlled to cut off the fuel supply to the combustion chamber and stop the combustion. In such a case, since the presence or absence of EGR does not particularly affect the NOx emission amount, the necessity of performing EGR is low, and EGR may not be performed.

  In an exhaust purification system having an exhaust purification device such as a catalyst or a particulate filter (hereinafter abbreviated as “filter”) in the exhaust passage, a process for recovering the exhaust purification ability of the catalyst or filter (hereinafter referred to as “catalyst regeneration process”). Can be included in the “operating state of the internal combustion engine in which EGR is not performed”.

  When catalyst regeneration is being performed in the exhaust purification device, the temperature of the exhaust gas discharged from the exhaust purification device may become very high. For example, during the filter regeneration process that oxidizes and removes PM deposited on the filter, the exhaust gas passing through the filter is heated by the reaction heat associated with the oxidation reaction of PM, so the exhaust gas discharged from the filter is very hot. become.

  Therefore, if EGR is performed while the catalyst regeneration process is being performed, hot exhaust gas flows into the intake system via the EGR passage. In that case, the temperature of the exhaust gas flowing through the EGR passage may exceed the cooling capacity of the EGR cooler and may not be sufficiently cooled in the EGR cooler. Therefore, it may be preferable to stop EGR when oxidation / reduction processing is performed in the exhaust gas purification apparatus.

When the frequency of scavenging the EGR passage by the scavenging means is low, unburned fuel and condensed water tend to gradually gather inside the EGR passage and exist in a relatively large particle size state. In such a state, even if high-pressure intake air is introduced into the EGR passage by the scavenging means, these unburned fuel and condensed water are not easily blown away, and these unburned fuel and condensed water are condensed from the inside of the EGR passage. There is a possibility that the scavenging time required to remove the water will be long or it may not be sufficiently removed.

  Therefore, in order to more reliably remove unburned fuel and condensed water from the EGR passage, it is preferable to scavenge the EGR passage as frequently as possible. In particular, when the operation state of the internal combustion engine is an operation state in which EGR is not performed, if the scavenging of the EGR passage is always performed, unburned fuel or condensed water existing in the EGR passage has a particle size of It can be removed by blowing away from the EGR passage in the stage before it becomes large, and it becomes possible to more reliably suppress the unburned fuel and condensed water from staying.

  Further, even if the operating state of the internal combustion engine is not an operating state in which EGR is not performed, the scavenging of the EGR passage may be performed if the intake pressure upstream of the supercharging device is higher than the exhaust pressure in the exhaust passage. May be performed.

  In this case, for example, when the EGR stop condition is not satisfied for a long period of time of a certain period or longer, for example, the EGR is temporarily stopped and forced even during EGR. Therefore, scavenging of the EGR passage can be performed. As a result, it is possible to more reliably suppress unburned fuel and condensed water from staying in the EGR passage, and to suppress occurrence of problems such as an increase in pressure loss in the EGR passage and a decrease in performance of the EGR cooler.

  INDUSTRIAL APPLICABILITY According to the present invention, in an exhaust gas purification system for an internal combustion engine having a low pressure EGR device capable of performing a large amount of EGR by recirculating exhaust gas upstream of a supercharging device, accumulation of soot and condensed water in the EGR passage The retention can be suppressed, and the occurrence of problems such as an increase in pressure loss in the EGR passage and a decrease in performance can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake and exhaust system. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders.

  The combustion chamber of the internal combustion engine 1 communicates with the intake passage 3 through the intake branch pipe 2. The intake passage 3 is provided with an intercooler 4 for cooling the gas flowing through the intake passage 3. Connected upstream of the intercooler 4 is a compressor 6 of a turbocharger 5 that operates using exhaust energy as a drive source.

  A throttle valve 10 is disposed upstream of the compressor 6. The throttle valve 10 is a flow rate adjusting device that adjusts the amount of fresh air flowing into the intake passage 3 by changing the cross-sectional area of the intake passage 3. The throttle valve 10 is connected to an ECU 22 to be described later via an electrical wiring, and the valve opening degree is controlled based on a control signal output from the ECU 22.

  An air cleaner 8 is provided upstream of the throttle valve 10. An EGR gas inlet 7 is provided in the intake passage 3 upstream of the compressor 6 and downstream of the throttle valve 10, and one end of an EGR passage 15 described later is connected thereto.

On the other hand, the combustion chamber of the internal combustion engine 1 communicates with the exhaust passage 11 via the exhaust branch pipe 21. A turbine 12 of the turbocharger 5 is provided in the exhaust passage 11. Downstream of the turbine 12, exhaust purification apparatuses 13 and 14 are provided for removing harmful substances such as particulate matter (hereinafter referred to as “PM”) and NOx in the exhaust from the exhaust.

  Examples of the exhaust purification devices 13 and 14 include a filter, a catalyst such as a NOx catalyst, an oxidation catalyst, and a three-way catalyst, or a device constituted by an appropriate combination thereof. The exhaust passage 11 is open to the atmosphere downstream of the exhaust purification device 14 so that the exhaust purified by the exhaust purification devices 13 and 14 is discharged.

  An EGR gas outlet 23 is provided in a portion of the exhaust passage 11 between the exhaust purification device 13 and the exhaust purification device 14, and one end of the EGR passage 15 is connected thereto. On the other hand, the other end of the EGR passage 15 is connected to the EGR gas inlet 7 of the intake passage 3 as described above, and the exhaust passage 11 downstream from the turbine 12 and the intake passage 3 upstream from the compressor 6 are connected by the EGR passage 15. Is communicated with.

  An EGR cooler 16 that cools the gas flowing through the EGR passage 15 is provided in the middle of the EGR passage 15, and an EGR valve 17 is disposed downstream of the EGR cooler 16. The EGR valve 17 is a flow rate adjusting device that adjusts the amount of exhaust gas flowing into the intake passage 3 via the EGR passage 15 (hereinafter referred to as “EGR gas amount”) by changing the flow passage cross-sectional area of the EGR passage 15. is there. The EGR valve 17 is connected to the ECU 22 via electrical wiring, and the valve opening degree is controlled based on a control signal output from the ECU 22.

  An intake air outlet 18 is provided in the intake passage 3 downstream of the compressor 6, and one end of a bypass passage 19 is connected thereto. The other end of the bypass passage 19 is connected to an intake inlet 9 provided in the EGR passage downstream of the EGR cooler 16 and upstream of the EGR valve 17. The intake passage 3 and the EGR passage 15 are communicated with each other by the bypass passage 19. Thereby, a part of the intake air pressurized by the compressor 6 is guided to the EGR passage 15 via the bypass passage 19.

  A bypass opening / closing valve 20 is arranged in the middle of the bypass passage 19. The bypass opening / closing valve 20 is a flow rate adjusting device that adjusts the amount of intake air that flows into the EGR passage 15 via the bypass passage 19 by changing the cross-sectional area of the bypass passage 19. The bypass on-off valve 20 is connected to the ECU 22 via electrical wiring, and the valve opening degree is controlled based on a control signal output from the ECU 22.

  The ECU 22 is an electronic control computer that includes a RAM, a ROM, a CPU, and the like. The ECU 22 detects or estimates various parameters representing the operating state of the internal combustion engine 1, such as the accelerator opening, the engine speed, and the engine load, and performs known control such as fuel injection according to the operating state of the internal combustion engine 1. The above-described throttle valve 10, EGR valve 17, and bypass opening / closing valve 20 are controlled, and scavenging control of the EGR passage 15 is executed.

  When the EGR valve 17 is controlled in the valve opening direction, the EGR passage 15 becomes conductive, and a part of the relatively low-pressure exhaust discharged from the exhaust purification device 13 flows into the EGR passage 15 and passes through the EGR cooler 16. It returns to the intake passage 3. The EGR gas recirculated to the intake passage 3 is pressurized by the compressor 6 together with fresh air, and is supercharged to the internal combustion engine 1. Thereby, a large amount of exhaust gas can be recirculated to the internal combustion engine 1.

  In this way, a large amount of exhaust gas can be recirculated to the internal combustion engine 1 by performing exhaust gas recirculation using the EGR device 24 including the EGR passage 15, the EGR cooler 16, and the EGR valve 17. Thus, the combustion temperature of the air-fuel mixture in the combustion chamber of the internal combustion engine 1 can be more reliably lowered. Thereby, the amount of NOx generated in the combustion process is greatly reduced.

  On the other hand, when a large amount of EGR is performed, the amount of unburned fuel discharged from the internal combustion engine tends to increase. Along with this, the amount of unburned fuel flowing into the EGR passage 15 may also increase. When the amount of unburned fuel flowing into the EGR passage 15 increases, unburned fuel tends to adhere to the inner walls of the EGR passage 15 and the EGR cooler 16. If EGR is continued in this state, soot in the EGR gas adheres to and accumulates on the unburned fuel, which may increase the pressure loss of the EGR passage 15 and decrease the cooling performance of the EGR cooler 16.

  Further, when the high-temperature exhaust gas is cooled by the EGR cooler 16, moisture in the EGR gas may be condensed and condensed water may be generated. When the amount of EGR gas increases, the amount of condensed water generated increases and accumulates in the EGR cooler 16 and the EGR passage 15, which may cause soot accumulation.

  On the other hand, in this embodiment, a part of the high-pressure intake air pressurized by the compressor 6 flows into the bypass passage 19 from the intake outlet 18 and passes from the intake inlet 9 to the EGR passage 15 via the bypass passage 19. Led. At this time, since the EGR valve 17 is closed, the high-pressure intake air flowing into the EGR passage 15 flows backward from the downstream side to the upstream side through the EGR passage 15 and flows into the exhaust passage 11 via the EGR cooler 16. become.

  Here, “upstream” and “downstream” of the EGR passage 15 are concepts based on the direction of the flow of EGR gas in the EGR passage 15 when EGR is performed by the EGR device 24. Therefore, “the intake air flows backward through the EGR passage 15” means that the intake air flows through the EGR passage 15 from the intake passage toward the exhaust passage.

  The intake air pressurized by the compressor 6 varies depending on the operating state of the internal combustion engine 1, but has a high pressure on the order of about 100 to 150 kPa. Therefore, when the high-pressure intake air flows back through the EGR passage 15, unburned fuel and condensed water existing inside the EGR passage 15 and the EGR cooler 16 are blown off and are carried to the exhaust passage 11 by the flow of intake air. Thereby, unburned fuel and condensed water adhering to the inner walls of the EGR passage 15 and the EGR cooler 16 are removed.

  Unburned fuel and condensed water blown off from the EGR passage 15 and the EGR cooler 16 and flowed into the exhaust passage 11 are purified when passing through the exhaust purification device 14 and discharged into the atmosphere.

  Thus, in the case of the present embodiment, scavenging of the EGR passage 15 is performed by intake air that contains almost no soot, unburned fuel, or the like and is higher in pressure than the exhaust gas flowing through the EGR passage 15 during EGR. For this reason, it is possible to perform the scavenging of the EGR passage 15 more reliably as compared with the conventional technique for scavenging the EGR passage by reversing the direction of the exhaust flow in the EGR passage.

  As a result, even if the amount of unburned fuel flowing into the EGR passage 15 increases with the increase in the EGR gas amount or the amount of condensed water generated in the EGR cooler 16 increases, the EGR device 24 It is possible to suppress unburned fuel and condensed water from staying inside. Thereby, it becomes possible to suppress the occurrence of problems such as an increase in pressure loss in the EGR passage 15 and a decrease in performance of the EGR cooler 16.

The scavenging of the EGR passage 15 as described above is performed when the internal combustion engine 1 is in a predetermined operation state. Specifically, scavenging of the EGR passage 15 is performed when the operating state of the internal combustion engine 1 is in an operating state in which EGR using the EGR device 24 is not performed. This is because when the scavenging of the EGR passage 15 is performed, the intake air flows backward from the downstream side of the EGR passage 15 to the upstream side.
This is because if the scavenging of the EGR passage 15 is executed when the internal combustion engine is in an operation state where EGR is to be performed, it is considered that the exhaust emission is affected.

  The operating state in which EGR is not performed by the EGR device 24 includes a case where the load of the internal combustion engine 1 is high, a case where the internal combustion engine is decelerating, or a case where catalyst regeneration processing is being performed in the exhaust purification device 13. It can be illustrated.

  This is because, if EGR is performed when the internal combustion engine 1 is in a high load state, the amount of smoke generated tends to increase. Therefore, the NOx emission reduction effect associated with the implementation of EGR and the smoke emission increase tendency This is because when the EGR is stopped, the total exhaust emission may be improved.

  Further, when the internal combustion engine is in a decelerating operation state when the engine speed is high, the internal combustion engine may be controlled to cut off the fuel supply to the combustion chamber and stop the combustion. In such a case, since the presence or absence of EGR does not particularly affect the NOx emission amount, the necessity of performing EGR is low, and EGR may not be performed.

  Further, when the catalyst regeneration process is being performed in the exhaust purification device 13, the temperature of the exhaust discharged from the exhaust purification device 13 may become very high. For example, when the exhaust emission control device 13 is configured to include a filter, a PM oxidation process for oxidizing the collected PM and removing it from the filter is appropriately executed. When the PM is oxidized in the filter, the exhaust gas passing through the filter is heated by the reaction heat generated when the PM undergoes an oxidation reaction, and the temperature of the exhaust gas discharged from the filter becomes high.

  If EGR is performed while such high-temperature exhaust is being exhausted from the exhaust purification device 13, the high-temperature exhaust flows into the intake passage 3 via the EGR passage 15. In this case, the temperature of the exhaust gas flowing through the EGR passage 15 may exceed the cooling performance of the EGR cooler 16 and may not be sufficiently cooled in the EGR cooler 16. Therefore, when the catalyst regeneration process is being performed in the exhaust purification device 13, it may be preferable to stop the EGR.

  Thus, in this embodiment, scavenging of the EGR passage 15 is performed when EGR using the EGR device 24 is not performed, but more preferably, EGR is always performed when EGR is not performed by the EGR device 24. The passage 15 may be scavenged.

  This is because when the frequency of scavenging of the EGR passage 15 is low, unburned fuel and condensed water in the EGR passage 15 and the EGR cooler 16 tend to gradually gather and exist in a large particle size state. . In such a state, even if scavenging is performed and high-pressure intake air is introduced into the EGR passage 15, these unburned fuel and condensed water are not easily blown off, and these unburned fuel are discharged from the EGR passage 15. This is because there is a possibility that the scavenging time required for removing water and condensed water may become long or may not be sufficiently removed.

  Accordingly, it is preferable to perform scavenging of the EGR passage 15 as frequently as possible when a condition that allows scavenging of the EGR passage 15 is established. By doing so, these can be efficiently blown off and removed from the EGR passage 15 at the stage before the particle size of unburned fuel or condensed water increases in the EGR passage 15.

  Hereinafter, scavenging control of the EGR passage 15 executed by the ECU 22 will be described based on the flowchart of FIG. The flowchart of FIG. 2 is a flowchart showing a routine for executing the scavenging control of the EGR passage 15, and this routine is repeatedly executed by the ECU 22 every predetermined period.

  First, in step 101, the ECU 22 detects or estimates the operating state of the internal combustion engine 1.

  Next, at step 102, the ECU 22 determines whether or not the operating state of the internal combustion engine 1 detected at step 101 satisfies an EGR stop condition. If an affirmative determination is made in step 102, that is, if it is determined that the operating state of the internal combustion engine 1 is an operating state in which EGR is not performed, the ECU 22 proceeds to step 104. On the other hand, if a negative determination is made in step 102, that is, if it is determined that the operation state of the internal combustion engine 1 is an operation state in which EGR is performed, the ECU 22 proceeds to step 103.

  In step 103, the ECU 22 executes EGR. Specifically, the ECU 22 controls the EGR valve 17 in the valve opening direction and closes the bypass flow rate adjustment valve 20. As a result, a part of the exhaust discharged from the exhaust purification device 13 flows into the EGR passage 15, flows through the EGR passage 15 while being cooled by the EGR cooler 16, and is guided to the intake passage 3.

  At this time, the ECU 22 calculates the target value of the EGR gas amount according to the operating state of the internal combustion engine 1 detected in step 101, and controls the valve opening degree of the EGR valve 17 so that the EGR gas amount becomes the target value. . Further, the ECU 22 calculates a target value of the mixture ratio of fresh air and EGR gas according to the operating state of the internal combustion engine 1, and the throttle valve 10 so that the ratio of the amount of fresh air and the amount of EGR gas becomes the target value. To control the opening degree.

  The fresh air and EGR gas mixed in the intake passage 3 upstream from the compressor 6 in this way are pressurized by the compressor 6 and supercharged to the internal combustion engine 1.

  FIG. 3 is a diagram showing the flow of EGR gas when EGR is performed in step 103. As shown in FIG. 3A, a part of the exhaust discharged from the exhaust purification device 13 returns to the intake passage 3 via the EGR passage 15.

  Returning to the flowchart of FIG. 2, when an affirmative determination is made in step 102, the ECU 22 proceeds to step 104 and scavenging the EGR passage 15. Specifically, the ECU 22 closes the EGR valve 17 and opens the bypass flow rate adjustment valve 20.

  As a result, a portion of the high-pressure intake air pressurized by the compressor 6 flows into the bypass passage 19 from the intake air outlet 18 and flows into the EGR passage 15 via the bypass passage 19. At this time, since the EGR valve 17 is closed, the intake air flowing into the EGR passage 15 flows in the direction of the EGR cooler 16.

  The high-pressure intake air introduced to the EGR passage 15 flows back through the EGR passage 15 from the downstream side to the upstream side while blowing off unburned fuel and condensed water existing in the EGR passage 15 and the EGR cooler 16, and the EGR gas outlet 23 Through the exhaust passage 11.

  FIG. 4 is a diagram showing the flow of intake air that flows backward through the EGR passage 15 when scavenging of the EGR passage 15 is performed in step 104. As shown in FIG. 4B, a part of the intake air pressurized by the compressor 6 is led from the intake air outlet 18 to the bypass passage 19 and flows into the EGR passage 15 via the bypass passage 19. It flows backward through the passage 15 and flows into the exhaust passage 11.

Thus, the scavenging means according to the present invention is realized by the ECU 22 executing step 104 of the scavenging control routine. As a result, in an exhaust gas purification system for an internal combustion engine equipped with a low pressure EGR device, unburned fuel and condensed water present in the low pressure EGR device are removed, and problems such as increased pressure loss and reduced performance of the low pressure EGR device are generated. It becomes possible to suppress.

  Various modifications may be made to the embodiments described above without departing from the spirit of the present invention. For example, in the above embodiment, an embodiment in which the present invention is applied to an exhaust gas purification system for an internal combustion engine provided with a so-called low pressure EGR device that recirculates exhaust gas downstream of the turbine upstream of the compressor as an EGR device has been described. In addition, a conventional EGR device (high pressure EGR device) that communicates the exhaust branch pipe and the intake branch pipe may be provided. In this case, since the present invention is an invention for removing unburned fuel and condensed water in the low pressure EGR device from the inside of the low pressure EGR device by the scavenging control, the scavenging control according to the present invention is not executed for the high pressure EGR device.

  Further, when scavenging the EGR passage 15, considering exhaust pressure in the exhaust passage 11, intake pressure in the intake passage 3 upstream from the compressor 6, pressure loss in the EGR passage 15, EGR cooler 16, EGR valve 17, etc. The opening degree of the EGR valve 17 may be adjusted so that the intake air flowing into the EGR passage 15 flows back through the EGR passage 15, and scavenging of the EGR passage 15 may be performed without fully closing the EGR valve 17.

  Further, in the above embodiment, scavenging of the EGR passage 15 is performed only when the EGR stop condition is satisfied. However, even if the EGR stop condition is not satisfied, the upstream side of the compressor 6 is upstream. The EGR passage may be scavenged when the intake pressure is higher than the exhaust pressure in the exhaust passage 11. Thus, for example, when the EGR stop condition is not satisfied for a long time of a certain period or longer, the EGR passage 15 can be forcibly scavenged. As a result, it is possible to more reliably suppress the unburned fuel and condensed water from staying in the EGR passage 15 and to suppress the occurrence of problems such as an increase in pressure loss in the EGR passage and a decrease in performance of the EGR cooler.

1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine in an embodiment of the present invention. It is a flowchart which shows the scavenging control routine in the Example of this invention. It is a figure which shows the flow of EGR gas when EGR is performed in the Example of this invention. It is a figure which shows the flow of the intake which scavenges an EGR channel when the scavenging of an EGR channel is performed in the example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake branch pipe 3 ... Intake passage 4 ... Intercooler 5 ... Turbocharger 6 ... Compressor 7 ... EGR gas inlet 8 ... Air cleaner 9 ... Intake inlet 10 ... Throttle valve 11 ... Exhaust passage 12 ... Turbine 13 ... Exhaust purification device 14 ... Exhaust purification device 15 ... EGR passage 16 ... EGR cooler 17 ... EGR valve 18 ... Intake intake port 19 ... Bypass passage 20 ... Bypass on-off valve 21 ... Exhaust branch pipe 22 ... ECU
23 ... EGR gas outlet 24 ... EGR device

Claims (5)

A supercharging device for supplying pressurized intake air to the internal combustion engine;
An EGR passage that recirculates part of the exhaust gas flowing through the exhaust passage of the internal combustion engine to the upstream side of the supercharging device of the intake passage of the internal combustion engine;
An EGR flow rate adjusting device for adjusting an amount of exhaust gas recirculated to the intake passage via the EGR passage;
A bypass passage for allowing a portion of the intake air pressurized by the supercharging device to flow into the EGR passage;
At least one of the EGR stop conditions is satisfied when the internal combustion engine is in a high-load operation state or when a process for recovering the exhaust purification ability of the catalyst or the particulate filter provided in the exhaust passage is being executed. when, it guides the intake air to the EGR passage through the bypass passage, and scavenging means for backflow to the upstream side of the intake from the downstream side of the EGR passage by controlling the EGR flow regulating device,
An exhaust gas purification system for an internal combustion engine, comprising: In Claim 1, the EGR flow control device is an EGR valve provided in the EGR passage,
An EGR cooler for cooling the exhaust gas flowing through the EGR passage is provided upstream of the EGR valve in the EGR passage,
The bypass passage is a passage that connects the EGR passage downstream from the EGR cooler and upstream from the EGR valve and the intake passage downstream from the supercharger,
The bypass passage is provided with a bypass on-off valve that opens and closes the bypass passage,
The exhaust gas purification system for an internal combustion engine, wherein the scavenging means opens the bypass on-off valve and closes the EGR valve when at least one of the EGR stop conditions is satisfied . The EGR control means according to claim 2, further comprising an EGR control means for recirculating exhaust gas from the exhaust passage to the intake passage upstream of the supercharger by opening the EGR valve,
An exhaust gas purification system for an internal combustion engine , wherein the exhaust gas recirculation is not performed by the EGR control means when at least one of the EGR stop conditions is satisfied . In claim 2,
Even when the EGR stop condition is not satisfied, the scavenging means forcibly forces the EGR passage when the intake pressure upstream of the supercharging device is in an operating state in which the exhaust pressure is higher than the exhaust pressure in the exhaust passage. An exhaust gas purification system for an internal combustion engine characterized by performing scavenging .   In claim 4,
  The scavenging means forcibly scavenges the EGR passage when the EGR stop condition is not satisfied for a certain period or longer.

Images