JP2010151075A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for recirculating desired quantity of low pressure EGR gas by reducing pressure loss when low pressure EGR gas flows through a low pressure EGR filter in an exhaust gas recirculation device for an internal combustion engine. <P>SOLUTION: This exhaust gas recirculation device includes: a turbocharger 6 including a turbine 6b disposed in an exhaust gas passage 5 of the internal combustion engine 1 and a compressor 6a disposed in an intake air passage 4 of the internal combustion engine 1; a low pressure EGR passage 31 taking part of exhaust gas from the exhaust gas passage 5 at a downstream of the turbine 6b as low pressure EGR gas and recirculating the low pressure EGR gas to the intake air passage 4 at an upstream of the compressor 6a; a low pressure EGR cooler 33 disposed in the low pressure EGR passage 31 and cooling the low pressure EGR gas flowing through the low pressure EGR passage 31; and a low pressure EGR filter 34 disposed in the low pressure EGR passage 31 at a downstream of the low pressure EGR cooler 33 and collecting PM in the low pressure EGR gas flowing through the low pressure EGR passage 31. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

The internal combustion engine may include an EGR passage that recirculates a part of the exhaust discharged from the internal combustion engine to the intake passage as EGR gas. When the EGR gas is introduced into the internal combustion engine through the EGR passage, the combustion temperature of the internal combustion engine is lowered by the heat capacity of the inert gas in the EGR gas, and the amount of NOx generated along with engine combustion can be reduced. In an internal combustion engine having such an EGR passage, an EGR cooler that cools the EGR gas flowing through the EGR passage in order to maintain or lower the temperature of the EGR gas at a temperature that can lower the combustion temperature of the internal combustion engine. May be arranged in the middle of the EGR passage. Furthermore, a technique is disclosed in which a particulate filter (hereinafter referred to as an EGR filter) that collects exhaust system foreign matter in the EGR gas is disposed in the EGR passage upstream of the EGR cooler (see, for example, Patent Document 1). . When the exhaust system foreign matter is collected by the EGR filter in this manner, the exhaust system foreign matter that has circulated through the EGR passage does not return to the intake passage, and damage to the intake system and the internal combustion engine can be avoided.
JP 2005-16390 A JP 2008-150955 A JP 2000-249003 A JP 2001-227324 A

  However, when the EGR filter is arranged in the EGR passage upstream of the EGR cooler as in the technique described in Patent Document 1, the pressure loss when the high-temperature EGR gas flows through the EGR filter increases, and the EGR gas However, it was difficult to secure a desired amount of EGR gas.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce a pressure loss when low-pressure EGR gas flows through a low-pressure EGR filter in an exhaust gas recirculation apparatus for an internal combustion engine, and to achieve a desired amount. The present invention provides a technique for refluxing low pressure EGR gas.

In the present invention, the following configuration is adopted. That is, the present invention
A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR passage that takes a part of the exhaust as low-pressure EGR gas from the exhaust passage downstream of the turbine and returns the low-pressure EGR gas to the intake passage upstream of the compressor;
A low pressure EGR cooler that is disposed in the low pressure EGR passage and cools the low pressure EGR gas flowing through the low pressure EGR passage;
A low pressure EGR filter that is disposed in the low pressure EGR passage downstream of the low pressure EGR cooler and collects exhaust system foreign matter in the low pressure EGR gas flowing through the low pressure EGR passage;
An exhaust gas recirculation device for an internal combustion engine.

In the present invention, the low pressure EGR filter is disposed in the low pressure EGR passage downstream of the low pressure EGR cooler. For this reason, since the low pressure EGR gas flowing into the low pressure EGR filter is cooled by the low pressure EGR cooler, the temperature is low. Here, the low-pressure low-pressure EGR gas has a gas density higher than that at a high temperature, and the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter is lower than that at a high temperature at the same flow rate. Therefore, according to the present invention, since the low-pressure EGR gas flowing into the low-pressure EGR filter is low in temperature, the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter can be reduced, and the low-pressure EGR gas easily recirculates. The gas can be refluxed.

In the present invention, the following configuration is adopted. That is, the present invention
A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR passage that takes a part of the exhaust as low-pressure EGR gas from the exhaust passage downstream of the turbine and returns the low-pressure EGR gas to the intake passage upstream of the compressor;
An upstream low pressure EGR cooler that is disposed in the low pressure EGR passage and cools the low pressure EGR gas flowing through the low pressure EGR passage;
A low pressure EGR filter that is disposed in the low pressure EGR passage downstream of the upstream low pressure EGR cooler and collects exhaust system foreign matter in the low pressure EGR gas flowing through the low pressure EGR passage;
A downstream low-pressure EGR cooler that is disposed in the low-pressure EGR passage downstream of the low-pressure EGR filter and cools the low-pressure EGR gas flowing through the low-pressure EGR passage;
Cooler switching control means for cooling the low pressure EGR gas by the upstream low pressure EGR cooler during normal operation of the internal combustion engine, and for cooling the low pressure EGR gas by the downstream low pressure EGR cooler during filter regeneration control of the low pressure EGR filter. ,
An exhaust gas recirculation device for an internal combustion engine.

  In the present invention, the low pressure EGR gas is cooled by the upstream low pressure EGR cooler during normal operation of the internal combustion engine, and the low pressure EGR gas is cooled by the downstream low pressure EGR cooler during filter regeneration control of the low pressure EGR filter.

  For this reason, during normal operation of the internal combustion engine, the low-pressure EGR gas flowing into the low-pressure EGR filter is cooled by the upstream low-pressure EGR cooler and thus has a low temperature. Here, the low-pressure low-pressure EGR gas has a gas density higher than that at a high temperature, and the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter is lower than that at a high temperature at the same flow rate. Therefore, according to the present invention, during the normal operation of the internal combustion engine, the low pressure EGR gas flowing into the low pressure EGR filter is low in temperature, so that the pressure loss when the low pressure EGR gas flows through the low pressure EGR filter can be reduced, and the low pressure EGR gas is recirculated. It is easy to recirculate a desired amount of low-pressure EGR gas.

  On the other hand, at the time of filter regeneration control of the low pressure EGR filter, the low pressure EGR gas flowing into the low pressure EGR filter is not cooled by the upstream low pressure EGR cooler and is at a high temperature. Here, in the filter regeneration control of the low pressure EGR filter, the exhaust pressure foreign matter collected by the low pressure EGR filter is oxidized and removed by raising the temperature of the low pressure EGR filter. Therefore, according to the present invention, at the time of filter regeneration control of the low pressure EGR filter, since the low pressure EGR gas flowing into the low pressure EGR filter is at a high temperature, the temperature of the low pressure EGR filter can be easily increased.

  During filter regeneration control of the low pressure EGR filter, the low pressure EGR gas flowing out from the low pressure EGR filter is cooled by the downstream low pressure EGR cooler to a low temperature. Therefore, even during the filter regeneration control of the low-pressure EGR filter, the low-temperature low-pressure EGR gas similar to that during normal operation of the internal combustion engine can be introduced into the internal combustion engine, and the amount of NOx generated due to engine combustion can be reduced.

The upstream-side low-pressure EGR cooler and the downstream-side low-pressure EGR cooler cool the low-pressure EGR gas by exchanging heat between the low-pressure EGR gas and the cooling medium, and can supply the cooling medium individually. The cooler switching control means supplies the cooling medium to the upstream low-pressure EGR cooler without supplying the cooling medium to the downstream low-pressure EGR cooler during normal operation of the internal combustion engine, and performs filter regeneration control of the low-pressure EGR filter. The cooling medium may be supplied to the downstream low pressure EGR cooler without supplying the cooling medium to the upstream low pressure EGR cooler.

  According to the present invention, the low pressure EGR gas can be cooled by the upstream low pressure EGR cooler during normal operation of the internal combustion engine, and the low pressure EGR gas can be cooled by the downstream low pressure EGR cooler during filter regeneration control of the low pressure EGR filter.

  An exhaust purification device disposed in the exhaust passage downstream of the turbine and upstream of a connection site with the low-pressure EGR passage, the exhaust purification device purifying the exhaust gas flowing through the exhaust passage, and raising the temperature of the exhaust purification device When the control for recovering the performance of the exhaust gas purification apparatus accompanied by the control is performed, the filter regeneration control of the low pressure EGR filter may be performed.

  According to the present invention, at the time of filter regeneration control of the low pressure EGR filter, a part of the exhaust gas whose temperature has become high by the control for recovering the performance of the exhaust gas purification device accompanied by raising the temperature of the exhaust gas purification device is used as the low pressure EGR gas. Flow into. Therefore, since the low pressure EGR gas flowing into the low pressure EGR filter becomes higher in temperature, the temperature of the low pressure EGR filter can be more easily increased.

  According to the present invention, in the exhaust gas recirculation apparatus for an internal combustion engine, the pressure loss when the low pressure EGR gas flows through the low pressure EGR filter can be reduced, and a desired amount of the low pressure EGR gas can be recirculated.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas recirculation apparatus for an internal combustion engine according to the present embodiment is applied and an intake system and an exhaust system thereof.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders 2 that form a combustion chamber together with a piston. The internal combustion engine 1 is mounted on a vehicle. Each cylinder 2 of the internal combustion engine 1 is provided with a fuel injection valve 3 that injects fuel at an appropriate amount and timing. An intake passage 4 and an exhaust passage 5 are connected to the internal combustion engine 1.

  In the middle of the intake passage 4 connected to the internal combustion engine 1, a compressor 6a of a turbocharger 6 that operates using exhaust energy as a drive source is disposed. An air flow meter 7 that outputs a signal corresponding to the amount of fresh air flowing through the intake passage 4 is disposed in the intake passage 4 upstream of the compressor 6a. The air flow meter 7 measures the intake air amount (fresh air amount) of the internal combustion engine 1. An intercooler 8 that performs heat exchange between the intake air and the outside air is disposed in the intake passage 4 downstream of the compressor 6a. These intake passages 4 and the devices arranged in the intake passages 4 constitute an intake system for taking intake air into the internal combustion engine 1.

  On the other hand, a turbine 6 b of the turbocharger 6 is arranged in the middle of the exhaust passage 5 connected to the internal combustion engine 1. The turbine 6b is driven by exhaust gas flowing through the exhaust passage 5, and the compressor 6a rotates together with the driven turbine 6b to supercharge intake air flowing through the intake passage 4.

An exhaust purification device 9 is disposed in the exhaust passage 5 downstream of the turbine 6b. The exhaust emission control device 9 includes an oxidation catalyst and a particulate filter (hereinafter simply referred to as a filter) disposed at the subsequent stage of the oxidation catalyst. The filter collects PM (particulate matter, soot) as exhaust system foreign matter contained in the exhaust gas flowing into the exhaust gas purification device 9 and purifies the exhaust gas.

  The filter carries a NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst). The NOx catalyst occludes NOx in the exhaust when the internal combustion engine 1 has a high oxygen concentration as in the normal operation, and the air-fuel ratio of the inflowing exhaust decreases and the oxygen concentration in the exhaust decreases. In addition, when a reducing agent such as fuel is present, the NOx occluded is released and reduced to restore the NOx occlusion performance. The NOx catalyst also stores SOx together with NOx in the exhaust when the internal combustion engine 1 has a high oxygen concentration, such as during normal operation. When the oxygen concentration in the exhaust gas decreases and the reducing agent such as fuel is present, the stored SOx is released and reduced to restore the NOx storage performance.

  However, the PM collection performance of the filter of the exhaust purification device 9 and the NOx storage performance of the NOx catalyst are limited. For this reason, in order to recover these performances, the exhaust gas purification apparatus 9 performs so-called NOx reduction control, S regeneration control (SOx poisoning recovery control), and filter regeneration control (PM oxidation removal control). Control to restore the performance of 9 is performed.

  In the NOx reduction control, when the NOx occlusion amount occluded in the NOx catalyst becomes a predetermined amount or more, fuel is added as a reducing agent from a fuel addition valve (not shown) disposed in the internal combustion engine or the exhaust passage 5, and the exhaust purification device 9 The air-fuel ratio of the exhaust gas flowing into the exhaust gas is reduced, and NOx is released and reduced from the NOx catalyst.

  In the S regeneration control, when the SOx occlusion amount occluded in the NOx catalyst exceeds a predetermined amount, fuel is added as a reducing agent from the internal combustion engine or the fuel addition valve, and the exhaust gas is exhausted by the oxidation heat of the fuel reacted with the oxidation catalyst or NOx catalyst While the temperature of the purification device 9 is raised, the air-fuel ratio of the exhaust gas flowing into the exhaust purification device 9 is lowered, and SOx is released and reduced from the NOx catalyst.

  In the filter regeneration control, when the PM collected by the filter exceeds a predetermined amount, fuel is added from the internal combustion engine or the fuel addition valve, and the exhaust purification device 9 is raised by the oxidation heat of the fuel reacted with the oxidation catalyst or the NOx catalyst. It warms and oxidizes and removes PM collected by the filter.

  As described above, the control of recovering the performance of the exhaust gas purification device 9 is performed other than during the normal operation of the internal combustion engine 1, so that the performance of the exhaust gas purification device 9 is maintained. Note that the S regeneration control and the filter regeneration control correspond to control for recovering the performance of the exhaust purification device 9 that involves raising the temperature of the exhaust purification device 9 in the present invention.

  The exhaust passage 5 and the devices arranged in the exhaust passage 5 constitute an exhaust system for exhausting exhaust gas from the internal combustion engine 1.

  The internal combustion engine 1 is provided with a high pressure EGR device 20 that recirculates (recirculates) a part of the exhaust gas flowing through the exhaust passage 5 to the intake passage 4 at a high pressure. The high pressure EGR device 20 includes a high pressure EGR passage 21 and a high pressure EGR valve 22.

  The high pressure EGR passage 21 connects the exhaust passage 5 upstream of the turbine 6 b and the intake passage 4 downstream of the intercooler 8. Exhaust gas is fed into the internal combustion engine 1 at high pressure through the high pressure EGR passage 21. The exhaust gas that is circulated through the high-pressure EGR passage 21 and refluxed is high-pressure EGR gas.

  The high-pressure EGR valve 22 adjusts the amount of high-pressure EGR gas flowing through the high-pressure EGR passage 21 by adjusting the passage sectional area of the high-pressure EGR passage 21. The high pressure EGR valve 22 is opened and closed by an electric actuator.

  The internal combustion engine 1 is provided with a low pressure EGR device 30 that recirculates (recirculates) a part of the exhaust gas flowing through the exhaust passage 5 to the intake passage 4 at a low pressure. The low pressure EGR device 30 includes a low pressure EGR passage 31, a low pressure EGR valve 32, a low pressure EGR cooler 33, and a low pressure EGR filter 34.

  The low pressure EGR passage 31 connects the exhaust passage 5 downstream of the exhaust purification device 9 and the intake passage 4 upstream of the compressor 6 a and downstream of the air flow meter 7. Exhaust gas is fed into the internal combustion engine 1 at low pressure through the low pressure EGR passage 31. The exhaust gas that flows back through the low-pressure EGR passage 31 is low-pressure EGR gas.

  The low pressure EGR valve 32 adjusts the amount of the low pressure EGR gas flowing through the low pressure EGR passage 31 by adjusting the passage sectional area of the low pressure EGR passage 31. The low pressure EGR valve 32 is opened and closed by an electric actuator.

  The low-pressure EGR cooler 33 is disposed in the low-pressure EGR passage 31 upstream of the low-pressure EGR valve 32 and the low-pressure EGR filter 34, performs heat exchange between the low-pressure EGR gas and the engine cooling water, and flows through the low-pressure EGR passage 31. Cool the gas. As a result, the temperature of the low-pressure EGR gas is maintained or lowered to a temperature at which the combustion temperature of the internal combustion engine 1 can be lowered. The engine cooling water in this embodiment corresponds to the cooling medium of the present invention. The cooling medium is not limited to engine cooling water, and a gas such as air can also be used.

  The low-pressure EGR filter 34 is disposed in the low-pressure EGR passage 31 downstream from the low-pressure EGR cooler 33 and collects PM as exhaust system foreign matter in the low-pressure EGR gas flowing through the low-pressure EGR passage 31. Here, since the exhaust gas that becomes the low-pressure EGR gas has already passed through the exhaust gas purification device 9, PM is also reduced, but the low-pressure EGR filter 34 further collects PM. As the low pressure EGR filter 34, for example, a metal filter or the like is used. When PM is collected by the low pressure EGR filter 34 in this way, it is possible to prevent the PM that has circulated through the low pressure EGR passage 31 from returning to the intake passage 4 and damaging the intake system and the internal combustion engine 1.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. In addition to the air flow meter 7, a crank position sensor 11 and an accelerator position sensor 12 are connected to the ECU 10 through electrical wiring, and output signals from these various sensors are input to the ECU 10. On the other hand, the fuel injection valve 3 and the actuators of the high-pressure EGR valve 22 and the low-pressure EGR valve 32 are connected to the ECU 10 through electric wiring, and these devices are controlled by the ECU 10.

  Conventionally, since the low-pressure EGR filter is disposed in the low-pressure EGR passage upstream of the low-pressure EGR cooler, high-temperature low-pressure EGR gas that is not cooled by the low-pressure EGR cooler flows into the low-pressure EGR filter. In this case, the high-temperature low-pressure EGR gas passes through the low-pressure EGR filter as indicated by A in FIG. 2 showing the relationship between the temperature of the low-pressure EGR gas and the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter. The pressure loss at the time of circulation became high, the low-pressure EGR gas was difficult to recirculate, and it was difficult to secure a desired amount of the low-pressure EGR gas. For this reason, attempts to recirculate a desired amount of low-pressure EGR gas may lead to deterioration in fuel consumption.

  Therefore, in this embodiment, the low pressure EGR filter 34 is arranged in the low pressure EGR passage 31 downstream of the low pressure EGR cooler 33.

  According to this embodiment, the low-pressure EGR gas flowing into the low-pressure EGR filter 34 is cooled by the low-pressure EGR cooler 33 and thus has a low temperature. Here, the low-pressure low-pressure EGR gas has a higher gas density than the high-temperature low-pressure EGR gas, and the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter 34 at the same flow rate is indicated by a mark B in FIG. Thus, it becomes lower than the A mark in FIG. 2 when the temperature is high. Therefore, according to this embodiment, since the low-pressure EGR gas flowing into the low-pressure EGR filter 34 is low in temperature, the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter 34 can be reduced, and the low-pressure EGR gas easily recirculates. Of low pressure EGR gas can be refluxed. Therefore, the fuel efficiency is not deteriorated when the desired amount of EGR gas is recirculated.

<Example 2>
Next, Example 2 will be described. In this embodiment, parts different from the above embodiment will be described, and description of similar parts will be omitted.

  FIG. 3 shows a schematic configuration of the internal combustion engine and its intake system / exhaust system according to the present embodiment. In this embodiment, as shown in FIG. 3, a low pressure EGR cooler 35 is provided in the low pressure EGR passage 31 downstream of the low pressure EGR filter 34 and upstream of the low pressure EGR valve 32. Hereinafter, the low pressure EGR cooler 33 on the upstream side of the low pressure EGR filter 34 is referred to as an upstream low pressure EGR cooler 33. Further, the low pressure EGR cooler 35 on the downstream side of the low pressure EGR filter 34 is referred to as a downstream low pressure EGR cooler 35.

  The upstream low-pressure EGR cooler 33 and the downstream low-pressure EGR cooler 35 perform heat exchange between the low-pressure EGR gas and the engine cooling water, and cool the low-pressure EGR gas flowing through the low-pressure EGR passage 31. Here, a cooling water passage 33 a that supplies engine cooling water to the upstream low-pressure EGR cooler 33 and collects engine cooling water from the upstream low-pressure EGR cooler 33 is provided. In addition, a cooling water passage 35 a that supplies engine cooling water to the downstream low-pressure EGR cooler 35 and collects engine cooling water from the downstream low-pressure EGR cooler 35 is provided. The cooling water channels 33a and 35a are individually provided independently. In each of the cooling water passages 33a and 35a, cooling water valves 33b and 35b for controlling supply / stop of the engine cooling water to the upstream low pressure EGR cooler 33 or the downstream low pressure EGR cooler 35 are arranged. The cooling water valves 33b and 35b are opened and closed by an electric actuator, and these actuators are connected to the ECU 10 via electric wiring, and the cooling water valves 33b and 35b are controlled by the ECU 10.

  In this embodiment, the low pressure EGR gas is cooled by the upstream low pressure EGR cooler 33 during normal operation of the internal combustion engine 1. Therefore, during normal operation of the internal combustion engine 1, the cooling water valve 35 b is closed so that the engine cooling water is not supplied to the downstream low pressure EGR cooler 35, and the engine cooling water is supplied to the upstream low pressure EGR cooler 33. The cooling water valve 33b is opened.

  On the other hand, a part of the high-temperature exhaust gas flowing out from the exhaust purification device 9 when the S regeneration control and the filter regeneration control are performed on the exhaust purification device 9 is introduced into the low-pressure EGR passage 31 as a high-temperature low-pressure EGR gas. Filter regeneration control of the low pressure EGR filter 34 that oxidizes and removes PM collected by the low pressure EGR filter 34 using EGR gas may be performed.

At this time, if the low-pressure EGR gas is cooled by the upstream low-pressure EGR cooler 33, the high-temperature low-pressure EGR gas cannot be supplied to the low-pressure EGR filter 34. For this reason, it is desired to prohibit the low-pressure EGR gas from being cooled by the upstream low-pressure EGR cooler 33. However, if only the low-pressure EGR gas is prohibited from being cooled by the upstream-side low-pressure EGR cooler 33, the high-temperature low-pressure EGR gas is introduced into the internal combustion engine 1, and the combustion temperature of the internal combustion engine 1 is greatly reduced. Thus, the amount of NOx generated with engine combustion cannot be reduced.

  Therefore, at the time of filter regeneration control of the low pressure EGR filter 34, the low pressure EGR gas is cooled by the downstream low pressure EGR cooler 35. Therefore, at the time of filter regeneration control of the low pressure EGR filter 34, the cooling water valve 33b is closed so that the engine cooling water is not supplied to the upstream low pressure EGR cooler 33, and the engine cooling water is supplied to the downstream low pressure EGR cooler 35. Then, the cooling water valve 35b is opened.

  According to this embodiment, during normal operation of the internal combustion engine 1, the low-pressure EGR gas flowing into the low-pressure EGR filter 34 is cooled by the upstream low-pressure EGR cooler 33 and thus has a low temperature. Here, the low-pressure low-pressure EGR gas has a higher gas density than the high-temperature low-pressure EGR gas, and the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter 34 at the same flow rate is indicated by a mark B in FIG. Thus, it becomes lower than the A mark in FIG. 2 when the temperature is high. Therefore, according to the present embodiment, during the normal operation of the internal combustion engine 1, the low pressure EGR gas flowing into the low pressure EGR filter 34 is low in temperature. The gas is easy to reflux, and a desired amount of low-pressure EGR gas can be refluxed. Therefore, the fuel efficiency is not deteriorated when the desired amount of EGR gas is recirculated.

  On the other hand, at the time of filter regeneration control of the low pressure EGR filter, the low pressure EGR gas flowing into the low pressure EGR filter 34 is not cooled by the upstream low pressure EGR cooler 33 and is at a high temperature. Therefore, according to the present embodiment, the low pressure EGR gas is not cooled by the upstream low pressure EGR cooler 33 during the filter regeneration control of the low pressure EGR filter 34. Thereby, the low pressure EGR gas flowing into the low pressure EGR filter 34 can be maintained at a high temperature as the high temperature exhaust gas flowing out from the exhaust purification device 9 when the S regeneration control and the filter regeneration control of the exhaust purification device 9 are performed. Therefore, the temperature of the low-pressure EGR filter 34 can be easily raised, and PM adhering to the low-pressure EGR filter 34 can be oxidized and removed. Further, since the high-temperature low-pressure EGR gas passes through the upstream low-pressure EGR cooler 33 before flowing into the low-pressure EGR filter 34, the PM adhering to the upstream low-pressure EGR cooler 33 can be oxidized and removed.

  At the time of filter regeneration control of the low pressure EGR filter 34, the low pressure EGR gas flowing out from the low pressure EGR filter 34 is cooled by the downstream low pressure EGR cooler 35 and becomes a low temperature. Thereby, the temperature of the low-pressure EGR gas flowing out from the low-pressure EGR filter 34 is maintained or lowered to a temperature at which the combustion temperature of the internal combustion engine 1 can be lowered. Therefore, even during the filter regeneration control of the low-pressure EGR filter 34, the low-temperature low-pressure EGR gas similar to that during normal operation of the internal combustion engine 1 can be introduced into the internal combustion engine 1, and the amount of NOx generated due to engine combustion can be reduced. Can be reduced.

  Next, the cooler switching control routine according to this embodiment will be described. FIG. 4 is a flowchart showing a cooler switching control routine according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 10 that executes this routine corresponds to the cooler switching control means of the present invention.

  In step S101, the upstream low-pressure EGR cooler 33 is used on the assumption that the internal combustion engine 1 is in normal operation. Specifically, the cooling water valve 35b is closed and the cooling water valve 33b is opened.

In step S102, it is determined whether or not the low pressure EGR filter 34 needs filter regeneration control. Specifically, it is determined that the low pressure EGR filter 34 needs to be subjected to filter regeneration control, for example, when a predetermined use time is exceeded from the previous filter regeneration control of the low pressure EGR filter 34.

  If a negative determination is made in step S102, this routine is once ended. If an affirmative determination is made in step S102, the process proceeds to step S103.

  In step S103, it is determined whether the S regeneration control or the filter regeneration control of the exhaust purification device 9 is being performed.

  If a negative determination is made in step S103, this routine is once ended. If an affirmative determination is made in step S103, the process proceeds to step S104.

  In step S104, the low pressure EGR valve 32 is controlled to open. The opening amount of the low pressure EGR valve 32 to the opening side may be obtained in advance, for example, fully open. Further, when the low pressure EGR valve 32 is opened to some extent and the flow of the low pressure EGR gas is not hindered, the processing of this step may not be performed.

  In step S105, the low pressure EGR cooler 35 is used on the downstream side assuming that the low pressure EGR filter 34 is in the filter regeneration control. Specifically, the cooling water valve 33b is closed and the cooling water valve 35b is opened.

  According to the cooler switching control routine described above, during normal operation of the internal combustion engine 1, the pressure loss when the low-pressure EGR gas flows through the low-pressure EGR filter 34 can be reduced, and a desired amount of the low-pressure EGR gas can be recirculated. . On the other hand, at the time of filter regeneration control of the low pressure EGR filter, the high pressure low pressure EGR gas can be supplied to the low pressure EGR filter 34 to easily raise the temperature of the low pressure EGR filter 34 and the low pressure EGR gas flowing out from the low pressure EGR filter 34 is downstream. Cooling with the low-pressure EGR cooler 35 allows low-temperature low-pressure EGR gas to be introduced into the internal combustion engine 1.

  The exhaust gas recirculation apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake system / exhaust system thereof according to Embodiment 1. FIG. It is a figure which shows the relationship between the temperature of the low pressure EGR gas which concerns on Example 1, and the pressure loss at the time of low pressure EGR gas distribute | circulating a low pressure EGR filter. It is a figure which shows schematic structure of the internal combustion engine which concerns on Example 2, and its intake system / exhaust system. 7 is a flowchart illustrating a cooler switching control routine according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Intake passage 5 Exhaust passage 6 Turbocharger 6a Compressor 6b Turbine 7 Air flow meter 8 Intercooler 9 Exhaust purification device 10 ECU
11 Crank position sensor 12 Accelerator position sensor 20 High pressure EGR device 21 High pressure EGR passage 22 High pressure EGR valve 30 Low pressure EGR passage 31 Low pressure EGR passage 32 Low pressure EGR valve 33 Low pressure EGR cooler (upstream low pressure EGR cooler)
33a Cooling water channel 33b Cooling water valve 34 Low pressure EGR filter 35 Downstream low pressure EGR cooler 35a Cooling water channel 35b Cooling water valve

Claims (4)

A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR passage that takes a part of the exhaust as low-pressure EGR gas from the exhaust passage downstream of the turbine and returns the low-pressure EGR gas to the intake passage upstream of the compressor;
A low pressure EGR cooler that is disposed in the low pressure EGR passage and cools the low pressure EGR gas flowing through the low pressure EGR passage;
A low pressure EGR filter that is disposed in the low pressure EGR passage downstream of the low pressure EGR cooler and collects exhaust system foreign matter in the low pressure EGR gas flowing through the low pressure EGR passage;
An exhaust gas recirculation device for an internal combustion engine, comprising: A turbocharger having a turbine disposed in an exhaust passage of an internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR passage that takes a part of the exhaust as low-pressure EGR gas from the exhaust passage downstream of the turbine and returns the low-pressure EGR gas to the intake passage upstream of the compressor;
An upstream low pressure EGR cooler that is disposed in the low pressure EGR passage and cools the low pressure EGR gas flowing through the low pressure EGR passage;
A low pressure EGR filter that is disposed in the low pressure EGR passage downstream of the upstream low pressure EGR cooler and collects exhaust system foreign matter in the low pressure EGR gas flowing through the low pressure EGR passage;
A downstream low-pressure EGR cooler that is disposed in the low-pressure EGR passage downstream of the low-pressure EGR filter and cools the low-pressure EGR gas flowing through the low-pressure EGR passage;
Cooler switching control means for cooling the low pressure EGR gas by the upstream low pressure EGR cooler during normal operation of the internal combustion engine, and for cooling the low pressure EGR gas by the downstream low pressure EGR cooler during filter regeneration control of the low pressure EGR filter. ,
An exhaust gas recirculation device for an internal combustion engine, comprising: The upstream low-pressure EGR cooler and the downstream low-pressure EGR cooler cool the low-pressure EGR gas by exchanging heat between the low-pressure EGR gas and the cooling medium, and can supply the cooling medium individually.
The cooler switching control means supplies the cooling medium to the upstream low pressure EGR cooler without supplying the cooling medium to the downstream low pressure EGR cooler during normal operation of the internal combustion engine, and performs filter regeneration control of the low pressure EGR filter. 3. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 2, wherein a cooling medium is supplied to the downstream low pressure EGR cooler without supplying a cooling medium to the upstream low pressure EGR cooler. An exhaust purification device that is disposed in the exhaust passage downstream of the turbine and upstream of a connection portion with the low-pressure EGR passage, and purifies exhaust gas flowing through the exhaust passage;
The filter regeneration control of the low-pressure EGR filter is performed when the control for recovering the performance of the exhaust purification device accompanied by raising the temperature of the exhaust purification device is performed. An exhaust gas recirculation device for an internal combustion engine.

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