JP2008309125A - Exhaust gas recirculation system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of recirculating exhaust gas without declining engine efficiency in an exhaust gas recirculation system for an internal combustion engine. <P>SOLUTION: The exhaust gas recirculation system for the internal combustion engine is provided with a turbocharger wherein a turbine is arranged on an exhaust passage of the internal combustion engine and a compressor is arranged on an intake passage and with an EGR passage 31 for connecting the exhaust passage with the compressor. The compressor comprises an impeller 50 and a shroud 52 formed around the impeller 50, and the EGR passage 31 is connected to the shroud 52 on the downstream side from a portion 53 having the narrowest cross section of the passage surrounded by the impeller 50 and the shroud 52. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

There is known a low pressure EGR device that includes a turbocharger having a turbine in an exhaust passage and having a compressor in an intake passage, and returns a part of exhaust flowing downstream from the turbine to an intake passage upstream from the compressor (for example, , See Patent Document 1). There is also known an EGR device that recirculates exhaust gas by connecting an exhaust passage upstream of the impeller in the turbine housing and an intake passage downstream of the impeller in the compressor housing (for example, a patent). Reference 2).
JP 2003-193852 A Japanese Patent Laid-Open No. 6-147027

  By the way, in order to introduce the EGR gas into the intake passage, the pressure on the exhaust passage side must be higher than the intake passage side of the EGR passage. However, in the low-pressure EGR device, since the EGR passage is connected downstream of the turbine and the catalyst, the pressure on the exhaust side is low. Therefore, the exhaust pressure may be increased by closing the exhaust throttle valve, or the intake pressure may be decreased by closing the intake throttle valve. However, closing the exhaust throttle valve or the intake throttle valve causes a reduction in engine efficiency.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of recirculating exhaust gas without reducing engine efficiency in an exhaust gas recirculation system for an internal combustion engine. To do.

In order to achieve the above object, an exhaust gas recirculation system for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas recirculation system for an internal combustion engine according to the present invention is:
A turbocharger in which a turbine is arranged in the exhaust passage of the internal combustion engine and a compressor is arranged in the intake passage;
An EGR passage connecting the exhaust passage and the compressor;
With
The compressor includes an impeller and a shroud formed around the impeller. An EGR passage is connected.

  As the impeller rotates, intake air flows through a passage surrounded by the impeller and the shroud. Here, in the passage surrounded by the impeller and the shroud, there is a portion where the passage cross-sectional area is the narrowest (hereinafter referred to as a throat). Then, when the intake air passes through the throat, the pressure of the intake air decreases here. That is, by connecting the EGR passage to the shroud immediately downstream of the throat, the pressure difference between the exhaust passage side and the intake passage side of the EGR passage can be increased. This makes it possible to easily introduce EGR gas into the intake passage.

Further, since the EGR gas does not pass through the upstream end of the impeller (hereinafter referred to as the leading edge), the leading edge is not damaged by the foreign matter contained in the EGR gas. Furthermore, since EGR gas can be introduced without closing the intake throttle valve or the exhaust throttle valve, a decrease in engine efficiency can be suppressed.

  According to the exhaust gas recirculation system for an internal combustion engine according to the present invention, exhaust gas can be recirculated without causing a decrease in engine efficiency.

  Hereinafter, specific embodiments of an exhaust gas recirculation system for an internal combustion engine according to the present invention will be described with reference to the drawings.

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

  An intake passage 3 and an exhaust passage 4 are connected to the internal combustion engine 1. In the middle of the intake passage 3, a compressor housing 5a of a turbocharger 5 that operates using exhaust energy as a drive source is provided.

  An intercooler 6 for exchanging heat between the intake air and the outside air is provided in the intake passage 3 downstream of the compressor housing 5a.

  On the other hand, a turbine housing 5 b of the turbocharger 5 is provided in the middle of the exhaust passage 4. An exhaust purification catalyst 10 is provided in the exhaust passage 4 downstream of the turbine housing 5b.

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

  The low pressure EGR passage 31 connects the exhaust passage 4 downstream of the exhaust purification catalyst 10 and the compressor housing 5a. Through this low pressure EGR passage 31, the exhaust gas is recirculated at a low pressure. In this embodiment, the exhaust gas recirculated through the low pressure EGR passage 31 is referred to as low pressure EGR gas.

  The low pressure EGR valve 32 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. Further, the EGR cooler 33 exchanges heat between the low-pressure EGR gas passing through the EGR cooler 33 and the cooling water of the internal combustion engine 1 to lower the temperature of the low-pressure EGR gas.

  Next, FIG. 2 is a cross-sectional view of a location where the low pressure EGR passage 31 is connected in the turbocharger 5.

An impeller 50 is stored in the compressor housing 5a. The impeller 50 rotates around the shaft 51. A shroud 52 is formed in the compressor housing 5 a around the impeller 50. The shroud 52 is formed along the rotation locus of the impeller slightly outside the rotation locus of the impeller 50 in order to guide intake air to the impeller 50. Intake air flows through a passage surrounded by the shroud 52 and the impeller 50. In the passage surrounded by the shroud 52 and the impeller 50, there is a portion (hereinafter referred to as a throat 53) where the cross-sectional area is the narrowest, and the throat 53 increases the flow velocity of the intake air.
In FIG. 2, the throat 53 is indicated by a broken line. Therefore, when the intake air passes through the throat 53, the pressure of the intake air decreases.

  In the shroud 52 immediately downstream of the throat 53, a slit 301 leading to the chamber 300 formed in the shroud 52 is opened. The position and size of the opening of the slit 301 are set so that, for example, the inside of the slit 301 has a negative pressure. Further, the length of the slit 301 in the direction of intake air flow may be, for example, 10% of the meridional surface length of the impeller 50. Further, the slit 301 may be set so that the center of the opening of the slit 301 is the position where the pressure of the intake air is lowest.

  A low pressure EGR passage 31 extending from the exhaust passage 4 is connected to the chamber 300. Since the chamber 300 and the slit 301 can be handled as a part of the low pressure EGR passage 31, the following description will be made assuming that the chamber 300 and the slit 301 are a part of the low pressure EGR passage 31. In other words, the low pressure EGR passage 31 communicates the exhaust passage 4 downstream of the exhaust purification catalyst 10 and the intake passage that is immediately downstream of the throat 53 and surrounded by the impeller 50 and the shroud 52.

  In the low pressure EGR device 30 configured as described above, the pressure on the intake passage 3 side of the low pressure EGR passage 31 is low because the pressure of the intake air is reduced in the throat 53. That is, the difference between the pressure on the exhaust passage 4 side of the low pressure EGR passage 31 and the pressure on the intake passage 3 side becomes large. Therefore, the low pressure EGR gas can be easily introduced into the intake passage 3.

  Here, if the low pressure EGR passage 31 is connected to the exhaust passage 4 downstream of the exhaust purification catalyst 10, the exhaust reaches the low pressure EGR passage 31 after passing through the turbine housing 5 b and the exhaust purification catalyst 10. For this reason, the pressure on the exhaust passage 4 side of the low-pressure EGR passage 31 may become low, and the EGR gas may not flow easily. However, according to the present embodiment, since the low pressure EGR passage 31 is connected immediately downstream of the throat 53, the intake passage 3 side of the low pressure EGR passage 31 becomes negative pressure by the intake air that has passed through the throat 53. Thereby, since the pressure difference between the exhaust passage 4 side and the intake passage 3 side of the low pressure EGR passage 31 becomes large, EGR gas can be easily introduced. Further, since it is not necessary to close the intake throttle valve or the exhaust throttle valve, it is possible to suppress a decrease in the efficiency of the internal combustion engine 1.

  Further, when the low pressure EGR passage 31 is connected to the upstream side of the compressor housing 5a, for example, when the exhaust purification catalyst 10 is broken, the fragments of the exhaust purification catalyst 10 together with the low pressure EGR gas are upstream of the impeller 50. Collide with. Since the shape of the upstream end of the impeller 50 greatly affects the performance of the turbocharger 5, the performance of the turbocharger 5 is degraded when the upstream end of the impeller 50 is damaged.

  On the other hand, in the present embodiment, since the low pressure EGR passage 31 is connected to the downstream side of the upstream end of the impeller 50, the exhaust does not pass through the upstream end of the impeller 50. That is, since it is possible to prevent, for example, fragments of the exhaust purification catalyst 10 from colliding with the upstream end of the impeller 50, damage to the upstream end of the impeller 50 can be prevented. Thereby, the performance fall of the turbocharger 5 can be suppressed. Further, it is possible to suppress PM in the low pressure EGR gas from adhering to the upstream end of the impeller 50.

  In the present embodiment, the low pressure EGR passage 31 is connected to the exhaust passage 4 downstream of the exhaust purification catalyst 10, but is connected upstream of the exhaust purification catalyst 10 or upstream of the turbine housing 5b. May be. The turbocharger 5 can also be a variable capacity turbocharger.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas recirculation system for an internal combustion engine according to an embodiment is applied and an intake / exhaust system thereof. It is sectional drawing of the location where a low voltage | pressure EGR channel | path is connected in a turbocharger.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Turbocharger 5a Compressor housing 5b Turbine housing 6 Intercooler 10 Exhaust purification catalyst 30 Low pressure EGR passage 31 Low pressure EGR passage 32 Low pressure EGR cooler 50 Low pressure EGR cooler 50 Impeller 51 Shaft 52 Shroud 53 Throat 300 Chamber 301 Slit

Claims (1)

A turbocharger in which a turbine is arranged in the exhaust passage of the internal combustion engine and a compressor is arranged in the intake passage;
An EGR passage connecting the exhaust passage and the compressor;
With
The compressor includes an impeller and a shroud formed around the impeller. An exhaust gas recirculation system for an internal combustion engine, wherein an EGR passage is connected.

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