Structure of the exhaust gas recirculation passage

Abstract

This system aims to achieve both the suppression of condensate concentration and the suppression of variations in EGR gas volume. [Solution] The structure of an exhaust gas recirculation passage that returns a portion of the exhaust gas generated by combustion to the cylinder where combustion occurred, comprising: an introduction pipe 2 that guides the exhaust gas to the cylinder side; first branch pipes 3A, 3B that branch into multiple branches at the tip of the introduction pipe 2; second branch pipes 4A to 4D that branch into multiple branches at the tips of the first branch pipes 3A, 3B; a connecting passage 5 that connects one of the second branch pipes 4B that branches from any one of the first branch pipes 3A and another second branch pipe 4C that branches from another first branch pipe 3B; and a flow obstruction section 6 that provides resistance to condensed water flowing along the inner surface of the connecting passage 5.

Description

Technical Field

[0001] The present invention relates to a structure of a passage for performing exhaust gas recirculation in which a part of exhaust gas generated by combustion of an air-fuel mixture is mixed into the air-fuel mixture.

Background Art

[0002] An example of this type of passage structure is described in Patent Document 1. The structure described in Patent Document 1 has an introduction passage for introducing exhaust gas from an exhaust system of an engine, and the introduction passage is bifurcated at its tip side to form a first gas passage portion and a second gas passage portion. These gas passage portions communicate with a gas chamber. A plurality of gas distribution passages for distributing and supplying recirculation gas (EGR gas) to cylinders of the engine are provided in the gas chamber, and partition walls, which are the wall surfaces at the locations where these gas distribution passages open, are divided by ridges. Therefore, although each gas distribution passage communicates with each other using the gas chamber as a so-called header, since the ridges protrude toward the inside of the chamber, the flow of condensed water between the openings on the gas chamber side of the gas distribution passages is blocked or suppressed by the ridges. As a result, it is said that condensed water can be prevented from flowing to a specific combustion cylinder in the engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the structure of the EGR gas passage to the combustion cylinder described in Patent Document 1, EGR gas is distributed from the gas introduction passage to the first and second gas passage sections. However, the distributed EGR gas is merged in the gas chamber, and then the EGR gas is distributed from the gas chamber to the gas distribution passage and sent to the combustion cylinder. Therefore, condensed water contained in the EGR gas or condensed water generated during the process of reaching the gas chamber merges in the gas chamber. Since the gas chamber has a single cavity inside, if centrifugal force acts due to the vehicle turning, etc., the condensed water will concentrate in a specific gas distribution passage. In the configuration described in Patent Document 1, although a protrusion is provided, the protrusion does not divide the inside of the gas chamber into multiple cavity sections, so it may not be possible to sufficiently prevent the concentration of condensed water in a specific combustion cylinder.

[0005] To avoid the concentration of condensed water, it is conceivable to divide the gas distribution passages and the passages leading to them, making each independent. For example, the inlet passage could be divided into two branch passages, and each branch passage could be further divided into two more branch passages before the EGR gas is guided to each combustion cylinder. With such a configuration, just before entering the combustion cylinder, the passages are divided and independent, so the condensed water at the point where the gas is guided to a specific combustion cylinder will not move to the other combustion cylinders. However, in a configuration where the passage is divided into multiple sequentially in this way, the amount of EGR gas may vary between combustion cylinders. For example, if combustion occurs continuously in two adjacent combustion cylinders, and combustion occurs in two other combustion cylinders with a time interval, the EGR gas will flow continuously through one of the branch passages branching from the inlet passage, and then flow through the other branch passage. Since EGR gas has inertia, a delay occurs when switching the flow path from one branch passage to the other, and this causes a variation in the amount of EGR gas between combustion cylinders. Increasing the amount of EGR gas introduced increases the variation in EGR gas volume between combustion cylinders.

[0006] This invention was made in view of the above technical problems, and aims to provide an exhaust gas recirculation passage structure that can suppress both the concentration of condensate and the variation in the amount of EGR gas. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a structure for an exhaust gas recirculation passage that recirculates a portion of the exhaust gas generated by combustion back to the cylinder where the combustion occurred, characterized in that it comprises: an introduction pipe that guides the exhaust gas to the cylinder side; a first branch pipe that branches into a plurality of branches at the tip of the introduction pipe; a second branch pipe that branches into a plurality of branches at the tip of the first branch pipe; a connecting passage that connects a second branch pipe that branches from any one of the first branch pipes and another second branch pipe that branches from another first branch pipe; and a flow obstruction section that provides resistance to condensed water flowing along the inner surface of the connecting passage. [Effects of the Invention]

[0008] In this invention, the pipelines that guide exhaust gas to the cylinders branch off from the inlet pipeline and are ultimately independent of each other, so that the movement of condensed water between cylinders is prevented at each branching point. Furthermore, the variation in exhaust gas volume between the first branch pipelines due to the inertia of the exhaust gas is eliminated or suppressed by the connecting passages. In addition, since flow obstruction sections are provided in the connecting passages, the concentration of condensed water toward a specific cylinder is prevented or suppressed. In short, according to this invention, both variation in exhaust gas volume and the concentration of condensed water can be prevented or suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an embodiment of the present invention. [Modes for carrying out the invention]

[0010] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0011] The exhaust gas recirculation passage according to the present invention is for recirculating a portion of the exhaust gas produced by the combustion of a fuel-air mixture in the engine cylinders back into the cylinders, and is installed between the engine's exhaust system and the intake system, such as an intake manifold. An example is schematically shown in Figure 1. The exhaust gas recirculation passage 1 shown here has an inlet pipe 2 that is connected to the engine's exhaust system (not shown) and guides the exhaust gas G to the intake side. At the tip of the inlet pipe 2, there are two first branch pipes 3A and 3B that branch into multiple (two in the example of Figure 1). These first branch pipes 3A and 3B may be configured by joining two pipes in a bifurcated manner and connecting them to the tip of the inlet pipe 2. Alternatively, two pipes may be branched and connected to a header pipe, and that header pipe may be connected to the inlet pipe 2. Furthermore, since the exhaust gas (i.e., EGR gas) G flowing through the inlet pipe 2 is divided and flows into the first branch pipes 3A and 3B, each of the first branch pipes 3A and 3B may be about half the diameter of the inlet pipe 2.

[0012] Branch pipelines are provided to send exhaust gas G from each of the first branch pipelines 3A and 3B to multiple cylinders (not shown). That is, at the end of each of the multiple (two) first branch pipelines 3A and 3B, there are multiple (two in the example of Figure 1) second branch pipelines 4A, 4B, 4C, and 4D that branch off. In the example shown in Figure 1, one pair of second branch pipelines 4A and 4B are connected to one first branch pipeline 3A, and the other pair of second branch pipelines 4C and 4D are connected to the other first branch pipeline 3B. Each pair of second branch pipelines 4A and 4B (or 4C and 4D) may be configured by joining two pipes in a bifurcated manner and connecting them to the end of the first branch pipeline 3A (or 3B). Alternatively, two pipes may be branched and connected to a header pipe, and that header pipe may be connected to the first branch pipeline 3A (or 3B). Furthermore, since the exhaust gas G flowing through the first branch pipes 3A and 3B is divided and flows into each of the second branch pipes 4A, 4B, 4C, and 4D, each of the second branch pipes 4A, 4B, 4C, and 4D may be about half the diameter of the first branch pipes 3A and 3B.

[0013] In the example shown in Figure 1, the second branch lines 4A, 4B, 4C, and 4D are connected to cylinder #1, cylinder #2, cylinder #3, and cylinder #4, respectively, from left to right in Figure 1. The ignition sequence is cylinder #1 → cylinder #3 → cylinder #4 → cylinder #2. Therefore, exhaust gas G is sent continuously to cylinder #3 and cylinder #4, and then to cylinder #2 and cylinder #1. In terms of the pipelines through which the exhaust gas G flows, exhaust gas G flows through one of the first branch lines 3B for the duration of the two ignitions, and then flows through the other first branch line 3B. In other words, the system switches from supplying exhaust gas G to cylinder #1 to supplying exhaust gas G to cylinder #3, and then switches from supplying exhaust gas G to cylinder #4 to supplying exhaust gas G to cylinder #2.

[0014] In the example shown in Figure 1, a connecting passage 5 is provided that connects the second branch pipe 4B on one side of the first branch pipe 3A with the second branch pipe 4C on the other side of the first branch pipe 3B. This connecting passage 5 is a passage that connects one side of the first branch pipe 3A with the other side of the first branch pipe 3B on the side of the second branch pipes 4A, 4B, 4C, and 4D. Therefore, instead of providing the connecting passage 5 between the second branch pipe 4C that connects to the second cylinder #2 and the second branch pipe 4C that connects to the third cylinder #3, it may be provided between the second branch pipe 4A that connects to the first cylinder #1 and the second branch pipe 4D that connects to the fourth cylinder #4.

[0015] The connecting passage 5 functions to merge the pipelines or exhaust gas G separated by the first branch pipelines 3A and 3B. Therefore, it is provided with flow obstruction sections to prevent or suppress the movement and merger of condensed water as the exhaust gas G merges. Examples of these flow obstruction sections include bends and uneven areas inside the connecting passage 5. In the example shown in Figure 1, the inclined section 6 provided in the connecting passage 5 serves as the flow obstruction section. The inclined section 6 is the part of the passage that is inclined at a predetermined angle with respect to a straight line connecting the connection points (or open ends) to the second branch pipelines 4B and 4C at both ends of the connecting passage 5. In the example shown in Figure 1, inclined sections 6 are provided at both ends of the connecting passage 5. The angle is preferably greater than, for example, 4 degrees.

[0016] In the exhaust gas recirculation passage 1 with the configuration shown in Figure 1, the exhaust gas G flowing through the inlet pipe 2 is split into two at the tip of the inlet pipe 2 and heads toward the first branch pipes 3A and 3B. Since these first branch pipes 3A and 3B are independent of each other, even if condensation occurs inside each, that condensation will not concentrate on either the first branch pipe 3A or 3B side due to centrifugal force or other factors.

[0017] The exhaust gas G is further divided into two at the ends of each first branch pipe 3A, 3B and flows into each second branch pipe 4A, 4B, 4C, 4D, and then sent to cylinders #1 to #4, which are connected to each of the second branch pipes 4A, 4B, 4C, 4D. Even in this case, since each of the second branch pipes 4A, 4B, 4C, 4D is independent of each other, even if condensation occurs inside each, it is prevented or suppressed from concentrating that condensation in any of the second branch pipes 4A, 4B, 4C, 4D or any of the cylinders #1 to #4 due to centrifugal force or the like.

[0018] As mentioned above, in the example shown in Figure 1, exhaust gas G is sent to one of the first branch pipes 3A (or 3B) for two ignitions, and then to the other first branch pipe 3B (or 3A). When the flow of exhaust gas G switches in this way, the inertia of the exhaust gas G can cause variations in the amount of exhaust gas. In that case, a difference in gas flow rate or pressure occurs at the outlet side of each first branch pipe 3A, 3B, that is, between one second branch pipe 4B and the other second branch pipe 4C. As a result, the exhaust gas G flows through the connecting passage 5, correcting any imbalance or variation in the amount of gas for cylinders #1 to #4.

[0019] Furthermore, when centrifugal force acts on the condensed water due to the vehicle turning, the flow of the condensed water is blocked or suppressed by the inclined section 6 described above in the connecting passage 5. As a result, even if the outlet sides of each of the first branch pipes 3A and 3B, that is, one second branch pipe 4B and the other second branch pipe 4C, are connected by the connecting passage 5, it is possible to avoid or suppress the condensed water from flowing and accumulating in the direction of the centrifugal force, and consequently concentrating in specific cylinders #1 to #4. In short, the structure of the exhaust gas recirculation passage described above makes it possible to suppress both the concentration of condensed water and the variation in the amount of EGR gas.

[0020] In the above-described embodiment, an example configured for a four-cylinder engine has been shown. However, the present invention can be implemented for engines having a number of cylinders other than four cylinders. Therefore, the number of the first branch pipelines and the number of the second branch pipelines are not limited to the numbers shown in the above-described embodiment.

Explanation of Signs

[0021] 1 Exhaust gas recirculation passage 2 Introduction pipeline 3A, 3B First branch pipeline 4A, 4B, 4C, 4D Second branch pipeline 5 Connection passage 6 Inclined portion (flow obstruction portion) G Exhaust gas (EGR gas) #1~#4 Cylinders

Claims

[Claim 1] A structure for an exhaust gas recirculation passage that recirculates a portion of the exhaust gas generated by combustion back into the cylinder where the combustion occurred, An introduction pipe for guiding the exhaust gas to the cylinder side, The first branch pipeline, which branches into multiple lines at the tip of the aforementioned inlet pipeline, The first branch pipeline has a second branch pipeline that branches into multiple branches at its tip, A connecting passage that links one second branch pipeline that branches off from one first branch pipeline with another second branch pipeline that branches off from another first branch pipeline, A flow obstruction section that provides resistance to condensed water flowing along the inner surface of the connecting passage A structure for an exhaust gas recirculation passage characterized by having the following features.

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