JP2003343264A - Method for connecting inner tube of double tube exhaust manifold and inner tube connecting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To thin an inner tube by enhancing the strength of the connecting part of the inner tube, to improve an exhaust gas purifying performance, and to reduce the cost of a catalyst in a double tube exhaust manifold. <P>SOLUTION: A method for connecting the inner tube of the double tube exhaust manifold having an outer tube 4 and an inner tube 3 disposed in an interior at an interval to the inner peripheral surface of the tube 4, so that the tube 3 is constituted of two members of at least first inner tube 7 and second inner tube 8 has a step of inserting the connecting end 71 of the tube 7 into the connecting end 81 of the tube 8 so that both the tubes 7, 8 can axially relatively move. The method comprises the steps of folding the connecting end 81 of the tube 8 to the inside of the tube to form a folding part 82 having a smaller inner diameter than the connecting end 71 of the tube 7, and press injecting the end 71 to the folding part 82. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner pipe connecting method and an inner pipe connecting structure for a double pipe exhaust manifold.

[0002]

2. Description of the Related Art Conventionally, in order to warm up a catalyst provided in an exhaust system faster and to exert an exhaust gas purifying function earlier, a double pipe exhaust composed of an inner pipe and an outer pipe for heat insulation covering the outer periphery thereof. Manifolds are known. The inner pipe is configured by two pipe members connected so as to be relatively movable in the axial direction in order to absorb the difference in thermal expansion between the inner pipe and the outer pipe, which is generated based on the temperature difference and the difference in thermal expansion coefficient.

Further, in the above-mentioned double pipe exhaust manifold, the inner pipe is made thinner to suppress the heat loss of the inner pipe, to improve the exhaust gas purification performance and to reduce the cost of the catalyst. .

[0004]

However, there is a problem in that the workability and durability are deteriorated when the inner tube is made thinner. In particular, when the inner pipe is formed from a pipe material by branch pipe processing such as hydroforming, the wall thickness of the end portion of the branch pipe becomes large, so that the processing height of the connection end portion is limited and the sufficient connection margin. Cannot be secured. Therefore, there is a problem that it is difficult to reduce the wall thickness.

The present invention has been made in view of the above problems. The purpose of the present invention is to increase the strength of the connecting portion and to make the inner pipe thinner, thereby improving the exhaust gas purification performance and the catalyst. An object of the present invention is to provide an inner pipe connecting method and an inner pipe connecting structure of a double pipe exhaust manifold, which can reduce the cost.

[0006]

In order to achieve the above object, in the inner pipe connecting method for a double pipe exhaust manifold according to the first aspect of the present invention, the outer pipe and the inner peripheral surface of the outer pipe are spaced from each other. And an inner pipe disposed inside, and the inner pipe is composed of at least two members of a first inner pipe and a second inner pipe,
In the inner pipe connecting method of the double pipe exhaust manifold, the connecting end of the first inner pipe is inserted into the connecting end of the second inner pipe so as to connect the both so as to be relatively movable in the axial direction. The end portion is folded back to the inside of the can to form a folded portion, and the connection end portion of the first inner pipe is inserted into this folded portion.

According to a second aspect of the present invention, in the inner pipe connecting method of the double pipe exhaust manifold according to the first aspect, the inner diameter of the folded portion is smaller than the outer diameter of the connecting end portion of the first inner pipe. The feature is that it is set.

In the inner pipe connecting structure of the double pipe exhaust manifold according to the third aspect of the present invention, the outer pipe and the inner peripheral surface of the outer pipe are arranged inside the inner pipe with a space provided therebetween. Is composed of at least two members of a first inner pipe and a second inner pipe, and the connecting end of the first inner pipe is inserted into the connecting end of the second inner pipe to connect them so as to be relatively movable in the axial direction. In the inner pipe connecting structure of the double pipe exhaust manifold, the second inner pipe includes a folded-back portion, which is folded back toward the inside of the can, at a connection end portion thereof, and the folded-back portion is a connection end portion of the first inner pipe. It is characterized by being in pressure contact with the outer circumference.

[0009]

According to the present invention, since the wall thickness of the connecting end portion of the second inner pipe can be supplemented by the folded portion, the inner pipe can be made thinner. In particular, in the case of an inner pipe that is formed from a pipe material by using branch pipe processing such as hydroforming, it is possible to suppress strength reduction due to metal thinning at the connection end, and to reduce the connection margin between inner pipes (startup of branch pipe Cost) can be raised to the processing limit.

Furthermore, by setting the inner diameter of the folded-back portion to be smaller than the outer diameter of the connecting end portion of the first inner pipe, the connecting end portions of both inner pipes are set to the size of the press-fitting tolerance, and the caulking processing of the connecting portion is performed. Since it is unnecessary, the cost can be reduced by reducing the number of steps.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment for realizing an inner pipe connecting structure of a double pipe exhaust manifold of the present invention will be described below with reference to the drawings.

First, the structure will be described. FIG. 1 is an overall view showing an exhaust system of an engine to which an inner pipe connecting method for a double pipe exhaust manifold according to the present invention is applied, and FIG. 2 is an enlarged sectional view of an essential part of FIG. Is a 6-cylinder V-type engine, 2 is a catalyst, 3 is an inner pipe, 4 is an outer pipe, 5 is an exhaust pipe, and 6 is a head flange.

As shown in FIG. 1, the double pipe exhaust manifold of this embodiment uses a catalyst 2 provided in the exhaust system to utilize heat of exhaust gas discharged from a 6-cylinder V-type engine 1. As shown in FIG. 2, the inner pipe 3 and the outer pipe 4 covering the outer periphery of the inner pipe 3 have a double structure in order to warm up more quickly and exert the purifying function earlier. The inner pipe 3 and the outer pipe 4 are separated from each other by a gap holding member (not shown) and are blocked by an air layer. Therefore, the heat of the exhaust gas passing through the inner pipe 3 does not easily escape from the outer pipe 4 to the outside, so that the catalyst 2 can be warmed early after the engine is started.

The inner pipe 3 is composed of two members, a first inner pipe 31 and a second inner pipe 32, which are connected so as to be relatively movable in the axial direction. This is because the inner tube 3 side has a function of absorbing a thermal expansion difference generated based on a temperature difference or a thermal expansion coefficient difference between the inner tube 3 and the outer tube 4.

Returning to FIG. 1 in more detail, this double pipe exhaust manifold is provided on both side surfaces of a 6-cylinder V-type engine 1 having two cylinder banks, and each double pipe exhaust manifold is ,
Three inner pipes 3 are provided according to the number of cylinders, and these three inner pipes 3 are integrated into one on the downstream side and are connected to the catalyst 2 via an exhaust pipe 5.

As shown in FIG. 2, the inner pipe 3 is composed of three first inner pipes 7 connected to the head flange 6 side and a second inner pipe 8 integrated on the downstream side. ing.
The second inner pipe 8 is provided with three connecting end portions 81 formed by hydroforming the pipe material to form a branch pipe portion and then punching the branch pipe portion.

The connecting end portion 81 of the second inner pipe 8 is shown in FIG.
As shown in FIG. 5, a folded-back portion 82 is provided that is folded back inside the tube. The folded-back portion 82 is formed by bending the end portion of the branch pipe portion into the pipe inner side by press-fitting a die of a predetermined shape into the branch pipe portion of the inner pipe 3 that has been punched from the outside of the pipe.

Since the die is set to have a diameter smaller than the outer diameter of the connecting end portion 71 of the first inner pipe 7, the inner diameter D2 of the connecting end portion 81 is as shown in FIG. Connection end 71
The outer diameter D1 is smaller than the outer diameter D1, and both connection end portions 71 and 81 are set to the dimensions of the press-fitting tolerance.

Next, the operation will be described. [Connecting Method of First Inner Tube and Second Inner Tube] First, as shown in FIG. 4, the connecting end portion 71 of the first inner tube 7 is press-fitted into the connecting end portion 81 of the second inner tube 81. At this time, since the inner diameter D2 of the connection end portion 81 is set to be smaller than the outer diameter D1 of the connection end portion 71, the connection end portion 71 elastically deforms the folded portion 82 of the connection end portion 81 to the outside of the pipe. It is inserted into the inside of the connection end 81 while making it.

In the connected state shown in FIG. 3, since the folded portion 82 is in pressure contact with the outer peripheral surface of the connecting end portion 71,
Sealing property is secured without rattling of the connection part. Further, the first inner pipe 7 and the second inner pipe 8 are relatively movable in the axial direction.

Next, the effect will be described. (1) By providing the folded-back portion 82 on the connection end portion 81 of the second inner pipe 8, the wall thickness of the connection end portion 81 becomes about twice as large as that of the conventional one, so that the hydroforming with large thickness reduction is possible. Also in the second inner pipe 8 formed by processing, it is possible to suppress a decrease in strength due to the processing thinning of the connection end portion 81, and it is possible to increase the strength.

(2) Even in the second inner pipe 8 formed by hydroforming with a large amount of wall thinning, the connection end 81 can be increased to the processing limit, so that the connection allowance can be set large and the connection can be made. The sealability of the part can be improved.

(3) Since the inner diameter D2 of the folded portion 82 is set to be smaller than the outer diameter D1 of the connecting end portion 71 of the first inner pipe 7, both connecting end portions 71 and 81 are set to the dimensions of the press-fitting tolerance. , Caulking the connecting part is not required. Therefore, it is possible to reduce costs by reducing the number of steps.

(Other Embodiments) The embodiments of the present invention have been described above. However, the specific configuration is not limited to the present embodiment, but is defined in each claim of the claims. Design changes and additions are allowed without departing from the gist of the invention.

[Brief description of drawings]

FIG. 1 is an overall view showing an exhaust system of an engine to which an inner pipe connecting method for a double pipe exhaust manifold of the present invention is applied.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a cross-sectional view showing a connecting end portion of a first inner pipe and a second inner pipe.

FIG. 4 is a cross-sectional view showing a method of connecting the first inner pipe and the second inner pipe.

[Explanation of symbols]

16-cylinder V-type engine 2 catalyst 3 inner tube 4 outer tube 5 exhaust pipe 6 head flange 7 First inner tube 71 Connection end 8 Second inner tube 81 Connection end 82 Folding part

Claims (3)

[Claims] 1. An outer tube and an inner peripheral surface of the outer tube are formed with an inner tube disposed inside the outer tube with a space therebetween. The inner tube is composed of at least a first inner tube and a second inner tube. In the inner pipe connecting method of the double pipe exhaust manifold, the connecting end portion of the first inner pipe is inserted into the connecting end portion of the second inner pipe to connect the both so as to be relatively movable in the axial direction. An inner pipe connecting method for a double pipe exhaust manifold, characterized in that the connecting end of the pipe is folded back to the inside of the can to form a folded back portion, and the connecting end of the first inner pipe is inserted into this folded back portion. 2. The inner pipe connecting method for a double pipe exhaust manifold according to claim 1, wherein an inner diameter of the folded portion is set to be smaller than an outer diameter of a connecting end portion of the first inner pipe. Inner pipe connection method for double pipe exhaust manifold. 3. The outer pipe and the inner peripheral surface of the outer pipe are composed of an inner pipe which is disposed inside with a space therebetween, and the inner pipe is composed of at least a first inner pipe and a second inner pipe. In the inner pipe connection structure of the double pipe exhaust manifold, the connection end portion of the first inner pipe is inserted into the connection end portion of the second inner pipe to connect the both so as to be relatively movable in the axial direction. The pipe has, at its connection end, a folded-back portion that is folded back toward the inside of the can. This folded-back portion is in pressure contact with the outer circumference of the connection end of the first inner pipe. Pipe connection structure.