JP2008267264A - Exhaust pipe for multicylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust pipe preventing generation of harmful vortexes while using an advantage of the exhaust pipe made of a steel pipe. <P>SOLUTION: In the exhaust pipe 15 for a multicylinder engine, a front end of a second exhaust pipe 14a is connected with a first exhaust pipe 12, and an angle θ1 between a center line 16 of the first exhaust pipe 12 and a center line 17 of the second exhaust pipe 14, is set at an acute angle. The first exhaust pipe 12 and the second exhaust pipe 14 are made of steel pipes. The front end of the second exhaust pipe 14 is stretch-shaped to form an angle θ2 with respect to the centerline 17 of the second exhaust pipe. The front end of the second exhaust pipe is partially stretch-shaped. A stretched part by the stretch shaping serves to eliminate harmful vortexes conventionally caused by flow confluence. The exhaust pipe made of the steel pipe for preventing the harmful vortexes is thus provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust pipe for a multi-cylinder engine made of steel pipe.

In a multi-cylinder engine, an exhaust pipe is extended from the exhaust port of each cylinder, but two exhaust pipes may be assembled into one for the purpose of improving the layout and performance of the exhaust pipe (for example, Patent Documents). 1).
JP 2003-222020 (FIGS. 1 and 4) JP 2001-227338 A (FIG. 1)

Patent document 1 is demonstrated based on the following figure.
FIG. 6 is a view for explaining a conventional exhaust pipe for a multi-cylinder engine. First to fourth exhaust pipes 101, 102, 103, 104 are combined into one by an exhaust collecting portion 105. Before that, the tip of the second exhaust pipe 102 is connected to the first exhaust pipe 101 in an acute angle state, and the two exhaust pipes 101 and 102 merge into one.

  FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 6, and the first exhaust pipe 101 is manufactured with a so-called “monaka” structure. That is, the upper half 113 having the flange 112 at the end of the semi-cylinder 111 is obtained by press-forming from a steel plate. Similarly, the lower half 116 having the flange 115 at the end of the semi-cylinder 114 is obtained by press forming from a steel plate. And the flange 115 is piled up on the flange 112, and both are joined by welding. 117 is a bead.

  Since it is a structure, the shape of the exhaust pipes 101 to 104 can be freely selected. However, in FIG. 6, the flanges 112, 112 project to the left and right and occupy the space around the exhaust pipes 101 to 104, which hinders the layout of the exhaust pipes 101 to 104.

And since it welds in the form which the flanges 112 and 112 overhang, welding processing cost increases. Moreover, since the flanges 112 and 112 project, the appearance is deteriorated.
Furthermore, in the structure, since press molding is essential, it is necessary to increase the number of parts and prepare a mold, which increases material costs and processing costs.

  Further, in FIG. 7, the exhaust pipe is heated to a high temperature due to the exhaust gas, thermal expansion occurs, an upward force acts on the upper half 113, and a downward force acts on the lower half 116. In the structure in which the flange 112 and the flange 115 are joined by welding, the flange 112 and the flange 115 are easy to open in a V shape with the bead 117 as a fulcrum. For this reason, the problem remains that the strength is not stable in the structure.

  Most of the structural problems are caused by flanges. Therefore, a flangeless structure is proposed in Patent Document 2.

Patent document 2 is demonstrated based on the following figure.
FIG. 8 is a diagram for explaining another conventional exhaust pipe for a multi-cylinder engine. First to fourth exhaust pipes 121, 122, 123, and 124 extend from the multi-cylinder engine 120, and the first exhaust pipe is shown. The fourth exhaust pipe 124 joins 121, the third exhaust pipe 123 joins the second exhaust pipe 122, and the tip of the second exhaust pipe 122 connects to the first exhaust pipe 121 on the downstream side. Connected at an acute angle.

FIG. 9 is an enlarged view of 9 parts in FIG. 8, the tip of the second exhaust pipe 122 is cut obliquely, and the tip of the second exhaust pipe 122 is connected to the first exhaust pipe 121. Yes. 125 is a bead.
Since there is no flange like the structure, the appearance is good and the layout is easy.

  FIG. 10 is a view for explaining the exhaust flow. The first exhaust gas 126 flows through the first exhaust pipe 121, and the second exhaust gas 127 flows through the second exhaust pipe 122. When the second exhaust gas 127 is merged with the first exhaust gas 126, a large vortex 128 is generated in the first exhaust pipe 121 on the downstream side of the portion where the second exhaust pipe 122 is connected. To do. In addition, it has been found that the vortex 129 is generated in the first exhaust pipe 121 also on the upstream side of the portion where the second exhaust pipe 122 is connected. These vortices 128 and 129 induce flow turbulence, making it difficult for exhaust gas to flow.

The generation of the vortices 128 and 129 becomes more remarkable as the angle θ1 formed by the first exhaust pipe 121 and the second exhaust pipe 122 is closer to 90 °. Therefore, a measure for reducing the angle θ1 is effective.
As the angle θ1 is reduced, the flow of exhaust gas becomes smoother, but on the other hand, welding on the acute angle side (left side in the figure) (FIG. 9, bead 125) becomes difficult and the number of welding steps increases. In addition, the welding stress increases and the risk of breakage from that portion increases.

  Therefore, there is a need for an exhaust pipe that can prevent the generation of harmful vortices while taking advantage of the exhaust pipe made of steel pipe.

  An object of the present invention is to provide an exhaust pipe capable of preventing the generation of harmful vortices while taking advantage of the exhaust pipe made of steel pipe.

  In the first aspect of the invention, the tip of the second exhaust pipe is connected to the first exhaust pipe extending from the multi-cylinder engine in an acute angle state, and the two exhaust pipes merge into one. In the exhaust pipe for a cylinder engine, the first exhaust pipe and the second exhaust pipe are steel pipe exhaust pipes, and the first exhaust pipe has an exhaust gas in accordance with a connection portion of the second exhaust pipe. An egg-shaped hole is formed so as to flow, and the tip of the second exhaust pipe is partially stretched so as to fit the egg-shaped hole.

  The invention according to claim 2 is characterized in that the tip of the second exhaust pipe is partially stretched and formed so as to form an angle of 10 ° to 30 ° with the center line of the second exhaust pipe.

  In the invention according to claim 1, an oval hole is formed in the first exhaust pipe so that the exhaust gas flows in accordance with a connection portion of the second exhaust pipe. The tip of the second exhaust pipe is partially stretched. The overhanging part formed by overhanging plays a role of eliminating harmful vortices that have conventionally occurred during merging. As a result, a steel pipe exhaust pipe capable of preventing the generation of harmful vortices can be provided.

  By providing the overhanging portion, a smooth flow of the exhaust gas can be ensured, and therefore it is not necessary to forcibly incline the second exhaust pipe with respect to the first exhaust pipe. The angle formed by the first exhaust pipe and the second exhaust pipe can be freely selected, and the welding work when connecting the second exhaust pipe to the first exhaust pipe is facilitated, and the number of welding processes is increased. Can be reduced.

  In addition, the steel pipe for the second exhaust pipe is cut obliquely so that the tip becomes elliptical. The tip of such a steel pipe is formed by a bulging forming method (an overhang forming method). At the time of forming, only the tensile force associated with the diameter expansion is applied to the steel pipe, and there is no fear of wrinkles or breakage, so that the finished shape is good.

  In the invention which concerns on Claim 2, the front-end | tip of the 2nd exhaust pipe made an angle of 10 degrees-30 degrees with the centerline of the 2nd exhaust pipe. If it is less than 10 °, the generation of vortices becomes remarkable. On the other hand, if the angle exceeds 30 °, the thinning of the second exhaust pipe becomes noticeable and the rigidity decreases. By keeping the overhang angle in the range of 10 ° to 30 °, it is possible to suppress the stress of the welded portion and maintain the strength while suppressing the generation of vortices.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a perspective view of an exhaust pipe including an exhaust pipe for a multi-cylinder engine according to the present invention, and four exhaust pipes 11 to 14 extend from the multi-cylinder engine 10. For convenience, the second exhaust pipe 12 from the left in the figure will be referred to as the first exhaust pipe 12, and the leftmost exhaust pipe 14 will be referred to as the second exhaust pipe 14.

  That is, the tip of the second exhaust pipe 14 is connected to the first exhaust pipe 12 at an acute angle, and the two exhaust pipes merge into one. The multi-cylinder engine exhaust pipe 15 refers to an exhaust pipe including such a merging portion.

  FIG. 2 is a cross-sectional view of an exhaust pipe for a multi-cylinder engine according to the present invention. The exhaust pipe 15 for a multi-cylinder engine has a first exhaust pipe 12 connected to the tip of a second exhaust pipe 14 and a first An angle θ1 formed by the center line 16 of the exhaust pipe 12 and the center line 17 of the second exhaust pipe 14 is an acute angle (less than 90 °).

The first exhaust pipe 12 and the second exhaust pipe 14 are steel pipe exhaust pipes. And the front-end | tip of the 2nd exhaust pipe 14 is extended | stretched and formed so that the angle of (theta) 2 may be made with respect to the centerline 17 of a 2nd exhaust pipe. Reference numeral 18 denotes an overhang portion.
The angle θ2 is selected from the range of 10 ° to 30 °.

  FIG. 3 is a view taken in the direction of the arrow 3-3 in FIG. 2, and the first exhaust pipe 12 has an oval hole 23 in which a crescent 22 is attached to an ellipse 21. In FIG. 2, the exhaust gas flows from the left to the right in the first exhaust pipe 12. The overhanging portion 18 at the angle θ2 is provided on the downstream side of the exhaust flow. That is, the tip of the second exhaust pipe 14 is characterized by being partially stretched so as to fit the oval hole 23.

FIG. 4 is an explanatory view of the operation of the exhaust pipe for a multi-cylinder engine. In the comparative example shown in FIG. 4A, a large vortex 128 is generated in the first exhaust pipe 121 on the downstream side and the upstream side of the second exhaust pipe 122. 129 has occurred.
On the other hand, in the embodiment shown in (b), there is no fear that harmful vortices are generated due to the presence of the overhanging portion 18, and the exhaust gases smoothly merge.

  According to the experiments by the present inventors, when the angle θ2 is 10 ° or more, the flow of exhaust gas becomes particularly good. This tendency is hardly related to the magnitude of the angle θ1 if the angle θ1 shown in FIG. 2 is in the range of 40 ° to 80 °.

Next, a method for processing the tip of the second exhaust pipe 14 will be described below.
FIG. 5 is a view for explaining a second exhaust pipe processing method. In FIG. 5A, the tip of the cylindrical steel pipe 25 is cut along a cutting line 26.
As shown in (b), the steel pipe 25 is fitted into the die 27, and then the punch 28 is press-fitted into the steel pipe 25 as indicated by the white arrow. The die 27 is provided with a recess 29 having an angle θ2. A convex portion 31 corresponding to the concave portion 29 is provided on the punch 28.

As shown to (c), the 2nd exhaust pipe 14 provided with the overhang | projection part 18 and the flange 32 can be obtained.
That is, the steel pipe 25 for the second exhaust pipe 14 (FIG. 2) is cut obliquely so that the tip becomes elliptical. The tip of such a steel pipe 25 is formed by a bulging forming method (an overhang forming method). At the time of forming, only the tensile force associated with the diameter expansion is applied to the steel pipe 25, and there is no fear of wrinkling or breaking, so that the finished shape is good.

  However, a thin-walled portion is generated with the stretch forming. Thinning becomes more conspicuous as the overhang amount (angle θ2 in the embodiment) increases. Therefore, the angle θ2 is limited to 30 °.

  Returning to FIG. 2, since the overhanging portion 18 is provided, a smooth flow of the exhaust gas can be secured, and therefore the second exhaust pipe 14 does not need to be inclined with respect to the first exhaust pipe 12. . The angle θ1 formed by the first exhaust pipe 12 and the second exhaust pipe 14 can be freely selected, and the welding work when connecting the second exhaust pipe 14 to the first exhaust pipe 12 is easy. Thus, the number of welding steps can be reduced.

  In the bulging forming method (extrusion forming method), the diameter of the tip of the steel pipe 25 may be expanded with a high-pressure liquid instead of the punch 28. Therefore, the molding method is not limited to the examples.

  The present invention is suitable for an exhaust system of a multi-cylinder engine.

1 is a perspective view of an exhaust pipe including an exhaust pipe for a multi-cylinder engine according to the present invention. 1 is a cross-sectional view of an exhaust pipe for a multi-cylinder engine according to the present invention. FIG. 3 is a view taken along arrow 3-3 in FIG. 2. It is operation | movement explanatory drawing of the exhaust pipe for multi-cylinder engines. It is a figure explaining the processing method of the 2nd exhaust pipe. It is a figure explaining the conventional exhaust pipe for multi-cylinder engines. FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 6. It is a figure explaining another conventional exhaust pipe for multi-cylinder engines. FIG. 9 is an enlarged view of 9 parts in FIG. 8. It is a figure explaining an exhaust flow.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Multi-cylinder engine, 12 ... 1st exhaust pipe, 14 ... 2nd exhaust pipe, 15 ... Exhaust pipe for multi-cylinder engines, 17 ... Center line of 2nd exhaust pipe, 18 ... Overhang part, 23 ... Egg Shape hole, θ2 ... An angle with respect to the center line of the second exhaust pipe.

Claims (2)

In the exhaust pipe for a multi-cylinder engine, the tip of the second exhaust pipe is connected to the first exhaust pipe extending from the multi-cylinder engine in an acute angle state, and the two exhaust pipes merge into one.
The first exhaust pipe and the second exhaust pipe are steel pipe exhaust pipes,
In the first exhaust pipe, an egg-shaped hole is formed so that exhaust gas flows in accordance with a connection portion of the second exhaust pipe, and the second exhaust pipe is fitted to the egg-shaped hole. An exhaust pipe for a multi-cylinder engine, characterized in that the tip of the cylinder is partially overmolded.   2. The multi-cylinder engine according to claim 1, wherein a tip of the second exhaust pipe is partially stretched and formed so as to form an angle of 10 ° to 30 ° with respect to a center line of the second exhaust pipe. Exhaust pipe.

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