EXHAUST MANIFOLD

An exhaust manifold includes a head flange member, a plurality of branch pipe parts and a collector pipe part. The head flange member has a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine. Each of the branch pipe parts has an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface. The collector pipe part is connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts. An area of the cylinder head mounting surface is smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2012-051413, filed on Mar. 8, 2012. The entire disclosure of Japanese Patent Application No. 2012-051413 is hereby incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an exhaust manifold that that is attached to a cylinder head of an internal combustion engine and allows exhaust gas to pass through.

2. Background Information

Japanese Laid-Open Patent Application No. 2004-52715 presents a known conventional exhaust manifold. This conventional exhaust manifold has a hollow dual pipe structure comprising an inner pipe covered by an outer pipe. A head flange is fixed to one end of each of the branch pipes of the inner pipe, and the other ends of the inner pipes are connected to a collector inner pipe. The head flange has through holes provided between adjacent branch pipes, and a flat surface of the head flange located on the opposite side as the branch pipes is attached to the cylinder head of an engine (internal combustion engine) such that the openings of the branch pipes are aligned with the exhaust ports of the cylinder head.

SUMMARY

With the conventional exhaust manifold explained above, since the cylinder head is constantly cooled with circulating cooling water and the head flange is fastened to the cylinder head, the head flange of the exhaust manifold looses heat to the cylinder head and is cooled. Meanwhile, the inner pipes of the branch pipes and the outer pipes covering the inner pipes are at a high temperature because high-temperature exhaust gas flows through the inner pipes and the branch pipes are not cooled by cooling water or the like. Consequently, a large temperature difference exists between the head flange and the outer pipe and inner pipe connected to the head flange and a difference between an elongation or expansion amount of the head flange in a lengthwise direction caused by heat and an elongation amount of the inner and outer pipes in a lengthwise direction caused by heat becomes large.

The present invention was conceived in view of the problem just explained and its object is to provide an exhaust manifold that can prevent the durability of the exhaust manifold from declining due to a difference of thermal expansion between the head flange and the inner and outer pipes.

An exhaust manifold according to one aspect includes a head flange member, a plurality of branch pipe parts and a collector pipe part. The head flange member has a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine. Each of the branch pipe parts has an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface. The collector pipe part is connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts. An area of the cylinder head mounting surface is smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.

With this arrangement, a contact surface area between the cylinder head and the mounting surface of the head flange member that contacts the cylinder head is smaller than the cross sectional area of the head flange main body portion. Consequently, the amount of heat transferred from the head flange to the cooled cylinder head is small and the head flange can be maintained at a higher temperature. As a result, the difference between the thermal expansion amounts of the head flange and the branch pipe parts can be reduced and the durability of the exhaust manifold can be improved.

In the exhaust manifold as described above, a surface of the flange main body portion and the cylinder head mounting surface are preferably connected with a step-shaped level difference in-between. With this arrangement, the contact surface area between the cylinder head and the mounting surface of the head flange member can be made smaller than the cross sectional area of the head flange main body with a simple and inexpensive method.

In the exhaust manifold as described above, the head flange member preferably defines a through hole in a position that avoids the branch pipe parts. With this arrangement, the contact surface area with respect to the cylinder head can be reduced further and the difference between the thermal expansion amounts of the head flange and the branch pipes can be reduced further.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure:

FIG. 1 is a perspective view of an exhaust manifold according to one embodiment of the present invention.

FIG. 2 is a frontal plan view of a head flange member of the exhaust manifold according to the embodiment.

FIG. 3 is a cross sectional view of the head flange member taken along a section line S1-S1 shown in FIG. 2.

FIG. 4 is a cross sectional view of the head flange member taken along a section line S2-S2 shown in FIG. 2.

 DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

The overall constituent features of the exhaust manifold according to one embodiment will now be explained based on FIG. 1. The exhaust manifold 2 according to the embodiment is attached to a side face of a cylinder head 1a of an engine 1 comprising an internal combustion engine using bolts (not shown).

The exhaust manifold 2 comprises a head flange member 20, a thin-walled inner pipe (not shown) including a plurality of inner branch pipes (four in this embodiment) and an inner collector pipe (not shown) connected to the inner branch pipes, a thick-walled outer pipe 3 that covers the inner pipe such that a gap exists between the outer circumference of the inner pipe and the inner circumference of the outer pipe 3, and a spacer (not shown). For example, a hollow dual-pipe structure disclosed in Japanese Laid-Open Patent Application No. 2004-52715 may be utilized to form the inner branch pipes, the collector pipe and the outer pipe 3 of this embodiment.

The head flange member 20 has a flange main body portion 2a having a cylinder head mounting surface that is fixed to the cylinder head 1a and a surface that is fixed by welding to exhaust gas upstream end portions of the inner pipe and the outer pipe. A plurality of exhaust gas flow holes (four in this embodiment) are provided in the flange main body portion 2a in positions aligned with exhaust ports formed in the cylinder head 1a. The structure of the head flange member 20 will be explained in more detail below.

The inner pipe is inside the outer pipe 3 and cannot be seen in FIG. 1. The inner pipe has four branch inner pipes and a collector inner pipe. The exhaust gas upstream end portions of the branch inner pipes are securely attached by welding to the head flange member 20 such that they are aligned with the positions of the exhaust ports. The exhaust gas downstream end portions of the branch pipes are connected to an exhaust gas upstream end portion of the collector inner pipe. An exhaust gas downstream end portion of the collector inner pipe bends downward from one location on an undersurface.

The outer pipe 3 comprises branch outer pipes 3a to 3d that cover the four branch inner pipes from the outside such that a gap exists in-between, a collector outer pipe 3e that covers the collector inner pipe from the outside such that a gap exits in-between, and an exhaust outer pipe portion 3f that covers the downwardly bent exhaust gas downstream end portion of the collector inner pipe from the outside such that a gap exists in-between. Spacers are disposed between the outer pipe 3 and the inner pipe in several locations to maintain the gaps. The spacers are made of for example, a metal mesh.

The branch inner pipe and/or the branch outer pipes 3a to 3d correspond to the branch pipe parts of this embodiment, and the collector inner pipe and/or the collector outer pipe 3e correspond to the collector pipe part of this embodiment.

The structure of the head flange member 20 will now be explained in more detail based on FIGS. 2 to 4. FIG. 2 is a frontal view of the head flange member 20 as seen from the surface of the cylinder head 1a onto which the head flange member 20 mounts. In FIG. 2, the cylinder head mounting surface is shown with hatching. FIG. 3 is a cross sectional view taken along the section line S1-S1 of FIG. 2. The upper side in FIG. 3 is the mounting surface side that attaches to the cylinder head 1a, and the lower side is the side having the surface that attaches to the inner pipe and the outer pipe 3. FIG. 4 is a cross sectional view taken along the section line S2-S2 of FIG. 2. The upper side in FIG. 4 is the mounting surface side that attaches to the cylinder head 1a, and the lower side is the side having the surface that mates with the inner pipe and the outer pipe 3.

As shown in FIGS. 2 to 4, the head flange member 20 has a plate-shaped flange main body portion 2a, portions 21a to 21d located on one side of the flange main body portion 2a, i.e., the side having the surface that attaches to the cylinder head 1a, and a portion 25 located on the other side of the flange main body portion 2a, i.e., the side having the surface that attaches to the inner pipe and the outer pipe 3 on the opposite side of the flange main body portion 2a as the surface that attaches to the cylinder head 1a.

The portions 21a to 21d on the side having the cylinder head mounting surface that attaches to the cylinder head 1a correspond to portions indicated with hatching in FIG. 2, and, as shown in FIGS. 3 and 4, are configured to protrude toward the cylinder head 1a from the flange main body portion 2a such that a step-shaped level difference exists between the portions 21a to 21d and the flange main body portion 2a. In other words, the cylinder head mounting surface of the portions 21a to 21d is disposed outwardly of a surface of the flange main body portion 2a when viewed along a direction parallel to the cylinder head mounting surface as shown in FIG. 2. The height of the step-shaped level difference is set to 1 mm in this embodiment, but it is acceptable to set a different height. As illustrated in FIG. 2, the cylinder head mounting surface or the contact surface area (area of the hatched portions in FIG. 2) between the cylinder head 1a and the surface portions 21a to 21d on the cylinder head side of the flange main body portion 2a is much smaller than the cross sectional surface area of the flange main body portion 2a and the surface area of the portion 25 on the pipe side of the flange man body portion 2a. As used herein, the cross sectional surface area of the flange main body portion 2a refers to a cross sectional surface area of the plate-shaped flange main body portion 2a as taken along a plane substantially parallel to the cylinder head mounting surface (i.e., a horizontal plane in FIG. 3).

The portions 21a to 21d on the cylinder head side comprise portions that surround the peripheries of four exhaust gas inlet holes 22a to 22d formed to correspond to the four exhaust ports provided in the cylinder head 1a and portions that surround the peripheries of eight bolt holes 23a to 23d through which bolts are inserted to mount the manifold to the cylinder head 1a. The pair of bolt holes 23a, 23b, 23c, 23d corresponding to each of the exhaust ports is positioned diagonally with respect to a line joining the centers of the exhaust ports. The portions 21a to 21d on the side having the surface that attaches to the cylinder head 1a are configured to be independent entities corresponding to each of the exhaust ports, and adjacent portions 21a to 21d do not join each another directly.

Meanwhile, the flange main body portion 2a has a cross sectional surface area larger than the other portions 21a to 21d and 25, and a total of three through holes 24a, 24b, and 24c are formed between adjacent holes of the four exhaust gas inlet holes 22a to 22d. The through holes 24a, 24b, and 24c provided to further reduce the surface area of the head flange member 20 that contacts the cylinder head 1a.

Four recesses for attaching to the inner pipe and the outer pipe 3 are formed in the portion 25 on the side having the surface that attaches to the inner pipe and the outer pipe 3 in positions corresponding the exhaust ports. The inner pipe and the outer pipe 3 are arranged such that the exhaust gas upstream end portions are inserted into these recesses and the head flange member 20 is welded to the inner pipe and outer pipe 3. Thus, the surface area of the portion 25 on the pipe side is smaller than the cross sectional surface area of the flange main body portion 2a but slightly larger than the contact surface area of the portions 21a to 21d on the cylinder head side.

With the exhaust manifold 2 configured as explained heretofore, the exhaust gas discharged from the cylinders of the engine 1 exits the exhaust ports of the cylinder head 1a, passes through the exhaust gas inlet holes 22a to 22d of the flange main body portion 2a, and flows to into the branch inner pipes. The exhaust gas that flows into the branch inner pipes enters the collector inner pipe and is combined into a single flow passage before discharged downward from the exhaust gas downstream end portion. When the exhaust gas flows through the inner pipes, the outer pipe 3 serves to suppress the temperature drop of the exhaust gas in the inner pipes.

A catalytic converter is provided downstream of the exhaust manifold, and exhaust gas exiting the exhaust manifold activates the cleaning effect of the catalytic converter because it has been held at a high temperature in the exhaust manifold. As a result, the exhaust gas cleaning effect is accelerated. Downstream of the catalytic converter, the exhaust gas passes through an exhaust pipe and a muffler before being released to the outside of the vehicle.

During the operation explained above, the inner pipe and the outer pipe 3 of the exhaust manifold are at a high temperature due to the high-temperature exhaust gas. Meanwhile, the head flange member 20 of the exhaust manifold looses heat to the cylinder head 1a because a surface on one side of the head flange member 20 contacts the cylinder head 1a, which is constantly cooled by cooling water while the engine 1 is running.

However, in the exhaust manifold according to the embodiment, the contact surface area between the one surface of the head flange member 20 and the cylinder head 1a is slightly smaller than the cross sectional surface area of the flange main body portion 2a. Consequently the amount of heat lost is small. As a result, the head flange member 20 can be held at a higher temperature and, thus, parts of the exhaust manifold can be prevented from becoming damaged due to a concentration of strain caused by a difference of thermal expansion.

The effects obtainable with the exhaust manifold according to the embodiment will now be reiterated. With the exhaust manifold according to the embodiment, the contact surface area between the surface on the one side of the head flange member 20 and the cylinder head 1a is slightly smaller than the cross sectional surface area of the flange main body portion 2a. Consequently, the temperature decrease of the head flange member 20 resulting from contact with the cylinder head 1a can be suppressed. Thus, the parts of the exhaust manifold can be prevented from being damaged due to a concentration of strain caused by a difference of thermal expansion.

Since the aforementioned difference of surface areas can be obtained by configuring the head flange member 20 such that the portions on the side having the surface that attaches to the cylinder head 1a join the flange main body portion 2a through a step-shaped level difference, that is, by removing portions other than the portions on the side having the surface that attaches cylinder head 1a side from the flange main body portion 2a, the head flange member 20 can be fabricated easily and inexpensively.

Since the head flange member 20 has through holes 20a to 20c in positions that avoid the branch inner pipes and the outer pipe, the contact surface area between the head flange member 20 and the cylinder head 1a can be reduced further and the temperature decrease of the head flange member 20 can be suppressed further.

Although the present invention is explained based on the embodiments, the present invention is not limited to these embodiments. The present invention includes design changes that do not depart from the scope of the invention.

For example, although the engine 1 is a four-cylinder type, the invention is not limited to a four-cylinder engine and a six-cylinder engine is also acceptable. The exhaust manifold according to the illustrated embodiment has a hollow dual-pipe structure, but the invention is not limited to such a structure.

Also, the shape of the head flange member 20 and the shapes of the portions on the side of the head flange member 20 having the surface that attaches to the cylinder head can be different from the embodiment.

General Interpretation of Terms

In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.

While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

1. An exhaust manifold comprising:

a head flange member having a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine;
a plurality of branch pipe parts with each of the branch pipe parts having an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface; and
a collector pipe part connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts,
an area of the cylinder head mounting surface being smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.

2. The exhaust manifold according to claim 1, wherein

a surface of the flange main body portion and the cylinder head mounting surface are connected with a step-shaped level difference in-between.

3. The exhaust manifold according to claim 1, wherein

the head flange member defines a through hole in a position that avoids the branch pipe parts.

4. The exhaust manifold according to claim 1, wherein

the cylinder head mounting surface is disposed outwardly of a surface of the flange main body portion when viewed along a direction parallel to the cylinder head mounting surface.
Patent History
Publication number: 20130232959
Type: Application
Filed: Mar 5, 2013
Publication Date: Sep 12, 2013
Applicant: CALSONIC KANSEI CORPORATION (Saitama-shi)
Inventor: Kazuya UCHIDA (Saitama-shi)
Application Number: 13/785,719
Classifications
Current U.S. Class: Common Receiver Having Inlets From Plural Cylinder (i.e., Exhaust Manifold) (60/323)
International Classification: F01N 3/00 (20060101);