Patent Publication Number: US-2013232959-A1

Title: Exhaust manifold

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 S 1 -S 1  shown in  FIG. 2 . 
         FIG. 4  is a cross sectional view of the head flange member taken along a section line S 2 -S 2  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  1   a  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  2   a  having a cylinder head mounting surface that is fixed to the cylinder head  1   a  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  2   a  in positions aligned with exhaust ports formed in the cylinder head  1   a.  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  3   a  to  3   d  that cover the four branch inner pipes from the outside such that a gap exists in-between, a collector outer pipe  3   e  that covers the collector inner pipe from the outside such that a gap exits in-between, and an exhaust outer pipe portion  3   f  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  3   a  to  3   d  correspond to the branch pipe parts of this embodiment, and the collector inner pipe and/or the collector outer pipe  3   e  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  1   a  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 S 1 -S 1  of  FIG. 2 . The upper side in  FIG. 3  is the mounting surface side that attaches to the cylinder head  1   a,  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 S 2 -S 2  of  FIG. 2 . The upper side in  FIG. 4  is the mounting surface side that attaches to the cylinder head  1   a,  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  2   a,  portions  21   a  to  21   d  located on one side of the flange main body portion  2   a,  i.e., the side having the surface that attaches to the cylinder head  1   a,  and a portion  25  located on the other side of the flange main body portion  2   a,  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  2   a  as the surface that attaches to the cylinder head  1   a.    
     The portions  21   a  to  21   d  on the side having the cylinder head mounting surface that attaches to the cylinder head  1   a  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  1   a  from the flange main body portion  2   a  such that a step-shaped level difference exists between the portions  21   a  to  21   d  and the flange main body portion  2   a.  In other words, the cylinder head mounting surface of the portions  21   a  to  21   d  is disposed outwardly of a surface of the flange main body portion  2   a  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  1   a  and the surface portions  21   a  to  21   d  on the cylinder head side of the flange main body portion  2   a  is much smaller than the cross sectional surface area of the flange main body portion  2   a  and the surface area of the portion  25  on the pipe side of the flange man body portion  2   a.  As used herein, the cross sectional surface area of the flange main body portion  2   a  refers to a cross sectional surface area of the plate-shaped flange main body portion  2   a  as taken along a plane substantially parallel to the cylinder head mounting surface (i.e., a horizontal plane in  FIG. 3 ). 
     The portions  21   a  to  21   d  on the cylinder head side comprise portions that surround the peripheries of four exhaust gas inlet holes  22   a  to  22   d  formed to correspond to the four exhaust ports provided in the cylinder head  1   a  and portions that surround the peripheries of eight bolt holes  23   a  to  23   d  through which bolts are inserted to mount the manifold to the cylinder head  1   a.  The pair of bolt holes  23   a,    23   b,    23   c,    23   d  corresponding to each of the exhaust ports is positioned diagonally with respect to a line joining the centers of the exhaust ports. The portions  21   a  to  21   d  on the side having the surface that attaches to the cylinder head  1   a  are configured to be independent entities corresponding to each of the exhaust ports, and adjacent portions  21   a  to  21   d  do not join each another directly. 
     Meanwhile, the flange main body portion  2   a  has a cross sectional surface area larger than the other portions  21   a  to  21   d  and  25 , and a total of three through holes  24   a,    24   b,  and  24   c  are formed between adjacent holes of the four exhaust gas inlet holes  22   a  to  22   d.  The through holes  24   a,    24   b,  and  24   c  provided to further reduce the surface area of the head flange member  20  that contacts the cylinder head  1   a.    
     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  2   a  but slightly larger than the contact surface area of the portions  21   a  to  21   d  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  1   a,  passes through the exhaust gas inlet holes  22   a  to  22   d  of the flange main body portion  2   a,  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  1   a  because a surface on one side of the head flange member  20  contacts the cylinder head  1   a,  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  1   a  is slightly smaller than the cross sectional surface area of the flange main body portion  2   a.  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  1   a  is slightly smaller than the cross sectional surface area of the flange main body portion  2   a.  Consequently, the temperature decrease of the head flange member  20  resulting from contact with the cylinder head  1   a  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  1   a  join the flange main body portion  2   a  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  1   a  side from the flange main body portion  2   a,  the head flange member  20  can be fabricated easily and inexpensively. 
     Since the head flange member  20  has through holes  20   a  to  20   c  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  1   a  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.