Abstract:
Branching pipes connect a surge tank to an intake manifold of an internal combustion engine. The branching pipes are made such that each gas column of the internal combustion receives a uniform intake volume. This is achieved by either making each branching pipe of the same length, or by adjusting the inside diameters of the branching pipes, thereby creating a flow delay of the intake into the gas columns, resulting in uniform intake volume. The inside diameters of the branching pipes are either made uniformly of a different diameter, or, alternatively, the inside diameters of the branching pipes include throttles for reducing the diameter of the branching pipe at a localized portion. In both cases, a flow delay of the intake into the gas columns is compensated, resulting in a uniform intake volume. The branching pipes of the present invention result in an improved output performance for the internal combustion engine; provide for smooth branching paths; reduce intake resistance; allow the intake manifold to be made compact and light; reduce fuel consumption; improve power performance; allow the internal combustion engine to be made compact; allow easier mounting in automobiles; and allow automobiles to be lighter.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an intake device for internal combustion engines. More specifically, the present invention relates to an intake device for internal combustion engines that allows the lengths of branching paths to be uniform, thereby improving output performance of the internal combustion engine. Additionally, the present invention relates to an intake device for internal combustion engines having smooth branching paths, thereby reducing intake resistance. The present invention relates to an intake device for internal combustion engines having a more compact and lightweight intake manifold, thereby reducing fuel consumption and improving power performance. Finally, the present invention relates to an intake device for internal combustion engines having a more compact internal combustion engine, thereby improving ease of mounting in an automobile and making the automobile lighter. 
     In conventional internal combustion engines mounted in cars, an intake device is disposed to guide intake gas into a plurality of gas columns. In this conventional intake device, there is an intake manifold that guides the intake gas to the gas columns. A throttle body adjusts the air intake. 
     Referring to FIG. 16, an internal combustion engine  202 , mounted in an automobile (not shown), includes a cylinder block  204  having an oil pan  210 . A cylinder head  206  is covered by a head cover  208 . In this conventional internal combustion engine  202 , a plurality of gas columns, e.g., four gas columns numbers 1-4 (not shown in the figure), are arranged in a row. An intake device  212  is positioned at cylinder head  206 . 
     Air intake device  212  includes a throttle body  214  and an intake manifold  216 . Throttle body  214  adjusts air intake using an internal throttle valve (not shown in the figure). Intake manifold  216  guides intake gas to the gas columns. 
     Referring to FIG. 17, an attachment flange  218  attaches to cylinder head  206 . First through fourth branching pipes  220 - 1 - 220 - 4  correspond to the first through fourth gas columns numbers 1-4. A surge tank  222  restricts intake gas ripples. 
     Surge tank  222  is positioned at a gas column row center C along a gas column row direction D formed by the four gas columns numbers 1-4 of internal combustion engine  202 . The ends of first through fourth branching pipes  220 - 1 - 220 - 4  connect to attachment flange  218 . The other ends of first through fourth branching pipes  220 - 1 - 220 - 4  connect to surge tank  222 . 
     With this conventional intake manifold  216 , first and second branching pipes  220 - 1  and  220 - 2  connect to attachment flange  218  on one side of gas column center C along gas column row direction D. The other end of first and second branching pipes  220 - 1  and  220 - 2  connect to a side wall  224  of surge tank  222  facing one side of gas column direction D. Also, in intake manifold  216 , third and fourth branching pipes  220 - 1  and  220 - 2  connect to attachment flange  218  on the other side of gas column center C along gas column row direction D. The other end of third and fourth branching pipes  220 - 3  and  220 - 4  connect to an opposite side wall  226  of surge tank  222 , facing the other side of gas column direction D. 
     Thus, with conventional intake manifold  216 , first through fourth branching pipes  220 - 1 - 220 - 4  are disposed symmetrically around gas column row center C, connecting attachment flange  218  with surge tank  222 . This allows first through fourth branching paths  228 - 1 - 228 - 4  to have uniform lengths. 
     This type of intake device for internal combustion engine is disclosed in Japanese laid- open patent publication number 5-180091, Japanese utility model publication number 2549543, and Japanese laid-open utility model publication number 5-21161. 
     In the disclosure in Japanese laid-open patent publication number 5-180091, the branching pipes are all grouped together and connected lengthwise to the surge tank. A contact section is disposed where the intake manifold attachment flange abuts the main engine unit. A chamber is disposed below the intake path of the contact section. A partitioning wall is disposed to partition the chamber into upper and lower divisions, and a communicating section is disposed to connect the two divisions. Communicating paths are disposed to connect the intake paths of each of the gas columns to one of the divisions, and an EGR path is disposed to send exhaust gas to the other chamber. 
     Referring to FIG. 15, the disclosure in Japanese utility model publication number 2549543 is roughly similar to what is shown in the figure. The path width of the curving intake pipes connected to the surge tank are roughly uniform. The cross-sections thereof are formed so that the curvature at the outside of the curve is greater than the curvature at the inside of the curve. 
     The cross-section shapes of the curving branches of the intake manifold are formed as ellipses so that their centroids are positioned closer toward the outside of the curves rather than at the centers of the intake pipes. 
     However, with the conventional intake devices of internal combustion engines, there are cases when the surge tank cannot be disposed at the center of the gas column row due to restrictions imposed by how the internal combustion engine is mounted in the automobile and the like. 
     Referring to FIG. 18, for example, in intake manifold  216  of intake device  212  a center C 1  of surge tank  222  is offset by a distance M toward a third gas column #3 toward one side of gas column row direction D. 
     With manifold  216  having surge tank  222  offset in this manner, first through fourth branching pipes  220 - 1  through  220 - 4  are disposed so that the path lengths of first and second branching paths  228 - 1  and  228 - 2  of first and second branching pipes  220 - 1  and  220 - 2  are longer than the path lengths of third and fourth branching paths  228 - 3  and  228 - 4  of third and fourth branching pipes  220 - 3  and  220 - 4 . 
     Thus, with this conventional intake device  212 , the path lengths of first through fourth branching paths  228 - 1  through  228 - 4  cannot be made uniform. The non-uniformity results in variations in intake air flow through first through fourth gas columns #1 through #4. This reduces the output performance of internal combustion engine  202 . 
     The path lengths of first through fourth branching paths  228 - 1  through  228 - 4  can be made uniform by having first and second branching pipes  220 - 1  and  220 - 2  formed with a larger curvature, resulting in a tighter curve, compared to third and fourth branching pipes  220 - 3  and  220 - 4 . 
     Referring to FIGS. 19 and 20, compared to branching pipe  220 , as shown in FIG. 19, formed with a small curvature resulting in a more gradual curve, branching pipe  220 , as shown in FIG. 20, is formed with a larger curvature, resulting in a tighter curve. This leads to increased intake resistance due to the tighter curve in branching path  228 . Thus, the output performance of the internal combustion engine is reduced. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an intake device for an internal combustion engine which overcome the foregoing problems 
     It is a further object of the present invention to provide an intake device for an internal combustion engine which allows the length of the branching paths to be uniform, thereby improving output performance. 
     It is another object of the present invention to provide an intake device for an internal combustion engine which has smooth branching parts, thereby reducing intake resistance. 
     It is yet a further object of the present invention to provide an intake device for an internal combustion engine which has a more compact and lightweight design, thereby reducing fuel consumption, improving power performance, improving the ease of mounting in an automobile, and making the automobile lighter. 
     Briefly stated, the present invention provides a branching pipes connecting a surge tank to an intake manifold of an internal combustion engine. The branching pipes are made such that each gas column of the internal combustion receives a uniform intake volume. This is achieved by either making each branching pipe of the same length, or by adjusting the inside diameters of the branching pipes, thereby creating a flow delay of the intake into the gas columns, resulting in uniform intake volume. The inside diameters of the branching pipes are either made uniformly of a different diameter, or, alternatively, the inside diameters of the branching pipes include throttles for reducing the diameter of the branching pipe at a localized portion. In both cases, a flow delay of the intake into the gas columns is compensated, resulting in a uniform intake volume. The branching pipes of the present invention result in an improved output performance for the internal combustion engine; provide for smooth branching paths; reduce intake resistance; allow the intake manifold to be made compact and light; reduce fuel consumption; improve power performance; allow the internal combustion engine to be made compact; allow easier mounting in automobiles; and allow automobiles to be lighter. 
     According to an embodiment of the present invention, there is provided an intake device for an internal combustion engine comprising: attachment means for attaching the intake device to an intake manifold having at least first and second gas columns on the internal combustion engine; at least first and second branching pipes, each connecting one of the at least first and second gas columns to a surge tank; the surge tank having a center positioned a prescribed distance from a center of the at least first and second gas columns; and the at least first and second branching pipes connecting to the surge tank such that first and second branching pipes, corresponding to first and second gas columns having consecutive intake timings, connect, facing each other, at opposite sides of the surge tank. 
     According to a feature of the present invention, there is provided an intake device for an internal combustion engine comprising: attachment means for attaching the intake device to an intake manifold, having at least first and second gas columns, on the internal combustion engine; at least first and second branching pipes, each connecting one of the at least first and second gas columns to a surge tank; the surge tank having a center positioned a prescribed distance from a center of the at least first and second gas columns; the at least first and second branching pipes having a corresponding at least first and second inside diameters; the first branching pipe, having a shorter path length than the second branching pipe, has a larger diameter than a diameter of the second branching pipe, whereby a flow delay of the intake into the at least first and second gas columns is compensated, resulting in a uniform intake volume; and the at least first and second branching pipes connecting to the surge tank such that first and second branching pipes, corresponding to first and second gas columns having consecutive intake timings, connect, facing each other, at opposite sides of the surge tank. 
     According to a further feature of the present invention, there is provided an intake device for an internal combustion engine comprising: attachment means for attaching the intake device to an intake manifold having at least first and second gas columns on the internal combustion engine; at least first and second branching pipes, each connecting one of the at least first and second gas columns to a surge tank; the surge tank having a center positioned a prescribed distance from a center of the at least first and second gas columns; the first branching pipe, having a longer path length than the second branching pipe, has a throttle projecting from an inside wall of the first branching pipe, whereby a flow delay of the intake into the at least first and second gas columns is compensated, resulting in a uniform intake volume; and the at least first and second branching pipes connecting to the surge tank such that first and second branching pipes, corresponding to first and second gas columns having consecutive intake timings, connect, facing each other, at opposite sides of the surge tank. 
     In the present invention, there is an intake manifold that includes an attachment flange attached to an internal combustion engine. A plurality of branching pipes, corresponding to a plurality of gas columns, are arranged in a row on the internal combustion engine. A surge tank restricts intake gas rippling. The gas columns are attached to side walls of the surge tank, which are perpendicular to a gas column row direction, so that the branching pipes corresponding to gas columns having consecutive intake timings are connected facing each other along the gas column row direction. 
     In each of the plurality of branching pipes, one end is connected to the attachment flange to form a row along the gas column row direction. The other ends of the branching pipes, connected to the attachment flange to one side of a gas column row center of the plurality of gas columns, and other ends of branching pipes, connected to the attachment flange to another side of the gas column row center, are connected to side walls of the surge tank, perpendicular to the gas column row direction, so that the pipes face each other in an asymmetrical manner along the gas column row direction. The plurality of branching pipes is formed so that branching paths are uniformly long. The plurality of branching pipes is preferably formed from a plate material shaped in the form of pipes with a gradual curve having a small curvature. One end of the plurality of branching pipes is connected to the attachment flange. The other end is connected to the surge tank, which is offset to either side of a gas column row center of the plurality of gas columns along the gas column row direction. 
     In the intake device for internal combustion engines according to the present invention, the surge tank has side walls that face perpendicular to the gas column row direction. Branching pipes, corresponding to the gas columns having sequential intake timings, are connected to these side walls so that they face each other along the gas column row direction. The other ends of the branching pipes, connected to the attachment flange at one side of the gas column row center along the gas column row direction and the other ends of the branching pipes connected to the attachment flange at the other side of the gas column row center along the gas column row direction, are connected to the side walls of the surge tank so that they face each other and are asymmetrical. The branching paths are preferably formed to have uniform lengths, being preferably formed of plate materials in the shape of pipes. The pipes are formed with gradual curves having small curvatures. One end of each of the pipes is connected to the attachment flange, and the other end is connected to the surge tank, which is offset along the gas column row direction to one side or the other of the gas column center of the plurality of gas columns. 
     With this intake device, the branching pipes are formed from plate materials that is easily shaped. This allows the branching pipes to be formed so that the branching paths have uniform lengths. As a result, the branching paths are easily formed with uniform lengths, even if the surge tank is offset along the gas column row direction. The branching pipes, which are formed so that the branching paths have uniform lengths, are connected facing each other so that they are asymmetrical along the gas column row direction. Branching pipes corresponding to gas columns that have consecutive intake timings are connected facing each other along the gas column row direction. This allows the branching pipes, whose branching paths have uniform lengths, to be formed having large curvatures without having tight curves. As a result, the projection of the branching pipes in the gas column row direction is kept small while the shapes of the branching paths are made smooth. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan drawing of an intake manifold of an intake device according to an embodiment of the present invention. 
     FIG. 2 is a perspective drawing of an intake manifold. 
     FIG. 3 is a side-view drawing of an internal combustion engine mounted in an automobile. 
     FIG. 4 is a plan drawing showing a first connection arrangement for the first and the second branching pipes to the surge tank. 
     FIG. 5 is a plan drawing showing a second connection arrangement for the first and the second branching pipes to the surge tank. 
     FIG. 6 is a plan drawing showing a first connection arrangement for the third and the fourth branching pipes to the surge tank. 
     FIG. 7 is a plan drawing showing a second connection arrangement for the third and the fourth branching pipes to the surge tank. 
     FIG. 8 is a plan drawing showing a first pipe arrangement of the first through the fourth branching pipes to the surge tank. 
     FIG. 9 is a plan drawing showing a second pipe arrangement of the first through the fourth branching pipes to the surge tank. 
     FIG. 10 is a plan drawing showing a third pipe arrangement of the first through the fourth branching pipes to the surge tank. 
     FIG. 11 is a plan drawing of an intake manifold where the surge tank is offset from the gas column row center toward the gas column along the gas column row direction. 
     FIG. 12 is a plan drawing showing an intake manifold according to a first alternative embodiment. 
     FIG. 13 is a plan drawing of an intake manifold according to a second alternative embodiment. 
     FIG. 14 is a schematic plan drawing of a sample implementation in an internal combustion engine of a V- 8  gas column internal combustion engine. 
     FIG. 15 is a schematic front-view drawing of a sample implementation in an internal combustion engine of a V- 8  gas column internal combustion engine. 
     FIG. 16 is a perspective drawing of a conventional internal combustion engine. 
     FIG. 17 is a plan drawing of an intake manifold where the surge tank is positioned at the gas column row center according to conventional technology. 
     FIG. 18 is a plan drawing of an intake manifold where the surge tank is offset from the gas column row center toward the third gas column along the gas column row direction according to conventional technology. 
     FIG. 19 is a partially cut-away plan drawing of a branching pipe that is gradually curved with a small curvature. 
     FIG. 20 is a partially cut-away plan drawing of a branching pipe that is tightly curved with a large curvature. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 3, an automobile  2  has an internal combustion engine  6  located in an engine compartment  4 . A transmission gearbox  8  connects with internal combustion engine  6 . Internal combustion engine  6  includes a cylinder block  10 , a cylinder head  12 , a head cover  14 , and an oil pan  16 . 
     A plurality of gas columns are arranged in a row, e.g., first through fourth gas columns #1-#4 (not shown in the figure). An exhaust manifold  18  is disposed on one side of cylinder head  12 . An intake device  20  is disposed on the other side of cylinder head  12 . The intake sequence of internal combustion engine  2  is the first gas column #1; the third gas column #3; the fourth gas column #4; and the second gas column #2. 
     An intake manifold  24  is disposed on a throttle body  22  which adjusts the intake volume using an internal throttle valve (not shown in the figure). Intake manifold  24  guides intake gas into the gas columns. 
     Referring to FIGS. 1 and 2, intake manifold  24  includes an attachment flange  26  attached to cylinder head  12 . First through fourth branching pipes  28 - 1  through  28 - 4  correspond to first through the fourth gas columns #1 through #4. A surge tank  30  restricts intake gas ripples. 
     Attachment flange  26  is preferably formed as a rectangular plate oriented lengthwise along a gas column row direction D. Attachment flange  26  is formed with first through fourth flange openings  32 - 1  through  32 - 4  arranged in a row along gas column row direction D. First through fourth flange openings  32 - 1  through  32 - 4  communicate with first through fourth intake ports (not shown in the figure) of first through fourth gas columns #1 through #4. On the other side of attachment flange  26  are first through fourth side connectors  34 - 1  through  34 - 4 , corresponding to first through fourth flange openings  32 - 1  through  32 - 4 . 
     First through fourth branching pipes  28 - 1  through  28 - 4  are preferably formed from plates shaped as pipes having small curvatures, resulting in gentle curves. Inside first through fourth branching pipes  28 - 1  through  28 - 4  are first through fourth branching paths  36 - 1  through  36 - 4 . 
     On first through fourth branching pipes  28 - 1  through  28 - 4  are disposed first through fourth flange fitting sections  38 - 1  through  38 - 4 , which connect on one end to first through fourth flange side connectors  34 - 1  through  34 - 4  of attachment flange  26 . On the other end are first through fourth tank fitting sections  40 - 1  through  40 - 4 , which connect to first through fourth tank-side connecting openings  60 - 1  through  60 - 4 , which are described later, of surge tank  30 . 
     Surge tank  30  is preferably a hollow rectangle having side walls  42  and  44  facing either side of the gas column row direction D. A facing wall  46  and a rear wall  48  face toward and away from attachment flange  26 . A bottom  50  is at the bottom of surge tank  30 , and a ceiling  52  is at the top of surge tank  30 . 
     Surge tank  30  is disposed so that a center C 1  is offset from a gas column row center C by a distance M toward third gas column #3 at one side of gas column row direction D. A stay  54 , formed as a curved plate, connects to attachment flange  26 . 
     On ceiling  52  of surge tank  30  is a body attachment seat  56  to which attaches a throttle body  22 . An air entry opening  58  on throttle body  22  attaches on a body attachment seat  56 . 
     First and second tank-side connection openings  60 - 1  and  60 - 2  are on first side wall  42  of surge tank  30  facing one end of gas column row direction D. Third and fourth tank-side connection openings  60 - 3  and  60 - 4  are on second side wall  44  facing the other end of gas column row direction D. 
     First tank-side connection opening  60 - 1  is in the vicinity of attachment flange  26  of first side wall  42  of surge tank  30 . Second tank-side connection opening  60 - 2  is away from attachment flange  26  on first side wall  42  of surge tank  30  Third tank-side connection opening  60 - 3  is in the vicinity of attachment flange  26  of second side wall  44  of surge tank  30 . Fourth tank-side connection opening  60 - 4  is away from attachment flange  26  of second side wall  44  of surge tank  30 . The curved line indicated by arrow E shows the intake sequence of first through fourth branching paths  36 - 1  through  36 - 4 . 
     The following is a description of how the structure described above works. 
     Intake manifold  24  is on intake device  20  of internal combustion engine  2 . Attachment flange  26  attaches to cylinder head  12 . First through fourth branching pipes  28 - 1  through  28 - 4 , corresponding to first through fourth gas columns #1 through #4, connect intake manifold  24  with surge tank  30 , thereby restricting intake gas rippling. 
     Intake manifold  24  is disposed so that center C 1  of surge tank  30  is offset by a distance M from gas column row center C toward third gas column #3 toward one side of gas column row direction D. Intake manifold  24 , having surge tank  30  offset in this manner, results in path lengths of first and second branching paths  36 - 1  and  36 - 2  of first and second branching pipes  28 - 1  and  28 - 2  being longer than third and fourth branching paths  36 - 3  and  36 - 4  of third and fourth branching pipes  28 - 3  and  28 - 4 . Therefore, first and second branching pipes  28 - 1  and  28 - 2  must be shortened. 
     When first and second branching pipes  28 - 1  and  28 - 2  are connected to surge tank  30 , the connection arrangement shown in FIG. 5 will result, wherein first branching path  36 - 1  is too long compared to the connection arrangement shown in FIG.  4 . This makes it difficult to form uniform lengths with third and fourth branching paths  36 - 3  and  36 - 4 , as well as second branching path  36 - 2 . Thus, for the connections between first and second branching pipes  28 - 1  and  28 - 2  and surge tank  30 , the connection arrangement shown in FIG. 4 allows easier shortening of paths, thereby forming uniform lengths as compared to the connection arrangement shown in FIG.  5 . 
     When third and fourth branching pipes  28 - 3  and  28 - 4  are connected to surge tank  30 , the connection arrangement shown in FIG. 7 will result, wherein fourth branching path  36 - 4  is too long compared to the connection arrangement shown in FIG.  6 . Fourth branching pipe  28 - 4  will project by a distance A along gas column row direction D, resulting in a larger structure. Thus, when connecting third and fourth branching pipes  28 - 3  and  28 - 4  to surge tank  30 , the connection arrangement shown in FIG. 6 will be more compact compared to the connection arrangement shown in FIG.  7 . 
     By forming connections as shown in FIG.  4  and FIG. 6, intake device  20  allows the path lengths of first through fourth branching paths  36 - 1  through  36 - 4  to be made shorter and more uniform. Furthermore, the overall structure of the intake device  20  is made more compact. 
     Intake device  20  includes intake manifold  24 , with attachment flange  26  connecting first through fourth branching pipes  28 - 1  through  28 - 4  with surge tank  30 . Surge tank  30  is disposed so that its center C 1  is offset toward third gas column #3 at one side of gas column row direction D. First through fourth branching pipes  28 - 1  through  28 - 4 , which are preferably formed from plates shaped as pipes, are curved gradually having a small curvature. This shape allows first through fourth branching paths  36 - 1  through  36 - 4  to have uniform lengths. 
     First through fourth flange fitting sections  38 - 1  through  38 - 4 , at one end of first through fourth branching pipes  28 - 1  through  28 - 4 , are arranged in a row along gas column row direction D and connected to first through fourth flange-side connectors  34 - 1  through  34 - 4  of attachment flange  26 . First through fourth tank fitting sections  40 - 1  through  40 - 4 , on the other end of first through fourth branching pipes  28 - 1  through  28 - 4 , connect to first through fourth tank-side connection openings  60 - 1  through  60 - 4  on side walls  42 , 44  of surge tank  30 . 
     Surge tank  30 , which is offset from gas column row center C toward third gas column #3 at one side of gas column row direction D, has side walls  42  and  44  facing either side of gas column row direction D. First and third branching pipes  28 - 1  and  28 - 3 , corresponding to first and third gas columns #1 and #3, are consecutive in intake timing and connect to side walls  42  and  44  so that they face each other along gas column row direction D. Second and fourth branching pipes  28 - 2  and  28 - 4 , corresponding to second and fourth gas columns #2 and #4, are also consecutive in intake timing and connected to side walls  42  and  44  so that they face each other along gas column row direction D. 
     First tank-side connection opening  60 - 1  of surge tank  30  is proximate to attachment flange  26  of first side wall  42 . Second tank-side connection opening  60 - 2  of surge tank  30  is distal to attachment flange  26  on first side wall  42 . Third tank-side connection opening  60 - 3  of surge tank  30  is proximate to attachment flange  26  on second side wall  44 . Fourth tank-side connection opening  60 - 4  of surge tank  30  is distal to attachment flange  26  of second side wall  44 . 
     As a result, first through fourth branching pipes  28 - 1  through  28 - 4  are arranged so that first and second tank-fitting sections  40 - 1  and  40 - 2 , at the ends of first and second branching pipes  28 - 1  and  28 - 2 , connect to side wall  42  of surge tank  30 . Side walls  42  and  44  are perpendicular to gas column row direction D, in an asymmetrical manner. First and second tank-fitting sections  40 - 1  and  40 - 2  face third and fourth tank-fitting sections  40 - 3  and  40 - 4 , which are at the ends of third and fourth branching pipes  28 - 3  and  28 - 4 . Third and fourth tank-fitting sections  40 - 3  and  40 - 4  attach to side wall  44  of surge tank  30 . 
     First through fourth branching pipes  28 - 1  through  28 - 4  of intake device  20  are preferably formed of a plate material that is easily shaped. With such a material, first through fourth branching pipes  28 - 1  through  28 - 4  are formed so that first through fourth branching paths  36 - 1  through  36 - 4  have a uniform length. This allows first through fourth branching paths  36 - 1  through  36 - 4  to be easily formed with uniform lengths even if surge tank  30  is offset along gas column row direction D. 
     Furthermore, first through fourth branching pipes  28 - 1  through  28 - 4 , which are formed with first through fourth branching paths  36 - 1  through  36 - 4  having uniform lengths, connect so that they face each other asymmetrically along gas column row direction D. First and third branching pipes  28 - 1  and  28 - 3 , which correspond to first and third gas columns #1 and #3 and which have consecutive intake timings, are disposed facing each other along gas column row direction D. Second and fourth branching pipes  28 - 2  and  28 - 4 , which correspond to second and fourth gas columns #2 and #4 and which have consecutive intake timings, are disposed facing each other along gas column row direction D. This structure allows first through fourth branching pipes  28 - 1  through  28 - 4 , for which first through fourth branching paths  36 - 1  through  36 - 4  are formed with uniform lengths, to have gradual curves with small curvature, without requiring tight curves having large curvature. This allows the shape of first through fourth branching paths  36 - 1  through  36 - 4  to be smooth, while minimizing projection of first through fourth branching pipes  28 - 1  through  28 - 4  along gas column row direction D. 
     As a result, intake device  20  reduces variations in the output generated from first through fourth gas columns #1 through #4, since the path lengths of first through fourth intake paths  36 - 1  through  36 - 4  are uniform. This improves the output performance of internal combustion engine  6 , reduces projections of first through fourth branching pipes  36 - 1  through  36 - 4  in the direction of gas column row direction D, allows smoother shapes for first through fourth branching paths  36 - 1  through  36 - 4  thereby reducing intake resistance, and allows intake manifold  24  to be lighter and more compact. By making intake manifold  24  lighter and more compact, fuel consumption is reduced, power performance is improved, and internal combustion engine  6  is made more compact. This makes it easy for internal combustion engine  6  to be mounted in automobile  2  while allowing automobile  2  to be lighter. 
     Referring specifically to FIG. 1, in this embodiment of the present invention, second branching pipe  28 - 2  is disposed above first branching pipe  28 - 1 . Fourth branching pipe  28 - 4  is disposed above third branching pipe  28 - 3 . However, it is also possible to have the pipes arranged as shown in FIGS. 8 through 11. 
     Referring to FIG. 8, in the pipe arrangement shown, first branching pipe  28 - 1  is above second branching pipe  28 - 2 . Fourth branching pipe  28 - 4  is above third branching pipe  28 - 3 . 
     Referring to FIG. 9, in the pipe arrangement shown, second branching pipe  28 - 2  is above first branching pipe  28 - 1 . Third branching pipe  28 - 3  is above fourth branching pipe  28 - 4 . 
     Referring to FIG. 10, in the pipe arrangement shown, first branching pipe  28 - 1  is above second branching pipe  28 - 2 . Tthird branching pipe  28 - 3  is above fourth branching pipe  28 - 4 . 
     The same advantages as the embodiment described above are provided, even if the relationship between first and second branching pipes  28 - 1  and  28 - 2 , and the relationship between third and fourth branching pipes  28 - 3  and  28 - 4  are changed. 
     Referring back to FIG. 1, surge tank  30  is offset from gas column row center C toward third gas column #3 at one side of gas column row direction D. First through fourth branching pipes  28 - 1  through  28 - 4  connect to surge tank  30 . 
     Referring now to FIG. 11, similar advantages are obtained when surge tank  30  is offset from gas column row center C toward second gas column #2 at the other side of gas column row direction D. As in the first embodiment of the present invention, first through fourth branching pipes  28 - 1  through  28 - 4  connect to surge tank  30 . 
     Referring to FIG. 12, there is shown a first alternative embodiment of the present invention. Surge tank  30  is offset from gas column row center C toward third gas column #3 at one side of the gas column row direction. A first and second path diameter d 1  and d 2  of first and second branching paths  36 - 1  and  36 - 2  of first and second branching pipes  28 - 1  and  28 - 2  are larger than a third and fourth path diameters d 3  and d 4  of third and fourth branching paths  36 - 3  and  36 - 4  of third and fourth branching pipes  28 - 3  and  28 - 4 , which have shorter path lengths. 
     First and second path diameters d 1  and d 2  of first and second branching paths  36 - 1  and  36 - 2 , having shorter path lengths, are formed larger than third and fourth path diameters d 3  and d 4  of third and fourth branching paths  36 - 3  and  36 - 4 , which have shorter path lengths. As a result, the flow delay of the intake air into first and second gas columns #1 and #2 is compensated, and the intake air volumes for first through fourth gas columns #1 through #4 are uniform. 
     By varying the first through the fourth path diameters d 1 -d 4  based on the path lengths of the first through the fourth branching paths  36 - 1 - 36 - 4 , the intake air volumes for the first through the fourth gas columns #1-#4 can be made uniform. 
     Referring to FIG. 13, there is shown a second alternative embodiment of the present invention. Surge tank  30  is offset from gas column row center C toward third gas column #3 at one side of the gas column row direction. A third and a fourth throttle  62 - 3  and  62 - 4  are on third and fourth path diameters d 3  and d 4  of third and fourth branching paths  36 - 3  and  36 - 4  of third and fourth branching pipes  28 - 3  and  28 - 4 , which have longer path lengths compared to first and second path diameters d 1  and d 2  of first and second branching paths  36 - 1  and  36 - 2  of first and second branching pipes  28 - 1  and  28 - 2 . Third and fourth throttles  62 - 3  and  62 - 4  serve to reduce third and fourth path diameters d 3  and d 4 . 
     Third and fourth throttles  64 - 3  and  64 - 4  are on third and fourth branching paths  36 - 3  and  36 - 4 , which have longer path lengths, in order to reduce third and fourth path diameters d 3  and d 4 . First and second throttles  62 - 1  and  62 - 2  (not shown in the figure) are not disposed on first and second branching paths  36 - 1  and  36 - 2 , which have shorter path lengths, in order to reduce first and second path diameters d 1  and d 2 . This structure provides compensation for the intake air flow delay to first and second gas columns #1 and #2, allowing the intake air volumes at first through fourth gas columns #1 through #4 to be uniform. 
     First through fourth throttles  62 - 1  through  62 - 4  can be varied according to the path lengths of first through fourth branching paths  36 - 1  through  36 - 4 , so that the intake air volume at first through fourth gas columns #1 through #4 are further equalized. Also, the intake resistance of the branching pipes is reduced and the intake air volumes is made uniform, by providing larger path diameters for the sections with gradual curves having small curvature, and by providing small path diameters for the sections with tight curves having large curvature. 
     In the internal combustion engine of the embodiments described above, first through fourth gas columns #1 through #4 are arranged in a row. However, it is also possible to implement the present invention for a V-type gas column internal combustion engine, with the intake manifolds attached to the cylinder banks on each side. 
     Referring to FIG. 14, there is shown a sample implementation of the present invention with a V- 8  gas column internal combustion engine  102  mounted in an automotive engine compartment (not shown in the figure). Internal combustion engine  102  includes cylinder heads  106 R and  106 L and head covers  108 R and  108 L mounted over a roughly V-shaped cylinder block  104 . Cylinder banks  110 R and  110 L are disposed in a V-shaped arrangement. An oil pan  112  is disposed below cylinder block  104 . 
     Internal combustion engine  102  of the V- 8  gas column can have, for example, four first-side first through fourth gas columns R#1 through R#4 (not shown in the figure) arranged in a row on first-side cylinder bank  110 R. Also, on second-side cylinder bank  110 L, four second-side first through fourth gas columns L#1 through L#4 (not shown in the figure) are arranged in a row. 
     In internal combustion engine  102 , an intake device  116  is disposed in a bank space  114 , between cylinder banks  110 R and  110 L. Intake device  116  includes an intake manifold  118  and a throttle body (not shown in the figure). 
     Intake manifold  118  includes first-side first through fourth branching pipes  122 R- 1  through  122 R- 4 , which correspond to a first-side attachment flange  120 R attached to a first-side cylinder head  106 R and first-side first through fourth gas columns R#1 through R#4. Second-side first through fourth branching pipes  122 L- 1  through  122 L- 4 , which correspond to a second-side attachment flange  120 L, have second-side first through fourth gas columns L#5 through L#8. A surge tank  124  restricts intake gas rippling. 
     First-side first through fourth branching pipes  122 R- 1  through  122 R- 4 , which are preferably formed from plates shaped as pipes, have gradual curves with small curvatures. First-side first through fourth branching pipes  122 R- 1  through  122 R- 4  are formed internally so that first-side first through fourth branching paths  126 R- 1  through  126 R- 4  have uniform lengths. Second-side first through fourth branching pipes  122 L- 1  through  122 L- 4 , which are preferably formed from plates shaped as pipes, have gradual curves with small curvatures and are also formed internally so that first-side first through fourth branching paths  126 L- 1  through  126 L- 4  have uniform lengths. 
     Surge tank  124  is a hollow, roughly rectangular body including side walls  128  and  130  perpendicular to the ends of gas column row direction D. Side walls  132 R and  132 L face side attachment flanges  120 R and  120 L. A bottom  134  is at the bottom of surge tank  124 . A ceiling  136  at the top of surge tank  124 . A body attachment seat  138 , for attaching a throttle body, is disposed on ceiling  136 . An air entry opening  140  is disposed on body attachment seat  138  to allow air in from the throttle body. 
     Surge tank  124  is disposed so that its center C 1  is at an offset of a distance M from gas column row center C toward third gas columns R#3 and L#3 of gas column row direction D. 
     First through fourth gas columns R#1 through R#4 and L#1 through L#4 (not shown in the figure) of internal combustion engine  102  are arranged as a row on each of cylinder banks  110 R and  110 L, respectively. First through fourth branching pipes  122 R- 1  through  122 R- 4  and  122 L- 1  through  122 L- 4  of intake device  116  connect symmetrically to surge tank  124 . 
     The following will describe how first through fourth branching pipes  122 R- 1  through  122 R- 4 , which communicate with first through fourth gas cylinders R#1 through R#4 of cylinder bank  110 R, are connected. 
     One end of first through fourth branching pipes  122 R- 1  through  122 R- 4  connect to first-side attachment flange  120 R. The other end of first and second branching pipes  122 R- 1  and  122 R- 2  connect to first side wall  128  of surge tank  124 , facing one end of gas cylinder direction D. The other end of third and fourth branching pipes  122 R- 3  and  122 R- 4  connect to second side wall  128  of surge tank  124 , facing the other end of gas cylinder direction D. 
     With these first through fourth branching pipes  122 R- 1  through  122 R- 4 , first and third branching pipes  122 R- 1  and  122 R- 3 , which correspond to first and third gas columns R#1 and R#3 and which have consecutive intake timings, connect to side walls  128  and  130  of surge tank  124  so that they face each other along gas column row direction D. Second and fourth branching pipes  122 R- 2  and  122 R- 4 , which correspond to second and fourth gas columns R#2 and R#4 and which have consecutive intake timings, connect to side walls  128  and  130  so that they face each other along gas column row direction D. 
     Also, with these first through fourth branching pipes  122 R- 1  through  122 R- 4 , the other ends of first and second branching pipes  122 R- 1  and  122 R- 2 , which connect to attachment flange  120 R to one side of gas column row center C along gas column row direction D, and the other ends of third and fourth branching pipes  122 R- 3  and  122 R- 4 , which connect to attachment flange  120 R to the other side of gas column row center C along gas column row direction D, connect to side walls  128  and  130 , so that they are asymmetrical along gas column row direction D. 
     Thus, in intake device  116 , first through fourth branching pipes  122 R- 1  throgh  122 R- 4 , which communicate with first through fourth gas columns R#1 through R#4, are preferably formed with easily shaped plate material. As a result, first through fourth branching pipes  122 R- 1  through  122 R- 4  are formed so that the lengths of first through fourth branching paths  126 R- 1  through  126 R- 4  are uniform. Thus, even if surge tank  124  is offset along gas column row direction D, first through fourth branching paths  126 R- 1  through  126 R- 4  are easily made with uniform lengths. 
     Furthermore, in intake device  116 , first through fourth branching pipes  122 R- 1  through  122 R- 4  connect facing each other so that they are asymmetrical along gas column row direction D. First and third branching pipes  122 R- 1  and  122 R- 3 , which correspond to first and third gas columns R#1 and R#3 and which have consecutive intake timings, connect facing each other along gas column row direction D. Likewise, second and fourth branching pipes  122 R- 2  and  122 R- 4 , which correspond to second and fourth gas columns R#2 and R#4 and which have consecutive intake timings, connect facing each other along gas column row direction D. As a result, first through fourth branching pipes  122 R- 1  through  122 R- 4 , which have uniform lengths for first through fourth branching paths  126 R- 1  through  126 R- 4 , are formed with gradual curves having small curvatures rather than with tight curves having large curvatures. Thus, the projections of first through fourth branching pipes  122 R- 1  through  122 R- 4 , along gas column row direction D, is kept small while the shapes of first through fourth branching paths  126 R- 1  through  126 R- 4  are kept smooth. 
     As a result, in intake device  116  of V- 8  gas cylinder internal combustion engine  102 , first through fourth branching paths  126 R- 1  through  126 R- 4  have uniform lengths. Thus, variations in the output generated from first through fourth gas cylinder R#1 through R#4 is reduced, the output performance of internal combustion engine  102  is improved, the projection along gas cylinder row direction D of first through fourth branching pipes  122 R- 1  through  122 R- 4  is minimized, the shapes of first through fourth branching paths  126 R- 1  through  126 R- 4  are made smooth thereby reducing intake resistance, and intake manifold  118  is made lighter and more compact. The lighter and more compact intake manifold  118  reduces fuel consumption and improves power performance, while allowing internal combustion engine  102  to be more compact. This further allows internal combustion engine  102  to be more easily mounted in an automobile, resulting in the automobile being lighter. 
     First through fourth branching pipes  122 L- 1  through  122 L- 4 , which communicate with first through fourth gas columns L#1 through L#4 of cylinder bank  110 L of internal combustion engine  102 , are symmetrical with first through fourth branching pipes  122 R- 1  through  122 R- 4  described above. By forming first through fourth branching pipes  122 L- 1  through  122 L- 4  in a similar manner as first through fourth branching pipes  122 R- 1  through  122 R- 4  described above, they are connected with a similar connection arrangement to surge tank  124 . 
     Thus, in intake device  116 , first through fourth branching pipes  122 L- 1  through  122 L- 4 , which communicate with first through fourth gas cylinder L#1 through L#4 of cylinder bank  110 L of internal combustion engine  102 , are formed similar to first through fourth branching pipes  122 R- 1  through  122 R- 4  as described above. First through fourth branching pipes  122 L- 1  through  122 L- 4  are formed so that first through fourth branching paths  126 L- 1  through  126 L- 4  have uniform lengths. Thus, even if surge tank  124  is offset along gas column row direction D, first through fourth branching paths  126 L- 1  through  126 L- 4  are easily made with uniform lengths. First through fourth branching pipes  122 L- 1  through  122 L- 4 , which have uniform lengths for first through fourth branching paths  126 L- 1  through  126 L- 4 , are formed with gradual curves having small curvatures rather than with tight curves having large curvatures. Thus, the projections of first through fourth branching pipes  122 L- 1  through  122 L- 4 , along gas column row direction D, is kept small while the shapes of first through fourth branching paths  126 L- 1  through  126 L- 4  are kept smooth. 
     As a result, in intake device  116  of V- 8  gas cylinder internal combustion engine  102 , first through fourth branching paths  126 L- 1  through  126 L- 4  have uniform lengths. Thus, variations in the output generated from first through fourth gas cylinder L#1 through L#4 is reduced, the output performance of internal combustion engine  102  is improved, the projection along gas cylinder row direction D of first through fourth branching pipes  122 L- 1  through  122 L- 4  is minimized, the shapes of first through fourth branching paths  126 L- 1  through  126 L- 4  are made smooth thereby reducing intake resistance, and intake manifold  118  is made lighter and more compact. The lighter and more compact intake manifold  118  reduces fuel consumption and improves power performance, while allowing internal combustion engine  102  to be more compact. This allows internal combustion engine  102  to be more easily mounted in an automobile, resulting in the automobile being lighter. 
     As described above, the intake device for internal combustion engines according to the present invention allows branching pipes to be formed so that their branching paths have uniform lengths. Even if the surge tank is offset along the gas column row direction, the branching paths are easily be formed with uniform lengths. Also, the branching pipes, having uniformly long branching paths, are formed without forming tight curves having large curvatures. The projection of the branching pipes, in the direction of the branching pipe row direction, is kept small, and the shapes of the branching pipes are kept smooth. 
     As a result, this intake device for internal combustion engines reduces variations in the power generated by the gas columns through the uniform lengths of the intake paths. The output performance of the internal combustion engine is improved. The projection of the branching pipes in the gas column row direction is kept small. The branching paths are kept smooth, thereby reducing intake resistance. The intake manifold is made compact and light. The compactness and lightness of the intake manifold allows fuel consumption to be reduced and improves overall power performance. This allows the internal combustion engine to be made more compact, resulting in the internal combustion engine being more easily mounted in an automobile, allowing the automobile to be lighter. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.