Abstract:
An exhaust manifold maintains the EGR ratio constant irrespective of a change in shape of the exhaust manifold and includes exhaust gas inlet sections connected to the exhaust ports of respective cylinders of the engine; a main pipe section configured so that exhaust gas entering from the exhaust gas inlet sections is collected inside the main pipe section; an EGR gas taking-out section for extracting, as EGR gas, a part of the exhaust gas; and an exhaust gas discharge section for discharging the exhaust gas. The main pipe section has formed thereon a curved section provided between the exhaust gas inlet sections and curved in a shape protruding to the side opposite the exhaust gas inlet sections. The curved section has a recess which is formed by causing a portion of the outer peripheral surface of the curved section to be recessed toward the inside of the main pipe section.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to structure of an exhaust manifold having an EGR gas taking-out section. 
       BACKGROUND ART 
       [0002]    Conventionally, a small internal combustion engine such as a diesel engine or a gasoline engine has high general-purpose properties and is employed for various purposes such as an agricultural machine, a construction machine and a ship (loaded machine). Accordingly, loading space of the internal combustion engine is various corresponding to the loaded machine, and the loading space of the internal combustion engine may be small. 
         [0003]    In an internal combustion engine having a DPF (Diesel Particulate Filter) effective for dealing with regulation of exhaust gas, the ratio of the space for the DPF to the space for the whole internal combustion engine is large. 
         [0004]    Therefore, different specifications are set about the loading position of the DPF in the internal combustion engine so as to follow the installation position and exhaust direction of the loaded machine. 
         [0005]    For example, as the loading position of the DPF in the internal combustion engine, the construction in which a DPF  200  is arranged above a manifold  210  as shown in  FIG. 12(   a ) and the construction in which the DPF  200  is arranged above a flywheel  220  as shown in  FIG. 12(   b ) are provided. 
         [0006]    When the loading position of the DPF is changed, the shape of the exhaust manifold is also changed. 
         [0007]    For example, in the construction in which the DPF is arranged above the exhaust manifold ( FIG. 12(   a )), an exhaust outlet of the exhaust manifold must be directed upward, whereby the shape of the exhaust manifold as shown in the Patent Literature 1 is employed. 
         [0008]    In the construction in which the DPF is arranged above the flywheel ( FIG. 12(   b )), the exhaust outlet of the exhaust manifold must be directed to the flywheel, whereby the shape of the exhaust manifold as shown in the Patent Literature 2 is employed. 
         [0009]    Furthermore, as a measure for reducing NOx and the like discharged from the internal combustion engine, in addition to the DPF, a method is employed in which a part of exhaust gas discharged from the internal combustion engine is returned to the intake as EGR gas (EGR: Exhaust Gas Recirculation). In this method, mixture ratio of the exhaust gas (EGR gas) and new air (EGR ratio) is changed corresponding to the positional relation between an EGR taking-out section and an exhaust gas discharge section guiding exhaust gas to a silencer in the exhaust manifold. 
       PRIOR ART REFERENCE 
     Patent Literature 
       [0010]    Patent Literature 1: the Japanese Patent Laid Open Gazette 2007-177693 
         [0011]    Patent Literature 2: the Japanese Patent Laid Open Gazette 2006-132408 
       DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
       [0012]    As mentioned above, when the position of the EGR taking-out section and the exhaust gas discharge section in the exhaust manifold is changed corresponding to the loading position of the DPF, the EGR ratio is also changed. Accordingly, there is a problem in that an operation program of a valve controlling the EGR ratio must be amended. 
         [0013]    Therefore, the present invention provides an exhaust manifold in which an EGR ratio is substantially fixed when loading position of a DPF is changed. 
       Means for Solving the Problems 
       [0014]    The above-mentioned problems are solved by the following means of the present invention. 
         [0015]    According to the present invention, an exhaust manifold includes exhaust gas inlet sections connected to exhaust ports of cylinders of an engine, a main pipe section communicated with the exhaust gas inlet sections and collecting exhaust gas flowing from the exhaust gas inlet sections, an EGR gas taking-out section taking out a part of the collected exhaust gas as EGR gas, and an exhaust gas discharge section discharging the other part of the exhaust gas. In the main pipe section, a curved section projectingly curved oppositely to the exhaust gas inlet sections is formed between the exhaust gas inlet sections. In the curved section, a recess is formed by recessing a part of an outer peripheral surface of the curved section toward an inside of the main pipe section, and an EGR gas taking-out section is extendingly provided from a part of the outer peripheral surface opposite to the recess. A center of an inlet opening of the EGR gas taking-out section is offset from an axis in lengthwise direction of the main pipe section. 
         [0016]    According to the present invention, a center of an opening of the exhaust gas discharge section is offset from the axis in the lengthwise direction of the main pipe section. 
         [0017]    According to the present invention, the exhaust gas discharge section is provided at a center in the lengthwise direction of the main pipe section. 
         [0018]    According to the present invention, the exhaust gas discharge section is provided at an end of the main pipe section oppositely to the EGR gas taking-out section. 
       Effect of the Invention 
       [0019]    The present invention brings the following effects. 
         [0020]    According to the present invention, the exhaust gas flowing into the EGR gas taking-out section is limited to the exhaust gas flowing from the specific exhaust ports. Accordingly, when the position of the exhaust gas discharge section in the exhaust manifold is changed and the shape of the exhaust manifold is changed, the change of the EGR ratio by the change of flow of the exhaust gas caused by the shape of the exhaust manifold can be reduced. Therefore, the EGR ratio is fixed regardless of the change of the shape of the exhaust manifold, whereby it is not necessary to change the EGR ratio control program though the shape of the exhaust manifold is changed. The exhaust manifold can be selected following the loaded position of the DPF in the internal combustion engine without changing the EGR ratio. 
         [0021]    According to the present invention, the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized regardless of the change of the shape of the exhaust manifold (the change of the position of the exhaust gas discharge section in the exhaust manifold). 
         [0022]    According to the present invention, the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized. 
         [0023]    According to the present invention, the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]    [ FIG. 1 ] A perspective view of an exhaust manifold according to a first embodiment. 
           [0025]    [ FIG. 2 ] A side view of the exhaust manifold according to the first embodiment. 
           [0026]    [ FIG. 3 ] A plan view of the exhaust manifold according to the first embodiment. 
           [0027]    [ FIG. 4 ] An arrow sectional view of the line X-X in  FIG. 3 . 
           [0028]    [ FIG. 5 ] A perspective view of an exhaust manifold according to a second embodiment. 
           [0029]    [ FIG. 6 ] A side view of the exhaust manifold according to the second embodiment. 
           [0030]    [ FIG. 7 ] A plan view of the exhaust manifold according to the second embodiment. 
           [0031]    [ FIG. 8 ] A rear view of the exhaust manifold according to the second embodiment. 
           [0032]    [ FIG. 9 ] A perspective view of a conventional exhaust manifold. 
           [0033]    [ FIG. 10 ] A graph of EGR ratios of the exhaust manifold according to the first embodiment, the exhaust manifold according to the second embodiment and the conventional exhaust manifold when a driving condition of a multi-cylinder internal combustion engine is 1mode. 
           [0034]    [ FIG. 11 ] A graph of EGR ratios of the exhaust manifold according to the first embodiment, the exhaust manifold according to the second embodiment and the conventional exhaust manifold when the driving condition of the multi-cylinder internal combustion engine is  4 mode. 
           [0035]    [ FIG. 12 ] A perspective view of a loading position of a DPF in the internal combustion engine. (a) is a perspective view of the case in which the DPF is arranged above the exhaust manifold. (b) is a perspective view of the case in which the DPF is arranged above a flywheel. 
       
    
    
     DESCRIPTION OF NOTATIONS 
       [0000]    
       
           1  exhaust manifold 
           2  exhaust manifold 
           10  exhaust gas inlet section 
           20  main pipe section 
           21  curved section 
           30  EGR gas taking-out section 
           40  exhaust gas discharge section 
           50  exhaust gas inlet section 
           60  main pipe section 
           61  curved section 
           70  EGR gas taking-out section 
           80  exhaust gas discharge section 
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    An explanation will be given on an exhaust manifold  1  according to the present invention. In below explanation, an internal combustion engine is a four-cylindered diesel engine (hereinafter, referred to as engine), and the exhaust manifold  1  attached to the four-cylindered diesel engine is explained. As shown in  FIG. 1 , the lengthwise direction of the exhaust manifold  1  is regarded as the longitudinal direction, and directions perpendicular to the lengthwise direction of the exhaust manifold  1  are respectively regarded as the vertical and lateral directions. 
         [0049]    An explanation will be given on the exhaust manifold  1  according to a first embodiment of the present invention. 
         [0050]    A DPF is disposed above the exhaust manifold  1  according to the first embodiment, and the axis (lengthwise direction) of the DPF is in parallel to an axis A ( FIG. 2 ) of the exhaust manifold  1  (the same as  FIG. 12(   a )). 
         [0051]    As shown in  FIGS. 1 ,  2  and  3 , the exhaust manifold  1  includes a plurality of exhaust gas inlet sections  10  (in this embodiment, exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d ), a main pipe section  20 , an EGR gas taking-out section  30  and an exhaust gas discharge section  40 . The exhaust gas inlet sections  10 , the main pipe section  20 , the EGR gas taking-out section  30  and the exhaust gas discharge section  40  are formed integrally. 
         [0052]    The exhaust manifold  1  is provided and connected to an exhaust port of a cylinder head fixed to an upper portion of a cylinder block, and exhaust gas discharged from the cylinders (not shown) of the engine is collected to the main pipe section  20  via the exhaust gas inlet sections  10 . Then, the collected exhaust gas is discharged from the exhaust gas discharge section  40  via the DPF and a silencer to the outside, and a part of the collected exhaust gas is taken out as EGR gas from the EGR gas taking-out section  30  via an EGR pipe and supplied to an intake side. 
         [0053]    The exhaust gas inlet sections  10  are connected to the exhaust port of the engine. The number of the exhaust gas inlet sections  10  is the same as that of the cylinders of the engine, and each of the exhaust gas inlet sections  10  is opened leftward parallel and has the same opening area as that of the cylinders. The exhaust gas inlet sections  10  are provided so that the first exhaust gas inlet section  10   a,  the second exhaust gas inlet section  10   b,  the third exhaust gas inlet section  10   c  and the fourth exhaust gas inlet section  10   d  are arranged in this order at predetermined intervals along the lengthwise direction of the main pipe section  20  from the end of the side at which the EGR gas taking-out section  30  is extendingly provided (rear side). 
         [0054]    The exhaust gas from the cylinders of the engine via the exhaust gas inlet sections  10  (the exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d ) are collected in the main pipe section  20 . The main pipe section  20  is pipe-like shaped and communicated with the exhaust gas inlet sections  10 . When the exhaust manifold  1  is attached to the engine, the main pipe section  20  is extended in parallel to a crankshaft of the engine. The shape of the main pipe section  20  will be described later. 
         [0055]    At the EGR gas taking-out section  30 , a part of the exhaust gas collected in the main pipe section  20  is taken out as EGR gas. The EGR gas taking-out section  30  is pipe-like shaped and narrower than the main pipe section  20  and extendingly provided downward while the upper end of the EGR gas taking-out section  30  is communicated with the lower surface of the middle portion in the lengthwise direction of the main pipe section  20 . In detail, as shown in  FIG. 3 , the EGR gas taking-out section  30  is extendingly provided downward from the position in the lower surface between the exhaust gas inlet sections  10   a  and  10   b  and close to the exhaust gas inlet section  10   b  and decentered (offset) rightward from an axis A in the lengthwise direction of the main pipe section  20 . The lower portion of the EGR gas taking-out section  30  is curved toward the center in the lengthwise direction of the main pipe section  20 , that is, forward, and the tip of the EGR gas taking-out section  30  is opened and connected to the EGR pipe (not shown). 
         [0056]    In the exhaust gas discharge section  40 , the exhaust gas collected in the main pipe section  20  except for the part taken out as the EGR gas is discharged to the outside of the exhaust manifold  1 . The exhaust gas discharge section  40  is pipe-like shaped and thicker than the main pipe section  20 , and the lower end of the exhaust gas discharge section  40  is extendingly provided slantingly upward from the upper portion of the center in the lengthwise direction of the main pipe section  20 . In detail, as shown in  FIGS. 3 and 4 , the exhaust gas discharge section  40  is extendingly provided slantingly upward from the position in the lower surface between the exhaust gas inlet sections  10   b  and  10   c  and close to the exhaust gas inlet section  10   b  and decentered (offset) rightward from an axis A in the lengthwise direction of the main pipe section  20 . Namely, the exhaust gas discharge section  40  is extendingly provided so as to go away from the cylinder head. The opening at the tip of the exhaust gas discharge section  40  is connected to an exhaust route having a catalytic device and a silencer (not shown). The exhaust gas discharge section  40  is projected oppositely to the projecting direction of the EGR gas taking-out section  30  when viewed in front (see  FIG. 4 ). The center of the opening of the exhaust gas discharge section  40  is offset from the axis A in the lengthwise direction of the main pipe section  20  when viewed in plan (see  FIG. 3 ). The EGR gas taking-out section  30  is provided symmetrically to the exhaust gas discharge section  40  about the center of the exhaust gas inlet section  10   b  when viewed in side (see  FIG. 2 ). 
         [0057]    Next, an explanation will be given on the shape of the main pipe section  20 . 
         [0058]    As shown in  FIGS. 1 ,  2  and  3 , the main pipe section  20  is pipe-like shaped by casting, and the axis A in the lengthwise direction is disposed longitudinally. At the left side of the main pipe section  20 , the exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d  are provided. 
         [0059]    The exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d  are projected leftward (along the crosswise direction) at predetermined intervals in the lengthwise direction of the main pipe section  20 , and the tips thereof are opened. The center of opening of each of the exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d  is in agreement with the axis A in the lengthwise direction of the main pipe section  20  when viewed in side (see  FIG. 2 ). 
         [0060]    The front portion of the main pipe section  20  is curved rightward (oppositely to the exhaust gas inlet section  10   b ) at the position closer top the front side from the longitudinal center and near the exhaust gas inlet section  10   b  when viewed in plan (see  FIG. 3 ) so as to form a curved section  21 , and extended leftward and rearward so as to form the exhaust gas inlet section  10   d.  As shown in  FIGS. 1 and 3 , the EGR gas taking-out section  30  is extendingly provided downward from the lower portion of the curved section  21 . Namely, the upper end of the EGR gas taking-out section  30  is communicated with the lower surface of the curved section  21 . 
         [0061]    By providing the curved section  21  at the middle of the route of exhaust gas from the exhaust gas inlet sections  10   a,    10   b,    10   c  and  10   d  via the main pipe section  20  to the exhaust gas discharge section  40 , the route of exhaust gas is curved at the curved section  21  so that the exhaust gas can flow into the EGR gas taking-out section  30  easily. Since the upper opening of the EGR gas taking-out section  30  is positioned at the curved section  21  closer to the exhaust gas inlet section  10   a  than the part at which exhaust gas from the exhaust gas inlet section  10   a  joins exhaust gas from the exhaust gas inlet section  10   b,  whereby the exhaust gas from the exhaust gas inlet section  10   a  can be taken out from the EGR gas taking-out section  30  easily. Namely, the exhaust gas from the specific exhaust gas inlet section ( 10   a ) can be taken out from the EGR gas taking-out section  30  easily, whereby the exhaust gas can be taken out more stably than the case of taking out a part of exhaust gas collected in the main pipe section  20  once, and change of EGR ratio can be made small. 
         [0062]    Furthermore, a recess  22  is formed in the upper portion of the curved section  21 . 
         [0063]    As shown in  FIG. 4 , the recess  22  is formed by recessing a part of the outer peripheral surface of the curved section  21  toward the inside of the main pipe section  20 . Namely, the recess  22  is formed by recessing a part of the upper portion of the curved section  21  downward and leftward. Concretely, the curved section  21  is recessed substantially U-like when viewed in side and substantially L-like when viewed in front sectionally. The rear end of the curved section  21  is positioned substantially at the center of the EGR gas taking-out section  30  when viewed in plan (see  FIG. 3 ), and the lower end of the longitudinal center of the curved section  21  is positioned above the front end of the EGR gas taking-out section  30 . Furthermore the EGR gas taking-out section  30  is extendingly provided from the part of the outer peripheral surface of the curved section  21  opposite to the recess  22 . The area of the recess  22  is not more than substantially half the sectional area of the main pipe section  20  not having any recess. 
         [0064]    Since the recess  22  is formed in the upper portion of the curved section  21 , the exhaust gas from the exhaust gas inlet section  10   a  flowing in the upper portion is curved leftward and downward by the recess  22 , whereby a part of the exhaust gas can flow into the EGR gas taking-out section  30  easily. 
         [0065]    By providing the recess  22 , a part of the exhaust gas from the second exhaust gas inlet section  10   b  can easily join the exhaust gas from the first exhaust gas inlet section  10   a  and flow into the EGR gas taking-out section  30 . Therefore, the exhaust gas flowing into the EGR gas taking-out section  30  is limited to the exhaust gas flowing from the specific exhaust ports, that is, the first exhaust gas inlet section  10   a  and the second exhaust gas inlet section  10   b,  whereby the change of the EGR ratio can be made small stably. 
         [0066]    Next, an explanation will be given on an exhaust manifold  2  according to a second embodiment of the present invention. 
         [0067]    A DPF is disposed before the exhaust manifold  2  according to the second embodiment, and the axis (lengthwise direction) of the DPF is arranged perpendicularly to an axis C of the exhaust manifold  1  ( FIG. 6 ) (the same mode as  FIG. 12(   b )). 
         [0068]    As shown in  FIGS. 5 ,  6  and  7 , the exhaust manifold  2  includes a plurality of exhaust gas inlet sections  50  (in this embodiment, exhaust gas inlet sections  50   a,    50   b,    50   c  and  50   d ), a main pipe section  60 , an EGR gas taking-out section  70  and an exhaust gas discharge section  80 . The exhaust gas inlet sections  50 , the main pipe section  60 , the EGR gas taking-out section  70  and the exhaust gas discharge section  80  are formed integrally. 
         [0069]    The exhaust manifold  2  is provided and connected to an exhaust port of a cylinder head fixed to an upper portion of a cylinder block, and exhaust gas discharged from the cylinders (not shown) of the engine is collected to the main pipe section  60  via the exhaust gas inlet sections  50 . Then, the collected exhaust gas is discharged from the exhaust gas discharge section  80  via the DPF and a silencer to the outside, and a part of the collected exhaust gas is taken out as EGR gas from the EGR gas taking-out section  70  via an EGR pipe and supplied to an intake side. 
         [0070]    The exhaust gas inlet sections  50  are connected to the exhaust port of the engine. The number of the exhaust gas inlet sections  50  is the same as that of the cylinders of the engine, and each of the exhaust gas inlet sections  50  is opened leftward parallel and has the same opening area as that of the cylinders. The exhaust gas inlet sections  50  are provided so that the first exhaust gas inlet section  50   a,  the second exhaust gas inlet section  50   b,  the third exhaust gas inlet section  50   c  and the fourth exhaust gas inlet section  50   d  are arranged in this order at predetermined intervals along the lengthwise direction of the main pipe section  60  from the end of the side at which the EGR gas taking-out section  70  is extendingly provided (rear side). 
         [0071]    The exhaust gas from the cylinders of the engine via the exhaust gas inlet sections  50  (the exhaust gas inlet sections  50   a,    50   b,    50   c  and  50   d ) are collected in the main pipe section  60 . The main pipe section  60  is pipe-like shaped and communicated with the exhaust gas inlet sections  50 . When the exhaust manifold  2  is attached to the engine, the main pipe section  60  is extended in parallel to a crankshaft of the engine. The shape of the main pipe section  60  will be described later. 
         [0072]    At the EGR gas taking-out section  70 , a part of the exhaust gas collected in the main pipe section  60  is taken out as EGR gas. The EGR gas taking-out section  70  is pipe-like shaped and narrower than the main pipe section  60  and extendingly provided downward while the upper end of the EGR gas taking-out section  70  is communicated with the lower surface of the middle portion in the lengthwise direction of the main pipe section  60 . In detail, as shown in  FIG. 7 , the EGR gas taking-out section  70  is extendingly provided downward from the position in the lower surface between the exhaust gas inlet sections  50   a  and  50   b  and close to the exhaust gas inlet section  50   b  and decentered (offset) rightward from an axis C in the lengthwise direction of the main pipe section  60 . The lower portion of the EGR gas taking-out section  70  is curved toward the center in the lengthwise direction of the main pipe section  60 , that is, forward, and the tip of the EGR gas taking-out section  70  is opened and connected to the EGR pipe (not shown). 
         [0073]    In the exhaust gas discharge section  80 , the exhaust gas collected in the main pipe section  60  except for the part taken out as the EGR gas is discharged to the outside of the exhaust manifold  2 . The exhaust gas discharge section  80  is pipe-like shaped and thicker than the main pipe section  60  and communicated with the front end of the main pipe section  60 . In detail, the exhaust gas discharge section  80  is to the end of the main pipe section  60  at the side (front side) opposite to the side at which the EGR gas taking-out section  70  is provided (rear side) in the lengthwise direction, and is extendingly provided rightward and forward from the basal portion of the fourth exhaust gas inlet section  50   d.  The tip of the exhaust gas discharge section  80  is opened forward and connected to an exhaust route having a catalytic device (DPF) and a silencer (not shown). The exhaust gas discharge section  80  is extendingly provided aslant from the front end of the main pipe section  60  so as to go away from the cylinder head when viewed in plan (see  FIG. 7 ), and the center of the opening is offset from the axis C in the lengthwise direction of the main pipe section  60 . The center of the opening of the exhaust gas discharge section  80  is arranged on the extension of the axis C in the lengthwise direction of the main pipe section  60  when viewed in side (see  FIG. 6 ). 
         [0074]    As mentioned above, by offsetting the center of the opening of the exhaust gas discharge section  80  from the axis C in the lengthwise direction of the main pipe section  60 , average exhaust pressure in the exhaust manifold  2  can be fixed. 
         [0075]    Next, an explanation will be given on the shape of the main pipe section  60 . 
         [0076]    As shown in  FIGS. 5 ,  6  and  7 , the main pipe section  60  is pipe-like shaped, and the axis C in the lengthwise direction is disposed longitudinally. At the left side of the main pipe section  60 , the exhaust gas inlet sections  50   a,    50   b,    50   c  and  50   d  are provided. 
         [0077]    The exhaust gas inlet sections  50   a,    50   b,    50   c  and  50   d  are projected leftward (along the crosswise direction) at predetermined intervals in the lengthwise direction of the main pipe section  60 , and the tips thereof are opened. The center of opening of each of the exhaust gas inlet sections  50   a,    50   b,    50   c  and  50   d  is in agreement with the axis C in the lengthwise direction of the main pipe section  60  when viewed in side (see  FIG. 6 ). 
         [0078]    As shown in  FIG. 7 , a curved section  61  is formed in the rear portion of the main pipe section  60 . The curved section  61  is disposed oppositely to the exhaust gas discharge section  80 , between the first exhaust gas inlet section  50   a  and the second exhaust gas inlet section  50   b  and closely to the second exhaust gas inlet section  50   b  so as to be curved and projected rightward (oppositely to the opening of the exhaust gas inlet section  50 , that is, oppositely to the cylinder block). Namely, the curved section  61  is formed by curving the rear portion of the main pipe section  60  L-like when viewed in plan. The curved section  61  is offset rightward from the axis C in the lengthwise direction of the main pipe section  60 . 
         [0079]    The upper end of the EGR gas taking-out section  70  is communicated with the lower surface of the curved section  61 . 
         [0080]    By providing the EGR gas taking-out section  70  in the curved section  61  as mentioned above, exhaust gas flowing from the first exhaust gas inlet section  50   a  is directed mainly leftward by touching the curved section  61 , and a part of the exhaust gas is directed downward. Accordingly, the exhaust gas flowing from the first exhaust gas inlet section  50   a  is apt to flow into the EGR gas taking-out section  70 . 
         [0081]    Since exhaust gas flowing from the second exhaust gas inlet section  50   b  flows oppositely to the exhaust gas flowing from the first exhaust gas inlet section  50   a,  the exhaust gas flowing from the second exhaust gas inlet section  50   b  joins the exhaust gas flowing from the first exhaust gas inlet section  50   a  and flows toward the exhaust gas discharge section  80  along the direction of the main flow. 
         [0082]    Therefore, the exhaust gas flowing into the EGR gas taking-out section  70  is limited to the exhaust gas flowing from the specific exhaust port, that is, the first exhaust gas inlet section  50   a,  whereby the change of the EGR ratio can be made small stably, 
         [0083]    Furthermore, a recess  62  is formed in the upper portion of the curved section  61 . 
         [0084]    As shown in  FIG. 6 , the recess  62  is formed by recessing a part of the outer peripheral surface of the curved section  61  toward the inside of the main pipe section  60 . The recess  62  is formed between the first exhaust gas inlet section  50   a  and the second exhaust gas inlet section  50   b  and closely to the second exhaust gas inlet section  50   b  so that the upper surface of the recess  62  is substantially V-like shaped when viewed in side. As shown in  FIG. 7 , a valley line D which is the lower end of the recess  62  passes through the center of the inlet opening of the EGR gas taking-out section  70  when viewed in plan. Namely, the EGR gas taking-out section  70  is extendingly provided from a part of the outer peripheral surface of the curved section  61  opposite to the recess  62 . 
         [0085]    By providing the recess  62  in the curved section  61  as mentioned above, the exhaust gas flowing from the first exhaust gas inlet section  50   a  is directed downward by the recess  62 , whereby a part of the exhaust gas is apt to flow into the EGR gas taking-out section  70 . 
         [0086]    By providing the recess  62 , a part of the exhaust gas flowing from the second exhaust gas inlet section  50   b  is apt to join the exhaust gas flowing from the first exhaust gas inlet section  50   a  and flow into the EGR gas taking-out section  70 . Therefore, the exhaust gas flowing into the EGR gas taking-out section  70  is limited to the exhaust gas flowing from the specific exhaust ports, that is, the first exhaust gas inlet section  50   a  and the second exhaust gas inlet section  50   b,  whereby the change of the EGR ratio can be made small stably. 
         [0087]    Next, an explanation will be given on the EGR ratio of each of the exhaust manifold  1  according to the first embodiment and the exhaust manifold  2  according to the second embodiment of the present invention. 
         [0088]    Firstly, an explanation will be given on a conventional exhaust manifold  100  fir comparing the EGR ratio of each of the exhaust manifold  1  and the exhaust manifold  2 . 
         [0089]    As shown in  FIG. 9 , similarly to the exhaust manifold  1  and the exhaust manifold  2 , the conventional exhaust manifold  100  includes a plurality of exhaust gas inlet sections  110  (in this embodiment, exhaust gas inlet sections  110   a    110   b,    110   c  and  110   d ) communicated with the exhaust ports of the engine (not shown), a main pipe section  120  collecting the exhaust gas flowing from the exhaust gas inlet sections  110 , an EGR gas taking-out section  130  taking out a part of the exhaust gas collected in the main pipe section  120  as EGR gas, and an exhaust gas discharge section  140  discharging the exhaust gas collected in the main pipe section  120  except for the exhaust gas taken out as the EGR gas to the outside of the exhaust manifold  100 . 
         [0090]    The main pipe section  120  does not have such recess and curved section that the exhaust manifold  1  and the exhaust manifold  2  have, and is straight pipe-like shaped. At one of the ends of the main pipe section  120 , the exhaust gas discharge section  140  is provided coaxially to an axis E in the lengthwise direction of the main pipe section  120 , and the EGR gas taking-out section  130  is provided in the lower portion of the main pipe section  120  opposite to the exhaust gas discharge section  140 . 
         [0091]    When the conventional exhaust manifold  100 , the exhaust manifold  1  and the exhaust manifold  2  are operated under driving conditions determined by regulation of exhaust gas (1mode and 4mode), the EGR ratio is improved as shown in  FIGS. 10 and 11 . 
         [0092]    As mentioned above, each of the exhaust manifold  1  and the exhaust manifold  2  includes the exhaust gas inlet sections (the exhaust gas inlet sections  10 , the exhaust gas inlet sections  50 ) connected to the exhaust ports of the cylinders of the engine, the main pipe section (the main pipe section  20 , the main pipe section  60 ) communicated with the exhaust gas inlet sections and collecting exhaust gas flowing from the exhaust gas inlet sections, the EGR gas taking-out section (the EGR gas taking-out section  30 , the EGR gas taking-out section  70 ) taking out a part of the collected exhaust gas as EGR gas, and the exhaust gas discharge section (the exhaust gas discharge section  40 , the exhaust gas discharge section  80 ) discharging the other part of the exhaust gas. In the main pipe section, the curved section (the curved section  21 , the curved section  61 ) projectingly curved oppositely to the exhaust gas inlet sections is formed between the exhaust gas inlet sections. In the curved section, the recess (the recess  22 , the recess  62 ) is formed by recessing a part of the outer peripheral surface of the curved section toward the inside of the main pipe section. The EGR gas taking-out section is extendingly provided from the part of the outer peripheral surface opposite to the recess. The center of the inlet opening of the EGR gas taking-out section is offset from the axis in the lengthwise direction of the main pipe section. 
         [0093]    According to the construction of the exhaust manifold  1  and the exhaust manifold  2 , the exhaust gas flowing into the EGR gas taking-out section is limited to the exhaust gas flowing from the specific exhaust ports. Accordingly, when the position of the exhaust gas discharge section in the exhaust manifold is changed and the shape of the exhaust manifold is changed, the change of the EGR ratio by the change of flow of the exhaust gas caused by the shape of the exhaust manifold can be reduced. Therefore, the EGR ratio is fixed regardless of the change of the shape of the exhaust manifold, whereby it is not necessary to change the EGR ratio control program though the shape of the exhaust manifold is changed. The exhaust manifold can be selected following the loaded position of the DPF in the internal combustion engine without changing the EGR ratio. 
         [0094]    In the exhaust manifold  1  and the exhaust manifold  2 , the center of the opening of the exhaust gas discharge section (the exhaust gas discharge section  40 , the exhaust gas discharge section  80 ) is offset from the axis in the lengthwise direction of the main pipe section (the main pipe section  20 , the main pipe section  60 ) 
         [0095]    According to the construction of the exhaust manifold  1  and the exhaust manifold  2 , the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized regardless of the change of the shape of the exhaust manifold (the change of the position of the exhaust gas discharge section in the exhaust manifold). 
         [0096]    Furthermore, in the construction of the exhaust manifold  1 , the exhaust gas discharge section  40  is provided at the center in the lengthwise direction of the main pipe section  20 . 
         [0097]    According to the construction of the exhaust manifold  1 , the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized. 
         [0098]    Furthermore, in the construction of the exhaust manifold  2 , the exhaust gas discharge section  80  is provided at the end of the main pipe section  60  oppositely to the EGR gas taking-out section  70 . 
         [0099]    According to the construction of the exhaust manifold  2 , the average exhaust pressure in the exhaust manifold can be fixed. Accordingly, the change of the amount of the EGR gas caused by the discharge direction of the exhaust gas can be reduced, whereby the amount of the EGR gas taken out from the EGR gas taking-out section can be stabilized. 
       INDUSTRIAL APPLICABILITY 
       [0100]    The present invention can be employed for an engine having an EGR (Exhaust Gas Recirculation), especially an engine having a DPF (Diesel Particulate Filter).