Fixing structure for exhaust manifold and exhaust manifold

Abstract

A fixing structure for an exhaust manifold that is to be fixed to a cylinder head by a bolt B comprises a fixing part 20 that extends to the outside from the exhaust manifold. The fixing part 20 comprises: a flange part 21 that has an insertion hole 22 into which the bolt is inserted; and a pair of wall surface parts 23 that are separated from each other and are formed to cover both side surfaces of the inserted bolt. The pair of wall surface parts 23 are continuous with the flange part 21 at one end, contact the cylinder head at the other end, and are sloped so as to become shorter from the one end toward the cylinder head. This fixing structure for an exhaust manifold makes it possible to securely fix joined parts of members that repeatedly expand and contract due to heating and cooling, regardless of whether an expensive alloy is used.

Description

Exhaust manifold fixing structure and exhaust manifold

[0001] The present invention relates to an exhaust manifold fixing structure and an exhaust manifold.

[0002] Exhaust system components for internal combustion engines used in passenger cars, trucks, and other construction, industrial, and agricultural vehicles include turbo housings and exhaust manifolds. These exhaust system components repeatedly expand and contract as they heat up and cool down, potentially causing gas leaks between components due to thermal expansion of fastening parts at the joints between the components. Furthermore, in recent years, exhaust gas temperatures have tended to rise in response to improved fuel efficiency in line with environmental regulations, resulting in increasingly greater temperature changes experienced by exhaust system components. This has created a demand for exhaust system components that are less susceptible to gas leaks.

[0003] Therefore, in order to improve thermal deformation resistance and prevent gas leakage, for example, the invention described in Patent Document 1 uses ferritic spheroidal graphite cast iron in which V or the like is added to high SiMo cast iron for exhaust system parts, and the invention described in Patent Document 2 uses ferritic spheroidal graphite cast iron in which V, Nb, and W are added to high SiMo cast iron for exhaust system parts.

[0004] Patent No. 3936849 Patent No. 5232620

[0005] However, these spheroidal graphite cast irons are known to be prone to casting defects (e.g., shrinkage cavities), which significantly affect casting productivity. Furthermore, although they can improve heat deformation resistance, they tend to be expensive because they require the addition of expensive alloys.

[0006] Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional technology and to provide a fixing structure for an exhaust manifold that can firmly fix the joints between components that repeatedly expand and contract due to heating and cooling, regardless of whether or not expensive alloys are used.

[0007] The fixing structure for an exhaust manifold of the present invention is a fixing structure for an exhaust manifold fixed to a cylinder head by bolts, the fixing structure comprising a fixing portion extending outward from the exhaust manifold, the fixing portion including a flange portion having an insertion hole into which the bolt is inserted, and a pair of spaced-apart wall portions formed to cover both side surfaces of the inserted bolt, one end of the pair of wall portions continuing to the flange portion and the other end contacting the cylinder head. In this invention, the pair of wall portions of the fixing portion are shaped so as to cover only a portion of the bolt by being spaced apart from each other rather than to cover the entire periphery of the bolt. This reduces the contact area of ​​the fixing portion with the cylinder head compared to when the entire periphery of the bolt is covered, suppressing temperature rise of the components constituting the fixing portion and thermal expansion of the bolt, resulting in a strong fixing of the components to each other.

[0008] The pair of wall portions are preferably inclined so that their height decreases from the one end toward the cylinder head. By configuring in this manner, the contact area of ​​the fixing portion with the cylinder head is further reduced, which further suppresses temperature increases in the members constituting the fixing portion and thermal expansion of the bolt, thereby enabling the members to be firmly fixed together to prevent gas leakage.

[0009] The flange portion preferably has a length in the thickness direction shorter than the length of the wall portion, which preferably suppresses thermal expansion of the bolt and enables the members to be firmly fixed together to prevent gas leakage.

[0010] The exhaust manifold of the present invention is characterized by having a plurality of the exhaust manifold fixing structures described above. By having a plurality of exhaust manifold fixing structures, the components can be firmly fixed to each other to prevent gas leakage.

[0011] Of the fixing portions, it is preferable that the insertion hole of a central fixing portion located in the longitudinal center of the exhaust manifold has a smaller hole diameter than the insertion holes of the other fixing portions. By configuring in this way, it is possible to perform positioning with high precision.

[0012] Of the fixing parts, it is preferable that the insertion holes of the left-end fixing part and / or the right-end fixing part located at both ends in the longitudinal direction of the exhaust manifold are elliptical in shape, and the longitudinal width of the ellipse is longer than the hole diameter of the insertion holes of the other fixing parts. By configuring at least one of the insertion holes of the left-end fixing part and the right-end fixing part in this manner, it is possible to position the fixing part in the up, down, left, and right directions using the insertion hole of this fixing part and the insertion hole of the central fixing part.

[0013] The exhaust manifold preferably has a reduced-weight portion in the partition wall between the exhaust passages or between the EGR passage and the exhaust passage on the surface that contacts the cylinder head. This configuration makes the exhaust manifold less susceptible to direct thermal effects from the cylinder head, suppresses thermal expansion of the exhaust manifold, and reduces misalignment between the cylinder head and the exhaust manifold.

[0014] According to the exhaust manifold fixing structure of the present invention, the joints between the members, which repeatedly expand and contract due to heating and cooling, can be firmly fixed so as to prevent gas leakage.

[0015] (1) A perspective view of an exhaust manifold according to an embodiment, and (2) a perspective view seen from the opposite direction. FIG. 1 is a view of the exhaust manifold according to an embodiment as seen from the cylinder head side. FIG. 2 is a perspective view showing a fixing structure of the exhaust manifold according to an embodiment. FIG. 3 is a top view showing a fixing structure of the exhaust manifold according to an embodiment. FIG. 4 is a cross-sectional view showing a fixing structure of the exhaust manifold according to an embodiment.

[0016] An exhaust manifold according to an embodiment of the present invention will be described with reference to Figures 1 to 5. However, this embodiment is merely an example, and the present invention is not limited to this embodiment. In addition, although the same reference numerals are used for the same components in the embodiment, when distinguishing between the same components based on their installation positions, alphabets such as a, b, etc. are added to the reference numerals to distinguish them.

[0017] 1 to 5, an exhaust manifold 10 of this embodiment includes an exhaust manifold body 11. The exhaust manifold body 11 has a base end 12 formed in one exhaust passage and having a plurality of branch pipes 14 branching off from each other. A base end flange 121 is provided on the base end 12, and the base end flange 121 and a flange of a turbocharger (not shown) are fixed together with bolts.

[0018] Exhaust passages 15 are formed inside the branch pipe 14. Each of the multiple exhaust passages 15 is connected to a corresponding exhaust port in a cylinder head (not shown). In addition, since an EGR (Exhaust Gas Recirculation) system (not shown) is connected to the exhaust manifold body 11, an EGR exhaust passage 16 is formed to send exhaust gas to the EGR. A reduced-weight portion 17 is provided between the exhaust passage 15a adjacent to the EGR exhaust passage 16 and the EGR exhaust passage 16, and a reduced-weight portion 18 is provided between the exhaust passages 15b and 15c.

[0019] The exhaust manifold body 11 is provided with fixing portions 20 for fixing the cylinder head and the exhaust manifold. Fixing portions 20a to 20d are provided at the upper portions of the exhaust passages 15a to 15d, respectively, and fixing portions 20e to 20h are provided at the lower portions of the exhaust passages 15a to 15d, respectively. Furthermore, fixing portions 20i and 20j are provided on the diagonally upper left side (above the end side of the exhaust manifold body 11) and diagonally lower right side (below the exhaust passage 15a side adjacent to the exhaust manifold body 11) of the EGR exhaust passage 16 in FIG. 2 . By providing fixing portions 20 corresponding to the exhaust passages 15 and the EGR exhaust passage 16 in this way, gas leakage can be efficiently prevented.

[0020] Each fixing portion 20 extends outward from the exhaust manifold body 11. Specifically, each fixing portion 20 includes a flange portion 21, the one formed on the upper side of the exhaust manifold body 11 extending upward, and the one formed on the lower side of the exhaust manifold body 11 extending downward. The flange portion 21 has a bolt insertion hole 22 in its center.

[0021] As shown in Figure 5, the fixing portion 20 is fixed to the cylinder head by a bolt B. The bolt B is inserted into an insertion hole 22 from the exhaust manifold 10 side toward the cylinder head side. In this embodiment, a stud bolt is used as the bolt B, and is fixed using both a collar K and a hexagonal nut N. The bolt B is inserted through the insertion hole 22, and the bearing surface of the collar K contacts and is held by the flange portion 21. By providing the flange portion 21 in this manner, the axial force of the bolt B can be uniformly transmitted and maintained, which prevents the bearing surface of the flange portion 21 from collapsing due to the bolt B, collar K, and hexagonal nut N, and allows the axial force of the bolt B to be maintained.

[0022] The fixing portion 20 also has a pair of wall surface portions 23 that are continuous with the flange portion 21 at one end in the width direction. Each of the pair of wall surface portions 23 is shaped to cover only the sides of an inserted bolt. The pair of wall surface portions 23 are spaced apart from each other, so an opening 24 is formed between the pair of wall surface portions 23. Therefore, when a bolt B is inserted through the insertion hole 22, the bolt B is exposed from the opening 24. In other words, the pair of wall surface portions 23 are not connected to each other on the outer circumferential side (upper part in FIG. 5 ) of the exhaust manifold main body 11, and when the bolt B is inserted into the insertion hole 22, the bolt B is exposed from the opening 24.

[0023] The pair of wall portions 23 contact the cylinder head at the end (the other end in the width direction) opposite the flange portion 21. In this embodiment, the wall portion 23 of the fixing portion 20 is shaped to cover only the side surface of the bolt rather than to cover the entire periphery of the bolt at the portion where it connects to the cylinder head. This makes it possible to reduce the contact area of ​​the fixing portion 20 with the cylinder head compared to when the wall portion 23 covers the entire surface of the bolt B, suppressing temperature rise in the components that make up the fixing portion 20 and reducing thermal expansion, thereby enabling the components to be firmly fixed.

[0024] If the wall portion were cylindrical and continuous from the flange portion, covering the entire circumference of the bolt, the higher the temperature of the heat transferred from the cylinder head, the greater the deformation of the bolt due to thermal expansion and the deterioration of the mechanical properties of the part, resulting in a decrease in strength. In addition, the fastening axial force applied to the bolt would cause plastic deformation of the bolt, reducing the axial force and the fastening force. In contrast, in this embodiment, the contact area between the pair of wall portions 23 and the cylinder head is small, making it difficult for heat to be transferred to the fixing portion 20, thereby suppressing deformation of the bolt B due to thermal expansion. As a result, the fixing portion 20 can maintain the strength of the bolt B itself and prevent plastic deformation, thereby firmly fixing the exhaust manifold 10 to the cylinder head. Furthermore, by providing such a fixing portion 20, it is possible to obtain an exhaust manifold 10 that does not leak exhaust gas, has few defects as a cast part, and is highly productive, using bolts and exhaust system component materials made of cost-effective materials (e.g., chromium-molybdenum steel) without changing the materials of the fastening components or the exhaust manifold 10 themselves.

[0025] Furthermore, in the fixing portion 20, the pair of wall portions 23 do not cover the entire outer periphery of the bolt, but rather the open portion 24 is formed so that the pair of wall portions 23 only cover a portion of the outer periphery of the bolt, thereby improving the heat dissipation of the bolt B. This makes it possible to suppress deformation of the bolt B due to thermal expansion. The fixing portion 20 can maintain the strength of the bolt B itself and prevent plastic deformation, allowing for strong fixation.

[0026] Furthermore, the contact surface of the fixing portion 20 that comes into contact with the cylinder head is a machined surface, which can result in casting defects (for example, shrinkage cavities) and reduce productivity. However, in the fixing portion 20 of this embodiment, the wall portion is cylindrical and continues from the flange portion 21, and the area of ​​the contact surface is smaller than when the wall portion covers the entire periphery of the bolt. This reduces the impact of defects on productivity. Furthermore, the provision of the open portion 24 reduces the material weight and the amount of processing, thereby reducing costs.

[0027] Furthermore, one end of the pair of wall surfaces 23 in the width direction is provided continuously from the same height as the flange portion 21, and the other end, i.e., the cylinder head side, is provided so as to be lower than this one end. In other words, the pair of wall surfaces 23 are provided with an inclination so as to be lower toward the cylinder head side. By inclining the pair of wall surfaces 23 in this way, it is possible to further reduce the area of ​​the contact surface between the wall surfaces 23 and the cylinder head, which reduces the temperature rise of the members constituting the fixing portion 20 and reduces the range of thermal expansion and contraction, thereby enabling the members to be firmly fixed.

[0028] The pair of wall surface portions 23 are preferably formed so that the height H1 of the other widthwise end, i.e., the cylinder head side (the height from the lower end of the insertion hole 22 to the upper end of the wall surface portion 23 at the cylinder head side end), is higher than the bolt center H2 of the bolt B inserted into the insertion hole 22, but lower than the height H3 of the flange portion 21 (the height from the lower end of the insertion hole 22 to the upper end of the flange portion). If the height H1 on the cylinder head side is lower than the bolt center H2 of the inserted bolt B, sufficient surface pressure will not be applied between the cylinder head and the exhaust manifold 10, which may result in gas leakage. Furthermore, the angle of inclination of the pair of wall surface portions 23 is preferably 110 to 130 degrees, for example.

[0029] The distance between the open portions 24, i.e., the distance between the pair of wall portions 23, is preferably 150 to 170% of the bolt diameter. If it is more than 170%, sufficient surface pressure cannot be applied between the cylinder head and the exhaust manifold, which may cause gas leakage, and if it is less than 150%, it is susceptible to the thermal effects of the cylinder head.

[0030] The thickness of the flange portion 21 is preferably shorter than the length of the wall portion 23, for example, approximately 8 to 12 mm, preferably approximately 10 mm. If the thickness of the flange portion 21 is longer than the length of the wall portion, heat dissipation from the bolt may be insufficient. In particular, if the thickness of the flange portion 21 is greater than approximately 12 mm, heat dissipation from the bolt may be insufficient. If the thickness is less than 8 mm, the bearing surface strength may be compromised when the collar K or nut N comes into contact with the bearing surface of the flange 21, resulting in deformation of the bearing surface. While the thickness of the flange portion 21 does not necessarily have to be shorter than the length of the wall portion 23, such a thickness effectively suppresses thermal expansion of the bolt and firmly secures the components together to prevent gas leakage.

[0031] Each insertion hole 22 also functions to position the exhaust manifold 10 when it is fixed. In this embodiment, the insertion hole 22b of the fixing portion (central fixing portion) 20b located toward the center of the exhaust manifold 10 in the longitudinal direction has a smaller diameter than the other insertion holes 22, and therefore has a smaller clearance for the inserted bolt B. Therefore, the insertion hole 22b of the fixing portion (central fixing portion) 20b can be positioned in the vertical and horizontal directions. When fixing the exhaust manifold 10 to the cylinder head, a bolt is first inserted into this insertion hole 22b, and then the positioning in the vertical and horizontal directions is determined. Note that, although positioning is performed using the insertion hole 22b as a reference in this embodiment, positioning can also be performed using any of the insertion holes 22 in the longitudinal direction as a reference. Furthermore, the insertion hole 22d of the fixing portion 20d located toward the longitudinal end of the exhaust manifold 10 is elliptical, and the longitudinal width of the ellipse is larger than the diameter of each of the other insertion holes 22. In this case, because the longitudinal width of the ellipse of the insertion hole 22d is long, even if the exhaust manifold experiences significant thermal expansion, this expansion can be absorbed by this hole, thereby preventing misalignment between the cylinder head and the exhaust manifold 10. In this embodiment, only the insertion hole 22d of the fixing part 20d, which is the right end fixing part, is elliptical, but the insertion hole 22i of the fixing part 20i, which is the left end fixing part, may also be elliptical.

[0032] Furthermore, by providing the recessed portions 17, 18 in the exhaust manifold 10, it is possible to suppress the occurrence of defects in the machined surface of the exhaust manifold body 11 and reduce the material weight and the amount of processing.

[0033] The present invention is not limited to the above-described embodiment. The configuration of the exhaust manifold body 11 is an example, and the present invention is not limited to this structure. Furthermore, the fastening parts are also an example, and the shape of the bolts, etc. are not limited.

[0034] REFERENCE SIGNS LIST 10 Exhaust manifold 11 Exhaust manifold body 12 Base end portion 14 Branch pipe 15 Exhaust passage 16 EGR exhaust passage 17, 18 Recessed portion 20 Fixing portion 21 Flange portion 22 Insertion hole 23 Wall portion 24 Opening portion B Bolt K Collar N Hexagonal nut

Claims

1. A fixing structure for an exhaust manifold that is fixed to a cylinder head with bolts, the fixing structure comprising a fixing portion extending outward from the exhaust manifold, the fixing portion comprising a flange portion having an insertion hole into which the bolt is inserted, and a pair of wall surface portions that are spaced apart and are formed to cover both sides of the inserted bolt, one end of the pair of wall surface portions continuing to the flange portion and the other end contacting the cylinder head, and the pair of wall surface portions are sloped so that their height decreases from the one end toward the cylinder head.

2. The exhaust manifold fixing structure according to claim 1, wherein the length of the flange portion in the thickness direction is shorter than the length of the wall portion.

3. An exhaust manifold comprising a plurality of the exhaust manifold fixing structures according to claim 1 or 2.

4. An exhaust manifold as described in claim 3, characterized in that the insertion hole of the central fixing portion located in the longitudinal center of the exhaust manifold among the fixing portions has a smaller hole diameter than the insertion holes of the other fixing portions.

5. An exhaust manifold as described in claim 3, characterized in that the insertion holes of the left end fixing portion and / or the right end fixing portion located at both longitudinal ends of the exhaust manifold among the fixing portions are elliptical in shape, and the longitudinal width of the ellipse is longer than the hole diameter of the insertion holes of the other fixing portions.

6. An exhaust manifold according to claim 3, characterized in that the exhaust manifold has a reduced-weight portion in the partition wall between the exhaust passages or between the EGR passage and the exhaust passage on the surface that contacts the cylinder head.

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