Fastening structure and fastening structure design method

Abstract

To design a fastening structure with due consideration given to effects that occur when the fastening structure thermally expands.SOLUTION: In a fastening structure 100 for fastening an exhaust manifold 10 to a cylinder head 30 of an engine, a bolt 50 passes through a flange 12 and is inserted and fixed into a bolt hole 36 provided in the cylinder head 30. The flange 12 has a contact surface 18 that contacts a mounting surface 32 of the cylinder head 30, and an inclined surface 20 that is inclined to the contact surface 18. Inside the bolt hole 36, in a range from the mounting surface 32 of the cylinder head 30 to a specified length, a clearance 38 is provided between the bolt 50 and the cylinder head 30.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a fastening structure and a method for designing a fastening structure. [Background technology]

[0002] Patent Document 1 discloses a fastening structure for fastening an exhaust manifold to a cylinder head of an engine. The cylinder head has exhaust port openings that open to the outside of the cylinder head. The branch pipes of the exhaust manifold have flanges at their ends. The flanges are fastened to mounting surfaces that surround the exhaust port openings, thereby connecting the exhaust manifold openings to the exhaust port openings.

[0003] The flange becomes thinner as it moves away from the branch pipe. That is, the flange has a contact surface that contacts the mounting surface and an inclined surface that is inclined relative to the contact surface. Bolts pass through the inclined surface of the flange and are inserted into bolt holes in the cylinder head. When nuts are tightened onto the bolts, a compressive force acts on the inclined surface of the flange. In this way, the exhaust manifold is fastened to the cylinder head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent Application Publication No. 3203048 Summary of the Invention [Problem to be solved by the invention]

[0005] The fastening structure is designed only by considering the relationship between the static friction coefficient of the inclined surface and the angle that the inclined surface makes with respect to the contact surface, and therefore does not fully consider the effects that occur when the fastening structure is thermally expanded. [Means for solving the problem]

[0006] The means for solving the above problems and their effects will be described below. According to one aspect of the present disclosure, there is provided a fastening structure for fastening an exhaust manifold to a cylinder head of an engine, the cylinder head having an opening of an exhaust port that opens to the outside of the cylinder head, a branch pipe of the exhaust manifold having a flange at an end, the flange being fastened to a mounting surface that surrounds the opening of the exhaust port, so that the opening of the exhaust manifold is connected to the opening of the exhaust port, the flange having a first end and a second end that are on opposite sides of the branch pipe and contact the mounting surface, a fixing member fixing the first end of the flange to the cylinder head, a bolt passing through the second end of the flange and being inserted into a bolt hole provided in the cylinder head and fixed, a nut being fastened to the bolt so that the second end of the flange is fixed to the cylinder head, a direction perpendicular to the mounting surface that contacts the second end of the flange is a first direction, and a direction in which the first end and the second end of the flange are aligned is a second direction, A direction perpendicular to the two directions is a third direction, and as viewed in the third direction, the second end of the flange has a contact surface that contacts the mounting surface of the cylinder head and an inclined surface that is inclined relative to the contact surface so as to approach the contact surface as it moves away from the branch pipe, and when the nut is fastened to the bolt, a compressive force acts on the inclined surface, and in a cross section that is a plane stretched by the second direction and a central axis of the bolt, before thermal expansion of the fastening structure, the bolt is inserted into the bolt hole from a part of the nut that applies the compressive force to the inclined surface. the length of the entire portion of the bolt that is not in contact with the bolt hole, from the point where the bolt contacts the bolt hole, is x0; the amount of deformation of the bolt in the axial direction of the bolt due to thermal expansion of the fastening structure is Δx; the amount of change in force with which the nut compresses the second end portion, in the cross section, due to thermal expansion of the fastening structure is ΔF; the angle that the inclined surface makes with respect to the contact surface in the cross section is θ; the distance from the tip of the first end portion at the contact surface of the flange to the center of the bolt hole in the cross section before thermal expansion of the fastening structure is 1;The linear expansion coefficient of the cylinder head in the cross section is α, h and the linear expansion coefficient of the flange is α f and the linear expansion coefficient of the bolt is α b and the temperature change of the cylinder head during thermal expansion of the fastening structure is ΔT h and the fastening structure thermal expansion The temperature change of the flange at this time is ΔT f and the temperature change of the bolt during thermal expansion of the fastening structure is ΔT b and before thermal expansion of the fastening structure, the spring constant of the flange at a portion of the flange sandwiched between the cylinder head and the bolt in the cross section is K f and the spring constant of the bolt in the axial direction of the bolt is K b and the limit load at which any one of the cylinder head, the flange, and the bolt undergoes plastic deformation is F C and the limit displacement at which either the flange or the bolt undergoes plastic deformation is Δx c and the limit strain in the axial direction of the bolt at which the bolt plastically deforms is ε bc If we assume that

[0007]

number

[0008] A fastening structure that satisfies all of the above relational expressions is provided. According to the above configuration, it is possible to accurately reflect the influence that occurs when the fastening structure thermally expands in the design of the fastening structure.

[0009] In the above fastening structure, a clearance may be provided between the bolt and the cylinder head within the bolt hole within a range from the mounting surface of the cylinder head to a specified length.

[0010] The bolt does not come into contact with the cylinder head within the bolt hole within a specified length from the mounting surface of the cylinder head. During thermal expansion of the fastening structure, the bolt is more likely to be able to deform inside the bolt hole. This reduces the likelihood of the bolt undergoing plastic deformation due to thermal expansion compared to when the bolt is only allowed to deform outside the bolt hole.

[0011] In other words, the portion of the bolt that is not constrained by the cylinder head (the portion with clearance) also stretches. The dimensions of the portion where the bolt stretches are secured, allowing stress to be distributed over a wider area without enlarging the fastening structure outward. This suppresses plastic deformation and fracture of the bolt due to thermal expansion. Furthermore, the increase in compressive force acting on the flange, which is the fastened member, due to the bolt stretching is suppressed. Therefore, plastic deformation of the flange can also be suppressed.

[0013] BookAccording to one aspect of the disclosure, there is provided a method for designing a fastening structure for fastening an exhaust manifold to a cylinder head of an engine, the cylinder head having an exhaust port opening that opens to the outside of the cylinder head, a branch pipe of the exhaust manifold having a flange at an end, the flange being fastened to a mounting surface surrounding the opening of the exhaust port so that the opening of the exhaust manifold is connected to the opening of the exhaust port, and the flanges are located on opposite sides of the branch pipe and are in contact with the mounting surface. a fixing member fixes the first end of the flange to the cylinder head; a bolt passes through the second end of the flange and is inserted into a bolt hole provided in the cylinder head to fix the first end; a nut is fastened to the bolt to fix the second end of the flange to the cylinder head; a direction perpendicular to the mounting surface that contacts the second end of the flange is a first direction; a direction in which the first end and the second end of the flange are aligned is a second direction; A direction perpendicular to the second direction is a third direction, and as viewed in the third direction, the second end of the flange has a contact surface that contacts the mounting surface of the cylinder head and an inclined surface that is inclined with respect to the contact surface so as to approach the contact surface as it moves away from the branch pipe, and when the nut is fastened to the bolt, a compressive force acts on the inclined surface, and in a cross section that is a plane stretched by the second direction and a central axis of the bolt, before thermal expansion of the fastening structure, the bolt is pulled out from a portion of the nut that applies the compressive force to the inclined surface. the length of the entire portion of the bolt that is not in contact with the bolt hole up to the point where it comes into contact with the bolt hole is x0, the amount of deformation of the bolt in the axial direction of the bolt due to thermal expansion of the fastening structure is Δx, the amount of change in force with which the nut compresses the second end portion in the cross section due to thermal expansion of the fastening structure is ΔF, the angle that the inclined surface makes with respect to the contact surface in the cross section is θ, and the distance from the tip of the first end portion at the contact surface of the flange to the center of the bolt hole in the cross section before thermal expansion of the fastening structure is 1,The linear expansion coefficient of the cylinder head in the cross section is α, h and the linear expansion coefficient of the flange is α f and the linear expansion coefficient of the bolt is α b and the temperature change of the cylinder head during thermal expansion of the fastening structure is ΔT h and the fastening structure thermal expansion The temperature change of the flange at this time is ΔT f and the temperature change of the bolt during thermal expansion of the fastening structure is ΔT b and before thermal expansion of the fastening structure, the spring constant of the flange at a portion of the flange sandwiched between the cylinder head and the bolt in the cross section is K f and the spring constant of the bolt in the axial direction of the bolt is K b and the limit load at which any one of the cylinder head, the flange, and the bolt undergoes plastic deformation is F C and the limit displacement at which either the flange or the bolt undergoes plastic deformation is Δx c and the limit strain in the axial direction of the bolt at which the bolt plastically deforms is ε bc If we assume that

[0014]

number

[0015] A method for designing a fastening structure is provided, which designs the fastening structure so as to satisfy all of the above relational expressions. With the above configuration, it is possible to accurately reflect the influence of thermal expansion of the fastening structure in the design of the fastening structure. For example, it is possible to determine x0 from parameters other than x0 so that all of the above relational expressions are satisfied. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a fastening structure according to one embodiment. [Figure 2]FIG. 2 is a perspective view of the fastening structure shown in FIG. 1, with members downstream of the flange omitted. [Figure 3] FIG. 3 is a perspective view illustrating a space into which a bolt extends in the fastening structure shown in FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view of one of the upper bolts in the fastening structure shown in FIG. [Figure 5] FIG. 5 is a diagram showing a normal fastening structure different from this embodiment, for the purpose of promoting understanding of the fastening structure according to this embodiment. [Figure 6] FIG. 6 is a diagram showing the force applied to the flange in the normal fastening structure of FIG. [Figure 7] FIG. 7 is a diagram showing the force applied to the bolt in the normal fastening structure of FIG. [Figure 8] FIG. 8 is a diagram for explaining thermal expansion of the fastening structure shown in FIG. [Figure 9] FIG. 9 is a diagram for explaining thermal expansion of the flange in the fastening structure shown in FIG. [Figure 10] FIG. 10 is a diagram for explaining thermal expansion of the flange in the fastening structure shown in FIG. [Figure 11] FIG. 11 is a diagram for explaining thermal expansion of the flange in the fastening structure shown in FIG. [Figure 12] FIG. 12 is a diagram for explaining thermal expansion of the bolt in the fastening structure shown in FIG. [Figure 13] FIG. 13 is a diagram showing the force applied to the bolt after thermal expansion of the fastening structure shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] A fastening structure and a method for designing a fastening structure according to an embodiment will be described below with reference to the drawings. <Fastening structure 100> The fastening structure 100 will be described with reference to FIGS.

[0018] As shown in Fig. 1, a fastening structure 100 fastens an exhaust manifold 10 to a cylinder head 30 of an engine. An exhaust pipe 60 is provided downstream of the exhaust manifold 10.

[0019] As shown in Figure 2, the cylinder head 30 has two exhaust port openings 34 for each cylinder that open to the outside of the cylinder head 30. As shown in Figure 1, the branch pipe of the exhaust manifold 10 has a flange 12 at its end. The flange 12 is fastened to a mounting surface 32 that surrounds the exhaust port openings 34. As shown in Figure 2, this connects the two openings 22 of the exhaust manifold 10 to the two exhaust port openings 34.

[0020] As shown in FIG. 1, flange 12 has first and second ends 14 and 16 on opposite sides of a branch pipe of exhaust manifold 10 and in contact with mounting surface 32 . First, a structure for fastening the exhaust manifold 10 to the cylinder head 30 of the engine at the first end 14 shown in FIG. 1 will be described. Two bolts 40, two nuts 42, and one lower holder 44 shown in FIG. 2 constitute a fixing member 46. The fixing member 46 fixes the first end 14 of the flange 12 to the cylinder head 30. Specifically, the fixing member 46 fixes the first end 14 of the flange 12 to the cylinder head 30 in the following procedure. First, two bolts 40 are inserted into two bolt holes provided in the cylinder head 30. The two bolts 40 are parallel to a first direction X, which is perpendicular to the mounting surface 32. Next, the lower holder 44 is installed on the cylinder head 30 so that the two bolts 40 extend through the two through holes of the lower holder 44, respectively. Next, two nuts 42 are tightened to the two bolts 40. As a result, the lower holder 44 and the cylinder head 30 form a pocket that receives the flange 12. The first end 14 of the flange 12 is then inserted into the pocket.

[0021] Next, a structure for fastening the exhaust manifold 10 to the cylinder head 30 of the engine at the second end 16 will be described. At the second end 16 shown in FIGS. 1 and 2, two bolts 50 extend through two cavities 24 shown in FIG. 3. Each of the two cavities 24 opens on the side opposite the first end 14. FIG. 3 is a diagram of the fastening structure 100 shown in FIG. 2, with the two nuts 52 and washers 54 omitted. When the first end 14 is inserted into the pocket, the two bolts 50 are already inserted into and fixed in two bolt holes 36 provided in the cylinder head 30. Each of the two cavities 24 opens on the side opposite the first end 14. Therefore, the flange 12 passes through the sides of the two bolts 50, resulting in the state shown in FIG. 3, where the two bolts 50 are located in the two cavities 24. Next, the washers 54 and two nuts 52 are fastened to the bolts 50 in this order.

[0022] 3, each bolt 50 does not contact the flange 12 within the cavity 24. This is intended to prevent the flange 12 from pressing sideways on the two bolts 50 when the flange 12 thermally expands. This makes it possible to prevent the flange 12 from applying unnecessary force to the two bolts 50 when the flange 12 thermally expands.

[0023] As shown in FIG. 4 , a bolt 50 penetrates the second end 16 of the flange 12 and is inserted into a bolt hole 36 provided in the cylinder head 30 to be fixed. A nut 52 is fastened to the bolt 50, thereby fixing the second end 16 of the flange 12 to the cylinder head 30. A first direction X is a direction perpendicular to a mounting surface 32 that contacts the second end 16 of the flange 12. A second direction Y is a direction in which the first end 14 and the second end 16 of the flange 12 are aligned. A third direction Z is a direction perpendicular to the first direction X and the second direction Y. When viewed in the third direction Z, the second end 16 of the flange 12 has a contact surface 18 that contacts the mounting surface 32 of the cylinder head 30 and an inclined surface 20 that is inclined relative to the contact surface 18 so that the inclined surface 20 approaches the contact surface 18 as it moves away from the branch pipe. When the nut 52 is fastened to the bolt 50, a compressive force is applied to the inclined surface 20 via a washer 54. Within the bolt hole 36, a clearance 38 is provided between the bolt 50 and the cylinder head 30 within a range from the mounting surface 32 of the cylinder head 30 to a specified length. cb indicates the specified length.

[0024] <Thermal expansion of normal fastening structures> 5 to 7, thermal expansion of a normal fastening structure different from this embodiment will be described for the purpose of promoting understanding of the fastening structure 100 according to this embodiment. In the normal fastening structure, a bolt 1050 and a nut 1052 fix the flange 1012 to the cylinder head 1030. The bolt 1050 is perpendicular to the mounting surface 1032 of the cylinder head 1030.

[0025] 5 to 7, the flange 1012, the bolt 1050, and the nut 1052 are shown by solid lines before thermal expansion, and the flange 1012, the bolt 1050, and the nut 1052 are shown by chain double-dashed lines after thermal expansion.

[0026] The parameters used in the following explanation are as follows: The thickness of the flange 1012 in the axial direction of the bolt 1050 before thermal expansion is x0. x0 is also the length of the bolt 1050 before thermal expansion. The deformation amount of the flange 1012 in the axial direction of the bolt 1050 due to thermal expansion is Δx. Δx is also the deformation amount of the bolt 1050 due to thermal expansion. The force that the nut 1052 acts on the flange 1012 in the axial direction of the bolt 1050 is called the bolt axial force. The change in the bolt axial force due to thermal expansion is ΔF. The linear expansion coefficient of the flange 1012 is α f The linear expansion coefficient of bolt 1050 is α b is. thermal expansion The temperature change of flange 1012 at this time is ΔT f The temperature change of bolt 1050 due to thermal expansion is ΔT b The spring constant of the flange 1012 at the portion of the flange 1012 that is sandwiched between the cylinder head 1030 and the bolt 1050 is K f The spring constant of the bolt 1050 in the axial direction of the bolt 1050 is K b is.

[0027] First, let us consider the flange 1012. If the flange 1012 is not constrained by the nut 1052, the flange 1012 will expand by x0·α f ΔT f In reality, the flange 1012 is restrained by the nut 1052. Therefore, when the flange 1012 thermally expands, the bolt axial force changes by ΔF and the thickness of the flange 1012 changes by Δx, achieving a balanced state. This balanced state is shown in Figure 6. Therefore, the deformation amount Δx of the flange 1012 is as follows:

[0028]

number

[0029] Next, let us focus on the bolt 1050. If the flange 1012 does not exist, the bolt 1050 will expand by x0·α b ΔT b In reality, due to thermal expansion, a force is generated in the flange 1012 that stretches the bolt 1050 via the nut 1052. When the bolt 1050 thermally expands, the bolt axial force changes by ΔF and the thickness of the bolt 1050 changes by Δx, achieving a balanced state. This balanced state is shown in Figure 7. Therefore, the deformation amount Δx of the bolt 1050 is as follows:

[0030]

number

[0031] From equations (1) and (2), the following equation (3) is obtained.

[0032]

number

[0033] From equations (1) and (3), the following equation (4) is obtained.

[0034]

number

[0035] <Thermal expansion of the fastening structure 100> 8 to 13, the thermal expansion of the fastening structure 100 will be described. The thermal expansion of the fastening structure 100 can be explained using the same concept as the thermal expansion of a normal fastening structure.

[0036] 8 to 13 show the flange 12, cylinder head 30, bolt 50, and nut 52 by solid lines before thermal expansion. 8 to 13 show the flange 12, cylinder head 30, bolt 50, and nut 52 by chain double-dashed lines after thermal expansion. 8 to 13 are views of the fastening structure 100 as seen in a cross section that is a plane stretched by the second direction Y and the central axis M of the bolt 50 shown in FIG. 4. As shown in FIG. 8, the contact point CP between the lower holder 44 and the flange 12 remains stationary even when the fastening structure 100 undergoes thermal expansion.

[0037] The parameters used in the following description are as follows. Some parameters are defined in a cross section, which is a plane spanned by the second direction Y and the central axis M of the bolt 50. In the cross section, before thermal expansion of the fastening structure 100, the length of the entire portion of the bolt 50 that is not in contact with the bolt hole 36, from the point where the nut 52 applies a compressive force to the inclined surface 20 to the point where the bolt 50 contacts the bolt hole 36, is x0. The amount of deformation of the bolt 50 in the axial direction of the bolt 50 due to thermal expansion of the fastening structure 100 is Δx. The amount of change in the force with which the nut 52 compresses the second end 16 in the cross section due to thermal expansion of the fastening structure 100 is ΔF. In the cross section, the angle that the inclined surface 20 forms with respect to the contact surface 18 is θ. This angle is an acute angle. In the cross section, before thermal expansion of the fastening structure 100, the distance from the tip of the first end 14 at the contact surface 18 of the flange 12 to the center of the bolt hole 36 is l. The linear expansion coefficient of the cylinder head 30 in the cross section is α h The linear expansion coefficient of the flange 12 is α f The linear expansion coefficient of bolt 50 is α b The temperature change of the cylinder head 30 during thermal expansion of the fastening structure 100 is ΔT h The fastening structure 100 thermal expansion The temperature change of flange 12 at this time is ΔT f The temperature change of the bolt 50 during thermal expansion of the fastening structure 100 is ΔT bBefore the thermal expansion of the fastening structure 100, the spring constant of the flange 12 at the portion of the flange 12 sandwiched between the cylinder head 30 and the bolt 50 in the cross section is K f The spring constant of the bolt 50 in the axial direction of the bolt 50 is K b The limit load at which any of the cylinder head 30, the flange 12, and the bolt 50 undergoes plastic deformation is F C The limit displacement at which either the flange 12 or the bolt 50 undergoes plastic deformation is Δx c The limit strain in the axial direction of the bolt 50 at which the bolt 50 undergoes plastic deformation is ε bc is.

[0038] First, attention is focused on the flange 12. The deformation amount Δx of the bolt 50 in the axial direction of the bolt 50 is also the deformation amount of the flange 12 in the axial direction of the bolt 50 due to thermal expansion. As shown in FIG. 8, the central axis L of the bolt hole 36 before the fastening structure 100 undergoes thermal expansion coincides with the central axis M of the bolt 50 before the fastening structure 100 undergoes thermal expansion.

[0039] As shown in FIG. 9, the position of the bolt hole 36 changes from point P to point P' as the flange 12 thermally expands. Point P' is on the central axis L' of the bolt hole 36 after the fastening structure 100 has thermally expanded. The amount of deformation Δx of the flange 12 in the axial direction of the bolt 50 is considered in the axial direction of the bolt 50 with point P as the reference point. The distance from point P to point P' is expressed as l·α f ΔT f This means that when the point P is used as the reference point and the axial direction of the bolt 50 is considered, the flange 12 is in the axial direction of the bolt 50 at a distance of l·α f ΔT f In addition, when the flange 12 is not restrained by the nut 52, the flange 12 extends by x0·α in the axial direction of the bolt 50 due to thermal expansion of the flange 12 in the axial direction of the bolt 50. f ΔT fTherefore, when the flange 12 is not restrained by the nut 52, the deformation of the flange 12 is (x0 + l sinθ)α f ΔT f This becomes:

[0040] The above-mentioned K f is expressed as the following equation (5).

[0041]

number

[0042] Here, E is the Young's modulus of the flange 12. A is the cross-sectional area of ​​the portion of the flange 12 that is sandwiched between the cylinder head 30 and the nut 52. When the fastening structure 100 thermally expands, the contact point between the nut 52 and the flange 12 shifts. That is, when the fastening structure 100 thermally expands, the thickness of the portion of the flange 12 that is sandwiched between the cylinder head 30 and the nut 52 changes. Hereinafter, this portion will be referred to as the sandwiched portion. Due to this change, the spring constant of the flange 12 changes. f From K f The thermal expansion of the flange 12 and the cylinder head 30 contributes to the change in thickness of the sandwiched portion. As shown in FIG. 10, the thickness of the sandwiched portion changes from l·α f ΔT f As shown in FIG. 11, the thermal expansion of the cylinder head 30 acts to cancel out the contribution of the thermal expansion of the flange 12 to the change in thickness of the sandwiched portion. Specifically, due to the thermal expansion of the cylinder head 30, the thickness of the sandwiched portion increases by l·α h ΔT h ·sinθ. Therefore, K f The following equation (6) for ' is obtained.

[0043]

number

[0044] As a result of thermal expansion, the force with which the nut 52 presses against the flange 12 increases. As a result of thermal expansion, the force with which the nut 52 presses against the flange 12 changes by ΔF, and the thickness of the flange 12 changes by Δx, achieving a state of balance. This state of balance is shown in Figure 8. By considering the same thermal expansion as in the normal fastening structure described above, the following equation (7) can be obtained for the deformation amount Δx of the flange 12 in the axial direction of the bolt 50.

[0045]

number

[0046] Next, attention will be focused on the bolt 50. As shown in Fig. 12, as the fastening structure 100 thermally expands, the position of the base of the bolt 50 changes from point Q to point Q'. Point Q' is on the central axis M' of the bolt 50 after the fastening structure 100 has thermally expanded. The deformation amount Δx of the bolt 50 in the axial direction of the bolt 50 is considered in the axial direction of the bolt 50 with point Q as the reference.

[0047] Due to thermal expansion of the cylinder head 30, the position of the root of the bolt 50 changes by l·α h ΔT h This means that, when considering the axial direction of bolt 50 with point Q as the reference, bolt 50 moves by l·α h ΔT h This means that it has been extended by sinθ.

[0048] Thermal expansion generates a force in the flange 12 that stretches the bolt 50 via the nut 52. When the bolt 50 thermally expands, the bolt axial force changes by ΔF and the length of the bolt 50 changes by Δx, achieving a state of balance. This state of balance is shown in Figure 13. By considering the same as the thermal expansion of the normal fastening structure described above, the following equation (8) is obtained for the deformation amount Δx of the bolt 50 in the axial direction of the bolt 50.

[0049]

number

[0050] From equations (7) and (8), the following equation (9) is obtained.

[0051]

number

[0052] From equations (8) and (9), the following equation (10) is obtained.

[0053]

number

[0054] Here, ΔF is F C is smaller than Δx c and the strain ε of the bolt 50 is ε bc This is required to prevent plastic deformation of any of the cylinder head 30, the flange 12, and the bolts 50. Here, the strain ε of the bolts 50 is Δx / x0. Therefore, the following equation (11) is obtained.

[0055]

number

[0056] The fastening structure 100 is designed to satisfy the relationships (9), (10), and (11). <Effects of this embodiment> (1) According to this embodiment, it is possible to accurately reflect the influence that occurs when the fastening structure 100 undergoes thermal expansion in the design of the fastening structure 100.

[0057] (2) Inside the bolt hole 36, the bolt 50 does not come into contact with the cylinder head 30 within a range from the mounting surface 32 of the cylinder head 30 to a specified length. When the fastening structure 100 thermally expands, the bolt 50 is more likely to be able to deform even inside the bolt hole 36. Therefore, compared to when the bolt 50 is only allowed to deform outside the bolt hole 36, the probability that the bolt 50 will undergo plastic deformation due to thermal expansion can be reduced.

[0058] In other words, the portion of the bolt 50 that is not constrained by the cylinder head 30 (the portion where the clearance 38 is provided) also extends. The dimensions of the portion where the bolt 50 extends can be ensured, and stress can be dispersed over a wider range, without enlarging the fastening structure 100 outward. Plastic deformation and breakage of the bolt 50 due to thermal expansion can be suppressed. Furthermore, an increase in compressive force acting on the flange 12, which is the fastened member, due to the extension of the bolt 50 is suppressed. Therefore, plastic deformation of the flange 12 can also be suppressed.

[0059] (3) According to this embodiment, it is possible to accurately reflect the influence that occurs when the fastening structure 100 thermally expands in the design of the fastening structure 100. For example, it is possible to determine x0 from parameters other than x0 so that all of the above relational expressions (9), (10), and (11) are satisfied.

[0060] <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0061] In the above embodiment, two bolts 40, two nuts 42, and one lower holder 44 constitute the fixing member 46. However, this is merely an example. For example, the lower holder 44 and the cylinder head 30 may be an integral part.

[0062] In the above embodiment, two bolts 50 and two nuts 52 secure the second end 16 of the flange 12 to the cylinder head 30. However, this is merely an example. The number and arrangement of the bolts 50 and nuts 52 can be changed as appropriate.

[0063] Instead of the void 24 in the above embodiment, a through hole may be provided in the second end portion 16 . A hollow cylindrical collar may be provided between the nut 52 and the washer 54. The washer 54 can be omitted.

[0064] In the above embodiment, the clearance 38 is provided inside the bolt hole 36 to ensure the size of x0. If the size of x0 can be ensured, the clearance 38 can be omitted, provided that the relational expressions (9), (10), and (11) are all satisfied. [Explanation of symbols]

[0065] 10...Exhaust manifold 12...Flange 14...First end 16…Second end 18…Contact surface 20…Slope surface 30...Cylinder head 32...Mounting surface 36...Bolt hole 38...Clearance 50...volts 52...Nut 100…Fascinating structure

Claims

1. A fastening structure for fastening an exhaust manifold to a cylinder head of an engine, the cylinder head has an exhaust port opening that opens to the outside of the cylinder head, The branch pipe of the exhaust manifold has a flange at an end thereof, the flange is fastened to a mounting surface surrounding the opening of the exhaust port, thereby connecting the opening of the exhaust manifold to the opening of the exhaust port; the flange has a first end and a second end on opposite sides of the branch pipe and in contact with the mounting surface; a fixing member fixing the first end of the flange to the cylinder head; a bolt passing through the second end of the flange and inserted into a bolt hole provided in the cylinder head to be fixed; a nut is fastened to the bolt, thereby fixing the second end of the flange to the cylinder head; a direction perpendicular to the mounting surface that contacts the second end of the flange is a first direction; a direction in which the first end and the second end of the flange are aligned is a second direction; a direction perpendicular to the first direction and the second direction is a third direction, When viewed in the third direction, the second end of the flange has a contact surface that contacts the mounting surface of the cylinder head and an inclined surface that is inclined with respect to the contact surface so as to approach the contact surface as it becomes farther from the branch pipe, When the nut is fastened to the bolt, a compressive force acts on the inclined surface, In a cross section that is a plane stretched by the second direction and the central axis of the bolt, before thermal expansion of the fastening structure, the length of the entire portion of the bolt that is not in contact with the bolt hole from the portion of the nut that applies the compressive force to the inclined surface to the portion of the bolt that is in contact with the bolt hole is x ０ and a deformation amount of the bolt in the axial direction of the bolt due to thermal expansion of the fastening structure is Δx; a change in force with which the nut compresses the second end portion within the cross section due to thermal expansion of the fastening structure is ΔF; an angle θ formed by the inclined surface with respect to the contact surface in the cross section; a distance from a tip of the first end of the contact surface of the flange to a center of the bolt hole in the cross section before thermal expansion of the fastening structure is 1; The linear expansion coefficient of the cylinder head in the cross section is α ｈ and The linear expansion coefficient of the flange is α ｆ and The linear expansion coefficient of the bolt is α ｂ and The temperature change of the cylinder head during thermal expansion of the fastening structure is ΔT ｈ and The temperature change of the flange during thermal expansion of the fastening structure is ΔT ｆ and The temperature change of the bolt during thermal expansion of the fastening structure is ΔT ｂ and Before the fastening structure is thermally expanded, the spring constant of the flange at the portion of the flange that is sandwiched between the cylinder head and the bolt in the cross section is K ｆ and The spring constant of the bolt in the axial direction of the bolt is K ｂ and The limit load at which any one of the cylinder head, the flange, and the bolt undergoes plastic deformation is F Ｃ and The limit displacement at which either the flange or the bolt undergoes plastic deformation is Δx ｃ and The limit strain in the axial direction of the bolt at which the bolt plastically deforms is ε ｂｃ If we assume that [Equation 1] Satisfy all of the above relationships Fastening structure.

2. A clearance is provided between the bolt and the cylinder head within the bolt hole within a range from the mounting surface of the cylinder head to a specified length. The fastening structure according to claim 1 .

3. A method for designing a fastening structure for fastening an exhaust manifold to a cylinder head of an engine, comprising: the cylinder head has an exhaust port opening that opens to the outside of the cylinder head, The branch pipe of the exhaust manifold has a flange at an end thereof, the flange is fastened to a mounting surface surrounding the opening of the exhaust port, thereby connecting the opening of the exhaust manifold to the opening of the exhaust port; the flange has a first end and a second end on opposite sides of the branch pipe and in contact with the mounting surface; a fixing member fixing the first end of the flange to the cylinder head; a bolt passing through the second end of the flange and inserted into a bolt hole provided in the cylinder head to be fixed; a nut is fastened to the bolt, thereby fixing the second end of the flange to the cylinder head; a direction perpendicular to the mounting surface that contacts the second end of the flange is a first direction; a direction in which the first end and the second end of the flange are aligned is a second direction; a direction perpendicular to the first direction and the second direction is a third direction, When viewed in the third direction, the second end of the flange has a contact surface that contacts the mounting surface of the cylinder head and an inclined surface that is inclined with respect to the contact surface so as to approach the contact surface as it becomes farther from the branch pipe, When the nut is fastened to the bolt, a compressive force acts on the inclined surface, In a cross section that is a plane stretched by the second direction and the central axis of the bolt, before thermal expansion of the fastening structure, the length of the entire portion of the bolt that is not in contact with the bolt hole from the portion of the nut that applies the compressive force to the inclined surface to the portion of the bolt that is in contact with the bolt hole is x ０ and a deformation amount of the bolt in the axial direction of the bolt due to thermal expansion of the fastening structure is Δx; a change in force with which the nut compresses the second end portion within the cross section due to thermal expansion of the fastening structure is ΔF; an angle θ formed by the inclined surface with respect to the contact surface in the cross section; a distance from a tip of the first end of the contact surface of the flange to a center of the bolt hole in the cross section before thermal expansion of the fastening structure is 1; The linear expansion coefficient of the cylinder head in the cross section is α ｈ and The linear expansion coefficient of the flange is α ｆ and The linear expansion coefficient of the bolt is α ｂ and The temperature change of the cylinder head during thermal expansion of the fastening structure is ΔT ｈ and The temperature change of the flange during thermal expansion of the fastening structure is ΔT ｆ and The temperature change of the bolt during thermal expansion of the fastening structure is ΔT ｂ and Before the fastening structure is thermally expanded, the spring constant of the flange at the portion of the flange that is sandwiched between the cylinder head and the bolt in the cross section is K ｆ and The spring constant of the bolt in the axial direction of the bolt is K ｂ and The limit load at which any one of the cylinder head, the flange, and the bolt undergoes plastic deformation is F Ｃ and The limit displacement at which either the flange or the bolt undergoes plastic deformation is Δx ｃ and The limit strain in the axial direction of the bolt at which the bolt plastically deforms is ε ｂｃ If we assume that [Equation 2] The fastening structure is designed to satisfy all of the above relational expressions. How to design fastening structures.

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