Fastening structure and saddle-ride type vehicle

Abstract

The purpose of the present invention is to achieve a structure advantageous for weight reduction and improved sealing performance.　In this fastening structure, a case member (23a) is provided with a case-side seal surface (32a) joined to a cover member (23b, 30), and a female threaded part (33, 333), the cover member (23b, 30) is provided with a cover-side seal surface (42a) overlapping the case-side seal surface (32a), a through hole (43a) through which a screw member (51) to be fastened to the female threaded part (33, 333) passes, and a boss part (43), and the case member (23a) and the cover member (23b, 30) are provided with bulging parts (34, 44, 144, 234, 244, 334) bulging from the female threaded part (33, 333) and the boss part (43) toward regions that do not overlap the seal surfaces (32a, 42a), and overlapping the screw member (51) in the axial direction.

Description

Fastening Structure and Straddle-Type Vehicle 【0001】 The present invention relates to a fastening structure and a straddle-type vehicle. 【0002】 In recent years, in order to enable more people to have access to affordable, reliable, sustainable, and advanced energy, research and development on weight reduction that contributes to energy efficiency have been carried out. Conventionally, a straddle-type vehicle having a bolt fastening structure for joining a plurality of joining members using bolts is known (see, for example, Patent Document 1). In the technique described in Patent Document 1, a crankcase having a female screw portion and a crankcase cover formed with a bolt hole through which a bolt passes are provided, and the crankcase and the crankcase cover are joined by screwing the bolt into the female screw portion in a state where the bolt passes through the bolt hole. 【0003】 Japanese Patent Application Laid-Open No. 2011-174423 【0004】 By the way, in the present technology related to weight reduction, it is desired to achieve both weight reduction and improvement of sealing performance. For example, when the seat surface is compressed by the fastening force of the bolt, there is a concern that the joint portion may undergo minute deformation, resulting in a partial decrease in the surface pressure of the sealing surface. Further, when the boss diameter of the joint portion is increased to enhance the strength of the joint portion, there is a concern that interference with other components or an increase in weight may occur. The present application aims to achieve a structure advantageous for weight reduction and improvement of sealing performance in order to solve the above problems. And by extension, it contributes to energy efficiency. 【0005】This specification includes all the contents of Japanese Patent Application No. 2024-216252, filed on December 11, 2024. To achieve the above objective, the fastening structure of the present invention is a fastening structure for fastening a case member and a cover member, wherein the case member has a case-side sealing surface that is joined to the cover member and a plurality of female screw portions around or on the case-side sealing surface, the cover member has a cover-side sealing surface that overlaps with the case-side sealing surface, a through hole through which a screw member fastened to the female screw portion passes, and a boss portion having a seating surface for the screw member, and the case member and the cover member have bulging portions that bulge out from the female screw portion and the boss portion in a region that does not overlap with the respective sealing surfaces and that overlap in the axial direction of the screw member. 【0006】 According to the present invention, a fastening structure advantageous for weight reduction and improved sealing performance can be provided. 【0007】 Figure 1 is a side view of a saddle-type vehicle according to an embodiment of the present invention. Figure 2 is a side view of the power unit. Figure 3 is a perspective view showing the fastening member of region A in Figure 2 together with the surrounding configuration. Figure 4 is a view of region A from a different direction than Figure 3. Figure 5 is a view showing the female thread portion of the case body together with the surrounding configuration. Figure 6 is a view showing the boss portion of the case cover together with the surrounding configuration. Figure 7 is a schematic diagram showing the periphery of the fastening structure. Figure 8 is a view showing the female thread portion having a predetermined member nearby together with the surrounding configuration. Figure 9 is a view showing the lower opening of the case body together with the surrounding configuration. Figure 10 is a perspective view showing the fastening structure of the oil pan. Figure 11 is a view showing the fastening structure according to Embodiment 2 of the present invention. Figure 12 is a view showing the fastening structure according to Embodiment 3 of the present invention. Figure 13 is a view showing the positional relationship between the case body and the case-side bulge portion used to explain Embodiment 4 of the present invention. 【0008】 Embodiments of the present invention will be described below with reference to the drawings. In the description, directions such as front, back, left, right, and up and down refer to directions relative to the vehicle body unless otherwise specified. In each figure, the symbol FR indicates the front of the vehicle body, the symbol UP indicates the top of the vehicle body, and the symbol LH indicates the left side of the vehicle body. 【0009】[Embodiment] Figure 1 is a side view of a saddle-type vehicle 10 according to an embodiment of the present invention. The saddle-type vehicle 10 is a vehicle comprising a body frame 11, a power unit 12 supported by the body frame 11, a front fork 14 that supports the front wheel 13 in a steerable manner, a swing arm 16 that supports the rear wheel 15, and a seat 17 for the rider. The saddle-type vehicle 10 is a vehicle in which the rider sits by straddling the seat 17. The seat 17 is provided above the rear of the body frame 11. 【0010】 The vehicle frame 11 comprises a head pipe 18 located at the front end of the vehicle frame 11, a front frame 19 located behind the head pipe 18, and a rear frame 20 located behind the front frame 19. The front end of the front frame 19 is connected to the head pipe 18. The seat 17 is supported by the rear frame 20. 【0011】 The front fork 14 is supported by a head pipe 18 so that it can be steered left and right. The front wheel 13 is supported by an axle 13a provided at the lower end of the front fork 14. The steering handle 21, which is held by the rider, is attached to the upper end of the front fork 14. 【0012】 The swingarm 16 is supported by a pivot shaft 22 which is supported by the vehicle frame 11. The pivot shaft 22 is an axis that extends horizontally in the vehicle width direction. The pivot shaft 22 is inserted through the front end of the swingarm 16. The swingarm 16 swings up and down around the pivot shaft 22. The rear wheel 15 is supported by an axle 15a provided at the rear end of the swingarm 16. 【0013】 The power unit 12 is positioned between the front wheel 13 and the rear wheel 15 and is supported by the vehicle frame 11. The power unit 12 is an internal combustion engine. The power unit 12 comprises a crankcase 23 and a cylinder section 24 that houses a reciprocating piston. An exhaust device 25 is connected to the exhaust port of the cylinder section 24. The output of the power unit 12 is transmitted to the rear wheel 15 by a drive force transmission member that connects the power unit 12 to the rear wheel 15. 【0014】The saddle-type vehicle 10 also includes a front fender 26 that covers the front wheel 13 from above, a rear fender 27 that covers the rear wheel 15 from above, a step 28 on which the rider places their feet, and a fuel tank 29 that stores the fuel used by the power unit 12. The front fender 26 is attached to the front fork 14. The rear fender 27 and step 28 are located below the seat 17. The fuel tank 29 is supported by the vehicle frame 11. 【0015】 Figure 2 is a side view of the power unit 12. The crankcase 23 of the power unit 12 has a case body (case member) 23a and a case cover (cover member) 23b that covers the case body 23a from the outside in the vehicle width direction. The case body 23a is a case that houses the crankshaft and the gear group that constitutes the power transmission system, and is formed as a case with openings that open to the left, right and downward. The case cover 23b is attached to the left and right sides of the case body 23a so as to cover the left and right openings of the case body 23a and is fastened to the case body 23a by a plurality of fastening members (screw members) 51. 【0016】 An oil pan 30, which functions as an oil reservoir for oil that lubricates various parts of the power unit 12, is located at the bottom of the crankcase 23. The oil pan 30 is attached to the bottom of the case body 23a so as to cover the opening at the bottom of the case body 23a, and is fastened to the case body 23a by a plurality of fastening members (screw members) 51. The case body 23a, the case cover 23b, and the oil pan (cover member) 30 are box-shaped structures with at least one side open. 【0017】 Examples of fastening members 51 include flange bolts and combinations of washers and bolts. 【0018】Figure 3 is a perspective view showing the fastening member 51 in region A of Figure 2 along with its surrounding configuration, and Figure 4 is a view showing region A from a different direction than Figure 3, in which the fastening member 51 is represented by a dashed line. The outer end portion in the vehicle width direction of the case body 23a is denoted as the case end portion 32. The inner end portion in the vehicle width direction of the case cover 23b is denoted as the cover end portion 42. As shown in Figures 3 and 4, a boss portion 43 is formed in the cover end portion 42 of the case cover 23b through which the fastening member 51 passes. Also, a female thread portion 33 is formed in the case end portion 32 of the case body 23a, through which the fastening member 51 that has passed through the boss portion 43 is fastened. The cover end portion 42 and the case end portion 32 are connected when the fastening member 51 passes through the boss portion 43 and is fastened to the female thread portion 33. 【0019】 Figure 5 shows the female thread portion 33 of the case body 23a along with its surrounding structure, viewed from the outside in the vehicle width direction. The case end portion 32 of the case body 23a has a female thread portion 33 and a case-side sealing surface 32a extending in two directions from the periphery of the female thread portion 33. The female thread portion 33 is formed as a substantially cylindrical boss in which a female thread hole 33a for screwing into the fastening member 51 is formed. Here, the case end portion 32 is formed as an endlessly extending rib around the opening on the outside in the vehicle width direction of the case body 23a, and the female thread portion 33 is formed at intervals on this case end portion 32. 【0020】 In Figure 5, the area below the female thread portion 33 corresponds to the inner circumference of the case end portion 32, and the area above the female thread portion 33 corresponds to the outer circumference of the case end portion 32. In this embodiment, the female thread portion 33 is provided offset to the outer circumference of the case end portion 32, or in other words, offset to the outer circumference of the case-side sealing surface 32a. This suppresses irregularities on the inside of the case caused by the boss portion 43 and the female thread portion 33. The female thread portion 33 is provided on the outer circumference of the case end portion 32 at predetermined intervals. 【0021】Figure 6 shows the boss portion 43 of the case cover 23b along with its surrounding structure, viewed from the inside in the vehicle width direction. As shown in Figure 6, the cover end portion 42 of the case cover 23b has a boss portion 43 and a cover-side sealing surface 42a extending in two directions from the periphery of the boss portion 43. The boss portion 43 is formed as a substantially cylindrical boss with a through hole 43a through which the fastening member 51 passes. Here, the cover end portion 42 is formed as an endlessly extending rib shape around the opening on the inside of the case cover 23b in the vehicle width direction, and the boss portion 43 is formed at intervals on this cover end portion 42. 【0022】 In Figure 6, the area below the boss portion 43 corresponds to the inner circumference of the cover end portion 42, and the area above the boss portion 43 corresponds to the outer circumference of the cover end portion 42. In this embodiment, the boss portion 43 is provided offset to the outer circumference relative to the cover end portion 42, or in other words, it is provided offset to the outer circumference relative to the cover-side sealing surface 42a. 【0023】 The cover end portion 42 is positioned to overlap with the case end portion 32, and the boss portion 43 is positioned to overlap with the female thread portion 33. More specifically, the cover-side sealing surface 42a of the cover end portion 42 and the case-side sealing surface 32a of the case end portion 32 are formed to be the same or similar in shape, and are positioned so that the sealing surfaces 32a, 42a overlap in the insertion and removal direction of the fastening member 51. In addition, the mating surface of the boss portion 43 and the mating surface of the female thread portion 33 are formed to be the same or similar in shape, and are positioned so that the mating surfaces overlap in the insertion and removal direction of the fastening member 51. The through hole 43a and the female thread hole 33a are coaxial in the insertion and removal direction of the fastening member 51. 【0024】 When the cover end 42 and the case end 32 are connected, the cover-side sealing surface 42a of the cover end 42 and the case-side sealing surface 32a of the case end 32 are in flush contact. Also, the boss portion 43 and the female thread portion 33 are in flush contact. As a result, the gap between the case cover 23b and the case body 23a is properly sealed. 【0025】As described above, the fastening member 51 penetrates the boss portion 43 provided on the case cover 23b and screws into the female thread portion 33 provided on the case body 23a, so that the case end portion 32 and the cover end portion 42 come into contact flush with each other, and the case body 23a and the case cover 23b can be fastened together while sealing the gap. 【0026】 By the way, if the case cover 23b is modified by adding material to improve its sealing performance, it will increase the weight of the saddle-type vehicle 10. Therefore, in this embodiment, in order to reduce weight and improve sealing performance, bulges 54 are provided on both the female thread portion 33 and the boss portion 43. In the following description, when each bulge 54 is described separately, the bulge 54 provided on the female thread portion 33 will be referred to as the "case-side bulge 34," and the bulge 54 provided on the boss portion 43 will be referred to as the "cover-side bulge 44." 【0027】 As shown in Figures 3 and 4, the case-side bulge (the bulge of the case member) 34 is integrally formed with the side surface of the female thread portion 33. As shown in Figure 5, the case-side bulge 34 has a shape that bulges radially from the female thread portion 33 and is provided in a region that does not overlap with the case-side sealing surface 32a. The case-side bulge 34 is fan-shaped when viewed in the direction of insertion and removal of the fastening member 51, and is a columnar rib having the same length as the female thread portion 33 or a shorter length than the female thread portion 33 in the direction of insertion and removal of the fastening member 51. 【0028】 The case-side bulge 34 is positioned to overlap with the cover-side bulge 44 in the insertion and removal direction of the fastening member 51, and makes surface contact with the cover-side bulge 44 when the case cover 23b and the case body 23a are fastened together. In this embodiment, the case-side joining surface 35 that makes surface contact with the cover-side bulge 44 is formed on the same plane as the end face of the female screw portion 33 and the case-side sealing surface 32a of the case end portion 32. 【0029】As shown in Figures 3 and 4, the cover-side bulge 44 is integrally formed with the side surface of the boss portion 43. As shown in Figure 6, the cover-side bulge 44 has a shape that bulges radially from the boss portion 43 and is provided in a region that does not overlap with the cover-side sealing surface 42a. The cover-side bulge 44 is fan-shaped when viewed in the direction of insertion and removal of the fastening member 51, and is a columnar rib having the same length as the boss portion 43 or a shorter length than the boss portion 43 in the direction of insertion and removal of the fastening member 51. 【0030】 Of the cover-side bulge portion 44, the cover-side joining surface 45 that makes surface contact with the case-side bulge portion 34 is formed on the same plane as the end face of the boss portion 43 and the cover-side sealing surface 42a of the cover end portion 42. 【0031】 As described above, in this embodiment, the fastening structure 50 between the case body 23a and the case cover 23b is provided with a bulge 54 on each of the case body 23a and the case cover 23b that bulges out from the female thread portion 33 and the boss portion 43 in an area that does not overlap with the respective sealing surfaces 32a and 42a, and that overlaps in the axial direction of the fastening member 51. As a result, the compressive strength of the fastening portion is improved, and the tilting of the case cover 23b can be suppressed. Furthermore, compared to the case in which build-up material is applied to the entire fastening portion, the increase in weight can be suppressed. This prevents a partial decrease in surface pressure on the sealing surfaces 32a and 42a while suppressing the increase in weight, which is advantageous for weight reduction and improved sealing performance. 【0032】 In this configuration, as shown in Figures 5 and 6, the bulging portion 54 is provided on the outer circumference relative to the female screw portion 33 and the boss portion 43. As a result, when a load is applied to the case cover 23b in a direction that causes it to tilt toward the case body 23a, the bulging portion 54 can receive the force in the tilting direction, thereby suppressing tilting toward the case body 23a. 【0033】Furthermore, as shown in Figures 5 and 6, when viewed in the insertion / removal direction of the fastening member 51, the case-side joining surface 35 of the case-side bulge 34 is formed to have the same shape as the cover-side joining surface 45 of the cover-side bulge 44. As a result, when the case body 23a and the case cover 23b are fastened together, the case-side joining surface 35 and the cover-side joining surface 45 of the case body 23a and the case cover 23b can be brought into full contact, and the compressive strength of the fastened portion can be efficiently improved. 【0034】 Furthermore, as shown in Figures 5 and 6, when viewed in the insertion direction of the fastening member 51, the bulge 54 is provided on the bisector L3 that bisects the seal angle θ formed by the imaginary lines L1 and L2 in the direction in which the seal surfaces 32a and 42a extend. This makes the surface pressure acting on the seal surfaces 32a and 42a more uniform, which is advantageous for improving sealing performance. Regarding the seal angle θ, it can be either the acute or obtuse angle side, but when the bulge 54 is provided on the acute angle side, it is preferable to use the angle on the obtuse angle side as the reference, and when the bulge 54 is provided on the obtuse angle side, it is preferable to use the angle on the acute angle side as the reference. 【0035】 As shown in Figure 6, when viewed in the insertion direction of the fastening member 51, it is preferable that the length L4 from the center of the through hole 43a to the outer end of the cover-side bulge 44 be 1.3 to 1.7 times the radius L5 of the boss portion 43. This makes it possible to effectively increase the strength of the boss portion 43 while avoiding an increase in the weight of the case cover 23b due to the cover-side bulge 44. 【0036】 Figure 7 is a schematic diagram showing a side cross-section of the fastening structure 50. As shown in Figure 7, in the insertion direction view of the fastening member 51, the length L6 of the case-side bulge 34 in the bulging direction is preferably more than half the diameter L7 of the fastening member 51 from the female thread portion 33, and the width L8 of the bulge 54, which corresponds to the length of the bulge 54 in the direction perpendicular to the bulging direction, is preferably 0.8 to 1.2 times the diameter L7 of the fastening member 51. This makes it possible to effectively increase the strength of the female thread portion 33 while avoiding an increase in the weight of the case body 23a due to the case-side bulge 34. 【0037】As shown in Figure 7, in the insertion direction of the fastening member 51, it is preferable that the length L9 of the cover-side bulge 44 is at least half the length L10 of the boss portion 43. This makes it possible to effectively increase the strength of the boss portion 43 while avoiding an increase in the weight of the case cover 23b due to the cover-side bulge 44. 【0038】 Figure 8 shows a female screw portion 33 having a predetermined member 60 nearby, along with its surrounding configuration. Note that the position and size of the case-side bulge 34 and the cover-side bulge 44 are not limited to those described above and may be changed as appropriate. For example, as shown in Figure 8, there is a predetermined member 60 near the female screw portion 33, and due to the influence of the predetermined member 60, it may not be possible to provide the case-side bulge 34 on the bisector L3 of the case-side sealing surface 32a. The predetermined member 60 is, for example, a part of the case body 23a, a vehicle part attached to the case body 23a, or a wiring component arranged around the case body 23a. In such a case, as shown in Figure 8, the case-side bulge 34 may be provided at a position offset from the bisector L3. The cover-side bulge 44 is provided at a position offset from the bisector L3 of the cover-side sealing surface 42a so as to overlap with the case-side bulge 34. This makes it possible to provide the bulge 54 while avoiding the predetermined member 60. 【0039】 As shown in Figure 2, the oil pan 30 is also connected to the lower part of the crankcase 23 by a fastening structure 50. The oil pan 30 is fastened to the case body 23a so as to cover the lower opening of the case body 23a. That is, the case body 23a has the configuration of the fastening structure 50 on the case body 23a side around the lower opening, and the upper part of the oil pan 30 has the configuration of the fastening structure 50 on the case cover 23b side. 【0040】 Figure 9 shows the lower opening of the case body 23a along with its surrounding configuration. As shown in Figure 9, the case body 23a is provided with a case end portion 32 that extends around the lower opening, and the case end portion 32 is provided with a female threaded portion 33, a case-side sealing surface 32a that extends in two directions from the periphery of the female threaded portion 33, and a case-side bulge portion 34 that bulges out from the side surface of the female threaded portion 33. 【0041】Figure 10 is a perspective view showing a fastening structure including the female thread portion 33 in area C of Figure 9, and shows the fastening structure of the oil pan 30. The fastening structure of the oil pan 30 is the same as the fastening structure 50 described above, and the same parts are denoted by the same reference numerals. The oil pan 30 includes a boss portion 43 that overlaps the female thread portion 33, and a cover-side bulge portion 44 that bulges out from the side surface of the boss portion 43. When the fastening member 51 penetrates the boss portion 43 provided on the oil pan 30 and screws into the lower female thread portion 33 of the case body 23a, the case end portion 32 and the cover end portion 42 are joined, and the cover-side bulge portion 44 and the case-side bulge portion 34 make surface contact. As a result, the oil pan 30 is connected to the lower part of the case body 23a. 【0042】 Furthermore, a gasket may be provided between the case body 23a and the case cover 23b, or between the case body 23a and the oil pan 30. 【0043】 In the fastening structure 50 of the oil pan 30, the boss portion 43 and the female thread portion 33 are positioned on the outer circumference of the cover end portion 42 and the case end portion 32. As a result, the internal irregularities of the case caused by the boss portion 43 and the female thread portion 33 are suppressed, and thus the flow of oil into the oil pan 30 is not obstructed. 【0044】As described above, in the fastening structure 50 that fastens the case body 23a and the case cover 23b or the case body 23a and the oil pan 30, the case body 23a includes a case-side seal surface 32a that is joined to the case cover 23b or the oil pan 30, and a plurality of female screw portions 33 around the case-side seal surface 32a or on the case-side seal surface 32a. The case cover 23b or the oil pan 30 includes a cover-side seal surface 42a that overlaps the case-side seal surface 32a, a through hole 43a through which a fastening member fastened to the female screw portion 33 passes, and a boss portion 43 having a seating surface of the fastening member 51. The case body 23a includes a case-side bulging portion 34 that bulges into a region that does not overlap the case-side seal surface 32a from the female screw portion 33 and overlaps in the axial direction of the fastening member 51. The case cover 23b or the oil pan 30 includes a cover-side bulging portion 44 that bulges into a region that does not overlap the cover-side seal surface 42a from the boss portion 43 and overlaps in the axial direction of the fastening member 51. According to this, since the respective bulging portions 34 and 44 of the case body 23a and the case cover 23b or the oil pan 30 overlap in the axial direction of the fastening member 51 in a region that does not overlap the seal surfaces 32a and 42a, the compressive strength of the fastening portion is improved, and tilting toward the bulging portions 34 and 44 can also be suppressed. Thereby, while suppressing an increase in weight, it is possible to prevent a situation in which the surface pressure of the seal surfaces 32a and 42a partially decreases, which is advantageous for weight reduction and improvement of sealing performance. 【0045】 The bulging portions 34 and 44 have the same shape on a case-side joining surface 35 that functions as a mating surface of the case body 23a and a cover-side joining surface 45 that functions as a mating surface with the case cover 23b or the oil pan 30. According to this, it is possible to effectively receive the pressure from the case cover 23b or the oil pan 30. 【0046】 The cover-side bulging portion 44 of the case cover 23b or the oil pan 30 has a height that is at least half the height of the boss portion 43 of the case cover 23b or the oil pan 30. According to this, it is possible to effectively increase the strength of the boss while avoiding an increase in the weight of the case cover 23b or the oil pan 30. 【0047】The cover-side bulging portion 44 of the case cover 23b or the oil pan 30 has a length from the center of the through-hole 43a that is 1.3 to 1.7 times the radius of the boss portion 43. According to this, it is possible to effectively increase the strength of the boss portion 43 while avoiding an increase in the weight of the case cover 23b or the oil pan 30. 【0048】 Each of the bulging portions 34 and 44 is located on the bisector L3 of the seal angle θ formed by the seal surfaces 32a and 42a that extend in two directions from the bulging portions 34 and 44 or their peripheries. According to this, it is possible to evenly balance the surface pressure of the seal surfaces 32a and 42a. 【0049】 The case-side bulging portion 34 of the case body 23a is provided outside the case body 23a with respect to the female screw portion 33. According to this, the unevenness inside the case is suppressed, and the flow of the internal oil becomes good. 【0050】 The case-side bulging portion 34 of the case body 23a bulges from the female screw portion 33 by a length of at least half the diameter of the fastening member 51 as viewed in the insertion direction of the fastening member 51, and has a width that is 0.8 to 1.2 times the diameter of the fastening member 51. According to this, it is possible to effectively increase the strength of the boss portion 43 while avoiding an increase in the weight of the case cover 23b or the oil pan 30. 【0051】 [Embodiment 2] An explanation will be given of Embodiment 2 to which the present invention is applied. In this Embodiment 2, portions having the same configuration as those in the above-described embodiment (hereinafter, Embodiment 1) are denoted by the same reference numerals, and the description thereof will be omitted. 【0052】Figure 11 shows a fastening structure 50 according to Embodiment 2 of the present invention. In Embodiment 1, in the insertion direction of the fastening member 51, the length L9 of the cover-side bulge 44 was more than half the length L10 of the boss portion 43. More specifically, the length of the cover-side bulge 44 in the insertion direction of the fastening member 51 was shorter than the length from the cover-side sealing surface 42a of the case cover 23b to the seating surface of the fastening member 51. In Embodiment 2, the length L11 of the cover-side bulge 144 (bulge of the cover member) is equal to the length L12 of the boss portion 43 from the cover-side sealing surface 42a of the case cover 23b to the seating surface of the fastening member 51. In other words, the cover-side bulge 144 is exposed on the same plane as the end face of the boss portion 43 on the side into which the fastening member 51 is inserted (the surface of the boss portion that contacts the seating surface of the fastening member). Because the cover-side bulge 144 extends to the surface of the boss portion 43 that contacts the seating surface of the fastening member, the height-direction shape of the boss portion 43 becomes uniform, and the strength of the boss portion 43 is further increased. 【0053】 [Embodiment 3] Embodiment 3, to which the present invention is applied, will now be described. In this Embodiment 3, parts configured in the same way as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted. 【0054】 Figure 12 shows a fastening structure 50 according to Embodiment 3 of the present invention. In Embodiment 1, the case-side joining surface 35 and the cover-side joining surface 45 were substantially the same. In Embodiment 3, the case-side joining surface 235 and the cover-side joining surface 245 have different shapes. More specifically, by enlarging the case-side bulge 234 (bulge of the case member), the case-side joining surface 235 (joint surface of the case member) is larger than the cover-side joining surface 245, and a step is formed between the case body 23a and the case cover 23b. Thus, the case-side joining surface 235 of the case body 23a may be larger than the cover-side joining surface 245 of the case cover 23b. This allows the case-side joining surface 235 of the case body 23a to stably support the case cover 23b and the oil pan 30, which is advantageous for improving the compressive strength of the fastening portion and can increase the strength of the boss portion 43. In addition, tilting of the case body 23a toward the bulge 54 side can be further suppressed. 【0055】 Furthermore, in Embodiment 1, the cover-side bulge 44 was a columnar bulge provided on the boss portion 43. In Embodiment 3, as shown in Figure 12, the cover-side bulge 244 is formed as a cone-shaped bulge that narrows in width towards the seating surface side of the fastening member 51 and tapers to a point. Even in this case, the cover-side bulge 244 and the case-side bulge 34 are in full contact, so they can effectively receive pressure from the case cover 23b or the oil pan 30. 【0056】 [Embodiment 4] Embodiment 4, to which the present invention is applied, will now be described. In this embodiment 4, parts configured in the same way as in Embodiment 1 are denoted by the same reference numerals and their description is omitted. 【0057】 Figure 13 is a diagram showing the positional relationship between the case body and the case-side bulge portion used to describe Embodiment 4 of the present invention. In Embodiment 1, as shown at P1 in Figure 13, the female thread portion 33 is positioned externally, offset to the outside of the case-side sealing surface 32a of the case end portion 32. That is, in a view in the insertion direction of the fastening member 51, the female thread portion 33 is provided bulging outwards. In Embodiment 4, as shown at P2 in Figure 13, the female thread portion 333 is positioned internally, offset to the inside of the case-side sealing surface 32a of the case end portion 32. That is, the female thread portion 333 is formed to be on the inside in the thickness direction of the annular structure, and in a view in the insertion direction of the fastening member 51, the female thread portion 333 is provided bulging inwards. As a result, in a view in the insertion direction of the fastening member 51, the bulge portion 334 and the fastening structure do not protrude outwards, resulting in a good appearance. 【0058】 The female thread portion 33 may also be centrally positioned on the case-side sealing surface 32a of the case end portion 32, as shown at P3 in Figure 13. In this case, as shown at P3 in Figure 13, even if the case-side bulge is offset outward, the outward protrusion of the bulge portion 34 and the fastening structure can be suppressed, resulting in a good appearance. 【0059】 [Other Embodiments] The embodiments described above are merely one aspect of the present invention and can be modified and applied as needed without departing from the spirit of the present invention. 【0060】 In the embodiments described above, examples of applying the present invention to the fastening structure 50 between the case body 23a and the case cover 23b, and to the fastening structure 50 between the case body 23a and the oil pan were explained, but the present invention may also be applied to other fastening structures. In the embodiments described above, the shapes of the boss portion 43, the female thread portions 33, 333, and the bulging portions 34, 44, 144, 234, 244, 334 may be changed as appropriate. 【0061】 In the embodiments described above, one bulge 34, 44, 144, 234, 244, and 334 was provided for each of the female threaded portions 33, 333 and the boss portion 43. However, multiple bulges 34, 44, 144, 234, 244, and 334 may be provided. That is, bulges may be provided on both the acute and obtuse angles of the seal angle. Alternatively, bulges 44, 144, and 244 may be provided only for the boss portion 43 of the case cover 23b and the oil pan 30. For example, the female threaded portions 33, 333 may be enlarged relative to the boss portion 43, and bulges 44, 144, and 244 may be provided only for the boss portion 43 of the case cover 23b and the oil pan 30 so as to make surface contact with the enlarged female threaded portions 33, 333. 【0062】 [Configurations supported by the above embodiment] The above embodiment supports the following configurations. 【0063】(Configuration 1) A fastening structure for fastening a case member and a cover member, wherein the case member has a case-side sealing surface that is joined to the cover member and a plurality of female threads around or on the case-side sealing surface, the cover member has a cover-side sealing surface that overlaps with the case-side sealing surface, a through hole through which a screw member fastened to the female threads passes, and a boss portion having a seating surface for the screw member, and the case member and the cover member have bulging portions that bulge out from the female threads and the boss portion in areas that do not overlap with the respective sealing surfaces and that overlap in the axial direction of the screw member. 【0064】 (Configuration 2) The fastening structure according to Configuration 1, wherein the bulging portion has the same shape as the mating surface of the case member and the mating surface of the cover member. With this configuration, the pressure from the cover member can be effectively received. 【0065】 (Configuration 3) The fastening structure according to Configuration 1 or 2, wherein the bulging portion of the cover member has a height of at least half the height of the boss portion of the cover member. This makes it possible to effectively increase the strength of the boss while avoiding an increase in the weight of the cover member. 【0066】 (Configuration 4) The fastening structure according to any one of Configurations 1 to 3, wherein the bulging portion of the cover member has a length from the center of the through hole that is 1.3 to 1.7 times the radius of the boss portion. This allows for an effective increase in the strength of the boss while avoiding an increase in the weight of the cover member. 【0067】 (Configuration 5) The fastening structure according to any one of Configurations 1 to 4, wherein each of the bulging portions is located on the line bisector of the sealing angle formed by the sealing surface extending in two directions from the bulging portion or its periphery. This makes it possible to balance and equalize the surface pressure of the sealing surface. 【0068】(Configuration 6) The bulging portion of the case member is provided on the inside of the case member relative to the female screw portion, in the fastening structure described in any one of Configurations 1 to 5. With this, the bulging portion is not exposed to the outside, resulting in a good appearance. 【0069】 (Configuration 7) The bulging portion of the case member is provided on the outside of the case member relative to the female screw portion, the fastening structure according to any one of Configurations 1 to 6. This suppresses irregularities inside the case and improves the flow of oil inside. 【0070】 (Configuration 8) The fastening structure according to any one of Configurations 1 to 7, wherein the bulging portion of the cover member is exposed on the same plane as the end face of the boss portion on the side into which the screw member is inserted. With this, the processed surface is the same as the seating surface of the screw fastening portion, so the shape in the height direction of the boss portion is made uniform, and the strength of the boss portion is further increased. 【0071】 (Configuration 9) The bulging portion of the case member bulges out from the female thread portion for a length of more than half the diameter of the screw member when viewed in the insertion direction of the screw member, and has a width of 0.8 to 1.2 times the diameter of the screw member, according to any one of Configurations 1 to 8. This makes it possible to effectively increase the strength of the boss while avoiding an increase in the weight of the cover member. 【0072】(Configuration 10) A saddle-type vehicle equipped with a fastening structure for fastening a case member and a cover member, wherein the case member has a case-side sealing surface that is joined to the cover member and a plurality of female screw portions around or on the case-side sealing surface, the cover member has a cover-side sealing surface that overlaps with the case-side sealing surface, a through hole through which a screw member fastened to the female screw portion passes, and a boss portion having a seating surface for the screw member, and the case member and the cover member have bulging portions that bulge out from the female screw portion and the boss portion in a region that does not overlap with the respective sealing surface and overlap in the axial direction of the screw member. 【0073】 10 Saddle-type vehicle 23a Case body (case member) 23b Case cover (cover member) 30 Oil pan (cover member) 32a Case side sealing surface 33 Female thread portion 33a Female thread hole 34 Case side bulge (bulge of case member) 35 Case side joining surface (matching surface of case member) 42a Cover side sealing surface 43 Boss portion 43a Through hole 44 Cover side bulge (bulge of cover member) 45 Cover side joining surface (matching surface of cover member) 50 Fastening structure 51 Fastening member (threaded member) 144 Cover side bulge (bulge of cover member) 234 Case side bulge (bulge of case member) 235 Case side joining surface (matching surface of case member) 244 Cover side bulge (bulge of cover member) 245 Cover-side joining surface (matching surface of cover member) 333 Female thread portion 334 Case-side bulge portion (bulge portion of case member)

Claims

1. In a fastening structure (50) for fastening a case member (23a) and a cover member (23b, 30), the case member (23a) has a case-side sealing surface (32a) that is joined to the cover member (23b, 30), and a plurality of female threaded portions (33, 333) around or on the case-side sealing surface (32a), and the cover member (23b, 30) has a cover-side sealing surface (42a) that overlaps with the case-side sealing surface (32a), and a through hole (43a) through which a screw member (51) fastened to the female threaded portions (33, 333) passes, and a boss portion (43) having a seating surface for the screw member (51), The fastening structure comprises a case member (23a) and a cover member (23b, 30) that bulge out from the female thread portion (33, 333) and the boss portion (43) in areas that do not overlap with the respective sealing surfaces (32a, 42a), and that overlap in the axial direction of the thread member (51), with bulging portions (34, 44, 144, 234, 244, 334).

2. The fastening structure according to claim 1, wherein the bulging portions (34, 44, 144, 334) have the same shape at the mating surfaces (35, 45) of the case member (23a) and the cover member (23b, 30).

3. The fastening structure according to claim 1, wherein the bulging portion (44) of the cover member (23b, 30) has a height of at least half the height of the boss portion (43) of the cover member (23b, 30).

4. The fastening structure according to claim 1, wherein the bulging portions (44, 244) of the cover members (23b, 30) have a length from the center of the through hole (43a) that is 1.3 to 1.7 times the radius of the boss portion (43).

5. The fastening structure according to claim 1, wherein each of the bulging portions (34, 44, 144, 234, 244, 334) is located on the bisector of the seal angle (θ) formed by the seal surfaces (32a, 42a) extending in two directions from or around the bulging portion (34, 44, 144, 234, 244, 334) or its periphery.

6. The fastening structure according to claim 1, wherein the bulging portion (34, 234) of the case member is provided on the inside of the case member (23a) relative to the female thread portion (33).

7. The fastening structure according to claim 1, wherein the bulging portion (334) of the case member (23a) is provided on the outside of the case member (23a) relative to the female thread portion (333).

8. The fastening structure according to claim 1, wherein the bulging portion (44) of the cover member (23b, 30) is exposed on the same plane as the end face of the boss portion (43) on the side into which the screw member (51) is inserted.

9. The fastening structure according to claim 1, wherein the bulging portions (34, 234, 334) of the case member (23a) bulge out from the female threaded portions (33, 333) for a length of more than half the diameter of the screw member (51) when viewed in the insertion direction of the screw member (51), and have a width of 0.8 to 1.2 times the diameter of the screw member (51).

10. A saddle-type vehicle (10) equipped with a fastening structure (50) for fastening a case member (23a) and cover members (23b, 30), wherein the case member (23a) has a case-side sealing surface (32a) that is joined to the cover members (23b, 30), and a plurality of female threaded portions (33, 333) around or on the case-side sealing surface (32a), and the cover members (23b, 30) have a cover-side sealing surface (42a) that overlaps with the case-side sealing surface (32a), and a boss portion (43) through which a screw member (51) fastened to the female threaded portions (33, 333) passes, and a seating surface for the screw member (51), The case member (23a) and the cover members (23b, 30) are provided with bulging portions (34, 44, 144, 234, 244, 334) that bulge out from the female threaded portion (33, 333) and the boss portion (43) in areas that do not overlap with the respective sealing surfaces (32a, 42a), and that overlap in the axial direction of the threaded member (51), in a saddle-type vehicle.

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