Screw member

Abstract

A screw member (10) is provided with a head part (20) and a shaft part (30) extending from the head part (20). The shaft part (30) has: a columnar first shaft part (33); and a columnar second shaft part (34) extending between the first shaft part (33) and the head part (20) and having an outer diameter smaller than the outer diameter of the first shaft part (33). The head part (20) has a seating part (22) configured to receive a load from a seating object (S) on which the head part (20) is seated. The seating part (22) has a convex surface (22c) that curves in a convex shape toward the seating object (S) between the outer peripheral edge (22a) and the inner peripheral edge (22b) of the seating part (22).

Description

Screw material

[0001] The present disclosure relates to a screw member.

[0002] As described in Patent Document 1, a screw member for fastening multiple components together is known. The screw member fastens, for example, a main body that houses equipment and the like to a lid. In this case, the main body has an opening that opens toward the outside of the main body. The screw member fastens the lid to the main body so that the lid covers the opening from the outside of the main body.

[0003] The screw members are detachable from the main body and the lid. For example, when inspecting the equipment stored inside the main body, the fastening of the main body and the lid by the screw members is released. This allows the lid to be removed from the main body, making it possible to access the inside of the main body from outside through the opening in the main body.

[0004] When screws are used to fasten the main body and the lid, a plurality of insertion holes for inserting the screws are formed on the outer periphery of the opening of the main body and the outer periphery of the lid. For example, the plurality of insertion holes formed in the main body and the plurality of insertion holes formed in the lid are positioned so that their axes coincide with each other. The screws are fastened to the main body by being inserted into these insertion holes.

[0005] Normally, the pitch between the insertion holes formed in the main body and the pitch between the insertion holes formed in the lid are the same. However, due to factors such as the machining accuracy of at least one of the main body and the lid, the pitch between the insertion holes formed in the main body and the pitch between the insertion holes formed in the lid may differ. The greater the number of insertion holes formed in the main body and the lid, the greater the difference in pitch size, which accumulates and can become significant. When a difference in the pitch size between the insertion holes in the main body and the lid occurs, the axes of the multiple insertion holes formed in the main body and the multiple insertion holes formed in the lid do not coincide, resulting in a misalignment. When a screw member is inserted into the misaligned insertion holes in the main body and the lid, the screw member may be inserted into each insertion hole with its axis inclined relative to the axes of the insertion holes in the main body and the lid.

[0006] In some cases, a floating nut is provided on the main body. In this case, even if the screw is inserted at an angle between the insertion hole in the main body and the insertion hole in the lid as described above, the angle of the screw is reduced and the screw is fixed to the floating nut. This allows the screw to fix the lid to the main body.

[0007] Registered Utility Model No. 3063831

[0008] When the difference between the outer diameter of the screw member and the diameter of the insertion hole is small, the clearance between the screw member inserted into the insertion hole and the insertion hole becomes small. In this case, even if a measure to reduce the inclination of the screw member is taken using the floating nut or the like, there is a risk that the inclination of the screw member inserted into the insertion hole will not be sufficiently reduced due to interference between the screw member and the insertion hole.

[0009] Furthermore, the screw may be fixed with its axis slightly tilted relative to the axis of the insertion hole. In this case, the head of the screw is seated at an angle relative to the seating object. This results in a line contact between the head of the screw and the seating object, which may result in an insufficient contact area between the head and the seating object. If the contact area is not sufficiently secured, the screw may be easily loosened, which is undesirable.

[0010] In one aspect of the present disclosure, there is provided a screw member including a head and a shank extending axially from the head. The shank includes a columnar first shank extending in the axial direction and a columnar second shank extending in the axial direction between the first shank and the head in the axial direction and having an outer diameter smaller than that of the first shank. The head includes a seat configured to receive a load from a seating object on which the head sits. The seat has a convex surface that curves convexly toward the seating object between an outer peripheral edge and an inner peripheral edge of the seat.

[0011] FIG. 1 is a perspective view showing a screw member according to an embodiment. FIG. 2 is a cross-sectional view showing the screw member according to an embodiment. FIG. 3 is an enlarged perspective view showing a portion of the screw member according to an embodiment. FIG. 4 is a perspective view showing seating according to an embodiment. FIG. 5 is a perspective view showing seating according to an embodiment. FIG. 6 is a cross-sectional view for explaining insertion of a screw member into the first insertion hole and the second insertion hole when the axis of the first insertion hole and the axis of the second insertion hole coincide with each other. FIG. 7 is a cross-sectional view for explaining insertion of a screw member into the first insertion hole and the second insertion hole when the axis of the first insertion hole and the axis of the second insertion hole coincide with each other. FIG. 8 is a cross-sectional view for explaining insertion of a screw member into the first insertion hole and the second insertion hole when the axis of the first insertion hole and the axis of the second insertion hole do not coincide with each other. FIG. 9 is a cross-sectional view for explaining insertion of a screw member into the first insertion hole and the second insertion hole when the axis of the first insertion hole and the axis of the second insertion hole do not coincide with each other. Fig. 10 is a perspective view showing seating in a modified example. Fig. 11 is a perspective view showing seating in a modified example. Fig. 12 is a side view showing a guide portion in a modified example. Fig. 13 is a side view showing a guide portion in a modified example. Fig. 14 is a side view showing a guide portion in a modified example.

[0012] An embodiment of a screw member will be described below with reference to the drawings. <Screw member> As shown in Figures 1 and 2, the screw member 10 includes a screw body 11. Furthermore, the screw member 10 includes a washer 40 and a guide portion 50. The screw body 11, the washer 40, and the guide portion 50 are each made of metal. The screw body 11 includes a head portion 20 and a shank portion 30. In other words, the screw member 10 includes the head portion 20 and the shank portion 30. The direction in which the axis of the shank portion 30 extends is referred to as the axial direction X.

[0013] <Head portion> The head portion 20 has a columnar shape extending in the axial direction X. In this embodiment, the head portion 20 has a cylindrical shape extending in the axial direction X. The head portion 20 may have a shape other than a cylindrical shape, such as a polygonal pillar shape. The head portion 20 has a first head portion end surface 21. The head portion 20 has a second head portion end surface 22 that serves as a seat portion, which will be described later. The first head portion end surface 21 is located at one end of the head portion 20 in the axial direction X, and the second head portion end surface 22 is located at the other end of the head portion 20 in the axial direction X.

[0014] The first head end surface 21 is, for example, a plane extending perpendicular to the axis of the head 20. A head hole 23 is formed in the first head end surface 21. The head hole 23 opens at the first head end surface 21. In this embodiment, the head hole 23 is hexagonal when viewed from the axial direction X. The head hole 23 may have a polygonal shape other than a hexagonal shape.

[0015] 1 and 3 , the shank 30 extends from the head 20 in the axial direction X. Of the two ends of the shank 30 in the axial direction X, the end connected to the head 20 is the connection end 31, and the end opposite the connection end 31 is the insertion end 32. In other words, the shank 30 has the connection end 31 connected to the head 20. The shank 30 has the insertion end 32 on the side opposite the head 20 in the axial direction X. The connection end 31 is connected to the second head end surface 22.

[0016] As shown in FIGS. 1 and 2 , the shaft portion 30 has a first shaft portion 33 and a second shaft portion 34. The first shaft portion 33 has a columnar shape extending in the axial direction X. For example, the first shaft portion 33 has a cylindrical shape extending in the axial direction X. A first threaded portion 35 is formed on an outer peripheral surface 33a of the first shaft portion 33. In other words, a male thread is formed on the first shaft portion 33. In this embodiment, the first threaded portion 35 corresponds to the male thread formed on the first shaft portion 33. The outer peripheral surface 33a of the first shaft portion 33 has crest portions 35a and valley portions 35b formed alternately in the axial direction X. The first threaded portion 35 is formed over the entire outer peripheral surface 33a of the first shaft portion 33.

[0017] Of the two ends of the first shank 33 in the axial direction X, one end functions as the insertion end 32, and the other end is connected to the second shank 34. The first shank 33 corresponds to the entire portion of the shank 30 between the second shank 34 and the insertion end 32 in the axial direction X.

[0018] The second shank 34 is columnar and extends in the axial direction X between the first shank 33 and the head 20 in the axial direction X. For example, the second shank 34 is cylindrical and extends in the axial direction X. The second shank 34 is a non-threaded portion with no thread grooves formed on its surface. In other words, the first shank 33 has a male thread, while the second shank 34 does not have a male thread. Of the two ends of the second shank 34 in the axial direction X, one end functions as the connecting end 31 that connects to the head 20, and the other end is connected to the first shank 33. In other words, the second shank 34 corresponds to the entire portion of the shank 30 between the first shank 33 and the connecting end 31 in the axial direction X.

[0019] As shown in FIG. 2 , the second shank 34 has an outer diameter smaller than that of the first shank 33. The outer diameter of the first shank 33 is also referred to as the first diameter D1. The outer diameter of the second shank 34 is also referred to as the second diameter D2. The second diameter D2 is smaller than the first diameter D1. Note that, because the first threaded portion 35 is formed on the outer peripheral surface 33a of the first shank 33, the outer diameter of the first shank 33 varies depending on the position of the first shank 33 in the axial direction X. In this embodiment, the first diameter D1 is the outer diameter of the first shank 33 measured at a position where the outer diameter is largest. For example, the second diameter D2 may be 60% of the first diameter D1. The outer diameter of the first shank 33 measured at a position where the outer diameter is smallest is also referred to as the third diameter D3. In this embodiment, the second diameter D2 is smaller than the third diameter D3.

[0020] <Guide Portion> As shown in FIGS. 1 and 2 , the guide portion 50 is located at the insertion end 32. The guide portion 50 extends from the insertion end 32 toward the opposite side from the head portion 20. The guide portion 50 has an inclined portion 52 whose outer diameter decreases with increasing distance from the insertion end 32 in the axial direction X. Furthermore, in this embodiment, the guide portion 50 has a connecting portion 51. The connecting portion 51 is, for example, cylindrical and extends in the axial direction X. One end of the connecting portion 51 in the axial direction X is connected to the insertion end 32, and the other end is connected to the inclined portion 52. For example, the outer diameter of the connecting portion 51 is larger than the outer diameter of the second shank 34. In this embodiment, the inclined portion 52 is hemispherical. In this embodiment, the portion of the guide portion 50 in the axial direction X other than the connecting portion 51 corresponds to the inclined portion 52.

[0021] <Washer> As shown in Figures 2, 4, and 5, a through hole 41 that penetrates in the axial direction X is formed in the washer 40. The washer 40 has a contact surface 43. The contact surface 43 is a plane that extends perpendicular to the axis of the washer 40. The washer 40 has an opposing surface 42. The contact surface 43 is located at one end in the axial direction X, and the opposing surface 42 is located at the other end in the axial direction X. The through hole 41 opens at both the opposing surface 42 and the contact surface 43.

[0022] A second threaded portion 45 is formed on the inner peripheral surface 44 of the washer 40. In other words, a female thread is formed in the through hole 41. The second threaded portion 45 formed in the through hole 41 corresponds to the female thread. On the inner peripheral surface 44 of the washer 40, the crest portions 45a and the valley portions 45b of the second threaded portion 45 are formed so as to be alternately positioned in the axial direction X. The second threaded portion 45 is formed over the entire inner peripheral surface 44 of the washer 40.

[0023] The diameter of the through hole 41 is also referred to as a fourth diameter D4. Note that, because the second thread portion 45 is formed on the inner peripheral surface 44 of the washer 40, the diameter of the through hole 41 varies depending on the position of the through hole 41 in the axial direction X. In this embodiment, the fourth diameter D4 is the diameter of the through hole 41 measured at the position where the diameter of the through hole 41 is smallest.

[0024] The fourth diameter D4 is smaller than the first diameter D1 and equal to or larger than the third diameter D3. The fourth diameter D4 may be larger than the third diameter D3 as long as the second threaded portion 45 and the first threaded portion 35 can be threadedly engaged with each other. The shank 30 is inserted into the through hole 41 of the washer 40. The washer 40 is configured to be displaceable in the axial direction X by being rotated relative to the shank 30 while the second threaded portion 45, which serves as an internal thread, is threadedly engaged with the first threaded portion 35, which serves as an external thread.

[0025] When the washer 40 is rotated in the first direction with the second threaded portion 45 threadedly engaged with the first threaded portion 35, the second threaded portion 45 threads into the first threaded portion 35 and the washer 40 is displaced in the axial direction X so as to move away from the second shank 34. By rotating the washer 40 in the first direction with the washer 40 positioned around the insertion end 32, the second threaded portion 45 and the first threaded portion 35 are disengaged from each other, making the washer 40 removable from the shank 30. This releases the washer 40 from its integration with the screw body 11.

[0026] When the washer 40 is rotated in a second direction, which is the opposite direction to the first direction, with the washer 40 positioned around the insertion end 32, the second threaded portion 45 and the first threaded portion 35 threadably engage with each other, and the washer 40 is attached to the shank 30. This causes the washer 40 to be integrated with the screw body 11. When the washer 40 is rotated in the second direction with the second threaded portion 45 threadably engaged with the first threaded portion 35, the washer 40 is displaced in the axial direction X so as to approach the second shank 34 while the second threaded portion 45 threadably engages with the first threaded portion 35.

[0027] The fourth diameter D4 is larger than the second diameter D2. Therefore, when the washer 40 is rotated in the second direction with the second threaded portion 45 threadedly engaged with the first threaded portion 35 and the washer 40 positioned around the boundary portion 30a between the first shank portion 33 and the second shank portion 34 in the axial direction X, the second threaded portion 45 and the first threaded portion 35 are disengaged from each other. This causes the washer 40 to be displaced in the axial direction X from around the first shank portion 33 to around the second shank portion 34. Therefore, the second shank portion 34 is inserted into the through hole 41. The washer 40 is disposed between the head portion 20 and the first shank portion 33 in the axial direction X. The washer 40 is displaceable in the axial direction X between the head portion 20 and the first shank portion 33 in the axial direction X.

[0028] When the washer 40 is positioned around the second shank 34, the head 20 prevents the washer 40 from moving to one side of the second shank 34 in the axial direction X, and the first shank 33 prevents the washer 40 from moving to the other side of the second shank 34 in the axial direction X. This prevents the washer 40 from falling off the second shank 34.

[0029] 2 and 3 , the second head end surface 22 serving as the seating portion is configured to receive a load from a seating object S on which the head 20 is seated. The second head end surface 22 serving as the seating portion has, for example, an annular shape extending from the connecting end 31 when viewed from the axial direction X. Therefore, the second head end surface 22 serving as the seating portion has an outer peripheral edge 22 a and an inner peripheral edge 22 b. The inner peripheral edge 22 b of the second head end surface 22 and the connecting end 31 are connected to each other.

[0030] The second head end surface 22 serving as a seating portion has a convex surface 22c that curves convexly toward the seating object S between an outer peripheral edge 22a and an inner peripheral edge 22b of the second head end surface 22. In this embodiment, the convex surface 22c is provided over the entire area between the outer peripheral edge 22a and the inner peripheral edge 22b of the second head end surface 22. In this embodiment, the entire second head end surface 22 serving as a seating portion corresponds to the convex surface 22c.

[0031] 1 and 2 , the opposing surface 42 has an annular shape extending around the through hole 41 when viewed from the axial direction X. The opposing surface 42 faces the head 20 in the axial direction X. Specifically, the opposing surface 42 faces the second head end surface 22, which serves as a seat, in the axial direction X. The opposing surface 42 faces the convex surface 22c in the axial direction X. The opposing surface 42 has a concave surface 42c that curves concavely along the convex surface 22c.

[0032] The concave surface 42c in this embodiment is provided over the entire area between the outer peripheral edge 42a and the inner peripheral edge 42b of the opposing surface 42. The seating object S on which the second head end surface 22 serving as a seat sits is the opposing surface 42. Therefore, in this embodiment, the entire opposing surface 42 is the concave surface 42c and corresponds to the seating object S.

[0033] <Fixing a First Member and a Second Member Using a Screw Member> As shown in FIG. 6 , the screw member 10 can fix a first member 61 and a second member 62. A first insertion hole 61a is formed in the first member 61. A second insertion hole 62a is formed in the second member 62. The first member 61 and the second member 62 are arranged so that the first insertion hole 61a and the second insertion hole 62a are connected to each other. The second member 62 is, for example, a main body that houses equipment (not shown) therein. The first member 61 is, for example, a cover that covers the opening of the second member 62. In this case, the opening of the second member 62 can be blocked by fixing the first member 61 and the second member 62 together. By releasing the fixation between the first member 61 and the second member 62, the interior of the second member 62 can be accessed through the opening of the second member 62.

[0034] The screw member 10 is inserted into the first insertion hole 61a and the second insertion hole 62a communicating with the first insertion hole 61a to fix the first member 61 and the second member 62. The screw member 10 inserted into the first insertion hole 61a and the second insertion hole 62a is pulled out from the first insertion hole 61a and the second insertion hole 62a, thereby releasing the fixation between the first member 61 and the second member 62. In this embodiment, the first member 61 and the second member 62 overlap each other in the direction in which the axes of the first insertion hole 61a and the second insertion hole 62a extend.

[0035] In this embodiment, no grooves for female threads are formed on the end surface of the first member 61 that defines the first insertion hole 61a or the end surface of the second member 62 that defines the second insertion hole 62a. The diameters of the first insertion hole 61a and the second insertion hole 62a are equal to or larger than the outer diameter of the first shank 33. This allows the first shank 33 to be inserted into the first insertion hole 61a and the second insertion hole 62a.

[0036] For example, a floating nut 63 for fixing the screw member 10 is attached to the second member 62. In detail, the floating nut 63 is fixed to a second surface 62b, which is one of both end surfaces of the second member 62 in the thickness direction, and is located on the side opposite to the surface that contacts the first member 61.

[0037] The floating nut 63 has, for example, a nut main body 64 and a cover 66. The nut main body 64 has an internally formed female thread 65. The cover 66 has a cover opening 67. The cover 66 is attached to the second member 62 by, for example, a bolt B. This allows the cover 66 to be attached to the second member 62 so as to cover the second surface 62b of the second member 62. An accommodation space is defined between the cover 66 and the second member 62. The nut main body 64 is provided in this accommodation space. The nut main body 64 is displaceable within the accommodation space. In the axial direction X, the second insertion hole 62a in the second member 62, the internally formed female thread 65 in the nut main body 64, and the cover opening 67 in the cover 66 are in communication with one another.

[0038] <When the axes of the first insertion hole and the second insertion hole are aligned> Next, a case will be described in which the first member 61 and the second member 62 are fixed using the screw member 10 in a situation in which the axes of the first insertion hole 61 a and the second insertion hole 62 a are aligned. Note that the following description will be given by way of example of a case in which the first member 61 and the second member 62 extend in the direction of gravity.

[0039] When the first member 61 and the second member 62 are fixed using the screw member 10, the screw member 10 is inserted sequentially into the first insertion hole 61a and the second insertion hole 62a. At this time, the guide portion 50 is inserted into the first insertion hole 61a before the shank portion 30. The guide portion 50 has an inclined portion 52 whose outer diameter decreases with increasing distance from the insertion end 32 in the axial direction X. Even if the axis of the screw member 10 and the axis of the first insertion hole 61a are misaligned, the guide portion 50 is inserted into the first insertion hole 61a while the opening edge 61c of the first insertion hole 61a formed on the first surface 61b, which is the surface of the first member 61 facing the screw member 10, abuts against the outer surface of the inclined portion 52. After the guide portion 50 is inserted into the first insertion hole 61a, the shank portion 30 is inserted into the first insertion hole 61a in this order: the first shank portion 33, then the second shank portion 34. Therefore, the guide portion 50 guides the insertion of the shaft portion 30 into the first insertion hole 61a.

[0040] As shown in FIG. 7 , the guide portion 50 and the first shank portion 33 pass through the first insertion hole 61a and the second insertion hole 62a in that order, and then are exposed from the opening of the second insertion hole 62a in the second surface 62b of the second member 62. By rotating the screw body 11, the first threaded portion 35 of the first shank portion 33 and the female threaded portion 65 of the nut body portion 64 of the floating nut 63 threadably engage with each other outside the second insertion hole 62a. This fixes the screw member 10 to the second member 62 via the floating nut 63. In this way, the first member 61 and the second member 62 are fixed by the screw member 10. Note that the screw body 11 can be rotated, for example, by an operator rotating a tool (not shown) inserted into the head hole 23.

[0041] The second shank 34 is located inside the first insertion hole 61 a and the second insertion hole 62 a in a state in which the first member 61 and the second member 62 are fixed by the screw member 10. Because the outer diameter of the second shank 34 is smaller than the outer diameter of the first shank 33, the end face of the first member 61 that defines the first insertion hole 61 a and the end face of the second member 62 that defines the second insertion hole 62 a are separated from the second shank 34 in a direction perpendicular to the axis of the screw body 11.

[0042] When the first member 61 and the second member 62 are fixed by the screw member 10, the contact surface 43 contacts the first member 61, and the opposing surface 42 faces the head 20 in the axial direction X. Specifically, the contact surface 43 of the washer 40 contacts a portion of the first surface 61b of the first member 61 around the first insertion hole 61a. The opposing surface 42 of the washer 40 faces the second head end surface 22 serving as a seating portion of the head 20. A concave surface 42c formed on the opposing surface 42 and a convex surface 22c formed on the second head end surface 22 contact each other. When the first member 61 and the second member 62 are fixed by the screw member 10, the second head end surface 22 serving as a seating portion receives a load from the opposing surface 42 as a seating object S on which the head 20 sits.

[0043] The washer 40 is sandwiched between the head 20 and the first member 61 in the axial direction X. After passing through the inside of the nut body 64 of the floating nut 63, the guide portion 50 is exposed to the outside of the floating nut 63 through the cover opening 67 of the cover portion 66. The first shank 33 is inserted into the nut body 64. At this time, the first threaded portion 35 of the first shank 33 and the female threaded portion 65 of the nut body 64 are engaged with each other. This fixes the first shank 33 to the floating nut 63.

[0044] As a result of the first shaft portion 33 being fixed to the floating nut 63, the head 20 presses the washer 40 against the first member 61. By applying a load from the head 20 and the washer 40 to the first member 61 and by fixing the first shaft portion 33 to the second member 62 via the floating nut 63, the first member 61 and the second member 62 are fixed to each other.

[0045] <Case where the axes of the first insertion hole and the second insertion hole do not coincide> Next, a case where the first member 61 and the second member 62 are fixed using the screw member 10 in a situation where the axes of the first insertion hole 61 a and the second insertion hole 62 a do not coincide will be described. Note that the following description will be given by way of example of a case where the first member 61 and the second member 62 extend in the direction of gravity, similar to FIGS. 6 and 7 .

[0046] 8, the guide portion 50 and the first shank 33 are sequentially inserted into the first insertion hole 61a and the second insertion hole 62a, similar to the case where the axes of the first insertion hole 61a and the second insertion hole 62a are aligned as described above with reference to FIGS. 6 and 7. At this time, if the axes of the first insertion hole 61a and the second insertion hole 62a are not aligned, the screw member 10 will be in a tilted position when the first shank 33 is inserted from the first insertion hole 61a to the second insertion hole 62a. With the screw member 10 in this tilted position, the second shank 34 is inserted into the first insertion hole 61a and the second insertion hole 62a.

[0047] As shown in FIG. 9 , by rotating the screw body 11, the first threaded portion 35 of the first shank 33 and the female threaded portion 65 of the nut body 64 of the floating nut 63 threadably engage with each other outside the second insertion hole 62a. The nut body 64 displaces depending on the inclination of the screw body 11. For example, the more the first threaded portion 35 of the first shank 33 threads into the female threaded portion 65 of the nut body 64, the more the nut body 64 displaces. In this way, the screw member 10 is fixed to the second member 62 via the floating nut 63. As the first threaded portion 35 of the first shank 33 threads into the floating nut 63, the inclination of the screw member 10 is alleviated. FIG. 9 illustrates a case where the inclination of the screw member 10 still occurs even after the inclination of the screw member 10 is alleviated. When the screw member 10 is tilted in position, the axis of the shank 30 is tilted with respect to the axis of the first insertion hole 61a and the axis of the second insertion hole 62a.

[0048] The second shank 34 is positioned inside the first insertion hole 61 a and the second insertion hole 62 a when the first member 61 and the second member 62 are fixed by the screw member 10. At this time, the second shank 34 is inclined inside the first insertion hole 61 a and the second insertion hole 62 a. However, the end face of the first member 61 that defines the first insertion hole 61 a and the end face of the second member 62 that defines the second insertion hole 62 a are separated from the second shank 34 in a direction perpendicular to the axis of the screw body 11.

[0049] With the first member 61 and the second member 62 fixed by the screw member 10, the contact surface 43 contacts the first member 61, and the opposing surface 42 faces the head 20 in the axial direction X. At this time, the screw body 11 is tilted, but the washer 40 is not tilted. Therefore, the contact surface 43 of the washer 40 contacts the portion of the first surface 61b of the first member 61 around the first insertion hole 61a.

[0050] As the screw body 11 tilts, a portion of the convex surface 22c approaches the opposite concave surface 42c. As a result, at least a portion of the convex surface 22c and at least a portion of the concave surface 42c come into contact with each other. The remaining convex surface 22c moves away from the concave surface 42c as the screw body 11 tilts.

[0051] At the portion of the convex surface 22c and the concave surface 42c where they contact each other, with the first member 61 and the second member 62 fixed by the screw member 10, the second head end surface 22 as a seating portion receives a load from the opposing surface 42 as a seating object S on which the head 20 sits. At the portion of the convex surface 22c and the concave surface 42c where they contact each other, the head 20 presses the washer 40 against the first member 61. The first member 61 and the second member 62 are fixed by the application of this load from the head 20 and the washer 40 to the first member 61 and the fixation of the first shaft portion 33 to the second member 62 via the floating nut 63.

[0052] [Operations and Effects of the Present Embodiment] The operations and effects of the present embodiment will be described. (1) The shank 30 has a columnar first shank 33 extending in the axial direction X and a columnar second shank 34 extending in the axial direction X between the first shank 33 and the head 20 in the axial direction X and having an outer diameter smaller than that of the first shank 33. Therefore, when the second shank 34 is inserted into the first insertion hole 61 a in the first member 61 and the second insertion hole 62 a in the second member 62 that serve as fixation targets with the screw member 10, interference between the second shank 34 and the first insertion hole 61 a and the second insertion hole 62 a can be suppressed. Therefore, even if the diameters of the first insertion hole 61 a in the first member 61 and the second insertion hole 62 a in the second member 62 are relatively small, tilt of the screw member 10 inserted into the first insertion hole 61 a and the second insertion hole 62 a can be sufficiently reduced. The head 20 also has a second head end surface 22 serving as a seating portion configured to receive a load from the seated object S on which the head 20 is seated. The second head end surface 22 serving as a seating portion has a convex surface 22c that curves convexly toward the seated object S between the outer peripheral edge 22a and the inner peripheral edge 22b of the second head end surface 22. Therefore, compared to a case in which the head 20 does not have the convex surface 22c, it is possible to ensure a sufficient contact area, which is an area where the head 20 and the seated object S come into contact with each other. Therefore, it is possible to suppress loosening of the screw member 10 caused by an insufficient contact area.

[0053] (2) The screw member 10 includes a washer 40 having a through hole 41 formed therein that penetrates in the axial direction X. The washer 40 has an opposing surface 42 that faces the head 20. The seating target S is the opposing surface 42. The opposing surface 42 faces the convex surface 22c in the axial direction X and has a concave surface 42c that curves concavely along the convex surface 22c. Therefore, when the screw member 10 is attached to a first member 61 and a second member 62 that are targets to be fixed by the screw member 10, the head 20 and the washer 40 abut against each other, thereby preventing the head 20 from abutting against the first member 61 that is the target to be fixed by the screw member 10. As a result, the head 20 abuts against the first member 61 that is the target to be fixed by the screw member 10, thereby preventing deformation of the first member 61 that is the target to be fixed. Furthermore, when the head 20 is seated on the washer 40, the convex surface 22c of the head 20 comes into contact with the concave surface 42c of the washer 40, so that a contact area where the head 20 and the seating object S come into contact with each other can be further secured compared to when the seating object S does not have the concave surface 42c. Therefore, loosening of the fixation of the screw member 10 caused by an insufficient contact area can be further suppressed.

[0054] (3) The first shank 33 is formed with a first threaded portion 35 as a male thread. The through hole 41 is formed with a second threaded portion 45 as a female thread. The washer 40 is configured to be displaceable in the axial direction X by rotating with respect to the shank 30 while the second threaded portion 45 as a female thread is threadedly engaged with the first threaded portion 35 as a male thread. Therefore, the washer 40 can be inserted up to the second threaded portion 45 by rotating with respect to the shank 30 while the second threaded portion 45 as a female thread is threadedly engaged with the first threaded portion 35 as a male thread. The washer 40 is integrated with the shank 30 when inserted into the second threaded portion 45. Therefore, the screw member 10 can be attached to and detached from the first member 61 and the second member 62, which are targets to be fixed by the screw member 10, with the washer 40 integrated with the shank 30, improving workability.

[0055] (4) The shank 30 has an insertion end 32 on the opposite side of the head 20 in the axial direction X. The screw member 10 includes a guide portion 50 extending from the insertion end 32 toward the opposite side of the head 20. The guide portion 50 has an inclined portion 52 whose outer diameter decreases with increasing distance from the insertion end 32 in the axial direction X. Therefore, when the screw member 10 is inserted into the first insertion hole 61a of the first member 61, which is the target of fixation by the screw member 10, the outer surface of the guide portion 50 abuts against the opening edge 61c of the first insertion hole 61a. Since the screw member 10 is inserted into the first insertion hole 61a while abutting against the opening edge 61c, the shank 30 is guided into the first insertion hole 61a. Therefore, the screw member 10 can be easily inserted into the first insertion hole 61a of the first member 61, which is the target of fixation.

[0056] [Modifications] The embodiment can be modified as follows: The embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0057] As shown in FIGS. 10 and 11 , the concave surface 42c may be formed in a portion of the opposing surface 42. For example, as shown in FIG. 10 , grooves 46 may be formed in the opposing surface 42. The grooves 46 extend linearly between the inner edge and the outer edge of the washer 40. Four grooves 46 are formed in the opposing surface 42. The concave surface 42c is located in a portion of the opposing surface 42 where no grooves 46 are formed. The shape and number of grooves 46 formed in the opposing surface 42 can be changed as appropriate. Furthermore, as shown in FIG. 11 , a flat surface 47 may be provided on the opposing surface 42. The flat surface 47 has a flat shape extending in a direction perpendicular to the axis of the washer 40. The flat surface 47 extends in an annular shape along the inner edge of the washer 40. The concave surface 42c is located in a portion of the opposing surface 42 where no flat surface 47 is formed. The position of the flat surface 47 on the opposing surface 42 can be changed as appropriate. When a flat surface 47 is formed on the opposing surface 42, a flat surface extending along the flat surface 47 may be provided on the portion of the second head end surface 22 serving as the seating portion of the head 20 that faces the flat surface 47.

[0058] As shown in Figures 12, 13, and 14, the shape of the guide portion 50 may be changed. For example, as shown in Figure 12, the guide portion 50 may have an end surface portion 53. The end surface portion 53 is connected to the inclined portion 52. The end surface portion 53 is located at the end of the screw member 10. The end surface portion 53 may be, for example, a plane perpendicular to the axis of the shank portion 30. Also, for example, as shown in Figure 13, the inclined portion 52 of the guide portion 50 may be conical extending in the axial direction X. Note that the inclined portion 52 may have a pyramidal shape other than a conical shape. Also, for example, as shown in Figure 14, the inclined portion 52 of the guide portion 50 may be conical extending in the axial direction X, and the guide portion 50 may have an end surface portion 53. The end surface portion 53 may have a configuration similar to that of the end surface portion 53 shown in Figure 12.

[0059] The head hole 23 may be omitted from the head 20. In this case, the operator can rotate the screw 10 by gripping and rotating the head 20. A thread groove may be formed on the outer surface of the second threaded portion 45.

[0060] The connecting portion 51 may be omitted from the guide portion 50. In this case, the inclined portion 52 may be connected to the insertion end 32, for example. The entire guide portion 50 may function as the inclined portion 52.

[0061] The guide portion 50 may be omitted from the screw member 10. In this case, for example, the insertion end 32 of the screw member 10 may function as the end of the screw member 10. The second threaded portion 45 as a female thread may be omitted from the through hole 41 of the washer 40. In this case, for example, the inner circumferential surface 44 of the washer 40 that defines the through hole 41 may be cylindrical extending in the axial direction X. For example, a slit may be formed in part of the washer 40, and the second shank 34 may be inserted into the through hole 41 through this slit, and then the slit may be closed to position the washer 40 around the second shank 34.

[0062] The concave surface 42c may be omitted from the washer 40. The washer 40 may be omitted from the screw member 10. In this case, the seating object S is a portion of the fixed object fixed by the screw member 10 that faces the head 20 in a state fixed by the screw member 10. For example, the seating object S may be the first surface 61b of the first member 61. In such a case, the seating object S may or may not have the concave surface 42c.

[0063] The object to be fixed by the screw member 10 may be one member such as the first member 61, or may be three or more members. In this case, at least one insertion hole formed in the object to be fixed by the screw member 10 may be a through hole without a thread groove, or may be a female screw with a thread groove.

[0064] [Additional Notes] The technical ideas that can be understood from the above-described embodiment and modifications will be described below. <Supplementary Note 1> A screw member that is inserted into a first insertion hole formed in a first member and a second insertion hole formed in a second member and communicating with the first insertion hole to fix the first member and the second member, the screw member comprising: a head; and a shank portion extending in an axial direction from the head, wherein the shank portion has a columnar first shank portion extending in the axial direction, and a columnar second shank portion that extends in the axial direction between the first shank portion and the head in the axial direction and has an outer diameter smaller than an outer diameter of the first shank, the second shank portion is located inside the first insertion hole and the second insertion hole in a state in which the first member and the second member are fixed by the screw member, the head has a seat portion that is configured to receive a load from a seating object on which the head sits in a state in which the first member and the second member are fixed by the screw member, and the seat portion has a convex surface that is convexly curved toward the seating object between an outer circumferential edge and an inner circumferential edge of the seat portion.

[0065] <Supplementary Note 2> A screw member according to Supplementary Note 1, comprising: a washer having a through hole formed therethrough in the axial direction; the second shank being inserted into the through hole; the washer having a contact surface at one end in the axial direction that comes into contact with the first member when the first member and the second member are fixed by the screw member, and an opposing surface at the other end in the axial direction that faces the head in the axial direction; the seating object is the opposing surface; and the opposing surface faces the convex surface in the axial direction, and has a concave surface that curves concavely along the convex surface.

[0066] <Supplementary Note 3> The screw member according to Supplementary Note 1 or Supplementary Note 2, wherein the shank has an insertion end on an opposite side to the head in the axial direction, and includes a guide portion extending from the insertion end to an opposite side to the head and guiding insertion of the shank into the first insertion hole, and the guide portion has an inclined portion whose outer diameter decreases with increasing distance from the insertion end in the axial direction.

[0067] S...seating object, X...axial direction, 10...screw member, 20...head, 22...second head end surface (as seating portion), 22a...outer peripheral edge, 22b...inner peripheral edge, 22c...convex surface, 30...shank portion, 32...insertion end, 33...first thread portion, 34...second thread portion, 35...first thread portion (as male thread), 40...washer, 41...through hole, 42...opposing surface, 42c...concave surface, 45...second thread portion (as female thread), 50...guiding portion, 52...inclined portion.

Claims

1. A screw member including a head and a shaft portion extending axially from the head, wherein the shaft portion has a columnar first shaft portion extending in the axial direction and a columnar second shaft portion extending in the axial direction between the first shaft portion and the head in the axial direction and having an outer diameter smaller than that of the first shaft portion, the head has a seating portion configured to receive a load from a seating target on which the head is seated, and the seating portion has a convex surface that curves convexly toward the seating target between an outer peripheral edge and an inner peripheral edge of the seating portion.

2. The screw member according to claim 1, further comprising a washer having a through hole formed therethrough in the axial direction, the washer having a facing surface facing the head, the seating target being the facing surface, and the facing surface having a concave surface that faces the convex surface in the axial direction and curves concavely along the convex surface.

3. The screw member according to claim 2, wherein a male screw is formed on the first shaft portion, a female screw is formed in the through hole, and the washer is configured to be displaceable in the axial direction by being rotated with respect to the shaft portion while the female screw is screwed onto the male screw.

4. The screw member according to any one of claims 1 to 3, wherein the shaft portion has an insertion end on the side opposite to the head in the axial direction, and includes a guide portion extending from the insertion end to the side opposite to the head, and the guide portion has an inclined portion whose outer diameter decreases as it moves away from the insertion end in the axial direction.

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