FASTENING TOOL WITH EARTH FUNCTION

Abstract

A fastening tool according to the invention includes: a female screw member (10) having an inverse screw that is fixed to the first member (1); a collar bolt (11) that is screwed with the female screw member (10); a fastening bolt (27) that is inserted into a center hole (19) of the collar bolt (11) from the second member side (2) and rotates the collar bolt (11) through a torque transmitter (25), thereby moving the collar bolt to a position colliding with the second member (2); and a fastening nut (33) that is fixed to the first member (1). An earth claw (21) protruding toward the second member (2) is formed at an outer periphery of an end surface of the collar bolt (11) facing the second member. The earth claw (21) is configured to bite into the second member (2) in an axial direction due to axial force generated by screwing the fastening bolt (7) with the fastening nut (33), thereby breaking an insulating coating layer (3) and thus ensuring electrical conduction.

Claims

1. A fastening tool with an earth function that fastens a first member and a second member to each other while keeping a mutual clearance, comprising: a female screw member having an inverse screw that is fixed to the first member; a collar bolt that is screwed with the female screw member; a fastening bolt that is inserted into a center hole of the collar bolt from the second member side and rotates the collar bolt through a torque transmitter, thereby moving the collar bolt to a position colliding with the second member; and a fastening nut that is attached to the first member and is screwed with a male screw of the fastening bolt, wherein an earth claw having elasticity is formed at an outer periphery of an end surface of the collar bolt facing the second member by protruding toward the second member and forming a rear surface thereof into a recess.

2. The fastening tool with the earth function according to claim 1, wherein the earth claw is configured to bite into the second member in an axial direction due to axial force generated by screwing the fastening bolt with the fastening nut.

3. The fastening tool with the earth function according to claim 1, wherein the torque transmitter is configured to be plural leaf springs formed around the center hole of the collar bolt.

4. The fastening tool with the earth function according to claim 1, wherein the collar bolt includes a flange formed on the end surface thereof facing the second member and the earth claw is plurally formed at an outer periphery of the flange.

5. The fastening tool with the earth function according to claim 4, wherein the earth claw is configured to have a shape of obliquely protruding toward an outer periphery from a surface of the flange.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] [FIG. 1]

[0021] FIG. 1 is a central vertical sectional view illustrating a state where a fastening tool according to the invention is attached to a first member.

[0022] [FIG. 2]

[0023] FIG. 2 is a central vertical sectional view illustrating a state where a fastening bolt is inserted into a collar bolt.

[0024] [FIG. 3]

[0025] FIG. 3 is a central vertical sectional view illustrating a state where the collar bolt is moving.

[0026] [FIG. 4]

[0027] FIG. 4 is a central vertical sectional view illustrating a state where the collar bolt collides with a second member.

[0028] [FIG. 5]

[0029] FIG. 5 is a central vertical sectional view illustrating a state where the fastening bolt starts to be screwed with a fastening nut.

[0030] [FIG. 6]

[0031] FIG. 6 is a central vertical sectional view illustrating a state of a fastening completion.

[0032] [FIG. 7]

[0033] FIGS. 7-A and 7-B are a front view and a plan view of the collar bolt.

[0034] [FIG. 8]

[0035] FIGS. 8-A and 8-B are diagrams for describing operation of an earth claw.

DESCRIPTION OF EMBODIMENTS

[0036] An embodiment of the invention will be described below. FIG. 1 is a central vertical sectional view illustrating a state where a fastening tool according to the invention is attached to a first member 1. A second member 2 is positioned so as to be slightly spaced apart from the first member 1. An insulating coating layer 3 is formed on a surface of the second member. For convenience of description, as illustrated in FIG. 1, the second member 2 is assumed to be on an upper side of the first member 1 in the following description. In this embodiment, the second member is a painted body panel of a vehicle, but is not naturally limited thereto.

[0037] Reference numeral 10 represents a cylindrical female screw member, and reference numeral 11 represents a collar bolt which is screwed with the female screw member 10. Both of them are made of metal. In this embodiment, the female screw member 10 is held inside a resinous clip 12. The resinous clip 12 is provided with a pair of leg portions 13 on lower ends thereof, and an elastic claw 15 provided with a projection 14 on the outside thereof is projected upward at a tip of the leg portion 13. When the leg portions 13 are inserted and pushed into attachment holes 16 formed on the first member 1, the elastic claws 15 pass through the attachment holes 16 while elastically being deformed inward, the projections 14 come in contact with a rear surface of the first member 1 as illustrated in FIG. 1, and the clip 12 and the female screw member 10 are fixed to an upper surface of the first member 1. In addition, the female screw member 10 can be fixed to the first member 1 using various fixing units which are not principal part of the invention.

[0038] A female screw 17 of the female screw member 10 is an inverse screw (leftward screw), and a male screw 18 of the collar bolt 11 is also similar. The collar bolt 11 is a cylindrical body having a center hole 19, and a circular flange 20 is formed on an upper end surface of the collar bolt which faces the second member 2. As illustrated in FIGS. 7-A and 7-B, a plurality of earth claws 21 is formed at an outer periphery of the end surface of the flange 20. An inclination angle of the earth claws 21 is preferably 15 to 30 degrees with respect to a flange surface. Each of the earth claws 21 is configured to have elasticity in such a manner that the outer side thereof protrudes upward toward the second member 2 and the rear surface thereof is formed into a recess 22. Four earth claws 21 are formed at equal intervals in this embodiment, but the number of the earth claws is arbitrary and is preferably to be two to six. The outer periphery of the flange 20 is bent upward by press working, thereby forming such an earth claw 21. In addition, since edges 23 of the earth claws 21 are portions which bite into an insulation coating layer, it is preferable to have an aculeate shape. In a state of a fastening start, the collar bolt 11 is deeply screwed into the female screw member 10 in FIG. 1, and the flange 20 is accommodated in a recess 24 formed at a top of the resinous clip 12.

[0039] A torque transmitter 25 is provided in a center hole 19 of the collar bolt 11. The torque transmitter 25 can transmit torque up to predetermined torque, but has a function of not transmitting the torque due to slip when exceeding the predetermined torque. In this embodiment, the torque transmitter 25 includes plural leaf springs. As illustrated in FIG. 1, a part of a peripheral wall of a cylinder 26 is bent inward, thereby forming the leaf spring, and the cylinder 26 is pressed into the center hole 19 of the collar bolt 11. The torque transmitter 25 is a unit which is engaged with a male screw 28 of a fastening bolt 27, which is inserted into the center hole 19 of the collar bolt 11, while being elastically deformed and thus transmits rotational torque of the fastening bolt 27 to the collar bolt 11. The torque transmitter 25 is not limited to the leaf spring, but a conventionally-known resin or various torque transmitters can be used.

[0040] An ordinary bolt having a head portion 29 and a shaft portion 30 can be used as the fastening bolt 27. Bolt insertion holes 31 and 32 are formed in the first member 1 and the second member 2, respectively. In addition, a fastening nut 33 is attached to the rear surface of the first member 1. The fastening nut 33 is attached to the first member 1 in an arbitrary manner and may be attached to the rear surface of the first member 1 by, for example, welding.

[0041] A fastening method using a fastening tool according to the embodiment will be described below.

[0042] First, as illustrated in FIG. 1, the female screw member 10 is fixed to the first member 1 by the clip 12. Next, as illustrated in FIG. 2, the fastening bolt 27 is strongly inserted into the center hole 19 of the collar bolt 11 from the bolt insertion hole 32 of the second member 2, and thus the male screw 28 is engaged with the torque transmitter 25 of the collar bolt 11. As illustrated in FIG. 2, the leaf spring as the torque transmitter 25 is elastically deformed outward and comes in closely contact with the male screw 28 of the fastening bolt 27. When the fastening bolt 27 rotates in a screwing direction (right direction) from this state, the collar bolt 11 also rotates due to the action of the torque transmitter 25, but a screwed portion between the collar bolt 11 and the female screw member 10 is in an inversely screwed (leftward screwed) state. Moreover, the female screw member 10 is fixed to the first member 1. For this reason, the collar bolt 11 moves in an axial direction so as to get out of the female screw member 10 while rotating and advances toward the first member 1 as illustrated in FIG. 3.

[0043] When the fastening bolt 27 further rotates, the flange 20 on the upper surface of the collar bolt 11 collides with the rear surface of the second member 2 as illustrated in FIG. 4. When reaching the state illustrated in FIG. 3, the collar bolt 11 can no longer move in the axial direction, so that torque required for rotating the fastening bolt 27 is rapidly raised. Then, when the torque required for rotating the fastening bolt exceeds the transmissible torque of the torque transmitter 25, the torque transmitter 25 malfunctions and the fastening bolt 27 independently moves downward as illustrated in FIG. 5 while being slipped from the surface of the torque transmitter 25. When the torque transmitter 25 is configured by the leaf spring, the fastening bolt 27 can quickly move while being slipped. Then, finally, as illustrated in FIG. 6, the male screw 28 of the fastening bolt 27 is screwed with the fastening nut 33 on the rear surface of the first member 1 and the first member 1 and the second member 2 are fastened to each other while keeping a clearance.

[0044] In the state where the collar bolt 11 abuts on the second member 2 as illustrated in FIG. 4, the edge 23 of the earth claw 21 contacts with the second member 2 as illustrated in FIG. 8-A. In this state, the insulating coating layer 3 of the second member 2 has not been broken. In a state of a fastening completion as illustrated in FIG. 6, however, since a large axial force (tightening force in the axial direction) is generated by the fastening, the earth claw 21 is elastically deformed and thus the edge 23 of the earth claw 21 bites into the insulating coating layer 3 of the second member 2 due to reaction force thereof as illustrated in FIG. 8-B. Therefore, it is possible to ensure an electrical conduction with the second member 2. Since the biting is performed in the axial direction by the large axial force due to the fastening, the insulating coating layer 3 can be surely broken.

[0045] In the case of using the fastening tool according to the invention as described above, the first member 1 and the second member 2 positioned so as to be spaced apart from each other can be fastened to each other while keeping a mutual clearance. Moreover, the insulating coating layer 3 of the second member 2 is broken by the earth claw 21 at the same time of the fastening and thus the fastening tool and the second member 2 can be electrically conducted to each other. In addition, since the first member 1 has no insulating coating layer on, it can ensure the electrical conduction as indicated by the arrow in FIG. 6 by letting the female screw member 10 contacted to the first member 1. Therefore, it is possible to ensure the electrical conduction between the first member 1 and the second member 2 using the fastening tool according to the invention.

REFERENCES SIGNS LIST

[0046] 1: first member [0047] 2: second member [0048] 3: insulating coating layer [0049] 10: female screw member [0050] 11: collar bolt [0051] 12: clip [0052] 13: leg portion [0053] 14: projection [0054] 15: elastic claw [0055] 16: attachment hole [0056] 17: female screw of female screw member [0057] 18: male screw of collar bolt [0058] 19: center hole [0059] 20: flange [0060] 21: earth claw [0061] 22: recess [0062] 23: edge [0063] 24: recess [0064] 25: torque transmitter [0065] 26: cylinder [0066] 27: fastening bolt [0067] 28: male screw [0068] 29: head portion [0069] 30: shaft portion [0070] 31: bolt insertion hole [0071] 32: bolt insertion hole [0072] 33: fastening nut