Fastening device

A fastening device permitting two separate members to be fixed together with a relative interval between them including a bolt with a male screw portion formed at a front end side of a cylindrical shaft portion thereof and a spacer having a female screw portion engaging a male screw portion and screw-fastens with a screw of a first member side and rotates while receiving a rotation torque from the bolt and moves up to a position in which it comes into a contact with a second member. The root diameter of a male screw portion is smaller than the diameter of a cylindrical shaft portion while the inside diameter of the female screw portion is larger than the diameter of the cylindrical shaft portion. Consequently, the cylindrical shaft portion can be passed through the female screw portion even if the diameter of the cylindrical shaft portion is not reduced in diameter by cutting processing.

BACKGROUND OF THE INVENTION

The present invention relates to a fastening device for fastening two separate members with each other with a relative interval between them.

Conventionally, the fastening devices for fastening two members with a relative interval between them have been already disclosed in the technical field of automobile and the like. For example, Japanese Patent Application Laid-Open No. 2002-347656 has disclosed a fastening device comprising a sleeve welded on one component of the two separate members, a spacer screw-fastening with the sleeve through an inverse screw and a bolt having a male screw portion capable of screw-fastening with a female screw portion formed in the spacer at a front end of a shaft portion.

The male screw portion of the bolt of this fastening device is coated with adhesive agent capable of transmitting a predetermined torque to the spacer and when the bolt is tightened, the spacer is rotated due to a transmission torque, so that it is pulled out from the sleeve. However, because if the spacer comes into a contact with the other member, it cannot rotate further, the male screw portion formed at the front end of the bolt is released from the female screw portion and advanced so as to screw-fasten with the female screw portion of the sleeve, so that the two members are fastened with each other with an interval by the spacer. To allow the bolt to be advanced quickly at this time, it is preferable to obtain a structure capable of passing through the female screw portion of the spacer without rotating the shaft portion of the bolt.

Because such a bolt is produced at the front end portion of a cylindrical blank according to the method of rolling the male screw portion, the root diameter of the male screw portion is formed smaller than the blank diameter (diameter of a cylindrical portion) of the bolt. Thus, because the inside diameter of the female screw portion of the spacer which screw-fastens with the male screw portion is smaller than the diameter of the cylindrical portion of the bolt, the cylindrical portion of the bolt cannot pass through the female screw portion of the spacer. Thus, the cylindrical portion of the bolt needs to be reduced in diameter by additional processing such as cutting processing and plastic deformation so that it is capable of passing through the female screw portion of the spacer. For the reason, processing steps for the bolt increases and further, manufacturing cost rises.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been accomplished to solve the above described conventional problem and an object of the invention is to provide a fastening device which enables a bolt to be produced by rolling at a low cost and is capable of fixing together two separate members with a relative interval between them like the conventional product.

To achieve the above-described object, according to the present invention, there is provided a fastening device comprising a bolt in which a male screw portion is formed at a front end of a cylindrical shaft portion thereof and a female screw portion which engages the male screw portion of the bolt, the fastening device further comprising a spacer which is screw-fastened with a screw of the first member side and rotated while receiving a rotation torque from the bolt through a torque transmitting means provided between the both so that it moves up to a position apart from the first member in which it collides with a second member, when the spacer moves to the position in which the spacer collides with the second member, the male screw portion of the bolt being released from the female screw portion of the spacer so as to fix the first member and the second member together, wherein the root diameter of the male screw portion of the bolt is smaller than the diameter of the cylindrical shaft portion while the inside diameter of the female screw portion of the spacer is larger than the diameter of the cylindrical shaft portion of the bolt.

The screw of the first member side may be formed in the sleeve provided on the first member or directly in the first member. Further, the screw of the spacer which screw-fastens with the screw of the first member side may be of inverse screw or of normal screw. Further, the female screw portion which screw-fastens with the male screw portion of the bolt released from the female screw portion of the spacer may be a nut welded on one member or a nut which is held by one member such that it can be played. As the torque transmitting means provided between the male screw portion of the bolt and the female screw portion of the spacer, various means such as a method of modifying part of the thread and covering part of the thread with elastic agent can be adopted appropriately as well as the method with adhesive agent.

The fastening device of the present invention is used for fixing the first and second members kept separately with a relative interval between them and the male screw portion of the bolt is fastened with the female screw portion of the spacer so as to transmit a torque to the spacer and the spacer is moved up to a position in which it collides with the second member. Because with this condition, the rotation of the spacer is stopped, the male screw portion of the bolt is released from the female screw portion of the spacer and advanced so as to fix the first member and the second member together, like the conventional fastening device.

However, because in the fastening device of the present invention, the root diameter of the male screw portion of the bolt is smaller than the diameter of the cylindrical shaft portion and the inside diameter of the female screw portion of the spacer is larger than the diameter of the cylindrical shaft portion of the bolt, the cylindrical shaft portion of the bolt can be passed through the female screw portion of the spacer even if the diameter of the cylindrical portion of the bolt is not reduced in diameter by additional processing such as cutting processing and plastic deformation. Because the bolt can be produced by only rolling and no additional processing is needed for the cylindrical shaft portion, manufacturing cost does not rise so much. Although according to the present invention, engagement between the male screw portion of the bolt and the female screw portion of the spacer is shallower than in the conventional product, by providing at least one of the male screw portion of the bolt and the female screw portion of the spacer with a torque transmitting means, the rotation force of the bolt can be transmitted effectively to the spacer so that the spacer can be pulled out smoothly and securely from the sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIGS. 1-6show the first embodiment of the present invention and the fastening device of this embodiment comprises a bolt1, a spacer10and a sleeve20. The bolt1is constituted of a head portion2, a cylindrical shaft portion3and a normal screw type male screw portion4formed on a front end thereof. The male screw portion4is formed by rolling a blank having the same diameter as the cylindrical shaft portion3and the cylindrical shaft portion3is not subjected to reduction of its diameter by cutting processing or the like. Thus, as shown inFIG. 2, the thread diameter d3 of the male screw portion4of the bolt1is larger than the diameter d1 of the cylindrical shaft portion3and the root diameter d4 of the male screw portion4is smaller than the diameter d1 of the cylindrical shaft portion3. In the meantime, a rod portion5, which is smaller in diameter than the root diameter d4 of the male screw portion4, is formed at the front end of the male screw portion4. According to this embodiment, the male screw portion4is coated with adhesive agent S as a torque transmitting means for transmitting a rotation force of the bolt to the spacer10. The adhesive agent S used here is nylon which is marketed in the name of “TORQ-PATCH” having a permanent plasticity. However, the torque transmitting means is not restricted to the adhesive agent S but it is permissible to adopt an appropriate means by, for example, transmitting a predetermined torque by deforming part of the thread.

The spacer10is comprised of a cylindrical portion11and a sheet-like portion13extending outward from an outer periphery of one end of the same cylindrical portion11. An inverse screw type male screw portion12is formed in the outer peripheral face of the cylindrical portion11. A screw hole14smaller than the inner diameter of the cylindrical portion11is formed in the central portion of the sheet-like portion13. A female screw portion15capable of screw-fastening the male screw portion4of the bolt1is formed in the peripheral face of this screw hole14. As described later, the crests of the threads of the female screw portion15of the spacer10are cut out in a predetermined quantity.

The sleeve20has an inner diameter substantially equal to the outer diameter of the cylindrical portion11of the spacer10and has a cylindrical portion21extending slightly longer than the cylindrical portion11. A female screw portion22which is an inverse screw capable of screw-fastening the male screw portion12formed on the outer peripheral face of the cylindrical portion11of the spacer10is formed in the inner peripheral face of the cylindrical portion21.

Further, a sheet-like portion23having a predetermined thickness is provided at an end portion of the cylindrical portion21of the sleeve20such that it closes an opening portion of the cylindrical portion21. This sheet-like portion23is in a larger diameter than the cylindrical portion21and a screw hole24having a smaller diameter than the inner diameter of the cylindrical portion21is made substantially in the central portion of the sheet-like portion23. A female screw portion25capable of screw-fastening the male portion4of the bolt1is formed in the peripheral face of this screw hole24. This female screw portion25has a normal thread shape corresponding to the male screw portion4of the bolt1.

The male screw portion4of the bolt1screw-fastens with the female screw portion15of the spacer10. As shown inFIG. 2, the section of the thread of the male screw portion4of the bolt1is triangular and the section of the thread of the female screw portion15of the spacer10is substantially trapezoidal because its crest is cut out. The inner diameter d2 of the female screw portion15is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1. That is, the root diameter d4 of the male screw portion4of the bolt1is smaller than the diameter d1 of the cylindrical shaft portion3and the inside diameter d2 of the female screw portion of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1. Thus, there is a relation of d2>d1>d4.

To form the configuration in which the crests of the threads of the female screw portion15are cut out, it is permissible to, after the screw shape is formed on the peripheral face of the screw hole14of the spacer10, cut out the crests of the threads so that the inside diameter thereof is constant or after the screw hole14whose inside diameter is of the aforementioned constant diameter is formed, form the screw shape in the peripheral face of the screw hole14.

A method for maintaining and fixing the two separate members using the aforementioned fastening device will be described with reference toFIGS. 3-6. Here, a case of fastening a first member40with a second member50located at a distance L1 with an interval maintained will be described. The first member40is, for example, a side plate of automobile and the second member50is, for example, automobile front pillar.

As shown inFIG. 3, first, the sleeve20is fixed to the first member40. More specifically, after the cylindrical portion21of the sleeve20is inserted into the through hole41provided in the first member40, the sheet-like portion23is brought into a contact with an face opposite to the insertion direction of the sleeve20of the first member40and both the members are fixed together by welding. The spacer10is screw-fastened with the sleeve20completely until the sheet-like portion13of the spacer10makes a contact with the cylindrical portion21of the sleeve20. As described previously, according to this embodiment, the spacer10is screw-fastened with the sleeve20through the inverse screw.

Next, the bolt1is inserted into the through hole51made in the second member50from the opposite side of the first member40. Then, if the bolt1is rotated in the normal screwing direction (clockwise direction) with the male screw portion4of the bolt1screw-fastened with the female screw portion15of the spacer10, a rotation torque is transmitted from the bolt1to the spacer10through the adhesive agent S which is a torque transmitting means provided between the both so that the bolt1and the spacer10are rotated integrally in the normal direction.

Due to the rotation of this spacer10, the spacer10screw-fastened with the sleeve20through the inverse screw is rotated in a loosening direction so that it is moved in the direction of escaping from the sleeve20. Then, as shown inFIG. 5, the spacer10moves until the sheet-like portion13makes contact with the second member50. When the position shown inFIG. 5is reached, the spacer10reaches a condition in which it is never rotated further due to friction resistance. Thus, if a predetermined torque is applied to the bolt1, the male screw portion4of the bolt1passes through the female screw portion15of the spacer10and escapes therefrom, so that as shown inFIG. 6, it advances further and is screwed through the female screw portion25of the sleeve20.

Because as described above, the inside diameter d2 of the female screw portion15of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1, after the cylindrical shaft portion3of the bolt1passes through the female screw portion15of the spacer10and escapes therefrom, it can pass through the female screw portion15of the screw hole14smoothly. Although the threads of the male screw portion4and the female screw portion15do not engage completely, there is no problem in terms of fastening strength because this condition is not a final fixing condition.

The bolt1advances until its male screw portion4reaches the female screw portion25formed in the screw hole24of the sleeve20and the male screw portion4screw-fastens with the female screw portion25of the sleeve20. Consequently, the first member40can be installed to the second member50strongly with an interval L1. Because at this time, the adhesive agent S applied to the male screw portion4of the bolt1adheres to the inside of the screw hole24of the sleeve20also, there is obtained an auxiliary effect of blocking loosening between the female screw portion25formed in the screw hole24and the male screw portion4.

As described above, because as for the fastening device of this embodiment, the inside diameter d2 of the female screw portion15of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1, the cylindrical shaft portion3of the bolt1can pass through the screw hole14of the spacer10smoothly, so that the cylindrical shaft portion3of the bolt1does not need to be reduced in diameter by cutting or the like. For the reason, a bolt produced by normal rolling processing can be employed, so that the fastening device can be provided at a lower cost than conventionally.

Second Embodiment

Although according to the first embodiment, the diameter of the sleeve20is set larger than the diameter of the spacer10and the both are screw-fastened with each other under conditions in which the spacer10is accommodated within the sleeve20, according to the second embodiment shown inFIG. 7, the diameter of the spacer10is set larger than that of the sleeve20, and the spacer10and the sleeve20are screw-fastened with each other under conditions in which the sleeve20is accommodated in the spacer10. The spacer10is comprises of the cylindrical portion11and the sheet-like portion13provided so as to close one opening portion of the cylindrical portion11and the female screw portion16is formed in the inner peripheral face of the cylindrical portion11. The screw hole14is made substantially in the central portion of the sheet-like portion13. The female screw portion15capable of screw-fastening with the male screw portion4of the bolt1is formed in the peripheral face of this screw hole14.

The sleeve20has an outside diameter substantially equal to the inside diameter of the cylindrical portion11of the spacer10and has a slightly longer cylindrical portion21than the cylindrical portion11. A male screw portion26capable of screw-fastening with the female screw portion16formed in the inner peripheral face of the cylindrical portion11of the spacer10is formed in the outer peripheral face of the cylindrical portion21. According to the second embodiment also, the root diameter d4 of the male screw portion4of the bolt1is smaller than the diameter d1 of the cylindrical shaft portion3and the inside diameter d2 of the female screw portion15of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3. Thus, there is a relation of d2>d1>d4.

According to the fastening device of the second embodiment also, the sleeve20is fixed to the first member and the bolt1is screw-fastened with the spacer10screw-fastened with this sleeve20through the inverse screw and rotated. The bolt1and the spacer10are screw-fastened with each other through the male screw portion4having the torque transmitting means and the female screw portion15of the spacer10. Because the inside diameter d2 of the female screw portion15is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1, after the male screw portion4of the bolt1passes through the screw hole14while screw-fastening with the female screw portion15of the spacer10, the cylindrical shaft portion3passes through the screw hole14smoothly. The contact area between the spacer10and the second member can be increased by forming the spacer10in a large diameter.

Third Embodiment

According to the third embodiment shown inFIGS. 8-11, the sleeve20is fixed to a first member40with a clip30. A nut31is welded on the rear face of the first member40. The other structure is the same as the first embodiment. As shown inFIG. 9, the bolt1is inserted into the female screw portion15of the spacer10through a through hole51of the second member50and rotated while transmitting a torque to the spacer10through the torque transmitting means so as to move the spacer10up to a position corresponding to the second member50inFIG. 10. After that, the male screw portion4of the bolt1is released from the female screw portion15of the spacer10and the bolt1is advanced and then, it is screw-fastened with a nut31welded on the rear face of the first member40.

Because according to the third embodiment, the root diameter d4 of the male screw portion4of the bolt1is smaller than the diameter d1 of the cylindrical shaft portion3and the inside diameter d2 of the female screw portion15of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1, there is a relation of d2>d1>d4. Although according to the first embodiment, the female screw portion25is formed in the spacer20, the third embodiment is different from the first embodiment in that the nut31is employed.

Fourth Embodiment

According to the above respective embodiments, an inverse screw is employed between the spacer10and the sleeve20and the bolt head portion of the spacer10is moved by a rotation of the bolt1. However, as indicated in this embodiment, it is permissible to employ a normal screw between the spacer10and the sleeve20. That is, as shown inFIG. 12, the sleeve20fixed on the first member40has the spacer10which is screw-fastened therewith through a normal screw portion33provided on the outer peripheral portion.

Thus, if the bolt1having the torque transmitting means is driven into the male screw portion4so as to rotate the spacer10, the spacer10is moved to the front end side of the bolt1as shown inFIG. 13and strikes a second member50so that it is stopped. According to this embodiment, a nut31is held by a nut holder34on the rear face of the second member50such that it is capable of being played within a certain area, the nut is automatically centered by the front end portion of the bolt1. Thus, if the bolt1is driven further from the condition ofFIG. 13, the male screw portion4of the bolt1is released from the female screw portion15of the spacer10, so that it is screw-fastened with the nut31on the rear face of the second member50and the fastening is completed.

Fifth Embodiment

Although the above-described respective embodiments all employ the spacer10and the sleeve20, an example that no sleeve20is employed will be described as the fifth embodiment shown inFIGS. 15-18. That is, according to the fifth embodiment, the first member40is directly provided with a female screw70and as shown inFIG. 15, the spacer10is driven into this female screw70together with the bolt1. The female screw70is of a normal screw and the spacer10moves until its front end comes into a contact with the second member50as shown inFIG. 16. Although not shown, according to this embodiment, by modifying part of the thread of the male screw portion of the bolt1, a torque transmitting means is produced.

Because the spacer10cannot rotate if the condition shown inFIG. 16is reached, the male screw portion4of the bolt1is released from the female screw portion15of the spacer10and advanced as shown inFIG. 17, so that it is screw-fastened with the nut31welded on the rear face of the second member50and the fastening is completed. According to the fourth and fifth embodiments also, the root diameter d4 of the male screw portion4of the bolt1is smaller than the diameter d1 of the cylindrical shaft portion3and the inside diameter d2 of the female screw portion15of the spacer10is larger than the diameter d1 of the cylindrical shaft portion3of the bolt1, there is a relation of d2>d1>d4 like the other embodiments.

The fastening devices of all the above-described embodiments can be manufactured with only rolling at a low coat without post processing of the bolt1. Further, two separate members can be fixed together with a relative interval like the conventional products. Needless to say, the nut31which can be played like the fourth embodiment can be used for the third embodiment and the fifth embodiment.