JP5080523B2 - Fastening structure - Google Patents

Description

  The present invention relates to a structure for suppressing potentiometric corrosion in a fastening structure.

  Conventionally, steel bolts are used for fastening automobile parts. In addition, it is known to reduce the weight of a vehicle by manufacturing automotive parts using a magnesium alloy. However, when a magnesium alloy automotive part is fastened with a conventionally used iron bolt, the potential (ionization tendency) of the magnesium alloy and iron is greatly different, so the potential is low (ionization tendency is high). Potential difference corrosion occurs on the alloy side. Thereby, the contact area of a volt | bolt and automotive components reduces, and the fastening axial force of a volt | bolt falls.

  Therefore, it is known that the corrosion of the magnesium alloy part is suppressed by coating the bolt or by providing a chemical-treated washer between the bolt and the magnesium alloy.

  In Patent Document 1, a washer is interposed between a bolt and a magnesium alloy part, and a convex portion surrounding the side surface of the washer is provided on the magnesium alloy member, and this convex portion is preferentially corroded. A technique for suppressing corrosion of a contact surface between a bolt and a magnesium alloy part is described.

JP 2008-32038 A

  However, each of the conventional techniques has a problem that the cost increases.

  An object of the present invention is to suppress the progress of potentiometric corrosion while suppressing an increase in cost.

The present invention relates to a fastening structure including a bolt and a member that is fastened by the bolt and is made of a metal having a lower potential than the bolt. And the protrusion is pushed into the member when the bolt is fastened.

Further, the present invention provides a fastening structure including a nut and a member that is fastened by the nut and configured by a metal having a lower potential than the nut. It has the projection part formed automatically, and a projection part is pushed into a member at the time of nut fastening, It is characterized by the above-mentioned.

  According to the present invention, at least one of the bolt head and the nut is provided with a protrusion formed continuously on the outer periphery of the surface in contact with the member, and the protrusion is pushed into the member when the bolt or nut is fastened. Even if potential difference corrosion occurs between the bolt or nut and the member, it is possible to suppress the corrosion from proceeding from the outer peripheral side to the center side of the bolt or nut due to the protrusion as a wall.

It is a block diagram which shows the structure of the fastening structure in this embodiment. It is a block diagram which shows the structure of the fastening structure in a prior art example. It is an enlarged view which shows the range A of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram showing a configuration of a fastening structure in the present embodiment. The fastening structure 10 includes a bolt 1 and a nut (not shown), and an automotive part 2 fastened by the bolt 1 and the nut. The bolt 1 is an iron bolt and is used for fastening the automotive part 2. The bolt 1 includes a head portion 5 and a shaft portion 6, and has a flange portion 3 having a diameter larger than that of the head portion 5 on the shaft portion side of the head portion 5. Therefore, when the bolt 1 is fastened, the flange portion 3 of the bolt 1 is pressed against the automotive part 2. The automotive part 2 is, for example, a mission case or an oil pan, and is made of a magnesium alloy for weight reduction.

  When moisture adheres between the flange part 3 of the bolt 1 and the magnesium alloy part 2 in a state where the magnesium alloy part 2 is tightened with the bolt 1, the potential difference corrosion is applied to the part in contact with the flange part 3 in the magnesium alloy part 2. Will occur. That is, since the electric potential (ionization tendency) of iron constituting the flange portion 3 and magnesium constituting the magnesium alloy part 2 is greatly different, the local battery using both as electrodes and water existing between the two as an electrolyte solution. And a local current flows from the precious metal iron to the base metal magnesium. As a result, magnesium becomes metal ions and dissolves in water as an electrolyte solution, so that the magnesium alloy part 2 is corroded.

  Since the potential difference corrosion is caused by moisture adhering from the outside, it is generated from the outer peripheral side of the flange portion 3 and gradually proceeds to the center side of the bolt 1. As corrosion progresses and the stress generating part of the magnesium alloy part 2 is eroded, the contact area between the flange part 3 and the magnesium alloy part 2 decreases, and the fastening force of the bolt 1 decreases.

  Therefore, in the present embodiment, as shown in FIG. 1, a protruding portion 4 that protrudes in the pressing direction is provided along the outer peripheral edge of the surface 3 a that is the flange portion 3 and pressed against the magnesium alloy component 2. The protruding portion 4 is formed in a wedge shape so that the thickness decreases toward the tip, and is provided over the entire circumference of the flange portion 3.

  Since magnesium is harder than magnesium alloy and iron, when the magnesium alloy part 2 is fastened with the bolt 1, the tip of the protrusion 4 is pushed into the magnesium alloy part 2 by the fastening force.

  Here, the effect of this embodiment by providing the projection part 4 in the flange part 3 of the volt | bolt 1 is demonstrated, comparing with the conventional volt | bolt. FIG. 2 is a configuration diagram showing a configuration of a fastening structure according to a conventional example.

  As shown in FIG. 2, in the conventional example, when moisture adheres between the flange portion 3 and the magnesium alloy part 2, the magnesium alloy part 2 is corroded, and the corrosion progresses one after another toward the center of the bolt 1. Go.

  On the other hand, in this embodiment, since the protrusion 4 is pushed into the magnesium alloy part 2, even if corrosion occurs, the protrusion 4 becomes a wall and the progress of corrosion can be suppressed.

  This corrosion inhibiting action will be further described with reference to FIG. 3 which is an enlarged view of range A in FIG. When the corrosion of the magnesium alloy part 2 occurs in the vicinity of the outer peripheral end of the flange portion 3, the protrusion 4 is pushed into the magnesium alloy part 2, so that the corrosion is caused by the protrusion 4 and the magnesium alloy part 2. It progresses in the downward direction of FIG. That is, it is possible to prevent the protrusion 4 from becoming a wall and causing corrosion to proceed toward the center side of the bolt 1 (left direction in FIG. 3).

  In any case, the corrosion reaches the tip of the protrusion 4 and then proceeds toward the center of the bolt 1, but the progress of corrosion is suppressed as compared with the conventional example in which the protrusion 4 is not provided. The In particular, it is possible to suppress and prevent the progress of the fastening stress directly below the flange where the stress is most concentrated.

  As described above, in the present embodiment, the protrusion 4 is provided in the vicinity of the outer peripheral end of the surface 3a of the flange 3 of the bolt 1 that is pressed against the magnesium alloy component 2, and the protrusion 4 is the magnesium alloy component 2. Therefore, it is possible to prevent the potential difference corrosion from proceeding from the outer peripheral side to the center side of the bolt 1 by using the protrusion 4 as a wall. Thereby, it can prevent that corrosion advances to the bolt center side, the contact area of the volt | bolt 1 and the magnesium alloy components 2 falls, and the fastening force of the volt | bolt 1 falls. Further, since the progress of corrosion can be suppressed with a simple structure in which the protrusions 4 are formed on the bolt 1, an increase in cost can be suppressed (corresponding to claim 2).

  Moreover, since the protrusion part 4 is provided in the surface 3a pressed by the magnesium alloy components 2 of the flange part 3 over a perimeter, it can further suppress progress of corrosion to the bolt 1 center side. Correspondence).

  The present invention is not limited to the embodiment described above, and various modifications and changes can be made within the scope of the technical idea.

  For example, in the present embodiment, the bolt 1 is described as a flanged bolt, but a bolt without the flange portion 3 may be used, and the protrusion 4 may be provided on the surface of the bolt head that is pressed against the automotive component 2. The same effect as this embodiment can be obtained (corresponding to claim 1).

  Further, in the present embodiment, the automotive part 2 is fastened by the bolt 1, but it may be fastened by using a nut or a nut with a flange instead of the bolt 1. In this case, the same effect as this embodiment can be obtained by providing the protrusion 4 on the surface of the nut or the flange portion of the nut that is pressed against the automotive part 2 (corresponding to claims 5 and 6). ).

  Furthermore, even if a washer is interposed between the bolt 1 or the nut and the automotive part 2 and the protrusion 4 is provided on the surface of the washer that is pressed against the automotive part 2, the same effect as the present embodiment is achieved. Can be obtained (corresponding to claims 3 and 7).

  In addition, when providing the projection part 4 in the above-mentioned volt | bolt, a bolt with a flange, a nut, a nut with a flange, or a washer, all may provide the projection part 4 over a perimeter, or it may provide it in several places (claim). Corresponding to items 4 and 8).

  In the present embodiment, the cross-sectional shape of the protrusion 4 is described as a wedge shape, but other shapes may be used as long as the shape is pushed into the magnesium alloy component 2 when the bolt 1 is fastened.

  In this embodiment, the projection 4 is pushed into the magnesium alloy part 2 when the bolt 1 is fastened. However, a groove having a shape corresponding to the projection 4 is provided in the magnesium alloy part 2 in advance. Also good.

  Furthermore, in this embodiment, although the example in which the protrusion 4 is formed along the outer peripheral end has been described, the surface pressure of the pressed surface 3a may be increased, and the protrusion 4 is formed on the inner side of the outer peripheral end. Also good.

DESCRIPTION OF SYMBOLS 1 Bolt 2 Parts made from magnesium alloy 3 Flange part 3a Surface 4 Projection part 5 Head part 6 Shaft part 10 Fastening structure

Claims (8)

In a fastening structure comprising a bolt and a member fastened by the bolt and made of a metal having a lower potential than the bolt,
The head portion of the bolt has a protrusion formed continuously on the outer periphery of the surface on the surface pressed against the member when the bolt is tightened, and the protrusion is pushed into the member when the bolt is tightened. The fastening structure characterized by this. The head of the bolt has a flange portion larger in diameter than the head between the member,
2. The fastening structure according to claim 1, wherein the projecting portion is continuously provided on an outer periphery of a surface of the flange portion that is pressed against the member, and is pushed into the member when the bolt is fastened. . A washer interposed between the bolt and the member;
2. The protrusion according to claim 1, wherein the protrusion is continuously provided on an outer periphery of a surface that is the washer and is pressed against the member when the bolt is fastened, and is pushed into the member when the bolt is fastened. Fastening structure.   The fastening structure according to any one of claims 1 to 3, wherein the protrusion is provided over the entire circumference along the outer periphery. In a fastening structure comprising a nut and a member that is fastened by the nut and is made of a metal having a lower potential than the nut,
The nut has a protrusion continuously formed on an outer periphery of the surface on a surface pressed against the member when the nut is tightened, and the protrusion is pushed into the member when the nut is tightened. Fastening structure. The nut has a flange portion larger in diameter than the nut between the member and
The fastening structure according to claim 5, wherein the protrusion is continuously provided on an outer periphery of a surface of the flange that is pressed against the member, and is pushed into the member when the nut is fastened. . A washer interposed between the nut and the member;
The said protrusion part is a said washer, and is continuously provided in the outer periphery of the surface pressed by the said member at the time of the said nut fastening, It is pushed into the said member at the time of the said nut fastening. Fastening structure.   The fastening structure according to any one of claims 5 to 7, wherein the protrusion is provided over the entire circumference along the outer periphery.

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