JP2015094434A - Fastening structure for dissimilar metal member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure that can facilitate component management and mounting work while preventing electrolytic corrosion in fastening a case that comprises dissimilar metal and a case cover to each other.SOLUTION: A case cover 20 made of magnesium alloy is superposed on a case 10 made of aluminum alloy, sandwiching an insulation gasket 30, and is coupled by using a bolt 40 made of steel. The insulation gasket includes: a main portion 31 sandwiched between mating surfaces of the case and the case cover; and an auxiliary portion 35 that is connected to the main portion via a connection piece 34 and is sandwiched between a head 41 of the bolt and the case cover. A flange 38 is erected from an outer peripheral predetermined range of the auxiliary portion. Since a portion in which ionization reaction may occur is insulated by one component, the number of component is reduced and mounting is facilitated. Since a portion of the auxiliary portion pressed by the head 41 is formed to have a conical shape in the free state, the portion functions as a conical spring washer, and thus looseness of the bolt can be inhibited without using an additional spring washer.

Description

  The present invention relates to a fastening structure for dissimilar metal members that prevents electrolytic corrosion due to a potential difference in ionization tendency between members fastened to each other.

Recently, vehicles have been required to be lighter, and in case of transmissions mounted on vehicles, the case cover is made of a similar metal such as steel, and the case cover is attached to the opening. Material changes such as dissimilar metals such as light magnesium alloys are underway.
Here, when different metals are in direct contact, a local battery is formed due to a potential difference when water or the like is present, and in the above case, so-called electrolytic corrosion that corrodes a magnesium alloy member having a low potential due to an ionization tendency. Occurs.

  As a countermeasure for this, for example, in Japanese Patent Laid-Open No. 5-125567, when a magnesium alloy member is attached to a steel strength member with a steel bolt, between the strength member and the magnesium alloy member, and between the steel bolt and the magnesium alloy. A washer or bush with a hard anodized film formed on the surface of each aluminum alloy is interposed as an insulating member between the base members, so that the magnesium alloy base member and the strength member are not in direct contact, and the steel bolt and magnesium The alloy-based member is also prevented from contacting directly. This prevents the magnesium alloy-based member from being corroded.

JP-A-5-125567

  However, in the above-mentioned JP-A-5-125567, in order to avoid contact between a magnesium alloy member having a low potential due to ionization and a steel bolt and a strength member having a high potential due to ionization, Two parts, a bush on the steel bolt side and a washer on the strength member side, are required across the member, resulting in an increase in the number of man-hours for parts management and assembling work, resulting in a cost increase.

  Therefore, in view of the above-described conventional problems, an object of the present invention is to provide a fastening structure for dissimilar metal members that can easily manage parts and assemble and reduce costs while preventing electrolytic corrosion.

Therefore, in the present invention, a second metal member having a lower ionization tendency than that of the first metal member is superimposed on the first metal member, and the first metal member is different from the second metal member. Fastening structure of dissimilar metal member in which the second metal member is pressed and fixed to the first metal member by the coupling member having the pressing portion located on the opposite side, and the coupling member is more ionized and has a higher potential than the second metal member. In
An insulating gasket is disposed between the first metal member and the second metal member;
The insulating gasket is connected to the main portion sandwiched between the mating surfaces of the first metal member and the second metal member, and to the main portion via the connection piece, and the second metal member and the coupling member are connected in the overlapping direction. It has a sub-part sandwiched between the pressing part.

  According to the present invention, it is necessary to separately set up a gasket to be disposed between the coupling member and the second metal member in addition to the gasket for preventing electrolytic corrosion between the first metal member and the second metal member. In addition, it is possible to insulate a portion where an ionization reaction can occur with a single component, facilitating assembly work, and reducing the number of components, thereby reducing costs.

It is a figure which shows the structure of embodiment of this invention. It is a figure which shows the state which removed the case cover and the volt | bolt in embodiment. It is sectional drawing which shows the insulation gasket of a free state. It is a figure which shows the change of the corrosion amount by the separation distance of steel and a magnesium alloy.

Hereinafter, an embodiment in which the present invention is applied to a case cover fastening portion for a transmission case will be described.
FIG. 1: shows the structure of the fastening structure concerning Embodiment, (a) is a partial top view, (b) is the AA part sectional drawing in (a). FIG. 2 is a view showing a state in which the case cover and the bolt are removed from FIG.
The case 10 is made of an aluminum alloy, and has an opening 18 at the upper end, as shown in FIG. 2, and a flange portion 12 having a flat fastening surface 13 around the entire upper surface along the opening edge. The opening 18 may be circular, rectangular or any other shape.

In particular, as shown in FIG. 1 (b), because of the bolt connection between the case 10 and the case cover, the boss portion 15 bulges outward from the side wall 11 of the case 10 along the opening edge at a predetermined interval.
A screw hole 16 is formed in the boss portion 15 so as to extend in parallel with the overlapping direction of the case cover 20 with respect to the case 10. In the boss portion 15, the flange portion 12 is widened so that the boss portion 15 includes the boss portion 15, and the upper end of the screw hole 16 is open to the fastening surface 13. On the other hand, the lower end of the screw hole 13 includes the pilot hole and does not penetrate the boss portion 15.

The case cover 20 is made of a magnesium alloy, covers the opening 18 of the case 10, and the lower peripheral surface is a lower mounting surface 23 that faces the fastening surface 13 of the case 10 and has a flat entire circumference. A mounting seat portion 25 having a predetermined plate thickness corresponding to the boss portion 15 of the case 10 is also provided on the periphery, and the lower surface of the mounting seat portion 25 forms a part of the lower mounting surface 23. A bolt through hole 26 corresponding to the screw hole 16 of the case 10 is formed in the mounting seat portion 25.
The upper surface of the mounting seat portion 25 is a flat upper mounting surface 27 that is parallel to the lower mounting surface 23.

An insulating gasket 30 is sandwiched between the case 10 and the case cover 20. The insulating gasket 30 is formed by coating an entire surface with nitrile rubber using an aluminum alloy plate as a core metal.
As shown in FIG. 2, the insulating gasket 30 includes a main portion 31 that forms a frame of the above-described arbitrary shape that is closed corresponding to the mating surfaces of the case 10 and the case cover 20, that is, the fastening surface 13 and the lower mounting surface 23. The main portion 31 is disposed between the fastening surface 13 of the case 13 and the lower mounting surface 23 of the case cover 20.
The width of the main portion 31 is also set to be equal to the width of the fastening surface 13 and the lower mounting surface 23. More preferably, as shown by the phantom line in FIG. That is, it is preferable to protrude outward from the outermost peripheral edge of the fastening surface 13 and the lower mounting surface 23. A portion of the main portion 31 corresponding to the boss portion 15 of the case 10 (boss portion corresponding portion 32) is formed with a first through hole 33 (see FIG. 1B) corresponding to the screw hole 16. .

  As shown in FIG. 1B, from the outermost peripheral edge of the boss portion corresponding portion 32 of the main portion 31, the connecting piece 34 extends outward by a predetermined amount, then bends at a right angle and extends vertically upward, A sub-part 35 extending inward and parallel to the main part 31 is connected to the tip. When the main portion 31 is protruded from the outermost peripheral edge of the fastening surface 13 and the lower mounting surface 23, the connection piece 34 may extend immediately vertically upward from the outermost peripheral edge of the boss portion corresponding portion 32.

As shown in FIG. 2, the sub-part 35 has a second through-hole 37 that is aligned with the first through-hole 33 of the main part 31 when viewed from above, and the disc is centered on the second through-hole 37. A bolt seat 36 is formed. A flange 38 extends upward from the outer peripheral edge of the bolt seat 36 except for a predetermined range including a connection portion with the connection piece 34.
FIG. 3 shows the insulating gasket 30 in a free state, and is a cross-sectional view taken along the line BB in FIG. As shown in FIG. 3, the disk-shaped bolt seat portion 36 of the sub portion 35 has a cone shape in which the hole edge side of the second through hole 37 at the center is higher than the peripheral edge.
The distance between the upper surface of the main part 31 and the lower surface of the sub part 35 (periphery thereof) is set to match the plate thickness of the mounting seat part 25 of the case cover 20.
The nitrile rubber of the insulating gasket 30 described above is preferably coated after molding.

The insulating gasket 30 having the main portion 31 sandwiched between the case 10 and the case cover 20 is in a state where the second through hole 37 of the sub portion 35 is aligned with the bolt through hole 26 of the mounting seat portion 25. 35 is seated on the upper mounting surface 27 of the mounting seat 25, in other words, the insulating gasket 30 has a configuration in which the mounting seat 25 of the case cover 20 is sandwiched between the main portion 31 and the sub-portion 35.
Further, the case 10 and the case cover 20 are aligned with the screw hole 16 of the boss 15 and the bolt through hole 26 of the mounting seat 25 by an alignment pin (not shown).
In this state, the screw shaft 42 of the steel bolt 40 passes through the second through hole 37 of the sub part 35, the bolt through hole 26 of the mounting seat part 25, and the first through hole 33 of the main part 31, and the boss The case cover 20 is coupled to the case 10 by being screwed into the screw hole 16 of the portion 15.

Generally, the tightening torque of the bolt is large and fluctuates depending on the surface roughness of the mating seat surface by die-casting or the like. Here, since the seat surface of the bolt 40 with respect to the head 41 is the insulating gasket 30 coated, High axial force can be obtained while tightening with torque. Further, since the head 41 of the bolt 40 has a hook, it can be tightened more smoothly.
The bolt seat portion 36 having the cone shape of the sub portion 35 functions in the same manner as a disc spring washer that is elastically deformed into a flat state by screwing the bolt 40, and the bolt 40 is prevented from loosening. Unlike general spring washers, there is no cut on the circumference, so even if water is applied after fastening, water does not enter the bolt through hole 26 of the case cover 20 from around the bolt seat portion 36.
Further, the bolt 40 is screwed at the case 10 and the boss portion 15, and there is a potential difference in ionization tendency between the steel and the aluminum alloy which are the respective materials. Ingress of water etc. is blocked.
Therefore, there is no risk of electrolytic corrosion in the internal space of the bolt through hole 26 and the screw hole 16 along the screw shaft 42 of the bolt 40.

Here, fastening of aluminum alloy members with steel bolts is widely used. However, according to predetermined test conditions such as salt water immersion, a predetermined amount of corrosion (thinning amount) is naturally applied to an aluminum alloy brought into contact with steel. Is recognized.
FIG. 4 is a graph showing the results of determining the change in the corrosion amount due to the separation distance between the steel and magnesium alloy under the same test conditions as those for the steel and aluminum alloy.
Under the test conditions where the corrosion amount / time of the aluminum alloy in contact with the steel was 2.5, if the steel and the magnesium alloy had a separation distance of about 8 mm, a practical electric power similar to the fastening with the steel bolt of the aluminum alloy member was obtained. Anti-food performance will be obtained. Therefore, the height of the flange 38 of the sub part 35 is set so that the shortest distance S between the bolt 40 (steel) and the case cover 20 (magnesium alloy) avoiding the flange 38 shown in FIG. 3 is 8 mm. The increase in material cost is suppressed by stopping at the height.

  In the fastening operation, the insulating gasket 30 is attached by first pulling up the side of the auxiliary portion 35 of the insulating gasket 30 in the free state far from the connecting piece 34 with a finger, thereby bending the connecting piece 34 and inwardly opening the auxiliary portion 35 (opening 18). The opening is opened toward the side), and the mounting seat 25 of the case cover 20 is fitted between the main portion 31 and the sub-portion 35, whereby the sub-assembly of the case cover 20 and the insulating gasket 30 is obtained. At this time, the mounting seat portion 25 may be aligned with the sub portion 35 by inserting the case cover 20 at a position shifted from the sub portion 35 in the circumferential direction and then rotating in the circumferential direction.

  Then, the main assembly 31 of the insulating gasket 30 is opposed to the case 10, and the subassembly is overlaid on the case 10 (fastening surface 13) after alignment. The sub-portion 35 having the opening is initially inclined with respect to the mounting seat portion 25 of the case cover 20, but according to tightening (screwing) of the bolt 40 in which the screw shaft 42 is inserted from the second through hole 37. It is pushed by the head 41 of the bolt 40 and is seated on the upper mounting surface 27 of the mounting seat 25 so that the mounting seat 25 is sandwiched between the main portion 31 and the sub portion 35. Further, by further tightening, the cone-shaped bolt seat portion 36 is elastically deformed and becomes flat.

In the present embodiment, the aluminum alloy case 10 corresponds to the first metal member in the invention, the magnesium alloy case cover 20 corresponds to the second metal member, and the steel bolt 40 corresponds to the coupling member. In particular, the head 41 of the bolt 40 corresponds to the pressing portion.
Moreover, the bolt seat part 36 of the sub part 35 corresponds to the contact part with the pressing part.

The embodiment is configured as described above, and the case cover 20 made of magnesium alloy is stacked on the case 10 made of aluminum alloy, and the head 41 is positioned on the opposite side of the case cover 20 from the case 10. The bolt 40 has a fastening structure in which the case cover 20 is pressed and fixed to the case 10. An insulating gasket 30 is disposed between the case 10 and the case cover 20, and the insulating gasket 30 is connected to the fastening surface 13 of the case 10 and the case. A main portion 31 sandwiched between the lower mounting surface 23 of the cover 20 and a sub-portion 35 connected to the main portion 31 via the connection piece 34 and sandwiched between the head 41 of the bolt 40 and the case cover 20. As a result, in addition to the gasket for preventing electric corrosion between the case 10 and the case cover 20, the gasket disposed between the bolt 40 and the case cover 20 is used. Separately it is not necessary to set until note, since it is possible to insulate the parts ionization reactions may occur in 1 part, reduce ease and component count assembling, cost reduction due to obtain.
(Effects corresponding to claims 1 and 2)

The sub-portion 35 of the insulating gasket 30 has a second through-hole 37 through which the screw shaft 42 of the bolt 40 passes, and the bolt seat portion 36 that contacts the head 41 of the bolt 40 is centered on the second through-hole 37. Since it has a cone shape, the bolt seat portion 36 functions in the same way as a disc spring washer, and the bolt 40 is prevented from loosening without a separate spring washer.
Since the spring washer is unnecessary, there is no possibility of water intrusion into the space along the screw shaft 42 from the cut.
(Effects corresponding to claim 3)

Since the sub-portion 35 of the insulating gasket 30 is provided with a flange 38 around the bolt seat portion 36 except for the vicinity of the connection portion 34 to the connection piece 34, water is likely to accumulate around the bolt fastening portion of the case cover 20. Even if it is a shape, generation | occurrence | production of the ionization reaction between the volt | bolts 40 is prevented reliably.
(Effects corresponding to claim 4)

  In the embodiment, the bolt 40 is used as a coupling member for fixing the case cover 20 to the case 10, and the screw shaft 42 passes through the mounting seat portion 25 of the case cover 20 and is screwed into the screw hole 16 of the case 10. The head 41 of the bolt 40 presses the bolt seat portion 36 of the insulating gasket 30 as a pressing portion. However, the present invention is not limited to this, and the coupling member may be a mounting seat portion of the case cover 20 from the boss portion 15 of the case 10. 25, and a bolted portion 36 of the insulating gasket 30 that presses against the bolt seat portion 36 as a pressing portion. It is good also as composition to do.

In the embodiment, the case 10 of the transmission is made of an aluminum alloy, the case cover 20 is made of a magnesium alloy, and the bolt 40 is made of steel. However, in the present invention, the case 10 and the case cover 20 tend to be ionized and have a potential. The present invention can be applied to various combinations made of different kinds of metals.
In many fields, steel is used as the coupling member. For example, the case 10 may also be made of steel, and the case cover 20 is made of an aluminum alloy. 30 can be used as it is.
Further, the insulating gasket is not limited to that of the embodiment, and any appropriate gasket can be selected as long as it can prevent generation of an ionization reaction between the case and the case cover.
Furthermore, the present invention is not limited to the parts of the vehicle transmission, and can be applied to fastening any dissimilar metal member.

DESCRIPTION OF SYMBOLS 10 Case 11 Side wall 12 Flange part 13 Fastening surface 15 Boss part 16 Screw hole 18 Opening 20 Case cover 23 Lower mounting surface 25 Mounting seat part 26 Bolt through-hole 27 Upper mounting surface 30 Insulating gasket 31 Main part 32 Boss part corresponding part 33 1st 1 through hole 34 connecting piece 35 sub-part 36 bolt seat 37 second through hole 38 flange 40 bolt 41 head 42 screw shaft

Claims (4)

A second metal member having a lower ionization tendency than the first metal member is superimposed on the first metal member, and a pressing portion is provided on the opposite side of the first metal member to the first metal member. In the fastening structure of the dissimilar metal member, the second metal member is pressed and fixed to the first metal member by the positioned coupling member, and the coupling member is more ionized and has a higher potential than the second metal member.
An insulating gasket is disposed between the first metal member and the second metal member;
The insulating gasket includes a main portion sandwiched between mating surfaces of the first metal member and the second metal member, and the second metal member in the overlapping direction connected to the main portion via a connection piece. A fastening structure for dissimilar metal members, comprising: a sub-portion sandwiched between the pressing portion of the coupling member. The coupling member is a bolt whose screw shaft passes through the second metal member and is screwed into the first metal member, or an implant that is implanted in the first metal member and penetrates the second metal member. It is a set of bolt and mating part,
2. The fastening structure for dissimilar metal members according to claim 1, wherein the pressing portion is the head of the bolt or the fitted portion paired with the implanted bolt.   3. The sub-portion has a through hole through which the screw shaft or the implanted bolt penetrates, and a contact portion with the pressing portion has a cone shape with the through hole as a center. The fastening structure of the dissimilar metal member as described in 2.   The said sub part is provided with the flange extended in the direction spaced apart from the said main part in the circumferential direction predetermined range except the connection part with the said connection piece of the periphery surrounding the said contact part. The fastening structure of the dissimilar metal member as described in 2.

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