Drain Bolt Mounting Structure

Abstract

A drain bolt mounting structure comprises a bottomed hole formed on an outer surface of an oil pan to extend continuously with a drain hole of the oil pan, a female thread formed on an inner peripheral surface of the drain hole; a drain bolt including a shaft portion having a male thread threadingly engageable with the female thread of the drain hole and a head portion formed at one end portion of the shaft portion; a press-in member formed of a second metal containing aluminum which has a higher standard electrode potential than a first metal forming the oil pan, the press-in member being configured to be pressed into the bottomed hole; and a crushing member configured to be crushed between the press-in member and the head portion of the drain bolt.

Description

CROSS-REFERENCE TO RELATED APPLICATIONThe present application claims priority to Japanese Patent Application No. 2009-297894 filed on Dec. 28, 2009 which is hereby incorporated by reference in its entirety for all purposes.BACKGROUND ART1. Field of the InventionThe present invention relates to a drain bolt mounting structure for sealably closing a drain hole provided in an oil pan formed of metal containing magnesium, in a fluid-tight state.2. Description of the Related ArtAn engine mounted in a vehicle such as a motorcycle includes a cylinder head, a cylinder block, a crankcase, an oil pan, etc. The crankcase accommodates a crankshaft and an oil pump. The oil pan is provided with a drain hole at a bottom portion thereof. The drain hole is sealably closed by a drain bolt or the like in a fluid-tight state. Upon the engine running, the oil pump is actuated by the rotation of the crankshaft, and oil reserved in the oil pan is pumped by the oil pump to be fed to driving members and com...

AI Technical Summary

Benefits of technology

The present invention addresses the above described conditions, and an object of the present invention is to provide a drain bolt mounting structure which allows the drain bolt to be mounted more easily and efficiently, can surely attain a highly sealed state, and can prevent the drain bolt from coming loose due to electric corrosion.

In such a configuration, since the press-in member is pressed into the bottomed hole formed on the outer surface of the oil pan, it is possible to prevent the press-in member from coming off from the bottomed hole when the drain bolt is detached from the oil pan. When the drain bolt is re-mounted to the oil pan, a messy operation, for example, re-positioning of the press-in member and pressing of the press-in member into the bottomed hole, is not necessary. Thus, the drain bolt is mounted more easily and more efficiently.

In addition, since the press-in member is pressed into the bottomed hole such that the outer peripheral surface of the press-in member is tightly fitted to the inner peripheral surface of the bottomed hole, a highly sealed state is surely attained between the inner peripheral surface of the bottomed hole and the outer peripheral surface of the press-in member. Since the crushing member is crushed and deformed between the press-in member and the head portion of the drain bolt by tightening the drain bolt, the crushing member and the press-in member are tightly fitted to each other and the crushing member and the head portion of the drain bolt are tightly fitted to each other. Thus, a highly sealed state is attainable between the crushing member and the press-in member and between the crushing member and the head portion of the drain bolt. This makes it possible to prevent the oil from leaking from the oil pan to an outside of the oil pan through the drain hole.

Since the bottom surface of the bottomed hole which is a part of the oil pan is formed of the first metal containing magnesium and the press-in member configured to contact the bottom surface of the bottomed hole is formed of the second metal containing aluminum which has a higher standard electrode potential than the first metal, the electric corrosion of the bottom surface of the bottomed hole can be suppressed by reducing a standard electrode potential difference between the bottom surface of the bottomed hole and the press-in member. Since a highly sealed state is surely attained between the inner peripheral surface of the bottomed hole and the outer peripheral surface of the press-in member as described above, water such as rain water can be prevented from entering the clearance between the bottom surface of the bottomed hole and the press-in member, which makes it possible to prevent the electric corrosion of the bottom surface of the bottomed hole due to the water. Therefore, degradation and deformation of the bottom surface of the bottomed hole due to the electric corrosion, which will cause the drain bolt to come loose, is effectively prevented.

In such a configuration, since at least the surface of the crushing member which is opposite to the press-in member has a lower hardness than the surface of the press-in member which is opposite to the surface of the crushing member, the crushing member can be preferentially crushed while suppressing damage to the press-in member when tightening the drain bolt. By changing only the crushing member damaged by the crushing into a new one, a product quality can be maintained for a longer period of time. Since the crushing member is formed of the third metal containing inexpensive aluminum, the crushing member can be changed into a new one at a low cost.

In such a configuration, leakage of oil from the oil pan, and entry of water such as rain water into the oil pan can be surely prevented because of a sealing function of the O-ring.

Problems solved by technology

In a case where an oil pan formed of magnesium or magnesium alloy is used to provide, for example, a lightweight engine, the oil pan is required to be subjected to an electric corrosion resistance treatment, because magnesium has a very low standard electrode potential and is likely to be electrically corroded due to contact with other metal (dissimilar metal contact).

Thus, the bolt (12) is not easily and efficiently mounted.

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