Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
1999-06-28
2001-08-14
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S294000, C384S297000
Reexamination Certificate
active
06273612
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a sliding bearing having an overlay layer, and more particularly to a sliding bearing having an improved heat emission property.
A sliding bearing, used, for example, for bearing a crankshaft or a crank pin of an engine, has an overlay layer of a uniform thickness formed on a bearing surface, made of a bearing alloy such as an Al alloy or a Cu alloy, over an entire circumference thereof. Such an overlay layer is made of a soft alloy, such as a Sn base alloy, a Pb base alloy, an Al base alloy, or a resin material. The overlay layer is formed in order to provide the bearing alloy with properties of conformability, foreign matter embeddability and anti-seizure property with respect to a mating shaft.
Lubricating oil is supplied to a sliding bearing, which serves to prevent a solid to solid contact between the bearing and the mating shaft and also has a function of transmitting heat generated during operation, that is, the function of cooling the bearing contact portion.
While the bearing contact portion is thus cooled by the lubricating oil, the sliding bearing itself is also required to have a function of heat emission to the outside. However, in the conventional sliding bearing, the above-mentioned overlay layer of a uniform thickness is formed over the entire circumference thereof, and particularly where the overlay layer is made of a resin material, heat is less liable to emit to the outside through the sliding bearing since the overlay layer has a low thermal conductivity, and therefore there has been encountered a problem that heat emission through the sliding bearing can not be effected adequately.
SUMMARY OF THE INVENTION
Thus, it is an object of the invention to provide a sliding bearing with an overlay layer, which has an excellent heat emission property.
In the conventional sliding bearings, an overlay layer, having a uniform thickness of about 3 to 20 &mgr;m, is formed on the bearing over the entire circumference thereof. With regard to improvement of the thickness and a material type of the conventional overlay layer, various efforts have been made to maintain its initial properties. The conventional sliding bearings have depended for the cooling on lubricating oil, and effective measures for promoting heat emission from the bearing structure have not been taken sufficiently.
In the sliding bearing of the present invention, having such a technical background, an overlay layer is improved so as to promote the heat emission property of the sliding bearing without affecting the original function of the overlay layer.
According to the invention, there is provided a sliding bearing wherein a load, applied to a bearing alloy surface adapted in a cylindrical shape, varies in a circumferential direction;
wherein an overlay layer is formed on a portion of the bearing alloy surface to which a higher load is applied; and
wherein a thickness of the higher load-side overlay layer decreases gradually from the central portion thereof toward both circumferential outward directions.
In the construction in which the thickness of the higher load-side overlay layer decreases gradually from the central portion thereof toward the opposite circumferential ends thereof, since the amount of heat, transmitted to the bearing alloy through the thin portions of the overlay layer, is greater, the amount of heat radiated to environment through the sliding bearing increases even if the overlay layer is present. The situation is the same as above also in the case of no overlay layer in the circumferential end regions.
The conformability and anti-seizure property of the overlay layer with respect to the mating shaft do not need to be uniform and high enough over the entire circumference. Namely, if that portion of the bearing alloy, to which a high load is applied, does not have sufficient original properties, it is necessary to form the overlay layer on this portion so as to enhance the properties, whereas those portions of the bearing alloy, to which a small load is applied, exhibit the sufficient original properties. Under the circumstances, in the above constructions, the overlay layer is provided on that portion of the bearing alloy surface to which a high load is applied, and therefore the conformability and anti-seizure property of the overlay layer (which are the functions to be originally achieved by the overlay layer) for the mating shaft are by no means inferior to those of the conventional sliding bearing.
According to one feature of the invention, a region of formation of the higher load-side overlay layer extends circumferentially from the central portion toward both circumferential directions in an angle range of 30 to 80 degrees so that the region includes a main load-supporting portion to which a highest load is applied.
For example, in the case of a diesel engine for an automobile, a main load-supporting portion of a sliding bearing for supporting a crankshaft or a crank pin extends circumferentially over an angle of about 30 degrees, and such angle for a gasoline engine is larger than it. Therefore, according to the above feature, the main load-supporting portion, required to have improved properties including the conformability and the anti-seizure property, is covered with the overlay layer.
According to another feature of the invention, a region of formation of the higher load-side overlay layer extends circumferentially from the central portion toward each of the circumferential directions in an angle range of 80 to 90 degrees so that the region includes a main load-supporting portion to which a highest load is applied, and the thickness of the higher load-side overlay layer decreases gradually from the central portion thereof toward each of the circumferential directions in an angle range of 30 to 70 degrees, and the thickness of each of the residual portions of the overlay layer other than the thickness-decreasing portion, the residual portions extending circumferentially outwardly from the thickness-decreasing portion, is uniform or increases gradually toward the circumferential outward direction.
The thickness of the overlay layer, disposed outwardly of the overlay layer extending circumferentially from the central portion toward each of the opposite ends in the range of 30 to 70 degrees, is uniform or is increasing gradually toward the opposite circumferential ends. Therefore, for example, in the sliding bearing comprising two bearing halves assembled together, even if the circumferential ends are shifted with respect to each other, premature fatigue of the bearing alloy due to a localized contact of the shifted ends with the mating shaft can be prevented.
According to still another feature of the invention, the higher load-side overlay layer at the circumferential central portion has a largest thickness at the respective opposite axial end portions in an axial direction of the bearing.
At an initial stage of use of the sliding bearing, the mating shaft tends to contact the both opposite axial end portions of the bearing surface in a localized manner. Therefore, the thickness of the overlay layer is increased at the opposite axial end portions, and thereby, the conformability of the opposite end portions can be improved.
According to a further feature of the invention, the higher load-side overlay layer, extending over a circumferential angle range of 30 to 70 degrees from the circumferential central portion toward each of the circumferential directions, has a largest thickness at the respective opposite axial end portions in an axial direction of the bearing, and the respective residual portions extending circumferentially outwardly from the circumferential central region decreases gradually toward the axial end portion of the bearing.
The sliding bearing, comprising two bearing halves assembled together, is used, for example, in an engine of an automobile, and when the bearing halves are pushed hard against each other, the central portion of the bearing half in the axial direction may be inwardly deformed or depresse
Hiramatsu Nobutaka
Ono Akira
Shibayama Takayuki
Yamamoto Koichi
Yoshimi Hiroshi
Browdy and Neimark
Daido Metal Company LTD
Footland Lenard A.
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