Hydrodynamic type porous oil-impregnated bearing and bearing device

DETAILED DESCRIPTION Objects of the invention are: (1) To reduce the number of parts of the bearing to 2, while reducing the cost, making it easier to increase the degree of accuracy of the parts, and adapting them for mass production; (2) To provide a construction such that the retained oil is circulated through the bearing clearance and the bearing interior, thereby retarding oil degradation.
(3) To find a bearing specification which allows hydrodynamic effects to be exerted irrespective of the presence of the openings in hydrodynamic-pressure-generating grooves in order to make the bearing design industrially feasible.
When a bearing surface of a bearing body 1 is provided with hydrodynamic-pressure-generating grooves (inclined grooves of the herringbone or spiral type), the flow of oil, as seen in an axial section, is as shown, for example, in FIG.
2.
The oil flows in, as indicated by arrows, from openings in the bearing surface 17 (inner surface) of the bearing body 1 into a bearing clearance 4 between the bearing surface 17 and a rotary shaft 2, to maintain an appropriate oil circulation, it is desirable that the openings be substantially uniformly distributed over the hydrodynamic-pressure-generating grooves 5 and ridges 6 between the grooves (see FIG.
7).
When the proportion of the openings in the surface is decreased, the oil moves with difficulty; reversely, when it is increased, the oil moves with less difficulty.
Further, the viscosity of the retained oil also has to do with the oil movement, such that the lower the viscosity, the greater the ease with which the oil moves and such that the higher the viscosity, the less the ease with which the oil moves.
In addition, in this specification, the term "openings" means those portions of pores forming the porous structure of the bearing body of porous material which open to the surface.
A combination of high opening percentage and low viscosity though allowing extremely smooth movement of oil, has the trouble that since the oil exuded into the bearing clearance 4 by the action of the hydrodynamic-pressure-generating grooves 5 is easily pushed back into the interior of the bearing body, the hydrodynamic effects will be lessened to the extent not only that rotation with high accuracy can not be maintained but that the contact between the shaft 2 and the bearing body 1 causes wear of the bearing body 1 to impair the bearing functions