Patent Application
20170058954
The present invention generally relates to a seal, and more particularly, to a non-contact seal surrounding a rotating shaft that contacts the shaft when stationary.
Conventional bearing assemblies include a housing, a bearing mounted in the housing, and a shaft mounted in the bearing for rotation relative to the housing. Seals are provided between the housing and shaft to prevent contaminants outside the housing from entering the housing and damaging the bearing. As will be appreciated by those skilled in the art, relative motion occurs between the seal and the shaft, causing wear. In order to reduce seal wear, a small gap or clearance is provided between the seal and the shaft so the seal and the shaft do not contact as the shaft turns in the seal. This reduces seal wear and increases the life of the bearing assembly.
Lubricant is introduced into the housing of the bearing assembly to reduce wear and friction between the moving parts. During operation, the lubricant in the housing is pressurized to prevent contaminants from entering the housing through the clearance where the contaminants could damage the bearing and reduce bearing life. During shutdown when the shaft is stationary, lubricant pressure drops, permitting contaminants to enter the housing through the clearance provided in conventional assemblies. Further, when the assembly is splashed with water such as when washed, water can enter the bearing assembly through the clearance, potentially causing bearing damage and reducing life. Although non-metallic seals have been introduced, these seals have limited wear resistance and temperature capabilities. Thus, there is a need for seals that permit lubricant to enter the gap between the seal and shaft as the shaft rotates, but that fully contacts the shaft when stationary to prevent contaminants and water from entering the bearing assembly.
In one aspect, the present disclosure includes a bearing assembly, comprising a housing having an interior cavity adapted to hold a lubricant. The housing also has an opening extending from the interior cavity to an exterior of the housing, an inward facing seal mounting surface, and an inward facing bearing seat. The bearing assembly also includes a bearing positioned in the interior cavity of the housing. The bearing has a central axis, as well as, an outer race mounted in the inward facing bearing seat of the housing and an inner race centered on the central axis and freely rotatable in the outer race. Further, the bearing assembly includes a shaft mounted in the inner race of the bearing for rotation with the inner race about the central axis of the bearing. The shaft has an outer surface extending along the shaft from the interior cavity through the opening to the exterior of the housing. At least part of the outer shaft aligned with the opening has a sealing diameter. The assembly includes a seal mounted in the seal mounting surface of the housing and around the outer surface of the shaft. The seal is positioned axially along the shaft between the interior cavity of the housing and the exterior of the housing to inhibit contaminants from entering the interior cavity of the housing through the opening and damaging the bearing. The seal includes an annular body having a bearing side facing the bearing, an opening side opposite the bearing side, and an inner surface facing the outer surface of the shaft. The inner surface has a tapered portion spaced from the outer surface of the shaft by a clearance gap having a predetermined axially varying width. The width of the clearance gap decreases from the bearing side toward the opening side. The inner surface also includes an axially extending sealing portion having an inner diameter corresponding to the sealing diameter of the outer surface of the shaft and forming a sealing interface with the outer surface of the shaft. The interface supports tribological film lubrication when the shaft rotates relative to the housing to reduce shaft wear. Further, the seal contacts the shaft when the shaft is stationary relative to the housing to prevent contaminants from entering the interior cavity of the housing through the interface.
In another aspect, the present disclosure includes a seal for use in a bearing assembly having a housing, a bearing positioned in the housing, a shaft mounted in the bearing for rotation and having a radially outward facing surface extending through an opening in the housing. The seal comprises an annular body having a bearing side adapted for facing the bearing when installed in the bearing assembly. The body has an opening side opposite the bearing side and an inner surface facing the outer surface of the shaft. The inner surface has a tapered portion spaced from the outer surface of the shaft by a clearance gap having a predetermined axially varying width. The width of the clearance gap decreases from the bearing side toward the opening side. The inner surface also includes an axially extending sealing portion having an inner diameter corresponding to the sealing diameter of the outer surface of the shaft and forming a sealing interface with the outer surface of the shaft. The interface supports tribological film lubrication when the shaft rotates relative to the housing to reduce shaft wear and contacts the shaft when the shaft is stationary relative to the housing to prevent contaminants from entering the interior cavity of the housing through the interface.
In still another aspect, the present disclosure includes a seal for use in a bearing assembly having a housing, a bearing positioned in the housing, a shaft mounted in the bearing for rotation and having a radially outward facing surface extending through an opening in the housing. The seal comprises an annular body having a bearing side adapted for facing the bearing when installed in the bearing assembly and an opening side opposite the bearing side. Further, the annular body includes a radial section extending between an inner boundary and an outer boundary. The body also includes an outer axial section extending axially from the outer boundary of the radial section and an inner axial section extending axially from the inner boundary of the radial section. The inner axial section has an inner surface adapted for facing the shaft when installed in the bearing assembly. The inner surface includes a tapered portion having a predetermined axially varying radius, the radius decreasing from the bearing side toward the opening side The inner surface also includes an axially extending sealing portion having an inner diameter corresponding to the sealing diameter of the outer surface of the shaft and forming a sealing interface with the outer surface of the shaft. The interface supports tribological film lubrication when the shaft rotates relative to the housing to reduce shaft wear and contacts the shaft when the shaft is stationary relative to the housing to prevent contaminants from entering the interior cavity of the housing through the interface.
Other objects and features will be in part apparent and in part pointed out hereinafter.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring to
As illustrated in
The housing 12 has the interior cavity 30, which is sized, shaped, and arranged to receive the bearing 14. As illustrated, the bearing enclosure member 32 of the housing 12 defines a radially inward facing bearing seat 40 for holding the bearing 14 to prevent it from moving transverse to a central axis A of the bearing or axially away from the shaft receiving member 34. The shaft receiving member 34 includes an axial face 42 configured to engage the bearing 14 and inhibit the bearing from moving axially in the housing 12. The interior cavity 30 is in fluid communication with a lubricant source (not shown) via an inlet 44 (
The opening 18 in the housing 12 extends between the interior cavity 30 and the exterior of the housing. In the illustrated housing 12, the shaft receiving member 34 defines the opening 18. The opening 18 is sized and shaped to receive a portion of the shaft 16 permitting the shaft to freely rotate in the opening. The shaft receiving member 34 of the illustrated assembly 10 includes an axially extending collar 46 that surrounds a larger diameter portion of the shaft outside of the interior cavity 30. A small clearance is provided between the collar 46 and the shaft 16 to inhibit contaminants from entering the interior cavity 30.
The housing 12 is configured to mount the seal 20 adjacent the opening 18 between the interior cavity 30 and the exterior of the housing. A radially inward facing seal mounting surface 50 sized for receiving the seal 20 is provided in the housing 12 to secure the seal in the proper position relative to the shaft opening 18. As illustrated, the shaft receiving member 34 of the housing 12 includes the seal mounting surface 50, but in other embodiments the seal mounting surface may be included in other portions of the housing without departing from the scope of the invention.
As further shown in
As shown in
The inner race 54 of the bearing 14 receives the shaft 16 for rotation relative to the housing 12 about the center axis A. In some cases, the inner race 54 of the bearing 14 is press fit on the shaft 16 so the shaft rotates mutually with the inner race about the central axis. Some shafts 16 include a thin sleeve 60 overlying the outward facing surface 58 of the shaft the sleeve is axially aligned with the seal 20 to provide a suitable surface for contacting the seal 20 to reduce shaft wear and increase the useful life of the shaft. In some instances, the sleeve 64 is a SPEEDI-SLEEVE® shaft sleeve available from SKF USA Inc., which is a Delaware corporation having place of business in Lansdale, Pa. As will be appreciated by those skilled in the art, the outward facing surface 58 of the shaft 16 or that of the sleeve 60, when present, forms a sealing land or diameter, generally designated 62.
The seal 20 has a one piece annular body that is mounted on the sealing diameter 62 of the outward facing surface 58 of the shaft 16 and positioned axially between the interior cavity 30 of the housing 12 and the exterior of the housing to inhibit contaminants from entering the interior cavity and damaging the bearing 14. As shown in
Referring to
As further shown in
Referring to
Most lubrication specialists agree that friction may be at its highest level during the boundary lubrication regime at startup, low speed, or high load conditions. The boundary lubrication regime occurs when asperities of two lubricated surfaces are in physically contact and moving relative to each other. This condition presents a potential for abrasion and/or adhesion. Because friction is high in the boundary lubrication regime, wear is believed to be more likely in this regime. Accordingly, lubrication engineers and tribologists have suggested that as much as seventy percent of wear occurs during machinery startup.
Generally speaking, the boundary lubrication regime is dramatically reduced as lubricant flow increases and the lubricant film becomes thicker between the surfaces in motion. As film thickness increases, the potential for asperity contact is reduced and the coefficient of friction drops dramatically through a condition known as mixed lubrication. As the lubricant film thickness increases, the system moves into the full film or hydrodynamic lubrication regime. During the hydrodynamic lubrication regime, such as when a full film of lubricant completely separates a turbine shaft from its support, there is little risk of asperity contact and the viscosity of the lubricant is sufficient to support the shaft and lubricate the support. During the full hydrodynamic lubrication regime, friction between the surfaces is extremely low, and for all practical purposes, non-existent. What little friction that is present is primarily in the lubricant itself, as the molecular structures of the lubricant shear during operation.
In view of the foregoing, it can be seen that a seal of relatively simple construction can be used to seal the housing opening of a bearing assembly around a shaft. Further, an inner surface of the seal 20 may be sized to support a tribological lubricant film when the shaft 16 rotates but to contact the shaft when stationary to prevent contamination and water from entering the housing.
Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.
When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions, products, and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
