Patent Application
20130175763
This disclosure relates generally to seals for shafts or other rotatable members or elements.
Shaft seals are used in various types of machinery and equipment in the automobile industry, as well as in many other industries, for sealingly engaging a rotatable or slidable shaft. Such seals typically have a non-lubricant (air or other atmosphere) side and a lubricant (e.g., oil) side and one or more sealing lips that engage the shaft and tend to keep the lubricant from leaking from the lubricant side to the non-lubricant side (whether the shaft is rotating, sliding, or stationary). Various seal shapes, configurations, and arrangements have been devised to accomplish this and to divert lubricant back to the non-lubricant side of the seal.
One type of such a seal arrangement includes one or more spiral grooves recessed into the sealing lip or alternately formed between spaced-apart ribs protruding in a generally radial inward direction from the lip (both arrangements hereinafter collectively referred to as “grooves”). These grooves are disposed on the active shaft-engaging surface of the sealing lip and serve to capture the migrated (or “leaked”) lubricant and hydrodynamically pump it back to the lubricant side as a result of the relative rotation between the seal and the shaft about which the seal is disposed. Such grooves have frequently been open to the lubricant side of the seal, thus providing fluid communication with the lubricant thereon. In some applications, however, such an open-groove arrangement can sometimes create the potential for static lubricant leaks when the shaft is stationary or for air leaks during pressurization testing of the machinery on which the seal is being used.
To address these potential leaks, the groove or grooves in one exemplary shaft seal arrangement do not extend all the way to the seal lip's leading or free edge that faces or is oriented toward the lubricant side. Rather, the groove is interrupted short of the free edge by way of a static dam or band, for example, disposed between the groove or grooves and the sealing lip free edge. Any lubricant that migrates past the sealing lip edge on the lubricant side is captured in the grooves, and its fluid pressure grows until it reaches a value that exceeds the seal lip opening pressure. When the lip opens under the influence of this built-up fluid pressure, the lubricant is directed back toward the lubricant side due to relative rotation between the seal and the shaft on which the seal is disposed.
Lubricant then gradually migrates back between the sealing lip and the shaft again when the shaft is rotating or during static conditions when the shaft is not rotating. In some embodiments of this type of seal arrangement, the shape or configuration of the groove or grooves is such that an induction zone is formed by one portion of the grooves and a booster zone is formed by a different portion of the grooves adjacent the static dam. In such an arrangement, the fluid pressure grows relatively slowly in the induction zone and relatively quickly in the booster zone until the opening pressure is exceeded.
The use of a static band or dam in such seals thus advantageously avoids or at least minimizes static or dynamic leakage as well as reducing problems resulting from insufficient fluid flow (e.g., lubricant coking or carbonization, etc.). By maintaining some amount of lubricant in the groove or grooves in the sealing lip's active sealing surface prior to the static dam liftoff, seal lip lubrication is improved, thereby reducing wear and extending seal life. Although this type of shaft seal arrangement has performed well, the present disclosure seeks to provide even further improvements in seal lip lubrication and seal life in order to meet increasingly demanding shaft sealing applications.
Still other types of radial shaft seals are of a type having an elastomeric body bonded to a metal case in which the active shaft-engaging portion of the lip can be made of polytetrafluoroethylene (PTFE), or at least has a PTFE portion, or other materials. Such seal designs of this type can have their leading or free ends of the PTFE lip surface or lip portion facing either the air (atmosphere or non-lubricant) side or the lubricant side of the seal. In such designs where the free edge of the sealing lip faces the lubricant side, however, installation difficulties have sometimes been experienced, necessitating the use of special fixtures and special precautions so as not to nick or damage the surface of the PTFE material during assembly and destroy the functionality of the seals.
In response to such difficulties, radial shaft seals with PTFE shaft-engaging surfaces have been developed where the free end of the lip seal extends toward the air (non-lubricant) side of the seal rather than toward the lubricant side. Optionally, this type of seal can also have an oil side excluder lip seal, an air (non-lubricant) side dust excluder lip seal, and an elastomeric static seal extending from the elastomeric portion of the seal. This type of seal can be a one-piece sealing element, but can also advantageously be of a composite or “sandwiched” construction with a PTFE material for a primary shaft-engaging lip portion having grooves therein, as described above, and another elastomeric material for an elastomeric lip body to which the grooved shaft-engaging lip portion is preferably bonded. Examples can be found in U.S. Pat. No. 6,428,013, the entire disclosure of which is incorporated herein by reference.
Although all of the exemplary seal arrangements discussed above have been effective and have performed advantageously, the present disclosure seeks to further improve the seal's ability to retain lubricant between the sealing lip's active shaft-engaging surface and the shaft.
According to the present disclosure, a seal for a shaft or other rotatable member or element includes a sealing lip, an active lip surface oriented toward the lubricant side of the seal and having a shaft-engaging lip surface portion thereon, and a lubricant vent providing communication between the shaft engagement surface portion and the lubricant side. In some examples of seal arrangements according to the disclosure, such a lubricant vent can include an opening or orifice formed in a grooved (or even a non-grooved) sealing lip and providing substantially direct fluid communication between shaft-engaging lip surface and the lubricant side of the seal. Alternatively, in other seal arrangements, a channel extending through or along at least a portion of the lip can be used to provide fluid communication (either alone or in conjunction with an opening or orifice through the lip) between the shaft-engaging lip surface and the lubricant side of the seal. Such a channel configuration is especially advantageous in applications where the lip protrudes toward the air (non-lubricant) side of the seal and/or in applications where the sealing lip is of a composite or sandwiched construction, as mentioned above.
In one version of a lubricated seal according to the present disclosure the hydrodynamic pumping of lubricant tends to create a vacuum (or low pressure condition) after lift off of the seal lip free edge or static dam, which helps pull lubricant through the lubricant vent opening or to maintain an adequate supply of lubricant between the seal lip's shaft-engaging surface and the shaft as well as helping the shaft-engaging lip portion to maintain sealing contact with the shaft. This substantially minimizes lubricant coking and lubricant degradation, thus even further reducing wear and extending seal life, even in demanding high-temperature, high-speed applications.
Further advantages and additional areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examples disclosed herein are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
The drawings described herein are presented merely for illustration of selected example embodiments. They do not depict all possible implementations of the disclosure and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts or elements throughout the several views of the drawings
Example embodiments will now be described more fully with reference to the accompanying drawings. Such example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that some specific details need not be employed, that example embodiments may be embodied in many different alternate forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element's or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Such spatially relative terms may also encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass an orientation of above or below, depending upon a device's depicted orientation in the drawings. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
With reference to
The seal 20 includes a central opening 36 through which the shaft 28 is disposed. The diameter of opening 36 is dimensioned to be less than the diameter of the shaft 28 to provide a fluid-tight seal therebetween as the portion of the seal 20 proximate the opening 36 deforms as the seal 20 is positioned on the shaft 28.
The seal 20 has a conically-shaped sealing lip 40 extending axially and radially toward the shaft 28. The sealing lip 40 has an active side or surface 44 with a seal-engaging surface portion 45 that engages the shaft 28, a non-active side or surface 48 that is opposite the active surface 44 and does not engage the shaft 28, and a free or leading seal lip edge 52. Part of the active surface 44 is exposed to the air (non-lubricant) side 49 while the non-active surface 48 and seal lip edge 52 are exposed to the lubricant side 50.
At least one groove 60 (two grooves are shown, for example, in
Due to the relative rotation between the shaft-engaging surface portion 45 of the active surface 44 and the shaft 28, the groove 60 captures lubricant that seeps or migrates past the seal lip edge 52 and hydrodynamically pumps it past the seal lip edge 52 back to the lubricant side 50.
The groove 60 can be a single groove that extends helically or spirally along the active surface 44 between a beginning point 64 and a termination point 68, as shown in
The groove 60 stops short of reaching the seal lip edge 52 and is interrupted by a static band or dam 70 disposed between the seal lip edge 52 and the termination point 68. The static dam 70 is preferably disposed adjacent the seal lip edge 52 and is in direct sealing contact with the shaft 28. To further facilitate the hydrodynamic pumping of lubricant back to the lubricant side 50, the groove 60 can include two distinct regions 74 and 76. The first region 74 functions as an induction zone while the second region 76 functions as a booster zone. In the induction zone 74 shown for purposes of illustration, the groove 60 has a cross-sectional area that is substantially constant, although other uniform or non-uniform cross-sectional shapes can also be employed. In contrast, the booster zone 76 has a cross-sectional area that diminishes, ultimately decreasing to zero, as the groove 60 extends to the termination point 68 adjacent the static dam 70. In one embodiment, the width W of the groove 60 in both the induction zone 74 and the booster zone 76 can be the same while the depth of the groove 60 in the induction zone 74 is different from the depth of the groove 60 in the booster zone 76. Specifically, in the induction zone 74 the depth of the groove 60 is substantially constant, while in the booster zone 76 the depth of the groove 60 diminishes as the groove 60 approaches the termination point 68. Thus, the cross-sectional area of the groove 60 in the induction zone 74 is substantially constant while the cross-sectional area of the groove 60 in the booster zone 76 approaches zero as the groove 60 approaches the termination point 68. This diminishing cross-sectional area of the groove 60 in the booster zone 76 advantageously facilitates the return of lubricant from the groove 60 back to the lubricant side 50, as described below.
Referring now to
In operation, the fluid pressure within the groove 60 thus continues to grow until a critical value, i.e., the opening pressure of the seal lip edge 52 and the static dam 70 (represented by line 84 in
The physical shape and dimensions of the groove 60 are chosen to provide a pumping rate that is equal to or greater than the expected leakage rate of lubricant past the seal lip 52 for the expected life of the seal 20, taking into account the expected increase in this leakage rate due to seal wear or other factors over the life of the seal.
In order to further improve the life and performance of the seal 20, the seal lip 40 is provided with one or preferably a number of lubricant vents 65 in the form of openings or orifices through the sealing lip 40 at the shaft-engaging surface portion 45 of the active surface 44. Six of such lubricant vents 65 are shown for example in
The provision of one or more lubricant vents 65 at the shaft-engagement portion 45 of the seal 20 allows the seal 20 to meet ever-increasing demands for longer durability and higher shaft speeds in the marketplace. In the dynamic state described above, the hydrodynamic pumping of the first sealing element will create a vacuum between the sealing engaging portion 45 and the shaft 28. This vacuum will help pull lubricant through the lubricant vents 65 as well as help the seal-engaging surface portion 45 to maintain contact with the shaft 28. This flow of lubricant through the lubricant vents 65 helps to assure lubrication and cooling of the seal-engaging surface portion 45 in order to further avoid and minimize lubricant degradation and carbonization in the pumping region in contact with the shaft, as well as reducing sealing lip temperatures. All of these improvements contribute to extended durability and life of the seal 20.
As shown in
Referring now to
The decreasing cross-sectional area of the groove 160 in the booster zone 176 causes the fluid pressure of the lubricant flowing through the lubricant vent 165 into the groove region between the seal-engaging surface 145 and the shaft (not shown in
Referring now to
Referring to
Referring another to still another exemplary alternate embodiment, the seal 220C of
In order to obtain the lubrication benefits and advantages discussed above in connection with other examples of seals according to the disclosure, the lubricant between the shaft 428 and the grooves 460 in the active shaft-engaging surface 444 is pumped under dynamic conditions through a gap 459 at the end of primary lip portion 451, through the lubricant vent channel 447, through the lubrication vent opening 465, and back to the lubricant side 450 of the seal 420. This also tends to create a vacuum in the gap 459 to help the secondary lip portion 453 maintain contact with the shaft under dynamic conditions.
In
Another version of an exemplary seal configuration somewhat similar to that of
While the present disclosure has been described and illustrated with reference to specific embodiment examples, it should be appreciated that these embodiments are merely illustrative and exemplary and that variations that depart from the embodiments shown are intended to be within the scope of the present disclosure. For example, while a variety of geometries are shown for the cross-sectional configuration of the groove or grooves, it should be appreciated that these cross-sectional geometries are merely exemplary and that other cross-sectional geometries can be employed. The shape of land portions of the active and shaft-engaging surfaces can vary, such as for example, with a width that varies and/or may be reduced to a generally “point” or “line” shape or configuration.
Additionally, while the seal has been shown with reference to various sealing lip, mounting portion and casing arrangements, it should be appreciated that these are merely exemplary and that other configurations that allow an active surface of a seal to engage with a shaft or other rotatable element or member can alternately be employed. Moreover, a seal according to the disclosure does not need to seal directly against the outer diameter of a shaft, but can alternately have a shaft-engaging surface portion that seals against a component attached to a shaft, such as a flat area or surface of an axial slinger or flange, with lubricant pumping in a generally radial direction. Furthermore, while the depiction of multiple grooves in
Furthermore, as mentioned above, it should be appreciated that while the pumping element is described as grooves, the use of raised ribs on the active surface of the seal may also be utilized in lieu of the grooves although all of the benefits of the present disclosure may not be realized. Moreover, it should be appreciated that while the shaft is described as being a rotary shaft, it could be stationary and the seal or a component attached to it could rotate about the shaft.
Seals according to the principles of the disclosure, can be made from a variety of material compositions. For example, materials for the dynamic seal can include plastic, synthetic or natural rubber, or any of a wide variety of known elastomers, such as PTFE, TPE (thermoplastic elastomers), TPV (thermoplastic volcanizates), and FlouroXprene® material, a composition described in U.S. Pat. No. 6,806,306, among others. While particular materials of construction have been disclosed as being among those suitable for use in the seal, it should be appreciated that such a list is merely illustrative and not exhaustive of the types of materials that can be used to form a seal according to the principles of the present disclosure.
Thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. The foregoing description of example embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
