GB2208243A - Unitized lip seal - Google Patents

Description

1 22M 8 2 43 UNITIZED EXCIUSION SEA1

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relate.s. generally to shaft seals and more particularly relates to a debris-excluding shaft real with an extended life expectancy achieved through ninimization of frictional contact between rotating sealing surfaces and through entrapment of abrasive contaminants within a porous filter element.

Description of Prior Developments

Prior debris-excluding seals have traditionally experienced various operational pr oblems including the generation of excessive beat via frictional contact between rotating seal elements. This frictional heat is primarily caused by the relatively high contact forces existing between the rotating seal elements. While these high contact forces were believed necessary to effect a reliable seal, they have beer, shjw!-, to cause rapid wear between the rotating sealing surfaces and have significantly reduced seal life.

One approach to overcome this heating problen is to avoid contact between the rotating elements by providing a small clearance therebetweerj. Bowever this approach presents another problem wherein debris passes through, or is entrapped within the clearance space. This condition results in extremely rapid abrasive wear of the sealing elements as well as wear of the rotating shaft.

It has generally beer, assumed that by providine a plurality 1 of engagement Points between rotating seal elements so as to f orm a plurality or series of sealing surfaces, a more effective barrier to debris would result. Thus, known debris excluding eeals generally provide several points of contact between the rotating real elements to form a series of sealing surfaces. Bowever, each contact point acts as a source of frictional heat, which as noted above, adversely affects seal life.

A particularly difficult sealing problem arises in those applications where dirt excluding Beals must accommodate significant shaft runout and/or shaft-to-bore misalignment. Prior seals have not proven effective in these cases and have not beer, well accepted by industry.

Another inconvenience associated with existing dirt excluding seals is the difficulty of properly and accurately aligning the stationary seal element with respect to the rotating seal element during installation of the seal assembly about a shaft.

1r) those instances where a seal is provided with hydrodynamic features, an additional problem often arises. While the hydrodynamic pu=ping effect serves to prevent lubricant from 1-o passing bey:)nd the seal lip, a vacu,= is generated which tends,, draw or suck air beneath the lip fro= the surrounding environment or, the dry or air side of the seal. If the air contains any contaminants such as dust particles, the contaminants are also drawn under the seal lip. This not only accelerates lip wear and reduces seal life but it also results in contaminanted lubricant and/or wear of internal moving parts.

When a real produces a hydrodynamic action a surprisingly large pressure differential is developed across the seal lip. As noted, a vacuum effect is created or) the air or dry side of the seal while ambient pressure is present within the wet or inner side of the seal. This condition can result in large contact forces between the lip and shaft if an air tight seal is formed therebetween. This contact force c an be reduced by allowing a Emall amount of air to be drawn past the seal lip eD as to mini=ize the pressure differential., Ezwever, by drawing air beneath the seal lip, the problem of contanination arises.

Moreover, large contact forces such as described above generate excessive frictional beat. In some instances this heat between the shaft and lip becomes;;'ro great that the lubricant which flows against and beneath the lip breaks down and becomes carbonized. This carbonized lubricant then bonds to the lip and/zr shaft and forms, a deposit or build-up of hardened carbon. This build-up then prevents continuous contact between the lip and shaft and Tesults in real. leakage.

a need exists for a unitized dirt-excluding shaft real which minimizes the generation of frictional beat by reducing the contact f0Tee between rotating sealing surfaces thereby extending seal life and protecting shaft finish.

A need also exists for a seal. which prevents contaminants such as dust particles from passing beneath a seal lip, particularly in those cases where the seal is Lgenerating a hydrodynarnic effect, yet which avoids large contact forces between the seal lip and the shaft.

SUMMARY OF THE 11;VE?x"LION.

W The present invention has been designed to fulfillthe needs noted above and therefore has as a primary object the provision of a unitized dirtexcluding shaft seal having extended life expectancy and improved perfZTMatiCt, Particularly in those applications where extremely tusty aTd dirty operating conditions prevailt Typical applications include fTzn't crankshaft seals for off-road engines as well as drive shaft and axle seals for, earth moving machinery.

or ameliorate one or moreof or to provide improvements genera-lly., 7-Z_ 1 Another object is to provide a dirt-excluding shaft real which minimizes the contact forces between rotating seal elements so as to minimize the production of frictional heat and correspondingly reduce the drag force of the seal on the shaft.

t Still another object is to provide a dirt-excluding shaft real which employs a single line of contact between a stationary seal case and a rotating seal lip so as to further reduce frictional heat.

Another object is to prevent airborne particles from contacting a seal lip and to prevent such particles from being drawn under the lip, particularly in those cases where the particles are drawn toward the lip by a vacuum created by hydrodynamic effects.

Yet another object of the present invention is to facilitate the handling, installation and alignment of a dirt excluding shaft seal about a shaft.

Another object is to provide a dirt-excluding seal which effectively accommodates significant anourits of shaft Tunout as well as sigrAficant misalignment between the seal bore housing and the shaft.

The present invention is generally directed to a unitized dirt-excluding seal which includes a static exclusion element arranged in limited contact with a rotating exclusion element. The rotating element is pressed or bonded to a shaft so as to rotate with the shaft. These coacting sealing elements provide an initial or primary barrier to exclude contaminants such as dust and abrasive particles from the interior of the seal. The contaminants are thus prevented from passing from the environment surrounding the seal to an interior region within the seal, wherein lubricart^or bearing surfaces are located.

A secondary barrier may be incorporated with the seal to further prevent the passage of contaminants therethrough. The secondary barrier may take the form of a foam or felted filter that contacts or nearly contacts an interior portion of the rotating element. Additional Oealing lips may be provided on the interior of the primary and/or secondary barrier to. serve as conventional lubricant seals. These conventional seal elements may allow small amounts of ambient air to pass beyond the seal lip so as to prevent excessive loading between the lip and shaft yet without allowing passage of contaminants past the lip. This is possible because of the presence of the filter which traps the airborne contaminants before they contact the seal lip so that only clean filtered air reaches the interior seal lip.

Various other objects, features and attendant advantages of the present invention will be more fully appreciated frz)IL the following detailed description when considered in connection with the accompanying drawings, in which the sane reference numbers designate the same or corresponding parts throughout.

i BRIEF DESCRIPTION OF THE DRAWINGS

Pi EUT e 1 is a fragmental axial sectional vi ey of a conventional rotary shaft lip seal pTovided with a debTiS exclusion lip of known design;.

Fie.uTe 2 is a fragmental axial sectional view of a unitized exclusion lip seal according to the invention; Figure 3 is a fragmental sectional view of the shaft engaging portion of the unitized exclusion seal of Figure 2 showing the proper positioning of the case flange in phantom; FigaTe 4 is a fragment: al sectional view of an alternate embodiment of the unitized; exclusion seal combined witha polytetrafluoroethylene radial lip seal; i c Figure 5 is a fragmental sectional view of yet another embodiment of the unitized exclusion seal combined with a conventional elastomeric radial lip seal; Figure 6 is a fragmental sectional view of still another embodiment of the unitized exClUBior) seal provided with a secondary filter to absorb airborne contaminants; and Figure 7 is a fragmental sectional view of still another embodiment of the unitized exclusion seal provided with a secondary filter to absorb airborne contaminants.

DETAI1ED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As seen in Fi&are 1, a conventional one-piece dirt excluding shaft seal (1) includes a dirt exclusion lip (3) and an oil sealing lip (5) each engaging a rotating shaft (7). This traditional design depends on dynamic irtereference between the lips and shaft to maintain ar, adequate seal. The exclusion lip (3) is intended to run on an oil film which tends to attract dust particles fro= the air. When the oil and dust particles mix, an abrasive slurry is formed which accelerates seal wear and leads to seal failure.

In use, heat is generated by friction between the seal lips (3), (5) and the shaft. The frictional heat pr:)duced by the exclusion lip (3) is transferred along the shaft and raises the shaft temperature to a value above that which would result from the sole use of the oil sealing lip (5) in the absence of dirt exclusion lip (3). Moreover, frictional heat generated by the oil sealing lip is transferred to the shaft and raises shaft temperature adjacent the exclusion lip as well. This increased shaft temperature adversely affects the life of each lip and correspondingly reduces the effective life of the seal. Beat from the frictional contact with the shaft causes the elastomeric or polymeric lip material to beoome hard and brittle and eventually chip and break, thereby causi tg a leak.

C- As seen in Figure 2, a basic embodiment of the present invention is directed to a two-piece unitized shaft seal (9) which is mounted over shaft (7) and, press fit within the boTe of a seal housing (11). The unitized' seal includes an annular case member (13) and an annular shaft ev gaging member (15). Typically, the shaft engaging member is pressed onto or bonded to the shaft and rotates with the shaft', while the case member remains static within the housing or bore (11).

Member (15) may be f:)rZed of any non-metallic engineering material such as an elastomeric or thermoplastic material. Preferred materials include:carboxylated nitrile and which are highly resistant to abrasilor,, car, withstand high operating temperatures, are easily mOlded and have good resistance to chemical attack. The case member (13) is preferably formed of a metallic material for efficiently conducting heat from me=ber (15) towards housing (11) where it is dissipated without raising the temperature of the shaft.

Member (15) is provided with an annLilar unitiziLF channel (17) which not only prevents disengagement of members (13) and (15) prior to installation but also aids in the installation of the unitized seal. That is,:channel (17) serves to axially align the shaft engaging member (15) with respect to the radial flange (19) of the case nembeT. The radial inner extremity (20) of the flange is properly and automatically disposed between the radially extending walls (21) of the channel upon installation. Little, if any additional adjustment is required once the unitized seal is seated within its housing.

An important feature of the unitized real is the relative 1 axial widths of the channel (11'7) and the flange (19). In order to minimize or prevent unwanted '.contact between the internal walls 1 (21) of the channel and the surfaces of the flange, the width A of the flange should be less than the width B of the channel. Moreover, a clearance C should be maintained between the radial innermost end face of the flange and the floor of the channel to prevent contact therebetween in the event of excessive radial shaft runout and/or excessive radial shaft whip.

In order to prevent disassembly of the shaft engaging member (15) from the case member (13), channel (17) is bounded by annular radial ridges or projections (23). These projections, while preferably formed of a resilient material, are radially short and axially thick to resist axial deflection upon contact with the radial inner extremity of flange (19). Such contact may occur during handling and installation of the seal, but once the seal is correctly installed, this contact is avoided or minimized by the dimensioning noted above.

The shaft engaging member (15) is further provided with a radially outwardly projecting lip element (25). As seen as Figure 3, the lip element may be formed with a relatively thin and resilient end portion (27). The tip (29) of the end portion is axially extended toward and over channel (17) to ar, extent which ensures a proper contact pressure range between the tip and ar, outer surface portion of the flange. This contact pressure should range from aPProximatelY 0.5 oz. to 25.0 oz. for most practical applications.

AT, additional advantage is gained by this dimensioning of the flange, channel and tip. By erisuTimg a biased interference fit between tip (29) and flange (19) over an axial extent X as shown in Figure 3, axial end play of shaft (7) will not result in a loss of contact between the tip (29) and flange (19) within a tolerance of X. The degree of interference X may be varied depending upon the acceptable limits of contact force and shaft end play.

In the event of shaft runout or shaft whip, contact will be t i el maintained between tip (29) and flange (19) since relative radial movement between these real hembers does not affect the axially directed sealing contact forIce therebetweer). This is riot the case, however, for conventional seals such as shown in Figure 1 which rely upon radial sealing forces. The axial widths D and E of the lip element (25) and Ithe end portion (27), respectively, should be generally less that the thicknesses F, G of either of the radial projections (23) so that the specified light contact pressure range is maintained between the tip (29) and the flange (19).

A definite advantage is gained by providing a single circumferential line or band'4 of continuous contact between tip (29) and flange (19) in that the frictional heat generated along this annular contact line i;s limited to a single soj-ce and location and is thus adequately controlled and significantly reduced. Little if any heat ils transferred from this contact area to the shaft. Moreover, thit contact needs no lubricant so that attraction and accumulation of airborne particulate contaminants by oil or the like is avoided., Installation of the unitized seal is simplified by its design. The seal is simply piessed axially into housiLg (11) in a conventional manner after the shaft engaging member has been radially stretched over the shaft. The radial projections (23) of the shaft engaging member prevent its disengagement from the case member during installation du! e to the relatively stiff resistance to deflection provided by thei,shoTt height and wide axial width of the projections. Once seatedivithin housing bore (11), either the case or the shaft engaging 1 member may be exially shifted if desired, to attain single point contact therebetween at tip (29).

Thus, the radially inner end portion or extremity 20 of shaft (19) may be aligned without contact within channel (17) during use.

Another embodiment of the invention is shown in Figure 4 wherein case member (13) is rE4ially and axially stepped at (31) to provide an annular mounting ridge (33) against which a polytetrafluoroethylene (PM) lip element (35) Is clamped in a known fashion. A sealing gasket (37) is provided between the lip element and the clamping member (39) to prevent leakage in a conventional gasket arrangement.

Figure 5 depicts another embodiment wherein an elastomeric seal lip (41) is bonded to the case member in a common configuration. In both Figures 4 and 5, it can be appreciated that the frictional heat developed by the dirt exclusion portion of the seal is limited to the flange (19). This heat is transferred from the metal flange to the seal housing (11) where it is dissipated without adversely affecting either seal lip element (35) or (41).

Since most elastomeTs and thermoplastics resist heat transfer, little if any heat is transferred through lip element (25) of the shaft engaging member to the shaft. This significantly enhances the life of the seals and protects the shafts. Moreover, the light contact pressure between the cantelevered tip (29) of lip element (25) and the flange (19) even further reduces frictional beating of the seals.

A fuTtheT refinement of the invention is shown in Figure 6. Although the seal shown in Figure 6 appears similar to that shown in Figure 4, a significant improvement is incorporated in the design of Figure 6. While this embodiment includes a primayy dust excluding portion composed of annular shaft engaging member (15) and flange (19) as descTibed above, a secondary porous annular filter element (45) is clamped between step (33) of metal care (13) and lip element (35) with the inner case or clamping member (39). One or more gaskets (47) may be clamped between the filter and case arid/or between the filter and lip element. The gaskets, preferably rubber washers, prevent lubricant from passing between the radial- outermost tip of the lip (35) and casing (13). This in turn prevents the lubricant from wicking through the foam 41 filter element and reducing its effectiveness.

As EL secondary barrier to dust and other particulate contaminants, the filter (45) its arranged to be in contact with the rotating shaft engaging member (15) or at least in near contact therewith. Filter (45) is preferably formed of a felted polyurethane foam since polyurethane foam has excellent resistance to abrasion an ensures a long operational life. The mesh or pore size of the foam is preferably within the range of I to 500 microns.

As further seen in Figure,6, lip element (35) is provided with spiral grooves or slits (49) for generating a hydrodynamic pumping action which tends to, pump lubricant inwardly in the direction of arrow (51). This pumping action tends to create a vacuum around the outer side of the lip as at (53). This vacuum in turn tends to draw in particulate airborne contaminants past the dirt and dust excluding elements 15 and 19.

By arranging filter (45) between the dust excluding elements 15 and 19 and the lip element (35), all particulate matter drawn I past the first contaminant excluding barrier (15,19) is embedded within the pores of the filter.45) and is prevented from reaching the lub7icant sealing lip (35). This significantly increases seal life and allows contact forces between lip element (35) and shaft (7) to be reduced.

Thall. is, in order to prevent coritarminants from being drawn past lip element (35), prior designs have maintained large contact forces between the lip and shaft:so as to form an air-tight seal. This approach often failed because at high rotative speeds the lip was unable to maintain contact with the shaft and contaminants would thus gain entry to the lubricant side of the seal. Furthermore, the high contact forces augmented by the hydrodynamically induced pressure differential carbonized the lubricant as discussed above.

t 1 C The seal shown in Figure 6 need not and preferably does not maintain an air-tight seal but rather maintains a light contact to allow a small amount of filtered air to flow past lip element (35). This air flow tends to neutralize any hydrodynamically induced pressure differential and thereby prevents. excessive lip-to-shaft contact forces.

As shown in Figure 7, the two-stage Beal may be used without the lip Beal (35) so as to serve only as a dust guard. Moreover, the filter (45) may be used with any of the embodiments Bhown in Figures 2, 4 or 5 as well- It is also possible to bond the filter (45) to the rotating element (15) instead of clanping or bonding the filter to the metal case (13).

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

h 1 11 0

Claims (6)

1 CLAIM:

1. A unitized seal for excuding debris from a portion of a rotating shaft, comprising:

an annular shaft-engaging member having an annular channel with a predetermined. width formed therein, said channel bounded by wall surfaces extending radially outwardly from said shaft-engaging member; a lip element provided on said shaft-engaging member, said lip element formed with a ti. P portion; and a seal case member comprising a radially inwardly projecting flange having a radial inner extremity formed with a width less thar, said predetermiped width, said flange positioned within said channel and in contact with said lip element.

2. The seal of claim 1, further comprising a seal lip element mounted to said case memli.er for sealing lubricant between said seal lip element and said rotating shaft.

3. The seal of clair 1, ifurther cozpTisir,g filter means disposed adjacent said shaft engaging member for entrapping contaminants within said filter means.

4. The seal of claim 1, further comprising a seal lip element mounted to said case member for sealing lubricant between said real lip element and said rotating shaft, and filter means axially disposed between said shaft engaging member and said seal lip for entrapping contaminants within said filter means.

1 1 1

5. A unitized seal substantially as described herein with reference to the accompanying drawings.

6. A method of forming a unitized seal substantially as described herein with reference to the accompanying drawings.

1 c Published 1988 at The Patent Office. State House. 66'71 High Holborn. London WClR 4TP. PurLher copies may be obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con. 1187.