MXPA01005467A - Hydrodynamic seal and method of manufacture - Google Patents

Abstract

A hydrodynamic shaft seal assembly and method of forming hydrodynamic grooves involves forming a spiraling open channel portion in the face of the seal element, and cutting a flex-enhancing portion extending from the open channel portion further into the seal element to enhance the flexibility of the seal without further enlarging the open channel portion.

Description

HYDRODYNAMIC SHUTTER AND MANUFACTURING METHOD DESCRIPTION OF THE INVENTION This invention relates generally to hydrodynamic seals and more particularly to the formation of hydrodynamic undercuts in such seals. Hydrodynamic shaft seals are conventionally made by molding, protruding or cutting a spiral notch or other hydrodynamic or auxiliary obturator structure. The hydrodynamic notch interacts with the rotating shaft to pump any lubricating oil that may find its outlet under the lower part of the plug next to the oil in the plug. Hydrodynamic aids often take the form of a spiral notch as illustrated, for example, in U.S. Patent No. 4,739,998, or an open spiral channel as illustrated, for example, in U.S. Patent No. 3,857,156. Each of the above hydrodynamic configurations has its advantages and disadvantages. Spiral notches generally extend deeper into the seal than do open spiral channels and such that they generally increase the shutter's flexibility to a greater degree than channels do. The increased flexibility advantageously decreases the required sealing force that the plug must exert on the shaft to effect a fluid-tight seal, thereby decreasing wear and prolonging the life of the plug. The closed nature of such notches, however, provides less pumping action of fluid than an open spiral channel. Open spiral channels have higher fluid pumping capacity due to the relatively larger fluid volume capacity they offer, although they are generally less effective in increasing the flexibility of the seals. There is an upper limit for the size of such open channels. Making them too large in an effort to increase flexibility can impart the static sealing capabilities and / or lead to excessive hydrodynamic pumping action, which are detrimental to the performance of the plug. It is a main object of the present invention to provide a hydrodynamic shaft seal having the benefits of both the aforementioned closed notch and the open channel hydrodynamic auxiliaries without their inherent disadvantages. A hydrodynamic shaft seal assembly comprising a carrier, a sealing member mounted on the carrier for sealingly coupling a relatively rotating shaft, and at least one hydrodynamic feature formed on the sealing member having an open channel portion is provided. spiral and at least one cut that increases the spiral flexibility that extends from the portion of an open channel in the sealing member. The shaft seal in this manner is a hybrid of the types between a hydrodynamic obturator of open channel type and a hydrodynamic obturator of the closed notch type. The open channel portion utilizes the optimized hydrodynamic pumping action and decreases entrapment of debris while the cut that increases flexibility optimizes shutter flexibility without sacrificing the sealing and hydrodynamic sealing capabilities of the obturator. The invention also provides a method for forming such a hydrodynamic notch in an axle plug comprising forming the portion of the open spiral channel in a face of the axle plug together with the formation of the cutting portion that increases the flexibility extending in the shutter from the open channel portion. Shaft seals formed according to the method of the invention share the same advantages discussed in the foregoing. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will become more readily appreciated when considered in conjunction with the following detailed description and accompanying drawings, wherein: Figure 1 is an end view of a shaft seal radial type prepared according to the invention; Figure 2 is an enlarged cross-sectional view taken generally along the lines 2-2 of Figure 1; Figure 3 is an enlarged fragmentary sectional view of the obturator projection portion of the shaft seal showing details of the hydrodynamic feature according to the preferred embodiment of the invention; Figure 4 is a fragmentary cross-sectional view of a shutter assembly embodying the present invention shown assembled between a rotating shaft and a stationary hole in a housing; Figure 5 is an enlarged cross-sectional view of a portion of the sealing protrusion in the installed condition; Figures 6 and 7 illustrate a preferred method for forming the hydrodynamic characteristics according to the invention; and Figure 8 illustrates an alternative hydrodynamic seal construction. With reference initially to Figures 1, 2 and 4 a hydrodynamic shaft seal assembly constructed in accordance with a presently preferred embodiment of the invention is generally shown at 10 and comprises a sealing element mounted on a carrier 14 for installation within a orifice 16 of a housing 18 for sealingly coupling a relatively rotatable shaft member 20 such that it contains a fluid, and typically lubricating oil, on a side 22 of the oil of the seal assembly and to exclude contaminants on a side 24 of air axially opposite of the assembly 10. The sealing element 12 is in the form of a plate or pellet made of a polymeric material, and preferably a polytetrafluoroethylene (PTFE) compound which is cut from a tubular billet. The fillers can be added to the pellet material to specifically adopt the pellet for its intended use. Suitable fillers include glass fibers, molybdenum disulfide, graphite and bronze. The plug element 12 includes a radial portion 26 fixed to the carrier 14 and a flexible radial inner portion 28 extending radially inward from the carrier 14 and terminating in a sealing protrusion 29 for the sealed coupling to the shaft 20. The term " "shaft" as used herein includes a rotating shaft itself as well as a wear sleeve equivalent rotatable and movable with the shaft in a known manner to provide a sealing surface that may or may not be used with the assembly. of shutter. As best shown in Figure 2, the carrier 14 includes a metal outer case 30 and a metal inner case 32 having nested cylindrical body portions 34, 36 terminating at one end in the axially spaced annular end tabs 38, 40. which extend radially inwardly of the respective body portions 34, 36 and which define an annular space 42 between them in which the radial outer portion 26 of the sealing element 12 is disposed. An elastomeric sealing gasket 44 is also disposed within the space 42 between the end tab 38 of the outer case 30 and the radial outer portion 26 of the sealing element 12. The end flange 40 of the inner case 32 is forced towards the outer end flange 38 of the outer case 30 so that the radial outer portion 26 and the sealing gasket 44 are hermetically compressed between the end flanges 38, 40 for fixing the shutter element 2 securely in the carrier 14 and to prevent leakage of oil passing the sealing gasket 44. An end portion 46 of the outer case 30 is flanged on the free edge 48 of the inner case 32 which serves to lock the members 30, 32 of the case securely in the compressed condition.

Those skilled in the art will recognize the above described fastening arrangement to secure a sealing element, and particularly one made of polytetrafluoroethylene (PTFE), as is well known. The invention contemplates other carrier constructions and forms for securing the obturator element 12 to the carrier 14 in such a way, for example, that it joins in place to hold the obturator element 12 to a carrier 14 which is likewise a technique known in the art. as described, for example, in U.S. Patent No. 5,024,364 commonly owned by the assignee of the present invention and its description is incorporated herein by reference. According to the invention, the radial inner portion 28 of the sealing element 12 is formed with hydrodynamic characteristics generally indicated at 50 which operate during the relative rotation of the shaft 20 to generate a hydrodynamic pumping action which acts to return any oil that may travel to through the shaft 20 to the back of the obturator to the oil side 22 of the obturator assembly 10 in the direction of the arrow 52. In this way, any oil that finds its outlet between the shaft 20 and the sealing projection 29 will be returned from new to oil side 22 of plug assembly 10 by the action of 50 hydrodynamic characteristics. The hydrodynamic characteristics by themselves are known in the art and are usually in the form of an open spiral channel or spirally closed notch. The hydrodynamic feature 50 according to the present invention is a hybrid of the open channel and hydrodynamic auxiliary types of the closed notch type. According to the invention, the sealing element 12 is formed with a spiral open channel portion 54 in combination with at least one spiral cutting portion 56 which increases the flexibility extending from the open channel portion 54 in the shutter element 12 to provide greater flexibility to the shutter element 12. Figures 2, 3, 6 and 7 show the shutter element 12 in a relaxed or tension free state before installation on the shaft 20. It will be noted that the open channel portion 54 has walls 58, 60 that are separated from each other in a sealing surface 62 of the sealing element 12 and converges or is inwardly in a base or bottom 64 of the open channel portion 50 below the surface 62. The open channel portion 54 is generally V-shaped preferably in a cross section, and a wall 60 may be parallel to a longitudinal axis A of the obturator member 12, while the other wall 58 is inclined at a predetermined acute angle a with respect to the axis, and preferably in the range of approximately 25 a Four. Five. The invention contemplates a construction where both walls are inclined to provide an angle α included for example, in the range of about 50 to 90 °, as illustrated in Figure 8. Thus, the open channel portion 54 is devoid of the material of sealing element, as its walls separate. The open channel portion 54 defines a predetermined open volume space in which the oil can be collected and redirected through the hydrodynamic pumping action back to the oil side 22 of the plug assembly 10 during operation. The size and configuration of the open channel portion 54 and the cutting portion 56 are selected to provide optimum hydrodynamic action and seal flexibilities while retaining good static seal. The invention achieves these objectives through the combination of the open channel and the closed cut notch portions. Each portion is designed to meet the needs of a particular application with the above objectives in mind. The scrubber illustrated in the drawings, for example, is designed for a motor shaft seal application. The size, proportion and / or geometry of the hydrodynamic portions 54,56 can be altered to meet the specific needs of a particular application to achieve the desired objectives. Also, a single or multiple lead spiral combination notch may be employed having the features of the invention.

Figures 6 and 7 illustrate a presently preferred method for forming hydrodynamic auxiliaries according to the invention to include the open channel and cutting portions 54, 56 that increase flexibility respectively. The basic process for forming a PTFE sealing member from a tubular billet is described in US Patent No. 3,857,156, the disclosure of which is incorporated herein by reference. A tubular template is mounted on a tool holder and rotates about its axis with an external face 66 thereof exposed. A pair of spiral cross-sections are machined by a tool 68 in the element 66 of the obturator element 12 to provide the resulting open channel portion 54 and the cutting portion 56 that increases flexibility. The cuts intersect in such a way that they remove the material to provide the open channel portion 54 while retaining at least one cut extending beyond the open channel portion defining the closed cut portion 56 that increases flexibility . The other cut is angularly offset with respect to the first cut and extends from a location C on the face 66 that is radially spaced from the location of A of the first cut in the shutter in convergent relation to the first cut, in a location D which is at or slightly beyond a point of intersection X with the first cut at an intermediate location of ends A, B of the first cut. The intersecting cut separates the material necessary to form the open channel portion 54 and leaves an intact portion of the location of the intersection X to the base B of the first cut corresponding to the cutting portion 56 that increases flexibility. As illustrated in Figure 7, two cutting portions that increase the cut may result. In Figure 8, the angle of the cuts is greater and cross-linked to provide the double-cut increase portions, which extend from the open channel portions. It will be appreciated that the cross cut is only one way to form the open channel portion 54 to provide a spiral channel devoid of the shaft seal material, and is the preferred method. However, those skilled in the art will appreciate that other techniques currently used to form open channel type blends can be employed, such as forging, modeling, and embossing and the like in combination with a process step to form the cutting portion 56 that extends from the open channel portion in the obturator element 12 to provide increased flexibility. When the plug 10 is installed, as shown in Figure 4, there is interference from the shaft which flexes the radially inner portion 28 axially, causing the projection 29 of the plug member 12 to fall against the shaft 20 providing a collar-type plug of the shaft 20. As best illustrated in Figures 4 and 5, the cutting portions 56 open up slightly when the obturator flexes on the shaft, which has the effect of reducing the radial sealing force that the plug member 12 it exerts on the shaft 12 when installed, when compared to a plug without the cutting portion 56 added. The reduced load beneficially decreases the wear on the sealing element due to frictional contact and, in doing so, prolongs the operating life of the sealed element 12. It will also be appreciated from Figures 4 and 5 that the bending caused by the cutting portion 56 does not greatly alter the volume or geometry of the cutting portion 56, particularly at the location where the projection 29 engages the shaft 20. Obviously, Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it will be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.

Claims (18)

1. CLAIMS 1. A hydrodynamic shaft seal assembly characterized in that it comprises: a carrier; a shutter member mounted on the carrier for sealingly coupling a relatively rotating shaft; and at least one hydrodynamic groove formed in the sealing member having an open channel portion and at least one cutting portion that increases the flexibility extending from the open channel portion in the sealing member to increase the flexibility of the sealing member . The shaft seal assembly according to claim 1, characterized in that the open channel portion has opposite walls thereof converging on a bottom of the open channel portion and a cutting portion extends from the walls of the open channel portion. open channel portion. 3. The shaft seal assembly according to claim 2, characterized in that the sealing member includes a sealing surface and the walls of the open channel portion are separated from each other on the sealing surface. The shaft seal assembly according to claim 3, characterized in that at least one of the walls is positioned at a predetermined angle relative to a longitudinal axis of the sealing member. The shaft seal assembly according to claim 4, characterized in that one of the walls is parallel to the longitudinal axis. The shaft seal assembly according to claim 5, characterized in that another of the walls is positioned at an angle in the range of approximately 25-45 ° with respect to the axis. The shaft seal assembly according to claim 4, characterized in that both walls are arranged at an angle relative to the longitudinal axis. The shaft seal assembly according to claim 2, characterized in that the cutting portion comprises a cutting extension of one of the walls of the open channel portion. The shaft seal assembly according to claim 8, characterized in that the cutting portion is accommodated at a predetermined angle relative to a longitudinal axis of the sealing member. The shaft seal assembly according to claim 1, characterized in that the cutting portion extends to a first predetermined axial distance within the sealing member and the cutting portion extends to a second predetermined axial distance in the sealing member. larger than that of the first distance. The shaft seal assembly according to claim 1, characterized in that the spiral hydrodynamic feature is formed by machining spiral cuts within the sealing surface of the sealing member with one of the cuts intersecting and extending beyond the other cut. so as to remove the sealing member material on the sealing surface corresponding to the open channel portion and provide a remaining cut extending from the open channel portion beyond the sealing member to define the cutting portion. The shaft seal assembly according to claim 1, characterized in that the hydrodynamic feature is cut into the sealing member and includes a cut that extends to a predetermined depth in the sealing member from the sealing surface and terminates within the member. shutter in a bottom of the same and another cut of smaller depth crosses and intersects a cut between the sealing surface and the bottom of a cut. 13. A shaft seal assembly characterized in that it comprises: a carrier; a sealing member made of PTFE material mounted on the carrier and having a sealing surface that couples the shaft; and at least one hydrodynamic feature machined into the sealing surface engaging the shaft, including a spiral open channel portion devoid of the sealing member material and a cutting portion that increases the flexibility extending from the open channel portion. in the shutter member. A method for forming a spiral hydrodynamic feature in an axle plug, characterized in that it comprises: forming a spiral open channel portion in a face of the plug; and cutting a cutting portion that increases the spiral flexibility in the shutter extending from the open channel portion. The method according to claim 14, characterized in that the open channel portion is formed by cutting the sealing member. 16. The method of compliance with the claim 14, characterized in that the open channel portion is formed by removing the obturator material and the cutting portion is formed by machining a cut from the open channel portion in the obturator. 17. The method according to claim 16, characterized in that it includes forming the sealing member from PTFE. 18. A method for forming at least one spiral hydrodynamic characteristic in a PTFE shaft seal characterized in that it comprises: a PTFE shaft seal having a sealing surface; and machining the obturator surface of the shaft seal to form a hydrodynamic open spiral channel portion and a closed cutting portion that increases the spiral flexibility extending from the open channel portion.