SEAL AND SCRAPER ASSEMBLY FOR BALL BEARING SCREWS AND THE LIKE

Abstract: A seal and scraper assembly for a ball screw (10) and nut (11) actuator has a resilient seal ring (22) for reception by the nut which includes a radially internal helical thread (14) mating with the screw groove (12). The seal ring further has a radially compressible annular lip (28) extending at an angle in an axially outboard direction from the outer periphery (22b) of the ring to engage and be radially compressed by the nut (11). A rigid, annular mount ring (23) also has an internal thread received by the screw groove which has an axially inboard portion (23e) interfitting with the seal ring so as to permit relative axial movement of the seal ring (22) and mount ring (23), while preventing relative rotation of the rings.

Description: The invention relates to a ball screw and nut assembly comprising: a) an axially extending screw having an external helical thread and a ball receiving helical groove for the reception of a series of balls, b) a nut having an internal helical groove, bounded at least at one end by a seal and scraper assembly receiving end surface portion, received on said screw, c) said helical grooves of the screw and nut forming a raceway, d) balls received in said raceway permitting relative rotation and translation of said nut and screw with relatively low frictional impedance, e) a non-rigid, resilient, annular seal ring housed by said nut in said receiving portion at at least one end of the nut and having an axially inboard section and an axially outboard section, f) said seal ring including a radially internal helical thread projection received by and mating with said screw groove, g) said seal ring further having at its inboard section a radially compressible lip integrated with its outer periphery and extending at an acute angle from said outer periphery to engage and be radially compressed by said nut, h) a comparatively rigid, annular mount ring at said end of the nut, at least partly outboard of the seal ring, and having an axially inboard portion interfitting with said seal ring, i) the mount ring also having a radially internal thread received by and mating with said screw groove, and j) parts being provided for preventing relative rotation of the mount ring and the nut. A ball screw and nut assembly of this type is known from US-A-4,407,511. With this known assembly the helical thread projection is provided at the axially outboard section of said seal ring whereas said lip extends in an axially inboard direction. It is the object of the present invention to provide a ball screw and nut assembly of the above mentioned type which is effective to wipe a grease from the screw and retain it within the nut more effectively with less imposition of torque resistance, while at the same time providing a device which seals the inboard operating parts from ice, foreign particles, and high pressure water in a manner which greatly expands the areas in which ball screw assemblies incorporating the invention can be utilized. According to the present invention this object is solved by the following features: k) said helical thread projection is provided at the inboard section of said seal ring, l) said lip extends in an axially outboard direction, m) the mount ring and the seal ring have interfitting parts permitting relative axial movement of the seal ring and the mount ring. Other aspects of the invention are subject matter of the independent claims 7 and 13 and of the subclaims. An embodiment of the invention is shown in the drawing. Figure 1 is an elevational view of a typical ball screw and nut assembly which incorporates the invention; Figure 2 is a greatly enlarged, fragmentary, sectional elevational view, showing the assembly of the present invention in sealing position within one end of a nut; Figure 3 is a still more enlarged, fragmentary, sectional elevational view of the resilient portion of the seal ring only; Figure 4 is a transverse sectional view, taken on the line 4-4 of Figure 2; Figure 5 is an edge elevational view of the mount ring only; Figure 6 is an inner end elevational view thereof; Figure 7 is an inner end elevational view of the resilient seal ring only; and Figure 8 is an opposite, outer end elevational view thereof. Referring now more particularly to the drawings, and in the first instance to Figure 1, a typical ball screw and nut assembly comprises a screw 10, assembled with a nut 11. The screw 10 has a continuous helical thread 10a, and a continuous helical groove 12 of semi-circular cross section providing a raceway for balls 13, which permit relative rotation and translation of the nut 11 and screw 10 with relatively low frictional impedance. As Figure 2 indicates, the nut 11 has a mating internal helical groove 14, bounded by a helical projection 14a in the usual manner, and ball returns 15 which span a number of turns of the helical groove 12, to provide for ball recirculation. A clamp plate 16, secured by fasteners 17, may be provided to secure the ball returns 15 in position. Trunnions T can be provided on the nut 11 to facilitate mounting the ball screw and nut assembly in position. Provided at each end of nut 11, in the conventional manner, are stop surface shoulders 18, to cooperate with stop surfaces 19 provided on stops 20 which secure to the screw 10. The stops define the relative axial movement of the screw 10 and nut 11 which is permitted. As Figure 2 particularly indicates, the nut 11, at each end, may be counterbored as at 21, to provide an inset internal peripheral surface 21a, and a radial wall 21b. The counterbores 21 provide scraper and seal receiving surfaces at each end of the nut 11, which are of the character particularly disclosed in Figures 2-8. Each seal and scraper assembly comprises a resilient seal ring 22, and a mating outboard mount ring 23. While nut 11 and screw 10 are normally formed of a rigid metallic material, both the members 22 and 23 may be formed from non-metallic materials. Mount ring 23 is typically a rigid ring formed from a material such as a phenolic plastic, whereas ring 22 may be formed from an elastomeric nitrile, or other suitable resilient and rubber-like material. The mount ring 23 may also be formed of metal. Typically the seal ring 22 will have a durometer rating in the range 40 - 90. As Figures 2, 5 and 6 particularly indicate, the outboard part of the mount ring 23 comprises an axially outer annular flange 23a, provided with axial slots 23b to receive set screws or tangs 11a which project radially inwardly from the nut 11 and prevent relative rotation between the mount ring 23 and the nut 11. Alternatively the slots may be provided in the nut and the tangs on the mount ring 23. Axial and radial float of the mount ring 23 with respect to the nut 11 is, however, permitted by the construction. The slots 23b are provided in axially projecting keys 23c and 23d of differing arcuate extent, which are disposed in 180° opposing relation. Between these keys, diametrically reduced, axially inboard seal-mounting end 23e and intermediate web portion 23f are provided. A series of radially projecting teeth 23g of rectangular configuration are provided on the end 23e between the projecting keys 23c and 23d, as shown in Figures 5 and 6. The radially internal surface of mount ring 23 is helically threaded to closely mate with the thread 10a and groove 12 of screw 10, and the thread is of such axial extent that up to two helical turns of the screw groove 12 are spanned by the radially inwardly projecting ring thread 23h. Thread 23h is accommodated in the screw groove 12 and defines helical groove portion 23i which receives the thread 10a of screw 10, as indicated in Figure 2. As Figure 2 further illustrates, resilient seal ring 22 comprises an axially inboard section 22a and an axially outboard section 22b, which has slots 22c and 22d, respectively, for receiving the keys 23c and 23d. Provided between the slots 22c and 22d, are splines 22e and grooves 22f, which interfit with the teeth 23g provided on the ring 23. Teeth 23g are of considerably shorter axial extent than the grooves 22f which receive them. Retention lips 22h are provided on seal ring 22 between the slots 22c and 22d, and maintain the mount ring 23 and seal ring 22 in axially assembled position, while permitting them some axial float. In a typical assembled position of the assembly, there will be an axial space 24 between the flange 23a and lip 22h, and an axial space 25 between the lip 22h and the end 23e and its teeth 23g. There will likewise be an axial space 26 between the end 23e of mount ring 23 and the inboard section 22a of the seal ring 22. Similarly; an axial space 27 will be present between the inner end wall of the seal ring 22, and the radial wall 21b. The inboard section 22a of seal ring 22 includes a radially outer annular wall 22i (see particularly Figures 2 and 3), having an integral lip 28 which, in non-compressed condition, extends at an acute angle in an outboard direction, as shown in Figure 3. When the seal is in inserted position, the lip 28 is collapsed radially and functions as a sealing surface, in the manner illustrated in Figure 2. Radially inward of wall 22i, and spaced circumferentially as at 29 from the wall 22i, are wiper thread projections 22j, which wipe the grease or lubricant from the screw and tend to return it in an inboard direction. Internally the seal ring 22, inboard of splines 22e, is threaded to match the screw 10, and thus has, in addition to the thread projection 22j, the thread grooves 22 1 , all of which collectively function as both seals and scrapers. The interrupted scraper threads have ends 22k which project radially inward of the remaining portions of the threads and are compressed when the ends are in engagement with the screw groove 12. The internally threaded portion of the seal ring 22 spans at least one turn of the screw thread 10a, and extends into the adjacent groove 12 on each side thereof. As particularly shown in Figure 7, the thread projection 22j is interrupted by several generally radial scraper surfaces 30 intersecting the radial direction of the screw 10 at an oblique angle. Circumferentially spaced from each scraper surface 30, and spaced a distance circumferentially therefrom as at 31, is an axially inclined lubricant return surface 32 opposite the surface 30, for the purpose of directing the lubricant axially inward relative to the outer end of the nut. The scraper surface 30 has a leading edge 30a, which in its uncompressed state, extends radially inwardly of the thread projection 22j, and accordingly is radially compressed when installed in position, as indicated in Figure 2. Each scraper surface 30 is connected to outer wall 22i of the seal ring 22 by a web 33, with the front surface of the web also functioning as a portion of the scraper surface 30. Thread projection 22j is of sufficient extent to seal along the thread form of screw 10, so that the interruptions created by scraper surface 30, and return surface 32, do not provide axially open flow passages through which lubricant can escape. In operation, the composite assembly formed by seal ring 22 and mount ring 23, is allowed to move axially in the counterbore 21 to allow for axial lash between the nut 11 and screw 10. At the same time, the seal ring 22 is permitted to float axially with respect to the mount ring 23, to relatively adjust to manufacturing tolerances and permit lip 28 to compress to maintain continuous circumferential contact. Relative rotation and translation of the screw 10 and nut 11, causes the internal thread projections 22j of the seal ring 22 to scrape or wipe lubricant from the groove 12, and redirect it in an axially inward direction. The internally threaded surface of ring 23 shields the thread projections 22j from outside influence, and further, of course, could function as a grease scraper and retainer on an emergency basis in the event of damage to the internal threads of seal ring 22. With the lip 28 extending in a direction toward the mount ring 23, when wash water under high pressure seeking to enter the nut enters the space radially inward of compressed lip 28 and exerts a pressure in the radial direction x , it causes the annular lip 28 to only more tightly seal. Lip 28 alleviates manufacturing imperfections in the sense that it allows the thread projections 22j to conform to the screw thread 10a without undue frictional impedance, while, at the same time, relieving undue internal grease pressure such that vent holes for eliminating these pressures need not be provided. The square tooth spline structure provided to intermesh the seal ring 22 and the mount ring 23 at 23g and 22e, aids in combatting any radial movement between the seal ring 22 and the mount ring 23. With the construction indicated, outside dynamic water pressures may be tolerated without entrance of water to the interior of the nut 11. The internal threads of the mount ring 23, prevent the ingression of foreign material such as sand, dust, frost and ice into the nut, and remove it from screw 10. In a sense, the mount ring 23 operates as an ice-breaker, and shields the seal ring 22 from ice particles and the like, which may be seeking to enter the assembly along the external thread surface of screw 10. Finally with the two-piece construction which has been described, a change of either seal ring 22 or mount ring 23 in the assembly is easily accomplished, and the assembly is easily made and oriented to assure an exact fit within the nut 11.

Claims: A ball screw and nut assembly comprising: a) an axially extending screw (10) having an external helical thread (10a) and a ball receiving helical groove (12) for the reception of a series of balls (13), b) a nut (11) having an internal helical groove (14), bounded at least at one end by a seal and scraper assembly receiving end surface portion, received on said screw (10), c) said helical grooves (12, 14) of the screw (10) and nut (11) forming a raceway, d) balls (13) received in said raceway permitting relative rotation and translation of said nut (11) and screw (10) with relatively low frictional impedance, e) a non-rigid, resilient, annular seal ring (22) housed by said nut (11) in said receiving portion at at least one end of the nut and having an axially inboard section (22a) and an axially outboard section (22b), f) said seal ring (22) including a radially internal helical thread projection (22j) received by and mating with said screw groove (12), g) said seal ring (22) further having at its inboard section (22a) a radially compressible lip (28) integrated with its outer periphery and extending at an acute angle from said outer periphery to engage and be radially compressed by said nut (11), h) a comparatively rigid, annular mount ring (23) at said end of the nut (11), at least partly outboard of the seal ring (22), and having an axially inboard portion (23e) interfitting with said seal ring (22), i) the mount ring (23) also having a radially internal thread (23h) received by and mating with said screw groove (12), and j) parts being provided for preventing relative rotation of the mount ring (23) and the nut (11), characterized by the following features, k) said helical thread projection (22j) is provided at the inboard section (22a) of said seal ring (22), l) said lip (28) extends in an axially outboard direction, m) the mount ring (23) and the seal ring (22) have interfitting parts permitting relative axial movement of the seal ring (22) and the mount ring (23). The assembly of claim 1 wherein said interfitting parts on the mount ring (23) and seal ring (22) comprise circumferentially arranged splines (22e), grooves (22f) and teeth (23g). The assembly of claim 1 wherein said inboard section (22a) of the seal ring (22) has a radially inner scraper portion defined by said helical thread projection (22j), and a radially outer seal portion defined by said lid (28); said scraper and seal portions being radially spaced and connected by compressible connecting web sections. The assembly of claim 1 wherein said helical thread projection (22j) is circumferentially interrupted by recess portions providing a generally radial scraper surface (30) on one radial marginal side and an axially inclined grease return deflecting surface (32) on the other; and said helical thread projection (22j) on the inboard section (22a) of the seal ring (22) has at least one complete turn disposed to block grease from passing axially through said interruptions in a direction toward said mount ring (23). The assembly of claim 1 wherein each mount ring internal thread (23h) has up to two helical turns. The assembly of claim 4 wherein said inboard section (22a) of the seal ring (22) has a radially outer annular wall (22i) radially spaced from said interrupted internal helical thread projection (22j). A seal and scraper assembly for a ball screw and nut actuator having an axially extending screw (10) with an external helical thread (10a) and a ball receiving groove (12), and a nut (11), having an internal helical groove (14) bounded at least at one end by a seal and scraper assembly receiving end surface portion, received on said screw, with said grooves (12, 14) of the screw (10) and nut (11) forming a raceway for balls (13) permitting relative rotation and translation of said nut (11) and screw (10) with relatively low frictional impedance, said seal and scraper assembly comprising: a) a non-rigid, resilient, annular seal ring (22) for reception by said nut (11) in said receiving portion at at least one end of the nut and having an axially inboard section (22a) and an axially outboard section (22b), b) said seal ring (22) including a radially internal helical thread projection (22j) received by and mating with said screw groove (12), c) said seal ring (22) further having at its inboard section (22a) a radially compressible lip (28) integrated with its outer periphery and extending at an acute angle from said outer periphery to engage and be radially compressed by said nut (11), d) a comparatively rigid, annular mount ring (23) at said end of the nut (11) having an axially inboard portion (23e) interfitting with said seal ring (22) to prevent relative rotation between the rings (22, 23), e) the mount ring (23) also having a radially internal thread (23h) received by and mating with said screw groove (12), and f) parts being provided for preventing relative rotation of the nut (11) and the mount ring (23), characterized by the following features: g) said helical thread projection (22j) is provided at the inboard section (22a) of said seal ring (22), h) said lip (28) extends in an axially outboard direction. The assembly of claim 7 wherein the mount ring (23) and the seal ring (22) have interfitting means preventing relative rotation of the rings while permitting some relative axial floating movement of the seal ring and mount ring to achieve independent seating of seal ring thread projection (22j) and mount ring internal thread (23h) in the screw groove (12). The assembly of claim 8 wherein said interfitting parts on the mount ring (23) and seal ring (22) comprise circumferentially arranged axially parallel spline and groove connections consisting of splines (22e) on the one of the mount ring and seal ring and grooves (22f) on the other, and wherein the splines (22e) are of different axial length than the grooves (22f). The assembly of claim 9 wherein said inboard section (22a) of the seal ring (22) has a radially inner scraper portion defined by said helical thread projection (22j) and a radially outer seal portion defined by said lip (28); said scraper and seal portions being radially spaced by compressible connecting web sections. The assembly of claim 8 in which said interfitting means comprises parts of differing axial length. The assembly of claim 8 wherein shoulder means on said mount ring (23) and seal ring (22) form a trap restricting total separation of said mount ring and seal ring. A method of sealing the threads of a ball screw and nut assembly having an axially extending screw (10) with an external helical groove (12), and a nut (11) with an internal helical groove (14) bounded by a thread seal receiving end surface portion which is received on the screw, with the helical grooves (12, 14) of the screw and nut forming a raceway for balls (13) permitting relative rotation and translation of the nut and screw, with relatively low frictional impedance, and wherein a resilient seal ring (22) has an inboard section (22a) with a radially internal helical thread projection (22j) adapted to be received by the screw groove (12), and is provided with a rigid mount ring (23) with a radially internal thread (23h) adapted also to be received by the screw groove (12), the mount ring (23) and seal ring (22) having interfitting parts capable of preventing their relative rotation while permitting relative axial movement of the rings, said method comprising the steps of: a) axially relatively moving the seal ring (22) and mount ring (23) to interfit the interfitting parts thereof to form an assembly; b) relatively moving an interfitted seal ring (22) and mount ring (23), and a nut (11), axially to position the seal ring and mount ring in said receiving end surface portion of the nut and restrain relative rotation of the nut and assembly; c) relatively rotating the nut (11) and screw (10) to thread the screw into the nut, and the seal ring (22) and mount ring (23); and d) relatively axially moving the seal ring (22) and mount ring (23) to permit each to adjust independently to the helical configuration of the screw groove (12).

Inventors: BENTON, ROBERT L., MARTINSONS, DAINIS O.
Applicants: THOMSON SAGINAW BALL SCREW COMPANY, INC.
Application year: 1989
Main classification: F16H25
IPC codes: F16J15, F16H25