Abstract:
There is described a seal assembly for sealing the gap between a rotary member and a fixed member, so as to prevent passage of a fluid from a first to a second environment located on opposite sides of the gap; the seal assembly has a first ring integral with the rotary member, a second ring integral with the fixed member, and an elastically deformable sealing member integral with the second ring and in turn having at least one lip cooperating in fluidtight manner with a mating portion of the first ring; and, on the side cooperating with the mating portion, the sealing member has a spiral groove which, in use, produces a fluid-dynamic pumping effect to pump the fluid away from the sealing area and towards the first environment.

Description:
The present invention relates to a seal assembly for a rotary member. 
     BACKGROUND OF THE INVENTION 
     In mechanical design, friction must be reduced by lubricating rotary members in an oil bath, and numerous applications call for immersing portions of the rotary members in the oil bath, while other portions, adjacent to them, operate in a sealed, oil-free environment. To do this, seal assemblies are known, as described for example in U.S. Pat. No. 5,348,312, which are housed inside the gap defined between a normally fixed, hollow casing and a rotary member housed inside the casing, and which, in use, seal the gap to prevent oil flow into the dry environment. 
     More specifically, seal assemblies of the above type are axially symmetrical with respect to the axis of the rotary member to which they are fitted, and comprise a metal inner ring integral with the rotary member; a metal outer ring fixed to the casing; and sealing members made of elastically deformable polymer material and interposed between the inner ring and the rotary member, between the outer ring and the casing, and between the rings themselves. 
     More specifically, the inner ring comprises an axial portion fitted to the inner ring; and two radial portions extending from respective opposite ends of the axial portion and inwards of the gap between the casing and the rotary member. In the example described in U.S. Pat. No. 5,348,312, the radial portion facing the oil bath is of a larger extension than the other radial portion, and terminates close to the casing. 
     In axial half-section, the outer ring is substantially L-shaped, and comprises an axial portion, and a radial portion extending from one end of the axial portion. More specifically, the radial portion of the outer ring is adjacent to the smaller-extension radial portion of the inner ring, and defines, with the other radial portion of the inner ring, a sealing chamber between the two rings. 
     The sealing members comprise a first seal pressed between the axial portion of the inner ring and the rotary member; and a second seal completely covering the outer ring and interposed between the outer ring and the casing to seal the chamber between the two rings. 
     More specifically, on the side facing the oil bath, the second seal has a lip which provides for contact sealing in contact with the larger-extension radial portion of the rotary inner ring. 
     The above contact seal has the typical drawback of producing rapid wear of the lip of elastomeric material. 
     To at least partly eliminate the above drawback, the lip has a number of concentric, radially equally spaced, circumferential grooves to reduce the contact surface and, therefore, friction with the rotary inner ring. Though it provides for prolonging the working life of the seal with the sealing lip, the above solution is not altogether satisfactory. 
     Seal assemblies are also known, as illustrated for example in U.S. Pat. No. 4,974,869, in which the sealing lip has no grooves, and the radial portion of the metal inner ring has a single spiral groove. In actual use, the sealing lip engages the spiral groove rotating integrally with the rotary member, thus again providing for contact sealing. Moreover, as the inner ring rotates integrally with the rotary member, the spiral groove produces a fluid-dynamic “pumping” effect of the air between the lip and the inner ring, which forces the oil towards the oil environment, thus enhancing sealing performance. 
     In this case too, extensive sliding contact between the spiral groove on the inner ring and the sealing lip of elastomeric material produces severe mechanical wear, and so greatly reduces the working life, of the lip. Moreover, the thinness of the inner ring and the technical difficulties encountered in machining it prevent the formation of deeper grooves shaped to vary airflow, so that the working life of the seal assembly and the effectiveness of the fluid-dynamic “pumping” effect remain limited. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a seal assembly for a rotary member, designed to eliminate the aforementioned drawbacks typically associated with known seal assemblies. 
     According to the present invention, there is provided a seal assembly as claimed in the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows an axial section of a seal assembly for a rotary member, in accordance with the present invention; 
         FIG. 2  shows a larger-scale, axial half-section of the  FIG. 1  seal assembly; 
         FIG. 3  shows a larger-scale section of a detail of the seal assembly in  FIGS. 1 and 2 ; 
         FIG. 4  shows a section along line IV-IV in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIGS. 1 and 2 , number  1  indicates as a whole a seal assembly housed in the gap  2  defined between a hollow casing  3  and a rotary member, e.g. a shaft  4 , of axis A, housed inside casing  3 . On opposite sides of seal assembly  1 , gap  2  comprises an environment  5  for containing a lubricating oil bath; and an environment  6  from which oil must be kept out, and which in use contains air. 
     Seal assembly  1  comprises an inner ring  7  integral with shaft  4 ; an outer ring  8  integral with casing  3 ; and an elastomeric member  9  interposed between rings  7  and  8  and carried by ring  8 . 
     Inner ring  7  comprises an axial portion  10  pressed in fluidtight manner onto shaft  4 , and from the opposite ends of which respective radial portions  11 ,  12  project inside gap  2 . One ( 11 ) of the radial portions faces environment  5 , and extends almost up to casing  3 , while the other ( 12 ) faces environment  6 , and is of a much smaller extension than radial portion  11 . 
     Outer ring  8  comprises an axial portion  13 , from the end of which facing environment  6  a contoured portion  14  projects towards axial portion  10  of inner ring  7 . Axial portion  13  is partly fitted in fluidtight manner to casing  3 , and partly defines, by means of a shoulder  22  and with casing  3 , a seat  23  for housing part of elastomeric member  9 , as described in detail later on. As shown in  FIGS. 1 and 2 , axial portion  13  of outer ring  8  extends facing axial portion  10  of inner ring  7 . 
     With particular reference to  FIG. 2 , as of axial portion  13 , contoured portion  14  comprises a radial portion  15  extending towards shaft  4  and approximately along an extension of radial portion  12 ; a substantially axial portion  16  extending towards environment  5 ; and a radial portion  17  defining a free end of outer ring  8 . 
     Elastomeric member  9  substantially comprises a contoured portion  18  fitted to the surface of portion  14  of outer ring  8  facing environment  6 , and secured to portion  14 ; and a sealing lip  20  projecting from contoured portion  18 , and cooperating with radial portion  11  of inner ring  7 . 
     More specifically, contoured portion  18  cooperates with portions  15 ,  16  and  17  of portion  14  of outer ring  8 , has a free end engaging seat  23  of outer ring  8 , and is secured at the opposite end to the free end of portion  17 . 
     Sealing lip  20  ( FIGS. 2 and 3 ) extends from the end of contoured portion  18  secured to portion  17  of outer ring  8 , and comprises, in succession towards its own free end, an axial portion  19 ; an oblique portion  21  sloping towards casing  3 ; and a radial portion  25  cooperating in fluidtight manner with radial portion  11  of inner ring  7 . Lip  20  tapers in section towards its free end, and is bounded by two surfaces  31 ,  32  facing portion  14  of outer ring  8  and portion  11  of inner ring  7  respectively. 
     Lip  20  comprises, on surface  32 , a number of alternating, equally spaced solid elements  33  and hollow elements  34  conferring a serrated appearance to the lip. Proceeding from radial portion  25  towards contoured portion  18 , each pair of solid and hollow elements  33 ,  34  is bounded by a sharp edge  35  substantially perpendicular to surface  31 ; by a convex intermediate portion  36  sloping towards surface  31 ; and by a bottom portion  38  parallel to surface  31 . In each solid element  33  cooperating with portion  11  of inner ring  7 , sharp edge  35  and the adjacent portion of intermediate portion  36  combine to define a fluidtight sealing edge  26 . 
     An important aspect of the present invention lies in the equally spaced hollow elements  34  of surface  32  being defined by a spiral groove  27  of constant pitch and depth ( FIG. 4 ), and which, in use, produces a thrust effect to push the oil particles from the sealing region towards the oil environment  5 , as explained in detail later on. 
     The equally spaced sealing edges  26  defined by spiral groove  27  on lip  20 , and inner ring  7  and outer ring  8  fitted respectively to shaft  4  and casing  3 , provide for sealing gap  2  between shaft  4  and casing  3 . 
     More specifically, elastomeric member  9  defines, with inner ring  7 , an annular chamber  29  communicating with environment  6 , and defines, with outer ring  8 , an annular chamber  24  radially outwards with respect to annular chamber  29  and communicating with environment  5 . 
     More specifically, chamber  29  is bounded radially inwards by axial portion  10  of inner ring  7 , and radially outwards by contoured portion  18  and lip  20  of elastomeric member  9 . Chamber  29  is bounded axially, on the environment  5  side, by radial portion  11  of inner ring  7  interacting with lip  20 , and communicates, on the opposite side, with environment  6  via an annular opening  30  defined between radial portion  12  of inner ring  7  and the portion of elastomeric member  9  secured to portion  15  of outer ring  8 . 
     A washer  28  is fitted inside chamber  29  to filter any foreign particles and let air through. More specifically, washer  28  is interference-fitted radially between axial portion  10  of inner ring  7  and the portion of elastomeric member  9  secured to axial portion  16  of outer ring  8 , and part of its surface facing environment  5  cooperates with the portion of elastomeric member  9  secured to radial portion  17  of outer ring  8 . 
     As shaft  4  rotates, the air flowing axially from environment  6  into chamber  29  through washer  28  is subjected by spiral groove  27  on lip  20  to a fluid-dynamic pumping effect which pumps it between lip  20  and radial portion  11  or inner ring  7 , so that any oil from environment  5  in the sealing area is forced back into environment  5  and so prevented from flowing into environment  6 . 
     To direct the air flowing into chamber  29  towards radial portion  25  of lip  20 , elastomeric member  9  has a further annular lip  37  projecting from the portion of the elastomeric member secured to portion  17  of outer ring  8 . Lip  37  defines a constriction  41  along the airflow into chamber  29 , so as to accelerate airflow towards lip  20 . 
     Moreover, when shaft  4  is stopped, lip  37  collects any oil left between groove  27  of lip  20  and radial portion  11  of inner ring  7 , and which could leak into chamber  29 . And, when shaft  4  is started again, the oil collected in the gap defined between lip  37  and axial portion  19  of lip  20  is pumped out of chamber  29  by a combination of centrifugal force and the fluid-dynamic pumping effect produced by spiral groove  27  of lip  20 . 
     More specifically, in axial half-section, lip  37  is substantially L-shaped, and, proceeding towards its free end, comprises a first radial section  39  facing axial portion  10  of inner ring  7 ; and a second portion  40  facing environment  5  and sloping slightly towards casing  3 . 
     The advantages of seal assembly  1  according to the present invention will be clear from the foregoing description. 
     In particular, providing lip  20  with equally spaced sealing edges  26  defined by spiral groove  27  produces a fluid-dynamic air pumping effect on the oil, thus greatly reducing mechanical wear of lip  20 , which only cooperates superficially with inner ring  7 , without penetrating it. More specifically, the reduction in wear of lip  20  has been found to be due to the formation, in use, of a sort of air cushion between lip  20  and the mating surface of inner ring  7 . 
     In other words, sealing between lip  20  and inner ring  7  is predominantly fluid-dynamic. 
     Moreover, spiral groove  27  being formed in an elastomeric material injection molded in an easily machined mold, the shape and depth of groove  27  can be varied as required to conform more closely to given operating requirements, and in particular to achieve a marked increase in the fluid-dynamic “pumping” effect and in the working life of seal assembly  1 . 
     Clearly, changes may be made to seal assembly  1  as described and illustrated herein without, however, departing from the scope of the accompanying Claims. 
     In particular, elastomeric member  9  may comprise a number of separate bodies fitted to outer ring  8 . 
     Spiral groove  27  may be a multiple spiral. 
     Finally, washer  28  may be replaced by an appendix of elastomeric member  9 , which defines a seal for liquid or particle material, but does not interfere with inner ring  7 , so as to let air through.