Abstract:
A seal assembly seals a gap between a fixed member and a rotating member housed therein, to prevent flow of oil from a first environment to a second environment of the gap. The assembly includes a first ring fitted to the rotating member, a second ring fitted to the fixed member, an elastically deformable seal attached to the second ring and comprising a first lip cooperating in a fluid-tight manner with a first mating portion of the first ring, and a spiral groove on the first lip to generate, during rotation of the rotating member, a fluid-dynamic pumping action to pump oil from a sealing area to the first environment. A second lip of the seal forms a contact seal with a second mating portion of the first ring when the rotating member is stopped, and a configuration detached from the second mating portion during rotation of the rotating member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of European Patent Application No: 07425697.5, filed on Nov. 6, 2007, the subject matter of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a seal assembly for a rotating member, in particular for a shaft of a vehicle engine, to which the following description specifically refers but without any loss of generality. 
         [0003]    In the field of mechanical design, there is a need to reduce friction by lubricating the rotating members in an oil bath. In many applications some portions of the rotating members need to be immersed in an oil bath while other adjacent portions thereof work in a sealed, oil-free environment. In order to satisfy this need, seal assemblies are known, as described for example in patent EP-B-1586799, which are housed inside the gap defined between a normally fixed, hollow casing, and a rotating member housed therein. During the rotation of the rotating member, said assemblies seal said gap in order to prevent oil flowing into the dry environment. 
         [0004]    In particular, said seal assemblies are axially symmetrical with respect to the axis of the rotating member to which they are fitted and essentially consist of a radially inner ring that is made of metal and fitted to the rotating member, a radially outer ring, also made of metal and fitted to the casing, and a sealing member made of elastically deformable polymeric material, interposed between said rings. 
         [0005]    More specifically, the elastomeric member is attached to the outer ring and has a lip on the side facing the oil bath, said lip being suitable to create a contact seal with a relative mating portion of the inner ring. 
         [0006]    To limit the drawback typical of contact seals, namely the rapid wear of the elastomeric material in use in the area of cooperation with the metal ring, the sealing lip is provided with a spiral groove, which fulfils two purposes:
       it achieves a sealing effect simply by creating a surface contact between the elastomeric lip and the inner ring, without the former having to penetrate the latter; and   as the inner ring rotates integrally with the rotating member, it generates a fluid-dynamic “pumping” effect on the air between the sealing lip and said inner ring, which forces the oil towards the oil environment and enhances sealing performance.       
 
         [0009]    While the solution described above is extremely advantageous with respect to other known solutions in terms of wear and functionality of the seal assembly when the rotating member is used, it is however capable of further improvement. 
         [0010]    In particular, it has been observed that seal assemblies of the type described above cannot guarantee perfect sealing of the dry environment when the rotating member is stopped and is arranged on a slope with respect to the horizontal or whenever, with the rotating member stopped, the oil level is above the half-way mark on said rotating member. 
         [0011]    In the above condition, part of the seal assembly could be in the oil bath and, in static conditions, the sealing lip provided with the spiral groove is not able to guarantee the same sealing effect that is generated in dynamic conditions, i.e. with the support of the fluid-dynamic pumping action that pushes the oil towards the oil environment. 
         [0012]    The above condition could occur for example when the vehicle on which the rotating member is mounted is parked on a slope or when said rotating member is installed at an oblique angle on said vehicle. 
       SUMMARY OF THE INVENTION 
       [0013]    An object of the present invention is to produce a seal assembly for a rotating member, which overcomes the drawback associated with the seal assemblies that are known and described above. 
         [0014]    This object is achieved by the present invention, which relates to a seal assembly to seal the gap between a rotating member and a fixed member housing said rotating member, to prevent the flow of a first fluid from a first environment to a second environment arranged on opposite sides of said gap, said seal assembly comprising:
       a first ring fitted to said rotating member;   a second ring fitted to said fixed member;   elastically deformable sealing means attached to said second ring and comprising at least a first lip suitable to cooperate in a fluid-tight manner with a first mating portion of said first ring; and   a spiral groove provided in the area of cooperation between said first lip and said first mating portion to generate, during the rotation of said rotating member, a fluid-dynamic pumping effect that pushes said first fluid away from the sealing area towards the first environment; said fluid-dynamic effect being obtained by generating a flow of a second fluid from said second environment to said first environment by means of said groove and due to the rotation of said rotating member;       
 
         [0019]    characterized in that said sealing means comprise a second lip suitable to cooperate with a second mating portion of said first ring, axially interposed between said first mating portion and said second environment; said second lip assuming a configuration in which it forms a contact seal with said second mating portion when said rotating member is stopped, and a configuration in which it is detached from said second mating portion during the rotation of said rotating member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    In order to better understand the present invention, a non-limiting preferred embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  shows an axial section of a seal assembly for a rotating member, according to the present invention; 
           [0022]      FIG. 2  shows an axial half-section on an enlarged scale of the seal assembly in  FIG. 1 ; and 
           [0023]      FIG. 3  shows a section similar to that in  FIG. 1  with reference to a vehicle application, in which the rotating member and the seal assembly according to the invention are shown in a sloping position with respect to the horizontal and partially in an oil bath in a static condition. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    In the attached drawings, number  1  indicates, as a whole, a seal assembly housed in the gap  2  defined between a hollow casing  3  with axis A and a rotating member, for example a shaft  4  of a vehicle, housed coaxially inside said casing  3 . On axially opposite sides of the seal assembly  1 , the gap  2  comprises an environment  5  for containing a lubricating oil bath, and an environment  6  into which the oil must not be allowed to flow and which, in use, contains air. 
         [0025]    The seal assembly  1  comprises a radially inner ring  7  integral with the shaft  4 , a radially outer ring  8  integral with the casing  3  and an elastomeric member  9  interposed between the rings  7  and  8  and attached to said ring  8 . 
         [0026]    The inner ring  7  comprises an axial portion  10  pressed in a fluid-tight manner onto the shaft  4 , and from the opposite ends of which respective radial portions  11 ,  12  project inside the gap  2 . One of the radial portions ( 11 ) faces the environment  5  and extends almost up to the casing  3 , while the other (12) faces the environment  6  and extends for a much shorter distance than the radial portion  11 . 
         [0027]    The outer ring  8  comprises an axial portion  13  from the end of which facing the environment  6  a contoured portion  14  projects towards the axial portion  10  of the inner ring  7 . 
         [0028]    The axial portion  13  is partially fitted in a fluid-tight manner to the casing  3  and partly defines, by means of a shoulder  15 , with said casing  3 , a seat  16  for housing part of the elastomeric member  9 , as described in more detail later on in this document. 
         [0029]    As shown in the attached drawings, the axial portion  13  of the outer ring  8  extends facing the axial portion  10  of the inner ring  7 . 
         [0030]    With particular reference to  FIG. 2 , starting from the axial portion  13 , the contoured portion  14  comprises a radial section  17  extending towards the shaft  4  and approximately along the extension of the radial portion  12 , a substantially axial section  18  extending towards the environment  5  and a radial section  19  defining a free end of the outer ring  8 . 
         [0031]    The elastomeric member  9  essentially comprises a contoured portion  20  fitted to the surface of the portion  14  of the outer ring  8  facing the environment  6  and anchored to said portion  14 , and a sealing lip  21 , projecting in a cantilevered manner from the contoured portion  20  and cooperating with the radial portion  11  of the inner ring  7 . 
         [0032]    In particular, the contoured portion  20  cooperates with the sections  17 ,  18  and  19  of the portion  14  of the outer ring  8 , has a free end that engages with the seat  16  of said outer ring  8  and is anchored, on the opposite end, to the free end of the section  19 . 
         [0033]    The sealing lip  21  ( FIG. 2 ) extends from the end of the contoured portion  20  anchored to the section  19  of the outer ring  8  and comprises, in succession towards its free end, an axial portion  22 , an oblique portion  23 , sloping towards the casing  3 , and a radial portion  25  cooperating in a fluid-tight manner with the radial portion  11  of the inner ring  7 . 
         [0034]    The sealing lip  21  tapers in section towards its free end and is delimited by two surfaces  26 ,  27 , respectively facing the portion  14  of the outer ring  8  and the portion  11  of the inner ring  7 . 
         [0035]    The surface  27  of the lip  21  is provided with a plurality of alternating, equally spaced solid elements  28  and hollow elements  29 , conferring a serrated appearance to said surface. 
         [0036]    The solid elements  28  of the surface  27  define, in correspondence with the outside edge thereof, respective sealing edges that cooperate with the radial portion  11  of the inner ring  7 . 
         [0037]    The equally spaced hollow elements  29  of the surface  27  are defined by a spiral groove  30  having a constant pitch and constant depth suitable to produce, during the rotation of the rotating member  4 , a fluid-dynamic pumping action on the air from the environment  6  to the environment  5  so as to push any oil particles in the sealing area towards said environment  5 , as described in detail later on in this document. 
         [0038]    Advantageously, the elastomeric member  9  comprises an additional static sealing lip  31  that extends towards the axial portion  10  of the inner ring  7  starting from the end of the contoured portion  20  anchored to the section  19  of the outer ring  8 ; the lip  31  being able to assume a configuration in which it forms a contact seal (attached drawings) with the axial portion  10  of the inner ring  7 , when the rotating member  4  is stopped, and a configuration in which it is detached (not illustrated) from said axial portion  10 , during the rotation of the rotating member  4  and due to the effect of the depression created by the air flow along the groove  30  as a result of said rotation. In practice, without any external action, the lip  31  is spring loaded towards the configuration in which it forms a contact seal with the axial portion  10  of the inner ring  7  and is detached from said portion due to the fluid-dynamic pumping effect generated by the groove  30  on the air inside said groove when the shaft  4  is made to rotate. 
         [0039]    As shown in  FIGS. 1 and 2 , the area of cooperation between the sealing lip  31  and the inner ring  7  is axially interposed between the environment  6  and the area of cooperation by the sealing lip  21  with said inner ring  7 . 
         [0040]    The sealing lip  31  has a truncated conical shape with axis A and decreases in section towards the environment  5  and towards the area of cooperation with the axial portion  10  of the inner ring  7 . 
         [0041]    According to a preferred embodiment of the present invention, the sealing lip  31  is also provided, radially inwards, with an annular projection  32 , in correspondence with which it cooperates with the axial portion  10  of the inner ring  7 . 
         [0042]    The elastomeric member  9  comprises a truncated conical appendix  33  with axis A, the tapered end of which is opposite that of the lip  31  and extends towards the inner ring  7  starting from the end of the contoured portion  20  anchored to the section  19  of the outer ring  8 . The appendix  33  delimits, with the inner ring  7 , an opening  34  of a suitable size to permit the flow of air, in all conditions, while also defining a filter for any foreign particles. 
         [0043]    In use, when the vehicle is parked, i.e. the shaft  4  is stopped, the lip  31  is arranged in the configuration in which it forms a contact seal with the axial portion  10  of the inner ring  7 . Also when the shaft  4  and the seal assembly  1  are on a slope with respect to the horizontal ( FIG. 3 ), any oil (the free surface of which is indicated by the letter L) coming from the environment  5  that flows past the seal provided by the lip  21  (only optimal during the rotation of said shaft  4 ) would not reach the environment  6  in any case, due to the sealing effect provided by the additional lip  31 . 
         [0044]    When the shaft  4  is made to rotate, i.e. when the engine of the vehicle is started, the oil contained in the annular chamber  35 , delimited between the inner ring  7  and the lips  21  and  31 , is pumped out of said chamber  35  again thanks to the combined action of the centrifugal force and the fluid-dynamic pumping effect generated by the spiral groove  30  of said lip  21 . 
         [0045]    Moreover, in this situation a depression effect is produced in the chamber  35 , with the subsequent detachment of the lip  31  from the axial portion  10  of the inner ring  7 . 
         [0046]    At this point, the air can enter the chamber  35  axially from the environment  6 , through the opening  34  and the gap formed between the lip  31  and the axial portion  10 ; said air is pushed towards the environment  5  due to said fluid-dynamic pumping effect generated by the groove  30 , producing a similar thrust effect on the oil particles in the sealing area, which are thus prevented from flowing into the environment  6 . 
         [0047]    It is important to note that thanks to the opening  34  and the gap between the lip  31  and the axial portion  10  of the inner ring  7  there is a narrowing of the section along the air flow in the chamber  35 , which causes an acceleration of said air flow towards the lip  21 . 
         [0048]    The advantages that can be achieved with the seal assembly  1  produced according to the present invention are apparent from an examination of the characteristics thereof. 
         [0049]    In particular, with the shaft  4  stopped, the additional lip  31  guarantees the sealing of the gap  2  even if the shaft  4  is arranged at an oblique angle with respect to the horizontal, so that the seal assembly  1  is partially in the oil bath. 
         [0050]    Moreover, the lip  31  does not obstruct the air flow from the environment  6  to the environment  5  when the shaft  4  is rotating; in said condition, the lip  31  is immediately pushed into the configuration in which it is detached from the inner ring  7  as a result of the depression created in the chamber  35  due to the fluid-dynamic pumping effect of the spiral groove  30 . 
         [0051]    Moreover, the inclusion of the lip  31  in seal assemblies  1  installed in internal combustion engines enables said engines to pass the pneumatic test in the cold condition, to verify the correct installation of the various components, without requiring any additional operations. 
         [0052]    As is known, said test essentially consists of blocking the engine outlets and introducing pressurized air into said engine in order to check for any pressure drops. Without the lip  31 , the test can only be passed by placing sealing additives on the groove  30  of the lip  21 , such as gel or wax products. 
         [0053]    Finally, the presence of the projecting member  32  guarantees the spring return of the lip  31  into the position in which it forms a contact seal with the axial portion  10  of the inner ring  7  when the shaft  4  is stopped. 
         [0054]    Lastly, it is clear that modifications and variations may be made to the seal assembly  1  described and illustrated herein without departing from the scope of the present invention as set forth in the appended claims. 
         [0055]    In particular, the elastomeric member  9  could consist of several separate elements fitted to the outer ring  8 .