Abstract:
A seal for a mass transit power transmission coupling. The seal is made at least partially of a polymeric material and configured such that the sealing surface moves radially outward under the centrifugal force created by rotation of the coupling beyond a predetermined speed. When the rotational speed of the coupling drops below the predetermined speed, the sealing surface moves radially inward and seals the coupling to prevent loss of the oil lubrication typically used on such couplings.

Description:
TECHNICAL FIELD  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/356,220 filed Feb. 12, 2002, and incorporated by reference herein. The invention relates generally to a seal which changes dimensions during operation and, more specifically, an annular elastic seal which has an inner sealing diameter which expands due to centrifugal force when the seal rotates at or above a predetermined speed. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Mass transit systems such as subway rail cars utilize power transmission couplings between the rail cars to transfer rotational power from car to car. These transmission couplings must be able to transfer power from one shaft to another, even when the shafts are misaligned such as when the cars are going around a corner or the cars buckle. Each shaft has a gear attached thereto which is housed on different sides of the coupling. The couplings utilize gears having mating teeth to enable the power transmission to the shafts while allowing them to be misaligned from each other. The gears are required to be lubricated to ensure proper movement of the gears within the housing, prevent premature wear of the gear teeth, and reduce heat build up. The gears are typically required to be lubricated with oil as opposed to grease. A seal is positioned at each end of the coupling to prevent oil from leaking out of the coupling. These prior art seals are attached to the housing of the transmission coupling and have a sealing inner diameter which registers against one of the shafts or an extended hub portion of the associated gear. These seals must flex and are therefore typically made of an elastomeric oil resistant material.  
           [0003]    The problem with these prior art seals is that the movement caused by misalignment of the shafts and relative axial movement of the shaft/extended hub portion of the gear, causes the seal to fail prematurely. The oil may then be able to migrate out of the coupling, resulting in damage to the coupling gears and potentially leading to failure of the coupling and contamination of the surrounding equipment and subway platform.  
           [0004]    Therefore, there remains a need in the art for a new seal which overcomes the limitations of the prior art while still providing effective oil retention.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention to provide an improved seal. These and other advantages are provided by an annular seal for use on a mass transit coupling having a ring gear hub and axle shaft positioned in a co-rotating housing, the seal comprising a seal body demountably attached to the housing; an inner sealing diameter of the seal body which seals against at least one of the ring gear hub and the axle shaft when the seal is rotating below a predetermined rotational speed and wherein the inner sealing diameter expands due to centrifugal force when the seal is rotating at or above the predetermined speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention and developments thereof are described in more detail in the following by way of embodiments with reference to the drawings, in which:  
         [0007]    [0007]FIG. 1 is a perspective view of a prior art power transmission coupling;  
         [0008]    [0008]FIG. 2 is a side elevational and partial cut-away cross sectional view of the prior art power transmission coupling of FIG. 1;  
         [0009]    [0009]FIG. 3 is a cross-sectional view of the prior art power transmission coupling of FIG. 1 showing misalignment of the hub gears;  
         [0010]    [0010]FIG. 4 is a cross-sectional view of a power transmission coupling utilizing the seal of the present invention;  
         [0011]    [0011]FIG. 5 is a cross-sectional view of a rotating power transmission coupling utilizing the seal of the present invention.  
         [0012]    [0012]FIG. 6 is a cross-sectional view of a power transmission coupling utilizing another embodiment of the seal of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Turning now to FIG. 1 which illustrates a typical power transmission coupling assembly  20  of the type suitable for use with the present invention. The prior art coupling  20  comprises a two-piece ring gear or ring gear housing  22  bolted together at the center by a plurality of fasteners  24 . Each end of the coupling  20  is attachable to a power transmission shaft of adjacent rail cars (not shown). A prior art seal  26  is shown attached to the ring gear  22  by a plurality of fasteners  28 . The seal  26  seals against the surface of a hub gear or ring gear hub  30  moveably positioned within the ring gear housing  22 .  
         [0014]    Referring now to FIG. 2, the prior art coupling assembly of FIG. 1 is shown in greater detail. Coupling assembly  20  comprises a hub gear  30  on either side of the assembly which are attached to the ends of opposing rotatable transmission shafts (not shown). The hub gears  30  have special gear teeth  32  about their outside diameter which mate with special internal gear teeth  34  of the ring gear  22 . The gear teeth  32 ,  34  are designed to allow movement in an axial direction and at an angular orientation from the centerline A of the coupling assembly  20 . The hub gears  30  are biased outward from the center of the ring gear  22  by springs  36  which register against a retainer  38  attached to each half of ring gear  22 . A pair of seals  26  are attached to the ends of the ring gear  22 . The seal  26  comprises a seal plate  42  typically made of steel and a seal portion  44  made of a elastomeric oil-resistant material. Seal portion  44  has an inside diameter which registers against the outside diameter of a hub extension portion  46  of the hub gear  30 . A seal portion  44  may also include a steel ring  45  between the interface of the elastomeric material and the steel hub gear  30 .  
         [0015]    Referring now to FIG. 3, the prior art coupling of FIG. 1 is shown in cross section to show the types of displacement possible with the coupling assembly  20 . The three types of displacement of the shaft misalignment is shown. Axial misalignment X, angular misalignment θ, and radial misalignment Y are possible during operation of the coupling assembly  20 . These movements often occur at high frequency, typically as high as 5000 rpm or 80 hertz and, when misaligned, the flexing of the rubber at this frequency will fail the seal due to flexural fatigue in as little as 6 weeks. Desired life is 5 to 10 years.  
         [0016]    An improved seal  10  of the present invention is shown in FIG. 4. Seal  10  is also made of an oil resistant elastomeric material having a plurality of ribs or bellows  12 , shown in this cross-section as accordion-like ribbing, leading to an inner diameter sealing surface  14 . The ribs  12  enable the seal to stretch and retract to accommodate the range of motion of the mating outside diameter hub extension surface  46 . The specialized geometry of seal  10  enables it to handle the rigorous application of use in a coupling assembly  20 . In operation, the power transmission shafts (not shown), hub gears  30 , and ring gear  22  are all rotating at the same speed and in the same rotational direction. As the rotational speed of the coupling assembly  20  approaches a predetermined speed, the centrifugal force on the inner diameter sealing surface  14  pulls the inner diameter sealing surface  14  radially outward away from the outside diameter hub extension surface  46  as best shown in FIG. 5. Therefore, the seal  10  is not subjected to the high frequency movements of the hub gear  30  because it is no longer in contact with the hub gear  30 . The lubrication oil is unable to escape as the centrifugal force holds the fluid against the ring gear  22 . As the rotational speed of the coupling assembly  20  slows below a predetermined speed, the inner diameter sealing surface  14  retracts until it contacts and seals against the hub gear  30 . The lubrication oil is thus sealed in the coupling assembly. In an alternate embodiment, seal  10  has radial cuts or slits (not shown) which help allow the inner diameter sealing surface  14  to move radially outward under the centrifugal force.  
         [0017]    In another alternate embodiment shown in FIG. 6, the seal  10 ′ is shaped at least partially as an elliptical tube  52  having thin side walls  54  as shown on the left side of the FIG. 6. The thin side walls  54  collapse to allow the inner diameter sealing surface  14 ′ to expand under the centrifugal force as shown on the right side of FIG. 6. The tube  52  may have one or more holes (not shown) to allow air flow into or out of the tube to aid in deformation. Conversely, the tube may be filled with a liquid (not shown) to help to aid in deformation expansion of the inner diameter sealing surface.  
         [0018]    It is contemplated that there are innumerable configurations that could be employed and not be beyond the scope of the present invention. For example, the density of the inner diameter sealing surface  14  could be increased or made of a heavier material to promote movement under the centrifugal force. Any seal configurations and material that can expand and retract automatically under centrifugal forces are contemplated by the present invention.  
         [0019]    Although the present invention has been described above in detail, the same is by way of illustration and example only and is not to be taken as a limitation on the present invention.