Patent Abstract:
A retaining device or snap-ring for retaining a mating hub and drum within a transmission is provided. The device is insertable into a groove along the inner circumference of a circular flange and includes a main outer loop, an opening for dividing the snap-ring into two deflectable curvilinear portions and at least partially defined by a tabular extension projecting from each curvilinear member. The tabular extensions provide sufficient surface area for applying deflective or compressive force to the snap-ring and are contoured to facilitate use of a deflection tool. The snap-ring further comprises an externally-projecting secondary loop for reducing deflection force, or an internally-projecting secondary loop for increasing deflection force. The snap-ring may be used within a double-flange hub having a plurality of slots for facilitating insertion of the secondary loop and the tabular extensions within the flange groove.

Full Description:
TECHNICAL FIELD 
     The present invention relates to an improved snap-ring retaining device for use within a vehicle transmission. 
     BACKGROUND OF THE INVENTION 
     A circlip or snap-ring is a substantially circular or annular retaining device having a break or opening which divides the ring into two interconnected curvilinear members. The members may be deflected or flexed to facilitate insertion into a mating groove. Snap-rings are typically formed, stamped, or otherwise constructed from a relatively thin layer of metal which directs a retaining or clamping force along the circumference or periphery of the snap-clip when properly inserted into the groove. The directional force is most commonly used to retain or clamp together various mating components. 
     The force vector imparted by the snap-ring varies with the type or style of snap-ring that is used and the location of the ring relative to the parts retained or mated. Two main styles of snap-ring are available: an internal snap-ring positioned within a mating internal groove and used for applying outwardly-directed clamping force, and an outer snap-ring positioned within a mating external groove for applying inwardly-directed clamping force. Of these two main types of snap-ring, internal snap-rings are of particular beneficial use within an automatic vehicle transmission. 
     With an internal snap-ring, the ring is compressed or contracted by deflecting the curvilinear beams or members of the ring and then inserted or “snapped” into a continuous groove cut into an inner circumferential surface of a drum, shaft, cylinder, or other component having an approximately circular cross section. Once inserted into the groove, the snap-ring is then released or retracted into its installed position, directing circumferential clamping force along the groove wall within the relatively restricted space of the groove. In this manner a snap-ring may restrict or minimize any undesirable lateral or axial motion between two or more mating parts, such as within a flange or flanges of a clutch hub and a mating drum within a transmission clutch assembly. 
     The insertion and removal of a snap-ring during the transmission assembly or build process may be relatively time or material intensive due to the difficulty of accessing various confined areas within the housing. For instance, a person installing a snap-ring must often insert or place the ring into an area having limited accessibility or installation clearance, while simultaneously exerting a substantial amount of force on the curvilinear beams of the snap-ring in order to open or close the ring. The space and force limitations may be considerable enough to necessitate the use of special-purpose capital equipment, potentially adding substantial cost to the assembly process. Additionally, the requisite strength or rigidity for higher-load applications may require a snap-ring formed from a proportionately thicker layer of material, which in turn may lead to an undesirable increase in overall axial space within a transmission case or other housing, resulting in the need for a larger case and/or the re-arrangement of other components within the system. 
     SUMMARY OF THE INVENTION 
     Accordingly, an improved retaining device is provided having a primary or main loop, a variable-width or compressible opening dividing the main loop into adjoining curvilinear beams or portions operable to exert a circumferential force when inserted into a mating groove or channel, and an additional minor or secondary loop connecting the curvilinear portions, and operable to modify the deflection or compressive force required to compress or deflect the curvilinear portions. 
     In one aspect of the invention, the opening comprises a plurality of generally parallel tabular extensions, each extension having sufficient surface area for applying compressive force to the main loop for flexing or bending of the curvilinear portions to facilitate installation of the retaining device. The tabular extensions are further configured to prevent rotation of the snap-ring within the mating circumferential groove. 
     In another aspect of the invention, a retaining device having an improved compressive or deflection force is provided in which an externally-projecting secondary loop reduces the compressive force required to compress or deflect the curvilinear portions of the main loop, thereby facilitating the installation of the retaining device. 
     In another aspect of the invention, a retaining device having improved rigidity is provided in which an internally-projecting secondary loop increases the compressive or deflection force required to compress or deflect the curvilinear portions of the main loop, thereby providing increased rigidity to the main loop. 
     In another aspect of the invention, a circular flange assembly is provided for use within a vehicle transmission, in which a substantially annular retaining device having a main loop and a minor secondary loop is inserted into continuous circumferential or peripheral groove in a flange wall, the main loop having a plurality of tabular extensions configured to prevent rotation of the main loop within the circumferential or peripheral groove. 
     In another aspect of the invention, a clutch assembly is provided for use within a vehicle transmission, in which an improved snap-ring retaining device is insertable in the mating grooves of a dual-flanged clutch hub and mating clutch drum to thereby retain the clutch hub and drum. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view of an improved snap-ring according to the invention having an outwardly-projecting secondary loop; 
         FIG. 1B  is a plan view of an improved snap-ring according to the invention having an inwardly-projecting secondary loop; 
         FIG. 2A  is a plan view of a clutch drum in combination with an improved internal snap-ring; 
         FIG. 2B  is a side view of a double-flange clutch hub in combination with an improved snap-ring; 
         FIG. 3A  is a schematic illustration showing a load deflection of a simplified straight or linear beam; 
         FIG. 3B  is a schematic illustration showing an exemplary load deflection of a modified straight beam having the secondary outer loop of this invention; and 
         FIG. 3C  is a schematic illustration showing a load deflection of a modified straight beam having a secondary inner loop. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures, there is shown in  FIG. 1A  a substantially annular or circular snap-ring  10   a  comprising a primary or main loop  20  having a width  11  and configured by a main radius  44  drawn from a main center point  32 . An outwardly-projecting minor or secondary extend loop  22   a , preferably circular in shape, is configured by a secondary radius  46   a  drawn from a secondary center point  30   a , the extend loop  22   a  projecting radially outward from the circular periphery of main loop  20 . A pair of tabular extensions or tabs  24   a ,  24   b , preferably aligned in a substantially parallel manner and positioned approximately 180° opposite secondary loop  22   a , define a normal unflexed or “free state” break or opening  26   a  in main loop  20 . The unflexed opening  26   a  is represented by the phantom or dotted-line profile in  FIG. 1A . Center points  30   a ,  32  are preferably aligned along a main loop axis  38  bisecting main loop  20  and secondary extend loop  22   a . Thus, main loop  20  has a first and second curvilinear beam portion  40 ,  42  being at least partially flexible, compressible, or deflectable, by actuating tabs  24   a ,  24   b  disposed at the end of portions  40 ,  42 , respectively. When curvilinear portions  40 ,  42  are deflected by the application of a contracting clamping force to tabs  24   a ,  24   b , a reduced-width or compressed opening  26   b  results, as shown by the solid line in  FIG. 1A . 
     In a preferred embodiment, main radius  44  and secondary radius  46   a  are proportionately related by a ratio of approximately 25:1, with compressed opening  26   b , when substantially flexed or compressed, having a width approximately 0 to 5% of main radius  44 . When curvilinear portions  40 ,  42  are in a “free state”, i.e. undeflected or unflexed, tabs  24   a ,  24   b  preferably form an unflexed opening  26   a , as shown by the phantom line in  FIG. 1A , with a relative angle of approximately 40° between tabs  24   a ,  24   b , although those skilled in the art will recognize that other deflection angles and loop ratios may be adapted and modified as necessary depending on the application. Tabs  24   a ,  24   b  are further preferably configured with a notch or series of notches  25  being sized and/or shaped to fit a ring compression tool (not shown), such as a pair of pliers, for assisting in compressing and inserting ring  10   a  into, for example, a flange groove in the wall of a clutch housing. 
     Turning to  FIG. 2A , a circular drum  54 , depicted herein as a representative clutch drum, is shown with a captive snap-ring  10   a  as described hereinabove. Snap-ring  10   a  is inserted into a channel or peripheral flange groove  50  positioned along the inner circumferential or peripheral surface  52  of the drum  54 , the groove represented in  FIG. 2A  as a dotted line. A first window or slot  55   a  is positioned at one end of drum  54  generally opposite secondary loop  22   a , slot  55   a  being appropriately sized to accept the elastically-deflectable tabs  24   a ,  24   b  of snap-ring  10   a  to prevent relative rotation or spin of the snap-ring  10   a  within the flange groove  50 . To obtain the rotational balance as well as to accommodate insertion and flexing of secondary outer loop  22   a , the bottom or opposite end of the drum  54  likewise has a substantially similar and preferably identical slot  55   b  positioned approximately 180° opposite slot  55   a . Once compressed or deflected and inserted into flange groove  50 , and subsequently released, snap-ring  10   a  returns to a position short of “free state” or unflexed opening  26   a  (See  FIG. 1A ), and so exerts a continuous outward circumferential clamping force along the surface of groove  50 , thereby providing axial support and noise reduction between the mating parts, such as, for example, between clutch drum  54  of  FIG. 2A  and mating clutch hub  62  of  FIG. 2B . 
     Clutch hub  62  of  FIG. 2B  has a continuous outer circumferential channel or hub groove  60  disposed between a first and second flange  63   a ,  63   b . Snap-ring  10   a  is inserted into groove  60  between flanges  63   a ,  63   b  and compressed at tabular extensions  24   a ,  24   b  (see  FIG. 1A ) as described previously herewithin. While holding snap-ring  10   a  in a compressed position, hub  62  is inserted into mating clutch drum  54  (see  FIG. 2A ). Tabular extensions  24   a ,  24   b  are held in compressed position until hub  62  is fully inserted into clutch drum  54 . Once the snap ring  10   a  is aligned with flange groove  50 , the tabular extensions  24   a ,  24   b  of snap-ring  10   a  are released, and the snap-ring  10   a  partially opens or decompresses to at least partially fill mating flange groove  50  (see  FIG. 2A ) while remaining at least partially within hub groove  60 . Tabular extensions  24   a ,  24   b  snap into place within slot  55   a , thereby preventing relative rotation of the snap ring  10   a  within grooves  50 ,  60 . For example, in the case of clutch hub  62  of  FIG. 2B , the snap-ring  10   a  would thereby retain the hub and drum, as would any splines on the mating surfaces of clutch drum  54  and hub  62 . For simplicity, mating splines are not shown on surface  52  of clutch drum  54  of  FIG. 2A  or on flanges  63   a ,  63   b  of hub  62  of  FIG. 2B , which are the respective mating surfaces on which splines could be employed. By utilizing the described double-flange design, the contact area or power density between snap-ring  10   a  and flanges  63   a ,  63   b  is thereby doubled, which may permit the amount and/or type of metal strengthening support components within the transmission component, such as splining, to be reduced in number and/or otherwise modified in appearance. 
     In an alternative embodiment of  FIG. 1B , a snap-ring  10   b  has an inwardly-projecting minor or secondary inner loop  22   b  having a center point  30   b  and a secondary radius  46   b . The primary advantages of a secondary inner loop are twofold. First, by positioning a secondary inner loop  22   b  on the inside of main loop  20 , the outer dimension or periphery of snap-ring  10   b  may be completely hidden within a groove positioned within a circular wall of, for example, a clutch hub. Additionally, in some circumstances installation space may be restricted or limited, and consequentially, a secondary extend loop of the type shown in  FIG. 1A  may not fit properly within the flange. Second, a secondary inner loop  22   b  may be used to enhance the rigidity of a snap-ring  10   b , as an inwardly-disposed secondary loop requires greater force to achieve a given amount of annular deflection than does an outer-loop design, as discussed hereinbelow. 
     The deflection effect on a main surface due to the addition of a secondary surface of various size and position may be explained by using the simplified linear-beam profile of  FIG. 3A  in which a straight beam  70   a  having a length L 1  is attached to ground  74  and subjected to an applied load P. In this example, load P imparts to beam  70   a  a deflection δ, in which δ=P*(L 1 ) 3 /(3*E*I). In this deflection equation, variable E is Young&#39;s Modulus, commonly referred to as the modulus of elasticity, with variable I being the moment of inertia. Those skilled in the art will recognize that Young&#39;s Modulus E is a material-specific quantity, with a stiffer material providing a reduced magnitude of deflection, while the moment of inertia I varies with the shape of the beam profile. 
       FIG. 3B  modifies the single-beam design by adding an outwardly-disposed minor beam  72   a  having a length L 2 . Under this modified configuration, the force-deflection equation is modified to δ=P*(L 1 +L 2 ) 3 /(3*E*I). That is, the addition of an outwardly-disposed minor-beam  72   a  increases deflection  6  for a given load P. In designing a snap ring according to the invention, deflection can therefore be customized by adapting a specific size and shape for the inner and outer loops, by changing ring material, or by modifying the shape of the ring, as indicated by the force-deflection equations. 
     By contrast,  FIG. 3C  shows an inwardly-disposed minor beam  72   b  having a length L 2  equal to length L 2  of  FIG. 3B . In this example, deflection δ=P*(L 1 −L 2 ) 3 /(3*E*I). The addition of minor-beam  72   b  therefore decreases deflection δfor a given load P, that is,  72   b  imparts stiffness or rigidity to the beam as described previously herewithin. When this deflection effect is applied to a curved beam or a beam of another non-linear shape, such as a snap-ring, the corresponding force-deflection equations consider the radii of the inner and outer loops in determining beam length and linear deflection. Note, however, that the general relationship of inverse proportionality between deflection and both moment of inertia and Young&#39;s Modulus, as illustrated in the simplified designs of  FIGS. 3A-C , holds true independent of beam shape and can be used by those skilled in the art to design a snap-ring for a given application, in accordance with the teachings of this invention. While the minor beams (secondary loop  22   a ,  22   b  of  FIGS. 1A ,  1 B) are preferably circular, they may also take another suitable shape such as an oval or a parabola to further increase or reduce the moment of inertia in the aforementioned manner. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Technology Classification (CPC): 5