Abstract:
A modular clutch assembly ( 15 ) comprising a first rotary member ( 16 ) having a first torque transfer surface ( 73  or  69 ), said first rotary member configured to rotate about an axis (x-x) and to rotationally couple to a first shaft ( 20 ), a second rotary member ( 22 ) configured to rotate about the axis and to rotationally couple to a second shaft ( 21 ), a pressure plate ( 23 ) configured to rotate about the axis, at least one of the second member and the pressure plate having a second torque transfer surface ( 78  or  66 ) opposing the first torque transfer surface, a spring element ( 29 ) configured to bias the opposed first and second torque transfer surfaces towards each other, and a pilot bearing ( 30 ) configured to act between the second member and the first shaft or the first member and the second shaft.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the field of clutches and, more particularly, to an improved modular clutch for preventing the transmission of excessive torque in, for example, hoist systems. 
       BACKGROUND ART 
       [0002]    Clutches are well known in the art and are generally used to transmit force between two rotating shafts. One of the shafts is typically attached to a motor, sometimes referred to as the driving member, and the other shaft provides output power for work to be done, often referred to as the driven member. The clutch connects the two shafts so that they can be either engaged so that they spin at the same speed, or decoupled and disengaged so they spin at different speeds. 
         [0003]    U.S. Pat. No. 1,807,210 is directed to a friction coupling and generally discloses a key gear having a hub, follower ring, spring and cylindrical shell. 
         [0004]    U.S. Pat. No. 2,953,911 is directed to a drive coupling and discloses a driven plate with radial grooves, hub, driving plate, pressure plate and clutch springs. 
         [0005]    U.S. Pat. No. 7,591,357 is directed to a crank shaft torque modulator and discloses a driven hub, clutch spring, carrier disk, thrust washer, crank shaft pulley and mounting hub. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiments, merely for purposes of illustration and not by way of limitation, the present invention provides a modular clutch assembly ( 15 ) comprising a first rotary member ( 16 ) having a first torque transfer surface ( 73  or  69 ), said first rotary member configured to rotate about an axis (x-x) and to rotationally couple to a first shaft ( 20 ), a second rotary member ( 22 ) configured to rotate about the axis and to rotationally couple to a second shaft ( 21 ), a pressure plate ( 23 ) configured to rotate about the axis, at least one of the second member and the pressure plate having a second torque transfer surface ( 78  or  66 ) opposing the first torque transfer surface, a spring element ( 29 ) configured to bias the opposed first and second torque transfer surfaces towards each other, and a pilot bearing ( 30 ,  105  or  106 ) positioned to act radially between the second member and the first shaft or the first member and the second shaft. 
         [0007]    The first rotary member may be a driving member and the second rotary member may be a driven member. The second member may have the second torque transfer surface ( 78 ) and the first member may comprise a third torque transfer surface ( 69 ) and the pressure plate may comprise a fourth torque transfer surface ( 66 ) opposing the third torque transfer surface. The pressure plate may be rotationally fixed ( 26 ,  31 ) relative to the second member. 
         [0008]    The assembly may further comprise an adjusting nut ( 32 ) configured to rotate about the axis and to couple to the second member, the first member, pressure plate, and spring element disposed between the second member and the adjusting nut, the adjusting nut having an inner surface ( 53 ) and the pressure plate having a surface ( 62 ) opposing the inner surface of the adjusting nut, and wherein the spring element acts between the inner surface of the adjusting nut and the surface of the pressure plate opposing the inner surface of the adjusting nut. The adjusting nut and the second member may be configured such that rotational movement of the adjusting nut relative to the second member adjusts the bias of the spring element. The assembly may further comprise a lock ( 35 ) configured to selectively inhibit rotation of the second member relative to the adjusting nut. 
         [0009]    The assembly may further comprise a second bearing ( 36 ) positioned to act radially between the second member and an external surface ( 38 ). The second member may comprise an outer journal ( 39 ) for receiving the second bearing. The pilot bearing ( 30 ) may be positioned directly between the second member and the first shaft. The pilot bearing ( 105 ) may be positioned directly between the first member and the second shaft. The pilot bearing ( 106 ) may be positioned directly between the second member and the first member. 
         [0010]    The second torque transfer surface may comprise a slot relief ( 40 ). The second torque transfer surface and the fourth torque transfer surface may each comprise a slot relief ( 40 ,  25 ). The first torque transfer surface may comprise a friction layer ( 100 ) and the third torque transfer surface may comprise a friction layer ( 101 ). The friction layer may be contoured or tapered. 
         [0011]    The spring element may comprise a first spring constant for a first range of deflection ( 103 ) and a second spring constant for a second range of deflection ( 104 ), wherein the second spring constant is less than about 25% of the first spring constant. The spring element may comprise a spring orientated about the axis and the pressure plate may comprise a pilot ring ( 41 ) configured to retain the spring in a position centered about the axis. 
         [0012]    In another aspect the invention provides a modular clutch assembly comprising a first rotary member having a first torque transfer surface, the first rotary member configured to rotate about an axis and to rotationally couple to a first shaft, a second rotary member configured to rotate about the axis and to rotationally couple to a second shaft, a pressure plate configured to rotate about the axis, at least one of the second member and the pressure plate having a second torque transfer surface opposing the first torque transfer surface, a spring element configured to bias the opposed first and second torque transfer surfaces towards each other, an adjusting nut configured to rotate about the axis and couple to the second member, the first member, pressure plate, and spring element disposed between the second member and the adjusting nut, the adjusting nut having an inner surface and the pressure plate having a surface opposing the inner surface of the adjusting nut, wherein the spring element acts between the inner surface of the adjusting nut and the surface of the pressure plate opposing the inner surface of the adjusting nut; and wherein the adjusting nut and the second member are configured such that rotational movement of the adjusting nut relative to the second member adjusts the bias of the spring element. 
         [0013]    An object of the invention is to provide an improved clutch. This and other objects and advantages will become apparent from the forgoing and ongoing written specification, the drawings and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a side view of an embodiment of the improved clutch. 
           [0015]      FIG. 2  is a vertical cross-sectional view of the clutch shown in  FIG. 1 , taken generally on line A-A of  FIG. 1 . 
           [0016]      FIG. 3  is a top exploded view of the clutch shown in  FIG. 1 . 
           [0017]      FIG. 4  is a bottom exploded view of the clutch shown in  FIG. 3 . 
           [0018]      FIG. 5  is a graph of the spring force for the clutch shown in  FIG. 1 . 
           [0019]      FIG. 6  is a side view of the clutch shown in  FIG. 1  acting between two shafts. 
           [0020]      FIG. 7  is a vertical cross-sectional view of the clutch and shafts shown in  FIG. 6 , taken generally on line B-B of  FIG. 6 . 
           [0021]      FIG. 8  is a vertical cross-sectional view of an alternative embodiment of the clutch shown in  FIG. 2 . 
           [0022]      FIG. 9  is a vertical cross-sectional view of a second alternative embodiment of the clutch shown in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0024]    Referring now to the drawings and, more particularly, to  FIGS. 2-4  thereof, this invention provides an improved clutch assembly, an embodiment of which is generally indicated at  15 . Assembly  15  generally includes adjusting nut  32 , spring  29 , pressure plate  23 , friction disk  16 , driven hub  22 , and pilot bearing  30 . An external bearing  36  may also be employed. As shown, clutch  15  is generally a cylindrical structure elongated along and orientated about axis x-x. 
         [0025]    As shown in  FIG. 2 , adjusting nut  32  is generally an annular structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  50 , rightwardly-facing vertical annular surface  51 , inwardly-facing horizontal cylindrical surface  52 , leftwardly-facing vertical annular surface  53 , inwardly facing horizontal cylindrical surface  54 , leftwardly-facing vertical annular surface  55 , inwardly-facing horizontal cylindrical surface  56 , and leftwardly-facing vertical annular surface  57 , joined at its outer marginal end to the left marginal end of cylindrical surface  50 . 
         [0026]    As shown in  FIG. 2 , pressure plate  23  is generally a ring-shaped annular structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  59 , rightwardly-facing vertical annular surface  60 , outwardly-facing horizontal cylindrical surface  61 , rightwardly-facing vertical annular surface  62 , outwardly-facing horizontal cylindrical surface  63 , rightwardly-facing vertical annular surface  64 , inwardly-facing horizontal cylindrical surface  65 , and leftwardly-facing vertical annular surface  66 , joined at its outer marginal end to the left marginal end of surface  59 . 
         [0027]    As shown in  FIG. 4 , four protrusions or tabs  26   a - 26   d  extend radially out from cylindrical surface  59 . Tabs  26   a - 26   d  are dimensioned to fit into corresponding slots  31   a - 31   d , which are described below. When tabs  26   a - 26   d  are positioned in slots  31   a - 31   d , respectively, pressure plate  23  is held such that it rotates with rotation of driven hub  22 . In addition, a number of radially extending reliefs  25  are cut into surface  66  of pressure plate  23 . These reliefs extend from surface  65  to surface  59  and are configured for dust collection and increased clutch pressure. 
         [0028]    Friction or driving hub  16  is generally a ring-shaped cylindrical structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  68 , rightwardly-facing vertical annular surface  69 , outwardly-facing horizontal cylindrical surface  70 , rightwardly-facing vertical annular surface  71 , inwardly-facing horizontal cylindrical surface  72 , and leftwardly-facing vertical annular surface  73 , joined at its outer marginal end to the left marginal end of surface  68 . 
         [0029]    As shown in  FIGS. 2 ,  6  and  7 , cylindrical surface  72  of driving hub  16  is splined and forms a bore configured to receive the correspondingly splined end of first shaft  20  for rotational engagement. Thus, when shaft  20  engages the splined bore formed by surface  72 , rotation of driving shaft  20  about axis x-x causes corresponding rotation of hub  16  about axis x-x. 
         [0030]    As shown in  FIG. 2 , driven hub  22  is generally a cylindrical annular structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  75 , rightwardly-facing vertical annular surface  76 , inwardly-facing horizontal cylindrical surface  77 , rightwardly-facing vertical annular surface  78 , inwardly-facing horizontal cylindrical surface  79 , rightwardly-facing vertical annular surface  80 , rightwardly and inwardly-facing frustoconical surface  81 , inwardly-facing horizontal cylindrical surface  82 , leftwardly-facing vertical annular surface  83 , outwardly-facing horizontal cylindrical surface  84 , leftwardly-facing vertical annular surface  85 , outwardly-facing horizontal cylindrical surface  86 , and leftwardly-facing vertical annular surface  87 , joined at its outer marginal end to the left marginal end of surface  75 . 
         [0031]    As shown in  FIGS. 2 ,  6  and  7 , cylindrical surface  82  of driven hub  22  is splined and forms a bore configured to receive the correspondingly splined end of second shaft  21  for rotational engagement. Thus, when shaft  21  engages the splined bore formed by surface  32 , rotation of driven hub  22  about axis x-x causes corresponding rotation of second shaft  22  about axis x-x. 
         [0032]    As shown in  FIGS. 2-4  and  7 , in this embodiment driving hub  16  includes conventional annular non-metallic composite friction liners  100  and  101  bonded to the outer portion of surface  73  and surface  69  of hub  16 , respectively. Friction liner  100  provides a desired contact area between surface  73  of driving hub  16  and surface  78  of driven hub  22 . Friction liner  101  in turn provides a desired contact area between surface  69  of hub  16  and surface  66  of pressure plate  23 . While in this embodiment liners  100  and  101  are bonded to hub  16 , alternatively they could be free floating. Also, liners  100  and  101  may be contoured to control the size, shape and location of the contact area and resulting torque between driving hub  16  and driven hub  22 . For example, liners  100  and  101  may have tapered or beveled outside and inside diameters on their leftwardly-facing and rightwardly-facing outer surfaces, respectively. 
         [0033]    As shown in  FIGS. 2 and 7 , surfaces  79  and  80  form an annular ledge on which pilot bearing  30  is positioned. As shown in  FIG. 2 , pilot bearing  30  is generally a ring-shaped cylindrical structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  90 , rightwardly-facing vertical annular surface  91 , inwardly-facing horizontal cylindrical surface  92 , and leftwardly-facing vertical annular surface  93 , joined at its outer marginal end to the left marginal end of cylindrical surface  90 . As shown, the diameter of outer cylindrical surface  90  is slightly less than the diameter of surface  79  such that pilot bearing  30  fits within and abuts cylindrical surface  79  of driven hub  22 . 
         [0034]    As shown in  FIG. 7 , inner cylindrical surface  92  of bearing  30  is configured to receive the left marginal end of shaft  20  and to act as a bearing surface with respect to that left marginal end portion of rotating shaft  20  that protrudes beyond the left side of the bore defined by surface  72  of friction hub  16 . Pilot bearing  30  allows for rotation of shaft  20  about axis x-x while holding the end of shaft  20 , and therefore friction hub  16 , in proper alignment. 
         [0035]    Surfaces  86  and an inner portion of surface  87  of hub  22  form outer journal  39  for receiving outer bearing  36 . As shown in  FIG. 7 , bearing  36  is generally a ring-shaped cylindrical annular structure orientated about axis x-x and bounded by outwardly-facing horizontal cylindrical surface  95 , rightwardly-facing vertical annular surface  96 , inwardly-facing horizontal cylindrical surface  97 , and leftwardly-facing vertical annular surface  98 , joined at its outer marginal end to the left marginal end of outwardly-facing horizontal cylindrical surface  95 . Inwardly-facing horizontal cylindrical surface  97  of bearing  36  is configured to bear against the outer cylindrical surface  86  of driven hub  22 , and the outer cylindrical surface  95  of bearing  36  is configured to bear against an external surface  38 . Thus, bearing  36  allows for rotation of driven hub  22  about axis x-x relative to external surface  38  while holding driven hub  22  in proper alignment. 
         [0036]    As shown in  FIGS. 2-4 , spring  29  bears on one side against surface  53  of adjusting nut  32  and on the other side against opposing surface  62  of pressure plate  23 . In operation, spring  29  presses against surface  53  of adjusting nut  32  and surface  62  of pressure plate  23 , causing friction hub  16  to be compressively clamped between pressure plate  23  and driven hub  22 . This encourages driven hub  22  to rotate together with friction hub  16  through contact friction at friction liners  100  and  101 . When the driving torque exceeds the friction torque, driven hub  22  will slip relative to friction hub  16 , resulting in shaft  21  no longer rotating at the same speed as shaft  20 . 
         [0037]    Inner cylindrical surface  56  of adjustment nut  32  is threaded and outer cylindrical surface  75  of driven hub  22  is corresponding threaded such that adjusting nut  32  can be rotationally connected to driven hub  22 . As shown, spring  29 , pressure plate  23 , friction hub  16 , and pilot bearing  30  are orientated between adjustment nub  32  and driven hub  22  and, in this embodiment, housed within and between adjustment nut  32  and driven hub  22 . Accordingly, rotation of adjustment nut  32  in one direction relative to driven hub  22  causes nut  32  and hub  22  to move closer together, thereby decreasing the distance between surface  53  of nut  32  and surface  62  of plate  23  and increasing the countering bias of spring  29 . Rotation of adjustment nut  32  in the other direction relative to driven hub  22  increases the gap between such surfaces and decreases the bias of spring  29 . The ability in this way to adjust the gap between surfaces  62  and  53  allows for the spring bias to be adjusted as desired. Thus, if over time either spring  29  losses its elasticity or if any of liner  100 , liner  101 , surfaces  69  and/or  73  of driving hub  16 , surface  66  of pressure plate  23  and/or surface  78  of driven hub  22  are worn away, adjustment nut  32  may be screwed down relative to driven hub  22  to maintain the desired bias of spring  29 . 
         [0038]    Cylindrical surface  63  of pressure plate  23  acts as a guide and serves to maintain the orientation of spring  29  about axis x-x. The inner surface of the bottom sections of spring  29  are dimensioned to fit around surface  63  of pressure plate  23  such that spring  29  is retained in proper alignment. 
         [0039]    As shown in  FIGS. 3-4 , notches  31   a - 31   d  are cut between surfaces  75  and  77  and into surface  76  of hub  22  at radial positions that correspond to the radial positions of tabs  26   a - 26   d , respectively, to provide locking engagement. Thus, the four rectangular-shaped tabs or notch keys  26   a - 26   d  are located on the outer edge of pressure plate  23  and fit into the corresponding notches  31   a - 31   d , respectively, in driven hub  22  to prevent pressure plate  23  from rotating relative to driven hub  22  when assembled. 
         [0040]    As shown, clutch spring  29  is arranged concentric to shafts  20  and  21 . In this embodiment, spring  29  is a Belleville spring, which allows for varying numbers of springs and spacers in varying arrangements to be employed as desired. Alternatively, a coil spring or other state of the art bias device or spring set may be employed. In this embodiment, spring  29  has a non-standard spring force displacement curve. As shown in  FIG. 5 , the force displacement curve for spring  29  includes region  102  of operation in which the bias force is relatively constant. As shown, spring  29  has a first spring constant in first range of deflection  103  and a different spring constant for second range of deflection  104 . In this embodiment, the spring constant for range  104  is less than about 25% of the spring constant for range  103 . The advantage of this arrangement is that the relatively flat or minimally sloped region  104  of the force-displacement curve allows a relatively constant force to be applied to the clutch even if the spring displacement changes due to clutch wear. 
         [0041]    As shown in  FIGS. 3-4 , outer surface  75  of driven hub  22  includes lock  35 . In this embodiment, lock  35  is a nylon plug that frictionally engages the inner threaded surface  56  of adjustment nut  32 , thereby restricting rotation of adjustment nut  32  relative to driven hub  22 . This allows for adjustment nut  32  to be screwed onto driven hub  22  to provide the desired gap between surfaces  62  and  53  and to prevent relative rotation thereafter. Alternative locking mechanisms may be employed, such as a locking screw or other state of the art thread locking device or method. 
         [0042]    As described, clutch  15  is a modular member in that may be easily placed into existing drive shaft assemblies, including without limitation hoist assemblies. All of the components of the clutch, other than bearing  36 , are housed between adjustment nut  32  and driven hub  22 . In addition, added strength is derived from having pilot bearing  30  and second bearing  36  acting on the same intermediate structure of driven hub  22 . Thus, clutch  15  may be quickly removed, installed or adjusted and reset. Clutch  15  also requires only one direct support bearing  36 . Drive shaft  20  is supported by pilot bearing  30 , which is internal or inside clutch  15 . In addition, the spline fit between drive shaft  20  and friction hub  16  controls unwanted radial movements and eliminates the need for a second direct support bearing. Spring  29  is designed to allow quick change of capacity. For example, four springs for a ½ horsepower rated clutch and two springs for a ¼ horsepower rated clutch may be used. In this embodiment, the use of Bellville springs designed with a relatively flat force curve helps tolerate clutch wear with minimal reduction in clutch torque. 
         [0043]    Clutch  15  is also configured for easy assembly. Adjustment nut  32  is tightened relative to driven hub  22  until spring  29  is flat, after which adjustment nut  32  is backed-off a minimal amount, preferably ⅛ to ¼ of a turn. The clutch is then set. As the clutch wears, the compressed height of the springs may increase and eventually the clutch torque would be reduced. With clutch  15 , the clutch can be reset by tightening adjustment nut  32  relative to driven hub  22  to flatten spring  29  and then by backing adjustment nut  32  off a minimal amount again. 
         [0044]    While a single pressure plate  23  and friction hub  16  are shown and described, multiple pressure plates and friction hubs may be used to increase torque transfer as desired. 
         [0045]    While in a first embodiment shown in  FIGS. 2-4  and  6 - 7  the radial pilot bearing  30  is shown as being held by driven hub  22  and acting directly between driven hub  22  and the protruding end of shaft  20 , other pilot bearing configurations may be used, examples of which are shown in  FIGS. 8 and 9 . In the alternative configuration shown in  FIG. 8 , driven hub  22  does not include surfaces  79  and  80  and the annular ledge formed thereby, but instead surface  78  of hub  22  extends and is joined at its inner marginal end to the right marginal end of the extension of surface  82  of hub  22 . And instead of surface  73  of friction hub  16  extending inwardly to surface  72  of hub  16 , an annular ledge is formed in friction hub  16  by inwardly-facing horizontal cylindrical surface  110  and leftwardly-facing vertical annular surface  110  of friction hub  16 . As shown in  FIG. 8 , surfaces  110  and  111  of friction hub  16  form an annular ledge on which pilot bearing  105  is positioned. Internal bearing  105  thereby acts directly between friction hub  16  and the protruding end of shaft  21 , rather than between driven hub  22  and the protruding end of shaft  20  as in the first embodiment. This is essentially a reversed configuration to the configuration shown in  FIGS. 2-4  and  6 - 7 . 
         [0046]      FIG. 9  shows yet another alternative pilot bearing configuration, in which internal radial bearing  106  acts directly between driven hub  22  and friction hub  16 , and only indirectly between driven hub  22  and shaft  20 . As shown in  FIG. 9 , instead of extending to surfaces  79  and then  80 , surface  78  of driven hub  22  extends to outwardly-facing horizontal cylindrical surface  114  of hub  22 , which in turn is joined to the extension of surface  82  of hub  22  by rightwardly-facing vertical annular surface  116  of hub  22 . And instead of surface  73  of friction hub  16  extending inwardly to surface  72  of hub  16 , an annular ledge is formed in friction hub  16  by inwardly-facing horizontal cylindrical surface  112  and leftwardly-facing vertical annular surface  113  of friction hub  16 . As shown in  FIG. 9 , surfaces  112  and  113  of friction hub  16  form an annular ledge and the inner portion of surface  78  and surface  114  form an opposing annular ledge between which pilot bearing  106  is positioned. Internal bearing  106  thereby acts directly between friction hub  16  and driven hub  22 , with shaft  20  constrained in turn by splined surface  72  of friction hub  16 . Like the first two embodiments, pilot bearing  106  provides a radial constraint while allowing axial rotation. 
         [0047]    The present invention contemplates that many changes and modifications may be made. Therefore, while the presently-preferred form of the modular clutch assembly has been shown and described, and several modifications and alternatives discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit and scope of the invention, as defined and differentiated by the following claims.