Abstract:
A flexible coupling assembly installed between a driving member and a driven machine or device. The flexible coupling assembly includes a one-way over-running clutch mechanism incorporated therein and transfers torque from the driving member to the driven device, while compensating for any angular and offset misalignment between two coupling members. The clutch mechanism provides driving torque in one rotational direction and over-running capability in the other, thereby accommodating large torque fluctuations from the driving member. This clutch mechanism is integrated within an intermediate housing assembly that is easily coupled between two jaw-type shaft couplings. Because the present invention eliminates the need for an intermediate shaft between the flexible coupling and a separate clutch mechanism, it further simplifies the installation of the assembly while reducing the overall space required.

Description:
This is a Continuation-In-Part of U.S. application Ser. No. 08/948,096, now U.S. Pat. No. 5,928,083, filed Oct. 9, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to flexible couplings between an output shaft, for example, of a motor and an input shaft of a driven device. More specifically, this invention relates to flexible couplings with an integrated one-way over-running clutch mechanism acting between the motor drive shaft and the driven device. 
     2. Discussion 
     Flexible couplings are used for transferring torque from output or drive shafts of devices such as an electrical motor or internal combustion engine, to input shafts of various machines or devices, such as fans, packaging machines or pumps. Both the driving shaft and driven shaft are attached to jaw-type coupling members that have interlocking extensions to couple the motor to the machine. A typical flexible coupling has an elastomeric coupling “spider” placed between these input and output coupling members. The spider is a flexible element with several legs, each of which fits between the pairs of adjacent “teeth” of the coupling members, which provides the unit with a degree of flexibility during operation, while still transferring the torque from the driving shaft to the driven shaft. The coupling teeth allow for a degree of axial offset while the flexibility of the spider permits angular mis-alignment between the motor and driven device without imposing high bearing loads on those devices. Without such a coupling, severe loading of the bearings in the motor or engine or in supportive “pillow blocks” could occur, causing reliability and durability problems. 
     In many types of machines, speed and transients occur during operation. Also, it might be necessary to prevent the load from “back driving” the motor or power source. It is therefore desired in certain machines to allow the driving shaft rotation to decelerate or even stop, relative to the driven shaft, while the driven shaft continues to rotate by inertia. In order to accomplish this, a clutch assembly is required between the output shaft of the motor and the input shaft of the driven device. This allows the driving shaft to stop, or even reverse direction, without suddenly stopping the rotation of the driven shaft. 
     Several one-way clutches or drives have been developed for use in various applications. For example, a one-way wrap spring clutch for an automobile belt driven alternator is disclosed in U.S. Pat. No. 5,598,913, issued to Monahan et al. The one-way over-running clutch pulley disclosed therein is mounted to the input shaft of the alternator, or other pulley driven device, and accommodates the rotational inertia of an accessory and thereby reduces the slipping and squealing of the belt when there is a large sudden deceleration of the engine. 
     Typically, a flexible coupling system includes a separate one-way drive or clutch which must be installed apart from the coupling. An intermediate shaft is required, and in some cases, extra couplings to allow for additional misalignment and pillow blocks for support of one or more of the shafts may also be required. To reverse the direction of the one-way drive, the entire assembly must be dismantled. Therefore, the previous systems are complicated, expensive, and may also require a large physical space in which to include all of the necessary components. 
     In view of the foregoing attributes of the prior art devices, there exists a need in the art for an improved clutch assembly for use in a flexible coupling between an output shaft of a motor and a driven shaft of a machine. 
     It is therefore a primary object of this invention to fulfill that need by providing a flexible coupling with a clutch assembly that can be easily incorporated between the coupling members of the flexible coupling, reducing installation costs and complexity. 
     It is a further object of this invention to provide a flexible coupling that has a clutch assembly integrated therein such that it has generally the same overall dimensions as a conventional flexible coupling. 
     It is another object of this invention to provide a flexible coupling with an integrated clutch assembly so that the assembly does not require an intermediate shaft or additional shaft supports. 
     It is yet another object of this invention to provide a flexible coupling with a clutch assembly that is easily assembled and serviced. 
     SUMMARY OF THE INVENTION 
     Briefly described, these and other objects are accomplished according to the present invention by providing a flexible coupling assembly with a one-way over-running clutch mechanism that is integrated within the flexible coupling. 
     The flexible coupling of the present invention includes first and second coupling members, two elastomeric coupling spiders and a cylindrical intermediate assembly containing a bearing assembly and clutch mechanism. The clutch assembly may be one of a variety of mechanisms, such as, but not limited to, wrap spring, sprag, or roller/ramp clutches. Because the clutch assembly is integrated within the flexible coupling, the overall dimensions of the coupling assembly are only increased a minimal amount over a conventional flexible coupling. Therefore, the overall space required for the flexible coupling of the present invention is significantly less than that required for a conventional flexible coupling and a separate clutch assembly. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the first embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the first embodiment of the present invention. 
     FIG. 2 is a cross-sectional view of the intermediate assembly taken along a line generally bisecting the assembly. 
     FIG. 2 a  is an alternate view of the region A—A of FIG. 2 with a spring of circular cross-section incorporated within the housing assembly. 
     FIG. 3 is a plan view of the first embodiment in its fully assembled state. 
     FIG. 4 is a cross-sectional view of the coupling teeth and spider taken generally along line  4 — 4  in FIG.  3 . 
     FIG. 5 is an exploded view of an alternate embodiment having the clutch assembly incorporated within one of the coupling members. 
     FIG. 6 is a cross-sectional view of a second embodiment of the intermediate assembly taken along a line generally bisecting the assembly. 
     FIG. 7 is a detailed view of the region  7  of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the drawings, there is shown in FIG. 1 an exploded view of the first embodiment of the present invention. The flexible coupling assembly, shown generally as  10 , includes an intermediate housing assembly  12  located between first and second coupling members  14  and  16 , with an elastomeric coupling element or “spider”  18  (hereinafter referred to as a coupling spider) between the intermediate assembly  12  and each coupling member  14  and  16 . The flexible coupling assembly  10  is attached at one end to a rotational input or driving member and at the other end to a rotationally driven device. The driving member may be an electric motor, internal combustion engine, or any other driving device capable of providing a rotational input to the coupling assembly  10 . 
     Each of the coupling members  14  and  16  have a bore  20  and  21  along the center axis  22  of one end  23  into which a rotational shaft is received. The diameter of the bores  20  and  21  are such that each bore  20  and  21  is slightly larger than the diameter of the desired driving shaft  24  of the driving motor (not shown) and driven shaft  26  of the driven machine (not shown), respectively. The attachment of the coupling members  14  and  16  to the driving and driven shafts  24  and  26  is not critical to this invention. However, clearly any number of known means for attachment that prevent relative rotation between the coupling members and their respective shafts can be applied according to the teachings of the present invention. Alternate methods include, but are not limited to, a shaft with a key or ridge along its outer surface corresponding to a keyway in the bore, corresponding splines on the shaft and bore, a set screw or coupling pin, or a shaft and bore of corresponding non circular cross-sectional shapes. 
     Opposite the shaft end  23 , the coupling members  14  and  16  each have a coupling surface  28  and  29  that is generally flat except for three “teeth” or extensions  30  and  31  protruding axially therefrom. The extensions  30  and  31  are spaced equidistantly apart on the coupling surface  28  and  29 , and are generally wedge shaped, with their side edges  32  tapering radially inward so that the outer edges  34  of the extensions are wider than the inner edges  36 , as best shown in FIG.  4 . However, more or less than three extensions, which may be of varying shape and spaced non-equidistantly apart, are clearly within the scope of the present invention. 
     The two coupling spiders  18  are made of rubber, polyurethane or other elastomeric material and have six legs  38  extending radially outward from a center portion  40 . In an alternate embodiment where the coupling members may have more or less than three extensions, the quantity of the legs  38  may be more or less, but is generally equal to twice the quantity of the extensions  30  and  31  protruding from each coupling member. Both end surfaces  42  of each coupling spider  18  are generally flat, with the length between the end surfaces  42  being substantially the same as the axial length of the extensions  30  and  31  on the coupling members  14  and  16 . In the first embodiment, the legs  38  are of a constant width. However, in an alternate embodiment where the shape and spacing of the extensions on the coupling members varies, the legs  38  of the spiders  18  will also vary accordingly, as detailed below. 
     The intermediate assembly  12  is generally cylindrical and is comprised of two end portions, more specifically a clutch envelope  44  and a clutch hub  46 , which have open ends  48  and  50 , respectively, and coupling surfaces  52  and  53  opposite the open ends  48  and  50 . The clutch envelope  44  and clutch hub  46  each have substantially smooth and flat surfaces  54  and  56  at their open ends  48  and  50  through which inner cylindrical surfaces  58  and  60  are formed with substantially equal diameters. Extending axially from its flat surface  54 , the clutch envelope  44  further includes a cylindrical axial extension  62  along its outer surface  64  which forms a second inner cylindrical surface  65  having a greater diameter than its inner cylindrical surface  58 . The clutch hub  46  on the other hand has a cylindrical recess  66  on its outer surface  68  which forms an intermediate cylindrical surface  69 . This intermediate cylindrical surface  69  has a diameter that is greater than the inner cylindrical surface  60 , but slightly less than the diameter of the second inner cylindrical surface  65  of the clutch envelope  44 . 
     The coupling surfaces  52  and  53  on the clutch envelope  44  and clutch hub  46  are substantially identical and are generally flat with a plurality of extensions  70  and  71  spaced equidistantly apart protruding therefrom. The extensions  70  and  71  are substantially the same quantity and length as the extensions  30  and  31  on the coupling members  14  and  16  and similarly include radially inward tapering edges  72 . Again, in an alternate embodiment having a different quantity of extensions on either of the coupling members, the number of extensions on each end portion is equal to the number of extensions on the corresponding coupling member. Furthermore, where the shape and spacing of the extensions on the coupling members differs from the first embodiment, the shape and spacing of the extensions  70  and  71  must be adapted accordingly, as detailed below. 
     The clutch envelope  44  and clutch hub  46  are press fit together around a rolling element bearing assembly  74  with inner and outer races  76  and  78  and a rolling element  75  to form the intermediate assembly  12 . As shown in FIG. 2, the axial extension  62  overlaps the rolling element bearing assembly  74  and cooperates with the corresponding recess  66  to secure the rolling element bearing assembly  74  therebetween. The smooth flat surfaces  54  and  56  are formed such that there is no contact between the clutch envelope  44  and the clutch hub  46  except through the rolling element bearing assembly  74 . Because there is no direct contact between the clutch envelope  44  and the clutch hub  46 , the rolling element bearing assembly  74  allows relative rotation between the two end portions. The rolling element bearing assembly  74 , which is illustrated as a ball bearing  75 , is located between inner and outer races  76  and  78 , where the inner race  76  is secured to the intermediate cylindrical surface  69  on the recess  66  of the clutch hub  46  and the outer race  78  is secured along the inner cylindrical surface  65  of the cylindrical axial extension  62 . While not shown, the bearing  75  is permanently sealed so that additional lubrication over its useful life is not necessary. The arrangement of the bearing assembly around the clutch envelope  44  and clutch hub  46  also allows the bearing seals to function as the seals for the clutch assembly so that no additional seals are required. Obviously, other varieties of bearings, journal bearings for example, could be used in the present invention. 
     When the clutch envelope  44  and the clutch hub  46  are pressed together, the inner cylindrical surfaces  58  and  60  are coaxial with substantially the same diameters so that they define a cylindrical cavity  80  for receiving a clutch spring  82 . This is best shown in FIG.  2 . The two inner cylindrical surfaces  58  and  60  form a common cylindrical surface  83  which defines the spring receiving cavity  80 . The spring receiving cavity  80  further includes end walls  84  and  85  on the clutch envelope  44  and clutch hub  46 , respectively. 
     The clutch spring  82  is located within the spring receiving cavity  80  and is a coil or wrap spring which, in its uncompressed or free standing condition, has a diameter which is slightly greater than the diameter of the common cylindrical surface  83 . When received in the cavity  80 , the spring  82  frictionally engages with and exerts a radially outward normal force on both of the inner cylindrical surfaces  58  and  60 . The spring  82  is shown in FIG. 2 as having a circular cross-section. However, alternate embodiments, including a spring of rectangular cross-section, as shown in FIG. 3, oval or other shaped cross-section, are clearly envisioned to be within the scope of the present invention. 
     The clutch hub  46  may further include a threaded hole  86  through its coupling surface  53  and end wall  85  into the partial cavity defined by its inner cylindrical surface  60 . This hole  86  allows air to escape as the two end portions  44  and  46  are pressed together to prevent pressurizing the spring receiving cavity  80 , and allows for the introduction of grease after assembly, for example during routine maintenance of the flexible coupling  10 . A threaded plug  88  threads into the hole  86  to seal the spring receiving cavity  80  and contain lubricant (not shown) for the clutch spring  82  therein. This prevents the lubricant from leaking out or being contaminated by foreign materials, which in turn prolongs the life of the clutch mechanism. 
     The threaded hole  86  also assists in separating the two end portions  44  and  46  after the intermediate assembly  12  is pressed together. This is necessary when the unit requires servicing, as may be the case if, for example, the spring  82  breaks inside the cavity  80 , or when reversal of the driving direction of the clutch mechanism is desired. To separate the end portions  44  and  46 , a threaded bolt (not shown) is inserted through the hole  86  so that its threaded end contacts the end wall  84  of the cavity  80  on the clutch envelope  44 . As the bolt is tightened, the threaded end pushes against the clutch envelope  44 , forcing the two end portions apart. Reversal of the driving direction is then accomplished by replacing the spring  82  with an opposite wound spring (not shown). Although the threaded hole  86  is described as being only through the clutch hub  46 , clearly, the scope of the present invention includes such a threaded hole on either the clutch hub  46  or clutch envelope  44 , or both. 
     After the clutch envelope  44  and the clutch hub  46  are pressed together, their coupling surfaces  52  and  53  are located at opposite ends of the intermediate assembly  12  with the extensions  70  and  71  being thereby directed in opposite axial directions. The intermediate assembly  12  is then axially aligned with the driving and driven coupling members  14  and  16  so that the extensions  70  and  71  on the clutch envelope  44  and on the clutch hub  46  insert between the extensions  30  and  31  on the coupling members  14  and  16 . Prior to coupling the intermediate assembly  12  to the coupling members  14  and  16 , the coupling spiders  18  are inserted between the components which results in a leg  38  of the coupling spider  18  being between each pair of adjacent extensions  30  and  70 , and  31  and  71 . This is best shown in FIG. 3, which shows the completed assembly  10 , with the extensions  70  and  71  on each end portion  44  and  46  engaging the legs  38  of the coupling spiders  18  and thereby engaging the extensions  30  and  31  on each coupling member  14  and  16 . As seen in FIG. 3, the outer surfaces  92  of the legs  38  are visible between each adjacent pair of extensions  30  and  70 , and  31  and  71 , and the legs  38  are formed such that they fit firmly in place between the adjacent pairs of extensions  30  and  70 , and  31  and  71 , contacting the tapered edges  32  and  72  of the extensions  30 ,  31 ,  70  and  71 , and filling the gaps therebetween. As mentioned above, in alternate embodiments where the extensions on either component are not spaced equidistantly apart or are not wedge shaped, the extensions on the corresponding component and the legs of the spiders must be adapted accordingly. In any embodiment of the present invention, the extensions on the coupling members must correspond to and engage the legs of the spider and the corresponding extensions on the intermediate assembly  12 , thereby functioning as a means for connecting the driving shaft to the intermediate housing and finally to the driven shaft. 
     The generally flat coupling surfaces  28  and  52 , and  29  and  53  cooperate with the flat end surfaces  42  of the coupling spiders  18  so that the components couple firmly together. The elasticity of the coupling spider  18  and any clearance gaps between the coupling spider  18  and the extensions  30 ,  31 ,  70  and  71  provide the flexibility of the coupling assembly  10  by compressing or flexing to accommodate for angular misalignment of the drive and driven shafts, while also transferring the torque from the driving coupling member  14  through the intermediate assembly  12  to the driven coupling member  16 . This reduces any angular misalignment or offset loads that may be applied to the motor bearings (not shown) if the two shafts  24  and  26  are not aligned. Furthermore, the lengths of the extensions  30 ,  31 ,  70  and  71  compensate for axial offset between the coupling surfaces  28  and  52 , and  29  and  53  by allowing the coupling assembly to remain fully functional when there are small gaps between the flat ends of the coupling spider  18  and the flat coupling surfaces of the coupling members  14  and  16  and/or the intermediate assembly  12 . 
     The coupling surfaces  52  and  53  and extensions  70  and  71  of the clutch envelope  44  and clutch hub  46  are substantially the same so that the intermediate assembly  12  can be installed in either direction between the coupling members. For example, the clutch envelope  44  can be coupled with either the driving coupling member  14  or the driven coupling member  16  with no change in overall performance of the flexible coupling assembly  10 . To simplify the description of the present invention, however, the assembly is generally described with the clutch envelope  44  coupling with the driving coupling member  14 . 
     The identical coupling surfaces  52  and  53  of the clutch envelope  44  and clutch hub  46  simplifies installation of the flexible coupling because there is not a concern as to which direction each end must face. Furthermore, it is easier to match the intermediate assembly  12  of the present invention to existing flexible coupling components. Coupling members and corresponding coupling spiders are typically obtained as a matched set whose legs and extensions cooperate with one another. The coupling surfaces of the intermediate assembly can be selected to match the coupling surfaces of existing coupling members so the intermediate assembly can easily be applied to an existing system. This avoids having to acquire separate coupling members and coupling spiders for each end of the intermediate assembly, which would be more costly and further complicate the assembly process. An additional benefit of using a matched set of coupling members is that the system can easily be made operable if the intermediate assembly  12  fails and has to be temporarily removed for service, as the two coupling members  14  and  16  can then be extended to engage each other in the absence of the intermediate assembly  12 . 
     During operation, either the clutch envelope  44  or the clutch hub  46  may be driven by the driving coupling member  14 , which is driven by the driving shaft  24  of the motor or internal combustion engine. As mentioned above, to simplify the discussion, the clutch envelope  44  is described as coupling with the driving coupling member  14 . Rotation of the driving shaft  24  therefore causes a corresponding rotation of the clutch envelope  44 . If the clutch envelope  44  is accelerated relative to the clutch hub  46  in the driving direction, the intermediate assembly  12  of the present invention will transfer torque from the clutch envelope  44  to the clutch hub  46  and subsequently to the driven shaft  26  and finally to the driven device or machine. When the clutch envelope  44  is significantly decelerated relative to the rotational speed of the clutch hub  46 , the intermediate assembly  12  of the present invention allows for the clutch hub  46  to over-run or rotate relative to the clutch envelope  44  as the inertia from the driven device prevents the clutch hub  46  from decelerating as fast as the clutch envelope  44 . Previously, where no over-running occurred in the flexible coupling itself, the deceleration of the motor and the inertial over-running of the driven device subjected the motor to additional stress as the motor had to overcome the built up inertia within the driven device as it slowed. 
     In the first embodiment of the present invention, torque is transferred and slip is permitted because of the operation of the coil spring  82  within the spring receiving cavity  80  of the intermediate assembly  12 . To provide these complementary functions, the coil spring  82  is oriented in the cavity  80  so that it is “wound” in a direction which fosters the transmission of torque while still permitting slip. The winding of the spring  82  is such that when the clutch envelope  44  is positively driving or accelerating relative to the clutch hub  46 , the frictional engagement of the spring  82  with the inner cylindrical surface  58  of the clutch envelope  44  will cause the spring to experience compressive loading or unwinding. As the coil spring  82  is unwound, its freestanding outer diameter would effectively increase if it were not restrained by the inner cylindrical surfaces  58  and  60 . The frictional forces between the inner cylindrical surfaces  58  and  60  and the coils or volutes of the spring  82  result in increased compressive forces being built-up in the spring  82  along the helix of the spring thereby increasing the radially outward normal force being exerted on both the inner cylindrical surfaces  58  and  60  of the clutch envelope  44  and clutch hub  46 . As the normal force increases, the effect of the spring  82  is to lock the clutch envelope  44  to the clutch hub  46 , fostering the transfer of torque from the driving shaft  24  to the driven shaft  26 . Additionally, by having the spring  82  engage the inner cylindrical surfaces  58  and  60  of the clutch envelope  44  and clutch hub  46 , centrifugal forces induced by rotation of the intermediate assembly  12  are utilized to further enhance and increase the radially outward normal force exerted by the spring  82 . One additional benefit of this engagement between the exterior surface  94  of the spring  82  and the interior cylindrical surfaces  58  and  60  is that any lubricants used with the spring  82  are retained on the spring  82  under the influences of the centrifugal forces and are not drawn away. 
     When the speed of the driving shaft  24  is reduced, the inertia acting on the driven shaft  26  causes the clutch hub  46  to over-run the clutch envelope  44 . The winding direction of the spring  82  causes the effective outer diameter of the spring  82  to slightly reduce as the spring  82  “winds-up”. Corresponding with this reduction in the effective outer diameter of the spring  82 , the frictional forces between the inner cylindrical surfaces  58  and  60  and the coils of the spring  82  result in a decrease of the compressive forces along the helix of the spring  82  which can produce a decrease in the radially outward normal force exerted by the spring  82  on the inner cylindrical surfaces  58  and  60 . This in turn “unlocks” the inner cylindrical surfaces  58  and  60  from each other and the clutch hub  46  is permitted to over-run and rotate relative to the clutch envelope  44 . 
     Although the first embodiment includes the one-way over-running clutch as disclosed in U.S. Pat. No. 5,598,913, and discussed above, clearly the scope of the present invention includes other clutch assemblies that are capable of being incorporated into the intermediate assembly or coupling member of the flexible coupling assembly of the present invention. Examples of other clutch assemblies include, but are not limited to, sprag and roller/ramp clutches. 
     In the first embodiment, the clutch spring  82  is incorporated within the intermediate assembly  12 . As mentioned above, this allows the clutch assembly to be applied to various applications with minimal cost. The intermediate assembly can be matched with corresponding coupling members that have the appropriate diameter bore therethrough to fit between the intermediate assembly and any desired driving shaft and driven shaft. Replacing existing coupling members  14  and  16  to adapt the clutch assembly to the application is much less costly than replacing the entire intermediate assembly  12 . However, an alternate embodiment, shown generally as  100  in FIG. 5, could incorporate the clutch assembly  102  into one of the coupling members  104 . The clutch coupling member  104  may then be installed on either the driving shaft  24  or driven shaft  26 , as long as the selected shaft is of substantially the same diameter and shape of the bore  106  in the coupling member  104 . The alternate assembly  100  eliminates the need for a separate intermediate housing assembly and further eliminates one of the two coupling spiders  18  that are present in the first embodiment. The remaining elements and operation of the flexible coupling assembly  100  are otherwise the same as the first embodiment discussed above. 
     In a second embodiment of the present invention, as shown in FIG. 6, a clutch envelope  144  and a clutch hub  146  of an intermediate assembly  112  both include two cylindrical axial extensions. The clutch envelope  144  and the clutch hub  146  both include outer cylindrical axial extensions  154  and  155  ending in substantially smooth and flat surfaces  156  and  157 , respectively. The outer cylindrical axial extensions  154  and  155  have inner cylindrical surfaces  158  and  160 , which are formed with substantially equal diameters, and are bound between open ends  148  and  150 . 
     The clutch envelope  144  and the clutch hub  146  also both include inner cylindrical axial extensions  162  and  164 , respectively, which both have a smaller diameter than the inner cylindrical surfaces  158  and  160 . The inner cylindrical axial extension  164  has a smaller diameter than the inner cylindrical axial extension  162  to provide an inner cylindrical cavity  172  for a rolling element bearing assembly  174 . Like the clutch envelope  44  and clutch hub  46 , the clutch envelope  144  and clutch hub  146  are press fit together around the rolling element bearing assembly  174 , with inner and outer races  176  and  178  and a rolling element  175 . The clutch hub  146  further includes a spring  166  and a snap ring  168  that function to secure the rolling element bearing assembly  174  within the intermediate assembly  112 . 
     When the clutch envelope  144  and the clutch hub  146  are pressed together, the outer cylindrical extensions  154  and  155  are coaxial with substantially the same diameters so that they define an outer cylindrical cavity  180  for receiving a clutch spring  182 . The outer cylindrical cavity  180  is located outwardly from the inner cylindrical cavity  172  relative to a rotational axis  181  defined by the rotation of the clutch envelope  144  and clutch hub  146 . The two inner cylindrical surfaces  158  and  160  form a common cylindrical surface  183 , which defines the spring receiving outer cavity  180 . The clutch spring  182  is located within the spring receiving cavity  180  and is a coil or wrap spring which, in its uncompressed or free standing condition, has a diameter which is slightly greater than the diameter of the common cylindrical surface  183 . When received in the cavity  180 , the spring  182  frictionally engages with and exerts a radially outward normal force on both of the inner cylindrical surfaces  158  and  160 . 
     When in use, the intermediate assembly  112  will generate heat from the friction of the clutch spring  182  against the cylindrical surface  183  and the open ends  148  and  150 . Unlike the intermediate assembly  12  of the first embodiment, the intermediate assembly  112  positions the clutch spring  182  near the outer surfaces  184  and  186  of the assembly  112 . This position of the clutch spring  182  allows better cooling of the intermediate assembly  112  for several reasons. First, the outer cavity  180  is located closer to the outer surfaces  184  and  186 , which improves heat transfer from the clutch spring  182  to the environment. Second, the clutch spring  182  is located outwardly of the rolling element bearing assembly  174 . In the first embodiment, the rolling element bearing assembly  74  acts as an insulator and impairs the heat transfer. The outer surfaces  184  and  186  further include cooling fins  188 , which increase the surface area of the outer surface  184  and  186 , to assist in the heat transfer. Because of the increased heat transfer properties of the intermediate assembly  112 , the assembly  112  may be used in applications at higher speeds and for longer durations than the intermediate assembly  12  of the first embodiment. 
     As shown in FIG. 7, the intermediate assembly  112  also includes a seal  190  positioned between the outer cylindrical axial extensions  154  and  155  and a tab  192 . The seal  190  functions to prevent the ingress of dirt and contamination to the clutch spring  182  and to prevent egress of any lubrication from the clutch spring  182 . The seal  190  can be made in any suitable shape and from any suitable material, such as natural rubber or synthetic elastomers. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.