Abstract:
A coupling ( 20 ) having a driving member ( 22 ) with an inner surface ( 24 ), a driven member ( 26 ) having an outer surface ( 28 ), a flexible member ( 27 ) intervening between the surfaces ( 24, 28 ) exhibiting an elastic center (EC), and a pivot ( 32 ) cooperating between the members ( 22, 26 ) wherein an axial location of the pivot substantially coincides with the axial location of the elastic center (EC). In another aspect, a bonded Subassembly ( 34 ) is provided which, together with the driving member ( 22 ), forms the coupling ( 20 ). The subassembly ( 34 ) has a driven member ( 26 ) with first ( 40 ) and second ( 50 ) projecting portions extending from a main body portion ( 38 ). The first portion ( 40 ) has an outer surface ( 28 ) and the second portion ( 50 ) includes a bearing member. The flexible member ( 27 ) is bonded to the outer surface ( 28 ) and a third projection ( 42 ) extends from the main body portion ( 38 ). The axial location of the bearing member is substantially aligned axially with the position of the elastic center (EC). The coupling ( 20 ) find utility in drivelines for vehicles, such a personal watercraft.

Description:
FIELD OF THE INVENTION 
     The invention relates to torsional drive couplings. More particularly, the present invention is directed to a resilient torsional coupling including a resilient element. 
     BACKGROUND OF THE INVENTION 
     Flexible drive couplings are transmission devices that connect between a driving and driven member, such as in a drive train, to provide misalignment accommodation, torque carrying capability and appropriate stiffness for vibration isolation. Couplings are used, for example, in a drive train between an engine and a unit to be rotated, such as a jet drive unit in a personal watercraft or a propeller in a boat. The coupling&#39;s torsional stiffness is designed to minimize torsional vibrations that may cause damage to the drive train components. Moreover, such couplings, as taught in U.S. Pat. No. 4,516,956 to Staiert, and U.S. Pat. No. 4,041,730 to Kress may include a torque overload feature where the bonded member slips inside the housing after a limit torque is exceeded. This may occur, for example, when the driven component becomes jammed or when it strikes another object. 
     Further Prior Art couplings are shown in FIGS. 1 and 2. These coupling connect between a flywheel and a output shaft in a personal watercraft. Each coupling  10  includes a driving member  11 , a driven member  12 , and a elastomer member  13  positioned between them. The elastomer member  13  is bonded to the driven member  12  and is received in an interference fit (precompressed) and unbonded relationship in a pocket  14  formed in the driving member  11 . The FIG. 1 Prior Art coupling includes a low cocking stiffness of about 14,400 lbf.-in./radian (1,627 N-m/radian). This low stiffness prevents any parallel or cocking misalignment between the members  11 ,  12  from being converted into large radial forces which are then transmitted through engine mounts into the hull liner (frame), and finally to the operator of the personal watercraft. However, the FIG. 1 coupling includes a low radial stiffness, about 56,200 lbf./in. (9,835 N/mm). Any rotational unbalance present will be aggravated at higher rotational frequencies because the unbalance tends to move further outward from the central axis because of the low radial spring rate. Moreover, the concentricity between the driving and driven member can be poor when a low radial stiffness is provided, thereby possibly further aggravating any unbalance present. 
     To combat the low radial stiffness, a pivot bearing  15  was added in the FIG. 2 Prior Art coupling. This substantially increased the radial stiffness to approximately 219,000 lbf./in. (38,352 N/m), thereby improving any unbalance problem present. However, the positioning of the pivot bearing  15  is offset from the elastomer member  13 , therefore, any parallel or cocking misalignment between the members  11 ,  12  causes the elastomer member to be loaded in radial compression. This results in a much higher cocking stiffness (approximately 426,700 lbf.-in./radian (48,217 N-m/radian)) than compared in the FIG. 1 coupling, and, therefore, resultantly higher loads generated should any cocking or parallel misalignment be present. Moreover, because of the high cocking stiffness it may be necessary to shim various driveline components to minimized such cocking or parallel misalignment, thus increasing manufacturing costs. 
     Although, in general, these prior art couplings have adequate performance and/or durability, they each exhibit certain performance limitations. For example, the FIG. 1 embodiment exhibits low radial stiffness thereby, in some installations, this can lead to unwanted radial vibrations in the drive train due to rotational unbalances in, and concentricity between, the members  11 ,  12 . In an effort to provide increased radial stiffness, a pivot bearing  15  was added in the FIG. 2 embodiment. However, this pivot bearing  15  limits the degree of cocking misalignment that is achievable by the coupling as well as substantially increases the cocking stiffness thereof. 
     Accordingly, there has been a long felt, and unmet need for a coupling capable of transmitting torques, which exhibits both increased radial stiffness as well as low cocking stiffness. 
     SUMMARY OF THE INVENTION 
     The present invention is a resilient coupling providing increased radial stiffness and at the same exhibiting a low cocking stiffness. Moreover, the coupling can accommodate substantial cocking and/or parallel misalignment. The coupling is most useful for transmitting torque, accommodating misalignment, and reducing vibration in the driveline components of personal watercraft. 
     According to the invention, the coupling comprises a driving member including an inner surface; a driven member including an outer surface; a flexible member intervening between the outer surface and the inner surface, the flexible member including an elastic center; and a pivot cooperating between the driving and driven members wherein an axial location of the pivot substantially coincides with an axial location of the elastic center. 
     According to another aspect of the invention, the coupling comprises a driving member including a bridging portion, an outer projection axially extending from said bridging portion, and an inner projection axially extending from said bridging portion and spaced radially inward from said outer projection, said outer projection including an inner surface and said inner projection including a first bearing member, a driven member including a main body portion including first and second projecting portions projecting axially therefrom, an outer surface formed on said first projecting portion and a second bearing member formed on said second projecting portion, a flexible member bonded to said outer surface of said driven member and received in a radially precompressed and unbonded relation with said inner surface, said elastomer member including an elastic center, and a pivot formed by said first and second bearing members, wherein an axial location of said pivot substantially coincides with said elastic center. 
     According to a further aspect of the invention, a coupling is provided comprising a first member including a generally hollow cylindrical outer projection having an inner surface, and an generally cylindrical inner projection concentric with said outer projection, said inner projection including a first bearing member, a second member including a generally cylindrical first projecting portion and a second projecting portion generally concentric with said first projecting portion, said first projecting portion including an outer surface and said second projecting portion including a second bearing member, an annular flexible member bonded to said outer surface and received in a radially precompressed and unbonded relation with said inner surface, said flexible member including an elastic center, and a pivot formed by said first and second bearing members, and wherein axial location of said pivot substantially coincides with an axial position of said elastic center. 
     In yet another aspect, a bonded subassembly is provided which is adapted to be received in the driving member of a coupling. The bonded subassembly comprises a driven member including first and second projecting portions extending in an axial direction from a main body portion of said driven member, said first projecting portion including an outer surface formed thereon, said second projecting portion including a bearing member formed on a radially outward surface thereof, a flexible member bonded to an outer surface, said flexible member including an elastic center (EC), a third projection which projects in a axial direction from a main body portion in a direction opposite from said projecting portions, and an axial location of said bearing member is substantially axially aligned with an axial position of said elastic center. 
     In accordance with another aspect, the invention comprises a vehicle, comprising a structure; an engine mounted to said structure; a drive component interconnected to and rotated by said engine; a coupling secured to said first drive component, said coupling including a driving member including an inner surface, a driven member including an outer surface, a flexible member intervening between said outer surface and said inner surface, said flexible member including an elastic center, and a pivot cooperating between said driving and said driven members wherein an axial location of said pivot substantially coincides with an axial location of said elastic center; a second drive component interconnected to said coupling; and a drive unit interconnected to, and driven by, said second drive component. 
     The coupling advantageously provides significantly increased radial stiffness as compared to certain prior art couplings. 
     Further, the coupling advantageously provides such increased radial stiffness without appreciably affecting cocking stiffnesses, therefore, the propensity for driveline vibration is reduced. 
     Moreover, the coupling advantageously provides high torque carrying capacity while exhibiting a torque limitation feature. 
     The above-mentioned and further features, advantages, and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become better understood by reference to the description that follows, in conjunction with the appended drawings, in which: 
     FIG. 1 s a cross-sectioned side view of a flexible coupling according to the Prior Art; 
     FIG. 2 is a cross-sectioned side view of another flexible coupling according to the Prior Art; 
     FIG. 3 is an end view of the flexible coupling in accordance with the present invention; 
     FIG. 4 is a cross-sectioned side view of the coupling of FIG. 3 taken along line  4 — 4 ; 
     FIG. 5 is an end view of the bonded subassembly in accordance with the present invention; 
     FIG. 6 is a cross-sectioned side view of the bonded subassembly of FIG. 5 taken along line  6 — 6 ; 
     FIG. 7 is an end view of the inner member; 
     FIG. 8 is a cross-sectioned side view of the inner member of FIG. 7 taken along line  8 — 8 ; 
     FIG. 9 is an end view of the outer member; 
     FIG. 10 is a cross-sectioned side view of the outer member of FIG. 9 taken along line  10 — 10 ; 
     FIG. 11 is a representative torsional spring rate curve of the coupling in accordance with the present invention; and 
     FIG. 12 is a personal watercraft vehicle in which the coupling according to the present invention finds excellent utility. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A flexible elastomeric coupling  20  according to the invention is first illustrated in FIGS. 3 and 4. This coupling  20  provides a soft torsional stiffness in a drive train between a clutch, flywheel or other like driving component  18  and an output shaft or other like driven component  19 . By way of example, and not to be considered limiting, the coupling  20  described herein includes a torsional stiffness of about 4,500 lbf.-in./radian (508 N-m/radian), a radial stiffness of about 256,200 lbf./in. (44,835 N/mm) and a cocking stiffness of about 14,400 lbf.-in./radian (1,627 N-n/radian). And, in particular, it should be recognized that the present coupling  20  includes a radial stiffness of greater than 100,000 lbf./in. and yet exhibits a cocking spring rate of less than 100,000 lbf.in./radian, a feat not possible in either of the FIG. 1 or FIG. 2 prior art couplings. 
     According to the invention, the coupling  20  includes a driving member  22 , a driven member  26  spaced therefrom and a flexible member  27  intervening between them. Flexible member  27  preferably comprises a polymeric material, such as a flexible plastic or elastomer, and is preferably bonded to the generally cylindrical outer surface  28  of the driven member  26 . In its unassembled form, as best shown in FIG. 5 and 6, the flexible member  27  comprises an annulus of generally trapezoidal cross section. The most preferred flexible member  27  is a natural rubber elastomer exhibiting a hardness of between about  35  and  70  shore A and is bonded to the outer surface  28  of driven member  26  by conventional means, such as hot vulcanized bonding or cold bonding. 
     Now referring to FIGS. 3-6, the coupling&#39;s driven member  26  with the flexible member  27  bonded thereto comprises a bonded sub-assembly  34 . The bonded subassembly  34  is interference fit (precompressed) into a pocket  36  formed in the driving member  22 . The bonded subassembly  34  is inserted and driven into a funnel via considerable axial force thereby inserting subassembly  34  into the driving member  22  and, resultantly, precompressing the flexible member  17  in the range between about 15% and 35% radial precompression strain, and more preferably about 25%. This ensures significant frictional engagement between the outer surface  29  of the flexible member  27  and the inner surface  24  of the driving member  22 . Together, the subassembly  34  and the driving member  22  comprise the coupling  20 . 
     It should be recognized that the flexible member  27  is bonded to the driven member  26  and unbonded to the driving member  22 . Therefore, as the limit torque about the central axis A—A is exceeded, the surface  29  of flexible member  27  will slip relative to the inner surface  24  of driven member  26 , thereby providing an overload prevention feature to be described more thoroughly with reference to FIG.  11 . 
     As best shown in FIGS. 4-8, the driven member  26  includes a main body portion  38  having a first generally cylindrical projecting portion  40  extending axially therefrom in a first direction along the central axis A—A and a tapered projection  42  extending generally axially in the opposite direction from the body portion  38 . The driven member  26  also includes a circular bore  44  formed therethrough including a splined portion  46  for receiving the splined output shaft  19  (FIG.  3 ). Preferably, the driven member  26  is manufactured from an aluminum or brass material. The drive component output shaft  19  connects between the coupling  20  and the drive unit, such as the propulsion unit of a personal watercraft as shown in FIG.  12 . An o-ring groove  48  is formed in the tapered projection  42  for receiving the o-ring  17  (FIG.  3 ). An elastomer o-ring  17  (FIG. 4) is received in the groove  48  and prevents escape of any grease used to lubricate the splined section  46  and minimized debris exposure to the inner workings of the coupling  20 . The driven member  26  also includes a second projecting portion  50  spaced radially inward from, and concentric with, the first projecting portion  40 . The second projecting portion  50  includes a generally annular shape and includes a bearing member such as an arcuate surface  52  formed on a radially outer periphery thereof. Preferably, the surface  52  includes a generally spherical profile formed thereon of radius R. 
     In FIGS. 3,  4   9  and  10 , the driving member  22  is shown. The driving member  22  includes a radial bridging portion  21 , a generally cylindrical outer projection  23  extending substantially axially along axis A—A from the bridging portion  21 , and a generally annular inner projection  25  extending in a substantially axial direction from the bridging portion  21 . The outer projection  23  and inner projection  25  are generally concentric. A threaded bore  35  extends axially through the bridging portion  21  and a portion of the inner projection  25 . The driving member  22  is preferably manufactured from aluminum material. 
     An annular low-friction bushing  31  is received in a press fit relation in a slightly smaller bore  33  formed in an axial end of the inner projection  25 . The bushing  31  acts as a bearing member (it bears radial load) and is preferably manufactured from a steel band including an inner annular portion of Teflon® impregnated porous bronze. Lip  37  formed at the end of outer projection  23 , together with the inner surface  24  and bridging portion  21 , form a pocket  36  into which the flexible member  27  (FIGS. 4 and 6) is received. Wrench flats  39  are formed on the outer surface of the driving member  22  such that the coupling  20  may be torqued onto, and securely fastened, to the threaded stud  16  formed integral with the flywheel  18  (FIGS. 4,  12 ). This installation brings the frontal planar surface  41  of the driving member  22  securely into mating contact with the aft surface portion  18   a  of the flywheel  18 . 
     As best shown in FIGS. 4, the coupling  20  includes a rotational pivot  32 . The pivot  32  is formed by the interaction of a bearing member, such as the non-planar arcuate surface, on the second projecting portion  50  of the driven member  26  with a bearing member, such as the bushing  31 , formed on the inner projection  25  of the driving member  22 . The pivot  32  facilitates cocking and axial motion but substantially restrains radial motion between the members  22 ,  26 . 
     In the present invention, the axial location of the pivot  32  is substantially aligned with the axial location of the Elastic Center (EC) of the flexible member  27 . The Elastic Center (EC) is generally defined as the point in space positioned axially relative to the flexible member  27  where, if one member of the coupling  20 , for example, the driving member  22  is held stationary, and a radially-directed load is applied to the other member (the driven member  26 ) and through that point, there will be zero rotation of the loaded member, i.e., the driven member  26 . It should be understood that this assumes that the loading is applied with the driveline components disconnected. Orienting the elastic center EC substantially coincident with the axial location of the pivot  32  has the concomitant effect of maximizing the cocking misalignment that may be accommodated between the driving  22  and driven  26  members. Further, any radial loading applied passes directly through the elastic center of the flexible member  17  thereby minimizing cocking rotation thereof. Moreover, such location minimized the cocking stiffness of the coupling thereby minimizing vibration transmitted to the driveline components. The pivot  32  allows cocking rotation between the members  22 ,  26  by way of rotation of the arcuate surface  52  relative to the bushing  31 . In addition, the pivot limits radial movement between the members  22 ,  26  and increases the radial stiffness dramatically. 
     FIG. 11 illustrates a representative spring rate curve  43  where Torque (in lbf.inches) is plotted against Torsional Windup (in degrees) between the driving  22  and driven  26  members of the coupling  20 . The spring rate ΔY/ΔX is fairly linear within its operating range OR. Upon exceeding the limit torque (beyond the dotted line  45 ), the bonded subassembly  34  rotationally slips within the driving member  22  and addition angular deflection occurs without any significant increase in the torque. This protects driveline components from being over-torqued and over-stressed. By way of example, one embodiment of the invention will slip at 5,800 lbf.-inches of torque or greater at about 60 degrees or more. 
     Shown in FIG. 12 is a vehicle, such as a personal watercraft PWC, in which the coupling  20  of the present invention finds utility. The coupling  20  interconnects between the first and second drive components, i.e., a flywheel  18  and the output shaft  19 . The engine E is mounted to the hull liner or other frame structure F by a plurality of elastomer engine mounts M. Upon being started, the engine E rotates the flywheel  18  mounted thereto which, in turn, rotates the coupling  20 . The driven member  26  (FIG. 4) of the coupling  20  is connected to the shaft  19  and rotates therewith to rotate the pump components, for example the impeller I, in the propulsion drive unit PU thereby drawing water into the channel IC and propelling the vehicle, i.e., the personal watercraft PWC. 
     The coupling  20 , via its relatively high radial stiffness (greater than about 100,000 lbf./in. (17,510 N/mm)), exhibits excellent concentricity between the driving and driven components and helps to maintain the concentricity between the shaft  19  and flywheel  18 , thereby minimizing rotational unbalances transmitted into the mounts M and thereby into frame F. Further, the relatively low cocking stiffness of the coupling  20  (about 14,400 lbf.-in./rad. (1,627 N-m/radian)) minimizes forces transmitted into the mounts M and frame F as a result of any cocking misalignment between the flywheel  18  and shaft  19 . Accordingly, the coupling  20  of the present invention facilitates smooth operation of the driveline components of the personal watercraft PWC. Notably, the coupling according to the invention may find utility in other vehicles, such as ATV&#39;s, boats, motorcycles, etc. 
     The invention has been described in terms of preferred structure, however, the particular example given is meant to be illustrative and not limiting. For example, the driving and driven members can take alternate forms or their orientations may be reversed. Moreover, the pivot may be of other forms. Substitutions and equivalents as will occur to those skilled in the art are included within the scope of the invention as defined by the following claims.