Patent Publication Number: US-2022228642-A1

Title: Dual rate torsional coupling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/866,813, which was filed on Jun. 26, 2019, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF INVENTION 
     The subject matter disclosed herein relates to the design, assembly and operation of a dual rate torsional coupling. 
     BACKGROUND 
     Torsional couplers are used in machinery to functionally connect an input (e.g., an engine) with an output (e.g., a transmission). At present, there is a need for a torsional coupling having variable stiffness, which can be advantageous to provide a “soft” stiffness when a first stage is engaged and a “hard” stiffness when a second stage is engaged. 
     SUMMARY 
     The torsional coupling comprises many parts that all work together. Torque is applied to the inner member. The first stage (low torque) consists of a bonded part (rubber, inner and outer member) that is in series with a set of compression style coil springs. The torsional stiffness of the bonded part is approximately 25% of the resulting torsion stiffness provided by the coil springs. The second stage (high torque) the tangs on the inner member engage with a sprocket plate which locks out the first stage and transfers all torque through the coil springs. The coil springs are held in place by a unique geometry on the sprocket plate and the spring holders. The spring holders also prevent metal to metal contact between the coil springs and the housing portions. Surface effect damping occurs at very high torques when the rubber molded around the tangs on the inner member rub on the bumps on the lower housing portion. A thrust bearing is used to react axial forces and to eliminate any metal to metal contact. 
     In one aspect, a dual rate coupling is disclosed. The dual rate coupling comprises: an upper housing portion having an opening positioned about a center of the upper housing portion, a plurality of coil spring receivers, and a plurality of securing points positioned about an outer circumference of the upper housing portion; a lower housing portion having an opening positioned about a center of the lower housing portion, a plurality of coil spring receivers, and a plurality of securing points positioned about an outer circumference of the lower housing portion, wherein the lower housing portion mirrors the upper housing portion for the plurality of coil spring receivers and the plurality of securing points, wherein the opening of the lower housing portion is smaller in diameter than the opening of the upper housing portion and further comprises a circular wall defining the inner diameter of the dual rate coupling, the circular wall having a plurality of bumps oriented away from the center of the lower housing portion; an inner member having a circular opening in a center of the inner member, a mounting ring, a bonding element, a plurality of bolt holes, a plurality of tangs, an outer wall, and a lower edge, wherein the plurality of tangs protrude downwardly and circumferentially from the lower edge, wherein the circular opening is adjacent to the circular wall and bumps of lower housing portion; a thrust bearing positioned around the inner member opening; a sprocket plate having a plurality of bolt holes positioned to mirror the plurality of bolt holes of the inner member, a plurality of engagement recesses and a plurality of sprocket teeth interiorly positioned about an inner opening, and a plurality of coil spring recesses exteriorly positioned about an outer surface  56 ; an outer coil spring; an inner coil spring having a first end and a second end; at least two coil spring holders, each having an inner ring, the inner ring of one coil spring holder capable of being inserted within the first end of the inner coil spring and the other coil spring holder capable of being inserted within the second end of the inner coil spring, wherein the combination of the two coil spring holders and the inner and outer coil springs form a coil spring assembly, wherein the coil spring assembly is capable of being inserted into the coil spring recesses of the sprocket plate, wherein the combination of the coil spring assembly and the sprocket plate form a sprocket assembly; a tubeform assembly, the tube form assembly including the inner member, an outer member and a tubeform, wherein the outer member has a circular opening positioned about a center of the outer member, a flange and a bonding ring, wherein the flange is substantially perpendicular to the bonding ring, wherein the tubeform is disposed and bonded between the inner member and the outer member, wherein the tubeform is further bonded to and round each of the plurality of tangs thereby forming a plurality of protrusions, wherein the outer member is swaged into the tubeform after being bonded; wherein each engagement recess of the sprocket plate is capable of receiving a corresponding single protrusion between a pair of sprocket teeth and maintaining a gap between the corresponding single protrusion and at least one of the sprocket teeth; wherein the lower housing portion and the thrust bearing have the sprocket plate assembly positioned on top of the thrust bearing with a portion of each of the plurality of coil spring assemblies positioned in one of the coil spring receivers of the lower housing portion; wherein the tubeform assembly is secured to and on top of the sprocket plate assembly; wherein the upper housing portion is positioned on top of the sprocket plate assembly and disposed about the tubeform assembly, wherein a portion of each of the plurality of coil spring assemblies positioned in one of the coil spring receivers of upper housing portion; and wherein the upper housing portion and the lower housing portion are secured together. 
     In another aspect, a dual rate coupling is disclosed, the coupling comprising: a housing comprising: an upper housing portion having a main body, an opening formed in the main body of the upper housing portion, and a plurality of coil spring receivers arranged or positioned circumferentially about and extending away from the main body of the upper housing portion; a lower housing portion having a main body, an opening formed in the main body of the lower housing portion, and a plurality of coil spring receivers arranged or positioned circumferentially about and extending away from the main body of the lower housing portion; a sprocket plate comprising: an inner opening formed through a thickness of the sprocket plate, a plurality of sprocket teeth arranged or positioned circumferentially about an inner diameter of the inner opening, a plurality of engagement recesses, each engagement recess being defined between adjacent sprocket teeth, and a plurality of coil spring recesses arranged or positioned circumferentially about, and extending radially inwardly from, a perimeter of the sprocket plate; a tubeform assembly comprising: an inner member comprising: a mounting ring at a first longitudinal end of the inner member, a lower edge at a second longitudinal end (e.g., opposite the first longitudinal end) of the inner member, a bonding element in a form of an outer wall between the mounting ring and the lower edge, and a plurality of tangs attached to, and extending away from, the lower edge, the plurality of tangs arranged or positioned circumferentially around the lower edge; an outer member comprising: a bonding ring in a form of an outer wall that is substantially concentrically arranged or positioned about the bonding element of the inner member, and a flange extending away from the bonding ring, the outer member being rigidly secured to the sprocket plate via the flange; and a tubeform comprising an elastomeric material, wherein the tubeform is arranged or positioned between the bonding ring of the outer member and the bonding element of the inner member; wherein the tubeform assembly is arranged or positioned, relative to the sprocket plate, such that each of the plurality of tangs is positioned within a corresponding one of the plurality of engagement recesses; and a plurality of coil spring assemblies, each coil spring assembly comprising: an outer coil spring having a first end and a second end, and at least two coil spring holders, one of which is arranged or positioned at the first end of the outer coil spring and another of which is arranged or positioned at the second end of the outer coil spring, wherein each of the plurality of coil spring assemblies is positioned within a corresponding one of the plurality of coil spring recesses of the sprocket plate, such that the plurality of coil spring and the sprocket plate form a sprocket assembly; wherein the tubeform assembly is arranged or positioned on a first side of the sprocket plate assembly and secured to the sprocket plate; and wherein the upper housing portion is positioned on a first side of the sprocket plate assembly and disposed about the tubeform assembly and the lower housing portion is positions on a second side of the sprocket plate assembly, opposite the first side of the sprocket plate assembly. 
     In some embodiments, the coupling is a dual rate coupling. 
     In some embodiments of the coupling, the inner member comprises a circular opening in a center of the inner member; and the circular opening is adjacent to the circular wall of the lower housing portion. 
     In some embodiments, the coupling comprises a plurality of fastener holes arranged or positioned circumferentially about the sprocket plate and formed through the thickness of the sprocket plate. 
     In some embodiments of the coupling, the mounting ring has a plurality of holes formed through a thickness thereof in a direction of the lower edge. 
     In some embodiments, the coupling comprises a thrust bearing positioned around the inner member opening; wherein the lower housing portion and the thrust bearing have the sprocket plate assembly positioned on top of the thrust bearing with a portion of each of the plurality of coil spring assemblies positioned in one of the coil spring receivers of the lower housing portion. 
     In some embodiments of the coupling, the flange of the outer member is substantially perpendicular to the bonding ring. 
     In some embodiments of the coupling, the tubeform is bonded to the bonding element of the inner member and/or the bonding ring of the outer member. 
     In some embodiments, the coupling comprises a plurality of protrusions formed about opposing lateral sides and a radially inner side of the plurality of tangs, the plurality of protrusions comprising an elastomeric material. 
     In some embodiments of the coupling, the outer member is swaged into the tubeform after being bonded to the tubeform at the bonding ring thereof. 
     In some embodiments of the coupling, the plurality of protrusions are formed integrally with, or separate from, the tubeform. 
     In some embodiments of the coupling, the plurality of tangs, as well as the plurality of protrusions formed thereon, and the sprocket teeth are circumferentially distributed in an alternating pattern when the tubeform assembly and the sprocket plate are assembled together. 
     In some embodiments of the coupling, there is a gap between lateral surfaces of the protrusion and adjacent lateral edges of the engagement recesses, such that the inner member is rotatable, relative to the sprocket plate, until the gap is closed and the protrusion contacts the sprocket plate at a first angular position. 
     In some embodiments of the coupling, the tubeform is configured to react a rotary movement between the inner member and the sprocket plate, through the outer member, in shear to provide a first stage stiffness of the coupling. 
     In some embodiments of the coupling, after the protrusions are in contact with the sprocket teeth of the sprocket plate, the inner member and the sprocket plate are configured to rotate in unison at all angular positions beyond the first angular position. 
     In some embodiments of the coupling, when the inner member and the sprocket plate undergo a rotary movement beyond the first angular position, the sprocket plate is configured to exert a compressive force on the coil spring assemblies, such that the coil spring assemblies provide a second stage stiffness when compressed by the rotary movement of the of the inner member and the sprocket plate. 
     In some embodiments of the coupling, the second stage stiffness is greater than the first stage stiffness. 
     In some embodiments of the coupling, an arrangement pattern of the plurality of coil spring receivers of the lower housing portion mirrors an arrangement pattern of the plurality of coil spring receivers of the upper housing portion, wherein the opening of the lower housing portion comprises a ring having a plurality of bumps extending radially outwards from the opening of the lower housing portion. 
     In some embodiments of the coupling, a portion of each of the plurality of coil spring assemblies is positioned in one of the coil spring receivers of the upper and lower housing portions, respectively. 
     In some embodiments of the coupling, the bumps are positioned about the ring defining the opening of the lower housing portion, such that a radially inner surface of the protrusions contacts a corresponding one of the bumps when the inner member and the sprocket plate are rotated to a second angular position, the second angular position being a greater angular displacement than the first angular position. 
     In some embodiments of the coupling, contact between the protrusions and the bumps provides surface effect damping to the coupling, in addition to the first and second stage stiffnesses. 
     In some embodiments, the coupling comprises a plurality of securing points positioned about an outer circumference of respective flanges of the upper and lower housing portions, wherein the upper housing portion and the lower housing portion are secured together at the plurality of securing points. 
     In some embodiments of the coupling, one or more of the plurality of coil spring assemblies comprises an inner coil spring arranged or positioned concentrically within the outer coil spring, such that the inner coil spring is coaxial with the outer coil spring. 
     In some embodiments of the coupling, at least one of the coil spring holders comprises an inner ring, the inner ring of one coil spring holder capable of being inserted within the first end of the inner coil spring and the other coil spring holder capable of being inserted within the second end of the inner coil spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate a top and bottom perspective view of a dual rate coupling. 
         FIG. 2A  illustrates a side view of the dual rate coupling. 
         FIG. 2B  illustrates a top-sectional view of the dual rate coupling taken from  FIG. 1A  along line  2 B- 2 B. 
         FIG. 2C  illustrates a side-sectional view of the dual rate coupling taken from  FIG. 2A  along line  2 C- 2 C. 
         FIG. 2D  illustrates a side-sectional view of the dual rate coupling taken from  FIG. 2B  along line  2 D- 2 D. 
         FIG. 2E  illustrates a perspective detail view of the inner member of the dual rate coupling taken from  FIG. 2D . 
         FIGS. 3A and 3B  illustrate a top and bottom perspective view of an inner member of the dual rate coupling. 
         FIG. 4  illustrates a top perspective view of an outer member of the dual rate coupling. 
         FIG. 5  illustrates a top perspective view of a sprocket plate of the dual rate coupling. 
         FIGS. 6A and 6B  illustrate a perspective view of an upper and lower housing portions of the dual rate coupling. 
         FIGS. 7A and 7B  illustrate a perspective view of an outer coil spring and an inner coil spring of the dual rate coupling. 
         FIGS. 8A and 8B  illustrate a coil spring holder for the outer coil spring and the inner coil spring. 
         FIG. 9  illustrates a bottom perspective view of a tubeform of the dual rate coupling bonded between the inner member and the outer member. 
         FIG. 10  illustrates a top perspective view of the outer coil spring positioned in the sprocket plate of the dual rate coupling with the inner coil spring nested within the outer coils spring. 
         FIGS. 11A-11D  illustrate the process to assemble the dual rate coupling. 
     
    
    
     DETAILED DESCRIPTION 
     A dual rate torsional coupling is disclosed herein, the dual rate torsional coupling using both elastomeric and coil spring elements to be operable in transmitting high-torque inputs. The elastomeric element includes a bonded tubeform that rotatably interfaces with a sprocket element, in which the coil springs are captively retained. The elastomeric element is rotatable, relative to the sprocket element, to provide a first stage of torsional stiffness to the torsional coupling. After the elastomeric element has snubbed against the sprocket element, the coil spring elements are rotatably engaged (e.g., in compression) to provide a second stage of torsional stiffness. It is advantageous for the first stage to have a lower torsional stiffness value than the second stage. The coils springs and the bonded tubeform can be selected to provide a desired amount of torsional stiffness for each installation. The use of an elastomer in the bonded tubeform allows for a reduction and/or elimination of high frequency noise in the transition from the first stage to the second stage. 
     The dual rate coupling allows a softer initial stiffness which allows an engine to have a lower idle speed and reduces noise associated with gear rattle, while in neutral. Additionally, the torsional coupling disclosed herein has a safety mechanism, such that the dual rate torsional coupling is still able to transmit torque through the coil springs (e.g., the second stage) if the elastomeric element (e.g., the first stage) fails. 
     Referring to  FIGS. 1A and 1B , a dual rate torsional coupling, generally designated  10 , is illustrated in both a top and bottom isometric view. The coupling  10  comprises an inner member  12 , an outer member  14 , a tubeform  16 , a sprocket plate  18 , an upper housing portion  20 , a lower housing portion  22 , an outer coil spring  24 , an inner coil spring  26 , a coil spring holder  28 , and a thrust bearing  29 . 
     As shown in  FIGS. 3A and 3B , the inner member  12  has a generally cylindrical shape. The inner member  12  has a mounting ring  32 , a bonding element in the form of an outer wall  40 , a plurality of bolt holes  36 , and a plurality of tangs  38 . The mounting ring  32  has a generally annular shape and defines a first end of the cylindrical shape of the inner member  12 . The mounting ring  32  has an opening  30  centrally disposed through a thickness thereof in the longitudinal direction of the inner member  12 , the opening  30  being sized to allow a shaft to pass therethrough. While the opening  30  is shown as having a generally circular profile, the opening  30  can have any size and/or shape based on the particular use and shaft for which the coupling  10  is being manufactured to be interconnected with. In the example embodiment shown, the inner member has a plurality of bolt holes  36  formed in, and extending partially or entirely through, the mounting ring  32 . In some embodiments, inner member  12  may be connected to an input (e.g., an engine) or an output (e.g., a transmission) by, for example and without limitation, a splined interface, key ways, and/or taper lock hubs. Any suitably rigid connection between the inner member  12  and the inlet device or the outlet device may be provided without deviating from the scope of the subject matter disclosed herein. 
     The inner member  12  has an outer wall  40  extending away from the mounting ring  32  to define, along with tangs  38 , a height or length (e.g., in the longitudinal direction of extension of the cylindrical shape of the inner member  12 ) of the inner member  12 . The bolt holes  36  are circumferentially positioned and spaced about the mounting ring  32  between the outer wall  40  and the opening  30  of the inner member  12 . The bolt holes  36  extend generally in the longitudinal direction of the inner member  12  and have an internal thread pattern configured for attaching the coupling  10  to either of an input or an output. The outer wall  40  extends in the longitudinal direction to a lower edge  42 , from which each of the tangs  38  protrude in the longitudinal direction and/or circumferentially (e.g., inwardly). The outer circumferential surface of the outer wall  40  is configured as a bonding element to which the elastomeric tubeform  16  is bonded to couple the inner member  12  to the outer member  14 . The inner member  12  comprises an inner wall  70 , which is on a radially opposite surface from the outer wall  40  In one embodiment, the inner member  12  is machined from a ductile iron casting. However, any suitable material capable of reacting the loads and/or moments for a particular application and/or installation of the coupling  10  may be selected. 
     As shown in  FIG. 4 , the outer member, generally designated  14 , has a flange  44  and a bonding ring  46 . The flange  44  is substantially perpendicular to the bonding ring  46  and extends away from the bonding ring  46  in a substantially radially oriented direction. The outer member  14  is arranged or positioned concentrically about the outer wall  40  of the inner member  12 , such that the bonding ring  46  is adjacent to, but spaced apart from (e.g., by the tubeform  16 ), the outer wall  40  of the inner member  12 . The flange  44  has a plurality of notches  45  formed therein, extending radially inwardly from a perimeter of the flange  44 . The notches  45  are spaced circumferentially apart from each other about the flange  44 . The positions at which the notches  45  are formed in the flange correspond to attachment positions (e.g., threaded holes) at which the outer member  14  is to be securely attached to the sprocket plate  18  to rotatably lock the outer member  14  with the sprocket plate  18  to prevent relative rotary movements therebetween. In some embodiments, the outer member  14  made of steel and can be formed by a stamping process. However, any suitable material capable of reacting the loads and/or moments for a particular application and/or installation of the coupling  10  may be selected. 
       FIG. 9  shows the inner member  12  and the outer member  14  assembled together, being adjoined by the tubeform  16 , to form a tubeform assembly  86 . The tubeform  16  is disposed concentrically around the inner member  12 , such that the inner circumferential surface of the tubeform  16  is in contact with, and preferably bonded to, the outer wall  40  of the inner member  12 . The tubeform  16  is arranged or positioned concentrically between the outer wall  40  of the inner member  12  and the bonding ring  46  of the outer member  14 , so as to physically separate the inner member  12  from the outer member  14  about all or at least a portion of the circumference of the inner and outer members  12 ,  14  and prevent the inner member  12  from contacting, or being contacted by, the outer member  14  during operation of the coupling  10 . Preferably, the tubeform  16  is bonded to one or both of the outer wall  40  of the inner member  12  and the inner wall of the bonding ring  46  of the outer member  14 . The above are merely examples and it is contemplated that the tubeform  16  may be retained between the inner member  12  and the outer member  14  using any attachment mechanism that will allow the tubeform  16  to provide adequate damping performance. In the example shown, the inner member  12  is formed as a machined ductile iron casting and the outer member  14  is stamped from steel. 
     The tubeform  16  is further shown in  FIG. 9  as being bonded to, and at least partially around, the tangs  38  of the inner member  12 , thereby forming protrusions  48  made from the elastomeric material from which the tubeform  16  is formed. The protrusions are advantageously formed around at least both lateral sides of the tangs  38 , which each extend in a radial plane of the inner member  12 , and the inner circumferential surface of the tangs  38 , as shown in  FIG. 9 . In some embodiments, the outer circumferential surface of the tangs  38  can be covered by the protrusions  48 . The protrusions  48  are bonded to one or both of the tubeform  16  and an inner ring  49  formed on and/or in an inner circumferential channel of the inner member  12 . In some embodiments, the tubeform  16  can be entirely and/or partially preformed and installed in the position between the inner member  12  and the outer member  14  shown in  FIG. 9 . In some embodiments, the tubeform  16  can be formed in situ, for example, by an injection molding technique. In some embodiments, the protrusions  48  and the inner ring  49  can be separable and/or physically distinct from the generally annular main body portion of the tubeform  16 , defined as being between the inner member  12  and the outer member  14 . In some embodiments, the protrusions  48  and the inner ring  49  can be formed so as to be integral to the main body portion of the tubeform  16 . In some embodiments, the protrusions  48  and the inner ring  49  can be formed integral with each other and separable from the main body portion of the tube form and, in fact, the protrusions  48  and the inner ring  49  can be formed by a different technique (e.g., injection molding) from the method by which the tubeform  16  is formed. 
     A sprocket plate, generally designated  18 , is shown in  FIG. 5 . The sprocket plate  18  has an inner opening  52  formed therein. As shown, the inner opening  52  extends through a full thickness of the sprocket plate  18  to define a hole, or void, therein. The inner opening  52  is centrally located about (e.g., uniformly) a central axis of the sprocket plate  18 . In some embodiments, the inner opening  52  may be offset from the central axis and/or have a non-uniform profile. The sprocket plate  18  has, at an inner circumferential surface thereof as defined by the outer circumference of the inner opening  52 , engagement recesses, generally designated  50 , formed therein to define sprocket teeth  51  spaced circumferentially about the inner circumferential surface of the inner opening  52 , such that the engagement recesses  50  extend radially away from the inner circumferential surface of the inner opening  52 , with each of the engagement recesses  50  being spaced apart from adjacent engagement recesses  50  by one of the sprocket teeth  51 . The engagement recesses  50  are spaced circumferentially about the inner opening  52  in a pattern that is substantially identical to the pattern at which the tangs  38  of the inner member  12  are formed, such that the engagement recesses  50  are positioned so that each tang  38  (e.g., as formed in the protrusion  48 ) of the inner member  12  can be positioned within one of the engagement recesses  50  and spaced apart from each other by the sprocket teeth  51 . As such, a corresponding protrusion  48  of the inner member  12  is positioned between each set of adjacent sprocket teeth  51 . 
     The sprocket plate  18  has a plurality of coil spring recesses, generally designated  54 , which are formed in and extend radially inwardly from an outer circumferential surface  56  of the sprocket plate  18 . The coil spring recesses  54  are spaced circumferentially about the sprocket plate  18  and extend in the circumferential direction of the sprocket plate  18  to allow for installation of a coil spring assembly ( 88 ,  FIG. 10 ) therein. The length L (e.g., measured in a direction tangential to the circumferential surface  56  where the coil spring recess  54  is formed) of each coil spring recess  54  is selected based on the uncompressed length of the coil spring assembly to be installed therein and the amount and/or degree of pre-compression specified for a specified application. The sprocket plate  18  has holes  55  formed in and/or at least partially (e.g., entirely) through the thickness thereof. The holes  55  are spaced about the sprocket plate  18  to align with the notches  45  formed in the flange  44  of the outer member  14  (see  FIG. 4 ), such that fasteners can pass through the notches  45  and the holes  55  to rigidly couple the outer member  14  to the sprocket plate  18  to prevent and/or resist relative movements (e.g., torsional, lateral, and/or axial) between the sprocket plate  18  and the outer member  14 . The sprocket plate  18  may be stamped, laser cut, and/or formed steel. However, any material and type of forming may be used in forming the sprocket plate  18  that will produce a sprocket plate  18  having suitable strength, thickness, and material properties for a specific application. In an example embodiment, the sprocket plate  18  has a thickness of about 0.5 inches (in), however, the thickness may be selected based on the torque to be transmitted. In some preferred embodiments, the sprocket plate  18  has a rounded profile to aid in assembly (e.g., insertion of a coil spring assembly in a unitary manner) of the sprocket assembly (see, e.g.,  90 ,  FIG. 10 ) and prevent the coil spring assemblies from being dislodged from the coil spring recesses  54  during normal operation. 
     Referring to  FIGS. 6A and 6B , example embodiments of an upper housing portion, generally designated  20 , and a lower housing portion, generally designated  22 , are shown, respectively. In the example embodiment shown, the upper and lower housing portions  20 ,  22  are substantially mirror images of each other, with the exception of the central portions thereof. As shown in  FIG. 6A , the upper housing portion  20  has a central opening  58  formed through a thickness thereof to define a hole. The upper housing portion  20  has a flange  66 A extending radially away from a main body  64  of the upper housing portion  20 , the flange  66 A being offset from (e.g., not coplanar to) the main body  64  of the upper housing portion  20 . The flange  66 A and the main body  64  can be parallel or inclined relative to each other. The lower housing portion  22  has a flange  66 B extending radially away from a main body  74  of the lower housing portion  22 , the flange  66 B being offset from (e.g., not coplanar to) the main body  74  of the lower housing portion  22 . The flange  66 B and the main body  74  can be parallel or inclined relative to each other. The flanges  66 A,  66 B of the upper and lower housing portions  20 ,  22  have respective notches  62 A,  62 B formed therein, which are configured to have a fastener affixed thereto to secure the upper housing portion  20  against the lower housing portion  22 . In some embodiments, the upper and lower housing portions  20 ,  22  are connected to either of an input or an output (e.g., to whichever the inner member  12  is not connected) at any portion of the upper and lower housing portions  20 ,  22 , including, for example, at flanges  66 A,  66 B by passing fasteners through the notches  62 A,  62 B and into the input or the output (e.g., a shaft connected to the input or the output). The opening  58  formed in the upper housing portion  20  is shaped so that, when the tubeform assembly ( 86 ,  FIG. 9 ) is attached to the sprocket assembly ( 90 ,  FIG. 10 ) and the upper and lower housing portions  20 ,  22  are secured about the sprocket assembly  90 , the opening  58  is positioned adjacent to the outer surface of the bonding ring  46  of the outer member  14 . The upper and lower housing portions can be formed by any suitable technique, including a stamping technique. 
     Each of the upper and lower housing portions  20 ,  22  have coil spring receivers  60  formed in the respective main bodies  64 ,  74  thereof. Each of the coil spring receivers  60  are sized to accept a portion of an outer coil spring  24  (e.g., an arcuate portion of a whole length thereof) of the sprocket assembly  90  therein when the upper and lower housing portions  20 ,  22  are secured about the sprocket assembly  90 . Each coil spring receiver  60  formed in the upper housing portion  20  is substantially identical to a corresponding one of the coil spring receivers  60  formed in the lower housing portion  22 . As such, the arrangement, sizes, and shapes of the coil spring receivers  60  formed in the upper housing portion  20  is substantially identical (e.g., is mirrored about a plane defined by the flanges  66  of the upper and lower housing portions  20 ,  22  when assembled together). In some embodiments, two or more sets of spring assemblies ( 88 ,  FIG. 10 ) may be installed in a single sprocket assembly  90 , each spring assembly  88  of each set of spring assemblies  88  has a same length, but all of the spring assemblies  88  of, for example, a first set of spring assemblies  88  may have a different length from all of the spring assemblies  88  of, for example, a second (or third, fourth, et seq.) set of spring assemblies  88  of the sprocket assembly  90 . The different lengths in the first, second, third, et seq. sets of spring assemblies  88  can be, for example and without limitation, from one or more of using coil springs (see  24 ,  26 ,  FIGS. 7A, 7B ) that have different uncompressed lengths, applying a greater amount or degree of pre-compression to the coil spring assemblies  88 , and the like. In embodiments in which the sprocket assembly  90  uses two or more different sets of spring assemblies  88 , it is advantageous to mirror the distribution of these different sets of spring assemblies  88  radially about the longitudinal axis of the sprocket assembly  90  and/or the coupling  10  to avoid imparting moments to the sprocket that could cause cocking or other misaligning movements of the sprocket assembly  90  within the housing formed by the upper and lower housing portions  20 ,  22 . 
     The lower housing portion  22  has a thrust bearing surface  67  that extends radially inwardly from the main body  74  towards and opening  68  formed in the central area of lower housing portion  22 . The thrust bearing surface  67  is preferably not coplanar with (e.g., is vertically offset from) the main body  74  of the lower housing portion  22 . The opening  68  is formed through a thickness (e.g., partially or entirely) of the main body  74  of the lower housing portion  22 . The opening  68  is smaller (e.g., in diameter) than the opening  58  formed in the main body  64  of the upper housing portion  20 . The opening  68  is defined by a ring  69  having a substantially annular shape and extending substantially orthogonally away from the thrust bearing surface  67  and, when the upper and lower housing portions  20 ,  22  are assembled about a sprocket assembly  90 , which is in turn attached to a tubeform assembly  86 , the wall defining the opening  68  is arranged or positioned and held substantially adjacent to the inner wall ( 70 ,  FIG. 3B ) of the inner member  12 . The opening  68  provides the pilot diameter of the coupling  10 . The lower housing portion  22  also has bumps  72  formed in the wall of the opening  68 . The bumps  72  extend radially outwards from the wall of the opening such that the bumps are capable of contacting, or being contacted by, the protrusions  48  of the tubeform assembly  86  when the inner member  12  is rotated, along with the sprocket assembly  90  and relative to the lower housing portion  22 , to undergo a sufficiently large displacement as the result of a torsional input to the coupling  10 . This contact between the bumps  72  and the protrusions  48  provides surface effect damping during large amplitude rotary displacements of the components of the coupling  10 , such as between the tubeform assembly  86 , along with the sprocket assembly  90  when the protrusions  48  are laterally engaged against (e.g., in contact with) the side walls of the sprocket teeth  51 , and the bumps  72  formed in the ring  69  of the lower housing portion  22 , such that the bumps  72  extend radially outwards from the ring  69  in the direction of the sprocket plate  18 , the flanges  66 A/ 66 B of the upper and/or lower housing portions  20 ,  22 , and the like. 
     The lower housing portion  22  has coil spring receivers  60  formed in the main body  74  thereof and protruding out from (e.g., so as to be non-planar to) the main body  74 . The is flange  66 B of the lower housing portion  22  is shown as being offset from the main body  74  in a direction that is opposite from the direction in which the coil spring receivers  60  are offset from the main body  74 . When in an assembled orientation (e.g., when the upper and lower housing portions  20 ,  22  are positioned relative to each other for assembly about the sprocket assembly  90 ), the flanges  66 A,  66 B extend away from the respective main bodies  64 ,  74 , such that the flanges  66 A,  66 B are arranged or positioned adjacent to each other (e.g., in direct contact with, or only being separated by a gasket). In the assembled orientation, the main bodies  64 ,  74  of the upper and lower housing portions  20 ,  22  are spaced apart from each other by a distance greater than the thickness of the sprocket plate  18 , the main bodies  64 ,  74  being spaced apart from the respective flanges  66 A,  66 B by a band, ring, or ridge of material. In the assembled orientation, the coil spring receivers  60  of the upper housing portion  20  extend away from the main body  64  in an opposite direction from the direction in which the coil spring receivers  60  of the lower housing portion  22  extend away from the main body  74 , such that a cavity in which a corresponding one of the coil spring assemblies  88  is formed between each aligned pair of coil spring receivers  60  in the upper and lower housing portions  20 ,  22 , and with which the coil spring recesses  54  formed in the sprocket plate  18  are also aligned. 
     In some embodiments, the upper and lower housing portions  20 ,  22  are stamped from a steel, or ferrous, material, but any material providing the suitable strength, thickness and similar material properties will work as is known to those having skill in the art, including, for example, aluminum. In the example embodiment shown, which is made from steel, the thickness of upper and lower housing portions  20 ,  22  is between 0.04 and about 0.08 inches, with a preferred thickness of about 0.06 inches. In some embodiments, the upper and/or lower housing portions  20 ,  22  can be manufactured to any dimensions necessary for an application. 
       FIG. 2E  shows a partial sectional view of the coupling  10  in an assembled configuration. As shown in  FIG. 2E , the tubeform  16  has a plurality of protrusions  48  that surround, at least partially or wholly, the tangs  38  formed in the inner member  12 . It is advantageous for each protrusion to be bonded against at least the lateral and radially inner surfaces of a corresponding one of the tangs  38 . In the assembled state shown, each tang  38 , along with the protrusion  48  associated therewith, is arranged or positioned within one of the engagement recesses  50  formed in inner radial surface of the sprocket plate  18 , as defined by the gaps between adjacent sprocket teeth  51 . Since the protrusions  48  have a width (e.g., in the circumferential direction of the inner member  12 ) that is smaller than the width (e.g., in the circumferential direction of the sprocket plate  18 ) of the engagement recess  50  in which the protrusion is positioned, there is a gap  78  defined between the lateral edges of each protrusion  48  and the lateral edges of the engagement recess in which each protrusion  48  is positioned. The gap  78  allows for rotational movement of the protrusions  48 , along with the inner member  12 , towards a lateral edge of the engagement recess  50  in which the protrusion  48  is positioned. 
     After the inner member  12  has rotated, relative to the sprocket plate  18 , by an amount corresponding to the gap  78  between the protrusions  48  and one of the lateral edges of the engagement recesses  50 , the lateral wall of the protrusion  48  is engaged against (e.g., pressed against in the circumferential direction) the side edge of a corresponding one of the engagement recesses  50  of the sprocket plate  18 , the lateral surface of the protrusion providing compliant engagement (e.g., as a rubber-like layer) between the sprocket plate  18  and the tangs  38 . The protrusions  48  and tangs  38  are each held in an undeflected position (e.g., when no rotary force is being imparted) within one of the engagement recesses  50  by the tubeform  16 , which reacts rotary movements between the inner member  12  and the outer member  14 , which is rigidly attached to the sprocket plate  18 , such that the inner member  12  returns to the undeflected state, relative to the outer member  14  and, hence, the sprocket plate  18  when no rotary force is being imparted to the inner member  12 . In some embodiments, the gaps  78  on opposing sides of the protrusions  48  can be substantially uniform (e.g., being designed for uniformity, but allowing for tolerances during manufacture and assembly that may result in slight misalignments) between the lateral edges of the engagement recesses  50 . In other embodiments, the position of the protrusions  48  and tangs  38  within the engagement recesses  50  can be staggered, or offset, in the circumferential direction such that the gap  78  between the protrusion  48  and the engagement recess  50  is different (e.g., smaller or larger) on a first lateral side of the protrusion  48  than on a second lateral side of the protrusion  48 , opposite the first lateral side in the circumferential direction. In some embodiments, the position of the protrusions  48  and tangs  38  within the engagement recesses  50  can be staggered, or offset, in the circumferential direction such that the protrusion  48  is adjacent to, or in contact with, a lateral edge of the engagement recess  50  in a first direction, such that there is no gap, or only a nominal gap, between the lateral surface of the protrusion  48  and the lateral edge of the engagement surface  50  in the first direction, with the gap  78  being present only between a second lateral surface of the protrusion and the lateral edge of the engagement surface in a second direction, opposite the first direction. 
     Additionally, after the inner member  12  has been radially displaced by a first angular distance to a first angular position in the circumferential direction for the protrusions to contact one of the lateral edges of the engagement recesses  50 , the inner member  12 , the outer member  14 , and the sprocket plate  18  move in a unitary manner when radially displaced beyond the first angular position and the coil spring assemblies  88  are engaged to provide a second, increased, stiffness to the coupling  10  to resist and/or react further angular displacement beyond the first angular position. When a rotary force of sufficient magnitude is imparted to the coupling  10  (e.g., through the inner member  12 ), to cause the inner member  12 , the outer member  14 , and the sprocket plate  18  to be rotationally displaced beyond the first angular position, the inner member  12 , the outer member  14 , and the sprocket plate  18  will continue to rotate within the housing defined by the upper and lower housing portions  20 ,  22  as the coil springs  24 ,  26  are compressed within the coil spring recesses  60  formed in the upper and lower housing portions  20 ,  22  until the inner member  12 , the outer member  14 , and the sprocket plate  18  have been radially displaced by a second angular distance to a second angular position, which is further radially displaced than the first angular position. At this second angular position, the protrusions  48  are positioned adjacent to the bumps  72  formed in the ring  69  of the lower housing portion  22 . Upon the coupling  10  receiving (e.g., at the inner member  12 ) a rotary force of sufficient magnitude, the inner member  12 , the outer member  14 , and the sprocket plate  18  rotate beyond the second angular position, such that the radially inwardly-facing surface of the protrusions  48  make contact with, and are at least to some degree radially compressed by, the bumps  72  to create surface effect damping during large displacements (e.g., beyond the second angular position) of the coupling  10 . 
       FIGS. 7A and 7B  show example embodiments of outer and inner coil springs  24  and  26 , respectively. The outer and inner coil springs  24 ,  26  may be selected to have identical or different uncompressed lengths. The amount of allowable travel and/or compression for the outer and inner coil springs  24 ,  26  is based on the torque and stiffness needed for a given application. In order to form a coil spring assembly  88 , the inner coil spring  26  is disposed within the outer coil spring  24  spring, which are held together by a coil spring holder  28 , various aspects of which are shown in  FIGS. 8A and 8B . In the example embodiment shown in  FIG. 8A , the coil spring holder  28  has a circumferential wall  80  extending (e.g., in the axial, or lengthwise, direction of the coil spring assembly  88 ) from the inner contact surface of the coil spring holder  28  to secure the outer and inner coil springs  24 ,  26  within the coil spring assembly  88  and to prevent direct contact between the outer and inner coil springs  24 ,  26 , at least while the coil spring assembly  88  is in an undeflected state and, preferably, over the entire range of compression of the coil spring assembly  88 . The wall  80  has a same, substantially similar (e.g., allowing for manufacturing tolerances), or larger inner diameter than the outer diameter of the inner coil spring  26 , at least at the end  82 A of the inner coil spring  26  where the inner coil spring  26  is in compressive contact against the radially inner contact surface  85 A of the coil spring holder  28 . The wall  80  has a same, substantially similar (e.g., allowing for manufacturing tolerances), or smaller outer diameter than the inner diameter of the outer coil spring  24 , at least at the end  82 A of the outer coil spring  24  where the outer coil spring  24  is in compressive contact against the radially outer contact surface  85 B of the coil spring holder  28 . In some embodiments (e.g., in those having only a single coil spring), the wall  80  may be omitted. 
     The coil spring assembly  88  has another coil spring holder  28 , which can in some embodiments omit, but preferably includes, the wall  80 , that contacts the ends  82 A,  82 B of the inner and outer coil springs  26 ,  24  and defines an outer axial boundary of the coil springs assemblies  88 . The coil spring holders  28  have a hole  83  formed through the thickness (e.g., entirely) of the coil spring holder  28 . The holes  83  are aligned with each other, when the coil spring assemblies  88  are in an assembled state, and are configured to have an axially-oriented longitudinal member (e.g., a bolt, elongated rivet, etc. that passes within the inner circumference of the inner coil spring  26  and allows an undeflected, or nominal, length of each coil spring assembly  88  to be defined at a maximum value, which can correspond to the length L of one of the coil spring recesses  54  of the sprocket plate  18  in which the coil spring assembly  88  will be inserted during assembly of the coupling  10 . The longitudinal member is advantageous in that it provides a rigid connection between the opposing coil spring holders  28  to prevent, or at least minimize, lateral deflections or distortions of the coil spring assemblies  88 . The thickness, undeflected length, diameter, spring coefficient, material, and any other parameter of the outer and inner coil springs  24 ,  26  may be selected to provide a desired amount of damping to the coupling when the second stage stiffness is engaged. In some embodiments, the outer and inner coil springs  24 ,  26  may have different compressed spring lengths, for example, in embodiments wherein the radially inner contact surface  85 A of the coil spring holder  28  is staggered, or offset from, (e.g., not coplanar with) the radially outer contact surface  85 B of the coil spring holder  28 , such that, when the coil spring assembly  88  is in the assembled state, the inner coil spring  26  can have a length that is shorter or longer than a length of the outer coil spring  24 . 
     As shown in  FIG. 8B , the coil spring holders  28  advantageously have opposing sprocket alignment tabs  84  protruding from the sprocket-interface surface  87  thereof. The sprocket alignment tabs  84  define a slot, generally designated  81 , therebetween, the slot  81  having a width that is the same as, of greater than, a thickness of the sprocket plate  18 , such that the slot  81  can be used to secure the coil spring assembly  88  within a corresponding one of the coil spring recesses  54  formed in the sprocket plate  18 , as shown in  FIG. 10 .  FIG. 10  illustrates the coil spring assemblies  88  attached to the sprocket plate  18  to define a sprocket assembly  90 .  FIGS. 1A-2D  show the sprocket assembly  90  inserted within the housing defined by the upper and lower housing portions  20 ,  22 . When in the assembled state shown in at least  FIGS. 1A-2D , coil spring assemblies  88  are contained within the cavity defined by opposing pairs of the coil spring receivers  60  formed in the upper and lower housing portions  20 ,  22 . In some embodiments, the coil spring holder  28  is injection molded plastic, but any suitable material may be used without deviating from the scope of the subject matter disclosed herein. 
     The coupling  10  advantageously includes a thrust bearing  29 , which is shown in at least  FIGS. 2C-2E  positioned between the thrust bearing surface  67  of the lower housing portion  22 , the inner member  12 , and at least a radially inner portion of sprocket plate  18 , such as at least the sprocket teeth  51  and, in some embodiments, extending further radially outwardly beyond the sprocket teeth  51 , but terminating prior to the coil spring holders  60  formed in the upper and lower housing portions  20 ,  22 . The thrust bearing  29  provides for torsional rotation of the coupling  10 . 
     During operation, the coupling  10  has an elastomeric material (e.g., rubber) in the form of the tubeform  16  and the outer and inner coil springs  24 ,  26  of the coil spring assembly  88 , which are initially regarded as being in series (e.g., being activated sequentially as rotary displacement of the components of the coupling  10  progresses). Upon initial rotation of the inner member  12  relative to the outer member  14  and/or the sprocket plate  18 , each of the protrusions  48  moves within (e.g., rotate within) a corresponding one of the engagement recesses  50  of the sprocket plate  18 , ultimately one or more of (e.g., each of) the protrusions  48  contacting a lateral edge of the engagement recess  50 , defined by the sprocket teeth  51 , at the completion of the first stage stiffness. After the protrusions  48  have contacted the lateral edges of the engagement recesses  50 , the coil spring assemblies  88  are compressively engaged upon further rotary movement of the inner member  12 , along with the inner member  14 , and the sprocket plate  18 , to provide the second stage stiffness. In the example embodiment shown, the protrusions  48  contact the bumps  72  of the lower housing portion  22  to provide surface effect damping during the second stage stiffness, upon the coupling receiving a rotary force of sufficient magnitude to cause a rotation of the inner member  12 , the outer member  14 , and the sprocket plate  18  by a sufficient angle to align the protrusions  48  with the bumps  72 . The placement of the bumps  72  about the ring  69  of the lower housing portion  22  can be selected to provide engagement of the surface effect damping between the protrusions  48  and the bumps  72  at any desired angular position of the inner member  12 , the outer member  14 , and the sprocket plate  18 , relative to the housing formed by the upper and lower housing portions  20 ,  22 . In some embodiments, the bumps  72  may be non-uniformly arranged or positioned about the ring  69 , relative to the undeflected positions of the protrusions  48 , such that the protrusions  48  do not engage all of the bumps  72  at a same degree of angular displacement, but instead engage the bumps  72  in multiple sequential stages. 
     In some other embodiments, the bumps  72  may be arranged or positioned such that the protrusions  48  contact the bumps  72  of the lower housing portion  22  to provide surface effect damping and the first stage damping prior to the engagement of the second stage stiffness; in such embodiments, after the protrusions  48  have contacted the lateral edges of the engagement recesses  50  and the bumps  72 , the coil spring assemblies  88  are compressively engaged upon further rotary movement of the inner member  12 , along with the inner member  14 , and the sprocket plate  18 , to provide the second stage stiffness. 
     As shown in  FIG. 9 , the elastomeric tubeform  16  is attached (e.g., bonded, adhesively or otherwise) between, and spaces apart, the inner member  12  and the outer member  14 . In some embodiments, the outer member  14  is swaged into the tubeform  16 . In some embodiments in which the tubeform  16  is bonded between one or both of the inner member  12  and the outer member  14 , the resulting tubeform assembly  86  has a torsional stiffness within a range of about 50,000 pounds force-inch/degree and about 150,000 pounds force-inch/degree, inclusive. In some other such embodiments in which the tubeform  16  is bonded between one or both of the inner member  12  and the outer member  14 , the resulting tubeform assembly  86  has a torsional stiffness of about 90,000 pounds force-inch/degree. In some embodiments, the tubeform  16  is made from a natural elastomer, a synthetic elastomer, or combinations thereof. In some embodiments, the tubeform  16  can have a laminated structure, having a plurality of sequentially arranged or positioned layers of elastomeric material to form the tubeform  16 , the layers of which can be the same, different, alternating, or any suitable arrangement. The tubeform  16  is preferably pre-compressed between about 3% and about 10%, with a more preferred pre-compression of about 6.5%. The term pre-compression means that the tubeform  16  has an uncompressed thickness that is greater than a distance between the outer wall  40  of the inner member  12  and the inner surface of the bonding ring  46  of the outer member  14 , when the inner member  12  and the outer member  14  are concentrically arranged or positioned, such that the tubeform  16  is compressed to have a thickness in an assembled state that is less than (e.g., thinner than) than the uncompressed thickness of the tubeform  16 . The tubeform  16  according to some embodiments can be designed to experience only about a 25% strain at transition torque and only about a 30% strain at peak torque. 
     In the example embodiment of the coupling  10  shown, the tubeform  16  is bonded between the inner member  12  and the outer member  14 . After the tubeform  16  is bonded between the inner and outer members  12 ,  14 , the outer member  14  is swaged into the tubeform  16 , thereby forming the tubeform assembly  86 . In forming the example embodiment of the coil spring assembly  88  shown in at least  FIG. 10 , the inner coil spring  26  is inserted concentrically within (e.g., inserted along the longitudinal axis of) the outer coil spring  24  and a coil spring holder  28  is positioned on each of the opposing ends  82   a,    82   b  of the outer and inner coil springs  24 ,  26 , after the inner coil spring  26  has been inserted within outer coil spring  24 . In forming the example embodiment of the sprocket assembly  90  shown in at least  FIG. 10 , a plurality of the coil spring assemblies  88  are inserted into the coil spring recesses  54  of the sprocket plate  18 . In some embodiments, the coil spring assemblies  88  are pre-compressed, prior to insertion, to have a maximum length substantially corresponding to the length L of the coil spring recess  54  in which the coil spring assembly  88  is to be inserted. In some embodiments, the coil spring assemblies  88  are compressed during insertion within one of the coil spring recesses  54 . 
       FIGS. 11A-11D  show various stages of assembly of the coupling  10  according to the example embodiment shown herein. In the first step, shown in  FIG. 11A , the thrust bearing  29  is installed into lower housing portion  22 , generally concentrically about the hole  68  and generally surrounding the ring  69  and the bumps  72  formed therein. The thrust bearing  29  is installed within the lower housing portion  22  in a position in contact with the thrust bearing surface  67 . In the second step, shown in  FIG. 11B , after installation of the thrust bearing  29 , the sprocket assembly  90  is installed on top of thrust bearing  29 , generally concentrically about the ring  69  and the bumps  72  of the lower housing portion  22 . In the third step, shown in  FIG. 11C , the tubeform assembly  86  is coupled to the sprocket assembly  90 , such that a portion (e.g., the inner member  12 ) of the tubeform assembly  86  is rotatable, as least to some degree, relative to the sprocket assembly  90 , and specifically to the sprocket plate  18 , while another portion (e.g., the outer member  14 ) of the tubeform assembly  86  is rigidly attached (e.g., so as to prevent relative movements therebetween) to the sprocket assembly, and specifically to the sprocket plate. As shown in the example embodiment disclosed herein, a fastener (e.g., a bolt, rivet, and the like) is used to rigidly couple the outer member  14  of the tubeform assembly  86  to the sprocket plate  18 , thereby securing the tubeform assembly  86  on top of the sprocket assembly  90 . Any type of fastener suitable for coupling the outer member  14  to the sprocket plate  18  may be used. In the fourth step, shown in  FIG. 11D , the upper housing portion  20  is installed over the lower housing portion  22 , such that the sprocket assembly  90  and the tubeform assembly  86  are, at least partially, contained within the housing formed by the upper and lower housing portions  20 ,  22 . The upper housing portion  20  is positioned to at least partially surround the tubeform assembly  86 , such that at least a portion of the tubeform assembly protrudes from the hole  58  formed in the upper housing portion  20 . In some embodiments, the inner member  12  is positioned to protrude from, be coplanar with, or recessed within, the hole  58  formed in the upper housing  20 . After being positioned over the sprocket assembly  90  and the tubeform assembly  86 , in which position the flanges  66  of the upper and lower housing portions  20 ,  22  are positioned adjacent to and/or abutting (e.g., in direct or indirect contact with) each other, the upper and lower housing portions  20 ,  22  are secured to each other (e.g., by fasteners, spot welding, or any suitable attachment technique) at the notches  62 A,  62 B formed in the flanges  66 A,  66 B of the upper and lower housing portions  20 ,  22 . In some embodiments, the tubeform assembly  86  is secured to the sprocket by a spot welding technique, either in addition to or in place of the fasteners discussed elsewhere herein to secure the outer member  14  to the sprocket plate  18 , or by any other suitable type of attachment. The reference herein to “steps” is not to be interpreted as being an exhaustive list of steps and further sub-steps, or additional steps, may be included during the assembly of the coupling  10  disclosed herein. 
     Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.