Abstract:
A decoupler assembly that includes a hub, a drive member disposed about the hub, and a clutch coupling the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis and includes an inner clutch surface. The clutch includes a carrier, a plurality of arcuate springs, and a wrap spring. The carrier is received between the hub and the drive member. The arcuate springs are mounted to the carrier and are configured to transmit rotary power between the carrier and the hub. The wrap spring includes a proximal end, which is drivingly coupled to the carrier, and a plurality of helical coils that are engaged to the inner clutch surface of the drive member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/572,128 filed on Mar. 16, 2006 now U.S. Pat. No. 7,624,852, which is a National Stage of International Application No. PCT/CA04/01696 filed on Sep. 22, 2004, which claims the benefit of U.S. Provisional Application No. 60/504,934, filed on Sep. 22, 2003. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a decoupler assembly. Such decoupler assembly can be employed to transmit rotary power between a driving member and a driven member while permitting the driven member to be decoupled from the driving member so that the driven member may overrun or operate temporarily at a speed different from that of the driving member and to decouple or mechanically isolate the driven member from the driving member and reduce torsional vibrations transmitted therebetween. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     It is widely known in an automotive vehicle engine to transfer a portion of the engine output to a plurality of belt driven accessory components utilizing an endless serpentine belt. Typically, each belt driven accessory component includes a pulley drivingly engaged with the belt and the belt is driven by an output pulley coupled directly to the crankshaft. 
     Internal combustion engines operate as a pulse system, constantly accelerating and decelerating and causing engine vibrations. As a result of these changing speeds, the belt driven accessory components, which are driven by the crankshaft, are continually trying to speed up and slow down. This can result in unacceptable levels of noise and vibration along with reduced accessory drive component durability due to high fluctuating loads and vibrations. Additionally, rapid engine accelerations and deceleration, such as during transmission shifts and engine startup and shutdown, cause belt squeal from slippage between the belt and the pulley as well as heavy impact loading on the belt. 
     It is known to provide a decoupler assembly between the belt driven accessory component and the pulley to allow the belt driven accessory component to operate temporarily at a higher speed or “overrun” the pulley as the pulley oscillates with the speed of the engine. Examples of such decouplers are disclosed in the U.S. Pat. No. 6,083,130, issued to Mevissen et al. on Jul. 4, 2000 and the U.S. Pat. No. 5,139,463, issued to Bytzek et al. on Aug. 18, 1992. 
     It is also known to provide a decoupler assembly between the belt driven accessory and the pulley to isolate vibrations therebetween and allow overrunning, reducing noise and impact loads. An example of such a decoupler is disclosed in U.S. Pat. No. 6,044,943 issued to Bytzek et al. on Apr. 4, 2000. 
     However, it remains desirable to provide an improved decoupler assembly. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides a decoupler assembly that includes a hub, a drive member disposed about the hub, and a clutch coupling the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis and includes an inner clutch surface. The clutch includes a carrier, a plurality of arcuate springs, and a wrap spring. The carrier is received between the hub and the drive member. The arcuate springs are mounted to the carrier and are configured to transmit rotary power between the carrier and the hub. The wrap spring includes a proximal end, which is drivingly coupled to the carrier, and a plurality of helical coils that are engaged to the inner clutch surface of the drive member. 
     In another form, the present disclosure provides a decoupler assembly that includes a hub, a drive member, a clutch, which couples the hub and the drive member, and a lubricant. The hub has a rotational axis and includes a plurality of radially extending tabs. Each of the tabs has a leading edge and a trailing edge. The drive member is disposed about the hub for rotation about the rotational axis and includes an inner clutch surface. The clutch includes a carrier, a rim, a plurality of arcuate compression springs, a wrap spring and a non-metallic bumper. The carrier is received between the hub and the drive member and includes a carrier member and an insert. The carrier member defines a recess into which the insert is received and the insert includes a clutch stop. The rim is coupled to the carrier and configured to abut an end of the wrap spring in at least two locations. Each of the arcuate compression springs is mounted inside the carrier and engaged against an associated one of the leading edges of tabs of the hub. The wrap spring includes a proximal end and a plurality of helical coils that are engaged to the inner clutch surface of the drive member. The proximal end has an end face that is abutted against the clutch stop. The non-metallic bumper is coupled to the carrier. Contact between one of the trailing edges and the non-metallic bumper limits relative rotation between the carrier and the hub in a predetermined rotational direction. The lubricant is disposed between the carrier and the arcuate compression springs. 
     In yet another form, the present disclosure provides a decoupler assembly with a hub, a drive member and a clutch that couples the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis of the hub. The drive member has an inner clutch surface. The clutch includes a carrier, a plurality of springs and a wrap spring. The springs deflect in response to transmission of torque between the hub and the carrier when the torque has a magnitude that is within a predetermined range. The wrap spring is rotatably coupled to the carrier and has a plurality of coils that are engaged to the inner clutch surface. The decoupler assembly also includes a lubricant received between the carrier and the at least one spring. 
     In still another form, the present disclosure provides a decoupler assembly with a hub, a drive member and a clutch that couples the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis of the hub. The drive member has an inner clutch surface. The clutch includes a carrier, a plurality of springs and a wrap spring. The springs deflect in response to transmission of torque between the hub and the carrier when the torque has a magnitude that is within a predetermined range. The wrap spring is rotatably coupled to the carrier and has a plurality of coils that are engaged to the inner clutch surface. The clutch also includes a clip that is coupled to the carrier. The clip abuts an axial end of the wrap spring such that rotary power is transmitted between the carrier and the wrap spring through an interface at which the clip and the axial end abut one another. 
     In a further form, the present disclosure provides a decoupler assembly with a hub, a drive member and a clutch that couples the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis of the hub. The drive member has an inner clutch surface. The clutch includes a carrier, a plurality of springs and a wrap spring. The springs deflect in response to transmission of torque between the hub and the carrier when the torque has a magnitude that is within a predetermined range. The wrap spring is rotatably coupled to the carrier and has a plurality of coils that are engaged to the inner clutch surface. The carrier includes first and second shell members that are fixedly coupled to one another via rivets, fasteners or combinations thereof. 
     In still another form, the present disclosure provides a decoupler assembly with a hub, a drive member and a clutch that couples the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis of the hub. The drive member has an inner clutch surface. The clutch includes a carrier, a plurality of springs and a wrap spring. The springs deflect in response to transmission of torque between the hub and the carrier when the torque has a magnitude that is within a predetermined range. The wrap spring is rotatably coupled to the carrier and has a plurality of coils that are engaged to the inner clutch surface. The clutch includes a non-metallic bumper that limits rotation of the hub relative to the carrier. 
     In yet another form, the present disclosure provides a decoupler assembly with a hub, a drive member and a clutch that couples the hub and the drive member. The drive member is disposed about the hub for rotation about a rotational axis of the hub. The drive member has an inner clutch surface. The clutch includes a carrier, a plurality of springs and a wrap spring. The springs deflect in response to transmission of torque between the hub and the carrier when the torque has a magnitude that is within a predetermined range. The wrap spring is rotatably coupled to the carrier and has a plurality of coils that are engaged to the inner clutch surface. The carrier includes a rim element that contacts the inner clutch surface during operation of the carrier. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a front view of an engine of an automotive vehicle incorporating a decoupler assembly according to one aspect of the present disclosure; 
         FIG. 2  is an exploded perspective view of the decoupler assembly of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a portion of the decoupler assembly of  FIG. 1 , illustrating the drive hub and the bearing assembly in more detail; 
         FIG. 4  is an exploded perspective view of a portion of the decoupler assembly of  FIG. 1 , illustrating the drive hub, the upper and lower spring shells and the clutch element; 
         FIG. 5  is a plan view of a portion of the decoupler assembly of  FIG. 1 , illustrating the lower spring shell, the biasing members and the clutch element; 
         FIG. 6  is a plan view of the lower spring shell; 
         FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is a plan view of the upper spring shell, biasing members and clutch element; 
         FIG. 9  is an exploded perspective view of an assembly that includes the decoupler assembly of  FIG. 1  and a torsional vibration damper; 
         FIG. 10  is a plan view of a portion of the decoupler assembly of  FIG. 1  illustrated in an accelerating condition that facilitates driving engagement of the output pulley; and 
         FIG. 11  is a plan view of a portion of the decoupler assembly of  FIG. 1  illustrated in a decelerating condition that facilitates the overrunning of the output pulley relative to the drive hub. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     An example embodiment will now be described more fully with reference to the accompanying drawings. 
     Referring to  FIG. 1 , an internal combustion engine for an automotive vehicle is generally indicated at  10 . The engine  10  includes a plurality of belt driven accessory components  12 , such as an alternator, compressor, etc. A pulley  14  is operatively coupled to each of the belt driven accessory components  12  for driving the components  12  via rotation of the pulley  14 . The engine  10  also includes a crankshaft  16 , which generally provides the mechanical torque output resulting from the operation of the engine  10 . An endless serpentine belt  18  is seated about each pulley  14  of the belt driven accessory components  12 . The belt  18  is driven in a driven direction by the rotation of the crankshaft  16 , which causes rotation of the pulleys  14 . A crankshaft torque modulator or decoupler assembly  20  is operatively coupled between the crankshaft  16  and the belt  18 . 
     Referring to  FIG. 2 , the decoupler assembly  20  is shown in an exploded view and includes an output pulley  22  having an annular outer track  24  defined between a pair of spaced apart, raised and parallel rims  25  that seats the belt  18  therein. The output pulley  22  also includes an annular inner clutch surface  26  opposite and generally concentric with the outer track  24 . The output pulley  22  further includes a face plate  28  extending between the outer track  24  and the inner clutch surface  26 . A hollow, cylindrical hub  30  projects axially from the center of the face plate  28  concentric with the inner clutch surface  26  for defining a hub bearing surface  32 . 
     Referring to  FIGS. 2-4 , the decoupler assembly  20  also includes a drive hub  40 , preferably formed of metal, fixedly secured to the crankshaft  16  by any suitable fastener or connection means for rotation therewith. The drive hub  40  includes a generally cup-shaped cylindrical main body  42  defining an inner surface  44  and having a circumferential radial rim  45 . A bearing post  46  extends axially from the center of the main body  42  to a distal end. At least one, but preferably a plurality of tabs  48 ,  50  extends radially outwardly radial rim  45  of the main body  42 . Each tab  48 ,  50  includes a leading edge  52  extending generally perpendicularly from the main body  42  and a trailing edge  54  extending angularly from the main body  42 . 
     A bearing assembly  60  rotatably couples the output pulley  22  and the drive hub  40 . The bearing assembly  60  includes a circular inner race  62  surrounding by a circular outer race  64 . A plurality of ball bearings  66  are seated between the inner race  62  and outer race  64 . The inner race  62  is seated around the bearing post  46  of the drive hub  40  and the outer race  64  is press fit against the bearing surface  32  of the output pulley  22  to provide the rotatable connection therebetween. In the preferred embodiment, the inner race  62  projects axially beyond the outer race  64  to form a shoulder to receive a disc-shaped seal  68  thereon to seal the ball bearings  66  between the inner race  62  and outer race  64  and to seal an oil or grease lubricant within the bearing assembly  60  and output pulley  22 , as will be described in further detail herein below. However, the inner race  62  may be axial flush with the end of the outer race  64 . In such case, the seal  68  may be seated around an extended collar portion of the bearing post  46  to seal against the ends of both the inner race  62  and outer race  64 . The seal  68  may be separate or an integral part of the bearing assembly  60 . Alternatively, a bushing can be used instead of the bearing assembly  60 . Generally, the bushing would provide greater damping over the bearing assembly  60 . 
     Referring to  FIGS. 2 , and  4 - 7 , the decoupler assembly  20  further includes a lower spring shell  70  and an upper spring shell  100  operatively coupled to the drive hub  40 . Each of the shells  70 ,  100  is preferably molded of an organic plastic material. The lower spring shell  70  is generally disc-shaped and extends between cylindrical and generally concentric inner and outer surfaces  72 ,  74 . A radial rim element  75  projects radially from at least portions of the outer surface  74  forming a shelf or shoulder and outer peripheral bearing surface  77  for frictionally engaging and supporting the inner clutch surface  26  of the output pulley  22 . The radial rim element  75  as shown in the preferred embodiment extends only along portions of the periphery of the outer surface to reduce the weight of the lower spring shell  70 . However, it should be appreciated that the rim element  75  may be a contiguous circumferential rim extending around the entire periphery of the outer surface  74 . Further, the radial rim element  75  increases in its axial thickness incrementally and continuously around the circumference of the outer surface  74  to form a helical contour or ramped support surface  79 . At least one, but preferably a plurality of trenches  76  is formed and recessed in the lower spring shell  70  between the inner and outer surfaces  72 ,  74 . Each trench  76  extends arcuately between a first end  78  and a second end  80 . The trenches  76  are aligned end to end and arranged in a generally circular manner along the perimeter of the lower spring shell  70 . A retaining slot  82  extends diagonally between the adjacent ends of the trenches  76  from the outer surface  74  to a generally rectangular cavity  84 . An L-shaped or U-shaped blocking tab or clutch stop  85 , preferably formed of stamped metal, is seated in the cavity  84 . A plurality of cutouts  86  is formed in the outer surface  74  to reduce the weight of the lower spring shell  70  and to form a series of alternating undulations  88 ,  90  in the outer surface  74 . Additionally, a lubricant can be supported in the cutouts  86  for lubricating the inner clutch surface  26  of the output pulley  22 . The undulations  88  each include a bore  92  therethrough for receiving a fastener  94 , such as a rivet or screw, to fixedly secure the lower spring shell  70  to the upper spring shell  100 . The undulations  90  each include an elongated slot  96  for aligning with and engaging with the upper spring shell  100  as will be further described below. Further, the lower spring shell  70  includes an enlarged counter-balance block  98  formed between the inner surface  72  and the outer surface  74  positioned radially opposite the retaining slot  82  and cavity  84  to rotationally balance the lower spring shell  70 . 
     Referring to  FIGS. 2 ,  4 , and  8 , the upper spring shell  100  is also generally disc-shaped and extends between cylindrical and generally concentric inner and outer surfaces  102 ,  104 . At least one, but preferably a plurality of trenches  106  is formed and recessed in the upper spring shell  100  between the inner and outer surfaces  102 ,  104 . Each trench  106  extends arcuately between a first end  108  and a second end  110 . The trenches  106  are aligned end to end and arranged in a generally circular manner along the perimeter of the upper spring shell  100 . A raised blocking wall  112 ,  114  extends diagonally between each of the pair of adjacent ends of the trenches  106  from the outer surface  102  to the second end  110  of each trench  106  for abutting with the trailing edge  54  of each respective tabs  48 ,  50  of the drive hub  40 . Further, one of the blocking walls  112 ,  114  is arranged to overlay the clutch stop  85  to retain the stop  85  within the cavity  84  of the lower spring shell  70 . The upper spring shell  100  further includes an axially extending alignment tab  115  extending diagonally between the inner surface  102  and outer surface  104 . The alignment tab  115  is sized to be received within the retaining slot  82  to ensure correct orientation between the lower and upper spring shells  70 ,  100 . A plurality of cutouts  116  is formed in the outer surface  104  to reduce the weight of the upper spring shell  100  and to form a series of alternating undulations  118 ,  120  in the outer surface  104 . Additionally, a lubricant can be supported in the cutouts  116  for lubricating the inner clutch surface  26  of the output pulley  22 . The undulations  118  each include a bore  122  therethrough aligned axial with a corresponding bore  92  in the lower spring shell  70  for receiving the fastener  94  to fixedly secure the lower spring shell  70  to the upper spring shell  100 . The undulations  120  each include an axially projecting and slightly tapered tab  124  for aligning axially with a corresponding elongated slot  96  in the lower spring shell  70  and for providing a rigid connection to transmit torque between the lower spring shell  70  and the upper spring shell  100 . Further, the upper spring shell  100  includes an enlarged counter-balance block  126  formed between the inner surface  102  and the outer surface  104  positioned radially opposite the retaining slot  82  and cavity  84  in the lower spring shell  70  to rotationally balance the lower and upper spring shells  70 ,  100 . 
     The decoupler assembly  20  also includes a plurality of biasing members  130  in the form of helical coil springs. A biasing member  130  is supported in each of the radially and axially aligned trenches  76 ;  106  between the lower spring shell  70  and upper spring shell  100 . Each biasing member  130  extends arcuately between first and second spring ends  132 ,  134 . Approximately one-half of the first and second spring ends  132 ,  134  abuts the first and second ends  78 ,  80  of the trenches  76  in the lower spring shell  70  and the other one-half abuts the first and second ends  108 ,  110  of the trenches  106  in the upper spring shell  100 . When the lower and upper spring shells  70 ,  100  are aligned axially and radially and pressed together, the biasing members  130  are seated in the corresponding trenches  76 ,  106  between the lower and upper spring shells  70 ,  100 . The biasing members  130  may be preformed in an arcuate shaped corresponding to the arcuate shape of the trenches  76 ,  106  or may be straight and then bent into shape when seated within the trenches  76 ,  106 . It should also be appreciated that the biasing members  130  may include any compressible or resilient member seated within the trenches  76 ,  106 , such as a rubber strut type member or compressible fluid. Preferably, a lubricant, such as grease or oil, is disposed in the trenches  76 ,  106  to reduce friction between the biasing members  130  and the spring shells  70 ,  100 . Generally, the lubricant also enhances damping characteristics of the decoupler assembly  20 . The damping characteristics can be tuned for a particular application. That is, the damping characteristics can be decreased or increased, depending on the type of lubricant placed in the trenches  76 ,  106  and decoupler assembly  20 . 
     A clutch element  140  is disposed adjacent the inner clutch surface  26  of the output pulley  22 . More specifically, the clutch element  140  is a coil spring having a plurality of coils  142  extending helically between a proximal end  144  and distal end  146 . The proximal end  144  of the clutch element  140  is fixedly held in the retaining slot  82  in the lower spring shell  70 . The tip of the proximal end  144  of the clutch element  140  extends into the cavity  84  and abuts the clutch stop  85 . The clutch element  140  is supported by the radial rim element  75  such that the ramped support surface  79  of the rim element  75  correspondingly mates with the contour of the helical coils  142 . The coils  142  are outwardly frictionally engaged with the inner clutch surface  26 , such that rotational acceleration of the drive hub  40  relative to the output pulley  22  in the driven direction of the crankshaft  16  causes the coils  142  to expand radially outwardly to couple the drive hub  40  and output pulley  22 . The coils  142  grip the inner clutch surface  26  so that the output pulley  22  rotates with the drive hub  40 . Conversely, deceleration of the drive hub  40  relative to the output pulley  22  causes the coils  142  to contract radially inwardly. The coils  142  release grip of the inner clutch surface  26  to allow the output pulley  22  to overrun the drive hub  40 . Preferably, the coils  72  have a rectangular cross section. 
     Referring again to  FIG. 2 , the decoupler assembly  20  is assembled by seating the biasing members  130  in the trenches  76  of the lower spring shell  70 . The clutch stop  85  is placed in the cavity  84 . The clutch element  140  is positioned around the lower spring shell  70  and the proximal end  144  is recessed within the retaining slot  82  with the end thereof abutting the clutch stop  85 . The clutch element  140  is supported by the radial rim element  75  such that the helical coils  142  mate with the helical contour of the ramped support surface  79  formed by the rim element  75 . The drive hub  40  is then positioned in the center of the lower spring shell  70  such that the radial rim  45  is seated against the periphery around the inner surface  72  and the tabs  48 ,  50  are positioned between the adjacent ends of the trenches  76 . Next, the upper spring shell  100  is aligned axially and radially with the lower spring shell  70  such that the biasing members  130  are seated in the trenches  106  and the tabs  48 ,  50  are similarly positioned between the adjacent ends of the trenches  106 . The alignment tab  115  is arranged to be received within the retaining slot  82  to ensure proper orientation between the shells  70 ,  100  and to position the counter-balance blocks  98 ,  126  opposite the proximal end  144  of the clutch element  140 . The counter-balance block  126  should be arranged generally 180 degrees opposite the proximal end  144  of the clutch element  140 . The alignment tab  115  also engages and presses down on the proximal end  144  of the clutch element  140  to retain the end  144  within the retaining slot  82 . The upper spring shell  100  is similarly seated within the circumference of the clutch element  140 . The axially projecting and tapered tabs  124  are received within the corresponding slots  96  in the lower spring shell  70  to provide a rigid connection and transmit torque between the shells  70 ,  100 . The upper and lower spring shells  70 ,  100  are fixedly connected by passing the fasteners  94  through each of the axially aligned bores  92 ,  122 . 
     The bearing assembly  60  is press fit against the hub bearing surface  32  of the output pulley  22  and the seal  68  is pressed around the inner race  62  against the shoulder formed with the outer race  64  to seal the bearing assembly  60  and output pulley  22 . 
     The inner cavity of the output pulley  22  is filled with a lubricant, such as grease or oil as desired to reduce friction between the components and provide dampening. A disc-shaped cover plate  150  closes the output pulley  22  and covers the upper spring shell  100 . Preferably, the cover plate  150  includes an inner seal  152  for sealing engagement against the main body  42  of the drive hub  40  and an outer peripheral gasket  154  for sealing against the output pulley  22 , together providing a fluid tight sealed decoupler assembly  20 . The cover plate  150  may be fixedly secured to the output pulley  22  by roll forming the periphery of a lip  156  on the output pulley  22  against the circumferential outer surface of the cover plate  150 . 
     Referring to  FIGS. 2 and 10 , in operation, the engine  10  rotatably accelerates or decelerates the crankshaft  16  and the drive hub  40  in the driven direction V relative to the output pulley  22 . First, during normal acceleration, the tabs  48 ,  50  engage the first spring ends  132  of the biasing members  130 . Initially, the first spring ends  132  are rotatably displaced relative to the respective second spring ends  134  as the biasing members  130  are compressed against the second ends  80 ,  110  of the trenches  76 ,  106 . The amount of displacement of the second spring ends  134  during acceleration is directly proportional to the rate of acceleration of the drive hub  40  and the stiffness of the biasing members  130 . Eventually, the upper and lower spring shells  70 ,  100 , urged by the compressed biasing members  130 , accelerate with the drive hub  40 . That is, the transfer of torque or acceleration from the drive hub  40  to the upper and lower spring shells  70 ,  100  is slightly delayed during compression of the biasing members  130 . Acceleration of the upper and lower spring shells  70 ,  100  relative to the output pulley  22  causes the coils  142  to expand radially outwardly toward the inner clutch surface  26 . More specifically, the rotation of the lower spring shell  70  urges the blocking tab  85  against the proximal end  144  of the clutch element  140  to radially expand the coils  142  against the inner clutch surface  26 . The contour of the retaining slot  82  in the lower spring shell  70  supports the proximal end  144  of the clutch element  140  to prevent localized bending of the coils  142  and urge uniform radial expansion along the entire length of the helical coils  142  against the inner clutch surface  26 . The coils  142  grip the clutch surface  26  with sufficient friction so that the output pulley  22  rotates with the drive hub  40 , driving the belt  18 . 
     Referring to  FIGS. 2 and 11 , during rapid deceleration of the crankshaft  16  and drive hub  40 , which may be caused by transmission shift, engine startup or shutdown, etc., it is desirable to selectively allow the output pulley  22  to rotate at a greater speed than the drive hub  40 , or overrun the drive hub  40  and crankshaft  16  to prevent belt slip on the output pulley  22  causing belt squeal or noise. During such deceleration, the tabs  48 ,  50  decelerate to reduce the load or torque exerted on the first ends  132  of the biasing members  130 . The biasing members  130  are allowed to extend or rebound against the tabs  48 ,  50  to thus also reduce the torque on the upper and lower spring shells  70 ,  100 . The trailing edges  54  of the tabs  48 ,  50  engage the corresponding blocking walls  112 ,  114  on the upper spring shell  100  to maintain the acceleration of the spring shells  70 ,  100  with the acceleration of the hub  40 . Deceleration of the spring shells  70 ,  100  relative to the output pulley  22  causes the coils  142  to contract radially inwardly with respect to the inner clutch surface  26 . Contraction of the coils  142  allows the inner clutch surface  26  to slip relative to the clutch mechanism  140 , thereby allowing the output pulley  22  to operate at a higher speed (V) than the drive hub  40  and crankshaft  16  (V-.delta.), or overrun the crankshaft  16  and prevent belt slippage on the output pulley  22  and noise in the assembly. 
     Additionally, during normal acceleration and deceleration of the crankshaft  16  as a result of the engine combustion process, higher frequency oscillatory torsional vibrations and high impact loads are generated within the crankshaft  16 . The decoupler assembly  20  also decouples, dampens and mechanically isolates these torsional vibrations between the crankshaft  16  and the output pulley  20 . Specifically, oscillatory torsional vibrations from the crankshaft  16  are dampened or isolated from the output pulley  22  by the biasing members  130 . Oscillations of the crankshaft  16 , and thus drive hub  40 , act on the first ends  132  of the biasing members  130  to compress the biasing members  130  against the second ends  80 ,  110  of the trenches  76 ,  106 . The biasing members  130 , or arcuate coil springs, compress and expand continuously with the torsional oscillations of the drive hub  40  to dampen, isolate and absorb the vibration caused by the torsional oscillations. The biasing members  130  thus reduce the impact loads generated within the engine, which would normally be transferred through the crankshaft  16  and into the output pulley  22 , and consequently directly into the belt driven accessory components. In other words, the biasing members  130  lower the oscillatory acceleration and deceleration rates and introduce a phase shift between the input force by the drive hub  40  and the output response at the output pulley  22 . This phase shift manifests itself as a lowering of the system resonance. By lowering the resonance of the drive assembly, unwanted vibrations are attenuated and torsional displacements induced by a system resonance are eliminated, or avoided. 
     Thus, the decoupler assembly  20  allows the belt driven accessory components  12  to temporarily operate at a higher speed or “overrun” the crankshaft  16  as the rotational speed of the crankshaft  16  changes with the speed of the engine  10 , which results in smoother engine operation, less noise, and increased belt life. The decoupler assembly  20  also dampens or isolates torsional vibrations experienced between the crankshaft  16  and the belt  18  during operation of the engine  10 . 
     Although the decoupler assembly  20  is described above as part of an internal combustion engine, it should be appreciated that the decoupler assembly  20  can be implemented in any rotary or pulley-type belt drive system, such as a generator or a conveyer belt system, or in any system of rigid shafts with pulley or misalignment couplings where a hub load is not necessarily applied. 
     It should also be appreciated that the output pulley  22  can be adapted to accommodate any type of drive element, such as a plastic or rubber multi-rib belt, a “V” belt, or a synchronous belt. The output pulley  22  can also be adapted to accommodate other drive elements such as a steel flat belt, as used in a continuously variable transmission, for example, or a multi-link chain made of plastic or steel. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.