Abstract:
A decoupler assembly for transferring torque between a shaft and an endless power transmitting element. The decoupler assembly includes a clutch spring that is formed only of wire for transmitting rotary power between a carrier and a pulley. The decoupler assembly further includes a hub, that is configured to be coupled to a driven shaft, and a torsion spring that transmits rotary power between the carrier and the hub. A lubricant is disposed on the coils of the clutch spring. The pulley and the hub cooperate to define an annular cavity in which the torsion spring and the clutch spring are disposed. The torsion spring and the clutch spring are disposed axially between the carrier and the hub.

Description:
FIELD OF THE INVENTION 
   The invention relates to a belt drive assembly for driving belt driven accessories in an engine of an automotive vehicle, and more particularly, to a decoupling mechanism for allowing the belt driven accessories to operate temporarily at a speed other than the belt drive assembly. 
   DESCRIPTION OF THE RELATED ART 
   It is widely known in an automotive vehicle engine to transfer a portion of the engine output to a plurality of belt driven accessories utilizing an endless serpentine belt. Typically, each component includes an input drive shaft and a pulley coupled to a distal end of the drive shaft for driving engagement with the belt. An example of such a belt driven accessory is an alternator. 
   It is also known to provide a decoupler operatively coupled between the pulley and the alternator to allow the alternator drive shaft to “overrun” or rotate at a faster speed than the pulley and to allow the speed of the pulley to oscillate with respect to the alternator drive shaft due to oscillations in the engine speed. 
   Examples of 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 remains desirable to provide a decoupler that is easier to manufacture and has better durability over conventional decoupler designs. 
   SUMMARY OF THE INVENTION 
   In one form the present teachings provide a decoupler assembly for transferring torque between a shaft and an endless power transmitting element. The decoupler assembly can include a hub, a carrier, a torsion spring, a pulley, a clutch spring and a lubricant. The hub is configured to be coupled to the shaft such that the shaft co-rotates with the hub about a rotational axis. The carrier is rotatable relative to the hub. The torsion spring is concentric with the rotational axis of the hub and extends between a hub end and a carrier end and is configured to transfer rotary power between the hub and carrier. The pulley is rotatably coupled to the hub and has an outer periphery that is configured to engage the endless power transmitting element. The pulley has an inner surface formed therein. The clutch spring is formed only of wire and includes a first end, which is fixedly coupled to the carrier, a second end, which is located opposite the first end, and a plurality of coils that are disposed between the first and second ends. The clutch spring exits the carrier and extends toward the inner surface of the pulley such that at least one of the plurality of coils is engaged against the inner surface of the pulley when rotary power is transmitted from the pulley to the hub. The plurality of coils are configured to contract to at least reduce gripping engagement between the plurality of coils and the inner surface of the pulley in response to deceleration of the pulley relative to the carrier beyond a predetermined extent to permit the hub to rotate at a speed in excess of the pulley. The lubricant is disposed on coils of the clutch spring. The pulley and the hub cooperate to define an annular cavity in which the torsion spring and the clutch spring are disposed. The torsion spring and the clutch spring are disposed axially between the carrier and the hub. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a front view of an engine of an automotive vehicle incorporating a decoupler assembly according to one aspect of the invention; 
       FIG. 2  is an enlarged fragmentary sectional view of the decoupler assembly; 
       FIG. 3  is a perspective view of a clutch spring in the decoupler assembly; 
       FIG. 4  is a perspective view of a carrier for carrying one end of the clutch spring in the decoupler assembly; 
       FIG. 5  is a perspective view of the clutch spring assembled to the carrier; 
       FIG. 6  is an exploded perspective view of the decoupler assembly according to a second embodiment of the invention; 
       FIG. 7  is a cross sectional view of the decoupler assembly according to the second embodiment of the invention; and 
       FIG. 8  is a cross sectional view of the decoupler assembly according to a third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the figures, an engine for an automotive vehicle is generally indicated at  10  in  FIG. 1 . The engine  10  includes a crankshaft  12  driving an endless serpentine belt  14 , as commonly known by those having ordinary skill in the art. The engine  10  also includes a belt driven accessory  16  driven by the belt  14 . Described in greater detail below, a decoupler assembly  20  is operatively assembled between the belt  14  and the belt driven accessory  16  for automatically decoupling the belt driven accessory  16  from the belt  14  when the belt  14  decelerates relative to the belt driven accessory  16  and allowing the speed of the belt  14  to oscillate relative to the belt driven accessory  16 . Additionally, a detailed description of the structure and function of a decoupler assembly can be found in applicant&#39;s U.S. Pat. No. 6,083,130, which issued on Jul. 4, 2000 and is incorporated herein by reference in its entirety. 
   Referring to  FIG. 2 , the decoupler assembly  20  includes a hub  22  having opposite first  24  and second  26  ends and a generally cylindrical body  28  extending axially therebetween. The body  28  includes opposite inner  30  and outer  32  surfaces extending between the first  24  and second  26  ends of the hub  22 . The inner surface  30  includes a plurality of inner threads  33  adjacent the first end  24  for fixedly securing the hub  22  to a drive shaft  15  from the belt driven accessory  16 . A reduced diameter portion  34  is formed in the first end  24 . The reduced diameter portion  34  includes an outer mounting surface  36  having a smaller outer diameter than the body  28 . An abutment surface  38  opposite the second end  26  extends generally radially between the outer mounting surface  36  and the body  28 . An annular thrust washer  39  is seated on the outer mounting surface  36  adjacent the abutment surface  38 . 
   A socket  40  is formed in the second end  26  for receiving a suitable tool therein for rotatably threading the hub  22  onto the drive shaft  15 . An annular first flange  41  extends radially outwardly from the body  28  adjacent the second end  26 . The first flange  41  includes an outer flange surface  42  having a larger outer diameter than the body  28 . An annular surface  44  extends generally radially between the body  28  and the outer flange surface  42  opposite the second end  26 . A generally helical first slot  46  is formed in the annular surface  44  defining a first locating surface  48  therein. 
   A generally cylindrical pulley  50  is rotatably journaled to the hub  22 . More specifically, the pulley  50  extends between opposite first  52  and second  54  ends. The pulley  50  includes an inner surface  56  extending between the first  52  and second  54  ends. A ball bearing member  57  is coupled between the pulley  50  and the hub  22 . The bearing member  57  includes an inner race  58  fixedly secured to a portion of the outer mounting surface  36  and an outer race  59  fixedly secured to a portion of the inner surface  56  adjacent the first end  52  of the pulley  50 . A plurality of ball bearings  55  is rollingly engaged between the inner  58  and outer  59  races of the bearing member  57 . A cylindrical bushing  60  is journal mounted between the pulley  50  and the first flange  41 . The bushing  60  includes a sleeve wall  62  extending between a portion of the inner surface  56  adjacent the second end  54  and the outer flange surface  42  of the first flange  41 . A bushing flange  64  extends radially inwardly from the sleeve wall  62  and abuts the annular surface  44  in the first flange  41 . 
   The pulley  50  includes an outer periphery  66  with a plurality of V-shaped grooves  68  formed therein for rollingly engaging and guiding the belt  14 . 
   Referring to  FIGS. 2-5 , a one-way clutch assembly  70  is operatively coupled between the hub  22  and the pulley  50 . The clutch assembly  70  includes a clutch spring  71  and a carrier  75 . The clutch spring  71  includes a plurality of helical coils  72  extending between a bent or hooked proximal end  73  and an opposite distal end  74 . Preferably, the clutch spring  71  is formed from an uncoated, spring steel material and has a non-circular cross-section to improve frictional contact. Most preferably, the cross-section of clutch spring  71  is rectangular or square. The clutch spring  71  is press fitted into frictional engagement with the inner surface  56  of the pulley  50 . Preferably, a lubricant similar or compatible with grease used in the ball bearing member  57  is applied to minimize wear between the clutch spring  71  and the inner surface  56  of the pulley  50 . 
   The carrier  75  is rotatably mounted on the hub  22 . The carrier  75  is generally ring shaped and extends axially between opposite first and second sides  76 ,  78 . The carrier  75  defines a generally cylindrical inner surface  80  and a generally cylindrical outer surface  82 . A hooked slot  84  is formed in the second side  78  of the carrier  75  and is configured to retain the hooked proximal end  73  of the clutch spring  71 . A generally helical second slot  86  is formed in the second side  78  of the carrier  75  defining a second locating surface  88  generally opposing the first locating surface  48  formed in the annular surface  44 . 
   Referring to  FIG. 2 , a helical torsion spring  90  extends between hub  92  and carrier  94  ends. The torsion spring  90  is axially compressed between the first  48  and second  88  locating surfaces for transferring torque between the hub  22  and the carrier  75 . More specifically, the hub end  92  of the torsion spring  90  is retained in the first slot  46  of the hub  22 . Similarly, the carrier end  94  of the torsion spring  90  is retained in the second slot  86  in the second side  78  of the carrier  75 . Axial forces due to the compression of the torsion spring  90  retains the first side  76  of the carrier  75  in abutting engagement with the thrust washer  39 . The torsion spring  90  also allows relative movement between the carrier  75  and the hub  22  to accommodate changes in the speed of the pulley  50  due to generally oscillating changes in the operating speed of the engine. The torsion spring  90  and the clutch spring  71  are coiled in opposite directions. 
   A cap  100  is fixedly assembled to a flange  102  formed in the pulley  50  for preventing contaminants from entering the decoupler assembly  20  and for retaining the lubricant within the decoupler assembly  20 . 
   In operation, the engine  10  is started and the pulley  50  is accelerated and rotated in a driven direction by the belt  14  driven by the engine  10 . Acceleration and rotation of the pulley  50  in the driven direction relative to the hub  22  creates friction between the inner surface  56  of the pulley  50  and preferably all of the coils  72  of the clutch spring  71 . It should be appreciated that the clutch spring  71  will function even where at the onset at least one of the coils  72  of the clutch spring  71  is frictionally engaged with the inner surface  56  of the pulley  50 . The clutch spring  71  is helically coiled such that the friction between the inner surface  56  of the pulley  50  and at least one of the coils  72  would cause the clutch spring  71  to expand radially outwardly toward and grip the inner surface  56  of the pulley  50 . Continued rotation of the pulley  50  in the driven direction relative to the hub  22  would cause a generally exponential increase in the outwardly radial force applied by the coils  72  against the inner surface  56  until all of the coils  72  of the clutch spring  71  become fully brakingly engaged with the pulley  50 . When the clutch spring  71  is fully engaged with the inner surface  56 , the rotation of the pulley  50  is fully directed toward rotation of the drive shaft  15  of the belt driven accessory  16 . Additionally, centrifugal forces help to retain the clutch spring  71  in braking engagement with the inner surface  56  of the pulley  50 . 
   The rotational movement of the carrier  75  in the driven direction is transferred to the hub  22  by the torsional spring  90  such that generally the carrier  75 , thrust washer  39 , hub  22 , and the drive shaft  15  from the belt driven accessory  16  rotate together with the pulley  50 . Additionally, the torsional spring  90  resiliently allows relative movement between the carrier  75  and the hub  22  to accommodate oscillations in the speed of the pulley  50  due to corresponding oscillations in the operating speed of the engine  10 . 
   When the pulley  50  decelerates, the hub  22  driven by the inertia associated with the rotating drive shaft  15  and the rotating mass within the belt driven accessory  16  will initially “overrun” or continue to rotate in the driven direction at a higher speed than the pulley  50 . More specifically, the higher rotational speed of the hub  22  relative to the pulley  50  causes the clutch spring  71  to contract radially relative to the inner surface  56  of the pulley  50 . The braking engagement between the clutch spring  71  and the pulley  50  is relieved, thereby allowing overrunning of the hub  22  and drive shaft  15  from the belt driven accessory  16  relative to the pulley  50 . The coils  72  may remain frictionally engaged with the inner surface  56  while the pulley  50  decelerates relative to the clutch assembly  70  and the hub  22 . The coils  72  of the clutch spring  71  begin to brakingly reengage the inner surface  56  as the pulley  50  accelerates beyond the speed of the hub  22 . 
   Referring to  FIGS. 6 and 7 , a second embodiment of the decoupler assembly  20 ′ is shown, wherein elements of the alternative embodiment similar to those in the first embodiment are indicated by primed reference characters. The decoupler assembly  20 ′ is assembled between an output or crankshaft  106  of an engine and the belt  14 ′ to allow the belt  14 ′ to overrun the crankshaft  106 . The decoupler assembly  20 ′ includes a generally ring-shaped spring support  110 . The slot  46 ′ of the hub  22 ′ has a generally U-shaped cross section for retaining the spring support  110  therein. 
   A first tab  112  extends outwardly from the spring support  110 . A first notch  114  is formed in the hub end  92 ′ of the torsion spring  90 ′ for axially receiving the first tab  112  therein. Engagement between the first tab  112  and the first notch  114  prevents relative rotational movement of the hub end  92 ′ of the torsion spring  90 ′ relative to the spring support  110  and hub  22 ′. Similarly, a second tab  116  extends outwardly from the second locating surface  88 ′ of the carrier  75 ′. A second notch  118  is formed in the carrier end  94 ′ of the torsion spring  90 ′ for axially receiving the second tab  116  therein. Engagement between the second tab  116  and the second notch  118  prevents relative rotational movement of the carrier end  94 ′ of the torsion spring  90 ′ relative to the carrier  75 ′. 
   The pulley  50 ′ includes an outer periphery  120  for seating the belt  14 ′ therein and an inner flange portion  122 . The inner flange portion  122  has a generally U-shaped cross section defined by outer  124  and inner  126  pulley walls and a first connecting wall  128  extending radially therebetween. The carrier  75 ′ is retained between the outer  124  and inner  126  pulley walls and the first connecting wall  128  of the inner flange portion  122 , such that the carrier  75 ′ rotates with the pulley  50 ′. A second connecting wall  130  extends radially between the outer pulley wall  124  and the outer periphery  120 . 
   The carrier  75 ′ includes a slot or split  132 , which helps the carrier  75 ′ to flex and accommodate loads associated with the rotation of the decoupler assembly  20 ′. 
   Referring to  FIG. 8 , a third embodiment of the decoupler assembly  20 ″ is shown, wherein the body  28 ″ and first flange  41 ″ of the hub  22 ″ are formed separately and fixedly connected in a subsequent assembly operation. The body  28 ″ of the hub  22 ″ is generally cylindrical and extends between the first  24 ″ and second  26 ″ ends. The first flange  41 ″ includes a mounting portion  140 , which has a center bore  142  for receiving the outer flange surface  36 ″ of the hub  22 ″ therethrough. The first flange  41 ″ includes a generally U-shaped cross section defined by an end wall  134  extending radially between generally parallel inner  136  and outer  138  flange walls. The spring support  110 ″ is retained between the inner  136  and outer  138  flange walls and the end wall  134 , such that the spring support  110 ″ rotates with the first flange  41 ″. 
   The outer periphery  120 ″ and the inner flange portion  122 ″ of the pulley  50 ″ are formed separately and fixedly connected in a subsequent assembly operation using any suitable method, such as welding. The generally U-shaped cross section of the inner flange portion  122 ″ opens toward the first flange  41 ″. The carrier  75 ″ is retained between the outer  124 ″ and inner  126 ″ pulley walls and the first connecting wall  128 ″, such that the carrier  75 ″ rotates with the pulley  50 ″. 
   A ring plate  143  is mounted concentrically onto the outer mounting surface  36 ″ adjacent the abutment surface  38 ″. A thrust washer  144  is disposed between the first flange  41 ″ and the ring plate  143 . The thrust washer  144  is axially spaced apart from the end wall  134  of the flange  41 ″ for receiving the inner flange portion  122 ″ of the pulley  50 ″ therebetween. 
   A torsional vibration damper  146 , as known by those skilled in the art, is fixedly secured to the outer flange wall  138  of the first flange  41 ″ for dampening vibrations experienced at the crankshaft  106  associated with the operations of the engine. 
   The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modification and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.