Abstract:
An isolating decoupler comprising a hub for connection to a driving shaft, a pulley journalled to the hub, the pulley having a belt engaging surface, a spring engaged between the hub and a spring carrier, the spring radially expandable in a loading direction, a one-way clutch spring disposed radially inward of the spring engaged with the spring carrier and frictionally engagable with the pulley in a loading direction that is opposite the loading direction of the spring, the one-way clutch spring engagable with the hub whereby the frictional engagement of the one-way clutch spring with the pulley can be progressively released in an unloading direction, and an inertial member engaged with the hub through a damping member.

Description:
FIELD OF THE INVENTION 
     The invention relates to an isolating decoupler comprising a wrap spring disposed radially inward of a torsion spring engaged with a spring carrier and frictionally engagable with a pulley in a loading direction that is opposite that of the torsion spring, the wrap spring engagable with the hub whereby the frictional engagement with the pulley can be released. 
     BACKGROUND OF THE INVENTION 
     Diesel engine use for passenger car applications is increasing due to the benefit of better fuel economy. Further, gasoline engines are increasing compression ratios to improve the fuel efficiency. As a result, diesel and gasoline engine accessory drive systems have to overcome the vibrations of greater magnitude from crankshafts due to above mentioned changes in engines. 
     Due to increased crankshaft vibration plus high acceleration/deceleration rates and high alternator inertia the engine accessory drive system is often experiencing belt chirp noise due to belt slip. This will also reduce the belt operating life. 
     Crankshaft isolators/decouplers and alternator decouplers/isolators have been widely used for engines with high angular vibration to filter out vibration in engine operation speed range and to also control belt chirp. 
     Representative of the art is U.S. Pat. No. 7,591,357 which discloses a decoupler provided for transferring rotary movement between an engine driven crankshaft and a serpentine belt. The decoupler has a rotary driving member and a rotary driven member coaxially mounted with the driving member for relative rotary movement therewith. A decoupling assembly extends between the driving member and the driven member. The decoupling assembly selectively couples the driving and driven members when the driving member rotates relative to the driven member in a first coupling sense. The decoupling assembly uncouples the driving member from the driven, member when the driving member rotates relative to the driven member in a second sense opposite the first sense. A torsional vibration damper is mounted for rotation with one of the driving and driven members to cancel some of the vibrations generated by the engine. 
     What is needed is an isolating decoupler comprising a wrap spring disposed radially inward of a torsion spring engaged with a spring carrier and frictionally engagable with a pulley in a loading direction that is opposite that of the torsion spring, the wrap spring engagable with the hub whereby the frictional engagement with the pulley can be released. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is an isolating decoupler comprising a wrap spring disposed radially inward of a torsion spring engaged with a spring carrier and frictionally engagable with a pulley in a loading direction that is opposite that of the torsion spring, the wrap spring engagable with the hub whereby the frictional engagement with the pulley can be released. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises an isolating decoupler comprising a hub for connection to a driving shaft, a pulley journalled to the hub, the pulley having a belt engaging surface, a spring engaged between the hub and a spring carrier, the spring radially expandable in a loading direction, a one-way clutch spring disposed radially inward of the spring engaged with the spring carrier and frictionally engagable with the pulley in a loading direction that is opposite the loading direction of the spring, the one-way clutch spring engagable with the hub whereby the frictional engagement of the one-way clutch spring with the pulley can be progressively released in an unloading direction, and an inertial member engaged with the hub through a damping member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is a front of the device. 
         FIG. 2  is a back view of the device. 
         FIG. 3  is an exploded, view of the device. 
         FIG. 4  is a cross-section of the device. 
         FIG. 5  is a cross-section showing a wrap spring connection to the hub. 
         FIG. 6  is a detail of the clutch carrier. 
         FIG. 7  is a detail of the clutch carrier. 
         FIG. 8  is a detail of the torsional vibration damper. 
         FIG. 9  is a detail of the hub and torsion spring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a front view of the device. The device comprises a hub  6 , inertial member  2  and a pulley  24 . Hub  6  can be used to attach the device to an engine crankshaft (not shown). Damper  4  is disposed between hub  6  and inertial member  2 . Damper  4  comprises an elastomeric material suitable for damping oscillations of the inertial member. Pulley  24  has a profile suitable for engaging a power transmission belt, for example, a v-belt or multi-ribbed belt. Inertial damper  4  damps crankshaft oscillations caused by the engine cylinder firing events. 
       FIG. 2  is a back view of the device. The diameter of inertial member  2  is approximately the same as the diameter of pulley  24 , thereby rendering the device compact. 
       FIG. 3  is an exploded view of the device. Hub  6  comprises an outer cylindrical portion  61  and radial portion  62 . An end  180  of torsion spring  18  is engaged with a stop  65  on radial portion  62 . The other end  182  of torsion spring  18  engages clutch carrier  20 . Clutch carrier  20  is journalled to pulley  24  on a bushing  22 . Bushing  22  engages an inner cylindrical portion  240  of pulley  24 . 
     An end  160  of wrap spring  16  engages clutch carrier  20 . The other end  161  of wrap spring  16  is temporarily engageable with hub  6 , see  FIG. 5 . Sleeve  8  is press fit to cylindrical portion  240 . Cylindrical portion  240  is journalled to hub  6  through a bushing  14 . Wrap spring  16  comprises a coil spring. 
     Retaining ring  12  engages groove  63  in hub  6 . Thrust washer  10  bears upon ring  12 , thereby retaining sleeve  8  and pulley  24  in position on hub  6 . Sleeve  8  and pulley  24  are journalled to hub  6  through bushing  14 . In an alternate embodiment, bushing  14  may be replaced with ball bearings, needle bearings, roller bearings or any other suitable bearing known in the art. 
     Carrier  20  with bushing  22  are installed on the outer diameter of the pulley portion  240 , and each are thereby retained in place by sleeve  8 . Carrier  20  and bushing  22  can freely rotate relative to the pulley  24 . Sleeve  8  is press fit onto the pulley portion  240 . Thrust washer  10  is installed between sleeve  8  and retaining ring  12  thereby retaining pulley  24  on the hub  6 . Pulley  24  can axially move relative to hub  6  only in the amount of the clearances between retaining ring  12 , thrust washer  10 , groove  63  in hub  6  for retaining ring  12  and space between sleeve  8  and pulley portion  240 . 
     Wrap spring  16  is wound around hub  21  of carrier  20  with end  160  fixed against a tab  23 , see  FIG. 6 . Wrap spring  16  uses about two or three coils to frictionally lock wrap spring  16  about hub  21  of carrier  20 . Wrap spring end  160  and clutch carrier  20  are not moveable relative to each other due the connection. Wrap spring  16  is radially inward of torsion spring  18 , thereby disposed between the torsion spring  18  and the hub  6 . Wrap spring  16  is radially disposed between torsion spring  18  and pulley  24 . 
     Clutch carrier  20  receives torsion spring  18 . During operation torsion spring  18  is loaded in the unwinding direction, meaning the coils tend to radially expand under load. Wrap spring  16  is installed onto sleeve  8  with an interference fit, that is, the difference in diameter between, an inside diameter of the wrap spring and the outside diameter of the sleeve are dimensionally different which causes an interference which is approximately 0.3 mm to 0.5 mm. The material for sleeve  8  is selected to suitably support the wrap spring during locking and overrunning modes. 
       FIG. 4  is a cross-section of the device. When torque is applied to hub  6 , for example by an engine crankshaft (not shown), torsion spring  18  is loaded in the unwinding direction, thereby driving clutch carrier  20 . Loading in the unwinding direction means torsion spring  18  increases in radial diameter as the coils of the torsion spring expand. In turn clutch carrier  20  winds wrap spring  16  about sleeve  8 . Wrap spring  16  is loaded in the direction opposite that of the torsion spring, that is, wrap spring  16  is loaded in the winding direction. Loaded in the winding direction means spring  16  tends to decrease in radial diameter as the coils are loaded. As the load increases wrap spring  16  grips sleeve  8  by a progressively increasing frictional engagement which is caused by the sequential engagement of the wrap spring coils about sleeve  8 . The grip of wrap spring  16  causes sleeve  8  and thereby pulley  24  to rotate in unison with nub  6 . In this operating condition there is little or no relative motion between clutch carrier  20  and pulley  24 , although some oscillation may be present due to load variations. 
     When the engine decelerates the crankshaft speed is slowed, wherein pulley  24  may temporarily rotate faster than hub  6  due to inertia in the belt drive system driven by the belt which engages pulley  24  (belt system not shown). In the deceleration condition pulley  24  and sleeve  8  temporarily rotate faster than hub  6  and wrap spring  16 . This causes wrap spring  16  to unwind which causes wrap spring  16  to radially increase in diameter which releases the frictional grip with sleeve  8 . This allows pulley  24  to temporarily overrun hub  6 . During the overrun condition bushing  14 , thrust washer  10 , and bushing  22  all experience some relative motion. 
       FIG. 5  is a cross-section showing a wrap spring connection to the hub. If during operation the loading torque on torsion spring  18  exceeds a predetermined magnitude then hub  6  will continue to angularly advance relative to pulley  24 . In doing so, end  66  of wrap spring grove  64  will come into contact with end  161  of wrap spring  16  ( FIG. 5 ). This contact causes wrap spring  16  to partially unwind as the load increases, thereby partially expanding the radial diameter of wrap spring  16 . Partial unwinding of wrap spring  16  progressively releases the force of the frictional engagement (“grip”) with sleeve  8  and pulley  24  as the input torque increases, for example during extreme engine acceleration. The partial release of the grip of wrap spring  16  allows hub  6  to partially overrun pulley  24 , thereby allowing excessive torque to bleed off. This limits further loading thereby protecting the device and the components driven by the device from possible damage from overload conditions. 
       FIG. 6  is a detail of the clutch carrier. Clutch carrier  20  comprises portions  25   a ,  25   b ,  25   c  which support the volutes of torsion spring  18 . Each portion  25   a ,  25   b ,  25   c  is of a different height relative to the clutch carrier in order to support the helical form of the wrap spring. End  160  of wrap spring  16  engages member  23 . Portion  25   c  also functions as a torsion spring stop. Torsion spring end  182  bears upon torsion spring stop  25   c  during operation. 
       FIG. 7  is a detail of the clutch carrier. End  182  of torsion spring  18  engages stop  25   c  in a driving condition. End  160  of wrap spring  16  is engaged with member  23 . 
       FIG. 8  is a detail of the torsional vibration damper. Debris channel  200  allows debris to exit the device between the damper  2  and pulley  24 . The labyrinth form of channel  200  discourages debris from entering the space between the damper and pulley. 
       FIG. 9  is a detail of the hub and torsion spring. End  180  of torsion spring  18  engages a stop  65  on hub  6 . During operation torsion spring  18  is loaded in the unwinding direction causing end  180  to bear upon stop  65 . 
     Advantages of the device include the pulley is connected to the wrap spring and the bearing support and inertia are located primarily within the envelope of the device. A further advantage of the invention is that wrap spring  16  can carry a substantially higher load compared to a like wrap spring loaded in an unwinding direction. For example, the wrap spring disclosed in U.S. Pat. No. 7,591,357 has to be selected based on material strength and rigidity so the wrap spring will keep its form and shape under compression (the unwinding direction). If not properly designed at certain loads the prior art wrap spring can “buckle”. On the other hand the wrap spring in the invention is only subject to tension during loading which allows a substantially higher stress. 
     Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.