Abstract:
An isolator decoupler comprising a shaft, a pulley journalled to the shaft, a clutch carrier journalled to the shaft through a one-way clutch, a torsion spring engaged between the pulley and the clutch carrier, the torsion spring loadable in an unwinding direction, the torsion spring and the pulley having a predetermined clearance between a torsion spring outside diameter surface and a pulley inside diameter surface, and whereby the torsion spring outside diameter surface and a pulley inside diameter surface come into a progressive frictional engagement by torque load dependent radial expansion of the torsion spring.

Description:
FIELD OF THE INVENTION 
     The invention relates to an isolator decoupler having a torsion spring and pulley having a predetermined clearance between a torsion spring outside diameter surface and a pulley inside diameter surface, and whereby the torsion spring outside diameter surface and a pulley inside diameter surface come into a progressive frictional engagement by torque load dependent radial expansion of the torsion spring. 
     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. 7,766,774 which discloses a decoupler assembly for allowing an alternator to be rotatably driven by a serpentine belt in an engine of an automotive vehicle and for allowing the speed of the belt to oscillate relative to the alternator. A hub is fixedly carried by a drive shaft from the alternator for rotation therewith. A pulley is rotatably journalled to the hub by a ball bearing assembly. A bare, helical clutch spring is operatively coupled between the hub and pulley for transferring rotational movement from the pulley to the hub during acceleration of the pulley relative to the hub by the serpentine belt and for allowing the hub to overrun the pulley during deceleration of the pulley relative to the hub. A torque limiter, preferably a spring or sleeve, is wrapped about the torsion limiting outward expansion of the torsion isolating the torsion spring from torques above a predetermined limit. 
     What is needed is an isolator decoupler having a torsion spring and pulley having a predetermined clearance between a torsion spring outside diameter surface and a pulley inside diameter surface, and whereby the torsion spring outside diameter surface and a pulley inside diameter surface come into a progressive frictional engagement by torque load dependent radial expansion of the torsion spring. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is an isolator decoupler having a torsion spring and pulley having a predetermined clearance between a torsion spring outside diameter surface and a pulley inside diameter surface, and whereby the torsion spring outside diameter surface and a pulley inside diameter surface come into a progressive frictional engagement by torque load dependent radial expansion of the torsion spring. 
     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 isolator decoupler comprising a shaft, a pulley journalled to the shaft, a clutch carrier journalled to the shaft through a one-way clutch, a torsion spring engaged between the pulley and the clutch carrier, the torsion spring loadable in an unwinding direction, the torsion spring and the pulley having a predetermined clearance between a torsion spring outside diameter surface and a pulley inside diameter surface, and whereby the torsion spring outside diameter surface and a pulley inside diameter surface come into a progressive frictional engagement by torque load dependent radial expansion of the torsion spring. 
    
    
     
       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 cross section view of the inventive device. 
         FIG. 2  is an exploded view. 
         FIG. 3  is a side view of the inventive device. 
         FIG. 4  is a detail of the clutch carrier. 
         FIG. 5  is a detail of the thrust bushing. 
         FIG. 6  is a persepctive view of the thrust bushing and clutch carrier stops. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a cross section view of the inventive device. The isolator decoupler comprises a shaft  10 . Pulley  30  is journalled to shaft  10  by a needle bearing  20  disposed between the pulley  30  and the shaft  10 . A torsion spring  40  is engaged between pulley  30  and clutch carrier  50 . Clutch carrier  50  is journalled to shaft  10  through a one-way clutch  60 . For example, the spring rate for spring  40  is approximately 0.27 Nm/deg, although other spring rates may be selected by a user to suit the operational requirements of the device. 
     Pulley  30  is further journalled to shaft  10  by a bearing  70  which is disposed between pulley  30  and shaft  10 . 
     A thrust bushing  80  is disposed between clutch carrier  50  and bearing  70 . Dust cover  90  prevents debris from entering the device. Cover  33  is press fit to pulley  30 . An end of spring  40  engages receiving portion  34  of cover  33 . 
     In operation for either an engine acceleration or steady speed, spring  40  is loaded in the unwinding direction and the one-way clutch  60  is locked. Power is transmitted from a belt (not shown) to pulley  30  through spring  40 , clutch carrier  50  and one-way clutch  60  to shaft  10 . While it is loaded in a driving direction spring  40  is trying to unwind and as a result the spring outside diameter (OD) surface  42  expands radially outward by an increase in the radius of each spring volute (R). The maximum extent of unwinding of spring  40  is limited as each spring  40  volute outside diameter surface  42  which progressively comes into contact with the pulley  30  inside diameter (ID) surface  32 . The extent of unwinding is dependent upon the torque load applied, hence, as the torque load is increased the amount of spring surface  42  in contact with surface  32  progressively increases, and as the torque load decreases the amount of spring surface  42  in contact with surface  32  progressively decreases. 
     The clearance between the spring outside diameter and the pulley inside diameter (C) determines and limits the unwinding radial expansion of spring  40 , which in turn protects spring  40  from being overloaded. At full lock up, that is when spring surface  42  is fully expanded into contact with the surface  32 , spring  40  is fully confined within the pulley surface  32  thereby preventing damage even if the applied torque load continues to increase. 
     In an engine deceleration condition the driving belt (not shown) will slow and so will the pulley  30 , but, due to its inertia an alternator (not shown) connected to shaft  10  would not in most cases drop RPM&#39;s as quickly as the pulley  30 . In effect the alternator would be trying to drive the engine (not shown) and the power flow would be reversed. This could overspeed the system and cause belt chirp as the belt slips on the pulley. Using the inventive device, the difference in deceleration rates will cause the one-way clutch to decouple the overrotating shaft  10  from pulley  30 . The alternator and shaft  10  will continue to decelerate at its own rate until it approximately matches the speed of the pulley  30  at which time the one-way clutch  60  will reengage. Uncoupling in this manner prevents shocks from being applied to the belt system as the engine accelerates and decelerates during normal use. 
       FIG. 2  is an exploded view. Thrust bushing  80  is press fit into the inside diameter of pulley  30 . Bearing  70  engages a collar  11  of shaft  10 . Dust cover  90  snaps onto pulley  30 . One-way clutch  60  has an axial sliding fit to shaft  10  and will lock up on a torque reversal. Clutch carrier  50  is press fit to one-way clutch  60 . Torsion spring  40  volutes have a rectangular cross-section. The rectangular cross section increases the surface area available to contact the inner diameter of the pulley. Bearing  20  is a sliding fit to shaft  10 . 
     Thrust bearing  80  engages bearing  70  to prevent axial movement of pulley  30  and clutch carrier  50 . 
       FIG. 3  is a side view of the inventive device. Pulley engaging surface  31  is a multiple ribbed surface, but can accommodate any surface form including toothed, smooth or single V groove. 
       FIG. 4  is a detail of the clutch carrier. Spring receiving portion  52  receives an end of torsion spring  41  when the device is being operated in the driving direction. 
       FIG. 5  is a detail of the thrust bushing. Thrust bushing  80  comprises a steel ring that is press fit into the pulley inside diameter. Thrust bushing  80  comprises plastic  81  over-molded on the steel ring  82 . 
     The thrust bushing sliding surface  81  comprises stops  83  which engage with stops  51  on the clutch carrier  50 . When the loaded spring is released during operation the thrust bushing will limit spring and clutch carrier reverse travel by contact between stops  83  and stops  51  thereby preventing spring end  41  from slipping out of the spring hookup slot  52  in the clutch carrier  50 . Further, engagement of the stops limits a relative rotation of the clutch carrier, and thereby the torsion spring with respect to the pulley. 
     The device is manufactured as follows. The pulley ID is with a +−0.015 mm tolerance. The spring OD is ground with a tolerance +/−0.03 mm. During assembly grease is applied between the spring OD  42  and the pulley ID  32  to soften engagement of stops  51  and  83 . For example, given a spring OD=42 mm, during start up the spring OD will expand approximately 0.024 mm per degree. 
     During assembly thrust bushing  81  is installed so that stops  83  engage clutch carrier stops  51 . The function of the stops  83 ,  51  is to prevent the spring end  41  from slipping out from portion  52  during a spring energy release or load reversal. The stops are not intended to give any preload to spring  40  and are not in contact during a no load condition for the device. However, due to assembly process variations, the assembled device may have a negligible preload or very small gap between the stops  83 ,  51  or spring end receiving portion which can be adjusted during assembly process. 
     During start up the clutch carrier  50  and clutch carrier stop  51  will deflect approximately 60 degrees from its unloaded engagement position with the thrust bushing stop  83 .  FIG. 6  is a persepctive view of the thrust bushing and clutch carrier stops. 
     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.