Decoupler with tuned damping and methods associated therewith

Abstract

In an aspect, the invention relates to a decoupler that is positionable between a shaft (eg. for an alternator) and an endless power transmitting element (eg. a belt) on an engine. The decoupler includes a hub that mounts to the shaft, and a pulley that engages the endless power transmitting element, an isolation spring between the hub and the shaft. The decoupler provides at least a selected damping torque between the hub and the pulley.

1 . An endless drive arrangement for an engine, comprising:
 a crankshaft pulley mountable to a crankshaft from the engine;   an alternator pulley mounted to an input shaft of an alternator, wherein the alternator operates at at least a first switching frequency and a second switching frequency;   an endless drive member that is positioned to transfer power from the crankshaft pulley to the alternator pulley such that first order vibrations are produced at the crankshaft; and   a decoupler including
 a hub that is adapted to be coupled to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis, 
 a pulley rotatably coupled to the hub, the pulley having an outer periphery that is positioned to engage the endless power transmitting element, 
 an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub, 
 a first friction surface operatively connected with the pulley, 
 a second friction surface operatively connected with the hub, 
 a biasing member positioned to exert a bias force between the first and second friction surfaces, and 
 a retainer engaging the biasing member to maintain the bias force, 
   wherein the second switching frequency is near a natural resonance frequency of the decoupler and the bias force between the first and second friction surfaces generates a damping torque during relative rotational movement between the pulley and the hub which attenuates said first order vibrations so as to reduce a tendency of the alternator to operate at the second switching frequency, thereby reducing a tendency of the alternator of transmitting vibration to the decoupler at frequencies near the natural frequency.   
     
     
         2 . An endless drive arrangement as claimed in  claim 1 , wherein the natural frequency is about 15 Hz. 
     
     
         3 . An endless drive arrangement as claimed in  claim 2 , wherein the second switching frequency is in the range of about 5 Hz to about 20 Hz. 
     
     
         4 . An endless drive arrangement as claimed in  claim 1 , wherein the damping torque results in a peak-to-peak angular range of relative movement between the pulley and the hub of less than about 1 degree. 
     
     
         5 . An endless drive arrangement as claimed in  claim 1 , wherein the damping torque is selected such that a peak-to-peak angular range of movement between the pulley and the hub results in at least a selected fatigue life for the isolation spring. 
     
     
         6 . An endless drive arrangement as claimed in  claim 1 , wherein the decoupler includes a one-way clutch that enables the hub to overrun the pulley. 
     
     
         7 . A decoupler for an endless drive arrangement which includes a crankshaft-driven pulley, an alternator pulley mounted to an input shaft of an alternator which operates at at least first and second switching frequencies, and an endless drive member that is positioned to transfer power from the crankshaft pulley to the alternator pulley, wherein first order vibrations are produced at the crankshaft, the decoupler comprising:
 a hub that is mountable to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis;   a pulley rotatably coupled to the hub, the pulley having an outer periphery that is adapted to engage the endless power transmitting element;   an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub;   a first friction surface operatively connected with the pulley;   a second friction surface operatively connected with the hub;   a biasing member positioned to exert a bias force between the first and second friction surfaces; and   a retainer engaging the biasing member to maintain the bias force,   wherein the second switching frequency is near a natural resonance frequency of the decoupler and the bias force between the first and second friction surfaces generates a damping torque during relative rotational movement between the pulley and the hub which attenuates said first order vibrations so as to reduce a tendency of the alternator to operate at the second switching frequency, thereby reducing a tendency of the alternator of transmitting vibration to the decoupler at frequencies near the natural frequency.   
     
     
         8 . A decoupler as claimed in  claim 7 , wherein the natural frequency is about 15 Hz. 
     
     
         9 . A decoupler as claimed in  claim 8 , wherein the second switching frequency is in the range of about 5 Hz to about 20 Hz. 
     
     
         10 . A decoupler as claimed in  claim 7 , wherein the damping results in a peak-to-peak angular range of relative movement between the pulley and the hub of less than about 1 degree. 
     
     
         11 . A decoupler as claimed in  claim 7 , wherein the damping torque is selected such that a peak-to-peak angular range of movement between the pulley and the hub results in at least a selected fatigue life for the isolation spring. 
     
     
         12 . A decoupler as claimed in  claim 1 , wherein the decoupler includes a one-way clutch that enables the hub to overrun the pulley. 
     
     
         13 . A method for operating an engine accessory drive which includes a crankshaft-driven pulley, an alternator pulley mounted to an input shaft of an alternator operable at a plurality of switching frequencies, and an endless drive member that is positioned to transfer power from the crankshaft pulley to the alternator pulley, the method including:
 installing a decoupler for transferring torque between the alternator shaft and the endless drive member, the decoupler including (i) a hub coupled to the alternator shaft, (ii) a pulley rotatably coupled to the hub, the pulley having an outer periphery that engages the endless power transmitting element, (iii) an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub, (iv) a first friction surface operatively connected with the pulley, and (v) a second friction surface operatively connected with the hub;   rotating the crankshaft so as to rotate the engine accessory drive;   generating a damping torque during relative rotational movement between the decoupler pulley and the decoupler hub by engaging the first and second friction surfaces with sufficient force to attenuate first order vibrations from the engine in order to reduce the tendency of the alternator to operate at a switching frequency near a natural frequency of the decoupler, thereby reducing a tendency of the alternator to transmit vibration to the decoupler at frequencies near the natural frequency.   
     
     
         14 . A method as claimed in  claim 13 , wherein the natural frequency is about 15 Hz. 
     
     
         15 . A method as claimed in  claim 14 , wherein the second switching frequency is in the range of about 5 Hz to about 20 Hz. 
     
     
         16 . A method as claimed in  claim 13 , wherein the damping results in a peak-to-peak angular range of relative movement between the pulley and the hub of less than about 1 degree. 
     
     
         17 . A method as claimed in  claim 13 , wherein the damping is selected such that a peak-to-peak angular range of movement between the pulley and the hub results in at least a selected fatigue life for the isolation spring. 
     
     
         18 . A decoupler as claimed in  claim 13 , wherein the decoupler includes a one-way clutch that enables the hub to overrun the pulley.