Over-running decoupler with torque limiter

Abstract

A method for producing an over-running decoupler that is configured to transmit rotary power between a rotary member and a hub. The over-running decoupler includes a one-way clutch having a clutch spring, a carrier that is coupled to the clutch spring and at least one spring that resiliently couples the carrier to the hub. The method includes: establishing a desired fatigue life of the at least one spring; establishing a design deflection of the at least one spring during resonance, wherein deflection of the at least one spring at the design deflection during resonance does not reduce a fatigue life of the at least one spring below the desired fatigue life; and preventing resonance in the over-running decoupler by controlling a maximum deflection of the at least one spring such that the maximum deflection is less than or equal to the design deflection.

What is claimed is: 
     
       1. A method for producing of operating an over-running decoupler that is configured to transmit rotary power between a rotary member and a hub, comprising: providing wherein the decoupler includes a one-way clutch having a wrap spring, and a carrier that is coupled to the wrap spring; providing and at least one isolation spring that resiliently couples the carrier to the hub; the method comprising: 
 controlling a maximum deflection of the at least one isolation spring, wherein below the maximum deflection during relative rotation is a first direction between the rotary member and the hub, the one-way clutch couples the rotary member and the hub, 
 and wherein upon reaching the maximum deflection during relative rotation in the first direction an a clutch feature, engageable with an end of the wrap spring to cause the wrap spring to coil more tightly, engages the end of the wrap spring engages a limit surface on one of the rotary member and the hub to prevent radial expansion of the wrap spring clutch to and limit torque transfer between the rotary member and the hub, 
 and wherein during relative rotation in a second direction between the rotary member and the hub, the one-way clutch decouples the rotary member and the hub. 
 
     
     
       2. The method of  claim 1 , wherein the maximum deflection is selected so as not to reduce a fatigue life of the at least one isolation spring below a desired fatigue life. 
     
     
       3. The method of  claim 1 , wherein the maximum deflection is selected at least partly based on a rotational inertia of at least one device that is driven through the over-running decoupler. 
     
     
       4. The method of  claim 1 , wherein the maximum deflection is selected at least partly based on a peak torque of one or more devices driven through the over-running decoupler. 
     
     
       5. The method of  claim 1 , further comprising establishing a peak drive torque of a device that is to receive rotary power from the over-running decoupler and wherein the maximum deflection of the at least one isolation spring is greater than a deflection of the at least one isolation spring when a torque having a magnitude that is equal to the peak drive torque is transmitted through the over-running decoupler. 
     
     
       6. A method for operating a drive system having an endless power transmitting element and an over-running decoupler, comprising:
 providing a hub, a rotary member and a one-way clutch between the hub and the rotary member, the one-way clutch comprising a carrier, and a wrap spring, the wrap spring having a first end, which is engaged to the carrier, the wrap spring being configured to be drivingly coupled to a radially inner surface of the rotary member; 
 providing at least one isolation spring disposed between the carrier and the hub; 
 operating the drive system under a first set of operating conditions to cause coupling of the wrap spring to the rotary member to facilitate transmission of torque through the over-running decoupler; 
 limiting torque transfer between the wrap spring and the rotary member in response to an increasing torque transfer resulting in a deflection of the at least one isolation spring by an amount that is greater than or equal to a predetermined spring deflection; and 
 operating the drive system under a second set of operating conditions to cause decoupling of the wrap spring from the rotary member to prevent transmission of torque through the over-running decoupler, 
 wherein the wrap spring has a second end on a side that is opposite the first end, the second end being contacted by one of the rotary member and the hub to coil at least a portion of the wrap spring radially inwardly away from a radially inner surface of the rotary member to thereby initiate the decoupling of the over-running decoupler when the amount by which the at least one isolation spring has deflected is greater than or equal to the predetermined spring deflection. 
 
     
     
       7. The method of  claim 6 , wherein the at least one isolation spring comprises a helical coil spring that is disposed concentrically about a rotational axis of the over-running decoupler. 
     
     
       8. The method of  claim 6 , wherein the rotary member comprises a pulley, a roller or a sprocket. 
     
     
       9. The method of  claim 6 , wherein the predetermined spring deflection is selected to provide the at least one isolation spring with at least a predetermined fatigue life. 
     
     
       10. A method for producing of operating an over-running decoupler that is configured to transmit rotary power between a rotary member and a hub, comprising: providing wherein the decoupler includes a one-way clutch having a wrap spring, and a carrier that is coupled to the wrap spring ; providing and at least one isolation spring that resiliently couples the carrier to the hub; the method comprising: 
 controlling a maximum torque of the at least one spring decoupler, wherein below the maximum torque during relative rotation in a first direction between the rotary member and the hub, the one-way clutch couples the rotary member and the hub, 
 and wherein upon reaching the maximum torque an end of the wrap spring engages a limit surface clutch feature on one of the rotary member and the hub to cause the wrap spring to coil more tightly to thereby prevent radial expansion of the wrap spring clutch to and limit torque transfer between the rotary member and the hub, 
 and wherein during relative rotation in a second direction between the rotary member and the hub, the one-way clutch decouples the rotary member and the hub. 
 
     
     
       11. The method of  claim 10 , wherein the maximum torque so as not to reduce the fatigue life of the at least one isolation spring below the desired fatigue life. 
     
     
       12. The method of  claim 10 , further comprising establishing a peak drive torque of a device that is to receive rotary power from the over-running decoupler and wherein the maximum torque that is transmitted through the over-running decoupler is greater than the peak drive torque. 
     
     
       13. The method of  claim 10 , wherein the maximum torque is selected at least partly based on a rotational inertia of at least one device that is driven through the over-running decoupler. 
     
     
       14. The method of  claim 10 , wherein the maximum torque is selected at least partly based on a peak torque of one or more devices driven through the over-running decoupler. 
     
     
       15. A decoupler, comprising:
 a rotary driving member;   a rotary driven member coaxially mounted with the driving member for relative rotary movement therewith;   a decoupling assembly extending between the driving member and the driven member, the decoupling assembly including an isolation spring and a one-way clutch mechanism, the isolation spring being a torsional spring having a first end engaging one of the driven and driving members and a second end engaging a carrier, and the one-way clutch mechanism including a wrap spring having a first end engaging the carrier, a second end, and a plurality of coils helically extending frictionally engaging only the other of the driven and driving members;   wherein one of the driving member and the driven member includes a clutch feature which, upon a predetermined degree of relative rotation between the driving and the driven members, is engageable with the second end of the wrap spring to cause the wrap spring to coil more tightly;   wherein, during relative rotation in a first direction between the driving member and the driven member, the wrap spring couples the rotary member and the hub, and wherein, during relative rotation in the first direction the isolation spring deflects, and wherein, when the isolation spring reaches a maximum deflection the clutch feature engages the second end of the wrap spring to limit engagement of the wrap spring with the other of the driven and driving members, thereby limiting torque transfer between the driving member and the driven member; and   wherein, during relative rotation in a second direction between the driving member and the driven member, the one-way clutch decouples the driving member and the driven member.   
     
     
       16. A drive system having an endless power transmitting element driving one or more accessories, comprising:
 an over-running decoupler including a hub connected to an accessory shaft, a rotary member driven by the endless power transmitting element, and an isolator disposed between the rotary member and the hub;   the isolator including an isolation spring, a carrier and a one-way clutch, wherein the isolation spring has a first end engaged with the carrier and the one-way clutch comprises a wrap spring having a first end engaged with the carrier, the wrap spring having a plurality of coils engaged only with and configured to be drivingly coupled to a radially inner clutch surface;   wherein the drive system operates under a first set of operating conditions to cause coupling of the wrap spring to the radially inner clutch surface to facilitate transmission of torque through the over-running decoupler, wherein torque transfer between the wrap spring and the radially inner clutch surface is limited in response to an increasing torque transfer resulting in a deflection of the at least one isolation spring by an amount that is greater than or equal to a predetermined spring deflection, said limited torque transfer being carried out through the wrap spring, which has a second end on a side that is opposite the first end, the second end being contacted by a feature on one of the rotary member and the hub to coil at least a portion of the wrap spring radially inwardly away from the radially inner clutch surface to thereby initiate the decoupling of the overrunning decoupler when the amount by which the at least one isolation spring has deflected is greater than or equal to the predetermined spring deflection; and   wherein the drive system is operated under a second set of operating conditions to cause decoupling of the wrap spring from the rotary member to prevent transmission of torque through the over-running decoupler.