Belt tensioner with spring actuated band brake damping

Abstract

A belt tensioning device having an improved damping mechanism for damping movements of the pivoted structure rotatably carrying the pulley with respect to the fixed structure. The damping mechanism includes a strap and a ring mounted on their respective fixed and pivoted structures and with respect to one another such that the strap engages the ring with a gripping action sufficient to provide (1) a relatively high resistance to frictional sliding movement between the strap and ring in one direction correspond to the direction of untensioning of the belt with the pulley and (2) a relatively low resistance to frictional sliding movement between the strap and ring in an opposite direction corresponding to the direction of belt tensioning. A spring is included in the mount for enabling the relatively high resistance and relatively low resistance to vary in response to the existence of predetermined vibrations such that the gripping action between strap and ring is relieved sufficient to enable movement therebetween in both directions to take place at substantially reduced resistance levels.

What is claimed is: 
     
       1. In a belt tensioning device comprising a fixed structure,   a pivoted structure mounted with respect to said fixed structure for pivotal movement about a first axis between first and second limiting positions,   a belt engaging pulley rotatably carried by said pivoted structure for rotational movement about a second axis parallel with said first axis,   spring means acting between the fixed and pivoted structures for resiliently biasing said pivoted structure to move in a direction away from said first limiting position toward said second limiting position with a spring force which decreases as said pivoted structure is moved toward said second position, and   curved surface means operatively associated with one of said structures,   elongated means operatively associated with the other of said structures having a central extent engageable with said curved surface means and connecting means outwardly of the opposite ends of said central extent,   means mounting said connecting means and said curved surface means on their respective structures and with respect to one another such that the central extent of said elongated means engages said curved surface means with a gripping action sufficient to provide (1) a relatively high resistance to frictional sliding movement between the central extent of said elongated means and said curved surface means in one direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction toward said first position and (2) a relatively low resistance to frictional sliding movement between the central extent of said elongated means and said curved surface means in an opposite direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction away from said first position,   said mounting means including said spring means for enabling said relatively high resistance and said relatively low resistance to vary together (1) in proportion to changes in said spring force and (2) in response to the existence of predetermined vibrations such that said gripping action between the central extent of said elongated means and said curved surface means is relieved sufficient to enable movement between the central extent of said elongated means and said curved surface means in both directions to take place at substantially reduced resistance levels.   
     
     
       2. A belt tensioning device as defined in claim 1 wherein said elongated means comprises a flexible strap. 
     
     
       3. A belt tensioning device as defined in claim 2 wherein said spring means comprises a torsional coil spring having one end connected with said pivoted structure, said mounting means including means for connecting the opposite end of said coil spring with the connecting means on one end of said strap and means for connecting the connecting means on the other end of said strap in fixed relation on said fixed structure. 
     
     
       4. A belt tensioning device as defined in claim 3 wherein said curved surface comprises an exterior cylindrical surface fixed with respect to said pivoted structure in concentric relation with respect to said first axis. 
     
     
       5. A belt tensioning device as defined in claim 4 wherein the central extent of said strap is greater than 180° of said exterior cylindrical surface and less than 300° thereof. 
     
     
       6. A belt tensioning device as defined in claim 4 wherein said exterior cylindrical surface is provided by a ring of resinous plastic fixed to said pivoted structure. 
     
     
       7. A belt tensioning device as defined in claim 4 wherein said strap is formed of steel. 
     
     
       8. A belt tensioning device as defined in claim 4 wherein said pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt on said belt engaging pulley, the gripping action force between the central extent of said strap and said exterior cylindrical surface acting on said pivoted structure in a direction extending through the bisector of the angle of engagement therebetween, loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       9. A belt tensioning device as defined in claim 1 wherein the pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt with said belt engaging pulley, the gripping action force between said elongated means and said curved surface means loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       10. In a belt tensioning device comprising a fixed structure,   a pivoted structure mounted with respect to said fixed structure for pivotal movement above a first axis between first and second limiting positions,   a belt engaging pulley rotatably carried by said pivoted structures for rotational movement about a second axis with said first axis,   spring means acting between the fixed and pivoted structures for resiliently biasing said pivoted structure to move in a direction away from said first limiting position toward said second limiting position with a spring force which decreases as said pivoted structure is moved toward said second position, and   curved surface means operatively associated with one of said structures,   elongated means operatively associated with the other of said structure engageable with said curved surface means,   means mounting said elongated means and said curved surface means on their respective structures and with respect to one another such that said elongated means engages said curved surface means with a gripping action sufficient to provide (1) a relatively high resistance to frictional sliding movement between said elongated means and curved surface means in one direction corresponding to the pivotal movement of said pivoted with respect to said fixed structure in a direction toward said first position which is greater than 70% of the instantaneous spring force and (2) a relatively low resistance to frictional sliding movement between said elongated means and said curved surface means in an opposite direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction away from said first position,   said mounting means including said spring means for enabling said relatively high resistance and said relatively low resistance to vary together (1) in proportion to changes in said spring force and (2) in response to the existence of predetermined vibrations such that said gripping action between said elongated means and said curved surface means is relieved sufficient to enable movement between said elongated means and said curved means in both directions to take place at substantially reduced resistance levels.   
     
     
       11. A belt tensioning device as defined in claim 10 wherein said elongated means comprises a flexible strap having a central extent engageable with said curved surface means and opposite ends extending outwardly from said central extent. 
     
     
       12. A belt tensioning device as defined in claim 11 wherein said spring means comprises a torsional coil spring having one end connected with said pivoted structure, said mounting means including means for connecting the opposite end of said coil spring with one end of said strap and means for connecting the opposite end of said strap in fixed relation on said fixed structure. 
     
     
       13. A belt tensioning device as defined in claim 12 wherein said curved surface means comprises an exterior cylindrical surface fixed with respect to said pivoted structure in concentric relation with respect to said first axis. 
     
     
       14. A belt tensioning device as defined in claim 13 wherein the central extent of said strap is greater than 180° of said exterior cylindrical surface and less than 300° thereof. 
     
     
       15. A belt tensioning device as defined in claim 13 wherein said exterior cylindrical surface is provided by a ring of resinous plastic fixed to said pivoted structure. 
     
     
       16. A belt tensioning device as defined in claim 13 wherein said strap is formed of steel. 
     
     
       17. A belt tensioning device as defined in claim 13 wherein said pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension action on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt on said belt engaging pulley, the gripping action force between the central extent of said strap and said exterior cylindrical surface acting through the bisector of the angle of engagement therebetween loading said sleeve bearing in a direction tending to balance the load. 
     
     
       18. A belt tensioning device as defined in claim 10 wherein the pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt with said belt engaging pulley, the gripping action force between said elongated means and said curved surface means loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       19. In a belt tensioning device comprising a fixed structure,   a pivoted structure mounted with respect to said fixed structure for pivotal movement above a first axis between first and second limiting positions,   a belt engaging pulley rotatably carried by said pivoted structure for rotational movement about a second axis parallel with said first axis,   spring means acting between the fixed and pivoted structures for resiliently biasing said pivoted structure to move in a direction away from said first limiting position toward said second limiting position with a spring force which decreases as said pivoted structure is moved toward said second position, and   curved surface means operatively associated with one of said structures,   elongated means operatively associated with the other of said structures having a central extent engageable with said curved surface means and connecting means outwardly of the opposite ends of said central extent,   means mounting said connecting means and said curved surface means on their respective structures and with respect to one another such that the central extent of said elongated means engages said curved surface means with a gripping action sufficient to provide (1) relatively high resistance to frictional sliding movement between the central extent of said elongated means and said curved surface means in one direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction toward said first position and (2) a relatively low resistance to frictional sliding movement between the central extent of said elongated means and said curved surface means in an opposite direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction away from said first position,   said mounting means including second spring means for enabling said relatively high resistance and said relatively for enabling said resistance to vary together in response to the existence of predetermined vibrations such that said gripping action between the central extent of said elongated means and said curved surface means is relieved sufficient to enable movement between the central extent of said elongated means and said curved surface means in both directions to take place at substantially reduced resistance levels.   
     
     
       20. A belt tensioning device as defined in claim 19 wherein said elongated means comprises a flexible strap. 
     
     
       21. A belt tensioning device as defined in claim 20 wherein said spring means comprises a torsional coil spring having one end connected with said pivoted structure, said mounting means includes means for connecting said second spring means with said fixed structure and with the connecting means on one end of said strap and means for connecting the connecting means on the other end of said strap in fixed relation on said fixed structure. 
     
     
       22. The device as defined in claim 21 wherein said curved surface means comprises an exterior cylindrical surface fixed with respect to said pivoted structure in concentric relation with respect to said first axis. 
     
     
       23. A belt tensioning device as defined in claim 22 wherein the central extent of said strap is greater than 180° of said exterior cylindrical surface and less than 300° thereof. 
     
     
       24. A belt tensioning device as defined in claim 22 wherein said exterior cylindrical surface is provided by a ring of resinous plastic fixed to said pivoted structure. 
     
     
       25. A belt tensioning device as defined in claim 22 wherein said strap is formed of steel. 
     
     
       26. A belt tensioning device as defined in claim 22 wherein said pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt on said belt engaging pulley, the gripping action force between the central extent of said strap and said exterior cylindrical surface acting on said pivoted structure in a direction extending through the bisector of the angle of engagement therebetween, loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       27. A belt tensioning device as defined in claim 19 wherein the pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt with said belt engaging pulley, the gripping action force between said elongated means and said curved surface means loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       28. In a belt tensioning device comprising a fixed structure,   a pivoted structure mounted with respect to said fixed structure for pivotal movement above a first axis between first and second limiting positions,   a belt engaging pulley rotatably carried by said pivoted structure for rotational movement about a second axis parallel with said first axis,   first spring means acting between the fixed and pivoted structures for resiliently biasing said pivoted structure to move in a direction away from said first limiting position toward said second limiting position with a spring force which decreases as said pivoted structure is moved toward said second position, and   curved surface means operatively associated with one of said structures,   elongated means operatively associated with the other of said structures engageable with said curved surface means,   means mounting said elongated means and said curved surface means on their respective structures and with respect to one another such that said elongated means engages said curved surface means with a gripping action sufficient to provide (1) a relatively high to frictional sliding movement between said elongated means and said curved surface means in one direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction toward said first position which is greater than 70% of the instantaneous spring force and (2) a relatively low resistance to frictional sliding movement between said elongated means and said curved surface means in an opposite direction corresponding to the pivotal movement of said pivoted structure with respect to said fixed structure in a direction away from said first position,   said mounting means including second spring means for enabling said relatively high resistance and said relatively low resistance to vary together in response to the existence of predetermined vibrations such that said gripping action between said elongated means and said curved surface means is relieved sufficient to enable movement between said elongated means and said curved surface means in both directions to take place at substantially reduced resistance levels.   
     
     
       29. A belt tensioning device as defined in claim 28 wherein said elongated means comprises a flexible strap having a central extent engageable with said curved surface means and opposite ends extending outwardly from said central extent. 
     
     
       30. A belt tensioning device as defined in claim 29 wherein said mounting means includes means for connecting said second spring means with said fixed structure and with one end of said strap and means for connecting the opposite end of said strap in fixed relation on said fixed structure. 
     
     
       31. A belt tensioning device as defined in claim 30 wherein said curved surface means comprises an exterior cylindrical surface fixed with respect to said pivoted structure in concentric relation with respect to said first axis. 
     
     
       32. A belt tensioning device as defined in claim 31 wherein the central extent of said strap is greater than 180° of said exterior cylindrical surface and less than 300° thereof. 
     
     
       33. A belt tensioning device as defined in claim 31 wherein said exterior cylindrical surface is provided by a ring of resinous plastic fixed to said pivoted structure. 
     
     
       34. A belt tensioning device as defined in claim 31 wherein said strap is formed of steel. 
     
     
       35. A belt tensioning device as defined in claim 31 wherein said pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt on said belt engaging pulley, the gripping action force between the central extent of said strap and said exterior cylindrical surface acting on said pivoted in a direction extending through the bisector of the angle of engagement therebetween, loading said sleeve bearing in a direction tending to balance the load. 
     
     
       36. A belt tensioning device as defined in claim 28 wherein the pivoted structure is mounted on said fixed structure by a sleeve bearing which is unequally loaded by the force of the belt tension acting on said pivoted structure in a direction extending through the bisector of the angle of wrap of the belt with said belt engaging pulley, the gripping action force between said elongated means and said curved surface means loading said sleeve bearing in a direction tending to balance the unequal belt load thereon. 
     
     
       37. A belt tensioner comprising, a fixed structure,   a pivoted structure,   a belt tensioning pulley mounted on said pivoted structure for rotational movement about a rotational axis,   said pivoted structure being mounted on said fixed structure for pivotal movement about a fixed pivotal axis parallel with said rotational axis between a first position wherein said belt tensioning pulley can be transversely aligned with a loosely trained belt and a second position,   spring means for resiliently biasing said pivoted structure in a direction toward said second position with a spring torque which varies as the position of the pivotal structure approaches said second position permitting manual movement of said belt tensioning pulley into said first position against such resilient bias so that upon manual release the resilient bias moves said belt tensioning pulley into an intermediate operating static equilibrium position in tensioning engagement with the belt wherein the spring torque is equal and opposite to a belt load torque which varies with the variation in the spring torque as the intermediate operation position approaches said second position due to belt elongation by maintaining the belt load force generally constant and varying the lever arm to said pivotal axis through which the belt load force acts, .Iadd.the spring torque at any intermediate operating position being provided by the instantaneous spring force at the intermediate operating position and the lever arm to the pivotal axis through which the instantaneous spring force acts, .Iaddend.   means for damping the pivotal movements of said pivoted structure as a result of dynamic belt load forces varying from the generally constant belt load force when the belt is moving,   said damping means including sliding friction surface means for establishing a damping torque resistance to pivotal movement of said pivoted structure in a direction toward said first position by virtue of the pressure of interengagement of said sliding friction surface means and the position of interengagement of said sliding friction surface means from said pivotal axis of a magnitude sufficient to prevent movement in said direction in response to dynamic increases in the constant belt load force .Iadd.within 70% of the instantaneous spring force.Iaddend., and   means operable in response to the application of vibratory forces to said sliding friction surface means independent of the dynamic belt load forces for instantaneously releasing the damping torque resistance to pivotal movement in said direction established by said sliding friction surface means so that instantaneous movement in said direction can take place which would otherwise be prevented.   
     
     
       38. A belt tensioner as defined in claim 37 wherein said sliding friction surface means establishes a damping torque resistance to pivotal movement of said pivoted structure in a direction toward said second position which is less than the damping torque resistance to pivotal movement in a direction toward said first position and said damping torque resistance releasing means is operable to instantaneously release the damping torque resistance to pivotal movement in the direction toward said second position. 
     
     
       39. A belt tensioner as defined in claim 38 wherein said damping means includes a band brake assembly including a ring operatively associated with one of said structures and a band operatively associated with the other of said structures, said band and ring having interengaging surfaces constituting said sliding friction surface means. 
     
     
       40. A belt tensioner as defined in claim 39 wherein said releasing means comprises a spring resiliently connecting one end of said band to said fixed structure, said spring being tuned to said independent vibratory forces. .Iadd. 
     
     
       41.  A belt tensioner as defined in claim 37 wherein said sliding friction surface means is operable to establish a damping torque resistance of a magnitude sufficient to prevent movement in said direction in response to dynamic increases on the constant belt load force within 200% of said instantaneous spring force. .Iaddend. .Iadd.42. A belt tensioner comprising, a fixed structure,   a pivoted structure,   a belt tensioning pulley mounted on said pivoted structure for rotational movement about a rotational axis,   said pivoted structure being mounted on said fixed structure for pivotal movement about a fixed pivotal axis parallel with said rotational axis between a first position wherein said belt tensioning pulley can be transversely aligned with a loosely trained belt and a second position,   spring means for resiliently biasing said pivoted structure in a direction toward said second position with a spring torque which decreases as the position of the pivotal structure approaches said second position permitting manual movement of said belt tensioning pulley into said first position against such resilient bias so that upon manual release the resilient bias moves said belt tensioning pulley into an intermediate operating static equilibrium position in tensioning engagement with the belt wherein the spring torque is equal and opposite to a belt load torque which varies with the variation in the spring torque as the intermediate operation position approaches said second position due to belt elongation by maintaining the belt load force generally constant and varying the lever arm to said pivotal axis through which the belt load force acts,   the spring torque at any intermediate operating position being provided by the instantaneous spring force at the intermediate operating position and the lever arm to the pivotal axis through which the instantaneous spring force acts,   interengaging sliding friction damping surfaces operatively associated with said fixed structure and said pivoted structure for damping the pivotal movements of said pivoted structure as a result of dynamic belt load forces varying from the generally constant belt load force when the belt is moving,   said interengaging damping surfaces presenting sliding friction therebetween sufficient to establish a damping torque resistance to pivotal movement of said pivoted structure in a direction toward said first position by virtue of the pressure of interengagement of said damping surfaces and the position of interengagement of said damping surfaces from said pivotal axis of a magnitude sufficient to prevent movement in said direction in response to dynamic increases in the constant belt load force within 78% of said instantaneous spring force,   said interengaging damping surfaces and the operative association thereof respectively with said fixed structure and said pivoted structure being operable in response to the application of vibratory forces to said damping surfaces through said fixed structure independent of the dynamic belt load forces to instantaneously release the damping torque resistance to pivotal movement in said direction established by said damping surfaces so that instantaneous movement in said direction can take place which   
     
     
        would otherwise be prevented. .Iaddend. .Iadd.43.  A belt tensioner as defined in claim 42 wherein the sliding friction between said interengaging damping surfaces is operable to establish a damping torque resistance of a magnitude sufficient to prevent movement in said direction in response to dynamic increases in the constant belt load force within 200% of said instantaneous spring force. .Iaddend. .Iadd.44. A belt tensioner as defined in claim 43 wherein said interengaging damping surfaces establish a damping torque resistance to pivotal movement of said pivoted structure in a direction toward said second position which is less than the damping torque resistance to pivotal movement in a direction toward said first position. .Iaddend. .Iadd.45. A belt tensioner as defined in claim 44 wherein said interengaging damping surfaces include a first damping surface on a ring operatively associated with one of said structures and a second damping surface on a band operatively associated with the other of said structures. .Iaddend. .Iadd.46. A belt tensioner as defined in claim 45 wherein said second damping surface is operatively associated with said fixed structure and the operative association is operable to effect said release. .Iaddend. .Iadd.47. A belt tensioner as defined in claim 46 wherein the operative association of said second damping surface with said fixed structure includes a fixed connection between one end of said band and said fixed structure, an opposite end of said band being connected with one end of a torsion coil spring constituting a said spring means, an opposite end of said torsion coil spring being connected to said pivoted structure. .Iaddend.