Tensioner with secondary damping

Abstract

A tensioner comprising a shaft, a base, a pivot arm pivotally engaged with the base, a pulley journalled to the pivot arm, a first spring urging a first damping member into a frictional engagement with the pivot arm, the first spring engaged with the base, the first damping member imparting a damping force greater in a first pivot arm direction than in a second pivot arm direction, and a second spring disposed in the pivot arm and urging a second damping member into a frictional engagement with a base surface, the base surface comprises an arcuate form having a radius that is variable from a minimum value to a maximum value.

Claims

1. A tensioner comprising: a shaft (2); a base (4); a pivot arm (11) pivotally engaged with the base; a pulley (12) journalled to the pivot arm; a first spring (5) urging a first damping member (6) into frictional engagement with the pivot arm, the first spring engaged with the base, the first damping member imparting a damping force greater in a first pivot arm direction than in a second pivot arm direction; and a second spring (9) disposed in the pivot arm and urging a second damping member (10) into frictional engagement with a base surface (42), the base surface comprises an arcuate form having a radius (R1) that is variable from a minimum value to a maximum value.

2. The tensioner as in claim 1, wherein the first spring is a torsion spring.

3. The tensioner as in claim 1, wherein the second spring is a compression spring.

4. The tensioner as in claim 1, wherein the second damping member and the second spring are disposed in the pivot arm.

5. The tensioner as in claim 4, further comprising a cover over the second damping member.

6. The tensioner as in claim 5, wherein the cover further comprises a brush portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 is a front perspective view of the tensioner.

(3) FIG. 2 is a rear perspective view of the tensioner.

(4) FIG. 3 is a rear plan view of the tensioner.

(5) FIG. 4 is a front exploded view of the tensioner.

(6) FIG. 5 is a rear exploded view of the tensioner.

(7) FIG. 6 is a chart of damping torque and spring force.

(8) FIG. 7 is a chart of damping torque versus arm angle.

(9) FIG. 8 is a detail of the spring cover.

(10) FIG. 9 is a plan view of the base.

(11) FIG. 10 is a profile of surface 42.

(12) FIG. 11 is a plan view of the first damping member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(13) FIG. 1 is a front perspective view of the tensioner. Tensioner 100 comprises pivot arm 11 which is pivotally mounted to base 4. Pulley 12 is journalled to pivot arm 11. Pulley 12 may engage a multi-ribbed belt or v-belt. Lugs 41 are used to attach the tensioner base to a mounting surface such as a vehicle engine (not shown). Lugs 41 receive fasteners such as bolts (not shown).

(14) FIG. 2 is a rear perspective view of the tensioner. Accordion spring 9 is disposed within cavity 110. Cavity 110 is within pivot arm 11. Spring 9 bears upon damping member 10. Spring 9 is a compression type spring with a spring rate of 177 N/mm by way of example. Damping member 10 is disposed in cavity 110. Damping member 10 is fully contained within pivot arm 4.

(15) An arcuate surface 101 of damping member 10 frictionally engages surface 42 of base 4. The frictional engagement between surface 42 and surface 111 damps an oscillatory movement of the pivot arm 11 relative to base 4. Cover 8 is attached to pivot arm 11 by screws 7. Screws 7 engage holes 111. Plug 1 is used to prevent contamination from entering the tensioner. Pivot shaft 2 acts as a pivot for pivot arm 11.

(16) FIG. 3 is a rear plan view of the tensioner. Pivot arm 11 engages stop 44 which then defines the limits of travel of arm 11. Arcuate surface 101 of damping member 10 frictionally engages surface 42 of base 4. Surface 42 has a cam profile, meaning, radius R1 of surface 42 smoothly varies from a lesser value to a greater value in a circumferential direction about the base, see FIG. 9 and FIG. 10. The cam profile of surface 42 has the effect of increasing or decreasing the damping force generated by damping member 10 depending upon the position of pivot arm 11 in its arc of pivotal movement.

(17) FIG. 4 is a front exploded view of the tensioner. Pivot arm 11 is press fit to shaft 2. Pivot bushing 3 is housed in base 4. Bushing 3 allows shaft 2 to pivot in base 4. One end 52 of spring 5 engages base 4. The other end 51 of spring 5 engages damping mechanism 6. Spring 5 is a torsion spring.

(18) Base 4 comprises arcuate surface 42 that is engaged by damping member 10. Surface 42 increases the amount of damping by damping member 10 as pivot arm 11 moves away from a belt by increasing the load from accordion spring 9 through compression of spring 9. Damping member 10 damps movement of pivot arm by engagement of the sides of member 10 with pivot arm cavity 110.

(19) Frictional surface 101 of damping member 10 engages surface 42 of base 4. The damping force generated by damping member 10 can be tuned by changing the spring rate of spring 9. Frictional force (damping) is the product of the normal force (N) and the coefficient of friction ().

(20) FIG. 5 is a rear exploded view of the tensioner. Frictional surface 61 of damping member 6 engages an inner surface 112 of arm 11. Damping member 6 imparts a damping force on arm 11 that is greater in a first pivot arm direction (loading) than in a second pivot arm direction (unloading), namely, the damping is asymmetric.

(21) Referring to FIG. 11, damping member 6 engages torsion spring 5 at end 51. FIG. 11 is a plan view of the first damping member. Damping member 6 further comprises an outer arcuate friction surface 61 for engagement with the pivot arm surface 112. Damping member 6 comprises first 80 and second 82 spring contact points for operatively connecting to spring end 51. Damping member 6 comprises a channel 62 for receiving spring end 51. Damping member 6 as shown has an arcuate form.

(22) Also shown are the forces acting on the damping member. A first damping force T.sub.L acts on a movement of the pivot arm 11 in a first direction away from a belt and a second damping force T.sub.un acts on a movement of the pivot arm in a second direction toward an endless member, the first damping force being greater than the second damping force.

(23) In the stationary position torsion spring 5 spring torque, T.sub.spr, creates reactions N1 and N2 on first and second contact points 80, 82. The other end of the spring engages the base 4 which is constrained from rotation, resulting in a torque. Damping mechanism 6 is substantially constrained in a predetermined position relative to the pivot arm by end 51.

(24) T.sub.L is greater than T.sub.un. is the coefficient of friction between surface 61 and surface 112. T.sub.L is a torque in the loading direction. T.sub.un is a torque in the unloading direction.

(25) FIG. 6 is a chart of damping torque and spring force. The effect of the first damping member 6 and the second damping member 10 is shown as the arm 11 is wound from an initial starting position to engagement with a belt, belt not shown.

(26) FIG. 7 is a chart of damping torque versus arm angle with and without the secondary damping mechanism. One can see the torque is significantly less for the single damping member (A) when compared to the hysteresis for the combination with the second damping member (B).

(27) FIG. 8 is a detail of the spring cover. Cover 8 comprises brush portion 81. Brush portion 81 acts as a seal to prevent entry of debris into cavity 110 and damping member 10. Portion 81 engages an exterior of base 4. Screws 7 engage holes 82.

(28) FIG. 9 is a plan view of the base. Surface 42 is an arcuate surface outwardly disposed on base 4. Radius R1 gradually increases from a minimum value at stop 44 to a maximum value as indicated by the arrow in a circumferential direction. The slope of surface 42 may vary from a minimum at the arrow to a maximum at stop 44 as well if required. The location of stop 44 is not key to the position of surface 42, it is simply referred to here as a convenient reference. Receiving portion 45 engages end 52 of spring 5, thereby preventing spring 5 from rotating about shaft 2.

(29) FIG. 10 is a profile of surface 42. For example, in the present embodiment surface 42 has a 4 mm increase in radius R1 over about 180. This profile is an example only and other profiles for surface 42 are possible to fit the needs of a user. Each profile will determine the damping characteristic contributed by damping member 10. Radius R1 is with respect to the pivot axis of the pivot arm. The pivot axis is the center of shaft 2.

(30) 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 and method without departing from the spirit and scope of the invention described herein.