MXPA98008145A - Ba tensioner - Google Patents

Abstract

The present invention relates to a tensioner for tensioning a power transmission belt and of the type with a pivot arm, a pulley fixed to the pivot arm for coupling the belt and receiving a load from the belt, a pivot in the form of a cantilevered kingpin member with a fixed end attached to the pivot arm, at least one pivot bearing, a base member supporting the pivot, a torsion spring operatively connected to bias the position of the pivot arm relative to the pivot member; base: friction the sliding surfaces to dampen the oscillating movements of the pivot arm, and wherein the improvement comprises: the base member has a bottom wall interconnecting a cantilevered post and a cantilevered annular base member which together define an annular cavity; the annular pivot member has an open end protruding into the annular cavity so that the annular pivot member is positioned within the annular base member; ote interposed between an outer surface of the annular pivot member and an inner surface of the annular base member, and the bearing have an internal surface that provides both bearing and friction bearing to dampen the oscillatory sliding movements of the annular pivot member with the connected pivot arm, and the spring has a restricted first end between the first and second locations at a free end of the post and a restricted second end between a third location at the free end of the annular pivot member and a fourth location juxtaposed to the Lower wall of the limb

Description

BAND TENSIONER DESCRIPTION OF THE INVENTION The invention relates to an automatic belt tensioner with a torsion spring and deflects the position of a pivot arm to which a belt-engaging pulley is fixed, but more particularly, the invention refers to a "Zed" type tensioner wherein a radial center plane for the pulley is laterally offset from an axis for a pivot about which the pivot arm swings. Automatic band tensioners have a pivot arm that moves pivotally relative to a base. A pulley is pivotally mounted to the pivot arm and a spring between the pivot arm and the base deviates the position of the pivot arm to place the pulley against an endless belt of a belt drive system to tension the belt at the time. that receives a load induced by the band. In some applications, it is preferred to have a bearing so that the pivot is in a common radial plane with the pulley to simplify or reduce the loads that must be carried by the bearing. Within this category of tensioners, there is a type that has a bearing that provides both bearing support and damping to the pivotal oscillatory movements of a pivot arm. Such a tensioner is described in United States Patent 4,723,934 (B 1 4,723,934). Another example of a tensioner having a bearing that provides both bearing support and damping for the pivotal movements of a pivot arm is described in U.S. Patent No. 5,478,285. An example of a "Zed" type tensioner is disclosed in U.S. Patent No. 4,473,362 wherein the tensioner has a pivot arm attached to a deviated annular pivot member that supports the pivot arm and swings on a pole insured to a base. A torsion spring is used in which one end of the spring is constrained at two points by a connection to the pivot arm, and the other spring end is constrained by a connection to the base and a connection by means of a damping mechanism that it includes a spring coil that presses against a bushing which in turn exerts pressure against the annular pivot member. A bushing type bearing positioned radially inwardly of the spring and positioned between the post and the annular member has a bearing surface supporting the annular member with its interconnected pivot arm. The pivot bearing in connection with the damping mechanism cushions the oscillating movements of the pivot arm. A problem with this type of tensioner is that the amount of damping available is limited in some way because the pivot bearing and the damping mechanism are located radially inward of the torsion spring and operate at a radius that is substantially less than the length of the pivot arm. Another example of a "Zed" type tensioner is described in United States Patent Application No. 08 / 828,216 and has: a pivot arm, a pivot pin connected on one side to the pivot arm, a member of generally "trough tube" shaped base holding at least one low friction bearing supporting the pivot pin, a torsion spring with one end restricted and fixed to the pivot arm and another end restricted and fixed to the base . The tensioner has a damping mechanism wherein one end of the spring is operatively connected to a damping mechanism that includes a shoe with an external friction surface that rose against an inner wall of the base member to effect damping. A feature associated with the tensioners of this type is that substantially all damping is by means of the damping mechanism; it degenerates very little cushioning in pivot bearing in response to a load of the belt received on a pulley. According to the invention, a tensioner is provided which is useful in front end accessory belt drive systems with V-shaped ribs used in automotive applications. The belt tensioner of the invention is of the "Zed" type with: a pivot arm, a pulley fixed to the pivot arm for coupling the belt and receiving a load of the belt, a pivot in a shape of an annular pivot member cantilever with a fixed end attached to the pivot arm, at least one pivot bearing, a base member supporting the pivot, a torsion spring operatively connected between the pivot arm and the base and wherein both the bearing support as the damping for the oscillatory movements of the pivot arm is provided first by means of a pivot bearing. The base has a bottom wall from which a draw-off post and a draw-off annular base member which together define an annular cavity extend. The annular pivot member is positioned within the annular base member with the pivot bearing positioned therebetween. A wide position is achieved between the reactive force of the belt load and the reactive force of the spring load while the torsion spring is operatively connected or "latched" to deflect the position of the pivot arm relative to the base. A first spring end is restricted between the first and second places at an open end of the pole. A second end of the spring is constrained between a location at the free end of the annular pivot member and the location juxtaposed with the lower wall of the base member.

The advantage of the "hooking" of the spring is that it provides a wide position for the reactive forces effected by the bearing and results in wear of the bearing which does not substantially inhibit the alignment of the pulley over the operating life of the tensioner. In addition, the "engaged" spring is such that the force of the belt received in the pulley and a spring force in the annular pivot member combine to provide a damping force that makes the pivot bearing reaction. Another advantage of the invention is that the pivot bearing is located radially outside the torsion spring to provide a high percentage of damping. These and other objects or advantages of the invention will be apparent after reviewing the drawings and the description thereof wherein: Figure 1 is a cross-sectional view of the tensioner of the invention taken along line 1-1 of Figure 2; Figure 2 is a partial schematic view taken in the S-S direction and the cross-sectional view along the line 2-2 of Figure 1 illustrating various components and forces associated with the tensioner; and Figure 3 is a partial schematic view taken in the S-S direction and the cross-sectional view taken along the line 3-3 of Figure 1 illustrating various components and forces associated with the tensioner. With reference to Figures 1-4, a tensioner 10 with a pulley 12 is typically used in conjunction with a belt driving system 14 that includes a band 16 constrained by various pulleys (not shown) and a tensioner pulley 12. The pulley 12 couples the band 16 to adjust the tension of the band. When coupled with the band, the pulley 12 receives a load of the band in the form of the tension TI, T2 of the band of the intervals 18, 20 of the adjacent band. The tension TI, T2 of the band (or load) is combined to generate a component BF of force along the band, along a bisector of an angle formed between the band intervals 18, 20 and acting symbolically at point A. The web force component acting at point A, when axially deviated from the pin 22 of the tension pin, generates a complicated internal load including forces and moments. Tensioners with such axial deviation are known as "Zed" type tensioners. The tensioner 10 is of the mechanical type and includes a base member 24, a torsion spring 26, a pivot arm 28 that oscillates about the pivot axis 22, and a ball bearing 30 fixed to the pivot arm for pivotally mounting the pulley 12.

The base member 24 has a lower wall 32 from which a lifting post 34 and a lifting-based ring base member 6 which together define an annular pocket 38 extend. The base member 24 has an open end 40 and is oriented so that its bottom wall 32 and the open end 40 face toward the pivot arm 28. One or more ears 42 can be integrally formed with bolt receiving holes 44 of the base member and used to secure the tensioner with fasteners to a motor (not shown) to be part of the belt drive system 14. A pivot in the form of an annular pivot member 46 has a fixed end 48 formed as an integral part of the pivot arm 28. An open end of the annular pivot member protrudes into the annular recess 38 so that the annular pivot member it is placed inside the annular base member 36. At least one pivot bearing 52 preferably of the polymeric type is interposed between an outer surface 54 of the annular pivot member and an inner surface 56 of the annular base member. The bearing contains an internal surface 58 that provides both bearing support and friction for damping for the oscillatory sliding movements of the annular pivot member with the pivot arm connected. The pivot bearing, the annular member and the annular base member have any complementary shapes with respect to each other such as cylindrical or tapered. A second bearing 60 preferably also of the polymeric type, it is placed on the post 34. Optionally, the pivot bearing and a second bearing can be formed together as a mixed bearing which is generally in the form of a "tundish tube". An extension of the pivot arm 28 and the integral fixed end 48 can include a flat radial plate 64 extending circumferentially juxtaposed with a wall 66 of the open end 48 of the annular base member 36. Optionally, the pivot bearing includes a radial flange 68 positioned between the radial planar plate of the pivot arm and the wall of the annular base member. The pivot arm 28 is secured to the lift post 34 of the base member 24 by a fastener such as a bolt 70 or a flanged or stacked washer. The bolt 70 extends through a hole 72 formed in the pivot arm 28 where the hole has a larger diameter than an external diameter of the fastener to secure a clearance 74 between the two parts. As it is assembled, the radial flange 68 functions as a thrust washer and dust cover between the base and the pivot arm and also serves to help maintain a radial alignment of the pivot arm relative to the base member. A sealing disc 75 between the bolt head and the pivot arm 'acts as a thrust washer carrying an axially extending load generated by the torsion spring on the assembly. The axially extending load helps to improve the spring tail YES, S2, S3 hooks. The pulley 12 is rotatably mounted to the pivot stroke 28 by means of a ball bearing 30 which is placed on a journal 67 formed of the pivot arm 28. The ball bearing 30 is retained in the journal by a fastener such as a pin 76 and a washer 78. Optionally, a stop for limiting the annular movements of the pivot arm can be included and formed between the base member and the pivot arm which are best illustrated in Figure 3. An arched outward cut 80 it is formed in the annular pivot member leaving the radial walls 82, 84 formed comps of the radial wall. A projection 86 formed of the lower wall 32 of the base member protrudes in the arcuate outward cut. The projection 86 in conjunction with the stops 82, 84 formed of the annular pivot member limits the oscillatory movements of the pivot arm. The torsion spring is placed in the annular cavity 38 between the lift post 34 and the base member 36 and is operatively connected to deflect the position of the pivot arm relative to the base member.

With more particular reference to Figures 1 and 2, a first end 88 of the spring 26 has a tail 90 bent radially inward which extends into a slot 92 formed in the free end of the lift post 34. A pin 94 is placed in a second slot 96 formed in the free end of the lifting post 96. A first end of the spring is restricted between a first SI in the slot 92 and a second place S2 in the pin 94. All the loads of the springs in the places SI, S2 are carried directly by the lifting post 34 of the base member 24. With reference to Figures 1 and 3, a second end 98 of the spring 24 has a tail 100 bent radially outwardly extending in a radial groove 102 formed in the free end of the annular pivot member 46. A bushing 104 is placed over the second bearing juxtaposed with the lower wall 32 of the base member. The second end of the spring is constrained between a third place S3 at the free end of the annular pivot member and a fourth place S4 in the bushing juxtaposed to the lower wall of the base member. The load from the end of the spring in the place S4 is transmitted to the bushing 104, then to the second bearing 60, and then to the lifting post 34 of the base member. The tail 100 of the second end of the spring imparts a spring force FS to the annular pivot member II at some point B that corresponds to the place where the spring is restricted in place S3. The band force imparted at point A and the spring force imparted at point B have the same general direction and are carried by the annular pivot member. The pivot bearing 52 supports the annular pivot member whereby the force of the band BF and the spring force FS are balanced by a reaction force N. There is friction between the sliding surface of the annular pivot arm member and the Pivot arm bearing that acts to dampen the oscillating movements of the pivot arm. The sliding surfaces operate at a mean radius DR which may be greater or less than a radius PR of the pivot arm. Both the pivotal movements and the damping are carried out by means of the pivot bearing. There is a small amount of damping effected between the bushing 104 and the second bushing 60. As illustrated more particularly in FIG. 3, the location of the web force BF moves from point A to point A 'in conjunction with the angular movements X of the pivot arm. However, there is very little change in the direction of the BF band force. The annular pivot member moves angularly with angular movements of the pivot arm, and therefore, the groove of the spring moves to a new location 106 as represented by the dotted lines in the angle Y (which is equal to the angle X ). The location of the spring force FS moves from point B to point B '. The force FS imparted by the spring at point B changes direction as it moves to point B 'and remains substantially perpendicular to the slot at its new location 106. The web force BF and the spring force FS are They combine to effect a damping force in the bearing that is balanced by the reaction force N. The large diameter DR of the bearing (ie it forms outside the torsion spring) together with its length suppresses wear and misalignment of the pulley. The foregoing description was made for the sole purpose of illustrating and is not intended to limit the scope of the invention which will be determined by the appended claims.

Claims (7)

1. A tensioner for tensioning a power transmission belt and of the type with a pivot arm; a pulley fixed to the pivot arm to engage the band and receive a load from the band; a pivot in the form of a member of the draw-off annular pivot with a fixed end attached to the pivot arm; at least one pivot bearing; a base member that supports the pivot; a torsion spring operatively connected to deflect the position of the pivot arm relative to the base member; fiction between sliding surfaces to dampen _ the oscillating movements of the pivot arm; and wherein the improvement comprises: the base member has a lower wall interconnecting a lift post and a draw-off annular base member which together define an annular cavity; the annular pivot member has an open end protruding into the annular cavity so that the annular pivot member is positioned within the annular base member; the pivot bearing interposed between an outer surface of the annular pivot member and an inner surface of the annular base member, and the bearing have an inner surface that provides both bearing and friction bearing to dampen the oscillating sliding movements of the pivot member Cancel with the pivot arm connected; and the spring has a restricted first end between the first and second locations at a free end of the post and a second restricted end between a third location at the free end of the annular pivot member and a fourth location juxtaposed in the lower wall of the limb member. base. The tensioner according to claim 1, characterized in that the second end of the spring is retained in a position on the annular pivot member in a circumferential location so that a force imparted by the spring to the third place in combination with a force The band generated by the band load generates a reaction force in the bearing to effect damping. The tensioner according to claim 1, characterized in that it includes the post having a portion of the substantially cylindrical surface juxtaposed to the bottom wall, a post bearing positioned on the post, and a bushing placed on the post bearing juxtaposed to the second end and a coil of the spring, and wherein the cylindrical surface, the post bearing and the spring coil define the fourth place juxtaposed to the bottom wall of the base member where the second end of the spring is restricted. The tensioner according to claim 3, characterized in that the pivot bearing and the post bearing are formed together as a mixed element which is generally in the form of a tundish tube. The tensioner according to claim 3, characterized in that the pivot bearing, the annular pivot member and the annular base member are additionally tapered in relation to one another. The tensioner according to claim 3, characterized in that the pivot arm has a radial flat plate extending in a circumferential shape juxtaposed to the open end of a wall of the annular base member, and the pivot bearing includes a flange radial placed between the flat radial plate of the pivot arm and the open end wall of the annular base member. The tensioner according to claim 3, characterized in that the base member includes a projection extending from the base wall and in an arched groove in the open end of the annular pivot member, the groove and projection together restrict the movement of the pivot arm to a predetermined angular amount.