MXPA98002222A - Ba tensioner - Google Patents

Abstract

The present invention relates to a tensioner for tensioning a power transmission belt and of the type having a pivot arm, a pulley fixed to the pivot arm for coupling the belt and receiving a belt load, a pivot pin fixed to the pivot arm, a base member which generally has a tubular pan shape with an internal cantilevered wall having an orifice, an outer wall, a receiving pocket of the annular spring defined between the inner and outer walls, and a lower wall that interconnects the inner and outer walls and faces an open end, at least one bushing that supports the pivot pin, a spring operatively connected between the pivot arm and the base member, a damping mechanism, and where the improvement comprises: the base member oriented with its bottom wall juxtaposed to the pivot arm and with the open end of the base member facing away from the pivot arm; pivot r connected at a first end and protruding from one side of the pivot arm and connected near n second end in at least one point of the resor

Description

BAND TENSIONER DESCRIPTION OF THE INVENTION The invention relates to a tensioner with a torsion spring that deflects the position of a pivot arm to which a belt coupling pulley is fixed, but more particularly, the invention relates to a tensioner of type "Zed" in which a central radial plane for the pulley deviates laterally from an axis for a pivot pin and around which the pivot arm oscillates. 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 an eccentric cylindrical member that supports the pivot arm and rotates about a secured pivot to a base. A torsion spring is used where one end of the spring is stopped at two points by a connection to the pivot arm, and the other spring end is stopped by a connection at the base. A sleeve of the individual socket type on the pivot has a bearing surface that supports the cylindrical member connected to the pivot arm. A housing surrounds and defines a ring for the spring. The stacked annular walls of the spring housing of the tensioner together with a cylindrical damping mechanism, located radially inward of the spring, tends to make the tensioner housing bulky for a tensioner that imparts moderate tension (e.g. 22.7 kg ( 50 lbs)) and damping (for example 30-40%) in a band of propulsion power transmission per band of the front end fitting. Another problem associated with the tensioner '362 is that unequal pressure loads introduced into an individual bearing surface of the bushing can result in uneven wear of the bushing and misalignment of the concurrent pulley. A tensioner design that reduces volume while providing comparable band tension capacity (eg, 22.7 kg (50 lbs) band tension) with a comparable pivot arm length, is described in the United States Patents. United Nos. 5,449,328 and 5,458,541 and having the same assignee (INA Walslager Schefseffler Kg). The "INA" tensioners are more compact than the patent tensioner -'362 in that the INA tensioners exclude the requirement of sharp annular walls in a spring housing. A representation of the INA tensioners as described in the '328 and' 541 patents is represented herein by means of Figure 6. With reference to Figure 6, the prior art tensioner includes a pivot arm, a pivot pin connected on one side of the pivot arm, a base member of generally "tubular pan" shape with two ferrules supporting the pivot pin, a disk-type countermeasure mechanism, and a torsion spring with a end stopped at two points by means of the pivot arm, and an opposite end stopped at two points by the base. The points to stop the ends of the torsion spring are not used together with a mechanism to generate a force to help balance a hub load that must be supported by the bushings. The base member includes a cantilevered inner wall, a cantilevered outer wall and a bottom wall interconnecting the inner and outer walls. An annular spring receiving cavity is defined between the external and internal walls. The lower wall of the base faces an open end of the base member located next to the pivot arm. With such an arrangement, the pivot pin is supported in a cantilevered manner by the internal wall of the base and wherein the lower wall, supporting the internal cantilevered wall, is spaced at a maximum distance away from a central radial plane of the pulley. The separation of the lower wall deteriorates the stiffness of the inner wall to support the pivot pin and maintain good alignment of the pulley. The restricted connection of the ends of the spring to the pivot arm and the base results in a bearing load that allows the pivot to "wiggle" or misalign with the wear of the bearing because the loads relative to the bearing surface are in directions opposite and are significantly greater than a load imparted on the pulley by a taut band. Although the INA tensioner is of a compact design, optimal for a reduced volume, also presents inherent rigidity and alignment problems due to: the orientation of the base with its open end facing the pivot arm and its lower wall separated at a maximum distance from the pulley; the spring engages at one end with two points directly stopped by the pivot arm and at the other end with two points directly stopped at the base; and a flat disk damping mechanism that operates together with a compression force generated by the torsion spring that allows the axial movement of the pulley with the wear of the disk and therefore the misalignment of the pulley. In response to the force BF 'of the belt on the pulley, the separated bushings are BL1, BL2 loaded in opposite directions. As the bushings wear out, the pivot pin will wiggle with the sliding of the concurrent pulley. As the friction surface of the disc type damping mechanism wears, the pulley will move in a direction PM resulting in further misalignment of the pulley.

According to the invention, a tensioner is provided which is particularly useful in front-end V-cranked-end attachment propulsion systems used in automotive applications where the minimum volume of the tensioner combined with maximum alignment of the tensioner is important. pulley on the expected life of the tensor. The band tensioner of the invention is of the "Zed" type with: a pivot arm, a pivot pin connected to one side of the pivot arm, a base member of generally "tubular tub" shape that holds at least a bushing supporting the pivot pin, a torsion spring with one end stopped and fixed to the pivot arm and another end stopped and fixed to the base. A base member includes a cantilevered internal wall, a cantilevered outer wall and a bottom wall interconnecting the inner and outer walls. The base member is oriented with its bottom wall juxtaposed to the pivot arm to provide rigidity to support the pivot pin. The pivot pin has one end connected to and protrudes from one side of the pivot arm. The pivot arm has another end spaced apart from the pivot arm to which a second spring end is connected. In a preferred embodiment, the second end is operatively connected to a damping mechanism that produces a reaction force generally in the same direction as the web force introduced into the pulley by a web tensioned by a web propulsion system. An advantage of the invention is that a translated volume tensioner having improved stiffness for supporting a pivot pin is provided and has the option of including a spring force that is responsive, which can be oriented to be generally of the same direction as the load of hub in order to generally balance a load on the separate bearings for good alignment of the pulley. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects or advantages of the invention will be evident, after reviewing the drawings and the description thereof where; Figure 1 is a cross-sectional view of the tensioner of the invention taken along the line 1-1 of Figure 2: Figure 2 is a partial schematic view illustrating various components and forces associated with the tensioner, the Figure 3 is a partial cross-sectional view similar to Figure 2 illustrating a damping mechanism and taken along a line 3-3 of Figure 1, but where the view is rotated to have the same orientation of the components of Figure 2; Figure 4 is a view taken along line 4-4 of Figure 1; Figure 5 is a view similar to Figure 1, but showing an alternative embodiment of the invention; Figure 6 is a cross-sectional view of a prior art tensioner; Figure 7 is a view similar to that of Figure 1, but showing another embodiment of a tensioner of the invention; Figure 8 is a view taken along line 8-8 of Figure 7; and Figure 9 is a view taken along line 9-9 of Figure 7, but where the view is rotated to have substance] in the same orientation as Figure 3. Referring to Figures 1- 4, a tensioner 10 with a pulley 12 is typically used in conjunction with a belt propulsion system 14 which includes a belt 16 stopped by several pulleys (not shown) and which includes the pulley 12 of the tensioner. The pulley 12 of the tensioner couples the band 16 to adjust the tension of the band. When coupled with the band, the pulley 12 of the tensioner receives a band load in the form of the band tension TI, T2 of the adjacent sections 18, 20 of the band. The tension TI, T2 of band (or load) is combined to generate a component BF of band strength along a bisector or an angle formed between the band sections 18, 20. The band strength component, by axially deviating from a pivot pin 22 of the turnbuckle, generates a complicated hub load that includes forces and moments that are symbolically represented (ie not specifically) by the arrow HL. The tensioner 10 is of the mechanical type and includes a base member 24, a torsion spring 26, a pivot arm 28 connected to the pivot pin and a ball bearing 30 attached to the pivot arm and rotatably mounted to the pulley 12. The base member 24 with its usual form of "tubular batten" has an internal cantilevered wall 32 having a hole 34, an external cantilevered wall 36, and a lower wall 38 interconnecting the internal and external walls. The base member 24 is oriented in such a manner that its lower wall 38 is juxtaposed with the pivot arm and with an open end 40 facing away from the pivot arm. The lugs 42, 44 with the bolt receiving holes 46 can be formed integrally from the base member and are used as a means for securing the tensioner with the bolts 47, 48 to a motor (not shown) to be part of the belt propulsion system. . The pivot pin 22 is connected at one end 50 to the pivot arm 28. In the preferred embodiment shown, the pivot pin is formed as an integral part of the pivot arm. Optionally, a labyrinth seal 52 is formed of a circumferential portion of the pivot arm 54 and an adjacent circumferential portion 56 of the bottom wall. The pulley 12 is rotatably mounted to the pivot arm 28 by means of the ball bearing 30 on a projecting arrow 58 formed of the pivot arm. The bearing is retained on the projecting arrow by means of a bolt 60. The bushings 62, 64 are preferably of the polymeric type and are located in the hole 34 of the inner wall to support the pivot pin with the fixed pivot arm. The bushings may include a flange 66 as a thrust bearing between the bottom wall and the pivot arm. Optionally, an individual bushing can be used to support the pin of the pivot wherein the bushing has two spaced apart surfaces as shown hereinafter in Fig. 5. A cover 68 is attached to a second end 71 of the pivot pin by means of a threaded bolt or a serrated fastener 70 as shown. The torsion spring 26 is located in a receiving cavity 72 of the annular spring defined between the internal and external walls 32 of the base member. As illustrated in Figure 4, the base member 24 has two separate points 74, 76 formed from the projections of the base where the point 74 is formed from the inner wall 32 and the point 76 is formed from the outer wall. 36 to restrict a first end 78 of the spring.

Optionally, a retainer for limiting the angular movements of the pivot arm may be included and formed between the base member and the pivot arm which is better illustrated in Figure 4. An arcuate groove 82 or notch is formed in the base member in a position juxtaposed to the pivot arm. A projection 84 formed of the pivot arm protrudes into the slot. The projection 84 together with the detents 86, 88 formed from the base at the ends of the slot limits the oscillating movements of the pivot arm. The projection 84 is shown positioned against the retainer 86 formed from the base and in dotted form against the detent 88. A second end 90 of the spring 26 is constrained or retained at one or more points at or near the second end 71 of the pivot pin. In the embodiment illustrated by Figure 3, the second end 90 of the spring 26 is constrained at a point near the second end of the pivot arm by means of the cover 68 where at least one point 92 or projection is formed of the cap. A second point for restricting the end of the spring may be formed from the outer wall 36 such as to form a point similar to the base 76, but in the preferred embodiment, the second spring restriction point is by means of a damping mechanism which includes a shoe 94 with an external arcuate friction surface 76 which couples an additionally internally arcuate surface 98 formed from a portion of the inner wall of the external wall of the base member. Optionally, the shoe has a liner 100 that defines the friction surface 96 and is attached to the shoe during the molding of the shoe or by the teeth 102 that conform to the formed complementary portions of the shoe. The shoe has a ramp surface 106 which couples a ramp surface 108 of a projection 110 formed of the lid. A second sliding surface 112 formed from the shoe defines a second contact point for restricting the end 90 of the spring. A closure member 114 such as one made of plastic material, it is fixed to the open end 40 of the base member to seal the damping mechanism from the contaminants. With reference to Figure 2, the shoe 94 imparts a reaction force 116 to the projection 110, and the spring end 90 imparts a reaction force 118 to the point of the spring contact 92 of the cap. The two forces 116, 118 are combined in a resultant force RF which is imparted to the end 71 of the pivot pin and has a direction which is generally the same as that of the web force BF. The resultant force, having the same general direction as the band force, can be used to optimize the charges to the bushes for good alignment of the pulley as discussed hereinafter.The damping mechanism including the shoe 94 moves the same number of degrees with respect to the annular wall of the base member as the pivot arm. The maximum angular movement of the damping mechanism is controlled by means of the arcuate groove 82 and the detents 86, 88, which is approximately plus or minus 25 °. However, and during use, the pivot arm only needs to move more or less an angle A (Figure A) which for most purposes, is within plus or minus 20 degrees. Of course, as the damping mechanism moves, the resultant force also changes the direction substantially in the same amount. Referring to Figure 5, another embodiment of the tensioner 120 of the invention is illustrated. The tensioner has substantially the same arrangement of parts as that described above together with Figures 1-4. The main difference relates to the configuration of the pivot pin 120 which is tapered to eliminate a machining operation and an internal wall 122 having a corresponding taper with a tapered bore 124 wherein a tapered bushing 126 having a push tab 128 is inserted. The bushing 126 has a notch 130 that divides the bushing into two separate bearing surfaces 132, 134. One of the aspects of the invention is that torsion springs are operated which have a wide spring rate such that they induce high band forces (i.e. up to 31.78 Kg (70 lbs)) to a power transmission band. When higher web tensions are required, an elongate pin 136 can be used to secure the cover 68 to the pivot pin 120 and improve the bending moment of the tapered pin. The use of a longitudinally grooved pin has the advantage of allowing the cap to be rotated to a desired angular position to adjust the torsion spring rate within a small tolerance band of, for example, approximately 1,362 kg (3 pounds) ). The toothed pin is pressed into position, which cuts complementary ridges on the cover and the hole. The operation of the tensioner of Figure 5 is substantially the same as that of Figure 4. Therefore, the operation of the tensioner is shown primarily together with Figure 5 where the pivot arm has been rotated to its tension position. band for coupling with a power transmission band (not shown). A band introduces a BF band force to the pulley and the damping mechanism introduces a resultant RF reaction force that substantially has the same direction as that of the band force. In response to this, the bearing surfaces 132, 134 support the pivot pin with two bearing forces of BF1, BF2 that are substantially in the same direction, but opposite that of the web force and the reaction force. The bearing surfaces can be sized for an average bearing pressure such that they wear radially and substantially at the same speed. With such an arrangement of the component parts, the pulley has a good alignment for a long period of time. In other words, the wear of the bearings is such that they will not allow the pivot pin to wiggle for a long period of time. The support for the pivot pin of the tensioner of the invention has greater rigidity than that of a comparable prior tensioner because the lower wall of the base member supporting the inner wall (ie the support wall of the pin of pivot) deviates as much as possible from a radial center RP plane for the pulley for a Zed type tensioner. As illustrated in Figure 5, the bottom wall 138 is located from the plane RP. of radial center for the pulley, at approximately the same distance SB from where the spring is connected to the base member. A radial center BFC plane for the bearing forces (ie the midpoint between the bearing forces BF1 and BF2) is located at a distance PB from the radial plane. The other end of the spring is connected to the pivot / cover arm at a distance SP from the radial plane. As is easily determined from Figure 5, the ratio of SB to PB is less than one and the relation SP to PB is greater than one. In contrast, the prior art has opposite relationships and they reflect a different construction and stiffness. With reference to the prior art tensioner of Figure 6, the bottom wall is located from a radial center plane RP 'for the pulley, approximately the same distance SB' where the spring makes contact with the bottom wall. A radial center BFC plane for a midpoint for the bearing load BL1 and BL2 is located at a distance PB 'from the radial plane RP' for the pulley; and the spring is connected to the pivot arm at a distance SP 'from the radial plane of the pulley. As can easily be determined from Figure 6, the ratio of SB 'to PB' is greater than one and the ratio of SP 'to PB' is less than one. An additional embodiment of the tensioner 142 of the invention is described in Figures 7-9. The tensioner has substantially the same arrangement of parts as described in conjunction with Figure 1-6 except for a cover, the provision of a second damping spring and a constant damping provision produced together with the second spring. With reference to Figures 7 to 8, the tensioner 142 has a torsion spring 144 for biasing the position of the pivot arm 28, a cover 146, a cushion spring 148, a washer 150 and an elongate fastener 152. The torsion spring 144 is restricted to the base member 24 at two separate points and in the same manner as illustrated in Figure 4 for the tensioner of Figure 1. However, the other end 154 of the spring 144 is restricted in two. dots 156-158 which are projections formed from a first side 147 of the lid 146 as illustrated in Figure 8. With reference to Figure 9, the damping spring 148 has an end 160 constrained at two points 162, 164 formed as projections on a second side 149 facing opposite to the lid 146. A second end 166 of the damping spring 148 is constrained at a point 168 or a formed projection of the lid. The second end of the spring is restricted at a second point by means of a damping mechanism similar to that described for Figure 3 and with the same parts that includes a shoe 94 with an external friction surface 96 that couples an arcuate surface 98 in addition internal that is in a portion of the inner wall of the base member. The shoe has a ramp surface 106 which couples a ramp surface 170 formed of the lid and a sliding surface 112 which defines a second point of the spring contact to restrict the end 170 of the spring.

The orientation of the damping mechanism of Figure 9 is arranged to be substantially in the same circumferential position as the damping mechanism of Figure 3 so as to provide a similar reaction RF 'force which is oriented to be substantially the same as that illustrated in Figure 5. With such orientation, the reaction force of the damping spring is used to substantially balance the loads of the web force as it is effected by the bushing 172 substantially in the same manner as illustrated together with the Figure 5. However, the reaction force RF 'remains a constant force because the damping spring 148 exerts a constant force on the shoe. In other words, the damping force does not vary with the angular position of the pivot arm in the manner that is exemplified by the tensioner in Figure 5.. Figures 7-8 illustrate how the operation of the tensioner can be easily changed from a shape that has a variable damping to a shape that has a constant damping, by exchanging a minimum number of component parts, ie two springs and a lid. The above detailed description is used for the purpose of illustrating and is not intended to limit the scope of the invention to be determined by the appended claims.

Claims (14)

1. CLAIMS 1. A tensioner for tensioning a power transmission band and the type that has a pivot arm; a pulley fixed to the pivot arm for coupling the band and receiving a band load; a pivot pin attached to the pivot arm; a base member which generally has a tubular batten shape with a cantilevered internal wall having an orifice, an outer wall, a receiving pocket of the annular spring defined between the inner and outer walls, and a lower wall interconnecting the inner walls and external and facing an open end; at least one bushing supporting the pivot pin; a spring operatively connected between the pivot arm and the base member; a damping mechanism; and wherein the improvement comprises: the base member oriented with its bottom wall juxtaposed to the pivot arm and with the open end of the base member facing away from the pivot arm; and the pivot pin connected at a first end and protruding from one side of the pivot arm and connected near a second end at at least one point of the spring. The tensioner according to claim 1, characterized in that it comprises: a cover attached to a second end of the pivot pin; and the spring has a first end constrained at two spaced points of the base member near the bottom wall and having a second end restricted in at least one point by means of a spring contact portion formed of the cap. 3. The tensioner in accordance with the claim 2, characterized in that it comprises: the second end of the spring has an extension that engages and presses a shoe of the damping mechanism against a portion of the juxtaposed internal wall of the external wall of the base member to dampen the oscillating movement of the arm of pivot. 4. The tensioner in accordance with the claim 3, characterized in that it comprises the second end of the spring is retained in a position on the lid in a circumferential location in such a way that, a reaction force imparted by the spring to the lid and the pivot pin has a direction that is inside of ± 10 ° of a plane of a belt load imparted to the pulley. The tensioner according to claim 2, characterized in that the cover with its spring contact portion is adjustable to a desired angular position relative to a longitudinal axis of the pivot pin, and the cover is fixed to the pivot pin by middle of a bra. The tensioner according to claim 5, characterized in that the pivot pin and the fastener have grooves oriented longitudinally and interdigitably. The tensioner according to claim 1, characterized in that the pivot pin is formed as an integral part of the pivot arm. 8. The tensioner in accordance with the claim 1, characterized in that the lower wall is separated at a distance SB from a plane of radial center of the pulley and the pivot pin is supported by means of two bearing forces, the middle point between which is a center plane located at a distance PB from the radial center plane where the ratio of SB to PB is less than one. The tensioner according to claim 1, characterized in that it comprises a closure fixed to the open end of the base member. 10. The tensioner in accordance with the claim 1, characterized in that a labyrinth seal is formed of a circumferential portion of the pivot arm and an adjacent circumferential portion of the lower wall. The tensioner according to claim 7, characterized in that it comprises the pivot pin having a length over which it is at least partially supported by at least a bushing and wherein the fastener has a length greater than the length supported by the bushing. 12. The tensioner in accordance with the claim 1, characterized in that it comprises: a cover joined to a second end of the pivot pin and having a first side with two separate points for restricting the spring and? N second side facing opposite; the spring in the form of a torsion spring has a first end restricted at two spaced points of the base member near the bottom wall, and having a second end restricted at the two separate points of the first side of the cap; and a damping spring having a first end restricted at two spaced points of the second side facing opposite to the cover, and a second end which is restricted at a third point on the second side of the cover, the spring having an extension that engages and presses a shoe of the damping mechanism against a juxtaposed internal wall portion of the outer wall of the base member to dampen the oscillating movements of the pivot arm. 13. The tensioner in accordance with the claim 12, characterized in that the damping spring has the shape of at least one partial coil of a torsion spring. 14. The tensioner in accordance with the claim 13, characterized in that the second end of the damping spring is restricted in a position on the lid which is in a circumferential location such that a reaction force imparted by the damping spring to the lid and the pivot pin has a duration which is within ± 10 ° of a plane of a belt load imparted to the pulley.