MXPA96006526A - Cushion mechanism for a ten - Google Patents

Abstract

The present invention relates to a tensioner for tensioning a power transmission belt and the type with a base, a pivotal arm that rotates around a pivot secured to the base, a pulley attached to the pivot arm to engage with the belt and receive a band load, a torsion spring with one end connected to the pivot arm and another end interconnected through the base and generating a spring force operating with a shock absorbing means that generates a normal force component towards part of a cylindrical member and towards a cylindrical surface, and wherein the improvement to the damper means comprises: a brake shoe with i) an external arcuate friction surface, which engages a complementary internal surface of the cylindrical member and ii) first and second internal ramp surfaces , opposite each other, with a space intercepted in an apex or vertex of an angle defined between the two ramp surfaces, the base has a surface ie of complementary ramp slidingly engaging with the first ramp surface of the brake shoe, the spring end interconnecting through the base has a slidably engaging extension and applies the spring force generated to the second ramp surface of the brake shoe. the brake shoe, and whereby the spring force applied to the second ramp surface in combination with a reactive force on the first ramp surface of the brake shoe generates the normal force

Description

MK? AMTRMO DK AMORTIGUATION FOR A TENSIONER BACKGROUND OF THE INVENTION The invention relates to a tensioner with a shock absorber mechanism or a belt drive system that includes such a tensioner or tensioner. More particularly the invention relates to a tensioner with a torsion spring that controls the position of a pivot arm to which a belt coupling pulley is rotatably mounted. The tensioner of the invention with its damper mechanism is particularly useful for controlling the tension of a V-shaped ribbed drive system such as a front end accessory drive for applications in automobile engines. A tensioning mechanism is used to automatically control the tension of a V-ribbed band of a front-end accessory drive for applications in automobile engines, such a tensioner has a pivotal arm that rotates about a pivot fixed to the base and uses a bushing With a sleeve on the pivot to provide a bearing surface for the rotating pivot arm, many such bushings are made of plastic and are subject to wear during the expected life of the tensioner. Frequently a torsion spring is used with one end connected to the pivot arm and the other end interconnected through the base to control the position of the pivotal arm and the position of a pulley added with respect to a band, the spring is also used to generate an operative spring force with damping means which generate a normal force component towards a sliding friction surface to prevent or dampen the oscillating movements of the pivot arm. In some designs of tensioners, the support for the pulley is in the same radial plane as the hub, so that the loads on the hub are kept to a minimum and the wear of this does not lead appreciably to a free play of the pivotal arm with a subsequent misalignment of the pulley during the operational life expected of the tensioner. Examples of web tensioners with the pulley support aligned in a common linear plane with the pivot arm pivot bushing are presented in U.S. Patents 4,696,663 and 5,045,031. Another belt tensioner design, centralizes the place of the pivot arm between opposingly wound torsion springs and locates the pulley support half way between the nylon insert bushings. The symmetrical spring of the springs and the place of the bushings results in uniform wear of each bushing. An example of such a tensioner is presented in the SAE Technical Paper Series Number 790699. The problems of such tensioners include: their volume because the design of the two springs makes them unsuitable to adjust them within the limits of available spaces: their cost , due to the numerous parts associated with the design of the two springs, and their lack of an ingenious damping mechanism. A tensioner design that solves the problems of volume, cost and damping of the aforementioned SAE tensor is shown in U.S. Patent 4,473,362. This has a pivot arm attached to a displaced cylindrical member that supports the pivotal arm and rotates on a pivot fixed to a base. Only one torsion spring is used with one end connected to the pivot arm and the other end to the base. A single sleeve of the sleeve type on the pivot has a surface supporting the cylindrical member. The radial plane of a pulley support is offset in relation to the sleeve bushing that introduces a moment or torque with a load that must be made by the hub. Such tensioners are sometimes referred to as "Zed" type tensioners because of the displacement of the pulley with respect to its support or base structure. Unequal pressure loads introduced into the bearing surfaces of the bushing can result in excessive bushing wear and misalignment of the pulley.

The belt of a drive system using such "Zed" type tensioners engages with the pulley and generates a belt force on the pulley that is transmitted to the cylindrical member (hereinafter referred to as "bucket loading"). As explained in the above-mentioned patent "362 the unequal loads on the bushing is reduced by a damping means which generates a normal force component acting generally in the same direction as the band force component transmitted to the cylinder member, although the orientation of the band force with the force component certainly decreases some of the bushing load and related wear problems, it is missing in some belt drive situations because the normal force component of the damper means is insufficient to balance a moment generated by the band force that is displaced from the cylindrical member that carries the bucket load and the insulated bushing or only has the tendency to be chamfered, as the change in pressure loads occur when the pivot arm oscillates between directions of agreement clockwise and counterclockwise In one direction of the pivotal arm the friction force generated by the damper mechanism it is added to the loads on the bushing, while in the opposite direction of the movement of the pivot arm the friction loads are subtracted.

Eventually the chamfering of the bushing due to uneven wear allows the cylindrical member and the linked pivotal arm to wobble causing misalignment of the pulley with respect to the belt. When manufactured such tensioners can have pulleys aligned by more or less 0.5 °, but after extensive use bevelling the hub causes misalignment of the pulley as high as plus or minus 1.5 °. S ^ TMARTP PE Tiift TWIYMCTQM According to the invention a tensioner is provided which is particularly useful in drive systems, V-ribbed end-face accessories used in automotive applications, where the alignment of the pulley during the life of the tensioner is important. The tensioner of the band of the invention is of the "Zed" type with a pivotal arm attached to a displaced cylindrical member that supports the pivotal arm and rotates on a pivot fixed to the base. A bush of the sleeve type on the pivot has a bearing surface supporting the cylindrical member. A pulley is attached to the pivotal arm to engage a band of a driving system and receive a band load that generates a band force component that is transferred to the cylindrical member (hub load). The bucket load and the normal force component generated by the damping mechanism are carried by at least one or two bushings having two axially spaced support surfaces or carriers. The bushings have an axial length of the size of the carrier surfaces for an average pressure contact so that such carrier surface is radially worn with the same rate. The carrier surfaces that wear out basically with the same rate ensure an alignment of the pulley during the expected life of the tensioner. In some belt drive systems the normal force component generated by the damper mechanism is sufficient to balance the bucket load and provide the necessary average pressure contact in the carrier surfaces to wear out with basically the same radial rate. In such circumstances and in accordance with another aspect of the invention, a damping mechanism is provided, where the normal force generated by the damping means is greater than the force of the spring that activates the damping mechanism. The damper means has a brake shoe with an outer arcuate surface that engages the inside of a second cylindrical member to provide friction to the surface therein slides. The brake shoe has two opposing internal ramp surfaces where one of the Ramp surfaces slidably engage a ramp surface complementary to the base and the other ramp surface slidably engages an extension of the end of the spring that applies the spring force to the brake shoe. The angle between the two ramp surfaces and the direction of the forces are such that a normal force component transferred to the brake shoe is greater than the applied spring force. Another advantage of the invention is a damping mechanism that generates a higher normal force that can be used for secondary advantages such as increased damping. These and other advantages of the invention will be made apparent by the drawings and the description that follows: Figure 1 is a schematic front view of a front end accessory impuleion system including a strip tensioner according to the invention. Figure 2 is an enlarged partial schematic view taken essentially from line 2-2 of the Figure 1 illustrating several component forces associated with the tensioner. Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2 except for the pulley shown in a quarter cross section. Figure 4 is a schematic view taken along line 4-4 of Figure 4 with the pulley removed to illustrate the force components associated with the invention. Figure 5a is a schematic cross-sectional view of the bushings of Figure 4 and shows schematically the component forces transferred to the bushings when the pivot arm moves in the clockwise direction. Figure 5b is a view similar to Figure 5a but showing the component forces when the pivot arm moves in the counterclockwise direction. Figure 5c is a composite view showing how the component forces of Figure 5a and 5b can be averaged to effect an average pressure contact on the bearing surface of the hub. Figure 6 is an alternative embodiment of a bushing having two carrier surfaces spaced apart to receive an average pressure contact as illustrated in Figure 5a. Figure 7 is an enlarged, interrupted view generally of line 7-7 of Figure 3 and showing the damping mechanism of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Figures 1 and 2, a tensioner 10 with a pulley 12 is illustrated as a component part of a belt drive system including a belt 16 and several pulleys. By way of example, the band 16 is driven around a running pulley 18, a water pump / fan pulley 20, a power control pulley 22, an alternator pulley 24, a vacuum pulley 26, and a Tensioner Pulley 12. The tensioner pulley 12 engages the web 16 and is illustrated in various positions to schematically show how the pulley moves to tension the tension of the web. The pulley of the tensioner 12 engages with the band 16 and receives a band load in the form of the web tension Tl and T2 of the adjacent band lights 28, 30. The voltage Tl and T2 (or load) is combined to generate a band force component BF along a bisector or angle formed between band lights 28 30. The band force component is displaced axially from a pivot 32 of the tensioner, and generates a complicated cube load including forces and moments which are represented symbolically (that is, not specifically) by the arrow HL. Referring to Figures 2-4 the tensioner 10 is of the mechanical type and includes a base 34, a tension spring 36 with one end 38 connected to a pivotal arm 40 and another end 42 interconnected through the base generating a spring force which operates with a shock absorbing means 34. The pivotal arm 40 is attached to a cylindrical member 46 which supports the pivotal arm 40 and rotates on the pivot 32. The sleeve bushings 48 and 50 are preferably of the polymeric type and are located in the pivot to support the cylindrical member that is attached to the pivot arm. The bushings may include flanges 52 and 54 as a thrust support for the cylindrical member and a flanged fastener such as a bolt 56 that retains the pivot arm. The pulley 12 is rotatably mounted to the pivot arm 40 such that by means of a ball bearing 58 on a journal 60 formed on the pivot arm. The support is retained on the journal as by a bolt 62. The ears 64 and 66 with holes for receiving bolts 68 and 70 can be used as means for mounting the tensioner to a machine or engine not shown, as part of the belt drive system. A second cylindrical member 72 which is displaced from the pivotal arm and is coaxial with the first cylindrical member 46 provides a box for the torsion spring and the d & damping 44. The second cylindrical member penetrates a cylindrical depression 64 formed in the box in a manner somewhat similar to the so-called telescopic. A seal against dust maintains a clean environment for the spring and damping means 64. The second cylindrical member is also part of the damping means. Referring more particularly to Figures 2, 3, 4 and 7 the damper means 44 is a mechanism including an extension 78 of the spring end 42, a brake shoe 80 with an outer arcuate friction surface 82 that engages a supplementary inner surface 84 of the second cylindrical member 72 The brake shoe has opposite internal ramp surfaces opposite one another with an intercept of space at a vertex A, optionally the brake shoe has a liner 90 which defines the friction surface 82 and is attached to the shoe for example by the teeth 92 that fit into the grooves 94 formed in the shoe. The end of the spring 42 interconnecting through the base 34 is bent around a protrusion 96 (shown as a post) formed from the base or attached to the base. The extension 78 of the spring end slidably engages within the ramp surface 88 formed in the brake shoe. The base includes a protrusion 100 (shown as a post) formed from the base or joined to the base and has a complementary ramp surface slidingly engaging with the ramp surface 88 formed in the brake shoe. The spring 36 under torsion applies a substantially normal spring force SF to the inner ramp surface 86 by pressing the inner side of the ramp surface 88 of the shoe against the complementary ramp surface 102 of the base and pressing the liner against the surface of the complementary inner side 84 of the second cylindrical member 72 causing a reaction force SF that is applied to the shoe. The spring force SF applied to the inner side of the ramp surface 86 in combination with the reactive force RF on the inner side of the ramp surface 88 generates a normal force NF that is equal and opposite to the force 104 carried on the surface Complementary 84 of the second cylindrical member 72. The normal force NF thus generated is generally in the same direction (generally parallel) to the band force BF. The magnitude of the spring force can be varied by changing the angle A between the internal ramp surfaces and the direction of the spring force SF. The greater the angle, the greater the normal force. The angle A between the internal ramp surfaces may be about 60 to 140 °, but more preferably the angle will be about 90 to 120 °. The magnitude, direction and location of the band force and the normal force of a tensioner can optionally be used to give the desired magnitude of the carrier surface of a bushing arranged on the pivot for an average pressure contact, so that each surface of support wear radially at the same rate basically. Referring to Figure 3 the band force BF being displaced from the cylindrical member 46 functions to apply a moment of force in the clockwise direction to the cylindrical member 46 in the cross section shown in Figure 4. The normal force NF which operates against the second cylindrical member causes in a moment arm 126 to move the cylindrical member in a counterclockwise direction in the plane of the cross section in Figure 4. The forces introduced to the cylindrical member are carried by the bushings 48.50 each having a carrier surface supporting the cylindrical surface and can be represented by a supporting force component BC1, BC2. The support surfaces are spaced a distance D. The force component BC1 operates on a moment arm 128 with respect to the web force BF and the support surface component BC2 operates on a moment arm 130 with respect to the force of support BF. Referring to Figure 5a each support 48, 50 has a support surface BSl, BS2 that supports a load CL1, CL2 when the pivot arm is rotated in the clockwise direction of the hands. As is known in the art, a damping mechanism generates a force that is added to the loads carried by the supports or bearings when the pivotal arm moves in one direction and subtracts the loads carried by the supports or bearings when the pivotal arm moves in a direction equal to the hands of the clock. As illustrated in Figure 5a the load CL1 introduced to the support surface BCl in the clockwise direction is greater than the load CL2 introduced to the support surface BC2 in the when the pivot arm moves in the direction of clock hands . Referring to Figure 5b the loads on the support surface basically change when the pivot arm moves in the opposite direction or counterclockwise direction. As illustrated, the load CC1 which is introduced to the loading surface BCl is smaller than the load CC2 introduced to its supporting surface BC2, when the pivot arm moves in the counterclockwise direction. The loads CL1 and CC1 can be averaged to determine an average load that must be carried by the support surface BCl. Similarly, the load CL2 and CC2 can be averaged to determine the loads that must be carried by the support surface BC2. It is probable that the charges thus averaged are not the same as illustrated in Figure 5c. The average load CAÍ (equal and opposite to the BC2) is greater than the average load CA2 (equal or set to the wing BC2). According to the invention, the support surface BCl and the BC2 have an axial length BL1 and BL2 which determines the size of the support surface for an average pressure contact PB1 and PB2 such that each support surface is radially worn essentially with the same rate. As illustrated in Figure 5c the bushing 48 has a larger axial length BL1 than the bushing 50 having the length BL2, so that the pressure contact PCl almost equals the PC2. Of course if the bushings were made of different materials to have different wear rates, the length of the bushings could be determined for a pressure contact that would produce basically the same radial wear rate. A tensioner according to the invention was constructed with a pulley with a diameter of 76.2 mm and a torsion spring of 100.8 pounds with the following characteristics: Average BF 108 lb 49.03 Kg Average NF 156 lb 70.82 Kg Average SF 123 lb 55.84 Kg Average RF 69 lb. 31.32 Kg 126 54.5 mm 128 23.3 mm 130 42.5 mm D 9.7 mm CL1 216 lb 98.06 Kg CL2 102 lb. 46.30 Kg CC1 77 lb. 34.95 Kg CC2 164 lb 74.45 Kg CAI 146.5 lb 66.51 Kg CA2 133 lb 60.38 Kg BL1 10 mm BL2 9 mm PCl 636 lb / in. * 44.52 Kg / cm2 PC2 640 lb / in2 44.80 Kg / cm Referring to the above the average normal force NF is greater than the average spring force which is in accordance with the characteristics of the present invention.

Claims (5)

1. RE I V I N D I CAC I S E S 1. - A tensioner for tensioning a power transmission band and of the type consisting of a base, a pivotal arm that rotates on a pivot fixed to the base; a pulley attached to the pivotal arm for coupling the band and receiving a band load; a torsion spring with one end connected to the pivot arm and another end connected through the base and generating a spring force operating with a damping means that generates a normal force component for moving a cylindrical member to a cylindrical surface, and wherein the improvement of the buffer means comprises: a brake shoe with i) an upper arched friction surface on the complementary internal side of the cylindrical member ii) surface of first and second internal ramps that oppose each other with a space interceptor at a vertex at a defined angle between two ramp surfaces; the base has a complementary ramp surface that slidably engages with the first ramp surface of the brake shoe; the spring end interconnects through the base having an extension that slidably engages with and applies the spring force generated to the second ramp surface of the brake shoe; and whereby the spring force applied to the second ramp surface in combination with a reactive force on the first ramp surface of the brake shoe generates the normal force.
2. 2. Tensioner according to claim 1, wherein the angle between the two ramp surfaces is approximately 60 to 40 °.
3. 3. Tensioner according to claim 1, wherein the angle between the two ramp surfaces is approximately 90 to 120 °.
4. 4. Tensor according to claim 1, wherein the brake shoe includes an aggregate liner that defines the arcuate friction surface.
5. 5. Tensioner according to claim 1, wherein the normal force generated by the damping means is greater than the spring force. A belt tensioner of the "Zed" type with a pivotal arm attached to a cylindrical member and including a spring-activated damping mechanism with a brake shoe having frontally opposite interior ramp surfaces, which operate in such a way as to provide a normal force greater than a spring force applied to a brake shoe which engages the cylindrical member.