TENSIONING DEVICE FOR FLEXIBLE DRIVE ELEMENT

Abstract: A tensioning device (10) for a flexible drive element (16), the tensioning device comprising a first tensioning member (40) having a first contact surface (58), and a second tensioning member (140) having a second contact surface (158). Straps (34,36) and positioning devices (42,44,142,144) secure the first and second tensioning members a selected distance away from one another. In one arrangement, the positioning devices form a ratchet-like mechanism arranged such that the force required to move the tensioning members toward one another is smaller than the force required to move the tensioning members away from one another. The tensioning device may be operated without any means securing the tensioning device with respect to the sprockets.

Description: The present invention relates to tensioning devices for drive systems that include flexible drive elements such as drive chains and drive belts. The present invention is adapted for use with a conventional drive system in which a driven sprocket and a drive sprocket are connected by a flexible drive element such as a drive chain. In such an arrangement, it is well known that the proper functioning of the drive system and the operating life of the drive chain can be significantly enhanced by maintaining the two drive chain runs between the sprockets in tension such that significant slack does not occur in either run. One common means of providing such tension is to resiliently bias the sprockets away from one another. However, a more common and typically more convenient arrangement is to provide a tensioning device that biases one or both drive chain runs inward towards the other run at a point intermediate the sprockets. A number of examples of this latter type of tensioning device are disclosed in the prior art. However, in the great majority of prior tensioning devices, the tensioning device is adapted to operate in a particular drive system, e.g., to operate with a given arrangement of sprockets and drive chain. One result of the fact that prior tensioning devices have been adapted for specific applications is that in essentially all cases, prior tensioning devices have been mounted or secured to a support that is fixed with respect to the sprocket axies. Through use of such a support arrangement, the position of the tensioning device between the sprockets can be controlled, to maintain the tensioning device at the optimum position. The use of fixed supports has been viewed as especially important for tensioning devices adapted to operate with sprockets that are or may be horizontally positioned with respect to one another. In such a horizontal arrangement, the weight of the tensioning device does not affect its position, i.e., the position of the tenisoning device between the sprockets is not in any way controlled by gravity acting on the tensioning device. A further feature of essentially all prior art tensioning devices is that in such devices, the surfaces contacting the two runs of drive chain and urging them inward have either been fixed in position with respect to one another, or resiliently biased towards one another by springs or similar means. A result of the resilient biasing technique is that it adds complexity to the tensioning device, and the resilient means are themselves subject to wear over time. Tensioning devices having fixed distances between their contact surfaces cannot be adjusted as the chain experiences increased wear. Thus, the tensioning force provided by the device decreases over time, at least in those arrangements where the sprockets are horizontally positioned with respect to one another. A further result of a fixed distance between contact surfaces is that the tensioning device cannot be used with different sizes sprockets. US 3,941,006 discloses a tensioning device for a drive system having a flexible, endless drive element, the tensioning device comprising first and second tensioning members, having first and second contact surfaces respectively, for contacting the drive element; positioning means for securing the first and second tensioning members to one another, the positioning means comprising at least one connecting member extending between the first and second tensioning members, the connecting member securing the tensioning members a fixed distance apart from each other during operation of the drive system with the first and second contact surfaces facing one another and in contact with first and second runs of the drive element respectively which pass between the tensioning members and freely support the tensioning device on the endless chain drive element; and adjustment means for permitting at least one tensioning member to be secured to the connecting member at a plurality of positions such that the spacing between the contact surfaces can be adjusted. US 2,210,276 discloses a tensioning device for a drive system having a flexible, endless chain drive element, the tensioning device comprising first and second tensioning members having first and second contact surfaces, a positioning means for securing the first and second tensioning members a selected distance away from one another such that the first and second contact surfaces are spaced apart from and facing one another and in use make sliding contact with first and second runs respectively of the chain drive element, the positioning means including means for adjusting the spacing between the contact surfaces to thereby adjust the tensioning device so as to cause the tensioning device to apply a suitable tensioning force to the drive element, the positioning means further including ratchet means arranged such that the force required to advance the ratchet so as to move the tensioning members toward one another is smaller than the force required to retract the ratchet so as to move the tensioning members away from one another. The present invention provides a tensioning device as defined in claim 1. As a result of the described arrangements, the positioning means holds the tensioning members a fixed distance from one another during operation of the drive system. Therefore when the tensioning device is in contact only with the drive element, the tensioning device can respond to fluctuations in load on the drive element by moving in a direction parallel to the drive element at the points of contact between the drive element and the tensioning members. In a preferred arrangement, the positioning means includes first and second connecting members, each connecting member extending between and secured to the first and second tensioning members. The connecting members are spaced apart by a distance sufficient to permit the drive element to pass between the connecting members. Preferably, at least one of the tensioning members can be entirely disengaged from the connecting members. An other preferred feature is that the connecting members is elongated along an axis extending between the tensioning members, and torsionally compliant along such axis, such that the tensioning members can rotate with respect to one another about such axis, in response to misalignement between the first and second runs of the drive element. The invention also provides a tensioning device as defined in claim 9. In a preferred embodiment, each connecting member includes a series of openings spaced along its length, to permit the tensioning members to be positioned at a selected distance from one another. In another embodiment, each connecting member includes a series of closely spaced, crosswire extending serrations, and each tensioning member includes a fastening member having a blade-like edge and means for forcing the edge against the connecting member, to secure the tensioning member to the connecting member. Figure 1 is a side elevational view of one embodiment of the tensioning device of the present invention used in connection with a drive chain; Figure 2 is a perspective view of the tensioning device of Figure 1; Figure 3 is a cross-sectional view taken along line 3-3 of Figure 1; Figure 4 is an exploded perspective view of the tensioning device of Figure 1; Figure 5 is a perspective view of a second preferred embodiment of the invention; Figure 6 is a partial perspective view of a third preferred embodiment of the present invention. Figures 1 and 2 illustrate tensioning device 10 of the present invention used in connection with a conventional drive system that includes sprockets 12 and 14 interconnected by drive chain 16. An upper run 20 of the drive chain extends between the upper sides of sprockets 12 and 14, and lower run 22 extends between the lower sides of the sprockets. Depending upon which of sprockets 12 and 14 is driven and upon the direction of such drive, either upper run 20 or lower run 22 will be placed under tension by the driving mechanism. However, in the absence of the tensioning device of the present invention, the other run will be slack, thereby increasing chain wear and ultimately leading to the possibility that the chain will come off one of the sprockets. Tensioning device 10 comprises upper assembly 30 and lower assembly 32 interconnected by straps 34 and 36. Upper assembly 30 includes block 40 that engages upper run 20, and lower assembly 32 includes block 140 that engages lower run 22. The blocks (tensioning members) are connected to the straps (connecting members) by ratchet-like arrangements, described below, such that the blocks can be moved toward one another upon application of a comparatively small force, but can be moved away from one another only upon application of a comparatively large force, or by use of a separate tool. Thus during operation of the tensioning device, straps 34 and 36 hold the upper and lower assemblies in fixed position with respect to one another, despite the tension exerted by drive chain 16 tending to move blocks 40 and 140 away from one another. However, the tensioning device of the present invention can readily be adjusted to decrease the separation between the blocks during the life of the drive chain, to take up slack caused by increasing drive chain wear. Furthermore, when the tensioning device of the present invention is installed on a drive chain or other flexible drive means, the distance between the blocks can be varied over a wide range, and the tensioning device can therefore be used for a wide range of sprocket sizes and distances between the upper and lower runs. A further important feature of the present invention is that it is capable of operation without any means for positioning the tensioning device on runs 20 and 22 between the sprockets. This is true for all positions of the sprockets with respect to one another, including the horizontal position shown in Figure 1. It is also true regardless of which of sprockets 12 and 14 is the drive sprocket and regardless of the direction of rotation of the sprockets. The tensioning device of the present invention therefore provides a device having a wide range of applications to different drive systems. It is to be understood that the present invention is also applicable to drive systems in which the flexible drive element comprises and O-ring, a V-belt or other drive belt, a rope, a bead chain, or any other flexible drive element. In a conventional tensioning arrangement, the upper and lower assemblies or their equivalents are resiliently mounted to an external structure such that they can move in directions normal to the drive elements, to accommodate the inevitable fluctuations in load or tension during operation of the drive system. By contrast, in the tensioning device of the present invention, the tensioning members are secured a fixed distance from one another, but the tensioning device can move along the drive element to accommodate fluctuations. This movement along the drive element provides a very effective vibration and shock absorber mechanism. In addition, unlike a conventional arrangement, shock and vibration are not transmitted through the tensioning devices to an external structure. Referring now principally to Figure 4, upper assembly 30 comprises block 40 and blade member 42 and clip 44 as adjustement means. Similarly, lower assembly 32 comprises block 140, blade member 142 and clip 144. In the preferred embodiment illustrated in Figures 1-4, the elements of the upper and lower assemblies are identical to one another, and a numbering scheme is used in which elements of the lower assembly are assigned reference numerals 100 greater than the reference numerals of the corresponding elements of the upper assembly. Where the context permits, reference in the following description to an element of one of assemblies 30 and 32 shall be understood as also referring to the corresponding element in the other assembly. Block 40 includes center portion 46 from which identical sidewalls 48 and 50 extend to form U-shaped channel 52. The side of center portion 46 that faces inwardly into channel 52 comprises contact surface 58 flanked by rails 54 and 56. The rails and contact surface have a common arcuate shape, and the height of the rails above the contact surface is constant, to thereby form convex groove 60 that extends the full length of channel 52. Upper run 20 of drive chain 16 rides in groove 60, as best indicated in FIGURE 3. Rails 54 and 56 keep the sides of chain 16 away from sidewalls 48 and 50, thereby minimizing friction between the drive chain and the block. The surface of center portion 46 that faces away from channel 52 includes projections 62 and 64 at opposite longitudinal ends of the center portion, and mounting surface 66 between the projections. Mounting surface 66 includes lateral edges 68 and 70. The inner edges of projections 62 and 64 include lips 72 and 74 that are slightly overhanging with respect to the adjacent portions of mounting surface 66. Blade member 42 includes end sections 80 and 82 and center section 84. Center section 84 includes laterally extending blades 86 and 88. The outer edges of blades 86 and 88 include tips 90 and 92 that are angled slightly out of the plane of the blade member in a direction away from mounting surface 66 and block 40. The function of blades 86 and 88 is described below. Clip 44 includes side pieces 100 and 102 interconnected by top pieces 104 and 106. Side piece 100 comprises center portion 108 that is shaped to form a shallow, inwardly facing, U-shaped groove. Center portion 108 is flanked by end portions 110 and 112. Similarly, side piece 102 comprises center portion 114 flanked by end portions 116 and 118, center portion 114 also being shaped to form a shallow, inwardly facing, U-shaped groove. Top piece 104 interconnects end portions 110 and 116, and top piece 106 interconnects end portions 112 and 118. Blade members 42 and 142 and clips 44 and 144 are preferably constructed of a metal such as steel. Blocks 40 and 140 and straps 34 and 36 are preferably constructed from a lower friction material such as ultra high molecular weight polyethylene (UHMW). A low-friction material available under the trademark NYLONTRON is also suitable. Upper assembly 30 is formed by placing blade member 42 on mounting surface 66, and then forcing clip 44 over the top and sides of block 40 such that the longitudinal edges of top pieces 104 and 106 are retained under lips 72 and 74 respectively. The longitudinal extent of blade member 42 is slightly less than the distance between lips 72 and 74. Similarly, the lateral extent of end sections 80 and 82 are slightly less than the lateral extent of the block. However, tips 90 and 92 extend slightly over respective edges 68 and 70, as best illustrated in Figure 3. The formation of lower assembly 32 is identical to that of the upper assembly. Clips 44 and 144 are formed such that straps 34 and 36 can be inserted in the slots formed by the center portions of the clips and the adjacent sidewalls of the corresponding blocks. For example, the upper end of strap 34 may be inserted through the slot formed by center portion 108 of clip 44 and the adjacent lateral surface of block 40, as shown in FIGURES 2 and 3. When strap 34 is so inserted, the strap makes contact with tip 90, as illustrated in FIGURE 3. Because tip 90 is angled slightly upward and away from block 40, the result is a ratchet-like arrangement in which strap 34 can be moved upward in the slot upon application of a comparatively small force, but can be moved downward in the slot only upon application of a large force, or by manipulation of blade 86 by a separate tool. The U-shaped openings between center section 84 and end sections 80 and 82 of blade member 42 permit insertion of a screwdriver or other tool under the blades, such that the blades can be raised above mounting surface 66 to move tip 90 or 92 upward and away from the block. Such upward movement of the blade tips disengages the tips from the straps, to thereby permit the straps to be moved downwardly with respect to the upper assembly. The connections between lower assembly 32 and straps 34 and 36 are identical to that described for the upper assembly. When the tensioning device of the present invention is initially applied to a drive chain, drive belt or other flexible drive mbmer, straps 34 and 36 are first inserted a short distance into one of the assemblies, such as the upper assembly, and the partially-formed tensioning device comprising the upper assembly and straps is then placed over one of the runs of the drive chain. The other assembly is then placed on the opposite side of the other drive chain run, and the straps are inserted into that assembly. The upper and lower assemblies are then manually moved closer together until the tensioning device exerts an appropriate force on the drive chain runs. When the drive system is in operation, the drive chain runs pass through grooves 60 and 160 of blocks 40 and 140, respectively. When the blocks are spaced an appropriate distance from one another, the tensioning device maintains a fixed average position between the sprockets during operation of the drive system, without the use of any auxiliary means to position the tensioning device with respect to the sprockets. The best separation of the blocks may readily be determined by initially setting the blocks a comparatively large distance apart, and then operating the drive system and gradually decreasing the block separation until the optimum position is found. As the drive system experiences wear over a comparatively long time period, drive chain 16 will exhibit increased amount of slack. Adjustment for such slack can again be readily made by manually forcing the blocks together, again until the optimum position is found. Removal of the tensioning device from the drive chain can best be accomplished by means of a screwdriver or the like, to force blade tips away from the straps, as described above. A second preferred embodiment of the tensioning device of the present invention is illustrated in FIGURE 5. This embodiment comprises upper assembly 170 and lower assembly 172 interconnected by straps 174 and 176. Straps 174 and 176 each include a series of equal sized, vertically spaced openings 178. Upper assembly 170 and lower assembly 172 each includes block 180, U-shaped bracket 182 and a pair of plates 184 positioned on opposite sides of the assembly. Each block 180 may have a shape and composition similar to that of blocks 40 and 140 of FIGURES 1-4. Brackets 182 are fastened to their respective blocks by any suitable means such as screws or rivets. Threaded shafts 186 extend laterally from either side of brackets 182 (only two shafts 186 shown in FIGURE 5). Shafts 186 are dimensioned so that they can pass through openings 178 in straps 174 and 176. Each plate 184 includes a centrally positioned opening 188 through which shafts 186 can also pass. Washers 190 and wing nuts 192 are provided for securing the plates and straps to brackets 182. In order to secure upper assembly 170 and lower assembly 172 to one another at a predetermined spacing from one another, nuts 192, washers 190 and plates 188 are removed from the assembly, as shown in the upper right portion of FIGURE 5, and shafts 186 are positioned in the appropriate openings 178. The plates, washers and nuts are then secured together, as shown in the lower portion of FIGURE 5, to produce a complete tensioning device assembly. Unlike the embodiment of FIGURES 1-4, the embodiment of FIGURE 5 does not include a ratchet-like mechanism for securing the upper and lower assemblies to the straps. However the tensioning device of FIGURE 5 can readily be adjusted to decrease or increase the separation between the blocks during the life of the drive chain, for example, to take up slack caused by increasing drive chain wear. Like the embodiment of Figures 1-4, the embodiment of Figure 5 is also capable of operation without any means for positioning the tensioning device to an external structure. This is true for all positions of the sprockets with respect to one another, and regardless of which of sprockets 12 and 14 (see Figure 1) is the drive sprocket, and regardless of the direction of rotation of the sprockets. A third embodiment of the tensioning device of the present invention is illustrated in partial view in Figure 6. Figure 6 illustrates upper assembly 200 secured to straps 204 and 206. Each of the straps includes a series of closely spaced horizontal serrations. Upper assembly 200 includes block 210 and bracket 212, the bracket being secured to the block by any suitable means (not shown) such as by rivets. The lateral sides of block 210 include channels to accommodate the straps. Threaded shaft 220 extends upwardly from bracket 212, or extends upwardly from block 210 through an opening in bracket 212. V-shaped spring metal cup 222 is positioned between straps 204 and 206, and includes a central opening through which shaft 220 extends. The clip may be secured to the upper assembly via wing nut 224 and one or more washers. By tightening wing nut 224, clip 222 is forced downward, forcing the outer, blade-like edges of the clip to bear against the inner, serrated surfaces of straps 204 and 206, thereby securing the upper assembly to the straps. In contrast with the embodiment of Figure 5, this arrangement permits an essentially continuous adjustment of the position of the upper and lower assemblies with respect to one another.

Claims: A tensioning device (10) for a drive system having a flexible, endless drive element (16), the tensioning device comprising first and second tensioning members (40, 140), having first and second contact surfaces (58, 158), respectively, for contacting the drive element; positioning means (30, 32, 34, 36) for securing the first and second tensioning members to one another, the positioning means comprising at least one connecting member (34, 36) extending between the first and second tensioning members, the connecting member securing the tensioning members a fixed distance apart from each other during operation of the drive system with the first and second contact surfaces facing one another and in contact with first and second runs of the drive element respectively which pass between the tensioning members and freely support the tensioning device on the endless drive element; and adjustment means (42, 44) for permitting at least one tensioning member to be secured to the connecting member at a plurality of positions such that the spacing between the contact surfaces can be adjusted, characterized in that said endless, flexible drive element is a chain drive element, the first and second contact surfaces (58, 158) are stationary with respect to the respective tensioning members (40, 140) and in use make sliding contact with the first and second runs respectively of the flexible endless chain drive element (16), and, in use, the tensioning device responds to fluctuations in load on the endless flexible chain drive element by moving in a direction parallel to the chain drive element at the points of contact between the chain drive element and the tensioning members (40, 140). A tensioning device according to claim 1, wherein the positioning means (30, 32, 34, 36) includes first and second connecting members (34, 36), each connecting member extending between and secured to the first and second tensioning members (40, 140), the connecting members being spaced apart by said fixed distance which is sufficient to permit the drive element (16) to pass between the connecting members. A tensioning device according to Claim 2, wherein at least one of the tensioning members (40, 140) can be entirely disengaged from the connecting members (34, 36). A tensioning device according to claim 1 or claim 2, wherein the at least one connecting member (34, 36) is elongated along an axis extending between the tensioning members (40, 140) and torsionally compliant along such axis, whereby the tensioning members can rotate with respect to one another about said axis in response to misalignment between the first and second runs of the drive element (16). A tensioning device according to claim 2 or claim 3, wherein the positioning means (30, 32, 34, 36) includes ratchet means (90, 92, 34, 36, 222, 204, 206) arranged such that the force required to advance the ratchet so as to move the tensioning members (40, 140) toward one another is smaller than the force required to retract the ratchet so as to move the tensioning members (40, 140) away from one another and the positioning means (30, 32, 34, 36) and ratchet means (90, 92, 34, 36; 222, 204, 206) are arranged in use to maintain the tensioning members (40, 140) said fixed distance apart irrespective of the tension in the flexible drive element (16). A tensioning device according to any of claims 1 to 4, wherein each connecting member (174, 176) includes a plurality of openings (178) spaced along the length of the connecting member between the tensioning members (180), and wherein each tensioning member includes a projection (186) adapted to pass through one of said openings in the connecting member for connecting the tensioning member to the connecting member. A tensioning device according to claim 5, wherein each connecting member (34, 36, 204, 206) includes a series of closely spaced serrations extending in a direction normal to the length of the connecting member, and wherein each tensioning member (40, 140; 180) includes a fastening member (42, 222) having a blade-like edge (90, 92), and means (86, 88; 224) for forcing the blade-like edge against the connecting member to secure the tensioning member to the connecting member. A tensioning device according to any preceding claim wherein each tensioning member (40, 140) is shaped to form a channel (52) in one surface thereof, the channel including an elongated central portion comprising the respective contact surface (58, 158), flanked by a pair of rails (54, 56) that extend outward from the contact surface on either side thereof, the contact surface and rails defining a groove (60) through which the flexible drive element (16) rides, the height of the rails above the contact surface being less than the thickness of the flexible drive element. A tensioning device (10) for a drive system having a flexible endless chain drive element (16), the tensioning device comprising first and second tensioning members (40, 140) having first and second contact surfaces (58, 158), a positioning means (30, 32, 34, 36) for securing the first and second tensioning members a selected distance away from one another such that the first and second contact surfaces are spaced apart from and facing one another, and in use make sliding contact with first and second runs respectively the positioning means including means (42, 44) for adjusting the spacing between the contact surfaces to thereby adjust the tensioning device so as to cause the tensioning device to apply a suitable tensioning force to the drive element, the positioning means further including ratchet means (90, 92, 34, 36, 222, 204, 206) arranged such that the force required to advance the ratchet so as to move the tensioning members toward one another is smaller than the force required to retract the ratchet so as to move the tensioning members away from one another; characterized in that the positioning means (30, 32, 34, 36) and ratchet means (90, 92, 34, 36, 222, 204, 206) are arranged in use to maintain the tensioning members (40, 140) a fixed distance apart irrespective of the tension in the flexible endless chain drive element (16) and the tensioning device (10) is freely supported on the endless chain drive element (16) which has first and second runs engaging said first and second contact surfaces (58, 158) respectively. A tensioning device according to claim 9, wherein each tensioning member (40, 140) comprises a block that includes the respective contact surface (58, 158), and wherein the positioning means (30, 32, 34, 36) includes a pair of straps (34, 36) extending between the first and second tensioning members, and includes engagement means (92, 108, 184, 186) for connecting the straps to the tensioning members, said engagement means comprising a pair of fastening means and engagement members (42, 142) for securing the engagement members to the blocks, said fastening means comprising a clip (44) shaped so as to form a pair of slots (100, 102) through which the respective straps extend and each of said engagement members comprising a blade (86, 88), the blades extending into the respective slots so as to engage the straps when the straps are inserted into the slots, thereby providing the ratchet means. A tensioning device according to claim 10, wherein each blade (86, 88) includes a tip (92) that is angled away from the block to which the blade is mounted. A tensioning means according to claim 11, wherein each engagement means comprises a blade member (42) shaped to form the blades (86, 88), each blade member being shaped so as to form openings adjacent the blades whereby a tool may be inserted between the blade and the block to move the blade out of contact with the respective strap (34, 36).

Inventors: MATSON, LES, SELA, RICHARD
Applicants: MOXEE INNOVATIONS CORPORATION
Application year: 1987
Main classification: F16H7
IPC codes: F16H7