Tensioning device for flexible drive element

A tensioning device (10) for a flexible drive element (16), the tensioning device comprising a first tensioning member (40) shaped to form a channel (52) having a first contact surface (58), and a second tensioning member (140) shaped to form a channel (152) having a second contact surface (158). Straps (34, 36) and engagement means (42, 44, 142, 144) secure the first and second tensioning members a selected distance away from one another by means of 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. Grooves (60, 160) are provided in the respective channels to maintain the sides of the flexible drive element out of contact with the channel sides.

FIELD OF THE INVENTION 
The present invention relates to tensioning devices for drive systems that 
include flexible drive elements such as drive chains and drive belts. 
BACKGROUND OF THE INVENTION 
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 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 tensoning 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 axles. 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 tensioning 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 disadvantage 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 disadvantage of a fixed distance between contact surfaces is that 
the tensioning device cannot be used with different sized sprockets. 
SUMMARY OF THE INVENTION 
The present invention provides a tensioning device that overcomes a number 
of the limitations of prior tensioning devices. The tensioning device of 
the present invention is adapted for use with a drive system having a 
flexible drive element extending between sprockets, pulleys or the like. 
The tensioning device comprises first and second tensioning members, and 
positioning means for securing the first and second tensioning members a 
selected distance away from one another. The first tensioning member is 
shaped to form a channel in one surface thereof, the channel including an 
elongated portion having a first contact surface. Similarly, the second 
tensioning member is shaped to form a channel in one surface thereof, the 
channel including an elongated portion having a second contact surface. 
The positioning means positions the first and second tensioning members 
such that the first and second contact surfaces are spaced apart from and 
facing one another. The positioning means inlcudes means for adjusting the 
spacing between the contact surfaces, to thereby adjust the tensioning 
apparatus, so as to cause the tensioning apparatus to apply a suitable 
force to the drive element. In a preferred aspect, the positioning means 
includes 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 positioning means may include a pair of straps extending between the 
first and second tensioning members, and engagement means for connecting 
the straps to the tensioning members. The engagement means comprises a 
pair of engagement members such as blades, and fastening means for 
securing the blades to the tensioning member. The fastening means 
preferably comprises a clip shaped to form a pair of slots through which 
the respective straps extend. The blades extend into the respective slots, 
so as to engage the straps. Each blade includes a tip that is angled away 
from the associated tensioning member, to thereby provide the ratchet-like 
mechanism. Openings are provided adjacent the blades, such that a tool may 
be inserted between each blade and the corresponding tensioning member, to 
move the blade out of contact with the strap. In another preferred aspect, 
each channel includes an elongated central portion comprising the contact 
surface, flanked by a pair of rails that extend outward from the contact 
surface to either side thereof. The contact surface and rails define a 
groove through which the flexible drive element rides, the height of the 
rails above the contact surface being less than the thickness of the 
flexible drive element. The flexible drive element is thereby kept out of 
contact with the sides of the channel, to minimize friction between the 
drive element and the tensioning members.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIGS. 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 are connected to the straps 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 FIG. 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 a drive belt or cable 
interconnects two pulleys or the like, and its use and construction for 
such a drive system is identical to that described herein for the sprocket 
and drive chain arrangement. 
Referring now principally to FIG. 4, upper assembly 30 comprises block 40, 
blade member 42, and clip 44. Similarly, lower assembly 32 comprises block 
140, blade member 142 and clip 144. In the preferred embodiment 
illustrated in the Figures, 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 FIG. 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 projection 62 and 64 
includes 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 low friction material such as ultra high 
molecular weight polyethylene (UHMW). A low-friction material available 
from duPont 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 FIG. 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 FIGS. 2 and 3. When 
strap 34 is so inserted, the strap makes contact with blade 90, as 
illustrated in FIG. 3. Because blade 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 tip 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 is 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 member, 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 runn, 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. 
While the preferred embodiment of the invention has been illustrated and 
described, it should be understood that variations will be apparent to 
those skilled in the art. For example, in certain applications, it may be 
found desirable to connect blocks 40 and 140 such that the blocks are 
secured a selected distance from one another but are free to rotate about 
an axis extending between the blocks. Accordingly, the invention is not to 
be limited to the specific embodiments illustrated and described, and that 
the true scope and spirit of the invention are to be determined by 
reference to the following claims.