Torsionally elastic power transmitting device and drive

A shock-absorbing torsionally elastic power transmitting device is described having resilient cushioning means loaded with modulus-increasing fibrous reinforcement, adapted to be interposed between mating lugs of a hub and rim configured to accommodate high torque levels simultaneously with relatively large angular deflections. The fibrous reinforcement is preferably aligned in the principal direction of displacement of the cushions under load. In another aspect, a torsionally elastic power transmitting device is used with V- or V-ribbed belt friction drive sheaves subject to slippage, to absorb torsional shocks and minimize heat build-up.

CROSS REFERENCES TO RELATED APPLICATIONS 
Copending and commonly assigned U.S. patent applications Ser. No. 900,459, 
filed Apr. 27, 1978 entitled "Shock Absorbing Sprocket and Drive 
Assembly", and Ser. No. 85,655, filed Oct. 17, 1979 entitled "Resilient 
Cushions For Elastic Isolator Power Transmission Devices", disclose 
shock-absorbing power transmission assemblies and resilient cushions for 
use therein, and are hereby incorporated by reference. In one aspect the 
present invention is drawn particularly to a cushioning means to 
compensate for very high peak loading, and to obtain a much flatter 
torque/angular deflection curve. 
BACKGROUND OF THE INVENTION 
This invention relates to rotary driven members and more particularly to 
torsionally elastic power transmission assemblies capable of absorbing or 
isolating torsional shocks and vibrations in a power drive train. 
Power transmitting devices are known which are capable of dampening or 
isolating torsional shock loading and minimizing noise and vibration by 
the use of resilient cushioning means. Rubber cushions, for instance, are 
adapted to yieldingly transmit rotary motion between mating lugs of an 
integral hub and rim assembly. Typical known applications include 
cushioned sprockets for use with roller chain or synchronous belting 
(timing belts), direct gear drives, and torque transmission between shafts 
(flexible couplings), for instance. Various industrial applications are 
contemplated including those set forth in Koppers Company "Holset 
Resilient Couplings" catalog, March, 1973. Additional relevant prior art 
include, for instance, Croset U.S. Pat. No. 2,873,590, Kerestury U.S. Pat. 
No. 3,314,512 and the above-referenced copending applications. 
The rubber cushions used in the torsionally elastic couplings of the 
referenced copending applications were especially effective in smoothing 
out vibrations and modulating torque peaks for the primary drive of 
motorcycles using synchronous drive belts. However, it was found that when 
subjected to abusive driving techniques, such as "speed shifts" where gear 
shifts are made without letting off on the throttle, the driven spocket 
experienced very high torque peaks. During the speed shift the torsionally 
elastic driver sprocket assembly would wind up (along the "soft" portion 
of the torque deflection curve) allowing the driven sprocket to slow down. 
Subsequently when the flattened or "stiff" portion of the torque 
deflection curve was reached as the cushions filled their associated 
cavities, a large torque was suddenly applied causing a very high peak 
load on the drive due to inertial effects. In some cases the belt failed 
by tooth shear or breaking of the tensile reinforcement. 
It is a primary object of this aspect of the invention to overcome the 
problems associated with such abusive conditions and to provide an 
elastomeric cushion spring having desirable spring rate and damping 
properties allowing much higher torques to be transmitted while still 
operating on the initial sloped ("soft") portion of the torque deflection 
curve, and simultaneously accommodating relatively large angular 
deflections for the drive. 
In another vehicular application there is a trend toward extensive use of 
dynamically unbalanced four and six cylinder diesel and other engines 
exhibiting severe speed excursions at low rpm, especially for automobiles 
and trucks which are particularly vibration prone. Accessory drives for 
these engines transmit power from the crankshaft sheave to various driven 
sheaves usually linked with a number of separate V-belts or V-ribbed 
belts, or in the case of the so-called serpentine drive with a single 
V-ribbed belt, all working on a friction drive principle. These rough 
running engines, particularly the four and six cylinder diesels, have such 
high rpm excursions at idle speeds (below about 1000 rpm) that V-ribbed 
belts and other friction drive belts undergo tremendous slippage and 
elastomeric material shear relative to the tensile section, causing the 
belt and sheaves to heat up to such temperatures that in severe cases the 
belts have failed after only a single hour of operation on the drive. 
In this latter aspect it is a primary object of this invention to overcome 
the slippage and heat build-up problems aforementioned associated with 
V-belt or V-ribbed or similar type friction drives. Examples of serpentine 
drives and other belt configurations useful in this aspect of the 
invention, and which drives and configurations are hereby incorporated by 
reference, include those disclosed in Fisher et al. U.S. Pat. No. 
3,951,006. 
SUMMARY OF THE INVENTION 
Briefly described, in one aspect the invention pertains to a 
shock-absorbing torsionally elastic power transmitting device including a 
rotatable input drive means; a rotatable output driven means; and 
resilient spring cushions linking the input drive means to the output 
driven means in power transmitting relation and displaceable under load, 
the cushions comprising bodies of elastomeric material loaded with 
modulus-increasing dispersed fibrous reinforcement. 
In an another aspect, the invention is directed to a shock-absorbing 
torsionally elastic belt sprocket or sheave assembly including a rotatable 
hub having at least two lugs protruding radially therefrom; a rotatable 
rim with at least two radially inwardly extending ears adapted to matingly 
engage the lugs of the hub, and having a peripheral surface configured to 
engage an endless power transmission belt; and resilient cushions 
interposed between the lugs and ears, comprising elastomeric material in 
which is embedded discrete reinforcement fibers functioning to 
substantially increase the dynamic modulus of the cushions. 
In another aspect, the invention pertains to a shock-absorbing, speed 
excursion reducing torsionally elastic single or multiple V-belt or 
V-ribbed belt power transmission friction drive assembly comprising: a 
plurality of sheaves having a peripheral surface provided with at least 
one V-shaped groove on its driving surface adapted to receive the belt in 
driving relation; at least one of said sheaves being shock-absorbing and 
including a rotatable hub having at least two lugs protruding therefrom, a 
rotatable rim with at least two radially inwardly extending ears adapted 
to matingly engage the lugs of the hub (and whose peripheral surface is 
formed with said at least one V-shaped groove), and resilient elastomeric 
cushions interposed between the lugs and ears in driving relation; and a 
single or multiple V-belt or V-ribbed belt trained about the sheaves in 
friction driving relation. 
Other aspects will become apparent from a reading of the description and 
claims.

PREFERRED EMBODIMENTS OF THE INVENTION 
The invention will be described with reference to a primary drive sprocket 
for a motorcycle in FIGS. 1-3, and as a crankshaft sheave for an 
automobile in FIGS. 5 and 6; however the power transmission assembly and 
cushioning means of the invention may be employed in various applications 
wherever torsional flexibility and elastic isolation between the hub and 
rim members is required in the transmission of rotary motion. For example, 
the devices of the invention are suitable for use in such diverse 
applications as transmission drives for business machines, tractive 
drives, air conditioner compressor drives, direct gear drives, chain 
drives, various belt drives, and in flexible couplings. 
Referring first to FIGS. 1-3, a power transmission belt drive 10 for the 
primary drive of a motorcycle (linking engine output to 
transmission/clutch input) includes a shock-absorbing torsionally elastic 
drive sprocket 12 configured in accordance with the invention, a driven 
sprocket 14 which may be of conventional design, and a positive drive 
power transmission belt 16 trained about and linking sprockets 12 and 14 
in synchronous driving relationship. Alternatively, the shock-absorbing 
sprocket may be the driven sprocket rather than the driver sprocket, 
either in the primary or secondary drive (linking transmission output to 
rear wheel) of a motorcycle. 
The endless power transmission belt 16 is preferably formed of a polymeric 
body material 17 in which is embedded a tensile member 19. A plurality of 
teeth 18 are formed on the driving surface of the belt of a predetermined 
pitch to make mating engagement with corresponding teeth 20 of the 
shock-absorbing sprocket, and with the teeth of sprocket 14 (not shown). 
The shock-absorbing sprocket assembly 12 of the invention is generally 
composed of a central hub 24 (input drive), outer rim 26 (output driven 
means), resilient spring cushioning means 28 and 30, flange bearings 31, 
32 sandwiching the hub (with bearing 31 being integral with hub 24), and a 
pair of rim surfaces 34, 36 integral with the rim and forming radial 
bearing surfaces, e.g., 33 (FIG. 1), with each of the flange bearings 31, 
32. 
The hub 24 has at least two generally radially protruding lugs 38, 40 which 
serve to transmit torque to the rim. Depending upon the application and 
size of the sprocket assembly, it may be preferable to use at least three 
such lugs, to prevent any thrust-induced wobbles in the assembly. The 
major diameter of the hub as measured from tip-to-tip of lugs 38 and 40 in 
FIG. 2, is somewhat less than the internal diameter of the rim to allow 
clearance for rotative movement. A portion of the internal bore of the hub 
is splined to form a journaled fit with splines 44 formed on the 
motorcycle crankshaft 42. The crankshaft, which protrudes from housing 46, 
is threaded at its tip 48 to receive lock nut 50 which, together with lock 
plate 51 holds the sprocket in retained assembly. 
The hub and its radially extending lugs are mounted for limited rotational 
movement within the internal cavity of rim 26. In addition to carrying 
teeth 20 about its circumference, the rim also has a plurality of inwardly 
extending ears 52, 54 adapted to mate with the lugs 38, 40 of the hub, 
torque being transmitted from the hub member lugs to the ears of the 
toothed rim member through the resilient cushioning means 28 in the 
forward direction and reversing cushions 30 in the opposite direction. It 
is preferred that the cushion means be precompressed (interference fit), 
as shown, with its side surfaces exerting a biasing force against the lugs 
and ears of the assembly, the advantages including initial elimination of 
free play, and reduction of free play due to compression set after 
extended use. 
The cushioning means is configured with respect to the rim and hub to 
define a captive void volume or cavity (under no load) to permit, in use, 
angular deflection of the hub relative to the rim. The void volume and 
angular deflection may be tailored to the specific application. The 
captive void volume shown in FIGS. 2 and 3 is determined by the total 
volume occupied by the resilient cushion 28 together with side clearances 
56, 58 i.e., the bound volume between lug 40 of the hub and ear 52 of the 
rim, side bearing plates 31 and 32, and arcuate connecting portions 60 and 
62 of the hub and rim, respectively. 
The resilient cushioning means preferably is configured to have arcuate top 
and bottom surfaces 70, 72, diverging side surfaces 74, 76 and 
substantially planar and preferably generally parallel front and rear 
faces 78, 80. 
In accordance with one aspect of the invention, the cushioned spring 
members 28, 30 are comprised of bodies of suitable elastomeric material 
loaded with modulus and hysteresis-increasing fibrous reinforcement. It is 
preferred that the fibers are generally uniformly dispersed within the 
elastomeric matrix, as shown in FIG. 4 which is a schematic drawing of an 
S.E.M. photomicrograph of a transverse section of the cushion, at 36X. The 
elastomeric matrix itself preferably has good compression set, high 
fatigue life, and resistance to any environmental materials, such as oil 
and grease in accordance with the application. For instance, nitrile 
rubber compounds have been found useful in the motorcycle sprocket 
application. Various natural and synthetic rubbers may be utilized and 
blends thereof, also with other compatible polymeric materials such as 
thermoplastic resins as well as some thermosets. 
The reinforcing fibers must be compatible with the elastomeric matrix and 
for this purpose may be coated or treated to achieve adhesion with the 
base elastomer. Various organic and inorganic fibers are useful and the 
specific choice will be again dictated by the particular application. In 
general, organic fibers made from polyester, nylon, rayon, cellulosics 
such as hard and soft woods, cotton linters, aramids, and the like are 
useful; typical inorganic fibers blendable with the elastomeric cushions 
include fiber glass, metallic fibers, carbon fibers and the like. The 
fibers may typically have lengths averaging from about 0.4 to about 12.7 
millimeters and more preferably from about 1 to about 6.4 millimeters, and 
aspect ratios preferably from about 30:1 to about 350:1 and more 
preferably from about 50:1 to about 200:1. 
Although the loading levels of the fibers based on the finished resilient 
cushions will vary in accordance with the application and 
modulus/dampening characteristics required, in general it is preferred to 
employ from about 3 to about 50, more preferably from 3 to about 30 and 
most preferably from about 4 to about 10 percent fibers by volume based on 
the overall cushion volume. 
Although not narrowly critical, it has been found highly advantageous to 
orient the fibers 64 predominantly at right angles to the principal 
direction in which the cushions are placed under load. If directions of 
the principal strains are known, an efficient use of fibers is to orient 
them along these maximum and/or minimum principal strain axes. With 
respect to FIGS. 3 and 4, in use the cushions 28 and 30 are displaced both 
in a direction parallel to the axis of rotation of the assembly as well as 
circumferentially, so as to tend to fill up the adjacent side cavities 56, 
58 respectively and to scrub circumferentially along the inner surface 62, 
of the driven rim. As seen in FIG. 4, the bulk 64 of the individual fibers 
are generally aligned in this axial direction, whereby under load the 
individual aligned fibers 64 in the cushions are placed in tension to 
thereby resist displacement of the cushions in the direction tending to 
fill the adjoining captive void cavities. This has the result of very 
substantially increasing the transverse modulus of the cushion in use. 
In certain other applications and depending upon the shape of the 
individual cushion, and the positioning of the adjacent cavities which 
will define the principal strain axes, a random orientation of the 
embedded fibers may be useful. 
Although fiber loading is known to normally reduce fatigue resistance of an 
elastomeric part, and produce a somewhat poorer compression set, with the 
subject invention these problems are largely overcome by designing the 
cushion with respect to the adjoining cavities so that minimum strain 
levels are imposed axially on the cushion. The higher modulus material 
thereby undergoes less strain and hence the fatigue resistance and 
compression set problems are substantially minimized. 
It is another aspect of the invention in its preferred form to utilize 
fibrous loading material which swells appreciably when contacted with 
environmental materials, such as oil and grease used in bearings of the 
hub and rim. In this manner the cushions swell appreciably and this 
swelling offsets a portion or all of the compression set which is induced 
after extended flexing of the cushions under cyclic loading and unloading. 
As a working example, cellulosic fibers marketed under the name Santoweb K 
(Monsanto Company) formed of a hardwood cellulosic fiber of approximately 
0.018 to 0.025 mm average fiber diameter, with a typical average aspect 
ratio of 55, was used. This fiber was treated for improved adhesion to 
nitrile and then uniformly dispersed at a level from about 4 to about 8 
percent by volume in a banbury mixer with a typical nitrile (NBR) rubber 
compound additionally comprising carbon black loading, oil extender, 
accelerators and vulcanizing agents. After thorough dispersion the 
resilient blocks were molded so as to orient the fibers as shown in FIG. 
4. These blocks had a tensile strength at break of 1500 psi, elongation at 
break of 100 percent, a durometer of 88 Shore A, compression set of 32 
percent after 22 hours at 212.degree. F. (compressed to 25 percent of 
original height), a compression set of 57 percent after 70 hours at 
250.degree. F., and an increase of 17 percent in volume after immersion in 
railroad airbrake grease (A.A.R. Specification No. M-914) for one week at 
212.degree. F. Thus, significant swell took place which tends to offset 
compression set during use. 
Although it is preferred to use cushions which are solid, in appropriate 
applications perforations or holes such as disclosed in copending 
application Ser. No. 85,655, referred to above, may be used to provide the 
advantages disclosed in that application. 
The torque/angular deflection curve ("D") for the resilient cushions of 
this aspect of the invention (FIGS. 1-4) compared with prior art cushions 
(curves A and B) and an experimental cushion (curve C) without fiber 
loading are shown in FIG. 7. All curves were generated using the sprocket 
assembly of FIGS. 1-3 of the drawings. Curve A is the torque deflection 
relationship using a standard nitrile elastomeric stock with holes 
penetrating the cushions in the axial direction, as shown in the 
aforementioned copending Ser. No. 85,655. Curve B utilizes the same 
material and construction as Curve A with the exception that the blocks 
were solid (no holes). In each of Curves A and B the breakover point or 
"knee" 66, 66' was less than about 50 lb-ft. torque. Curve C on the other 
hand represents a special carboxylated nitrile stock of high modulus 
purposely compounded to attempt to achieve a much higher torque at the 
breakover point 71. Curve D, of the invention, however, achieved a 
significantly higher breakover point 73 approximating 190 lb-ft. torque, 
providing a much greater ability to withstand torque transients in the 
drive train, with minimal backlash and simultaneously accommodating 
angular deflections of preferably greater than 8 degrees. The resilient 
cushions used with respect to Curve D employed the nitrile compound 
discussed in the above example loaded with 6% by volume Santoweb K. 
The fiber-loaded cushion represented by Curve D above has successfully 
solved the "speed shift" problem mentioned above, for motorcycle drives. 
Although not narrowly critical, the slope of the torque/deflection curve 
(below the "knee") is preferably from about 0.02 to about 0.2, more 
preferably from about 0.03 to about 0.09 for the function degrees/lb-ft. 
The high modulus cushion enables slopes within these desirable ranges to 
be obtained. Simultaneously, the corresponding breakover point ("knee") is 
preferably at least about 100 lb-ft., more preferably at least about 150 
lb-ft. of torque. 
In FIG. 5, an alternative application is shown in which a shock-absorbing 
torsionally elastic belt sheave 12' is employed in a serpentine accessory 
drive for a transverse mounted diesel automobile engine. In this example, 
sheave 12' is coupled directly to the engine crankshaft. Sheave 12' is 
coupled in driving relationship to a backside water pump sheave 75 (to 
which an offtake belt, not shown, may couple a vacuum pump), air 
conditioner sheave 77, alternator sheave 79 and power steering sheave 81, 
a tension applying backside idler 83, all coupled by serpentine belt 85. 
In general, at least three sheaves are linked by the belt in driving 
relation. As shown more clearly in FIG. 6, belt 85 may be a typical 
reinforced endless power transmission belt of V-ribbed construction whose 
individual ribs 91 wedge into or make frictional contact with 
corresponding V-grooves 89 formed on the driving circumference of sheave 
87. The use of a torsionally elastic sheave 12' in this application 
constructed in accordance with the invention using cushions 28', 30' of 
high modulus (preferably fiber loaded) or unloaded cushions of relatively 
soft elastomeric material results in a number of advantages including 
reduction of engine rpm excursions and induced vibration or wobble, as 
well as damping torque peaks in the drive train. This has been found to 
translate into tremendously longer belt and drive life. 
In an actual comparative test on a transverse mounted 90.degree. V-6 diesel 
engine serpentine accessory drive of the type shown in FIG. 5, three 
different crank sheaves 12' were employed. Change in rpm (excursion) at a 
given rpm level approximating engine idle was measured as was sheave 
temperature (qualitatively). The first crankshaft sheave was the control, 
a standard sheave of the type shown partially in FIG. 6, without provision 
of any elastomeric blocks or other torque compensation. The second and 
third crankshaft sheaves employed the compensator sheave 12' of the 
invention using, respectively, cushions 28', 30' loaded with from about 4 
to about 8 volume percent Santoweb K per the example mentioned previously 
herein, and unloaded relatively soft elastomeric cushions 28', 30' made of 
35 percent acrylonitrile NBR reinforced with carbon black and having a 
modulus of 600 psi at 100 percent elongation, and a tensile strength of 
about 1800 psi at break (350 percent elongation). With the control, the 
excursion defined as the maximum change in rpm per engine cylinder from 
idle (600 rpm) was about 13 rpm; with the compensator of the invention 
using high modulus fiber reinforced cushions the excursion was about 9 
rpm; and for the compensator of the invention using relatively soft 
cushions the excursion was only about 2.5 rpm. The control sheave (without 
torsional compensation) caused the belt to slip about 6 degrees and the 
sheave became so hot after a few minutes of engine operation that it 
scorched the V-ribbed belt. The torsionally elastic sheave with the high 
modulus fiber-loaded cushion became hot but did not burn or scorch the 
belt. The third torsionally elastic sheave, with the softer cushions, 
heated only slightly whereby it was possible to hold onto the sheave (by 
hand) virtually indefinitely. Of course, the lower the rpm excursion, the 
lower the vibration level, belt slip and belt elastomeric material shear 
and the longer the expected belt and drive train life. With low excursions 
it is also possible to reduce flywheel weight, etc. 
In the drive embodiment of FIG. 5 it is preferred to limit the captive void 
volume between the cushions 28', 30' and adjacent sheave components (i.e., 
hub, rim, etc.) so as to achieve angular deflections from about 0.1 to 
about 8, more preferably from about 3 to about 7 degrees at 100 lb-ft. 
torque. 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the invention, it will be apparent to those 
skilled in this art that various changes and modifications may be made 
therein without departing from the spirit or scope of the invention.