Note: Descriptions are shown in the official language in which they were submitted.
Ihis is a divisional application of application Serial No. 300,820
filed on June 29, 1981.
This invention relates to rotary driven members and more particularly
to torsionally elastic power trallsmission assemblies capable of absorbing or
isolating torsional shocks and vibrations in a power drive train.
Power transmitting devices are known which are capable of dampen:irlg
or isolating torsional shock loading and millimiæi.llg 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 includes, for instance, Croset United States Patent No.
2,873,590, and Kerestury United States Patent No. 3,314,512.
Prior rubber cushions used in torsionally elastic couplings were
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 lctting off on the throttle, the driven
sprocket experienced very high torque peaks. During the speed shift the tor-
sionally 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 deflec-
tion 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
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due to inertial efEects. In some cases the belt Eailed by bo-th tooth shear or
breaking of the tensile reinforcement.
The problems associated with such abusive conditions are believed
to be overcome by provision of an elastomeric cushion spring havi~g desirable
spring ra-te and damping properties allowing much higher torques to be trans-
mitted while still operating on the initial sloped ("soft") portion of the
torque deflection cu-ve, and simultaneously accommodatillg relatively large
angular deflections for the drive.
In another vehicular application there is a trend toward extensive
use o:E dynamically unbalanced four and six cylinder diesel and other engines
exhibiting severe speed excursions a-t 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 under-
go 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 failéd after only a single hour of operation on
the drive.
In this latter aspect it is an object of this invention to overcosne
the slippage and heat build-up problems aforementioned associated with V-belt
or V-ribbed or similar type friction drive. Examples of serpentine drives
and other belt configurations useful in this aspect of the invention, include
those disclosed in Fisher et al. United States Patent No. 3,951,006.
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Briefly described~ in one aspect the invention relates to a shock--
absorbing torsionally elastic power -transmitting device including a rotatable
imput drive means; a rota-table output driven means; and resilient spring
cushions linking the input drive means -to the outpu-t driven means in power
transr~itting relation and dispaceable unde:r load, the cushions comprising
bodies of elastomeric material loaded with modulus and hysteresis increasing
fibrous reinforcement.
In another aspect, the i.nvention relates to a shock-absorblng tor-
sionally elastic bel-t sprocket or sheave assembly including a rotatable hub
having at least two lugs protruding radi~lly therefrom; a rotatable rim with
at leas-t 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 resilien-t cushions interposed between~the
lugs and ears, comprising elastomeric material in which is embedded discrete
reinforcement fibers functioning to substantially increase -the dynamic modulus
and hysteresis of the cushions.
~ he invention provides a shock-absorbing torsionally elastic
single or multiple V-belt or V-ribbed belt power transmission accessor-y drive
assembly for use with an engine exhibiting substantial speed excursions at
low rpm, comprising: a plurality of sheaves each having a peripheral surface
provided with a-t least one V-shaped groove on its driving surface adapted to
receive the belt in driving relation: at least one of said sheaves being a
shock-absorbing crankshaft sheave assembly, adapted to be coupled to the crank-
shaf-t of the engine, and including a rotatable hub having at least two lugs
protruding therefrom, a ro-tatable rim having at least two radially inwardly
extending ears adapted to indirectly matingly engage the lugs of the hub and.
having a peripheral surface formed with said a-t least one V-shaped groove, and
B
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resilient elas-tomeric cushions i.nterposed is cavities be-tween -the lugs and
ears in driving relation; said crankshaf-t sheave being provided with a
captive void vol.ume defined as an individual cavity volume less the volume
occupied by the cushion contained in tha-t cavi.ty of such amount to allow, in
operation, the hub and rim to undergo relative angular deflections of from
about .1 to abou-t 8 degrees, and a single of multiple V-belt or V-ribbed
belt trained about the sheaves in friction driving relation.
P~.~ - 3a -
Other aspects will become apparent :Erom a reading of the description
ancl c:laims.
The invention in its preferred embodiments will be morc particularly
described by reference to the accompanying drawings, in which like parts are
designated by like numerals in the vari,ous figures~ and in which:
Figure 1 is a partial cutaway view of a power transmissiorl drive
using a synchronous belt;
Figure 2 is a sectional view of the leftmost sprocket of Pigure 1,
taken along section 2-2 of Figure 3;
Flgure 3 is a partial sectional view of the sprocket taken along
section 3-3 o-f Figure 2;
Figure 4 is an enlarged view of a sectioned portion of a rubber
cushion as shown at 4-4 of Figure 3;
Figure 5 is a schematic view of a serpentine V-ribbed belt
drive for an automobile using a torsionally elastic sheave;
Figure 6 is a partial sectional view along 6-6 of Figure 5; and
Figure 7 is a graph of angular deflection versus torque for the
sprocket shown in E~igures 1-3, comparing d:iE-Eerent cushion:ing mater:ials.
The clescription w:ill refer to a primary dr:ive sprocket :Eor a motor-
cycle in Fi.gures 1-3, and a crankshaft sheave :Eor an automobile in F:igures 5
and 6. ~lowever the power transmission assembly and cushioning means may be
employed in various applications wherever torsional flexibility a:nd elastic
isolation between the hub and rim members is requ:ired i.n the transmiss:i.on o:E
rotary motion. For example, the devices are suitable :Eor use in such d:iverse
applications as transmission drives :Eor business machines, trac-tive drives, air
conditioner compressor drives, dlrect gear drives, chain dr:ives, va-rious belt
drives, and i.n flexi.ble couplings.
Re-ferring first to Figures 1-3, a power transmission belt drive 10 for
the prirnary drive of a motorcycle (linking engine output to transmission/clutch
input) includes a shock-absorbing torsionally elastic drive sprocket 12 con-
figured 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 drivi.ng relationship.
Alternatively, the shock-absorbing sprocket may be the driven sprocket rather
tnan 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 poly-
meric 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 2C of the shock-
absorbing sprocket, and with the teeth of sprocket 14 (not shown).
The shock-absorbing sprocket assembl.y 12 is generally composed of a
central hub 24 linput drive), outer rim 26 (output driven means), resilient
spring cushioning means 28 and 30, flange bearings 31, 32 sandwiching the hub
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~z~
~with bearing 31 being integral Wit]l hub 24), and a pair of rim surfaces 34,
36 integral with the rim and forming radial bearing surfaces, e.g., 33 (Figure
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 appl:ication arld
size of the sprocket assembly, it may be preferable to use at least three such
lugs, to prevent any thrust-indllced wobbles in the assembly. The major diameter
of the hub as measured Erom tip-to-t:ip of lugs 38 and 40 in Figure 2, is
somewhat less than the interl~al diameter oE the rim to allow clearance for
rotative movement. A portion oE the internal bore of the hub is splined to Eorm
a journaled fit with splines 44 Eormed 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 ex-tending lugs are mounted for limited
rotational movement within the internal cavity of rim 26. In addition to carry-
ing 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 3û in the opposite direction. It is preferred that the
cushion means be precompressed (interference fit) as shown, with its side sur-
faces exerting a biasing force against the lugs and ears oE 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,
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angular deElec-tio1l of the hub rolative to -the -rim. The void volume and angul-
ar deflection may be tailored to the speciEic application. The cap-tive void
volume shown in Figures 2 and 3 is determ:ined by -the total volurne occupied bythe resilient cushion 28 together with side clearances 56, 58 i.e., the bound
volume between lug 40 of the hub and ear 52 o:E the rim, side bear:ing plates
31 and 32, and arcuate connecting portions 60 and 62 of the hub and rim, res-
pectively.
The resilient cushioning means preEerably is conE:igured to have
arcuate top and bottom su:rEaces 70, 72, d:ivergir1g side surEaces 74, 76 and
substantially planar and preferably generally parallel front ancl rear faces 78,80.
In accordance with one aspect, the cushioned spring members 28, 30
are comprised o:E bodies of suitable elastomeric material loaded with modulus
and hysteresis-increasing fibrous reinforcement. It is preEerred that the
fibers are generally uniformly dispersed within the elastomeric matrix,
as shown in Figure 4 which is a schematic drawing of an S.E.M. photomicrograph
of a transverse section of the cushion, at 36X. The elastomeric matrix itselE
preferably has good compression set, high fatigue life, and resistance to any
environmental materials, such as oil and grease in accordance with the appli-
cation. For instance, nitrile rubber compounds have been found useful in the
motorcycle sprocket application. Various natural and synthe-tic 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 speci-
fic 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 custlions i.nclude fiber glass, metallic
fibers, carbon fibers and the like. The :fibers may typically have lengths aver-
aging from about .4 to about 12.7 millimeters and more preferably from about
1 to about 6.4 millimeters, and aspect ra-tios pre:Eerably 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 flnish~d
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 fi.bers 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 stra.in axes. With respect to Figures 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 circumferent-
ially along the inner surface 62, of the driven rim. As seen in Figure 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.
63
In certain other applications and clepending upon -the shape oE the
individual cushion, and the positioning of the adjacen-t cavities which will
define the principal strain axes, a random orientation of the embecldecl 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, these
problems are ]argely overcome by des;gning the cushion W;til 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.
In another aspect, it is preferred to utilize fibrous loading material
which swells appreciably when contacted with enviro-nmental materials, such as
oil and grease used in bearings of the hub and rim. In this manner the cushions
swell appreciably and this swelling off-sets 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
trademark Santoweb K (Monsanto Company) formed of a hardwood cellulosic fiber
of approximately .018 to .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 addi-
tionally comprising carbon black loading, oil extender, accelerators and
vulcanizing agents. After thcrough dispersion the resilient blocks were molded
so as to orient the fibers as shown in Figure ~. 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~F. (com-
pressed to 25 percent of original height), a compression set of 57 percent after
9 _
70 hours at 250~F., and an increase of 17 pe:rcent in volume after immerSiOJI
in railroad airbrake grease (A.A.R. SpeciEica-tion No. ~-914) for one week at
212F. Thus, significarlt swell took place which tends to offset compression
set during use.
Al-though it is preferred to use cushions which are solid, in appro-
priate applications per:Eorations or holes may be used to provide the advantages
disclosed in -that application.
The torque/angular deElect;on curve ("D") Eor the resiLicn-t cushions
of this aspect (Figures 1-4) compared with prior art cushions (Curves A and B)
and an experimental cushion (curve C) without Eiber loading are shown in Figure
7. All curves were generated using the sprocket assembly of Figures 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. 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, 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. (Trademark).
The fiber-loaded cushion represented by Curve D above has success-
fully solved the "speed shift" problem mentioned above, for motorcycle drives.
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~ lthougllllot narrowly critica:L, -the slope of the torque/cleflection
curve ~below -the "knee") is preEerab]y from about .02 to about .2, more prefer-
ably from about .03 to about .09 for the function degrees/lb-Et. The high
modulus cushion enables slopes within these desirable ranges to be obtained.
Simultaneously, the corresponding breakovcr point ("knee") is preferably at
least about 100 lb-t. more preferably at least 150 lb-ft of torque.
In Figure 5, an alternative app:Lication is shown ;n which a shock-
absorbing torsionally elastic belt sheave 12' is employecL in a serpentine
accessory drive for a transverse mounted diesel automobile engi.ne. In th:is
example, sheave 12' is coupled directly to the engine crankshaft. Shcave 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 shea-ve 79 and power steering sheave 81, a tension applying backside
idler 83, all coupled by serpentine belt 85. In gelleral, at least three sheaves
are li.nked by the belt in driving relation. As shown more clearly in Figure 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
using cushions 28', 30' of high modulus (preferably fiber loaded) or unloaded
cushions of relatively soft elastomeric material results in a number of advant-
ages 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- V-6 diesel
engine serpentine accessory drive of the type shown in Figure 5, three different
crank sheaves 12' were employed. Change in rpm ~excursion) at a given rpm level
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approximating engine idle was measured as was sheave temperature (qualitatively).
The first crankshaEt sheave was the control, a standard sheave of the type shown
partially in Figure 6~ without provision o-E ally elastomeric blocks or other
torque compensation. The second and thircl crankshaft sheaves employed the com-
pensator sheave 12' of the invention using, respectively, cushions 28', 30'
loaded with from about 4 to about 8 volume percent Santoweb K. (-trademark) per
the example mentioned previously herein, and unloaded relatively soft elasto-
meric cushions 28', 30' made of 35 percent acrylonitrile ~BR reinEorced with
carbon black and having a modulus of 600 psi at 100 percent elongation, and a
tensile strength oE 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 using high
modulus fiber reinforced cushions the excursion was about 9 rpm; and for the
compensator using relatively soft cushions the excursion was only about 2.5 rpm.
The control sheave (without torsional compensation) caused the belt to slip
about G degrees and the sheave became so hot after a few minutes of engine opera-
tion 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) virtual-
ly indefinitely. Of course, the lower the rpm excursionJ the lower the vibration
level, belt slip and belt elastomeric material shear and the longer the expect-
ed belt and drive train life. With low excursions it is also possible to reduce
flywheel weight, etc.
In the drive embodiment of Figure 5 it is preferred to limit the cap-
tive void volume between the cushions 28', 30' and adjacent sheave components
(i.e., hub, rim, etc.) so as to achieve angular deflections from about .1 to
about 8, more preferably from about 3 to about 7 degrees at 100 Ib-ft. torque.
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