Note: Descriptions are shown in the official language in which they were submitted.
35~3
This application is related to my earlier filed application Serial No.
319,851, filed January 18, 1979 entitled "Drive S~stem". In m~ said earlier
application I disclosed and c'Laimed a variable diameter pulley in which the
pulley diameter varied in infinite increments between minimum and maximum diam-
eter in response to load changes imposed by the driven element. As disclosed
and claimed in said earlier application, the pulley assembly comprises a hub, a
pair of parallel sideplates mounted concentric to the hub, a first one of the
sideplates is fixed to the hub and the second one of the sideplates is movable
about the hub or pulley axis relative to the first sideplate. Since the first
sideplate is fixed to the hub it is often referred to in this specification as a
fixed plate, while the second sideplate is often referred to as the movable plate.
Also, the slots may be referred to as cams and the pins as cam followers. A
plurality of pairs of curved slots (cams), are provided in the fixed plate sur-
face and an equal number of pairs of straight slots (cams), are provided in the
movable plate. A plurality of arcuate belt-engaging segments are located be-
tween the plates and two pins (cam followers), extend from each side o-F each
segment and are received in an appropriate one of the slots. '['ho slots in the
fixed plate are curved and arranged so that relative movement betwoon plates
causes the segment to follow thc slots to e~f~ect a net radial movement of tho
segment. In the basic pulloy as~embly, a sp-ring or othcr resilient means norlllal-
ly urges the movable plate to tlle ]imit oE its relative motion in a direction
that posi.tlons the bolt-engaging sogmonts to (leEine maxilllum pulley diumotor. ln-
creased bolt tension roslllting from groator loa~l causos tho nrcuato segmorlts to
Eollow the curves towurd the hllh thus rodllcing pulloy dilllllotcr and bolt sl)ood
wi.th a consequent change in power ratio. My said earlior appLication also di.s-
closed and claimed a drive system in whlch two variable dianleter pulleys connected
by a belt were utilized whereby when the larger pulley, driven by a crank and
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pedal, was subjected to increased load it underwent a reduction in diameter J
~ith an automatic proportionate increase in diameter of the smaller driven
pulley on the bicycle wheel. The net effect is that the ratio of diameter of
the driving pulley to that of the driven pulley was changed.
The present application contains all the subject matter of my earlier,
application along with amplification and clarification of such subject matter.
Additionally, I wish to herein disclose and claim an improved spring and arrange-
ment thereof for urging the movable plate normally into position whereby the
arcuate segments define maximum pulley diameter. Also, I disclose and claim
herein ways and means for selecting and achieving distinct patterns of power andspeed variations. For instance, there may be definite automatic shifting se-
quences and/or dwell at selected speed levels.
TECIINICAL FIELD
This invention relates to variable diameter pulleys and drive systems
incorporating at least two such pulleys interconnected by an endless belt. More
particularly, the invention is directed to a load responsive pulley that auto-
matically reduces in diameter in response to increased belt tension and increases
diameter in response to easi,ng of belt tension thus changing the speed and power
ratios between driving and driven pulleys to accommodate load changes.
BACKGROUND O~ TIIE INVEN'rlON
Drive systems utilizing pulleys or sprockets and flexible dra~t means
such as chains or belts trainod thereabout are well known. It is equally well
known to provide for changes ln the cliameter of oither or both tho cl-rivinK ordriven pulley to accommodate changes in imposed load. In bicyclos, the most
commonly used variable speed/output drive requires a plurality of drivin~
sprockets at both the crank and driven wheel. A shi,ftin~ mechanism changes the
chain from sprocket to sprocket. Although this system is in wicle use, it does
35~3
suffer from the disadvantages, inter alia, that ~1) the shifting is not automatic
but requires deliberate effort by the operator; ~2) the chains often slip off the
sprockets causing much inconvenience; and (3) the several speeds and power ratios
available are fixed and may or may not be optimum for a given situation.
~ arious devices have been proposed to provide a load responsive system
to automatically vary the driving sprocket diameter in response to load changes.
One such arrangement, as described in United States Patent 3,995,508, utilizes a
driving sprocketassembly comprising a pair of spaced apart plates mounted on a
hub. One plate is fixed to and rotates with the hub while the other is free to
rotate about the hub axis. The fixed plate is provided with a plurality of
spiral slots while the movable plate has an equal number of straight radially
extending slots. A plurality of small sprockets are carried between the plates
and each sprocket is provided with laterally extending elements, such as pins
that are received in the slots. A spring co-acts between the plates urging them
to the relative angular position that moves the sprockets farthest from the hub
to define maximum effective sprocket diameter. In such prior arrangement, in-
creased load forces the pins and sprockets to follow the slots toward the hub
thus reducing sprocket diameter. In the arrangement described, the resulting
chain slack is taken up by a separate take-up device. Although the device de-
scribed appears generally to be workable, it suffers from the disadvantages thatit is limited to a chaln and is not adaptable to belts. Chains are undesirable
due to initlal as w011 as replaccment cost, and also because they frequently
malfunction due to Eailure to engage the sprockets procisely. Moreover, the
range of speed and power ratio change is limited sinco thc ~liameter of the small
sprocket i5 ~`ixed.
Systems have also been proposed utilizing belts which are dcsirable
because they are relatively inexpensive, require little or no maintenance and,
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3 ~ 3
even more importantly, are not required to engage sprocket teeth hence will not
jump off the pulley, but will maintain continuous contact. An early belt driven
system, as described in United States Patent No. 672,962, employs a pulley having
a pair of spaced-apart plates fixed to a hub and at least one other plate rotat-
able relative to the hub and fixed plate. There is a plurality of spirally
curved slots in the fixed plate and an equal number of straight radial slots in
the movable plate. Arcuate belt-engaging segments between the plates have later-
ally extending guides that are received in the slots and mechanical means rotate
the plates manually to move the segments and vary the pulley diameter. This
system ls not automatic. Also, the belt-to-pulley contact is erratic because
the arcuate segments tend to roll in the direction of belt travel. Additionally,
the rolling or tilting of the segments causes the segment guides to bind in the
straight radial slots thus seriously hampering operation of the entire drive.
Another proposal, as disclosed in British Patent No. 159,790, utilizes
a pulley assembly that has a fixed and a movable plate mounted concentric to a
hub. Each plate is provided with a plurality of pairs of parallel spirally
extending curved slots. The curves of the two plates are îdentical, but extend
in opposite directions. Arcuate belt-engaging segments are positioned between
the plates, each segment being provided wlth pins that are received in the slots
2~ in both plates. The pulley diameters cannot vary automatically. Instead, complex
means are provided to manually acljust the relative angular positions of the
plates to effcct radial movement of the segments. The structure requires parallel
slots which cannot gulde the scgments raclially except with pronounced tilting or
rolling which reduces belt-to-pulley contact
ln summary, of the several prlor arrangements clescri~ed above, only
the manually shiftable multiple sprocket chain drive has enjoyed any success.
The load responsive chain and sprocket drive disclosed in U.S.A. Patent
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~1~3593
3,995,508 apparently suffers from the disadvantages of frequent misengagement of
sprocket and chain while the prior belt and pulley arrangements do not and cannot
provide sufficient and reliable belt-to-pulley contact throughout their range of
operations for acceptable operation.
BRIEF DESCRIPTION OF THE INVENTION
It is the principal object of the present invention to provide a belt-
engaging pulley the diameter of which is variable automatically in response to
various tension loads imposed thereon yet presents for belt engagement a maximum,
uniform and predictable area over its entire range.
Another object is the provision of a load-responsive pulley of the type
described in which a variety of patterns of the speed and power ratios may be
achieved.
An important related object is the provision of a pulley of the type
described in which the rate of change and force requirements therefor may be
predetermined by selection of spring strength and slot configuration.
Still another object is provision of a load-responsive variable diam
eter pulley in which arcuate belt-engaging segments move smo~thly through a
variety of patterns, including steps or dwells and/or infinite positions yet
achieve a net radial movement relative to the pulley ax:is.
A further object is the provision, in a variablo cliallleter pulley of
thc type described, of an improved sprlng for normally mainta:i.n:i.ng the pulley at
nlaximum effectlve dlametor.
Another related object i.s prov.i.slon of an automat:ic load-rosponsive
drive systcm incorporatlng two variable cliameter pulloys functionally connected
by an endless belt trained theroabout.
In a.ccordance with the invention, the foregoing and probably other
objects are achieved by a pulley assembly having a hub, a first sideplate con~
-- 5 --
5~33
centricc to said hub and fixed thereto, a second sideplate concentric to said hub
and rotatable a6Out said hub relative to said first sideplate, a plurality of
pairs of curved slots in said first sideplate said slots extending outwardly and
in the direction of rotation o~ said first sideplate and a plurality of slots
in said movable second sideplate. These slots extend from a location adjacent
the outer end of said curved slots in said first sideplate to a location adjacent
the inner ends of said curved slots. A plurality of arcuate belt-engaging seg-
ments are located between said first and second sideplates. Pins extending
laterally from opposite sides of said arcuate segments, said pins being received
in said slots. Resilient means act between said first and second plates to bias
said second plate to the position where said belt-engaging segments are at the
limit of their outward travel in said slots, and said slots in said first and
second sideplates are coordinated to the location of said pins on said arcuate
segments so that, at all locations in said slots, the chord of each arcuate belt-
engaging segment forms a right angle with a radius of said hub.
Also, in accordance with a preferred embodiment of the invention,a drive
system is presented employing two variable diameter pulleys functionally connect-
ed by an endless belt trained successively thereabout. In another embodiment
which is especially useful on bicycles, the driven pulley in the rear wheel is
relatively small compared to the pedal-operated driving pulley and there :is no
spring co-acting between plates of the small pulley.
My inventLon is preclicatod on the basic discovory tllat the slot con-
Piguration must be selected, ompiriclllly i~ necessary, so that the arcuate seg-
ments always bear the same geollletric rclationship to a racl-ius of thc pulley
throughout the entlre range of pulley diameter. [n accordanco with this require-
mellt, the chord o~ each arcuate segment must always be normal to a radius o~ the
pulley. To achieve this, the invention requires pairs of slots, at least in the
,
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~3593
fixed plate, that are coordinated with the cam follower pins on the arcuate seg-
ments to maintain the normal relationship throughout the travel. It is a re-
quirement that the individual slots of each pair of slots in the fixed plate not
be parallel to each other.
As will become more apparent, the invention also provides the ability
to select from an infinite variety of patterns for speed and power ratio varia-
tions.
In accordance with another feature of the invention, a horseshoe-
shaped spring is mounted to interact between the fixed plate and the movable
plate to bias them toward that relative angular displacement which provides maxi-
mum pulley diameter.
BRIEP DESCRIPTION OF THE DRAWINGS
In order that the invention may be more readily understood and carried
into effect, reference is made to the accompanying drawings and description
thereof which are offered by way of example only and not in limitation of the
invention, the scope of which is defined by the appended claims, including equiv-
alents thereof, rather than any preceding description.
ln the drawings:
Figure 1 is a partial top view of a bicycle having a drive system em-
bodying the invention.
Figure 2 i.s side view of the drivc shown in Figure I some parts beingomitted and some hLdden parts showll in dotted lines, all or purposes oE clarity.
Figure 3 Ls an enlarged sectional view takon in thc plalle of line 3 - 3
of Pigure 2 and looking in the direction of arrows 3.
Figure 4 is an enlarged sectional view taken in the plane o~ line 4 - 4
of Figure 2 looking in the direction of arrows 4.
Figure 5 is a pictorial view o one of the arcuate belt-engaging
.
. - 7 _
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sectors employed in the invention.
Figure 6 is an exploded view of a pulley of the type illustrated in
Figures 1 - 4 but em~odying a modified spring arrangement.
Pigure 7 is an exploded view of a modification of the pulley illus-
trated in Figures 1 - 4 and in which two essentially identical sideplates 26 areemployed to provide increased stability.
Figure 8 is a view similar to Figure 1 illustrating a drive embodying
the modified pulley illustrated in Figure 7.
Figure 9 is a side view of the drive shown in Figure 8 with some parts
omitted and others shown in dotted lines for clarity.
Figure 10 is a sectional view taken in the plane of line 10 - 10 of
Figure 9 looking in the direction of arrows lO.
Figure l] is a sectional view taken in the plane of line 11 - 11 of
Figure 9 looking in the direction of arrows 11.
Figure 12 is a sectional view taken in the plane of line 12 - 12 of
Figure 8 illustrating in detail the horseshoe spring biasing the fixed and movable
plates to that angular displacement which results in maxiMum pulley diameter.
Figure 13 is a sectional view taken in the plane of line 13 - 13 of
Pigure 12 looking in the direction of arrows 12.
2a Figure 14 is a sectional vicw taken in the plane of line 14 - 14 of
Pigure 12 looking in the direction of arrows 14.
Pigure 15 is a view dcpictin~ three sequential positions of a pulley
and certain parts theroof during operation, some parts are omitted and others
shown in dotted lines for clarity. 'I'he pulley illustrated in Figure 15 has thccurved cam slots in the flxed plate and straight cam slots in the movable plate
as illustrated in Figures 1 - 2.
Figures 16 - 18 inclusive are enlarged partially cut away views of the
"
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~35~3
portions enclosed respectively by lines 16, 17 and 18 of Figure 15, i]lustrating
in greater detail relative movement of components during the operational se-
quence shown in Figure 15.
Figure 19 is a view similar to Figure 15, but showing an operational
sequence of a pulley in which the cam slots in both the fixed and movable plates
are curved.
Figures 20 - 22 inclusive are enlarged partially cut away views of the
portions enclosed respectively by lines 20, 21 and 22 of Figure 19.
Figure 23 is a view, similar to Pigure 15 but of a modified pulley in
which the straight cam slots are positioned differently from those of the pulley
s,hown in ~igure lS.
Pigures 24 . 26 inclusive are enlarged partially cut away views of the
portions enclosed respectively by lines 24, 25 and 26 of Figure 23.
~ igure 27 is a view similar to Figure 15 but in which the cam slots in
the movable plate 27 are zig-zag or stepped rather than continuous.
Figures 28 - 30 inclusive are enlarged partially cut away views of the
portions enclosed respectively by lines 28, 29 and 30 of Figure 27.
Figure 31 is a view similar to ~igure 15 but of a pulley embodying a
modification in which the cam slots in the fixecl plate are irregular to provide
a stepped rather than continuous variation ot` pulley diameter.
~ igures 32 - 34 inclusive are enlargcd partially cut away views o~ the
portions enclosed respectively by the llnes 32, 33, and 34 of Piguro 31.
Dl~'.TAILEID DLSCI~IPrl':[ON OP Tllr D!~AW'[NGS
~ igures 1 - 5 illustrate a prc~errod oInI)odinlent o~ the pulley o~ the
invention as well as a bi,cyclo drive system cmbody:ing the inventlon.
As illustrated, the drivc system, designatecl generally 10, is mounted
on a bicycle Il which is shown fr-gmentarily and Includes chaLn stays or rear
. .
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3~3
wheel supports 12 and 13, bottom bracket or crank assembly housing 14, seat tube
15J down tube 16, a rear wheel axle 17 and a wheel 19 having usual spokes 18,
the wheel being fixed to the frame by usual wing nuts 20 and 21.
The drive system includes a variable diameter pulley assembly 22 se-
cured to and rotatable with a crank 23. The crank may be of any conventional
design and will, if in a bicycle, include pedals, a hub, and a transverse portion
extending through the crank assembly housing 14. The drive also includes a re-
latively smaller variable diameter pulley assembly 24 secured to and rotatable
with the rear wheel. An endless V belt 25 is trained about the two pulleys. In
the drive as illustrated, the small variable diameter pulley not only contributes
to enhanced operation of the drive but acts as a belt slack take-up device. If
desired, to accommodate special conditions, the small pulley may be replaced
with a fixed diameter pulley and a separate belt slack take-up device provided.
However, such an arrangement is not the equivalent of the illustrated drive sys-
tem embodiment. Rather, it is a modification useful under different conditions.
The load responsive variable diameter pulley 22 comprises spaced apart
plates 26 and 27. One plate 26 is fixed to the crank 23 by means of an integral
central support plate 35 which is in turn secured to the crank 23 adjacent one
end oi` the crank assembly housing 1~ by a typical cone. The cono is referred to
herein as a hub. The other plate 27 ls mounted for relativo angular ~lotion
about the extended annular section 2~ of the support plato :~S and, oE courso,
about the axis of the pulley and hub.
A central support plato 36 is socured to the movablo plato 27 in
spaced relationship to the central support plate 35 thereby to deEine an en-
closure for a spring. The extended annular section 28 provides bearing surEaces
for the movable plate 27 and the support plate 36. It also ensures spacing be-
tween support plates 35 and 36.
- 1 0
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~35~3
For controlling net radlal movement of the belt-engaging segments 30,
curved slots (cams) 29 are provided in the surface of the fixed plate 26. Cam
follower pins 31 extend laterall~ from opposite sides of the segment and are
received in the slots. The slots 29 are arranged in pairs - onepair for each
segment. As noted, the individual curved slots, although of similar configura-
tion need not be identical and cannot be parallel to each other. To predetermine
the amount of angular movement and thus the amount of overload needed to effect
change in the pulley diameter straight slots 33 are provided in the movable plate
27. The pinS 31 which extend through the arcuate segments are received in the
slots 33. A flanged nut 32 may be used to hold the pins in place.
A plurality of coil springs 37 are connected between pins 38 on the
central support plate 36 of the movable plate 27 and pins 39 on the central sup-
port plate 35 of the fixed plate 26. These springs bias the plates toward an
angular displacement at which the arcuate segments are at the limit of their out-
ward travel thus defining maximum diameter of the pulley 22.
The smaller variable diameter pulley 24 driving the rear wheel is
similar in construction to pulley 22. It comprises spaced-apart fixed and movable
plates 40 and 41, with pairs of curved slots ~cams~ 42 in the fi,xed plate 40 and
straight slots (cams) 43 in the movable plate 41. Cam Eollowers, formcd as
threaded pins 46 extending laterally from the arcuate segmcntx 45 are received
in the slots 42 cmd 43 rospectively. A flanged nut 47 may bc usod to rctain the
pin in placc.
As shown in Figure 5 tho arcuate 'belt-engaging sogmonts 30 and 45, com-
prise a curved body 60 with upstanding sidowalls 61 and 62 tho inner surEaces of
which are slanted to accommodate a V bolt and suitably roughencd to onhance fric-
tional engagement with the belt. Transverse holes are drillecl through the seg-
ments to accommodate the pins 31 and 46. The belt-engaging segments Eor both
- 11 -
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~1~;35~
pulleys are selected so that at minimum pulley diameter the segments come to-
gether to form a circular continuous belt-engaging surface. Obviously, as the
segments move outwardly the surface becomes discontinuous, however, the total
area of belt-engagement remains essentially the same. This is achieved in ac-
cordance with this invention by insuring that the chord of the segment is normal
to a radius of the pulley. Thus the area of belt-engagement is always essential-
ly uniform and definitely predictable.
Unlike pulley 22, the smaller pulley 24 does not have any spring bias-
ing the components to maximum diameter. Instead, in the drive system shown, the
taut belt 25 wraps around the pulley and the applied tension prevents the segments
from moving outwardly in the slots.
When the large pulley is at maximum diameter and the small pulley at
minimum diameter, as shown in ~igures 1 - 4, the drive is in a normal load posi-
tion. This is the position where greatest speed is achieved. It is also the
position of minimum power output. When the diameter of the large pulley 22 de-
creases and/or the diameter of the small pulley 23 increases, a lower speed is
transmitted to the wheel 19, but the power output is greater hence it is easier
to climb a steep hill. 'Ln my drive, chsmges in pulley diameters und thus speed
'~ and power are achieved automatically. In operation, if the hicyclc stslrts uphil'l,
increased resistsmce is transmitted through tho rear wheel 19, pul1Oy 2~ and
belt 25 - to the belt-ellgslging soglllonts 30 on tho Is~rgo ~Iriving pllLLey 22. When
the increased load ovorcomos tho oppos-inR forco of springs X7, tllo holt pull on
the sogments will causo tho cam f'ollowor pins ~1, acting in slots 33 to offoct
rotation oE the plato 27 agsllnst tho urgLng of tho splirlgs X7. 'I'his csluses tho
cam -follower p:ins 81 to move also along tho curved CUIIIS 29 ill the f'ixed plate
thus eEecting a net inward radial movornent oE the belt-ongslg-ing segments and
reducing pulley diameter. This movement stops when the resulting increased
12 -
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~ ~35~
spring tension of~sets the load. Whene~er there is a reducti~n in diameter of
the large pulley there will be a lessening of tension in the lower run of the
belt. The reduced tension or slack permits the belt to pull the segments 45
outwardly in the slots thus increasing the diameter of the smaller pulley 24.
The action of the two pulleys is proportional and, for all practical purposes,
simultaneous. The result is a smooth effortless changing of speed and ability
to handle varying loads. When all the slack or reduced belt tension disappears
the diameter of both pulleys stabilizes until a further load variation is sensed.
In the illustrated embodiment, the smaller pulley does not reauire a
spring because the belt will pull the sectors outwardly until all slack is takenup. A spring can be employed if desired for any reason, but it is not necessary
for this application as the desired expansion and contraction of thc rear pulleyis achieved automatically in the drive assembly of the invention. ~ drive utiliz-
ing a spring on both pulleys to bias them toward maximum diameter is not the
equivalent of that illustrated but is a separate modification useEul under dif-
~erent conditions where, for instance, a smaller range of chan~e can be tolerated.
~igure 6 is an exploded view of a pulley similar to that shown in
~igllres 1 - 4, but with a modified spring and consequent changes in structure to
accommodate such spring. Also, the crank assembly and housing are omitted. The
pulley, as shown in ~igure 6, comprises a fixed plate 26, a mcvable plate 27, a
central support plate 35 to which tlle Eixed plate 26 is securcd by suitable
screws 34 to hold it in spaccd-apart rclationship to tho movablc p~lato 27.
A simple but strong horseslloe spring 63 is locatod in the rocoss do-
flned between plates 35 and 36. Ono end-piece 64 of the spring is suitllbly so-
cured, as by a machine screw 65 to the central support plato 3fi o~ tho movable
plate 27 and at end piece 66 to the central support plate 35 ot the fixed plate
which is in turn connected by screws 34 to the fixed plate 26. The horseshoe
3593
spring is compact yet strong enough to af~ect the high torques encountered dur-
ing operation of a bicycle. It replaces the several smaller springs 37 shown in
Figures 1 - 4. The horseshoe spring is installed so that it is almost fully ex-
panded whereby relative angular motion of plate 27 will force the spring ends
toward each other. As in the pulley illustrated in Figures 1 - 4 the fixed plate27 has curved cam slots 29 while the movable plate has straight cam slots 33,
only a few of which are shown.
Figures 7 - 14 illustrate a modification of the pulley useful in situ-
ations where high forces are involved. 'I'he pulley is similar to that shown in
la Pi~gure 6 but includes a pair of identical fixed plates 26 held in spaced-apart
relationship by a spacer 68. 'I'he two plates 26, the spacer and the central sup-
port plate 35 are all held together by suitable machine screws 71, threaded even-
tually into an annular member 69 integral to the support plate 35. The member 69corresponds to the extension 28 of Figures 3 and 6. It is required that the two
plates 26 be mounted so their cam slots are exactly aligned with each other.
Then, when the segments 30 are in place the pins 31 will pass through the curvedslots 29 in both of the plates 26 then through the straight slots 33 i.n the mov-
able plate 27 which is mounted face to face and closely adjacent the inboard oneof. the fixed plates 26. A horseshoe spring 63 ;s connected to co-act hetween the
2a ~ixed plate 26 and the movable plate 27 by securin~ its ends 64 and 66 to central
support plates 35 and 36.
~'igure 15 lllustratcs a soquonco o~ oporation of tllo pulloy whon an
increased load is lmposed theroon as when tho bicyclo climhs a h:ill. In the
normal position, as shown in tho top diagralll, the pulley is at maximum dialneter.
In the center dia~ram the crank and fixed plate have rotated about 22.5 de~rces
while the movable plate has rotated an equal amount in the opposite direction
to crank rotation; and in the bottom diagram, the crank and fixed plate as well
- 14 -
3593
as the movable plate have rotated 45 degrees, a total relative displacement of
90 degrees; and the arcuate segments have moved to the innermost position. One
end of the pins 31 on the arcuate segment follow the curved slots 29 in the
plate 26 while the opposite ends follow the straight slots 33 in the movable
plate 27. The head of the pins 31 and the flanged nuts 32 at the opposite end
hold the pins in the slots. The net movement of the arcuate segment is radially
invard thus decreasing the pulley diameter. In the bicycle drive system of the
invention any decrease in the diameter of the large pulley automatically causes
a proportionate increase in the diameter of the small pulley. The increase in
lQ the small pulley diameter is effected by the belt pulling on the segments where-
by the pins 46 follow the curved slots 42 and straight slots 43 in the side-
plates.
The changes in diameter of both pulleys will continue until the spring
de~lection has completely offset the increased load or the pins (cam followers)
reach the end of slots (cams) whichever occurs first. In other words, the spring
is deflected as it senses increased torque thereby effecting decrease in diam-
eter of the large pulley. This results ;.n a change in belt tension that causes
an increase in the diameter of the small pulley. It will be appreciated that
changes in belt tenslon are complex. The tension increases in upper or working
run of the belt under increased load, but at the same time decrcases on the lower
run. Thus, there :Ls some slack on the lowcr run. Ihe combination ot increased
tension on the upper run and decreased tcns:ion on the lower run is what causes
expansion o~ the small pulley. ~`he amount Oe dLameter increase being limited
by tension of the belt when this llmited slack is taken up. [n any event, the
maximum range Oe diameter changes is eixed by the length of the slots, the
strength of the spring and/or the length of the belt.
It is critical to proper operation that the arcuate belt-engaging seg-
- 15 -
S~3
ments move radially ~ithout tilting. Tilting causes loss of bel~ contact thus
reducing drive efficiency due to belt slippage. Thus, the curves in both plates
must be selected so that as the belt-engaging segments move along the curves the
e~fective chord of the arcuate belt-engaging surface is always normal to a radi-
us from the pulley axis. This relationship is illustrated in Figures 16 18
where the chord 81 is shown to be at right angle to the pulley's radius 82
regardless of position of the segment in the slot. Care must be taken to ensure
that it is the chords of the arcuate segments that are maintained normal to a
radius of the pulley. 'I'he chord may not be the same as a line between the pins.
However, a line between the pins whether or not normal to a radius, must maintain
the same geometric relationship to a radius of the pulley.
In all embodiments shown in the drawings, a chord of the arcuate seg-
ments and a line between the pins coincide, but as noted, this is not necessary.
Also, as shown, the pin ends 31 and 32 are directly opposite each other. This is
convenient, but not necessary as the pairs of curves in the first and second
sideplates may be offset from each other.
Pigures 19 - 22 are similar to ~igures 15 - 18, but show a construction
in which the slots 73 in the movable plate 27 are simply the reverse of the
curves 29 in the fixed plate 26. With the curved slots 73 a greater ovcrload
is, required to move the arcuatc sector inwardly. 'rhis is so because therc must
be more displacement of the spring when the arcuate sogment followx a longcr
spiral path than when it follows the shortcr racl;al path.
I1igures 23 - 26 are similar to Figuros 'l5 - l8 but the stra;ght slots
74 in the movable plate 27 are not parallel to a radius of thc pulley betweell
them. Instead, one nf the slots lies on a rad;us. In this posi.tion the slots
75 require a smaller load to decrease the pulley diameter than do either the
curved slots 73 or the straight slots 33 of the embodiment shown in Figures 19 -
593
22, because as~ noted, a slot configuration that requires the smallest spring de-
flection for full travel of the arcuate segments will be the most sensitive to
overload.
Figures 27 - 30 are similar to Figures 15 -18, except that the illus-
trated embodiment employs a zig-zag slot 76 in the movable plate. This provides
a dwell or a stepped speed change at one or more radial locations of the segment.
That is, when overload is first applied, it will move the arcuate segment in-
wardly to that part of the slot 76 that is approximately parallel to the belt-
engaging surface of the arcuate segment. If the overload has then been offset
lQ by spring deflection the arcuate segment will not move any further inwardly. On
the other hand, if the overload is not offset by the spring, it will continue
to deflect the spring until the arcuate segment has traversed the center part of
the slot and if at that point the overload is still not offset by the spring the
segment (by the pins in the slots) moves in along the inboard part of the slot
to minimum diameter. Thus, although the movable plate rotates whenever there is
an increased load not offset by the spring, when the segment is in a dwell posi-
tion of the slots such plate movement will not cause radial movement of the seg-
ment so there will be no diameter change even though some spring deflect:ion is
occurring. In other words, there is a range of overload that can bo accommodated
2Q at each dwell place without change in pulley diameter.
~ igures 31 - 34 are similar to ~igures 15 - 18, but illustrato an em-
bodiment of tho pulley in which an irrcgular slot 77 is providod in the eixed
plate 26. Thc operation o~ this pulley wi!l, likc that illl~stratcd in l1iguros
27 - 30, proivde a dwell at one or morc radial locat1ons in thc slot. ~t cach
dwell, there will be a range of overloud at which no ~`urther inward shifting oE
the arcuate segment will occur, but once the load range o~ that dwell section is
exceeded, inward shifting of the arcuate segment will resume.
- 17 -
35~3
Obviously, the number of dwell portions in the zig_zag slot 76 of
Figures 27 - 3a and the irregular slot 77 may vary according to the use to which
the pulley and any drive embodying it are to be put.
As previously noted the slots in both the fixed and movable plates
must be carefully defined so that the effective chord of each arcuate segment
at all times defines a right angle wi~h a radius from the pu]ley axis. An en-
tirely suitable way to define the curves is to trace the path the pins or cam
followers 31 take as they move outwardly while maintaining the necessary right
angle intersection between such chord and pulley radius. The chord of the seg-
ment may be taken across the bottom of the ~ or, if the pins 31 and 32 are pro-
perly placed, a line between them can be used as the chord.
In the foregoing description, the large and small pulleys are de-
scribed as having the same construction. This is not entirely correct. For
instance, as shown in Pigure 11, the fixed and movable plates 40 and 41 are suit-
ably secured to an axially offset pla~e that is in turn fastened to a free wheel-
ing clutch assembly mounted concentrically to the rear shaft 17. The construc-
tion of Figure 4 is similar.
Although the invention has been described in connect;on with thc use of
V belts and a bicycle drive system, it will be appreciated that other types of
2~ belts may be used and the pulley ~nd drive systems employed in other vehicles or
in industrlal application.
