US2603978A - Extensible pulley - Google Patents

Description

y 1952 E. E. J. GAISSET EXTENSIBLE PULLEY Filed Feb. 7. 1949 4 Sheets-Sheet 2 July 22, 1952 E. E. J. GAISSET EXTENSIBLE PULLEY 4 Sheets-Sheet 3 Filed Feb. 7. 1949 July 22, 1952 E. J. GAISSET EXTENSIBLE PULLEY 4 Sheets-Sheet 4 Filed Feb. 7. 1949 Patented July 22, 1952 EXTENSIBLE PULLFY- Edmond E. J. Ga'l'sset, Carcassonne, Aude, France Application February '7, 1949, Serial No. 74,874

In France February 9, 1948 According to the relative position of the two,

disks, the opening at the intersection of two paired slots into which is engaged the support of a'rim element, is located nearer to or further from the centre of the pulley, this enabling to vary the diameter of this pulley.

The object of my invention is to improve extensible pulleys formed by radially movable rim segments.

One of the'objects of the invention is the suppression of noise and wear occurring in known pulleys.

Another object of the invention is a better guiding of the radial motion of the rim elements.

Another object of the invention is the suppression of the causes of wear and tear of straps due to a sudden change in curvature owing to the discontinuity of the periphery of these pulleys.

The invention will be made fully apparent in the following description, reference being had to the accompanying drawings in which:

Fig. 1 is a side elevation diagram of a known pulley.-

Fig. 2 is a cross-section along line IlT I I of I Fig. 1.

Figs. 3 and 4 are two similar side elevations of a pulley according to the invention, at its maxi-' mum and minimum diameters respectively, the

paired flanges being in position in Fig. 3, and the inner flange only being apparent in Fig. 4.

"Fig.' 5 is a cross-section along line VV of Fig.3.

Fig. 6 is a diagram showing the extreme positions of a rim element of the pulley, and an intermediate position.

Fig.. '7 is a side elevation of another embodi- 1929 and No.-859,008 of August 11, 1939, filed in the applicants name.

This pulley has two sides each of which is 6'Claims. ((31. 74- 230.22) I formed by two disksan inner one i, and an outer one 2which are integral with two coaxial sleeves 3 and 4 respectively, the latter being secured to shaft 5.

In disks l and 2 are provided curvilinear slots 6 regularly distributed over each one of them, but the slots in one of the disks are directed in the opposite way relatively to the slots in the, ad.- joining' one. The tips of pins 1 integral with each rim element 9, cross curvilinear quadrilateral openings 8 at the intersections of slots 6 provided in the paired disks. If slots 6 have the shape of logarithmic spirals whose tangent makes.

a constant angle of with the radius vector, two spirals provided in two'adjoining disks always out at right angles, so that, if pins 1 have a square cross-section, they arecentred and guidwards the centre or the periphery, by thesame' amount. Moreover, these elements are kept in a constant, direction relatively to the disks, because a rotation of pins 1 in openings 8 cannot occur owing to the shape of the pins. Rim .ele-

ments 9 thus form together an extensible pulley rim either for a flat strap or for trapezoidal ones if grooves 9a are provided. The diameter of this a pulley may be altered by causing anyhow disks I and 2 to rotate relatively to one another. This.

rotation may merely be the result of centripetal forces exerted by the strap on the elements,-on

the one hand, and of centrifugal forces exerted on rim elements 9, on theother hand, this causing the pulley to automatically adjust according to the assigned resistant or driving couple.

This pulley, although very attractive in principle, nevertheless bears numerous disadvanjamed in openings 8. Anyway, in order to allow sliding, a certain clearance is required, this causing noise and wear.

sage in every-position, .to pins l ofrim elements? 9. Eachfof these pins 7 is freely held, at its tips, at one end of a tie-rod l6 and at one end of a corresponding tie-rod H, the other ends of these;

tie-rods being hinged upon pivots I8, l9 respectively, carried by flanges H), H respectively; tierods |6 being inversely directed relativelyto tie-- rods l1.

Owing to this arrangement, a rim element-9 supported by two tie-rods I6 and two tie-rods HE may occupy any position between that corre sponding to themaximun'r diameter of the pulley (Fig- 3), and that corresponding to the minimum diameter (Fig.4) by a. mere relative rotatior of the two flanges ID'and II.

Flanges ID and II are only designedjto carry. pivots l8 and I9 and to prevent any lateral'displacement of tie-rods I5, I! and rim elements 9.-

In this example, the pulley comprises eight rim elements. It may-be shown by calculation that ifipivots. l8} [9 are distributed over a circumference of'radius- 0.83Z, with I being the operative length. ofthe tie-rods, the maximum radius. of the-.pulleyis approximately Z, whereas the minimumlradius. may be. as low as. 0.32 roughly see Fig.5); I

Fig. 5 showsthearrangement andlsizebipivtats.

181.19,, designed to allow ireelmovement. of tie.-

rods. l6;v I! between theirextreme positions with-.

outhindering. each other, even if they are. rectilinear; and. the .more. so, if they are bent,

The angle between twov corresponding tie-rodstion-, a change: in the ratio of 1:9fiwhich isvery convenient forpractical use.

.However,..if. aratio greater than. 1:3 between.

the extreme diameters, is'required. twosets of L-shaped tie-rods and. 20' (Fig. '7) may be 1 carrying? the considered rim element 9.

In the shown example, tie-rods l6, as well as tie-rods ll, being alternately placed in two parallel planes, if it is assumed that the thickness of the tie-rods is equal to that of the flanges which all have the same thickness, the overall dimensions on either side of the pulley may be reduced to six times the thickness of a disk.

The position of pins I determines that of rimv elements-9: However, for? the pull'ey, to; fulfill its function, it'is important that those rim-elements 9 be prevented from rotating about these pins 1 during rotation of the pulley, under the exertion oi tangential forces due to the strap.

A" firstmeans to achieve this result consists in. securing. each rinr element 9 by means of a fiat (Fig. 8). whose outline is such that its edges 213a andZlbbe in contact with pins 7' of the next rim elements on either side of pin 1 The angular interval 0 between pins 1 and 7 remaining-constant, edges 2|.afand. 21b. of keyll. are

incontact with. pins E." whateverbe the diameter assignedtothepulley.

The. set of keys. [IE-shown in full I linein the case ofthe minimum diameterandin. brokenline in thev case oi. the maximum diameter-prevents the -rotation .of,.thefour rim. elements .9. about an angleof i It should be notedthat the. radius of curvature of each rim element must be at the most-equal.

to; the. minimum-radius .oi the pulley in the. state of maximum contraction, so: that no. impacttakes. place in the strap during passage from 01168182- menttathe other.

Another wayof preventing: rotation of. rim. elements Q about theirpins 1, consists insecuring these pins-tetheends-of one of the sets'of tie-- rods I 6. or- [1-,- and freely holding them at theends :Qf'thzB: tie-rods-o-i theother set. 1

Under thoseconditions, each rim elementfl; lies along, a y direction. depending on. the position of; the tie-rod to'which'it issecured. During changes:

in dimensions. oi the pulley, the angle: a made by the axis of each of these rim elements-and the radius of the: pulley passing through itspin,

used in'stead'of. the previous sets of tie-rods l6- and Hf These tie-rods 2d, 201 are arranged so.

that. pins '1 hel'd'at'their ends. be always situated inside the. concavity of the following" L-shaped'" 'tie-rod;

Slots 6 similar to those of Fig. 1 but a'little wider are provided for the free-displacement of pins 'l'. The positionsof the tie-rods giving the maXimum'di'a-meter are shown in full line, and

the positions giving the minimum diameter are shown in broken line;

Inf: practice, the. tie-rods are given the smallestpossible thickness, so as to. decrease the. lateral overall dimensions-of the whole.

As shown. in Fig. 5, tie-rods l5 hinged upon pivots 18 carried.

ment' large. enough for their rim'to be-tangent is altered by a certain angle when the tie-rod? moves-"(Fig 6 For .theserim: elements to always remain tangent: to =the strap--wrapping them, it. is. enough-"for. their radius of curvature to be. at

least equal to.the: distance dbetween pins 1 and the primitiverioircle 22- (Fig. 6)='of the pulley-,xbutjt. is:necessary;1in order to avoid exaggerated bendings of the strap that the radius of curvature thus;

determined be greater-than. the radius of. the

pulley ofminimum diameter required bythe normal use of said strap. As a matter of fact; particularly: in the case of trapezoidal straps,. it-is known that there is, for each'of them,.a. minimum:

diameter or the. pulley around which: it maybe wound: without excess-oi strain or wear.

The simplest solution consists in giving'the elementsa radius: of curvature-:1" equal to. the

minimum radius Of the pulley compatible with.

the strap;:.in making the: support'pin' oflthese. elements: coincide with their centre of curvature, and in giving these elements a peripheral develop? to the strap, at the points atwhich the strap comes into contact-with the elements, during-their rotation about the pins. This conditionentails producing the periphery. of the. element at. least entail pulley comprises six rim-elements and that the peripheral development of each of them is very nearlya complete circle, it maybe easily seen in Fig. that the smallest possible radius of the pulley is 3r. If it is wanted tohave avariation of 1.130 3 between the smallest and the largest diameters ,of the pulley, the diameter of. the pulley at its maximum extension will be 181', i. e.: this pulley -will be veryheavyand clumsy. Anyhow,

itis easy: to see that if the-number of elements is greater,- the minimum diameter, andhence the maximum diameterare greater.

It will be shown hereunder that it is possible to obtainextensible pulleys with elements whose radiusof curvature is very nearly the minimumallowable radius, these pulleys being liable to be .reducedjdown to a radius a little greater than th'eQminimum radius. Indeed, for a rim element 9i o figliven. curvature to be utilizable inan exten-.

sible ipulley according tothe invention without damage to the strap, it is necessary- .That, .the tangential plane common to two successive r'imelements, really touches the circular cylindrical portion represented by each of them and not the. extension of that cylindrical portion outside the element} I r j Thatffrom the pointof contact ofthe. strap to, the point at which that strap tangentially leavestheelementin question, the arc of the element subtended by thestrap must be equal to n being'the number of elements in the pulley.

7 In other words,.these two conditions mean that it is necessary that the bending of the-strap entirely occurs on the cylindrical surface of the rim element, i. e., that the strap leaves the rim element}! on either side tangentially to its cylindrical surface, and not around itsouter edge. Ifthese conditions are not complied with, the

strap wrapping .two consecutive-elements and ofiering,. owing toits tension. an intermediate rectilinear portior i, makes a certain angle with the tangent. at the point of contact with one of the elements, this-entailing a sudden increase infthe curvature of the strap around the outer edge of the rim element, thus overstraining its On the contrary, these-two conditions are complied with .ifthe peripheral development of eacho fLtheseelements is at leastequal to the arc" Mean position means the position (B in-Fig.

in which the symmetry plane of each element 9' passes through theaxis ofv the pulley; and formswith theltie-rod an angle 18 equal to-themean of, the maximum angle 8" and theminimumi angle 5" 'made by that tie-rod with the radius passing through the pin carrying the-rim element during its displacement betweenthe extreme" positionsl Iffor instance; 3= 58;. and [SW- 5.0";

: through the axis of thepulley.

6? the mean position corresponds to 6:64. which determines a value for the radius of the pulley. For this position the rim element will be wedged to the tie-rod so that its symmetry plane passes It may be proved that'by: conveniently choosing the wedging of each-element 9 relatively toxone ofthe tie-rods It or I'Lthe change in direction o'f.the elements, in other words, the angle made by the symmetry plane of an element with the diametrical plane of. the pulley passing through pin] supporting it, may be reduced to a minimum not'exceeding in practice a few degrees.

Ihe peripheral development of each of theele- I ments thuszdefined by observation of the'conditions of correct operation of the strap, may nevertheless be so great that'it assigns a value yet too large for. the minimum diameter. of the pulley, i.. e. diameter obtained when all elements are brought; ,in contact with each other, owing to centripetal motion.. 1 I 1 This fact will be clearly apparent in the descriptionigiven with'reference to-Fig. 9 showing a way of coping with this disadvantage.

In that figure, one half of an eightrim element pulley-has been shown, i. e. four of these elements 911,-91), 90, 911. The centres of curvature of. these elements are locatedin C1, C2, C3, C4 i. e. the radius of-curvature ris'far superior: to distance d between thecentre of pins land the primitive circle 22 of the-pulley. Pins 1 are regularly distributed overa circle '23 having a variable radius equal to R'd, B being the radiusof the primitive circle 22 of the pulley-for the considered posi-f tion of the tie-rods and pivots.

-' It is noted in theiigure; thatelements 9 a the first one, is secured to tie-rod ISM-whereas the second one is secured to tie-rod llc. 'I'hesame' occurs in thecase of the other elements which are alternately secured to tie-rods of'set l6 and of set 11. As the two tie-rods I67) and He for instance, in the relative-rotation of the two flanges l0 and H remain symmetrical about-plane 24-, elements 9b and -90. will also remain thus in wedged relatively to their-respectivetie rods, so

r y (for the radius of curvature of the element) increased. by twice the arc -(for a radius equal.

; srmmet qal with c3, 5 a ou p .25

as to -i'ulfill this; condition, forany determinedposition. In practice, their wedgingrelatively to.

their respective tierod is ensured in such-:a way that, in the position defined as the mean position, the plane of symmetry of each of these elements 9 coincides with: the diametrical plane of; the

pulleymassing-through the joint axis of the 'cor-- mum'ra'dius'ofthe pulley. Element 9b bein'g -symmetrical with element Qc'about plan'e '24, centre of curvature C2 of elementilb isfalso symmetricalwith centre of curvature Ci oi'element 9c, ile.

Consequently, the common tangent AB of these two elements is paralleland equal toCz'Ca. v

If the-alternationin securing the elements to tie-rods lfiiand llis kept, centre of curvature C1 of element Sais also symmetrical about plane24' with centre Caof element 9b; similarly, centre C4 every position, if they have been appropriately The figure is assumed to bedrawn for aposi- As: the. strap wrapszeachi element over arransle of an'element and thediametrical planepassingthrough itslpin remains small, the sidesof the polygon are little'different from eachother and no disturbance of operationis caused for the pulley. And this arrangement-offers'the great advantage of reducing the" peripheral development of each element.

Assuming element 9b has the same direction as elements 9a and 90 which lie on either" side of it, which practically meansthat all elements are secured to "the set oftie-rods IT, for in stance. Under these conditions, during a change in dimension of the pulley, every element turns aboutipins: T in the same direction. Hence, elemer'it Bbwoccupies the position shown by dotted lines '9b (Fig. '9) and its centre of curvature is'thenin 0's. The common tangent A'B'to elements 9b and 9c is thenequal and parallel" to C3C'2. But, it-may be noticed in the drawingthat point:A.*is virtual, i. e. it does not lie on element 9 but on itsextension. In order to enable the strap totangentiallyreach element S'b, i. e. avoid bending it on the edge of element 9'!) along aradi'usincompatible with'its proper operation, the peripheral development of each element should be increased'at least by the length A'F; It is obvious that this inc'rease in the peripheral development: of the elements restricts the possibility of reducing the'diameter of the pulley because ef the premature engagement into contact the pins and" the primitive circle 2 2 of the pulley.-

*It is-sufiici ent', inorder to ensure a correct operation of 1 the'strap that for the an-" gular variation :1. of the elements relatively to the meanpositionfthe distance between'the two centree of curvature 0203 be greater-than that between. the edges of both elements which are.

moved; apart} owingtothat symmetrical position andthat'the edges moved nearer owing to it-donottoucnor are just in-contact.

The-keeping of these two, conditions enables us, todeterminethe maximum valueof the radius;

of. curvature of the rim elements, starting from' the'maximum angular variation, the minimum radius of the pulley and the distance between pins 'ljofjelements 9fand primitive circle22.

fIIhus,- for instance, for an angular variation notexceeding-i", a minimum primitive diameter of 150 mm., and a distance between the and the primitive circleequalto' mm-., theradius of curvature: of an element may be equal? to- 60 mm.

The peripheral length of the element is: then 55.7 mm., which corresponds'to a subtendedangle at the centre of 53 for that element.

- The radius ofi curvature of "an element is; in

that case, three" times the distance between apirr and the primitive circle of the pulley.

The proposed arrangement obviously im lies; an even number of elements; 1

WhatI claim is 1; An extensiblepulley carried by ashaftcomprising a sleeve adapted to rotate around said shaft; two annular flanges coaxial with said J shaft and secured tothe ends of said sleeve;-two

the shaft between the sets of tielrods hingedtoj the former flanges. v

'2. An extensible pulley comprising four; par

allel, coaxial flanges, the two outer flanges being fast with onefanother and the twofinner flanges being fast with one another and arranged for rotation relatively to the two outer flanges; a plurality, of tie rods pivotally mounted on each'of. said flanges; the-,number-of" tie rodsjas'soci'ated, with each flange being the same; and a plurality of rim elements arranged forfree radial displacement between the two inner flanges, each rim element being supported by four corresponding tie rods respectively associated withthe four flanges.

3. extensible pulley comprising four parallel," coaxial flanges, the two'outer flanges being. fast with one another'and the two inner flangesbeing fast with one another and. arranged" for rotation relatively to the two outer flanges; a;

plurality of tie rods pivotally mounted oneach of' saidflanges along a circle coaxial therewith and regularly distributed thereon, the number of tierods associated with eachflange being; the same; and a plurality Offrim elements arranged;

for free radial displacement between the two in;

ner' flanges,;each rim element being supportediby four'corre'sp'onding tie'rods respectively associe" ated'with the four flanges.

'4': extensible'pulleycomprising four par-.-

allel,"coaxial'fl'a nges, the two outer-flanges being;

fast with one another and the two inner flanges being fast with one another and arranged for rotation relatively to the two outer flanges; a plurality of tie rods pivotally mounted on, each.

of said flanges through pivotsregularly distrib-v uted' along a circle coaxial therewith, the conesponding pivots carried on flanges fast with, one another being" coaxial, and'all'the-tie rods as"- sociated with flanges fast with one anotherhaving the same shape and size, the number-citierods associated with each flange being thesame;

and a plurality of rim elements arranged for-"free radial displacement between "the two inner flanges, each rim element beingsupported, by"

fourcorresponding tie rods respectively associ 9 carrying at the other end of the corresponding rim elements, the convexity of said angle-shaped tie rods being outwardly directed and the interval between successive pivots associated with 'a. same flange being smaller than the length of the pivoted arm of the angle-shaped tie rods.

6. An extensible pulley comprising four parallel, coaxial flanges, the two outer flanges being last with one another and the two inner flanges being fast with one another and arranged for rotation relatively to the two outer flanges; a plurality of tie rods pivotally mounted on each of said flanges, the number of tie rods associated with each flange being the same; and a plurality of rim elements arranged for free ra-. dial displacement between the two inner flanges, each rim element being supported by four corresponding tie rods respectively associated with the tour flanges, said rim element being secured to the tie rods associated with one 01' the pairs of flanges fast with one another and hingedly 10 connected to the tie rods associated with the other pair of flanges fast with one another, each rim element having a substantially cylindrical. operative surface the radius of curvature of which is at least equal to the distance between the support axis of the rim element and the envelope cylinder of all the rim elements.

EDMOND E. J. GAISSET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 698,854 Pratt Apr. 29, 1902 2,004,224 Silber June 11, 1935 FOREIGN PATENTS Number Country 1 Date 6,349 Great Britain of 1903

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