US2419797A - Change-speed conversion unit - Google Patents

Description

April 9, 1947. w. 5. SMITH ETAL 2,419,797

CHANGE-SPEED CONVERSION UNIT Filed April 29, 1944 4 Sheets-Sheet 1 INVENTO 5- April 29, .1947.

wp's. SMITH ETAL.

CHANGE-SPEED CONVERSION UNIT 4 Sheets-Sheet 2 Filed April 29, 1944 I...- III.

April 29, 1947. w, s, sM r 2,419,797

CHANGE-SPEED CONVERSION UNIT Filed April 29, 1944 4 Sheets-Sheet 3 I 0 j v v a] 5.

April 29, 1947. w s, SM|TH ETAL 2,419,797

CHANGE-SPEED CONVERSION UNIT Filed April 29, 1944 I N 4 Sheets-Sheet 4 Patented Apr. 29, 1947 Wilfred Sydney Smith, Bedford, and Fredrick James Walters, Bedford Park, London, England Application April'29, 1944, Serial No. 533,360 In Great Britain June 4, 1942 Ill-Claims. l The subject of this invention is a changespeed transmission unit.

Of necessity, certain classes of machine tools and machinery have to run, not at one fixed.

speed, but at alternative speeds according :to the nature of the work on which they areengaged.

This change of speed has usually been efiected either by-means of a train of gears, orby countershaits and standard cone pulleys, limiting the speed changes to something like three or four 'in number, and normally making it necessary to stop or-slow down the machineto effectthe speed change.

Machines fitted with gear boxes or geared mo- .tors are more compact, but more costly. Machines fitted with cone pulleys are cheaper but need overhead shafting and countershafting taking up much more :room and using much more metal.

Machines fitted with gear boxes are easily converted to individual driving, that -is,'by a motor on the machine'if a change-over is required from group driving, thatis, by line shafting, but machines fitted with cone pulleys have not been easily converted to unit driving.

The chief object of this invention is to provide a change speed. transmission unit suitable for converting cone driven machine tools to individual drive, or for giving speed changes on single pulley drives, in which the advantages of a geared unit as regards space taken up and ease of conversion are obtained at something like half the cost, without recourse to toothed gears :or clutches. A further object is to obtain a total of not less than seven speeds (or possibly 9 speedsaccording to the type of unitemployed) on a three-step cone pulley instead of the three or four speeds normally obtained from gearboxes or other forms of transmission units, giving twelve speeds if required on a fourstep cone pulley, without the necesity of stopping or slowing down the machine When a change of speed is required.

According to the invention, an input shaft to receive a constant drive is'assoc'iated with a secondary shaft driven from the said input shaft-and on one of which shafts are provided change speed pulleys driven at different speeds to engage a belt, which belt engages a pulley loosely mounted on the other shaft and which belt remains constantly in one path determined by a pulley on the machine that is to be driven, lateral movement of the complete unit, by displacing the shafts and pulleys thereon relatively to the *belt,

causing the belt to assume the speed of the pun I 2 ley which at the time is passed under it, and thereby to effect changes in the speed to "be transmitted to the machine. The-constant drive may be obtained either from a motor on the unit, or if required by a direct drive from line shafting to the input shaft, when the advantages of a geared head machine would'be obtained with additional speed changes-whilst running. .The power transmitted by'the motor does not fall with :a reduction in speed. The :transmission unit can be combined with ordinary or modifiedcone driving gear, whereby agreatly increased range of speeds is obtained, with .the advantage of being able to obtain speed :changes whilst the machine is running.

For certain classes of machinerya quick "reverse in direction of rotation is necessary. Reversal can easily'be obtained electrically-but'electrio reverse has the disadvantage that specially wound motors are necessary if frequent reversals are required. Also the motor and machine'must be allowed to come to rest in one direction :of rotation before being switched over to the ;opp.o site direction. It is therefore obvious that if :a reversal in the machine could be obtained whilst the motor continued to run in the same direction of rotation, several advantages would :be gained including a saving of time in any .particular operation. It is therefore proposed that where thus required, the reversal should be .obtained in the unit and not electrically.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawings.

Figure 1 represents in end elevation a device for embodying one form of the invention.

Figure 2 represents the same device in front elevation.

Figure 3 is an end elevation of a modified form.

Figure .4 is a front elevation of the device shown in Figure .3.

Figures 5 to 11 represent details hereinafter described.

Figure 12 is a diagram illustrating the path of the belt I! in Figure 3.

Figures '13, 14 and 15 illustrate a'modification in which a reversal .of the drive can be obtained in the unit and not electrically, Figure 13 representing a front elevation of the unit with the guards removed to reveal the driving arrangements, and Figures 14 and 15 are diagramsillustrating the method of obtaining reversal in this 3 modification, in which different reference numerals are used for the sake of clearness.

As will be shown the units detailed in Figures 1, 2, 3 and 4 are basically the same and differ only in their method of operation. In both types the principle employed is identical and for equivalent units the.driving components are interchangeable.

Referring first to Figures 1 and 2, G indicates a bracket or frame on which the whole of the conversion unit is mounted, this bracket being movable in either direction along a base plate Y. A indicates a standard high speed electric motor, mounted with its starter B on an adjustable plate C hinged at C. From a V grooved pulley 2| on the shaft of the motor, V ropes l2 drive a similarly grooved pulley I3 on a shaft E, which may be termed the main shaft or in this case the input shaft of the unit, the ratio of this drive depending on the ultimate speeds required. In the case of a three-step cone machine the speed of the input shaft would normally be the middle speed required on the machine. The input shaft E is carried by two ball bearing plummer blocks F, F, which are in turn carried in slots P in the main bracket G. The base plate C of the motor A is hinged at C to the bracket G, and is adjustable by means of a nut which when the motor is tilted backward, can be inserted in the part of the bolt C between the plate C and the frame G. The plate C is slotted for the free passage of the bolt C and the bracket G is threaded to engage the said bolt; when the bolt is screwed back to release the plate C the motor can be tilted backward and a nut C can be inserted on that portion of the bolt which is to be between the bracket G and plate C, thereby holding the plate C secure between the bolt head and the nut C this arrangement being duplicated on the other side of the unit. The nut C when not required can be placed on the free end of the bolt C as shown in Figure 1, so that it will be handy for use when it is required. In the position shown, in which the plate C is held closely against the frame, the nut is unnecessary, as the plate is prevented from moving by the bolt C Adjustment of the .belt tension of the initial drive from the motor A to the input shaft E is thus obtained.

'On the input shaft E are two fast pulleys H and K, Figure 2. The pulley H is suitable for the use of a fiat belt, and the pulley K is V grooved to receive V ropes S for driving a counter-shaft or secondary shaft L. This shaft L is carried by two ball bearing plummer blocks P, P, secured on the bracket G, and on the said shaft L are three fast transmission pulleys M, N and O. M is driven by flexible transmission elements, ropes S, while the two latter pulleys are V grooved and drive back by ropes S on to the driven pulleys Q and R, which are loose on the shaft E, each of these pulleys Q and B being made integrally with a fiat or crown faced change speed pulley Q, R of the same diameter and face width as the change speed pulleys H. The ratio of the drives NQ and OR are in the same proportion, but one is a step-up and the other a step-down drive. Consequently the fiat belt pulleys Q, H and R, running side by side, revolve at three different rates of speed. Due to the fact that the shaft E, on which these pulleys rotate, is revolving in the same direction as the loose pulleys QQ' and RR, the speed of these pulleys relatively to the shaft is not great, and gun-metal bushed pulleys, or ball bearing pulleys,

4 with provisions for lubrication, are adequate for the job. The width of the fiat belt pulley H, and of the flat belt pulley portions Q and R, is either the same as the face width of the machine cone pulleys or is sufficient to transmit whatever power is required.

The lay-out is made as compact as possible, this minimizing the length of the V ropes S operatively connecting the shafts E and L and reducing the possibilities of their stretching. The said ropes are all of the same section and length, are all doing the same amount of work, and are all in motion at the same time, consequently any stretch that occurs is uniform, and it can be taken up by raising the plummer blocks P in the slots P in the bracket G, as shown in Figures 1, 2, 3 and 4 an eye-bolt 4| can be attached to the top plummer blocks, which eye-bolt passes through a lug on the bracket G, when adjustment can be obtained by tightening a nut on the eye-bolt, on top of the lug, thus drawing the plummer blocks P and. shaft L away from the shaft E.

Between the pulleys N and O on the shaft L is a loose jockey pulley T, running on ball bearings above which is another loose jockey pulley U (also running on ball bearings) on a shaft V carried in adjustable saddles W which are supported on the bracket G, by means of threaded studs X which are secured in the bracket G but are free to rotate within same. The shaft V is adjustable, in that it can be raised or lowered by means of the threaded studs X the rotation of which studs causes the saddles W to be raised or lowered on their threads. The saddles are threaded to take the studs, so that rotation of the studs causes the saddles to rise or fall. Alternatively, spring adjustment may be employed as shown in Figures 5 and 6 where the supporting saddles W are fitted in studs 3| which are secured to the bracket G. Around the top portions of these studs, springs X are located by a lug 23 in the bracket G and by the saddles W themselves, and a fiat belt I! is fitted with the springs compressed, the springs thus automatically taking up any slack in the belt due either to belt stretch or to moving the belt from step to step of the machine cone pulley, the point being that shaft V is adjustable.

The bracket G, which carries the whole of the equipment, including the motor and its starter, is movable backwards and forwards on a base plate Y, by means of a square threaded lea-d screw I4, which passes through the base plate and is located by the operating hand-wheel Z at one end and a collar Y at the other end. In the base of the bracket G are two threaded nuts or lugs to mesh with the square threaded lead screw, the arrangement being such that when the operating hand-wheel Z is turned, the bracket G with its equipment travels backwards or forwards along the base plate Y and can be left in any position along the said base plate.

A flat belt I! (see Figures 3 and 12) is passed around the driving pulley H to the back of the jockey pulleys T and U and runs across at short centres to the middle step of the machine tool step cone pulley Hi. When the motor is connected and started, the speed at which the machine rotates can be adjusted by the operating hand-wheel Z, which draws one of the driving pulleys Q, H or R, with their different speeds under the flat driving belt I! which then assumes the speed of the pulley over which it is running and drives the machine accordingly,

should additional speeds be required, the hat belt II can be moved from-the centrestepof the machine cone :pulley l8 as in Figure 3 and run on to either of the other steps, th flat belt driving tension being maintained by the top ijockey pulley U, on the adjustable shaft *V. Thus with the existing three step cone pulley on the machin tool, a maximum of three Speeds can be obtained in each step, according to whether Q, H or R (with their different driving speeds) is the driving pulley. Consequently, a total of'nine "speeds is possible.

The conversion unit issmall vandcompact and can be bolted direct on to the machine, thus making it individually or unit driven, and becoming .partcf the machine. It can be secured at any angle as the bracket G- not only slides on the machined seats of the base plate Y, but on shafts Ci by which the bracket is attached to the base plate. The shafts G are fixed in the base plate Y and the bracket G is slidable on them. Thus, if necessary, the unit could be .inverted as the bracket G would be securelyiheld :hy shafts G on which it would then travel when the operating hand-wheel Z was actuated.

Referring now to Figures 3 and 4, instead of shafts G bein fixed in a base plate, and the bracket G sliding on these shafts, the said shafts are fixed in the bracket G, and are themselves slidable in the supporting bracket Y, which takes the place of the base plate Y in the example illustrated in Figures 1 and 2. For changingspeeds, movement of the bracket G is effected by turning the three-armed capstan type hand lever Z" at the top of the unit, which causes an upright operating shaft 4 to rotate. A pinion ion theshaft 4 meshes with arack 6 (Figure 4) which connects the two upright portionscf the bracket this rack and the bracket G being preferably cast in one piece. The pitch diameter of the-pinion is .such that when one .of the knobs of :the three-armed lever .Z' is moved to the front, it brings one of-the driving-pulIeys Q, H or R underneath the flat belt l-I driving the machine to obtain a selected speed. The shaft :4, on which-the pinion is mounted is located in .ahole drilled for this'purpose in the supporting bracket Y and is made rigid by a supporting-saddle 8, which is also bolted to the bracket Y. The collar 1 prevents the pinion being lifted out of mesh with-the rack.

In this modification it is found convenient to make the top jockey pulley U and shaft V adjustable .by springs. As shown in Figure .3, the supporting saddles W are fixedto shafts 32 which are sunk into the bracket G. Around the tree portion (that .is, the part not secured in saddle W and therefore free to move up and down in the bracket G) or each shaft 32 springs X are located byzsaddles W at the :top and by a shoulder 33 in casting G at the bottom so that if the flat :belt H is fitted whilethespringsare compressed, the springs automatically take up any slack in the belt'dueto stretch ortomoving the belt from step tester-of the cone pull y- Themotor A is fitted on slide rails 0, instead of on a hin ed plate 'C as in Figures 1 and 2. By means of an adjusting bolt 25, the slide rails can be moved up or .down the machined and slotted back :ofthe bracket G. Slots in the rails also provide for lateral movement, so that it is possible to move the motor either vertically or horizontally; thus the fitting of any motoris simple, and the :ne- .cessity of drilling holding-down bolt-holes is avoided. The input shaft drive from :the motoris 6 taken directlyatovthelupper; shaftL, and this :can

also be donein-the case-of theexamplezshownin Figures .1 and. 2 when so required. An extension 9 on :thebottom shaft can beused for taking an auxiliary, drive, .for example to a machine tool suds pump. The extension could alternatively be on the inputshaft. It will be noted that any drivetakencff theextensionQ will be at a constant speed, although the unit and machine speeds maybechanged by the capstantype control lever or hand wheel. A metalguard 21 is fitted across the front of'th'e unit, .both as a safety precaution and-to prevent suds pump splash or swarf'being carried into the unit. .sAnother metal guard 28 (shown open in Figure 4 to expose "the grooved pulleys ,to-view) completely encases the connecting driv MK.

It will be evident that the units hereinbefore described in Figures .1 and;2'and in Figures3 and respectively are basically the same, that .is,the mechanisms vare identical .in principle, and for equivalent units, thedriving components are interchangeable, but for certain applications one method of operation-either hand-wheel control or three point capstan control lever-may .be more advantageous than the :other.

With the unitshown in Figures 1 and 2, the extent of movement of the bracket is sufiicient to allowof three speeds being obtainedon each step of the cone pnlley,;but with the unit shown in. Figures 3 and 4, it may'in some cases be inconvenient to permit the amount of traverse necessary to give the three speedson the largest and-smallest steps of'the driven cone Pulley, and the unit can be arranged to give three speeds onzthe middle step, and twoeach on the largest and smallest steps, while reducing the width of the bracket by twice the .width of each step of the cone pulley. The two shafts may be parallel vertically as shown or in any other plane.

It is not intended that the conversion unit should be used solely for converting group driven machines :to individual drive. It can be built into new installations, opposite either a single diameter .or step cone pulley ,of the type described hereinafter when speed changes are required.

Many machine tools are still manufactured with cone pulley drives, due to the expense of the alternative forms of change speed drivessuch astoothedgears.

Inv suchnew installations it is proposed that the cone pulley on "the'machine tool should be made as "shown in Figures 7 and 8, with an inclined rise ,29:steppingaup one diameter to the other instead of each diameter rising vertically to the next. The adjustable top shaft V of the conversion unit, carried insaddles W as already referred to, will in such cases'be spring controlled as described with reference to Figures 3, 44, 5 and 6.

To enable the advantage of quick speed changes itO be obtained on existing machines, which might be ,fltl'led with the standard type of step cone'pulley in which the diameter falls vertically from one step to the next, it is proposed to supply separate inclined wedge shaped rising sections 38 as shown in Figures 9, 10 and 11. These 'will be made in a variety of sizes, to suit the varying drops in diameter likely to be encountered. Two or more of these must be fitted to each step by means of a set screw, against the wall separating one diame er of the cone from the other, thereby supplying the flat belt with theslead-itrequires.

When these risers are applied .to ex sting machines, the narrower fiat belt might not be capable of transmitting the necessary power, so that if necessary to compensate for the loss in belt width due to the fitting of the rise, a thicker belt can -be employed to transmit the power required.

The travel of carriage or bracket G will be so arranged that at the conclusion of the complete speed range on any one step of the machine cone pulley the flange dividing the grooved pulley and fiat face portions of pulleys Q and R will push the fiat belt from that step on to the next diameter step. When the belt is pushed from a larger to a smaller diameter step, the tension in the springs will be such that they immediately adjust the top shaft V so that the correct driving tension is maintained on the belt.

Similarly, when the belt is pushed from a smaller to a larger diameter as it engages the inclined rise on the machine cone pulley, the tension in the fiat belt will be increased, thus compressing the spring X, causing a reduction in the height of the top shaft V, and allowing the belt to pass on to the next diameter of the machine cone pulley.

In this way, not only would three speeds be obtained on each step of the machine cone whilst running, without the necessity of stopping or slowing down, but the full range of the unit could be obtained on the other two steps without having to stop or slow down to adjust the belt from one step to the other on the machine cone.

The jockey pulleys on the unit are so arranged that the fiat belt H has an arc of contact, or gripping surface on the pulley H of something like 250 degrees, as compared with an average drive of about 140 degrees lap around the smaller pulley, so that a very good drive is provided.

It should also be noted that where necessary or expedient due to the conditions under which the unit may be called upon to work, the drives NQ, OR or MK can be effected by means of chains, or toothed gears at fixed centres, instead of by V ropes. The principle of operation and layout otherwise remain exactly as described.

It will be seen that the change speed unit herein described is a compact means of converting group driven plant to individual drive, and/or of obtaining speed changes in the drive on to any form of pulley, whether of cone or single diaameter. It permits three speed changes to be obtained whilst running on any single pulley diameter, and when used in conjunction with three-step existing cone pulleys allows a total of nine speeds to be obtained without the use of clutches. The use of inclines between the steps of the cone pulleys renders it unnecessary to stop or slow down the machine when making any change, and the operator can pass rapidly, without pause, to any speed in the range that he may require. It is important that such drives as suds pump drives should run at constant speed although the main drive varies, and this can be effected by the method described. Any standard motor can be easily fitted to the unit without the necessity of drilling holes at varying centres due to the slots in the side rails and the possibility of vertical adjustment. In using the capstan three point control lever, positive indications of speed are obtained by observing which of the three knobs is at the front.

The method of obtaining a reversal of the drive is illustrated in Figures 13 to 15. Here, as previously described, either shaft may be taken as the input shaft. In Figure 13 the unit is driven 8 through the input shaft pulley which causes the top shaft to rotate at any desired speed. On this shaft three other fast pulleys are secured, namely, transmission pulleys 5|, 53 and change speed pulley 51.

From the pulley 5| the drive is taken at any required ratio to the combined pulley 52 which runs loose on the secondary shaft, and which is combined'with a fiat belt pulley portion as previously described.

From the transmission pulley 53 a similar drive is taken to the pulley 54, which is fast on the secondary shaft and causes this shaft to rotate at any desired speed according to the ratio of the drive.

Usually drives 5| to 52 and 53 to 54 have the same ratio, one being a speed-up, the other a step-down.

The fiat face pulley 55 is also secured to the secondary shaft so that it rotates at the same speed as the pulley 54, thus pulleys 52 and 55 rotate side by side at different speeds of revolutions per minute.

A loose pulley 58 of th same diameter and width as the fiat face portion of pulley 52 and pulley 55 is located between pulleys 55 and 54 and thus runs opposite the fixed pulley 51 which has the same diameter and width on the top shaft (input shaft).

A loose pulley 56 carried on to the top shaft is located between fast pulleys 5| and 51 and runs opposite the flat faced portion of pulley 52, and pulley 55 is equal in diameter to them and its width is equal to their combined width.

The method of operating the unit is exactly the same as hereinbefore described according to the type of unit, and the flat belt connecting the unit to the machine is arranged as previously detailed, and as shown in diagrams Figures 14 and 15 which represent the arrangement in side view.

When the unit is operated the flat belt is driven either by pulley 52, or 55 in one direction of rotation at their different speeds, but when on operation the unit moves across for the belt to engage pulleys 58 and 51, the driving function is transferred from the bottom to the top shaft and is obtained from the pulley 51, with the result that although pulley 51 is rotating in the same direction as the other driving pulleys 52 and55, the direction of rotation of the belt is reversed as will be made clear by reference to Figures 14 and 15, Figure 14 representing the drive when taken from either of the bottom driving pulleys 52 or 55, Figure 14 representing the drive when taken from pulley 51. It will be observed that as the driving function is transferred from pulley 5-5 to 51, or vice versa, the resulting action of the pulleys is first to slow down, then to brake, and then reverse the direction of rotation of the belt, because as the pulleys move under the belt, they are tending to pull it in opposite directions.

The top shaft is indicated at 60, and the cone or other pulley on the driven machine at 6|.

Thus the reverse is immediate as the unit applies its own brake. The motor and the extension shaft 59 which drives the auxiliary (such as suds pump) continue to rotate in the same direction throughout. Thus two speeds forward and one in reverse are possible on any single diameter step of the machine pulley.

In the same manner if it was required it would be possible to introduce a third drive on the right-hand side of the bracket (outside the bracket) to give a total of three speeds forward and one reverse.

What we claim and desire to secure by Letters Patent of the United States is:

1. In a change speed unit, an input shaft adapted to receive a constant drive, and associated therewith a secondary shaft adapted to be driven at constant speed from said input shaft; transmission members associated with said shafts, driving change speed pulleys adapted to be driven at different speeds by means of said shafts and transmission members and arranged upon said input shaft; a belt, a driven pulley loosely mounted on said secondary shaft; said belt adapted to be engaged alternatively by each one of said driving change speed pulleys on said input shaft and to engage said driven pulley loosely mounted on said secondary shaft; an output pulley arranged to be driven by said belt and for driving a machine; means for displacing said change speed unit laterally and relatively to said belt, so as to cause said belt to assume the speed of that of said driving change speed pulleys which at the time is passed under it, thereby to effect changes in the speed of said output pullay and the machine driven thereby.

2. A change speed unit as set forth in claim 1 including a motor arranged for deriving therefrom the constant drive of said input shaft.

3. A change speed unit as set forth in claim 1 including a motor arranged for deriving therefrom the constant drive of said input shaft, a base plate for said motor, a frame carrying said change speed unit, said base plate hinged to said frame.

4. A change speed unit as set forth in claim 1 including a motor arranged for deriving therefrom the constant drive of said input shaft, a frame carrying said change speed unit, and slide rails on said frame, said slide rails adapted to mount thereon said motor adiustably for fourway movement.

5. A change speed unit as set forth in claim 1 wherein a base plate in fixed spatial relationship to said driven machine is provided and said unit is slidably arranged on said base plate and relatively to said belt; said transmission members including fast pulleys on said secondary shaft and loose pulleys on said input shaft and flexible transmission elements for engaging said fast and loose pulleys, said fast pulleys arranged to drive back, by means of said flexible transmission elements onto said loose pulleys and to impart to them speeds at variance with the speed of said input shaft and for thus to impart various speeds to said change speed pulleys and through said belt to said output pulley and said machine driven thereby according to the position of the unit relatively to said fixed base plate and said belt.

6. In a change speed unit, an input shaft adapted to receive a constant drive and associated therewith a secondary shaft adapted to be driven at constant speed from said input shaft; change speed pulleys comprising driving and driven pul- 10 leys arranged oppositely of one another on said shafts, transmission pulleys arranged in opposite pairs on said shafts and including driving transmission pulleys fast on said input shaft and driven transmission pulleys loose on said secondary shaft, flexible transmission elements connecting said driving and driven transmission pulleys whereby speeds at variance with the speed of the input shaft are imparted to said transmission pulleys; said change speed driving pulleys arranged for being driven at different speeds by means of said shafts and said transmission pulleys; a belt associated with said change speed pulleys, an output pulley adapted to be driven by aid belt and to drive a machine; a base plate disposed in fixed spatial relation to said machine, said unit mounted slidably on said base plate and relatively to said belt for causing, on displacement of said unit, the belt to assume the speed of that of said driving change speed pulleys which by such displacement is at the time passed under it, thereby to effect changes in the speed of said output pulley and said machine driven thereby.

'7. A change speed unit as set forth in claim 1 wherein said output pulley is a cone driving gear whereby to obtain a greatly increased range of speeds for said machine.

8. A change speed unit as set forth in claim 1 wherein said output pulley is a step cone and inclined risers are provided at the lateral faces of said steps for joining each step of said cone to next, said risers consisting of wedge shaped sections secured to said faces.

9. A change speed unit as set forth in claim 1 wherein means are provided on at least one of said input and secondary shafts for taking a constant drive from said shaft to an auxiliary mechanism.

10. A change speed unit as set forth in claim 1, said change speed pulleys including fast and loose pulleys in opposite pairs on each of said input and secondary shafts, means for displacing said unit relatively to said belt, said unit, by various displacements with relation to said belt, adapted to engage said belt with a fast pulley on said secondary shaft to transmit to said belt a drive in one direction, and to engage said belt with a fast pulley on said input shaft to reverse the direction of said drive.

WILFRED SYDNEY SMITH. FREDRICK JAM'ES WALTERS.

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

UNITED STATES PATENTS Number Name Date 2,029,053 Brennen Jan. 28, 1936 35,729 Butler et a1 June 24, 1862 955,920 Stevens Apr. 26, 1910

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