US2617248A - Overwind preventer - Google Patents

Description

Patented Nov. 11, 1952 UNITED STATES PATENT OFFICE OVERWIND PREVENTER Foster H. Brown, Brooklyn, N. Y.

Application December 31, 1948, Serial No. 68,630

9 Claims.

This invention relates to main-spring barrel assemblies, especially those used in watches. It is, however, equally appropriate to any other device, horological or not, employing a main-spring barrel.

The majority of jeweled watches are now provided with mainspring-drum chambers smaller than a five-grain aspirin tablet, i. e. less than three-eighths of an inch in diameter.

It is obvious that, if any watch is forced beyond full-wound condition while being wound, some part may rupture.

Devices heretofore proposed are, basically, internal brake mechanisms with contracting shoes. They are designed and constructed so that a section or sections of the shoe or band can be contracted and pulled away from contact with part or parts of the drum-wall surface by the action of the radial components of the power of the mainspring. In other words, this functional movement decreases the size of the band, thus reducing the amount of static friction or holding power between the band and the drum wall. In use, this action continues until the holding power of the band is overcome by the power of the mainspring, at which time the band slips.

The present invention is also, basically, an internal brake mechanism, except that, unlike the prior art, its shoe or band does not contract or reduce its traction.

An object of the present invention is to provide an efiicient safety barrel mechanism, the shoe of which is of equal radius and cross-section in all its parts and, to all intents and purposes, remains in one hunderd per cent contact with the barrel wall under all conditions and at all times.

A further object is to provide a barrel clutchband construction without any torque-producing characteristics whatsoever and to provide a surface for the mainspring which, to all intents and purposes, is equal to the surface of a naked barrel wall, hence eliminating any possibility of increasing inter-coil mainspring friction and allowing the mainspring unrestricted functional freedom at all times.

A further object of this invention is to provide a mainspring-barrel clutch which has an established and non-varying kinetic frictional factor higher than the full torque of the mainspring, thus eliminating any and all leaping tendencies or characteristics which the shoe band might have.

Another object of this invention is to provide a barrel-clutch band which can be easily inserted in, removed from, or reinserted in, the drum, or replaced, independently of the mainspring.

A further important object of this invention is to provide, by means of the substantial difference in the feel of the winding tension, a silent, smooth and commercially acceptable full-wound signal. Such a signal is provided by the clutch in accordance with the invention when it goes into action.

In accordance with the present invention, these objects are accomplished by providing a clutch, the inner member of which is made of mainspring stock having a length such that, when inserted within the outer member (the barrel or mainspring housing), its ends abut and it forms, virtually, a continuous and concentric circle. This end-to-end jointure, plus the fact that the said inner member is preferably constructed from the same material as that of its associated mainspring, results in a clutch-shoe construction which occupies the same amount of space as is occupied by a single layer of mainspring stock.

This construction is also advantageous in that it is applicable to conventional mainsprings and housings. The only basic requirement is a hookless barrel. The clutch design is such that it can be easily manufactured, and its cost is less than that of many current mainspring-to-barrel connections.

The clutch is particularly adaptable for use to prevent damage caused by overwinding, such as a ruptured spring, or, in the event that the spring does not break from the overwinding, to prevent the excessive tension from causing damage to the associated mechanism, such as twisting off the stem, damaging or breaking teeth of one or more gears, or other damage. In the event that the main-spring should break because of in erent characteristics, the clutch yields to the shock and tends to prevent the possibility of resulting damage. The fact that the clutch requires only a small amount of space, is a most important advantage, particularly in wrist watches, in which the main-spring barrel is often one-quarter of an inch or less in diameter. Such barrels are. in fact, Lilliputian power houses.

Other obj cts and further advantages 0* the invention will become apparent from the following description and from the accompanying drawings which show, by way of example, several embodiments of the invention.

In the drawings,

Fig. 1 is a frOnt view of a barrel assembly, including a clutch in accordance with my invention, the barrel cover being removed to show the interior of the barrel.

Fig. 2 is a cross section taken approximately on the line 22 of Fig. 1, with the cover in pla e.

Fig. 3 is a View similar to Fig. 1, but showing another embodiment of the invention in which the peripheral wall of the barrel is tapered, or frusto-conical.

Fig. 4 is a cross section taken approximately on the line 44 of Fig. 3.

Fig. 5 is an edge view of the clutch shoe removed from the main-spring assembly of Fig. 3.

Fig. 6 is a view of the inner face of the clutch shoe shown in Fig. 5.

Fig. 7 is a view similar to Fig. 5 but showing another form of clutch shoe.

Fig. 8 is a face view of the clutch shoe shown in Fig. 7.

Fig. 9 is a fragmentary edge view of the clutch shoe and a connecting member in accordance with another modification.

Fig. 10 is a fragmentary view similar to Fig. 9 showing still another embodiment.

Fig. 11 is a graph showing the relation between the torque and the turns of a characteristic mainspring as the spring is wound up and then allowed to unwind.

A main-spring assembly as shown in Figs. 1 and 2 of the drawings, comprises a housing, drum or barrel I, an arbor 2, a main-spring 3, and a clutch shoe 4, the latter being, in accordance with the present invention. While the particular mainspring barrel assembly illustrated in the drawings is intended for use in a watch, the invention is also applicable to clocks and other spring driven devices, and as before stated, to other types of barrels. It will be understood that the mainspring assembly for a watch is actually very much smaller than shown in the drawing. In a pocket watch the diameter of the barrel may be from one half to three quarters of an inch, while the barrel of a wrist watch may be one quarter inch or less in diameter. The assembly is shown on an enlarged scale in the drawings for greater clarity.

The housing or barrel I may be formed of' any suitable material such as metal or plastic and comprises a back or bottom wall II, an annular peripheral wall I2 and av removable cover I3. The cover I 3 snaps into place against an annular shoulder I4 provided on the inside of the peripheral wall I2, being normally held in place by the resilience and frictional contact of the barrel and the cover. The barrel wall I 2 has a circular inner surface which is utilized for engagement by the clutch member 4.. The barrel shown in the drawings by way of example is a going barrel provided with a series of teeth around its periphery for. driving the succeeding member of the device. The bottom Wall I I and the cover I3 are provided at their centers with alignedv circular Openings. to receive the arbor 2.

It should be here noted that the examples shown are not intended to limit this invention to going barrels alone. The word barrel is meant to imply any housing construction suitable for a barrel assembly.

The arbor 2 has circular bearing surfaces 2I and 22 adapted to engage the holes in the bottom wall II and the cover I3 of the barrel. Intermediate the bearing surfaces 2| and 22 the arbor has a cylindrical portion 23 of enlarged diameter about which the main-spring 3 is adapted to be Wound. One side of the cylindrical portion 23 is preferably flattened, as indicated at 24 (Fig. l) and provided with a hook 25 adapted. to engage a slot or hole in the inner end of the main-spring to connect the main-spring. with the arbor. It will be understood that other suitable connecting means may be used. The ends of the arbor project beyond the bottom wall I I and the cover I3, respectively, and are provided with pivot or bearing portions 26 and 27, respectively, for rotatably mounting the arbor in suitable bearings. One end of the arbor, usually the end that projects through the bottom wall II, terminates in a non-circular or squared end portion 28 which provides for a driving connection with suitable winding mechanism for the main-spring 3. A pawl and a ratchet wheel (not shown) are customarily associated with either the arbor or the winding mechanism to hold' the POW?!) 95 $11 main-spring after it is wound.

The main-spring 3 is formed of a strip or ribbon of tempered spring steel, or. a suitable alloy, which is wound in spiral form about the arbor 2. In Fig. 1 the inner end 3I of the main-spring is attached to the arbor, for example, by the hook 25, while the outer end 32 is connected with the clutch shoe 4, as will be more fully described below. The width of the main-spring is slightly less than the distance between the bottom wall I I and the cover I3 of the barrel, so that the mainspring fits in the barrel without binding edgewise. The length and thickness of the main-spring are preferably such that the spring occupies approximately half of the free area inside the barrel, i. e., the area between the arbor and the peripheral wall formed by the inside surface of the clutch shoe. In Figs. 1 and 2 the main-spring is shown fully wound, in which condition it is closely Wrapped around the arbor 2. As the main-spring runs down its turns or coils gradually expand and separate from one another. When the mainspring is fully run down, itscoils or convolutions have expanded and lie one against the other inside the periphery of the clutch. As. will be more fully explained below, a feature of the present invention is. that the clutch shoe 4 does not appreciably decrease the space available for the main-spring and it providesa smooth, concentric, circular wall for the spring at all times.

The clutch shoe. 4, in accordance with the present invention, is made of a strip or ribbon of spring stock. The width of the strip is substantially equal to thewidth of. the inner surface of the peripheralv wall. I2 between the bottom II and the cover I 3 of the barrel. Its length is substantially equal to the inner circumference of the peripheral wall I2. Its thickness is of the same order as the thickness of the main-spring, as will be more fully explained. below.

In its relaxed condition, before it is put into the barrel it may be straight, as shown in Fig. '7, or curved, as shown in Fig. 5, the radius of curvature being greater than the radius of the barrel. Alternatively, the clutch shoe may be reversely curved, or it may have the end portions curved in one direction. The opposite ends M are substantially square, although the corners are preferably slightly rounded, as shown in Fig. 6, and/or the ends 4| are toed-up slightly, as indicated in Fig. 7, sothat there is no tendency for the clutch shoe ends to dig into the barrel wall. This further improves its action.

In inserting the clutch shoe in the barrel, it is preferably coiled into approximate circular shape with the ends overlapping and slipped edgewise into the barrel. The clutch ring is then spread and the ends are snapped into abutting relationship, so that they press against one another in a flush-butt joint. to maintain. the circularity of the shoe and hold it in. contact with the barrel wall throughout its circumference. This construction produces novel and surprising results. The thin clutch shoe now develops its own tension, which is utilized to produce the resulting eificient traction, and in addition, the shoe now can never upset the normal main-spring torque. If a somewhat shorter clutch shoe were used, the opposite ends would. meet at an angle some- What: like the apex of a. heart. In other words, the adjacent end portions of the clutch shoe would tend to straighten out and extend somewhat chordwise across corresponding sectors of the circle formed by the peripheral wall of the barrel. However, in accordance with the present invention, thfi length of the clutch member 4 and the pressure of the abutting ends 4| are such that the clutch member is held in circular form substantially corresponding to, and in contact with, the inner periphery of the barrel wall l2 throughout its entire inner circumference. The barrel shoe maintains this concentricity and its true circular shape at all times. The outside surface of the clutch or barrel shoe being substantially equal in area to the inside surface of the peripheral wall of the barrel, and the shoe being therefore in contact with the barrel throu hout its entire periphery, the maximum area of traction and frictional engagement is thereby provided. The barrel shoe maintains this substantially 100% bearing surface at all times.

The outer end of the main-spring 3 is attached to or connected with the clutch member 4 in any suitable manner. In the form illustrated in Figs. 1, 2, 5 and 6, the clutch member 4 is provided with a punched-out or extruded hook 43 which engages a hole with which the outer end of the main sprin is provided. In the form shown in Figs. '1 and 8 the clutch member 4 is provided with a hole 44 which is adapted to be engaged by a hook provided on the outer end of the main-spring.

When the outer end of the main-spring is connected directly to the clutch member 4, as in Figs. 1 and 2, the point of connection is preferably placed at least a short distance from the abutting ends 4| of the clutch shoe so that there is no tendency for the clutch-shoe ends to separate or for the end to which the main-spring is connected to be pulled away from the barrel wall by the radial component of the pull of the mainspring when the spring is fully wound.

Preferably, the point of connection is in the trailing or rear half of the clutch shoe so that the major portion of the shoe is pushed rather than pulled around the inner periphery of the barrel by the main-spring, the direction of movement being as indicated by the arrow a. The pushing action also provides a self-energizing eifect which increases the slipping resistance or traction of the clutch. In other words, considering the direction of rotation of the clutch, the outer end of the main-spring is preferably connected to clutch member 4 at a point at least a short distance ahead of the abutment. By virtue of this arrangement the major portion of the shoe is pushed and tends to expand under the influence of the main-spring, and the clutch thereby tends to become self-energizing.

The outer end of the clutch member 4 and the inner surface of the peripheral wall [2 of the barrel are smooth. It should be noted here that the clutch and the main-spring are lubricated in any manner appropriate for the main-spring itself. The slipping resistance of the clutch, or in other words, the torque that will be held by the clutch without slipping, can be varied by varying the pressure with which the opposite ends 4| of the clutch member 4 abut one another. This, in turn, is determined by the length of the clutch shoe in relation to the inner circumference of the barrel wall, and also by its relative thickness.

Because of the inherent characteristics of the thin flexible clutch shoe, it closely hugs the barrel wall surface, conforming to it in shape, and thereby, in resisting movement, provides maximum traction or adhesion between itself and the housing wall. It has been found that a clutch shoe approximately half the thickness of its associated main-sprin functions satisfactorily and is sufficient to hold full main-spring torque in self-winding timepieces, as in these no signal is required, or even desirable. In other cases, where a strong signal is desirable, it has been found that a slight increase in the thickness of the clutch shoe relative to its main-spring thickness adds considerably to its holding power, all other dimensions remaining the same. In fact, these barrel shoes can be made so tight that they never slip. It holds its original traction value indefinitely and in its preferred form is self-energizing.

In production manufacturing, desired traction or pressure can be assured merely by adhering to usual precision methods in the making of the parts. In fitting a clutch shoe to an individual barrel, it is preferably made slightly longer than the calculated length and either or both ends may then be trimmed off slightly until the shoe fits with just enough tightness to provide the desired traction.

Fig. 11 is a graph illustrating the operational characteristics of a typical main-spring. The abscissae of the curve w represent turns of the member of the barrel assembly through which the spring is wound, and the abscissae of the curve 11. represent turns of the member of the assembly through which the mechanism is driven. The ordinates indicate the proportionate amount of torque at various stages between fully wound and fully unwound. The upper curve w represents the torque required to wind the mainspring, while the lower curve it represents the torque delivered by the main-spring in unwinding. The point ;f on the curve w represents the point at which the mainspring is fully wound. At this point the coils of the mainspring are adjacent one another, being compactly wound around the arbor 2, as illustrated in Fig. 1. Up to the point I, the torque has gradually increased, as indicated by the curve w. Further winding of the main-spring starts to pull its outer end away from the barrel, as shown at 32 in Fig. 1, and the torque increases at a rapid rate, as indicated by the dotted portion 0 of the curve w, representing overwinding of the main-spring. The point B represents the approximate point at which the mainspring will rupture or some part of the associated mechanism will give way if the overwinding is continued.

The holding power, traction, or slipping point of the clutch is preselected, as indicated above, so as to hold the torque of the fully wound mainspring, and preferably slightly more. Hence, the clutch will not slip until the main-spring is fully wound, but will slip before the spring or some other part of the mechanism breaks or is damaged. Preferably, the holding power of the clutch is slightly more than the maximum power of the mainspring, so that the traction of the clutch can be felt by a person winding the mainspring, thus giving a clear indication or signal that the spring is fully wound. While latitude is permissible in the selection of the slipping point, it should be between the points 1 and B on the curve w shown in Fig. 11, and preferably in the lower half of the range. The slipping point has been indicated, by way of example, on the curve 10, at point S. After the slipping point or traction of the clutch has been established by properly selecting the material and determining the dimensions of the shoe or inner member 4, it will retain its value indefinitely. When the slipping point of the clutch is reached, it creeps or slips silently and smoothly, and at the same rate at which the mechanism is overwound. As the slipping point or traction value of the clutch is greater than the maximum torque of the main-spring; full main-spring power-is held, and an unmistakable and commercially acceptable signal is provided. This is of particular importance in timepieces or other small mechanisms, as it is essential for the main-spring to be wound fully and for the full power of the mainspring to be held in order that the mechanism can run satisfactorily for the prescribed period of time. 7

In winding and operating tests made with several conventional self-winding or automatic timepieces, havinga 72-tooth barrel driving a 12-tooth center pinion and providing six hours of running time per barrel revolution, it. was found that using the original drag units and main-springs, the main-spring assemblies were able,,on the average, to develop and store sufficient main-spring energy to drive the barrel from four, to five revolutions. Further tests made with the same barrels, but substituting clutch shoes according to this invention, and appropriately longer main-springs, made possible by the lesser space requirements of the clutch, showed an average development of over six driving turns. It should be particularly noted that this extra reserve power is always added to the most favorable portions of the power curve, that is, to the top. This invention, on each full winding, thus provides a gain in some of these examples of as much as two full turns of favorable reserve power, or twelve hours of additional running time, thereby doubling the length of the most desirable section of the power curve.

A clutch in accordance with this invention does not appreciably change the generally accepted proportions for a correctly proportioned hoe rological barrel assembly.

The operating characteristics of a main-spring, and in particular, the uniformity of its torque curve, do not depend entirely on the dimensions of the barrel. The uniformity of power flow, however, depends somewhat on the material from which the spring is made, its dimensions, proportions, hardness and resiliency. If the mainspring is too soft, it sets (becomes permanently deformed in use) and loses much of its power. As a general rule, the desirable characteristics of a spring increase with an increase in hardness. Therefore, since clutch member 4 is not subjected to repeated flexing or bending it can be relatively hard, and hardness of this member is desirable because it increases the traction and general efficiency of the clutch, all other things remaining equal.

The embodiment of my invention shown in Figs. 3 and 4 is similar in most respects to that shown in Figs- 1 and 2, and corresponding parts are designated by the same reference numerals. There. are, however, two principal differences. The first is that the inner peripheral wall of the barrel. slopes slightly, being of greater diameter adjacent the bottom wall H. The second is in the method of connecting the main-spring with the clutch.

As will be seen in Fig. 4, the inner surface of the peripheral wall [2 of the barrel is frustroconical rather than cylindrical", as shown in Fig. 2. The larger diameter of the chamber is at a point adjacent the bottom wall H of the barrel. The inclination of the wall is slight, being, for example, from one to five degrees to the axis of the barrel, and preferably about two degrees. The" flexible clutch member 4 adopts a correspending shape so as to conform with the inner surface of the peripheral barrel wall It, and, when the clutch slips from time to time in preventing overwinding of the main-spring, due to this novel design, the shoe always tends to hunt toward, and therefore remains at, the bottom of the barrel. An inclined barrel wall also makes it practical to use a clutch in coverless or open barrel constructions.

The connection between the main-spring and. the clutch member l in the embodiment of Figs. 3 and 4 is provided by a tongue or pushed link 5|. One end of the link 5| engages a hook 52 provided at the outer end of the main-spring. The other end engages a hook or projection 4-3 provided on the inner face of the clutch member 4, for example, by being stamped out of the clutch member itself (Fig. 3). The link 5| is preferably arcuate, as shown, in order to conform with the curvature of the main-spring and the clutch shoe whenthe main-spring is fullyrun down. The link 5|, and for that matter, any tongue end, permits the outer end of the main-spring to move inwardly and away from the barrel wall, hence tending to augment the pressure of the clutch member 4 as the main-spring is wound up. It has the further advantage of avoiding any tendency of the mainspring to pull inwardly on the clutch member 4 when the spring is tightly wound. By reason of this fact, the point of connection between the link El and the clutch memher 4 with respect to the abutting ends 4! of. the clutch member, is not as critical.

Figs. 9 and 10 show still other means of conneeting the main-spring with the clutch member. In Fig. 9, a novel type of brace 5| is riveted to the clutch member 4 as indicated at 53. The opposite end of the brace 51 engages a hook 52 on the outer end of the main-spring, as for example, in Fig. 3. The push brace 5i is sufficiently flexible to allow the outer end of the main-spring to move inwardly and away from the peripheral wall formed by the clutch shoe as the spring is wound up. Brace constructions are favored by some horological engineers, as they tend to hold the unwinding main-spring more concentric. thus tending to reduce friction between the main-spring coils as they unwind. Fig. 9 shows the brace in the relative position it assumes when the main-spring is nearly wound up.

In the embodiment shown in Fig. 10, one end of the tongue 5i is riveted to the outer end of the main-spring, as indicated at 54. The opposite end of the tongue engages a hook 43 provided. on the clutch member 4. Tongue-ended main-springs are extensively used and readily obtainable. The clutch in accordance with the present invention is thus readily applicable to use with standard types of main-springs.

It will. be understood that the various features shown in the several figures are mutually interchangeable in any suitable barrel assembly. For example, the means for connecting the mainspring with the clutch member shown in Figs. 3, 9 and 10 can also be used in the embodiment of Figs. 1 and 2. Likewise, the main-spring and clutch member shown in Figs. 1, 2, 5 and 6, as well as the clutch member shown in Figs- 7 and 8 may be used with. an inclined barrel wall, as illustrated in Figs. 3 and 4.

Many additional advantages other than those heretofore mentioned will be readily apparent tothose skilled in the art.

For example, where more than one barrel assembly is used in a single device, with the arbors geared to a single winding key, this invention eliminates both the risk of one short mainspring taking all the winding strain and the need of setting up equally, and, in use, should either main-spring lose a turn, the equal tension of both is simply re-established as turning the winding key and thereby slipping the tighter spring by means of the clutch brings the lesser tensioned Spring up to full tension, at which point they are equalized, even if inadvertently improperly synchronized when first set up.

Still other desirable applications and modifications will be apparent to those skilled in the art within the scope of the invention claimed.

I claim:

1. A main-spring assembly comprising a barrel having an annular wall, a main-spring within the barrel, an arbor for engaging the inner end of the main-spring, a clutch member for operatively connecting the outer end of the mainspring to the barrel, and means for connectin the clutch member with the said outer end of the main-spring, said clutch member adapted to fit in place within the barrel between the barrel and the main-spring and being formed of a single turn of material with its ends in flush abutting relationship and being of a length to exercise a pressure against the barrel wall.

2. A main-spring assembly comprising a barrel having an annular wall, a main-s ring within the barre an arbor for engaging the inner end of the main-spring, and a clutch for operatively connecting the other end of the main-spring to the barrel, said clutch adapted to fit in place within the barrel between the barrel and the main-spring and being formed of a single turn coil with its ends abutting and flush with one another, and having projecting means thereon for engagement with the said other end of the main-spring.

3. A mainspring assembly comprising a barrel having an annular wall, a mainspring within the barrel, an arbor for engaging the inner end of the mainspring, and a clutch for operatively connecting the other end of the mainspring to the barrel, said clutch adapted to fit in place within the bar rel between the barrel and the mains ring and being formed of a sin le turn coil with its ends abutting and flush with one another and having an aperture therein adapted to be engaged by a projecting means on the said other end of the mainspring.

4. A mainspring assembly comprising a barrel having an annular wall, a mainspring within the barrel, an arbor for engaging the inner end of the mainspring, a clutch for operatively engaging the barrel, said clutch adapted to fit in place within the barrel between the barrel and the mainspring and being formed of a single turn coil with its ends abutting and flush with one another and readily disconnectible means operatively connecting the other end of the mainspring with the clutch member at a point spaced from the end of said member.

5. A mainspring assembly comprising a barrel having an annular wall, a mainspring within the barrel, an arbor for engaging the inner end of the mainspring, a clutch for operatively engaging the barrel, said clutch adapted to fit in place within the barrel between the barrel and the mainspring and being formed of a single turn coil with its ends abutting and flush with one another and a push link operatively connecting the other end of the mainspring with the clutch member.

iii

6. In a mainspring assembly the combination with a barrel having an annular wall and a mainspring within said barrel, of a clutch member comprising a strip of spring material of substantially the same cross-section and characteristics as that of the mainspring and of a length substantially equal t the inside circumference of said annular wall, said member bein connected with one end of the mainspring and being fitted within said wall with its ends abutting and flush with one another to hold said member in frictional contact with said wall throughout substantially its entire circumference and provide a substantially constant resistance to slipping appreciably greater than the maximum torque of said spring.

'7. In a mainspring assembly, the combination with a barrel having a side wall and an annular wall having a frusto-conical inner surface with the larger diameter adjacent said side wall, and a mainspring in said barrel, of a clutch member com rising a strip of spring material having a length at one side edge substantially equal to the maximum internal circumference of said annular wall and a length at the other side edge substantially equal to the minimum internal circumference of said annular wall, said strip being connected with one end of said mainspring and being fitted in said barrel with its ends abutting in a flush butt joint t maintain substantially the entire outer surface of said strip in contact with the inner surface of said barrel.

8. In a mainspring assembly. the combination with a barrel having a side wall and an annular wall having a frusto-conical inner surface with its larger diameter adjacent said side wall and a mainspring in said barrel, or a clutch member readily detachably connected with the outer end of said spring and comprising a single turn of resilient strip material friction-ally engaging the inner surface of said annular wall and having its ends meeting in a single thickness fiush butt joint.

9. A mainspring assembly comprising a barrel having an annular wall, a mainspring within the barrel, an arbor for engaging the inner end of the mainspring, a clutch member for operatively connecting the other end of the mainspring to the barrel, and means for connecting the clutch mem ber with the outer end of the mainspring, said clutch member adapted to fit in place within the barrel between the barrel and the mainspring and being formed of a single turn of material with its ends in flush abutting relationship and being of a length to form a substantially true circle.

FOSTER H. BROWN.

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

UNITED STATES PATENTS Number Name Date 397,504 Karthaus Feb. 12, 1889 448,191 Fasoldt Mar. 10, 1891 497,429 Jobson May 16, 1893 1,091,561 Carlstrom Mar. 31, 1914 1,52 .0' 3 Odom Jan. 6, 1925 1,619,943 Lehwess Mar. 8, 1927 1,962,056 Colomb June 5, 1934 FOREIGN PATENTS Number Country Date 145,733 Switzerland May 16, 1933

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