US2798915A

US2798915A - Snap acting mechanism

Info

Publication number: US2798915A
Application number: US401768A
Authority: US
Inventors: James P Watson
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-01-04
Filing date: 1954-01-04
Publication date: 1957-07-09
Anticipated expiration: 1974-07-09

Description

J. P. WATSON 2,798,915

SNAP ACTING MECHANISM July 9, 1957 2 Shee ts-Sheet l Filed Jan. 4, 1954 JAMES P. WA TSON 9 IN VEN TOR.

HUEBNER, BEEHLER 9 WORREL 8 HERZ/G 4' AT TOR/ 15K? July 9, 1957 J. P. WATSON SNAP ACTING MECHANISM 2 Sheets-Sheet 2 Filed Jan. 4, 1954 JAMES P. WATSON:

INVENTOR.

HUEBNER BEEHLER,

- V WORREL a! HERZ/GQ BY A TTORNEYS United States Patent O SNAP ACTING MECHANISM James P. Watson, Lynwood, Calif. Application January 4, 1954, SerialNo. 401,768

4 Claims. Cl. 200-69) This invention relates to snap acting mechanisms, and more particularly to a snap acting switch of the type which moves abruptly from one attitude or position to another attitude or position.

It is an object of this invention to provide an improved snap acting mechanism, especially in the form of a snap acting switch, which has high contact pressure between theengaged portions of the switch, when in the closed position.

It is another object of this invention to provide a snap acting mechanism which requires a relatively low force to operate, yet which has high contact pressure between the engaging portions of the mechanism, more particularly between the contact portions of the switch.

It is another object of this invention to provide an improved snap acting mechanism, and more particularly an improved snap acting switch, having a high ratio between the contact pressure and the force required to operate the switch.

While it is generally recognized that it is desirable to break an electric contact as rapidly as possible, it is often not appreciated that in many instances it is equally desirable to rapidly make the contact. This is particularly true in the common incandescent house lighting where tungsten filament lamps are used, for the initial current through a tungsten filament is often as high as twenty times the steady state current, when the filament is hot. Thus as the contacts of a lamp switch approach each other, a small arc is formed which carries an extremely heavy current. Thus it is very important that the contacts engage rapidly as well as disengage rapidly. It is accordingly an object of this invention to provide a snap acting mechanism, and more particularly a snap acting switch, in which a quick make-and-break operation is effected.

It is another object of this invention to provide an improved snap acting element suitable for use in a snap acting mechanism such as an electric switch.

The advantages and features of the present invention have particular applicability to the type of switch disclosed in my copending patent application, Serial No. 326,737, filed December 18, 1952, although the features and advantages of the present invention are not limited to use or incorporation with such a switch.

In accordance with these objects and with other objects which will become apparent hereinafter, the present invention will now be described with reference to the accompanying drawings wherein:

Fig. 1 is a fragmentary external perspective view showingthe present mechanism as it may be incorporated into the standard of a tablelarnp.

Fig. 2 is a fragmentary longitudinal section taken on line 2-2 in Fig. 1.

Fig. 3 is a cross section taken on line 3--3 in Fig. 2.

Fig. 4 is a fragmentary longitudinal section taken on line 44 in Fig. 2.

Figs. 5, 6, 7 and 8 are fragmentary cross sections taken Substantially in the plane 4-4 of'Fig. 2.

i that lead upward from the base 16 to the bulb at the- Patented July 9, 1957 Fig. 9 is a fragmentary exploded view showing the snap acting elements of the present mechanism in detail.

Fig. 10 is a fragmentary perspective View showing the cam actuating means or member which operates the snap acting elements of Fig. 9.

Referring to the drawings, 16 designates the base of a table lamp surmounted by an upright standard 17, to the upper end of which is secured a lamp socket capable of receiving a two filament lamp bulb (not shown). Such lamps are known in the art and comprise two filaments of unequal wattage, which are electrically brought out from the lamp base in the person of three terminals. Such a lamp may be operated in any one of three modes, namely, the low Wattage filament alone, with the high wattage filament alone, or both filaments together.

Mounted within the upright standard 17 is a switch mechanism constructed in accordance with the present invention. In the example shown, this mechanism has four different positions of operation, so as to adapt it for operating the above mentioned two-filament lamp. One of the four positions is the off position, while the other three positions are the three possible combinations of lamp filament connections alluded to above.

The switch mounted within the standard 17 is operated by a ring 18 disposed circumjacent the lamp body or standard 17. The ring 18 is secured to and around the ends of an actuating shaft 19, which extends diametrically and horizontally across the ring 18 and through the standard 17. The ring 18 may be manually oscillated back and forth employing the shaft 19 as an axis, thus rocking the shaft 19 and actuating the switch mechanism within the standard 17 in a manner which will be described hereinafter.

, The ring 18 is secured to the shaft 19 by cooperating mating means which will now be described. Embedded into the ring 18 at diametral points thereon, are caps 21, which have rectangular recesses 23 facing toward the shaft 19.. The ends of the shaft 19 are relieved to form corresponding rectangular projections 22, which engage or mate within the recesses 23 in the caps 21 to thus secure the ring 18 around the shaft 19. Such a construction makes possible a very simple assembly operation. The ring 18, being made of springable material such as metal or plastic, is simply compressed and distorted slightly as it is placed over the shaft 19, this distortion being inward at right angles tothe shaft 19, so that the ring is slightly elongated in the direction of the shaft 19. When the projections 22 are opposite the recesses 23, the ring 18 is released, whereupon it resumes its normal unstressed attitude causing it to engage the shaft 19 in the manner shown in Figs. 1 and 2. The rectangular nature of the engagement between the projections 22 and recesses 23 causes oscillation of the ring 18 to be imparted correspondingly to the shaft 19.

For convenience of assembly the standard 17 is made of two parts by being portioned along a horizontal plane 24 coinciding with the horizontal shaft 19..

Within the standard 17 is formed a cavity through which the shaft 19 passes. Within this cavity is mounted the switch mechanism of the present invention, shown particularly in Figs. 2, 3, and 4. The switch mechanism comprises a cylindrical insulating body 26 which substantially fills thecavity in the upright 17. A deep recess 27 is formed downwardly in the body 26, which is capped by an insulating flanged cover 28. The walls 29 at each side of the recess 27 are slotted from the top down, to facilitate installation of the shaft 19 in the: body 26.

Extending vertically the full length of the body 26 and throughthe cover 28 are a pair of diametrically spaced bores 20, through which are passed the wires 3 top of the standard 17, and to the switch terminals, to be described hereinafter.

Also extending vertically the full length of the body 26 and cover 28 are a pair of diametrically spaced peripheral grooves 25 which accommodate long bolts 30 that secure the upper and lower sections of the upright 17 together. The bolts 30 also secure the switch body 26 within the standard 17.

Freely rotatably mounted over the shaft 19 is an actuating means or member 31 embodying a clutch which selectively causes the member 31 to be engaged or disengaged by the shaft 19. The shaft 19 is resiliently biased to a given angular position by a pair of springs 35. The showing of these springs has been omitted from Fig. 3 in the interest of clarity, but one such spring is shown in Fig. 2. Springs 35 bear inwardly against opposite sides of a flat lug 40 extending outward from the shaft 19. Springs 35 thus permit shaft 19 to oscillate, but constantly bias it toward a central position. Such clutch and centering means are of the type disclosed in the above mentioned pending application, Serial No. 326,737, to which reference is hereby made for the details thereof. The clutch portion of the actuating means or member 31 is embodied in an enlarged portion 32. On the extended smaller portion of the actuating member 31 are formed a pair of actuating

cams

33 and 34. As best seen in Fig. 10, the cam 34 is generally cylindrical in shape and is provided with four arcuate depressions 37 spaced equally about the periphery thereof.

Between the depressions 37 there are thus left four equally spaced lobes 39, each of which constitutes an actuating or operating member for the switch arm, to be described hereinafter. The cam 33 is spaced axially from cam 34 and also includes four arcuate depressions 36. The depressions 36 are not spaced equally about the cam periphery, but instead are spaced in pairs, the respective depressions of each pair being continguous and spaced substantially 45 degrees apart. That is to say, a pair of radial lines, from the center of the shaft 19 when passed through the low points or centers of contiguous depressions 36 would be approximately 45 degrees apart. On the cam 33 there are thus only two operating lobes 38, between the two pairs of depressions 36. Between adjacent depressions of a given pair there is a small rounded lobe 38a which follows the peripheral contour of the member 31, and which completes the concavity of contiguous depressions 36. The lobes 38a are not switch actuating members, however.

The

lobes

38 and 39, respectively, constitute actuating, engaging, or contact portions of the cams, respectively, which serve to actuate respective switch elements or members, which will now be described. The cam 33, especially its lobes 38, actuates, or operates upon, an elongate leaf spring member 41, which constitutes a first switch arm. The leaf spring 41 is made of springy sheet metal and is divided into at least two longitudinal portions by longitudinal slotting. In the particular embodiment shown there are two such slots 42 and 43 (Fig. 9), which divide the leaf spring member 41 into a plu rality, in this case three, parts or portionsa central portion 44, and another portion comprising the two side parts or portions 46. As shown in Fig. 9, the portions are joined together at each end to form an integral structure constituting the leaf spring member 41. In the embodiment shown in Fig. 9, the central portion 44 is stretched longitudinally, so that it is longer than the side portions 46 and hence must bow outwardly on one side or the other of the plane of the shorter side portions 46, as clearly seen in Figs. -8.

The bottom end of the elongate leaf spring member 41 is bent at right angles to form an integral base 47 which is secured to the insulating body 26, at the bottom of the cavity 27, through the intermediacy of a heavier metal conducting base 48, to be described. more fully hereinafter. The free upper end of the leaf spring memr 4 her 41 is formed arcuately, as shown at 49, to constitute a movable switch contact. The normal attitude of the leaf spring member 41, that is, the one in which it is stressed the least, is as shown in Figs. 7, 8, and 9, with the bowed portion 44 extending inwardly and with the contact portion 49 moved outwardly, away from the actuating member 31.

The free contact end 49 is thus normally in engagement with some form of output member, in this case a stationary contact 51 (Fig. 4) which is disposed against the wall of the cavity 27 near the upper end thereof, and which has a horizontal portion 52 extending into a recess on the top surface of the insulating body 26. The portion 52 is circular and has a circular hole therethrough through which may be passed a mounting screw 53 threaded into the body 26, as shown in Fig. 4. The mounting screw 53 also passes through a contact grommet 54 mounted in the cap or cover 28. The grommet 54 and screw 53 thus constitute one terminal of the switch mechanism, said terminal leading directly to the stationary contact 51, selectively engageable and disengageable by the switch arm 41.

The elongate leaf spring member 41 is positioned to be actuated by the cam 33. On the other side of the shaft 19 from the member 41, but spaced axially along the shaft, so as to be engageable by the cam 34, is a similar leaf spring member 56. Like the leaf spring member 41, the member 56 also has a base 57, which rests atop the base 47 of the member 41. The free upper end of the member 56 is likewise bent into the form of an outwardly facing are 60 which forms a movable electrical contact. This contact is normally in engagement with a stationary contact 58 placed on the wall of the cavity 27 opposite the stationary contact 51 but spaced axially along the shaft 19 therefrom. The stationary contact 58 extends upwardly through a slot in the cover 28 and has a horizontal portion 59 extending over the top surface of the cover 28. The portion 59 is secured to cover 28 by a terminal grommet 62 in which is threaded a screw 61. The grommet 62 and screw 61 constitute a second terminal of the switch, which leads directly to the stationary contact 58, selectively engageable by the leaf spring switch arm 56.

The

cams

33 and 34 are both somewhat narrower, axially, than are the respective central sections or

portions

44 and 81 of the resilient

leaf spring member

41 and 56. Thus as the cam actuating means or member 31 is rotated, the respective earns 33 and 34 operate only upon the respective central portions of the resilient switch arms, leaving the side portions free of contact or engagement by the cams.

In order to rentrain the actuating means or member 31 selectively in its sevesal positions of operation, a resilient detent means or member is provided. This means is in the form of an upright resilient arm 64 (Fig. 9), which is bent outwardly and then returned to form a recessed portion 66. This recessed portion is of just sufficient length to receive resiliently one of the lobes 39 of the cam 34; and the arm 64 is disposed opposite to the cam 34. Integral with the arm 64 is formed, at right angles thereto, a base 67, similar to the

bases

47 and 57, which overlies the base 57, as seen in Figs. 9 and 4.

Referring to the

cams

33 and 34 as pictured in Figs. 5-8, and 10, it will be seen that there are eight different positions of operation of the actuating means 31 with each complete revolution thereof. Thus a 45 degree rotation of the member 31 is required to move from one discrete position to the next. Since there are four different switch combinations of the

switch arms

41 and 56, as seen in Figs. 5-8, it follows that there will be two complete cycles of operation with each revolution of the actuating member 31. In four of these discrete positions the recess 66 of the detent arm 64 will be engaged by one of the lobes 39 of the cam 34, as exemplified by the positions shown in Figs. 6 and 8. In

be opposite a depression 37 of the cam 34. In such positions, however, the cam member 31 will be resiliently restrained by engagement of the bowed central portion 81 of the switch arm 56 in one of the arcuate depressions 37 of the cam 34, as will be described more in detail hereinafter. Thus each of the eight discrete positions of the actuating member 31 is provided with a resilient detent means which holds the member 31 resiliently in that discrete position.

The four

bases

48, 47, 57 and 67 are clamped together as shown in Fig. 4- by a pair of rivets 68 (Fig. 2) which pass through pairs of holes 69 formed in each of the several bases. The

bases

67 and 48 are appreciably heavier or thicker than are the

bases

57 and 47 which are made of light spring material, and thus these top and bottom bases serve as washers to integrate the entire base assembly.

Extending upward from the bottom base 48 and integral therewith, is an elongate portion 71 which is disposed contiguous to the side wall of thecavity 27. At the top of the insulating base or body 26, the conductor 71 is bent horizontally into a shallow recess in the top surface of the body 26 and there terminates in an annular terminal portion 72 (Fig. 9). This portion 72 is contacted by a grommet 73 (Fig. 4) mounted in the cover 28. Through the grommet '73 and terminal 72 extends a terminal screw 74 threaded into the base 26, as shown in Fig. 4. The screw 74 and grommet 73 constitute the third terminal of the switch, this terminal being common to both of the

movable switch arms

41 and 56.

Also formed integral with the base 48 are a pair of

upstanding backing members

76 and 77 which have projecting

portions

78 and 79, respectively, engaging the respective side portions of the

switch arms

41 and 56, as best seen in Figs. 58. These

backing members

76 and 77 form fulcrums about which the resilient switch members 51 and 56 are bent.

The operation of the present snap acting mechanism will now be described with particular reference to Figs. 5-8. The normal position of the resilient switch arms 41 and 56that is, the position in which they are stressed the least, is that shown in Fig. 7. In this case it will be noted that the respective free ends of each of the

switch arms

41 and 56, are moved outward into engagement with their respective stationary contacts 51 and 58. In this position the bowed central portion 44 of the arm 41 nests within one of the arcuate depressions 36 formed on the cam 33. Similarly, the bowedcentral portion 81 of the switch arm 56 nests with in one of the arcuate depressions 37 of the cam 34. Thus the cam 33 serves as a back-up member or brace for the arm 41 which keeps the arm 41 pressed firmly against the stationary contact 51. This backing action serves to greatly enhance the contact pressure between the contact end 49 of the arm 41 and the stationary contact 51. The contact pressure between the

members

56 and 58 is similarly enhanced by the backing action of the cam 34.

As the cam actuating means 31 is rotated clockwise from the position shown in Fig. 7 to that shown in Fig. 8, the upper right-hand lobe 39 bears against the inwardly bowed portion 81 of the arm 56 and slides longitudinally therealong. As the lobe 39 slides along the central portion 81, it follows an arcuate path and thus bears with increasing pressure against the central portion 81 tending to press the central portion 81 outwardly. It has been found in practice that as the lobe 39 runs along the central portion 81 and presses thereinto, a small wave is formed on the central section 81 running immediately ahead of the lobe 39. When the central portion 81 has been pressed far enough outward past the plane of the unbowed side portions of the spring member 56, the central portion 81 snaps suddenly and abruptly past the dead center position and onto the other side of the plane Tof.the.unbowed side sectionsof thespring arm 56. After the central portion 81 suddenly snaps past dead center, it occupies the position shown in Fig. 8.

This snapping action is simultaneously accompanied by a sudden snapping of the free end 82 of the member 56 away from its stationary contact 58, thus opening that portion of the switch mechanism. In moving from the position shown in Fig. 7 to that shown in Fig. 8, the cam actuating member 31 has moved through 45 degrees. In this position, as shown in Fig. 8, the lobe 39 is pressed firmly into and against the arcuate or bowed portion 81, restraining the switch arm 56 in open position against its natural, resilient tendency to snap outward. The cam member 31 is resiliently restrained in this position by the engagement of the opposite lobe 39 in the recessed portion 66 of the resilient detent arm 64.

During this operation of the cam 34 upon the central portion 81 of the switch arm 56, the cam 33 has also moved, with respect to the bowed central portion 44 of the switch arm 41. This movement of the cam 33, however, has not affected the position of the switch arm 41, since the bowed portion 44 has simply moved from a nested position in one of the arcuate depressions 36 to a corresponding nested position in the immediately adjacent depression 36, as shown in Fig. 8.

A further 45 turn of the actuating member 31 in a clockwise direction leads from the position shown in Fig. 8 to the position shown in Fig. 5. In this turn the lobe 39 steadily recedes away from the bowed central portion 81. In this receding action the bowed portion 81 follows the lobe 39 closely by virtue of its natural resilient bias in that direction. When the lobe 39 has receded sufficiently, the bowed portion 81 again snaps past center, i. e., past the plane of the unbowed side portions, to the position shown in Fig. 5, whereupon, and simultaneously therewith, the free end 82 snaps suddenly back into engagement with its stationary contact 58.. Thus both the make-and-break operation of the switch arm are done abruptly and with suddenness, which is highly desirable in switching operations, particularly when applied to tungsten incandescent illuminating bulbs.

During the movement from the position shown in Fig. 8 to that shown in Fig. .5, the lobe 38 of the cam 33 is slid with increasing pressure against the bowed central portion 44 of the switch arm 41. As described in connection with the lobe 39, the lobe 38 likewise rides longitudinally against the bowed portion 44 of the arm 41 until the bowed portion snaps past center, to the position shown in Fig. 5, this snapping being accompanied by the simultaneous snapping of the free end 49 awa from its stationary contact 51. In the position shown in Fig. 5, the detent recess 66 is no longer occupied by one of the lobes 39. However, the cam actuating .member 31 is nonetheless resiliently held in this position by the nesting of the bowed portion 81 in the corresponding depression 37 of the cam 34.

An additional clockwise turn of 45 degrees carries the switch from the position shown in Fig. 5 to that shown in Fig. 6, in which the bowed portions of both of the

arms

41 and 56 are under pressure by their respective cam lobes and hence both switches are open. A further turn of 45 degrees carries the switch from the position shown in Fig. 6 to that shown in Fig. 7, where this present explanation started. It is thus seen that four different switch combinations are effected by a degree rotation of the cam actuating member 31. Hence there are two cycles in a corrrplete revolution of the actuating member 31. t

The present invention may be practiced by elongate leaf spring members such as 41, which have any number of elongate slots 42. In this case it is preferred and desirable to have a cam section operating upon eachof the outwardly bowed portions. A multiplicity of such bowed sections is preferred in heavy duty switches where a large contact surface is desired between the stationary and movable contacts.

It is also within the contemplation of the present invention that where a leaf spring member having two slots is employed, the two outer sections may be the lengthened and bowed sections, if desired, leaving the central section shorter and unbowed. In this case it is preferred to have a pair of spaced cams operating simultaneously upon the two outer bowed sections of the leaf spring.

It is also within the contemplation of the present invention that a return cam may be employed, i. e., a cam which bears against the unbowed portion of the leaf spring to return the spring to its position of lesser stress. For example, a pair of cams may be placed opposite and in selective engagement with the side portions 46, which bear against the leaf spring member 41 and press it back outwardly in operating from the position shown in Fig. 6 to that shown in Fig. 7. This alternate arrangement provides a positive actuation for the switch arm, instead of relying on the natural resiliency thereof, to return it to the closed or outer position illustrated for example in Fig. 7.

It is further within the contemplation of the present invention that the backing of the switch arm in its closed or engaged position, illustrated in Fig. 7, may be achieved by nesting the relaxed bowed portion of the svw'tch in an arcuate depression which is in a stationary member, rather than in the rotatable cam portion of the switch. In this case there would simply be a movable or cam portion which would project movably out from the stationary backing cavity in an arcuate path to actuate the switch to its open position.

In some cases backing or reinforcing of the bowed portion may be desirable for both positions of the switch, as for example, in a double throw switch where good contact pressure is desired in both throws of the switch arm. In this case stationary backing members with concavities to receive the bow may be provided on one or both sides of the switches in position to nest with the bowed portion as it snaps back and forth.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein but is to be accorded the full scope of the claims.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Actuating member comprising a body, an actuating shaft rotatably mounted in said body and protruding at each side thereof, an actuating ring of elastic material disposed circumjacent said body, and mating means between the ends of said shaft and diametral areas on said ring, the distance between said areas when said ring is unstressed being less than the length of said actuating shaft, whereby said ring may be mounted to said shaft by being distorted within the elastic limit and released with said mating means in mating engagement.

2. Cam actuated switch comprising in combination a pair of rotatably mounted earns, a pair of switcharms disposed, one on each side of said cams, one of said witch arms being positioned to be actuated by one of said cams and the other of said switch arms being positioned to be actuated by the other of said cams, one of said cams embodying four discrete operating lobes effec tive to actuate its corresponding switch arm through four cycles with each revolution of said cam, and the other of said cams embodying two discrete lobes effective to actuate its corresponding switch arm through two cycles with each revolution of said cams, whereby four different combinations of switch positions are effected for the two switch arms.

3. Switch mechanism comprising an elongate leaf spring member composed of at least two longitudinal portions separated by a longitudinal slot and joined together at each end, one of said leaf spring portions being longer than the other so that it must bow out, on one side or the other, of the plane of the shorter of said portions; means mounting said leaf spring member firmly at one end, the other end being free to oscillate back and forth; an electrical contact on the free end of said leaf spring member; and a cam rotatably mounted on an axis substantially transverse to the length of said elongate spring member, and substantially parallel to the plane of said shorter portion of said leaf spring member, said cam bearing against said bowed portion and sliding longitudinally thereagainst with increasing pressure until said bowed portion snaps past said plane, thereby to move the free end of said leaf spring member with a snap action, in a direction generally opposite to the direction of snapping of said bowed portion, said cam having an arcuate depression with a lobe at each end thereof, said longer portion of said leaf spring member nesting within said depression and against said cam in the unsnapped position of said leaf spring member.

4. Switch mechanism comprising an elongate leaf spring member composed of at least two longitudinal portions separated by a longitudinal slot and joined together at each end, one of said leaf spring portions being longer than the other, so that it must bow out, on one side or the other, of the plane of the shorter of said portions; means mounting said leaf spring member firmly at one end, the other end being free to oscillate back and forth; an electrical contact on the free end of said leaf spring member; an actuating member including a contact portion engaging the bowed portion of said leaf spring memher and mounted to move longitudinally and inward against said bowed portion so as to slide longitudinally therealong with increasing pressure thereagainst, starting near one end of said bowed portion and progressing toward the center, until said bowed portion snaps past dead center onto the other side of the plane of said shorter portion of said leaf spring member, thereby to move the free end of said leaf spring member with a snap action, in a direction generally opposite the direction of snapping of said bowed portion; and backing means having an arcuate depression therein in which resides said bowed portion of said leaf spring member when said actuating member is in minimum pressure engagement with said bowed portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,741,406 Decker Dec. 31, 1929 1,913,992 Mabie June 13, 1933 1,960,020 McGall May 22, 1934 2,059,712 Schellenger Nov. 3, 1936 2,182,715 Yeske Dec. 5, 1939 2,240,770 Hammerly May 6, 1941 2,262,306 Thompson Nov. 11, 1941 2,314,592 McCormick Mar. 23, 1943 2,335,388 Conradty Nov. 30, 1943 2,338,305 Simmon Ian. 4, 1944 2,512,306 Clark June 20, 1950 2,540,421 Broch Feb. 6, 1951 2,574,429 Wood Nov. 6, 1951 2,582,034 Hausler Ian. 8, 1952 2,604,316 OBrien July 22, 1952 2,654,817 Brenton Oct. 6, 1953 2,700,079 Haydon Jan. 18, 1955 FOREIGN PATENTS 348,686 Great Britain May 13, 1931 560,583 Great Britain Apr. 11, 1944 965,142 France Feb. 8, 1950