US2705272A - Shock proof switch - Google Patents

Description

March 29, 1955 M. J. DOBES ETAL 2,705,272

SHOCK PROOF SWITCH Filed Aug. 19, 1950 7 Sheets-Sheet l INVENTORS. M w/96. J. 0055: 14/165 .w/n/

March 29, 1955 Filed Aug. 19, 1950 M. J. DOBES ETAL 2,705,272

snocx PROOF SWITCH 7 Sheets-Sheet 2 Xio l IN V EN TORS.

MICHAEL J. 0 555 JflMES H. 5 1/771 March 29, 1955 Filed Aug. 19, 1950 M. J. DOBES ET AL SHOCK PROOF SWITCH 7Sheets-Sheet3 Mam J. 0 86.5 14/955 MJ/W/F/ March 29, 1955 M. J. DOBES ETAL 2,705,272

SHOCK PROOF SWITCH Filed Aug. 19, 1950 7 Sheets-Sheet 5 filwflez .Z A0565 1 1/ 155 .4. SM/ TH March 29, 1955 V M. J. DOBES ETAL 2,705,272

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Much 29, 1955 Filed Aug. 19, 1950 M. J. DOBES ETAL SHOCK PROOF SWITCH 7 Sheets-Sheet 7 IN VEN TOR-3.

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United States Patent SHOCK PROOF SWITCH Michael J. Dobes, Euclid, and James H. Smith, Cleveland, Ohio, assignors to The National Acme Company, Cleveland, Ohio Application August 19, 1950, Serial No. 180,332

2 Claims. (Cl. 200-166) This invention relates to switches and more particularly to a switch which will not be jarred or shaken out of contact by a sudden impact.

Until recently, there has been very little need for switches carrying moderately large current which could not be shaken to break the contact. Most switches were firmly mounted and were not subject to impact or shock. However, more recently a demand has arisen for a switch which will maintain its contacts closed in spite of impact or the like. Such switches may be used on fast moving vehicles, ordinance or other devices subject to vibration or impact.

These shockproof switches must be protected against overloading and should have protection against failure of power in addition to being shockproof. Moreover, these parts must be such as to be substantially unmoved by the shock also. One such type of overload relay is shown in our csopending application Serial No. 166,326, filed June In addition to satisfying the above requirements, the switch embodying the present invention is operated quickly by a snap action device and has improved type contacts which reduce the amount of arcing, and substantially reduce the harmful effects of such arcing by their formation.

A more complete understanding of our invention may be derived from reference to the accompanying drawings and description which form a part of the specification.

In the drawings:

Fig. 1 is a side elevational view of a switch embodying our invention, some parts being broken away to show underlying parts;

Fig. 2 is a top plan view of the switch with the cover removed;

Fig. 3 is a top plan view of the snap action alone, the cover being broken away to show underlying parts;

Fig. 4 is a medial sectional view of the device shown in Fig. 3 along line 4-4 of that figure;

P Fig. 5 is a medial sectional view along line 5-5 of F Fig. 6 is a detailed sectional view along line 6-6 of Fig. 7 is a detailed sectional view along line 7-7 of Fig. 4;

8 is a detailed sectional view along line 8-8 of ig.

Fig.9 is a sectional view of the switch contacts and the housing separated from their surroundings taken along line 9-9 of Fig. 10;

Fig. 10 is a sectional view along line 10-10 of Fig. 9;

Fig. 11 is a wiring diagram showing one possible circuit for the switch;

Fig. 12 is a side sectional view of the movable contact assembly separated from surrounding parts;

Fig. 13 is an end elevational view of the contact assembly shown in Fig. 12;

Fig. 14 is an exploded top plan view of the contact assembly, showing its relation to the fixed contacts;

Fig. 15 is a detailed side elevational view of the main contact member alone;

Fig. 16 is a detailed end elevational view of the contact member;

b Fig. 17 is a detailed top plan view of the contact mem- Fig. 18 is a detailed side elevational view of a jaw member of the movable contacts; and

Fig. 19 is a detailed top plan view of the jaw member.

Briefly, our invention comprises a housing in which are 2,705,272 Patented Mar. 29, 1955 mounted the switch elements. The overload relays which are preferably of the shockproof type as disclosed in our aforementioned co-pending application, are mounted on one side and are adapted to be reset or held in an emergency running position from outside the housing. A snap action device adapted to operate a linearly moving member is disposed centrally of the housing. This device is spring-biased to an off position but may be turned on by turning a handle from the exterior of the housing. The switch is then locked in that position by a pawl means until released either by the handle or by a solenoid trip which acts to trip the switch in the event of power failure or overload. The contact assembly is mounted in the housing opposite the overload relays and includes movable contacts operated in a linear direction by the snap action mechanism. The contacts are of a novel type in that the movable contacts grip the stationary contacts with a pair of fingers which holds the contacts together unless deliberately pulled apart. In addition, the fingers are engaged with the fixed contact members for a considerable space after the main seat of the movable contact has been moved away. Thus, any arcing in the switch when the contacts are opened takes place between the fingers and the fixed contacts and at a different location from the main contact surfaces. Thus any pitting of the contacts because of arcing is localized in an area remote from the main contact surfaces. This condition prolongs the useflllll life of the contacts as will be evident to those skilled in t e art.

More particularly and referring to the figures, the switch is enclosed in a housing 11 having a cover 12 fixed thereto by screws 13. A pair of overload relays 14 is mounted in one end of the housing on mounting bosses 15. In the cover above the relays 14, is mounted a push button member 16 which is biased outwardly of the cover by a spring 17. A bar 18 is fixed to the end of this pushbutton transversely of the cover to extend over the reset members 19 of both overload relays 14. This bar 18 is guided by a groove 20 in the cover thus preventing any rotation or misalignment.

The cover 12 also provides bearing surfaces for the main switch operating shaft 22. The end of this shaft extending within the cover is formed with a male coupling 23 adapted to engage a mating female coupling member 24 on the snap action mechanism to drive it. This may be a simple tongue and groove arrangement as shown, or may take any of several other forms. A hand wheel 26 or other operating lever is fixed to the other end of the shaft 22 and the assembly is urged outward of the cover 12 by a spring 27. This urging is resisted by the engagement of the coupling member 23 with a shoulder 28 formed in the cover. Gasket material 29 may be interposed between the member 23 and the shoulder 28 to prevent leakage of corrosive material into the switch. The pressure on this gasket also creates a frictional force which helps to prevent inadvertent turning of the wheel 26. Additional packing material 25 is disposed in an annular groove at the outer surface of the cover and is held in place by the spring 27.

The snap action mechanism is enclosed in a separate housing 30 mounted onbosses 31 formed in the main switch housing 11, and is held there by screws 32 extending through holes in ears 33 formed on the housing 30. A cover 34 for the housing 30 is held in place by screws 35.

The snap action (Figs. 3-8) is driven by a shaft 36 formed at one end with the coupling member 24. Immediately adjacent the coupling part 24, the shaft is journalled in the cover 34. A spring holding drum 37 is pinned to the shaft 36 below the cover and is surrounded by a fiat coil spring 38 held in a notch 39 in the drum 37. The other end 40 of the spring is hooked around a post 41 either formed as a part of the cover 34 or rigidly attached thereto. This spring 40 serves to bias the shaft 36 toward one position which, as will appear later, is the position where the switch contacts are separated or open and the switch is 01?.

Below the drum 37 the shaft is formed with a pair of diametrically oppposed key ways 43. A driving memposed, is freely journalled on the shaft 36, both above and below the member 44. An almost completely annular slot 50 (Fig. 6) is formed in both driving and driven members leaving only relatively narrow bridge portions 51 connecting the outer and inner rings on each member. A flat ring shaped spring 52 of the type disclosed in the Jeffrey Patent No. 2,270,951 is disposed in the slot 50 and resists relative angular displacement between the driving and driven members. Thus, if the driving member 44 were to be turned by the wheel 26 through the shaft 36, the driven member 47 would follow it unless constrained by external means. In the latter case, the two members 44 and 47 would be angularly displaced (Fig. 6), the driving member turning with the shaft and the driven member held stationary. The spring 52 then stores up a certain amount of energy which, if released suddenly, would snap the driven member into line with the driving member again. A washer 53 may be disposed about the shaft 36 between the drum 37 and the driven member 47 to serve as a spacer.

The holding means for the driven member comprises two similar sets of pawls (Figs. 3, 6, and 8) mounted in the housing and adapted to engage notches 55 formed in the driven member. Each set of pawls is journalled on a post or shaft 56 or 56a having one end 57 extending into the housing 30 and adapted to be supported by the cover 34 at the other end 58. The post 56 extends the full depth of the housing 30 while the post 56a is somewhat shorter so that the housing may be cut away beneath it to form a depending rib 60 (Fig. to which a release lever 61 is pivoted for a purpose to be made clear hereinafter.

Each set of pawls comprises two slightly different pawl members 62 and 62a. The pawls are similar as viewed from the top (Figs. 3 and 6) each having a notch engaging point 63 and an enlarged end 64 through which the shaft 56 or 56a extends. In the elevational view (Fig. 8) the pawls are somewhat different. The pawls 62 are formed as a rectangle with a pair of shaft engaging arms 65 extending outwardly and spaced somewhat from the edges of the rectangle. The pawls 62a are formed from a similar rectangle having a pair of arms 65a extending from the top and bottom edges of the rectangle and adapted to engage the shaft 56 or 56a in the spaces outside the arms 65. A post 66 is also formed on each pawl 62a to serve as an auxiliary release as will appear hereinafter. A small coil spring 67 is coiled about the shafts 56 and 56a in the space between thearms 65. Each end of this spring engages one of the pawls 62 or 62a and tends to hold it resiliently against the driven member 47 as best shown in Fig. 6. The pawls are spaced on their shafts by bushings 68 which locate the pawls in position to engage the driven member 47.

It will be noted that each member of the pair of the pawls 62 and each of the pawls 62a is disposed diametrically opposite its mating member in the housing 30 (Figs. 3 and 6). This symmetry is required to make shockproof the snap action mechanism. It is clear that with such spacing, an impact or shock tending to release one of the pawls will, at the same time, tend to drive the other similar pawl into tighter engagement with its notch and, as a result, an impact will never release both pawls to allow movement of the snap action.

The points of the pawls 62 and 62a are spaced apart somewhat further than the notches 55 so that only one of each set of pawls is engaged at any one time. The movement from the point where one pawl is engaged to the point where the other is engaged is utilized to operate the switch. This is accomplished through a gear and crank arrangement which results in linear move ment of a switching member. More particularly the driven member 47 is formed with a set of gear teeth 69 on its lower part nearest the post 56. Enmeshed with these teeth 69 is a frictional pinion 70 formed on a crank member 71 rotatably journaled on the post (Fig. 5). A crank arm 72 near the lower end of the member 71 extends toward the center of the housing 30 beneath the end of the shaft 36, and is loosely disposed in a slot 73 formed in an operating member 74 of the switch. A pin 75 extending through the operating member 74 and the crank arm 72 holds the two members in operative relationship. The hole 76 in the arm 72 is made either considerably larger than the pin 75 or is slotted some- 72 and the operating member 74, thus permitting truly linear movement of the member 74 "while the arm 72 moves angularly.

The movement of the operating member 74 thus caused by the driven member 47 is made a snap movement by the action of a spring, either the spring 38 or spring 52. The driven member 47 is held against movement by either of a pair of pawls 62 or 62a until released. When released, one of the springs will be stressed so that it will snap the member 47 to its alternate position. This release is accomplished by either of two release means. For manual operation, the driving member 44 is formed with cam portions 78 (Figs. 3 and 6) on its outer surface. Each cam portion consists of an inclined plane adapted to move the engaged pawl out of its notch 55. The cams 78 are spaced so that this disengagement takes place only after the driving and driven members are displaced angularly, enough so that the spring 52 will snap the driven member to its alternate position where the other of the pawls will be engaged. Cam portions 78 are provided for each of the pawls 62 or 62a, however, so that manual operation will be effective to snap the switch either off or on. Stop members in the form of arms 79 extending outwardly from the driven member 47 adapted to engage abutments 80 formed in the housing 30 are provided to prevent over travel of the driven member 47 or the switch operating member 74. In the illustrated embodiment, the arms 79 serve a second purpose. The slot 48 is so extensive that it almost completely divides the driven member 47 into two parts. The only material holding the upper and lower part together is at the arms 79. It will be recognized however, that this condition need not exist and that the only reason the slot extends through so great an extent of the outer surface is that the points 63 of the pawls are widely spaced and therefore the cam 78 on the driving member 44 must be able to engage them at the widely spaced points.

For automatically opening the switch, a second pawl release means is provided. This is operated in case of power failure or of an overload and is tripped by means later described. The release mechanism is operated by the trip lever 61 which, as stated before, is pivotally mounted on a rib 60 formed in the housing 30. This lever extends downward from the housing 30 in position to be tripped by the trip means, and extends upward through a slot 82 (Fig. 7) formed in the housing. A bushing 83 (Figs. 4, 5 and 7) staked into the housing 30 provides bearing means both for the rotary parts'of the release mechanism and for the lower end of the shaft 36. A washer 84 set into a counterbored hole in the housing 30 and surrounding the top of the bushing 83 covers the bushing and provides a floor on which the member 47 may slide. Beneath the washer 84 and journalled on the outer surface of the bushing is a stepped member or plate 85 formed with a step 86 (Fig. 7). The upper end of the lever 61 is positioned to engage this step 86 to rotate the plate slightly about the bushing. A pair of extending fingers 87 are disposed in milled grooves at opposite edges of the stepped member 85 and are pivoted thereto by pins 88 extending through ears 89. The arms are guided between the edge 90 of a hollow in the housing and the bottom 91 of the milled grooves, in a direction to engage the posts 66 on the pawls 62a. A small post 92 may be formed in the housing 30 to serve as an additional guide for the fingers 87.

The pawls 62a are placed to hold the switch in the contact closed" or on position. When the lever 61 moves the plate 85 in a counterclockwise rotation (Fig. 7) the fingers 86 are further extended and engage the posts 66 to release the pawls 62a. As noted above, the spring 38 is stressed to urge the shaft 36, and therefore the driving member 44, to a contact open or off position but this tendency is overcome by the heavier spring 52 which holds the driving and driven members in line. However, when the pawls 62a are released, there is nothing opposing the spring 38 since the driven member is then free to turn, so the switch is snapped to the off position by the spring 38. The spring 67 is effective not only to hold the pawls 62 and 62a against the member 47 but also resets lever 61 by pressing the fingers 87, through the posts 66 on the pawls 62a, to move the plate 85 in a clockwise direction, thus returning it to its normal position.

what to allow a sliding movement between the arm 85 The means which trips the lever'61 comprises a solenoid 94 mounted on bosses 95 in the housing 11 by screws 96 (Fig. 1). The solenoid is of customary formation and is provided with a headed bar 97 fixed to the armature 98. A spring 99 is engaged between the head 100 on the bar 97 and the yoke 101 which is fixed to the stator of the solenoid. Thus the armature is urged outwardly of the stator. The normal position when the switch is on, however, is for the armature to be drawn in, since a part or all of the current going through the switch also passes through the winding of the solenoid. In the normal switch on position therefore, the head 100 on the bar 97 is held to the left (Figs. 1 and 2) and away from the lever 61. It is, however, aligned with the lower end of that lever and when the solenoid is deenergized, either by a failure of power from the source or by an open circuit somewhere else, the head 100 will trip the lever 61 to cause the switch to be opened. The overload relays 14 are reconnected in the circuit including the solenoid winding as described hereinafter. Thus when an overload in the circuit causes one of the relays -14 to be opened by a process explained in our aforesaid copending application, the current through the solenoid winding is shut off, and the switch is opened by the snap action mechanism as described.

A wall 104, of insulating material is fixed to the side of the snap action housing 30 by screws 105. This wall which may extend beyond the sides of the housing slightly, as shown, serves several purposes. One of the most important purposes is to increase the creepage distance between the terminals on the overload relays 14 and the snap action housing 30. A further purpose is to insure that the eyelets used to make connections to the overload relays do not come in electrical contact with the housing 30. A still further purpose will be apparent when the nature of the overload relays is considered. These relays 14 are of the type which is released by a maximum temperature. It is desirable, therefore, that the snap action mechanism and its housing 30 be insulated at least from direct exposure to the heat from the heating elements. The wall 104 is made of insulating material and therefore is effective to protect the snap action from this heat also.

A separate contact housing 107 for the main switch contacts is supported on bosses 108 formed in the switch housing 11 and is held thereto by screws 109 extending through holes 110 in cars 111 on a plate 112 on each side of the housing. The housing 107 is held in place between the plates 112 by screws 113 (Fig. 10).

A plurality of fixed contact members are mounted in vertically separated pairs in the housing 107. Each member is formed with a cylindrical contact portion 116, preferably a silver jacket, and a stem portion 117 of reduced diameter which extends through a wall of the housing and is threaded near its end. A nut 118 secures the contact member in the housing. Each of the stems extends through a contact strip 119 or 119a and is electrically connected therewith because of the clamping action of the nut 118. The strips 119 are disposed in grooves 120 and are provided with terminal screws 121 to which wires may be attached. In order that all connections to the contacts may be made at the top of the housing, the contact strips 119a extending from the lower contacts to the top of the housing are embedded in grooves in the housing and are separated from each other for proper creepage distance by ribs 123. One rib is cut away at 122 to provide for a jumper 154 which is connected between two adjacent contacts 116 as will be described later. Terminal screws 124 are threaded into insert 125 in the housing which hold the strip 119a in place.

The movable contacts 126 are carried by a block 127 of insulating material slidably disposed in grooves 128 in the housing 107. This block is connected to the operating member 74 which extends from the snap action device by a plate 129 staked on the end of the member 74 (Fig. 4) and held to the block 128 by screws 130 (Fig. 10). Thus, the block 127 is moved by the operating member 74 in response to action of the snap action mechanism.

The contacts 126 are disposed in slots in the block 127 and are slidably journalled on a screw 132 threaded into an insert 133 moulded in the block 127. The threads of the screw are preferably somewhat smaller than the body, thus providing a shoulder which will seat against a washer 136 and hold the screw firmly, although it is extended from the block. The contacts 126 are formed with a hole 134 and are thereby journalled on the extending body part and are kept from sliding off by a head 137. A pair of compression springs 138 on each contact 126 hold the contacts against the head 137. One end of each spring 138 is held in place on its contact by studs 139 and the other end is disposed in a hole 140 formed in the block 127.

The contacts 126 have the general formation of the letter H (Figs. 12 and 15) lying on one side. The cross piece 142 of the H is formed with the hole 134 which is journalled on the screw 132 as described above. The legs 143 of the H are similar, each carrying a contact making part for engagement with the contact portion 116 of the fixed contact. The right hand ends (Figs. 9, 10, 12, and 15) of the legs are formed with flanges 145 which support the studs 139.

The other ends of the legs 143 carry a block 146 formed with a substantially semicylindrical concave surface 147 which is preferably inlaid with silver and which contacts the portion 116 of the stationary contacts. Pivotally mounted on the outer surface of each leg 143 are a pair of fingers 148. These fingers are journalled on a pin 149 pressed into the contact member 126. A spring 150 is coiled about the pin 149 and engages the fingers to urge them toward each other. The fingers, however, are held apart by their engagement with the bottom of slots 152 cut into the side of the block 146. The ends 153 of the fingers 148 extend beyond the edge of the block and are rounded convexly. The slots 152 are of such depth that the space between the ends 153 of the fingers is normally somewhat less than the diameter of the part 116 of the stationary contacts. Thus the fingers are adapted to grasp the part 116 as shown in the dashed lines in Fig. 10.

The operation of the contact part of the switch is controlled by the snap action mechanism as described above. As the operating member 74 is pushed to the left (Figs. 1, 9, and 10) the block 127 is slid with it. The movable contact members 146 are thus carried by the block toward the fixed contacts. As the fingers 148 engage the part 116 of the fixed contacts, they are pressed apart by the camming action of the part 116 on the rounded ends 153. As the motion continues to the left, the fingers grasp the part 116. Further motion of the block 127 presses the movable contacts against the fixed posts 116 and compresses the springs 138 thus holding the movable contacts firmly against the posts 116 providing better electrical contact. The surface 147 engages the surface of part 116 and is held there at least partly by the grasp of the fingers 148. The spring 150 and fingers 148 may be so proportioned that considerable efiort is required to break the grasp, thus preventing a breakage of contact due to shock. It may be noted here that the block 127 which carries the contacts 126 is rigidly held in place by action of the latches or pawls 62a in the snap action device, so that the fingers need hold against the inertia of the contact piece 126 only, and in this they are assisted by the compression springs 138.

When the switch is opened by action of the snap action, it will be noted that the fingers are in contact with the sides of the part 116 of the stationary contacts after the main contact surfaces have been separated. Thus the fingers act to delay the final break of the circuit and therefore reduce any tendency to arc. Moreover, since the fingers are at the sides, any arcing that does result will pit or burn only the sides of the contacts and will not affect the principal contact surfaces. The result is a much longer lived set of contacts.

It is apparent that the contact fingers 148 need not extend around the part 116 of the fixed contacts to achieve the latter result. As best shown in Figs. 14 and 19 it is also conceived that the fingers 148a should extend substantially tangentially to the surface of the jacket 116. With this form, the grasping force on the jacket 116 is considerably less. However, this form retains many of the benefits of the prior described device. In case of a shock tending to free this type of contact from the fixed contact, there might be a slight movement against the spring 138. However, the fingers 148a extend beyond the block 146, a distance sufiicient so that no matter how severe the shock, they will always remain in contact with the jacket 116. Thus while the contact resistance might be momentarily increased somewhat there still would not be a breaking of the circuit. It is obvious that this latter form retains all the benefits of the former insofar as freedom of the contact surfaces from arcing is concerned.

A wiring diagram showing the method of wiring the switch is shown in Fig. 11. This diagram is for three phase alternating current using three wires. However, it is apparent that single phase alternating current, or direct current could also be used merely by bypassing one of the overload relays shown diagrammatically at 14. Further types of wiring diagram will be readily apparent to those skilled in the art.

In the diagram the power enters the switch through three leads 155 to either the upper or lower fixed contacts indicated at 116a, c, e, and g. Since four contacts are provided, a jumper 154 is used between two of them 116a and c to make connection of the wire more simple. The moving contacts 126- are adapted to close the circuit joining together fixed contacts 116a and b, 1160 and d, 116e and f, and 116g and h. The main load circuit leads from contact 116d through contact strips 158 heater 156 of one of the overload relays to the motor 157 and from contact 116 directly to the motor 157 and from contact 116h through contact strips 158 and the other heater 156 to the motor 157. Since two of the three leads pass through the heaters 156, it is obvious that an overload in any phase will cause overheating of the heater and consequent opening of the overload relay circuit.

The auxiliary control circuit leads from contact 116b through the trip solenoid 94 to the dual contacts 159 of the first overload relay 14 thence through the contacts 159 of the second relay and to the fixed contact 116h. Thus if either of the overload relays becomes 'an open circuit because of overheating, the solenoid 94 will be de-energized and the switch will be tripped open by the means described above. Since the heaters 156 are a part of the circuits of all three phases, it is clear that an overload in any one of the phases will cause the solenoid 94 to open the switch.

It is obvious that for single phase or direct current use, the pair of fixed contacts 116a and f could simply be omitted and the device would operate satisfactorily. However, by a simple rewiring to bypass the second pair of overload contacts 159 and to connect the first pair directly to fixed contact 116i and not use the pair of contacts 116g and h. This would save the energy used in the heater 156 of the second overload relay. Many other possibilities will appear to those skilled in the art, the above described circuits being merely illustrative of possible uses.

Having thus described our invention in an embodiment thereof, we are aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of our invention.

We claim:

1. In a switch having at least one pair of spaced cylmdrical fixed contacts, and movable contact carrier means, movable contact means comprising an H-shaped member having a cross member and a pair of leg members, said cross member being slidably disposed on said carrier means, spring means engaged between said carrier means and one end of each of said pair of leg members, the other end of said leg members being formed with parti-cylindrical seats for engagement with said fixed contacts, finger members pivoted to said leg members and extending beyond the seat ends of said leg members toward said fixed contacts, said fingers being adapted to remain engaged with said fixed contacts after the engagement of said seats and fixed contacts has been broken.

2. In a switch having a support, and contact means mounted in said support; movable contact means comprising a contact seat block having a curved surface for engagement with said contact means, at least a pair of opposed contact fingers pivoted about a common point on said contact seat block and extending beyond said contact seat curved surface, biasing means urging said contact fingers toward each other whereby said contact fingers will be first to engage said contact means in said support when the contact seat block is relatively moved toward engagement with said contact means.

References Cited in the file of this patent UNITED STATES PATENTS 1,199,478 Mahoney Sept. 26, 1916 1,354,764 Kellner Oct. 5, 1920 1,992,036 Meier Feb. 19, 1935 2,064,632 Schmitt Dec. 15, 1936 2,254,914 Rugg Sept. 2, 1941 2,376,652 Bassett May 22, 1945 2,411,894 Peters Dec. 3, 1946 2,414,956 Kyle, Jr. et al. Ian. 28, 1947 2,432,782 McClain Dec. 16, 1947 2,498,250 Cole Feb. 21, 1950 2,523,370 Jefirey Sept. 26, 1950 FOREIGN PATENTS 142,858 Switzerland Oct. 15, 1930 318,262 Great Britain Dec. 1, 1930 375,947 Great Britain July 7, 1932 447,735 Great Britain Aug. 17, 1934 461,095 Great Britain Feb. 10, 1937 468,224 Germany Nov. 9, 1928 912,284 France Apr. 23, 1946

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