US2661766A - Hydraulic apparatus - Google Patents

Description

Dec. 8, 1953 c, E A M 2,661,766

HYDRAULIC APPARATUS riginal Filed March 12, 1947 2 Sheets-Sheet l b X Fl 6. 4

109 INVENTOR.

CECIL E. ADAMS BY cum Dec. 8, 1953 c. E. ADAMS 2,661,766

HYDRAULIC APPARATUS Original Filed March 12, 194'? 2 Sheets-Sheet 2 3 IN V EN TOR.

5 CECIL E. ADAMS BY 7% KMW Pat ented Dec. 8, 1953 2,661,766 HYDRAULIC APPARATUS Cecil E. Adams, Columbus, Ohio, as'signor to The I Denison Engineering Company, Ohio, a corporation of Ohio Columbus,

,originalapplication March 12, 1947, Serial No,

743,127, now Patent No. 2,569,213, datedv Sep- 'tember 25, 1951. Divided and this application June 15, 1948, Serial N 33,211

1 a This application is a division of my copending application, Serial No. 734,127, filed March 12, 1947 for Hydraulic Motor Control Apparatus now Patent No. 2,569,213, dated September 1951. 6

- This invention relates generally to the science or hydraulics and is particularly directed to a hydraulic circuit and hydraulic apparatus contained within the hydraulic circuit.

One of the objects of the invention is to provide a hydraulic circuit for hydraulic apparatus of the type having a movable element, the circuit including means for causing delayed action of the movableelement in the apparatus.

Another object of the invention is to provide a time-delay valve for use in a hydraulic circuit containing a power cylinder, the latter having a piston for reciprocatory movement in the cylinder, the time-delay'valve being-operative to cause the piston to remain in a certain position for a predetermined period of time before completing a desired cycle of movement.

Another object of the invention is to provide a time-delay mechanism for use in a hydraulic circuit, the time-delay mechanism being operated principally by hydrostatic pressure.

A still further object of the invention is to provide a time-delay mechanism of the type mentioned in the preceding paragraphs with means for varying the length of the delay caused by such mechanism. a

Another object of the invention is to provide a hydraulic circuit with a time-delay mechahism which is fully automatic in operation, thus eliminating any additional requirements for action on the part of the operator of the mechanism in which the hydraulic circuit is incorporated.

' Still another object of the invention is to provide a hydraulic circuit including a source of fluid pressure and a power unit with acontrol mechanism including a fluid pressure responsive valve which is operative to efiect automatic forward and reverse action of the power unit and providing the circuit with a time-delay mechanism for causing the power unit to be retarded in its transition from forward to reverse operation.

Another object is to provide a time-delay mechanism of the type mentioned in the preceding paragraph which is set for operation by a pressure drop in the system and becomes operative when the pressure'drop is diminished.

Still another object of the invention is to p v de a time-delay mechanism for use in a r .6 Claims. (01. 137-689) hydraulic circuit, themechani'sm having a spool valvebiased by a spring toward a closed position and opened in opposition t'othe spring by fluid pressure when certain'action takes place in the hydraulic system, the spool valvebeing closed by the spring when the above-mentioned condition changes, the movement of the spool valve to the closed position being retarded by a slow dissipation of fluid from the space in front of the spool valve} An object of the invention also is to provide a hydraulic press having a hydraulic circuit including a source of fluid pressure, a power cylinder'for operating the'ram of the press, a valve mechanism for controlling the operation of the power cylinder,this mechanism having an automaticreversing valve moved in one direction by fluid pressure, and a time delay mechanism for applying fluid pressure to the reversing valve to' maintain the same in a position to direct fluid pressure from the source to a certain portion of the power unit; the'time-delay mechanism includes a spool valve which is biasedtoward a closed position by a spring and toward an open position in opposition to'the spring by a pressure differential existing when fluid "is directed from the pressure source to the power cylinder to cause movement of the ram in one direction, the spring serving to return the spool valve to a closed position when the pressure differential is diminished by the interruption of ram movement, the time-delay mechanism including an orifice through which fluid is displaced by the spool in moving toward a closed position, the resistance-caused i by the orifice retarding the movement ot the spool to delay the closing of the valve, 'this' delay' 'serving to lengthen the period of time fluid pressure is applied to the reversing valve and consequently the time period during which the ram exerts pressure on the work prior to making a return stroke.

An object also is to provide a time-delay mechanism of the type mentioned in the preceding paragraph with a fixed orifice and means for changing the potential travel of the spool to vary the length of the delay caused by the mech- It'is an' object of the invention to provide a hydraulic circuit for a hydraulic mechanism of the typehaving a cylinder with a reciprocatory piston anda control mechanism for governing theoperation of thepiston, the control mechanism having-a reversing valve which is main tained in aposition to cause movement of the piston'ina selected direction through the utilization of fluid discharged from the cylinder while the piston is moving in such direction, the cessation of fluid discharge, due to the interruption of movement of the piston, permitting the reversing valve to shift to a position to cause reverse movement or the piston, the circuit being provided with a mechanism for delaying the shifting of the reversing valve for a predetermined time after the piston stops moving, the time-delay mechanism being automatically set for operation when the piston moves in theselected direction and released for operation when the piston stops moving in such direction.

Another object is to provide a time-delay mechanism for a hydraulic circuit; which mechanism is provided with a flow resisting element consisting of a group of reduced orifices spaced in a series whereby the effect of a single minute orifice may be secured without the danger of stoppage attendant thereto, the use of a group of larger orifices also permittingthe employment. of substantial material and still maintain :the ratio of diameter to length of orifice. most conducive to a minimization of the effect of changes in viscosity of the hydraulic fluid due to temperature variations.

Further obj ects and advantages of the present invention will be apparent from the following description, reference being had to'the accom panying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the drawings:

a Fig. 1 is a plan view of the time-delay valve formed in accordance with the present invention.

Fig. 2 is a detail horizontal sectional view taken through the valve shown in Fig. 1.

Fig. 3 is a detail "sectional view taken through a portion of the valve on the plane indicated by the .line III-III of Fig. 2.

Fig. 4 is a similar view on an enlarged scale taken through a portion of the valve on the plane indicated by the line IV--IV of Fig. 3.

Fig. 5 is a diagrammatic view of a hydraulic system for a hydraulic power cylinder, the time delay mechanism shown in Figs. 1 to 4 being incorporated therein.

Referring more particularly to the drawings and especially to Fig. 5 thereof, the numeral designates a hydraulic system in which the timedelay valve, indicated generally by the numeral 2 l is connected. The circuit 20 includes a source of fluid pressure 22 having a fluid reservoir 23, a motor-driven pump 24 and a relief valve 25 for limiting the pressure generated by the pump 24.

The circuit also includes a power cylinder 2'5 and a control valve mechanism 21 for governing the movement of a piston 28 contained within the power cylinder. The mechanism 21 may be of any suitable type, that illustrated corresponding to a control valve mechanism'forming the subject matter of my copending application Serial No. 589,163, filed April 19, 1945, now Patent No. 2,491,355, issued December 13, 1949. This valve mechanism includes a body 30 having -a bore 3! and a plurality of annular grooves 32 to 31, in-

clusive, spaced longitudinally of the bore 3 I; This bore 31 receives for sliding movement a sleeve member 38 which is provided with a plurality of sets, 40 to 41' inclusive, of-latera-lly extending ports which sets of ports are spaced longitudinally of the sleeve, these ports registering in certain positions of movement of the sleeve, with certain of the grooves 32 to 31. The sleeve receives .a shuttle valve spool 48 which is provided with an external groove 53 for connecting certainsets of-pv sn different positions of longitudinal movement in the sleeve. This spool is biased toward the lower end of the sleeve by a coil spring 5| disposed between the spool and a cap 52 secured to the upper end of the sleeve. I

A shipper rod 53 projects from the lower end of the sleeve 38 through a cover 54 which is secured to the bottom of the body 30. This shipper rod receives a collar 55 for engagement by an arm 56 which is carried by a ram 51 projecting from the under side of piston 28. When the arm 56 engages collar 55 movement will be transmitted to the shipper rod 53 and sleeve 38; this movement takes place only when the piston 28 is moving in an upward direction adjacent the termination of its upward stroke. Normally, the

sleeve 38 is held in a centered position by a coil spring 58 surrounding the shipper rod and engaging a washer 60 at its upper end and a stop collar til at its lower end. The washer Bil is arranged to engage a shoulder 62 which surrounds the lower end of bore 3 I, this shoulder serving to limit the upward movement of the washer. Collar 5.! engages the bottom wall of a counterbored hole through which the shipper rod 53 projects; this arrangement permits movement of the sleeve in either direction in opposition to the force of the spring 58. When the sleeve 38 is moved upwardly by the final stage of upward movement of the piston 28, ports 44 will be in registration with groove 34 so that fluid flowing from the pressure source to groove 35 will be conducted through the interior of the sleeve 38 and ports 44 to groove 34 I from which it may flow through a second bore ing from the pressure source into 63 to a groove 64 which communicates with groove 36 and from groove 36 through ports 46, the interior of the sleeve 38 above spool 48 and outwardly therefrom through ports 41 to groove 31 from which the fluid will flow through the upper end of bore 63 and through conduit 65 to reservoir 23. When the fluid follows this path pump 24 will operate under no load.

The body 30 is also provided with an annular groove 66 in communication with bore 63 below the point of communication of such bore with groove 34. Groove 66 communicates with groove 32 as at 61, communication between bore 63 and groove 32 over this path being normally precluded by a land 68 formed on a spool I0 disposed for longitudinal adjustment in bore '63. Spool 10 has an external groove H above land 68, this groove normally providing for fluid flow from groove 34 to groove 64. When it is desired to initiate an operation of the power cylinder, spool 10 is lowered through the actuation of a crank pin I2 until a land 13, at the upper end of spool 10 blocks groove 64, at which time groove II will establish communication between groove 34 and groove 66. With spool It so positioned fluid flowgroove 35 will pass through ports 45 to the interior of the sleeve 38 and outwardly therefrom through .ports 44 to groove 34; this fluid then flows into bore 63 and downwardly to groove 65 from which it will flow to groove 32.

r The fluid enters the sleeve 38 through ports 40 and exerts an upward force on the shuttle valve spool 48. This force moves the shuttle valve in opposition to the spring 5| to cause groove 50 to establish communication between ports 45- and 46. At this time fluid introduced to groove 35 from the source of fluidpressure will flow through ports 45 to the interior of the sleeve 38 and out:- wardly therefrom through ports 46 to groove 36. This fluid will then flow through passage I4 to the acumen upper end of power cylinder 28; the force of this fluid willact upon piston 28 to'urge it in a downward direction. This movement of, the piston discharges fluid from the lower end of the power cylinder through line to groove 33. Such fluid will then flow through ports 42'into a transverse passage 18 formed in the shuttle valve spool 48. From this passage fluid will be discharged through an axial passage 11 in the shuttle valve and an extension 18 thereof in cap 52 to the groove 31 from which it will flow to the reservoir 23. Due to the restriction of port 11 a back pressure will lie-built up in passage 16, port 42, groove 33, and line 15} as well as in the bottom portion of power cylinder 28. This back pressure will be. transmitted through a reduced passage 80 in the lower portion of the shuttle valve to the lowerend of the chamber in sleeve 38 beneath the shuttle valve, this pressure tending to retain the shuttle valvetin an elevated position during downward movement of the piston 28.

Under normal conditions the back pressure will fall when piston 28 ceases to-move in a downward direction for any reason, and when this occurs spring. 5| will return the shuttle valve to a lowered position in which fluid pressure from the pump 24 will be directed to the under side of the piston 28 while the upper end of the power cylinder will be in communication with the reservoir 23. At this time the force of the fluid will move the iston 28 and ram 51 in' an upward direction in the return stroke of the ram. When the ram and piston approach the upper limit of this return stroke, arm 56 will engage collar 55 on the shipper rod 53 and move spool 38 upwardly until ports 44 again register with groove 34 at which time fluid pressure from the source will be directed to the reservoir 23. It will be understood at this time that in the initial portion of the downward stroke of piston 28 arm 58 moves away from collar 55 permitting spring 58 to return'sleeve 38 'to its normal position in which ports '44 are not in registration with groove 34. After this initial movement spool 18 may be returned to its normal position either through the manual actuation of crank pin 12 or automatically under the influence of spring 8I disposed between lower end of the spool 18 and the bottom cover 54. 7

As set forth in the above-mentioned copending application crank pin 12 may be employed to set spool 18 for the automatic operation of the power cylinder; that is, spool 18 will be retained in its lowered position in which groove 1I therein continuously establishes communication between groove 34 and groove 88. When spool 18 is so disposed the final stage of upward movement of piston 28 will cause the registration of ports 44 with groove 34 and fluid from the source of pressure may then flow directly to groove 32 to initiate another cycle of operation of the power cylinder. The mechanism and operation thus far described are identical with those of the copending application mentioned, the foregoing description having been given merely to facilitate the understanding of the present invention.

On some occasions in the use of the press mechanism above described, it is desirable in the operation of ram 51, to cause this ram to hesitate or dwell at the lower end of the downward or power stroke before the return stroke is initiated. One such occasion is found in the formation of belts for sanding machines wherein the ends of the belts are coated'with adhesive and" pressed together with the press ram, the overlapped ends communication between being squeezed together 6: a predetermined time period to permit the adhesive to set. Another occasion is in the formation of die cast or certain plastic materials wherein the material is sub- 'jected to ram pressure while being heated or while in a fluid or plastic state. To effect this hesitation or dwell of the. ram, a time-delay mechanism indicated by the numeral 2 I, has been disposed in the hydraulic circuit. This time-delay mechanism is so constructed and connected in the system that its operation will be accomplished hydraulically and fully automatically. The timedelay mechanism 2| includes a bore 82 in a body 83, which body is provided with a pair of ports 84 and 85 spaced longitudinally of the bore 82. Port 85 is connected by line 85 with groove 38 in body '38; port 84 is connected by line 81 with groove 32. Bore 82 slidably receivesa spool 88 in which an annular groove 98 is provided, this spool also having a wide land 9| at one end which normally obstructs communication between ports 84 and 85. A narrower land 92 adjacent the opposite end of the spool prevents communication between the groove 98 and the end 89 of bore 82 adjacent the corresponding end of the spool. This end of bore 82 is connected by-a line 93 with line 86, line '93 having a check valve 94 disposed therein; this check valve permits unrestricted fluid flow from line 86 into the end 88 of bore 82 and prevents fluid flow outwardly through line 93. A second line 95 also extends from this end of the bore 82 to line 86, line 95 having flow-restricting means 96 disposed therein; the purpose of this flowrestricting means will be set forth hereinafter.

The spool 88 is normally advanced toward a position to block communication between ports '84 and 85 by a coil spring 91 disposedbetween the end of a socket in the spool and a shoulder 98 on a stop screw I88, threadedly received in a cap ID! for body 83. Stop screw I88 has an exteriorly disposed knob I82 by means of which this screw is adjusted in or out to regulate the degree of movement of spool 88. In the innermost position thereof stop screw I88 retains spool 88 in position to prevent communication between ports 84 and 85 and renders the time-delay mechanism ineffective. By adjusting the screw outwardly a distance sufiicient to permit spool 88 to move far enough so that groove 98 on the spool will establish-communication between ports 84 and 85, the time-delay mechanism may be rendered operative. The degree of outward movement of the stop screw will determine the length of the time- 'delay period.

restricted orifice I83 disposed in such line. Due to the orifice I83 fluid flow to the power cylinder 26, when shuttle valve48 is in elevated position,

will be restricted. Fluid will, therefore, be caused to fiow through lines 88 and 93 to the end of bore 82; this fluid will move spool 88 in opposition to spring 81 until the inner end of stopscrew I88 is engaged by the inner 'end of the socket in the spool. Immediately after spool 88 starts to move in opposition to spring 91 groove 98 will establish ports 84 and 85 and some of the fluid from the source of pressurewill be directed through line 81 to groove 32 and the under side of the shuttle valve. As long as piston pressure differential will exist on opposite sides of the orifice I 83, -the higher pressure of this pressure differential being applied through lines 85 and 93, as above*described,-to the end of the'spool opposite the spring 91. .The lower pressure applied to the opposite end of 'thespool throughline I04 which isconnected' with, the uppe'rjendof t power cylinder 26. 'While' this'pressure' differential exists, spool 88, willbeheld against the action of spring .91. After the pistcnand ram cease to move the pressure differential'is dissipated causing equal pressures at opposite endsof the spool '88, thus permitting spring 91 to move spool 88 toward a closed position. Fluid pressure beneath the shuttle valve 48 will be maintained through lines 85 and 81 until spool 88 returns to a position to, interrupt communication between ports B and 85; This movement of spool 88 is retarded by the restricting means .95. which opposes fluid flow from the end of the bore'82, this fluid flow being caused by movement of piston 88 under the influence of spring 91.

, Whenspool 88 interrupts fluid flow from line 86 to line 8?, pressure beneath shuttle valve 48 will be dissipated and spring 5| will .return the shuttle valve to its lowered position wherein fluid pressure .from the source will be .directedinto the lower end of the power cylinder; the return stroke er the piston and ram will then be effected.

It is importantto note that in the operation of the power unit the shuttle valveAB is retained in an elevated position or a position to cause movement of the piston in aworking stroke, by the fluid being discharged from the power unit. In order to effect such a discharge, it is, necessary that a flow of fluid'fromthe pressure source to the power unit be maintained] While such flow is taking place,.the pressure differential employed to cook or set the time-delay spool for operation serves also to hold the spool ready for action. The stopping of the piston 28 .in any manner permits the instantaneous dissipation of the pressure differential which starts the operation of the time-delay. One feature of the mechanism shown and described is that the shuttle spool and the time-delay spool are held against movement by spring force indirectly by the movement of the same element, namely the piston 28. The initiation of the period of the delay is thus dependent upon the operation of the element to which the delaying action is applied. It will be observed that in varying the length of the time-delay caused by this mechanism the distance travelled by spool 88 is varied permitting more or less fluid to be directed into the end of bore 82 for discharge through the restricting means 96. In all positions of adjustment of the time-delay mechanism the diameter of the orifices in the restricting means 95 remains the same.

Figs. 1 to 4, inclusive, disclose the actual construction of one form of the time-delay mecha- -nism. It will beobserved from Figs. 3 and 4 that the-check valve 9:! and flow-restricting means 96 are embodied in one piece of the valve, these elements being carried by and movablerwith the spool '88. This spool has a transversely extending passage 105, see Fig. 3, which communicates with -a longitudinally extending passage I06; this passage terminates in a socket lill formed in the spool 88. The socket receives a substantially cylindrical check valve body 108 which is urged by a spring J09 toward the inner end of the socket ill-1. Body 198 has a-resilient gasket I 10 provided on its inner end for engagement 'with the inner end of the socket 101. T-hi-sgasket and the manner of mounting spool 1-08 for movement permits relatively unrestricted .fluid flowirom bore H16, around gasket 4 H1 and into socket 101; but :preyen-ts the reverse new of ;.fiuid -'over this path.

When spring moves spool 88 toward a closed position fluid must flow rrom the end otthe bore 82 through the flow restricting means 96 which is contained within the check valve body 108. This flow restricting means comprises a series of spaced wafers or disks i H in which orifices I12 are provided. A series of waters is employed to permit the use of larger orifices while the effect of a small ,or minute orifice is secured. The wafers are formed of thin material to reduce the deleterious effects of changes in the viscosity of the 011 due to temperature variations. 1

The disks ill are clamped between spacers H3 which comprise ring-like members positioned be' tween adjacent disks. This arrangement provides a series of chambers separated by the disks H1 and communicating -only through the orifices therein. Due to the alternate restrictions and chambers the fluid will be repeatedly accelerated and declera'ted so that the force of the fluid will be continuously lessened until the effect of a minute orifice is secured.

It has been determined that by forming an orifice through which fluid is to flow, in a thin piece of material, the effect of the orifice on the flow will be afiected less by changes in viscosity due to temperature variations than if the orifice is formed in thick material.

By using relativelylarge orifices the disks may be formed of heavier material while the most desirable ratio of orifice diameter to lengthis maintained. Li a single minute orifice were employed and an attempt were made to retain the same diameter to length ratio, the material would be so thin that a failure thereof would immediately result.

I claim:

1. A time delay valve comprising a body provided with a chamber, an intermediate port extending from said chamber and a laterally extending port on either side of said intermediate port; a spool element disposed for movement in said chamber and normally obstructing communic-ation between said ports; a passage formed in said spool to establish communication between one of said laterally extending ports and one-end of said chamber; spring means normally urging said spool element toward said one end .of said chamber; a check valve having an orifice disposed in the passage in said spool, said check valve serving to permit relatively unrestricted fluid flow fromsaid port to said chamber end and controlled fluid flow in the opposite direction, said spool be ing movable in response to a higher pressure in said one end of said chamber than in the other end to a position in which communication be tween said intermediate port and the port communicating with said one end of said chamber is established; and means for regulating the discanoe-said spool is moved bysuch pressure.

2. A time delay valve comprising a body provided with a chamber and first and second laterally extending ports spaced longitudinally .of said chamber and communicating therewith, all of said ports being spaced from the front .end -.of said chamber; a spool member disposed for sliding movement in said chamber; resilient means yieldably urging said spool member toward :the front end of the chamber, said spool preventing communication between the first and second lateral ports when in such position; apair of passages in said spool member for establishing communication between the first lateral port when :fluid pressure is supplied thereto and the front en of said chamber at the end of said spool; a check 9 valve in one of said passages, said check valve permitting fluid flow from the first lateral port to the front end of said chamber and preventing flow in the opposite direction; and a series of small orifices in the other of said passages to retard fluid flow therethrough.

3. A time delay valve comprising a body provided with a chamber and first and second laterally extending ports spaced longitudinally of said chamber and communicating therewith, said ports being spaced from the front end of said chamber; a spool member having an external groove disposed for sliding movement in said chamber; resilient means yieldably urging said spool member toward the front end of the chamber, said spool preventing communication between said first and second lateral ports when in such position; a pair of passages for establishing communication between the groove in said spool, when fluid pressure is supplied to said first lateral port, and the front end of said chamber at the end of said spool; a check valve in one of said passages, said checl: valve permitting fluid flow Y from said groove to the front end of said chamber and preventing reverse flow; and a series of spaced orifices in the other passage to retard fluid flow therethrough.

4. A time delay valve comprising a body having a chamber and first and second laterally extending ports communicating therewith, said ports being spaced from the front end of said chamber and longitudinally of said body; a spool member having an external groove disposedin said chamber for sliding movement; spring means in said body urging said spool toward the front end of said chamber, said spool preventing communication between said first and second ports when disposed in such position, the groove in said spool establishing communication between such ports when moved in opposition to said spring; a pair of passages for establishing communication between the groove in said spool and the forward end of the chamber beyond the corresponding end of said spool; a check valve in one of said passages to permit fluid flow to the forward end of said chamber and prevent flow from such end through the passage; and a restriction in the other passage to provide limited flow therethrough.

5. A time delay valve comprising a, body having a chamber and first and second laterally extending ports communicating therewith, said ports being spaced from the front end of said chamber and longitudinally of said body; a spool member having an external groove disposed in said chamber for sliding movement; spring mean in said body urging said spool toward the front end of said chamber, said spool preventing communication between said first and second ports when disposed in such position, the groove in said spool establishing communication between such ports when moved in opposition to said spring; a pair of passages for establishing communication between the groove in said spool and the forward end of the chamber beyond the corresponding end of said spool; a check valve in one of said passages to permit fluid flow to the forward end of said chamber and prevent flow from such end through the passage; and a plurality of thin wall members dividing a portion of the other passage into a series of chambers, said wall members having reduced orifices to establish limited communication between said chambers.

6. A time delay valve comprising a body having a chamber and first and second laterally extending ports communicating therewith, said ports being spaced from the front end of said chamber and longitudinally of said body; a spool member having an external groove disposed in said chamber for sliding movement, spring means in said body urging said spool toward the front end of said chamber, said spool preventing communication between said first and second ports when disposed in such position, the groove in said spool establishing communication between such ports when moved in opposition to said spring; an adjustable stop member in said body for limiting the extent of movement of said spool in opposition to said spring; a pair of passages for establishing communication between the groove in said spool and the forward end of the chamber beyond the corresponding end of said spool; a check valve in one of said passages to provide fluid flow through such passage to the forward end of said chamber and prevent fiow in the opposite direction; and a restriction in the other passage to provide limited flow therethrough.

, CECIL E. ADAMS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 270,573 Blake Jan. 16, 1883 419,447 Hussey Jan. 14, 1890 441,995 Wheeler Dec. 2, 1890 559,881 Ahrens May 12, 1896 1,379,092 Fraccascia May 24, 1921 2,004,904 ,Peo June 11, 1935 2,411,930 Mathys Dec. 3, 1946 2,416,722 Waldie Mar. 4, 1947

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