US2628731A - Hydraulically operated tractor shovel - Google Patents

Description

Feb. 17, 1953 G. REUTER 2,628,731

HYDRAULICALLY-OPERATED TRACTOR-SHOVEL.

Filed Sept. 17. 1949 4 Sheets-Sheet 1 INVENTOR GOrrFR/ED REL/TEE BY ///;C WM 723 Feb. 17, 1953 G. REUTER 2,

HYDRAULICALLY-OPERATED TRACTOR SHOVEL Filed Sept. 17. 1949 4 Sheets-Sheet 3 INVENTOR l Q GOTTFR/ED PEUTER a fi/mKfl Patented Feb. 17, 1953 HYDRAULICALLY OPERATED TRACTOR SHOVEL Gottfried Renter, South Milwaukee, Wis., assignor to Bucyrus-Erie Company, South Milwaukee, Wis., a corporation of Delaware Application September 17, 1949, Serial No. 116,391

is usually designed for attachment to a conventional tractor and consists of a transverse bucket, two arms pivoted 0n the tractor for pushing and lifting the bucket, and means to raise and lower the arms. The last-mentioned means usually consists of one or two hydraulic cylinders actuated by a pump driven by the engine of the tractor. The bottom of the bucket is usually concave toward the front in vertical cross-section,

the ends being closed by flat plates. The bottom of the bucket is pivoted for dumping about a horizontal transverse axis on the front end of the lift arms, and the dumping and return move,- ment of the bucket about this axis is usually effected by means of one or two double-acting hydraulic cylinders actuated by the pump and mounted on the lift arms.

The principal objects of the invention are to provide a material-handling implement in which:

(1) A very fast hydraulically-operated positive bucket dump is obtained without increasing normal pump capacity.

(2) The fast bucket dump utilizes the same fluid output from the pump and main control valve as is used for hydraulically lowering or raising the bucket lift arms at normal speed.

3) The speed-force ratio at the bucket-dump piston is increased to roduce the fast bucket dump without increasing speed of flow from the pump and main control valve.

(at) The increase of speed-force ratio at the bucket-dump piston occurs automatically responsive to a predetermined speed oi return flow from the bucket-dump cylinder to the maincontrol valve.

(5) Means is provided to render the means for changing the bucket-cylinder speed-force ratio inoperative automatically when the bucket is used in dumped or partially-dumped, position to bulldoze backwards.

(6) lilieans is provided to prevent excess buildup of pressure in the bucketsdump control cylinder its supply line after the end of the fast dumpstroke without increasing dumping time.

In addition to the principal objects, above stated, a number of novel and useful details have 4 Claims. (01. 214- 140) been. workedout. which will be readily evident as the description progresses.

The, invention consists in the novel parts, and in the combination and arrangement thereof, which. are defined in the appended claims, and of which two embodiments. are, exemplified in the accompanyingcdrawings, which are hereinafter particularly described and explained.

Throughout the description, the. same reference number is applied to the same member or to similar members.

Figure 1 is a general side elevation of the tractor shovel embodying the invention, with control lever and linkage to the valve stems omitted (see Figures 10-12)..

Figure 2 is a plan view of the same tractor shovel, also with control lever and linkage omitted. I

Figure, 3 is an enlarged vertical section of the short-circuit valve (for obtaining fast dump) showing the plungers of this valve in normal closed position.

Figure 4 is a similar section taken along the line 4 -l of Figure 3.

Figure 5 is a similar I section taken along line 5-5 of Figure 3.

Figure 6 is similar to Figure 3,. but shows the valve plungers raised in open position.

Figure 7 is an enlarged vertical section of a second embodiment of the, short-circuit valve, showing all valve plungersin normal closed. position.

Figure 8 is an enlarged horizontal section of the selector valve (for switching the. hydraulic controls from the lift arms to thebucket or vice versa) showing the plunger of this valve in position for operation of the lift arms.

Figure 9 is similarto Figure 8, but with the plunger in position for operation of the bucket.

Figure 10 shows the control-lever linkage 'i'or controlling the selector valve and the main control valve of the hydraulic unit.

Figure 11 is an enlarged, side view of the control lever showing its five fore-and-ait operating positions.

Figure 12 is a rear elevation of the control lever showing its two selector valve positions.

Figure 13 is a schematic diagram showing the hydraulic circuit for controlling the lift arms and the bucket and the direction of flow therein when the control lever is set in bucket-slow-dump position.

Figure 14 is similar to Figure 13, but shows the flow whenthe control lever is set in bucket fastdump position.

Referring now to Figures 1 and 2, it is seen that H is a conventional tractor, mounted on creeping traction units I2, which are pivoted on propelling shaft 3 and have considerable freedom to oscillate independently about said shaft to conform to unevenness of the ground.

Pivoted to each side of cradle frame H on the tractor as at rearward point I5 is a forwardlyprojecting lift arm I6. These arms are connected at their front end by cross-beam l1, and serve to support and impel bucket 2 I. They are raised and lowered by the following-described mechanism. To an intermediate point |8 on each arm l6 there is pivoted an hydraulic cylinder-piston assembly 20 which is also pivotally supported at a rearward and relatively-low point IS on the cradle frame M. The two cylinders are inter connected and their pistons are actuated by pressure fluid supplied from a conventional hydraulic unit 3| (hereinafter described) mounted at the front of the tractor. The bottom of bucket 2| is pivoted at 22 to the forward end of lift arms l6. Two pairs of ears 23 welded to the rear of bucket 2| are drilled for a pin connection at 24 to link arms 25 which are each pin-connected at their rear end 26 to a cross-head 21 grooved to slide on a. T-shaped rail 28 welded to the top of each lift arm Hi. The rear of each cross-head 26 is attached at 29 to piston rod 30a of bucket-dump control cylinder-piston assembly 30 mounted on each lift arm l6. Cylinder-piston assemblies 30 are double-acting, and pressure fluid therefor is supplied through selector valve 4| and shortcircuit valve 6| from hydraulic unit 3| which will now be described.

At the front end of the tractor engine there is mounted a conventional hydraulic unit 3|. which is driven by the tractor and comprises a hydraulic storage tank or tanks, a hydraulic pump, a control valve for the control of the flow to and from the pump, and various incidental conduits, relief valves, and one-way valves. Since this hydraulic unit is well known in the art and forms no part of my present invention, it is merely shown schematically in the figures. the hydraulic unit has two fluid ports 32R and 32L which are connected (as hereinafter described) to the raise and lower ends respectively of the cylinder assemblies which the hydraulic unit controls. The plun er 34 of the control valve of the hydraulic unit has five positions to control the flow of fluid to and from the pump in five cases as follows:

(1) "Raise position.-Fluid under pressure is delivered by the pump through the raise port 32R of the hydraulic unit to the raise end of the cylinders; return fluid from the lower" end of the cylinders through the lower port 32L of the hydraulic unit into the pump intake and tank.

(2) "Hold position-Fluid under pressure is delivered by the pump to the tank and then back into the pump again without leaving the hydraulic unit. Fluid ports 32R and 32L of the hydraulic unit are blocked o f. Hence the cylinder pistons are locked in position.

(3) Slow lower position.Fluid is delivered by the pump to the tank and then back into the pump. But the fluid ports 32R and ML of the hydraulic unit are not entirely blocked off, there being a slow flow of fluid, under pressure of the weight of the bucket, from the raise end of the cylinders, to the raise port 32R of the hydraulic unit, and thence through a bleeder in the control valve of the hydraulic unit to the tank Suffice to sav that and the pump intake. In this "slow lowering" position fluid is drawn into lower" end of th! cylinders from lower port 32L, to compensatl for the fluid drawn out of the cylinder at its othm end.

(4) "Lower position.Fluid under pressure h delivered by the pump through the lower" pori 32L of the hydraulic unit to the "lower end c: the cylinders; return fluid passing from thi "raise end of the cylinders through the raise port 32R of the hydraulic unit into the pump intake.

(5) "Float position-Raise and lower' ports 32R. and 32L of the hydraulic unit am hence the raise and lower ends of the cylin ders intercommunicate and communicate, wifl flow permitted in either direction through tb control valve and tank of the hydraulic unfl Hence the piston is free to float in its cylindel Turning now to the subject matter of the in vention, the hydraulic circuit leading from th raise and lower" ports 32R and 321.- respec tively of hydraulic unit 3| through selector val! 4| (hereinafter described) and short-circuit val 6| (hereinafter described) to the raise ai lower ends of the lift-arm cylinders 20 a bucket cylinders 30, will now be described.

Turning to Figures 8-9 and 13-14, it is see that the selector valve 4|, which is mounted f0 convenience above the tractor engine behind t1 hydraulic unit, has ports 42R and 42L located (1 its side adjacent the hydraulic unit and con nected respectively to ports 32R and 32L of th hydraulic unit through conduits 33R and 33L (so Figure 2) On the other side of the selector vali there are two pairs of ports. The outer pair I and 43L are connected respectively to the raist and lower ends 20R and 20L of lift-arm cylir ders 20 through conduits 45R and 45L. The it ner pair 44R and L are connected respective to the raise and lower ends 30R and ML i bucket cylinders 30, through conduits 46R ar; 46L, short-circuit valve 6| (hereinafter dscribed), and conduits 66R, 61R, and 66L.

There are six chambers in the selector valve. three for the "raise side of the circuit and three for the lower" (or dump") side of the circuit. Ports 42R and 42L lead into chambers 41R and L respectively; ports 43R. and 43L (to lift-arm cylinders) into chambers 48R and 48L respectively; and ports 44R and L (to bucket cylinders and short-circuit valve) into chambers 49R and 49L respectively.

Connection between these chambers is through annular recesses 5|R, 5|C, and 5|L in plunger 50 which is shiftable along its longitudinal axis into one of t o positions in its seat.

In the lift-arm" control position (Figure 8) of plunger 50, chamber "R is connected through annular recess SIR to chamber 48R and chamber "L is connected through annular recess 5|L to chamber 48L, connection to chambers 49R and 49L (to bucket cylinders 30) being blocked off by lands 52 and 53 respectively of plunger 50. Accordingly the lift arms alone are operable by the control valve of hydraulic unit 3|, the bucket being locked in a hold position.

In the bucket control position (Figure 9) of plunger 50, chamber HR is connected through annular recess 5 IC to chamber 49R, and chamber L is connected through annular recess 5|L to chamber 49L; connection to chambers 48R and L (to lift-arm cylinders) being blocked off by land 52 and 54 respectively of plunger 50. Accordingly the bucket alone is operable by the control valve of the hydraulic unit 3|, the liftarms being locked in a "hold position.

Short-circuit valve 6| has five ports connected externally as follows (see Figures 2-5, 13 and 14) Port 62 is connected by conduit 66R to the raise (bucket relatch) end 30B. of one of the bucket .cylinders 30. Port 63 is connected by conduit 61R to the raise (bucket relatch) end 30R of the other bucket cylinder. Port 64 is connected by conduit 468. to the bucket raise (relatch) port 44B. of selector valve 4|. Port 65 is connected by conduit 66L to the lower (bucket dump) end 30L of one of the bucket cylinders. Port 66 is connected by conduit 46L to the lower (bucket dump) end 30L of the other bucket cylinder and also by the same conduit to lower (dump) port ML of selector valve 4|.

Short-circuit valve 6| (Figures 3-6) has a gravity-closing shuttle plunger II seated and shiftable vertically in vertical-cylindrical seat 12, and a gravity-closing check-valve consisting of plunger 8| seated and shiftable vertically invertical seat 82. Seat I2 opens at its bottom end into passage I3 which interconnects ports 62 and 63, at its top into passage I4 leading to port 64,

and at its lower side into passage 11 leading to the bottom end of seat 82 of check-valve 8|. Seat 82 opens at its sides into ports 65 and 66 through passages I5 and I6 respectively.

Both plungers II and BI are normally held by gravity in lowered position (Figure 3), so that passage of fluid through passage 11 is blocked oil;

Shuttle plunger II has a longitudinal bored passage I8 that opens at its lower end into passage I3 and at its upper end through radial holes 19 into external annular depression 80 which is open to the upper portion of seat I2.

When shuttle plunger II is lifted into raised position, by fluid from ports 62-63 and passage I3 hitting the underside of the plunger, the head of the plunger covers and blocks off flow of fluid outwardly through bore I8, radial holes I9, passage I4 and port 64, except for the small flow through relief hole 19a in the head of the plunger (this hole prevents excessive build-up of pressure in the raise and lower ends of the bucket cylinders); and at the same time passage II is uncovered and flow of fluid from ports 6263 and passage I3 into passage 11 occurs with the result that one-way plunger 8| is raised by the fluid pressure on its underside and fluid flows on out through the interior of seat 92, passages I5|6, and ports 6566.

Turning now to Figure '7, we see a second embodiment of the short-circuit valve, in which the relief hole I90. in the head of shuttle-plunger II is replaced by a two-step relief valve connected in parallel with the shuttle valve and consistin of vertically-slidable plunger 9| having a conical bottom surface and a hollow stem 92 at its upper end for seating the lower end of load regulating spring 94 which is seated at itsupper end against spring guide flange 95. Plunger 9| is normally held by spring 94 seated on valve seat 96. In this position plunger-stem 92 cover and blocks flow of fluid from passage 93 below plunger 9| into passage 98, into chamber 91 above plunger 9| and thence into passages 99 and I4 which lead to port 64. In this closed position plunger 9| has only a relatively-small effective pressure area (equal to the cross-section area of passage 93), and accordingly a relatively-large pressure in passage 13-93 is required initially to open the valve by pushing plunger 9| up against spring 94. Once the valve is open. however, the effective pressure: area of plungerv 9| is increased to its entire cross-section area, and accordingly only a relatively-low pressure of the bypassed fluid is required to keep plunger 9| open against spring 94.

Turning now to Figures to 12, it is seen that the valve plunger 34 of hydraulic unit 3| and selector valve plunger 50, each of which is shiftable along its longitudinal axis, are. actuated by a common hand control lever I00 mounted on the tractor beside the operator.

Fore-and-aft movement of control lever I00 aboutits pivot IN on quadrant I02 shifts main control valve plunger 34 into its five operating positions of raise, hold, slow lower," lower, and "float above described. To accomplish this, control-lever I00 is connected to plunger 34 by reach rod I03 universally connected at I04 to lever I00. reach rod I06 universally connected at I05 to rod I03, lever I0I pivotally connected at I08 to rod I06, vertical lever shaft I09 rigidly connected at its upper end to the fulcrum |I0 of lever I01 and mounted on the tractor to pivot about its axis, lever III rigidly connected at its fulcrum NZ to shaft I09, transverse reach rod 3 pivotally connected at M4 to lever III, and anchor II5 pivotally connected at one end I I6 to rod 3, and rigidly connected at the other end to the plunger 34. Notches are provided in quadrant I02 so that: the control lever I00 can beheld in each of its five operating positions.

Sideways movement of control lever I00 about the horizontal longitudinal axis of lever shaft I II which is journalled on the side of the tractor at III? and H9, and upon which quadrant I02 is rigidly mounted, shifts the selector valve plunger 50 into its two operating positions of lift-arm control and bucket control. To accomplish this, control lever I00 actuates plunger 50 through quadrant I02, lever shaft III, lever I rigidly connected at |2I to shaft II'I, reach rod I22 pivoted at I23 to the end of lever I20, and anchor-l24 having universal connection I25 to rod I 22, and rigid connection to plunger 50. Outward sideways movement of the control lever I00 throws the selector valve plunger 50 into liftarmcontrol position, and inward movement into bucket-control position.

Turning'now to Figures 13 and 14, inwhich the circuit of the hydraulic system is represented schematically and fluid flow is represented by arrows for the cases of slow. dump and fast dump respectively of the bucket, it is seen that for these as well as all other bucket-control cases, the selector valve plunger 50 is in bucket-com trol'position so that ports 43R and 43L to the lift cylinders 20 are blocked off bythe selector valve, which is open to allow passage of fluid from the hydraulic unit 3| to the bucket cylinders through conduits 40R and 46L and short-circuit valve 6|.

When the operator now moves the control lever I00 forward from hold into slow lower position for slow dumping of the bucket (see Figures 11 and 13) this causes fluid to flow from the lower port 32L of the hydraulic unit 3| through ports 42L and ML of the selector valve 4|, and thence through conduits 46L and 66L and ports -456 of short-circuit valve 6| to the rear lower" (i. e., dump ends 30L of bucket cylinders 30, thereby causing the pistons of these cylinders tomove forward and the fluid in the forward part of the cylinders to be expelled through raise (or relatch) ports 30R to ports 6263 of the short-circuit valve BI, and thence through bore I8 and radial holes I (Figure 4) of shuttle plunger II out through port E4 and conduit 46R to port 44R of the selector valve, and thence through the selector valve to port 32R of the hydraulic unit 3!. In this slow dump case the flow of fluid through shuttle-plunger II of the shortcircuit valve BI is not fast enough to lift the shuttle plunger from its seated position, so that a short-circuit through passage I1, valve seat 82, and ports 05-66 of the short-circuit valve to the lower (i. e., dump) ends 30L of the bucket cylinders is blocked.

When, however, the operator puts the control lever I00 forward further into lower position for fast dumping of the bucket (see Figures 12 and 14), this causes the fluid to travel faster through the ports 62-63 of the short-circuit valve and to hit the underside of shuttle plunger II with such force that it instantly moves up, blocking all flow (except bleeding through relief hole 19a) through plunger 1| and port 64, and uncovering passage TI so that the fluid expelled from the raise end 30R of the bucket cylinders is now short-circuited past check-valve plunger 8| and out through ports 65--66 back to the bucket cylinders through their lower i. e., dump) end 30L. Thus a connection is estab lished between the front and rear ends of the bucket cylinders and return flow to the hydraulic unit is eliminated except for the above-mentioned bleeding through hole 1911 the function of which will be explained hereinafter. Therefore the fluid from the lower port 32L of the hydraulic unit will now serve merely to compensate for piston-rod displacement of the bucket cylinders 20, and accordingly movement of the pistons of these cylinders will be greatly accelerated producing a very fast dump, even faster than a gravity dump. This makes it possible for the operator to get rid of sticky material in his bucket and to speed up the digging operation and. at the same tim retain full control of his bucket.

It will be seen that when fluid at lower position speed is supplied by the hydraulic unit to the bucket cylinders, the short-circuit valve then automatically reduces the effective bucket-dump pressure area of the pistons of cylinders 30 to the cross-sectional area of their piston rods and thereby increases the speed-force ratio of the bucket cylinders. obtain a fast bucket dump with the relatively slow flow of fluid that is available from the hydraulic unit (and is normally sufllcient for lowering or raising the lift-arms), and at the same time to have a, common hydraulic unit and a common control lever for both the lift arms and the bucket, with analogous operating functions for each.

When the operator moves the control lever I00 ba to hold position, flow through ports 32R and 32L of hydraulic unit 3| is blocked, and since plungers II and BI of the short-circuit valve will then be in their normal gravity closed position, there will be no connection between ends 30L and ends 30R of the bucket cylinders 30 so that their pistons will be held stationary. If, however, the shuttle-plunger II is by chance stuck in its raised short-circuit position, and fluid in the lower" end 30L of cylinders 30 is under pressure due to bulldozing backward with the bucket in dumped position, plunger 8| will block the short-circuit between the ends of the cylinder and thereby prevent a decrease in the eflective pressure area of the piston and a corresponding excessive increase in fluid pressure in the cylinder.

In this way it is possible to When the operator moves the control lever II still further back to raise position for return ing the bucket to its normal carrying positiq this causes fluid to flow from the raise port 3! of the hydraulic unit 3!, through ports 42R an R of the selector valve 4|, and thence throul conduit 46R, port 64 of short-circuit valve 0 radial holes 19 and bore 18 of plunger II whi is held by gravity and fluid pressure in its seat! position (Figure 3), and thence out through p01! 62 and 03 through conduits 06R and 61R respel tively to the raise ports 30R of the buck! cylinders 30, thereby causing the pistons of thq cylinders to move rearwardly and the fluid in tl rear chambers of the cylinders to be expello through the lower ports 30L, through conduit ML and ESL and ports 5565 of the short-circll valve GI, and thence through ports ML and 41 of the selector valve 4| to port 32L of hydraull unit 3 I. In this bucket-return case, both pluni ers 7| and 8! are held by gravity and by fiui pressure in their seated. position so that short circuit flow between the ports MR and am through passage '5'? is blocked.

Relief hole a in the head of shuttle plunge II prevents excessive build-up of pressure in th shorted dump circuit. Hole 19a also serves t relieve pressure in the lower and raise end SQL and 351?. of the cylinders by returnin fluid to the raise port MB of the hydraulic uni 3| when the end of the dumping stroke is reached In order, however, to develop less heat, if th operator should leave the control lever I 00 i1 fast-dump position after dumping has been com pieted, it is desirable to return the fluid to thl raise port 32R, at as low pressure as possible since then less engine horsepower is required Accordingly as an alternative to relief hole 191:, a two-step relief valve may be connected in pare allel with the shuttle valve. This alternativ. embodiment is shown in Figure 7 and operatel as follows. When and only when pressure 1'! high, the plunger 9| will open, since the effective pressure area to open it when closed is small. Immediately after opening however, the effective pressure area is increased to the full cross-section area of the plunger, and accordingly pressure required to keep the plunger open is reduced, and so long as the plunger remains open any oil that is bypassed and returned to the raise port 32R of hydraulic unit 3| is returned at low pressure.

Having now described and illustrated two forms of the invention, it is to be understood that the invention is not to be limited to the specific form or arrangement of parts herein described and shown.

I claim:

1. In a tractor propelled material-handling apparatus the combination of: a main frame, a lifting and lowering frame attached to the main frame; a bucket rockingly supported by said lifting and lowering frame; means to raise and lower said lifting and lowering frame; a double-acting cylinder-piston assembly having one end sup ported by one of said frames and the other end pivotally connected to the bucket; hydraulic means to feed pressure fluid selectively into the chamber at one end of the cylinder of said assembly to rock the bucket into dumping position and into the chamber at the other end of the cylinder to restore the bucket to digging and carrying position; said hydraulic means including a fluid supply tank, a pump, piping and a control valve for the selective control of the flow of such pressure fluid; and a normally-closed short-circuit valve connected between said chambers and adapted to open for a predetermined setting of said control valve of said hydraulic means to feed pressure fluid into the chamber at said one end of the cylinder to dump the bucket; said short-circuit valve being connected in the piping between said second-mentioned chamber and the main control valve in such a manner that when open it blocks substantially all return flow from said second-mentioned chamber to the main control valve and diverts it into the other end of the cylinder.

2. A material-handling apparatus according to claim 1, further characterized by the fact that in the circuit between said second-mentioned chamber and the main control valve, the shortcircuit valve is in parallel with a normally-closed one-way valve that opens responsive to a predetermined fluid pressure in said second-mentioned chamber to permit a relief flow of fluid from said second-mentioned chamber to the main control valve, and remains open responsive to a pressure that is lower than said predetermined fluid pressure.

3. In a tractor-propelled material handling apparatus the combination of; a main frame, a lifting and lowering frame attached to the main frame; a bucket rockingly supported by said lifting and lowering frame; means to raise and lower said lifting and lowering frame; a double-acting cylinder-piston assembly having one end supported by one of said frames and the other end pivotally connected to the bucket; hydraulic means to feed pressure fluid selectively into the chamber at one end of the cylinder of said as-.

sembly to rock the bucket into dumping position and into the chamber at the other end of the cylinder to restore the bucket to digging and carrying position; said hydraulic means includso ing a control valve for controlling the flow of such pressure fluid adapted to be set selectively to feed such pressure fluid into the first-mentioned chamber at one or the other of two predetermined speeds of flow; and a short-circuit valve connected between said chambers and between said second-mentioned chamber and the control valve in such a manner that, when the control valve is set to feed pressure fluid into said firstmentioned chamber at the lower of said predetermined speeds of flow, the short-circuit valve blocks flow between said chambers and provides an opening for return flow from the secondmentioned chamber to the control valve, and that, when the control valve is set to feed pressure fluid into said first-mentioned chamber at the higher of said predetermined speeds of flow, the short-circuit valve provides an opening for flow of pressure fluid from said second-mentioned chamber to said first-mentioned chamber and blocks substantially all return flow from said second-mentioned chamber to the control valve.

4. A material-handling apparatus according to claim 3, further characterized by the fact that in the circuit between said second-mentioned chamber and the main control valve, the short-circuit valve is in parallel with a normallyclosed one-way valve that opens responsive to a predetermined fluid pressure in said secondmentioned chamber to permit a relief flow of fluid from said second-mentioned chamber to the main control valve, and remains open responsive to a pressure that is lower than said predetermined fluid pressure.

GOT'I'FRIED REUTER.

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

UNITED STATES PATENTS Number Name Date 2,267,284 Livers Dec. 23, 1941 2,431,032 Ernst Nov. 18, 1947 2,517,582 Lull Aug. 8, 1950

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