US2870826A - Liquid fuel distributing systems for combustion engines - Google Patents

Description

2,870,826 LIQUID FUEL DISTRIBUTING SYSTEMS FOR COMBUSTION ENGINES I Filed Nov. 20, 1957 Jan. 27, 1959 R/J. .THORPE ETAL 2 Sheets-Sheet 1 INVENTORS ROBERT J.THORPE, DONALD F. WINTERS.

FIG. 2.

Jan. 27, 1959 IR. J. THORPE ETAL LIQUID FUEL DISTRIBUTING SYSTEMS FOR COMBUSTION ENGINES Filed Nov. 20, 1957 2 Sheets-Sheet 2 FUEL FLOW DISTRIBUTION PRESSURE DROP (P.8J.)

INVENTORS ROBERT J. THORPE DONALD F. WINTERS UnitedStates Patent LIQUID FUEL DISTRIBUTING SYSTEMS FOR COMBUSTION ENGINES} Application Noveinber 20, 1957, Serial No. 697,691 6 Claims. (Cl. 158-36) Winters, Westinghouse Elec- East Pittsburgh, Pa., a corporation This invention relates to a liquid distributing system, more particularly to a system for distributing liquid from a common supply to a plurality of dispensing nozzles at uniform pressure and has foran object to provide an improved and highly reliable system of the above type.

Although the invention provides a liquid distributing system which is susceptible of wide and diversified application, the system is primarily intended for distributing liquid fuel to an internal combustion engine, for example an aviation gas turbine engine, and is especially advantageous for fuel distribution in turbojet engines having a wide flight speed range or spectrum. Turbojet engines of this type require fuel distribution systems which uniformly a distribute fuel to the dispensing nozzles throughout a wide flow range, on the order of 40 to 1 and within a pressure drop range extending from a minimum of about 50 lbs/sq. in. to a maximum of about 200 lbs/sq. in.

Accordingly, it is a further object of the invention to provide a liquid fuel distributing system for uniformly distributing fuel to a plurality of nozzles throughout a' wide flow range and Within pressure drop limits suitable for a wide flight spectrum aviation engine.

in accordance with the invention, there is provided a system for distributing fuel to a plurality of dispensing or injecting nozzles including a manifold communicating with a supply pipe and a plurality of positive displacement pumps having their inlets and outlets connected to each other in a series hydraulic loop-servo circuit which is connected at its ends to the supply pipe. In the servo circuit there is interposed a valve, responsive to differential pressure, for controlling the total or cumulative fuel pressure rise across all of the pumps at a desired value. Each of the pumps is coupled to an associated set of positive displacement-fuel actuated motors having their inlets connected to the manifold and their outlets connected individually to the injecting nozzles.

Thus, as fuel at suitable pressure and in metered quantity is delivered to the manifold by the supply pipe, it

flows into the inlets of the fuel actuated motors to drive the same and is thence delivered to the nozzles at a re,-

duced pressure. Since the motors drive the pumps, the

total pressure drop occurring across each set of motors is r substantially equal to the pressure rise across the associated pump. By suitable adjustment of the valve, the total pressure rise in the servo-loop circuit,.and accordingly the pressure drop at the nozzles, may be closely controlled at any desired value.

2,870,826 Patented Jan. 27, 1959 ICE drawings, forming a part of this application, in which:

Fig. 1 is a diagrammatic transverse sectional view of an aviation turbojet engine having an embodiment of the invention incorporated therein;

Fig. 2 is an enlarged axial sectional view of one of the pump and motor units shown in Fig. 1; i

Fig. 3 is a transverse sectional view taken on line III- III of Fig. 2, looking in the direction of the arrows;

Fig. 4 is a view similar to Fig. 1, but illustrating a second embodiment of the invention; and

Fig. 5 is a chart illustrating the performance curve attained with the invention and representative curves at tained with prior art devices.

Referring to the drawings in detail, in Fig. 1 there is shown a typical aviation turbojet engine 10 having a fuel distributing system 11 formed in accordance with the invention.

Since the turbojet engine 10 does not form a part of the invention, it has been shown diagrammatically in transverse section taken through the fuel combustion chamber 12 and looking in upstream direction. As well known in the art, the turbojet engine 10 has an outer tubular casing 13 encompassing the usual air compressor and gas turbine portions (not shown), coupled for joint operation by a centrally disposed rotatable engine shaft chamber 12 by an annular row of dispensing or injecting The valve may be of the fixed adjustment type when the distribution system is employed with a suitable fuel metering control mechanism. However, a manually adjustable valve mechanism, responsive to suitable engine operating conditions such as rotational speed of the shaft, may be employed for selectively controlling the pressure rise in the servo circuit and accordingly the distribution pressure at the fuel nozzles.

The foregoing and other objects are effected by the innozzles 18, which may be of any suitable variable area type or vaporizing type, as desired. As well known in the art, the nozzles 18 are uniformly spaced from each other to admit fuel in highly atomized or otherwise finely divided condition in a uniform pattern to the combustion chamber, thereby to promote a good fuel/ air mixture and to obviate formation of localized hot spots.

The fuel system 11 has a supply pipe 19, provided with fuel from any suitable source (not shown), communicating with an annular manifold 20 which is mounted concentrically with the engine 10. The fuel supply pipe 19 has interposed therein a main fuel pump 21 and a fuel metering control mechanism 22 of any suitable type for regulating the flow of fuel from the pump 21 into the manifold 20, as well known in the art.

In accordance with the invention, the fuel manifold 20 has attached thereto at uniformly spaced intervals a plu- 'rality of motor-pump units, generally designated 23, forregulating the delivery of fuel from the manifold 24] to the nozzles 18. Since the motor-pump units 23 may be identical, only one will be defined, it being understood that the others are arranged and formed in a similar manner. Asbest shown in Figs. 2 and 3, the motorpump unit 23 has a pump element 24 and a plurality of motor elements 25 similar to the pump element 24 but of slightly smaller capacity. The motor elements 25 and the pump element 24, as illustrated, are of the positive displacement rotary vane type.

The pump element 24 includes a rotor member 26 mounted on a shaft 27 which is rotatably mounted in a generally cylindrical housing 28 provided with a fuel inlet 29 and a fuel outlet 30. The rotor 26 has a plurality of vanes 31 slidable radially to maintain abutment with the inner surface of the housing 28 during rotation of the shaft, thereby to translate fuel .from' the pump inlet 29 to the pump outlet 30.

pressure in closing direction. 7 provided with an inlet 50 and an outlet port 51, the

form flow throu'gh all of the; fuel injectingn zles'18.

The motor elements 25 are similar to the setup element 24 andareindividually provided withvaned rotors 32 mounted to the shaft 27 and having-fluid inlets and outlets 33 and 34, respectively. The motor outlets 34 are (as shown in fig. l) connegted to "the asspciatgd fuel injecting nozzles 1% by individual conduits 35 while the motor inlets 33 (as shown in Fig. 2) co-mniunicate witha manifold 36 for-med in the housing 28 and having a common inlet 37 formed therein which is connected to the annular manifold 20. 'Dhus, fuel from the annular manifold is delivered to the riianifiolddti through the common inlet 37 and thence divided for how through each of the inlets 33 toprovide motivating fuel to each of ,the motor elements 25. s

Thus, it will be seen that the motor elements and the pump element 24 rotate jointly'and at the same speed, the motor elements25 receiving motivating fuel from the common inlet 37 and jointly driving the pump element 24, while the pump element 24 is fed fuel through the pump inlet 29 and'delivers it through an outlet 38 communicating with the outlet 30.

The pump elements 24 are connected to each other 'in a loop-servo circuit by a plurality of conduits 39 connected at their upstream ends to the pump outlets and at their downstream ends to the pump inlets 29, therebyfonning a series flow circuit from one pump to the next. The first pump element '24 in the servo cir- -cuit (disposed at nine ocloclt in Fig. 1) has its inlet 29 connected to the supply pipe 19 by a conduit '40,

thereby to provide the servo-loop circuit with fuel at supply pipe values, while the outlet of the last pump element 24 in'the servo circuit (disposed at seven oclock in Fig. '1 has :itsjoutlet 39 connected to adiiferentia'l pressure valve 42 by a conduit 43.

The differential valve 42 has a housing Within which is mounted a, slidable valve member '44 having a pair ,of spaced lands 4-5 and 46 connected to each other and biased upwardly by a spring "47. lIhe upper end-of the va1ve, 42:is connected 'to the supply pipe 19 by a conduit 48, while tlie'lower end of the housing-is connected to one of the fuel nozzle conduits by a conduit 49, thereby to provide supply fuel pressure upon the slidable valve 44in'opening direction and fuel nozzle The valve 42 is further latter being regulatedby the lower land 46. The outlet port 51 is connected to the supply pipe 19 by a conduit 52. Thus, it will-be seen that the servo l-oop circuit is provided with fuel from. the supply pipe 19 flowing through the cohduit' itl and the pump elements 24 by way of the conduits '35 and thence through con- 'duit 43, the differential pressure'valve"42 and conduit 52 back to the supply pipe 19,

The fuel system 11 operatesint'he following manner. As fuel, pumped by the'ina'i-npunip 21, is delivered to the m anifold w at regulated-flow rate-Fund pressure values by thefuelcontrol -22,t he rotors -32 of-th e rnotoi' elements 25 are driven "and'the fuel ejected therefrom through the outlets 34 is delivered to each of the asseciated nozzles 18 at a reduced pressure value, Since the motor rotors 32' of each motor pu-m'p unit 23 are interlocked, the fuel delivered tceach of the fuel nozzles 18 is uniform in volume, insofar as each of the motorpump units 23 is concerned. However, since the pump elements 24 are driven b'ythiehnotor elements 25, and since each of the pump "elements '24 is coiiiiectedto all of the other pump elements in the 'servo-loopcirciiit by conduits 39, the pumped fuel intust passth'rsu h each of the pump elements 24. in this manner, 'th e puinped volume is equal for all pump elements "24, hence the R. P. M. s of all pumps "are equal, thereby insuring uniform flow through the motor elements andhni- The motor elements zs perrormwancm riv' ing is effected across each of the motor elements 25, and the sum of the work accomplished by each of the motorpump units 23 is converted to the pressure rise across the associated pump element 24. Accordingly, the sum of the pressure rises across each of the pump elements 24 is transmitted to the valve 42 by the conduit 43. The valve 42 serves to regulate the total pressure rise in the loop=servo *circuit at a preselected value to insure that the pressure drop across the motor elements is main tained within certain preselected limits in the following manner. s

As fuel from. the supply line 19 is delivered to the fuel manifold 20 by the fuel metering control 22 at a se lected rate of flow, the motor rotors 32 of each of the motor-pump units 23 are rotated and, in turn, drive the associated pump rotors 24. The resulting pressure drop across the motor elements 25 is transmitted to the valve 42 by the conduit 49, thereby modifying the position of the valve land 46 a's re'quired to regulate the area of the valve port 51. The pressure rise across the pump elements 24 is thus regulated by the valve and concomitantly controls the pressure drop across the motor elements 25 in a manner to permit uniform dist'ributidn of fuel to each of the injector nozzles 18.

During operation of the engine 10, the fuel rate to the injectornozzles 18 may bein'creased or decreased within prescribed limits by the fuel metering control 22, for reasons well known in the art. Should the fuel metering control 22 be adjusted for an increased flow rate so that the fuel from the supply pipe 19 is delivered to the manifold 20 at a higher flow rate, the motor elements 32 rotate 'at a faster rate, thereby 'to deliver fuel to the fuel nozzles "18 at a higher rat'e as indicated by the fuel metering control 22. Such increase in flow rate of the motor elemen s 'will momentarily result in an increase in pressure amp across the motor elements with'a momenta'r'y increase in the pressure rise "across the pump elements. The momentary increase inpr'essuire drop across "the htoto'r'elemen'ts, however, 'isf't'raiism'itted 'to the "differential valve 42 by the conduitflti as 'afpre'ssure increase, moving the valve land 46 downwardly to increase the 'area of the outlet port 51 until a stabilized position'is obtained wherein the desired pressure rise in the servo-loop circuit 'is attained.

Should the fuel metering control 22 be adjusted for a reduced -flow rate, the rate at which fuel is delivered 'tlirough'the manifold 20to the motor-pump elements 23 is reduced and hence is effective to reduce the rotational 'speed of the motor elements 25 and create a'smaller pressure drop across the motor elements with reduced rate of flow to the nozzles 18. Themomentarydecreasein'pressure drop across the motor elements 25 is effective to provide a decreasing pressure rise across the pump elements 24. However, the decrease in pressure drop across'the motor elements is effective as a decrease in pressure at "valve '42, "permitting thevalve land 46 to "movelin upwere direction, 'thereby decreasing the effective'ar'e'a er 'tlieport 51 or the valve and restoring the -."pres's'u'ie rise "value.

Re'fer'ringto the chart in Fig. '5,whereinthe abscissa denotes the'pressur'e dropin pounds per square 'inchof the distribution system (effective across the motor elements 25) and the ordinate denotestheratio'of fuel flow rates metered by the metering control 22 within its range, the curve A graphically illustrates the operating characteristics of the abovedes'cribedsysem. "In'aviatiou jet propulsion engines having awide flight speed "spectrum, for adequate performance, the maximum and minimum practical pressure drops in the distribution system-is about 200 pounds per square inch and 50 pounds per square inch, respectively, and the desired fuel-flowrate ranges from a minimum to rna iimum of aboutl to 49. It will be r eadily seen that the straight line tPOI-tl Ol'l of curve -A lies within the above mentioned limits,thusindicatiiig that 'theifivntidnds highly suitable for' 'a-via'tion engines amass having a wide flight speed spectrum. More particularly, it will be noted thatat minimum fuel flow rate ofl the pressure drop is about 80 pounds per square inch, while at the maximum flow rate of 40 the pressure drop is 150 pounds per square inch. i i

For comparison purposes, curve B, depicting performance characteristics of a conventional fixed orifice fuel distributor, and curve C, depicting performance charac teristics of aknown fuel distributor orifices, are also shown on the chart.

It will readily be apparent, by referring to curve B, that the fuel distributor of the fixed orifice type has limited application value, since the pressure drop across the orifice is too low for proper distribution at low flowrate values and quickly rises to excessive pressure values at a practical maximum flow rate of about 10. q The variable orifice area distributor is considerably better than the fixed orifice distributorand may be employed in wide flight spectrum engines, since itca n deliver fuel at rates ranging from to 40 withinthe pressure drop limits of 50 p. s. i. to 200 p. s. i. However, at flow rates of less than 10 the fuel pressure drop is lower than desired. In addition, the variable "area dis tributor requires extreme manufacturing precision in order to uniformly distribute fuel to a plurality of nozzles.

In Fig. 4 there is shown a fuel distributing system of somewhat modified form. Since most of the structure has already been described'in connection with the first embodiment, that structure is designated by the same reference numerals heretofore employed.

In this embodiment, a suitable bypass conduit 55 is provided communicating with the inlet and the outlet of the main fuel pump 21, whereby to permit recirculation of excess fuel pumped by the fuel pump 21. The rate at which the excess fuel recirculates therethrough is regulated by a differential pressure valve 56 having a port 57 controlled by a slidable piston valve member 58. The

having variable area pistonvalve is subjected to opposing fuel pressures of the supply pipe 19 transmitted thereto by conduit 48 and distribution pressure of the injector nozzles 18 transmitted thereto by conduit 49. t

i A fuel control valve 60 is interposed betweenthe conduits 43 and 52 for regulating the cumulative fuel pressure rise in the servo-loop circuit of the pump elements 24, and accordingly the pressure drop across the motor elements 25. The fuel control valve 60 has a housing 61 within which is rotatably mounted a hollow cylindrical member 62 driven in any suitable manner (not shown) by the engine shaft 14 and provided with a pair of axially spaced ports 63 and 64 communicating with the conduits 52 and 43, respectively. Within the rotatable member 62, there is slidably disposed a piston valve member 65 having .a land 66 arranged to vary the area of the port 64. The

upper end of the valve member 65 has a circular platform 67 upon which is received a helical speeder spring 68 for biasing the valve member 65 downwardly, i. e. in the direction to open the port 64. The bias of the speeder spring 68 is adjustable by a pivoted throttle lever 69 having a cam portion 70 for adjusting a plunger 71 which abuts the speeder spring 68. Thus as the throttle lever is rotated in clockwise direction, from the off position shown, the spring bias is increased. A plurality of suitable flyweight members 72, pivoted to the rotatable cylinder 62, are employed for opposing the downward bias of the speeder spring 68 on the valve member 65.

In operation, the throttle lever 69 is manually moved in clockwise direction to a selected engine speed setting, thereby biasing the valve member 65 downwardly in a direction to open the port 64. As the rotatable cylinder 62 is rotated by the engine shaft 18 the centrifugal force of the fiyweights 72 is effective to oppose the bias of the spring and stabilize the valve 65. Hence fuel flows through the servo-loop circuit including the pump elements 24, conduit 43, valve ports 64 and 63, and conduit 52 to the supply pipe 19 at a suitable controlled cumulative pressure rise value which is equal to the sum of the individual pressure rise values across each of the pump elements 24. Accordingly, the individual pres sure drop values acrosseach of the motor elements are controlled, in the manner described in connection with the first embodiment, to provide fuel at equal flow rate to the fuel injecting nozzles.

The fuel flow distribution rate maybe increased by moving the throttle lever 69 inclockwise direction, thereby to increase the bias of the speeder spring 68 on the valve member 65. As the bias of the speeder spring is increased, the valve port 64 is opened to a'greater degree by the valve member 65 and "the position of the valve member is stabilized by the opposing centrifugal force of the fly-weights acting against the speeder spring. Thus, the pressure rise in the servo-loop circuit is correspondingly decreased, with attendant reduction in the pressure drop across the motor elements 25. The thus reduced pressure drop across the motor elements 25 is transmitted to the valve 56 through the conduit 49 as a pressure increase, moving the piston valve 58 upwardly to reduce the effective area of the port 57 and increasing the fuel flow through the conduit 19 to the manifold 20. Conversely, the fuel flow distribution rate may be decreased by moving the throttle lever 69 in counterclockwise direction, thereby decreasing the bias: of the speeder spring 68. j The pressure rise in theservoaloop circuit is correspondingly increased with attendant increase in pressure drop across the motor units 25, thereby causing the effective area of the valve port 57 to be increased, increasing the flow rate through the recirculation conduit 55 and decreasing the fuel flow rate through conduit 19 to the manifold 20. l i It will be noted that in the embodiment shown in Fig. 1, the fuel metering control 22 is of conventional type and thatfall of the fueldelivered to the injector nozzles 18 passes through the control 22. However, in the embodiment shown in Fig. 4 the fuel control valve 60 is effective toregulate the fuel flow rate through conduit 19, although only the fuel flow through the servo-loop circuit traverses through the valve.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

What is claimed is: j t

1. A liquid distributing system comprising a liquid manifold, a liquid supply pipe communicating with said manifold, a plurality of positive displacement liquid pumps, a plurality of sets of positive displacement liquid actuated motors, each of said sets of motors being mechanically coupled to and driving an associated one of said pumps, each of said sets of motors having their inlets connected to said manifold, conduit structure connecting the inlets and outlets of said pumps in a series hydraulic circuit, valve structure disposed in said conduit structure for controlling the pressure rise across said pumps, the pressure rise across said pumps being effective to maintain a regulated pressuredrop across said motors, and a plurality of liquid dispensing nozzles, each of said nozzles being connected to the outlet of an associated motor.

. 2. A liquid distributing system comprising a liquid manifold, a liquid supply pipe communicating with said manifold, a plurality of positive displacement liquid pumps, a plurality of sets of positive displacement liquid actuated motors, each of said sets of motors being mechanically coupled to and driving an associated one of said pumps, each of said sets of motors having its inlets connected to said manifold, conduit structure connecting the inlets and outlets of said pumps in a series,

duit structure for regulating the pressure rise across said pumps,xsaid valve being responsive to the differential pressure between the "liquid "in the outlet "of one or said motors andfrlre liq in insatd'snpply pip 'and a pl ralit 6f li'qur'd "dispensing nozzles, each of said nozzles 'bein connected'to "the outlet ef'an associated motor.

3. A liquid 'dist'ribiiti'ng system comprising a liquid manifold, a liquid supply pipe communicating 'vv'ith said manifold, a main um insa'id supplypipe for deliverin ressurized liquid to said manifold, alplura'lity of positive displacement "pumps, "a pluralit of "sets of positive displacement liquid actuated "meters, each of said sets of meters being mechanicall "coupled to and driving an associated one of said positiv .l'rs tace'ment pum s, each of said sets of motors having'its inlets 'connect'ed to"'said manifold, conduit "structure connectin the inlets and oiitlets or said positive displacement pumps in a series hydraulic circuit, a valve disposed in said conduit structure 'forco'n'trolling 't-hepres's'ure rise across said positive dis lacement pum s, means for automatically regulating said valve, means including a ditferen'tial pressure relief valve- 'for-permitting recirciilati'o'n of eX'ce'ss'liquid about said ina-in pump, said differential pressure relief valve being responsive to-liquidgp'ressure at the outlet o'fone of said motors and a plurality of'liquiddispensing nozzle's, 'each ofsaid nozzles being connected to the outlet of an associated motor.

4'. A"fu'el distributing sysasm "fer fuel "combustionapparatus including a'tubular "wall structure "and a plurality of nozzles for injecting fuel thereinto, comprising a fuel manifold, a fuel supply pipe communicating with said manifold, 'a 'plurality of ositive displacementpumps, a plurality offsets er positive displacement "fuel actuated motors mechanically connected to said pumps, each of said sets ef' rnerorsfhav'in ifs "inlets connected "to said manifold "and its outlets "connected f Said "'iJOZZl'CS, "60hfnuirst'ruetur e connecting'the inlet xaird outlets "o f said positive displacement umps in a loop servo circuit, "a valve disposed "in said conduit st'ru'ctiire fofcontrolling the cumulative fuel pressure rise '"acr'o'ss all of "said positive displacement pum s, the "pressure rise across said positive displacementpurnps 'being effective 'to'maintain a controlled pressure drop acrosssaid 'm'ot'ors,'andme'ans for automatically regulating said valve.

5; A fuel distributing Systemfor an internal "combustion engine having a fuel combustion chamber for pro viding hot motive gases of combustion, a plurality of fuel injection nozzles for delivering fuel t'o'said chamber and a rotary shaft driven by said motive gases; comprising a fuel manifold, a fuel supply pipe "communicating'vvi th said manifold, ta main fuel pump in said supply pipe for 8 i; delivering pressurized fuel to said manifold, a plurality 'of's'e'cond'ary pumps, a plurality of positive displacement fuel actuated motors mechanically coupled to saidpumps, each er said motors having its inlet connected t g-s-said rnani'foldand its outlet connected toan associated one of said nozzles, conduit structure progressively connectin'g'the inlets and outlets of said secondary pumps in .a loop-servo circuit, said conduit structure connecting the inlet of theffirs't 'one'of said secondary pumps to said suppl 'p'ip'e andthe outlet ofthe last one of said secondary pumps to said supply pipe, a valve disposed'in said 'conduit'structure 'be't weenthe outlet of said last secondary'pu'mp"and'said'supply pipe for controlling the cumulative fuel pressure rise across all of said secondary pumps, isaid se'condary pumps being substantially identical and the pressure rise across said secondary pumps being effective to maintain a controlled pressure drop across each of said motors, and condition responsive "means 'for automatically regulating said valve in response "to 'a variable condition in-said engine.

'6. A liquid. fuel distributing system for an internal combustion engine having a rotary shaft, a fuel combustion chamber for providing hot motive gases of combu'stion'for driving said shaft, and a plurality of fuel in jection nozzles for delivering fuel to said chamber; comprising a fuelmanifold, a 'fuel supply pipe communicating 'Withsaid manifold, -a main 'fuel pump .in said supply pipe for deliveringpressurized fuel to said manifold, alplurality of secondary positive displacement pumps, a plurality of positive displacement fuel actuated motors mechanically coupled to said pumps, each of said motors having its inlet connected to said manifold and its outlet connected to one of said nozzles, conduit structure serially connecting the inlets and outlets of said secondary pumps in a loop-servo circuit, said conduit structure connecting the inlet of 'the "first one of saidsecondary pumps and the outlet of the'last one of said secondary Pumps to said supply pipe; and a valve interposed in s'aid co'nduit structure for r'egulatingthe fuel pressure rise insaid loop s'ervo circuit, said valvehaving a portcommunicating with said conduit structure, a movable valve member for regulating the effective area of said port, and means responsive to the speed of said rotary shaft for controlling the movement of said valve member.

References Cited in the file of this patent UNITED STATES PATENTS 2,430,264 Wiega'nd Ietal.. Nov.-4, 1947 12,566,734 .Lawrenc'e etal Sept. 4, 1951 2,599,680 Weeks .June 10, 1952

Images