US2642717A - Fluid pressure control apparatus for free piston machines - Google Patents

Description

Patented June 23, 1953 FLUID PRESSURE CONTROL APPARATUS FOR FREE PISTON MACHINES Ralph T. Whitney, Irwin, Pa., assigner to Westinghouse Air Brake Company, Aa corporation of Pennsylvaniay Application December 9, 1947, Serial No. 790,547

4 Claims.

This invention relates to control apparatus for free piston machines of the type usually embodying two opposed piston assemblages operable by expansion of hot gases generated in a combustion ychamber common to both assemblages, for effecting pumping or compression of a gas such as air.

In the copending application of A. J. Bent, Serial No. 762,771, led July 22, 1947, now Patent No.v 2,608,052, and assigned to the assignee of the present application, there is disclosed control apparatus for controlling a free piston machine of the above type, in which each piston assemblage comprises a power piston, an air compressor piston, and a direct bounce piston secured together. By expansion of hot gases in a combustion chamber during normal running of the machine the power pistons of both piston assemblages are forced outwardly, causing air to be compressed in and displaced from respective chambers at one side of the air compressor pistons and to be compressed in respective direct bounce chambers at the end of the direct bounce pistons. By expansion of the air compressed in the direct bounce chambers during the outward stroke of the assemblages, a return inward stroke of said assemblages is effected, advancing the air compresser pistons in the direction of respective reverse bounce chambers at their opposite sides, and causing the power pistons to move in the direction of the common combustion chamber for compressing combustion air supplied thereto dur-` ing the previous outward stroke.

In the a-bovementioned application, means are disclosed whereby during running of `the free piston machine the reverse bounce chambers are continuously open to a source of fluid under pressure for pressurizing said chambers. Also during starting and warm-up of the machine, the reverse bounce chambers remain open to the source of fluid under pressure, but normally closed vent valve means are opened at this time which vent said chambers to the atmosphere to thereby rel duce pressure of fluid therein. It will therefore be apparent that during starting and warm-up considerable fluid under pressure from the source may be lost to the atmosphere via the vreverse bounce chambers; for sake of economy this loss of iiuid under pressure is undesirable. It is therefore a prime object of the invention to provide means for preventing such loss.

According to this object, I provide a fluid pressure operable valve device associated with the control apparatus disclosed in the aforementioned application which is automatically operable to y cut olf communication between the source of fluid p devices describedbriefly in the present applica- 1 under pressure and the reverse bounce-chambers when the vent valve means are open, and to reestablish said communication when said vent valve means are closed, for thereby preventing the above described unnecessary loss of fluid under y pressure from said source.

Other objects and advantages of the invention hereinafter will become obvious from the following more detailed description thereof.

In the accompanying drawing; Fig. 1 is a diagrammatic view of Aa free piston machine with a portion of the control apparatus therefor, in which apparatus the invention is embodied; and Fig. 2 is a partial plan view of an operators control device shown in elevation in Fig. 1.

. c Description Thefrce piston machine and the control apparatus therefor embodying the invention may be substantially the same as that fully disclosed and described in the aforementioned copending application, to which reference may be made, in view of which that portion of said control apparatus directly pertinent tothe invention and necessary for a clear understanding thereof is shown in the drawing in detaiLfor detailed description of other Y lgenerator type comprising ra casing containing two opposite, coaxially arranged power pistons 2, 2a slidablymounted therein. Between the respective ends of the two power pistons 2, 2a is formed a combustion chamber 3 which is common to both. By burning fuel supplied from a nozzle 4 in combustion chamber 3, hot expansible combustion gases are generated for dri-ving'the .power Y pistons 2, 2a through power strokes in opposite directions. To supply combustion and scavenger air to the combustion chamber 3, aninlet port 5 is provided and arranged to be uncovered by` powerpiston 2a near the end of its power stroke and after an exhaust port 6 has been uncovered by power piston 2 substantially at the end of its power stroke. machine is intended to be employed as a gas generator for driving a gas turbine or the like, eX- haust port 6 is connected to a delivery pipe 1 for conveying the hot exhaust gases to said turbine (not shown). The inlet port 5 is connected to a duct 8 adapted to be supplied with air compressed by the free piston machine itself, as will be pointed out. y

Since the particular free pistonk To the opposite respective ends of the two power pistons are attached, in coaxial relationship therewith, two larger air compressor pistons 9, 9a slidably mounted in suitable bores in the casing. As power pistons 2, 2a are driven through their power strokes, pistons 9, Sa are advanced in the direction of respective air compressing chambers I al; their one side, compressing air, previously admitted thereto via respective inlet valves I I, for discharge into the duct 8 via respective discharge valves I2.

Attached to the air compressor pistons 9, 9a opposite power pistons 2, 2a and in coaxial relationship therewith, are two direct bounce pistons I3, I3a, respectively, which are-advancedin the i direction of respective direct bounce chambers I4 formed in the casing by an end -wall and suitable bores in which the bounce pistons are slidably guided. Air trapped in the direct bounce chambers I4 is compressed by the direct bounce pistons I3, I3a during the'power stroke of the power pistons 2, 2a, and this compressed air in each of said chambers acts as a spring for cushioning the pistons at the end of said power stroke-as well as provides stored energy to actuate the pistons through a return stroke. It will be appreciated that the pressure of air in the chambers I0 acting on pistons`9, 9a' may-also partially aid in return of the entire piston assemblages.

During the returnvstroke of the power pistons 2, 2a, as substantially effected through the bounce pistons I3, I3a, the air compressor pistons `9, v9a are caused to move in the ldirection' of respective reverse bounce chambers I5, compressing air trapped therein, and by expansion of 'said air at the end of said return stroke. aiding the power pistons 2, 2a to repeat their power strokes as above described, compressing air admitted to the chambers I0 during said return stroke.

The two piston assemblages are connected together for symmetrical movement'by two oppositely arranged toothed racks I1 and I8 connected at one end to the air comp-ressor pistons 9, 9a, respectively, and operatively connected to each other by a meshing pinion I9 arranged torotate on a xed axis.

The two direct bounce chambers I4 are connected one with the other by way :of ports and chambers 2I in the casing, andapipe 22 connecting said .chambers 2I. -Ther-pipe 22 is adapted to be connected to mea-ns (notshown) for regulating the'amount of air in theV direct bounce chambers I4 to alter the running characteristics of the free piston machine forreasons which are of no concern to the'present invention.

The two reverse bouncechambers I5 are connected one with the other by way of a pipe' 25. During starting of the free piston machinefas will be described hereinafter, the pipe is adapted to be supplied with compressed air from an operators .control device 26 mounted on a pipe bracket 21 and having an operators handle 26a, by way of passages 29, 29a in said bracket, the former passage being connected to an-outlet port 30 in said control device.

One or more starting valve devices'3l are associated with the casing of the free piston machine for each reverse bounce chamber I5, each starting valve device comprising a vent valve 32 arranged to open inwardly of said cha-mberfor establishing a communication from said chamber to atmosphere by way of a port '33, and a spring chamber 34 which is open to atmosphere via a port or .ports 35 in thecasingof eachdevice. A spring 36 in each valve device 3I.is arranged to urge the valve 32 toward a normally closed position, and a piston in each device connected to said valve is arranged to be operated by fluid under pressure supplied to a chamber 38 to open said valve against action of said spring. The chambers 38 in all of the starting valve devices are connected toa common controlpipe 39 which in turn is adapted to be connected to' control means (not shown) for controlling supply and release of iluid under pressure thereto during starting and warm-up of the free piston machine, as will be described hereinafter.

According to the invention, a fluid pressure 'operated valve device 40 is provided interposed in the communication between the operators control valve device 26 and the pipe 25 connected rtothe reverse bounce chambers I5 in the free piston machine. The valve device 40 comprises a casing 4I removably mounted on the pipe bracket 21. The casing 4I is provided with a chamber 42 open at one end to the passageZS at one side of a valve seat 43 which is disposed in said chamber. At an opposite side of valve seat 43, the chamber 42 is open to the passage 29a. connected to pipe 25. Disposed in chamber 42 is a normally unseated valve 44 arranged for engagement with seat 43 to close off passage 29 from passage 29a.

The valve 44 is operatively connected to a stem 45 which extends through an opening ina casing partition wall 46 separating chamber 42 from a, spring chamber 41. Chamber 41 is open to atmosphere via a port 48 in casing 4I, and to prevent leakage of fluid under pressure from chamber 42 past stem 45 into said chamber 41, a sealing-ring is disposed in a groove vinthe opening through the partition wall 46 for slidable sealing contact with the outer surface of said stem. A compression spring` 49 is disposed in chamber 41 interposed between the partition wall 46 and a piston 50 which is operatively connected to the stem 45 and exposed to said chamber on its one side. At the opposite side of piston 50 there is a pressure chamber 5I which is adapted to be supplied with fluid under pressure for causing movement of saidpiston in the direction of chamber 41 to close Avalve 44. Pressure chamber 5I is connected to the control p ipe 39 byway of a passage 52 in the casing-4|, a registering passage 52a in pipe'bracket 21, anda pipe 53, so that fluid under pressuresupplied via said control pipe 39 for effecting opening of vent valves 32 will also at the same time be supplied to said'pressure chamber 5I to effect closure of lvalve 44 for cutting oil communication between the reverse bounce chambers I5 and the source of fluid under pressure in passage 29.

Prior to starting the free piston machine, the operators lever 26a, of the operators control device 26 Ywill be moved to stop position ('Fig.2), if not' already in such position, in which position means (not shown) comprised in the control apparatus are so conditioned as to assure that the piston assemblages will be disposed in innermost lrest positions, in which they are shown in the drawing, with chambers I4, I0, I5 in saidrnachine, chambers 38 in starting valve devices 3I, and chamber 5I in valve device Y4I) all opento the atmosphere. Vent valves 32 in devices 3I are thus closed by springs 36 and valve A44 in device 40 is opened by spring'49.

In effecting normal starting of the free piston machine, described in detail in the aforementioned. application, the operators handle26a'of device 26 is moved to Start position, shown'in Fig. 2,"where'upon fluid under pressure is initially'supplied via port 30 to passage 29, thence to passage 29a and pipe 25 to the reverse bounce` chambers I5. Pressure of fluid thus supplied to the reverse bounce chambers I5"and acting on one'faceof Vthe pistons 9, 9a is thereby'increased sulciently tov cause the piston assemblages to moveoutwardly; said pistons 9, 9a moving in the direction of respectiver chambers I0, and after closure vof inlet valves*` I I, thus causing air previously admitted to said chambers to be displaced at'slight compression into the duct 8 via the discharge Vvalve devices I2;'pistons I3, I3a` moving in the direction o'f respective-direct bounce chambers I4 toextreme outer positions; and pistons 2, 2a movingoutwardly and consecutively uncovering, respectively, the exhaust port 6 and the inlet port 5, thus allowing air from ductv 8 to flow into the combustionchamber 3, sweeping any stale air from said chamber out through said port 6. At the time that the pistons; I3, I3a reach their outermost or starting positions, automatic means (not shown) .are rendered responsive to effect supply of fluid at a'chosen pressure to the direct bounce chambers I4 for charging same therewith. After the direct bounce chambers I4 have become `fully charged, automatic means (not shown) are automatically rendered responsive to eiect supply of fluid under pressure to the fluid pressure operated startingv-alve devices 3l via control pipe 39 to cause the vent valves 32 to be opened suddenly. Opening of vent valves 32 opens the reverse-bounce chambers I5 to the atmosphere via ports 33, thus suddenly reducing pressure of fluid acting*l on the re'- spective faces of the pistons 9, 9a, and t'hereby allowing the fluid under pressure with which the direct bounce chambers I4 were charged to expand against the pistons I3, I3a and cause inward movement of the piston assemblages; pistons 9, 9a moving in the direction of the reverse bounce chambers I5; and pistons 2, 2a moving through a compression stroke. in the direction of the common Vcombustion chamber 3, covering yports 5, 6 and compressing air ,therebyk trapped in chamber 3. 'At somepoint in the inward stroke of the piston assemblages, by timing means (not shown) comprised in the control apparatus, uid under pressure is vented from the control pipe 39 to allow the vent valves 32 to close before the pistons 9, 9a reach their innermost extreme positions so that during subsequent movement,

pressure of fluid in the reverse bounce chambers will build up. Substantially at the time that 'the power pistons 2, 2a reach their inner dead-center positions, the air in the combustion chamber 3 is compressed sulciently to be of suflicientlyV high temperature to ignite fuel injected into said chamber from nozzle 4. By burning of the fuel in the combustion chamber 3, hot expansible gases are generated which, acting on the power pistons 2, 2a, together with the pressure'of fluid l in the reverse bounce chambers I 5 acting on pistons 9, 3a, causes the piston assemblages to move outwardly. Outward movement of the piston assemblages at this time effects compression of fluid under pressure trapped in the direct bounce chambers I4 for thereby storing energy to be expended in effecting subsequent inward stroke of said assemblages; effects displacement of air admitted to chambers I0 into the duct 8 where same may be compressed to greater or less degree; and effects exhaust of combustion gases from the combustion chamber 3 through the port Ii` upon being uncovered by piston 2 and subsequent r`scavenging and rensupply of combustion air'from vent valves 32` remaining closed, to again com `press combustion air in the chamber 3 for burningr -fuel for'the return stroke, while pressure'of fluid in the reverse bounce chambers I5 is maintained for aiding said return." If'the'machine' is running smoothly, thek piston assemblages auto'- matically repeat their inward and y outward strokes in the manner above describedand the control lever 26a of the operatorscontroldevice 2-8 is moved'to running zone, indicated inFig;

2, for effecting vcontrol of pressure of fluidhinithe reverse -bounce 'c'.h'ainbers' I5 and direct vvbounce chambers I4 to change operating conditions of the machiney for reasons yof 'no concernfto the present invention. f f 7'7" If, however, at time of starting, with the-dperators control lever 26a in Start possitionan'd during the initial inward stroke offthe piston as'- semblages for actuating the power pistons- 2, 2a throughfan initial compression stroke to compress combustion air in chamber`3, ldue to low initial temperature of the lubricant on the cylin-I der walls, for example, the viscous drag of said lubricant may so slow down said assemblages, together with the restraining action of pressure of fluid trfippedin the reverse bounce chambers: I5 after closure of vent valves 32, that compression of `air in the chamberr 3 will be insufcientto cause ignition of fuel therein, in which case the machine does notstart, or it may make a few strokes after an initial ignition and then die. To obviate` any such difficulty in starting, in the control apparatus disclosed inthe `aforementioned application, means are provided for efecting'a continuoussupply of fluid under pressure' to the .control pipe 39, thence to the pressure chambers in the'starting valve devices 3| for causing the v ent valves 32 to beheld open, so that the aboveinated. With the vent' valves 32'Vthu's' hel'dwopn the piston a'ssemblageswill continue to oscillate as in normal running, and after the machine has been allowed to warm up, sulciently, it is stopped and restarted in the normal manner above described. f

According to the invention, when fluid under pressure is supplied to the control pipe 39 for opening the vent'valves 32 in the starting valve devices 3I, it will also flow from said control pipe to pipe 53 and thence through passage 52a in pipe bracket 21, and the registering passage 52 in casing 4I of valve -device 40 inte chamber 5I thereof. `Pressure of rfluid thus supplied to chamber passage 29a connected via pipe 25 to the reverse y bounce chambers I5 in the free piston machine I. It will be appreciated that closure of valve 44 will be effected substantially at the same time thatvent valves 32V `are caused to open, sol that particularly during warm-up of the machine, much compressed air from the operators control device will be saved.

.It-'will' thus be seen that I have providedmeans particularly fadapted `for use -with `control iapparatus of the type disclosed in the aforementioned application which is automatically operative, when the vent valves .are opened, to Avent fluid .under pressure from reverse. bounce chambers in-.the freepiston machine, to close off communication between thesource of fluid .under pressure and Asaid chambers, thereby effecting considerable saving in fluid under pressure during starting tandV warm-up of said machine.

:Havingnow described the invention, what I claimas new and desire to secure by Letters Patent, is: v :1. The combination with an internal -combustionfree piston engine comprising a casing having aireverse bounce chamber, a iluid .pressure supply port and a fluid pressure .exhaust port opening thereto, ofstarting .control `apparatus forrsaid engine comprising an operators control lever having a start position and means operable by said lever in said start .position to establish a fluid pressure supply communication to said sup- -ply port, interlock means-for closing said supply communication from -said operators control device to said reverse bounce chamber, vent valve means operable to establish a fluidpressure. release communication between said exhaust port andthe atmosphere,.and means connecting both said interlock. means and said vent valve means togetherfor operation in unison.

`2. `The combination with an internal combustion free piston engine comprisinga casing having a reversebounce chamber, afluidlpressure supply port and a fluid pressureexhaust port opening thereto,V of starting .apparatus for said engine comprising-an.operator.s control device operable to.. establish afluidpressuresupply communication for conveyinguid under .pressure v'to said fluid pressuresupply portto .start said engine, vent valve means operable by fluid under pressure t0 open said exhaust port vto atmosphere, andinterlock means responsive to supply of operating fluid-under pressure toA said vent valve means to linterrupt-said supply kvcommunication between. said operatorTs control device and said supply port. l

3. The combination with an internal combustion free piston'engine comprising a casing havlnga reverse bounce chamber, of starting means foresaid* engine comprising an operators control device operable tov supply iluid under pressure to said reverse bounce chamber to start saidengine, vent valve means operable by fluid underpressure .to vent said reverse bounce chamber to atmosphere, and interlock means responsive to supply of operating fluid under pressure to said vent valve means to interrupt supply of.fluid under pressure from said operators control device to s aid reverse bounce chamber.

4. The combination Withan internal combustion free'piston'engine comprising a casing having a reverse 'bounce chamber open to a lluid pressure supply conduit, of an operators control device operable to supply fluid under pressure to said supply conduit, vent valve means responsive to supply and release of iluid under pressure .to a rst chamber to open and close, respectively, communication between said vreverse bounce chamber and atmosphere, interlock valve means responsive to release and `supply of fluid under pressure to'a vsecond chamber to establish and disestablish, respectively, communi c a ti o n through' said supply conduit, andl control f circuit means 'connected to'said rst and second chambers for conveying fluid under pressure simultaneously -to both said first chamber andsaid second chamber and simultaneouslyfrom both said first chamber and said second chamber.

RALPH T. WHITNEY.

References Citedin the ille of this patent AUNITED STATES PATENTS Number Name Date 2,168,828 Pateras Pescara Aug..8, 1939 n2,430,066 Lewis Nov. 4, 1947 :2,434,280 y Morain Jan. 13, 1'948 *2,435,970v Lewis Feb. 17, 1948

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