US2815641A - Starting system for free piston engines - Google Patents

Description

De 10, 1957 R. P. RAMsEY ETA.

v STARTING SYSTEM FOR FREE `PISTON ENGINES Filed Jan. 16, 1952 l5 Sheets-Sheet 1 ww SN Snnentors: Rosana/"P ZZAMSEY, YKrLLARn MURAIN.

' v/ v v (Ittomeg S R. P. RAMSEY ETAL STARTING SYSTEM FOR FREE PIsToN ENGINES Filed Jan. 1s, 195;

Dec. 10, 1957 sshee'ts-sneet 2 nventors:

FnERTZ- FAn/rss2, y

WILLAHD A.M/JRAIN.

Gftmegs Dec. 10, 1957 R. P. RAMsEY Erm.

STARTING sYsTEN EoR FREE PIsToN ENGINES A 3 Sheets-Sheet 3 Filed Jan. 16, 1952 zlvl/ENTOR.5 ROBERTPPAMSEY I/l/L/ ARDAIYORA/N ATTORNEYS Unie STARTING SYSTEM FOR FREE PISTGN ENGINES Application: January 16 1952, Serial No. 266,764

7 Claims. (Cl. 60-14) Thiszinvention'y relates to starting of free piston engines, and has for itsA primary object, the provision of a starting system in which the` pressures existing; in the several cylinders; atA the end ofthe starting` stroke are at, or very close to, the: pressures to be expected during normal running of the engine.

Free piston engines in which airis relied upon to return! the'` pistonsl to the center or. compression position have, in the past, been started by injecting a charge of air behind the pistons in the bounce cylinders to drive them together. The bounce or energy accumulator cylinders normally run with, a very closely controlled increase and decrease in pressure soithat the quantity of air trapped inthe cylinders must be closely controlled. It almost invariably happens that the quantity of air required to drive' the. pistons ona starting, stroke differs considerably from` the quantity desirable for running, so that the quantity of the starting air must be changed rapidly at the end of the starting stroke, leaving a precisely predetermined quantity in. the cylinder. This, in some types of engi-nes, is difficult to accomplish.

Certain free piston engines are` of the type in which all of the energy developed during an outward stroke. of, the pistons is accumulated behind. the compressor pis.- tons and returned to the cycle as work in. a compressor cylinder, and work in compressing; the air in the power cylinder, during the inward stroke. It has been hereh tofore` proposed to start engines of this type by controlling exactly the pressure and volume ot the starting airv by segregating the air in a separate chamber, and subsequently opening this chamber to the. rear end of the compressor cylinders. This procedure usually requires that the pis tons be located properly, prior tostarting,y at some intermediate position between the. extremities of a. normal stroke. One object of the present invention is to avoid the necessity of. precise piston positioning,y the pistons being permitted to move to the full inward position..

Other types of free piston engines extract the work of compressing air from the cycle during the outward stroke of the pistons. Such engines use a separate bounce cylinder. into the bounce cylinders of these engines and to remove a part of the` air when the pistons reach the innermost position. There is, thus, a necessity for precise timing of the air removing valves which must be closed during a very short interval when the pistons are traveling at high. speed, as well as the usual accurate control of the pressure and volume of the starting air.

It will thus be seen that the previously known starting systems are such that a proper energy balance in the engine at the end of the starting stroke is diiiicult to obtain. The present invention comprises means tor introducing starting air to force the pistons apart, rather than together, for the initial stroke. Such a departure from the known practice makes it possible to eliminate precise timing of unloading valves, and greatly facilitates the establishment of a properly balanced system as well as giving other advantages hereinafter explained.

Itr has been proposed to inject the starting airv Naterit rice In the accompanying drawings, Fig. 1 is a diagram-- matic longitudinal sectional view of a free piston engine having a starting system in accordance with the present invention; Fig. 2 is. a group of pressure curves for the: several chambers in which pressure variations occur;` Fig. 3 is. a somewhat diagrammatic view, partly in section of al suitable starting bottle and control valve.;v Fig. 4 is a centralvertical section of avent control, valve, shown. somewhat diagrammatically, and Fig., 5 is a. central sectionalview of a modified, air operated, airy feed valve.

Referring to the drawings, and particularly Fig. l, ther free piston engine there diagrammatically disclosed includes opposed piston and cylinders symmetrical with respect, to the center so that only one need be described. A center power cylinder 10 is provided in which a power piston` 12` reciprocates, the piston 12 controlling the en,- gine exhaust ports 14 in the usual manner. The opposed piston of. the set controls air inlet ports 16.

The power piston is made integral with or connected tota compressor piston 17 operating in a compressor cylinder 118 and. dividing that cylinder into a compressor front chamber 20- and a compressor rear chamber 22.

Extending rearwardly of the compressor piston is a third piston section 24 which is the energy accumulating or bounce piston. This piston works in a bounce cylinder 26 and divides the cylinder into a bounce front chamber 28` and a, bounce rear chamber 30.

A suitable scavenging connection 32 connects the compressor space 20 and the inlet ports in the power cylinder. Pressure equalizing line 33 connects the compressor rear chambers 22 on each side of the center of the engine, an equalizing line 34- connects the bounce rear spaces Sil, and a third equalizing line, 35 connects the bounce` front chambers 28 which will be hereafter referred to simply as theA bounce chambers.

The: engine is provided with a pressure regulating der vice 4.6,- to control the air pressure in the bounce chamf bersl 28@ tomaintain the energy balance during variations in load, but this unit forms no part of the present invention, so that it is indicated only as a box in. the equalizing line. 35 that` connects the controlled chambers.

The starting` system of the present invention takes its air from any suitable source, designated 44. The several valves by which the flow of air from the source is regulated are sho-wn as separate, unrelated units, although it should be expressly understood that the valves may be grouped for easy sequential operation in a manner well known in the art. As the valves by which air is introduced into the system` are, in themselves, old and well known, they are` not shown or described in detail. In practice the valves are grouped for operation` by a single device such as a4 hand wheel which has certain prede.- terrnined positions, six in the present instance.

Valve 50 is a, three-way valve having feed and vent, positions. The valve in its feed position operates to conduct air from supply source 44 through, pipe 5l to a shut-ofi valve 52 ahead of the bounce pressure regulator 4) to render the regulator temporarily inoperative. The regulator is so arranged that it operates to maintain a predetermined pressure in the bounce chambers 28 and must, therefore,v beI taken out of operation during any starting cycle in which the pressure in the bounce chambers is considerably different than normal during most of the starting period.

In the execution of the invention shown in the drawings, a second three-way supply valve 55 is connected be tween the supply source 44 and a starting air bottle 56', the valve being interposed i'n a line 5'7. The starting air bottle is charged to a predetermined pressure and preferably has a predetermined volume. It is held out of commimication with the engine by a quick opening valve Si which is pneumatcally operated as hereinafter described. If desired, the three-way valve 55 may be eliminated and the bottle 56 charged continuously through a small, non-return valve. It is only necessary that bottle 56 contain enough air at the proper pressure to effect a start whenever required.

A third valve is indicated at 60. This Valve operates to supply air through a check valve 61 to the bounce chamber equalizing line 35. The introduction of air into the bounce chambers 28 continues until the pistons reach their innermost or center position at which time valve 60 can be closed, discontinuing the introduction of air into the bounce chambers.

A vent control valve for the bounce chambers is provided which is designated 70 and is operated next in the sequence. In the feed position of this valve, inwardly opening vent valves 72, associated with vent ports 71 provided in the periphery of the accumulating chambers 28 are opened, these valves being connected at their stems with pistons 74 operating in cylinders 75 against springs 76. So long as pressure is maintained on the lower face of pistons 74 the vent valves will remain open. A latch comprising a pneumatically operated bar 77 is provided adjacent each of the vent valves 72. The latches are urged into engagement with the stems of valves 72 and are removed therefrom by the introduction of air ahead of pistons 78 to which the latch bars are connected.

It will be seen that by sequentially operating valves S0, S, 60 and 70 that the bounce pressure regulator 40 has been temporarily rendered ineffective, the starting bottle 56 has been charged, the pistons have been moved to their center positions and chambers 28 have been vented. Valve 70 may then be moved to vent position removing the air pressure from the face of the vent valve control pistons 74, but the valves themselves will not close since the latch bars 77 operate to prevent this movement.

At the same time that the starting bottle 56 is charged by opening valve 55 thus introducing air into line 57, air passes into the end of a valve control cylinder 80 and behind piston 81 as can be seen in Fig. 3. A check valve 84 is interposed in the branch of line 57 between the three-way charging valve 55 and the starting bottle 56. Pressure of air behind piston 81 maintains valve 58 closed until cylinder 80 is vented by moving valve v55 to its vent position.

When the pistons have been moved to their center position and the accumulator cylinders vented by opening vent valves 72, the starting operation is initiated by rotating valve 55 to vent position and permitting the air in cylinder 80 to escape. Piston 81 thus has its rear face at substantially atmospheric pressure while the head of the valve 58 to which it is connected is subject to the full pressure of the air in starting bottle S6. This causes the quick opening valve 58 to move rapidly outwardly and to permit the starting air in the bottle to expand into equalizer conduit 34 which connects the bounce rear spaces at each end of the engine. Valve 58 may be shrouded at the top and bottom so that the passages which it controls are opened and closed gradually. It will be seen that before the shroud of valve 58 leaves seat 58a the valve body has already attained a considerable velocity so that the period over which the valve is fully opened is relatively short. When the valve 58 seats on seat 58b the ow is first rapidly shut off by the protruding shroud and the valve has a tendency to seat easily and without exerting destructive forces on the valve seat. The effect of the shroud is to effectively open and close valve 58 at high speed even though the acceleration and deceleration of the valve body are kept low for structural reasons. The damping action of the shroud on the valve head can be augmented by itting piston S1 relatively closely in cylinder 80 and spacing the air connection to the cylinder ,a short distance from theend of the cylinder. This causes a small quantity of air to be trapped behind the piston 81 at the end of its movement which air can act as a cushion for the valve body 58.

Air into the bounce rear spaces 30 starts the pistons on their first outward stroke. The vent valves 72 being open, the air in the bounce chambers 28 remains at substantially atmospheric pressure until ports 71 controlled by vent valves 72 are covered by the pistons 24 at which time the air pressure in the bounce chambers begins to rise. The increase in the pressure in the bounce chambers operates through a check valve 100 and line t 101 to the front face of the pneumatically actuated latches 77 causing the latches to be withdrawn and permitting the vent valves 72 to close. It will be seen that the time of closure of valves 72 is not critical and that this closure can take place at any time in the interval when the ports 71 are tirst covered and when these ports are uncovered by the pistons on their next inward stroke.

The pressure of the starting air from bottle 56, after passing valve 58 into the equalizing line 34 to bounce rear spaces 30, exerts its force on the rear faces of the bounce pistons only for the time required to accelerate the pistons to the proper velocity to store therein the kinetic energy required for the remainder of the outward stroke. The starting air may, at this time be vented from the bounce rear spaces 30, and ports 102 controlled by outwardly opening check valves 103 are provided in the walls of the chambers 30 for this purpose. These valves may be of any suitable type, but are preferably reed valves hinged to swing outwardly a predetermined distance from their ports. The pressure in the cylinder will drop rapidly, and should reach atmospheric pressure at about the end of the outward stroke of the pistons, and prior to the time the pistons commence to return.

The operation of the starting system may best be followed from the pressure-stroke diagrams comprising Fig. 2. The top line of diagrams corresponds to the pressures existing in the several chambers on the right-hand side of the engine shown in the drawing. This first diagram represents the pressures existing in the power cylinder and indicates that the pressure is atmospheric in the beginning of the first outward stroke or starting stroke. A suction is created in the power cylinder which reaches a given value depending on the leakage past the rings of the piston and remains at that value until point A is reached at which time one of the pistons uncovers the exhaust ports 14 which immediately relieves the vacuum. 1n the power cylinder. The power cylinder then maintains a substantially atmospheric pressure until the completion of the outward starting stroke. The second diagram indicates the conditions existing 1n the chamber at the rear of the compressor piston indicated at 22. This chamber begins its outward stroke at atmospheric pressure and draws a gradually increasing vacuum during the entire outward stroke so that the pressure declines on a substantially logarithmic curve.

The pressure in the compressor front space 20 is next indicated, and it will be seen that this chamber shows a gradual increase in pressure due to the movement of the compressor piston in a direction tending to decrease the size of the space in which the air is disposed, reaching some predetermined value above atmospheric pressure at the end of the outward starting stroke. The value reached at the end of the stroke is somewhat above atmospheric pressure and there is some flow from the compressor cylinder 20 into the scavenging header 32 and into the power cylinder. It is found that the power cylinder has an appreciable pressure at the conclusion of the first outward stroke, due largely to the inability of the air to transfer instantaneously to the cylinder 10 and out the exhaust ports 14.

The bounce rear chamber is the chamber into which air is injected through equalizer pipe 34 from the starting I' serment bottle 56.4 Thus this chamber commences they out-wardstroke at a very high pressure corresponding tothe pressure of the expanded air from the starting bottle. This pressure is maintained until ports 102A areuncovered by the outwardly traveling bounce pistons; The air' inA this chamber then expands down to atmospheric pressure by exhausting through the check valves lll-3 at aI rate determined by the size of the passages, by the resistance of. the check valves and the configura-tion of the elements which the air must pass in escaping. The energy imparted to the pistons by the expansion indicated and by the stored kinetic energy is suicient to carry outy the entire startingstroke and may be increased or decreased at the selection of the designer. The check Valves 103- operate to maintain atmospheric pressure in the bounce rear spaces at the position selected for the ports during normal operation of the machine with normal variations above and below this pressure as the volume of the spaces changes The pressureV in the bounce chambers is indicated by the last diagramy in the upper line and it will be seen thattthe air in these chambers stays at substantially atmospheric pressure until such time as the ports 71 are covered by the bounce piston in its outward stroke. Thereafter, the pressure in the now-closed bounce spaces rises rapidly. Valves 72 are open during the outwardA stroke of. the bounce piston and are closed by the pressure increase in the bounce chambers 2b, air being displaced through` check valve lll@ and line 101 to act on the front face of piston 78 and withdrawing the latch bar 77 from beneaththe shoulder on the stern of valve 72. Thereafter the valves 72 remain closed during normalrunning. There is ample time for valves 72 to close.

The inward compression stroke which is brought about by the outward stroke above described is the result largely of the energy stored in bounce chambers 28 and may be followed from the second line of diagrams which comprise Fig. 2.

The energy in the bounce chamber 28 expands down from the peak reached at the outermost position of the pistons to a pressure less than atmospheric when the pistons have co-mpleted their inward stroke. This expansion is indicated by the curved graph line at the lower right of Fig. 2. A small amount of energy is expanded in the bounce rear space 30 as indicated, this chamber maintaining atmospheric pressure for most of the inward travel but rising at the inner end of the stroke when ports at 102 are covered by the bounce piston.

A slight contribution of energy from the compressor cylinder 2li results from the re-expansion of air trapped in the end of this cylinder at the end of the rst outer r stroke and returned to the cycle on the rst inward stroke. Thereafter, the chamber 2i) is at somewhat less than atmospheric pressure since air is entering the compressor cylinder through its inlet valves designated 23 in Fig. 1.

The compressor rear operates to return energy to the cycle since the vacuum that has existed in this space at the end of the outward starting stroke is relieved and the chamber comes up to slightly more than atmospheric pressure at the end of the stroke. These chambers may conveniently be vented by an outwardly opening check valve 31 in the equalizing line 33 which connects them.

As above noted the power cylinder commences the rst compression stroke with a positive pressure, in the order of 2.5 lbs., existing therein by reason of the inertia of the air column supplied during the starting stroke. This pressure is increased after the exhaust and scavenging ports are closed on the usual compression curve and reaches a peak when the pistons are at their closest inner position. Substantially all of the energy that was stored in the bounce chambers 23 is expended in increasing the pressure in the power cylinder and the pressure therein reaches a sufficient value to cause compression ignition of fuel injected into the cylinders if the engine is operated on a diesel cycle or to compress a charge of gas for spark ignition if the engine is operated on gas on an Otto cycle.

A. fuel injector F has` been diagrammatically indicated Asabove noted, valves 72.are.closed, at any time during.

the interval when: the ports 71V are closed by the bounce pistons-moving outwardly on. the startingstro-ke and'w-hen these same.` ports areV uncovered by the bounce pistons moving inwardly onx the compression stroke. There is thus no critical time when. the valves are required to` be closed since this interval in the cycle is relatively long.

After the enginehas completedI its first inward compression stroke asindicated in Fig.` 2 all of the cylinders will be some increase in. pressure in the' compressor cyl inder 20 when the engine is operating under load since the engine exhausts at well above atmospheric pressure,

dependingonthe load to which itis subjected, and the compression pressure. in thechambers 2li must be greater than the exhaust pressure fromy the power cylinder for proper scavenging; This effect is, of course, compensated'y for by the bounce governorr operating in a known manner` An alternatey form ofcontrol valve for introducing a predetermined and limited quantity of air from `a storage bottle tol the equalizer pipe 34 and thus into the bounce rear chambers isshown in Fig. 5. This valve operates on the principle that relatively unrestricted communication is desired: 'between the storage bo-ttle and the 'equalizer' pipe 34 for a. limitedk period of time, which period can be increased 4or decreased depending, on the velocity imparted to a control element, and the volume of starting air will be directly related to the time dur ing which the storage bottleA is allowed to communicate with the conduit that passes air to the engine. ln the construction shown, the valve comprises a casing 13G closed at one ,end by a head 132 which hasy a central `guiding boss 134 for operating. stem 136 to which a control piston4 138 is connected. Appropriate packing isprovided for stem 136 in boss 134 to prevent the Ileakage of high pressure starting. air. A cylinder liner 142 is disposed within body 130 and has a plurality of large .and relatively unrestricted ports 144 intermediate its length. The interior `of the cylinder formed by liner 142 is in open and unrestricted communication with the air storage bottlef indicated diagrammatically at S6. Piston 138 has a relatively long skirt or outer surface and is provided with a series `of holes 146 in its periphery. The piston skirt is supported by a series of spaced webs 148 which connect the periphery of the piston to the actuating rod 136. The piston tits sufficiently tightly in cylinder 142 that so long as the holes 146 are 4out of registry with ports 144 no air passes into the ports into the equalizer pipe 34. However, when .ports 146 are brought into coincidence with the peripheral series of ports 144 air passes freely from the interior of the cylinder through holes 146, ports 144 and into equalizer pipe 34.

Any suitable means may be used to reciprocate the piston 138 and thus bring its peripheral holes into registry with the ports. As diagrammatically indicated in Fig. 5 the actuator preferably takes the form of a small pneumatic cylinder 150 in which a piston 152 is mounted and attached to a pist-on rod 154 which is detachably connected by any suitable device to piston rod 136. Cy1- inder 150 may be made double acting, that is air may be introduced into either end and controlled exhaust provided 4at the opposite end thus furnishing very close governing of the .speed of Imovement of the actuating piston. The air supply and discharge .pipes are indicated at 156 and 158.

As piston 138 is moved longitudinally, Iits ports 146 pa-ss over ports 144 in the cylinder wall, and during the time required for this passage the source of air pressure, whether it be storage bottle 56 or its equivalent, is in direct communication with equalizer pipe 34 and ythus with the chambers in the engine which receive the starting air. As the interval is made longer or shorter by slowing down or speeding up the rate of travel of piston 138 the quantity of starting air can be varied. Any suitable automatic or manual valve arrangement may be used to control the supply to pipes 156 and 158 for this purpose.

lIt will be appreciated that the invention has been diagrammatically indicated in the drawing and no attempt has been made to indicate the proper relative size of the ports or their mechanical construction since, for the most part, the valves are conventional units except for the vent Valve 72 and its associated parts, the quick opening valve 58 and its `operator and the air metering valve formed by piston 138. These have, therefore, been shown in more detail for a more complete understanding of the invention.

What we claim is:

1. A starting means for rapidly stabilizing a free piston engine having a power cylinder, a compressor cylinder and a bounce cylinder, connected power, compressor and bounce pistons in said cylinders, the piston in said bounce cylinder dividing said cylinder into front and rear chambers, said starting means comprising a source of air under pressure, means to connect said source of air to o-ne of said cylinders to charge said cylinder and to position said pistons near the inner end of their stroke, means to trap air at predetermined pressure n the front chamber of said bounce cylinder, valve means to vent said charged cylinder operable after the pistons have been positioned, means to introduce starting air at high pressure and in predetermined volume into one of said cylinders and against the rear face of that one of said pistons in said one cylinder to drive said connecte-d pistons outwardly .against air in said bounce cyl-inder, and means to close said vent valve means operable during sai-d outward stroke.

2. A starting means in accordance with claim 1 in which said valve means to vent said charged cylinder comprises a plurality of valves in a peripheral series in the wall of the cylinder short of the end thereof, and said means to close said vent valves is actuated in the interval between the time when the adjacent one of said connected pistons .passes said valves in a covering and an uncovering direction.

3. A starting means in accordance with claim 2 in which said means to close said vent valves are actuated by air from said bounce cylinder, said air 'being com` pressed to operating pressure by outward movement of said connected pistons.

4. A starting means in accordance with claim 1, and means -to vent the cylinder into which starting air is introduced.

5. A starting means in accordance with claim 4 in which said vent means comprises piston controlled ports in the wall of said cylinder into which starting airis introduced.

6. A starting means in accordance with claim 5, and outwardly opening check valves associated with said ports, .whereby the pressure in said cylinder is reduced to atmospheric pressure at or prior to the end of said outward stroke and maintained substantially at said pressure thereafter.

7. A starting means for rapidly stabilizing a free piston engine having a power cylinder, a compressor cylinder and a bounce cylinder, connected power, compressor and bounce pistons in said cylinders, the piston in said bounce cylinder dividing said cylinder into front and rear chambers, and the piston in said compressor cylinder dividing said compressor cylinder into front and rear chambers, said starting means comprising a source of air under pressure, means to position said pistons near the inner end of their stroke with the power piston at substantially the position corresponding to maximum compression, means to trap air at predetermined pressure in the front chamber of said -bounce cylinders when said pistons are so positioned, Iand means to introduce starting air from said source at high pressure and in predetermined Volume into one of said cylinders and against the rear face of that one of said pistons disposed in said one cylinder to -drive said connected pistons outwardly against said air trapped in said bounce cylinder, whereby the energy stored in said trapped air at the end of said outward stroke causes a substantially normal return `stroke of said pistons to the inner position.

References Cited in the le of this patent UNITED STATES PATENTS 2,215,326 Ianicke Sept. 17, 1940 2,423,720 Mllejans et al. July 8, 1947 2,434,778 Welsh Ian. 20, 1948 2,434,877 welsh Jan. 20, 1948 2,439,482 Meitzler Apr. 13, 1948 2,600,251 Lewis et al June 10, 1952

Images