US2583115A - Control for free piston engines - Google Patents

Description

CONTROL FOR FREE PISTON ENGINES Filed May 24, 1950 INVENTOR. l/V/Wa/"d A. Mara/n H TTOPNEYS Patented Jan. 22, 1952 UNITED STATES PATENT OFFICE =-2,-583,115 CONTROL FOR FREE ris'roN'ENemr's Willard A. Morai'n, Hamilton, Ohio, assignor, by

mesne assignments, to Baldwin-Lima-Hamil- 'ton Corporatioma corporation=of Pennsylvania 'KpplicationMayM, lssofseriarno.163,974

"4 Claims. (01. 123-46) This invention relates to free piston internal combustion engines and is particularly directed 'to a siinplified meohanism -foreontrolling the return-'strokeof the pistonsin such aneng'ine.

I n the operation of free pistonengines, some means inust be provided to return the pistons to the'pro'per position'within the engine cylinder'for oo'n'iiii ess'ion or the change' of ai r therein. Where -the engine is used on'a p'art of'an air compressor operating at constant load, the re-expansion eny of theair in the compressor may be -utilizecl to return the pistons. However, in the case of the engine being used as a power gas generator and operating at variableload, it is necessary to resort to the useof an additional cylinder or chamber wherein the proper .piston restoringenergy can be developed. Such a, chamber is known asa bounce chamber, and by-adding air to or venting this chamber it is possible to govern "the inward piston stroke within relatively close limits.

It is known in the art toaccomplish control of the bounce chamber energy in various ways. 'See, for example, the patent to -Lewis;2,4=3 5,970. The present invention is primarily directed to a simplified control structure in which the bounce chamber energy is related to theloadon the en- :gine, the latter being reflected in "a change in exhaust pressure. I

I The primary object of the invention ie to provide a control device of the above character whiehissimple-andefiicient in operation and which is not likely to get out of adjustmenta'fte'r long continued use. v

Another object of 'the invention is to provide a control for a Spowergas generator that is operated in conjunction with a turbine of hired noz- 'zle area, the control being arranged to corr late gas generator bounce "pressure a'n'd 'eihaus't to frfai'titai'n proper stroke length in the gas "gen- "er ator. g V g g I other objects'and advantages or the invention will "become apparent from the following specification, reference being had to the accom an ing drawings in'which: f

Fig. 1 is"a diagrammaticvi-ewj aruy i'nseoti on, of a free piston engine embodying the present "contra device; I

v Fig. 2 is a'central'verticalsectional view somewhat diagrammatic, of 'a suitable control deviceenib'odying' the invention and Fig. 3 is "a fragmentary sectional'view of a modmention introducing additional 'CO'ntlol ressure.

feliing to the erawings, the present iriVen- "flail is shown in connection "with 2. ires piston '2 'power gas generatordesignated generally =1 0, "h'avi'ri'g'a't 'e'a'chenda bounce chamber H connected b'y-an equalizing line 12. The-gasg-e'nerajtor includes the usual integral multiple pistons fitt'ing in power cylinders M, compressor cylinders l-il and the bounce cylinders or chambers H. The compressor cylinder 16 is also utilized as a reverse bounce chamber H in a manner set forth in the above identified Lewis patent. it will be appr'e ciated that, if the *engine is to operate broompres'sion ignition the power pistons must reach an inward pointsuch that the air'betweenthe'm is at the proper temperature and pressure "to ignite "an injected fuel charge, but must not approach each other'too closely, thereby restricting the volume into which the fuel may be injected or 'raisingthe temperature and pressure of the air charge beyond practical limits. Excessive "pressure in the bounce chambers will also tend to stall the engine by restricting the'length of the outward strokes of the piston's'and preventing proper scavenging of the power cylinder. It is therefore, important that the energy available in the bounce chambers for returning the pistons be maintained at the proper level'required for a given load condition. Further, it is not desirable that the devices intendedto control the piston restoring energy be responsive to each minute "change in stroke length, since such devices will exhibit a tendency to hunt abovea'nd below the proper 'ener y level. It is *sufiicient that pro"- nou'n'ced trends toward changes in stroke length 'be followed, 'so that "the present invention in'tr'oducesfoscillation clamping means in the control circuit.

"The present invention comprises regulating valvemeans constructed and arranged to 've'n'to'r add air to the bounce chambers as the engine exhaustpressure decreaseso'r increases. Broadly, control of the stroke length of'a free piston engine by regulating the quantity "of air in bounce chamber is known in "the are-but prior devices have relied 'on complicated equipment to balance pressures in various engine chambers, and have proved di'fiicult'to adjust'an'd maintain.

The valve means of the present invention'is'im dicated somewhat diagrammatically in 'Fig. 2 and comprises a body 20 having an upper connection 22 to the engine-exhaustline/aconnection 24- to a source of highpressur'e air-such as a 'storage bottle -25, and twoco'nnection's, 2 8'and 30, 'to the bounce c linder equalizing line 1 2.

Connection 28 is deliberately restricted ''so that small fluctuations do not aifec't the control ele' r'rieiits. The damped" con'n'ection thus provided permits the control to respond to variations in the mean pressure in the bounce chamber equalizing line and not to the maximum and minimum pressures therein. No attempt has been made to indicate the manner in which the valve body is assembled.

A cylinder 32 at the top of the valve body 20 communicates directly with connection 22, and a piston 34, working in this cylinder is thus subjected to the control pressure which may be either exhaust pressure, or the sum of exhaust and reverse bounce pressures, at all times. Piston 34 is biased inwardly of its cylinder by a regulating spring 36 interposed between an extension 31 of the piston and a head 38 of a movable valve seat 40. Head 38 is attached at the center of a diaphragm 42, the outer edge of which is sealed in the body 26.

The movable valve seat 40, of which head 38 forms the upper end, is guided for linear movement in a bore 44 of the body 20, by a packed piston-like flange 46 and is provided with a central passage 48 which opens into a vented chamber 50 above the diaphragm. A valve 52 normally closes passage 46 by sealing engagement with the lower end of the movable valve seat 48.

Valve 52 is preferably provided with a guiding stem 54 which cooperates with a suitably formed part of the body 29 to assure linear movement to the valve. The valve is biased upwardly by a spring 56 interposed between a plate valve 58 and a stationary body part Bil, the plate valve engaging a stem extension 62 of the valve 52. Valve 52 is limited in its upward movement by a series of projections 64 extending into the bore :3

44 in the path of movement of the valve.

A chamber 66 around valve 52 communicates with damped connection 28 to the direct bounce cylinder equalizing line 12 by means of passages 68 and 12. Thus, when the valve is opened by a separating movement ofseat and the head of the valve, chamber 66 and hence the bounce cylinders will be vented through passage 48 and chamber 50.

Passage l2 in the body 20 opens into a chamber '14 below the diaphragm 42 so that the underside of the diaphragm is subjected to the existing mean pressure in the bounce cylinder equalizing line and is urged upwardly thereby. This force is opposed by the force exerted by the control pressure acting on piston 34 and transmitted through spring 36 and head 38. Proper selection of the relative areas of piston 34 and diaphragm 42 makes it possible to provide a control suitable for a wide range of systems, primary dependence being on the operating characteristics of the associated turbine or other gas consumer.

Suitable means are also provided to add air to the bounce chambers by opening communication between high pressure air connection 24 and bounce cylinder charging line 30. This connection is controlled directly by a lower valve 80 disposed in a chamber 82 in the body 20, the chamber 82 being constantly connected to the source of high pressure air.

Lower valve Bil is carried by a stem 84 formed on the lower side of a piston 86 working in a cylinder 88 in the valve body. The stem 84 has a central passage 90 extending through it which communicates with the cylinder 88 above the piston 86, but the passage is restricted at its upper end, as by an orifice 92. The lower face of piston 86 is subject to the pressure of chamber 82 and the charging air by reason of a direct- 1y connecting passage 94. Thus, the upper and lower faces of the piston are under the same pressure when conditions are'stable, but if cylinder 88 were suddenly vented and pressure in the upper piston face relieved, it will be seen that the pressure on the lower piston face would predominate until air passing through the restricted end of passage 90 could again fill the cylinder to the initial pressure. Under certain conditions of unbalanced pressure, then, piston 84 moves upwardly in its cylinder and charging valve 80 is opened. A spring 96 biases the piston downwardly to close valve 80 when the pressures again balance on the upper and lower faces of piston 86.

Cylinder 88 is controlled at its upper end by plate valve 58, and is vented, when this valve is opened, through passage 10, into the bounce air control circuit. The cylinder could be vented to atmosphere, but it is preferred to conserve the available air.

In operation, assuming the power gas generator to be running at normal stroke and frequency properly to supply gas to an associated turbine T, the control device above described will come into operation only upon a deviation from the proper operating conditions. If the control pressure rises for any reason the pressure in top cylinder 32 rises and piston 34 moves outwardly against the tension of regulating spring 36. Diaphragm 42 is thus lowered and the movable valve seat 40 and its associated valve 52 are likewise lowered so that plate valve 58 is opened while valve 52 remains closed. This condition would also be realized if for any reason the bounce spaces become undercharged and limited the pressure under diaphragm 42.

When plate valve 58 leaves its seat, air in lower cylinder 88, being under full supply pressure, rushes into the control system through passages 10 and I2. The forces On the two faces of lower piston 86 are thus unbalanced, there being a greater pressure on the lower face than on the upper. The piston is thus moved upwardly in its cylinder and the lower valve is moved off its seat against the action of spring 96. High pressure air from the storage bottle 26 thus enters the bounce chamber equalizing line and the bounce cylinders themselves. Thus more energy becomes available to force the engine pistons towards each other on the compression stroke, compensating for the increased exhaust pressure or scavenging air.

As the bounce pressure is raised to the point where the desired balance is again reached, the pressure on the under side of diaphragm 42 forces the diaphragm and its associated movable valve seat 40 upwardly allowing spring 55 to again seat plate valve 58 and prevent further escape of air from lower cylinder 88. As air from the high pressure source continues to pass through passage and the restriction 92, the pressure above and below lower piston 86 soon becomes balanced and spring 96 can move the piston and valve 80 downwardly to seat the latter and close communication to charging line 30.

If for any reason the exhaust pressure is reduced from the normal operating condition, or if for any reason the bounce cylinders become overcharged, diaphragm 42 is moved upwardly to compress spring 38 due to the now excessive pressure on its under face. The movable valve seat 40 is thus moved away from valve 52 since the valve can follow the seat only to the limit determined by the projections 54 in the bore 44. Since passage 48 is now open, venting into chamber 50 and to atmosphere can take place from the bounce cylinder equalizing line through damped connection 28, passages 72, and 68. As the pressures are again balanced, diaphragm 42 will return to its normal position and valve 52 will again close.

It will thus be seen that the bounce energy will be adjusted in accordance with changes in load as reflected in a variation of the exhaust pres- L sure and, at any given load condition, will be corrected for under-charge or over-charge resulting from any other cause such as leakage past the pistons, etc.

In the modification shown in Fig. 3, additional control pressure is introduced by extending a line I00 from a reverse bounce equalizing line I02 connecting the two reverse bounce chambers ll. The line I00 is connected to the top cylinder 32 which is now broken down into two axially concentric cylinders 32, 32a. Cylinder 32 is connected to the exhaust line through conduit 22 while cylinder 32a is connected by line I00 to the reverse bounce equalizing line. Piston 34 is now shown as a stepped piston comprising a lower portion 34a operating in cylinder 32a and an upper portion 34 operating in cylinder 32. The composite piston is thus subjected to the sum of the reverse bounce pressure and the exhaust pressure and a significant variation in either will cause operation of the elements heretofore described to increase or decrease the bounce pressure of the engine. If the reverse bounce pressure is increased the frequency of operation of the engine is likewise increased in accordance with the disclosure of Lewis Patent 2,435,970. An increase in reverse bounce pressure causes an increase in the direct bounce pressure but operation of the present engine with the over-all eiTect that the engine runs at a higher frequency and greater load and supplies considerably more gas to the turbine or other consumer.

The addition of control by means of the reverse bounce pressure is also advantageous in the event that the system includes more than a single free piston power gas generator since control of the frequency of operation is more readily obtainable by variation in the reverse bounce pressure than by any other means so that more accurate synchronism can be maintained between a multiplicity of gas generators.

While the invention has been disclosed in connection with a particular form and disposition oi! the parts numerous modifications and changes may be made without departing from the scope of the appended claims.

What I claim is:

1. In an apparatus for controlling a free piston engine having a chamber in which air is compressed by a movement of the free pistons and subsequently utilized to return energy to the system by re-expansion, the improvement comprising an element subject on one side to the average pressure in said chamber and on the opposite side to a second pressure which reflects an op-- erating characteristic of the free piston engine, a valve seat attached to and movable with said element, a valve normally closed on said valve seat and disposed to follow the movements thereof, means to limit the movement of said valve in one direction to eifect a separation of said valve and seat upon continued movement of said seat in one direction, a second valve opened by movement of said first valve in the opposite direction, and means operated in response to an opening of said second valve to admit air to said chamber.

2. The improvement defined in claim 1 in which said last means includes a cylinder in communication with a source of high pressure air, and a piston controlled valve normally closing communication between said cylinder and said engine chamber, said piston controlled valve normally closing communication between said cylinder and said engine chamber, said piston controlled valve being opened when said second valve is opened.

3. The improvement defined in claim 1 in which said element comprises a diaphragm urged in one direction by pressure in said engine chamber and in the opposite direction by a pressure corresponding to engine exhaust pressure.

4. The improvement defined in claim 1 in which said element comprises a diaphragm urged in one direction by pressure in said engine chamber and in the opposite direction by a pressure corresponding to the sum of engine exhaust pressure and pressure in an engine reverse bounce cylinder.

WILLARD A. MORAIN.

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

UNITED STATES PATENTS Number Name Date 2,053,720 Huck Sept. 8, 1936 2,077,802 Martin Apr. 20, 1937 2,352,891 Graves July 4, 1944 2,434,280 Morain Jan. 13, 1948 2,467,513 Welsh Apr. 19, 1949

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