US2355924A - Free piston machine - Google Patents

Description

R. PATERAS PEscARA 2,355,924

FREE PI STON MACHINE Aug. 15, 1944.

Filed Nov. 25, 1941 2 Sheets-Sheet 1 M20 b q I I P pm 5 Inventar y iiorneys.

Aug. 15, 1944- R. PATERAS PESCARA FREE PISTON MACHINE Filed Nov. 25, 1941 2 Sheets-Sheet 2 E401. PA T5645 wgcz m gggg Patented Aug. 15, 1944 or of one-tenth to Societe dEtudes et de Participations, Eau, 'Gaz, Electricite, Energie S. A., Geneva, Switzerland Application November 25, 1941, Serial No. 420,433 In France September 3, 1941 9 Claims.

The present invention relates to free piston machines, that is to say machines for the, production of gas under pressure including one or several reciprocating elements the length of stroke of which can vary freely within certain limits,

contrary to what takes place, for instance, in machines including connecting rods and crankshafts.

The invention is more especially, although not exclusively, concerned, among these machines, with those in which the discharge pressure is variable, and in particular those in which, furthermore, at least a portion of the compression work takes place during the return stroke of the reciprocating element's. And it is still more espe- 'cially concerned with the auto-generators of this kind, the expression auto-generator" designating a free piston machine in which at least a portion of the airfed by the compressor part ofthe machine serves the scavenging and the feed of the motor part of the same, the mixture of burnt gases and excess of scavenging air being sent to an expansion receiver, such for instance as a turbine.

The object ofthe present invention is to provide a machine of this kind which is better adapted to meet the requirements of practice than 7 those used for the same purpose up to the present time.

' According to an essential feature of the present invention, the machine is provided with a pneumatic energy accumulator capable of giving back tothe reciprocating element or elements, during the return stroke thereof, energy stored up during the outward strokes, the energy brought into play in the pneumatic accumulator or accumulators being automatically varied by means of a source of gas under pressure controlled by a device operating as a function of at least one characteristic of operation of the machine, and, furthermore, this control device is influenced, on the one hand, by variations of the pressure existing in the accumulator or accumulators for i a given position of thereciprocating element or elements and, on the other hand, by variations of the length of the stroke of said element or.elements.

.According to another feature of the invention,

the control device, or the means for regulating it, is arranged in such manner that the law ac-- cording to which this device operates in response to variations of the discharge pressure, or of a pressure varying in accordance with this discharge pressure, is a non-linear law.

According to still another feature of "the invention, means are provided for varying the energy which produces the return of the reciprocating element or elements in accordance with the altitude at which the machine is working.

.Other featuresof the present invention will result from the following detailed description 0 some specific embodiments thereof.

Preferred embodiments of the present invention will be hereinafter described, with reference to the accompanying drawings, given merely by way of example, and in which: f

Fig; 1 is a diagrammatical view of a free piston machinemade according to an embodiment of the invention;

Figs. 2, 3 and 4 are diagrams for illustrating the operation of a machine according to the invention;

Fig. 5 is a view, similar to Fig. 1, of a free piston machine made according to a second embodiment of the invention;

Fig. 6 is a diagram for facilitating a good 1111- i derstanding of the operation of the machine according to Fig. 5.

In the following description, it will be supposed that the machine that is being considered is of the free piston type and constitutes a variable discharge pressure auto-generator in which at least a portion of the compression work is produced during the return strokes.

Concerning the general construction of the machine, itis of any suitable type and for instance it includes the following parts:

a. A cylinder I, constituting the motor cylinder and in which are mounted two pistons 2 and 2 adapted to cooperate, respectively, ,when they are close to the outer ends of their strokes, with an inlet port 3 and an outlet port 4;

b. Two compressor pistons F5 and 5 radially slidable in cylinders 6 and 6 respectively, are

rigid with the motor pistons, and the inner faces of said compressor pistons ensure, owing to the provision of inlet valves I and outlet valves 8, the ieedof air under pressure to a fiuidtight case 9 which surrounds the motor cylinder l;

c. Between these motor pistons, there is provided a synchronizing mechanism, of the ty shown in my Patent Number 2,075,133, and consists, for instance, of a system of levers oscillating about a fixed axis andhaving their opposed ends interrelated, by means of connecting rods, with the two reciprocating elements moving in opposed directions;

d. Accumulators are provided'for accumulating, during the outward strokes of the pistons, an

amount of energy to be given back to said pistons during the compression strokes, which are the return or inward strokes thereof, and these energy accumulators are constituted, for instance, by causing the outer faces of pistons 5 and 5 to cooperate with the end portions of cylinders 6 and 8 These accumulators are designated, in the following description, by letters A and A, respectively;

e. In order to obtain, as it will be hereinafter more fully described, that the energy brought into play in accumulators A and A may vary in accordance with the discharge pressure of the machine, I provide an intermittent communication between said accumulators and a source of air under pressure or a discharge chamber, ac-

cording as the amount of air present in the accumulators is too great or too small.

In particular, and as it will be hereinafter supposed, I utilize, as source of air under pressure and also as discharge chamber, a space in which the existing pressure is a characteristic of the machine. For instance, I make use of casing 9, in which there is a pressure substantially equal to the discharge pressure (in the following description, I will designate, for simplification purposes, the pressure in said casing 9 by the expression discharge pressure).

In this case, I interpose, between pneumatic accumulators A and A and casing 9,. a distributing system such that, on the one hand, when the working conditions are stable, it maintains these accumulators separated from said casing, and, on the other hand, when there is a variation of the working conditions, said system enables air contained in casing 9 to pass into the accumulators,

,or inversely.

This distributing system is constituted by a kind of slide valve l0, mounted in a reservoir II which is constantly in communication with casing 9, this slide valve including two chambers or compartments I9 and M respectively provided with ports I2 and 12 adapted, when either of them is brought opposite a fixed port l3, to connect the corresponding compartment with conduits I 4 M leading to accumulators A and A orifice l3 being closed when slide-valve I is in neutral position (position shown by Fig. l).

I provide, in the walls of compartments I0 and i0, respectively, check valves I5 which permit only of air passing from compartment I 0 into' reservoir II and casing 9 and check valves I5 which permit onl of air passing from reservoir H and casing 9 into chamber I0 I provide means for coupling this distributing device to the movable element, or instance the piston, of a system including cylinder l6 and piston l1, one of the faces of this piston being subjected to the discharge pressure, through a conduit l8, while its other-face is subjected to the action of a spring IS. The whole is arranged in such manner that an increase of the discharge pressure produces a displacement of the slide valve such that orifice I2 comes opposite orifice l3, and that, inversely, a reduction of this pressure causes orifice It to come opposite said orifice l3. 7

Concerning the correcting or controlling means which are to ensure the return of distributor l0 into neutral position, after each variation of the working conditions, said correcting means are operated, according to a feature of the invention, both in accordance with the pressure existing, for a given position of the piston, in the pneumatic accumulator or accumulators and in accordance with the length of thepiston stroke. For this purpose, preferably, I make use of the mean pressure in the accumulator or accumulators, or of a pressure the value of which depends upon said mean pressure, this last mentioned pressure being also variable in accordance with the length of stroke of the accumulator piston, as well as in accordance with the initial accumulator pressure.

In the embodiment of the invention illustrated by Fig. 1, I utilize, as controlling factor, the pressure 10 existing in a space 20 which is in corn munication with the inside of accumulator A through a calibrated aperture 2|, preferably adjustable by means of a needle valve 22.

Preferably, I make use of the pressure existing in space 20 for adjusting the tension of spring l9 which brings back distributing member ID into position, Consequently, this pressure is caused to act on a piston 23 which is acted upon by a spring 24. This piston acts, through a transmission the detail of which will be hereinafter more fully described, upon a push-piece 25 against which spring I9 is bearing. The whole is arranged in such manner that an increase of pressure in space 20 corresponds to an increase of the tension of spring l9.

An auto-generator made as above described will work in the following manner:

Supposing that the discharge pressure passes from a value p for which distributor ID was in neutral position, to a higher value 9 piston I1 is displaced against the action of spring [9 and orifice I2 is brought opposite orifice IE. Air under pressure present in casing 9 can then, during the portion of the stroke for which the discharge pressure is higher than the pressure in the accumulators, flow past check valves l5 and come, through conduits hi and it into said accumulators, where it increases the mass of air present therein. 1 Ii, on the contrary, the discharge pressure had decreased, distributing member [0 would have been displaced in the opposite direction and orifice l2 would come opposite orifice I3, thus permitting a portion of the air present in the accumulators to return into casing 9 through check valves I5 during the portions of the piston strokes for which the pressure in said accumulators is higher than the pressure in said casing.

The return of distributing member ID into its neutral position, in which orifice l3 cannot communicate either with I2 and with I2 is obtained by the variation of the pressure conditions in the accumulators, which variation produces a modification of the pressure existing in space '20, and, consequently, a variation of the tension of spring l9.

Supposing that the communication between accumulator A and space 20 is obtained only through one or several calibrated orifices such as 21, the pressure existing in space 20 is substantially equalto the mean pressure in accumulator A The diagram of Fig. 2 shows how the pressure conditions in the accumulators are influenced by the utilization, as factor for controlling the work- In this diagram, solid line a represents for a given stable state of conditions, corresponding to a given pressure of discharge of the machine, the variation of the pressure in the accumulator when the stroke length l of the reciprocating element is relatively short, the mean pressure which tcorresponds to this curve of variation being equal If, at a given time, the length of stroke of the reciprocating system passes from value I to a higher value L, without any variation of the discharge pressure of the machine, this increase first causes the mean pressure to pass to a higher value. This increased mean pressure, acting on piston 23, destroys the state of equilibrium of system l0l1 and causes distributing member ID to move in such manner that a portion of the air present in the accumulators passes into casing 9 through check valves I5 The increase of the device in the same manner discharge'pressure of the machine would have done.

The equilibrium will be restored and, consequently, device ill-J1 will return into its neutral position when, for longer strokes of the pistons, the pressure variation in the accumulator will correspond to the dotted line b of Fig. 2, the mean pressure which corresponds to this curve being again equal to pm.

Although the machine can work satisfactorily with the arrangement just above described, it seems advantageous to make use of the following supplementary ieatures,'which may eventually be used separately.

According to one of these supplementary features, the control device l--i| is arranged in such manner as to work, in response to 'variations of the discharge pressure existing in casing 9, according to a non-linear law.

For this purpose, according to the embodiment illustrated by Fig. l, I act on the transmission interposed between piston 23 and push-piece 25.

In this embodiment of the invention, this transmission is provided with a bell-crank lever 26 adapted to pivot about anaxis 21, one of the ends of said lever being coupled at 28 with piston 23, while the other end 25 thereof acts on push- -piece 25. r

If this lever were utilized alone, the control device would work in accordance with a law corresponding to the straight line 0 of Fig. 3 of the drawings, in which the abscissas represent the discharge pressure pd of the auto-generator, while the ordinates represent the pressures pm in the accumulator.

In order to obtain a non-linear characteristic curve, for instance a curve in the form of a broken line, I proceed as follows:

I provide, above the end 29 of lever 28, a push piece 30, rigid with a piston 3i which is subjected, on one side thereof, to the action of a spring 32, and, on the other side, to the pressure existing in casing 9, this pressure being fed through a conduit 33 to the upper part of a cylinder 34 inside which-piston 3| is movable. As long as the dischar e pressure of the autoegenerator has not reached a value equal to spring 32 keeps push piece 30 away from the end 29 of lever 26, but once the discharge pressure has been reached, the push-piece bears against said end of lever 26 and this with a force which is the greater as the discharge pressure is higher.

Consequently, when the discharge pressure has a value lower than the operation of the control device corresponds to line 0, but once this value of the discharged pressure has been exceeded, the working of the control device corresponds to line 0 the inclination of which is smaller than that of line c.

When the auto-generator is mounted on a vehicle, for instance an aircraft, intended to work at different altitudes, it is useful, according to another feature of the present invention, to provide a supplementary control element which influences control device i0l'l in accordance with the value of the altitude.

In order to obtain this result, I have, in the embodiment shown by Fig. 1, provided a barometric box system 35 adapted to pivot a lever 36 ciprocating elements. Owing to this feature, I

obtain a modification of the law according to which the return energy varies as a function of the length of stroke.

For this purpose, I provide, in order to connect accumulator A and space 20, in addition to cali brated orifice 2i and parallelly thereto, a kind of by-pass 38 controlled by a check valve 38 subjected to the action of a spring 40. According to the direction in which check valve 38 opens, the pressure in space 20 is lower or higher than the mean pressure of the accumulator. In the embodiments of the invention illustrated by Figs. 1 and 5, this check valve is arranged in such manner that it permits a portion of the air under pressure present in space 20 to escape into accumulator A when the pressure in said accumulator is lower than that existing in said space 20, while this check-valve prevents passage of air from accumulator A into space 20 through said by-pass. Consequently, the pressure in this space 20 is lowerthan the mean pressure in accumulator A The action or by-pass 38 results from the diagram of Fig.4. In this diagram the three curves d d, (1 represent the variation of the pressure in the accumulator. The horizontal lines pm thu pin are the mean pressures corresponding respectively to these three curves. Finally, the horizontal lines pr pr pr are the pressures existing in'space 20. These last mentioned pressures are lower than the corresponding mean pressures 17m pin 17m with respective differences equal to Apr, Am, hm, these differences being due to the provision of the by-pass and the check valv interposed between the accumulator and space 20.

If the tension of spring 40 is invariable, the

"value Ap is a function of A F2 Si being the area of calibrated orifice 2i and S: the area of the check valve 39.

In order to determine this value Ap, I may act either on the area of the passage through calibrated orifice 2! by means of a needle valve 22, or on the tension of the spring 40 of check valve 39. This adjustment may be effected automatically in accordance with an operating factor of the machine, the latter including at least one generator of gas under pressure and at least one receiver machine, for instance a turbine.

This factor may advantageously consist in one of the working pressures of the generator.

According to still another feature of my invention, the pressure Dr in space 20 is regulated as a function of the working pressure of the generator in such manner that, under stable working c0nditions,'this pressure is always of the same value. The difference op between the mean pressure in the accumulator and pressure n must therefore increase as a function of the working pressure in such manner that this result is obtained.

"The diagram of Fig. 6 shows, for three differout working pressure conditions of accumulator Ar, corresponding to three different feed pressures of the auto generator:

a. The curves e1, e2, 63 of the pressure in the accumulator as a function of the length of stroke,

for these three working conditions:

b. The horizontal lines giving the mean ,pressures in the accumulator corresponding respectively to these three curves;

c. The horizontal dotted line giving the value oi pressure pr, pm, pm, pr: in space 20, which remains the same for the three working conditions that are being considered, the difference between pm and-p1- being equal to An", while that between pm and Dr is Ap" and that between pm and pr is An .A machine working in accordance with the conditions illustrated by the diagram of Fig. 6 is shown by Fig. 5. V

In this embodiment of my invention, the area of the cross section of calibrated orifice 2| is variedby means of a needle valve H the position of which is variable in accordance with the value of the working pressure or discharge pressure in casing 9.

In order to obtain the desired working ofthis needle valve, this casing is connected, through a casing 42, with a cylinder 43 in which can move,

' section of aperturell remains constant.

The shape and size of the element which varies the cross section through orifice 2|, and the force of spring 44 are chosen in such manner that the differences Ap', Ap" and Ap' that are obtained are those illustrated by Fig. 6. g

The fact that the same regulating pressure pr is maintained in space 20 whenever the working conditions of the machine are stable and irrespective of the value of the mean pressure pm in the accumulator, permits of obtaining an important simplification of the device which controls the value of the pressures in the accumulators. Asa matter of fact, as shown by Fig. 5, the pressure p: existing in space 20 can then be caused to act directly on the piston I? of dis- I f tributing device it), without interposing mechanical means. It suffices to connect space 20, through a conduit 41, with the space 8 inside cylinder IB and above piston l1 and to subject the lower side of said piston to .the action of a spring 49, the portion of cylinder Iii in which this spring is housed being provided with an orifice 50 which connects this portion of the cylinder with the atmosphere.

The device of Fig. will work in the following manner:

Supposing that the discharge pressure of the 7 generator, and therefore the pressure in casing 9, increases, this increase produces a displacement of needle valve ll in the, direction which reduces the section of flow through calibrated orifice 2|. Consequently, the pressure in space drops, which causes distributing member Ill to move in such manner that the orifice it" thereof is brought opposite orifice l3, so as to permit an under pressure present in casing 5 to pass space 20 has returned to its initial value since,

due to the increase of the pressure in casing 9, the'section of flow through orifice 2i is now smaller than precedingly. In view of the fact that the pressure in space 20 has come back to its former value, distributing member i0 has come back into the neutral position shown by Fig. 5, whereby the whole is again ready to operate for a new variation of the working pressure.

Of course, when the working pressure in casing 9 decreases, the operations above described take place in the opposite direction.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efiicient embodiments of the present invention, it should be well understood that I do not wish to be limited thereto as there might be changes made therein without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. A free piston machine of the type described which comprises, in combination, a motor cylinder and a compressor cylinder, at least one reciprocating structure movable in the axial direction of said cylinders, including a motor piston and a compressor piston rigid with each other and adapted to cooperate with said motor cylinder and said compressor cylinder, respectively, a pneumatic accumulator associated with said reciprocating structure for storing up energy during the outstrokes of the pistons and giving back said energy to said structure during the return strokes thereof, a source of gas under pressure, control means, responsive to variations of at least one working -factor or the machine, for producing an interchange of gas between said accumulator and said source when such variations occur, and means responsive both to "said structure, for regulating said control means.

2. A free piston machine of the type described which comprises, in combination, a motor cylinder and a compressor cylinder, at least one reciprocating structure movable in the axial direction of said cylinders, including a motor piston and a compressor piston rigid with each other and adapted to cooperate with said motor cylinder and said compressor cylinder, respectively, a pneumatic accumulator associated with said reciprocating structure for storing up energy during the outstrokes of the pistons and giving back said energy to said structure during the return strokes thereof, a chamber containing gas under pressure, control means responsive to variations of the discharge pressure from said compressor cylinder, for producing an interchange of gas between said accumulator and said chamber when such variations occur, and means responsive both to variations of the pressure existing in said accumulator for a given position or said reciprocating structure and to variations of stroke of the reciprocating movement said structure, for regulating said control means.

3. A free piston machine of the typedescribed, which comprises, in combination, a motor cylinder and a compressor cylinder,v at least one reciprocating structure movable in the axial direction of said cylinders, including a motor piston and a compressor pistonrigid with each other and adapted to cooperate with said motor cylinder and said compressor cylinder, respectively, a pneumatic accumulator associated with said reciprocating structure for storing up energy during the outstrokes of the pistons and giving back said energy to said structure during the return strokes thereof, a casing arranged to receive the compressed gas from said compressor cylinder, control means responsive to variations of the pressure in said casing, for producing an interchange of gas between said casing and said accumulator when such variations occur, and means for returning said control means into neutral position, said return means being responsive both to variations of the pressure existing in said accumulator for a given position of said reciprocating structure and to variations of the stroke of the movement of said structure.

4. A free piston machine of the type described, which comprises, in combination, a motor cylinder and a compressor cylinder, at least one reciprocating structure movable in the axial direction of said cylinders, including a motor piston and a compressor piston rigid with each other and adapted to cooperate: with said motor cylinder and said compressor cylinder, respectively, a pneumatic accumulator associated with said reciprocating structure for storing up energy during the outstrokes of the pistons and giving back said energy to said structure during the return strokes thereof, a casing arranged to receive the compressed gas from said compressor cylinder, control means responsive to variations of the pressure in said casing, for producing an interchange of gas between said casing and said accumulator when such variations occur, and

means for returning said control means into neutral position, said return means being re,- sponsive to variations of the pressure existing in said accumulator for a given position 01' said reciprocating structure, to variations of the stroke of the reciprocating movement 01' said structure, and also to variations of the atmosmospheric pressure. 5. A free piston machine ofthe type described,

which comprises, in combination, a. motor cylinder and a compressor cylinder, at least one reciprocating structure movable in the axial direction of said cylinders, including a motor piston and a compressor piston rigid with eachother and adapted to cooperate with said motor cylinder and said compressor cylinder, respectively, a pneumatic accumulator associated with said reciprocating structure for storing up energy durin the outstrokes of the pistons and giving back said energy to said structure during the return strokes thereof, a casing arranged to receive the compressed gas from said compressor cylinder, control means responsive'to variations of the pressure in said casing for producing an interchange of gas between said casing and said accumulator when such variations occur, and return means for bringing back said control means into neutral position, said return means being adjustable in response to variations of the mean pressure in said accumulator.

6. A free piston machine of the type described, which comprises, in combination, a motor cylinder and a compressor cylinder, at least one reciprocatingstructure movable in the axial direction of said cylinders, including a motor piston and a compressor piston rigid with, each other and adapted to cooperate with said motor cyl inder and said compressor cylinder, respectively,

- a pneumatic accumulator including a piston and a cylinder respectively rigid with the above mentioned pistons and cylinders, adapted to form, during the outstrokes of the reciprocating structure, a compressed gascushion which produces,

the return strokes of the pistons, a casing adapted to receive the compressed gas from said compressor cylinder, control means responsive to variations of the pressure in said casing for interconnecting said casing and said accumulator in one direction or the other according as the pressure in said casing has increased or decreased, a chamber communicating with the inside of said accumulator through a small calibrated orifice, and means for elastically returning said control means into neutral position, said return means being responsive to variations of the pressure in said chamber.

1. A machine according to claim 6 further including a connection between said chamber and the inside of said accumulator adapted to bypass said calibrated orifice, said connection consisting of a conduit, a check valve in said conduit and elastic means for urging said check valve toward the closed position thereof. I

8. A free piston machine of the type described, which comprises, in combination, a motor cylinder and a compressor cylinder, at least one reciprocating structure movable in the axial direction of said cylinder, including a motor piston and a compressor piston rigid with each other and adapted to cooperate with said motor cyl-, inden and said compressor cylinder, respectively, a pneumatic accumulator including a piston and a cylinder respectively rigid with the above mentioned pistons and cylinders, adapted to form, during the outstrokes of the reciprocating structure, a compressed gas cushion which produces the return strokes of the pistons, a casing adapted to receive the compressed gas from said compressor cylinder, control means responsive to variations of the pressure in said casing for interconnecting said casing and said accumulator in one direction or the other according as the pressure in said casing has increased or decreased, a chamber communicating with the inside of said accumulator through a small calibrated orifice, means for returning said control means into neutral position, said return means being responsive to variations of the pressure in said chamber, and means operative by variations of the pressure on said casing for varying the section of flow through said calibrated orifice in accordance with said pressure in the casing.

9. A machine according to claim 8 in which the last mentioned means are adapted to keep the pressure in said chamber at the same value for all stable working conditions.

RAUL PA'I'ERAS PESCARA.

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