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Publication numberUS3347215 A
Publication typeGrant
Publication dateOct 17, 1967
Filing dateApr 8, 1965
Publication numberUS 3347215 A, US 3347215A, US-A-3347215, US3347215 A, US3347215A
InventorsR. P. Pescara
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Free piston engines
US 3347215 A
Abstract  available in
Images(3)
Previous page
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Claims  available in
Description  (OCR text may contain errors)

Oct. 17, 1967 P. PESCARA FREE PISTON ENGINES 5 Sheets-Sheet 1 Filed April 8, 1965 JNVENTOR Rea) Quilter-a5 pescara BY 774%J /Jv, ATTORNEYS Oct. 17, 1967 R. P. PESCARA 3,347,215

FREE PISTON ENGINES Filed April 8, 1965 3 Sheets-Sheet 2 I D j;

INVEN TOR Raul der'ds pescara MMM ATTORNEYS Oct. 17, 1967 P. PESCARA FREE PISTON ENGINES 3 Sheets-Sheet 3 Filed April 8, 1965 QWN iuqu

U f @YW so s QQN INVE/V TOR W7m1 ATTORNEYS Qdbi/ wwmm 3,347,215 Patented Oct. 17, 1967 8 Claims. in. 123-46) The invention relates to free piston engines which may be operated as well as compressors delivering compressed air or as autogenerators delivering a hot mixture of gases under pressure constituted by compressed air and uncompletely expanded combustion gases. The invention includes in particular the so called tandem free piston engines that is to say engines the driving parts of which comprise two motor cylinders and motor pistons operating therein according a two-stroke cycle, said pistons reciprocating in phase opposition in the respective motor cylinders. In other words the pistons in one of said cylinders perform their compression strokes while the pistons in the other cylinder performs their Working strokes.

The object of the invention is to improve such engines and in particular to improve the stability of their operation.

Another object of the invention is to improve the volumetric yield of the compressor cylinders of said engines.

Further objects of the invention in connection more particularly with the tandem free piston engines are to improve their ability to be operated as autogenerators for the supply of gases under variable pressures.

According to the invention and in connection with the tandem free piston engines the pressure of the air to be compresed in the compressor cylinders is controlled at the starting of the compression stroke of the compressor pistons reciprocating in said compressor cylinders.

In connection with free piston engines the compressor cylinders of which are double acting compressors, part of the air compressed in the clearance volume defined in each of the compressor cylinders by the corresponding compressor piston, when the latter reaches one of its dead end centres, is transferred in the compartment of each of said compressor cylinders opposite said clearance volume.

Still according to the invention the pneumatic accumulator of return energy of a free piston engine, in which the fuel injector means provided in the motor cylinder supply the energy for operating the outwards stroke of the motor pistons, comprises a cylinder in which two pistons are imparted opposite reciprocations, said pistons confining a cushion of air which acts as the pneumatic accumulator.

Other objects of the invention will appear as the description of illustrative but not limitative embodiments proceeds in connection with the following drawings in which:

FIG. 1 shows diagrammatically an axial section of a tandem free piston engine according to the invention;

FIGS. 2 and 3 show various embodiments according to the invention of a free piston engine;

FIG. 4 shows diagrams of the working cycle of a compressor piston of a free piston engine according to an embodiment of the invention shown in FIG. 2 or 3, as compared with the diagram of a classical free piston engine.

In FIG. 1 there is shown a tandem free piston autogenerator established according to an embodiment of the invention. The autogenerator is provided with two preferably coaxial motor cylinders a and b, in each of which reciprocate two opposite motor pistons respectively designated at 10, 2a and 1b, 2b.

The motor pistons working in one of said motor cylinders are respectively connected with the pistons reciprocating in the other motor cylinder in a manner such that the pistons operating in one of said cylinders perform their outwards strokes or working strokes, while the pistons operating in the other cylinder perform their in- Wards strokes or compression strokes.

For instance, as shown in FIG. 1, rigid connections are provided, on the one hand, between the exterior pistons 1a and 2b and, on the other hand, between the two interior pistons 2a and 1b. The two exterior pistons 1a and 2b may be connected by rods 3 and 4 whereas the two interior pistons 2a and 1b are cast in a single piece.

The two groups of the pistons 1a, 2a and 2b, 1b are provided with usual means (not represented) for the synchronisation of their strokes.

Advantageously, the supply of the motor cylinders a and b with air under pressure and the exhaust from said motor cylinders of a hot mixture under pressure of air and uncompletely expanded combustion gases are respectively controlled by the motor pistons themselves.

To that eifect, said cylinders are provided with inlet ports respectively designated at 5a and 5b and with exhaust ports respectively designated at 60 and 6b. The exhaust ports 6a are connected with an outlet pipe 7a and the ports 6b communicate with an outlet pipe 71), both of said outlet pipes supplying a common collector 8 which is connected through a pipe 9 with a turbine or any other receiver machine to supply the same with the driving gases which escape from said motor cylinders a and b.

Each of said motor cylinders a and b is provided with one or several fuel injectors 10 which are fed by a pump (not represented) which supply said motor cylinders with fuel when their respective motor pistons come close to their interior dead end centres.

The compressor part of the autogenerator comprises advantageously two double acting compressor elements one of which is located at one of the ends of said autogenerator and the other of which is located between the two motor cylinders. For instance the motor piston 1a is integral with a compressor piston 11a which reciprocates in a compressor cylinder 12a provided, in each of its extremities, with suction valves 13a and delivery valves 140, these latter valves connecting, either directly or through a delivery duct 150, the interior of said compressor cylinder with the interior of a casing 16a surrounding the motor cylinder a and constituting the air reservoir associated with said cylinder.

Each of the above mentioned rods 3 and 4 is secured by one of its extremities to the compressor piston 11a and by another of its extremities to a transverse head 21 rigid with the motor piston 2b.

The second compressor element comprises a compressor piston 11b provided between the motor pistons 20 and lb, rigid therewith and forming with them a single block, said compressor piston 11b reciprocating in a compressor cyiinder 12b inserted between the two motor cylinders a and b. The compressor cylinder 12b is provided in each of its extremities, on the one hand, with suction valves 13b and, on the other hand, with delivery valves 14b, these latter valves delivering compressed air either directly or through a duct 15b, into the casing 161) which surrounds the motor cylinder b and constitutes its air reservoir.

It must be noted that the rods 3 and 4 which interconnect the motor pistons la and 2b pass through the compressor piston lib.

According to a particularly advantageous embodiment of the invention applicable to normal free piston engines as well as to tandem free piston engines provided with double acting compressor elements, part of the air compressed in the clearance volume defined in the compressor cylinder by the compressor piston, when the latter approaches one of its dead end centres, is transferred to the compartment of said compressor cylinder opposite to said clearance volume with respect to said compressor piston.

The compressor cylinders 12a and 12b are both provided with two series of ports, respectively, designated at 170, 18a and 17b, 18]). These ports are respectively connected by ducts designated at 190, 20a and 19b, 20b, with the clearance volumes defined in the compressor cylinders, by the compressor piston when the latter approach their respective dead end centres.

In addition these ports are so located in their respective compressor cylinders that, when the compressor piston working in each cylinder approaches one of its dead end centres, they be uncovered, at llfiHSt partially by the respective compressor piston on the side thereof, opposite to said clearance volumes. The greater the stroke of the compressor piston, the greater the length of said ports which is uncovered.

The time of opening of said ports increases simultaneously with the increase of the length on which said ports are uncovered by the corresponding compressor piston at the end of a stroke thereof. Thus one obtains, on the one hand, a decrease of the pressure in the cushion of compressed air in said clearance volumes, such decrease varying in function of the length of said stroke, and, on the other hand, an increase of the starting pressure of the air previously sucked in the compartments of said motor cylinder opposite to said clearance volumes, said air being compressed during the next stroke in the opposite directions of said compressor pistons.

These series of ports confer to the free piston engine and in particular to the tandem free piston engine a great stability since, upon an increase of the strokes of the compressor pistons, the energy accumulated in the clearance volumes of said compressor cylinders is decreased and the resistant work during the subsequent strokes is increased.

Of course, the converse occurs when said strokes decreases.

These two phenomena, reduction of the accumulated energy and increase of the resistant energy, cooperate to impart a good stability to the engine.

In FIG. 1, the piston assemblies respectively constituted by the pistons 10, 11a and 21!, 11b are shown in their internal dead end centres, the compressor pistons 11a and 11b having respectively uncovered the ports 18a and 1712 on about half of their length.

FIG. 2 shows a free piston engine comprising a single motor cylinder 30 associated with two double acting compressor elements embodied according to the invention. Two opposite hollow motor pistons 31a and 3111 closed at their end nearest the center of motor cylinder 30 reciprocate therein, said motor pistons being respectively rigid with two hollow compressor pistons 32 reciprocating in compressor cylinders 33 located on either sides of the motor cylinder 30. The latter comprises furthermore inlet ports 42 and exhaust ports 43 the opening of which is controlled, respectively, by the motor pistons 31a and 31b.

Injector means 34 supply the energy for operating the outwards strokes of the piston assemblies 31a, 32 and 31b, 32. The motor pistons 31a, 311; are slidable on guiding members 35 provided in the neighboring compressor cylinder 32 and passing through said compressor pistons, said guiding members confining, within said hollow motor pistons cushions of air 44 which act as pneumatic accumulators of energy for restoring the same to said piston assemblies for the return strokes thereof.

In the same manner as in FIG. 1 each of said compressor cylinders 33 is provided in both of its extremities with inlet valves 38 and with delivery valves 39, the latter valves communicating either directly or through ducts 40 with a casing 41 surrounding the motor cylinder 30.

Concerning the compressor double acting elements of said free piston engine it is constituted in a manner similar to the compressor elements shown in FIG. 1 with the difference, however, that each of the compressor cylinders 33 is provided in its middle with a single series of poIts 36 connected with the two extremities or clearance volumes of said compressor cylinder by a manifold 37. In the same time each of said compressor pistons 32 is given a length almost equal to the half of the length of the cylinder so that said piston, when reaching one of its dead end centres, uncovers the ports 36 on a length varying with its stroke by one of its faces opposite to the clearance volume, then defined in the compressor cylinder, said piston uncovering the same ports by its other face in a similar fashion when it reaches its opposite dead end centre.

This embodiment of the ports operates in exactly the same fashion as the one shown in FIG. 1.

Another advantage of these ports consist in the improvement of the volumetric yield of the compressor cylinders such an improvement resulting from the reduction of the pressure existing in the clearance volume at the end of a compression stroke and from the increase of the starting pressure in the compartment opposite said clearance volume and containing air to be compressed and delivered in the casing 41.

This improvement of the volumetric yield is diagrammatically represented in FIG. 4 which shows, on the one hand, the pressure diagram of a classical free piston engine provided with the double acting compressor cylinders in mixed dotted lines and a diagram established in similar conditions for the same engine when provided with the ports according to the invention in full lines. The axis of abscissae records the displacements of the compressor piston in the compressor cylinder of the engine whereas the axis of ordinates records the pressure in one of the two compartments defined by said piston in said cylinder in function of the position of the former in the latter.

Concerning first the case of an engine devoid of said ports, the pressure for instance in the compartment 33a at the left hand side of the compressor piston 32, is shown at A when said piston starts its outward stroke. The pressure in the compartment 33a increases up to the point B at which the delivery, through delivery valves 39, into the casing 41 of the air compressed in the compartment 33a is started.

The pressure in said compartment 33a continues to increase a little owing to the concomitant increase of the pressure in the casing 41 (since the inlet ports 42 and outlet ports 43 of said motor cylinder have been closed by the motor pistons 31a and 31b) until point C which corresponds to the left hand side dead end centre of the compressor piston 32.

The latter then starts its inward stroke whereby the pressure in this compartment 33a decreases until point D where the suction valves 38 open and permit suction of air from outside, into the compartment 33a until piston 32 reaches again its right hand side dead end centre A.

Considering now the diagram of the same compressor element provided with ports such as 36 the pressure in the compartment 33a at the starting of the outward stroke of the piston 32 is shown in A this pressure being higher than in the preceding case owing to the fact that some of the air compressed in the right hand side clearance volume 33b has been transferred into the compartment 33a through ports 36. The delivery of the compressed air from the compartment 33a in the casing 41 thus starts earlier, in B than in the foregoing case.

The pressure in compartment 33a continues to increase until the right hand side of piston 32 starts to uncover the ports 36 in C From this time on the pressure in compartment 33a decreases until E time at which the piston 32 reaches its exterior dead end centre, owing to the transfer of air under pressure from the compartment 33a to the opposite compartment in said compressor cylinder through the manifold 37.

However when the piston 32 starts its inwards stroke the suction of air in the compartment 33a will start for a position D of the piston 32 nearer its exterior dead end centre than in the preceding case.

In the same fashion the pressure will start increasing in the compartment 33a before the end of the inward stroke of said piston, namely in F owing to the fact that the ports 36 start to be uncovered by said piston and permit the transfer of part of the air contained in the compartment 33b through the manifold 37.

It will be appreciated that the invention provides for an increase of the surface limited by the curves A B C,, E, D F A,, which surface corresponds to the volumetric yield of the engine.

Considering again the case of the tandem free piston engine according to further embodiments of the invention, the delivery of such an engine may be modified in an even more important manner, especially in the case where a reduced delivery is required, by suppressing the injection of fuel in one of the motor cylinders, for instance in the motor cylinder b.

In this case cylinder b acts only as a pneumatic accumulator of energy which stores energy when the motor pistons 1a and 2a reciprocating in the other cylinder perform their working stroke, the cushion of compressed air in the cylinder b restoring the energy accumulated to the pistons 1b and 2b and consequently to the pistons 1a and 2a, to ensure their respective return strokes to bring back the latter pistons in the position for which the injection in the motor cylinder a and the self-ignition of fuel is operated.

In the conditions which have been described, a very efficient cushion is obtained in the cylinder b since air is compressed therein by two pistons moving in opposite directions.

It is therefore even possible to build an engine of this nature without providing any injector means in said cylinder b which then becomes a simple pneumatic accumulator of return energy with opposite free pistons.

Such engine is shown in FIGURE 3 in which the elements identical to those of FIG. 1 have been designated by the same reference numbers.

The motor cylinder b of FIG. 1 is replaced, in the engine according to FIG. 3, by a cylinder c acting only as a pneumatic cushion not connected anymore with the collector 8 feeding the receiver machine or turbine through pipe 9.

The ports which permit communication of the interior of this cylinder with the interior of the casing 16b are designated by 23. These ports form two groups controlled respectively by the pistons 1b, 2b. The axial distance between these groups of ports is greater than the axial distance between the groups of ports b and 6b shown in FIG. 1.

The only object of the ports 23 is to adapt the original pressure in the cushion C to the pressure of operation of the autogenerator, said ports 23 being uncovered by the respective pistons 1b and 211 only when they come very close to their exterior dead end centres.

Finally in FIG. 3 the casing 16b is connected through a duct 24 with the casing 16a surrounding the cylinder a which is the only motor cylinder of the engine shown FIG. 3.

It should be noted that the combination of a cushion controlled by opposite pistons with compressor elements provided with the transverse ports as described hereabove leads to an engine having a particularly important stability.

While the invention has been described in connection with particularly prefered embodiments it will be understood that the invention is not limited to these embodiments but is intended to encompass all alternatives, modifications and equivalents, as may be properly included within the spirit and scope of the invention as defined by the appended claims.

What I claim is:

1. A free piston engine comprising a motor cylinder and a double acting compressor cylinder, a motor piston reciprocating in said motor cylinder, at double acting compressor piston rigid with said motor piston reciprocating in said compressor cylinder, a casing surrounding said motor cylinder, valve controlled connection means between said casing and respectively both extremities of said compressor cylinder, a series of ports in said compressor cylinder so located therein as to be uncovered, at least partially, by said compressor piston at the side thereof opposite to the clearance volume defined by said compressor piston in said compressor cylinder upon termination of a stroke of said compressor piston, communication means connecting said ports to said clearance volume whereby air is transferred from said clearance volume to the compartment defined by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

2. A free piston engine comprising a motor cylinder and a double acting compressor cylinder, a motor piston reciprocating in said motor cylinder and a double acting compressor piston rigid with said motor piston reciprocating in said compressor cylinder, said motor piston and said compressor piston forming a piston assembly, fuel injector means in said motor cylinder for supplying the energy for the outwards stroke of said piston assembly, a system comprising a piston element and a cylinder element, the one of said elements being rigidly connected with said piston assembly, said system confining a cushion of air acting as a pneumatic accumulator of energy for restoring the same to said piston assembly for the return inwards stroke thereof, a casing surrounding said motor cylinder, valve controlled connection means between said casing and respectively both extremities of said compressor cylinder, a series of ports in said compressor cylinder so located therein as to be uncovered, at least partially, by said compressor piston at the side thereof opposite to the clearance volume defined by said compressor piston in said compressor cylinder upon termination of a stroke of said compressor piston, communication means connecting said ports to said clearance volume whereby air is transfered from said clearance volume to the compartment defined by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

3. A free piston engine comprising a motor cylinder and a double acting compressor cylinder adjacent said motor cylinder, a hollow motor piston, closed at its end the nearest the center of said motor cylinder, reciprocating in said motor cylinder, a hollow double acting compressor piston reciprocating in said compressor cylinder, said double acting compressor piston forming with said motor piston a piston assembly, a guiding member for said motor piston in said compressor cylinder and passing through said compressor piston, said motor piston being slidable on said guiding member, fuel injector means in said motor cylinder to supply the energy for the outwards stroke of said piston assembly, a cushion of air acting as a pneumatic accumulator of energy within the cavity defined in said hollow motor piston beyond the extremity of said guiding member for restoring said energy to said piston assembly for the return inwards stroke thereof, a casing surrounding said motor cylinder and adjoining said compressor cylinder, valve controlled connection means between said casing and respectively both extremities of said compressor cylinder, a series of ports in said compressor cylinder so located therein as to be uncovered, at least partially, by said compressor piston at the side thereof opposite to the clearance volume defined by said compressor piston in said compressor cylinder upon termination of a stroke of said compressor piston, communication means connecting said ports to said clearance volume whereby air is transferred from said clearance volume to the compartment defined by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

4. A tandem free piston engine comprising a first motor cylinder, first opposite motor pistons reciprocating therein, a second motor cylinder and second opposite motor pistons reciprocating therein, said first and second motor pistons being respectively interconnected in a manner such that said first motor pistons and second motor pistons reciprocate respectively in said first and second motor cylinders in phase opposition with respect to one another, at least one double acting compressor cylinder, a double acting compressor piston rigid, with one of said first motor pistons, reciprocating in said double acting compressor cylinder, a casing surrounding said first motor cylinder, valve controlled connection means between said casing and respectively both extremities of said compressor cylinder, a series of ports in said compressor cylinder so located therein as to be uncovered, at least partially, by said compressor piston at the side thereof opposite to the clearance volume defined by said compressor piston in said compressor cylinder upon termination of a stroke of said compressor piston, communication means connecting said ports to said clearance volume whereby air is transferred from said clearance volume to the compartment defined by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

5. A tandem free piston engine according to claim 4 wherein said first motor cylinder and second motor cylinder are coaxial.

6. A tandem free piston engine comprising a first motor cylinder, first opposite pistons reciprocating therein, a second motor cylinder coaxial with said first motor cylinder and second opposite motor piston reciprocating therein, a central double acting compressor cylinder between said first and second motor cylinders, a double acting compressor piston, rigid with respectively one of said first motor pistons and one of said second motor pistons, reciprocating in said central compressor cylinder, a first casing and a second casing surrounding respectively said first motor cylinder and said second motor cylinder, valve controlled connection means between said central compressor cylinder and respectively said first casing and second casing, a series of ports so located therein as to be uncovered, at least partially, by said compressor piston, at the side thereof opposite to the clearance volume defined by said compressor piston in said compressor cylinder upon termination of its stroke, communication means connecting said ports to said clearance volume, whereby air is transferred from said clearance volume to the compartment defined by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

7. A tandem free piston engine comprising a first motor cylinder, first opposite pistons reciprocating therein, a second motor cylinder coaxial with said first motor cylinder and second opposite motor pistons reciprocating therein, a rigid connection between the one of said first motor pistons and the one of said second motor pistons which reciprocate in the halves the nearest from one another of said respective first and second motor cylinders, a rigid connection between the other respective first and second motor pistons, a first double acting compressor cylinder, a first double acting compressor piston reciproeating therein and rigid with one of said first motor pistons, a second double acting compressor cylinder, a second double acting compressor piston reciprocating therein and rigid with one of said second motor pistons, 21 first and a second casings respectively surrounding said first and second motor cylinders, valve controlled connection means between said first casing and respectively both extremities of said first compressor cylinder, valve controlled connection means between said second casing and respectively both extremities of said second compressor cylinder, series of ports in each of said compressor cylinders so located therein as to be uncovered, at least partially, by the corresponding double acting compressor piston at the side thereof opposite to the clearance volume defined in said compressor cylinder by said corresponding compressor piston upon termination of its stroke, communication means connecting said ports to the corresponding clearance volume, whereby air is transferred from said clearance volume to the compartment defined, by said compressor piston in said compressor cylinder opposite to said clearance volume when said compressor piston terminates said stroke.

8. A tandem free piston engine comprising a first motor cylinder, first opposite motor pistons reciprocating therein, a second motor cylinder and second opposite motor pistons reciprocating therein, said first and second motor pistons being respectively interconnected in a manner such that said first motor pistons and second motor pistons reciprocate respectively in said first and second motor cylinders in phase opposition with respect to one another, at least one double acting compressor cylinder, a double acting compressor piston rigid with one of said first motor pistons, reciprocating in said double acting compressor cylinder, a casing surrounding said first motor cylinder, valve-controlled connection means between said casing and, respectively, both extremities of said compressor cylinder, said double acting compressor piston having a dead-end center position at each end of the double acting compressor cylinder, and stabilizing means including means responsive to the position of the compressor piston controlling the initial pressure of the air in the double acting compressor cylinder on the side of the compressor piston next to undergo compression to correct for deviations of the compressor piston from its dead-end center position by varying said initial pressure to produce a variation in the stroke of the double acting compressor piston to restore it to its dead-end center positions and thereby stabilize same.

References Cited UNITED STATES PATENTS 2,075,133 3/1937 Pescara 12346 2,147,935 2/1939 Steiner 123-46 2,189,497 2/1940 Pescara 12346 2,554,762 5/1951 Welsh et al. 123-46 X FOREIGN PATENTS 44,028 7/ 1934 France.

MARK NEWMAN, Primary Examiner.

WENDELL E. BURNS, Examiner.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3501087 *May 20, 1968Mar 17, 1970Benaroya HenryTandem,free-piston machines
US4403577 *Dec 18, 1980Sep 13, 1983Henry BenaroyaFree piston internal combustion engines
US4678407 *Jun 23, 1980Jul 7, 1987Henry BenaroyaMulti-tandem free piston machine
US4831972 *May 4, 1988May 23, 1989Barnwell Edward AInternal combustion engine
US4924956 *Feb 9, 1988May 15, 1990Rdg Inventions CorporationFree-piston engine without compressor
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Classifications
U.S. Classification123/46.00R, 417/340
International ClassificationF02B75/02, F02B71/02, F02B71/00
Cooperative ClassificationF02B2075/025, F02B71/02
European ClassificationF02B71/02