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Publication numberUS3583155 A
Publication typeGrant
Publication dateJun 8, 1971
Filing dateSep 26, 1969
Priority dateSep 26, 1969
Publication numberUS 3583155 A, US 3583155A, US-A-3583155, US3583155 A, US3583155A
InventorsSchuman Mark
Original AssigneeSchuman Mark
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Double piston engine
US 3583155 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney-Cullen, Sloman & Cantor ABSTRACT: A cylinder separated into two opposed portions interconnected by an elongated gas passageway which is constantly heated at one end and constantly cooled at its opposite end. Gas is forced back and forth through the passageway by a free piston arranged within the cylinder portion between the heated passageway end and adjacent cylinder end and by a driven piston arranged in the opposite cylinder portion. The free piston is reciprocated by the pressure of the heated gas on one face and the pressure on its opposite fact of gas compressed by the free piston itself. The driven piston is connected to a power takeoff shaft and is reciprocated on its drive stroke by the pressure of the cooled gas from the passageway and on its return stroke by a mechanical means, such as a flywheel, aided by reduced gas pressure against the driven piston.


INVENTOR MARK SCHUMAN ATTORNEYS DOUBLE PISTON ENGINE BACKGROUND OF INVENTION This invention relates to a pistontype engine of the type utilizing an external heat source for providing heated gas within the cylinder. In the past, such engines typically utilized a heated gas such as steam, fed into the engine cylinder to move a drive piston coupled to a power takeoff shaft.

At times, such engines have included a pair of pistons, both coupled to takeoff power shafts or have utilized one or two free pistons with suitable mechanisms for power takeoff.

Such prior engines have been relatively expensive and inefficient and typically have included discharging the heated gases from the cylinder after the drive stroke, then con densing, pumping, heating and returning the gas at high pressure to the cylinder. This is contrasted with the engine herein which is adapted for recycling a gaseous mixture substantially within the cylinder, and at the piston frequency.

SUMMARY OF INVENTION Summarizing, the invention herein contemplates combining a free piston with a driven piston within the same cylinder, utilizing a recycled gas or vapor which is heated from external sources and is also cooled from external sources in order to provide maximum operating efficiency and economy and overall clean operation.

More specifically, the invention contemplates providing a free piston at one'end of the cylinder, a driven piston coupled to a power takeoff at the opposite end, with the two cylinder portions being interconnected by elongated gas passageways which are externally heated at the free piston end and cooled at the driven piston end for movement of heated and cooled gas respectively into the opposite cylinder ends for driving the driven and free pistons. The free piston is constantly oscillated and its oscillation or reciprocation is controlled for controlling the power output of the engine.

These and other objects and advantages of this invention will become apparent upon reading the following description of which the attached drawings form a part.

DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectional elevational view schematically showing the engine herein.

FIG. 2 is a cross-sectional view taken in the direction of arrows 2-2 of FIG. 1.

FIG. 3 is an enlarged, fragmentary view of a portion of a piston and the cylinder wall.

FIG. 4 is an end view ofthe free piston.

FIG. 5 is a cross-sectional view taken in the direction of arrows 5-5 of FIG. 1.

FIGS. 6 through 9, inclusive, show steps in the operating cycle of the engine for one particular set of valve adjustments.

FIG. 10 is a view similar to FIG. 1, but showing a modifica tion.

DETAILED DESCRIPTION The engine 10 is formed of an elongated, closed cylinder 11 containing a free piston 12 at one end and a driven piston 13 near the opposite end. The driven piston is connected by a pivot 14 to a connecting rod 15 in turn connected to a suitable flywheel 16 to which the power output shaft 17 is connected.

The middle of the cylinder, between the pistons, is blocked by a tiller 20 which includes a number of elongated spaced apart plates 21 each having gas passageways 22 extending therethrough. The plates are spaced apart and the gaps between them are blocked by end spacers 23 located at their upper and lower ends. Central spacers 24 divide the gaps between the plates into upper heating spaces 25 and lower cooling spaces 26.

Referring to FIG. 2, a suitable heat source 37 illustrated schematically as coils is connected by a heated fluid inlet 28 and outlet 29 into each of the upper heating spaces 25. The

purpose is to heat the upper ends of the passageways by heating the plates near their upper ends. Such heating means, for example, could be in the form ofa fossil-fueled heater, heating a liquid circulated through the inlet 28, the heating spaces 25 and the outlet 29. Alternatively, coils could be placed within the heating spaces 25 for heating the upper ends of the plates and conveying fluid which has been heated. The particular form of heater may vary depending upon cost, availability and efficiency. For example, in some places a solar heater would be more economical whereas in other places an electrical type heater might be more economical.

Similarly, a cooling source 30, also schematically shown as coils, provides cooling liquid into the lower cooling spaces 26 through inlets 31 and out outlets 32. Any suitable and conventional cooling means can be used such as a refrigerating apparatus, cooled water in an available pool or body of water, air cooling, etc.

It is desirable to provide the maximum difference in temperature in heating source and cooling source, consistent with economies, and to provide substantially constant or uniform heat and cooling at the upper and lower ends of the passageways respectively, for a given power output.

Preferably, both the free piston 12 and the driven piston 13 are hollow with their exterior piston walls 35 being formed of a gas pervious material, such as sintered metals through which gas may leak. Thus, a gas bearing is formed between the walls of the pistons and the cylinder wall to avoid piston-cylinder contact and wear. Each piston is provided with a piston check valve 36 for receiving gas on its compression stroke, which in the case of the free piston is the bottom of its stroke and in the case of the driven piston is the top of its stroke. The check valves otherwise are closed.

In addition, the opposing faces of each of the pistons are bent or otherwise formed into V-shaped or sawtoothlike fins. The end spacers 23 are correspondingly formed into mating or interfitting fins for meshing with the fins of the pistons and thereby considerably increasing the speed of heat transfer and the percentage of gas moved between the opposed faces of the pistons, and therefore the ultimate efficiency of the engine.

A pressurized surge tank 40 is provided outside of the cylinder and is connected by a pipe 411 to the space 42 above the free piston through an adjustable, spring-loaded throttle valve 43 of conventional construction. The tank is likewise connected through a pipe 44 to the space 45 below the free piston, through a similar throttle valve 46.

In addition, the surge tank 40 is also connected by a pipe 47 to the space 48 above the driven piston 13, again through the same type of throttle valve 49.

A bypass or shunt pipe 51 connects the space 48 above the driven piston to the cylinder portion beneath the driven piston, with a spring-loaded throttle valve 52 for adjusting the pressure of the gas above the driven piston. This affects the amount of gas undergoing the temperature cycle and thus the rate of converting thermal energy into mechanical energy. This may also be affected by the other throttle valves.

OPERATION The general operation of the engine is as follows: The free piston 12 reciprocates upwardly and downwardly, being driven upwards by the upward movement of the driven piston and the heating of the gas coming from space 45. As the free piston moves upwards it compresses the gas above it and below the top of the cylinder to the point where that compressed gas serves to drive the piston back downwardly again. Thus, in effect, the free piston is simply bounced up and down by the heated, compressed gas below it and by the gas which it itself has compressed above it. By adjusting the throttle valves 43 and 46, the stroke of the free piston is controlled, particularly as to amplitude by controlling the pressure from the pressurized surge tank. The surge tank pressure may be adjusted by the throttle valve 49.

On the downstroke of the free piston, the gas, due to the downward movement of the pistons and the heating from heating spaces 25, is pushed and expands downwardly, at high pressure, into the space 48 above the driven piston which thereby drives the driven piston downwardly. The driven piston returns upwardly by the inertia of the flywheel 16 or by some other suitable mechanical mechanism, as is conventional in engines, and aided by the drop in pressure caused by cooling of the gas due to cooling spaces 26.

As can be seen, the gas reaching the finned face of the free piston is'heated. When the gas is driven downwardly towards the driven piston, it is cooled at the lower ends of the passageways 22, thereby reducing the pressure between the pistons during the upstroke of the driven piston and increasing the pressure during the downstroke of the driven piston.

The two pistons generally are timed to operate on the same cycle of movements upwardly and downwardly, but normally the free piston will lag the driven piston some predetermined amount of the cycle, such as by one-quarter cycle.

FIGS. 6 through 9 illustrate successive steps in a single cycle of engine operation. FIG. 6 shows the driven piston 13, threequarters of the way up on its upstroke. The free piston, lagging the driven piston by about one-quarter cycle is halfway up on its upstroke. Gas (shown by arrows) is being forced upwardly through the passageways 22 into the space below the free piston 12, the gas being heated near the tops of the passageways.

At this portion of the cycle, the throttle valves 43, 46 and 49 are closed as is the check valve 52.

In FIG. 7, the driven piston 13 is one-quarter way down on its downstroke, while the free piston I2 is at its top dead center. At this point, the gas from the space 45 beneath the free piston is just beginning to flow back into the passageways 22 and downwardly. At this point, throttle valve 46 is cracked open by its spring loading and some of the gas from space 45 flows into the surge tank 40, which in this example, is kept at a relatively low pressure.

In FIG. 8, the driven piston 13 is three-quarters of the way down on its downstroke and the free piston is halfway down on its downstroke. Now, the gas is freely flowing from the space 45 beneath the free piston through the passageways and into the space 48 above the driven piston, the gas being cooled as it passes through the lower ends of the passageways.

Here, the throttle valve 49 is open for flow of gas from the surge tank into the space 48 above the driven piston. Simultaneously, the throttle valve 52 has opened to permit gas to recharge the space 48 above the driven piston to the desired minimum pressure.

FIG. 9 shows the driven piston again on its upstroke, about one-quarter of the way up with the free piston at its bottom dead center. The pistons are so formed that they do not actually make contacts with the mating fins but simply closely approach them and this is done by proper dimensioning of the connecting rod 15 as well as by the pressure in the free piston end ofthe cylinder.

Here, the gas is now beginning to flow upwardly again. Throttle valve 43 is opened by means of its spring loading to permit gas flow as shown by the arrows. The throttle valves 49 and 52 are about to close. Cooling of the gas in the space 48 reduces the pressure on the driven piston during its upstroke.

The cycle repeats itself in the usual engine fashion in the manner as described above,

A higher pressure stored in the surge tank 40 and applied by means of valves 43 and 46 to the gas trapped in spaces 42 and 45, above and below the free piston, would affect the amplitude of oscillation of the free piston, the amount of gas undergoing the temperature cycle and therefore, the power output.

A change in the pressure of gas trapped in space 42 relative to that trapped in space 45 will cause an upward or downward shift in the mean position of the free piston, and likewise will affect the power output.


FIG. 10 illustrates a modification substantially the same as that shown in FIG. 1. However, in FIG. 10, the bypass pipe 51 and check valve 52 have been replaced by a bypass pipe 60 which leads from the space below driven piston 13 to a throttle valve 61 and pipe 62 into the space 48 above the driven piston. In addition, a pipe 63 connects space 42, above the free piston 12, through a check valve 64 (shown schematically) to a dome 65 formed on the upper end of the cylinder. That dome receives a domed portion 66 formed on the upper end ofthe free piston 12.

Another pipe 71 communicates through a check valve 67 and a passageway 68 formed in modified outer vane 69 into the space 70 formed in the free piston.

With this construction, trapped gas in the dome 65 and in the space 70 in the free piston is compressed during the respective up and down movement of the free piston to prevent any possibility of the piston bottoming against the cylinder on its upward stroke or against the fins on the downward stroke.

The throttle valve 61 may also serve for adjusting the average pressure in the entire portion of the apparatus above the driven piston and thereby, may serve as an additional power control.

Also added to the apparatus is an additional surge tank connected through a throttle valve 81 to the pipe 47 which communicates with the space 48 above the driven piston. The surge tank 80 also is connected to another throttle valve 82 communicating through a passage 83 into the space 84 located between the outer vanes,just above the driven piston. The throttle valve 81 and 82 are spring loaded for presetting to a predetermined pressure.

Valve 81 serves to store a chosen pressure in the surge tank 80. For a power change in the system, valve 82 opens during a portion of the stroke to apply the stored pressure from surge tank 80 into the central region or space 84 for changing the pressure in the region between the two pistons.

For example, valve 81 may be normally closed, with its valve wafer down and seated, but opening at the maximum pressure when the driven piston is three-quarters of the way up on its upstroke. The valve 81 may then close when the piston is three-quarters on the way down on a valve stroke.

Valve 82 is normally closed, but may be adjusted to open at the maximum cylinder pressure, when driven piston 13 is onequarter of the way down on its downstroke, to release stored pressure into the area 84 to increase the drive pressure against the driven piston.

As can be seen, these additions to the basic system described in FIG. 1, provides for more flexibility and better control of the operation.

Having fully described an operative embodiment of this invention, I now claim:

1. An engine comprising a closed free piston cylinder portion containing a reciprocating free piston having opposite piston faces, and a driven piston cylinder portion containing a reciprocating driven piston;

the two cylinder portions being interconnected by an elongated gas passageway extending within the cylinder for conveying gas into and between them, with the two pistons reciprocating towards and away from their adjacent passageway ends so that each forces gas through the passageway towards the other;

means for constantly heating the passageway adjacent to the free piston cylinder portion, and means for constantly cooling the passageway adjacent to the driven piston cylinder portion for respectively heating and cooling the gas passing through the passageway;

the free piston being alternately reciprocated by the pressure of the heated gas, received in its cylinder portion from the passageway, applied against one face thereof and by the pressure of gas compressed between its opposite face and the adjacent end of the piston portion;

and the driven piston being alternately reciprocated by the pressure of the cooled gas received from its adjacent passageway end and by a means for reciprocating the driven piston back towards its passageway end.

2. An engine as defined in claim 1, and said cylinder portions being formed of the opposite end portions of a single cylinder, the pistons reciprocating towards and away from each other, with means blocking the central portion of the cylinder between the pistons, except for said passageway.

3. An engine as defined in claim 2, and said blocking means including elongated plates extending between the pistons, each having gas passageways extending to the cylinder end portions between the opposed piston faces.

4. An engine as defined in claim 3, and with the opposed piston faces each being formed into an axially elongated, sawtoothlike fin configuration, and correspondingly shaped fins formed on the blocking means between the plates and extending between and mating with their adjacent piston face fins.

S. An engine as defined in claim 1, and including a source of compressed gases connected through a throttle valve to the free piston cylinder portion at each of the opposite ends ofthe free piston for controlling the pressure ofthe gas upon the opposite faces of the free piston and therefor the stroke of the free piston.

6. An engine comprising a closed cylinder having a free piston in one end and a driven pistonl coupled to a power takeoff means in its opposite end, with the pistons being reciprocally fitted within the cylinder and with the two piston containing cylinder ends connected by at least one elongated passageway extending within the cylinder through which gas may freely pass to the opposed faces of the two pistons;

means for externally, constantly heating the passageway at the free piston end thereof and for externally, constantly cooling the passageway at the driven piston end thereof for thereby respectively heating and cooling gas moved through the passageway by reciprocation ofthe pistons.

7. An engine as defined in claim 6 above, and said passageway being formed lengthwise through an elongated plate extending between the pistons .and fixed within the cylinder, the cylinder being blocked against movement of gas between the pistons except for the passageway; and said heating and cooling means being applied to the upper and lower end portions, respectively, of the plate.

8. An engine as defined by claim 6 above and with the opposing faces of the two pistons each being formed in a sawtoothlike fin configuration; and means blocking the cylinder between the piston opposing faces except for the passageway, said means including sawtoothlike fins arranged for fitting between and mating with the adjacent piston fins.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3767325 *Jun 20, 1972Oct 23, 1973Schuman MFree piston pump
US3782859 *Dec 7, 1971Jan 1, 1974Schuman MFree piston apparatus
US3807904 *Feb 18, 1972Apr 30, 1974Schuman MOscillating piston apparatus
US3889465 *Jun 24, 1974Jun 17, 1975Motoren Werke Mannheim AgApparatus for controlling the power of a hot-gas piston engine
US4044558 *Sep 10, 1975Aug 30, 1977New Process Industries, Inc.Thermal oscillator
US4271669 *Aug 2, 1978Jun 9, 1981Keller Arnulf AReciprocating-piston engine, especially hot-gas engine or compressor
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U.S. Classification60/520, 60/521, 60/522
International ClassificationF02G1/043, F02G1/00
Cooperative ClassificationF02G1/0435
European ClassificationF02G1/043F