Thermally driven piston apparatus

A closed cylinder contains a thermally driven free piston oscillating between hot and cold ends of the cylinder which ends are respectively connected to a thermal lag heating chamber and a turbine/cooling chamber. A thermal regenerator is provided within a cylinder bypass which bypasses a portion of the cylinder between hot and cold rebound chambers which include, respectively, the hot and cold ends of the cylinder. The hot rebound chamber also includes the thermal lag heating chamber. The heating chamber has sufficient thermal lag properties for substantially heating gas therein as the piston is rebounding away from the hot end of the cylinder, thereby sustaining piston oscillation. The cyclical heating and cooling of the working gas in the heating and cooling chambers and in the regenerator as the displacer piston coasts up and down within the bypass region of the cylinder between the rebound chambers produces a modulated pressure for driving the turbine via a nozzle-like conduit interposed between the cylinder and the turbine. The modulated pressure is augmented by orienting the hot end of the bypass and an inlet port of the thermal lag heating chamber so that, while the piston is coasting toward the cold end of the cylinder, gas flowing into the hot end of the cylinder via the bypass is directed into the cylinder in a stream which passes into the heating chamber inlet port and thence into the heating chamber for further heating therein while the piston is still coasting toward the cold end of the cylinder. The overall cycle of this heat engine is regenerative and may loosely be referred to as a modified Stirling cycle. The turbine or motor may drive a generator or alternator to produce electrical power. The turbine may be replaced by a different rotary motor or other fluid driven load.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to energy converters and more 
particularly to an energy converter which utilizes a regenerative gas 
cycle and an oscillatory gas flow through the regenerator. 
2. Description of the Prior Art 
Various energy converters have been previously disclosed utilizing a 
modified Stirling cycle and a free or semi-free piston which alternately 
displaces gas back and forth between a hot space (a hot chamber) and cold 
space (a cold chamber) via a thermal regenerator as the piston oscillates 
in a cylinder. The temperature difference between the hot and cold 
chambers is maintained by means of a heating means or chamber and a 
cooling means or chamber and this alternate displacement of gas causes an 
alternate heating and cooling of the gas by the heating and cooling 
chambers and by the regenerator connecting these two chambers. This 
alternate heating and cooling results in a cyclical variation or 
modulation of the gas pressure. This modulated pressure may in turn be 
used to drive a load, such as a working piston, which may also be a free 
piston and which typically oscillates up to about 90.degree. out of phase 
with respect to the displacer piston, and the oscillating working piston 
may do mechanical, pneumatic, or electro-magnetic work. The displacing and 
working pistons may also be combined so as to form a single complex piston 
having a displacing piston mounted on a working piston and moving relative 
to the working piston to accomplish its function. Or, the displacing 
piston may be porous and act as an oscillating regenerator to accomplish 
its function. 
The modulated pressure energy developed by means of the displacing or 
working piston can be used for fluid pumping purposes by means of check 
valves which rectify the modulated pressure, or, as described within my 
copending application, Ser. No. 502,748, filed Sept. 3, 1974, now U.S. 
Pat. No. 3,973,771 entitled Illusion Amusement Device and as also 
described and illustrated herein, a pressure driven load, such as for 
example, a turbine, may be driven directly by such a device without the 
use of check valves, by means of the pressure modulated fluid of such a 
device issuing from a nozzle which directs the reciprocating fluid against 
the load. 
I have previously invented a free piston, Stirling type device such as 
described above and various embodiments of this device are described and 
illustrated within my U.S. Pat. Nos. 3,782,859, entitled "Free Piston 
Apparatus, " and 3,767,325, entitled "Free Piston Pump." The free piston 
of this device can be of simple and integral construction, and it is a 
completely free piston. The piston is reversed by means of a gaseous 
spring, which does not wear out, as compared with a mechanical spring, and 
the means for reversing the direction of motion of the free piston, twice 
each cycle, is relatively independent of the load, whereby the device is 
essentially stall-free. Since the free piston is guided by means of the 
cylinder itself, there is no need for a separate guidance apparatus or for 
accurate alignment of such a guidance apparatus with the cylinder. In 
addition, in the simplest form of my device, the single free piston is the 
only moving part required for developing the cyclical pressure variation. 
To my knowledge, none of the other Stirling-type free piston energy 
converters have all of these advantages features. 
However, my approach to this family of devices appears to have a slight 
disadvantage which most, if not all, of the other devices do not have. In 
one of its simplest forms, my device has a single heating chamber. The 
sole heating chamber, in contrast with the other devices, serves as a 
thermal lag heating chamber for driving the free piston and, also in 
contrast with these other devices, the sole heating chamber is not located 
in the cylinder bypass, where it would each cycle heat substantially all 
of the gas forced from the cold chamber to the hot chamber via the bypass. 
Instead, the sole heating chamber is disposed outside of the bypass and 
communicates with the hot end of the cylinder by means of a separate 
heating chamber port which is located beyond the bypass. The heating 
chamber port is located in or very near the hot end-wall of the cylinder, 
whereby the heating chamber communicates with the hot end of the cylinder 
while the hot bypass port is blocked by the piston side-wall during the 
hot rebound portion of the cycle, during which portion of the cycle the 
heating chamber functions not only as part of the hot rebound chamber but 
also as a thermal lag heating chamber for sustaining piston oscillation 
(see my U.S. Pat. No. 3,807,904, entitled "Oscillating Piston Apparatus," 
for a relatively thorough description of a thermal lag heating chamber; my 
U.S. Pat. No. Re. 27,740, entitled "Oscillating Free Piston Pump," also 
discusses thermal lag heating). 
The heating of the gas forced by the piston into the heating chamber during 
this hot rebound portion of the cycle, in addition to the heating of the 
gas forced into the heating chamber during the next portion of the cycle 
as a result of the increasing pressure in the cylinder while the piston 
coasts within the bypass region in a direction away from the hot cylinder 
end, combine to essentially provide the cyclical heating by the heating 
chamber of gas forced from the cold chamber to the hot chamber via the 
regenerator in the bypass. While it is normally desirable for all of the 
gas being forced through the regenerator to be heated by the heating 
chamber each cycle, and while this goal is apparently substantially 
accomplished by the other Stirling type devices of which I am aware, it is 
difficult to say, in the case of my device, just how much of this forced 
gas enters the sole heating chamber of my simplified device each cycle 
during the above two portions of my cycle. Certainly a substantial amount 
of such gas does enter my heating chamber for heating therein such cycle; 
however, this amount may well be substantially less than 100% of such gas, 
the main problem occurring during the above-mentioned coasting portion of 
the cycle while the piston iscoasting in the bypass region in a direction 
away from the hot end of the cylinder (toward the cold end of the 
cylinder) primarily because the bypass flow is not angled toward the 
heating chamber. Although the advantages of my approach, discussed first, 
may out-weigh this slight disadvantage, discussed last, it nevertheless is 
the prime object of the present invention to correct this slight 
deficiency without introducing any new deficiency. 
SUMMARY OF THE INVENTION 
The present invention is a modified Stirling cycle energy converter which 
utilizes, as in the case of my Free Piston Apparatus and my Free Piston 
Pump, referenced above, a cylinder, a cylinder bypass containing a 
regenerator, a free piston oscillating within the cylinder between hot and 
cold ends of the cylinder, a gaseous rebound chamber at each end of the 
cylinder beyond the bypass, one of the rebound chambers including a 
thermal lag heating chamber for supplying heat energy to the gas for 
sustaining the piston oscillation; and a cooling chamber for cooling gas 
flowing into the cold end of the cylinder. However, within the present 
invention, the cooling chamber is provided by a load in the form of a 
turbine which is connected pneumatically, with or without the use of check 
valves, to the cold end of the cylinder so as to be driven by means of the 
oscillatory temperature and pressure developed within the cylinder/turbine 
system as a result of both the alternate and simultaneous heating and 
cooling of the gas (or other compressible fluid). The thermal lag heating 
chamber is connected to the opposite, or hot, end of the cylinder and, 
also in contrast with the two last named patents, the bypass and heating 
chamber are constructed, oriented, and connected to the hot end of the 
cylinder in such a manner as to utilize the nozzle effect of the hot 
bypass conduit such that the fluid flowing through the bypass into the hot 
end of the cylinder is directed by the hot bypass conduit into the 
cylinder in a concentrated stream which flows toward and thence into and 
perhaps even through the heating chamber for heating therein as the piston 
coasts within the bypass region in a direction toward the cold end of the 
cylinder. Thus, the thermal lag heating chamber not only operates to heat 
the working gas during the hot rebound portion of the cycle (while the hot 
end of the bypass is blocked by means of the piston), for sustaining 
piston oscillation, but also serves as a heating chamber for heating 
substantially all of the fluid flowing into the hot end of the cylinder 
via the bypass while the piston is coasting toward the cold end of the 
cylinder. 
Accordingly, it is an object of the present invention to provide a new and 
improved energy converter utilizing a free oscillating piston. 
Another object of the present invention is to provide a new and improved 
energy converter utilizing a modified Stirling cycle, wherein the energy 
converter utilizes a cylinder containing a free piston which oscillates 
within the cylinder between hot and cold ends of the cylinder. The 
cylinder has a bypass which contains a regenerator and which bypasses a 
sufficient portion of the cylinder so that the piston coasts while it is 
within the bypass region. A hot rebound chamber is provided at the hot end 
of the cylinder beyond the bypass for reversing the piston motion and 
includes a thermal lag heating chamber communicating with the hot end of 
the cylinder for driving the piston during the hot rebound portion of the 
oscillatory cycle. The thermal lag heating chamber and the hot end of the 
bypass are configured, oriented, and connected to the hot end of the 
cylinder such that, while the piston is coasting in a direction toward the 
cold end of the cylinder, most, or even substantially all, of the fluid 
flowing into the hot end of the cylinder via the bypass is directed by 
means of the bypass is a stream which flows to, and thence into, the 
thermal lag heating chamber for heating therein during this coasting 
portion of the cycle. 
A further object of the present invention is to provide a new and improved 
energy converter utilizing a free piston oscillating within a cylinder 
between hot and cold ends thereof, a bypass containing a regenerator and 
bypassing a portion, and only a portion, of the cylinder, the bypass 
connecting the hot and cold ends of the cylinder together while the bypass 
is not blocked by the oscillatory piston. Means are also provided for 
heating fluid flowing into the hot end of the cylinder and for feeding 
cool fluid into the cold end of the cylinder, the hot end of the bypass 
being connected to the cylinder side-wall at an acute angle with respect 
to the cylinder axis so that fluid flowing into the hot end of the 
cylinder via the hot end of the bypass has a velocity component along the 
cylinder axis in a direction away from the cold end of the cylinder, such 
angling of the hot bypass end tending to improve the power output and 
efficiency of the energy converter. 
An additional object of the present invention is to provide a new and 
improved energy converter utilizing a modified Stirling cycle, wherein the 
displacing piston is in the form of a free piston which coasts within a 
bypass region of a cylinder, wherein the working member of the energy 
converter is a turbine, and wherein the turbine housing provides cooling 
for energy converter.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Reference now being made to FIG. 1, there is illustrated a closed cylinder, 
generally indicated by the reference character 1, having a side-wall 2, 
and end-walls 3 and 4 at opposite ends of the cylinder. As a result of a 
thermal lag heating chamber; generally indicated by the reference 
character 5, and a turbine/cooling chamber, generally indicated by the 
reference character 6, which are respectively connected to opposite ends 
of the cylinder, as more particularly described later, the cylinder 1, 
during operation, has a cold end adjacent and including end wall 3 and a 
hot end adjacent and including end wall 4. A free piston 7 oscillates 
between and separates the hot and cold ends of cylinder 1 and the cylinder 
also has a bypass, generally indicated by the reference character 8, 
containing a regenerator 9. 
The regenerator 9 and bypass 8 communicate with the cold end of the 
cylinder by means of a cold bypass conduit 10 terminating in a cold bypass 
port 11 in the side-wall 2 of the cylinder in the cold end of the 
cylinder, and similarly, the regenerator and bypass are connected to the 
hot end of the cylinder by means of a hot bypass conduit 12 which 
terminates in a hot bypass port 13 in the cylinder side-wall 2 in the hot 
end of the cylinder. Thus, the bypass connects the hot and cold ends of 
the cylinder via the bypass 8 (and regenerator 9) while free piston 7 is 
coasting in either direction within the cylinder bypass region between 
bypass ports 11 and 13. The coasting of the piston is facilitated by means 
of the low fluid flow impedance of the cylinder bypass, which impedance is 
the same for fluid flow in either direction through the bypass. The 
coasting steps, however, when the side-wall of the piston 7 traverse 
either of the ports 11 or 13, at which time the bypass port and bypass are 
blocked or restricted by the piston side-wall and the piston then 
compresses the gas within the corresponding end of the cylinder. The 
compression of the gas causes the piston to rebound away from this end of 
the cylinder toward the opposite end of the cylinder, and thus, the cycle 
of piston oscillation has two coasting portions interspersed with two 
rebound portions. 
As the piston coasts toward the cold end of the cylinder, that is, coasts 
upward as seen in FIG. 1, which may arbitarily be considered as the first 
coasting portion of the oscillatory cycle, cold gas is forced by the 
piston downwardly through the bypass and into the hot end of the cylinder. 
The regenerator, during operation, has a positive temperature gradient 
directed toward the hot end of the cylinder, because of the alternate flow 
of the cold gas downward and the hot gas upward within the bypass and 
through the regenerator, and consequently, the cold gas forced downwardly 
through the bypass by the upwardly coasting piston is warmed by the 
regenerator and simultaneously cools the regenerator before it is 
directed, by means of the hot bypass conduit 12, into the hot end of the 
cylinder in a concentrated stream which flows toward and into an inlet 
port 16 of heating chamber 5. Thus conduit 12 acts as a crude nozzle and 
guiding means for directing the warmed fluid substantially immediately 
into the heating chamber for immediate initiation of heating of the fluid 
by and within the heating chamber. 
Heating chamber inlet port 16 may be in the cylinder side-wall 2 on the 
opposite side of the cylinder axis from bypass port 13, that is, 
180.degree. around the cylinder from port 13, as illustrated in FIGS. 1 
and 2, and is further from the cold end of the cylinder than is port 13. 
Thus the hot bypass conduit 12, and the stream of gas flowing therethrough 
into the hot end of the cylinder, are oriented at an acute angle with 
respect to the cylinder axis, such that this flow of warmed or heated gas 
through hot bypass port 13 and into the hot end of the cylinder has a 
substantial velocity component along the cylinder axis in a direction away 
from the cold end of the cylinder. 
Heating chamber inlet port 16 is connected to heating chamber 5 by means of 
heating chamber inlet conduit 17. Thus, substantially all of the warmed 
gas is directed by means of hot bypass conduit 12 in a stream which flows 
into, and through a segment of, the hot end of the cylinder, thence 
through port 16 and conduit 17, and into heating chamber 5 for substantial 
additional heating therein during this portion of the cycle while the 
piston is coasting toward the cold end of the cylinder. Port 16 may, as 
shown in FIG. 1, have a larger cross-sectional area than that of port 13 
so as to facilitate entry of substantially all of the directed stream into 
conduit 17 and heating chamber 5. In addition, conduit 17 has a mean flow 
axis which is approximately aligned with the mean flow axis of conduit 12 
so as to further facilitate passage of the stream into heating chamber 5. 
Heating chamber 5 may also have an optional, separate outlet conduit 20 
which communicates with the hot end of the cylinder by means of a heating 
chamber outlet port 21 which, as illustrated in FIG. 1, may be in the hot 
end wall 4 of the cylinder. By allowing the gas to return to the hot end 
of the cylinder after being heated within the heating chamber, entry of 
the directed gas stream via port 16 and conduit 17 into the heating 
chamber is further facilitated. Conduit 20 and port 21 facilitate passage 
or circulation of most of the directed fluid completely through the 
heating chamber and back into the hot end of the cylinder during the first 
coasting portion of the cycle. The increased circulation of the fluid 
through the heating chamber increases the heating of the directed fluid in 
the heating chamber during the first coasting portion of the cycle, 
thereby producing a greater pressure increase in the cylinder during this 
first coasting portion of the cycle. In addition, it should be noted that 
conduit 20 and port 21 are oriented, located, and configured so as to 
avoid interference with the above-mentioned directed stream by the gas 
returning from the heating chamber to the hot end of the cylinder via port 
21, as will be discussed below in connection with FIG. 2. Thus, because of 
these features, substantially all of the directed stream from the hot end 
of the bypass enters, and is heated by and within, the heating chamber 
during this first coasting portion of the cycle, causing a substantially 
greater increase in the gas pressure within the cylinder during this 
upward coasting portion of the cycle than occurred in my above-mentioned 
Free Piston Apparatus and Free Piston Pump which did not feature a bypass 
angled toward a thermal lag heating chamber inlet port. If port 16 and 
conduit 17 are quite large, the directed fluid may circulate both into and 
out of the heating chamber via this port and conduit during the first 
coasting portion of the cycle, whereby the advantages of conduit 20 and 
port 21 for facilitating the desired flow of fluid into and out of the 
heating chamber during this first coasting portion of the cycle are 
diminished, whereby conduit 20 and port 21 become less necessary and 
desirable. Port 16 may alternatively be located within the hot end wall 4 
of the cylinder. 
This increasing pressure, due to the heating of the fluid by and within the 
regenerator and heating chamber as the piston coasts toward the cold end 
of the cylinder, forces gas from the cold end of the cylinder into turbine 
6 via load conduit 24. Load conduit 24 communicates with the cylinder by 
means of load port 25 in the cylinder side-wall and also communicates with 
the interior of the housing 26 of the turbine by means of a turbine 
housing port 27. Conduit 24 acts as a crude nozzle so as to direct the gas 
in a stream toward blades 29 of the turbine rotor 30 as each of the blades 
is disposed above the rotor axis and opposite port 27. The directed stream 
is deflected by the blades 29, thereby providing impulses against the 
blades which drive rotor 30 in a clockwise direction as denoted by the 
arrow. As the rotor spins, the additional rotor blades successively come 
into line with the conduit or nozzle 24 and are in turn driven by means of 
the directed stream. The turbine rotor may be connected to an alternator 
or generator, thereby converting the heat energy into electrical energy, 
or, alternatively, the turbine may drive other types of loads. 
The fluid stream, after deflection by the rotor blades, is cooled by the 
turbine housing 26, thus concentrating the gas within the turbine and 
tending to reduce the pressure in the turbine, thereby augmenting the gas 
flow into the turbine, whereby greater pneumatic power for driving the 
turbine is derived as a result of this cooling of the working fluid by the 
turbine housing 26. Various means, not shown, may of course be provided 
for cooling the housing 26, such as for example, cooling fins and a fan. 
One preferred position for load port 25 is a location having the same 
longitudinal position along the length of the cylinder as that of cold 
bypass port 11, as illustrated in FIG. 1. Thus, ports 11 and 25 are the 
same distance from cold end wall 3 of the cylinder, and in this manner, 
the upward coasting piston simultaneously blocks and restricts flow 
through cold bypass port 11 and load port 25 by means of the traversal of 
these ports by the piston sidewall, whereupon the coasting away from the 
hot end of the cylinder stops and the piston compresses the gas trapped 
within the upper or cold rebound chamber comprising the cold cylinder end. 
It is noted that the cold rebound chamber acts as a gaseous compression 
spring for slowing, stopping, and reversing the direction of motion of the 
piston during this cold rebound portion of the oscillatory cycle. 
Subsequently, the second coasting portion of the cycle commences as the 
free piston unblocks ports 11 and 25 and coasts away from the cold end of 
the cylinder, thereby forcing hot gas from the hot end of the cylinder to 
the cold end of the cylinder via the bypass. This flow of gas in the 
bypass heats the regenerator, and the gas in turn is cooled by the 
regenerator as it is fed into the cold end of the cylinder during this 
second coasting portion of the cycle. The cooling of the gas in the bypass 
causes a drop in the cylinder pressure which draws cooled gas from the 
turbine back into the cold end of the cylinder via the load conduit 24 and 
ports 27 and 25. 
The gas flowing into port 27 and conduit 24 during this second coasting 
portion of the cycle is drawn diffusely from within the turbine housing, 
and this diffuse flow retards the rotation of the turbine rotor almost 
insignificantly. This is contrasted with the nozzle or directional stream 
effect occurring when gas flows from the cylinder into the turbine via 
nozzle 24 and port 27 during the first coasting portion of the cycle, 
which nozzle effect causes substantial work to be done by the gas upon the 
rotor 30. I have built a simple, thermally driven, free piston/turbine 
model which demonstrates this asymmetric nozzle effect, as well as some of 
the other features of the device illustrated in FIG. 1. 
Free piston 7, which is coasting away from the cold end of the cylinder, 
eventually reaches and traverse the hot bypass port 13 and therefore 
blocks flow in the bypass, whereupon this second coasting portion of the 
cycle terminates and the piston compresses the gas in the hot rebound 
chamber comprising the hot end of the cylinder, heating chamber 5, and 
conduits 17 and 20. The hot rebound chamber acts as a gaseous spring so as 
to reverse the direction of the piston motion and to cause the piston to 
rebound away from the hot end of the cylinder and to move toward the cold 
end of the cylinder. During this hot rebound portion of the cycle while 
port 13 is blocked by the piston, the piston first draws a small amount of 
gas from the turbine and then, after the piston motion is reversed, forces 
a small amount of gas into the turbine, thereby doing a small amount of 
work upon the turbine during the hot rebound cyclic portion. The hot 
rebound portion of the cycle ends when the hot bypass port 13 is uncovered 
by the piston, the cycle of piston oscillation thereby being completed. 
The piston then begins coasting away from the hot end of the cylinder, 
that is, the piston commences the first portion of the next cycle. 
The heating chamber 5, which is heated by an external heat source 35, has, 
of course, a higher temperature than the hot end (the lower end) of the 
regenerator. The heating chamber 5 has sufficient thermal lag properties, 
so that the gas within the heating chamber (and thus the gas within the 
hot rebound chamber) is heated continuously by the heating chamber (and 
perhaps also by the hot end of the cylinder) throughout the hot rebound 
portion of the cycle, so as to augment the speed and kinetic energy of the 
piston as it rebounds toward the cold end of the cylinder, thereby 
sustaining piston oscillation. This continuous heating is facilitated if 
the heating chamber contains at least one heated passageway which is 
elongated and has a length and breadth which are substantially greater 
than the passageway width, several of such thermal lag passageways being 
illustrated in FIG. 1 as passageways 36 (see my U.S. Pat. NO. 3,807,904 
for a discussion of thermal lag driving of a piston). Also, the passageway 
width is typically greater than the width of a heated passageway of a 
conventional heating chamber. 
This continuous or substantially continuous heating of the gas in the hot 
rebound chamber during the hot rebound cycle portion causes the mean gas 
temperature, and therefore also the pressure, of the gas within the hot 
rebound chamber to substantially lag the instantaneous geometrical 
compression ratio of the hot rebound chamber (the ratio of maximum volume 
to instantaneous volume), whereby the maximum temperature, and the maximum 
pressure, within the hot rebound chamber are attained substantially after 
the maximum instantaneous compression ratio is reached and while the 
piston is accelerating away from the hot end wall 4. Thus there is a 
substantially greater average pressure in the hot rebound chamber and 
against the lower face of the piston while the piston is rebounding away 
from the hot end wall 4 than the average pressure is the hot rebound 
chamber during the early part of the hot rebound portion of the cycle 
while the piston is moving toward the hot end wall 4 of the cylinder. This 
produces a substantially greater piston kinetic energy at the end of the 
hot rebound portion of the cycle than at the beginning of the hot rebound 
portion of the cycle, even allowing for some energy loss due to such 
factors as sliding friction, viscous losses, and leakage of gas between 
the piston and cylinder sidewalls, as well as the small amount of work 
done by the piston upon the turbine (via the working gas) during the hot 
rebound portion. 
This thermo-pneumatic augmentation of the piston energy, during the hot 
rebound portion of the cycle, is sufficient to overcome various piston 
energy losses throughout the cycle, such as to example, piston-cylinder 
leakage, thermal transfer losses between the gas and its enclosing walls, 
and viscous losses, such as for example, windage within the regenerator, 
so that the piston oscillation is nevertheless sustained in spite of these 
losses. The thermal lag heating is also sufficient to maintain piston 
oscillation in spite of most any severe load on the device, such as, for 
example, a complete stalling of the turbine (a very unlikely event). This 
is because the piston is essentially a displacer piston rather than a 
working piston, whereby its oscillation is essentially independent of the 
load, because of the bypass. Thus, the load is driven primarily by the 
alternate heating and cooling of the gas rather than by direct compression 
of the gas by the piston. 
It should also be understood that the heating of the gas required during 
the hot rebound portion for sustaining piston oscillation is also 
contingent upon the directed stream, flowing into port 16 from the bypass, 
being cooler than the heated passageways 36 that must heat this fluid. 
Thus the means for sustaining piston oscillation must include either a 
cooling of the working fluid elsewhere in the device during a portion of 
the cycle, such as for example, within the turbine, or some other means in 
addition to the regenerator for feeding cool gas into the cylinder, such 
as for example, by means of a cooling chamber in the bypass, or a supply 
of cold gas being pumped by means of the energy converter. 
The hot and cold ends of the cylinder may be thought of as first and second 
variable volumes separated by the free piston. The bypass connects the 
first and second volumes but is restricted when either of the volumes has 
values in a minimum range, as a result of blockage of the bypass ports by 
the piston. 
A simple, manually operated, piston-cylinder type starter 40, connected 
pneumatically to the lower end of the cylinder by means of a starter 
conduit 41, provides a pneumatic impulse against the piston for initiating 
the piston oscillation. 
Referring now to FIG. 2, there is illustrated therein a bottom view of the 
cylinder, the bypass, and the heating chamber inlet conduit of FIG. 1, as 
viewed in the direction of arrows 2--2 in FIG. 1. Shown in this 
substantially external view of the hot end of the cylinder is port 21 by 
which port the heating chamber outlet conduit 20 communicates with the hot 
end of the cylinder. Port 21 is provided in the hot end wall 4 of the 
cylinder and is offset from the cylinder axis so as to avoid undue 
interference by the fluid flowing into the hot end of the cylinder via the 
port 21 with the directed hot bypass fluid stream flowing from hot bypass 
port 13 toward and into heating chamber inlet port 16. 
As illustrated in FIG. 3, there is shown an alternate connecting means 
between the cylinder and the turbine. The alternate connecting means is 
not believed to provide any additional novelty, and thus is not described 
in great detail. However it is seen that the alternate connecting means 
essentially comprises conduit 24, modified so as to include a check valve 
and surge tank in order to provide a smooth unidirectional flow from the 
nozzle to the turbine. The alternate connecting means further includes a 
substantially separate return path or conduit 28 for the gas returning to 
the cold end of the cylinder from the turbine, the return path containing 
a second check valve for obtaining unidirectional flow in the return path 
from the turbine to the cold end of thecylinder. The alternate connection 
reduces the small amount of power lost due to the periodic backward flow 
through the nozzle; however such connection also adds some complexity, 
service lifetime considerations, and small power losses of its own. 
The working fluid of this device can be a gas, a vapor, or most any 
compressible fluid. Some liquid may be present, but it must not interfere 
too much with the piston oscillation. Of course, some gases would provide 
a greater thermodynamic efficiency than others. 
The turbine is only one example of a load for the thermally powered source 
of oscillatory pressure variation described herein; other fluid-driven 
rotary or non-rotary motors or other loads may of course be driven by 
means of this device. By using check valves, the device may be used for 
unidirectionally pumping or compressing gas. The thermal energy required 
for the cooling and heating operations described above for operating the 
device can be derived from the gas or other fluid being pumped, or from 
other pressure driven loads. A cooling chamber may be located in the 
bypass between the regenerator and the cold end of the cylinder to provide 
the required cooling; similarly a heating chamber may be disposed in the 
bypass between the regenerator and the hot end of the cylinder as long as 
it does not heat the fluid in the bypass so much that it destroys the 
ability of the thermal lag heating chamber to further heat the fluid 
sufficiently to sustain the piston oscillation. 
The configuration of the heating chamber of this device can be adapted in 
various ways to absorb and utilize heat from most any heat source - even 
solar heat. For example, the energy converter of this invention could be 
used to convert solar radiant energy into electrical energy, for purposes 
such as providing electrical energy for a home. Thus the solar energy can 
be focused or semi-focused onto a radiation collector which is configured 
to act as the heating chamber of the engine of this invention. The waste 
heat discharged by the engine, for example the heat drawn from the turbine 
housing by a fan which cools the turbine housing, can be used to heat the 
home, to heat hot water for the home, and even to supply heat for air 
conditioning the home (by replacing the gas flame of a gas powered air 
conditioning unit) (or air-conditioning can be provided by using one 
engine, less the turbine, running "forward," as described herein, to drive 
a modified second engine running "backard " to provide cooling - see FIG. 
16 of my U.S. Pat. No. 3,782,859). Another example of a heat source for 
powering the engine of the present invention is a flame -- as from burning 
a fuel, such as for example, kerosene, propane, wood, or even garbage. 
Most any source of waste heat may be used if a sufficient temperature 
differential is available. 
The thermal lag heating technique does not appear to be a very powerful 
means for driving the free piston, and it may or may not be a highly 
efficient means for driving the piston, but it does not need to be either 
a powerful or efficient piston driving means since the piston, because of 
the bypass and regenerator, is primarily a displacer piston rather than a 
working piston, and therefore requires relatively little energy to sustain 
its oscillation, especially if the cylinder is vertically oriented, which 
orientation practically eliminates piston -- cylinder friction. In 
addition, the thermal lag heat energy which is not converted into piston 
kinetic energy is essentially not wasted since it provides the required 
cyclical heating of the working gas and therefore facilitates development 
of the Stirling type pressure variation for doing work upon the load while 
the piston is coasting up and down in the cylinder, and therefore is 
efficiently used. Thus, the work done upon the turbine or other load comes 
essentially from the heating and cooling operations and not from direct 
compressive work by the piston. The primary purpose of the piston is thus 
to cyclically displace the gas in order to facilitate the heating and 
cooling in the desired cyclical manner, whereby the energy required to 
sustain the piston oscillation is much less than if the piston were a 
working piston which more directly performed work upon the load. For these 
reasons, it is feasible for the free piston of this invention to be driven 
in the simple, thermal lag manner. 
Besides simplicity, another advantage of avoiding the use of a working 
piston as the primary moving part of the engine is that the displacer 
piston oscillation is affected relatively little by the load, whereby the 
energy converter is essentially stall-free, because of the bypass and the 
thermal lag means for sustaining piston oscillation. For example, if the 
rotor 30 were held stationary, piston oscillation would continue as long 
as the heating and cooling rates were adequate. Or, if there were no rotor 
and the single free piston device were used as a pump for storage of gas 
in high and low pressure surge tanks, neither a large nor a zero 
difference in pressure between the two tanks would stall the piston 
assuming adequate heating and cooling were still provided. 
For generating electrical power, one advantage of using a turbine instead 
of a working piston, as the working member of the engine, is the higher 
speed of the turbine which does not have to stop twice each cycle as a 
working piston does. A high turbine speed is further facilitated by the 
high speed gas flow through conduit 24 which has a much smaller 
cross-sectional area for flow than does cylinder 1. This difference in 
cross-sectional area acts as a gas speed multiplying factor for augmenting 
the rotational speed of the turbine. Thus, the piston-cylinder of this 
invention can serve as a Stirling-type compressor for a turbine in place 
of the usual turbo-compressor. This substitution is especially 
advantageous when the engine is of small or medium size, since 
conventional turbo-compressors become very inefficient in small sizes. The 
simplicity, long life, silent operation and low cost are also advantages, 
no matter what the driven load may be. 
The device can be turned upside down without increasing the piston-cylinder 
friction, whereby the hot end of the cylinder and the heating chamber 
would then be on top and the cold end of the cylinder, and perhaps the 
starter, would be on the bottom. In addition, the device can also be 
operated at any other angles within a gravitational field as long as the 
higher piston-cylinder friction can be accommodated by the means for 
sustaining piston oscillation. 
In the device of FIG. 1, the piston can be reversed in direction at the top 
of the cylinder merely by gravity, if the cold bypass port is higher than 
the uppermost travel of the upper face of the piston. The cold rebound 
chamber as described herein would not then be necessary. 
Since the piston is not a working piston, it can be very light, whereby the 
energy required to reverse its direction of motion and sustain its 
oscillation is small. Another advantage of the piston being light in 
weight is that piston-cylinder friction is low even when the cylinder is 
not vertical. A further advantage of the light weight or low mass of the 
piston is that the vibration of the device would be minimal. However, if 
it is desired to eliminate any tendency of the device to vibrate along the 
cylinder axis, two in-line cylinders may be used, with the pistons 
synchronized to move in phase in opposite directions by suitable 
synchronizing means, such as, for example, described and/or illustrated in 
my patents referenced hereinabove. While my thermally powered model does 
not demonstrate all of the features illustrated in FIG. 1, it does utilize 
the basic configuration described and/or illustrated in by above-mentioned 
patents for obtaining synchronization. The model demonstrates two 
thermally powered free pistons oscillating synchronously and oppositely, 
whereby the tendency of the device as a whole to vibrate is essentially 
zero. 
The turbine may alternatively be connected to the cylinder at positions 
thereof along the cylinder axis other than the illustrated position, such 
as for example, at the cold end wall of the cylinder or, if the turbine 
housing is not cooled, at the hot end of the bypass region. Still further, 
the turbine housing may be heated and the turbine used as a thermal lag 
heating chamber in place of the chamber 5. It would then communicate with 
the cylinder as does chamber 5, and cooling for the energy converter could 
then be provided by means such as a cooling chamber in the bypass between 
the regenerator and the cold bypass port. However, if the turbine is 
operated hot, as in these last two examples, there probably would be some 
undesirable transfer of heat to the turbine bearings, as well as perhaps 
some undesirable heat flow to a generator or alternator driven by the 
turbine. 
Free piston 7 is of simple and integral construction, and thus, all 
segments of the free piston move together as a unit and the 
cross-sectional dimensions of the piston are constant throughout the 
length of the piston. 
The terms hot, warm, cool, and cold, as used herein, are relative terms. 
For example, the cold end of the cylinder may feel warm or hot to the 
touch even though it is cooler than the hot end of the cylinder. Either of 
the terms warm or hot implies a higher temperature than either of the 
terms cool, or cold. 
The thermodynamic cycle of the present invention is essentially 
regenerative but, strictly speaking, it utilizes neither a Stirling cycle 
nor an Ericsson cycle, both of which are regenerative gas cycles. However, 
because Stirling type engines are relatively well known and utilize a 
displacer piston, the device may, in a broad sense, be referred to as a 
Stirling type device, and the cycle may loosely be referred to as a 
modified Stirling cycle. 
Due to the motion of piston 7 as well as the movement of heated gas 
returning from heating chamber 5 to the hot end of the cylinder, during 
the first coasting portion of the cycle, the heated fluid stream directed 
into the hot end of the cylinder by the hot bypass conduit may not travel 
exactly in a straight line toward the heating chamber inlet port. The 
particular geometry of the hot end of the cylinder, with its deflecting 
surfaces, may also influence the path of the directed stream within the 
cylinder. Thus, for reasons such as these, the heating chamber inlet port 
and conduit may have to be disposed somewhat off-axis with respect to the 
mean flow axis of the hot bypass conduit, in order to readily admit 
substantially all of the directed stream from the hot end of the bypass. 
Although the bypass is described herein as being blocked and unblocked by 
the piston side-wall, other means can be used to block and unblock the 
bypass at the proper times, whereby the bypass, in a structural sense, 
would not necessarily be restricted to bypassing only a portion of the 
cylinder, and could then theoretically bypass the entire cylinder. Thus, 
for example, the bypass could be blocked or closed by a pressure sensitive 
valve or a piston position sensitive valve. As shown in FIG. 7 of my U.S. 
Pat. No. 3,782,859, for example, a face of the piston can have a rod or 
nipple which periodically enters a small cylinder at the end of the main 
cylinder in which the piston travels, and operates a pressure sensitive 
valve in the small cylinder. 
Obviously, many other modifications and variations of the present invention 
are possible in light of the above teachings. It is to be understood 
therefore that within the scope of the appended claims, the present 
invention may be practiced otherwise than as specifically described 
herein.