Note: Descriptions are shown in the official language in which they were submitted.
I-IE I~TlC Rl.SONANT l':L~rON
ST:tl~LING _NGrNE COMPRESSOR A_T_~NATOI~ IIAVING
ilYDI~AIJI.IC COUP_ING DIAI'_IACM
TECHNICAL FIEL~
~ ... . _ __
This inverltion re.Lates to nn improved Stirling
engine and in particular to all :improved free-piston Stirling engine
having a hydraul:ic coupl:i.ng to an output melllbe:r such as a compresYor
of a heat pump.
BACKGROUND A~T
The Stirling eng:ine is a cLosed-cycle engine ~.lth
cyclic recirculat:lon oE the work:Lng f:Lu.i.d. Power :is produced by
compressing the workillg flu:id at a l.ow temperature and exrunding it
at a high temperature. The requi.red heal: is added continual.Ly
durlng expans:ion of tlle working gas i.ns.ide the engine througil a
heat exchanger wal.L. Since this wal:L has a high heat capnclty,
it i.s not possib.Li~ to rapi.dly heat and cool the same wall; there-
Eore, the working gas is alternately shuttled between two stationary
variable volume chambers in the working space, held respectively
at high and low temperatures and called the hot space and the cold
space.
The alternating heating and cool:ing of the same
wor~ing gas would inherently waste quantities of heat, so a
regenerator is placed between the hot and cold sources in the
path of the working gas. Heat
.~
~ ~ID ~73Pc~r
7~-3
~2~
1 is stored in the regenerator as the gas moves from
the hot space toward the cold space and is then re~
leased to the working gas as i~ passes back through
the regenerator in moving from the cold space to the
hot space.
The conventional Stirling engine includes two
pistons: one, called the displacer, is a lightweight
body mounted on a rod which moves the displacer to
shuttle the working gas between the hot and cold
spaces; the other, called the power piston, is of
heavier construction and is responsible for the work
transfer over the cycle.
The motions of the power and displacer pistons
can be considered from a first order perspective, to
give rise to three pressure wave components, two o~
which occur with.in the cold space or engine compres-
sion space. The first pressure component, called the
power piston pressure wave, is associated with the
motion of the power piston. Physically, this is the
pressure wave which would exist in the engine if the
displacer piston were held fixed and the power piston
were oscillated sinusoidally9 The amplitude of the
power piston pressure wave is related to the springi-
ness of the engine and is primarily a function of the
engine pressure, enclosed volume, piston area, and
piston mass~
.
The second component is associated with the mo-
tion of *he displacer piston and is called ~he dis-
placer piston pressure wave9 Physically, this is the
pressure wave which would exist in the compression
space volume if the power piston were fixed and the
displacer piston were oscillated sinusoidally9 This
wave is the result of two generally conflicting
. HD-5473PCT
~'7~
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1 effects: the first is the change in pressure which
results from moving the displacer rod in and out of
the engine volume; the second is the change in pres-
sure which occurs due to the change in gas tempera-
ture as the working fluid is shuttled between thehot and cold spaces in the engine. As the displacer
moves toward the engine hot space, the first effect
tends to increase the pressure and the second effect
tends to decrease the pressure. For any practical
engine operating point, the temperature effect more
than o~fsets the volume efect. As a consequence,
the displacer pressure wave leads the displacer mo-
tion by 180.
The third component of the pressure wave occurs
in the expansion space volume or the hot space and is
due to seal leakage. This component results from the
pressure drop across the seal and is proportional to
the pressure amplitude, leading the pressure by gao.
It i5 inimical to yood engine efficiency and is the
subject of considerable development effort to mini-
mize. The sum of these three components is the pres- -
sure wave in the working space; if there were no
pressure drop in the heat exchanger duct, this wave
would lead the power piston motion.
2~ The pressure wave components in the expansion
and compression spaces may further be broken down in-
s to two elements: first, the basic pressure wave and,
- second, the pressure drop due to flow through the heat
- exchanger duct. I'he basic pressure wave approximates
the pressure wave which would be measured in the mid-
dle of the heat exchanger duct. The expansion space
pressure is the basic pressure plus the pressure drop
between the middle of the heat exchanger duct and the
expansion space~ The compression space pressure is
HD~5473PCT
1 found ln a similar manner. The forces which are
exerted on the power piston and the displacer, because
of the basic pressure wave, are obtained by multiply-
ing the magnitude of this pressure wave by the area of
the power piston face and the displacer rod area, re-
spectively. These forces, which are 180 out-of-
phase with the pressure wave, are in a ratio of ap-
proximately 10:1. The power is proportional to the
component of the force phasor which is normal to the
displacement vector. As a consequence of the dis-
placer rod area, the engine does feed power into the
displacer through the rod area, and if the rod area
is large enough, this power will exceèd the power
dissipated through the heat exchangers. The lag angle
between the engine pressure wave and the power piston
phasor is referred to as the engine pressure anyle.
A low-pressure angle corresponds to a peaked or
springy PV diagram while a high-pressure angle cor-
responds to a more oval or flat PV diagr~m~ From a
thermodynamic per~pective, a flat PV diagram is more
desirable than a peaked PV diagram since the flat
diagram has a lower peak-to-peak pressure ratio and,
hence, a smaller temperature vari.ation of the gas in
the compression and expansion space volume, and there-
fore, lower thermal mixing and thermal energy losses.The thermal mixing loss is the irreversibility which
occurs when gas from the heater or cooler enters the
expansion or compression space volume at a tempera-
ture signficantly different fxom the gas temperature
within the vol~meO The thermal entry loss is the
loss which occurs when gas from the expansion or com-
pression space enters the heater or cooler ~t a tem-
perature significantly different from the heater or
cooler metal temperature.
ilD~5~73P~T
-5-
l The uni~ue feature of free-piston Stirling en
gines is that the piston motions are determined by
the state of a balanced dynamic system of springs and
masses, rather than a mechanical system.
The free-piston Stirling engine is an ideal
vehicle to power residential-sized heat exchangers.
It is extremely ~uiet, indeed virtually silent, in
operationO It can be designed to be heated by any
fuel whatsoever, and therefore is able to utilize the
cheapest and most available fuel at any particular
timer By using the same fuel for both heating and
cooling, the seasonal demand on particular power
sources can be substantially leveled to the benefit
of the distrihution system. The free-piston Stirling
engine is sealed so the working fluids within the
pressure vessel are not subject to loss through the
shaft seals of conventional mechanical output Stirling
engines. However, in a closed hermetic system uti-
lizing moxe th~n one working fluid, it is necessary
that they be separated. In addition, the lubrication
within the sealed vessel must be maintainPd at the
correct pressure and properly separated from the other
working fluids, particularly the engine working fluid.
Power modulation of a Stirling engine heat pump
alternator is theoretically controllable by control~
ling the pressure of the wor~ing gas in ~he engine.
However, this also has the effect of altering the en-
gine frequency which in turn can alter the frequency
of ~he electric output of the system. In-some situa-
tions, it may be desirable to regulate the power ou~put while maintaining the system frequency constant. -
~ HD-5~73PCT
7 ~ A, ~ ~
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1 As the power requiremellts for the heat pump inW
crease in hot or cold weather, this condition must be
sensed by the system which must automatically adjust
the operating parameters to produce a higher output
power. The conventional technique for accomplishing
the power modulation is to adjust the time interval
in which the compressor operates. This is inherently
inefficient because of start-up power surges and the
other known inefficiencies in operating a high-power
output device intermittently to produce low power out-
put levels. A much more efficient method would be to
run a system continuously but modulate the input
energy to produce a controlled output power as
desired~
Disclosure of the Invention
- ,
It is an object of this invention to provide a
free-piston Stirling engine having a displacer sprung
to ground and a hermetic separation of the engine
working fluid and the power piston. The engine is
coupled to ~ gas compressor havin~ a P-V diagram ro-
tated 90 to the engine P-V diagram/ so anenergy stor-
age mass is incorporated in the compressor to absorb
energy from the engine during the high power output
portion of its c~cle, and to deliver that stored
Z5 energy to the compress~or during the high power demand
portion of its cycle.
. ~ ,
A power diaphragm is provided to seal the woxk-
- ing gas in the working space, and a hydraulic coupling
between the power diaphragm and the power ~iston pro
vides a uniform backing for the diap~ragm and a means
for selecting the stroke of the power pistonO The
displacer is supported for axial oscillation on a
post fixed relative to the vessel and incorporates a
" HD-5~73PCT
7~3
-7Y
1 gas spring between the post and the displacer. A mid-
stroke porting arrangement is provided to maintain the
equality of the gas spring and working gas mean pres-
sures. A control is provided for continuously modu-
lating the engine power in response to system demands.
Brief Descr_ption of the Drawings
The invention and its many objects and advan-
,~ages will be come more clear upon reading the follow-
ing description of the preferred embodiment in con-
junction with the following drawings, wherein:
Figs. lA and lB are the top and ~ottom sections,
respectively, of a sectional elevation of a Stirliny
engine driven alternator/compressor made in accordance
with this invention;
Fig. 2 is a plan view along lines 2-2 in Fig. lB;
Fig. 3 is an exploded view of portions o~ the
gas compressor piston cylinder assembly shown in
Fig. 1~;
Fig. 4 is a sectional plan view along lines 4-4
in Fig. lA;
Fig. 5A is a combined temperature-entropy graph
of the engine and the compressor of the embodiment
shown in Fig. l;
Fig 5B is a combined pressure volume diagram of
'25 the engine working gas and the compression spaces in
the compressor;
' , Fig. 5C is a schematic diagram of the Stirling
engine and compressor of the embodiment shown in
Fig. l; and
Fig. 6 is a schematic view of the controls for
the device shown in Fig. 1.
HD 5~73PCT
, ~_
1 Description of the Preferred Em~odiment
Referring now to the drawings wherein like refer-
ence characters de5ignate identical or corresponding
parts, and more particularly to Fig. 1 thereof, a
Stirling engine powered alternator-compressor is shown
having a Stirling engine working section 10 and a
power section which includes a compressor-alternator
assembly 12. The power section and the working sec~
tion are coupled through a lower hydraulic chamb~r 14.
The distal end (the top end in Fig. lA) of the
compressor-alternator assembly 12 is coupled through
an upper hydraulic chamber 16 to a bounce space 18.
The workiny section 10 and the alternàtor-compressor
are all enclosed within a hermetically sealed ~essel
17 having a vertical axis.
Broadly, the energy flow through the system be-
gins with heat input to the heater head 20 of the en-
gine which heats a charge of working gas contained
within the working space of the engine working sec-
tion lOo A displacer 22 moves axially in a recipro-
cating manner in the working space and causes the
working gas to cycle between the hot end defined by
the heater head 20 and the opposite end which is kept
cold by a cooler 24. The cyclic heating and cooling
of the working gas causes a periodic pressure wave
which is transmitted through a flexible engine dia-
phrasm 26 to the hydraulic fl~id in the hydraulic
chamber 14 where it drives a compressor cylinder 28
to compress a gas or vapor such as Freon refrigerant
in conjunction with a fixed piston 30. The other end
of the compressor cylinder 28, operating in a hy-
draulic chamber 1~, is similar in shape to the first
mentioned end of the comp.ressor cylinder operating
in the hydraulic chamber 14 and is coupled tnrough
HD~5473PCT
3~
~ -.
1 the hydraulic fluid in the chamber 16 and a bounce
diaphragm 31 to the gas spring bounce space 18. An al--
ternator armature 32 is fastened to the compressor
cylinder 28 and oscillates with it opposite a fixed
alternator stator 34 to produce electrical output
power.
The engine displacer 22 oscillates axially in a
working space which is defined by the inner surfaces
of the heater head 20, a cylindrical regenerator
housing 36 to which the heater head 20 is screwed, a
cylindrical cooler housing 38 to which the regenera-
tor housing is attached by bolts 40, a base member 42,
and the engine diaphragm 26. A shell 46 is an,chored
to the base 42 at 47 and extends downwardly therefrom
coaxially through the working space~ The shell 46
has an axial opening 48 in the lower end thereof for
directing the flow of working gas in close proximity
to the heater head for the purpose of heat.ing the gasO
The displacer 22 includes a top portion S0 having
an outside cylindrical wall 52, a flat radially ex-
tending annular roof 54 and coaxial sleeve 56 extend-
ing into the middle of the displacer 22. The end of
the sleeve 56 i5 enlarged and closed by an end wall57
to form a chamber 53. The bottom end of the cylin-
drical wall 52 texminates in an inwardly extendingradial flange 60 and a small,axially extending lip 62
! to which is fastened the top edge of a cylindrical
body 64 having a closed rounded bottom end 66. Three
di,sc-shaped stiffen r elements 68 to hold the shape
of the.'cylindrical body 64 and act as heat- shields.
The center of each of the stiffener members 68 is
punctured by a small hole 70 for enabling the interior
of the displacer to pressurize equally throughout.
HD-5473PCT
2~
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l The base 42 includes a plinth 72 fastened by an
axial screw 74 to the central portion of the base 42
and held against rotation with respect thereto by a
locating pin 76. An integral axial post 78 depends
from the plinth 72 in snug fitting relation to the
sleeve 56~ The interior of the axial post 78 is pres-
surized, by a system which will be described below,
and provided with a series of smal~ holes 79 which ad-
mit pressurized gas to the interface between the post
78 and the sleeve 56 to act as a gas bearing. A hole
80 is drilled in the sleeve ~axially midway between
the series of holes 79 to act as a gas bearing drain.
The re~enerator housing 36 encloses an annular
cylindrical regenerator 81 composed of a network of
fine high-temperature wires such as Nichrome or
Inconel. 'rhe wires are arranged in a screen or mesh
configuration which presents a minimal impedance t~
the gas flow through the regenerator while presenting
a substantial surface area to the gas to facilitate
the heat exchange between the wire and the gas. The
connection between the regenerator housing and the
heater head 20 and the cooler 24 facilitates easy in-
spection and replacement of the regenerator should
that be necessary.
The cooler 24 includes the cooler housing 38 pre
senting an annular space betw'een the inner surface of
the cooler housing 38 and the outer surface of the
shell 46~ A cooler assembly is secured in the annu-
- lar space and sealed therein as by brazing'or other
30 secure means to prevent any mixing between' ~he c'oolant
and the engine working fluid. The cooler is an annu-
la assembly having a top plate 84 and a bottom plate
85, both of which are perforated with a multitude of
~, ~ID~5~73PC'r
--11~
1 closely spaced small diameter aligned holes~ A
plurality of fine tubes 86 are brazed at their ends
between the top and bottom plates 84 and 85 to pro-
vide a gas passage between the plates with a very
large heat exchange surface area. A set of three
radial baffles 87 is arranged between the top and
bottom plates and alternately fastened at outer and
inner circumferential edges to the cooler housing 38
and shell 46, respectively, thereby providing a ser-
pentine path for the coolant. An inlet connection 89and an outlet connection 89' are provided for con-
nection to coolant lines for circulation of a liquid
coolant such as water or liquid Freon through the
cooler and an external heat exchanger (not shown) for
effective cooling of the working gas. The baffle
arrangement makes maximal use of the coolant by
creating high rates of flow around the tubes and a
multi-pass, counter-current flow for optimal heat
exchangP .
The base member 42 includes an outer ~lange 88
having holes 90 formed therethrough for receiving
bolts 92 which fasten the base 42 to the power sec-
tion 12 of the vessel. The top face of the base 42
is formed in a shallow concavity 94 which, with the
engine diaphragm 26, forms a portion 95 of the cold
space or engine working gas compression space. The
face 94 also-serves as a limit surface to prevent ex-
cessive downward deflection of the diaphragm 26.
, The base member 42 includes a series-c~ passages
96 extending completely through and establishing com-
munication between the cooler and the portion 95 of
the compression space. A second set of passages 98
formed through the base 42 at a position radially
,, .
~ llD~5473PCT
'7;~
1 inward of the passages 96 establishes communication
between the portion 95 of the worklng gas compression
space and a second or lower portion 100 of th2 working
gas compression space bounded between the top face
102 of the displacer and the bottom face 104 of the
plinth 72.
The diaphragm 26 lies in a plane which is per-
pendicular to the axis of vessel 17 and approximately
coaxial therewith. This has the advantage of great
compactness and rugged construction. It is made pos
sible because the displacer drive arrangement is lo-
cated within the displacer and therefore does ~ot
require external driving mechanisms. An additivnal
advantage of this arrangement, as will appear more
clearly in the following description, is the compact
connection o the power section, directly to the same
vessel with the engine. This makes possible a low
cost, unitary power module in which all power trans-
mission is within the vessel and the only connections
to the vessel are fuel lines and power take-off lines
from the compressor and alternator.
The gas flow path of the Stirling engine will
now be described in connection with the theoretical
or ideal Stirling engine cycle as shown in the
temperature-entropy and pressure-volume diagrams of
Figs. SA and 5B, At an arbitrarily selected starting
point, the displacer 22 is at its lowermost position
with the dome-shaped bottom portion of the ~isplacer
close to the dome-shaped bottom portion of the ~hell
46, and the engine diaphragm 26 in its uppermost po-
sition away from the top face 94 of the base member4
In this configuration, the gas volume is maximum and
the gas temperature and pressure are minim~. This
~ HD~547~PCT
7~
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l is point A on the pressure~volume and temperature-
entropy diagrams. The process A-B is performed by
the diaphragm 26 moving downwardly toward the face 94
of the base member 42. This process is an isothermal
compression of the cold working gas wherein the heat
occasioned by the compression of the gas is trans-
ferred from the gas to the cooler 24. At position B
the diaphragm is at its lowermost position against
the face 94 of the base 42 and the displacer is-at its
lowermost position with the rounded end 66 of the dis-
placer 22 close to the rounded bottom end of the shell
46. At this point, the volume, temperature, and en-
tropy are all at their minimum values.
The next motion is the motion of the displacer
moving upwardly away from the curved bottom face of
the shell 46 toward the bottom face 104 of the plinth
72. This displacer motion causes the gas to be dis-
placed from the cold space at the top end of the en-
gine through the cooler and then through the regenera-
tor where it i6 reheated by the heat deposited in theregenerator during the last c~cle, and then passes
between the heater head 20 and the shell 46 where it
i5 heated at constant volume by heat transfer from the
heater head 20. When the displacer 22 reaches its
uppermost position, the gas, still at minimum volume
but now at maximum pressure a~;d temperature, does work
? on the diaphragm, driving the diaphragm upward in the
process C-D which is an isothermal expansion of the
working gas where heat is transferred to the working
f~uia at the maximum cycle temperature of the external
source. The displacer again moves downward to dis-
place the hot gas toward the cold zone, during which
it passes through the regenerator and deposits its
heat into the regenerator where it is cooled at
~7~ 1D-S473P~r
1 constant volume. Thi5 is the process D-A in which the
pressure and temperature drop at constant volume. The
cycle then repeats itself at t,he natural fre~uency of
the system. If the heat which is transferred to the
working fluid from the regenerator matrix is the same
as that transferred from the fluid to the matrix, then
only the external heat tranfer processes remain; the
efficiency is consistent with the Carnot cycle effi-
ciency. The advantage of the Stirling engine cycle
is that the two isentropic processes of the Carnot
cycle are replaced by two constant volume processes
which increase the area under the P-V diagram result-
ing in higher specific work output levels without re-
sorting to very high pressures and high swept,volumes.
The ideal c~cle described assumes that the proc-
esses are thexmodynamically reversible. That is, the
expansion and compression processes are isothermal
and that infinite heat rates exist in addition to in-
finite heat capacities. The ideal analysis neglects
the effects of reyenerator matrix voids, clearance
spaces and cylinder pockets. In addition, the dis-
placer and engine diaphragm are assumed to move in a
discontinuous manner whereas, in reality, the motion
is smooth and continuous. Therefore, the theoretical
P-V and T-S diagrams are rounded off as shown in the
oval shaped curves. Aerodynamic and mechanical losses
are also neglected. Incl,usion of these losses, of
course, results in a lower nbt cycle output power and
lower efficiency. The addition of heater and co~ler
- 30 components changes the real heat transfer ~o a more
- adiabatic si~uation rather than the assume'd-isothermal
processes. Penalties in additional aerodynamic flow
losses and increased dead volume result. The use of -
practical equipment imposes one'additional reality;
that the fluid is heated not only as it flows to the
~ S~73PCT
1 expansion space, but also as it flows in the reverse
direction from the expansion space to the cooler.
The cooling process is also penalized in this manner
as well. These losses have been minimized by this
engine design to maximize the engine efficiency toward
the ideal Carnot efficiency.
Turning back again to Fig. 1, the power section
will now be described. The hermetic vessel 17includes
a cast aluminum casing 106 having a lower flange
107 to which the outer flange 88 of the base member
42 is bolted by the bolts 92. The casing 106 includes
an integral hydraulic cylinder 108 which is coaxial
with the vessel axis. The hydraulic cylinder 108
terminates at a top end 110 and flares on its bottom
end in a web 111 with a concave face extending outward
to the same diameter as the concave face 94 on the
base member 42. The bottom face 112 of the casing 106
serves a function corresponding to the concave face 94
- o-f the base 42, namely to prevent excessive deflec-
tion of the engine diaphragm 26 and al50 to provide a
wide area over which the engine working gas can act
through the engine diaphragm 26 to displace a si~-
nificant volume of hydraulic fluid to act in the hy-
draulic cylinder 108.
The hydraulic cylinder 108, which is cast i~-
tegrally with the case 106 anl~ therefore is of the
same material, is lined with a sleeve 114 of high-
strength, wear-resistant material such as stainless
steel. The sleeve is retained in position by a spi~
der 116 having an outer ring 118 which fits into a
recess 120 at the lowex end of the hydraulic cylin-
der 108. The spider also includes a series of arms
122 extending inwardly to a center disc 124.
HD-5473PCT
-16-
1 A piston assembly 125, shown exploded in Fig, 3,
is mounted for axial reciprocation in the vessel 17
and includes a cup-shaped lower end member 126 at-
tached to the cylinder 28 and operating in the hy-
draulic cylinder 108. The piston lower end member
126 includes a lower working face 128 which, with the
top face of the engine diaphragm 26, defines the lcwer
hydraulic chamber 14. The flexiny of the diaphragm
26 in response to a pressure wave generated in the
working gas in the Stirling engine working space dis~
places~ hydraulic fluid upwardly in the hydraulic cham-
ber ~ to drive the piston 126 upwardly in the hy-
. ~
draulic cylinder 108.
The piston assembly 125 is substantially s ~ net-
rical about the transverse plane 4-4, except for an
elongation of the top piston member 126' to provide a
threaded mounting collar for the linear alternator
armature, as will he described below. A hydraulic
cylinder 108' lined with a sleeve 114' is disposed at
the top end of the vessel 17 to receive a cup~shaped
top end member 126' of the piston 125. The end face
128' of the top end member 12~' of the piston 125,
along with the bolu~ce diaphragm 31, defines a top hy-
. draulic chamber ~' which cooperates with a bounce
space 18 to balance the:piston 125 dynamically so
that it will produce two power strokes for each cycle
of the engine working space. The following detailed
description of the piston assembly 125 lower end will
be understood to apply also to the symmetrically iden-
tical structure of the top end, therefore the descrip-
~ion will not be repeated for the top end~
An axial boss 131 is formed inside the piston
end member 126 extending inward, away from the piston
~ ID~5473PCT
7~
l7
1 face 128. The boss is hollow, defining an axial well
132 opening in the face 128 of the piston. The well
132 receives one end of a centering spring 134 which
is biased between the end wall of the well 132 and
the top face of the dlsc 124. A similar centering
spring 134' acts i~ a symmetrically identical well
opening in the top end 126' of the piston 125 to exert
a centering force on the piston in its cylinders 108
and 108'.
An inlet val~e seat disc 138 is fastened to the
top end of the central boss 131 by a screw fastener
140 or the like. The diameter of the inlet val~e
seal disc 138 is smaller than the inner diameter of
the piston lower end member 126 to provide an annular
passage 142 through which gas to be compressed can
flow into the compression space, as will be described
below. A series of inlet openings 144, formed in the
inlet valve disc~ are controlled by an annular valve
reed 145 for admitting gas to be compressed and pre-
venting the exodus of gas from the compression cham-
ber as it is compressed, all to be described presently.
A series of apertures 146 is formed through the side-
wall of the piston lower end member 126 for the pur-
pose of admitting gas to be compressed into the com-
pression chamber.
The top inside periphery of the piston lower endmember 126 is internally threaded at 150 and screwed
onto a threaded portion 152 of the cylinder 28. The
c~linder 28 is threaded to and becomes part-of the
piston 125, but it functions as a moving cylinder re-
ciprocating on the fixed piston 30. Thus the piston
125-cylinder 23 assembly has both piston and cylinder
functions. The cylinder 28 includes a loweF end 154
. ~ ~ID-5~73PCT
7~3'~
-18~
1 having a diameter identical to the diameter of the
inlet valve seat disc 138, An annular groove 156 in
the end face of the cylinder 28 receives an 0-ring
158 to seal the junction of the cylinder 28 to the in-
let valve seat disc 138. The inside lower edge of thecylinder 28 is notched at 159 to receive a stop ring
160 which extends over the inlet valve reed 145 to
retain the reed during the suction stroke in which gas
flo~sthrough the inlet openings, around the reed 145,
and into the compression chamber 161. The end of the
cylinder 28 is necked down at 162 in the vicinity of
the apertures 146 in sidewall of the piston end mem-
ber 126 to provide the aforementioned annular gas pas-
sage 142 for gas passing from the interior of ~.he cas-
ing 106 into the compression space. An oval slot 163
extends through both sides of the central section of
the cylinder 28 between the threaded portions 152 and
152' to provide clearance for the cylinder 28 to re-
ciprocate around the pipe 182, to be described below.
A cylindrical boss 164, best shown in Fig. 4, is
formed in the side of the casing 106 at the center of
the midstroke position of the piston 125. A corres-
ponding boss 166 is formed in the wall of the casing
106 diametrically opposite the boss 164. A bore 168
extends completely through the boss 164 perpendicular
to the vessel axis, and an aligned bore 170 extends
partially into the boss 1~6.
. ~
. The fixed piston 30 is disposed in the center of
the cylinder 28. The fixed piston 30 incIu~es a pis~
ton body 172 and an exhaust valve disc 174 screwed to
the end of the piston body 172 by a screw 176 or the
like. An annular exhaust valve reed 178 lies over
a series of openings 179 in the exhaust valve
. HD~5~73PCT
-19~
1 disc 174 for exhausting gas which has been compressed
between the inside face of the inlet valve disc 138
and the outside face of the exhaust valve disc 174,
which space constitutes the compression space 161 of
the gas compressor. In a manner sirnilar to the inlet
valve arrangement, the lower end of the piston body
172 is notched to receive a valve stop ring which is
held in place ln its notch by the outlet valve disc
174. A series of gas channels 180 communicate between
-a plenum behind the exhaust valve reed 178 and a cen-
tral transverse bore 181 extending to the bore 168 in
the boss 164 and the bore 170 in the boss 166.
A pipe 182 extends through the bore 168 in the
boss 164, the slots 163 in the cylinder 28, the bore
181 in the piston body 172 and into the bore 170 in
the boss ].~6. A screw 184 is threaded into an in-
ternally threaded hole in the end of the pipe 182 to
fasten the pipe to the casing 106. An 0-ring 186
seals the pipe lg2 in the bore 168 of the boss 164
and a corresponding 0 ring 188 seals the pipe in the
bore 170 of the boss 1~6. The pipe 182 extends
through the central transverse bore 181 in the piston
body 172 to secure the piston 30 in place in the cas-
ing lOG and to establish fluid communication from the
interior of the piston 30 to the exterior of the case
106. This communication is established by a recess
190 which connects the channels 180 in the piston
body 172 with an aperture 192 in the pipe 182, which
aperture permits gas to flow rom the pi~ton interior
into the interior 194 of the pipe 182O A-fittin~ 196
. is ~hreaded into an internally threaded portion at
the end of the boss 164 for connection to external
gas lines by which the compressed gas may be piped
to its use, as in a heat pump.
'7~
- 20 -
Ttle manner of asselllbLy of the colllpr~s.sor apl)artus
will now be described. The exhaust valve discs 174 alld l74' are
screwed to the ends of the plston body L72 whicll is then inserted
into the cylinder 28. The inlet valve seat discs 138 and 138 ~lre
screwed to the interior top of the central boss 131 on the two
piston end portions l26 and 126', respective:ly, arld the two piston
end portions 126 are screwed onto the cyLinder 28 at the threaded
portion 152. The lower end ]26 of the piston cylinder assembly i9
then inserted into the hydraulic cylinder 108 and the pipe l82 is
slid through the bore 168, the slots 163 in the central portion of
the cylinder 28, the bore 181 in the piston body l72, and into the
bore 170. The screw 18~ is threaded into tlle threaded hoLd in the
end of the pipe 182 to secure the assemb1y into posit:ion.
The d5laphragms 26 and 31 hclve a number of functiolls
in the system. One important function is providing a hermetic and
thermal separatlon of the engine and compressor working gases. Any
intermixing of the working gases would have 1 deleterious effect on
the performance of the engine or the compressor because of the
particular characteristics of the working gases in the thermodynamic
cycles they perform. It is desirable, therefore, that there be a
"hard" or hermetic separation of the working gases, and this precludes
the use of sliding seals. One technique for providing the hermetic
separation of working gases in an internal compressor is a spring tube.
While such arrangement works well, there is a thermal penalty introduced
by the close proximity of the engine working gas to the compressor
working gas across a metal interface of large surface area. The engine
.~
~ 5~73PC'r
~ 1 ~ 7 ~
1 working gas in the cold compression space is consider-
ably hotter than the compressor working gas at suc~
tlon pressure, and the transfer of heat throu~h the
spring tube to the compressor suction gas imposes an
efficiency penalty to the compressor. The design of
the invention disclosed herein substantially reduces
that heat transfer and thereby improves the effi-
ciency potential of the compressor.
The hydraulic coupling between the diaphragms
and the compressor provides an ideal backing for the
diaphragms by eliminating stress concentrations and
also providesan ideal environment in which the pistons
126 and 126' can operate with low friction and uni-
form temperature. This hydraulic fluid would cause
severe problems if it leaked into the engine, but
- such leakage is positively prevented by the hermetic
sealing of the diaphragms,
This design has two degrees of freedom which is
a simple arrangement to control, thereby simpli~ying
the system controls. The controls are described be-
low and will be seen to be uncomplicated, inexpensive
and reliable fluid controls~ This simplification is
made possible by the use of diaphragms which eliminate
at least one degree of freedom in the system.
An alternator housing 2Q0 having top and bottom
flanges 202 and 204 is secured to the casing 106 by
means of bolts 206 which secure the bottom flange 204
to a top flange 205 of the case 106. The housing 200
includes a depending hydraulic cylinder 108' con-
nected to a top web 210 of the housing 200~ The top
surface 212 of the web 210 is slightly concave to pro-
vide a backstop for the bounce space diaphragm 31.
/ HD~5~73PCT
-22-
1(,
1 An upper end hydraulic chamber ~ is defined between
the diaphragm 31, the top surface 212 of the web 210,
the interior of the hydraulic cylinder 108', and the
top face of the upper piston end member 126'. The
function of the hydraulic chamber ~ ~ in conjunction
with the bounce space 18 will be described below.
Except for the linear alternator armature mounting
ring, the top end portion of the piston cylinder as
sembly is symmetrically identical to the lower end
-portion.
A linear alternator is mounted in the housing
200 for generating electrical power. The alternator
includes an armature 32 fastened to a support cylinder
216 of the upper piston end member 126'. The alterna~
tor armature includes a depending internally threaded
collar 218 which flares outwardly in a funnel-shaped
section 220 and is joined to a cylindrical sleeve 222
which supports the alternator armature 32. The arma~
ture stator 34 is fastened to the inside surface o~
the alternator housing 200 in radial alignment with
the transverse midplane of the alternator armature.
A top dome 225 is fa~tened to the alternator
housing 200 by bolts extending through holes in a
bottom radial flange 226 and aligned holes in the
top flange 202 on the alternator housing. The d~ome
225 encloses a control space 227 which is separated
~ from the bounce space 18 by a partition 228O The bot~
- tom face of the dome 225 is slightly concave to pro-
vide a backing for the diaphragm 31 and includes a
3G spider 229 ~hich provides a backing for the diaphrag~
31 while permitting working gas which fills the bounce
space 18 to flow freely between the top face of the
diaphragm 31 and the bounce space 18.
~ID-5473PCT
2"~
-23-
1 In operationl a pressure wave in the engine
working space causes the engine diaphragm 26 to de-
flect upwardly, displacing hydraulic fluid in the hy-
draullc chamber 14 into the hydraulic cylinder 108
where it drives the plston-cylinder 126/28 upwardly,
The valve reed 145 is forced shut against the seat
disc 138 and the exhaust valve reed 178 opens to ex-
haust refrigerant compressed in the compression space
151.
The top end 126' of the piston 125 simultane-
ously moves upwardly in the hydraulic cylinder 108',
displacing hydraulic fluid into the hydraulic chamber
16 and flexing the bounce diaphragm 31 upwardly tcward
the bounce space 18. The gas compressed in the bounce
space acts as a spring, storing energy which is re-
turned to the piston-cylinder 126/28 when it is
driven downwardly on the return stroke.
The fastigium of the compressor cycle coincides
with the minimum enthalpy of the engine cycle and
therefore the coupling between engine and compressor
must account for this inherent mismatch~ This cou-
pling is accomplished by providing the piston-cylinder
assembly 126/28 with a mass which absorbs energy from
the hydraulic chamber 14 in the form of inertia (mv2)
which is transferred to the gas in the compression
chamber 161 and also via the ~iaphragm 31 to the gas
in the bounce space 18,
At the end of the up-stroke, the piston-cylinder
126/23 is momentarily staticnary, all its inertial
energy having been converted to gas pressure in the
compression chamber 161 and the bounce space 18, and
electrical energy by the alternator. The energy in
~ flD-5473PCT
1 the bounce space 18 and some of the energy in the
compression space 161 is now returned to the piston-
cylinder 126/28 by the expansion of the compressed
gas. The piston-cylinder 126/28 moves downwardly,
compressing gas in the upper compression chamber 161'
and displacing hydraulic fluid in the hydraulic cylin-
der 108 which flows into the hydraulic chamber 14 and
pushes the diaphragm 26 into the upper portion of the
working gas compression space. The mass of the mov-
ing elements, the spring constants of the gas com-
pression spaces 161 and 161', and the bounce space 18
are selected so that the natural fre~uency of the
power piston system is near the natural frequency of
the displacer system. The hydraulic fluid pressure
and working gas pressure is adjustable, as explained
in detail below, and the gas spring/damping efect of
the compressor is self-regulating, so the systems may
be held in correct relationship to each other.
The apparatus disclosed can be used as a heat
pump in which refrigerant having a low boiling tem-
perature, such as Freon R22 or the like is compressed
by the compressor and the electrical demands of the
system such as blowers, pumps, and solenoids can be
supplied by the linear alternator. The cold refri~-
érant enters the case 106 at suction pressure at aninlet fitting 224. It fills the lnterior o the al-
ternator housing 200, coo~ing,the stator windings 34,
and fills the interior of the case 106. From there
it can be drawn into the compression chamber at each
- 30 end of the piston-cylinder assembly where it is com-
pressed and expelled at exhaust pressure through the
pipe 182 and the fitting 196 to the external heat
exchangers.
~ID-5473PCT
-~5-
1 The control system for starting the engine and
controlling the power output is shown in Fig. 8.
After a temperature differenti~l is established be-
tween the heater head 20 and the cooler 24, it may be
necessary to give the displacer an initial movement
to initiate working gas circulation and start the en-
gine. That movement is given in the system by pres-
surizing both hydraulic chambers 14 and 16 to a pres-
sure higher than the mean pressure of the working gas
,in the engine and in the bounce space 18O This will
cause the diaphragms 26 and 31 to flex outwardly away
from the hydraulic chambers. The hydraulic pressure
can then be released suddenly causing the diaphragms
to bounce inwardly toward the gas compressor ~hereby
causing a pressure wave in the working space in the
Stirling engine 10 which causes an initial movement
of the displacer.
The hydraulic chambers 14 and 16 are pressurized'
by an oil pump 230 which pressurizes oil in an oil
supply line 234 to about 20 psi higher than the mean
hydraulic pressure in the hydraulic chambers 14 and
16. The high pressure oil supply line 234 from the
oil pump 230 is connected to a starter control 232.
The starter control includes a spool valve having a
valve body 235 in which is formed a center oil pas-
sage 236 and two end passages 238 and 240. The spool
valve includes a spool valve,'element 242 biased in
,. the start position (to the left) by a spring 244 and
is moved to the normal running position (to the right)
by a solenoid 246. An axial passage 247 running
through the valve,'element 242 enables the element to
move in the'valve body 235 without pressure cushions
developing at its ends.
~ID-5~73PC'~
72
-~6-
1 The operation of the starter control 232 is as
follows: The pump 230 ls energized to pressurize hy-
draulic fluid in the line 234. The spring 244 holds
the starter control valve element 242 in the start
position (to the left in F.ig. 8) wherein fluid com-
munication is established between the line 234 con-
nected to the end passage 238 through the interior
of the valve body to the center passage 236. The cen-
ter passage 236 is connected to an oil line 252 which
-links both hydraulic chambers 14 and 16, whereby the
chambers may be pressurized. After the hydraulic
chamber pressure has reached the desired magnitude,
the solenoid 246 is energized and moves the element
242 against the spring force to the left (to the po-
sition illustrated in Fig. 8) establishing fluid com-
munication between the oil line 252, through the cen-
ter passage 236 and Ollt the end passage 240 to the
distal portion 253 of the oil supply line, connected
to the high pressure section 234 through a restric-
tion 255, and thence to an oil sump, as will be explained below. This permits the oil pressure in the
hydraulic chambers 14 and 16 to drop suddenly causing
the diaphragm 26 to flex away from the engine working
space and causing a sudden drop in the pressure of
the working gas. The gas spring 58 will sense that
pressure drop somewhat slower than the displacer top
and bottom faces and therefore the displacer will
move downwardlv in the shell.~6, displaci.ng working
? gas through the regenerator to the cooler, thus start-
- 30 ing the working ga~ circulation and the engine cycle.
.
' The oil line 252 also serves to establish com-
munication between the hydraulic chambers 14 and 16
at the midstroke position of the piston cylinder as-
sembly 126/28 to equalize the pressure in the two
~ ~ 7~ D-5~73P("~
--27-
1 chambers. As shown .in Fig. lA, a passage 254 leads
from an opening in the well 132 of the piston end
sections 126 through a web (not shown) in the piston
end member 126 and out through an opening 256 in the
S wall of the piston end member 126. A corresponding
opening 258 in the hydraulic cylinder liner 114 opens
to an annular groove 259 in the inside wall of the
hydraulic cylinder 108 which in turn leads to an oil
passage 260 in a web 262 extending from the hydraulic
-cylinder 108 and the wall of the case 106. The open-
ing 258 in the cylinder liner 114 is aligned with the
opening 256 in the piston wall at the midstroke posi-
tion of the piston-cylinder assembly, thereby es-
tablishing communication through the oil passage 260,
through the midstroke balancing line 252 connected to
a connector 263 on the wall of the case 106, and
through a corresponding passage 264 through the al-
ternator housing 200 to a corresponding midstroke
balancing oil passage system in the top piston end
member 126'. This passage system permits the oil
pressure in the two hydraulic chambers 14 and 16 to
equalize at the midstroke position of the piston-
cylinder assembly 126/28 to ensure dynamic centering
of the midstroke position in the housing, and the al-
ternator armature 32 in the statox 34.
The mean hydraulic fluid pressure in the hy-
draulic chambers 14 and i6 must be equal to the mean
. working gas pressure in the compression space in the
engine and the bounce space 18 in the top.end section
- 30 2~5. To maintain this equality, a pressure control
270 is provided having a body 272 defining kherein a
- cylindrical chamber which houses a cylindrical
plunger 276. One end 274 of the plunger 276 is con-
nected to a long roll diaphragm 278 such as a
flD-5~73PCT
-2~-
1 Bellowfram, and the other end 275 controls an oil
drain port, as will be explained presently. The
Bellowfram separates the chamb'er into two ends: one
end 279 is connected by a capillary gas line 280 to
the bounce space 18 to insure that the gas pressure
behind the Bellowfram 278 is at the engine working gas
mean pressure. The other end 281 of the chamber i5
connected to the oil line 253 and thence through the
restriction 255 to the high-pressure oil supply line
234. The restriction 255 normally reduces the hy-
draulic pressure to about the mean fluid pressure in
the engine.
The end 275 of the plunger 276 is disposèd near
the oil drain port 282 in the wall of the chamber ~81
which can be covered and uncovered by the plunger 276.
When the pressure of the working gas is higher than
the hydraulic pressure, the pressure in the gas end
279 of the pressure control 270 is higher than the
pressure in the f]uid end 281 and moves the plunger
276 toward the end 281, sealing off the drain port
282. ~he normally open passage through the start con-
trol 232 between the end passage 240 and the center
passage 236 permits the pump 230 to raise the pressure
of the hydraulic fluid through the restriction 25~ in
the hydraulic chambers 14 and 16 during the midstroke
position of the piston cylinder assembly until the'h~-
draulic and working gas press~res are equal~
: ;
When the hydraulic fluid pressure is higher than
the mean working gas pressure, the plunger 276 moves
toward'the gas end 279 of the pressure control 2io,
: uncovering the drain port 282 and permitting hydraulic
fluid to bleed out of the fluid end chamber 281~ The
back pressure is thus relieved and hydraulic fluid
~ID-5~73PCT
-~29-
1 can flow from the chambers 14 and 16 through the mid-
stroke pressure halancing line 252, the starter con-
trol val~e, and the oil line connecting the end pas-
sage 240 to the line 253 downstream of the restriction
255, until the hydraulic fluid pressure and the work-
ing gas pressure are equalized.
Power modulation is achieved by controlling the
pressure of the working gas in the engine~ Essen-
-tially, the technique for controlling the gas pressure
in the working space is to selectively connect the
control volume 227 in the top section 225 of fhe ves-
sel to the working space through a check valve which
permits gas to flow in the desired direction during
the portion of the cycle in which the space to receive
the gas is at a lower pressure than the space frorn
which the gas is supplied. For example, if it is de-
sired to lower the pressure of the working gas in the
working space of the engine, a power modulation con-
trol 290 will permit gas flow from the working space
to the control volume 227 during the high-pressure
periods of the engine cycle, but prevent flow of gas
in the opposite direction from the control volume.
The power modulation control 290 includes a
body 292 having a pressure increase solenoid 294
mounted on one end and a pressure decrease solenoid
296 mounted on the other end. ~he solenoids 294 and
296 are connected to a con~rol element 298 which
slides axially in a bore 300 in the power modulation
: cohtrol ~ody 292. A pair of centering spr-ings 302
and 304 bear against opposite shoulders on the control
element 298 to center the element in the bore when ~he
two solenoids are deenergized. The center portion of
the control element 298 is relieved at 306 to provide
IID- 5 4 7 3PCrr
:~ ~ 7 ~ ~ 3 4
30-
1 gas flow between a center port 307 and a right port
309 or left port 311 when the control elemerlt is dis-
placed to the right or left, respectivel~, in the bore
300, but prevent gas flow when the eIement is centered
S An inflow check valve 308 and an outflow check valve
310 axe provided to permit the flow of gas into and
out of the control body 292 depending on the position
of the control element 298. The center gas port 307
from the control element body 292 is connected to the
control volume by a fluid line 314. The right and
left ports 309 and 311 are connected by fluid lines
to the working spac by a fluid line 316.
In operat~on, when it is desired to increase
the power of the system, the increase solenoid 296 is
energizèd pulling the control element 298 to the left
in Fig. 8, thereby establishing fluid communication
between the lines 314 ~nd 316 through the check valve
310 and the control body passages to permit fluid
flow from the control chamber through the ralieved
portion 306 in the control element and hence through
the fluid line 316 into the bounce space 18 at the
working space in the Stirling engine and the engine
working space. The fluid flow occur~ only during the
low-pressure portions of the Stirling engine cycle
since the control chamber pressure is lower than the
maximum cycle pressure of the gas in the working
spaceO The engine working gas pressure is thus in
creased which increases the engine power.
, 1
. When it is desired to decrease the power in the
30 Stirling engine,.the decrease solenoid 294-~s ener-
gized to puil the control element 298 to the right
against the force of the spring 304. Communication
is established between the inlet check valve 308 and
~ID-5973PCT
-31-
1 the central gas passage 307 so that fluid can flow
from the Stirling engine working space during the
high-pressure periods of its c~cle through the check
valve 308 and the control passage to the central pas-
sage 307 and thence through the line 314 into the
control chamber 227. The pressure of the working gas
in the Stirling engine and the bounce space is thus
reduced, and the engine power is reduced.
The system described above provides a Stirling
engine powered compressor-alternator which is sealed
to prevent the loss of working gases and lubricant,
and is provided with positive internal sealed separa~
tion of the engine working fluid from the comprèssor
working fluid. The sealing is achieved by diaphragms
operating in hydraulic chambers to give an incompres-
- sible linkage between the power piston and the dia-
phragm, without creating a stress concentration zone
on the diaphragms~ The engine cycle and the compres-
sor cycle are made concordant by the mass and damping
of the power piston and linear alternator armature.
The system power output and internal pressure balanc-
ing are automatically controlled, making possible
contlnuous power modulation in response to external
power demand. The internal electrical power require-
ments are provided by the linear alternator, makingthe system completely independent of the vulnerable
external grid so that a gas fuel source is the only
' 5' energy requirement.
Gbviously, numerous modifications and variations
of the above described preferred embodiment~are pos-
sible in view of this disclosure. It is, therefore,
to be expres~ly understood that these modifications
and variations r and the equivalents thereof, may be
. HD-5~73PCT
-32-
1 practiced while remaining within the spirit and
scope of the invention which is defined by the fol-
lowing claims, wherein we claim:
. I
,,
,
