Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to regenerative
Stirling cycle engine systems.
This application is a division of copen~ng Canadian
application Serial No. 273562 filed March 9, 1977
Xnown control methods for controlling the power
of a regenerative Stirling engine do so by changing the
means pressure prevailing in the working chambers of the
engine, such engine typically having a hot chamber and a
cold or low temperature chamber per cyclinder, these
being separated from one another and adapted to be alter-
nately reduced and enlarged in volume by a piston movable
in the cylinder. The hot chamber is connected to the cold
chamber within the same engine cylinder or to a cold chamber
in another cylinder (operating in a phase-displ'acement
manner) by way of a flow path having a regenerator and
cooler therein.
To control power, the mean pressure prevailing in
the working chambers is so modified that a high pressure
is present in the chambers at a high engine torque demand
and a low pressure at a low torque demand. These pressure
levels; as well as varying intermediate levels, are
achieved by means of a compressor driven by the engine and
which is effective to pump the working medium into a
reservoir. In the case of a power reduction, the reservoir
is maintained at a typically high pressure. A compressor
for this task has to meet very high standards. It must
have a high pressure ratio, must operate without lubrication
of the piston and must be sealed to prevent the escape of
hydrogen. These re~uirements can be met only with dif-
ficulty, if they are met at all, and only at great expense.
Such compressors may be separate units or may be exten-
sions of the piston extending into close-fitting auxiliary
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cylinders. The piston extensions may be one or more in
number and usually extend from the bottom side of the
principal piston. In addition to the increased complexity
and cost of utilizing a system which is compressor
actuated to transfer gases to or from the working chambers
to a reservoir, there is the additional problem that
pumping of the working medium out of the working chambers by
the small compressors takes place relatively slowly.
Separate small compressors have become a popular
means of implementing mean pressure control which in turn
provides torque control for the engine. Mean pressure
control systems of the prior art have emphasized the
need for equalizing the mean pressures in the different
working chambers, separated by double acting pistons.
However, such prior art systems employ injection or
ejection of high pressure from one working chamber at a
time which creates a temporary inequilibrium lasting
for 3 or 4 cycles of the engine until mean pressures
stabilize again. What is needed is a mean pressure control
system which eliminates independent compressors and yet
provides a temporary inequilibrium in mean pressures
during a torque demand change commensurate with the
inequilibrium now experienced by prior art systems.
In accordance with the present invention, there
is provided a regenerative Stirling cycle engine system,
comprising: (a) means defining a hot gas volume containing
a gas having a low or high density and respectively a
high or low thermal conductivity; ~b) means defining a
low temperature gas volume in communication with the
hot gas volume, each low temperature gas volume being
associated with one hot gas volume to define a pair of
cycling volumes; (c) piston means associated with each
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pair of cycling volumes and being in communication with
at least the low temperature gas volume for varying the
low temperature volume in timed relation to the variations
in the hot gas volume; (d) thermal regenerator and cooling
means intercoupling the hot gas volume and the low temperatNre
gas volume of each pair of cycling volumes to provide
reversible thermodynamic gas flow therebetween during
changes in volume; (e) means coupled to the means defining
a hot gas volume for.releasing thermal energy thereinto;
(f) means coupled to the piston means for deriving working
energy from the system; (g) means providing a one-way
fluid connection between adjacent low temperature volumes
in series; (h) means fluidly connecting the pair of
volumes; and (i) control means selectively permitting
fluid communication through any two selected and adjacent
low temperature volumes of means (g) one of the low
temperature volumes undergoing compression or is at a
compressed condition, while allowing continuous one-way
fluid communication from the selected and adjacent low
temperature volumes to a reservoir so that if the instan-
taneous pressure of the reservoir is greater than the
communicated low temperature volume, one low temperature
space will pump fluid i~to the other lower temperature
~paae to be raised in pressure therein.
In the present invention, the -~x~sity for a
separate and distinct compre.ssor is eliminated and
wor~ing fluid is transferre~ from the wor~ing chambers
a reservoir. The use of a reservoir in this way permits
rearrangement of the closed working fluid system to
realize weights and cost savings while retaining or
improving system relLability.
The invention herein is particularly adaptable
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to a double-acting Stirling cycle hot gas engine of a
kind having a plurality of engine cylinders, each
receiving a reciprocating piston therein dividing the
engine cylinder into an upper chamber containing gas at
a high temperature level and a lower chamber containing
gas at a low temperature level~ Each of the pistons
have integrally connected thereto one or more pumping
pistons, which during operation of the engine, recipro-
cate in an axial direction. According to the prior art
of Stirling double-acting piston engines, these pumping
pistons extend into an adjacent pumping cylinder provided
with two check valves to control gas conduits, one gas
conduit leading from the lower chamber of the respective
engine cylinder to the pump cylinder, and the other gas
conduit operating to assist in the alleviation of gases
from the pump cylinder. The pumping pistons, working
in the-pumping cylinder, together with the appertaining
conduits and valves, constitute an arrangement whereby
it is possible to vary the quantity of working gas
employed in the engine in order to vary the power output
of the engine.
In an engine of the type described, it is common
to connect the conduit leading from the pumping cylinder
to a gas storage tank (reservoir) and to include a stop
valve in said conduit to stop the gas flow as soon as a
predetermined pressure is reached in the tank. ~ach
pumping piston will be operating on an enclosed volume of
gas behaving as a gas spring. Several disadvantages
result from such an arrangement, among which include the
drawback that the piston rings, working in the pumping
cylinder, will be exposed to severe stresses whenever
the engine is operat-ing, even during periods when the
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pumping pistons are not pumping fluid to the tan~. In
addition, the cost and weight related to the use of such
pumping cylinders and pumping pistons, are undesirable
when making an automotive application of such engine.
The invention is described further, by way of
illustration, with reference to the accompanying drawings
in which:
Figure 1 is a schematic layout of substantially
the entire working fluid system of a regenerative Stirling
engine embodying the principles of this invention; and
Figure 2 is an enlarged sectional view of a portion
of piston and cylinder showing an alternative mode for
a valve used in the system of Figure 1.
Turning now to Figure 1, the closed working fluid
system 10 of a regenerative Stirling engine comprises a
plurality of cylinders 11, 12, 13 and 14, each divided
respectively by reciprocating pistons 15, 16, 17 and 18
into two chambers, spaces or volumes (see lla, llb, 12a,
12b, 13a, 13b, 14a and 14b). Chambers lla, 12a, 13a and
14a may be considered a hot or high temperature chamber
for purposes of expansion and the others llb, 12b, 13b and
14b may be considered a cold or low temperature chamber
for purposes of compression. Each of the cold chambers
are connected by a first means 19 to an adjacent hot
chamber in progressive series. The means 19 includes for
each pair of hot and cold cham~ers a conduit 20, a cooling
mechanism 21 for extracting heat from the closed wor~ing gas
and a regenerator ~2 for storing heat units of the gas passing
therethrough or for releasing heat units upon fluid movement
3~ in the reversed direction. The fluid in the closed working
circuit may preferably be hydrogen maintained at a relatively
high mean pressure to present excellent thermal conductivity.
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The fluid in conduits 20 is heated by an external heating circuit
j 23 surrounding a substantial portion of each of said conduits
¦ 20, promoting heat transfer to the gases therein and elevating
the gas ~emperature to about 1300F. Pssembly 5 is a means for
¦ deriving work energy from the system 10, such as mechanical swash
plate assembly.
Due to the separation of each pair of hot and cold
chambers by a piston, both ends of the dividing ~piston act as a
work surface, hence the term double-acting piston arrangement.
The pistons are all connected to a common mechanical driven
! means 24, which assure that the pistons will be operating 90
out of phase with the next most leading or trailing piston.
¦ In automotive applications, the shaft tor~ue of the
engine must be varied over a large range during normal operation
of the vehicle. Torque control or power control is accomplished
by changing the mean cycle pressure of the working gas within
the variable volume chambers lla, llb, 12a, 12b, 13a, 13b, 14a
and 14b. Such pressure variations are usually from a pressure
minimum of 25 atmospheres to a pressure maximum of over 200
atmospheres. This invention proposes to connect the compression
spaces ~cold spaces llb, 12b, 13b and 14b of adjacent cylinders
in a manner which will allow engine compression strokes by way
~ of said pistons 15, 16, 17 and 18 to work consecutively to
¦ produce a sufficient pressure head to fill a gas reservoir means
25 used in the pressure regulation of the closed working system
10. The reservoir means 25 contains two separate reservoirs
25a and 25b for additional novel purposes herein; a novel valve
27 responsive to high and low ranges of the mean pressure in the
working system 10 serves to regulate the pressures in the two
` reservoirs.
¦ When the closed working system 10 is su~stantially
filled with high pressure gas, leaving the reservoirs sub-
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stantially depleted and at their low end of a predetermined
¦ pressure range, such as may occur at full throttle for the engine,
5 any change of pressure from this condition must involve transferof gas from the cylinders to the reservoir To this end~ a first
means 26 provides a one-way fluid communication to the reservoirs
25. ~eans 26 comprises conduits 28, 29, 30 and 31 respectively
leading from each of the cold chambers and which comm~nly connect
to passage 32: to insure one-way communication from ~he cold
cham~ers, check-valves 33, 34, 35 and 36 are interposed respec-
tively in conduits 28-31. The passage 32 will be referred to as
the Pmax. line, always containing the maximum pressure in the
cold chambers except during a transient change of mean pressure
during deceleration or acceleration of the vehicle. Pmax. is
assured by the orientation of said check valves 33-36 per-
mitting flow only to the reservoirs. Similarly, passage 50
acts as a P min. or minimum chamber pressure line, always con-
taining the minimum pressure in the cold chambers as assured by
the opposite orientation of one-way valves 52-55 permitting
flow only to the cold cham~ers from the reservoirs by way of
a passage or conduit path including 39 or 40, 57, ~6, 91 and
95.
Valve 27 directs fluid in passage 32 to one of the two
reservoirs 25a or 25b. Valve 27 comprises a valve housing 37
defining a cylindrical bore 38 in which is slidable a closely
fitting spool valve 39. Passage 32 by way of passaae 57
connects with a center position of the bore 38 and passages 39
and 40 connect with off-center positions of said bore. Passage
39 connects also with the low pressure range reservoir 2Sa and
~ passage 40 connects with high pressure range reservoir 25~.
¦ - One end 27a of spool valve 27 receives a high reservoir
pressure force from passage 40 via conduit 43 causing the spool
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to be biased to the left; the other end 27a is biased to the
right by force of a spring 44 and the force of the minimum
pressure in the working cylinders via passage 50 and conduit 45
The minimum pressure results from the one-way communication
to the cold chambers provided by conduits 46, 47, 48 and 49
commonly connected to passage 50 which in turn conne~ts at 51
to said conduit 45; the one-way check valves 52, 33, 54 and 55
insure fluid flow only into said cylinders causing the pressure
in passage 50 to ~e at about the minimum cycle pressure for the
system except during transient changes in mean pressure in the
cold chambers.
A second means 41 is employed to direct fluid from the
reservoirs and inject said fluid into one cylinder at any one
moment by a timed valve 42 for purposes of increasing the mean
wor~ing pressure in response to a demand for more engine tor~ue
~'eans 41 comprises conduit 56 which connects also to passage 57
at 58. A gate valve assembly ~9, responsive to a change in
eng~ne torque demand, directs fluid to flow through first means
26 or through second means 41. The assembly has a gate valve
60 interrupting passage 32 and a gate valve 61 interrupting
conduit 56. Fluid flow permitted through conduit 56 is carried
by passage 62 to the timed valve 42. Timing of the injection
of reservoir fluid into any one cylinder is important to reduce
or eliminate negative work on the added fluid hy the associated
piston. To this end the injection is timed to occur at the end
of the compression cycle and substantially during the expansion
cycle. Obviously this re~uires a control to orchestrate this
type of injection among the several cylinders each operating at
¦ a different phase from the other.
¦ The timing of injection of reservoir pressure into
~ only one cylinder at any one moment is modified in one respect.
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It has been found that the disadvantage of negative work, ~hich
would occur if all cold chambers were injected simultaneously
is outweighed by the disadvantage of slow engine response when
the mean pressure reaches a certain level. Thus, a switch-over
valve assembly 90 is employed to permit injection simultaneouslv
into all of the cold chambers by a path through conduits 3g or
40, ~7, ~6, 91, 95, 45, ~0 and each of 46, 47, 48 and 49 when
the mean pressure is sensed to be above a middle level. During
the initial stage of acceleration, the mean pressure wlll be
below the middle level and valve 90 will be in the other position
bloc~ing communication to 95, but permitting communication to
94 which in turn is bloc~ed by one-way valves 33-36 from
entering the cold chambers.
Timed valve 42 has a valve element 63 which causes
to rotate at a speed synchronous with phase changes in the
cylinders 11-14, whereby fluid communication between passage 62
and one of the passages 64, ~5, 66 or 67 is permitted through
opening 63a at the precise moment when injection of higher
pressure fluid is best to effect a desired torque change. One-
way check valves 68, 69, 70 and 71 insure injection of fluid
into the cylinders.
A third means 72 interconnects the cold spaces in a most
important manner. Means 72 comprises pairs of conduits 73-74,
75-76, 77-78, and 79-80, each pair of conduits connect separately
to the interior cylinder 83 of a timed valve 81. The timed
valve has a rotor valve member 82 which rotates in synchronous
phase with the phase changes of the cylinders 11-14 so that
a communication through valve opening 82a and through any one
pair of passages is permitted at the precise time when one of
¦ the cold chambers associated with the pair of passages is
¦ undergoing compression Qr has completed compression. ~he latter
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¦ is preferable to provide the greatest opportunity for a
¦ particular cold space to transfer fluid to the reservoir means
before a communication is established to allow transfer to
the next trailing cQld chamber. Complete cut-off of the
I communication between cold chambers can be established by the
sizing of the opening 82a; however, as a practical matter,
the check valves 6, 7, 8 and 9 will function to limit the
communication.
Thus, the cold spaces are connected in seq~ential series
so that the pistons 15-18 may perform one or more phase pumping
functions to increase pressure beyond the maximum cycle pressure.
The increased pressure is permitted to flow back to the
reservoirs for restoring pressure therein. The third means 72
is made to operate in conjunction with the opening of passaoe
3~ by actuating gate valves 84, 85, 86 and 87 and gate valve - -,
60 through a linkage 88 to open and close simultaneously.
~ en the demand for engine shaft torque is reduced,
indicated by a reduced throttle opening or position, the mean
cycle pressure (P mean) must be reduced by transferring fluid
(hydrogen) from the engine to the reservoir means. ~-ate valve
60 is opened and gate valve 61 is closed. During a portion of
a cycle at some operating condition where the maximum cycle
pressure (P max.) is greater than the reservoir pressure (Pr)~
' fluid will flow through one of the check valves 33-36 and gate
valve 60, airectly to the reservoirs 25. S~en P max. is less
than Pr~ fluid cannot flow from the reservoirs to the cold
chambers thro~gh passage 32 ~P max.) because of the check valves
33-36; fluid will flow into the adjacent trailing compression
!space during or at the end of the associated compression stroke
of the cold space from which fluid is flowing. The latter is
permitted for each cold space in series timing as controlled by
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valve 81. ~uch transferred fluid ~ill then be further compressed
~to an even higher pressure head and allbwed to flow to the
reservoir system when P max. is instantaneously greater than P
in any subsequent cold chamber, or again to the next adjacent
trailing compression space.
The timed valve 81 may be constructed as shown with a
valve seat arranged as circular interior cylinder having openings
equi-circumferentially arranged thereabout. Each set of adjacent
~openings aré fluidly connected to adjacent compression spaces,
¦said sets being arranged in an order according to the series
connections of cylinders. The central rotor valve rotates
within the cylinder at a speed so that a valve or opening 82a
(having a dimension effective to span two adjacent passage
openings) will connect a set of openings substantially during
the compression phase of one of the associated cold spaces.
Actuation of rotor valve 82 can be by mechanical drive train or
by hydraulic means pulsing said member in phase with the
pressure variations of the cold spaces.
A simpler mode of making the valve 81 may be use of
a groove 97 in the upper end of each piston rod 96 tsee Figure 2).
~hen the piston rod substantially reaches bottom dead center at
or near the completion of the compression stroke, a communication
through groove 97 and passage 98 is established. Passage 98
~and one-way valve 99) act as any of the passages 73, 76, 78,
80 with a respective chec~-valve 6, 7, 8 or 9. Passage 98 lea~s
to the next trailing cold chamber. Phase timing is achieved by
the action of the piston rod.
The reservoir system 25 stores all of the hydrogen gas
or fluid required to raise the engine mean cycle pressure from
the minimum level of about 25 atmospheres to a maximum in excess
of 200 atmospheres. The pressure will range from slightly above
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P min. (that pressure which exists in an expanded cold space)
to the highest engine operating pressure, depending upon the
reser~oir system volume. With a simple reservoir ~ystem ~x~n~ng
to the prior art employing a single bottle, the H2 would, in the
most difficult situation, have to be compressed 200 atmospheres
resulting in the imposition of extremely high forces on anyone
pumping piston. To overcome this, a dual reservoir system is
employed. This reservoir system has a shuttle or spool valve
assembly 27 which distributes pressure to one of two reservoirs
25a and 25b. ~eservoir 25b is utilized for the high pressure
range of the engine when the engine mean cycle pressure is
high. Reservoir 25a is used for the low pressure range, when
the mean cycle pressure is low. This reduces the m~m operat~
pressure ratio (imposed on the integral series pumping system)
during compression and also reduces the work of compression.
The balance of such forces on opposite ends of the spool valve
determines the position of the spool valve to communicate
passage 57 with either passage 39 for reservoir 25a or passage
40 for reservoir 25b.
