U.S. patent number 3,699,770 [Application Number 05/147,355] was granted by the patent office on 1972-10-24 for stirling engine control system.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to James E. Bennethum.
United States Patent |
3,699,770 |
Bennethum |
October 24, 1972 |
STIRLING ENGINE CONTROL SYSTEM
Abstract
A working gas control system for a double acting hot gas engine
particularly adapted for vehicle installation and including a
manually adjustable system for variably controlling the pressure of
the engine working gas to provide for load control of the engine.
The system includes a gas reservoir for working gas to supply the
engine system with gas at a suitable mean working pressure through
an operator actuator control system. A gas supply tank is provided
to maintain a predetermined minimum gas pressure in the
reservoir.
Inventors: |
Bennethum; James E. (Rochester,
MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
22521234 |
Appl.
No.: |
05/147,355 |
Filed: |
May 27, 1971 |
Current U.S.
Class: |
60/521;
60/525 |
Current CPC
Class: |
F02G
1/05 (20130101); F02G 2270/50 (20130101) |
Current International
Class: |
F02G
1/00 (20060101); F02G 1/05 (20060101); F03g
007/06 () |
Field of
Search: |
;60/24 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schwadron; Martin P.
Assistant Examiner: Ostrager; A. M.
Claims
What is claimed is:
1. A power control system for a hot gas engine of the type having a
plurality of closed variable volume working chambers each having a
hot space and a cold space and adapted to contain a working gas,
said engine including means for heating and for cooling such
working gas and means to transfer such gas between said hot and
cold chambers while passing it through a working cycle, said
control system comprising: a gas storage reservoir means including
a gas reservoir and a supply tank interconnected by a pair of
conduits, one of which contains a pressure regulator valve to
control the flow of gas from said supply tank to said reservoir and
the other containing a one-way check valve connecting said
reservoir to said supply tank, first gas transfer means connecting
said reservoir with said engine working chambers for unidirectional
gas flow from said reservoir to the individual chambers, second gas
transfer means connecting said reservoir with said engine working
chambers for unidirectional gas flow from the individual chambers
to said reservoir, regulating means arranged to control the
admission to and exhaust from said working chambers of working gas
through said first and second gas transfer means respectively and a
gas pump in said second gas transfer means between said regulating
means and said reservoir and adapted to aid the return flow of gas
to said reservoir when the return flow of gas is below a
predetermined pressure relative to the pressure of gas in the
reservoir while permitting direct return flow of gas to said
reservoir when the return flow of gas is above a predetermined
pressure relative to the pressure of gas in the reservoir.
2. A power control system according to claim 1 wherein said gas
reservoir is sized in respect to the volumes of said engine working
spaces and the components of said first and second gas transfer
means such that said volumes can be supplied with gas from said
reservoir to the maximum mean working pressure condition from only
said reservoir, additional gas from said supply tank flowing to
said reservoir at a predetermined pressure below the maximum mean
working pressure through said pressure regulator valve.
3. A power control system according to claim 1, further including
bypass valve means interconnecting out of phase pairs of said
closed variable volume working chambers to permit the bypassing of
gas from said out of phase working chambers to effect rapid
reduction of engine output torque thereby and pressure responsive
means and manually actuated lever means in said regulating means to
effect operation of said bypass valve means.
Description
This invention relates to hot gas engines and more particularly to
a gas control system for a closed cycle hot gas engine such as a
double acting Stirling cycle engine.
It is known in the art to provide means for controlling hot gas
engines of the Stirling cycle type by varying the pressure of the
working gas in the engine working spaces. Such pressure variations
have been accomplished by supplying gas from external storage means
to the engine working space and exhausting gas from the working
spaces to the storage means through the operation of suitable
transfer and control means including a gas compressor. Normal
practice has been to use one small high pressure external gas
reservoir to store the working gas and to serve as the source of
gas to fill the engine during operation. However, it has been found
that the use of such small high pressure reservoirs for the gas is
disadvantageous because the high pressure of the gas maintained in
the reservoir requires relatively high compressor input power to
refill the reservoir with gas discharged from the hot gas engine
and the use of a high pressure reservoir did not allow the system
to make use of the hot gas engine's own pumping ability to directly
refill the gas reservoir from the working spaces of the hot gas
engine under certain engine operating conditions.
It is therefore the principal object of this invention to improve
hot gas engine control systems whereby the power required for
refilling the reservoir with gas exhausted from the engine is
reduced.
Another object of this invention is to improve a hot gas engine
control system whereby engine response times are small and
independent of the engine duty cycle.
These and other objects of the invention are attained by means of
an engine control system in which working gas is supplied to the
engine by normal gas pressure flow from a supply reservoir through
an engine pressure control system; a gas supply tank being provided
to supply makeup gas to maintain a minimum gas pressure in the
reservoir and to serve as a secondary reservoir to which gas can be
bled if the pressure in the main reservoir exceeds a predetermined
pressure at engine shutdown. Engine power is varied in a known
manner by varying the gas pressure in the engine working space with
pressure responsive regulating means being utilized to maintain the
desired working space pressure by sensing the mean pressure in the
working space and controlling the gas supply and exhaust in
accordance with desired pressure requirements. The regulating means
includes manually adjustable pressure selection means which are
actuated by the vehicle operator such as through a conventional
foot pedal to manually select the desired working gas pressure. The
variation of this manual selection means thus varies the engine
output torque and provides engine operation similar to that of the
throttle controlled internal combustion engine.
For a better understanding of the invention, as well as other
objects and further features thereof, reference is had to the
following detailed description of the invention to be read in
connection with the accompanying drawings, wherein:
FIG. 1 is a cross sectional view of a double acting, four-cylinder,
in line, hot gas engine of the Stirling cycle type;
FIG. 2 is a schematic illustration of the gas supply and pressure
control system for the engine of FIG. 1;
FIG. 3 is a diagrammatic representation of the fluid pumping means
in the system of FIG. 2;
FIG. 4 is a schematic illustration of the inlet and exhaust system
to the engine of FIG. 1; and,
FIG. 5 is a sectional view showing the pressure control system of
the gas supply and pressure control system of FIG. 2.
Referring now to the drawings, a four-cylinder, double acting, in
line, hot gas engine, generally designated by reference numeral 10,
includes cylinders 11 mounted on and partially closed at one end by
an intermediate block 12 which in turn is supported on an engine
crankcase 13. The cylinders 11 terminate in closed ends 14 at one
end thereof and are partially closed at the opposite end by the
apertured reduced portion 15 of the intermediate block 12.
Intermediate block 12 with annular apertured end caps 16 secured
thereto support part of a rolling seal structure 17 for each
piston. Each rolling seal structure may be of the type disclosed in
U.S. Pat. No. 3,568,436 issued Mar. 9, 1971 in the names of Francis
E. Heffner and Richard R. Toepel.
A non-vented piston 18 is slidably received in each of the
cylinders 11 and is suitably connected at one end to the piston rod
portion 19 of a crosshead piston 21 slidably received in a
crosshead cylinder portion 22 of the crankcase 13, which may also
be provided with crosshead piston liners 23. Each crosshead piston
21, in turn, is connected by a connecting rod 24 to a crankshaft 25
journaled in the crankcase 13, the connecting rods 24 being
connected at their upper ends to the crosshead pistons 21 by pins
26 retained in the crosshead pistons by retaining rings 27.
The interiors of the cylinders 11 are separated by their respective
pistons 18 into hot chambers 28 formed at the ends 14 of the
cylinders, and cold chambers, not numbered, formed at the opposite
ends thereof. Canister-like members 30 encircle each of the
cylinders and support therein suitable coolers 31 and regenerators
32. A heater, not shown, which may be a burner or other suitable
heating device, is located above the canisters 30. A plurality of
tubes 33 extend from the ends 14 of the cylinders through the
heaters to the regenerators 32 of each cylinder. Connecting tubes
34 connect the coolers 31 of one cylinder with the cold chamber end
of the next appropriately phased cylinder.
Thus, four separate gas containing working spaces are formed, each
made up of the hot and cold chambers of adjacent cylinders
connected through heater tubes 33, regenerators 32, coolers 31 and
connecting tubes 34 in a known manner as shown in U.S. Pat. No.
3,538,706 issued Nov. 10, 1970 to Richard R. Toepel.
Referring to FIG. 2, there is shown schematically a control system
diagram for supplying the working gas to the engine 10. A supply of
working gas is contained in a supply tank 40 and a reservoir 41,
the supply tank 40, which serves as a secondary reservoir being
connected to the reservoir 41, by a supply conduit 42 with a
pressure regulator 43 therein and by a return conduit 44 with a
pressure relief valve 45 therein. The reservoir 41 is connected to
a manifold type fill header 46 for supplying working gas to the
engine by means of a conduit 47 through an engine pressure control
regulator, generally designated 48, and by conduit 49. A solenoid
shuttoff valve SV-1 is placed in the conduit 47 to shut off the
flow of gas from the reservoir to the pressure control regulator 48
when the engine is not in operation and it can be controlled by a
conventional switch, not shown.
The fill header 46 is connected by valve controlled conduits 51 to
the engine and gases are dumped from the engine through valve
controlled conduits 52 to a manifold type dump header 53 which in
turn is connected by conduit 54 to the engine pressure control
regulator 48 and then by conduit 55 through a plurality of
compressor gas chambers or accumulators 56 and 56a, and conduit 58
to the reservoir 41. Compressor gas chambers 56 and 56a are
actuated by a compressor pump 57, as described hereinafter.
Referring now to FIG. 3, there is shown diagrammatically the fluid
pumping system for the engine which includes the compressor gas
chambers 56 and 56a and the compressor pump 57. As shown, the
device includes a pair of compressor gas chambers 56 and 56a in the
form of accumulators, both of which incorporate movable wall means
such as diaphragms 61 which divide these accumulators into first
and second chambers 62 and 63, respectively.
Chambers 62 are connected through spring biased check valves 64 and
conduit 58 to the reservoir 41. The valve openings for the check
valves 64 include metal anti-extrusion flaps 65 which prevent
damage to the diaphragms while permitting flow to the check valves
64. The chambers 62 are also connected through spring biased poppet
inlet valves 66 and conduit 55 with the engine pressure control
regulator 48 and therethrough with the working space of the engine
10. The valves 64 and 66 are arranged to permit flow from the
engine working space to either chamber 62 and from either chamber
62 to the reservoir 41, but to prevent flow in the opposite
direction as well as to prevent flow between the two chambers
62.
Chambers 63 of the compressor gas chambers 56 and 56a are connected
through spring biased anti-extrusion devices 67 and conduits 68 and
68a, respectively, to spaced portions of the housing 70 of a spool
type selector valve. Valve housing 70 also includes drain lines 71
and 71a located adjacent its ends and a hydraulic supply line 72
which connects with the output of the compressor pump 57 in the
form of an oil pump, the drain lines 71 and 71a being connected to
the inlet of pump 57. The compressor pump 57 receives pressurized
oil drained from lines 71 and 71a and oil bypassed through supply
line 72 in a manner described in detail hereinafter.
Reciprocally disposed within valve housing 70 is a valve spool 73
which includes oppositely disposed end portions in the form of
actuator rods 74 and 74a.
Each of the actuator rods 74 and 74a are selectively reciprocated
by means of pivotally connected levers 75 and 75a, respectively,
which in turn are pivoted clockwise and counterclockwise,
respectively, by means of hydraulic actuated plungers 76 and 76a of
pressure actuators 78 hydraulically connected to conduits 68 and
68a, respectively.
When the valve spool 73 is in the position shown in FIG. 3, the
valve acts to connect hydraulic supply line 72 with conduit 68a,
while conduit 68 is connected with drain line 71. In its second
position, in which the spool valve 73 is moved to the right with
reference to FIG. 3, it connects hydraulic supply line 72 with
conduit 68 while conduit 68a is then connected with the drain line
71a.
The hydraulic system also includes a pressure release valve 81
connected with the outlet of the compressor pump 57 and is arranged
to bypass fluid therefrom to the compressor pump inlet at a
predetermined pressure. A bypass valve 82 is also connected to both
the inlet and outlet of the compressor pump 57 and includes a valve
spool 83 which is spring biased in an opening direction wherein the
pump inlet and outlet are connected. A diaphragm actuator 84, at
one end of spool 83, is acted on by gas pressure in conduit 55
through connection therewith by a line 85 for a purpose to be
subsequently described.
The operation of the above-described compressor system is as
follows. Compressor pump 57 in the form of an oil pump is driven
intermittently, by an electric drive motor, not shown, the
operation of which is controlled by a switch SW-1 actuated by valve
spool 83 of bypass valve 82. When, however, the compressor pump is
in operation and the valve spool 73 is in the position shown in
FIG. 3, oil is pumped through line 72 and conduit 68a to chamber 63
of the accumulator 56a. This forces diaphragm 61 upwardly reducing
the size of chamber 62 therein and forcing any gas in this chamber
out of accumulator 56a and past check valve 64 through conduit 55
to the reservoir 41.
When the gas in chamber 62 is exhausted and diaphragm 61 bears
against the sides of the accumulator 56a, the hydraulic pressure in
line 68a increases to force the plunger 76a of pressure actuator 78
associated with this line to the left, as shown in FIG. 3, to
rotate the lever 75a counterclockwise to move the spool valve 73 to
the right, as shown in this figure, thus connecting line 68a with
drain line 71a. At the same time, line 72 is connected with conduit
68 so that the compressor pump 57 begins to fill chamber 63 of
accumulator 56 forcing out of it any gas which may be present in
its chamber 62 in the same manner as was done with accumulator 56a.
When all gas is exhausted from accumulator 56, the pressure in line
68 will increase, actuating the plunger 76 of pressure actuator 78
connected to this line to rotate the lever 75 associated therewith
in a clockwise direction to move the spool valve 73 to the left, to
the position as shown in FIG. 3, after which the above-described
cycle is again repeated.
While the above-described pumping action is taking place in one
accumulator, the full volume of the remaining accumulator is always
available to receive a charge of gas from the engine 10 through the
dump header 53, conduit 54, engine control system 48 and conduit
55.
Thus, when accumulator 56a is being discharged and the engine is
cycled for full load to idle, the complete charge of gas is
receivable through conduit 55 and check valve 66 into chamber 62 of
accumulator 56. Since the gas is received under pressure, it easily
forces out of chamber 63 the oil contained therein, which passes
through conduit 68 and drain line 71 to the inlet of pump 57.
When the pumping cycle on accumulator 56a is then completed, the
valve spool 73 is moved as previously described and the discharge
of gas from accumulator 56 is begun. At this time, accumulator 56a
is available to receive an additional charge of gas from the engine
working space through conduit 55 and check valve 66 to chamber 62
of the accumulator 56a.
Whenever the gas pressure in line 55 drops to a predetermined low
pressure, such that further pumping action of the compressor is not
required, the reduced pressure on diaphragm actuator 84 permits the
valve spool 83 to move to the left, as seen in FIG. 3, opening the
bypass valve 83 and bypassing hydraulic fluid discharged from the
pump 57 back to the pump inlet. This stops further gas pumping
action until increased inlet pressure in line 55 again closes the
bypass valve 82. In addition, when the spool valve 83 moves to the
left, as described above, the contacts of switch SW-1 are opened
thus deenergizing the electric motor used to drive the pump 57.
However, as will be described hereinafter, when dumping of gas from
the engine is initiated by an operator to reduce mean pressure in
the working spaces of the engine 10, between, for example, mean
pressures of 1,500 to 1,100 pounds per square inch absolute, using
a preferred working embodiment of such an engine, the engine 10
dumps through the dump header 53, regulator 48 and accumulators 56
and 56a directly into the reservoir 41. At this range of gas
pressure, depending of course on the actual gas pressure in
reservoir 41, gas entering into chambers 62 of the accumulators 56
and 56a would immediately flow back out through the valves 64 to
the reservoir 41 and no work output from the compressor pump would
be required. Below 1,100 pounds per square inch dump pressure, or
otherwise as necessary, the compressor pump 57 is used to pump the
gas back into the reservoir 41 in the manner described.
Referring now to FIG. 4, there is illustrated schematically in
greater detail that portion of the gas flow system, outlined in
broken lines in FIG. 2, relating to the interconnection of conduits
between the fill header 46, engine 10 and dump header 53. As shown,
the fill header 46 is connected by a conduit 51 to each of the
cylinders 11 (the four cylinders in this figure being further
identified as cylinders CYL-1, CYL-2, CYL-3 and CYL-4), of the
engine 10 through a cooler 31, regenerator 32 and heater tubes 33
for each of the cylinders, with each cylinder also being connected
with the next cylinder, in the appropriate phasing order, by
conduits 34 to provide four working spaces as previously described.
Conduits 34 are also in communication with the conduits 52
interconnecting the cylinders to the dump header 53. Conduits 51
leading to out of phase cylinders CYL-1 and CYL-3 are adapted to be
placed in communication with each other by solenoid actuated bypass
valve SV-2 in connecting conduit 86, while out of phase cylinders
CYL-2 and CYL-4 are adapted to be placed in communication with each
other by solenoid actuated bypass valve SV-3 in connecting conduit
87.
In order to operate the engine at varying output torques and speeds
ranging from idle to full rated load, the pressure control
regulator 48, as actuated by an operator, is used to vary the
pressure of the working gas in the working spaces of the engine 10.
The pressure control regulator 48 is connected by the conduit 47 to
reservoir 41 in which a supply of working gas, preferably hydrogen,
is kept under pressure.
Pressure control regulator 48 controls the supply of gas to the
cylinders of the engine 10 through conduit 49 and fill header 46
connected to the engine, as previously described.
Pressure control regulator 48 is also connected to the engine
working spaces through conduit 54 and dump header 53 to control the
exhaust of gas from the working spaces through these conduits.
Exhausted gas is transmitted to gas compressors 56 and 56a which
increase the pressure of gas if necessary before it is returned to
reservoir 41.
Pressure control regulator 48 may be made in any suitable form;
however, a preferred arrangement for such a system is schematically
shown in FIG. 5 of the drawings. As shown, the regulator 48
includes a fill valve 101 connecting through line 47 with reservoir
41 and through line 49 to the fill header 46 for the engine 10.
Oppositely disposed from the fill valve is a dump valve 102. Dump
valve 102 connects through conduit 54 with the dump header 53 to
the engine working spaces and through line 55 with gas compressors
56 and 56a.
A pivotally mounted actuating lever 103 is arranged between these
valves 101 and 102 so as to open the fill valve 101 upon a downward
movement and open the dump valve 102 upon an upward movement of the
lever. Adjusting means such as screws 104 are provided to properly
adjust the valve positions. The adjustments are preferably such
that all valves are closed with the lever in an intermediate
position and the dump valve 102 opens upon a slight upward movement
and the fill valve opens upon a slight downward movement of the
lever from the position shown.
This system further includes a cylinder 105 carrying a reciprocable
piston 106, one end of which engages the underside of lever 103.
The lower face of piston 106 is acted upon by gas pressure supplied
through a capillary line 49a connecting the cylinder 105 with the
engine working spaces. The capillary line acts to restrict gas flow
so that cyclic pressure variations in the engine working spaces are
not transmitted to cylinder 105, but changes in the mean working
pressure due to operation of the gas pressure control system are
followed by the pressure in the cylinder 105.
The upper surface of lever 103 is engaged by a spring 107 which is
partially compressed by a follower 108 controlled by a rotatably
mounted cam 110. Cam 110 is in turn actuated by a gear 111 engaged
by a rack 112 which is mechanically connected through linkage 113
with a manually actuated foot pedal 114. Adjustable stop means 115
are provided to be engaged by an abutment 116 on the rack to limit
travel of the manual actuating means.
Beneath lever 103, an overspeed governor mechanism is provided
comprising rotating flyweights 117 which engage a reciprocable
shaft 118 urging the shaft upwardly against a spring 120 to engage
the lower surface of lever 103. Flyweights 117 are rotated at a
speed proportional to engine speed through mechanism, not
shown.
When the engine is in operation, an increase in engine torque is
obtained by moving pedal 114 in a counterclockwise direction. This
moves rack 112 leftwardly rotating cam 110 so as to increase the
downward force of follower 108 on spring 107. Assuming the mean
working pressure acting on piston 106 is less than that called for,
lever 103 is pivoted downward by the bias of the spring, opening
valve 101 and permitting pressurized gas to flow from the reservoir
41 to the engine fill header 46 and then to the working spaces of
the cylinders 11 of engine 10 to increase the working pressure
therein. The increase in mean working pressure is transmitted
through line 49a to cylinder 105 acting against piston 106 and
urging lever 103 upwardly until, when the desired pressure is
reached, lever 103 resumes a neutral position closing valve 101 and
shutting off the flow of gas.
If a decrease in engine torque is desired, pedal 114 is moved
clockwise and through cam 110 reducing the downward bias of spring
107 and permitting piston 106 to move lever 103 upwardly opening
dump valve 102. This permits the exhaust of gas from the working
space through dump header 53 and lines 54 and 55 to the gas
compressor 56 and 56a for return back into reservoir 41.
In case of an engine overspeed, flyweights 117 urge shaft 118 into
engagement with lever 103 moving it upwardly and acting to exhaust
working gas from the engine through the opening of dump valve
102.
The regulator 48 also includes a switch SW-2 actuated by lever 103
and a pressure actuated switch SW-3 in the electrical circuit for
solenoid actuated bypass valves SV-2 and SV-3 used to effect rapid
reduction of output torque from engine 10, as shown in FIG. 4.
Switch SW-2 is a normally open switch which is closed, depending
upon position of adjusting screw 104, when lever 103 moves upward
for opening dump valve 102. Switch SW-3, a normally closed switch,
is opened by a pressure actuator 121 connected to conduit 49a
whenever the pressure in this conduit is above a predetermined
pressure, for example, above a pressure of 1,100 psia in the
embodiment of the system disclosed.
Although the engine control system of the invention can be designed
for any size engine or gas pressure conditions, a brief description
of the system as applied to the engine disclosed operable under
predetermined pressure conditions is as follows:
Fill of gas to the hot gas engine is always from the reservoir 41
through the engine pressure control regulator 48 and aforesaid
conduits to the engine 10 by normal pressure flow. When the engine
is empty, the reservoir contains a gas, such as hydrogen, at a
pressure of 2,000 psia. Sufficient hydrogen is in the reservoir 41
to allow filling the entire engine system with gas at 1,500 psia
mean working pressure. If leakage should occur during engine
operation, the pressure in the reservoir 41 could drop below 1,200
psia at maximum engine pressure conditions. However, the supply
tank 40, which serves as a secondary reservoir, is provided for
makeup and contains sufficient gas therein to maintain a minimum
gas pressure in the reservoir of 1,200 psia. The supply tank 40
also acts as a secondary reservoir for gas to bleed from the
reservoir 41 if the pressure of the gas therein exceeds 2,000 psia
at shutdown of the engine.
During normal engine operation, the operator actuates the foot
pedal 114 to control the engine mean gas pressure through the
pressure control regulator 48 as previously described. As more
power is required, the pedal 114 is depressed further to further
open the fill valve 101 resulting in higher mean working pressures
in the engine. When the pedal 114 is lifted, a dump is initiated,
in the manner previously described, to reduce the mean pressure of
the gas in the engine through the discharge of gas therefrom.
As previously described, in the embodiment of the system disclosed,
between mean pressures of 1,500 psia and 1,100 psia, the engine
dumps gas directly into the reservoir 41, with the filling or
dumping time being limited only by the line sizes of the
interconnecting conduits between the various components of the
system. Below a pressure of 1,100 psia for the dump gas, the
compressor pump 57 is required to pump the gas back into the
reservoir, the compressor pump 57 being sized so as to effect rapid
pumping of the gas back into the reservoir 41, when necessary, up
to a pressure of 2,000 psia.
While one of the accumulators 56 or 56a is connected to the
discharge side of the compressor pump to effect compression of the
gas contained in the compressor accumulator, the oil chamber of the
other accumulator is connected to the inlet of the compressor pump
to create a suction within the accumulator chamber to further
induce gas flow to the gas chamber of the accumulator from the dump
header 53. The charge of gas thus drawn into this accumulator will
then be compressed and forced back into the reservoir 41. The
accumulator chambers are then reversed and the process continues
until the operator calls for a fill of gas to the engine or the
engine idle conditions have been reached. As previously described,
an idle speed governor with flyweights 117 therein is built into
the engine pressure regulator to effect dumping at excessive engine
speeds.
By making the reservoir 41 about equal in volume to the volume of
the working spaces in the engine 10 and its associated piping,
optimum operating results can be obtained. With the reservoir thus
sized, it has been found that the reservoir need not be too large,
as compared to previously known systems, and that the pressure of
the gas in the system can be set so that the engine can be filled
to the maximum gas pressure condition, so that, under normal
conditions, the pressure of the gas remaining in the reservoir is
about 200 psi above the minimum cycle gas pressure at full engine
load conditions.
However, at full engine load conditions, the maximum working
pressure of the gas is considerably higher than the pressure of the
gas remaining in the reservoir 41 and allows the gases dumped from
the working spaces of the engine to be, in effect, pumped by the
engine directly to the reservoir 41 with no extra compression of
the gas by work output by the compressor pump 57. This direct
dumping of gas from the engine working spaces can be done until the
engine maximum cycle pressure gets to within approximately 200 psi
of the pressure of the gas remaining in the reservoir 41. Below
this pressure differential, the gas must be pumped into the
reservoir 41 by operation of the compressor pump 57, but about
one-third of the gas in the engine working spaces can be dumped
back to the reservoir in this manner.
When compression is required, it is desirable to reduce the power
required for operation of the compressor pump 57 to a minimum. This
is accomplished by using a small low pressure reservoir 41 and by
reducing the pressure differential against which the compressor
pump 57 must operate. In the arrangement shown in FIG. 3, the inlet
or suction to the compressor pump 57 is from an accumulator which
is being charged with dumped gas from the engine, which gas is
already under some pressure. Thus, the oil pump must perform work
only to compress the dumped gas to overcome a pressure differential
which is that existing between the engine maximum pressure and the
pressure in the reservoir 41.
From the above description of the subject control system, it is
apparent that there is provided a control system arrangement
requiring the least engine power to operate. This advantage is
obtained by means of the following:
The use of a reservoir of about equal volume with that of the
engine to take full advantage of the engine's pumping ability.
The use of a separate supply tank which allows the system to be
maintained at optimum pressure conditions for extended periods of
operation and independent of leakage or system temperature
changes.
The use of a pressurized compressor pump inlet which reduces the
head requirement to a minimum.
The use of a non-vented piston which reduces the engine gas
inventory and therefore the compressor pumping capacity
requirement.
The use of the bypass torque control to reduce engine output torque
while the compressor system is dumping gas and extend the time
available for pumping thus reducing the horsepower requirement of
the pump.
* * * * *