Note: Descriptions are shown in the official language in which they were submitted.
~ 2 5~7~ ~ ~
--1--
~aclcKI-oull~ oE tl~e lnvelltioll
~ evi.ces rulllling witll tllelr natural Ereyuency, S~CIl as free
pi.9 ~011 nlaCIlille5, tllelr EreqUellCy 0~ cyclic syeed is a unctioll o~ tlle
ellergy illpUt portion an~ energy output portion oE tlle device, sucll as
tlle p~wer piS~OII energy input portioll and compressor plston energy
ou~put l~ortion oE a Lree plstoll engllle compressor. In otller words
Llle spee~l o~ sucll an engllle colll~)ressor will vary in a glverl flxed
na~llral relationsllip witll variations oE compres~or volumetric flow
all~ colnF)ressor llltake yressures all~/or discllarge pressures. Tllus,
in a lleat ywlll), for exanlple, a greater volu~netric flow rate is typ-
ica:lly re~luired at tlle lower intake an~ discllarge pressures involved
ill opera~illg at low alnbient teml)eratures. ~lowever, even at maxinlulll '
piStOII stroke, no~ on:ly is ~lle volumetric outpu~ per stroke re~uced
by tlle lower intalce pressure, but tlle ra~e of volumetric flow is
Eur~ller substalltlally re~uced by tlle lower natural frequency wllicl
tlle ellg.ille coolpressor will assume un~er tlle influellce of botll tlle
lower intake and ~iscllarge pressures.
lllis Lixed natural relationslllp llas not lleretofore been controlle~
eLEicientl.y over a range wi~e enougll to prevent or vvercome, in a
practicable Illanller~ tlle problelll ~ust ~escribe~, an~ specifically to
provide Eor all improved lillear Eree piston engine capable of driving,
any one oE a nulllber oE ~iEEerent ~ypes of energy absorbillg deYices.
ln all eEEort to provi~e sonle extent of spee~ control Eor macllilles
sucll as Lree piStOII engille colopressors, one previous proposal involve~
a ~evice in wllicll tlle reciprocatillg free piston masses lla~ llollow
portiolls wllicll could ~e Eille~ to varylng ~egrees witll a li(lui~ sucl
~257S~
--2--
as oil and, thus, by variation of the reciprocating masses, the speed
was to be controlled within a rather limited range, since the cyclic
speed varies with the mass according to the equation:
@2 2
JS1 F ds = m V /2 (~)
which for a given characteristic engine, can be reduced to:
(S F ds CX~ m n (II)
J 1
when F is the driving force, s the stroke and sl and s2 the inner and
outer limits of the stroke of m (the reciprocating or driven mass~,
V the velocity of the mass and n the cyclic speed. As equation II
10 -shows, the mass would have to be reduced for instance to one quarter
to obtain twice the cyclic speed which, in practice, would be a most
difficult and most likely impraetical result to achieve.
In connection with the use of free piston engine gas generators
(gasifiers) Eor supplying exhaust gas to drive a turbine, prior efforts
15 have been made, as in Lewis, U.S. patent 2,435,970, to control the
frequency of a free piston engine by means of an additional bounce
chamber in conjunction with a bounce chamber on the back side of a
load compressor piston to seek lower and higher frequency limits than
would be possible without such an additional bounce chamber. While
20-Lewis suggested that his desired operation could be accomplished with
the help of governors responsive to various operating conditions to
adjust or respond to pressures in a number of engine locations, in- -
cluding direct (positive) and reverse (negative) bounce chambers and
other portions of his gasifier, the Lewis patent does not disclose
25 an engine and control combination capable of meeting the problems
recognized and solved by the present inventor in the manner described
in this application.
Summary of the Invention
; This invention involves the recognition of a need for a free piston
30-engine which could vary engine speed over a very wide range and for
selective use with any one of a number of different types of energy
absorbing devices and with rather simple control elements. The de-
sired wide control range for such an engine can be achieved by use
of specially located and constructed bounce chambers, and moreover
35 by means of lower pressures in such specially located bounce chambers
~L2575~8
--3--
capable of operating without a pressurized reservoir of high pressure
bounce control fluid. In cases where the energy absorbing device in-
volves a compressor or heat pump, such a combination is capable of
operating the control section with a separate fluid from that of the
~working compressor or heat pump section, and with less complex con-
trol elements than would otherwise be needed. For certain uses it
also recognizes a need for a vibration-free compressor with an engine
speed controller and a contamination-free compressor for compressing
freon or the like.
-The present invention accordingly includes a speed control device
that allows changing the speed of a free piston engine compressor or
similar energy absorbing device (EAD) within wide margins, or main-
taining the speed of a free piston engine-driven electric generator
or alternator within very narrow margins, independent from conditions
5-of the energy input section or the energy absorbing section which may,
in the case of the generator require a very wide range of control to
maintain a substantially constant speed, and in the case of compressor
or heat pump EADIs, require substantial speed changes needed, for ex-
ample, as compressor demand changes from low volume-high pressure to
20 high volume-low pressure operation, and which in both instances is
the very opposite of what the engine would do or the manner in which
it would respond, if it did not include the control means and the
structural arrangement and relative location of bounce chambers of this
invention.
-- The present invention thus provides a variable stroke free piston
engine which can be selectively connected to any one of several diE-
ferent energy absorbing devices, and in which the engine speed (fre-
quency of reciprocation) can be controlled and adjusted in response to
an extremely broad range of changes in the demands on a specific energy
30~absorbing device (EAD) connected to and driven by the piston engine.
I have found that the desired range of control forces can be effec-
tively provided by adjustment of the working pressures in two bounce
chambers specifically located at an intermediate position along the
axis of a reciprocating piston rod assembly in a free piston engine
35~which has a power piston at one end and a connecting means at the
other end for driving connection with a movable member of the selec-
ted energy absorbing device. A bounce piston unit having oppositely
di~rected and oppositely acting bounce piston faces compresses the air
~25~5~3
--4--
or gas in one bounce chamber during a power piston expansion stroke of
the piston rod assembly from the power piston end toward the EAD con-
nection end and then compresses the air or gas in the other bounce
chamber during the return (i,e. compression) stroke of the power piston.
Thus the invention provides a negative first botmce chamber at a
relative location between one bounce piston working face and the power
piston end of the piston rod assembly, and a positive second bounce
chamber at a relative location between the other bounce piston working
face and the EAD end of ~he piston rod assembly. In the preferred
lO embodiments, the first and second bounce chambers are most efficient-
ly and effectively provided by a single bounce cylinder in which op-
posite faces of only one double-acting bounce piston are used to
s,eparate the two bounce chambers, thus eliminating half of the fric-
tional losses that would be developed between the usual piston rings
15 ~and the inner bounce cylinder wall surfaces, if the bounce piston unit-
had two piston members, and also minimizing the net pressure differen-
tials between the two chambers separated by such a single bounce piston.
The invention further provides control means for such machines
which includes at least one pair of bounce chamber pressure control
20 -openings (one opening in each bounce chamber), and at least one pair
of variably (e.g., incrementally or interm~ttently) adjustable bounce
pressure control valves (one for each of the bounce chamber control
openings of said pair). Each control valve oE said one pair, when
opened partially, fully, incrementally or intermittently, provides
25 -for direct connection of the bounce chamber, through its bounce cham-
ber pressure control opening, to the ambient atmospheric air outside
the bounce cylinder. Each of said controls valves is further connected
to its respective bounce chamber control opening for variably and sub-
stantially simultaneously adjusting each of the variable pressure
30 -control valves of said pair and thereby similarly changing (i.e. in
the same direction~ both upwardly or both downwardly) the respective
bounce chamber working pressures in response to changes in the de-
mands on the particular EAD involved.
In the preferred embodiments, the control valves of said one pair
35 are located and arranged to adjust the maximum outlet pressures for
each bounce chamber. It is also possible to arrange such valves to
adjust the minimum inlet pressures for each bounce cllamber, or even
to provide two such control valve pairs, one pair for inlet pressures
.
~25~
--5--
and one pair for outlet pressures.
The invention also provides for the further combination of means
for relatively adjusting at least one pair of the respective variable
pressure control valves in opposite senses, thereby making it possible
5 to shift the successive top dead center positions of the po~"er piston
in its power cylinder in response to a signal from an engine efficiency
sensing means which indicates relative efficiency or inefficiency
of combustion and operation of the engine. Such a signal can be made
available, for example, from a knock sensor of the type responsive to
10 and indicative of incipient knocking in the power cylinder, i.e. at
a top dead center position of the power piston just short of tllat at
which actual knocking might occur.
Such a knock-sensing means is shown, ror exal)mle, in llly prior United
States patent no. 3,853,100.
- I have found that the use of two such bounce chambers, with a
double-acting bounce piston in a single bounce cylinder which is sub-
stantially greater in cross sectional area than that of the power -
piston in its power cylinder, provides adequate forces on the recip-
rocating piston rod assembly to control very efficiently and effec-
20-tively the engine speed required to meet the wide range of changes in
the demands on certain E~D's, such as electric linear generators,
heat pumps, hydrostatic pumps, process gas compressors, and gas or oil
field compressors. As a practical matter, the effectiveness of such
controls is preferably enhanced by having each face of the double-
25~acting bounce piston substantially greater in cross section area thanthat of the power piston by a factor in the range from at least 1.5
to at least ~ times the power piston area, and in some applications as
much as 10 times the effective power piston area. With such large
area ratios, I have found that most load demands on the E~D can be
30 -controlled by using ambient atmospheric air as a readily available
control fluid, thus eliminating any need for a special source of highly
pressuri~ed air or gas as a control fluid for the bounce chambers. It
also substantially eliminates the need for high starting pressures.
In a free piston engine, the cyclic speed of the reciprocating
35_assembly varies closely with the square root of the total mean or
average force driving the reciprocating assembly. In the present
invention as just described the cyclic speed can be substantially al-
tered by raising or lowering the pressures in each of the bounce
~2~.7~
--6--
chambers, since tlle component forces driving the bounce piston are a
product of their respective piston areas and the corresponding pressures
acting on the~. By assuming commonly-employed mean effecti-ve pressures
of the engine or power cylinder it can be shown that to double the
5 cyclic engine speed the bounce pressures PB will have to be increased
by approximately three times the product of the mean effective engine
pressure M~P times the ratio of the power piston area AE over the
bounce piston area AB, i.e. P~ is nearly equal to 3 MEP (AE/AB).
This clearly shows the great advantage of the present invention of
lO providing the freedom to select the cross sectional areas of the two
bounce chambers (and of their corresponding piston) independent of the
areas of the power piston, and of the compressor piston (if any).
Thus doubling the engine speed of a free piston engine according to the
above example will be possible with mean effective bounce pressures of
15-only 75% that of the mean effective pressure of the power section, if the
bounce piston area will be 4 times that of the power piston, which in a
typical engine ecompressor application will be entirely practical. This
contrasts sharply with previously shown designs in which the mean effec-
tive bounce pressures would have to be in excess of three times the mean
20-effective pressure of the power section or more than 4 times as high as
the pressures required according to the present invention.
Thus to control the mean bounce chamber force in a ratio of ten
to one, it is simply necessary to operate the bounce chamber intake
pressure between atmospheric pressure of 14.7 psia and 1.47 psia.
25-This may be accomplished by restricting the cross-section upstream of
the intake valve correspondingly. These below-atmospheric bounce in-
let control pressures are practicable for large speed changes as a
result of the large bounce piston area and the double-acting bounce
piston unit possible according to this invention. This confirms the
30-substantial advantage of the present invention in providing a large
area for each speed control piston face, so that a very wide range
of control of the engine speed can be obtained with use of ambient
air at atmospheric pressure as the control fluid.
A further advantage in having the bounce chamber of the speed con-
35-trol section independent of the selected energy absorbing device,
such as the compressor piston of a compressor or heat pump, is that
the maximum pressures in the bounce chanbers of the speed control
section of the present invention can be kept to a minimum. ~[oreover,
when the energy absorbing device to be removably attached
to the outer end of the engine power assembly includes a com;
pressor piston in a compressor cylinder, this compressor cylinder
can also be constructed to provide a further (third) bounce chamber
between the outer end of the engine and the compressor piston. Such
a third bounce chamber can be used at the back side of the compressor
piston in such a way as to help keep the bounce pressures in the
two speed control bounce chambers of the engine substantially equal
and thus to their lowest possible maximum cylinder pressure.
In some applications, such as in heat pumps and air conditioners,
it is also desirable to have an initial load to avoid mechanical con-
tact between the piston assembly and cylinder head during start up
and other transient conditions. In this case one or both chambers
of the speed control bouncer can be made to temporarily act as
15 -compressors until the refrigerant compressor is able to assume the
power input from the driver or power section. Similar situations
exist, for example, in free piston eng:ine electric generators which
could be similarly controlled by the speed control bouncer.
The invention is thus not merely in the use or control oE
bounce piston control pressures alone or the use of two bounce cham-
bers as a control. It also involves the specific relative location
of bounce piston faces and bounce chambers to provide adequate con-
trol piston areas without blocking or limiting the area for the EAD
connection end of the engine. This further makes possible the pro-
vision and use of an optimum number of piston faces and an optimumassignment of power and control functions to such piston faces,
including the allocation of speed control functions to the specif-
ically located oppositely-acting bounce chambers and bounce piston
faces and the possibility of using ambient atmospheric air as a
con~rol fluid to provide a wide range of control in a manner com-
patible with the selective attachment of different energy absorb-
ing devices.
Brief Description of the Drawings.
Fig. 1 of the accompanying drawing is a schematic showing
of one embodiment of the invention;
~2~7~
z
Fig. 2 is a work diagrain in which the work is plotted
vertically with reference to the expansion and compression strokes
plotted horizontally for the power piston oE an engine unit;
Fig. 3 is a work diagram for a bouncer unit;
-Fig. 4 is a work diagram for a compressor unit;
Fig. 5 is a work diagram for a scavenging unit;
Fig. 6 is a work diagram for a bouncer unit having different
inlet and outlet valve pressure settings from that of Fig. 3 allow-
ing the bouncer at these settings to act as a compressor;
--Fig. 7 is a work diagram for a negative bouncer in the com~
pressor cylinder;
Fig. 8 is a schematic showing of a modification of the inven-
tion.
Fig. 9 is a fragmentary sectional view of the modification of
15 -Fig. 8, taken along line 9-9 of Fig. 8;
Fig. 10 is a schematic showing, similar to Fig. ],of another
preferred embodiment of the invention;
Fig. 11 i5 a schematic showing, similar to Fig. 1~ of another
modification of the invention; and
- Fig. llA is a partial schematic view of a preferred modification
of the device of Fig. 11.
Description of the Preferred Embodiments
In the preferred embodiment of the invention, which is illus-
trated in Fig. 1, the reference numeral 10 designates a free-piston
25 -engine power cylinder which has a fuel inlet 11, an air inlet 12,
an exhaust outlet 13 in a power section lOp of the cylinder, and
conventional air inlet and outlet check valves in a scavenging air
section lOs thereof. A power piston 15 is connected to a bounce
bounce piston 16 by a piston rod 17 extending through a bearing 14
30 -in a wall between said pistons. Scavenging air may be suitably
delivered from lOs to lOp through a conduit 12a by using the inner
face (i.e. the right hand face, as viewed in Fig. l) of the power
piston 15 as a scavenging piston during the expansion stroke of
piston 15 toward the right.
~ A double-acting bounce piston 16 is located in a common bounce
~L257~
cylinder 18 having piston rod bearings 19 and 20 and air flow inlet
openings 21 and 22, one on each side of piston 16. Piston 16 divides
cylinder 18 into a negative first bounce chamber 18n and a positive
second bounce chamber 18p, respectively.
- The respective bounce chambers are provided with pressure
control means which include a pair of pressure control inlet openings
21 and 22, one in each bounce chamber, and a pair of pressure con-
trol outlet openings 25 and 26, one in each bounce chamber. An
adjustable pressure-actuated inlet control or check valve 23 is
10 -located in opening 21, and a similar or identical adjustable check
valve 24 is located in opelling 22. Outlets 25 and 26 are provided
with variably adjustable pressure-actuated high pressure outlet
control valves 27 and 28 to control air flow out of the cylinder and
thereby the maximum working pressures and the bounce energy in the
15 -bounce chambers.
An energy absorbing device,illustrated as a compressor cylinder 29
at the cuter end of the engine,has~-an outlet{pening 30witha check valve 31
therein, aninlet opening 32 with a checkvalve 33 therein and a compressor
piston 3~ therein. Piston 34 is connected to bounce piston 16 by a piston
20 rod 35,preferably through a bellows seal 36attheotherend ~ cylinder 29.
Inlet valves 23 and 24 have tension springs for normally clos-
ing the valve elements therein, each being manually adjustable to
change the pressure drop across each valve. In the simplest case,
where the clearance volume in each of the two bounce chambers is
25~equal, the pressure drop across the valves would be simultaneously
lowered or raised to control the cyclic speed of the machine. The
boxes 23a and 24a have conventional manually adjustable means therein
for adjustably changing the spring tension. To change the spring
tension automatically, the adjustable means may be actuated by a
30 sensor responsive to changes in demands on the selected energy ab-
sorbing device, such as the temperature of a space to be heated or
the engine speed required for a specific application. For the
compressor of Fig. 1, for example, a conventional speed responsive
or temperature responsive sensor 37 may be connected to controls
3s~23a and 24a through a suitable mechanism 38. In general, the
sensor may be responsive to compressor flow, changes in temperature
I
~2~
--10--
needs and/or cyclic speed requirements of tile engine, or to com-
binations thereof, or to other suitable control signals. The sensing
means itself may be of a known type but is connected tllrough a
mechanism 38 which variably ancl.substarltinlly simultaneously and
similarly (i.e. in t~le same direction) adjusts each of the variable
pressure control valves 23 and 24 and thereby similarly changes the
respective wo-rking pressures in bounce chambers 18n and 18p. Suitable
mecllanisms are furtt~er described llerein in connection with Fig.s. 10
and ll.
For otllerwise substantial]y con.qtallt conditions of the maclline
of Fig. l, cyclic speed would be increased by reducing tile pressure
drop across the bounce cllamber intake valves, that is, by increasing
the mean effective pressure, and consequently the energy level in the
bounce chambers, and vice versa, to decrease the cyclic speed. To
15 insure proper functioning and prompt adjustment of bounce chamber
pressures, the present control means includes bleed means providing
a substantially continuously open limited leakage path of small
effective cross section primarily out of each bounce chamber. Such
leakage paths are provided, for example, by tlle small bleed openings
loa and 18b in Fig. l.
All of valves 23,24,27 and 28 are located and constructed for direct
connection between the corresponding bounce chambers and ambient atmos-
pheric air outside the bounce cylinder. Non-pressure-actuated valves
(not shown) may also be provided in series with or in lieu of the valves
23 and 24.
The outlet valves 27 and 28 have compression springs therein for nor-
mally holding the valves closed. They likewise have conventional means
25a and 25b for adjusting their compression. Automatic means can be pro-
vided as shown in Fig. ll to adjust these valves in a manner similar to
that for valves 23 and 24. Such adjustment may be in addition to or in place
of the means for valves 23 and 24. In many machines it is most effective
to provide such automatic variable adjustment and control for the outlet
valves 27 and 28 only, nad insure proper functioning by providing any
required flow into the bounce chambers through preset inlet check valves
23 and 24, in which case the small bleed openings 18a and 18b can be
eliminated.
In the operation of the machine, combustion of fuel in the chmaber to
the left of piston 15 causes the power assembly (power piston 15, bounce
3L%~7S~8
--1 1--
piston 16 and piston rod 17,35) and attached compressor piston 34 to move
to the right. This causes a build-up of pressures in the scai~enge ai-r cham-
ber 10s to the right of piston
15, in the positive bounce chamber 18p at the rigllt face of piston
5 16 and in the compression chamber 29c to the right of piston 34. A
reduced pressure occurs in the negative bounce chamber 18n at the
left face of the bounce piston 16. The chamber 29a to the left of
compressor piston 34 may be exposed to amhient atmosphere, but
should preferably be constructed to provide a third bounce chamber
10 between the compressor challlber and bounce chclnlber 18p for establish-
ing the basic work balarlce between the work in the power section and
the work in the compressor section. The energy stored in the bounce
chambers is regained by their use to return the power assembly and
compressor piston to their left hand positions for the next power
15 stroke.
In drawing Figures 2 through 7, the work diagrams have the
power stroke lines shown as solid lines while the return lines are
shown as broken lines. It can thus be seen that the net work per
cycles of each unit of the machine is the difference in the areas
20 under each oE the lines. In order to prevent one or more of the
pistons Erom striking the end of the enclosing cylinder, the valves
in the bouncer unit may be adjusted ~eml)or,lrily to cause Lhe l)~ullcer
to act as a compressor and, thereby, temporarily increase the load
to absorb the energy of the engine.
In the event that the invention is operating in a heat pump
that presents a mismatch problem between demand and capacity, par~
ticularly for heating in cold weather conditions, all that has to be
done to compensate for a normal drop in capacity at low ambient
temperatures, is to adjust the inlet valves 23 and 24 in Fig. l, or
30 123a and 124a in Flg. 8, or the respective valves in Figs. 10 and ll,
to increase the pressure in the bounce chambers and thus increase the
speed of the machine. Tllis may be done automatically by sensor 37
or 137 sensing outside air temperature and adjusting the valves in
accordance with it or, if no sensor is provided, by adjusting the
35 valves manually.
The pistOn rod and power assembly in the engine of Fig. l thus
provides two pistons with a total of four working Eaces, one for
the power section, one for the scavenging section, and t~o for the
hounce cilambers oE the control section. ~hen this assembly is con-
3L2~8
nected to the working piston oE a compressor type of energy absorb-
ing device, the two additional piston faces provided by such r,70rking
piston can also be fully utilized, i.e. one face as a compressor
working face, and the other face as a bounce control piston face
for a further (i.e. third) bounce chamber control section. Thus
a maximum range of speed control is obtainable within the general
constraints imposed by the maximum allowable cylinder pressures and
space limitations.
The modification of the invention illustrated in Fig. 8 is
10 basically the same in relative location and control of bounce
chambers as that of Fig. 1 in that it has a power cylinder 110 at
one end, a connection to a compressor 129 at the other end, and a
bouncer assembly 118 with separate negative and positive bounce
cylinders 118a and 118b providing negative and positive bounce
15 chambers 118n and 118p, respectively, between the power piston end
of the power assembly and the opposite end of the piston rod,
which is attached to drive the compressor piston. However, a Braun
counterbalanoing mechanism 139, such as disclosed in U.S.A. Patent
3,501,088 and a small compressor 140 have been added to provide a
20 vibration free compressor and a higher pressure air source for
varying the air pressure in the bounce chambers. A sensor and
control means 137 controls the air pressures in the bounce chambers
in response to engine speed. Air flows from auxiliary compressor
140, through conduit 140a to sensor controlled means 137 and
25 through conduits 138 to valve adjusters 123a and 124a.
The negative bounce chamber is designated by numeral 118n and
the positive by 118p. Other elements similar to those of Fig. 1,
have numbers differing by 100. Thus fuel inlet lll, air inlet
112 receiving scavenging air through conduit 112a from chamber
30 llOs, exhaust openin~ 113, openings 121, 125, 122, 126, 130 and
132 correspond to openings 11, 12, 13, 21, 25, 22, 26, 30 and 32
in Fig. 1.
The operation of the Fig. 8 and 9 modification is the same as
that of Fig. 1 except that the smaller diameter bouncer pistons
35 require higher air pressures to properly adjust the bounce pres-
sures. The smaller bounce pistons are necessary to enable the
~L2~
-13-
counterbalancing outer racks to straddle the bouncer cylinders as
they move in the opposite direction to the movernent of the pistons.
FiK. 10 is a schematic diagram similar to Fig. 1, showing
another preferred emboidment of the present invention, in which the
S variable stroke free piston machine includes a power assembly with
a piston 215 at one end of the axially movable piston rod 217, 235
and with a connection means 235a at the second or~outer end of the
piston rod for selective and removable driving connection to an
appropriate energy absorbing device 229 which could be the piston
10 of a compressor, as in Fig. 1, or an axially reciprocable electric
generator mernber, or the piston of a heat pump assembly. Between
power piston 215 and the connection 235a, the power assembly in-
cludes a double-acting bounce piston 216, which moves back and -
forth axially within a bounce cylinder 218, so that the respective
15 faces 216n and 216p of piston 216 divide the bounce cylinder 218
into an inner or negative first bounce chamber 218n between the
power piston and the bouncer piston, and an outer or positive
second bounce chamber 218p on the opposite side of the bouncer
piston 216, i.e. between the bouncer piston and the outer piston
20 rod end carrying the load connection 235a for the working member of
the energy absorbing device or load. To achieve the desired range
and flexibility of control within practical limits for such a total
power assembly, the effective cross sectional area of the double-
acting bouncer piston 216, is substantially greater than that of
25 the power piston, as already described, by a factor in the range
from at least 1.5 to at least 4 times the area of the power piston
215.
Elements in Fig. 10 which correspond to similar elements in
Fig. 1 are given numbers in the 200 series, with the last two
30 numbers corrPsponding generally to the similarly numbered parts in
Fig. 1. Thus the controls for the bounce chambers 218n and 218p
include respective inlet openings 221 and 222 controlled by spring
loaded inlet valves 223 and 224. These valves are biased down-
wardly in Fig. 10 by adjustable springs 223a and 224a, which are
35 connected respectively to the outer ends 241 and 242 of a generally
horizontal control lever 243 pivoted on a hori~ontal (as shown)
~7~4~
-14-
axis or shaft 244 carried by a vertically movable support slider
246. This slider is supported in turn for limited vertical movement
within a tubular vertical housing 247 having its upper end secured
to the bottom of the bounce cylinder 218 or a corresponding frame
portion.
The vertical position of the mo-vable support slider 246 may be
adjusted by a vertically movable link 248 having its lower end
pivoted on shaft 2ll4 and its upper end 249 pivoted at 251 to one
end ofi a two-armed lever 252 pivoted at an intermediate point 253
10 to another supporting bracke~ or frame member 254. The outer end
256 of lever arm 252 can be positioned along a scale 257 to estab-
lish a relatively lower or higher pressure range simultaneously
within each of the bounce chambers 218n and 218p, by pushing the
pivot point 244 of the control lever 243 downwardly to a greater
15 or lesser degree and thus increasing or reducing to a corresponding
extent the tension of springs 223a and 224a which control the en-
trance of atmospheric air to both bounce chambers at the low end
of the pressure range which is achieved in such chambers as the
volume of each bounce chamber approaches its maximum.
The relative position of lever arm 252 may be controlled
manually or automatically. In Fig. 10, an automatic control is
shown, in which the outer end 256 of lever arm 252 is connected as
shown schematically at 258 to a speed responsive or temperature
responsive controller shown schematically at 259.
As in the device of Fig. l, the respective bounce chambers
218 n and 218p are provided with constantly-open bleed openings
or orifices 218a and 218~', respectively. These orifices provide
limited but desirable and substantially continuous leakage of air
from the bounce chambers to help reach the desired bounce pressures
30 for which the inlet valves 223 and 224 are being controlled.
In this case, as in Fig. l, the bounce chambers are provided
with pressure relief openings 225 and 226, which are capable of
su~stantial relief of pressure from stroke to stroke, at what-
ever maximum pressure range has been established by the variable
35 pressure relief valves 227 and 228. The relief pressure for these
valves can again be set by manual adjustment of the spring tension
~2~
-15-
therein or, as further described in Fig~ 11, tlley may be controlled
substantially simultaneously (due to the rapid back and forth
strokes of the bouncer piston 216 with the piston rod assembly Z17,
235) to control tlle apparatus by correspondingly limiting the
maximum pressures within the two bounce chambers.
A further feature of the control mechanism shown in Fig. 10
involves the possibility of relative adjustment of the inlet pres-
sures in either bounce chamber to slightly different levels than
exist at their respective operational settings. For this purpose,
10 the lever arm 243 includes an integral downwardly projecting adjust-
ing arm 261 perpendicular to arm 243 which can be controlled at its
lower end 262 to rock the complete lever member 243, 261 in a clock-
wise or counterclockwise direction around its supporting pivot 244,
in response to control signals from another sensor, such as the
15 well-known knock sensors for signaling incipient knocking of an
engine within its power cylinder.
As shown in Fig. 10, the lower end 262 of lever arm 261 may be
normally urged to the right by a connecting link 263 pivotally con-
nected at 263a to a horizontally movable piston 264, urged to the
20 right in Fig. 10 by spring 266 within cylinder 267. The rocking of
the lever arm 261 to the right in Fig. 10 will reduce the tension of
spring 224a and correspondingly increase the tension of spring 223a,
so that air can enter bounce chamber 21Bp at a slightly higher
pressure in chamber 218p and could enter bounce chamber 218n at a
25 slightly lower pressure in chamber 218n than existed just before
such movement of lever end 262 to the right. If a lower entrance
pressure setting is desired for the bounce chamber 218p and a
higher entrance pressure for the bounce chamber 218n, then the lower
end of lever arm 261 can be pushed to the left in Fig. 10 by
30 admission of air under appropriate pressure to the control chamber
268 at the right of piston 264.
Such pressure can be applied under the control of a normally
closed solenoid valve 269 which can be opened to admit compressed
air or gas, either from the scavenge pump of such an engine or from
35any other source of pressure indicated generally at 271, which
supplies the necessary pressurized control air or gas through check
-16-
valve 272. The chamber 268 in which piston Z64 can be mo~ed against
the urging of spring 266 by an increase of pressure within the
chamber is also provided with a bleed opening 273, in order to per-
mit reduction of pressure irl chamber 268 and corresponding movement
of piston 264 back to the right under the influence of spring 266,
to the extent that the normally closed solenoid valve 269 is not
being actuated in response to a signal indicating incipient knock at
the power cylinder. Such a knock sensing device is indicated
schematically at 274 in Fig. 10.
Thus, if the total engine cond.itions involving power
piston, bounce piston and load member or energy absorbing device
are such that the piston rod of the power assembly is being driven
back on its compression stroke to such a degree as to lead to in-
cipient or actual knocking, the signal from a well-known type of
- 15 knock sensor will open the normally closed solenoid valve to increase
the pressure in chamber 268, move piston 264 and lever arm 262
gradually to the left, and thus rock the lever arm 243 so as to in-
crease the tension of spring 224a~ decrease the tension of spring
223a, and thus substantially simultaneously (because of the fre-
20 quency of the engine strokes) make it more difficult for air to
enter the bounce chamber 218p, less difficult for
air to enter,
218n, and thus rapidly estab:lish a lower range of pressure in the
positive bounce chamber, with a corresponding reduction in the force
25 e~erted against face 216p of the double-acting bounce piston during
the return or compression stroke of the piston assembly, and a
corresponding and substantially simultanious increase in the pressure
range within chamber 218n, which, in turn, will reduce the work
available in chamber 218p in contributing to the inward compression
30 stroke of the piston rod and similarly increase the resistance of
the pressure in chamber 218n to the inward compression stroke of the
piston rod and thus eliminate or prevent knocking in the power
cylinder.
When the knock sensor signal is thus eliminated, valve 269 will
35 resume its normally closed position, and the escape of pressure from
chamber 268 through bleed opening 273 will reverse the control
;7~
-17-
process, all of which happens within sllort time intervals, in viel,J
of the relatlvely high frequency of reciprocation of the piston rod
in this type of free piston engine. The "top-dead center" position
of the power piston wilL inte~lnittelltly (withirl these short time
intervals) oscillate between thè incipient knock position and a
small distance short of this point of maxlmum engine e~ficiency,
irrespective o~ where the position of incipient knocking may occur
under the influence of operating conditions such as engine intake
air temperature, air-to-fuel ratio, thrott~e position, octane number
of fuel, altitude and others. Thus the engille is enabled to operate
under any nominal setting at the point of the highest efficiency
that its general condition is capable of.
The device of Fig. 10 further emphasizes the advantages of
providing a single bounce cylinder with closed ends through which a
piston rod assembly, with a power piston at one end and an energy
absorbing load device connection at the other end can reciprocate
axially, and in which the rod is provided with a dOuble-acting
bounce piston inside the bounce cylinder, wllich defines two bounce
chambers of substantially equal circular cross section. Thus equal
and opposite absolute volume changes are available in the two bounce
chambers as the piston rod moves axially back and forth. The pro-
vision of two such oppositely acting bounce chambers in this par-
ticular location and relative arrangement between the power piston
and load connection ends of the power assembly facilitates the rapid
and accurate control of the pressure ranges in such bounce chambers
for optimum engine performance.
Moreover, the preferred pro-vision of bounce piston faces (cross-
sectional areas) which are not only substantially equal to each
other in the respecti~e bounce chambers, but are also substantially
larger, as shown in Figs. 1 and 10, than the area of the power
piston, makes it possible to provide total bounce chamber forces
(i.e. piston area times instantaneous pressure) great enough to
establish and/or maintain the desired high degree of control over
the operation of the piston rod and power assembly under the varying
load and frequency conditions required by whatever specific energy
absorbing device (e.g., con~pressor piston, heat pump assembly piston,
-18-
or axially movable electric generator member) is selected for
connection to tlle outer en~ of the pis~on rod.
Small changes in the bounce inlet valve pressures at the low
ends of each bounce chamber pressure range, as established by the
settings of the bounce chamber variable pressure inlet vavles, can
result in much higher ratios of pressure differences at the high
ends of such bounce chamber pressure ranges, while the maximum
pressures at sucll high ranges can also be controlled by the settings
of the respective bounce cllamber variable pressure relief valves.
The small constantly-open bleed openings, such as 218a and 218b,
further provide limited inlet and outlet functions in each bounce
chamber, and their function should be included in certain cases.
Such function can also be nchieved as part of the construction or
operation of the variable pressure bounce chamber valves, or by
15 limited leakage along the shaft seals at the respective end walls
of the bounce chambers, or even by limited leakage around the
periphery of the bounce piston from one bounce chamber to the other.
In all cases, however, the desired functions of such bleed openings
should be supplemented (or provided) by at least one pair (one in
20 each bounce chamber) of variable bounce chamber pressure inlet
control valves, or one pair (one in each bounce chamber) of variable
bounce chamber pressure relieE valves, or preferably by both such
pairs.
Fig. ll shows an embodiment of the invention in which the
desired control of the free piston machine is specifically achieved
by a pair of pressure relief outlets 325 and 326 (one in each of the
bounce chambers 318n and 318p). These pressure relief outlet means
are controlled by variable pressure outlet valves 327 and 328 as
shown schematically in Fig. ll. A pair of small constantly-open
30 bleed openings 318a and 318b (one in each of the bounce chambers
318n and 318p), is also provided. Both the bleed openings and the
variable pressure relief valves are shown, for example, as located
in the axial end walls of bounce chamber 318, which are also
provided with central bearing portions and seals at 319 and 320 to
receive the axially movable piston rod assembly 31~, 335. This rod
has a power piston 315 at its inner end and a connection 335a at
31Z~;7~
-19~
its outer end for readily removable connection to a moving member
334 of a selected energy absorbing devlce 329 which is also removably
secured to the outer end of the machine at 341.
~lements in Fig. 11 which correspond to similar elements in other
figures are given numbers in tlle 300 series, with the last t~Jo numbers
corresponding generally to the similarly-numbered parts in Fig. 1.
Thus the power piston 315 moves axially witllin a power cylinder 310
and compresses the appropriate fuel m-ixture in combustion cllamber
310p during a compression stroke of the power assembLy 317, 335 and
its associated parts from right to left in Fig. 11. Combustion of
the fuel mixture in chamber 310p then drives the power piston315 and
associated piston rod to the right in Fig. 11 in the appropriate
power stroke needed for operation of the energy absorbing device
member 334. The double-acting bounce piston 316 carried by the
piston rod divides the cylindrical bounce chamber 318 into a first
bounce chamber 318n toward the power piston end of the machine and a
second bounce chamber 318p toward the load connection means at the
other end of the machine. These bounce chambers are used for control
of tlle macllille, and the colltrols inclu~le ll~e collsLalltLy opell restrictcdopenings 318a and 318b, respectively (one in each chamber) in
combination with the pair of pressure relie~ openings 325 and 326
controlled by variable pressure valve members 327 and 328, respec-
tively described above. The closing forces oE the valves are
adjustably set by spring members 343 and 344 which are compressed
between the valves and two respective control abutments 345 and 346.
Abutment 345 projects upwardly from a slider member 347 which is
supported for relative sliding within the hollow receiving chamber
348 of a telescoping outer slider member 349. Slider 349, in turn,
is relatively slidable along the same axis as member 347 within the
channel 351 of a slide support 352 secured to the bottom of bounce
cylinder 318 or to an appropriate frame member of the engine.
A spring 353 positioned within the chamber or recess 348 in
outer slider 349, i,e between the inner end of recess 348 and the
supported end of slider member 347, normally urges the two slider
members 347 and 349 in oppositely outward directions, tending to
reduce the spring pressures applied at 343 and 344 to the relief
~L2~;^754~3
-20-
valve members 327 and 328.
To provide for relative movement of sliders 347 and 349 toward
each other to reduce the distance between abutments 345 and 346 and
thus increase the spring pressures on outlet valves 327 and 328, the
inner slider member 3~7 is provided witll an extension shaft 354
extending axially througll tlle outer slider 349 to a piston 356 within
a control cylinder 357 at the outer end of slider member 349 which
carries abutment 346. To move the respective sliders 347 and 349
and tlleir abutments 345 and 346 toward eacll other, pressure may be
increased within the cylinder chamber 358 at the left side (as
viewed in Fig. 11) of piston 356.
For this purpose, a variable pressure regulator valve 359
connected to a source 360 of pressurized air or gas can feed such
pressurized fluid througll inlet 362 into chamber 358 in response to
signals from a suitable sensor shown scl-ematically at 361, such as a
signal from a speed responsive sensor indicating an undesired de-
crease in speed or frequency of the free piston machine. A vent
355 keeps the outer end of cylinder 357 at ambient pressure, so
piston 356 is free to move out in response to pressure increases in
chamber 358.
The increased valve closing pressures of springs 343 and 344
can thus provide increased maximum pressure levels within the
respective bounce chambers 318n and 318p to increase the speed of
engine operation until the signal from the speed regulator permits
regulator valve 359 to close. At that point, pressure will be
relieved within chamber 358 oE the slider cylinder 357 by means of
the small bleed orifice 363. If the pressure drops to a point where
the sliders move apart far enough to cause another undesired drop
in engine speed, the control process just described will be repeated,
so that the engine speed may vary sliglltly in a cyclical manner
close to the desired engine speed. This control arrangement responds
to undesired decreases in speed, but it should be understood that such
a control system could also be made responsive to undesired increases
in engine speed.
As further shown in Fig. 11, the slider members 347 and 349 and
their spring-controlling abutments 345 and 346 can be moved axially
~2~i7~
-21-
as a unit to increase the rel:ief pressure imposed by spring 342 and
simultaneously decrease the spring pressure imposed by spring 344,
or vice versa. For this purpose, a piston 364, rigidly connected
to the outer end of slider 349 is recei~ved in a control cylinder
367 fixed to a stationary engine part or frame at 366. A spring
365 between the outer end of slider 349 and the inner end (left
end, as viewed in ]~ig. 11) of rixed cyl-inder 367 normaLIy urges
the total assembly of sliders 347 and 349 in a direction (]eft in
Fig. ll) to apply maximulll spring pressllre at 343 on relief valve
327 and to apply minimum spring pressure at 344 on relief valve
328.
To position the sliders against the force of spring 365, the
pressure in cylinder chamber 368 may be controlled, for example,
in response to signals from a known knock sensor 374 of the type
described in connection with Fig. 10. Thus the signal from such an
incipient knock snnsor can open a solenoid-controlled valve 369 to
feed compressed air or gas from an appropriate source 371 (such as
the scavenge pump chamber 310s or any other suitable source of
pressure) through a check valve 372 into the inlet of chamber 368.
Such pressure on the inner face of piston 364 will exceed the
ambient pressure through the open end of cylinder 367 against the
outer face of piston 364 and will thus urge the sliders 347 and 349
jointly toward fixed cylinder 367, and hold the sliders in an
operating position where the respective bounce chamber maximum
pressures are expected to provide satisfactory engine performance.
The pressure available from source 371, and the effective area of
piston 364, must be great enough to overcome the force from spring
365, and move the sliders far enough to the right (in Fig. 11) to
reduce the maximum outlet pressure at bounce pressure control valve
328, and result in engine performance which DO longer provides a
knock sensor signal. Valve 369 will then close, and bleed orifice
373 will provide for slow release of pressure from chamber 368 to
let the sliders move back and increase the bounce relie pressure
at valve 326, so that the engine operation can again approach the
incipient knocking point, where operation is generally believed to
be most efficient. Thus the upper dead center position of power
~L'257~
-22-
piston 315 can cycle within a narrow range close to the incipient
knock point to maintain the desired efficiency of engine operation.
The control systems shown in Fig. 11 operate to provide the
desired bounce chamber pressure ranges by variably controlling the
maximum pressures within such chambers, without relying on the
controls at the low pressure ends of such ranges as more fully
described in connection with Fig. 10.
Fig. llA shows a preferred modification of the device of Fig.
11, in which the pair oE small constantly open bleed openings 318a
10 and 318b are replaced by inlet openings 321 and 322 controlled by
one-way inlet valves 323 and 324 for the respective bounce chambers
318n and 318p. The inlet pressure at which the inlet valve will
open may be preset, or variably adjusted as shown schematically at
323a and 324a, and the inlet valves are provided with restricted
15 orifices 323b and 324b which are "upstream" from the bounce chamber
inlet openings and one-way valve portions. Such restricted orifices
are open directly to the ambient air at atmospheric pressure and
are restricted primarily to limit the rate at which air can be
sucked into the respective bounce chambers during the intervals in
20 which the one-way check valves are open. Such restricted orifices
may be as small as .02 inclles in eEFective dlameter, to limit the
inward flow of ambient air when the inlet valves are opened. The
inlet valves are thus useEul in providing for limited replacement
- of control air within the respective bounce chambers, while the
25 major control of bounce chamber working pressures is achieved as
described in connection with Fig. 11 by the indicated variable
adJustments of the maximum pressures at which the respective
bounce chamber exhaust valves 327 and 328 will be opened. The
inlet check valves can be set, however, to let the control means
30 work with higher bounce pressures.
The modifications of Figs. 11 and llA have both safety and
operating advantages in providing a particularly wide range of
bounce chamber control pressures primarily by controlling the
maximum pressures in such chambers.
Thus the present invention provides a wide range of control
possibilities by providing at least one "negative" or inner bounce
~L2~7~;4~3
-23-
chamber positioned toward the power piston end of such an engine,
i.e. between a bounce piston face on the piston rod of the engine
and the power piston itself7 in combination with a so-called
"positive" or outer bounce chamber positioned toward the outer end
of the engine, i.e. between the inner bounce chamber and the load
connection means at the other end of the piston rod of the free
piston engine assembly.
The availab]e flexibility of control providecl by such relative
locations and by the indicated relative cross sectional areas of the
lO bounce chambers helps to make possible the use of different energy
absorbing devices with the same basic power unit, by selectively
and removably connecting such different devices, as shown
schematically at 335a and 341 in Fig. 11, to the closed outer end
of the outer bounce chamber or to some other appropriate frame part,
15 and by using the same power assembly and piston rod 317, 335 to
drive the desired movable member 334 of the particular energy
absorbing device chosen for a specific application.
When the energy absorbing device is a working compressor (or
pump), as specifically shown in Fig.l, the invention provides a
20 relative location of engine parts which permits the compressor or
puml) chamber to be separate(l Erom, and tl~ereLy eEEectiveLy sealed
off from the engine speed controlling bounce cylinders. Tllis
permits use of a working fluid in the compressor or pump chamber
which is different from e.g. incompatible with the controlling
25 fluid, such as air, which is used in the engine bounce cylinders.
While the invention is specifically iLlustrated in a free piston
engine far driving compressOr, it may also be used in such an engine
for driving an electric alternator or some other energy absorbing
device (EAD) that is subject to varying loads as described herein, or
30 which requires an engine responsive to a wide range of changes
demanded by a particular load device. Modifications may be made in
the embodiments described herein within the intent and scope of the
following claims.
