Note: Descriptions are shown in the official language in which they were submitted.
KC ~ I J ' A ~ 'CA 0 2 2 17 8 6 4 1 9 9 7 - 1 0 - 0 9 ,1
PCTt2~I~96/00157
operation and ccntrol c,f a ~ree pia t~n ~greg~te
The invention relates to the cperation and contxol o~ a
free pi~ton aggregate.
n general, the aggregate in question is a ~ree pi~ton
S aggregate in which the compre~sion of combustion ga~ takes
place with the aid of a hydraulic~ly moved fre~ piston
and in which the ~ree piston mai~ly supplie~ hydraulic
er.ergy. ~ore speci~ically, t~e aggregate in question i3
the ~o-call~d Po~ma o~ ~P-aggregate, whlch was ~irst
described ln the Dutch paten~ applicatlon ~8.1440~, in
which only one pis~on is ~Se~ per combustion cyli~der and
the ~~e~uency and power control are realized ~y keeping
the rree piston in a 8tationary position at ~he end o~
eac~ expansicn 3troke during a longer or shorter waitin~
period.
~n the ~ree piston aggregates the movemen~ o~ the ~ree
piston or, rather, ~e ~ree piston combi~a~io~, is not a
~orced movement, such as is ~he ca8e in a crank-conrecting
rod engine. ~n tne latter case t~e combus~ion piston is
connected to the crankshaft and makes a lorced harmonic
.o~ement, whi~e the move~ent and timing o~ the free piston
must take place ~y op~ration and control ol the ~co~usti-
on)sas and liquid ~low, the p~e~sure of which delermines
~5 the moveme~t of the free piston. This operation and
control for attai~ing ~n opti~al movement o~ ~he ~ree
pistcn largely takeQ place by remotely operating certain
~as and liquid ~alves Dy means of electric control sign~ls
gcln~ out from the ce~tral c~ntrol electronics. The main
points here are the ~uick opening and closing o~ specific
valves with su~ficiently large passages that in~luence
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speci~ic ~lows of liq~ids and gases, which determine the
free pist~n movement and thus also the opti~al action of
the ~ree pi~ton aggregate.
A further embodime~t of the ~-ee piston aggregate or free
piston en~ine is described in the interna~ional patent
application WO 93/l0342 Al. This document sho~s the free
piston engine with a com~ustion pi3ton that is connected
to a plunger ~ection in a cylinder via a rod. ~n the Lo~er
Dead Centre of the combu~tion ~iston the plunger section
closes off a main ~o ~ pressure acc~mulator. The plunger
section c~n be acti~a~ed from the ~ by an auxiliary
ch~n~.l to the pressure accu~ulat~r, in whic~ a starting
val~e is arranged.
A disac~vant~ge OI the known free piston aggregate~ is that
hy~raulic -hro_tlin~ los6es usual~y occur when so~.e ~alves
do nct cpen or close quic~ly enough ~nd/or have a pagsage
that is too ~all. ~notrer disad~antage is that imDerfec~
20 gas-~iliing of th~ combustion cylinder ta~e~ place in th~
kno~L free piston aggrega~e3, owing to t~e f~ct t~at the
chargin~ device is mechanically coupled to the mo~em~n~ of
the combustion piston, ~hich is not opti~al, al~o in ~iew
o~ ~he eiectronicall~ cont-olled wai ting per~ oas of the
free pis~on. A third disadvantQge is that the known ~ree
pis~on aggre~tes have a rather i~r~cate co~d~it and
~al~e configur~tion. A fourth disadvan~age is that, in the
knowT. conduit config~ra~icn of '~ree piston ergines, flow
and leakage losses occur at the fast-mo~ing ~i~tons and
rod~ and durin~ the waiting periods or ~he ~ree pis~on.
It i~ an cb; ect o~ the inventior to prov~ide an improved
free piston a~gregate.
According to a ~irst aspect of ~he inventio~ a device for
~enerating a ~as~ ~ovement as de~cribed in claim 1 is
provided tc that end.
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Claims 2 - 17 pro~ide advantageous embodiment~ for ~his
device.
A device is herew1th pro~ided ~or generating a relatively
large a~d p~werful and, in particular, ~ast movement,
controlle~ remotely and with very littly e~ergy, which
movement can be implemented within a ve_y ~hort period o~
time after ~he co~trol signal. The moveme~t is mai~ly used
~or operatir.g ~arious ~ypes o~ hydraulic and pneumatic
lo valves, either slidi~g val~es or completely sealing
seatlng valves. ~ach time, the movement i5 bro~ght a~out
by one or more hydraul~cally opera~ed adju~ting piston~s~.
The c~e~rice for tne valve opera~ion according to the in~en-
15 tion always coTnprises a hydraulic adjusting piston, whichpiston can also ke ir.te~preted as a plunger ~ombination,
with which the valve that has ~o be operated is
~;~trcjlled. The fa~t movenle~t ~ron~ the initial ~osition to
the final position of the val~e ~ake~; place under the
û inrluence of hydrau~ic ~high) pre~sure on one side of the
ad~usting pistsn. The high pressure medium ~lows towards
the pre~3ure side of the adjusting pis~on via a main that,
in the initial pos~tion, is closed by the aajusting pis~on
itself. The adjusti~g piston mu~t therefore be moved
2s acros3 a very ~mall initial distance 7n orQer ~o open this
main.
Thi~ inilial movemen~ may take place with mechanica~,
electromagnetical and electrodynamical means because no
(high) pressure is exerted on the two sides o~ ~he adjus-
ting piston in the initial po~iti~n ~nd the adju~ing
piston can move f~eely to ~he e~tent that, in ~he ca~ç of
movement ~rom the i~itial posi~ion, no pressure ~uild-~p
can occur by d~splaee~ent of liouid ax a result ~ 6aid
3 ~ moveme~t .
The initial mo~ment i~ preferably achieve~ wieh hydraulic
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means under the influence of an electric ~ignal to ~ast-
working elestroval~es with a small pGssage, i~ which, via
a narrow auxiliary channel, pres~ure medium ~low6 to~ards
the pressure side o~ ~he adju~ting pi~ton. In the starting
position, the pressure 5~ de of t~.e adjusting piston is
connected with low pre6sure, as a ~esul~ o. which a po5-
sible leakage ~low to said pre~u~e ~ide cannot lead tc
pressure build-up ~nd unwa~ted movement of the adjustl~g
piston,
~ith the device according co the l~v~nti~n it ~ poss~ble
to realize a dou~le-acting ~mbodimen~ ky using a second
adjusting piston, as a result of which ~he valve opera~ed
by the a~juj~ing pisto~3 will be able to open ve-y ~uic~ly
arter a contro; signal as well a3 clo~e ~ery ~uic~ly ~_ter
a csnt_cl signal.
Clai~s 18 and 19 offer an applicatio~ cf the device for a
~alve as~embly.
2Q
Clai~s 2~ - 22 o~er an apDlicatio~ of ~he device ~or
operating 3 ga. va~ve ~or a combustion chamber, and the
gas or sup~'y valves used the-e~ith
~5 Accordirg ~o a seco~d a~ect of the invention, a free
piston a~gregate ~ith a device fo~ char~ing ~he c~mbustion
chamber o~ a f~_e pis~or aggregate, and ~he pr~ssure-
cha~gi~s devlce itsel~ a_e pro~ided, as descri~ed in
claims 23 - 26.
With this aspec~ of the inventio~, a free piston agg~a~e
a~d a de~ice are provided ~ith which the ~re~h air or gas
supply to ~he combus~ian chamber is con.rolled. T~e de~ice
ls ~uch, that the quantity o~ fresh gas and ~hus al~a the
develop~ent o~ the p~essure in t~e eo~bu~tio~ cylinder can
be operated and controlled remotely, ror every stroke, by
the con~rol elect~onics.
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The ope~~ation and control cf tke fresh gas flow towards
the com~u5tlon cy~inder takes place by means of a piston
gas p~mp that is hyd-aulically dri~en with the same ~re-
quency as the free piC~on. The gas pump piston draw~ in
fresh gas during the final part o~ the COmp~es~iO~ stroke
of the free pi~t~n and/or du~in~ the initial part of the
expan~ion stroke . ~hen, bef ore the beginning o~ the next
compression stroke, the compres~ion o~ the dr~wn-in Iresh
ga~ in the ~aq pump cylin~er commences. The moment the
deli~ery stroke o~ the g~s piston begins is determined
h-ith a control signal fro~ the control electronics to a
~~ast-working hyd~a~lic ~alve that admits pressu_e ~Qdium
to the hydrauli~ piston that a~ti~ate~ the pump piston.
The ga~ pump cylinde~ ~s connected to the combustion
c-~linder ~Jia a conduit in wh~h a non-~eturn gas val~e ~r
a~. opex~ted gas valve are present. The no~.-return ~alve
opens when the pressure in ~he ~as pump ~yl i~der is higher
than the pres~ure i~ the coF~bustion cylinder. In ~his
case, the beginning o.~ the delivery ~troke of ~he gas ~ump
piston i~ regulated in su~h a way tna~ ~he non-return
~alve opens during ~he oompression stro~e of the ~ree
pi5to~ within a period of ti~e beginning shortly ~efore
the exhaust poxts of the co~bustion cylinder ~lo~e un~il
we~l before the end o~ the compression stroke of the com-
~us~i~n piston. In the case o~ ar act~ated saS -~al~e to
the c~mbustion cyli~der, the gas pressu~e i~ the gas pump
cylinder ca~ rise ~nsiderably hi3her ~han the pressure in
the combu5~ ion cylinder before said ~alve is opened. The
mo~ent o~ opening is then determined by ~he oontrol
èlectronics. In ~his ~ase too, howevex, the moment o~
opening will lie within the indicated pe~iod of ti~e,
since, when opening takes place well be~ore the exhaust
ports close, ~resh a r or ~resh combustion gas wiil disap-
pear through the exhaust ports without ha~ins ~een used,as a result. ~he ~as ~rom ~he gas pump reaches the combus-
tion cylinder ~ia a conduit that debouches i~ the head or
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in the cy'i~er wall of the combustion cylinder. The
actua~d gas ~al~e is opened by an adju5tin~ pi~ton, a6
described before
~he moment ~he gas valve opens, the ga~ pump piston will
u~ually ~till be moving and the delivery action will
ccntinue during the compression ~t_oke of the combustion
pis~on as well, with the ad~anta~e that the pressure
difference at whic~ fre~h gas is sup~ d (and t~erewith
o the qua~tity of press~re energy needed far each stroke)
can be a~ low a~ possible on average. The mome~t the
deli~ery s~roke of the sa~ pump co~ences ~nd ends i~
p~incipally determined ~y the operation o~ t~e
hyd~aulically actuated valve that co~trols the supply and
discharge ~o ~he hyd~aulic cylinder or the ga~ pump. By
control~ing the opening and clo~ing times of th~s
hydraulic ~alve and of the gas ~alve, the quantity o~
supplied fresh air or fresh combustion gas per ~troke can
be operated and controlle~ by the control elect-onic~.
2C
Accordi~g to a thi~d a~pect ar ~he invc~tion, a free
piston asgregate is pro~ided suc~ as described in the
claim~ 27 - 5~.
wit~ tni~ aspect of the in~e~i3n~ a s~eci~ic embodiment
is Sivcn of Ihe li~uid suDply and discharge t~ the --ixst
and s~co~d displacement ~pa~e on either side o~ the
~ydraulic co~pression piston o~ the ~ree pisto~ co~-
bination~ It in~-ol~es various conduit con~igurations with
or wit~out r.on-retu~n val~es and/or valves that can be
quickly and remotely actuate~, with which the mo~ement3 of
the free pis~on are con~rolled. ~epending on the indicated
con~iguration, specific ac~antages are attained leading to
limi~ation of the occurring leakaye loss an~/or
si~pli~ica~ion o~ ~he embodiment. The attained
simpli~ication consists of a limitation of ~he number of
~alves and/Gr a limitation of the nu~bex of d~splacement
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spaces upto two at the least by integrating the energy and
the compression piston, in addition to ~ich the mir~lly
required number of high pressure accumulatoxs can be
reduced to two in certain cases.
The em~odiment~ have the advantage tha~ leakage ~ia rod
~nd pis~on seal~ at the hydrauli~ co~pression pi~ton i~
reduced a~ a result o~ the ~act that the ~upply of
nydraulic medium fr~ space~ with high pressure via con-
dui ts ~o the co~pres3ion cylinder is prevented during ,he
wai~ing period o~ ths ~ree pis_on near the lower dead
cen~re with ~he aid or non-return valves and actua~ed
val~e~ in gaid con~uit~. T~is embodiment according to _he
in~J~ntion h~s a great n~be_ of v~_iants a~d example~ of
applicatio~. 'n one of the varian~s, the second
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displacement space is permanently connected to a space
with a pressure that is as low as possible and said second
displacement space is therefore never connected to a space
with high pressure when the machine is working normally.
However, in order to prevent too strong a spring-back of
the free piston after the end of the expansion stroke, a
new device is required for release of the pressure medium
in the first displacement space as soon as the free piston
comes to a standstill in the lower dead centre. In other
variants a simplified embodiment is described in which the
conduit to the first displacement space as well as the
conduit to the second displacement space are provided with
a fast-working actuated valve, as a result of which ports
in the cylinder wall of the hydraulic compression cylinder
are prevented, the interception of the free piston at the
end of the expansion stroke is improved, the leakage via
the piston and rod seals is reduced and a number of valves
can be integrated into a compact combination of valves.
Finally, an embodiment is described in which, under cer-
tain circumstances, the third displacement space can beintegrated with the first and second, while, for a number
o~ embodiments, the number of hydraulic accumulators can
be reduced from three to two as well.
The invention will be elucidated below on the basis of a
number of figures.
Figure 1 shows a known embodiment of a hydraulic free
piston aggregate;
figure 2 shows a single-acting valve actuation with one
adjusting piston;
figure 3 shown a double-acting valve actuation with two
adjusting pistons;
figure 4 shows a valve actuation with an auxiliary adjus-
CA 02217864 1997-10-09
ting piston;
figure 5 shows a charging of the combustion part of a free
piston aggregate with a separate hydraulically 'driven
piston gas pump;
figure 6 shows embodiments of an actuated gas valve in the
head or wall of the combustion cylinder;
figure 7 shows embodiments of the supply and discharge of
hydraulic medium to the hydraulic compression cylinder of
the free piston aggregate;
figure 8 shows a release device for pressure medium in the
first and third displacement space of the free piston
aggregate;
figure 9 shows an embodiment with two actuated valves to
the hydraulic compression cylinder of the free piston
aggregate;
figure 10 shows an embodiment with upto two integrated
displacement spaces and upto two integrated accumulators.
Figure 1 shows a known hydraulic free piston engine or
~ree piston aggregate. The way it works is described
below. The combustion piston 7 moves within the combustion
cylinder 15, which combustion piston 7 is connected via
rod 35 to the hydraulic piston 8 and to the plunger 9. The
piston 8 moves within a cylinder 17 and, therewith, forms
the first, displacement space 1 (with pressure ~) and the
second displacement space 2 (with pressure ~ ). The left-
hand annular piston surface of piston 8 is smaller than
the right-hand annular piston surface. Together with the
plunger cylinder 18, the plunger 9 ~orms the third
displacement space 3. The combustion engine portion
especially comprises the combustion cylinder 15 and the
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combustion piston 1 and acts as a two-stroke combustion
engine with exhaust- 13 and inlet-ch~nnel 14. During the
expansion stroke (the movement to the right), hydraulic
medium is forced from space 1 into high pressure compres-
sion accumulator 4 in which the pressure Pca prevails. Thesupply into accumulator 4 first goes mainly via the wide
ch~nnel 19 and, after it has been closed by the piston 8,
via non-return valve 11. Liquid is also forced from space
3 (with pressure Pac) into the high pressure accumulator
5, in which pressure Paa prevails, via non-return valves
32 and 30. Liquid under high pressure Pca is also supplied
from accumulator 4 to displacement space 2 via channel 10.
By supplying energy to accumulator 4 and 5, the piston 8
comes to a standstill in the lower dead centre (LDC) at
the end of the expansion stroke. In order to start the
compression stroke (movement to the left), the valve 12
must open. The time that passes from the moment the free
piston comes to a standstill in the LDC and the moment the
starting valve 12 opens and the compressions stroke com-
mences, is the waiting period of the free piston. Thiswaiting period is controlled with starting valve 12, and
thus the stroke frequency of the free piston is also
determined, as well as the quantity o~ pressurized oil
produced per unit of time.
After the starting valve 12 has been opened the compressi-
= on stroke commences, during which the pressure medium
flows with high pressure from the compression accumulator
4 to space 1 and with low pressure PL from the low pressure
accumulator 6 to space 3. At the same time, liquid flows~rom the second displacement space 2 into compression ac-
cumulator 4. During the movement to the left the piston
plunger combination is slowed down by the compressed gases
in the combustion cylinder 15 and finally comes to a
standstill in the upper dead centre (UDC), i.e. the left-
most position. Just be~ore the UDC is reached, combustion
commences and the pressure within the combustion cylinder
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very quickly rises.
The free piston starts the expansion stroke and subse-
quently comes to a standstill in the LDC. At this moment
liquid under high pressure is still present in space 1 and
space 3.
Owing to the elasticity of the liquid, the free piston
rebounds to the left even before the starting valve 12
opens. During this movement to the left a counterforce is
experienced, however, under the influence of the pressure
Ptc in the second displacement space 2 that is connected
to the accumulator 4. Owing to this counterforce, the free
piston comes to a standstill again within a very short
period of time, even before channel 19 is released by the
piston 8. Subsequently, the free piston moves to the left
again, until the pressure in space 1 has risen so much
that the piston comes to a standstill. In this way the
free piston oscillates with ~;m;n;shing amplitude near the
LDC and finally comes to a complete standstill, especially
as a result of frictional losses. The high pressure in
space 2 is necessary in order to prevent the free piston,
under the influence of the elasticity of the oil in space
1 and 3, from rebounding too far upto past the port of
channel 19, as a result of which an unwanted new stroke is
made and the operation can no longer be controlled with
starting valve 12.
In this embodiment of the free piston engine, space 2 is
under high pressure during the waiting period and oil will
leak via the rod seal 16. Here, it is difficult to seal
properly because of the varying temperatures caused by the
proximity of the hot combustion piston to which rod 25 is
attached. The combination of varying temperatures,
extremely high piston speed and high pressure is undesired
from a viewpoint of limitation of leakage losses.
CA 02217864 1997-10-09
During the waiting period, leakage also occurs from ac-
cumulator 4 via channel 19 along the seal between piston 8
and the cylinder wall. Differences in temperature occur
less frequently here, but there is a longer leakage gap,
however, owing to the larger diameter of piston 8.
Figure 2a shows the basic embodiment of the movement
device according to th~invention. The adjusting piston 51
moves within cylinder,~. This adjusting piston 51, in the
depicted first position or initial position, closes the
main 59 in the wall of the cylinder. The piston or plunger
combination 51 (figure 2b), together with the cylinder ~,
forms a first displacement space 61 and a second displace-
ment space 79. The piston or plunger combination can move
towards the second, most right-hand position and, via rod
28, moves the mass M that mainly consists of a valve slide
or valve of an air- or hydraulic piston or a gas valve.
In the first position of the adjusting piston 51 the first
displacement space is connected to low pressure PL. The
second displacement space 79 is also connected to low
pressure PL via a large channel 72a. The main 59 is under
high pressure Ph. The adjusting piston 51 can move from
the first position without pressure build-up by displacing
hydraulic medium in space 79. After a small first or
initial movement to the right the adjusting piston 51
opens the main channel 59, causing hydraulic medium under
high pressure to flow in and causing the adjusting piston
51 or the plungers 51 with the mass M to move to the
second end position very quickly. The means for generating
the initial movement are described in the figure descrip-
tion and at figures 2c - 2e, as well as the means to move
the adjusting piston back to the first position again.
Figure 2cshows a drawing of the movement device according
to the invention, which is used for operating a hydraulic
valve 96. To this end, the valve 96, which may serve as
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CA 02217864 1997-10-09
starting valve 12 of the free piston aggregate, is
operated by the fast-working adjusting piston 51 that
moves under the influence of a medium under high pressure
that flows in via electrovalve 74 in auxiliary channel 56
and via main 59 that is opened by the adjusting piston 51.
In the initial position valve 96 is closed. Via re-setting
valve 68 the main 59 (with large passage) is under high
pressure Ph and auxiliary channel 56 is connected to low
pressure Pl via actuating valve 73. The adjusting piston
51 does not start moving because space 61 is under low
pressure and main 59 is closed off and the very slight
hydraulic imbalance is compensated by the left seating
seal with spring ~.5~
As soon as the control electronics close off the electri-
cally operated actuating valve 73 and open actuating valve
74, space 61 is pressurized, causing the adjusting piston
51 to move and, subsequently, main 59 to open, after whic~
a fast movement to the right takes place and valve 96
opens.
Under the influence of the pressure difference between Px
and Py, which pressures may be deduced from the present
pressures in the free piston aggregate, the re-setting
valve 68 switches and moves to the left. For Px a choice
can be made out o~ Pca, Pcc or P~c, to be combined with
PTC~ Pca and Pcc, respectively for Py. In this case Px-Py
will first become negative during the compression stroke
(68 switches to the left) while Px-Py will become positive
(68 switches to the right) at the end of said stroke and
during the expansion stroke. In the left position of valve
68 the main 59 will come under low pressure, after which
the adjusting piston 51, under the spring force of spring
83, moves to the left and closes the valve 96. The star-
ting valve 96 is now closed again.
Meanwhile, the control electronics have closed actuating
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valve 74 and opened 73, ca~ising space 61 to be connected
to low pressure.
At a certain moment in time, the pressure difference Px-Py
reverses its sign, as a result of which re-setting valve
68 switches to the right. Main 59 will now be under high
pressure again and the initial position has been reached
again.
In figure 2c, the possibility of channels to the high
pressure level Ph and the low pressure level Pl are also
indicated on the righthand side in cylinder 71, with small
non-return valves 115 and 116 in said channels. If neces-
sary, these serve to decelerate the adjusting piston 51
lS that moves quickly to the right, by means of pressure
build-up in space 79 during the final part of the stroke
to the right of adjusting piston 51.
The valve operation according to figure 2c brings about a
fast-working and electrically controllable valve adjust-
ment, in which use can be made of small and very fast-wor-
king electrovalves (73, 74), which may be obtained on the
market, and of standard sliding valves (96).
In figure 2d the initial movement is brought about mecha-
nically with the aid of a short, powerful current surge
through coil 128, as a result of which, via the pin con-
nected to the coil cup 128, a force is exerted to the
right on the adjusting piston 51. The moment port 47 is
closed,~the port to channel 59 is opened. The non-return
valve ~ , to be mounted if necessary, makes it possible
to close port 47 slightly earlier, as a result of which
the possibility of a brief leakage from channel 59 via
space 61 into port 47 and to low pressure PL in space 79 is
prevented or greatly reduced. After channel 59 has been
switched back to low pressure via the (non-depicted) re-
setting valve 68, the adjusting piston moves to the left
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again under the influence of spring 55. The port to chan-
nel 59 closes first or simultaneously with port 47. If
channel 59 should close slightly earlier, the r~ n;ng
kenetic energy is converted to throttling heat via the
leakage gap at channel 59.
In figure 2e port 72a is connected to the pressure Pac in
the third displacement space 3 of the energy cylinder of
the free piston aggregate and channel 59 is connected to
the pressure Paa in the energy accumulator 5. During the
waiting period of the free piston in the expansion positi-
on and during the compression stroke, the pressure Pac is
lower than Paa. The adjusting piston 51 can then open
valve 96 and, under the influence of the pressure diffe-
rence Paa-Pac, will remain in the second position. After
the expansion stroke has commenced, Pac rises to a level
that is equal to or higher than Paa, as a result of which
the adjusting piston, owing to the spring force and the
slight pressure difference present, moves back to the
first position during the expansion stroke. The time that
is required for this back-movement can be influenced by
the spring force and possibly by a resistance with, para-
llel thereto, a non-return valve in channel 59 in order to
achieve that valve 96 closes shortly before the end of the
expansion stroke and, before that moment, maintains a
large passage from the first displacement space 1 to the
compression accumulator 4.
In the double-acting movement device according to the
invention of figure 3, the valve actuating rod 28 is
operated by two adjusting pistons 51 and 52. The opening
of valve 96 takes place by adjusting piston 51 in a way
that corresponds with the one described at figure 2c.
After the starting valve has been opened, the adjusting
piston 51 opens channel 63 and brings it into connection
with the pressure Ph in adjusting cylinder 71, causing re-
setting valve 68 to switch to the right, counter to the
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spring force of spring 67. By switching the re-setting
valve 68, channel 59 and thus also 63 will be put under
low pressure and main 60 under high pressure. The spring
67 cannot switch valve 68 to the left, however, because
non-return valve 65, bridged by the pre-stressed non-
return valve 66, prevents it from doing so. The pressure
required to open 66 c~nnnot be generated by spring 67.
Owing to the pressure in main 60, the adjusting piston 52
can now move to the left after an electric command from
the control electronics of the free piston aggregate,
closing electrovalve 73 and opening 76. Valve 96 will now
close. This closing takes place by adjusting piston 52 in
a way that corresponds with the one described for adjus-
ting piston 51. As soon as valve 96 (which may serve as
starting valve 12) is closed, the adjusting piston 52
connects channel 64 to the space 62 under high pressure.
Re-setting valve 68 switches to the left, as a result of
which the initial position is reached again.
Figure 4 indicates how, in the case of a heavy adjusting
piston and the mass moved by it, the speed of response of
the adjusting piston 51 can be increased by means o~ an
auxiliary adjusting piston 51a. It works as ~ollows.
After the actuating valve 74 has been opened, space 61
will be pressurized. The actuating valve switches very
quickly, but has a very small passage, which decelerates a
quick start of the relatively large adjusting piston 51.
Therefore the auxiliary adjusting piston 51a is present,
which, owing to its small mass, low spring force of spring
83a and small piston surface, can move to the left more
quickly, opening channel 59a in the process, which has a
larger passage than actuating valve 74. Owing to this
larger passage to space 61, the adjusting piston 61 can
now also move more quickly and open main 59. When the
adjusting piston 51 moves back under the influence of low
pressure in space 61, the auxiliary adjusting piston 51a
-
CA 02217864 1997-10-09
returns to its initial position under the influence of the
spring force of spring 83a.
Figures 5a-d depict the free piston engine of figure 1
with the charging device.
In figures 5a and Sb the gas supply channel 46 debouches
in the head of the combustion cylinder, but channel 46 can
also debouch in the wall of the combustion cylinder 15 and
be closed off there by the combustion piston 7. This
embodiment of figures 5c and d entails that the closing of
the gas supply from pressure space 137 is now attended to
by the combustion piston. This ensures guaranteed, extre-
mely fast closing. The supply valve 45 is embodied as an
actuated valve 45a (figure 5c) or as a non-return valve 45
(figure 5d) and can now close much more slowly during the
period of time that passes4from the moment the combustion
piston closes off channell~ until the moment the combus-
tion piston re-opens channel ~ during expansion.
The exhaust port 13 of the combustion cylinder is also
indicated. Port 46, with non-return valve 45 or actuated
valve 45a, is connected via channel 44 to the charging
cylinder 42 within which the scavenging piston 128 moves.
This piston 128 is connected via rod 119 to the hydraulic
piston 121 which moves within the hydraulic cylinder 127.
Via fast-working and remotely operable valves 123, 124 or
the valves 123 - 126, the spaces 120, 122 may be connected
to high or low pressure. Air supply to the charging
cylinder 137 takes place via the channel with non-return
valve 41, in which the valve 41 is an operated valve or a
non-return valve.
The charging device works as follows. Proceeding from the
depicted initial position with the combustion piston 2 in
the lower dead centre (LDC), the combustion piston 7 moves
to the left and compresses the gas in cylinder 15 as soon
AMENDED SHEET
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- 17 -
as the exhaust port 13 is closed by the piston 7. Before
the moment the combustion piston 7 commences the compres-
sion stroke starting from the LDC, the supply of hydraulic
medium under high pressure to the hydraulic cylinder 127
is opened, under the influence of which the scavenging
piston 12 8 moves upwards. The scavenging piston 12 8 can
generally compress the gas in the scavenging cylinder
faster than the combustion piston 7 compresses the gas in
the combustion cylinder, because, among other things, the
scavenging piston is comparatively much lighter and/or
makes a shorter stroke. As a result of this and of a
commencement of the scavenging piston before the beginning
of the compression stroke of the combustion piston, the
gas pressure in the scavenging cylinder 137 can be higher
than the gas pressure in the combustion cylinder 15 at the
beginning of the compression stroke, causing gas to flow
from the scavenging or charging cylinder 137 via non-
return valve 45 into the combustion cylinder 15. This gas
supply is ended shortly after the scavenging piston has
reached the end of its stroke or by the fact that the
scavenging piston is brought to a standstill by the clo-
sing of the supply of hydraulic medium to cylinder 127
with the aid of the hydraulic valves present. Subsequent-
ly, the combustion piston 7 continues its movement to the
left until the upper dead centre (I~DC) is reached.
The scavenging piston must commence its movement to the
left before the combustion piston has started its own
movement to the left. As a result, the very moment the
combustion piston commences there will be an over-pressure
present in the scavenging cylinder and gas will flow to
combustion cylinder 15 via channel 44, 46. This flow of
gas subsequently increases as a result of the quickly
rising gas pressure in the scavenging cylinder. After the
supply of hydraulic pressure medium into cylinder 127 has
stopped, the speed of the scavenging piston will quickly
drop to zero, causing the pressure difference between
CA 022l7864 l997-lO-09
- 18 -
scavenging and combustion cyilnder to decrease as well. As
a result of the fact that the combustion piston 7 con-
tinues moving upwards, the pressure in the combustion
cylinder continues to rise, initially resulting in an
equilibrium of pressure, followed by an over-pressure in
the combustion cylinder. Non-return valve 45 will now
close. Subsequently, the scavenging piston 128, under the
influence of the remaining gas pressure in the scavenging
cylinder 137 and as a ~r~ts~ t of the pressure of hydraulic
medium ln thfe space j~h c~ the hydraulic piston 12,~, will
move ¦~wn~T~ , in the course of which the pressure in the
scavenging cylinder 137 decreases and, finally, air or gas
is drawn in via non-return valve 41 and air filter 118,
until the scavenging piston reaches the initial position
again. The important aspect of this device is the pos-
sibility to control the amount of supplied air or gas via
channel 46 by letting the movement of the scavenging
piston to the left take place sooner or later. When the
scavenging piston starts comparatively long before the
combustion piston does, an over-pressure will already have
built up in the scavenging cylinder the moment the combus-
tion piston commences and gas will already flow into the
combustion cylinder. Owing to the fact that, generally
speaking, the exhaust port 13 is still open here, the
supplied air from the scavenging cylinder will be able to
leave the combustion cylinder again via the exhaust port.
This is, of course, effective scavenging. After the ex-
haust port has been closed, the remaining volume of air in
the scavenging cylinder will be fed under low pressure
into the combustion cylinder and participate in the com-
bustion process. When the scavenging piston commences
later, at a moment in time chosen in such a way that the
supply of gas is just commencing via conduit 46 the moment
the combustion piston closes off the exhaust port, all the
air supplied from the scavenging cylinder will be used for
charging. If commencement takes place at an even later
moment in time, the charging will diminish because the
AMENDED SHEET
CA 02217864 1997-10-09
~ -- 19
pressure in the combustlon cylinder at which supply from
the scavenging cylinder takes place, is higher. The degree
and nature of the charging can therefore be remotely
controlled by the control electronics, in addition to
which the early start may also result in a comparatively
big charging.
By using an actuating valve 45a in the head or wall of the
combustion cylinder, the operation and control o~ the
fresh gas filling of said cylinder is enhanced even fur-
ther. The actuated gas valve makes it possible to start
the charging piston sooner and to build up the pressure in
the pump cylinder 137 further, until approximately the
moment the exhaust port 13 closes and the gas valve opens.
The greater pressure difference between pump cylinder 137
and combustion cylinder 15 will cause the ~resh gas to
flow to the combustion space more quickly and more gas to
be supplied during the very short period of time of 5 - 10
m.sec. that is available therefor. On the other hand, said
greater pressure dif~erence increases the amount of energy
that is required for the charging by the required higher
end pressure. The opening and closing times of the hydrau-
lic valves 123 - 126 and the gas valve 45a must therefore
be optimized by the control electronics in order to attain
a mimimal energy demand for each desired air addition via
channel 46. This is possible with the charging device
according to the invention.
For the control o~ the movement of the charging piston
128, the hydraulic valves 123 - 126 are used. The hydrau-
lic piston 121 can also be embodied as a single-acting or
double-acting adjusting piston 51 and 52, just like those
in figures 2c, 3, 6g of 6i. The valves 123 and 124 can be
embodied as a three-way valve that is moved by a double-
or single-acting adjusting piston or as two open-close
valves that are ~perated by a single-acting adjusting
piston 51. ,~c c~?
AMENDED S~IEET
CA 02217864 l99i-10-09
- 20 -
sc~/~;~
The ~hargi ~ piston 128 can also be controlled by a four-
way valve moved by a single- or double-acting adjusting
piston as described at figures 2, 3, 6g or 6i, for
instance.
The charging device according to the invention can also be
used for the supply of fuel. To this end, fuel is injected
on the places indicated with a triangle. Injection im-
mediately into the combustion cylinder is possible too, of
course. Injection of fuel into the charging part has the
advantage that more time is available for evaporation and
mixing before the fuel reaches the combustion cylinder as
an air-fuel mixture, together with the charging air.
Figure 6a shows an embodiment of the supply valve 45a that
is to be mounted into the wall of the cylinder. One objec-
tion here is the present space 46 in which air or gas
remains behind that is brought into contact with the
burning gas mixture in the combustion cylinder during the
expansion stroke. The volume 46 causes a small pressure
drop in the combustion cylinder as soon as the port in the
cylinder wall is opened. This pressure drop decreases the
energetic efficiency of the machine.
When combustible gas is fed in ~from _~ -E_ - ~
g~a ~, the dead volume of gas 46 will not participate in
the combustion cycle, as a result of which the fuel effi-
ciency of the machine will decrease further.
It is therefore important to make the dead volume 46 as
small as possible.
Figure 6b shows an embodiment of the supply valve 45a with
a very small dead volume. When gas pressure is present in
the combustion cylinder during the second part of the
expansion stroke, the valve may not open and must then be
kept closed by a considerable force on valve stem 28.
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CA 02217864 1997-10-09
Figure ~3t shows an embodiment of the supply valve 45a with
a minimal dead volume, a passage that is as large as
possible and a light valve disc 45a. Here, the valve disc
is a ring or band around the outer wall 38 of the
cylinder, in which the wall is provided with holes 46 all
around, which holes are opened or closed by rotation of
the valve disc 45. To this end the valve disc, too, is
provided with holes 36 that correspond with the holes 46
in the cylinder wall 38 when the valve is open. The
rotation of the valve disc is made possible on account of
the fact that it is provided with a cam 37 to which the
operating rod 28 is attached. By moving the rod 28 back
and forth, the valve disc is rotated.
If there is a ring 45a, it must consist of two parts that
are connected to each other after they have been placed in
a slot around the combustion cylinder. If a band is used,
it must have a joint that is bridged by ~pring Lenslon or
by a fixed connection.
Figure 6d shows how the band-shaped valve disc can be
locked up between two annular sealing surfaces 38 and 39.
The dlvided band can now have a light-weight construction
and will be able to contact the outer sealing area 39 when
there is pressure in the combustion space, and be able to
contact the inner sealing area 38 when there is pressure
from outside the combustion cylinder (in the pressure
space that encloses the outer side of the combustion
cylinder here). The surface 39 has holes 35 that corres-
pond with the holes 46.
Figures 6e - 6i relate to the hydraulic valve control. The
supply valve 45a can also be operated mechanically in a
way that is customary for crankshaft combustion enginges,
with rotary cams, the movement being transferred to the
valve disc mechanically or hydraulically. Owing to the
very fast opening and closing on account of the very short
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CA 02217864 1997-10-09
W 096/32576 PCT~NL96/0~157
- 22 -
period of time of 5 - 10 msec that are available for the
total charging period, valve operating times of a ~ew
milliseconds are necessary here. Major forces occur as a
result, which preferably should be generated by hydrau-
lically operated adjusting cylinders. The fast movementsdo call for comparatively large adjusting pistons, high
hydraulic pressures, large passages, while electric or
mechanical control valves are necessary that are light to
operate and work fast.
These combined requirements can be better met when the
valve controls according to the invention, described in
the following, is used. The valve controls in figures 6e
and 6f are, on account of the constructive adaptation and
the necessary fast opening and fast closing, rather meant
to be mounted in the upper area of the cylinder head,
while the figures 6g - 6i show valve controls that are
more suitable for valves that are placed in the wall of
the combustion cylinder.
Figures 6e and 6f show the usual embodiment o~ a spring-
loaded sealing gas valve in the head of the combustion
cylinder. The valve stem 28 is moved by two adjusting
pistons 51 and 52, in a way as described at figure 3. In
the depicted closed position in figure 6e, no resulting
force is exerted on the first adjusting piston by the
medium in space 61. In this embodiment, the opening of the
valve is commenced with the aid of the fast little elec-
trovalves 73 and 74. Via the large main 59, the pressure
medium can now flow in, on account of which the first
adjusting piston 51 opens the valve 45a with considerable
force and high speed. When this movement to the right
takes place, the liquid escapes from the second
displacement space 62, via the second main 60 and subse-
quently via the re-setting valve 68 into a space with low
pressure PL' At the same time liquid with low pressure PL
flows via channel 70 into the displacement space 53 of
CA 022l7864 l997-lO-09
holding cylinder 89.
As soon as the first adjusting piston 51 has reachecl ~
open position or second end position, the following takes
place. Channel 63 is connected to the first displacement
space 61 with high pressure by the first adjusting piston,
while channel 64 is connected to the space 79 with low
pressure by the second adjusting piston 52. This will
cause the re-setting valve 68 to move quickly to the
right. As a result, the pressure in the first displacement
space 61 decreases via main 59 and the pressure in the
second displacement space 62 increases via main 60 and the
pressure in the displacement space 53 of the holding
cylinder 89 increases via channel 70.
In this second end position, the second displacement space
62 iS connected via auxiliary channel 57 to low pressure
and the connection between main 60 and the second
displacement space is closed off5 by the second adjusting
piston as well. The valve disc ~ is now kept open by the
pressure in the holding cylinder 89, opposing the spring
i~orce of spring 55, while the :Eirst and second
displacement spaces are connected to low pressure and the
first and second adjusting piston do not exert a resulting
force on the valve disc ~.45
Owing to the fact that channels 63 and 64 are now con-
nected to the pressure-free spaces 61 and 79, re-setting
valve 68 would be able to spontaneously switch back to the
left position under the influence of spring 67. The non-
return valve 66 through which the through-flow must take
place is spring-loaded, however, and the power of spring
67 iS not large enough to open the non-return valve 66.
4~
A sta~le open or second position of the supply valve ~'is
obtained with this.
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CA 02217864 1997-10-09
- 24 -
The closing of the supply valve is subsequently started
with the aid of electrovalves 73 and 76. Valve 73 is
closed first, after which 76 is opened. This causes main
60 to be opened by the second adjusting piston 52, after
which the valve disc moves to the left with great force
and speed. When the closed position is reached, channel 64
is connected to the high pressure in the second
displacement space 62, while channel 63 is connected to
the low pressure in space 79 via non-return valve 66. The
re-setting valve 68 switches to the left as a result and
the initial position is reached again.
Figure 6f shows an embodiment with a small first adjusting
piston 51 and a larger second adjusting piston 52. The
first displacement space 61 is brought under pressure by
closing valve 73 and then opening valve 74, starting from
the position depicted in the drawing. The first adjusting
piston starts off the initial movement to the right and,
after a slight displacement, opens the main 59 after which
the first adjusting piston quickly reaches the second45end
position. When this open position of the supply valve ~ is
reached, channel 63 is connected to the hlgh pressure in
displacement space 61 and channel 64 is connected to the
low pressure in space 79, causing the re-setting valve 68
to switch to the right. Main channel 60 is now brought
under high pressure, so that a~ter the closing of valve 75
and the4~pening of valve 76 the closing movement of supply
valve ~ will commence. The permanent high pressure in
displacement space 61 and the force to the right that the
~irst adjusting piston continues to exert are unable to
prevent the closing movement from taking place because the
piston surface of the second adjusting piston 52 is larger
than the surface of 51.
When the closed position is reached, channel 64 is brought
under pressure and channel 63 is connected to the low
pressure space 79, causing the re-setting valve 68 to
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CA 02217864 1997-10-09
- 25 -
switch to the left and return to the depicted position.
Valve 73 is open then, and 74 is cl3~sed so that a stable
closed position of the supply valve ~ is attained.
The embodiment according to figure 6f has a disadvantage
as compared to that of figure 6e in that there is a larger
adjusting cylinder and it has the advantage that there is
a simpler re-setting valve and no holding piston.
Figure 6g shows an embodiment that corresponds to the
embodiment of figure 6e as far as its operation is con-
cerned. In this case there is no holding pi5ston 89 because
the band or ring-shaped valve member ~1 stays in any
position when the operating force is cut off. Another
difference is the operation of the re-setting valve 68.
Here, the re-setting valve is operated by pressure dif-
ferences that occur in the displacement spaces of a free
piston aggregate. Operation as indicated in figure 6e is
possible here as well, however.
As far as the operating pressures indicated in ~igure 6g
for the re-setting valve 68 are concerned, i.e. Ptc, Pca,
Pcc, the following serves to elucidate. In ~igure 1 of the
free piston aggregate, 2 is the back pressure cylinder
with the pressure Ptc, 1 is the compression cylinder with
the pressure Pcc and 4 is the energy cylinder with the
pressure Pac. The pressures in the pressure accumulators
4, 5 and 6 are: Pca, Paa and PL During the compression
stroke (the movement to the left) liquid is forced through
pipe 10 to the accumulator 4. The pressure Ptc is
therefore higher than Pca in accumulator 4. For Pcc the
reverse holds during the compression stroke: Pcc is lower
than Pca. During the expansion stroke the following ap-
plies: Pcc is larger than Ptc and Ptc is smaller than Pca
and Pac is larger than Paa. The pressure di~ferences Ptc-
Pca and Pca-Pcc and Ptc-Pcc are positive during the
compression stroke and negative during the expansion
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CA 02217864 1997-10-09
- 26 -
stroke. By connecting these pressures to points Px and Py,
the re-setting valve 68 in figure 6g will therefore switch
to the right during the compression stroke and to the left
during the expansion stroke. The speed-dependent component
of these pressure differences is largest in the second
half of the compression stroke and the first half of the
expansion stroke because the piston speeds are highest
then. When choosing the connecting points of x and y on
the conduit system of the free piston, the speed and ac-
celerating component in the pressure difference must betaken into account in order to be able to use them op-
timally.
The pre-stressed non-return valves 91 and 92 that do not
open until a certain pre-pressure has been reached, ensure
that valve 68 does not switch until the pressure dif-
ference Px-Py has reached a certain threshold value.
Figure 6h shows a valve embodiment with a very small dead
space 46 in accordance with what is stated at figure ~. 6
During the second half of the expansion stroke there is
rather high gas pressure in the combustion cylinder. Valve
45a may not open then and counterforce cylinder 80 is
present to ensure this, exerting a permanent force to the
right that is large enough to keep valve 45a closed during
the second part of the expansion stroke. This permanent
force could also be exerted by a strong spring, for that
matter, which spring would have to be strong enough to
ensure that the valve 45a cannot be opened under the
influence of the pressure of the gas medium.
In this embodiment only a first adjusting piston 51 is
present that is larger than the counterforce piston 81 and
can therefore quickly open the adjusting piston (opposing
the action of the counterforce piston) in accordance wit~h
the procedure described above.
AMENDED SHEET
CA 02217864 1997-10-09
G 3 G'rlCf nG7~ ~7u~J_ 27
In the open positio ~ of valve ~ oil flows under high
pressure via channel~65 to the operatlng cylinder of the
non-return valve 68, which will switch to the right as a
result. This will cause the pressure in the main 59 and in
the first displacement space 61 to fall out. The first
adjusting piston will now move to the right (to the closed
position) under the influence of the counterforce piston
81. In order to prevent too fast a closing, an adjustable
restriction 84 might be necessary that slows down the flow
into counterforce cylinder 80.
In this embodiment the re-setting valve 68 may also be
operated by pressure differences that occur in the free
piston aggregate as described at figure 6g. In that case,
non-return valve 82 and the adjustable restriction 84 are
unnecessary and the conduits 6~ and 87 are left out. Valve
4~ will open quickly and will not close until re-settlng
valve 68 has been switched by the external pressures Pcc,
Ptc and Pca.
Figure 6i shows an embodiment in which, just as in figure
6h, only a first adjusting piston 51 is present to quickly
open the band-shaped supply valve ~, also indicated in
figure 6d. 45
Starting from the position in the drawing, first the
electrovalve 73 will close and electrovalve 74 will open.
High-pressure oil now flows through the auxiliary channel
56 to the first displacement space 61. Piston 51 commences
the m4Ovement to the right and opens main 59. The supply
valve ~ will now open quickly, during which holes 46, 36
and 35 correspond with one another. In the open position
channel 63 is opened by the first adjusting piston 51. Oil
under high pressure flows vla non-return valve 65 to the
operating cylinder of the re-setting valve 68. This valve
now switches to the right, causing channel 97 to be
brought under pressure and piston 98 and the first adjus-
AMENDED SHEET
CA 02217864 1997-10-09
- 28 -
ting piston S1 to move to the left. If necessary, this
movement is slowed down by the adjustable restriction 95
that is bridged by non-return valve 96 (for the purpose of
quickly opening the supply valve~
45~
When the closed position is reached, channel 64 is con-
nected to high pressure by piston 98, causing the adjus-
ting valve 68 to switch to the left. Electrovalve 74 had
already closed when the open position was reached and 73
is opened before the closed position is reached so that
the initial position is reached again.
Generally speaking, it can be said that the electrovalves
73 - 76 may also be replaced by mechanically operated
valves that are moved by a rotary cam. This also holds for
the re-setting valves 68 that can be switched either
mechanically via a rotary cam or electrically or with the
aid of the pressures occurring in the free piston ag-
gregate or by opening and closing the ports in the adjus-
ting cylinders. The described control of the supply valve45a with the aid of a first and/or second adjusting piston
can also be used for controlling other gas or liquid
valves or valves that form a part of known crank shaft or
free piston engines. In this way, the control in figures
6e and 6f, for instance, can also be used for the
electrohydraulic operation of inlet and exhaust valves of
known two-stroke and four-stroke engines. The valves can
then be opened and/or closed very quickly and be
controlled by the electronics, the camshaft being left
out. In many instances in which the actuated valves open
near the lower dead centre and close before the end of the
expansion stroke, one re-setting valve can operate several
adjusting cylinders.
In view of the high valve speeds, buffering may be neces-
sary. To that end, figure 6j shows the known pos-
sibilities. 140 and 146 are restrictions that are adjus-
AMENDtD Si''cT
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CA 02217864 1997-10-09
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- 29 -
table or not.
As indicated above, use may also be made of a gas non-
return valve 45 in ~h~nnel 44 to cylinder 15. In that case
closing takes place slowly via a spring and for those
reasons valve 45 is preferably placed in the wall of the
combustion cylinder. A closing time then runs from the
moment the combustion piston port in the cylinder wall
closes off until the moment said piston re-opens the port.
It is an object of the invention to reduce the occurring
leakage losses by means of a specific control of the flows
of liquid to the hydraulic compression cylinder 17 and
also to keep the spring-back of the free piston small. A
first embodiment thereof is shown in figure 7a, in which
the dotted line indicates the non-return valve 107. This
valve offers passage to compression accumulator 4 via the
port in the cylinder wall and channel 19, but prevents the
flow of liquid from accumulator 4 to the port in the
cylinder wall and, therewith, leakage via the piston
sealing to the first displacement space 1. In this em-
bodiment according to the invention, the liquid, during
the entire compression stroke, will only be able to flow
to the first displacement space via the starting valve 12.
To that end, starting valve 12 must be ~;m~qioned more
largely and may not close until after the UDC. At the
description of the valve embodiments there is an in-
dication as to how such a valve may be realized.
Figure 7a also shows a drawing of a second embodiment
according to the invention. In the drawing the combustion
portion has been left out because, in figure 7a and those
following, it is the same as the one in figure 1.
In this second embodiment the second displacement space is
connected to accumulator 4 via channel 10. In channel 10 a
non-return valve 26 is accommodated that only offers
CA 02217X64 1997-10-09
W 096/32576 PCT~L96/00157 - 30 -
passage to the accumulator, but that blocks the flow from
the accumulator to the second displacement space and,
therewith, also leakage loss via channel 10 and the rod
seal 16.
The embodiment is also characterized by the connection
between the first and second displacement space via chan-
nel 29, in which a non-return valve 27 is accommodated
that only offers passage in the direction of the second
displacement space 2. Ch~nn~l 29 connects the right part
of space 1 with the left part of space 2 and has a connec-
tion via channel 28 with a port in the wall of the
hydraulic cylinder 17 that is closed by piston 8 during
the final part of the expansion stroke and the first part
of the compression stroke. (Channels 19 and 28 are not
interconnected via the ports in the wall of the cylinder
77). This embodiment works as follows.
At the end of the expansion stroke the free piston comes
to a standstill. The piston 8 will spring back to the left
under the influence of the compressibility of the volume
of oil in spaces 1 and 3. Meanwhile, the piston undergoes
a counterforce under the influence of the pressure in the
second displacement space 2, which occurs as a result of
the initial pressure and the rise in pressure caused by
compression of the (rather large) volume of oil in space 2
during the spring-back, and channel 29 is closed by non-
return valve 27 while c~nnel 10 only offers passage when
the pressure via valve 26 to accumulator 4 is high enough.
Under the influence of the pressure build-up in space 2,
the piston comes to a standstill and subsequently moves to
the right. This movement to the right and leakage via rod
seal 16 cause the pressure in space 2 to fall. After
several oscillations of very small, declining amplitude,
the free piston comes to a complete standstill, while the
pressure in spaces 1, 2 and 3 drops below level Pca,
depending on the leakage proportion between the gap seal
CA 02217864 1997-10-09
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- 31 -
of piston 8 and the rod seal 16.
A combination with the non-return valve 107 described
above, will cause the leakage during the waiting periods
to become low because, during said waiting period, both
the high pressure accumulators 4 and 5 are closed and the
pressure in the displacement spaces can fall to the
minimum level PL-
10 ~After opening the starting valve 12, the compressionstroke commences and moves the free piston to the left.
While doing so, the liquid in the second displacement
space 2 is pressed to accumulator 4 under high pressure.
As soon as the piston 8 opens the port of channel 28 in
the wall of the cylinder 17, the liquid can flow from the
second displacement space to the first displacement space
via a large channel 28, 29. Therefore, in the presence of
channel 28, non-return valve 27 may be small.
At the end of the expansion stroke, channel 28 is closed
again by piston 8. At a further movement to the right, the
liquid flows from space 1 into space 2 via non-return
valve 27 until the piston comes to a standstill in the
LDC.
The starting valve 12 can be embodied in accordance with
figure 2. This valve is operated by an adjusting piston 51
in conformity with earlier descriptions. Here, valve 12
corresponds with the actuated valve 96 and is opened by
means of a control signal from the control electronics of
the free piston aggregate and must open quickly enough to
be able to handle the increasing flow of oil to the first
displacement space withouth great flow losses. Valve 96 is
closed in the initial position of the free piston in the
LDC. After the opening, the compression stroke commences.
Under the influence of this pressure difference Ptc-Pcc
that is created between points Px and Py of the re-setting
CA 02217864 1997-10-09
- 32 -
valve 68 in figure 2c, for instance, valve 68 switches to
the left, after which valve 96 closes. After the UDC, the
pressure difference Ptc-Pca reverses the sign and switches
68 to the right, as a result of whlch the initlal position
is reached again.
Figure 7b shows an embodiment of the hydraulic portion of
the free piston engine in which channel 28 as in figure
has been left out. The non-return valves 26 and 27 must
have greater dimensions here. For the rest, the operation
and the technical effect are comparable to the embodiment
of figure 7a.
Figure 7c shows an embodiment of non-return valve 27, 30
or 11, in which the closing force of the valve may be
enhanced hydraulically. To this end a piston 90 is pre-
sent, which will exert a force onto valve disc 93 in the
closing direction of the non-return valve when there is
pressure difference over said piston. Space 98 is con-
nected to the discharge channel 29 of the non-return
valve. As long as space 104 is kept at the same pressure
level as 98, only the valve spring provides the per-
manently present closing force.
As soon as the pressure in space 104 is decreased with
respect to that in space 98, an extra closing force
develops. This extra closing force is necessary at valve
11 in those cases in which channel 19 has been le~t out
for the sake of minimal leakage and at valve 27 if channel
28 has been left out. This device is also necessary for
valve 30 i~ valve 32 has been left out. At two o~ the
present discharge channels the second (smaller) valve may
be provided with a heavy spring to prevent after-flow
after the free piston has come to a standstill in the LDC.
The enhancement of the closing force according to the
invention therefore serves to achieve that the valves in
question, notwithstanding the weak closing spring, never-
~ AMENDE~ SHEET
CA 02217864 1997-10-09
theless close quickly after the free piston has come to a
standstill in the LDC. To that end, the enhancement of the
closing force is activated during the final part of the
expansion stroke. The fast closing decreases the springing
back of the free piston after the LDC because the pressure
fall in spaces l and 3 commences earlier. Enhancement of
the closing force according to the invention is a general-
ly usable means for fast closing non-return valves with
nevertheless little flow losses.
On account of the fact that, in the cases indicated, the
non-return valve in question must handle the entire dis-
charge from spaces 1 and 3, even at the highest speed o~
the free piston, and must therefore have a relatively
large and heavy construction, the enhancement of the valve
force is necessary in the indicated embodiments according
to the invention. The activation of the enhancement of the
lo4
closing force takes place by connecting space ~ to a
level of low pressure with the aid of electrically or
hydraulically operated valves or by connection to a point
of the conduit system at which the development of the
pressure already follows the desired pattern, as is
described at figures 7f and 7g, for instance.
Figure 7d shows an embodiment of the hydraulic portion of
the ~ree piston engine in which space 2 is permanently
connected to a pressure accumulator 33 in which there is a
pressure Pm that is lower than Pca but high enough to
prevent cavitation in space 2 during the expansion stroke.
Owing to the fact that Pm is lower than Pca, the leakage
via the rod seal 16 will decrease as well. At the same
time, however, a stronger spring-back of the free piston
with respect to the embodiment according to figure 1 will
take place. In order to overcome this drawback, a release
valve is suggested in the embodiments according to the
invention, which release valve is described at figures 8a
and 8b.
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Figure 7e shows an embodiment of the free piston aggregate
according to the invention in which channel 19 (whether or
not provided with non-return valve 107) of figures(1, , ~C6~d
~ has been left out. The advantage of leaving out
channel lS is that, during the waiting period of the free
piston, leakage can no longer occur from the high pressure
accumulator ~ via channel 19. In this embodiment, the flow
of liquid from accumulator 4 takes place via starting
valve 12 during the entire compression stroke. This valve
12 must therefore offer a large passage and may only close
after the UDC. By subsequently closing the starting valve
12 shortly before the LDC is reached, a small non-return
valve 11 may be used. In order to ensure that this is
accomplished, the operation of valve 12 may for instance
be carried out according to figure 3, in which the control
electronics determine the exact closing time.
Figure 7f shows an embodiment in which both channel 19 and
channel 28 have been left out. The statement at figure 7b
applies here as well.
The enhancement of the closing force may be easily ob-
tained here for valve 27, by connecting space 104 o~
figure 7c to main 60 of figure 3. On account of the fact
that channel 60 is connected to low pressure during the
closed position of the starting valve 12 and said closed
position only occurs during the ~inal part o~ the expan-
sion stroke and during the waiting period, also the enhan-
cement of the closing force will be active during said
period.
Figure 7g shows an embodiment in which channels 19 and 28
have been left out and displacement space 2 is permanently
connected to accumulator 105 with pressure Pm. It should
be noted that the non-return valve 32 to accumulator 5 has
been le~t out here too. This means that enhancement o~
closing force must be applied ~or valve 30. The control o~
A~ L~t i,E
CA 022l7864 l997-lO-09
W 096/32576 PCT~L96/00157
- 35 -
the enhancement of the closing force may here be obtained
by connecting space 104 of figure 7c to ch~nn~l 94 of
figure 7g with a port in the cylinder wall 17, or to main
60 of figure 3. Owing to the fact that channel 94 is only
connected to the lower pressure Pm during the righthand
position of the free piston, the hydraulic enhancement of
the closing force is only active during that time.
Figure 8a shows a drawing of the signaller for a release
valve 100 in figure 8b. This release valve is necessary
because the pressure in displacement space 2 to Pm has
been decreased, which may cause the spring-back of the
free piston to increase too much. The signaller works as
follows. Piston 90 is connected to the valve disc 93 of
the non-return valve of figure 7c. The spring-mounted pin
106 breaks off the connection with piston 90 just before
non-return valve 93 closes. The free piston then still
moves to the LDC and will come to a standstill at a known
period of time after pin 106 has broken off the contact
with piston 90. Breaking off the contact with the pin 106
that has electrically insulated bearings entails the
breaking of the electric contact of point 109 with mass.
This results in an electric signal to the control
electronics of the free piston engine. The control
electronics convert this signal into a starting signal :Eor
the release valve, taking correction data, if any, into
account. This starting signal arrives at exactly the right
moment when, as a result of the opening of the release
valve 100 on time, the liquid pressure in displacement
spaces 1 and 3 has fallen to PI~ the moment the piston comes
to a standstill in the LDC. Spring-back no longer takes
place then and the problems connected therewith stay away.
Figure 8b shows a diagram of the release valve 100. This
valve is operated by an adjusting piston 51 and functions
in accordance with the description for the starting valve
of figure 2. In this case, however, valve 96 of the star-
CA 02217864 1997-10-09
ting valve 96, present as well, is constructed in such a
way that, simultaneously with the opening of the connec-
tion between space 1 and the compression accumulator 4,
the connection between channel 113 and low pressure PL is
interrupted and vice versa. As a result, the release valve
l~o ~ only has ef~ect as along as starting valve 12 is closed
and is put out of operation when valve 12 opens. In the
case of the highest stroke frequency and a zero waiting
period, the startlng valve will open before the free
piston reaches the LDC. The release valve will not be in
operation then, but that is unnecessary in this situation
anyhow, because the free piston has to start on the next
compression stroke after it has reached the ~DC.
In this embodiment, channel 59 in figure 8b can be con-
nected to channel 59 of figures 2 or 3 or be operated by
an electrovalve or another valve that connects 59 to a
space of high or low pressure.
As far as the connection of space 1 and space 3 to the
release valve 100 is concerned, it is necessary to accom-
modate the non-return valves 111 and 112 in order to
prevent an unwanted flow from space 1 to space 3 or vice
versa from occurring.
In ~igure 9a an embodiment of a free piston aggregate with
valve kl is given. It works as follows. In the depicted
position the starting valve 12 and valve kl are closed and
the free piston is located at the expansion-end position
near the lower dead centre. In order to start the free
piston 8, both the starting valve 12 and valve kl are
opened. Pressure oil now flows via the starting valve into
the first displacement space 1 and from the second
displacement space 2 into the compression accumulator 4
3s via valve K1. During the first part of the expansion or
energy stroke to the right, pressure oil flows from the
first displacement space l via the starting valve 12 and
AMENDED SHEET
_ CA 022l7864 l997-lO-09
W O 96/32576 PCTnYL96/U0157 - 37 -
via non-return valve 11 into the compression accumulator
4, while pressure oil flows from the first displacement
space 1 into the second displacement space via non-return
valve 27. =Shortly before the end of the expansion stroke
(in the position indicated by the dotted line) valve kl
and starting valve 12 are both closed.
During the subsequent final part of the expansion stroke,
the hydraulic medium flows from the first displacement
space 1 via non-return valve 11 into accumulator 4 and
pressure medium flows from the first displacement space 1
via non-return valve 27 into the second displacement space
2 until the free piston 8 comes to a standstill in the
lower dead centre.
The non-return valves 11 and 27 will now close and the
initial position is reached again. When the free piston
springs back to the left, the pressure in the second
displacement space will rise, causing said spring-back to
be very slight.
In embodiment 9b a valve kl is present in conduit 29. This
valve is bridged by non-return valve 27. During the
compression stroke of the free piston 8 less oil will now
flow through the starting valve 12, as a result of which a
smaller one may be used.
In figure 9c conduit 10 has been added to embodiment 9b
again. This has been done for the purpose of preventing
high rises in pressure in the first displacement space
during the spring-back of the free piston. In order to
decrease leakage when the piston is at a standstill, non-
return valve 2 6 has been introduced.
In embodiments 9a and 9b starting valve 12 and valve kl
must open simultaneously in order to ensure an immediate
start. In embodiment 9c kl may open a bit later than 12.
CA 02217864 1997-10-09
- 38 -
In all embodiments 9a - 9c kl may close a bit sooner or
later than starting valve 12. In all embodiments 9a - 9c,
11 and 27 are small non-return valves with a relatively
high closing force.
5 ~
/ In figure 9d, the embodiment of valves 12 and kl is given.
/ These valves must open very quickly and also close at a
/ rather specific moment ln time and are controlled by a
signal of little energy issued by the control electronics
of the free piston aggregate. In order to meet these
requirements and the requirement of a large passage, these
valves may be operated as indicated in figure 3.
In figure 9d, Cwhich corresponds with figure 3~ the adjus-
ting piston operates a sliding or scavenging valve 132that opens both the starting valve and kl in one position,
and, in the other position, closes both the valves. In the
embodiment that is in conformity with figures 9b and 9e,
conduit 24 is connected to space 1, while conduit 29 is
connected to space 2 and conduit 23 to accumulator 4.
Valve 132 can also be moved by a single adjusting piston
according to figure 2e.
In figure 9e the non-return valve 11 and the starting
valve 12 are combined, while the non-return valves 27 and
kl are com~ined as well. The operation of the adjusting
pistons 51 and 52 is described at ~igure 6f. Operation in
conformity with figure 6i and figure_ 2c is possible as
well.
The yoke 142 that is moved by the adjusting pistons pushes
both the non-return valves 11 and 27 open at the same
time. After the closing movement of yoke 142 to the left
has taken place, valves 11 and 27 work as normal non-
return valves, offering passage from space 1 via conduit24 into accumulator 4 via conduit 23 and into space 2 via
conduit 29, respectively. The combined valve in figure 9e
AMEN~ED SHEET
CA 02217864 1997-10-09
= 39
holds all the valves shown in figures 9b and 9c. The non-
return valves 11 and 27 may also be placed one after the
other and as shown in figure 9f.
In figure 9f a single adjustlng piston 51 is used that can
press open the two non-return valves 11 and 27. The way
the adjusting piston works is described at 2e. ~ere,
pressure Paa must be larger than or equal to Pca.
In the embodiment according to 9f t is also possible to
connect channel 59 to pressure Pca in accumulator 4 and
72a to pressure Pcc in the first displacement space 1. In
this case, as soon as pressure Pcc in space 1 has risen
until above the value Pca in accumulator 4 during the
expansion stroke of the free piston after the non-return
valve 11 has been opened, adjusting piston 51 will move to
the left under the influence of the pressure difference
Pcc-Pca and the spring force. After this, non-return
valves 11 and 27 operate independently of the adjusting
piston 51. These valves may be provided with a relatively
strong closing spring that does not bring about any extra
loss of pressure when said non-return valves are kept open
by adjusting piston 51 until just before the end of the
expansion stroke. A decelerated movement to the left of 51
may therefore be needed and, if necessary, is achieved
with non-return valve 121 and the flow resistance 122.
Actuation by means of adjustion piston 51 in conformity
with figure 9f, as described here, may also be used, com-
bined with only non-return val2v~jll a~s~ starting valve, or
combined with valves 96 and 13~ hen hese movements with
an adjusting piston 51 take place, 72a is always connected
to the outlet of the actuated valve. The movement of non-
return valve 11 on its own, or 11 and 27, may also be
brought about with an actuation in conformity with figure
2c or 2d, while the re-setting valve 68, however, is
operated via channels in the wall of the adjusting
cylinder in accordance with the operation of re-setting
AMEND~D SHEET
CA 02217864 1997-10-09
- 40 -
valve 68 in figures -6h and 6i.
e
Figures lOa - 10~ show embodiments in which the third and
second displacement spaces are integrated. The supply to
the energy accumulator 5 takes place from space 2 via non-
return valve 30, except in fi=gure lOc. In embodiment lOa
the low pressure accumulator- 6 and the compression ac-
cumulator 4 are integrated as well. In embodiment lOc the
energy and compression accumulators are integrated. All
this will result in low-leakage embodiments according to
the invention, which are relatively simple but do have the
disadvantage that the lowest pressure level (which was PL
at first) will end up being higher and the pressure
variations in the energy accumulator 5 should be small by
preference or necessity. For some applications this need
not be a problem, however.
~ ~igure lOa, which has been derived from the embodiment
according to figures 7a and 7b, liquid is pressed into the
energy accumulator 5 during the compression stroke with a
pressure Paa that is higher than Pca. The compression
pressure Pca is the lowest system pressure and is kept as
low as possible by giving piston 8 a relatively large
diameter. The energy supplied from accumulator 4 to the
free piston, less the hydraulic energy given out at ac-
cumulator 5, is available for the gas compression. At the
expansion stroke all the energy given out by the combus-
tion gases to the free piston is supplied to the compres-
sion accumulator 4. The energy users are connected between
Paa and Pca. The pressures Pca and Paa are basically
constant. However, Paa may be increased by supplying
liquid to 5 at an increased pressure Paa during a part of
the compression stroke and by supplying liquid to 4 during
the remaining part of the stroke. This can be done with
the aid of a short-circuit conduit 38 with a cut-off
valve. This conduit is indicated in the figure by means of
the dotted line. When the cut-off valve is open, the
A~ENDED SHEET
CA 02217864 1997 - lO-09
-- 41
increased pressure in 5 is attainable.
The embodiments 10~ and lOc have been derived from those
in figures 7b and 7d. The free piston engine pumps liquid
from the medium pressure accumulator with pressure Pm (the
lowest system pressure here) into the energy accumulator 5
or into the integrated accumulator 4/5.
In embodiment lOb, Pca is lower than Paa. In lOc, Paa and
Pca are equal and high. The pressure ratios are determined
by the difference between the left- and righthand piston
surface of piston 8. Pressure Pm is so high that cavitati-
on in the second displacemen~ space still cannot take
place during the expansion stroke. The pressure level Paa
is basically constant but may be increased in lOb by
partial supply from space 2 during the compression stroke
via conduit 38.
_
Figures lOd and lOe show an embodiment in which the func-
tion of the first and third displacement space is integra-
ted. Paa is equal to or higher than Pca depending on the
fuel supply. The users are connected between 4 and 5.
Figure lOd has been derived from the embodiment according
to figures 7d and 7g, while the embodiment lOe has been
derived from figures 7a, 7b, 7e and 7f. In lOd, the stroke
volume of the second displacement space can be kept
relatively small and Pm can be kept relatively low by
using the release valve o~ figures 8a and 8b.
JK/ES
; r' ~r~"n Er' ~ E~
