CA1094334A - Hot gas reciprocating machine - Google Patents
Hot gas reciprocating machineInfo
- Publication number
- CA1094334A CA1094334A CA298,337A CA298337A CA1094334A CA 1094334 A CA1094334 A CA 1094334A CA 298337 A CA298337 A CA 298337A CA 1094334 A CA1094334 A CA 1094334A
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Abstract
ABSTRACT:
A hot gas reciprocating machine, comprising a free piston, one surface of which varies the volume of a working space, while its other surface bounds a buffer space of constant pressure, there being provided a control mechanism which is formed by an auxiliary cylinder and an auxiliary piston which is movable therein, said control mechanism maintaining a given central position of the free piston by instantaneously opening a connection between the buffer space and the auxiliary cylinder space.
A hot gas reciprocating machine, comprising a free piston, one surface of which varies the volume of a working space, while its other surface bounds a buffer space of constant pressure, there being provided a control mechanism which is formed by an auxiliary cylinder and an auxiliary piston which is movable therein, said control mechanism maintaining a given central position of the free piston by instantaneously opening a connection between the buffer space and the auxiliary cylinder space.
Description
3~
PHN. 8698.
The invention relates to a hot gas reciprocating machine, comprising at least one working space in which a working medium performs a thermodynamic cycle, said work~
ing space comprising a compression space and an expansion space of mutually different mean temperatures during operation which are'connected to each other via heat ' ~
exchangers, including a regenerator, there being provided ~ ~:
at least one'free piston which is reciprocatable in a '~
cylinder and one surface of which'varies the volume of the working space, whilst its other surface forms a part of the boundary of a buffer space which also contains working medium during operation at an at least substantially con- :
stant pressure'which'corresponds to the mean working ~.
medium pressure in the working space, there being provided ~ 15 a control mechanism for maintaining a given central posi-- tion of the free piston by the instantaneous opening of a connection between the buffer space and a space in which a variable pressure'prevails, said control mechanism com-prising two eLemen~s which are constructed as an auxiliary ~'~
cylinder and an auxiliary piston, which is movable therein so as to vary the volume'of ~he auxiliary cylinder space, '~
one'of said elements being connected to the free piston whilst the other element is rigidly arrangedr the auxiliary ,;
piston being 33~
provided with at least one duct, one end of which opens into the auxiliary piston wall, cooperating with the auxiliary cylinder wall, where it corresponds, in a given position of the auxiliary piston, to at leas one duct S in the auxiliary cylinder wall which communicates with the buffer space.
Within the scope of the present invention, hot gas reciprocating machines are to be understood to mean cold gas refrigerators, hot gas engines and heat pumps.
A hot gas reciprocating machine of the described kind has been proposed in our Canadian Patent 1,054,383 which issued on May 15, 1979 (Figs. 4 and 5).
In the proposed hot gas reciprocating machine, the end of the duct in the auxiliary piston which is remote from the buffer space opens into the working space of the machine, so that a given central position of the free piston is maintained in that an open connection ; exists instantaneously between the buffer space and the working space. Depending on the situation, working medium then flows from the buffer space to the working space or in the reverse direction.
This construction has a drawback in that the thermodynamic cycle taking place in the working space is adversely affected. The maximum/minimum pressure ratio of the working medium participating in the cycle is affected whilst at the same time a phase shift occurs, ,. ~
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i.e. the phase difference between the pressure variation and the volume variation of the working medium in the working space change~.This leads to a reduction of the e*ficiency of the machine.
The invention has for its object to provide an improved hot gas reciprocating nnachine of the described kind in which the control of the central positi~n of ` the free piston is so that the thermodynamic cycle is not subject to negative inf~uences.
In order to realize this object, the hot' gas reciprocating machine in accordance with the invention is characterized ln that the other end of the ~uct in the auxiliary piston opens in-to the au~iliary cylillder space.
~ preferred embod:iment of the!hot gas reci-proca-ting machine in accordance with the invention is , characterized in tha't the rigidly arranged element is adjustable with respect to the cy~inder in the direction of the cylinder axis.
The central position of the free piston'is thus adjustable. -~
' A further preferred embodiment of the hot '- gas reciprocating machine in accordance with the invention is characterized in that the element wh}ch is connected to the free piston is adjustable in the axial direction with respect to the free piston.
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The central position of the piston is thus also adjustable.
Preferably, both elements are accommodated in the buffer space for si~e considerations.
The invention will be described in detail hereinafter with reference to the drawing which diagrammatically shows, besides two graphs ~hich illustrate the principle, some embodiments of the hot gas reciprocating machine (not to scale).
Fig. 1 is a longitudinal sectional vie~r of a cold gas refrigerator in which the control mechanism for maintaining a given central position of the free piston comprises àn auxiliary piston which is rigidly arranged in the b'uffer spac~e and which is reciprocata'ble in an auxiliary cylinder which is connected to the free piston.
Fig. 2 graphically illustrates thepressure (P) as a function of the'time (t) for the working medium ¦P1) participating in the cycle in the working space of the 20 ' hot gas reciprocating machine shown in Fig~ 1, for the working ~ dium (P2) in the buffer space, and for the working medium (P3) in the auxiliary cylinder space Or said machine.
Fig. 3 is a longitudinal sec-tional view of a hot gas engine for genera-ting electrical energy (generator) in which the auxiliar~r piston is connected to the free piston and is movable in an auxiliary cylinder connected to the buffer space.
~94334 .
Fig. 4 is a longitudinal sectional view of a cold gas rafrigerator, cornprising an auxiliary cylinder ~ which is ~gidly arranged in the buffer space and an ; au~iliary piston which is coupled to the free pis-ton to be'axially adjustable.
`~ ~ig. 5 is a longitudinal sectional view of a cold gas refrigerator, comprising an auxiliary piston which is connec-ted to the free piston and an auxiliary cylinder which is arranged in the buffer spaoe to be axially adjustable.
Fig. 6 is a longitudinal sectional view of a cold gas re~rigerator in which the expansion piston forms a free piston which is pro~ided with an auxiliary piston which is'reciprocatable in an auxiliary cylinder~
Fig. 7 shows a sligrhtly modified ~ersion of the hot gas engine sho~n in Fig. 3.
which is on the same sheet as Figure 2 Fig. 8,/graphically shows the pressure (P) as a function of the time (t) for the working medium (Pl) participating in the cycle of-the worklng space of the hot gas engine of Fig. 7, for the working medium (P2) in the buffer space, and for the working medium (P3) in the auxiliary cylinder space, P3 being in phase with Pl.
The~reference numeral 1 in Fig. 1 denotcs a cylinder in ~hich a free piston 2 and a free dis-placer 3 are reciprocatable a-t a mutual phase difference.
_~_ L33~
PHN. 8698.
Between the ~orking surface 2a of the piston 2 and the working surface 3a of displacer 3 a compression space 4 is present which accommodates a cooler 5. The upper - working surface 3b of the displacer 3 bounds an expansion space 5 which constitutes the working space in conjunc-tion with the compression space 4. The displacer 3 accommodates a regenerator 7 which is accessible for working medium on its lower side`via bores 8 and on its upper side via bores 9. The machine comprises a freezer 10 as a heat exchanger for the exchange of heat between expanded, cold working medium and an object to be cooled.
When the piston 2 and the displacer 3 move at a mutual phase difference during operation, a working medium (for example, helium or hydrogen) in the working lS space of the machine is alternately compressed and expanded~ cold being produced due to the expansion.
The compression of the working medium takes place when substantially all of it is present in the compression space 4. The working medium successively flows via the cooler 5, while giving off compression heat, the bores 8, thè regenerator 7 while giving off hea~, and the bores 9 to the expansion space 6. Expansion of the working medium : :
takes place when substantially all the working medium is present in the expansion space 6. The working medium then flows back again along the described path in the reverse order, after having taken up heat in the freezer 10 r ~ 09~3 from the object to be cooled (not shown~, the heat previously stored in the regenerator 7 also being taken up again.
. The lower side 2b of the free piston 2 bounds a buffer space 11 whlch also contains working medium during operation at a substantially constant pressure which.corresponds to the mean working medium pressure in the working space. The lower side 2b of the piston supports a llght-wèight sleeve 12 of a non-magnetic and non--magnetisabIe material such as hard paper or alumin:i.um. ~round the sleeve 12 an electrical c~rrent conductor i.s wound to form an armature coil 13 whereto currellt supply wires 13 and 15 are connected, said wires being brougllt out through the wall of the hollsing 16 which is connected to the cylinder 1 in a gastight manner~
said wlres being provided with electrical contacts 17 and 18, respectively, on the outside. The armature coil 13 is reciprocatable in the axial direction of the piston 2 in an annular gap 19 in which a permanent magnetic fielcl prevails, the lines of force of which extend in radial directions~ transversely of the movement di.rection of the armature coil.
The permanent magnetic field is obtained in the present c~ase by means of an annular permanent magnet 20 comprising poles on its upper and lower side, a~soft-iron ring 21, a solid soft-iron cylinder 22S
and a soft-iron circular dis~ 23.
33~
The permanent magnet and the soft-iron components together constitute a closed magnetic circuit, i.e. a circuit of closed magnetic lines o*
force. During operation, the contacts 17 and 18 are connected to an electrical alternating current source (for`example, the mains) having a frequency f (for example, 50 Her~). Under theinfluence of the permanent magnetic field in the gap 19, Lorentz forces which are alternately dlrected upwards and downwards are exerted on the armature coil 13 carrying alter-nating current, with the result that the assembly formed by the piston 2, t;he sleeve 12 and the armature coil 13 starts to resonate. This is effected so that the resonant frequency oi~ the system formed by the moving assembly and the working medium in the working ` space is at least substantially equal to the alternating current frequency fO (a deviation of 10% is still acceptable). The wor~ing medium in the working space then acts as a spring system. The alternating current need deliver only so much energy to the resonant system of piston/armature coil assembly and working medium, via the armature coil 13, as is required to compensate for the work performed by the working medium and the friction losses. ~he displacer 3 locally has a smaller diameter, so that an aImular intermediate space 2l~
is ~ormed between the cylinder 1 and the displacer 3.
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The wall of the cylinder 1 is provided with a projection 25. A resilient element 26 is connected on the one side to the projection 25 and on the other side to the annular face 27 of the displacer-3.
The resilient slement 26 limits the s-troke of the displacer 3 and constitutes a mass/spring system in conjunction therewith, so that the displacer, like the piston, performs a purely harmonic movement of the same frequency as the piston, but at a phase difference with respect thereto. The spring constant of the resiliellt el.ement 26 and the mass of the displacer 3 are chosen so that the frequency ~1 at i~hich -this system is àble to resonate is higher than the resonant frequency of the system .formed by the piston/armature coil assembly and the working medium. During operation, at eq~lal vibration frequencies o~ the piston 2 and .
displacer 3, the volume variation of the expansion space then leads the pressure variation occurring in thls space, ~ with the result that cold is produced ln the expansion .~ 20 space 6.
An auxiliary piston 28, connected to the soft-iron cylinder 22 via a rod 29~ is rigidly arranged in the buffer space 11. The au~iliary pis-ton~28 is . movable in an auxiliary cylinder 30 l~hich is connected to the frse piston 2 and can thus vary the volume of the space 31.
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In the auxiliary.piston 28 there is provided a duct system 32 which communicates at one end with the space 31 an~ which at the other end opens at di.fferent . .locations into the au~iliary piston wall (32a), cooperating with the auxiliary cylinder wall, where it co-operates .with ports 33 in the wall of the auxiliary cylinder 30.
The por$s 33 are in open communication with the buffer space 11. As appears from Fig. 2, the cycle pressure P1 in the working space 4,6 of-Fig. 1 is higher than th0 pressure P2 in the buffer space 11 during the time interval..A. Due to leakage via the gap.34 between the wall of the pisto~ 2 and. the cylinder 1, working mediu~l then flows from the working space 4,6 to the buffer space 11. During the time interval B (Fig.2), however, the pressure in t;he buffer space 11 is higher than that in the working space 4, 6, so that medium then flows from the buffer space 11, via the gap 34, to the working space 4, 6. However, the pressure of the medium flowing from the working space during the interval A is higher than the pressure of the medium flowing from the buffer space during the interval B. This means that the medium volume flows to and from the working space are equal, but not the mass flows. The medium mass flow to - the buffer space 11 is larger than that to the working space 4, 6. As a result,the piston 2 would gradually assume a higher central posi.tion, which means that the .
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central positiorl of the piston would be displaced in the direction towards the compression space 4.
This is prevented by the operation ~.-the : control mechanism formed by the auxiliary piston 28 and the aiuxiliary cylinder 30~ .
hen the piston reciprocates at the desired nominal central position, the ports 33 pass the duct 32a at the insta~ts t17 t2 and t3 (Fig.2) at which the pressures in the working space, the buffer space and the auxiliary cylinder space are equal. No working mediurn then flows through the ports 33 and the duct system 32If the mean po~sition of the piston 2 is shi~ted upwards due to a rnedium mass flow fromthe compression space l~ vla the gap 34~ to the buffer space 11 which is larger than the medium mass flow-in the reverse direction, the ports 33 pass the ducts 32a during the downward movement of the piston 2 at an instant~ ~or example t4, whicll is later than t2, whilst during the upward movement of the piston 2 the port.s 33 pass the .ducts 32a at the instant t ~lich is earlier than the instant t3. As a result, at the instan-ts t4 and t5, at which the pressure P3 in the auxiliary cylinder space 31 is higher than the pressure P2 in the buffer space 11, working medlum flows from the auxiliary cylinder space 31, .25 via the duct system 32 and the ports 33, to the buffer space 11. The pressure level in the auxiliary cylinder , PHN. 8698.
space 31 thus decreas~s, which causes an additional reversing, downwards directed force on the piston 2, so that the original central position is restored.
Should the mean position of the piston 2 be displaced downwards, for example, under the influence o~ its own weight, i.e. in the direction of the soft-iron cylinder 22, the ports 33 pass the ducts 32a during the upwards movement of the piston 2 at an instant, for example t6, which is later than tl (Fig. 2); during the downward movement of the piston 2, they pass at an instant t7 which is earlier than t2. At the instants t6 and t7, at which the pressure P2 in the buffer space 11 exceeds the pressure P3 in the auxiliary cylinder space 31, working medium then flows :Erom the buffer space 11, via the ports 33 and the duct system 32, to the auxiliary cylinder space 31. The mean pressure in the auxiliary cylinder space 31 then increases r with the result that the mean piston position is moved upwards to the original central positionO
Parts of the hot gas engine shown in Fig. 3 which correspond to the parts of the cold gas refrigerator shown in ~ig. 1 are denoted by the same reference numerals~
Therein, the compression space 4 communicates, via the cooler 5, the regenerator 7 which is rigidl~
arranged in a cylinder 40, and a heater 41, with the expansion space 6. The heater 40 comprises a number of 133~ ~
; . .
pipes 42 wtlich are connected at one end to the regenera-tor 7 and at the other end to an annular duct ~3, and also comprises a number of pipes 44 ~hich are connected at one end to the annular duct 43 and at the other end to the 0xpansion space 6.
Heat origincLting from a burner device 45 is given off to the working medium flowing through the heater pipes 42, 44 during operation. The burner device 45 comprises a burner 46 with a fuel inle-t 47 and an air inlet 4~ After having given off heat to the heater l~l, arranged inside a housing 49, the combustion gases leave the housing 49 via thc outlet 50.
The displacer 3 is coupled, via a displacer rod 51, to a drive system not shown. During operation f the hot gas engine, during which the displacer 3 and the piston 2 move at a mutual phase difference, the thermal energy applied -to the heater 41 is utilised to drive -the piston 2, so that electrical energy is generated in the armature coil 13. I~hen the displacer 3 is provided with an electrodynamic drive, part of the electrical energy generated in the armature coil 13 and be used, after the starting of the hot gas engine, for powering the armature coil coupled to the displacer rod 3.
AI1 auxiliary piston 53, being reciprocatable in an auxiliary cylinder 5~, is connected tothe free -14~
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piston 2 via a rod 52. The auxiliary piston 53 varies the'volume of the auxiliary cylinder space 55. In the auxili'ary piston 53 there is provided a duct 56, one end of which opens into the auxiliary cylinder spaGe 55, 5 ~ whilst its other end cooperates with a port 57 in the wal~ of the auxiliary cylinder 54, said port 57 being in open communication with the buffer space 11 via a duct 58.
The control of the central position of the piston 2 is identical to that shown in Fig. 2, so that no f'urther description is required~
Parts of the cold gas refrigerator shown in Fig.4 which correspond to parts of -the machine shown in Fig. 1, are,deno-ted by -the same reference numerals.
Irl the present case, a bore 61 with a thread 60 is provided in the piston 2, a rod 62 being screwed -therein in a gastight manner, said rod supporting an auxiliary piston 63 which is reciprocatable in an auxiliary cylinder 6~ provided with ports 65. In the situation shown, the buffer space 11 is in open communication, via theports 65 and a duct sys-tem 66 in the auxiliary piston 63, with the auxiliary cylihder space 67. The operation of the control mechanism for the central position is identical to that described with re~erence to Fig.1.
The desired central position of the piston 2 can be adjusted by screwing the rod 62 further into or out of the bore 61.
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Parts of the~cold gas refrigerator shown ,~
in Flg. 5 which correspond to those of ~ig. 4 are denoted - by the same reference numerals.
- The rod 62 is now rigidly connected to the piston Z, the auxiliary cylinder 64 being adjustable in the axial direction by means of an adjusti~g screw 70 in a bush 71. Thus, the central position of the piston 2 ; is again adjustable, an advantage being obtained in that ; the adjustment can be externally performed during operation.
Fig. 6 shows a cold gas refrigerator, com-pri.sing a cylinder 80 which accommodates a compression piston 81 which is connected, via a piston rod 82, to a drive system 83 in the crank case space 83a.
The compression piston 81 varies the volumeo~ a com' pression space 84 when it moves. The compression space 84 and the freezer 87, with an expansion space 88.
The expansion space 88 is bounded by an expansion piston 89, the other end of whlch bounds a buffer space 90 which contains working medium at a pressure which is equal to the mean working medium pressure in the expansion ; space 88. The expansion piston 89 is connected to a piston rod 91 which supports an auxiliary piston 92 - which varies the volume of the space 93 inside an auxiliary cylinder 94 when it moves.
~ duct 95 is provided in the auxiliary piston 92 and a port 96 is provided in the auxiliary cylinder 94 .
10~33~
In the situation shown, the buffer space 90is in open commullication, via the port 96 and the duct 95, with the auxiliary cylinder space 93. The operation of the central position control mechanism for the piston 89, *ormed by the awciliary piston 92 and the auxili.ary cylinder 94, is identical to that described with ref~rence to Fig. 1~ . .
. Obviously, the compression piston 8l.may also be constructed-as a free piston provided with a .
central position control system, for example, as shown in Fig.1. The cranlc case space 83a may form one integral unit wïth the buf*er space 90, if desired.
The reference numerals of Fig.3 are used for all parts of the hot gas engine shown in Fig.7.
The present hot gas engin3 di~*ers *romthat sho~n in Fig. 3 only in that now the upper side o* the au~iliary piston 53 varies the volume of the auxiliary . cylinder space 55. This means that the pressurb variation P3 in the auxiliary cylinder .space 55 is now in phase with the pressure variatlon P1 in the compression space 4, which is shown in Fig. 8.
.en the mean position of the piston 2 moves upwards again, the duct 56 passes the port 57, during the do1~nward movement of the piston 2, a-t the lnstan-t t4 25. which i9 later than t2, whllst during the upward movement of the piston 2, the duct 56 passes the port 57 at 1;he . -17-.
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~ instant t5 which is earlier than the instant t5.
J As a result, at the ins-tants t~ and t5, at which the pressure P2 in the buffer space 11 is higher than the pressure P3 in the auxiliary cylinder space 55, working medium flows from the buffer space 11, via the ~ duc~ 58, the port 57 and the duct 56, to the auxiliary '. . cylinder space 55, so that the pressure level in the latter space increases. Thus, the piston 2 is driven . back -to its original central position again.
0 When the mean position of the piston 2 moves downwards, the duct 56 passes theport 57, during the opward movement of the piston 2, at an instant t6 ~h.ich is later than t1 (Fig.8), and passes this port ¦ during the downward movement of the piston 2 at an :instant t7 which is earlier~ than t2. At the instants t6 and t7, the pressure P3 in the auxiliary cylinder space 55 is : higher than the pressure P2 in the buffer space 11.
Wor~ing medium then flows from the auxiliary cylinder space 55 to the buffer space 1.1. The pressure level in i 20 the auxiliary cylinder space 55 decreases, with the result that the piston 2 assumes thehlgher, original central position aeain.
It will be obvious that the central position control system functions when the variable pressures in the wor~ing space and the auxiIiary cylinder space are in phase (Fig.8) as well as whell said pressures . are i~ counter-phase (180 phase difference) (Fig.2).
PHN. 8698.
The invention relates to a hot gas reciprocating machine, comprising at least one working space in which a working medium performs a thermodynamic cycle, said work~
ing space comprising a compression space and an expansion space of mutually different mean temperatures during operation which are'connected to each other via heat ' ~
exchangers, including a regenerator, there being provided ~ ~:
at least one'free piston which is reciprocatable in a '~
cylinder and one surface of which'varies the volume of the working space, whilst its other surface forms a part of the boundary of a buffer space which also contains working medium during operation at an at least substantially con- :
stant pressure'which'corresponds to the mean working ~.
medium pressure in the working space, there being provided ~ 15 a control mechanism for maintaining a given central posi-- tion of the free piston by the instantaneous opening of a connection between the buffer space and a space in which a variable pressure'prevails, said control mechanism com-prising two eLemen~s which are constructed as an auxiliary ~'~
cylinder and an auxiliary piston, which is movable therein so as to vary the volume'of ~he auxiliary cylinder space, '~
one'of said elements being connected to the free piston whilst the other element is rigidly arrangedr the auxiliary ,;
piston being 33~
provided with at least one duct, one end of which opens into the auxiliary piston wall, cooperating with the auxiliary cylinder wall, where it corresponds, in a given position of the auxiliary piston, to at leas one duct S in the auxiliary cylinder wall which communicates with the buffer space.
Within the scope of the present invention, hot gas reciprocating machines are to be understood to mean cold gas refrigerators, hot gas engines and heat pumps.
A hot gas reciprocating machine of the described kind has been proposed in our Canadian Patent 1,054,383 which issued on May 15, 1979 (Figs. 4 and 5).
In the proposed hot gas reciprocating machine, the end of the duct in the auxiliary piston which is remote from the buffer space opens into the working space of the machine, so that a given central position of the free piston is maintained in that an open connection ; exists instantaneously between the buffer space and the working space. Depending on the situation, working medium then flows from the buffer space to the working space or in the reverse direction.
This construction has a drawback in that the thermodynamic cycle taking place in the working space is adversely affected. The maximum/minimum pressure ratio of the working medium participating in the cycle is affected whilst at the same time a phase shift occurs, ,. ~
~L0~33~
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. I .
i.e. the phase difference between the pressure variation and the volume variation of the working medium in the working space change~.This leads to a reduction of the e*ficiency of the machine.
The invention has for its object to provide an improved hot gas reciprocating nnachine of the described kind in which the control of the central positi~n of ` the free piston is so that the thermodynamic cycle is not subject to negative inf~uences.
In order to realize this object, the hot' gas reciprocating machine in accordance with the invention is characterized ln that the other end of the ~uct in the auxiliary piston opens in-to the au~iliary cylillder space.
~ preferred embod:iment of the!hot gas reci-proca-ting machine in accordance with the invention is , characterized in tha't the rigidly arranged element is adjustable with respect to the cy~inder in the direction of the cylinder axis.
The central position of the free piston'is thus adjustable. -~
' A further preferred embodiment of the hot '- gas reciprocating machine in accordance with the invention is characterized in that the element wh}ch is connected to the free piston is adjustable in the axial direction with respect to the free piston.
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, .
The central position of the piston is thus also adjustable.
Preferably, both elements are accommodated in the buffer space for si~e considerations.
The invention will be described in detail hereinafter with reference to the drawing which diagrammatically shows, besides two graphs ~hich illustrate the principle, some embodiments of the hot gas reciprocating machine (not to scale).
Fig. 1 is a longitudinal sectional vie~r of a cold gas refrigerator in which the control mechanism for maintaining a given central position of the free piston comprises àn auxiliary piston which is rigidly arranged in the b'uffer spac~e and which is reciprocata'ble in an auxiliary cylinder which is connected to the free piston.
Fig. 2 graphically illustrates thepressure (P) as a function of the'time (t) for the working medium ¦P1) participating in the cycle in the working space of the 20 ' hot gas reciprocating machine shown in Fig~ 1, for the working ~ dium (P2) in the buffer space, and for the working medium (P3) in the auxiliary cylinder space Or said machine.
Fig. 3 is a longitudinal sec-tional view of a hot gas engine for genera-ting electrical energy (generator) in which the auxiliar~r piston is connected to the free piston and is movable in an auxiliary cylinder connected to the buffer space.
~94334 .
Fig. 4 is a longitudinal sectional view of a cold gas rafrigerator, cornprising an auxiliary cylinder ~ which is ~gidly arranged in the buffer space and an ; au~iliary piston which is coupled to the free pis-ton to be'axially adjustable.
`~ ~ig. 5 is a longitudinal sectional view of a cold gas refrigerator, comprising an auxiliary piston which is connec-ted to the free piston and an auxiliary cylinder which is arranged in the buffer spaoe to be axially adjustable.
Fig. 6 is a longitudinal sectional view of a cold gas re~rigerator in which the expansion piston forms a free piston which is pro~ided with an auxiliary piston which is'reciprocatable in an auxiliary cylinder~
Fig. 7 shows a sligrhtly modified ~ersion of the hot gas engine sho~n in Fig. 3.
which is on the same sheet as Figure 2 Fig. 8,/graphically shows the pressure (P) as a function of the time (t) for the working medium (Pl) participating in the cycle of-the worklng space of the hot gas engine of Fig. 7, for the working medium (P2) in the buffer space, and for the working medium (P3) in the auxiliary cylinder space, P3 being in phase with Pl.
The~reference numeral 1 in Fig. 1 denotcs a cylinder in ~hich a free piston 2 and a free dis-placer 3 are reciprocatable a-t a mutual phase difference.
_~_ L33~
PHN. 8698.
Between the ~orking surface 2a of the piston 2 and the working surface 3a of displacer 3 a compression space 4 is present which accommodates a cooler 5. The upper - working surface 3b of the displacer 3 bounds an expansion space 5 which constitutes the working space in conjunc-tion with the compression space 4. The displacer 3 accommodates a regenerator 7 which is accessible for working medium on its lower side`via bores 8 and on its upper side via bores 9. The machine comprises a freezer 10 as a heat exchanger for the exchange of heat between expanded, cold working medium and an object to be cooled.
When the piston 2 and the displacer 3 move at a mutual phase difference during operation, a working medium (for example, helium or hydrogen) in the working lS space of the machine is alternately compressed and expanded~ cold being produced due to the expansion.
The compression of the working medium takes place when substantially all of it is present in the compression space 4. The working medium successively flows via the cooler 5, while giving off compression heat, the bores 8, thè regenerator 7 while giving off hea~, and the bores 9 to the expansion space 6. Expansion of the working medium : :
takes place when substantially all the working medium is present in the expansion space 6. The working medium then flows back again along the described path in the reverse order, after having taken up heat in the freezer 10 r ~ 09~3 from the object to be cooled (not shown~, the heat previously stored in the regenerator 7 also being taken up again.
. The lower side 2b of the free piston 2 bounds a buffer space 11 whlch also contains working medium during operation at a substantially constant pressure which.corresponds to the mean working medium pressure in the working space. The lower side 2b of the piston supports a llght-wèight sleeve 12 of a non-magnetic and non--magnetisabIe material such as hard paper or alumin:i.um. ~round the sleeve 12 an electrical c~rrent conductor i.s wound to form an armature coil 13 whereto currellt supply wires 13 and 15 are connected, said wires being brougllt out through the wall of the hollsing 16 which is connected to the cylinder 1 in a gastight manner~
said wlres being provided with electrical contacts 17 and 18, respectively, on the outside. The armature coil 13 is reciprocatable in the axial direction of the piston 2 in an annular gap 19 in which a permanent magnetic fielcl prevails, the lines of force of which extend in radial directions~ transversely of the movement di.rection of the armature coil.
The permanent magnetic field is obtained in the present c~ase by means of an annular permanent magnet 20 comprising poles on its upper and lower side, a~soft-iron ring 21, a solid soft-iron cylinder 22S
and a soft-iron circular dis~ 23.
33~
The permanent magnet and the soft-iron components together constitute a closed magnetic circuit, i.e. a circuit of closed magnetic lines o*
force. During operation, the contacts 17 and 18 are connected to an electrical alternating current source (for`example, the mains) having a frequency f (for example, 50 Her~). Under theinfluence of the permanent magnetic field in the gap 19, Lorentz forces which are alternately dlrected upwards and downwards are exerted on the armature coil 13 carrying alter-nating current, with the result that the assembly formed by the piston 2, t;he sleeve 12 and the armature coil 13 starts to resonate. This is effected so that the resonant frequency oi~ the system formed by the moving assembly and the working medium in the working ` space is at least substantially equal to the alternating current frequency fO (a deviation of 10% is still acceptable). The wor~ing medium in the working space then acts as a spring system. The alternating current need deliver only so much energy to the resonant system of piston/armature coil assembly and working medium, via the armature coil 13, as is required to compensate for the work performed by the working medium and the friction losses. ~he displacer 3 locally has a smaller diameter, so that an aImular intermediate space 2l~
is ~ormed between the cylinder 1 and the displacer 3.
_g_ . : :
~433;~
l~
The wall of the cylinder 1 is provided with a projection 25. A resilient element 26 is connected on the one side to the projection 25 and on the other side to the annular face 27 of the displacer-3.
The resilient slement 26 limits the s-troke of the displacer 3 and constitutes a mass/spring system in conjunction therewith, so that the displacer, like the piston, performs a purely harmonic movement of the same frequency as the piston, but at a phase difference with respect thereto. The spring constant of the resiliellt el.ement 26 and the mass of the displacer 3 are chosen so that the frequency ~1 at i~hich -this system is àble to resonate is higher than the resonant frequency of the system .formed by the piston/armature coil assembly and the working medium. During operation, at eq~lal vibration frequencies o~ the piston 2 and .
displacer 3, the volume variation of the expansion space then leads the pressure variation occurring in thls space, ~ with the result that cold is produced ln the expansion .~ 20 space 6.
An auxiliary piston 28, connected to the soft-iron cylinder 22 via a rod 29~ is rigidly arranged in the buffer space 11. The au~iliary pis-ton~28 is . movable in an auxiliary cylinder 30 l~hich is connected to the frse piston 2 and can thus vary the volume of the space 31.
".
- 1 ow ~ 9D~
.
.
.
In the auxiliary.piston 28 there is provided a duct system 32 which communicates at one end with the space 31 an~ which at the other end opens at di.fferent . .locations into the au~iliary piston wall (32a), cooperating with the auxiliary cylinder wall, where it co-operates .with ports 33 in the wall of the auxiliary cylinder 30.
The por$s 33 are in open communication with the buffer space 11. As appears from Fig. 2, the cycle pressure P1 in the working space 4,6 of-Fig. 1 is higher than th0 pressure P2 in the buffer space 11 during the time interval..A. Due to leakage via the gap.34 between the wall of the pisto~ 2 and. the cylinder 1, working mediu~l then flows from the working space 4,6 to the buffer space 11. During the time interval B (Fig.2), however, the pressure in t;he buffer space 11 is higher than that in the working space 4, 6, so that medium then flows from the buffer space 11, via the gap 34, to the working space 4, 6. However, the pressure of the medium flowing from the working space during the interval A is higher than the pressure of the medium flowing from the buffer space during the interval B. This means that the medium volume flows to and from the working space are equal, but not the mass flows. The medium mass flow to - the buffer space 11 is larger than that to the working space 4, 6. As a result,the piston 2 would gradually assume a higher central posi.tion, which means that the .
.
~0~33~
.
central positiorl of the piston would be displaced in the direction towards the compression space 4.
This is prevented by the operation ~.-the : control mechanism formed by the auxiliary piston 28 and the aiuxiliary cylinder 30~ .
hen the piston reciprocates at the desired nominal central position, the ports 33 pass the duct 32a at the insta~ts t17 t2 and t3 (Fig.2) at which the pressures in the working space, the buffer space and the auxiliary cylinder space are equal. No working mediurn then flows through the ports 33 and the duct system 32If the mean po~sition of the piston 2 is shi~ted upwards due to a rnedium mass flow fromthe compression space l~ vla the gap 34~ to the buffer space 11 which is larger than the medium mass flow-in the reverse direction, the ports 33 pass the ducts 32a during the downward movement of the piston 2 at an instant~ ~or example t4, whicll is later than t2, whilst during the upward movement of the piston 2 the port.s 33 pass the .ducts 32a at the instant t ~lich is earlier than the instant t3. As a result, at the instan-ts t4 and t5, at which the pressure P3 in the auxiliary cylinder space 31 is higher than the pressure P2 in the buffer space 11, working medlum flows from the auxiliary cylinder space 31, .25 via the duct system 32 and the ports 33, to the buffer space 11. The pressure level in the auxiliary cylinder , PHN. 8698.
space 31 thus decreas~s, which causes an additional reversing, downwards directed force on the piston 2, so that the original central position is restored.
Should the mean position of the piston 2 be displaced downwards, for example, under the influence o~ its own weight, i.e. in the direction of the soft-iron cylinder 22, the ports 33 pass the ducts 32a during the upwards movement of the piston 2 at an instant, for example t6, which is later than tl (Fig. 2); during the downward movement of the piston 2, they pass at an instant t7 which is earlier than t2. At the instants t6 and t7, at which the pressure P2 in the buffer space 11 exceeds the pressure P3 in the auxiliary cylinder space 31, working medium then flows :Erom the buffer space 11, via the ports 33 and the duct system 32, to the auxiliary cylinder space 31. The mean pressure in the auxiliary cylinder space 31 then increases r with the result that the mean piston position is moved upwards to the original central positionO
Parts of the hot gas engine shown in Fig. 3 which correspond to the parts of the cold gas refrigerator shown in ~ig. 1 are denoted by the same reference numerals~
Therein, the compression space 4 communicates, via the cooler 5, the regenerator 7 which is rigidl~
arranged in a cylinder 40, and a heater 41, with the expansion space 6. The heater 40 comprises a number of 133~ ~
; . .
pipes 42 wtlich are connected at one end to the regenera-tor 7 and at the other end to an annular duct ~3, and also comprises a number of pipes 44 ~hich are connected at one end to the annular duct 43 and at the other end to the 0xpansion space 6.
Heat origincLting from a burner device 45 is given off to the working medium flowing through the heater pipes 42, 44 during operation. The burner device 45 comprises a burner 46 with a fuel inle-t 47 and an air inlet 4~ After having given off heat to the heater l~l, arranged inside a housing 49, the combustion gases leave the housing 49 via thc outlet 50.
The displacer 3 is coupled, via a displacer rod 51, to a drive system not shown. During operation f the hot gas engine, during which the displacer 3 and the piston 2 move at a mutual phase difference, the thermal energy applied -to the heater 41 is utilised to drive -the piston 2, so that electrical energy is generated in the armature coil 13. I~hen the displacer 3 is provided with an electrodynamic drive, part of the electrical energy generated in the armature coil 13 and be used, after the starting of the hot gas engine, for powering the armature coil coupled to the displacer rod 3.
AI1 auxiliary piston 53, being reciprocatable in an auxiliary cylinder 5~, is connected tothe free -14~
,.
~0~33~
..
piston 2 via a rod 52. The auxiliary piston 53 varies the'volume of the auxiliary cylinder space 55. In the auxili'ary piston 53 there is provided a duct 56, one end of which opens into the auxiliary cylinder spaGe 55, 5 ~ whilst its other end cooperates with a port 57 in the wal~ of the auxiliary cylinder 54, said port 57 being in open communication with the buffer space 11 via a duct 58.
The control of the central position of the piston 2 is identical to that shown in Fig. 2, so that no f'urther description is required~
Parts of the cold gas refrigerator shown in Fig.4 which correspond to parts of -the machine shown in Fig. 1, are,deno-ted by -the same reference numerals.
Irl the present case, a bore 61 with a thread 60 is provided in the piston 2, a rod 62 being screwed -therein in a gastight manner, said rod supporting an auxiliary piston 63 which is reciprocatable in an auxiliary cylinder 6~ provided with ports 65. In the situation shown, the buffer space 11 is in open communication, via theports 65 and a duct sys-tem 66 in the auxiliary piston 63, with the auxiliary cylihder space 67. The operation of the control mechanism for the central position is identical to that described with re~erence to Fig.1.
The desired central position of the piston 2 can be adjusted by screwing the rod 62 further into or out of the bore 61.
~~5 , ` ~111943~4 ~ .
.
Parts of the~cold gas refrigerator shown ,~
in Flg. 5 which correspond to those of ~ig. 4 are denoted - by the same reference numerals.
- The rod 62 is now rigidly connected to the piston Z, the auxiliary cylinder 64 being adjustable in the axial direction by means of an adjusti~g screw 70 in a bush 71. Thus, the central position of the piston 2 ; is again adjustable, an advantage being obtained in that ; the adjustment can be externally performed during operation.
Fig. 6 shows a cold gas refrigerator, com-pri.sing a cylinder 80 which accommodates a compression piston 81 which is connected, via a piston rod 82, to a drive system 83 in the crank case space 83a.
The compression piston 81 varies the volumeo~ a com' pression space 84 when it moves. The compression space 84 and the freezer 87, with an expansion space 88.
The expansion space 88 is bounded by an expansion piston 89, the other end of whlch bounds a buffer space 90 which contains working medium at a pressure which is equal to the mean working medium pressure in the expansion ; space 88. The expansion piston 89 is connected to a piston rod 91 which supports an auxiliary piston 92 - which varies the volume of the space 93 inside an auxiliary cylinder 94 when it moves.
~ duct 95 is provided in the auxiliary piston 92 and a port 96 is provided in the auxiliary cylinder 94 .
10~33~
In the situation shown, the buffer space 90is in open commullication, via the port 96 and the duct 95, with the auxiliary cylinder space 93. The operation of the central position control mechanism for the piston 89, *ormed by the awciliary piston 92 and the auxili.ary cylinder 94, is identical to that described with ref~rence to Fig. 1~ . .
. Obviously, the compression piston 8l.may also be constructed-as a free piston provided with a .
central position control system, for example, as shown in Fig.1. The cranlc case space 83a may form one integral unit wïth the buf*er space 90, if desired.
The reference numerals of Fig.3 are used for all parts of the hot gas engine shown in Fig.7.
The present hot gas engin3 di~*ers *romthat sho~n in Fig. 3 only in that now the upper side o* the au~iliary piston 53 varies the volume of the auxiliary . cylinder space 55. This means that the pressurb variation P3 in the auxiliary cylinder .space 55 is now in phase with the pressure variatlon P1 in the compression space 4, which is shown in Fig. 8.
.en the mean position of the piston 2 moves upwards again, the duct 56 passes the port 57, during the do1~nward movement of the piston 2, a-t the lnstan-t t4 25. which i9 later than t2, whllst during the upward movement of the piston 2, the duct 56 passes the port 57 at 1;he . -17-.
.
~,~
' ' , ~ .. ' ,.
~09433~
~ instant t5 which is earlier than the instant t5.
J As a result, at the ins-tants t~ and t5, at which the pressure P2 in the buffer space 11 is higher than the pressure P3 in the auxiliary cylinder space 55, working medium flows from the buffer space 11, via the ~ duc~ 58, the port 57 and the duct 56, to the auxiliary '. . cylinder space 55, so that the pressure level in the latter space increases. Thus, the piston 2 is driven . back -to its original central position again.
0 When the mean position of the piston 2 moves downwards, the duct 56 passes theport 57, during the opward movement of the piston 2, at an instant t6 ~h.ich is later than t1 (Fig.8), and passes this port ¦ during the downward movement of the piston 2 at an :instant t7 which is earlier~ than t2. At the instants t6 and t7, the pressure P3 in the auxiliary cylinder space 55 is : higher than the pressure P2 in the buffer space 11.
Wor~ing medium then flows from the auxiliary cylinder space 55 to the buffer space 1.1. The pressure level in i 20 the auxiliary cylinder space 55 decreases, with the result that the piston 2 assumes thehlgher, original central position aeain.
It will be obvious that the central position control system functions when the variable pressures in the wor~ing space and the auxiIiary cylinder space are in phase (Fig.8) as well as whell said pressures . are i~ counter-phase (180 phase difference) (Fig.2).
Claims (4)
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A hot gas reciprocating machine, comprising at least one working space in which a working medium per-forms a thermodynamic cycle, said working space compris-ing a compression space and an expansion space of mutually different mean temperatures during operation which are con-nected to each other via heat exchangers, including a regenerator, there being provided at least one free piston which is reciprocatable in a cylinder and one surface of which varies the volume of the working space, whilst its other surface forms a part of the boundary of a buffer space which also contains working medium during operation at an at least substantially constant pressure which corresponds to the mean working medium pressure in the working space, there being provided a control mechanism for maintaining a given central position of the free piston by the instan-taneous opening of a connection between the buffer space and a space in which a variable pressure prevails, said control mechanism comprising two elements which are con-structed as an auxiliary cylinder and an auxiliary piston which is movable therein so as to vary the volume of the auxiliary cylinder space, one of said elements being con-nected to the free piston whilst the other element is rigidly arranged, the auxiliary piston being provided with at least one duct, one end of which opens into the auxiliary piston wall, cooperating with the auxiliary cylinder wall, where it corresponds, in a given position of the auxiliary piston, to at least one duct in the auxiliary cylinder wall which communicates with the buffer space, characterized in that the other end of the duct in the auxiliary piston opens into the auxiliary cylinder space.
2. A hot gas reciprocating machine as claimed in Claim 1, characterized in that the rigidly arranged element is adjustable with respect to the cylinder in the direction of the cylinder axis.
3. A hot gas reciprocating machine as claimed in Claim 1, characterized in that the element which is connected to the free piston is adjustable in the axial direction with respect to the free piston.
4. A hot gas reciprocating machine as claimed in Claim 1, 2 or 3, characterized in that both elements are accommodated in the buffer space.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,337A CA1094334A (en) | 1978-03-06 | 1978-03-06 | Hot gas reciprocating machine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,337A CA1094334A (en) | 1978-03-06 | 1978-03-06 | Hot gas reciprocating machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094334A true CA1094334A (en) | 1981-01-27 |
Family
ID=4110924
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA298,337A Expired CA1094334A (en) | 1978-03-06 | 1978-03-06 | Hot gas reciprocating machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1094334A (en) |
-
1978
- 1978-03-06 CA CA298,337A patent/CA1094334A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry |