FR2742215A1 - STIRLING COOLER WITH ROTARY STEERING - Google Patents

Abstract

In a Stirling cycle cooler comprising rotary control means for driving in phase shifted translation for a compression piston (3) limiting a compression chamber (23) and a displacement piston (5) limiting an expansion chamber (13) and constituting a regenerative exchanger on a circuit for circulating a thermodynamic fluid in a closed circuit between said chambers, said drive means comprise an element (35) for mechanical connection of the two pistons to one another which is guided linearly around of an eccentric (4) mounted off-center on a rotary motor shaft (6), in a median part (71) intermediate between two lateral branches (72,73) terminated by ends (74,75) for attachment to each of said pistons (3,5) respectively.

Description

STIRLING COOLER WITH ROTARY STEERING

  The present invention relates to a Stirling cycle cooler of the type comprising means with rotary piloting for displacement displacement in phase shift for a compression piston limiting a compression chamber and a displacing piston limiting a expansion chamber and constituting regenerative exchanger on a circuit for circulating a thermodynamic fluid in

  closed circuit between said chambers.

  To cool electronic components which must be maintained in cryostatic conditions, more and more coolers are used which use a reversible thermodynamic cycle called Stirling, consisting in subjecting a thermodynamic working fluid to a compression phase at hot temperature. and an expansion phase at cold temperature, separated by two intermediate phases o, theoretically at

  constant volume, the fluid passes through a regulated material

  generator which captures the own cooling energy of the cold fluid leaving the expansion phase to restore it to the hot fluid upon its return from the compression phase to

the relaxation phase.

  To operate according to this principle of the Stirling cycle, known cryogenic coolers include a closed circuit of thermodynamic fluid, generally a high purity gas such as helium, between a compression chamber at hot temperature whose volume is variable under the control of 'a pressure oscillator, and an expansion chamber at cold temperature delivering to the component to cool the cooling power released by the expansion of the thermodynamic fluid. Between these two chambers, both in the forward direction and in the return direction, the circuit is at least partially constituted by a regenerator which is produced in the form of an elongated tube containing

the regenerative material.

  As in practice, this regenerator is generally itself mobile at the limit of the volume of the expansion chamber, the notion of its movement often takes precedence over its function of regenerator in terminology, which leads to designate it by the terms of tube or displacement piston, or displacement exchanger. It nevertheless retains its primary function of being traversed by the fluid during heating or cooling, in theory excluding expansion and compression, by the fact that

  its displacements are out of phase with respect to the modi-

  volume fications of the hot chamber of the pressure oscillator. However, it also plays an important role in regulating the thermodynamic cycle through the loss of

charge it implies.

  Among these coolers, the present invention provides an improvement to those which, more precisely, take the form of one-piece systems, o rotary type motor means which serve to drive in translation a compression piston limiting the hot temperature chamber in the pressure oscillator, also control the movements of the regenerator, in translation in a cryostatic well terminated by the expansion chamber at cold temperature from where the frigories

  produced are transmitted to the element to be cooled.

  By its characteristics, as will be described and claimed below, the invention aims in particular to reduce manufacturing costs and to

  improve the operating conditions of such coolers

  Stirling cycle dissectors with common rotary piloting

  to the compression piston and to the displaced displacement piston

  nerator. In its preferred forms of implementation, it makes it possible in particular to increase safety and the service life in operation, in particular by reducing the number of mechanical connections with fragile articulation, of limiting the risks of contamination of the thermodynamic fluid and of fouling of the circuit which it borrows, to facilitate the synchronization and the shift in time of the four thermodynamic phases of the cycle. Mainly, while in known embodiments of this type, we can not do otherwise than to transmit the movement of a rotary motor shaft, by transforming it into a rectilinear movement for entrainment of the pistons, by means of a crankshaft involving a

  eccentric mounted on the motor shaft and two connecting rods

  abutments on the eccentric in angularly offset positions

  stretching, generally 90 degrees, and respectively articulated on each of the pistons, the invention provides for replacing the two connecting rods by a single linear element of mechanical transmission which follows the movements of the eccentric and connects the two pistons one to the other. 'other. This element also has the advantage of being able, in combination, to play the role of the pneumatic connection conduit for the

  circulation of thermodynamic fluid.

  The invention therefore essentially relates to a Stirling cycle cooler of the type comprising means with rotary piloting for displacement in phase shifted for a compression piston limiting a compression chamber and a displacing piston limiting a expansion chamber and constituting regenerative exchanger on a circuit for circulating a thermodynamic fluid in a closed circuit between said chambers, in which the drive means comprise a mechanical connection element of the two pistons with each other which is guided linearly around a mechanism eccentric mounted off-center on a rotary drive shaft, in a middle intermediate part between two between two lateral branches terminated by attachment points on each of said

pistons respectively.

  According to a secondary characteristic of the invention, this element is a flexible tube not

  compressible also constituting a circulation conduit

  lation of the thermodynamic working fluid between the compression chamber and an inlet end in the displacer tube opposite to a cold end limiting the expansion chamber. Said element then combines the functions of

  mechanical connection and pneumatic connection.

  According to another characteristic of the invention, such an element is structured and configured in such a way that it fulfills a spring function which advantageously combines with its mechanical connection function, and

  preferably also its pneumatic connection function.

  The remainder of this description will highlight

  other characteristics of the invention, with particular regard to the production of an eccentric movement transmission mechanism between a rotary shaft and the two pistons and compliance with the four phases

  of practical operation in Stirling cycle.

  It will be seen in particular that this mechanism advantageously comprises a semi-circular holding and guiding cage which is mounted on a crankshaft eccentric having a groove in which the piston-to-piston connecting element is engaged, and that such a cage is advantageously of semi-circular shape, in order to tighten said element in its receiving groove only on a part of the periphery of the eccentric, where it does not have to play flexibility during the operating cycle and where it is desirable that a central point of its middle part

  either stuck in a fixed position on the eccentric.

  It will also be seen that the mechanical connection element between the two pistons, preferably produced in the form of a conductive tube of the thermodynamic working fluid, is advantageously claimed by a natural open configuration of its middle part before mounting on the eccentric , and that it thus succeeds in limiting the mechanical stresses generated by the rotary piloting of the pistons, and in particular, in balancing the radial forces imposed by the compression piston on its liner in its dynamic displacement and thus significantly reducing the effects selective wear

  on the walls of the compressor piston jacket.

  In addition, its spring function preferably involves two curvatures which it forms in its lateral branches, each with a concavity in the opposite direction to that of its median part around the eccentric, so as to maintain each branch in axial alignment with

  the piston corresponding to the vicinity of the attachment point.

  The remainder of this description, set out in

  non-limiting title, relates to a particular form of

  concrete realization of the invention, however preferred.

  It is illustrated by the figures in the appended drawings, in which: - Figure 1 shows a Stirling cycle cooler according to the invention, in a cross-sectional view; - Figure 2 shows the same cooler in its mechanical parts in a partial longitudinal sectional view; - Figure 3 shows the organs of the piston drive mechanism in cavalier representation; - Figure 4 illustrates the configuration of the mechanical and pneumatic connection tube between pistons at rest in order to also play the role of spring; - And Figures 5a to 5d schematically illustrate the kinematics of the deformations followed by this tube, in control of the displacement of the pistons by the mechanism to

  eccentric, during the four phases of the thermo cycle

  dynamic. It should be noted that in these drawings, the scale has not always been perfectly respected, in the sole concern of facilitating their understanding, and that on the other hand, we have sought to keep the same references for the same elements of a figure to another. As already indicated, coolers of the rotary pilot type following a Stirling thermodynamic cycle are already known. They are preferably produced in miniature and monobloc form to be used for the cryogenic cooling of electronic components, although they can also be used in other fields, like all those which involve superconductors having to be maintained at cryogenic temperature.

  Particularly in the optoelectronics industry

  culier, they are useful for cooling for example a

  infrared detector or any other sensor whose temperature

  Cold operating temperature is between 80 K and K. They are particularly appreciated for their high efficiency under low mass constructions, suitable for use in portable systems. On the other hand, they sin by their price when their quality of yield loses interest, which is the case in particular of the applications which are satisfied with a working temperature in the range of cold temperatures called

  intermediate, around 120-150 K.

  A known embodiment of a one-piece miniature Stirling cooler with rotary engine and integrated cold probe is described in particular in the French publication entitled "Engineering Techniques, Electronic Treaty" by Damien FEGER, with pages numbered E4070.

  n 1 to 11. In this publication, the concept of a cooling

  Low cost rotary Stirling straightener is particularly

  felt in figure 14, where we can clearly see a city

  brequin which drives the compression piston and the porous displacing piston, or regenerator, by means of two rigid and independent rods, articulated at their two ends, which are arranged at 90 degrees of angle

one from the other.

  In accordance with the present invention, the cooler described here differs essentially from the previous one in that the mechanical entrainment of the compression piston, as well as the mechanical entrainment of the porous displacing piston, are achieved by means of a single and unique connecting element, linearly disposed between the compression piston and the inlet of the displacing piston, while being driven by means of an eccentric mechanism similar to a crankshaft. By getting rid of the linkage system, we already save money

  important in manufacturing and maintenance cost.

  In accordance with the embodiment described, the mechanical connection is combined with the pneumatic connection necessary for the circulation of the working fluid. Indeed the linear element is a flexible and non-extensible tube,

  but also non-compressible, which conducts the thermo-

  dynamic between the compression chamber limited by the compression piston and the entry of the displacer piston of regenerative material which it crosses between this entry and

  the cold end of this piston limiting the expansion chamber.

  It is therefore no longer necessary to make holes in the cooler housing to communicate the compression chamber with the entry of the displacer piston, a hole that can be seen clearly on the art cooler

  previous shown in Figure 14 mentioned above.

  In addition, and at best by giving the linear connection a shape and a stiffness chosen so that it behaves like a spring having infinite fatigue, it is ensured that the life of the device is improved compared to known devices, avoiding in particular that the displacements of the displacing piston lead to premature wear of its guide tube on a preferential generator, due to the radial forces which are always exerted in the direction opposite to the compression piston. In Figure 1 of the drawings here attached, we

  recognizes elements known to themselves to be cool

  existing Stirling & piloting dissectors, namely a casing 2, enclosing a pressure oscillator which ensures the compression of the thermodynamic fluid at each operating cycle by a compression piston 3, a displacement piston 5 of elongated shape, movable in translation in a guide tube 55 outside the pressure oscillator, and a crankshaft mechanism whose eccentric 4 is rotatably mounted, but in the off-center position, on a drive shaft 6, centered on the axis of the cylindrical volume

internal of housing 2.

  By means of this mechanism, the shaft 6 is used both to drive the compression piston 3 in translation and to control the translational movements of the displacing piston 5. The two pistons 3 and 5 are movable in radial directions of the volume internal cylindrical of the casing 2, but angularly offset from each other by degrees, in order to ensure the desired phase shift between the

stages of the thermodynamic cycle.

  The pressure oscillator is provided with ears 22 on the periphery of the casing 2, which are intended for mounting the

  cooler by fixing on a support (not shown).

  The compression piston 3 limits a compression chamber 23 of the thermodynamic fluid at the bottom of a fixed jacket 26 for guiding the piston constituting both the cylinder head 29 of the compressor and the closure plug for

a radial tap 24 of the casing 2.

  The displacement piston 5 extends between an inlet end 51 situated in the hot zone on the side of the pressure oscillator and a cold end 53 situated at the end

  opposite, a relief chamber 13 is provided.

  In this extremity radially distant from the oscil-

  pressure lator, its guide tube 55 ends with a cold plate 52 for mounting a component & to cool 54, affixed against the cold end so as to receive at best, by thermal conduction, the cooling power

  produced by the expansion of the working fluid.

  At the inlet end, it can be seen in FIG. 1 that the displacing piston is kept sliding in a radial connection 25 of the casing 2, fitted internally with a fixed ring 27. With this, a piece of concentric interface 78, which terminates the body of the piston beyond its guide tube 55, secured in tight connection with the casing 2, and which surrounds a passage channel of the

  fluid 58, arranged along its axis.

  In a conventional manner in itself, the displacing piston and its guide tube 55 together constitute what is commonly called a cold finger, and this piston plays the role of thermal regenerator, being filled with a porous material suitably chosen for this purpose. effect, generally consisting of a stack of metal grids inside a thermal insulating tube. The component to be cooled 54 is, for example, an infrared detector. A space is maintained between the cold plate which supports it and the tip of the cold finger, in order to avoid the transmission of vibrations. The cold finger is completely surrounded by a thermal insulation envelope 59, with a double wall under vacuum, which is only mentioned in the figure. It is connected, generally by welding or gluing, to the radial tap 25 at its hot zone 51. This produces the one-piece construction of the cooler recommended by the invention and conforms to the concept of cold probe.

  integrated, the cold finger representing a cryostat well.

  For the position of the mobile elements shown in FIG. 1, the expansion chamber 13 is reduced to its minimum volume, the cold end of the displacer piston 5 being at the end of its travel towards the component to be cooled at the bottom of the guide tube 55. The compression piston 3 is on the contrary distant from the cylinder head 29 at the bottom of its jacket 26 at the level of the compression chamber 23. The position is that of the operating phase described further on in

reference to Figure 5d.

  According to the invention, the drive of the compression piston 3 and of the porous displacing piston 5 from the movement of the crankshaft eccentric 4 is effected by means of a connecting element 35 which, in the present case, is more particularly a connecting tube 35 to ensure both the mechanical connection and the

  pneumatic connection between the two pistons.

  This connecting tube 35 is fixed at each end, by brazing or welding between metal parts, on the one hand with the compression piston 3 and on the other hand with the porous displacing piston 5, more precisely with the channel 58 which admits the pressure modulation in the porous regenerative material contained in the displacing piston, and there by means of a miniature bellows at low

stiffness 69.

  The connecting tube 35 is of circular or ovoid cross-section which remains constant, over a non-extensible length, while it has the flexibility necessary to deform at each revolution of the axis of the eccentric 4, bending elastically between the eccentric and each of its ends 74, 75 completed

  by its attachment points on the two pistons.

  Each of the fasteners at these attachment points is preferably carried out as far as possible from the axis of the crankshaft, in order to reduce the radial forces of the pistons on their liners and to lengthen the life of the sliding seal. Thus, on the side of the compression chamber, the piston 3 is hollow and the tube 35 is fixed on it (at 77, FIG. 1) on the side of the compression chamber 23, flush with its cap and beyond. an empty annular space 33 internal to the piston. This design provides the equivalent of a great length of

  connecting rod without interfering with lateral travel.

  Figure 2 being in section along a diametrical plane of the pressure oscillator, it shows a housing 11 in extension of the housing 2 which encloses the electric motor 10 driving the shaft 6 of the cooler, with its stator 12 and its rotor 14. The crankshaft 6, constituted by the axis of the rotor, is rotatably mounted on ball bearings and it is provided with a flywheel 15 which makes it possible to optimize the shape of the mechanical torque required by the cooler and thereby reduce power consumption. Through the bottom wall of the casing 11, we see a metal rod 16 which shows the loading of the working gas cooler made there. The

  watertight electrical bushings necessary for the supply

  electric motor are located in the same place,

  but they were not represented.

  The motor casing 11 is integral with the casing 2 by a connection between their respective walls which is impermeable to the working gas filling the internal volume. the electric winding of the stator is therefore isolated by an organic resin with low degassing of impurities which would come

pollute the working gas.

  The constitution of the spring crankshaft mechanism

Figures 1,2 and 3.

  The eccentric 4 is cantilevered at the end of the shaft 6, on an axis 61, which is in practice of reduced section as in FIG. 2 and 3. The body of the eccentric 4 is made of a annular ring 42 in which the external cage of a miniature ball bearing system 62 is slidably engaged slidingly on the axis 61 by its internal cage. The use of a pair of mounted twin bearings as illustrated can reduce the rolling torque. The ball bearing 17 supporting the shaft 6 on the crankcase 6 on this side is

split in the same way.

  As regards the eccentric, the ring 42 is started by a circular groove 43 in which the connecting tube 35 is housed. The latter is partially enclosed therein and held by means of a cage 44 which forms a semi-circular ring. circular around the ring 42, so

  which it defines with it a corresponding throat diameter

  laying precisely on that of the tube 35 in the vicinity of a central point 63 of the cage 44. However, by deviating from this central point, it can be seen in FIG. 1 that the cage 44 has internally a flared periphery towards the edges of its semi-circular shape, such as 45, which has the consequence that it leaves the tube 35 more free to deform during its drive by the crankshaft mechanism. FIGS. 5a to 5d clearly show how the engine movement is transmitted by the crankshaft and the tube 35 to the pistons 3 and 5 so as to ensure the four phases of a Stirling cycle, while FIG. 4 represents the configuration presented by the tube 35 naturally, before mounting around the eccentric and fixing to the pistons. The geometric shape chosen is particularly well suited so that the tube 35 ensures

  the spring effect sought after according to the invention.

  It should be emphasized in this connection that the

  Lement of the four essential phases of the cycle by using the movement transmission spring tube according to the invention, is closely linked to the operation of the finger

  cold. Due to the presence in it of a reg-

  generator necessarily crossed by the thermo-fluid

  dynamic, both in the forward direction from the compression chamber to the expansion chamber and in the return direction, which regenerator consists of an elongated porous tube, the fluid necessarily undergoes significant pressure drops which translate in favor of the maintenance of its phase shifted. In other words, the operating energy to be brought in from the outside is essentially to move the compression piston, both in traction and in thrust, hence the clearly wider section of this piston . As described here, the tube 35 breaks down into three parts in its linear configuration. We distinguish in the figures, and in particular in Figure 4, a middle part 71, which forms an arc intended to fit on the eccentric on either side of the fixed central point already mentioned. This middle part is intermediate between two lateral branches 72 and 73, each of which ends in a straight end 74 or 75

  towards the point of attachment to the corresponding piston.

  The spring tube 35 is mounted pretended on the eccentric 4 from a natural curvature of its middle part 71 whose angular opening is greater than that of the eccentric, therefore less concave than that of the cage 44 which maintains it in the groove of the latter, as it appears in FIG. 4. This is how we ensure, during operation, a pretensioning effect which tends to open the angle of 90 degrees between the axes of the pistons, and which contributes to keeping the tube 35 in alignment with the axes of the pistons in the vicinity of the respective attachment points, by virtue of an initial flexibility constraint which is balanced in dynamics. The advantage of this arrangement is particularly noticeable in the case of the compressor piston, because it results in a considerable reduction in selective wear and tear on a preferential generator of its jacket which is deplored.

  in previously designed coolers.

  In the same concern, it is provided that the middle part 71 extends over a length which corresponds substantially to that of a semicircle around the eccentric, and that the two lateral branches 72 and 73 which are made for move away from it to the pistons at the ends of the tube 35, themselves form convex bumps, in curves whose concavity is turned in the opposite direction to that of the middle part 71, before joining the rectilinear shape that 'they have at their ends 74, 75, in the immediate vicinity of the points

  of attachment to their respective pistons.

  Thanks to such a configuration, and according to rules which are perfectly within the reach of metallurgists to translate in terms of manufacturing the requirements posed here, we obtain that in operation, once it is linked to the eccentric, the tube 35 behaves in practice as a linear mechanical connecting element having the properties of a spring with high stiffness and that its deformations best follow those which correspond to

  a linear translation of the pistons.

  These arrangements combine in their effects with the choice of a bellows 69 of low stiffness, the essential role of which is to absorb, by its flexibility, the lateral deviations with respect to an axial alignment of the corresponding lateral branch 73 of the tube 35 in the vicinity. immediately from its point of attachment with the displacing piston, and not to allow a longitudinal extension or retraction. Indeed, despite the limited stiffness of such a bellows, the consequences on the actual stroke of the piston are low, given the maintenance of the movement already imposed by the intrinsic surface forces of which the displacer piston is seat. Furthermore, the bellows 69, advantageously

  made of stainless steel like the connecting tube itself

  even, is easily capable of containing the dynamics of pneumatic pressure, insofar as it is located in the internal volume of the casing 2, and therefore subjected externally to the loading pressure. In certain variant embodiments of the invention, it will however be preferable to replace such a bellows connection with a ball joint mounting of the end of the tube 35 in the body of the displacer, more precisely in its interface part 78, including the channel 58 remains in communication through the ball joint

  with the tube 35 for the passage of the working gas.

  When the tube 35 is in place in the operating cooler, it deforms slightly by elastic flexibility of its curved parts during the rotation of the eccentric axis 61 around the axis of the motor shaft 6, however that, due to the realization of the eccentric 4 in two concentric parts rotating one inside the other, the groove in which it is held by the cage 44 freely follows its small displacement.

  This is illustrated by Figures Sa to 5d, in which it has been sought to show both the deformations of the curves of the tube 35 and the displacement of its points of attachment to the pistons at its opposite ends, schematically representing the assembly for four typical positions during a cycle. Note, however, that the representation remains theoretical in relation to what continuous rotation can give in practical reality. In accordance with these figures, the end linked to the compression piston passes from the position A1 for maximum reduction of the compression volume to the position A3 at the end of compression (FIG. 5c) passing through the intermediate quarter-cycle position A2. It then returns to position A1 in FIG. Sa by passing substantially through the same intermediate position A2 in FIG. 5d. At the same time, the end linked to the displacing piston starts from an intermediate position B1 (FIG. 5a) to come to its retracted position B2 corresponding to a maximum volume of the expansion chamber (FIG. 5b), then it returns to the position Bl (FIG. 5c) before reaching towards position B3 in FIG. 5d, corresponding to the minimum volume of the

relaxation room.

  From one phase to another, the middle part of the spring tube 35 bears partly on the bottom of the groove 43, but also on the guide cage 44 itself, taking into account its flared edges and the pretension of the tube. The efforts are exerted mainly on the side of the lateral branch attached to the compression piston, o moreover, the problem of axial alignment is less posed, for this reason, the curvature of the convex bump of the tube of this side was made knowingly more inflated in amplitude than that of the side of the displacer piston. The thrust axes are shown diagrammatically by the lines X1, X2, X3 passing through the center

eccentric axis.

  We will now specify somewhat the materials used in the constitution of the cooler which is the subject of the figures, as well as the dimensioning of its

  constituent elements, choosing a particular example

  particularly advantageous for a low-cost device, both in production cost and in costs

operation and maintenance.

  In general, helium is used as the working gas in known coolers, but for operation at intermediate cold temperatures, of the order of 120 to 150 K, it is better here to use air, nitrogen, argon, or preferably neon. The tube 35 is made of a steel of good ductility in stainless quality, such as the ZO10 type, semi-hard annealed steel. It is implemented in a circular section pipe. The tube 35 may, for example, have a linear length of 44 mm, for a mobility of its ends over a distance of the order of 1 mm, and a passage section equivalent to that of a circular diameter of 1.5 mm under a wall thickness of microns. The respective diameters of the two pistons are for example 6 mm for a displacing piston offering a regenerator length of 41 mm, and 14 mm for the piston

compression.

  In an embodiment with integrated cold probe as described above, the main casing 2, the engine casing 11 and the guide tube 55 of the displacing piston together constitute a tight monolithic enclosure for the working gas, which fills its internal volume under the

static loading pressure.

  In this enclosure are located all the movable elements of the cooler of the invention. With a view especially to low cost, it can be made of plastic of the technical type. Its different parts are manufactured by molding and assembled with a tight connection of the walls by gluing. If one adds a surface metallization on the internal side, one avoids the consequences of a potential degassing of the organic constituents and the phenomenon of hygroscopicity. At least for the body of the compressor casing 2, a material of good mechanical strength with high thermal conductivity is used in order to ensure the rejection of the heat of compression to the outside. The same material may be suitable for the crankcase for the same reasons, especially if it has insulating properties

  clean to facilitate watertight electrical crossings.

  The heat rejection can be further improved if it is planned to keep the choice of a metallic material (stainless steel) for the cylinder head 29 of the compressor and the jacket 26 of the compression piston, made in one piece, the piston compression 3

  itself being metallic in nature.

  The dynamic seal between the compression piston and its jacket is provided for example by a coating of polytetrafluoroethylene preferably impregnated with a sliding additive to reduce the coefficient of friction between piston and jacket. The same type of coating can be applied to the displacement piston to facilitate its sliding, especially

  in its part mounted on the compressor housing.

  A plastic material based on the same resins as the casing or compatible resins can also be used for the tube 55 for guiding the displacing piston,

  with the proviso that it is desirable that it be thermi-

  only insulating, like the tube forming the clean wall of the displacing piston and that it is impermeable to the working gas. For both, we are looking for materials with a low coefficient of thermal expansion in order to

  limit any variation in the length of the cold finger.

  Also in the case of temperate operation

  cold intermediate rature and in a low cost perspective, the thermal insulation envelope of the cold finger does not strictly need to be under vacuum, and a filling of inerting gas in a double wall of

  plastic may be appropriate.

  The interface piece 78 of the displacing piston is of cylindrical shape, and it is bonded in the tube specific to the displacer for sealing in static pressure which is here sufficient. Indeed, as the working gas is forced through the porous regenerator along its axis by the pressure modulation conducted by the tube 35 located in the internal pressurized volume in the casing 2, there is no longer any need for static sealing as previously requested by the holes through the casing which made the fluid enter laterally into the displacer tube from the compression chamber.

  But of course, this description does not mean to be limiting. In particular, and even the case

  if necessary by using substantially the same plastic material for the casing of the cold finger and the casing, it may be preferable to assemble them by metal joint and screwing rather than by gluing, when the aim is interchangeability

cold finger.

Claims (18)

  1 / Stirling cooler & cycle of the type comprising rotary drive means of phase shifted translation for a compression piston (3) limiting a compression chamber (23) and a displacer piston (5) limiting a expansion chamber ( 13) and constituting a regenerative exchanger on a circuit for circulating a thermodynamic fluid in a closed circuit between said chambers, characterized in that said drive means comprise an element (35) for mechanical connection of the two pistons (3,5) l to each other   which is guided linearly around an excent mechanism   plate (4) mounted off-center on a rotary motor shaft (6), in a middle part (71) intermediate between two lateral branches (72,73) terminated by points   of attachment to each of said pistons respectively.   2 / cooler according to claim 1, charac-   terized in that said connecting element (35) is produced in the form of a tube also constituting a conduit for circulation of the thermodynamic working fluid between said compression chamber and a channel (58) for entering a hot zone (51 ) of the opposite displacement piston (5)   at a cold end (53) limiting said expansion chamber.   3 / cooler according to claim 1 or 2, characterized in that said connecting element (35) is   structured and configured to ensure that   spring effect constantly tending to balance the radial forces imposed by the piston   compression on his shirt in his dynamic displacement.   4 / cooler according to one of claims 1   to 3, characterized in that said eccentric (4) is surrounded by a semi-circular cage (44) defining with it a groove (43) for guiding said connecting element (35) in which the latter is clamped fixed in a point central of its middle part (71).   5 / cooler according to claim 4, characterized in that said cage (44) has internally   a flared circumference towards the edges of its semi-shape circular.   6 / Cooler according to any one of the res-   dications 1 to 5, characterized in that said connecting element (35) is pretended to be mounted on said eccentric (4) from a natural curvature of its middle part (71) with an angular opening greater than that of said eccentric.   7 / cooler according to one of claims 1 to   6, characterized in that said connecting element is shaped in each of its lateral branches (72,73) according to a curvature of concavity opposite to that of said median part (71), which tends, in operation, to maintain it along the axis of the corresponding piston in sound   end terminated by its point of attachment thereon.   8 / cooler according to claim 6 or 7, characterized in that said connecting element (35)   has the properties of a spring with high stiffness.   9 / cooler according to one of claims 1 to   8, characterized in that said connecting element (35) is fixed to the displacing piston (5) by means of a bellows (69) selectively allowing lateral deviations from an axial alignment of its corresponding lateral branch (73 ) at the point of attachment with said displacement piston.   / Cooler according to one of claims 1 to 8   characterized in that said connecting element is fixed to the   displacer piston by a ball joint mounting.   11 / Cooler according to one of claims 1 to   10, characterized in that said connecting element (35) is fixed to the compression piston (3) on the side of the compression chamber (23), beyond an annular space vacuum (33) internal to the piston.   12 / cooler according to one of claims 1 to   11, characterized in that said eccentric is produced in two parts (42,61) mounted to rotate one inside the other by ball bearing (62).   13 / cooler according to one of claims 1 to   12, characterized in that said connecting element (35) and said eccentric (4) are located in the internal volume   a casing (2) sealed to said thermodynamic fluid.   14 / cooler according to claim 13, charac-   terized in that said casing (2) is in tight sealed connection with a motor casing (11) enclosing a motor driving said shaft (6).   / Cooler according to claim 13 or 14, characterized in that said casing (2) is in sealed integral connection with a tube (55) for guiding said displacement piston (5).   16 / cooler according to claim 15, charac-   in that in a monobloc embodiment, all the mobile elements which it comprises are located in a   enclosure filled with static thermodynamic fluid.   17 / A cooler according to claim 2, combined   possibly with one of the claims which   depend, characterized in that said channel (58) is formed in an interface part (78) slidably mounted in a casing (2) limiting a pressurized volume of working gas.   18 / Cooler according to one of claims 1 to   17, characterized in that said displacement piston (5) is limited by a tube   19 / Chiller according to any one of the res-   dications 1 to 18, characterized in that said housing (2) and / or said motor housing (11) and / or said guide tube (55) together constitute a monolithic sealed enclosure for thermodynamic fluid.   20 / Cooler according to claim 19, characterized in that said housing (2), said motor housing (11), an envelope (59) of cold finger, and possibly said guide tube (55), are made of   plastic and assembled by gluing.