WO2010139323A2

WO2010139323A2 - Stirling cooling arrangement

Info

Publication number: WO2010139323A2
Application number: PCT/DK2010/000081
Authority: WO
Inventors: Poul Erik Hansen; Ana Mari Tataru Kjaer; Klaus Reinwand
Original assignee: Danfoss Compressors Gmbh
Priority date: 2009-06-05
Filing date: 2010-06-01
Publication date: 2010-12-09
Also published as: DE102009023977A1; WO2010139323A3

Abstract

Stirling cooling arrangement with a driving unit (2) having a housing (47-49) and at least one piston (5, 6) that is driven by a linear motor (8, 9) along a piston axis (7) in a cylinder (29), and a displacer unit (3) that is connected to the driving unit (2) via a gas-carrying connection (24) and comprises at least one displacer (14) that is movable in a displacer housing (15) along a displacer axis (16), the linear motor (8, 9) comprising an armature (10, 11) that is connected to the piston (5, 6) and arranged between an inner stator (31 ) and an outer stator (32), and a coil arrangement (35, 35'). It is endeavoured to achieve a good efficiency. For this purpose, in the radial direction the coil arrangement (35, 35') is arranged inside the armature (10, 11).

Description

Stirling cooling arrangement

The invention relates to a Stirling cooling arrangement with a driving unit having a housing and at least one piston that is driven by a linear motor along a piston axis in a cylinder, and a displacer unit that is connected to the driving unit via a gas-carrying connection and comprises at least one displacer that is movable in a displacer housing along a displacer axis, the linear motor comprising an armature that is connected to the piston and arranged between an inner stator and an outer stator, and a coil arrangement.

Such a Stirling cooling arrangement is, for example, known from EP 1 348 918 A1.

A cooling arrangement working in accordance with the Stirling principle has a relatively good relation between achievable cooling capacity and mass. From a design point of view, it is thus well suited for mobile applications.

As, however, in connection with mobile applications, for example a cooling ar- rangement for a portable cooling box, it is also required to take along the power supply, it is particularly essential for the cooling arrangement to have a good efficiency. The good efficiency is of course also a goal for stationary applications.

The invention is based on the task of providing a good efficiency.

With a Stirling cooling arrangement as mentioned in the introduction, this task is solved in that in the radial direction the coil arrangement is arranged inside the armature.

Arranging the coil arrangement inside the armature in the radial direction causes that the length of the conductor, through which the current flows inside the coil arrangement, can be kept shorter. This has two advantages. Firstly, less copper is required, so that mass can be saved. Secondly, with the same current intensity, less ohmic losses appear. Inside the armature, sufficient space is available, so that the coil arrangement can be made with a relatively large conductor cross-section, so that the current can be sent through at a sufficient current intensity. Thus, the current generates a magnetic field that can generate the forces required to move the piston. The armature that is usually provided with permanent magnets lies on a relatively large radius, so that relatively much force can be generated.

Preferably, the coil arrangement is accommodated in the inner stator. Thus, the coil arrangement is mechanically held by the inner stator. This gives a good coupling of the magnet field generated by the coil arrangement at the inner stator and thus a good efficiency.

Preferably, the inner stator is made of two parts arranged after one another along the piston axis. This simplifies the manufacturing. In a simple manner, it is possible to integrate the coil arrangement in the inner stator. For this purpose, merely one of the two parts, of which the inner stator is assembled, must have a recess, in which the coil arrangement can be accommodated. The other part then acts as some kind of cover. Of course, it is also possible to provide both parts with recesses together forming a hollow in which the coil arrangement can be accommodated.

It is preferred that the two parts have the same design. This simplifies the manufacturing. The two parts then only have to be joined with opposite orienta- tion to provide the required recess for the coil arrangement. In certain cases, it may be necessary to turn the two parts by 180° in relation to one another around the piston axis, for example when the two parts comprise openings for the entry of electrical connections.

Preferably, the inner stator and/or the outer stator are made as sintered elements). A sintered part is relatively expensive in manufacturing. When using a sintered part or a sintered element, however, a good space utilisation and a good magnetic flux occur. Also the shaping of the sintered parts or sintered elements is freer, so that within certain limits almost any desired shape can be realised.

Preferably, the inner stator and the housing are connected by means of a join- ing element arrangement that comprises at least one deformation zone. The joining element of the joining element arrangement can, for example, comprise a rivet, whose deformation zone is then formed by a closing head. The joining element arrangement can also be a pin, whose end is provided with a head. An annular element can then be pressed around the other end of this pin. If the connection can be achieved by means of the deformation of a joining element, it will be sufficient during manufacturing to act upon the joining element arrangement by means of an axial force. This can be done in a simple press. Complicated movements for making the joint between the housing and the inner stator are therefore not required.

Preferably, the joining element is made as an electrical conductor that is connected to the coil arrangement. The joining element then meets another task, namely conducting electrical current to the coil arrangement. If the joining element is led through the housing, the electrical current can be supplied from the outside.

Alternatively or additionally, it may be provided that the joining element arrangement comprises a joining element that is connected to the inside of the housing. Thus, it is avoided to make an opening in the housing, which is particu- larly advantageous, if the gas accommodated inside the cooling arrangement has already been pressurised to a certain pressure and/or comprises relatively small molecules, like for example helium. In this case, it is advantageous to avoid all unnecessary openings in the housing.

Preferably, the axial position of the outer stator in the housing is fixed by means of a radially yielding element. A radially yielding element can, for example, be a lock ring or an annular spring. The radially yielding element can wedge or cling itself to the inner wall of the housing. A groove can also be provided in the inner wall of the housing for the accommodation of the radially yielding element. Preferably, the outer stator is supported in the housing in the radial direction, at least one channel being provided between the outer stator and the housing. Thus, the housing retains the outer stator radially. As, however, during the re- ciprocating movement of the armature a certain gas volume has to be displaced out of the gap between the inner stator and the outer stator, in which the armature moves, at least one channel is provided through which the displaced gas can flow axially past the outer stator to reach an area between the linear motor and the piston. Here a sufficiently large buffer space is available, in which the gas can enter without significantly increasing the pressure. Thus, the movement of the armature is not impeded by a gas buffer.

Preferably, at least one section of the channel is formed by a groove on the outer stator. Such a groove can be provided without problems, without exces- sively impeding the magnetic flux through the outer stator. In many cases, it is easier to provide a groove in the outer stator than to deform the housing accordingly.

Preferably, at least one section of the channel is formed by a deformation in an end face of the housing. Also here a path is then available, through which the gas can be displaced that is pressed out by the movement of the armature in the gap. In the end face of the housing, it is particularly easy to make a recess, if, at least in this area, the housing is made as a deep-drawn part of sheet metal. During deep-drawing (or another deformation kind) the recesses can be formed at the same time.

Preferably, the armature is formed as a cylinder with a bottom wall, the bottom wall comprising at least one through opening. The bottom wall gives the cylinder-shaped armature a relatively large mechanical stability. Also the fixing means, with which the armature is connected to the piston, are arranged in the bottom wall. The fact that at least one, usually more, through openings are provided in the bottom wall causes that also here a possibility exists for the gas that is trapped between the armature and the inner stator can escape or flow in during a movement of the armature. Thus, also here the formation of a pressure buffer or a lower pressure is avoided, which has a positive effect on the efficiency, as the armature does not have to come up with additional forces during its movement.

Preferably, the driving unit has two pistons arranged in a common cylinder, each piston being movable by a linear motor. The two linear motors do then work at opposite phase. This means that the two pistons are moved towards each other or away from each other at the same time. As two pistons are available, each piston only has to displace half the amount of gas. Accordingly, also only half the stroke amplitude and half the electromotive force is required in each linear motor. This, the dimensions of the linear motors can be kept small, which again has a positive effect on the dimensions of the complete driving arrangement.

Preferably, the coil arrangements of the two linear motors are arranged so that with the same current supply they show oppositely directed effects. In the simplest case, this can be achieved in that the current flows through the coil arrangements in different directions. In this case the oppositely directed movements of the two pistons occur automatically, if both coil arrangements are con- nected to the same current connection.

In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing:

Fig. 1 a schematic cross-section through a Stirling cooling arrangement,

Fig. 2 a partial section M-Il according to Fig. 1, and

Fig. 3 a perspective view of a modified embodiment, partially in section.

A Stirling cooling arrangement 1 comprises a driving unit 2 and a cooling arrangement 3. In the present case, the driving unit 2 has a cylinder block 4, in which two pistons 5, 6 are arranged. The two pistons 5, 6 are movable in coun- terphase along a piston axis 7. They are driven by electric magnets 8, 9 acting upon armatures 10, 11 , which again are connected to the pistons 5, 6 via piston rods 12, 13. In Fig. 2 the piston axis 7 extends from the left to the right and in Fig. 1 perpendicularly to the drawing plane.

The cooling arrangement 3 comprises a displacer 14 that is movable in a dis- placer housing 15 along a displacer axis 16. The displacer 14 and the pistons 5, 6 are not mechanically coupled with each other. They work with a phase offset of approximately 90° to each other.

The displacer housing 15 is guided through an isolating wall 17. It extends on both sides of the isolating wall 17. In this connection, the side facing the driving unit 2 is called the "hot side", and the side of the displacer housing 15 arranged on the other side of the isolating wall 17 is called the "cold side". A first heat exchanger 18 is provided at the hot side, and a second heat exchanger 19 is pro- vided at the cold side. A regenerator 20 is arranged between the heat exchangers 18, 19. The heat exchangers 18, 19 and the regenerator 20 are arranged in an annular gap that is formed between the displacer housing 15 and a cylinder 21 of the displacer housing 15.

The two heat exchangers 18, 19 and the regenerator 20 must, however, not necessarily be arranged in the displacer housing 15, if it is ensured otherwise that the displacer housing 15 comprises a cold side and a hot side.

On the cold side of the displacer housing 15 a cooling member 22 is fixed, a ventilator 23 ensuring an air flow through the cooling member 22. As the cooling member 22 is in heat conducting connection to the cold side of the displacer housing 15, the cooling member 22 discharges heat to the displacer housing 15, said heat being transferred to the hot side of the displacer housing by means of the Stirling process.

The displacer housing 15 and the driving unit 2 are connected to each other via a pipe 24 that has a curved section 25. The pipe 24 ends in an end face of the displacer housing 15, that is, substantially perpendicular to the displacer axis 16. The pipe 24 ends in the driving unit 2 in a section of approximately 45° with basis in a peak 26 of the driving unit 2.

On the hot side of the displacer housing 15 a further cooling member 27 is ar- 5 ranged that is connected to a ventilator 28. The ventilator 28 generates an air flow through the cooling member 27 to discharge heat that has been transported from the cold side to the hot side by means of the cooling arrangement 3. o The two linear drives 8, 9 are made mirror-inflected, a central plane 30 being the symmetry plane. In the following, therefore only linear drive 8 will be explained in detail. The linear drive 8 comprises an inner stator 31 and outer stator 32. An annularly extending gap 33 is provided between the inner stator 31 and the outer stator 32, the armature 10 being inserted in said gap 33. In the gap5 33, the armature 10 carries permanent magnets 34.

The inner stator 31 accommodates a coil arrangement 35, that is, the inner stator 31 retains the coil arrangement 35 mechanically. At the same time, the inner stator 31 forms a path for the magnetic flux that is generated by the coil ar- o rangement 35, when the current is led through the coil arrangement 35. For this purpose, the coil arrangement 35 has two connections 36, 37. The current flows through the coil arrangement 35 in such a manner that the current entering through the connection 36 enters in the drawing plane (in relation to the view in Fig. 2), and is then led in a circle around the piston axis 7. If the coil arrange-5 ment 35 was viewed from the right, the current would flow anti-clockwise.

The inner stator 31 is made up of two parts 38, 39, which are made to be identical. In order to form the inner stator 31 , one of the two parts 38, 39 is lifted up or turned down by 180° and turned by 180° in relation to the piston axis 7. Then o the two parts 38, 39 are joined and connected to each other in the axial direction by a joining element 40, onto which a disc 41 is pressed. The joining element 40 is also connected to the connection 37 of the coil arrangement 35. Each of the parts 38, 39 has an annular recess 42, 43. When the two parts 38, 39 have been joined; the two recesses 42, 43 form an annular hollow, in which the coil arrangement 35 can be located. Each of the two parts 38, 39 comprises a radially internal through opening 44 and a radially external through opening 45 in an end face. Both through openings 44, 45 are connected to one another by means of a recess 46. In connection with the part 38, the internal through opening 44 serves the purpose of guiding the connection 37 through. In connection with the part 39, the radially external through opening 45 serves the purpose of guiding the connection 36 through.

Both parts 38, 39 are made as sintered elements. With sintered elements, the freedom with respect to shaping is relatively large. Further, without larger additional efforts, sintered material often has a good magnetic conductivity.

The outer stator 32 can also be a sintered element. The outer stator is made so that on the radial inside it is supported on a housing element 47. Together with a housing element 48 that surrounds the second linear drive 9, and an annular element 49 that connects the two housing elements 47, 48, the housing element 47 forms the housing. The pipe 24 that ends in the cylinder block 4 and is con- nected to the cylinder 29, and an electrical connection 50 that is connected to the connection 36 of the coil arrangement 35, are guided through the annular element 49.

In the axial direction, the outer stator is held in the housing element 47 by means of a radially yielding element 58. The radially yielding element can be an annular spring that clings to the inner wall of the housing element 47 because of its spring force. However, also a groove or a projection can be made in the inner wall of the housing element 47, so that the outer stator 32 can be fixed by means of a lock ring that opens radially outward.

The outer stator 32 comprises an axis-parallel groove 51 that forms an axially extending channel together with the housing element 47. The housing element 47 has an end face 51 that comprises deformations 53, through which radial grooves 54 are formed. The grooves 51 , 54 then form a channel, through which the gas can flow that is displaced or sucked in during a movement of the armature 10 in the gap 33. The gas can flow into an area 55 between the armature 10 and the cylinder block 4. Here, a sufficient buffer volume is available, so that a movement of the armature 10 is not impeded by the formation of a gas buffer.

The armature 10 is made as a hollow cylinder with a bottom wall 56. The bottom wall comprises several through openings 57. By means of the through openings 57, the gas that exists between the armature 10 and the inner stator 31 can escape into the chamber 55 during a movement of the armature in the direction of the inner stator 31. During a movement in the opposite direction, the gas can then be sucked in through the through openings 57.

As mentioned above, the driving unit 2 has two pistons 5, 6 that are driven in counterphase. This is achieved in a simple manner in that current flows through the coil arrangement 35 with a first current direction, while current flows through the coil arrangement 35' of the second linear motor 9 with the opposite current direction. Thus, the two coil arrangements 35, 35' can be supplied with current through the same electrical connection 50. This current is an AC current, which then automatically leads to the counterphase movement of the two pistons 5, 6. The current is then led out via the joining elements 40 through the front wall 52 of the housing elements 47, 48. This merely assumes that the joining element 40 is capable of conducting the current. In many cases, it may be favourable to provide an electrical conductor that is isolated in the circumferential direction, not shown in detail, in the joining element 40. In this case, it is avoided that the housing elements 47, 48 are energised. Uncritical, however, is a missing isolation, if the joining elements 40 are connected to a ground connection.

The cooling arrangement 1 works in accordance with the Stirling process as follows:

The Stirling cooling arrangement 1 works in accordance with the Stirling process. The Stirling process is a thermo-dynamic cyclic process consisting of two isothermal and two isochoric state changes of a gas. When the two pistons 5, 6 are moved towards each other, they take the gas from the cylinder 29 through the pipe 24 into the cooling unit 3. Here, it flows through the regenerator 20 that - absorbs heat from the gas. The temperature of the gas decreases with constant volume (1^st isochoric state change). The colder gas on the "cold side" of the displacer housing 15 absorbs heat from the outside. Its volume increases with constant temperature (1^st isothermal state change). The displacer 14 is displaced by the gas against the force of a spring in the direction of the driving unit 2. When the displacer 14 is moved back again, the gas is again led through the regenerator 20, where it absorbs the stored heat. The temperature increases. The volume remains constant (2^nd isochoric state change). On the hot side the gas then discharges heat to the environment at constant temperature and reducing volume (2^nd isothermal state change). The cyclic process starts over again. The required driving output is generated by the pistons 5, 6 displacing the gas into the cooling unit 3 and sucking it back from there again. In this con- nection, the pistons 5, 6 on the one side and the displacer 14 on the other side move at a phase offset of 90°.

Claims

Patent Claims

1. Stirling cooling arrangement with a driving unit (2) having a housing (47- 49) and at least one piston (5, 6) that is driven by a linear motor (8, 9) along a piston axis (7) in a cylinder (29), and a displacer unit (3) that is connected to the driving unit (2) via a gas-carrying connection (24) and comprises at least one displacer (14) that is movable in a displacer hous- ing (15) along a displacer axis (16), the linear motor (8, 9) comprising an armature (10, 11) that is connected to the piston (5, 6) and arranged between an inner stator (31) and an outer stator (32), and a coil arrangement (35, 35'), characterised in that in the radial direction the coil arrangement (35, 35') is arranged inside the armature (10, 11).

2. Cooling arrangement according to claim 1 , characterised in that the coil arrangement (35, 35') is accommodated in the inner stator (31).

3. Cooling arrangement according to claim 1 or 2, characterised in that the inner stator (31) is made of two parts (38, 39) arranged after one another along the piston axis (7).

4. Cooling arrangement according to claim 3, characterised in that the two parts (38, 39) have the same design.

5. Cooling arrangement according to one of the claims 1 to 4, characterised in that the inner stator (31) and/or the outer stator (32) are made as sintered element(s).

6. Cooling arrangement according to one of the claims 1 to 5, characterised in that the inner stator (31) and the housing (47-49) are connected by means of a joining element arrangement (40, 41) that comprises at least one deformation zone.

7. Cooling arrangement according to claim 6, characterised in that the joining element (40) is made as an electrical conductor that is connected to the coil arrangement (35).

8. Cooling arrangement according to claim 6 or 7, characterised in that the joining element arrangement (40, 41) comprises a joining element that is connected to the inside of the housing.

9. Cooling arrangement according to one of the claims 1 to 8, characterised in that the axial position of the outer stator in the housing (47-49) is fixed by means of a radially yielding element (58).

10. Cooling arrangement according to one of the claims 1 to 9, characterised in that the outer stator (32) is supported inside the housing (47-49) in the radial direction, at least one channel being provided between the outer stator (32) and the housing (47-49).

11. Cooling arrangement according to claim 10, characterised in that at least one section of the channel is formed by a groove (51) on the outer stator (32).

12. Cooling arrangement according to claim 10 or 11 , characterised in that at least one section of the channel is formed by a deformation (53) in an end face (52) of the housing (47-49).

13. Cooling arrangement according to one of the claims 1 to 12, characterised in that the armature (10) is formed as a cylinder with a bottom wall (56), the bottom wall (56) comprising at least one through opening (57).

14. Cooling arrangement according to one of the claims 1 to 13, characterised in that the driving unit (2) has two pistons (5, 6) arranged in a common cylinder (29), each piston being movable by a linear motor (8, 9).

15. Cooling arrangement according to claim 14, characterised in that the coil arrangements (35, 35') of the two linear motors (8, 9) are arranged so that with the same current supply they show oppositely directed effects.