Displacer assembly for a cryo-cooler

Abstract

Displacer assembly for a cryo-cooler comprises a displacer body 10 movable in a housing 23 of a displacer; a rod 22 transferring movement of a motor 14 to the displacer body; and wherein the rod is co

Description

The present invention relates to a displacer assembly for a cryo-cooler at a displacer including such a displacer assembly. Further, the present invention relates to a cryo-cooler comprising such a displacer. Cryo-coolers are designed to reach cryogenic temperatures below 120K. Common cryocoolers, such as Gifford-McMahon (GM-coolers) comprise a displacer having a displacer body in a housing that is movable within the housing from a first position to a second position in a reciprocating manner in order to displace a coolant such as helium. In order to generate the reciprocating movement of the displacer body in the housing of the displacer device, the rotational movement of an electromotor need to be transferred by a yoke into the linear movement. Movement of the yoke is transferred via a rod to the displacer body. Due to the movement of the yoke, a radial force is applied to the displacer body creating an increased wear of the seal of the first stage displacer. Hence, lifetime of the cryo-cooler is decreased and replacement of the seal in shorter intervals becomes necessary. It is an object of the present invention to provide a displacer assembly with an increased lifetime and improved reliability of the displacer seal. The problem is solved by a displacer assembly according to claim 1, a displacer device according to claim 9 and a cryo-cooler according to claim 10. The displacer assembly for a cryo-cooler according to the present invention comprises a displacer body configured to be movably arranged in a housing of a displacer device. In particular, the displacer body forms a first stage displacer of a cryo-cooler. The displacer assembly further comprises a rod to transfer movement of an electromotor to the displacer body. Thus, by the rod reciprocating movement of the displacer body inside the housing is facilitated. Therein, the rod is connected to the displacer body by a hinged connection. Contrary to the prior art, the rod is not fixedly connected to the displacer body. By the hinged connection between the rod and the displacer body radial force, applied by a yoke, is compensated and not transferred to the displacer body due to the hinged connection. Consequently, wear of a seal of the displacer body is reduced and the lifetime of the displacer is increased. Preferably, the hinged connection is provided by a ball connected to the rod and a correspondingly shaped recess in the displacer body or vice versa, i. e. a recess shaped in the rod and a ball provided by the displacer body. Therein, the ball is arranged in the recess. By arranging the ball in the recess, movement between the rod and the displacer or pivoting movement relative between the displacer body and the rod is feasible in order to mitigate radial forces applied by the yoke of the displacer device. Instead of a ball, a cylinder can be provided and connected to the rod and a correspondingly shaped recess in the displacer body is configured to receive the cylinder in order to form the hinged connection. Alternatively the cylinder is provided by the displacer body and a corresponding recess is arranged in the rod receiving the cylinder. Since by the yoke radial force is only generated in two opposite directions, movability of the hinged connection provided by a cylinder is sufficient in order to mitigate radial forces in these two directions. Preferably, the recess is at least partially closed by a cap element connected to the displacer body. Hence, the recess is at least partially closed by the cap element thereby maintaining the ball or cylinder of the rod in the recess of the displacer body. Consequently, for assembly, first the ball or cylinder can be arranged in the recess and subsequently the cap element can be mounted or connected to the displacer body thereby reducing the size of the opening of the recess such that the ball or cylinder cannot slip out of the recess anymore. Preferably, the rod comprises a transfer element wherein the transfer element is connected to the rod by a threaded connection, wherein the hinged connection is at least in part provided by the transfer element. Hence, rod and displacer body can be either connected by the hinged connection. Consequently, first, the hinged connection can be established between the displacer body and the transfer element and subsequently the rod can be connected to the transfer element via the threaded connection. Thus, connection between an electromotor and the displacer can be built in a reasonable manner simplifying service and disassembly of the displacer device. Preferably, the displacer assembly comprises a cap element connected to the displacer body in particular by a threaded connection, wherein the recess is built by the cap element. Hence, connection between the cap element and displacer body is releasable and the hinged connection between the rod and the displacer body is at least in part provided by the cap element. Preferably, the displacer body forms a first stage displacer, wherein at an end of the displacer body opposite to the rod, a connection element is disposed to be connected to a second stage displacer, wherein the connection element is built as snap-fit connection. Hence, the second stage displacer can be connected to the displacer body of the first stage displacer by a snap-fit connection thereby simplifying assembly and disassembly of the displacer assembly. Preferably, the snip-fit connection comprises a spherical snap-element connected to the displacer body of the first stage displacer and a correspondingly shaped recess in the second stage displacer body. Preferably, the recess in the second stage displacer body is provided in a second cap element of the second stage displacer body. Preferably the second cap element is connected to the second stage displacer body by a threaded connection. Hence, either by the snap-fit connection or the threaded connection between the second cap element of the second stage displacer body, the connection between the first stage displacer body and the second stage displacer body is releasable. In an aspect of the present invention a displacer device for a cryo-cooler is provided comprising a housing and a displacer assembly as described before. Further the displacer device comprises an electromotor and a yoke connected to the rod in order to transfer rotational movement of the electromotor into reciprocating movement of the displacer body. In an aspect of the present invention a cryo-cooler is provided comprising a displacer device as described before. In the following the present invention is described in more detail with reference to the accompanying figures. The figures show: Figure 1 a first embodiment of the displacer device according to the present invention, Figure 2 a detailed view of the displacer device of Figure 1 and Figure 3 another embodiment of the displacer assembly of the present invention. In the following it is referred to Figures 1 and 2. The displacer device according to the present invention comprises a first stage displacer body 10, disposed in a housing. Therein, the first stage displacer body 10 is moveable within the housing 12 in a reciprocating manner. Further, the displacer device comprises an electromotor 14 schematically indicated in Figure 1. The electromotor 14 comprises a rotating driveshaft 16, wherein a cam element 18 is connected to the driveshaft 16 interacting with a yoke 20 in order to transfer the rotating movement of the electromotor 14 into a reciprocating movement of the first stage displacer body 10. Therein, the reciprocating movement of the yoke 20 is transferred to the first stage displacer body 10 by a rod 22. The rod 22 is supported by a first bearing 30 and a second bearing 32. In addition a seal 28 surrounds the rod 22 in order to provide a fluid or gas barrier between the area of the electromotor 14 and the internal volume of the housing 12. At a first end 33 of the first stage displayer body 10 a seal assembly is provided. The seal assembly comprises an elastomeric O-ring 36 surrounded by a rigid seal element 34.. In the prior art, the seal element 34 is prone to wear due to radial forces applied by the yoke 20. However, according to the preset invention the rod 22 is connected to the first stage displacer body 10 by a hinged connection 24 such that the rod 22 can pivot around the connection between the rod and the displacer body. Therein, the hinged connection 24 comprises in the example of the figures a ball 25 connected to the rod 22 and a correspondingly shaped recess 26 in the first stage displacer body 10 in particular at the first end 33 of the first stage displacer body 10. Thus, radial forces are mitigated by the hinged connection 24 and excessive wear of the seal element 34 can be prevented. Instead of a ball 25, also a cylinder could be implemented provided a hinged connection between the rod 22 and the first stage displacer body 10. Therein, in the embodiments shown in Figures 1 and 2, the recess 26 is partially closed by a first cap element 38, wherein by the first cap element 38 connected to the first end 33 of the first stage displacer body 10, the ball 25 is maintained in the recess 26. Referring to Figure 3 showing a different embodiment of the displacer assembly, wherein same or similar features are indicated by the same reference signs. In the embodiment of Figure 3, the first stage displacer body 10 comprises a first cap element 38', wherein the recess 26 is provided by the first cap element 38. Further, the ball 24 is connected to the rod 22 by a transfer element 44, wherein the connection between the transfer element 44 and the rod 22 is provided by a threaded connection. Also the first cap element 38 may be connected to the first stage displacer body 10 via a threaded connection 40. Furthermore, the first stage displacer body 10 comprises a second end 35 opposite to the first end 33, wherein a first end 57 of a second stage displacer 46 is connected. Therein, connection of the second stage displacer body 46 is provided by a snap-fit connection provided by spherical elements 50 separated by a gap 52 in order to create flexibility to allow snap-in of the snap elements 50 into a recess 56 that is correspondingly shaped. Therein, the recess 56 may be provided by a second cap element 48 connected to the first end 37 of the second stage displacer body 46 by a threaded connection 54. Hence, the second stage displacer body 46 can be easily and releasably connected to the first stage displacer body 10. In addition, due to the spherical shaped snap-fit elements 50 radial forces or tilting of the first stage displacer body 10 is not transferred to the second stage displacer body 46 reducing radial forces applied to the second stage displacer body 46. Hence, by the hinged connection between the rod 22 and the first stage displacer body 10, radial forces a compensated or mitigated. Thus, wear of the seal element 34 is reduced and lifetime of the displacer device is increased. Reference list 10 first stage displacer body 12 housing 14 electromotor 15 drive shaft 18 cam element 20 yoke 22 rod 24 hinged connection 25 ball 26 recess 28 seal 30 first bearing 32 second bearing 33 first end 34 seal element 35 second end 36 o-ring 37 first end 38 cap element 38' cap element 40 threaded connection 44 transfer element 46 second stage displacer body 48 second cap element 50 snap-fit element 52 gap 54 threaded connection 56 recess

Claims

1. Displacer assembly for a cryo-cooler comprising:a displacer body to be movably arranged in a housing of a displacer,a rod to transfer a moment of a motor to the displacer body,wherein the rod is connected to the displacer body by a hinged connection.

2. Displacer assembly according to claim 1, wherein the hinged connection is provided by a ball or cylinder connected to the rod and a correspondingly shaped recess in the displacer body, wherein the ball or cylinder is arranged in the recess.

3. Displacer assembly according to claim 2, wherein the recess is at least partially closed by a cap element connected to the displacer body.

4. Displacer assembly according to any of claim 1 to 3, wherein the rod comprises a transfer element, wherein the transfer element is connected to the rod via a threaded connection, wherein the hinged connection is at least in part provided by the transfer element.

5. Displacer assembly according to any of claim 1 to 4, comprising a cap element connected to the displacer body, wherein the recess is built by the cap element.

6. Displacer assembly according to any of claim 1 to 5, wherein the displacer body forms a first stage displacer, wherein at an end of the displacer body opposite to the rod, a connection element is disposed to be connected to a second stage displacer, wherein the connection element is built as snap-fit connection.

7. Displacer assembly according to claim 6, wherein the snap-fit connection comprises a spherical snap-element connected to the displacer body and a correspondingly shaped recess in a second stage displacer body.

8. Displacer assembly according to claim 7, wherein the recess in the second stage displacer body is provided in a second cap element of the second stage displacer body.

9. Displacer device of a cryocooler comprising a housing, a displacer assembly according to any of claim 1 to 8, an electromotor and a yoke connected to the rod in order to transfer rotational movement of the electromotor into reciprocating movement of the displacer body.

10. Cryo-cooler comprising a displacer device according to claim 9.

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