Discussion of the Related Art [0002] Generally, a cooler is an apparatus for generating cooling effect through the processes of compression, expansion, etc. of working fluid, such as helium, hydrogen or the like.

Such a cooler is used to cool small-sized electronic goods or superconductor material to an ultra low temperature.

[0003] A heat regenerating type cooler, such as Stirling cooler and GM cooler is mainly used as a cooler. In these coolers, reliability is enhanced by lowering the operation speed, changing the shape of a rubbed sealing material or removing moving parts.

[0004] Meanwhile, it is required to develop a cryogenic cooler with a high reliability so that there is no need to repair for a long period of time. As a result, the lubricationless pulse tube cooler is developed. The lubricationless pulse tube cooler is an apparatus to implement cryogenic refrigeration at an open end of a tube by using the principle in which a gas having a constant temperature is periodically injected into the tube one end of which is closed and thus the pressure is changed. If the turbulence component in the gas flow is small, a very great temperature gradient is obtained.

[0005] FIG. 1 illustrates a cooler according to the conventional art. Referring to FIG. 1, a cooler includes a driving part 100, a radiating part 200 and a refrigerating part 300 as a whole. The driving part 100 compresses a coolant gas through linear reciprocating movement of a piston 140 by electromagnetic interaction of a linear motor 130 into high temperature and pressure state. The driving part 100 includes a shell tube 120, a linear motor 130, a piston 140, a cylinder 150, a leaf spring 160 and a spring support 170. The shell tube 120 has a space therein, and is fixedly coupled with a frame 110 with concentrically circled with inner/outer radiating parts 210,220 having a displacer 310 inserted therein. The linear motor 130 includes a stator 130a and an armature 130b, and is installed in the shell tube 120. The piston 140 is fixed to one end of the armature 130b of the linear motor 130 so that linear reciprocating movement is made by the electromagnetic mutual interaction of the linear motor 130. The cylinder 150 is fixedly coupled with a frame 110 at the center in the inside the frame 110 such that the linear reciprocating movement of the piston 140 that is inserted therein with concentric to the inner radiating part 210 is evenly transmitted to the displacer 310. The leaf spring 160 is fixedly supported at an end of a displacer rod 320 such that the position of the displacer rod 320 inserted into the piston 140 is concentric with the piston 140 and the inner radiating part 210. One end of the spring support 170 is fixed at the shell tube 120 so as to fixedly support the leaf spring 160 and the other end is fixedly coupled with the leaf spring 160.

[0006] The radiator part 200 includes the inner radiating part 210 fixed to the frame 110 of the external circumferential surface of the displacer 310 to absorb the heat of the coolant gas compressed in high temperature and high pressure by the piston 140, and the outer radiating part 220 fixed to the external circumferential surface of the inner radiating part 210, for radiating the heat of the coolant gas transmitted from the inner radiating part 210 to the outside of the cooler 10.

[0007] The refrigerator part 300 includes the displacer 310, a regenerator 330 and a cooling side part 350. The displacer 310 is formed as one body with the displacer rod 320 and fixedly inserted into the inner radiating part 210 to perform the linear reciprocating movement within the elastic deformation range of the leaf spring 160 fixed at one end of the displacer rod 320 through compression of the coolant gas pressed by the piston 140.

The regenerator 330 coupled with the displacer 310 accumulates the sensible heat of the coolant gas in high temperature and high pressure state and compressed and delivered into the displacer 310 by the piston 140. After the coolant gas is expanded, the regenerator 330 transmits the heat to the coolant gas in a low temperature expanded in an expansion space thereby compensating for the temperature of the coolant gas. The cooling side part 350 is provided at the position which is an expansion space (P) away from the regenerator 330. The coolant gas passing through the regenerator 330 is expanded in the expansion space to exchange heat with the outside to lower its temperature.

[0008] The operation of the cooler 1 constructed as above is described hereinafter. In the linear motor 130, electromagnetic interaction of the stator 130a and the armature 130b allows the armature 130b to move linearly. This linear movement also makes the piston 140 fixed at one end of the armature 130b to move linearly. At this time, the linear movement of the piston 140 allows the coolant gas, such as helium or hydrogen stored in the compression space, to be compressed. A portion of the compressed coolant gas is released out of the cooler 10 via the radiating part 200, and the other portion is injected into the regenerator 330 through the displacer 310. At this time, the displacer 310 linearly moves into the expansion space by the compressed coolant gas. The compressed gas injected into the regenerator 330 delivers heat to store thermal energy while the gas passes through the regenerator 330, and moves into the expansion space.

At this time, the compressive force of the piston 140 is reduced, so that the displacer 310 moves into the compression space through linear reciprocating movement. Thereafter, the coolant gas that has moved into the expansion space is cooled to an ultra low temperature state. The expanded coolant gas in low temperature state is given the accumulated heat while passing through the regenerator 330 into the compression space. As described above, the cooler performs cooling operation by repeating the above-described operation cycle.

[0009] As shown in FIG. 2, the regenerator 330 coupled with the displacer 310 includes a housing 340 concentrically coupled with a cylinder of the displacer 310, a heat accumulation member 344 inserted to the inside of the housing 340, and an end cap 348 adhered to a front end of the housing 340. The heat accumulation member 344 contacts with the coolant gas to exchange heat. The heat accumulation member 344 receives energy from the coolant gas to store the energy and return it back. So, it is desired that the heat accumulation member 344 has a large heat exchanging area and a great specific heat, and is made of the material that has a low heat transfer coefficient.

[0010] The heat accumulation member 344 is made in a soft powder type, a small ball type or a random wire type.

Specifically, material of each type of the heat accumulation members 344 depends on the temperature band in which the cooler is used. In general, the random wire type heat accumulation member made of stainless material is usually employed for the regenerator of the cooler used for cryogenic refrigeration of about 77 °K. The random wire type heat accumulation member is made in the form of a bundle of fine wires. Accordingly, in order to insert the random wire heat accumulation member into the regenerator, the random wire heat accumulation member is made using a die considering its structural characteristic and inserted into the housing.

[0011] However, the regenerator to which the conventional random wire type heat accumulation member is applied, is high in cost and takes too much time to allow the random wire type heat accumulation member that has a random shape to have a concrete shape. Since the random wire is bundled, the heat transfer is so easy that the efficiency of the regenerator is lowered.

[0012] In addition, while the random wire type heat accumulation member is inserted into the housing of the regenerator, the heat accumulation members are not uniformly pressed throughout the whole area of the housing at the same interval. In other words, since the random wires having a specific shape, inserted first into the housing are pushed by a portion of the random wires inserted later into the housing, the random wires at the rear portion of the inside of the housing are highly dense and the random wires at the front portion of the inside of the housing are low dense. Therefore, the uniform ventilation is not maintained throughout the whole housing, thereby the cooler performance is lowered.

SUMMARY OF THE INVENTION [0013] Accordingly, the present invention is directed to a regenerator for a cooler that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[0014] An object of the present invention is to provide a regenerator for a cooler provided with a heat accumulation member including a plurality of stacked mats made in a housing by a vacuum sintering method.

[0015] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0016] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a regenerator for a cooler includes: a housing coupled to a displacer and having a space therein; a heat accumulation member in which a plurality of mats provided from a base mat prepared in advance are inserted into the housing; and an end cap adhered to a front end of the housing [0017] The plurality of mats are made of random wire material and stacked in series in the housing. The thickness of the mat or the number of the mats inserted into the housing is varied depending on heat transfer rate and/or ventilation inside the housing.

[0018] In another aspect of the present invention, a heat accumulation member inserted into a regenerator for a cooler comprises a plurality of mats stacked inside a housing.

[0019] The plurality of mats are made of random wires that are same material.

[0020] In another aspect of the present invention, a method of forming a heat accumulation member comprises the steps of: (a) forming a base mat by vacuum-sintering random wires pressed in advance; (b) forming a plurality of mats having a specific shape by punching the base mat; and (c) inserting the plurality of mats into a housing in series.

[0021] The thickness of the mat is varied depending on intensity of the pressing step. At least one mat is formed from the base mat in the step (b). The number of the mats inserted into the hosing is varied depending on closeness between the mats.

The shape of the mats is one selected from the group consisting of a circle, a rectangle and a polygon.

[0022] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS [0023] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment (s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: [0024] FIG. 1 illustrates a cooler according to the conventional art.

[0025] FIG. 2 illustrates a regenerator for the cooler shown in FIG. 1.

[0026] FIG. 3 illustrates a regenerator for a cooler according to a preferred embodiment of the present invention.

[0027] FIG. 4 is a flow chart to illustrate a method of adapting a heat accumulation member to a regenerator for a cooler according to a preferred embodiment of the present invention.

[0028] FIGS. 5 and 6 are diagrams to illustrate a method of adapting a heat accumulation member to a regenerator for a cooler according to another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0029] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0030] FIG. 3 illustrates a regenerator for a cooler according to a preferred embodiment of the present invention.

Referring to FIG. 3, a regenerator for a cooler according to an embodiment of the present invention includes a housing 42 coupled to a displacer 32 and having a space therein, a heat accumulation member 44 inserted into the housing 42, and an end cap 46 adhered to a front end of the housing 42.

[0031] The heat accumulation member 44 is comprised of a plurality of mats that are processed in a specific shape. The plurality of mats are made of random wire materials, and stacked in series in the housing 42. The plurality of the mats are prepared to match the diameter of the housing 42 by a punching process. The thickness of each of the mats is varied depending on a heat transfer rate and/or ventilation in the inside of the housing 42. In other words, in case the heat transfer rate and/or the ventilation is not adequate, then thin mats are inserted into the housing. The number of the mats inserted into the housing also may be varied depending on the heat transfer rate and/or the ventilation in the inside the housing 42. If the heat transfer rate and/or the ventilation is not adequate, the less number of mats are inserted into the housing 42. As described above, the heat transfer rate and/or the ventilation in the inside the housing 42 can be adjusted using the thickness of the mat and the number of the mats such that the best heat transfer rate and/or the optimum ventilation can be maintained in the inside of the housing 42.

[0032] In the case of the conventional art in which the random wire type heat accumulation member having a specific shape is inserted into the housing, the random wires inserted first into the housing are pushed by the random wires inserted later into the housing, so that the uniform ventilation is not implemented in the whole housing.

[0033] However, in the present invention, the mat inserted first into the housing are not pushed by the mat inserted later into the housing, instead the plurality of the mats are stacked in series in the housing 42, thereby the uniform ventilation is realized in the whole housing.

[0034] A method of forming a heat accumulation member of a regenerator for a cooler is described below. FIG. 4 is a flow chart to illustrate a method of employing a heat accumulation member to a regenerator for a cooler according to an embodiment of the present invention. FIGS. 5 and 6 are schematic views to illustrate a method of employing a heat accumulation member to a regenerator for a cooler according to anther embodiment of the present invention. Specifically, FIG. 5 is a schematic view to illustrate a method of forming a plurality of mats from the random wire type heat accumulation member and FIG. 6 is a schematic view to illustrate a method of inserting a plurality of the mats into the housing.

[0035] First, easily available random wires are pressed by a press machine (S511). Here, the press machine used is a general press machine. When the pressing of the random wires is performed, the heat transfer rate and/or ventilation in the inside the housing should be considered. In other words, after the heat transfer rate and/or ventilation inside the housing are grasped in advance, the press intensity for the random wires is controlled according to the grasped parameters to obtain the optimal thickness.

[0036] As shown in FIG. 5, the pressed random wires are vacuum-sintered in a sintering furnace to form a base mat 47.

(S513). Here, the sintering furnace can be any one of the conventional machines that can perform vacuum sintering. It is desired that the base mat 47 should have a greater area if possible. This is because more number of mats can be made from the base mat when the base mat has the greater area and thus the production cost can be reduced.

[0037] The base mat 47 formed by the above-mentioned vacuum sintering process is punched to separate a plurality of mats 48 having a constant shape from the base mat 47 (S515). Here, the mats may be made in a shape of circle, rectangle or polygon, and the shape of the mats is varied based on the shape of the housing.

Preferably, more mats are made from the base mat if possible, and the size of the mats should be substantially the same as the size of the inside of the housing. More preferably, the size of the mats is slightly less than the size of the base mat if possible, so that the mats are not placed tightly in the housing or move loosely in the housing when inserting the mats into the housing.

[0038] As shown in FIG. 6, the plurality of the mats 48 separated from the base mat 47 are inserted in series into the housing 42 prepared in advance (S517). In this case, the number of the mats inserted into the housing 42 may be varied depending on the heat transfer rate and/or the ventilation in the housing 42. In the other words, in case the heat transfer rate and/or the bad ventilation is not adequate, the less number of mats are inserted into the housing 42. Thus, the closeness between the mats 48 and 48'is adjusted according to the heat transfer rate and/or the ventilation in the housing so that the optimal heat transfer rate and/or the optimal ventilation are maintained.

[0039] In the case of the conventional art in which random wires are pressed as one body and then inserted into a housing, heat transfer through the inside of the housing happened easily, and thus much loss in the heat transfer is resulted.

[0040] However, in the present invention, since the plurality of mats 48 are sequentially inserted into the housing 42 in series, boundary layers between mats 48 and 48'are formed to delay the heat transfer, making possible to decrease the loss in the heat transfer.

[0041] As described above, according to the regenerator for the cooler of the present invention, a plurality of mats are stacked in the housing in series, so that the uniform ventilation is realized throughout the housing to improve the cooling efficiency of the cooler.

[0042] In addition, boundary layers are formed between neighboring mats, so that the heat transfer is delayed to reduce the loss in the heat transfer.

[0043] According to the method of forming heat accumulation member of a regenerator for a cooler of the present invention, a plurality of mats are made once from the base mat formed by vacuum sintering process to reduce the production cost.

[0044] A plurality of the mats can be made to be matched with the shape of the housing, so that the regenerator for a cooler can be applied more widely.

[0045] In addition, the thickness of the mats and the number of the mats inserted into the housing can be determined according to the heat transfer rate and/or ventilation of the housing, such that the optimal heat transfer rate and/or the optimal ventilation are always realized.

[0046] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.