Abstract:
An integrated piston operating assembly for a linear compressor and a method for manufacturing the same are provided. The integrated piston operating assembly includes a piston coupling boss coupled to a piston, a plurality of magnets disposed in a cylindrical arrangement concentric with the piston coupling boss, and a linking member formed of a resin for connecting and thus integrating the piston coupling boss with the plurality of magnets. The magnets and piston coupling boss are secured to the linking member as the linking member is injection molded. By integrating the piston operating assembly of the linear compressor, geometric and assembling tolerances are improved, while deterioration of persistence due to processing and assembling processes is prevented.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a linear compressor for compressing refrigerant by using a reciprocating piston. More particularly, the present invention relates to a piston operating assembly for the linear compressor and a method for manufacturing the same. 
     2. Description of the Prior Art 
     Generally, a linear compressor compresses a refrigerant by reciprocating a piston with a changing magnetic field. Such a compressor is shown in FIGS. 1 through 3. 
     As shown in the drawings, the linear compressor includes a cylinder portion  10 , a piston  20 , a piston operating assembly  30  and an external lamination portion  40 , all of which are disposed in a chamber  1 . 
     As shown in FIG. 2, the piston operating assembly  30  includes a magnet holder  32 , which is a hollow cylinder having a hole formed in an outer circumference thereof, a magnet  33  inserted in the hole of the magnet holder  32 , a magnet cover  35  press fit on the outer circumference of the magnet holder  32  to prevent any accidental separation of the magnet  33  from the magnet holder  32 , and a linking member  31  having a hole formed on the center portion thereof for receiving the piston  20 . The linking member  31  is connected to one end of the magnet holder  32 . 
     The piston  20  is a hollow cylinder, having one end attached to a suction valve  25  and the other end coupled to the linking member  31  of the piston operating assembly  30 . The piston  20  can be secured to the linking member  31  by one of a number of methods, such as welding, etc. 
     The cylinder portion  10  includes a cylinder  11 , in which the piston  20  is received for reciprocating movement, an internal lamination  13  inserted about the outer circumference of the cylinder  11 , and a coil  15  wound about the center portion of the internal lamination  13 . 
     An external lamination portion  40  includes an external lamination  41  formed a predetermined distance from the internal lamination  13 , a housing  43  for supporting the external lamination  41 , and a frame  42 . 
     The operation of the linear compressor constructed as above will be described below. 
     First, when Alternating Current (AC) voltage is applied to the coil  15  of the internal lamination  13 , a magnetic field having N-S poles is generated between the internal and external laminations  13  and  41 , respectively. Due to the presence of the permanent magnet  33  disposed between the internal and external laminations  13  and  41 , a force in an axial direction is generated according to Flemming&#39;s left-hand rule. As the N-S poles of the magnet  33  are varied, the magnet  33  reciprocates, and accordingly, the piston  20  also reciprocates. 
     Next, a refrigerant is introduced into the chamber  1  through an inlet tube  3  by the reciprocating movement of the piston  20 . The refrigerant flows through the piston  20  and the suction valve  25  and into a compressing chamber  5 . When the refrigerant is compressed in the compressing chamber  5 , the refrigerant is then discharged through an outlet tube  7 . 
     The conventional linear compressor, however, has several shortcomings. First, some parts of the compressor require forceful coupling methods, such as force fit, welding, etc., to secure the parts together. For example, the piston  20  and linking member  31  are welded together, as are the linking member  31  and the magnet holder  32 . Further, the magnet holder  32  must undergo processes like cutting, punching and welding. The force of the couplings and heat distortion of the respective parts produce an internal stress that affects the integrity of the parts. Further, the conventional linear compressor has a complex and lengthy assembly process, while producing a high possibility of defective products. As a result, productivity and throughput are deteriorated. 
     The manufacturing process of the magnet holder  32  is described in greater detail with reference to FIG.  3 . First, a metal plate  32   a  of a predetermined size is prepared. Then, the metal plate  32   a  undergoes a rolling process. Next, the ends of the metal plate  32   a  are welded together to form a hollow cylinder  32   b . The hollow cylinder  32   b  is then punched to form a plurality of holes  32   c  therein. Finally, in order to prevent any accidental separation of the magnets  33  from the hollow cylinder  32   b , a magnet cover  35  is force fit onto the outer circumference of the hollow cylinder  32   b.    
     In the conventional linear compressor, the different sizes of and deviations among the magnets  33  make it difficult to press fit or force fit the magnet cover  35 . When the magnet cover  35  is forcefully press fit, without taking into consideration the different sizes of the magnets  33 , those magnets  33  that are more fragile can be broken. 
     Further, according to a conventional way of assembling the piston operating assembly  30  of the linear compressor, an error in concentricity occurs when the piston  20  and the magnet holder  32  are welded to the linking member  31 , and errors in circularity and concentricity occur when press fitting the magnet  33 , which is press fit in the magnet holder  32 , in the magnet cover  35 . Accordingly, productivity and throughput deteriorate. Further, since there are numerous parts that must be assembled together, all of which affect the geometric tolerance of the piston operating assembly  30 , the assembly tolerance is increased due to an accumulation of the tolerances of the respective parts. When the geometric tolerance and the assembly tolerance exceed a predetermined degree, the same becomes a defect factor, which can cause problems, such as a malfunction of the linear compressor, etc. 
     In addition, in the conventional method of assembling the linear compressor, a non-magnetic metal is used to form the magnet holder  32 , thereby preventing a leakage of the magnetic force from the magnet  33 . The non-magnetic metal of the conventional linear compressor, however, has a relatively higher conductivity, which hinders a complete absence of the magnetic force leakage from the magnet  33 . Accordingly, due to the leakage of the magnetic force from the magnet  33 , the compression efficiency of the linear compressor is negatively affected. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome the above-mentioned problems of the prior art. Accordingly, it is an object of the present invention to provide a piston operating assembly for a linear compressor having a piston coupling boss coupled with a piston, a plurality of magnets, and a linking member. The linking member connects the piston coupling boss with the magnets, all of which are integrally secured to the linking member when the linking member is injection molded. Thus, the integrated piston operating assembly has improved geometric and assembling tolerances and no deterioration of persistence. 
     It is another object of the present invention to provide a method for manufacturing a piston operating assembly for a linear compressor. In the present method the processes are simplified while resulting in a higher productivity. 
     The above object is accomplished by a piston operating assembly of a linear compressor for compressing a refrigerant with a piston that linearly reciprocates due to a magnetic field. The piston operating assembly includes a piston coupling boss for coupling to the piston, a plurality of magnets disposed in a cylindrical arrangement concentric with respect to the piston coupling boss, and a linking member for connecting and thus integrating the piston coupling boss and the plurality of magnets. The linking member is formed of an injection molded resin, and the piston coupling boss and the magnets are coupled to the linking member at the same time that the linking member is injection molded. 
     Each of the magnets has a stepped portion that is formed along a boundary thereof. 
     The above object is also accomplished by a method for manufacturing a piston operating assembly for a linear compressor. The method includes the steps of preparing a plurality of magnets and a piston coupling boss, assembling the plurality of magnets and the piston coupling boss in a core mold, and mounting the core mold in an injection molding machine. The method further includes injecting a molding resin into the core mold to form an integrated piston operating assembly, with the plurality of magnets and the piston coupling boss fixed in the molding resin. The completed integrated piston operating assembly is then separated from the core mold, once the injection molding is finished. 
     Accordingly, the piston operating assembly of the linear compressor has improved geometric and assembling tolerances and persistence. In addition, the method of manufacturing such piston operating assembly is greatly simplified and results in an increase in productivity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and other features and advantages of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a sectional view of a conventional linear compressor; 
     FIG. 2 is a sectional view of a piston operating assembly for the conventional linear compressor of FIG. 1; 
     FIG. 3 illustrates the steps for manufacturing a conventional magnet holder for the conventional linear compressor of FIG. 1; 
     FIG. 4 is a plan view of a plurality of magnets, which are employed in a piston operating assembly for a linear compressor, in accordance with the present invention; 
     FIG. 5 is a sectional view of a piston coupling boss, which is employed in the piston operating assembly for the linear compressor, in accordance with the present invention; 
     FIG. 6 is a perspective view of the piston operating assembly for the linear compressor, in accordance with the present invention; 
     FIG. 7A is a plan view of a core mold, which is used to manufacture the piston operating assembly of FIG. 6; 
     FIG. 7B is a cross-sectional view taken generally along the line I—I of FIG. 7A; 
     FIG. 8 is a sectional view of the core mold of FIGS. 7A and 7B shown mounted in an injection molding machine during manufacture of the piston operating assembly of FIG. 6; and 
     FIG. 9 is a flow chart illustrating the steps in a method for manufacturing the piston operating assembly of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of the present invention will be described below with reference to the accompanying drawings. 
     FIG. 6 is a perspective view of a piston operating assembly  50  for a linear compressor in accordance with the present invention. 
     The piston operating assembly  50  includes a plurality of magnets  51  disposed in a cylindrical arrangement and spaced from each other at equal intervals, a hollow piston coupling boss  52  concentrically disposed within the cylindrical arrangement, and a linking member  53  for connecting the cylindrical arrangement to an end of the piston coupling boss  52 . The magnets  51 , piston coupling boss  52 , and linking member  53  are preferably secured together simultaneously with the formation of the linking member  53 . 
     In order to compress a refrigerant, a piston reciprocates in the cylinder of a linear compressor. The piston operating assembly, which moves the piston within the cylinder of the compressor, includes a piston coupling boss  52  that has a screw portion  52   b  (FIG.  5 ). The screw portion  52   b  includes threads that engage the threads formed at one end of the piston. The integrated piston operating assembly is preferably injection molded using a molding resin. As shown in FIG. 5, in order to increase the coupling force between the piston coupling boss  52  and the molding resin, a female screw portion  52   b  is formed in one end of the piston coupling boss  52 , while a raised portion  52   a  is formed at the opposite end. It is further preferable that the piston coupling boss  52  is made of a brass. 
     Because of the changes of magnetic field between the internal and external laminations  13  and  41 , the magnets  51  cause the piston to reciprocate. Each magnet  51  has a stepped portion formed around its boundary. As shown in FIG. 4, each magnet  51  is a square plate having a predetermined radius of curvature. The two opposite sides of the magnet  51  are processed to have an L-shaped cross-section, while the other two opposite sides of the magnet  51  are processed to have an upended L-shaped cross-section. By processing the sides of the magnet  51  to have L-shaped and upended L-shaped cross-sections, the coupling force between the piston operating assembly  50  and the molding resin is increased when the piston operating assembly  50  is integrally formed by injection molding. 
     The molding resin is preferably a non-magnetic and non-conductive thermosetting resin, such as a bulk molding compound composed of polyester as a main material, glass fiber as a reinforcing material, filler, and catalyst, etc. 
     In the piston operating assembly  50  for the linear compressor of the present invention, since the piston coupling boss  52  and the plurality of magnets  51  are integrally formed in the integrated molding resin, which forms the linking member  53 , the separate process steps of assembling the magnets  51  and press fitting the magnet cover  35  are no longer required. In addition, the assembly of the piston is completed by screwing the piston onto the piston coupling boss  52 . 
     The integrated piston operating assembly  50  reciprocates due to a changing magnetic field, which is generated by the internal lamination  13  and coil  15  disposed within the cylindrical arrangement of magnets  51 , and the external lamination  41  disposed outside the cylindrical arrangement of magnets  51 . When the piston operating assembly  50  reciprocates, the piston, which is coupled with the piston operating assembly  50 , also reciprocates linearly within the cylinder. Accordingly, the refrigerant is drawn into the compressing chamber and then compressed. 
     A method for manufacturing the piston operating assembly  50  for the linear compressor in accordance with the preferred embodiment of the present invention will be described below with reference to FIGS. 7-9. 
     As illustrated in FIG. 9, the method for manufacturing the integrated piston operating assembly  50  includes the steps of preparing a plurality of magnets  51  and a piston coupling boss  52  (step S 100 ), assembling the plurality of magnets  51  and the piston coupling boss  52  in a core mold  60  (FIGS. 7A and 7B) and mounting the core mold  60  in an injection molding machine (step S 200 ), integrally injection molding the piston operating assembly  50  with the plurality of magnets  51  and the piston coupling boss  52  (step S 300 ), and then separating the completed the piston operating assembly  50  for the linear compressor from the core mold  60  when the molding process is finished (step S 400 ). 
     In the preparation step S 100 , the magnets  51  and the piston coupling boss  52 , which are made by separate processes, are prepared for assembly into the core mold  60 . In this embodiment, one piston coupling boss  52  and eight magnets  51  are used. Accordingly, eight magnets  51  and one piston coupling boss  52  are prepared. The magnets  51  are initially non-magnetized magnets. 
     In the mold mounting step S 200 , the eight magnets  51  and the piston coupling boss  52  are assembled in the core mold  60 . The core mold  60  is then mounted between an upper mold  70  and a lower mold  80  of the injection molding machine. The core mold  60  has a plurality of linear projections  61  (FIGS. 7A and 7B) that are formed on the outer circumference thereof. The linear projections  61  extend parallel to the axis of the core mold  60  and are spaced apart at equal intervals to accommodate the magnets  51 . In order to magnetize the non-magnetic magnets  51 , additional magnets  62  are disposed within the core mold  60 . Further, a screw portion is formed at the center of the core mold  60 , to secure the piston coupling boss  52 . The piston operating assembly  50  of the present invention has less geometric error, for example, less error in concentricity, since a relatively shorter piston coupling boss  52  is secured thereto by injection molding. In contrast, in a conventional piston operating assembly, a longer piston is welded onto the linking member. 
     After the core mold  60  is mounted in the injection molding machine, the injection molding process begins. A molding resin is injected in the direction indicated by an arrow P in FIG. 8 into the core mold  60 . The molding resin fills in the area of the core mold  60  that is indicated by the cross-hatching in FIG. 8 to surround the piston coupling boss  52  and the magnets  51 . As a result, the integrated piston operating assembly  50  is formed at step S 300 . Gravity helps to draw the molding resin down through the gaps defined between the plurality of projections  61  of the core mold  60  to surround the magnets  51 , so that the magnets  51  are fixedly secured by the molding resin. 
     After a predetermined time period, the molding resin solidifies and cools. At step S 400  the completed piston operating assembly  50  is then removed from between the upper and lower molds  70  and  80 , respectively, of the injection molding machine. 
     The present method for manufacturing the piston operating assembly  50  improves the geometric and assembly tolerances of the resulting piston operating assembly, by eliminating forceful coupling methods for securing the piston coupling boss and the magnets to the linking member. The magnets  51  and the coupling boss  52  are each coupled to the linking member  53  as the linking member  53  is injection molded. 
     Furthermore, the present method for manufacturing the piston operating assembly  50  for the linear compressor improves productivity, since the numerous assembly process steps are simplified by injection molding. The L-shaped cross-section of the magnets  51  secures the magnets to the linking member  53 , thereby eliminating the need for a separate magnet cover. In addition, the piston is easily connected to the piston operating assembly  50 , by matingly engaging the threads at the end of the piston with the screw portion  52   b  of the piston coupling boss  52 . 
     As stated above, a preferred embodiment of the present invention is shown and described. Although the preferred embodiment of the present invention has been described, it is understood that the present invention should not be limited to this preferred embodiment. Various changes and modifications can be made by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed.