Abstract:
A linear compressor includes a cylinder block in which a compressing chamber is formed; and an inner core having a plurality of electric steel plates disposed around the cylinder block. The cylinder block extends into spaces between the electric steel plates so that the cylinder block is integrally formed with the inner core. Each of the electric steel plates includes an insertion projection extending from a surface toward the cylinder block and an insertion step extending upward and downward from the insertion projection to form a concave between the surface and the insertion step, the cylinder block extending into the concave to interlock with the inner core.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a linear compressor and, more particularly, to an inner core/cylinder block assembly for a linear compressor and a method for assembling the same. 
     2. Description of the Related Art 
     In general, a linear compressor is used in a refrigeration system that provides refrigeration energy by having a refrigerant undergo the successive process of compressing, condensing, expanding and evaporating. The linear compressor has a linear motor, which is driven by electromagnetic force created by the alternate direction change of magnetic flux, to compress the refrigerant at high temperature and pressure. 
     FIG. 1 shows a conventional linear compressor, and FIG. 2 shows an inner core of the conventional linear compressor. 
     As shown in the drawings, the conventional linear compressor comprises an airtight container  10 , a driving part generating a driving force in the airtight container  10 , and a compressing part inhaling, compressing and discharging a refrigerant by using the driving force of the driving part. 
     The compressing part comprises a piston  11  and a cylinder block  13  provided with a compressing chamber  12  in which the piston  11  is slidably disposed. On one end of the cylinder block  13  is mounted a cylinder head  16  in which an inhaling chamber  14  and a discharging chamber  15  are provided for guiding the refrigerant to the inside and outside of the compressing chamber  12 , respectively. 
     The driving part comprises an inner core  20  coupled on an outer surface of the cylinder block  13 , a stator  30  spaced away from the inner core  20  at a predetermined distance, a permanent magnet  22  disposed between the inner core  20  and the stator  30  to interact with an electric field formed by the stator  30 . 
     The stator  30  includes a cylindrical bobbin  31 , coils  32  wound around the bobbin  31 , and outer core  33  inserted into the bobbin  31 . 
     On the lower end of the piston  11  is provided a fixing shaft  11   a  with a frame  40  for fixing the permanent magnet  22 . A resonant spring  41  for elastically supporting the piston  11  is connected to the lower end of the fixing shaft  11   a  to raise compressing force of the piston  11 . 
     The inner core  20  is made by piling up rectangular-shaped electric steel plates  21  and is arranged radially along the outer circumference of the cylinder block  13 . Korean laid-open patent No. 96-39553 discloses a method for piling the steel plates  21  and assembling the inner core  20  and the cylinder block  13 . This will be described hereinafter with reference to FIG.  2 . 
     Each steel plate is first magnetized by a magnetic flux generating device (not shown), then the magnetized steel plates  21  are radially disposed about a holder  50 . 
     The holder  50  includes a cylindrical main body  51 , an inner extending portion  52  extending inwardly at the lower end of the main body  51 , and an outer extending portion  53  extending outwardly at the lower end of the main body  51 . The inner extending portion  52  is provided with a plurality of screw holes  52   a  so that the holder  50  can be coupled on the lower end of the cylinder block  13  by a screw  54 . Each magnetized steel plate  21  is disposed on the outer extending portion  53 . 
     The magnetized steel plates  21  disposed on the holder  50  are fixed by an adhesive, thereby obtaining a radially piled inner core  20 . And, the holder  50  is coupled to the cylinder block  13  by screw-coupling the screws  54  through the screw holes  52   a , thereby completing the coupling process of the holder  50  to the cylinder block  13 . 
     However, in the conventional compressor, to dispose the steel plate  21  on the holder  50 , a special magnetic flux generating device is required, making the manufacturing process complicated. In addition, since the steel plates  21  are attached on the holder  50  by an adhesive, the same may be easily removed by external force, deteriorating the performance of the compressor. Furthermore, to assemble the inner core  20  on the cylinder block  13 , additional fastening members such as the holder  50  and the screws  54  are required, lowering the productivity and increasing the manufacturing costs. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to solve the above problems. 
     It is an objective of the present invention to provide a linear compressor which can be easily manufactured with the low costs and a method for manufacturing the same. 
     To achieve the above objective, the present invention provides a linear compressor comprising a cylinder block in which a compressing chamber is formed; and an inner core having a plurality of electric steel plates disposed around the cylinder block, wherein the cylinder block extends into spaces between the electric steel plates so that the cylinder block is integrally formed with the inner core. 
     Each of the electric steel plates comprises an insertion projection extending from a surface toward the cylinder block and an insertion step extending upward and downward from the insertion projection to form a concave between the surface and the insertion step, the cylinder block extending into the concave to interlock with the inner core. 
     According to another aspect of the present invention, a method for manufacturing the linear compressor comprising the steps of punching each of the electric steel plates; radially stacking the electric steel plates; welding the electric steel plates to form the inner core; inserting the inner core into a cast mold for casting the cylinder block; pouring molten material into the cast mold and applying pressure to the cast mold so that the molten material is filled into spaces between the electric steel plates, thereby making the inner core integral with the cylinder block. 
     The punching step further comprises the steps of forming an insertion projection on a surface of the electric steel plate; and forming an insertion step on the insertion projection. The stacking step further comprises the steps of preparing a jig having an insertion groove; and stacking the electric steel plates along the jig in a semi-cylindrical shape by inserting the insertion step into the insertion groove. 
     The welding step further comprises the step of welding the electric steel plates along the insertion steps. The method further comprises the step of making a pair of inner cores inserted into the cast mold. 
     The punching step further comprises the steps of forming an insertion projection on a surface of the electric steel plate and forming an insertion step on the insertion projection to form a concave between the insertion step and the surface. 
     The molten material is filled into the concave during the pouring step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a sectional view of a conventional linear compressor; 
     FIG. 2 is a perspective view illustrating an inner core of a conventional linear compressor; 
     FIG. 3 is a sectional view of a linear compressor according to a preferred embodiment of the present invention; 
     FIG. 4 is a perspective view illustrating a punching process of an inner core of a linear compressor according to a preferred embodiment of the present invention; 
     FIG. 5 is a perspective view illustrating a piling process of an inner core of a linear compressor according to a preferred embodiment of the present invention; 
     FIG. 6 is a side view illustrating a welding process of an inner core of a linear compressor according to a preferred embodiment of the present invention; 
     FIG. 7 is a sectional view illustrating a die casting process of an inner core on a cylinder block of a linear compressor according to a preferred embodiment of the present invention; and 
     FIG. 8 is a sectional view taken along line A—A of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 3 shows a linear compressor according to a preferred embodiment of the present invention. 
     The inventive linear compressor comprises an airtight container  100 , a driving part generating a driving force in the airtight container  100 , and a compressing part inhaling, compressing and discharging a refrigerant by using the driving force of the driving part. 
     The compressing part comprises a piston  101 , and a cylinder block  103  provided with a compressing chamber  102  in which the piston  101  is slidably disposed. On one end of the cylinder block  103  is mounted a cylinder head  106  in which an inhaling chamber  104  and a discharging chamber  105  are provided for guiding the refrigerant to the inside and outside of the compressing chamber  102 , respectively. A valve plate  107  on which inhaling valve  104   a  and discharging valve  105   a  are formed is mounted between the cylinder block  103  and the cylinder head  106  to open and close the inhaling chamber  104  and the discharging chamber  105 , respectively. 
     The driving part comprises an inner core  110  coupled around the cylinder block  103 , a stator  120  disposed away from the inner core  110  at a predetermined distance, and a permanent magnet  115  disposed between the inner core  110  and the stator  120  to interact with an electric field formed by the stator  120 . 
     As a feature of the present invention, the inner core  110  is integrally coupled to the cylinder block  103  without using a coupling member. This will be described more in detail hereinbelow. 
     In addition, the stator  120  includes a bobbin  121  of a cylindrical shape having a recess for winding coils at the outer circumference thereof, coils  122  wound in the coil winding recess of the bobbin  121 , and outer core  123  inserted into the bobbin  121 . 
     On the lower end of the piston  101  is provided a fixing shaft  101   a  with a frame  140  for fixing the permanent magnet  115 . A resonant spring  141  for elastically supporting the piston  101  is connected to the lower end of the fixing shaft  101   a  by means of a bolt  142  to raise compressing force of the piston  101 . 
     The structures of the inner core  110  and the cylinder block  103  will be described hereinafter with reference to FIGS. 4 to  8 . 
     Generally, the inner core  110  of the linear compressor is made by piling a plurality of rectangular electric steel plates. As shown in FIG. 4, the electric steel plate  111  of the present invention is made by punching a material plate  111   a  by a press  150  while it is conveyed by a conveying system (not shown). As shown in FIG. 5, in the punching process, an insertion projection  112  is formed on a surface of the electric steel plate  111  and an insertion step  113  is formed extending from an extreme end of the insertion projection  112  in upper and lower directions, thereby forming a concavity  114  between the surface of the electric steel plate  111  and the insertion step  113 . 
     The electric steel plate  111  having undergone the punching process forms the inner core  110  through a stacking process. At this point, semi-cylindrical jigs  210  and  220  are prepared to guide the stacking process of the electric steel plate  111 . 
     Describing more in detail, the jigs  210  and  220  are separated in upper and lower sides, and the insertion step  113  of the electric steel plate  111  is disposed between the upper and lower jigs  210  and  220 . 
     Lower and upper ends of the respective upper and lower jigs  210  and  220  are provided with a circumferential insertion groove  211  and  221  in which the insertion step  113  of the electric steel plate  111  is inserted. That is, in a state where the insertion groove  211  of the upper jig  210  and the insertion groove  221  of the lower jig  220  is in an opposing state to each other, the insertion step  113  of the electric steel plate  111  is inserted into the insertion groove  211  and  221 . Accordingly, the electric steel plates  111  are stacked in a semi-cylindrical shape while being guided by the shape of the jigs  210  and  220 , thereby forming the inner core  110 . 
     When the stacking process is completed, as shown in FIG. 6, a welding process is conducted to fix the stacked electric steel plates  111 . The welding process is conducted along a central portion  113   a  of the insertion step  113 . 
     At this point, the length L of the insertion step  113  should be designed to be larger than a sum of the depth D 1  of the insertion groove  211  of the upper jig  210  and the depth D 2  of the insertion groove  221  of the lower jig  220 . This is to obtain a space for welding the electric steel plates  111  along the central portion  113   a  of the insertion step  113 . 
     When the welding process is completed, the jigs  210  and  220  are removed from the inner core  110 . 
     After the above, an assembling process is conducted for assembling the inner core  110  with the cylinder block  103 . This will be described more in detail hereinafter. 
     Generally, the cylinder block  103  is made of a nonmagnetic material through a die casting process. In the die casting process, as shown in FIG. 7, a cast mold  300  is first prepared to cast the cylinder block  103 , and a nonmagnetic molten material is poured into the cast mold  300 . At this point, before pouring the molten material into the cast mold  300 , a pair of inner cores  110  are inserted into the cast mold  300  such that the insertion steps  113  of the pair of inner cores  110  face a center of the cast mold  300  to make the pair of inner cores cylindrical. 
     After the above, the molten material is poured into the cast mold  300 , then a pressure is applied to the cast mold  300 . At this point, as shown in FIG. 8, the molten material is filled into spaces between the electric steel plates  111  and the concavity  114  formed on each of the electric steel plates  111 . That is, the inner core  110  is integrally formed with the cylinder block  103 . Preferably, the molten material is aluminum. 
     In addition, during the die casting process, a cylindrical core  301  is disposed on a central portion of the cast mold  300  to form the compressing chamber  102  (see FIG. 3) within the cylinder block  103 . 
     As described above, the electric steel plates of the inventive linear compressor can be easily stacked by using jigs, making the manufacturing process simple. Furthermore, the inner core formed by welding the stacked electric steel plates is integrally coupled to the cylinder block during the die casting process, thereby conventional coupling members such as a holer and screws and the assembling process of the same being unnecessary, the productivity being raised, and the manufacturing costs being decreased. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.