The present invention relates to a reciprocating compressor including a driving motor unit having a crank shaft and a compressor unit having a cylinder, and more particularly, to a reciprocating type compressor having an improved combination structure between a piston and a connecting rod. 
A reciprocating compressor, that is, a hermetic compressor which has been widely used for compressing a coolant, is comprised of an air-tight external housing, a driving motor unit and a compressor unit both of which are installed in the external housing.  A crank shaft which is connected with a rotor in the driving motor unit, is connected with a piston accommodated in a cylinder and reciprocated by a connecting rod, thereby converting a rotational force of the crank shaft into a reciprocal movement of the piston.  The piston reciprocates in the cylinder to thereby compress fluids such as a coolant flowing into the cylinder. 
FIG.  5 is an exploded perspective view showing an example of the connection of a connecting rod and a piston which is adopted in a conventional reciprocating type compressor.  FIG.  6 is a sectional view showing an example of the assembly of the connecting rod and the piston thereof.  As shown in FIGS.  5 and 6, a larger eye 102 into which an eccentric crank pin 109 of a crank shaft 113 is inserted is formed on one end of a connecting rod 101, and a smaller eye 105 into which a piston pin 104 is inserted is formed on the other end thereof.  An insertion hole 106, into which the end of the connecting rod 101 at the side of the smaller eye 105 is inserted, is formed in the piston 103 along the axial direction, which piston has a cylindrical external surface which contacts the inner wall of a cylinder 110.  A piston pin hole 107 into which the piston pin 104 is inserted perpendicularly to the axial direction is formed to communicate with the insertion hole 106. 
The piston pin 104 is formed as a tubular body, and passes through the piston pin hole 107 of the piston 103 and the smaller eye 105 of the connecting rod 101, to thereby connect the piston 103 and the connecting rod 101 on order to enable them to rotate relatively to each other.  To prevent the piston pin 104 from being released from the piston 103 and the connecting rod 101 in the connection state, a fixing pin 108 is inserted into a fixing hole 115 formed on the piston pin 104 perpendicularly to the lengthwise direction thereof via a fixing pin hole 114 formed on the piston 101, to maintain the piston pin 104. 
During assembly of the piston 103 and the connecting rod 101, the end of the connecting rod 101 at the side of the smaller eye 105 is at first inserted into the insertion hole 106 of the piston 103, and then the piston pin 104 is inserted into both the piston pin hole 107 formed on the piston 103 and the smaller eye 105 of the connecting rod 101.  Then, the fixing pin 108 for preventing the piston pin 104 from being released is inserted into the fixing hole 115 via the fixing pin hole 114, to complete the assembly of the connecting rod 101 and the piston 103. 
Meanwhile, in such a conventional reciprocating compressor, since the insertion hole 106 into which the end of the connecting rod 101 is inserted is formed on the piston 103, the length of the piston 103 becomes longer.  Accordingly, the surface area of the piston 103 becomes larger and a frictional force between the piston 103 and the inner wall surface of the cylinder 110 increases, which causes the lowering of performance of the compressor.  Also, since there are a plurality of such elements as the piston pin hole 107, the smaller eye 105, the insertion hole 106, the fixing pin hole 114 and the fixing hole 115 which require a highly precise fabricating process, the overall manufacturing cost becomes high.  Also, since the connection structure between the connecting rod 101 and the piston 103 is relatively complex, it takes much working time to assemble them.