Hermetic compressor

1. A compression device, comprising:

a case;

a stator within the case;

a rotor within the stator;

a crank shaft coupled to the rotor;

a compressor, coupled to the crank shaft, to suction and compress a refrigerant and to discharge the compressed refrigerant into the case;

a first bearing, coupled to the compressor, to support a first portion of the crank shaft; and

a second bearing to support a second portion of the crank shaft spaced apart from the first portion,

wherein a diameter of the crank shaft is greater than or equal to 0.114 times an outer diameter of the stator, and

wherein the diameter of the crank shaft is less than or equal to 0.138 dines the outer diameter of the stator,

wherein the compressor comprises:

a cylinder coupled to the first bearing, the cylinder forming a compression space together with the first bearing;

a rolling piston coupled to the crank shaft to perform an orbiting motion within the compression space of the cylinder; and

a vane to partition the compression space into a suction chamber and a discharge chamber and linearly moving in response to the orbiting of the rolling piston, and

wherein the second bearing comprises:

a frame welded onto an inner circumferential surface of the case at one side of the stator;

a housing coupled to the crank shaft so as to allow for rotation of the crank shaft, the housing being detachably coupled to the frame;

a plurality of first protrusions located on an outer circumferential surface of the frame, the plurality of protrusions being welded onto the inner circumferential surface of the case and spaced apart from one another at predetermined intervals along a circumferential direction; and

a plurality of second protrusions located on an outer circumferential surface of the housing for support at the frame,

wherein a number of the plurality of first protrusions equals a number of the plurality of second protrusions, and wherein the plurality of first protrusions and the plurality of second protrusions overlap each other.

2. The compression device of claim 1 , wherein the first beating includes a plurality of bearing plates coupled to upper and lower sides of the cylinder shielding the compression space.

3. The compression device of claim 1 , wherein a bearing protrusion is located at a center of the housing, and a bearing member is mounted in the bearing protrusion such that the crank shaft is inserted therein to be supported.

4. The device of claim 1 , wherein the rotor and stator are located between the first and second portions of the crank shaft.

5. The device of claim 1 , further comprising: an oil storage area within the case, wherein a passage to guide oil pumped up from the oil storage area toward the second bearing is included through the crank shaft in the axial direction.

6. The device of claim 1 , wherein a difference between the outer diameter of the stator and an interior diameter of the case is less than 10% of the interior diameter of the case.

7. The device of claim 6 , wherein the difference between the outer diameter of the stator and the interior diameter of the case is less than 5% of the interior diameter of the case.

8. The device of claim 1 , wherein the diameter of the crankshaft is substantially constant from a first end of the stator to a second end of the stator.

9. The device of claim 8 , wherein the outer diameter of the stator is substantially constant from the first end to the second end of the stator.