Sealed compressor

Abstract

A hermetic compressor includes a cylindrical hole ( 117 ) forming a compression space ( 115 ) and having a tapered portion ( 127 ) so as to increase its inner diameter from the top dead center to the bottom dead center of a piston ( 123 ). The piston ( 123 ) is reversed in its inclination direction with respect to the axial center of the cylindrical hole ( 117 ) in the initial stage of the compression stroke. This reduces the contact between the piston ( 123 ) and the cylindrical hole ( 117 ) at the time of the reversal, as compared with the case in which the piston ( 123 ) is reversed in its inclination direction in the middle or later stage of the compression stroke. As a result, the hermetic compressor is reliable and has low noise level.

1 . A hermetic compressor comprising:
 an airtight container having lubricating oil therein;   an electric element; and   a compression element, the compression element being driven by the electric element, and the electric element and the compression element being housed in the airtight container;   the compression element including:
 a shaft having a main shaft portion and an eccentric shaft portion, the main shaft portion being rotatable by the electric element, and the eccentric shaft portion moving in unison with the main shaft portion; 
 a cylinder block having a cylindrical hole and a bearing, the cylindrical hole forming a compression space, and the bearing supporting the main shaft portion; 
 a piston reciprocable in the cylindrical hole; and 
 a connection mechanism for connecting the eccentric shaft portion and the piston, wherein 
   the cylindrical hole includes a tapered portion so as to increase an inner diameter thereof from a top dead center to a bottom dead center of the piston, and   the piston is reversed in an inclination direction thereof with respect to an axial center of the cylindrical hole in an initial stage of a compression stroke.   
     
     
         2 . The hermetic compressor of  claim 1 , wherein
 the piston is reversed in the inclination direction thereof with respect to the axial center of the cylindrical hole at a moment when the piston comes into contact with the tapered portion at an edge on a compression space side thereof.   
     
     
         3 . The hermetic compressor of  claim 1 , wherein
 the cylindrical hole includes a straight portion having a uniform inner diameter in an axial direction, the straight portion being formed in a region adjacent to the tapered portion and corresponding to an upper end on the compression space side of the piston when the piston is near the top dead center position.   
     
     
         4 . The hermetic compressor of  claim 3 , wherein when the straight portion has an axial length L 1 ,
 the compression space has a minimum inner diameter D 1 ,   the piston has an outer diameter D 2 ,   the eccentric shaft portion has an eccentricity “e” with respect to the main shaft portion,   a connection center of the connection mechanism and the piston, and an end face on the compression space side of the piston have a distance L 2  therebetween,   the main shaft portion whose rotation angle is 0 (zero) degrees when the piston is in the top dead center position has a rotation angle “θ”, and   the axial center of the compression space and the tapered portion form an angle “α” therebetween,   the angle “α” and a dimension value “γ” satisfy Mathematical Formula 2, the dimension value “γ” being expressed by Mathematical Formula 1 based on the D 1 , the D 2 , the L 1 , the L 2 , the “e”, and the “θ”;
   γ={3( D 1− D 2)/2}/{ L 1− L 2+2 e (1−cos θ)}  Mathematical Formula 1
 
   0.4Γ≦tan(α)≦2.0γ where α>0  Mathematical Formula 2
 
   
     
     
         5 . The hermetic compressor of  claim 4 , wherein
 when the piston is in the bottom dead center position, at least a bottom end of the piston is exposed from the cylindrical hole, and   the rotation angle “θ” of the main shaft portion is in a range of π to 4 π/3 (rad).   
     
     
         6 . The hermetic compressor of  claim 1 , wherein
 the piston is provided on an outer surface thereof with a concave oil supply groove, the oil supply groove being communicated with the airtight container near the bottom dead center of the piston.   
     
     
         7 . The hermetic compressor of  claim 3 , wherein
 the bearing and the compression space are arranged in such a manner that a third center line and a second center line cross each other, the third center line being parallel to a first center line representing an axial center of the bearing, and the second center line representing an axial center of the compression space.   
     
     
         8 . The hermetic compressor of  claim 7 , wherein
 when the straight portion has an axial length L 1 , the compression space has a minimum inner diameter D 1 , the piston has an outer diameter D 2 , the eccentric shaft portion has eccentricity “e” with respect to the main shaft portion, a connection center of the connection mechanism and the piston and an end face on the compression space side of the piston have a distance L 2  therebetween, the main shaft portion whose rotation angle is zero degrees when the piston is in the top dead center position has a rotation angle “θ”, the first center line and the third center line have a distance “s” therebetween, and the axial center of the compression space and the tapered portion form an angle “α” therebetween, the angle “α” and a dimension value “γ” satisfy Mathematical Formula 2, the dimension value “γ” being expressed by Mathematical Formula 3 based on the D 1 , the D 2 , the L 1 , the L 2 , the “e”, the “θ”, and the “s”;
   γ={3( D 1− D 2)/2}/{ L 1− L 2+2 A}   Mathematical Formula 3,
 
   wherein  A ={( e   2 (1−cos θ) 2   −s   2 }  Mathematical Formula 4
 
   
     
     
         9 . The hermetic compressor of  claim 8 , wherein
 when the piston is in the bottom dead center position, at least a bottom end of the piston is exposed from the cylindrical hole, and   the rotation angle “θ” of the main shaft portion is in the range of π to 4 π/3 (rad).