Screw Fluid Machine

Abstract

A screw fluid machine that suppresses power loss by preventing a residual volume from being generated at a discharge-side end face while thinning a tooth tip of a male rotor is provided. In a screw fluid machine in which a male rotor 2 including a plurality of teeth and a female rotor corresponding to the male rotor 2 are rotated to compress and convey a fluid, when viewed in an axial direction, a cross-sectional tooth profile 21d in a first section in the vicinity of an end portion on a discharge side of the male rotor 2 is formed thick so as to be located outside a pitch point-centered circle CP at a tooth tip and on an advancing surface side of the tooth tip, and a cross-sectional tooth profile 21s in a second section in the vicinity of an end portion on a suction side is formed thin so as to be located inside the pitch point-centered circle CP. A cross-sectional tooth profile of the male rotor 2 between the first section and the section in the axial direction is configured to continuously change from a second cross-sectional shape to a first cross-sectional shape.

What is claimed is: 
     
         1 . A screw fluid machine, comprising:
 a male rotor including twisted male teeth and rotating about a first rotation center;   a female rotor including twisted female teeth and rotating about a second rotation center parallel to said first rotation center; and   a casing including an accommodating chamber that rotatably accommodates said male rotor and said female rotor in a meshed state,   wherein said male rotor and said female rotor are rotated to convey a fluid between a suction port and a discharge port in a state where pressure of the fluid is changed,   said male rotor is formed such that a cross-section orthogonal to said first rotation center at a discharge-side end face has a first cross-sectional shape in which a length from any point in a rotor advancing direction from a tooth tip of each tooth to a pitch point of the tooth is equal to or longer than a length from said tooth tip to said pitch point, and   when viewed in an axial direction, said male rotor is formed such that a section exists in which a cross-section orthogonal to said first rotation center at a predetermined position between a suction-side end face and said discharge-side end face has a second cross-sectional shape in which a length from a predetermined point in said male rotor advancing direction of a tooth tip of each tooth to a pitch point of the tooth is shorter than a length from said tooth tip to said pitch point.   
     
     
         2 . The screw fluid machine according to  claim 1 ,
 wherein, when viewed in the axial direction, said male rotor has a transition section between a section having the first cross-sectional shape and a portion having the second cross-sectional shape of said male rotor, in which the cross-section of said male rotor changes continuously from the second cross-sectional shape to the first cross-sectional shape.   
     
     
         3 . The screw fluid machine according to  claim 2 ,
 wherein the cross-section of said male rotor at the suction-side end face is formed with the second cross-sectional shape.   
     
     
         4 . The screw fluid machine according to  claim 3 ,
 wherein, when viewed in the axial direction, said male rotor in a section from the suction-side end face to said transition section is formed with the same cross-sectional shape as the second cross-sectional shape, and   when viewed in the axial direction, said male rotor in a section from said transition section to said discharge-side end face is formed with the same cross-sectional shape as the first cross-sectional shape.   
     
     
         5 . The screw fluid machine according to  claim 4 ,
 wherein a tooth profile on an advancing surface side of said tooth tip in the second cross-sectional shape of said male rotor is formed such that a product of an angle and a lead, the angle being formed by sequentially connecting an intersection point where a normal line drawn from a point on an advancing surface intersects a pitch circle, a center of said male rotor, and said tooth tip with a straight line, is not larger than an axial length of said transition section.   
     
     
         6 . The screw fluid machine according to  claim 3 ,
 wherein, when viewed in the axial direction, a section having a third cross-sectional shape in which a length from any point in said rotor advancing direction from a tooth tip of each tooth to a pitch point of the tooth is equal to or longer than a length from said tooth tip to said pitch point and a second transition section in which the cross-section of said male rotor changes continuously from the third cross-sectional shape to the second cross-sectional shape are provided between the suction-side end face and the section having the second cross-sectional shape.   
     
     
         7 . The screw fluid machine according to  claim 6 ,
 wherein the first cross-sectional shape and the third cross-sectional shape are the same shape.   
     
     
         8 . The screw fluid machine according to  claim 1 ,
 wherein a shape of said male rotor on a front side from said tooth tip is configured such that, in a section having the first cross-sectional shape, said tooth tip coincides with or is located outside a pitch point-centered circle having the pitch point as a center and passing through said tooth tip and, in the section having the second cross-sectional shape, a contour of said tooth tip is located inside said pitch point-centered circle, and   a cross-sectional shape of said female rotor perpendicular to a rotation axis direction is a shape corresponding to a cross-sectional shape of said male rotor.   
     
     
         9 . The screw fluid machine according to  claim 1 ,
 wherein a lubricating liquid is supplied into said accommodating chamber that compresses the fluid.   
     
     
         10 . A screw fluid machine, comprising:
 a male rotor including twisted male teeth and rotating about a first rotation center;   a female rotor including twisted female teeth and rotating about a second rotation center parallel to said first rotation center; and   a casing including an accommodating chamber that rotatably accommodates said male rotor and said female rotor in a meshed state,   wherein said male rotor and said female rotor are rotated to convey a fluid between a suction port and a discharge port in a state where pressure of the fluid is changed,   when viewed in an axial direction of a rotation axis, said male rotor is formed such that cross-sectional shapes orthogonal to the rotation axis are sequentially formed in sections having a second cross-sectional shape, a transition shape that changes continuously, and a first cross-sectional shape from a suction-side end face toward a discharge-side end face,   a cross-sectional tooth profile in the section having said first cross-sectional shape has a cross-sectional shape coinciding with or located outside a pitch point-centered circle at a tooth tip and on an advancing surface side of said tooth tip,   a cross-sectional tooth profile in the section having the second cross-sectional shape has a cross-sectional shape located inside said pitch point-centered circle at said tooth tip and on the advancing surface side of said tooth tip, and   in the section having the transition shape, a cross-sectional tooth profile of said male rotor has a shape that changes continuously from the second cross-sectional shape to said first cross-sectional shape.   
     
     
         11 . The screw fluid machine according to  claim 10 ,
 wherein an axial length of the section having the transition shape is shorter than axial lengths of the section having said first cross-sectional shape and the section having the second cross-sectional shape, and is larger than a maximum axial width Lv of a space V res  that becomes a residual volume.   
     
     
         12 . The screw fluid machine according to  claim 11 ,
 wherein the section having the second cross-sectional shape occupies one-half or more of a length of said male rotor in a rotation axis direction, and   the section having the transition shape is disposed in a latter half region close to a discharge side of said male rotor.   
     
     
         13 . The screw fluid machine according to  claim 12 ,
 wherein a length of the section having said first cross-sectional shape in the rotation axis direction is shorter than a length of the section having the transition shape in the rotation axis direction.   
     
     
         14 . A screw fluid machine, comprising:
 a male rotor including twisted male teeth and rotating about a first rotation center;   a female rotor including twisted female teeth and rotating about a second rotation center parallel to said first rotation center; and   a casing including an accommodating chamber that rotatably accommodates said male rotor and said female rotor in a meshed state,   wherein said male rotor and said female rotor are rotated to convey a fluid between a suction port and a discharge port in a state where pressure of the fluid is changed,   said male rotor is configured such that cross-sectional shapes orthogonal to a rotation axis are sequentially formed in sections having a first cross-sectional shape, a second transition shape that changes continuously, a second cross-sectional shape, a first transition shape that changes continuously, and said first cross-sectional shape from a suction-side end face toward a discharge-side end face of the rotation axis,   a cross-sectional tooth profile in the section having said first cross-sectional shape has a cross-sectional shape coinciding with or located outside a pitch point-centered circle at a tooth tip and on an advancing surface side of said tooth tip,   a cross-sectional tooth profile in the section having the second cross-sectional shape has a cross-sectional shape located inside said pitch point-centered circle at said tooth tip and on the advancing surface side of said tooth tip,   in the section having the second transition shape, a cross-sectional tooth profile changes continuously from the first cross-sectional shape to the second cross-sectional shape, and   in the section having the first transition shape, a cross-sectional tooth profile changes continuously from the second cross-sectional shape to the first cross-sectional shape.   
     
     
         15 . The screw fluid machine according to  claim 14 ,
 wherein a total length of the section having the first cross-sectional shape in a rotation axis direction is shorter than a total length of the section having the first cross-sectional shape in the rotation axis direction.