Screw pump and screw gear

Abstract

A screw pump is provided with a pair of screw rotors serving as fluid transfer bodies. With respect to a rotation angle (x) around an axis of each of the screw rotors, a change of a lead angle (θ) from a winding start angle ( 0 ), which is the rotation angle (x) corresponding to a leading end of a spiral groove, to a winding end angle (E), which is the rotation angle (x) corresponding to a trailing end of the spiral groove, can be expressed by a lead angle change function θ(x). The lead angle change function θ(x) is structured by a combination of a plurality of change functions θ 1 (x) and θ 2 (x) having different manners of changing. It is possible to arbitrarily set a manner in which the lead angle (θ) changes in accordance with a combination of a plurality of change functions θ 1 (x) and θ 2 (x). Therefore, it is possible to arbitrarily set a fluid compression characteristic of the pump in a relation with an axial length (L) of the screw rotor.

1 . A screw gear having a portion in which a lead angle is continuously changed from a leading end to a trailing end of a spiral groove,
 wherein, in the case of expressing, as a lead angle change function, a change of said lead angle from a winding start angle serving as a rotation angle corresponding to the leading end of said spiral groove to a winding end angle serving as a rotation angle corresponding to a trailing end of said spiral groove with respect to a rotation angle of said screw gear around an axis, said lead angle change function is constituted by a combination of a plurality of change functions having different manners of changing.   
   
   
       2 . The screw gear according to  claim 1 , wherein a predetermined rotation angle between said winding start angle and said winding end angle is set as a switch angle, wherein said lead angle change function includes a first change function corresponding to an angle range from said winding start angle to said switch angle, and a second change function corresponding to an angle range from said switch angle to said winding end angle, and wherein said second change function expresses the change of the lead angle by a gentler change degree than said first change function. 
   
   
       3 . The screw gear according to  claim 1 , wherein each of said change functions constituting said lead angle change function is constituted by a monotone changing function gradually increasing the lead angle in accordance with change of said rotation angle from said winding start angle to said winding end angle. 
   
   
       4 . The screw gear according to  claim 1 , wherein the following expressions are satisfied:
   θ1( x )=Deg S+k 1· x  (in this case 0<x<M)       k 1=(Deg M −Deg S )/(2π r·M )     θ2( x )=Deg M+k 2·( x−M ) (in this case M<x<E)       k 2=(Deg E −Deg M )/(2π r·E )       L 1=1/k1·log(sin(Deg S+k 1·2π r·M )/Sin(Deg S ))       L 2=1/k2·log(sin(Deg M+k 2·2π r·E )/Sin(Deg M ))       L=L 1+ L 2   
     in which x: rotation angle,  0 : winding start angle, E: winding end angle, M: switch angle corresponding to a rotation angle x set between the winding start angle  0  and the winding end angle E, DegS: winding start lead angle corresponding to a lead angle at the winding start angle  0 , DegE: winding end lead angle corresponding to a lead angle at the winding end angle E, DegM: switch lead angle corresponding to a lead angle at the switch angle M, θ 1 (x): change function indicating a change of the lead angle in an angle range (0<x<M) from the winding start angle  0  to the switch angle M, θ 2 (x): change function indicating a change of the lead angle in an angle range (M<x<E) from the switch angle M to the winding end angle E, k1 and k2: constants, r: radius of a pitch circle of the screw gear, L: entire length in an axial direction of the screw gear, L 1 : length in an axial direction of the screw gear corresponding to the angle range 0<x<M, L 2 : length in an axial direction of the screw gear corresponding to the angle range M<x<E. 
   
   
       5 . (canceled) 
   
   
       6 . A screw pump apparatus comprising:
 a pair of screw gears mating with each other; and   a pump chamber accommodating the screw gears,   wherein the screw gears rotate while mating with each other, whereby a fluid sucked into the pump chamber is transferred in an axial direction of the screw gears while being compressed within said pump chamber,   wherein an actuation chamber for compressing the fluid is defined between adjacent thread ridge portions in the axial direction of each screw gear,   wherein each screw gear has a portion in which a lead angle is continuously changed from a leading end to a trailing end of a spiral groove, and   wherein, in the case of expressing, as a lead angle change function, a change of said lead angle from a winding start angle serving as a rotation angle corresponding to the leading end of said spiral groove to a winding end angle serving as a rotation angle corresponding to a trailing end of said spiral groove with respect to a rotation angle of each screw gear around an axis, said lead angle change function is constituted by a combination of a plurality of change functions having different manners of changing.