Male and female screw rotor assembly with specific tooth flanks

An oil-cooled type screw rotor assembly having a female rotor and a male rotor adapted to rotate around parallel axes in meshing condition, wherein a leading side flank, as viewed in a normal direction of rotation, of said female rotor includes a first leading side flank formed by an arc of a radius R.sub.1 centered at a point outside of a pitch circle of said female rotor and a second leading side flank formed by an arc of a radius R.sub.2 centered at a point within said pitch circle, a trailing side flank of said female rotor includes a first trailing said flank generated by an arc of teeth end of said male rotor having a radius R.sub.5 centered at a point on a line interconnecting centers of rotations of said rotors and a second trailing side flank formed by an arc of a radius R.sub.3 smaller than the radius R.sub.2 of said second leading side flank of said female rotor centered at a point within said pitch circle, and wherein a tooth contour of teeth of said male rotor is substantially generated by the arcs of said leading side flanks and trailing side flanks of said female rotor.