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Screw rotor machine and rotor profile therefor

  • US 4,435,139 A
  • Filed: 02/03/1982
  • Issued: 03/06/1984
  • Est. Priority Date: 02/06/1981
  • Status: Expired
First Claim
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1. Screw rotor machine for a working fluid comprising a casing with a working space provided with spaced apart low pressure and high pressure ports for communication with low pressure and high pressure channels, respectively, and including at least two intersecting bores with parallel axes, a number of rotors disposed in said bores and intermeshing in pairs, each rotor having helical lands and intervening grooves, whereby a pair of communicating groove portions form a chevron-shaped chamber having its base end disposed in a plane transverse to the axes of the rotors and adjacent to the high pressure port of the machine, one rotor of each pair being of female rotor type formed such that at least the major portion of each land and groove is located inside the pitch circle of the rotor, the other rotor of the pair being of male rotor type formed such that at least the major portion of each land and groove is located outside the pitch circle of the rotor, the lands of one rotor following the envelopes developed by the grooves of the other rotor to form a continuous sealing line between the rotors, each rotor groove being provided with a primary flank forming the peripherally outer wall of the leg of said chamber comprised of a female rotor groove and the peripherally inner wall of the leg of said chamber comprised of a male rotor groove, respectively, and a secondary flank forming the other wall of the related leg of the chamber, characterized in that in a plane perpendicular to the rotor axes at least the primary flank of each male rotor groove comprises a first flank portion adjacent to the pitch circle and extending outwardly therefrom, that the tangent to said first flank portion in its pitch point, where it intersects with the pitch circle, and a radial line from the centre of the rotor through the pitch point form an angle therebetween falling within the range of 0.25 rad to 0.75 rad, when measured outside the pitch circle from the tangent towards the groove, and that the radius of curvature of said first flank portion in its pitch point has a length exceeding the product of the pitch radius and the sine function of said pitch point angle between the tangent and the radial line.

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