The invention relates to a screw rotor machine for a compressible working medium with a screw cam rotor provided with gudgeons at its ends and a hollow screw thread rotor provided with bearing surfaces and surrounding the screw cam rotor which are rotatably journalled in a housing for rotation around mutually sideways displaced rotation axes which are fixed relative to the housing and coaxial with the gudgeons and the bearing surfaces respectively which rotors during rotation form chambers between their screw cams and screw threads which chambers move from end to end of the rotors while changing their volume.
In screw rotor machines of this and the closely related type where the screw thread rotor is stationary and forms a stator there are a number of suggestions as regards the choice of profile for the cooperating screw cams and screw threads of the rotors. This is shown for example in Swedish patent specification No. 85,331 and U.S. Pat. specifications Nos. 1,892,217 and 2,553,548. Hitherto existing combinations of working profiles with associated rotor journallings and drivings have, however, mostly been complicated, difficult to manufacture, and hardly suitable for effective work at high pressures and rpm.