Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
1998-11-12
2001-10-02
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
C418S201300, C029S888023
Reexamination Certificate
active
06296461
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to plural screw positive displacement machines comprising a housing having at least two intersecting bores the axes of which are coplanar in pairs, and usually parallel, and male and female rotors mounted for rotation about their axes which coincide one with each of the housing bore axes. The rotors each have helical lands which mesh with helical grooves between the lands of at least one other rotor, the or each male rotor having as seen in cross section a set of lobes corresponding to the lands and projecting outwardly from its pitch circle. Each female rotor has as seen in cross section a set of depressions extending inwardly of its pitch circle and corresponding to the grooves of is the female rotor(s). The number of lands and grooves of the male rotor(s) being different to the number of lands and grooves of the female rotor(s).
BACKGROUND OF THE INVENTION
Examples of such machines, which may be used as compressors or expanders are disclosed in GB 1,197,432, GB 1,503,488 and GB 2,092,676.
SUMMARY OF THE INVENTION
A plural screw positive displacement machine according to the invention is characterised in that, the profiles of at least those parts of the lobes projecting outwardly of the pitch circle of the male rotor(s) and the profiles of at least the depressions extending inwardly of the pitch circle of the female rotor(s) are generated by the same rack formation. The lobes are curved in one direction about the axis of the male rotor(s). The depressions are curved in the opposite direction about the axis of the female rotor(s). The portion of the rack which generates the higher pressure flanks of the rotors being generated by rotor conjugate action between the rotors.
Advantageously, a portion of the rack, preferably that portion which forms the higher pressure flanks of the rotor lobes, has the shape of a cycloid. Alternatively, this portion may be shaped as a generalized parabola, for example of the form: ax+by
q
=1.
Normally, the bottoms of the grooves of the male rotor(s) lie inwardly of the pitch circle as “dedendum” portion and the tips of the lands of the female rotor(s) extend outwardly of its pitch circle as “addendum” portions. Preferably, these dedendum and addendum portions are also generated by the rack formation.
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City University
Denion Thomas
Flynn ,Thiel, Boutell & Tanis, P.C.
Trieu Thai-Ba
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