Gas compressor of the scroll type having delayed suction closing capacity modulation

A gas compressor of the positive displacement scroll type comprising

• a. a first wrap element defining inner and outer flank surfaces of generally spiroidal configuration about a first axis and extending between first and second axial tip portions;
• b. a second wrap element defining inner and outer flank surfaces of generally spiroidal configuration about a second axis and extending between first and second axial tip portions, said first and second wrap elements being disposed in intermeshing, angularly offset relationship with their respective axes generally parallel;
• c. end plate means comprising a first end plate sealingly affixed to the first axial tip portion of said first wrap element and a second end plate sealingly affixed to the first axial tip portion of said second wrap element, the second axial tip portions of said first and second wrap elements extending to a point in substantial sealing relationship to said second and first end plates respectively;
• further comprising means for maintaining said second wrap element and end plate in a fixed position;
• d. drive means operative to drive said first wrap element and end plate in an orbital path with respect to said second wrap element and end plate such that moving line coaction between the inner facing flank surface of said first wrap element and the outer facing flank surface of said second wrap element, and between the outer facing flank surface of said first wrap element and the inner facing flank surface of said second wrap element, defines between said end plate means first and second moving volumes originating at a radially outer portion of said wrap elements and progressing radially inwardly to a radially inner portion thereof, said volumes being bounded initially by a single, leading moving line of coaction so as to define a suction volume;
• then by both leading and trailing lines of coaction so as to define a closed moving volume which is progressively reduced in volume as it moves radially inwardly;
• and finally by a single trailing line of coaction so as to define a discharge volume;
• e. port means for admitting a working gas at a suction pressure to said suction volumes and for discharging compressed gas from said discharge volume;
• and
• f. unloader means for selectively varying the capacity of said gas compressor comprising
• i. a first passage extending through said second end plate at a first location in communication with said first and second closed moving volumes at least at the time they are formed by said trailing lines of coaction, to a location in communication with working gas normally at suction pressure during operation of said compressor, said first passage having a dimension in a radial direction such that, as said first wrap element undergoes relative orbital motion with respect thereto, a closed moving volume lying on either side thereof is placed in communication with said first passage as the first wrap element passes thereover;
• ii. a second passage extending through said second end plate at a location in communication with said first and second closed moving volumes at least from the time they are no longer in communication with said first passage and until they progress radially inwardly to predetermined positions, to a location in communication with working gas normally at suction pressure during operation of said compressor, said second passage being disposed radially inwardly from said first passage and having a dimension in a radial direction such that, as said first wrap element undergoes relative orbital motion with respect thereto, a closed moving volume lying on either side thereof is placed in communication with said second passage as said first wrap element passes thereover;
• and
• iii. valve means for selectively blocking flow through said first and second passages whereby said gas compressor operates, at a relatively high capacity;
• and for permitting flow through said passages whereby gas is exhausted via said passages from said closed moving volumes as they are reduced in volume until they have progressed radially inwardly to the aforesaid predetermined positions, whereby the capacity of said gas compressor is reduced.