Patent ID: 6341951
Filing Date: 2002-01-29
Classification: F01C,F04C

Abstract:
A combination double screw rotor assembly, comprising:a casing, said casing comprising an inside wall defining a receiving chamber, an inlet, and an outlet; a first rotor, said first rotor comprising a shaft axially-rotatably mounted in said casing, a low pressure screw rotor element and a high pressure screw rotor element respectively mounted on said shaft of said first rotor in a direction from said inlet toward said outlet, and a spiral thread raised around a periphery thereof and extending over the low pressure screw rotor element and high pressure screw rotor element of said first rotor, the spiral thread of said first rotor being comprised of a first spiral thread segment raised around a periphery of the low pressure screw rotor element of said first rotor and defining a uniform long pitch, and a second spiral thread segment raised around a periphery of the high pressure screw rotor element of said first rotor and defining a uniform short pitch; a second screw rotor, said second screw rotor comprising a shaft axially-rotatably mounted in said casing and disposed in parallel to said shaft of said first screw rotor, a low pressure screw rotor element and a high pressure screw rotor element respectively mounted on said shaft of said second rotor in the direction from said inlet toward said outlet, and a spiral thread raised around the periphery thereof and extending over the low pressure screw rotor element and high pressure screw rotor element of said second rotor, the spiral thread of said second rotor being comprised of a first spiral thread segment raised around a periphery of the low pressure screw rotor element of said second rotor and defining a uniform long pitch, and a second spiral thread segment raised around a periphery of the high pressure screw rotor element of said second rotor and defining a uniform short pitch, the first spiral thread segment and second spiral thread segment of the spiral thread of said second screw rotor being respectively meshed with the first spiral thread segment and second spiral thread segment of said first screw rotor; two sets of axle bearings respectively mounted in said casing near said outlet to support the shaft of said first rotor and the shaft of said second rotor; and a plurality of keyless axle bushes respectively fastened to the shaft of said first screw rotor and the shaft of said second screw rotor in a region near said inlet, each keyless axle bush including a tapered inner sleeve, a tapered outer sleeve disposed around the tapered inner sleeve, and a nut that urges the tapered inner sleeve into engagement with the tapered outer sleeve to secure the respective low pressure screw rotor elements of said first screw rotor and said second screw rotor to the respective shafts; wherein the use of said keyless axle bushes allows the region near said inlet to be maintained free of axle bearings, thereby preventing evaporated lubricating grease from being drawn by a reverse flow into said inlet.