Rotary expansible chamber devices – Grooved abutting cylinder-rotating member end surfaces – Non-working fluid directed to groove
Reexamination Certificate
2000-06-07
2001-11-06
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Grooved abutting cylinder-rotating member end surfaces
Non-working fluid directed to groove
C418S077000, C418S079000, C418S201100, C418S203000
Reexamination Certificate
active
06312239
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a screw-type compressor comprising a housing in which are arranged a primary rotor and a secondary rotor each having a shaft and a screw rotor.
Screw-type compressors are used for compressing a gaseous substance, e. g. air, and making it available as compressed gas. From DE-A-42 27 332 a screw-type compressor is known wherein a motor-driven primary rotor drives a secondary rotor. The shafts of the primary and secondary rotors are radially supported in roller bearings at both ends. Further, each shaft of the two rotors is axially supported in a plurality of ball bearings at one end. Said axial bearings carry the forces, which occur between the screw rotors during gas compression, in axial direction of the primary and the secondary rotor. The antifriction bearings produce heat during operation, which leads to inhomogeneous heat distribution and thus to stresses in the shaft. From DD-PS 84 891 and U.S. Pat. No. 3,811,805 compressors are known whose primary and secondary rotors are each provided with axial bearings which are configured as slide bearing and thus produce less heat. U.S. Pat. No. 3,275,226 describes a screw-type compressor wherein the primary and secondary rotors are axially supported by antifriction bearings with the primary rotor being additionally axially supported by a disk. The multitude of bearings for the primary and the secondary rotor render the configurations of the known screw-type compressors complicated and their manufacture expensive.
SUMMARY OF THE INVENTION
It is the object of the invention to simplify and improve support of the primary and the secondary rotors in a screw-type compressor.
In the screw-type compressor according to the invention the secondary rotor is axially supported by the primary rotor. Only the primary rotor comprises an axial bearing part which is supported in an axial bearing part of the housing. The secondary rotor is thus directly supported by the housing only via radial bearings. The secondary rotor however is no longer directly supported by the housing via its own axial bearing. The axial forces of the secondary rotor are transmitted via its screw rotor to the screw rotor of the primary rotor. The axial bearing of the primary rotor, formed by the axial bearing parts of the primary rotor and the housing, thus takes up all axial forces of the primary rotor and the secondary rotor.
By omission of the axial bearing between secondary rotor and housing the overall complexity with regard to support of the primary and the secondary rotor is reduced by at least one (axial) bearing.
An axial bearing supported by the housing is provided only for the primary rotor with the majority of the axial forces occurring during gas compression acting upon said bearing. The secondary rotor, upon which acts a considerably less amount of the axial forces produced during gas compression, is supported via the tooth flanks of its screw rotor at the screw rotor of the primary rotor.
The primary rotor is provided with the only axial bearing since larger axial forces act upon the primary rotor than on the secondary rotor. In this configuration only the relatively low axial forces of the secondary rotor need to be transmitted via the screw rotor teeth onto the primary rotor. Generally the secondary rotor may also be axially supported via an axial bearing at the housing while the primary rotor is axially supported via the screw rotors at the secondary rotor and thus does not comprise its own axial bearing connected with the housing.
In a preferred embodiment the axial bearing formed by the axial bearing parts is configured as slide bearing. The radial bearings, too, may be executed as slide bearings. The configuration of the axial slide bearing is simpler than that of an antifriction bearing and thus facilitates low-cost manufacture of the screw-type compressor. Slide bearings further present the advantage that they do not produce any appreciable heat so that the rotor shafts remain stressfree even at high speeds. The slide bearing may be lubricated with the same medium which is also used as lubricating and sealing agent in the compression chamber of the screw-type compressor. Oil or water may serve as gliding, lubricating and sealing fluid. However, air may also be used as slide bearing fluid.
When the primary rotor is belt-driven, an antifriction bearing is preferably used as radial bearing on the drive side since slide bearings are not suited for accommodating extremely high radial stresses.
In a preferred embodiment axial thrust forces of the secondary rotor are axially countered by the primary rotor exclusively via the front end faces of the meshing teeth of the screw rotors bearing against a bearing disk. The teeth of the screw rotors may be configured such that only very low axial forces or none at all occur on the secondary rotor so that these low axial thrust forces of the secondary rotor can without any problems be transmitted via the secondary screw rotor teeth to the primary rotor. A further means for transmitting the axial forces from the secondary rotor to the primary rotor is not required.
The secondary rotor preferably comprises an axial tensioning means which axially biases the secondary rotor. The axial tensioning means is not provided with a stop which could support the secondary rotor but applies a constant biasing force to the secondary rotor, preferably the secondary rotor shaft, the biasing force substantially corresponding to the anticipated axial stress acting on the secondary rotor during gas compression. The tensioning means thus substantially compensates for the axial forces acting upon the secondary rotor so that only very low axial forces or none at all have to be transmitted from the secondary rotor to the primary rotor. In a preferred embodiment the axial tensioning means is configured as a hydraulic tensioning means acting upon the shaft or the screw rotor of the secondary rotor. The tensioning means may also be supplied with air.
The axial bearing part of the primary rotor is preferably arranged on the screw rotor of the primary rotor. It is not the shaft of the primary rotor but the screw rotor of the primary rotor which is supported by the housing. The screw rotor, at which occur the axial forces produced by pressure generation as well as those transmitted by the secondary rotor, is directly supported by the housing which takes up the axial forces without any transmission via another component. Thus the primary rotor does not apply any axial stresses to the shaft so that the shaft is loaded to a smaller degree by corresponding torques and shearing forces.
In a preferred embodiment the axial bearing part of the primary rotor is configured as an axial front wall of the screw rotor. The axial bearing part of the housing is executed as an annular disk-shaped running face with the two axial bearing parts together forming the slide bearing. The front wall of the primary rotor screw rotor thus forms a bearing face supported on the ring-shaped running face of the housing. In this configuration no bearing-specific parts must be provided on the primary rotor. This renders manufacture of the primary rotor less expensive.
In an alternative embodiment the primary rotor comprises a slide bearing disk on an axial front end face of the screw rotor, which forms, together with an axial bearing part running face of the housing, the slide bearing.
On a front end face of the rotor of the primary rotor a ring-shaped slide bearing disk is provided which forms a closed radial running surface.
The screw rotor front wall or the slide bearing disk preferably comprises substantially radial grooves for a gliding fluid. The gliding fluid, which is introduced near the shaft or at the basis of the screw rotor, can be fed by the centripetal forces via said grooves to the outside. In this way a gliding film is produced over the overall radius and circumference of the screw rotor.
In a preferred embodiment the grooves take an arcuate path with the outer end of each groove, as seen in radial direction, be
Diller Ramik & Wight
KT Kirsten Technologie-Entwicklung GmbH
Vrablik John J.
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