Pumps – Motor driven – Motor rotor intermediate coaxial pump rotors
Reexamination Certificate
1999-03-31
2001-02-27
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Motor rotor intermediate coaxial pump rotors
C417S423500, C417S355000, C417S423700, C310S179000
Reexamination Certificate
active
06193473
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compressor assembly, in particular to a compressor assembly comprising a compressor having a rotatable impeller and a motor driving the compressor, the impeller and the motor being linked by a direct drive.
BACKGROUND OF THE INVENTION
Compressors having an impeller rotatable within a compressor casing are well known in the art. Such compressors include both centrifugal compressors or radial flow compressors and axial flow compressors. In centrifugal or radial flow compressors, the fluid being compressed is caused by the rotating impeller to flow along a passageway in which the cross sectional area normal to the flow gradually decreases in the direction of flow. Axial compressors operate by causing the fluid to be compressed to flow along a passage of constant or substantially constant cross sectional area. An example of such a compressor is disclosed in U.S. Pat. No. 4,428,715.
Compressors of the aforementioned types may be driven by a range of motors, such as internal combustion engines, and turbines. However, in many applications it is both preferable and desirable to drive centrifugal and axial flow compressors using electric motors. Typically, induction or synchronous electric motors have been employed to drive compressors. To date, a major drawback associated with the use of electric motors to drive rotating impeller compressors has been the linkage between the electric motor and the compressor impeller. A given compressor will have a specific speed of rotation of the impeller in order to achieve the compression duty required of it. At the same time, an induction electric motor will have an optimum speed of rotation, at which the torque output is at a maximum. Heretofore, in order to link the compressor with a suitable electric drive motor, it has been necessary to employ an arrangement of one or more gears. In this way the different optimum speeds of rotation of the compressor and the electric motor can be accommodated. A particular problem arises in the case of high speed centrifugal compressors, having power requirements of the order of 200 horsepower or less. Such compressors are often required to operate at speeds in excess of 50,000 rpm. The optimum speed of rotation of an induction electric motor suitable for this duty is far lower than the speed of rotation required of the high speed compressor, requiring a gear assembly to be employed in the drive assembly of the compressor. However, for such compressors, the high costs of incorporating an arrangement of gears in the drive assembly results in a significant economical disadvantage. This in turn has led to other forms of compressors, such as screw compressors, being favored for such duties.
Accordingly, there is a need for a compressor assembly in which the requirement for a gear assembly in the drive is dispensed with and in which the compressor and the electric motor are directly linked.
SUMMARY OF THE INVENTION
According to the present invention there is provided a compressor assembly comprising:
a compressor having a compressor casing comprising a fluid inlet and a fluid outlet;
an impeller rotatable within the compressor casing;
a switched reluctance motor;
a rotatable drive shaft assembly extending from the switched reluctance motor into the compressor casing;
the impeller being mounted on the drive shaft assembly and rotatable therewith within the compressor casing; and
the switched reluctance motor comprising a stator and a rotor, the rotor being mounted on the drive shaft assembly and rotatable therewith.
It has surprisingly been discovered that a switched reluctance motor may be employed to drive a rotating impeller compressor using a direct drive configuration, that is one in which the impeller of the compressor and the rotor of the motor are directly connected and rotate at the same speed. It has been found that the use of a switched reluctance motor to drive the rotatable impeller of a compressor allows the gear assembly or gear box to be dispensed with and a direct drive assembly to be employed.
The compressor may be either an axial flow compressor or a centrifugal or radial flow compressor. The preferred embodiment of the present invention employs a centrifugal or radial flow compressor.
The compressor assembly of the present invention is particularly suitable for operation at high speeds of rotation. Accordingly, the compressor preferably rotates at a speed greater than 25,000 rpm, more preferably at a speed greater than 50,000 rpm.
Although any size or rating of compressor may be used, the compressor assembly of the present invention offers particular advantages when the compressor has a power input requirement of less than 200 horse power.
The compressor assembly preferably comprises first and second compressors having first and second compressor casings, each of the first and second compressor casings comprising a fluid inlet and a fluid outlet. First and second impellers are located within and rotatable within the first and second compressor casings respectively. The first and second impellers are mounted on the drive shaft assembly and rotatable therewith. Such a compressor assembly may comprise two separate compressors driven from the same switched reluctance motor. More preferably, however, the two compressors are combined to form a two-stage compressor assembly. In such an arrangement, the fluid outlet of the first compressor casing communicates with the fluid inlet of the second compressor casing. In a two compressor assembly or two-stage compressor assembly, the switched reluctance motor is most conveniently disposed between the first and second compressor casings, with the rotor of the switched reluctance motor being mounted on the drive shaft assembly between the first and second impellers.
References in this specification to a “drive shaft assembly” are to a linkage transferring drive from the switched reluctance motor to the impellers of the compressor assembly. The drive shaft assembly provides a direct drive between the rotor of the switched reluctance motor and the impellers. Such a drive is characterized by the motor and the impeller rotating at the same speed. The drive shaft assembly may comprise one or more individual shafts linked by couplings so as to allow the drive to be transferred. A most convenient and advantageous assembly is one in which the rotor of the switched reluctance motor and the impeller are mounted on a single shaft.
A preferred embodiment of the present invention is a two stage centrifugal compressor assembly comprising:
a first compressor casing having a fluid inlet and a fluid outlet;
a first impeller rotatable within the first compressor casing;
a second compressor casing having a fluid inlet and a fluid outlet;
a second impeller rotatable within the second compressor casing; and
a switched reluctance motor disposed between the first and second compressor casings and comprising a stator and a rotor rotatable within the stator;
a drive shaft; wherein the first impeller, second impeller and the rotor are mounted on the drive shaft and rotatable therewith; and
the fluid outlet of the first compressor casing communicates with the fluid inlet of the second compressor casing.
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Landes Forrest G.
Mruk Gerald K.
Weber Peter J.
Cooper Turbocompressor, Inc.
Pwu Jeffrey
Tassel Kurt D. Van
Van Tassel & Associates
VandenHoff Deborah G.
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