Rotary kinetic fluid motors or pumps – Runner has planetary motion or rotates around oblique or...
Reexamination Certificate
2002-07-24
2003-10-21
Nguyen, Ninh H. (Department: 3745)
Rotary kinetic fluid motors or pumps
Runner has planetary motion or rotates around oblique or...
C415S122100, C415S216100, C415S231000
Reexamination Certificate
active
06634853
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power driven machinery, such as compressors, and, more particularly, to centrifugal compressors.
Due to the power that drives them and the need for durability, machines such as compressors tend to be heavy and bulky. The bulk involved requires that considerable space be dedicated to machines such as compressors, and it has long been desired to reduce their space requirements, not only for more advantageous use of space in buildings and the like, but also to reduce the size of the machines for purposes of shipping, maintenance, repair, etc. In the case of a compressor, for example, the output shaft from an electric motor, internal combustion engine, or the like is coupled to a drive shaft of the compressor. The drive shaft transmits power from the power source through an arrangement of gears to another shaft, on which an impeller is mounted. Very often, where more than one stage of compression is necessary, one or more additional impellers are mounted on still other shafts. All of this tends to add to the size of the compressor.
Furthermore, the input shaft to the compressor must be precisely aligned with the output shaft from the motor or the like to avoid excessive vibration, premature bearing failure and other problems. In addition, the gears tend to be noisy, and there are a number of places at which high-pressure gas from gas handling portions of the compressor can leak into areas containing the gears and other drive elements. In addition, a large seal around the input shaft has been required and, in some cases, notches in the seal, designed to prevent seals from rotating, that can lead to seal distortion as the temperature rises. Moreover, many step up gear drives employ a single stage of step up, thereby making the pitch line velocities of the gears and the gear noise level higher, and gear efficiency lower. In addition, gear size is unnecessarily large. With a single stage of gear step up, the drive shaft and the impeller shaft [input and output] must be offset, requiring more expensive machining and assembly and the windage loss of the gears traveling through the gas in the drive compartment is higher than necessary because the gear diameter is greater and the gear velocity is higher than necessary. The power windage loss from a gear is usually proportional to the fifth power of the diameter. With many shaft bearings, there tends to be some movement between bearing surfaces and the shaft such that the shaft is slightly eccentric to the bearings, which in turn increases the likelihood of significant leakage of the impeller cavity to the gear cavity.
As with all rotary machinery, particularly machinery that rotates at a high speed, vibration is an important consideration, and vibration is likely to be excessive if the critical speed of the rotor is below the operating speed of the rotor, the critical speed being the speed at which vibration begins. Each impeller develops pressure from the inside to the outside and, as a result, each impeller has a thrust force developed toward the inlet side. These thrust forces must be borne by some portion of the compressor.
SUMMARY OF THE INVENTION
By the present invention, a centrifugal compressor for air or other gases is provided which is compact and lightweight compared with known centrifugal compressors of similar capacity. In addition, the centrifugal gas compressor according to the present invention has numerous other improved characteristics, such as reduced noise and vibration, increased ease of installation, improved sealing between the gear cavity and the compressor cavity, as well as smaller and more efficient sealing between the compressor and the atmosphere. Furthermore, aspects of the compressor according to the present invention result in lower costs for machining and assembly than known compressors.
The foregoing and other advantages result from the construction of the compressor of the present invention. Misalignment of a coupling of the drive shaft of the motor, engine or the like to the drive shaft of the compressor is accommodated by the structure of the compressor shaft, including the thinness and flexibility of the compressor input shaft. The compressor input shaft is a thin quill shaft positioned within a hollow shaft so that most of the length of the hollow shaft overlaps the quill shaft. The quill shaft is fixed to the hollow shaft only at the internal ends of the quill shaft and the hollow shaft, thereby reducing the overall length of the compressor input shaft system compared to the input shaft systems of compressors in which the thin quill shaft is mounted external to the compressor. Thus, according to the present invention, the full length of the quill shaft between the coupling to the motor at one end and the attachment to the hollow shaft at the other end is available to accommodate strain and misalignment, but without increasing the length of the compressor input shaft system by the entire length of the compressor input shaft and without adversely affecting the performance of the hollow shaft.
The diameter of the thin quill shaft can be minimized because no keyways are used to connect the shaft to the coupling hub. Keyways inherently experience increased stress concentrations relative to the rest of a shaft. Therefore, shafts having keyways must be made sufficiently large in diameter to withstand the higher stresses of the keyways. A hub is mounted by friction on the outer end of the thin quill shaft, the hub being connected by a flexible coupling with the motor drive shaft. The inner end of the thin quill shaft is secured by friction in the inner end of the hollow shaft. Since the drive shaft of the compressor according to the present invention is a round shaft without keyways, the drive shaft has no increased stress concentrations in some areas. As a result, the diameter of the shaft can be made smaller. This reduces weight and permits the use of a smaller shaft seal having lower rubbing speeds, lower costs, and less friction loss.
In addition to accommodating misalignment of the coupling, the small diameter of the quill shaft allows the shaft seal between the gas in the compressor and the atmosphere to be minimized, due to the smaller diameter of the seal. The smaller diameter of the seal reduces the speed at which surfaces of the seal rub on one another and thereby reduces wear on the seal and the possibility of leakage.
Of the parts of the seal that rub on one another, it is preferred that one is carbon and that the other is silicone carbide. These materials operate together with a low coefficient of friction to reduce wear. Furthermore, the carbon seal is devoid of notches and other irregularities and, therefore, is better able to maintain its true flatness without distortion. Notches are commonly used in seals to receive complementary formations and thereby prevent the seals from rotating due to the friction between the mechanical parts. Upon the heating due to friction, the areas of the seals around the notches expand differently from other areas of the seals, thereby causing distortion of the seals. In contrast, the compressor according to the present invention includes a circular spring finger to grip the carbon seal part and thereby prevent it from rotating due to friction.
Two stages of gear ratio step up are used in the compressor according to the present invention. As a result, the pitch line velocities of the gears are much lower than the pitch line velocities of a single stage step up gear. This makes for better efficiency and a lower noise level. Furthermore, the use of a two-stage gear ratio step up enables the compressor drive shaft and the compressor impeller shaft to be coaxial, rather than offset from one another, as in a single stage gear ratio step up. The coaxial arrangement reduces the cost of machining and assembly. Furthermore, the diameters of the gears in the two-stage gear ratio step up arrangement are smaller than in a single stage arrangement, and the gear velocities are lower. As a result, the powe
Nguyen Ninh H.
Sea Solar Power, Inc.
Shannon John P.
Venable LLP
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