Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-03-03
2001-06-05
Thorpe, Timothy S. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C418S191000
Reexamination Certificate
active
06241490
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a multirotor vacuum pump including at least two rotor arranged in the pump housing and cooperating with each other so that as a result of their mutual contactless movement relative to each other, working chambers, into which a to-be-pumped gas is fed, are formed.
Multirotor vacuum pumps of the type described above find a particularly wide application in chemical industry and in semiconductor technology as dry pump systems. Dry pump systems are characterized in that no oil is contained in their compression or expansion chambers for lubrication, reduction of a dead volume and similar purposes. Therefore, they are capable of producing a completely hydrocarbon-free vacuum. To obtain optimal pumping characteristics, a plurality of pump stages can be arranged in a single one after another.
In conventional multirotor vacuum pumps, two or more pistons are rotatably arranged in a single housing. The pistons are mounted on shafts supported in bearing plates arranged at one or both of opposite ends of a shaft. The rotation of the pistons is synchronized by gear sets so that a uniform rolling off of the pistons without any contact there-between, with maintaining minimal clearances, can take place. The bearings and the gear sets should be separated from the working chambers with suitable seals to prevent oil or similar working medium from penetrating into the chambers and to prevent, on the other hand, the pumped harmful gases from penetrating into the gear sets and the space, where the bearing are located, as these gases can contaminate or even destroy the lubricant. The sealing can be effectively established by using a seal gas.
In the conventional multirotor vacuum pumps, the drive motor is located outside of the pump housing and, for its connection to the main shaft, a shaft leadthrough is necessary. Dependent on the pump use and/or design, one or more rather expensive seals need be provided for the shaft leadthrough.
A serious drawback of the conventional pumps of the above-described type consists in their rather expensive construction. This results from relative large dimensions of the pump, numerous pump components, and from their rather complicated assembly. Moreover, such important components of a pump as seals between separate stages, seal gas arrangements, and elements of oil supply are often unaccessible in the known construction and need much improvement.
Accordingly, an object of the present invention is to provide a dry multirotor vacuum pump in which the foregoing drawbacks are eliminated.
A further object of the present invention is to provide a dry multirotor vacuum pump which while insuring optimal pump characteristics, would have small dimensions which would insure a space-saving and easy mounting of the pump.
A still further object of the present invention is to provide a dry multirotor vacuum pump in which the seals, the seal gas elements and the elements of the oil supply are optimally adapted to the novel concept of the pump.
SUMMARY OF THE INVENTION
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a dry multirotor vacuum pump of the type described above in which at least one of the at least two rotors has a hollow somewhat bell-shaped profile, and the drive is formed as an external rotor motor having the rotor elements arranged on an inner surface of the at least one of the at least two rotors, and stator elements fixedly mounted inside the at least one of the at least two rotors opposite the rotor elements.
The rotors occupy a very large portion of the pump volume. This space until now has not been used because of the large dimensions of the rotors. By providing at least one hollow rotor having a bell-shaped profile, it became possible to completely integrate the drive system in the interior of this rotor and, thus, use the space which until the present time has not been used. This reduces the dimensions of the pump to a substantial degree.
The locations of the bearings are encapsulated with respect to the pumping space, and the need for shaft leadthrough has been eliminated. The novel design of the dry multirotor vacuum pump provides additional advantages which consist in that the electrical conductors for feeding power to the drive elements and the cooling medium conduits can be arranged in the shaft of the main rotor.
A bell-shaped profile is a structure that results in a large diameter of the rotor. In case of a multirotor pump, with the stages being arranged axially one behind the other, there exists a problem of providing appropriate sealings between the stages. E.g., providing radial shaft seals results in high speeds at the border surfaces because of large diameters. This leads to unacceptable high temperatures and to wear. In addition, it is desirable that the seals act in direction opposite to the return flow between stages. In order to take these conditions into account, it is proposed to provide contactless seals between the stages and formed as screw pumps. The screw pump provide for a pressure ratio acting opposite to the return flow.
To insure that no oil penetrates into the pumping space and, vice versa, no process gas penetrates into the gear set space, it is necessary to create a seal gas barrier between the gear set space and the pumping space. A critical problem here is metering. Because as a seal gas, as a rule, an inert gas is used, it is necessary to keep the gas consumption low. On the other hand, no risk should be taken to endanger the sealing function by using a too little gas amount. To fulfill these contradictory requirements, until now, rather expensive seal gas devices for controlling the seal gas pressure, for monitoring the seal gas sealings, and the like were necessary. According to the invention, to keep an optimal gas consumption, elements of the seal gas sealing are formed of a porous material, with the seal gas consumption being dependent on the wall thickness of the seals and the permeability of the porous material. At that, care should be taken that the seal gas pressure is above the range in which blocking of the seal material takes place. Because of the distribution of the seal gas in the sealing and along the surfaces defining a clearance between seals and the rotor, a gas cushion is provided which prevents a gas exchange between the gear set space and the pumping space.
For feeding oil to the bearings, symmetrically arranged screw pumps, which are arranged on the inner side of the control rotor, are used. For further delivery of the oil, according to the invention, bores are formed inside respective shafts. This also promotes an optimal use of the available space.
The inventive pump has a compact construction while insuring, at the same time, optimal pump characteristics. It also makes possible an easy space-saving mounting of the inventive pump. At that, the components of the power supply, cooling medium supply, and sealings can be optimally adapted to the new pump design.
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patent: Re. 32055 (1985-12-01), Schibbye et al.
patent: 3969042 (1976-07-01), Bachler
patent: 4457680 (1984-07-01), Gable
patent: 4551073 (1985-11-01), Schwab
patent: 4770609 (1988-09-01), Uchida et al.
patent: 5051060 (1991-09-01), Fleischmann et al.
patent: 5346361 (1994-09-01), Jurgill et al.
patent: 5927863 (1999-07-01), De Bock
Brown & Wood LLP
Gray Michael K.
Pfeiffer Vacuum GmbH
Thorpe Timothy S.
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