Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Patent
1990-01-13
1992-05-05
Bertsch, Richard A.
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
417 18, 417 44, 417 45, 417 53, 417205, 417243, 318432, F04D 2700
Patent
active
051102641
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention generally relates to the field of vacuum pumps useful to evacuate an enclosed space. More particularly, the invention details a vacuum pump which incorporates a variable speed motor rotationally driving a compressor. The motor is electronically controlled to increase in speed in inverse proportion to the density of the air or gas being evacuated from the enclosed space. Thereby, the compressor and motor operate at maximum efficiency, reducing the evacuation time and energy requirements.
The most common types of vacuum pumps are designed for constant displacement and/or constant speed operation. These vacuum pumps are designed to have a peak efficiency at a selected inlet and outlet air or gas density. During the time interval required to evacuate an enclosed space, these vacuum pumps operate at the peak efficiency for only a brief time. During the majority of the evacuation interval, the constant displacement constant speed vacuum pumps are not operating efficiently, requiring longer evacuation intervals and higher amounts of power. Furthermore, the weight and bulk of these types of vacuum pumps is adversely affected.
Additionally, current vacuum pumps generally utilize oil or a liquid lubricant for reducing friction and wear within moving components. For some applications, these lubricants may be a source of contamination for the air being evacuated from the enclosure. When the air is being exhausted to a clean environment, contamination is not acceptable. Thus it would be desirable to eliminate the necessity for liquid lubricants where there is a potential for contamination.
It is therefore an object of the present invention to provide a vacuum pump which operates efficiently throughout the evacuation interval. A further object of the invention is to provide a vacuum pump which does not require liquid lubricants which may potentially contaminate the evacuated exhaust stream.
SUMMARY OF THE INVENTION
The vacuum pump system of the present invention basically consists of a motor driven compressor, aftercoolers, an electronic controller, a shutoff valve, a check valve and interconnecting plumbing and wiring. A coolant or heat sink medium is also required for circulation through the aftercoolers to remove the heat of compression. The system is particularly designed and described for use in evacuating an airlock on a space station, and recovery of the air therefrom.
In operation, the electronic controller controls the current to the motor driven compressor at a constant level to develop constant drive torque. The resulting compressor speed depends on the density of the air at the inlet and the discharge pressure. On initial run-up in a simple pumpdown cycle from a chamber pressurized to 14.7 pounds per square inch (psia) the rotor rapidly reaches approximately 25 to 40 percent of the design speed before the motor, running at design current, is fully loaded. As the evacuation progresses, the rotor accelerates as 1/.sqroot.p.sub.in, where p.sub.in is the inlet air density. The compressor design speed thus matches the density at the airlock final pumpdown pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the vacuum pump system of the present invention.
FIG. 2 is a cross sectional view of a preferred design for a motor driven compressor for use in the system of FIG. 1.
FIG. 3 is a schematic representation of an alternative design for the vacuum pump system incorporating a pair of two stage motor driven compressors.
FIG. 4 is a schematic representation of the electronic controller and electrical circuitry of the system of FIG. 1.
FIG. 5 is a graphical representation of motor speed and torque as a function of inlet gas density.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The variable speed vacuum pump system 10 is depicted schematically in FIG. 1. The vacuum pump system 10 includes a two stage motor driven compressor 12, a pair of aftercoolers 14, 16, an electronic controller 18, a shutoff valve 20, and a check valve 2
REFERENCES:
patent: 4105372 (1978-08-01), Mishina et al.
patent: 4125345 (1978-11-01), Yoshinagha et al.
patent: 4525125 (1985-06-01), Matsumoto et al.
patent: 4878813 (1989-11-01), Miki
Abel David B.
Allied-Signal Inc.
Bertsch Richard A.
Miller Terry L.
Scheuermann David W.
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