Rotary expansible chamber devices – Working member has planetary or planetating movement – Helical working member – e.g. – scroll
Reexamination Certificate
1998-10-13
2001-02-27
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Working member has planetary or planetating movement
Helical working member, e.g., scroll
C418S055400, C418S141000, C277S398000
Reexamination Certificate
active
06193487
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to a fluid displacement device. More particularly, it relates to a scroll-type fluid displacement device for vacuum pump application.
BACKGROUND OF THE INVENTION
Scroll-type fluid displacement devices are well known. For example, U.S. Pat. No. 801,182 to Leon Creux, discloses a scroll device including two scroll members, each having a circular end plate and a spiroidal or involute scroll element. The scroll elements have identical, spiral geometry and are interfit with an angular and radial offset to create a plurality of line contacts between their spiral curved surfaces. Thus, the interfit scroll elements define and seal off at least one pair of fluid pockets. By orbiting one scroll element relative to the other, the line contacts are shifted along the spiral-curved surfaces, thereby changing the volume of the fluid pockets. This volume increases or decreases depending upon the direction of the scroll elements' relative orbital motion. Thus, the device may be used either to compress or expand fluids.
Known scroll-type fluid displacement devices, whether operating as expanders or compressors, can be used as vacuum pumps. However, both face a substantial potential for overheating.
Where an expander is used as a vacuum pump, ambient air will re-expand to the discharge pockets because the air pressure in the discharge pockets is much lower than the ambient air pressure. Re-expansion of ambient air in this fashion consumes energy and frequently causes overheating. A discharge valve can be employed to reduce re-expansion of the ambient air to some extent, but, it cannot eliminate re-expansion and such valves frequently malfunction.
When a compressor is used as a vacuum pump and the inlet air of the compressor is at atmospheric pressure during the start-up period, or due to leakage to ambient, the heat associated with the re-expansion and compression process is damaging to the compressor because there usually is no lubrication or internal cooling allowed. The re-expansion and compression heat causes excessive thermal growth of the scroll elements, resulting in galling between tips and bases of the scroll elements.
U.S. Pat. No. 3,994,636 discloses a tip seal mechanism for radial sealing between the compression pockets in a scroll-type fluid displacement device. In this device, as shown in the drawings as in
FIG. 7
, tip seals
101
and
201
are placed in spiral grooves
102
and
202
formed in the middle of the tips of a scroll vanes
103
and
203
, respectively. These tip seals
101
and
201
run continuously along spiral grooves
102
and
202
, from the central region to the periphery of the scroll members
103
and
203
, respectively. The seals
101
and
201
are urged by either a mechanical device, such as elastic material, or by pneumatic force to contact the bases
204
and
104
of the other scroll member
203
and
103
, respectively. This arrangement provides radial sealing. However, the width of the tip seal is smaller than the width of the scroll vane. There are tangential leakage passages A—A and B—B in scroll element
103
, for example, at the both sides of the tip seal
101
. These leakage passages lower the volumetric and energy efficiency of the scroll device.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to overcome the above-mentioned shortcomings of a scroll-type fluid displacement device in a vacuum pump application.
It is also an object of the invention to provide a scroll-type vacuum pump wherein excessive heat normally associated with the re-expansion and compression process in such a device is eliminated.
It is another object of the invention to provide a scroll-type vacuum pump which achieves these ends by, among other things, utilizing an expander and a compressor in the same pump.
It is still another object of the present invention is to provide a shaft seal mechanism which seals off the suction chamber of the expander from both the ambient and the discharge chamber of the expander.
Yet another object of the present invention is to provide a seal arrangement at the tip of a scroll element which effectively provides radial and tangential sealing without tip-base galling.
The foregoing and other objects are realized in accord with the present invention by providing an expander-compressor, two stage vacuum pump, built in the same body and sharing the same drive shaft. The first stage is a scroll-type expander. It is in series with a scroll-type compressor, which is the second stage. The volume of the suction pockets of the second stage, the compressor, is not significantly smaller than the volume of the discharge pockets of the first stage device, the expander. Thus, the amount of heat associated with the re-expansion and compression process is reduced. The two stage pump also includes a double shaft seal mechanism which seals off the suction chamber of the expander from both the ambient and the discharge chamber of the expander.
The two stage pump of the invention further includes a labyrinth structure on the tip of each scroll element to tightly control the axial gap between the tips and bases of the mating scroll elements. The labyrinth structure comprises an arrangement of small lips, with thin and low walls, forming a maze on each tip of each of the scroll elements. When thermal growth of the scroll elements causes the labyrinth lips to press against the base of a mating scroll element, the labyrinth lips are sufficiently weak that the contact pressure between the lips and base deforms the lips on the scroll by removing interferencing material without causing tip or base galling. Thus, the labyrinth lips can produce an extremely close axial clearance between the scroll tips and bases. Radial and tangential leakage flow between compression pockets is significantly reduced because good radial and tangential sealing is achieved.
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Brinks Hofer Gilson & Lione
Mind Tech Corporation
Vrablik John J.
LandOfFree
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