Rotary expansible chamber devices – Working member has planetary or planetating movement – Helical working member – e.g. – scroll
Reexamination Certificate
1999-07-16
2001-09-18
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Working member has planetary or planetating movement
Helical working member, e.g., scroll
C418S055500, C418S057000
Reexamination Certificate
active
06290478
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a back-pressure chamber for a scroll compressor wherein seals are positioned to reduce a thrust force between the two scroll members.
Scroll compressors are widely utilized in refrigerant compression applications. Generally, a scroll compressor includes two scroll members each having a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. A motor drives one scroll member to orbit relative to the other. Most scroll compressors have an axially compliant design. In this design, either the orbiting or non-orbiting scroll is allowed to move axially towards the other to minimize leakage between the floor of the scroll base and tips of the opposed scroll wraps by loading one scroll member against the other. This loading prevents the formation of gaps between the floor and tips of the scroll, thus minimizing leakage losses.
However, when the scrolls are loaded against one another, it is possible to damage the scroll components if the created thrust load becomes too high. Further, unwanted frictional losses also increase with increased loading. Thus, it is a goal of a scroll compressor designer to minimize the load as much as possible, while keeping the floor and the tip of the interfitting scroll wrap in contact with each other to avoid leakage.
There are several forces acting on the non-orbiting and orbiting scroll members, shown schematically in FIG.
1
. As illustrated for the case of radially compliant orbiting scroll, a projection of a radial gas force vector F
rad
passes through a center line of the orbiting scroll
24
, and acts at the midpoint of the wrap height. A tangential gas force vector F
tg
is perpendicular to the radial gas force and also acts at the midpoint of the wrap height. An axial gas force F
ax
is applied normal to the floor or plane of the orbiting scroll. As shown in
FIG. 2
, to assure that positive contact is maintained between the interfitting scroll members in axial direction, it is necessary to establish a F
BC
force which compensates for the force F
ax
separating the two scroll members, and also compensates for an overturning moment M
ov
which tips the orbiting scroll member relative to the non-orbiting scroll member. The overturning moment M
ov
is a product of F
tg
and an overturning moment arm L
ov
where L
ov
extends from the center of orbiting scroll bearing the center of the wraps. The radial gas force F
rad
also in theory has an impact on the overturning moment M
ov
, but its effect is typically of a second order and is normally neglected in calculations of the overturning moment.
The compensating force F
BC
has been provided by tapping a pressurized fluid to a chamber behind one of the two scroll members. Pressurization of this chamber, known as a back-pressure chamber
28
establishes the compensating force F
bc
to counteract the separating force F
ax
, and the overturning moment M
ov
. Typically, back-pressure chambers are defined by at least two seal surfaces, that seal the back-pressure chamber from the suction pressure. The refrigerant is tapped to this chamber through an opening in one of the two scroll members to establish pressure in the back chamber that is higher than suction pressure. Since the pressure in the back chamber exceeds suction pressure, the compensating force F
bc
counteracts the separating force F
ax
, and the overturning moment M
ov
.
As shown in
FIG. 3
, in prior art designs of back-pressure chambers
28
, both an inner seal
12
and an outer seal
10
have been positioned concentrically with respect to the crankcase bore
14
. This crankcase seal arrangement while capable of creating a force that counteracts the separating force has the drawback of requiring a high back-pressure chamber force F
bc
. As a result, a high thrust load as mentioned above has been encountered between the interfitting scroll members. It is a goal of this invention to reduce the thrust load between the interfitting scroll members.
SUMMARY OF THE INVENTION
In disclosed embodiments of this invention, at least one seal defining boundary of a back-pressure chamber is positioned off-center relative to a rotational axis of the shaft driving an orbiting scroll member. Because of the seal eccentricity, the back-pressure force vector F
bc
is also positioned eccentrically with respect to the shaft rotational axis. This eccentricity can be defined by a distance e. As a result of seal eccentricity, a moment M
BC
in the back-pressure chamber is created which is equal to F
bc
e. The position of the eccentric seals or seals may be selected in such a way that the moment M
BC
counteracts the action of the scroll overturning moment M
ov
, at the time during the cycle when F
tg
reaches its maximum value.
Stated another way, the position of the seal eccentricity may be chosen to provide the maximum benefit at the time when the scrolls are most prone to separate, which occurs when F
tg
is at maximum.
These and other features of the present invention can be best understood from the following specification and drawings, the following which is a brief description.
REFERENCES:
patent: 4992032 (1991-02-01), Barito et al.
patent: 5040956 (1991-08-01), Barito et al.
patent: 5085565 (1992-02-01), Barito
patent: 5622488 (1997-04-01), Tojo et al.
patent: 5857844 (1999-01-01), Lifson et al.
patent: 5989000 (1999-11-01), Tomayko et al.
patent: 421910 A1 (1990-09-01), None
patent: 478269 A1 (1991-09-01), None
patent: 631063 86 (1988-11-01), None
patent: 631063 87 (1988-11-01), None
patent: 631063 88 (1988-11-01), None
patent: 3172592 (1991-07-01), None
patent: 5-141201 (1993-06-01), None
patent: 9203413 (1992-03-01), None
Carlson & Gaskey & Olds
Denion Thomas
Scroll Technologies
Trieu Theresa
LandOfFree
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