Controlled contact pressure for scroll compressor seal

Details Controlled contact pressure for scroll compressor seal Controlled contact pressure for scroll compressor seal

1999-07-16

2001-05-01

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

C277S390000, C277S399000, C418S055400

Reexamination Certificate

active

06224059

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to seals for defining a scroll compressor back pressure chamber wherein the contact pressure between the seal and the scroll member is reduced compared to the prior art.
Scroll compressors are widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members face each other. The two scroll members each have a base with a generally spiral wrap extending from the base. The two spiral wraps interfit to define compression chambers. One scroll member is driven to orbit relative to the other. As the one scroll member orbits relative to the other, the intermitting spiral wraps move and decrease the volume of the compression chambers. In this way, refrigerant is compressed.
While scroll compressors do have several advantages, they also raise many design challenges. As an example, a separating force is created between the two scroll members as the refrigerant is compressed. The separating force tends to move the two scroll members away from each other. This reduces sealing contact between the two scroll members and leads to efficiency losses.
To address the separating force, scroll compressor designers create a “back pressure” chamber behind one of the two scroll members. Compressed fluid is tapped to the back pressure chamber and creates a force which opposes the separating force. The back pressure chamber is defined behind the base of one of the two scroll members by inner and outer sealing surfaces.
In one type of scroll compressor, the back pressure chamber is defined behind the orbiting scroll member, and includes two separate seals, with one at a radially inner position and one at a radially outer position. Pressurized refrigerant is tapped to a chamber defined between the two seals and creates the back pressure force.
In another type scroll compressor, the back pressure chamber is defined behind the non-orbiting scroll, and a single large seal with two sealing areas is utilized. The present invention has more benefit to the first type scroll compressor; however, aspects of the present invention may also prove beneficial to the second type scroll compressor.
The first type scroll compressor is shown in
FIG. 1. A
scroll compressor
20
incorporates a crankcase
22
receiving an orbiting scroll member
24
. A pair of seals
26
and
28
define a back pressure chamber
30
. A fixed scroll member
32
is positioned opposed to the orbiting scroll member. While the present invention is shown with the back pressure chamber defined behind the orbiting scroll
24
, it should be understood that aspects of this invention might also apply to scroll compressors having the back pressure chamber defined behind the fixed, or non-orbiting scroll member. Further, while a pair of seals are shown, aspects of this invention might apply to scroll compressors having a single large seal.
As shown in
FIG. 2A
, seals
26
and
28
include a seal jacket
30
having a rear wall
32
, and inwardly extending lips
34
and
36
. A coil spring
38
is positioned in each seal jacket. The seal portions
34
abut a rear surface
40
of the orbiting scroll member
24
. The spring
38
tends to bias the lip
34
into contact with the scroll member rear surface
40
.
A gas pressure force on the seal jacket
34
also forces the seal jacket
34
into rear surface
40
, in addition to the coil spring
38
. As shown in
FIG. 2B
, inward of lips
34
and
36
, the lips see the full pressure P in the back pressure chamber
30
. However, outwardly of the lips
34
and
36
, there is a restriction against flow. Thus, there is a pressure gradient from P downwardly toward a lower pressure. As shown in
FIG. 2C
, there is a gradient of the contact force between the lip
34
and
36
and the rear surface
40
of scroll member
24
which is generally reversed from the gradient shown in FIG.
2
B. As shown, the force is very large adjacent the rear wall
32
, and becomes smaller adjacent the inner edges of lips
34
and
36
. Adjacent the inner edges of lips
34
and
36
, the pressure outwardly of the lips is generally equal to the pressure inwardly, and thus the pressures are cancelled. However, due to the pressure gradient the contact force does become larger approaching the rear wall
32
.
Thus, adjacent the rear wall
32
, there is a contact force against the rear surface
40
which is undesirably high. Orbiting scroll
24
orbits relative to the seals. This contact force can lead to undue seal wear and premature seal failure.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, a seal for a scroll compressor back pressure chamber has a smaller contact area adjacent to the scroll member than is found adjacent to a housing member which receives the seal. In one preferred embodiment, this smaller force is provided by a thin sheet which includes a tab providing the contact area with the scroll member. Stated another way, there is structure on the seal for allowing pressurized gas in the back pressure chamber to move between the seal and the rear surface of the scroll member over the majority of the radial thickness of the seal surface. Stated yet another way, the seals each include an inner seal surface facing a housing and an outer seal surface facing the scroll member. The outer seal surface is provided with a tab extending for a portion of the radial thickness of the outer seal surface. The tab extends away from a lip surface of the outer seal surface and toward the scroll member, such that only the tab contacts the rear surface of the scroll member. The pressure in the back pressure chamber is communicated along the lip portion up to the tab portion.
In a most preferred embodiment, the invention is utilized in a scroll compressor having the back pressure chamber defined behind the orbiting scroll, and wherein generally U-shaped seal jackets are utilized in conjunction with a coil spring.
In embodiments of this invention, the tab may be formed at a position spaced inwardly of the rear wall, or alternatively may be generally aligned with the rear wall. In further embodiments, the sheet includes an extending lip which extends outwardly of the upper lip of the seal. The present invention also discloses an embodiment wherein a single seal sheet is associated with both the inner and outer seals that define the back pressure chamber. A pair of spaced ribs extend upwardly from the single sheet, and provide the smaller contact area.
With the present invention and its several embodiments, the use of the smaller contact area ensures that there is the full back pressure chamber P along the great majority of seal area. Thus, the force imbalance described above will not occur over as large an area. Instead, the force imbalance is generally cancelled, or at least controllable. In fact, the contact force between the seal and the scroll member from gas pressure can be eliminated. The contact force can be limited to a coil spring force, and the scroll compressor designer will have more control over this contact force.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.


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