Rotary expansible chamber devices – Working member has planetary or planetating movement – Helical working member – e.g. – scroll
Reexamination Certificate
2000-12-27
2002-04-09
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Working member has planetary or planetating movement
Helical working member, e.g., scroll
C418S055500, C418S057000
Reexamination Certificate
active
06368088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a mechanism for regulating back pressure of a scroll compressor. More particularly, the present invention relates to a mechanism for automatically regulating back pressure of a fixed scroll of a scroll compressor.
2. Background of the Invention
Scroll compressors have been widely employed in air conditioners. An example of the scroll compressors is shown in Taiwan Patent Publication No. 263024.
FIG. 1
of the attached drawings shows a conventional scroll compressor. The conventional scroll compressor comprises a pair of scrolls, respectively called fixed scroll
10
and rotating scroll
11
. The fixed scroll
10
is in general fixed and thus not rotatable, while the rotating scroll
11
is rotatable with respect to the fixed scroll
10
. The rotation of the rotating scroll
11
drives working fluid, such as coolant, from a low pressure chamber
12
located on the back side of the rotating scroll
11
to a high pressure chamber
13
located on the back side of the fixed scroll
10
and thus compressing the working fluid.
Also referring to
FIG. 7
which shows plots of the back pressure and scroll separation force of a scroll compressor vs. pressure difference between the high pressure chamber
13
and the low pressure chamber
12
. In
FIG. 7
, Curve A represents the scroll separation force occurring during the operation of the scroll compressor. The term “scroll separation force” as used herein indicates the force caused by the compressed working fluid acting between and thus tending to separate the fixed scroll
10
and the rotating scroll
11
. This may lead to leakage of the compressed working fluid between the scrolls
10
.
The scroll separation force changes in accordance with the operation conditions of the compressor. An example of the operation conditions of the scroll compressor that affects the scroll separation force is the pressure difference &Dgr;P between the high pressure chamber
13
and the lower pressure chamber
12
of the scroll compressor. During the operation of the scroll compressor, it is common to make use of the pressure difference between the high pressure chamber
13
and the low pressure chamber
12
, serving as a back pressure acting upon the fixed scroll
10
, to overcome the scroll separation force and thus eliminating leakage of working fluid between the scrolls
10
,
11
caused by the separation of the scrolls
10
,
11
.
In the conventional design of the scroll compressor shown in
FIG. 1
, forces caused by the pressure difference &Dgr;P act upon a boss
100
and a plurality of back pressure carrying pins
14
to provide the desired back pressure for retaining the fixed scroll
10
in position.
Curve B of
FIG. 7
shows the distribution of the back pressure employed in the conventional design. In the conventional design, only a single point of the back pressure curve is taken into consideration. Namely, the design is based on a “fixed” back pressure. The fixed point is usually the most frequently occurring back pressure of the scroll compressor, such as pressure difference &Dgr;P
2
of FIG.
7
. The design is done by adding a desired margin to the corresponding scroll separation force. This is the back pressure desired to overcome the separation force and keep the scrolls
10
,
11
together. The back pressure is the sum of the forces acting upon the boss
100
and the pins
14
and it is in general equal to the sum of the scroll separation force plus the safety margin. The overall surface area of the boss
100
and the pins
14
can thus be determined which in turn determines the slope of Curve B.
The conventional design is particularly suitable for scroll compressors that operate under fixed pressure difference. By suitably selecting the overall surface area of the boss
100
and the pins
14
, a sufficient back pressure may thus be obtained to overcome the scroll separation force. However, when a scroll compressor does not work in a fixed pressure difference condition, such as the condensation temperature and the evaporation temperature changing with the surroundings, the conventional design suffers the following disadvantages:
(1) When the scroll compressor is operating in a low pressure difference zone, namely the difference between the condensation temperature and the evaporation temperature is small, such as the zone between zero pressure difference and &Dgr;P
2
of
FIG. 7
, the back pressure (Curve B) is close to the scroll separation force (Curve A) causing an insufficiency of back pressure. Satisfactory sealing between the scrolls may not be kept and leakage of working fluid occurs.
(2) When the scroll compressor is operating in a high pressure difference zone, namely the difference between the condensation temperature and the evaporation temperature is large, such as the zone between &Dgr;P
2
and &Dgr;P
3
of
FIG. 7
, the situation is reversed. With the increase of the pressure difference, the back pressure acting on the fixed scroll
10
via the boss
100
and the pins
14
is increased and may significantly exceeds the desired back pressure thereby leading to undesired friction and thus wearing between the scrolls
10
,
11
and between the rotating scroll
11
and the support frame
15
. Damage of the parts and waste of electrical power that is used to drive the rotating scroll
11
may thus be caused.
Increasing the overall surface area of the boss
100
and the pins
14
results in a steep slope of Curve B. This, although helping solving the insufficient back pressure problem encountered in a low pressure difference operation condition, excessively increases the back pressure in the high pressure difference operation condition, resulting in reduction of the service life of the parts. Thus, there always needs a compromise between the leakage problem caused by insufficient back pressure and the wearing problem caused by excessive back pressure.
It is thus desirable to have a back pressure regulation mechanism for overcoming the above mentioned problems.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a back pressure regulation mechanism for a scroll compressor which help maintaining a suitable back pressure for all operation conditions. In other words, when the scroll compressor is operating in a low pressure difference condition, the back pressure regulation mechanism provides a sufficient back pressure to the fixed scroll in order to avoid leakage of the compressed working fluid. On the other hand, when the scroll compressor is operating in a high pressure difference condition, the back pressure regulation mechanism limits the back pressure applied to the fixed scroll to a desired value so as to avoid excessive back pressure acting upon the fixed scroll and thus alleviating wearing occurring on the parts of the compressor.
In accordance with the present invention, the back pressure regulation mechanism comprises a plurality of back pressure regulation devices engaging with the fixed scroll and a boss extending from the fixed scroll. The back pressure regulation devices provide a force acting on the fixed scroll, the force being proportional to the pressure difference during the operation in a low pressure difference zone, while being constant during the operation in a high pressure difference zone. Thus when scroll compressor is operating in the low pressure difference zone, the force provided by the back pressure regulation device, plus a force provided by the boss, both resulting from the pressure difference, is sufficient to compensate the scroll separation force and thus eliminating leakage problem and when the scroll compressor is operating in a high pressure difference zone, the constant force provided by the back pressure regulation devices limit the increased amount of the force acting upon the fixed scroll and thus alleviating the excessive back pressure problem.
An illustrative example of the back pressure regulation device in accordance with the present invention comprises a b
Chang Yu-Choung
Hsiao Tse-Liang
Lai Ching-Feng
Liang Kun-I
Yang Chun-Chung
Industrial Technology Research Institute
Vrablik John J.
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