Thrust ball bearing and open-type scroll compressor

Details Thrust ball bearing and open-type scroll compressor Thrust ball bearing and open-type scroll compressor

2000-06-07

2001-11-06

Denion, Thomas (Department: 3748)

Rotary expansible chamber devices

Working member has planetary or planetating movement

Helical working member, e.g., scroll

C384S615000, C384S255000, C384S492000

Reexamination Certificate

active

06312235

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to open-type scroll compressors, and relates in particular to an open-type scroll compressor that can be operated in the critical region of a cooling medium such as carbon dioxide to provide vapor compression cooling cycles.
2. Description of the Background Art
From the standpoint of environmental protection, there has been proposals, in recent years, to use carbon dioxide gas as a replacement for freon gas as a working gas (cooling medium) to provide cooling cycles (referred to as CO
2
cooling cycles), for example, in a Japanese Patent Application, First Publication Hei
7-18602
. The operation of the CO
2
-based cooling cycle is similar to that of the conventional vapor compression cooling cycle based on freon. That is, as shown in
FIG. 7
(using a Mollier diagram for CO
2
) by an A-B-C-D-A cycle, the compressor compresses gas-phase CO
2
(A-B), and the compressed high temperature gaseous CO
2
is cooled in a heat dissipater (gas cooler) (B-C). Next, the gas pressure is reduced (C-D) in a pressure reducer, and the condensed liquid-phase CO
2
is vaporized (D-A) so that the latent heat of vaporization is gained from an external fluid medium such as air thus resulting in cooling the external fluid.
However, because the critical temperature for CO
2
is 31° C. which is lower than that of freon, which is the conventional cooling medium, so that when the outside temperature is high, such as during the summer season, the temperature of CO
2
in the heat dissipater circuit becomes higher than the critical temperature of CO
2
. In other words, CO
2
does not condense at the exit-side of the heat dissipater (line BC does not cross saturated liquid line SL). Also, because the conditions at the exit-side (point C) of the heat dissipater are determined by the discharge pressure of the compressor and the temperature of CO
2
at the exit-side of the heat dissipater and the temperature of CO
2
at the exit-side of the heat dissipater is determined by the heat releasing capability of the heat dissipater and the outside temperature (not controllable), the temperature at the exit-side of the heat dissipater cannot be controlled in practice. Therefore, it follows that it is possible to control the conditions at the exit-side (point C) of the heat dissipater by controlling the discharge pressure of the compressor (heat dissipater exit-side pressure). In other words, to obtain sufficient cooling capacity (enthalpy difference) when the external temperature is high such as during the summer season, it is necessary to increase the heat dissipater exit-side pressure as shown by a cycle E-F-G-H-E. For this reason, it is necessary to increase the operating pressure of the compressor for CO
2
-based cooling cycle compared with that for conventional freon-based cooling cycle.
For example, in an automobile air conditioner, operating pressure required for conventional R134-based (freon-based) compressor is about 3 kg/cm
2
while it is 40 kg/cm
2
for CO
2
based compressor, and the stationary pressure is about 15 kg/cm
2
for R134 (freon) while that for CO
2
is 100 kg/cm
2
. Therefore, it is necessary for the compressor to be built to withstand the pressure of such a high magnitude.
An example of the compressor used in the conventional automobile air conditioner is shown in FIG.
8
. As shown in this diagram, a spiraling scroll
52
is provided inside a housing
51
, and a fixed scroll
53
for engaging with the spiraling scroll
52
is situated above the spiraling scroll
52
.
Inside a cylindrical boss
54
formed in the center section of the outer surface (lower surface in the diagram) of the end plate
52
a
of the spiraling scroll
52
, an eccentric shaft
55
is freely rotatably supported by a scroll bearing
56
, which also serves as the radial bearing. The eccentric shaft
55
is able to rotate eccentrically with a radius p by means of an eccentric drive, which is omitted from the diagram.
Also, between the outer surface periphery of the end plate
52
a
and the fixed frame
57
fixed to the housing
51
, a thrust ball bearing
58
is provided to support the spiraling scroll
52
.
This thrust ball bearing
58
is comprised by a pair of ring shaped race members
59
mounted on the fixed frame
57
and the spiraling scroll
52
and balls
60
intervening between the race members
59
. On opposing surfaces of the pair of race members
59
, spiraling race grooves
61
are disposed in several places for providing rolling motion of the balls
60
. These race grooves
61
are formed in an arc shape such that the profile radius of the groove is slightly larger than that of the balls
60
.
The operation of the thrust bearing so constructed will be explained below. The spiraling scroll
52
is driven by the eccentric shaft
55
to produce spiral revolution with a scroll radius &rgr;. During the motion, the fixed frame
57
is coupled to the spiraling scroll
52
by means of the balls
60
intervening between the race members
59
, and, because the rolling range of the balls
60
is restricted by the race grooves
61
, the spiraling scroll
52
is prevented from self-rotating about its own axis.
Also, a large axial load is applied to the spiraling scroll
52
by the pressure from the compressed gas, but the axial load is supported by the balls
60
and the race members
59
.
The thrust ball bearing
58
described above not only supports the load in the thrust direction but also prevents self-rotation of the spiraling scroll
52
.
In other words, because the fixed frame
57
and the spiraling scroll
52
are coupled by means of the balls
60
, the race grooves
61
of the race members
59
on the fixed frame side slide against the balls
60
, and the race grooves
61
of the race members
59
on the spiraling scroll side slide against the balls
60
.
Specifically, as shown in
FIG. 9
, while the ball
60
is under the load Ft in the axial direction generated by the compressed gas acting, it is also under a pressing force Fh acting in the left/right direction resulting from the tendency of the spiraling scroll
52
to self-rotate about its own axis. The ball
60
exerts a reaction force to this pressing force Fh to prevent self-rotation of the spiraling scroll
52
.
However, because the ball
60
is rolling on the race groove
61
, the pressing force Fh acting in the left/right direction causes the ball
60
to slide against the race groove
61
, thereby generating friction at the interface. For this reason, lubrication film between the ball
60
and the race groove
61
is lost and the mechanical loss is increased, and the ball
60
and race groove
61
are worn by the friction to lead to shortening the service life of the bearing.
Frictional effects become significantly higher the higher the load on the bearing. This effect becomes particularly severe when CO
2
is used as the working gas because the compressed gas pressure is higher compared with freon gas, and presents a problem that the bearing service life is reduced considerably.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a thrust ball bearing that can withstand higher loading than conventional thrust ball bearings while preventing frictional effects between the moving parts, and to provide an open-type scroll compressor incorporating such a thrust ball bearing.
The object has been achieved in a thrust ball bearing comprising: a first thrust plate for providing spiral revolution; a second thrust plate opposing the first thrust plate; a retaining device, provided with retaining cavities for retaining a ball in each cavity, disposed between the first thrust plate and the second thrust plate; and balls retained in said retaining cavities; wherein a radius &rgr; of spiral revolution of the first plate, a diameter d of the balls and a diameter D of the retaining cavity are related by an expression D≧d+&rgr;.
In this thrust ball bearing, because the diameter of each retaining cavity is related by the expression D≧d+

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