Scroll fluid machine having multistage compressing part

Rotary expansible chamber devices – Multistage – One working chamber stage encircles another

Reexamination Certificate

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Details

C418S055200

Reexamination Certificate

active

06659743

ABSTRACT:

BACKGROUND TO THE INVENTION
1. Field of the Invention
The present invention relates to a scroll fluid machine which compresses fluid, expands fluid and delivers fluid under pressure and more particularly to a scroll fluid machine having a multi-stage compressing part which compresses fluid having been compressed by a front-stage compressing part and cooled, and further compresses the fluid with a back-stage compressing part.
2. Description of the Related Art
Heretofore, it was possible to increase the compression ratio by increasing the number of wrap turns. However, increasing the compression ratio results in problems such as having an unnecessarily large structure and also incurring a decline in the life of the bearings and sealing parts owing to the high temperatures generated by the compression of the fluid.
Hence, the structure of the cooler needs to be enlarged in order to cool the revolving scroll and the stationary scroll using greater amount of cooling energy of the cooler than usual. In a scroll fluid mechanism, fluid is obtained from the outer circumference of the revolving scroll base and the fluid is compressed by reducing the fluid-compressing pocket, in which the fluid is obtained, toward the center and the compressed fluid is discharged from the discharge port disposed at the center region. Therefore, a highly developed technique is required in order to cool the center region effectively.
By the aforementioned reason, a multi-stage compression scroll fluid machine is required wherein a cooler is disposed adjacent to the scroll fluid mechanism and a compressing part of the scroll fluid machine is separated into two stages so that a compressed fluid from a front compressing stage is led to and cooled in said cooler and the cooled fluid is introduced to a back compressing stage to compress again. Said multi-stage compression scroll fluid machine is able to obtain a desired compression ratio without reaching a higher temperature than usual, by compressing at a front stage to a pressure such that the temperature is limited to what the scroll fluid machine is designed to withstand, and then passing the compressed fluid through an intermediate cooler, and then further compressing at a back-stage until reaching the same limited temperature as at the front-stage compression.
The aforementioned multi-stage compression scroll fluid machine wherein a compressing part of the scroll fluid machine is separated into two stages so that a compressed fluid from a front compressing stage is led to and cooled in a cooler and the cooled fluid is introduced to a back compressing stage to compress again has been publicly known by the publication of unexamined application Shou54-59608.
An obtained fluid compressing characteristic curve L
1
, L
2
of a prior art is shown in
FIG. 6
, where the vertical axis denotes a fluid pocket pressure P
3
and the horizontal axis denotes a rotational angle &ohgr; of a revolving scroll driving shaft (a crank shaft). Compressing behavior along the characteristic curve is as follows. The obtained fluid in the fluid pocket of a pressure P
0
indicated by “a” is compressed to a pressure P
1
indicated by “b” where the compressed fluid is cooled. The cooled fluid is further compressed along the curve L
2
to the point “d” of the fluid pressure P
3
(the discharge pressure).
Meanwhile, the fluid pressure pocket volume corresponding to a given rotational angle of the rotational driving shaft varies with production errors which are brought about in the production of such as a stationary scroll wrap, a revolving scroll wrap, a revolving scroll driving shaft or a crankshaft for preventing the rotation of the revolving scroll. Directing our attention to the characteristic curve L
2
of the back compressing stage, a variation in inner pressure by an amount &Dgr;P of the fluid pocket containing compressed fluid of the sealed space corresponding to a given angle rotational amount &Dgr;&ohgr; of the revolving scroll driving shaft is generated with each compressor.
As shown in
FIGS. 4 and 5
, fluid pressure pockets are formed as depicted as sealed spaces S inside and T outside of a revolving scroll wrap. These sealed spaces communicate with a discharge port after forming last compression chambers so that compressed fluids in the last compression chambers are mixed together in the discharge port to discharge to the outside of the compressor. Therefore, the discharge pressure at the discharge port varies so as to result in over-compression or insufficient compression owing to the variation in inner pressure by an amount &Dgr;P of the fluid pocket containing the compressed fluid of each sealed space such as the sealed space S and T corresponding to the given angle of rotation &Dgr;&ohgr; of the revolving scroll driving shaft.
SUMMARY OF THE INVENTION
The present invention has done in the light of the aforementioned problem and has an object of offering a scroll fluid machine having a multi-stage compressing part which is characterized in that the volumes of sealed spaces corresponding to the given angle of rotation of the revolving scroll driving shaft show less variation.
The first part of the present invention is characterized in that in a scroll fluid machine having a multi-stage compressing part which compresses fluid with a back-stage compressing part, the fluid having been compressed by a front stage compressing part and cooled, a reduction ratio &Dgr;Y of a volume of a compression chamber is smaller in a back compressing part than in a front compressing part, &Dgr;Y being expressed by &Dgr;Y={A(n−1)−An}/A(n−1)}, where A is the volume of a compression chamber defined by a scroll wrap and a scroll mirror plane, A(n−1) is the volume of a compression chamber at the rotational angle &Dgr; &ohgr;(n−1), An is the volume of a compression chamber at the rotational angle &Dgr; &ohgr;n and &Dgr;&ohgr; is the rotational angle of a driving shaft of a revolving scroll.
According to the first part of the present invention, as the reduction ratio &Dgr;Y of the volume of the compression chamber is smaller in the back compressing part than in the front compressing part, the reduction ratio &Dgr;Y of the volume of the compression chamber defined by the scroll wrap and the scroll mirror plane corresponding to the rotational angle of the scroll driving shaft is small so that a varying extent of a pressure P in the sealed space which forms the volume of the compression chamber is small. Thus, a characteristic curve of said pressure P in the sealed space inclines gently. Consequently, a multi-stage compression scroll fluid machine having less variation in inner pressure of the fluid pocket containing the compressed fluid of each sealed space by an amount &Dgr;P and a stable discharge pressure can be offered.
The second part of the present invention is characterized in that in a scroll fluid machine having a multi-stage compressing part which compresses fluid with a back stage compressing part, the fluid having been compressed by a front stage compressing part and cooled, a distance between the mirror planes of the wraps in the back-stage compressing part is larger than a distance between the mirror planes of the wraps in the front-stage compressing part.
According to the second part of the present invention, in the back-stage compressing part where the pressure of the sealed space is larger than the front-stage compressing part corresponding to the given rotational angle of the scroll driving shaft, a volume reduction ratio by compression is smaller in a degree proportioned to a longer distance between the mirror planes of the wraps so that a varying extent of a pressure P in the sealed space which forms the volume of the compression chamber is small. Thus, a characteristic curve of said pressure P in the sealed space inclines gently. Consequently, a multi-stage compression scroll fluid machine having only a small variation in inner pressure of the fluid pocket containing the compressed fluid of each sealed space by an amount &Dgr;

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