Sliding vane compressor with end face inserts or rotor

A sliding vane compressor has a housing and a rotor mounted in the housing. The rotor has axial endfaces which are juxtaposed with respective housing surfaces from which they must be kept at a predetermined spacing. This spacing is obtained by mounting in open recesses of the axial rotor endfaces respective elements of a material having a higher coefficient of thermal expansion than the material of the rotor itself. As the compressor comes up to operating temperatures the resulting thermal expansion of these elements causes them to protrude beyond the axial rotor endfaces by a distance corresponding to the desired spacing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to compressors. 
More particularly, the invention relates to sliding vane compressors. 
2. The Prior Art 
One of the problems which are encountered with prior-art sliding vane 
compressors is how to maintain the required amount of play (i.e., spacing) 
between the axial endfaces of the rotor and the juxtaposed surfaces of the 
chamber in which the same is mounted. This spacing, between each axial 
rotor endface and the juxtaposed chamber surface, is generally about 0.05 
mm; it is set and maintained by means of axial pressure bearings. These 
are mounted on the rotary shaft of the compressor and support the rotor 
against the housing walls having the aforementioned chamber surfaces. Such 
bearings, e.g., needle bearings or roller bearings, must be high-precision 
bearings which are correspondingly expensive. Also, the juxtaposed 
surfaces of the housing and the rotor must be precision machined to make 
them as planar as possible, and all elements must be assembled with the 
greatest care to assure their proper cooperation. All of these factors 
combine to make the prior-art compressors of the type in question rather 
expensive. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved sliding vane 
compressor which is not subject to the prior-art disadvantages. 
Another object is to provide such a compressor wherein the spacing 
necessary between the rotor endfaces and the juxtaposed chamber surfaces 
will set and maintain itself as a function of the operation of the 
compressor. 
Still a further object is to provide a compressor of the type in question 
which is much simpler and less expensive to construct than those of the 
prior art. 
Pursuant to the above objects, and still others which will become apparent 
hereafter, one aspect of the invention resides in a sliding vane 
compressor of the type having a housing and a rotor journalled for 
rotation in a chamber of the housing so that the axial endfaces of the 
rotor are juxtaposed with slight clearance relative to cooperating housing 
surfaces. In such a compressor, the invention provides means bounding a 
plurality of recesses in each axial endface of the rotor; and an insert 
received in each of the recesses and being of a material having a 
relatively low coefficient of friction and having a coefficient of thermal 
expansion which is higher than that of the material of the rotor so that, 
upon reaching a predetermined temperature, the inserts expand and extend 
across the respective clearance into contact with the housing surfaces to 
prevent direct contact between the same and the axial endfaces of the 
rotor. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS 
A conventional sliding vane compressor, i.e., a compressor according to the 
prior art, is illustrated in FIG. 1. It has a housing which is essentially 
composed of a center section 1, a left endsection or cover 2 and a right 
endsection or cover 2'. The covers 2, 2' are screw-threaded into the open 
ends of the annular center section 1. 
The center section 1 is formed with a chamber 8 of cylindrical outline 
which is circumferentially bounded by an inner surface of the section 1; 
the axial ends of the chamber 8 are closed by the inwardly directed 
surfaces of the covers 2, 2'. The inner circumferential surface of the 
section 1 may be elliptical or circular (in the latter case it is 
non-coaxial with chamber 8) and forms the cam track which dictates 
movement of the sliding vanes during operation of the compressor 3 mounted 
in the chamber 8. The outer circumferential surface of rotor 3 is 
cylindrical and defines with the inner circumferential surface of the 
section 8 two fluid compartments of approximately sickel-shaped 
configuration. 
The rotor 3 has a central bore 10 in which an end portion of a rotary shaft 
6 is press-fitted. The shaft is journalled for rotation in two sleeve 
bearings which, in turn, are mounted in a tubular part of the left-hand 
cover 2, as shown. 
There are also provided axial needle bearings 7 which are arranged 
coaxially with the shaft 6 and serve to support the rotor 3 in axial 
direction. It is these bearings 7 which determine the amount of play 
(i.e., the spacing) between the axial endfaces of the rotor 3 and the 
therewith juxtaposed planar inner surfaces of the covers 2, 2'. This 
spacing amounts at each axial end of the rotor to about 0.05 mm and must 
be set extremely precisely. It will be appreciated that if the spacing is 
too small it will permit contact between the rotor and the respective 
cover with the resulting frictional losses, whereas, if the spacing is too 
great, leakage losses will develop in the compressor. 
The rotor 3 is provided with several radial slots 4 in which the respective 
vanes 5 are tightly but slidably received and guided. The radially outer 
edges of the sliding vanes 5 are in sliding engagement with the inner 
circumferential surface of the section 1 so as to subdivide the 
afore-mentioned fluid compartments into individual cells. Each of the 
fluid compartments has a suction (low-pressure) region and a high-pressure 
region. The suction region communicates with a fluid inlet 8' whereas the 
high-pressure region of each fluid compartment communicates (via not 
illustrated valves) with the interior 9 of a cupped outer housing which 
surrounds and is connected to the inner housing 1, 2, 2'. It is this 
interior 9 which constitutes the pressure chamber of the compressor; in 
operation it contains an oilsump 19 in its lower region. 
The compressor according to the present invention corresponds in most 
aspects to the prior-art compressor shown in FIG. 1. In fact, it differs 
from the same only in the details shown and explained with reference to 
the embodiments of FIGS. 2-4 and 5, respectively. Therefore, a repeated 
illustration of the entire compressor is not considered to be necessary. 
According to a first embodiment of the invention, illustrated in FIGS. 2-4, 
the rotor 3' has a center bore 10 (corresponding to the one of the rotor 3 
in FIG. 1) in which the shaft 6 (FIG. 1) is to be mounted. Unlike the 
prior art, however, the rotor 3' is provided in its axial endfaces with 
circumferentially distributed recesses (e.g., blind bores) in each of 
which a plate or otherwise shaped member 11 is mounted (e.g., adhesively, 
by press-fitting or in another suitable manner). The plates 11 are of a 
material having a relatively low coefficient of friction and a coefficient 
of thermal expansion which is greater than that of the rotor material 
(usually steel). A suitable material for the plates is aluminum, although 
other materials suitable for this purpose will be readily apparent to 
those skilled in the art. 
At room temperature the outer exposed surfaces of the plates 11 are flush 
with the respective axial endface 3a of the rotor 3' (see FIG. 3). 
However, when the rotor 3' (installed in the compressor of FIG. 1) reaches 
the operating temperature of the compressor, then the plates 11 expand and 
project outwardly from the axial endfaces 3a, due to the fact that the 
coefficient of thermal expansion of the plates 11 is greater than that of 
the rotor 3'. The projecting plates 11 then contact the inner surfaces of 
the covers 2, 2' (as shown for cover 2 in FIG. 4) and thus space the axial 
endfaces 3a from the covers 2, 2'. In other words: as the rotor 3' reaches 
operating temperature the necessary spacing between the covers 2, 2' and 
the axial endfaces 3a is automatically established and it is maintained 
until the temperature of rotor 3' drops again below operating temperature 
(i.e., the compressor is shut down). The extent of such projection may be 
up to about 0.1 mm in all embodiments, but about 0.002 to 0.003 mm has 
been found particularly advantageous. 
It will be clear that during start-up of the compressor respective endfaces 
3a will be in contact with the covers 2, 2'. However, the heat produced by 
this frictional contact will quickly cause the plates 11 to expand and 
establish the desired spacing (FIG. 4) so that the start-up phase with its 
friction losses will only be of brief duration. 
Evidently, a compressor (similar to the one in FIG. 1) using the rotor 3' 
of FIGS. 2-4 does not require the bearings 7 shown in FIG. 1, so that 
these may be omitted. In some special cases it may be desirable to retain 
such bearings; however, even then the invention will proffer its benefits 
because due to the presence of the rotor 3' it is possible under such 
circumstances to use bearings which are manufactured to much less exacting 
tolerances (and hence less expensive) and also to assemble the compressor 
to less exacting tolerance specifications. 
Another embodiment of the invention is illustrated in FIG. 5. The rotor 3" 
as shown there is again suitable for use in a compressor of the type and 
construction shown in FIG. 1. It has a center bore 10' for the shaft 6 
(not shown). 
In the embodiment of FIG. 5 the weight of the rotor 3" is reduced by 
forming the same with axially throughgoing hollows 12' (e.g., bores or the 
like) in the axial ends of which the plates 11' are mounted. Each of these 
plates is provided with a (preferably centrally arranged) passage 13 
communicating with the respective hollow 12'. The number and 
circumferential distribution of the hollows 12' may correspond to that 
shown for the recesses and plates 11 in FIG. 2. Suitable channels (not 
illustrated) are provided via which the hollows 12' are filled (e.g., via 
the shaft 6) with oil from the sump 19. 
The operation of the embodiment in FIG. 5 is identical with that in FIGS. 
2-4, insofar as the plates 11 are concerned. In addition, however, the oil 
in the hollows 12' flows--during operation of the compressor--through the 
passages 13' and lubricates the areas of contact between the plates 11' 
and the covers 2, 2'. 
Although in the embodiment of FIGS. 2-4 plates 11, 11' are flush with the 
endfaces 3a, it will be understood from FIG. 5 that in special cases they 
can be made to project from these endfaces (in all embodiments) by a small 
amount (e.g., about 0.002 mm) while still at room temperature, as shown 
with reference to the faces 3a' in FIG. 5. The operation will not be 
changed thereby. 
It is also possible for the plates 11, 11' to have a different 
configuration than that shown in the drawings. 
While the invention has been illustrated and described as embodied in a 
sliding vane compressor, it is not intended to be limited to the details 
shown, since various modifications and structural changes may be made 
without departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fiarly constitute essential 
characteristics of the generic or specific aspects of this invention.