Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
16 BACKGROUND OF THE INVENTION
17
18 l This invention relates to improvements in a centrifugal
19 compressor combined with a turbine to provide a turbosupercharger,
a gas turbine or the like. More specifically, the invention is
21 directed to means for preventing the leakage of lubricating oil
22 1 in such turbine-compressor units.
23 ' In a centrifugal compressor combined with a turbine in
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24 the manner under consideration herein, negative pressure builds
up at the back of its impeller (i.e., on that side of the impeller
26 directed toward the turbine) under some operating conditions. This
27 ~ negative impeller back pressure causes the lubricating oil used
28 in the turbine-compressor unit to leak through sealing rings by
29 suction. The development of such undesirable negative pressure in
~ the prior art turbine-compressor unit will be later explained in
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further detail with reference to the accompanying drawings.
SUMMARY OF THE INVENTION
It is an object of an aspect of this invention to
minimize the development of negative pressure at the back of an
impeller in the centrifugal compressor of a turbine-compressor
unit such as a turbosupercharger and hence to prevent the leak-
age of lubricating oil for all practical purposes.
An object of an aspect of the invention is to attain
the first recited object by extremely simplified means which
can be easily incorporated in a turbine-compressor unit without
any substantial alteration of its existing parts and without
adding to the cost of the unit.
In accordance with one aspect of this invention there
is provided in a centrifugal compressor combined with a
turbine so as to be driven thereby, wherein the compressor
includes an impeller having a disc with means defining gas
passages thereon, the improvement comprising front and rear
walls defining therebetween an annular throat which surrounds
; the periphery of said impeller and through which passes a gas
accelerated by said impeller, said throat having a width less
than the width of said gas passages at the periphery of said
impeller.
It should be understood that by the term-"width"
as used herein or in the appended claims is meant the dimen-
sion in the direction parallel to the axis of the compressor.
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In accordance with another aspect of this invention there
is provided a turbine-compressor unit comprising a compressor
having an impeller, a turbine having a turbine wheel, shaft
means connecting said turbine whee:L and said impeller, where-
by said impeller may be driven in response to rotation ofsaid turbine wheel, bearing means for supporting said shaft
means, a bearing housing containing a chamber adapted to
receive lubricating oil and in which said bearing means is
located and through which a part of said shaft means passes,
oil seal means located between said chamber and said impeller,
:said compressor having a cover with a front wall and said
bearing housing ~aving a flange with a rear wall, said cover
and flange being secured together and defining a chamber in
which said impeller is housed, said impeller including a disc
15 having a front surface with blades projecting therefrom :
defining gas passages, said front and rear walls defining ~
therebetween an annular throat which surrounds the outer : -
periphery of said impeller and through which gases accele-
rated by said impeller pass, said rear wall being projected
.20 toward said front wall beyond the outer peripheral edge of
said front surface of said impeller and extending substan-
tially parallel to the portion of said front surface of said
impeller at the outer periphery of said impeller, thereby
reducing the development of negative pressure at the back
of said impeller and on the side of said oil seal means
adjacent said impeller and remote from said chamber, where-
by the tendency of lubricating oil to be sucked passed said
oil seal is reduced.
The above and other objects, features and advantages :~
of this invention and the manner of attaining them will
;become more clearly apparent, and the invention itself will
best be understood, by reference to the following description
taken in connection with the accompanying drawings.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
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3 FIG. 1 is a fragmentary axial sectional view of a prior
art centrifugal compressor combined with a turbine~ not shown, the
view being explanatory of the problem existent with the prior art;~
6 FIG. 2 is a graphical representation of pressure varia- ;
7 I tion at various parts of the prior art compressor of FIG. 1 in
8 comparison with airflow;
9 I FIG. 3 is an axial sectional view of a turbosupercharger
incorporating the novel concepts of this invention; r
11 l FIG. 4 is a detail view showing on an enlarged scale
12 part of the centrifugal compressor in the turbosupercharger of
13 I FIG. 3,
14 I FIG. 5 is a graphical representation of pressure varia-
' tion at various parts of the centrifugal compressor of FIG. 3 in
16 ~ comparison with airflow; and
17 I FIG. 6 is a graphical representation of relationship
18 I between pressure ratio and airflow at various impeller speeds in
19 I the centrifugal compressor of FIG. 3. 1,
21 DETAILED DESCRIPTION
22 l
23 It is considered essential that the above noted problem
24 ~ with the prior art turbine-compressor unit be shown and described
¦ in some more detail~ the better to make clear the features and ¦
26 advantages of this invention. In FIG. 1 there is shown at 10 the
27 1 impeller of the centrifugal compressor which is combined with the
28 ~ unshown turbine, located at the right as seen in the drawing, to
29 1I provide the turbine-compressor unit in accordance with the prior
l art.
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1 In this type of turbine-compressor unit~ lubricating oil
2 1ll in a chamber 12 is not to leak through sealing rings 14 and 16 at
3 relatively high ratio of throat pressure ~2 to inlet pressure ~
4 because then impeller back pressure p3 is relatively high. How-
¦ ever~ at low throat pressure p2 ~as at high and low idling time
in the case of a turbosupercharger), the impeller back pressure
7 ~ ~3 becomes negative, with the result that the oil in the chamber
8 ~ 12 leaks through the sealing rings 14 and 16 by suction. Such oil
9 leakage is even more liable to occur as upon clogging of the air
I cleaner through which the compressor draws air in.
11 ~ The graph of FIG. 3 plots the curves of the pressure at
12 ~ and adjacent points a~ b and c in the prior art compressor of
13 FIG. 1 against the airflow therethrough, as ascertained by experi-
14 ment, with the impeller at a constant rotative speed. It will be I
I observed that the aforesaid impeller back pressure ~3 becomes ne- ¦
16 I gative as the airflow exceeds the value labeled GB1.
17 ¦ In FIG. 3 this invention is shown adapted for a turbo-
18 I supercharger employed usually to increase induction system pres-
19 sure in an internal combustion engine. The turbosupercharger
~ broadly comprises an exhaust gas turbine 20 powered by the energy ¦
21 j in the engine exhaust gases which otherwise would be wasted, and
22 a centrifugal compressor 22 driven by the turbine.
23 I The turbine 20 has a housing 24 within which a turbine
24 , wheel 26 is fixedly mounted on a shaft 28 extending into a bearingl
2~ I housing 30 to be journaled in a bearing 32. The compressor 22 has¦
26 a cover or casing 34 accommodating an impeller 36 which comprises ¦
27 a disc 38 and blades 40 defining the usual gas passages on the
28 ~) fron~ surface of the disc and which is mounted on the burbine dri-
29 ! ven shaft 28 to be rotated thereby. The turbine housing 24~ the
30 I bearing housing 30 and the compressor cover 34 are rigidly inter-
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1 connected by means which permit ready disassembly of the unit.
2 It will be seen that a spacer sleeve 42 is arranged be-
3 I tween the bearing 32 and the impeller 36, and an annular insert 44
4 ~ is fluid-tightly installed between this spacer sleeve and the
~ bearing housing 30 via sealing rings 46 and 48. ~nother sealing
6 ring is mounted at 50 on the shaft 28. Thus, the bearing housing
7 32 has formed therein a chamber 52 in which there is filled lubri-
I cating oil.
9 I The construction of the turbosupercharger as so far de-
sribed is conventional~ and therein lies no feature of this in-
11 I vention. The operation of the turbosupercharger as a whole is
12 also believed to be clearly apparent to those skilled in the art.13 I The centrifugal compressor 22, to which this invention
14 ~ is specifically directed, has an inlet 54, an annular throat 56,
I a spiral outlet passage 58, and an outlet which is not shown. It
16 1I must be mentioned here that the throat 56 around the periphery of
17 the impeller 36 is defined by a front wall 60 forming part of the
18 I compressor cover 34 and a rear wall 62 forming part of the flange
19 I on the bearing housing 30. Gas is drawn into the compressor 22
through the inlet 54 as the impeller 36 is rotated by the turbine
21 1 20. On flowing through the passages in the rotating impeller, the
22 1, gas is given an acceleration and emerges under pressure from the
23 compressor outlet after flowing through the throat 56 and outlet
24 passage 58. The compressed gas is of course utilized for super-
~ charging the engine.
26 1 In accordance with this invention, as illustrated on an ¦
27 1 enlarged scale in FIG. 4~ the width x of the annular throat 56 in
28 '1 the compressor 22 is made smaller than the width X of the impel-
29 ler passages at the periphery of the impeller. For reduction of
I the width of the throat 56, the rear wall 62 projects toward the
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1 front wall 60 a distance d beyond the peripheral edge 64 of the
2 1I front surface of the impeller disc 38.
3 1I Preferably, the distance d should be in the range of
4 from about 1/10 to 3/10 the distance W between the front wall 60
1 and the notional line passing the edge 64 of the impeller disc and
6 I drawn perpendicular to the axis of the compressor 22. It has also
7 been found out that the constricted throat 56 can be substantially
8 I prevented from adversely affecting the performance of the compres-
g sor if the rear wall 62 has its edge opposite to the impeller 36
I beveled or rounded as indicated at 66 in FIG. 4.
11 The relationship between airflow and pressure at and
12 I adjacent points a', b1 and c', FIG. 4~ at a constant impeller
13 speed in the inventive compressor of FIG. 3 was ascertained by
14 I experiment, with the results as graphically represented in FIG. 5.
I Comparison should be made between the curve c~ and the curve c,
16 j also given in FIG. 5, which represents the pressure variation ad-
17 ~ jacent the point c in the prior art compressor of FIG. 1.
18 I FIG. 6 is a graphical representation of the relationship¦
19 ~ between the ratio of throat pressure p2 to inlet pressure ~1 and
20 1l airflow as ascertained experimentally at various impeller speeds
21 ~ N1 through N4. It should be noted that the region of negative
22 ~ pressure e is materially lessened in comparison with the negative
23 pressure region f of the prior art compressor of FIG. 1.
24 It is evident from these results that the measure taken
by this invention is highly effective to minimize the development
26 of negative pressure at the back of the impeller 36. The oil fil-
27 led in the chamber 52 of the turbine-compressure unit can thus be ¦
28 substantially prevented from leaking through the insert 44 by the j
29 I, extremely simple means.
While this invention has been shown and described very
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1 specifically as adapted for a turbosupercharger~ the invention is
2 also adaptable for a gas turbine or the like. It is also under-
stood that the invention is not to:be restricted by the exact de-
4 tails of this disclosure, as numerous modifications or changes of
5 ¦I such details will readily occur to those skilled in the art with-
6 ¦ out departing from the spirit or scope of the invention as expres-
7 ~ sed in the following claims.
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