GB1574942A

GB1574942A - Centrifugal compressor combines with a turbine

Info

Publication number: GB1574942A
Application number: GB1649177A
Authority: GB
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 1977-04-20
Filing date: 1977-04-20
Publication date: 1980-09-10

Description

(54) A CENTRIFUGAL COMPRESSOR COMBINED WITH A TURBINE (71) We, KABUSHIKI KAISHA KOMATSU SEISAKUSHO, a Corporation duly organised under the laws of Japan of 3-6, 2-chome Akasaka, MinatoLku, Tokyo, Japan, do hereby declare the invention for which we pray that a Patent may be granted to us, and the merhod by which it is to be performed to be particularly described in and by the following statement: This invention relates to improvements in a centrifugal compressor combined with a turbine to provide a turbosupercharger, a gas turbine or the like. More specifically, the invention is directed to means for preventing the leakage of lubricating oil in such turbinecompressor units.

In a centrifugal compressor combined with a turbine in the manner under consideration herein, negative pressure builds up at the back ob its impeller (i.e., on that side of the impeller directed toward the turbine) under some operating conditions. This negative impeller back pressure causes the lubricating oil used in the turbine-compressor unit to leak through sealing rings by suction.

As described in Japanese laid open publication No. 50-138410 published on November 5, 1975, it has been proved effective to make the width of an annular throat through which a gas accelerated by an impeller passes into a spiral passage less wide than the width of the usual passages in the impeller as measured at its periphery.

With providing such configurations, the development of negative pressure at the back of the impeller under various operating conditions is minimized, so that lubricating oil in the turbine-compressor unit can be prevented from leakage by suction. It should be understood that by the term "width" as used herein is meant the dimension in the direction parallel to the axis of the compressor.

It is an object of the present invention to minimize the development of negative pressure at the back of an impeller in the centrifugal compressor od a turbine-compressor unit such as a turbosupercharger and hence to prevent the leakage of lubricating oil for all practical purposes.

According to the present invention there is provided a centrifugal compressor combined with a turbine so as to be driven thereby comprising an impeller having a disc with means defining gas passages on its front surface, 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 rear wall projecting toward said front wall beyond the peripheral edge of said front surface of said impeller disc by a dls- tance which is in the range of from about 0.2 to 0.35 the axial width W of the impeller passages at the periphery of said impeller, said rear wall having a rounded corner ow posite to said impeller with the radius of said rounded corner being in the range of from about 0.15 to 0.2 W.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is an axial sectional view of a turbo; supercharger in accordance with the invention; Fig. 2 is a detail view to an enlarged scale of part of the centrifugal compressor in the turbosupercharger of Fig. 1; Fig. 3 is a graphical representation of adiabatic efficiency of the compressor, impeller back pressures and lubricating oil leakage through seal rings by suction, respectively, as a function of the overhang length of the rear wall of the housing wherein the front edge ob the impeller is plotted as zero point as illustrated in Fig. 2; and Fig. 4 is a graphical representation of relationship between pressure ratio and air flow at various impeller speeds in the centrifugal compressor of Fig. 1.

Referring now to Fig. 1, this invention is shown applied to a turbosupercharger employed to increase induction system pressure in an internal combustion engine. The turbosupercharger broadly comprises an exhaust gas turbine 20 powered by the energy in the engine exhaust gases which otherwise would be wasted, and a centrifugal compressor 22 driven by the turbine.

The turbine 20 has a housing 24 within which a turbine wheel 26 is fixedly mounted on a shaft 28 extending into a bearing housing 30 to be journaled in a bearing 32. The compressor 22 has a cover or casing 34 accommodating an impeller 36 which comprises a disc 38 and blades 40 defining the usual gas passages on the front surface of the disc and which is mounted on the turbine driven shaft 28 to be rotated thereby. The turbine housing 24, the bearing housing 30 and the compressor cover 34 are rigidly interconnected by means which permit ready disassembly od the unit.

It will be seen that a spacer sleeve 42 is arranged between the bearing 32 and the impeller 36, and an annular insert 44 is fluidtightly installed between this spacer sleeve and the bearing housing 30 via sealing rings 46 and 48. Another sealing ring is mounted at 50 on the shaft 28. Thus, the bearing housing 32 has formed therein a chamber 52 in which there is filled lubricating oil.

The construction of the turbosupercharger as so far described is conventional, and therein lies no feature of this invention. The operation of the turbosupercharger as a whole is also believed to be clearly apparent to those skilled in the art.

The centrifugal compressor 22, to which this invention is specifically directed, has an inlet 54, an annular throat 56, a spiral outlet passage 58, and an outlet which is not shown.

It must be mentioned here that throat 56 around the peripheTy of the impeller 36 is defined by a front wall 60 forming part d the compressor cover 34 and a rear wall 62 forming part of the flange 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 20. On flowing through the passages in the rotating impeller, the gas is given an acceleration and emerges under pressure from the compressor outlet after flowing through the throat 56 and outlet passage 58. The compressed gas is of course utilized for supercharging the engine.

In accordance with this invention, as illustrated on an enlarged scale in Fig. 2, the width x of the annular throat 56 in the compressor 22 is made smaller than the width W of the impeller passages at the periphery of the impeller. For reduction of the width of the throat 56, the rear wall 62 projects toward the front wall 60 a distance "d" beyond the peripheral edge 64 of the front surface od the impeller disc 38.

In order to enhance adiabatic efficiency of the compressor 22, a corner 66 of the rear wall 62 facing the impeller 36 should be rounded.

Experiments were conducted to determine the preferable overhang distance "d" and radius "R" of the corner 66. The results are shown in Fig. 3.

Adiabatic efficiency of the compressor, im peller back pressures "Ps" and oil leakage through seal rings 46 and 48 by suction are plotted with varying length "d" from 0.4 W to -0.2 W. Minus W means that the rear wall 62 does not overhang impeller disc 38, a design which is typical to the conventional compressors employed in the turbosuper charger.

Radius of the corner 66 of the rear wall 62 is varied in three levels, i.e. 0.08 W, 0.16 W and 0.32 W.

As illustrated by the graph of Fig. 3 when the distance "d" exceeds 0.35 W, adiabatic efficiency of the compressor drops significantly.

On the other hand, however, if the distance "d" is shorter than 0.2 W, lubricating oil begins to leak through seal rings 46 and 48.

Therefore it is reasonably concluded that the overhang distance "d" of the rear wall 62 should be from about 0.2 W to 0.35 W in order to attain required performance of this invention.

Observing the relationship between adiabatic efficiency of the compressor and radius "R" of the rounded corner 66 of the rear wall 62, it is noted that adiabatic efficiency of the compressor is decreased significantly when the radius "R" of the rounded corner 66 is 0.08 W. It is proved by the experiments, however, if radius "R" of the rounded corner exceeds 0.2 W, lubricating oil tends to leak through seal rings 46 and 48. Accordingly, radius "R" of the rounded corner 66 should be about 0.15 W to 0.2 W to attain better results according to the present invention.

Fig. 4 is a graphical representation of the relationship between the ratio of throat pressure P2 to inlet pressure P1 and airflow as ascertained experimentally at various impeller speeds 20,000 rpm to 60,000 rpm. In Fig. 4, reference character "A" represents rated output state of the engine, "B", "C", "D" denote respectively maximum torque state, high idling state and low idling state. It should be noted that the region of negative pressure "E" is materially lessened and therefore negative impeller back pressure can hardly be developed during normal operating conditions of the engine.

It is evident from these results that the measure taken by this invention is highly effective to minimize the development of negative pressure at the back of the impeller 36.

The oil in the chamber 52 of the turbine compressor unit can thus be substantially prevented from leaking through the insert 44 by the extremely simple means.

While this invention has been shown and described specifically as adapted for a turbosupercharger, the invention is also adaptable for a gas turbine or the like.

WHAT WE CLAIM IS: 1. A centrifugal compressor combined with

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. driven by the turbine. The turbine 20 has a housing 24 within which a turbine wheel 26 is fixedly mounted on a shaft 28 extending into a bearing housing 30 to be journaled in a bearing 32. The compressor 22 has a cover or casing 34 accommodating an impeller 36 which comprises a disc 38 and blades 40 defining the usual gas passages on the front surface of the disc and which is mounted on the turbine driven shaft 28 to be rotated thereby. The turbine housing 24, the bearing housing 30 and the compressor cover 34 are rigidly interconnected by means which permit ready disassembly od the unit. It will be seen that a spacer sleeve 42 is arranged between the bearing 32 and the impeller 36, and an annular insert 44 is fluidtightly installed between this spacer sleeve and the bearing housing 30 via sealing rings 46 and 48. Another sealing ring is mounted at 50 on the shaft 28. Thus, the bearing housing 32 has formed therein a chamber 52 in which there is filled lubricating oil. The construction of the turbosupercharger as so far described is conventional, and therein lies no feature of this invention. The operation of the turbosupercharger as a whole is also believed to be clearly apparent to those skilled in the art. The centrifugal compressor 22, to which this invention is specifically directed, has an inlet 54, an annular throat 56, a spiral outlet passage 58, and an outlet which is not shown. It must be mentioned here that throat 56 around the peripheTy of the impeller 36 is defined by a front wall 60 forming part d the compressor cover 34 and a rear wall 62 forming part of the flange 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 20. On flowing through the passages in the rotating impeller, the gas is given an acceleration and emerges under pressure from the compressor outlet after flowing through the throat 56 and outlet passage 58. The compressed gas is of course utilized for supercharging the engine. In accordance with this invention, as illustrated on an enlarged scale in Fig. 2, the width x of the annular throat 56 in the compressor 22 is made smaller than the width W of the impeller passages at the periphery of the impeller. For reduction of the width of the throat 56, the rear wall 62 projects toward the front wall 60 a distance "d" beyond the peripheral edge 64 of the front surface od the impeller disc 38. In order to enhance adiabatic efficiency of the compressor 22, a corner 66 of the rear wall 62 facing the impeller 36 should be rounded. Experiments were conducted to determine the preferable overhang distance "d" and radius "R" of the corner 66. The results are shown in Fig. 3. Adiabatic efficiency of the compressor, im peller back pressures "Ps" and oil leakage through seal rings 46 and 48 by suction are plotted with varying length "d" from 0.4 W to -0.2 W. Minus W means that the rear wall 62 does not overhang impeller disc 38, a design which is typical to the conventional compressors employed in the turbosuper charger. Radius of the corner 66 of the rear wall 62 is varied in three levels, i.e. 0.08 W, 0.16 W and 0.32 W. As illustrated by the graph of Fig. 3 when the distance "d" exceeds 0.35 W, adiabatic efficiency of the compressor drops significantly. On the other hand, however, if the distance "d" is shorter than 0.2 W, lubricating oil begins to leak through seal rings 46 and 48. Therefore it is reasonably concluded that the overhang distance "d" of the rear wall 62 should be from about 0.2 W to 0.35 W in order to attain required performance of this invention. Observing the relationship between adiabatic efficiency of the compressor and radius "R" of the rounded corner 66 of the rear wall 62, it is noted that adiabatic efficiency of the compressor is decreased significantly when the radius "R" of the rounded corner 66 is 0.08 W. It is proved by the experiments, however, if radius "R" of the rounded corner exceeds 0.2 W, lubricating oil tends to leak through seal rings 46 and 48. Accordingly, radius "R" of the rounded corner 66 should be about 0.15 W to 0.2 W to attain better results according to the present invention. Fig. 4 is a graphical representation of the relationship between the ratio of throat pressure P2 to inlet pressure P1 and airflow as ascertained experimentally at various impeller speeds 20,000 rpm to 60,000 rpm. In Fig. 4, reference character "A" represents rated output state of the engine, "B", "C", "D" denote respectively maximum torque state, high idling state and low idling state. It should be noted that the region of negative pressure "E" is materially lessened and therefore negative impeller back pressure can hardly be developed during normal operating conditions of the engine. It is evident from these results that the measure taken by this invention is highly effective to minimize the development of negative pressure at the back of the impeller 36. The oil in the chamber 52 of the turbine compressor unit can thus be substantially prevented from leaking through the insert 44 by the extremely simple means. While this invention has been shown and described specifically as adapted for a turbosupercharger, the invention is also adaptable for a gas turbine or the like. WHAT WE CLAIM IS:

1. A centrifugal compressor combined with

a turbine so as to be driven thereby comprising an impeller having a disc with means defining gas passages on its front surface, 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 rear wall projecting toward said front wall beyond the periplheral edge of said front surface of said impeller disc by a distance which is in the range of from about 0.2 to 0.35 the axial width W of the impeller passages at the periphery of said impeller, said rear wall having a rounded corner opposite to said impeller with the radius of said rounded corner being in the range of from about 0.15 to 0.2 W.

2. A centrifugal compressor combined with a turbine, substantially as herein described with reference to and as illustrated in the accompanying drawings.