CENTRIFUGAL GAS COMPRESSOR OR PUMP COMPRISING A TOOTHED RING AND A COWL

Abstract

A centrifugal gas compressor or pump comprising a body, a wheel rotatably mounted within the body around a wheel axis, the wheel comprising a hub, a set of blades fastened to the hub, the body comprising a diffuser placed on the periphery of the wheel and a fluid intake placed facing the hub, the blades comprising a first edge facing the intake and a second edge facing the diffuser so that a fluid travels from the intake to the diffuser, the second edges being located inside a blade-enveloping cylinder centred on the wheel axis. The wheel comprises a toothed ring fastened to the wheel, which extends radially past the enveloping cylinder to form a diffuser wall.

Description

TECHNICAL FIELD

The invention relates to a rotating machine such as a compressor of a centrifugal type for a gaseous fluid or a pump for a liquid. In particular, it concerns the diffusion system of such a machine.

BACKGROUND ART

Rotating machines such as a compressor of a centrifugal type or a pump are widely used in industry, in particular in the field of combustion engines. In particular, a turbine coupled on the same shaft to a compressor is used to form a turbocompressor. The turbine is supplied by the exhaust gases of an engine and drives the compressor which compresses the fresh air to supercharge the engine. Certain compressors are driven by an electric motor.

FIGS. 6 and 7 show a centrifugal compressor 11 according to the prior art. The compressor 11 includes a compressor body 111 and a rotating part rotatively mounted in the compressor body 111 around a wheel axis A. The rotating part comprises a compressor wheel 112 mounted on a rotating shaft 114 in a bearing 113 of the compressor body 111. The compressor wheel 112 comprises a hub 1120 and a set of blades 1121 attached to the hub. The compressor body 111 also comprises an axial opening placed opposite the hub 1120 and which comprises an intake 1110. The compressor body 111 comprises a volute 1112 around the compressor wheel 112. The volute 1112 comprises a peripheral opening placed on the periphery of the compressor wheel 112 and leads to an outlet 1113 which extends substantially in a direction tangent to the compressor wheel 112. The peripheral opening is called a diffuser 1111. The blades 1121 comprise a first edge 11211, called a leading edge, opposite the axial opening 1110 and a second edge 11212, called a trailing edge, opposite the diffuser 1111 so that the gases circulate from the axial opening 1110 to the diffuser 1111 being driven by the compressor wheel 112. The shape of the blades 1121 is designed so that the gases receive mechanical energy by the compressor wheel 112, that principally being accelerated, the kinetic energy thus obtained then being converted into pressure in the volute.

Certain compressor wheel versions are cowled and comprise for this purpose a cowl attached to the blades, the section of which mates with that of the guide wall.

Machines of the same type can be used for a fluid no longer gaseous, but liquid. In this case, the term pump is used instead of compressor.

The speed of the fluid at the diffuser is high such that the friction losses along the diffuser wall related to the viscosity of the fluid are high. At this level, the tangential component of the speed of the fluid is very high and often predominant. The aim of the invention is to reduce these friction losses.

DETAILED DESCRIPTION

With these targets in mind, the object of the invention is a centrifugal gas compressor or pump comprising a body, a wheel rotatively mounted in the body around a wheel axis, the wheel comprising a hub, a set of blades attached to the hub, the body comprising a diffuser placed on the periphery of the wheel and a fluid intake placed opposite the hub, the blades comprising a first edge opposite the axial opening and the second edge opposite the diffuser so that a fluid circulates from the intake to the diffuser, the second edges being located inside a blade-enveloping cylinder centered on the wheel axis, the wheel comprising at least one ring attached to the wheel and which extends radially beyond the blade-enveloping cylinder to form a diffuser wall.

A result of the ring is that the diffuser zone comprises a wall which rotates at the same speed as that of the wheel. The difference between the average speed of the fluid and this wall is greatly reduced which allows the friction losses at this level to be greatly reduced. Thus, less losses on the kinetic energy of the fluid are obtained in the diffuser and, therefore, on the energy supplied in the form of pressure at the volute outlet. It can also be seen that the wheel is submitted to pressure forces the resultant of which is an axial force. In particular, the pressure which is presented on the face of the wheel which carries the blades is in general very different to the one opposed to it. The modification in the size of this face which results from adding the ring beyond the first edge of the blades also modifies this result. Thus, it is possible to adjust this result, in particular in the case of a turbocompressor where the turbine wheel and the compressor wheel exert axial forces in opposite directions.

In a particular manner, the ring is inserted with play in a bore of the compressor body and is placed in such a way that its diffuser side face is in the same plane as the wall of the volute at this level. The gas flow which leaves the ring continues to be guided without discontinuity by the wall of the volute thus avoiding the creation of load losses.

According to an additional characteristic, the body comprises a volute around the diffuser.

According to an embodiment, the ring extends from the hub.

In a particular embodiment, the wheel comprises a cowl attached to the blades. According to an improvement, the ring extends from the cowl. Thus, the diffuser zone comprises a wall possibly additional which rotates at the same speed as that of the wheel. This ring can be alone. In combination with the ring in the extension of the hub, the flow of the fluid is entirely channelled in this zone by the walls which substantially move at the same speed as the flow of the fluid, thus greatly reducing the friction losses. The balance of the pressure forces can be exerted in a direction opposite to that of the configuration with the ring in the extension of the hub.

In a particular embodiment, the cowl and the blades are in one piece.

According to another arrangement, the ring and the wheel in the extension of the hub are in one piece. Thus the wheel is provided with high mechanical strength. Manufacture requires only a few modifications in the manufacturing technique.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and other features and advantages of the invention will become apparent on reading the following description, the description making reference to the appended drawings:

FIG. 1 is a longitudinal cross-sectional view of a machine fulfilling the function of compressor in accordance with a first embodiment of the invention;

FIG. 2 is a detailed view taken along the lines II of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a turbocompressor comprising a turbine and a compressor in accordance with the invention;

FIGS. 4 and 5 are views similar to FIG. 2 of a compressor wheel, but according to a third and a fourth embodiment of the invention;

FIG. 6 is a longitudinal cross-sectional view through line VI-VI of FIG. 7 of a centrifugal compressor according to the prior art; and

FIG. 7 is a view of the compressor, the body being shown by a cross-sectional view through line VII-VII of FIG. 6.

DETAILED DESCRIPTION

A compressor 21 in accordance with a first embodiment of the invention, such as shown on FIGS. 1 and 2, includes a compressor body 211 and a rotating part rotatively mounted in the compressor body 211 around a wheel axis A. The rotating part includes a compressor wheel 212 mounted on a rotating shaft 214 on a bearing of the compressor body 211. The compressor wheel 212 comprises a hub 2120 and a set of blades 2121 attached to the hub 2120. The compressor body 211 also includes an axial opening placed opposite the hub 2120 and which comprises an intake 2110. The compressor body 211 includes a volute 2112 around the compressor wheel 212. The volute 2112 includes a peripheral opening forming a diffuser 2111, placed on the periphery of the compressor wheel 212 and leading to an outlet 2113 which substantially extends in a direction tangential to the compressor wheel 212. The blades 2121 include a first edge 21211 opposite the gas intake and a second edge 21212 opposite the diffuser 2111. The gases circulate from the intake 2110 to the diffuser 2111 being driven by the compressor wheel 212. The shape of the blades 2121 is designed so that the gases accelerate when passing through the compressor wheel 212 by means of the energy supplied by the wheel. The second edges 21212 extend substantially parallel to the wheel axis A and are contained in a virtual cylinder called blade-enveloping cylinder C.

In compliance with the invention, the hub 2120 extends beyond the fictive cylinder C in the form of a ring 21201. The ring 21201 thus delimits the diffuser 2111 on one of its sides. The ring 21201 is inserted with play in a bore 2114 of the compressor body 211 and is placed in such a way that its diffuser 211 side face is in the same plane as the wall of the volute 2112 at this level.

In operation, the shaft 214 is rotationally driven by drive means, not shown, at a speed which can be higher than 200,000 revolutions per minute. A gas flow is established between the gas inlet 2110 and the outlet 2113. The speed of the gas at the outlet of the wheel, at the second edge of the blades, has a tangential component generally higher than the radial component. The relative speed between the ring and the gas flow is essentially the radial component and is therefore much lower than the speed of the gas flow against the fixed wall of the diffuser according to prior art. It can be seen that the losses related to the friction along the wall rendered rotative are substantially divided by two in relation to the fixed wall case, or even more in certain operating modes where the gas speed has a dominant tangential component.

In the embodiment shown on FIG. 3, a turbocompressor comprises a turbine 30 and a compressor 31 in compliance with the invention. The wheels 302, 312 of the turbine 30 and of the compressor 31 are mounted on the same shaft 32, which is rotatively mounted by means of a bearing 33 placed between the body of the compressor 311 and the body of the turbine 301. The bearing 33 is formed, in this example, by two ball bearings.

The turbine 30 includes a turbine body 301 and a rotating part rotatively mounted on the turbine body 301 around the wheel axis A. The rotating part includes a turbine wheel 302 which comprises a hub 3020 and a set of blades 3021 attached to the hub 3020. The turbine body 301 includes a turbine volute 3012 around the turbine wheel 302. The volute 3012 comprises an intake 3013 which extends substantially in a tangential direction and leads to a nozzle 3011 placed on the periphery of the turbine wheel 302. The turbine body 301 also comprises an axial opening placed opposite the hub 3020 and which acts as an outlet 3010 for the gases. The turbine body 301 comprises a guide wall 3014 opposite the blades 3021 of the turbine wheel 302 in such a way as to leave only a small space between the blades 3021 and the turbine body 301. The purpose of the nozzle 3011 is to channel the gases which enter by the intake 3013 into the turbine volute 3012 to be directed to the blades 3021 of the turbine wheel 302 with an appropriate direction and speed. The shape of the blades 3021 is designed so that the gases are decompressed by passing through the turbine wheel 302 and restore energy to it.

In the same way as for compressor 31, the turbine wheel 302 includes a ring 30201 extending from the hub 3020 beyond the blade-enveloping cylinder C′. The ring 30201 forms one of the walls of the nozzle 3011.

According to a third embodiment, shown on FIG. 4, the wheel 402 of a compressor also comprises a cowl 4022 attached to the blades 4021 and channelling the gases between the cowl and the hub 4020. The cowl 4022 forms one piece with the blades 4021 but can be attached by other means. In compliance with the invention, the cowl is extended by a second ring 40220 opposite the ring 40201 which extends the hub. Thus, the diffuser 4011 comprises two walls which delimit it and are rotative to limit the friction losses.

According to a fourth embodiment, shown on FIG. 5, the wheel 502 of a compressor also includes a fixed cowl 5022 on the blades 5021, but only in the most peripheral part of the wheel 502. The cowl 5022 forms one piece with the blades 5021, but can be attached by other means. In compliance with the invention, the cowl is extended by a second ring 50220, substantially parallel to the ring 50201 which extends the hub. Thus, the diffuser 5011 comprises two walls which delimit it and which are rotative to limit the friction losses.

The invention is not limited to the embodiments described above which are provided only as an example. For instead, the ring could equip only the cowl, the machines can circulate a liquid instead of a gaseous fluid.

Claims

1. A centrifugal gas compressor or pump comprising a body, a wheel rotatively mounted in the body around a wheel axis the wheel comprising a hub, a set of blades in attached to the hub, the body comprising as diffuser placed on the periphery of the wheel and a fluid intake placed opposite the hub, the blades comprising as first edge opposite the intake and a second edge opposite the diffuser so that a fluid circulates from the intake to the diffuser, the second edges being located inside a blade-enveloping cylinder centered on the wheel axis, wherein the wheel comprises at least one ring, attached to the wheel and which extends radially beyond the blade-enveloping cylinder to form a wall of the diffuser.

2. A compressor or pump according to claim 1, wherein the body comprises a volute around the diffuser.

3. A compressor or pump according to claim 2, wherein the ring is inserted with play into a bore of the compressor body and is placed in such a way that its diffuser side face is in the same plane as the wall of the volute at this level.

4. A compressor or pump according to claim 1, wherein the ring extends from the hub.

5. A compressor or pump according to claim 1, wherein the wheel comprises as cowl attached to the blades.

6. A compressor or pump according to claim 5, wherein the ring extends from the cowl.

7. A compressor or pump according to claim 4, wherein the cowl and the blades are in one piece.

8. A compressor or pump according to claim 4, wherein the ring forms one piece with the wheel extending from the hub.