WO1995014158A1

WO1995014158A1 - Bearing for air cycle machine

Info

Publication number: WO1995014158A1
Application number: PCT/US1994/012504
Authority: WO
Inventors: Jeffrey Faul; Kenneth B. Groves; Debra Lear Sutton
Original assignee: Fmc Corporation
Priority date: 1993-11-15
Filing date: 1994-10-28
Publication date: 1995-05-26
Also published as: AU8097194A; TW265386B; IL111623A0

Abstract

An air cycle machine has a turbine side and a compressor side. In operation the air cycle machine runs with both turbine and compressor at pressures above ambient, but not at equal pressures. The common shaft for the turbine and compressor is supported on a fluid bearing. Cross transfer of gas may occur between the turbine and compressor through the bearing. The bearing is vented to ambient through passages (33, 37) so that any cross transferring turbine or compressor fluid is dumped into ambient.

Description

BEARING FOR AIR CYCLE MACHINE

SUMMARY OF THE INVENTION

An air cycle machine has a machine case and a compressor and expander included therein. The machine further has a common shaft for mounting the compressor and expander, the common shaft being supported by a fluid bearing within the machine case. A centrally disposed vent is formed within the machine case extending from the fluid bearing and a low pressure sump is communicated with the vent so that during operation of the air cycle machine when both the compressor and expander are at higher pressures relative to the sump, cross transfer of gas between the compressor and the expander is prevented.

In an air cycle machine having a machine case, a compressor and a turbine are mounted on a common shaft with the shaft being supported on a fluid bearing within the machine case. An improvement is provided wherein the machine case has a vent passage extending between the fluid bearing and a pressure volume at a lower state than either the turbine or the compressor. The invention further relates to a method of preventing cross-transfer of gas between a turbine side and a compressor side of an air cycle machine wherein the machine has a machine case and a common turbine/compressor shaft. The shaft is supported in the case by a fluid bearing. The method includes the step of venting the air bearing to a pressure lower than the compressor or turbine pressures.

BRIEF DESCRIPTION OF THE DRAWING

The figure is a sectional view of an air cycle machine incorporating the present invention. DESCRIPΗON OF THE PREFERRED EMBODIMENTS Air cycle machines are used in systems which take in contaminated air and provide clean air as an output. One such system is a regenerable collective protection system (RCPS) wherein clean air flow is used to drive a turbine or expander in the air cycle machine and wherein the turbine, through a common shaft supported by an air bearing, drives a compressor which compresses the contaminated air flow in the system prior to cleansing the contaminated air. It may be seen that the purpose of the RCPS would suffer considerable detriment if contaminated air was allowed to leak through the air bearing supporting the common shaft for the turbine and compressor into the clean air flow which drives the turbine. The invention disclosed herein relates to a means for preventing such cross transfer from one air flow to the other air flow through the air cycle machine.

The figure shows a section, considerably simplified, of a typical air cycle machine 11 for use in applications such as just discussed hereinbefore. The air cycle machine has an outer case 12 having an air inlet 13 wherein air flows into the air cycle machine as indicated by arrow 14. The inflowing air is compressed by a compressor stage 16 and is caused to flow out of the compressor outlet 17 as indicated by arrow 18. The compressor stage 16 is mounted on one end of a shaft 19 which extends through the case 12, having a turbine 21 mounted on the opposite end thereof. The turbine is driven by input air in the direction of arrow 22 entering through a turbine inlet 23 in the case 12. The turbine input air drives the turbine 21, thereby driving the compressor 16, and then exits the case of the air cycle machine through a turbine outlet opening 24 in the direction of flow indicated by arrow 26 of the figure.

The shaft 19 on which the turbine 21 and the compressor 16 are mounted is in some instances supported for slow speed rotation by a thrust bearing 27 at one end and a radial bearing 28 at the other end. High speed rotation of the shaft 19 is supported on a fluid bearing, which may be oil or may be gas such as air. The figure will first be considered to depict a machine utilizing an air bearing for supporting the shaft 19 for high speed rotation. An opening 31 through the case 12 receives the shaft 19 for rotation therein. Labyrinth seals 29 are formed along specified lengths of the shaft and shaft opening in a fashion well known to those of skill in this art. However, higher pressure at the compressor stage 16 creates a tendency for cross transfer of air from the compressor stage along the length of shaft 19 and through the seals to the turbine stage 21 as hereinbefore described.

To avoid the aforementioned cross transfer an annular groove 32 is formed in the wall of the shaft receiving passageway 31 which communicates with a radially extending vent passage 33 which vents cross transfer air through the outer wall of the case 12 in the direction of arrow 34. Similarly, another annular groove 36 is formed in the wall of the shaft receiving passage 31 which is connected to a second radially extending vent passage 37. The vent passage 37 also extends through the outer wall of the case 12 allowing cross transfer air to be vented from the case to ambient as indicated by arrow 38. Since, during operation, both the compressor stage 16 and the turbine stage 21 are functioning at pressures higher than ambient, any cross transfer air from either the compressor stage or the turbine stage will be vented through the vent passages 33 and/or 37 to ambient.

The figure also shows in dotted lines an isolated oil sump 39 coupled to the vent passage 33. In the case of a liquid bearing, such as an oil bearing for supporting the shaft 19 within the shaft passage 31, cross transfer gas flowing from either the compressor section 16 or the turbine section 21 would migrate toward the isolated oil sump 39 in the direction of the arrow 34. The isolated oil sump is kept at a pressure below the pressure in either the compressor or the turbine stages to assure cross transfer gas flow toward the sump 39. The sump 39 may be vented to ambient through a vent 41 , as shown in the figure, to assure the differential in pressures which will cause the described flow of cross transfer gas.

The aforementioned feature in an air cycle machine eliminates cross transfer potential in that component in an RCPS and thereby maintains system integrity. The vented air cycle machine isolates the clean air stream from the contaminated air stream in an RCPS by directing the vent path for each stream to the contaminated ambient atmosphere. Since turbine pressure and compressor pressure are both necessarily above ambient pressure, any leak from either the turbine side or the compressor side of the air cycle machine will result in a positive flow of leaked air to the atmosphere.

As a result, in one application of the disclosed invention, the chemical protection level of an RCPS is enhanced.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

Claims

WHAT IS CLAIMED IS:

1. An air cycle machine having a machine case containing a compressor and an expander positioned therewithin, the machine further having a common shaft for mounting the compressor and expander, the common shaft being supported by a fluid bearing within the machine case, comprising a centrally disposed vent within the machine case extending from the fluid bearing, and a low pressure sump communicating with said vent so that during operation when both compressor and expander are at higher pressure relative to said sump, cross transfer of gas between compressor and expander is prevented.

2. An air cycle machine as in claim 1 wherein said fluid bearing is an oil bearing and wherein said low pressure sump is an isolated oil sump.

3. An air cycle machine as in claim 1 wherein said fluid bearing is an air bearing, and wherein said low pressure sump is ambient.

4. In an air cycle machine having a machine case, a compressor and a turbine mounted on a common shaft with the shaft being supported on a fluid bearing within the machine case, the improvement wherein the machine case has a vent passage extending between the fluid bearing and a pressure volume at a lower state than either the turbine or the compressor.

5. An air cycle machine as in claim 4 wherein said fluid bearing is a liquid bearing and wherein said pressure volume comprises an isolated liquid sump.

6. An air cycle machine as in claim 5 wherein said isolated liquid sump comprises a vent to ambient pressure.

7. An air cycle machine as in claim 4 wherein said fluid bearing is a gaseous bearing, and wherein said pressure volume comprises ambient.

8. A method of preventing cross transfer of gas between a turbine side and a compressor side of an air cycle machine having a machine case and a common turbine/compressor shaft supported in the case by a fluid bearing, comprising the step of venting the air bearing to a pressure lower than the compressor or turbine pressures.

9. The method of claim 8 wherein the fluid bearing is an air bearing, and wherein the step of venting comprises the step of venting to ambient.

10. The method of claim 8 wherein the fluid bearing is a liquid bearing and wherein the step of venting comprises the step of venting to a low pressure liquid sump.

11. The method of claim 10 further comprising the step of venting the liquid sump to ambient.