Axial thrust balancing device

Abstract

An axial thrust balancing mechanism for a rotating shaft apparatus such as a rotary pump provides self-regulating thrust compensation while avoiding contact and wear between rotating and static elements. A rotor fixed to the shaft includes a cylindrical male section proximal to but not extending within a cylindrical female section of a non-rotating stator, such that a gap formed therebetween is varied in width by shaft displacements caused by axial thrusts. Pressurized fluid within the female section applies a thrust-compensating force to the rotor that is controlled by the gap size. The female section is larger in diameter than the male section, thereby preventing any contact therebetween. The disclosed mechanism can be combined with a thrust-compensating drum so as to reduce the thrust to a residual level that can be regulated. The rotor and stator can be stepwise varied to provide a plurality of gaps and intermediate chambers therebetween.

Claims

1. An apparatus comprising: a housing; at least one impellor fixed to a shaft that is rotatable within the housing, said at least one impellor and shaft being subject to an axial displacement caused by an axial thrust; a thrust compensating mechanism that is distinct and separated from all impellors that are fixed to said shaft, said thrust compensating mechanism including: a first segment that is longitudinally and rotationally fixed to and coaxial with the rotatable shaft; and a second segment that surrounds the rotatable shaft while being longitudinally and rotationally fixed to the housing; one of the first and second segments being a male segment having a first cylindrical outer surface that is terminated by a first circular leading edge; the other of the first and second segments being a female segment containing a first cylindrical passage, said first cylindrical passage being terminated at a front face of the female segment by a first circular opening that is larger in diameter than the first circular leading edge of the male segment, when the shaft is not axially displaced, said first circular leading edge of the male segment being proximal to the first circular opening of the female segment without entering into the first cylindrical passage of the female segment, so that a first pressure release gap is formed between the first leading edge of the male segment and the first circular opening of the female segment through which pressurized fluid is able to flow from a high pressure region to a first lower pressure region, whereby an axial compensating force opposed to said axial thrust is applied to the first segment by the pressurized fluid, said first pressure release gap being reduced in size by said axial displacement, such that the compensating force is increased when the axial thrust and axial displacement are increased, and the size of the pressure release gap is consequently decreased.

2. The apparatus of claim 1, wherein the apparatus is a compressor.

3. The apparatus of claim 1, wherein the apparatus is a turbine.

4. The apparatus of claim 1, wherein the apparatus is a pump rotating as a turbine.

5. The apparatus of claim 1 wherein the apparatus is a turbo pump.

6. The apparatus of claim 5, wherein the apparatus is a multi-stage turbo pump.

7. The apparatus of claim 5, wherein the female segment is configured so as to be filled with fluid that leaks past an impeller of the turbo pump.

8. The apparatus of claim 1, wherein the low pressure region is a fluid inlet region of the apparatus.

9. The apparatus of claim 1, wherein the apparatus further comprises a thrust reducing drum mechanism that is configured to oppose but not eliminate the axial thrust, said drum mechanism comprising a cylindrical drum section configured to rotate within and relative to a non-rotating passage, a radial gap being formed between the drum and passage having a radial gap size that is independent of said axial displacement, one but not both of said drum and passage being longitudinally fixed to the shaft, a residual axial thrust that is not compensated by the drum mechanism being regulated by the thrust regulating mechanism.

10. The apparatus of claim 1, wherein: said male element further comprises a second cylindrical outer surface that is terminated by a second circular leading edge, said second cylindrical outer surface being smaller in diameter than said first cylindrical outer surface, said second cylindrical outer surface extending into said first cylindrical passage of the female element; and said female element further contains a second cylindrical passage extending inward from said first cylindrical passage, said second cylindrical passage being terminated at the first cylindrical passage by a second circular opening that is smaller in diameter than the first circular opening but larger in diameter than the second circular leading edge of the male segment; when the shaft is not axially displaced, said second circular leading edge of the male segment being proximal to the second circular opening of the female segment without entering into the second cylindrical passage of the female segment, so that a second pressure release gap is formed between the second leading edge of the male segment and the second circular opening of the female segment through which the pressurized fluid is able to flow from the first lower pressure region to a second lower pressure region, said second lower pressure region being lower in fluid pressure than said first lower pressure region, said second pressure release gap being reduced in size by said axial displacement: wherein the pressurized fluid sequentially traverses the first and second pressure release gaps as it flows from the high pressure region to the second lower pressure region.

11. The apparatus of claim 1, wherein the apparatus is configured such that a magnitude of the compensating force will rise to at least 90% of a magnitude of the axial thrust before the circular leading edge of the male segment enters the cylindrical passage of the female segment.

12. The apparatus of claim 1, wherein the male segment is smaller in diameter than all of the impellors that are fixed to the shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified cross sectional illustration of a thrust compensating disk of the prior art;

(2) FIG. 2 is a simplified cross sectional illustration of a thrust compensating drum of the prior art;

(3) FIG. 3A is a side view of a rotary pump to which embodiments of the present invention are applicable;

(4) FIG. 3B is a sectional view of the pump of FIG. 3A;

(5) FIG. 4 is a magnified cross-sectional view of a region of the pump of FIG. 3B where an embodiment of the present invention is implemented;

(6) FIG. 5 is a magnified cross-sectional view of the embodiment of FIG. 4, shown in a low-thrust configuration;

(7) FIG. 6 is a magnified cross-sectional view of the embodiment of FIG. 4, shown in a high-thrust configuration;

(8) FIG. 7 is a cross-sectional view of an embodiment that includes step-wise rotor and stator regions that form two pressure relief gaps with an intermediate chamber therebetween; and

(9) FIG. 8 is a graph of compensating thrust as a function of axial shaft position in an embodiment of the invention, where the graph compares points generated by computational fluid dynamics with an analytical curve.

DETAILED DESCRIPTION

(10) An axial thrust balancing mechanism for a rotating shaft apparatus is disclosed that provides self-regulating thrust compensation, similar to a balancing disk, and is thereby able to provide complete or nearly complete cancellation of axial thrust, while at the same time avoiding virtually any possibility of contact and wear between rotating and static elements of the balancing mechanism. The disclosed device is referred to herein as a hybrid balancing mechanism, because it combines advantages associated with balancing disks (self-regulating thrust compensation) and balancing drums (axial contact between the rotating and static elements is impossible) into a single mechanism. The device is applicable to any rotating shaft apparatus that is subject to axial thrust, including but not limited to turbo pumps, compressors, turbines, and turbochargers.

(11) FIG. 3A is a side view of a multi-stage rotary pump in which an embodiment of the present invention is included. FIG. 3B is a sectional view of the pump of FIG. 3A, where the plurality of impeller stages is clearly visible. FIG. 4 is an enlargement of the region behind the final impellor stage in the region indicated in FIG. 3B. It can be seen in FIG. 4 that the disclosed embodiment includes a balancing drum section that is formed by a first region 200 of the rotor element that is contained within a first region 106 of the stator element. In addition, the embodiment includes a hybrid balancing section including a second region 400 of the rotor element that is smaller in diameter but located just outside of a corresponding region 402 of the stator element, such that an intermediate chamber 404 is formed within the second region 402 of the stator element wherein fluid can be collected. The area that is circled in FIG. 4 is enlarged in FIG. 5.

(12) With reference to FIG. 5, the rotor 400 and stator 402 elements are configured such that the rotor element 400 is coaxial with the stator element 402 and of smaller diameter. This difference in diameters 502 represents a minimum gap 502 between the rotor 400 and stator 402 elements. However, unlike the balancing drum 200 of FIG. 2, according to the present invention the rotor element 400 is positioned adjacent to the stator element 402, rather than within the stator element 402. As a result, during normal operation the pressure relief gap 500 that is formed between the rotor and stator elements in this region is neither horizontal nor vertical, but instead varies in both direction and size as the shaft 102 is axially shifted by applied axial thrust.

(13) In FIG. 5, the thrust is relatively low, causing the rotor element 400 to be spaced apart from the stator element 402 such that the effective pressure relief gap 500 between the intermediate chamber 404 and the collection chamber 112 is tipped at an angle of approximately 55 degrees from horizontal. In FIG. 6, the thrust has been increased, causing the shaft 102 to shift to the right, thereby narrowing the gap 500 and shifting its direction closer to horizontal. Because the gap 500 is narrower, the pressure difference across the rotor 400 is increased, thereby compensating for the increased thrust. In embodiments, the angle of the pressure relief gap 500 can vary between zero degrees and 70 degrees, depending on the axial thrust and resulting displacement of the shaft.

(14) Accordingly, a feedback effect is established by the disclosed thrust compensation mechanism that is similar to the feedback provided by a thrust compensation disk such as FIG. 1. However, the disclosed mechanism does not pose any danger of direct contact between the rotor element 400 and stator element 402, because the rotor element 400 is smaller in diameter than the stator element 402, such that there is a minimum gap 500 that is always maintained between them. If the rotating shaft 102 is displaced by a large offset, the rotor element 400 will simply enter into the interior of the stator element 402, and will function much like the compensating drum 200 of FIG. 2.

(15) As discussed above, the embodiment of FIGS. 4-6 combines a balancing drum (106, 200, 110) with a hybrid balancing mechanism (402, 400, 404) of the present invention. Accordingly, fluid collected in the leakage chamber 104 is required to flow through the drum gap 110 before reaching the intermediate chamber 404. The fluid then flows through the angled gap 500 before reaching the collection chamber 112. In general, the drum gap 110 and the minimum rotor/stator clearance 502 of the hybrid balancing section can be the same size or different sizes, depending on the requirements of the embodiment.

(16) In some embodiments the disclosed hybrid balancing mechanism is the only thrust compensation that is provided, and in some of these embodiments, the disclosed mechanism compensates for at least 90% of the thrust that is developed by the impeller or other shaft-mounted apparatus.

(17) In the embodiment of FIG. 7, the fluid flowing from the leakage chamber 104 to the collection chamber 112 is required to flow through a first variable angle gap 500 and into an intermediate chamber 604 before flowing through a second variable angle gap 700 and into the collection chamber 112. In embodiments, this approach increases the feedback effect of the disclosed mechanism, by enhancing the changes in leakage chamber pressure as a function of axial movement of the shaft 102. In a similar manner, various embodiments include three or more variable gaps and intermediate chambers.

(18) FIG. 8 is a plot of simulated CFD (computational fluid dynamics) data points and an analytical model illustrating the compensating thrust provided by an embodiment as a function of axial position of the rotating shaft 102. It can be seen that in this specific application, when the axial position is in the steepest region of the curve, a shift of the axial position of only 0.1 mm results in a change in the compensating thrust of approximately 2000 pounds. It should be noted, however, that these quantities will vary considerably depending on the specific application.

(19) The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application.

(20) The invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein and is not inherently necessary. However, this specification is not intended to be exhaustive. Although the present application is shown in a limited number of forms, the scope of the invention is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof. One of ordinary skill in the art should appreciate after learning the teachings related to the claimed subject matter contained in the foregoing description that many modifications and variations are possible in light of this disclosure. Accordingly, the claimed subject matter includes any combination of the above-described elements in all possible variations thereof, unless otherwise indicated herein or otherwise clearly contradicted by context. In particular, the limitations presented in dependent claims below can be combined with their corresponding independent claims in any number and in any order without departing from the scope of this disclosure, unless the dependent claims are logically incompatible with each other.