US20090191072A1

US20090191072A1 - Pump for high g-load applications

Info

Publication number: US20090191072A1
Application number: US12/361,986
Authority: US
Inventors: Charles B. Kendall
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-01-29
Filing date: 2009-01-29
Publication date: 2009-07-30

Abstract

A pump for high G-load applications comprises a motor assembly coupled to an impeller mounted in a rigid housing and support structure. The motor assembly further comprises a rotor specifically designed to support large radial forces. The rotor is supported by two bearing assemblies. A stator that interacts with the rotor is supported by two rings that position it in the housing. The impeller acts upon a working fluid via an axial inlet and tangential outlet, which comprises a diffuser section to improve the overall pump efficiency. In an aspect, a first distance between the first bearing and the second bearing defines a bearing span, and the first bearing comprises a bearing bore, wherein a ratio of the bearing span to the bearing bore comprises less than 10:1.

Description

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to Provisional Application No. 61/024,264 entitled “Pump for High G-load Applications” filed Jan. 29, 2008, hereby expressly incorporated by reference herein.

BACKGROUND

The described aspects relate to a centrifugal type pump used in high gravity (G)-load applications.
Centrifugal pumps are used on a number of rotating machines. One of the most common applications is on medical computed tomography (CT) scanners for circulating coolant for the imaging components. It should be understood, however, that centrifugal pumps may be used in any number of other applications, such as in aircraft, ships, industrial equipment, etc. In recent years the rotational speed of state of the art CT scanners has increased to 0.30 seconds/revolution with most manufacturers designing machines capable of 0.20 seconds/revolution. The components on these machines are thus subjected to enormous G-loading, sometimes in excess of 20 Gs. A given G-load is the numerical ratio of any applied force to the gravitational force at the earth's surface. The prior art comprises several pumps for severe duty applications where leak tightness and durability are required. Although used on rotating equipment, none of these designs are capable of extremely high G-loads, e.g. in excess of 20 Gs, and long operational life, e.g. in excess of 50,000 hours. Most of the prior art pumps use a standard design motor rotor and bearing arrangement which limits its functional capabilities. Thus, a pump for extended high G-load service, and in some aspects, with reduced risk of leakage, is needed.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.
In an aspect, for example, a pump for high G-load applications comprises a housing, a stator mounted within the housing, and a rotor rotatably positioned within the stator and mounted to the housing. The rotor is mounted to the housing by a first bearing and a second bearing. A first distance between the first bearing and the second bearing defines a bearing span, and the first bearing comprises a bearing bore. In an aspect, a ratio of the bearing span to the bearing bore comprises less than 10:1.
To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed aspects will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the disclosed aspects, wherein like designations denote like elements, and in which:

FIG. 1 is an isometric view of one aspect of a high G-load pump;

FIG. 2 is a partial cross-sectional view of the pump of FIG. 1;

FIG. 3 is an axially exploded view of the pump of FIG. 1;

FIG. 4 is an exploded view of one aspect of an assembly of an impeller and a rotor of the pump of FIG. 1;

FIG. 5 is a partial cross-sectional view of one end of the pump of FIG. 1;

FIG. 6 is a front view of one aspect of a bundle of wires from the end view of FIG. 4;

FIG. 7 is a partial cross-sectional view of one end of the pump, similar to FIG. 4, wherein the pump is adapted to tolerate a misalignment of the rotor;

FIG. 8 is a cross-sectional view of an outlet tube along line 8-8 of the pump of FIG. 1; and

FIG. 9 is a partial cross-sectional view of one aspect of the pump of FIG. 1.

DETAILED DESCRIPTION

Various aspects are now described with reference to the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details.
A pump for high G-load applications comprises a motor assembly coupled to an impeller mounted in a rigid housing and support structure. The motor assembly further comprises a rotor specifically designed to support large radial forces. The rotor is supported by two bearing assemblies. A stator that interacts with the rotor is supported by two rings that position it in the housing. The impeller acts upon a working fluid via an axial inlet and tangential outlet, which comprises a diffuser section to improve the overall pump efficiency.
In one aspect, the risk of leaks is effectively reduced or eliminated in this design by allowing the stator to be wetted by the pumped fluid. Typically there would be seals to keep the stator from being wetted, however, in some aspects, the stator is potted or encapsulated with a material that fluidly seals the stator, thereby eliminating the need for seals and hence reducing risk of leaks. Also, in some aspects, the pumped working fluid includes electrically non-conductive fluids. However, conductive fluids may also be pumped if the stator is encapsulated in an electrically-resistive material such as epoxy.
To achieve very high G-load capabilities, for example, over 20 G forces or over 30 G forces or even over 60 G forces, the mass of the components, and in particular the rotating components, are kept as low as possible. The pressure developed by the pump is proportional to the square of the impeller diameter, and thus increasing the diameter is often used to increase the pressure rating of a pump for a given speed. However, increasing impeller diameter creates a larger axial force component across the motor bearings due to the low pressure zone generated on the impeller face. As bearing life is a function of both axial and radial loads, keeping the axial loads as low as possible allows for increased radial loading for a given bearing size. This is accomplished by using a high speed brushless direct current (DC) motor system with a relatively small impeller. For example, for a CT scanner application, the impeller may be generally less than 3 inches in diameter.
To further improve the load carrying capabilities of the pump, oversized bearings are used with the front bearing being of the angular contact variety that can support the axial loads that are generated during operation. For example, for a CT scanner application, the oversized bearings may have generally greater than a 10 mm bore, wherein the size of the bore is proportional to the size of the bearings. The loads are the result of the aforementioned low pressure zone on the impeller face, as well as loads due to gravity as may be present in CT systems operated with the gantry in a non-vertical orientation. Additionally, the increased motor efficiency gained by use of a brushless DC type motor results in a stator with a shorter overall length. This relatively shorter length combined with the oversized bearings result in a rotor with a relatively very high transverse stiffness. For example, prior art devices typically have a bearing span to bearing bore ratio of greater than 10:1. In one aspect, the disclosed device has a bearing span to bearing bore ratio in the range of about 8:1 to about 4:1, where the bearing bore is proportional to the size of the bearing, or in some cases a ratio of about 6:1, although other ratios of equal to or less than about 10:1 or equal to or less than 9:1 can be feasible depending on the application. This increased stiffness helps to maintain bearing alignment during high G operation, thus increasing the operating life of the bearings.
Further, keeping the impeller weight to a minimum, and reducing induced axial forces are useful in improving bearing life. The impeller has several features that contribute to improved bearing life. Primarily, the impeller comprises slots in the rear face to minimize the axial pressure area. Secondarily, there is no front cover on the impeller, rather the front cover of the pump closely conforms to the impeller vanes.
Referring to FIG. 1, one aspect of pump 10 comprises body 12 with inlet tube 16, and outlet tube 14. During operation the pumped fluid enters via inlet 18 and exits via outlet 20.
Referring to FIGS. 2-4, one aspect of body 12 comprises rear end cap 26 and front end cap 24 enclosing ends of an external housing 32, within which the components of pump 10 are mounted. In one aspect, for example, end caps 24 and 26 are connected to housing 32 in a manner, such as by welding, to form a liquid tight seal at joints 28 and 30. Stator 34 is mounted within support rings 36, which properly center stator 34 within housing 32 along central axis 38. Rear bearing 40 is supported in rear end cap 26, while front bearing 42 is held in holder 44. Rotor 46 is supported by rear bearing 40 and front bearing 42, effectively positioning rotor 46 along central axis 38. O-ring 82, such as a rubber or elastic material, is mounted within rear end cap 26, extending toward rear bearing 40. O-ring 82 is deformable to accommodate some amount of axial misalignment between rotor 46 and housing 32. Impeller 52 is positioned on rotor 46 and held axially by clip 54. Rotation energy of rotor 46 is transmitted to impeller 52 via drive pin 56 (FIGS. 3-4). Stator 34 and rotor 46 define a motor assembly operable to rotate impeller 52 to pump fluid from inlet 18 to outlet 20.Referring specifically to FIG. 4, in one aspect, drive pin 56 is positioned cross axis to rotor 46. Slot 70 in impeller 52 receives drive pin 56 as impeller is axially held by clip 54, which seats in groove 71 in rotor 46.
Also, referring specifically to FIG. 2, internal face 58 of front end cap 24 is shaped to conform to the edge 60 of tapered blade 60 of impeller 52. For example, blades 60 may have a radially-decreasing axial length.
Referring now to FIGS. 2 and 5-7, in one aspect, motor wires 56 provide electricity to energize stator 34, thereby creating a magnetic field that interacts with magnets embedded in rotor 46, thus causing rotation of rotor 46. Wires 56 pass through opening 50 into well 48. Well 48 is filled with an encapsulant 60 to provide sealing and strain relief to motor wires 58. For example, encapsulant 60 may include, but is not limited to, materials such as a thermoset material, such as epoxy or urethane, a thermoset material with additives (such as alumina) to increase thermal conductivity without increasing electrical conductivity, or any non-electrically conductive material. In one specific aspect, now referring to FIG. 6, insulation 68 is stripped in region 62 to expose a plurality of wires or conductor strands 64. Strands 64 are splayed open to create gap(s) 66 between individual strands. During the encapsulation process, encapsulant 60 enters gap(s) 66 to provide liquid tight sealing around individual conductor strands 64. This prevents the fluid within pump 10 from migrating inside motor wires 56 between insulation 68 and conductor strands 64.
Also, referring to FIG. 7, o-ring 82 elastically engages rear bearing 40, allowing rear bearing 40 to position rotor 46 along axis 84, which permits an amount of misalignment 86 with respect to axis 38. For example, axis 38 may be centered within housing 32, and thus axis 84 represents a non-centered axis on which rotor 46 may be positioned. Such misalignment 86 may be desired when front bearing 42 is not mounted in housing 32 co-axially with axis 38, and thus o-ring 82 allows rear bearing 40 to be co-axial with front bearing 42 and rotor 46. The amount of misalignment 86 may be less than about 0.5 degrees in one aspect, or less than about 1 degree in another aspect, and less than about 2 degrees in a further aspect, where there is a tradeoff between amount of misalignment 86 and life and/or durability of the bearings. In other words, by allowing misalignment 86 when front bearing 42 is not co-axially mounted, o-ring 82 allows rear bearing 40 to remain co-axial with front bearing 42, thereby avoiding side loading on the bearings.
Referring now to FIG. 8, in one aspect, outlet tube 14 comprises throat region 76 having a first-sized internal opening and diffuser region 72 having a second-sized internal opening greater than first-sized internal opening. In one aspect, for example, second-sized internal opening of diffuser region 72 has a size that expands along the axial length as diffuser region 72 extends away from housing 32. In other words, diffuser region 72 has a variable-sized internal opening that increases in size as diffuser region 72 extends from housing 32. For example, in one aspect, internal walls of diffuser region 72 may be positioned at a divergent angle 74. Diffuser region 72 effectively pressurizes the pumped fluid flowing in direction 78 by exchanging flow velocity in throat region 76 for pressure at outlet 20. In other words, the opening size governs the flow rate, e.g. larger opening results in a slower flow rate and vice versa, and the rim speed of the impeller controls the pressure, e.g. higher speed results in greater pressure, and vice versa. As such, outlet tube 14 serves to increase the pump efficiency.
Referring now to FIG. 9, pump 10 is arranged to be suitable for the pumping of electrically conductive fluids. In one aspect, stator 34 is coaxially mounted to housing 32 along central axis 38 via support rings 36. Insulation media 80 is positioned within housing 32 in a manner to completely encapsulate stator 34, effectively insulating stator 34 from the pumped fluid. For example, insulation media 80 may be molded within housing 32, between stator 34 and rear end cap 26, effectively sealing stator 34 from fluid pumped by the rotating impeller 52. Insulation media 80 may include, but is not limited to, materials such as a thermoset material, such as epoxy or urethane, a thermoset material with additives (such as alumina) to increase thermal conductivity without increasing electrical conductivity, or any non-electrically conductive material, and any other material capable of forming a seal to resist flow of a fluid.
In some aspects, for example, insulation media 80 and encapsulant 60 may be the same material. In other aspects, insulation media 80 and encapsulant 60 may have different viscosities during installation within pump 10. For example, the viscosity during installation may be referred to as the “as mixed” viscosity, which is prior to the material substantially curing or setting. For example, insulation media 80 may have a first viscosity, and encapsulant 60 may have a second viscosity, wherein the first viscosity is less than the second viscosity. It may be desirable for encapsulant 60 to have a greater viscosity than insulation media 80 in order to ensure that encapsulant 60 adheres to each of the plurality of splayed motor wires 64. Further, it may be desirable for insulation media 80 to have a viscosity less than encapsulant 60 to allow insulation media 80 to fill all the nooks and crannies within housing 32 to fully seal stator 34. For example, in one aspect, insulation media 80 may have a viscosity of less than about 2000 centipoise, wherein in another aspect, the viscosity may be less than about 1500 centipoise, wherein in another aspect, the viscosity may be in the range about 1300 centipoise to about 700 centipoise, wherein in another aspect, the viscosity may be about 1000 centipoise. Further, for example, in one aspect, encapsulant 60 may have a viscosity of greater than about 2500 centipoise, wherein in another aspect, the viscosity may be greater than about 3500 centipoise, wherein in another aspect, the viscosity may be in the range about 2500 centipoise to about 4500 centipoise, wherein in another aspect, the viscosity may be in the range of about 3000 centipoise to about 4000 centipoise.
Additionally, in one aspect, device 10 has a bearing span 90 to bearing bore 92 ratio in the range of about 8:1 to about 4:1, where the bearing bore is proportional to the size of the bearing. In other aspects, bearing span 90 to bearing bore 92 ratio is about 6:1, although other ratios of equal to or less than about 10:1 or equal to or less than 9:1 can be feasible depending on the application. A reduced span to bore ratio, for example in the range of less than 8:1, increases the rotor stiffness between the bearings, helping to maintain bearing alignment, and keeping the rotor mass to a minimum. Additionally, a larger bearing bore, and hence bearing size, allows for increased radial loading for a given rotor size.
While the foregoing disclosure discusses illustrative aspects and/or embodiments, it should be noted that various changes and modifications could be made herein without departing from the scope of the described aspects and/or embodiments as defined by the appended claims. Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise.

Claims

1. A pump for high G-load applications, comprising:

a housing;

a stator mounted within the housing;

a rotor rotatably positioned within the stator and mounted to the housing by a first bearing and a second bearing, wherein a first distance between the first bearing and the second bearing defines a bearing span, wherein the first bearing comprises a bearing bore, wherein a ratio of the bearing span to the bearing bore comprises less than 10:1.

2. The pump of claim 1, wherein the ratio comprises less than 9:1.

3. The pump of claim 1, wherein the ratio is in a range between about 8:1 to about 4:1.

4. The pump of claim 1, wherein the ratio comprises about 6:1.

5. The pump of claim 1, wherein the bearing bore is proportional to a bearing size.

6. The pump of claim 1, wherein the housing comprises a first end and a second end, further comprising a first end cap fluidly sealed to the first end, a second end cap fluidly sealed to the second end, and an insulation media positioned between the stator, the housing and the first end cap to define a fluid seal.

7. The pump of claim 1, further comprising:

wherein the housing comprises a first end;

a first end cap fluidly sealed to the first end, wherein the first end cap comprises an internal wall defining an opening through the first end cap;

a plurality of motor wires electrically connected to the stator and extending through the opening, wherein the plurality of motor wires are spaced apart from one another within the opening thereby defining gaps between the plurality of wires; and

an encapsulant within the opening and filling the gaps between the plurality of wires, fluidly sealing each of the plurality of wires and the opening.

8. The pump of claim 7, further comprising:

wherein the housing further comprises a second end opposite the first end further comprising a second end opposite the first end;

a first end cap fluidly sealed to the first end;

a second end cap fluidly sealed to the second end; and

an insulation media positioned between the stator, the housing and the first end cap to define a fluid seal.

9. The pump of claim 7, further comprising an outer insulator containing a first length and a second length of the plurality of motor wires, wherein the first length and the second length are separated by a third length of the plurality of wires, wherein the third length is positioned within the opening.

10. The pump of claim 1, further comprising:

wherein the housing further comprises an axial inlet and a tangential outlet; and

an impeller connected to the rotor, wherein the impeller is operable to act upon a working fluid entering the pump via the axial inlet and pump the working fluid out of the tangential outlet.

11. The pump of claim 10, wherein the outlet comprises a diffuser region having a variable-sized internal opening that increases in size as diffuser region extends from housing.

12. The pump of claim 10, further comprising a holder mounted within housing and supporting the first bearing, wherein the holder and first bearing are axially positioned between the stator and the impeller.

13. The pump of claim 1, further comprising:

wherein the housing further comprises a first end and an opposing second end;

an insulation media positioned between the stator, the housing and the first end cap to define a fluid seal, wherein the insulation media comprises a first viscosity during installation;

an encapsulant within the opening and filling the gaps between the plurality of wires, fluidly sealing each of the plurality of wires and the opening, wherein the encapsulant comprises a second viscosity during installation, wherein the second viscosity is greater than the first viscosity.

14. The pump of claim 13, wherein the first viscosity is less than about 2000 centipoise, and wherein the second viscosity is greater than about 2500 centipoise.

15. The pump of claim 13, wherein the first viscosity is less than about 1500 centipoise, and wherein the second viscosity is greater than about 2500 centipoise.

16. The pump of claim 13, wherein the first viscosity is in a range of about 700 centipoise to about 1300 centipoise.

17. The pump of claim 13, wherein the first viscosity is about 1000 centipoise.

18. The pump of claim 13, wherein the second viscosity is in a range of about 2500 centipoise to about 4500 centipoise.

19. The pump of claim 13, wherein the second viscosity is in a range of about 3000 centipoise to about 4000 centipoise.

20. The pump of claim 13, further comprising an outer insulator containing a first length and a second length of the plurality of motor wires, wherein the first length and the second length are separated by a third length of the plurality of wires, wherein the third length is positioned within the opening.