Patent Publication Number: US-5158440-A

Title: Integrated centrifugal pump and motor

Description:
This application is a continuation of application Ser. No. 593,655, filed Oct. 4, 1990. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to electrically driven fluid pumps, and more particularly to electrically driven centrifugal pumps which require no shaft seals. 
     Centrifugal fluid pumps are well known in the hydraulic and pneumatic fields. They commonly consist of a motor to drive a shaft on which a fluid impeller is mounted. Generally, the fluid inlet port, or suction port, feeds fluid to the center, or hub, of the impeller. A number of impeller vanes generally project outward from the hub in spiral paths and are supported between shrouds which, together with the vanes, define pumping channels. The rotor is encased in a housing which channels the working fluid from the inlet port to the hub, or inducer, where it is inducted into the pumping channels between the vanes and shrouds. The centrifugal action of the impeller drives the working fluid outward to a diffuser at the periphery of the impeller disk where it enters a scroll shaped volute and, from there, is channelled to the discharge port of the pump. 
     The motor shaft, which supports the impeller, requires bearings which are sometimes lubricated by the working fluid, but, in many cases, they require separate lubrication due to incompatibility of the working fluid. In all cases, seals are required to prevent leakage of the working fluid around the impeller shaft where it enters the pump housing. After some time in service, the bearings may deteriorate to the point where they permit some radial displacement of the rotating shaft. This causes accelerated wear and deterioration of the shaft seal and results in leakage of the working fluid from the pump housing. 
     The foregoing illustrates limitations known to exist in present centrifugal pumps. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, this is accomplished by providing an impeller disk which also functions as a rotor for a brushless DC motor in a centrifugal fluid pump, comprising a hub section; at least one disk shaped shroud containing permanent magnets; a plurality of impeller blades projecting outward from the hub and fixed to a face of the shroud to define fluid pumping channels; and means for supplying fluid to the pumping channels. The pump including the impeller disk exhibits a novel construction in that the hub section includes inducer means for inducing fluid flow from one or more inlets to the pumping channels through openings in stator coils and the impeller disks. The impeller may be axially hydrodynamically balanced by providing rings for partially closing the gaps between the stator coils and the impeller so that a pressure is established in the gaps. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional elevation view illustrating one embodiment of a centrifugal pump according to the present invention; 
     FIG. 2 is a schematic sectional elevation view of another embodiment of the pump of the present invention; and 
     FIG. 3 is a fragmentary view along line 3--3 of the pump embodied in FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic cross sectional view of one embodiment of the pump of the present invention, which is seen to be laterally symmetrical about the vertical center plane represented by the centerline of FIG. 1. The housing 10 has an inlet port 11 and a discharge port 12 which are connected by means of inducer assembly 18, impeller shrouds 15, rotating vaneless diffuser 24, and volute 13. The pump fluid enters at the inlet port 11; divides and passes into the two sides of the inducer assembly 18; passes between the two impeller shrouds 15 through pumping channels 55 (shown in FIG. 3) which are defined by the spaces between neighboring impeller blades 21 and the impeller shrouds 15, between which the impeller blades 21 are disposed; passes through the rotating vaneless diffuser 24; then passes through the volute 13 and into discharge port 12. Between diffuser 24 and volute 13 a small amount of the high pressure fluid feeds back through axial thrust balance passages 45. These narrow passages provide the gap necessary for rotation of the rotor shrouds 15 between the stators 14 and, by admission of the feedback fluid, provide a hydrodynamic balance to counteract any axial thrusts of the rotor 15 so that it remains centered between stators 14. Axial thrust balancing rings 16 are provided in the balance passage 45 either on the surface of the stator can 17 or on a projection of housing 10. By narrowing the axial gap between the impeller shrouds 15 and stator cans 17 or housing 10, these rings cause an increase of fluid pressure in the balance passage 45 which enhances the axial thrust balance performance. 
     The alternative provided for placement of the axial thrust balancing rings 16 is required because, in some cases, stators 14 will not be canned or encapsulated. In such cases, it is necessary to place the axial thrust balancing rings 16 on projections of housing 10. Each half of housing 10 has a toroidal recess 33 in which a stator 14 is secured. In addition, recirculation passages 20 are provided to assure smooth inducer action at off-design flow rates. 
     The rotor assembly which includes inducer assembly 18, shrouds 15, impeller blades 21, and rotating diffuser 24 is supported on journals provided on the outside of the tubular axial extensions of shrouds 15 in radial magnetic bearings 35 and auxiliary bearings 40. During operation, the rotor is supported by the radial magnetic bearings 35 which have a large enough clearance to provide non-contact bearing support to the rotor. Should the magnetic bearings 35 fail to support the rotor, auxiliary bearings 40 are provided for the ensuing emergency rundown of the rotor only, and they have a smaller clearance than do magnetic bearings 35. 
     Impeller shrouds 15 each contain a peripheral array of permanent magnets required for a rotor in a brushless DC motor when used in conjunction with stators 14 containing the windings and electrical connections required for operation as a motor. Because impeller shrouds 15 contain permanent magnets, and because shrouds 15 are supported in radial magnetic bearings 35 and auxiliary bearings 40, there is no need for any shaft to penetrate the housing 10 and, thus, no need for rotary shaft seals which can cause wear of the shaft and will eventually leak. 
     FIG. 2 illustrates another embodiment of the pump of the present invention. In this case the housing 10 is composed of several sections, and it has two inlets 11. Otherwise, in all other respects, the pumps are functionally identical. For this reason, numbering of the various components has been retained consistent with that used in FIG. 1. 
     FIG. 3 shows a fragmentary schematic sectional view of the rotor and housing along line 3--3 of FIG. 1. Vanes 21 are attached to shroud 15. Inducer assembly 18 feeds fluid to the impeller blades which pump it radially outward through pumping channels 55 defined by blades 21 and shrouds 15. Diffuser 24 is defined by that space between the two shrouds 15 radially outside that which is occupied by blades 21. Pressurized fluid from diffuser 24 is carried away through volute 13. 
     The particular design parameters for a given pumping application are determined by pressure and volume requirements, space constraints, working fluid properties, and desired orientation of inlet and discharge ports. These are the considerations that determine the diameter of the impeller shrouds 15, the spacing between the shrouds and consequently the width of the impeller blades 21, the size of diffuser 24 if needed, the size of inducer assembly 18, and the size and shape of the pump housing 10 and recirculation passages 20 which are provided to assure smooth inducer action at off-design flow rates. Stators 14 and impeller shrouds 15 are matched according to pumping power requirements. Stators 14 may or may not be encapsulated in cans 17, depending upon whether the working fluid is compatible with the stators. 
     This invention provides an integrated centrifugal pump and motor having the advantages of compactness, the ability to operate electronically at variable speeds, a shaftless rotor which requires no seals, non-contact radial bearing supports during operation, and hydrodynamic axial thrust balance for the rotor. These advantages are obtained when pumping either compressible or incompressible fluids.