Abstract:
A long life rotor pump combination of the type having a liquid filled rotor that uses the liquid being pumped to establish hydrodynamic bearings within the rotor incorporates a pump which can be expanded to include more than one impeller, providing an optionally higher flow rate. Thermal isolation between the motor housing and the pump housing is assured by restricting heat conductivity through the physical structures and through the liquid. The rotor enclosure is formed with a number of engaging but not joined elements maintained under compression established by forces exerted in securing the encompassing motor housing.

Description:
FIELD OF THE INVENTION 
     This invention relates to long life motor driven pump systems, and particularly pump systems of the type that employ the same liquid that is being pumped as lubricant within the motor housing, even though the liquid in the pump can vary widely in temperature and viscosity. 
     BACKGROUND OF THE INVENTION 
     Motor driven pump systems in which the rotor is enclosed within a liquid filled shell are known and are used in a number of applications. A significant advance in such systems has been provided by the teachings of U.S. Pat. No. 6,068,455, to Kenneth W. Cowans, issued May 30, 2000 and entitled “Long Life Pump System”. This type of pump system is particularly needed where the properties of the liquid being pumped may change substantially with time because of temperature and viscosity differences, as can occur in a temperature control system for semiconductor fabricating tools. Such systems must reliably operate over exceptionally long life spans in order that the expensive fabricating tools with which they are used need not be shut down periodically for pump or motor servicing. The system of the &#39;455 patent teaches how the same thermal transfer fluid that is being pumped can be within the interior of the closed rotor housing, and lubricate hydrodynamic bearings in an essentially athermal manner, regardless of the temperature and viscosity variations of the same fluid at the pump. The rotor interior is isolated from thermal variations in the pump to a sufficient degree by restricting interflow, and by limited heat conduction and convection paths. 
     Manufacturing costs and assembly techniques, however, are always of importance in units of this kind, particularly where volume production rates are required. Thus it can be very useful for the pump/rotor system to be so designed as to be externally fillable and made of interchangeable parts that can be readily assembled, but at the same time remain leak free for long periods when in service. Finding other means of cost reduction, as by simplification and standardization of parts, are other paramount objectives. Further, it is desirable to have greater versatility in system operation, such as the ability to vary the pump rate with minimal changes of components. In addition the unit should be compact and operate stably with minimal wear of the moving parts during its service life. These and other objectives are achieved, in accordance with the invention, by the novel configuration disclosed herein. 
     SUMMARY OF THE INVENTION 
     A regenerative turbine-type pump operated by an adjacent motor having a fluid-filled enclosed rotor disposes the rotor within a nonmagnetic cylindrical shell completed at each end by closure members which can provide bearing surfaces for a central shaft. One end of the shaft extends into the interior of the pump housing, to provide a rotatable mount for at least one impeller. The pump housing is secured to a motor housing, which itself encompasses the stator provided about the cylindrical shell. Thermal conductivity between the pump and motor is low because the units are designed to have minimal areal contact between abutting metal parts of relatively low conductivity. Alternatively, a low thermal conductivity element concentric with the shaft can be interposed between the two housings. The end structure for one end of the cylindrical shell comprises an end hub having a central bore open to the interior of the rotor shell, the end hub being maintained in position by a removable end cap for the motor housing. An interposed concentric compression spring about the central bore holds the end hub tightly against the end hub when the housing end cap is tightened in place, even though the end hub is not physically joined to the shell. The central bore in the end hub is closed by a closure member for the rotor shell which seats a fill valve for the thermal transfer fluid. Short central bores in the shaft from each end, with radial outlets into the rotor interior enable thermal transfer fluid to flow into the inner side of the bearings at each end of the rotor. After filling, the fluid volume within the rotor and about the hydrodynamic bearings stabilizes in temperature and is not destabilized in by immaterial amounts of fluid movement. 
     This arrangement provides a simplified shell construction about the rotor that is effectively scaled against leakage for long use periods. Nonetheless, it can be assembled and disassembled with replacement parts, because the concentric compression spring compensates for tolerance variations between parts. The spring, such as a Belleville spring, exerts a selected substantial compressive force along the central axis to maintain the rotor enclosure sealed after assembly. The end supports adjoining or coupled to the rotor shell usefully form journals for the shaft ends when surfaced with a noble metal, such as silver. Alternatively, integral hydrodynamic bearings for long life operation can be supported by sleeves inserted within the rotor shell as journals for bearings at each end of the shaft, and to account for size differences between the end supports and the rotor shaft. 
     Another useful aspect of the invention derives from limited heat conductive paths existing between the pump housing and the rotor enclosure provided by spaced apart legs on the pump housing engaging the motor housing and an inner ring engaging the rotor shell or an intervening isolator. Other alternative features of the construction include the inclusion of an integral rotor shell and end sleeve on the pump side, and a single end closure member on the fill side, reducing both the number of parts employed and the cost. 
     In accordance with another feature of the invention, the pump housing may be configured to receive an extended end on the rotor shaft, which end includes two axially spaced apart mounting surfaces for attachment of one or, alternatively, two impellers. Also, the impeller housing is configured with a base on the rotor side and an opposed end cap which can either be directly coupled to the base or to an interposed spacer element which mates between the base and end cap. When the insert and second impeller are included in the pump housing the flow paths for the thermal transfer fluid are still maintained in continuity between the inlet and outlet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a motor/pump combination in accordance with the invention 
     FIG. 2 is a cross-sectional view of the arrangement of FIG. 1 incorporating one impeller; 
     FIG. 3 is a perspective view, partially broken away, of parts of the interior of the combination of FIGS. 1 and 2; 
     FIG. 4 is a perspective view of a rotor enclosure that may be employed in the system; 
     FIG. 5 is a broken away perspective view of details of the rotor enclosure of FIG. 4; 
     FIG. 6 is a fragmentary perspective view, partially broken away, of the interior of the pump end of the unit, showing further details thereof; 
     FIG. 7 is an enlarged perspective view, partially broken away, of a portion of the rotor enclosure employing a compression spring, hydrodynamic bearing, and fill valve at the fill end of the unit; 
     FIG. 8 is a side sectional view of a modification of the pump end of the motor/pump assembly showing how one or two impellers may be alternatively employed; 
     FIG. 9 is a exploded perspective view of part of the modification of FIG. 8, depicting a housing body, end cap and an alternative interposable member for optionally increasing its interior chamber volume to permit the additional impeller to be used; 
     FIG. 10 is a side sectional fragmentary view of an alternative arrangement of the fill end of an assembly in accordance with the invention; and 
     FIG. 11 is a side sectional fragmentary view of an alternative arrangement of the pump end of an assembly in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to FIGS. 1 to  7 , a motor/pump combination in accordance with the invention includes a motor  10  of the type having an enclosed rotor  12  within a cylindrical rotor shell  14  having a length of thin-walled nonmagnetic material as its central section. The shell  14  includes, at what may be called the fill end, an opening formed by an edge  15  concentric with the central axis of the rotor  12 . A motor shaft  17  along the central axis extends in opposite directions from the rotor  12  to a first end at the pump side, and through the open end edge  15  of the shell  14  at its second or fill end. An extension of the cylindrical shell  14  on the first end comprises an end hub  18  forming a journal  19  (FIGS. 5 and 8) closely fitting about the shaft  17 . The journal  19  surface is plated with a noble metal, such as silver, to provide a suitably smooth, low friction surface in opposition to bearing surface on the shaft  17 , to maintain a hydrodynamic bearing effect upon rotation at a sufficient rate with the bearing gap being occupied by thermal transfer fluid. 
     Immediately about the outside of the thin walled length portion of the cylindrical shell  14  is a conventional stator  23  which in turn is encompassed by the exterior motor housing  25 , the central region of which has protruding lengthwise fins  26  aiding in dissipation of heat generated in consumption of electrical energy. Short longitudinal bolts  28  which pass through lugs  27  on the housing parts are engaged at each end by nuts  29  which secure the motor housing  25  to a first end cap  30  at the pump end, and to a second end cap  32  at the fill end. The second end cap  32  at the fill end includes a central bore  33  coextensive with and about the shaft  17 , and the wall of the body of the housing  25  includes an inner circumferential periphery  34  and an outer circumferential periphery  35  in this region. 
     The pump  36  is of the regenerative turbine type and comprises a pump housing fabricated as separate mating modules, with two engageable principal parts in this example. The two module construction is shown in FIGS. 1,  2 ,  3 , and  6 , while FIGS. 8 and 9 depict the three module variant. In both examples the pump housing has, closest to the motor, a pump body  40  with circumferentially spaced support legs  42 . These legs  42  engage, in separate quadrants, mating side surfaces  41  extending about the circumferential periphery of the first end cap  30  of the motor housing  25  at this radius. As best seen in FIGS. 1,  2 , and  6 , the support legs  42  have small radial and circumferential dimensions at their ends which contact the motor housing, and thus provide only small cross-sectional contact areas for thermal energy conduction in the central axis direction to or from the facing surfaces  41 . The pump body  40  is of cast metal, but not highly conductive. An inner ring  44  of thermally nonconductive material, such as a synthetic resin, is here disposed between the end hub  18  of the rotor shell  14  and the facing inner radial end  43  of the pump body  40 , as best seen in FIGS. 2 and 6. The thermal isolator or spacer ring  44  is sealed by O-rings  45  against each of the adjoining members. In one practical example of a 1500 watt motor, the isolator ring  44  is less than one half inch long, adequate to substantially attenuate thermal conduction along the central axis in the region close to the shaft  17  when the thermal transfer fluid at the pump varies from −40° C. to +120° C. Where the anticipated range of temperature variations in the fluid is less, direct contact can be employed without exceeding acceptable bearing temperature variations. 
     The housing of the pump  36  also includes a pump end plate  46  configured to mate with the pump body  40  portion so as to close off the end of the pump  36 , in both modular versions. The internal faces of the pump body  40  and end plate  46  have largely complementary concavities which, when the pump body  40  and pump end cap  46  are engaged in facing relation, define a shaped interior chamber  47  (FIG. 2) of generally circular form on both axial sides of the blades of an impeller. The chamber  47  extends to an outlet  48  formed in the pump body  40  which extends tangentially from the periphery of the interior chamber  47 , where an inset ring or annular groove  49  envelops the blades of an impeller mounted on the shaft  17 . The ring groove  49  portion of the chamber  47  is also in communication via a short channel with an inlet  50 , in the end plate  46 , that is parallel to the central axis and transverse to the plane of the ring groove  49 . The ring groove volume about the impeller blades is defined by opposing grooves  49   a  and  49   b  (as is seen in FIG. 9) disposed in the pump body  40  and pump end plate  46  respectively. An impeller  53  is coupled to the shaft  17  by a key  54  seated in a groove  55  in the shaft  17  and a corresponding axial groove in the inner bore of the impeller  53 . Rotary pumps with one impeller and having a body and end plate in this construction are known and further description of these elements would be superfluous for the single impeller version. 
     At the second or fill end of the shaft  17 , the open end of the cylindrical shell  14  is closed at the edge  15  by a transverse end or closure member  65  that has an interior bore closely spaced from the shaft  17  exterior. The body of the closure member  65  forms a cylindrical journal surface  67  plated with a noble metal, again typically silver, to provide hydrodynamic bearing support for a bearing surface  68  on the shaft  17 . This portion of the system is best seen in FIGS. 2,  4 ,  5  and  7 . The outer periphery of the end member  65  engages the circular edge  15  of the cylindrical shell  14 , the end section of which diverges slightly in this region, and is engaged against it axially by a separate end shoulder  70  and peripherally sealed by a circumferential O-ring  72 . The outer portion of the end member  65  protrudes to the fill end of the shaft  17  which includes a hollow and inset end section  74  used in the filling operation. A concave end cup  76  is received within the end of the hollow section  74  of the shaft  17 , and includes a radial flange  75  that extends outwardly from the central bore of the cup  76 . An O-ring  77  seals the joinder between the axial end of the end member  65  and the radial flange  75 . The exterior (i.e. fill end side) surface of the flange  75  is engaged on its flat side by a compression spring  78  concentric with and about the end bore  33  and by the housing end cap  32  on the other. A modern compression spring, such as a Belleville spring  78 , can exert a selected force (such as an 800 pound force in this instance) when fully engaged. An externally threaded fill valve  84  is seated in mating threads in the base portion of the interior of the end cup  76 , in communication will the inset opening in the hollow end section  74  of the shaft  17 . The interior of the hollow end section  74  opens to the interior of the rotor  12  enclosure via radial apertures  86 , which are on the rotor side of the bearing  68 . The fill valve  84  is conveniently the type known as a Schroeder valve, which opens to pressure inflow of the heat transfer fluid (in this instance) after its central valve stem has been depressed by an actuator pin in the liquid fill line (not shown). 
     At the first end of the shaft  17 , as seen in FIGS. 2,  5  and  7  an axial conduit  90  extends from the interior chamber  47  of the pump housing  38  into the interior of the rotor  14  enclosure, via at least one radial conduit  92  in the shaft  17  wall. This radial conduit  92  is also on the inner or rotor side of the bearing  19  region so that upon shaft  17  rotation there is sufficient flow into both sides for hydrodynamic operation. After the pump pressure on the heat transfer fluid has initially infiltrated the volume inside the rotor enclosure, there is thereafter no meaningful transfer of thermal energy from or to the rotor enclosure via the thermal transfer fluid. The radial size of the axial conduit  90  in the shaft  17  is substantial, so that the shaft  17  wall is thin, which reduces the heat conduction along the shaft  17  to the bearing region and the principal body of the shaft  17 . The size of the conduit  90  can be reduced by using, a nonconductive insert, such as a synthetic resin tube with a central passageway, without increasing heat conduction in the axial direction. 
     Accordingly, the system has a number of advantages, in addition to the requisite characteristics of low thermal conduction and thermal isolation between the closely coupled pump and rotor enclosures. The fill valve gives access to the rotor enclosure, so that on startup the interior can be filled and the hydrodynamic bearings immediately lubricated. Even though the elements at the fill end are physically separate and interchangeable, they are effectively sealed, by virtue of the force exerted by the motor housing on the rotor enclosure parts via the compression spring. With the selected force provided by the Belleville spring, and sealing provided by the O-rings, the desired leak free connections are established even though assembly and disassembly are feasible. Consequently, the substantial advantages of interchangeability of parts that are afforded by this design act to reduce material costs, assembly costs, and production costs. Tolerance variations are taken up between the various elements, which are held together in sealed relation by the compressive forces that are exerted. Disassembly involves only disengagement of the end cap of the motor housing from the remainder of the body. 
     The basic unit, moreover, is compact and less costly because the plated journal surfaces are integral parts of the rotor enclosure, reducing size requirements while easing assembly problems. Generally available, mass produced parts, such as the motor housing and pump housing are used without substantial modification. 
     In accordance with the present invention, moreover, the pump end may alternatively include, as seen in FIGS. 7 and 8, an optional spacer insert  51  of uniform width (except for interior concavities), which is configured to be interposed between the pump body  40  and the end plate  46 . The spacer insert  51  is configured with openings and passageways opposing the peripheral grooves  49   a ,  49   b  in the body  40  and end plate  46  to provide two annular interior passageway volumes, each receiving a different impeller  53  or  53 ′. The spaced apart impellers  53 ,  53 ′ are mounted on the shaft  17 , being seated in axially separated keyways  55 ,  56  on the shaft  17  and thus positioned within the interior chamber  47  of the pump  36 . These impellers  53 ,  53 ′ are of the type having a flat disk body  57  and peripherally spaced blades  58  mounted perpendicularly, to provide desired pressure and flow for given conditions of impeller velocity and size, and fluid viscosity. Small keys  54 ,  54 ′ (FIG. 9) fit into the keyways  55  or  56  and into longitudinal slots in the associated impeller to lock the impeller against turning relative to the shaft  17 . The impellers  53 ,  53 ′ find a stable axial position between the adjacent sidewalls in the pump housing when at operating speed. With this arrangement, the same two basic modules  42 ,  46  for the pump  36  can either be used with a single impeller, or, if a substantially higher flow rate is desired, the second impeller  53 ′ can be installed, with no other modification than insertion of the spacer insert  51 . Bolts  60  extending through holes in the pump modules along lines parallel to the central axis, are engageble in the motor housing  25 , to secure the modules together, and the pump  36  as a whole to the motor housing  25 . The interior chambers are peripherally sealed by O-rings  61 , one in the body  40  and the other (not visible) in one face of the insert  51 , while shaped depressions or apertures in the modules  40 ,  46  and  51  provide inlet-outlet flow paths no matter which alternative is used. 
     Use of the optional spacer insert in the pump body allows ready modification of the pump rate by easy disassembly of the end cap from the pump body, insertion of the spacer insert and a second impeller, and reassembly of the modules. The inlets, outlets and passageways are adequately sized for the increased flow. Only a short interval for refill of lost thermal transfer fluid is required. 
     An alternative configuration of the components of the assembly at the fill end of the housing  25  is shown in FIG.  10 . In this figure, elements that are identical or similar to elements in the prior views are correspondingly numbered, while only those which differ are given new numbers. Here at the fill end the transverse end member  65  and cup  76  are combined into a single closure member  100  formed as a step down tubular sleeve having a larger diameter section  102  and a smaller diameter section  104  adjoined by a radial transverse flange  106 . The smaller section  104  includes an inner female threaded surface  108  for receiving the fill valve  84 . The end edge portion  15  of the rotor shell  14  is axially engaged against a shoulder  109  on the enclosure  100  and circumferentially mates with the larger diameter section  102 , with sealing being assured by the O-ring  72 . A pair of low friction washers  111 ,  112  are disposed between the rotor side of the closure member  100  and the end of the rotor winding to provide a reactive surface against axial thrust that is found to exist in some circumstances. These washers  111 ,  112  are of “Rulon” plastic and are employed primarily only as a safeguard against the occasionally encountered thrust forces. The conduit path from the fill valve  84  into the inner side of the hydrodynamic bearing extends into the interior volume within the shaft wall  74  at the fill end of the shaft  17  then a central bore  113 , along the shaft  17 , and the one or more radial outlets  86  that open to the bearing. 
     In this instance, the shaft  17  design is seen to have an outer diameter opposing but spaced apart from the closure member  100 , with the gap being filled by a hollow sleeve  115 , the inner circumference of which functions as a plated journal in the hydrodynamic bearing structure. A two element Belleville spring  117  fitted against the radial flange  106  has two diverging spring segments  118 ,  119 , with the inner segment  118  fitting against the face of the radial flange  106  and the outer part of the outer segment  119  being axially engaged by a shoulder  120  in the housing end cap  32 . 
     The example of FIG. 10 therefore provides sealing using a single closure member  100  and makes the fill valve  42  more accessible to the fluid supply connection that is to be attached. It will generally be preferred to employ an enclosure having a inner bore sized to provide a close fitting, sliding reference for the fill end of the shaft  17 , thus establishing a hydrodynamic bearing. 
     A modification of the pump and of the assembly is shown in FIG. 11, again using a single impeller  53 . This Figure shows a stepped-down portion  130  on the pump side of the shaft  17  leading to an end portion  132  that is again of lesser diameter. Here again, a sleeve insert  134  is disposed between the exterior of the first stepped-down portion  130  of the shaft and the facing end sleeve  136  of the rotor shell  14 . The rotor shell  14  in this example is a single unit with the thin shell wall  138  along its principal length being integral with end sleeve  136  which encompasses the bearing sleeve  134 . The end sleeve  136  and an interior radial flange  144  of the pump housing, however, are in direct axial abutment and not separated by an interposed low thermal conductivity spacer. The abutting transverse surfaces encompass an O-ring  146 , but have only a small surface area of contact, and the opposing members are of relatively low thermal conductivity metal. The first end cap  30 ′, it should be noted, has a different shape than the corresponding element of FIGS. 1-3 but is the same in functional aspects. 
     In this arrangement, a typical motor, such as a 1000 watt motor, tends to operate at a temperature of about 40° C. above ambient, whereas the temperature of the fluid used in thermal transfer can typically vary from −40° C. to +120° C. Under these conditions, the contact surfaces between the rotor shell and pump housing, and the motor housing and the pump housing provide a thermal transfer of less than about 80 watts, which increases the bearing temperature less than 10° C. at the hot extreme and decreases the bearing temperature less than about 10° C. at the lowest temperature extreme. Consequently the hydrodynamic bearings are subjected only to minor temperature and viscosity variations and long life exposure is assured. If the temperature extremes are to be stretched appreciably, then a thermal isolator in the interior radial region may be preferred. 
     While there have been described above and illustrated in the drawings various forms and modifications, the invention is not limited thereto and incorporates all alternatives and variants within the scope of the appended claims.