Abstract:
A motor/pump system which uses an enclosed rotor shell, and also interior hydrodynamic bearings which are lubricated by the liquid being pumped, is arranged to minimize localized heating at the bearings to vaporization levels under high load conditions. To this end output pressure from the pump, which varies with load, is communicated into the rotor interior, without bulk fluid transfer. The increased pressure raises the vaporization temperature, automatically adjusting it with increased load to maintain the hydrodynamic bearing effect.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to pumps driven by motors having fluid filled rotors, and more particularly to such pumps which use pressurized liquids within the rotor to maintain hydrodynamic bearing surfaces.  
         BACKGROUND OF THE INVENTION  
         [0002]    A low cost and highly reliable pumping system for use in critical applications, such as applications in which a thermal transfer fluid is directed through a tool that must be maintained at a particular temperature, is provided by a system described in U.S. patent application Ser. No. 09/906,624, entitled “Pump System Employing Liquid Filled Rotor”, having Kenneth W. Cowans as inventor. In this system, the same thermal transfer fluid that is being pumped is also confined within a sealed rotor housing and used to serve as the fluid for supporting internal hydrodynamic bearings, even though the temperature of the thermal transfer fluid, as well as its viscosity, may be required by process conditions to vary within a substantial range. Typical thermal transfer fluids, such as a proprietary fluid sold under the trademark “Galden” or a fifty/fifty mixture of glycol and water, neither solidify nor vaporize even though the hot and cold temperature limits vary widely. The design of the motor and pump system is such that thermal energy transfers between them are limited in all respects, specifically conduction through solids, conduction in the liquid, and convection. Thus the mean temperature within the enclosed rotor varies little, even though the temperature of the fluid circulated by the pump is at a much higher or lower level.  
           [0003]    It has been found, however, that under certain high load conditions, the localized temperature of the hydrodynamic films at the bearings within the rotor shell can substantially increase. In fact, the temperatures in these specific volumes can approach the vaporization point if the thermal transfer fluid being pumped is also in a higher temperature range. While the motor structure can be redesigned so that conductive fins dissipate some of this localized heat, this adds undesirably to cost, and sacrifices compactness. It is therefore desirable to preclude such localized fluid vaporization problems without imposing limitations on the operation of the pump/motor system, or employing special cooling structures for the bearings.  
         SUMMARY OF THE INVENTION  
         [0004]    A pumping system employing a motor with a liquid filled rotor in accordance with the invention utilizes a regenerative turbine pump having an inlet angularly separated from the outlet for the pump, and an interior chamber in the pump housing that is in communication with an interior chamber within the fluid filled rotor of the motor. The passageways between the pump and the rotor communicate pressure without fluid transport, which would tend to equalize the temperature throughout the rotor chamber to the variable temperature at the pump.  
           [0005]    In accordance with the invention, however, the volume within the pump chamber which communicates with the rotor interior is opened via conduits to the higher pressure at the pump outlet. This higher pressure in turn is established within the rotor interior. Such communication does not affect the pump operation, inasmuch as the substantial differential between inlet and outlet pressure is maintained. However, the increase in pressure within the rotor interior, which is dependent on the load on the pump, is highly significant. Under periods of high pump loading, when the local hydrodynamic bearing temperature tends to reach a peak, the pressure at the bearings is correspondingly increased. This consequently increases the fluid vaporization temperature level, automatically counteracting any boil off tendency at the bearing, while not otherwise affecting operation. Consequently, catastrophic or bearing fatigue effects which would be inimical to the desired goal of long life reliable operation of the pump, are avoided.  
           [0006]    In a more specific example of a system in accordance with the invention, the regenerative turbine pump includes a turbine mounted within a pump housing that encompasses a protruding end of the motor shaft. The rotor housing incorporates bearing surfaces about the shaft on each axial side of the rotor. The pump inlet is parallel to the axis of rotation of the turbine, and the pump outlet is tangential relative to that the axis, the inlet and outlet being isolated from each other except for a circumferential channel about the turbine circumference. Blades on each side of the periphery of the turbine disk occupy most of the channel cross section. Fluid communication between the interior of the pump housing and the rotor shell interior is provided through an axial shaft conduit that extends between them. A small fluid interlink conduit in the pump housing between the pump outlet and the interior pump chamber hydraulically raises the interior rotor pressure with load via pathways extending between the high pressure turbine disk region and the rotor interior volume around the shaft. This provides pressure responsive temperature stabilization which avoids local heating in the bearing areas to levels which might approach the pressure adjusted vaporization temperature of the fluid.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    A better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 is a perspective view, partially broken away, of a variable temperature and variable load system for supplying thermal transfer fluid to a unit to be temperature controlled;  
         [0009]    [0009]FIG. 2 is a side sectional view of the pump and motor combination of FIG. 1;  
         [0010]    [0010]FIG. 3 is a fragmentary sectional view of the pump housing of FIG. 1, showing further details thereof;  
         [0011]    [0011]FIG. 4 is a fragmentary perspective view of the pump housing of FIG. 2, and  
         [0012]    [0012]FIG. 5 is a perspective exploded view of the components of the pump. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    In a system in accordance with the invention, referring now to FIGS.  1 - 5 , an induction motor  10  having a liquid filled rotor  12  with a shaft  14  end  15  extending from the rotor housing  13  is fully sealed against leakage, with the shaft end  15  extending to within a pump housing  18  with a narrow circumferential chamber for receiving a regenerative turbine pump  16  having a disk body  17  mounted on the shaft end  15 . The pump housing  18  is also enclosed except for an axial inlet  20  and a radial outlet  22 , each leading to an opposite side of a peripheral channel  23  that extends about the outer circumference of the disk  17 . The inlet  20  and the outlet  22  are angularly separated relative to the pump periphery, as is more clearly shown in FIG. 5. A central or second interior chamber  24  concentric with and about the shaft end  15  is defined between the pump housing  18  and adjacent rotor housing  13 . The chamber  24  is separated by a portion of the pump housing wall from the outlet port  22 . Turbine blades  29  on the opposite sides of the periphery of the disk body  17  are in communication with the inlet and outlet ports  20 ,  22 , respectively, and lie within the different sides of the peripheral channel  23 . The halves of the pump housing  18 , however, includes barriers which separate the flow at the inlet port from that at the outlet port  22  as seen in FIG. 5. the narrower circumferential chamber in the housing which receives the turbine disk body  17  has side wall surfaces which are spaced apart from, but close to, the body  17 .  
         [0014]    The pump  16  is driven by the motor shaft  14  to supply pressurized thermal transfer fluid to a temperature controlled processor unit or process tool  30  (FIG. 1 only), which may be a cluster tool for making precise parts, such as semiconductors. The induction motor  10  is operated by drive circuits  34  which respond to signals from a controller  36  to provide rotational velocity for the desired flow rate for the then current operating needs of the processor unit  30 . The temperature of the thermal transfer fluid that is being supplied is regulated prior to input to the unit  30  by a temperature control unit  38  also governed by the processor unit  30 .  
         [0015]    The housing  18  of the pump  16  includes a small (typically less than about 5 mm diameter) pressure communicating aperture  40  (FIGS.  2 - 4  only) between the inside wall of the outlet port  22  and the interior chamber  24  of the housing  18 . this aperture  40 , which is in this example between about 1 mm and about 1.5 mm in diameter, does not circulate fluid but raises the pressure to a higher level in the chamber  24 . The interior chamber  24  between the pump housing  18  and the rotor housing  13  communicates pressure through the turbine disk  17  volume via flow holes  42  (FIG. 5), small spacings (not readily visible at this scale) between the walls of the housing  18  and the disk body  17 , and into a pump end chamber  44  (FIGS. 2 and 3) about the shaft end  15 . An axial conduit  46  in the shaft end  15  is open to the end chamber  44 , and extends into the interior volume within the rotor housing  13 , where radial apertures  48  open into the pump housing  18  interior. These end openings of the apertures  18  are on the inside of a first hydrodynamic bearing  50  which is on the pump side of the rotor  12 , and which is formed by a smooth (e.g. silver) plating on the inner cylindrical surface of a part of the rotor housing  13 . Such an arrangement is reliable and particularly cost effective. At the opposite end of the rotor  12 , a second hydrodynamic bearing  52  (FIG. 2 only) is mounted about the shaft  14 , and comprises a like plated concentric structure receiving the shaft  14 . Pressure communication within the rotor housing  13  is thus via the gap between the shaft  14  and the rotor windings. The rotor housing  13  and pump housing  18  are both stationary, and a seal member  56  with interior O rings is disposed between these abutting surfaces, as seen in FIGS. 2 and 3.  
         [0016]    The pump  16  is effective in providing a high flow rate, at a given level, for a thermal transfer fluid such as “Galden HT 70” grade, or a 50/50 glycol/water mixture, which may be at temperatures from −40° C. to +70° C. At ambient pressures of one atmosphere, “Galden HT 70” has a boiling point of about 70° C., and while the temperatures needed for the process tool  30  of FIG. 1 do not approach this boiling point, the localized temperature in the immediate vicinity of the bearings  50 ,  52  may in fact approach or exceed such a level. Significant vaporization in the bearing gap would deteriorate the liquid film support and drastically or even catastrophically affect bearing life. Such conditions can occur when the maximum liquid that is being pumped involves heavy loading, i.e. high flow rates and pressures, because as noted above, the maximum temperature within the rotor housing  13  varies little more than 10° C. even though the liquid being pumped may vary across a range of 110° C. The localized temperature at the bearings under high stress can reach an absolute level of 110° C., which at one atmosphere, exceeds the boiling point of “Galden HT 70”.  
         [0017]    In accordance with the invention, however, the interconnection  40  between the high pressure outlet side of the pump  16 , the radial port  22  and the central chamber  24  increases the interior pressure within the rotor housing  13  essentially to the output pressure level of the output fluid. Since essentially no flow of thermal transfer fluid is involved, and only hydraulic pressure is communicated, an output pressure of 80 psi from the pump  15  raises the boiling point at the hydrodynamic bearings to about 115° C., and this gain of 45° C. in boiling point renders localized evaporization unlikely. Since the power to drive the pump  16  is roughly proportional to the pressure being delivered, the temperature at which the bearings  50 ,  52  will fail is automatically raised as the pressure is changed. This approach thus offers a low cost solution that avoids more expensive expedients for cooling the bearings.  
         [0018]    It will be appreciated that with different pump designs, other hydraulic pressure pathways may be used to communicate output pressure into the bearing regions. It should be noted that, with the presently described configuration, the higher pressure in the mid-region of the regenerative turbine disk does not introduce substantial back pressure to inflow or act to increase the stress on the pumping system. The peripheral channel and the turbine disk separate the incoming and outgoing flows so that they are adequately isolated and the pressure communicated into the rotor interior does not meaningfully increase motor load.  
         [0019]    While there have been described above the illustrated in the drawings various forms and modifications of systems in accordance with the invention it should be appreciated that the invention is not limited thereto but encompasses all versions and expedients within the scope of the appended claims.