Abstract:
Embodiments of the invention provide a pump assembly and a method for assembly the pump assembly. The pump assembly includes a stator assembly, a lower pump housing, an upper pump housing, a rotor assembly, and an isolation cup. The method includes coupling the stator assembly to the lower pump housing, overmolding an overmold material over the stator assembly and the lower pump housing, positioning the isolation cup over the overmold, and positioning the rotor assembly inside the isolation cup. The method further includes placing the upper pump housing over the rotor assembly and coupling the upper pump housing to the lower pump housing.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 61/235,274 filed on Aug. 19, 2009, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Cooling of computer systems has conventionally been accomplished through forced-air cooling systems, such as fans. However, liquid cooling systems provide better heat transfer compared to forced-air systems. In liquid cooling systems, a liquid coolant circulates through tubing around the computer system. As the liquid coolant circulates, heat is transferred from the computer system to the liquid coolant, thus cooling the computer system. The liquid coolant then circulates back to a cooling component where it is again cooled, and then recirculated around the computer system. Circulation of the liquid coolant can be accomplished using a pump. Conventional pumps for liquid cooling systems utilize drive magnets. Most magnetic drive pumps require a separate motor and can be bulky, making them a poor choice for use in small spaces near computer systems. 
       SUMMARY 
       [0003]    Some embodiments of the invention provide a pump assembly for pumping a fluid. The pump assembly includes a first pump housing, a second pump housing removably coupled to the first pump housing, and a motor assembly with a rotor assembly and a stator assembly. The stator assembly is positioned inside the first pump housing, and the pump assembly also includes an overmold substantially covering the stator assembly and an inside portion of the first pump housing. The pump assembly further includes an isolation cup positioned inside the first pump housing over the overmold. The isolation cup is coupled to the first pump housing and the rotor assembly is positioned inside the isolation cup. 
         [0004]    Some embodiments provide a method of assembling a pump assembly. The method includes coupling a stator assembly to a lower pump housing. The method also includes overmolding an overmold material over an inside portion of the stator assembly and an inside portion of the lower pump housing, positioning an isolation cup inside the lower pump housing over the overmold material, and positioning the rotor assembly at least partially inside the isolation cup. The method further includes securing a position of the rotor assembly by placing an upper pump housing over the rotor assembly and coupling the upper pump housing to the lower pump housing. 
         [0005]    Some embodiments of the invention provide a pump assembly including a first pump housing with an inlet and an outlet, and a second pump housing removably coupled to the first pump housing. The pump assembly also includes a pumping chamber fluidly connecting the inlet and the outlet, a motor chamber in fluid communication with the pumping chamber, and a stator assembly positioned in the second pump housing. The pump assembly further includes an overmold substantially covering the stator assembly and an inside portion of the second pump housing. The overmold substantially seals the stator assembly from fluid passing through the motor chamber and the pumping chamber. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a front view of a pump assembly according to one embodiment of the invention. 
           [0007]      FIG. 2  is a back view of the pump assembly of  FIG. 1 . 
           [0008]      FIG. 3  is a cross-sectional view of the pump assembly taken along line A-A of  FIG. 1 . 
           [0009]      FIG. 4  is a front perspective view of the pump assembly of  FIG. 1 . 
           [0010]      FIG. 5  is another front perspective view of the pump assembly of  FIG. 1 . 
           [0011]      FIG. 6  is a back perspective view of the pump assembly of  FIG. 1 . 
           [0012]      FIG. 7  is a side view of the pump assembly of  FIG. 1 . 
           [0013]      FIG. 8  is a schematic view of a pump assembly according to one embodiment of the invention. 
           [0014]      FIG. 9  is a flow diagram of a process for assembling a lower pump housing and a stator assembly of the pump assembly of  FIG. 1 . 
           [0015]      FIG. 10  is a front view of a stator assembly during the assembly process of  FIG. 9 . 
           [0016]      FIG. 11  is a perspective top view of a stator assembly and a lower pump housing during the assembly process of  FIG. 9 . 
           [0017]      FIG. 12A  is a bottom view of a lower pump housing during the assembly process of  FIG. 9 . 
           [0018]      FIG. 12B  is an inside view of a pump housing and a stator assembly during the assembly process of  FIG. 9 . 
           [0019]      FIG. 12C  is another bottom view of a lower pump housing during the assembly process of  FIG. 9 . 
           [0020]      FIG. 13  is a perspective view of a mold insert used during the assembly process of  FIG. 9 . 
           [0021]      FIG. 14A  is an inside view of a pump housing and a stator assembly during the assembly process of  FIG. 9 . 
           [0022]      FIG. 14B  is another inside view of a pump housing and a stator assembly during the assembly process of  FIG. 9 . 
           [0023]      FIG. 15  is a cross-sectional view of a pump assembly according to another embodiment of the invention. 
           [0024]      FIG. 16  is a flow diagram of a process for assembling a lower pump housing and a stator assembly of the pump assembly of  FIG. 15 . 
           [0025]      FIGS. 17A-17D  are perspective views of pump assembly components during the assembly process of  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings, whether mechanical or electrical. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0027]    The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
         [0028]      FIGS. 1-7  illustrate a pump assembly  10  according to one embodiment of the invention. The pump assembly  10  can include a lower pump housing  12  (as shown in  FIG. 2 ), an upper pump housing  14 , an inlet  16 , and an outlet  18 . In some embodiments, the pump assembly  10  can be a compact, magnetic drive, centrifugal pump with an integrated motor assembly  20 , as shown in  FIG. 3 . In some embodiments, a diameter of the pump assembly  10  can be about 7.2 inches and a thickness of the pump assembly  10  (i.e., from a top of the inlet  16  to a bottom of the lower pump housing  12 ) can be about 6.6 inches. 
         [0029]    In some embodiments, the pump assembly  10  can be used in various applications, such as agriculture and horticulture, automotive, brewery, cryogenics, dairy, medical, petrochemicals, pharmaceuticals, semiconductor manufacturing, thermal cooling, water treatment, chillers, aquariums, ponds, waterfalls, etc., to pump media such as fresh water, acids, combustible chemicals, corrosive chemicals, effluent, fuel, ground water, coolants, salt water, photochemicals, etc. 
         [0030]    In some embodiments, the pump assembly  10  can be used to circulate water or cooling fluid through tubing around small electronics or computer systems (not shown) to permit proper heat dissipation of the electronics or computer systems. The tubing can connect to the inlet  16  and the outlet  18  and the pump assembly  10  can circulate the fluid at about 75 gallons per minute (gpm) with about 40 feet of head pressure, in one embodiment. In addition, the motor assembly  20  can operate using an input voltage of about 400 volts., and the motor assembly  20  can dissipate about 250 kilowatts (kW) of heat while operating using the 400-volt input voltage, in one embodiment. 
         [0031]      FIG. 3  illustrates a cross section of the pump assembly  10 . As shown in  FIG. 3 , the motor assembly  20  can include a static shaft  22 , a rotor assembly  24 , bearings  26 , and a stator assembly  28 . The rotor assembly  24 , which can include a rotor  30  and an impeller  32 , can be supported by the static shaft  22  and the bearings  26 . The rotor assembly  24  can circumscribe the static shaft  22  and the stator assembly  28  can drive the rotor assembly  24  to rotate about the static shaft  22 . In some embodiments, the static shaft  22  and the bearings  26  can include one or more ceramic materials. 
         [0032]    The motor assembly  20  can provide an integrated permanent magnet brushless motor within the pump assembly  10 . By using the stator assembly  28  instead of a separate drive magnet coupled to an external motor, the pump assembly  10  can be substantially less expensive (e.g., due to of reduced material costs), lighter, quieter, and more compact than conventional pumps. In addition, the pump assembly  10  can have cleaner operation and increased life due to elimination of leakage paths and shaft seals, due to the permanent magnet drive current construction, and due to a reduced number of bearings and mass in motion. This also results in improved efficiency due to reduced power consumption. The pump assembly  10  can also be capable of handling aggressive media successfully, and be more reliable due to better thermal management in comparison to conventional pumps, as further described below. 
         [0033]    As shown in  FIG. 3 , the pump assembly  10  can include a pumping chamber  34  and a motor chamber  36 . The pumping chamber  34  can fluidly connect the inlet  16  and the outlet  18 . For example, fluid (e.g., water or liquid coolant) can be drawn into the pumping chamber  34  through the inlet  16  and forced out of the pumping chamber  34  through the outlet  18  by rotation of the impeller  32  within the pumping chamber  34 . In some embodiments, the rotor  30  and the impeller  32  can be a single integral part or two separate pieces coupled together. In addition, the rotor  30  can be positioned within the motor chamber  36  and the impeller  32  can be positioned within the pumping chamber  34 . As shown in  FIG. 3 , there are no seals between the pumping chamber  34  and the motor chamber  36 . As a result, fluid from the pumping chamber  34  can circulate through the motor chamber  36 . The circulating fluid can flow in between the static shaft  22  and the bearings  26  and the rotor  30 , thus providing lubrication for the bearings  26  and cooling for the motor assembly  20 . 
         [0034]    The stator assembly  28  can fit inside the lower pump housing  12 , and in some embodiments, the inside of the lower pump housing  12  (including the stator assembly  28 ) can be overmolded with an overmold material  38 , such as epoxy, silicone, or a similar material. The rotor assembly  24  can then be placed inside the overmolded lower pump housing  12  (including the stator assembly  28 ), and the upper pump housing  14  can be placed over the lower pump housing  12 . The upper pump housing  14  and the lower pump housing  12  can then be coupled together via fasteners  40  around the pump assembly  10 , as shown in  FIGS. 1-7 . Also, as shown in  FIG. 3 , the upper pump housing  14  can include a holding portion or holder  42  which can be positioned over and/or around a portion of the static shaft  22  when the upper pump housing  14  is coupled to the lower pump housing  12 . The holder  42  can help maintain the position the static shaft  22  within the pump assembly  10  and can also help prevent the static shaft  22  from rotation or lateral movement. In addition, the top bearing  26  can abut the holder  42 , as shown in  FIG. 3 . As a result, the holder  42  can also help prevent axial movement of the rotor assembly  24  along the static shaft  22 . In some embodiments, the pump assembly  10  can also include a self-priming channel (not shown) to permit self-priming. 
         [0035]    The overmold  38  can provide a liquid-tight seal between the pumping chamber  34  and the stator assembly  28 , as well as the motor chamber  36  and the stator assembly  28 , thus keeping the stator assembly  28  dry. The overmold  38  being in contact with fluid in both the pumping chamber  34  and the motor chamber  36  can also act as a heat sink for the stator assembly  28 . In addition, the overmold  38  provides better heat conducting capabilities than air, allowing heat to be released more rapidly to the circulating fluid in the pumping chamber  34  and the motor chamber  36  than in conventional pumps where the stator is surrounded by air. Thus, the overmold  38  can be a one-piece overmold that can isolate the stator assembly  28  from fluid and act as a heat sink for the stator assembly  28 . 
         [0036]    The overmold  38  can also provide high dielectric strength between windings  44  of the stator assembly  28  and the fluid in the motor chamber  36 , helping prevent leakage currents. The high dielectric strength and enhanced thermal transfer capabilities of the overmold  38  can allow the motor assembly  20  to operate at higher voltages than conventional pumps. The higher input voltage can permit the pump assembly  10  to operate at a faster speed, increasing the flow rate of the fluid being pumped compared to conventional pumps. The higher input voltage can also permit increased loads on the motor assembly  20 , reducing the risk of the motor assembly  20  falling out of synchronization due to over-loading. As a result, the pump assembly  20  can handle aggressive media better than conventional pumps with similar proportions. The overmold  38  can also provide an improved magnetic field around the motor assembly  20 , compared to conventional pumps with air gaps between the stator assembly  28  and the rotor assembly  24 . In addition, metals are prone to eddy currents in environments with a varying magnetic field. Thus, conventional induction-type motors with metal cans, which use a metallic separator between the rotor and the stator, generate additional heat inside of the motor due to the eddy currents. The overmold  38 , because it is not a metallic material, can reduce the risk of generated eddy currents within the pump assembly  10 . 
         [0037]    In some embodiments, the lower pump housing  12  can be made of stainless steel and can also act as a heat sink for the motor assembly  20  (e.g., to surrounding outside air). Also, in some embodiments, the lower pump housing  12  can include fins  46  around its outside, as shown in FIGS.  1  and  3 - 6 . The fins  46  can provide additional surface area for effective heat transfer from the lower pump housing  12 . Also, electrical connectors or lead wires  48  (as shown schematically in  FIG. 8 ) connected to the stator assembly  28  can be provided through one or more of the fins  44  or another bottom portion of the lower pump housing  12 . The lead wires  48  can electrically connect the stator assembly  28  to a controller  50 , as shown in  FIG. 8 , which can control operation of the pump assembly  10  (i.e., by providing power to, adjusting power to, and/or removing power from the stator assembly  28 ). The overmold  38  can completely isolate the lead wires  48  from fluid being pumped. In some embodiments, the controller  50  can be an external controller, as shown in  FIG. 8 . For example, the controller  50  can be completely separate from the pump assembly  10  or the controller  50  can be mounted to a rear or outside portion of the pump assembly  10 . In other embodiments, the controller  50  can be an internal controller positioned inside the pump assembly  10  (for example, sealed from the fluid by the overmold  38 ). In embodiments where the controller  50  is mounted on the pump assembly  10  or positioned inside the pump assembly  10 , the lower pump housing  12 , the upper pump housing  14 , and/or the overmold  38  can act as heat sinks to help cool the controller  50 . 
         [0038]      FIG. 9  illustrates an assembly process for manufacturing the stator assembly  28  and the lower pump housing  12  according to one embodiment of the invention. First, at step  52 , the stator assembly  28  can be wound using wire including, for example, a dielectric strength of about 4275 volts/millimeter (e.g., Aspen Motion Technologies Part No. 10039). Then, at step  54 , the stator assembly  28  can be dipped in a varnish with, for example, a dielectric strength of about 1300 volts/millimeter when wet and about 2500 volts/millimeter when dry (e.g., Aspen Motion Technologies Part No. 10912). The stator assembly  28  can be placed in an oven to cure after excess varnish has been drained from the stator assembly  28 . At step  56 , the stator assembly  28  can be dipped in varnish for a second time and placed in the oven to cure.  FIG. 10  illustrates the cured stator assembly  28  according to one embodiment of the invention. In addition, as shown in  FIGS. 10 and 11 , the lead wires  48  can be coupled to the stator assembly  28 . The lead wires  48  can electrically connect the stator assembly  28  to the controller  50 , as shown in  FIG. 8 . 
         [0039]    As step  58 , the stator assembly  28  and at least an inner portion of the lower pump housing  12 , as shown in  FIG. 11 , can be cleaned with alcohol and allowed to dry. At step  60 , the stator assembly  28  can be coated with an adhesive (e.g., Aspen Motion Technologies Part No. 10903 “Loctite 325” adhesive) and the inner portion of the lower pump housing  12  can be coated with an activator (e.g., Aspen Motion Technologies Part No. 10904 “Loctite 7380” activator). For example, a bottom portion and an outer circumference portion of the stator assembly  28  can be coated with the adhesive (i.e., portions which will come into contact with the lower pump housing  12 ), and an inner circumference portion and part of an inside bottom portion of the lower pump housing  12  can be coated with the activator (i.e., portions which will come into contact with the stator assembly  28 ). At step  62 , the stator assembly  28  can be placed inside the inner portion of the lower pump housing  12 , joining the adhesive and the activator. As shown in  FIGS. 12A and 12B , the lead wires  48  can be routed through a wire grommet  64  of the lower pump housing  12  when the stator assembly  28  is placed inside the lower pump housing  12 . The adhesive can be allowed to cure in order to couple together the stator assembly  28  and the lower pump housing  12 . 
         [0040]    At step  66 , the lead wires  48  can be secured to the combined stator assembly  28  and lower pump housing  12 . The lead wires  48  can be bonded in place through the wire grommet  64  using an epoxy (e.g., Aspen Motion Technologies Part No. 11490), as shown in  FIG. 12C , and allowed to cure. 
         [0041]    At step  68 , a mold insert  70 , as shown in  FIG. 13 , can be placed inside the lower pump housing  12  over the stator assembly  28  and the overmold material  38  (e.g., Aspen Motion Technologies Part No. R45-14701) can be transfer-molded around the insert  70  over an exposed portion of the stator assembly  28  and the lower pump housing  12 . More specifically, as shown in  FIG. 12B , a top portion  72  and an inner circumference  74  of the stator assembly  28  can be overmolded with the overmold material  38 , and an inside bottom portion  76  of the lower pump housing  12  can be overmolded with the overmold material  38 . The insert  70  can be constructed so that the overmold  38  has a varied thickness (e.g., from about 0.01 inch to about 0.1 inch). The overmolded lower pump housing  12  can be removed from the mold insert  70  when the overmold  38  is cool. 
         [0042]    As shown in  FIG. 13 , the insert  70  can include grooves  78 . The grooves  78  can translate to the overmold  38 , providing complimentary grooves  80 , as shown in  FIGS. 3 and 14A , for holding the static shaft  22  and the lower bearing  26  in their correct positions when the motor assembly  20  is placed inside the lower pump housing  12 . More specifically, the complimentary grooves  80  can substantially prevent the static shaft  22  from lateral movement within the lower pump housing  12 . In addition, the insert  70  can include protrusions (not shown), which translate to the overmold  30 , to provide fluid pathways between the pumping chamber  34  and the motor chamber  36  when the pump assembly  10  is assembled. 
         [0043]    At step  82 , an interface between the lower pump housing  12  and the stator assembly  28  can be sealed. In one embodiment, the lower pump housing  12  and the stator assembly  28  can be coated with an adhesion promoter (e.g., Aspen Motion Technologies Part No. 15660 “Dow Corning P5200 adhesion promoter”), allowed to cure, and then an exposed interface  84  between the stator assembly  28  and the lower pump housing  12  can be sealed with a potting compound (e.g., Aspen Motion Technologies Part No. 12136 “Dow Corning Sylhard 160 Potting Compound”), as shown in  FIGS. 14A and 14B . 
         [0044]    In some embodiments, as shown in  FIG. 15 , the pump assembly  10  can include an isolation cup  86 . The isolation cup  86  can separate the overmolded lower pump housing  12  from the pumping chamber  34  and the motor chamber  36 . As a result, the stator assembly  28 , as well as the overmold  38 , can be kept dry, preventing the overmold  38  from absorbing water. In some embodiments, the isolation cup  86  can also provide additional structural strength to the overmolded lower pump housing assembly  12 . The overmold  38 , through the isolation cup  86 , can continue to provide enhanced dielectric strength and help remove heat from the stator assembly  28 . In addition, the impeller  32  and the isolation cup  86  can be positioned relative to each other within the pump assembly  10  to allow fluid to flow from the pumping chamber  34  into the motor chamber  36 . In some embodiments, the isolation cup  86  can be constructed of Polyether Ether Ketone (PEEK) or a similar moldable material. 
         [0045]    The isolation cup  86  can include the complimentary grooves  80 , as shown in  FIG. 15 , for holding the static shaft  22  and the lower bearing  26  in their correct positions when the motor assembly  20  is placed inside the lower pump housing  12 , substantially preventing the static shaft  22  from moving within the lower pump housing  12 . In addition, in some embodiments, as shown in  FIG. 15 , the pump assembly  10  can also include spacers  88  (e.g., ceramic spacers) surrounding the static shaft  22  and the rotor assembly  24  can rotate about the spacers  88 . 
         [0046]      FIG. 16  illustrates an assembly process for manufacturing the pump assembly  10  according to another embodiment of the invention. At step  90 , the stator assembly  28  can be positioned inside the lower pump housing  12 , as shown in  FIG. 17A , and the inside of the stator assembly  28  and the lower pump housing can be overmolded with the overmold material  38  (as described above). At step  92 , the isolation cup  86  can be positioned inside the overmolded lower pump housing  12 . In some embodiments, the isolation cup  86  can be coupled to the lower pump housing  12  by fasteners  94 , as shown in  FIG. 17B . In addition, in some embodiments, an exposed interface between the isolation cup  86  and the lower pump housing  12  can be sealed (e.g., with a potting compound). At step  96 , the rotor assembly  24  can be positioned inside the isolation cup  86 , as shown in  FIG. 17C . At step  98 , the upper pump housing  14  can be placed over the lower pump housing  12 , as shown in  FIG. 17D , and the upper pump housing  14  and the lower pump housing  12  can be coupled together by the fasteners  40  around the outside of the pump assembly  10 . 
         [0047]    As described above, the fluid being pumped by the pump assembly  10  can lubricate the bearings  26  associated with the pump assembly  10  as well as help dissipate heat generated from the stator assembly  28 . In some embodiments, the pump assembly  10  can include additional features to prevent or minimize operation of the pump assembly  10  when no fluid is present, as described below. 
         [0048]    In some embodiments, the pump assembly  10  can include one or more internal or external sensors  100  (e.g., pressure sensors, force sensors, temperature sensors, and/or current sensors) to monitor dynamic operation of the pump assembly  10 , as shown schematically in  FIG. 8 . For example, one or more pressure sensors can be used to monitor pressure inside the pumping chamber  34 , as pressure will be greater when the pump assembly  10  is pumping fluid compared to air. One or more force sensors can be used to measure any force changes associated with the static shaft  22  (e.g., by positioning the force sensor on the static shaft  22  near the impeller  32 ), as a greater axial force can be exerted on the static shaft  22  when the pump assembly  10  is pumping fluid compared to air. One or more temperature sensors can be used to measure a temperature of the pump assembly  10 . The temperature sensors can detect the difference between pump operation with and without fluid because fluid present improves the pump assembly&#39;s ability to dissipate heat from the stator assembly  28 . Thus, an increase in temperature can indicate minimal or no fluid is being pumped. A current sensor can be used to measure current draw characteristics associated with the motor assembly  20 . For example, current draw associated with the motor assembly  20  can directly correspond to the amount of torque required to rotate the impeller. The current sensor can be used to help detect a wet pump assembly  10  or a dry pump assembly  10  because pumping fluid will require more torque on the rotor assembly  24  to turn at a given speed when compared to pumping air. 
         [0049]    One or more of the above-mentioned sensors  100  can be in communication with the controller  50 , as schematically shown in  FIG. 8 , and can be dynamically monitored via software of the controller  50 . In some embodiments, as long as the dynamic feedback provided from the sensors  100  provides a signal or signal range indicating the pump assembly  10  is operating wet (i.e., with fluid present), the controller  50  can allow the pump assembly  10  to continue to operate (i.e., continue providing power to the stator assembly  28 ). If the feedback provided reflects dry operation of the pump assembly  10  (i.e., when no fluid is being pumped), the controller  50  can remove power to the stator assembly  28 , stopping operation of the pump assembly  10 . In some embodiments, the sensors  100  (e.g., the pressure sensors) can be micro-electromechanical system (MEMS) based sensors. The controller  50 , in conjunction with the integrated motor assembly  20 , can provide improved controllability and throttle ability of the pump assembly  10  because the motor speed and/or the torque of the motor assembly  20  can be varied quickly and easily by the controller  50 . Adding one or more of the sensors  100  as part of a control loop for the pump assembly  10  can further improve the controllability and throttle ability due to faster, dynamic monitoring of torque, motor speed, and/or other motor assembly characteristics. 
         [0050]    To more accurately determine if the pump assembly  10  is attempting to operate without fluid, a combination of one or more of the above-mentioned sensors  100  can be used in some embodiments. The sensors  100  can be calibrated during normal operation of the pump assembly  10  to determine normal operating conditions. In some embodiments, the controller  50  can include pre-set operating conditions for each of the sensors  100  in a wet environment (i.e., a loaded environment, with fluid being pumped) and a dry environment (i.e., an unloaded environment, without fluid being pumped). In addition, the controller  50  can include sensing algorithms specific to each sensor  100 . For example, temperature measurements can require the pump assembly  10  to have operated for a period of time before the temperature change is measurable. As a result, the controller  50  can rely on temperature sensor measurements only after the time period has exceeded. In another example, as a pump assembly  10  ages and the bearings  26  wear, dynamics such as torque requirements can change. As a result, to prevent unnecessary shut-downs from current sensing, the controller  50  can require or automatically perform recalibration of the current sensor after a certain time period. 
         [0051]    It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the following claims.