Patent Publication Number: US-6702555-B2

Title: Fluid pump having an isolated stator assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic fluid pump. 
     2. Background Art 
     Use of fluid pumps in vehicle engine cooling systems and various industrial applications is well known. However, typical fluid pumps in both of these areas have inherent limitations. Typically in engine cooling systems, a coolant pump has a pulley keyed to a shaft. The shaft is driven by the engine via a belt and pulley coupling, and rotates an impeller to pump the working fluid. Fluid seals sometimes fail due to the side load from the drive belt, which tends to allow fluid to leak past the seal into the bearing. 
     U.S. Pat. No. 6,056,518, issued to Allen et al. on May 2, 2000, describes one attempt to overcome the shortcomings of prior art vehicle coolant pumps. The &#39;518 patent provides a fluid pump with a switched reluctance motor that is secured to a housing and rotates an impeller for pumping the fluid. This design eliminates the side load problem associated with keyed pulleys, but it is generally not intended for use where larger industrial pumps are required. 
     Industrial pumps are typically driven by an electric motor connected to the pump via a coupling, the alignment of which is critical. Misalignment of the coupling can result in premature pump failure, which leads to the use of expensive constant velocity couplings to overcome this problem. Moreover, industrial pump motors are typically air-cooled, relying on air from the surrounding environment. The cooling air is drawn through the motor housing leaving airborne dust and other contaminants deposited in the motor components. These deposits can contaminate the bearings, causing them to fail, or the deposits can coat the windings, shielding them from the cooling air and causing the windings to overheat and short out. 
     Accordingly, it is desirable to provide an improved fluid pump which overcomes the above-referenced shortcomings of prior art fluid pumps, while also providing enhanced fluid flow rate and control capability while reducing costs. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides an improved fluid pump with enhanced fluid flow rate and control capability that also reduces costs. 
     Another aspect of the invention provides a fluid pump that comprises a housing that has a housing cavity with an inlet and an outlet. A diffuser, at least a portion of which is attached to the housing, is substantially disposed within the housing cavity. The diffuser has an internal diffuser cavity, in which an electric motor stator assembly and a tubular member are located. The tubular member sealingly contacts the diffuser to isolate the stator assembly from the working fluid. An impeller is rotatably disposed near the inlet of the housing cavity. An electric motor rotor assembly is substantially and rotatably disposed within the tubular member, and it is connected to the impeller for pumping the fluid from the inlet to the outlet. 
     Yet another aspect of the invention provides a fluid pump that comprises a housing having a housing cavity with an inlet and an outlet. A diffuser having an internal diffuser cavity is substantially disposed within the housing cavity, and has at least a portion that is attached to the housing. An electric motor stator assembly and a tubular member are disposed within the diffuser cavity. The tubular member is in sealing contact with the diffuser; this isolates the stator assembly from the fluid. An impeller is rotatably disposed near the housing cavity inlet. A rotor having first and second sides is rotatably disposed within the tubular member, and a rotor shaft is attached to the rotor and connected to the impeller for pumping the fluid from the inlet to the outlet. 
     A further aspect of the invention provides a housing having a housing cavity with an inlet and an outlet. A diffuser, at least a portion of which is attached to the housing, is substantially disposed within the housing cavity. The diffuser includes an internal diffuser cavity, in which an electric motor stator assembly and a tubular member are located. The generally cylindrical tubular member forms a seal with the diffuser that isolates the stator assembly from the fluid. An impeller is rotatably disposed near the inlet of the housing cavity, and a rotor is rotatably disposed within the tubular member. The rotor has a rotor shaft that is attached to the impeller for pumping the fluid from the inlet to the outlet. The rotor shaft is supported within the tubular member by a shaft support apparatus. A circuit board assembly for controlling the pump is disposed within the diffuser cavity; it is electrically connected to the stator assembly and isolated from the fluid by the tubular member. 
    
    
     The above objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side sectional view of a fluid pump in accordance with the present invention; 
     FIG. 2 is a perspective view of a two-piece diffuser that can be used in the fluid pump shown in FIG. 1; 
     FIG. 3 is a perspective view of the impeller; 
     FIG. 4 is a side sectional view of a canister used to seal electrical components in the fluid pump from the working fluid; 
     FIG. 5 is a side sectional view of a second embodiment of the fluid pump where the canister is sealed with an O-ring; 
     FIG. 6 is a side sectional view of a third embodiment of the fluid pump having a rotor and rotor shaft with bearings supporting the rotor shaft disposed on both sides of the rotor; 
     FIG. 7 is a side sectional view of a fourth embodiment of the fluid pump where the rotor shaft is supported by ceramic bushings instead of bearings; 
     FIG. 8 is a side sectional view of a fifth embodiment of the fluid pump wherein the rotor is disposed within a ceramic bushing and the rotor shaft is not supported by bushings or bearings; 
     FIG. 9 is a side sectional view of a portion of a fluid pump housing having a stud terminal extending from the housing for connecting electric power and motor control circuits to the pump; 
     FIG. 10 is a detail view of the stud terminal shown in FIG. 9; and 
     FIG. 11 is a side sectional view of a portion of a fluid pump having a controller integrated into the pump and disposed within the pump housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     FIG. 1 shows a side sectional view of a fluid pump  10  in accordance with the present invention. The fluid pump  10  has a housing  12  that has an inlet  14  and an outlet  16 . The housing  12  defines an internal housing cavity  18  in which a diffuser  20  is located. The diffuser  20  shown in FIG. 1 includes a front portion  22 , a middle portion sub-assembly  24 , and a back portion  26 . The middle portion sub-assembly  24  of the diffuser  20  includes a vaned inner portion  25  and a diffuser ring  28 . The diffuser ring  28  is shrunk-fit to the vaned inner portion  25  to create the middle portion sub-assembly  24 . The diffuser ring  28  is captured between front and back pieces  30 ,  32  of the housing  12 . Because the front and back portions  22 ,  26  of the diffuser  20  are connected to the middle portion sub-assembly  24 , the diffuser  20  is held stationary within the housing cavity  18 . 
     Although the diffuser  20  is shown in FIG. 1 with a three-piece configuration, it can also be made from two pieces. FIG. 2 shows a two-piece diffuser  27 , including a front portion  29  having vanes  31 , and a back portion  33  having vanes  35 . The diffuser ring is removed in this view to more clearly illustrate the diffuser vanes  31 . The vanes  31 ,  35  are configured to optimize fluid flow through the pump  10 , and in particular, to straighten the fluid prior its leaving the outlet  16  (see FIG.  1 ). 
     The diffuser  20  has an internal diffuser cavity  34  in which a number of the pump components are located. A stator assembly  36  is located within the diffuser cavity  34  substantially within the back portion  26  of the diffuser  20 . The stator assembly  36  includes steel laminations, copper windings, and motor power leads. It is contemplated that the stator assembly  36  will be integrally molded to the back portion  26  of the diffuser  20 . Molding the back portion  26  out of a thermally conductive polymer will allow good heat transfer from the stator assembly  36  to the working fluid, which will be in contact with an outer surface  38  of the diffuser  20 . Also within the diffuser cavity  34  is a tubular member, which in this embodiment is a canister  40 . One of the functions of the canister  40  is to form a seal with the diffuser  20  to isolate the stator assembly  36  from the working fluid. 
     As seen in FIGS. 1 and 4, the canister  40  has a hollow cylindrical portion  42  that has an opening  44  surrounded by a lip  46 . Preferably, the canister  40  is made from a non-magnetic material and is thin so as to minimize eddy current braking losses. The canister  40  may be made from drawn stainless steel that has a wall thickness of 0.007-0.015 inches. The generally cylindrical shape of the canister  40  is well suited to the drawing process. It is understood however, that the canister  40  can be manufactured by processes other than deep drawing. In other embodiments, the canister  40  may be a tubular member open at both ends. Shown partially in phantom in FIG. 4 is a tubular member  47  having both ends open. Such a configuration requires the tubular member  47  to be sealed against the diffuser  20  at the inlet and outlet sides to ensure that the stator assembly  26  remains isolated from the working fluid. 
     Returning to FIG. 1, it is seen that a rotor assembly  48  which includes a rotor  50  attached to a rotor shaft  52  is disposed within the canister  40 . Attached to the rotor shaft  52  are bearings  54 ,  56  which support the rotor assembly  48 . When power is provided to the pump  10 , the stator assembly  36  generates a magnetic field which causes the rotor  50 , and therefore the rotor shaft  52 , to rotate. The rotation of the rotor shaft  52  turns an impeller  58  that is attached to one end of the rotor shaft  52 . The impeller  58 , shown in detail in FIG. 3, includes vanes  59  configured to pump the fluid from the inlet  14  to the outlet  16  as the impeller  58  rotates. 
     The stator assembly  36  and the rotor assembly  48  comprise the pump motor, which can be configured in a variety of ways to suit the requirements of different applications. For example, the rotor can be a magnet, if a brushless permanent magnet pump motor is desired. As an alternative, the pump can be driven by a switched reluctance motor, in which case the rotor  50  may be made of any ferrous metal (for example, see U.S. Pat. No. 6,056,518, describing a fluid pump using a switched reluctance motor.) Pumps using switched reluctance motors are particularly well suited to high temperature applications. 
     Because the pump  10  can be configured with many different types and sizes of pump motors, it can be used in a wide variety of applications. For example, when used in an automotive application, the pump motor can be powered by a low voltage DC power source. Small pumps such as this may be configured to have relatively low volumetric flow rates (40 gallons per minute (gpm) or less), with output pressures of less than two pounds per square inch (psi). Conversely, the pump  10  can be configured for a heavy-duty industrial application, in which case it may be driven by a three-phase induction motor with a high voltage AC power supply. A large industrial pump such as this can be configured to pump over 500 gpm at 25 psi. 
     During operation of the pump  10 , it is important that the working fluid does not come in contact with the stator assembly  36 . This is one of the functions of the canister  40 : to form a seal with the diffuser  20  so that the stator assembly  36  is isolated from the working fluid. In one embodiment, the canister  40  is attached to the diffuser  20  with an adhesive material that will also act to form a seal such that the stator assembly  36  is isolated from the working fluid. An alternative to this method is shown in FIG.  5 . In FIG. 5, a fluid pump  60  is configured substantially the same as the fluid pump  10  in FIG.  1 . However, the seal between the canister  62  and the diffuser  64  is accomplished not with an adhesive, but rather with an elastomeric material such as an O-ring  66  located in a groove  68  molded into the diffuser  64 . 
     When an O-ring seal such as that shown in FIG. 5 is used to isolate a stator assembly from the working fluid, the canister may be attached to the diffuser with an adhesive, or even threaded fasteners. Moreover, it is also possible to press fit the canister into the diffuser and thereby form a secure attachment. Adhesive bonding between the canister and the diffuser is another option. The methods described herein merely represent a few of the possible ways of attaching the canister and forming a seal to isolate the stator assembly. 
     Returning to FIG. 1, it is clear that as the working fluid is pumped from the inlet  14  to the outlet  16 , the stator assembly  36  remains isolated from the working fluid because of the seal between the canister  40  and the diffuser  20 . However, the components inside the canister  40 , unlike the stator assembly  36 , are in constant contact with the working fluid. Thus, the bearings  54 ,  56  as well as the rotor shaft  52  and the rotor  50  itself contact the working fluid as it is pumped from the inlet  14  to the outlet  16 . This eliminates the need for a seal at the opening  44  of the canister  40 . Although the rotor  50  experiences a greater drag when it rotates in liquid rather than air, a reduction in drag realized by the elimination of a shaft seal will often more than offset the additional drag resulting from the liquid. Because the working fluid will contact the bearings  54 ,  56  it is contemplated that these bearings will be ceramic, so that their useful life is increased and pump down time is therefore decreased. Non-ceramic bearings may of course be used, if the needs of a particular application so dictate. 
     In the embodiment shown in FIG. 1, both of the bearings  54 ,  56  are on the inlet side of the rotor  50 . This effectively cantilevers the rotor assembly  48 , which makes the pump  10  robust and easy to assemble. If necessary for a particular application, bearings may be positioned such that the rotor shaft is simply supported, rather than cantilevered. For example, the fluid pump  70  shown in FIG. 6 has a rotor assembly  72  that includes a rotor  74  attached to a rotor shaft  75 . In this embodiment, one bearing  76  attaches to the rotor shaft  75  on the inlet side of the rotor  74 , while a second bearing  78  attaches to the rotor shaft  75  on the outlet side of the rotor  74 . Thus, a rotor assembly used in the present invention may be supported in a number of ways depending on the needs of a particular application. 
     Bearings are just one type of support apparatus that may be used to provide support for the rotor assembly. For example, bushings, and in particular ceramic bushings, provide an alternative to bearings. FIG. 7 shows a fluid pump  80  having a configuration similar to that of the pump  10  shown in FIG.  1 . However, in this embodiment, the bearings  54 ,  56  have been replaced with ceramic bushings  82 ,  84 . The ceramic bushings  82 ,  84  support a rotor shaft  86  that has attached to it a rotor  88 . It is contemplated that the life of the ceramic bushings  82 ,  84  will exceed that of most bearings, even those that are at least partly ceramic. In addition, because the working fluid will be in almost constant contact with the bushings  82 ,  84  and the rotor shaft  86 , the wear on the rotor shaft  86  will be minimized as the working fluid acts as a lubricant at the interface of the bushings  82 ,  84  and the rotor shaft  86 . 
     FIG. 8 shows another embodiment  90  of the present invention. Here, the fluid pump  90  has a rotor assembly  92  that includes a rotor  94  and a rotor shaft  96 . In this design however, there are no bearings or bushings to support the rotor shaft  96 . Rather, ceramic bushings  98 ,  100  keep the rotor  94  centered within a canister  102 , and keep the rotor  94  from moving front to back. The bushings  98 ,  100  do not provide support for the rotor  94  during operation of the pump  90 . Instead, the rotor  94  floats within the electromagnetic field generated by a stator assembly  103 . This design eliminates losses due to friction that occur when bearings or bushings are used to support the rotor shaft. In addition, because the rotor is not actually in contact with the bushings  98 ,  100  while it is rotating, there is virtually no wear on the bushings  98 ,  100  and so their useful life is almost infinite. 
     In one embodiment of the present invention such as the pump  10  shown in FIG. 1, electrical wires for both power and motor control will connect to portions of the stator assembly  36  and exit the pump housing  12  at or near the circumferential portion  28 . Typically these wires will not be terminated, so as to allow for easy attachment to any kind of electrical connection required by the particular application. An alternative to having unterminated electrical wires exit the housing  12  is illustrated in FIG.  9 . In FIG. 9, a portion of a pump housing  104  is shown with a threaded stud terminal  106  attached. The stud terminal  106  is shown in detail in FIG.  10 . Here it is seen that the stud terminal  106  comprises a threaded stud  108  that traverses the pump housing  104  through an opening  110  in which there is placed a rubber grommet  112 . A nut  114  is threaded onto the threaded stud  108  from the outside of the pump housing  104 . This not only holds the threaded stud  108  in place, but also helps to seal the opening  110  so that the working fluid does not escape the housing  104 . Inside the pump housing  104 , the threaded stud  108  is electrically connected to a stator assembly such as  36  shown in FIG.  1 . The stud terminal  106  provides a convenient method to attach the electric power and motor control circuits to the fluid pump. 
     A typical fluid pump such as  10  shown in FIG. 1 will have eight wires connected to the stator assembly that either exit the pump housing with unterminated ends, or are each attached inside the pump housing to a stud terminal such as  106  shown in FIGS. 9 and 10. Of course, the number of wires connected to the stator assembly may be more or less than eight, depending on the particular application or applications for which the pump is configured. One way to reduce the number of wires leaving the pump housing or the number of stud terminals attached to the housing, is to integrate a motor controller into the fluid pump itself. Such a configuration is shown in FIG.  11 . Here, a portion of a fluid pump  114  is shown with a portion of a pump housing  116  having a housing cavity  118  in which there is a portion of a diffuser  120 . As in the other embodiments described above, a stator assembly  122  is attached to, or integrally molded with, a portion of the diffuser  120 . In this embodiment, a controller  124  is also attached to, or integrally molded with, a portion of the diffuser  120 . A canister  126  forms a seal with the diffuser  120  to isolate both the stator assembly  122  and the controller  124  from the working fluid. 
     This design has a number of important benefits. First, the portion of the diffuser  120  in contact with the stator assembly  122  and the controller  124  can be made from a thermally conductive polymer which allows heat transfer from both the stator assembly  122  and the controller  124  to the working fluid. Next, by locating the controller  124  inside the pump and connecting it directly to the stator assembly  122 , the possibility of having problems with the motor control due to electromagnetic interference (EMI) is greatly reduced or eliminated. In addition, integrating the controller  124  into the pump reduces the number of wires or stud terminals exiting the pump housing  116 , and it makes the entire pump design more compact. It is contemplated that in some applications the fluid pump of the present invention will be integrated into a system that has its own controller used to control other elements within the system. In such an application, it may be possible to configure the system controller to perform the additional task of controlling the fluid pump. Where there is not a system controller in a particular application, the integrated controller configuration shown in FIG. 11 is a convenient method for providing a fluid pump and controller in one compact package. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.