Abstract:
An integral motor and pump includes a casing having an inlet and an outlet, and a motor mounted within the casing. The motor includes a rotor member and a stator member. A tubular shaft circumscribing a central axis is received and fixed within the rotor. The tubular shaft is formed from a pair of axially overlapping tubular end portions and has an inner peripheral wall. An impeller is longitudinally spaced and press-fit within the inner peripheral wall of the shaft. The impeller includes a central, axially-extending body and a series of radially projecting blades, with each blade extending radially outward from the central body to the inner peripheral wall. When the motor is energized, the rotor turns, which in turn causes the impeller to rotate and draw fuel through the pump. When the motor is off, a flow path is maintained through the pump between the blades of the impeller.

Description:
CROSS-REFERENCE TO RELATED CASES  
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Application Serial No. 60/339,377; filed Dec. 10, 2001, the disclosure of which is expressly incorporated herein by reference 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to centrifugal fuel pumps, such as for aircraft applications.  
         BACKGROUND OF THE INVENTION  
         [0003]    Centrifugal pumps are commonly used to move fluid from one location to another, for example to remove fuel from an aircraft fuel tank and provide the fuel to remote equipment, e.g., to a turbine engine, or to move the fuel from tank to tank. Such pumps typically have a motor and an impeller enclosed within a casing or housing. The motor rotates the impeller, which in turn draws fluid through an inlet opening in the casing and discharges the fluid (typically under pressure) through an outlet opening. One common pump has an in-line design, where the impeller includes an axially-extending stem coupled to the drive shaft of the motor. Radially extending helical blades are formed integrally with the stem of the impeller and are enclosed by an axially-extending cylindrical shroud or sleeve. The stem and helical blades rotate within the shroud to draw the fluid into a volute chamber in the housing. The volute chamber converts the kinetic energy imparted to the fuel by the impeller into pressure and discharges-the fluid through the outlet in the housing. Such centrifugal pumps are available from a wide variety of manufacturers, including the assignee of the present invention. Exemplary pumps are also shown in Chu, U.S. Pat. No. 5,427,501; Carter, U.S. Pat. No. 3,652,186; Ridland, U.S. Pat. No. 2,846,952; Kalashnikov, U.S. Pat. No. 4,275,988; Davis et al, U.S. Pat. No. 4,142,839; and Bell, U.S. Pat. No. 3,038,410.  
           [0004]    In the Chu pump, as in many others, the volute chamber surrounds the impeller. A discharge housing is fluidly connected and fixedly coupled to a side of the casing, and directs the flow to the appropriate location (e.g., another fuel tank, to an engine, etc.). The volute chamber and discharge housing thereby take up additional space in the tank, and require additional components. They also add weight to the pump, and overall, increase the total cost of the pump and the system.  
           [0005]    In addition, a common requirement in aircraft applications is to maintain a fuel path if the pump is not operational, for example to maintain fuel flow to the engine in the event of a pump failure. Many pumps, particularly in-line pumps with shaft-mounted impellers, impede or prevent fuel flow through the pump when the pump is off. To create such a flow path, a by-pass fluid circuit is plumbed into the system. The bypass fluid circuit includes tubing, valves and sometimes even additional pump(s) that are used when the pump is off. Adding a bypass circuit in the system, of course, also adds space, requires additional components, and increases the weight and cost of the pump.  
           [0006]    In light of the drawbacks noted above, the pumps useful for aircraft applications tend to be large in size, complex, heavy and costly. Thus, it is believed there is a demand in the aircraft industry for an in-line centrifugal pump that is compact, light in weight, and has a structure which is simple to assemble and repair, and low cost to manufacture.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a novel and unique in-line centrifugal pump having a motor with an integral impeller. The impeller draws fluid from an inlet to an outlet when the pump is operational, while a flow path is maintained through the pump (with negligible pressure drop) when the pump is not operational. The pump is easy to assemble, has good reliability due to few rotating parts, and has a lower weight due to the compactness of the design. The cost of the pump is thereby reduced.  
           [0008]    According to the principles of the present invention, the pump includes a casing having an inlet and an outlet. A motor is mounted within the casing and includes an annular, rotatable rotor member and fixed stator member. A tubular shaft circumscribing a central axis is received within the rotor, and is fixed thereto. The shaft is co-axial with the inlet and outlet of the casing, and defines an inner peripheral wall. An impeller is longitudinally spaced and press-fit within the inner peripheral wall of the shaft. The impeller includes a central, axially-extending body and a series of helical blades, where each blade extends radially outward from the central body to the inner peripheral wall. When the motor is energized, the rotor turns, which in turn causes the impeller to rotate and draw fuel through the pump from the inlet to the outlet.  
           [0009]    When the motor stops, a flow path is maintained between the helical blades of the impeller from the inlet port to the outlet port. It has been found that there is little if no pressure drop across the impeller when the pump is non-operational which eliminates the need for a separate by-pass circuit.  
           [0010]    The shaft includes radially-inward projecting first and second shoulders forming axial stops for the impeller. The stops axially locate the impeller within the hollow central shaft. Preferably the shaft comprises a tubular inlet end portion and a tubular outlet end portion, with each portion being concentrically aligned and having an axially overlapping section which allows the end portions to be fixed together. Each end portion carries one of the shoulders forming the shoulders for the impeller.  
           [0011]    The central shaft further includes a pair of spaced apart, annular flange members, projecting radially outward from the shaft. Each of the inlet end and outlet end portions also carries one of the flange members. The rotor member is located between the annular flange members.  
           [0012]    A pair of bearing members outwardly support the tubular shaft in the casing. The bearing members are located on the axial opposite side of said flange members from the rotor member, with the flange members each constituting an axial support for the bearing members.  
           [0013]    Preferably, a vaned diffuser is supported in the tubular shaft on the downstream side of the impeller to optimize the pressure conversion at the impeller exit.  
           [0014]    Thus, as described above, an in-line centrifugal pump is provided that is easy to assemble, has good reliability due to fewer rotating parts, and has a lower weight due to the compactness of the design. It is believed this reduces the costs associated with the pump.  
           [0015]    Further features of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a side view of a pump constructed according to the principles of the present invention;  
         [0017]    [0017]FIG. 2 is an end view of the pump of FIG. 1 from the inlet end;  
         [0018]    [0018]FIG. 3 is an end view of the pump of FIG. 1 from the outlet end;  
         [0019]    [0019]FIG. 4 is a cross-sectional side view of the pump;  
         [0020]    [0020]FIG. 5 is an enlarged, cross-sectional side view of a portion of the pump. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Referring to the drawings, and initially to FIGS.  1 - 4 , a centrifugal pump is illustrated generally at  10 , constructed according to the principles of the present invention. The centrifugal pump includes an outer pump casing or housing, indicated generally at  12 , which encloses a motor, indicated generally at  14 , and an impeller, indicated generally at  16 . The centrifugal pump is preferably mounted in a conventional manner to a tank floor or end wall, or other appropriate support surface. Mounting pads or feet  23  extend radially outward from the bottom of housing  12  and can be attached to the support surface in a conventional manner, such as with bolts  24 .  
         [0022]    The motor casing  12  includes a body  25 , having a somewhat cylindrical configuration, and being enclosed at one end by an annular inlet cover  26 , and at the other end by an annular outlet cover  27 . Inlet cover  26  includes an annular elongated neck portion  28  which defines an inlet port  29 ; while outlet cover  27  includes an annular elongated neck portion  30  which defines an outlet port  32 . Neck portions  28 ,  30  are each concentrically aligned with each other and with the central axis “A” of the casing  12 . Appropriate bolts, as at  34 , fix the covers  26 ,  27  to the body  25 , and appropriate O-ring seals as at  35  are provided between these components to ensure a fluid-tight enclosure.  
         [0023]    The motor  14  is preferably a three-phase AC wet motor of a suitable explosion-proof sealed type for submerged operation, and includes thermal fuses for each phase. The motor  14  is located within an internal chamber  39  of the casing, and includes an annular rotor  41  surrounded by an annular stator  43 . Stator  43  is sealed and fits closely within the main body  25  of the casing, and is located and fixed against rotation with respect to casing  12  by an elongated L-shaped key  45 , which fits into a slot in the stator and a corresponding axial groove in the casing. An insulator layer  47  can be provided, as appropriate, between stator  43  and main body  25  as a spark arrester. Stator  43  is preferably of an otherwise conventional type, with wound coils embedded in a potting compound.  
         [0024]    Rotor  41  is also preferably conventional in design, and closely surrounds a hollow tubular shaft, indicated generally at  50 . Conventional means are used to fix the rotor with respect to the shaft, such as elongated ribs or knurls on the inside diameter of the rotor received in indentations or serrations along the outside diameter of the shaft. The rotor could also be keyed to the shaft such as described above with the stator and housing; or generally, any other means could be used to prevent relative rotation and axial movement of the rotor along the shaft.  
         [0025]    Shaft  50  circumscribes the central axis “A” of the pump, and defines a main fuel passage  51  through the pump shaft from inlet port  29  to outlet port  32 . Shaft  50  preferably comprises a two-piece design, with an inlet end portion  52  toward inlet port  29 , and an outlet end portion  54  toward outlet port  32 . The outlet end portion  54  is coaxial with and axially overlaps a section of the inlet end portion  52 . The outer end portion  54  can be fixed to the inlet end portion  52 , such as by welding.  
         [0026]    A pair of annular flanges  58 ,  59 , project radially outward from shaft  50 . Each flange  58 ,  59  has a tapered surface  60 ,  61 , respectively (see FIG. 5), which surfaces face inwardly toward each other. The flanges  58 ,  59  are axially spaced apart sufficient to closely receive rotor  41 , and the tapered surfaces facilitate axially locating rotor  41  along shaft  50 . Preferably, one flange  58  is provided integral (preferably unitary) with outlet end portion  54 ; while the other flange  59  is provided integral (preferably unitary) with inlet end portion  52 .  
         [0027]    Shaft  50  is supported on a bearing structure comprising a first carbon thrust/radial bearing  63  and a second carbon thrust/radial bearing  64 . First bearing  63  has one axial end located against a flat, outwardly-facing side  64   a  (FIG. 5) of flange  58  opposite from rotor  41 , and supported on its outer diameter by the annular base  65  of a first bearing sleeve  66 . A shoulder  67  projects radially inward from base  65  to support the other axial end of first bearing  63 . First bearing sleeve  66  has a radially outward projecting annular arm  68  which is fixed to a sidewall  69  of body  25  via bolts as at  70 .  
         [0028]    Likewise, second bearing  64  has one axial end located against a flat, outwardly-facing side  72  (FIG. 5) of flange  59  opposite from rotor  41 , and is supported on its outer diameter by the annular base  74  of a second bearing sleeve  75 , and at its other axial end by radial shoulder  76 . Second bearing sleeve  75  also has a radially outward projecting annular arm  77  which is fixed to a sidewall  78  of inlet cover  26  via bolts as at  80 . Straight pins  82  are provided between bearings  63 ,  64 , and their respective bearing sleeves  66 ,  75 , to locate and prevent relative rotation thereof.  
         [0029]    Bearings  63 ,  64 , in conjunction with flanges  58 ,  59  and sleeves  66 ,  75  properly axially and radially locate the shaft  50 , and allow smooth rotation thereof.  
         [0030]    A slight gap or clearance is provided between the ends of shaft  50  and the adjacent portions of covers  28 ,  30 , to prevent catching and binding, and to allow fluid communication/leakage into chamber  39  for lubrication of the bearings and to cool the motor. The use of carbon bearings, and the bearing design described above, allows the motor to dry-run, in the event of a drop in fuel, without overheating or damage to the bearings because of a loss of cooling fluid.  
         [0031]    The impeller  16  preferably comprises an inducer-type impeller which is received within and coupled to hollow tubular shaft  50 . To this end, referring now to FIG. 5, the impeller includes a central, axially-extending body  84 , having a conical tapered shape, with its narrow end  85  toward the inlet port  29 , and its wider end  86  toward the outlet port  32 ; and a series of helical or spiral blades or vanes, as at  87 , which project radially outward from central body  84  to shaft  50 . As should be well-know, the blades form channels which are configured to move fuel received in inlet port  29  toward outlet port  32 . Blades  87  are preferably formed unitary (in one piece) with body  84 , and have a common radial dimension such that they are all closely received, and preferably press-fit, within the shaft  50 , and preferably within the outlet end portion  54  of the shaft  50 , such that the impeller rotates with the rotation of shaft  50 . The blades  87  preferably extend the entire length of the body  84  from the narrow end  85  to the wider end  86  and can be configured in one or more flights. Preferably no additional mechanical attachment is necessary between the impeller and the shaft.  
         [0032]    A first, radially-inward directed annular shoulder  88  is provided in outlet end portion  54  to axially locate and support one axial end  86  of impeller  16  in shaft  50 ; while a second, radially-inward directed annular shoulder  89  is provided by the radially smaller end of inlet end portion  52  to axially locate and support the opposite axial end  85  of impeller  16  in shaft  50 .  
         [0033]    The dimensions of the central body  84 , blades  87  and shaft  50  are preferably chosen so as to maximize the capacity of the impeller for a particular application. These characteristics, as well as the rating of motor  14 , can be easily determined by those of ordinary skill in the art based on such factors as the dimensions and volumetric capacity of the pump and the intended rotational speed of the impeller.  
         [0034]    The assembly of the pump is facilitated by the above design. Specifically, the rotor  41  and stator  43  are initially located over outlet end portion  54  of shaft  50 , with one end of the rotor being supported against flange  58 . The impeller  16  is then inserted within the outlet end portion  54 , with one end  86  of the impeller being supported against first shoulder  88 . The inlet end portion  52  is then slid into the outlet end portion, with the other flange  59  supporting the other end of the rotor  41 , and the second shoulder  89  supporting the opposite end  85  of impeller  16 . The inlet end portion  52  and other end portion  54  are then fixed together, such as by welding. Bearing sleeves  66 ,  75  are attached to their respective sidewalls  69 ,  78 ; and the motor and impeller subassembly is then inserted within main body  25 . Bolts  34  are then tightened down to fix covers  28 ,  30  to opposite ends of the main body with bearings  63 ,  64  located between their respective bearing sleeve and shaft portion, to enclose the motor and impeller within the housing, and allow relative rotation of the rotor and impeller therewith.  
         [0035]    As should be appreciated, the assembly of the motor and impeller is thereby simplified, with fewer parts to reduce cost, reduce complexity, and reduce the necessity of repair and maintenance.  
         [0036]    Referring again to FIG. 4, a vaned diffuser, indicated generally at  94 , can be located in outlet cover  30 , downstream from impeller  16 , if necessary or desirable, to diffuse the fuel flow through the pump. Such a diffuser is illustrated as including a central, axial body  95 , which narrows toward the outlet port  32 , and a series of radial vanes  96 . Diffuser  94  can be attached to annular neck portion  30  in an appropriate manner, such as by press-fit or welding.  
         [0037]    Remote electrical communication with the motor of the pump is provided by an electrical connector, indicated at  98  in FIGS.  1 - 3 . Electrical connector  98  is conventional in design, and can include for example, a multi-pronged connection for control of each phase of the motor. Other electrical connectors, or a hard-wiring connection of the pump, can also be used.  
         [0038]    Also if necessary or desirable, a pressure transducer, indicated generally at  108 , can be mounted to the housing  14  via bolts  109 , to measure the pressure of fuel flow through the pump for control purposes. A passage  110  (FIG. 4) is provided internally of the casing into main fuel passage  51  for this purpose. Pressure transducer  108  is preferably of a conventional type, commercially-available in the marketplace, and chosen so as to be appropriate for the particular application. Electrical connector  98  can include additional prongs for communication with the pressure transducer, or the pressure transducer can be separately controlled.  
         [0039]    While a specific type of motor has been described, it should be apparent to those skilled in the art that the motor could also comprise rotor and stator configurations other than as described above; as well as drive means such as an air turbine, a hydraulic motor, or any other type of means for transferring energy to mechanical motion. In any case, the dynamic requirements of the motor can be easily determined knowing the requirements of the pump, e.g., the differential head necessary, the running speed, the liquid characteristics, and the available power supply.  
         [0040]    As should be appreciated, application of a control signal through connector  98  will energize the motor and cause rotation of rotor  41 . This in turn will cause rotation of impeller  16 , which will draw fuel from inlet port  29  and discharge the fuel through outlet port  32 , typically under pressure. When the motor is stopped, the rotor and impeller will likewise stop rotating. As can be seen in FIG. 2, a flow path through passage  51  is maintained between the impeller blades  87  to maintain fuel flow to the downstream components of the system (e.g., to the engine). It has been found that the impeller blades do not cause significant pressure drop for the fuel flow, which thereby eliminates the need for a separate by-pass circuit.  
         [0041]    While the present invention is particularly suited to be used as a fuel pump for aircraft applications, it is believed the pump may also be appropriate for other aerospace and non-aerospace applications where it is necessary to move a fluid from one location to another.  
         [0042]    Thus, as described above, an in-line centrifugal pump is provided that is easy to assemble, has good reliability due to fewer rotating parts, and has a lower weight due to the compactness of the design. The pump is thereby more cost-effective to produce.  
         [0043]    The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein should not, however, be construed as limited to the particular form described as it is to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims.