Abstract:
A method of increasing the pressure of a fluid in an aircraft centrifugal pump by forcing the fluid to make multiple passes through one impeller of the aircraft centrifugal pump is provided. It includes providing fluid through a pump inlet to an aircraft impeller inlet. The fluid then exits the impeller through a first set of discharge ports and the exiting fluid is directed to a second inlet on the same impeller. The fluid then exits the impeller through a second set of discharge ports to a pump outlet. Each pass through the impeller by the fluid increases the pressure thereof.

Description:
This application claims the benefit of U.S. Provisional Application Serial No. 60/134,271, filed on May 14, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to centrifugal pumps, and more particularly, to an improved impeller for use in a centrifugal pump. The present invention finds particular application in conjunction with an aircraft fuel pump, and it will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications. 
     2. Discussion of the Art 
     The structure and operation of centrifugal pumps is well known in the art. Briefly, fluid generally enters a pump inlet in an axial direction and due to the rotation of the impeller the fluid centrifugally flows radially outward through a set of channels defined between impeller blades. The fluid discharges from the impeller around the peripheral edge of the impeller. The centrifugal action of the fluid flowing outwardly through the channels creates a suction at the central area of the impeller which serves to continuously draw more fluid into the inlet of the pump. 
     The fluid discharged from the impeller is at a significantly higher pressure than the fluid entering the pump inlet. The major portion of the energy imparted to the fluid is converted to a pressure head by means of a volute, diffuse, or other system. 
     Impellers may generally be classified according to their flow arrangements. Single-suction impellers receive fluid through a single inlet on one face of the impeller. Double-suction impellers generally have fluid flowing onto opposed faces of the impeller. The fluid streams flowing into each face of a double-suction impeller are usually commingled within impeller fluid channels or at the periphery of the impeller before exiting the pump. 
     Centrifugal pumps may additionally be classified as either single-stage pumps or multi-stage pumps. Single-stage pumps are generally defined as those in which the pressure head was developed by a single pass through only a single impeller. Multi-stage pumps generally refer to pumps using two or more impellers operating in series. Additionally, a single impeller, double suction pump has been, heretofore, generally classified as a single-stage pump. 
     Multi-stage pumps are often used in applications that require large volumes of liquid to be delivered at high pressures. Each stage incrementally imparts rotational energy into the fluid thereby increasing the amount of pressure of the fluid at each stage. Although the delivery of a high volume of fluid at high pressures is desirable, several disadvantages are present in the prior art. 
     One disadvantage of multi-stage pumps is that substantial internal energy losses result from using additional impellers because each impeller frictionally interfaces with the surrounding pump casing or housing. The mechanical drag results in lower pump efficiency. 
     Another disadvantage is that each additional impeller stage adds volume and weight to the overall pump assembly. Increased volume or size may prevent installation of the pump unit in tight-fitting applications. Increased weight may cause inefficiencies in particular applications such as for use as an aircraft fuel pump where the load capacity of the aircraft is limited. 
     Therefore, it is desirable to provide an improved impeller for use in a centrifugal multi-stage pump that overcomes these problems and others. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved impeller for use in a single-impeller, multi-stage centrifugal pump is provided for minimizing these and other disadvantages of the prior art. 
     More particularly, a preferred embodiment of the present invention has an impeller provided with multiple inlets and corresponding sets of discharge ports. Multiple pump stages are accomplished by successively passing the fluid through the impeller by entry into the various inlets of the impeller. 
     A preferred embodiment of the centrifugal pump includes a housing having a pump inlet and a pump outlet that communicate with an internal chamber. A rotatable shaft drives a generally cylindrical impeller operatively received in the internal chamber. The impeller includes a first impeller face, a second impeller face opposite from the first impeller face, and a radial peripheral edge extending around the circumference of the impeller and interconnecting the first and second impeller faces. The impeller also includes a first impeller inlet located on one of the first and second impeller faces and a second impeller inlet located on one of the first and second impeller faces. Additionally, a first and second set of impeller outlet ports are located on the impeller. The first set of channels communicate between the first impeller inlet and the first set of impeller outlet ports disposed in the impeller while the second set of channels communicate between the second impeller inlet and the second set of impeller outlet ports disposed in the impeller. 
     According to a preferred method of the present invention increased pressure of a fluid in a centrifugal pump having a single impeller is provided. The method includes the steps of providing fluid through a pump inlet to a first impeller inlet. Fluid exiting the impeller through a first set of discharge ports is directed to a second inlet for a second pass through the same impeller. The fluid then exits the impeller through a second set of discharge ports at an increased pressure. Finally, the fluid is directed to a pump outlet. Of course, additional passes through the same impeller are possible. 
     A primary advantage of the present invention is reduced overall efficiency losses due to mechanical drag from using the subject single-impeller, multi-stage pump of the present invention. 
     A further advantage is realized by the multi-pass single impeller obtaining high discharge pressures without requiring a large impeller diameter. 
     Another advantage of the present invention over the prior art is that the overall pump weight is reduced. 
     Still another advantage is that the overall size of the pump is reduced. 
     Still other features and benefits of the invention will be apparent to those skilled in the art upon reading and understanding the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings. Of course, the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
     FIG. 1 illustrates a partial cross-sectional view of the impeller in one embodiment of the present invention. 
     FIG. 2 illustrates a partial cross-sectional view of the impeller in a second embodiment of the present invention. 
     FIG. 3 illustrates an exploded perspective view of the impeller in a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein like reference characters represent like elements. The impeller of the present invention may have any number of inlets on one or both of its faces. Each inlet represents the beginning of a separate pump stage. Thus, in a first pump stage the fluid enters a specific or first impeller inlet and is discharged from a first set of discharge ports in operative communication with the first inlet. The fluid is then routed to a second or successive impeller inlet to begin the second pump stage. Each stage, or pass through the impeller, incrementally increases the pressure of the fluid. The number of stages or passes that may be accomplished through a single impeller is theoretically unlimited, but in accordance with the present invention two or three passes are preferred. 
     Multiple passes through the improved single impeller of this invention provide high discharge pressures to be attained without many of the disadvantages of the prior art. As will be evident to those skilled in the art, a single impeller capable of multiple passes can be accomplished in a variety of manners. 
     With reference to FIG. 1, a centrifugal pump indicated generally by reference numeral  10  illustrates one embodiment of the present invention. The rotational components of the pump  10  includes an impeller  12  and a shaft  14 . The impeller  10  is connected to the shaft  14  by any known means. The shaft interconnects a drive output from a motor (not shown) to rotatably drive the impeller  12 . A housing or casing  16  includes an internal chamber  18  for operatively receiving the impeller  12  and the shaft  14 . The housing  16  also includes a pump inlet  20  and a pump outlet (not shown). 
     The pump inlet  20  is an axial inlet disposed adjacent a rotational axis of the impeller. The inlet  20  is in fluid communication with a first impeller inlet  22  located on a first face  24  of the impeller  12 . The first impeller inlet  22  is annularly disposed between a distal end  14 a of the shaft  14  and an interior wall  26  of the impeller  12 . The first impeller inlet leads to a first set of fluid channels  28  that extend through the impeller and connect the first impeller inlet to a first set of discharge ports  30 . The fluid channels may be of any variety as is well known in the art. 
     The first set of discharge ports  30  are located on a peripheral edge  32  of the impeller. Specifically, the first set of discharge ports  30  are axially spaced from a central axis  34  that extends perpendicular to the rotational axis of the impeller and generally parallel to the first face  24  of the impeller  12 . A first discharge chamber  36  is provided in the housing  16 . The first discharge chamber  36  receives the fluid from the first set of discharge ports  30  as it exits from the impeller. 
     The first discharge chamber  36  is connected to a second inlet chamber  38  by any known fluid communication means (not shown). For example, passages in the housing direct the fluid from the first discharge chamber to the second inlet chamber (shown in FIG. 1 as being located on an axially opposite end of the impeller from the first inlet chamber). The second inlet chamber  38  redirects fluid to a second impeller inlet  40  such that the fluid may enter the impeller  12  in a generally axial direction. The second impeller inlet  40 , located on a second face  42  of the impeller  12 , is annularly disposed between the shaft and the interior wall  44  of the impeller. The second impeller inlet  40  leads to a second set of fluid channels  46 . The fluid channels  46  proceed through the impeller and connect the second impeller inlet  40  to a second set of discharge ports  48 . Again, the fluid channels may be of any variety as is well known(i.e., radial, axial, circumferential, or a combination of these). 
     The second set of discharge ports  48  are located on the peripheral edge  32  of the impeller. Specifically, the second set of discharge ports  48  are axially offset from the central axis  34  in the direction of the second face  42  of the impeller. A second discharge chamber  50  is provided in the housing and is in fluid communication with the second set of discharge ports  48  to receive fluid as it exits the impeller from the second set of channels  46 . 
     Third and fourth inlet chambers  52 ,  54  are provided in the impeller to provide an actuator stage. The inlets are disposed on opposite ends or faces of the impeller and communicate with axially extending impeller inlets  56 ,  64 , respectively. The impeller inlets  56 ,  64  are located radially outward relative to the first impeller inlet  22  and communicate with a third set of fluid channels  58 . The fluid channels  58  extend radially through the impeller connecting the third impeller inlet to a third set of discharge ports  60 . As with the first and second set of discharge ports, the third set of discharge ports  60  are located on the peripheral edge  32  of the impeller and are axially offset on opposite sides of the central axis  34  in the direction of the first face and second faces of the impeller. Third discharge chambers  62 ,  70  are provided in the housing  16  and fluidly connect to the third set of discharge ports for receiving fluid as it exits the impeller from the third set of channels  58 . 
     The third and fourth discharge chambers  62  and  70  are connected to an actuator outlet (not shown). At a point before the actuator outlet, the fluid from the third and fourth discharge chambers  62  and  70  reconvenes and exits the pump  10  as a single fluid stream. 
     In operation, fluid enters the pump  10  through the pump inlet  20  and is axially directed into the first impeller inlet  22 . The motor (not shown) rotates the impeller  12  via the shaft  14 . The rotation of the impeller causes the fluid entering the first impeller inlet  22  to be centrifugally forced radially outwardly through the first set of fluid channels  28 . The fluid then exits the impeller  12  through the first set of discharge ports  30  and is received in the first discharge chamber  36 . As a result of the centrifugal forces, the fluid received in the first discharge chamber  36  is at a higher pressure than when the fluid first entered the impeller. 
     The fluid is then directed to the second inlet chamber  38  where the fluid is axially directed for reentry into the impeller. Fluid enters the second impeller inlet  40  and is again forced radially outwardly through a second set of fluid channels  46  due to the rotation of the impeller  12 . The fluid exits the impeller  12  through the second set of discharge ports  68  and is received in a second discharge chamber  50 . The fluid received in the second discharge chamber  50  is at an even higher pressure than when the fluid entered the impeller for the second time. 
     Although the third and fourth inlets, fluid channels, and discharge ports are intended for use as an actuator in FIG. 1, this embodiment illustrates how additional passages can be formed in the impeller without adversely affecting the function of the impeller. It will be understood by one skilled in the art that these additional passages could also be converted to third and fourth stages if appropriate. 
     With reference to FIG. 2, a second embodiment of the present invention is shown. Where possible, components in the FIG. 2 embodiments are identified by a “100” series to correspond with like components having the same last two digits in the embodiment of FIG. 1 (e.g., impeller  12  from FIG. 1 generally corresponds to impeller  112  in FIG.  2 ). A centrifugal pump  110  has an impeller  112  and a shaft  114 . The pump  110  includes a housing or casing  116  which includes an internal chamber  118  for operatively receiving the impeller  112  and the shaft  114 . Additionally, the casing  116  includes a pump inlet  120  and a pump outlet (not shown). 
     The pump inlet  120  is in fluid communication with a first impeller inlet  122  located on a first face  124  of the impeller  112 . The first impeller inlet  122  is annularly disposed on the first face  124 . The first impeller inlet  122  is in fluid communication with a first set of channels  128  that axially and radially extend and thereby connect the first impeller inlet to a first set of discharge ports  130 . The first set of discharge ports  130  are preferably located on a chamfered peripheral edge  131  which is located between an outer diameter  132  of the impeller and a second face  142  of the impeller. 
     A fluid communication means or passage  137  receives fluid from the first set of discharge ports  130  and redirects the fluid into a second impeller inlet  140 . The second impeller inlet  140  is annularly disposed on the second face  142  of the impeller and is in fluid communication with a second set of channels  146 . The fluid channels run through the impeller connecting the second impeller inlet  140  to a second set of discharge ports  140 . The first and second set of fluid channels  128  and  146  cross-over one another but are not in fluid communication with one another. In this manner, each pass through the impeller increases the pressure and a multi-stage pump is achieved with a single impeller. The second set of discharge ports  140  are located on the radial peripheral edge  132  and in fluid communication with the pump outlet such that fluid may be discharged from the pump upon completion of two passes through the impeller. 
     In operation, fluid enters the pump  110  through the pump inlet  120  and is axially directed into the first impeller inlet  122 . The impeller  112  rotates via the shaft  114  causing the fluid entering the first impeller inlet to be centrifugally forced radially outwardly through the first set of fluid channels  128  and exit the impeller  112  through the first set of discharge ports  130 . The exiting fluid is at a higher pressure than the fluid first entering the impeller. 
     The fluid is then directed through the fluid passage  137  to the second impeller inlet  140  where the fluid again enters the impeller. The rotation of the impeller imparts further energy to the fluid and forces the fluid radially outwardly. The fluid flows through the second set of fluid channels  146  and exits the impeller through the second set of discharge ports  168 . The fluid exiting the impeller for a second time is at an even higher pressure than the fluid exiting the impeller after the first pass. The fluid is then directed to the pump outlet after two passes through the impeller in which each pass incrementally increases the pressure of the fluid. 
     A third embodiment of the present invention is shown in FIG.  3 . An impeller  200  of the centrifugal pump is shown in a disassembled state and includes a first and second member  202  and  204 . Each member  202  and  204  includes a substantially planar face  202   a  and  204   a  disposed in facing relation and that allow members  202  and  204  to be abutted together. 
     The first member includes a hub  206  having a circular opening  208  that receives a drive shaft for rotational engagement. A first impeller inlet  210  is annularly disposed around the hub and is in fluid communication with a first set of flow channels  212 . The second member  204  defines the remainder of the first set of flow channels  212 . The first set of flow channels  212  connects the first impeller inlet  210  to a first set of discharge ports located on the first chamfered edge of the second member  204 . The second member  204  is substantially a mirror image of the first member. That is, a second impeller inlet (not shown) is annularly disposed around a second hub portion (not shown) in the same manner as the hub portion  206  of the first member  202 . A second set of flow channels  216  is partially defined by the second member  204 . The first member  202  defines the remainder of the second set of flow channels  216 . The second set of flow channels  216  connects the second impeller inlet to a second set of discharge ports  218  located on the second chamfered edge. 
     The first and second members  202  and  204  are joined together in any conventional manner. For example, the members  202  and  204  are brazed together once the fluid flow channels  212  and  216  are aligned. The respective sets of channels  212  and  216  cross over one another but are not in fluid communication with one another for reasons described above. The resultant impeller  200  has the capability of a two-stage pump achieved with only a single impeller.