Patent Publication Number: US-2022220959-A1

Title: Pump integrated with two independently driven prime movers

Description:
PRIORITY 
     The present application is a continuation of U.S. patent application Ser. No. 15/887,856 filed on Feb. 2, 2018, which is a continuation of U.S. patent application Ser. No. 14/944,368 filed on Nov. 18, 2015, now U.S. Pat. No. 9,920,755, which is a continuation of U.S. patent application Ser. No. 14/637,064 filed on Mar. 3, 2015, now U.S. Pat. No. 9,228,586, which is a continuation of International Application No. PCT/US2015/018342 filed on Mar. 2, 2015, which claims priority to U.S. Provisional Patent Application Nos. 61/946,374; 61/946,384; 61/946,395; 61/946,405; 61/946,422; and 61/946,433 filed on Feb. 28, 2014, each of which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to pumps and pumping methodologies thereof, and more particularly to pumps using two fluid drivers each integrated with an independently driven prime mover. 
     BACKGROUND OF THE INVENTION 
     Pumps that pump a fluid can come in a variety of configurations. For example, gear pumps are positive displacement pumps (or fixed displacement), i.e. they pump a constant amount of fluid per each rotation and they are particularly suited for pumping high viscosity fluids such as crude oil. Gear pumps typically comprise a casing (or housing) having a cavity in which a pair of gears are arranged, one of which is known as a drive gear, which is driven by a driveshaft attached to an external driver such as an engine or an electric motor, and the other of which is known as a driven gear (or idler gear), which meshes with the drive gear. Gear pumps, in which one gear is externally toothed and the other gear is internally toothed, are referred to as internal gear pumps. Either the internally or externally toothed gear is the drive or driven gear. Typically, the axes of rotation of the gears in the internal gear pump are offset and the externally toothed gear is of smaller diameter than the internally toothed gear. Alternatively, gear pumps, in which both gears are externally toothed, are referred to as external gear pumps. External gear pumps typically use spur, helical, or herringbone gears, depending on the intended application. Related art external gear pumps are equipped with one drive gear and one driven gear. When the drive gear attached to a rotor is rotatably driven by an engine or an electric motor, the drive gear meshes with and turns the driven gear. This rotary motion of the drive and driven gears carries fluid from the inlet of the pump to the outlet of the pump. In the above related art pumps, the fluid driver consists of the engine or electric motor and the pair of gears. 
     However, as gear teeth of the fluid drivers interlock with each other in order for the drive gear to turn the driven gear, the gear teeth grind against each other and contamination problems can arise in the system, whether it is in an open or closed fluid system, due to sheared materials from the grinding gears and/or contamination from other sources. These sheared materials are known to be detrimental to the functionality of the system, e.g., a hydraulic system, in which the gear pump operates. Sheared materials can be dispersed in the fluid, travel through the system, and damage crucial operative components, such as O-rings and bearings. It is believed that a majority of pumps fail due to contamination issues, e.g., in hydraulic systems. If the drive gear or the drive shaft fails due to a contamination issue, the whole system, e.g., the entire hydraulic system, could fail. Thus, known driver-driven gear pump configurations, which function to pump fluid as discussed above, have undesirable drawbacks due to the contamination problems. 
     Further limitation and disadvantages of conventional, traditional, and proposed approaches will become apparent to one skilled in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present disclosure with reference to the drawings. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention are directed to a pump having at least two fluid drivers and a method of delivering fluid from an inlet of the pump to an outlet of the pump using the at least two fluid drivers. Each of the fluid drives includes a prime mover and a fluid displacement member. The prime mover drives the fluid displacement member and can be, e.g., an electric motor, a hydraulic motor or other fluid-driven motor, an internal-combustion, gas or other type of engine, or other similar device that can drive a fluid displacement member. The fluid displacement members transfer fluid when driven by the prime movers. The fluid displacement members are independently driven and thus have a drive-drive configuration. The drive-drive configuration eliminates or reduces the contamination problems of known driver-driven configurations. 
     The fluid displacement member can work in combination with a fixed element, e.g., pump wall, crescent, or other similar component, and/or a moving element such as, e.g., another fluid displacement member when transferring the fluid. The fluid displacement member can be, e.g., an internal or external gear with gear teeth, a hub (e.g. a disk, cylinder, or other similar component) with projections (e.g. bumps, extensions, bulges, protrusions, other similar structures or combinations thereof), a hub (e.g. a disk, cylinder, or other similar component) with indents (e.g., cavities, depressions, voids or similar structures), a gear body with lobes, or other similar structures that can displace fluid when driven. The configuration of the fluid drivers in the pump need not be identical. For example, one fluid driver can be configured as an external gear-type fluid driver and another fluid driver can be configured as an internal gear-type fluid driver. The fluid drivers are independently operated, e.g., an electric motor, a hydraulic motor or other fluid-driven motor, an internal-combustion, gas or other type of engine, or other similar device that can independently operate its fluid displacement member. However, the fluid drivers are operated such that contact between the fluid drivers is synchronized, e.g., in order to pump the fluid and/or seal a reverse flow path. That is, operation of the fluid drivers is synchronized such that the fluid displacement member in each fluid driver makes contact with another fluid displacement member. The contact can include at least one contact point, contact line, or contact area. 
     In some exemplary embodiments of the fluid driver, the fluid driver can include motor with a stator and rotor. The stator can be fixedly attached to a support shaft and the rotor can surround the stator. The fluid driver can also include a gear having a plurality of gear teeth projecting radially outwardly from the rotor and supported by the rotor. In some embodiments, a support member can be disposed between the rotor and the gear to support the gear. 
     In exemplary embodiments, pumps and methods of pumping provide for a compact design of a pump. In an exemplary embodiment, a pump includes a pair of fluid drivers. In each of the pair of fluid drivers, a fluid displacing member is integrated with a prime mover. Each of the pair of fluid drivers is rotatably driven independently with respect to the other. In some exemplary embodiments, e.g., external gear-type pumps, the fluid displacing members of the fluid drivers are rotated in opposite directions. In other exemplary embodiments, e.g., internal gear-type pumps, the fluid displacing members of the fluid drivers are rotated in the same direction. In either rotation scheme, the rotations are synchronized to provide contact between the fluid drivers. In some embodiments, synchronizing contact includes rotatably driving one of the pair of fluid drivers at a greater rate than the other so that a surface of one fluid driver contacts a surface of another fluid driver. 
     In another exemplary embodiment, a pump includes a casing defining an interior volume. The casing includes a first port in fluid communication with the interior volume and a second port in fluid communication with the interior volume. A first fluid displacing member of a first fluid driver is disposed within the interior volume. A second fluid displacing member of a second fluid driver is also disposed within the interior volume. The second fluid displacing member is disposed such that the second fluid displacement member contacts the first displacement member. A first motor rotates the first fluid displacement member in a first direction to transfer the fluid from the first port to the second port along a first flow path. A second motor rotates the second fluid displacement member, independently of the first motor, in a second direction to transfer the fluid from the first port to the second port along a second flow path. The contact between the first displacement member and the second displacement member is synchronized by synchronizing the rotation of the first and second motors. In some embodiments the first motor and second motor are rotated at different revolutions per minute (rpm). In some embodiments, the synchronized contact seals a reverse flow path (or a backflow path) between the outlet and inlet of the pump. In some embodiments, the synchronized contact can be between a surface of at least one projection (bump, extension, bulge, protrusion, another similar structure or combinations thereof) on the first fluid displacement member and a surface of at least one projection (bump, extension, bulge, protrusion, another similar structure or combinations thereof) or an indent (cavity, depression, void or another similar structure) on the second fluid displacement member. In some embodiments, the synchronized contact aids in pumping fluid from the inlet to the outlet of the pump. In some embodiments, the synchronized contact both seals a reverse flow path (or backflow path) and aids in pumping the fluid. In some embodiments, the first direction and the second direction are the same. In other embodiments, the first direction is opposite the second direction. In some embodiments, at least a portion of the first flow path and the second flow path are the same. In other embodiments, at least a portion of the first flow path and the second flow path are different. 
     In another exemplary embodiment, a pump includes a casing defining an interior volume, the casing including a first port in fluid communication with the interior volume, and a second port in fluid communication with the interior volume. The pump also includes a first fluid driver with the first fluid driver including a first fluid displacement member disposed within the interior volume and having a plurality of first projections (or at least one first projection), and a first prime mover to rotate the first fluid displacement member about a first axial centerline of the first fluid displacement member in a first direction to transfer a fluid from the first port to the second port along a first flow path. In some embodiments the first fluid displacement member includes a plurality of first indents (or at least one first indent). The pump also includes a second fluid driver with the second fluid driver including a second fluid displacement member disposed within the interior volume. The second fluid displacement member has at least one of a plurality of second projections (or at least one second projection) and a plurality of second indents (or at least one second indent), the second gear is disposed such that a first surface of at least one of the plurality of first projections (or the at least one first projection) aligns with a second surface of at least one of the plurality of second projections (or the at least one second projection) or a third surface of at least one of the plurality of second indents (or the at least one second indent). The pump also includes a second prime mover to rotate the second fluid displacement member, independently of the first prime mover, about a second axial centerline of the second gear in a second direction to contact the first surface with the corresponding second surface or third surface and to transfer the fluid from the first port to the second port along a second flow path. 
     In another exemplary embodiment, a pump includes a casing defining an interior volume. The casing includes a first port in fluid communication with the interior volume and a second port in fluid communication with the interior volume. A first gear is disposed within the interior volume with the first gear having a plurality of first gear teeth. A second gear is also disposed within the interior volume with the second gear having a plurality of second gear teeth. The second gear is disposed such that a surface of at least one tooth of the plurality of second gear teeth contacts with a surface of at least one tooth of the plurality of first gear teeth. A first motor rotates the first gear about a first axial centerline of the first gear. The first gear is rotated in a first direction to transfer the fluid from the first port to the second port along a first flow path. A second motor rotates the second gear, independently of the first motor, about a second axial centerline of the second gear in a second direction to transfer the fluid from the first port to the second port along a second flow path. The contact between the surface of at least one tooth of the plurality of first gear teeth and the surface of at least one tooth of the plurality of second gear teeth is synchronized by synchronizing the rotation of the first and second motors. In some embodiments the first motor and second motor are rotated at different rpms. In some embodiments, the second direction is opposite the first direction and the synchronized contact seals a reverse flow path between the inlet and outlet of the pump. In some embodiments, the second direction is the same as the first direction and the synchronized contact at least one of seals a reverse flow path between the inlet and outlet of the pump and aids in pumping the fluid. 
     Another exemplary embodiment is directed to a method of delivering fluid from an inlet to an outlet of a pump having a casing to define an interior volume therein, and a first fluid driver and a second fluid driver. The method includes rotatably driving the first fluid driver in a first direction and simultaneously rotatably driving the second fluid driver independently of the first fluid driver in a second direction. In some embodiments, the method also includes synchronizing contact between the first fluid driver and the second fluid driver. 
     Another exemplary embodiment is directed to a method of delivering fluid from an inlet to an outlet of a pump having a casing to define an interior volume therein, and a first fluid displacement member and a second fluid displacement member. The method includes rotating the first fluid displacement member and rotating the second fluid displacement member. The method also includes synchronizing contact between the first fluid displacement member and the second fluid displacement member. In some embodiments, the first and second fluid displacement members are rotated in the same direction and in other embodiments, the first and second fluid displacement members are rotated in opposite directions. 
     Another exemplary embodiment is directed to a method of transferring fluid from a first port to a second port of a pump including a pump casing that defines an interior volume therein, the pump further including a first prime mover, a second prime mover, a first fluid displacement member having a plurality of first projections (or at least one first projection), and a second fluid displacement member having at least one of a plurality of second projections (or at least one second projection) and a plurality of second indents (or at least one second indent). In some embodiments the first fluid displacement member can have a plurality of first indents (or at least one first indent). The method includes rotating the first prime mover to rotate the first fluid displacement member in a first direction to transfer a fluid from the first port to the second port along a first flow path and rotating the second prime mover, independently of the first prime mover, to rotate the second fluid displacement member in a second direction to transfer the fluid from the first port to the second port along a second flow path. The method also includes synchronizing a speed of the second fluid displacement member to be in a range of 99 percent to 100 percent of a speed of the first fluid displacement member and synchronizing contact between the first displacement member and the second displacement member such that a surface of at least one of the plurality of first projections (or at least one first projection) contacts a surface of at least one of the plurality of second projections (or at least one second projection) or a surface of at least one of the plurality of indents (or at least one second indent). In some embodiments, the second direction is opposite the first direction and the synchronized contact seals a reverse flow path between the inlet and outlet of the pump. In some embodiments, the second direction is the same as the first direction and the synchronized contact at least one of seals a reverse flow path between the inlet and outlet of the pump and aids in pumping the fluid. 
     Another exemplary embodiment is directed to a method of transferring fluid from a first port to a second port of a pump that includes a pump casing, which defines an interior volume. The pump further includes a first motor, a second motor, a first gear having a plurality of first gear teeth, and a second gear having a plurality of second gear teeth. The method includes rotating the first motor to rotate the first gear about a first axial centerline of the first gear in a first direction. The rotation of the first gear transfers the fluid from the first port to the second port along a first flow path. The method also includes rotating the second motor, independently of the first motor, to rotate the second gear about a second axial centerline of the second gear in a second direction. The rotation of the second gear transfers the fluid from the first port to the second port along a second flow path. In some embodiments, the method further includes synchronizing contact between a surface of at least one tooth of the plurality of second gear teeth and a surface of at least one tooth of the plurality of first gear teeth. In some embodiments, the synchronizing the contact includes rotating the first and second motors at different rpms. In some embodiments, the second direction is opposite the first direction and the synchronized contact seals a reverse flow path between the inlet and outlet of the pump. In some embodiments, the second direction is the same as the first direction and the synchronized contact at least one of seals a reverse flow path between the inlet and outlet of the pump and aids in pumping the fluid. 
     The summary of the invention is provided as a general introduction to some embodiments of the invention, and is not intended to be limiting to any particular drive-drive configuration or drive-drive-type system. It is to be understood that various features and configurations of features described in the Summary can be combined in any suitable way to form any number of embodiments of the invention. Some additional example embodiments including variations and alternative configurations are provided herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
         FIG. 1  illustrates an exploded view of an embodiment of an external gear pump that is consistent with the present invention. 
         FIG. 2  shows a top cross-sectional view of the external gear pump of  FIG. 1 . 
         FIG. 2A  shows a side cross-sectional view taken along a line A-A in  FIG. 2  of the external gear pump. 
         FIG. 2B  shows a side cross-sectional view taken along a line B-B in  FIG. 2  of a the external gear pump. 
         FIG. 3  illustrates exemplary flow paths of the fluid pumped by the external gear pump of  FIG. 1 . 
         FIG. 3A  shows a cross-sectional view illustrating one-sided contact between two gears in a contact area in the external gear pump of  FIG. 3 . 
         FIGS. 4-8  show side cross-sectional views of various embodiments of external gear pumps that are consistent with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention are directed to a pump with independently driven fluid drivers. As discussed in further detail below various exemplary embodiments include pump configurations in which at least one prime mover is disposed internal to a fluid displacement member. In other exemplary embodiments, at least one prime mover is disposed external to a fluid displacement member but still inside the pump casing, and in still further exemplary embodiments, at least one prime mover is disposed outside the pump casing. These exemplary embodiments will be described using embodiments in which the pump is an external gear pump with two prime movers, the prime movers are motors and the fluid displacement members are external spur gears with gear teeth. However, those skilled in the art will readily recognize that the concepts, functions, and features described below with respect to motor driven external gear pump with two fluid drivers can be readily adapted to external gear pumps with other gear designs (helical gears, herringbone gears, or other gear teeth designs that can be adapted to drive fluid), internal gear pumps with various gear designs, to pumps with more than two fluid drivers, to prime movers other than electric motors, e.g., hydraulic motors or other fluid-driven motors, internal-combustion, gas or other type of engines or other similar devices that can drive a fluid displacement member, and to fluid displacement members other than an external gear with gear teeth, e.g., internal gear with gear teeth, a hub (e.g. a disk, cylinder, or other similar component) with projections (e.g. bumps, extensions, bulges, protrusions, other similar structures, or combinations thereof), a hub (e.g. a disk, cylinder, or other similar component) with indents (e.g., cavities, depressions, voids or similar structures), a gear body with lobes, or other similar structures that can displace fluid when driven. 
       FIG. 1  shows an exploded view of an embodiment of a pump  10  that is consistent with the present disclosure. The pump  10  includes two fluid drivers  40 ,  70  that respectively include motors  41 ,  61  (prime movers) and gears  50 ,  70  (fluid displacement members). In this embodiment, both pump motors  41 ,  61  are disposed inside the pump gears  50 ,  70 . As seen in  FIG. 1 , the pump  10  represents a positive-displacement (or fixed displacement) gear pump. The pump  10  has a casing  20  that includes end plates  80 ,  82  and a pump body  83 . These two plates  80 ,  82  and the pump body  83  can be connected by a plurality of through bolts  113  and nuts  115  and the inner surface  26  defines an inner volume  98 . To prevent leakage, O-rings or other similar devices can be disposed between the end plates  80 ,  82  and the pump body  83 . The casing  20  has a port  22  and a port  24  (see also  FIG. 2 ), which are in fluid communication with the inner volume  98 . During operation and based on the direction of flow, one of the ports  22 ,  24  is the pump inlet port and the other is the pump outlet port. In an exemplary embodiment, the ports  22 ,  24  of the casing  20  are round through-holes on opposing side walls of the casing  20 . However, the shape is not limiting and the through-holes can have other shapes. In addition, one or both of the ports  22 ,  44  can be located on either the top or bottom of the casing. Of course, the ports  22 ,  24  must be located such that one port is on the inlet side of the pump and one port is on the outlet side of the pump. 
     As seen in  FIG. 1 , a pair of gears  50 ,  70  are disposed in the internal volume  98 . Each of the gears  50 ,  70  has a plurality of gear teeth  52 ,  72  extending radially outward from the respective gear bodies. The gear teeth  52 ,  72 , when rotated by, e.g., electric motors  41 ,  61 , transfer fluid from the inlet to the outlet. In some embodiments, the pump  10  is bi-directional. Thus, either port  22 ,  24  can be the inlet port, depending on the direction of rotation of gears  50 ,  70 , and the other port will be the outlet port. The gears  50 ,  70  have cylindrical openings  51 ,  71  along an axial centerline of the respective gear bodies. The cylindrical openings  51 ,  71  can extend either partially through or the entire length of the gear bodies. The cylindrical openings are sized to accept the pair of motors  41 ,  61 . Each motor  41 ,  61  respectively includes a shaft  42 ,  62 , a stator  44 ,  64 , a rotor  46 ,  66 . 
       FIG. 2  shows a top cross-sectional view of the external gear pump  10  of  FIG. 1 .  FIG. 2A  shows a side cross-sectional view taken along a line A-A in  FIG. 2  of the external gear pump  10 , and  FIG. 2  shows a side cross-sectional view taken along a line B-B in  FIG. 2A  of the external gear pump  10 . As seen in  FIGS. 2-2B , fluid drivers  40 ,  60  are disposed in the casing  20 . The support shafts  42 ,  62  of the fluid drivers  40 ,  60  are disposed between the port  22  and the port  24  of the casing  20  and are supported by the upper plate  80  at one end  84  and the lower plate  82  at the other end  86 . However, the means to support the shafts  42 ,  62  and thus the fluid drivers  40 ,  60  are not limited to this design and other designs to support the shaft can be used. For example, the shafts  42 ,  62  can be supported by blocks that are attached to the casing  20  rather than directly by casing  20 . The support shaft  42  of the fluid driver  40  is disposed in parallel with the support shaft  62  of the fluid driver  60  and the two shafts are separated by an appropriate distance so that the gear teeth  52 ,  72  of the respective gears  50 ,  70  contact each other when rotated. 
     The stators  44 ,  64  of motors  41 ,  61  are disposed radially between the respective support shafts  42 ,  62  and the rotors  46 ,  66 . The stators  44 ,  64  are fixedly connected to the respective support shafts  42 ,  62 , which are fixedly connected to the casing  20 . The rotors  46 ,  66  are disposed radially outward of the stators  44 ,  64  and surround the respective stators  44 ,  64 . Thus, the motors  41 ,  61  in this embodiment are of an outer-rotor motor design (or an external-rotor motor design), which means that that the outside of the motor rotates and the center of the motor is stationary. In contrast, in an internal-rotor motor design, the rotor is attached to a central shaft that rotates. In an exemplary embodiment, the electric motors  41 ,  61  are multi directional motors. That is, either motor can operate to create rotary motion either clockwise or counter-clockwise depending on operational needs. Further, in an exemplary embodiment, the motors  41 ,  61  are variable speed motors in which the speed of the rotor and thus the attached gear can be varied to create various volume flows and pump pressures. 
     As discussed above, the gear bodies can include cylindrical openings  51 ,  71  which receive motors  41 ,  61 . In an exemplary embodiment, the fluid drivers  40 ,  60  can respectively include outer support members  48 ,  68  (see  FIG. 2 ) which aid in coupling the motors  41 ,  61  to the gears  50 ,  70  and in supporting the gears  50 ,  70  on motors  41 , 61 . Each of the support members  48 ,  68  can be, for example, a sleeve that is initially attached to either an outer casing of the motors  41 , 61  or an inner surface of the cylindrical openings  51 ,  71 . The sleeves can be attached by using an interference fit, a press fit, an adhesive, screws, bolts, a welding or soldering method, or other means that can attach the support members to the cylindrical openings. Similarly, the final coupling between the motors  41 ,  61  and the gears  50 ,  70  using the support members  48 ,  68  can be by using an interference fit, a press fit, screws, bolts, adhesive, a welding or soldering method, or other means to attach the motors to the support members. The sleeves can be of different thicknesses to, e.g., facilitate the attachment of motors  41 ,  61  with different physical sizes to the gears  50 ,  70  or vice versa. In addition, if the motor casings and the gears are made of materials that are not compatible, e.g., chemically or otherwise, the sleeves can be made of materials that are compatible with both the gear composition and motor casing composition. In some embodiments, the support members  48 ,  68  can be designed as a sacrificial piece. That is, support members  48 ,  68  are designed to be the first to fail, e.g., due to excessive stresses, temperatures, or other causes of failure, in comparison to the gears  50 ,  70  and motors  41 ,  61 . This allows for a more economic repair of the pump  10  in the event of failure. In some embodiments, the outer support members  48 ,  68  is not a separate piece but an integral part of the casing for the motors  41 ,  61  or part of the inner surface of the cylindrical openings  51 ,  71  of the gears  50 ,  70 . In other embodiments, the motors  41 ,  61  can support the gears  50 ,  70  (and the plurality of first gear teeth  52 ,  72 ) on their outer surfaces without the need for the outer support members  48 ,  68 . For example, the motor casings can be directly coupled to the inner surface of the cylindrical opening  51 ,  71  of the gears  50 ,  70  by using an interference fit, a press fit, screws, bolts, an adhesive, a welding or soldering method, or other means to attach the motor casing to the cylindrical opening. In some embodiments, the outer casings of the motors  41 ,  61  can be, e.g., machined, cast, or other means to shape the outer casing to form a shape of the gear teeth  52 ,  72 . In still other embodiments, the plurality of gear teeth  52 ,  72  can be integrated with the respective rotors  46 ,  66  such that each gear/rotor combination forms one rotary body. 
     In the above discussed exemplary embodiments, both fluid drivers  40 ,  60 , including electric motors  41 ,  61 and gears  50 ,  70 , are integrated into a single pump casing  20 . This novel configuration of the external gear pump  10  of the present disclosure enables a compact design that provides various advantages. First, the space or footprint occupied by the gear pump embodiments discussed above is significantly reduced by integrating necessary components into a single pump casing, when compared to conventional gear pumps. In addition, the total weight of a pump system consistent with the above embodiments is also reduced by removing unnecessary parts such as a shaft that connects a motor to a pump, and separate mountings for a motor/gear driver. Further, since the pump  10  of the present disclosure has a compact and modular design, it can be easily installed, even at locations where conventional gear pumps could not be installed, and can be easily replaced. Detailed description of the pump operation is provided next. 
       FIG. 3  illustrates an exemplary fluid flow path of an exemplary embodiment of the external gear pump  10 . The ports  22 ,  24 , and a contact area  78  between the plurality of first gear teeth  52  and the plurality of second gear teeth  72  are substantially aligned along a single straight path. However, the alignment of the ports are not limited to this exemplary embodiment and other alignments are permissible. For explanatory purpose, the gear  50  is rotatably driven clockwise  74  by motor  41  and the gear  70  is rotatably driven counter-clockwise  76  by the motor  61 . With this rotational configuration, port  22  is the inlet side of the gear pump  10  and port  24  is the outlet side of the gear pump  10 . In some exemplary embodiments, both gears  50 ,  70  are respectively independently driven by the separately provided motors  41 ,  61 . 
     As seen in  FIG. 3 , the fluid to be pumped is drawn into the casing  20  at port  22  as shown by an arrow  92  and exits the pump  10  via port  24  as shown by arrow  96 . The pumping of the fluid is accomplished by the gear teeth  52 ,  72 . As the gear teeth  52 ,  72  rotate, the gear teeth rotating out of the contact area  78  form expanding inter-tooth volumes between adjacent teeth on each gear. As these inter-tooth volumes expand, the spaces between adjacent teeth on each gear are filled with fluid from the inlet port, which is port  22  in this exemplary embodiment. The fluid is then forced to move with each gear along the interior wall  90  of the casing  20  as shown by arrows  94  and  94 ′. That is, the teeth  52  of gear  50  force the fluid to flow along the path  94  and the teeth  72  of gear  70  force the fluid to flow along the path  94 ′. Very small clearances between the tips of the gear teeth  52 ,  72  on each gear and the corresponding interior wall  90  of the casing  20  keep the fluid in the inter-tooth volumes trapped, which prevents the fluid from leaking back towards the inlet port. As the gear teeth  52 ,  72  rotate around and back into the contact area  78 , shrinking inter-tooth volumes form between adjacent teeth on each gear because a corresponding tooth of the other gear enters the space between adjacent teeth. The shrinking inter-tooth volumes force the fluid to exit the space between the adjacent teeth and flow out of the pump  10  through port  24  as shown by arrow  96 . In some embodiments, the motors  41 ,  61  are bi-directional and the rotation of motors  41 ,  61  can be reversed to reverse the direction fluid flow through the pump  10 , i.e., the fluid flows from the port  24  to the port  22 . 
     To prevent backflow, i.e., fluid leakage from the outlet side to the inlet side through the contact area  78 , contact between a tooth of the first gear  50  and a tooth of the second gear  70  in the contact area  78  provides sealing against the backflow. The contact force is sufficiently large enough to provide substantial sealing but, unlike related art systems, the contact force is not so large as to significantly drive the other gear. In related art driver-driven systems, the force applied by the driver gear turns the driven gear. That is, the driver gear meshes with (or interlocks with) the driven gear to mechanically drive the driven gear. While the force from the driver gear provides sealing at the interface point between the two teeth, this force is much higher than that necessary for sealing because this force must be sufficient enough to mechanically drive the driven gear to transfer the fluid at the desired flow and pressure. This large force causes material to shear off from the teeth in related art pumps. These sheared materials can be dispersed in the fluid, travel through the hydraulic system, and damage crucial operative components, such as O-rings and bearings. As a result, a whole pump system can fail and could interrupt operation of the pump. This failure and interruption of the operation of the pump can lead to significant downtime to repair the pump. 
     In exemplary embodiments of the pump  10 , however, the gears  50 ,  70  of the pump  10  do not mechanically drive the other gear to any significant degree when the teeth  52 ,  72  form a seal in the contact area  78 . Instead, the gears  50 ,  70  are rotatably driven independently such that the gear teeth  52 ,  72  do not grind against each other. That is, the gears  50 ,  70  are synchronously driven to provide contact but not to grind against each other. Specifically, rotation of the gears  50 ,  70  are synchronized at suitable rotation rates so that a tooth of the gear  50  contacts a tooth of the second gear  70  in the contact area  78  with sufficient enough force to provide substantial sealing, i.e., fluid leakage from the outlet port side to the inlet port side through the contact area  78  is substantially eliminated. However, unlike the driver-driven configurations discussed above, the contact force between the two gears is insufficient to have one gear mechanically drive the other to any significant degree. Precision control of the motors  41 ,  61 , will ensure that the gear positions remain synchronized with respect to each other during operation. Thus, the above-described issues caused by sheared materials in conventional gear pumps are effectively avoided. 
     In some embodiments, rotation of the gears  50 ,  70  is at least 99% synchronized, where 100% synchronized means that both gears  50 ,  70  are rotated at the same rpm. However, the synchronization percentage can be varied as long as substantial sealing is provided via the contact between the gear teeth of the two gears  50 ,  70 . In exemplary embodiments, the synchronization rate can be in a range of 95.0% to 100% based on a clearance relationship between the gear teeth  52  and the gear teeth  72 . In other exemplary embodiments, the synchronization rate is in a range of 99.0% to 100% based on a clearance relationship between the gear teeth  52  and the gear teeth  72 , and in still other exemplary embodiments, the synchronization rate is in a range of 99.5% to 100% based on a clearance relationship between the gear teeth  52  and the gear teeth  72 . Again, precision control of the motors  41 ,  61 , will ensure that the gear positions remain synchronized with respect to each other during operation. By appropriately synchronizing the gears  50 ,  70 , the gear teeth  52 ,  72  can provide substantial sealing, e.g., a backflow or leakage rate with a slip coefficient in a range of 5% or less. For example, for typical hydraulic fluid at about 120 deg. F, the slip coefficient can be can be 5% or less for pump pressures in a range of 3000 psi to 5000 psi, 3% or less for pump pressures in a range of 2000 psi to 3000 psi, 2% or less for pump pressures in a range of 1000 psi to 2000 psi, and 1% or less for pump pressures in a range up to 1000 psi. Of course, depending on the pump type, the synchronized contact can aid in pumping the fluid. For example, in certain internal-gear gerotor designs, the synchronized contact between the two fluid drivers also aids in pumping the fluid, which is trapped between teeth of opposing gears. In some exemplary embodiments, the gears  50 ,  70  are synchronized by appropriately synchronizing the motors  41 ,  61 . Synchronization of multiple motors is known in the relevant art, thus detailed explanation is omitted here. 
     In an exemplary embodiment, the synchronizing of the gears  50 ,  70  provides one-sided contact between a tooth of the gear  50  and a tooth of the gear  70 .  FIG. 3A  shows a cross-sectional view illustrating this one-sided contact between the two gears  50 ,  70  in the contact area  78 . For illustrative purposes, gear  50  is rotatably driven clockwise  74  and the gear  70  is rotatably driven counter-clockwise  76  independently of the gear  50 . Further, the gear  70  is rotatably driven faster than the gear  50  by a fraction of a second, 0.01 sec/revolution, for example. This rotational speed difference between the gear  50  and gear  70  enables one-sided contact between the two gears  50 ,  70 , which provides substantial sealing between gear teeth of the two gears  50 ,  70  to seal between the inlet port and the outlet port, as described above. Thus, as shown in  FIG. 4 , a tooth  142  on the gear  70  contacts a tooth  144  on the gear  50  at a point of contact  152 . If a face of a gear tooth that is facing forward in the rotational direction  74 ,  76  is defined as a front side (F), the front side (F) of the tooth  142  contacts the rear side (R) of the tooth  144  at the point of contact  152 . However, the gear tooth dimensions are such that the front side (F) of the tooth  144  is not in contact with (i.e., spaced apart from) the rear side (R) of tooth  146 , which is a tooth adjacent to the tooth  142  on the gear  70 . Thus, the gear teeth  52 ,  72  are designed such that there is one-sided contact in the contact area  78  as the gears  50 ,  70  are driven. As the tooth  142  and the tooth  144  move away from the contact area  78  as the gears  50 ,  70  rotate, the one-sided contact formed between the teeth  142  and  144  phases out. As long as there is a rotational speed difference between the two gears  50 ,  70 , this one-sided contact is formed intermittently between a tooth on the gear  50  and a tooth on the gear  70 . However, because as the gears  50 ,  70  rotate, the next two following teeth on the respective gears form the next one-sided contact such that there is always contact and the backflow path in the contact area  78  remains substantially sealed. That is, the one-sided contact provides sealing between the ports  22  and  24  such that fluid carried from the pump inlet to the pump outlet is prevented (or substantially prevented) from flowing back to the pump inlet through the contact area  78 . 
     In  FIG. 3A , the one-sided contact between the tooth  142  and the tooth  144  is shown as being at a particular point, i.e. point of contact  152 . However, a one-sided contact between gear teeth in the exemplary embodiments is not limited to contact at a particular point. For example, the one-sided contact can occur at a plurality of points or along a contact line between the tooth  142  and the tooth  144 . For another example, one-sided contact can occur between surface areas of the two gear teeth. Thus, a sealing area can be formed when an area on the surface of the tooth  142  is in contact with an area on the surface of the tooth  144  during the one-sided contact. The gear teeth  52 ,  72  of each gear  50 ,  70  can be configured to have a tooth profile (or curvature) to achieve one-sided contact between the two gear teeth. In this way, one-sided contact in the present disclosure can occur at a point or points, along a line, or over surface areas. Accordingly, the point of contact  152  discussed above can be provided as part of a location (or locations) of contact, and not limited to a single point of contact. 
     In some exemplary embodiments, the teeth of the respective gears  50 ,  70  are designed so as to not trap excessive fluid pressure between the teeth in the contact area  78 . As illustrated in  FIG. 3A , fluid  160  can be trapped between the teeth  142 ,  144 ,  146 . While the trapped fluid  160  provides a sealing effect between the pump inlet and the pump outlet, excessive pressure can accumulate as the gears  50 ,  70  rotate. In a preferred embodiment, the gear teeth profile is such that a small clearance (or gap)  154  is provided between the gear teeth  144 ,  146  to release pressurized fluid. Such a design retains the sealing effect while ensuring that excessive pressure is not built up. Of course, the point, line or area of contact is not limited to the side of one tooth face contacting the side of another tooth face. Depending on the type of fluid displacement member, the synchronized contact can be between any surface of at least one projection (e.g., bump, extension, bulge, protrusion, other similar structure or combinations thereof) on the first fluid displacement member and any surface of at least one projection(e.g., bump, extension, bulge, protrusion, other similar structure or combinations thereof) or an indent(e.g., cavity, depression, void or similar structure) on the second fluid displacement member. In some embodiments, at least one of the fluid displacement members can be made of or include a resilient material, e.g., rubber, an elastomeric material, or another resilient material, so that the contact force provides a more positive sealing area. 
     In the embodiments discussed above, the prime movers are disposed inside the fluid displacement members, i.e., both motors  41 ,  61  are disposed inside the cylinder openings  51 ,  71 . However, advantageous features of the inventive pump design are not limited to a configuration in which both prime movers are disposed within the bodies of the fluid displacement members. Other drive-drive configurations also fall within the scope of the present disclosure. For example,  FIG. 4  shows a side cross-sectional view of another exemplary embodiment of an external gear pump  1010 . The embodiment of the pump  1010  shown in  FIG. 4  differs from pump  10  ( FIG. 1 ) in that one of the two motors in this embodiment is external to the corresponding gear body but is still in the pump casing. The pump  1010  includes a casing  1020 , a fluid driver  1040 , and a fluid driver  1060 . The inner surface of the casing  1020  defines an internal volume that includes a motor cavity  1084  and a gear cavity  1086 . The casing  1020  can include end plates  1080 ,  1082 . These two plates  1080 ,  1082  can be connected by a plurality of bolts (not shown). 
     The fluid driver  1040  includes motor  1041  and a gear  1050 . The motor  1041  is an outer-rotor motor design and is disposed in the body of gear  1050 , which is disposed in the gear cavity  1086 . The motor  1041  includes a rotor  1044  and a stator  1046 . The gear  1050  includes a plurality of gear teeth  1052  extending radially outward from its gear body. It should be understood that those skilled in the art will recognize that fluid driver  1040  is similar to fluid driver  40  and that the configurations and functions of fluid driver  40 , as discussed above, can be incorporated into fluid driver  1040 . Accordingly, for brevity, fluid driver  1040  will not be discussed in detail except as necessary to describe this embodiment. 
     The fluid driver  1060  includes a motor  1061  and a gear  1070 . The fluid driver  1060  is disposed next to fluid driver  1040  such that the respective gear teeth  1072 ,  1052  contact each other in a manner similar to the contact of gear teeth  52 ,  72  in contact area  78  discussed above with respect to pump  10 . In this embodiment, motor  1061  is an inner-rotor motor design and is disposed in the motor cavity  1084 . In this embodiment, the motor  1061  and the gear  1070  have a common shaft  1062 . The rotor  1064  of motor  1061  is disposed radially between the shaft  1062  and the stator  1066 . The stator  1066  is disposed radially outward of the rotor  1064  and surrounds the rotor  1064 . The inner-rotor design means that the shaft  1062 , which is connected to rotor  1064 , rotates while the stator  1066  is fixedly connected to the casing  1020 . In addition, gear  1070  is also connected to the shaft  1062 . The shaft  1062  is supported by, for example, a bearing in the plate  1080  at one end  1088  and by a bearing in the plate  1082  at the other end  1090 . In other embodiments, the shaft  1062  can be supported by bearing blocks that are fixedly connected to the casing  1020  rather than directly by bearings in the casing  1020 . In addition, rather than a common shaft  1062 , the motor  1061  and the gear  1070  can include their own shafts that are coupled together by known means. 
     As shown in  FIG. 4 , the gear  1070  is disposed adjacent to the motor  1061  in the casing  1020 . That is, unlike motor  1041 , the motor  1061  is not disposed in the gear body of gear  1070 . The gear  1070  is spaced apart from the motor  1061  in an axial direction on the shaft  1062 . The rotor  1064  is fixedly connected to the shaft  1062  on one side  1088  of the shaft  1062 , and the gear  1070  is fixedly connected to the shaft  1062  on the other side  1090  of the shaft  1062  such that torque generated by the motor  1061  is transmitted to the gear  1070  via the shaft  1062 . 
     The motor  1061  is designed to fit into its cavity with sufficient tolerance between the motor casing and the pump casing  1020  so that fluid is prevented (or substantially prevented) from entering the cavity during operation. In addition, there is sufficient clearance between the motor casing and the gear  1070  for the gear  1070  to rotate freely but the clearance is such that the fluid can still be pumped efficiently. Thus, with respect to the fluid, in this embodiment, the motor casing is designed to perform the function of the appropriate portion of the pump casing walls of the embodiment of  FIG. 1 . In some embodiments, the outer diameter of the motor  1061  is less that the root diameter for the gear teeth  1072 . Thus, in these embodiments, even the motor side of the gear teeth  1072  will be adjacent to a wall of the pump casing  1020  as they rotate. In some embodiments, a bearing  1095  can be inserted between the gear  1070  and the motor  1061 . The bearing  1095 , which can be, e.g., a washer-type bearing, decreases friction between the gear  1070  and the motor  1061  as the gear  1070  rotates. Depending on the fluid being pumped and the type of application, the bearing can be metallic, a non-metallic or a composite. Metallic material can include, but is not limited to, steel, stainless steel, anodized aluminum, aluminum, titanium, magnesium, brass, and their respective alloys. Non-metallic material can include, but is not limited to, ceramic, plastic, composite, carbon fiber, and nano-composite material. In addition, the bearing  1095  can be sized to fit the motor cavity  1084  opening to help seal the motor cavity  1084  from the gear cavity  1086 , and the gears  1052 ,  1072  will be able to pump the fluid more efficiently. It should be understood that those skilled in the art will recognize that, in operation, the fluid driver  1040  and the fluid driver  1060  will operate in a manner similar to that disclosed above with respect to pump  10 . Accordingly, for brevity, pump  1010  operating details will not be further discussed. 
     In the above exemplary embodiment, the gear  1070  is shown as being spaced apart from the motor  1061  along the axial direction of the shaft  1062 . However, other configurations fall within the scope of the present disclosure. For example, the gear  1070  and motor  1061  can be completely separated from each other (e.g., without a common shaft), partially overlapping with each other, positioned side-by-side, on top of each other, or offset from each other. Thus, the present disclosure covers all of the above-discussed positional relationships and any other variations of a relatively proximate positional relationship between a gear and a motor inside the casing  1020 . In addition, in some exemplary embodiments, motor  1061  can be an outer-rotor motor design that is appropriately configured to rotate the gear  1070 . 
     Further, in the exemplary embodiment described above, the torque of the motor  1061  is transmitted to the gear  1070  via the shaft  1062 . However, the means for transmitting torque (or power) from a motor to a gear is not limited to a shaft, e.g., the shaft  1062  in the above-described exemplary embodiment. Instead, any combination of power transmission devices, e.g., shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices, can be used without departing from the spirit of the present disclosure. 
       FIG. 5  shows a side cross-sectional view of another exemplary embodiment of an external gear pump  1110 . The embodiment of the pump  1110  shown in  FIG. 5  differs from pump  10  in that each of the two motors in this embodiment is external to the gear body but still disposed in the pump casing. The pump  1110  includes a casing  1120 , a fluid driver  1140 , and a fluid driver  1160 . The inner surface of the casing  1120  defines an internal volume that includes motor cavities  1184  and  1184 ′ and gear cavity  1186 . The casing  1120  can include end plates  1180 ,  1182 . These two plates  1180 ,  1182  can be connected by a plurality of bolts (not shown). 
     The fluid drivers  1140 ,  1160  respectively include motors  1141 ,  1161  and gears  1150 ,  1170 . The motors  1141 ,  1161  are of an inner-rotor design and are respectively disposed in motor cavities  1184 ,  1184 ′. The motor  1141  and gear  1150  of the fluid driver  1140  have a common shaft  1142  and the motor  1161  and gear  1170  of the fluid driver  1160  have a common shaft  1162 . The motors  1141 ,  1161  respectively include rotors  1144 ,  1164  and stators  1146 ,  1166 , and the gears  1150 ,  1170  respectively include a plurality of gear teeth  1152 ,  1172  extending radially outward from the respective gear bodies. The fluid driver  1140  is disposed next to fluid driver  1160  such that the respective gear teeth  1152 ,  1172  contact each other in a manner similar to the contact of gear teeth  52 ,  72  in contact area  78  discussed above with respect to pump  10 . Bearings  1195  and  1195 ′ can be respectively disposed between motors  1141 ,  1161  and gears  1150 ,  1170 . The bearings  1195  and  1195 ′ are similar in design and function to bearing  1095  discussed above. It should be understood that those skilled in the art will recognize that the fluid drivers  1140 ,  1160  are similar to fluid driver  1060  and that the configurations and functions of the fluid driver  1060 , discussed above, can be incorporated into the fluid drivers  1140 ,  1160  within pump  1110 . Thus, for brevity, fluid drivers  1140 ,  1160  will not be discussed in detail. Similarly, the operation of pump  1110  is similar to that of pump  10  and thus, for brevity, will not be further discussed. In addition, like fluid driver  1060 , the means for transmitting torque (or power) from the motor to the gear is not limited to a shaft. Instead, any combination of power transmission devices, for example, shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices can be used without departing from the spirit of the present disclosure. In addition, in some exemplary embodiments, motors  1141 ,  1161  can be outer-rotor motor designs that are appropriately configured to respectively rotate the gears  1150 ,  1170 . 
       FIG. 6  shows a side cross-sectional view of another exemplary embodiment of an external gear pump  1210 . The embodiment of the pump  1210  shown in  FIG. 6  differs from pump  10  in that one of the two motors is disposed outside the pump casing. The pump  1210  includes a casing  1220 , a fluid driver  1240 , and a fluid driver  1260 . The inner surface of the casing  1220  defines an internal volume. The casing  1220  can include end plates  1280 ,  1282 . These two plates  1280 ,  1282  can be connected by a plurality of bolts. 
     The fluid driver  1240  includes motor  1241  and a gear  1250 . The motor  1241  is an outer-rotor motor design and is disposed in the body of gear  1250 , which is disposed in the internal volume. The motor  1241  includes a rotor  1244  and a stator  1246 . The gear  1250  includes a plurality of gear teeth  1252  extending radially outward from its gear body. It should be understood that those skilled in the art will recognize that fluid driver  1240  is similar to fluid driver  40  and that the configurations and functions of fluid driver  40 , as discussed above, can be incorporated into fluid driver  1240 . Accordingly, for brevity, fluid driver  1240  will not be discussed in detail except as necessary to describe this embodiment. 
     The fluid driver  1260  includes a motor  1261  and a gear  1270 . The fluid driver  1260  is disposed next to fluid driver  1240  such that the respective gear teeth  1272 ,  1252  contact each other in a manner similar to the contact of gear teeth  52 ,  72  in contact area  78  discussed above with respect to pump  10 . In this embodiment, motor  1261  is an inner-rotor motor design and, as seen in  FIG. 6 , the motor  1261  is disposed outside the casing  1220 . The rotor  1264  of motor  1261  is disposed radially between the motor shaft  1262 ′ and the stator  1266 . The stator  1266  is disposed radially outward of the rotor  1264  and surrounds the rotor  1264 . The inner-rotor design means that the shaft  1262 ′, which is coupled to rotor  1264 , rotates while the stator  1266  is fixedly connected to the pump casing  1220  either directly or indirectly via, e.g., motor housing  1287 . The gear  1270  includes a shaft  1262  that can be supported by the plate  1282  at one end  1290  and the plate  1280  at the other end  1291 . The gear shaft  1262 , which extends outside casing  1220 , can be coupled to motor shaft  1262 ′ via, e.g., a coupling  1285  such as a shaft hub to form a shaft extending from point  1290  to point  1288 . One or more seals  1293  can be disposed to provide necessary sealing of the fluid. Design of the shafts  1262 ,  1262 ′ and the means to couple the motor  1261  to gear  1270  can be varied without departing from the spirit of the present invention. 
     As shown in  FIG. 6 , the gear  1270  is disposed proximate the motor  1261 . That is, unlike motor  1241 , the motor  1261  is not disposed in the gear body of gear  1270 . Instead, the gear  1270  is disposed in the casing  1220  while the motor  1261  is disposed proximate to the gear  1270  but outside the casing  1220 . In the exemplary embodiment of  FIG. 6 , the gear  1270  is spaced apart from the motor  1261  in an axial direction along the shafts  1262  and  1262 ′. The rotor  1266  is fixedly connected to the shaft  1262 ′, which is couple to shaft  1262  such that the torque generated by the motor  1261  is transmitted to the gear  1270  via the shaft  1262 . The shafts  1262  and  1262 ′ can be supported by bearings at one or more locations. It should be understood that those skilled in the art will recognize that the operation of pump  1210 , including fluid drivers  1240 ,  1260 , will be similar to that of pump  10  and thus, for brevity, will not be further discussed. 
     In the above embodiment gear  1270  is shown spaced apart from the motor  1261  along the axial direction of the shafts  1262  and  1262 ′ (i.e., spaced apart but axially aligned). However, other configurations can fall within the scope of the present disclosure. For example, the gear  1270  and motor  1261  can be positioned side-by-side, on top of each other, or offset from each other. Thus, the present disclosure covers all of the above-discussed positional relationships and any other variations of a relatively proximate positional relationship between a gear and a motor outside the casing  1220 . In addition, in some exemplary embodiments, motor  1261  can be an outer-rotor motor design that is appropriately configured to rotate the gear  1270 . 
     Further, in the exemplary embodiment described above, the torque of the motor  1261  is transmitted to the gear  1270  via the shafts  1262 ,  1262 ′. However, the means for transmitting torque (or power) from a motor to a gear is not limited to shafts. Instead, any combination of power transmission devices, e.g., shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices, can be used without departing from the spirit of the present disclosure. In addition, the motor housing  1287  can include a vibration isolator (not shown) between the casing  1220  and the motor housing  1287 . Further, the motor housing  1287  mounting is not limited to that illustrated in  FIG. 6  and the motor housing can be mounted at any appropriate location on the casing  1220  or can even be separate from the casing  1220 . 
       FIG. 7  shows a side cross-sectional view of another exemplary embodiment of an external gear pump  1310 . The embodiment of the pump  1310  shown in  FIG. 7  differs from pump  10  in that the two motors are disposed external to the gear body with one motor still being disposed inside the pump casing while the other motor is disposed outside the pump casing. The pump  1310  includes a casing  1320 , a fluid driver  1340 , and a fluid driver  1360 . The inner surface of the casing  1320  defines an internal volume that includes a motor cavity  1384  and a gear cavity  1386 . The casing  1320  can include end plates  1380 ,  1382 . These two plates  1380 ,  1382  can be connected to a body of the casing  1320  by a plurality of bolts. 
     The fluid driver  1340  includes a motor  1341  and a gear  1350 . In this embodiment, motor  1341  is an inner-rotor motor design and, as seen in  FIG. 7 , the motor  1341  is disposed outside the casing  1320 . The rotor  1344  of motor  1341  is disposed radially between the motor shaft  1342 ′ and the stator  1346 . The stator  1346  is disposed radially outward of the rotor  1344  and surrounds the rotor  1344 . The inner rotor design means that the shaft  1342 ′, which is connected to rotor  1344 , rotates while the stator  1346  is fixedly connected to the pump casing  1320  either directly or indirectly via, e.g., motor housing  1387 . The gear  1350  includes a shaft  1342  that can be supported by the lower plate  1382  at one end  1390  and the upper plate  1380  at the other end  1391 . The gear shaft  1342 , which extends outside casing  1320 , can be coupled to motor shaft  1342 ′ via, e.g., a coupling  1385  such as a shaft hub to form a shaft extending from point  1384  to point  1386 . One or more seals  1393  can be disposed to provide necessary sealing of the fluid. Design of the shafts  1342 ,  1342 ′ and the means to couple the motor  1341  to gear  1350  can be varied without departing from the spirit of the present invention. It should be understood that those skilled in the art will recognize that fluid driver  1340  is similar to fluid driver  1260  and that the configurations and functions of fluid driver  1260 , as discussed above, can be incorporated into fluid driver  1340 . Accordingly, for brevity, fluid driver  1340  will not be discussed in detail except as necessary to describe this embodiment. 
     In addition, the gear  1350  and motor  1341  can be positioned side-by-side, on top of each other, or offset from each other. Thus, the present disclosure covers all of the above-discussed positional relationships and any other variations of a relatively proximate positional relationship between a gear and a motor outside the casing  1320 . Also, in some exemplary embodiments, motor  1341  can be an outer-rotor motor design that are appropriately configured to rotate the gear  1350 . Further, the means for transmitting torque (or power) from a motor to a gear is not limited to shafts. Instead, any combination of power transmission devices, e.g., shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices, can be used without departing from the spirit of the present disclosure. In addition, the motor housing  1387  can include a vibration isolator (not shown) between the casing  1320  and the motor housing  1387 . Further, the motor housing  1387  mounting is not limited to that illustrated in  FIG. 7  and the motor housing can be mounted at any appropriate location on the casing  1320  or can even be separate from the casing  1320 . 
     The fluid driver  1360  includes a motor  1361  and a gear  1370 . The fluid driver  1360  is disposed next to fluid driver  1340  such that the respective gear teeth  1372 ,  1352  contact each other in a manner similar to the contact of gear teeth  52 ,  72  in contact area  128  discussed above with respect to pump  10 . In this embodiment, motor  1361  is an inner-rotor motor design and is disposed in the motor cavity  1384 . In this embodiment, the motor  1361  and the gear  1370  have a common shaft  1362 . The rotor  1364  of motor  1361  is disposed radially between the shaft  1362  and the stator  1366 . The stator  1366  is disposed radially outward of the rotor  1364  and surrounds the rotor  1364 . Bearing  1395  can be disposed between motor  1361  and gear  1370 . The bearing  1395  is similar in design and function to bearing  1095  discussed above. The inner-rotor design means that the shaft  1362 , which is connected to rotor  1364 , rotates while the stator  1366  is fixedly connected to the casing  1320 . In addition, gear  1370  is also connected to the shaft  1362 . It should be understood that those skilled in the art will recognize that the fluid driver  1360  is similar to fluid driver  1060  and that the configurations and functions of fluid driver  1060 , as discussed above, can be incorporated into fluid driver  1360 . Accordingly, for brevity, fluid driver  1360  will not be discussed in detail except as necessary to describe this embodiment. Also, in some exemplary embodiments, motor  1361  can be an outer-rotor motor design that is appropriately configured to rotate the gear  1370 . In addition, it should be understood that those skilled in the art will recognize that the operation of pump  1310 , including fluid drivers  1340 ,  1360 , will be similar to that of pump  10  and thus, for brevity, will not be further discussed. In addition, the means for transmitting torque (or power) from the motor to the gear is not limited to a shaft. Instead, any combination of power transmission devices, for example, shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices can be used without departing from the spirit of the present disclosure. 
       FIG. 8  shows a side cross-sectional view of another exemplary embodiment of an external gear pump  1510 . The embodiment of the pump  1510  shown in  FIG. 8  differs from pump  10  in that both motors are disposed outside a pump casing. The pump  1510  includes a casing  1520 , a fluid driver  1540 , and a fluid driver  1560 . The inner surface of the casing  1520  defines an internal volume. The casing  1520  can include end plates  1580 ,  1582 . These two plates  1580 ,  1582  can be connected to a body of the casing  1520  by a plurality of bolts. 
     The fluid drivers  1540 ,  1560  respectively include motors  1541 ,  1561  and gears  1550 ,  1570 . The fluid driver  1540  is disposed next to fluid driver  1560  such that the respective gear teeth  1552 ,  1572  contact each other in a manner similar to the contact of gear teeth  52 ,  72  in contact area  78  discussed above with respect to pump  10 . In this embodiment, motors  1541 ,  1561  are of an inner-rotor motor design and, as seen in  FIG. 8 , the motors  1541 ,  1561  are disposed outside the casing  1520 . Each of the rotors  1544 ,  1564  of motors  1541 ,  1561  are disposed radially between the respective motor shafts  1542 ′,  1562 ′ and the stators  1546 ,  1566 . The stators  1546 ,  1566  are disposed radially outward of the respective rotors  1544 ,  1564  and surround the rotors  1544 ,  1564 . The inner-rotor designs mean that the shafts  1542 ′,  1562 ′, which are respectively coupled to rotors  1544 ,  1564 , rotate while the stators  1546 ,  1566  are fixedly connected to the pump casing  1220  either directly or indirectly via, e.g., motor housing  1587 . The gears  1550 ,  1570  respectively include shafts  1542 ,  1562  that can be supported by the plate  1582  at ends  1586 ,  1590  and the plate  1580  at ends  1591 ,  1597 . The gear shafts  1542 ,  1562 , which extend outside casing  1520 , can be respectively coupled to motor shafts  1542 ′,  1562 ′ via, e.g., couplings  1585 ,  1595  such as shaft hubs to respectively form shafts extending from points  1591 ,  1590  to points  1584 ,  1588 . One or more seals  1593  can be disposed to provide necessary sealing of the fluid. Design of the shafts  1542 ,  1542 ′,  1562 ,  1562 ′ and the means to couple the motors  1541 ,  1561  to respective gears  1550 ,  1570  can be varied without departing from the spirit of the present disclosure. It should be understood that those skilled in the art will recognize that the fluid drivers  1540 ,  1560  are similar to fluid driver  1260  and that the configurations and functions of fluid driver  1260 , as discussed above, can be incorporated into fluid drivers  1540 ,  1560 . Accordingly, for brevity, fluid drivers  1540 ,  1560  will not be discussed in detail except as necessary to describe this embodiment. In addition, it should be understood that those skilled in the art will also recognize that the operation of pump  1510 , including fluid drivers  1540 ,  1560 , will be similar to that of pump  10  and thus, for brevity, will not be further discussed. In addition, the means for transmitting torque (or power) from the motor to the gear is not limited to a shaft. Instead, any combination of power transmission devices, for example, shafts, sub-shafts, belts, chains, couplings, gears, connection rods, cams, or other power transmission devices can be used without departing from the spirit of the present disclosure. Also, in some exemplary embodiments, motors  1541 ,  1561  can be of an outer rotor motor design that are appropriately configured to respectively rotate the gears  1550 ,  1570 . 
     In an exemplary embodiment, the motor housing  1587  can include a vibration isolator (not shown) between the plate  1580  and the motor housing  1587 . In the exemplary embodiment above, the motor  1541  and the motor  1561  are disposed in the same motor housing  1587 . However, in other embodiments, the motor  1541  and the motor  1561  can be disposed in separate housings. Further, the motor housing  1587  mounting and motor locations are not limited to that illustrated in  FIG. 8 , and the motors and motor housing or housings can be mounted at any appropriate location on the casing  1520  or can even be separate from the casing  1520 . 
     Although the above embodiments were described with respect to an external gear pump design with spur gears having gear teeth, it should be understood that those skilled in the art will readily recognize that the concepts, functions, and features described below can be readily adapted to external gear pumps with other gear designs (helical gears, herringbone gears, or other gear teeth designs that can be adapted to drive fluid), internal gear pumps with various gear designs, to pumps having more than two prime movers, to prime movers other than electric motors, e.g., hydraulic motors or other fluid-driven motors, inter-combustion, gas or other type of engines or other similar devices that can drive a fluid displacement member, and to fluid displacement members other than an external gear with gear teeth, e.g., internal gear with gear teeth, a hub (e.g. a disk, cylinder, other similar component) with projections (e.g. bumps, extensions, bulges, protrusions, other similar structures or combinations thereof), a hub (e.g. a disk, cylinder, or other similar component) with indents (e.g., cavities, depressions, voids or other similar structures), a gear body with lobes, or other similar structures that can displace fluid when driven. Accordingly, for brevity, detailed description of the various pump designs are omitted. In addition, those skilled in the art will recognize that, depending on the type of pump, the synchronizing contact can aid in the pumping of the fluid instead of or in addition to sealing a reverse flow path. For example, in certain internal-gear gerotor designs, the synchronized contact between the two fluid drivers also aids in pumping the fluid, which is trapped between teeth of opposing gears. Further, while the above embodiments have fluid displacement members with an external gear design, those skilled in the art will recognize that, depending on the type of fluid displacement member, the synchronized contact is not limited to a side-face to side-face contact and can be between any surface of at least one projection (e.g. bump, extension, bulge, protrusion, other similar structure, or combinations thereof) on one fluid displacement member and any surface of at least one projection(e.g. bump, extension, bulge, protrusion, other similar structure, or combinations thereof) or indent (e.g., cavity, depression, void or other similar structure) on another fluid displacement member. Further, while two prime movers are used to independently and respectively drive two fluid displacement members in the above embodiments, it should be understood that those skilled in the art will recognize that some advantages (e.g., reduced contamination as compared to the driver-driven configuration) of the above-described embodiments can be achieved by using a single prime mover to independently drive two fluid displacement members. In some embodiments, a single prime mover can independently drive the two fluid displacement members by the use of, e.g., timing gears, timing chains, or any device or combination of devices that independently drives two fluid displacement members while maintaining synchronization with respect to each other during operation. 
     The fluid displacement members, e.g., gears in the above embodiments, can be made entirely of any one of a metallic material or a non-metallic material. Metallic material can include, but is not limited to, steel, stainless steel, anodized aluminum, aluminum, titanium, magnesium, brass, and their respective alloys. Non-metallic material can include, but is not limited to, ceramic, plastic, composite, carbon fiber, and nano-composite material. Metallic material can be used for a pump that requires robustness to endure high pressure, for example. However, for a pump to be used in a low pressure application, non-metallic material can be used. In some embodiments, the fluid displacement members can be made of a resilient material, e.g., rubber, elastomeric material, etc., to, for example, further enhance the sealing area. 
     Alternatively, the fluid displacement member, e.g., gears in the above embodiments, can be made of a combination of different materials. For example, the body can be made of aluminum and the portion that makes contact with another fluid displacement member, e.g., gear teeth in the above exemplary embodiments, can be made of steel for a pump that requires robustness to endure high pressure, a plastic for a pump for a low pressure application, a elastomeric material, or another appropriate material based on the type of application. 
     Pumps consistent with the above exemplary embodiments can pump a variety of fluids. The working fluid (or fluid) to be pumped by the external gear pump  10  can be either high viscosity liquid (e.g. engine oil) or low viscosity liquid (e.g. water). Here, high viscosity means a viscosity higher than 1 mPa·s at 25° C. and low viscosity means a viscosity equal to or lower than 1 mPa·s at 25° C. For example, the pumps can be designed to pump hydraulic fluid, engine oil, crude oil, blood, liquid medicine (syrup), paints, inks, resins, adhesives, molten thermoplastics, bitumen, pitch, molasses, molten chocolate, water, acetone, benzene, methanol, or another fluid. As seen by the type of fluid that can be pumped, exemplary embodiments of the pump can be used in a variety of applications such as heavy and industrial machines, chemical industry, food industry, medical industry, commercial applications, residential applications, or another industry that uses pumps. Factors such as viscosity of the fluid, desired pressures and flow for the application, the design of the fluid displacement member, the size and power of the motors, physical space considerations, weight of the pump, or other factors that affect pump design will play a role in the pump design. It is contemplated that, depending on the type of application, pumps consistent with the embodiments discussed above can have operating ranges that fall with a general range of, e.g., 1 to 5000 rpm. Of course, this range is not limiting and other ranges are possible. 
     The pump operating speed can be determined by taking into account factors such as viscosity of the fluid, the prime mover capacity (e.g., capacity of electric motor, hydraulic motor or other fluid-driven motor, internal-combustion, gas or other type of engine or other similar device that can drive a fluid displacement member), fluid displacement member dimensions (e.g., dimensions of the gear, hub with projections, hub with indents, or other similar structures that can displace fluid when driven), desired flow rate, desired operating pressure, and pump bearing load. In exemplary embodiments, for example, applications directed to typical industrial hydraulic system applications, the operating speed of the pump can be, e.g., in a range of 300 rpm to 900 rpm. In addition, the operating range can also be selected depending on the intended purpose of the pump. For example, in the above hydraulic pump example, a pump designed to operate within a range of 1-300 rpm can be selected as a stand-by pump that provides supplemental flow as needed in the hydraulic system. A pump designed to operate in a range of 300-600 rpm can be selected for continuous operation in the hydraulic system, while a pump designed to operate in a range of 600-900 rpm can be selected for peak flow operation. Of course, a single, general pump can be designed to provide all three types of operation. 
     In addition, the dimensions of the fluid displacement members can vary depending on the application of the pump. For example, when gears are used as the fluid displacement members, the circular pitch of the gears can range from less than 1 mm (e.g., a nano-composite material of nylon) to a few meters wide in industrial applications. The thickness of the gears will depend on the desired pressures and flows for the application. 
     In some embodiments, the speed of the prime mover, e.g., a motor, that rotates the fluid displacement members, e.g., a pair of gears, can varied to control the flow from the pump. In addition, in some embodiments the torque of the prime mover, e.g., motor, can be varied to control the output pressure of the pump. 
     While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.