Abstract:
A fluid metering/pumping device preferably includes a series of intermeshing gears. The fluid metering/pumping device includes an inlet port or area adjacent the intermeshing portion of each pair of gears within the series adjacent the point at which the pair of gears diverge. The device further includes a pressure loaded floating shoe adjacent the intermeshing portion of each pair of gears within the series adjacent the point at which the pair of gears converge. The device further includes a piston subjected to discharge pressure at each discharge port which conveys hydraulic pressure to each floating shoe. The device is configured to convey liquid from a main inlet stream of liquid, through the inlet ports or areas, and out of one or more discharge ports at substantially equal rates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. § 119(e) of Provisional Application Ser. No. 60/987,954 filed on Nov. 14, 2007, entitled FLUID METERING AND PUMPING DEVICE and whose entire disclosure is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    This invention relates generally to devices for regulating the flow of liquids, and more particularly, to flow dividers for dividing a stream of liquid, such as liquid fuel, into two or more smaller streams of liquid and to pumps for pumping a single flow of liquid to one or more locations in substantially accurate flow rates. 
         [0004]    2. Description of Related Art 
         [0005]    When working with liquids, it is often desirable to divide a single stream of liquid into several smaller, equal streams of liquid or several substantially accurate streams of liquid. This is typically done using a fluid metering device such as liquid flow divider, an equal-flow pump, or an equal-flow liquid motor. 
         [0006]    A typical prior art liquid flow divider is taught in U.S. Pat. No. 4,531,535 to Kiernan (hereinafter also referred to as “Kiernan”). As shown in FIG. 4 of Kiernan, such liquid flow dividers typically include multiple dividing units of two intermeshed spur gears. The various dividing units are typically linked together by a drive train that may include a drive line, drive shafts, or a sun gear. As a result of this linkage, all of the gears within the various dividing units rotate at substantially the same speed. 
         [0007]    Within each individual dividing unit, a liquid inlet port is positioned on one side of the intermeshing portion of the pair of spur gears, and a liquid discharge port is positioned on the other side of the intermeshing portion of the pair of spur gears. A housing is provided that conforms to the exterior portions of the spur gears that are not in communication with the liquid inlet port or the liquid discharge port. All of the various dividing units&#39; liquid inlet ports are in communication with a single, pressurized liquid source. 
         [0008]    In operation, pressurized liquid from the pressurized liquid source first enters each dividing unit&#39;s liquid inlet port. The pressurized liquid then causes the gears in each dividing unit to rotate in opposite directions so that each gear&#39;s teeth carry liquid from the liquid inlet port, around the exterior portion of the gear, and into the liquid discharge port. Because all of the dividing gears within the liquid flow divider are preferably the same size and shape, and because the gears are linked together by a central drive train so that all of the gears rotate at the same rate, the flow rate of liquid around each of the flow divider&#39;s various gears is identical to the flow rate of liquid around each of the flow divider&#39;s other gears. Since each dividing unit includes two gears that convey liquid from the dividing unit&#39;s liquid inlet port to the dividing unit&#39;s liquid discharge port, liquid flows through each dividing unit at a rate that is equal to two times the rate at which the liquid flows around a single gear. 
         [0009]    Accordingly, prior art liquid flow dividers are typically designed to include one dividing unit for each equal discharge stream that the flow divider is to produce. For example, if the flow divider is to produce ten equal discharge streams of liquid, the flow divider will include ten separate dividing units. As noted above, these dividing units are linked together by a drive train, such as a drive line or a central sun gear. 
         [0010]    U.S. Pat. No. 6,857,441 B2 to Flavelle shows away to simplify the drive train in such a flow divider. However, such prior art liquid flow dividers, including the flow dividers described above, have significant disadvantages. First, because the drive trains within these flow dividers are typically less robust than the other components within the flow dividers, the drive trains often break or otherwise malfunction. Secondly, a tolerance stack-up between the mating parts can result in excessive running clearances between the gear outer diameter (OD) and the case bore interior diameter (ID) which, in turn, results in excessive fluid slip between the inlet and discharge side of the gears and produces inaccuracies in the liquid flow streams. 
         [0011]    Accordingly, there is a need for improved liquid flow dividers, pumps and other fluid metering devices with parts having tolerances that can be more easily manufactured but still result in very close clearances between the gear OD and the case bore ID to reduce the fluid slip through the clearances which greatly improves the accuracy of the liquid flow stream or streams. 
         [0012]    A prior art approach to reducing the clearances between the gears and the housing in a pump is shown in U.S. Pat. No. 4,127,365 to Martinet al. (hereinafter also referred to as “Martin”). In Martin, a moveable suction shoe surrounds the meshing point of the gears, and the shoe also covers the suction port, where liquid enters the pump. The higher pressure at the pump&#39;s outlet bears on the full outside surface area of the shoe, and pushes it firmly against the ends of the gears and against the tips of the gear teeth. This greatly reduces slip in the pump, but causes a problem that the difference between suction pressure and discharge pressure increases because an increasingly large load has to be borne by the tips of the gear teeth as the shoe is pressed harder and harder against the gears. In practice, this effect limits the suction shoe concept to pumps that only operate at low differential pressures. Also, the suction shoe cannot be used in a flow divider as described above because, unlike a pump, either the inlet or outlet port of a flow divider may be at a higher pressure than the other port. 
         [0013]    In Martin, the lower pressure must at all times remain on the inside of the shoe. If the pressure inside the shoe becomes greater than the pressure outside the shoe, then the internal pressure will push the shoe away from the gears until the pump ceases moving any fluid. So, there is also a need for a way to balance the forces on the shoe, and to be able to control the forces whatever the pressure change at the pump or flow divider&#39;s port may be. All references cited herein are incorporated herein by reference in their entireties. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    The exemplary embodiments include a fluid metering or pumping device including first and second gears, a housing and a floating shoe. The second gear is disposed adjacent the first gear and intermeshes with the first gear. The housing surrounds the gears and seals them from outside liquid contact. Preferably, the housing is not in close contact with the gears, but still forms a chamber around the gears that is in liquid communication with a port that may be used to allow liquid either into or out of the pumps or fluid metering device. The floating shoe partially extends into the port of the pump, forming a first chamber defined by the port opening, the part of the shoe extending into the port, and the interior walls of the housing. Preferably, the floating shoe is not connected to the chamber surrounding the gears, but is in contact with both gears. The floating shoe forms a second chamber also defined by the outer surface of the gears between the contact point between the gears and the second chamber, and the gear mesh point. This second chamber is in liquid communication with the port that the shoe partially extends into, with the cross sectional areas of the second chamber formed by the gears and shoe, and the part of the shoe extending into the port being equal. In other words, the liquid pressure applied to the outward facing surface of the part of the floating shoe extending into the port is balanced with (e.g., equal to with a minimal force to maintain contact between the shoe and the gears) the liquid pressure applied to the inward facing surface of the shoe in the second chamber. By balanced, it is understood that some minimal force is preferred between the shoe and the gears to keep the gears in contact with the shoe even when the remaining pressures applied to the outward facing surface of the shoe extending into the port and to the inward facing surface of the shoe are equal. This minimal force may be applied by an additional force applied inward onto the shoe or outward against the gears. Alternative approaches for providing this minimal contact force include adjusting the surfaces of the shoe to acquire a slightly greater inward pressure than outward pressure, or a compression spring. 
         [0015]    Additional gears may be arranged adjacent the first two gears with at least one of the additional gears intermeshed with one of the first two gears and also intermeshed with each other to form a line or circle of intermeshed gears. In this scenario, each pair of gears contacts a separate floating shoe and forms multiple pumps or fluid metering devices. 
         [0016]    According to another exemplary embodiment, the floating shoe described above is divided into two members. The first member includes a part of the shoe that contacts the gears, and the second member includes a part of the shoe which extends into one of the liquid ports of the device. Both members are free to move towards or away from each other depending on the force exerted on them by the liquid in the two ports of the device. In this exemplary embodiment, which is configured with cross sectional areas of the inside facing walls of the shoe contacting the gears, with the outward facing wall of the part of the shoe extending into one port, and with the manner that the two pieces of the shoe fit together, a small centering force always presses the part of the shoe in contact with the gears towards the gears, regardless of which port contains a higher liquid pressure. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements, and wherein: 
           [0018]      FIG. 1  is a cross sectional side view of an exemplary embodiment of the invention perpendicular to a gears&#39; axis of rotation; 
           [0019]      FIG. 2  is a cross sectional side view of the embodiment of  FIG. 1  parallel to the gears&#39; axis of rotation; 
           [0020]      FIG. 3  is a cross sectional side view of a two piece shoe in accordance with the preferred embodiments of the invention; 
           [0021]      FIG. 4  is a cross sectional side view of a two piece shoe in accordance with the preferred embodiments of the invention; 
           [0022]      FIG. 5  is a cross sectional side view of a multi-section pump or flow divider in accordance with the preferred embodiments of the invention; and 
           [0023]      FIG. 6  is a cross sectional side view of a multi-section pump or flow divider with a central gear in accordance with the preferred embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The present invention provides a fluid metering device, such as a liquid flow divider or pump, that has tolerances that are more easily manufactured and have no tolerance stack-up between the gear OD and the pressure loaded shoe ID that will increase the fluid slip between the gear OD and the pressure loaded shoe ID. While not being limited to a particular theory, each gear in the metering or pumping unit intermeshes with adjacent gears, which eliminates the need for a separate drive train between the elements of multi-element units that are typically less robust than the other components in the unit. More particularly, a preferred liquid metering device includes two or more gears located adjacent to each other that intermesh with the adjacent gears. 
         [0025]      FIGS. 1 and 2  depict an exemplary fluid metering device  10  shown in cross-section perpendicular and parallel, respectively, to a gear&#39;s axis of rotation as will be described in greater detail below. As can best be seen in  FIG. 1 , the fluid metering device  10  includes a first gear  12 , a second gear  14 , a housing  16  and a floating shoe  18 . The second gear  14  is disposed adjacent the first gear  12  and intermeshes with the first gear. The housing  16  surrounds the gears and seals them from outside liquid contact exterior of the housing, except through the first and second port as will be discussed in greater detail below. Preferably, the housing  16  is not in close or touching contact with the gears  12 ,  14 , but still forms a first chamber  20  around the gears that is in liquid communication with a first port  22  that may be used to allow liquid either into or out of the fluid metering device  10 . 
         [0026]    The floating shoe  18  partially extends into the first port  22  of the housing  16 . Preferably, the floating shoe  18  is not connected to the first chamber  20  surrounding the gears  12 ,  14 , but is in contact with both gears. The floating shoe defines a second chamber  24  in liquid communication with the first port  22  that the shoe  18  partially extends into via a central bore  38  of the shoe. This second chamber  24  is around the gear mesh point and around one side of the gears. That is, the floating shoe  18  in contact with the pair of gears (e.g., the first and second gears  12 ,  14 ) contacts the tips  26  of the gear teeth  28 , and also covers the outer edge  30  of the gears to beyond their point of intermeshing, thus forming the second chamber  24  as a sealed cavity in the space between the pair of gears and the floating shoe. This second chamber  24  is connected, through the inside of the shoe  18 , to the first port  22  of the device  10 , with a first section  32  of the shoe extending out of the chamber  20  surrounding the gears  12 ,  14  and into the first port. 
         [0027]    While not being limited to a particular theory, the area of the outward facing or exterior wall of the first section  32  of the floating shoe  18  that extends into the first port  22  is preferably equal the cross-sectional surface area of the second chamber, including the interior wall of a second part  34  of the floating shoe  18  aligned with the tips  26  of the gear teeth  28  that is exposed to the pressure in the chamber  20  having the two gears  12 ,  14  and the interior surface space of the shoe. This preferred structural arrangement results in no net force on the shoe  18  from changing pressures at either the first port  22  or a second port  36  of the fluid metering device  10  as shown, for example, in  FIGS. 1 and 2 . 
         [0028]    It is noted that, as discussed above for the preferred embodiments, a minimal pressure should be maintained between the floating shoe  18  and the gears  12 ,  14  to ensure continuous contact between the shoe and the gears. This minimal pressure may be maintained by, for example, added pressure on the exterior wall of the first section  32  of the floating shoe  18 , or pressure within the first chamber  20  applied to the exterior facing wall of the shoe within the first chamber. Pressure may be added to the exterior wall of the first section  32  by added fluid pressure or mechanical pressure; such as a compression spring applied in a compressed state between the exterior wall of the first section  32  and a cover  56  over the first port  22  (see  FIG. 5 ). It is more appropriate to add mechanical pressure in very high pressure situations to offset any hysteresis in the device. The net effect is a balancing of the shoe in the device  10  and in contact with the gears regardless of changing pressures at either the first port  22  or a second port  36 . 
         [0029]    Sometimes it is desirable to have a controllable net force on the shoe, regardless of which port has the higher pressure. In this case, a two-piece shoe  40  as shown, for example, in the fluid metering device  10  of  FIGS. 3 and 4 , can be used. The two-piece shoe  40  is similar to the floating shoe  18 , and includes a first member  42  and a second member  44  cooperatively engageable and sharing a central bore  46  providing fluid communication between the first port  22  and the second chamber  24 . If the pressure is higher in the first port  22  that the two-piece shoe  40  extends into, the two members  42 ,  44  are pushed together—as can best be seen in FIG.  3 —and the resultant force on the floating two-piece shoe  40  is a small force proportional to the difference in pressure between the first port  22  and the second port  36 . 
         [0030]    Still referring to  FIGS. 3 and 4 , the differences in area inside the chamber  20  between the gears  12 ,  14  and the floating two-piece shoe  40 , and the area of the two-piece shoe exposed to the pressure in the port  22  can be biased to keep a small centering force that holds the two-piece shoe firmly against the gears. If the pressure in the port  22  is less than the pressure in the chamber  20  applied to the two-piece shoe  40 , the two parts of the two-piece shoe separate slightly. That is, the first member  42  of the shoe  40  may move toward the port  22  up to there the retaining ring  35  abuts the wall of the housing  16  adjacent the ring, yet the second member  44  remains in contact with the gears due to the pressure in the first chamber  20  applied toward the gears. Here, the differences in area inside and outside the two-piece shoe provide a small controllable centering force to hold the two-piece shoe against the gears, even with a reversal of the pressure difference. That is, the second member  44  is urged into contact with the gears regardless of which port contains a higher liquid pressure. 
         [0031]    It is understood that additional gears may be arranged adjacent the first two gears  12 ,  14  with at least one of the additional gears intermeshed with its adjacent one of the first two gears and also intermeshed with other additional gears to form a plurality of pairs of intermeshed gears. In this scenario each pair of gears contacts a separate floating shoe and forms multiple pumps or fluid flow dividers. In other words, when the fluid metering device includes multiple pumps or flow dividers, the gears may be arranged in a line, as can be seen for example in  FIG. 5 . 
         [0032]      FIG. 5  depicts a fluid metering device  50  with a plurality of gears forming adjacent alternate pairs of gears. For example, gear  12  interconnects with gear  14  to form one pair of gears, and gear  12  also interconnects with a gear  52  to form an adjacent alternate pair of gears. Each pair of adjacent alternate gears shares a respective floating shoe  40 , with each floating shoe having first and second members  42 ,  44  as discussed above, and with successive floating shoes located on alternate sides of the line of gears. Each floating shoe  40  is confined within the housing  54  by a grommet or cover  56  including an aperture  58  preferably aligned with the central bore  46  of the shoe. The cover  56  is a fastener attached to the housing  54  by any approach readily understood by a skilled artisan (e.g., friction, adhesion, force, threaded engagement) and may similarly partially cover the first ports  22  shown in the other figures. While  FIG. 5  shows gears arranged in a line, it is understood that the plurality of gears can be arranged in other forms while remaining within the scope of the invention. For example, the gears could be arranged in a curve, circle, polygon or some combination thereof while forming adjacent pairs of gears in contact with respective floating shoes. 
         [0033]      FIG. 6  depicts yet another exemplary embodiment, where the fluid metering device  60  is configured as a series of gears  62  arranged around a central gear  64  and all intermeshing with the central gear. In this example, the fluid metering device  60  includes a plurality of floating shoes  66 , with each floating shoe again connected to a pair of gears (e.g., the central gear  64  and one of the gears  62 ). Each floating shoe  66  includes a central bore  68  providing fluid communication between the first port  22  and the second chamber  24 , as is consistent with the floating shoes  18 ,  40  discussed above. While not being limited to a particular theory, in this embodiment, each gear  62  shares its matched floating shoe  66  with the central gear  64 . While the central gear  64  is shown significantly larger than each gear  62 , the relative proportions of the gears is not critical to the scope of the invention. It is understood that the relative proportions of the gears is influenced by several factors, including but not limited to the number and size of the floating shoes  66 , the alignment of the first ports  22  and floating shoes within the housing  70 , and the size of the paired gear (e.g., the central gear  64  for each of the series of gears  62 , and the respective gear  62  for the central gear  64 ). 
         [0034]    As can best be seen in  FIG. 2 , each floating shoe  18 ,  40  and  66  preferably connects to side plates  15  as would readily be understood by a skilled artisan. The side plates  15  extend from the floating shoe  18 ,  40 ,  66  about opposite sides of the gears  12 ,  14 ,  62 ,  64  to keep the gears laterally in place, that is, to prevent the gears from sliding off their intermeshed engagement with adjacent gears. It is also noted that each floating shoe also includes an elastic o-ring  25  and a retaining ring  35 . The elastic o-ring  25  provides a liquid seal between the floating shoe and its respective housing  16 ,  54 ,  70 . The retaining ring  35  keeps the floating shoe in a preferred orientation extending into the first port  22  preventing its extension further into the first port beyond the abutment of the retaining ring and the inner wall of the housing. 
         [0035]    It is understood that the fluid metering and pumping device described and shown are exemplary indications of preferred embodiments of the invention, and are given by way of illustration only. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, the gears may have teeth arranged preferably in a 1:1 ratio with matching teeth from adjacent gears, or may have some other intermeshed relationship, such as a 2:1 or 1:2 ratio with teeth from adjacent gears as long as the gears maintain their rotational communicative relationship. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only, and not for purposes of limitation. Without further elaboration, the foregoing will so fully illustrate the invention that others may, by applying current or future knowledge; readily adapt the same for use under various conditions of service.