Abstract:
The subject matter of this specification can be embodied in, among other things, a method that includes a gear pump includes gears having a gear root diameter and teeth having an addendum and pressure angle. A housing includes a fluid inlet and discharge, bearings configured to position the gear teeth in intermeshing contact across a fluid dam. The fluid dam includes a first face arranged at an angle to a split line, spaced apart from a center line at the split line a first distance towards the inlet, and extending from the first gear root diameter away from the center line to the first gear root diameter, and a second face arranged approximately perpendicular to the split line, spaced apart from the center line at the split line a second distance towards the outlet, and extending between the first gear root diameter and the second gear root diameter.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a gear pump, and more particularly to a fluid gear pump that includes a central fluid dam formed to reduce cavitation of the fluid being pumped. 
       BACKGROUND 
       [0002]    Gear pumps use meshed gears to pump fluid by displacement. Gear pumps exhibit positive or fixed displacement performance, meaning they pump a predetermined amount of fluid for each revolution. As the gears rotate they separate on an intake side of the pump, creating a void that is filled by the fluid being pumped. The fluid is carried in the spaces between the gear teeth about the outer peripheries of the gears to a discharge side of the pump. As the gears mesh, the fluid is displaced and flows out the discharge side of the pump. The intermeshing of the gears, along with the speed of rotation of the gears, effectively prevents leakage and backflow of the fluid being pumped. 
         [0003]    Cavitation is a term that is used to describe a phenomenon in which bubbles or “vapor cavities” can form in a fluid due to forces acting upon the fluid. Cavitation can be caused by rapidly dropping the pressure of a fluid. When subjected to higher pressure, the bubbles can implode, generating intense shockwaves. These shockwaves can cause wear in some mechanical devices. Vapor cavities that implode near solid surfaces can cause cyclic stresses through repeated exposure to such implosions. Repeated exposure can lead to surface fatigue of the solid surface and can cause a type of wear also referred to as “cavitation”. This type of wear can occur upon solid surfaces such as pump impellers, generally at locations where sudden changes in the pressures of liquids occur. 
       SUMMARY 
       [0004]    In general, this document describes a fluid gear pump that includes a central fluid dam formed to reduce cavitation of the fluid being pumped. 
         [0005]    In a first aspect, a gear pump includes a first gear having a first axis, a first gear root diameter, and a plurality of first gear teeth having a gear addendum and a gear set pressure angle. The gear pump also includes a second gear having a second axis, a second gear root diameter, and a plurality of second gear teeth having the gear addendum and the gear set pressure angle. A housing includes a fluid inlet and a fluid discharge, a first gear bearing and a second gear bearing configured to position the first gear and the second gear along a bearing center line extending between the first axis and the second axis on opposite sides of a bearing split line, the bearing split line extending through a midpoint between the first gear root diameter and the second gear root diameter and extending perpendicular to the bearing center line, the first gear bearing and the second gear bearing configured to position the first gear teeth and second gear teeth in intermeshing contact, and a central fluid dam. The central fluid dam includes a first face arranged at an angle to the bearing split line, spaced apart from the bearing center line at the bearing split line a first distance towards the fluid inlet, and extending from the first gear root diameter away from the bearing center line to the second gear root diameter, and a second face arranged approximately perpendicular to the bearing split line, spaced apart from the bearing center line at the bearing split line a second distance towards the fluid outlet, and extending between the first gear root diameter and the second gear root diameter. 
         [0006]    Various embodiments can include some, all, or none of the following features. The first distance can be in a range of about 35% to about 65% of a gear addendum away from the bearing center line towards the fluid inlet at the bearing split line. The first distance can be about 47% of the gear addendum. The angle to the center line can range from about the angle of the gear set pressure angle plus 5 degrees to about the angle of the gear set pressure angle minus 5 degrees. The angle to the center line can be about 25 degrees. The central fluid dam can also include a slot formed in the first face proximate the first gear, the slot extending approximately tangent to the first gear root diameter toward the fluid discharge, the slot having a slot width in the range of about 15% to about 44.6% of the gear addendum, and the slot having a slot depth in the range of about 15% to about 45% of a gear addendum. The slot depth can be about 33% of the gear addendum and the slot width can be about 25.3% of the gear addendum. The second distance can be in a range of about 90% to about 115% of a gear addendum away from the bearing center line towards the fluid discharge at the bearing split line. The second distance can be about 103.21% of the gear addendum. The central fluid dam can also include a vent formed in the second face proximate the second gear, the vent having a semi-circular cross-section extending into the second face, the vent having a radius approximately tangent to the second gear root diameter, and the vent being spaced apart from the bearing center line toward the fluid discharge a third distance in a range of about 50% to about 75% of a gear addendum. The third distance can be about 63% of the gear addendum. 
         [0007]    In a second aspect, a method for pumping a fluid includes providing a gear pump having a first gear having a first axis, a first gear root diameter, and a plurality of first gear teeth having a gear addendum and a gear set pressure angle, a second gear having a second axis, a second gear root diameter, and a plurality of second gear teeth having the gear addendum and the gear set pressure angle. The method also includes providing a housing having a fluid inlet and a fluid discharge, a first gear bearing and a second gear bearing configured to position the first gear and the second gear along a bearing center line extending between the first axis and the second axis on opposite sides of a bearing split line, the bearing split line extending through a midpoint between the first gear root diameter and the second gear root diameter and extending perpendicular to the bearing center line, the first gear bearing and the second gear bearing configured to position the first gear teeth and second gear teeth in intermeshing contact, and a central fluid dam. The central fluid dam includes a first face arranged at an angle to the bearing split line, spaced apart from the bearing center line at the bearing split line a first distance towards the fluid inlet, and extending from the first gear root diameter away from the bearing center line to the second gear root diameter, and a second face arranged approximately perpendicular to the bearing split line, spaced apart from the bearing center line at the bearing split line a second distance towards the fluid outlet, and extending between the first gear root diameter and the second gear root diameter. The method also includes providing the fluid at the fluid inlet to a collection of tooth spaces, driving the first gear, driving the second gear with the first gear, and urging the movement of the fluid in the collection of tooth spaces from the fluid inlet to the fluid discharge, wherein backflow of the fluid from the fluid discharge to the fluid inlet is impeded by the central fluid dam. 
         [0008]    Various implementations can include some, all, or none of the following features. The first distance can be in a range of about 35% to about 65% of a gear addendum away from the bearing center line towards the fluid inlet at the bearing split line. The first distance can be about 47% of the gear addendum. The angle to the center line can range from about the angle of the gear set pressure angle plus 5 degrees to about the angle of the gear set pressure angle minus 5 degrees. The angle to the center line can be about 25 degrees. The central fluid dam can also include a slot formed in the first face proximate the first gear, the slot extending approximately tangent to the first gear root diameter toward the fluid discharge, the slot having a slot width in the range of about 15% to about 44.6% of the gear addendum, and the slot having a slot depth in the range of about 15% to about 45% of a gear addendum. The slot depth can be about 33% of the gear addendum and the slot width can be about 25.3% of the gear addendum. The second distance can be in a range of about 90% to about 115% of a gear addendum away from the bearing center line towards the fluid discharge at the bearing split line. The second distance can be about 103.21% of the gear addendum. The central fluid dam can also include a vent formed in the second face proximate the second gear, the vent having a semi-circular cross-section extending into the second face, the vent having a radius approximately tangent to the second gear root diameter, and the vent being spaced apart from the bearing center line toward the fluid discharge a third distance in a range of about 50% to about 75% of a gear addendum. The third distance can be about 63% of the gear addendum. The systems and techniques described herein may provide one or more of the following advantages. First, cavitation of the fluid being pumped can be reduced. Second, erosion of pump components due to fluid cavitation can be reduced. Third, maintenance costs for the pump can be reduced. Fourth, the service life of the pump may be improved. Fifth, the pumping inefficiencies due to erosion of pump components may be reduced. 
         [0009]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional view of an example gear pump assembly. 
           [0011]      FIGS. 2A-2D  are perspective views of the example gear pump assembly. 
           [0012]      FIG. 3  is a side view of a collection of example gear teeth of the example gear pump assembly. 
           [0013]      FIG. 4  is an enlarged cross-sectional view of the example gear pump assembly. 
           [0014]      FIGS. 5 and 6  are enlarged cross-sectional views of a fluid dam of the example gear pump assembly. 
           [0015]      FIG. 7  is a flow diagram of an example process for pumping fluid with the example gear pump assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    This invention relates to a gear pump, and more particularly to a fluid gear pump that includes a central fluid dam formed to reduce cavitation of the fluid being pumped. In general, cavitation can accelerate the wear and reduce the pumping efficiency and lifespan of gear pump components, particularly gear teeth. By reducing cavitation, such wear can be reduced, and the efficiency and lifespan of the pump can be increased. 
         [0017]    Gear pump bearings can have inlet and discharge relief cuts in the face of the floating and stationary bearings. Such relief cuts can allow the fluid being pumped to flow out of the gear mesh to the top and bottom of the gear on the discharge side and flow into the gear mesh from the top and bottom of the gear on the inlet side. Such relief cuts leave some of the bearing material near the center line between the inlet and discharge to create a bearing dam. The bearing dam substantially seals the inlet from the discharge side to maintain pumping efficiency. In some embodiments, the shape of the bearing dam can have a significant impact on gear venting and filling, and therefore may impact the cavitation performance of the gear pump. 
         [0018]    Still speaking generally, the gear pump described in this specification includes a bearing dam with a geometry that reduces fluid cavitation and the damage that can result. The bearing dam geometry can be described using multiple methods to calculate the appropriate scale of the features for a given pump size. One such method is described herein to scale the geometry to a desired pump size by describing the features as a percentage of the gear addendum, which can also be referred to as the ‘standard gear addendum’, and be defined as 1/(gear pitch) for pump gears. 
         [0019]      FIG. 1  is a cross-sectional view of an example gear pump assembly  100 . The assembly  100  includes a housing  102 . The housing  102  includes a driving gear bearing  104  and a driven gear bearing  106 . The driving gear bearing  104  is configured to support a driving gear  114  rotationally at a driving gear axis  124 . The driven gear bearing  106  is configured to support a driven gear  116  rotationally at a driven gear axis  126 . The driving gear  114  includes a collection of driving gear teeth  134  extending radially outward from a root diameter  135 . The driven gear  116  includes a collection of driven gear teeth  136  extending radially outward from a root diameter  137 . 
         [0020]    A bearing center line  150  extends through both the driving gear axis  124  and the driven gear axis  126 . The gear bearings  104 ,  106  are configured such that the driving gear teeth  134  and the driven gear teeth  136  intermesh along the bearing center line  150 . A bearing split line  152  extends perpendicular to the bearing center line  150  through a center point  154  substantially centered between the root diameters  135  and  137  along the bearing center line  150 . 
         [0021]    The housing  102  includes a fluid inlet cavity  160  and a fluid discharge cavity  180 . In some embodiments, the fluid inlet cavity  160  and/or the fluid discharge cavity  180  may be formed as relief cuts in faces of the housing  102  and/or the gear bearings  104 ,  106 . In some embodiments, the fluid inlet cavity  160  and/or the fluid outlet cavity  180  may be molded, cast, etched, or otherwise formed within the housing  102 . The fluid inlet cavity  160  is in fluid communication with a fluid inlet (not shown), and the fluid discharge cavity  180  is in fluid communication with a fluid outlet (not shown). 
         [0022]    The fluid inlet cavity  160  includes a bearing dam inlet face  161 , and the fluid outlet cavity  180  includes a bearing dam outlet face  181 . The bearing dam inlet face  161  and the bearing dam outlet face  181  extend across the bearing split line  161  generally along the bearing center line  160  to form a central fluid dam  158 . In general, the assembly  100  is configured such that fluid pressure within the fluid inlet cavity  160 , coupled with predetermined geometry of the central fluid dam  158 , ports fluid flow to the intermeshed collections of gear teeth  134 ,  136  at predetermined timing to reduce the level of cavitation induced in the fluid being pumped. The aforementioned geometry of the central fluid dam  158  is discussed further in the descriptions of  FIGS. 4-6 . 
         [0023]      FIGS. 2A-2D  show exploded perspective views of the example gear pump assembly  100 . The housing  102  is removed in  FIGS. 2A-2D  to better illustrate the remaining internal components of the assembly  100 . 
         [0024]      FIGS. 2A and 2C  show front and back offset angle perspective views, respectively, of the assembly  100 . As shown in  FIG. 2A , the driving gear bearing  104  of  FIG. 1  includes a driving gear bearing half  204   a  and a driving gear bearing half  204   b . The driving gear  114  includes the driving gear teeth  134 , a central shaft portion  234   a  (e.g., a journal) extending axially from the driving gear teeth  134 , and a central shaft portion  234   b  extending axially from the driving gear teeth  134  opposite the central shaft portion  234   a . The driving gear bearing half  204   a  includes a bore  250   a , and the driving gear bearing half  204   b  includes a bore  250   b . The bore  250   a  is formed to accept insertion of and rotationally support the central shaft portion  234   a , and the bore  250   b  is formed to accept insertion of and rotationally support the central shaft portion  234   b , when the assembly  100  is in its assembled form. 
         [0025]    As shown in  FIG. 2A , the driven gear bearing  106  of  FIG. 1  includes a driving gear bearing half  206   a  and a driving gear bearing half  206   b . The driven gear  116  includes the driven gear teeth  136 , a central shaft portion  236   a  extending axially from the driven gear teeth  136 , and a central shaft portion  236   b  extending axially from the driven gear teeth  136  opposite the central shaft portion  236   a . The driven gear bearing half  206   a  includes a bore  250   c , and the driven gear bearing half  206   b  includes a bore  250   d . The bore  250   c  is formed to accept insertion of and rotationally support the central shaft portion  236   a , and the bore  250   d  is formed to accept insertion of and rotationally support the central shaft portion  236   b , when the assembly  100  is in its assembled form. 
         [0026]    The assembly  100  includes the central fluid dam  158  within the areas generally indicated as area  201  in  FIG. 2A  and area  202  in  FIG. 2C .  FIG. 2B  is an enlarged view of the bearing dam shown in area  201 , and  FIG. 2D  is an enlarged view of the bearing dam shown in area  202 . The central fluid dam  158  includes a central fluid dam half  258   a  that will be described with respect to  FIG. 2B , and a central fluid dam half  258   b  that will be described with respect to  FIG. 2D . 
         [0027]    Referring now to  FIGS. 2B and 2D , the central fluid dam halves  258   a  and  258   b  of the central fluid dam  158  includes an inlet face  260  and an outlet face  261 . The inlet face includes a slot  262  formed as a relief cut in the inlet face  260 . The outlet face  261  includes a vent  263  formed as a relief cut in the outlet face  261 . In the assembled form of assembly  100 , the central fluid dam halves  258   a  and  258   b , the driving gear teeth  134 , and the driven gear teeth  136  provide a barrier that substantially blocks the flow of fluid between the fluid inlet cavity  160  and the fluid discharge cavity  180  along the bearing split line  152  across the bearing center line  150 . The configuration of the inlet face  260 , the outlet face  261 , the slot  262 , and the vent  263  will be discussed further in the descriptions of  FIGS. 4-6 . 
         [0028]      FIG. 3  is a side view of a collection of example gear teeth  300 . In some embodiments, the gear teeth  300  can represent the driving gear teeth  134  and/or the driven gear teeth  136  of the example gear pump assembly  100 . 
         [0029]    The gear teeth  300  extend radially from a gear  302 . In some embodiments, the gear  302  can be the driving gear  114  or the driven gear  116 . The gear  302  has a root diameter  304 , which is the diameter at the base of a tooth space  306 . In some embodiments, the root diameter  304  can be the root diameter  135  or the root diameter  136 . The gear  302  also includes a pitch circle  308 . In some embodiments, the pitch circle  308  can be the circle derived from the number of the gear teeth  300  and a predetermined diametral or circular pitch, and can be the circle on which spacing or tooth profiles is established and from which the tooth proportions can be constructed. 
         [0030]    Each of the gear teeth  300  includes an addendum  310  and a dedendum  312 . The addendum  310  is the height by which the gear tooth  300  projects beyond the pitch circle  308 , while the dedendum  312  is the depth of the tooth space  306  between the pitch circle  308  and the root diameter  304 . As will be discussed in the descriptions of  FIGS. 4-6 , the geometry of the central fluid dam  158  can be partly based on the addendum  310 . 
         [0031]    Each of the gear teeth  300  also includes a pressure angle  320 . The pressure angle  320  is the angle at a pitch point  322  on the pitch circle  308  between the line of pressure which is normal to the tooth surface at pitch point  322 , and the plane tangent to the pitch circle  308 . In involute teeth such as the gear teeth  300 , the pressure angle  320  can be also described as the angle between a line of action  324  and a line  326  tangent to the pitch circle  308 . In some implementations, standard pressure angles can be established in connection with standard gear-tooth proportions. As will be discussed in the descriptions of  FIGS. 4-6 , the geometry of the central fluid dam  158  can be partly based on the pressure angle  320 . 
         [0032]      FIG. 4  is an enlarged cross-sectional view  400  of the example gear pump assembly  100  of  FIG. 1 . The view  400  shows the driving gear  114  and the driven gear  116 , arranged along the bearing center line  150  and on opposite sides of the bearing split line  152 . Visible between the driving gear  114  and the driven gear  116  is the central fluid dam  158 , with the inlet face  260 , the outlet face  261 , the slot  262 , and the vent  263 . 
         [0033]      FIGS. 5 and 6  are enlarged cross-sectional views of a central portion of the central fluid dam  158  of the example gear pump assembly  100  of  FIG. 100 . Referring now to  FIG. 5 , the discharge side of the central fluid dam  158  includes the outlet face  261 . The outlet face  261  is an edge that is substantially perpendicular to the bearing split line  152 . The outlet face  261  is located a distance  510  into the fluid discharge cavity  180  from the bearing center line  150 . In some embodiments, the distance  510  can be about 90% to about 115% of the gear addendum, e.g., the addendum  310  as shown in  FIG. 3 , into the fluid discharge cavity  180  away from the bearing center line  150 . In one example, the addendum can be about 0.1744227 and the distance  510  from the bearing center line  150  to the outlet face  261  can be approximately 0.1800, or approximately 103.21% of the addendum (e.g., 0.1800=approximately 1.0321×an addendum of 0.1744227). 
         [0034]    The vent  263  is formed in the discharge face  261  proximate the driven gear  116  (not shown in  FIG. 5 ). The vent  263  has a generally semi-circular cross-section extending into the discharge face  261  toward the bearing center line  150 . The vent  263  has a radius approximately tangent to the gear root diameter  137  of the driven gear  116  (not shown in  FIG. 5 ), the radius being in a range of about 40% to about 85% of the gear addendum. For example, the addendum can be about 0.1744227 and the radius can be 0.0940 or approximately 54% of the gear addendum (e.g., 0.0940=approximately 0.54×an addendum of 0.1744227). As shown, the vent  263  is spaced apart from the bearing center line  150  toward the discharge face  261   a  distance  520  in a range of about 50% to about 75% of the gear addendum, e.g., the addendum  310  of  FIG. 3 . In some embodiments, the distance  520  can be about 63% of the gear addendum. 
         [0035]    Referring now to  FIG. 6 , the fluid inlet cavity  160  side of the central fluid dam  158  includes the inlet face  260 . The inlet face  260  is a substantially straight edge that intersects the bearing split line  152  at a point represented by a point  610 . The point  610  is located a distance  615  of about 35% to about 65% of the gear addendum, e.g., the addendum  310  of  FIG. 3 , into the fluid inlet cavity  160  away from the bearing center line  150 . For example, the distance  615  from the point  610  on the bearing split line  152  to bearing center line  150  can be 0.0816, or approximately 47% of gear addendum (e.g., 0.0816=approximately 0.47×an addendum of 0.1744227) 
         [0036]    The inlet face  260  is angled into the fluid inlet cavity  160  away from the bearing center line  150  as it approaches the gear root diameter, e.g., the gear root diameter  304  of the driven gear  116  (not shown in  FIG. 6 ), at a face angle  620  approximately equal to the gear set pressure angle, e.g., the pressure angle  320 , +/− approximately 5 degrees. For example, the pressure angle  320  may be 28 degrees, and the face angle  620  can be about 25 degrees (e.g., pressure angle of 28 degrees−3 degrees=25 degrees). 
         [0037]    The slot  262  is formed in the inlet face  260  proximate the driving gear  114  (not shown in  FIG. 6 ). The slot  262  extends approximately tangent to the root diameter  135  of the driving gear  114  (not shown in  FIG. 6 ) away from the fluid inlet cavity  160  and toward the fluid discharge cavity  180 . The slot  262  has a slot width  640  in the range of about 15% to about 44.6% of the gear addendum, e.g., the gear root diameter  304 , and the slot  261  has a slot depth  650  in the range of about 15% to about 45% of the gear addendum. In some embodiments, the slot depth  650  of the slot  261  can be about 33% of the gear addendum. In some embodiments, the slot width  640  of the slot can be about 25.3% of the gear addendum. 
         [0038]      FIG. 7  is a flow diagram of an example process  700  for pumping fluid with the example gear pump assembly  100  of  FIG. 1 . The process  700  begins when a gear pump is provided ( 710 ). In some implementations, the gear pump can be the gear pump assembly  100  of  FIG. 1 . Fluid is provided ( 720 ) at a fluid inlet to a collection of tooth spaces. For example, fluid can be provided at the fluid inlet to the fluid inlet cavity  160 , where the fluid can flow into the tooth spaces  306  of  FIG. 3 . 
         [0039]    The first gear is then driven ( 730 ). For example, the driving gear  114  can be spun by an external force. The second gear is driven ( 740 ) with the first gear. For example, the driving gear teeth  134  can be intermeshed with the driven gear teeth  136  to transfer motion of the driving gear  114  to the driven gear  116 . 
         [0040]    Movement of the fluid in the collection of tooth spaces is urged ( 750 ) from the fluid inlet to the fluid discharge. Backflow of the fluid from the fluid discharge to the fluid inlet is impeded by the central fluid dam. For example, as the driving gear  114  and the driven gear  116  rotate, fluid occupying the tooth spaces  306  between the gear teeth  134 ,  136 , the gear roots  135 ,  137 , and the housing  102 , is urged from the fluid inlet cavity  160  to the fluid discharge cavity  180  and out the fluid discharge. Backflow of fluid from the fluid discharge cavity  180  to the fluid inlet cavity  160  is substantially blocked by the central fluid dam  158  and the intermeshed gear teeth  114 ,  116  across the bearing split line  152 . 
         [0041]    Although a few implementations have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.