Abstract:
A chamfer is formed in bearing blocks on either side of the hydraulic fluid inlet. The chamfer allows a family of pumps with varying hydraulic inlet sizes to have similar bearing block pressure profiles. The chamfer prevents the build up of hydraulic pressure immediately adjacent to the hydraulic inlet below a given inlet size so that the bearing block pressure profile for a family of pumps with different inlet sizes more nearly matches the pressure profile of the largest opening used in a particular design family. The sealing gasket on the side of the bearing block opposite the gears is designed to accommodate this single pressure profile. The result is an improved bearing life and reduced slippage over an entire family of pumps or motors of similar design.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Not applicable 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     No applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to rotary gear pumps and motors in general, and to the type having pressure balanced bearing block seals in particular. 
     So-called external gear pumps are used in hydraulic power applications, as both motors and pumps. Reasonable efficiency, long life, and low-cost are normally the design criteria for these widely used pumps and motors. An external gear pump has a pair of intermeshing gears. The gears incorporate shafts which are parallel and which are mounted in bearing blocks which seal the ends of the gears. The gears are contained within a housing and hydraulic oil is supplied at an inlet and is pumped to an outlet on the other side of the meshing gears. 
     External gear pumps or motors, when used in hydraulic power applications, operate with pressures of up to several thousand pounds per square inch (psi). The high differential pressure and the importance of efficiency makes pump slip a concern. Slip is the fluid flow which leaks from the high-pressure side of the pump or motor to the low-pressure side. The design of external gear pumps minimizes pump slip by careful attention to pump design details. One major source of pump slip is the seal between the end faces of the rotors/gears and opposed bearing blocks. The opposed bearing blocks contain the bearings into which the shafts on which the gears are mounted turn. 
     The bearing blocks are positioned above and below the rotors in a twin lobe passageway formed in the motor housing. Oil pressure is allowed to reach the distal sides of the bearing blocks, forcing them toward the end faces of the rotors. However, the bearing blocks necessarily must be supported with uneven pressure so as to match the pressure developed within the pump as the rotors turn to carrying fluid from the low-pressure side of the pump to the high-pressure side. If the pressure on the sides of the bearing blocks opposed to the end faces of the rotor are not adequately matched to the pressures developed between the gear teeth of the pump, excessive slippage or bearing block face wear will result. Proper balancing of pressure on the side of the bearing blocks opposite to the end faces of the rotor is typically accomplished by a sealing gasket which supplies different pressures to different portions of the bearing blocks. 
     The tooling costs for the fabrication of bearing blocks is high, as the finish and dimensions of the block require tight tolerances. Thus, a single block design is often used in several different pump designs. Typically a family of hydraulic pumps will be designed to accommodate a range of hydraulic fluid inlet sizes. The inlet size of the hydraulic pump causes a variation in the hydraulic loading on the bearing blocks. Therefore, the design of the sealing gasket has to the present time been a compromise. 
     What is needed is a family of external hydraulic gear pumps which can accommodate a variety of hydraulic fluid inlets with a single bearing block design which has better bearing block sealing and reduced bearing block face wear. 
     SUMMARY OF THE INVENTION 
     The external hydraulic gear pump of this invention incorporates a chamfer in the bearing blocks on either side of the hydraulic fluid inlet. The chamfer functions to cause a family of pump designs with varying hydraulic inlet sizes, to have similar bearing block pressure profiles. The chamfer prevents the buildup of hydraulic pressure immediately adjacent to the hydraulic inlet below a given inlet size so that the bearing block pressure profile for a family of pumps with different inlet sizes more nearly matches the pressure profile of the largest opening used in a particular design family. The sealing gasket on the side of the bearing block opposite the gears is designed to accommodate this single pressure profile. The result is an improved bearing life and reduced slippage, over an entire family of pumps and motors of similar design. 
     It is an object of the present invention to reduce the cost of producing a family of hydraulic pumps or motors. 
     It is another object of the present invention to provide a family of hydraulic pumps or motors wherein the needed hydraulic sealing pressure remains substantially constant over a range of hydraulic fluid inlet sizes. 
     It is a further object of the present invention to provide a family of hydraulic pumps or motors with reduced wear. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged isometric view of a bearing block incorporating the chamfer of this invention which allows more uniform pressure compensation for motors with varying inlet sizes. 
     FIG. 2 is an exploded isometric view of the pump with this invention showing the location and arrangement of the bearing blocks and bearing block hydraulic balancing seals. 
     FIG. 3 is a schematic illustrative view shown superimposed on a top view of the bearing block, the gear teeth, the block chamfer, three inlet ports of varying size, and the prior art balancing seal, and the improved balancing seal, which are positioned on the bottom of the bearing block, but shown superimposed on the top of a bearing block. 
     FIG. 4 is an exploded isometric view of an alternative embodiment pump with this invention showing the location and arrangement of the bearing blocks and bearing block hydraulic balancing seals. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to FIGS. 1-4 wherein like numbers refer to similar parts, a pump  22 , is shown in FIG.  2 . The pump  22  has a housing  24  which has a central bore  26  in which are mounted a first gear  28  mounted to a first shaft  30 , and a second gear  32  mounted to a drive shaft  34 . The drive shaft  34  has a spline  36  to allow the shaft to be connected to a mechanism to be driven, in the case of a motor, or to a drive source such as an electric motor in the case of the pump. The first shaft  30 , has a first bearing surface  38  which rides on a first bearing  40  in a first bearing block  42 . The first shaft  30  has a second bearing surface  44  which rides in a second bearing  46  in a second bearing block  48 . In a similar way the drive shaft  34  has a first bearing surface  50  which rides in a bearing  52  in the first bearing block  42  and a second bearing surface  54  which ride in a bearing  56  in the second bearing block  48 . 
     The pump housing  24  has an inlet  58  through which hydraulic fluid is supplied. As shown in FIG. 3, the first gear  28  and the second gear  32  intermesh so that only a small volume of hydraulic fluid moves toward the inlet  58  indicated by an arrow. The individual teeth  60  of the gears  28  and  32  rotate along the walls  62  of the central bore  26  of the housing  24  as indicated by arrows  64 . As the gear teeth  60  rotate they sweep along a substantial volume of hydraulic fluid which flows to the outlet  66  of the pump  22 . 
     As the gear teeth  60  rotate they move hydraulic fluid from the low-pressure side  68  to the high-pressure side  70  of the pump  22 . Pressure begins to build up in the hydraulic fluid when it becomes trapped between adjacent gear teeth  60  and the housing  24 . Thus, the beginning of pressure buildup starts when a volume of fluid is no longer in communication with low-pressure side  68  of the pump  22 . Pressure is built up along an arc such as that labeled α in FIG.  3 . The sealing surface  72  of the bearing block  42  as shown in FIG.  1  and as represented in FIG. 3 is sealed against the open sides  74  of the gears  28 ,  32 . In order to form a good seal, the bearing blocks  42 ,  48  are forced against the gear open sides  74  by hydraulic pressure which has access to the distal sides  76  of the bearing block  42 . 
     A sealing gasket  80 , as shown in FIG. 2, engages the distal sides  76  of the bearing blocks  42 ,  48 . The seal formed by the gasket  80  divides the bottom surface into a portion  82  which communicates with the high-pressure side of the pump, and a portion  84  which is in communication with the low-pressure side of the pump. The seal  80  is designed so that the high-pressure and low-pressure portions  82 ,  84  balance the pressure profile on the sealing surfaces  72  of the bearing blocks  42 ,  48 . The design of the seals  80  is complicated by the desirability of manufacturing a family of pumps with identical mechanical components differing only in the size of the hydraulic inlet  58 . 
     FIG. 1 shows a chamfer  88  which relieves a portion of the sealing surface  72  of the bearing block  42 . The effect of the chamfer  88  is to control the position where pressure begins to build up as the gear teeth  60  rotate as shown by arrow  64  toward the high-pressure side of the pump  22 . The bearing block  42  has a vertical surface  90  which engages the central bore  26  of the housing  24 . The bearing block has cylindrical surfaces  92  which form the waist of the figure eight of the bearing block  42 . The top and bottom of the figure eight have portions  94  which are relieved. The relieved portions  94  communicate with the high-pressure side  70  of the pump  22  as shown in FIG.  3 . The relieved portions  94  are in communication with a high-pressure side  70  of the pump  22  because the high-pressure fluid forces the bearing block  42  toward the low-pressure side of the pump housing  24 , opening up a small gap between the bearing block  42  and the wall  62  of the housing  24 . 
     FIG. 3 shows the size and positioning of three possible inlet openings  58 . For purposes of explanation a pair of lines  96  define an inlet of ⅞ inch diameter, a second pair of lines  98  define an inlet of 1{fraction (1/16)} inch diameter, and the third pair of lines  100  define an inlet of 1{fraction (5/16)} inch diameter. The right side of FIG. 3 shows three regions of pressure buildup corresponding to each of the three different diameters. Δ 1  is the region of pressure buildup which corresponds with an inlet diameter of 1{fraction (5/16)} inches; Δ 2  is the region of pressure buildup which corresponds with an inlet diameter of 1{fraction (1/16)} inches; and Δ 3  is the region of pressure buildup which corresponds with an inlet diameter of ⅞ inches. These pressure buildup regions correspond to the prior art. With prior art designs a sealing gasket  102  was selected based on Δ 3  which corresponded to the smallest inlet diameter  96 . This results in the prior art design having substantially sub-optimal bearing support for the larger inlets  98 ,  100 . In other words the oil pressure profile on the distal sides  76  in the prior art approach does not match the oil pressure on the sealing sides  72 , for the larger in the openings. 
     As can be seen from FIG. 3 the buildup of pressure within the space between gear teeth  60 , begins when a space is isolated from the inlet  58 , and is complete when the space between gear teeth  60  communicates with, the high-pressure side which occurs when the space between gear teeth  60 , overlies the relieved portion  94  of the bearing blocks  42 ,  48 . Isolation from the inlet  58  is controlled by either the inlet or the chamfer  88 . The effect of the chamfer  88  is to substantially eliminate the effect the inlet diameter has on the beginning of pressure buildup. 
     The effect of the chamfer  88  is shown on the left-hand side of FIG. 3 where pressure buildup regions α and φ are very nearly the same. The pressure buildup region φ is controlled by the size of the chamfer, and is the same for the ⅞ inch inlet  96  and the 1{fraction (1/16)} inch inlet  98 . The largest inlet  100  at 1{fraction (5/16)} is slightly larger than the chamfer  88  and results in the pressure buildup region α. Because the pressure buildup regions α and φ are very nearly the same, a sealing gasket  104  can be designed which is more optimal for hydraulic pumps with a range of inlet sizes. In the example shown in FIG. 3, the prior art gasket  102  optimized for the ⅞ inch inlet  96 , extends about 71 degrees from the symmetry  106 , while the improved sealing gasket  104  extends only about 54.6 degrees from the symmetry axis  106 . 
     So that the same bearing block  42  may be used in pumps and motors, and two identical bearing block  42  may be used in a single pump or motor, the bearing blocks  42 ,  48  are identical and symmetric such that a chamfer  88  is positioned next to both the inlet  58  and the outlet  66 , however when positioned near the outlet the chamfer has little or no effect. 
     In the same way, the sealing gasket  104  is made to function symmetrically by duplicating it about the symmetry axis  106 , shown in FIG.  3  and thus in actually use has the shape shown in FIG. 2 for the sealing gasket  80 . 
     It should be understood that the chamfer  88  differs substantially from features used in prior art motor designs which prevented the over-rapid buildup of pressure as the teeth  60  move into the region of pressure buildup. Such prior art features include a very shallow groove in the sealing surface  72 , designed to prevent a pressure spike due to the incompressibility of the hydraulic fluid. The chamfer  88  differs from such a feature designed to prevent chatter due to the incompressibility of the working fluid, because it substantially changes the pressure buildup profile, while the anti-chatter features only prevent a pressure spike, but do not allow free flow of fluid into the gap between gear teeth. The chamfer  88  as, is shown in FIG. 1 as a simple relieving of the surface  72  which allows free flow of hydraulic the chamfer  88  does not result in the removal of so much material that the vertical surfaces  90  which engages the bearing blocks  42 ,  48  with the walls  62  of the housing  24  are significantly reduced in bearing area. 
     FIG. 4 shows an alternative embodiment hydraulic pump  122 , where the arrangement of the bearing blocks  142 ,  148  and the seals  180  are optimized for a pump in which the gears  128 ,  132  rotate in a single direction. Because the pump gears rotate only in a single direction a “3” shaped seal  180  is all that is necessary. Because the pump  122  rotates in only a single direction chamfers  188  are only required on the low-pressure side of the pump  122 . 
     The low-pressure side of the pump  122  is considerably lower pressure generally than the low-pressure side of a similar hydraulic motor. The hydraulic pump  122  of FIG. 4 utilizes this fact to facilitate lubrication of the shaft bearings  140 ,  156 . Provision is made on the bearing surfaces  172  of the bearing blocks  142 ,  148  to drain oil to the low-pressure side from the shaft bearings  140 ,  156 , by connecting the shaft bearings with the low-pressure side of the pump to facilitate bearing lubrication. This is accomplished by passageways  155  in the bearing surfaces  172  of the bearing blocks  142 ,  148  and on the underside of the blocks by similar passages  157 . 
     The high-pressure openings formed by the end portions  94  of the bearing blocks in FIG. 1 are designed to allow rapid filling of the gear teeth with hydraulic fluid. Openings at the end of the bearing blocks are larger in a motor where it is desirable to fill the gears rapidly with fluid, than in a pump  122  where filling is more readily affected. 
     The precise shape of the U-shaped indentations  159  at the neck of the figure eight shaped bearing blocks as shown in FIG. 4 are designed for tool path economy and positioning exactly where the spaces between the gear teeth  160  are connected with the high- and low-pressure sides of the pump  122 . 
     The pump housing  124  in FIG. 4 has a high-pressure outlet (not shown) to which hydraulic fluid is pumped. The chamfer  188 , which controls the pressure profile on the bearing blocks, faces the low-pressure inlet  166 . 
     It should be understood that although a hydraulic pump is described in the claims, the term hydraulic pump should be understood to include a hydraulic motor, because the hydraulic pump and motor can be identical in structure, much as an electric motor can operate as a generator. 
     It should also be understood that the term fluid inlet refers to the low-pressure side of the pump, and should also be understood as referring to the low-pressure (fluid outlet) side of a hydraulic motor, so that the invention when claimed as a motor reads on a hydraulic pump. Similarly the term fluid outlet refers to the high-pressure side of the hydraulic pump and should also be understood as referring to the high-pressure (fluid inlet) side of a hydraulic motor, so that the invention when claimed as a pump reads on a hydraulic motor. Moreover, fluid described as flowing from the low-pressure side to the high-pressure side in a pump, should be understood to include fluid flowing from the high-pressure side to the low-pressure side in a motor. 
     It should be understood that the hydraulic motor or pump can be used in a wide variety of applications. See, for example, U.S. Pat. No. 6,010,321 to Forsythe et al. which is incorporated herein by reference. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces such modified forms thereof as come within the scope of the following claims.