Patent Publication Number: US-6659748-B1

Title: Axial compensation in an inner geared pump for a closed circuit

Description:
The invention relates to an internal geared machine, especially an internal geared pump. Such machines are known from numerous publications, for example EP 0 563 661 A1 and its counterpart. U.S. Pat. No. 5,354,188, which is incorporated by reference herein. 
     Said pump has axially moving discs, so-called axial discs bordering on the rotating toothed parts of the internal toothed ring gear and the pinion. Said axial discs are movable in axial direction. They are pressed against the rotating toothed parts by means of an axial pressure derived from the working pressure so as to compensate the gap between the housing and the toothed part. 
     With frequency converters a constant displacement pump can be turned into a variable capacity pump by means of speed control. Such a pump has considerable advantages over a variable piston pump. The noise level during operation is much lower, it has a longer service life and uses less energy. 
     Problems always arise when machines of the above described type have to operate in reverse and when the pressure range changes. For example, there are numerous applications where it is desirable to have an internal geared pump operating both clockwise and counterclockwise. So far, no solution has been found for the cases where such a pump has to operate in a closed circuit. 
     For high pressure applications an axial compensation is also required. Both axial pressure surfaces of said axial discs are pressurized at the same time. The side connected with high pressure is pressurized with high pressure and the other side is pressurized with the feeder pressure, which is approx. 10 bar. 
    
    
     The invention is discussed in more detail by means of the drawing showing the following: 
     FIG. 1 shows an axial-vertical sectional view of an internal geared pump. 
     FIG. 2 shows a circuit with an internal geared pump of the invention. 
     FIG. 3 shows an axial sectional view of a section of a first version of an internal geared pump. 
     FIG. 4 again shows an axial sectional view of a section of a second version of an internal geared pump. 
     FIG. 5 shows an axial disc in an axial sectional view in accordance with the illustrations in FIGS. 3 and 4. 
     FIG. 6 is a top view of the left surface of the axial disc of FIG.  5 . 
     FIG. 7 is a top view of the right surface of the axial disc of FIG.  5 . 
    
    
     The internal geared pump shown in FIG. 1 comprises the following substantial components: an external toothed pinion  1 , an internal toothed ring gear  2 , a filling consisting of two filler pieces  3 ,  4 , a stop pin  5  and a housing  6 . 
     The pinion  1  is seated eccentrically relative to the ring gear  2 . See center M 1  of the pinion and center M 2  of the ring gear. A straight line in a dot-and-dash pattern is applied through the two centers M 1  and M 2 . Said line defines a plane of symmetry whose relevance will be discussed below. 
     The sickle-shaped space between the pinion  1  and the ring gear  2  is filled with a filling. Said filling comprises the two filler pieces  3 ,  4 . The stop pin  5  is mounted in the housing  6  and has a certain play. The illustration shows that the stop pin has two supporting surfaces  5 . 1 ,  5 . 2 . The front ends of the two filler pieces  3 ,  4  are supported against the supporting surfaces  5 . 1 ,  5 . 2 . 
     Furthermore, the two filler pieces  3 ,  4  are longitudinally divided in a manner known in the art. Therefore, they are based on an inside part  3 . 1 ,  3 . 2  and  4 . 1 ,  4 . 2 , respectively, but each filler piece  3 ,  4  could just as well consist of one single part. 
     The housing has two pressure connections  6 . 1 ,  6 . 2 . The two pressure connections are provided on both sides of the plane of symmetry  7 . The housing also has a leakage outlet  6 . 3  which, in this case, is located precisely on the plane of symmetry  7 . 
     In detail, FIGS. 3 and 4 show the following: Axial discs  21 ,  22  are provided between the two walls of the housing  6  and the pinion  1 . In the first version as per FIG. 3, axial pressure fields  23 ,  24  are incorporated directly in the axial pressure discs  21 ,  22 . As is well known and disclosed in the aforementioned U.S. Pat. No. 5,354,188, the pressure fields bear on the walls of housing  6  and press axial discs  20 ,  21  against gears  1  and  2 . 
     In the second version as per FIG. 4, the axial fields  25 ,  26  are incorporated in the walls of the housing  6 . 
     Said axial pressure fields are also seen in FIG. 6 where they are shown as axial pressure fields  23 . 
     The axial discs  21 ,  22  are provided with control fields  27 ,  28  on their inner sides, i.e. on the sides facing the pinion  1 . Again, as disclosed in U.S. Pat. No. 5,354,188, control fields  27  and  28  apply pressure on discs  21  and  22  that oppose pressure fields  23  and  24 . Also see FIG.  7 . According to the invention, the control fields  27 ,  28  have a special feature: they are provided with slots. See slots  30  in FIG.  7 . The arrangement is such that the recesses formed by the slots  30  are in communication with the recesses formed by the control fields  27 ,  28 . Through-bores  31 ,  32  are also provided to enable the pressure medium coming from the internal gear pump to enter the spaces on the opposite sides of discs  21  and  22  to create the pressure fields. See FIGS. 6 and 7. 
     Note the symmetrical configuration with regard to the axial pressure fields, the control fields and the control slots. The control slots  30  are configured such that the volume of the recesses they are forming increases starting from the tip of each control slot toward the control field. As a result, the pressure is building relatively slowly in the control fields so as to prevent excessive wear or even damage to the machine. 
     Between the axial pressure fields  23 ,  24  and the respective walls of the housing  6 , or between the axial pressure fields  25 ,  26  and the axial discs  21 ,  22  a so-called axial piston can be provided, which substantially has the same shape as the respective control field  23  shown in FIG.  6 . 
     FIG. 2 illustrates internal geared pump  14  in an exemplary enclosed circuit arrangement to drive reversible piston  11 . 1  disposed in cylinder  11 . 2 . The input of pump  14  is connected to sump  18  and the output  16  connected through check valves  19  and  20  in lines  12  and  13  to power hydraulic device  11 . Pressure relief valve  15  is connected in the return line  17  to sump  18 .