Abstract:
An axial piston pump of the swash-plate variety having a rotating cylinder block and pistons movable in a longitudinal direction within bores formed in the block, and having a reversing capacitance for reducing pressure pulsations. For the further reduction of such pulsations, one or more channels, each having an associated discharge opening, are formed into a web of the valve plate of the pump to sequentially couple the reversing capacitance into fluid communication with the cylinder bores passing across the web.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Application No. DE 198 59 328.7, filed Dec. 22, 1998, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an axial piston pump of a swash plate variety having a driven rotating cylinder block or drum and a large number of cylinder bores arranged radially therein, each of the bores being separated within the cylinder drum by a web of cylinder drum material. Pistons are arranged in each of the cylinder bores to be reciprocatingly movable in an axial, linear direction relative to the rotation of the cylinder drum between, at the end of a de-compression stroke, a bottom dead center position and, at the end of a compression stroke, a top dead center position. A valve plate having a low pressure connection port and a high pressure connection port also is provided, with the low and high pressure connection ports being separated in the valve plate by a web of valve plate material. The rotation of the cylinder drum causes the cylinder bores to be aligned in alternating fashion with the low-pressure connection port and the high-pressure connection port. Concurrently, the cylinder bores sweep past the web in the valve plate separating the low and high pressure connection ports, whereupon a reversing capacitance in fluid communication with the sweeping cylinder bore via at least one channel is supplied through the valve plate to mitigate the effects of a pressure pulsation. 
     The structure and operation of axial piston pumps of the type herein involved is described in further detail in the publication “Measures For The Reduction Of High-Pressure-Side Pulsations Of Hydrostatic Swash Plate Units” by Marcus Jarchow, Dissertation 1997, Aachen Institute of Technology, Verlag Mainz, Aachen, and in the following U.S. Pat. Nos.: 3,250,227; 3,667,867; 3,774,505; 4,037,521; 4,212,596; 4,366,627; and 5,123,815. The Jarchow publication deals in particular with the problem of high-pressure-side pulsations, and sets forth a solution which involves a reversing capacitance. In this regard, in order to avoid compression oil flows when each individual cylinder bore of the cylinder block is aligned with the high-pressure connection port, it is necessary to adjust the pressure forming in the cylinder bore through the compression movement of the piston to the pressure prevailing on the high-pressure side of the control base in its high-pressure connection port. Through the use of a reversing capacitance, this adjustment is effected by admitting compression oil under high pressure into the cylinder bore. This reversing capacitance is formed in the control base via a channel in communication with the cylinder bores of the rotating cylinder block and, respectively, via an additional channel with the high-pressure connection port. 
     It has been observed, however, that the undesirable high-pressure-side pulsations continue to occur in attenuated form even with the use of a reversing capacitance. In this regard, the clearing of the channel extending from the reversing capacitance through the web between each of the cylinder bores results in an abrupt pressurization of the cylinder bore as the compression oil is admitted under high pressure from the reversing capacitance. An object of the present invention therefore is to further reduce the development of pulsations in an axial piston pump, and to ensure a less abrupt alignment of the cylinder bore with the high-pressure connection port. 
     BROAD STATEMENT OF THE INVENTION 
     Broadly, the present invention is directed to the provision of one or more channels, each having an associated discharge opening, which are formed in the web of the valve plate to couple the reversing capacitance in fluid communication sequentially with each of the cylinder bores passing across the web. 
     According to one exemplary embodiment of the invention, at least two such channels are provided which are arranged on an arc defined by the low and high pressure connection ports. Optionally, the discharge openings and their associated channels may have the same or different diameters. 
     According to another exemplary embodiment of the invention, particularly if two channels are provided, the discharge openings of the channels are connected with each other via a recess formed in the web of the valve plate, such recess surrounding the discharge openings. 
     For a further improvement of a positioning of the cylinder bores the discharge openings of the channels extending from the reversing capacitance to each of the cylinder bores via the web formed on the valve plate are equipped with adjoining guide-in notches and/or guide-out notches. In one exemplary embodiment, the first discharge opening relative to the direction of rotation of the cylinder block is provided with a longer guide-in notch and a shorter guide-out notch adjoining the discharge opening. In addition, in the case of two channels being formed through the valve plate web, the second discharge opening relative to the direction of rotation of the cylinder block is provided with a shorter guide-in notch and a longer guide-out notch. Similarly, if a recess is formed surrounding the discharge openings of the two channels, this recess may be provided with a guide-in notch and/or a guide-out notch. 
     The present invention, accordingly, comprises the apparatus and method possessing the construction, combination of elements, and arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantages of the invention includes an axial piston pump construction which reduces undesirable high-pressure-side pulsations. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein: 
     FIG. 1 shows a swash plate-type axial piston pump in a generally schematic representation; 
     FIG. 2 shows the reversal of one of the pistons of the pump of FIG. 1 while occluded by a supplied reversing capacitance; 
     FIG. 3 is a top view of the fixed valve plate of the pump of FIG. 1 showing an arrangement of the discharge openings of the channels provided to couple the cylinder bores into fluid communication with the reversing capacitance; 
     FIG. 4 shows an alternative embodiment of the discharge opening arrangement of FIG.3; and 
     FIG. 5 shows another alternative embodiment of the discharge opening arrangements of FIGS.  3  and  4 . 
    
    
     The drawings will be described further in connection with the following Detailed Description of the Invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     An important element of the axial piston pump construction shown in FIG. 1 is a cylinder block or drum  10  which will be readily understood to be rotatable by a drive (not shown) coupled to the drum via a shaft  9 . Cylinder bores  11  are spaced-apart radially in the outer area of the cylinder block, with a piston  12  being received with each of the bores  11  to be reciprocatingly movable in a linear, axial direction. A ball,  13 , of each of the pistons  12  is supported on one face of cylinder block  10  within the socket  14  of a guide shoe  15  disposed outside of cylinder block  10 . Guide shoe  15  bears upon a rotationally stationary swash plate  16  such that the rotation of cylinder block  10  in relation to the swash plate  16  can be converted into a linear motion of the pistons  12  in cylinder bores  11 , which motion is directed axially relative to the axis of rotation of block  10 . 
     A valve plate  20  is arranged fixedly on the face of cylinder block  10  opposite swash plate  16 . High pressure connection ports, commonly referenced at  18 , are formed to extend along an arc over a portion of the circumference of the valve plate  20 , with corresponding low pressure connection ports, referenced at  19  in the views of FIGS. 2-5, also being formed in the control plate for the low-pressure range. As may be seen with additional reference to FIGS. 2-5, connection ports  18  and  19  are separated a web  26 , of material in valve plate  20  (FIG.  2 ). 
     A transition of the connection of cylinder bore  11  with low-pressure connection port  19  and high pressure connection port  18  is shown schematically in FIG. 2, such reversal being effected by means of a reversing capacitance. For this purpose, a reversing capacitance  23  is formed in connection plate  17  from which the two channels commonly referenced at  24  extend to the face of cylinder block  11  and empty into a corresponding discharge opening, commonly referenced at  27  in each of the views of FIGS. 3-5. A resistance,  25 , each is provided in each of the channels  24 . 
     Looking next to FIG. 2, the control sequence of the pump of FIG. 1 is illustrated with reference to three cylinder bores  11  and their associated pistons  12  which are adjacently-arranged in cylinder block  10 . Each of the cylinder bores  11  is separated from an adjacent bore by a web, commonly referenced at  21 , of the cylinder block material. In the left-most illustration, the cylinder bore  11  communicates with low-pressure connection port  19 , with piston  12  still moving in the direction of its bottom dead center position such that oil is suctioned from the low-pressure connection port  19 . Continuing with the center illustration of FIG. 2, piston  12  is now moved to its bottom dead center position  22  wherein the discharge opening  27  of channel  24  is occluded by web  21 . As the rotation of cylinder block  10  continues, the discharge opening  27  of channels  24  is unblocked, and the pressure in the cylinder bore  11  is increased with the incipient piston stroke via the supply of compression oil from reversing capacitance  23 . Concluding with the right-most, the cylinder bore  11  is now in communication with the high-pressure connection port  18  as the compression stroke of piston  12  proceeds in the direction of its top dead center position. However, the pressure in bore  11  previously has been increased to such an extent that during the connection of the bore  11  to the high-pressure connection port  18 , the pressure surge and consequently the pulsation in rotating cylinder block  10  is correspondingly reduced. 
     An arrangement according to the present invention of two or more channels  24  is next revealed in the several views of FIGS. 3-5. As may be seen in FIG. 3, two discharge openings  27  of two corresponding channels  24  (FIG. 2) can be arranged in web  26  of valve plate  20 . Web  26  separates low-pressure connection port  19  and high-pressure connection port  18 , with channels  24  being arranged on the partial arc defined by connection ports  18  and  19 . 
     With reference now to FIG. 4, discharge openings  27  may be seen to be provided with correspondingly-arranged guide-in notches  28  and guide-out notches  30 , respectively, the first discharge opening  27  being provided with a guide-in notch  28  having a longer extension and a shorter guide-out notch  30  in the direction of rotation of cylinder block  10  from low-pressure connection port  19  to high-pressure connection port  18 . In turn, the second discharge opening  27  located forwardly in the direction of rotation first has a shorter guide-in notch  28  and a longer guide-out notch  30  directed towards high-pressure connection port  18 . These guide-in and guide-out notches  28  and  30  are each variable in number, shape, position and size and can thus be designed appropriately to optimize the reversing process. 
     Another exemplary embodiment of the invention is shown in FIG. 5 wherein the discharge openings  27  of two channels  24  are in communication with each other via a surrounding recess  27  to effect a still further graduation of the activation characteristics. Preferably, recess  29  may be designed to be kidney or oblong-shaped and to be arranged on the arc defined by connection ports  18  and  19 . Additionally, guide-in and guide-out notches may be provided at the beginning and ending portions of recess  29 . 
     Although not shown in greater detail, it will be appreciated that discharge openings  27  and channels  24  may be configured as having the same or different diameters. Discharge openings  27  and their adjoining channels  24  also may have variable diameters, and further may be arranged in varied angular positions relative to each other. 
     As it is anticipated that certain changes may be made in the present invention without departing from the precepts herein involved, it is intended that all matter contained in the foregoing description shall be interpreted as illustrative and not in a limiting sense. All references cited herein are expressly incorporated by reference.