Hydrostatic piston machine unit

Abstract

A hydrostatic piston machine unit, which is in particular designed as a hydrostatic axial piston machine unit, comprises at least two driving mechanisms that can be driven synchronously and have displacement pistons which each perform a reciprocating motion in operation and are provided for delivery into a common pressure line. The hydrostatic piston machine unit has a jointly assigned precompression volume for the at least two driving mechanisms.

Claims

1. A hydrostatic piston machine unit comprising: a first driving mechanism including first displacement pistons that are arranged in a first rotating cylinder part that defines a plurality of first cylinder spaces, each first cylinder space is configured to be alternately connected via a first respective connecting opening to a first low-pressure control port and a first high-pressure control port of a first stationary control part, on which two first changeover regions are arranged between the first low-pressure control port and the first high-pressure control port, the first displacement pistons configured to reverse direction of motion within the two first changeover regions at respective first dead center positions; a second driving mechanism including second displacement pistons that are arranged in a second rotating cylinder part that defines a plurality of second cylinder spaces, each second cylinder space configured to be alternately connected via a second respective connecting opening to a second low-pressure control port and a second high-pressure control port of a second stationary control part, on which two second changeover regions are arranged between the second low-pressure control port and the second high-pressure control port, the second displacement pistons configured to reverse direction of motion within the two second changeover regions, each of the first and second displacement pistons performing a reciprocating motion in operation so as to deliver fluid into a common pressure line or a common pressure connection via the respective first or second high-pressure control port; at least one cavity defining at least one precompression volume that is jointly assigned to both the first and second driving mechanisms; a first connecting line arranged in one of the two first changeover regions so as to connect the first cylinder spaces to a first cavity of the at least one cavity; and a second connecting line arranged in one of the two second changeover regions so as to connect the second cylinder spaces to the first cavity, wherein the first cavity is connected permanently in a restricted manner to the common pressure connection via a third connecting line.

2. The hydrostatic piston machine unit according to claim 1, wherein: the at least one cavity includes the first cavity and a second cavity; one of the first and second cavities defines a first precompression volume of the at least one precompression volume provided for changeover from the first and second low-pressure control ports to the first and second high-pressure control ports; and the other of the first and second cavities defines a second precompression volume of the at least one precompression volume provided for changeover from the first and second high-pressure control ports to the first and second low-pressure control ports.

3. The hydrostatic piston machine unit according to claim 1, wherein: each of the first respective connecting openings is configured to be connected in the one of the first changeover regions to the at least one cavity via a first outlet, which is arranged in the one of the first changeover regions, of the first connecting line, at the earliest when a connection to one of the first high-pressure control port and the first low-pressure control port is still restricted and before there is an overlap with the other of the first high-pressure control port and the first low-pressure control port; and each of the second respective connecting openings is configured to be connected in the one of the second changeover regions to the at least one cavity via a second outlet, which is arranged in the one of the second changeover regions, of the second connecting line, at the earliest when a connection to one of the second high-pressure control port and the second low-pressure control port is still restricted and before there is an overlap with the other of the second high-pressure control port and the second low-pressure control port.

4. The hydrostatic piston machine unit according to claim 3, wherein: within a first angular range, one of the first respective connecting openings is open simultaneously to the first cavity and to a first respective control port of the first high-pressure and low-pressure control ports to which a changeover is being made, and to match a pressure in the first cavity to a pressure in the first respective control port, pressure fluid flows between the first respective control port and the first cavity via the one of the first respective connecting openings and via the first connecting line; and within a second angular range, one of the second respective connecting openings is open simultaneously to the first cavity and to a second respective control port of the first high-pressure and low-pressure control ports to which a changeover is being made, and to match a pressure in the first cavity to a pressure in the second respective control port, pressure fluid flows between the second respective control port and the first cavity via the one of the second respective connecting openings and via the second connecting line.

5. The hydrostatic piston machine unit according to claim 1, wherein: the hydrostatic piston machine unit is an axial piston machine unit of swash plate design; and the first rotating cylinder part and the second rotating cylinder part are arranged in axial alignment with one another.

6. The hydrostatic piston machine unit according to claim 5, wherein the first and second rotating cylinder parts are driven via a common shaft.

7. The hydrostatic piston machine unit according to claim 1, wherein the first and second driving mechanisms each have the same number of respective first and second displacement pistons and are rotationally offset relative to one another by a half piston pitch in such a way that each of the first displacement pistons reverses direction of motion in a center of an angular interval between two of the second displacement pistons, and each of the second displacement pistons reverses direction of motion in a center of an angular interval between two of the first displacement pistons.

8. The hydrostatic piston machine unit according to claim 1, wherein: the first and second driving mechanisms are rotationally offset relative to one another in such a way that each of the first displacement pistons reverses direction of motion in a center of an angular interval between two of the second displacement pistons, and each of the second displacement pistons reverses direction of motion in a center of an angular interval between two of the first displacement pistons; and alternately either only one of the first cylinder spaces or only one of the second cylinder spaces is connected directly to the first cavity.

9. The hydrostatic piston machine unit according to claim 1, further comprising: a common housing accommodating the first and second driving mechanisms, the common housing defining the at least one cavity; a further pressure connection, which is common to the first and second driving mechanisms; and the pressure connection and the further pressure connection are formed on the common housing.

10. The hydrostatic piston machine unit according to claim 1, wherein the hydrostatic piston machine unit is a hydrostatic axial piston machine unit.

11. The hydrostatic piston machine unit according to claim 1, wherein the first cavity has a greater cross-sectional area than the first and second connecting lines.

12. A hydrostatic piston machine unit comprising: a first driving mechanism including first displacement pistons that are arranged in a first rotating cylinder part that defines a plurality of first cylinder spaces, each first cylinder space is configured to be alternately connected via a first respective connecting opening to a first low-pressure control port and a first high-pressure control port of a first stationary control part, on which two first changeover regions are arranged between the first low-pressure control port and the first high-pressure control port, the first displacement pistons configured to reverse direction of motion within the two first changeover regions at respective first dead center positions; a second driving mechanism including second displacement pistons that are arranged in a second rotating cylinder part that defines a plurality of second cylinder spaces, each second cylinder space configured to be alternately connected via a second respective connecting opening to a second low-pressure control port and a second high-pressure control port of a second stationary control part, on which two second changeover regions are arranged between the second low-pressure control port and the second high-pressure control port, the second displacement pistons configured to reverse direction of motion within the two second changeover regions, each of the first and second displacement pistons performing a reciprocating motion in operation so as to deliver fluid into a common pressure line or a common pressure connection via the respective first or second high-pressure control port; at least one cavity defining at least one precompression volume that is jointly assigned to both the first and second driving mechanisms; a first connecting line arranged in one of the two first changeover regions so as to connect the first cylinder spaces to a first cavity of the at least one cavity; and a second connecting line arranged in one of the two second changeover regions so as to connect the second cylinder spaces to the first cavity, wherein the first cavity defines a first precompression volume of the at least one precompression volume, and the first precompression volume corresponds to a volume of one of the first and second cylinder spaces.

13. The hydrostatic piston machine unit according to claim 12, wherein the first cavity is connected permanently in a restricted manner to the common pressure connection via a third connecting line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An illustrative embodiment of a hydrostatic piston machine according to the disclosure which is designed as a variable-displacement double axial piston pump of swash plate design is illustrated in simplified form in the drawings. The disclosure is now explained in greater detail with reference to the figures of these drawings, in which:

(2) FIG. 1 shows a longitudinal section through the illustrative embodiment perpendicularly to the pivoting axes of the swash plates, and

(3) FIG. 2 shows a schematic illustration with a plan view of the control ports of both component pumps and the connection of two precompression volumes.

DETAILED DESCRIPTION

(4) The hydrostatic axial piston machine according to the figures is provided as a variable-displacement axial piston pump for the purpose of supplying pressure medium to one or more hydraulic loads, e.g. hydraulic cylinders, in an open hydraulic circuit. It is embodied as a swash plate design. An open hydraulic circuit means that the axial piston pump receives pressure medium via a low-pressure or suction connection and discharges it to the hydraulic loads via a high-pressure connection and that the pressure medium flowing away from the hydraulic loads flows back into a tank. The volume flow of the axial piston pump is proportional to the drive speed and to the displacement, which is the quantity of pressure medium delivered in each revolution.

(5) The hydrostatic axial piston pump shown is a “double pump”, in which a first driving mechanism 9 and a second driving mechanism 10 are accommodated in a common multipart housing 8. The housing 8 has a central housing part 11, on which a high-pressure connection 12 and a low-pressure connection 13 are formed as work connections on opposite side walls and which has a central passage for a drive shaft 14 with an axis of rotation 15. Extending out from the low-pressure connection 13 in the central housing part 11 are two low-pressure passages 16, of which one emerges at a first end wall 17 perpendicular to the axis of rotation 15 and one emerges at a second end wall 18 of the central housing part 11, said second end wall being situated opposite the first end wall and likewise being perpendicular to the axis of rotation 15. Extending out from the high-pressure connection 12 in the central housing part 11 are two high-pressure passages 19, of which one emerges at the first end wall 17 and one emerges at the second end wall 18 of the central housing part 11. The outlets of the passages 16 and 19 in the end walls 17 and 18 are curved in the form of circular arcs and, for example, extend over an angle of approximately 120 degrees. The side walls having the work connections 12 and 13, and the passages 16 and 19, extend outside the section plane of FIG. 1 and are therefore indicated only by dashed lines.

(6) A first pot-shaped housing part 25 is flanged to the central housing part 11 on one side, that facing in the direction of the axis of rotation 15, and a second pot-shaped housing part 26 is flanged to the central housing part 11 on the opposite side. The first driving mechanism 9 is accommodated by the first pot-shaped housing part 25, and the second driving mechanism 10 is accommodated by the second pot-shaped housing part 26.

(7) Driving mechanism 9 comprises a cylinder barrel 30, in which circular-cylindrical cylinder spaces 31 which extend at a slight slope to the axis of rotation 15 and are open on that side of the cylinder barrel which faces away from the central housing part 11, are uniformly distributed and lie on the same pitch circle. In the text which follows, the cylinder spaces are referred to as cylinder bores because of their circular-cylindrical cross section, even if they are not or not exclusively produced by boring from solid material. A displacement piston 32 is guided in a longitudinally movable manner in each cylinder bore 31. In housing part 25, a swash plate 33 is mounted so as to be pivotable about a pivoting axis 34 perpendicularly intersecting the axis of rotation 15. In operation, the displacement pistons 32 are supported on the swash plate 33 via piston shoes 35 held on the pistons. The cylinder barrel 30 is coupled to a component shaft 36, passing through it, of the drive shaft 14 in a manner secure against relative rotation but allowing axial movement, and in operation is rotated about the axis of rotation 15 by means of the drive shaft 14.

(8) In the axial direction, the cylinder barrel 30 is supported on a control plate 37, which forms a control part and is held nonrotatably on the end wall 17 of the central housing part 11. The control plate 37 has two arc-shaped control slots 38 and 39 passing through it, wherein the low-pressure control slot 38 is open toward the outlet of one low-pressure passage 16 extending in the central housing part 11, and the high-pressure control slot 39 is open toward the outlet of one high-pressure passage 19 extending in the central housing part 11. Thus, the low-pressure control slot 38 is the low-pressure control port, and the high-pressure control slot 39 is the high-pressure control port. The high-pressure control slot 39 exposed to the high pressure in operation is divided by narrow webs into a plurality of partial slots to ensure that the control plate 37 has a high strength in the region of the control slot 39.

(9) An elongate connecting opening 40 provides a fluidic connection from each cylinder bore 31 to that end of the cylinder barrel 30 which faces the control plate 37. Said barrel rests by means of the end having the connecting openings 40 against the control plate 37 and, in operation, slides across the control plate. The two control slots 38 and 39 of the control plate 37 are situated on the same pitch circle as the connecting openings 40. In operation, there is a high pressure (e.g. a pressure of 200 bar) in the high-pressure control slot 39, while, in operation, there is a low pressure (e.g. a pressure of less than 5 bar), in particular tank pressure, in the low-pressure control slot 38. Between the high-pressure control slot 39 and the low-pressure control slot 38 there are two changeover regions on the control plate, namely a changeover region 41, in which the connecting openings 40 change over from an open fluidic connection to the low-pressure control slot 38 to an open fluidic connection to the high-pressure control slot 39, and a changeover region 42, in which the connecting openings 40 change over from an open fluidic connection to the high-pressure control slot 39 to an open fluidic connection to the low-pressure control slot 38.

(10) It is also within the two changeover regions that the dead center positions in the stroke motion of the pistons are located, at which the pistons are plunged furthest into a cylinder bore (inner dead center position) or project furthest out of a cylinder bore (outer dead center position). In the present case, the outer dead center position is in changeover region 41, and the inner dead center position is in changeover region 42.

(11) In FIG. 1, two displacement pistons 32 are depicted in the section plane. For the sake of simplicity, the illustration is chosen so that it is not possible for two displacement pistons simultaneously to be in the section plane, even if there is an uneven number of displacement pistons and the angular interval between the displacement pistons is the same.

(12) The component shaft 36 of the drive shaft 14 is rotatably mounted in the central housing part 11 and, in a manner not shown specifically, in the base of the first pot-shaped housing part 25 by means of rolling bearings.

(13) Driving mechanism 10 comprises a cylinder barrel 50, which is of identical design to the cylinder barrel 30 of the first driving mechanism 9 and in which cylinder bores which extend at a slight slope to the axis of rotation 15 and are open on that side of the cylinder barrel which faces away from the central housing part 11, are uniformly distributed and lie on the same pitch circle. A displacement piston 52 is guided in a longitudinally movable manner in each cylinder bore. In housing part 26, a swash plate 53 of identical design to swash plate 33 is mounted so as to be pivotable about a pivoting axis 54 perpendicularly intersecting the axis of rotation 15 and parallel to pivoting axis 34. In operation, the displacement pistons 52 are supported on the swash plate 53 via piston shoes 55 held on the pistons. Cylinder barrel 50 is coupled to a component shaft 56, passing through it, of the drive shaft 14 in a manner secure against relative rotation but allowing axial movement, and in operation is rotated about the axis of rotation 15 in synchronism with cylinder barrel 30 by means of the drive shaft 14.

(14) The component shaft 56 of the drive shaft 14 is rotatably mounted in the central housing part 11 and, in a manner not shown specifically, in the base of the second pot-shaped housing part 26 by means of rolling bearings. Within the central housing part 11, the two component shafts 36 and 56 are coupled to one another for conjoint rotation via a coupling sleeve 43.

(15) In the axial direction, the cylinder barrel 50 is supported on a control plate 57, which, just like control plate 37, is formed with a high-pressure control slot 39, with a low-pressure control slot 38 and with two changeover regions 41 and 42 and is arranged as a mirror image of control plate 37.

(16) The two cylinder barrels 30 and 50 are arranged offset relative to one another by half a piston pitch in the direction of rotation. In the case of five cylinder bores, for example, the piston pitch is 72 degrees. In corresponding fashion, the offset between the two cylinder barrels would be 36 degrees. In the case of six cylinder bores, for example, the piston pitch is 60 degrees. In corresponding fashion, the offset between the two cylinder barrels would be 30 degrees. In the case of nine cylinder bores, for example, the piston pitch is 40 degrees. In corresponding fashion, the offset between the two cylinder barrels would be 20 degrees.

(17) Otherwise, driving mechanism 10 operates in exactly the same way as driving mechanism 9, and therefore reference can be made to the corresponding description in respect of driving mechanism 9.

(18) In order, during the changeover from the low-pressure control slot 38 to the high-pressure control slot 39, to keep pressure peaks in the cylinder bores 31, nonuniform flow and pressure pulsations in the high-pressure control slot 39 and hence in the high-pressure connection 12 of the axial piston pump and in the entire hydraulic system within which the axial piston pump is used to a low level, a fluid volume 65 of defined size is provided, which is designed as a cavity in the central housing part 11 and from which a bore 66 passing through the central housing part 11 and control plate 37 and having an outlet 67 in changeover region 41 starts. After a dead center position of the displacement pistons 32, the outlet 67 is closer to the high-pressure control slot 39 than to the low-pressure control slot 38. The bore 66 has a certain restricting effect or a restrictor is arranged therein. Starting from fluid volume 65 there is a further bore 68, which passes through the central housing part 11 and control plate 57 and has an outlet 69 in changeover region 41 of control plate 57. After a dead center position of the displacement pistons 52, the outlet 69 is likewise closer to the high-pressure control slot 39 than to the low-pressure control slot 38 of control plate 57. Bore 68 also has a certain restricting effect or is provided with a restrictor.

(19) As an option, fluid volume 65 can additionally also be connected permanently directly to the high-pressure side of the pump. This is indicated in FIG. 2 by a bore 70, in which a restrictor is arranged or which acts as a restrictor.

(20) During the operation of the pump, the connecting openings 40 in the cylinder barrels 30 and 50 move over the control slots 38 and 39 and the changeover regions 41 and 42. Initially, a connecting opening 40—say connecting opening 40 of cylinder barrel 30—is still open to the low-pressure control slot 38. The tank pressure prevails in the corresponding cylinder bore 31. There is high pressure in fluid volume 65.

(21) As a cylinder barrel 30 is rotated further, the connecting opening 40 leaves the low-pressure control slot 38 of control plate 37 and comes into overlap with the outlet 67 of bore 66, initially with a connection to the low-pressure control slot 38 that is at most still greatly restricted, with the result that a fluidic connection is established between cylinder bore 31 and fluid volume 65. Pressure fluid then flows from fluid volume 65 into cylinder bore 31, with the result that the pressure therein rises and the pressure in fluid volume 65 falls. The inflow of pressure fluid into cylinder bore 31 ends when the pressure prevailing in said bore is the same as that prevailing in fluid volume 65. The pressure medium in cylinder bore 31 is now precompressed, and therefore a fluid volume of the same type as fluid volume 65 is also referred to as a precompression volume.

(22) As cylinder barrel 30 is rotated further, the connecting opening 40 reaches the high-pressure control slot 39 and increasingly covers the latter. As a result, a fluidic connection is created not only between the high-pressure control slot 39 and cylinder bore 31 but also between the high-pressure control slot 39 and fluid volume 65, with the result that pressure fluid then flows out of the high-pressure control slot 39 into cylinder bore 31 and into fluid volume 65. When the connecting opening 40 comes out of overlap with the outlet 67 of bore 66, there is once again high pressure in fluid volume 65.

(23) A connecting opening 40 in cylinder barrel 50 then leaves the low-pressure control slot 38 of control plate 57 and, with a connection to the low-pressure control slot 38 that is initially at most still greatly restricted, comes into overlap with the outlet 69 of bore 68, with the result that a fluidic connection is established between the corresponding cylinder bore 31 and fluid volume 65. Pressure fluid then flows from fluid volume 65 into the cylinder bore 31 of cylinder barrel 50, with the result that the pressure in the cylinder bore rises and the pressure in fluid volume 65 falls. The inflow of pressure fluid into cylinder bore 31 ends when the pressure prevailing in said bore is the same as that prevailing in fluid volume 65. The pressure medium in cylinder bore 31 is then precompressed.

(24) As cylinder barrel 50 is rotated further, the connecting opening 40 reaches the high-pressure control slot 39 and increasingly covers the latter. As a result, a fluidic connection is created not only between the high-pressure control slot 39 and cylinder bore 31 but also between the high-pressure control slot 39 and fluid volume 65, with the result that pressure fluid then flows out of the high-pressure control slot 39 into the cylinder bore and into fluid volume 65. When the connecting opening 40 comes out of overlap with the outlet 69 of bore 68, there is once again high pressure in fluid volume 65.

(25) For the two driving mechanisms, therefore, just one precompression volume is provided, and this is effective during the transition of a cylinder bore from the low-pressure control slot to the high-pressure control slot of a control plate.

(26) In addition, a fluid volume of defined size is provided for the changeover of a cylinder bore 31 from the high-pressure control slot 39 to the low-pressure control slot 38. This fluid volume 75 is likewise designed as a cavity in the central housing part 11. Starting from fluid volume 75 there is a bore 76 passing through the central housing part 11 and control plate 37 and having an outlet 77 in changeover region 42. After a dead center position of the displacement pistons 32, the outlet 77 is closer to the low-pressure control slot 38 than to the high-pressure control slot 39. The bore 76 has a certain restricting effect or a restrictor is arranged therein. Starting from fluid volume 75 there is a further bore 78, which passes through the central housing part 11 and control plate 57 and has an outlet 79 in changeover region 42 of control plate 57. After a dead center position of the displacement pistons 52, the outlet 79 is likewise closer to the low-pressure control slot 38 than to the high-pressure control slot 39 of control plate 57. Bore 78 also has a certain restricting effect or is provided with a restrictor.

(27) As an option, fluid volume 75 can additionally also be connected directly to the low-pressure side of the pump. This is indicated in FIG. 2 by a bore 80, in which a restrictor is arranged or which acts as a restrictor.

(28) When a connecting opening 40, after leaving the high-pressure slot 39 of a control plate 37 or 57, comes into overlap with the outlet 77 or 79, pressure medium flows out of the corresponding cylinder bore 31 into fluid volume 75. The pressure in the cylinder bore falls and the pressure in fluid volume 75 rises until the pressures are equal. The cylinder bore is then partially decompressed. When the connecting opening is then simultaneously in overlap with the low-pressure control slot 38 and an outlet 77 or 79, the pressure in the cylinder bore and in fluid volume 75 falls to the low pressure. Although fluid volume 75 thus brings about a partial decompression of the cylinder bore, a fluid volume of this kind is also referred to somewhat inaccurately as a precompression volume (PCV).

LIST OF REFERENCE SIGNS

(29) 8 housing 9 first driving mechanism 10 second driving mechanism 11 central housing part 12 high-pressure connection 13 low-pressure connection 14 drive shaft 15 axis of rotation of 14 16 low-pressure passages 17 end wall of 11 18 end wall of 11 19 high-pressure passages 25 first pot-shaped housing part 26 second pot-shaped housing part 30 cylinder barrel 31 cylinder 32 displacement pistons 33 swash plate 34 pivoting axis of 33 35 piston shoe 36 component shaft of 14 37 control plate 38 control slot in 37 and 57 39 control slot in 37 and 57 40 connecting opening 41 changeover region 42 changeover region 43 coupling sleeve 50 cylinder barrel 52 displacement pistons 53 swash plate 54 pivoting axis of 53 55 piston shoe 56 component shaft 57 control plate 65 fluid volume 66 bore 67 outlet of 66 68 bore 69 outlet of 68 70 bore 75 fluid volume 76 bore 77 outlet of 76 78 bore 79 outlet of 78 80 bore