Abstract
A hydrostatic axial piston machine includes a control disk that has a permanent relief field and at least one hydrostatic auxiliary relief field.
Claims
1. A hydrostatic axial piston machine, comprising: a control disk having a permanent relief field and at least one hydrostatic auxiliary relief field configured to be supplied with pressure medium; and a cylinder drum supported on the control disk, the auxiliary relief field having a release pressure that is set in a manner dependent on a rotational speed of the cylinder drum.
2. The hydrostatic axial piston machine according to claim 1, wherein the at least one auxiliary relief field is configured for the compensation of rotational-speed-dependent disturbance variables.
3. The hydrostatic axial piston machine according to claim 1, wherein the pressure medium supply has a pressure medium flow limitation mechanism.
4. The hydrostatic axial piston machine according to claim 1, wherein the pressure medium is drawn or picked off via a high-pressure side of the axial piston machine.
5. The hydrostatic axial piston machine according to claim 1, wherein the at least one auxiliary relief field is configured to be connected to one or more of a hydraulic capacity and a hydraulic pump.
6. The hydrostatic axial piston machine according to claim 1, wherein the pressure medium is a discharged oil.
7. The hydrostatic axial piston machine according to claim 1, wherein a first auxiliary relief field is arranged in a tilting direction.
8. The hydrostatic axial piston machine according to claim 7, wherein the arrangement of the auxiliary relief field effects an enlargement of a support circle radius on the control disk.
9. The hydrostatic axial piston machine according to claim 7, wherein the tilting direction is inclined at an angle of approximately 5-45 relative to a dead center axis or central axis of the control disk.
10. The hydrostatic axial piston machine according to claim 7, wherein a second auxiliary relief field is arranged diametrically with respect to the first auxiliary relief field.
11. The hydrostatic axial piston machine according to claim 1, wherein the relief pressure of the auxiliary relief field is configured to be controlled or regulated as a function of the rotational speed of the cylinder drum.
12. The hydrostatic axial piston machine according to claim 8, wherein the tilting direction is inclined at an angle of approximately 5-45 relative to a dead center axis or central axis of the control disk.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Particularly preferred exemplary embodiments of the hydrostatic axial piston machine according to the disclosure are illustrated in the drawings. The disclosure will now be discussed in more detail on the basis of the figures of said drawings, in which:
[0035] FIG. 1 shows a first exemplary embodiment of the pressure medium supply of the auxiliary relief field on the control disk by way of a non-adjustable nozzle,
[0036] FIG. 2 shows a second exemplary embodiment of the auxiliary relief field according to the disclosure by way of an adjustable nozzle,
[0037] FIGS. 3a and 3b are schematic illustrations of the tilting of the cylinder drum in a radial view and an axial view,
[0038] FIG. 4 shows an exemplary embodiment of the control disk with an auxiliary relief field according to the disclosure arranged in the tilting direction,
[0039] FIG. 5 shows a further exemplary embodiment of a control disk with auxiliary relief field according to the disclosure, and
[0040] FIG. 6 shows a typical variable-rotational speed and variable-pressure load cycle of an axial piston machine according to the disclosure.
DETAILED DESCRIPTION
[0041] FIG. 1 shows an exemplary embodiment of the hydrostatic auxiliary relief field 1 of the hydrostatic axial piston machine on a control disk 2 which is, according to the disclosure, supplied with pressure medium by way of an auxiliary pump 4. The auxiliary relief field is arranged approximately centrally on the outer circumference of a high-pressure kidney-shaped control port 32, by way of which the cylinders of a cylinder drum (compare FIG. 3) are connected to the high-pressure side of the axial piston machine. Furthermore, the control disk 2 has a low-pressure kidney-shaped control port 34, by way of which the cylinder bores are connected to the low-pressure side. With regard to the underlying mode of operation of the axial piston machine, reference is made to the introductory part of the description and to FIG. 3. The high-pressure kidney-shaped control port 32, the low-pressure kidney-shaped control port and the auxiliary relief field 1 are situated in elevated regions of the control disk 2, against which the cylinder drum bears with a greater or lesser gap dimension. The elevated region in which the auxiliary relief field 1 is situated is very narrow and is separate from the elevated region in which the high-pressure kidney-shaped control port and the low-pressure kidney-shaped control port are situated. The gaps that arise between the elevated region surrounding the auxiliary relief field and the cylinder drum may be regarded as a nozzle via which pressure medium can flow out of the auxiliary relief field into the housing (not illustrated in any more detail) of the axial piston machine and which is denoted in the figures by the reference numeral 3.
[0042] The auxiliary relief field 1 is arranged on a control disk 2 at an angle of approximately 90 relative to the top dead center TDC of the piston position. In the exemplary embodiment as per FIG. 1, the supply of pressure medium to the auxiliary relief field 1 is realized by way of an auxiliary pump 4. The auxiliary pump 4 delivers pressure medium via a main line to a non-adjustable nozzle 6 and via the latter into the auxiliary relief field 1. The pressure medium flows out of the latter into the housing. The pressure in the main line between the auxiliary pump 4 and the nozzle 6 is measured by way of a manometer 8. An auxiliary line branches off from the main line, which auxiliary line is equipped with a pressure-limiting valve 12 which does not allow the pump pressure to increase beyond a particular value. This is realized by way of the drainage of excess pressure medium into a tank 14, which is open to the atmosphere. An auxiliary pump 4 is used which is such that it always delivers more pressure medium than flows out via the nozzles 6 and 3. The excess amount flows off via the pressure-limiting valve 12 into the tank. Thus, the pressure in the main line is equal to the pressure predefined by the pressure-limiting valve.
[0043] The relief pressure that prevails in the auxiliary relief field 1 is defined by pressure division by way of the nozzles 3 and 6. The latter nozzle 6 particularly preferably has a diameter of 4 mm. If, for example, the throughflow cross section of the nozzle 3 is equal to the throughflow cross section of the nozzle 6, the pressure in the auxiliary relief field 1 is equal to half of the pump pressure. If, by contrast, the cylinder drum lifts off slightly from the control disk, the throughflow cross section of the nozzle 3 becomes larger, and the pressure on the auxiliary relief field decreases. If the cylinder drum approaches the control disk in relation to a position with half pump pressure in the auxiliary relief field, the throughflow cross section of the nozzle 3 becomes smaller, and the pressure on the auxiliary relief field increases. This results in self-regulation of the pressure in the auxiliary relief field and thus self-regulation of the action of the auxiliary relief field. If the relief of the cylinder drum changes in the surface region surrounding the high-pressure kidney-shaped control port and the low-pressure kidney-shaped control port owing to a change in the rotational speed or the working pressure, the relief by way of the auxiliary relief field changes oppositely thereto.
[0044] A further secondary line with a 2/2-way valve 16 branches off from the main line. In an open position of the 2/2-way valve 16, the pressure medium can flow off out of the main line via the secondary line into the tank 14. The pressure in the main line and thus also in the auxiliary relief field is then the tank pressure. The auxiliary relief field is inactive. In the closed state of the 2/2-way valve 16, the pressure level and the main line is maintained.
[0045] The pressure prevailing at the auxiliary relief field 1 can be measured by way of a manometer 10. The manometers 8 and 10 are provided primarily for testing purposes.
[0046] FIG. 2 shows a second exemplary embodiment, in which the hydrostatic pressure relief field 1 on the control disk 2 can be supplied with pressure medium via the high-pressure side of the axial piston machine. The illustrated control disk 2 from FIG. 2 is identical to the control disk 2 from FIG. 1. For the supply of pressure medium to the auxiliary relief field, pressure medium flows out of the high-pressure kidney-shaped control port 32 via a nozzle 15 with a constant throughflow cross section to a branching point 17, from which three lines extend. One line leads, without further throttle cross sections, to the auxiliary relief field 1. In terms of circuit layout, the auxiliary relief field 1 and the branching point 17 are the same. A second line leads to the tank 14. In the exemplary embodiment as per FIG. 1, a 2/2-way switching valve 16 is incorporated into said line. In an open position of the 2/2-way valve 16, the pressure medium flows off to the tank 14, which leads to a release of pressure and thus to a dissipation of the relief pressure in the auxiliary relief field 1, or prevents a pressure build-up in the auxiliary relief field 1. The pressure on the auxiliary relief field is then equal to the housing pressure, which in turn may be equal to a tank pressure. A third line likewise leads to the tank 14. A nozzle 18 with an adjustable throughflow cross section is incorporated into said line. Thus, the nozzle 18 and the nozzle 3, which is formed by the gaps between the edge of the auxiliary relief field 1 and the cylinder drum, are connected in parallel with one another. The nozzles 3 and 18 arranged in parallel with one another are in turn arranged in series with respect to the nozzle 15. In the closed position of the 2/2-way switching valve, the pressure in the auxiliary relief field 1 is defined by pressure distribution between the nozzle 15, on the one hand, and the nozzles 3 and 18, on the other hand. By way of the adjustable nozzle 18, it is possible for the effective cross section of the combination composed of the nozzles 3 and 18 connected in parallel to be varied. If a small throughflow cross section of the adjustable nozzle 18 is selected, the pressure in the auxiliary relief field 1 is higher than if the throughflow cross section of the adjustable nozzle 18 were selected to be relatively large. Furthermore, as in the exemplary embodiment as per FIG. 1, the throughflow cross section of the nozzle 3 self-evidently also influences the pressure level in the auxiliary relief field 1. If the throughflow cross section of the nozzle 3 is equal to zero, then only the nozzle 18 together with the nozzle 15 determines the pressure in the auxiliary relief field 1. By way of the adjustable nozzle 18, it is thus also possible to set a maximum pressure in the auxiliary relief field.
[0047] The pressure level at the auxiliary relief field 1 can be measured by way of the manometer 10.
[0048] FIGS. 3a and 3b show schematic illustrations of the axial piston machine. FIG. 3a is a longitudinal section of the axial piston machine, in particular of the cylinder drum 20 and of the control disk 2 against which the cylinder drum 20 bears. FIG. 3b shows the cylinder drum 20 in a cross section. It is possible to see the oblique positioning of a swashplate 26 of the axial piston machine. At the top dead center TDC, the piston 24 is situated in its deployed position in the cylinder 22. The bearing point 30 is the central point on the oblique axis 26. In the event of an increase of the rotational speed, the centrifugal forces acting on the piston 24 become continuously greater, such that, owing to the pistons 24 being deployed to different extents, the running surface of the cylinder drum 20 becomes seated increasingly obliquely on the running surface of the control disk 2, owing to the tilting moment M.sub.ges as per FIG. 3b. The tilting point 31 is situated not at the top dead center TDC of the piston 24 on the dead center axis or central axis y but so as to be offset with respect thereto by an angle of approximately 15.
[0049] The control disk 2 from FIG. 4 shows the arrangement of the auxiliary relief field 1 in the region of the tilting point 31 of the cylinder drum 20. This exemplary embodiment is preferably realized for the above described compensation or prevention of the tilting of the cylinder drum 20 on the control disk 2. The kidney-shaped control port 32 of the high-pressure side of the axial piston machine is equipped with intermediate webs. The kidney-shaped control port 34 of the low-pressure side is, by contrast, of continuous form. The auxiliary relief field 1 extends over an angle of approximately 5-30 with respect to the dead center axis or central axis y. The permanent relief field 38 is formed over the entire circumference of the control disk 2 and corresponds to the motor relief. Together with the activated auxiliary relief field 1, a pump relief is realized. The arrangement of the auxiliary relief field 1 increases the support circle radius 42. As described, the cylinder drum 20, when it lifts off at one side, pivots about the outer edge of the support circle radius 42, which in the prior art is characterized by the outer diameter of the permanent relief field 38. This situation arises if the punctiform residual pressing force lies outside the support circle radius 42. Owing to the arrangement of the auxiliary relief field 1 radially outside the permanent relief field 38, the support circle radius 42 is increased, which corresponds to a new support circle radius 44 which extends to the outer edge of the auxiliary relief field 1.
[0050] A control disk 2 with two diametrically arranged auxiliary relief fields 1 and 40 is shown in FIG. 5. The second auxiliary relief field 40 generates, together with the first auxiliary relief field 1, an additional stability moment for the compensation or prevention of the tilting of the cylinder drum 20 on the control disk 2. In the second auxiliary relief field 40, the pressure behaves oppositely to the first auxiliary relief field 1 owing to the above-described self-regulating effect. The matter of which pressure conditions prevail in the respective auxiliary relief field 1/40 is dependent on the respective oblique positioning of the cylinder drum 20 on the control disk 2. The control disk 2 as per 5 is suitable in particular for an axial piston machine with two-quadrant operation.
[0051] FIG. 6 shows a variable-rotational-speed and variable-pressure load cycle which is typically realized by way of an axial piston machine according to the disclosure. The upper curve shows the pressure profile 46 of the axial piston machine within the load cycle. By contrast, the lower curve shows the rotational speed profile 48 of the axial piston machine within the load cycle. It can be seen from the rotational speed profile 48 that, within the load cycle, the rotational speeds of the axial piston machine lie almost entirely in a range close to zero or in a very high range at around 3000 rpm. In these two situations, the above-discussed intensely varying rotational-speed-dependent disruptions arise, which it is sought to compensate by way of the one or more auxiliary relief fields 1 and 40 according to the disclosure, by virtue of said auxiliary relief field(s) being supplied with pressure medium in rotational-speed-dependent fashion according to the disclosure. Specific disruptions would, as already discussed in the introduction, be the omission of the hydrodynamic component of the permanent relief field 38 at low rotational speeds close to zero and the tilting of the cylinder drum 20 at high rotational speeds owing to the centrifugal forces of the deployed piston 24 in the cylinder 22 or the tilting of the cylinder drum 20 upon a change from motor operation to pump operation in the low rotational speed range.
LIST OF REFERENCE DESIGNATIONS
[0052] 1 Auxiliary relief field
[0053] 2 Control disk
[0054] 3 Nozzle
[0055] 4 Auxiliary pump
[0056] 6 Nozzle
[0057] 8 Manometer p.sub.1
[0058] 10 Manometer p.sub.2
[0059] 12 Pressure-limiting valve
[0060] 14 Tank
[0061] 15 Nozzle
[0062] 16 2/2-way valve
[0063] 17 Branching point
[0064] 18 Nozzle
[0065] 20 Cylinder drum
[0066] 22 Cylinder
[0067] 24 Piston
[0068] 26 Swashplate
[0069] 28 Slide shoe bearing arrangement
[0070] 30 Bearing point
[0071] 31 Tilting point
[0072] 32 High-pressure kidney-shaped control port
[0073] 34 Low-pressure kidney-shaped control port
[0074] 38 Permanent relief field
[0075] 40 Second auxiliary relief field
[0076] 42 Small support circle radius
[0077] 44 Large support circle radius
[0078] 46 Pressure profile
[0079] 48 Rotational speed profile
[0080] Angle
[0081] TDC Top dead center
[0082] BDC Bottom dead center
[0083] M.sub.ges Tilting moment
[0084] y Dead center axis or central axis
