ADJUSTING DEVICE FOR AN AXIAL PISTON MACHINE

Abstract

The present disclosure relates to an adjusting device for adjusting the swash plate of an axial piston machine comprising an adjusting piston, which is connected to the swash plate of the axial piston machine via an adjusting lever, and a regulator for adjusting the adjusting pressure acting on the adjusting piston in dependence on a control force acting on a control piston of the regulator, wherein the adjusting piston is connected to the control piston via a feedback spring.

Claims

1. An adjusting device for adjusting a swash plate of an axial piston machine comprising: an adjusting piston, which is connected to the swash plate of the axial piston machine via an adjusting lever, and a regulator which adjusts adjusting pressure acting on the adjusting piston in dependence on a control force acting on a pot-shaped control piston of the regulator, wherein the adjusting piston is connected to the pot-shaped control piston via a feedback spring, wherein the feedback spring is at least partly received in a cylindrical recess of the pot-shaped control piston.

2. The adjusting device according to claim 1, wherein the pot-shaped control piston is arranged in a control piston receiving bore and that the adjusting piston is arranged in an adjusting piston receiving bore such that the control piston receiving bore and the adjusting piston receiving bore merge into each other, wherein the adjusting piston receiving bore has a larger diameter than the control piston receiving bore.

3. The adjusting device according to claim 1, wherein the cylindrical recess is filled with hydraulic oil at adjusting pressure level, wherein at least one axial bore, preferably exactly one axial bore, is provided in a bottom of the pot-shaped control piston extending towards a side of the pot-shaped control piston opposite the cylindrical recess so that oil at adjusting pressure level reaches the side of the pot-shaped control piston opposite the cylindrical recess.

4. The adjusting device according to claim 3, wherein a diameter of the at least one axial bore is smaller than a diameter of the cylindrical recess of the pot-shaped control piston and the at least one axial bore and the cylindrical recess have a cylindrical shape with their rotating axis being aligned coaxially.

5. The adjusting device according to claim 2, wherein both cross-sectional surfaces of the pot-shaped control piston on which oil at adjusting pressure level is acting in opposite directions are of a same size, so that an unwanted shift in position of the pot-shaped control piston by the adjusting pressure is avoided.

6. The adjusting device according to claim 5, wherein the pot-shaped control piston is formed as a stepped piston and is inserted into the control piston receiving bore via a ring so that resulting cross-sectional surfaces of opposing end faces of the pot-shaped control piston are of a same size.

7. The adjusting device according to claim 6, wherein the ring is arranged at a position close to an end on a side opposite a bottom of the cylindrical recess of the pot-shaped control piston.

8. The adjusting device according to claim 2, wherein a free volume of the control piston receiving bore, a free volume of the cylindrical recess of the pot-shaped control piston and a volume of the adjusting piston receiving bore being fluidly connected to the cylindrical recess of the pot-shaped control piston each are filled with hydraulic oil at an adjusting pressure level.

9. The adjusting device according to claim 1, wherein at least one adjusting pressure bore is provided in a side wall of the pot-shaped control piston, in particular in a side wall of the cylindrical recess, to allow oil flow into or out of the cylindrical recess dependent on an axial position of the pot-shaped control piston, and wherein said at least one adjusting pressure bore is a radial bore extending only in radial direction through the side wall of the pot-shaped control piston and said at least one adjusting pressure bore preferably extends from a groove formed in an outer surface of the pot-shaped control piston, said groove preferably being formed as an annular groove.

10. The adjusting device according to claim 9, wherein the pot-shaped control piston comprises a certain number of circumferentially arranged adjusting pressure bores which are connected to each other via a groove provided in the side wall of the cylindrical recess.

11. The adjusting device according to claim 1, wherein one end of the feedback spring is supported on a bottom of the cylindrical recess and its other end rests against the adjusting piston.

12. The adjusting device according to claim 2, wherein a regulator housing is inserted in the control piston receiving bore, in which the pot-shaped control piston is shiftably seated.

13. The adjusting device according to claim 1, wherein the pot-shaped control piston comprises in its side wall only bores extending in radial direction or diagonal radial direction through the side wall, in particular for fluidly connecting any of a regulating pressure bore, a high-pressure bore and a tank bore provided in a regulator housing.

14. The adjusting device according to claim 1, wherein oil connections to the pot-shaped control piston are guided through bores extending radially or obliquely radially through a regulator housing.

15. The adjusting device according to claim 1, wherein the cylindrical recess comprises a portion with a reduced inner diameter formed in the cylindrical recess at its end close to a bottom of the cylindrical recess, wherein the reduced inner diameter is adapted to an outer diameter of the feedback spring.

16. The adjusting device according to claim 1, wherein a tappet is guided through the pot-shaped control piston proceeding from the adjusting piston, wherein at a free end of the tappet a spring plate is arranged and wherein the feedback spring on one hand is supported on the spring plate and on another hand on a bottom of the cylindrical recess of the pot-shaped control piston.

17. The adjusting device according to claim 1, wherein the regulator is configured as a volumetric flow regulator or as a power regulator.

18. The adjusting device according to claim 1, wherein the feedback spring has a non-linear spring characteristic with a progressively rising force-spring travel characteristic curve.

19. The adjusting device according to claim 2, wherein the control piston receiving bore and the adjusting piston receiving bore are aligned coaxially to each other.

20. The adjusting device according to claim 2, wherein the control piston receiving bore and the adjusting piston receiving bore are aligned at an angle to each other and/or are aligned in a manner shifted parallel to each other with respect to their respective axes.

21. A method of assembling an adjusting device for adjusting a swash plate of an axial piston machine comprising: an adjusting piston, which is connected to the swash plate of the axial piston machine via an adjusting lever, and a regulator which adjusts adjusting pressure acting on the adjusting piston in dependence on a control force acting on a control piston of the regulator, inserting the adjusting piston into an adjusting piston receiving bore from one side and inserting the control piston into a control piston receiving bore from another side; connecting the adjusting piston receiving bore to the control piston via a feedback spring, which is at least partly received in a pot-shaped recess of the control piston; and wherein the control piston receiving bore and the adjusting piston receiving bore merge into each other, and the adjusting piston receiving bore has a larger diameter than the control piston receiving so that a shoulder is formed.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] FIGS. 1A and, 1B show the schematic representation of a volumetric flow regulator (FIG. 1A) and a power regulator (FIG. 1B).

[0020] FIG. 2 shows a sectional representation through a part of an adjusting device according to a first embodiment of the present disclosure in a first working position.

[0021] FIG. 3 shows the adjusting device according to FIG. 2 in another working position.

[0022] FIG. 4 shows a partly sectional representation through an adjusting device according to a second embodiment of the present disclosure.

[0023] FIG. 5 shows a partly sectional representation of an adjusting device according to a third embodiment of the present disclosure.

[0024] FIG. 6 shows the embodiment of FIG. 5 with an explanation of the acting forces.

[0025] FIG. 7 shows a sectional representation through a part of an adjusting device according to a fourth embodiment of the present disclosure.

[0026] FIG. 8 shows a sectional representation through a part of the adjusting device according to a fifth embodiment of the present disclosure.

[0027] FIG. 9 shows a diagram representation of the spring characteristic of a feedback spring used according to the present disclosure.

[0028] FIG. 10. shows a diagram with the family of characteristic curves for a power regulator according to the present disclosure.

DETAILED DESCRIPTION OF THE FIGURES

[0029] The adjusting device described below serves for adjusting the swash plate of an axial piston machine. The construction of a corresponding axial piston machine is known for example from EP 1 220 990 B 1. With respect to the constructive details reference therefore is made to the disclosure presented there.

[0030] The subject-matter of the present disclosure is an adjusting device by means of which the adjusting piston for adjusting the swash plate is adjustable over a large stroke range. FIGS. 1A and 1B schematically show the construction of the adjusting device in two design variants. FIG. 1A represents an adjusting device 10 that comprises a volumetric flow regulator 12. The volumetric flow regulator 12 is adjoined by the only purely schematically represented adjusting piston 14 with connected adjusting lever 36. On the opposite side a closure and adjusting unit 16 is arranged. The volumetric flow regulator 12 substantially includes a control piston 18 that has a pot-shaped recess 20. Into the pot-shaped recess 20 of the control piston 18 a feedback spring 22 protrudes, which connects the control piston 18 to the adjusting piston 14 shown here only schematically. The adjusting piston 14 connected to the swash plate of the axial pistion machine 100. Reference numeral 24 designates the control unit 24 for the control piston 18, which represents the hydraulic ports for high pressure, tank recirculation and regulating pressure as well as the adjusting pressure bore.

[0031] FIG. 1B shows a corresponding adjusting device 10 with a power regulator 12. On the one side, there is likewise arranged a closure and adjusting unit 16. The control piston 18 here is also formed with a pot-shaped recess 20, wherein with respect to its pot shape it is received in the corresponding control piston receiving bore 34 rotated by 180 degrees with respect to the volumetric flow regulator. In the power regulator 12 there is also provided a feedback spring 22 that dips into the pot-shaped recess 20 of the control piston 18. This spring 22, however, here on the one hand is supported on the bottom of the pot-shaped recess 20 and on the other hand on a spring plate 26 that via a tappet 28 is connected to the adjusting piston 14 and thus to the adjusting lever 36 adjoining the same. The adjusting piston 14 connected to the swash plate of the axial pistion machine 100.

[0032] FIGS. 2 and 3 show a constructive exemplary embodiment for a volumetric flow regulator according to FIG. 1A. In a housing part 30 belonging to the otherwise axial piston machine an adjusting piston receiving bore 32 as well as a control piston receiving bore 34 are provided. As shown in FIG. 2, the diameter of the adjusting piston receiving bore 32 is greater than that of the control piston receiving bore 34 so that a shoulder is formed. In the adjusting piston receiving bore 32 the adjusting piston 14 is longitudinally shiftably seated, which is adjoined by an adjusting lever 36. With its end not shown here the adjusting lever 36 extends to the likewise swash plate of an axial piston machine. In the control piston receiving bore 34 a regulator housing 38 is inserted, in which a control piston 18 configured as a stepped piston is shiftably seated. The control piston 18 includes a pot-shaped recess 20. On the correspondingly formed bottom of the pot-shaped recess a feedback spring 22 is supported, which with its other end rests against the adjusting piston 14. The feedback spring 22 thus extends from the control piston receiving bore towards the adjusting piston receiving bore.

[0033] The free volumes of the control piston receiving bore 34 and the adjusting piston receiving bore 32 each are filled with hydraulic oil at adjusting pressure level. This hydraulic oil also fills the pot-shaped recess 20. In the lateral wall of the control piston 18, which encloses the pot-shaped recess 20, an adjusting pressure bore 40 is provided through which the hydraulic oil can enter. In the regulator housing 38 a control pressure bore 42, a regulating pressure bore 44, a high-pressure bore 46 and a tank bore 48 are provided, through each of which hydraulic oil flows in cooperation with the control piston 18 configured as a stepped piston to actuate the adjusting piston 14. As this mode of operation is known, no further description is needed here.

[0034] As compared to known constructions, this design also leads to a shortened design because instead of a proportional magnet adjoining the closure and adjusting unit 16 in the longitudinal extension an arbitrarily placeable pilot control unit is provided, which is connected to the aforementioned control pressure bore 40 arranged laterally in the regulator housing 38.

[0035] As shown here in the drawing, embodiments of the oil connections to the control piston 18 are guided through bores extending radially or obliquely radially through the regulator housing 38. To create a flow cross-section sufficient for an oil connection by providing for an installation space as small as possible with respect to the longitudinal extension of the regulator, a plurality of bores each with a smaller diameter are made instead of a single bore along an imaginary circle enclosing the shell surface of the regulator housing 38. With respect to the outside of the regulator housing 38, the bores of an oil connection are located on a groove base of a continuous outer radial groove correspondingly incorporated into the housing. The groove corresponds to the above-mentioned imaginary circle. By this measure, radial bores associated for an oil connection contribute to the intended oil flow of the hydraulic oil with the same effectiveness. For the illustrated exemplary embodiment these are the control pressure bores 42, the regulating pressure bore 44, the high-pressure bore 46 and the tank bore 48.

[0036] The arrangement of the adjusting pressure bore 40 in the wall of the control piston 18 represents a particularity of the present disclosure. Usually, the adjusting pressure bore 40 also is provided as a radial bore in the regulator housing 38. As a measure for limiting the overall length of the control piston 16 and thus for a compact construction of the regulator, the distances between the adjacent annular spaces that contain the bore are to be designed as small as possible. However, limits are obtained here for the minimum distances. The longitudinal portion of the control piston 18 on which the contours of control edges are applied requires a certain extension so as to have a clearly defined and reproducible dependence between the axial position of the control piston 18 and the pressure loss occurring across the control edge. In addition, adjacent volumes, in which desirably and due to the function greatly differing oil pressure levels, are at a certain distance from each other in order to avoid too much oil leakage here. A certain oil leakage always exists with correspondingly movable parts, which also is necessary as a lubrication for the movement of the control piston 18 in the interior of the regulator housing 38. When this leakage however becomes too high, an unnecessarily high power loss is obtained in the regulator. In the extreme case, too high a leakage also can lead to an unwanted influence on the position of the control piston 18. The leakage between adjacent annular spaces can be reduced for example by applying one or more radial grooves acting as split ring seals on the shell surface of the control piston. Such additional radial grooves however are not shown in FIG. 2 for reasons of simplification.

[0037] By shifting the adjusting pressure bore 40 into the outer wall of the control piston 18 the distance between the individual bores in the regulator housing 30 is increased so that even with a reduced overall length of the regulator the distance between the individual bores is comparatively larger. The entirely unwanted leakage on the outside of the regulator housing 18 thereby is suppressed sufficiently without an increased manufacturing effort being required for this purpose.

[0038] Via the adjusting pressure bore 40 the hydraulic oil enters into the free cavity of the control piston receiving bore 34 with the desired adjusting pressure via the existing fluid connection also into the free regions of the adjusting piston receiving bore 32. As shown in FIG. 2, a bore 50 penetrating the remaining region of the control piston 18 is provided from the blind hole bottom of the control piston 18. Thereby, an oil connection is created so that the existing hydraulic pressure on both sides applies the adjusting pressure on the control piston 18. Desired compensation is used to avoid an unwanted shift in the position of the control piston 18 by the adjusting pressure created by both cross-sectional surfaces of the control piston 18 on which the adjusting pressure acting in opposite directions is applied is of the same size. In the exemplary embodiment shown here, this compensation is created in that the control piston 18 formed as a stepped piston is inserted into the regulator housing 38 via a mounting ring 52.

[0039] In the representation of FIG. 2 the adjusting piston 14 and hence the adjoining adjusting lever 36 is maximally deflected. In FIG. 3 the adjusting device of FIG. 2 is shown in another position. Here, the adjusting piston 14 and hence the adjoining adjusting lever 36 is fully retracted. This representation clearly shows that the feedback spring 22 in the contracted condition is almost completely received in the pot-shaped recess 20 of the control piston 18. By this construction a minimum overall length is achieved.

[0040] FIG. 4 shows an adjusting device 10 in a constructive configuration that corresponds to the schematic representation according to FIG. 1B. Here, a power regulator 12 is integrated. Components are configured in the same way as in FIGS. 2 and 3. In a housing 30 of a axial piston machine, an adjusting piston receiving bore 32 and a control piston receiving bore 34 are provided here as well. In the adjusting piston receiving bore 32 an adjusting piston 14 with adjoining adjusting lever 36 also is inserted here again. Here, the adjusting piston 14 is shown in the fully retracted position. In this embodiment, the adjusting lever 36 is connected to the feedback spring 22 via a tappet 28 at whose end a spring plate 54 is arranged. The opposite side of the feedback spring 22 rests against the bottom of the control piston 18 which here likewise is provided with a pot-shaped recess 20. Thus, in this design variant the feedback spring 22 also dips into the pot-shaped recess 20 of the control piston 18. Through the lateral wall of the control piston 18 the adjusting pressure bore 40 also extends in the embodiment shown here, whereby the same advantages are obtained as in the embodiment described above. Furthermore, a tank bore 48, a regulating pressure bore 44 and a high-pressure bore 46 are provided.

[0041] The control piston receiving bore 34 and the adjusting piston receiving bore 32 are aligned coaxially to each other in the embodiments of FIGS. 2 and 3 and in the embodiment of FIG. 4. As a result, the control piston 18 and the adjusting piston 14 also extend coaxially to each other. This design variant however has the disadvantage that the adjusting piston 14 connected to the swash plate of a axial piston machine 100 via an adjusting lever 36 compensates a transverse force introduced via the adjusting lever 36, which leads to a non-uniform action on the adjusting piston 14 in the adjusting piston receiving bore 32.

[0042] This problem is solved by the constructive configuration of the adjusting devices according to FIGS. 5 and 6, 7 and 8, respectively.

[0043] FIG. 5 represents an adjusting device 10 corresponding to the construction of the adjusting device according to FIG. 3, wherein the adjusting piston 14 here likewise is in the same position as in FIG. 3. However, in this design variant the adjusting piston receiving bore 32 is angled by an angle with respect to the control piston receiving bore 34. The force compensation of the transverse force applied via the adjusting lever 36, which is achieved thereby, can be illustrated with reference to the forces depicted in FIG. 6. The equilibrium of forces at the adjusting piston 14 is shown there, wherein FL designates the longitudinal component of the adjusting force, FQ designates the transverse component of the adjusting force, and FR designates the restoring force of the piston. In the exemplary embodiment shown here, a typical angle of about 2 is indicated, which leads to an obtuse angle of 178, at which the respective middle axes of the control piston receiving bore 34 on the one hand and the adjusting piston receiving bore 32 on the other hand are aligned relative to each other. This only is an exemplary indication of an angle. In accordance with the present disclosure, an even greater or smaller obtuse angle can also be employed here.

[0044] FIG. 8 likewise shows an angled design variant of an adjusting device, here however as a power regulator 12 as shown in FIG. 4. According to this representation, the control piston receiving bore 34 likewise is angled with respect to the adjusting piston receiving bore 32. In this embodiment, the tappet 28 is guided obliquely into the adjusting piston 14.

[0045] In the design variant according to FIG. 7, a compensation of the transverse force is achieved in that the axis A of the control piston receiving bore 34 and the axis B of the adjusting piston receiving bore 32 are shifted parallel to each other, i.e. offset. With a corresponding adjustment of the offset, the transverse component of the adjusting force, which is applied by the adjusting lever 36, also can be compensated thereby.

[0046] In all design variants the feedback spring 22 can be formed as a spring with a non-linear spring characteristic, i.e. here with a progressively rising force-spring travel characteristic curve, in particular in the design variants of the adjusting device that include a power regulator 12. In FIG. 9 the corresponding spring characteristic curve is shown. There, the compressive force exerted on the spring provided there is plotted over the provided reduction in length of the compressive spring. The characteristic curve shown here has an exemplary character. One common feature of the springs depicted on the right side in three different contraction widths and of that spring which has the characteristic map shown on the left side is the presence of three areas in which the spring has different spring stiffnesses. This is revealed in the characteristic map due to the presence of three straight portions with different slopes. With reference to the illustrated spring this is shown best in the first representation in which the lowest contraction exists. The adjacent spring windings here have a distinctly larger distance. In the middle length portion of the spring a distinctly smaller distance of adjacent spring windings can be seen and in the lower region this distance is even smaller.

[0047] When viewing a contraction of such a spring the following is to be observed. Proceeding from a very small and rising application of force, all spring windings contribute to a length contraction in a region I. The spring windings between which the smallest distance is present without the presence of a contraction force and a contraction force present within the region I contact each other after the exceedance of a certain force. As soon as this has occurred, no contribution is made in these windings to a further reduction of the spring length in connection with a further increase of the contraction force. From an exceedance of a yet higher threshold value an additionally continuously increasing contraction force only leads to a compression of those spring windings which still have a distance from their adjacent winding.

[0048] In accordance with the present disclosure it is also possible to use coil springs that have another number of contraction areas or due to other embodiments have a non-linear force-spring travel characteristic curve, for example due to having a cone-shaped contour etc. Instead of coil springs other springs with a corresponding spring characteristic can also be used. For example, combinations with a coil spring are conceivable that is supported by a disk spring at one or both spring ends or is supported on a stack of disk springs. These disk springs can also have different stiffnesses.

[0049] By using a corresponding non-linear feedback spring, a characteristic curve that approaches the course of a hyperbola pHD*Q=constant at a constant rotational speed can be achieved in a power regulator as it is shown for example in FIG. 4 or 8. This means that the product of the stroke of the engine pistons and the pressure level at the high-pressure outlet of the axial piston machine is constant. In the aforementioned formula pHD designates the high-pressure level at the high-pressure outlet of the hydraulic pump or at the inlet of the hydraulic motor. Q is the discharged volumetric flow of the hydraulic pump or the received volumetric flow of the hydraulic motor, i.e. here of the axial piston machine. By adjusting different pretensions of the non-linear feedback spring, a family of characteristic curves indicated corresponding to the representation of FIG. 10 is obtained. A limit here on the one side is given at the maximum high pressure and on the other side at the maximum stroke of the engine pistons, i.e. the limit stop.