Patent Application
20190145389
This application claims priority to Swiss Patent Application No. 01365/17 filed Nov. 11, 2017, entitled “Adjusting Device For An Axial Piston Machine,” the entire contents of which is hereby incorporated by reference in its entirety for all purposes.
This present disclosure relates to an adjusting device for adjusting the swash plate of an axial piston machine.
The design of an axial piston machine in a swash plate construction is known for example from DE 10 2012 015 503 A1. In such hydrostatic machines the delivery/absorption volume is adjustable by pivoting a swash plate against which a plurality of pistons rest that are guided in a cylinder drum. The pivoting of the swash plate is affected via a corresponding adjusting device. The requirements for high efficiencies and high power densities imposed on axial piston machines require the adjustability of the swash plate over an angular range as large as possible. This means that the adjusting piston of the adjusting device has a large stroke range.
From EP 1 220 990 B1 there is known an adjusting device for adjusting the swash plate of an axial piston machine, in which the adjusting piston is adjustable over a large stroke range. Via a feedback spring, the adjusting piston which is connected to the swash plate of the axial piston machine via an adjusting lever is connected to the control piston of that regulator which serves for adjusting the adjusting pressure acting on the adjusting piston in dependence on a control force acting on the control piston of the regulator. An adjusting device of simple and robust design thereby is created to adjust the swash plate of an axial piston machine in a swash plate construction, in which the adjustment path of the adjusting piston exerts the desired retroactive effect on the position of the control piston. As the feedback spring follows the comparatively long adjustment range of the adjusting piston, the same has a rather great length. This leads to the fact that the entire regulator also has a large length dimension.
It therefore is the object of the present disclosure to construct an adjusting device for adjusting the swash plate of an axial piston machine which is compact, wherein the overall length is reduced.
In accordance with the present disclosure, this object is solved by an adjusting device for adjusting the swash plate of an axial piston machine includes the combination of an adjusting piston that 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. The feedback spring according to the present disclosure is at least partly received in a pot-shaped recess of the control piston. Thereby, a compact arrangement is achieved.
In contrast to the already known solution from EP 1 220 990 B1, in which the feedback spring with some windings could dip into the partly hollow-drilled adjusting piston, the formation of the pot-shaped recess of the control piston according to the present disclosure provides for a much shorter overall length. The control piston is constructed much longer than the adjusting piston due to functional reasons. The pot-shaped recess of the control piston can be designed so long that substantially the entire feedback spring can be received in the same in the compressed condition.
Accordingly, the control piston is arranged in a control piston receiving bore and the adjusting piston is arranged in an adjusting piston receiving bore, wherein the control piston receiving bore and the adjusting piston receiving bore merge into each other, in one embodiment. The adjusting piston receiving bore has a larger diameter than the control piston receiving bore. The adjusting piston receiving bore and the control piston receiving bore thus form a shoulder in the adjusting device housing so that during an assembly the adjusting piston is inserted into the adjusting piston receiving bore from one side, while the control piston is inserted into the control piston receiving bore from the other side.
According to one embodiment of the present disclosure the control piston receiving bore and the adjusting piston receiving bore are coaxially arranged in the adjusting device housing. This coaxial arrangement leads to the control piston being guided in the control piston receiving bore and the adjusting piston arranged in the adjusting piston receiving bore also are arranged on one axis, wherein they are axially offset on the axis. During the assembly, the control piston and the adjusting piston are inserted from one side into a uniform bore with a nominal diameter. Due to the inventive stepped design of the receiving bores with different diameters, the housing can be dimensioned smaller in the region of the control piston arranged in the smaller control piston receiving bore.
The coaxial alignment of control piston and adjusting piston corresponding to the aforementioned embodiment however is disadvantageous, as the adjusting piston connected to the swash plate of the axial piston machine via an adjusting lever compensates a transverse force introduced via the adjusting lever, which leads to a non-uniform action on the adjusting piston in the adjusting piston receiving bore. As a compensation of this transverse force the present disclosure provides two alternative design variants.
The first design variant consists in that the control piston receiving bore and the adjusting piston receiving bore are aligned at an angle to each other. The angle is chosen such that the transverse force applied onto the adjusting piston at one end via the adjusting lever is compensated via the correspondingly angled control piston and the spring guided by the same.
An alternative design variant consists in that the control piston receiving bore and the adjusting piston receiving bore are arranged offset from each other such that the corresponding transverse force likewise is compensated.
According to another aspect of the present disclosure the pot-shaped recess not only receives the feedback spring, but at the same time is filled with hydraulic oil at adjusting pressure level. The hydraulic oil gets into the pot-shaped recess of the control piston via corresponding bores in the side wall. The circumferentially arranged adjusting pressure bores can be connected to each other via a groove provided in the side wall of the pot-shaped recess. The oil connection between the cavity in the control piston and in the adjusting cylinder is effected in an axial direction. To avoid that in the regulator the position of the control piston is influenced by the adjusting pressure, a compensation is created. For this purpose an additional oil connection is created, by which the oil under the adjusting pressure also reaches the front side of the control piston facing away from the spring. For this purpose an axial bore is provided towards the side of the control piston opposite the pot-shaped recess.
According to another embodiment of the present disclosure the control piston is stepped on the outside and is mounted in the control piston receiving bore via a ring in its portion close to the end on the side opposite the bottom of the control piston. Via this ring, both cross-sectional surfaces of the control piston, which each are urged in opposite directions by the adjusting pressure, have the same size.
According to another embodiment of the present disclosure a tappet is guided through the control piston proceeding from the adjusting piston, wherein at the free end of the tappet a spring plate is arranged and wherein the feedback spring is supported on the spring plate and on the bottom of the pot-shaped recess of the control piston. This type of construction is a power regulator.
In accordance with the present disclosure, such power regulators and also volumetric flow regulators can be used as regulators.
According to another aspect of the present disclosure, which is employed in power regulators, the feedback spring has a non-linear spring characteristic. There is used a one-part spring with a non-linear spring characteristic. It is advantageous when the feedback spring has a progressively rising force-spring travel characteristic curve. Such a spring characteristic provides for a simple construction of a power regulator, in which the control piston and the adjusting piston are non-positively connected via such a common spring. Via a corresponding spring characteristic a regulator characteristic curve can be generated, which comes very close to a mathematically exact hyperbola (pHD*Q=constant).
Further features, details and advantages will be explained in detail with reference to the exemplary embodiments illustrated in the Figures.
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 B1. With respect to the constructive details reference therefore is made to the disclosure presented there.
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.
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.
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.
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.
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
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.
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
In the representation of
The control piston receiving bore 34 and the adjusting piston receiving bore 32 are aligned coaxially to each other in the embodiments of
This problem is solved by the constructive configuration of the adjusting devices according to
In the design variant according to
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
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.
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.
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
| Number | Date | Country | Kind |
|---|---|---|---|
| 01365/17 | Nov 2017 | CH | national |
