This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2012 015 503.4, filed on Aug. 4, 2012 in Germany, the disclosure of which is incorporated herein by reference in its entirety.
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The disclosure relates to a hydrostatic axial piston machine of swash plate design.
An axial piston machine of this type is disclosed, for example, in DE 10 2008 038 435 A1. In said hydrostatic machines, the delivery/displacement volume can be adjusted by pivoting of a pivot cradle, against which a multiplicity of pistons bear which are guided in a cylinder barrel. In the known embodiment, the pivoting of the pivot cradle takes place via a countercylinder and an actuating cylinder, the countercylinder loading the pivot cradle in one direction and the actuating cylinder loading it in the opposite direction. A counterpiston of the countercylinder is loaded with the pump pressure in the usual way, whereas an actuating piston of the actuating cylinder is loaded with control oil via a regulating valve. A valve slide of the regulating valve can be adjusted counter to the force of a return spring, the prestress of said return spring depending on the pivoting angle of the pivot cradle. The valve slide of the regulating valve is situated in its regulating/basic position when the actuating force which acts electrically or electrohydraulically on the valve slide is in equilibrium with the force of the return spring; the pivot cradle is then set to a pivoting angle which is proportional to the actuating force which acts at the regulating valve.
In the known axial piston machine, the return spring is coupled via a linkage to the counterpiston, the regulating valve and the return spring being attached to the housing of the axial piston machine and the linkage protruding out of the housing of the axial piston machine into the attached valve housing.
The attached valve housing with the return spring requires a considerable amount of installation space; in addition, the construction of the housing of the axial piston machine is relatively complex, since the linkage has to be guided through it in a suitable way.
Under the type designation A4CSG, Bosch Rexroth AG presents an axial piston machine with electro-proportional adjustment, the adjustment mechanism of which is described in detail in DE 100 63 526 C1. In this solution, the regulating valve and the countercylinder are likewise coupled mechanically via a driver and are arranged transversely with respect to the axis of a drive shaft which is connected to the cylinder barrel, and are attached to the housing of the axial piston machine. This variant exhibits the same disadvantage as the above-described prior art: as a result of the attachment of the housings for the regulating valve and for the return spring, the radial dimensions of the axial piston machine are comparatively great. In contrast, the disclosure is based on the object of providing a compact hydrostatic axial piston machine.
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This object is achieved by a hydrostatic axial piston machine having the features of the disclosure.
Advantageous developments of the disclosure are the subject matter of the subclaims.
The axial piston machine according to the disclosure is configured with an electro-proportional adjustment of the pivoting angle of a pivot cradle, a counterpiston of a countercylinder and/or an actuating piston of an actuating cylinder acting on said pivot cradle. Said actuating piston can be actuated by means of a proportionally adjustable regulating valve, the valve slide of which is loaded via a return spring with a returning force which is dependent on the pivoting angle. A multiplicity of pistons which are guided in the cylinder barrel which is connected operatively to a drive shaft are supported on the pivot cradle. According to the disclosure, in the region between its end section on the regulating-valve side and the end section which is remote from the regulating valve, the return spring is attached on the pivot cradle. As a result of this geometry, the overall length of the axial piston machine can be reduced considerably, since the attachment usually takes place on the other side of the return spring.
In one preferred exemplary embodiment of the disclosure, the regulating spring is attached indirectly to the pivot cradle.
The regulating spring can be supported, for example, on a spring sleeve, the pivot cradle then being connected to the spring sleeve in a non-positive or positively locking manner by way of a driver.
In an alternative solution, the spring sleeve can be supported on the housing side via a bearing spring.
A very compact solution is obtained if the bearing spring is arranged coaxially with respect to the return spring, it being possible for both springs to lie behind one another.
In order to make sufficient support possible, the spring force of the bearing spring is preferably selected to be greater than the spring force of the return spring.
The overall length of the axial piston machine can be reduced further if the sleeve which supports the return spring has, on the bottom side, a receptacle for an end section of the bearing spring, with the result that both springs overlap one another in sections.
In one exemplary embodiment of the disclosure, the return spring is arranged laterally offset with respect to the actuating cylinder or with respect to the countercylinder.
The orientation of the structural elements can be selected in such a way that the countercylinder, the actuating cylinder and the return spring lie parallel to the drive-device axis.
BRIEF DESCRIPTION OF THE DRAWINGS
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In the following text, preferred exemplary embodiments of the disclosure will be explained in greater detail using diagrammatic drawings, in which:
FIG. 1 shows a longitudinal section through a hydrostatic axial piston machine according to the disclosure of swash plate design,
FIG. 2 shows a diagrammatic side view of the open housing of the axial piston machine according to FIG. 1,
FIG. 3 shows an outline sketch of the construction of an adjusting device of a pivot cradle of the axial piston machine according to FIGS. 1 and 2, and
FIG. 4 shows a variant of an adjusting device for a pivot cradle of the axial piston machine.
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It is presumed in the following comments that the principle construction of an axial piston machine of swash plate design is known, with the result that only the structural elements which are essential for understanding the disclosure will be explained here. Otherwise, reference is made to the specialist literature, for example the prior art which was indicated at the outset.
The axial piston machine 1 has a drive device with a drive shaft 2 and a pivot cradle 4 which is mounted pivotably in the housing. The drive shaft 2 is mounted via antifriction bearings 6 in the housing with a cup-like housing part 8 and a cover 10. The drive shaft 2 is connected fixedly to the cylinder barrel 12 so as to rotate with it, in which cylinder barrel 12 a multiplicity of working pistons 14 are guided displaceably. The latter in each case delimit a working space 16 with a cylinder bore, which working spaces 16 can be brought into a pressure medium connection with high pressure or low pressure via a disk cam. During the rotation of the cylinder barrel 12, the pistons 14 slide with piston shoes 18 on the sliding face of the pivot cradle 4. The adjustment of the delivery/displacement volume and therefore of the piston stroke takes place via an adjusting device 20, the basic construction of which is explained in the prior art described at the outset.
In accordance with said prior art, an adjusting device 20 of this type has a countercylinder 22, the counterpiston 24 of which is connected via a ball joint 26 to the pivot cradle 4. The pump pressure acts in a pressure space 28 of the countercylinder 22, with the result that the end face of the counterpiston 24 is always loaded with pump pressure. In the position which is shown in FIG. 1, the pivot cradle 4 is pivoted out to a maximum value of, for example, +20°, the counterpiston 24 being retracted completely. Here, the counterspring 30 is loaded with a maximum stress. The right-hand end section of the counterspring 30 in FIG. 1 is supported on a spring collar 32 which can be displaced along the counterpiston 24, the displacement path being delimited by a shoulder 34 (see also FIG. 3) on the outer circumference of the counterpiston 24. The other, left-hand end section of the counterspring 30 in FIG. 1 bears against a supporting part 36, the construction of which will be explained later using FIG. 3. As is apparent from FIG. 1, the supporting part 36 for its part is supported on the ball joint 26 and therefore on the pivot cradle 4. The axial spacing between the supporting part 36 and the spring collar 32 when in contact with the shoulder 34 is selected in such a way that the counterspring 30 is loaded with a prestress.
Offset diametrically with respect to the countercylinder 24, an actuating cylinder 38 acts on the pivot cradle 4, the actuating piston 40 of which actuating cylinder 38 delimits an actuating space 42. Merely a proportional magnet 45 of the regulating valve 44 can be seen in the illustration according to FIG. 1. The regulating valve 44 itself is not visible in the section according to FIG. 1 and lies, for example, approximately on the same circumferential circle as the countercylinder 22 below the plane of the drawing in FIG. 1. It goes without saying that the regulating valve 44 can also be positioned in a different way.
Via said regulating valve 44, control oil can be fed to the actuating space 42 or a control oil connection to the tank can be opened in a controlled manner. The actuating piston 40 has a greater diameter than the counterpiston 24. The actuating piston 40 is also connected via a ball joint 46 to the pivot cradle 4. The actuating cylinder 40 is engaged around by an actuating spring 48 which acts on one side via a spring collar 54 on a shoulder 50 and on the other side on a spring collar 52 which for its part is supported via the ball joint 46 on the pivot cradle 4. The axial spacing of the spring collar 52 from the shoulder 50 is in turn selected in such a way that the actuating spring 48 is loaded with a prestress.
In order to set the pivoting angle which is shown in FIG. 1, the pump pressure prevails both in the actuating space 42 and in the pressure space 28, with the result that the pivot cradle 4 is adjusted to its maximum pivoting angle in the manner shown, on account of the greater diameter of the actuating piston 40. As has been explained, the counterpiston 24 is retracted completely in this position of the pivot cradle 4, the spring collar 32 then coming into contact with a shoulder of the housing and rising up from the shoulder 34, with the result that the counterspring 30 is stressed. In principle, the adjustment of the pivoting angle in the direction of a reduction of the delivery/displacement volume takes place by the control oil connection to the tank connector being controlled via the regulating valve 44 and the pivoting taking place accordingly via the resulting moment which acts on the pivot cradle. The desired pivoting angle is maintained when there is an equilibrium of moments.