CN114810531A - Variable displacement hydraulic unit - Google Patents

Abstract

The invention provides a variable displacement hydraulic unit. The variable displacement hydraulic unit includes a housing accommodating at least one rotating assembly whose displacement is variably adjustable by a swing element tiltable about a swing element tilting axis perpendicular to a rotation axis of the rotating assembly and drivable by at least one servo unit including: a servo cylinder integral with the housing; a servo plunger movable in the servo cylinder, wherein a servo plunger head of the servo plunger is pressurizable in the servo cylinder such that movement of the servo plunger connected with the swinging element by a servo plunger shaft tilts the swinging element; wherein the servo unit is arranged in the housing on the side of the oscillating element opposite to the side on which the cylinder of the rotating group is located and adopts a working direction substantially parallel to the axis of rotation of the rotating group.

Description

Variable displacement hydraulic unit

Technical Field

The technical field of the present invention relates to a variable displacement hydraulic axial plunger unit having an oscillating element for adjusting the displacement of the rotating group of the hydraulic unit. Furthermore, the technical field of the invention also relates to a variable displacement hydraulic single unit or a variable displacement hydraulic series unit, and also to a hydrostatic transmission equipped with such a hydraulic unit. For the hydraulic tandem unit and the hydrostatic transmission according to the invention, a plurality of rotary assemblies are arranged in a common housing. According to the invention, the displacement of at least one of the rotating assemblies is adjustable. The invention also relates to a hydrostatic transmission having a variable displacement hydraulic axial piston unit in combination with one or more radial piston units.

Background

Hydraulic units and hydrostatic transmissions are commonly used in propulsion applications for transferring mechanical energy from a drive motor to a consumer propelled by hydraulic or mechanical energy. Since the available space is often limited by the vehicle manufacturer, a compact hydraulic unit is typically employed. For example, such a hydraulic unit or power plant may be incorporated into a tractor and mounted on or in its mechanical gearbox. Here they must be adapted to be placed in some frame of the tractor, e.g. the leg room of the driver.

Disclosure of Invention

In order to reduce the installation space of the hydraulic unit or the hydrostatic transmission, direct displacement control is the preferred method of adjusting the displacement of the rotating group. Specifically, mechanical systems including joysticks (levels) and/or rods (rod) are used to transmit operator control commands of a desired displacement to the respective rotating assemblies. In some application scenarios, the pivoting movement of the pivoting element is performed from the outside by a screw-mounted servo unit, but this special servo unit takes up valuable installation space.

Accordingly, there is a need in the art to provide a tilting system for a rocking element. The tilting system can variably adjust the displacement of at least one rotating assembly of a hydraulic axial piston unit or a hydrostatic transmission having a rotating assembly. Here, the given shape of the available space of a device equipped with such a hydraulic unit is not enlarged. The displacement regulating system of the invention should be based on a hydraulic servo system. Furthermore, the Displacement Control system of the present invention may be controlled by Manual Displacement Control (MDC), Hydraulic Displacement Control (HDC), and/or Electronic Displacement Control (EDC). In addition, the proposed displacement regulation system should allow high variability and simple switching to allow mechanical position feedback with optional electrical position feedback, or mechanical position feedback, and/or optional electrical position feedback, load dependent and/or load independent displacement control can be used.

The technical problem underlying the present invention is solved by a variable displacement hydraulic axial plunger unit according to claim 1. Further, the dependent claims, which directly or indirectly refer to claim 1, describe preferred embodiments of the invention.

In order to solve the technical problem to be solved by the present invention, the present invention provides a variable displacement hydraulic axial plunger unit equipped with a housing in which at least one rotating assembly is accommodated. The displacement of at least one rotating assembly can be variably adjusted by means of a swivel element which can be tilted about a tilt axis which is oriented perpendicularly to the axis of rotation of the rotating assembly. The oscillating element of the invention, or so-called swashplate, can be driven by at least one servo unit comprising a servo cylinder housed in a casing. A servo piston arranged in the servo cylinder can be pressurized at its servo piston head, so that the movement of the servo piston (which is connected to the oscillating element by a servo piston shaft) tilts the oscillating element. According to the invention, the servo unit is located in the housing of the hydraulic axial piston unit or hydrostatic transmission. Furthermore, the servo unit is arranged on the side of the oscillating element remote from the cylinder of the rotating group. In order to be able to tilt the pivoting element about a pivoting element tilting axis, the servo unit according to the invention uses a working direction which is substantially parallel to the axis of rotation of the rotating assembly, wherein the point of application of force, i.e. the point of fixation of the servo piston shaft to the pivoting element, is arranged laterally spaced from the pivoting element tilting axis in order to generate a tilting moment about the tilting axis.

Contrary to the prior art, the servo unit according to the invention is arranged on the side of the wobble element (swash plate) where no cylinder block is arranged. The servo units according to the prior art are then arranged on the same side of the oscillating element as the displacement piston or cylinder, respectively. For the internal servo unit, the housing of the hydraulic unit should be arranged to be able to accommodate the servo unit also therein. In the prior art, the servo cylinder and the servo plunger are arranged parallel to the rotating assembly, which makes the housing larger in radial dimension than a comparative housing that only needs to cover the rotating assembly.

The invention proposes to arrange the servo unit on the other side of the swash plate, wherein the servo cylinder can be part of the housing. The servo cylinder may here be a separate part or, in a preferred embodiment, the servo cylinder may be formed integrally with the housing of the hydraulic unit and located inside the housing of the hydraulic unit.

According to the invention, the servo piston is arranged in the servo cylinder so that the servo piston head can be pressurized by the servo pressure and such that its servo piston shaft projects towards the oscillating element substantially parallel to the axis of rotation of the rotating assembly. The fixed point of the servo plunger shaft is thus displaced beside the tilting axis of the tilting element, so that the servo unit generates a force in the linear direction on the tilting element, which force generates a moment about the tilting axis of the tilting element. Thus, when the servo plunger is pushed out of the servo cylinder, the servo plunger shaft transmits a linear force parallel to the axis of rotation of the rotating assembly, thereby causing a tilting movement of the oscillating element.

Preferably, the servo plunger shaft may be hingedly connected to the tilting element, the lateral distance of the fixed point of the servo plunger to the tilting axis of the tilting element decreasing as seen in the direction of the rotation axis of the turning assembly as the tilting element tilts/rotates about the tilting axis of the tilting element. Furthermore, the servo plunger skirt can preferably be designed convex, for example spherical, in order to compensate for lateral movements of the fixing point of the servo shaft. The seal which can be provided on the servo plunger skirt is preferably an elastic seal which is arranged to be able to maintain a sealing contact with the servo cylinder inner wall during the servo plunger curve-linear movement.

According to the invention, the servo plunger shaft can be connected to the oscillating element, for example by means of a ball joint, a hinge joint, a pin joint or the like, preferably with a cap (socket) provided thereon, into which the projecting end of the servo plunger shaft can be inserted or placed, so that a linear force in a direction parallel to the axis of rotation of the swivel assembly can be transmitted to the oscillating element without generating lateral forces on the lateral surface of the servo cylinder.

In an embodiment of the invention, it is conceivable that the servo cylinder may be connected to the housing in such a way that the servo cylinder can pivot about a point of rotation or an axis parallel to the tilting axis of the tilting element to compensate for a lateral movement of the fixing point of the servo plunger shaft on the tilting element. These pivotal movements of the servo plunger need not be very large, only a slight inclination of the longitudinal axis of the servo unit (servo cylinder axis) has to be compensated.

In another embodiment of the invention, the fixing of the servo plunger shaft on the wobble element may be arranged in such a way that the end of the servo plunger shaft can slide on the wobble element, so that the servo cylinder and the servo plunger longitudinal axis can be kept parallel to the rotation axis of the turning assembly when the wobble element is tilted about the wobble element tilt axis. This fixing can be achieved, for example, by the servo plunger shaft being in sliding engagement on the wobble element to which it is connected, or, for example, by the end of the servo plunger shaft being received in a slit perpendicular to the tilt axis of the wobble element in a manner allowing a certain degree of linear displacement. In a simple embodiment, the free end of the servo plunger shaft may be convex, such that lateral movement relative to the wobble element may be compensated by a rolling movement on the wobble element, wherein the servo plunger is tilted due to the convex shape of the servo plunger skirt.

According to the invention, the servo unit can be used for a rotating assembly having a wobble element for adjusting the displacement from a zero position to a maximum position in one direction or vice versa. Alternatively, the servo unit may be used with a rotating assembly having a variable displacement element that can be tilted from one maximum position on one side to another maximum position on the other side. Thus, the high pressure side can be interchanged with the low pressure side while maintaining the rotational direction. In either case, the end stop of the tilting movement can be realized either by the servo plunger head abutting against the bottom of the servo cylinder or by providing an end stop fixed to the housing on the side of the sliding surface of the oscillating element. If the rotary assembly is equipped with a swivel element which can be tilted in both directions relative to a neutral position, the servo plunger is preferably arranged in this neutral position in a half-position, i.e. a half-stroke position, of the possible stroke in the servo cylinder of the servo unit.

For embodiments with a wobble element that can tilt in two directions, it is preferred to provide two servo units according to the invention, i.e. a pair of servo units, on either side of the wobble element tilt axis. By such a pair arrangement, in the neutral position of the oscillating element (no displacement of the rotary assembly), the pressures to which the two servos are subjected are the same, so that this neutral position can be defined and maintained, in which the moments that may be generated by the two servos cancel each other out. More preferably, in such an embodiment, pairs of servo units may be provided on the side of the oscillating element remote from the cylinder of the rotating group. For example, another pair of servo units may be arranged in parallel, so that four servo units are distributed on the oscillating element, forming a cuboid around the rotation axis. In other words, the working directions of the servo units are arranged in four different quadrants when the swash plate is viewed in the direction of the axis of rotation of the rotating assembly. Here, the quadrant is formed by the intersection of the tilting axis of the oscillating element with a plane perpendicular to the tilting axis of the oscillating element and contains the entire rotation axis of the rotating assembly. This particular arrangement allows the forces acting on the swash plate to be balanced, since the four points of application on the side of the swash plate opposite the cylinder block prevent the swash plate from tilting with respect to a plane parallel to the tilting axis of the oscillating element and perpendicular to the rotation axis of the rotating group.

The person skilled in the art will thus appreciate that when a symmetrical arrangement with respect to the tilting axis of the oscillating element is not possible, asymmetrical lateral deviations can be compensated by adjusting the diameters of the servo cylinder and the servo piston, respectively, to compensate for the moment that can be generated by each servo unit.

Preferably, in another embodiment of the present invention in which the tilting element can be tilted in both directions about the tilting axis of the tilting element, when one servo plunger located on one side with respect to the tilting axis of the tilting element is pushed out of the servo cylinder, the other servo plunger located on the other side of the tilting axis of the tilting element is pressed into the servo cylinder due to the tilting motion of the tilting element. The same holds true if, according to the invention, two or more pairs of servo units are arranged symmetrically with respect to the tilting axis of the oscillating element on the side of the oscillating element opposite the cylinder.

The servo pressure for pressurizing the at least one servo plunger in the servo cylinder may be provided by an internal or external pressure source, no matter how many servo units are employed for moving/tilting the oscillatory member. For this purpose, the internal or external pressure source can be controlled by a control unit in a manner known in the art. This means that the servo pressure level provided to the servo cylinder can be controlled hydraulically, mechanically, electromechanically, electronically or in any other way known to the person skilled in the relevant art. For this purpose, in a special embodiment, the servo pump can be fastened by means of screws on the outside of the housing of the hydraulic unit according to the invention. However, the person skilled in the art may also consider the possibility of using the system pressure and the pressure reducing valve in order to control the servo pressure level supplied to the servo cylinder. The internal system pressure can be provided, for example, by a charge pump of the closed hydraulic system.

Since the amount of servo fluid (hydraulic fluid or even air) used for moving the servo plunger in the servo cylinder is relatively small, the servo unit/servo units according to the invention can be provided with servo pressure by means of a small working fluid line, and therefore the servo system for adjusting the displacement according to the invention can be used in a load-dependent servo pressure control manner, whatever type of pressure source is used. These fluid lines can be installed and adjusted in a simple and variable manner as desired. Here, use of flexible tubes or hoses is suggested, which are well known to the person skilled in the art.

As described above, the swinging member can be tilted about its swinging member tilting axis by means of the servo units provided on the opposite sides of the swinging member and the sliding surfaces against which the working plungers in the cylinders of the rotating assemblies abut. If the oscillating element is tilted from its initial position, the oscillating element can be returned to its initial position by means of a further servo unit, which can be arranged symmetrically with respect to the axis of tilting the oscillating element, for example on the same side of the oscillating element. In another embodiment, this can also be achieved by means of a servo spring which is compressed when the pendulum element is tilted/displaced from the initial position.

If the oscillating element can only tilt in one direction, the oscillating element can be returned to its initial position by means of servo springs on the same side of the oscillating element, symmetrically arranged with respect to the axis of inclination of the oscillating element. The maximum angle of inclination can thus be defined by the maximum compression of the servo spring or, for example, by an end stop formed on the housing. However, such an embodiment is only possible if the wrap angle of the cradle bearing of the rocking element is larger than 180 °.

Preferably, according to the present invention, if the swing member can be tilted in either direction, a plurality of springs may be positioned on the side of the swing member where the cylinder is provided. In this way, the expansion of the servo unit on the extension of the longitudinal axis of the servo unit causes more or less compression of the servo spring located opposite the servo unit.

Preferably, when the oscillating element of the rotating assembly is equipped with a servo unit according to the invention, a corresponding servo spring means can be provided for each servo unit on the other side of the oscillating element. In this case, when the paired servo springs are located on the side of the sliding surface of the swinging member, at least one spring may be provided on either side of the tilting axis of the swinging member. Preferably, the servo spring is pre-stressed when the oscillating element is in the neutral position. In this way, two, four or more servo springs are able to keep the oscillating element in a neutral position, since the spring force is able to generate a tilting moment on the same height of the oscillating element, but the direction of the moments is different, so that the moments can compensate each other. According to the invention, such a pair of servo-spring arrangements (which may preferably be arranged symmetrically with respect to the tilting axis of the oscillating element) is called a return device, since it is able to return the neutral position of the oscillating element as described previously. It will be appreciated by those skilled in the art that compensation of the spring force is required when it is not possible to arrange the servo springs symmetrically, as is well known.

In order for the servo spring to act on the oscillating element, it is necessary to provide the servo spring with a support, which can preferably be fixed with the housing. Such a bearing surface or the like may be formed on the housing or on a so-called end cover of the hydrostatic unit, for example. Typically, the servo spring may be oriented such that its longitudinal axis is parallel to the axis of rotation of the rotating assembly and is attached to the oscillating element in an articulated manner similar to a servo plunger shaft, but on the other side of the oscillating element. For this purpose, preferably, a spring seat may be used. By using a spring seat and a spring guide, the servo spring can be installed with a preload. Within the scope of the present disclosure, a mounting assembly including a servo spring, at least one spring seat, and a spring guide may be referred to as a servo spring assembly. Preferably, the servo spring device further comprises a connecting device for connecting the servo spring device to the oscillating element.

Preferably, since these servo springs can be supported by their ends remote from the oscillating element on bearing elements on a bearing surface fixed to the housing, they can also provide an end stop for the angle of inclination of the oscillating element. This can be achieved, for example, by means of an outer tube or an inner rod which is suitably adjusted in its length and which also serves as a guide. However, the end stop may also be realized by means of a minimum length of the spring (i.e. a length in a state of maximum compression).

As previously mentioned, the servo spring may be guided within the outer tube or by an inner rod to be able to provide an end stop for the tilting angle of the rocking element. These tubes or rods may also be adapted to provide one or two spring seats for the servo spring. Preferably, one of these servo spring seats can be designed to be able to adjust the pretensioning force of the servo spring when the pendulum element is in the neutral position, for example by screwing the spring seat in or out relative to the guide. When using such adjustable spring seats, advantages can also be achieved in the assembly of the hydrostatic unit or the transmission.

In another aspect of the invention, particularly for a bi-directional tiltable swash plate having one or more pairs of servo springs on the swash plate sliding surface side, the servo spring arrangement can be used to hold the swash plate in its cradle bearing when the swash plate is tilted about the tilt axis. Since the servo unit according to the invention is located on the other side of the swash plate, which faces away from the cylinder block, the servo unit pushes the swash plate away from its cradle bearing when tilting the swash plate. To compensate for this, the servo spring arrangement according to the invention can be used, since the servo spring arrangement can also provide a swash plate holding force downwards against the tilting force of the servo piston to hold the swash plate in its cradle bearing.

Drawings

In the following figures, exemplary embodiments of a servo unit, a servo spring arrangement and combinations thereof according to the present invention are shown, as previously described. In the embodiments shown in the following figures, different possibilities of devices are shown, which can be combined with each other without leaving the spirit of the inventive concept, wherein combinations not described are also included in the present invention. Furthermore, the embodiments of the present invention do not limit the scope of the present invention. The following figures show:

FIG. 1 is a schematic diagram of a first embodiment according to the present invention;

FIG. 2 is a schematic diagram of a second embodiment according to the present invention;

FIG. 3 is a cross-sectional view of a third embodiment according to the present invention;

FIG. 4 is a cross-sectional view of a fourth embodiment according to the present invention;

FIG. 5 is a detailed view of a fifth embodiment according to the present invention;

FIG. 6 is a schematic illustration of a fifth embodiment according to the present invention;

fig. 7 is a rear view of the embodiment according to fig. 4.

Detailed Description

Fig. 1 is a schematic view of a first embodiment of the invention, showing an end cap 4, with a drive shaft 2 of a rotating assembly 5 mounted in the end cap 4. The turning assembly 5 is rotatable with respect to the axis of rotation 6. The displacement of the rotating assembly 5 may be adjusted by means of a swinging element 7, the swinging element 7 being shown in a neutral position in which there is no stroke of the displacement plunger of the rotating assembly 5. The oscillating element 7 can be tilted in a clockwise or counterclockwise direction by means of the servo plunger 14. The servo plunger 14 shows a servo plunger head 15. The servo plunger head 15 can be pressurized in a servo cylinder (not shown) so that the servo plunger 14 guided by the servo plunger skirt 18 transmits a linear force along the servo plunger shaft 16 to the oscillating element 7 in order to tilt/rotate the oscillating element 7, thereby setting the displacement of the rotating group 5. When the pendulum element 7 is tilted by means of one of the servo plungers 14, the active servo plunger 14 moves to the right and the non-pressurized inactive servo plunger moves to the left. As can be gathered from fig. 1, the hydraulic unit 1 according to fig. 1 is in a neutral position, i.e. the rotary group 5 does not produce any displacement, and therefore the pressure acting on the two servo plungers 14 is the same.

Fig. 2 is a side view of another embodiment according to the present invention. In the embodiment shown in fig. 2, only one servo-plunger 14 is arranged to move the oscillating element 7 in either direction about the oscillating element tilt axis 8. If the tilting element 7 is tilted about the tilting axis 8 of the tilting element, one of the two servo spring means 25 shown in fig. 2 is compressed, thereby generating a reaction force to the pressure force acting on the servo plunger 14, i.e. on the servo plunger head 15. In this arrangement, the servo pressure is proportional to the servo spring force, so that the servo pressure can be adjusted/set to obtain an intermediate position between the maximum angle and the minimum angle. As in fig. 1, in the embodiment of fig. 2, the servo-plunger 14 is arranged on the opposite side of the oscillating element to the cylinder 52 of the rotating group 5. This makes the design of the entire hydraulic unit 1 very compact. As will be apparent to those skilled in the art from fig. 1 and 2, the end cap 4 forms part of a housing 3 of the hydraulic unit, which housing 3 accommodates the components shown in fig. 1 and 2.

Fig. 3 shows an exemplary embodiment of a cross-sectional view of a hydraulic unit 1 according to the present invention. It can be seen that the hydraulic unit according to the invention shows a very compact design. The displacement of the hydraulic unit 1 can be adjusted by means of the servo unit 10. The servo unit 10 is provided integrally with the housing 3 of the hydraulic unit 1. As shown in fig. 3, the servo unit 10 includes a servo cylinder 12 and a servo plunger 14, and the servo unit 10 is disposed on the opposite side of the oscillating member 7 from the cylinder body 52 of the rotating assembly 5 (which adjusts the displacement by means of the oscillating member 7). In fig. 3, two servo spring arrangements 25 are shown which are capable of exerting opposing forces on the servo unit 10. The servo spring means 25 are thus connected to the oscillating element 7 in an articulated manner, as will be explained in detail below. The same applies to the servo plunger shaft 16, since the fixed point 33 on the rocking element 7 performs a circular arc movement when the rocking element 7 is tilted about the rocking element tilting axis 8.

In fig. 3, it is also shown that the servo spring 22 is guided by an internal guide 27, which internal guide 27 also provides the servo spring 22 with a spring seat 26. The spring seat 26 can be moved parallel to the axis of rotation 6 of the hydraulic unit 1 in order to adjust the servo spring force. At the other end of the servo spring 22, a spring seat 23 is fixed to a first end 24 of a servo spring arrangement 25 in order to pretension the servo spring 22. Together with a spring seat 26 on the second end of the servo spring 22, an embodiment of a servo spring arrangement 25 is shown, wherein the servo spring arrangement 25 can be installed as a mounting assembly into the hydraulic unit 1. In the case of unpressurized servo unit 10, the pretension of the servo spring 22 can be used to define the neutral position of the hydraulic unit 1.

FIG. 4 is a cross-sectional view of another embodiment of the present invention, showing a compact hydrostatic transmission 100. The hydrostatic transmission 100 includes a hydrostatic unit 1. The displacement of the hydrostatic unit 1 may be adjusted by tilting the pendulum element 7. For this purpose, one servo unit 10 can be arranged on each side of the axis of rotation 6. Each servo unit 10 comprises a servo plunger 14. The servo plunger head 15 of the servo plunger 14 may be pressurized by the servo pressure in the servo cylinder 12. When the servo plunger head 15 in the servo cylinder 12 is pressurized, the servo plunger 14 moves along the servo cylinder wall toward the swinging member 7 under the guidance of its servo plunger skirt 18, thereby tilting the swinging member 7. When the oscillating element 7 is tilted, the servo plunger shaft 16 performs a rotational movement fixed to a fixed point 33 of the oscillating element 7. To compensate for the rotary movement of the fixing point 33, the servo plunger skirt 18 is convex, so that the servo plunger shaft 16 in the neutral position of the oscillating element 7 is parallel to the axis of rotation 6 of the swivel assembly 5 and can pivot around a small angle so as not to interfere with the rotary movement of the oscillating element 7. As will be apparent to those skilled in the art from fig. 4, when the oscillating element 7 is tilted away from its neutral position, the tilt angle of the two servo piston shafts 16 can be changed with respect to the zero position of the oscillating element 7, due to the convex shape of the servo piston skirt 18. When in such a tilted orientation, the servo plunger skirt 18 is also able to seal with the servo cylinder 12.

On the other side of the oscillating element 7 in the embodiment of fig. 4, two servo spring devices 25 can counteract the servo pressure of one of the two servo units 10. The first end 24 of the servo spring means 25 is thus also fixed to the oscillating element 7 in an articulated manner, so that the substantially longitudinal axis of the servo spring means 25 can follow the rotational movement of a fixed point 34 on the oscillating element 7 (in fig. 4, below the fixed point 33 of the servo plunger shaft 16). If one of the two servo units 10 in fig. 4 is pressurized with servo pressure, the corresponding servo spring arrangement 25 on the other side of the compression oscillating element 7 is compressed, providing a reaction force to the servo force in the servo cylinder 12. The other servo spring means 25 is elongated or decompressed.

As shown in fig. 3, the device of fig. 4 also comprises a servo spring force adjustment device 29, by means of which the pretension of the servo spring devices 25 (i.e. the servo springs 22) can be set and adjusted such that, when the pivoting element 7 is in the neutral position, the pretension of the two servo spring devices 25 is equal and the pivoting element 7 can be positioned in the neutral position. The servo spring means 25 thus form a return means 20 for returning the oscillating element 7 to the neutral position.

By means of fig. 5 and 6, a detailed view of the servo device according to the invention is shown, wherein the method for assembling the servo plunger 14 and the servo spring device 25 to the oscillating element 7 is shown. In particular with regard to the fixing point 33 of the servo plunger shaft 16 to the oscillating element 7, it can be seen that the end of the servo plunger shaft 16 is designed with an exemplary spherical shape, so that the servo plunger shaft 16 can be mounted in a cap formed in the oscillating element 7. The servo plunger 14 is again fixed to the oscillating element 7, for example by moving the servo plunger 14 in a direction parallel to the axis of rotation 6 towards its fixing point 33. Subsequently, the servo plunger 14 can be rotated, for example, by 90 ° about an axis parallel to the tilting axis 8 of the tilting element, in order to fix the servo plunger 14 in its end position. For example, the second servo plunger 14 in fig. 3 shows such a fixed position, wherein the second servo plunger 14 is located in the drawing plane behind the unassembled servo plunger 14 in the foreground.

Similarly, the servo spring means 25 can be fixed to the oscillating element 7 with a bayonet catch. The servo spring means 25 is here inserted with its spherical first end 24 into the swivel element 7 in a direction parallel to the swivel element tilting axis 8 and then rotated from a vertical direction perpendicular to the swivel axis 6 to a horizontal position parallel to the swivel axis 6, similarly to the position of the second servo spring means 25. In another embodiment, for example, the servo spring means 25 is rotated about its longitudinal axis before being rotated into the horizontal position, in order to engage with the oscillating element 7. Here, several forms of joining the two parts with a mortise lock are known to those skilled in the art. However, the mortise lock for fixing the servo plunger 14 and the servo spring device 25 on the swinging member 7 is a new technology compared to the prior art.

Fig. 6 shows the wobble element servo unit assembly 70 ready to be mounted into the housing 3 of the axial plunger unit. The wobble element servo unit assembly 70 may be installed into a servo unit as shown in fig. 4, for example. The rotating assembly 5 with the drive shaft 6 can be mounted between the servo spring means 25 in a subsequent assembly step of the hydraulic unit.

Fig. 7 shows an example of a hydrostatic transmission, in which the two rotary assemblies 5 are arranged in parallel and only the displacement of the left rotary assembly 5 is adjustable. For this purpose, the servo unit 10 according to the invention is installed (hidden by the rotating group 5 and the oscillating element 7) and four servo spring devices 25 are installed in four positions. These four positions can be considered as two pairs of symmetric positions. The servo unit 10 and the servo spring means 25 of each pair are arranged on each side of the tilting axis 8 of the oscillating element and on each side of the rotation axis 6, the rotation axis 6 being located in the centre of the rotating assembly 5. Such a four-quadrant arrangement is preferred in order to keep the wobble element symmetrically in its neutral position in the absence of servo pressure. On the other hand, such a four-point support of the oscillating element 7 makes it possible to prevent undesired pivoting movements of the oscillating element 7 and, in the worst case, rotation or oscillation of the rotating assembly 5, since the oscillating element 7 is supported in the lateral, vertical or horizontal direction by at least two servo spring devices 25 when the oscillating element 7 is tilted to the maximum tilting position by means of the servo pressure acting in the servo unit 10.

From the above disclosure and the figures and claims it is understood that the hydraulic unit 1 according to the invention has many possibilities and advantages compared to the prior art. Those skilled in the art will further recognize that further modifications and changes may be made to the hydraulic unit according to the present invention without departing from the spirit and scope of the present invention. Accordingly, such modifications and changes are within the scope of the claims and are covered thereby. It should be further understood that the examples and embodiments described above are for illustrative purposes only and that various modifications, changes, or combinations thereof suggested to persons skilled in the art are to be included within the spirit and purview of this application.

List of reference numerals

1 variable displacement hydraulic unit

3 case

4 end cap

5 rotating assembly

6 axis of rotation

7 swinging element

8 tilting axis of oscillating element

9 sliding surface/sliding surface side

10 servo unit

12 servo cylinder

13 servo cylinder bottom

14 servo plunger

15 servo plunger head

16 servo plunger shaft

18 servo plunger skirt

19 working direction

20 resetting device

22 servo spring

23 spring seat

24 first end servo spring

26 spring seat

27 internal guide device

28 external guide device

29 servo spring force adjusting device

32 stop surface

33 fixed point

34 fixed point

52 cylinder body

54 displacement plunger

70 swinging element servo unit assembly

100 hydrostatic transmission

200 control unit

Claims (20)

1. A variable displacement hydraulic unit (1) comprising a housing (3), the housing (3) accommodating at least one rotating assembly (5), the displacement of the at least one rotating assembly (5) being variably adjustable by means of a pendulum element (7), the pendulum element (7) being tiltable about a pendulum element tilt axis (8) perpendicular to a rotation axis (6) of the at least one rotating assembly (5) and being drivable by at least one servo unit (10), wherein the servo unit (10) comprises:

a servo cylinder (12) integral with the housing (3);

a servo piston (14) which is movable in the servo cylinder (12), wherein a servo piston head (15) of the servo piston (14) can be pressurized in the servo cylinder (12) such that a movement of the servo piston (14) tilts the pendulum element (7), wherein the servo piston (14) is connected to the pendulum element (7) by a servo piston shaft (16),

wherein the servo unit (10) is arranged inside the housing (3) on the side of the oscillating element (7) opposite to the side on which the cylinder (52) of the rotating group (5) is located, and adopts a working direction (19) substantially parallel to the rotation axis (6) of the rotating group (5).

2. The variable displacement hydraulic unit (1) as claimed in claim 1, characterized in that the variable displacement hydraulic unit (1) comprises a plurality of servo units (10), the working directions (19) of the plurality of servo units (10) being substantially parallel to each other.

3. A variable displacement hydraulic unit (1) according to claim 1, comprising two servo units (10), the two servo units (10) being symmetrically arranged with respect to the tilting axis (8) of the oscillating element, such that movement of one servo plunger (14) towards the rotating assembly (5) brings the other servo plunger (14) into the corresponding servo cylinder (12).

4. A variable displacement hydraulic unit (1) as claimed in claim 3, comprising two pairs of servo units (10), each pair of servo units (10) being arranged with one servo unit (10) on each side of the tilting axis (8) of the tilting element.

5. A variable displacement hydraulic unit (1) according to any one of claims 1 to 4, wherein the servo plunger skirt (18) of the servo plunger head (15) is convex or spherical.

6. A variable displacement hydraulic unit (1) according to any one of claims 1 to 5, wherein the servo plunger shaft (16) is connected with the oscillating element (7) by means of an articulation.

7. The variable displacement hydraulic unit (1) according to any one of claims 1 to 6, wherein the connection of the servo plunger shaft (16) to the oscillating element (7) is any one of the following connections: ball joint, hinge joint, pin joint, comprising a cap on the oscillating element (7), into which cap the protruding end of the servo plunger shaft (16) can be inserted, so that linear forces in the direction of the servo plunger shaft (16) can be transmitted onto the oscillating element (7) or vice versa.

8. A variable displacement hydraulic unit (1) according to any one of claims 1-7, wherein the servo cylinder (12) is a bore provided in the housing (3) or a cylinder fixed inside the housing (3).

9. A variable displacement hydraulic unit (1) according to any one of claims 1 to 8, wherein at the neutral position of the oscillating element (7) the rotating group (5) does not produce displacement and the servo plunger (14) is located at half the possible stroke position in the servo cylinder (12).

10. A variable displacement hydraulic unit (1) according to any one of claims 1 to 9, wherein tilting movement is provided by a stop surface (32) fixed at the housing (3).

11. A variable displacement hydraulic unit (1) according to any one of claims 1-10, wherein the servo cylinder (12) is pressurizable by a servo pressure provided by a pressure source internal or external to the variable displacement hydraulic unit (1) and controlled by a control unit.

12. A variable displacement hydraulic unit (1) as claimed in claim 11, wherein the external pressure source is a bolt-on pressure source with hydraulic fluid or air as working fluid.

13. A variable displacement hydraulic unit (1) as claimed in claim 11 or 12, wherein the magnitude of the servo pressure is provided in a load dependent manner.

14. A variable displacement hydraulic unit (1) according to any one of claims 1 to 13, wherein at least one servo spring (22) is located on the opposite side of the oscillating element (7) from the at least one servo unit (10) and on the sliding surface side (9) of the oscillating element (7); the at least one servo spring (22) is used to provide a restoring force to the oscillating element (7) when the oscillating element (7) is tilted from an initial position by the respective servo unit (10).

15. A variable displacement hydraulic unit (1) as claimed in any one of claims 1 to 14, characterised in that each servo unit (10) is assigned at least one servo spring (22).

16. A variable displacement hydraulic unit (1) as claimed in any one of claims 1 to 15, further comprising: a resetting device (20), the resetting device (20) being used to hold or reset the oscillating element (7) in a neutral position; at the neutral position, the stroke of the displacement plunger (54) is zero; wherein the reset means (20) comprises at least two servo springs (22), a first end (24) of a servo spring (22) being arranged on the sliding surface side (9) of the oscillating element (7) such that the forces of the servo springs are balanced when the oscillating element (7) is in the neutral position, wherein a second end (26) of the at least two servo springs (22) is connected with a fixation point (33) fixedly arranged in the housing (3), the fixation point (33) being arranged at an end cap (4) of the variable displacement hydraulic unit (1).

17. Hydraulic unit (1) according to claim 16, characterised in that said at least two servo springs (22) are arranged on the sliding surface side (9) of the oscillating element (7) symmetrically with respect to the oscillating element tilting axis (8).

18. A variable displacement hydraulic unit (1) as claimed in claim 16 or 17, characterised in that the reset means (20) provides an end stop (4) for the maximum angle of inclination of the rocking element (7) in either direction of inclination.

19. A variable displacement hydraulic unit (1) as claimed in any one of claims 14 to 18, wherein the servo spring (22) is in a pre-tensioned state in the initial position of the oscillating element (7).

20. Variable displacement hydraulic unit (1) according to any one of claims 14-19, wherein the servo spring (22) is guided by internal or external guiding means (27, 28) and/or connects the first end (24) to the swinging element (7) and the second end (26) to the fixed point (33) by means of an articulated connection, wherein the guiding means (27, 28) comprise, at least at the first end (24), a spring seat (23) against which the servo spring (22) can abut.

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