Abstract
A variable displacement hydraulic unit with a housing in which a rotating group is housed, wherein the displacement volume of the rotating group is variably adjustable by means of a swivel element able to tilt around a tilt axis perpendicular to the rotational axis of the rotating group. The swivel element can be actuated by at least one servo unit including a servo cylinder integrated in the housing and a servo piston moveably within the servo cylinder. The head of the servo piston can be pressurized in the servo cylinder such that a movement of the servo piston coupled to the swivel element via a servo piston shaft tilts the swivel element; wherein the servo unit is located within the housing on that side of the swivel element on which no rotating group is located, and follow a working direction substantially parallel to the rotational axis of the rotating group.
Claims
1. A variable displacement hydraulic unit with a housing in which a rotating group is housed, wherein the displacement volume of the rotating group is variably adjustable by means of a swivel element tiltable around a tilt axis perpendicular to the rotational axis of the rotating group, which swivel element can be actuated by at least one servo unit comprising: a servo cylinder integrated in the housing; a servo piston moveably within the servo cylinder, wherein the head of the servo piston can be pressurized in the servo cylinder, such that a movement of the servo piston, which is coupled to the swivel element via a servo piston shaft, tilts the swivel element; wherein the servo unit is arranged within the housing on that side of the swivel element on which no rotating group is located, and follows a working direction substantially parallel to the rotational axis of the rotating group.
2. The hydraulic unit according to claim 1, wherein the hydraulic unit comprise more than one servo unit with working directions substantially parallel to each other.
3. The hydraulic unit according to claim 1, comprising two servo units arranged symmetrically with regard to the swivel element tilt axis, such that the movement of one servo piston towards the rotating group causes the other servo piston to enter into the respective servo cylinder.
4. The hydraulic unit according to claim 3, comprising two pairs of servo units, with each pair having one servo unit on either side of the swivel element tilt axis.
5. The hydraulic unit according to one of the preceding claims, wherein a skirt of the servo piston head shows a convex or spherical shape.
6. The hydraulic unit according to claim 1, wherein the servo piston shaft is connected to the swivel element in an articulated manner.
7. The hydraulic unit according to claim 1, wherein the connection of the servo piston shaft to the swivel element is a kind of ball joint, hinge joint, pin joint or similar, comprising a calotte on the swivel element into which a convex end of the servo piston shaft can be inserted, such that linear forces in direction of the servo piston shaft can be transmitted to the swivel element and vice versa.
8. The hydraulic unit according to claim 1, wherein the servo cylinder is a bore in the housing or a cylinder fixed to the inner side of the housing.
9. The hydraulic unit according to claim 1, wherein, in a neutral position of the swivel element, the rotating group do not show a displacement volume and the servo piston(s) are at half way of their possible stroke in the servo cylinder.
10. The hydraulic unit according to claim 1 wherein a tilt movement is provided by means of a stop surface stationary at the housing.
11. The hydraulic unit according to claim 1, wherein the servo cylinder can be pressurized by a servo pressure provided by a pressure source internal or external to the hydraulic unit and controlled by a control unit.
12. The hydraulic unit according to claim 11, wherein the external pressure source is a bolt-on pressure source having hydraulic fluid or air as working fluid.
13. The hydraulic unit according to claim 11, wherein the height of the servo pressure is provided in a load dependent manner.
14. The hydraulic unit according to claim 1, wherein a servo spring is located at the swivel element opposite to a servo unit and on the sliding surface side of the swivel element, in order to provide a restoring force to the swivel element when the swivel element is tilted away from an initial position by the allotted servo unit.
15. The hydraulic unit according to claim 1, wherein to each servo unit at least one servo spring is allotted.
16. The hydraulic unit according to claim 1, comprising restoring means for holding or restoring the swivel element into a neutral position, in which the stroke of the displacement pistons is zero, wherein the restoring means comprise at least two servo springs arranged with a first end on the sliding surface side of the swivel element, such that in neutral position of the swivel element the servo spring forces are balanced, and wherein the servo springs are attached with their second end to a fixing point stationary within the housing, preferably at the end cap of the hydraulic unit.
17. The hydraulic unit according to claim 16, wherein the servo springs are arranged symmetrically with respect to the tilt axis on the sliding surface side of the swivel element.
18. The hydraulic unit according to claim 16, wherein the restoring means provide for an end stop of a maximum tilt angle of the swivel element in either direction of tilt.
19. The hydraulic unit according to claim 14, wherein, in the initial position of the swivel element, the servo spring(s) is/are pre-tensioned.
20. The hydraulic unit according to claim 14, wherein the servo spring(s) is/are guided by internal or external guiding means and/or is/are attached with a first end in an articulated manner to the swivel element and with the second end to the fixing point, wherein the guiding means comprise at least at their first end a spring seat on which the servo spring can abut.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In the following Figures, exemplary embodiments for the servo unit, for the servo springs, for the servo spring arrangements, and for combinations thereof according to the invention, as described before, are presented. In the embodiments shown in the following Figures, different possibilities of arrangement are shown, which can be combined with each other without leaving the spirit of the inventive concept, wherein combinations not described are covered by the invention as well. Further, the presented embodiments do not limit the scope of the invention. The following Figures show:
[0030] FIG. 1 is a schematic view of a first embodiment according to the invention;
[0031] FIG. 2 is a schematic view of a second embodiment according to the invention;
[0032] FIG. 3 is a sectional view of a third embodiment according to the invention;
[0033] FIG. 4 is a sectional view of a fourth embodiment according to the invention;
[0034] FIG. 5 is a detailed view of a fifth embodiment according to the invention;
[0035] FIG. 6 is a schematic view of the fifth embodiment according to the invention; and
[0036] FIG. 7 is a rear view of the embodiment according to FIG. 4.
DETAILED DESCRIPTION
[0037] FIG. 1 is a schematic view of a first embodiment of the invention, showing an end cap 4 in which a drive shaft 2 of a rotational group 5 is mounted. Rotational group 5 is rotational with regard to a rotational axis 6. The displacement volume of rotational group 5 is adjustable by means of a swivel element 7 which is shown in a neutral position in which displacement pistons of the rotational group 5 do not show any stroke. Swivel element 7 can be tilted by means of servo piston 14 in either direction clockwise or counterclockwise. Servo pistons 14 show a servo piston head 15 which can be pressurized in a servo cylinder (not shown) so that servo piston 14, guided by a servo skirt 18, transmits a linear force along servo shaft 16 towards the swivel element 7 in order to tilt/rotate swivel element 7, thereby setting the displacement volume of rotational group 5. When the swivel element 7 is tilted by means of one of the servo pistons 14, the active servo piston 14 is moving towards the right and the non-active servo piston which is not pressurized is moving to the left. As can be derived from FIG. 1, the hydraulic unit 1 according to FIG. 1 is in its neutral position, i.e. the rotating group 5 does not show any displacement volume, hence equal pressure acts on both servo pistons 14.
[0038] In the schematic view of FIG. 2a side view of another embodiment according to the invention , only one servo piston 14 is arranged in order to move the swivel element 7 around its tilt axis 8 in either direction. If the swivel element 7 is tilted around the swivel element tilt axis 8, one of the two servo spring arrangements 25 shown in FIG. 2 is compressed, thereby generating a counterforce to the pressure force acting on servo piston 14, respectively on servo piston head 15. The servo pressure force is proportional to the servo spring force in this arrangement, such that intermediate positions between a maximum angle and a minimum angle can be obtained by adjusting/setting the servo pressure. As well as in FIG. 1, the servo piston 14 in the embodiment of FIG. 2 is arranged at the side of the swivel element opposite to the cylinder block 52 of the rotating group 5. This provides for a very compact design of the whole hydraulic unit 1. A person skilled in the art derives from FIG. 1 as well as from FIG. 2 that the end cap 4 constitutes part of the hydraulic units housing 3 involving the components shown in FIGS. 1 and 2.
[0039] An exemplary embodiment showing a sectional cut of a hydraulic unit 1 according to the invention is shown with FIG. 3. It can be seen that the hydraulic unit according to the invention shows a very compact design. The displacement volume of the hydraulic unit 1 can be adjusted by means of a servo unit 10, which is arranged integrally with the housing 3 of the hydraulic unit 1. As shown with FIG. 3, the servo units 10, comprising a servo cylinder 12 and a servo piston 14, are arranged on the opposite side of the swivel element 7 than a cylinder block 52 of a rotating group 5 whose displacement volume can be adjusted by means of the swivel element 7. In FIG. 3, two servo spring arrangements 25 are shown which are able to counteract to the servo unit 10. Thereby, the servo spring arrangements 25 are connected to the swivel element 7 in an articulated manner, as will be shown in more detail further on. The same is valid for servo piston shaft 16, as the fixing point 33 on the swivel element 7 performs a circular motion when the swivel element 7 tilts around the swivel element tils axis 8.
[0040] In FIG. 3, it is also shown that the servo springs 22 are guided by an internal guiding means 27 which also provides a seat 26 for servo spring 22. Seat 26 can be moved parallel to the rotational axis 6 of the hydraulic unit 1 in order to adjust the servo spring forces. On the other end of servo springs 22, a spring seat 23 is fixed at a first end 24 of servo spring arrangement 25 in order to pre-tension servo spring 22. Together with the spring seat 26 on the second end of servo spring 22, an embodiment for a servo spring arrangement 25 is shown in which the servo spring arrangements 25 can be mounted as an assembly group into the hydraulic unit 1. The pre-tensioning forces of the servo springs 22 can be used to define the neutral position of hydraulic unit 1 in case the servo unit 10 is non-pressurized.
[0041] In FIG. 4, another embodiment according to the invention is shown in a sectional view, showing a compact hydrostatic transmission 100 comprising a hydrostatic unit 1 which is adjustable in its displacement volume by means of tilting a swivel element 7. For this, two servo units 10 are arranged on either side of rotational axis 6. Each servo unit 10 comprising a servo piston 14, whose servo piston head 15 can be pressurized by a servo pressure in a servo cylinder 12. When the servo piston-head 15 in the servo cylinder 12 is pressurized, the servo piston 14 moves guided by its servo skirt 18 along the servo cylinder walls towards the swivel element 7, thereby tilting the swivel element 7. When the swivel element 7 is tilted, the fixation points 33 of the servo piston shafts 16 to the swivel element 7 perform a rotational motion. In order to compensate this rotational movement of fixations points 33, the servo piston skirts 18 show a convex shape, so that the servo piston shaft 16 in neutral position of the swivel element 7 is parallel to rotational axis 6 of the rotational group 5 and can pivot around a small angle in order to not impede the rotational motion of the swivel element 7. A person with skills in the relevant art detects from FIG. 4 that, when the swivel element 7 is tilted out of its neutral position, the inclination angle of both servo piston shafts 16 can be changed with respect to a zero position of the swivel element 7 due to the convex shape of the servo piston skirt 18. The servo piston skirts 18 are also capable of providing a sealing with the servo cylinder 12 in such an inclined orientation.
[0042] On the opposite side of swivel element 7 in the embodiment of FIG. 4, two servo spring arrangements 25 can counteract the servo pressure in one of the two servo units 10. Thereby, the first ends 24 of the servo spring arrangements 25 are also fixed to the swivel element 7 in an articulated manner, such that a basically longitudinal axis of the servo spring arrangements 25 can follow the rotational movement of fixation points 34 on swivel element 7 (in FIG. 4 below fixing points 33 of the servo piston shafts 16). If one of the two servo units 10 in FIG. 4 is pressurized with a servo pressure, the corresponding servo spring arrangement 25 on the other side of swivel element 7 is compressed, thereby providing a counterforce to the servo force in servo cylinder 12. The other servo spring arrangement 25 is elongated or decompressed, respectively.
[0043] As shown with FIG. 3, the arrangement of FIG. 4 also comprises servo spring force adjustment means 29 with which the pre-tension of the servo spring arrangements 25, i.e. the servo springs 22, can be set and adjusted such that the per-tensioning forces in a neutral position of the swivel element 7 of both servo spring arrangements 25 are equal and capable of positioning the swivel element 7 in the neutral position. Thus, the servo spring arrangements 25 form restoring means 20 for the neutral position of the swivel element 7.
[0044] With FIGS. 5 and 6, a detailed view of an inventive servo arrangement according to the invention is shown, wherein a method for assembling servo pistons 14 and servo spring arrangements 25 to the swivel element 7 are shown. Especially for the fixing point 33 of servo shaft 16 to the swivel element 7, it can be seen that the end of servo shaft 16 is designed in an exemplary spherical form, so that the servo shaft 16 can be mounted in a calotte formed in the swivel element 7. The servo piston 14 is then fixed to swivel element 7 by moving the servo piston 14 in a direction parallel to the rotational axis 6 towards its fixing point 33, for example. Subsequently, the servo piston 14 can be rotated around an axis parallel to the swivel element tilt axis 8 by, e.g., 90 for fixing the servo piston 14 in its end position. The second servo piston 14 in FIG. 3 is shown is such a fixed position, for instance, wherein the second servo piston 14 is located in the drawing plane behind the non-assembled servo piston 14 in the foreground.
[0045] In an analogous way, servo spring arrangement 25 can be fixed to the swivel element 7 in a kind of bayonet lock. Here, servo spring arrangement 25 is inserted into the swivel element 7 parallel to swivel element tilt axis 8 with its ball-like first end 24, then pivoted from the vertical orientation into a horizontal position parallel to the rotational axis 6, and similar to the position of the second servo spring arrangement 25. In another embodiment, the servo spring arrangement 25 is rotated around its longitudinal axis before pivoting into the horizontal position in order to engage with swivel element 7, for example. Here, a person skilled in the art knows several forms of connecting two parts by a bayonet like lock. However, bayonet locks for fixation of servo pistons 14 as well as of servo spring arrangements 25 on a swivel element 7 are new over the state of the art.
[0046] In FIG. 6, a swivel element servo unit assembly group 70 is shown ready for being mounted into an axial position unit housing 3, for example, into the servo unit shown with FIG. 4. The rotating group 5 with drive shaft 6 could be mounted between the servo spring arrangements 25 in a following assembly step of the hydraulic unit.
[0047] FIG. 7 shows an example for a hydrostatic transmission in which two rotating groups 5 are arranged in parallel, wherein only the left one of FIG. 7 is adjustable in its displacement volume. For this, the servo units 10 according to the invention which are hidden by the rotating group 5 and the swivel element 7 are mounted as well as four servo spring arrangements 25 at four locations. These four locations can be seen as two pairs of symmetrical locations. The servo units 10 and the servo spring arrangements 25 of each pair are arranged on either side of the swivel element tilt axis 8 and on either side of rotational axis 6, which is in the center of rotational group 5. Such a four-quadrant arrangement is preferred in order to symmetrically hold the swivel element in its neutral position in case that servo pressure is absent. On the other hand, such a four-point support for the swivel element 7 prevents from non-desired pivot motions of the swivel element 7 and, in the worst case, of pivoting or vibrating of the rotating group 5, as the swivel element 7 is laterally as well as vertically, or horizontally, supported by at least two servo spring arrangements 25in case the swivel element 7 is tilted to maximum tilt position by means of a servo pressure acting in the servo unit 10.
[0048] From the above disclosure and the accompanying Figures and claims, it will be appreciated that the hydraulic unit 1 according to the invention offers many possibilities and advantages over the prior art. It will be appreciated further by a person skilled in the relevant art that further modifications and changes could be made to the hydraulic unit according to the invention without parting from the spirit and scope of this invention. Hence, such modifications and changes are within the scope of the claims and covered by them. It should be further understood that the examples and embodiments described above are for illustrative purposes only and that various modifications, changes or combinations of embodiments in the light of thereof, which will be suggested to a person skilled in the relevant art, are included in the spirit and purview of this application.
