Manual displacement control arrangement for an axial piston pump

Abstract

Displacement control device for variably adjusting the displacement of an axial piston hydraulic pump including a rotary shaft rotatable around a shaft axis. A torque can be applied for rotating the rotary shaft to open and close servo pressure lines to adjust the displacement volume of the axial piston hydraulic pump. Concentric to the shaft axis in a mid-portion of the rotary shaft a detent sleeve is positioned having an abutment area onto which, in the neutral position, a sliding element abuts. The detent sleeve, in operating conditions is rotatably fixed with the rotary shaft and turns with the rotary shaft and for neutral position adjustments in non-operating conditions, the detent sleeve and the rotary shaft are detachable from each other such that the rotary shaft can be turned relative and independently within the detent sleeve, which is held in its neutral position by the sliding element.

Claims

1. A displacement control device for variably adjusting the displacement volume of a hydraulic axial piston pump comprising a rotary shaft mounted rotatable in a housing around a rotary shaft axis of the rotary shaft, said rotary shaft having a first end and a second end, wherein the rotary shaft is configured to open and close servo pressure lines arranged within the housing when a torque is applied to the second end, which protrudes outside of the housing, wherein the servo pressure lines are configured to conduct hydraulic fluid to and from a servo adjusting unit capable of adjusting the displacement volume of the axial piston pump, said rotary shaft further comprising a mid-portion located between the first end and the second end, wherein a detent sleeve is positioned concentric to the rotary shaft axis in the mid-portion of the rotary shaft, the detent sleeve comprising an abutment area onto which, in a neutral position of the displacement control device, a sliding element abuts, the sliding element being mounted pre-stressed in the housing and exerting a resilient force onto the detent sleeve transverse to the rotary shaft axis, wherein the detent sleeve in operating conditions of the displacement control device, is rotatably fixed to the rotary shaft and turns with the rotary shaft, wherein, for neutral position adjustments in non-operating conditions, the detent sleeve and the rotary shaft are detachable from each other, such that the rotary shaft is configured to be turned independently within the detent sleeve which is held in its neutral position by the resilient force of the sliding element onto the abutment area.

2. The displacement control device according to claim 1, wherein the abutment area is a flattened portion formed on the detent sleeve onto which a flat front face of the sliding element is configured to abut fully-faced in the neutral position of the displacement control device.

3. The displacement control device according to claim 2, wherein the sliding element and the abutment area are designed such that the detent sleeve is fixed axially with regard to the rotary shaft when the sliding element engages with the detent sleeve.

4. The displacement control device according to claim 2, wherein the abutment area is a recess formed in the detent sleeve into which a protrusion of the sliding element is configured to be inserted.

5. The displacement control device according to claim 4, wherein the sliding element and the recess are designed such that the detent sleeve is fixed axially with regard to the rotary shaft when the sliding element engages with detent sleeve.

6. The displacement control device according to claim 1, wherein the abutment area is a depression into which, in the neutral position of the displacement control device, a convex surface of the sliding element is configured to engage.

7. The displacement control device according to claim 6, wherein a protrusion of the sliding element engages the detent sleeve laterally and thereby prevents rotational motion of the detent sleeve.

8. The displacement control device according to claim 7, wherein the sliding element and the depression are designed such that the detent sleeve is fixed axially with regard to the rotary shaft when the sliding element engages with the detent sleeve.

9. The displacement control device according to claim 1, wherein the abutment area is a recess formed in the detent sleeve into which a protrusion of the sliding element is configured to be inserted.

10. The displacement control device according to claim 4, wherein the sliding element and the recess are designed such that the detent sleeve is fixed axially with regard to the rotary shaft when the sliding element engages with the detent sleeve.

11. The displacement control device according to claim 1, wherein a feedback sleeve is attached to the first end of rotary shaft, wherein the feedback sleeve is rotatable with respect to the housing and with respect to the rotary shaft, wherein a feedback element attached to a displacement element of the hydraulic axial piston pump is capable of feeding back the position of the displacement element of the hydraulic axial piston pump and engages with the feedback sleeve eccentrically, such that a motion of the displacement element and therefore of the feedback element causes a rotation of the feedback sleeve relative the rotary shaft, thereby opening and/or closing the servo pressure lines.

12. The displacement control device according to claim 11, wherein an offset of a feedback element axis to a tilt axis of the displacement element is different from a distance of the feedback element axis to the rotary shaft axis.

13. The displacement control device according to claim 12, wherein the offset is bigger than the distance.

14. The displacement control device according to claim 1, wherein an eccentric pin having an eccentric axis is located at the first end of the rotary shaft, wherein the eccentric axis provides a rotational axis for a feedback link, whose first end is coupled to a control spool and whose second end comprises an elongated hole section for receiving a second end of a feedback element attached to a displacement element, such that a motion of the displacement element causes a rotation of the feedback link and shifts the control spool.

15. The displacement control device according to claim 14, wherein the eccentric pin is integrally formed on the first end of the rotary shaft.

16. The displacement control device according to claim 14, wherein the elongated hole section is U-shaped.

17. The displacement control device according to claim 14, wherein the elongated hole section is capable of exerting an elastic force onto the second end of the feedback element for providing a clearance-free engagement of the second end of the feedback element and the elongated hole section.

18. The displacement control device according to claim 1, wherein the hydraulic axial piston pump is of the swashplate type or the bent axis type, wherein a displacement element of the hydraulic axial piston pump is configured to be swiveled to positive and/or negative displacement angles.

19. The displacement control device according to claim 1, wherein the torque applied to the second end of the rotary shaft is configured to be generated manually, mechanically, pneumatically, electro-mechanically or hydraulically.

20. The displacement control device according to claim 1, wherein a lever is fixed to the second end of the rotary shaft or is fixed to the detent sleeve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of a displacement control device according to the invention are depicted in more detail in the appended drawings, which do not limit the scope of the inventive idea. All features of the disclosed and illustrated embodiments may be combined in any desired combination with one another within the scope of the invention. For this purpose:

(2) FIG. 1 shows schematically a hydraulic circuit diagram of an exemplary hydraulic pump with a displacement control device according to invention;

(3) FIG. 2 shows a cross section of an exemplary embodiment of a displacement control device according to the invention with a first alternative to feedback the displacement element position to the displacement control device;

(4) FIG. 3 depicts a side view of the displacement control device of FIG. 2 without housing;

(5) FIG. 4 is a partial cross-section along the plane B-B of FIG. 3

(6) FIG. 5 is a partial cross-section along the plane C-C of FIG. 3;

(7) FIG. 6 is a partial cross-section along the plane D-D of FIG. 3;

(8) FIG. 7 shows in an exploded view another embodiment of a displacement control device according to the invention with a second alternative to feedback the displacement element position to the displacement control device.

DETAILED DESCRIPTION

(9) FIG. 1 shows schematically a hydraulic circuit diagram of an exemplary hydraulic pump 100 with a displacement control device 1 according to invention. The displacement control device 1 is fed with hydraulic fluid under pressure via charge pressure line 50 leading from the hydrostatic piston pump 100 to charge pressure port P of the displacement control device 1. The displacement control device 1 according to FIG. 1 is shown in the neutral position in which the hydrostatic piston pump 100 does not show any displacement volume. Hereby servo pressure ports A and B are both connected via corresponding discharge ports T to discharge line 60 connected to tank 80. Thus both servo piston sides 35A and 35B of servo piston 35 are at the same pressure level, here at tank pressure level, and the servo piston 35 is centered via its servo piston springs 37A and 37B. Hence, displacement element 4 of hydrostatic piston pump 100 is in its neutral positon too, and no displacement volume flow rate is generated by hydrostatic piston pump 100. This neutral position of displacement element 4 is fed back via feedback element 3 to displacement control device 1.

(10) FIG. 2 shows an exemplary embodiment of a displacement control device 1 according to the invention in cross-section. The displacement control device 1 is housed in a housing 20, preferably not part of the hydraulic machine housing. The shown hydraulic machine of this embodiment is exemplarily of the swashplate type. For reason of simplicity only, part of a displacement element 4, here a swashplate, and a feedback element 3 associated therewith is shown. The displacement element 4, here the swashplate, is tiltable in two directions about a tilt axis 16, wherein the tilt angle determines the volumetric flow rate of the hydraulic machine. These features and the manner of operation of such a hydraulic machine are well known to a person skilled in the relevant art, such that further explanations thereto can be omitted at this point. In the following, the terms “displacement element” and “swashplate” will be used synonymously with the same reference numeral 4.

(11) Feedback element 3 which is generally pin or rod shaped and having a longitudinal axis 15, is fixedly attached with a first end 23 to the swashplate 4. Thus, the feedback element 3, in particular the first end 23 participates in any tilt motion of the swashplate 4 with a curvature-like motion. The longitudinal axis 15 of feedback element 3 is laterally offset from the tilt axis 16 of swashplate 4 by a distance “a” as shown in FIGS. 2 and 3. The second end 24 of feedback element 3 extends into the interior of the displacement control device 1 and engages a feedback sleeve 2 which is rotatable supported in housing 20. Feedback sleeve 2 has a slot 21 extending in a radial direction, in which slot 21 the second end 24 of feedback element 3 is slidable, as depicted in FIG. 6, in order to enable the curvature-like motion of the feedback pin 3, i.e. of second end 24 of feedback pin 3 within the feedback sleeve 2, and transfer the curvature-like motion into a rotational motion of feedback sleeve 2 around the rotary shaft axis 13. In an inner bore of feedback sleeve 2 a first end 11 of a generally cylindrical rotary shaft 10 is held rotatable around the rotary shaft axis 13 as well. Thereby, feedback sleeve 2 and rotary shaft 10 can rotate independently from each other.

(12) Feedback sleeve 2 has several ports 25A, 25B, 25P and 25T which can be put in fluid connection with charge pressure line 50, discharge pressure line 60 and with servo pressure lines 40 and 45 all located partially within housing 20 of displacement control device 1. The lines 40, 45, 50 and 60 are connected with the respective ports 25A, 25B, 25P and 25T, what is shown in FIG. 5 in greater detail. The first end 11 of rotary shaft 10 comprises two recesses 26L and 26R in the region of the ports 25A, 25B, 25P and 25T. Between the recesses 26L and 26R a bridge 27 of rotary shaft 10 acts as a barrier or seal between charge pressure port 25P and the discharge port 25T. Port 25A and 25B connected to servo pressure lines 40 and 45 are not visible in FIG. 2 as they are located in the back respectively in the front of the bridge 27. In the situation of displacement control device 1 shown in FIG. 2, which again corresponds to the neutral position or zero position of displacement control device 1, no fluid flow is possible between one of servo pressure lines 40 or 45 and charge pressure line 50. Nor a fluid communication of the other one of servo pressure lines 40 or 45 with discharge line 60 is enabled. This will be explained in more detail with FIG. 5 below.

(13) The mid portion 14 of rotary shaft 10 is surrounded by a detent sleeve 5. A second end 12 of rotary shaft 10 protrudes outside of housing 20. This second end 12, for instance, as shown in the embodiment of FIG. 2, is threaded and can be fixedly connected to the adjoining end of detent sleeve 5 by means of a nut or counter-nut 19, wherein the detent sleeve 5 abuts with its other end on a shoulder 29 on rotary shaft 10 beneath the first end 11 of rotary shaft 10. According to the embodiment of FIG. 2, a lever 6 is attached to detent sleeve 5 which enables the rotation of detent sleeve 5 together with rotary shaft 10 relative to feedback sleeve 2. In operation of the hydraulic device rotary shaft 10 and detent sleeve 5 are jointly fixed together in order that a torque applied to the second end 12 of rotary shaft 10 causes the rotary shaft 10 to rotate together with detent sleeve 5. As it will be explained in more detail with the description of FIG. 5, a rotation of the rotary shaft 10 enables a fluid connection between the charge pressure line 50 and of servo pressure lines 40 or 45 and another fluid connection of discharge line 60 with the other one of servo line 40 or 45 in order to command the displacement element 4 of the hydrostatic piston pump 100 to another displacement volume flow rate.

(14) Loosening of nut 19 enables a free and relative rotation of rotary shaft 10 with respect to detent sleeve 5, which permits a precise adjustment of the neutral position of a displacement control device 1 according to the invention, as the detent sleeve 5 is held in a fixed rotational and axial position by a sliding element 8. For this purpose, detent sleeve 5 comprises an abutment area 7 into which the sliding element 8 can engage. Preferably the abutment area 7 shows a flattened portion 7a onto which a flat front face 8a of the siding element 8 is pushed resiliently by means of a spring 17. Thereby spring 17 is held pre-stressed in housing 20 by a cap or—in general—by a stopper 18, preferably screwed-in in the housing 20.

(15) As can be derived from FIG. 2, the sliding element 8 is pushed towards the stopper 18 when a torque is applied to the second end 12 of rotary shaft 10. Here, for instance, by means of lever 6. When the detent sleeve 5 is rotated the flat front face 8a leaves the planar contact on the flattened portion 7a. This planar contact is transferred by the rotational motion of the detent sleeve 5 to a linear contact. As this linear contact is eccentric to the rotary shaft axis 13, the resilient force of spring 17 generates a restoring torque via the eccentric line contact. This restoring torque is used to hold the detent sleeve in place, when the rotary shaft 10 has to be adjusted to the zero or neutral position of the hydrostatic axial piston pump in a first adjustment process when putting the hydrostatic axial piston pump into service for the first time or after maintenance.

(16) In the following figures and description, the same reference numerals will be used where appropriate to denote similar parts, or features, in order to facilitate an explanation of the invention.

(17) FIG. 3 depicts a side view of the displacement control device 1 of FIG. 2, however, without the housing 20. Swashplate 4 and feedback element 3 are shown in operation condition. Of particular note are the positions and geometrical relationships of the distance “a” of the longitudinal axis 15 of the feedback element 3 and the tilt axis 16 of the displacement element 4 as well as the offset “b” of the longitudinal axis 15 of the feedback element 3 and the axis of rotation 13 of the feedback sleeve 2. Thereby the distance “a” is larger than the offset “b” which means that a small change in the tilt angle of the swashplate 4 cause a big feedback response to the feedback sleeve 2, which means further that the displacement control device 1 according to the invention allows big rotational angles at the rotary shaft 10 for commanding the displacement volume of the hydrostatic piston pump 100. This finally provides for a precise, smooth (i.e. not agitated) and better controllable control of the hydrostatic piston pump as it is not oversensitive.

(18) In FIG. 3 are shown three planes B-B, C-C and D-D that indicate the respective position of the detailed cross-sections of the displacement control device 1 of FIG. 3 that are depicted in the following FIGS. 4 to 6.

(19) FIG. 4 depicts a cross section taken in plane B-B of FIG. 3, i.e. at the mid-level of a reset mechanism 28, comprising sliding element 8, spring 17 and stopper 18. Clearly visible is an abutment area 7 with a flattened portion 7a of a recess or depression 7b in detent sleeve 5 against which a flat front face 8a of sliding element 8 abuts in full planar contact. In this configuration the forces acting on detent sleeve 5 and rotary shaft 10 are balanced. Rotation of detent sleeve 5 with respect to reset mechanism 28 causes a deviation from the full contact between the flattened portion 7a located at detent sleeve 5 and the flat front face 8a of sliding element 8. Depending on the direction of the rotation, contact is in this case only between the edges or peripheral regions of the flattened portion 7a and the flat front face 8a. As spring 17 exerts a force via sliding element 8 on detent sleeve 5, a restoring momentum acts on detent sleeve 5 that counteracts the applied rotation. This is due to the position of the line contact between detent sleeve 5 and sliding element 8, which is laterally offset from the common axis of rotation 13 of detent sleeve 5 and rotary shaft 10. Thus, reset mechanism 28 tends to restore the neutral position state of the displacement control device 1 shown in FIG. 3.

(20) In FIG. 5 a different cross section taken in plane C-C is shown. This cross-section is taken at the level of ports 25A, 25B, 25P and 25T in feedback sleeve 2, wherein the recesses 26L and 26R and the bridge 27 of rotary shaft 10 can be seen as well. In the operational condition shown in FIG. 5 the solid section 27/bridge 27 of rotary shaft 10 together with the recess 26L left of the bridge 27 enables a hydraulic fluid connection of the charge pressure line 50 with the servo pressure line 45 leading, for instance, to servo piston side 35A (see FIG. 1). This position of the bridge 27 also enables together with the recess 26R on the right side of the bridge 27 discharging of hydraulic fluid from the other servo piston side, here for instance, to servo piston side 35B (see FIG. 1) via servo discharge line 60 to a region with lower pressure, e.g. to tank 80. The situation shown in FIG. 5 is just after rotating lever 6 in one direction around rotational axis 13 of rotary shaft 10. The feedback sleeve 2 is still its initial position, however, feedback sleeve 2 will be turned by means of the feedback element 3 (not shown in FIG. 5), for instance, in the counter-clockwise direction until the discharging of the non-charged servo piston side, here servo piston side 35B, is disabled. The position of the rotary shaft 10 and therewith of bridge 27 will remain as shown in FIG. 5, however, the fluid cross section between charge pressure port 25P and servo pressure port 25A will be reduced due to the rotation of the feedback sleeve 2.

(21) FIG. 6 shows a third cross section taken in plane D-D of FIG. 3 taken at the level of feedback sleeve 2. The second end 24 of feedback element 3 extends into slot 21 of feedback sleeve 2, and is in a slide-able but close contact with the sidewalls 22 of slot 21. As the feedback element 3 moves in a curvature-like motion, e.g. a circular arc centred on the axis of tilt 16 of swashplate 4 slot 21 is necessary to compensate the change in the distance between the axis 15 of feedback element 3 and the common axis of rotation 13 of feedback sleeve 2 and rotary shaft 10 upon any displacement of feedback element 3.

(22) FIG. 7 depicts, in an exploded view, another embodiment of a displacement control device 1 according to the invention. Therewith a second alternative for feeding back the position of the displacement element 4 to the displacement control device 1 is depicted. However, the neutral setting adjustability allowing a relative and independent rotational motion between the rotary shaft 10 and the detent sleeve 5 when loosening the nut 19 is maintained as descript above with FIGS. 2 and 3. This is shown in the upper part of FIG. 7 in an described manner by means of the exploded view. An loosened nut 19 does not press the detent sleeve 5 any longer on a shoulder 29 on rotary shaft 10 separating the mid-portion 14 of rotary shaft 10 from the first end 11 of rotary shaft 10. Thereby, the rotary shaft 10 can be rotated within the longitudinal bore of detent sleeve 5, whilst detent sleeve 5 is hold rotationally fixed in position by means of the spring forces of spring 17. Thus, if the rotary shaft 10 is brought into its neutral position the nut 19 can be tighened (again) to fix and define the neutral position of the inventive displacement control device 1.

(23) The rotary shaft 10 is in its neutral position, when the displacement element 4 is its neutral position in which the hydraulic axial piston unit 100 do show any displacement volume. The displacement element 4 is situated in the neutral position if the pressures acting on both sides 35A and 35B of the servo piston 35 are balanced (see FIG. 1). In the embodiment of FIG. 7 a feedback link 32 feeds back to the control spool 33 the position of the feedback element 3 attached to displacement element 4. Control spool 33 serves in this embodiment for opening and closing the servo lines 40 and 45 as well as servo charge line 50 and servo discharge line 60 in an adequate manner to forward the demand set at the displacement control device 1 to the servo adjusting unit 38 (see FIG. 1). For this purpose an eccentric pin 30 is located at the first end 11 of rotary shaft 10. This eccentric pin 30 is rotatable supported around a rotational axis 31 in the mid-portion 32C of the feedback link 32. An elongated hole section 34 at the second end 32B of the feedback link 32 is engaged rotatable free with the second end of feedback element 3 attached to displacement element 4. On the other side the feedback link 32 is coupled in an articulated manner with its first end 32A to the control spool 33, such that any motion of the feedback element 3 or the eccentric pin 30 due to a rotation of the displacement element 4 or the rotary shaft 10 is transmitted to control spool 33. Thereby either the rotational axis 31 of the eccentric pin 30 or the longitudinal feedback element axis 15 constitutes the axis of rotation.

(24) By means of this arrangement the feedback link 32 is in an defined position in the zero displacement volume condition of the hydraulic axial piston unit 100 and is capable to provide via the rotational axis 31 and the eccentric pin 32 the neutral position for rotary shaft 10. As can be derived from FIG. 7 this neutral position of rotary shaft 10 can be aligned with the rotational neutral position of detent sleeve 5 simply by openning and tighen nut 19. The neutral position of the detent sleeve 5 is kept fixed by means of the sliding element 8 which is prestressed by spring 17.

(25) When implementing the invention the eccentric pin 30 can be formed integrally at the first end 11 of the rotary shaft 10 or can be a separate part attached to the rotatory shaft 10, for instance at shoulder 29. Elongated hole section 34 can be an oblong hole in the feedback link 32 or e.g. for assembling reasons in the shape of an U. Thereby an elongated hole is preferred due to the curvature-like motion the feedback element 3 at the displacement element 4 can perform. In another preferred embodiment of the invention the elongated hole section 34 is capable to exert an elastic force onto the second end 24 of the feedback element 3 for providing a clearance-free engagement of the second end 24 of the feedback element 3 and the elongated hole section 34. This can be realized e.g. when applying a U-shaped elongated hole section by inserting a spring or other elastic material into the elongated hole section.

(26) Finally with the inventive displacement control device 1 a quick, simple, robust and comfortable neutral setting device is provided, which reliable admits the individual neutral setting of a hydraulic axial piston unit thereby compensating manufacturing and assembly tolerances within the whole hydraulic axial piston unit.

(27) While the present disclosure has been illustrated and described with respect to particular embodiments thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.