This application claims foreign priority benefits under U.S.C. § 119 from German Patent Application No. 10 2021 205 359.9 filed May 26, 2021, the content of which is hereby incorporated by reference in its entirety.
The present invention is related to variable displacement hydraulic units, specifically to manual displacement control devices of variable displacement hydraulic units.
Hydrostatic units equipped with manual displacement control devices often comprise a rotatable input shaft, on which a torque can be applied to by the system operator in order to adjust the displacement volume of the hydrostatic unit. Diverse manual displacement control devices and mechanisms can be applied to convert the rotational movement of the input shaft to hydraulic pressure acting on a servo unit in order to tilt a displacement element of the hydrostatic unit. If the operator displacement command changes, the servo pressure increases or decreases, and the inclination angle of the displacement element is changed. A mechanical position feedback is provided to indicate the operator that the intended adaptation of the inclination angle of the displacement element is reached, when the displacement of the pump is consistent with the input signal applied to the input shaft.
Due to manufacturing tolerances of the components of the hydraulic unit, particular its displacement control devices, the relative positions of the mechanical feedback element and the input shaft of the control unit for providing servo pressure to the servo unit has to be coincidently in the zero position when the hydraulic unit is in its neutral position. As the manual displacement control device installed to a variable displacement hydraulic unit after its assembly, the zero position of the manual displacement control may not coincide with the neutral position of the hydraulic unit. Subsequently the mechanical relations in the feedback chain leads to an asymmetrical behavior of the manual displacement control unit. This can even cause the input lever to be in a non-centered starting position, which as a result negatively influences the control behavior of the hydraulic unit. This also may lead to asymmetric rotational angles of the input shaft, even though an adjustable centering mechanism for bringing the input shaft to its rotational zero position.
It is therefore the objective of the invention to provide a manual displacement control device, which is adjustable to the neutral position of a variable displacement hydraulic unit after being assembled and installed to the hydraulic unit and which manual displacement control device shows a symmetrical rotational behavior when setting the displacement of the hydraulic unit.
The objective according to the invention is solved by a manual displacement control device according to claim 1 and a hydraulic unit according to claim 10. Preferred embodiments are disclosed in the dependent subclaims.
The manual displacement control device according to the invention is applicable for variable displacement hydraulic units, which are equipped with a servo unit capable of operating a variable tiltable displacement element in order to set the displacement volume of the variable displacement hydraulic unit. The control device according to the invention comprises an input shaft, which is mounted rotatable about an input shaft axis in an input shaft block. The input shaft protrudes from the input shaft block with a first end, on which a rotating torque can be mounted. The control device further comprises a control spool housed in a control housing. The control spool can be moved by means of rotation of the input shaft for controlling servo pressure, which can be guided to and from the servo unit. Depending on the servo pressure, the servo unit interacts with the displacement element of the variable displacement hydraulic unit and thereby controls the displacement of the hydraulic unit. A feedback transmitting element is provided for transmitting the displacement element position to the control unit and the input shaft. The feedback transmitting element can pivot about a feedback pivot axis, which is oriented basically parallel to the input shaft axis. The feedback transmitting element comprises a first end portion for interacting with the control spool and a second end portion for receiving a mechanical feedback signal of a feedback element connected to the displacement element of a hydraulic unit, such that a mechanical feedback chain is provided between the feedback element and the control spool of the control unit. The actuation signal induced at the first end of the input shaft displaces the control spool thereby changing the pressures in the servo unit which leads to a change of inclination angle of the displacement element, which causes a displacement of the feedback element that is transferred back to the control spool by a pivoting motion of the feedback transmitting element.
According to the invention positioning means are provided, which are capable of adjusting and fixing the lateral position of the input shaft with respect to the control housing in a direction basically perpendicular to the input shaft axis and basically perpendicular in direction of a centering force exerted on the input shaft. The centering force is exerted by a centering mechanism in order to bring the input shaft into a zero rotational position when no rotating torque is applied to the first end of the input shaft. This lateral adjustability of the position of the input shaft minimizes the asymmetric behavior when controlling the hydraulic unit displacement as all manufacturing and/or assembling tolerances of the involved parts can be compensated.
In contrast to a rotational or angular compensation of tolerances, the lateral movement of the input shaft is capable of adjusting the geometric relationship between the control spool and the feedback element via the feedback transmitting element without superimposing the lateral adjustment movement with the rotational control movement. In other word, the feedback pivot axis is not moved on a circular path, what would superimpose a later control action applied to the input shaft and therefore would cause an asymmetrical control behavior. According to the invention, the feedback transmission element is moved on a straight path due to the lateral movement of the input shaft, resulting in a symmetrical behavior when controlling the displacement of the hydraulic unit. A person skilled in the art understand that a lateral deviation of the input shaft, e.g., caused by manufacturing and/or assembly tolerances of the input shaft block with respect to the control housing and/or the hydraulic unit housing, would lead to a displacement of the control spool as the rotational centring mechanism acting on the input shaft intends to rotate the input shaft in a torque less position. This is done in art usually by means of an elastic restoring force. Hence, a lateral deviation of the input shaft causes an increased restoring force at the centering mechanism, which will/can be released by rotating the input shaft leading to an asymmetric rotational position of the input shaft in both rotational directions. According to the invention such a lateral deviation can be compensated by providing positioning means allowing to correct the lateral position of the input shaft with respect to the input shaft block/housing.
In a specific embodiment, inclined surfaces are formed on opposite sides of the input shaft block such that wedge surfaces of wedge-shaped parts of the positioning means having through holes can be pressed by means of fixation bolts on the inclined surfaces to fix the input shaft block on the control housing. Preferably, the wedge surfaces of the wedge-shaped parts face each other and therefore exert a force in the direction of the opposite wedge-shaped part if they are pressed on the inclined surface of the input shaft block. According to the invention, one of the fixation bolts can be loosened, whereas the other fixation bolt is tightened in order to move the input shaft block in the direction of the loosened fixation bolt and relative to the control housing. The loosened fixation bolt allows an upwards motion of the corresponding wedge-shaped part, providing space for the movement of the input shaft block, especially, the inclined surface on the input shaft block. The tightened fixation bolts force the input shaft block towards the other side, where the fixation bolt is loosened. When the correct respectively the tolerance compensated position of the input shaft is reached both fixation bolts are tightened and the input shaft block is fixed/locked in this position. This lateral adjustability of the input shaft block can be done in a direction basically perpendicular to the force for centering the input shaft to its zero rotational position and basically perpendicular to the input shaft axis.
Preferably, the control housing comprises guiding means adjacent to screw holes for screwing-in the fixation bolts. This guiding means maintain the distance between the wedge-shaped parts constant in direction of the lateral movability of the input shaft block, when one of the fixation bolts is loosened or tightened. The guiding means thereby not only prevent a lateral movability of the wedge-shaped parts but can also prohibit tilting of the wedge-shaped parts, which could lead to blockage of the wedge-shaped parts on the inclined surfaces of the input shaft block, which would counteract the functionality of the control device according to the invention.
The wedge-shaped parts can show a circular base surface and the guiding means can comprise annular grooves formed in the control housing. With this geometric arrangement, the wedge-shaped parts are guided in every direction but the direction towards or away from the input shaft block. This means that the wedge-shaped parts can only slide on the inclined surfaces towards to or away from the input shaft block, when one of the fixation bolts is loosened or tightened, thereby forcing the input shaft block to move in the direction perpendicular to the input shaft axis and perpendicular to the rotational centering force, i.e., the input shaft rotational restoring force.
Preferably, in one embodiment of the invention the direction and/or the magnitude of the centering force of the centering mechanism is adjustable by adjustment means. Thereby, the restoring force, which rotationally restores the input shaft back to its zero position after being rotated, can be adapted to the desired stirring behavior and to the tolerance compensated position of the input shaft.
In another embodiment the feedback pivot axis can be defined by an eccentric pin located eccentrically at the second end of the input shaft. This means that the feedback pivot axis is displaced when the input shaft is rotated. In one specific embodiment according to the invention, this causes the feedback transmission element to shift the control spool lateral thereby opening and closing control edges to vary the servo pressure acting in the servo unit for adjusting the angular position of the displacement element.
In an alternative embodiment the feedback pivot axis can be defined by a support pin located eccentrically on a regulating pin accommodated rotatable in the control housing parallel to the input shaft axis. In this embodiment, the input shaft does not necessarily move/shift a cylindrical control spool, but rotate a control sleeve for guiding hydraulic pressure to and from a servo unit, which control sleeve is mechanically connected to the feedback transmitting device and arranged around the input shaft to the servo unit.
The feedback transmitting element can comprise an elongated hole for receiving a feedback pin attached to the displacement element of the hydraulic unit and indicating the position of displacement element. As the displacement element rotates around its tilt axis and the feedback pin is attached eccentrically to the displacement element to fulfil its function, the free end of the feedback pin describes a circular trace when the displacement element tilts. To allow this circular movement an elongated hole is provided in the feedback transmitting element.
Preferably, the centering mechanism for the input shaft is housed in the input shaft block. In this configuration, it is not required to provide a separate angular adjustment means for the centering mechanism, as it would be when the centering mechanism is not arranged within the input shaft block. When the input shaft block is laterally displaced by, e.g., the wedge-shaped parts, the centering mechanism moves accordingly, and the relative position between the input shaft block and the centering mechanism does not change. In contrast to that, if a centering mechanism and input shaft block are arranged separately, the relative position of the two parts change when the position of the input shaft axis is calibrated/adjusted to eliminate the assembling tolerances. Then the centering mechanism has to be readjusted afterwards in order to fulfill its functionality correctly.
According to the invention, a hydraulic unit can be equipped with a manual displacement control device according to the invention as descript above. In one embodiment the control housing of the manual displacement control device preferably is part of the hydraulic unit housing, wherein the positioning means are located close to the first end of the input shaft, e.g., in order to be able to adjust/to adapt the lateral position of the input shaft relative to the hydraulic unit housing and/or the neutral position of the displacement element.
According to the invention, the wedge-shaped parts of the positioning means can be guided by guiding means on the hydraulic unit housing in direction perpendicular to the rotation restoring force. This means that the guiding means prevent the wedge-shaped parts from moving in direction of the restoring force.
The hydraulic unit can comprise a tiltable displacement element having a feedback pin attached thereto. One end of the feedback pin is received by the second end portion of the feedback transmitting element. Thereby, a mechanical feedback chain between the displacement element and the control spool is established via the feedback transmitting element, wherein the feedback transmitting element, in one embodiment of the invention can rotate around an eccentric pin arranged at the second end of the input shaft. Hence a movement of the feedback pin causes a displacement of the control spool. When the input shaft is rotated the feedback transmitting element is displaced by the eccentric pin thereby shifting the control spool, as the feedback transmitting element can rotate around the feedback pin.
In a preferred embodiment of the invention the neutral position of the displacement element is assured by means of the a servo unit having at least one servo piston and at least one servo spring, wherein these two parts of the servo unit are arranged on opposite sides of the displacement element with regard to a sliding surface on which reciprocating working pistons are supported. The exact setting of the neutral position of the displacement element is a safety issue for hydraulic unit when the servo unit is without pressure as in an idling condition no hydraulic force should be generated in order to stop a vehicle from driving, e.g. For setting/finding this exact real neutral position of the displacement element hydraulic units frequently are calibrated on a test stand in order to compensate manufacturing and assembly tolerances affecting the neutral position of the displacement element. It is a further objective of the invention to provide a device with the help of which the neutral position of the displacement element can be set/calibrated already when assembling the hydraulic unit.
For assuring that the servo unit in a pressure balanced or pressure-less state does not exert any spring restoring forces on the displacement element in its neutral position a variably/adjustable fixable servo spring bracket is provided according to the invention having an end stop surface for every servo spring of the servo unit. During assembly of the hydraulic unit the real neutral position deviating from the theoretical neutral position can be blocked temporarily by means of auxiliary blocking means. To this blocked neutral position of the displacement element the end stop surfaces of the servo spring bracket can be aligned such that the end stop surfaces, i.e., the servo spring bracket, are parallel to a sliding surface on the displacement element on which the working pistons of rotational group of the hydraulic unit are supported. In other words, the servo spring bracket is aligned with its end stop surfaces to the real neutral position of the displacement element. On these end stop surfaces the servo springs can abut preferably with servo spring seats, and further (full) expansion of the servo springs is limited by means of these end stop surfaces. To the servo spring seats servo spring rods are attached with a first end and traverse the servo spring bracket towards the displacement element where they abut at a lay-on point without any gap and free of spring forces in the neutral position of the displacement element as the servo spring travel path is limited by means of the end stop surfaces on which the servo spring seats abut.
In one preferred embodiment on either side of the tilt axis of the displacement element one servo spring is arranged such that the neutral position of the displacement element is held securely by the servo spring rods as every movement of the displacement element would cause one servo spring to be compressed. For this the second ends of the servo spring rods are formed in a manner that they can exert a pushing force on the displacement element however not a tensile force. In one embodiment the second ends of the servo spring rods can show a semi-circular shape in order for the servo spring rod to be able to follow the circular movement of the lay-on point when the displacement element is deflected by means of a servo piston force exerted on the opposite side of the displacement element. For this the joint of the second ends of the servo spring rods and the lay-on point of the displacement element in one embodiment is formed as kind of pivot joint.
For adjusting the servo spring bracket to neutral position of the displacement element a person skilled in the art will find various possibilities, however in a preferred embodiment of the invention a combination of fixation bolts with adjustable threaded sleeves is used. Thereby, it is equivalent if the threaded sleeves are screwed into the bracket for adjusting and keeping constant a distance between the servo spring bracket to the housing of the hydraulic unit or if the threaded sleeves are screwed on the fixation bolts in order to maintain the desired distance of servo spring bracket to the hydraulic unit housing. In both alternatives the servo spring bracket is fixed to the hydraulic unit housing by means of the fixation bolts. Needless to say, for a person skilled in the relevant art that when tightening the fixation bolts the threaded sleeves have to be secured against turning to not modify the adjusted distance and to support the servo spring bracket in an orientation in which the end stop surfaces are parallel to the sliding surface on the displacement element when the displacement element is in its neutral position.
This neutral position adjustment according to the invention is applicable to any hydraulic unit independent of the number of servo springs and servo pistons installed for changing the displacement of a variable displacement hydraulic unit. It is imaginable that the invention is applicable to both kinds of hydraulic units, deflectable in one direction only or deflectable in both directions. Thereby, displacement forces can be exerted on the displacement element by at least one servo piston on one side of the displacement element and supported by at least one servo spring arrangement on the other side as described above.
Once the neutral position of the displacement element is adjusted according to the invention and the assembly is forwarded to install the manual displacement device (MDC), the lateral adjustment of the input shaft of the MDC can be done directly in the assembly line as the neutral position of the displacement element is already adjusted/calibrated. Hence according to the invention there is no need to calibrate the neutral position and subsequently to adjust the lateral position of the input shaft of the manual displacement control (MDC) on a test stand. In other words, the neutral position calibration by means of the servo spring bracket adjustment described above provides the preconditions for the lateral position adjustment/calibration of the input shaft of the manual displacement control (MDC).
The hydraulic units to which the invention can be applied to can be of the axial or radial piston type. In detail, the hydraulic unit can be of the swashplate or bent-axis type, in case the axial piston design is selected.
The invention described above in general is now detailed further with the help of annexed Figures, in which preferred embodiments and preferred design possibilities are shown. However, these preferred embodiments do not limit the scope of the inventive idea. The shown preferred embodiments can be combined with one another without leaving the spirit of the invention. Furthermore, modifications within the possibilities of the knowledge of a person with skills in the relevant art can be implemented without leaving the spirit of the invention. In the Figures, it is shown:
A centering mechanism 35 is provided at the input shaft block 15 in order to force/restore the input shaft 10 and the lever 6 back to the starting position, when no torque is applied to the lever 6. The centering force/torque of the centering mechanism 35 can be adjusted via adjustment means 50, e.g., an eccentric mechanism and/or a pre-tensioned spring. Input shaft block 15 is fixed to a control housing 20 via fixation bolts 42 pressing onto wedge-shaped parts 44, which exert a holding force on the input shaft block 15. A lateral adjustability of the input shaft block 15 is provided, when one of the fixation bolts 42 is loosened and the other fixation bolt 42 is tightened. Gaps 49, which are visible between the input shaft block 15 and the wedge-shaped parts 44, restrict the lateral movability of the input shaft block 15. If the input shaft block 15 is moved either to the left or right direction in the plane of
Three intersection lines, marked with the letters A to C are shown with
In the following, the functionality of the positioning means 40 according to the invention is explained on behalf of a movement to the left in the view of
In
In the specific embodiment shown with the Figures, a rotation of the input shaft 10 around the input shaft axis 13 leads to a lateral displacement of the eccentric pin 16, which causes—as best can be seen in
Manufacturing and mounting tolerances negatively influence the functionality of this mechanical feedback chain and, therefore, have to be eliminated by adjusting the position of the eccentric pin 16 and therewith the position of the feedback pivot axis 33 after the manual displacement control device 1 has been assembled. Simultaneously, the neutral position of the hydraulic unit has to be defined accurately as this neutral position is the initial point for tolerance compensation of a hydraulic unit. In other words, a calibration of the input shaft 10 should be done when the displacement element 4 is held in its neutral position, preferably in the real neutral position in which manufacturing and assembly tolerances influencing the neutral position are compensated.
According to the invention, the adjustment of the lateral position of the input shaft 10 and therewith of the eccentric pin 16 to the neutral position of the displacement element 4 is achieved by the combination of inclined surfaces 17 at the input shaft block 15 and the wedge surfaces 47 at the wedge-shaped parts 44. Thereby, a lateral movability of the input shaft axis 13 and the feedback pivot axis 33 in a direction perpendicular to the sectional line C-C is provided as descript in detail above.
With
According to the invention the orientation/positioning of the servo spring bracket 68 can be adjusted by means of a variable adjustable fixing system. In the embodiment shown in the
In
While the present disclosure has been illustrated and described with respect to a particular embodiment 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.
Number | Date | Country | Kind |
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102021205359.9 | May 2021 | DE | national |