CN110792568A

CN110792568A - Torque control and feedback device

Info

Publication number: CN110792568A
Application number: CN201910680940.2A
Authority: CN
Inventors: 陈用毅; 卡斯滕·菲宾
Original assignee: Danfoss Power Solutions GmbH and Co OHG
Current assignee: Danfoss Power Solutions GmbH and Co OHG
Priority date: 2018-07-25
Filing date: 2019-07-25
Publication date: 2020-02-14
Anticipated expiration: 2039-07-25
Also published as: DE102018212419A1; CN110792568B

Abstract

A torque control and feedback device for a hydraulic axial piston unit of swash plate construction includes a displacement control unit for setting the angle of inclination of the swash plate. The feedback base is coupled to the swash plate such that the feedback base may rotate with the swash plate. The feedback piston in the feedback base may be pressurized by hydraulic fluid taken from the high pressure side to exert a rocker torque on the pivotable rocker. A torque control valve having a torque control valve spool reacts against the rocker bias to counteract the rocker torque, thereby enabling opening or closing of a servo connection line connected to the servo unit to adjust the tilt angle theta of the swash plate by means of servo pistons located in the servo unit.

Description

Torque control and feedback device

Technical Field

The present disclosure relates generally to a torque control and feedback device and, more particularly, to a control and feedback device for a variable displacement hydraulic axial piston unit of swash plate type construction equipped with a servo system. A method for swashplate tilt angle position control is also disclosed.

Background

Variable displacement hydraulic axial piston units are generally known and are used to convert adjustable pressurized fluid flow into mechanical energy and vice versa. The flow of pressurized fluid is used to drive actuators such as cylinders or hydraulic motors associated with moving machine tools, linkages, and/or propulsion applications. Based on the requirements of the actuator, the displacement of the hydraulic axial piston unit is increased or decreased such that the actuator moves the tool, the connecting rod and/or the propulsion application at a desired speed and/or a desired force. A typical variable displacement hydraulic axial piston unit used is known as a swash plate hydraulic axial piston unit. Variable displacement hydraulic axial piston units have a rotating cylinder block with axially movable pistons that engage a tiltable swash plate that varies the stroke of the pistons. The displacement of the hydraulic axial piston unit is proportional to the stroke of the piston within the cylinder and the inclination angle of the swash plate.

To selectively specify the position of the swashplate, displacement control is used in response to a command input to change the swashplate position. The displacement control takes many forms, but in most cases it allows the operator to manually select the desired swashplate position and corresponding hydraulic axial piston unit displacement. Historically, the swash plate of a hydraulic axial piston unit has been tilted to a desired angle by one or more actuators connected to one side of the swash plate in response to an operator command. When the actuator is extended or retracted, the swash plate is tilted about the pivot axis. This is usually done by a servo unit comprising a servo piston whose position in a servo cylinder is set by conducting hydraulic fluid under servo pressure on one or both sides of the servo piston. The servo pressure acting on the servo piston and against the servo spring is usually regulated by a control unit comprising a control spool. One or more solenoid valves associated with the control spools are controlled in response to various inputs to direct pressurized fluid to the actuators/servo pistons to extend the actuators, or to exhaust fluid from the actuators to retract the actuators, to adjust the inclination angle of the swash plate.

Although the above-described electromagnetic actuators are functionally adequate to control a hydraulic axial piston unit, they may be problematic in some situations. For example, when the power supply to the solenoid actuator fails or when the input for controlling the solenoid actuator fails, the inclination angle of the swash plate may be incorrectly adjusted or not adjusted at all. The position of the swash plate angle is transmitted, for example, mechanically to a feedback spring which is positioned itself by a balance of forces generated on the control spool. The feedback spring force is transmitted back to the control spool by feedback of the position of the swashplate, for example, by a feedback pin attached to the swashplate. Thereby, the position of the control spool in the control spool cylinder is adjusted to a swash plate position different from the command position. Therefore, corrections are ultimately needed to meet the operator input signals. Thus, fluctuations in the hydraulic pressure in the working line, in particular in the high-pressure-conducting working line, lead to an adjustment of the position of the control valve member, since only the swashplate position is fed back to the control valve member.

Instead of mechanical feedback, electronic proportional swash plate angular position control is also used in the prior art. However, all these feedback controls have expensive electronic and/or mechanical and/or hydraulic swash plate angle position feedback means to feed the swash plate angle back to the control unit. In addition, the assembly of the feedback mechanism between the swash plate or servo piston and/or the control valve spool requires a great deal of effort.

All in all, this results in high costs for building a system to achieve full control of the hydraulic axial piston unit. The main object of the present invention is therefore to propose a simple, precise and cost-effective device and a method for providing rotational angular position control on a hydraulic machine. Thus, swashplate angular position feedback should result in adjustment of the swashplate angular position in accordance with the high pressure levels occurring at the hydraulic axial piston units. Further, it is an object of the present invention to combine a swashplate position feedback signal and a high pressure level signal to adjust the performance of a hydraulic axial piston unit to an operator input command.

Disclosure of Invention

The object of the invention is achieved by a torque control and feedback device according to claim 1, which can be used in a hydraulic axial piston unit of swash plate construction, comprising a displacement control unit to control the inclination angle Θ of a swash plate having a swash plate inclination axis. The feedback base is coupled to the swashplate such that the feedback base is rotatable with the swashplate about a swashplate tilt axis. The feedback base includes a feedback piston with a first end received in a feedback chamber. The first end of the feedback piston may be pressurized by hydraulic fluid taken from the high pressure side of the hydraulic axial piston unit. The torque control and feedback device of the present invention further comprises a pivotable rocker having a sliding surface against which a second end of the feedback piston slidably abuts, such that the feedback piston, which may be pressurized, is capable of generating a rocker torque about the rocker axis when the swash plate is tilted. Since the magnitude of the rocker torque is composed of the pressure on the feedback piston, depending on the high pressure of one of the working lines of the hydraulic axial piston unit, and the magnitude of the lever arm, depending on the size of the swash plate inclination angle, the rocker torque varies with the inclination angle theta of the swash plate and the high pressure level of the hydraulic axial piston unit.

This combined feedback signal on the rockers is in the form of rocker torque, which includes the swash plate angle, i.e., the swash plate position and the high pressure level in one of the working lines, received by a torque control valve having a torque control valve spool biased against the rocker, e.g., by a torque control valve spring, to counteract the rocker torque. The torque control valve spool can open or close a servo connection line connecting the high pressure side of the hydraulic axial piston unit with the servo unit, wherein the servo unit can adjust the inclination angle theta of the swash plate by means of the servo pistons located in the servo unit. The performance of the hydraulic axial piston unit is thus adjusted in dependence on the swash plate angle and the (high) pressure level of the system pressure.

In a preferred embodiment, in the rest state of the hydraulic axial piston unit, the swash plate is preferably oriented such that the longitudinal direction of the feedback pistons intersects the rocker axis. By doing so, no torque is generated around the rocker axis (further: rocker torque) because there is no lever arm. When the hydraulic axial piston unit is in an operational (deflection) state, the swash plate is controlled to the aforementioned swash plate angular position so that the hydraulic axial piston unit provides the required amount of displacement to deliver the required hydraulic or mechanical output. When the swash plate deviates from its initial position, the second end of the feedback piston moves in sliding contact along the sliding surface of the rocker and generates a corresponding rocker torque, which consists of the magnitude of the hydraulic force on the feedback piston and the magnitude of the swash plate inclination angle, which constitutes the magnitude of the lever arm.

The hydraulic pressure on the first end of the feedback piston is thus dependent on the high pressure level in one of the working lines of the hydraulic axial piston unit, which is led to the feedback chamber in which the first end of the feedback piston is located. Therefore, the high pressure level is preferably directed to the feedback chamber through the pressure relief vent. Thus, if one of the pressure on the feedback pistons or the swash plate angle changes, the rocker torque will also change. This change in the rocker torque caused by a change in the tilt angle or pressure breaks the balance of forces on the pivotable rockers, provided that the hydraulic axial piston unit operates before constant operating conditions.

Thus, according to the invention, a counter-balancing force on the pivotable rocker, i.e. a counter-balancing torque on the rocker, is provided by the torque control valve piston controlling the torque valve to stably maintain the rocker in a constant operating state of the hydraulic axial piston unit. The torque control valve piston is biased to bear against the pivotable rocker, preferably on the opposite side of the sliding surface of the pivotable rocker. The biasing force is generated, for example, by a torque control valve spring that resists the rocker torque that is intended to rotate the rocker about the rocker axis and cause a change in the output of the hydraulic axial piston unit.

The swash plate angle remains stable when the torque generated by the feedback piston is equal to the torque generated by the force on the spool of the torque control valve, which closes the hydraulic connection line between the high pressure side of the hydraulic axial piston unit to the servo unit. If the magnitudes of the reaction torques on the pivotable rockers are different from each other, the torque control valve spool is displaced in the torque control valve cylinder, thereby opening a hydraulic connection line from the high pressure side to the servo unit, or opening a discharge line from the servo unit to the low pressure region, to increase or decrease the swash plate inclination angle. Thus, according to the present invention, a change in the rocker torque is detected by a torque control valve whose torque control valve pistons are displaced to change the pressure conditions in the servo unit, thereby causing an adjustment of the swash plate inclination angle.

It is clear that the force on the torque control valve piston for generating a counter torque against the rocker torque can be in any suitable way, wherein the use of a torque control valve spring is only one possibility considered by the person skilled in the art. Such a force on the torque control valve piston may also be generated, for example, hydraulically, mechanically, electrically or pneumatically or by a combination thereof.

According to the invention, the position of the pivotable rocker reflects the actual swash plate angle and the current high pressure level under continuous operating conditions of the hydraulic axial piston unit. Thus, the swashplate tilt angle and the current high pressure level are continuously sensed by the torque control valve, which maintains the pivotable rocker in a constant rotational position relative to its rocker axis by reversing torque. The rocker leaves this rotational position when the angle of inclination of the swash plate changes (e.g. due to operator input), or when the high pressure level in the hydraulic axial piston unit changes (e.g. due to a change in the load on the hydraulic axial piston unit). To adjust the swash plate angle to the performance requirements of the hydraulic axial piston unit, the torque control valve adjusts the pressure level in the servo unit until stable operating conditions are again achieved.

According to the invention, a commonly known control unit for specifying or setting the inclination angle, such as an Electrical Displacement Control (EDC) or a Hydraulic Displacement Control (HDC) or any other known control unit, may be used in order to set the required performance for the hydraulic axial piston unit.

The invention is suitable for hydraulic axial piston pumps and hydraulic axial piston motors. Thus, the hydraulic axial piston unit may be of an open or closed configuration. A hydraulic axial piston unit capable of delivering hydraulic fluid in both directions may also be equipped with the torque control and feedback arrangement of the present invention. If a hydraulic axial piston unit with two conveying directions is used, the axis of the pivotable rocker is preferably situated in line with the swash plate at an angle of inclination equal to zero.

In a preferred embodiment of the invention, the feedback base is fixed to the swash plate and is rotatable about a swash plate tilt axis, representing a substantially disc-shaped design, the axis of rotation of which coincides with the swash plate tilt axis. When the swash plate is in its initial position, for example when the hydraulic axial piston unit is stationary at an inclination angle equal to zero, the feedback piston is arranged in a feedback cylinder fixed to or integrated in the feedback base such that the longitudinal direction of the feedback piston intersects the rocker axis. It will be apparent to one of ordinary skill in the art that the initial position may also be such that the angle of inclination of the swashplate is at a maximum. In the case of a bidirectional hydraulic axial piston unit, the initial position is preferably an angle of inclination equal to 0 °.

The feedback base is disc-shaped or rod-shaped or any other shape, preferably rotatably coupled to the swash plate, and may be rotated by a feedback pin attached to the swash plate. Thus, the feedback pin acts as a coupling element between the swash plates, with the feedback base transmitting any rotational movement of the swash plates. It will be apparent to those skilled in the art that the attachment of the feedback pin to the swashplate and feedback base may be of any suitable design that enables the feedback base to rotate with the swashplate about the swashplate axis as the angle of inclination changes.

The feedback base is preferably designed to accommodate a feedback chamber in which the feedback piston is slidably guided. A feedback spring is also positioned in the feedback chamber, prestressing the feedback piston towards the sliding surface on the pivotable rocker. In another embodiment, the feedback chamber is integral with the feedback base and is connected to the high pressure side of the hydraulic axial piston unit to feed back the high pressure level of the hydraulic axial piston unit to the pivotable rocker via the feedback piston. Thus, the hydraulic connection of the feedback chamber to the high pressure side of the hydraulic axial piston unit may be direct. Preferably, however, the high pressure level acting on the feedback piston is reduced, for example by an orifice, to decrease in proportion to the high pressure level. Thus, depending on the swash plate angle of inclination, pressure from the high pressure level present is fed back to the lever arm by the feedback piston on the pivotable rocker. This combined/joint feedback signal of the high pressure and the inclination angle of the swash plate constitutes the feedback rocker torque of the invention on the pivotable rocker, thereby feeding back two operating parameters of the hydraulic axial piston unit simultaneously. Preferably, the force of the feedback spring, which also pushes the feedback piston towards the pivotable rocker, is low compared to the hydraulic force, but is also high enough to keep the feedback piston in contact with the slidable surface, even when the hydraulic axial piston unit is stationary.

On the pivotable rocker, the reaction torque of the torque control device also acts about the pivotable rocker axis, wherein the rocker axis is preferably fixed relative to the housing of the hydraulic axial piston unit. Preferably, the torque control valve is also fixedly mounted in the housing of the hydraulic axial piston unit. Thus, the counter torque of the torque control valve piston counteracts the feedback rocker torque of the feedback piston, which exhibits a constant lever arm. In a preferred embodiment, the torque control valve piston also exerts a constant force on the rocker. Thus, in this preferred embodiment, the reverse torque is constant under all operating conditions. In this case, the control torque is set by design and is adjusted, for example, when the hydraulic axial piston unit is put into use. However, it will be apparent to those skilled in the art that the force with which the torque control valve spool presses against the rocker arm may also be adjusted, for example, according to the requirements of the hydraulic axial piston unit. It is also conceivable that the force with which the torque control valve spool presses against the rocker is controlled, for example, derived from and/or referenced to the high-pressure side of the hydraulic axial piston unit. Thus, a redundant control of the inclination angle of the swash plate can be achieved.

As mentioned above, in a preferred embodiment, the feedback base rotates about an axis, which preferably coincides with the swashplate axis. It is therefore logical for this preferred embodiment to configure the sliding surface of the rocker with a concave curvature which is in the neutral position of the rocker, i.e. concentric with the feedback base axis and the swash plate axis. Such an embodiment shows in particular a torque control and feedback arrangement which can be used for all volume sizes of hydraulic axial piston units, since only the forces on the torque control valve piston have to be adapted to the maximum high pressure level achievable, which is usually the same, for example for hydraulic axial piston units of the same product family.

In a preferred embodiment, the neutral position of the rocker is reached when two equal magnitudes of reaction torque are applied to the rocker, i.e., the feedback rocker torque applied by the feedback piston on the sliding surface is equal to the control torque applied by the torque control valve spool on a different rocker surface than the sliding surface. In this neutral position of the pivotable rocker, the torque control valve maintains the pressure in the hydraulic unit and the swash plate angle condition by, for example, closing the servo connection line and the discharge line, thereby keeping the swash plate angle constant because the pressure in the servo unit remains constant. For example, when the operator or control unit controls the swash plate angle to another position, the torque on the rocker changes as the lever arm changes. The high pressure level in the hydraulic axial piston unit is changed at the same time as the inclination angle of the swash plate is changed. This occurs as long as a new balance between feedback torque and torque control is achieved on the pivotable rocker.

In a simple implementation of the invention, the control torque realized on the rocker by the torque control valve (i.e. the control valve spool) is constant for a given setting; however, the torque generated by the feedback piston varies with the force exerted on its first end by the hydraulic fluid under pressure from the high pressure side and the lever arm adjusted by the servo unit by adjusting the swash plate inclination angle. To reach the equilibrium point of operation again, the swash plate angle is changed by the torque control valve displacing the torque control valve spool to accommodate the pressure conditions in the servo unit.

As can be seen by those skilled in the art in one embodiment of the invention, the torque control valve may be a two/three way valve, preferably of proportional type construction or any other suitable valve for controlling the pressure conditions within the servo unit to ultimately adjust the swash plate angle.

In an alternative embodiment of the invention, a solenoid is arranged at the torque control and feedback device, which solenoid is controlled by a control unit, e.g. an Electronic Torque Controller (ETC), which may act on the pivotable rocker in place of the rocker torque generated by the feedback piston. Such pressure control may also be accomplished by another control spool acting on the pivotable rocker to limit the pressure level on the high pressure side of the hydraulic axial piston unit, for example, by using a pressure limiting valve. Such a pressure limiting valve generates a pilot pressure acting on the torque control valve.

Drawings

Exemplary embodiments of the inventive torque control device are shown in more detail in the accompanying drawings, which do not limit the scope of the inventive concept. All features of the disclosed and described embodiments can be combined with each other in any desired combination within the scope of the invention. For this purpose, the figures show:

FIG. 1 schematically illustrates a first embodiment of the torque control and feedback arrangement of the present invention in a first initial position;

fig. 2 schematically shows the embodiment of the inventive torque control and feedback device of fig. 1 in an operating state of a hydraulic axial piston unit.

Fig. 3 schematically shows a preferred embodiment of the invention in a side view.

Detailed Description

Fig. 1 schematically shows a hydraulic axial piston unit 100 with an inventive torque control and feedback arrangement according to the present invention. For the purpose of explaining the torque control and feedback arrangement of the present invention, FIG. 1 shows only an open-circuit hydraulic axial piston pump 100 of swash plate type construction. The hydraulic axial piston pump 100 shown in fig. 1 is driven by a motor M and is capable of delivering pressurized hydraulic fluid in one direction. The hydraulic axial piston pump 100 depicted in FIG. 1 is in its initial position, showing the swash plate angle Θ equal to zero. In the direction of the swash plate 4 in the lower part of fig. 1, a feedback base 8 is shown, which comprises a feedback chamber 9, in which feedback chamber 9 a first end 11 of a feedback piston 10 is guided in the longitudinal direction and is urged outwards by a feedback spring 13. In this position of the swash plate 4 according to fig. 1, the feedback piston 10 points in the direction of the rocker axis 17 of the pivotable rocker 15 and does not generate a feedback torque about the rocker axis 17 on the rocker 15. Thus, the second end 12 of the feedback piston 10 abuts on a sliding surface 16 on the rocker 15. On the opposite side of the pivotable rocker 15, the torque control valve spool 22 exerts a reverse torque, referred to herein as a control torque, on the rocker 15 at a distance from the rocker axis 17 and reacts the feedback torque generated by the feedback piston 10. In the case of fig. 1, the torque control valve spring 21 urges the torque control valve spool 22 to the initial position of the torque control valve 20, in which position the servo connection line 27 is disconnected from the servo unit 25, the servo connection line 27 connecting the high pressure side of the hydraulic axial piston unit 100 with the servo unit 25. In this initial position of the torque control valve 20, a discharge line 51 leading to the tank 50 is connected to the servo unit 25, as shown in fig. 1. The servo unit 25 is therefore pressureless and does not apply any force to the swash plate 4.

As further shown in fig. 1 and 2, the servo unit 25 is connected to the control unit 2 for controlling the hydraulic axial piston unit 100 in dependence of inputs, such as operator inputs. Fig. 2 depicts an operator input (e.g., via the control unit 2) to provide a servo pressure/servo force to the servo unit 25 that deflects the swashplate 4 to an angle theta greater than zero. The operating situation shown in fig. 2 shows that the two torques exerted on the rocker 15 compensate for one another, since in their initial position the torque control valve 20 does not connect the servo unit 25 to the servo connection line 27. The feedback torque formed by the lever arms shown and the resulting pressure force, which is exerted on the rocker slide surface 16 of the pivotable rocker 15, are thus formed by the pressure force in the feedback chamber 9 acting on the first end 11 of the feedback piston 10 and the spring force of the feedback spring 13 and the lever arm corresponding to the tilt angle of the swash plate. The torque generated by the torque control valve spool 22 compensates/reacts against this feedback torque, urging the rocker in the opposite direction on the surface opposite the sliding surface 16 by the force generated by the torque control valve spring 21.

It is detectable to those skilled in the art that when the inclination angle of the swash plate 4 changes, the torque exerted on the pivotable rocker 15 by the second end 12 of the feedback piston 10 changes, whereby the pivotable rocker 15 rotates, for example, counterclockwise, so that the torque control valve spool 22 moves to a position where the servo connection line 27 is connected to the servo unit 25. When the pressure at the servo piston unit 25 increases, the servo piston 26 moves the swash plate 4 back towards zero to reduce the lever arm on the rocker 15 until a balancing torque acts on the rocker 15. If the torques are balanced, the servo connection 27 is closed again.

It will be apparent to those skilled in the art that the examples given in fig. 1 and 2 are for illustrative purposes only and that the operation of the torque control and feedback arrangement of the present invention is explained in a simple exemplary manner. As can be derived from the embodiments of fig. 1 and 2, the torque control and feedback arrangement of the present invention is also applicable to any other hydraulic axial piston unit showing one or both directions of delivery, which is of an open or closed circuit type construction, independent of functioning as a hydraulic pump or motor. Furthermore, the torque control valve 20 as shown in fig. 1 and 2 is also a simple embodiment. It may also be a three-position/four-way valve, etc. Finally, in the operating state of the hydraulic axial piston unit 100 with variable amplitude and variable lever arm, the feedback torque of the feedback piston 10 on the pivotable rocker 15 is compensated by the control torque generated by the torque control valve 20, wherein the desired swash plate inclination angle Θ is obtained. If the desired swash plate angle is not achieved, the torque control valve 20 automatically controls the pressure level in the servo unit 25 to move the swash plate 4 to the inclination angle theta such that the balance of the two torques acting on the rockers compensate each other.

Furthermore, the force exemplarily exerted on the torque control valve spool 22 by the torque control valve spring 21 is a simplified embodiment, which may also be realized by a hydraulic pilot pressure or a magnetic or mechanical force generated by a solenoid.

Fig. 3 schematically shows a preferred embodiment of the invention in a side view in the direction of the swash plate inclination axis 5. As can be derived from fig. 3, the rocker axis 17 at the rocker 15 is parallel to the swash plate axis 5. It can also be seen that the feedback pin 6, which is fixed to the swash plate 4, rotates the feedback base 8 when the swash plate is tilted to the equilibrium state shown in fig. 3. When the swash plate 4 is tilted, the feedback piston 10 slides with its second end 12 on the sliding surface 16, whereby the rocker 15 rotates. When the rocker 15 rotates, the torque control valve spool 22 in the torque control valve 20 moves, the servo connection line 27 is thereby opened or closed (refer to fig. 1 or 2), and the servo unit 25 of the displacement hydrostatic axial piston unit adjusts the swash plate inclination angle Θ.

By means of the invention, not only is a reliable swash plate angle adjustment device unit provided, but also a device is provided which combines the feedback signal of the pressure and the swash plate angle of inclination in a simple and reliable manner to adjust the displacement of a hydraulic axial piston unit of swash plate construction.

List of reference numerals

2 displacement control unit

3 case

4 swash plate

5 inclined axis of swash plate

6 feedback pin

8 feedback base

9 feedback chamber

10 feedback piston

11 first end

12 second end

13 feedback spring

15 rocking bar

16 sliding surface

17 rocker axis

20 torque control valve

21 torque control valve spring

22 torque control valve spool

23 torque control valve cylinder

25 servo unit

26 servo piston

27 servo connection line

30 control unit (ETC)

40 Pressure Controller (PC)

50 liquid box

51 discharge line

100 hydraulic axial piston unit

Theta Angle of inclination

EDC electric displacement controller

HDC hydraulic displacement controller

MDC manual displacement controller

ETC electronic torque controller

PC pressure controller

Claims

1. A torque control and feedback device for a hydraulic axial piston unit (100) of swash plate construction, comprising:

-a displacement control unit (2), the displacement control unit (2) being adapted to set an inclination angle (Θ) of a swash plate (4) having a swash plate inclination axis (5),

-a feedback base (8), the feedback base (8) being coupled to the swash plate (4) such that the feedback base (8) is rotatable together with the swash plate (4) about the swash plate inclination axis (5), wherein the feedback base (8) comprises a feedback piston (10), a first end (11) of the feedback piston (10) being pressurizable by hydraulic fluid taken from a high pressure side of the hydraulic axial piston unit (100),

-a pivotable rocker (15), the pivotable rocker (15) having a sliding surface (16), the second end (12) of the feedback piston (10) slidably abutting on the sliding surface (16) such that the pressurized feedback piston (10) can generate a rocker torque around a rocker axis (17) which varies with the inclination angle (Θ) of the swash plate (4) and the high pressure level of the hydraulic axial piston unit (100), wherein

-a torque control valve (20), said torque control valve (20) having a torque control valve spool (22), said torque control valve spool (22) being biased against said rocker (15) to counteract said rocker torque, thereby enabling opening or closing of a servo connection line (27) connecting the high pressure side of the hydraulic axial piston unit (100) and a servo unit (25), thereby adjusting the inclination angle (Θ) of the swashplate (4) by means of a servo piston (26) located in the servo unit (25).

2. Torque control and feedback device according to claim 1, wherein the displacement control unit (2) is an electric displacement control device (EDC), a hydraulic displacement control device (HDC) or a manual displacement control device (MDC).

3. The torque control and feedback device according to claim 1 or 2, wherein the feedback base (8) is coupled to the swash plate (4) by a feedback pin (6) coupled to a mechanical feedback unit of the displacement control unit (2).

4. Torque control and feedback device according to any of the preceding claims, wherein said feedback base (8) is substantially disc-shaped and said feedback piston (10) is housed with its first end (11) in a feedback chamber (9), said feedback chamber (9) being integral with said feedback base (8) and connected to said high pressure side of said hydraulic axial piston unit (100).

5. Torque control and feedback device according to claim 4, wherein a feedback spring (13) is arranged in said feedback chamber (9), said feedback spring (13) forcing said feedback piston (10) towards said sliding surface (16).

6. Torque control and feedback device according to claim 5, wherein the force of said feedback spring (13) is adjustable.

7. A torque control and feedback device according to any of the preceding claims, wherein said rocker axis (17) is fixed relative to a housing (3) of the torque control and feedback device.

8. A torque control and feedback device as claimed in any one of the foregoing claims, wherein said sliding surface (16) exhibits a concave curvature concentric with the swash plate inclination axis (5) in a neutral position of the rocker (15).

9. A torque control and feedback device according to any one of the preceding claims, wherein in a neutral position of the rocker (15) the torque control valve (20) closes the servo connection line (27).

10. A torque control and feedback arrangement as claimed in any preceding claim, wherein said torque control valve (20) is a two-position, three-way proportional valve.

11. The torque control and feedback device according to any of the preceding claims, wherein the torque control valve (20) comprises a torque control valve spring (21), said torque control valve spring (21) forcing said torque control valve spool (22) into said initial position.

12. The torque control and feedback device according to any one of the preceding claims, further comprising a solenoid (30) controlled by an Electronic Torque Controller (ETC), said solenoid (30) being able to act on said rocker (15) to replace said rocker torque generated by said feedback piston (10).

13. Torque control and feedback device according to any of the preceding claims, further comprising a Pressure Controller (PC) able to act on said rocker (15) to limit the pressure level of said high pressure side of the hydraulic axial piston unit (100).

14. Torque control and feedback device according to any of the preceding claims, wherein the swash plate (4) is tiltable from a neutral position towards positive and negative inclination angles (Θ).

15. Torque control and feedback device according to any of the preceding claims, wherein said hydraulic axial piston unit (100) is an open circuit hydraulic unit or a closed circuit hydraulic unit.