Method for Operating an Axial Piston Machine of Swashplate Design

Abstract

A method for operating an axial piston machine of swashplate design, in which a swashplate is settable by means of an adjustment device, and in which a controlled variable of the axial piston machine is regulated by predetermining a manipulated variable. Under the assumption of a constant intended value of the controlled variable, a future profile of the controlled variable is ascertained using a model of the axial piston machine in which respective current values of at least one operating variable of the axial piston machine, which comprises the controlled variable, and a current value of the manipulated variable are taken into account. A value to be set for the manipulated variable is ascertained and set taking into account the future profile of the controlled variable.

Claims

1. A method for operating an axial piston machine having a swashplate comprising: setting the swashplate with an adjustment device; regulating a controlled variable of the axial piston machine by predetermining a manipulated variable; ascertaining, under an assumption of a constant intended value of the controlled variable, a future profile of the controlled variable using a model of the axial piston machine in which respective current values of at least one operating variable of the axial piston machine, which comprises the controlled variable, and a current value of the manipulated variable are taken into account; and ascertaining and setting a value to be set for the manipulated variable by taking into account the future profile of the controlled variable.

2. The method according to claim 1, further comprising: ascertaining the value to be set for the manipulated variable using an optimization calculation, in which a deviation of the current value of the controlled variable from the constant intended value and the current value of the manipulated variable are taken into account.

3. The method according to claim 1, wherein a pivot angle, a rotational speed, a pressure of the axial piston machine or a variable respectively correlating therewith is used as the controlled variable.

4. The method according to claim 1, further comprising: taking into account geometric dimensions of the axial piston machine and/or of the adjustment device in the model of the axial piston machine.

5. The method according to claim 1, further comprising: using a hydraulic adjustment cylinder and an electro-proportional valve for setting the adjustment cylinder as the adjustment device.

6. The method according to claim 1, wherein the at least one operating variable of the axial piston machine comprises a rotational speed of the axial piston machine and/or a degree of adjustment of the swashplate and/or operating variables of the adjustment device.

7. The method according to claim 1, wherein the manipulated variable comprises an actuation variable for actuating the adjustment device.

8. The method according to claim 1, further comprising: predetermining maximum and/or minimum values for the at least one operating variable and/or the manipulated variable.

9. The method according to claim 1, wherein a computing unit having a regulator is configured to carry out the method.

10. The method according to claim 1, wherein a computer program prompts a computing unit to carry out the method when the computer program is executed on the computing unit.

11. The method according to claim 1, wherein the computer program is stored on a machine-readable storage medium.

12. An axial piston machine comprising: a swashplate; an adjustment device configured to set the swashplate; and a computing unit configured to execute program instructions for setting the swashplate with the adjustment device, regulating a controlled variable of the axial piston machine by predetermining a manipulated variable, ascertaining, under an assumption of a constant intended value of the controlled variable, a future profile of the controlled variable using a model of the axial piston machine in which respective current values of at least one operating variable of the axial piston machine, which comprises the controlled variable, and a current value of the manipulated variable are taken into account, and ascertaining and setting a value to be set for the manipulated variable by taking into account the future profile of the controlled variable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 schematically shows an axial piston machine, by means of which a method according to the disclosure can be carried out.

[0050] FIG. 2 schematically shows a course of the method according to the disclosure in a preferred embodiment.

[0051] FIG. 3 shows measurement results when carrying out a method according to the disclosure in a preferred embodiment.

[0052] FIG. 4 shows measurement results when carrying out a method according to the disclosure in a further preferred embodiment.

[0053] FIG. 5 shows measurement results when carrying out a method according to the disclosure in a further preferred embodiment.

DETAILED DESCRIPTION

[0054] FIG. 1 schematically illustrates an axial piston machine 100, here in the form of an axial piston pump, of swashplate design. In the cross-sectional view shown, two pistons 110 are shown, which are guidable in the housing 105 and which are supported on a swashplate 120. During operation as a pump, the housing 105 and hence also the pistons 110 are rotated about the axis of rotation 125.

[0055] In this manner, fluid is suctioned in on the side of the piston 110 illustrated here on the left-hand side, said fluid being compressed by the rotation and being output on the side of the piston 110 illustrated here on the right-hand side.

[0056] The swashplate 120 and hence the pivot angle can be adjusted by means of an adjustment device 130. Here, the adjustment device 130 comprises an adjustment cylinder 131, which engages with the swashplate 120 at a distance r.sub.V from a pivot cradle of the swashplate, and an electro-proportional valve 131 with two coils or electromagnets, to which the voltages u.sub.1 and u.sub.2, respectively, can be applied, and which serves to set or regulate the adjustment cylinder pressure in the adjustment cylinder 130.

[0057] FIG. 2 schematically illustrates a course of the method according to the disclosure in a preferred embodiment, by means of which it is simultaneously also possible to explain a structure and a measurement setup for the model-predictive regulation carried out within the scope of the disclosure, using the example of an axial piston machine having an electro-proportional adjustment as shown in FIG. 1.

[0058] A regulator 181, which may be part of a computing unit or a control apparatus 180, receives an intended value y.sub.r as an input. From this, it is possible to ascertain an actuating signal or a value for the manipulated variable u.sub.m. In order to prevent adhesion in the regulation valve, a so-called dither signal D.sub.S can be superposed onto the actuating signal u.sub.m of the regulator 181. With the aid of the block 183, the resultant signal u.sub.m can be converted into the two voltages u.sub.1 and u.sub.2 of the coils.

[0059] The currents i.sub.1 and i.sub.2 of the two coils, the adjustment degree =tan()/tan(.sub.max) and the rotational speed n.sub.t=.sub.t/(2) form measured variables at the axial piston machine 100 for the regulator 181 in this case. Here, the two currents i.sub.1 and i.sub.2 are combined to a current i.sub.m by calculation. The valve spool position s.sub.V of the valve and the adjustment cylinder pressure p.sub.V are defined as non-measurable variables for the subsequent application and reconstructed or estimated using an extended Kalman filter 182 as an observer. However, within the scope of trials or a test setup, these may also be measured for comparison purposes; however, they are not included in the calculation of the regulating algorithm.

[0060] In order to suppress disturbances and parameter variations, the observer can be extended by a disturbance variable model with a constant disturbance. As a consequence, the stationary accuracy of the regulation can be improved.

[0061] FIG. 3 illustrates measurements using the pivot angle regulator according to the aforementioned IPG method. To this end, the adjustment degree in %, the voltage u.sub.m in V, the valve spool position s.sub.V in mm and the current i.sub.m in A are plotted, over time t in s in each case. Here, the reference signs V.sub.1, V.sub.2 and V.sub.3 are used to denote the respective variable profiles for voltage restrictions of 7 V, 10 V and 13 V, as also indicated in the diagrams in the second row from the top by means of dashed lines.

[0062] Here, the dashed line in the diagrams in the first row from the top represent intended values for the adjustment degree; the dashed line in the diagrams in the third row from the top represent a stop restriction.

[0063] It is clearly visible that the regulator always drives into the manipulated variable constraint and therefore realizes the maximum possible adjustment speed. Similar results can also be obtained using the DSS method.

[0064] FIG. 4 illustrates a measurement for a pivot angle regulation using the DSS method, in which a state constraint for the current in the regulator is taken into account. Here, the adjustment degree in %, the voltage u.sub.m in V and the current i.sub.m in A are plotted, over the time t in s in each case. Here, the reference signs V.sub.4 and V.sub.5 denote the respective variable profiles for current restrictions of 2 A and 5 A, as also indicated in the right-hand diagram by means of a dashed line.

[0065] The effect of the restriction of the measured current i.sub.m can be clearly identified. The time-averaged current profile is restricted on account of the superposed dither signal. As soon as the current limit has been reached, the regulator reduces the voltage.

[0066] FIG. 5 illustrates measurements using the rotational speed regulator according to the IPG method. Here, a rotational speed n.sub.t in 1/min, the voltage u.sub.m in V and the adjustment degree in % are plotted, over the time t in s in each case. Here, discontinuous intended prescriptions with different target rotational speeds are considered in each case.

[0067] Here too, it is possible to identify that the regulator is able to take into account the constraint on the manipulated variable. Further, the diagrams in the second row from the top illustrate an acceleration of the axial piston machine from a standstill position. This represents a particular challenge for the regulator on account of the high coefficient of static friction in the shaft of the axial piston machine.

[0068] Now, in particular, the proposed method can be used for the pivot angle adjustment, the rotational speed regulation and the pressure regulation for any axial piston machine of swashplate design.

[0069] An example of such an application lies in the use for vehicles with partial or complete hydraulic power transfer by way of axial piston machines. Using the pivot angle regulator, it is possible to regulate the volumetric flow. If the axial piston machine can be decoupled from the drivetrain by way of a switchable coupling, it is possible to synchronize the rotational speed with that of the drivetrain by way of the rotational speed regulator.

[0070] It is possible to set the drive torque of the axial piston machine by way of a pressure regulation. When the axial piston machine supplies work hydraulics, it is likewise possible, by way of the proposed method, to set the volumetric flow and hence, for example, also the adjustment speed or the pressure and hence, for example, the force on the actuator in turn.