Axial piston pump for a hydrostatic propulsion drive, hydrostatic propulsion drive with the axial piston pump, and method for control

Abstract

A hydrostatic axial piston pump has adjustable swept volume and is configured for fluidic connection to a hydraulic motor of a hydrostatic propulsion drive in a hydraulic circuit. The hydrostatic axial piston pump includes an adjusting unit configured to adjust the swept volume. The adjusting unit has an actuating cylinder with a first actuating pressure chamber, in which a first actuating pressure can be set via a first pressure reducing valve. The first actuating pressure is dependent on a first current at a first electromagnet of the first pressure reducing valve. An electronic control device is configured to store a model of the first current in a manner which is dependent on a requested speed.

Claims

1. A hydrostatic axial piston pump for a speed-controlled hydrostatic propulsion drive, the hydrostatic axial piston pump having an adjustable swept volume, the hydrostatic axial piston pump comprising: an adjusting unit configured to adjust the swept volume, the adjusting unit including an actuating cylinder with a first actuating pressure chamber, in which a first actuating pressure is set via a first pressure reducing valve, the first actuating pressure being dependent on a first current at a first electromagnet of the first pressure reducing valve; an electronic control device configured to store a model of the first current in a manner which is dependent on a speed that one of (i) can be requested and (ii) is requested; and an adaptation device configured to adapt the model in a manner which is dependent on the first current and an actual speed which one of (i) can be assigned and (ii) is assigned to the first current, wherein the hydrostatic axial piston pump is included in a hydraulic circuit for fluidic connection to a hydraulic motor.

2. The hydrostatic axial piston pump according to claim 1, further comprising: a regulating device configured to correct a deviation of the actual speed from the requested speed.

3. The hydrostatic axial piston pump according to claim 2, wherein first output values of the regulating device and the electronic control device are linked to the first current via a first operator.

4. The hydrostatic axial piston pump according to claim 3, wherein the adaptation device is configured adapt a model of the regulating device in a manner which is dependent on the first current and the actual speed which one of (i) can be assigned and (ii) is assigned to the first current.

5. The hydrostatic axial piston pump according to claim 4, wherein the adaptation device is configured to adapt a model of the electronic control device and the model of the regulating device in such a way that a first output value of the regulating device one of (i) is minimized and (ii) is zero.

6. The hydrostatic axial piston pump according to claim 2, wherein the regulating device is configured to deactivate following one of (i) an adaptation operation and (ii) a start up.

7. The hydrostatic axial piston pump according to claim 1, wherein the adaptation device is configured to deactivate following one of (i) an adaptation operation and (ii) a start up.

8. The hydrostatic axial piston pump according to claim 1, wherein the adaptation device includes a cancelation condition of the adaptation at least in a manner which is dependent on the first current and the actual speed which one of (i) can be assigned and (ii) is assigned to the first current.

9. The hydrostatic axial piston pump according to claim 5, wherein the respective model in each case has a static part and a dynamic part.

10. The hydrostatic axial piston pump according to claim 1, wherein the hydraulic circuit is a closed hydraulic circuit.

11. A hydrostatic propulsion drive, comprising: a hydraulic motor; and an hydrostatic axial piston pump having an adjustable swept volume, the hydrostatic axial piston pump including (i) an adjusting unit configured to adjust the swept volume, the adjusting unit including an actuating cylinder with a first actuating pressure chamber, in which a first actuating pressure is set via a first pressure reducing valve, the first actuating pressure being dependent on a first current at a first electromagnet of the first pressure reducing valve, (ii) an electronic control device configured to store a model of the first current in a manner which is dependent on a speed that one of can be requested and is requested, and (iii) an adaptation device configured to adapt the model in a manner which is dependent on the first current and an actual speed which one of can be assigned and is assigned to the first current, wherein the hydrostatic axial piston pump is connected fluidically to the hydraulic motor in a closed hydraulic circuit, wherein the hydrostatic axial piston pump is coupled to a drive machine, and wherein the hydraulic motor is coupled to an output.

12. A method for controlling at least one of (i) a hydrostatic axial piston pump and (ii) a propulsion drive, the method comprising: performing a model-based determination of at least a first current assigned to a requested speed using a model; actuating a first electromagnet by way of the determined first current; and adapting the model in a manner dependent on an actual speed and at least the determined first current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will now be described in greater detail on the basis of the figures of said drawings, in which:

(2) FIG. 1 shows a hydraulic circuit diagram of an axial piston pump according to the disclosure in accordance with a first exemplary embodiment,

(3) FIG. 2 shows a logic circuit diagram of a propulsion drive according to the disclosure with the axial piston pump according to FIG. 1 and a method according to the disclosure which is stored therein, in adaptation operation which is based on the pivoting angle,

(4) FIG. 3 shows a logic circuit diagram of the propulsion drive according to the disclosure in accordance with FIG. 2 and the method according to the disclosure which is stored therein, in adaptation operation which is based on the speed, and

(5) FIG. 4 shows a logic circuit diagram of the propulsion drive according to the disclosure in accordance with FIGS. 2 and 3 and the method according to the disclosure which is stored therein, in purely controlled operation.

DETAILED DESCRIPTION

(6) FIG. 1 shows a circuit diagram of the exemplary embodiment of an axial piston pump 1 according to the disclosure. Only those components of the axial piston pump which are essential to the disclosure will be described. Said axial piston pump 1 has a housing 2, on which two working connectors A, B are formed, to which in each case one working line (not shown) of a closed circuit is closed. By way of a hydraulic motor (not shown) which is incorporated fluidically into the circuit, a hydrostatic propulsion drive according to the disclosure for a mobile machine (not shown) is thus formed.

(7) The axial piston pump 1 is configured with a swash plate 4, the pivoting angle α.sub.P of which can be set via an adjusting unit 6. A double-acting actuating cylinder 8 serves for this purpose which has a first actuating pressure chamber 10.sub.1 and a second actuating pressure chamber 10.sub.2 which acts counter to the former.

(8) A first pilot pressure p.sub.st1 acts in the first actuating pressure chamber 10.sub.1 in the direction of an enlargement of the pivoting angle α.sub.P and therefore in the direction of an enlargement of the swept volume V.sub.P of the axial piston pump 1. This is counteracted by a second actuating pressure p.sub.st2 in the second actuating pressure chamber 10.sub.2 in the direction of a reduction of the pivoting angle α.sub.P and therefore in the direction of a reduction of the swept volume V.sub.P of the axial piston pump 1. An actuating pressure difference Δp.sub.st=p.sub.st1−p.sub.st2 can be defined here, said actuating pressure difference Δp.sub.st always acting in the direction of an enlargement of the pivoting angle α.sub.P or the swept volume V.sub.P in accordance with the definition in the exemplary embodiment.

(9) The driving mechanism 14 of the axial piston pump 1 and, moreover, also a feed pump 16 are driven via a drive shaft 12 of said axial piston pump 1. The drive shaft 12 is driven by a diesel engine (not shown), and rotates at a rotational speed n.sub.P. Said rotational speed n.sub.P acts together with the actuating pressure difference Δp.sub.st in the direction of an enlargement of the pivoting angle α.sub.P. More specifically, an increase in the rotational speed n.sub.P acts in this way.

(10) A characteristic of the axial piston pump 1 is stored in an electronic control unit 18 as formulae and/or as characteristic diagrams or characteristic curves.

(11) Furthermore, the rotational speed n.sub.P, the actuating pressure difference Δp.sub.st and the high pressure HD are measured. In this way, operating points of the axial piston machine 1 according to the disclosure can be actuated, without a feedback in the sense of a regulating circuit being necessary for this purpose.

(12) The two actuating pressures p.sub.st1, p.sub.st2 are actuated via two pressure reducing valves 20.sub.1, 20.sub.2. The latter have in each case one electric magnet a, b, which electric magnets are connected via a respective electric line 22.sub.1, 22.sub.2 to the electronic control unit 18.

(13) The two pressure reducing valves 20.sub.1, 20.sub.2 are designed in such a way that the respective actuating pressure p.sub.st1, p.sub.st2 is proportional to the respective current strength I.sub.1, I.sub.2.

(14) The two pressure reducing valves 20.sub.1, 20.sub.2 are supplied on the inlet side by the feed pump 16 via a feed pressure line 24.

(15) FIG. 2 shows a logic circuit diagram of a hydrostatic propulsion drive 26 with the axial piston pump 1 according to FIG. 1, the latter being shown in a manner which is reduced to the abovementioned components of adjusting unit 6, actuating cylinder 8, driving mechanism 14 and control unit 18. The propulsion drive 26 has a propulsion drive train 28 and an operator interface 30. The propulsion drive train 28 comprises the axial piston pump 6, 8, 14 with an adjustable swept volume V.sub.P=f(α.sub.P), and a hydraulic motor 32 which is configured with a constant displacement volume V.sub.M. They are both arranged in a closed, hydraulic circuit, as described above. Furthermore, the propulsion drive train 28 has a detection device 34 for the detection of the actual value of a driving speed v.sub.ist.

(16) For the definition of a speed request, the operator interface 30 (HMI) has an accelerator pedal 36, an inching pedal 38, cruise control 40, and further operating elements 42.

(17) The control unit 18 has an interpretation device 44 for the conversion of the speed request of the operator into a speed specification or required speed v.sub.soll. In addition, the control unit 18 has a calculation device 46 for the calculation of a requested pivoting angle α.sub.P,Soll of the axial piston pump 1 according to FIG. 1 from the requested speed v.sub.soll.

(18) Furthermore, the control unit 18 has a control device 48, a regulating device 50 which can be superordinate or is superordinate with respect to the former, an adaptation device 52, and an estimation device 54.

(19) According to FIG. 2, a deflection of the accelerator pedal 36 which is signal-connected to the interpretation device 44 takes place. Said interpretation device 44 converts the driver's request into a requested speed v.sub.soll which is entered into the calculation device 46. In the latter, with the assumption of a constant motor 32 with a constant displacement volume V.sub.M, the calculation of a corresponding setpoint pivoting angle α.sub.Psoll takes place. Said setpoint pivoting angle is entered into the control device 48 and into the regulating device 50. Characteristic diagrams and in each case one model of the first current I.sub.1 in a manner which is dependent on the requested pivoting angle α.sub.Psoll, that is to say in a manner which is indirectly dependent on the requested speed v.sub.soll, are stored in the two devices 48, 50. From the respective model and characteristic diagram, the devices 48, 50 determine first output values I.sub.1ff with regard to control (“feed-forward”) and I.sub.1fb with regard to regulation (“feed-back”). The two output values I.sub.1ff and I.sub.1ft are then added at a first operator 56 to form the first current I.sub.1. This actuates the first electromagnet a via electric line 22.sub.1 according to FIG. 1, and brings about a first actuating pressure p.sub.st1 in the first actuating pressure space (10.sub.1) there via the first pressure reducing valve 20.sub.1 which is actuated by way of said first current I.sub.1. An actual pivoting angle α.sub.Pist results therefrom at the axial piston pump 6, 8, 14 according to FIG. 2, which actual pivoting angle α.sub.Pist leads to a pressure medium volumetric flow Q.sub.P at the rotational speed n.sub.P of the axial piston pump and drive machine. Via the abovementioned balance, the output rotational speed n.sub.M which is proportional to the actual speed v.sub.ist results therefrom at the hydraulic motor 32. The actual speed v.sub.ist is detected by the detection device 34 and is reported to the estimation device 54. The latter estimates the actual pivoting angle, since this is not detected. The estimated actual pivoting angle is called α.sub.Pest. It is entered into the regulating device 50 as a second input variable, in addition to the setpoint value α.sub.Psoll of the pivoting angle. In this way, the expensive detection of the actual pivoting angle α.sub.Pist can be dispensed with, and regulation can nevertheless take place. In addition, the actual speed v.sub.ist is entered into the adaptation device 52 together with the first current I.sub.1, on which it is based. In the course of this, the learning and adaptation algorithm which is stored there changes the model parameters of the models which are stored in the devices 48 and 50 and/or the characteristic diagrams of the first current I.sub.i, with the result that the first output value I.sub.1fb of the regulating device 50 becomes smaller and smaller as the adaptation increases, that is to say the regulation decreases.

(20) The adaptation device 52 is preferably configured in such a way that, during the course of the adaptation operation, a constantly improved match between the parameters of the models which are used and the parameters of the models which are actually present results.

(21) In this way, ageing effects of the components can also be taken into consideration in the control of the axial piston pump 1. This results in a consistently satisfactory driving behavior.

(22) As a result of the depicted adaptation of the characteristic diagrams and/or parameters, the control by means of the control device 48, in particular, is improved more and more, with the result that the regulation by way of the regulation device 50 can be dispensed with completely from a certain time or cancelation criterion. This case is shown in FIG. 4. The regulating device 50, the adaptation device 52 and the estimation device 54 are then deactivated (not shown graphically).

(23) Since only control and no longer regulation then takes place, the axial piston pump and the propulsion drive have a robustness, for example, against sensor failure. In this case, a measurement of the actual speed v.sub.ist can then be dispensed with. The omission of sensor systems is to be valued highly, since a sensor failure which is possible at any time usually has very unfavorable effects on the speed control.

(24) In order to learn the required parameters and characteristic diagrams, however, a temporary use of a sensor for the actual speed v.sub.ist and a pivoting angle sensor for the actual pivoting angle α.sub.ist can prove appropriate in the learning and adaptation phase, in order to shorten the learning and adaptation phase.

(25) The adaptation of the parameters and/or the characteristic diagrams can take place by way of a step of “local adaptation of points in the characteristic diagram” and/or a step of “shifting of characteristic curves”. It is an advantage of the characteristic curve shifting that points which are not accessed during operation are also adapted. For this purpose, a model approach is necessary which describes, for example, a linear link of the variable to be estimated with the pivoting angle. It can be a disadvantage of the characteristic curve shifting that a deterioration of some points occurs if the assumed link (for example, linear link) is incorrect.

(26) FIG. 3 shows one variant of the propulsion drive 26 according to FIG. 2, in the case of which the determinations of the pivoting angle α.sub.Psoll from the requested speed v.sub.soll and of the estimated actual pivoting angle α.sub.pest from the actual speed v.sub.ist are dispensed with, since the control device 48 and the regulating device 50 are active in a directly speed-dependent manner, that is to say without a reconstruction of the pivoting angle α from the speed v. In this case, the actual speed v.sub.ist is entered directly into the regulating device 50, and the setpoint speed v.sub.soll is entered directly into the control device 48 and the regulating device 50.

(27) Advantages of the disclosure are a simplification and cost reduction as a result of the omission of an EP-regulated pump, improved performance as a result of precise speed tracking, reduced start up complexity, since required parameters are set and learned autonomously, an increase in safety, since a detection using measuring technology is required only temporarily and purely controlled operation becomes possible after start up, and the achieving of a consistent machine behavior over the service life in the case of continuous use of the adaptation device 52, since wear phenomena are compensated for by way of the adaptation of the parameters and/or the characteristic diagrams in the vehicle controller.

(28) An axial piston pump for a hydrostatic propulsion drive is disclosed, with a hydraulically adjustable swept volume and an adjusting unit for this purpose, an adjusting pressure of the adjusting unit acting in a proportional manner with respect to an adjusting current, on which adjusting pressure the swept volume and indirectly a volumetric flow and a driving speed are dependent. Here, a control device is provided, in which a model and/or characteristic diagram of the adjusting current is stored in a manner which is dependent on a requested speed. According to the disclosure, a learning and/or adaptation device is provided, via which the model and/or characteristic diagram can be adapted in a manner which is dependent on the adjusting current and an actual speed which can be assigned or is assigned to it.

(29) In addition, a hydrostatic propulsion drive with the axial piston pump is disclosed. Furthermore, a mobile machine, in particular a municipal vehicle, a wheel loader, an agricultural machine, such as a sprayer or a combine harvester, or the like, is disclosed, with a hydrostatic propulsion drive of this type. In addition, a method for controlling the axial piston pump and/or the propulsion drive is disclosed.