METHOD FOR DETERMINING A PRESENT STATE OF WEAR OF A HYDROSTATIC MACHINE

Abstract

The present invention relates to a method for determining a present state of wear of a hydrostatic machine during the operation of the hydrostatic machine. The hydrostatic machine comprises a drive with variable rotational speed and a hydrostatic pump, wherein the drive is designed to drive the hydrostatic pump for generating a volume flow of a fluid, and wherein the hydrostatic machine is connected to a fluid transport channel in which the fluid is transported in a manner driven by the hydrostatic machine. The method has a step for determining a first torque of the drive at a specified drive vector. Furthermore, the method has a step for ascertaining a second torque of the drive at the specified drive vector using a first calculation method, and in addition, the method has a step for determining the present state of wear of the hydrostatic machine using a second calculation method, in order to compare the first determined torque and the second ascertained torque to one another.

Claims

1. A method for determining a present state of wear of a hydrostatic machine during the operation of the hydrostatic machine comprising a drive with variable rotational speed and a hydrostatic pump, wherein the drive is designed to drive the hydrostatic pump in order to generate a volume flow of a fluid, and wherein the hydrostatic machine is connected to a fluid transport channel of a hydraulic drive system in which the fluid is transported from the hydrostatic machine to the hydraulic drive system in a driven manner, comprising the following steps: determining a first torque of the drive at a specified drive vector; ascertaining a second torque of the drive at the specified drive vector using a first calculation method; and determining the present state of wear of the hydrostatic machine using a second calculation method, in order to compare the first determined torque and the second ascertained torque to one another.

2. The method according to claim 1, wherein the step of determining a first torque of the drive comprises ascertaining a product of a consumption of current of the drive and a proportional factor.

3. The method according to claim 1, wherein the step of determining a first torque of the drive comprises measuring the first torque with a torque sensor.

4. The method according to claim 1, wherein the first calculation method comprises the use of at least one lookup table, and a value for the second torque of the drive is calculated from the lookup table.

5. The method according to claim 4, wherein the first calculation method comprises a physical model of a the hydrostatic machine, and a value for the second torque of the drive is derived from the physical model.

6. (canceled)

7. The method according to claim 5, wherein the first and/or the second calculation method are stored and executed locally in a computer program with program code of a control unit of the hydrostatic machine.

8. The method according to claim 1, wherein the first calculation method comprises a multivariate regression for evaluating a D-dimensional grid using drive and torque pairs.

9. The method according to claim 1, wherein the second calculation method ascertains a ratio, namely a quotient, of the first determined torque at a specified drive vector to a the second ascertained torque at the specified drive vector.

10. The method according to claim 1, wherein the second calculation method ascertains a ratio, namely a mean value, from a set of quotients for wear values in a given time window, wherein each of the quotients is the quotient of the first determined torque at a specified drive vector to the second ascertained torque at the specified drive vector.

11. The method according to claim 1, wherein the drive vector comprises: a rotational speed of the drive, the hydraulic fluid type, a first pressure of the fluid, the first pressure being the pressure applied to the hydrostatic pump at the working output, a second pressure of the fluid, the second pressure being the pressure fed into the hydrostatic pump, a present delivery volume of the hydrostatic machine, a viscosity of the fluid, and/or a temperature of the fluid.

12. (canceled)

13. (canceled)

14. An electrohydrostatic pump device comprising a hydrostatic pump, a drive with variable rotational speed, means for determining a first torque of the drive, and an electronic control unit capable of performing a method according to claim 1.

15. A computer program comprising program code for performing a method according to claim 1 when the computer program is executed on an electronic device.

Description

[0051] The present invention is explained in more detail below using the exemplary embodiments specified in schematic figures of the drawings. In the figures:

[0052] FIG. 1 is a schematic illustration of a simplified hydraulic system;

[0053] FIG. 2 is a flowchart of an embodiment of the method according to the invention; and

[0054] FIG. 3 is an example of a variation of the power state.

[0055] The accompanying drawings are intended to impart a further understanding of embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the mentioned advantages result with regard to the drawings. The elements of the drawings are not necessarily shown to scale relative to one another.

[0056] In the figures of the drawing, identical, functionally identical, and identically acting elements, features, and components are respectively provided with the same reference signs unless stated otherwise.

[0057] FIG. 1 shows a schematic illustration of a simplified hydraulic system. The hydraulic system in the illustrated form comprises a hydrostatic machine 10, a cylinder 30, preferably a hydraulic cylinder. The hydraulic cylinder 30 is connected to the hydrostatic machine 10 via fluid channels 20 (further necessary components of the hydraulic system, which are of little relevance to the present invention, are not shown). In the simplified form, the hydrostatic machine 10 comprises a hydrostatic pump 12 which is driven by a drive 11, preferably an electric motor with variable rotational speed n. The connection between the drive 11 and the hydrostatic pump 12 can be implemented, for example, via a shaft, transmission, etc. During operation of the hydrostatic machine 10, the shaft has a specific rotational speed n. The hydrostatic pump 12 is connected via the fluid channels 20 (supply and return flow) to a hydraulic cylinder 30, for example a differential cylinder. Differential cylinders are known in the prior art and have a piston, a piston rod, and two cylinder chambers. The hydrostatic pump 12 pumps the hydraulic liquid via the fluid channels 20 to the cylinder 30. By pumping the hydraulic liquid into the respective pressure chamber of the hydraulic cylinder 30, the piston and the piston rod are moved in the respective direction (retraction/extension of the cylinder). In addition, FIG. 1 shows the drive 13 as a control unit for the drive 11 of the hydrostatic machine 10. The currents for driving the drive 11 are provided and controlled via the drive 13. Furthermore, the consumption of current, for example the nominal consumption of current of the drive 11, can be measured via the drive 13. Internal measuring instruments or methods can be used for this purpose. From the measured present consumption of current and a proportional factor, a first torque M.sub.1eff of the drive 11 can be ascertained. Furthermore, the rotational speed n.sub.1 of the drive 11 can be determined via the drive 13. The rotational speed n.sub.1 may be contained in the drive vector. In an alternative or combined embodiment, the hydrostatic machine 10 can have a torque sensor 40 and a sensor 40 for detecting the rotational speed n.sub.1. The torque sensor 40 and the rotational speed sensor 40 for detecting the rotational speed n.sub.1 can be introduced into the hydrostatic machine 10 in such a way that they determine the first torque M.sub.1,eff of the drive 11 and the rotational speed n.sub.1. Using a first calculation method, a second torque of the drive 11 can be ascertained at a specified drive vector. The first calculation method may comprise the use of a lookup table and/or of a physical model of a hydrostatic machine 10 and/or a machine learning module. A present state of wear w of the hydrostatic machine 10 can be determined using a second calculation method. For this purpose, in the second calculation method, the first determined torque M.sub.1,eff and the second ascertained torque are compared to one another as follows:

[0058] M.sub.1,eff = f(V.sub.1, n.sub.1, ΔP, v) wherein M.sub.1,eff corresponds to the determined first torque of the drive 11 at a corresponding drive vector, and the drive vector comprises a delivery volume v.sub.1, a rotational speed n.sub.1, a differential pressure ΔP, and/or a value for the viscosity v of the fluid. Embodiments according to the invention may take into account one or a plurality of parameters for a drive vector. The differential pressure ΔP can be detected by means of a pressure sensor 50 which ascertains the pressure difference from the pressures P.sub.A, P.sub.B. The state of wear w or the health index HI of the hydrostatic machine 10 results from w = M.sub.1,100% / M.sub.1,eff, where M.sub.1,100% corresponds to the second torque ascertained by the first calculation method.

[0059] FIG. 2 shows a flow chart according to a preferred embodiment of the method according to the invention. In the shown embodiment, the method 1 comprises a plurality of steps. In a first step S1, a first torque of the drive 11 is determined at a specified drive vector. In a second step S2, a second torque of the drive 11 is ascertained at the specified drive vector, using a first calculation method. In a third step S3, the present state of wear of the hydrostatic machine 10 is determined using a second calculation method. The first determined torque and the second ascertained torque are compared to one another.

[0060] FIG. 3 shows an example of the curve of the state of wear w in % and/or the health index HI in % of a hydrostatic machine 10, as could occur over a particular useful life d. The curve 74 constitutes the variation of the state of wear w in % (y-axis 71) and/or of the health index HI in % over a useful life d (x-axis 72). Over the useful life d, values for the differential pressure ΔP, the delivery volume V.sub.1, the rotational speed n.sub.1, and the value for the viscosity v of the fluid are detected for a drive vector at particular intervals (100, 200, etc.). Table 1 lists exemplary values for the differential pressure, the delivery volume, the rotational speed, and the viscosity. For this drive vector, a first torque M.sub.1,eff is determined by measuring the current of the drive 11 and using a proportional factor, and/or by measuring by means of a torque sensor. By means of a first calculation method, a second torque M.sub.1,100% is ascertained for the corresponding drive vector. The first torque and the second torque are compared to one another using a second calculation method, and result in the state of wear w or the health index HI. It can be seen in FIG. 3 that the health index HI in % worsens over the useful life, which is represented by the falling curve 74. Furthermore, FIG. 3 shows a boundary line 70. This boundary line 70 represents a region in which the state of wear w, represented by the curve 74, reaches a value at which maintenance or servicing measures should be taken in order to remedy the wear in the hydrostatic machine 10 or to limit negative consequences for a hydraulic system to a minimum. In addition, the curve 73 shows how the curve 74 can be extrapolated for the application of predictive maintenance. A prediction can thus be made about the time profile of the state of wear. This extrapolation can be achieved by linear regression, as shown in FIG. 3, or alternatively with the aid of Markov chains, Kalman filters, and/or machine learning algorithms. A history of the state of wear is required for this purpose. In an advantageous manner, an operator of the system can plan, prepare, or perform necessary maintenance procedures of the machine using the information about the state of wear. In FIG. 3, the points marked with “X” represent the corresponding measurement points of the state of wear, and the curve 74 is ascertained via the simulation/extrapolation with the aid of the aforementioned methods (Markov chains, etc.).

[0061] It can be seen from Table 1 that the determined first torque M.sub.1,eff has a higher value than the second ascertained torque M.sub.1,100%. This can be attributed to friction within the hydrostatic machine 10 or the hydrostatic pump 12. The result is a worsened health index Hl. The health index HI steadily decreases over the useful life d. This index can be used for a wear prognosis and/or a simulation of the state of wear and can result in predictive maintenance.

TABLE-US-00001 Time [d] Δp [bar] V.sub.1 [cmm] n.sub.1 [rpm] v [cSt] M.sub.1,100% [Nm] M.sub.1,eff [Nm] HI [%] 100 100 19 1250 98 35.72 35.73 99.97 200 150 14.25 500 83 39.98 40.00 99.94 300 10 19 2500 95 3.94 3.95 99.81 400 100 19 1300 72 35.62 36.02 98.90 500 150 14.25 575 82 40.02 42.26 90.47

[0062] Finally, it should be pointed out that the description of the invention and the exemplary embodiments are basically not to be understood as limiting with regard to a particular physical realization of the invention. All features explained and shown in conjunction with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention in order to simultaneously realize their advantageous effects.

[0063] The scope of protection of the present invention is defined by the claims and is not limited by the features explained in the description or shown in the figures.

TABLE-US-00002 List of reference signs 1 Method 10 Hydrostatic machine 11 Drive 12 Hydrostatic pump 13 Drive 20 Fluid transport channel 30 Hydraulic cylinder 40 Torque sensor 50 Pressure sensor 60 Current detector 70 Wear limit 71 y-axis (health index) 72 x-axis (running time) 73 PM 74 State of wear (health index) S1-S3 Method steps P.sub.A, P.sub.B Pressure Q.sub.1 Volume flow V.sub.1 Delivery volume M.sub.1,eff Actual torque n Rotational speed