CN118896772A - Wear identification method for rolling bearing device of pivoting cradle of adjustable hydraulic press - Google Patents

Abstract

The invention relates to a method for detecting wear of a rolling bearing device (66, 68) of a pivot cradle (64) of a pivot device of an adjustable hydraulic machine (2), comprising: -manipulating (110) a pivoting means for pivoting the pivoting cradle (64) according to a preset target pivoting angle curve (70) over time; detecting (120) an actual pivot angle curve (72) over time during pivoting; -evaluating (130) an actual pivot angle curve (72) and a target pivot angle curve (70) for identifying at least one defined characteristic deviation (74, 76, 84, 86) of the actual pivot angle curve relative to the target pivot angle curve, the characteristic deviation being indicative of wear; and determining (140) that there is wear of the rolling bearing device (66, 68) when at least one defined characteristic deviation (74, 76, 84, 86) is identified.

Description

Wear identification method for rolling bearing device of pivoting cradle of adjustable hydraulic press

Technical Field

The invention relates to a method for detecting wear of a rolling bearing arrangement of a pivoting cradle of an adjustable hydraulic press, as well as to a computing unit and a computer program product for carrying out the method.

Background Art

In the hydraulic drive, an adjustable hydraulic machine can be used. For example, a variable displacement pump in the form of a swash plate axial piston machine can be used for a hydrostatic drive. The volume flow is proportional to the drive speed and the displacement volume, wherein the displacement volume and thus the volume flow can be varied steplessly by adjusting the pivoting cradle (swash plate). In such a swash plate axial piston machine, the piston conveying the hydraulic oil is arranged axially relative to the drive shaft, rotates therewith and is supported on the pivoting cradle by means of a sliding shoe. The pivoting cradle is usually supported by means of a rolling bearing or a sliding bearing, wherein the pivoting cradle is adjusted by rotating or pivoting the pivoting cradle in the rolling bearing, i.e. by varying the so-called pivot angle.

Summary of the invention

According to the invention, a method for detecting wear of a rolling bearing of a pivoting cradle of an adjustable hydraulic press is proposed, as well as a computing unit and a computer program product for carrying out the method. Advantageous embodiments are the subject matter of the dependent claims and the following description.

The invention uses the measure that a pivoting cradle of an adjustable hydraulic press is pivoted according to a target pivot angle curve and the corresponding actual pivot angle curve is evaluated to determine whether at least one defined characteristic deviation from the target pivot angle curve occurs. If at least one defined characteristic deviation is detected, it is determined that there is wear or potential wear of the rolling bearing arrangement of the pivoting cradle. This solution allows wear at the rolling bearing arrangement to be detected early, so that appropriate measures can be taken to prevent further damage.

At least one characteristic deviation is defined as a characteristic deviation for wear, i.e. as a phase or time period during the pivoting movement in which the actual pivot angle changes more slowly or more quickly relative to the target pivot angle curve. In other words, at least one characteristic deviation is suitably defined for indicating wear.

The wear to be detected is in particular the so-called "false brinelling" or "wavy formation" or "static marks".

The adjustable hydraulic machine is in particular an adjustable axial piston machine, for example a pivot plate machine or a bent-axis machine.

The computing unit according to the invention, for example a control unit of a hydraulic machine or of a hydraulic drive system of a working machine using a hydraulic machine, is designed, in particular in terms of programming, to carry out the method according to the invention.

In particular, if the executed controller is also used for other tasks and is therefore already present, it is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with program code for executing all method steps, since this results in particularly low costs. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs and others. It is also possible to download the program via a computer network (Internet, intranet, etc.).

Further advantages and embodiments of the invention are apparent from the description and the accompanying drawings.

It goes without saying that the features mentioned above and the features yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is schematically illustrated in the drawings using exemplary embodiments and is described in more detail below with reference to the drawings.

FIG1 shows the structure of a hydraulic system in a simplified diagram;

FIG2 shows an exemplary hydraulic press in cross-sectional view;

3A, 3B show characteristic deviations between the curves of the actual pivot angle and the target pivot angle or their time derivatives, which are indicative of wear;

4A, 4B show filtered plots of actual pivot angle and target pivot angle or related time derivatives;

FIG. 5 shows a flow chart according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows (simplified) the design of a hydraulic system in which the method according to the invention can be used.

Shown is an adjustable hydraulic machine 2 (in particular an adjustable hydraulic pump or variable displacement pump), which conveys a pressure medium (hydraulic fluid, usually hydraulic oil) from a first working connection 22 (which is hydraulically connected to a pressure medium tank, for example) to a second working connection 24, which is connected to a hydraulic drive system 6, for example, so that the hydraulic drive system is supplied with pressure medium via the hydraulic machine 2. The hydraulic drive system 6 usually includes one or more hydraulic loads (i.e. hydraulic cylinders and/or hydraulic motors) and valves, which control the flow of pressure medium into and out of the hydraulic loads.

The hydraulic machine 2 is adjustable, that is to say it has an adjustable displacement or adjustable displacement volume. The term "displacement" refers to the volume of pressure medium delivered per revolution of the hydraulic machine 2. The hydraulic machine 2 is in particular an axial piston machine, for example in a swash plate or slanted axis design, wherein the displacement corresponds to the pivot angle. The hydraulic machine 2 is driven by a motor 4, for example an internal combustion engine (in particular a diesel engine) or an electric motor.

The hydraulic machine 2 can be regulated in a pre-controlled electro-hydraulic manner. Here, for example, the pressure medium volume flow to the servo cylinder (Stellzylinder) of the hydraulic machine 2 is controlled by means of a control signal of a controller 12 of a directional valve (e.g., a proportional directional valve) that is electrically or electromagnetically controlled (the control signal is transmitted, for example, via a control line). The servo cylinder in turn regulates the displacement of the hydraulic machine 2, i.e., changes the pivot angle of the pivoting cradle (pivoting plate or swash plate). Different current intensities of the control signal correspond, for example, to different magnitudes of regulation of the directional valve and correspondingly to different magnitudes of pressure medium volume flow to the servo cylinder, so that the current intensity of the control signal corresponds to the displacement regulation speed, i.e., the rate of change (gradient) of the pivot angle of the hydraulic machine. The servo cylinder, the directional valve, and the pivoting cradle can be regarded as components of the regulating device of the hydraulic machine. The controller 12 (computing unit or electronic control device) is a controller of the hydraulic machine and/or the hydraulic system.

Furthermore, the hydraulic system can have one or more sensors. A pivot angle sensor 30 is provided which measures the pivot angle of the pivot cradle. The corresponding pivot angle measurement values can be transmitted from the pivot angle sensor 30 to the control unit 12, which detects them as the actual pivot angle. The pivot angle measurement values or the actual pivot angle are used in the embodiment of the method according to the invention for detecting wear on the rolling bearing arrangement of the pivot cradle.

Furthermore, a first pressure sensor 32 for measuring the pressure of the pressure medium at the first working connection 22 and/or a second pressure sensor 34 for measuring the pressure of the pressure medium at the second working connection 24 can be provided. The corresponding pressure measurement values can be transmitted from the pressure sensors to the control unit 12, which detects them and can, for example, implement a control and/or regulation method based on them in normal operation. A rotation speed sensor 36 can also be provided, which measures the rotation speed of the hydraulic machine 2 or the corresponding rotation speed of the motor 4, wherein the transmission ratio may be taken into account. The corresponding rotation speed measurement values can be transmitted from the pressure sensors to the control unit 12.

In normal operation, the control unit 12 receives a target value specification 38 , for example for the pressure or the pivot angle, and controls or regulates the hydraulic machine accordingly by adjusting the pivot angle, wherein measured values of sensors can be used.

In particular, the control unit 12 can perform a wear detection function according to the method according to the invention for detecting wear of a pivot cradle rolling bearing arrangement of a hydraulic press, for example by executing a corresponding computer program product, namely a wear detection computer program product 14 .

FIG2 shows an exemplary hydraulic press in a cross-sectional view, the function of which is briefly described below.

The drive shaft 51 is driven by a motor with torque and speed. The cylinder 60 is driven by the drive shaft through the meshing part and is in rotation. In each rotation, the piston 62 completes a stroke in the cylinder bore, the size of which is related to the tilting position of the pivoting cradle 64. The sliding shoe 63 is held and guided on the sliding surface of the pivoting cradle together with the piston through the pull-back plate 52. Due to the tilting position of the pivoting cradle, each piston moves back to its starting position through the bottom dead center and the top dead center during one rotation. Here, the pressure liquid corresponding to the stroke volume is delivered and discharged through two control gaps in the control plate 56. The pressure liquid flows into the enlarged piston space on the suction side 58. At the same time, the pressure liquid is pressed into the hydraulic system from the cylinder space through the piston on the high-pressure side 55. The pivot angle of the pivoting cradle 64 can be adjusted steplessly. Adjustment is performed by means of a servo piston (Stellkolben) 61, wherein the inflow and outflow of the pressure medium in the servo piston are controlled by a control valve 59 (for example, an electric proportional reversing valve). The piston stroke and thus the displacement volume are changed by adjusting the pivot angle. The pivot angle is adjusted hydraulically by a servo piston. The pivot cradle is flexibly mounted in a pivot bearing and is balanced by a reaction piston 53. When the pivot angle increases, the displacement volume increases; when the pivot angle decreases, the displacement volume decreases accordingly.

The pivot cradle 64 is supported in a rotatable manner about an axis perpendicular to the drawing plane. The pivot bearing is formed by a rolling bearing arrangement. Here, a bearing journal 66 arranged on the pivot cradle 64 is supported in a bearing cage 68 (indicated by a dotted line) arranged at the housing of the hydraulic press, thereby forming a sliding bearing arrangement or a rolling bearing arrangement (or rolling bearing).

Due to the micro-oscillations during the operation of the hydraulic press, wear phenomena in the form of so-called "false brinelling" or "wavy formation" or "static marks" appear on the contact surfaces of the rolling bearing assembly. Such wear phenomena should be detected as early as possible to avoid subsequent damage to the hydraulic press and the hydraulic circuit.

3A , 3B show characteristic deviations between the curves of the actual pivot angle and the target pivot angle or their time derivatives, which are indicative of wear.

In FIG. 3A , a target pivot angle curve 70 and an actual pivot angle curve 72 are plotted, wherein the pivot angle α is plotted against the time t. The target pivot angle curve 70 is a time curve of the target pivot angle (with which the hydraulic press is operated). In the example shown, the target pivot angle curve 70 is a linear curve with a constant rate of change of the target pivot angle. The actual pivot angle curve 72 is a time curve of the actual pivot angle (which is actually set by the hydraulic press and measured, for example, by means of a pivot angle sensor).

FIG. 3B shows a target rate of change curve 80 and an actual rate of change curve 82, wherein the rate of change The target rate of change curve 80 is a time curve of the time derivative or rate of change of the target pivot angle, which can be determined, for example, from the target pivot angle curve. In the example shown, the target rate of change curve 80 substantially corresponds to a constant target rate of change of the target pivot angle. The actual rate of change curve 82 is a time curve of the time derivative or rate of change of the actual pivot angle, which can be determined, for example, from the actual pivot angle curve or the actual pivot angle measured at consecutive time points.

In both figures, the sections in which characteristic deviations between the actual pivot angle and the target pivot angle or the curves of the corresponding rate of change occur are marked. With the aid of these characteristic deviations, wear at the bearings of the pivot cradle can be detected. The characteristic deviations shown are, on the one hand, deviations that represent a slowing down of the actual pivot angle change relative to the target pivot angle change 74, 84 (which corresponds, for example, to a stagnation of the bearing arrangement at a location with high sliding resistance) and, on the other hand, deviations that represent an acceleration of the actual pivot angle change relative to the target pivot angle change 76, 86 (which corresponds, for example, to a breakaway of the bearing arrangement from a location with high sliding resistance).

Their combination, for example a slowed actual pivot angle change 74, 84 followed by an accelerated actual pivot angle change 76, 86, also represents a characteristic deviation. Identification of the combination is advantageous because it allows for better differentiation from other possible disturbances in the pivoting movement, for example in the case of load changes of a hydraulic load supplied with pressure medium by a hydraulic press.

It is provided that such characteristic deviations for wear at the rolling bearing of the pivot cradle are identified by evaluating the actual pivot angle curve with reference to the target pivot angle curve in order to be able to determine whether wear is present. In this case, a distinction can be made between various so-called deviation characteristics. The evaluation can in particular include the application of a low-pass filter.

Fig. 4A, Fig. 4B (in addition to the curves showing the actual pivot angle and the target pivot angle) also show the filtered curves of the actual pivot angle and the target pivot angle or the related time derivatives. Fig. 4A, Fig. 4B are similar to Fig. 3A, Fig. 3B, wherein smoothed or low-pass filtered curves are additionally drawn.

In FIG. 4A , a target pivot angle curve 90 and an actual pivot angle curve 91 are plotted, wherein the pivot angle α is plotted relative to time t. In addition, a smoothed or filtered target pivot angle curve 92 and a smoothed or filtered actual pivot angle curve 93 are plotted, wherein the pivot angle α is again plotted relative to time t. The pivot angles of the filtered curves 92, 93 are rescaled here relative to the unfiltered curves 90, 91 in order to be able to better distinguish the curves. A low-pass filter is used so that the filtered target pivot angle curve 92 and the filtered actual pivot angle curve 93 can be determined from the target pivot angle curve 90 and the actual pivot angle curve 91, wherein in particular the same filter parameters are used for both.

FIG. 4B shows a smoothed or filtered target rate of change curve 98 and a smoothed or filtered actual rate of change curve 96, wherein the rate of change Plotted against time t. This is a quantity of the rate of change (Betrag). The filtered target rate of change curve 98 and the filtered actual rate of change curve 96 can be obtained, for example, as quantities of the time derivative of the filtered target pivot angle curve 92 or the filtered actual pivot angle curve 93, respectively. Alternatively, the quantities of the time derivatives of the target pivot angle curve 90 and the actual pivot angle curve 91 can be filtered with a low-pass filter (the quantity formation can also be equivalently The time derivative of the pivot angle curve is to be understood as follows: the pivot angle curve is understood as a function of the pivot angle assigned to each time point and the time derivative of the function is determined to obtain the time derivative of the pivot angle curve. When executed in a computing unit (e.g., by the controller 12 of FIG. 1 with the aid of the wear identification computer program product 14), the curve is usually given as a sequence for consecutive discrete time points (e.g., according to a time grid given by the processing frequency of the computing unit), so that the time derivative corresponds to the discrete derivative.

The evaluation for identifying wear is based in particular on a target rate of change curve and an actual rate of change curve, wherein an unfiltered rate of change curve (e.g. according to FIG. 3B ) or a filtered rate of change curve (e.g. according to FIG. 4B ) can be used. In general, therefore, the target rate of change curve and the actual rate of change curve are determined or calculated based on the target pivot angle curve and the actual pivot angle curve. In this case, the time derivatives of the target pivot angle curve and the actual pivot angle curve can be used directly or can be filtered additionally using a low-pass filter. The filtering can be performed before or after the formation of the time derivative. Preferably, the amount of the time derivative is used respectively.

In order to identify the first deviation feature, it can be checked within the framework of the evaluation whether the actual rate of change curve is lower than the target rate of change curve in a first time period, wherein the first time period has at least one first (temporal) minimum duration, and/or wherein the target pivot angle is changed in amount by at least one predetermined (first) minimum pivot angle change amount according to the target pivot angle curve in the first time period. In FIG. 3B , this corresponds to the slowed actual pivot angle change 84. In particular, it is checked whether the actual rate of change curve is lower than a predetermined portion of the target rate of change curve in the first time period (i.e., the portion of the actual rate of change according to the actual rate of change curve being lower than the target rate of change according to the target rate of change curve for all time points in the first time period). The "portion" can be expressed, for example, as a percentage (of the target rate of change). The portion can be determined, for example, according to the method (with or without filtering) used for determining or calculating the rate of change curve (actual rate of change curve and target rate of change curve). If a rate of change curve without filtering is used, the portion can, for example, be equal to or less than 95%, preferably equal to or less than 90%, more preferably equal to or less than 80%. When using a low-pass filter, the portion can, for example, be equal to or less than 50%, preferably equal to or less than 35%, more preferably equal to or less than 25%.

Achieving a quantitative change of the target pivot angle by at least one predetermined minimum pivot angle change within a first time period, this optional prerequisite involves that a sufficiently large change of the target pivot angle should be achieved within the first time period, or that the first time period has a sufficient time length corresponding to a first (temporal) minimum duration, in particular for excluding small fluctuations of the actual pivot angle near the target pivot angle. The minimum pivot angle change can be selected accordingly appropriately. For example, the minimum pivot angle change can be at least 5%, at least 10%, at least 15% or at least 20% relative to the maximum possible pivot angle change of the hydraulic press. The first minimum duration can be correspondingly determined using a target change rate according to a target change rate curve. The first minimum duration or the minimum pivot angle change can be determined, for example, by means of experiments and/or simulations.

Preferably, within the framework of the first deviation characteristic, it is possible to additionally check whether the actual rate of change curve is higher than the target rate of change curve by at least one predetermined multiple in the second time period that occurs after the first time period (i.e., for all time points in the second time period, the actual rate of change according to the actual rate of change curve is at least one multiple greater than the target rate of change according to the target rate of change curve). The second time period has in particular at least one second (temporal) minimum duration. The second minimum duration is preferably shorter than the first minimum duration. The second minimum duration can be specified relative to the first minimum duration, for example, as less than or equal to 0.5 times of the first minimum duration, less than or equal to 0.2 times of the first minimum duration, less than or equal to 0.1 times of the first minimum duration, or less than or equal to 0.05 times of the first minimum duration. In critical cases, the second time period can be a single time point (referred to as the first time point). The time interval between the first time period and the second time period should in particular be less than or equal to a predetermined maximum time interval. This maximum time interval can, for example, be determined relative to the first minimum duration like the second minimum duration, that is, as described above. The multiple is greater than 1 and can be appropriately selected, and can be, for example, equal to or greater than 2, equal to or greater than 3, or equal to or greater than 4.

If the actual rate of change curve in a second time period occurring after the first time period exceeds the target rate of change curve by at least a predetermined multiple, it can optionally be further checked within the framework of the first deviation feature whether the actual rate of change curve in a third time period occurring after the second time period (or the first time point) is below the target rate of change curve, wherein the third time period has at least a third (temporally) minimum duration, and/or wherein the target pivot angle is changed in amount by at least a predetermined (second) minimum pivot angle change amount according to the target pivot angle curve in the third time period. This corresponds to the following situation: wherein first a slowed actual pivot angle change occurs, which results in a difference in the actual pivot angle curve relative to the target pivot angle curve, after which an accelerated actual pivot angle change occurs that exceeds the target pivot angle curve, and then a further slowed actual pivot angle change occurs, which brings the actual pivot angle curve back to the target pivot angle curve.

It should be noted that the concepts of "first", "second", "third" ... are used in this application to distinguish between different elements that have the same name otherwise. Unless explicitly stated, they should not imply a specific order. The phrase "a time period or a time point that occurs after another time period or another time point" should not be construed as meaning immediately following, but there can also be a time interval between them.

According to another embodiment, in order to identify the second deviation feature, it can be checked within the framework of the evaluation whether the amount of the difference between the actual pivot angle curve and the target pivot angle curve or between the filtered actual pivot angle curve and the filtered target pivot angle curve exceeds a quantity threshold at at least one time point. In FIG. 3A , the corresponding time points are approximately at the beginning and end of the marked areas of the slowed down actual pivot angle change 74 , 84 and the accelerated actual pivot angle change 76 , 86 . The quantity threshold can be specified, for example, in degrees as an absolute value or relative to the maximum possible pivot angle of the hydraulic press. The maximum possible pivot angle is approximately 0 to 100% or (for a hydraulic press that can pivot through zero) -100% to +100%. The quantity threshold can be selected appropriately, in particular such that it is higher than the value of the amount of the difference between the (unfiltered or filtered) actual pivot angle curve and the (unfiltered or filtered) target pivot angle curve that occurs when running with wear-free rolling bearings. The quantity threshold can be approximately greater than 5% or greater than 10% relative to the maximum possible pivot angle.

Furthermore, the sign of the difference between the actual pivot angle profile and the target pivot angle profile can be taken into account.

In the following, further conceivable deviation characteristics are described, which can be used for an unfiltered or filtered actual pivot angle curve or a target pivot angle curve, respectively. For simplicity, the expressions "actual pivot angle curve" and "target pivot angle curve" are used, which can represent both, namely "unfiltered actual pivot angle curve" and "unfiltered target pivot angle curve" or "filtered actual pivot angle curve" and "filtered target pivot angle curve".

In order to identify the third deviation feature, within the framework of the evaluation, it is possible to check, for example, whether the actual pivot angle curve is above the target pivot angle curve by at least one first threshold value in a fourth time period or at a second time point, and whether the actual pivot angle curve is below the target pivot angle curve by at least one second threshold value in a fifth time period or at a third time point that occurs later than the fourth time period or the second time point. In FIG. 3A , this corresponds to, for example, a slowed actual pivot angle change 74.

In order to identify the third deviation feature, it is possible to further check within the framework of the evaluation whether the actual pivot angle curve is above the target pivot angle curve by at least one third threshold value in a sixth time period or at a fourth time point that occurs later than the fifth time period or the third time point. In FIG. 3A , this corresponds, for example, to a slowed actual pivot angle change 74 followed by an accelerated actual pivot angle change 76.

The first threshold value, the second threshold value and, if necessary, the third threshold value can be specified like the previous value threshold values and selected appropriately, in particular selected sufficiently high, in order to exclude as far as possible an erroneous determination of wear in the case of a non-wear bearing. The first threshold value, the second threshold value and, if necessary, the third threshold value can be, independently of one another, approximately greater than 5% or greater than 10% relative to the maximum possible pivot angle.

It is also conceivable that the signs of the differences are detected in the opposite order, ie an accelerated actual pivot angle change may be followed by a slowed actual pivot angle change.

In order to identify the fourth deviation characteristic, it can be checked within the framework of the evaluation whether the actual pivot angle curve is below the target pivot angle curve by at least one fourth threshold value in the seventh time period or at the fifth time point, and whether the actual pivot angle curve is above the target pivot angle curve by at least one fifth threshold value in the eighth time period or at the sixth time point later than the seventh time period or the fifth time point. In FIG. 3A , this corresponds to, for example, a slowed actual pivot angle change 74.

To identify the fourth deviation feature, a further check can additionally be performed within the scope of the evaluation: whether the actual pivot angle curve in a ninth time period occurring later than the eighth time period or the sixth time point or at the seventh time point falls below the target pivot angle curve by at least a sixth threshold value.

The fourth threshold value, the fifth threshold value and, if necessary, the sixth threshold value can be specified like the previous value threshold values and selected appropriately, in particular selected sufficiently high, in order to exclude as far as possible an erroneous determination of wear in the case of no wear on the bearing. The fourth threshold value, the fifth threshold value and, if necessary, the sixth threshold value can be, independently of one another, approximately greater than 5% or greater than 10% relative to the maximum possible pivot angle.

FIG. 5 shows a flow chart of a method for detecting wear of a rolling bearing of a pivot cradle of a pivot device of an adjustable hydraulic press according to an embodiment of the present invention.

Here, the pivoting device is controlled in step 110 to pivot the pivot cradle according to a preset target pivot angle curve over time. The target pivot angle curve is preset as a time series of target pivot angles (eg as a discrete sequence or a continuous sequence in a functional form).

In step 120, an actual pivot angle profile is detected over time during the pivoting. This is done in parallel with step 110. The actual pivot angle profile is, for example, a time series of the actual pivot angle of the pivot cradle, ie the true (actual) pivot angle, which is measured, for example, with a sensor (pivot angle sensor).

In step 130, the actual pivot angle curve is evaluated in order to identify at least one defined characteristic deviation in terms of wear relative to the target pivot angle curve. For this purpose, the difference between the actual pivot angle curve and the target pivot angle curve and/or between the actual rate of change curve and the target rate of change curve (based on the unfiltered or filtered curves, respectively) can be used, as described in conjunction with FIGS. 3A , 3B, 4A and 4B. The at least one defined characteristic deviation can in particular include one or more of the deviation features described in conjunction with FIGS. 3A , 3B, 4A and 4B.

Optionally, during evaluation 130, it can be first checked whether the target rate of change according to the target rate of change curve is equal to or greater than the rate of change assessment lower limit and/or equal to or less than the rate of change assessment upper limit. If this is not the case, the check on whether at least one characteristic deviation exists is omitted. In other words, only when the target rate of change curve is equal to or greater than the rate of change assessment lower limit and/or equal to or less than the rate of change assessment upper limit is it checked or identified whether at least one characteristic deviation exists. Therefore, during the evaluation, it is possible to exclude target rates of change that are not suitable for wear identification, for example very small (e.g. close to 0) or very large. The rate of change assessment lower limit and the rate of change assessment upper limit can be appropriately determined. The rate of change assessment lower limit is in particular greater than zero. The rate of change assessment upper limit is in particular less than the maximum rate of change of the pivot angle (e.g. determined by technology). It is considered here that the target rate of change or the target rate of change curve is determined as an absolute value, i.e. their determination includes quantitative formation.

If at least one defined characteristic deviation is detected, then in step 140 it is determined that wear or potential wear of the rolling bearing is present. The term "potential" refers to the fact that characteristic deviations can occur in principle due to measurement errors, fluctuations, etc. in the hydraulic system (for example, such deviations can occur when the pressure medium temperature is too low). This means that wear is detected in the sense of the method when at least one characteristic deviation is detected. If necessary, the method can be repeated when at least one characteristic deviation is detected in order to achieve a high degree of reliability that wear of the rolling bearing arrangement is actually present.

If no defined characteristic deviation is detected, it is assumed that there is no wear or that the wear is very low.

If (potential) wear is detected, a fault message can be generated and/or output, for example (for example via a display of the working machine in which the hydraulic system is used). Such a fault message can also be stored in the control unit, so that it can be read and evaluated, for example during maintenance work on the hydraulic system. In the case of a fault message, appropriate measures can be taken, such as replacing worn parts of the rolling bearing arrangement, to prevent further damage.

Claims (15)

1. A method for detecting wear of a rolling bearing arrangement (66, 68) of a pivoting cradle (64) of an adjustable hydraulic press (2), the method comprising: Controlling (110) a pivoting device of the hydraulic press (2) to pivot the pivoting cradle (64) according to a preset target pivot angle curve (70) over time; During the pivoting, detecting (120) an actual pivot angle curve (72) over time; evaluating (130) the actual pivot angle curve (72) and the target pivot angle curve (70) for identifying at least one defined characteristic deviation (74, 76, 84, 86) of the actual pivot angle curve relative to the target pivot angle curve, the characteristic deviation being indicative of wear; and When at least one defined characteristic deviation (74, 76, 84, 86) is detected, it is determined (140) that wear of the rolling bearing arrangement (66, 68) is present. 2. The method according to claim 1, wherein the target pivot angle curve (70) comprises a monotonic, in particular strictly monotonic, increase or decrease of the target pivot angle; and/or wherein the target pivot angle curve (70) comprises a linear curve of the target pivot angle having a predetermined rate of change different from zero. 3. The method according to any one of claims 1 or 2, wherein in the evaluation (130), an actual rate of change curve (82, 96) is determined as a quantity based on the rate of change of the actual pivot angle curve (72, 93) over time, and a target rate of change curve (80, 98) is determined as a quantity based on the rate of change of the target pivot angle curve (70, 92) over time; wherein at least one defined characteristic deviation as a first deviation characteristic comprises: the actual rate of change curve (82) is below the target rate of change curve (84) within a first time period; The first time period has at least a first minimum duration and/or the target pivot angle is changed by at least a predetermined minimum pivot angle change amount in the first time period according to the target pivot angle curve (70). 4. The method of claim 3, wherein it is checked whether the actual change rate curve is below a predetermined portion of the target change rate curve during the first time period in order to determine that the actual change rate curve (82, 96) is below the target change rate curve (84, 98) during the first time period. 5. The method of claim 4, wherein the fraction is less than or equal to 0.95; and/or wherein the fraction is less than or equal to 0.5. 6. The method according to any one of claims 3 to 5, wherein the first deviation feature further comprises: In a second time period occurring after the first time period, the actual change rate curve (82) is higher than the target change rate curve (84) by at least a predetermined multiple; The second time period has at least one second minimum duration. 7. The method according to claim 6, The second minimum duration is shorter than the first minimum duration, in particular, less than or equal to 0.5 times of the first minimum duration; and/or Wherein, the multiple is equal to or greater than 2. 8 . The method according to claim 6 , wherein a time interval between the first time period and the second time period is less than or equal to a predetermined maximum time interval. 9. The method according to any one of claims 3 to 8, Wherein, determining the actual rate of change curve (82, 96) includes: calculating the rate of change of the actual pivot angle over time based on the actual pivot angle curve (72), and calculating a quantity measuring the rate of change of the calculated actual pivot angle over time; and/or Wherein, determining the target change rate curve (80, 98) includes: calculating the rate of change of the target pivot angle over time according to the target pivot angle curve (70), and A quantity is calculated that measures the rate of change of the calculated target pivot angle over time. 10. The method according to claim 9, Wherein, determining the actual change rate curve (96) further comprises: applying a low pass filter before or after calculating the rate of change of the actual pivot angle over time; and/or Wherein, determining the target change rate curve (98) further comprises: A low pass filter is applied before or after calculating the rate of change of the target pivot angle over time. 11. A method according to any one of claims 3 to 10, wherein, in the evaluation (130), the presence of at least one defined characteristic deviation (74, 76, 84, 86) of the actual pivot angle curve relative to the target pivot angle curve is checked or identified only when the target rate of change according to the target rate of change curve (80, 98) is equal to or greater than a rate of change assessment lower limit and/or equal to or less than a rate of change assessment upper limit. 12. The method according to any of the preceding claims, wherein the at least one defined characteristic deviation as a second deviation characteristic comprises: The magnitude of the difference between the actual pivot angle curve (72) and the target pivot angle curve (70) or between the filtered actual pivot angle curve (93) and the filtered target pivot angle curve (92) exceeds a magnitude threshold at at least one point in time. 13. A computing unit (12) comprising a processor, the computing unit being configured in such a way that it performs the method according to any of the preceding claims. 14. A computer program product (14) comprising instructions which, when the program is executed by a computer, cause the computer to perform the method according to any one of claims 1 to 12. 15. A computer-readable data carrier having a computer program stored thereon, characterized in that when the computer program is executed by a processor, all method steps of the method according to any one of claims 1 to 12 are implemented.