Method for detecting wear of a rolling bearing of a swivel cradle of an adjustable hydraulic machine

Abstract

Method for detecting wear of a rolling bearing (66, 68) of a swivel cradle (64) of an adjustable hydraulic machine (2), comprising Controlling (110) a swiveling device of the hydraulic machine (2) to swivel the swivel cradle (64) according to a predetermined target swivel angle profile (70) over time; Recording (120) a temporal actual swivel angle progression (72) during swiveling; Evaluating (130) the actual swivel angle profile (72) and the target swivel angle profile (70) in order to identify at least one defined characteristic deviation (74, 76, 84, 86) of the actual swivel angle profile from the target swivel angle profile, which indicates wear; and Determine (140) that wear of the rolling bearing (66, 68) is present when at least one defined characteristic deviation (74, 76, 84, 86) is detected.

Description

[0001] The present invention relates to a method for detecting wear of a rolling bearing of a pivoting cradle of an adjustable hydraulic machine as well as a computing unit and a computer program for carrying out the method. Background of the invention

[0002] Adjustable hydraulic machines can be used in hydraulic drives. For example, variable displacement pumps in the form of swash plate axial piston machines can be used for hydrostatic drives. The volumetric flow is proportional to the drive speed and the displacement, whereby the displacement and thus the volumetric flow can be continuously varied by adjusting a swash plate cradle. In such swash plate axial piston machines, the pistons that deliver the hydraulic oil are arranged axially to the drive shaft, rotate with it and are supported on the swash plate by means of sliding shoes. The swash plate is typically mounted on rolling or plain bearings, whereby the swash plate is adjusted by rotating or pivoting the swash plate in the rolling bearing, i.e. by changing the so-called pivot angle.

[0003] The patents DE 10 2015 200 574 A1, DE 10 2014 225 147 A1, DE 10 2004 056 996 A1 and US 2014 / 0 039 809 A1 are known from the prior art. Disclosure of the invention

[0004] According to the invention, a method for detecting wear on a rolling bearing of a pivoting cradle of an adjustable hydraulic machine, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0005] The invention utilizes the measure of pivoting the pivoting cradle of an adjustable hydraulic machine according to a target pivot angle profile and evaluating a corresponding actual pivot angle profile to determine whether at least one defined characteristic deviation from the target pivot angle profile occurs. If the at least one defined characteristic deviation is detected, it is determined that wear or potential wear of the pivoting cradle's rolling bearing is present. This procedure allows wear on the rolling bearing to be detected early, making it possible to take appropriate measures to prevent further damage.

[0006] The at least one characteristic deviation is defined as a deviation characteristic of wear, i.e., as phases or time periods during the swivel movement in which a delayed or accelerated change in the actual swivel angle occurs compared to the desired swivel angle curve. This means that the at least one characteristic deviation is defined to indicate wear.

[0007] The wear that needs to be detected is in particular so-called “false brinelling” or “ribbing” or “standstill marking”.

[0008] The adjustable hydraulic machine is in particular an adjustable axial piston machine, e.g. a swash plate machine or a bent axis machine.

[0009] A computing unit according to the invention, e.g. a control unit of the hydraulic machine or of a hydraulic drive system of a work machine in which the hydraulic machine is used, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0010] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, especially if an executing control unit is also used for additional tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0011] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0012] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0013] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description Fig. Figure 1 shows a sketch of the structure of a hydraulic system. Fig. 2 shows an exemplary hydraulic machine in a cross-sectional view. Fig. 3A, Fig. 3B shows characteristic deviations, which indicate wear, between the curves of the actual swivel angle and the target swivel angle or their time derivatives. Fig. 4A, Fig. 4B show filtered curves of the actual swivel angle and the target swivel angle or of associated time derivatives. Fig. 5 shows a flowchart according to an embodiment of the invention. Detailed description of the drawing

[0014] Fig. Figure 1 shows (simplified) the structure of a hydraulic system in which the method according to the invention can be used.

[0015] An adjustable hydraulic machine 2 (in particular an adjustable hydraulic pump or variable displacement pump) is shown, which conveys pressure medium (hydraulic fluid, typically a hydraulic oil) from a first working port 22 (which is hydraulically connected, for example, to a pressure medium tank) to a second working port 24, which is connected, for example, to a hydraulic drive system 6, so that the latter is supplied with pressure medium by the hydraulic machine 2. The hydraulic drive system 6 typically comprises one or more hydraulic consumers (i.e., hydraulic cylinders and / or hydraulic motors) and valves that control the inflow and outflow of pressure medium to and from the hydraulic consumers.

[0016] The hydraulic machine 2 is adjustable, i.e., it has an adjustable displacement or an 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, e.g., with a swashplate design or a bent-axis design, wherein the displacement corresponds to a pivot angle. The hydraulic machine 2 is driven by a motor 4, e.g., an internal combustion engine, in particular a diesel engine, or an electric motor.

[0017] The adjustment of the hydraulic machine 2 can be carried out in a pilot-controlled electro-hydraulic manner. In this case, the volume flow of pressure medium to an actuating cylinder of the hydraulic machine 2 is controlled by means of a control signal (which is transmitted, for example, via a control line) from a control unit 12 of an electrically or electromagnetically controlled directional control valve (e.g. a proportional directional control valve). The actuating cylinder, in turn, adjusts the displacement of the hydraulic machine 2, i.e., changes the swivel angle of a swivel cradle (swash plate or swash plate). Different current intensities of the control signal correspond, for example, to different adjustments of the directional control valve and correspondingly different volume flows of pressure medium to the actuating cylinder, so that the current strength of the control signal corresponds to a speed of adjustment of the displacement, i.e., a rate of change (gradient) of the swivel angle of the hydraulic machine.The actuating cylinder, the directional control valve, and the swivel cradle can be considered part of the hydraulic machine's adjustment device. Control unit 12 (processing unit or electronic control) is a control unit of the hydraulic machine and / or the hydraulic system.

[0018] The hydraulic system can further comprise one or more sensors. A swivel angle sensor 30 is provided, which measures the swivel angle of the swivel cradle. Corresponding swivel angle measurements can be transmitted from the swivel angle sensor 30 to the control unit 12, which records them as the actual swivel angle. The swivel angle measurements or actual swivel angles are used in embodiments of the method according to the invention to detect wear on the roller bearing of the swivel cradle.

[0019] Furthermore, a first pressure sensor 32, which measures the pressure of the pressure medium at the first working port 22, and / or a second pressure sensor 34, which measures the pressure of the pressure medium at the second working port 24, can be provided. Corresponding pressure measured values ​​can be transmitted from the pressure sensors to the control unit 12, which records them and can, for example, implement a control and / or regulation method based thereon during regular operation. A speed sensor 36 can also be provided, which measures the speed of the hydraulic machine 2 or a corresponding speed of the motor 4, whereby a transmission ratio may also be taken into account. Corresponding speed measured values ​​can be transmitted from the pressure sensors to the control unit 12.

[0020] During regular operation, the control unit 12 receives, for example, a setpoint value 38 for a pressure or a swivel angle and controls or regulates the hydraulic machine accordingly by adjusting the swivel angle, whereby measured values ​​from the sensors can be used.

[0021] The control unit 12 can, in particular, implement a wear detection function according to a method according to the invention for detecting wear of a pivoting cradle rolling bearing of the hydraulic machine, e.g., by executing a corresponding computer program, i.e., a wear detection computer program 14.

[0022] Fig. 2 shows an exemplary hydraulic machine in a cross-sectional view; the function of the hydraulic machine is briefly described below.

[0023] A drive shaft 51 is driven by a motor with torque and speed. A cylinder 60 is driven by gearing via the drive shaft and set in rotation. With each revolution, pistons 62 perform a stroke in cylinder bores, the length of which depends on the inclination of a pivoting cradle 64. Sliding shoes 63 are held and guided with the pistons by a retraction plate 52 on the sliding surface of the pivoting cradle. Due to the inclination of the pivoting cradle, each piston moves past the bottom and top dead center during one revolution back to its starting position. During this process, the hydraulic fluid corresponding to the stroke volume is supplied to and removed through two control slots in a control plate 56. On a suction side 58, hydraulic fluid flows into the expanding piston chamber. At the same time, on a high-pressure side 55, the hydraulic fluid is forced from the cylinder chamber into the hydraulic system by the pistons.The swivel angle of the swivel cradle 64 is continuously adjustable. Adjustment is achieved by means of a control piston 61, with the inflow and outflow of pressure medium to the control piston controlled by a control valve 59 (e.g., an electroproportional directional control valve). Adjusting the swivel angle changes the piston stroke and thus the displacement volume. The swivel angle is adjusted hydraulically via the control piston. The swivel cradle is mounted smoothly in swivel bearings and is kept in balance by a counter piston 53. Increasing the swivel angle increases the displacement volume; decreasing it decreases accordingly.

[0024] The pivoting cradle 64 is mounted for rotation about an axis perpendicular to the plane of the drawing. The pivot bearings are formed by roller bearings. Bearing pins 66, which are arranged on the pivoting cradle 64, are mounted in bearing shells 68 arranged on the housing of the hydraulic machine (indicated by dashed lines), thus forming a plain bearing or roller bearing (or a rolling bearing).

[0025] Micro-oscillations during operation of the hydraulic machine can cause wear on the contact surfaces of the rolling bearings in the form of so-called "false brinelling," "ribbing," or "standstill markings." The occurrence of this wear phenomenon should be detected as early as possible to prevent subsequent damage to the hydraulic machine and the hydraulic circuit.

[0026] Fig. 3A, Fig. 3B shows characteristic deviations, which indicate wear, between the curves of the actual swivel angle and the target swivel angle or their time derivatives.

[0027] In Fig. 3A shows a target swivel angle curve 70 and an actual swivel angle curve 72, with the swivel angle α plotted against time t. The target swivel angle curve 70 is the time curve of the target swivel angle (with which the hydraulic machine is controlled). In the example shown, the target swivel angle curve 70 is a linear curve with a constant rate of change of the target swivel angle. The actual swivel angle curve 72 is the time curve of the actual swivel angle (which is actually set by the hydraulic machine and measured, for example, using a swivel angle sensor).

[0028] In Fig. 3B shows a target change rate curve 80 and an actual change rate curve 82, with the change rate α̇ being plotted against time t. The target change rate curve 80 is the time curve of the time derivative or the rate of change of the target swivel angle, which can be determined, for example, from the target swivel angle curve. In the example shown, the target change rate curve 80 essentially corresponds to a constant target change rate of the target swivel angle. The actual change rate curve 82 is the time curve of the time derivative or the rate of change of the actual swivel angle, which can be determined, for example, from the actual swivel angle curve or the actual swivel angles measured at successive points in time.

[0029] In both figures, sections are marked in which characteristic deviations occur between the curves of the actual swivel angle and the target swivel angle or the corresponding rates of change. Based on these characteristic deviations, it can be seen that there is wear on the bearing of the swivel cradle. The characteristic deviations shown are, on the one hand, deviations that indicate a delayed actual swivel angle change 74, 84 compared to the target swivel angle change (this corresponds, for example, to the bearing getting stuck at a point with high sliding resistance), and, on the other hand, deviations that indicate an accelerated actual swivel angle change 76, 86 compared to the target swivel angle change (this corresponds, for example, to the bearing breaking away from a point with high sliding resistance). Combinations of these, such asa delayed actual swivel angle change 74, 84 followed by an accelerated actual swivel angle change 76, 86, represent characteristic deviations. The detection of combinations is useful because it allows a better differentiation from other possible disturbances (e.g. in the case of load changes of the hydraulic consumers which are supplied with pressure medium by the hydraulic machine) of the swivel movement.

[0030] By evaluating the actual swivel angle curve, it is intended to detect deviations from the target swivel angle curve that are characteristic of wear on the swivel cradle's rolling bearing, in order to determine whether wear is present. A distinction can be made between various so-called deviation characteristics. The evaluation can, in particular, include the application of a low-pass filter.

[0031] Fig. 4A, Fig. 4B show filtered curves of the actual swivel angle and the target swivel angle or of the associated time derivatives (in addition to curves of the actual swivel angle and the target swivel angle). Fig. 4A, Fig. 4B are similar to the Fig. 3A, Fig. 3B, where smoothed or low-pass filtered curves are also shown.

[0032] In Fig. 4A shows a target swivel angle curve 90 and an actual swivel angle curve 91, with the swivel angle α being plotted against time t. Additionally, a smoothed or filtered target swivel angle curve 92 and a smoothed or filtered actual swivel angle curve 93 are shown, with the swivel angle α again being plotted against time t. The swivel angle of the filtered curves 92, 93 is rescaled here compared to the unfiltered curves 90, 91 in order to better distinguish the curves. A low-pass filter is used to determine the filtered target swivel angle curve 92 and the filtered actual swivel angle curve 93 from the target swivel angle curve 90 and the actual swivel angle curve 91, with the same filter parameters being used for both.

[0033] In Fig. 4B shows a smoothed or filtered target change rate curve 98 and a smoothed or filtered actual change rate curve 96, with the change rate α̇ plotted against time t. In each case, this represents the absolute value of the change rate. The filtered target change rate curve 98 and the filtered actual change rate curve 96 can, for example, each be obtained as the absolute value of the time derivative of the filtered target swivel angle curve 92 and the filtered actual swivel angle curve 93, respectively. Alternatively, the filtered target change rate curve 98 and the filtered actual change rate curve 96 can be obtained by filtering the absolute value of the time derivatives of the target swivel angle curve 90 and the actual swivel angle curve 91 with the low-pass filter (the absolute value can also be formed equivalently after filtering).The term "time derivative of a swivel angle curve" is to be understood as above in the sense that the swivel angle curve is understood as a function that assigns a swivel angle to each point in time, and the time derivative of this function is determined to obtain the time derivative of a swivel angle curve. When implemented in a computing unit (e.g., by the control unit 12 of the . Fig. 1 by means of a wear detection computer program 14), the courses are typically given as sequences for successive discrete points in time (e.g., corresponding to a time grid given by a processing frequency of the computing unit), so that the time derivatives are correspondingly discrete derivatives.

[0034] The evaluation to detect wear is based in particular on the target change rate curve and the actual change rate curve, whereby the unfiltered (e.g. according to Fig. 3B) or the filtered change rate curves can be used (e.g. according to Fig. 4B). Generally speaking, a target change rate curve and an actual change rate curve are determined or calculated based on the target swivel angle curve and the actual swivel angle curve. The time derivatives of the target swivel angle curve and the actual swivel angle curve can be used directly, or additional filtering with a low-pass filter can be performed. Filtering can occur before or after the time derivatives are calculated. Preferably, the absolute value of the time derivative is used in each case.

[0035] As part of the evaluation, in order to identify a first deviation characteristic, it can be checked whether the actual change rate curve lies below the target change rate curve in a first time period, wherein the first time period has at least a first (temporal) minimum duration and / or wherein, in accordance with the target swivel angle curve in the first time period, an amount change of the target swivel angle by at least a predetermined (first) minimum swivel angle change amount occurs. This corresponds to Fig. 3B of the delayed actual swivel angle change 84. In particular, it is checked whether, in the first time period, the actual change rate curve lies below a predetermined fraction of the target change rate curve (i.e., for all points in time in the first time period, the actual change rate corresponding to the actual change rate curve lies below the fraction of the target change rate corresponding to the target change rate curve). The fraction can be expressed, for example, as a percentage (of the target change rate). The fraction can be determined, for example, depending on the method used (with or without filtering) to determine or calculate the change rate curves (actual change rate curve and target change rate curve). If change rate curves are used without filtering, the fraction can be, for example, 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 fraction can be, for example,equal to or less than 50%, preferably equal to or less than 35%, more preferably equal to or less than 25%.

[0036] The optional requirement that the target swivel angle changes by at least a predetermined minimum swivel angle change amount in the first time period refers to the fact that a sufficiently large change in the target swivel angle should occur in the first time period or that the first time period has a sufficient length of time corresponding to the first (temporal) minimum duration, in particular in order to exclude minor fluctuations in the actual swivel angle around the target swivel angle. The minimum swivel angle change amount can be selected accordingly. For example, the minimum swivel angle change amount can be at least 5%, at least 10%, at least 15%, or at least 20%, based on a maximum possible swivel angle change of the hydraulic machine. The first minimum duration can be set accordingly using the target change rate in accordance with the target change rate curve.The first minimum duration or the minimum amount of change in the swivel angle can be determined, for example, by means of tests and / or simulations.

[0037] Additionally, within the scope of the first deviation characteristic, it can preferably be checked whether, in a second time period occurring after the first time period, the actual change rate profile is at least a predetermined factor higher than the target change rate profile (i.e., for all points in time in the second time period, the actual change rate corresponding to the actual change rate profile is at least a factor higher than the target change rate corresponding to the target change rate profile). The second time period in particular has at least a 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 the first minimum duration, as less than or equal to 0.2 times the first minimum duration, as less than or equal to 0.1 times the first minimum duration, or as less than or equal to 0.05 times the first minimum duration. In the limiting case, the second time period can be a single point in time (referred to as the first point in time). In particular, a time interval between the first and the second time period should be less than or equal to a predetermined maximum time interval. The maximum time interval can, for example, be specified like the second minimum duration, i.e., as described above, relative to the first minimum duration. The factor is greater than one and can be chosen appropriately; for example, the factor can be equal to or greater than 2, equal to or greater than 3, or equal to or greater than 4.

[0038] Furthermore, optionally within the scope of the first deviation characteristic, if in the second time period, which occurs after the first time period, the actual change rate curve is above the target change rate curve by at least the predetermined factor, it can be checked whether in a third time period, which occurs after the second time period (or the first time point), the actual change rate curve is below the target change rate curve, wherein the third time period has at least a third (temporal) minimum duration and / or wherein, in accordance with the target swivel angle curve in the third time period, an amount change of the target swivel angle takes place by at least a predetermined (second) minimum swivel angle change amount.This corresponds to a situation in which initially a delayed actual swivel angle change occurs, which leads to a difference between the actual swivel angle curve and the target swivel angle curve, then an accelerated actual swivel angle change occurs, which exceeds the target swivel angle curve, and then another delayed actual swivel angle change occurs, which returns the actual swivel angle curve to the target swivel angle curve.

[0039] It is noted that the terms "first," "second," "third," etc., are used in this application to distinguish different, otherwise identically named elements. They are not intended to imply a particular order unless explicitly stated. The phrase used, that a period of time or a point in time occurs after another period of time or another point in time, is not necessarily to be understood as immediately following; rather, there may also be a period of time in between.

[0040] According to a further embodiment, in order to detect a second deviation characteristic, it can be checked during the evaluation whether the amount of the difference between the actual swivel angle curve and the target swivel angle curve or between the filtered actual swivel angle curve and the filtered target swivel angle curve exceeds a threshold value for at least one point in time. Fig. 3A, corresponding points in time are approximately at the beginning and end of the marked ranges of a delayed actual swivel angle change 74, 84 and an accelerated actual swivel angle change 76, 86. The absolute value threshold can be specified as an absolute value, e.g., in degrees, or relative to a maximum possible swivel angle of the hydraulic machine. The maximum possible swivel angle is approximately from 0 to 100% or from -100% to +100% (for zero-swivel hydraulic machines). The absolute value threshold can be suitably selected, in particular such that it lies above values ​​of the absolute value of the difference between the (unfiltered or filtered) actual swivel angle curve and the (unfiltered or filtered) target swivel angle curve, which occur during operation with wear-free rolling bearings. Relative to the maximum possible swivel angle, the absolute value threshold can be approximately greater than 5% or greater than 10%.

[0041] Furthermore, the sign of the difference between the actual swivel angle curve and the target swivel angle curve can be taken into account.

[0042] Further possible deviation characteristics are described below, each of which is applicable to the unfiltered or filtered actual swivel angle curve or target swivel angle curve. For simplicity, the terms "actual swivel angle curve" and "target swivel angle curve" are used, which can mean both, i.e., "unfiltered actual swivel angle curve" and "unfiltered target swivel angle curve" or "filtered actual swivel angle curve" and "filtered target swivel angle curve."

[0043] For example, to detect a third deviation characteristic, the evaluation can check whether, in a fourth time period or at a second point in time, the actual swivel angle curve is above the target swivel angle curve by at least a first threshold value, and in a fifth time period or at a third point in time that occurs later than the fourth time period or the second point in time, the actual swivel angle curve is below the target swivel angle curve by at least a second threshold value. This corresponds to Fig. 3A e.g. the delayed actual swivel angle change 74.

[0044] Furthermore, to detect the third deviation characteristic, the evaluation can also check whether, in a sixth time period or at a fourth point in time that occurs later than the fifth time period or the third point in time, the actual swivel angle curve is at least a third threshold value above the target swivel angle curve. This corresponds to Fig. 3A e.g. the delayed actual swivel angle change 74 followed by the accelerated actual swivel angle change 76.

[0045] The first, second, and, if applicable, third threshold values ​​can be specified like the above threshold value and selected appropriately, in particular sufficiently high to exclude, as far as possible, the erroneous detection of wear in a wear-free bearing. Relative to the maximum possible pivot angle, the first, second, and, if applicable, third threshold values ​​can independently be approximately greater than 5% or greater than 10%.

[0046] The detection of the reverse sequence of the signs of the difference is also conceivable, ie an accelerated actual swivel angle change possibly followed by a delayed actual swivel angle change.

[0047] Accordingly, in order to detect a fourth deviation characteristic, it can be checked during the evaluation whether, in a seventh time period or at a fifth point in time, the actual swivel angle curve is below the target swivel angle curve by at least a fourth threshold value and, in an eighth time period or at a sixth point in time that occurs later than the seventh time period or the fifth point in time, the actual swivel angle curve is above the target swivel angle curve by at least a fifth threshold value. This corresponds to Fig. 3A e.g. the delayed actual swivel angle change 74.

[0048] Furthermore, in order to detect the fourth deviation characteristic, it can also be checked during the evaluation whether, in a ninth time period or at a seventh point in time that occurs later than the eighth time period or the sixth point in time, the actual swivel angle curve is below the target swivel angle curve by at least a sixth threshold value.

[0049] The fourth, the fifth and, if applicable, the sixth threshold value can be specified in the same way as the above-mentioned threshold value and can be suitably selected, in particular sufficiently high, in order to exclude, as far as possible, an erroneous detection of wear in a wear-free bearing. In relation to the maximum possible swivel angle, the fourth, the fifth and, if applicable, the sixth threshold value can independently of one another be approximately greater than 5% or greater than 10%.

[0050] Fig. 5 shows a flow chart according to an embodiment of the invention, ie the method for detecting wear of a rolling bearing of a pivoting cradle of a pivoting device of an adjustable hydraulic machine.

[0051] In step 110, the swivel device is controlled to swivel the swivel cradle according to a predetermined temporal target swivel angle profile. The target swivel angle profile is specified, for example, as a temporal sequence of target swivel angles (e.g., as a discrete sequence or as a continuous sequence in the form of a function).

[0052] In step 120, a temporal profile of the actual swivel angle is recorded during swiveling. This occurs parallel to step 110. The actual swivel angle profile is, for example, a temporal sequence of actual swivel angles, ie, of the actual (actual) swivel angles of the swivel cradle, which are measured, for example, with a sensor (swivel angle sensor).

[0053] The actual swivel angle curve is evaluated in step 130 in order to detect at least one defined deviation from the target swivel angle curve, which is characteristic of wear. For this purpose, as in connection with the Fig. 3A, Fig. 3B, Fig. 4A and Fig. 4B, the difference between the actual swivel angle curve and the target swivel angle curve and / or between the actual change rate curve and the target change rate curve can be used (each based on unfiltered or filtered curves). In particular, the at least one defined characteristic deviation can be one or more of the Fig. 3A, Fig. 3B, Fig. 4A and Fig. 4B described deviation characteristics.

[0054] During evaluation 130, it can optionally first be checked whether the target change rate according to the target change rate curve is equal to or greater than a lower change rate evaluation limit and / or equal to or less than an upper change rate evaluation limit. If this is not the case, the check to determine whether at least one characteristic deviation exists is omitted. In other words, the check or detection of whether at least one characteristic deviation exists only occurs if the target change rate curve is equal to or greater than a lower change rate evaluation limit and / or equal to or less than an upper change rate evaluation limit. Target change rates that are not suitable for wear detection, e.g., those that are very small (e.g., close to 0) or very large, can thus be excluded from the evaluation. The lower and upper change rate evaluation limits can be set appropriately.The lower rate of change evaluation limit is, in particular, greater than zero. The upper rate of change evaluation limit is, in particular, smaller than a maximum (e.g., technically determined) rate of change of the swivel angle. Here, it is assumed that the target rate of change or the target rate of change curve are determined as absolute values, i.e., that their determination includes the calculation of an absolute value.

[0055] If the at least one defined characteristic deviation is detected, it is determined in step 140 that wear or potential wear of the rolling bearing is present. The term "potential" refers to the fact that, in principle, a characteristic deviation could occur as a result of measurement errors, fluctuations, or the like in the hydraulic system (for example, similar deviations could occur if the pressure medium temperature is too low). Thus, wear within the meaning of the method is detected upon detection of the at least one characteristic deviation. If necessary, the method can be repeated upon detection of the at least one characteristic deviation in order to achieve a high degree of certainty that wear of the rolling bearing is actually present.

[0056] If no defined characteristic deviation is detected, it is assumed that there is no or only slight wear.

[0057] If (potential) wear is detected, an error message can be generated and / or displayed (e.g., via a display on the machine in which the hydraulic system is used). It is also possible to store such an error message in the control unit so that it can be read and evaluated during maintenance work on the hydraulic system, for example. If an error message is detected, appropriate measures can then be taken to prevent further damage, such as replacing wear parts in the rolling bearings.

Claims

[1] Method for detecting wear of a rolling bearing (66, 68) of a pivoting cradle (64) of an adjustable hydraulic machine (2), comprising Controlling (110) a swivel device of the hydraulic machine (2) in order to swivel the swivel cradle (64) in accordance with a predetermined temporal target swivel angle profile (70); detecting (120) a temporal actual swivel angle curve (72) during swiveling; Evaluating (130) the actual swivel angle profile (72) and the desired swivel angle profile (70) in order to detect at least one defined characteristic deviation (74, 76, 84, 86) of the actual swivel angle profile from the desired swivel angle profile, which indicates wear; and Determining (140) that wear of the rolling bearing (66, 68) is present when the at least one defined characteristic deviation (74, 76, 84, 86) is detected. [2] Method according to claim 1, wherein the desired swivel angle profile (70) includes a monotonic, in particular strictly monotonic, increase or decrease of the desired swivel angle; and / or wherein the desired swivel angle profile (70) includes a linear profile of the desired swivel angle with a predetermined, non-zero rate of change. [3] Method according to one of claims 1 or 2, wherein during the evaluation (130) an actual change rate profile (82, 96) is determined as the amount of a temporal change rate based on the actual swivel angle profile (72, 93) and a desired change rate profile (80, 98) is determined as the amount of a temporal change rate based on the desired swivel angle profile (70, 92); wherein the at least one defined characteristic deviation includes, as a first deviation characteristic, that in a first time period the actual change rate profile (82) is below the desired change rate profile (84); wherein the first time period has at least a first minimum duration and / or wherein, in accordance with the desired swivel angle profile (70), an amount-related change in the desired swivel angle by at least a predetermined minimum swivel angle change amount occurs in the first time period. [4] Method according to claim 3, wherein it is checked whether in the first time period the actual change rate curve is below a predetermined fraction of the desired change rate curve in order to determine that in the first time period the actual change rate curve (82, 96) is below the desired change rate curve (84, 98). [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] A method according to any one of claims 3 to 5, wherein the first deviation characteristic further includes in a second time period occurring after the first time period, the actual change rate curve (82) is at least a predetermined factor higher than the desired change rate curve (84); wherein the second period of time has at least a second minimum duration. [7] Method according to claim 6, wherein the second minimum duration is shorter than the first minimum duration, in particular less than or equal to 0.5 times the first minimum duration; and / or where the factor is equal to or greater than 2. [8] Method according to claim 6 or 7, wherein a time interval between the first and the second time period is less than or equal to a predetermined maximum time interval. [9] Method according to one of claims 3 to 8, wherein determining the actual change rate curve (82, 96) includes: Calculating the rate of change of the actual swivel angle according to the actual swivel angle curve (72), and Calculating the magnitude of the calculated time rate of change of the actual swivel angle; and / or wherein determining the desired change rate curve (80, 98) includes: calculating the time rate of change of the desired swivel angle corresponding to the desired swivel angle curve (70), and Calculate the magnitude of the calculated time rate of change of the desired swivel angle. [10] The method of claim 9, wherein determining the actual rate of change history (96) further includes: Applying a low-pass filter before or after calculating the time rate of change of the actual tilt angle; and / or wherein determining the desired rate of change curve (98) further includes: applying a low-pass filter before or after calculating the time rate of change of the desired swivel angle. [11] Method according to one of claims 3 to 10, wherein during the evaluation (130) the presence of the at least one defined characteristic deviation (74, 76, 84, 86) of the actual swivel angle curve from the desired swivel angle curve is only checked or detected if the desired change rate corresponding to the desired change rate curve (80, 98) is equal to or greater than a lower change rate evaluation limit and / or equal to or less than an upper change rate evaluation limit. [12] Method according to one of the preceding claims, wherein the at least one defined characteristic deviation includes, as a second deviation characteristic, that the amount of the difference between the actual swivel angle profile (72) and the desired swivel angle profile (70) or between a filtered actual swivel angle profile (93) and a filtered desired swivel angle profile (92) exceeds an amount threshold value for at least one point in time. [13] Computing unit (12) comprising a processor, which is configured to carry out the method according to one of the preceding claims. [14] Computer program (14) comprising instructions which, when executed by a computer, cause the computer to carry out the method according to one of claims 1 to 12. [15] A computer-readable data carrier on which the computer program according to claim 14 is stored.

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