Device and method for determining a state, in particular a wear state, of a displacement unit

Abstract

1. Device and method for determining a state, in particular a wear state, of a displacement unit. 2. A device for determining a state, in particular a wear state, of a displacement unit (8) is disclosed, comprising a fluid line (12, 14) connected to a high-pressure side of the displacement unit (8); at least one fluid device (18) fluidically connected to the fluid line (12, 14), which enables a fluid pressure build-up upstream of itself in the fluid line (12, 14); a pressure sensor (20, 22) in each case, which detects a system parameter in the form of the fluid pressure (p, p') upstream of each fluid device (18) in the fluid line; and an evaluation device (24) which is configured such that it determines the state of the displacement unit (8) as a function of at least one system parameter (p, p').

Description

[0001] The invention relates to a device and a method for determining a condition in the form of a wear condition of a displacement unit.

[0002] From EP 1 960 666 B1, a device and a method for condition monitoring in axial piston machines are known. The device has a detection unit that includes sensors attached to and in the axial piston machine for detecting operating data, in particular pressure in a high-pressure line of the axial piston machine, and for detecting monitoring data. The operating data and the monitoring data are each analyzed in the time domain or in the time-frequency domain by means of an evaluation unit connected to the detection unit.In a diagnostic unit connected to the evaluation unit, the analyzed operating and monitoring data are linked, and an output unit connected to the diagnostic unit can trigger a pre-alarm indicating an upcoming maintenance and a main alarm indicating a critical machine condition for further operation and which can activate an emergency switch.

[0003] DE 10 2015 206 403 A1 discloses a device and method for leakage measurement for a hydraulic arrangement in a displacement unit, with a fluid line connected to a high-pressure side of the displacement unit, at least one fluid device fluidically connected to the fluid line which enables a fluid pressure build-up upstream in the fluid line, each with a pressure sensor which measures a system parameter in the form of the fluid pressure upstream of the respective fluid device in the fluid line ( p, p ') recorded, an evaluation unit which is set up in such a way that it depends on at least one system size ( p , p') the state of the displacement unit is determined, a further fluid device which divides the fluid line into a fluid line section connected to the displacement unit and another fluid line section and which is designed in such a way that it allows fluid pressure transmission from one fluid line section to the other fluid line section, in particular from a predefinable pressure threshold and blocks it in the opposite direction.

[0004] DE 10 2020 112 660 A1 discloses a method for determining the instantaneous wear state of a hydrostatic machine. Comparable devices and methods are also disclosed in DE 10 2011 075 870 A1, DE 10 2019 170 820 A1 and DE 10 2020 127 285 B3.

[0005] Based on this prior art, the invention aims to provide a device for determining the wear state of a displacement unit, which allows for an accurate determination of the condition with reduced effort in carrying out the condition assessment.

[0006] This problem is solved by the features of claim 1 in its entirety.

[0007] According to claim 1, the device has a fluid line connected to a high-pressure side of the displacement unit; at least one fluid device fluidically connected to the fluid line, which enables a fluid pressure build-up upstream of itself in the fluid line; a pressure sensor in each case, which detects a system parameter in the form of the fluid pressure upstream of the respective fluid device in the fluid line; and an evaluation device, which is configured such that it determines the condition, in particular the wear condition, of the displacement unit as a function of at least one system parameter.

[0008] It was initially recognized that, with increasing wear compared to its new condition, a given displacement unit must be driven at a higher speed, at least in certain areas, to generate a predetermined fluid pressure, or, put another way, that at a given speed it delivers a lower fluid pressure, at least in certain areas. These findings are fundamental to the present invention, which is described in claim 1.

[0009] The features of claim 1, in particular the fluid device, enable a fluid pressure to be built up, maintained, and optionally reduced again in the fluid line as a system variable depending on a corresponding control of the displacement unit, wherein a change in the curve of the fluid pressure is recognizable in the corresponding curve profile of the fluid pressure that is significant for the state of the respective displacement unit, which characterizes a characteristic operating point of the displacement unit in which the theoretical volume flow of the displacement unit corresponds to its volumetric losses, and wherein a comparison of system variables, in particular the fluid pressure, at the operating point or at least of one parameter dependent on these, in particular of the displacement unit, with corresponding reference values ​​allows an accurate conclusion to be drawn about the state of the displacement unit.Fluid pressure changes can occur during a diagnostic run, startup, or shutdown of a fluid system in the form of a consumer arrangement. The system parameters are processed exclusively in the time domain by the evaluation unit. This results in lower processing power for the evaluation unit, lower sensor sampling rates, and smaller data volumes compared to at least partial processing in the frequency domain. Consequently, condition monitoring can be performed with minimal effort. Furthermore, the device is located outside the displacement unit, allowing it to be combined with any displacement unit at any time, for example, retrofitted after the displacement unit has been sold.

[0010] Furthermore, another fluid device is provided, which divides the fluid line into a fluid line section connected to the displacement unit and another fluid line section, and which is designed in such a way that it allows fluid pressure transmission from one fluid line section to the other fluid line section, in particular from a predefinable pressure threshold, and blocks it in the opposite direction.

[0011] Furthermore, a temperature sensor is provided which, as an additional system parameter, detects the temperature of the fluid flowing through the displacement unit, thus contributing to the determination of the system's condition. This fluid temperature can be measured by the temperature sensor in the fluid line or in a tank from which the displacement unit draws fluid and / or in which the consumer assembly discharges fluid.

[0012] In a preferred embodiment, the displacement unit is hydrostatically and / or speed-controlled. Particularly preferably, the displacement unit is designed as a pump, preferably a constant-displacement pump. The fluid used can be hydraulic fluid, in particular hydraulic oil, so that the fluid components of the device are designed accordingly as hydraulic components.

[0013] The respective fluid device in the form of a fluid control device can be set up in such a way that the fluid pressure is built up upstream in the fluid line at least to a predetermined pressure and / or by appropriate control of the respective fluid device.

[0014] In a further preferred embodiment, a fluid device is designed as a consumer arrangement that can be operated at a nominal pressure and is connected to the fluid line, in particular to an end of the fluid line facing away from the displacement unit. The consumer arrangement can include a controllable valve arrangement that, when appropriately controlled, enables the aforementioned pressure build-up and / or a pressure relief valve set to the nominal pressure, which protects the consumer arrangement against pressures exceeding the nominal pressure.

[0015] In a further preferred embodiment, a device is provided that determines the drive speed of the displacement unit, which is then included as an additional system parameter in the determination of the system's state. This device can be designed as a speed sensor that detects the speed at the displacement unit or at an electric motor driving the displacement unit. The speed of the electric motor and the displacement unit can be the same.

[0016] In another preferred embodiment, a hydraulic accumulator is provided which is connected to the fluid line, in particular the further fluid line section, in order to compensate for a pressure drop.

[0017] In a further preferred embodiment, the nominal or load pressure of the consumer arrangement is detected, preferably by means of the additional pressure sensor, and this pressure is included as a system parameter in determining the system's state. The additional fluid pressure detected by the additional pressure sensor can correspond to the nominal or load pressure of the consumer arrangement.

[0018] In another preferred embodiment, a device is provided that determines a swivel angle of the displacement unit, which is included as a further system parameter in the determination of the state. The displacement unit is designed as a variable displacement pump, for example as an axial piston pump.

[0019] The invention further relates to a method for determining the condition, in particular the wear condition, of a displacement unit, particularly using a device described above, comprising the following method steps: building up fluid pressure in a fluid line upstream of at least one fluid device fluidically connected to the fluid line, wherein the fluid line is connected to the high-pressure side of the displacement unit; acquiring a system parameter in the form of the respective fluid pressure in the fluid line upstream of the respective fluid device; determining the condition of the displacement unit as a function of at least one system parameter, and determining at least one operating point of the displacement unit characteristic of the condition by calculating the theoretical volume flow rate. Q th the displacement unit and its volumetric losses Q Leck corresponds.

[0020] In a preferred embodiment, the state is also determined as a function of at least one of the following additional system parameters: a drive speed of the displacement unit; a swivel angle of the displacement unit; and a temperature of the fluid flowing through the displacement unit.

[0021] In a further preferred embodiment, the drive speed of the displacement unit is determined at least by one of the following possibilities: detected by means of a speed sensor; derived from a signal attributable to an electrical control of the electric motor for driving the displacement unit; and derived from sound signals emitted by the displacement unit.

[0022] In a further preferred embodiment, at least one of the following change processes is carried out over a period of time to determine the operating point: the drive speed of the displacement unit is changed; a nominal or load pressure of a consumer arrangement connected to the fluid line, in particular to the end of the fluid line furthest from the displacement unit, is changed; and a swivel angle of the displacement unit is changed. It is particularly preferred that the drive speed, the nominal or load pressure, and / or the swivel angle are increased and / or decreased during the change process, preferably first increased and then subsequently decreased again, or vice versa.

[0023] In a further preferred embodiment, the sampling period of the respective curve profile of the fluid pressure or a curve profile dependent on it during the increase or decrease of the drive speed of the displacement unit is up to 3 seconds, preferably approximately 0.5 or 2.5 seconds, and / or the sampling rate is 100 to 300 Hertz, preferably 200 Hertz.

[0024] In a further preferred embodiment, during the modification process the drive speed of the displacement unit is reduced from a positive value towards zero, in particular in a ramp-like manner, while the curve of at least one respective fluid pressure is initially essentially constant, in particular corresponding to the nominal pressure value of the consumer arrangement, and subsequently begins to fall when a certain speed is undershot, which represents the significant change in the curve.

[0025] In a further preferred embodiment, the future state, in particular the wear state, and / or the remaining service life of the displacement unit, is estimated based on a temporal analysis of the change in at least one system variable at the operating point or a parameter dependent thereon, in particular the displacement unit. Accordingly, the device and method according to the invention can serve to determine the future state, in particular the wear state, and / or the remaining service life of the displacement unit.

[0026] In another preferred embodiment, the drive speed is used of DAD the displacement unit at the operating point, of the respective fluid pressure p DAD at the operating point and, if applicable, the geometric conveying volume V g of the displacement unit, a parameter is calculated, in particular the parameter λ = n DAD ⋅ V g p DAD of the displacement unit. "DAD" stands for pressure-displacement speed. Because the leakage flow of the displacement unit increases with increasing temperature due to the decreasing viscosity of the hydraulic fluid, the parameter λ = Q Leck Δ p p The displacement unit is temperature-dependent and is compared using a reference parameter at the same temperature by performing a final comparison. λ compared to the displacement unit.

[0027] The following is the formula for volumetric efficiency that is fundamental to the present invention. η vol [%] explained in more detail: η vol = Q eff Q th = Q th − Q Leck Q th = Q th − λ ⋅ Δ p P Q th This is Q eff for the actual, i.e. effective, volume flow rate of the displacement unit, Q th for the calculated, theoretical volume flow rate of the displacement unit, Q Leck for the internal leakage flow of the displacement unit, λ for the characteristic parameter of the displacement unit, and Δ p Pfor the pressure difference falling across the displacement unit, which corresponds to the fluid pressure p on the high-pressure side of the displacement unit, if the displacement unit draws from a tank where ambient pressure prevails.

[0028] At the aforementioned characteristic operating point with the drive speed of DAD and the fluid pressure p DAD corresponds to the theoretical volume flow rate Q th the displacement unit and its internal leakage flow Q Leck , so that the volumetric efficiency η vol The displacement unit is equal to zero. This corresponds to... Q th = V g · n = Q Leck = λ · Δ p P , where V g where represents the geometric delivery volume of the displacement unit and n represents the drive speed of the displacement unit.

[0029] The device and method according to the invention for determining a state, in particular a wear state, of a displacement unit will be explained in more detail below with reference to the drawing.

[0030] This shows in principle representation Fig. 1 partly in the form of a hydraulic circuit diagram and partly in block representation the device according to the invention for determining a state of a displacement unit; Fig. 2 a speed curve plotted over time for a displacement unit according to Figs. 1 ; Fig. 3 shows a pressure curve plotted over time on the high-pressure side of the displacement unit. Figs. 1 , which is derived from the speed curve profile according to Figs. 2 is dependent; Fig. 4 above shows a partial speed curve according to Figs. 2 and below, partially dependent pressure curve profiles according to Figs. 3of displacement units exhibiting different wear states, wherein the pressure curve profiles are shown in the region of their respective significant change in profile, which characterize an operating point characteristic of the respective displacement unit for that state; Fig. 5 a pressure curve profile magnified in the region of the significant change in profile and plotted against the rotational speed of the displacement unit; Fig. 6 curve profiles of the parameter plotted against the wear state of the displacement unit λ the displacement unit as a function of the temperature of the fluid flowing through the displacement unit; and Figs. 7 and 8 each show in a block diagram the process of the method according to the invention.

[0031] The in Figs. 1The illustrated device for determining the condition, in particular the wear condition, of a displacement unit 8 has, according to a first embodiment, a pressure supply connection P and a fluid line 12, 14 connected at one end to the pressure supply connection P. In addition, there are two fluid devices 18 (only one is shown in the figures) fluidically connected to the fluid line 12, 14 and a pressure sensor 20, 22, which measures a system parameter in the form of the fluid pressure in the fluid line 12, 14 upstream of each fluid device 18. p, p' The fluid devices 18 each enable a fluid pressure build-up upstream of themselves in the fluid line 12, 14, and the evaluation device 24 is configured such that it is dependent on at least one system parameter. p, p' the condition, in particular the wear condition, of the displacement unit 8 was determined.

[0032] The hydrostatic displacement unit 8 is connected to the pressure supply port P, i.e., one end of the fluid line 12, 14, with its high-pressure side. The displacement unit 8 is designed as a speed-controlled pump 10, preferably as a constant-speed pump, which can be driven by an electric motor 26.

[0033] At the other end of the fluid line 12, 14, a consumer connection A is provided, to which a fluid device (not shown in the figures) is fluidically connected. This fluid device can be described as one with a nominal pressure p NoseThe system shall be designed as an operable consumer arrangement. A further fluid device 18 is connected in the fluid line 12, 14 and divides the fluid line 12, 14 into a fluid line section 12 fluidically connected to the pressure supply port P and a further fluid line section 14 fluidically connected to the consumer port A. The further fluid device 18 is configured such that it allows fluid pressure transfer from the pressure supply port P to the consumer port A above a predefinable pressure threshold, which is in particular approximately the nominal pressure. p Nose The consumer arrangement corresponds to the flow of water from the consumer connection A to the pressure supply connection P, and the flow is permanently blocked. The further fluid device 18 is designed as a check valve 28, in particular a spring-operated one, which opens in the direction of the consumer connection A.

[0034] A device 30 is provided for determining the drive speed n of the pump 10, which serves as a speed sensor 32 for detecting the speed. n of the electric motor 26. In addition, a pressure sensor 20 is provided, which is connected to the fluid line section 12 and measures the fluid pressure in the fluid line section 12. p The fluid line section 12 can also be connected to a temperature sensor 34, which can detect the fluid temperature T in the fluid line section 12. Furthermore, a hydraulic accumulator 36 can be connected to the other fluid line section 14 to compensate for any pressure losses in the other fluid line section 14, for example, due to leakage flows from the consumer assembly. The speed sensor 32, the pressure sensor 20, and the temperature sensor 34 are electrically connected to the evaluation unit 24. The drive speed thus detected n of pump 10, the fluid pressure pand the temperature T each represent a further system parameter that is included in the determination of the state using the evaluation unit 24.

[0035] The preceding statements regarding the first embodiment apply accordingly to a second embodiment of the device.

[0036] In addition, in the second embodiment, a further pressure sensor 22 is connected to the further fluid line section 14 and detects a further fluid pressure in the further fluid line section 14. p' , which is included as a further system parameter in the determination of the state. The additional pressure sensor 22 is electrically connected to the evaluation unit 24. The additional fluid pressure p' can withstand the nominal pressure p Nose The consumer arrangement corresponds to this. Due to a pressure loss when flowing through the check valve 28, a pressure difference occurs, so that the pressure pso that the pressure difference is greater than the pressure p'. With a good design of the check valve 28, the pressure difference is rather small.

[0037] The following explains in more detail the inventive method carried out by the evaluation unit 24 in the time domain: To determine the state of the pump 10, a characteristic operating point of the pump 10 is determined, in which the theoretical volume flow Q th the volumetric losses of pump 10 Q Leck corresponds to, that is, the volumetric efficiency η vol The pump is 10 zero.

[0038] To determine this operating point, the drive speed n of pump 10 is measured within the framework of a Figs. 2 shown change process over a time period [s] from approximately zero to a predefinable rotational speed value n [ min -1< ] increased and then reduced again to approximately zero. The rotational speed ncan at least be increased to such an extent that the fluid pressure prevailing on the high-pressure side of pump 10 p at least the nominal pressure p Nose the consumer arrangement is reached. The drive speed n is detected during the change process by means of the speed sensor 32 and can have an essentially triangular shape n V The described process can, in principle, have an ascending ramp followed by a descending ramp 41. This occurs simultaneously with the corresponding change in drive speed. n In the first embodiment, a pressure sensor 20 is used in the fluid line section 12 to measure a pressure in the fluid line section. Figs. 3 shown fluid pressure curve p V and the temperature T in the fluid line section 12 is detected by means of the temperature sensor 34. In the second embodiment, the fluid pressure profile is also measured by means of the additional pressure sensor 22. p' V or p Nose,Vin the further fluid line section 14. The sampling period AZ of the respective fluid pressure profile during the reduction of the drive speed. n Pump 10 can be used as in Figs. 3 The sampling time is approximately 0.5 seconds, or, as shown in the figure, for example 2.5 seconds (not shown), with a sampling rate of approximately 200 Hz. The same applies to the period during which the drive speed n increases.

[0039] After recording 38 ( Figs. 7 ) of the system sizes n, p, p', T can the values ​​of each system size n, p, p', T Data filtering can be performed, for example, by calculating an average of the respective system size values. n, p, p', T from the last recorded system size values n, p, p', T in the sense of a moving average.

[0040] The in Figs. 3 shown fluid pressure curve p VThe pressure sensor 20, plotted over time [s], is essentially trapezoidal, thus exhibiting an ascending and a descending ramp 42, between which the fluid pressure profile p V has a substantially constant part 44 and in particular the nominal pressure profile p Nose,V corresponds to the consumer arrangement. The fluid pressure profile p V In the transition from its essentially constant part 44 to its rising or falling ramp 42, it describes a significant change in course 46 in the form of a kink, which characterizes the aforementioned characteristic operating point.

[0041] The significant change in the course 46 results from the fact that any pump will stop operating below a certain drive speed. n , namely the drive speed of DADat the aforementioned operating point, it is no longer able to maintain the fluid pressure prevailing in the fluid flow direction behind the check valve 28. p' or nominal pressure p Nose to apply to the consumer arrangement so that the volume flow via the check valve 28 is reduced when the specified drive speed is undershot n comes to a complete standstill and the check valve 28 closes. Starting from a specific rotational speed... of DAD further decreasing speed n The fluid pressure also drops. p continuously decreasing, with the fluid pressure p' or p Nose due to the check valve 28 closing towards the pressure supply connection P, the pressure can be maintained at least in the short term by means of the hydraulic accumulator 36.

[0042] In Figs. 4 are above part of the descending ramp 41 of the rotational speed n [ min-1< ] and below at least partially the essentially constant part 44 and the descending ramp 42 of the rotational speed n dependent fluid pressure p [bar] Several pumps 10 are shown in principle, which differ in their wear condition. The rotational speed n and the fluid pressure p are plotted against time [s]. The different wear states of the pumps 10 are shown in Figs. 4 This can be recognized by the fact that the fluid pressure p the most worn pump 10 already at a higher speed n and the fluid pressure p the least worn pump 10 at a relatively lower speed n falls, each time with the formation of the significant change in the course 46 of the pressure curve. p V . Upon reaching the speed n The fluid pressure delivered by each pump 10 is equal to zero. pAlso zero, regardless of their respective wear condition. In an ideal pump, the pressure would still be present; naturally, the delivered volume flow would be zero.

[0043] The aforementioned operating point is shown in the fluid pressure curve. p V located by the evaluation unit 24 using an evaluation algorithm 48.

[0044] In the first embodiment of the device, a time-dependent change profile is calculated using the evaluation algorithm 48, in particular by calculating the pressure gradient using (backward) difference quotient calculation. p ˙ V = dp V dt The fluid pressure of pressure sensor 20 is generated. Subsequently, the change process is described. ṗ V by performing an interim comparison of the change trend 48 ṗ V with corresponding reference values ​​49 in the form of limit values, the significant change in the course 46 of the pressure curve. p V localized.

[0045] In the second embodiment of the device, the significant change in the course 46 in the pressure curve is p V [bar] according to Figs. 5 by performing an intermediate comparison of the pressure curve progression p V with reference values ​​49 in the form of limit values ​​Δ p RV,min , Δ p RV,max located, among which the significant change in course 46 is found. In Figs. 5 is the pressure curve profile p V above the rotational speed n [ min -1< ] plotted. In the calculation of the limit values ​​Δ p RV,min , Δ p RV,max The additional fluid pressure detected by means of the further pressure sensor 20 flows p' or p Nose with one. In Figs. 5 is the fluid pressure p DAD in the respective localized significant change in course 26, i.e. at the operating point, marked with a cross.

[0046] Alternatively or additionally to applying limit values, pattern recognition can be used to evaluate the respective curve progression. Pattern recognition can be implemented within the framework of artificial intelligence, neural networks, and / or machine learning.

[0047] As shown above, when localizing the significant change in course 46, not only a fluid pressure value is regularly used. p DAD Not one value is determined, but several, which, for example, fall between the limit values. Therefore, the multiple determined fluid pressure values ​​can be used. p DAD further averaging 50 to obtain an average fluid pressure value p DAD to be obtained at the operating point.

[0048] Based on the significant change in the course of the fluid pressure, 46 p Once the operating point has been determined, at least one system parameter is calculated, either by performing a final comparison (60). n DAD , p DAD , T DADAt the operating point, each comparison is made directly with at least one corresponding reference system parameter and / or using the recorded system parameters, rotational speed. of DAD and fluid pressure p DAD at the operating point as well as a pump parameter 56, possibly in the form of the geometric delivery volume V g of pump 10, a calculation of at least one parameter, possibly in the form of the parameter λ = n DAD ⋅ V g p DAD l min ⋅ bar the pump 10, which is compared at least with a corresponding reference parameter 64.

[0049] Because the leakage current Q Leck The parameter of pump 10 increases due to the decreasing viscosity of the hydraulic fluid with increasing temperature T. λ = Q Leck Δ p p The pump 10 is temperature-dependent. In Figs. 6 is the corresponding temperature dependence of the parameter λ The pump 10 is shown, in which a first to third parameter λ the pump 10 during a first T1 or second T 2 or third T 3. Temperature is plotted against the wear condition of the pump. This is T 3, in particular approximately 70°C, greater than T 2, in particular approximately 50°C, greater than T 1, in particular approximately 30°C. The wear condition is divided into different zones along the x-axis: New 88, Zone I (Green), Zone II (Yellow), Zone III (Light Red), and Zone IV (Dark Red), with the wear condition increasing with increasing zone number. The color coding of the zones is based on a traffic light, which can serve as an indicator of the wear condition for a user. The viscosity value of the hydraulic fluid at the temperature T 1 corresponds approximately to twice the viscosity value of the hydraulic fluid at that temperature. T 2 , which in turn is approximately twice the viscosity of the hydraulic fluid at the temperature T3 corresponds to this. Accordingly, the calculated parameter λ the pump 10 and the corresponding reference parameter λ The final comparison included comparing the measured fluid temperature T with each other 60.

[0050] Based on the result of the respective final comparison 60, the state of the pump 10 is then determined, which can be forwarded by the evaluation unit 24 via a state output 66 to a display 54, which shows a user the state of the pump 10 and which can in particular be designed as the aforementioned traffic light.

[0051] It can also include a buffer 68 for recorded system sizes. n , p, p', T and a memory of 70 for system sizes present at the operating point n DAD , p DAD , T DADand / or at least one parameter dependent on system sizes, in particular pump 10, may be provided. Furthermore, a (trend) analysis 72 based on a temporal analysis of the system sizes can be performed. n DAD , p DAD , T DAD at the operating point or of the parameter dependent on system sizes, a future wear condition and / or the remaining service life 74 of the pump 10 can be estimated.

[0052] The pump 10, the electric motor 26, which drives the pump 10 via a shaft, and power electronics 78, such as a frequency converter 80 or an inverter, which controls the electric motor 26, are part of a variable-speed electro-hydraulic unit 76 ( Figs. 8 ).

[0053] Furthermore, a machine control unit 82 is provided, for example for controlling the consumer arrangement, such as a programmable logic controller (PLC) or a (main) control unit, which specifies at least one setpoint, such as a rotational speed, a flow rate, a position, a pressure and / or a velocity, etc. The machine control unit can be configured either as shown in Figs. 8 shown with the power electronics 78 or, as not shown in the figures, with the evaluation unit 24, communicating and transmitting at least the setpoint there.

[0054] The evaluation unit 24 requests the execution of the inventive method from the power electronics 78 by means of a query 84, for example, after a predefinable number of operating hours of the consumer arrangement. The power electronics 78 subsequently confirms the query 84 by issuing a confirmation 86 and, if the consumer arrangement is in a suitable state, initiates the method by means of a corresponding change process, for example, a corresponding change in the drive speed. n of pump 10. A suitable system state exists, for example, when the system is not operating under load and / or is about to be shut down.

[0055] To determine the state of the displacement unit 8, the drive speed n of the displacement unit 8 can also be set to a constant value, which depends on the drive speed. ndependent fluid pressure p can be detected and the detected fluid pressure p or a parameter dependent on it, in particular the displacement unit 8, is compared with at least one corresponding reference value.

Claims

1. Apparatus for determining a condition in the form of a wear condition of a displacement unit (8), having - a fluid line (12, 14) connected to a high-pressure side of the displacement unit (8), - at least one fluid device (18) fluidically connected to the fluid line (12, 14), which enables a build-up of fluid pressure in the fluid line (12, 14) upstream of said fluid device, - a pressure sensor (20, 22) in each case which acquires a system variable in the form of the fluid pressure (p, p') in the fluid line upstream of the respective fluid device (18), - an evaluation device (24), which is set up in such a manner that it determines the condition of the displacement unit (8) as a function of at least the one system variable (p, p'), - a further fluid device (18), which divides the fluid line into a fluid line portion (12), which is connected to the displacement unit (8), and a further fluid line portion (14) and which fluid device is set up in such a manner that it permits a transfer of fluid pressure from the one fluid line portion (12) to the further fluid line portion (14), in particular above a predefinable pressure threshold, and blocks it in the opposite direction, and - a temperature sensor (34), which detects a temperature (T) of the fluid flowing through the displacement unit (8), which temperature is included as a further system variable in the determination of the condition.

2. Apparatus according to claim 1, characterised in that a fluid device is configured as a consumer assembly which can be operated at a nominal pressure (pnom).

3. Apparatus according to claim 1 or 2, characterised in that the further fluid device (18) is configured as a check valve (28) which opens away from the displacement unit (8) in the direction of a consumer port (A).

4. Apparatus according to one of the preceding claims, characterised in that at least one of the following components is additionally provided: - a device (30), which determines the speed (n) of the displacement unit (8), which is included as a further system variable in the determination of the condition; and - a hydraulic accumulator (36) connected to the further fluid line (14).

5. Method for determining a condition in the form of a wear condition of a displacement unit (8) using an apparatus according to the preceding claims, with the following method steps: - building up a fluid pressure (p, p') in a fluid line (12, 14) upstream of at least one fluid device (18) fluidically connected to the fluid line, wherein the fluid line (12, 14) is connected to a high-pressure side of the displacement unit (8), - acquiring a system variable in the form of the respective fluid pressure (p, p') in the fluid line (12, 14) upstream of the respective fluid device (18), - determining the condition of the displacement unit (8) as a function of at least the one system variable (p, p'), and that, for - determining the condition of the displacement unit (8), at least one operating point of the displacement unit (8), which is characteristic for the condition, is determined in which the theoretical volume flow (Qth) of the displacement unit (8) corresponds to its volumetric losses (Qleak)).

6. Method according to Claim 5, characterised in that the condition is additionally determined as a function of at least one of the following further system variables: - a speed (n) of the displacement unit (8); and - a temperature (T) of the fluid flowing through the displacement unit (8).

7. Method according to Claim 5 or 6, characterised in that, for determining the condition of the displacement unit (8), at least the one system variable (n, p, p', T) is compared with at least one corresponding reference system variable and / or a parameter (λ), in particular of the displacement unit (8), is determined as a function of at least the one system variable (n, p, p', T), which parameter is compared with at least one corresponding reference parameter, wherein the condition of the displacement unit (8) is defined based on the result of this respective final comparison (60).

8. Method according to one of Claims 5 to 7, characterised in that, for determining the operating point, at least one of the following change processes is carried out over a period of time: - the speed (n) of the displacement unit (8) is changed; and - a nominal (pnom) or load pressure of a fluid device configured as a consumer assembly is changed.

9. Method according to one of Claims 5 to 8, characterised in that, while passing through the respective change process, a curve (pV) of at least one respective fluid pressure (p, p') or a curve (ṗV, ΔpRV,V) dependent thereon is at least partially determined and, using this curve, a significant profile change is localised in this curve (pV) of the fluid pressure (p, p'), which profile change marks the operating point.

10. Method according to one of Claims 5 to 9, characterised in that the curve (ṗV, ΔpRV,V) dependent on at least one respective fluid pressure (p, p') describes the change over time (ṗV) of at least one respective fluid pressure (p, p') or the pressure difference (ΔpRV,V) between a further fluid pressure (p'), which is detected by means of a further pressure sensor (22) in a further fluid line portion (12), and a fluid pressure (p), which is detected by means of a pressure sensor (20) in a fluid line portion (20).

11. Method according to one of claims 5 to 10, characterised in that, to localise the significant profile change, the curve (ṗV, ṗV, ΔpRV,V) determined is compared with at least one corresponding reference value at least partially by carrying out an interim comparison (48).

12. Method according to one of claims 5 to 11, characterised in that the respective system variable (nDAD, pDAD, TDAD) present at the operating point is used for the final comparison (60).

13. Method according to one of claims 5 to 12, characterised in that, to determine the condition of the displacement unit (8), the speed (n) of the displacement unit (8) is specified as constant, the respective fluid pressure (p, p') dependent on the speed (n) is determined and the respective fluid pressure (p, p') determined or a parameter dependent thereon, particularly of the displacement unit (8), is compared with at least one corresponding reference value.

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