CN117769627A

CN117769627A - State monitoring system

Info

Publication number: CN117769627A
Application number: CN202280027922.4A
Authority: CN
Inventors: 安德烈亚斯·舒马赫
Original assignee: Danfoss Power Solutions GmbH and Co OHG
Current assignee: Danfoss Power Solutions GmbH and Co OHG
Priority date: 2021-04-21
Filing date: 2022-02-24
Publication date: 2024-03-26
Also published as: DE102021203992B3; EP4295061A1; WO2022223180A1

Abstract

A condition monitoring system embedded in a hydraulic circuit is disclosed, the condition monitoring system comprising a primary sensor device for continuously sensing a first physical operating parameter of a hydraulic propulsion unit. A storage unit is provided on the primary sensor device for storing sensed and/or processed data. The condition monitoring system further comprises a computing unit for processing the sensed data. The status information of the propulsion unit is obtained by applying status monitoring methods and/or predictive maintenance methods to the propulsion unit. The output unit indicates status information of the propulsion unit and/or communicates status information of the propulsion unit to the indicator and/or the control unit and/or the vehicle controller.

Description

State monitoring system

The present invention relates to a hydraulic circuit. More particularly, the present invention relates to a condition monitoring system for a hydraulic circuit. The invention further relates to a method for monitoring the state of a hydraulic circuit.

The condition monitoring system is applied in a work vehicle equipped with a hydraulic circuit (e.g. equipped with a hydraulic propulsion unit) and may perform different tasks, for example by monitoring relevant system variables to predict product failure or by recording relevant system variables to provide an improved basis. Additionally, the condition monitoring system can improve the safety of the hydraulic circuit and the work vehicle in which the hydraulic circuit is installed, because the possibility of dangerous accidents can be monitored. The condition monitoring system provides a basis for predictive maintenance systems in which relevant system parameters are continuously monitored and maintenance measures are recommended if the monitored parameter(s) deviate significantly from the design values.

Typically, sensors are required to detect the operating state of the monitored system, and a computing unit and a memory unit are required for data storage and sensor data processing. Software algorithms must be designed to calculate the desired results from the sensor data. As condition monitoring systems become increasingly important in the field of work vehicles, manufacturers of hydrostatic circuits must cover a wide range of applications. Thus, the hydrostatic component/unit provider of the work vehicle needs to design a condition monitoring system for each different application. Because the components of the condition monitoring system are distributed throughout the work vehicle, a synergistic effect cannot be used.

DE 11 2014 000 132 T5 discloses a control device which adjusts the capacity ratio between a hydraulic motor and a hydraulic pump in a closed hydraulic circuit. The control device comprises a determination unit that determines whether the operator wants to slow down the work vehicle and adapts the capacity ratio in dependence of the operator's command.

It is therefore an object of the present invention to provide a condition monitoring system for a hydraulic circuit, for example to implement propulsion or work functions. The system should be able to monitor the hydraulic circuit and communicate the status of the circuit without the need to custom-tailor the underlying structure to the circuit, wherein the system according to the invention should be inexpensive and versatile. Further, the hydrostatic circuit according to the invention should be equipped with a low cost and flexible applicable condition monitoring system. The present invention should further provide a method for monitoring the status of an associated hydraulic circuit and predicting the maintenance time point.

The object of the invention is achieved by: a condition monitoring system according to claim 1, a hydrostatic unit according to claim 10, a hydraulic circuit according to claim 11, and a method for monitoring the condition of a hydraulic circuit and predicting maintenance time points according to claim 14. Preferred embodiments of the invention are disclosed in the corresponding dependent claims.

The condition monitoring system according to the invention is embedded in a hydraulic circuit. The term "embedded" refers to a condition monitoring system integrated as an electronic system into the mechanical and/or hydraulic perimeter of the hydraulic circuit and performing some function as part of the entire unit. The condition monitoring system includes a primary sensor device for continuously sensing a first physical operating parameter of the hydraulic circuit. The primary sensor means senses at least a first physical parameter and converts the physical parameter into an electrical signal. The main sensor device may be connected to a power source if, for example, power is required to perform the conversion from the physical domain to the signal domain. However, as known to those skilled in the relevant art, there are also sensors that do not require a power connection to generate an output signal, such as a photoelectric sensor or a hall sensor.

The condition monitoring system according to the invention comprises a storage unit on the primary sensor for storing sensed and/or processed data. The electrical energy may be supplied to the storage unit via a power supply to which the main sensor device is connected.

The condition monitoring system further comprises a calculation unit for processing the sensed data in order to determine the condition information of the hydraulic circuit, preferably according to a condition monitoring method and/or a predictive maintenance method applied to the hydraulic circuit. The computing unit is at least capable of receiving sensed data or reading sensed data from the memory unit and writing processed data to the memory unit. The computing unit may also be capable of reading the processed data from the storage unit or even overwriting the sensed data if, for example, significant errors in the sensed data are to be corrected.

The condition monitoring system further comprises an output unit for indicating the determined condition information of the hydraulic circuit and/or for communicating the determined condition information of the hydraulic circuit to an indicator and/or a control unit and/or a vehicle controller.

The status information determined by the calculation unit and indicated and/or communicated by the output unit may comprise performance characteristics of the main components of the hydraulic circuit or performance characteristics of the hydraulic circuit itself, and/or efficiency values of the hydraulic circuit, and/or other parameters suitable for indicating the status of the hydraulic circuit. The status information determined according to the present invention may be directly indicated via an output unit (e.g. by using a display) or may be sent to an information processing device (e.g. an indicator and/or a control unit and/or a vehicle controller) for further processing and/or for display.

The condition monitoring system according to the present invention may further include: at least one slave sensor for sensing a second physical operating parameter; and a communication path between the at least one slave sensor and the master sensor for communicating the sensed value of the at least one slave sensor to the master sensor. The second physical operating parameter may be from the same physical domain as the first physical operating parameter sensed by the primary sensor device, or may be from a different physical domain. If more than one slave sensor is provided, each sensor may sense a different physical operating parameter, or some of the slave sensors may sense the same physical operating parameter at different locations in the hydraulic circuit. The concept of the invention also covers that the same physical operating parameter is sensed by more than one slave sensor, or by both slave and master sensors, if for example a measurement error has to be detected in a reliable manner. The communication path between the at least one slave sensor and the master sensor may be a unidirectional communication path via which, for example, sensed data may be transmitted only from the slave sensor to the master sensor, or may be a bidirectional communication path via which sensed data from the slave sensor may be transmitted to the master sensor, and information and commands from the master sensor may be transmitted to the slave sensor.

According to the inventive concept, the master sensor device, the storage unit, the calculation unit, the output unit, the at least one slave sensor and/or the communication path(s) may be designed as an integral part or group of components (in other words, an encapsulation) that may be arranged or fastened to the inside/outside of the hydrostatic unit of the hydraulic circuit or to the inside/outside (e.g. at the outer surface) of the hydraulic circuit itself. In one embodiment of the invention, the storage unit, the calculation unit and the output unit are integrated in a main sensor device, which is arranged inside the hydrostatic unit of the hydraulic circuit. This facilitates handling of the components during and after assembly of the condition monitoring system according to the invention, and also facilitates mounting of the condition monitoring system to a hydraulic circuit or a hydrostatic unit. The concept of the present invention also contemplates that one or more slave sensors and/or communication paths to and from the slave sensors are arranged separately from other aforementioned components that may form an integral part or assembly of the hydraulic circuit.

In one embodiment of the invention, the primary sensor (comprising at least a storage unit, and which may be designed as a group of components comprising computing power and output power) may be regarded as a "smart" head of the system that collects and processes data sensed by the secondary sensor. In general, the slave sensor is cheaper than the master sensor device, since the slave sensor is not equipped with a memory unit, a calculation unit or an output unit, so that the total cost of the condition monitoring system can be reduced. The provision of such an intelligent master sensor device and at least one slave sensor for sensing a physical signal at a location remote from the master sensor device forms a cost-effective condition monitoring system. However, since all data is stored in the central main sensor device, no information is lost. Furthermore, this facilitates data processing, since information can be exchanged between the master sensor and the slave sensor(s) only during the measurement step and not during subsequent data processing (performed only at the master sensor device).

The first and/or second physical operating parameters may be selected from the group comprising: hydraulic input and/or output pressure, hydraulic fluid temperature, hydraulic circuit temperature, hydraulic fluid flow, displacement angle, rotational or linear/longitudinal speed, acceleration/deceleration, hydraulic fluid viscosity, vibration, noise level, ambient temperature, roughness, deformation, and/or comparable parameters. If more than two physical operating parameters are monitored, those parameters may also be selected from the list above, however, other parameters not mentioned may also be sensed.

The determined status information may be continuously processed by a predictive maintenance method to determine the remaining time until the end of the next maintenance service or life cycle. Preferably, the processing of the state information is performed by the computing unit based on the sensed data stored in the storage unit. The term "continuous" refers to performing processing at regular intervals, the length of which depends on, for example, available computing power, available storage capacity, and the system being monitored. Various predictive maintenance methods are known to those skilled in the art, wherein the sensed physical signals, the corresponding sensors, the amount of memory required by the memory unit, and the computing power of the computing unit will be selected based on: predictive maintenance methods to be applied, and intervals at which the predictive maintenance methods are performed.

The main sensor device according to the invention may be a multi-physical field sensor capable of measuring more than one physical operating parameter in succession. The physical operating parameters measured by the multiple physical field sensors may be from the same physical domain, such as an electrical domain or a hydraulic domain, or may be from different physical domains, such as a combination of electrical and hydraulic domains.

The communication path between the one or more slave sensors and the master sensor may be a wire line, a LAN or WLAN system, a bus system, a network or internet (cloud) interface, etc. Because each type of communication path has its advantages and disadvantages over other communication paths, the particular type must be selected according to system requirements. For example, the wire line may be the most cost effective type of communication path, while the WLAN system is not limited to the space constraints imposed by the design of the hydraulic circuit.

In one embodiment of the invention, the calculation unit is adapted to receive continuously sensed values of the physical operating parameter of the hydraulic circuit. From these parameters, the calculated speed (rotational or longitudinal/linear speed) of the hydrostatic unit of the hydraulic circuit can be determined. The calculation unit is further adapted to determine a deviation value between the calculated speed and the sensed speed of the hydrostatic unit of the hydraulic circuit. The calculation unit is further adapted to store the deviation values chronologically starting from the point in time when the hydraulic circuit is put into use or is started to operate.

The calculated rotational or longitudinal/linear speed of the hydrostatic unit may be determined, for example, based on the output pressure of a hydraulic pump arranged in the hydraulic circuit. The correlation between pressure and speed can be deduced from a physical model of the system or from measurements recorded during operation of the hydraulic circuit under experimental conditions. The calculated speed represents a nominal system behavior, wherein the measured speed may be regarded as a performance indicator of the current system behavior. By determining a deviation value between the calculated speed and the sensed speed of the hydrostatic unit, a measure of the degree of deviation of the performance of the hydraulic circuit from nominal system behavior is obtained. These values may be stored chronologically, for example in a memory unit of the condition monitoring system. Depending on the use, these values may alternatively be stored sorted by quantitative value or in a database format. Preferably, the time-sorted deviation values are used to predict the system behavior by comparing the curve of the deviation values with a reference curve in order to predict the point in time when maintenance is required or a system failure may occur.

The output unit may issue an alarm signal if the deviation value is greater than a predetermined threshold value during a period of time longer than a predetermined limit. This means that the current system behavior deviates significantly from the nominal system behavior during the relevant time period. By selecting limits for the predetermined period of time and the magnitude of the predetermined deviation threshold, the system designer can influence the behavior of the condition monitoring system. The lower the deviation threshold and the shorter the associated time period is set, the faster the system reacts to the deviation. If, in contrast, a high magnitude of the relevant time period and the deviation threshold is predetermined, an alarm signal is sent only if the calculated rotational speed deviates significantly from the sensed rotational speed over a long period of time. Experiments can be conducted on the monitored system to evaluate which magnitudes of the deviation thresholds and which durations of the relevant time periods provide a suitable combination of robust system behavior and reliable maintenance predictions.

The hydrostatic unit equipped with the condition monitoring system according to the invention may be part of a hydraulic circuit of the open hydraulic circuit type or of the closed hydraulic circuit type, wherein preferably at least the hydrostatic pump is equipped with the condition monitoring system according to the invention.

It is further preferred that at least one hydrostatic actuator (e.g. a hydrostatic motor) of the hydraulic circuit is equipped with a slave sensor according to the invention, wherein the condition monitoring system monitors the condition of both the hydrostatic pump and the at least one hydrostatic motor. This arrangement optimally utilizes the concept of a locally divided master and slave sensor and thus provides an efficient option for monitoring the status of a hydraulic circuit comprising more than one hydrostatic unit (hydrostatic displacement device).

The condition monitoring system of the present invention may also be applied to hydraulic circuits including hydrostatic pump-cylinder systems. The hydrostatic pump-cylinder system according to the invention comprises at least one hydrostatic cylinder driven by the hydrostatic pump, wherein, according to the invention, the hydrostatic pump is equipped with a condition monitoring system and the at least one hydrostatic cylinder is equipped with a slave sensor. The condition monitoring system monitors the condition of both the hydrostatic pump and the at least one hydrostatic cylinder. Similar to the condition monitoring of a hydraulic circuit comprising a hydrostatic motor and a hydrostatic pump, the hydraulic circuit with the hydrostatic pump and the hydrostatic cylinder comprises at least two hydrostatic units (displacement devices) arranged in different positions of the circuit. Therefore, a plurality of sensors are required to measure and monitor the state of the loop, but only one of these sensors (the main sensor device) is equipped with a computing device, such as a memory unit or a computing unit. The sensor data is centrally processed at the primary sensor device and provided to an output unit that displays the processed data and/or communicates processed status information of the loop to a superordinate unit (e.g. to the vehicle). At the upper level, the status information may be displayed using indicators and/or other visual interfaces, and/or may be further processed by the control unit and/or the vehicle controller.

According to the present invention, there is provided a method for monitoring a state of a hydraulic circuit and predicting a maintenance time point of the hydraulic circuit, the method comprising:

in a first step a), the speed (rotational or longitudinal speed) of the hydrostatic unit of the hydraulic circuit is calculated based on sensed values of the operating parameters of the hydraulic circuit at predetermined points in time during its operation. The selection of the predetermined point in time may be based on, for example, a time pattern with a constant time step, but may also be based on different rules to obtain the predetermined time step, e.g. the calculation may be triggered when one of the sensed values exceeds a predetermined threshold.

The (theoretical) speed of the hydrostatic unit may be calculated in various ways based on sensed values of the operating parameters, for example based on the system pressure or the vibration frequency, wherein the parameters providing the basis for the calculation may be directly or indirectly related to the speed. The basis of the calculation for determining the speed can also be deduced from empirical values collected from measurements or experiments. It is preferable to perform the calculation based on an empirical relationship between the calculated speed of the hydraulic circuit and the sensed operating parameter, as this requires less computational power. The empirical relationship may be obtained, for example, by: the elements of the matrix used as a scale factor between the measured parameter and the velocity are tuned during the experiment so that a reliable estimate/calculation of the velocity can be obtained with a low computational effort by multiplying the vector containing the measured system parameter with the matrix comprising the tuned values.

The relationship between the calculated speed and the sensed value of the system parameter can also be obtained by: a look-up table is compiled or a physical equation representing the hydraulic circuit is approximated with a low order taylor series. However, one skilled in the relevant art will find different solutions that require less calculation of the speed from the measured system parameters.

In step b), the actual speed of the hydrostatic unit is sensed at the predetermined point in time, at which the parameters providing the basis for the calculation have been measured. Depending on the particular application, the speed of the hydrostatic unit may be sensed during the entire operation of the hydraulic circuit, or the speed of the hydrostatic unit may be sensed only when a trigger signal is provided at a predetermined point in time.

In step c), an absolute deviation value representing the deviation of the calculated speed from the sensed (actual) speed is determined at a predetermined point in time. By comparing the calculated rotational speed with the sensed rotational speed, an indication of the degree of significance of the deviation of the system behaviour from the designed system behaviour is obtained. Such deviations are expressed in terms of absolute deviation values. Thus, a conclusion about the current state of the hydraulic circuit can be drawn from the absolute deviation value.

The absolute deviation value may be filtered according to its temporal resolution and scattering. If absolute deviation values are frequently calculated and the value distributions are significant, a moving average filter, for example, may be applied to facilitate further processing of the absolute deviation values. However, the absolute deviation value may also be further processed in an unfiltered manner, or a different filter technique may be applied.

During operation of the hydraulic circuit, steps a) to c) are repeated periodically. This repetition is marked as step d).

In step e), a signal is output if the absolute deviation value exceeds a predetermined tolerance threshold for the deviation for a period of time longer than a predetermined period of time. The predetermined tolerance threshold and the predetermined time period are set by the system designer depending on the application. The higher the predetermined deviation threshold is set, the greater the deviation between the calculated (theoretical) speed and the sensed (actual) speed, i.e. the nominal system behavior and the current system behavior, before the output signal is generated. The measurement error, singularity or short term effect may affect the absolute deviation value and eventually cause an output signal, which may be excluded from being considered as a fault state by the state monitoring method according to the present invention by setting a minimum duration of the predetermined period. The periodic repetition of steps a) to c) does not necessarily lead to the steps a) to c) being performed in a strict temporal pattern. Steps a) to c) may alternatively be performed when a periodically monitored operating state becomes true, for example when the system pressure rises above a certain value.

According to the present invention, the predictive maintenance signal may be output, for example, when a first allowable threshold of the absolute deviation value is exceeded during a time interval greater than a predetermined time period. If the second allowable threshold of the absolute deviation value is exceeded, a fault signal may be output. Preferably, the first allowable threshold, which represents a point in time at which predictive maintenance is required, is lower than the second allowable threshold, which represents a point in time at which the hydrostatic circuit is highly likely to fail. For example, the first threshold value of the absolute deviation value is greater than 50rpm. For example, the second threshold value of the absolute deviation value is greater than 100rpm.

Preferably, the first and/or second allowable threshold is defined by a system designer or operator, for example before activating a method on the hydraulic circuit for monitoring the state of the hydraulic circuit and predicting the maintenance time point of the hydraulic circuit. According to the invention, the predetermined threshold value may be stored in a memory unit of the main sensor device of the condition monitoring system, for example.

In one embodiment of the invention, the magnitude of the first and/or second allowable threshold may be changed during operation of the hydraulic circuit by, for example, service or maintenance personnel. The values that may have been defined by the system designer may be adapted to the specific characteristics of the particular vehicle/system to which the condition monitoring method according to the invention is applied, preferably by means of updates implemented by the system designer or operator, or also by means of e.g. self-learning algorithms or other computational or artificial intelligence means.

The invention generally described above will now be described in further detail with the aid of the accompanying drawings, in which preferred embodiments and preferred design possibilities are shown. However, these preferred embodiments do not limit the scope of the inventive concept. The preferred embodiments shown may be combined with each other without departing from the spirit of the invention. Further, modifications may be implemented within the scope of the possibilities of knowledge of a person skilled in the relevant art without departing from the spirit of the invention. In the following figures, the following are shown:

FIG. 1 schematically illustrates a condition monitoring system according to the present invention;

FIG. 2 schematically illustrates a second embodiment of a condition monitoring system according to the present invention;

fig. 3 shows a flow chart of a method according to the invention;

fig. 4 shows schematically a diagram of absolute deviation values as a function of operating time.

In fig. 1, a hydraulic circuit 1 comprising a condition monitoring system 10 according to the invention is schematically shown. The hydraulic circuit 1, which in this case serves as a hydraulic propulsion unit 1, comprises two hydrostatic units, i.e. a hydraulic pump 2 providing hydraulic pressure to a hydraulic motor 6, wherein the pump 2 and the motor 6 are arranged in a closed-loop hydraulic circuit. The closed loop comprises a high pressure line 3 connecting the pump outlet with the motor inlet, and a low pressure line 5 connecting the motor outlet with the pump inlet. The pump 2 is driven by an internal combustion engine 4 which is connected to the pump 2 via a shaft or a gear arrangement.

The hydraulic pressure generated by the pump 2 is transmitted via the high-pressure line 3 to a hydraulic motor 6, where it is converted into mechanical energy and supplied via a shaft or gear arrangement to a mechanical consumer 8. The condition monitoring system 10 is arranged in the high pressure line 3 at the outlet of the hydraulic pump 2. The condition monitoring system 10 comprises a main sensor device 12 that senses data 14 from the high pressure line 3. In this case, the main sensor device 12 may sense, for example, the outlet pressure of the hydraulic pump 2, the volumetric flow through the pump and/or through the high pressure line 3, and/or other system parameters (such as temperature or flowability). The storage unit 16 is arranged on the main sensor device 12. Sensed data 14 from the primary sensor device 12 is stored in a memory unit 16. The computing unit 20 is connected to the storage unit 16 by a data connection and exchanges the sensed data 14 and/or the processed data 18 with the storage unit 16. In addition to or in lieu of the sensed data 14, the processed data 18 may be stored on the storage unit 16. The calculation unit 20 processes the sensed data 14 and calculates status information about the hydraulic circuit/propulsion unit 1 based on the sensed data 14, the application status monitoring method and/or the predictive maintenance method (e.g., the predictive maintenance method according to the embodiment shown in fig. 3). The condition monitoring system 10 further comprises an output unit 24 capable of receiving data, in particular the condition information 22, from the computing unit 20. The status information 22 of the propulsion unit 1 may be indicated directly by the output unit 24, for example via a visualization device. However, the status information may also be communicated by the output unit 24 to an information processing device 26 (e.g., an indicator, a control unit, and/or a vehicle controller).

The various parts of the condition monitoring system 10 shown in fig. 1 (i.e. the main sensor device 12, the storage unit 16, the calculation unit 20 and the output unit 24) may be provided as e.g. an integral part or group of components or as e.g. one microcontroller in combination with a sensor. However, the sensor device 12 and the units 16, 20, 24 for storing, information and outputting signals may also be provided as separate parts. Further, the condition monitoring system 10 according to the described preferred embodiment is an integral part of the propulsion unit 1 and may be arranged inside the housing or outside the housing of the hydraulic propulsion unit 1.

One skilled in the relevant art will recognize that the high pressure line 3 and the low pressure line 5 may be interchanged. Similarly, the pressure in the low pressure line 5 may be measured by the primary sensor means without departing from the spirit of the invention. The condition monitoring system according to the invention may also comprise a plurality of sensors in the high pressure line 3 and/or the low pressure line 5 in order to determine the pressure difference.

Fig. 2 schematically illustrates a second embodiment of a condition monitoring system 10 according to the present invention. In the present example, the condition monitoring system 10 is integrated into the hydraulic circuit/propulsion unit 1. The second embodiment of the condition monitoring system 10 includes all the elements of the condition monitoring system 10 according to the first embodiment shown in fig. 1. The condition monitoring system 10 according to the second embodiment further comprises a number of slave sensors 30 which sense additional physical operating parameters of the hydraulic propulsion unit 1. For example, the rotational speed of an input shaft connected to the hydraulic pump 2, or the rotational speed of an output shaft connected to the motor 6 is monitored. Additionally, pressure sensors are provided at the inlet and outlet of the hydraulic pump 2 and the hydraulic motor 6. The slave sensor 30 is connected to the master sensor device 12 via a communication path 32. Information between the master sensor device 12 and the slave sensor 30 is exchanged via a communication path 32. For example, the master sensor device 12 can send commands to the slave sensors 30, while the slave sensors 30 provide sensed data 14 to the master sensor device 12.

Preferably, only the main sensor device 12 is provided with means capable of performing a computing action, such as the storage unit 16 and/or the computing unit 20. Because the slave sensors 30 of this embodiment are not equipped with a computing device, the master sensor 12 coordinates the measurements performed by the slave sensors 30 via the communication path 32. In systems that include high complexity, because a large number of system components must be monitored, if one master sensor has insufficient storage and/or computing power to process and store all data received from slave sensors 30, more than one intelligent master sensor device 12 may be provided, for example. Depending on the system environment in which the condition monitoring system 10 is installed, the communication path 32 may be provided as a wire line, a LAN or WLAN system, a bus system, a network or internet interface (which may also be a cloud interface), or the like. Thus, the communication path 32 is not limited to a visual connection, but may also be a wireless technology, e.g. bluetooth or infrared connection may be applied.

Fig. 3 schematically shows a method for monitoring the state of the hydraulic circuit 1 and predicting the maintenance time point of the hydraulic circuit 1. In step a), the rotational speed 40 of the hydrostatic unit 6 is calculated based on the sensed data 14, i.e. sensed values of the operating parameters suitable for performing the calculation. Preferably, the calculation in step a) is repeatedly performed (e.g. performed periodically) at predetermined points in time. The interval at which the computation is performed may be selected, for example, based on a balance requirement between high resolution of the computed data and minimizing storage requirements.

In step b), the rotational speed 42 of the hydrostatic unit 6 is sensed by the sensor means 30, preferably at the same predetermined point in time as the predetermined point in time at which the rotational speed is calculated in step a). The calculation of the operating parameters in step a) may be done by way of example by a main sensor device 12 equipped with calculation means. The sensing of the rotational speed 42 of the hydrostatic unit 6 in step b) (illustratively the rotational speed measured at the shaft connecting the hydrostatic unit/motor 6 with the mechanical consumer 8) may be performed by the slave sensor 30 without computational power. However, the inventive concept also covers the use of different sensor types and the use of more than one sensor for measuring an operating parameter.

In step c), an absolute deviation value 44 is determined by comparing the calculated rotational speed 40 with the sensed rotational speed 42, i.e. by comparing two values measured and sensed, respectively, preferably at the same predetermined point in time. Thus, the absolute deviation value 44 represents the deviation of the calculated speed 40 from the sensed rotational speed 42.

During operation of the hydraulic circuit 1, steps a) to c) are repeated periodically or at least repeatedly. This is indicated by step d).

In step e), a signal 46 is output if the absolute deviation value 44 exceeds a predetermined tolerance threshold during a period of time longer than a predetermined period of time.

In fig. 4, a diagram is shown that visualizes the development of the absolute deviation value 44 over the operating time of the hydraulic circuit 1. The absolute deviation value 44 is calculated from the sensed rotational speed 42 and the calculated rotational speed 40 over time. The first and second tolerance thresholds 50, 52 are visualized, wherein the first tolerance threshold 50 comprises an absolute value lower than the second tolerance threshold 52. As an example, the magnitude of the first threshold may be assigned to 50rpm and the magnitude of the second threshold may be 100rpm. According to step e) of the method of fig. 3, a predictive maintenance signal 56 may be output if the absolute deviation value 44 exceeds a first threshold. If the absolute deviation value 44 exceeds the second allowable threshold 52 for a longer time span than the predetermined period 54, a fault signal is output at the end 58 of the predetermined period 54 indicating that the hydraulic propulsion unit is likely to be faulty.

The predetermined period of time 54 may be set to one hour or several hours, for example. However, one skilled in the relevant art will conclude that the predetermined time period(s) 54 may be defined, for example, to be within a range of seconds, minutes, hours, or days without departing from the scope of the invention. If more than one time period is defined, the time periods may include the same duration or different durations.

From the above disclosure and the drawings and claims, it should be appreciated that the condition monitoring system 10 and method for monitoring the condition of the hydraulic circuit 1 and predicting the maintenance time point provide a number of possibilities and advantages over the prior art. It will be further appreciated by those skilled in the relevant art that further modifications and variations to the state monitoring system 10 and method for monitoring the state of the hydraulic circuit 1 known in the art may be made to the state monitoring system and method according to the present invention without departing from the spirit and scope of the present invention. Accordingly, all such modifications and changes are intended to be within the scope of the claims and are intended to be covered by the claims. It should be further understood that the examples and embodiments described above are for illustrative purposes only and that various modifications, changes, or combinations of embodiments suggested to persons skilled in the relevant art and accordingly are included within the spirit and purview of this invention.

List of reference numerals

1. Hydraulic circuit/propulsion unit

2. Hydraulic pump/hydrostatic unit

3. High pressure pipeline

4. Internal combustion engine

5. Low pressure pipeline

6. Hydraulic motor/hydrostatic unit

8. Machine consumption device

9. Vehicle controller

10. State monitoring system

12. Main sensor device

14. Sensed data/sensed value

16. Memory cell

18. Processed data

20. Calculation unit

22. Status information

24. Output unit

26. Information processing apparatus

30. Slave sensor

32. Communication path

40. Calculated rotational speed

42. Sensed rotational speed

44. Absolute deviation value

46. Signal signal

50. First allowable threshold

52. Second allowable threshold

54. For a predetermined period of time

56. Predictive maintenance signal

58. End of predetermined time period

Claims

1. A condition monitoring system (10) for arrangement or fastening to a hydrostatic unit, the condition monitoring system being embedded in a hydraulic circuit (1), the condition monitoring system comprising:

-a main sensor device (12) for continuously sensing a first physical operating parameter of the hydraulic circuit (1);

-a storage unit (16) on the primary sensor (12) for storing sensed and/or processed data (14, 18);

-a calculation unit (20) for processing the sensed data (14) in order to determine status information (22) of a hydrostatic unit of the hydraulic circuit (1);

-an output unit (24) for indicating status information (22) of the hydrostatic unit of the hydraulic circuit (1) and/or for communicating status information (22) of the hydrostatic unit of the hydraulic circuit (1) to an indicator and/or a control unit and/or a vehicle controller (9).

2. The condition monitoring system (10) of claim 1, further comprising:

-at least one slave sensor (30) for sensing a second physical operating parameter;

-a communication path (32) between the at least one slave sensor (30) and the master sensor (12) for communicating the sensed values (14) sensed by the at least one slave sensor (30) to the master sensor (12).

3. The condition monitoring system (10) according to claim 1 or 2, wherein the master sensor device (12), the storage unit (16), the calculation unit (20), the output unit (24), the at least one slave sensor (30) and/or the communication path (32) are designed as an integral part or group of components arranged inside or outside a hydrostatic unit in the hydraulic circuit (1).

4. A condition monitoring system (10) according to one of claims 1 to 3, wherein the first and/or second physical operating parameter is selected from the group comprising: hydraulic input and/or output pressure, hydraulic fluid temperature, hydraulic circuit (1) temperature, hydraulic fluid flow, displacement angle, speed, acceleration/deceleration, hydraulic fluid viscosity, vibration frequency, noise level, ambient temperature, roughness, deformation.

5. The condition monitoring system (10) according to any one of the preceding claims, wherein the determined condition information (22) is continuously processed by a predictive maintenance method to determine a remaining time until the end of a next maintenance service or life cycle.

6. The condition monitoring system (10) according to any one of the preceding claims, wherein the main sensor device (12) is a multi-physical field sensor capable of continuously measuring more than one physical operating parameter.

7. The condition monitoring system (10) according to one of claims 2 to 6, wherein the communication path (32) is a wire line, a LAN or WLAN system, a bus system, a network or internet (cloud) interface or the like.

8. The condition monitoring system (10) according to one of claims 1 to 7, wherein the calculation unit (20) is adapted to receive continuously sensed values (14) of a physical operating parameter of the hydraulic circuit (1), from which continuously sensed values a calculated speed (40) of a hydrostatic unit in the hydraulic circuit (1) can be determined, and to determine a deviation value of the calculated speed (40) from a sensed speed (42) of the hydrostatic unit, and to store the deviation values in time sequence starting from a point in time when the hydraulic circuit (1) is put into operation or in use.

9. The condition monitoring system (10) of claim 8, wherein the output unit (24) issues an alarm signal if the deviation values are greater than a predetermined threshold (50, 52) during a time period longer than a predetermined time period (54).

10. A hydrostatic unit equipped with a condition monitoring system (10) according to any one of claims 1 to 9.

11. Hydraulic circuit (1) of the open hydraulic circuit or of the closed hydraulic circuit type, wherein at least the hydrostatic pump (2) is equipped with a condition monitoring system (10) according to one of claims 1 to 9.

12. Hydraulic circuit (1) according to claim 11, wherein at least one hydrostatic motor (6) is equipped with a slave sensor (30) according to claim 2, and wherein the condition monitoring system (10) monitors the condition of both the hydrostatic pump (2) and the at least one hydrostatic motor (6).

13. Hydraulic circuit (1) comprising at least one hydrostatic cylinder driven by a hydrostatic pump (2), wherein the hydrostatic pump (2) is equipped with a condition monitoring system (10) according to one of claims 1 to 9, and the at least one hydrostatic cylinder is equipped with a slave sensor (30) according to claim 2, and wherein the condition monitoring system (10) monitors the condition of both the hydrostatic pump (2) and the at least one hydrostatic cylinder.

14. A method for monitoring a status of a hydraulic circuit (1) and predicting a maintenance time point of the hydraulic circuit (1), the method comprising the steps of:

a) Determining a calculated speed (40) of the hydrostatic unit based on the sensed value (14) of the operating parameter at a predetermined point in time during operation of the hydraulic circuit (1);

b) Sensing the speed of the hydrostatic unit at the predetermined point in time according to step a);

c) Determining an absolute deviation value (44) representing a deviation of the calculated speed (40) from the sensed speed (42) at the predetermined point in time (54);

d) Periodically repeating steps a) to c) during operation of the hydraulic circuit (1);

e) A signal (46) is output if the absolute deviation value (44) exceeds a predetermined tolerance threshold (50, 52) for the deviation during a time period longer than a predetermined time period (54).

15. The method of claim 14, wherein the predictive maintenance signal (56) is output when a first allowable threshold (50) of the absolute deviation value (44) is exceeded, and wherein the fault signal is output if a second allowable threshold (52) of the absolute deviation value (44) is exceeded.