A variable load working condition hydraulic oil source pressure early warning method and system

Abstract

This invention relates to the field of hydraulic system condition monitoring and fault early warning technology, and discloses a method and system for early warning of hydraulic oil source pressure under variable load conditions. The method collects hydraulic system operating parameters and extracts transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters under variable load transient conditions. These two parameters are mapped to a preset two-dimensional state phase plane for discrimination. When a characteristic point falls into the critical state region, active micro-amplitude excitation frequency domain verification is triggered. A test excitation frequency that adaptively avoids the system's inherent harmonics is selected, and a micro-amplitude excitation signal is injected into the hydraulic system to obtain the actual pressure response amplitude at a specific frequency and generate an early fault alarm signal. This invention overcomes the shortcomings of traditional fixed threshold methods, which are prone to false alarms, and can adaptively distinguish between normal physical delays and abnormal pressure build-up hysteresis, achieving early warning of hidden faults before a significant deviation in steady-state pressure occurs.

Description

Technical Field

[0001] This invention relates to the field of hydraulic system condition monitoring and fault early warning technology, specifically to a method and system for early warning of hydraulic oil source pressure under variable load conditions. Background Technology

[0002] The hydraulic power system is the core power unit of large industrial equipment, and its operating status directly affects the safety and stability of the entire machine. In practical engineering applications, hydraulic equipment is usually under variable load conditions, and frequent load switching can cause transient changes in the system's output pressure and flow rate.

[0003] Currently, the monitoring and early warning of hydraulic system pressure generally adopts a fixed steady-state pressure threshold method. This method is applicable to a certain extent when the system is in a stable operating phase. However, when the hydraulic system is under transient conditions with varying loads, the compressibility of the fluid itself and the inertia of the mechanical actuators will produce a normal physical pressure build-up delay. Existing fixed threshold monitoring mechanisms cannot distinguish this normal physical delay from abnormal pressure build-up delays caused by increased oil gas content, internal component wear, etc. To avoid frequent false alarms during normal operating condition switching, existing technologies usually choose to relax the dead zone threshold for alarms. This approach directly leads to a decrease in the sensitivity of the early warning system, causing the control system to only trigger an alarm in the late stage of a fault, when hydraulic components have suffered serious damage and steady-state pressure fluctuates significantly. At this point, the hidden fault has often evolved into irreversible physical damage, which can easily cause unplanned equipment shutdowns and secondary damage to related components, failing to meet the engineering requirements for early warning of hidden faults in hydraulic systems in industrial settings. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a hydraulic oil source pressure early warning method and system under variable load conditions. This solves the problem that existing hydraulic system pressure early warning methods primarily rely on fixed pressure thresholds under steady-state conditions, making it difficult to distinguish between normal physical pressure build-up lag and abnormal pressure build-up lag caused by oil gas deterioration or internal pump wear under variable load transient conditions. This results in low sensitivity for early warning of hidden faults and a tendency to generate false alarms during frequent changes in operating conditions.

[0005] The first aspect of this invention provides a method for early warning of hydraulic oil source pressure under variable load conditions, comprising the following steps: Collect hydraulic system operating status parameters, including the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the hydraulic oil temperature; The variable load transient condition is identified based on the rate of change of the actual displacement signal of the variable mechanism. Under the variable load transient condition, the transient pressure response hysteresis time is determined based on the time difference between the moment when the rate of change of the actual displacement signal of the variable mechanism reaches the extreme value and the moment when the rate of change of the actual pressure of the main oil circuit reaches the corresponding extreme value. The dynamic volumetric stiffness characterization parameter is determined based on the relationship between the rate of change of the actual pressure of the main oil circuit and the rate of change of the theoretical output flow determined based on the actual speed of the motor and the actual displacement signal of the variable mechanism. The transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters are mapped to a preset two-dimensional state phase plane for discrimination. The two-dimensional state phase plane uses the dynamic volumetric stiffness characterization parameters as the abscissa and the transient pressure response hysteresis time as the ordinate. The normal state region, critical state region and severe fault region are divided by the first state boundary and the second state boundary. When the feature point falls into the critical state region, active micro-amplitude excitation frequency domain verification is triggered. In the active micro-amplitude excitation frequency domain verification, the fundamental frequency of the variable pump flow pulsation and its harmonic frequencies are determined based on the current actual speed of the motor and the number of plungers of the hydraulic pump, and the test excitation frequency is determined under the condition of avoiding the fundamental frequency of the variable pump flow pulsation and its harmonic frequencies. A micro-amplitude excitation signal is injected into the hydraulic system according to the test excitation frequency. The actual pressure of the main oil circuit is separated in the frequency domain to obtain the actual pressure response amplitude at the test excitation frequency. An early fault alarm signal is generated based on the ratio between the actual pressure response amplitude and the corresponding reference pressure response amplitude.

[0006] Furthermore, the transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters are extracted under variable load transient conditions, specifically including: According to the preset sampling period, the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit and the hydraulic oil temperature are synchronously acquired based on a unified time base, and a time correspondence relationship is established for each synchronously acquired operating status parameter. The theoretical effective bulk modulus of hydraulic oil under the current working conditions is determined based on the hydraulic oil temperature and the actual pressure of the main oil circuit. The theoretical output flow rate is determined based on the actual speed of the motor and the actual displacement signal of the variable mechanism, combined with the displacement conversion factor of the hydraulic pump.

[0007] Furthermore, based on the rate of change of the actual displacement signal of the variable mechanism, the transient load condition is identified, and the transient pressure response hysteresis time is determined, specifically including: The actual displacement signal of the variable mechanism is monitored in real time. When the absolute value of the rate of change of the actual displacement signal of the variable mechanism reaches or exceeds the preset trigger threshold, the variable load transient feature extraction cycle is entered. Within the time window corresponding to the variable load transient feature extraction cycle, the first moment when the rate of change of the actual displacement signal of the extracted variable mechanism reaches its maximum absolute value. Based on the direction of change of the actual displacement signal of the variable mechanism at the first moment, within the preset pressure response search time window after the first moment, search for the extreme value of the actual pressure change rate of the main oil circuit that corresponds to the direction of change and whose absolute value of the pressure change rate reaches the preset effective threshold of the pressure response, and determine the moment corresponding to the extreme value of the actual pressure change rate of the main oil circuit as the second moment. The time difference between the second moment and the first moment is taken as the transient pressure response hysteresis time.

[0008] Furthermore, the dynamic volumetric stiffness characterization parameters are determined in the following way: Extract the maximum absolute value of the actual pressure change rate and the maximum absolute value of the theoretical output flow rate change within the current variable load transient feature extraction period; When the maximum absolute value of the theoretical output flow rate change is not lower than the preset effective lower limit of the flow rate change, the ratio of the maximum absolute value of the actual pressure change of the main oil circuit to the maximum absolute value of the theoretical output flow rate change is determined as the dynamic volumetric stiffness characterization parameter. When the maximum absolute value of the theoretical output flow rate change is lower than the preset effective lower limit of the flow rate change, the current variable load transient feature extraction cycle is marked as an invalid cycle.

[0009] Furthermore, the first state boundary and the second state boundary are determined based on the dynamic volumetric stiffness characterization parameters, the equivalent volume of the main oil circuit, the theoretical effective bulk elastic modulus corresponding to the effective extreme moment of the actual pressure change rate of the main oil circuit, and the system's inherent time offset parameters, respectively. Wherein, the threshold of the first transient pressure response hysteresis time corresponding to the first state boundary is equal to the sum of the product of the system's inherent time offset parameter, the first boundary calibration coefficient, the dynamic volumetric stiffness characterization parameter, and the equivalent volume of the main oil circuit, divided by the theoretical effective bulk elastic modulus. The second transient pressure response hysteresis time threshold corresponding to the second state boundary is equal to the sum of the product of the system's inherent time bias parameter, the second boundary calibration coefficient, the dynamic volumetric stiffness characterization parameter, and the equivalent volume of the main oil circuit, divided by the theoretical effective bulk elastic modulus; and the second boundary calibration coefficient is greater than the first boundary calibration coefficient.

[0010] Furthermore, when the transient pressure response hysteresis time is less than the first transient pressure response hysteresis time threshold, the feature point is determined to be in the normal state region. When the transient pressure response hysteresis time is not less than the first transient pressure response hysteresis time threshold and less than the second transient pressure response hysteresis time threshold, the feature point is determined to be in the critical state region. When the transient pressure response hysteresis time is not less than the second transient pressure response hysteresis time threshold, the feature point is determined to be located in the severe fault zone. When the feature point is in the critical state region, after the current variable load transient feature extraction cycle ends, the rate of change of the actual displacement signal of the variable mechanism and the rate of change of the actual pressure of the main oil circuit are continuously detected. When both fall back to the corresponding preset stable range, active micro-amplitude excitation frequency domain verification is performed.

[0011] Furthermore, the test excitation frequency was determined in the following way: Based on the currently collected actual motor speed and the number of plungers inside the hydraulic pump, the fundamental frequency of the variable pump flow pulsation is calculated, and the harmonic frequencies of each order within the preset order range are determined according to the fundamental frequency of the variable pump flow pulsation. Within the test excitation frequency band allowed by the electro-proportional relief valve, multiple candidate test frequencies are generated according to a preset frequency search step size; Select candidate test frequencies from multiple candidate test frequencies whose absolute differences from the fundamental frequency of the variable pump flow pulsation and the harmonic frequencies of each order are not less than the preset frequency avoidance interval. When there are multiple candidate test frequencies that meet the conditions, the minimum frequency interval between each candidate test frequency and the nearest variable pump flow pulsation fundamental frequency or harmonic frequency is determined, and the candidate test frequency with the largest minimum frequency interval is determined as the test excitation frequency.

[0012] Furthermore, a micro-amplitude excitation signal is injected into the hydraulic system, and an early fault alarm signal is generated based on the actual pressure response amplitude, specifically including: When the electro-proportional relief valve is in the preset dynamic pressure regulation working range, and the rate of change of the actual displacement signal of the variable mechanism and the rate of change of the actual pressure of the main oil circuit are both in the corresponding preset stable range, a sinusoidal test signal with a set amplitude and test excitation frequency will be superimposed on the basic pressure regulation command of the electro-proportional relief valve. By using bandpass filtering with the test excitation frequency as the center frequency, the actual pressure signal of the main oil circuit is separated in the frequency domain and the actual pressure response amplitude is extracted. Based on the current hydraulic oil temperature, the current actual pressure of the main oil circuit, and the test excitation frequency, the corresponding reference pressure response amplitude is determined from the pre-established reference response calibration relationship; The ratio of the actual pressure response amplitude to the reference pressure response amplitude is calculated to obtain the frequency domain response amplitude ratio; when the frequency domain response amplitude ratio is lower than the preset alarm threshold, an early fault alarm signal is generated.

[0013] Furthermore, after a feature point falls into a severe fault zone or an early fault alarm signal is generated, the following steps are also included: Obtain the normal reference characterization parameters corresponding to the current hydraulic equipment and the current working range, and determine the safety limit factor based on the deviation of the current dynamic volumetric stiffness characterization parameters from the normal reference characterization parameters; Based on the safety limit coefficient, fault degradation control is implemented. The upper limit of the maximum displacement command of the power source under fault degradation state is determined as the product of the safety limit coefficient and the original maximum displacement command upper limit under normal operation state. The upper limit of the highest set pressure under fault degradation state is also determined as the product of the safety limit coefficient and the original highest set pressure upper limit under normal operation state. Based on the maximum displacement command limit and the maximum set pressure limit of the power source, the maximum displacement output capacity of the power source module and the maximum pressure setting value of the electro-proportional relief valve are respectively limited.

[0014] A second aspect of the present invention provides a hydraulic oil source pressure early warning system under variable load conditions, used to execute the above-mentioned hydraulic oil source pressure early warning method under variable load conditions, comprising: The parameter extraction module is used to collect the operating status parameters of the hydraulic system, including the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the hydraulic oil temperature. It identifies the transient working condition of variable load based on the rate of change of the actual displacement signal of the variable mechanism, extracts the transient pressure response hysteresis time based on the transient response relationship between the actual displacement signal of the variable mechanism and the actual pressure of the main oil circuit, and determines the dynamic volumetric stiffness characterization parameters based on the relationship between the rate of change of the actual pressure of the main oil circuit and the rate of change of the theoretical output flow. The state discrimination module is used to map the transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters to a preset two-dimensional state phase plane for discrimination. The two-dimensional state phase plane is divided into normal state region, critical state region and severe fault region by the first state boundary and the second state boundary. When the feature point falls into the critical state region, active micro-amplitude excitation frequency domain verification is triggered. The frequency domain verification and early warning module is used to determine the fundamental frequency and harmonic frequencies of the variable pump flow pulsation based on the actual speed of the motor and the number of plungers inside the hydraulic pump during active micro-amplitude excitation frequency domain verification. Under the condition of avoiding the fundamental frequency and harmonic frequencies of the variable pump flow pulsation, the test excitation frequency is determined. A micro-amplitude excitation signal is injected into the hydraulic system according to the test excitation frequency. The actual pressure of the main oil circuit is frequency-domain separated to obtain the actual pressure response amplitude under the test excitation frequency. An early fault alarm signal is generated based on the ratio between the actual pressure response amplitude and the corresponding reference pressure response amplitude.

[0015] This invention provides a method and system for early warning of hydraulic oil source pressure under variable load conditions. It has the following beneficial effects: 1. This invention constructs a two-dimensional state phase plane by extracting transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters under variable load conditions, and sets the state boundary of the phase plane as a linear slope function based on the system's inherent hysteresis time and volumetric stiffness. This mechanism changes the traditional early warning logic that relies on a single fixed pressure threshold, and can adaptively distinguish between normal physical delays under variable load conditions and abnormal pressure build-up hysteresis caused by oil deterioration or internal leakage, thus reducing the false alarm rate of the hydraulic system when frequently switching operating conditions.

[0016] 2. After determining that the system characteristics have entered a critical state, this invention triggers active micro-amplitude excitation frequency domain verification. Based on the current motor speed and the number of plungers, it calculates and avoids the inherent pulsating harmonic frequencies of the hydraulic pump, adaptively selecting the test excitation frequency. This frequency avoidance method prevents spectral aliasing between the test signal and the system's inherent noise. Subsequently, combined with bandpass filtering to extract the actual pressure response amplitude, it can quantitatively assess the degree of attenuation of the dynamic stiffness of the hydraulic oil source, thereby achieving early warning of hidden faults before a significant deviation in the system's steady-state pressure occurs.

[0017] 3. After generating an early fault alarm signal, this invention triggers a fault-tolerant degradation control command, synchronously limiting the upper limit of the maximum displacement command of the power source and the maximum set pressure of the system according to a preset safety factor. This mechanism, upon confirming early performance degradation in the hydraulic system, proactively reduces the output load of hydraulic components, preventing the equipment from performing extreme actions while malfunctioning. This prevents overall system collapse and secondary damage caused by the deterioration of local faults, thus improving the operational safety of the equipment. Attached Figure Description

[0018] Figure 1 This is a diagram illustrating the architecture of the hydraulic oil source pressure early warning system under variable load conditions according to the present invention. Figure 2 This is a flowchart illustrating the overall workflow of the hydraulic oil source pressure early warning method under variable load conditions of the present invention. Figure 3 This is a logic diagram of the multidimensional physical parameter synchronous acquisition and basic parameter calculation of the present invention; Figure 4 This is a schematic diagram illustrating the principle of transient physical feature extraction in this invention. Figure 5 This is a schematic diagram of the two-dimensional state phase plane mapping principle of the present invention; Figure 6 This is a schematic diagram of the frequency adaptive active micro-amplitude excitation and frequency domain separation verification principle of the present invention; Figure 7 This is a logic diagram of the fault-tolerant control linkage and safety protection mechanism of the present invention; Figure 8 This is a time series curve of transient feature extraction under varying load in an embodiment of the present invention; Figure 9This is a diagram of the two-dimensional state phase plane and feature point migration trajectory in an embodiment of the present invention; Figure 10 This is a spectral distribution diagram of the active micro-amplitude excitation frequency domain separation verification in an embodiment of the present invention; Figure 11 This is a sensitivity comparison curve between the early warning method of this invention and the traditional early warning method during the fault evolution cycle. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See attached document Figure 1 This invention provides a hydraulic oil source pressure early warning system under variable load conditions, including a data acquisition module, a power source module, a control valve module, and a main control module.

[0021] The data acquisition module is used to collect operating status parameters of the hydraulic system during operation, including displacement sensors, high-frequency pressure sensors, temperature sensors, and speed sensors.

[0022] A displacement sensor is installed at the variable displacement mechanism of the power source module to collect the actual displacement signal of the variable displacement mechanism. A high-frequency pressure sensor is installed at the main oil circuit outlet of the hydraulic system to collect the actual pressure of the main oil circuit. A temperature sensor is installed in the main oil circuit to collect the hydraulic oil temperature. A speed sensor is installed corresponding to the drive motor of the power source module to collect the actual speed of the drive motor.

[0023] The power source module includes an electro-hydraulic servo variable pump, which is used to adjust the displacement of the variable mechanism according to the displacement control command output by the main control module, and output hydraulic oil to the main oil circuit of the hydraulic system.

[0024] The control valve module includes an electro-proportional relief valve. The inlet of the electro-proportional relief valve is connected to the main oil circuit of the hydraulic system, and the outlet is connected to the return oil circuit. It is used to regulate and limit the working pressure of the main oil circuit.

[0025] The main control module is electrically connected to the acquisition module, power source module, and control valve module. The acquisition module transmits the acquired actual displacement signals of the variable mechanism, actual motor speed, actual pressure of the main oil circuit, and hydraulic oil temperature to the main control module via an industrial communication bus.

[0026] The main control module stores a hydraulic parameter calculation program and a bandpass filter processing program. The hydraulic parameter calculation program is used to calculate the theoretical effective bulk modulus of elasticity based on the hydraulic oil temperature and the actual pressure of the main oil circuit, and to calculate the theoretical output flow rate based on the actual speed of the motor and the actual displacement signal of the variable mechanism. The bandpass filter processing program is used to perform bandpass filtering on the high-frequency pressure signal with the selected dynamic test frequency as the center frequency during subsequent dynamic testing.

[0027] The main control module outputs displacement control commands to the power source module and pressure regulation commands to the control valve module based on the operating status of the hydraulic system. When the dynamic test conditions are met, the main control module generates a micro-amplitude sinusoidal test excitation signal and superimposes it onto the pressure regulation command, causing the electro-proportional relief valve to produce a micro-amplitude dynamic response corresponding to the dynamic test frequency, thereby applying a test disturbance for pressure response detection to the main oil circuit.

[0028] See attached document Figure 2 This invention provides a method for early warning of hydraulic oil source pressure under variable load conditions, comprising the following steps: S100 synchronously acquires the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the temperature of the hydraulic oil according to the preset sampling period. Based on the hydraulic oil temperature and the actual pressure of the main oil circuit, it calculates the theoretical effective bulk modulus of the hydraulic oil under the current working condition, and calculates the theoretical output flow of the power source module based on the actual speed of the motor and the actual displacement signal of the variable mechanism.

[0029] S200: Calculate the rate of change of the actual displacement signal of the variable mechanism and compare its absolute value with the preset trigger threshold; when the absolute value of the rate of change of the actual displacement signal of the variable mechanism reaches or exceeds the preset trigger threshold, enter the variable load transient feature extraction cycle.

[0030] Within the variable load transient feature extraction period, the moments when the actual displacement change rate of the variable mechanism reaches its extreme value and the moments when the actual pressure change rate of the main oil circuit corresponding to the current pressure change direction reaches its extreme value are determined. The transient pressure response hysteresis time is calculated based on the time difference between the two extreme moments. At the same time, the maximum absolute value of the actual pressure change rate of the main oil circuit and the maximum absolute value of the theoretical output flow rate change rate are extracted respectively, and the ratio between the two is calculated to obtain the dynamic volumetric stiffness characterization parameters.

[0031] S300 constructs a two-dimensional state discrimination plane with the dynamic volumetric stiffness characterization parameter as the horizontal axis and the transient pressure response hysteresis time as the vertical axis, and divides the two-dimensional state discrimination plane into normal state region, critical state region and severe fault region according to the predetermined state boundary.

[0032] The dynamic volumetric stiffness characterization parameters and transient pressure response hysteresis time obtained from the current variable load transient feature extraction cycle are used to form the current feature point, and the current feature point is mapped to the two-dimensional state discrimination plane. The current state of the hydraulic oil source is determined according to the positional relationship between the current feature point and the state boundary.

[0033] S400, when the current feature point falls into the critical state region, the main control module calculates the variable pump flow pulsation fundamental frequency and its harmonic frequency based on the actual speed of the motor and the structural parameters of the power source module, and selects a dynamic test frequency within the preset allowable test excitation frequency band that maintains a preset minimum frequency avoidance interval with the variable pump flow pulsation fundamental frequency and its harmonic frequency.

[0034] When the dynamic test conditions are met, a micro-amplitude sinusoidal test excitation signal corresponding to the dynamic test frequency is generated and superimposed on the pressure regulation command of the control valve module. The main control module performs bandpass filtering on the main oil circuit pressure signal collected during the test, extracts the actual pressure response amplitude at the test frequency, and determines the corresponding theoretical reference amplitude based on the current hydraulic oil temperature, the actual pressure of the main oil circuit, and the dynamic test frequency.

[0035] Calculate the frequency domain response amplitude ratio of the actual pressure response amplitude to the theoretical reference amplitude, and compare the frequency domain response amplitude ratio with the preset alarm threshold; when the frequency domain response amplitude ratio meets the preset alarm conditions, output a fault alarm signal.

[0036] S500, when the current feature point falls into the severe fault zone, or when step S400 outputs a fault alarm signal, the main control module executes fault degradation control linkage, generates a safety limit coefficient based on the deviation of the dynamic volumetric stiffness characterization parameter from the normal reference characterization parameter, and reduces the maximum displacement command limit of the power source module and the maximum set pressure limit of the control valve module according to the safety limit coefficient, so as to limit the maximum output capacity of the hydraulic oil source under abnormal conditions.

[0037] See attached document Figure 3 In step S100, the main control module synchronously collects the operating status parameters of the hydraulic system and calculates the theoretical effective bulk modulus and theoretical output flow rate under the current operating conditions based on the synchronous collection results. This includes the following steps.

[0038] S101, the main control module acquires the operating status parameters of the hydraulic system synchronously according to a preset sampling period based on a unified time base synchronization and timestamp alignment mechanism. The operating status parameters include the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the hydraulic oil temperature.

[0039] To meet the signal extraction requirements for pressure response at subsequent dynamic test frequencies and for the pulsating harmonic components of the variable pump flow, the synchronous sampling frequency of the main control module is higher than twice the highest analysis frequency in the signal to be acquired, and a sampling frequency margin is reserved according to the transition bandwidth required for bandpass filtering. The highest analysis frequency is the highest frequency among the dynamic test frequency and the variable pump flow pulsating harmonic frequency to be analyzed.

[0040] The displacement sensor, speed sensor, high-frequency pressure sensor, and temperature sensor in the acquisition module are respectively set at their corresponding measurement positions. The main control module uses the distributed clock synchronization function of the industrial communication bus to establish a unified time base among the acquisition nodes and sends a synchronization sampling trigger signal to the acquisition module. Each acquisition node completes the sampling and data latching of the corresponding operating status parameters based on the same synchronization trigger time, and adds a timestamp under the unified time base to the sampled data to reduce the impact of clock deviation and bus transmission delay difference between different acquisition nodes on the data time correspondence.

[0041] For the inherent fixed response hysteresis of each sensor and the time offset caused by the fixed hydraulic propagation path, the corresponding time compensation amount can be obtained in advance through calibration and compensated in the synchronously acquired data; alternatively, the fixed time offset that is not compensated separately can be uniformly included in the inherent time offset parameter of the system used in the subsequent two-dimensional state discrimination plane.

[0042] After synchronous acquisition, the main control module obtains the actual displacement signal of the variable mechanism corresponding to the same sampling time t. Actual motor speed Actual pressure and hydraulic oil temperature The above parameters will be used as the basis for subsequent theoretical parameter calculations and transient feature extraction.

[0043] S102, the main control module determines the hydraulic oil temperature based on the current sampling time. and the actual pressure of the main oil circuit Calculate the theoretical effective bulk modulus of pure hydraulic oil under the current operating conditions. .

[0044] The effective bulk modulus of hydraulic oil varies with pressure and temperature. To obtain a theoretical reference value corresponding to the current operating conditions, the main control module pre-stores the basic bulk modulus of the target hydraulic oil, as well as pressure and temperature compensation parameters, and performs calculations according to a preset temperature-pressure compensation empirical formula. Theoretical effective bulk modulus. Determined according to the following formula: ; In the formula, for The theoretical effective bulk modulus of hydraulic oil at any given time; For the target hydraulic oil at the reference pressure and reference temperature The basic bulk modulus of elasticity under the given conditions; Sampling time The actual pressure of the main oil circuit; Sampling time The temperature of the hydraulic oil; The preset reference pressure; The preset reference temperature; This is a pressure compensation factor used to eliminate pressure difference terms. The dimensions of the unit make It is a dimensionless quantity; This is a temperature compensation coefficient used to eliminate temperature difference terms. The dimensions of the unit make It is a dimensionless quantity; Represented by natural constant An exponential function with base 0.

[0045] , and The reference pressure can be determined based on the physical properties of the target hydraulic oil, or it can be obtained through calibration tests on the target hydraulic oil under different temperature and pressure conditions. Specifically, it is based on the reference pressure. and reference temperature The bulk modulus of elasticity obtained under the condition is used as ; Obtain the bulk elastic modulus of the target hydraulic oil under multiple pressure and temperature combinations. and based on Establish parameter fitting relationships and determine them through least squares fitting. and For cases where the target hydraulic oil properties are determined based on their physical properties, the bulk modulus of elasticity corresponding to different pressures and temperatures in the hydraulic oil property data can be used as... The above fitting was performed; for the results obtained from calibration tests, the bulk modulus of elasticity corresponding to each pressure and temperature combination was measured by changing the test pressure and hydraulic oil temperature. Then the above fitting was performed. The result was... , and Pre-stored in the main control module. Reference pressure and reference temperature With determination The reference operating conditions used at that time correspond to the benchmark operating conditions.

[0046] The aforementioned theoretical effective bulk modulus is used to characterize the theoretical reference state under current pressure and temperature conditions without considering actual deterioration factors such as oil gas content, emulsification, and internal leakage of the hydraulic system, and serves as the basic parameter for subsequent dynamic state discrimination.

[0047] S103, the main control module adjusts the motor speed according to the actual speed. and the actual displacement signal of the variable mechanism Combined with the displacement conversion factor of the power source module Calculate the theoretical output flow rate of the power source module at the current sampling time. .

[0048] For electro-hydraulic servo variable displacement pumps, the actual displacement of the variable mechanism determines the theoretical displacement per revolution, and the actual speed of the motor determines the number of revolutions per unit time. Therefore, when the actual displacement of the variable mechanism and the theoretical displacement per revolution have a preset correspondence, the theoretical output flow rate... Determined according to the following formula: ; In the formula, The theoretical flow rate output from the power source module to the main oil circuit at sampling time t; This is the displacement conversion factor for the power source module, used to characterize the theoretical displacement of the variable pump per revolution corresponding to the unit actual displacement of the variable mechanism; The actual speed of the motor at sampling time t; The variable is the actual displacement signal of the mechanism at sampling time t; the constant 60 is used in... When using revolutions per minute as the unit, the motor speed is converted to revolutions per second.

[0049] when When expressed using actual length, angle, or normalized displacement... Dimensions and The representation forms match so that and The product of represents the theoretical displacement of the variable pump per revolution at the current position of the variable mechanism. The parameters can be determined based on the structural parameters or factory calibration data of the electro-hydraulic servo variable pump and pre-stored in the main control module.

[0050] The formula obtained above The theoretical output flow rate, which does not take into account the volumetric efficiency loss and internal leakage of the variable pump, is used to characterize the theoretical oil supply capacity of the power source module determined by the current speed and the actual displacement of the variable mechanism, and serves as the basis for subsequent calculations of the theoretical output flow rate change rate and dynamic volumetric stiffness characterization parameters.

[0051] See attached document Figure 4In step S200, the main control module identifies the variable load condition based on the changes in the actual displacement signal of the variable mechanism, and after triggering the variable load transient feature extraction cycle, extracts the time characteristics and amplitude change characteristics between the actual displacement change of the variable mechanism and the pressure response of the main oil circuit to obtain the transient pressure response hysteresis time and dynamic volumetric stiffness characterization parameters. Specifically, this includes the following steps.

[0052] S201, the main control module processes the actual displacement signal of the synchronously acquired variable mechanism. Perform first-order difference or first-order derivative processing to obtain the actual displacement change rate of the variable mechanism, and compare the absolute value of the actual displacement change rate of the variable mechanism with the preset trigger threshold to determine whether the hydraulic system has entered the variable load condition.

[0053] In this embodiment, the variable load condition refers to a condition where a change in load, controlled by the hydraulic oil source, causes a step change, a ramp change, or other changes in the actual displacement of the variable mechanism that exceed a preset rate of change. The main control module stores a preset length of sliding data buffer during the continuous acquisition of operating status parameters to preserve the operating status data prior to the triggering of the variable load condition.

[0054] When the absolute value of the actual displacement change rate of the variable mechanism is greater than or equal to the preset trigger threshold When the trigger condition for variable load is met, the main control module determines that the condition is met and enters the variable load transient feature extraction cycle. The variable load transient feature extraction cycle includes a preset length data segment stored in the sliding data buffer before the trigger time, and a pressure response data segment after the trigger time; among which, the pressure response data after the trigger is continuously collected until the actual pressure change rate of the main oil circuit falls back to the preset stable range, or the duration reaches the preset maximum extraction time. .

[0055] When the absolute value of the actual displacement change rate of the variable mechanism is less than the preset trigger threshold At this time, the main control module maintains continuous acquisition of operating status parameters and does not start the current variable load transient feature extraction cycle.

[0056] in, The threshold for triggering variable load conditions is used to distinguish between normal steady-state fluctuations and displacement changes of the variable mechanism that can trigger transient feature extraction. During the threshold calibration process, the actual displacement signal of the variable mechanism is continuously collected under normal steady-state operation of the hydraulic oil source. The absolute value of the actual displacement change rate of the variable mechanism is calculated, and the upper limit of the change rate corresponding to normal steady-state fluctuations is determined. Subsequently, within the hydraulic oil source's designed response bandwidth, the minimum load change sufficient to generate an effective variable load response is applied to obtain the corresponding actual displacement change rate of the variable mechanism. ;Will Set at and Between, to satisfy The threshold was verified through multiple tests under normal steady-state and variable load conditions. Pre-stored in the main control module; This represents the maximum allowed duration of the single-cycle transient feature extraction period under varying load.

[0057] S202, within the variable load transient feature extraction cycle, the main control module calculates the actual displacement change rate of the variable mechanism and the actual pressure change rate of the main oil circuit respectively, and determines the transient pressure response hysteresis time based on the time when the extreme values ​​of the two occur.

[0058] The main control module first determines the moment when the absolute value of the actual displacement change rate of the variable mechanism reaches its maximum value within the feature search time window corresponding to the current variable load transient feature extraction cycle. Specifically, it is expressed as: ; In the formula, This refers to the moment when the absolute value of the actual displacement change rate of the variable mechanism reaches its maximum value within the current variable load transient feature extraction cycle. This is the actual displacement signal of the variable mechanism corresponding to sampling time t; The actual rate of change of displacement of the variable mechanism; This indicates the time position at which the corresponding function reaches its maximum value.

[0059] Sure Then, the main control module... Starting from the preset pressure response search time window, the extreme value of the actual pressure change rate of the main oil circuit corresponding to the actual displacement change direction of the current variable mechanism is searched.

[0060] when When the actual displacement rate of the variable mechanism at a given time is positive, the main control module searches for the positive extreme value of the actual pressure change rate in the main oil circuit; when... When the actual displacement rate of the variable mechanism at a given time is negative, the main control module searches for the negative extreme value of the actual pressure change rate in the main oil circuit. The absolute value of the searched extreme value of the actual pressure change rate in the main oil circuit should also be greater than or equal to the preset effective pressure response threshold. The extreme moment of the rate of pressure change that satisfies the above conditions is denoted as . .

[0061] To uniformly represent the above directional matching relationship, let: ; Then the extreme moment of pressure response It can be represented as: ; Where, the range of values ​​for t is limited to those of... Within a preset pressure response search time window starting from [starting point], and satisfying the following: ; In the formula, The extreme moment of the actual pressure change rate of the main oil circuit corresponding to the actual displacement change direction of the current variable mechanism; The actual pressure of the main oil circuit at sampling time t; s is the actual pressure change rate of the main oil circuit; s is the direction indicator. When the actual displacement of the variable mechanism changes in the positive direction, s takes 1, and when the actual displacement of the variable mechanism changes in the negative direction, s takes -1. This is the effective threshold for pressure response, used to exclude small fluctuations and interference peaks in the pressure signal. The effective threshold for pressure response is determined through pre-calibration: Under normal steady-state operation of the hydraulic oil source, the actual pressure of the main oil circuit is collected, the absolute value of the rate of change of the actual pressure in the main oil circuit is calculated, and the upper limit of the rate of change corresponding to normal pressure fluctuations is determined. Subsequently, the minimum load change that can generate an effective variable load pressure response is applied to obtain the corresponding peak value of the actual pressure change rate in the main oil circuit. In order to satisfy Determine the effective threshold of pressure response within the range And it is pre-stored in the main control module.

[0062] In satisfying Under these conditions, the main control module calculates the time difference between the two physical moments mentioned above to obtain the transient voltage build-up hysteresis time. When no pressure change rate that meets the direction matching condition is found within the preset causal search interval, or when the absolute value is less than the effective threshold of the pressure response, the current feature extraction cycle is marked as an invalid cycle, and subsequent two-dimensional state phase plane mapping is not performed. ; In the formula, the transient pressure build-up hysteresis time This represents the time hysteresis characteristic of the hydraulic system's pressure build-up response when facing sudden load changes. For differential differentiation and extremum search of discrete sampled data, those skilled in the art can use sliding window differencing or parabolic fitting to find the extremum; the underlying data processing is well-known in the field and will not be elaborated upon here.

[0063] When there are no directional matching conditions within the preset pressure response search time window and the absolute value of the actual pressure change rate of the main oil circuit reaches... When the effective pressure response reaches its extreme value, the main control module marks the current variable load transient feature extraction cycle as an invalid cycle and does not use the data of this cycle to perform feature point mapping of the subsequent two-dimensional state discrimination plane.

[0064] S203, the main control module constructs dynamic volumetric stiffness characterization parameters to characterize the dynamic volumetric response characteristics of the hydraulic oil source based on the correspondence between the theoretical output flow rate change and the main oil circuit pressure response during the variable load transient process. .

[0065] Fluid continuity relationships indicate that pressure changes in a hydraulic system are related to the net flow rate entering the pressurized volume, the effective bulk modulus, and the equivalent pressurized volume. Considering that the compressibility of the hydraulic oil, internal leakage, pipeline volume, and the dynamic response of the power source in a real system all affect the pressure build-up characteristics during variable load processes, this embodiment does not include... It is used as a direct measurement of the actual physical volumetric stiffness, and as a dynamic characteristic parameter characterizing the transient pressure response capability of the hydraulic oil source.

[0066] The main control module extracts the maximum absolute value of the actual pressure change rate and the maximum absolute value of the theoretical output flow rate change within the current variable load transient characteristic extraction period, and calculates the dynamic volumetric stiffness characterization parameters according to the following formula. : ; In the formula, This is a parameter characterizing dynamic volumetric stiffness; This represents the maximum absolute value of the actual pressure change rate in the main oil circuit within the current variable load transient feature extraction period. The maximum absolute value of the theoretical output flow rate change rate within the same variable load transient feature extraction period; The theoretical output flow rate calculated in step S103; This represents the theoretical output flow rate change rate. The dimensions are determined by the units used for the actual pressure and theoretical output flow rate of the main oil circuit.

[0067] In calculation Previously, the main control module would effective lower limit of preset flow rate change Comparison. When Less than When this occurs, it indicates that the current theoretical output flow change is insufficient to form an effective transient response reference. The main control module marks the current variable load transient characteristic extraction cycle as an invalid cycle and does not execute it. The ratio is calculated to avoid the calculation result being abnormally amplified due to an excessively small denominator.

[0068] in, The effective lower limit of the theoretical output flow rate change rate is determined based on the flow fluctuation range under normal operating conditions, the displacement measurement resolution of the variable mechanism, and the motor speed measurement resolution, and is pre-stored in the main control module.

[0069] Under the condition that the current variable load transient feature extraction cycle is effective, the dynamic volumetric stiffness characterization parameters Used to characterize the degree of transient pressure change in the main oil circuit corresponding to a unit change in theoretical output flow rate, and compared with the transient pressure response hysteresis time. Together they serve as input parameters for the subsequent two-dimensional state discrimination plane.

[0070] See attached document Figure 5 In step S300, the main control module constructs a two-dimensional state discrimination plane based on the dynamic volumetric stiffness characterization parameters and transient pressure response hysteresis time obtained in step S200, and determines the current state of the hydraulic oil source through the positional relationship between the current feature point and the preset state boundary. Specifically, this includes the following steps.

[0071] S301, the main control module constructs a two-dimensional state discrimination plane, and the two-dimensional state discrimination plane uses dynamic volumetric stiffness to characterize parameters. The horizontal axis represents the transient pressure response hysteresis time. The vertical axis is denoted as .

[0072] Within the equipment calibration range corresponding to this embodiment, when the dynamic pressure response capability of the hydraulic oil source decreases, the dynamic volumetric stiffness characterization parameter... Typically, this reduces the transient pressure response hysteresis time. The corresponding increase. Based on the dynamic volumetric stiffness characterization parameters With transient pressure response hysteresis time The main control module, in conjunction with the dynamic response relationship of the hydraulic system and the bench calibration parameters of the same model of equipment, sets the first state boundary and the second state boundary in the two-dimensional state discrimination plane to determine the relationship between them.

[0073] Specifically, the main control module acquires the moment when the actual pressure change rate of the main oil circuit reaches the effective extreme value determined in step S202. The corresponding theoretical effective bulk modulus of elasticity, and denoted as The main control module is based on the theoretical effective bulk modulus. Equivalent volume of main oil circuit Dynamic volumetric stiffness characterization parameters And pre-calibrated boundary parameters, respectively, determine the first state boundary function and the second state boundary function.

[0074] The first-state boundary function is expressed as: ; The second-state boundary function is expressed as: ; In the formula, The threshold value for the first transient pressure response hysteresis time is used to divide the normal state region and the critical state region. The second transient pressure response hysteresis time threshold is used to distinguish between the critical state region and the severe fault region; This is the first state boundary function; This is the boundary function for the second state; These are the dynamic volumetric stiffness characterization parameters obtained in step S203; The equivalent volume of the main oil circuit; The moment when the actual pressure change rate of the main oil circuit reaches its effective extreme value The corresponding theoretical effective bulk modulus; and They are the first boundary calibration coefficient and the second boundary calibration coefficient, respectively, and satisfy the following conditions: ; This is the system's inherent time offset parameter.

[0075] Among them, the system's inherent time offset parameters This is used to characterize the fixed response hysteresis of the variable mechanism, the fixed response hysteresis of the sensor, and the time deviation caused by the fixed hydraulic propagation path. The fixed hysteresis component, which has already undergone time compensation in step S101, will not be counted again. .

[0076] When the actual pressure of the main oil circuit is calculated using pressure units, the theoretical output flow rate is calculated using volume units consistent with the equivalent volume of the main oil circuit, and a unified time unit is used for calculation, the result obtained in step S203 is... and The product of these has the dimension of time.

[0077] First boundary calibration coefficient Second boundary calibration coefficient Dimensionless calibration coefficients were used. During the bench calibration of the same type of hydraulic equipment, normal state, preset performance degradation state, and severe performance degradation state were set respectively. Multiple variable load tests were performed, and the dynamic volumetric stiffness characterization parameters under each state were obtained. and transient pressure response hysteresis time Based on the principle of distinguishing between normal state samples and preset performance degradation state samples using the first state boundary, and distinguishing between preset performance degradation state samples and severely performance degradation state samples using the second state boundary, the following is determined: and and make .

[0078] The main control module divides the two-dimensional state discrimination plane into a normal state region, a critical state region, and a severe fault region based on the first and second state boundary functions. The normal state region indicates that the transient pressure build-up hysteresis and dynamic pressure response capability of the hydraulic oil source are within the normal calibration range. The critical state region indicates that the dynamic response characteristics deviate from the normal range but have not yet reached the level of a severe fault, requiring further confirmation through active micro-amplitude excitation frequency domain verification. The severe fault region indicates that the degradation of the dynamic response characteristics has exceeded the second state boundary, reaching the trigger condition for fault degradation control.

[0079] If the transient pressure response hysteresis time corresponding to the current feature point satisfies: ; Then it is determined that the current feature point is located in the normal state area.

[0080] If the transient pressure response hysteresis time corresponding to the current feature point satisfies: ; Then it is determined that the current feature point is located in the critical state region.

[0081] If the transient pressure response hysteresis time corresponding to the current feature point satisfies: ; Then it is determined that the current feature point is located in a severe fault zone.

[0082] Equivalent volume of main oil circuit First boundary calibration coefficient Second boundary calibration coefficient and the system's inherent time offset parameters The parameters are determined by the structural parameters of the same type of hydraulic equipment and bench test data, and are pre-stored in the main control module.

[0083] Among them, the equivalent volume of the main oil circuit This refers to the connected pressurized oil volume corresponding to the pressure detection location of the high-frequency pressure sensor, which participates in the compression response during pressure changes. For the pipeline section, the oil volume inside the pipe is calculated based on the inner diameter and length of each connecting pipe segment; for the internal cavity of the hydraulic component, the corresponding pressurized volume is determined based on the structural dimensions or factory volume parameters of the hydraulic component, and the volumes of all pressurized oil connected to the pressure detection location are added together to obtain the final volume. .

[0084] System inherent time offset parameters Determined through bench testing on normal hydraulic equipment, this method characterizes the fixed response hysteresis of uncompensated variable mechanisms, fixed response hysteresis of sensors, and time offset caused by fixed hydraulic propagation paths; obtained under multiple normal operating conditions. and After the corresponding data is obtained, the fixed time offset is calibrated according to the time relationship between the first state boundary and the second state boundary.

[0085] First boundary calibration coefficient Second boundary calibration coefficient Based on the bench test data of the aforementioned normal state, preset performance degradation state, and severe performance degradation state, the first state boundary is determined such that it is located between the normal state sample and the preset performance degradation state sample, and the second state boundary is located between the preset performance degradation state sample and the severe performance degradation state sample.

[0086] S302, the main control module will use the dynamic volumetric stiffness characterization parameters obtained from the current variable load transient feature extraction cycle. and transient pressure response hysteresis time Composition of current feature points The current feature point is then compared with the first and second state boundaries determined in step S301 to determine the state region where the current feature point is located.

[0087] When the current feature point is in the normal state zone, the main control module determines that the current detection result does not meet the state judgment condition of abnormal dynamic response performance of hydraulic oil source, maintains the current pressure and flow control, and ends the current variable load transient feature extraction cycle.

[0088] When the current feature point is in the critical state region, the main control module determines that the current dynamic volumetric response feature has deviated from the normal state. Since the feature deviation may be caused by transient fluctuations during extreme load changes, or may be related to changes in oil state or internal leakage of the hydraulic system, the main control module does not directly output a fault alarm signal. Instead, after the current transient feature extraction cycle of the variable load ends, it further determines whether the hydraulic system has recovered to a stable state that meets the dynamic test requirements.

[0089] Specifically, the main control module continuously monitors the actual displacement change rate of the variable mechanism and the actual pressure change rate of the main oil circuit within a preset waiting time. When both fall back to their corresponding preset stable ranges, the main control module enters the frequency adaptive active micro-amplitude test excitation and frequency domain separation verification process in step S400. If the two do not fall back to their corresponding preset stable ranges simultaneously after the preset waiting time has elapsed, the frequency domain verification is not performed, and the status determination is re-performed in subsequent detection cycles.

[0090] The preset stability range is used to exclude obvious variable load transient processes, and its value is determined based on the fluctuation range of the actual displacement change rate of the variable mechanism and the actual pressure change rate of the main oil circuit during normal steady-state operation of the hydraulic system; the preset waiting time is determined based on the allowable time required for the hydraulic system to recover from the variable load transient process to the stable operating state.

[0091] When the current feature point is located in the severe fault zone, the main control module determines that the dynamic response characteristics of the current hydraulic oil source have reached the judgment conditions of a severe fault state, and enters the fault degradation control linkage process in step S500 to limit the maximum displacement command limit of the power source module and the maximum set pressure limit of the control valve module.

[0092] See attached document Figure 6 In step S400, after step S300 determines that the current feature point is in the critical state region and the hydraulic system has recovered to a stable state that meets the dynamic test requirements, the main control module adaptively selects the dynamic test frequency based on the variable pump flow pulsation frequency, applies a micro-amplitude sinusoidal test excitation to the main oil circuit through the control valve module, and separates and extracts the pressure response at the test frequency to further determine whether the dynamic response performance of the hydraulic oil source has deteriorated. Specifically, this includes the following steps.

[0093] S401, the main control module calculates the fundamental frequency of the variable pump flow pulsation and its harmonic frequencies based on the current actual speed of the motor and the number of plungers in the power source module.

[0094] During operation, the electro-hydraulic servo variable pump sequentially completes the oil suction and discharge processes according to the pump shaft rotation cycle, thus forming periodic flow pulsations related to the motor speed and the number of plungers. The main control module uses the actual motor speed obtained at the current sampling time... The fundamental frequency of the variable pump flow pulsation is calculated according to the following formula. : ; In the formula, The fundamental frequency of the flow pulsation of the variable pump, in Hz; The actual speed of the motor at the current sampling time, when When the unit is revolutions per minute, the constant 60 is used to convert the rotational speed to revolutions per second; Z is the number of plungers in the power source module that participate in the periodic oil intake and exhaust.

[0095] After obtaining the fundamental frequency of the variable pump flow pulsation, the main control module calculates the corresponding harmonic frequencies of each order according to the following formula: ; In the formula, Let k be the harmonic frequency of the k-th order variable pump flow pulsation; k is the harmonic order, taken as a positive integer. The main control module pre-sets the highest harmonic order to be analyzed. And for k=1,2,…, The corresponding frequency is tracked, where k=1 corresponds to the fundamental frequency of the variable pump flow pulsation. Based on the flow pulsation spectrum characteristics of the variable pump and the permissible test excitation frequency band, in specific implementation, the first three to the first five harmonics that can cover the main flow pulsation energy frequency range can be selected.

[0096] Number of plungers Z and highest harmonic order The preset parameters corresponding to the power source module are stored in the main control module.

[0097] S402, the main control module selects a dynamic test frequency within the allowable test excitation frequency band of the control valve module, so that the dynamic test frequency maintains a preset minimum frequency avoidance interval with the variable pump flow pulsation fundamental frequency and the harmonic frequencies of each order to be analyzed.

[0098] Based on the dynamic response capability of the electro-proportional relief valve, the permissible test excitation frequency band is predetermined. .in, To allow the lower limit frequency of the test excitation band, The upper limit of the allowed test excitation frequency band is determined based on the frequency response test results of the electro-proportional relief valve and its drive circuit, and is pre-stored in the main control module.

[0099] The main control module searches for the step size according to a preset frequency. Generate candidate test frequencies within the allowed test excitation frequency band. The frequency intervals between the candidate test frequency and the fundamental frequency of the variable pump flow pulsation, as well as the harmonic frequency to be analyzed, are calculated respectively. The candidate test frequency should satisfy: ; In the formula, Candidate test frequencies; For the first The flow pulsation frequency of a variable pump; The highest harmonic order to be analyzed; The frequency clearance interval currently used is used to limit the minimum frequency distance that should be maintained between the candidate test frequency and the flow pulsation frequency of each variable pump.

[0100] When multiple candidate test frequencies meet the above conditions, the main control module compares the minimum distance between each candidate test frequency and the most recent variable pump flow pulsation frequency, and selects the candidate test frequency with the largest minimum distance as the dynamic test frequency. ,Right now: ; In the formula, The selected dynamic test frequency; Candidate test frequencies; A set of candidate test frequencies that meet the requirements of the permissible test excitation frequency band and the minimum frequency clearance interval; is the frequency of the k-th order variable pump flow pulsation; k is the harmonic order. The highest harmonic order used in dynamic test frequency avoidance judgment; Indicates the set of candidate test frequencies The candidate test frequency that makes the minimum frequency interval within the parentheses reach its maximum value is selected.

[0101] Preset minimum frequency avoidance interval The effective half-bandwidth and transition bandwidth are determined based on the subsequent bandpass filtering process to ensure that the pressure response at the test frequency can be separated from the frequency components of the flow pulsation of adjacent variable pumps.

[0102] When the allowed test excitation frequency band does not contain the current requirement When the required candidate test frequency is selected, the main control module reduces the frequency avoidance interval according to the preset adjustment step size, but the adjusted frequency avoidance interval must not be less than the preset minimum allowable frequency avoidance interval. ,and The minimum frequency separation condition required for subsequent bandpass filtering should still be met.

[0103] When the frequency avoidance interval is reduced to If a suitable dynamic test frequency cannot be obtained after the test, the main control module will not perform the current dynamic test and will re-execute the dynamic test frequency selection after the actual speed of the motor changes or after entering the next test cycle.

[0104] S403, Determine the dynamic test frequency Then, the main control module determines whether the electro-proportional relief valve and hydraulic system currently meet the test excitation application conditions.

[0105] The main control module determines whether the electro-proportional relief valve is within the pre-calibrated dynamic pressure regulation range based on the current pressure regulation command, and checks whether the actual displacement change rate of the variable mechanism and the actual pressure change rate of the main oil circuit are within the preset stable range of step S302. The dynamic pressure regulation range is determined through a pre-calibration test of the electro-proportional relief valve: under normal hydraulic system operation, the pressure regulation command of the electro-proportional relief valve is changed step by step, and the main oil circuit pressure response corresponding to each pressure regulation command is recorded. Low command ranges where the valve port does not form an effective pressure regulation response and saturation ranges close to the maximum pressure regulation capacity are excluded, and the intermediate range where changes in the pressure regulation command can cause a continuous and stable pressure response is determined as the dynamic pressure regulation range. When the electro-proportional relief valve is within the dynamic pressure regulation range, and both the actual displacement of the variable mechanism and the actual pressure of the main oil circuit have reached a stable state, the main control module generates a frequency of... The small-amplitude sinusoidal test excitation signal.

[0106] The small-amplitude sinusoidal test excitation signal can be expressed as: ; In the formula, For a moment The small-amplitude sinusoidal test excitation signal; To test the amplitude of the excitation signal; For dynamic testing frequency; To test the duration of the stimulus process.

[0107] The main control module superimposes the micro-amplitude sinusoidal test excitation signal onto the basic pressure regulation command of the control valve module. The superimposed control command is expressed as follows: ; In the formula, This is a superimposed control command sent to the control valve module; This is the baseline pressure adjustment command when no test stimulus is applied; This is a small-amplitude sinusoidal test excitation signal.

[0108] Test excitation signal amplitude Based on the control response characteristics of the electro-proportional relief valve and the detection resolution of the high-frequency pressure sensor, pre-calibration is performed, and the following conditions are met: ; In the formula, The minimum test excitation amplitude required to enable the electro-proportional relief valve to produce a pressure response that can be effectively identified by a high-frequency pressure sensor; The maximum test excitation amplitude that will not cause the base pressure of the main oil circuit to deviate from the allowable range of variation.

[0109] Micro-amplitude sinusoidal test excitation signal duration preset number A complete cycle, corresponding test duration for: ; In the formula, The duration of a single test stimulus; The preset number of complete incentive cycles; This refers to the dynamic testing frequency. The value of should be chosen so that the pressure response at the test frequency has a sufficient stable data segment for subsequent amplitude extraction.

[0110] After receiving the superimposed control command, the control valve module generates a dynamic test frequency for the electro-proportional relief valve. The corresponding minute periodic adjustment action, thereby applying a small pressure disturbance with a known test frequency to the main oil circuit without changing the basic pressure control target of the main oil circuit.

[0111] During the test excitation, the main control module continuously acquires the main oil circuit pressure signal collected by the high-frequency pressure sensor, and recalculates the variable pump flow pulsation fundamental frequency and its harmonic frequencies based on the real-time updated actual motor speed.

[0112] When the actual speed of the motor changes, the dynamic test frequency is affected. When the interval between the frequency of the flow pulsation of any variable pump to be analyzed no longer meets the current minimum frequency clearance requirement, the main control module cancels the current micro-amplitude sinusoidal test excitation signal, stops the current pressure response amplitude extraction, and re-executes step S402 for dynamic test frequency selection.

[0113] When the minimum frequency clearance requirement is still met between the dynamic test frequency and the variable pump flow pulsation frequency, the main control module sets the center frequency of the bandpass filter to the current dynamic test frequency. The filter bandwidth is set according to the interval between the dynamic test frequency and the most recent variable pump flow pulsation frequency.

[0114] Let the effective half-bandwidth of the bandpass filter be... The transition bandwidth is Then its frequency setting satisfies: ; In the formula, To use dynamic test frequency The effective passband half-width centered on the center; This represents the transition bandwidth of the bandpass filter from the passband to the stopband. Through the aforementioned frequency constraints, the variable pump flow pulsation frequency is ensured to be outside the filter passband corresponding to the test frequency.

[0115] The main control module uses bandpass filtering to suppress low-frequency baseline pressure fluctuations and variable pump flow pulsation frequency components in the main oil circuit pressure signal, obtaining a dynamic test frequency. The pressure response signal is identified by its primary frequency components, and the actual pressure response amplitude is extracted using envelope detection. .

[0116] in, This refers to the pressure response amplitude at the test frequency generated by the hydraulic oil source in response to a micro-sinusoidal test excitation signal under the current operating conditions.

[0117] S404, the main control module determines the corresponding reference pressure response amplitude based on the current hydraulic oil temperature, the actual pressure of the main oil circuit and the dynamic test frequency, and judges the dynamic response performance based on the ratio between the actual pressure response amplitude and the reference pressure response amplitude.

[0118] The main control module pre-stores a three-dimensional reference response calibration table. The three-dimensional reference response calibration table uses hydraulic oil temperature, main oil circuit base pressure and dynamic test frequency as input parameters, and the reference pressure response amplitude under the corresponding working condition as the output parameter.

[0119] During the test, the main control module adjusts the current hydraulic oil temperature... Actual pressure of main oil circuit and dynamic test frequency The reference pressure response amplitude is determined according to the following correspondence. : ; In the formula, This represents the baseline pressure response amplitude under the current temperature, pressure, and test frequency conditions. This indicates the pre-calibrated correspondence between three-dimensional reference responses; The current hydraulic oil temperature; This represents the current actual pressure of the main oil circuit; This represents the current dynamic testing frequency.

[0120] when , or When located between adjacent calibration nodes, the main control module interpolates the reference pressure response data of the adjacent calibration nodes to obtain the corresponding... The effective calibration range is the hydraulic oil temperature range, main oil circuit pressure range, and dynamic test frequency range that were actually calibrated when establishing the three-dimensional reference response calibration table, denoted as follows: , and Each upper and lower limit is determined by the minimum and maximum calibration nodes of the corresponding calibration parameters, respectively. When the current temperature, the actual pressure of the main oil circuit, or the dynamic test frequency is not within the corresponding calibration range mentioned above, the main control module will mark this frequency domain verification as invalid and will not make fault judgments based on data that exceeds the calibration range.

[0121] The three-dimensional reference response calibration table is obtained by pre-calibrating a hydraulic device with the same structure and parameter configuration as the hydraulic device under test. During calibration, hydraulic oil that meets the preset normal state requirements is used, and test excitations are applied under different hydraulic oil temperatures, main oil circuit pressures, and test frequencies, and the corresponding pressure response amplitudes are recorded.

[0122] To ensure the comparability of field test data with benchmark data, the benchmark calibration process and the field testing process use the same test excitation amplitude, test excitation duration, dynamic pressure regulation operating range of the electro-proportional relief valve, high-frequency pressure sensor installation location, and pressure response filtering and amplitude extraction methods. The obtained calibration data is pre-stored in the main control module.

[0123] When the reference pressure response amplitude Greater than the preset effective lower limit At that time, the main control module calculates the frequency domain response amplitude ratio according to the following formula. : ; In the formula, This is the ratio of the frequency domain response amplitude; This is the actual pressure response amplitude extracted during the current testing cycle; This represents the reference pressure response amplitude corresponding to the current temperature, pressure, and dynamic testing frequency.

[0124] when At this time, the main control module marks the current frequency domain verification period as invalid, does not perform the frequency domain response amplitude ratio calculation, and cancels the micro-amplitude sine test excitation signal superimposed on the pressure regulation command.

[0125] The main control module will calculate the frequency domain response amplitude ratio. With preset alarm threshold A comparison is made, in which: ; When the following conditions are met: ; When the main control module determines that the dynamic pressure response performance of the current hydraulic oil source has reached the fault alarm condition, it outputs a fault alarm signal.

[0126] when When the main control module determines that the frequency domain verification result does not meet the fault alarm conditions, it cancels the micro-amplitude sine test excitation signal superimposed on the pressure regulation command, restores the basic pressure regulation command, and ends the frequency domain verification cycle.

[0127] alarm threshold By pre-calibrating, the lower limit of the frequency domain response amplitude ratio under normal conditions of hydraulic equipment of the same model was obtained. The upper limit of the ratio of frequency domain response amplitude to the preset abnormal state In order to satisfy At that time, Set between the two, and ensure that it is not lower than the minimum permissible frequency response amplitude ratio corresponding to the minimum allowable dynamic response performance of the hydraulic equipment. .

[0128] It should be noted that the decrease in frequency domain response amplitude ratio can reflect the decline in the overall dynamic response performance of hydraulic oil source caused by factors such as increased gas content in hydraulic oil, changes in oil state, and increased internal leakage of the system. However, this embodiment does not further distinguish specific fault types based on the single frequency domain response amplitude ratio result.

[0129] When the frequency domain response amplitude ratio reaches the fault alarm condition, the main control module first cancels the micro-amplitude sine test excitation signal, then outputs the fault alarm signal, and enters the fault degradation control linkage process in step S500.

[0130] See attached document Figure 7 In step S500, when step S300 determines that the current feature point is located in a severe fault zone, or when step S400 outputs a fault alarm signal, the main control module determines a safety limit coefficient based on the deviation of the dynamic volumetric stiffness characterization parameter from the normal reference characterization parameter, and limits the maximum displacement command limit of the power source module and the maximum set pressure limit of the control valve module based on the safety limit coefficient. Specifically, this includes the following steps.

[0131] S501, the main control module calculates the basic safety limit coefficient based on the deviation of the dynamic volumetric stiffness characterization parameter, and determines the final safety limit coefficient in combination with the triggering conditions of the fault degradation control linkage.

[0132] The main control module obtains the dynamic volumetric stiffness characterization parameters calculated in step S203. And obtain the normal reference characterization parameters corresponding to the current hydraulic equipment model and the current working range. The deviation of the characterization parameter is calculated according to the following formula. : ; In the formula, This represents the deviation of the dynamic volumetric stiffness characterization parameter from the normal reference characterization parameter; These are the pre-calibrated normal reference characterization parameters for the current hydraulic equipment within the corresponding working range; These are the current dynamic volumetric stiffness characterization parameters obtained in step S203.

[0133] when Not less than At that time, that is The basic safety limit factor remains at 1; when At this time, the main control module reduces the basic safety limit coefficient proportionally based on the deviation of the characterization parameters and imposes a lower limit on the calculation results. Basic safety limit coefficient Determined according to the following formula: ; In the formula, Basic safety limit factor; This is a system degradation mapping ratio coefficient used to determine the proportional relationship between the deviation of the dynamic volumetric stiffness characterization parameter and the degree of reduction in output capability; To preset the minimum safety limit factor, and satisfy ; This indicates that the larger value among the parameters within the parentheses is selected.

[0134] because It is a dimensionless proportionality constant, therefore Dimensions and Corresponding to the reciprocal; when for and When normalization is performed in the same way, It can be set as a dimensionless calibration coefficient accordingly.

[0135] The main control module further determines the final safety limit coefficient based on the trigger source of the fault degradation control linkage. .

[0136] When the fault degradation control linkage is triggered only by entering the severe fault zone from the current feature point, the final safety limit factor is determined according to the following formula: ; When the fault degradation control linkage is triggered solely by the fault alarm signal output in step S400, the final safety limit factor is determined according to the following formula: ; When the current feature point is located in a severe fault zone and step S400 simultaneously outputs a fault alarm signal, the final safety limit factor is determined according to the following formula: ; In the formula, This is the final safety limit factor; This is the critical fault limitation factor; This is the fault alarm limit coefficient; This indicates that the minimum value among the parameters within the parentheses should be taken. Both the critical fault limit coefficient and the fault alarm limit coefficient are less than 1, and not lower than the minimum safety limit coefficient allowed by the system. .

[0137] Through the above processing, in the event of a severe fault or frequency domain verification failure, the final safety limit factor is... Keep it less than 1 to put the hydraulic oil source into a degraded operation state; if the fault degrade control linkage of step S500 is not triggered, the above output limit is not executed, and the hydraulic system maintains the original control upper limit.

[0138] Normal reference characterization parameters System degradation mapping ratio coefficient Minimum safety limit factor Severe Fault Limitation Factor and fault alarm limit coefficient The parameters are determined based on the bench calibration results of the same type of hydraulic equipment and are pre-stored in the main control module. When the normal dynamic response characteristics differ across different operating ranges, the main control module retrieves the corresponding normal baseline characterization parameters according to the current operating range. .

[0139] S502, the main control module is based on the final safety limit factor. Adjust the maximum displacement command limit of the power source module and the maximum set pressure limit of the control valve module respectively.

[0140] The main control module obtains the preset maximum displacement command limit under normal operating conditions of the hydraulic system. and the original maximum pressure limit The maximum displacement command limit under fault degradation state is calculated according to the following formula: ; The maximum set pressure limit under fault degradation conditions is calculated using the following formula: ; In the formula, This represents the maximum allowable displacement command for the variable pump under fault degradation conditions. The preset upper limit of the original maximum displacement command of the variable pump under normal operating conditions of the hydraulic system; Set the maximum allowable pressure limit for the electro-proportional relief valve under fault degradation conditions; The preset maximum pressure limit of the electro-proportional relief valve under normal operating conditions of the hydraulic system; The final safety limit coefficient determined in step S501.

[0141] After completing the above calculations, the main control module updates the control command limiting parameters of the power source module and the control valve module, ensuring that the displacement command of the variable mechanism sent to the power source module does not exceed the limit. And ensure that the pressure setting command sent to the control valve module does not exceed Therefore, in the event of a severe fault or a confirmed fault in the frequency domain verification, the maximum displacement output capacity of the power source module and the maximum allowable pressure setting value of the control valve module are limited respectively.

[0142] The following is a specific numerical example of the system in actual operation, using the variable load condition of the mold clamping hydraulic circuit of a 1000-ton injection molding machine as an example: (1) S100 status synchronous acquisition and basic parameter calculation: See attached document Figure 8When the system is in the pressure holding preparation stage, the acquisition module synchronously obtains the current motor speed as 1500 rpm, hydraulic oil temperature as 45℃, actual pressure of main oil circuit as 15.0 MPa, and displacement signal of variable mechanism as 80% (corresponding to theoretical maximum single-rotation displacement of 100 mL / r).

[0143] Based on the internally stored ISOVG46 hydraulic oil property parameter table, the main control module directly calculates that the theoretical effective bulk modulus of pure hydraulic oil under the current working conditions is 1650MPa, and the current theoretical output flow rate of the power source module is 120L / min.

[0144] (2) Extraction of transient features of S200 variable load: See attached document Figure 9 When the injection molding machine performs a high-pressure mold closing action, the load changes abruptly. The main control module detects that the actual displacement change rate of the variable mechanism reaches 150% / s, exceeding the preset trigger threshold (50% / s), and the system immediately enters the variable load transient feature extraction cycle.

[0145] Within the sliding data window, the main control module locks the moment when the actual displacement change rate of the variable mechanism reaches its extreme value at 1.250 seconds, and then captures the moment when the actual pressure change rate of the main oil circuit reaches its extreme value (200 MPa / s) at 1.285 seconds. The time difference between the two is the transient pressure response hysteresis time, which is 35 ms. Simultaneously, based on the maximum absolute value of the maximum pressure change rate and the theoretical output flow rate change rate, the dynamic volumetric stiffness characterization parameter is obtained as 0.42 MPa / (L / min).

[0146] (3) S300 two-dimensional state phase plane discrimination: See attached document Figure 10 The main control module calls a two-dimensional state boundary model calibrated based on the same model of injection molding machine (the equivalent volume is known to be 20L, and the system's inherent hysteresis is 10ms). The judgment results show that, under the premise that the dynamic volumetric stiffness characterization parameter is 0.42MPa / (L / min), the hysteresis time in the normal state should be less than 25ms, and the hysteresis time in the severe fault boundary should be greater than 50ms.

[0147] Since the current extraction hysteresis time is 35ms, the feature point (0.42, 35) falls right into the critical state region, indicating that the dynamic pressure build-up capability of the hydraulic oil source has shown a suspicious decline (there may be an early increase in gas content or slight internal leakage).

[0148] (4) S400 frequency adaptive micro-amplitude excitation and frequency domain verification: See attached document Figure 11 To further confirm whether performance degradation has occurred, the system automatically initiates a verification test after the mold closing pressure stabilizes.

[0149] The main control module consulted a table and found that the pump has 9 plungers. Based on the current speed of 1500 rpm, the fundamental frequency of the variable pump flow pulsation was determined to be 225 Hz, and the second harmonic was 450 Hz. To ensure that the frequency avoidance interval is greater than 50 Hz, the main control module adaptively selected 340 Hz as the dynamic test frequency within the allowable frequency range (100 Hz-500 Hz) of the electro-proportional relief valve.

[0150] The system superimposed a 340Hz micro-amplitude sinusoidal test excitation with a duration of 0.5 seconds and an amplitude of 0.5MPa onto the pressure regulation command. After bandpass filtering, the actual pressure response amplitude at 340Hz was obtained as 0.32MPa.

[0151] Consulting the three-dimensional reference response calibration table, it was found that the standard response amplitude of a 340Hz excitation at 45℃ and 15.0MPa should be 0.45MPa. The frequency domain response amplitude ratio is 0.32 / 0.45=0.71, which is lower than the preset alarm threshold of 0.8. The system accurately outputs a fault alarm signal, confirming that the decrease in dynamic stiffness is caused by oil emulsification with gas.

[0152] (5) S500 fault-tolerant control linkage and safety protection: Due to the triggering of a fault alarm, the main control module generated a safety limit factor of 0.85. The system immediately implemented degraded control, limiting the maximum displacement command limit of the power source from 100% to 85%, and the maximum set pressure from 25MPa to 21.25MPa, effectively preventing system collapse or secondary damage caused by operating at extreme limits while malfunctioning.

[0153] To verify the effectiveness and advancement of this invention, a comparative verification experiment was conducted on a comprehensive hydraulic test bench equipped with an electro-hydraulic servo pump power source. The experiment tested the "traditional fixed pressure threshold early warning method" and the "variable load dynamic phase plane and frequency domain verification early warning method of this invention".

[0154] The experiment simulated two typical hidden faults in a hydraulic system during long-term operation: Fault A (oil deterioration and gas content): By injecting a small amount of air into the main oil tank, the air content of the hydraulic oil gradually increases from the normal 0.5% to 5.0%.

[0155] Fault B (minor internal wear and leakage in the pump): A bypass parallel adjustable flow valve is connected to simulate the gradually increasing internal leakage at the pump inlet over time.

[0156] Comparison of effects data: Comparison of sensitivity of early fault warning: For fault A, since the increase in gas content has a minimal impact on the absolute pressure value under steady state, the traditional method only issues an alarm when the gas content reaches 4.5% (causing severe cavitation noise in the main pump and exceeding the limit of steady-state pressure fluctuation); while the method of this invention successfully issues an early warning 120 working hours in advance when the gas content reaches 1.5%, that is, by extending the transient pressure build-up hysteresis time (the point falls into the critical zone) and decreasing the frequency domain response amplitude ratio (down to 0.75).

[0157] Comparison of false alarm rates under variable load conditions: For frequent step load switching conditions (simulating 5 sudden load changes per minute), traditional methods, unable to distinguish between "normal physical response delay" and "insufficient pressure build-up due to faults," generated 14 false alarms in 1000 consecutive tests. In contrast, the method of this invention, by constructing a "two-dimensional state phase plane" incorporating flow rate and stiffness, allows dynamic characteristic parameters to adaptively match the operating conditions, resulting in a false alarm rate of 0 in 1000 tests.

[0158] This system not only enables online evaluation without affecting the normal operation of the main system, but also has an overwhelming advantage in the advance of identification and the accuracy of judgment of early hidden faults in hydraulic systems, realizing a fundamental transformation from "threshold dead zone alarm" to "dynamic performance prediction".

[0159] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for early warning of hydraulic oil source pressure under variable load conditions, characterized in that, Includes the following steps: The system collects hydraulic system operating status parameters, including the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the hydraulic oil temperature. It identifies variable load transient conditions based on the rate of change of the actual displacement signal of the variable mechanism. Under these transient conditions, it determines the transient pressure response hysteresis time based on the time difference between the moment when the rate of change of the actual displacement signal of the variable mechanism reaches its extreme value and the moment when the rate of change of the actual pressure of the main oil circuit reaches its corresponding extreme value. Furthermore, it determines dynamic volumetric stiffness characterization parameters based on the relationship between the rate of change of the actual pressure of the main oil circuit and the rate of change of the theoretical output flow rate determined based on the actual speed of the motor and the actual displacement signal of the variable mechanism. The transient pressure response hysteresis time and the dynamic volumetric stiffness characterization parameter are mapped to a preset two-dimensional state phase plane for discrimination. The two-dimensional state phase plane uses the dynamic volumetric stiffness characterization parameter as the abscissa and the transient pressure response hysteresis time as the ordinate. It is divided into normal state region, critical state region and severe fault region by the first state boundary and the second state boundary. When the feature point falls into the critical state region, active micro-amplitude excitation frequency domain verification is triggered. In the active micro-amplitude excitation frequency domain verification, the fundamental frequency of the variable pump flow pulsation and its harmonic frequencies are determined based on the current actual motor speed and the number of plungers in the hydraulic pump. The test excitation frequency is determined under the condition of avoiding the fundamental frequency of the variable pump flow pulsation and its harmonic frequencies. A micro-amplitude excitation signal is injected into the hydraulic system according to the test excitation frequency. The actual pressure of the main oil circuit is frequency-domain separated to obtain the actual pressure response amplitude at the test excitation frequency. An early fault alarm signal is generated based on the ratio between the actual pressure response amplitude and the corresponding reference pressure response amplitude.

2. The hydraulic oil source pressure early warning method under variable load conditions according to claim 1, characterized in that, Under the aforementioned variable load transient condition, determining the transient pressure response hysteresis time and the dynamic volumetric stiffness characterization parameter specifically includes: According to the preset sampling period, the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit and the hydraulic oil temperature are synchronously acquired based on a unified time base, and a time correspondence relationship is established for each synchronously acquired operating state parameter; The theoretical effective bulk modulus of the hydraulic oil under the current operating conditions is determined based on the hydraulic oil temperature and the actual pressure of the main oil circuit. The theoretical output flow rate is determined based on the actual speed of the motor and the actual displacement signal of the variable mechanism, combined with the displacement conversion factor of the hydraulic pump.

3. The hydraulic oil source pressure early warning method under variable load conditions according to claim 2, characterized in that, The step of identifying the variable load transient condition based on the rate of change of the actual displacement signal of the variable mechanism and determining the transient pressure response hysteresis time specifically includes: The actual displacement signal of the variable mechanism is monitored in real time. When the absolute value of the rate of change of the actual displacement signal of the variable mechanism reaches or exceeds the preset trigger threshold, the variable load transient feature extraction cycle is entered. Within the time window corresponding to the variable load transient feature extraction cycle, extract the first moment when the rate of change of the actual displacement signal of the variable mechanism reaches its maximum absolute value. Based on the direction of change of the actual displacement signal of the variable mechanism at the first moment, within the preset pressure response search time window after the first moment, search for the extreme value of the actual pressure change rate of the main oil circuit that corresponds to the direction of change and whose absolute value of the pressure change rate reaches the preset effective threshold of the pressure response, and determine the moment corresponding to the extreme value of the actual pressure change rate of the main oil circuit as the second moment. The time difference between the second moment and the first moment is taken as the transient pressure response hysteresis time.

4. The hydraulic oil source pressure early warning method under variable load conditions according to claim 3, characterized in that, The dynamic volumetric stiffness characterization parameters are determined in the following manner: Extract the maximum absolute value of the actual pressure change rate of the main oil circuit and the maximum absolute value of the theoretical output flow rate change within the current variable load transient feature extraction period; When the maximum absolute value of the theoretical output flow rate change is not lower than the preset effective lower limit of the flow rate change, the ratio of the maximum absolute value of the actual pressure change of the main oil circuit to the maximum absolute value of the theoretical output flow rate change is determined as the dynamic volumetric stiffness characterization parameter. When the maximum absolute value of the theoretical output flow rate change is lower than the preset effective lower limit of the flow rate change, the current variable load transient feature extraction period is marked as an invalid period.

5. The hydraulic oil source pressure early warning method under variable load conditions according to claim 2, characterized in that, The first state boundary and the second state boundary are determined based on the dynamic volumetric stiffness characterization parameter, the equivalent volume of the main oil circuit, the theoretical effective bulk elastic modulus corresponding to the effective extreme moment of the actual pressure change rate of the main oil circuit, and the system's inherent time offset parameter, respectively. Wherein, the first transient pressure response hysteresis time threshold corresponding to the first state boundary satisfies: The first transient pressure response hysteresis time threshold is equal to the sum of the product of the system's inherent time bias parameter, the first boundary calibration coefficient, the dynamic volumetric stiffness characterization parameter, and the equivalent volume of the main oil circuit, divided by the theoretical effective bulk modulus. The second transient pressure response hysteresis time threshold corresponding to the second state boundary satisfies: The second transient pressure response hysteresis time threshold is equal to the sum of the product of the system's inherent time bias parameter, the second boundary calibration coefficient, the dynamic volumetric stiffness characterization parameter, and the equivalent volume of the main oil circuit, divided by the theoretical effective bulk modulus. Furthermore, the second boundary calibration coefficient is greater than the first boundary calibration coefficient.

6. The hydraulic oil source pressure early warning method under variable load conditions according to claim 5, characterized in that, When the transient pressure response hysteresis time is less than the first transient pressure response hysteresis time threshold, the feature point is determined to be in the normal state region. When the transient pressure response hysteresis time is not less than the first transient pressure response hysteresis time threshold and less than the second transient pressure response hysteresis time threshold, the feature point is determined to be located in the critical state region. When the transient pressure response hysteresis time is not less than the second transient pressure response hysteresis time threshold, the feature point is determined to be located in the severe fault area; When the feature point is located in the critical state region, after the current variable load transient feature extraction cycle ends, the rate of change of the actual displacement signal of the variable mechanism and the rate of change of the actual pressure of the main oil circuit are continuously detected. When both fall back to the corresponding preset stable range, the active micro-amplitude excitation frequency domain verification is performed.

7. The hydraulic oil source pressure early warning method under variable load conditions according to claim 1, characterized in that, The test excitation frequency is determined in the following way: Based on the currently collected actual motor speed and the number of plungers inside the hydraulic pump, the variable pump flow pulsation fundamental frequency is calculated, and the harmonic frequencies of each order within the preset order range are determined according to the variable pump flow pulsation fundamental frequency. Within the test excitation frequency band allowed by the electro-proportional relief valve, multiple candidate test frequencies are generated according to a preset frequency search step size; From the plurality of candidate test frequencies, select candidate test frequencies whose absolute differences from the variable pump flow pulsation fundamental frequency and the harmonic frequencies of each order are not less than a preset frequency avoidance interval. When there are multiple candidate test frequencies that meet the conditions, the minimum frequency interval between each candidate test frequency and the nearest variable pump flow pulsation fundamental frequency or harmonic frequency is determined, and the candidate test frequency with the largest minimum frequency interval is determined as the test excitation frequency.

8. The hydraulic oil source pressure early warning method under variable load conditions according to claim 7, characterized in that, The process of injecting a micro-amplitude excitation signal into the hydraulic system and generating an early fault alarm signal based on the actual pressure response amplitude specifically includes: When the electro-proportional relief valve is in the preset dynamic pressure regulation working range, and the rate of change of the actual displacement signal of the variable mechanism and the rate of change of the actual pressure of the main oil circuit are both in the corresponding preset stable range, a sinusoidal test signal with a set amplitude and the test excitation frequency is superimposed on the basic pressure regulation command of the electro-proportional relief valve. By using bandpass filtering with the test excitation frequency as the center frequency, the acquired actual pressure signal of the main oil circuit is separated in the frequency domain, and the actual pressure response amplitude is extracted. Based on the current hydraulic oil temperature, the current actual pressure of the main oil circuit, and the test excitation frequency, the corresponding reference pressure response amplitude is determined from the pre-established reference response calibration relationship; Calculate the ratio of the actual pressure response amplitude to the reference pressure response amplitude to obtain the frequency domain response amplitude ratio; When the frequency domain response amplitude ratio is lower than the preset alarm threshold, the early fault alarm signal is generated.

9. The hydraulic oil source pressure early warning method under variable load conditions according to claim 1, characterized in that, After the feature point falls into the severe fault zone or the early fault alarm signal is generated, the method further includes: Obtain the normal reference characterization parameters corresponding to the current hydraulic equipment and the current working range, and determine the safety limit factor based on the deviation of the current dynamic volumetric stiffness characterization parameters from the normal reference characterization parameters; Based on the safety limit coefficient, fault degradation control is performed. The upper limit of the maximum displacement command of the power source under fault degradation state is determined as the product of the safety limit coefficient and the original maximum displacement command upper limit under normal operation state. The upper limit of the highest set pressure under fault degradation state is determined as the product of the safety limit coefficient and the original highest set pressure upper limit under normal operation state. Based on the maximum displacement command limit of the power source and the maximum set pressure limit, the maximum displacement output capacity of the power source module and the maximum pressure setting value of the electro-proportional relief valve are respectively limited.

10. A hydraulic oil source pressure early warning system under variable load conditions, used to execute a hydraulic oil source pressure early warning method under variable load conditions as described in any one of claims 1-9, characterized in that, include: The parameter extraction module is used to collect hydraulic system operating status parameters, including the actual displacement signal of the variable mechanism, the actual speed of the motor, the actual pressure of the main oil circuit, and the hydraulic oil temperature; it identifies variable load transient conditions based on the rate of change of the actual displacement signal of the variable mechanism, extracts the transient pressure response hysteresis time based on the transient response relationship between the actual displacement signal of the variable mechanism and the actual pressure of the main oil circuit, and determines the dynamic volumetric stiffness characterization parameters based on the relationship between the rate of change of the actual pressure of the main oil circuit and the rate of change of the theoretical output flow rate. The state discrimination module is used to map the transient pressure response hysteresis time and the dynamic volumetric stiffness characterization parameters to a preset two-dimensional state phase plane for discrimination. The two-dimensional state phase plane is divided into a normal state region, a critical state region, and a severe fault region by a first state boundary and a second state boundary. When a feature point falls into the critical state region, active micro-amplitude excitation frequency domain verification is triggered. The frequency domain verification and early warning module is used to determine the fundamental frequency and harmonic frequencies of the variable pump flow pulsation based on the actual speed of the motor and the number of plungers inside the hydraulic pump during the active micro-amplitude excitation frequency domain verification. It then determines the test excitation frequency while avoiding the fundamental frequency and harmonic frequencies of the variable pump flow pulsation, injects a micro-amplitude excitation signal into the hydraulic system according to the test excitation frequency, performs frequency domain separation on the actual pressure of the main oil circuit to obtain the actual pressure response amplitude at the test excitation frequency, and generates an early fault alarm signal based on the ratio between the actual pressure response amplitude and the corresponding reference pressure response amplitude.

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