Hydraulic fatigue test apparatus and method for high pressure hydrogen storage cylinders

Abstract

The application discloses a kind of hydraulic fatigue test device and method for high-pressure hydrogen storage bottle, the test device includes oil tank, hydraulic power unit, multistage pressurization unit, hydraulic compensation unit, detection unit and control unit;The oil inlet of hydraulic power unit is connected with oil tank, and the oil outlet is connected with the inlet of multistage pressurization unit by first pipeline;The outlet of multistage pressurization unit is connected with the inlet of hydrogen storage bottle by second pipeline;The outlet of hydrogen storage bottle is connected to oil tank by third pipeline, and pressure relief valve is provided on third pipeline;The cavity of hydraulic compensation unit is connected with second pipeline;Control unit is connected with hydraulic power unit, hydraulic compensation unit, detection unit.This application can realize the pressure stability of ±0.15MPa level, and ensure the high fidelity of fatigue load waveform.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage cylinder testing technology, and particularly relates to a hydraulic fatigue testing device and method for high-pressure hydrogen storage cylinders. Background Technology

[0002] High-pressure hydrogen storage cylinders are key hydrogen storage equipment for hydrogen fuel cell vehicles, and their fatigue life and safety performance directly affect the commercial application prospects of the entire vehicle. Currently, mainstream technologies are focused on the research and testing of hydrogen storage cylinders with pressure ratings of 70 MPa and above. Hydraulic fatigue testing is the core method for evaluating the lifespan and reliability of hydrogen storage cylinders under alternating loads, and its testing accuracy and reliability are crucial for the safety certification of the cylinders.

[0003] Traditional hydraulic fatigue testing equipment typically consists of a hydraulic pump station, a one-way booster cylinder, a solenoid directional valve, a piping system, and a simple controller. Its control strategy usually employs open-loop control or classic PID closed-loop control. However, when faced with testing conditions of 70MPa ultra-high pressure and high-frequency cycling, this traditional technology reveals the following inherent defects, making it difficult to meet the requirements of high-precision testing:

[0004] (1) Low pressure control accuracy and severe waveform distortion: Under ultra-high pressure, the compressibility of the oil is significantly enhanced (isothermal compressibility coefficient β≈5.2×10). -10 Pa -1 Meanwhile, the composite material hydrogen storage cylinder body will undergo significant elastic expansion deformation (circumferential strain) under high pressure. >0.4%). These two factors together lead to a decrease in the system cavity stiffness, making its pressure highly susceptible to overshoot and oscillation. In fatigue testing, this directly manifests as a significant deviation between the actual output pressure curve and the target waveform, with pressure fluctuations typically exceeding ±5% of full scale (FS), severely impacting the accuracy and validity of the test data.

[0005] (2) The system's heat accumulation effect is prominent, affecting test safety and lifespan: To achieve high-efficiency testing, the test frequency is usually required to be higher than 1Hz. At this high frequency, the throttling loss inside the hydraulic system, fluid viscous friction, and the hysteresis effect of the composite hydrogen storage cylinder will generate a large amount of heat. Due to the lack of an effective thermal management mechanism in traditional devices, the heat cannot be dissipated in time, causing the temperature of the surface of the hydrogen storage cylinder and the system oil to rise continuously, with the temperature rise ΔT often exceeding 15℃. Excessive temperature will not only accelerate the aging of the seals and cause leakage, but also change the mechanical properties of the tested hydrogen storage cylinder material, causing the fatigue test results to deviate from the actual working conditions, and may even cause safety risks due to "thermal runaway".

[0006] (3) Inaccurate life prediction model, limited engineering guidance significance: The testing and control strategies of traditional devices are relatively crude and do not fully consider the inherent anisotropic characteristics of composite materials and the nonlinear cumulative effect of fatigue damage. The life prediction model based on ideal assumptions cannot accurately reflect the actual damage evolution process of hydrogen storage cylinders under complex alternating loads, resulting in a deviation of more than 20% between the predicted life and the actual life, making it difficult to provide accurate and reliable data support for the design optimization and safe service life assessment of hydrogen storage cylinders. Summary of the Invention

[0007] The purpose of this invention is to provide a hydraulic fatigue testing device and method for high-pressure hydrogen storage cylinders, so as to solve at least one of the above-mentioned defects.

[0008] This invention solves the above-mentioned technical problems through the following technical solution: a hydraulic fatigue testing device for high-pressure hydrogen storage cylinders, comprising:

[0009] The hydraulic power unit has its oil inlet connected to the oil tank.

[0010] The multi-stage booster unit has its inlet connected to the oil outlet of the hydraulic power unit via a first pipeline, its outlet connected to the inlet of the hydrogen storage cylinder via a second pipeline, and the outlet of the hydrogen storage cylinder connected to the oil tank via a third pipeline. A pressure relief valve is provided on the third pipeline.

[0011] A hydraulic compensation unit, the cavity of which is connected to the second pipeline, and the cavity is pre-filled with hydraulic oil;

[0012] The detection unit is used to detect the instantaneous volumetric elastic deformation, real-time temperature, real-time pressure, and real-time flow rate of the hydrogen storage cylinder.

[0013] The control unit, connected to the hydraulic power unit, hydraulic compensation unit, detection unit, and pressure relief valve, is used to: during the pressurization phase, coordinately control the hydraulic power unit and hydraulic compensation unit based on the instantaneous volumetric elastic deformation, target pressurization rate, initial volume of the hydrogen storage tank, and stable and efficient flow rate to eliminate errors and disturbances and achieve precise pressurization; during the pressure holding phase, control the hydraulic compensation unit based on the real-time temperature and target temperature, or the real-time pressure and target pressure, to eliminate errors caused by temperature changes or internal leakage; and during the pressure relief phase, control the pressure relief valve based on the instantaneous volumetric elastic deformation, target pressure reduction rate, initial volume, and real-time flow rate to achieve smooth and shock-free pressure relief.

[0014] In this embodiment, during the pressurization phase, the control unit calculates the main flow command and the compensation flow command based on the instantaneous volumetric elastic deformation, the target pressurization rate, the initial volume of the hydrogen storage tank, and the stable and efficient flow rate. Based on the main flow command, it controls the hydraulic power unit to operate, providing the basic flow rate to the hydrogen storage tank. Based on the compensation flow command, it controls the hydraulic compensation unit to operate, providing the compensation flow rate to the hydrogen storage tank to eliminate errors and disturbances. During the pressure holding phase, it calculates the first compensation displacement based on the real-time temperature and target temperature, or the real-time pressure and target pressure. Based on the first compensation displacement, it controls the hydraulic compensation unit to operate, eliminating errors caused by temperature changes or internal leakage. During the pressure relief phase, it calculates the opening degree of the pressure relief valve based on the instantaneous volumetric elastic deformation, the target pressure reduction rate, the initial volume, and the real-time flow rate. Based on the opening degree, it controls the pressure relief valve to operate in real-time, achieving smooth and shock-free pressure relief.

[0015] This invention controls the hydraulic power unit according to the main flow command, which delivers oil from the tank to the hydrogen storage cylinder, providing a stable and efficient basic flow rate. It also controls the hydraulic compensation unit according to the compensation flow command, providing a compensation flow rate to the hydrogen storage cylinder and eliminating errors and instantaneous disturbances in real time. This coarse-adjustment + fine-adjustment mode ensures the accuracy of the flow input from the source, thereby achieving precise tracking of the pressure curve and reducing pressure fluctuations from ±5%FS to an extremely high level of ±0.15MPa.

[0016] During the pressure holding phase, any minute temperature change (e.g., thermal expansion and contraction) or pressure leakage can disrupt pressure stability. To address this issue, this invention actively monitors these disturbances (temperature, pressure) and counteracts their impact on the total volume of the hydrogen storage tank by precisely adjusting the displacement of the hydraulic compensation unit. This achieves true static high-precision pressure holding, providing an extremely stable pressure environment for fatigue life testing.

[0017] During the pressure holding phase, temperature is used as the core control variable to adjust the hydraulic compensation unit. This allows the device to not only sense the temperature but also actively offset pressure fluctuations caused by temperature changes through volume compensation. Although it cannot directly cool the pressure, it eliminates the negative impact of temperature changes on pressure, prevents test data distortion and safety risks caused by temperature runaway, and improves the reliability and safety of the test.

[0018] Volumetric elastic deformation is a key parameter that directly reflects the mechanical behavior (stiffness change, etc.) of composite hydrogen storage cylinders under load. High-precision pressure and temperature data eliminate the interference of systematic errors on material behavior analysis. These data can capture the anisotropic response of materials and the process of nonlinear damage accumulation, providing a high-quality data source for accurate life prediction.

[0019] Furthermore, the multi-stage booster unit is a three-stage booster unit, which includes a first accumulator, a second accumulator, and a first-stage booster cylinder, a second-stage booster cylinder, and a third-stage booster cylinder connected in sequence. The inlet of the first-stage booster cylinder is connected to the oil outlet of the hydraulic power unit through a first pipeline, and the outlet of the third-stage booster cylinder is connected to the inlet of the hydrogen storage cylinder through a second pipeline. The first accumulator is connected to the pipeline between the first-stage booster cylinder and the second-stage booster cylinder, and the second accumulator is connected to the pipeline between the second-stage booster cylinder and the third-stage booster cylinder.

[0020] In this embodiment, a multi-stage pressurization unit enables the device to operate at a lower initial pressure while achieving extremely high output pressure. The multi-stage pressurization ensures that each stage only undertakes a portion of the pressurization task, resulting in a more rational piston area ratio, a more compact structure, and reduced load and mass on each piston stage. This leads to smoother movement and reduced inertial impact. Ultimately, this results in lower overall energy consumption, smoother operation, and less noise and vibration, laying the foundation for high-precision pressure control. By rationally allocating the pressurization ratio, the significant pressure difference can be distributed across each stage of the seals, significantly reducing the harshness of the operating conditions for each seal and greatly extending the seal life and maintenance cycle of the entire pressurization unit.

[0021] The core functions of the first and second accumulators are to absorb pressure pulsations, compensate for leaks, and stabilize pressure. Specifically, the first and second accumulators can effectively absorb pressure pulsations generated in their respective stages, preventing them from being transmitted to the next stage or the hydrogen storage tank. At the same time, the first and second accumulators can also compensate for internal leaks, providing replenishment when a large flow rate is needed instantaneously, ensuring pressure stability.

[0022] Preferably, the pressure ratio of the first-stage booster cylinder is 1:10, the pressure ratio of the second-stage booster cylinder is 1:15, and the pressure ratio of the third-stage booster cylinder is 1:20.

[0023] Furthermore, the hydraulic compensation unit includes a compensation cylinder, a drive motor, a linear motion mechanism, and a hydraulically controlled check valve; the drive motor is controlled by the control unit and its output end is connected to the linear motion mechanism; the linear motion mechanism is connected to the piston rod inside the compensation cylinder, and is used to convert the motion of the drive motor into the linear motion of the piston rod;

[0024] The cavity of the compensation cylinder is connected to the second pipeline via the hydraulic check valve.

[0025] In this embodiment, the drive motor (such as a servo motor) receives electrical signal commands from the control unit and drives the linear motion mechanism to convert rotational motion into high-precision linear motion, thereby driving the piston rod in the compensation cylinder to move linearly back and forth. Specifically, during the pressurization stage, the drive motor, according to the compensation flow command, precisely pushes the piston towards the inside of the cylinder through the linear motion mechanism, reducing the volume of the compensation cylinder and thus pumping the oil inside into the second pipeline. This provides a small-flow, high-response compensation flow to the gas storage cylinder, which, combined with the base flow output from the hydraulic power unit, ensures the accuracy and stability of the pressurization process. During the pressure holding stage, the drive motor operates under the command corresponding to the first compensation displacement, pushing the piston rod to make minute reciprocating movements through the linear motion mechanism to maintain constant pressure: when the pressure drops (e.g., the oil temperature decreases or there is a minor leak), the piston rod moves inward, supplementing the main oil circuit with a small amount of high-pressure oil, achieving positive pressure compensation; when the pressure rises (e.g., the oil temperature rises), the piston rod moves outward, receiving a small amount of high-pressure oil from the main oil circuit, achieving negative pressure compensation. During the depressurization phase, the hydraulic compensation unit does not actively control pressure or is in a standby state.

[0026] Furthermore, the test device also includes a heat exchange unit located between the hydraulic power unit and the multi-stage pressurization unit; the control unit is also used to calculate the temperature rise based on the real-time temperature of the hydrogen storage cylinder, and to activate the heat exchange unit when the temperature rise is greater than the temperature rise threshold or the real-time temperature is greater than the temperature threshold, thereby realizing active thermal management.

[0027] By directly reducing the temperature of the oil entering the hydrogen storage cylinder through the heat exchange unit, the temperature rise is effectively controlled within the allowable range, directly solving the problem of heat accumulation. The fatigue performance of the composite material of the tested hydrogen storage cylinder is highly correlated with temperature. By reducing the oil temperature through the heat exchange unit, a test environment close to isothermal or controllable temperature is provided for the hydrogen storage cylinder. This makes the load conditions applied to the hydrogen storage cylinder purer, and the obtained fatigue life data can more accurately reflect its performance under design conditions, improving the accuracy of life prediction.

[0028] Furthermore, the control unit is also used to calculate the material attenuation coefficient based on the peak pressure and valley pressure in each cycle during the cyclic control phase; calculate the real-time pressure amplitude based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; calculate the pressure amplitude attenuation rate based on the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude attenuation rate is greater than a set percentage threshold, calculate the second compensation displacement based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles; and control the hydraulic compensation unit to work based on the second compensation displacement to achieve long-cycle online pressure compensation.

[0029] The initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle, where n ≤ N.

[0030] In this embodiment, the device no longer passively executes a fixed pressure curve, but actively senses the microscopic changes in the hydrogen storage cylinder material and adjusts the test load in real time to compensate for the stiffness reduction caused by material fatigue. This ensures that the pressure amplitude applied to the hydrogen storage cylinder is stable and realistic throughout the fatigue test, thereby improving the test accuracy and the accuracy of life prediction.

[0031] Based on the same concept, the present invention also provides a hydraulic fatigue testing method for high-pressure hydrogen storage cylinders, based on the hydraulic fatigue testing device described above, the testing method including a pressure-increasing stage, a pressure-holding stage and a pressure-releasing stage;

[0032] During the pressurization phase, the instantaneous volumetric elastic deformation of the hydrogen storage cylinder is obtained, and the main flow command and compensation flow command are calculated based on the instantaneous volumetric elastic deformation, the target pressurization rate, the initial volume, and the stable and efficient flow rate.

[0033] The hydraulic power unit is controlled to operate according to the main flow command to provide a basic flow to the hydrogen storage tank; the hydraulic compensation unit is controlled to operate according to the compensation flow command to provide a compensation flow to the hydrogen storage tank to eliminate errors and disturbances.

[0034] During the pressure holding stage, the real-time temperature and real-time pressure of the hydrogen storage cylinder are obtained, and a first compensation displacement is calculated based on the real-time temperature and target temperature, or the real-time pressure and target pressure. The hydraulic compensation unit is controlled to work based on the first compensation displacement to eliminate errors caused by temperature changes or internal leakage.

[0035] During the depressurization phase, the instantaneous volumetric elastic deformation and real-time flow rate of the hydrogen storage cylinder are obtained. The opening degree of the depressurization valve is calculated based on the instantaneous volumetric elastic deformation, the target depressurization rate, the initial volume, and the real-time flow rate. The depressurization valve is controlled to operate in real time based on the opening degree to achieve smooth and shock-free depressurization.

[0036] Furthermore, the specific calculation process for the main flow command and the compensation flow command is as follows:

[0037] The theoretical flow rate during the boost phase is calculated using the following formula:

[0038] ;

[0039] in, This represents the theoretical flow rate during the boost phase; This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t. Indicates the set target boost rate; Indicates the effective compression ratio;

[0040] The main flow instruction is calculated using the following formula:

[0041] ;

[0042] in, Indicates the main flow command; Indicates stable and efficient traffic; Indicates the safety factor;

[0043] The compensation flow command is calculated using the following formula:

[0044] ;

[0045] in, This indicates a compensation flow command; This represents the estimated value of the disturbance flow.

[0046] Furthermore, the specific calculation formula for the first compensation displacement is as follows:

[0047] ,or ;

[0048] ;

[0049] ;

[0050] in, Indicates the first compensation displacement; This indicates the amount of compensation caused by temperature changes; Indicates the amount of compensation caused by internal leakage; This indicates the cross-sectional area of ​​the piston in the hydraulic compensation unit; This indicates the total volume of the second pipeline and the gas cylinder; Indicates the target temperature; This indicates the real-time temperature of the hydrogen storage cylinder; Indicates the bulk modulus of the oil; , , These represent the first proportional coefficient, the first integral coefficient, and the first differential coefficient, respectively. Indicates target pressure; This indicates the real-time pressure of the hydrogen storage tank; Indicates time.

[0051] Furthermore, the specific calculation process for the opening degree of the pressure relief valve is as follows:

[0052] The specific formula for calculating the flow compensation coefficient is as follows:

[0053] ;

[0054] in, Indicates the flow compensation coefficient; Indicates the calibration constant; This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t.

[0055] The theoretical flow rate during the pressure relief phase is calculated using the following formula:

[0056] ;

[0057] in, This represents the theoretical flow rate during the pressure relief phase. Indicates the set target rate of voltage reduction; Indicates the effective compression ratio;

[0058] The product of the flow compensation coefficient and the theoretical flow rate during the pressure relief stage is used as the corrected flow rate, which is then converted into the opening value. The specific conversion formula is as follows:

[0059] ;

[0060] in, Indicates the opening value; Indicates corrected flow rate; This indicates the rated flow coefficient of the pressure relief valve;

[0061] The specific formula for calculating the opening correction value is as follows:

[0062] ;

[0063] in, This indicates the opening correction value; , These represent the second proportional coefficient and the second integral coefficient, respectively. This represents the real-time flow rate at the outlet of the hydrogen storage cylinder; t represents time.

[0064] The final opening degree of the pressure relief valve is obtained by calculating the sum of the opening degree value and the opening degree correction value.

[0065] Preferably, the specific formula for calculating the instantaneous volumetric elastic deformation is as follows:

[0066] ;

[0067] in, This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t. This indicates the circumferential strain of the hydrogen storage cylinder; This indicates the initial volume of the hydrogen storage cylinder.

[0068] Furthermore, the experimental method also includes long-cycle online pressure compensation during the cyclic control phase, specifically including:

[0069] The material attenuation coefficient is calculated based on the peak and valley pressures in each cycle.

[0070] The real-time pressure amplitude is calculated based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; wherein, the initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle;

[0071] The pressure amplitude attenuation rate is calculated based on the real-time pressure amplitude and the initial pressure amplitude.

[0072] When the pressure amplitude attenuation rate is greater than a set percentage threshold, a second compensation displacement is calculated based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles; where n≤N;

[0073] The hydraulic compensation unit is controlled to operate according to the second compensation displacement to achieve long-cycle stable pressure compensation.

[0074] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0075] The hydraulic fatigue testing device provided by this invention improves performance by introducing a hydraulic compensation unit and coordinating its work with the hydraulic power unit and multi-stage booster unit, combined with multi-parameter sensing and intelligent control algorithms. Specifically, this improvement is reflected in the following aspects:

[0076] This invention employs a unique "feedforward-feedback composite control" strategy. During the pressurization phase, the total required flow rate is decomposed into a base flow rate provided by the hydraulic power unit and a compensation flow rate provided by the hydraulic compensation unit, achieving coordinated coarse and fine flow rate regulation. During the pressure holding phase, based on temperature and pressure deviations, the hydraulic compensation unit performs minute volumetric compensation to actively offset pressure drift caused by thermal expansion and contraction and leakage. This mechanism fundamentally suppresses pressure overshoot and fluctuations, achieving pressure stability at the ±0.15MPa level and ensuring high fidelity of fatigue load waveforms.

[0077] This invention embeds temperature as a core control variable directly into the pressure holding control process. The control unit drives the hydraulic compensation unit to perform volume compensation based on the deviation between the real-time temperature and the target temperature. This not only stabilizes the pressure but also proactively eliminates the impact of temperature changes on core test parameters from a control perspective. Combined with pre-cooling by the heat exchange unit, a dual thermal management mechanism of "physical cooling + control compensation" is formed, effectively controlling the surface temperature rise ΔT of the hydrogen storage cylinder at an extremely low level, avoiding safety risks and material performance test distortions caused by thermal runaway.

[0078] The testing apparatus of this invention, through a high-precision detection unit, can capture the instantaneous volumetric elastic deformation, reflecting the mechanical state of the material, in real time. During the cyclic control phase, the control unit can adaptively adjust its output based on changes in the instantaneous volumetric elastic deformation, compensating for stiffness decay caused by material fatigue damage and ensuring a constant pressure amplitude applied to the hydrogen storage tank throughout its entire lifespan. This provides high-quality, interference-free load-strain data for lifespan prediction, fundamentally solving the prediction bias (>20%) problem caused by neglecting material anisotropy and damage accumulation, and laying a solid foundation for achieving accurate assessments with an amplitude decay rate of <3% after 30,000 cycles.

[0079] This invention encompasses a precise control strategy for the entire process of pressurization, pressure holding, and pressure relief. Particularly during the pressure relief phase, the opening of the pressure relief valve is precisely calculated based on the instantaneous volumetric elastic deformation and the target pressure reduction rate, achieving smooth and controllable pressure relief. This avoids hydraulic shock to pipelines and hydrogen storage cylinders, further improving equipment reliability and test repeatability. Attached Figure Description

[0080] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0081] Figure 1 This is a schematic diagram of the hydraulic fatigue testing device in an embodiment of the present invention;

[0082] Figure 2 This is a flowchart of the hydraulic fatigue test method in an embodiment of the present invention.

[0083] Explanation of reference numerals in the attached diagram: 1-Flow meter, 2-Pressure sensor, 3-Temperature sensor, 4-Strain gauge, 5-Pressure relief valve, 6-First-stage booster cylinder, 7-Second-stage booster cylinder, 8-Third-stage booster cylinder, 9-Hydraulic compensation unit, 10-Heat exchange unit, 11-Oil tank, 12-Variable frequency piston pump, 13-Control unit, 14-Hydraulic check valve. Detailed Implementation

[0084] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. 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.

[0085] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0086] Example 1

[0087] like Figure 1 As shown, the hydraulic fatigue testing device for high-pressure hydrogen storage cylinders provided in this embodiment of the invention includes an oil tank 11, a hydraulic power unit, a multi-stage pressurization unit, a hydraulic compensation unit 9, a detection unit, and a control unit 13; the oil inlet of the hydraulic power unit is connected to the oil tank 11, and the oil outlet is connected to the inlet of the multi-stage pressurization unit through a first pipeline; the outlet of the multi-stage pressurization unit is connected to the inlet of the hydrogen storage cylinder through a second pipeline; the outlet of the hydrogen storage cylinder is connected to the oil tank 11 through a third pipeline, and a pressure relief valve 5 is provided on the third pipeline; the cavity of the hydraulic compensation unit 9 is connected to the second pipeline.

[0088] The main oil circuit is formed by the hydraulic power unit, the first pipeline, the multi-stage booster unit, and the second pipeline. The compensation oil circuit is formed by the hydraulic compensation unit 9. The main oil circuit and the compensation oil circuit are connected in parallel to provide oil flow to the hydrogen storage cylinder. The third pipeline is the pressure relief pipeline, which is used to provide a pressure relief path with less resistance to the hydrogen storage cylinder during the pressure relief stage.

[0089] In a specific embodiment of the present invention, the multi-stage booster unit is a three-stage booster unit, comprising a first accumulator, a second accumulator, and a first-stage booster cylinder 6, a second-stage booster cylinder 7, and a third-stage booster cylinder 8 connected sequentially. The inlet of the first-stage booster cylinder 6 is connected to the outlet of the hydraulic power unit via a first pipeline, and the outlet of the third-stage booster cylinder 8 is connected to the inlet of the hydrogen storage cylinder via a second pipeline. The first accumulator is connected to the pipeline between the first-stage booster cylinder 6 and the second-stage booster cylinder 7 via a three-way connector or a block-type integrated valve block, and the second accumulator is connected to the pipeline between the second-stage booster cylinder 7 and the third-stage booster cylinder 8 via a three-way connector or a block-type integrated valve block. The first pipeline is a low-pressure pipeline, and the second pipeline is a high-pressure pipeline.

[0090] The oil undergoes three stages of pressurization, gradually increasing its pressure until it reaches the target pressure of 70 MPa.

[0091] In a specific embodiment of the present invention, the hydraulic compensation unit 9 includes a compensation cylinder, a drive motor, a linear motion mechanism, and a hydraulically controlled check valve 14. The drive motor is controlled by a control unit 13, and its output end is connected to the linear motion mechanism. The linear motion mechanism is connected to the piston rod inside the compensation cylinder, and is used to convert the motion of the drive motor into the linear motion of the piston rod. The cavity of the compensation cylinder is connected to a second pipeline through the hydraulically controlled check valve 14. In this embodiment, the drive motor is a servo motor, and the linear motion mechanism is a ball screw pair.

[0092] The cavity of the compensating cylinder (consisting of the cylinder body and its internal piston, with the piston connected to the piston rod) is pre-filled with hydraulic oil. This cavity is connected to a second pipeline via a hydraulically controlled check valve 14. The hydraulically controlled check valve 14 is configured to allow oil to flow from the cavity of the compensating cylinder to the second pipeline, achieving positive pressure compensation. When it is necessary to replenish oil to the cavity of the compensating cylinder, the control unit 13 sends an opening signal to the pilot control port of the hydraulically controlled check valve 14, forcibly opening the valve and allowing the oil in the second pipeline to flow back into the container of the compensating cylinder. The hydraulic compensation unit 9 has no independent circulating power source; its oil replenishment comes from the pressure of the main oil circuit itself, achieving unidirectional hydraulic coupling with the main oil circuit.

[0093] Because the ball screw assembly itself has the self-locking characteristic of irreversible transmission, when the servo motor stops rotating, the ball screw assembly can effectively lock the piston rod of the compensating cylinder in the current position, maintain the volume of the second pipeline unchanged, and form a mechanical sealing barrier.

[0094] In this embodiment, a Type IV hydrogen storage cylinder (plastic liner, carbon fiber winding) with a nominal volume of 50L was selected as the test specimen, and the initial volume was calibrated. It is 0.05m 3 The hydraulic power unit uses a variable frequency piston pump 12 with a rated speed of 3000 rpm; the pressure ratio of the first-stage booster cylinder 6 is 1:10, the pressure ratio of the second-stage booster cylinder 7 is 1:15, and the pressure ratio of the third-stage booster cylinder 8 is 1:20; the servo motor of the hydraulic compensation unit 9 has a rated torque of 10 N·m, and the lead of the ball screw pair is 5 mm; the pressure sensor 2 has a range of 100 MPa and an accuracy of 0.1%FS; the temperature sensor 3 (Pt100) has a range of -50℃ to 150℃ and an accuracy of 0.5℃; the control unit 13 uses an embedded controller combining ARM Cortex-M7 and FPGA; the pressure relief valve 5 is an electromagnetic proportional valve. During the pressure boosting and holding stages, the electromagnetic proportional valve is closed, and high-pressure oil enters the hydrogen storage tank; during the pressure relief stage, the electromagnetic proportional valve is open, and high-pressure oil flows back to the oil tank 11 through the pressure relief pipeline.

[0095] In a specific embodiment of the present invention, the test apparatus further includes a heat exchange unit 10, which is disposed between the hydraulic power unit and the multi-stage pressurization unit. In this embodiment, the heat exchange unit 10 is a heat exchanger.

[0096] The complete oil path is as follows: oil tank 11, variable frequency plunger pump 12, heat exchanger, first stage booster cylinder 6, first accumulator, second stage booster cylinder 7, second accumulator, third stage booster cylinder 8, second pipeline, hydrogen storage cylinder, electromagnetic proportional valve, oil tank 11; compensation cylinder, second pipeline, hydrogen storage cylinder.

[0097] The detection unit detects the instantaneous volumetric elastic deformation, real-time temperature, real-time pressure, and real-time flow rate of the hydrogen storage cylinder. In this embodiment, the detection unit includes a strain gauge 4, a temperature sensor 3, a pressure sensor 2, and a flow meter 1. The temperature sensor 3 is attached to the surface of the hydrogen storage cylinder and is used to detect the real-time temperature of the hydrogen storage cylinder; the pressure sensor 2 is attached to the wall of the hydrogen storage cylinder cavity and is used to detect the real-time pressure inside the hydrogen storage cylinder; the flow meter 1 is used to detect the real-time flow rate at the outlet of the hydrogen storage cylinder; the strain gauge 4 is attached to the surface of the hydrogen storage cylinder and is used to detect the circumferential strain of the hydrogen storage cylinder, and then the instantaneous volumetric elastic deformation of the hydrogen storage cylinder is calculated based on the circumferential strain. The specific calculation formula is as follows:

[0098] (1)

[0099] in, This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t, in meters (m). 3 ; This represents the circumferential strain of the hydrogen storage cylinder, and is dimensionless. This indicates the initial volume of the hydrogen storage cylinder.

[0100] Initial volume of hydrogen storage cylinder The initial volume of the hydrogen storage tank can be obtained by calibration using deionized water. The specific process is as follows: inject deionized water into an empty hydrogen storage tank until the pressure reaches atmospheric pressure (P0=0.1MPa), and then detect the injected volume using a high-precision flow meter 1 (accuracy ±0.1%). Deionized water was used for initial volume calibration to eliminate the risk of electrochemical corrosion that may be caused by ions in the water, to avoid the influence of dissolved gases on measurement accuracy, and to ensure compatibility with the hydraulic fatigue testing device, thereby guaranteeing the accuracy of the calibration results and the safety of the test.

[0101] The control unit 13 is connected to the hydraulic power unit, the hydraulic compensation unit 9, the detection unit, and the pressure relief valve 5. The single hydraulic fatigue test process of the hydrogen storage cylinder includes a pressurization stage, a pressure holding stage, and a pressure relief stage. During the pressurization stage, the control unit 13 calculates the instantaneous volumetric elastic deformation based on the circumferential strain of the hydrogen storage cylinder collected by the strain gauge 4 (see formula (1)). The set target pressurization rate and the initial volume of the hydrogen storage tank. The system calculates the main flow command and the compensation flow command using a stable and efficient flow meter 1. Based on the main flow command, it controls the operation of the variable frequency plunger pump 12. The frequency converter of the variable frequency plunger pump 12 receives the main flow command (converted into a speed signal) and drives its internal three-phase asynchronous motor to precisely adjust the speed within the range of 500-3000 rpm. The asynchronous motor drives the pump head to draw low-pressure oil from the oil tank 11. The oil is delivered to the three-stage pressurization unit through the first pipeline. After three stages of continuous pressurization, high-pressure oil (e.g., pressure of 70 MPa) is output. The high-pressure oil is delivered to the hydrogen storage cylinder through the second pipeline, providing a basic flow to the hydrogen storage cylinder efficiently and stably through the main oil circuit. Simultaneously, the control unit 13 controls the servo motor of the hydraulic compensation unit 9 to work according to the compensation flow command. The servo motor then drives the ball screw pair to precisely advance the piston rod of the compensation cylinder (moving towards the inside of the cylinder) at a speed of 0.1-5 mm / s. The volume of the compensation cylinder decreases, and an additional, controlled compensation flow is injected into the second pipeline to accurately compensate for the lag in the rate of pressure rise caused by the volume elastic deformation of the hydrogen storage tank and the compressibility of the flow, thus eliminating errors and disturbances.

[0102] Stable and efficient flow rate refers to the flow rate that a hydraulic power unit (such as a variable frequency piston pump 12, a fixed displacement piston pump driven by a servo motor, a proportional variable pump, or a servo variable pump) can output stably and efficiently. Taking a variable frequency piston pump 12 as an example, the process of obtaining stable and efficient flow rate is as follows:

[0103] Plot specific curves for the variable frequency piston pump 12 at a specific speed, including flow-head (pressure) curves and flow-efficiency curves; analyze the entire device and calculate the total pressure required at different flow rates (the resistance of the pipeline that needs to overcome the net head), obtaining the demand curve; determine the stable operating point from the intersection of the flow-head (pressure) curve and the demand curve; determine the efficiency of the stable operating point based on the flow-efficiency curve; if the efficiency of the stable operating point is in the high-efficiency zone, then the flow rate of the stable operating point is the stable high-efficiency flow rate; if the efficiency of the stable operating point is not in the high-efficiency zone, change the speed of the variable frequency piston pump 12, and repeat the steps of plotting specific curves, plotting demand curves, determining the stable operating point, determining the efficiency of the stable operating point, and judging whether the efficiency is in the high-efficiency zone, until a stable high-efficiency flow rate is obtained.

[0104] When pressure sensor 2 detects that the real-time pressure reaches the set peak value (e.g., the nominal working pressure or rated filling pressure of the hydrogen storage cylinder; for vehicle-mounted hydrogen storage cylinders, the highest standard is 70 MPa), control unit 13 controls the hydraulic power unit to reduce its speed or stop working, stopping the supply of basic flow. Simultaneously, it controls the hydraulic compensation unit 9 to stop working, stopping the supply of compensation flow, and the device enters the pressure holding stage. During the pressure holding stage, the device may experience abnormal pressure increases due to temperature changes or extremely small internal leaks (<0.1 mL / min) causing pressure drops. Control unit 13 calculates the first compensation displacement based on the real-time temperature collected by temperature sensor 3 and the set target temperature, or the real-time pressure collected by pressure sensor 2 and the set target pressure. Based on the first compensation displacement, control unit 9 operates to eliminate errors caused by temperature changes (abnormal pressure increases) or internal leaks (pressure drops), ensuring that pressure fluctuations are strictly controlled within an extremely high precision of ≤±0.15 MPa throughout the entire pressure holding stage.

[0105] Specifically, if a temperature change causes an abnormal increase in pressure, the first compensation displacement is calculated based on the real-time temperature collected by temperature sensor 3 and the set target temperature. The servo motor is then reversed based on the first compensation displacement, and the piston rod of the compensation cylinder is moved outward to receive a small amount of high-pressure oil from the main oil circuit, thus achieving negative pressure compensation. If a very small internal leak (<0.1mL / min) causes a pressure drop, the first compensation displacement is calculated based on the real-time pressure collected by pressure sensor 2 and the set target pressure. The servo motor is then rotated forward based on the first compensation displacement, and the piston rod of the compensation cylinder is moved inward to replenish a small amount of high-pressure oil to the main oil circuit, thus achieving positive pressure compensation.

[0106] After the pressure holding time ends, the control unit 13 issues a command to open the pressure relief valve 5, and the device enters the pressure relief stage. During the pressure relief stage, the control unit 13 calculates the instantaneous volumetric elastic deformation based on the circumferential strain of the hydrogen storage cylinder collected by the strain gauge 4 (see formula (1)). Based on the instantaneous volumetric elastic deformation, the set target pressure drop rate, the initial volume, and the real-time flow meter 1, the control unit 1 calculates the opening degree of the pressure relief valve 5. Based on the opening degree, the control unit controls the real-time action of the pressure relief valve 5, achieving a smooth and shock-free pressure relief process and avoiding damage to the hydrogen storage cylinder, sensors, etc. caused by a sudden drop in pressure. When the pressure sensor 2 detects that the real-time pressure has dropped to the set valley value, the control unit 13 controls the pressure relief valve 5 to close, ending the pressure relief stage.

[0107] The hydraulic fatigue test of the hydrogen storage cylinder needs to be performed Nmax times. Therefore, after a complete "pressurization-holding-depressurization" cycle, the timer or counter in the control unit 13 automatically triggers the start of the next cycle. The "pressurization-holding-depressurization" process is repeated according to the set number of cycles Nmax (e.g., 30,000 times) to achieve fully automatic continuous operation. The cycle frequency (e.g., 0.1~2Hz) can be preset according to the test requirements. During the entire cycle control process, the temperature sensor 3 monitors the real-time temperature of the hydrogen storage cylinder surface. If the detected temperature rise is greater than the set temperature rise threshold (e.g., 5℃) or the real-time temperature is greater than the set temperature threshold (e.g., 45℃), the control unit 13 dynamically reduces the cycle frequency (e.g., from 1.2Hz to 1.08Hz) and simultaneously starts the heat exchanger to reduce the temperature of the injected oil, preventing the hydrogen storage cylinder from overheating at the source and achieving active thermal management.

[0108] In order to overcome the performance degradation caused by tens of thousands of pressure cycles (such as increased internal leakage, seal creep, etc.), the control unit 13 also performs online prediction and compensation of long-cycle pressure during the cycle control phase. When the pressure amplitude decay rate is greater than the preset percentage threshold (e.g., 3% or 2.5%), the control unit 13 automatically triggers the compensation mechanism to keep the pressure output stability at an extremely high level.

[0109] Specifically, in the cyclic control phase, the control unit 13 calculates the material attenuation coefficient based on the peak pressure and valley pressure in each cycle; calculates the real-time pressure amplitude based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; calculates the pressure amplitude attenuation rate based on the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude attenuation rate is greater than the set percentage threshold, calculates the second compensation displacement based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles, and controls the hydraulic compensation unit 9 to work based on the second compensation displacement to achieve long-cycle online pressure compensation; wherein, the initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle.

[0110] Throughout the fatigue test, the device automatically and synchronously records and stores all data such as time-pressure curves, cycle number-temperature, and cycle number-compensation displacement (first compensation displacement and second compensation displacement), providing complete and accurate data support for evaluating the fatigue life and safety performance of hydrogen storage cylinders.

[0111] Example 2

[0112] like Figure 2 As shown, based on the hydraulic fatigue testing device in Embodiment 1 of the present invention, the hydraulic fatigue testing method for high-pressure hydrogen storage cylinders provided in this embodiment includes the following steps:

[0113] Step 1: Preparation before the experiment: Obtain the initial volume of the gas storage cylinder.

[0114] Obtain the initial volume of the gas storage cylinder. The specific process is as follows: Deionized water is injected into an empty hydrogen storage cylinder to atmospheric pressure (P0=0.1MPa), and then the injected volume is detected by a high-precision flow meter (accuracy ±0.1%) to obtain the initial volume of the hydrogen storage cylinder. Deionized water was used for initial volume calibration to eliminate the risk of electrochemical corrosion that may be caused by ions in the water, to avoid the influence of dissolved gases on measurement accuracy, and to ensure compatibility with the hydraulic fatigue testing device, thereby guaranteeing the accuracy of the calibration results and the safety of the test.

[0115] Step 2: During the pressurization stage, the circumferential strain of the hydrogen storage cylinder is obtained using strain gauges. The instantaneous volumetric elastic deformation of the hydrogen storage cylinder is calculated based on the circumferential strain, as shown in Formula (1). In this embodiment, the sampling period of the strain gauge is 10s.

[0116] Step 3: Calculate the main flow command and compensation flow command based on the instantaneous volumetric elastic deformation, target pressure boosting rate, initial volume, and stable high-efficiency flow rate.

[0117] In a specific embodiment of the present invention, the specific calculation process for the main flow command and the compensation flow command is as follows:

[0118] Step 3.1: Calculate the theoretical flow rate during the boost stage. The specific calculation formula is as follows:

[0119] (2)

[0120] in, This represents the theoretical flow rate during the boost phase; This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t. This indicates the set target boost rate; in this embodiment, the target boost rate is 3 MPa / s. Indicates the effective compressibility factor (unit: Pa). -1 This coefficient, which integrates key parameters such as hydraulic oil compressibility and pipeline elasticity, can be obtained through experimental calibration. In this embodiment, Specifically, it is 1.72 × 10 -9 / Pa.

[0121] Step 3.2: Calculate the main flow command. The specific calculation formula is as follows:

[0122] (3)

[0123] in, Indicates the main flow command; Indicates stable and efficient traffic; This represents the safety factor. It is a number slightly less than 1. In this embodiment, The value range is 0.92 to 0.98.

[0124] Step 3.3: Calculate the compensation flow command. The specific calculation formula is as follows:

[0125] (4)

[0126] in, This indicates a compensation flow command; This represents the estimated disturbance flow rate, which can be estimated in real time by the disturbance observer in the control unit.

[0127] Step 4: Control the hydraulic power unit to work according to the main flow command to provide the basic flow to the hydrogen storage tank; control the hydraulic compensation unit to work according to the compensation flow command to provide the compensation flow to the hydrogen storage tank to eliminate errors and disturbances.

[0128] Specifically, the control unit controls the operation of the variable frequency plunger pump according to the main flow command. The inverter of the variable frequency plunger pump receives the main flow command (converted into a speed signal) and drives its internal three-phase asynchronous motor to precisely adjust the speed within the range of 500-3000 rpm. The asynchronous motor drives the pump head to draw low-pressure oil from the oil tank. The oil is delivered to the three-stage pressurization unit through the first pipeline. After three stages of continuous pressurization, high-pressure oil (e.g., pressure of 70 MPa) is output. The high-pressure oil is delivered to the hydrogen storage tank through the second pipeline, providing a basic flow to the hydrogen storage tank efficiently and stably through the main oil circuit. At the same time, the control unit controls the servo motor of the hydraulic compensation unit according to the compensation flow command. The servo motor then drives the ball screw pair to precisely advance the piston rod of the compensation cylinder (moving it towards the inside of the cylinder) at a speed of 0.1-5 mm / s. The volume of the compensation cylinder decreases, injecting an additional, controlled compensation flow into the second pipeline to precisely compensate for the lag in the pressure rise rate caused by the volume elastic deformation of the hydrogen storage tank and the compressibility of the flow, thus eliminating errors and disturbances.

[0129] Step 5: Obtain the real-time pressure of the hydrogen storage cylinder and determine whether the real-time pressure has reached the set peak value. If so, control the hydraulic power unit and hydraulic compensation unit to stop working and enter the pressure holding stage.

[0130] When the pressure sensor detects that the real-time pressure has reached the set peak value (e.g., the nominal working pressure or rated filling pressure of the hydrogen storage cylinder; for vehicle-mounted hydrogen storage cylinders, the highest standard is 70 MPa), the control unit controls the hydraulic power unit to reduce its speed or stop working, stopping the supply of basic flow. At the same time, it controls the hydraulic compensation unit to stop working, stopping the supply of compensation flow, and the device enters the pressure holding stage.

[0131] Step 6: During the pressure holding stage, obtain the real-time temperature and real-time pressure of the hydrogen storage cylinder.

[0132] Step 7: Calculate the first compensation displacement based on the real-time temperature and target temperature, or the real-time pressure and target pressure, and control the hydraulic compensation unit to work based on the first compensation displacement to eliminate errors caused by temperature changes or internal leakage.

[0133] If a temperature change causes an abnormal increase in pressure, a first compensation displacement is calculated based on the real-time temperature collected by the temperature sensor and the set target temperature. This first compensation displacement is then used to control the servo motor to reverse, causing the piston rod of the compensation cylinder to move outward, drawing a small amount of high-pressure oil from the main oil circuit to achieve negative pressure compensation. In this embodiment, the first compensation displacement caused by the temperature change... The specific calculation formula is as follows:

[0134] (5)

[0135] (6)

[0136] in, This indicates the amount of compensation caused by temperature changes; This indicates the cross-sectional area of ​​the piston inside the compensation cylinder; This indicates the total volume of the second pipeline and the gas cylinder; Indicates the target temperature; This indicates the real-time temperature of the hydrogen storage cylinder; The bulk modulus of oil is a physical constant that represents the compressibility of oil, with a value of approximately 1400~2000 MPa.

[0137] If a very small internal leak (<0.1 mL / min) causes a pressure drop, a first compensation displacement is calculated based on the real-time pressure collected by the pressure sensor and the set target pressure. This first compensation displacement is then used to control the servo motor to rotate forward, causing the piston rod of the compensation cylinder to move inward, replenishing the main oil circuit with a small amount of high-pressure oil, thus achieving positive pressure compensation. In this embodiment, the first compensation displacement caused by the change in internal leakage... The specific calculation formula is as follows:

[0138] (7)

[0139] (8)

[0140] in, Indicates the amount of compensation caused by internal leakage; This represents the first proportionality coefficient; the larger the pressure deviation, the larger the compensation displacement, used for rapid response. This represents the first integral coefficient, which is proportional to the sum of all pressure deviations over a period of time. It is used to eliminate static errors (such as a slow pressure drop caused by a continuous small leak). The integral term is key to achieving accurate compensation. This represents the first differential coefficient, which is proportional to the rate of change of pressure deviation. It predicts the future trend of pressure deviation, making the response smoother and reducing overshoot. Indicates the target pressure (e.g., 70 MPa); This indicates the real-time pressure of the hydrogen storage tank; Indicates time.

[0141] The hydraulic compensation unit is controlled based on the first compensation displacement, and the pressure is controlled within 70MPa±0.15MPa during the entire pressure holding stage.

[0142] Step 8: Determine if the pressure holding time has been reached. If so, proceed to the pressure relief stage and control the pressure relief valve to open.

[0143] After the pressure holding time ends, the control unit issues a command to open the pressure relief valve, and the oil in the hydrogen storage cylinder flows back to the oil tank through the pressure relief pipeline, and the device enters the pressure relief stage.

[0144] Step 9: During the depressurization stage, the circumferential strain of the hydrogen storage cylinder is obtained using strain gauges and the real-time flow rate of the hydrogen storage cylinder is obtained using a flow meter. The instantaneous volumetric elastic deformation of the hydrogen storage cylinder is calculated based on the circumferential strain, as shown in Formula (1).

[0145] Step 10: Calculate the opening degree of the pressure relief valve based on the instantaneous volumetric elastic deformation, target pressure reduction rate, initial volume, and real-time flow rate. Control the pressure relief valve to operate in real time based on the opening degree to achieve smooth and shock-free pressure relief.

[0146] In a specific embodiment of the present invention, the specific calculation process for the opening degree of the pressure relief valve is as follows:

[0147] Step 10.1: Calculate the flow compensation coefficient. The specific calculation formula is as follows:

[0148] (9)

[0149] in, Indicates the flow compensation coefficient; This represents the calibration constant, determined through no-load calibration tests, with a typical value of 1.05. This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t.

[0150] Step 10.2: Calculate the theoretical flow rate during the pressure relief stage. The specific calculation formula is as follows:

[0151] (10)

[0152] in, This represents the theoretical flow rate during the pressure relief phase. Indicates the set target rate of voltage reduction; This represents the effective compression factor.

[0153] Step 10.3: Using the flow compensation coefficient Theoretical flow rate during the depressurization phase The product of these values ​​is used as the corrected flow rate and converted into an opening value. The specific conversion formula is as follows:

[0154] (11)

[0155] in, Indicates the opening value; Indicates corrected flow rate; This indicates the rated flow coefficient of the pressure relief valve.

[0156] Step 10.4: Calculate the opening correction value. The specific calculation formula is as follows:

[0157] (12)

[0158] in, This indicates the opening correction value; , These represent the second proportional coefficient and the second integral coefficient, respectively. This indicates the real-time flow rate at the outlet of the hydrogen storage cylinder, measured by a flow meter. Indicates time. In this embodiment, It is 0.8. It is 0.2.

[0159] Step 10.5: Calculate the sum of the opening value and the opening correction value to obtain the final opening of the pressure relief valve.

[0160] The final opening degree of the pressure relief valve is calculated in real time according to steps 10.1 to 10.5, and the opening degree of the pressure relief valve is adjusted in real time to achieve smooth and shock-free pressure relief. When the pressure sensor detects that the real-time pressure has dropped to the set valley value, the control unit controls the pressure relief valve to close, ending the pressure relief stage and completing one hydraulic fatigue test.

[0161] In a specific embodiment of the present invention, in order to overcome the performance degradation (such as increased internal leakage, seal creep, etc.) caused by tens of thousands of pressure cycles, the test method also includes long-cycle online pressure compensation during the cycle control phase, specifically including the following steps:

[0162] Calculate the material attenuation coefficient based on the peak and trough pressures in each cycle;

[0163] The real-time pressure amplitude is calculated based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; where the initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle.

[0164] The pressure amplitude attenuation rate is calculated based on the real-time pressure amplitude and the initial pressure amplitude.

[0165] When the pressure amplitude decay rate is greater than the set percentage threshold, the second compensation displacement is calculated based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles.

[0166] The hydraulic compensation unit operates according to the second compensation displacement control, achieving long-cycle stable pressure compensation.

[0167] In this embodiment, a single cycle is a complete pressurization-holding-depressurization process. Real-time pressure is collected at different sampling times within a single cycle using a pressure sensor, thereby determining the peak pressure (i.e., maximum real-time pressure) and trough pressure (i.e., minimum real-time pressure) for each cycle. The difference between the peak and trough pressures in each cycle is calculated to obtain the instantaneous pressure amplitude for that cycle. The material attenuation coefficient is calculated based on a mathematical model of exponential decay.

[0168] (13)

[0169] in, This represents the instantaneous pressure amplitude in the i-th cycle; Indicates the initial pressure amplitude; This represents the material attenuation coefficient in the i-th cycle.

[0170] Taking the natural logarithm of both sides of equation (13), we obtain a linear relationship:

[0171] (14)

[0172] By fitting a linear relationship between the natural logarithm of the instantaneous pressure amplitude and the number of cycles, the material attenuation coefficient (fitting slope) can be obtained. This leads to the formula for calculating the real-time pressure amplitude:

[0173] (15)

[0174] in, Indicates real-time pressure amplitude; Indicates the number of iterations; This represents the material attenuation coefficient. In this embodiment, the calculated material attenuation coefficient is 1.69 × 10⁻⁶. -6 .

[0175] The formula for calculating the pressure amplitude attenuation rate is:

[0176] (16)

[0177] Based on the calculated pressure amplitude attenuation rate and the set percentage threshold, it is determined whether to calculate the second compensation displacement, and then perform long-cycle pressure stability compensation. Every 1000 cycles, the pressure amplitude attenuation rate is calculated according to formula (16), and then a determination and compensation are performed. In this embodiment, the percentage threshold is 2.5%. That is, in When the displacement exceeds 2.5% (approximately after 15,000 cycles), the control unit calculates the second compensation displacement. The specific calculation formula is as follows:

[0178] (17)

[0179] in, Indicates the second compensation displacement; This represents the average value of the instantaneous volumetric elastic deformation in the first n cycles (in this embodiment, n is 100); This indicates the cross-sectional area of ​​the piston inside the compensation cylinder. The direction of the second compensation displacement is determined based on the target pressure and the real-time pressure: when the target pressure is greater than the real-time pressure, the servo motor is controlled to rotate forward, causing the piston rod of the compensation cylinder to move inward and replenish a small amount of high-pressure oil to the main oil circuit, achieving positive pressure compensation; when the target pressure is less than the real-time pressure, the servo motor is controlled to rotate in reverse, causing the piston rod of the compensation cylinder to move outward and receive a small amount of high-pressure oil from the main oil circuit, achieving negative pressure compensation; when the target pressure equals the real-time pressure, the second compensation displacement is zero. A single pulse output by the servo motor corresponds to a displacement of 0.001 mm.

[0180] In this embodiment, the initial circulation frequency is set to 1Hz. During the circulation control process, the control unit dynamically adjusts the circulation frequency based on the real-time temperature collected by the temperature sensor. Specifically, when the temperature rise rate of the hydrogen storage tank exceeds the temperature rise threshold, or when the real-time temperature of the hydrogen storage tank exceeds the temperature threshold, the circulation frequency is controlled to decrease; simultaneously, the heat exchanger can be started to actively reduce the temperature of the injected oil.

[0181] During the specific test, the hydraulic fatigue testing device operated continuously and successfully completed 30,000 pressure cycle tests. Throughout the test, the pressure curve was smooth, the pressure amplitude decay rate was only 2.8%, and the highest surface temperature of the hydrogen storage cylinder remained stable below 58°C, successfully verifying the high precision, high reliability, and excellent thermal management capabilities of the testing device and method of this invention.

[0182] The above description only discloses specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or modifications that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydraulic fatigue testing method for high-pressure hydrogen storage cylinders, characterized in that, The hydraulic fatigue testing device includes a hydraulic power unit, a multi-stage pressurization unit, a hydraulic compensation unit, a detection unit, and a control unit. The inlet of the hydraulic power unit is connected to an oil tank. The inlet of the multi-stage pressurization unit is connected to the outlet of the hydraulic power unit via a first pipeline, and the outlet of the multi-stage pressurization unit is connected to the inlet of the hydrogen storage cylinder via a second pipeline. The outlet of the hydrogen storage cylinder is connected to the oil tank via a third pipeline, and a pressure relief valve is installed on the third pipeline. The cavity of the hydraulic compensation unit is connected to the second pipeline and is pre-filled with hydraulic oil. The detection unit is used to detect the instantaneous volumetric elastic deformation, real-time temperature, real-time pressure, and real-time flow rate of the hydrogen storage cylinder. The control unit is connected to the hydraulic power unit, the hydraulic compensation unit, the detection unit, and the pressure relief valve. The test method includes a pressurization phase, a pressure holding phase, and a pressure release phase; During the pressurization phase, the instantaneous volumetric elastic deformation of the hydrogen storage cylinder is obtained, and the main flow command and compensation flow command are calculated based on the instantaneous volumetric elastic deformation, the target pressurization rate, the initial volume, and the stable and efficient flow rate. The hydraulic power unit is controlled to operate according to the main flow command to provide a basic flow to the hydrogen storage tank; The hydraulic compensation unit is controlled to operate according to the compensation flow command to provide compensation flow to the hydrogen storage tank in order to eliminate errors and disturbances; During the pressure holding stage, the real-time temperature and real-time pressure of the hydrogen storage cylinder are obtained, and a first compensation displacement is calculated based on the real-time temperature and target temperature, or the real-time pressure and target pressure. The hydraulic compensation unit is controlled to work based on the first compensation displacement to eliminate errors caused by temperature changes or internal leakage. During the depressurization phase, the instantaneous volumetric elastic deformation and real-time flow rate of the hydrogen storage cylinder are obtained. The opening degree of the depressurization valve is calculated based on the instantaneous volumetric elastic deformation, the target depressurization rate, the initial volume, and the real-time flow rate. The depressurization valve is controlled to operate in real time based on the opening degree to achieve smooth and shock-free depressurization.

2. The hydraulic fatigue testing method according to claim 1, characterized in that, The multi-stage booster unit is a three-stage booster unit, which includes a first accumulator, a second accumulator, and a first-stage booster cylinder, a second-stage booster cylinder, and a third-stage booster cylinder connected in sequence. The inlet of the first-stage booster cylinder is connected to the oil outlet of the hydraulic power unit through a first pipeline, and the outlet of the third-stage booster cylinder is connected to the inlet of the hydrogen storage tank through a second pipeline. The first accumulator is connected to the pipeline between the first-stage booster cylinder and the second-stage booster cylinder, and the second accumulator is connected to the pipeline between the second-stage booster cylinder and the third-stage booster cylinder.

3. The hydraulic fatigue testing method according to claim 1, characterized in that, The hydraulic compensation unit includes a compensation cylinder, a drive motor, a linear motion mechanism, and a hydraulically controlled check valve; the drive motor is controlled by the control unit and its output end is connected to the linear motion mechanism; the linear motion mechanism is connected to the piston rod inside the compensation cylinder and is used to convert the motion of the drive motor into the linear motion of the piston rod. The cavity of the compensation cylinder is connected to the second pipeline via the hydraulic check valve.

4. The hydraulic fatigue testing method according to claim 1, characterized in that, The test apparatus also includes a heat exchange unit located between the hydraulic power unit and the multi-stage pressurization unit. The control unit is also used to calculate the temperature rise based on the real-time temperature of the hydrogen storage cylinder, and to activate the heat exchange unit when the temperature rise exceeds a temperature rise threshold or the real-time temperature exceeds a temperature threshold, thereby achieving active thermal management.

5. The hydraulic fatigue testing method according to any one of claims 1 to 4, characterized in that, The control unit is also used to calculate the material attenuation coefficient based on the peak pressure and valley pressure in each cycle during the cyclic control phase; calculate the real-time pressure amplitude based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; calculate the pressure amplitude attenuation rate based on the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude attenuation rate is greater than a set percentage threshold, calculate the second compensation displacement based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles; and control the hydraulic compensation unit to work based on the second compensation displacement to achieve long-cycle online pressure compensation. The initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle, where n ≤ N.

6. The hydraulic fatigue testing method according to claim 1, characterized in that, The specific calculation process for the main flow command and the compensation flow command is as follows: The theoretical flow rate during the boost phase is calculated using the following formula: ； in, This represents the theoretical flow rate during the boost phase; This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t. Indicates the set target boost rate; Indicates the effective compression ratio; The main flow instruction is calculated using the following formula: ； in, Indicates the main flow command; Indicates stable and efficient traffic; Indicates the safety factor; The compensation flow command is calculated using the following formula: ； in, This indicates a compensation flow command; This represents the estimated value of the disturbance flow.

7. The hydraulic fatigue testing method according to claim 1, characterized in that, The specific calculation formula for the first compensation displacement is as follows: ,or ; ； ； in, Indicates the first compensation displacement; This indicates the amount of compensation caused by temperature changes; Indicates the amount of compensation caused by internal leakage; This indicates the cross-sectional area of ​​the piston in the hydraulic compensation unit; This indicates the total volume of the second pipeline and the gas cylinder; Indicates the target temperature; This indicates the real-time temperature of the hydrogen storage cylinder; Indicates the bulk modulus of the oil; , , These represent the first proportional coefficient, the first integral coefficient, and the first differential coefficient, respectively. Indicates target pressure; The value 't' represents the real-time pressure of the hydrogen storage tank; 't' represents time.

8. The hydraulic fatigue testing method according to claim 1, characterized in that, The specific calculation process for the opening degree of the pressure relief valve is as follows: The specific formula for calculating the flow compensation coefficient is as follows: ； in, Indicates the flow compensation coefficient; Indicates the calibration constant; This indicates the initial volume of the hydrogen storage cylinder; This represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t. The theoretical flow rate during the pressure relief phase is calculated using the following formula: ； in, This represents the theoretical flow rate during the pressure relief phase. Indicates the set target rate of voltage reduction; Indicates the effective compression ratio; The product of the flow compensation coefficient and the theoretical flow rate during the pressure relief stage is used as the corrected flow rate, which is then converted into the opening value. The specific conversion formula is as follows: ； in, Indicates the opening value; Indicates corrected flow rate; This indicates the rated flow coefficient of the pressure relief valve; The specific formula for calculating the opening correction value is as follows: ； in, This indicates the opening correction value; , These represent the second proportional coefficient and the second integral coefficient, respectively. This represents the real-time flow rate at the outlet of the hydrogen storage cylinder; t represents time. The final opening degree of the pressure relief valve is obtained by calculating the sum of the opening degree value and the opening degree correction value.

9. The hydraulic fatigue testing method according to claim 1, characterized in that, The experimental method also includes long-cycle online pressure compensation during the cyclic control phase, specifically including: The material attenuation coefficient is calculated based on the peak and valley pressures in each cycle. The real-time pressure amplitude is calculated based on the material attenuation coefficient, the initial pressure amplitude, and the number of cycles N; wherein, the initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle; The pressure amplitude attenuation rate is calculated based on the real-time pressure amplitude and the initial pressure amplitude. When the pressure amplitude attenuation rate is greater than a set percentage threshold, a second compensation displacement is calculated based on the average value of the instantaneous volumetric elastic deformation in the previous n cycles; where n≤N; The hydraulic compensation unit is controlled to operate according to the second compensation displacement to achieve long-cycle stable pressure compensation.

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