Hydraulic fatigue test device and method for high-pressure hydrogen storage cylinder

Abstract

The invention discloses a hydraulic fatigue test device and method for a high-pressure hydrogen storage cylinder. The test device comprises an oil tank, a hydraulic power unit, a multi-stage pressurization unit, a hydraulic compensation unit, a detection unit and a control unit, an oil inlet of the hydraulic power unit is connected with the oil tank, and an oil outlet is connected with an inlet of the multi-stage supercharging unit through a first pipeline; an outlet of the multi-stage supercharging unit is connected with an inlet of the hydrogen storage bottle through a second pipeline; an outlet of the hydrogen storage bottle is connected to the oil tank through a third pipeline, and a pressure release valve is arranged on the third pipeline; the accommodating cavity of the hydraulic compensation unit is connected with the second pipeline; the control unit is connected with the hydraulic power unit, the hydraulic compensation unit and the detection unit. According to the invention, the pressure stability of + / -0.15 MPa can be realized, and the high fidelity of the fatigue load waveform is ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen storage bottle testing, and particularly relates to a hydraulic fatigue test device and method for a high-pressure hydrogen storage bottle. BACKGROUND

[0002] The fatigue life and safety performance of a high-pressure hydrogen storage bottle, as key hydrogen storage equipment for a hydrogen energy fuel cell vehicle, are directly related to the commercial application prospect of the vehicle. At present, mainstream technologies are committed to the research and testing of 70 MPa and above pressure grade hydrogen storage bottles. Hydraulic fatigue testing is a core means for evaluating the life and reliability of hydrogen storage bottles under alternating loads, and the testing precision and reliability are crucial for the safety certification of the gas cylinder.

[0003] A conventional hydraulic fatigue test device is usually composed of a hydraulic pump station, a one-way pressure boosting cylinder, an electromagnetic reversing valve, a pipeline system, and a simple controller. Its control strategy mostly adopts open-loop control or classic PID closed-loop control. However, in the face of 70 MPa ultra-high pressure and high-frequency cycle test conditions, the conventional technology exposes the following inherent defects, which are difficult to meet the high-precision testing requirements:

[0004] (1) Low pressure control precision and serious waveform distortion: In the ultra-high pressure environment, the compressibility of the oil is significantly enhanced (isothermal compression coefficient β ≈ 5.2 × 10 -10 Pa -1 ), and at the same time, the composite hydrogen storage bottle body will produce obvious elastic expansion deformation (hoop strain > 0.4%) under high pressure. These two factors together cause the system cavity stiffness to decrease, making the pressure prone 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 a pressure fluctuation range usually greater than ± 5% of the full scale (FS), which seriously affects the accuracy and effectiveness of the test data.

[0005] (2) System thermal accumulation effect is prominent, affecting test safety and life: To achieve high efficiency testing, the test frequency is usually required to be higher than 1 Hz. At this high frequency, the throttling loss, fluid viscous friction in the hydraulic system, and the hysteresis effect of the composite hydrogen storage bottle will generate a large amount of heat. Since the conventional device lacks an effective thermal management mechanism, the heat cannot be dissipated in time, causing the temperature of the hydrogen storage bottle surface and the system oil to continuously rise, with a temperature rise ΔT often exceeding 15℃. Excessive temperature not only accelerates the aging of the seal and causes leakage, but also changes the mechanical properties of the tested hydrogen storage bottle material, making the fatigue test results deviate from the true working conditions, and even may cause safety risks due to "thermal runaway".

[0006] (3) The life prediction model is inaccurate, and the engineering guidance is limited: the test and control strategy of the traditional device is relatively extensive, and the inherent anisotropic characteristics of the composite material and the nonlinear accumulation effect of fatigue damage are not fully considered. The life prediction model based on ideal assumptions cannot accurately reflect the actual damage evolution process of the hydrogen storage bottle under complex alternating loads, resulting in a deviation of more than 20% between the predicted life and the actual life, which makes it difficult to provide accurate and reliable data support for the design optimization and safety use cycle evaluation of the hydrogen storage bottle. SUMMARY

[0007] The purpose of the present application is to provide a hydraulic fatigue test device and method for high-pressure hydrogen storage bottles to solve at least one of the above-mentioned defects.

[0008] The present application solves the above technical problems by the following technical solutions: a hydraulic fatigue test device for high-pressure hydrogen storage bottles, comprising: a hydraulic power unit, the oil inlet of which is connected to an oil tank; a multi-stage pressurization unit, the inlet of which is connected to the oil outlet of the hydraulic power unit through a first pipeline, the outlet of which is connected to the inlet of the hydrogen storage bottle through a second pipeline, and the outlet of the hydrogen storage bottle is connected to the oil tank through a third pipeline, and a pressure relief valve is arranged on the third pipeline; a hydraulic compensation unit, the cavity of which is connected to the second pipeline, and the cavity is pre-filled with hydraulic oil; a detection unit for detecting the instantaneous volumetric elastic deformation, real-time temperature, real-time pressure and real-time flow rate of the hydrogen storage bottle; and a control unit connected to the hydraulic power unit, hydraulic compensation unit, detection unit and pressure relief valve, for controlling the hydraulic power unit and hydraulic compensation unit in the pressurization stage according to the instantaneous volumetric elastic deformation, target pressurization rate, initial volume of the hydrogen storage bottle and stable efficient flow rate to eliminate errors and disturbances and achieve accurate pressurization; for controlling the hydraulic compensation unit in the pressure maintaining stage according to 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 for controlling the pressure relief valve in the pressure relief stage according to the instantaneous volumetric elastic deformation, target depressurization rate, initial volume and real-time flow rate to achieve smooth and impact-free pressure relief.

[0009] In the embodiment, the control unit calculates a main flow instruction and a compensation flow instruction according to the instantaneous volumetric elastic deformation, the target pressure increasing rate, the initial volume of the hydrogen storage bottle and the stable and efficient flow in the pressure increasing stage; controls the hydraulic power unit to work according to the main flow instruction, so as to provide a basic flow for the hydrogen storage bottle; controls the hydraulic compensation unit to work according to the compensation flow instruction, so as to provide a compensation flow for the hydrogen storage bottle, and eliminate errors and disturbances; calculates a first compensation displacement according to the real-time temperature and the target temperature, or the real-time pressure and the target pressure in the pressure maintaining stage, and controls the hydraulic compensation unit to work according to the first compensation displacement, so as to eliminate errors caused by temperature changes or internal leakage; and calculates the opening of the pressure relief valve according to the instantaneous volumetric elastic deformation, the target pressure decreasing rate, the initial volume and the real-time flow in the pressure decreasing stage, and controls the pressure relief valve to act in real time according to the opening, so as to realize smooth and impact-free pressure relief.

[0010] The control unit controls the hydraulic power unit to work according to the main flow instruction, and the hydraulic power unit is used to deliver oil in the oil tank to the hydrogen storage bottle, so as to stably and efficiently provide a basic flow for the hydrogen storage bottle; the control unit controls the hydraulic compensation unit to work according to the compensation flow instruction, and the hydraulic compensation unit is used to provide a compensation flow for the hydrogen storage bottle, and eliminate errors and instantaneous disturbances in real time. The coarse adjustment + fine adjustment mode guarantees the accuracy of the flow input from the source, so as to realize accurate tracking of the pressure curve, and reduce the pressure fluctuation from ± 5% FS to ± 0.15 MPa, which is a very high level.

[0011] In the pressure maintaining stage, any slight temperature change (for example, thermal expansion and cold contraction) or pressure leakage will destroy the pressure stability. In view of this problem, the present application actively monitors the disturbance amount (temperature, pressure), and offsets the influence of the disturbance amount on the total volume of the hydrogen storage bottle by precisely adjusting the displacement of the hydraulic compensation unit, so as to realize truly static high-precision pressure maintaining, and provide a very stable pressure environment for fatigue life test.

[0012] In the pressure maintaining stage, temperature is used as a core control variable to adjust the hydraulic compensation unit, so that the device can not only sense temperature, but also actively offset the pressure fluctuation caused by temperature change through volumetric compensation. Although the device cannot directly refrigerate, the negative influence of temperature change on pressure is eliminated, the test data distortion and safety risk caused by out-of-control temperature are prevented, and the reliability and safety of the test are improved.

[0013] The volumetric elastic deformation is a key parameter directly reflecting the mechanical behavior (stiffness change, etc.) of the composite hydrogen storage bottle under load, and high-precision pressure and temperature data eliminate the interference of system error on material behavior analysis. These data can capture the anisotropic response and nonlinear damage accumulation process of the material, and provide a high-quality data source for accurate life prediction.

[0014] Further, the multi-stage supercharging unit is a three-stage supercharging unit, the three-stage supercharging unit comprises a first accumulator, a second accumulator, and a first-stage supercharging cylinder, a second-stage supercharging cylinder and a third-stage supercharging cylinder connected in sequence; the inlet of the first-stage supercharging cylinder is connected with the oil outlet of the hydraulic power unit through a first pipeline, and the outlet of the third-stage supercharging cylinder is connected with the inlet of the hydrogen storage bottle through a second pipeline; the first accumulator is connected with the pipelines between the first-stage supercharging cylinder and the second-stage supercharging cylinder, and the second accumulator is connected with the pipelines between the second-stage supercharging cylinder and the third-stage supercharging cylinder.

[0015] In the embodiment, the multi-stage supercharging unit is adopted to enable the device to work at a lower primary pressure and achieve an extremely high output pressure; the multi-stage supercharging enables each stage to undertake only part of the supercharging task, the piston area ratio is more reasonable, the structure is more compact, the load and mass of each piston are reduced, the movement is more stable, and the inertial impact is reduced. Ultimately, the device as a whole has lower energy consumption, more stable operation, smaller noise and vibration, and lays a foundation for high-precision pressure control. By reasonably allocating the supercharging ratio, a large pressure difference can be decomposed to each seal, which significantly reduces the harshness of the working condition of each seal, greatly prolongs the sealing life and maintenance period of the entire supercharging unit.

[0016] The core role of the first accumulator and the second accumulator is to absorb pulsation, compensate leakage and stabilize pressure. Specifically, the first accumulator and the second accumulator can effectively absorb the pressure pulsation generated in the stage to prevent it from being transmitted to the next stage or the hydrogen storage bottle; at the same time, the first accumulator and the second accumulator can also compensate internal leakage, provide supplement when a large flow is needed in an instant, and ensure pressure stability.

[0017] Preferably, the supercharging ratio of the first-stage supercharging cylinder is 1:10, the supercharging ratio of the second-stage supercharging cylinder is 1:15, and the supercharging ratio of the third-stage supercharging cylinder is 1:20.

[0018] Further, the hydraulic compensation unit comprises a compensation oil cylinder, a driving motor, a linear motion mechanism and a hydraulic control check valve; the driving motor is controlled by the control unit and its output end is connected with the linear motion mechanism; the linear motion mechanism is connected with a piston rod in the compensation oil cylinder, and is used for converting the movement of the driving motor into the linear movement of the piston rod.

[0019] The cavity of the compensation oil cylinder is connected with the second pipeline through the hydraulic control check valve.

[0020] In the embodiment, the driving motor (such as a servo motor) receives an electrical signal instruction from the control unit, drives the linear motion mechanism to convert the rotary motion into high-precision linear motion, and then drives the piston rod in the compensation oil cylinder to move linearly. Specifically, in the pressure boosting stage, the driving motor accurately pushes the piston to move inward in the cylinder body according to the compensation flow instruction through the linear motion mechanism, so that the volume of the compensation oil cylinder decreases, and the oil in the compensation oil cylinder is pressed into the second pipeline, thereby providing a small flow and high response compensation flow for the gas storage cylinder, which is superimposed with the basic flow output by the hydraulic power unit to ensure the accuracy and stability of the pressure boosting process. In the pressure maintaining stage, the driving motor works under the instruction corresponding to the first compensation displacement, and drives the piston rod to move slightly through the linear motion mechanism to maintain the pressure constant: when the pressure decreases (such as oil temperature decrease or slight leakage), the piston rod moves inward to supplement a small amount of high-pressure oil to the main oil line to realize positive pressure compensation; when the pressure rises (such as oil temperature rise), the piston rod moves outward to receive a small amount of high-pressure oil from the main oil line to realize negative pressure compensation. In the pressure relief stage, the hydraulic compensation unit does not actively control the pressure or is in a standby state.

[0021] Further, the test device further comprises a heat exchange unit, the heat exchange unit is arranged between the hydraulic power unit and the multi-stage pressure boosting unit; the control unit is further configured to calculate a temperature rise according to a real-time temperature of the hydrogen storage cylinder, and start the heat exchange unit when the temperature rise is greater than a temperature rise threshold or the real-time temperature is greater than a temperature threshold, to realize active thermal management.

[0022] The heat exchange unit directly reduces the temperature of the oil entering the hydrogen storage cylinder, effectively controls the temperature rise within the allowable range, and directly solves the problem of heat accumulation; the fatigue performance of the composite material of the measured hydrogen storage cylinder is highly related to the temperature, and the heat exchange unit reduces the oil temperature to provide a test environment close to isothermal or controllable temperature for the hydrogen storage cylinder, which makes the load condition applied to the hydrogen storage cylinder more pure, the fatigue life data obtained more truly reflects the performance of the hydrogen storage cylinder under the design working condition, and the accuracy of life prediction is improved.

[0023] Further, the control unit is further configured to calculate a material attenuation coefficient according to the peak pressure and the valley pressure in each cycle in the cycle control stage; calculate a real-time pressure amplitude according to the material attenuation coefficient, an initial pressure amplitude and a number of cycles N; calculate a pressure amplitude attenuation rate according to the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude attenuation rate is greater than a set percentage threshold, calculate a second compensation displacement according to the average of the instantaneous volume elastic deformations in the first n number of cycles, and control the hydraulic compensation unit to work according to the second compensation displacement, to realize long-period pressure online compensation.

[0024] The initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle, and n≤N.

[0025] In the embodiment, the device no longer passively executes a fixed pressure curve, but actively senses micro changes in the hydrogen storage bottle material and adjusts the test load in real time to compensate for the stiffness decay caused by material fatigue, ensuring that the pressure amplitude applied to the hydrogen storage bottle is stable and true throughout the fatigue test process, improving test accuracy and the accuracy of life prediction.

[0026] Based on the same concept, the application also provides a hydraulic fatigue test method for a high-pressure hydrogen storage bottle, based on the hydraulic fatigue test device described above, the test method comprising a pressure increasing phase, a pressure maintaining phase and a pressure releasing phase;

[0027] In the pressure increasing phase, the instantaneous volumetric elastic deformation of the hydrogen storage bottle is obtained, and the main flow instruction and the compensation flow instruction are calculated according to the instantaneous volumetric elastic deformation, the target pressure increasing rate, the initial volume and the stable efficient flow;

[0028] The hydraulic power unit is controlled according to the main flow instruction to provide the basic flow for the hydrogen storage bottle, and the hydraulic compensation unit is controlled according to the compensation flow instruction to provide the compensation flow for the hydrogen storage bottle to eliminate errors and disturbances;

[0029] In the pressure maintaining phase, the real-time temperature and the real-time pressure of the hydrogen storage bottle are obtained, and the first compensation displacement is calculated according to the real-time temperature and the target temperature, or the real-time pressure and the target pressure, and the hydraulic compensation unit is controlled according to the first compensation displacement to eliminate errors caused by temperature changes or internal leakage;

[0030] In the pressure releasing phase, the instantaneous volumetric elastic deformation and the real-time flow of the hydrogen storage bottle are obtained, and the opening degree of the pressure releasing valve is calculated according to the instantaneous volumetric elastic deformation, the target pressure decreasing rate, the initial volume and the real-time flow, and the pressure releasing valve is controlled according to the opening degree to realize smooth and impact-free pressure releasing.

[0031] Further, the specific calculation process of the main flow instruction and the compensation flow instruction is as follows:

[0032] The theoretical flow in the pressure increasing phase is calculated, and the specific calculation formula is as follows:

[0033] ;

[0034] Wherein, represents the theoretical flow in the pressure increasing phase; represents the initial volume of the hydrogen storage bottle; represents the instantaneous volumetric elastic deformation of the hydrogen storage bottle at time t; represents the set target pressure increasing rate; Indicates the effective compression ratio;

[0035] The main flow instruction is calculated using the following formula:

[0036] ;

[0037] in, Indicates the main flow command; Indicates stable and efficient traffic; Indicates the safety factor;

[0038] The compensation flow command is calculated using the following formula:

[0039] ;

[0040] in, This indicates a compensation flow command; This represents the estimated value of the disturbance flow.

[0041] Furthermore, the specific calculation formula for the first compensation displacement is as follows:

[0042] ,or ;

[0043] ;

[0044] ;

[0045] 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.

[0046] Furthermore, the specific calculation process for the opening degree of the pressure relief valve is as follows:

[0047] The specific formula for calculating the flow compensation coefficient is as follows:

[0048] ;

[0049] wherein, represents a flow compensation coefficient; represents a calibration constant; represents an initial volume of the hydrogen storage bottle; represents an instantaneous volume elastic deformation amount of the hydrogen storage bottle at time t;

[0050] calculating a theoretical flow rate of the pressure relief stage, and the specific calculation formula is:

[0051] ;

[0052] wherein, represents a theoretical flow rate of the pressure relief stage; represents a set target pressure reduction rate; represents an effective compression coefficient;

[0053] taking the product of the flow compensation coefficient and the theoretical flow rate of the pressure relief stage as a corrected flow rate, and converting it into an opening value, and the specific conversion formula is:

[0054] ;

[0055] wherein, represents an opening value; represents a corrected flow rate; represents a rated flow coefficient of the pressure relief valve;

[0056] calculating an opening correction value, and the specific calculation formula is:

[0057] ;

[0058] wherein, represents an opening correction value; , respectively represent a second proportional coefficient and a second integral coefficient; represents a real-time flow rate of the hydrogen storage bottle outlet; and t represents time;

[0059] calculating the sum of the opening value and the opening correction value to obtain a final opening of the pressure relief valve.

[0060] Preferably, the specific calculation formula of the instantaneous volume elastic deformation amount is:

[0061] ;

[0062] wherein, represents an instantaneous volume elastic deformation amount of the hydrogen storage bottle at time t; represents a hoop strain of the hydrogen storage bottle; represents an initial volume of the hydrogen storage bottle.

[0063] Further, the test method further comprises a long-period pressure online compensation of the cycle control stage, and specifically comprises:

[0064] A material attenuation coefficient is calculated according to the peak pressure and the valley pressure in each cycle;

[0065] A real-time pressure amplitude is calculated according to the material attenuation coefficient, an initial pressure amplitude and a cycle number N; wherein the initial pressure amplitude refers to a difference between the peak pressure and the valley pressure in the first cycle;

[0066] A pressure amplitude attenuation rate is calculated according to the real-time pressure amplitude and the initial pressure amplitude;

[0067] When the pressure amplitude attenuation rate is greater than a set percentage threshold, a second compensation displacement is calculated according to an average of instantaneous volume elastic deformations in the previous n cycle numbers; wherein n<=N;

[0068] The hydraulic compensation unit is controlled according to the second compensation displacement, so as to realize long-period pressure stable compensation.

[0069] Compared with the prior art, the present application has the following beneficial effects:

[0070] The hydraulic fatigue test device provided by the present application brings performance improvement through the introduction of the hydraulic compensation unit and the fine division and cooperation with the hydraulic power unit and the multi-stage pressurization unit, combined with multi-parameter sensing and intelligent control algorithm, which is specifically embodied in the following aspects:

[0071] The present application realizes coarse-fine collaborative adjustment of flow by decomposing total demand flow into basic flow provided by the hydraulic power unit and compensation flow provided by the hydraulic compensation unit in the pressurization stage through the unique "feedforward-feedback compound control" strategy; in the pressure maintaining stage, according to temperature deviation and pressure deviation, the hydraulic compensation unit is used for small volume compensation, which actively offsets pressure drift caused by thermal expansion and contraction and leakage. This mechanism fundamentally suppresses pressure overshoot and fluctuation, and can realize pressure stability of ±0.15MPa level, ensuring high fidelity of the fatigue load waveform.

[0072] The present application directly embeds temperature as a core control variable into the pressure maintaining control process. The control unit drives the hydraulic compensation unit to perform volume compensation according to the deviation between real-time temperature and target temperature, which not only stabilizes the pressure, but also actively eliminates the influence of temperature change on the core test parameter from the control level. Combined with the front physical cooling of the heat exchange unit, a double thermal management mechanism of "physical cooling + control compensation" is formed, which effectively controls the hydrogen storage bottle surface temperature rise ΔT at a very low level, avoiding the safety risk and material performance test distortion caused by thermal runaway.

[0073] The test device of the present application can capture the instantaneous volumetric elastic deformation reflecting the mechanical state of the material in real time through a high-precision detection unit. In the cycle control stage, the control unit can adaptively adjust the output according to the change of the instantaneous volumetric elastic deformation, compensate for the stiffness decay caused by material fatigue damage, and ensure that the pressure amplitude applied to the hydrogen storage bottle is constant throughout the service life. This provides high-quality and interference-free load-strain data for life prediction, fundamentally solves the prediction deviation (> 20%) problem caused by not considering material anisotropy and damage accumulation, and lays a solid foundation for achieving precise evaluation of 30000 cycle amplitude decay rate < 3%.

[0074] The present application covers the precise control strategy of the whole process of pressure boosting, pressure maintaining and pressure relief. In particular, in the pressure relief stage, the pressure relief valve opening is accurately calculated according to the instantaneous volumetric elastic deformation and the target pressure relief rate, realizing smooth and controllable pressure relief, avoiding hydraulic impact on the pipeline and the hydrogen storage bottle, and further improving the reliability of the equipment and the repeatability of the test. BRIEF DESCRIPTION OF DRAWINGS

[0075] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only one embodiment of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0076] Figure 1 is a structural schematic diagram of the hydraulic fatigue test device in the embodiment of the present application;

[0077] Figure 2 is a flow chart of the hydraulic fatigue test method in the embodiment of the present application.

[0078] Explanation of reference numerals: 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 plunger pump, 13-control unit, 14-hydraulic control check valve. DETAILED DESCRIPTION

[0079] The technical solutions in the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0080] 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.

[0081] Example 1

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The oil undergoes three stages of pressurization, gradually increasing its pressure until it reaches the target pressure of 70 MPa.

[0086] 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.

[0087] The compensation oil cylinder is pre-filled with hydraulic oil in a cavity (i.e. formed by the compensation oil cylinder body and the piston in the compensation oil cylinder body, and the piston is connected with the piston rod), and the cavity is connected to the second pipeline through a hydraulic control one-way valve 14. The conduction direction of the hydraulic control one-way valve 14 is configured to allow the oil to flow from the cavity of the compensation oil cylinder to the second pipeline, so as to realize positive pressure compensation; when it is necessary to supplement oil into the cavity of the compensation oil cylinder, the control unit 13 sends an opening signal to the pilot control port of the hydraulic control one-way valve 14, so as to forcibly open the hydraulic control one-way valve 14, and the oil in the second pipeline can flow reversely into the container of the compensation oil cylinder. The hydraulic compensation unit 9 has no independent circulating power source, and the oil supplement comes from the pressure of the main oil circuit itself, so that the one-way hydraulic coupling with the main oil circuit is realized.

[0088] Since the ball screw pair itself has the irreversible transmission self-locking characteristic, when the servo motor stops rotating, the ball screw pair can effectively lock the piston rod of the compensation oil cylinder at the current position, maintain the volume of the second pipeline unchanged, and form a mechanical sealing barrier.

[0089] In the embodiment, the test piece is a Type IV (plastic liner, carbon fiber winding) hydrogen storage bottle with a nominal volume of 50L, and the calibrated initial volume is 0.05m 3 ; the hydraulic power unit is a variable frequency plunger pump 12 with a rated speed of 3000rpm; the pressure increasing ratios of the first-stage pressure increasing cylinder 6, the second-stage pressure increasing cylinder 7 and the third-stage pressure increasing cylinder 8 are 1:10, 1:15 and 1:20 respectively; the rated torque of the servo motor of the hydraulic compensation unit 9 is 10N·m, and the lead of the ball screw pair is 5mm; the range of the pressure sensor 2 is 100MPa, and the accuracy is 0.1%FS; the range of the temperature sensor 3 (Pt100) is-50℃~150℃, and the accuracy is 0.5℃; the control unit 13 is an embedded controller combining ARMCortex-M7 and FPGA; and the pressure relief valve 5 is an electromagnetic proportional valve. In the pressure increasing stage and the pressure maintaining stage, the electromagnetic proportional valve is closed, and the high-pressure oil enters the hydrogen storage bottle; in the pressure relief stage, the electromagnetic proportional valve is opened, and the high-pressure oil flows back to the oil tank 11 through the pressure relief pipeline.

[0090] In the specific embodiment of the application, the test device further comprises a heat exchange unit 10 arranged between the hydraulic power unit and the multi-stage pressure increasing unit. In the embodiment, the heat exchange unit 10 is a heat exchanger.

[0091] The complete oil path is: the oil tank 11, the variable frequency plunger pump 12, the heat exchanger, the first-stage pressure increasing cylinder 6, the first accumulator, the second-stage pressure increasing cylinder 7, the second accumulator, the third-stage pressure increasing cylinder 8, the second pipeline, the hydrogen storage bottle, the electromagnetic proportional valve, the oil tank 11; the compensation oil cylinder, the second pipeline, the hydrogen storage bottle.

[0092] 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 the embodiment, the detection unit comprises 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 in the hydrogen storage cylinder; the flow meter 1 is used to detect the real-time flow rate of the hydrogen storage cylinder outlet; the strain gauge 4 is attached to the surface of the hydrogen storage cylinder and is used to detect the hoop strain of the hydrogen storage cylinder, and then the instantaneous volumetric elastic deformation of the hydrogen storage cylinder is calculated according to the hoop strain, and the specific calculation formula is:

[0093] (1)

[0094] wherein, represents the instantaneous volumetric elastic deformation of the hydrogen storage cylinder at time t, unit: m 3 ; represents the hoop strain of the hydrogen storage cylinder, dimensionless; represents the initial volume of the hydrogen storage cylinder.

[0095] The initial volume of the hydrogen storage cylinder can be obtained by using the deionized water calibration method, and the specific process is as follows: deionized water is injected into the empty hydrogen storage cylinder to normal pressure (P0=0.1 MPa), and then the injection volume is detected by a high-precision flow meter 1 (accuracy ±0.1%), and the initial volume of the hydrogen storage cylinder is obtained. The initial volume is calibrated by using deionized water, which aims to eliminate the risk of electrochemical corrosion caused by ions in water, avoid the influence of dissolved gas on the measurement accuracy, and ensure the compatibility with the hydraulic fatigue test device, so as to ensure the accuracy of the calibration result and the safety of the test.

[0096] The control unit 13 is connected with 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 comprises a pressure rising stage, a pressure maintaining stage and a pressure relief stage. In the pressure rising stage, the control unit 13 calculates the instantaneous volumetric elastic deformation according to the hoop strain of the hydrogen storage cylinder collected by the strain gauge 4 (see formula (1)), and sets the target pressure rising rate according to the instantaneous volumetric elastic deformation , the set target pressure rising rate and the initial volume of the hydrogen storage cylinder and stable high-efficiency flow meter 1 main flow instruction and compensation flow instruction; according to the main flow instruction control variable frequency piston pump 12 work, variable frequency piston pump 12 frequency converter received main flow instruction (converted into speed signal), drive its internal three-phase asynchronous motor in the 500-3000 rpm range accurate adjustment speed, asynchronous motor drive pump head, from the oil tank 11 low pressure oil, oil through the first pipeline to the three-stage supercharging unit, after three-stage continuous supercharging output high pressure oil (for example, the pressure is 70MPa), high pressure oil through the second pipeline to the hydrogen storage bottle, through the main oil road for hydrogen storage bottle high efficiency, stable provide basic flow. At the same time, the control unit 13 according to the compensation flow instruction control hydraulic compensation unit 9 servo motor work, servo motor in turn drive ball screw pair with 0.1-5mm / s speed accurate compensation oil cylinder piston rod (towards the inside of the cylinder) advances, compensation oil cylinder volume decreases, injects a additional, controlled compensation flow to the second pipeline, to accurately compensate for the pressure rise rate lag due to the volume elasticity of hydrogen storage bottle and flow compressibility, eliminates the error and disturbance.

[0097] Stable high-efficiency flow refers to the flow value that the hydraulic power unit (such as variable frequency piston pump 12, servo motor driven quantitative piston pump, proportional variable pump or servo variable pump, etc.) can output stably and efficiently. Taking the variable frequency piston pump 12 as an example, the process of obtaining stable high-efficiency flow is as follows:

[0098] Draw the specific curve of variable frequency piston pump 12 at a certain speed, including flow-head (pressure) curve and flow-efficiency curve; analyze the whole device, calculate the total pressure required at different flow (need to overcome the resistance of the pipeline of net head), get the demand curve; determine the stable working point from the intersection of flow-head (pressure) curve and demand curve; determine the efficiency of stable working point based on flow-efficiency curve; if the efficiency of stable working point is in the high efficiency area, the flow of stable working point is stable high-efficiency flow; if the efficiency of stable working point is not in the high efficiency area, change the speed of variable frequency piston pump 12, repeat the steps of specific curve drawing, demand curve drawing, stable working point determination, stable working point efficiency determination and efficiency in high efficiency area judgment, until the stable high-efficiency flow is obtained.

[0099] When the pressure sensor 2 detects that the real-time pressure reaches the set peak value (for example, the nominal working pressure or the rated filling pressure of the hydrogen storage cylinder, and the maximum standard is 70 MPa for the vehicle-mounted hydrogen storage cylinder), the control unit 13 controls the hydraulic power unit to reduce the rotating speed or stop working to stop the supply of the basic flow, and controls the hydraulic compensation unit 9 to stop working to stop the supply of the compensation flow, so that the device enters the pressure maintaining stage. In the pressure maintaining stage, there may be temperature changes that cause abnormal pressure rise or extremely small internal leakage (<0.1 mL / min) that causes pressure drop. The control unit 13 calculates the first compensation displacement according to the real-time temperature collected by the temperature sensor 3 and the set target temperature, or the real-time pressure collected by the pressure sensor 2 and the set target pressure, and controls the hydraulic compensation unit 9 to work according to the first compensation displacement, so as to eliminate the errors caused by temperature changes (abnormal pressure rise) or internal leakage (pressure drop), and ensure that the pressure fluctuation is strictly controlled within an extremely high precision of ≤±0.15 MPa throughout the pressure maintaining stage.

[0100] Specifically, if the temperature changes cause abnormal pressure rise, the first compensation displacement is calculated according to the real-time temperature collected by the temperature sensor 3 and the set target temperature, and the servo motor is controlled to reverse according to the first compensation displacement, so that the piston rod of the compensation oil cylinder moves outward to receive a small amount of high-pressure oil from the main oil path, thereby realizing negative pressure compensation; if the extremely small internal leakage (<0.1 mL / min) causes pressure drop, the first compensation displacement is calculated according to the real-time pressure collected by the pressure sensor 2 and the set target pressure, and the servo motor is controlled to rotate forward according to the first compensation displacement, so that the piston rod of the compensation oil cylinder moves inward to supplement a small amount of high-pressure oil to the main oil path, thereby realizing positive pressure compensation.

[0101] After the pressure maintaining time ends, the control unit 13 issues an instruction to control the pressure relief valve 5 to open, so that the device enters the pressure relief stage. In the pressure relief stage, the control unit 13 calculates the instantaneous volume elastic deformation amount (see formula (1)) according to the circumferential strain of the hydrogen storage cylinder collected by the strain gauge 4, calculates the opening degree of the pressure relief valve 5 according to the instantaneous volume elastic deformation amount, the set target pressure reduction rate, the initial volume and the real-time flow meter 1, and controls the pressure relief valve 5 to act in real time according to the opening degree, so as to realize a smooth and impact-free pressure relief process, and avoid damage to the hydrogen storage cylinder, sensors and the like caused by sudden pressure drop. When the pressure sensor 2 detects that the real-time pressure decreases to the set valley value, the control unit 13 controls the pressure relief valve 5 to close, and ends the pressure relief stage.

[0102] The hydraulic fatigue test of the hydrogen storage cylinder needs to be performed Nmax times, so after a complete "pressure increase-pressure maintenance-pressure relief" cycle ends, the timer or counter in the control unit 13 automatically triggers the start of the next cycle. The "pressure increase-pressure maintenance-pressure relief" process is repeated according to the set cycle number Nmax (for example, 30000 times) to achieve automatic continuous movement. The cycle frequency (for example, 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 surface of the hydrogen storage cylinder in real time. If the detected temperature rise is greater than the set temperature rise threshold (for example, 5°C) or the real-time temperature is greater than the set temperature threshold (for example, 45°C), the control unit 13 dynamically reduces the cycle frequency (for example, 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 from the source and achieving active thermal management.

[0103] In order to overcome the performance degradation (for example, increased internal leakage, seal creep, etc.) caused by tens of thousands of pressure cycles, the control unit 13 also performs online prediction and compensation of long-period pressure during the cycle control phase, and when the pressure amplitude decay rate is greater than the preset percentage threshold (for example, 3% or 2.5%), the control unit 13 automatically triggers the compensation mechanism to maintain the pressure output stability at a very high level.

[0104] Specifically, during the cycle control phase, the control unit 13 calculates the material attenuation coefficient based on the peak pressure and the 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 decay rate based on the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude decay rate is greater than the set percentage threshold, calculates the second compensation displacement based on the average 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 online compensation of long-period pressure; wherein the initial pressure amplitude refers to the difference between the peak pressure and the valley pressure in the first cycle.

[0105] During the entire fatigue test process, the device automatically synchronously records and stores all time-pressure curves, cycle number-temperature, cycle number-compensation displacement (first compensation displacement and second compensation displacement), and other data, providing complete and accurate data support for evaluating the fatigue life and safety performance of the hydrogen storage cylinder.

[0106] Embodiment Two

[0107] As shown in Figure 2 Based on the hydraulic fatigue test device in Embodiment One of the present application, the hydraulic fatigue test method for high-pressure hydrogen storage cylinders provided in this embodiment includes the following steps:

[0108] Step 1, Preparation before test: Obtain the initial volume of the gas cylinder.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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:

[0113] Step 3.1: Calculate the theoretical flow rate during the boost stage. The specific calculation formula is as follows:

[0114] (2)

[0115] 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.

[0116] Step 3.2: Calculate the main flow command. The specific calculation formula is as follows:

[0117] (3)

[0118] in, Indicates the main flow command; Indicates stable and efficient traffic; Safety factor is a number slightly less than 1, in the embodiment, the value range is 0.92~0.98.

[0119] Step 3.3, calculate the compensation flow instruction, the specific formula is:

[0120] (4)

[0121] wherein, represents the compensation flow instruction; represents the disturbance flow estimation value, which can be estimated in real time by the disturbance observer of the control unit.

[0122] Step 4, control the hydraulic power unit to work according to the main flow instruction, and provide the hydrogen storage cylinder with the basic flow; control the hydraulic compensation unit to work according to the compensation flow instruction, and provide the hydrogen storage cylinder with the compensation flow to eliminate errors and disturbances.

[0123] Specifically, the control unit controls the variable frequency plunger pump to work according to the main flow instruction, the frequency converter of the variable frequency plunger pump receives the main flow instruction (converted into a speed signal) to drive the internal three-phase asynchronous motor to accurately adjust the speed in the range of 500-3000 rpm, the asynchronous motor drives the pump head to extract low-pressure oil from the oil tank, the oil is transported to the three-stage supercharging unit through the first pipeline, and high-pressure oil (for example, the pressure is 70 MPa) is output after three-stage continuous supercharging, the high-pressure oil is transported to the hydrogen storage cylinder through the second pipeline, and the hydrogen storage cylinder is efficiently and stably provided with the basic flow through the main oil way. At the same time, the control unit controls the servo motor of the hydraulic compensation unit to work according to the compensation flow instruction, and the servo motor drives the ball screw pair to accurately advance the piston rod of the compensation oil cylinder (move to the inside of the cylinder) at a speed of 0.1-5 mm / s, the volume of the compensation oil cylinder decreases, and an additional controlled compensation flow is injected into the second pipeline to accurately compensate for the pressure rise rate hysteresis caused by the volumetric elastic deformation and flow compressibility of the hydrogen storage cylinder, and eliminate errors and disturbances.

[0124] Step 5, obtain the real-time pressure of the hydrogen storage cylinder, and judge whether the real-time pressure reaches the set peak value, if so, control the hydraulic power unit and the hydraulic compensation unit to stop working, and enter the pressure maintaining stage.

[0125] When the pressure sensor detects that the real-time pressure reaches the set peak value (for example, the nominal working pressure or the rated filling pressure of the hydrogen storage cylinder, and for the vehicle-mounted hydrogen storage cylinder, the highest standard is 70 MPa), the control unit controls the hydraulic power unit to reduce the speed or stop working to stop the supply of the basic flow, and controls the hydraulic compensation unit to stop working to stop the supply of the compensation flow, and the device enters the pressure maintaining stage.

[0126] Step 6, during the pressure maintaining stage, the real-time temperature and the real-time pressure of the hydrogen storage cylinder are obtained.

[0127] Step 7, the first compensation displacement is calculated according to the real-time temperature and the target temperature, or the real-time pressure and the target pressure, and the hydraulic compensation unit is controlled to work according to the first compensation displacement, so as to eliminate the error caused by temperature change or internal leakage.

[0128] If the temperature change causes the pressure to abnormally rise, the first compensation displacement is calculated according to the real-time temperature collected by the temperature sensor and the set target temperature, and the servo motor is controlled to reverse according to the first compensation displacement, so that the piston rod of the compensation oil cylinder moves outward to receive a small amount of high-pressure oil from the main oil circuit, thereby realizing negative compensation of pressure. In this embodiment, the specific calculation formula of the first compensation displacement caused by temperature change is as follows:

[0129] (5)

[0130] (6)

[0131] Wherein, represents the compensation amount caused by temperature change; represents the cross-sectional area of the piston in the compensation oil cylinder; represents the total volume of the second pipeline and the gas cylinder; represents the target temperature; represents the real-time temperature of the hydrogen storage cylinder; represents the bulk modulus of oil, which is a physical constant representing the compressibility of oil, and its value is about 1400-2000 MPa.

[0132] If the extremely small internal leakage (<0.1 mL / min) causes the pressure to drop, the first compensation displacement is calculated according to the real-time pressure collected by the pressure sensor and the set target pressure, and the servo motor is controlled to rotate forward according to the first compensation displacement, so that the piston rod of the compensation oil cylinder moves inward to supplement a small amount of high-pressure oil to the main oil circuit, thereby realizing positive compensation of pressure. In this embodiment, the specific calculation formula of the first compensation displacement caused by internal leakage change is as follows:

[0133] (7)

[0134] (8)

[0135] Wherein, represents the compensation amount caused by internal leakage; represents the first proportional coefficient, the larger the pressure deviation, the larger the compensation displacement, which is used for rapid response; ​​represents the first integral coefficient, proportional to the cumulative sum of all pressure deviations in the past period of time, used to eliminate static errors (such as slow pressure drop caused by continuous small leakage), and the integral term is the key to achieve accurate compensation; represents the first differential coefficient, proportional to the rate of change of pressure deviation, predicts the future trend of pressure deviation, makes the response more stable and reduces overshoot; represents the target pressure (for example, 70 MPa); represents the real-time pressure of the hydrogen storage cylinder; represents time.

[0136] According to the first compensation displacement, the hydraulic compensation unit is controlled, and the pressure is controlled within 70 MPa±0.15 MPa throughout the pressure maintaining stage.

[0137] Step 8, judge whether the pressure maintaining time is reached, if yes, enter the pressure relief stage and control the pressure relief valve to open.

[0138] After the pressure maintaining time is over, the control unit issues an instruction to control the pressure relief valve to open, 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.

[0139] Step 9, in the pressure relief stage, the hoop strain of the hydrogen storage cylinder is obtained by using the strain gauge, and the real-time flow of the hydrogen storage cylinder is obtained by using the flowmeter, and the instantaneous volume elastic deformation of the hydrogen storage cylinder is calculated according to the hoop strain, as shown in formula (1).

[0140] Step 10, the opening of the pressure relief valve is calculated according to the instantaneous volume elastic deformation, the target pressure relief rate, the initial volume and the real-time flow, and the pressure relief valve is controlled to act in real time according to the opening, so as to realize smooth and impact-free pressure relief.

[0141] In the specific embodiment of the present application, the specific calculation process of the opening of the pressure relief valve is as follows:

[0142] Step 10.1, calculate the flow compensation coefficient, and the specific calculation formula is as follows:

[0143] (9)

[0144] wherein, represents the flow compensation coefficient; represents the calibration constant, which is determined by the no-load calibration test, and the typical value is 1.05; represents the initial volume of the hydrogen storage cylinder; represents the instantaneous volume elastic deformation of the hydrogen storage cylinder at time t.

[0145] Step 10.2, calculate the theoretical flow in the pressure relief stage, and the specific calculation formula is as follows:

[0146] (10)

[0147] wherein, represents the theoretical flow rate of the pressure relief phase; represents the set target pressure relief rate; represents the effective compression coefficient.

[0148] Step 10.3, compensating the flow rate with the flow rate compensation coefficient and the product of the theoretical flow rate of the pressure relief phase as the corrected flow rate, and converting it into an opening value, and the specific conversion formula is:

[0149] (11)

[0150] wherein, represents the opening value; represents the corrected flow rate; represents the rated flow rate coefficient of the pressure relief valve.

[0151] Step 10.4, calculating the opening correction value, and the specific calculation formula is:

[0152] (12)

[0153] wherein, represents the opening correction value; , respectively represent the second proportional coefficient and the second integral coefficient; represents the real-time flow rate at the outlet of the hydrogen storage bottle, which is measured by a flow meter; represents time. In this embodiment, is 0.8, is 0.2.

[0154] Step 10.5, calculating the sum of the opening value and the opening correction value to obtain the final opening of the pressure relief valve.

[0155] According to steps 10.1 to 10.5, the final opening of the pressure relief valve is calculated in real time to adjust the opening of the pressure relief valve in real time, so as to realize smooth and impact-free pressure relief. When the pressure sensor detects that the real-time pressure is reduced to the set valley value, the control unit controls the pressure relief valve to be closed, the pressure relief phase is ended, and one hydraulic fatigue test is completed.

[0156] In the specific embodiment of the present application, in order to overcome the performance degradation (such as increased internal leakage, sealing creep, etc.) caused by tens of thousands of pressure cycles, the test method further includes long-period pressure online compensation in the cycle control phase, and specifically includes the following steps:

[0157] The peak pressure and the valley pressure in each cycle are used to calculate the material attenuation coefficient;

[0158] The real-time pressure amplitude is calculated according to 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;

[0159] The pressure amplitude attenuation rate is calculated according to the real-time pressure amplitude and the initial pressure amplitude;

[0160] When the pressure amplitude attenuation rate is greater than the set percentage threshold, the second compensation displacement is calculated according to the average of the instantaneous volume elastic deformation amount in the previous n cycles;

[0161] The hydraulic compensation unit is controlled according to the second compensation displacement to realize long-period pressure stable compensation.

[0162] In this embodiment, a single cycle is a complete process of pressure rising, pressure maintaining and pressure releasing. The real-time pressure at different sampling times in a single cycle is collected by a pressure sensor, so that the peak pressure (i.e. the maximum real-time pressure) and the valley pressure (i.e. the minimum real-time pressure) in each cycle can be determined; the difference between the peak pressure and the valley pressure in each cycle is calculated, i.e. the instantaneous pressure amplitude in the cycle is obtained; the material attenuation coefficient is calculated based on the mathematical model of exponential decay law:

[0163] (13)

[0164] Wherein, represents the instantaneous pressure amplitude in the i th cycle; represents the initial pressure amplitude; represents the material attenuation coefficient in the i th cycle.

[0165] Taking the natural logarithm of both sides of formula (13), a linear relationship is obtained:

[0166] (14)

[0167] The natural logarithm of the instantaneous pressure amplitude is linearly fitted with the number of cycles, so that the material attenuation coefficient (fitting slope) can be obtained. Further, the calculation formula of the real-time pressure amplitude can be obtained:

[0168] (15)

[0169] Wherein, represents the real-time pressure amplitude; represents the number of cycles; represents the material attenuation coefficient. The calculated value of the material attenuation coefficient in this embodiment is 1.69 × 10 -6 .

[0170] The calculation formula of the pressure amplitude attenuation rate is:

[0171] (16)

[0172] According to the calculated pressure amplitude decay rate and the set percentage threshold, it is determined whether to calculate the second compensation displacement, and then the long-period pressure stabilization compensation is performed. The pressure amplitude decay rate is calculated according to formula (16) once every 1000 cycles, and then a determination and compensation are performed. In the embodiment, the percentage threshold is 2.5%. That is, when the pressure amplitude decay rate is greater than 2.5% (after about 15000 cycles), the control unit calculates the second compensation displacement, and the specific calculation formula is as follows:

[0173] (17)

[0174] wherein, represents the second compensation displacement; represents the average value of the instantaneous volumetric elastic deformation in the previous n cycles (in the embodiment, n is 100); represents the cross-sectional area of the piston in the compensation oil cylinder. The compensation direction of the second compensation displacement is determined according to 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, the piston rod of the compensation oil cylinder is controlled to move inward, a small amount of high-pressure oil is supplemented to the main oil circuit, and positive pressure compensation is realized; when the target pressure is less than the real-time pressure, the servo motor is controlled to rotate reversely, the piston rod of the compensation oil cylinder is controlled to move outward, a small amount of high-pressure oil is accepted from the main oil circuit, and negative pressure compensation is realized; when the target pressure is equal to 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.

[0175] In the embodiment, the initial cycle frequency is set to 1 Hz. During the cycle control process, the control unit dynamically adjusts the cycle frequency according to the real-time temperature collected by the temperature sensor. Specifically, when the temperature rise rate of the hydrogen storage bottle is greater than the temperature rise threshold, or the real-time temperature of the hydrogen storage bottle is greater than the temperature threshold, the cycle frequency is controlled to decrease; at the same time, the heat exchanger can also be controlled to start to actively reduce the temperature of the injected oil.

[0176] In the specific test process, the hydraulic fatigue test device is continuously operated, and 30000 pressure cycle tests are successfully completed. During the entire test process, the pressure curve is smooth, the pressure amplitude decay rate is only 2.8%, the maximum temperature on the surface of the hydrogen storage bottle is stably below 58℃, and the high precision, high reliability and excellent heat management capability of the test device and the test method of the present application are successfully verified.

[0177] The above only discloses specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or modifications within the technical scope disclosed by the present application, which shall be covered within the protection scope of the present application.​

Claims

1. A hydraulic fatigue testing device for a high-pressure hydrogen storage cylinder, characterized by, The test device comprises: a hydraulic power unit, an oil inlet of which is connected to an oil tank; a multi-stage pressurization unit, an inlet of which is connected to an oil outlet of the hydraulic power unit through a first pipeline, an outlet of which is connected to an inlet of the hydrogen storage bottle through a second pipeline, and an outlet of the hydrogen storage bottle is connected to the oil tank through a third pipeline, and a pressure relief valve is arranged on the third pipeline; a hydraulic compensation unit, a cavity of which is connected to the second pipeline, and the cavity is pre-filled with hydraulic oil; a detection unit for detecting the instantaneous volume elastic deformation, real-time temperature, real-time pressure and real-time flow rate of the hydrogen storage bottle; and a control unit connected to the hydraulic power unit, the hydraulic compensation unit, the detection unit and the pressure relief valve, for, in the pressurization stage, cooperatively controlling the hydraulic power unit and the hydraulic compensation unit according to the instantaneous volume elastic deformation, the target pressurization rate, the initial volume of the hydrogen storage bottle and the stable and efficient flow rate, so as to eliminate errors and disturbances and realize accurate pressurization; for, in the pressure maintaining stage, controlling the hydraulic compensation unit according to the real-time temperature and the target temperature, or the real-time pressure and the target pressure, so as to eliminate errors caused by temperature changes or internal leakage; and for, in the pressure relief stage, controlling the pressure relief valve according to the instantaneous volume elastic deformation, the target depressurization rate, the initial volume and the real-time flow rate, so as to realize smooth and impact-free pressure relief.

2. The hydraulic fatigue test apparatus according to claim 1, characterized by The multi-stage pressurization unit is a three-stage pressurization unit, which comprises a first accumulator, a second accumulator, and a first-stage pressurization cylinder, a second-stage pressurization cylinder and a third-stage pressurization cylinder connected in sequence; an inlet of the first-stage pressurization cylinder is connected to an oil outlet of the hydraulic power unit through a first pipeline, and an outlet of the third-stage pressurization cylinder is connected to an inlet of the hydrogen storage bottle through a second pipeline; the first accumulator is connected to the pipelines between the first-stage pressurization cylinder and the second-stage pressurization cylinder, and the second accumulator is connected to the pipelines between the second-stage pressurization cylinder and the third-stage pressurization cylinder.

3. The hydraulic fatigue testing apparatus of claim 1, wherein The hydraulic compensation unit comprises a compensation oil cylinder, a driving motor, a linear motion mechanism and a hydraulic control check valve; the driving 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 a piston rod in the compensation oil cylinder, for converting the motion of the driving motor into the linear motion of the piston rod; the cavity of the compensation oil cylinder is connected to the second pipeline through the hydraulic control check valve.

4. The hydraulic fatigue testing apparatus of claim 1, wherein The test device further comprises a heat exchange unit arranged between the hydraulic power unit and the multi-stage pressurization unit; the control unit is further used for calculating the temperature rise according to the real-time temperature of the hydrogen storage bottle, and starting the heat exchange unit when the temperature rise is greater than a temperature rise threshold or the real-time temperature is greater than a temperature threshold, so as to realize active thermal management.

5. The hydraulic fatigue testing apparatus according to any one of claims 1 to 4, characterized by The control unit is further configured to calculate a material attenuation coefficient according to the peak pressure and the valley pressure in each cycle in a cycle control stage; calculate a real-time pressure amplitude according to the material attenuation coefficient, an initial pressure amplitude, and a number N of cycles; calculate a pressure amplitude attenuation rate according to the real-time pressure amplitude and the initial pressure amplitude; calculate a second compensation displacement according to an average of the instantaneous volumetric elastic deformations in the previous n cycles when the pressure amplitude attenuation rate is greater than a set percentage threshold; and control the hydraulic compensation unit to work according to the second compensation displacement, so as to realize long-period pressure online compensation. The initial pressure amplitude refers to a difference between the peak pressure and the valley pressure in the first cycle, and n≤N.

6. A hydraulic fatigue test method for a high-pressure hydrogen storage cylinder, characterized by, The test method comprises a pressure increasing stage, a pressure maintaining stage, and a pressure releasing stage. In the pressure increasing stage, an instantaneous volumetric elastic deformation of the hydrogen storage bottle is obtained, and a main flow instruction and a compensation flow instruction are calculated according to the instantaneous volumetric elastic deformation, a target pressure increasing rate, an initial volume, and a stable high-efficiency flow. The hydraulic power unit is controlled to work according to the main flow instruction, so as to provide a basic flow for the hydrogen storage bottle. The hydraulic compensation unit is controlled to work according to the compensation flow instruction, so as to provide a compensation flow for the hydrogen storage bottle, so as to eliminate errors and disturbances. In the pressure maintaining stage, a real-time temperature and a real-time pressure of the hydrogen storage bottle are obtained, and a first compensation displacement is calculated according to the real-time temperature and a target temperature, or the real-time pressure and a target pressure, so as to eliminate errors caused by temperature changes or internal leakage. In the pressure releasing stage, an instantaneous volumetric elastic deformation and a real-time flow of the hydrogen storage bottle are obtained, and an opening degree of a pressure releasing valve is calculated according to the instantaneous volumetric elastic deformation, a target pressure decreasing rate, an initial volume, and the real-time flow, so as to control the pressure releasing valve to act in real time, so as to realize smooth and impact-free pressure releasing.

7. The hydraulic fatigue test method according to claim 6, characterized by The specific calculation process of the main flow instruction and the compensation flow instruction is as follows: The theoretical flow in the pressure increasing stage is calculated, and the specific calculation formula is as follows: ； wherein, represents a theoretical flow rate of the pressure increasing stage; represents an initial volume of the hydrogen storage cylinder; represents an instantaneous volume elastic deformation amount of the hydrogen storage cylinder at the time t; represents a set target pressure increasing rate; represents an effective compression coefficient; The main flow instruction is calculated, and the specific calculation formula is as follows: ； wherein, represents a main flow rate command; represents a stable high efficiency flow rate; represents a safety factor; The compensation flow instruction is calculated, and the specific calculation formula is as follows: ； wherein, represents a compensation flow rate command; represents a disturbance flow rate estimation value.

8. The hydraulic fatigue test method according to claim 6, characterized by The specific calculation formula of the first compensation displacement is as follows: , or ; ； ； wherein, represents a first compensation displacement; represents a compensation amount caused by temperature change; represents a compensation amount caused by internal leakage; represents a cross-sectional area of a piston in a hydraulic compensation unit; represents a total volume of a second pipeline and a gas cylinder; represents a target temperature; represents a real-time temperature of a hydrogen storage cylinder; represents a bulk modulus of oil; , , respectively represent a first proportional coefficient, a first integral coefficient, and a first differential coefficient; represents a target pressure; represents a real-time pressure of a hydrogen storage cylinder; and t represents time.

9. The hydraulic fatigue test method according to claim 6, characterized by The specific calculation process of the opening degree of the pressure releasing valve is as follows: The flow compensation coefficient is calculated, and the specific calculation formula is as follows: ； wherein, represents a flow compensation coefficient; represents a calibration constant; represents an initial volume of the hydrogen storage cylinder; represents an instantaneous volume elastic deformation amount of the hydrogen storage cylinder at time t; The theoretical flow in the pressure releasing stage is calculated, and the specific calculation formula is as follows: ； wherein, represents the theoretical flow rate of the pressure relief phase; represents the set target pressure reduction rate; represents the effective compression coefficient; The product of the flow compensation coefficient and the theoretical flow in the pressure releasing stage is taken as a correction flow, and the specific conversion formula is as follows: ； wherein, represents an opening value; represents a correction flow rate; represents a rated flow rate coefficient of the pressure relief valve; The opening degree correction value is calculated, and the specific calculation formula is as follows: ； wherein, represents an opening degree correction value; , respectively represent a second proportional coefficient and a second integral coefficient; represents a real-time flow rate of the hydrogen storage bottle outlet; t represents time; The sum of the opening degree value and the opening degree correction value is calculated, so as to obtain the final opening degree of the pressure releasing valve.

10. The hydraulic fatigue test method according to claim 6, characterized by The test method further comprises long-period pressure online compensation in the cycle control stage, and specifically comprises the following steps: A material attenuation coefficient is calculated according to the peak pressure and the valley pressure in each cycle. A real-time pressure amplitude is calculated according to the material attenuation coefficient, an initial pressure amplitude, and a number N of cycles; the initial pressure amplitude refers to a difference between the peak pressure and the valley pressure in the first cycle. calculating a pressure amplitude attenuation rate according to the real-time pressure amplitude and the initial pressure amplitude; when the pressure amplitude attenuation rate is greater than a set percentage threshold, calculating a second compensation displacement according to an average of the instantaneous volume elastic deformation amounts in the previous n times of the cycle; wherein n≤N; controlling the hydraulic compensation unit to work according to the second compensation displacement, so as to realize long-period pressure stable compensation.

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