A high-energy-density dual-piston hydraulic accumulator and its working method

Abstract

This invention discloses a high-energy-density dual-piston hydraulic accumulator and its working method, belonging to the field of hydraulic energy storage technology. It includes a variable-diameter dual-piston chamber formed by the combination of two piston chambers, one smaller and one larger. Each dual-piston chamber contains two interconnected pistons connected by a connecting mechanism, dividing the variable-diameter dual-piston chamber into three chambers: upper, middle, and lower. Oil ports are located at the top and bottom of each chamber. A gas cylinder is connected to the side of the larger piston chamber near the smaller piston chamber via a pipeline, thus making the upper and lower piston chambers oil chambers and the middle piston chamber a gas chamber. Due to the smaller diameter of the upper chamber and the larger diameter of the lower chamber, the rod rises, reducing the volume of the middle piston chamber and compressing the air in the middle piston chamber for energy storage. Its structure is simple, small in size, low in cost, and its energy density is twice that of traditional accumulators.

Description

Technical Field

[0001] This invention relates to the field of hydraulic energy storage technology, and is particularly applicable to a high-energy-density dual-piston hydraulic accumulator and its working method. Background Technology

[0002] Hydraulic transmission is one of the important forms of transmission in modern industry. With the rapid development of industries such as engineering machinery, automobiles, and aerospace, the requirements for transmission systems in related products are constantly increasing. Hydraulic transmission systems, with their advantages of high power ratio, high reliability, and stepless speed regulation, have gradually become one of the most important energy transmission methods in modern industrial equipment.

[0003] However, with the rapid development of the global economy and the increasing use of fossil fuels, the resulting problems of fossil energy depletion and environmental pollution have attracted growing attention. Improving energy efficiency is a key focus in addressing these issues. Therefore, it is necessary to improve the energy efficiency of hydraulic systems to achieve green, low-carbon, and sustainable production, thereby alleviating energy shortages. Recovering, storing, and reusing energy within hydraulic systems is an important method for improving their energy efficiency.

[0004] Employing appropriate and efficient energy storage methods to effectively store energy in hydraulic systems is essential for achieving energy conservation and emission reduction. Piston accumulators are a commonly used hydraulic energy storage device in excavator hydraulic systems. They convert hydraulic energy into compressed gas energy at appropriate times for storage, and release this compressed gas energy back into hydraulic energy when needed to replenish the hydraulic system. Currently, gas-loaded hydraulic energy storage technology is widely used in energy recovery in construction machinery and vehicle braking energy recovery. However, in practical applications, while hydraulic accumulators have a higher power density than other energy storage components, their energy density is far lower than commonly used fuel cells, and they suffer from drawbacks such as large size and high cost. Furthermore, due to energy losses in the system, the output pressure of traditional accumulators when releasing energy is slightly lower than the hydraulic oil pressure when storing energy. Therefore, additional hydraulic pump supply is often required to ensure the normal operation of the hydraulic system, which not only complicates the entire hydraulic system but also reduces efficiency. Summary of the Invention

[0005] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a high-energy-density dual-piston hydraulic accumulator and its operating method. It utilizes two piston chambers of different sizes and a matching piston to increase the pressure within the air chamber, and employs an electromagnetic directional valve to ensure that the output hydraulic pressure is greater than the pressure during storage, thus solving the problem of excessively low output pressure of the accumulator.

[0006] To achieve the above technical objectives, the present invention provides a high-energy-density dual-piston hydraulic accumulator, comprising a variable-diameter dual-piston chamber formed by the combination of two piston chambers, one smaller and one larger. Each dual-piston chamber contains two interconnected pistons, one smaller and one larger, connected by a connecting mechanism. The upper piston of the interconnected piston moves in the smaller-diameter piston chamber above the variable-diameter dual-piston chamber, while the lower piston moves in the larger-diameter piston chamber below the variable-diameter dual-piston chamber. The two pistons are connected by a piston rod, and the interconnected pistons divide the variable-diameter dual-piston chamber into three chambers: an upper piston chamber located from the small piston to the top of the piston chamber, a middle piston chamber between the two pistons, and a lower piston chamber from the large piston to the bottom of the large piston chamber. Oil ports are located at the top and bottom of the variable-diameter dual-piston chamber. A gas cylinder is connected to the side of the large piston chamber near the small piston chamber via a pipeline, thus making the upper and lower piston chambers oil chambers and the middle piston chamber a gas chamber. Due to the smaller diameter of the upper chamber and the larger diameter of the lower chamber, the rod rises, reducing the volume of the middle piston chamber and compressing the air in the middle piston chamber for energy storage.

[0007] Specifically, it includes a lower cylinder and an upper cylinder. The lower cylinder has a lower end cap at its bottom, with an oil inlet at its center. The upper cylinder has an upper end cap at its top, with an oil inlet at its center. The openings of the lower and upper cylinders are connected and sealed to form a variable-diameter double-piston cylinder body, with a smaller upper cylinder and a larger lower cylinder. The lower cylinder contains a lower piston, and the upper cylinder contains an upper piston. A piston rod connects the lower and upper pistons, and the piston rod is connected to the lower piston at its center via a lower spherical hinge. The pistons in the lower and upper chambers are connected at their center via a spherical hinge, enabling linkage between them. The upper chamber piston and the upper chamber end cap form the upper liquid chamber within the double-piston cylinder, while the upper and lower chamber pistons form the gas chamber within the double-piston cylinder. The lower chamber piston and the lower chamber end cap form the lower liquid chamber within the double-piston cylinder. The side of the lower cylinder near the upper cylinder is connected to a gas cylinder that communicates with the gas chamber via a pipeline. During energy storage, the upper liquid chamber is connected to the oil tank, and the initial pressure in the gas cylinder is greater than the inlet oil pressure of the lower liquid chamber, thereby increasing the internal energy of the stored gas.

[0008] A method for operating a high-energy-density dual-piston hydraulic accumulator, wherein the lower chamber oil inlet and the upper chamber oil inlet are connected by pipelines to solenoid valves that control the inlet and outlet of high-pressure oil, the steps of which are as follows:

[0009] During energy storage, the solenoid valve is de-energized and operates in the right position. The upper chamber oil inlet is connected to the oil tank, and high-pressure oil enters the lower chamber liquid chamber of the accumulator through the lower chamber oil inlet. The increased pressure in the lower chamber liquid chamber pushes the lower chamber piston, causing the piston rod to move upward, compressing the gas in the gas chamber. The pressure in the gas cylinder increases, and the hydraulic energy in the lower chamber liquid chamber is converted into the gas pressure internal energy of the gas chamber and the gas cylinder. During this process, the upper chamber liquid chamber is connected to the oil tank. The upper chamber piston is not subjected to hydraulic pressure, and the piston rod is subjected to three forces: the hydraulic pressure in the lower chamber liquid chamber, and the gas pressure acting on the lower and upper chamber pistons respectively. When storing energy, the piston rod moves at a constant speed, thus obtaining the current force balance equation. During energy storage, because the gas chamber pressure is increasing, the hydraulic pressure in the lower chamber liquid chamber increases slowly until the lower chamber liquid chamber pressure reaches its maximum pressure, at which point energy storage is no longer possible, and the piston rod stops moving. At this point, energy storage is complete.

[0010] When energy is released, the solenoid valve is energized and operates in the left position. The oil circuits of the upper and lower liquid chambers of the accumulator are connected. High-pressure oil is connected to the upper and lower liquid chambers through the pipeline. At this time, the pressure in the upper and lower liquid chambers is equal, and the internal energy in the gas cylinder is released. At this time, the piston rod is subjected to four forces and moves downward. The internal energy of the gas chamber and the gas cylinder is converted into hydraulic energy and output through the pipeline. When releasing energy, the pressure in the gas chamber is equal to the pressure in the lower liquid chamber, while when storing energy, the pressure in the gas chamber is greater than the pressure in the lower liquid chamber. Therefore, the oil pressure when releasing energy is greater than the oil pressure when storing energy, thus achieving the effect of pressurization.

[0011] Furthermore, since the upper liquid chamber is connected to the oil tank when storing energy, and the hydraulic pressure is 0, only the total volume of the lower liquid chamber is considered when storing energy. The initial position of the piston rod is at the lowest end, so the initial volume of the lower liquid chamber is 0, and the final state of the lower liquid chamber is the maximum allowable pressure, which is the state when the piston rod rises to the limit position.

[0012] When storing energy, let the initial pressure of the lower chamber be P. y1 The pressure at the end of the lower chamber is P. y2 The initial volume of the air chamber is V q1 ;

[0013] In the initial state, the force exerted on the piston rod by the upper liquid chamber is:

[0014] P y1 A2+P q1 (A1-A0)=P q1 (A2-A0) (6)

[0015] In the final state, the pressure in the lower chamber reaches the maximum inlet pressure, resulting in the following force on the piston rod:

[0016] P y2 A2+P q2(A1-A0)=P q2 (A2-A0) (7)

[0017] By combining equations (6) and (7), the relationship between the pressure in the gas chamber and the pressure in the lower liquid chamber can be obtained:

[0018]

[0019] From this, we can understand the relationship between the volume of the air chamber and the volume change of the lower liquid chamber (13):

[0020]

[0021] Using the gas law, the pressure in the gas chamber is determined by P. q1 Rise to P q2 The following relationship must be satisfied:

[0022] P q1 V q1 n =P q2 V q2 n (10)

[0023] In the formula: P y1 P represents the initial high-pressure oil pressure in the lower chamber; y2 The pressure of the lower chamber high-pressure oil in the final state; P q1 P represents the initial pressure of the air chamber. q2 V represents the pressure in the gas chamber at the final state; A1 is the piston area in the upper chamber; A2 is the piston area in the lower chamber, A2 > A1; A0 is the cross-sectional area of ​​the piston rod; V q1 V is the initial volume of the air chamber; q2 ΔV is the final volume of the air chamber. y ΔV represents the change in the liquid chamber volume of the accumulator in this invention. q This represents the change in air cavity volume;

[0024] Substituting equation (8) into equation (10) yields...

[0025]

[0026] Substituting equation (11) into equation (9), we obtain the current cavity liquid pressure from P. y1 Rise to P y2 Afterwards, the change in volume of the lower chamber fluid cavity, ΔV y :

[0027]

[0028] Furthermore, the stored energy is calculated using the formula for the energy of a gas as a work quantity:

[0029]

[0030] Substituting equation (11) into the equation and simplifying, we can obtain the expression for the energy density μ2:

[0031]

[0032] The pressure P in the lower chamber at the initial state y1 The pressure P at the end state y2 Initial volume V of the air chamber q1 When all are the same, comparing equation (3) and equation (12), since It can be seen that the volume change of the accumulator liquid chamber of the present invention is larger than that of the traditional accumulator, and the volume of oil stored is larger.

[0033] Comparing the energy density expression μ1 of a conventional energy storage device with the energy density expression μ2 of this invention, it can be seen that the energy density of the energy storage device of this invention is higher than that of a conventional energy storage device. times; due to Therefore, the energy density μ2 of the present invention is greater than the energy density μ1 of a conventional energy storage device;

[0034] The increase in energy density is related to the cross-sectional areas A1 and A2 of the two pistons. The larger A1 is, that is, the closer A1 is to A2, the greater the energy density. If the maximum pressure in the gas chamber is P... qmax The maximum pressure in the liquid chamber is P. ymax From equation (8), we can obtain:

[0035]

[0036] As can be seen from equation (15), the larger A1 is, the greater the energy density of the accumulator and the greater the maximum pressure P in the liquid chamber. ymax It is determined by the actual working conditions. If A1 is to be increased, the maximum pressure P of the air chamber needs to be increased. qmax However, the maximum air pressure of the accumulator is limited, thus restricting the maximum value of A1, which is limited by the maximum pressure P of the oil to be stored. ymax The maximum pressure P in the air chamber qmax When the energy density approaches the target value, A1 is very small, so the energy density cannot be increased. Therefore, the ratio of A1 to A2 should be selected reasonably according to the actual working conditions.

[0037] Furthermore, the pressure in the gas chamber during energy release is the same as the pressure P at the end of the energy storage state. q2 Force analysis of the piston rod:

[0038] P y ′A2+P q2 (A1-A0)=P q2 (A2-A0)+P y ′A1 (16)

[0039] We can obtain:

[0040]

[0041] In the formula: A1 is the effective cross-sectional area of ​​the upper piston rod cavity; A2 is the effective cross-sectional area of ​​the lower piston cavity, A2 > A1; A0 is the cross-sectional area of ​​the piston rod; P y ′ represents the high-pressure oil pressure in the hydraulic chamber when energy is released;

[0042] Therefore, it can be concluded that the output high-pressure oil pressure during energy release is the same as the high-pressure oil pressure during energy storage. Therefore, the accumulator of the present invention can play a role in boosting pressure.

[0043] Beneficial effects:

[0044] 1) The accumulator of this invention increases the pressure of the air chamber compared to traditional piston accumulators, thereby increasing the stored energy. It can release greater force within the same volume. In excavators, while only needing to store the energy required for boom descent, the weight and volume of the accumulator can be reduced, lowering costs.

[0045] 2) Due to the throttling pressure difference in the hydraulic system, traditional accumulators are insufficient to push the piston rod upward when releasing energy, so a booster pump is needed to increase the pressure to push the boom upward. However, the accumulator of this invention can boost the pressure through an electromagnetic reversing valve when releasing energy, thus pushing the boom upward, simplifying the hydraulic system and improving the dynamic performance of the system.

[0046] 3) By calculating the energy density of both, the energy density of the energy storage device of the present invention under this operating condition is twice that of the conventional energy storage device.

[0047] Instruction manual illustrations

[0048] Figure 1 This is a schematic diagram of the high energy density dual-piston hydraulic accumulator of the present invention;

[0049] Figure 2 This is a schematic diagram of the working principle of the high energy density dual-piston hydraulic accumulator of the present invention, wherein (a) is a schematic diagram of energy storage and (b) is a schematic diagram of energy release.

[0050] In the diagram: 1. Lower chamber oil inlet; 2. Lower chamber end cap; 3. Lower chamber liquid chamber; 4. Lower chamber piston; 5. Lower chamber spherical hinge; 6. Piston rod; 7. Lower chamber cylinder; 8. Upper chamber cylinder; 9. Upper chamber spherical hinge; 10. Upper chamber piston; 11. Upper chamber end cap; 12. Upper chamber oil inlet; 13. Upper chamber liquid chamber; 14. Gas chamber; 15. Gas chamber air inlet; 16. Gas cylinder. Detailed Implementation

[0051] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0052] like Figure 1 As shown, a high-energy-density dual-piston hydraulic accumulator includes a lower cylinder 7 and an upper cylinder 8. The lower cylinder 7 has a lower end cap 2 at its bottom, with a lower end cap 2 having a lower end cap 1 at its center. The upper cylinder 8 has an upper end cap 11 at its top, with an upper end cap 11 having an upper end cap 12 at its center. The openings of the lower cylinder 7 and the upper cylinder 8 are connected and sealed to form a variable-diameter dual-piston cylinder body with a smaller upper diameter and a larger lower diameter. The lower cylinder 7 contains a lower piston 4, and the upper cylinder 8 contains an upper piston 10. A piston rod 6 connects the lower piston 4 and the upper piston 10, and the piston rod 6 is connected to the lower piston 4 at its center via a lower spherical hinge. The piston rod 6 is connected to the center of the upper chamber piston 10 via the upper chamber spherical hinge 9, thereby enabling linkage between the lower chamber piston 4 and the upper chamber piston 10. The upper chamber piston 10 and the upper chamber end cap 11 form the upper chamber liquid chamber 13 in the double piston cylinder, the upper chamber piston 10 and the lower chamber piston 4 form the gas chamber 14 in the double piston cylinder, and the lower chamber piston 4 and the lower chamber end cap 2 form the lower chamber liquid chamber 3 in the double piston cylinder. The side of the lower chamber cylinder 7 near the upper chamber cylinder 8 is connected to a gas cylinder 16 that communicates with the gas chamber 14 via a pipeline. When storing energy, the upper chamber liquid chamber 13 is connected to the oil tank, and the initial pressure in the gas cylinder 16 is greater than the oil inlet pressure of the lower chamber liquid chamber 3, thereby increasing the internal energy of the stored gas.

[0053] like Figure 2 As shown, a method for operating a high-energy-density dual-piston hydraulic accumulator is described, wherein the lower chamber oil inlet 1 and the upper chamber oil inlet 12 are connected by pipelines to solenoid valves that control the inflow and outflow of high-pressure oil. The steps are as follows:

[0054] During energy storage, the solenoid valve is de-energized and operates in the right position. The upper chamber oil inlet 12 is connected to the oil tank, and high-pressure oil enters the lower chamber liquid chamber 3 of the accumulator through the lower chamber oil inlet 1. The increased pressure in the lower chamber liquid chamber 3 pushes the lower chamber piston 4, which in turn pushes the piston rod 6 upward, compressing the gas in the gas chamber 14. The pressure in the gas cylinder 15 increases, and the hydraulic energy in the lower chamber liquid chamber 3 is converted into the internal pressure energy of the gas chamber 14 and the gas cylinder 16. During this process, the upper chamber liquid chamber 13 is connected to the oil tank. The upper chamber piston 10 is not subjected to hydraulic pressure, and the piston rod 6 is subjected to three forces: the hydraulic pressure in the lower chamber liquid chamber, and the gas pressure acting on the lower chamber piston 4 and the upper chamber piston 10 respectively by the gas chamber 14. When storing energy, the piston rod 6 moves at a constant speed, thus obtaining the current force balance equation. During energy storage, because the pressure in the gas chamber 14 is increasing, the hydraulic pressure in the lower chamber liquid chamber 3 is increasing slowly until the pressure in the lower chamber liquid chamber 3 reaches its maximum, at which point energy storage is no longer possible, and the piston rod 6 stops moving. At this point, energy storage is complete.

[0055] When energy is released, the solenoid valve is energized and operates in the left position. The oil circuits of the upper liquid chamber 3 and the lower liquid chamber 13 of the accumulator are connected. High-pressure oil is connected to the upper liquid chamber 3 and the lower liquid chamber 13 through the pipeline. At this time, the pressure of the upper liquid chamber 3 and the pressure of the lower liquid chamber 13 are equal, and the internal energy in the gas cylinder 16 is released. At this time, the piston rod 6 is subjected to four forces and moves downward. The internal energy of the gas chamber 14 and the gas cylinder 16 is converted into hydraulic energy and output through the pipeline. When releasing energy, the pressure of the gas chamber 14 and the pressure of the lower liquid chamber 13 are equal. However, when storing energy, the pressure of the gas chamber 14 is greater than the pressure of the lower liquid chamber 13. Therefore, the oil pressure when releasing energy is greater than the oil pressure when storing energy, thus achieving the effect of pressurization.

[0056] High-energy-density dual-piston hydraulic accumulator energy storage principle

[0057] For accumulators with the same initial gas volume and initial pressure, the pressure change in the liquid chamber is the same. If the volume of stored oil is large, the energy storage density of the accumulator is high. The high energy storage density of the present invention will now be explained.

[0058] Traditional accumulators rely on changes in the volume and pressure of their filling chamber to achieve filling and discharging functions. According to the gas law, if the liquid chamber pressure changes from P... y1 Rise to P y2 Then the air chamber pressure also changes from P q1 Rise to P q2 It satisfies the following relationship:

[0059] P q1 V q1 n =P q2 V q2 n (1)

[0060] In the formula: P q1 P represents the initial pressure of the air chamber. q2 V represents the pressure in the gas chamber at the final state; n is the polytropic exponent, n = 1.4 for an adiabatic process, V q1 V is the initial volume of the air chamber; q2 The final volume of the air chamber; ΔV q This represents the change in air cavity volume.

[0061] available

[0062]

[0063] Simplification yields the change in the liquid chamber volume of a traditional accumulator, ΔV. q :

[0064]

[0065] The stored energy is essentially the work done by the liquid on the piston, which is converted into the internal energy of the gas. The stored energy is calculated by the following formula:

[0066]

[0067] Substituting equation (2) into the equation and simplifying, we can obtain the expression for the energy density μ1.

[0068]

[0069] The principle of the high energy density dual-piston hydraulic accumulator of the present invention for storing energy is as follows: Figure 2 As shown in (a). When storing energy, the solenoid valve is de-energized and operates in the right position. The oil inlet 12 of the upper chamber of the accumulator is connected to the oil tank. High-pressure oil enters the liquid chamber 3 of the lower chamber of the accumulator through the oil inlet 1 of the lower chamber, pushing the piston rod 6 to move upward, compressing the gas in the gas chamber 14, increasing the pressure in the gas cylinder 16, and converting the hydraulic energy into the internal energy of the gas chamber and the gas cylinder.

[0070] In order to compare with conventional accumulators, the pressure P of the accumulator liquid chamber in the initial state of the present invention is... y1 The pressure P at the end state y2 Initial volume V of the air chamber q1 It is equivalent to traditional energy storage devices.

[0071] Force analysis of the piston rod in the initial state:

[0072] P y1 A2+P q1 (A1-A0)=P q1 (A2-A0) (6)

[0073] Force analysis of the piston rod in the final state:

[0074] P y2 A2+P q2 (A1-A0)=P q2 (A2-A0) (7)

[0075] By combining equation (6-7), the relationship between the air chamber pressure and the liquid chamber pressure can be obtained:

[0076]

[0077] According to the structure of the accumulator of the present invention, the relationship between the changes in gas chamber volume and liquid chamber volume can be understood as follows:

[0078]

[0079] According to the gas law, if the pressure in the gas chamber is P q1 Rise to P q2 The following relationship must be satisfied:

[0080] P q1 V q1 n =P q2 V q2 n (10)

[0081] In the formula: P y1 P represents the initial high-pressure oil pressure in the lower chamber; y2 The pressure of the lower chamber high-pressure oil in the final state; P q1 P represents the initial pressure of the air chamber. q2 V represents the pressure in the gas chamber at the final state; A1 is the piston area in the upper chamber; A2 is the piston area in the lower chamber, A2 > A1; A0 is the cross-sectional area of ​​the piston rod; V q1 V is the initial volume of the air chamber; q2 ΔV is the final volume of the air chamber. y ΔV represents the change in the liquid chamber volume of the accumulator of this invention. q This represents the change in air cavity volume.

[0082] Substituting equation (8) into equation (10) yields...

[0083]

[0084] Substituting equation (11) into equation (9), we can obtain the result when the liquid chamber pressure changes from P. y1 Rise to P y2 Afterwards, the change in the volume of the liquid cavity, ΔV y :

[0085]

[0086] The stored energy is calculated using the formula for the energy of a gas as a work quantity:

[0087]

[0088] Substituting equation (11) into the equation and simplifying, we can obtain the expression for energy density μ2.

[0089]

[0090] The pressure P of the liquid chamber in the initial state y1 The pressure P at the end state y2 Initial volume V of the air chamber q1 When all are the same, comparing equation (3) and equation (12), since It can be seen that the volume change of the accumulator's liquid chamber is greater than that of a conventional accumulator, and the volume of oil stored is larger. By definition, the accumulator of this invention has a higher energy storage density than conventional accumulators.

[0091] Comparing the energy density expression μ1 of a conventional energy storage device with the energy density expression μ2 of this invention, it can be seen that the energy density of the energy storage device of this invention is higher than that of a conventional energy storage device. Times. Due to Therefore, the energy density μ2 of this invention is greater than the energy density μ1 of a conventional accumulator.

[0092] The increase in energy density is related to the cross-sectional areas A1 and A2 of the two pistons. The larger A1 is, that is, the closer A1 is to A2, the greater the energy density. If the maximum pressure in the gas chamber is P... qmax The maximum pressure in the liquid chamber is P. ymax From equation (8), we can obtain:

[0093]

[0094] As can be seen from equation (15), the larger A1 is, the greater the energy density of the accumulator and the greater the maximum pressure P in the liquid chamber. ymax It is determined by the actual working conditions. If A1 is to be increased, the maximum pressure P of the air chamber needs to be increased. qmax However, the maximum air pressure of the accumulator is limited, thus restricting the maximum value of A1. This is when the maximum pressure P of the oil to be stored... ymax The maximum pressure P in the air chamber qmax When the energy density approaches the target value, A1 becomes very small, meaning the energy density cannot be increased. Therefore, the appropriate ratio of A1 to A2 must be chosen based on actual operating conditions.

[0095] High-energy-density dual-piston hydraulic accumulator energy release principle

[0096] The principle of the high energy density dual-piston hydraulic accumulator of the present invention for storing energy is as follows: Figure 2 As shown in (b). When releasing energy, the solenoid valve is energized and operates in the left position. The upper chamber 3 and the lower chamber 13 of the accumulator are connected. High-pressure oil connects the upper and lower chambers through the pipeline. The internal energy in the gas cylinder 16 is released, the piston rod 6 moves downward, and the internal energy of the gas chamber and the gas cylinder is converted into hydraulic energy.

[0097] When releasing energy, the pressure in the gas chamber is the same as the pressure P at the end of the energy storage state. q2 Force analysis of the piston rod:

[0098] P y ′A2+P q2 (A1-A0)=P q2 (A2-A0)+P y ′A1 (16)

[0099] We can obtain:

[0100]

[0101] In the formula: A1 is the effective cross-sectional area of ​​the upper piston rod cavity; A2 is the effective cross-sectional area of ​​the lower piston cavity, A2 > A1; A0 is the cross-sectional area of ​​the piston rod; P y ′ represents the high-pressure oil pressure in the hydraulic chamber when energy is released;

[0102] Therefore, it can be concluded that the output high-pressure oil pressure during energy release is the same as the high-pressure oil pressure during energy storage. Therefore, the accumulator of the present invention can play a role in pressurization.

[0103] Example 1

[0104] The energy storage density of conventional energy accumulators and the energy accumulator of this invention is compared by applying them to the potential energy recovery system of an excavator boom.

[0105] A medium-sized excavator's boom is driven by two hydraulic cylinders. The piston and piston rod diameters are 120mm and 85mm respectively, with a stroke of 1.7m. The total volume of one cylinder is calculated to be 19.2L. Therefore, approximately 38.4L of hydraulic oil enters the accumulator with each boom descent. The pressure in the lower chamber of the hydraulic cylinder during descent is approximately 12MPa. In a hydraulic system, flow requires a pressure difference, and flow necessitates a pressure difference. Excavator hydraulic systems are relatively complex, typically containing multiple throttling circuits. To control the speed of the boom cylinders, the minimum pressure difference between the boom cylinder and the accumulator is 1MPa.

[0106] Recovering energy from the excavator boom using a traditional piston accumulator.

[0107] Given that the lower chamber pressure during boom descent is approximately 12 MPa and the system throttling pressure difference is 1 MPa, the working pressure of a traditional accumulator during storage can be estimated to be 11 MPa. During release, due to the throttling pressure difference of 1 MPa, the hydraulic oil pressure entering the lower chamber of the boom is approximately 10 MPa, which is insufficient to push the piston rod upward. Therefore, a hydraulic pump is needed to supplement the pressure in order to push the boom upward when the accumulator releases energy.

[0108] When storing energy, if the pressure in the accumulator's liquid chamber rises from 7 MPa to 11 MPa and the volume change of the liquid chamber is 38.4 L, the initial volume of the conventional accumulator can be calculated using equation (3):

[0109]

[0110] The stored energy can be calculated from equation (4):

[0111]

[0112] The energy density μ1 can be calculated from equation (5):

[0113]

[0114] (2) Energy recovery using the energy storage device of the present invention

[0115] The maximum pressure during energy recovery is:

[0116] P amax ≈12MPa-△P=11MPa (21)

[0117] To ensure that the pressurized pressure is sufficient to lift the boom, the lower boom chamber pressure must be at least 13 MPa. Therefore, the minimum working pressure during release is:

[0118] P bmin ≈13MPa + ΔP = 14MPa (22)

[0119] In the formula: ΔP is the system throttling pressure difference.

[0120] When storing energy, if the pressure in the accumulator's liquid chamber rises from 7 MPa to 11 MPa, the pressure in the gas chamber can be calculated from the pressure in equation (8). Rise to It can be calculated from the minimum working pressure:

[0121]

[0122] We can obtain A2 = 2A1. After the boom descends once, approximately 38.4L of hydraulic oil enters the accumulator. The initial volume of the accumulator can be calculated using equation (12).

[0123]

[0124] The stored energy can be calculated from equation (13):

[0125]

[0126] The energy density can be calculated from equation (14) as follows:

[0127]

[0128] In summary, under the excavator's energy recovery operation, the high-pressure oil in the lower chamber enters the accumulator through the system. The pressure in the accumulator's liquid chamber rises from 7MPa to 11MPa, and the pressure in the air chamber rises from 14MPa to 22MPa. During release, the accumulator is pressurized, and the pressure in the liquid chamber drops from 22MPa to 14MPa. After being throttled by 1MPa by the system, the pressure is higher than the minimum pressure in the lower chamber of the boom, which is 13MPa. Therefore, the boom can be raised.

Claims

1. A high energy density dual piston hydraulic accumulator, characterized by: The variable-diameter double piston chamber consists of two piston chambers, one smaller and one larger. Each double piston chamber contains two interconnected pistons connected by a piston rod (6). The upper piston moves in the smaller diameter piston chamber above the variable-diameter double piston chamber, while the lower piston moves in the larger diameter piston chamber below. The interconnected pistons divide the variable-diameter double piston chamber into three chambers: an upper piston chamber located between the small piston and the top of the piston chamber; a middle piston chamber between the two pistons; and a lower piston chamber located between the large piston and the bottom of the large piston chamber. Oil ports are located at the top and bottom of the variable-diameter double piston chamber. The large piston chamber of the double piston chamber is connected to the side of the small piston chamber via a pipeline. There is a gas cylinder (16), so that the upper piston chamber and the lower piston chamber are the upper liquid chamber (13) and the lower liquid chamber (3), and the middle piston chamber is the gas chamber (14). Due to the small diameter of the upper chamber and the large diameter of the lower chamber, the rod rises and the volume of the middle piston chamber decreases, compressing the air in the middle piston chamber to store energy. The upper chamber oil inlet (12) is connected to the oil tank. The lower chamber oil inlet (1) and the upper chamber oil inlet (12) are connected to a solenoid valve that controls the inlet and outlet of high pressure oil through a pipeline. When storing energy, the solenoid valve is de-energized and the solenoid valve works in the right position. When releasing energy, the solenoid valve is energized and the solenoid valve works in the left position. The oil circuits of the upper liquid chamber (3) and the lower liquid chamber (13) of the accumulator are connected.

2. A high energy density dual piston hydraulic accumulator according to claim 1, wherein, Specifically, it includes a lower cylinder (7) and an upper cylinder (8). The lower cylinder (7) has a lower end cap (2) at its bottom, and a lower oil inlet (1) is opened at the center of the lower end cap (2). The upper cylinder (8) has an upper end cap (11) at its top, and a higher oil inlet (12) is opened at the center of the upper end cap (11). The openings of the lower cylinder (7) and the upper cylinder (8) are connected and sealed to each other, thus forming a variable-diameter double piston cylinder body with a smaller upper diameter and a larger lower diameter. The lower cylinder (7) has a lower piston (4), and the upper cylinder (8) has an upper piston (10). A piston rod (6) is provided between the lower piston (4) and the upper piston (10) to connect them. The piston rod (6) is connected to the lower piston (4) at its center by a lower spherical hinge (5). The upper chamber piston (10) is connected at its center by an upper chamber spherical hinge (9), thereby enabling linkage between the lower chamber piston (4) and the upper chamber piston (10). The upper chamber piston (10) and the upper chamber end cap (11) form an upper chamber liquid chamber (13) in the double piston cylinder, the upper chamber piston (10) and the lower chamber piston (4) form a gas chamber (14) in the double piston cylinder, and the lower chamber piston (4) and the lower chamber end cap (2) form a lower chamber liquid chamber (3) in the double piston cylinder. The side of the lower chamber cylinder (7) near the upper chamber cylinder (8) is connected to a gas cylinder (16) that communicates with the gas chamber (14) through a pipeline. When storing energy, the upper chamber liquid chamber (13) is connected to the oil tank. The initial pressure in the gas cylinder (16) is greater than the oil inlet pressure of the lower chamber liquid chamber (3), thereby increasing the internal energy of the stored gas.

3. A method for operating one or two high-energy-density dual-piston hydraulic accumulators, characterized in that, The lower chamber oil inlet (1) and the upper chamber oil inlet (12) are connected to a solenoid valve that controls the inlet and outlet of high-pressure oil via pipelines. The steps are as follows: When storing energy, the solenoid valve is de-energized and operates in the right position. The upper chamber oil inlet (12) is connected to the oil tank. High-pressure oil enters the lower chamber liquid chamber (3) of the accumulator through the lower chamber oil inlet (1). The increased pressure in the lower chamber liquid chamber (3) pushes the piston rod (6) upward by pushing the lower chamber piston (4), compressing the gas in the gas chamber (14). The pressure in the gas cylinder (15) increases, and the hydraulic energy in the lower chamber liquid chamber (3) is converted into the gas pressure internal energy of the gas chamber (14) and the gas cylinder (16). During this process, the upper chamber liquid chamber (13) is connected to the oil tank. The upper chamber piston (10) is not subjected to hydraulic pressure, while the piston rod (6) is subjected to three forces: the hydraulic pressure in the lower chamber liquid cavity, and the gas pressure in the gas cavity (14) acting on the lower chamber piston (4) and the upper chamber piston (10). When storing energy, the piston rod (6) moves at a constant speed, thus obtaining the current force balance equation. When storing energy, the pressure in the gas cavity (14) is increasing, and the hydraulic pressure in the lower chamber liquid cavity (3) is increasing slowly until the pressure in the lower chamber liquid cavity (3) reaches the maximum pressure, at which point energy cannot be stored, and the piston rod (6) stops moving. At this point, energy storage is complete. When energy is released, the solenoid valve is energized and operates in the left position. The oil circuits of the upper liquid chamber (3) and the lower liquid chamber (13) of the accumulator are connected. High-pressure oil is connected to the upper liquid chamber (3) and the lower liquid chamber (13) through the pipeline. At this time, the pressure of the upper liquid chamber (3) and the pressure of the lower liquid chamber (13) are equal. The internal energy in the gas cylinder (16) is released. At this time, the piston rod (6) is subjected to four forces and moves downward. The internal energy of the gas chamber (14) and the gas cylinder (16) is converted into hydraulic energy and output through the pipeline. When energy is released, the pressure of the gas chamber (14) and the pressure of the lower liquid chamber (13) are equal. However, when energy is stored, the pressure of the gas chamber (14) is greater than the pressure of the lower liquid chamber (13). Therefore, the oil pressure when releasing energy is greater than the oil pressure when storing energy, thus achieving the effect of pressurization.

4. The operating method of the high energy density dual-piston hydraulic accumulator according to claim 3, characterized in that, Since the upper liquid chamber (3) is connected to the oil tank when storing energy, the hydraulic pressure is 0. Therefore, when storing energy, only the total volume of the lower liquid chamber (13) is considered. The initial position of the piston rod (6) is at the lowest end. Therefore, the initial volume of the lower liquid chamber (13) is 0. The final state of the lower liquid chamber (13) is the maximum allowable pressure. The piston rod (6) rises to the limit position. When storing energy, let the initial pressure of the lower chamber (13) be... The pressure in the lower chamber (13) at the end of its state is: The initial volume of the air chamber is ; In the initial state, the upper liquid chamber (3) exerts the following force on the piston rod (6): （6）， In the final state, the pressure in the lower chamber (13) reaches the maximum inlet pressure, and the piston rod (6) is subjected to the following forces: （7）， By combining equations (6) and (7), the relationship between the pressure in the air chamber (14) and the pressure in the lower liquid chamber (13) can be obtained: （8）， From this, we can understand the relationship between the volume of the air chamber (14) and the volume change of the lower liquid chamber (13): （9）， Using the gas law, the pressure in the gas chamber (14) is determined by... Rise to The following relationship must be satisfied: （10）， In the formula: This represents the initial high-pressure oil pressure in the lower chamber. The pressure of the lower chamber high-pressure oil in the final state; This represents the initial pressure of the air chamber. The pressure in the air chamber at the final state; The area of ​​the piston in the upper chamber; The area of ​​the lower chamber piston is... ; This is the cross-sectional area of ​​the piston rod; This represents the initial volume of the air chamber. This refers to the final volume of the air chamber. This refers to the change in the liquid chamber volume of the accumulator in this invention. This represents the change in air cavity volume; Substituting equation (8) into equation (10) yields... （11）， Substituting equation (11) into equation (9), we obtain the pressure of the current cavity fluid chamber (13) from... Rise to Subsequently, the change in volume of the lower chamber fluid cavity (13) : （12）。 5. The operating method of the high energy density dual-piston hydraulic accumulator according to claim 3, characterized in that, The stored energy is calculated using the formula for the energy of a gas as a work quantity: （13）， Substituting equation (11) into the equation and simplifying, we can obtain the energy density. expression: （14）， Pressure of the lower chamber (13) in the initial state Pressure at the end state Initial volume of air chamber (14) When all are the same, comparing equation (3) and equation (12), since Therefore, it can be seen that the volume change of the accumulator liquid chamber of the present invention is larger than that of the traditional accumulator, and the volume of oil stored is larger. Compare the energy density expressions of ordinary accumulators And the energy density expression of the present invention It can be seen that the energy density of the energy storage device of the present invention is higher than that of conventional energy storage devices. times; due to Therefore, the energy density of this invention Greater than the energy density of ordinary energy storage devices ; The increase in energy density is related to the cross-sectional area of ​​the two pistons. and related, The larger, that is The closer to The higher the energy density, the greater the maximum pressure in the air chamber. The maximum pressure in the liquid chamber is From equation (8), we can obtain: （15）， From equation (15), we can see that The larger the accumulator, the greater its energy density and the higher its maximum liquid chamber pressure. It is determined by the actual working conditions; if you want to increase... This requires increasing the maximum pressure in the air chamber. However, the maximum air pressure of the accumulator is limited, which restricts its operation. The maximum value when the maximum pressure of the oil to be stored is... The maximum pressure of the air chamber When approaching, at this time The energy density is very small, meaning it cannot be increased; therefore, it needs to be selected appropriately based on actual operating conditions. and The ratio of .

6. The operating method of the high energy density dual-piston hydraulic accumulator according to claim 3, characterized in that, When releasing energy, the pressure in the gas chamber is the same as the pressure at the end of the energy storage state. Force analysis of piston rod (6): （16）， We can obtain: （17）， In the formula: The effective cross-sectional area of ​​the upper piston rod cavity; The effective cross-sectional area of ​​the lower chamber piston is... ; Let be the cross-sectional area of ​​the piston rod; This refers to the high-pressure oil pressure in the liquid chamber when energy is released. Therefore, it can be concluded that the output high-pressure oil pressure during energy release is the same as the high-pressure oil pressure during energy storage. Therefore, the accumulator of the present invention can play a role in boosting pressure.

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