Hydraulic axle with energy storage features

Abstract

A closed circuit, self-contained hydraulic axle includes an electric motor, a hydraulic cylinder configured to be connected to a load, and a main pump driven by the electric motor to pump hydraulic fluid through the circuit. Pressure connections of the pump are connected to respective chambers of the cylinder such that a cylinder rod is configured to extend and retract depending on a direction of flow of the hydraulic fluid through the main pump. The hydraulic axle includes a main accumulator connected to the pump via a first control valve, an energy storage accumulator connected to the pump via a second control valve, and a supply pump. The hydraulic axle is switchable between a first operating mode in which no energy is stored in the energy storage accumulator and a second operating mode in which energy is stored in the energy storage accumulator.

Description

Background Technology

[0001] A hydraulic shaft is a hydraulic device that includes an actuator in the form of a hydraulic cylinder and a hydraulic or electro-hydraulic control device or circuit that uses hydraulic fluid to actuate the actuator. This type of hydraulic shaft is a compact, powerful drive and is ideally suited for applications requiring the application of large forces and energy over extended periods or in applications with limited space. Hydraulic shafts can be used in a variety of industrial automation applications, such as presses, plastics machinery, and bending machines. In many applications, hydraulic shafts are designed to achieve at least two types of motion: rapid transmission motion and force-applying motion. Summary of the Invention

[0002] In some hydraulic shaft applications, the hydraulic shaft needs to provide high energy to the load only during actuator extension and low energy during actuator retraction. In one example application, the load is a secondary linear pump that fills during actuator retraction and supplies energy to the fluid during actuator extension. To reduce power spikes during load cycles, techniques are often employed to store energy during the lower load portion of the cycle. This stored energy can then replenish the actuator's prime mover during periods of high power demand, similar to how batteries store power in hybrid vehicles.

[0003] To achieve this hydraulic objective, a closed-loop (e.g., vent and reservoir free loop) hydraulic shaft is provided, comprising a prime mover that controls speed and force applied to a load via an oil-filled hydraulic gear system employing mechanical advantage and a conversion from rotational to linear motion. More specifically, the hydraulic shaft includes an electric motor driving a bidirectional hydraulic master pump, a differential region, and a single-lever actuator receiving hydraulic fluid from the master pump via a hydraulic loop, wherein ports of the master pump are respectively connected via lines to the actuator chamber, such that the lever is configured to extend and retract according to the flow direction of the hydraulic fluid through the master pump. The hydraulic shaft includes a main accumulator connected to the loop via a first control valve and an energy storage accumulator connected to the loop via a second control valve.

[0004] The hydraulic shaft can be used in a first operating mode and a second operating mode. In the first operating mode, the hydraulic shaft operates in a conventional manner and the energy storage accumulator is isolated. In the second operating mode, the hydraulic shaft operates in an energy storage mode, in which the main accumulator is isolated and the energy storage accumulator is activated. The hydraulic shaft can switch between modes during operation, thereby allowing for appropriate energy storage.

[0005] During each actuator cycle, a variable supply pump is used to store hydraulic fluid in an energy storage accumulator, and the energy stored in the energy storage accumulator can be varied.

[0006] The energy storage feature can be disabled when there is no load in either direction. The hydraulic shaft will not store energy when the first and second control valves are de-energized.

[0007] In some aspects, the closed hydraulic circuit includes a hydraulic shaft. The hydraulic shaft includes an electric motor and an actuator. The actuator includes a cylinder, a piston disposed within the cylinder, and a rod, the piston dividing the internal space of the cylinder into two chambers, and the rod having a first end connected to the piston and a second end configured to be connected to a load. The hydraulic shaft includes a bidirectional hydraulic master pump driven by the electric motor to pump hydraulic fluid through the hydraulic circuit. Pressure connections of the master pump are connected via first and second lines to corresponding chambers of the actuator, such that the rod is configured to extend and retract according to the flow direction of the hydraulic fluid through the master pump. The hydraulic shaft includes a main accumulator connected to the first line via a third line, and a first control valve disposed in the third line between the first line and the main accumulator. Additionally, the hydraulic shaft includes an energy storage accumulator connected to the first line via a fourth line, and a second control valve disposed in the fourth line between the first line and the energy storage accumulator. The hydraulic shaft is switchable between a first operating mode in which no energy is stored in the energy storage accumulator, and a second operating mode in which energy is stored in the energy storage accumulator.

[0008] In some embodiments, the hydraulic shaft switches between a first operating mode and a second operating mode by controlling a first control valve and a second control valve.

[0009] In some embodiments, the hydraulic shaft operates in a first operating mode when the first control valve allows hydraulic fluid to flow to the main accumulator and the second control valve is closed. Additionally, the hydraulic shaft operates in a second mode when the first control valve isolates the main accumulator from the first line and the second control valve is open.

[0010] In some embodiments, the energy storage accumulator is configured to store variable energy during each actuation cycle of the actuator.

[0011] In some embodiments, the amount of energy stored in the energy accumulator varies depending on the load applied to the rod.

[0012] In some embodiments, the hydraulic shaft includes a supply pump driven by a second electric motor. The second motor has a variable speed, and the supply pump is configured to control the pressure of hydraulic fluid stored in an energy storage accumulator.

[0013] In some embodiments, when the hydraulic shaft is in a first operating mode, the hydraulic shaft is configured to actuate an actuator via a hydraulic circuit, wherein the hydraulic fluid in the hydraulic circuit is driven by a main pump, excess hydraulic fluid from the actuator is stored at low pressure in a main accumulator, and the energy storage accumulator is isolated from the hydraulic circuit. Additionally, when the hydraulic shaft is in a second operating mode, the hydraulic shaft is configured to actuate an actuator via a hydraulic circuit, wherein the hydraulic fluid in the hydraulic circuit is driven by a main pump, the main accumulator is isolated from the hydraulic circuit, and excess hydraulic fluid from the actuator is stored at high pressure in an energy storage accumulator.

[0014] In some embodiments, the main accumulator is a low-pressure accumulator configured to operate at a pressure corresponding to the pressure associated with the low-pressure side of the hydraulic circuit, and the energy storage accumulator is a high-pressure accumulator configured to operate at a pressure corresponding to the pressure associated with the high-pressure side of the hydraulic circuit.

[0015] In some embodiments, the actuator is a differential area actuator with a single rod.

[0016] In some embodiments, the hydraulic shaft has no vent and no hydraulic fluid reservoir.

[0017] In some embodiments, when the hydraulic shaft is in the second operating mode and hydraulic fluid is stored under pressure in the energy storage accumulator, the pressure drop across the pressure connection of the main pump is reduced.

[0018] In some embodiments, the main accumulator is configured to store hydraulic fluid at a first pressure, and the energy storage accumulator is configured to selectively store fluid at a second pressure higher than the first pressure.

[0019] In some embodiments, the energy storage accumulator is configured to release the stored fluid under a second pressure during the movement of the rod.

[0020] In some aspects, a method is provided for providing energy storage in a closed hydraulic circuit and a reservoir-less hydraulic system. The hydraulic system includes an electric motor and an actuator. The actuator includes a cylinder, a piston disposed in the cylinder, the piston dividing the internal space of the cylinder into two chambers, and the rod having a first end connected to the piston and a second end configured to be connected to a load. The hydraulic system includes a bidirectional hydraulic master pump driven by the electric motor to pump hydraulic fluid through the hydraulic circuit. A pressure connection of the master pump is connected via a first line and a second line to a corresponding chamber of the actuator, such that the rod is configured to extend and retract according to the flow direction of the hydraulic fluid through the master pump. The hydraulic system includes a main accumulator connected to the first line via a third line, and a first control valve disposed in the third line between the first line and the main accumulator. The hydraulic system includes an energy storage accumulator connected to the first line via a fourth line, and a second control valve disposed in the fourth line between the first line and the energy storage accumulator. Additionally, the hydraulic system includes a supply pump connected to the second line. The method includes the step of transferring oil from the main accumulator to the energy storage accumulator via the supply pump.

[0021] In some embodiments, the hydraulic system can switch between a first operating mode and a second operating mode, in which no energy is stored in the energy accumulator and in the second operating mode, energy is stored in the energy accumulator.

[0022] In some embodiments, the hydraulic system switches between a first operating mode and a second operating mode by controlling a first control valve and a second control valve.

[0023] In some embodiments, the hydraulic system operates in a first operating mode when the first control valve allows hydraulic fluid to flow to the main accumulator and the second control valve is closed, and operates in a second mode when the hydraulic system is configured such that the first control valve isolates the main accumulator from the first line and the second control valve is open.

[0024] In some embodiments, the energy storage accumulator is configured to store variable energy during each actuation cycle of the actuator.

[0025] In some embodiments, the amount of energy stored in the energy accumulator varies depending on the load applied to the rod. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the hydraulic circuit of the hydraulic shaft shown in the figure.

[0027] Figure 2 This is a diagram of the bearing area defined by the actuator cylinder, where area A1 is the area of ​​the piston on the piston side of the cylinder, A2 is the area of ​​the piston on the rod side of the cylinder, A3 is the area of ​​the rod, and A2 = A1 – A3. Detailed Implementation

[0028] refer to Figure 1 The independent hydraulic shaft 100 is a compact and powerful drive for moving load 13 and can be used in industrial machines such as presses, bending machines, and plastics machinery. The hydraulic shaft 100 includes a variable-speed electric motor referred to as a prime mover 1. The prime mover 1 controls the speed and force applied to load 13 via an oil-filled hydraulic gear system that employs mechanical advantage and the conversion from rotational to linear motion. More specifically, the prime mover 1 drives a main hydraulic pump 2, which in turn supplies hydraulic fluid to a hydraulic linear actuator 12 via a hydraulic circuit 102. The main hydraulic pump 2 has a fixed displacement per revolution, and the actuator 12 has a linear displacement per volume input. In the hydraulic circuit 102, the hydraulic fluid volume is a closed reservoir with no atmospheric discharge. Considering the differential volume of the actuator 12, the hydraulic shaft 100 includes a main accumulator 11 that stores excess hydraulic fluid during the cycle of the actuator 12. Additionally, the hydraulic shaft 100 includes an energy storage accumulator 10, which can be used to replenish the prime mover 1 during periods of high power demand and reduce power peaks during load cycles. The energy storage characteristics of the hydraulic shaft 100 will be discussed below along with details of the hydraulic circuit 102.

[0029] Actuator 12 is a linear hydraulic cylinder comprising a cylinder 12a, a piston 12b disposed within the cylinder 12a, and a single-ended rod 12c connected to the piston 12b and providing a mechanical connection between the piston 12b and the load 13. The piston 12b seals relative to the inner surface of the cylinder 12a and divides the internal space of the cylinder 12a into two sealed chambers, such as a piston-side chamber 12d and an annular rod-side chamber 12e. By changing the relative pressure within the piston-side chamber 12d and the rod-side chamber 12e, the piston 12b can move between a forward position (not shown) and a retracted position (shown). The movement of the piston 12b towards the forward position provides the working stroke of the hydraulic shaft 100. Hereafter, references to "actuator extension" correspond to the state of actuator 12 in which the piston 12b is moving toward or in the forward position, and references to "actuator retraction" correspond to the state of actuator 12 in which the piston 12b is moving toward or in the retracted position. The reference to "actuator cycle" refers to the movement of the piston from the reference position to the fully extended position, then to the fully retracted position, and then back to the reference position.

[0030] refer to Figure 2Actuator 12 is a differential area double-acting cylinder. Specifically, the piston area A1 and the annular area A2 are not equal. The piston area A1 corresponds to the area on which pressure is applied to the piston 12b, and the annular area A2 corresponds to the area on which pressure is applied to the opposite side of the piston 12b minus the area A3 of the rod 12c. With equal hydraulic fluid supplied to the piston-side or rod-side chambers 12d, 12e, actuator 12 will move faster during retraction due to the reduced volumetric capacity. When the pressure is equal at the piston-side chamber 12d and the rod-side chamber 12e, actuator 12 can apply more force during extension because the piston area A1 associated with the piston-side chamber 12d is larger than the annular area A2 associated with the rod-side chamber 12e. If equal pressure is applied to both chambers 12d, 12e, and assuming the load 13 is not large enough to counteract the differential force, actuator 12 will extend due to the higher resultant force on the piston-side chamber 12d.

[0031] When actuator 12 is used in closed hydraulic circuit 102, it is necessary to store the differential volume V of hydraulic fluid generated by the movement of actuator 12. D The differential volume V of the hydraulic fluid in actuator 12 D It is a function of the differential areas A1 and A2, through which hydraulic fluid moves during the extension and retraction of actuator 12. When actuator 12 extends, the volume V of hydraulic fluid in the cylinder is... EXT Equals area A1 * actuator stroke. When actuator 12 retracts, volume V RET Equals area A2 * actuator stroke. Differential volume V D Corresponding to volume V EXT and volume V RET The difference between them, and therefore equal to the rod volume V. ROD The rod volume V ROD This is equivalent to A3 * actuator stroke.

[0032] Refer again Figure 1 The main hydraulic pump 2 is connected to a hydraulic line system forming a closed hydraulic circuit 102 at its two pressure connections 2a and 2b. The first pressure connection 2a is connected to the piston-side chamber 12d of the actuator 12 via lines 21 and 22, and the second pressure connection 2b is connected to the rod-side chamber 12e of the actuator 12 via lines 20 and 23.

[0033] Loop 102 includes a main accumulator 11, which is a low-pressure pneumatic expansion chamber sized to store excess hydraulic fluid volume from actuator 12. The main accumulator 11 is connected to line 20 via a first branch line 27, which also includes a pressure reducing valve 9. The pressure reducing valve 9 is an infinite position valve whose position (e.g., pressure threshold setting) is determined by regulator 14. During normal operation of loop 102 (e.g., loop operation without energy storage features), the pressure threshold of regulator 14 is set relatively low, allowing excess hydraulic fluid, compression / decompression volume, and thermal expansion or contraction volume to be stored in the main accumulator 11. Hydraulic fluid from loop 102 enters the main accumulator 11 via lines 22, 21, 20, and 27 through pressure reducing valve 9 during actuator retraction, and re-enters loop 102 either via line 25 through supply pump 4 or via lines 25 and 28 through anti-cavitation check valve 7 during actuator extension.

[0034] The supply pump 4 is unidirectional and driven by the variable speed motor 3. The supply pump 4 receives hydraulic fluid from the main accumulator 11 via the low-pressure line 25 and discharges the hydraulic fluid to the first pressure connection 2a of the main hydraulic pump 2 via lines 30 and 21. A first check valve 5, located in line 30, prevents fluid from flowing from the first pressure connection 2a to the supply pump fluid outlet 4a. Additionally, a second check valve 6, located in line 24, prevents fluid from flowing from the second pressure connection 2b to the supply pump fluid outlet 4a.

[0035] In addition to the main accumulator 11, loop 102 also includes an energy storage accumulator 10, which is configured to store energy during the reduced load portion of the cycle. The energy storage accumulator 10 is a gas-filled accumulator connected to line 20 of loop 102 via a second branch line 26. A control valve 8 is disposed in the second branch line 26 between the energy storage accumulator 10 and line 20. The control valve 8 is a normally closed, two-way solenoid valve.

[0036] Pipelines 20, 21, 22, 23, 26, and 27 are located on the high-pressure side of hydraulic circuit 102. Pipelines 24 and 30 are located in the medium-pressure section of circuit 102. Pipelines 25 and 28 are located on the low-pressure side of hydraulic circuit 102.

[0037] The hydraulic shaft 100 can be used in a first operating mode and a second operating mode. In the first operating mode, the hydraulic shaft 100 operates in a conventional manner and the energy storage accumulator 10 is isolated. In the second operating mode, the hydraulic shaft 100 operates in an energy storage mode, in which the main accumulator is isolated and the energy storage accumulator is activated. The hydraulic shaft 100 can switch between the first and second operating modes during operation, thereby allowing energy to be properly stored in the system.

[0038] By operating the hydraulic shaft 100 in a second operating mode (e.g., energy storage mode), energy can be stored during actuator retraction. The stored energy can then be used to reduce power peaks during actuator extension, thereby supplementing prime mover power during actuator extension. This can be advantageous, for example, in applications where load 13 requires high energy only during actuator extension and minimal energy during actuator retraction.

[0039] During operation of the hydraulic shaft 100 in the second operating mode, control valve 8 and pressure reducing valve 9 are energized during actuator 12 movement. As a result, normally closed control valve 8 opens, allowing hydraulic fluid to flow to energy storage accumulator 10. Simultaneously, the pressure threshold of pressure reducing valve 9, controlled by regulator 14, is set relatively high, thereby isolating main accumulator 11 from circuit 102. During actuator retraction (e.g., the reduced load portion of the actuator cycle), hydraulic fluid flows from piston-side chamber 12d to rod-side chamber 12e via lines 22, 21, main hydraulic pump 2, and lines 20 and 23. Main hydraulic pump 2 draws volume V from actuator 12 corresponding to area A1. EXT The hydraulic fluid. The pressure in the piston-side chamber 12d drops to the pressure of the energy storage accumulator 10, the initial pressure of which has been preset by the supply pump 4. The rod-side chamber 12e of the actuator 12, corresponding to area A2, will receive a portion of this hydraulic fluid, while the differential volume V... D The remaining volume will be stored in the energy accumulator 10.

[0040] Differential volume V D The hydraulic fluid is pushed into the energy storage accumulator 10 under pressure. The pressure of the hydraulic fluid stored in the energy storage accumulator 10 determines the energy available in the hydraulic circuit 102. Due to the physical characteristics of the system, the pressure P on area A2... A2 Pressure P at area A1 A1 Proportional:

[0041] P A2 = P A1 * A1 / A2–F13 / A1.

[0042] The pressure ratio is directly related to the area ratio minus the force F13 applied by load 13.

[0043] The amount of energy stored in the energy storage accumulator 10 can be varied during each actuator cycle. This technique allows for optimization of energy storage capacity. The amount of energy stored in the energy storage accumulator 10 is the product of the discharged hydraulic fluid volume and the pressure at which that volume is discharged. Assuming the piston 12b and rod 12c complete their full stroke, the exchanged volume (e.g., differential volume V) D The actuator 12 is fixed at stroke A3*. When the actuator 12 is fully extended, the differential volume V is discharged.D The pressure at the point of application depends on the pressure of the energy storage accumulator 10. When the actuator 12 is fully extended, the pressure of the energy storage accumulator 10 also depends on the gas pre-charge pressure and the initial volume of hydraulic fluid in the energy storage accumulator 10. This initial volume can be increased by transferring hydraulic fluid from the main accumulator 11 to the energy storage accumulator 10 as the actuator 12 extends. In the illustrated embodiment, this is achieved via the supply pump 4 through lines 25, 30, 21, 20, and 26. As the pressure setting of the supply pump 4 increases, the flow of hydraulic fluid through the first check valve 5 will increase the pressure on actuator area A1 during the retraction phase. To maintain net force, hydraulic fluid will be diverted from the piston-side chamber 12d to the rod-side chamber 12e via the main pump 2. This will increase the pressure at A2, which in turn will increase the preset pressure of the energy storage accumulator 10 via valve 8. The preset pressure can be reduced by lowering the pressure set point of the supply pump 4. Subsequent system leakage causes a decrease in pressure in the energy storage accumulator 10. The supply pump 4 can be adjusted during operation, and a final hydraulic fluid exchange (filling or evacuation) occurs during the stroke of actuator 12. Depending on the cylinder stroke frequency, the hydraulic fluid can also be gradually exchanged over several stroke cycles. Therefore, the amount of energy stored in energy accumulator 10 can change when the load 13 changes.

[0044] The preset pressure of the energy storage accumulator 10 can be increased by increasing the pressure set point of the supply pump 4. Subsequently, adding oil from the supply pump 4 to the circuit causes the pressure in the energy storage accumulator 10 to increase.

[0045] During the extension of actuator 12, work is performed by hydraulic shaft 100, and hydraulic fluid flows from rod-side chamber 12e to piston-side chamber 12d. The extended portion of the actuator cycle corresponds to the increased load portion of the actuator cycle. Since the rod-side chamber 12e, corresponding to area A2, is smaller than the piston-side chamber 12d, corresponding to area A1, more hydraulic fluid is required to fill the piston-side chamber 12d than is available from the rod-side chamber 12e. At this time, pressurized hydraulic fluid from energy storage accumulator 10 is used to fill piston-side chamber 12d, thereby reducing the pressure drop across the two pressure connections 2a, 2b of the main hydraulic pump 2. This, in turn, reduces the torque required to rotate the main hydraulic pump 2, allowing the pump 2 to operate at lower power for a given speed.

[0046] The energy stored in the energy storage accumulator 10 is connected to port 2b of the pump 2, thereby allowing the release of the stored energy to be controlled by the prime mover 1.

[0047] In applications where load 13 varies over time, it may be desirable to change the amount of energy stored in energy storage accumulator 10 accordingly. Since the energy stored in energy storage accumulator 10 corresponds to the area under the curve representing the hydraulic fluid pressure versus volume within energy storage accumulator 10, this curve can be assumed to be linear for small changes in pressure. The volume of hydraulic fluid added to energy storage accumulator 10 corresponds to the differential volume V. D Or area A3 * stroke. If the pressure increases, the amount of stored energy increases linearly. In circuit 102, the supply pump 4 can be used to increase the hydraulic fluid pressure at check valve 5, main pump 2, and energy accumulator 10. Therefore, circuit 102 provides the ability to change the energy stored in accumulator 10 by changing the charging pressure from supply pump 4.

[0048] An exemplary application where the load varies over time may include a load 13 in the form of a fluid pump used to pump fluid into a tank (not shown). Initially, when the tank is empty, there is no load at the fluid pump. In this initial stage, the hydraulic shaft 100 can operate without energy storage. That is, the pressure reducing valve 9 can be set to a low-pressure point to allow hydraulic fluid to be stored in the main accumulator 11, while the control valve 8 is closed, thereby isolating the energy storage accumulator 10 from the circuit 102. When the tank is filled, the fluid pump experiences a load, thereby making the stored energy available. At this time, the pressure reducing valve 9 is set to a high-pressure point to isolate the main accumulator from the circuit 102, and the control valve 8 is opened. Additionally, a supply pump is used to direct fluid to the energy storage accumulator 10 and store it there under pressure, where the supply pump can be used to balance the pressure at the pressure connections 2a, 2b of the main pump, thereby reducing torque and increasing available power.

[0049] When there is no load in either direction, the energy storage feature can be disabled. This is achieved by de-energizing both control valve 8 and regulator 14 of pressure reducing valve 9. As a result, control valve 8 returns to its normally closed state, preventing hydraulic fluid from flowing to energy accumulator 10. Simultaneously, the pressure threshold of pressure reducing valve 9 is set relatively low, allowing hydraulic fluid to flow through pressure reducing valve 9 to main accumulator 11. With both control valve 8 and regulator 14 de-energized, the system will not store energy.

[0050] In some embodiments, electric motors 1, 3 and valves 8 and 9 / 14 are controlled by a general-purpose programmable controller (not shown), such as a programmable logic controller (PLC). A PLC may include input modules or points, a central processing unit (CPU), and output modules or points. The PLC receives information from connected input devices and sensors, processes the received data, and triggers the desired outputs according to its pre-programmed instructions. The instructions implemented by the PLC may be provided by a programming device or stored in a non-volatile PLC memory.

[0051] Selective illustrative embodiments of the hydraulic shaft have been described in detail above. It should be understood that only structures deemed necessary for clearly illustrating the hydraulic shaft have been described herein. Other conventional structures, as well as those dependent and auxiliary components of the hydraulic shaft, are assumed to be known and understood by those skilled in the art. Furthermore, while working examples of the hydraulic shaft have been described above, the hydraulic shaft is not limited to the above working examples, but various design changes can be implemented without departing from the hydraulic shaft set forth in the claims.

Claims

1. A closed hydraulic circuit including a hydraulic shaft, said hydraulic shaft comprising: Electric motor; An actuator includes a cylinder, a piston disposed in the cylinder, the piston dividing the internal space of the cylinder into two chambers, and the rod having a first end connected to the piston and a second end configured to be connected to a load. A bidirectional hydraulic main pump, driven by an electric motor, pumps hydraulic fluid through the hydraulic circuit. The pressure connection of the main pump is connected to the corresponding chamber of the actuator via a first line and a second line, such that the rod is configured to extend and retract according to the flow direction of the hydraulic fluid through the main pump. The main accumulator is connected to the first pipeline via a third pipeline; A first control valve is disposed in a third pipeline between the first pipeline and the main accumulator; An energy storage accumulator is connected to the first pipeline via a fourth pipeline; and The second control valve is located in the fourth pipeline between the first pipeline and the energy storage accumulator. The hydraulic shaft can switch between a first operating mode and a second operating mode. In the first operating mode, no energy is stored in the energy accumulator, while in the second operating mode, energy is stored in the energy accumulator.

2. The closed hydraulic circuit according to claim 1, wherein, By controlling the first control valve and the second control valve, the hydraulic shaft switches between the first operating mode and the second operating mode.

3. The closed hydraulic circuit according to claim 2, wherein... When the hydraulic shaft is configured such that the first control valve allows hydraulic fluid to flow to the main accumulator and the second control valve is closed, the hydraulic shaft operates in the first operating mode, and When the hydraulic shaft is configured such that the first control valve isolates the main accumulator from the first pipeline and the second control valve is open, the hydraulic shaft operates in the second operating mode.

4. The closed hydraulic circuit according to claim 1, wherein, The energy storage accumulator is configured to store variable energy during each actuation cycle of the actuator.

5. The closed hydraulic circuit according to claim 1, wherein, The amount of energy stored in the energy accumulator varies depending on the load applied to the rod.

6. The closed hydraulic circuit of claim 1, comprising a supply pump driven by a second electric motor having a variable speed, the supply pump being configured to control the pressure of hydraulic fluid stored in the energy storage accumulator.

7. The closed hydraulic circuit according to claim 1, wherein... When the hydraulic shaft is in the first operating mode, the hydraulic shaft is configured to actuate the actuator via the hydraulic circuit, wherein... The hydraulic fluid in the hydraulic circuit is driven by the main pump. Excess hydraulic fluid from the actuator is stored at low pressure in the main accumulator, and the accumulator is isolated from the hydraulic circuit. When the hydraulic shaft is in the second operating mode, the hydraulic shaft is configured to actuate the actuator via the hydraulic circuit, wherein the hydraulic fluid in the hydraulic circuit is driven by the main pump, the main accumulator is isolated from the hydraulic circuit, and excess hydraulic fluid from the actuator is stored at high pressure in the energy storage accumulator.

8. The closed hydraulic circuit according to claim 1, wherein, The main accumulator is a low-pressure accumulator configured to operate at a pressure corresponding to the pressure associated with the low-pressure side of the hydraulic circuit, and the energy storage accumulator is a high-pressure accumulator configured to operate at a pressure corresponding to the pressure associated with the high-pressure side of the hydraulic circuit.

9. The closed hydraulic circuit according to claim 1, wherein, The actuator is a differential area actuator with a single rod.

10. The closed hydraulic circuit according to claim 1, wherein, The hydraulic shaft has no vent and no hydraulic fluid reservoir.

11. The closed hydraulic circuit according to claim 1, wherein, When the hydraulic shaft is in the second operating mode and the hydraulic fluid is stored under pressure in the energy accumulator, the pressure drop on the pressure connection of the main pump decreases.

12. The closed hydraulic circuit according to claim 1, wherein... The main accumulator is configured to store hydraulic fluid under a first pressure, and The energy storage accumulator is configured to selectively store fluid at a second pressure higher than the first pressure.

13. The closed hydraulic circuit according to claim 12, wherein, The energy storage accumulator is configured to release the stored fluid under the second pressure during the movement of the rod.

14. A method for providing energy storage in a closed hydraulic circuit and a accumulator-free hydraulic system. The hydraulic system includes Electric motor; An actuator includes a cylinder, a piston disposed in the cylinder, the piston dividing the internal space of the cylinder into two chambers, and the rod having a first end connected to the piston and a second end configured to be connected to a load. A bidirectional hydraulic main pump, driven by the electric motor, pumps hydraulic fluid through the hydraulic circuit. The pressure connection of the main pump is connected to the corresponding chamber of the actuator via a first line and a second line, such that the rod is configured to extend and retract according to the flow direction of the hydraulic fluid through the main pump. The main accumulator is connected to the first pipeline via a third pipeline; A first control valve is disposed in a third pipeline between the first pipeline and the main accumulator; An energy storage accumulator is connected to the first pipeline via a fourth pipeline; The second control valve is disposed in the fourth pipeline between the first pipeline and the energy storage accumulator; and The supply pump connected to the second pipeline, The method includes Oil is transferred from the main accumulator to the energy storage accumulator via the supply pump.

15. The method according to claim 14, wherein, The hydraulic system can switch between a first operating mode and a second operating mode. In the first operating mode, no energy is stored in the energy accumulator, while in the second operating mode, energy is stored in the energy accumulator.

16. The method according to claim 15, wherein, By controlling the first control valve and the second control valve, the hydraulic system switches between the first operating mode and the second operating mode.

17. The method of claim 15, wherein When the hydraulic system is configured such that the first control valve allows hydraulic fluid to flow to the main accumulator and the second control valve is closed, the hydraulic system operates in the first operating mode, and When the hydraulic system is configured such that the first control valve isolates the main accumulator from the first line and the second control valve is open, the hydraulic system operates in the second operating mode.

18. The method according to claim 14, wherein, The energy storage accumulator is configured to store variable energy during each actuation cycle of the actuator.

19. The method of claim 14, wherein, The amount of energy stored in the energy accumulator varies depending on the load applied to the rod.

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