Electro-hydraulic hybrid drive system

Abstract

The present application relates to electro-hydraulic hybrid drive system, especially electro-hydraulic hybrid drive system with energy recovery function, comprising prime mover, main pump and main generator driven by the prime mover, overflow valve, electrochemical energy storage device powered by the main generator, at least one actuator assembly and oil tank or oil return low pressure rail, wherein, at least one common high pressure rail supplied by the main pump is further included, each of the actuator assembly comprises motor / generator, first hydraulic pump / motor, second hydraulic pump / motor and actuator, the motor / generator is electrically connected with the electrochemical energy storage device, suction control valve and oil outlet control valve are corresponded two by two, and the first hydraulic pump / motor is controlled in four quadrant operation, the second hydraulic pump / motor is hydraulically coupled with the actuator through pipeline.The present application can accurately control the speed of the motor / generator, reduce the required rated power of the motor / generator, and be modularized and expandable on the basis of energy recovery function.

Description

Technical Field

[0001] This invention relates to electro-hydraulic hybrid drive systems, and more particularly to electro-hydraulic hybrid drive systems with energy recovery functions. Background Technology

[0002] Hydraulic drives offer extremely high power density and excellent reliability. Traditional hydraulically driven machinery, such as mobile machines (e.g., excavators, loaders) and stationary machines (e.g., robotic arms), uses hydraulic systems to drive multiple actuators, achieving high-load movement of the entire machine. These hydraulic systems typically consist of a centralized power source and dedicated hydraulic valves for each actuator. However, under high-load conditions, the movement of each actuator is achieved by changing the flow rate of the fluid in the hydraulic system through flow control valves. This results in a significant amount of hydraulic power being dissipated as heat at the throttling points during operation, making the entire system highly inefficient.

[0003] The paper "A Study on the Boom Energy Regeneration System for a Hybrid Excavator," presented at the 7th International Conference on Fluid Dynamics (Kang B., Oh S., 2010), employs a sophisticated solution to recover the pressure drop in the flow line when the fluid flows back from the valve to the tank, as well as the energy generated during overload operation.

[0004] Presented at the 8th Scandinavian International Conference on Fluid Power, the paper "Cylinder Control with The Floating Cup Hydraulic Transformer" (Vael G., Achten P., and Potma J., 2003) offers a solution to improve the energy efficiency of hydraulic systems by using hydraulic transformer control instead of traditional hydraulic valve control. The hydraulic transformer is hydraulically coupled to each load, changing the pressure of a centralized power source to meet the load's demands. This solution eliminates flow throttling and achieves energy recovery; however, it is currently limited by unresolved issues such as market-standard size constraints, limited transformer ratios, and reduced efficiency under partial load.

[0005] Presented at the First Bratislava Symposium on Fluid Dynamics, "Energy Saving Hydraulic Actuators for Mobile Machines" (Rahmfeld R., and Ivantysynova M., 1998) proposed a scheme using displacement control instead of valve control. The movement of each actuator is controlled by adjusting the displacement of a hydraulic pump / motor dedicated to that actuator. The hydraulic pump / motor manages the full power of the load and is driven by a prime mover (such as the internal combustion engine of mobile machinery). This scheme eliminates flow throttling and allows for energy recovery, but its disadvantages include the high configuration cost of servo valve-controlled swashplate rotation and the currently difficult-to-improve efficiency reduction of hydraulic pumps or motors at partial displacement settings.

[0006] Presented at the 7th FPNI Fluid Dynamics Doctoral Symposium, "Electrohydraulic Compact-drives for Low Power Applications considering Energy-efficiency and High Inertial Loads" (Michel S., Weber J., 2012) offers an electrohydraulic speed control alternative to valve control. A hydraulic pump / motor driven by an electric motor / generator is hydraulically coupled to the actuator, and the actuator's movement is controlled by adjusting the pump / motor's speed. This approach eliminates flow throttling and enables energy recovery to improve energy efficiency. Excellent control performance is achieved through precise adjustment of the motor / generator speed while ensuring high-bandwidth control. However, all power managed by the load must come from the motor and the load itself. Therefore, when power increases to several kilowatts, bulky motors and expensive electronic drives are required, making this approach controversial and even infeasible. Furthermore, the energy required by the motor in mobile machinery must be provided by onboard equipment, necessitating the installation of high-power generators driven by internal combustion engines, high-performance energy storage devices, and electrical systems.

[0007] US Patent 62 / 801137, "Device Having Hybrid Hydraulic-Electric Architecture," provides an electrohydraulic hybrid solution with multiple pressure rails. This solution combines speed control with high-pressure and low-pressure rails shared throughout the device. By switching valves to correctly connect two ports of a variable-speed hydraulic pump / motor, two ports of the hydraulic actuator driving the load, the high-pressure rail, and the low-pressure rail, and by connecting one port of the hydraulic pump / motor to the high-pressure rail, power is hydraulically and electrically transmitted to or from the load. This solution reduces the rated power of the motor / generator and related electrical components (such as electronic drives, generators, and energy storage devices). However, it significantly increases the complexity in terms of overall system design and control outcomes. Each pressure rail must be individually supplied with oil, thus requiring additional components (such as motors, hydraulic pumps, electro-hydraulic valves, and hydraulic-pneumatic accumulators). Furthermore, this solution requires accompanying intelligent control algorithms and multiple sensors to enable the switching valves to respond quickly and be appropriately controlled to activate / deactivate each pressure rail at the correct time.

[0008] US Patent 62 / 697226, Dual Power Electro-hydraulic Motion Control System, provides an electro-hydraulic hybrid solution using Common Pressure Rail (CPR) technology. However, when the chamber on one side of the hydraulic cylinder piston rod is under high pressure, i.e. when the load is working, the hydraulic pump / motor connected to both ends of the common high pressure rail will not provide torque and pressure energy to the motor, and therefore does not have the function of energy recovery.

[0009] Meanwhile, in the two patents mentioned above, the hydraulic pump / motor is directly connected to the high-pressure common rail or oil tank, and it is also necessary to compensate for the flow difference caused by the asymmetry of its chambers when the actuator moves. This results in the centralized power source and each actuator being essentially designed as a single unit, which increases the complexity of the system design and makes it impossible to achieve system modularity and scalability. Summary of the Invention

[0010] The purpose of this invention is to provide a modular and scalable electro-hydraulic hybrid drive system that can precisely control the speed of a motor / generator, reduce the rated power required by the motor / generator, and has energy recovery capabilities.

[0011] An electro-hydraulic hybrid drive system includes a prime mover, a main pump and a main generator driven by the prime mover, an overflow valve, an electrochemical energy storage device powered by the main generator, at least one actuator assembly, and an oil tank or return low-pressure rail. It also includes at least one common high-pressure rail supplied by the main pump. Each actuator assembly includes a motor / generator, a first hydraulic pump / motor, a second hydraulic pump / motor, and an actuator. The motor / generator is electrically connected to the electrochemical energy storage device. The first and second hydraulic pumps / motors are sequentially mounted on the drive shaft of the motor / generator. The first hydraulic pump / motor is hydraulically coupled to the common high-pressure rail. The suction line connecting the first hydraulic pump / motor to the common high-pressure rail is equipped with two sets of suction control valves. The discharge line connecting the first hydraulic pump / motor to the oil tank or return low-pressure rail is equipped with two sets of discharge control valves. The suction and discharge control valves correspond to each other in pairs. All the suction and discharge control valves jointly control the four-quadrant operation of the first hydraulic pump / motor. The second hydraulic pump / motor is hydraulically coupled to the actuator through a pipeline.

[0012] The speed of the second hydraulic pump / motor is determined by the motor / generator. The torque acting on the second hydraulic pump / motor is jointly provided by the motor / generator that converts electrical energy and the first hydraulic pump / motor that converts pressure energy. While retaining the efficiency advantages and control performance of the motor / generator speed control system, the addition of the hydraulic pump / motor significantly improves the hydraulic power, greatly reducing the rated power of the motor / generator required for the actuator to move. This saves costs and improves the compactness and power density of the system.

[0013] The common high-pressure rail is hydraulically coupled only to the first hydraulic pump / motor, and the actuators are not connected to the common high-pressure rail. This allows each actuator assembly to be designed as an "independent" system, simplifying installation and further enabling the system to be modular and expandable, making it suitable for various mobile and stationary hydraulic machinery.

[0014] Based on the above scheme, a hydraulic accumulator connected to the public high-voltage rail is also included.

[0015] When the actuator is under load, the second hydraulic pump / motor can conversely provide torque to the motor / generator and the first hydraulic pump / motor, converting the originally dissipated energy into electrical energy and pressure energy, which are then transmitted to the electrochemical energy storage device and the hydraulic accumulator, respectively, to achieve energy recovery. This has substantial advantages in energy saving and emission reduction and can be further applied to various hydraulically driven industrial machines and equipment related to energy regeneration.

[0016] Based on the above scheme, each of the oil suction control valve (21) and oil discharge control valve (21') is composed of at least one electro-hydraulic digital valve, at least one electro-hydraulic proportional valve, or a combination of an electro-hydraulic digital valve and an electro-hydraulic proportional valve.

[0017] Based on the above scheme, the first hydraulic pump / motor is equipped with a first drain line that connects to the oil tank or the low-pressure return rail.

[0018] Based on the above scheme, the first hydraulic pump / motor is a constant displacement hydraulic pump, a numerical variable displacement hydraulic pump / motor, or a proportional variable displacement hydraulic pump / motor.

[0019] Based on the above scheme, the main pump supplies oil to the first common high-pressure rail and the second common high-pressure rail with different pressures through a two-position three-way valve. The suction line of the first hydraulic pump / motor connected to the first common high-pressure rail is equipped with two sets of suction control valves. The suction line of the first hydraulic pump / motor connected to the second common high-pressure rail is equipped with two sets of suction control valves. The discharge line of the first hydraulic pump / motor connected to the oil tank or the return low-pressure rail is equipped with four sets of discharge control valves. The suction control valves and discharge control valves correspond to each other in pairs. All the suction control valves and discharge control valves jointly control the four-quadrant operation of the first hydraulic pump / motor.

[0020] Based on the above scheme, each end of the pipeline located at both ends of the actuator is connected to a pressure reducing valve to protect the pipeline.

[0021] Based on the above scheme, the oil suction end and oil discharge end of the second hydraulic pump / motor form a closed loop with the actuator through pipelines. Each end of the pipeline located at both ends of the actuator is equipped with a pair of check valves, which further enhances the "independence" of the actuator components and facilitates modularization.

[0022] Based on the above scheme, each actuator assembly also includes a low-pressure accumulator, with the low-pressure ends of the check valve and pressure reducing valve connected to the low-pressure accumulator. By replacing the oil tank or return low-pressure rail with a low-pressure accumulator, the rated flow rate of the second hydraulic pump / motor can be reduced, thereby reducing the power consumption of the motor / generator, and the "independence" of the actuator assembly can be further improved, facilitating modularization.

[0023] Preferably, when the actuator is an asymmetric actuator, the check valve is a pilot-operated check valve.

[0024] Based on the above scheme, the second hydraulic pump / motor is equipped with a second drain line connected to the low-pressure accumulator.

[0025] Based on the above scheme, the second hydraulic pump / motor is an asymmetric hydraulic pump / motor. The return end of the second hydraulic pump / motor is connected to the oil tank or the low-pressure return rail, and the low-pressure ends of the check valve and the pressure reducing valve are also connected to the oil tank or the low-pressure return rail. An asymmetric hydraulic pump / motor is used as an extension design of the second hydraulic pump / motor.

[0026] Based on the above scheme, each actuator assembly further includes a three-position four-way valve. One end of the second hydraulic pump / motor is connected to one working port of the three-position four-way valve, and the other end is connected to the oil tank or the low-pressure return rail. The other working port of the three-position four-way valve connected to the second hydraulic pump / motor is also connected to the oil tank or the low-pressure return rail. The two working ports on the other side of the three-position four-way valve form a closed loop with the actuator through pipelines. The low-pressure end of the pressure reducing valve is connected to the oil tank or the low-pressure return rail. An extended design of the open-loop actuator assembly with the addition of a three-position four-way valve is also included.

[0027] Based on the above scheme, each actuator assembly further includes a third hydraulic pump / motor. One end of the second hydraulic pump / motor is connected to the actuator via a pipeline, and the other end is connected to an oil tank or a low-pressure return rail. The suction and discharge ends of the third hydraulic pump / motor form a closed loop with the actuator via pipelines. This is an extended design where the second hydraulic pump / motor is open-loop and the third hydraulic pump / motor is closed-loop.

[0028] Preferably, the third hydraulic pump / motor is mounted on the drive shaft of the motor / generator.

[0029] Preferably, each of the actuator components further includes an auxiliary motor / generator, with a third hydraulic pump / motor mounted on the drive shaft of the auxiliary motor / generator. This allows for an expanded design by adding an auxiliary motor / generator.

[0030] Preferably, the third hydraulic pump / motor has a third drain line connected to the oil tank or the low-pressure return rail.

[0031] Preferably, the low-pressure end of the pressure reducing valve is connected to the oil tank or the return low-pressure rail.

[0032] The advantages of this invention are:

[0033] (1) The speed of the second hydraulic pump / motor is determined by the motor / generator. The torque acting on the second hydraulic pump / motor is provided by the motor / generator that converts electrical energy and the first hydraulic pump / motor that converts pressure energy. While retaining the efficiency advantage and control accuracy of the motor / generator speed control system, the hydraulic power is significantly improved by adding a hydraulic pump / motor, which greatly reduces the rated power of the motor / generator required for the actuator to move, thus saving costs and improving the compactness and power density of the system.

[0034] (2) As can be seen from the previous point, in mobile machinery, the actuator requires less electrical energy to move, which can reduce the configuration of mobile power supply, save costs and improve the overall compactness of the machinery.

[0035] (3) When the actuator is under load, the second hydraulic pump / motor can provide torque to the motor / generator and the first hydraulic pump / motor, converting the originally dissipated energy into electrical energy and pressure energy, which are then transmitted to the electrochemical energy storage device and the hydraulic energy storage device, respectively, to realize energy recovery. It has the substantial advantages of energy saving and emission reduction, and can be further applied to various hydraulically driven industrial machines and equipment related to energy regeneration.

[0036] (4) The common high-pressure rail is hydraulically coupled only to the first hydraulic pump / motor, and the actuator is not connected to the common high-pressure rail, so that each actuator component can be designed as an "independent" system, thereby simplifying the installation and further making the system modular and expandable, making it suitable for various mobile and stationary hydraulic machinery. Attached Figure Description

[0037] Figure 1 A schematic diagram of the system in which this invention is applied to mobile hydraulic machinery;

[0038] Figure 2a Schematic diagram of a control valve alternative scheme of the present invention;

[0039] Figure 2b Schematic diagram of the second alternative control valve of the present invention;

[0040] Figure 2c Schematic diagram of the third alternative control valve of the present invention;

[0041] Figure 3 Schematic diagram of the first hydraulic pump / motor alternative of the present invention;

[0042] Figure 4 Schematic diagram of the public high-voltage rail alternative scheme of the present invention;

[0043] Figure 5 Schematic diagram of the second hydraulic pump / motor alternative of the present invention;

[0044] Figure 6 Schematic diagram of the actuator component alternative of the present invention;

[0045] Figure 7a A schematic diagram of the proposed alternative solution for adding a third hydraulic pump / motor;

[0046] Figure 7b A schematic diagram of the second alternative solution for adding a third hydraulic pump / motor in this invention. Detailed Implementation Plan

[0047] Example 1

[0048] like Figure 1This invention relates to a system schematic diagram of a mobile hydraulic machinery, an electro-hydraulic hybrid drive system, including a prime mover 1, a main pump 2 and a main generator 6 driven by an internal combustion engine 1, an overflow valve 5 for system protection, an electrochemical energy storage device 7 powered by the main generator 6, two actuator assemblies 8, and an oil tank or return low-pressure rail 18. It also includes a common high-pressure rail 3 supplied by the main pump 2 and a hydraulic accumulator 4 connected to the common high-pressure rail 3. Each actuator assembly 8 includes a motor / generator 9, a first hydraulic pump / motor 10, a second hydraulic pump / motor 11, an actuator 13, and a low-pressure accumulator 17. The motor / generator 9 is electrically connected to the electrochemical energy storage device 7. The first hydraulic pump / motor 10 and the second hydraulic pump / motor 11... Two hydraulic pumps / motors 11 are sequentially mounted on the drive shaft of the motor / generator 9. The first hydraulic pump / motor 10 is a fixed displacement hydraulic pump and is hydraulically coupled in the common high-pressure rail 3. The suction line of the first hydraulic pump / motor 10 connected to the common high-pressure rail 3 is equipped with two sets of suction control valves 21. The discharge line of the first hydraulic pump / motor 10 connected to the oil tank or return low-pressure rail 18 is equipped with two sets of discharge control valves 21'. The suction control valves 21 and discharge control valves 21' are paired, and all the suction control valves 21 and discharge control valves 21' together control the four-quadrant operation of the first hydraulic pump / motor 10. The second hydraulic pump / motor 11 is hydraulically coupled to the actuator 13 through the pipeline 12, and the actuator 13 drives the load 14.

[0049] Preferably, each of the oil suction control valve 21 and the oil discharge control valve 21' consists of an electro-hydraulic digital valve.

[0050] Each end of the pipeline 12 located at both ends of the actuator 13 is connected to a pressure reducing valve 16. The oil suction end and oil discharge end of the second hydraulic pump / motor 11 form a closed loop with the actuator 13 through the pipeline 12. Each end of the pipeline 12 located at both ends of the actuator 13 is provided with a pair of check valves 15. The low-pressure ends of the check valves 15 and the pressure reducing valves 16 are connected to the low-pressure accumulator 17.

[0051] Preferably, when the actuator 13 is an asymmetric actuator, the check valve 15 is a pilot check valve.

[0052] The rotational speed of the first hydraulic pump / motor 10 is controlled by the motor / generator 9, thereby adjusting the flow rate of the first hydraulic pump / motor 10 to meet the movement requirements of the hydraulic actuator 13. Typically, a pressure sensor monitors the pressure on both sides of the hydraulic actuator 13, a position sensor measures the position of the hydraulic actuator 13, and a speed sensor detects the speed of the motor / generator 9. After receiving signals from multiple sensors, the control algorithm activates the control valve 21 at an appropriate time, enabling the first hydraulic pump / motor 10 to provide the appropriate torque to the drive shaft of the motor / generator 9.

[0053] Alternatively, the pressure drop across the first hydraulic pump / motor 10 can be actively controlled by adjusting the pressure of the common high-pressure rail 3, rather than by activating the control valve 21 at the appropriate time, so that the first hydraulic pump / motor 10 can provide appropriate torque to the drive shaft of the motor / generator 9.

[0054] Therefore, the first hydraulic pump / motor 10 transfers energy from the common high-pressure rail 3 to the load 14, thereby reducing the energy that needs to be transferred from the electrochemical energy storage device 7 to the load 14 by the electric motor / generator 9. In other words, the motor / generator 9, as the control element of the actuator 13, ensures the movement requirements of the load 14 even though its rated power is significantly lower than the total power required for the movement of the load 14.

[0055] Example 2

[0056] like Figure 2a A schematic diagram of the control valve alternative of the present invention shows an actuator assembly 8. The suction line of the first hydraulic pump / motor 10 connected to the common high-pressure rail 3 is equipped with two sets of suction control valves 21. The discharge line of the first hydraulic pump / motor 10 connected to the oil tank or return low-pressure rail 18 is equipped with two sets of discharge control valves 21'. The suction control valves 21 and discharge control valves 21' are paired. Each set of suction control valves 21 and discharge control valves 21' consists of two electro-hydraulic digital valves. Other components are the same as in embodiment 1.

[0057] like Figure 2b The schematic diagram of the second alternative control valve of the present invention shows an actuator assembly 8. The suction line of the first hydraulic pump / motor 10 connected to the common high-pressure rail 3 is equipped with two sets of suction control valves 21. The discharge line of the first hydraulic pump / motor 10 connected to the oil tank or the return low-pressure rail 18 is equipped with two sets of discharge control valves 21'. The suction control valves 21 and discharge control valves 21' are paired. Each set of suction control valves 21 and discharge control valves 21' consists of an electro-hydraulic proportional valve. Other components are the same as in embodiment 1.

[0058] like Figure 2c The schematic diagram of the third alternative control valve of the present invention shows an actuator assembly 8. The suction line of the first hydraulic pump / motor 10 connected to the common high-pressure rail 3 is equipped with two sets of suction control valves 21. The discharge line of the first hydraulic pump / motor 10 connected to the oil tank or return low-pressure rail 18 is equipped with two sets of discharge control valves 21'. The suction control valves 21 and discharge control valves 21' are paired. Each set of suction control valves 21 and discharge control valves 21' consists of a combination of an electro-hydraulic digital valve and an electro-hydraulic proportional valve. Other components are the same as in embodiment 1.

[0059] Example 3

[0060] like Figure 3The schematic diagram of the first hydraulic pump / motor alternative of the present invention shows an actuator assembly 8, a first hydraulic pump / motor 10 which is a variable displacement hydraulic pump / motor, and other components are the same as in embodiment 1.

[0061] Preferably, the first hydraulic pump / motor 10 is a numerical variable displacement hydraulic pump / motor or a proportional variable displacement hydraulic pump / motor. The numerical variable displacement hydraulic pump / motor determines its value by the discrete value of the torque on the drive shaft, while the proportional variable displacement hydraulic pump / motor determines its value by adjusting the proportional value of the torque on the drive shaft.

[0062] Example 4

[0063] like Figure 4 This invention provides a schematic diagram of a common high-pressure rail alternative. It includes an actuator assembly 8. The main pump 2 supplies oil to the first common high-pressure rail 3 and the second common high-pressure rail 3' with different pressures via a two-position three-way valve 22. The suction line of the first hydraulic pump / motor 10 connected to the first common high-pressure rail 3 is equipped with two sets of suction control valves 21. The suction line of the first hydraulic pump / motor 10 connected to the second common high-pressure rail 3' is also equipped with two sets of suction control valves 21. The discharge line of the first hydraulic pump / motor 10 connected to the oil tank or the return low-pressure rail 18 is equipped with four sets of discharge control valves 21'. The suction control valves 21 and discharge control valves 21' are paired, and all the suction control valves 21 and discharge control valves 21' jointly control the four-quadrant operation of the first hydraulic pump / motor 10. Other components are the same as in Embodiment 1.

[0064] By using the first high-pressure rail 3 and the second high-pressure rail 3' with different pressures, instead of activating the control valve 21 at the appropriate time, the pressure drop across the first hydraulic pump / motor 10 is actively controlled, so that the first hydraulic pump / motor 10 can provide appropriate torque to the drive shaft of the motor / generator 9.

[0065] Example 5

[0066] like Figure 5 The schematic diagram of the second hydraulic pump / motor alternative of the present invention shows an actuator assembly 8. The second hydraulic pump / motor 11 is an asymmetric hydraulic pump / motor. The return oil end of the second hydraulic pump / motor 11' is directly connected to the oil tank or the low-pressure return oil rail 18 to replace the hydraulic pneumatic accumulator 17. The low-pressure ends of the check valve 15 and the pressure reducing valve 16 are both connected to the oil tank or the low-pressure return oil rail 18. Other components are the same as in embodiment 1.

[0067] Example 6

[0068] like Figure 6The schematic diagram of the alternative actuator assembly of the present invention shows an actuator assembly 8, which further includes a three-position four-way valve 23. One end of the second hydraulic pump / motor 11 is connected to one working port of the three-position four-way valve 23, and the other end is connected to the oil tank or the return low-pressure rail 18. The other working port of the three-position four-way valve 23 connected to the second hydraulic pump / motor 11 is connected to the oil tank or the return low-pressure rail 18. The two working ports on the other side of the three-position four-way valve 23 form a closed loop with the actuator 13 through the pipeline 12. The low-pressure end of the pressure reducing valve 16 is connected to the oil tank or the return low-pressure rail 18. Other components are the same as in Embodiment 1.

[0069] Example 7

[0070] like Figure 7a The present invention provides a schematic diagram of an alternative solution for adding a third hydraulic pump / motor. An actuator assembly 8 is included, which further includes a third hydraulic pump / motor 11'. The third hydraulic pump / motor 11' is mounted on the drive shaft of a motor / generator 9. One end of the second hydraulic pump / motor 11' is connected to the actuator 13 via a pipeline 12, and the other end is connected to an oil tank or a low-pressure return rail 18. The suction and discharge ends of the third hydraulic pump / motor 11' form a closed loop with the actuator 13 via the pipeline 12. The third hydraulic pump / motor 11' is equipped with a third drain pipeline 20' connected to the oil tank or the low-pressure return rail 18. The low-pressure end of the pressure reducing valve 16 is connected to the oil tank or the low-pressure return rail 18.

[0071] like Figure 7b The present invention includes a second alternative scheme with a third hydraulic pump / motor. An actuator assembly 8 further includes an auxiliary motor / generator 9' and a third hydraulic pump / motor 11'. The third hydraulic pump / motor 11' is mounted on the drive shaft of the auxiliary motor / generator 9'. One end of the second hydraulic pump / motor 11' is connected to the actuator 13 via a pipeline 12, and the other end is connected to an oil tank or a low-pressure return rail 18. The suction and discharge ends of the third hydraulic pump / motor 11' form a closed loop with the actuator 13 via pipeline 12. The third hydraulic pump / motor 11' is equipped with a third drain pipeline 20' connected to the oil tank or the low-pressure return rail 18. The low-pressure end of the pressure reducing valve 16 is connected to the oil tank or the low-pressure return rail 18.

[0072] The above embodiments are applicable to general-purpose multi-actuator mobile hydraulic machinery, but with simple modifications, they can be extended to general-purpose multi-actuator stationary hydraulic machinery. For design simplicity, the embodiments only show the case of two actuators and two high-pressure common rails, but even adding more actuators and high-pressure rails will not change the system's design principle. The above descriptions are merely preferred embodiments of the present invention. All equivalent changes and modifications made within the scope of the claims of this invention, including the two modifications described above, should fall within the scope of the claims of this invention.

Claims

1. An electro-hydraulic hybrid drive system, comprising a prime mover (1), a main pump (2) and a main generator (6) driven by the prime mover (1), an overflow valve (5), an electrochemical energy storage device (7) powered by the main generator (6), at least one actuator assembly (8), and an oil tank or return low-pressure rail (18), characterized in that: It also includes at least one common high-pressure rail (3) supplied by the main pump (2). Each of the actuator assemblies (8) includes a motor / generator (9), a first hydraulic pump / motor (10), a second hydraulic pump / motor (11), and an actuator (13). The motor / generator (9) is electrically connected to the electrochemical energy storage device (7). The first hydraulic pump / motor (10) and the second hydraulic pump / motor (11) are sequentially mounted on the drive shaft of the motor / generator (9). The first hydraulic pump / motor (10) is hydraulically coupled in the common high-pressure rail (3). (10) The suction line connected to the common high-pressure rail (3) is equipped with two sets of suction control valves (21). The outlet line connected to the first hydraulic pump / motor (10) and the oil tank or return low-pressure rail (18) is equipped with two sets of outlet control valves (21'). The suction control valves (21) and outlet control valves (21') correspond to each other. All the suction control valves (21) and outlet control valves (21') jointly control the four-quadrant operation of the first hydraulic pump / motor (10). The second hydraulic pump / motor (11) is hydraulically coupled to the actuator (13) through the pipeline (12). Each of the portions of the pipeline (12) located at both ends of the actuator (13) is connected to a pressure reducing valve (16); The suction end and the discharge end of the second hydraulic pump / motor (11) form a closed loop with the actuator (13) through the pipeline (12). The pipeline (12) is provided with a pair of check valves (15) at each end of the actuator (13).

2. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: It also includes a hydraulic accumulator (4) connected to the public high-voltage rail (3).

3. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: Each of the oil suction control valve (21) and oil discharge control valve (21') consists of at least one electro-hydraulic digital valve, at least one electro-hydraulic proportional valve, or a combination of an electro-hydraulic digital valve and an electro-hydraulic proportional valve.

4. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: The first hydraulic pump / motor (10) is equipped with a first drain line (19) that connects to the oil tank or the return low-pressure rail (18).

5. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: The first hydraulic pump / motor (10) is a constant displacement hydraulic pump, a numerical variable displacement hydraulic pump / motor, or a proportional variable displacement hydraulic pump / motor.

6. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: The main pump (2) supplies oil to the first common high-pressure rail (3) and the second common high-pressure rail (3') with different pressures through a two-position three-way valve (22). The suction line of the first hydraulic pump / motor (10) connected to the first common high-pressure rail (3) is equipped with two sets of suction control valves (21). The suction line of the first hydraulic pump / motor (10) connected to the second common high-pressure rail (3') is equipped with two sets of suction control valves (21). The discharge line of the first hydraulic pump / motor (10) connected to the oil tank or return low-pressure rail (18) is equipped with four sets of discharge control valves (21'). The suction control valves (21) and discharge control valves (21') correspond to each other. All the suction control valves (21) and discharge control valves (21') jointly control the four-quadrant operation of the first hydraulic pump / motor (10).

7. The electro-hydraulic hybrid drive system according to any one of claims 1-6, characterized in that: Each of the actuator components (8) further includes a low-pressure accumulator (17), and the low-pressure end of the check valve (15) and the pressure reducing valve (16) is connected to the low-pressure accumulator (17).

8. The electro-hydraulic hybrid drive system as described in claim 7, characterized in that: When the actuator (13) is an asymmetric actuator, the check valve (15) is a pilot check valve.

9. The electro-hydraulic hybrid drive system as described in claim 7, characterized in that: The second hydraulic pump / motor (11) is equipped with a second drain line (20) connected to the low-pressure accumulator (17).

10. The electro-hydraulic hybrid drive system as described in claim 1, characterized in that: The second hydraulic pump / motor (11) is an asymmetric hydraulic pump / motor. The return end of the second hydraulic pump / motor (11) is connected to the oil tank or the return low pressure rail (18). The low pressure ends of the check valve (15) and the pressure reducing valve (16) are both connected to the oil tank or the return low pressure rail (18).

11. The electro-hydraulic hybrid drive system according to any one of claims 1-6, characterized in that: Each actuator assembly (8) further includes a three-position four-way valve (23), one end of the second hydraulic pump / motor (11) is connected to one working port of the three-position four-way valve (23), and the other end is connected to the oil tank or return low-pressure rail (18). The other working port of the three-position four-way valve (23) connected to the second hydraulic pump / motor (11) is connected to the oil tank or return low-pressure rail (18). The two working ports on the other side of the three-position four-way valve (23) form a closed loop with the actuator (13) through the pipeline (12). The low-pressure end of the pressure reducing valve (16) is connected to the oil tank or return low-pressure rail (18).

12. The electro-hydraulic hybrid drive system according to any one of claims 1-6, characterized in that: Each of the actuator components (8) further includes a third hydraulic pump / motor (11'), one end of which is connected to the actuator (13) via a pipeline (12), and the other end is connected to an oil tank or a return low-pressure rail (18). The suction end and the discharge end of the third hydraulic pump / motor (11') form a closed loop with the actuator (13) via a pipeline (12).

13. The electro-hydraulic hybrid drive system as described in claim 12, characterized in that: The third hydraulic pump / motor (11') is mounted on the drive shaft of the motor / generator (9).

14. The electro-hydraulic hybrid drive system as described in claim 12, characterized in that: Each of the aforementioned actuator components (8) also includes an auxiliary motor / generator (9'), with a third hydraulic pump / motor (11') mounted on the drive shaft of the auxiliary motor / generator (9').

15. The electro-hydraulic hybrid drive system as described in claim 12, characterized in that: The third hydraulic pump / motor (11') is equipped with a third drain line (20') that connects to the oil tank or the return low-pressure rail (18).

16. The electro-hydraulic hybrid drive system as described in claim 12, characterized in that: The low-pressure end of the pressure reducing valve (16) is connected to the oil tank or the return low-pressure rail (18).

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