A crane luffing mechanism potential energy recovery system and a control method thereof

Abstract

This invention provides a potential energy recovery system and control method for a crane luffing mechanism. Through modular collaborative control of an energy conversion unit, an energy storage unit, a luffing control unit, and a control unit, the system can recover and store the gravitational potential energy generated by the luffing mechanism during the lowering of the boom. During the lifting of the boom, the recovered energy is released to assist power output, effectively replacing the throttling and overflow energy consumption method of traditional luffing systems, significantly reducing energy waste, while also reducing the heat generation of the hydraulic system and extending the service life of hydraulic components. The control unit can uniformly regulate the working status of each unit based on work instructions and real-time working condition signals, ensuring smooth and controllable luffing movements, balancing energy recovery efficiency and operational reliability. At the same time, it can rely on the energy storage unit to realize emergency drive in case of failure, improving the safety and adaptability of the entire machine operation.

Description

Technical Field

[0001] This invention relates to the field of energy-saving control technology for engineering machinery, and in particular to a potential energy recovery system and control method for a crane luffing mechanism. Background Technology

[0002] Cranes are core lifting equipment in infrastructure, ports, metallurgy, and other scenarios, and the luffing mechanism is the key actuator for realizing the pitching motion of the crane boom. In existing technologies, crane luffing mechanisms mostly adopt valve-controlled hydraulic drive systems. During the lowering of the crane boom with a load, the gravitational potential energy of the crane boom and the load is directly dissipated as heat energy through throttling and overflow of the control valve. This not only causes serious energy waste and results in low overall machine energy efficiency, but also accelerates the deterioration of hydraulic oil and the aging of seals and hydraulic components due to long-term overflow heat, shortening the system's service life and increasing maintenance costs.

[0003] Current solutions for potential energy recovery in crane machinery often suffer from incomplete system architecture and limited energy storage methods, failing to fully recover and utilize gravitational potential energy during the lowering process. Furthermore, they lack coordinated control logic for luffing drive and potential energy recovery, making it difficult to maximize recovery efficiency while ensuring the smoothness of luffing movements. In addition, most existing systems do not have emergency drive functions, which can lead to safety risks such as the crane boom failing to move when the main power unit malfunctions, thus failing to fully meet the energy-saving, reliable, and safe operation requirements of crane luffing systems. Summary of the Invention

[0004] The purpose of this invention is to provide a potential energy recovery system for a crane luffing mechanism, in order to solve the technical problems of serious waste of gravitational potential energy, low energy utilization efficiency, poor coordination of recovery control, and lack of emergency safety guarantee in the existing crane luffing system.

[0005] To achieve the above objectives, the present invention provides a potential energy recovery system for a crane luffing mechanism, comprising an energy conversion unit, an energy storage unit, a luffing control unit, a hydraulic actuation unit, and a control unit; The hydraulic actuator includes a luffing cylinder, which is used to output linear driving force to drive the crane boom to complete the pitching and luffing motion. The energy conversion unit is connected to the hydraulic circuit of the luffing cylinder through the luffing control unit. It is used to output hydraulic power in the forward direction to drive the luffing cylinder to move. It can also be driven by the load to run in the reverse direction when the boom is lowered, converting gravitational potential energy into storable energy. The energy storage unit is connected to the main oil circuit of the system to store the recovered energy and release pressure oil to assist in driving the luffing cylinder during the lifting of the boom. The luffing control unit is located in the oil circuit between the energy conversion unit and the luffing cylinder, and is used to control the direction, speed and on / off state of the luffing action; The control unit is electrically connected to the energy conversion unit, energy storage unit, luffing control unit and hydraulic actuator unit respectively, and is used to coordinate the control of potential energy recovery, energy storage and energy release according to the luffing operation command, the crane boom load detection signal and the position detection signal.

[0006] Furthermore, the energy conversion unit includes a variable displacement piston four-quadrant pump, a drive motor, and a pump oil direction control valve; the variable displacement piston four-quadrant pump is coaxially connected to the drive motor, and the pressure port of the variable displacement piston four-quadrant pump is connected to the main oil circuit of the system via the pump oil direction control valve; when the boom is raised, the drive motor drives the variable displacement piston four-quadrant pump to work in pump mode and output high-pressure oil; when the boom is lowered, the high-pressure oil drives the variable displacement piston four-quadrant pump to work in motor mode and reverses to drive the motor to generate electricity.

[0007] Furthermore, the energy storage unit includes a hydraulic accumulator group and an accumulator control valve; the hydraulic accumulator group is connected to the main oil circuit of the system via the accumulator control valve, and the accumulator control valve is electrically connected to the control unit; during the lowering operation, the accumulator control valve is turned on, and high-pressure oil is charged into the hydraulic accumulator group to complete the storage of hydraulic energy; during the lifting operation, the accumulator control valve is turned on at a preset opening degree, and the hydraulic accumulator group releases high-pressure oil to assist in the drive.

[0008] Furthermore, the energy storage unit also includes a battery pack, which is electrically connected to the drive motor and is used to store the electrical energy recovered by the drive motor.

[0009] Furthermore, the luffing control unit includes a luffing cylinder control valve and a flow regeneration valve; the luffing cylinder control valve is a three-position four-way proportional directional valve, with its inlet connected to the main oil circuit of the system, its two working ports respectively connected to the rodless chamber and the rod chamber of the luffing cylinder, and its return port connected to the oil tank; the flow regeneration valve is connected in parallel between the rodless chamber and the rod chamber of the luffing cylinder, and during the lowering operation, the flow regeneration valve is turned on, and the return oil from the rodless chamber is directly replenished to the rod chamber.

[0010] Furthermore, it also includes a first pressure sensor, a second pressure sensor, a position sensor, and a speed sensor; the first pressure sensor is disposed on the connecting pipeline between the luffing cylinder control valve and the rodless chamber of the luffing cylinder, and the second pressure sensor is disposed on the connecting pipeline between the luffing cylinder control valve and the rod chamber of the luffing cylinder; the position sensor is disposed at the boom and is used to collect boom angle and position signals; the speed sensor is disposed for the variable displacement piston four-quadrant pump and is used to collect pump speed signals; the signal output terminals of each sensor are connected to the control unit.

[0011] A method for controlling the potential energy recovery of a crane luffing mechanism, based on a potential energy recovery system for the crane luffing mechanism, includes the following steps: S1: The control unit receives the luffing operation command and determines whether the current luffing action is lifting or lowering; S2: If it is a lowering action, the control unit switches the system to the potential energy recovery mode, adjusts the recovery torque to match the current load, and converts the gravitational potential energy of the luffing mechanism into hydraulic energy and electrical energy respectively and stores them in the energy storage unit. S3: If a lifting action is detected, the control unit switches the system to auxiliary drive mode and controls the energy storage unit to release the stored energy according to the current lifting load size, so as to drive the luffing cylinder together with the energy conversion unit to complete the lifting action; S4: After the amplitude change operation is completed, the control unit closes the potential energy recovery circuit and the energy release circuit, and locks the energy storage state of the energy storage unit.

[0012] Furthermore, during the lowering process in step S2: the control unit collects the boom angle, lowering speed, and system pressure signals in real time, and dynamically adjusts the potential energy recovery torque and valve opening to ensure smooth luffing action while maximizing energy recovery efficiency; during the lifting process in step S3, dynamic power distribution is adopted: the control unit dynamically adjusts the output power of the energy conversion unit and the energy release ratio of the energy storage unit according to the remaining capacity of the energy storage unit, the luffing system pressure, and the load size, taking into account both power performance and energy saving effect.

[0013] Furthermore, during the system startup and shutdown phases, the control unit performs buffer control: first, it raises the system pressure or motor speed to a preset threshold, and then switches to normal operating mode; when stopping, it first gradually reduces the power and then cuts off the circuit to avoid hydraulic shock.

[0014] Furthermore, it also includes emergency control steps: when the control unit detects a failure of the energy conversion unit, it switches to emergency lowering mode, controls the accumulator control valve and the luffing cylinder control valve to operate, and uses the hydraulic accumulator group to provide power to control the crane boom to be lowered smoothly to a safe position.

[0015] The technical solution of this invention utilizes modular collaborative control of an energy conversion unit, an energy storage unit, a luffing control unit, and a control unit. This allows for the recovery and storage of gravitational potential energy generated by the luffing mechanism during boom lowering, and the release of this recovered energy during boom lifting to assist power output. This effectively replaces the traditional throttling and overflow energy consumption method of luffing systems, significantly reducing energy waste and lowering the heating level of the hydraulic system, thus extending the service life of hydraulic components. The control unit can uniformly regulate the working status of each unit based on work commands and real-time operating signals, ensuring smooth and controllable luffing movements while balancing energy recovery efficiency and operational reliability. Furthermore, the energy storage unit can be used for emergency fault response, improving the overall safety and adaptability of the machine. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a system structure diagram of the present invention.

[0018] Explanation of reference numerals in the attached drawings: 1-luffing cylinder, 2-drive motor, 3-variable displacement piston four-quadrant pump, 4-pump oil direction control valve, 5-relief valve, 6-accumulator, 7-accumulator control valve, 8-luffing cylinder control valve, 9-flow regeneration valve, 10-first pressure sensor, 11-second pressure sensor, 12-hoisting motor, 13-hoisting motor control valve. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] Example 1: like Figure 1 As shown, the present invention provides a potential energy recovery system for a crane luffing mechanism, which is mainly applied to large-tonnage truck cranes and crawler cranes. The system as a whole includes an energy conversion unit, an energy storage unit, a luffing control unit, a hydraulic actuation unit, and a control unit, and is equipped with a variety of sensing and detection elements.

[0023] The hydraulic actuator includes a luffing cylinder 1. The piston rod end of the luffing cylinder 1 is hinged to the crane boom, and the cylinder body end is hinged to the slewing platform. The extension and retraction of the piston rod drives the crane boom to complete the luffing action. The rodless chamber and the rod chamber of the luffing cylinder 1 are respectively connected to the corresponding working oil ports of the luffing control unit.

[0024] The energy conversion unit is the core of the system's main power and energy recovery, including a motor pump and a pump oil direction control valve 4. The motor pump consists of a variable displacement piston four-quadrant pump 3 and a drive motor 2 rigidly connected coaxially. The suction port of the variable displacement piston four-quadrant pump 3 is connected to the hydraulic oil tank, and the pressure port is connected to one end of the pump oil direction control valve 4. The other end of the pump oil direction control valve 4 is connected to the system's main oil circuit. The pump oil direction control valve 4 is a two-position control valve with a one-way oil replenishment function. It is electrically connected to the control unit. When the valve is de-energized, the pump outlet is disconnected from the main oil circuit, and the built-in one-way valve can achieve passive oil replenishment. When the valve is energized and conducting, the variable displacement piston four-quadrant pump 3 is fully connected to the system's main oil circuit, supporting both forward pumping and reverse motor power generation.

[0025] The energy storage unit adopts a hybrid hydraulic and electrical energy storage method, including an accumulator 6, an accumulator control valve 7, and a battery pack. The oil port of the accumulator 6 is connected to the main oil circuit of the system via the accumulator control valve 7. The accumulator control valve 7 is a proportionally controllable two-position valve, electrically connected to the control unit, and can adjust the valve opening to control the filling and releasing speed of the accumulator 6. The battery pack is electrically connected to the electronic control terminal of the drive motor 2 to store the electrical energy generated by the motor and can provide auxiliary power supply during lifting operations.

[0026] The luffing control unit includes a luffing cylinder control valve 8 and a flow regeneration valve 9. The luffing cylinder control valve 8 is a three-position four-way proportional directional valve, with its neutral position being O-type. The P port (oil inlet) is connected to the main oil circuit of the system, and the T port (oil return port) is connected to the oil tank. The A and B working oil ports are respectively connected to the rod chamber and rodless chamber of the luffing cylinder 1. By switching the valve core left and right, the flow direction of the pressure oil can be controlled, realizing the extension, retraction, and neutral position locking of the luffing cylinder 1. By proportionally adjusting the valve core opening, the oil flow rate can be controlled, and the luffing action speed can be adjusted.

[0027] The flow regeneration valve 9 is a two-position two-way control valve, connected in parallel to the oil circuit of the rodless chamber and the rod chamber of the luffing cylinder 1, and electrically connected to the control unit. When the flow regeneration valve 9 is turned on during the lowering operation, part of the high-pressure oil discharged from the rodless chamber can flow directly into the rod chamber to supplement the oil intake demand of the rod chamber, reduce the oil replenishment flow from the oil tank, and improve system efficiency.

[0028] The control unit adopts a crane vehicle controller. The system is equipped with a first pressure sensor 10, a second pressure sensor 11, a boom angle position sensor, and a pump speed sensor. The first pressure sensor 10 is installed in the working oil circuit between port B and the rodless chamber of the luffing cylinder 1 to detect the real-time working pressure of the rodless chamber. The second pressure sensor 11 is installed in the working chamber oil circuit between port A and the rod chamber of the luffing cylinder 1 to detect the real-time working pressure of the rod chamber. The angle position sensor is installed at the boom hinge point to detect the angle and position signals of the boom. The speed sensor is installed for the variable displacement piston four-quadrant pump 3 to detect the pump speed. The signal output terminals of all the above sensors are connected to the control unit. The control output terminal of the control unit is connected to the electromagnets of each control valve, the motor controller of the motor pump, and the pump displacement adjustment mechanism to achieve coordinated control of the entire system.

[0029] In addition, the main oil circuit of the system is equipped with a relief valve 5 in parallel to limit the maximum working pressure and prevent overload damage to components. The main oil circuit of the system is also connected in parallel with a hoisting operation circuit consisting of a hoisting motor control valve 13 and a hoisting motor 12. It shares a motor pump as a power source with the luffing circuit. The two circuits are independent of each other and can operate independently or work together to complete compound actions.

[0030] Working principle: I. Load lowering condition of the crane boom: When the control unit receives the luffing command from the driver and detects that the load meets the gravity-driven conditions, it determines that the current action is a loaded luffing action, and the system switches to the potential energy recovery mode. The specific working process is as follows: The control unit first calculates the target lowering speed and target recovery torque parameters based on the load pressure of the rodless chamber detected by the first pressure sensor 10 and the boom angle detected by the angle sensor. Then, it controls the left electromagnet of the luffing cylinder control valve 8 to be energized, and the valve core switches to the left position. An oil passage is formed inside the valve core with bidirectional communication between ports B and P, and bidirectional communication between ports A and T. Due to the gravity of the boom and the load, the piston rod of the luffing cylinder 1 is pulled back, the volume of the rodless chamber decreases, and the oil is compressed to form high pressure. The oil can flow in reverse through the valve passage and merge into the main oil circuit of the system.

[0031] The high-pressure oil discharged from the rodless chamber is divided into two paths: The first path is the flow regeneration branch: the control unit activates the flow regeneration valve 9, and part of the high-pressure oil discharged from the rodless chamber flows directly into the rod chamber pipeline through the flow regeneration valve 9 connected in parallel between the two chamber pipelines. This replenishes the oil demand of the rod chamber during the cylinder retraction process, reduces the amount of oil replenished from the oil tank, and achieves energy saving through flow regeneration. The second path is the energy recovery main branch: the remaining high-pressure oil is connected to port B of the luffing cylinder control valve 8; under pressure, the oil flows in reverse through the internal passage on the left side of the valve core, flows out from port P on the lower left of the valve body, and merges into the common high-pressure main oil circuit arranged horizontally below the valve group.

[0032] The high-pressure oil flowing into the main oil circuit is then divided into two paths to complete energy storage: Hydraulic energy recovery branch: The control unit opens the accumulator control valve 7, and part of the high-pressure oil is charged into the accumulator 6, converting the gravitational potential energy of the luffing mechanism into hydraulic energy for storage; the control unit dynamically adjusts the valve opening according to the pressure of the accumulator 6 and the lowering speed to ensure smooth lowering action.

[0033] Energy recovery branch: The control unit activates the pump oil direction control valve 4, and the remaining high-pressure oil flows in reverse into the variable piston four-quadrant pump 3, which drives the pump to work in motor mode, driving the coaxial drive motor 2 to rotate and generate electricity, converting hydraulic energy into electrical energy and storing it in the battery pack; the control unit adjusts the pump displacement and generator torque to match the load size and stabilize the lowering speed.

[0034] During the retraction of the hydraulic cylinder, the volume of the rod chamber increases, creating negative pressure. Under the action of the pressure difference, the hydraulic oil in the tank flows in reverse through the return oil line into the T port of the luffing cylinder control valve 8, and then replenishes the rod chamber from the A port through the AT connecting channel on the left side of the valve. Together with the oil in the flow regeneration branch, it maintains the oil inlet balance of the rod chamber. The entire lowering process adopts closed-loop control. The control unit collects signals of boom angle, lowering speed, rodless chamber pressure, and pump speed in real time, and dynamically adjusts the opening degree of each valve port and the recovery torque to maximize energy recovery efficiency while ensuring smooth luffing action without impact.

[0035] If the system is under light load and gravity is insufficient to drive the cylinder to retract smoothly, the system can switch to active lowering mode: control valve 8 of the luffing cylinder is switched to the right position, the high-pressure oil output by the main pump enters the rod chamber through port P and port A, actively driving the cylinder to retract, and the oil in the rodless chamber returns to the oil tank through port B and port T. This is the conventional throttling lowering mode, and no energy recovery is performed.

[0036] II. Lifting conditions of the crane boom: When the control unit receives a luffing hoisting command, it determines that the current action is a hoisting action and the system switches to energy-assisted drive mode. The specific working process is as follows: The control unit calculates the optimal allocation ratio between the active power output and the recovered energy release based on the load pressure detected by the first pressure sensor 10, the remaining pressure of the accumulator 6, and the remaining battery capacity. In the active power circuit, the drive motor 2 drives the variable displacement piston four-quadrant pump 3 to operate in pump mode, drawing oil from the oil tank and pressurizing it for output. The high-pressure oil flows into the main oil circuit of the system through the pump oil direction control valve 4.

[0037] Simultaneously, the auxiliary power circuit starts, and the control unit adjusts the opening of the accumulator control valve 7 according to a preset ratio. The accumulator 6 releases the stored high-pressure oil, which flows into the main oil circuit of the system. After merging with the high-pressure oil output from the main pump, they enter the P port of the luffing cylinder control valve 8. At this time, the electromagnet on the left side of the luffing cylinder control valve 8 is energized, and the valve core switches to the left position: the P port is connected to the B port in the forward direction, and the A port is connected to the T port. The high-pressure oil enters the rodless chamber of the luffing cylinder 1 through the B port, pushing the piston rod to extend and driving the boom to lift smoothly. The oil in the rod chamber flows back to the oil tank through the A port and the T port.

[0038] During the lifting process, the control unit monitors the main oil circuit pressure, cylinder extension speed and accumulator 6 pressure in real time, and dynamically adjusts the opening of the accumulator control valve 7 and the main pump output power. Under the premise of meeting the power requirements of operation, it maximizes the use of recovered energy, reduces the power consumption of the main pump, and achieves energy saving effect.

[0039] III. Operational completion status: After the luffing maneuver is completed and the operator releases the control lever, the control unit executes the standby lock logic: First, it de-energizes both electromagnets of the luffing cylinder control valve 8, causing the valve core to return to the neutral position. Utilizing the O-type neutral position function, it cuts off the P, T, A, and B oil ports, sealing the two chamber oil circuits of the luffing cylinder 1, thus mechanically locking the boom and preventing it from falling. Next, it de-energizes and closes the accumulator control valve 7, cutting off the oil circuit of the accumulator 6 and locking the accumulator 6's energy storage state. Then, it stops the motor pump, de-energizes the pump oil direction control valve 4, and cuts off the power circuit. In standby mode, the control unit continuously monitors the pressure in both chambers of the cylinder and the pressure in the accumulator 6. When an abnormal pressure drop occurs, it issues a timely warning to ensure the safety and reliability of the standby state.

[0040] IV. Emergency Fault Operation Conditions: When the control unit detects a malfunction in the motor pump (such as motor power failure or pump damage) and its inability to output power, the system automatically switches to emergency lowering mode. Lowering is then achieved through active drive by the accumulator 6, ensuring operational safety. The control unit opens the accumulator control valve 7, releasing stored high-pressure oil from the accumulator 6 as a temporary power source to power the main oil circuit, establishing high pressure at port P. Simultaneously, the control unit switches the luffing cylinder control valve 8 to the right position (lowering position), creating a pathway connecting port P and port A, and port B and port T. High-pressure oil enters the rod chamber of the luffing cylinder 1 through ports P and A, driving the cylinder to retract and smoothly lowering the boom. Low-pressure oil discharged from the rodless chamber flows back to the oil tank through ports B and T. The control unit adjusts the opening of the accumulator control valve 7 to control the lowering speed, safely lowering the boom to its lowest position and avoiding the safety risk of the boom being suspended and jammed in a fault situation, thus improving the overall safety performance of the machine.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A potential energy recovery system for a crane luffing mechanism, characterized in that, It includes an energy conversion unit, an energy storage unit, a variable amplitude control unit, a hydraulic actuator unit, and a control unit; The hydraulic actuator includes a luffing cylinder, which is used to output linear driving force to drive the crane boom to complete the pitching and luffing motion. The energy conversion unit is connected to the hydraulic circuit of the luffing cylinder through the luffing control unit. It is used to output hydraulic power in the forward direction to drive the luffing cylinder to move. It can also be driven by the load to run in the reverse direction when the boom is lowered, converting gravitational potential energy into storable energy. The energy storage unit is connected to the main oil circuit of the system to store the recovered energy and release pressure oil to assist in driving the luffing cylinder during the lifting of the boom. The luffing control unit is located in the oil circuit between the energy conversion unit and the luffing cylinder, and is used to control the direction, speed and on / off state of the luffing action; The control unit is electrically connected to the energy conversion unit, energy storage unit, luffing control unit and hydraulic actuator unit respectively, and is used to coordinate the control of potential energy recovery, energy storage and energy release according to the luffing operation command, the crane boom load detection signal and the position detection signal.

2. The potential energy recovery system for the crane luffing mechanism according to claim 1, characterized in that, The energy conversion unit includes a variable displacement piston four-quadrant pump, a drive motor, and a pump oil direction control valve. The variable displacement piston four-quadrant pump is coaxially connected to the drive motor, and the pressure port of the variable displacement piston four-quadrant pump is connected to the main oil circuit of the system via the pump oil direction control valve. When the boom is raised, the drive motor drives the variable displacement piston four-quadrant pump to operate in pump mode and output high-pressure oil. When the boom is lowered, the high-pressure oil drives the variable displacement piston four-quadrant pump to operate in motor mode and reverses to drive the motor to generate electricity.

3. The potential energy recovery system for the crane luffing mechanism according to claim 1, characterized in that, The energy storage unit includes a hydraulic accumulator group and an accumulator control valve; the hydraulic accumulator group is connected to the main oil circuit of the system via the accumulator control valve, and the accumulator control valve is electrically connected to the control unit; during the lowering operation, the accumulator control valve is turned on, and high-pressure oil is charged into the hydraulic accumulator group to complete the storage of hydraulic energy; during the lifting operation, the accumulator control valve is turned on at a preset opening degree, and the hydraulic accumulator group releases high-pressure oil to assist in the drive.

4. The potential energy recovery system for a crane luffing mechanism according to claim 2, characterized in that, The energy storage unit also includes a battery pack, which is electrically connected to the drive motor and is used to store the electrical energy recovered by the drive motor.

5. The potential energy recovery system for a crane luffing mechanism according to claim 1, characterized in that, The luffing control unit includes a luffing cylinder control valve and a flow regeneration valve. The luffing cylinder control valve is a three-position four-way proportional directional valve. Its inlet is connected to the main oil circuit of the system, and its two working ports are respectively connected to the rodless chamber and the rod chamber of the luffing cylinder. Its return port is connected to the oil tank. The flow regeneration valve is connected in parallel between the rodless chamber and the rod chamber of the luffing cylinder. During the lowering operation, the flow regeneration valve is turned on, and the return oil from the rodless chamber is directly replenished to the rod chamber.

6. The potential energy recovery system for a crane luffing mechanism according to claim 5, characterized in that, It also includes a first pressure sensor, a second pressure sensor, a position sensor, and a speed sensor; the first pressure sensor is installed on the connecting pipe between the luffing cylinder control valve and the rodless chamber of the luffing cylinder, and the second pressure sensor is installed on the connecting pipe between the luffing cylinder control valve and the rod chamber of the luffing cylinder; the position sensor is installed at the boom and is used to collect boom angle and position signals; the speed sensor is installed for the variable displacement piston four-quadrant pump and is used to collect pump speed signals; the signal output terminals of each sensor are connected to the control unit.

7. A method for controlling the potential energy recovery of a crane luffing mechanism, implemented based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: S1: The control unit receives the luffing operation command and determines whether the current luffing action is lifting or lowering; S2: If it is a lowering action, the control unit switches the system to the potential energy recovery mode, adjusts the recovery torque to match the current load, and converts the gravitational potential energy of the luffing mechanism into hydraulic energy and electrical energy respectively and stores them in the energy storage unit. S3: If a lifting action is detected, the control unit switches the system to auxiliary drive mode and controls the energy storage unit to release the stored energy according to the current lifting load size, so as to drive the luffing cylinder together with the energy conversion unit to complete the lifting action; S4: After the amplitude change operation is completed, the control unit closes the potential energy recovery circuit and the energy release circuit, and locks the energy storage state of the energy storage unit.

8. The control method according to claim 7, characterized in that, During the lowering process in step S2: the control unit collects the boom angle, lowering speed and system pressure signals in real time, and dynamically adjusts the potential energy recovery torque and valve opening; during the lifting process in step S3, dynamic power distribution is adopted: the control unit dynamically adjusts the output power of the energy conversion unit and the energy release ratio of the energy storage unit according to the remaining capacity of the energy storage unit, the pressure of the luffing system and the load size.

9. The control method according to claim 7, characterized in that, During system startup and shutdown, the control unit first increases the system pressure or motor speed to a preset threshold, and then switches to normal operating mode; when stopping, it first gradually reduces the power and then cuts off the circuit to avoid hydraulic shock.

10. The control method according to claim 7, characterized in that, It also includes emergency control steps: when the control unit detects a failure of the energy conversion unit, it switches to emergency lowering mode, controls the accumulator control valve and the luffing cylinder control valve to operate, and uses the hydraulic accumulator group to provide power to control the crane boom to be lowered smoothly to a safe position.

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