Tower crane movable arm variable amplitude hydraulic system and control method

Abstract

The invention discloses a tower crane movable arm variable amplitude hydraulic system and a control method. The variable amplitude hydraulic system comprises an oil tank, a motor, a plunger variable pump, a high-pressure filter, a first one-way valve, a pressure gauge, a pilot-operated overflow valve, a proportional direction valve, a shuttle valve, a second one-way valve, a third one-way valve, an oil return filter, a variable amplitude oil cylinder valve set, a variable amplitude oil cylinder and a displacement sensor. Wherein the variable-amplitude oil cylinder valve group comprises a first balance valve, a first stop valve, a second stop valve, a second balance valve, a first pressure sensor, a third stop valve, a fourth one-way valve, a fifth one-way valve, a fourth stop valve and a second pressure sensor; the system can meet the working stability and reliability when different amplitude variation angles, the stress direction of the amplitude variation oil cylinder and the stress change in real time, realizes the self-adaptive matching of the load, the power and the flow, meets the maximum power utilization, reduces the heating value of the system, reduces the energy consumption of equipment, and is high in control precision, quick in response and long in service life.

Description

Technical Field

[0001] This invention relates to the field of crane technology, specifically to a tower crane boom luffing hydraulic system and control method. Background Technology

[0002] Tower cranes, as an important construction equipment, are increasingly widely used in urban construction. The luffing mechanism of traditional luffing tower cranes is generally composed of a motor, brake, reducer, drum, wire rope and jib. The luffing is driven by the motor and the wire rope pulls the jib to perform pitching and swinging operations. However, the traditional structure has a long jib and a large operating radius, which is not suitable for operation in urban high-rise building clusters and narrow construction sites. The congested space on site also makes it very difficult to assemble and disassemble the tower crane on site.

[0003] Therefore, in the above-mentioned operating environment, tower crane booms typically adopt hydraulic luffing systems, which consist of luffing cylinders, hydraulic pump stations, and control systems. Compared with traditional motor-driven wire rope traction booms for luffing, hydraulic luffing has a shorter counterweight boom and a smaller operating radius, making it more advantageous for operation in urban high-rise building clusters and narrow construction sites. At the same time, it is also very convenient for on-site tower crane assembly, disassembly, and relocation.

[0004] Patent publication number CN110422778A discloses a boom luffing hydraulic system and a crane. The boom luffing hydraulic system includes: a hydraulic cylinder for driving the boom to pitch and swing, the hydraulic cylinder including a first chamber for discharging hydraulic fluid when the boom falls and a second chamber for introducing hydraulic fluid; a control valve including an inlet for introducing hydraulic fluid, a return port for discharging hydraulic fluid, a first fluid port and a second fluid port, the control valve having a first state where the inlet is connected to the first fluid port and a second state where the inlet is connected to the second fluid port; a balance valve connected between the first fluid port of the control valve and the first chamber of the hydraulic cylinder, and having a control fluid port for introducing hydraulic fluid to control the opening of the balance valve, the control fluid port communicating with the second fluid port of the control valve; and wherein the control valve further includes a valve body having a first valve chamber, a first valve core movably disposed in the first valve chamber to switch the control valve between the first state and the second state, and a pressure reducing valve. In this luffing hydraulic system and crane, when the boom is raised, the hydraulic pump outputs pressurized oil through inlet P, the first fluid port, and the balance valve into the rodless chamber via a mechanically operated control valve, pushing the boom to rise. The hydraulic oil discharged from the rod chamber returns to the oil tank through the back pressure valve. When the boom is lowered under gravity, the hydraulic pump outputs pressurized oil through inlet P, the control valve, the pressure reducing valve, and port B into the control port of the balance valve via a mechanically operated control valve. By controlling the pressure of the pressure reducing valve, the opening of the balance valve is controlled, thereby controlling the boom to descend smoothly.

[0005] However, this boom luffing hydraulic system technology has the following problems when used on tower crane booms: 1. Due to the gravity of the counterweight, boom, and load, the direction and magnitude of the force on the luffing cylinder change at different boom angles. When the luffing decreases to a point where the counterweight exceeds the force exerted on the cylinder by the boom and load, the luffing cylinder changes from compression to tension. The hydraulic system must actively provide retraction power through the cylinder to overcome the tension condition and prevent free fall. Therefore, this boom luffing hydraulic system is not suitable for tower crane booms; 2. Direct drive control using a mechanical joystick. 1. The valve design, due to manual operation, leads to long-term wear and aging of the valve core and sealing ring, and the mechanical transmission has gaps, resulting in low control accuracy of the luffing action, affecting work efficiency and safety; 2. The hydraulic pump in the luffing hydraulic system of this crane boom lacks load-sensing function. During the descent of the crane boom under gravity, the hydraulic pump is always working at full load, resulting in high heat generation in the luffing hydraulic system and a tendency to overheat; 3. This crane boom luffing hydraulic system lacks effective protection mechanisms such as overspeed, overpressure, and overstroke, which can easily lead to cylinder malfunction or damage to hydraulic components under sudden working conditions, posing a safety hazard. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a tower crane boom luffing hydraulic system and control method.

[0007] To achieve the above objectives: This invention provides a tower crane boom luffing hydraulic system, comprising an oil tank, a motor, a piston variable pump, a high-pressure filter, a first check valve, a pressure gauge, a pilot-operated relief valve, a proportional directional valve, a shuttle valve, a second check valve, a third check valve, a return oil filter, a luffing cylinder valve assembly, a luffing cylinder, and a displacement sensor. The variable amplitude cylinder valve group includes a first balance valve, a first shut-off valve, a second shut-off valve, a second balance valve, a first pressure sensor, a third shut-off valve, a fourth check valve, a fifth check valve, a fourth shut-off valve, and a second pressure sensor. Hydraulic oil is stored in the tank. The motor is connected to the variable piston pump. The suction port and discharge port of the variable piston pump are connected to the tank through suction pipes and discharge pipes, respectively. The pressure port of the variable piston pump is connected to the inlet of the high-pressure filter. The outlet of the high-pressure filter is connected to the inlet of the first check valve. The outlet of the first check valve is divided into three paths. The first and second paths are connected to the pressure ports of the pressure gauge and the pilot-operated relief valve, respectively. The third path is connected to the P” port of the proportional directional valve. Port 1 of the shuttle valve is connected to the B” port of the proportional directional valve, and the flow is then connected to port B1. Port 2 of the shuttle valve is connected to the A” port of the proportional directional valve, and the flow is then connected to port A1. The neutral port 3 of the shuttle valve is connected to the pilot pressure port X of the variable piston pump. The unloading port of the pilot-operated relief valve, the T" port of the proportional directional valve, the inlet of the second check valve, and the outlet of the third check valve converge and are connected to port T3. The outlet of the second check valve is connected to the oil tank via the return oil filter, and the inlet of the third check valve is used as the suction port to return the oil tank. Ports A1 and B1 are connected to ports A2 and B2 of the luffing cylinder valve group, respectively. Ports T2 and T3 of the luffing cylinder valve group are connected.

[0008] Port A2 is connected to port 2 of the first balancing valve and port 3 of the second balancing valve, with port 3 of the second balancing valve serving as the pilot port. Port B2 is connected to port 2 of the second balancing valve and port 3 of the first balancing valve, with port 3 of the first balancing valve serving as the pilot port. Port 1 of the first balancing valve is divided into three paths, connecting to the first shut-off valve, the check port of the fourth check valve, and the third shut-off valve, respectively. Port 1 of the second balancing valve is also divided into three paths, connecting to the second shut-off valve, the check port of the fifth check valve, and the fourth shut-off valve, respectively. The other end of the third shut-off valve is connected to the rodless chamber of the luffing cylinder and the first pressure sensor, while the other end of the fourth shut-off valve is connected to the rod chamber of the luffing cylinder and the second pressure sensor. The other ends of the first and second shut-off valves are connected in parallel and then merged with the inlets of the fourth and fifth check valves before being connected to port T2.

[0009] Furthermore, it also includes a safety valve, with the other end of the fourth shut-off valve connected to the rod chamber of the luffing cylinder, the second pressure sensor, and the pressure port of the safety valve; The other ends of the first and second shut-off valves are connected in parallel and then merged with the inlets of the fourth and fifth check valves and the unloading port of the safety valve before being connected to port T2.

[0010] Furthermore, the variable displacement piston pump is a Rexroth A11VO-LRDS series axial piston pump with a displacement of 40~260ml / r and a maximum pressure of 350bar, integrating power control, pressure cut-off and load sensing functions.

[0011] Furthermore, the proportional directional valve is a three-position four-way Y-type pilot-operated proportional valve, which receives a current signal of 4~20mA. Specifically, the valve core is in the neutral position when the input current signal is 12mA. When the current signal increases from 12mA to 20mA, the cylinder is extended; when the current signal decreases from 12mA to 4mA, the cylinder is retracted.

[0012] Furthermore, it also includes a PLC controller, whose input terminals are connected to the first pressure sensor, the second pressure sensor, the displacement sensor, and the variable amplitude rise / fall multi-position switch signal set on the driver's cab control panel. The output of the PLC controller is connected to the motor, the piston variable pump and the proportional directional valve. The PLC controller adjusts the valve core displacement of the proportional directional valve through the current signal to achieve proportional control of direction and flow. The first pressure sensor is used to monitor the pressure in the rodless chamber; the second pressure sensor is used to monitor the pressure in the rod chamber; and the displacement sensor is used to monitor the real-time stroke position of the luffing cylinder.

[0013] Furthermore, the PLC controller is also used to calculate the amplitude angle based on the stroke signal received by the displacement sensor and display it on the operating interface in the driver's cab. The formula for calculating the amplitude angle is as follows: , Where S is the length of the hydraulic cylinder when the boom is horizontal; L1 is the length of the support frame; L2 is the boom fulcrum length; This refers to the working stroke of the hydraulic cylinder during boom luffing. α is the angle between the fulcrum of the boom cavity and the support frame when the boom is horizontal; α' is the angle between the boom cavity fulcrum and the support frame when the boom is luffing; β is the angle between the boom and the fulcrum of the rod cavity when the boom is horizontal; The luffing angle is the angle between the boom and the horizontal plane when the boom is luffing.

[0014] Furthermore, the PLC controller is also used to realize the cross-gear shifting control of the variable amplitude hydraulic system: when shifting up a gear, the PLC controller realizes the smooth transition of the current signal through the incremental ramp algorithm, so that the hydraulic oil flow rate output by the piston variable pump increases smoothly; when shifting down a gear, the descending ramp algorithm is used to make the hydraulic oil flow rate output by the piston variable pump decrease smoothly.

[0015] Furthermore, the PLC controller is also used to implement pressure protection control: when the load pressure reaches the preset cut-off value of the plunger variable pump, the safety valve of the plunger variable pump opens to limit the system pressure; at the same time, the first pressure sensor monitors the rodless chamber pressure in real time and transmits the signal to the PLC controller. If the rodless chamber pressure is abnormal or exceeds the threshold, the PLC controller immediately triggers an alarm and executes a variable amplitude action stop command, forming a dual safety protection mechanism of pressure cut-off and real-time monitoring to ensure the safety and reliability of the system under overload conditions.

[0016] Furthermore, the PLC controller is also used to implement intelligent stroke protection control: when the stroke position approaches the preset protection threshold during the amplitude increase or decrease process, the PLC controller immediately triggers a deceleration command to make the system stop smoothly.

[0017] Furthermore, the PLC controller is also used to implement intelligent speed protection: when the gear position remains unchanged, the PLC controller compares the normal speed of the gear position with the real-time variable speed in real time: when the variable speed rises to 110% of the normal speed of the gear position, the gear position current increment received by the proportional directional valve of that gear position is reduced by 50%, automatically reducing the speed and locking the upshift function, which can only downshift and reduce the speed; when the variable speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is released. If the amplitude conversion speed continues to rise to 120% of the normal speed of the gear after the current increment of the gear decreases by 50%, the PLC controller will immediately stop the amplitude conversion action and trigger an overspeed alarm.

[0018] The present invention also provides a control method applied to the above-mentioned tower boom luffing hydraulic system, the control method comprising: Boom raising: The operator presses the "Pump on" button, the PLC controller controls the motor to be energized, driving the piston variable pump to run. The operator switches to the luffing raising gear 1 on the linkage. The PLC controller receives the switch signal of luffing raising gear 1 and outputs the corresponding current signal to control the opening of the proportional directional valve. The piston variable pump outputs hydraulic oil flow corresponding to the opening, which flows through the P" port and A" port of the proportional directional valve, the first balance valve, and the third shut-off valve to the rodless chamber of the luffing cylinder. At the same time, the second balance valve opens under the action of the pilot port pressure. The hydraulic oil in the rod chamber of the luffing cylinder flows back to the oil tank through the fourth shut-off valve, the second balance valve, the B" port and T" port of the proportional directional valve, the second check valve, and the return oil filter. The luffing cylinder is pushed out, and the boom begins to rise. During the boom luffing process, the X port of the piston variable pump receives the working oil pressure of the rodless chamber in real time through the shuttle valve. Based on its load sensing function, the pump body monitors the pressure difference between the input and output pressures of the proportional directional valve in real time. When the pressure difference increases, the pump automatically reduces the displacement; when the pressure difference decreases, the pump increases the displacement. Through dynamic adjustment, the pressure difference is always maintained at the set value. During the boom luffing process, the direction and magnitude of the force on the luffing cylinder are constantly changing. When the load on the luffing cylinder is within the constant power control starting pressure range set by the variable piston pump, the variable piston pump can output the maximum rated full flow. At this time, the luffing speed is directly controlled by the luffing gear of the control table. When the load exceeds the constant power starting pressure, the maximum output flow of the variable piston pump will be automatically adjusted according to the power control characteristic curve. At this time, constant power adjustment takes precedence over gear adjustment. By dynamically limiting the maximum luffing speed, the system adapts to the increasing load, thereby ensuring the stability and reliability of the system operation. During the boom luffing and raising process, the gears can be gradually switched if acceleration is required, depending on the load and operating conditions. During the boom luffing process, when the load pressure reaches the preset pressure cut-off value of the piston variable pump, the safety valve of the piston variable pump immediately opens to limit the pressure from continuing to rise, thereby ensuring the safety and reliability of the system under overload conditions. At the same time, the first pressure sensor monitors the real-time pressure status of the rodless chamber and transmits the pressure signal to the PLC controller. When the pressure in the rodless chamber is abnormal or exceeds the preset safety threshold, the PLC controller will quickly trigger an alarm signal and execute a luffing action stop command according to the preset overpressure protection parameters, forming a dual protection mechanism. When the boom rises to the working position, the operator switches the gear to the zero position. The PLC controller outputs a current signal according to the descent ramp algorithm, which controls the proportional directional valve to smoothly switch to the neutral position, so that the boom luffing stops. At this time, the luffing cylinder is locked and pressure is maintained under the action of the first balance valve and the second balance valve. At the same time, the motor delay power-off protection mechanism is triggered to ensure the safety and stability of the system. The control logic during boom descent is symmetrical to that during boom ascent.

[0019] Furthermore, the control method also includes handling situations involving skipping gear shifts: When shifting up a gear, the PLC controller uses an incremental ramp algorithm to achieve a smooth transition of the current signal, so that the hydraulic oil flow rate output by the piston variable pump increases smoothly; when shifting down a gear, a descending ramp algorithm is used to make the hydraulic oil flow rate output by the piston variable pump decrease smoothly.

[0020] Furthermore, the control method also includes How to handle situations where the amplitude is close to its limit: When the amplitude increases or decreases and the travel position approaches the preset protection threshold, the PLC controller immediately triggers a deceleration command to bring the system to a smooth stop.

[0021] Furthermore, the control method also includes handling situations where the luffing cylinder experiences cavitation failure: When the luffing cylinder is subjected to a load in the same direction and an extreme abnormality occurs during the boom luffing process, causing it to rapidly pull out and suck in air, the rodless chamber, through suction, draws hydraulic oil from the tank via port T5, the third check valve, the return oil pipes at ports T3 and T2, and the fourth check valve, thus replenishing the oil and preventing unstable luffing. Simultaneously, with the gear position unchanged, the PLC controller compares the normal speed of the gear position with the real-time luffing speed: when the luffing speed rises to 110% of the normal speed of the gear position, the proportional directional valve for that gear position receives a 50% reduction in the gear current increment, automatically reducing speed and locking the upshift function, allowing only downshifting and speed reduction; once the luffing speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is lifted. If the amplitude conversion speed continues to rise to 120% of the normal speed of the gear after the current increment of the gear decreases by 50%, the PLC controller will immediately stop the amplitude conversion action and trigger an overspeed alarm. When a suction failure occurs during the boom luffing and descent, the rod chamber is quickly replenished with oil through the fifth check valve. The PLC control logic is symmetrical with the lifting process, and the current regulation and speed protection mechanisms are executed in opposite directions, forming a two-way symmetrical fault protection system.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The luffing hydraulic system of this invention is equipped with a proportional directional valve. By receiving input signals from the PLC controller in the control box, the extension and retraction of the luffing cylinder are realized. According to the load of the boom, the input signal value can be adjusted in real time by switching the gear on the linkage table in the driver's cab to control the opening of the proportional directional valve, thereby controlling the output flow of the piston variable pump, and thus controlling the extension and retraction speed of the luffing cylinder. This achieves smooth raising and lowering of the tower crane boom with high control precision and fast response. Both the rodless chamber and the rod chamber are equipped with pressure-type balance valves with extremely low internal leakage, which can meet the pressure holding requirements of long-term boom locking operation. At the same time, when the boom changes at different operating angles and the load direction changes, the back pressure of the two balance valves can ensure the stability of the luffing cylinder when it is under load in the same direction during extension and retraction, effectively preventing free fall.

[0023] 2. The variable displacement piston pump of this invention is a power-controlled type, equipped with pressure cut-off and load sensing control functions. During boom luffing, the variable displacement piston pump uses a constant power control function, which is set with a constant power control starting pressure. When the load of the luffing cylinder is within the set constant power control starting pressure range, the variable displacement piston pump can output the maximum rated full flow. When the load exceeds the constant power starting pressure, the maximum output flow of the variable displacement piston pump will decrease, and it will be automatically adjusted through the constant power curve. At the same time, the pilot pressure port X of the variable displacement piston pump receives the real-time working oil pressure of the luffing cylinder through a shuttle valve. When the operator switches gears, it is used to adjust the opening of the proportional directional valve. When controlling the luffing speed, the system automatically compares the pressure difference between the input and output pressures of the proportional directional valve based on the load sensing function. When the pressure difference increases, the variable displacement pump automatically reduces its output displacement; when the pressure difference decreases, the variable displacement pump automatically increases its output displacement until the pressure difference returns to the set value. The power control and load sensing functions of the variable displacement pump achieve adaptive matching of load power, greatly reducing energy consumption while meeting the luffing speed requirements. When the load pressure of the luffing cylinder reaches the set pressure cutoff value, the safety valve of the variable displacement pump opens, and the pressure will no longer rise, ensuring the safety and reliability of the system under overload conditions.

[0024] 3. This invention significantly improves the operational performance of the boom luffing system through the coordinated control of PLC and load sensing system. The system uses displacement sensors to monitor the real-time stroke position of the luffing cylinder, and the PLC calculates and displays the luffing angle in real time, eliminating the conversion step of traditional angle sensors and achieving higher measurement accuracy. The proportional directional valve opening is controlled by a segmented ramp algorithm to achieve a smooth transition of hydraulic oil flow during gear shifts, effectively suppressing system shock. The load sensing system dynamically adjusts the displacement of the piston variable pump, maintaining full flow output within the constant power range and automatically limiting speed protection in case of overload. During the shutdown phase, a ramp algorithm is used to achieve smooth braking, and the balance valve locks the cylinder and delays power cutoff to ensure system safety. This solution simplifies the system structure and improves operational stability and safety while ensuring accuracy through the dual-purpose integration of displacement sensors and intelligent control strategies.

[0025] 4. This invention is particularly effective in tower crane boom luffing hydraulic systems. During boom luffing, it can ensure stability and reliability when the luffing cylinder experiences real-time changes in force direction and magnitude at different luffing angles. It achieves adaptive matching of load, power, and flow, maximizing power utilization, reducing system heat generation, lowering equipment energy consumption, and providing high control precision, fast response, and long service life. Attached Figure Description

[0026] Figure 1 This is a diagram of the variable-amplitude hydraulic system according to a preferred embodiment of the present invention; Figure 2 This is a control principle diagram of a preferred embodiment of the present invention; Figure 3 A simplified diagram of the boom luffing structure of the tower crane; The components include: oil tank 1, motor 2, plunger variable pump 3, high-pressure filter 4, first check valve 5, pressure gauge 6, pilot-operated relief valve 7, proportional directional valve 8, shuttle valve 9, second check valve 10, third check valve 11, return oil filter 12, luffing cylinder valve assembly 13, luffing cylinder 14, displacement sensor 15, first balance valve 13.1, first shut-off valve 13.2, second shut-off valve 13.3, second balance valve 13.4, safety valve 13.5, first pressure sensor 13.6, third shut-off valve 13.7, fourth check valve 13.8, fifth check valve 13.9, fourth shut-off valve 13.10, and second pressure sensor 13.11. Detailed Implementation

[0027] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0028] Example 1, see Figure 1 and Figure 2The tower boom luffing hydraulic system shown includes an oil tank 1, a motor 2, a piston variable pump 3, a high-pressure filter 4, a first check valve 5, a pressure gauge 6, a pilot-operated relief valve 7, a proportional directional valve 8, a shuttle valve 9, a second check valve 10, a third check valve 11, a return oil filter 12, a luffing cylinder valve group 13, a luffing cylinder 14, and a displacement sensor 15. The variable amplitude cylinder valve group 13 includes a first balance valve 13.1, a first shut-off valve 13.2, a second shut-off valve 13.3, a second balance valve 13.4, a first pressure sensor 13.6, a third shut-off valve 13.7, a fourth check valve 13.8, a fifth check valve 13.9, a fourth shut-off valve 13.10, and a second pressure sensor 13.11. Hydraulic oil is stored in tank 1. Motor 2 is connected to piston variable pump 3 via a coupling. The suction port and discharge port of piston variable pump 3 are connected to tank 1 via suction pipe and discharge pipe, respectively. The pressure port of piston variable pump 3 is connected to the inlet of high pressure filter 4. The outlet of high pressure filter 4 is connected to the inlet of first check valve 5. The outlet of first check valve 5 is divided into three paths. The first and second paths are connected to the pressure ports of pressure gauge 6 and pilot relief valve 7, respectively. The third path is connected to port P” of proportional directional valve 8. Port 1 of shuttle valve 9 is connected to port B” of proportional directional valve 8, and the flow is combined and connected to port B1. Port 2 of shuttle valve 9 is connected to port A” of proportional directional valve 8, and the flow is combined and connected to port A1. The neutral port 3 of shuttle valve 9 is connected to pilot pressure port X of piston variable pump 3. Preferably, proportional directional valve 8 and shuttle valve 9 are installed in a stacked combination. The oil discharge port of the pilot-operated relief valve 7, the T" port of the proportional directional valve 8, the inlet of the second check valve 10, and the outlet of the third check valve 11 are connected to the T3 port after they converge. The outlet of the second check valve 10 is connected to the oil tank 1 via the return oil filter 12, and the inlet of the third check valve 11 is used as the oil suction port to return to the oil tank 1. Ports A1 and B1 are connected to ports A2 and B2 of the luffing cylinder valve group 13, respectively. Ports T2 and T3 of the luffing cylinder valve group 13 are connected.

[0029] Port A2 is connected to port 2 of the first balancing valve 13.1 and port 3 of the second balancing valve 13.4, with port 3 of the second balancing valve 13.4 serving as the pilot port; Port B2 is connected to port 2 of the second balancing valve 13.4 and port 3 of the first balancing valve 13.1, with port 3 of the first balancing valve 13.1 serving as the pilot port; Port 1 of the first balancing valve 13.1 is divided into three paths, connecting to the first shut-off valve 13.2, the check port of the fourth one-way valve 13.8, and the third shut-off valve 13.7 respectively; Port 1 of the second balancing valve 13.4 is also divided into three paths, connecting to... Connect the check ports of the second shut-off valve 13.3 and the fifth check valve 13.9, and the fourth shut-off valve 13.10. Connect the other end of the third shut-off valve 13.7 to the rodless chamber of the luffing cylinder 14 and the first pressure sensor 13.6. Connect the other end of the fourth shut-off valve 13.10 to the rod chamber of the luffing cylinder 14 and the second pressure sensor 13.11. Connect the other ends of the first shut-off valve 13.2 and the second shut-off valve 13.3 in parallel with the inlets of the fourth check valve 13.8 and the fifth check valve 13.9 to port T2.

[0030] This invention uses shuttle valve 9 to detect the oil pressure in the rodless chamber and rod chamber of luffing cylinder 14 at both ends. When there is a pressure difference between the two sides, the shuttle valve will automatically open the high-pressure side oil circuit and feed back the pressure signal to the pilot pressure port X of plunger variable pump 3, thereby realizing dynamic adjustment of pump displacement. This design ensures that the system can adjust the oil supply pressure in real time according to load changes through mechanical pressure comparison, which not only improves the response accuracy of luffing action, but also avoids the delay problem of traditional electronic control scheme. In this embodiment, a safety valve 13.5 is also included, and the other end of the fourth shut-off valve 13.10 is connected to the rod chamber of the luffing cylinder 14, the second pressure sensor 13.11, and the pressure port of the safety valve 13.5; The other ends of the first shut-off valve 13.2 and the second shut-off valve 13.3 are connected in parallel and then merged with the inlet of the fourth one-way valve 13.8 and the fifth one-way valve 13.9, and the unloading port of the safety valve 13.5 before being connected to port T2. Among them, the first shut-off valve 13.2 and the second shut-off valve 13.3 are used to unload the pressure in the rodless chamber during maintenance of the luffing cylinder 14. More specifically, during maintenance of the luffing cylinder 14, the oil circuit of the rodless chamber can be connected to the oil tank by manually opening the shut-off valve, thereby quickly releasing the pressure in the chamber and ensuring safe unloading. The safety valve 13.5 is used for rapid overflow when the rod chamber of the luffing cylinder 14 is abnormally overpressurized, eliminating the safety hazard of cylinder explosion caused by the instantaneous increase in pressure in the rod chamber when the fourth shut-off valve 13.10 is mistakenly closed.

[0031] In this embodiment, the variable piston pump 3 is a Rexroth A11VO-LRDS series axial piston pump with a displacement of 40~260ml / r and a maximum pressure of 350bar, integrating power control, pressure cut-off and load sensing functions.

[0032] In this embodiment, the proportional directional valve 8 is a three-position four-way Y-type pilot-operated proportional valve, which is input with a current signal of 4~20mA. Among them, the input of 12mA is the valve core in the middle position. When the current signal increases from 12mA to 20mA, the control cylinder extends; when the current signal decreases from 12mA to 4mA, the control cylinder retracts.

[0033] In one embodiment, it also includes a PLC controller, the input terminals of which are connected to the first pressure sensor 13.6, the second pressure sensor 13.11, the displacement sensor 15, and the variable amplitude rise / fall multi-position switch signal set on the driver's cab control panel. The output of the PLC controller is connected to the motor 2, the piston variable pump 3 and the proportional directional valve 8. The PLC controller adjusts the valve core displacement of the proportional directional valve 8 through the current signal to realize the proportional control of direction and flow. The first pressure sensor 13.6 is used to monitor the pressure in the rodless chamber; the second pressure sensor 13.11 is used to monitor the pressure in the rod chamber; and the displacement sensor 15 is used to monitor the real-time stroke position of the luffing cylinder 14.

[0034] like Figure 3 As shown, in one embodiment, the PLC controller is also used to calculate the amplitude angle based on the stroke signal received by the displacement sensor 15 and display it on the operating interface in the driver's cab. The formula for calculating the amplitude angle is as follows: , Where S is the length of the hydraulic cylinder when the boom is horizontal; L1 is the length of the support frame; L2 is the boom fulcrum length; This refers to the working stroke of the hydraulic cylinder during boom luffing. α is the angle between the fulcrum of the boom cavity and the support frame when the boom is horizontal; α' is the angle between the boom cavity fulcrum and the support frame when the boom is luffing; β is the angle between the boom and the fulcrum of the rod cavity when the boom is horizontal; The luffing angle is the angle between the boom and the horizontal plane when the boom is luffing.

[0035] The PLC controller directly receives the stroke signal from the displacement sensor 15, calculates the boom luffing angle in real time, and displays it on the operator's cab interface. Compared with the traditional angle sensor measurement method that requires secondary conversion, its accuracy is significantly improved. At the same time, this solution reuses the displacement data for the overspeed calculation function, which not only avoids the need for additional sensor installation, but also simplifies the system structure and achieves efficient integration of a single sensor for dual purposes.

[0036] In one embodiment, the PLC controller is also used to implement cross-gear shifting control of the luffing hydraulic system: when shifting up a gear, the PLC controller uses an incremental ramp algorithm to achieve a smooth transition of the current signal, so that the hydraulic oil flow rate output by the piston variable pump 3 increases smoothly; when shifting down a gear, a descending ramp algorithm is used to make the hydraulic oil flow rate output by the piston variable pump 3 decrease smoothly. For example, when switching from luffing up gear 1 to luffing up gear 3, the current signal output by the PLC controller to the proportional directional valve 8 linearly increases from 14mA to 18mA within 2 seconds. To ensure a smooth increase in hydraulic oil flow from the variable piston pump 3 during acceleration, the PLC controller outputs a current signal to the proportional directional valve 8 when decelerating from luffing gear 3 to luffing gear 1. A descent ramp is set, linearly reducing the current signal from 18mA to 14mA within 2 seconds. This ensures a smooth decrease in hydraulic oil flow from the variable piston pump 3 during deceleration. This segmented ramp control strategy effectively suppresses system shocks caused by sudden flow changes during luffing by dynamically adjusting the proportional valve opening, thus ensuring the stability of the actuator's movement.

[0037] In one embodiment, the PLC controller is also used to implement pressure protection control: when the load pressure reaches the preset cut-off value of the plunger variable pump 3, the safety valve of the plunger variable pump 3 opens to limit the system pressure; at the same time, the first pressure sensor 13.6 monitors the rodless chamber pressure in real time and transmits the signal to the PLC controller. If the rodless chamber pressure is abnormal or exceeds the threshold, the PLC controller immediately triggers an alarm and executes a variable amplitude action stop command, forming a dual safety protection mechanism of pressure cut-off and real-time monitoring to ensure the safety and reliability of the system under overload conditions.

[0038] In one embodiment, the PLC controller is also used to implement intelligent stroke protection control: when the stroke position approaches the preset protection threshold during the luffing rise or fall process, the PLC controller immediately triggers a deceleration command to make the system stop smoothly. For example, when the protection threshold is set to ±20mm (this protection threshold can be adjusted according to different models), the first level of protection of "about to exceed the stroke" is triggered. At this time, the PLC controller will immediately intervene to control and instruct the luffing system to decelerate and stop smoothly. By intervening in advance, the mechanical shock and violent shaking of the luffing system that may be caused by this can be effectively eliminated, ensuring the safety and stability of the equipment operation. This avoids the sudden stop impact caused by the direct power cut-off of traditional limit switches, ensuring the safety and stability of the equipment operation.

[0039] In one embodiment, the PLC controller is also used to implement intelligent speed protection: When the gear position remains unchanged, the PLC controller compares the normal speed of the gear position with the real-time variable speed. When the variable speed rises to 110% of the normal speed of the gear position, the PLC controller reduces the gear position current increment received by the proportional directional valve 8 by 50%, automatically reducing speed and locking the upshift function, allowing only downshifting and speed reduction. Once the variable speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is lifted. If the variable speed continues to rise to 120% of the normal speed of the gear position after the gear position current increment has decreased by 50%, the PLC controller immediately stops the variable speed operation and triggers an overspeed alarm. By setting an intelligent speed protection mechanism, when the variable speed exceeds 110% of the normal speed of the gear position, the system automatically halves the current of the proportional directional valve to achieve smooth speed reduction, while locking the upshift function to prevent misoperation. If the speed continues to rise to 120% of the normal speed of the gear position, the operation is immediately stopped and an alarm is triggered, forming a tiered protection system. This strategy eliminates the response lag of traditional systems through real-time closed-loop regulation, reduces mechanical shock through gradient intervention, and has automatic recovery capabilities, which not only ensures operational safety but also improves work continuity and effectively reduces the risk of overload.

[0040] The present invention also provides a control method applied to the above-mentioned tower boom luffing hydraulic system, the control method comprising: Boom raising: The operator presses the "Pump On" button, energizing motor 2 and driving the variable displacement piston pump 3. The operator then shifts the boom to luffing position 1 on the control panel. The PLC controller receives the switching signal for luffing position 1 (the control current signal for luffing position 1 is in the 12-20mA range; for example, if luffing position 4 is set, the current for luffing position 1 is 14mA, luffing position 2 is 16mA, luffing position 3 is 18mA, and luffing position 4 is 20mA), and outputs the corresponding current signal to control the boom. For example, when the directional valve 8 opens, the plunger variable pump 3 outputs hydraulic oil flow corresponding to the opening degree. This flow passes through the P" port and A" port of the proportional directional valve 8, the first balance valve 13.1, and the third shut-off valve 13.7 to the rodless chamber of the luffing cylinder 14. At the same time, the second balance valve 13.4 opens under the action of the pilot port pressure. The hydraulic oil in the rod chamber of the luffing cylinder 14 flows back to the oil tank 1 from the fourth shut-off valve 13.10, the second balance valve 13.4, the B" port and T" port of the proportional directional valve 8, through the second check valve 10 and the return oil filter 12. The luffing cylinder 14 is pushed out, and the boom begins to rise. During the boom luffing process, the X port of the variable piston pump 3 receives the working oil pressure of the rodless chamber in real time through the shuttle valve 9. Based on its load sensing function, the pump body monitors the pressure difference between the input and output pressures of the proportional directional valve 8 in real time. When the pressure difference increases, the pump automatically reduces the displacement; when the pressure difference decreases, the displacement increases. Through dynamic adjustment, the pressure difference is always maintained at the set value. This closed-loop control keeps the pressure difference stable within the set range, which avoids overflow loss, ensures the smoothness of the actuator movement and the control accuracy, and significantly reduces the heat generation of the luffing hydraulic system, extends the life of key components, and reduces the energy consumption of the whole machine. During the boom luffing and raising process, the direction and magnitude of the force on the luffing cylinder 14 are constantly changing. When the load on the luffing cylinder 14 is within the constant power control starting pressure range set by the piston variable pump 3, the piston variable pump 3 can output the maximum rated full flow. At this time, the luffing speed is directly controlled by the luffing raising gear of the linkage table. When the load exceeds the constant power starting pressure, the maximum output flow of the piston variable pump 3 will be automatically adjusted according to the power control characteristic curve. At this time, constant power adjustment takes priority over gear adjustment. By dynamically limiting the maximum luffing speed, the system adapts to the increasing load, thereby ensuring the stability and reliability of the system operation. During the boom luffing and raising process, the gears can be gradually switched if acceleration is required, depending on the load and operating conditions. During the boom luffing process, when the load pressure reaches the preset pressure cut-off value of the piston variable pump 3, the safety valve of the piston variable pump 3 immediately opens to limit the pressure from continuing to rise, thereby ensuring the safety and reliability of the system under overload conditions. At the same time, the first pressure sensor 13.6 monitors the real-time pressure status of the rodless chamber and transmits the pressure signal to the PLC controller. When the pressure in the rodless chamber is abnormal or exceeds the preset safety threshold, the PLC controller will quickly trigger an alarm signal and execute a luffing action stop command according to the preset overpressure protection parameters, forming a dual protection mechanism. When the boom rises to the working position, the operator switches the gear to the zero position. The PLC controller outputs a current signal according to the descending ramp algorithm, which controls the proportional directional valve 8 to smoothly switch to the neutral position, so that the boom luffing stops. At this time, the luffing cylinder 14 is locked and pressure maintained under the action of the first balance valve 13.1 and the second balance valve 13.4. At the same time, the motor delay power-off protection mechanism is triggered to ensure the safety and stability of the system. The control logic during boom descent is symmetrical to that during boom ascent.

[0041] In one embodiment, the control method further includes handling situations involving skipped gear shifts: When shifting up a gear, the PLC controller uses an incremental ramp algorithm to achieve a smooth transition of the current signal, so that the hydraulic oil flow rate output by the piston variable pump 3 increases smoothly; when shifting down a gear, a descending ramp algorithm is used to make the hydraulic oil flow rate output by the piston variable pump 3 decrease smoothly.

[0042] In one embodiment, the control method further includes handling situations where the amplitude is close to its limit travel: When the amplitude increases or decreases and the travel position approaches the preset protection threshold, the PLC controller immediately triggers a deceleration command to bring the system to a smooth stop.

[0043] In one embodiment, the control method also includes handling a cavitation failure in the luffing cylinder 14: When the luffing cylinder 14 is subjected to a load in the same direction and an extreme abnormality occurs during the boom luffing process, and it is rapidly pulled out to suck in air, the rodless chamber, through suction, draws hydraulic oil from the oil tank 1 through port T5, the third check valve 11, the return oil pipes of ports T3 and T2, and the fourth check valve 13.7 into the rodless chamber to replenish the oil and prevent unstable luffing. At the same time, with the gear position unchanged, the PLC controller compares the normal speed of the gear position with the real-time luffing speed in real time: when the luffing speed rises to 110% of the normal speed of the gear position, the gear position current increment received by the proportional directional valve 8 of that gear position is reduced by 50%, automatically reducing the speed and locking the upshift function, allowing only downshifting and speed reduction; once the luffing speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is released. If the amplitude conversion speed continues to rise to 120% of the normal speed of the gear after the current increment of the gear decreases by 50%, the PLC controller will immediately stop the amplitude conversion action and trigger an overspeed alarm. When a suction failure occurs during the boom luffing and descent, the rod chamber is quickly replenished with oil through the fifth one-way valve 13.9. The PLC control logic is symmetrical with the lifting process, and the current regulation and speed protection mechanisms are executed in opposite directions, forming a two-way symmetrical fault protection system.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention includes the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0045] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A hydraulic system for a tower crane jib luffing, characterized in that: The hydraulic system comprises an oil tank (1), a motor (2), a piston variable pump (3), a high-pressure filter (4), a first check valve (5), a pressure gauge (6), a pilot overflow valve (7), a proportional directional valve (8), a shuttle valve (9), a second check valve (10), a third check valve (11), an oil return filter (12), an amplitude cylinder valve group (13), an amplitude cylinder (14) and a displacement sensor (15); The amplitude cylinder valve group (13) comprises a first balance valve (13.1), a first stop valve (13.2), a second stop valve (13.3), a second balance valve (13.4), a first pressure sensor (13.6), a third stop valve (13.7), a fourth check valve (13.8), a fifth check valve (13.9), a fourth stop valve (13.10) and a second pressure sensor (13.11); The hydraulic oil is stored in the oil tank (1), the motor (2) is connected with the piston variable pump (3), the suction port and the discharge port of the piston variable pump (3) are connected with the oil tank (1) through the suction pipeline and the discharge pipeline respectively, the pressure oil port of the piston variable pump (3) is connected with the inlet of the high-pressure filter (4), the outlet of the high-pressure filter (4) is connected with the inlet of the first check valve (5), the outlet of the first check valve (5) is divided into three paths, the first and second paths are connected with the pressure port of the pressure gauge (6) and the pilot overflow valve (7) respectively, and the third path is connected with the P" port of the proportional directional valve (8); the 1 port of the shuttle valve (9) is connected with the B" port of the proportional directional valve (8) and is connected with the B1 port after confluence; the 2 port of the shuttle valve (9) is connected with the A" port of the proportional directional valve (8) and is connected with the A1 port after confluence; the middle 3 port of the shuttle valve (9) is connected with the pilot pressure oil port X of the piston variable pump (3); The discharge port of the pilot overflow valve (7), the T" port of the proportional directional valve (8), the inlet of the second check valve (10) and the outlet of the third check valve (11) are connected with the T3 port after confluence, the outlet of the second check valve (10) is connected with the oil tank (1) through the oil return filter (12), and the inlet of the third check valve (11) is connected with the oil tank (1) as a suction port; the A1 port and the B1 port are connected with the A2 port and the B2 port of the amplitude cylinder valve group (13) respectively, and the T2 port of the amplitude cylinder valve group (13) is connected with the T3 port; A2 port is connected with 2 port of the first balance valve (13.1) and 3 port of the second balance valve (13.4), 3 port of the second balance valve (13.4) is a pilot port; B2 port is connected with 2 port of the second balance valve (13.4) and 3 port of the first balance valve (13.1), 3 port of the first balance valve (13.1) is a pilot port; 1 port of the first balance valve (13.1) is divided into three paths and is connected with the first stop valve (13.2), the non-return port of the fourth one-way valve (13.8) and the third stop valve (13.7); 1 port of the second balance valve (13.4) is also divided into three paths and is connected with the second stop valve (13.3), the non-return port of the fifth one-way valve (13.9) and the fourth stop valve (13.10); the other end of the third stop valve (13.7) is connected with the rodless cavity of the variable amplitude oil cylinder (14) and the first pressure sensor (13.6), the other end of the fourth stop valve (13.10) is connected with the rod cavity of the variable amplitude oil cylinder (14) and the second pressure sensor (13.11); the other ends of the first stop valve (13.2) and the second stop valve (13.3) are connected in parallel and then connected with the inlet of the fourth one-way valve (13.8) and the fifth one-way valve (13.9) and then connected with T2 port.

2. The hydraulic system for the luffing of the jib of a tower crane according to claim 1, characterized in that It also comprises a safety valve (13.5), the other end of the fourth stop valve (13.10) is connected with the rod cavity of the variable amplitude oil cylinder (14), the second pressure sensor (13.11) and the pressure port of the safety valve (13.5); The other ends of the first stop valve (13.2) and the second stop valve (13.3) are connected in parallel and then connected with the inlet of the fourth one-way valve (13.8) and the fifth one-way valve (13.9), the unloading port of the safety valve (13.5) and then connected with T2 port.

3. The hydraulic system for the jib luffing of a tower crane according to claim 1, characterized in that: The plunger variable pump (3) is a Rexroth A11VO-LRDS series axial plunger pump, the displacement is 40-260ml / r, the maximum pressure is 350bar, and the integrated power control, pressure cut-off and load sensing functions are integrated.

4. The hydraulic system for the jib luffing of a tower crane according to claim 1, characterized in that: The proportional directional valve (8) is a three-position four-way Y-type pilot proportional valve, and a 4-20mA current signal is input, wherein: input 12mA is the valve core middle position, when the current signal increases from 12mA to 20mA, the oil cylinder is controlled to extend; when the current signal decreases from 12mA to 4mA, the oil cylinder is controlled to retract.

5. The hydraulic system for the jib luffing of a tower crane according to claim 1, characterized in that: It also comprises a PLC controller, the input end of the PLC controller is connected with the first pressure sensor (13.6), the second pressure sensor (13.11), the displacement sensor (15) and the variable amplitude lifting / descending multi-gear switch signal set in the driver's room linkage platform; The output end of the PLC controller is connected with the motor (2), the plunger variable pump (3) and the proportional directional valve (8), the PLC controller adjusts the valve core displacement of the proportional directional valve (8) through the current signal to realize the direction and flow proportional control; The first pressure sensor (13.6) is used for monitoring the pressure of the rodless cavity; the second pressure sensor (13.11) is used for monitoring the pressure of the rod cavity, and the displacement sensor (15) is used for monitoring the real-time stroke position of the variable amplitude oil cylinder (14).

6. The hydraulic system for the jib luffing of a tower crane according to claim 5, characterized in that: The PLC controller is also used for calculating the luffing angle according to the stroke signal received by the displacement sensor (15) and displaying the luffing angle on the operation interface of the driver's room, and the calculation formula of the luffing angle is as follows: ， Wherein, S is the length of the oil cylinder when the boom is horizontal; L1 is the length of the support frame; L2 is the length of the boom support point; Working stroke of the cylinder when the boom is being luffing; Alpha is the angle between the rod cavity support point and the support frame when the boom is horizontal; Alpha' is the angle between the rod cavity support point and the support frame when the boom is luffing; Beta is the angle between the rod cavity support point and the boom when the boom is horizontal; is the amplitude angle, which is the angle between the boom and the horizontal plane when the boom is being luffed.

7. The hydraulic system for the jib luffing of a tower crane according to claim 5, wherein: The PLC controller is also used for realizing the over-grade gear shifting control of the luffing hydraulic system: when over-grade upshifting, the PLC controller realizes the smooth transition of the current signal through the incremental ramp algorithm, so that the hydraulic oil flow output by the plunger variable pump (3) is smoothly increased; when over-grade downshifting, the descending ramp algorithm is adopted, so that the hydraulic oil flow output by the plunger variable pump (3) is smoothly decreased.

8. The hydraulic system for the jib luffing of a tower crane according to claim 5, wherein: The PLC controller is also used for realizing the pressure protection control: when the load pressure reaches the preset cut-off value of the plunger variable pump (3), the safety valve of the plunger variable pump (3) is opened to limit the system pressure; at the same time, the first pressure sensor (13.6) monitors the pressure of the rodless cavity in real time and transmits the signal to the PLC controller, if the pressure of the rodless cavity is abnormal or exceeds the threshold value, the PLC controller immediately triggers an alarm and executes the luffing action stop instruction, forming a double safety guarantee mechanism of pressure cut-off and real-time monitoring, to ensure the safety and reliability of the system under overload working conditions.

9. The hydraulic system for the jib luffing of a tower crane according to claim 5, wherein: The PLC controller is also used for realizing the intelligent stroke protection control: when the luffing position approaches the preset protection threshold during the luffing up or down process, the PLC controller immediately triggers a deceleration instruction to make the system stop running smoothly.

10. The hydraulic system for the jib luffing of a tower crane according to claim 5, wherein: The PLC controller is also used for realizing the intelligent speed protection: under the condition that the gear position is unchanged, the PLC controller compares the normal gear speed with the real-time luffing speed in real time: when the luffing speed rises to 110% of the normal gear speed, the gear current increment received by the gear proportional directional valve (8) is reduced by 50%, the speed is automatically reduced, and the upshift function is locked, and only downshift and speed reduction are allowed; when the luffing speed returns to the normal gear speed, the rated current is reset and the upshift restriction is released; If the luffing speed continues to rise to 120% of the normal gear speed after the gear current increment is reduced by 50%, the PLC controller immediately stops the luffing action and triggers an overspeed alarm.

11. A control method applied to the tower crane jib luffing hydraulic system of any one of claims 1-10, characterized in that: The control method comprises: Boom up: The operator presses the "pump on" button, and the PLC controller controls the motor (2) to be powered on, driving the plunger variable pump (3) to operate. The operator pulls down the boom up 1 gear on the linkage table. The PLC controller receives the switch quantity signal of the boom up 1 gear and outputs the current signal corresponding to the gear position to control the opening of the proportional directional valve (8). The plunger variable pump (3) outputs the hydraulic oil flow corresponding to the opening, which passes through the P" port, A" port of the proportional directional valve (8), the first balance valve (13.1), the third stop valve (13.7) to the rodless cavity of the boom cylinder (14). At the same time, the second balance valve (13.4) is opened under the action of the pilot port pressure, and the hydraulic oil in the rod cavity of the boom cylinder (14) flows back to the tank (1) through the fourth stop valve (13.10), the second balance valve (13.4), the B" port and the T" port of the proportional directional valve (8), the second check valve (10) and the oil return filter (12). The boom cylinder (14) is pushed out, and the boom starts to rise; During the boom up process, the X port of the plunger variable pump (3) receives the working oil pressure of the rodless cavity in real time through the shuttle valve (9). Based on its load sensing function, the pump body monitors the pressure difference between the input pressure and the output pressure of the proportional directional valve (8) in real time. When the pressure difference increases, the pump automatically reduces the displacement. When the pressure difference decreases, the displacement increases. Through dynamic adjustment, the pressure difference is always maintained at the set value. During the boom up process, the force direction and size of the boom cylinder (14) are always changing. When the load of the boom cylinder (14) is within the constant power control starting pressure range set by the plunger variable pump (3), the plunger variable pump (3) can output the maximum rated flow. At this time, the boom running speed is directly controlled by the boom up gear of the linkage table. When the load exceeds the constant power starting pressure, the maximum output flow of the plunger variable pump (3) will be automatically adjusted according to the power control characteristic curve. At this time, the constant power adjustment is prior to the gear adjustment. The maximum speed of the boom is dynamically limited to adapt to the increasing load, thereby ensuring the stability and reliability of the system operation. During the boom up process, according to the load and operation condition, if acceleration is required, the gear can be gradually switched. During the boom up process, when the load pressure reaches the preset pressure cut-off value of the plunger variable pump (3), the safety valve of the plunger variable pump (3) opens immediately to limit the pressure from rising, thereby ensuring the safety and reliability of the system under overload conditions. At the same time, the first pressure sensor (13.6) monitors the real-time pressure state of the rodless cavity in real time and transmits the pressure signal to the PLC controller. When the pressure of the rodless cavity is abnormal or exceeds the preset safety threshold, the PLC controller will trigger an alarm signal and execute a boom action stop instruction according to the pre-set overpressure protection parameters, forming a double protection mechanism. When the jib is raised to the working position, the operator sets the gear to zero, and the PLC controller outputs a current signal according to the descending slope algorithm to control the proportional directional valve (8) to smoothly switch to the middle position, so that the jib is stopped, at this time, the jib cylinder (14) is locked and pressure-kept under the action of the first balance valve (13.1) and the second balance valve (13.4), and the motor delay power-off protection mechanism is triggered to ensure the safety and stability of the system; The control logic for the jib lowering is symmetrical to that for the jib raising, and the PLC controller reverses the opening of the proportional directional valve (8) through the current signal to control the retraction of the cylinder.

12. The control method according to claim 11, characterized in that: The control method further includes the following responses when the gear is shifted by-pass: When the gear is shifted up by-pass, the PLC controller realizes the smooth transition of the current signal through the incremental slope algorithm, so that the hydraulic oil flow output by the plunger variable pump (3) is smoothly increased; when the gear is shifted down by-pass, the descending slope algorithm is adopted to make the hydraulic oil flow output by the plunger variable pump (3) smoothly decreased.

13. The control method according to claim 11, characterized by: The control method further includes The response when the jib approaches the limit stroke: When the stroke position approaches the preset protection threshold during the jib raising or lowering, the PLC controller immediately triggers the deceleration instruction to make the system stop running smoothly.

14. The control method according to claim 11, characterized by: The control method further includes the response when the jib cylinder (14) is in a suction fault: When the jib cylinder (14) is rapidly pulled out for suction due to an extreme abnormal situation during the jib raising under the action of the same direction load, the rodless cavity quickly sucks the hydraulic oil in the tank (1) through the T5 port, the third one-way valve 11, the T3 port, the T2 port, the return oil pipeline, and the fourth one-way valve (13.7) to realize oil supplement to prevent the jib from being unstable; at the same time, under the condition that the gear remains unchanged, the PLC controller compares the gear normal speed with the real-time jib speed: when the jib speed rises to 110% of the gear normal speed, the gear current increment received by the proportional directional valve (8) is reduced by 50%, the speed is automatically reduced, and the upshift function is locked, only downshift and speed reduction are allowed; when the jib speed returns to the gear normal speed, the rated current is reset and the upshift restriction is removed; If the jib speed continues to rise to 120% of the gear normal speed after the gear current increment is reduced by 50%, the PLC controller immediately stops the jib action and triggers the overspeed alarm; When the suction fault occurs during the jib lowering, the rod cavity quickly supplements oil through the fifth one-way valve (13.9), and the PLC control logic is symmetrical to the rising process, and the speed protection mechanism is executed in the opposite direction, forming a bidirectional and symmetrical fault protection system.

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