An electro-hydraulic co-melting cylinder automobile crane luffing system and a control method thereof

Abstract

The application provides an electro-hydraulic co-mingling cylinder automobile crane luffing system and a control method thereof. The system comprises an electro-hydraulic co-mingling cylinder, a motor driving unit, a hydraulic buffer unit, a sensor unit and a controller. The traditional full hydraulic driving architecture is cancelled. The electric cylinder is used as the main driving, and the hydraulic buffer unit is used as the anti-impact auxiliary. The electro-hydraulic co-mingling cylinder adopts the coaxial integrated structure of the electric cylinder and the hydraulic cylinder. The hydraulic cavity is only responsible for buffering, pressure maintaining and energy absorption. The control method comprises five steps of system initialization and safety judgment, luffing starting soft starting, stable luffing electro-hydraulic cooperation, stopping positioning non-impact locking and abnormal working condition safety protection. The stable stage is divided into the light load high speed mode and the heavy load low speed mode. The three-level control strategy is adopted in the stopping stage. The application combines the advantages of the precise and efficient electric system and the anti-impact hydraulic system, realizes the non-impact, high precision and high reliable operation of the automobile crane luffing mechanism, and significantly improves the operation stability and the service life of the whole machine.

Description

Technical Field

[0001] This invention relates to the field of engineering machinery technology, and in particular to a luffing system for a truck crane with an electro-hydraulic fusion cylinder and its control method. Background Technology

[0002] The luffing mechanism of a truck crane is the core actuator that enables the boom's pitching motion and adjusts the working radius. Its performance directly determines the overall machine's operating accuracy, stability, safety, reliability, and service life. With the continuous advancement of electrification, intelligence, and green development trends in construction machinery, the technical shortcomings of traditional luffing systems are becoming increasingly apparent.

[0003] Currently, luffing systems for truck cranes are mainly divided into two categories: pure hydraulic drive and pure electric drive. Pure hydraulic drive luffing systems rely on hydraulic cylinders for power and have the advantages of strong impact resistance and high load-bearing capacity. However, they also suffer from problems such as low hydraulic system efficiency, high energy consumption, easy leakage and pollution, poor control precision, and slow response speed, making it difficult to meet the requirements of high-precision operation and energy conservation and emission reduction.

[0004] Pure electric luffing systems employ servo motors paired with electric cylinders for direct drive, offering significant advantages such as fast response, high control precision, simple structure, high efficiency, and zero pollution. They enable precise closed-loop position control and speed regulation, representing a crucial development direction for the electrification of construction machinery. However, pure electric cylinders, relying on mechanical transmission and motor torque output, suffer from weak impact resistance and poor buffering performance. During crane luffing starts, stops, and sudden load changes, they are highly susceptible to severe mechanical shocks, vibrations, and boom shaking. This not only seriously affects operational stability and lifting accuracy but also accelerates fatigue damage to the mechanical structure, reducing the overall machine's safety redundancy and service life.

[0005] Currently, there is no luffing system or control method that can effectively integrate the precise control advantages of electric systems with the shock-absorbing characteristics of hydraulic systems. This makes it impossible to effectively suppress impact loads, improve operational stability, and enhance structural safety while ensuring high-precision positioning. Therefore, developing a novel electro-hydraulic coordinated luffing system and its control method has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a luffing system for a truck crane with an electro-hydraulic fusion cylinder and its control method. Through the coaxial integrated design of the electric cylinder and the hydraulic cylinder and the electro-hydraulic coordinated control strategy under all working conditions, it retains the advantages of high precision, high efficiency and low energy consumption of pure electric drive, while solving the defects of poor impact resistance and easy vibration of pure electric cylinder, so as to realize the impact-free, high precision and high reliability operation of the luffing mechanism of the truck crane.

[0007] According to one objective of the present invention, the present invention provides a luffing system for a truck crane with an electro-hydraulic fusion cylinder, comprising an electro-hydraulic fusion cylinder, a motor drive unit, a hydraulic buffer unit, a sensor unit, and a controller; The electro-hydraulic fusion cylinder is hinged at both ends to the turntable and the root of the boom of the truck crane, respectively. The electric actuator and the hydraulic buffer chamber are coaxially integrated inside the electro-hydraulic fusion cylinder. The electric actuator serves as the active power output component, and the hydraulic buffer chamber is not connected to an external independent hydraulic power source and is only used for buffering and absorbing energy. The motor drive unit is mechanically connected to the input end of the electric actuator of the electro-hydraulic fusion cylinder, providing linear extension and retraction driving force to the electric actuator; The hydraulic buffer unit is connected to the hydraulic buffer chamber of the electro-hydraulic fusion cylinder through a hydraulic pipeline, and provides adjustable back pressure only to the hydraulic buffer chamber to achieve impact absorption and load adaptive pressure holding. The sensor units are respectively mounted on the boom hinge point, the electro-hydraulic fusion cylinder body, the hydraulic buffer unit pipeline, and the motor drive unit, and all sensor signal output terminals are electrically connected to the controller. The controller is electrically connected to the electrical control components of the motor drive unit and the hydraulic buffer unit respectively; the hoisting mechanism of the whole machine is equipped with an independent pure motor drive assembly, and the hoisting drive assembly is not interconnected with the hydraulic buffer unit of this luffing system by oil circuit or circuit; The system abandons the fully hydraulic active drive structure and uses an electric actuator to achieve closed-loop precise control of the luffing position. The hydraulic buffer chamber works with the hydraulic buffer unit to complete the shock resistance compensation under all working conditions, forming an electro-hydraulic collaborative shock-free luffing architecture.

[0008] Furthermore, the electro-hydraulic fusion cylinder adopts a coaxial and co-cavity integrated structure. The piston rod of the electric actuator is coaxially inserted inside the hydraulic buffer cavity. The extension and retraction of the piston rod synchronously changes the internal volume of the hydraulic buffer cavity. Passive buffering is achieved by relying on the compression of the closed hydraulic oil inside the cavity. The hydraulic buffer cavity does not output power to drive the boom movement.

[0009] Furthermore, the hydraulic buffer unit includes a first electro-proportional relief valve, a second electro-proportional relief valve, a directional switching valve, and a hydraulic oil tank. The inlet side of the directional switching valve has two pipelines that connect to the rodless chamber and the rod chamber of the hydraulic buffer cavity, respectively. The outlet side of the directional switching valve has one pipeline connected to the hydraulic oil tank via the first electro-proportional relief valve and the other pipeline connected to the hydraulic oil tank via the second electro-proportional relief valve. By switching the relief path through the directional switching valve, and by adjusting the set pressure of the two electro-proportional relief valves, the buffering stiffness of the hydraulic buffer cavity is changed in stages.

[0010] Furthermore, the sensor unit includes: an amplitude angle sensor installed at the hinge shaft of the boom, a stroke sensor fixed on the outer wall of the electro-hydraulic fusion cylinder, a load pressure sensor arranged at the force-receiving end of the cylinder hinge, a cavity pressure sensor installed on the oil outlet pipeline of the hydraulic buffer cavity, and a speed and torque sensor integrated on the servo motor body of the motor drive unit. All sensors collect operating parameters in real time and transmit electrical signals to the controller.

[0011] Furthermore, the motor drive unit consists of a servo motor and a servo driver. The output end of the servo motor is mechanically coupled to the ball screw transmission pair inside the electro-hydraulic fusion cylinder. The servo driver is controlled by the controller, and together with the controller, the position and speed of the electric actuator are controlled in a dual closed loop.

[0012] According to another objective of the present invention, the present invention provides a control method for an electro-hydraulic fusion cylinder of a truck crane luffing system, the method comprising the following steps: S1. Initialization self-test: The controller receives all the data collected by the sensors, including boom angle, cylinder stroke, load pressure, hydraulic chamber pressure, and motor operating parameters. It verifies whether the boom working stroke is within the safe range, locks the luffing action of the whole machine if it exceeds the limit, and pre-configures the motor PID parameters, hydraulic foundation back pressure, and buffer coefficient. S2, Start-up Soft Control: The controller drives the servo motor for low-speed soft start, and the electric actuator is connected to the position and speed dual closed-loop control, synchronously controlling the hydraulic buffer unit to build up pressure, so that the hydraulic buffer chamber can establish a basic back pressure in advance; S3. Steady-state coordinated control: The electric actuator, as the active component, continuously drives the boom pitching and tilting according to the target stroke. The controller dynamically adjusts the opening pressure of the two electro-proportional relief valves based on real-time load data. The hydraulic buffer chamber passively absorbs energy and replenishes the system stiffness in real time as the load changes. S4. Staged shutdown and locking: When the boom approaches the target position, the controller sequentially controls the electric actuator to decelerate and perform micro-position correction, and simultaneously controls the hydraulic buffer unit to stabilize and maintain pressure. Relying on the dual constraints of motor locking and hydraulic pressure maintenance, the controller achieves springback-free positioning. S5. Fault safety protection: When the system triggers any abnormal signal such as overload, instantaneous impact, underpressure, or power failure, the hydraulic buffer unit will prioritize depressurization and energy absorption, while the motor drive unit will perform speed limiting and brake protection.

[0013] Furthermore, step S3, steady-state coordinated regulation, is divided into two operating modes: When the load pressure is lower than the set light load threshold, the controller lowers the pressure of the corresponding electro-proportional relief valve, the hydraulic buffer chamber operates with low damping, and the system enters the light load high speed mode. When the load pressure exceeds the set heavy load threshold, the controller adjusts the pressure of the corresponding electro-proportional relief valve, the hydraulic buffer chamber provides high damping buffering, and the system enters the heavy load low speed anti-impact mode.

[0014] Furthermore, the graded shutdown lockout in step S4 adopts a three-stage progressive control: Speed ​​pre-deceleration stage: When the boom is at the first preset angle difference from the target, the electric actuator decelerates at a constant speed according to the preset deceleration curve; Position fine-tuning stage: When the distance between the boom and the target angle reaches the second preset value, the electric actuator switches to a micro-speed point-position closed loop to eliminate positioning deviation; Hydraulic pressure stabilizing section: After the position error meets the standard, the hydraulic buffer unit maintains constant pressure to absorb residual vibration and suppress boom rebound.

[0015] Furthermore, step S5 involves fault-tolerant protection and condition-specific control: Overload condition: The corresponding electro-proportional relief valve is fully opened for rapid pressure relief, and the electric actuator retracts at a limited speed; Instantaneous impact condition: The hydraulic buffer chamber stores and releases energy instantaneously, and the servo motor engages in damping control; Under pressure loss / power failure conditions: The hydraulic buffer unit's oil circuit self-locks and maintains pressure, and the servo motor's power failure causes the brake to lock the piston rod.

[0016] Furthermore, during boom lifting operations, the direction switching valve reverses to connect to the oil circuit where the first electro-proportional relief valve is located, and the controller adjusts the pressure of the first electro-proportional relief valve to match the lifting buffer; during boom lowering operations, the direction switching valve reverses to connect to the oil circuit where the second electro-proportional relief valve is located, and the controller adjusts the pressure of the second electro-proportional relief valve to match the lowering buffer.

[0017] The technical solution of this invention, through the integrated design of the coaxial and shared cavity electro-hydraulic fusion cylinder and the all-condition electro-hydraulic coordinated control, completely solves the industry pain points of weak impact resistance in pure electric luffing systems and low precision and high energy consumption in pure hydraulic systems. The hydraulic cavity only acts as a passive buffer and does not participate in active drive, retaining the advantages of electric drive systems such as ±0.05° high-precision positioning, over 90% transmission efficiency, and zero hydraulic leakage, while achieving impact absorption under all working conditions through adjustable hydraulic damping. The load-sharing adaptive buffer and three-level shutdown lock-up strategy effectively eliminate boom rebound and vibration, reducing structural fatigue damage by more than 30%. The comprehensive abnormal protection mechanism greatly improves safety redundancy, while the independent electric drive of the winch simplifies the system architecture, significantly reduces maintenance costs, and adapts to the electrification development needs of construction machinery. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a flowchart of the control method for the luffing electro-hydraulic fusion cylinder of a truck crane according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the luffing system of a truck crane with an electro-hydraulic fusion cylinder according to an embodiment of the present invention.

[0020] In the diagram: 1. Electro-hydraulic fusion cylinder; 2. Motor drive unit; 3. Hydraulic buffer unit; 31. First electro-proportional relief valve; 32. Second electro-proportional relief valve. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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 based on the specific circumstances.

[0024] Example 1 like Figure 1 and Figure 2 As shown in the figure, the electro-hydraulic fusion cylinder of the truck crane luffing system provided in this embodiment mainly includes an electro-hydraulic fusion cylinder 1, a motor drive unit 2, a hydraulic buffer unit 3, a sensor unit, and a controller.

[0025] One end of the electro-hydraulic fusion cylinder 1 is hinged to the crane turntable, and the other end is hinged to the boom, used to drive the boom to achieve luffing motion. The motor drive unit 2 is connected to the electric cylinder portion of the electro-hydraulic fusion cylinder 1, providing active power for the luffing motion. The hydraulic buffer unit 3 is connected to the hydraulic chamber of the electro-hydraulic fusion cylinder 1, used to provide buffering and shock protection. Sensor units are distributed in various key parts of the system to collect operating condition signals in real time. The controller is electrically connected to the motor drive unit 2, the hydraulic buffer unit 3, and the sensor units respectively, executing electro-hydraulic coordinated control logic. The crane's hoisting system 7 is driven independently by a pure electric motor, without any connection to the hydraulic circuit of the luffing system, achieving independent control of luffing and hoisting.

[0026] The electro-hydraulic fusion cylinder 1 is a coaxial integrated structure of an electric cylinder and a hydraulic cylinder, comprising an electric cylinder body, an electric cylinder piston rod, and a hydraulic cylinder cavity. The hydraulic cylinder cavity is nested inside the front end of the electric cylinder body and is coaxially arranged with the electric cylinder piston rod. The front end of the electric cylinder piston rod extends into the hydraulic cylinder cavity, dividing the hydraulic cylinder cavity into a rod-side cavity and a rodless cavity, which together form a hydraulic oil cavity. The hydraulic cylinder cavity is not connected to any active hydraulic power source; it achieves buffering, pressure holding, and impact energy absorption solely through changes in the hydraulic oil pressure within the hydraulic oil cavity. The electric cylinder internally employs a ball screw transmission mechanism to convert the rotational motion of the servo motor into the linear motion of the electric cylinder piston rod, achieving precise position control.

[0027] The hydraulic buffer unit 3 includes a first electro-proportional relief valve 31, a second electro-proportional relief valve 32, a directional switching valve, a hydraulic oil tank, and connecting pipelines. The inlet of the first electro-proportional relief valve 31 is connected to the rodless chamber of the hydraulic cylinder, and its outlet is connected to the hydraulic oil tank. The inlet of the second electro-proportional relief valve 32 is connected to the rod chamber of the hydraulic cylinder, and its outlet is connected to the hydraulic oil tank. The directional switching valve is a two-position four-way solenoid directional valve used to switch the connection between the hydraulic oil chamber and the two electro-proportional relief valves, thereby achieving the switching of buffer modes for luffing lifting and lowering. By adjusting the set pressure of the first electro-proportional relief valve 31 and the second electro-proportional relief valve 32, the hydraulic buffer stiffness can be continuously changed to adapt to the needs of different loads and working conditions.

[0028] The sensor unit includes a luffing angle sensor, an electric cylinder stroke sensor, a load pressure sensor, a hydraulic chamber pressure sensor, a motor speed sensor, and a motor torque sensor. The luffing angle sensor is installed at the hinge of the boom to detect the boom's luffing angle in real time; the electric cylinder stroke sensor is installed on the electro-hydraulic eutectic cylinder 1 to detect the extension stroke of the electric cylinder piston rod; the load pressure sensor is installed at the hinge between the electro-hydraulic eutectic cylinder 1 and the boom to detect the actual load on the luffing mechanism; the hydraulic chamber pressure sensor is installed on the pipeline of the hydraulic oil chamber to detect the real-time pressure of the hydraulic chamber; and the motor speed sensor and motor torque sensor are integrated on the servo motor to detect the motor's operating status.

[0029] The motor drive unit 2 includes a servo motor and a servo driver. The output shaft of the servo motor is connected to the ball screw of the electric cylinder via a coupling. The servo driver receives speed and position commands sent by the controller and drives the servo motor to run precisely, realizing dual closed-loop control of the electric cylinder's position and speed.

[0030] The controller adopts a high-performance PLC controller with a built-in electro-hydraulic coordinated control algorithm. It can synchronously control the operating status of the motor drive unit 2 and the hydraulic buffer unit 3 according to the real-time operating condition signals collected by the sensor unit, so as to realize electro-hydraulic coordinated control under all operating conditions.

[0031] Example 2 like Figure 1 As shown, this embodiment, based on embodiment 1, specifically explains the control of the luffing and hoisting operation: When the operator issues a luffing lifting command, the system first executes step S1, system initialization and safety judgment: the controller collects signals from the luffing angle sensor, electric cylinder stroke sensor, load pressure sensor, hydraulic chamber pressure sensor, and motor status to determine whether the boom is within the safe operating angle range. If it exceeds the safe range, the system prohibits operation and issues an alarm signal. At the same time, the controller completes the initialization configuration of the electric cylinder PID control parameters, hydraulic foundation back pressure, and buffer coefficient according to preset parameters.

[0032] Then, step S2, variable amplitude start soft start control, is entered: the controller sends a soft start command to the servo driver, the servo motor starts at an extremely low speed, and the electric cylinder enters the dual closed-loop control mode of position loop and speed loop; at the same time, the controller controls the direction switching valve to switch to the lifting buffer direction, adjusts the set pressure of the first electro-proportional relief valve 31 to the basic back pressure value, so that the rodless chamber of the hydraulic oil chamber establishes pre-clamping pressure, eliminates mechanical transmission clearance, avoids starting impact, and achieves smooth entry.

[0033] Next, in step S3, steady-state variable amplitude electro-hydraulic coordinated control: Based on the set target amplitude angle, the controller calculates the target stroke and speed curve of the electric cylinder, controls the servo motor to operate according to the preset curve, extends the electric cylinder piston rod, and drives the boom to lift smoothly. During this process, the controller collects signals from the load pressure sensor in real time to determine the current load size. If the load pressure is lower than the preset light load threshold (such as 30% of the rated load), the system enters the light load high speed mode. The controller reduces the set pressure of the first electro-proportional relief valve 31, and the hydraulic unit is in a low buffer state, reducing hydraulic damping and improving the system response speed and operating efficiency. If the load pressure is higher than the preset heavy load threshold (such as 70% of the rated load), the system enters the heavy load low speed mode. The controller increases the set pressure of the first electro-proportional relief valve 31, and the hydraulic unit is in a high buffer state, increasing hydraulic damping, strengthening the impact resistance, and preventing the boom from shaking.

[0034] When encountering a sudden change in load (such as a sudden sway of the hoisted object), the pressure in the hydraulic oil chamber will rise instantaneously. The first electro-proportional relief valve 31 will automatically overflow to absorb the impact energy. At the same time, the controller will adjust the motor torque to suppress boom vibration and maintain smooth luffing.

[0035] When the luffing mechanism approaches the target position, proceed to step S4 to stop positioning and lock without impact: Speed ​​pre-deceleration stage: When the angle of change is at the first preset value (e.g., 2°) from the target angle, the controller controls the electric cylinder to decelerate linearly according to the S-shaped deceleration curve to avoid sudden stop impact; Position fine-tuning stage: When the amplitude angle is close to the target angle by the second preset value (e.g., 0.2°), the electric cylinder switches to low-speed position closed-loop control and runs at an extremely low speed to gradually eliminate position deviation; Hydraulic pressure holding stage: When the position deviation is less than the allowable error (e.g., 0.05°), the controller controls the servo motor to lock at zero speed, while maintaining the set pressure of the first electro-proportional relief valve 31. The hydraulic oil chamber maintains a constant pressure, absorbs the remaining vibration energy, eliminates boom rebound, and achieves impact-free precise positioning.

[0036] Example 3 like Figure 1As shown, this embodiment, based on embodiment 1, specifically explains the control of the variable amplitude pullback condition: The control process for luffing and descent is basically the same as that for hoisting, except that: in step S2, the controller switches the direction switching valve to the descent buffer direction and adjusts the set pressure of the second electro-proportional relief valve 32 to the base back pressure value, so that the rod chamber of the hydraulic oil chamber establishes pre-clamping pressure; in step S3, during steady-state luffing, the set pressure of the second electro-proportional relief valve 32 is adjusted according to the load size to achieve adaptive buffering; in step S4, during the stop positioning stage, a three-level control strategy is also adopted to achieve shock-free locking.

[0037] During the luffing and descent process, if the boom shows an overspeed descent tendency, the pressure in the rod chamber of the hydraulic oil chamber will rise sharply. The second electro-proportional relief valve 32 will automatically overflow to provide reverse damping and limit the boom's descent speed. At the same time, the controller will control the motor to increase reverse torque to prevent the boom from going out of control.

[0038] Example 4 like Figure 1 As shown, this embodiment, based on embodiment 1, specifically explains the safety protection under abnormal operating conditions. Overload condition: When the load pressure sensor detects that the load exceeds 110% of the rated load, the controller immediately triggers the overload protection, controls the electro-proportional relief valve to quickly release pressure and absorb the overload energy, and controls the electric cylinder to retract at a limited speed, slowly returning the boom to a safe position to prevent structural overload damage.

[0039] Impact condition: When the hydraulic chamber pressure sensor detects that the hydraulic chamber pressure rises instantaneously and exceeds the preset impact threshold, the controller controls the electro-proportional relief valve to open fully, quickly releasing the impact energy. At the same time, it controls the electric cylinder to switch to damping control mode, reducing the motor response speed and reducing the transmission of impact load to the mechanical structure.

[0040] Pressure loss / power failure conditions: When the system detects pressure loss in the hydraulic circuit or power failure of the whole machine, the one-way valve in the hydraulic circuit will automatically close to achieve hydraulic self-locking and pressure maintenance. At the same time, the power failure brake of the electric cylinder will immediately brake, doubly locking the position of the boom to prevent the boom from slipping and ensuring the safety of personnel and equipment.

[0041] The beneficial effects of this invention are as follows: This invention adopts an integrated design of an electro-hydraulic fusion cylinder, which integrates the electric cylinder and the hydraulic cylinder in a common cavity and on the same axis. The hydraulic cavity only serves as a buffer unit and does not participate in active driving. This retains the advantages of high precision, high efficiency, low energy consumption, and no pollution of the pure electric drive system, while making full use of the strong impact resistance of the hydraulic system, thus solving the technical problem of pure electric cylinder luffing systems being easily damaged by impact.

[0042] This invention proposes a full-condition electro-hydraulic coordinated control strategy. For different stages such as luffing start-up, steady-state operation, stop positioning, and abnormal working conditions, corresponding control algorithms are designed to achieve deep coordination of the electro-hydraulic system, with impact-free luffing throughout the process, which significantly improves the stability of operation and hoisting accuracy.

[0043] The hydraulic buffer unit of this invention adopts a combination design of dual electric proportional relief valve and directional switching valve, which can dynamically adjust the buffer stiffness according to the load size and amplitude direction, realize adaptive buffer compensation, and take into account both the working efficiency under light load and the safety and stability under heavy load.

[0044] The hoisting system of this invention is driven independently by a pure electric motor and is not connected to the hydraulic circuit of the luffing system, which avoids mutual interference between systems, simplifies the system structure, and improves the reliability and maintainability of the whole machine.

[0045] This invention has a comprehensive safety protection mechanism for abnormal working conditions. In the event of overload, impact, pressure loss, power failure, etc., it can quickly respond and execute protective actions, effectively preventing the boom from going out of control and greatly improving the safety redundancy of the whole machine.

[0046] 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 luffing system for a truck crane with an electro-hydraulic fusion cylinder, characterized in that: It includes an electro-hydraulic fusion cylinder, a motor drive unit, a hydraulic buffer unit, a sensor unit, and a controller; The electro-hydraulic fusion cylinder is hinged at both ends to the turntable and the root of the boom of the truck crane, respectively. The electric actuator and the hydraulic buffer chamber are coaxially integrated inside the electro-hydraulic fusion cylinder. The electric actuator serves as the active power output component, and the hydraulic buffer chamber is not connected to an external independent hydraulic power source and is only used for buffering and absorbing energy. The motor drive unit is mechanically connected to the input end of the electric actuator of the electro-hydraulic fusion cylinder, providing linear extension and retraction driving force to the electric actuator; The hydraulic buffer unit is connected to the hydraulic buffer chamber of the electro-hydraulic fusion cylinder through a hydraulic pipeline, and provides adjustable back pressure only to the hydraulic buffer chamber to achieve impact absorption and load adaptive pressure holding. The sensor units are respectively mounted on the boom hinge point, the electro-hydraulic fusion cylinder body, the hydraulic buffer unit pipeline, and the motor drive unit, and all sensor signal output terminals are electrically connected to the controller. The controller is electrically connected to the electrical control components of the motor drive unit and the hydraulic buffer unit respectively; the hoisting mechanism of the whole machine is equipped with an independent pure motor drive assembly, and the hoisting drive assembly is not interconnected with the hydraulic buffer unit of this luffing system by oil circuit or circuit; The system abandons the fully hydraulic active drive structure and uses an electric actuator to achieve closed-loop precise control of the luffing position. The hydraulic buffer chamber works with the hydraulic buffer unit to complete the shock resistance compensation under all working conditions, forming an electro-hydraulic collaborative shock-free luffing architecture.

2. The luffing system of a truck crane with an electro-hydraulic fusion cylinder according to claim 1, characterized in that: The electro-hydraulic fusion cylinder adopts a coaxial and co-cavity integrated structure. The piston rod of the electric actuator is coaxially inserted inside the hydraulic buffer cavity. The extension and retraction of the piston rod synchronously changes the internal volume of the hydraulic buffer cavity. Passive buffering is achieved by the compression of the closed hydraulic oil inside the cavity. The hydraulic buffer cavity does not output the power to drive the boom movement.

3. The luffing system of a truck crane with an electro-hydraulic fusion cylinder according to claim 1, characterized in that: The hydraulic buffer unit includes a first electro-proportional relief valve, a second electro-proportional relief valve, a directional switching valve, and a hydraulic oil tank. The inlet side of the directional switching valve has two pipelines that connect to the rodless chamber and the rod chamber of the hydraulic buffer cavity, respectively. The outlet side of the directional switching valve has one pipeline connected to the hydraulic oil tank via the first electro-proportional relief valve and the other pipeline connected to the hydraulic oil tank via the second electro-proportional relief valve. The relief path is switched by reversing the directional switching valve, and the buffering stiffness of the hydraulic buffer cavity is changed in stages by adjusting the set pressure of the two electro-proportional relief valves.

4. The luffing system of a truck crane with an electro-hydraulic fusion cylinder according to claim 1, characterized in that: The sensor unit includes: an amplitude angle sensor installed at the hinge shaft of the boom, a stroke sensor fixed on the outer wall of the electro-hydraulic fusion cylinder, a load pressure sensor arranged at the force-receiving end of the cylinder hinge, a cavity pressure sensor installed on the oil outlet pipeline of the hydraulic buffer cavity, and a speed and torque sensor integrated on the servo motor body of the motor drive unit. All sensors collect operating parameters in real time and transmit electrical signals to the controller.

5. The luffing system of a truck crane with an electro-hydraulic fusion cylinder according to claim 1, characterized in that: The motor drive unit consists of a servo motor and a servo driver. The output end of the servo motor is mechanically coupled to the ball screw transmission pair inside the electro-hydraulic fusion cylinder. The servo driver is controlled by the controller and works with the controller to achieve dual closed-loop control of the position and speed of the electric actuator.

6. A control method for a luffing electro-hydraulic fusion cylinder of a truck crane, characterized in that: The luffing system of a truck crane using any one of the electro-hydraulic fusion cylinders described in claims 1 to 5 includes the following steps: S1. Initialization self-test: The controller receives all the data collected by the sensors, including boom angle, cylinder stroke, load pressure, hydraulic chamber pressure, and motor operating parameters. It verifies whether the boom working stroke is within the safe range, locks the luffing action of the whole machine if it exceeds the limit, and pre-configures the motor PID parameters, hydraulic foundation back pressure, and buffer coefficient. S2, Start-up Soft Control: The controller drives the servo motor for low-speed soft start, and the electric actuator is connected to the position and speed dual closed-loop control, synchronously controlling the hydraulic buffer unit to build up pressure, so that the hydraulic buffer chamber can establish a basic back pressure in advance; S3. Steady-state coordinated control: The electric actuator, as the active component, continuously drives the boom pitching and tilting according to the target stroke. The controller dynamically adjusts the opening pressure of the two electro-proportional relief valves based on real-time load data. The hydraulic buffer chamber passively absorbs energy and replenishes the system stiffness in real time as the load changes. S4. Staged shutdown and locking: When the boom approaches the target position, the controller sequentially controls the electric actuator to decelerate and perform micro-position correction, and simultaneously controls the hydraulic buffer unit to stabilize and maintain pressure. Relying on the dual constraints of motor locking and hydraulic pressure maintenance, the controller achieves springback-free positioning. S5. Fault safety protection: When the system triggers any abnormal signal such as overload, instantaneous impact, underpressure, or power failure, the hydraulic buffer unit will prioritize depressurization and energy absorption, while the motor drive unit will perform speed limiting and brake protection.

7. The control method for the luffing electro-hydraulic fusion cylinder of a truck crane according to claim 6, characterized in that: The steady-state coordinated regulation step S3 is divided into two operating modes: When the load pressure is lower than the set light load threshold, the controller lowers the pressure of the corresponding electro-proportional relief valve, the hydraulic buffer chamber operates with low damping, and the system enters the light load high speed mode. When the load pressure exceeds the set heavy load threshold, the controller adjusts the pressure of the corresponding electro-proportional relief valve, the hydraulic buffer chamber provides high damping buffering, and the system enters the heavy load low speed anti-impact mode.

8. The method for controlling the luffing electro-hydraulic fusion cylinder of a truck crane according to claim 6, characterized in that: The step S4 graded shutdown lockout adopts a three-stage progressive control: Speed ​​pre-deceleration stage: When the boom is at the first preset angle difference from the target, the electric actuator decelerates at a constant speed according to the preset deceleration curve; Position fine-tuning stage: When the distance between the boom and the target angle reaches the second preset value, the electric actuator switches to a micro-speed point-position closed loop to eliminate positioning deviation; Hydraulic pressure stabilizing section: After the position error meets the standard, the hydraulic buffer unit maintains constant pressure to absorb residual vibration and suppress boom rebound.

9. The method for controlling the luffing electro-hydraulic fusion cylinder of a truck crane according to claim 6, characterized in that: Step S5: Fault safety protection and working condition control: Overload condition: The corresponding electro-proportional relief valve is fully opened for rapid pressure relief, and the electric actuator retracts at a limited speed; Instantaneous impact condition: The hydraulic buffer chamber stores and releases energy instantaneously, and the servo motor engages in damping control; Under pressure loss / power failure conditions: The hydraulic buffer unit's oil circuit self-locks and maintains pressure, and the servo motor's power failure causes the brake to lock the piston rod.

10. The method for controlling the luffing electro-hydraulic fusion cylinder of a truck crane according to claim 6, characterized in that: When the boom is being lifted, the direction switching valve switches to connect to the oil circuit of the first electro-proportional relief valve, and the controller adjusts the pressure of the first electro-proportional relief valve to match the lifting buffer. When the boom is being lowered, the direction switching valve switches to connect to the oil circuit of the second electro-proportional relief valve, and the controller adjusts the pressure of the second electro-proportional relief valve to match the lowering buffer.

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