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**I. Introduction**
The traditional hydraulic system in cranes typically relies on valve control, where the flow rate of the hydraulic fluid is regulated by adjusting the opening of a multi-way valve. This method controls the speed of the actuator but often leads to energy loss and excessive heat generation within the system.
To address these issues, modern crane systems have adopted pump-controlled hydraulic technology. This approach ensures better coordination between the engine and the hydraulic system, allowing for more efficient use of engine power. By minimizing unnecessary energy consumption, this system helps save energy and enables smooth, stepless regulation of the crane’s operations.
Additionally, the system offers excellent shock absorption, significantly reducing hydraulic shocks that could otherwise damage components. This not only protects the hydraulic system but also extends the lifespan of its parts, enhancing the crane’s safety, reliability, and overall efficiency. The system integrates electrical control with hydraulic functions, making it a truly intelligent and integrated solution. It also includes features such as a retractable mechanism and an electrical telescopic single-cylinder latch function for enhanced performance.
**II. System Overview**
The system uses electro-hydraulic proportional pilot control to adjust the displacement of the actuator, enabling precise control over movement speed. It consists of a closed-loop rotary circuit, along with open circuits for the main and auxiliary oil lines.
In the swing circuit, a swash-plate variable displacement piston pump works in conjunction with a closed-loop fixed motor circuit. The pump's outlet connects to the motor's inlet, while the motor's outlet connects back to the pump's inlet, forming a closed loop without the need for valves. Adjusting the pump’s swashplate angle changes both the flow and direction of the pressure oil, allowing for smooth rotation and stable operation. A charge pump and charge device are included to improve pump speed and prevent cavitation.
The main oil circuits include the primary and auxiliary lifting lines, luffing lines, and telescoping lines. The main pump is a dual axial-variable pump, capable of independent adjustment to meet different operational requirements. With power regulators and load limiters, the system ensures optimal power distribution and prevents overloading. Proportional relief valves help manage pressure and flow, allowing for continuous and smooth speed control.
The entire system uses advanced electro-hydraulic proportional pilot control, where the pump's displacement is regulated by pilot oil pressure. The greater the displacement of the electronic remote control handle, the higher the current output, which increases the pressure of the proportional relief valve and, in turn, the pump's displacement. This allows for precise control over the actuator’s speed. The system supports both independent and combined oil supply to various actuators, offering a wide range of speed adjustments and smooth operation.
**III. Function Description**
1. **Swing Circuit**
The swing mechanism is crucial for the crane’s handling performance, operational efficiency, and structural stability. In addition to using on-demand pump control and fixed motor drive, the system also considers buffer and start-up performance. The closed-loop swing circuit eliminates the need for valves, and the pump’s swashplate angle adjusts the flow and direction of pressure oil, controlling the motor’s speed and rotation. A charge pump, filters, and pollution indicators are included to enhance performance and protect the system. A free-wheeling solenoid valve is used to allow the boom to float during heavy lifting, preventing damage from lateral forces.
2. **Main and Auxiliary Lifting Circuits**
Both the main and auxiliary lifting mechanisms feature fixed motors with high torque and built-in safety valves to prevent overload damage. The system uses a proportional pressure-reducing valve to control the main pump’s displacement, ensuring smooth lifting and lowering. When the pilot handle returns to neutral, the system unloads pressure, allowing the brakes to engage automatically. Lifting balance valves prevent stalling and ensure stable descent, improving safety.
3. **Luffing Circuit**
The luffing mechanism uses advanced gravity reduction principles and a proportional valve controlled directly by the pilot handle. When the cylinder force reaches a set value, the balance valve compensates for pressure, slowing down the speed to maintain boom stability during luffing.
4. **Telescoping Circuit**
The telescoping system uses a single-cylinder expansion principle driven by a telescoping cylinder. It can be manually or automatically controlled. During extension and retraction, the system ensures stability through locking mechanisms and a balancing valve. The dual-loop design prevents failure due to valve damage, ensuring safe and reliable operation.
5. **Auxiliary Oil Circuit**
The auxiliary circuit includes pilot control, counterweight, and cooling systems. A 3 MPa pilot pressure system powers the proportional valve and controls the main directional valve. The cooling system automatically activates when the oil temperature rises, using a load-sensing gear pump to drive the fan motor, ensuring optimal system performance.
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