Working principle of excavator
Hydraulic excavator is mainly composed of engine, hydraulic system, working device, traveling device and electrical control. The hydraulic system consists of hydraulic pumps, control valves, hydraulic cylinders, hydraulic motors, pipelines, fuel tanks, etc. The electrical control system includes monitoring panels, engine control systems, pump control systems, various sensors, solenoid valves, etc.
Hydraulic excavators generally consist of three major parts: working device, slewing device and traveling device. According to its structure and use, it can be divided into: crawler type, tire type, walking type, fully hydraulic, semi-hydraulic, full rotation, non-full rotation, general type, special type, articulated type, telescopic arm type and other types.
The working device is a device that directly completes the excavation task. It is articulated by three parts: boom, bucket, and bucket. The lifting and lowering of the boom, telescopic arm and bucket rotation are all controlled by reciprocating double-acting hydraulic cylinders. In order to meet the needs of various construction operations, hydraulic excavators can be equipped with a variety of working devices, such as excavation, lifting, loading, leveling, clamping, bulldozing, impact hammers and other working tools.
The slewing and traveling device is the body of the hydraulic excavator, and the upper part of the turntable is equipped with a power device and a transmission system. The engine is the power source of hydraulic excavators. Most of them use diesel. If the location is convenient, electric motors can also be used.
The hydraulic transmission system transmits the power of the engine to actuators such as hydraulic motors and hydraulic cylinders through hydraulic pumps to promote the movement of working devices to complete various operations.
How does the excavator hydraulic system work?
The excavator has three parts of hydraulic cylinders: the boom, the bucket, and the bucket. There are three hydraulic motors, one for left and right travel and one for rotation. These are controlled by reversing valves for oil supply. The oil comes out of the hydraulic pump and is distributed to the above actuators through the reversing valve. Most of the reversing valves of excavators are hydraulically controlled, which uses a stream of oil with low pressure to push the valve core of the reversing valve. Generally, medium-sized excavators use triple pumps. Two large pumps provide the pressure required for work. A small gear pump supplies oil to the control oil circuit. The control oil adjusts the position of the main oil line reversing valve spool through the control valve under the handle to realize the expansion and contraction of the boom arm and bucket cylinder. As well as the rotation and stopping of the hydraulic motor and the direction of rotation. The main oil line is equipped with a relief valve. If the pressure exceeds the limit value, it will open and the oil will return directly to the tank. Therefore, the system pressure is always maintained within a certain range. For the same reason, relief valves are also installed in the branches of each cylinder to achieve secondary pressure adjustment. Not only excavators, but the working principle of any hydraulic system is oil in the tank - pump - control element - actuator - oil tank. What are the functions of the reversing valve of the hydraulic control proportional valve and the function of the pilot valve connected in series with the reversing valve of the hydraulic control proportional valve
The inlet and outlet of the traditional reversing valve are controlled through a valve core, and the two oils The corresponding relationship between the mouth, hearing and opening has been determined as early as the valve core design and processing, and cannot be modified during use. As a result, the flow or pressure through the two oil ports cannot be independently controlled without affecting each other.
With the decline in the cost of microprocessor controllers and sensor components, and the continuous improvement of control technology, dual-spool control technology has been applied in the field of engineering machinery. The British company Utronics has used its own technology and patent advantages to develop a dual-spool multi-way reversing valve, which has been widely used in excavators, truck loaders, backhoe loaders and other products of JCB, Deere, DAWOO, CASE and other companies. . In order to adapt to the functional requirements of hydraulic systems for Chinese construction machinery products. With the continuous improvement of stability and automation control, Utronics' products have entered the Chinese market in a timely manner. The prototype debugging of XCMG (5t) loader and Zhanyang (8t) excavator has been initially completed and entered the testing stage.
1. Defects of the traditional single-spool directional valve
The hydraulic system composed of the traditional single-spool directional valve cannot reasonably solve the following problems between functions and control Contradiction:
(1) In order to improve system stability and reduce the impact of load changes on speed when designing a hydraulic system, we must either sacrifice some of the functions we want to achieve, or add additional hydraulic components, such as speed control valves , pressure control valve, etc., by increasing damping and increasing system speed stiffness to improve system stability. However, the increase in components will reduce efficiency and waste energy; it will also reduce the reliability of the entire system and increase costs.