The structure principle of excavator
Section 1 Overview
1. The overall structure of single bucket hydraulic excavator
The overall structure of the single-bucket hydraulic excavator includes power unit, working device, slewing mechanism, operating mechanism, transmission system, walking mechanism and auxiliary equipment.
excavator
The power unit, the main part of the transmission system, the slewing mechanism, auxiliary equipment, and the cab of the commonly used full-slewing hydraulic excavator are all installed on a rotatable platform, usually called the upper turntable. Therefore, the single bucket hydraulic excavator can be summarized into three parts: working device, upper turntable and walking mechanism.
excavator
The excavator uses a diesel engine to convert the chemical energy of diesel fuel into mechanical energy. The hydraulic plunger pump converts the mechanical energy into hydraulic energy. The hydraulic energy is distributed to each executive element (hydraulic cylinder, slewing motor + reducer, walking motor + Reducer), the hydraulic energy is converted into mechanical energy by the various actuators to realize the movement of the working device, the rotary movement of the rotary platform, and the walking movement of the whole machine.
2. Excavator power system
1. The power transmission route of the excavator is as follows
1) Traveling power transmission route: Diesel engine-coupling-hydraulic pump (mechanical energy is converted into hydraulic energy)-distribution valve-central rotary joint-traveling motor (hydraulic energy is converted into mechanical energy)-reduction gear box- Drive wheel-track chain crawler-realize walking
2) Rotary motion transmission route: diesel engine-coupling-hydraulic pump (mechanical energy is converted into hydraulic energy)-distribution valve-slewing motor (hydraulic energy is converted into mechanical energy)-reduction gear box-slewing bearing-realization turn around
3) Boom movement transmission route: Diesel engine-coupling-hydraulic pump (mechanical energy is converted into hydraulic energy)-distribution valve-boom cylinder (hydraulic energy is converted into mechanical energy)-to realize boom movement
4) Stick movement transmission route: Diesel engine-coupling-hydraulic pump (mechanical energy is converted into hydraulic energy)-distribution valve-stick cylinder (hydraulic energy is converted into mechanical energy)-to achieve stick movement
5) Bucket movement transmission route: Diesel engine-coupling-hydraulic pump (mechanical energy is converted into hydraulic energy)-distribution valve-bucket cylinder (hydraulic energy is converted into mechanical energy)-realizing bucket movement
2. Power plant
The power unit of single bucket hydraulic excavator mostly adopts upright multi-cylinder, water-cooled, one-hour power calibration diesel engine.
3. Transmission system
The single-bucket hydraulic excavator transmission system transmits the output power of the diesel engine to the working device, slewing device, and traveling mechanism. There are many types of hydraulic transmission systems used in single-bucket hydraulic excavators, which are traditionally classified according to the number of main pumps, power adjustment methods and the number of circuits. There are single-pump or double-pump single-loop quantitative system, double-pump double-loop quantitative system, multi-pump multi-loop quantitative system, double-pump double-loop sub-power regulated variable system, double-pump double-loop full power regulated variable system, multi-pump multi-loop quantitative Or variable mixing system and other six kinds. According to the oil circulation mode, it is divided into open system and closed system. According to the fuel supply mode, it is divided into series system and parallel system.
Where the main pump output flow is a fixed value hydraulic system is a quantitative hydraulic system; on the contrary, the main pump flow can be changed by the adjustment system is called a variable system. In the quantitative system, each actuator works according to the fixed flow supplied by the oil pump without overflow, and the power of the oil pump is determined by the fixed flow and maximum working pressure; in the variable system, the most common is the double pump double loop constant power variable The system is divided into power variable and full power variable. The sub-power variable control system is to install a constant power variable pump and a constant power regulator on each loop of the system. The power of the engine is evenly distributed to each oil pump; the full power control system has a constant power regulator that controls at the same time The flow rate of all oil pumps in the system changes, so as to achieve synchronization variables.
The return oil of the actuator in the open system flows directly back to the fuel tank, which is characterized by simple system and good heat dissipation effect. However, the oil tank has a large capacity, and there are many opportunities for the low-pressure oil circuit to contact air, and the air is easy to seep into the pipeline and cause vibration. The operation of single bucket hydraulic excavator is mainly the work of the oil cylinder, and the difference between large and small cylinders with cavities, frequent work and large heat generation, so most single bucket hydraulic excavators use open systems; The oil return path of the actuator does not return to the oil tank directly. Its characteristic structure is compact, the volume of the oil tank is small, there is a certain pressure in the oil return path, the air is not easy to enter the pipeline, the operation is relatively stable, and the impact during reversing is avoided . However, the system is more complicated and the heat dissipation conditions are poor. In partial systems such as the slewing device of the single-bucket hydraulic excavator, a closed circuit hydraulic system is used. In order to supplement the oil leakage caused by the forward and reverse rotation of the hydraulic motor, a charge pump is often provided in a closed system.
4. Slewing mechanism
The swivel mechanism makes the working device and the upper turntable swivel left or right for excavation and unloading. The slewing device of the single bucket hydraulic excavator must be able to support the turntable on the frame without tilting and make the slewing light and flexible. For this reason, single bucket hydraulic excavators are equipped with slewing support devices and slewing transmission devices, which are called slewing devices.
The transmission form of the slewing device of the full-rotation hydraulic excavator includes direct transmission and indirect transmission.
1) Direct drive. A drive pinion is installed on the output shaft of a low-speed high-torque hydraulic motor to mesh with the rotating gear.
2) Indirect transmission. An indirect transmission structure in which a high-speed hydraulic motor drives a rotary ring gear through a gear reducer. It has a compact structure, a large transmission ratio, and the gear force is better. The axial plunger hydraulic motor has basically the same structure as the same type of hydraulic oil pump, and many parts can be used in common, which is convenient for manufacturing and maintenance, thereby reducing costs. However, a brake must be installed to absorb the larger rotational moment of inertia, shorten the operating cycle time of the excavator, and improve production efficiency.
5. Walking mechanism
The walking mechanism supports the overall quality of the excavator and completes the walking tasks, mostly in the crawler type and the tire type.
6. Crawler walking mechanism
The basic structure of the crawler-type walking mechanism of the single-bucket hydraulic excavator is roughly the same as other crawler-type mechanisms, but it uses two hydraulic motors to drive a crawler each. Similar to the transmission of the slewing device, a high-speed small torque motor or a low-speed large torque motor can be used. The rotary excavator with two hydraulic motors in the same direction will travel in a straight line; if only one hydraulic motor is supplied with oil and the other hydraulic motor is braked, the excavator will steer around the track on the brake side, if there are two left and right hydraulic motors Reverse rotation, the excavation is about to turn in place.
All parts of the walking mechanism are installed on the integrated walking frame. The pressure oil input by the hydraulic pump actually enters the travel hydraulic motor by the multi-way reversing valve and the central rotary joint. After the motor converts the hydraulic energy into output torque, it is transmitted to the driving wheel through a gear reducer, and finally the crawler is wound to realize the excavator walk.
Single bucket hydraulic excavators mostly use combined structure crawlers and flat crawlers-no obvious spurs, poor adhesion, but sturdy and durable, less destructive to the road, suitable for hard rocky ground operations, or frequent transition operations. There are also three-track stab crawlers, which have a larger grounding area and a shallow depth of stab cut into the soil, which is suitable for excavator quarrying operations. After the implementation of standardization, it is stipulated that the excavator adopts rolled track shoes with light weight, high strength, simple structure and lower price. The triangular track shoe dedicated to the swamp can reduce the ground pressure and improve the passing capacity of the excavator on the loose ground.
The driving wheels of the single bucket hydraulic excavator are made of integral castings, which can be correctly meshed with the crawler belt and the transmission is stable. Excavator line
The driving wheel should be located at the rear when traveling, and the tension section of the crawler belt should be shorter to reduce friction, wear and power loss of the crawler belt.
Each track is equipped with a tensioning device to adjust the tension of the track to reduce vibration, noise, friction, wear and power loss. At present, single-bucket hydraulic excavators adopt hydraulic tensioning structure. The hydraulic cylinder and the internal buffer spring reduce the structural size.
7. Tyre walking mechanism
The walking mechanism of the wheel excavator consists of mechanical transmission and hydraulic transmission. Among them, the running mechanism of the hydraulically driven tire excavator is mainly composed of a frame, a front axle, a rear axle, a transmission shaft, and a hydraulic motor.
The traveling hydraulic motor is installed on the gearbox fixed to the frame, and the power is transmitted to the front and rear drive axles through the gearbox and drive shaft. Some excavators drive the wheels through the wheel-side reducer. The high-speed transmission method adopting hydraulic motor is reliable in use, and the vertical moving shaft of the upper and lower transmission boxes in the mechanical transmission is omitted, and the structure is simple and easy to arrange.
