Basic structure and working principle of excavator

Basic structure and working principle of excavator

Overall structure of single bucket hydraulic excavator

The overall structure of a single-bucket hydraulic excavator includes power unit, working device, slewing mechanism, control mechanism, transmission system, traveling mechanism and auxiliary equipment, as shown in the figure.

The power unit, main part of the transmission system, slewing mechanism, auxiliary equipment and cab of a commonly used full-rotation 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 traveling mechanism.

The excavator converts the chemical energy of diesel into mechanical energy through the diesel engine, and converts the mechanical energy into hydraulic energy through the hydraulic piston pump. The hydraulic energy is distributed to each actuator (hydraulic cylinder, swing motor + reducer, traveling motor + Reducer), each actuator converts hydraulic energy into mechanical energy to realize the movement of the working device, the rotary movement of the rotary platform, and the walking movement of the entire machine.

02

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 converted into hydraulic energy) - distribution valve - central rotary joint - traveling motor (hydraulic energy converted into mechanical energy) - reduction box - drive wheel ——Rail chain crawler——achieving walking

(2)

Rotary motion transmission route: diesel engine - coupling - hydraulic pump (mechanical energy converted into hydraulic energy) - distribution valve - rotary motor (hydraulic energy converted into mechanical energy) - reduction box - slewing bearing - realize rotation

(3)

Boom movement transmission route: diesel engine - coupling - hydraulic pump (mechanical energy converted into hydraulic energy) - distribution valve - boom cylinder (hydraulic energy converted into mechanical energy) - realize boom movement

(4)

Bucket movement transmission route: diesel engine - coupling - hydraulic pump (converting mechanical energy into hydraulic energy) - distribution valve - stick cylinder (converting hydraulic energy into mechanical energy) - realizing stick movement

(5)

Bucket movement transmission route: diesel engine - coupling - hydraulic pump (mechanical energy converted into hydraulic energy) - distribution valve - bucket cylinder (hydraulic energy converted into mechanical energy) - realization of bucket movement

1. Guide wheel 2. Center rotary joint 3. Control valve 4. Final drive 5. Travel motor 6. Hydraulic pump 7. Engine 8. Travel speed solenoid valve 9. Swing brake solenoid valve 10. Swing motor 11. Swing mechanism 12 , Slewing bearing 

2. Power unit The power unit of a single-bucket hydraulic excavator mostly uses an upright multi-cylinder, water-cooled, one-hour power calibrated diesel engine.

3. Transmission system The transmission system of single-bucket hydraulic excavator 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 for single-bucket hydraulic excavators, which are customarily classified according to the number of main pumps, power adjustment methods and the number of circuits. There are single-pump or double-pump single-circuit dosing systems, double-pump dual-circuit dosing systems, multi-pump multi-circuit dosing systems, dual-pump dual-circuit split power adjustable variable systems, double-pump dual-circuit full power adjustable variable systems, and multi-pump multi-loop dosing systems. Or variable mixing system and six other types. According to the oil circulation method, it is divided into open system and closed system. According to the oil supply mode, it is divided into series system and parallel system.

1. Drive plate 2. Coil spring 3. Stop pin 4. Friction plate 5. Shock absorber assembly 6. Muffler 7. Engine rear mounting seat 8. Engine front mounting seat

A hydraulic system in which the flow rate output by the main pump is a fixed value is a quantitative hydraulic system; conversely, a hydraulic system in which the flow rate of the main pump can be changed through an adjustment system is called a variable system. In the quantitative system, each actuator works according to the fixed flow rate supplied by the oil pump when there is no overflow. The power of the oil pump is determined according to the fixed flow rate and the maximum working pressure.

Among the variable systems, the most common one is the double-pump double-circuit constant power variable system, which is divided into divided power variable and full power variable. The split power variable regulation system installs a constant power variable pump and a constant power regulator on each circuit of the system, and the engine power is evenly distributed to each oil pump; the full power regulation system has a constant power regulator that simultaneously controls The flow rates of all oil pumps in the system change to achieve synchronized variables.

In the open system, the return oil of the actuator flows directly back to the oil tank, which is characterized by a simple system and good heat dissipation effect. However, due to the large capacity of the fuel tank, there are many opportunities for the low-pressure oil circuit to come into contact with air, and air can easily penetrate into the pipeline and cause vibration. The operation of a single-bucket hydraulic excavator is mainly based on the work of the oil cylinder, and the difference between large and small cylinders is large. They work frequently and generate a lot of heat. Therefore, the vast majority of single-bucket hydraulic excavators use open systems;

The oil return line of the actuator in the closed circuit does not directly return to the oil tank. It has a compact structure, a small oil tank volume, and a certain pressure in the inlet and return oil lines. It is difficult for air to enter the pipeline, and the operation is relatively smooth, which avoids Impact during reversal. However, the system is complex and the heat dissipation conditions are poor. In some systems such as the slewing device of a single-bucket hydraulic excavator, a closed-circuit hydraulic system is used. In order to compensate for 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. Rotary mechanism

The slewing mechanism rotates the working device and the upper turntable to the left or right for excavation and unloading. The slewing device of a single-bucket hydraulic excavator must be able to support the turntable on the frame without tilting and make the rotation light and flexible. For this reason, single-bucket hydraulic excavators are equipped with a slewing support device and a slewing transmission device, which are called slewing devices.

1. Brake 2. Hydraulic motor 3. Planetary gear reducer 4. Rotary ring gear 5. Lubricating oil cup 6. Central rotary joint

The transmission forms of the slewing device of the full-turn hydraulic excavator include direct transmission and indirect transmission.

1.Direct drive. A driving pinion is installed on the output shaft of a low-speed, high-torque hydraulic motor to mesh with the counter-rotating gear.

2.Indirect transmission. An indirect transmission structure in which a high-speed hydraulic motor drives a rotating ring gear through a gear reducer. It has a compact structure, a large transmission ratio, and good gear stress.

3.The structure of the axial piston hydraulic motor is basically the same as that of the same type of hydraulic oil pump. Many parts can be used in common, which facilitates manufacturing and maintenance, thereby reducing costs. 

4.However, a brake must be installed to absorb the large rotational inertia moment, shorten the excavator operation cycle time, and improve production efficiency. 5. Traveling mechanism The traveling mechanism supports the overall quality of the excavator and completes the walking task. It mostly uses crawler type and tire type.

6.Crawler traveling mechanism The basic structure of the crawler traveling mechanism of a single-bucket hydraulic excavator is roughly the same as that of other crawler mechanisms, but it mostly uses two hydraulic motors to drive one crawler each. Similar to the transmission of the rotary device, a high-speed low-torque motor or a low-speed high-torque motor can be used. A rotary excavator with two hydraulic motors in the same direction will drive in a straight line; if only one hydraulic motor is supplied with oil and the other hydraulic motor is braked, the excavator will turn around the crawler track on the braking side. If there are two hydraulic motors on the left and right Reverse rotation and the excavation is about to turn in place.

All parts of the traveling mechanism are installed on the integral execution frame. The pressure oil input by the hydraulic pump enters the traveling hydraulic motor through the multi-channel reversing valve and the central rotary joint. The motor converts the hydraulic energy into output torque and then transmits it to the driving wheel through the gear reducer, and finally winds the crawler track to realize the operation of the excavator. walk.

Most single-bucket hydraulic excavators use combined structure crawlers and flat crawlers - there are no obvious crawlers. Although the adhesion performance is poor, they are durable and have little damage to the road surface. They are suitable for operations on hard rock ground or operations that frequently change locations. There are also three-spur type crawlers, which have a large ground contact area and a shallow depth of the snails cutting into the soil, making them suitable for excavator quarrying operations. After the implementation of standardization, it was stipulated that excavators should use rolled track shoes that are light in weight, high in strength, simple in structure, and low in price. The triangular track shoes specially used in swamps can reduce the ground specific pressure and improve the excavator's ability to pass on loose soil.

7. Tire-type traveling mechanism The traveling mechanism of the tire-type excavator consists of two types: mechanical transmission and hydraulic transmission. The traveling 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 a gearbox fixed to the frame. The power is transmitted to the front and rear drive axles through the gearbox and transmission shaft. Some excavators drive the wheels through wheel reducers. The high-speed transmission method using a hydraulic motor is reliable and eliminates the need for vertical moving shafts of the upper and lower transmission boxes in mechanical transmission. The structure is simple and easy to arrange.