1. Engine
The 20 ton excavator is the largest model in the market. At present, there are at least dozens of brands that are produced and sold in China. However, the engine used for a long time has been concentrated in several brands. At present, we are using the direct injection diesel engine of Europe two emissions, and the European three engines are also exported. I think the direct injection engine is more suitable for China cheaper, easy to maintain, less electrical problems, the most important not to pick oil, I think the electric jet engine and fuel saving is not much related, Carter's engine is an electric spray, do anyone say he saves oil? Hitachi's 4HK1 is also less oil - saving.
Komatsu, modern, Liugong, old money 31, dragon workers, Yuchai and Zhonglian are all equipped with Cummins engine. Now there are two kinds of production and import of Dongfeng Cummins on the domestic market. In the automobile, they are basically in the early stage of China (except the bus), and all the excavators are imported. The characteristics of imported Cummins diesel engine: the new electric fuel injection of Cummins diesel engine, the accessories are very expensive; the old direct injection of Cummins, oil consumption, but convenient maintenance; imported models, low noise, low fuel consumption, durable, basically not too big shortcomings; import maintenance costs are a little high, cold cars start a slight time. Blue smoke and some engines do not fire well after long working hours, but this phenomenon is less.
Hitachi ZX-1 and -2, Daewoo -5-7, Dou Shan -7, 31, Xugong, XmD, Yi workers, Xu Wa, mountain and river intelligent, VO, JCB, Keith, Sumitomo assembly of the five bell engines.
Hitachi -3 uses 4HK1 model, EFI three emissions, many domestic manufacturers also choose, but only export type. The quality of the Isuzu engine is very good, the very common engine, the price is relatively cheap, the small trouble is less durable, the working condition is not important, easy to repair, and easy to maintain.
Kobelco -6 and the last generation of Kato, now the new 31 assembly of MITSUBISHI 6D34 engine, its characteristics are fuel saving. Now the MITSUBISHI 4M50 engine, Kato's latest generation of excavator is in use, there is no domestic production, the three phase of emissions. Mitsubishi engine is characterized by high power, low fuel consumption, easy maintenance, but because it belongs to Japan's right-wing Mitsubishi consortium, so relatively disgusted at home.
Carter series engine is equipped with Carter brand, featuring oil burning, durable, and Ma Lizu.
Hino Shengang 8 series, 4 cylinder three stage discharge the biggest characteristic is good reliability, less defect, other general, that is, fuel consumption, power general
Volvo and labor, Atlas assembly deutts engine, German quality, durable, reliable, but everything is under the premise of regular maintenance, there are problems, only professional personnel can be repaired, the price of accessories is high
German man engine, Dou Shan -9 assembly, presumably everyone has heard Mercedes Benz, is to provide Mercedes Benz engine manufacturers. Good quality, durable, high oil consumption.
Yanmar engine, in the field of small engines should be the world's leading, the domestic after-sales technical force is slightly weak, so in China Yanmar engine wind evaluation is not very good, it is considered difficult to repair the machine. In fact, this brand machine is very good, but the domestic matching can not keep up with, such as the top of the excavator, when most small excavators use Yanmar engine, in the design have fatal defects, causing the engine to be bad, the final result is that everyone thinks Yanmar is not good, in fact, Yanmar is lying in the gun.
The Dou Shan engine only assembled its own product, its performance is general and seldom used.
Yuchai engine, Yuchai excavator matching, Heng te 220, Shandong some excavator small plant equipment. Yulai is a domestic engine old, its sales volume has always been the first level in China. The characteristics of the Yulai engine are strong power, reliable quality and convenient maintenance. The share of the passenger car and light, medium and large freight car is really big, but the comparison of the application of the jade engine in heavy and heavy engineering machinery Less.
Two. Hydraulic pump
Hydraulic pump is the conversion of mechanical energy into liquid pressure energy. We usually see only gear pumps and plunger pumps. The common point between the two is that they produce pressure on liquids through volume changes. Difference: the organization is different, the volume position is different. The liquid volume of the gear pump is between the two gears, and the liquid volume is changed by the rotation of the gear, while the volume of the plunger pump is in each plunger cylinder.
1. Gear pump
Gear pumps are operated by closed movement in the form of two meshing gears. Gear pump is a gear transmission to provide power, gear pumps are quantitative pumps, mostly for low precision medium low pressure control. The gear pump is a common type of pump. Its main features are simple structure, convenient manufacturing, low cost, low price, small volume, light weight, good self-priming performance, insensitive to oil pollution and reliable work. Its main disadvantages are large flow and pressure pulsation, large noise and non adjustable displacement. It is widely used in various low-pressure systems. Gear pump requirements for oil liquid minimum, the earliest time because of low pressure, so generally used in low pressure system, now the pressure of the gear pump can be about 25MPA, often used in the mechanical pressure is not high, but his oil fluid pulsation, no variable, the advantage is good self suction performance.
The external gear pump is a hydraulic pump commonly used in hydraulic systems of loaders and some small excavators.
There is a gear with the same modulus and the same number of teeth in the pump body. The two ends of the gear are sealed by the pump cover. The end cover of the pump body and the gear slot of the gear form a sealed volume. The meshing of the two gear is divided into two parts of the oil suction cavity and the oil pressure chamber, and each other is not connected to each other in the work.
Because of the gear engagement, the volume of the seal gradually decreases, and the oil in the alveolus is squeezed and discharged from the oil outlet. Gear rotation, gear meshing caused by the size of oil absorption and discharge chamber volume changes, to achieve continuous oil absorption chamber, pressure chamber pressure oil.
2, plunger pump
The plunger pump is driven by the reciprocating movement of the piston. The plunger pump is a variable pump. It is used for high precision and high pressure control. The piston pump has high working pressure. The working pressure is generally 20 ~ 40MPa, up to 1000MPa; the structure is compact; the efficiency is high and the flow regulation is convenient and so on. Piston pump has high pressure, stable performance, high cost, minimum fluctuation, variable, often used in high-pressure systems and construction machinery. But its self-priming performance is the worst. For example, the main pump of the excavator is usually double pumps, the rated pressure is 34MPA, and the instantaneous maximum pressure can reach 39MPA. The reason why the pump oil pressure of plunger pump is higher than that of gear pump is because of its higher work efficiency and volumetric efficiency. At present, a large number of hydraulic excavators adopt swash plate variable axial piston pump. Usually, two pumps are used to connect two plunger pumps together with one shaft, so they are also called shaft pumps. The through shaft pump used on the excavator can also be connected with a small gear pump as a servo pump (that is, the pilot pump) to greatly simplify the excavator department. Chuan Qi's K3V pump is used more in the excavator.
Working principle of plunger pump
Working principle
When the engine drives the drive shaft to rotate, the connecting rod pushes the plunger in the cylinder body to reciprocate, and the side of the connecting rod drives the piston together with the cylinder body, and the oil tray is fixed. Under the action of the cam and the plunger spring, the plunger moves upward and downward to complete the oil pumping task. When the cam protruding part turns over, under the action of the plunger spring, the plunger moves downward, and the plunger part space is the vacuum in the pump oil chamber. At this time the inlet of the plunger sleeve will open, and the hydraulic oil on the oil pump enters the oil chamber of the pump, and the plunger is moved to the bottom and the oil is finished.
When the camshaft is transferred to the convex part of the cam, the plunger spring is compressed, the plunger moves upward, the hydraulic oil is pressed, and a part of the oil hole flows back to the upper oil cavity. When the top surface of the plunger covers the oil hole, the matching clearance between the plunger and the cylinder sleeve is small so that the oil distribution chamber at the top of the plunger becomes a sealed space, the plunger continues to rise, the oil pressure of the pump oil chamber rises rapidly. When the pump pressure is greater than the oil spring, the hydraulic pump is introduced and the high-pressure liquid enters the cylinder through the main operation valve.
When the plunger supply oil, the slant trough on the plunger connects with the oil back hole on the cylinder sleeve, the low pressure oil circuit of the pump chamber connects with the middle hole and the inclined slot of the plunger head, the oil pressure drops, and the oil outlet valve closes the oil supply under the action of the spring. The plunger continues to go up, and when the cam's protruding part turns away, the plunger goes down again to start the next cycle under the action of the spring.
Piston, cylinder, and flow plate
When the excavator is not working, the main control valve is in the middle, the high pressure oil is used in the main operation valve, the oil is returned under the control of the load sensitive control, some of the control pump continues to work, and a part of the oil tank is returned. My personal understanding is that the middle position of the main control valve is a large oil return line.
Structurally speaking, the plunger pump mechanism is complex, which can produce higher pressure, and the gear pump is slightly worse. The main pumps of large and medium-sized excavators are using plunger pumps, and some of them have linked gear pumps to provide pilot pressure. When the pressure is greater and the quantity is required, the plunger pump should be selected. When the pressure is small and the quantity is not required, the gear pump should be selected.
