The engine, the hydraulic pump, the distribution valve are the three main parts that people often say, the excavator is not powered by the engine as the automobile, through the gearbox and the transmission shaft to drive the whole vehicle, but through the engine to drive the hydraulic pump, and the hydraulic actuating components such as the hydraulic motor and the hydraulic cylinder by the high pressure hydraulic oil. Drive the whole vehicle movement? The engine provides power for hydraulic pumps, hydraulic pumps, hydraulic oil pipes, hydraulic motors, hydraulic cylinders, etc.
One, what is a plunger pump, what is a gear pump?
Hydraulic pump is the conversion of mechanical energy into liquid pressure energy. We usually see that there are gear pumps and plunger pumps for excavators and loaders.
Common ground: pressure is produced by volume changes.
Difference: the organization is different, the volume position is different. The volume of the fluid of the gear pump is between the two gears, and the volume of the liquid is changed by gear rotation. The displacement of the plunger pump is in the cylinder of each plunger.
The common large and medium excavators usually assemble the plunger pump and the gear pump together to form the hydraulic pump assembly. The general main pump is the plunger pump (the hydraulic pressure of the output hydraulic oil is larger) to the hydraulic motor, the hydraulic rotary motor and the hydraulic cylinder, and the pilot pump is the gear pump (the output pressure of the output hydraulic oil is small) to supply the valve to the distribution valve.
Main pump assembly
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.
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.
The main disadvantages are: large flow and pressure pulsation, large noise and no 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 (pilot pump), 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, good self suction performance.
Principle diagram of gear pump
Working principle
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 pump body, the end cover and the gear slot of the gear form a sealed volume. The meshing of the two gears divides the closed volume space into the oil suction cavity and the pressure chamber, and does not interconnect with 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. The gear is constantly rotating, and the volume of the oil suction and oil discharge cavity caused by the gear meshing causes changes in the volume of the oil suction chamber, and the oil pressure chamber continuously presses the oil.
A gear pump for a loader (double pump): a driving shaft drives two driven gears to work, and there are two oil suction cavities and two oil discharge cavities.
At present, the hydraulic system of the loader in China is basically a quantitative hydraulic system. The so-called quantitative hydraulic system means that the displacement of the hydraulic pump is not constant, basically with the gear pump, and there is a part of the export model, because of the high demand for the whole machine noise in foreign countries, the blade pump is used, and the remaining part of the model is matched. The variable hydraulic system is basically equipped with variable piston pump.
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.
The plunger pump has high pressure, stable performance, high cost, minimal pulsation, and variable variables, which are often used in high pressure systems and engineering construction machinery. But his self sucking performance is the worst.
Schematic diagram of plunger pump
When the engine drives the drive shaft (the left end of the upper drawing), the connecting rod pushes the plunger in the cylinder block to reciprocate, while 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 pump chamber. The plunger moves to the bottom of the oil pump, and the plunger is transported to the bottom and the oil to the end.
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, and the inclined slot on the plunger and the oil back hole on the cylinder sleeve, the low pressure oil circuit of the pump oil chamber and the middle hole and the inclined slot of the plunger head are supposed to pass through, the oil pressure drops, and the oil outlet valve closes the oil supply under the effect of the spring. The plunger continues upward, when the convex part of the cam is turned over, under the action of the spring, the plunger goes down again and starts the next cycle.
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 piston pump is higher than that of gear pump is due to 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 use of excavator on the shaft pump can also be connected to a pinion pump as a servo pump (that is, the pilot pump) to make the excavator's department greatly simplified.
