Engine 2113, hydraulic pump, distribution valve
For Xiaobai, who is just beginning to get in touch with the excavator 5261, 4102 must be wondering why the excavator is not powered by the engine like the 1653 car. It drives the vehicle forward through the gearbox and drive shaft, but uses the engine to drive the hydraulic pump to rotate. , The high-pressure hydraulic oil drives the vehicle to move through hydraulic actuators such as hydraulic motors and hydraulic cylinders.
The engine provides power for the hydraulic pump. The hydraulic pump, hydraulic tubing, hydraulic motor and hydraulic cylinder are driven by hydraulic pressure, and the distribution valve is controlled by hydraulic pressure.
What is a plunger pump and what is a gear pump?
Hydraulic pumps convert mechanical energy into hydraulic pressure energy. Commonly used are gear pumps and plunger pumps (for excavators and loaders).
Common point: all apply pressure to the liquid through volume change.
Difference: The mechanism is different, the volume is different, and the location 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 gears. The volume of the plunger pump is in each plunger cylinder.
Common large and medium-sized excavators generally combine a plunger pump and a gear pump into a hydraulic pump assembly. The main pump is generally a plunger pump (high output hydraulic oil pressure), which supplies oil to hydraulic travel motors, hydraulic swing motors, and hydraulic cylinders; the pilot pump is a gear pump (low output hydraulic oil pressure) that supplies oil to the distribution valve
Main pump assembly
When the two meshing gears rotate, the gear pump works by closing movement. The gear pump is a gear drive that provides power, and the gear pump is a fixed pump, mostly used for low-precision medium and low pressure control.
Its main features are: simple structure, convenient manufacturing, low cost, low price, small size, light weight, good self-priming performance, insensitive to oil pollution, and reliable operation.
The main disadvantages are: large flow and pressure pulsation, large noise, and non-adjustable displacement.
It is widely used in various low pressure systems. Gear pumps have the lowest oil requirements. At first, due to its low pressure, it was generally used in low-pressure systems (pilot pumps). At present, the pressure of gear pumps can reach about 25MPA, which is often used in machinery with low pressure requirements. However, its oil pulsation is large and cannot be changed, and it has the advantage of good self-priming performance.
External gear pumps are commonly used hydraulic pumps 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, and the two end faces of the gear are sealed by the pump cover. The pump body, the end cover and the tooth grooves of the gears form a sealed volume. The engagement of the two gears divides the sealed volume into two parts, namely the oil suction chamber and the oil pressure chamber. The two parts are not connected during operation. Due to the meshing of the gears, the volume of the seal gradually decreases, and the oil in the tooth groove is squeezed and discharged from the oil discharge port. With the continuous rotation of the gears, the volume of the oil suction chamber and the oil discharge chamber changes when the gears mesh, so that the oil suction chamber continuously sucks oil and the oil pressure chamber continuously presses oil. Loader gear pump (dual pump: one drive shaft drives two driven gears to work, with two oil suction chambers and two oil discharge chambers.
At present, the hydraulic systems of domestic loaders are basically quantitative hydraulic systems. The so-called quantitative hydraulic system means that the displacement of the hydraulic pump is constant, and the gear pump is basically the main one. There are also some export models. Because of the high noise requirements of the whole machine, vane pumps are used in foreign countries. The remaining models are equipped with Variable hydraulic systems are basically equipped with variable plunger pumps.
The plunger pump is powered by the reciprocating movement of the piston. The plunger pump is a variable pump mainly used for high-precision high-pressure control. The working pressure of the plunger pump is high, generally 20-40 MPa, up to 1000 MPa; structure Compact; high efficiency, convenient flow adjustment.
Plunger pumps have the characteristics of high pressure, stable performance, high cost, small pulsation, and variable capacity, and are often used in high-pressure systems and construction machinery. But his self-absorption performance is the worst.
When the engine drives the transmission shaft to rotate, the connecting rod drives the plunger to reciprocate in the cylinder, and the side of the connecting rod drives the piston to rotate with the cylinder, and the oil distribution plate is fixed.
When working, under the action of the cam and the plunger spring, the plunger repeatedly moves up and down to complete the oil pumping task. When the convex part of the cam rotates, the plunger moves downward under the action of the plunger spring, and the upper part of the plunger generates a vacuum for the pump oil chamber. At this time, the oil inlet on the plunger sleeve on the plunger opens, the hydraulic oil in the oil pump oil circuit enters the pump oil chamber through the oil inlet hole, the plunger moves to the bottom, and the oil intake ends.
When the camshaft turns to the cam protrusion to push up the rolling element, the plunger spring is compressed, the plunger moves upward, the hydraulic oil is pressed down, and a part of it flows back to the upper body oil cavity through the oil hole. When the top surface of the plunger covers the oil inlet, the oil distribution chamber at the top of the plunger becomes a sealed space due to the small fit gap between the plunger and the cylinder liner. The plunger continues to rise, and the oil pressure in the pump oil chamber rises rapidly. When the pump oil pressure is greater than the oil outlet spring, the hydraulic pump is pushed out, and the high-pressure liquid enters the oil cylinder through the main operating valve.
When the plunger supplies oil, it communicates with the chute on the plunger, the cylinder liner, and the return hole on the plunger, and the low-pressure oil passage in the pump oil chamber communicates with the plunger, the middle hole and the chute on the head. When the oil pressure drops, the oil outlet valve is closed under the action of the spring to stop the oil supply. The plunger continues to rise. When the convex part of the cam is turned over, under the action of the spring, the plunger falls again to start the next cycle.