Before that, the characteristics and disadvantages of gear pump and plunger pump are roughly introduced. This article will roughly introduce the working principle of gear pump and plunger pump.
1. Gear pump
External gear pump is a common hydraulic pump in the hydraulic system of loaders and some small excavators. There is a gear with the same module 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 sealed volume is composed of the pump body, the end cover and each tooth groove of the gear. The meshing of the two gears divides the sealed volume space into oil suction chamber and oil pressure chamber, and they are not connected with each other in work. Due to the meshing of the gear, the volume of the seal is gradually reduced, and the oil in the tooth groove is squeezed and discharged from the oil drain port. The continuous rotation of the gear changes the volume of the oil suction and oil discharge chamber caused by the meshing of the gear, so as to realize the continuous oil suction of the oil suction chamber and the continuous oil pressure of the oil pressure chamber.
The gear pump for the loader is a double pump. One drive shaft drives two driven gears to work, and there are two oil suction chambers and two oil discharge chambers.
At present, the domestic loader hydraulic system is basically a quantitative hydraulic system. The so-called quantitative hydraulic system means that the displacement of the hydraulic pump is unchanged, mainly gear pump; There are also some export models, which adopt vane pump because of the high requirements for the noise of the whole machine abroad; The remaining few models are equipped with variable hydraulic system, which is basically equipped with variable piston pump.
2. Plunger pump
When the engine drives the transmission shaft to rotate, the connecting rod pushes the plunger to move back and forth in the cylinder block. At the same time, the side of the connecting rod drives the piston to rotate together with the cylinder block, and the oil distribution plate is fixed.
During operation, under the action of cam and plunger spring, the plunger moves up and down repeatedly to complete the oil pumping task. When the convex part of the cam rotates, under the action of the plunger spring, the plunger moves downward, and the space above the plunger is the pump oil chamber to generate vacuum. At this time, the oil inlet on the plunger sleeve at the upper end of the plunger will open, and the hydraulic oil in the oil passage on the oil pump enters the pump oil chamber through the oil inlet hole. The plunger moves to the bottom, and the oil inlet is completed.
When the camshaft turns to the convex part of the cam to jack up the rolling element, the plunger spring is compressed, the plunger moves upward, the hydraulic oil is pressurized, and part of it flows back to the oil chamber of the upper body through the oil hole. When the top surface of the plunger covers the oil inlet hole, due to the small matching gap between the plunger and the cylinder liner, the oil distribution chamber at the top of the plunger becomes a sealed space. 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, push out the hydraulic pump, and the high-pressure liquid enters the oil cylinder through the main operating valve.
When the plunger supplies oil, the low-pressure oil circuit of the pump oil chamber is communicated with the middle hole and the inclined groove of the plunger head, the oil pressure drops, and the oil outlet valve is closed under the action of the spring to stop oil supply. The plunger continues to go up. When the convex part of the cam turns over, under the action of the spring, the plunger goes down again to start the next cycle.
