Gear pump type characteristics
2.1.1 type characteristics
(l) Classified gear pump is a hydraulic pump based on meshing principle. It is a kind of hydraulic pump with the simplest structure, the lowest price, the largest output and consumption in modern hydraulic technology. Its detailed classification is shown in Figure a. Among all kinds of gear pumps, because the gears of standard involute external meshing spur gear pump are easy to process and detect, they are most widely used. This kind of gear pump mostly uses a pair of gears with the same parameters, only a few special pumps have three or more gears.
(2) The characteristics are shown in the table below.
Characteristics of gear pump
主 要 缺 点
2.1.2 working principle
(1) Working principle and some key problems of involute external gear pump
① Working principle most involute external gear pumps use a pair of gears with the same parameters, and some special pumps have three or more gears.
Figure B shows the working principle of an involute external gear pump with a pair of gears. The driving gear 4 and driven gear 7 with the same geometric parameters are meshed in a sealed space composed of tooth profile, housing 1 and side cover plate. The housing 1, the side cover plate and each tooth Valley (between teeth) of the gear form many sealing working cavities 5. The gap between the top of the gear and the surface of the inner hole of the shell and between the end face of the gear and the side cover plate is very small, and the contact surface of the meshing teeth is in close contact, which plays a sealing role and separates the oil suction and pressure areas (distribution function). When the prime mover drives the driving gear 4 and the driven gear 7 to run in the direction shown in the figure through the transmission shaft 3, the volume between the teeth in the oil suction chamber 6 becomes larger due to the meshing separation of the teeth, resulting in a vacuum and sucking oil from the oil tank 8; the oil absorbed is carried to the oil pressure chamber 9 by the rotating Valley (between the teeth); and the oil pressure is sent to the system in the oil pressure chamber due to the reduction of the volume between the teeth. The pump shaft rotates for one circle, and each working chamber sucks and presses oil once. When the prime mover drives the pump to run continuously, the pump will press oil continuously and periodically.
(2) Working principle of involute gear pump
The working principle of involute internal gear pump is the same as that of involute external gear pump. As shown in Fig. I, a driving gear 1 and a larger driven gear (internal gear ring) 2 form a meshing pair, and both rotate in the same direction. The crescent plate 3 separates the oil suction chamber 4 from the oil pressure chamber 5. When the oil suction chamber is disengaged from the meshing, the volume between the teeth increases, forming a vacuum, and the oil enters the oil suction chamber under the action of atmospheric pressure to fill the teeth; when the two gears in the lower part of the oil pressure chamber enter the meshing, the volume between the teeth decreases, and the oil is hydraulically discharged.
Like the high-pressure external gear pump, the high-pressure internal gear pump can use the end clearance and radial clearance compensation to improve the volumetric efficiency, and its maximum working pressure has reached 32 MPa.
(3) The working principle of cycloid gear pump cycloid gear pump is also known as rotor pump, its tooth shape is cycloid, the outer rotor has one more tooth than the inner rotor. The working principle of cycloid gear pump is shown in Figure J. The shell 6 is provided with an oil suction port 7 through the oil tank and an oil pressure port 8 through the system. The outer rotor 4 has one more tooth than the inner rotor 2, and there is eccentricity e between the inner and outer rotors. During operation, all the teeth of the inner rotor are engaged. The meshing lines of the adjacent teeth, the shell and the oil distribution plates on both sides form several closed working cavities. As the inner rotor rotates clockwise around center 01, the outer rotor rotates at different speeds in the same direction around center 02.
The volume of each chamber changed. Therefore, the oil in the chamber is absorbed and pressed through the oil distribution plate oil suction window 5 and oil pressure window 3.
Like the external gear pump, the medium and high pressure cycloid gear pump adopts the end clearance compensation to improve the volumetric efficiency, and its maximum working pressure can reach 16MPa.