Among the hydraulic power units, the common hydraulic oil pumps mainly include vane pumps, gear pumps, and plunger pumps. Today, I will briefly talk about internal gear pumps.

There are two types of internal gear pumps: involute tooth shape and cycloid tooth shape. Its working principle and main features are the same as those of the external gear pump, except that the sizes of the two gears are different, and the moving internal gears rotate in the same direction at their respective centers.

Internal gear pump structure

In the involute internal gear pump, a crescent plate is installed between the pinion and the internal gear to separate the oil suction chamber and the oil pressure chamber. When the pinion drives the inner gear to rotate, the left half of the gear teeth are out of mesh to form a vacuum to complete the oil absorption process. The oil entering the tooth slot is brought to the oil pressure chamber, and the right half of the gear teeth are engaged to squeeze out the hydraulic oil, and the oil is discharged from the oil pressure port. Compared with the external gear pump, it has the advantages of small flow pulsation, more compact structure, light weight, low noise and high efficiency, and can also achieve no trapped oil phenomenon. The disadvantage is that the tooth shape is complex and requires special high-precision processing equipment.

In the cycloid internal meshing gear pump (also known as the cycloid rotor pump), the pinion and the internal gear differ by one tooth. When the pinion drives the internal gear to rotate, the teeth of all the pinions are meshed, forming several independent Seal the cavity, no need to set the crescent plate. With the meshing and rotation of the inner and outer gears, the volume of each sealing cavity changes, so as to absorb and press oil. It is characterized by compact structure, few parts, large working volume, high speed, smooth movement and low noise. However, due to the small number of teeth, the flow pulsation is large, and the gap leakage at the meshing position is large, so the working pressure of this pump is low (generally 2.5 ~ 7MPa), and it is usually used as an auxiliary pump for lubrication and oil replenishment.

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