Cycloid pump type and naming 

 The cycloidal rotor oil pump is an internal gear pump with a special tooth profile. 

 The internal gear ( outer rotor ) and its internal external gear ( inner rotor ) are engaged and rotated with each other. The tooth shape is formed according to the swing trajectory of the cycloid, so it is named after the scientific name of its trajectory, which is called cycloid pump.

The inner and outer rotors differ by one tooth. In Figure 1, the inner rotor is six teeth and the outer rotor is seven teeth. Because the inner and outer rotors are multi-tooth meshing, several sealing volumes are formed. When the outer rotor rotates around the center O2, the inner rotor rotates around the center O1 of the inner rotor in the same direction. At this time, the sealing volume C formed between the inner rotor tooth top A1 and the outer rotor tooth valley A2 ( the shade line part in Fig.1 ) gradually expands with the rotation of the rotor, so a local vacuum is formed. The oil is sucked into the sealing chamber from the oil distribution window b, and the sealing volume is the largest when it reaches the A1 ' and A2 ' positions. When the rotor continues to rotate, the sealing volume filled with oil gradually decreases, and the oil is squeezed, so the oil is discharged through another oil distribution window a, until the other teeth of the inner rotor are all engaged with the tooth concave A2 of the outer rotor, and the oil pressure is completed. Each rotation cycle of the inner rotor, each sealing volume composed of the tooth top of the inner rotor and the tooth valley of the outer rotor, completes the suction and pressure oil each time. When the inner rotor continuously rotates, the suction and discharge of the hydraulic pump is completed.