This is a hydraulic motor using inscribed gear, smaller than other motors, and can be operated at low speed as well as at high torque with the same output and powerful for radial and thrust load.  

This motor is composed of the following major components: a rotor-set, rotary valve, valve plate, drive shaft, and output shaft. The rotor-set (drawing-1) is composed of an outer rotor (5) fixed to the body and an inner rotor (6) biting at the inner side. Outer rotor has seven teeth and inner rotor has six teeth. The pressurized oil will flow in the following order: port, rotary valve(12), valve plate(13), and tooth chamber of the rotor-set. Half of the tooth chamber composed of the outer and inner rotor is connected to the high pressure side and the rest to the low pressure side (return side). The inner rotor will rotate in the direction where the volume of the tooth chamber increases. The relative position of the rotary valve and valve plate will be varied simultaneously with the rotation of the output shaft, and position of the pressurized oil in the rotor-set will also be varied. These rotations can be divided into (a) the orbital motion and (b) spin motion.  In this system only the spin motion can be transmitted, through the drive shaft, to the output shaft. The revolution of the inner rotor, as indicated in the drawing-2, will be the inversion of the teeth number of the inner rotor, that is 1/6 per one orbital rotation of the inner rotor. Therefore, the output torque will be 6 times that of other general hydraulic motors; so the result is the same as if a reducer (1:6) is fixed with the hydraulic motor; and that is the reason of low rotation and high torque.