There is no “rigid” kinematic connection between the centers of the rotors of the orbital hydraulic motor, which leads to non-standard changes in its output characteristics. A kinematic diagram of the movement of the rotors of an orbital hydraulic motor was developed, which made it possible to substantiate the kinematics of movement of its rotors and analyze the change in output characteristics. Abnormal changes in the output characteristics of this type of hydraulic motors are changes in the overall efficiency and changes in the angular speed of rotation of its shaft. When the gap between the rotors changes in the range of 0 to 0.4 mm, the overall efficiency of the positive displacement hydraulic machine decreases 3.6 times, which is explained by the increasing pour over between its rotors. The high value (0.92) and constancy of the volumetric efficiency of the orbital hydraulic motor is explained by the property of its rotors “self-sealing” in the process of moving, eliminating overflows. A decrease in the angular speed of rotation of the shaft of an orbital hydraulic motor 35 to 27 rad/s, with an increase in the gap of 0 to 0.4 mm, is explained by additional displacements of its inner rotor.

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