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.

The technology of rotors manufacturing for orbital hydraulic motors causes a certain form error of the gear surface. This leads to oscillations of the diametrical gap between the rotors. Such oscillations have a negative effect on the change in the output characteristics of the orbital motor. The previous studies on the issue consider the interaction between the rotors of orbital hydraulic machines as a gapless (theoretical) connection. The authors do not take into account that between the rotors of the orbital hydraulic motor , there is no rigid kinematic connection. This allows the internal rotor to move randomly within the diametrical gap (self-aligning). The study led to the development of the mathematical models that describe the relationship between the design features of the rotors and the output characteristics of an orbital hydraulic motor. To simulate the oscillation of the diametrical gap, the limiting deviations for the form error of the rotor gear surfaces have been substantiated. Investigations revealed that fluctuations in the form error of the rotor gear surface have a significant effect on the variation of the diametrical gap. The limiting deviations in the form errors of the gear surface manufacturing enabled to eliminate the oscillation of the diametrical gap and to ensure stability of the output characteristics for the orbital hydraulic motor.

The reliability of orbital hydraulic motors which are used in mechatronic systems with a hydraulic drive for active working tools on self-propelled machinery is a pressing engineering problem. To increase the reliability, a specific design method was proposed. It required development of a mathematical apparatus and a calculation algorithm. The mathematical tools allowed to realize the method for determination of hydraulic motor reliability by simulating changes in a technical state of the rotors in a hydraulic motor. A program, which has been developed, enabled modeling the conjugation of external and internal rotors. The program implemented an algorithm for the sequence of calculating the parameters for the external and internal rotors. The proposed program made it possible to obtain a three-dimensional image of zones with admissible interfaces which ensure the efficient and reliable operation of orbital motors. The modeling of working capacity change for an orbital motor has established some dependence. The changes in the number of teeth and overall dimensions of the rotor in the investigated range enabled to develop a standard size range for hydraulic machines, which operate in mechatronic drive systems for active working tools on self-propelled machinery.

The output characteristics of a planetary (orbital) hydraulic motor could be significantly improved if the kinematic diagrams for its working fluid distribution system are chosen correctly and substantiated. Fluctuations in the flow of the power fluid cause pulsation in the cavity of the input pressure of the hydraulic motor. This results to vibration of the hydraulic system elements. Thus, the hydraulic motor can be considered as a source of pulsation which leads to functional failures of the hydraulic system. As they run at low rotational speeds with high torque, planetary hydraulic motors are commonly applied for a hydraulic drive in active working tools of self-propelled machinery. It has been established that one of the main components of a planetary hydraulic motor, which causes pressure puls ations, is its distribution system. The frequency and amplitude of these pulsations depends on the kinematic diagram for the distribution system of the power fluid. Therefore, we studied how the kinematic diagram for the distribution system effects on the output characteristics of a planetary motor. Since the change in the capacity of a distribution system with various kinematic diagrams influences on the output characteristics of a planetary motor, the impact was investigated. The kinematic diagrams, which improve the output characteristics of planetary hydraulic motors, were justified.

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