Today, the hydraulic drive is increasingly used in agricultural machinery as motion drives, drives of working bodies, and drives of control systems. The power source of this type of drives is pumping stations based on piston-type pumps. This type of pump units has a number of advantages and disadvantages compared to gear pumps. The advantages include power, reliability, higher efficiency, the ability to smoothly regulate the flow of working fluid, and the disadvantages include increased requirements for the degree of purification of working fluids.
The article reviews known hydraulic schemes of agricultural machines, analyzes them, and identifies their advantages and disadvantages. One of the elements of these hydraulic systems is the pump supply control system depending on the load on the working bodies of the hydraulic system elements. The correct choice of the parameters of the elements of this system has a significant impact on the quality of its work as a whole. In order to study the influence of system parameters, the structure and principle of operation of the system for regulating the supply of the working liquid of the axial-piston pump are described, the coordinates of the movement of the center of the reduced force from the action of the plunger pairs on the cradle of the control system for the supply of the working liquid are calculated. The trajectory of its movement along the plane of the feeding adjustment cradle is determined. The proposed dependencies make it possible to determine the magnitude of the moment acting on the cradle depending on the magnitude of the eccentricity. it was found that the point of application of the combined force to the end of the cradle moves along a loop-like trajectory, symmetrical to the axis, parallel to the axis of rotation of the cradle. At the same time, the magnitude of the moment of the combined force acting on the cradle has a cyclic nature, the periodicity of which is determined by the angle of rotation of the cylinder block by a value equal to the angular distance between adjacent cylinders. The frequency of fluctuations of the moment of the combined force when rotating the cylinder block of the PVC 1.63 pump with a frequency of 1500 rpm is 450 Hz, which requires the development of measures to eliminate their negative impact on the operation of the pump supply regulator.
The moment of combined forces acting on the cradle from the side of the cylinder block depends on the pressure in the pump discharge line and the angle of rotation of the cylinder block. At a nominal pressure of 25 MPa, the range of fluctuations of the combined force moment acting on the PVC 1.63 pump cradle reaches 290 Nm. If the axes of the cylinder block and the trunnion of the cradle are in the same plane, the moment of combined forces acting on the cradle will change symmetrically relative to the axis of rotation of the cradle and periodically cause it to deviate in opposite directions. This nature of the load of the cradle interferes with the process of adjusting the angle of its inclination and, accordingly, the working volume of the pump.
In order to reduce the negative impact of the moment of the combined force on the quality of the regulation of the supply of the working fluid of the PVC 1.63 pump, it is recommended to introduce a shift of the axis of rotation of the cradle relative to the axis of the cylinder block by 5 mm.
