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To ensure high productivity of grain production reliable operation of grain cleaning equipment is required. The process of cleaning seed material is connected to significant vibration loads some of which have an impact on the separation process and the operational reliability of the machine components. To combat harmful vibrations a theoretical analysis of the beats occurring during the sieve separation of grain was made. The law of motion of the mass center of the sieve pan is derived as a function from time over a period of oscillating. The analytical solution of the obtained equation allows determining the horizontal and vertical displacements of the mass center at every moment of time. Based on this motion, accelerations and related inertial forces are determined. These forces take on sufficiently large values, which lead to beats of the indicated separation devices. To determine the forces leading to these beats, using the d’Alembert’s principle, equilibrium equations are compiled, the solution of which allows determining the total horizontal force and reaction force in the suspension. The equations of equilibrium include the forces of tension on bending of the suspension rods. It has been established that a rational choice of the geometric characteristics of these suspensions can significantly reduce the forces acting on the drive of the sieve pan and, as a result, on the horizontal and vertical runouts.

The most complete idea of the stability of the curvilinear motion of a tractor is given by the nature of the change in the trajectory of motion of its kinematic center and the coordinates of the turn: the abscissa and ordinate of the headland, showing both the transverse and longitudinal deviations of the machine-tractor unit, including those determining its productivity and the required quality of agricultural operations. According to the operating conditions, the methods of motion of the unit are chosen, both on the main array of the field and on the headland. The paper presents explicit equations for the analytical calculation of the theoretical coordinates of the points of the kinematic center trajectory of the tractor when it performs a circular loopless rotation, which allowed determining the theoretical trajectory of a complete cycle of circular loopless rotation of a tractor depending on the following parameters. These parameters are as follows: design - base, distances between the axes of the pivots, maximum angles of rotation of the internal wheels; operational - forward speed of a tractor, the angular speed of the steered wheels in the transverse plane. The author made the attempt to analyze and compare the most universal ways of turn: the front steered wheels and the front and rear steered wheels by turning them in different directions relative to the core.

One of the ways to increase the stability of movement and improve the manoeuvrability and controllability of a wheeled universal row-crop tractor in curvilinear motion is the choice of a rational turning method. To solve the tasks, the authors proposed a combined method of turning the tractor, which consists in crabbing in the entry into the rotation, after which the rear wheels automatically return to the neutral position and then the direction of movement in the established rotation and exit from the rotation uses front steering wheels. The article developed a methodology for determining the theoretical trajectory of the centre of mass of a wheeled tractor with a combined method of rotation for the three distinct sections of the movement included in it. Based on the conditions of smoothness and continuity, we glued together three characteristic sections of the curvilinear trajectory of the centre of mass and obtained a continuous non-linear piecewise smooth function of the investigated combined rotation method. It is possible to apply the research results for theoretical calculations of the parameters for the curvilinear motion of tractors, as well as other wheeled vehicles, that allows choosing rational laws to change the speed and control modes of turning the wheels, to identify the patterns of change for ensuring the necessary stability, manoeuvrability and controllability and confirming effectiveness in comparison with known and previously investigated laws.