| Summary: | The paper is focused on the issues of controllability of machine-tractor units based on wheel-type tractors during their non-straight driving on the soil surface, which is positioned at an angle to the horizon. There were obtained analytical expressions for the determination of the actual indicator of control λd, including both the power and the design parameters of the machine-tractor unit, which affect the abovementioned indicator in the longitudinal vertical plane. These expressions are obtained for the tractor driving on both road and also driving during field operation. In addition, the paper discusses the conditions under which there may occur the cross-slip of the tractor steering wheels in the transversal horizontal plane. As a result of this review, there were obtained the analytical expressions for determining the required indicator of the controllability λd of machine-tractor unit in the horizontal plane, excluding the possibility of lateral sliding of the unit by turning its steering wheels at a certain angle. These expressions are obtained for the two modes of the machine-tractor unit: for driving during transport on the road and during the operation in the field. The machine-tractor unit based on the wheel-type tractor with rear mounted 3-mouldboard plough was analytically investigated. By means of computer calculations, there was observed the fact that when moving in non-straight direction on the soil surface, inclined to the horizon at an angle of 12°, the machine-tractor unit is controllable only when the angles of the steering wheel of the given tractor do not exceed 9°. During the working movement (ploughing) of the given machine-tractor unit on an inclined field surface, its controllability will be preserved on condition that the angle of the tractor steering wheels does not exceed 11°. According to obtained results, it can be stated that the controllability of the machine-tractor unit is determined by the indicator of controllability, taking into account the value of the vertical load acting on the tractor steering wheels, the possibility of their turning in the horizontal plane, as well as the withdrawal of the machine-tractor unit from rectilinear motion and its movement on the field surface, inclined at an angle to the horizon.
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