Analysis of lateral reactions of soil on tractor wheels when turning

The objective of the research was to determine lateral reactions on tractor wheels from the side of the support surface in the "entrance to the turn" and "steady turn" sections of the circular loop-free turn. The objects of research included a mounted combined broad-cut unit KRSH-8,1+NP-5,4+LTZ-155+SST-18 and kinematic ways of turning the tractor (front steerable wheels; front and rear steerable wheels when turning relative to the frame in different directions). The calculation was performed by using a mathematical model of the curvilinear motion of a machine-tractor unit in an interactive programming environment Matlab/Simulink. It was assumed that the transition from rectilinear motion to a trajectory of great curvature followed the same law of uniform rotation of the steering wheel and, consequently, the same law of rotation of the steering wheels. The authors have established the negative effect of turning the rear wheels on the controllability and stability of the movement of the machine-tractor unit. When turning four controlled wheels, the instantaneous turning radius decreases, but the intensity and magnitude of its deviation from the specified trajectory of movement increase. The lateral force also increases with an increase in the speed of movement due to an increase in the centrifugal force of inertia and the moment of resistance to rotation due to a more intense dynamic effect of the micro profile of the support surface. In the simplest case, when the wheels of the front axle are the guides, the magnitude of the lateral reaction occurring on its wheels when entering a turn at a speed of 0.68 m / s is 6.6...8.8 times higher than on the wheels of the rear axle, and at a speed of 1.37 m / s it is 2.0... 2.3 times higher . With all steerable wheels the following results were obtained: at a speed of 0.68 m/s it was 1.16...1.20 times and at 1.37 m/s it was 1.50 ...1.52 times higher. The resulting character of the change in lateral reactions and their redistribution along the tractor axes is due to the values and ratios of tangential traction forces, rolling resistance forces and vertical forces on the wheels, their rolling conditions, changes in the position of the center of gravity of the machine-tractor unit, accelerations of vertical vibrations and geometric characteristics of turning. In all calculation options a more uniform distribution of lateral forces across the tractor axles when entering a turn with all controlled wheels obviously contributes to better controllability and stability of the unit, despite the fact that the vertical load on the front axle is 1.56...1.63 times higher than on the rear. At the same time the most favorable conditions of rolling wheels and realization of traction force occur. Thus, it is not advisable to control the tractor only with the front wheels when turning with frontal aggregation. Therefore, it is reasonable to use the method of turning the front and rear wheels at all stages of a circular loop-free turn to create the most favorable conditions for improving controllability and increasing the stability of movement on turns.