Improving controllability of curvilinear motion of caterpillar tractors by installation of a differential rotary actuator and tracking system

The subject of the study is an industrial caterpillar tractor of the traction class within the range of 10... 20 t equipped with a hydro-mechanical transmission based on a hydrodynamic torque transformer and with a differential rotary actuator. We indicated the advantages of using a hydraulic rotary actuator and justified that the issue of ensuring stable machine motion along a trajectory with different radii is relevant. We presented a mathematical model of motion of a caterpillar machine with two power paths connected through a planetary geared linkage mechanism and a tracking system for maintaining the constant radius while the steering wheel position remains unchanged. We studied the transient processes in the hydrodynamic transmission and hydrostatic rotary actuator when the machine enters a turn or turns round. We determined boundary ground conditions under which a tractor maneuvers continuously while performing technological operations. We developed a tracking system algorithm which maintains the constant trajectory radius of machine motion set by the hand-wheel regardless of internal and external disturbance, such as a leakage in hydraulic machines, skidding of the caterpillar track mover and changes of ground. In case of disturbances, the stability of machine motion along the radius trajectory set by the hand-wheel is achieved by adjusting the pump swash plate of the hydraulic rotary actuator and taking into account two values: the rotation speed of the hydrodynamic transformer turbine and the trajectory curvature of machine motion on the terrain, calculated on the basis of the GPS data. It was established that when entering the turn with the top gear, the pressure in the hydrostatic drive of the rotary actuator is 1.5 times the steady-state value. When entering the turn on heavy-textured soil, it lacks ground grip for maneuvering. When starting to turn round on the ground with a coefficient of resistance to turning more than 0.7, the pressure in the hydrostatic drive line reaches 40 MPa. The simulated stabilizing system of the motion trajectory of a slow-speed tracked vehicle confirmed the accuracy in the control of curvilinear motion.