TIRES PULL FORCE OF A TRACTOR IN THE 4X2 AND 4x4 SCHEMES WHEN IT MAKES A TUR

For developing the pull force, the tractive elements from the tractor generate slippage due to the adhesion between the tire and the soil. When the tractor moves straight forward, the pull forces and slippages do not change in the rear tires in the 4x2 scheme, neither the rear nor front tires in the 4x4 scheme. As the tractor makes a turn, these parameters change up to generate an instability torque, so that the engine has to develop a torque to overcome it and the driver has to keep forcibly the turn of the tractor toward the indicated side. In this work, were developed the equations to determine the tires pull force and slippage, according to turning radius for tractors having engaged the differential (4x2) and connected the front axle (4x4), considering the sum of the tires slippages, which corresponds to the total pull force developed by the tractor. The results indicated that while the tractor made a turn, as the turning radius decreased, the tire pull force and slip increased in the inner tire (4x2) and rear tire (4x4) and decreased in the outer tire (4x2) and front tire (4x4). For each total pull force needed, there was a limit condition to disengage the differential (4x2) and disconnect the front axle (4x4).