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Design and analysis of a novel electrohydraulic draft control system in agricultural machinery

Karakoç, Emir Murat
A three-point hitch system is a mechanism that controls the movement of various agricultural equipment. Connection dimensions between the equipment and working range of mechanisms are defined by standards. The mechanism is actuated by hydraulic cylinders and the required hydraulic power for movement is provided by a hydraulic pump. Constitutively, there are two types of methods to control the three-point hitch mechanism. Draft control is a type of control mechanism that ensures the tractor not to slip and minimizes the inefficiencies. The force applied from equipment to the tractor depends on the equipment depth, soil characteristics, and vehicle velocity. An excessive amount of load may cause slippage on tires, even stopping the tractor during tillage operations. In order to prevent this situation, draft control adjusts the depth of the three-point hitch mechanism under the soil according to the force value from the ground during the tillage process. As for the position control, the control mechanism arranges the height of the mechanism according to the given angle input. In this study, a three-point hitch draft control system is examined. Solid model of the three-point system is constructed by using computer-aided design software, PTC Creo 3.0® (CAD) and transferred to MATLAB®. With the transferred model, the tractor's hydraulic system consisting mainly of pumps, valves and cylinders, position and draft sensors and the controller are modeled, and the resulting system is created by using MATLAB Simulink module. Established kinematic equations of the three-point hitch mechanism are validated with ADAMs® simulation software. The aim of the thesis is to control the pulling force by the measured pressure transmitted to the main external lift cylinders, instead of using a force sensor, as opposed to the application in existing tractors. Simulations of the current model with force sensors and the simulations of the proposed model with pressure sensors are performed and the feasibility of the proposed scheme is discussed in detail.