ENGINEERING FOR RURAL DEVELOPMENT MODEL OF HYDROPNEUMATIC THREE POINT HITCH

Abstract. This paper presents a model of a hydropneumatic three point hitch system for farm tractors. A model of hydropneumatic three point hitch is derived to suit the control task of oscillations damping of the tractor aggregate. The reaction forces of the tractor hitch system hydraulic cylinder were determined, corresponding to different weight positions of the implement. The hitch mechanism is divided in three kinematic groups (unit of upper link and implement, unit of lift arm and unit of lower link) for calculations. From the simulation with the program Working Model it was established that the tractor hitch system lower link and mounted soil cultivation tool at low amplitude oscillations during transport can be simplified as a single beam. The necessary stiffness characteristics for beam suspension, depending on the implement weight and its position, were determined. Uses of hydraulic accumulators were provided for obtaining different stiffness characteristics of suspension. The volume and necessary charge pressure were determined for hydraulic accumulators. Keywords: hydropneumatic hitch, hydraulic accumulators. Introduction During tractor movement, with attached to the hitch-system working equipment (plough, harrow), over rough road surfaces oscillation of the machine takes place. These oscillations are a reason of pressure pulsations in the hydraulic hitch-system. The previous experiment [1] presents results of pressure oscillation investigation in the hydraulic hitch-system of the tractor Claas Ares ATX 557 during the motion around an artificial roughness test road. During the experiments oscillations at the different driving speed, different tire pressure, loading weight position and hitch-system oscillation damping (turned on/off) were investigated. The results of the experiments present maximum pressure peaks of 170 bar in the tractor hydraulic system. The hydraulic hitch-system with hydropneumatic accumulators allows adjusting the stiffness and damping characteristics of the hydraulic cylinder, limiting the pressure oscillation amplitude. In order to reduce the pressure maximal values during oscillations, a mathematical model of tractor hydraulic hitch system with hydropneumatic accumulators was developed. The mathematical model for the implement on the hitch system was simplified to the model of a single beam with different weight and moment of inertia. The results of calculations were compared with the results of the experiments