Research On Heat Dissipation Performance Of Oil Tank For Hydraulic Exoskeleton Robot

Hydraulic exoskeleton robot is an assistant tool used by many research institutes in the military field to help soldiers lighten their burden and enhance their individual combat capability.Its hydraulic system is faced with the problem of high temperature of hydraulic oil in the working process.Excessive oil temperature will lead to the decrease of oil viscosity,lubrication performance,volume efficiency and control performance.For hydraulic-driven exoskeleton robots,the size of the hydraulic tank is small because of the limitation of operating conditions.The heat dissipation of the hydraulic tank will directly determine the operation status and performance of the exoskeleton robots.The poor heat dissipation of the oil tank may cause the exoskeleton robots fail to work properly.Therefore,it is very important to adopt a reasonable heat dissipation structure for the long-time operation of the hydraulic exoskeleton robot.Through theoretical analysis of the heat dissipation principle of the oil tank and general measures to strengthen heat dissipation,the influence of structural parameters such as fin thickness,fin spacing and fin height on the heat dissipation performance of the oil tank has been studied by using CFD.Then the structure of the fuel tank is further optimized according to the field synergy principle.Finally,a new finned oil tank structure is proposed.It provides a reference for the optimal design of hydraulic tank.The main contents of this paper are as follows:(1)According to the requirements of structure,operation characteristics and control strategy of exoskeleton robot,the schematic diagram of hydraulic system has been designed.The geometric model of exoskeleton knee joint has been established to determine the position of hinge fixing point of hydraulic cylinder.Referring to CGA data,the parameters of hydraulic cylinder motion stroke and velocity have been obtained by using MATLAB software to analyze the angle and moment curve of knee joint.And the inlet parameters of hydraulic tank simulation are further calculated.Selection and design of main parts such as hydraulic cylinder,hydraulic pump,servo valve and hydraulic pipe have been done.(2)Through theoretical analysis of the heat dissipation principle of the hydraulic oil tank,the ways to improve the heat dissipation performance of the oil tank have been determined: increasing the heat dissipation area of the oil tank and improving the convective heat transfer coefficient of the oil tank.Referring to the commonly used measures to enhance heat transfer of oil tank and the limitations of operating conditions,the scheme of optimizing the structure of oil tank has been adopted to improve the heat transfer performance of oil tanks.The heating power,heat dissipation area and oil temperature rise of the hydraulic system have been calculated theoretically,and the inlet temperature parameters of the hydraulic oil during the simulation have been obtained.(3)An optimization structure model of oil tank has been proposed.Taking this model as the research object,a CFD-based heat transfer calculation model of oil tank has been established and its heat dissipation process has been simulated.The simulation results show that the oil temperature at the oil suction port of the optimized oil tank decreases significantly and the heat dissipation effect of the oil tank improves significantly.(4)The fin structure,widely used to enhance heat dissipation,has been applied to the oil tank.According to the geometric parameters of the fin structure,a simulation model has been established.The influence of fin spacing,fin height and fin thickness on the heat dissipation performance of the oil tank has been studied by using CFD software,and the fin structure parameters with the best heat dissipation performance have been obtained.Then,according to the principle of field synergy,the structure of finned oil tank has been further optimized by means of opening a circular hole in the area where the field synergy is poor.The simulation results show that the opening method can further improve the heat dissipation performance of the oil tank,save materials and reduce the weight of the oil tank.Finally,the optimized structure of the final oil tank has been obtained,which can be used as a reference for the design of the hydraulic oil tank.