In this study, in order to review the structural stability of a Sub-frame assembly mounted on a 5-ton dump truck with a telescopic cylinder type that can secure price competitiveness through cost reduction effect and an extended loading box that satisfies automobile safety standards, the 3D shape design technique for a main component parts is presented. In addition, structural analysis based on the finite element method is performed with the load condition applied to a safety factor 3.0 and boundary condition assigned to the lower part of the Sub-frame. By comparing and examining the maximum stress result from the structural analysis of the entire Sub-frame assembly and individual component and a yield strength of each material applied to each component, a design technique that can assure the structural stability of the Sub-frame assembly is presented.

The multistage double acting oil pressure cylinder can overcome limits of a stroke of cylinder. Development target of the multistage double acting oil pressure cylinder makes a overcome operation distance, in the case of transport of bodies or tension, contraction working. It's structure is composed that fluid flow pipelines are inserted in the cylinder. In the serial arrangement of reciprocating cylinders, the multistage double acting oil pressure cylinder can prevent a buckling or cylinder loss because assemble arrangement is simple type of insertion way. Using the MSC.Visual Nastran, the 3D simulation was executed. Through the 3D simulation, we ascertained that the multistage double acting oil pressure cylinder could be adapted to a elevation system.