A Special Transport Vehicle Hydraulic System Simulation Studies

Taking a special transport vehicle as the research object and the hydraulic lifting system as the principle line, the theories and methods of simulation of hydraulic system was discussed.Firstly, the total frame and function of the vehicle was analyzed, the hydraulic system was divided into three subsystems including HST, steering, lifting, and the engine power was distributed to the subsystems by gear distribution box. Then the finished vehicle hydraulic principle was researched. Closed circuit of flow coupled consisted of Variable pump and variable motor was used in The HST system. A load-sensing hydraulic pump was used in both steering and lifting systems, what's more the static loading-sensing hydraulic steering system including the completed hydraulic steering units and flow amplifier was used in steering system, the electro-hydraulic proportional control multi-way valve and the height electron feedback of the frame closed loop control was adopt to the self-equilibrium lifting in lifting system. The multi-way valve included two stages and the PWM on/off valve bridge displacement electron feedback closed loop control was used in determining the displacement of the host spool in pilot stage. Secondly, based on the basic hypothesis and rational simplification of the hydraulic systems, the simulation model was established in Easy5 software by choosing rational component models. Then, the steady state of all hydraulic systems was analyzed, including the kinematics and dynamics analysis and equivalent of actuators, in order to provided the rational boundary to the hydraulic system, the operation point including pressure, velocity etc. was calculated, so that the whole picture of working process was known and the parameter matching was checked, and the ranges was determined. At last, the simulation about dynamic performance was analyzed, the function and parameter matching of accumulator was analyzed, and the effect of some critical parameters on the overall performance of load-sensing system was investigated, simulation under different conditions of all hydraulic systems was executed, and the variation of some internal state variables was acquired. It was the most issue that must be cared was the stability in the hydraulic steering and lift system with the use of the load sensing and pressure compensation circuit. Specially, it would be unstable with the long pipe in feedback line and in entrance line, but the instability could be improved by increasing the resistance in feedback line and in pressure compensation line. The accumulators had good effect of absorbing shock in parallel with the cylinders in the hydraulic lift system. The motivation and the economical efficiency of the engine and the hydraulic system could be used to the full in the transient process by adjusting the displacement of the pump and motor rationally in the hydraulic driving system. The road wheel could response the change of the wheel rapidly, but a little slowing in starting process because of the long pipe which connected the steering units. The simulation results of all hydraulic systems manifested that the main could be used as the guidance for the debugging of the hydraulic systems, and be used as the theoretic foundation for improving and designing the hydraulic systems.