Investigation Into The Static And Dynamic Characteristics Of The Mass Flow Hydraulic Priority Valve

Hydraulic priority valve is one of the most important component on the load sensing hydraulic steering system, Inlet flux has been distributed to the steering circuit priority, and the others has been distributed to the hydraulic work circuit.the safe of the construction machine's diversion is impacted by the hydraulic priority valve directly, and the prominent loss of the power system is reduced by it. In this thesis, theoretical analysis, computational fluid dynamic (CFD) and static-dynamic analysis were used to investigate the hydraulic priority valve. Flow characteristics, pressure loss characteristics arid dynamic characteristic were analyzed. It was shown by numerical calculation that the numerical value of spring stiffness and pre-compression were bigger, the response to steering flow was more quickly, pressure loss of the valve was bigger. Methods and ideas of improve to the hydraulic priority valve were put forward.The main content of the thesis is as follows:In chapter 1, the background and significance of this thesis was presented. The working principle and current research progress on hydraulic priority valve and load sensing hydraulic steering system were reviewed. Lastly, the main research subjects were presented.In chapter 2, the orifice area of the hydraulic priority valve were deduce, and the variation curve of the orifice area can be obtained by the software Mathcad. The variation trend of the orifice area was decrease as the displacement of the spool when the displacement was less than 4.5mm, and the orifice area was magnify as the displacement of the spool when the displacement was more than 4.5mm. The pressure field, velocity field, and the spool's steady flow force can be calculated by using numerical analysis. The pressure loss of the valve was 1.41MPa when the inlet flow was 160L/min, the spool's steady flow force was bigger at the begin, and smaller as displacement.In chapter 3, the static mathematical model of the hydraulic priority valve has been founded, state parameter of the hydraulic priority valve under different condition were obtained by the program which was worked out, and the steering circuit's variation of the flow were analyzed under different conditions, priority valve has pressure compensation, to change the variation of the flow with steering gear is proportional to the open area, and the steering flow was impacted by the operating load. Reducing the variation of the steering flow and improving the sensitivity of the steering control can be obtained by adding the numerical value of spring stiffness and pre-compression, but also the pressure loss of the match oil window can be increased.In chapter 4, the model for the hydraulic priority valve has been founded with AMESim software, and the dynamic response curves under different conditions were obtained by the simulation. The dynamic characteristic of the valve under different conditions were obtained by analyzing and comparing the simulation curve. When the Steering Gear was in the medium, the larger of the orifice area, the larger of the Load pressure of the working circuit within a certain range, the smaller of the steering load, the bigger of the Bulk modulus Values, the Dynamic Response of the Hydraulic priority valve will be faster.At the end, some conclusions in this thesis are summarized and the future research proposals are suggested.