Investigation Into The Vibration Reduction Of The Flow-amplifier Type Steering Hydraulic System On Loader

Hydraulic steering part is one of the most important systems for loader.It directly impacts on safety,operational efficiency,energy consumption and operating comfort.In this thesis,theoretical analysis,numerical simulation and experimental study are used to investigate the performance of the flow amplifier valve used in the flow-amplifier type steering hydraulic system for large wheel loader.Vibration mechanism is analyzed. Based on the orifice optimum design of the flow amplifier valve,the vibration reduction method is put forward.Numerical simulation and test results show that the new flow amplifier valve reduces vibration obviously,thus the steering hydraulic system has good control performance,good operator comfort and some energy-saving effect.The main content of this thesis:In chapter 1,the background and significance of this thesis is presented.The history and current research progress on hydraulic steering system of wheel loader are reviewed.Lastly,the main research subjects are presented.In chapter 2,the characteristics and shortcomings of two pilot oil supply modes for the amplifying flow hydraulic steering system of loader are analyzed and corresponding solutions are put forward.The vibration mechanism of the enlarging flow hydraulic steering system is analyzed.Based on optimum design for orifice of the flow amplifier valve,a kind of vibration reduction method is put forward.In chapter 3,the orifice area of the flow amplifier valve is studied by numerical analysis.The characteristic curve of the orifice area is obtained and the idea of the orifice area magnification in the flow amplifier valve is proposed.The numerical results show that the orifice area curve and area magnification of the pilot valve in the new flow amplifier valve have good monotonicity and linearity.In chapter 4,the inner flow field of the flow amplifier valve is analyzed by numerical method.The results show that,under same working conditions,the axial and radial force on the main spool of the new flow amplifier valve is smaller than those of others.Due to lower starting acceleration,the vibration in the hydraulic steering system is reduced efficiently. In chapter 5,the mathematical model for the closing process of the main spool is built.The software MATLAB/Simulink is used to analyze the impacts of some factors on the closing process of the main spool.The results show that the closing speed of the main spool is very fast at the beginning,which acts 88.5%of the whole stroke within about a quarter of the closing time,then it slides slowly to its center position.It is concluded that the orifice area of the pilot in the main spool is the key factor to the closing process,and the closing time is very sensitive to the configuration of the pilot orifice area.In chapter 6,the enlarging flow hydraulic steering system is tested on the loader. The results show that the new flow amplifier valve reduces vibration obviously,thus the steering system has good control performance,good operator comfort and some energy-saving effect.At the end,some conclusions in this thesis are summarized and the future research proposals are suggested.