Research On Closed-loop Travel System Of Skid-steer Loader

Accompanied by the constantly expanding demand for high-response,high-precision and high-power hydraulic system in many industrial sectors andtechnological fields, the hydraulic drive technology has become more mature. Theskid-steer loader as the represented in the compact construction machinery field hascommonly adopted the hydrostatic transmission technology. As one of the corehydraulic system in the skid-steer loader, the closed-loop travel system dynamicquality has an important impact on the security, reliability and maneuverability of thewhole construction vehicles. Therefore, the key technology is to study how toimplement the quick response, precise control and steady work performance ofskid-steer loader.However, for the domestic skid-steer loader manufacturing enterprises, theresearch on dynamic characteristics of closed-loop travel system is still in its infancy,their design goal is to complete the implementation of the agency action cycle andmeet the system static performance requirements. This design method which based onstatic calculation tend to make the system in an unstable state, leading to theoccurrence of phenomena such as engine flameout.This dissertation is funded by the school-enterprise cooperation project"Research on loader hydraulic and transmission system analysis and dynamicsimulation comparative tests". Analyzed the dynamic characteristics of closed-looptravel system which is widely used in skid-steer loader, adopted the transfer functionmethod to derive the mathematical model as the theoretical basis, relied on theAMESim (Advanced Modeling Environment for Simulation of engineering systems)simulation software as a platform for dynamic analysis, combined with experimentalverification as the research ideas, then analyzed the main factors affecting thedynamic characteristics of the closed-loop travel system.The integrated research work mainly includes the following aspects:(1) Based on the characteristics analysis of the pump-control-motors andclosed-loop systems, the working principle of skid-steer loader travel system waselaborated. Due to the unreasonable power matching for construction machinerywhich caused issues such as flameout, discussed the technical principles of the fill-oilsystem and DA-control strategy to solve the related problem theoretically.(2) After creating the servo feedback mechanism of variable displacement pump and the closed-loop system mathematical model, the overall system transfer functionblock diagram was derived based on the principle of closed-loop travel system.Through qualitative analysis on the structural parameters of travel systems whichaffect dynamic characteristics shows that: Reduce the variable displacement pumpspool flow gain and pressure-flow variation coefficient of servo spool valve, increasethe spring stiffness conducive to improving the stability of the system pressure;Increase fluid bulk modulus or decrease the variable pump displacement gradient andthe DA orifice diameter conducive to improving the systems response characteristics.(3) Relying on the AMESim simulation software platform, created simulationmodel including the variable displacement pump with position servo feedback, theengine with speed regulation output characteristic, the DA-control valve with speedsensor features, and the overall system of skid-steer loader travel system. Through thebatch simulation of the component parameters, explicit the variable displacementpump servo control mechanism, the dynamic load and the main loop fluid affected onsystem dynamics, and verified the correctness of theoretical analysis. Aiming atseveral typical operating conditions of skid-steer loader, compared simulation curveand experimental curve parameters, verified the simulation model accuracy as well asprovided a method for follow-up optimization performance evaluation.(4) The experimental test program for skid-steer loaders of dynamic performanceof travel system was designed, Tests had been conducted on the factors such as servocontrol signals and displacement of variable displacement pump, the mechanical loadand so on, the experimental results verified the correctness of the related theoreticalanalysis. Proposed to adopt DA-control strategy to solve the problem of flameoutexisted in skid-steer loader. The experimental test shows that the optimizationprogram can effectively avoid the occurrence of travel system flameout phenomenon,ensure the stability and reliability of the systems.