| Construction vehicle is used extensively for the constructions, such asbuilding, mining, highway, railroad, port and the military engineering etc. Theyhave important function to ease the labor intensity and lower the engineeringcost, and relate directly to the national construction project. The workenvironment of the engineering machine is worse and the load is continualvariety, so the engineering machine requires higher efficiency in energy usingand transition. It is importance to raise the economy energy, operability, safetyand the driver's comfort of the engineering machine.Generally, automatic transmission of the engineering machinery is requiredto improve the performance of the power system because of their rugged,complicated and variable working conditions. The transmission system ofengineering machinery is generally hydrodynamic-mechanical transmissionsystem to improve the adaptive abilities to load. The control system forhydrodynamic-mechanical transmission can adjust ratio automatically accordingto the change of work condition, so it is able to achieve variable transmission ina certain rang. But transmission ratio is not continuous between the multi-rang.In the course of changing shift, there is impact to make driver feeluncomfortable, and rotation speed of the engine is unsteady that the exhaustionof the waste gas can be increase. In addition, the efficiency ofhydrodynamic-mechanical transmission is lower, thus the power and economicfeatures of construction vehicle are affected largely.The hydraulic transmission can provide the stable speed, and can be controlaccurately that variable transmission is able to come true. But the efficiency ofhydraulic transmission is lower. Hydraulic transmission of high-powerconstruction machinery vehicle is replaced by hydrostatic-mechanictransmission which has the perfect performance of continuously variabletransmission and could realize the large power transmission high efficiently.Hydrostatic-mechanic transmission makes the most of the power of engine andguarantees the driver to be comfortable at the same time. Hydrostatic-mechanictransmission has become leading direction in high-power constructionmachinery developing.Tied with the above discussion and analysis, the dissertation, aiming at theproblems of that the drive ratio of construction vehicle is discontinuity and thetransmission efficiency is lower, investigates the design of hydrostatic-mechanictransmission system. By incorporating the engine, hydrostatic-mechanictransmission gear-box and load to a dynamic system, the theoretical research ofthe performance in power and the economic features was carried on. In pursuitof promoting utilization ratio of power on vehicular transmission, thedissertation has designed the control system which controlled the pump toconstant rotation by adjusting pump displacement according to the changingrotation of engine. Study of this dissertation is as following:(1) The dissertation analyzes the evolution background and present researchsituation of hydrostatic-mechanic transmission technology in vehicle overseaand inland. And the application productions of the variable transmission inconstruction machinery are introduced. The key technology ofhydrostatic-mechanic transmission system is analyzed, and then thedevelopmental orientation of hydrostatic-mechanic transmission for vehicle ismade certain.(2) Aiming at the transmission demand for construction vehicle, a schemeof hydrostatic-mechanic transmission was designed, and the characteristics wereanalyzed. The control method used in the course of the transmission system hasgenerally summarized. According to working conditions and characteristics, thematching method for the co-operation characteristic of engine and variety ofload is developed. The control scheme can improve the power performance andeconomic feature of construction vehicle. The control methods for components,which are controlled, are analyzed.(3) According to various load and characteristics of transmission system,the dissertation introduces about using intelligence fuzzy controller to controlpower to constant for promoting utilization ratio of power. Fuzzy controllerleaves alone a precise model under traditional control theory.(4) The dissertation has set up mathematics model and transmitted functionof engine, variable volume pump, valve and cylinder, and also has simplified themodel according to request of the simulink. By means of computer simulation,the computer models of intelligent control on hydrostatic-mechanic transmissionfor construction vehicle are set up. The computer Simulink experiment was usedsimulink module of Matlab on the control system. The simulink result indicatesthat the fuzzy control system is effective to steady rotate speed of the enginewhen load has variety.(5) The insufficiencies which can be perfected in the future are pointed outin the dissertation.The dissertation validates the control system of hydrostatic-mechanictransmission is reliable. The fuzzy control strategy aiming to improving theefficiency of transmission is feasible.
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