Study On Design And Performance Of Composite Mechanical And Hydraulic Drive System

At present,construction vehicles are widely used in road transport.In the highway maintenance engineering,construction vehicles should not only have the transportation function but also have maintenance function.However,designing a special vehicle with the aforementioned functions is not necessary.So,the appropriate transformation of existing construction vehicles,especially its transmission system,will help adapt to the maintenance of stable low-speed operation requirements.This paper aims to research the transformation of traditional vehicle gearbox.Adding hydraulic transmission into mechanical gearbox will achieve hydraulic-mechanical transmission.It can not only meet the demand of high-speed transportation,but it can also adapt to the need of low-speed maintenance construction.Firstly,under the comprehensive analysis of the advantages of mechanical transmission and hydraulic transmission,this paper determines to use hydraulic-mechanical transmission technology.Considering the vehicle low-speed range,efficiency,applicability and so on,the final transmission scheme that the new hydraulic-mechanical transmission is installed between the engine and the gearbox is adopted;Then based on the construction vehicle low-speed operating requirement,it selects the closed hydraulic system with variable pumpconstant displacement motor.According to the matching principle,the main components in this transmission system and the hydraulic system pressure are selected;Furthermore,the power,traction and economy of this transmission system are calculated and analyzed.And in order to meet the requirements of vehicle operation quality,the control methods to keep the vehicle stable at low-speed are analyzed;Finally,with the use of hydraulic simulation software,the vehicle low-speed driving system is simulated.It includes the vehicle speed in terms of system starting and braking time's response,changed load's effects on the stability of the vehicle speed,the system pressure and gear reasonable speed range;The simulation results show that this low-speed stable system can meet the needs of construction vehicles.