The Design Of The Hydraulic Drive System On The Road-building Machinery Cooling Device

The cooling system fan of the road-building machinery at present mainly adopts the traditional crankshaft fixed transmitting ratio type driving, and the same cooling system fan is bearing the heat dissipation of the engine and hydraulic oil of road-building machinery transmission system, hydraulic lifting and steering system at the same time. The heat dissipation is great in intensity. This type of driving method caused the engine of road-building machinery has high start torque, long preheating time, undercooling at low-speed high-load and overcooling at high-speed low-load, unreasonable cooling, and too much power consumption by the fan, which decreased the power output, and the fix location of the fan is limited, and the operation noise is high.In the project we designed a cooling system of new style, which adopts two driving way using one electronic controlled unit together and rationally controls the cooling system of the engine and hydraulic oil separately. It can not only settle the problems of over heat of engine and undercooling of the hydraulic transmission system which often happen under construction of road-building machinery, but also put the fans separately , and the cooling is reliable and rational.The thesis describes in detail the cooling system operating principle, especially the parameter calculation and selection of the main hydraulic element of the hydraulic drive system on the road-building machinery engine cooling device, and the selecting and matching of proportional spill valve and other designs, etc. The feature and function to be performed of the system: Being different to the traditional single cooling system, this system divided the whole system into two parts: cooling system for engine and cooling system forhydraulic oil, and both of them are controlled by electronic controlled unit. The cooling system of engine adopted the way of hydraulic driving to realize the stepless speed regulation of the fan. The system can adjust the control-current of the proportional value according to the coolant temperature and the target coolant temperature so as to control the speed of the fan. The cooling system for the hydraulic oil adopts motor drive, then the electronic controlled unit controls the motor's starting and stopping according to the temperature of the hydraulic oil. The driving ways of these two kinds of fans work independently according to different cooling directions.The design scheme made after a large amount of science investigation and research and on-the-spot investigation can not only resolve the problems of over heat of engine and undercooling of hydraulic oil, but also have the following advantages: easy to fix, saving fuel, reducing noise, small volume, high power, etc. And good social economic efficiency will be achieved when this design is widely applied in the road-building machinery.