| According to different requirements, the wheel loader need to complete a series ofactions, such as shoveling, loading, unloading and transporting, under the serious workingconditions. So a lot of heat is generated from many heat sources in the system. In order toensure the high-efficiency and reliable work of the loader, the heat should be conducted intoatmosphere. Traditional loader cooling system usually contains one fan and several radiators.The cooling fan is driven by engine. So the rotation speed of cooling fan changes along withengine speed according to certain proportion. As a result, the system of loader may beovercooling or overheating. The form of one fan matching to several radiators can’t ensure thecooling requirement of systems because of many constraints, such as the space layout ofengine compartment and the mutual influence between the radiators. With the increasinglystrict requirement of energy saving and emission reduction and the increasing heat load ofmachine, the cooling system of loader is developing toward to intelligentization andmodularization. In this paper, taking the cooling system of a domestic50wheel loader asthe research object, aiming at the new intensive cooling system, from the view of reducing themutual influence between radiators, the driving characteristics of the cooling fan of theintensive cooling system were studied.Firstly, based on ε-NTU, the performance of radiators was forecasted. The heatdissipated power and pressure loss of vehicle coolant radiator and the engine coolant radiatorat different ambient temperature and different air flow were obtained. The results showed thatthe speed of cooling fan should be adjusted to change air flow flowing through the radiators tokeep the heat dissipated power of radiator constant. While the ambient temperature is low, thespeed of fan should be reduced to lower the air flow to avoid overheating. While ambienttemperature is high, the speed of fan should be increased to increase the air flow to eliminatethe effect of temperature difference on the heat dissipation power of radiator. But the pressure loss was increased when the air flow was increased, which led bigger shaft power of fan.Secondly, based on the test characteristics of cooling fan and the calculation formulas forperformance of cooling fan, the relationship between the speed of cooling fan and the staticpressure, the fan static efficiency or the shaft power was obtained respectively. The speed offan control model varied with environment temperature was obtained. According to the fittedformula, under the condition of invariable heat dissipation power, the driving characteristicsof cooling fan at different ambient temperature were obtained.Thirdly, the quantitatively and variably hydraulic drive of the cooling fan of the intensivecooling system were researched. In the quantitatively hydraulic drive system, the speed of fanwas controlled by electro-hydraulic proportional overflow valve. In the variably hydraulicdrive system, the speed of fan was controlled by variable pump. According to parametercalculation, the type and specification of the key hydraulic components were obtained. Thenthe dynamic characteristics of the system were analyzed by means of simulation under twoextreme operating conditions. One condition was the loader working under the maximum heatload at the ambient temperature of-30℃and the other one was at the ambient temperature of45℃. The difference of energy consumption was analyzed between the intensive coolingsystem and mechanical drive or conventional hydraulic drive of cooling fan. The resultshowed that hydraulic drive had obvious energy-saving effect at lower ambient temperatureand the energy consumption of hydraulic drive was more than mechanical drive when theambient temperature achieved a certain value compared with mechanical drive. Thequantitatively hydraulic drive was better than the variably hydraulic drive. Compared withconventional hydraulic drive, the power of pump and cooling fan of the intensive coolingsystem were lower. The higher the ambient temperature was, the better the result was.Lastly, the influence factors of the hydraulic drive of the intensive cooling system wereanalyzed. The simulation model of the intensive cooling system matched to a new cooling fanwas established. The dynamic characteristics and the energy consumption of the system wereanalyzed. The characteristics of the system and the utilization of hydraulic pump power underdifferent engine speed were analyzed. The effect of the resistance characteristic of back oilcircuit on the characteristics of the system was analyzed by means of changing the resistance characteristic of radiators. The effect of the temperature of the coolant at the inlet of the pumpon the characteristics of the system was analyzed by means of changing the thermoryticcharacteristics of the radiators. |
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