Research On Fuel-saving Of Hydrodynamic Transmission System For Wheel Loader

With the rapid development of economy, the energy requirement from societyis increased continuously. Recently the problems of energy crisis become very serious,the green economy on the theme of the fuel saving and consumption reduce hasbecome main melody of social development. The wheel loader is one constructionmachinery mainly on earth moving with feather of flexible moving, easy operation. itplays an important role in the development of economy construction, logistictransportation. In the fuel saving field of wheel loader, the strict regulation of energyconsumption is formulated to be a mandatory license for product permission inEurope and America, The fuel saving is also regarded as a basic policy of wheelloader developing, the standard of fuel consumption is formulated as an importantcriterion of product quality evaluation. The development of fuel saving and lowenergy consumption is already become the common agreement in the wheel loader.The hydrodynamic transmission system of wheel loader is mainly composedof engine, torque converter, power shift transmission and axle, the torque converterhas the advantages of simple structure, low manufacture cost, wide torque range andcontinuously variable power transmission. Low efficiency of the hydrodynamictorque converter is its main disadvantage and impacts the fuel consumption of wheelloader. According to the statistics, the power transmits from engine to the vehiclewheel by the torque converter with loss of around30%, of which80%loss comesfrom torque converter, therefore the research on fuel saving of hydrodynamictransmission system for wheel loader is important and has very big development space.The foreign research on fuel saving of hydrodynamic transmission system forwheel loader starts rather earlier and becomes to maturity. It is mainly concentrated onthe application of low speed engine, torque converter with free wheel stator, lock upclutch, manufacture accuracy improvement of the transmission, axle gears,optimization of engine match with torque converter to promote transmission systemfuel saving for wheel loader. In the new fuel saving era, it is mainly focus on CVTbased on application of the hydraulic and mechanical coupling, or the Hybrid fuelsaving. The torque converter is cancelled in both of the two solutions, the fuelconsumption of wheel loader is improved obviously. However it is hard to beaccepted by the market in the short term for industry as the high cost and technology.In the coming future, the wheel loader manufactures will continue to optimize the fuelsaving of hydrodynamic transmission system as main development route, as the sametime to reserve the next generation fuel saving plan of CVT and Hybrid.The traditional hydrodynamic transmission system is used in domestic wheelloader, which is mainly applied in the ZL50series type with the dual turbinesconverters. The research on the hydrodynamic transmission fuel saving is later thanoverseas, due to the big volume manufacture, fierce competition, and the pressure offoreign advanced fuel saving wheel loader, the research on the fuel saving ofhydrodynamic transmission for wheel loader is very urgent and has an importantpractical meaning.In the view of the former questions, combined with the national863planprojectof "PLM design critical technology faced on earth-moving mechanical powertransmission system"（2014AA041502）, this paper starts a series of fuel savingresearch on the hydrodynamic transmission system for wheel loader and comes toconclusion with some wheel loader prototypes from Guangxi Liugong MachineryCo.,Ltd as following：1. The fuel saving effect from low speed engine matching with low speedtorque converter is researched based on some ZL50wheel loader prototype, the lowspeed torque converter with dual turbines is designed by the CFD and the simulation design accuracy is verified from test accordingly. It comes to conclusion that the newmodel with the low speed torque converter matching with low speed engine outputsmore torque than the old high speed torque converter matching with high enginemodel. For the reliability of transmission, it is raised that optimize the torqueconverter overrun clutch gear sets speed ratios to keep the low speed model outputtorque not higher than the high speed model, at the condition of good match with lowspeed engine. Meanwhile the concept of a new inner cam design for overrun clutch israised, which can effectively decrease friction abrasion due to the frequent lock andunlock of clutch gears. Finally it comes to conclusion from field test that at the samepower performance, the wheel loader prototype with low speed engine can save fuelby13%than high speed model at the top ground speed, and save fuel by6%duringthe average load condition.2. The fuel-saving effect for the torque convert with free wheel stator andlockup clutch based on some wheel loader is researched. It is verified that the wheelloader with lockup clutch outputs31.7%accumulated power more, faster top groundspeed and less acceleration time than the model with no lockup clutch, the fuelconsumption at top ground speed in all transmission gears is decreased accordingly.The strategy of lockupclutch is also researched, the transmission shift ratio step israised to obtain the best lock up fuel saving. The wheel loader at the top ground speedwith and without free wheel stator is tested for fuel consumption comparison. Itcomes to conclusion that the wheel loader prototype with free wheel stator can savefuel by17%than the prototype with no free wheel stator. The comparison test ofpower performance between the torque converter with and with no lockup clutch isdeveloped based on some wheel loader. It comes to conclusion that the top groundspeed of wheel loader with lockup clutch in all transmission gears is higher than thewheel loader with no lockup clutch, as the shifts upper, the top ground speed isincreased more.3. The fuel saving focus on variable power engine match with torque converteris researched. It is raised that the variable engine power mode is defined by thematerial strength. The duty cycle is analyzed based on some wheel loader, and engine variable power curves are designed by the duty cycle. The power mode of engine isvaried by changing torque at the regulation speed range, changing torque at full loadcharacteristics range and in between to match with the same torque converter, thereasonability of matching is also analyzed. Every variable power model is integratedwith3different power curves such as power, standard and economy. After that thevariable power modes for wheel loader are set up to meet different duty cyclesrequirement. Finally the variable power engine prototype with optional regulationcurves is manufactured and assembled in the wheel loader for fuel test. It comes toconclusion that the wheel loader with power mode consumes more fuel by9.8%thanthe condition with economy mode during loose duty condition, and consumes morefuel by12.4%than the condition with economy mode at top ground speed condition.The research on fuel saving of hydrodynamic transmission system for wheelloader is developed, the feasible solutions are given in the paper, which is proved tobe valid combined with real machine from manufacture factory. The research not onlyprovides fuel saving solutions of hydrodynamic transmission system for wheel loaderdevelopment, but also gives some valuable reference on fuel saving of hydrodynamictransmission system for other construction machinery.