Research On Performance Of Double-impeller Torque Converter And Variable Capacity Matching For Loader

Loader is a sort of earthmoving machineries that are widely applied inengineering construction. Besides for running condition, loader also works undershovel mucking condition. The use requirement of loader could only be satisfiedwhen the output power of engine is dynamically and reasonably distributed betweentransmission system and hydraulic system. Typically, loader includes a torqueconverter (TC) positioned between engine and gearbox to adapt complex and variableworking conditions. The matching between TC and engine determines the powerperformance and fuel economy of loader. At present, the capacity characteristic of TCwidely used in loader is invariable. The matching performance of loader underrunning condition and shovel mucking condition cannot acquire the perfect effectsimultaneously when the matching between TC and engine is designed by full powermatching, part power matching or optimal matching method. However,double-impeller TC has the property of variable capacity, which can be used forsolving the matching problem of loader. To improve the performance of loader, in thisthesis variable capacity matching technique was researched in terms ofdouble-impeller TC design, characteristic prediction and matching performance basedon a7t loader. The main contents and conclusions are as follows.(1)Through analyzing working conditions of loader, the double-impeller TC withslip clutch was designed to replace the original three-element TC. Similar-designmethod was adopted to design the prototype of double-impeller TC, whose effectivediameter was425mm. The main and auxiliary impeller blades of double-impeller TCwere obtained by segmenting the impeller blades of the prototype. Then the structureand hydraulic control system of slip clutch were designed and the variable capacitycontrol method of double-impeller TC was analyzed.(2)The torque of working wheels of double-impeller TC at different slip ratios and different speed ratios was calculated using CFD method and the performance ofdouble-impeller TC under the conditions of two working impellers, one singleworking impeller and slipping was analyzed. Through building the force equilibriumequation of slip clutch and calculating the pressure of side cavity of double-impellerTC, the torque characteristic of slip clutch was obtained. Then the originalcharacteristics of double-impeller TC under different pressure control laws werecalculated by the combine of torque characteristics of double-impeller TC and slipclutch, which provided a basis for analyzing the variable capacity matchingcharacteristic of loader.(3)The mathematical models of engine and double-impeller TC were built andthe effect of using double-impeller TC on the input and output equilibrium runninglines of engine and TC was analyzed. The dynamic variable capacity matching modelbetween engine and double-impeller TC was built and the variable capacity matchingprocess of loader was simulated. Then the effect of using double-impeller TC on theparameters of matching performance in a working cycle was analyzed. The analysisresults of static and dynamic variable capacity matching characteristics indicated thatthe matching performance of loader using double-impeller TC changedinconspicuously under shovel mucking condition but improved significantly underrunning condition compared with the original one. The calculation results of powerperformance and fuel economy indicated that both of the power performance and fueleconomy of loader using double-impeller TC improved significantly compared withthe original one. Overall, the research shows that the variable capacity matchingbetween double-impeller TC and engine can simultaneously satisfy the userequirement of loader under the two typical working conditions and efficaciouslyimprove the performance of loader.