| Wheel loader is a kind of construction machinery with extensive uses, which is mainly used for shoveling and transporting bulk-solid material, unloading and leveling operations. In order to improve the adaptability of loader to violent changes of load, hydro-mechanical transmission is used in the transmission system in general, which can have the loader obtain advantages such as better traction characteristics, automatic adaptability to load fluctuation, the vibration and shocks reduced, flameout of engine avoided, and the engine power taken fully. Hydro-mechanical transmission is a key component in the hydro-mechanical transmission system, which uses hydrodynamic torque converter to complete transmission of power, realizing automatic transformation of output speed and torque. Different transmission gear pairs work to realize variable-speed function through combination and detachment of the shift clutch. Engine combined with torque converter can be regarded as a new power plant in driveline, properties of which directly influences power performance and economy of loader. The rational matching of engine and hydraulic torque converter is basis of traction force calculation of the whole vehicle and premise of the matching and optimization design of driveline for hydrodynamic transmission vehicle. Transmission system matched with engine reasonably makes the engine work near ideal area, which can not only reduce fuel consumption, but also reduce engine wear and improve engine life as well as reduce emissions.Reasonable transmission parameters are chosen in order to reach dynamic and fuel economic requirements after the parameters of whole vehicle are determined. Therefore, it has important real significance to optimize the performance and match of hydro-mechanical transmission with electro-hydrodynamic control as well as the entire transmission system.In this paper, combined with the project commissioned by enterprises, studies on the performance of the hydro-mechanical transmission and the matching of power train of ZL50 loader are conducted. The main research work is as follow: (1)The mathematical models of engine and hydrodynamic torque converter are established by means of least square method based on the basic parameters of 6CT8.3-C215 engine and YJH340 hydrodynamic torque converter. The curve of external and governing characteristics of engine, the curves of original performance as well as the loading parabolic of hydrodynamic torque converter are drawn by programming with MATLAB. The net torque curve of engine and the load parabola of torque converter are drawn in the same coordinate system, and the input characteristic curve of engine working together with hydrodynamic torque converter is got, their common working point is determined by means of analytical method, then the output characteristic of the engine working together with torque converter and every span's efficiency curve as well as output torque's theoretical curve of transmission are got through calculation. The matching results are unsatisfactory, so the diameter of circulatory circle of torque converter is optimized by use of the method of power matching, the optimal value is D = 0.350m.(2)The performance test of hydrodynamic mechanical transmission is conducted. The method of test is made based on machinery industry standard JB/T9720.2001. The content of tests include: no-load loss and transmission efficiency tests of 4WG.200 hydrodynamic mechanical transmission with torque converter. The results show that the highest efficiency of the first-speed, second-speed, third-speed and the forth-speed is respectively 0.732, 0.731, 0.719, 0.728; the no-load loss is respectively 8.125kW, 11.476kW, 13.830kW, 19.412kW. The results of theoretical calculation and experiment are compared, and the error is within the allowable range, which verifies the correctness of theoretical calculation.(3)On the basis of analyzing traction force balancing and traction power balancing of loader, the theoretical tractive performance curve of loader is drawn combined with the whole vehicles parameters and the common output characteristic as well as the transmission ratio of every span. After the match of engine and hydrodynamic torque converter, the vehicles performance can reach to the maximum speed and maximum traction requirements through analysis. The evaluation index of power performance and economy of loader is explained in detail, which provides necessary reference for the optimization of the parameters of hydrodynamic transmission system. (4)On the basis of traction characteristics calculation, optimization model is established which takes the maximum power efficiency for the objective function, and takes the maximum dynamic factor, the maximum climbable gradient , the road adhesion condition, and the relation between the transmission ratio of every span for constraint condition. The optimization of every span's transmission ratio is made by use of fuzzy optimize theory, and the optimization results are i1 = 4.181, i2 = 2.315, i3 = 1.101, i4 = 0.634. The maximum vehicle speed rises by 4.947%; the maximum traction force decreases by 2.251%; and the coverage area of speed-power rises by 8.115%, which means utilization ratio of the engine effective power is improved, reaching to the requirement of optimization design. It can be regarded as the optimization results are more reasonable than the original parameters.
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