Study on stepwise regression optimization of shift quality of heavy-duty tractor HMCVT based on five factors

Abstract

! Objectives | In order to improve the switching quality of heavy tractors equipped with hydro-mechanical continuously variable transmission(HMCVT), a model of power shift process was established by SimulationX software. [Methods] We made deep researches on the factors affecting power shift process and the relationship between the factors and the switching quality. The verification of model accuracy was done in indirect bench tests. Based on the simulation model,we carried out five factors and four levels orthogonal test,and figured out the speed drop and the dynamic load of each test. On the one hand, the experimental results were analyzed for extreme difference,the main factors affecting the speed drop were the load pressure,the flow rate of the clutch,and the oil pressure of hydraulic system. The main factors affecting dynamic load were the load pressure and the oil pressure of hydraulic system, and the influence of flow rate of the clutch was the lowest. On the other hand,stepwise regression analysis was used to move the factors that were not significant and establish a mathematical model of speed drop and significant influence factors(the oil pressure of hydraulic system,the flow rate of the clutch and the load pressure) . The mathematical model of dynamic load was also established by stepwise regression analysis,and the load pressure and the oil pressure of hydraulic system were the most affecting factors. After analysis,the results of extreme difference analysis were consistent with those of stepwise regression analysis,and the accuracy of stepwise regression analysis was proved. The results of orthogonal experiments showed that the oil pressure of hydraulic system was positively related to dynamic load,but inversely related to speed drop, the load pressure was positively related to speed drop, but inversely related to dynamic load. So the comprehensive power shift process evaluation index should be established to evaluate shift quality. We first calculated variance of 16 groups of speed drop date and 16 groups of dynamic load date,then the weight of speed drop and dynamic load were the ratio of the variance respectively. In order to study the influence of structural design parameters on the quality of shift process,we conducted single factor tests. During the experiments with single factor,the relationship between ratio of inner and outer diameters of friction plates and speed drop as well as that between ratio of inner and outer diameters of friction plates and the dynamic load were revealed,the relationship between the number of friction plates and speed drop as well as that between the number of friction plates and the dynamic load were revealed. | Rcsulls | During wet clutch engagement,the main factors affecting the speed drop were oil pressure, flow rate and load pressure,and the main factors affecting the dynamic load were oil pressure and load pressure. Among the structural design factors,the number of friction plates played a significant part in the quality of shift process,and the ratio of inner and outer diameters of friction plates had little connection with quality of shift process. [Conclusions] An analysis method for the improvement of shift quality and optimal design of the wet clutch was proposed in this paper. The method which combined the weight of variance with stepwise regression analysis provided reference for the research in related fields.