Study On Contamination Matching For Electro-hydraulic Shifting System In Power Shift Steering Transmission

The existence of contaminant particles is a major problem that limits the improvement of the reliability of electro-hydraulic shifting system in power-shift steering transmission. On the basis of theoretical analysis, mathematic modeling, numerical simulation and experimental validation, the multiple characteristics of contaminant particles and their affection on the performance degradation of the hydraulic components have been investigated. The strict sensitive size ranges(contaminant sensitivity) of particles, which decreasing the probabilities of contaminant lock and wear, is acquired as well. Moreover, numerical simulation of the contamination-control equations is applied to investigate the matching relationships between the contamination levels, the contaminant sensitivity, the filtration rate and the contaminant ingressive rate, which is seen as the theoretical basis for adaptable design and the appropriate control on contamination for the electro-hydraulic shifting system. Major scientific works are shown as the following:① By applying the multiple techniques of oil analysis, the shape, size and element characteristics of contaminant particles have been acquired. To classify and recognize the wear conditions as well as stochastically predict the degradation and failure period of electro-hydraulic shifting system, mathematical methods, such as the maximum likelihood estimation, the Robust Kernel Principal Component Analysis(RKPCA) and the Wiener process with a positive drift are adopted. Their eigenvalues have been applied to determine the threshold values on contamination control, which is crucial for the realization of condition-based maintenance and the extension of maintain interval.② The filter cake theory and the plastic deformation theory are combined to model the lock force and the wear process caused by contaminants. Both analytical and empirical studies of lock force show that the generation of lock force is due to the friction force between the filter cake and the spool when equilibrium. The lock force decreases as the hydraulic propulsive force increases since elevated hydraulic propulsive force tears the filter cake into pieces. Moreover, the model of contaminant wear indicates that a closer hardness values, a shorter contact length of the kinematic pair and a smaller diameter of spool will extend the valve’s life. On the contrary, a higher concentration of contaminants, a higher rate of large particles in the whole contaminants, and a higher temperature and pressure will definitely shorten the life. Both the sensitive size range of particles and its matching filtration precision have been deviated by the rule of the variational radial clearances between the kinematic pair.③ By considering the differential pressure flow and the variational clearance, a degrading process for gear pump and the equation for its life prediction have been modeled. The broken process of contaminants that passed through the leakage path from the gear ends to the end plates was applied in this model. Meanwhile the affections of the generation rate of wear debris, the average filtration rate, the displacement, the constructive parameters, and the contamination level have also been analyzed to increase the anti-contaminant capacities. The comparison results between the observation value and the theoretical value shows that the latter is more robust in evaluating the contaminant sensitivity. Later, both the threshold values of sensitive diameter and the best matching filter precision for gear pump have been derived by using the theory of the contaminant sensitivity.④ A dynamic filtration model has been established by defining re-filtered rate ? and re-contamined rate ?. Therefore a mathematic model of contamination control for the electro-hydraulic shifting system is derived from its block diagram. Under the constraints of the contaminant sensitivity, the contamination capacity and the differential pressure of the filters, the model has been testified for its accordance with the dynamic equilibrium theory by the contaminant matching simulation in MATLAB/Simulink. In the contamination matching design for the electro-hydraulic shifting system, a higher flow rate and a smaller fluid volume are beneficial for a higher purifying rate. The equilibrium time of filtering process decreases obviously when the filtration rate is in the range 1 ?? ?10. While in the range ? ?20, the filtration rate has inconspicuous effect on the equilibrium time.