Gear Pump Reliability Evaluation Based On Performance Degradation

The reliability test method of hydraulic pump based on traditional life test needs a long time and high cost,which can not meet the actual needs of reliability evaluation.The reliability evaluation method based on the performance degradation records the change rule of the performance characteristics of the products health state with time,and does not need to observe the failure.It provides a new way for the rapid evaluation of the reliability of the hydraulic pump.Taking the gear pump as the research object,considering that there are many uncertainties in the degradation process,such as individual difference of initial value,individual difference of degradation rate,random fluctuation of degradation trajectory and measurement error,the reliability evaluation technology of one-dimensional and two-dimensional performance degradation,the modeling and optimization design of step stress accelerated degradation test are studied.It provides theoretical support for the overall reliability evaluation of gear pump.The reliability evaluation of one-dimensional performance degradation of gear pump is carried out.Based on the Wiener process,a one-dimensional performance degradation model of gear pump considering multiple uncertainties is established,the life distribution under the definition of first hitting time failure is obtained,.and the relationship between the parameters of degradation model and reliability is established.Based on Bayesian theory and bootstrap,a two-step estimation method of model parameters for small sample degradation test is proposed.Monte Carlo simulation is used to verify the effectiveness of the model in characterizing the degradation process with various uncertainties and the effectiveness of the two-step parameter estimation method.The reliability evaluation of gear pump one-dimensional degradation based on volume efficiency is taken as an example.Compared with Wiener process model and linear degradation trajectory model,it is verified that the model can represent various uncertainties in performance degradation of gear pump.The control variable method is used to analyze the influence rule of degradation model parameters on reliability,and the main influence parameters of gear pump reliability are determined.The reliability evaluation of two-dimensional performance degradation of gear pump is carried out.Based on the one-dimensional degradation model,two performance characteristics degradation processes of gear pump are modeled respectively,and the reliability evaluation model considering the two-dimensional correlation is established by using the copula function.Under the guidance of the edge inference method,the two-step parameter estimation method is used to estimate the model parameters.The case study of the two-dimensional degradation reliability evaluation of gear pump based on volumetric efficiency and total efficiency is compared with the reliability evaluation based on the one-dimensional degradation model and the two-dimensional reliability evaluation without considering the correlation.Then the rationality of the reliability evaluation considering the two-dimensional degeneration correlation of gear pump is verified.The influence of correlation degree on two-dimensional reliability evaluation is analyzed.The step stress accelerated degradation model of gear pump is studied.Considering the influence of pressure and speed on the degradation rate,a two stress step-stress accelerated degradation model of gear pump is established based on the multi uncertainty one-dimensional degradation model.The two-step parameter estimation method of accelerated degradation model under the condition of small sample and the method of judging the failure mechanism consistency of step stress accelerated degradation test based on the principle of likelihood ratio test are given.The rationality of accelerated degradation model,the validity of parameter estimation method and failure mechanism consistency judgment method are verified by numerical examples.The optimal design of step stress accelerated degradation test of gear pump is carried out.The optimization model of step stress accelerated degradation test with the minimum progressive variance of B₁₀ life under normal service stress is established.The numerical case optimization analysis is carried out by using the traversal search algorithm.Under the constraints of total test time and the maximum stress,the optimal scheme of pressure,rotation speed and measurement times distribution of step stress accelerated degradation test of gear pump is obtained.And the parameter sensitivity analysis of the optimal test scheme is carried out.The control variable method is used to analyze the influence of the test variables on the optimal test scheme and optimization objective,which provides a reference for step stress accelerated degradation test of gear pump.