Time-Dependent Reliability Analysis And Synthesis Of Steering Mechanisms

Recently, the time-dependent kinematic reliability of mechanisms with uncertainty is oneof the hot issues of mechanism theory. The motion output of mechanisms is uncertaintybecause of the influences of the uncertainties (such as geometric dimensions, joint clearances,principle, environment and so on). This uncertainty would lead to the kinematic accuracyreliability decreasing or mechanism action unreliable. At present, most kinematic reliabilitymethods are only for the point reli-ability, which provides us with the likelihood of realizingthe desired function only at a specific instant regardless whether the function has beenrealized or not before that instant. Obviously, the reliability of mechanisms over the entirerange of the input motion is more reasonable and realistic than the point reliability. Therefore,the researches of time-dependent (interval) kinematic reliability analysis and synthesis ofmechanism with uncertainty have an extremely important theoretical and practical value. Inthis paper, we take integral steering mechanism and rack and pinion steering mechanism asthe objects of study, the time-dependent kinematic reliability analysis and synthesis ofsteering mechanisms are studied. The main research works are described as follows:(1) Based on the kinematic analysis of integral steering mechanism and rack and pinionsteering mechanism which are widely used in the automobile, the error probabilistic model ofsteering mechanisms are presented.(2) Combined the first order second moment method (FOSM) and the first-passagePoisson approximation method, the analytical expression of up-crossing and down-crossing arederived, and then the computing formula of the time-dependent reliability is established.Based on this works, the time-dependent reliability model of integral steering mechanism andrack and pinion steering mechanism are created and numerical examples are given. The resultsshow that the time-dependent reliability is always less than point reliability. Kinematicreliability meet point reliability does not mean that it can meet time-dependent reliability. Thus,time-dependent reliability is more reasonable than the traditional point reliability. Thetime-dependent kinematic reliability take the entire movement range as the target, it can reflectthe probability of realizing the desired function over the entire movement range.(3) A time-dependent reliability synthesis method is proposed for steering mechanismsynthesis. Taking the time-dependent reliability as object and constraint, the optimizationsynthesis model of integral steering mechanism is presented. Accordingly, a deterministicsynthesis model and point reliability synthesis model are proposed. A numerical example isgiven for verifying the effective of presented methods. The results show that thetime-dependent reliability optimization method superior to deterministic optimization method and point reliability optimization method. It can not only meet the reliability requirements butalso reduce the structure error of mechanism, and its optimal solution is more stable than theother two methods.