Study On Key Technologies In Automatic Mechanism Of A Combat Vehicle Gun

Automatic mechanism technology is one of combat vehicle gun's key Technologies.Because a new-type special ammuniton and rotating chamber technology have been used in a combat vehicle gun, while enhancing firing frequency, increasing the power, but also brings the corresponding technical problems, such as collectivity match, shell loading and positioning, etc. Based on the key beforehand project of the "eleventh five-year", the research is developed and aims at the automatic mechanism of a combat vehicle gun and its key technology using the theory of automatic weapon dynamics, multi-body dynamics, optimization design, probability distribution and mechanical reliability, which can provide theoretical foundation and design decision for engineering practice of such weapon systems. The main research content is as follows:(1) Collectivity structure and its working principle of this new type automatic mechanism of a combat vehicle gun are discussed. And then the shell loading and positioning movement, the firing movement and so on has carried on the kinematics match analysis. The shell loading and positioning technology is a key technology in this automatic mechanism.(2) Through load analysis of every part in cartridge retaining mechanism, motion differential equations of shell are built during its feeding and positioning time via dynamics theory of automatic weapons. And then numerical simulation is done base on this differential equations. Each item has its meaning; this builds theoretical foundation for understanding the dynamic response of mechanism system.(3) Virtual dynamic models of cartridge retaining mechanism and guided-chain ramming mechanism are built in multi-body system dynamic software based on the first kind of Lagrange equation via multi-body system dynamics theory.Through merging both dynamic models, the dynamic model of the shell loading and positioning system is acquired. Finally, rigid-flexible coupling dynamic model is builted via replacing some key parts with their flexible parts in dynamic model of cartridge retaining mechanism.And its simulation results and multi-body dynamics model are compared, results show that the two are basically the same. Equivalent spring stiffness of chain links and stiffness of all contact pairs in those dynamic models are calculated using finite element method. This will make virtual prototype and real physical prototype more consistent.(4) Based on the multidisciplinary integrated optimization platform, with buffer spring, braking spring, positioning spring's stiffness and pre-deformation as design variables, with proper positioning as constraint conditions, an experimental design is carried out on cartridge retaining mechanism for dynamic matching of three springs. Through dynamic matching experimental design, several groups of feasible design variables are obtained, and the preliminary design variables, and the probability density of shell displacement presents in three "island" state. For complex mechanical system with many elastic components and contact collisions, this method overcomes the disadvantage of the traditional methods which can hardly do dynamic matching design.(5) To reduce the contact forces between shell and retaining pawl, shell and hold down plate in the cartridge retaining mechanism, and prolong the life of those parts, with stiffness minimums of buffer spring, braking spring, positioning spring as objective functions, with three spring's stiffness and pre-deformation as design variables, with proper positioning as constraint conditions, multi-objective dynamic matching optimization design is conducted. And spring stiffness and pre-deformation are obtained. Based on this, considering the design problem of springs, multi-objective dynamic matching optimization design is conducted using hierarchical optimization design. The first layer is a global level, mainly consider the optimal design of shell proper positioning. The second layer is the local level, considering the optimal design of the spring.This kind of hierarchical optimization strategy can not only reduce the contact forces, design time cost,the number of design variables, but also consider more design factors. Hence, it has more practical meaning.(6) Using truncation distribution theory, the paper derives four kind of truncated distribution density functions and cumulative distribution functions of commonly used typical distributions and corresponding means, variances. On this basis, according to cumulative distribution functions of various truncation distributions, the sampling method of random variables is deduced, which is available for non-truncated distribution. The discussion of truncated distribution and sampling method is foundation for design variables in mechanism motion reliability analysis.(7) Discussing theory and its application of accurate analysis method (stress-strength interference model), approximate method (mean first-order second-moment method, JC method), and the numerical simulation method (Monte Carlo method) are discussed in motion reliability analysis. And then it is proved that trucated normal distribution don't have superposition in accurate analysis method.(8) Aiming at cartridge retaining mechanism which is multi-dimensional, strong nonlinear systems, with some motion reliability rules built, mechanism motion reliability analysis are done via numerical simulation method when random variables obey general distribution and truncated distribution respectively. At last, the data is compared with both,and the results show that random variables which obey truncated distribution is more accurate than the other when mechanism motion reliability analysis is done.