增压器压气机三维弹塑性接触的研究

以某柴油机涡轮增压器的压气机为例,采用由参变量变分原理导出的有限元参数二次规划法,并结合多重子结构技术分析求解叶轮与轴套、轴套与轴的三维弹塑性接触问题,针对不同的过盈量、转速和轴套壁厚进行了大量计算,获得了叶轮、轴套与轴之间接触应力的相应分布规律。分析表明随着叶轮与轴套间过盈量的减小,轴套的外表面与内表面的接触应力是线性减小的,而且内表面的接触应力减小较为迅速。因而在采用压力组装法时应严格控制轴套与轴的过盈量,使得轴套和轴间有足够的压力保证叶轮、轴套和轴不会相互脱离,又满足结构强度的要求,并使其产生的不良影响减至最小。当转速一定时,叶轮与轴套接触点的法向相对位移与叶轮的质量分布存在着明显的联系。建议采用非均匀的初始过盈量,以保证不发生相对位移和接触应力的均匀性。这些对于确定合理过盈量,改进设计和提高压气机的寿命,具有实际参考意义。

STUDY ON 3D ELASTOPLASTIC CONTACT PROBLEM OF TURBOCHARGER COMPRESSOR

A locomotive-type turbocharger compressor with 24 blades under combined centrifugal and interference-fit loading is used for the present analysis. The FE parametric quadratic programming (PQP) method which is developed based on the parametric variational principle (PVP) is used for the analysis of the stress distribution of 3-D frictional contact problem of impeller-shaft sleeve-shaft, and then, using the multi-level, multi-branch substructure technique of FE, makes it possible to precisely simulate complicated geometrical shapes of impeller and considerably enhances accuracy in numerical computation. The effects of fit tolerance and rotational speed, the displacement and the contact stress on the interference-fitting surfaces are discussed in detail. The contact stress of both the external and internal surface of shaft sleeve descends linearly with the increase of the rotational speed. At the same rotational speed, the contact stress of the external and internal surface of shaft sleeve decrease with the decrease of the amount of interference. And the contact stress of the internal surface decreases more quickly. To decrease the difficulty of the assembling process and make sure the safety of the working state, the amount of interference between the shaft sleeve and shaft by press-fitting should be controlled strictly to avoid the rapid increase of the contact stress. It is found there is obvious relationship between the mass distribution of impeller and normal relative displacement of contact points of impeller and shaft sleeve within the certain rotational speed. It is proposed that nonuniform initial interference value in the structural design would avoid relative displacement generated and ensure uniformity of the contact stress. The numerical results show the high accuracy and good convergence of the algorithm presented here. It provides an effective approach which achieves more reliable interference-fitted connections and more precise assembly accuracy with lower manufacturing cost in the structural design.