缸盖-缸垫-机体热弹性接触问题研究

Study on Thermoelastic Contact of Cylinder Head-Cylinder Head Gasket-Engine Block

为研究机械约束和热状态对缸盖与缸垫间热弹性接触非线性问题的影响规律,以某4气门柴油机为研究对象,建立了缸盖-缸垫-机体-螺栓的四体接触关系简化模型。采用增广拉格朗日乘子法作为接触算法,在不同的螺栓预紧力和热状态下,计算了缸盖底板的受力变形,揭示了标定工况热态下机械约束对缸盖底板相关部位接触应力和节点位移的影响规律,及标定预紧力时不同热状态对结果的影响。研究表明:当预紧力为标定值时,施加最高燃烧压力后,标定工况热态下缸盖底板正对缸圈处及排气门侧螺孔处的接触应力与冷态时相近,节点位移有所减小,不同热状态下螺孔处节点位移及正对缸圈处接触应力和节点位移的变化幅值均小于2%;除少数情况外,缸盖底板各相关部位的接触应力和节点位移随预紧力增大而增大。上述研究结果也说明:目前采用常温条件进行缸垫密封性试验基本上能够代表实用状态。

In order to study the influence of mechanical constraints and thermal state on thermoelastic contact nonlinear problem that between cylinder head and cylinder head gasket, a four-body contact simplified model of cylinder head-cylinder head gasket-engine block-bolts was built based on a four-valve diesel engine. Under different bolt preload and thermal state, contact state and deformation of cylinder head plate were calculated by using Augmented Lagrange multipliers as the contact algorithm. Then the influence of contact stresses and nodal displacements of mechanical constraints on some parts of the cylinder head plate were revealed in rated thermal state condition. Moreover the effect of different thermal state on the results was similarly revealed. The study makes clear that, when preload maintains the rated value and burst pressure is exerted, contact stresses in rated thermal state condition of the parts on cylinder head plate that against the cylinder ring and around the screw, which is on exhaust valve side, are similar with those values in cold state, while nodal displacements are reduced, and in different thermal states, the rates of change among the nodal displacements around the screw and both contact stresses and nodal displacements that against the cylinder ring are all less than 2 0 with few exceptions, contact stresses and nodal displacements of these parts of the cylinder head plate increase with the increases of the bolt preload. The results also show that cylinder head gasket sealing tests in normal temperature condition is roughly adequate to practical state.