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首页> 外文会议>2003 Fall Technical Conference of the ASME Internal Combustion Engine Division; Sep 7-11, 2003; Erie, Pennsylvania >Two Dimensional Effects in the Lubrication of the Cam-Tappet Contact
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Two Dimensional Effects in the Lubrication of the Cam-Tappet Contact

机译：凸轮-挺杆接触的润滑中的二维效应

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摘要

The cam-tappet contact experiences very high loads and the lubrication conditions are Elasto-Hydrodynamic (EHD). In EHD lubrication the oil film thickness (OFT) is mainly determined by the entrainment speed of the oil and the oil viscosity. Under the high load present in the cam-tappet contact the OFT reaches very small values in the order of magnitude of a fraction of one micrometer and asperity contacts cannot be avoided. In this situation the friction force has two components, a boundary and a viscous one, and non-Newtonian behavior of the oil prevails. The friction force is determined by the theological properties of the oil and the geometry of the contact (combined radius of curvature, cam width and combined asperity of the rubbing surfaces). For valve trains with bucket type tappets, the mechanism is design to rotate the tappet during engine operation. In this situation, both the entrainment speed and the radius of curvature are varying along the contact line determining variations in the OFT and, .consequently, variations in the contribution of the boundary friction component. Based on a simulation model that considers the tappet spin under the action of the friction force between cam and tappet, and the friction force between tappet and its bore, the entrainment speeds and their directions were calculated along the contact line. It was found that the boundary friction component reaches a maximum value at the inner edge of the cam, at the beginning of the valve-closing event. Because the boundary component of the friction force is mainly responsible for wear, an increased wear of this region should occur. Visual inspection of a used camshaft seems to confirm this finding.
机译：凸轮-tappet接触件承受很高的载荷，润滑条件为弹性流体力学（EHD）。在EHD润滑中，油膜厚度（OFT）主要取决于油的夹带速度和油粘度。在凸轮式止回阀触点中存在的高负载下，OFT达到非常小的值，约为一个微米的数量级，无法避免粗糙接触。在这种情况下，摩擦力具有两个分量，边界分量和粘性分量，并且油的非牛顿性行为占主导。摩擦力由油的流变学特性和接触件的几何形状（组合的曲率半径，凸轮宽度和组合的粗糙表面粗糙度）决定。对于带有铲斗式挺杆的气门机构，该机构设计为在发动机运行期间旋转挺杆。在这种情况下，夹带速度和曲率半径都沿着接触线变化，从而确定了OFT的变化，从而确定了边界摩擦分量的贡献的变化。基于一个在凸轮与挺杆之间的摩擦力的作用下考虑挺杆旋转以及挺杆与其孔之间的摩擦力的仿真模型，沿接触线计算了夹带速度及其方向。已经发现，在气门关闭事件开始时，边界摩擦分量在凸轮的内边缘处达到最大值。因为摩擦力的边界分量主要是磨损的原因，所以该区域的磨损会增加。目视检查二手凸轮轴似乎可以证实这一发现。

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