Heat generation and transfer in automotive dry clutch engagement

Abstract

Dynamic behaviour of automotive dry clutches depends on the frictional characteristics of the contact between the friction lining material, the flywheel, and the pressure plate during the clutch engagement process. During engagement due to high interfacial slip and relatively high contact pressures, generated friction gives rise to contact heat, which affects the material behaviour and the associated frictional characteristics. In practice excess interfacial slipping and generated heat during torque transmission can result in wear of the lining, thermal distortion of the friction disc, and reduced useful life of the clutch. This paper provides measurement of friction lining characteristics for dry clutches for new and worn state under representative operating conditions pertaining to interfacial slipping during clutch engagement, applied contact pressures, and generated temperatures. An analytical thermal partitioning network model of the clutch assembly, incorporating the flywheel, friction lining, and the pressure plate is presented, based upon the principle of conservation of energy. The results of the analysis show a higher coefficient of friction for the new lining material which reduces the extent of interfacial slipping during clutch engagement, thus reducing the frictional power loss and generated interfacial heating. The generated heat is removed less efficiently from worn lining. This might be affected by different factors observed such as the reduced lining thickness and the reduction of density of the material but mainly because of poorer thermal conductivity due to the depletion of copper particles in its microstructure as the result of wear. The study integrates frictional characteristics, microstructural composition, mechanisms of heat generation, effect of lining wear, and heat transfer in a fundamental manner, an approach not hitherto reported in literature.

中文概要

目的

本研究旨在凸显热效应在离合系统动态摩擦分析 中的重要性以及将其拓展到制动系统的可能性。

创新点

采用一种未被报道过的新方法从根本上整合摩擦 特性、微结构组分、产热机理、摩擦片磨损和传 热机制。

方法

基于能量守恒原理,针对由飞轮、摩擦片和压力 板构成的离合系统提出一种适用于工业应用的热分区网络解析模型。

结论

1. 通过实测得到的μ-ν 特性表明,新的摩擦片具 有磨损片子所不具备的温度敏感性。2. 通过对磨 损片子的微结构分析以及热导率变化的测量显 示,晶格结构中铜颗粒损耗会导致其导热性能减 弱。3. 使用摩擦计的测量结果显示新的摩擦片相 对于磨损片子具有更高的摩擦系数;较高的摩擦 系数减轻了离合器啮合时产生的界面滑移的程 度,从而减小了由于产热导致的摩擦功率损耗。 4. 根据本文发展的热学模型,新的摩擦片可通过 其优良的导热性将摩擦产生的热量释放出去。