Influences of friction-induced thermal phenomena and macroscopic surface features on the stability of a thin disk subjected to sliding contact
Abstract
Widespread use of disk clutches in transmissions has generated an interest in better understanding the dynamic behavior of clutches subjected to various operating conditions. The research conducted in this study focuses on thermal aspects of clutch engagement. It is divided into two parts: a study of transient fluid thermal effects during engagement and a study of thermally induced structural instability. Both portions of the research are concerned with the macroscopic behavior of clutches. The fluid thermal model is used to study torque transfer. Experimental data from a wet clutch dynamic test rig has been obtained for various initial temperatures and sliding speeds. By comparing analytical and experimental results it is shown that modeling thermal effects is important for accurately predicting characteristics such as peak torque and engagement time. The stability studies involve analyses of the conditions leading to divergence (static) and flutter (dynamic) instabilities when the clutch is operated under drag operating conditions. Static instabilities are shown to depend on sliding speed, friction coefficient, and temperature. A conservative estimate of the stability boundary can be determined by calculating two points on the boundary. Dynamic instability, which produces squeal vibrations, depends on sliding speed, friction coefficient, and temperature as well as the distribution of the stiffness of the friction material. Two types of instability boundaries are observed. For certain conditions, the stability boundary is “V”-shaped and a very small friction coefficient can cause an unstable response. For other conditions, the stability boundary is trough-shaped. Higher friction coefficients are needed to cause instability.
Degree
Ph.D.
Advisors
Sadeghi, Purdue University.
Subject Area
Mechanical engineering
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