Dynamic Responses of a Drivetrain System with Dry Friction Clutch under Time-Varying Normal Load Chengwu Duan a , Rajendra Singh b Acoustics and Dynamics Laboratory Department of Mechanical Engineering The Ohio State University Columbus, Ohio 43202, USA ABSTRACT This study aims to acquire a better understanding of the dynamic response of a dry friction (slip torque converter) clutch that is widely found in automatic transmissions. A drivetrain system is simplified as a two-degree of freedom torsional system for the sake of illustration. Friction clutch is treated as a power transmission path that is subjected to time-varying normal load. Under a sinusoidal torque excitation, three types of friction interface motions, namely pure stick, pure slip and stick-slip motions are determined via analytical or computational approaches. Transient time histories are of interest. It is observed that a well-tuned normal load could possibly attenuate the stick-slip transients even in the presence of the negative slope in friction-velocity characteristics. Plausible physical explanations are provided. 1 INTRODUCTION In this paper, we examine the slipping torque converter clutch (TCC) that is employed in automotive driveline system, as illustrated in Figure 1a. In particular, we investigate the nonlinear dynamics of a two-degree of freedom (2DOF) torsional system with a dry friction controlled path. Earlier work by Duan and Singh [1-2] had found significant stick-slips motions in this torsional system and. However, prior work assumed a time-invariant friction problem, i.e. constant normal load N . In this study, we investigate the effect of time-varying N for the same torsional system. Unlike the classical dry friction damper problem that has been examined by many researchers [3-5], the dry friction element of Figure 1a is a key path that transmits the mechanical power. The non-linear friction torque sf T is applied by an actuation pressure () Pt , and in this study, we assume () Pt to be harmonic along with a mean term. Figure 1b shows the schematic of a reduced automotive driveline system. Here, 1 I represents the combined torsional inertia of flywheel, 2 I is the inertia of friction shoe and pressure plate, 3 I is the wheel and vehicle sub-system that is assumed to be rigid. The governing equations for this system are: 1 1 1 2 ( , ) () sin( ) f e m p I T t T t T T t θ θ θ ω + − = = + && & & , (1a) 2 2 23 2 23 2 1 2 ( , ) f I C K T t θ θ θ θ θ + + = − && & & & . (1b) Here, 1 θ are 2 θ are absolute angular displacements; 23 C and 23 K are the lumped viscous damping and stiffness associated the automotive driveline. The engine torque excitation () e T t a Email: duan.19@osu.edu b Email: singh.3@osu.edu