Tribologic Analysis, Wear Evolution and Torque Trend Estimation of an LSD Clutch Pack

Tribologic Analysis, Wear Evolution and Torque Trend Estimation of an LSD Clutch Pack

Amedeo Tesi (University of Florence, Florence, Italy), Emanuele Galvanetto (University of Florence, Florence, Italy), Claudio Annicchiarico (University of Florence, Florence, Italy) and Renzo Capitani (University of Florence, Florence, Italy)
DOI: 10.4018/IJSEIMS.2017010102
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Abstract

The wear phenomenon in friction clutches involves a variation in the contact pairs characteristics, defining a decay of transmissible torque properties. For multidisk clutch packs installed in electro-actuated differentials, the friction torque evolution allows to define how wear decay can influence the dynamic of the vehicle where the differential is installed in. A tribological analysis of a molybdenum-coated clutch pack was made under typical working conditions in terms of temperature, normal load and sliding speed. Friction coefficient and wear rate trends were outlined to define material characteristics through block-on-ring tests. Metallurgic studies on the specimens used in tribologic tests validated the base material used in the samples. Results from experimental analyses were used as input for a numerical study regarding wear and pressure evolutions during clutch engagement. The application of Reye's theory and Archard's law on a FE model of the clutch led to the definition of an algorithm to estimate the friction torque generated by the clutch system and the its lifetime.
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Introduction

The dynamics of clutch pack installed inside electro-actuated differentials are highly influenced by the disks engagement behavior and their material properties. Torque transmission in differential clutch pack is guarantee by friction surfaces; lots of applications in motorsport field use commercial treated disks, typically treated with molybdenum-based coating or other treatments, with the aim to control as well is possible the vehicle dynamics. To keep a high performance level of the differential during its lifetime it is important to know how each component works, especially the internal clutch.

Tribologic studies on clutch apparatus were made in last years by Lingsten et al. (Lingesten, et al., 2012) developing an apparatus for continuous wear measurement with the aim to obtain more information about clutch characteristics. Another example of tribologic study has been made by Marklund et al. (Marklund & Larsson, 2008), where wet clutch characteristics have been described to obtain a friction coefficient trend in relation with the temperature and with the implementation of oil characteristics. The influence of surface topography on the friction characteristics of a sintered-treated clutch pack has been outlined by Nyman et al. (Nyman, Maki, Olsson et al., 2006). A large number of studies were carried out with the aim to evaluate the progressive wear trend in some contact, as it is possible to see in (Thompson & Thompson, 2006). In this work, Thompson et al. calculated wear strain in order to modify the elastic strain in an element using the Archard equation. Another Archard application could be found in Garleanu et al. work (Garleanu, Popovici, Garleanu et al., 2008); the Archard’s law was used to define wearing phenomenon in a FE domain, obtaining a medium level of prediction of wear. Andersson et al. (Andersson, Almqvist, & Larsson, 2011) and Liu et al. (Liu, Jang, & Barber, 2014) studied the application of Archard equation to define a modified pressure distribution. In Liu’s work the method was applied only on linear systems where full contact is maintained at all times, while in Andersson’s study the application of Archard’s wear equation outlined some important factors as roughness, temperature and lubricant additive-surface interaction. Kim et al. (Kim, et al., 2005) studied the implementation of wear trend analysis in oscillatory contacts. Adhesive wear was studied by (Waghmare, 2016) using an accurate FE model of asperity contact. An important study on the correlation among experimental campaigns and finite element analysis could be found in (Podra & Andersson, 1999), where wear trend was defined using a pin-on-disk apparatus and implemented in a FE domain. A detailed study on the tribological and mechanical characteristics of a brake disc using a FE approach was performed by (Belhocine, 2015) and later by (Ali Belhocine, 2016). On the friction characteristics definition, an important study was made by (Asif, Chandra, & Misra, 2013), evaluating the characteristics of brake pads material with the aim to provide improved manufacturing process. An optimization in the design of contact pairs production using a Taguchi approach was developed by (Zaharudin, Talib, Berhan, Budin, & Aziurah, 2012). Taguchi method was also followed by (Rajesh, 2013) in order to define a statistical model and analysis of SiC reinforced aluminum MMCs. The same approach was used by (Prasanta Sahoo, 2014) and (Priya Shekar Gajjal, 2015) with the aim to define optimized tribological relationship in different contact pairs.

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