Abstract: In traditional engine setups Belt Drive Systems (BDS) are in charge of power transmission from the crankshaft to the accessories. They are complex and critical dynamic mechanisms, involving contact mechanics and vibration phenomena. The hybridization of vehicles has increased the severity of the operating conditions of these systems that have become even more critical. The traditional alternator was substituted by a Belt-Starter Generator (BSG), an electric machine that can power the BDS in particular operating conditions to improve the Internal Combustion Engine (ICE) performance or to allow regenerative braking. The aim of the present work is to describe the design and the main characteristic of a test rig conceived to investigate in laboratory environment on the behaviour of belt drive systems in dynamic conditions. Two permanent magnet electric motors are used to replicate the dynamic behavior of crankshaft and BSG in a realistic, though controlled and repaetable, manner.68696

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Keywords: Automotive Control, Hybrid Vehicles, Belt Drive Systems, Dynamic Modeling, Front-End Accessory Drives, Model Based Control

1. INTRODUCTION

Belt Drive Systems (BDS) or Front-End Accessory Drives (FEAD) constitute the traditional power transmission mechanism to power the main internal combustion ancil- liaries such as the alternator, water pump and air con- ditioning pump. The torque generated by the Internal Combustion Engine (ICE) is transmitted by means of a serpentine belt that wraps around the driving and driven accessory pulleys of the drive systems.

BDS represent traditionally a complex and critical vehicle subsystem because of the performance specifications that need to be fulfilled. It usually in the severe ambient condi- tions of the engine compartment and is subject to highly dynamic excitations coming from the crankshaft harmon- ics. These harmonic excitation ,together with the inertia of the accessories (mainly the alternator), leads to vibrations of the belt and high tension fluctuations that can cause slippage and noise. To reduce these excitations a number of solutions have been developed including decoupling, filtering and overruning pulleys. The analysis of these phenomena led to the development of refined models of the belt pulley contact mechanics together with the definition of serpentine multi-pulley models to predict the dynamic response of serpentine belt-drive systems. A literature review shows that several research activities were carried out addressing separately the belt pulley mechanisms, see Bechtel et al. (2000), Rubin (2000), Hansson (1990), and the dynamic behavior of the transmission system, see Ul- soy et al. (1985), Hwang et al. (1994), Leamy and Perkins (1998). Only few attempts were done in the last 10  years

to bridge the gap between research on contact mechanics and dynamic analysis by Leamy and Wasfy (2002), Leamy (2003), Kong and Parker (2003). Tonoli et al. (2006) an- alyzed the effect of shear deflection of the belt on the rotational dynamic behavior of the transmission.

Additionally, the advent of hybrid technologies has seen the rise of a class of micro-hybrids that changes the oper- ating modes of the traditional belt drive systems. In this paradigm, the alternator is substituted with a Belt Starter Generator (BSG), an electrical machine able to work both as motor and as generator, causing a tight/slack span alternation when activated. The use of a BSG requires the introduction of a tensioning device able to keep the belt tension inside a safe range while preventing slippage facing the severe working conditions, see Cariccia et al. (2013). Several solutions have been proposed to satisfy this requirement, such as doble tensioners, decoupling tension- ers and active electromechanical or hydraulica tensioners. With the addition of active devices, such as the BSG and complex tensioners, the intelligent BDS (iBDS) becomes a complex and challenging mechatronic system.