SAE TECHNICAL PAPER SERIES2007-24-0138 Friction inside Wheel Hub Bearings: Evaluation through Analytical Models and Experimental Methodologies A. Sorniotti University of Surrey, School of Engineering E. Sampò, M. Velardocchia, E. Bonisoli, E. Galvagno Politecnico di Torino, Department of Mechanics Capri, Naples Italy September 16-20, 2007 2007-24-0138 Friction inside Wheel Hub Bearings: Evaluation thro ugh Analytical Models and Experimental Methodologies Aldo Sorniotti University of Surrey, School of Engineering Enrico Sampo’, Mauro Velardocchia, Elvio Bonisoli, Enrico Galvagno Politecnico di Torino, Department of Mechanics Copyright © 2007 SAE International ABSTRACT This paper presents an experimental methodology whi ch can be adopted to measure the friction torque of th e bearings in the wheel hubs of passenger vehicles. T he first section of the paper highlights the reasons w hy an experimental device is necessary to have an objecti ve evaluation of the performance of the bearing in ter ms of friction. In particular, the high level of approxim ation of the current formulas for the estimation of the fric tion inside a single bearing is discussed and demonstrat ed. An analytical methodology for the evaluation of the distribution of the axial load between the two bear ings of the wheel hub is presented. However, its practical application for the precise calculation of the dist ribution of the load has to be checked through experimental tests. The following part of the paper is focused o n the possible solutions which can be adopted to conceive a test rig to measure friction inside the bearings of wheel hubs by considering the effect of the real loads ac ting on the hubs of the vehicle (due to the forces between the tires and the road surface). The most efficient sol ution of test rig is developed and implemented for the evalu ation of the friction of the bearings of a 3-wheel low consumption vehicle. This solution, which can be properly sized according to the considered applicat ion, can be extended also to the evaluation of the performance, in terms of friction, of the hubs of s eries production passenger cars. INTRODUCTION Nowadays one of the most challenging targets in the field of automotive engineering is the reduction of fuel consumption. The major issues from this point of vi ew are related to the reduction of vehicle weight. In fact, vehicle weight exerts an influence both on the loss es related to tire rolling resistance and on the fuel consumption related to the acceleration of the vehi cle. Other major issues in the context of fuel saving technology are the optimization of tires performanc e in terms of their rolling resistance coefficients and of vehicle shape in terms of aerodynamics. Another key point is the optimization of the efficiency of the engine and transmission (with particular reference to the gearbox). However, car manufacturers and their suppliers, in order to obtain the best possible res ults, are trying to optimize also other components, like the bearings of the wheel hubs, which should theoretica lly give origin to a second approximation effect in ter ms of final result on the overall vehicle. Wheel hubs are usually characterized by a couple of separate taper roller bearings in the case of industrial vehicles, wherea s they are usually characterized by an integrated system o f two diagonal contact ball bearings in the case of passe nger cars. In most of the wheel hubs there is a unique external ring and two separate internal rings. The alternative integrated system adopts a slightly dif ferent setup with one internal and one external ring. One of the key points of wheel hub bearings is that they have to be optimized for a wide spectrum of working conditions, because of the significant variations o f the loads at the wheel hubs induced by the dynamics of the vehicle on the road. A first approximation evaluati on of the loa