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A significant percentage of energy is lost in internal combustion engines due to valve train friction. The reduction of friction losses of a valve train is an important factor to improve significantly fuel efficiency and consequently emissions reduction. The friction loss of valve train includes the losses of the individual components and factors, such as spring load, temperature, lubricant type, mass of components, operating conditions and others. The breakdown of the friction within the valve train is necessary for the implementation of effective optimization measures. This paper presents an analysis of some influence factors associated to friction loss, utilizing the Design of Experiments approach. The results are based on dynamic measurements on a single overhead camshaft (OHC) engine valve train, performed on a test rig developed for friction torque measurements.

As a common trend on the automotive development process, the increase in system efficiency became a major concern for design engineers nowadays. Several are the focuses at which such topic can be dealt with, including full systems upgrades, electrification and component level optimization. However, there are simpler ways to increase efficiency by only replacing construction concepts that have always been taken for granted. This is the case of replacing the sliding friction of the camshaft hydrodynamic bearings by rolling elements. The direct reduction of the power consumption, when applying rolling element bearings to the camshaft, is a straightforward method to increase the liquid torque available at the crankshaft, hence enabling downsizing. In this paper some design solutions and the structural integrity of the system will be assessed and, most of all, the reduction on the friction torque, hence the increase in system efficiency, which leads to CO₂ emission reductions.