Fuel economy sensitivity analysis for DLC coatings on tappets 2018-36-0027
Today there are efforts for greater energy conservation and reduction of greenhouse gas emissions. In this context, the fuel consumption of automobile engines remains an important study subject. A small gain in fuel consumption, even by 1% over existing levels, is an important achievement. Fuel efficiency is highly affected by engine torque losses which are generated by each engine subsystem. In valvetrains, for example, there are losses associated with the hydrodynamic bearings of the axes control valves, losses associated with interactions between tappet and bore, losses associated with cam and tappet interactions, etc… In valvetrains provided with mechanical bucket tappets, very applied due to its constructive simplicity, it is estimated that about 85% of the total torque losses are generated by interactions between the cam and the tappet. In order to minimize these losses by friction, coatings like diamond like carbon (DLC) can be applied on the normal production tappets. The fuel consumption of a light passenger vehicle, powered with an I3 engine, for example, with tappets coated with DLC, differs from the fuel consumption of the same vehicle equipped with normal production tappets. The percentage difference between these consumptions is determined by the use of enterprise software for the simulation of consumption cycles, resulting in a reduction of about 0.5% in the combined North American cycle. In addition, it was performed a sensitivity analysis in fuel economy, considering mathematical variations of engine torque losses, taking as reference the effects of using the tappets with DLC. A nonlinear behavior was discovered.