Integration of a CAM Phaser on an Engine to Reduce Fuel Consumption: A Comprehensive Approach to the System

The paper presented describes the application of a Continuously Variable Cam Phaser (CVCP) to an existing engine, with the scope of reducing significantly the engine specific fuel consumption at part load, through the reduction of pumping losses. A single vane-type cam phaser was adopted, which controls both intake and exhaust cam events simultaneously, thanks to the particular cam timing assembly used on the base engine (FIAT-GM Powertrain FIRE 1,4 16v). The cam phaser itself is powered by the same oil which lubricates the engine, through a three-way solenoid valve controlled by the Engine Management System (EMS) with an on-off duty cycle signal. The design and experimental activity done to introduce the CVCP on an existing engine is described, which must comply with a number of key features needed (advance and retard travel speed, precision in actuation, minimum oil leakage, no increase of oil pressure required, minimum additional oil mass flow required) and constraints required (reduced modifications of base engine and of production line, system cost). In particular the base engine structure, which features cam timing command through toothed belt, limited room in the cylinder head for oil and blow-by gases, hydraulic tappets, wide camshaft bearing diameter, no external oil/gas separator, determined the need to limit the overall oil mass flow within the cylinder head: this was required to avoid possible oil recirculation into the intake manifold through the crankcase venting system. For this and other reasons, an accurate and comprehensive optimization of all the components involved in the above described system was needed. An extensive experimental activity was performed, which included the cam phaser design optimization, the re-definition of camshaft bearing and hydraulic tappet clearances, the re-design of piston rings, some prescriptions for the cam phaser control strategies and calibration of the EMS. This development work achieved a system definition which solves all the main problems described above, with no additional costs with respect to (w.r.t.) the first version of the CVCP engine, since no additional parts have been required nor particular material or machining or configurations were prescribed. The described engine is currently in its industrialization phase: it is planned to produce about 1000 engines/day in the Italian FIRE engine manufacturing plant (Termoli).