Phasing Strategy for an Engine with Twin Variable Cam Timing 2002-01-1101
Twin camshaft phasing was applied to a 1.6l 4-cylinder 16-valve DOHC engine. Both camshafts - intake and exhaust - were equipped with continuously adjustable cam phasing units. Different operating strategies were compared with regard to mechanical feasibility, thermodynamics and calibration. Attractive part load fuel economy was achieved with two different phasing strategies. With regard to full load and idle a preferred twin camshaft phasing strategy was determined.
It was found favorable to shift the intake camshaft largely towards ‘advance’, and the exhaust camshaft towards ‘retard’. Maximum fuel economy improvement was 8% at 2500 rpm and 3 bar mean effective pressure. In the European drive cycle 5 % fuel economy improvement was obtained.
To achieve superior performance it is mandatory to combine twin camshaft phasing with an appropriate exhaust system and optimized cam events. The best exhaust system was found to be a 4-2-1 manifold with 2 closed coupled catalysts in the manifold secondaries. With such an exhaust system, a tuned intake manifold and optimized cam events, a mean effective pressure of 12 bar was demonstrated between 2000 rpm and 4500 rpm. Compared with the base engine the maximum torque increase at 2000 rpm amounted to 15 %. The average torque increase was 10 %.
The described phasing strategy led to a 50 % reduction in NOx feedgas emissions in the European drive cycle. This reduction, along with the homogenous, stoichiometric operation enables the twin camshaft phasing technology to fulfill the tightest emission regulations with customary fuel quality and standard aftertreatment technology.
