Cam Phaser Actuation Rate Performance Impact on Fuel Consumption and NOx Emissions Over the FTP-75 Drive Cycle

Variable valve timing technology allows more flexibility for modern engines to meet peak performance, fuel economy and low emissions targets while providing good driveability. The most common device to achieve such improvement and comply with new emissions legislation is the oil pressure actuated cam phaser. Calibration for variable valve timing using dynamometer testing at steady state is the base for mapping the intake and exhaust valves phasing positions for the range of engine speed and load.

Calibration is aimed at improving fuel economy and emissions levels while avoiding combustion instabilities. During a transient however, the actuation rate limitations of the cam phasing device, which depends on available oil pressure, cause the phaser to not meet the ECU timing map request. This lag alters the engine optimum operation. A proposed solution, the Cam Torque Actuated phaser or CTA, uses available cam torque energy to sustain high actuation rates independently of oil pressure. Comparing simulation results between a continuously variable CTA phaser and a state of the art vane type Oil Pressure Actuated phaser (OPA), a 1.76% and 22% benefit for fuel consumption and NOx emissions respectively was achieved over the entire FTP-75 drive cycle. This paper outlines the analytical approach and detailed simulation results of the phaser actuation rate performance impact on fuel consumption and engine out NOx emissions for a V6 3.5L gasoline engine over the FTP-75 drive cycle.