Experimental investigation of the valvetrain friction in actual engine operation conditions

Recently, the demands for improved fuel economy have been continually rising because of environmental protection policies, legislative pressures on emissions and increases in the price of oil. Reducing the friction power loss in a production engine may be regarded as one of the most effective technologies for improving fuel economy because the technology is cost effective and applicable to a great number of vehicles. This paper describes attempts to measure the torque needed to drive a camshaft and to examine the sources of the torque fluctuations in order to analyze the friction in valvetrains. The measurements were performed through a cam sprocket-type torquemeter, which was able to measure the torque of the valvetrain under actual engine operating conditions. In the cam torque measured, the fluctuations were mainly dependent on the primary oscillations caused by cam events and the secondary oscillations caused by the valvetrain natural frequency. The range of the fluctuations became greater at high speed because of the inertial mass. The resulting FMEP (friction mean effective pressure) of the valvetrain decreased, and the effective peak tension increased with an increase in the engine speed.