Analyzing Vibrations in an IC Engine Valve Train

This study analyzes the vibration characteristics of the valve train of a 2.0L SOHC Chrysler Corp. Neon engine over a range of operating speeds to investigate and demonstrate the advantages and limitations of various dynamic measurements such as displacement, velocity, and acceleration in this application. The valve train was tested in a motoring fixture at speeds of 500 to 3500 camshaft rpm. The advantages of analyzing both time and frequency domain measurements are described. Both frequency and order analysis were done on the data. The theoretical order spectra of cam displacement and acceleration were computed and compared to the experimental data. Deconvolution was used to uncover characteristic frequencies of vibration in the system. The theoretical cam acceleration spectrum was deconvolved from measured acceleration spectra to reveal the frequency response function of the follower system. The frequency response function of the valve spring was separately measured and deconvolved from the acceleration spectra. Significant coupling of the valve spring dynamic response and the cam input function at higher speeds is seen. The presence of a significant non-cam-lobe related 16th order vibration is found. Structural resonances at 576 Hz and 1.52 kHz are also detected. Recommendations regarding valve train test procedures are made.