This paper reports development of a measuring device built in a camshaft drive chain sprocket for detecting precise torque fluctuation with minimum change on the valve drive system dynamical characteristics. This torque measuring device (TMD) was designed to measure torque with minimum cross-talk with bending force or lateral force. To realize these functions, the disc portion of a chain sprocket that connects the teeth and the camshaft was carved to make thin plate area so that the strain gages placed on the area may have enough sensitivity to torque fluctuation. The signal from the circuit goes through frequency modulation and is transmitted to demodulation circuit via coil antennas. By this arrangement, almost perfect linearity was observed in the relationship of the TMD output voltage and the applied torque.
Using a model cylinder head unit of an in-line four cylinder gasoline engine driven by a variable speed electric motor, the TMD performance was evaluated. The measured waveforms were compared with ones calculated by AVL Tycon, multi-body dynamics simulation software. The low frequency features of the measured and calculated waveforms, such as the maximum amplitude, are found to be almost the same. This implies that the sensitivity of the measuring system was correct. However, the measured waveforms are not completely periodic. Waveform for each valve differs from one another. In addition, they contain irregular high-frequency damped free oscillation around valve opening timing. Such features are difficult to predict quantitatively by software in market. Further, because of high-sensitivity, torque fluctuation caused by chain engaging and disengaging was observable at high frequency range. These are the advantages of this technique over conventional ones.