An Experimental Study on Camshaft Impact Noise by Dynamic Coupling of Valve Train and Chain System

To improve the fuel efficiency and satisfy the strict emission regulations, the development of internal combustion engine gets more complicated in both hardware and software perspectives, and the margins for durability and NVH quality become narrower, which could result in poor NVH robustness in harsh engine operating conditions. In this paper, we investigate experimentally the camshaft impact noise mechanism relating the valve train and timing chain forces to detailed motion of the camshaft and the chain tensioner. After the initial investigation of identifying the impact timings and specific engine operating points when the noise occurs, the camshaft orbital motion inside of the sliding bearing is measured and visualized with the proximity sensors with calibration after sensor mounting, in addition to the chain tensioner movements. It is shown that the impact noise occurs at the event of the abrupt change of camshaft orbital motion, which results from the combined resultant force of valve train and timing chain forces. As the valve timing has significant effects on the breathing and combustion efficiency sequentially, only the timing chain force on the camshaft is modified in a way to reduce the abrupt change of movement of the camshaft. In conclusion, the mechanism of camshaft impact has been identified with the proper visualization of the camshaft movement together with the tensioner force-displacement diagram in problematic engine operation condition.