An in situ method is presented to identify ten engine inertia parameters and system dynamic stiffness from the frequency response functions. The ten engine inertia parameters and system dynamic stiffness are estimated from two distinct steps. The accuracy of the proposed technique is verified by finite element simulation, and then the generality is validated using an engine supported by a specially designed curved bar spring. The locations of the measure points on the results are also carefully investigated. The identification of system dynamic stiffness is validated comparing with the engine with an auxiliary plate, which shows good consistency with the results identified from the study.

A valve mechanism supports the working process of an engine cylinder, and a camshaft is a key component required to open and close a valve. When a camshaft loosens, the balance of the engine disrupts. In the meanwhile, the generalised force at its centre of gravity (CG) alters. This study proposed a novel technique to detect camshaft loosening based on recognising the generalised force at the CG of the engine. We conducted Hanning windowed interpolation of discrete spectra to extract the precise phase and amplitude by utilising the acceleration signals at the engine cylinder and mounts and cylinder head. We then accurately computed the generalised force at the CG. Finally, we accurately extracted the camshaft loosening features by analysing the main harmonic orders for the generalised force. As indicated by simulations, our method can be used to effectively detect combustion engine faults involving camshaft loosening.