Indirect measurement of main bearing loads in an operating diesel engine

This paper deals with the application of indirect measurement techniques to an operating diesel engine. Internal loads exciting the engine block during operation are not directly measurable with force sensors; they have to be assessed from the dynamic deformation of the structure. The idea is to use the structure itself as a multi-force sensor, which requires the knowledge of the transfer functions between considered excitations and measured responses. The first part is devoted to the description of the methodology. In Section 1, the extraction of uncorrelated deflection shapes from stationary measurements is presented. Then the pseudo-inversion technique, needed to invert the transfer system, is reviewed. Optimization of the inversion, based on a weighing technique, is presented in Section 3. Then a regularization process based on the truncated singular value decomposition and the L-curve principle is suggested. In the second part, a basic model of a drive train is used to directly assess internal excitations from the measured cylinder pressures. Outputs of this model are compared with excitations indirectly measured on the operating engine in a third part. The efficiency of the optimization and regularization processes is illustrated, and encouraging results are presented, allowing information on defects of the drive train model to be obtained. Finally, a ranking operation is realized on internal excitations to illustrate the strong interest of the results of indirect force measurement.