6. Conclusion

At low frequencies (0 to 100 Hz), the GMP can be considered as a solid body subjected to the excitations of the idealized mobile coupling (i.e. without play or deformation) and gases. The 40 to 100 Hz sub-range is particularly interesting, as it is a frequency band in which the GMP can be assimilated to a solid body under free-floating boundary conditions: this is the so-called "quiet" zone. This zone can be advantageously exploited to determine the inertial characteristics of the GMP using the inverse method. Above 100 Hz, modes such as exhaust face, flywheel bending, GMP, crankshaft torsion, support torsion and bending may appear. The elasticity of the GMP or the crankshaft is sufficient to explain the existence of non-integer and odd harmonics in four cylinders (and not just multiples of 1.5 or 1 in three cylinders), which enrich the vibration sonogram of the GMP supports (see example...