International Conference on Engineering Vibration edition:2015 location:Ljubljana date:7-10 September 2015
Quietness and reliability, together with efficiency and lightweight design, are key requirements to compete in current mechanical industry. Within the latter, gearboxes play an important role as the usual choice to transmit mechanical power with high energy density, especially when using cylindrical involute gears. Noise and vibration performance are strongly influenced by tooth microgeometry modifications. Typical modifications are applied along the profile and the lead of the teeth. Profile modifications mainly compensate for tooth deflections; lead modifications mainly compensate for angular misalignments. Both modification types yield optimal performance at a given operating condition (e.g. nominal transmitted torque under ideal alignment), minimizing the meshing excitation. One key operating condition for the gear pair is represented by the instantaneous centre distance between the gears. Centre distance variations affect mainly the pressure angle for the transmitted contact force, the total contact ratio and the active tooth height. Furthermore after a change in centre distance, the contacting surfaces on the tooth flanks shift with respect to each other; this yields a mismatch with respect to the theoretical start for the tooth profile modifications. A precision gear test rig, where operating conditions can be varied and tightly controlled, is used in this paper to evaluate the effects of centre distance variations on the dynamic behaviour of a spur gear pair. The dynamic behaviour is characterized relying on the so-called Static Transmission Error (STE). Spectral analysis of the STE provides an indication of the internal excitation generated by gear meshing. Results show that the STE is sensitive to small changes in centre distance (in the order of 0.1% of the nominal value). In particular, it is also observed that the transmitted torque for obtaining minimum STE peak to peak value changes significantly as a function of the centre distance.