Influence of Profile Modifications on Transmission Error and Noise of Spur Gears

All gear sets are tested on the facility described in Chapter 2. A clockwise torque is applied by the motor and the load is varied from 25 to 250 Nm, with 25 Nm incremental steps. Transmission error is measured at 200 rpm, assuming that for such speed dynamic effects are negligible. Data acquisition and elaboration is performed by means of the procedure described in the previous chapter; TE is measured for one complete revolution of the input shaft and thanks to the once-per-revolution signal of the two encoders, transmission error is measured, for every gear set, from the same pair of teeth in contact. Transmission error curves are shown in Figure 3.27; each diagram refers to a different gear set and colours are the same used to identify the various profile modifications. Pinion angular position is represented on the x-axis, while TE expressed in microns is shown on the y-axis; each curve corresponds to a different applied torque as reported in the legend. It is worth noting that, for every gear set, the mean value of the TE curves decreases as the torque increases; in fact, according to the theory, as the load increases, the delay of the driven gear increases; transmission error is then negative and its absolute value increases with the load. Each curve is composed by a low frequency component, correspondent to the once-perrevolution frequency of the input shaft and caused by pitch errors as well as gears runouts, and by high frequency components related to the gear mesh cycle. Since for every gear set, transmission error is measured from the same pair of teeth in contact, TE curves have the same low frequency component; the end value of each curve is not equal the initial value, since all possible combinations of meshing teeth are not made out: this would have occurred after a number of revolution of the input shaft equal to the number of teeth of the driven gear.