1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

As viewed, all depicted lubricated records share common features which are a high value of variance in low speed region followed by a linear decrease, which later enters into a speed-independent section. Location, where the slope diminishes, corresponds to a region, where the transition of the bearing to fully developed EHL film was predicted for each of lubricants by the model. For oil viscosity 22 cSt, the speed-independent section is missing, due to λ = 3 is per Figure 3 beyond the tested speed range. For the dry, unlubricated bearing, the progress of variance completely differs from the lubricated cases. Figure 6: Progress of signal feature: variance normalised by mean value of the signal, with depicted predictions of locations, where bearing enters the EHL regime.

Source: Own elaboration (2020) The hypothesis, that observed changes and behaviour of the signal indicate the state of the lubrication film is based on following argumentation further discussed in (Chmelar, 2020): 1. The characteristic changes correspond to predicted zones of bearing transition into EHL regime. It was observed for 3 different lubricant viscosities. 2. Minimum value of the signal, which is attributed to transition of roller between PZT elements, increases with the speed, but saturates when predicted EHL is achieved. It was illustrated by change of normalised variance slope in Figure 6. This behaviour is due to presence of lubrication film in the contact, for which the propagation speed of waves in the interface is lower than for direct metal – to-metal contact. The increase of propagation time then corresponds to less frequent direct contact of rolling element and race with increasing film thickness. The saturation at speeds of predicted EHL state then is attributed to full separation of the rolling element and race, so the propagation speed of waves is only driven by properties of lubrication film. 3. Very low increase of maximum value of the signal with the speed is attributed to its propagation in the interstices between rolling elements. The minor increasing trend is explained by growing amount of oil remaining in the interstices with the speed and therefore negatively influencing the propagation speed of waves at the interface.

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