A novel monitoring method of wet friction clutches based on the post-lockup torsional vibration signal

Abstract

Wet friction clutches play a critical role in vehicles equipped with automatic transmissions, power shift transmissions and limited slip differentials. An unexpected failure occurring in these components can therefore lead to an unexpected total breakdown of the vehicle. This undesirable situation can put human safety at risk, possibly cause long-term vehicle down times, and result in high maintenance costs. In order to minimize the negative impacts caused by the unexpected breakdown, an optimal maintenance scheme driven by accurate condition monitoring and prognostics therefore needs to be developed and implemented for wet friction clutches. In this paper, the development of a condition monitoring system that can serve as a basis for health prognostics of wet friction clutches with a focus in heavy duty vehicle applications is presented. The developed method is based on monitoring the dominant modal parameters extracted from the torsional vibration response occurring in the post-lockup phase, i.e. just after the clutch is fully engaged. These modal parameters, namely the damped torsional natural frequency fd and the decay factor σ, are computed based on the pre-filtered Hankel Total Least Squares (HTLS) method which has an excellent performance in estimating the parameters of transient signals with a relatively short duration. In order to experimentally validate the proposed monitoring method, accelerated life tests were carried out on five different paper-based wet friction clutches using a fully instrumented SAE#2 test setup. The dominant modal parameters extracted from the post-lockup velocity signals are then plotted in function of the service life (duty cycle) of the tested clutches. All the plots exhibit distinct trends that can be associated with the progression of the clutch degradation. Therefore, the proposed quantities can be seen as relevant features that may enable us to monitor and assess the condition of wet friction clutches. Since velocity sensor(s) is typically available in a transmission, the proposed monitoring method allows for the practical implementation.