Fast modelling and simulation of the dynamic behaviour of a wet multidisc clutch during the engagement phase

In recent years multidisc wet friction clutches are of great importance to manufacturers of automatic transmissions (ATs) for the automotive industry, particularly since the introduction of double-clutched ATs. Their main advantage compared to their dry-friction counterparts is that they ensure smooth engagement, high reliability and long service life. Their progressive engagement due to the developed Couette flow between the discs enables them to be used both as clutches and as brakes in order to control power flow in simultaneously engaged geared shafts in the AT. Due to the coupled nature between the mechanical and the fluid dynamics regimes governing their operation, these systems are highly complex to be treated analytically and instead numerical approaches have proven to provide better results. However, the numerical treatment of such problems provides only case-specific results, which cannot be generalised and are not able to provide a general insight in the complex dynamics of the device. Furthermore the computational cost and the associated modelling and simulation effort during the design phase is high, making the incorporation of such methods in iterative design processes and algorithms counterproductive. In this paper the modelling of the dynamic behaviour of a wet multidisc clutch during the engagement phase is performed, via the combination of analytical and numerical methods and conclusions are drawn about the effect of the main geometric, kinematic and dynamic design parameters on the clutch’s response. The dynamic modelling is performed by applying the principle of linear and angular momentum on each disc. The effect of the fluid film is taken into account through the solution of the governing Navier-Stokes equations via CFD analysis or by the use of semi-analytical solutions with high accuracy, where applicable. Therefore both the developed pressure field and the torque of the fluid film are calculated efficiently and used in the simulation of the system. The flow is assumed to be laminar and the discs rigid and flat