Abstract
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.
Highlights
Successful modelling and evaluation of a wet multidisc clutch is a fairly demanding and complicated process if treated analytically and numerical methods are employed to solve the coupled problem of solid and fluid mehcanics
A simplified configuration of a wet multiplate clutch is presented in Fig. 1 where the following two systems are indetified: the primary system consisting of the clutch input shaft engaged with the engine and the male discs and the secondary system consisting of the output shaft engaged with the housing and the female disks
The progressive engagement of the clutch due to the developed shear stresses applied by the Couette flow on the surface of the discs, implies the radial outflow of the fluid which is provided by the axial displacement of discs by means of a hydraulic actuator
Summary
Successful modelling and evaluation of a wet multidisc clutch is a fairly demanding and complicated process if treated analytically and numerical methods are employed to solve the coupled problem of solid and fluid mehcanics. The incorporation of such methods in the modelling of complete power transmission systems involving wet multidisc clutches [5], [6] (such us the well-known double clutch ATs) makes the total simulation proccess of the power-train consuming in terms of time and recourses. Aiming in the composition of wet clutch fast models that assist the design process in terms of computational cost, this paper proposes the use of semi-analytical methods in order to study the dynamic behavior of a multidisc wet clutch during the engagement phase
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