Driveline Modeling, Experimental Validation and Evaluation of the Influence of the Different Parameters on the Overall System Dynamics 2008-01-0632
The paper presents the driveline models conceived by the author in order to evaluate the main parameters for an optimal tuning of the driveline of a passenger vehicle. The paper deals with a full modal analysis of the contributions of the different parts. The implemented models permit to consider the non-linear driveline dynamics, including the effect of the clutch damper (in terms of non-linear stiffness and variable amplitude hysteresis in the case of the models in the time domain) and the halfshafts, the engine mounting system and the tires.
The influence of each component of the driveline on the overall frequency response of the system is presented. In particular, the paper demonstrates that the tire can be modeled like a non-linear damper within the rotational dynamics of the driveline and that it is the fundamental component contributing to the first order dynamics of the transmission. The equivalent damping coefficient of the tire can be derived as a function of the vehicle longitudinal speed.
The simplest model capable of taking into account the first order dynamics of the driveline has to consider the moments of inertia of the engine and the driveline, the stiffness of the halfshafts and the damping coefficient of the tires (which link the wheel to the equivalent inertia of the vehicle). The same model without the tire would be underdamped and characterized by too high natural frequencies. The model of the driveline, including the engine mounting system, is linked to a vehicle model conceived for the evaluation of the drivability and the comfort during the gearshift. In particular, it takes into account the vertical motion of the vehicle sprung and unsprung masses, body pitch dynamics and anti-dive/anti-lift dynamics of the suspension.
An analysis of the natural frequencies of the undamped and damped systems and of the vibration modes by considering the vehicle and driveline models (under linear and non-linear hypotheses) at increasing levels of complexity is discussed and derived. In particular, the natural frequencies related to the layout of the engine mounting system are discussed. The interaction between the natural frequencies of the driveline/engine mounting system and vehicle body motion is examined in terms of vertical displacement of sprung/unsprung masses and pitch angle of the vehicle. The most complex model deals with the interaction between suspension dynamics, engine mounting system dynamics and driveline dynamics.
The experimental validation of this sophisticated of the five models included in the paper is presented. Some examples of applications of the model, like real time simulation within the validation process of the control algorithm of an automated manual transmission system or the adoption for the prediction of the comfort during the gearshift process, are also considered.