Predictive Analysis for Engine/Driveline Torsional Vibration in Vehicle Conditions using Large Scale Multi Body Model

Driveline torsional vibration in vehicles equipped with an automatic gearbox can lead to increased fuel consumption. At low rpm the torque converter of the automatic gearbox is active. The earlier the torque converter can be disengaged and bypassed by a lock-up clutch, the better the efficiency of the engine. Torsional vibrations in the drivetrain could prevent this early locking of the torque convertor and thus lead to a higher fuel consumption. Furthermore, these torsional vibrations can also lead to lower driver comfort.

In order to improve the efficiency and the passenger comfort, a hybrid approach has been developed to predict the torsional vibrations of a full vehicle during a run-up manoeuvre on a chassis dyno, including transient effects. The hybrid approach is based on multi body modeling of the full car in LMS DADS, taking into account the flexibility of all major components of the powertrain.

This paper describes the specific application of this hybrid approach for the creation and use of a predictive model of a complete rear driven car with a 6 cylinder-4 stroke powertrain and automatic gearbox. The model is built in a step-by-step pragmatic approach based on multi body modelling and validated using experimental databases of critical components.

Using this model, several real live vehicle conditions are studied in a virtual way:

• full run up simulation with transmission in 3rd and 4th gear while the torque converter is in lock-up condition
• Idle condition with the transmission in drive and braking applied.

Other vehicle conditions can be simulated as well, the inputs that are required are the combustion forces corresponding to the manoeuvre, vehicle speed and the state of the gearbox. The model is built in a flexible way so that it can be extended to include more complex manoeuvres like gear shifting.

This kind of simulations enables one to:

1. 1
   identify operational excitation for specific engine orders;
2. 2
   predict engine bracket vibrations resulting from the operational excitation and prescribed dynamic boundary conditions;
3. 3
   predict driveshaft and propshaft torsional vibration, resulting from the operational excitation and prescribed loading;
4. 4
   predict operational deflection shapes of the car assembly under operational conditions

In a further stage, the virtual model is used to evaluate the influence of several design changes and to look for solutions that improve the efficiency and the NVH performance of the car. The adopted methodology is applicable for vehicle development purposes and has several advantages.