Engine developers and OEMs have mastered the small engine – less displacement, fewer cylinders, yet maintaining driving pleasure. Today, 4-cylinder engines are even commonplace in the luxury segment. Established measures – like fewer cylinders, higher cylinder pressure and early clutch lock-up – increase the speed irregularity in the lower engine speed range. The connected drivetrain is increasingly susceptible to vibration. So, to keep or even improve the expected driving pleasure, influencing parameters must be analyzed early in the concept phase of drivetrain development, and counter measures must be evaluated to reduce interior noise.
To achieve this, FEV developed a method to support drivetrain development from concept up to the start of production. The key component of this method is multi-body simulation of the drivetrain using FEV’s “Virtual Engine” software. The simulation result is either directly evaluated within the software, or serves as input for a subsequent Vehicle Interior Noise Simulation with “FEV VINS”, which combines the simulated excitations with the vehicle body transfer functions of the corresponding noise path.
As complex as necessary, as simple as possible
The complexity of the interior noise simulation can be varied depending on the existing input data and the target. This ranges from a pure simulation of the structure-borne noise with smoothed standard transfer functions, to the calculation of a more realistic interior noise using vehicle specific transfer functions, including combining measured airborne noise shares.
Also the complexity of the multi-body simulation can meet the requirements of the development process. In the concept phase, where only basic input data are available and very different configurations need to be quickly evaluated, a pure torsional vibration model can be set up. In the further course of the development process the model is extended to a full 3-D model by adding different sub-systems like wheel suspension.
As an example, the illustration shows Campbell diagrams of the interior noise for a full load run up. Here the simulated interior noise (right) can be compared to the measured noise (left), because vehicle specific transfer functions have been used.
In contrast to the measured noise the simulated noise only includes the noise shares caused by the drive train. The comparison shows that these are dominant in this vehicle below 100 Hz, especially for the ignition order. The measurement also includes non-rotatory excited noise shares. E.g. the high level of the fourth engine order at 100 Hz can be traced back to the orifice noise of the exhaust system.
Due to the shown variation possibilities of the simulation depth from pure torsional vibration models up to the calculation of realistic interior noise, the presented method can be effectively applied at all stages of the development process.