Reciprocal Powertrain Structure-borne Transfer Functions Synthesis for Vehicle Benchmarking 2007-01-2354
In order to characterize and summarize the structure-borne performance of the body and the NVH treatment of a group of vehicles independently from the type of powertrain, a reciprocal transfer function synthesis procedure is applied with respect to structure-borne noise.
Structure-borne transfer functions or Noise Transfer Functions (NTF) are useful to quantify the vehicle acoustic sensitivity to structure-borne noise. Direct NTF measurements are difficult to perform on full vehicle configuration due to modern cars congested engine bays, and often require engine dismantling to take into account all the individual structure-borne routes; traditional impact testing is also time consuming and limited to low frequencies.
In the reciprocal approach the full vehicle is acoustically excited in the interior passenger compartment by means of a Low Frequency and a Middle-High Frequency calibrated point sources to cover the whole structure-borne frequency range of investigation: all the transfer paths are thus excited, and measured, simultaneously. This implies a significant reduction in time requirements and an easier testing procedure compared with the direct method. The mechanical responses at the powertrain body mounting points from the two sources are summarized with a magnitude phase-less technique and synthesized to a single curve in the 40 - 1000 Hz range, a wider frequency range compared to direct measurements capabilities.
The same acoustic sources and a similar procedure are also applied to evaluate the air-borne transfer function performance of the full vehicle.
The presented procedure, complemented with reciprocal air-borne transfer functions, is part of the Vehicle Benchmarking Performance Program, and is well suited to quickly rank different vehicles with respect to both air- and structure-borne noise filtering performance.