The increasing trend toward electric and hybrid-electric vehicles (HEVs) has created unique challenges for NVH development and refinement. Traditionally, characterization of in-vehicle powertrain noise and vibration has been assessed through standard operating conditions such as fixed gear engine speed sweeps at varied loads. Given the multiple modes of operation which typically exist for HEVs, characterization and source-path analysis of these vehicles can be more complicated than conventional vehicles.
In-vehicle NVH assessment of an HEV powertrain requires testing under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. Generally, it is necessary to assess issues related to IC engine operation and electric motor operation (running simultaneously with and independent of the IC engine), under both motoring and regeneration conditions. Additionally, mode transitions, including IC engine start/stop must be assessed.
An analysis is presented here, which explores the differences in NVH performance of multiple HEVs currently available in the US-market. Measurements were conducted on these vehicles to assess noise and vibration at the powertrain-level and vehicle interior. Two of the vehicles included in this investigation were then chosen for a more in-depth comparative analysis. The analysis of these two vehicles included assessment of source level excitations and vehicle NVH sensitivities, in the context of boundary conditions driven by their hybrid system architectures.
Based on the powertrain and vehicle NVH performance assessments, methods were explored for developing powertrain level NVH targets. For the initial phase of this target cascading process, the analysis was limited to full load (IC engine operational) and part load (EV-only) modes. Based on in-vehicle performance, and vehicle sensitivity information, test procedures and targets were defined for powertrain radiated noise and mount vibration content.