Plug-in hybrid and range extender NVH – Challenges and Solutions

The automotive industry continues to develop new powertrain and vehicle technologies aimed at reducing overall vehicle-level fuel consumption. While the use of electrified propulsion systems is expected to play an increasingly important role in helping OEM’s meet fleet CO2 reduction targets, hybridized propulsion solutions can play a vital role in the electrification strategy of vehicle manufacturers. Plug-in hybrid and range extender vehicles show unique NVH challenges due to their different possible operation modes. First, the paper outlines different driveline architectures for PHEV and range extenders. Given the multiple general architectures, as well as operation modes which typically occur for these vehicles, characterizations and source-path analysis of these vehicles can be more complicated than conventional vehicles. In the following steps, typical NVH related challenges are highlighted and potential solutions for NVH optimization are discussed. While the overall noise levels being low in electrical mode, the NVH behavior of such vehicles can be objectionable due to the presence of tonal noise coming from electric machines and geartrain components. Additionally, road- and wind noise share can be relatively high during higher vehicle speed operation. The switch-over from pure electrical drive to operation with combustion engine introduces transient NVH challenges, such as engine start and – pending on the hybrid architecture- driveline torque disturbance related to change of the propulsion source. Downsizing and boosting of modern combustion engine increase the combustion related excitation and hence require detailed attention during vehicle NVH integration. Further, operation strategy of the combustion engine during operation must be refined for pleasant NVH while not compromising fuel economy of the vehicle. The NVH assessment of an PHEV drivetrains requires evaluations under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. 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 all operating conditions. Methods and case studies for this are outlined in this publication.