Part one of a four-part series on Automotive NVH comfort, this series is based on the paper, “Improving Vehicle NVH CAE Prediction Capability to Prevent Expensive Late Design Changes” written by Andrew Burke, Global NVH Manager at Altair.

Vehicle customers have an increasing expectation for refinement, which is a very important differentiator in a crowded market. Noise, vibration and harshness (NVH) performance is strongly linked to this perception of refinement and quality. In addition to the increasing expectation for refinement, there are also other trends that present many challenges for NVH Engineers, these include:

Drive for Light Weight Designs

Generally, reduction in weight has an adverse effect on NVH performance. This is due to having less mass and inertia to react forces and lighter designs may also compromise structural performance.

Electric Vehicles

Replacement of a traditional internal combustion engine (ICE) with an electric motor intuitively means that noise and vibration levels will be reduced. This is true for certain vehicle operating conditions and frequency ranges, but the loss of engine masking noise can expose other noise issues, which were previously not apparent to the customer. Efforts then have to be made to engineer solutions for these issues that were not a problem for vehicles with traditional engine installations.

Electric motors also generate noise and vibration, and the installation requires additional actuators and machines that bring their own NVH issues. These have to be understood and engineered during the electric vehicle or hybrid vehicle development.

An important aspect of NVH performance is sound quality. Many customers enjoy the driving experience of a vehicle fitted with an ICE simply due to the sound it generates. Electric motor sound quality is the subject of much debate and has to be considered and developed during the design process.

Smaller Engines with High Power Output

ICE technology has allowed development of smaller engines, with fewer cylinders, and with higher power output. Lighter more efficient ICEs are beneficial for fuel economy and the environment but can also have a detrimental effect on NVH performance. High power output means higher excitation and a smaller engine generally will have less mass and inertia to react this excitation. In addition, fewer cylinders can also introduce inherent engine imbalance issues.

Drive to Reduce Lead Times

Most vehicle manufacturers now offer a large portfolio of vehicles each with many variants and options. Customers expect that new models of these vehicles are also offered frequently. Supporting the engineering of this is very complex and resource heavy, and in order to manage this complexity the design process should be as efficient and fast as possible so that development lead times can be competitive.

CAE is already used in the automotive industry to develop vehicle performance. However, in order to meet the business and engineering challenges cited above, there is a greater, and essential, emphasis being placed on CAE to be used extensively as an integral part of the design process.

Does this mean that NVH CAE technology is at the stage that it can replace test based development and verification? The answer to this is currently no, and is the reason that work is being carried out to develop technologies to improve NVH CAE prediction capability. Current industry standard automotive simulation methods require development in order to capture the physical properties that are present in real vehicles. The inclusion of such effects as metal forming, bolt preload, contact, and acoustic trim porous materials are shown to significantly change NVH predictions compared to current modelling practices.

Don’t miss the next post in this series! We’ll discuss four common challenges faced by NVH engineers when working to address these trends and how to overcome them. Can’t wait for the next blog post? Go ahead and download the full paper here.