How can perceived vertical choppiness in the driver seat be improved in an electric vehicle
Examensarbete för masterexamen
Mobility engineering (MPMOB), MSc
It’s essential to understand both the positive and negative implications of the automobile industry’s transition from traditional internal combustion engine (ICE) vehicles to electric vehicles (EVs). One such negative impact is the vertical choppiness levels in an EV. Choppiness, considered a part of ride comfort, is defined as road-induced uneven pitch and bounce motions of the vehicle. It can be felt between the frequency ranges of 3 and 8 Hz. Choppiness is more predominant when the vehicle is driven over an irregular or rough surface. As humans have the lowest tolerance for vibrations between 3 and 8 Hz, high degrees of choppiness impact the abdomen region as well as the voice of the occupants. The ICE, together with its engine mounts, acts as a heavy mass damper, reducing vibration input to the driver and occupants’ seats at 3-8Hz, whereas the electric motor is not as heavy and has less potential to reduce choppiness, hence increasing choppiness in a BEV. It is crucial to think about the impact of choppiness because ride comfort is one of the most important elements a customer evaluates when buying a new vehicle. This thesis focuses on finding low cost solutions by examining the interaction of the driver in the seat with the suspension to reduce the choppiness without having a negative impact on the shake vibration region (8-20Hz). Air suspensions are one way to reduce the choppiness, but they cannot be used in every vehicle due to their high cost. The thesis proposal attempts to validate the potential of altering the seat characteristics, i.e., the seat spring and damping, in order to lower the levels of choppiness perceived in the driver’s seat of a BEV, using CAE ride models. The effects of the driver’s vertical seat bounce frequency on choppiness were investigated using these ride models, as well as design modifications that have an impact on choppiness levels. The results obtained from these models were also validated by comparing them with tests done on the actual vehicle on the shake rig. When these models were run on different virtual roads, the corresponding responses were recorded and used for further calculation of RMS acceleration values of the seat, which was the cost function chosen to quantify the choppiness levels of the ride models in accordance with the international standards in place for the effect of environmental vibration on operator health, efficiency, and comfort (ISO 2631).
choppiness , ride comfort , CAE ride models , seat parameters , validation , BEV , ICE , ISO 2631 , efficiency , RMS acceleration