Aerodynamics Development for a New EV Hatchback Considering Crosswind Sensitivity 2018-01-0715

An electric vehicle (EV) has less powertrain energy loss than an internal combustion engine vehicle (ICE), so its aerodynamic accounts have a larger portion of drag contribution of the total energy loss. This means that EV aerodynamic performance has a larger impact on the all-electric range (AER). Therefore, the target set for the aerodynamics development for a new EV hatchback was to improving AER for the customer’s benefit. To achieve lower aerodynamic drag than the previous model’s good aerodynamic performance, an ideal airflow wake structure was initially defined for the new EV hatchback that has a flat underbody with no exhaust system. Several important parameters were specified and proper numerical values for the ideal airflow were defined for them. As a result, the new EV hatchback achieves a 4% reduction in drag coefficient (C_D) from the previous model. A wind tunnel with a 0 degree yaw angle is generally used in new vehicle development, but this condition is different from the real world with a small yaw angle due to natural crosswinds. The new EV hatchback was also examined under a small yaw angle (4 degree) condition for practical use, and some crosswind sensitivity measures were applied. The mechanism causing an increase in aerodynamic drag was studied by observing asymmetrical airflow during the development process. Attention was focused on negative pressure growth, which is the root cause of leading aerodynamic drag from the rear end wake. To control the wake, the rear side spoiler shape was optimized. As a whole, considering the tendency that the difference in the 0 and 4 degree C_D becomes larger for vehicles with a better C_D, the aerodynamic drag increase of the new EV hatchback from a yaw angle of 0 to 4 degrees was concluded to be acceptable in comparison with the previous model.