Load distribution structure of rear bumper beam to enhance vehicle body energy absorption in rear-end collisions

Objective: This research focused on FMVSS301, which is required for higher energy absorption as a regulation for rear-end collisions. Since they are offset collisions, the deformation of the non-collision side frame, which does not directly contact the barrier, is less than on the collision side. The reason is that the rear bumper beam with curvature is deformed into a straight shape by the load from the barrier, resulting in an asymmetrical load distribution from the barrier that is biased toward the collision side. Therefore, the objective of this research was to construct a new bumper beam structure that reduces the difference in the load input to both frames and increases the energy absorption of the non-collision side frame.Method: The basic principle is to generate a counterforce against the lateral loads during transmitting the load from barrier to the frames. To achieve this, a bow-shaped rear bumper beam structure was devised. The rear bumper beam corresponds to the bow and the newly added connection plate to the string. The lateral load increase is suppressed and load distribution to the rear frame is maintained.Results: The designed rear bumper beam and rear components equipped with the rear bumper beam were both prepared and evaluated by drop test. With testing of the rear bumper beam, it was demonstrated that the load in the lateral direction, which conventionally generates over 80 kN, could be canceled. Tests of the rear component demonstrated that load distribution to the rear frame could be maintained, and the energy absorption of the non-collision side frame could be enhanced by 35 times. The total energy absorption of the barrier and the two frames was demonstrated to increase 2.9 times.Conclusion: The bow-shaped rear bumper beam was designed to distribute the load evenly to the collision and non-collision side frames, and to deform both frames, thereby achieving a higher energy absorption of the entire vehicle body. This is expected to be applicable to electric vehicles and FCVs, which require more energy absorption with increased vehicle weight.