Mechanisms of using knee bolster to control kinematical motion of occupant in reclined posture for lowering injury risk

Abstract

Reclining is a dangerous posture for occupants in moving vehicles, not only because it can easily induce submarining and cause abdominal injury, but also because it may increase risk of spinal injury. In this study, the THUMS 50th percentile model is used to simulate a reclined occupant under 30 km/h frontal impact and to study the effect of knee restraint on reclined occupant kinematics. The main findings are as follows. First, if the reclined occupant is restrained only by a seatbelt, the occupant kinematics in frontal collision can be very unfavourable. Second, if the knee bolster is positioned close to the knees and the recline angle is less than 60° from the vertical, the early knee restraint provided by the bolster can result in upper body rotation about the pelvis, without causing excessive spinal flexion.