Next-generation automotive restraints
Over the past 40 years, technology to reduce occupant injury in automotive collisions has advanced remarkably. Pre-crash shoulder belt tensioning is one promising new technology designed to reduce automotive crash injuries.
Current technology enables a seat belt to be tightened by about 10 cm (4 in) and air bags to be deployed simultaneously, milliseconds after a collision. However, pre-crash tensioning technology increases the opportunity to secure a passenger safely before a crash. Sensors and logic, designed to anticipate a crash, activate a motorized seat belt retractor that secures a shoulder belt around an occupant before a crash actually occurs.
The figure above shows the lumped mass model of an occupant subject to shoulder belt tensioning. There is an optimal position for occupants to minimize the effects of an automotive crash. Observational studies report that 10% of drivers and 22% of passengers in crashes were poorly positioned on impact.
The motorized shoulder belt tensioner is powerful enough to pull a forward-leaning occupant back to position prior to impact, provided the possibility of impact is determined sufficiently early. Such a system can reduce injury by repositioning the occupant and controlling occupant movement in pre-crash maneuvers. A motorized tensioning system also reduces injury for occupants who are seated correctly.
Craig Good, a partner at Collision Analysis conducted a research program to develop further understanding of the biomechanics of shoulder belt tensioning. The objective of this study was to experimentally measure the response of a diverse group of forward-leaning occupants to shoulder belt tensioning during straight-line, pre-crash braking (below), and then model the results. The study intended to develop and validate a mechanical model to characterize the biomechanical response of forward leaning volunteers during the motorized shoulder belt tensioning.
This seat-belted volunteer is subjected to motorized shoulder-belt tensioning while leaning forward.
The biomechanics of human exposure to shoulder belt tensioning in a vehicle environment must be understood to enhance protection of a diverse population. A previous study measured the upper torso biomechanics of three populations of forward leaning adult volunteers during motorized shoulder belt tensioning. The current study used a small representative group of volunteers of different sizes. This analysis was helpful in determining the requirements to enhance the protection of a varied group of occupants. The ultimate goal is to provide the best level of crash protection for all occupants using motorized shoulder belt tensioning.
The three dimensional model incorporated the biomechanical properties of the occupant populations, a motorized shoulder belt tensioner (DC motor and controller), and shoulder-belt webbing models. Model validation was achieved against the volunteer experiments for angular torso position, torso velocity, and shoulder belt moment applied to the torso.
Creating the model
Good used DynaFlexProTM (DFP) from MaplesoftTM to create a 2D occupant model, using the experimentally measured data for validation. DFP is a software package for modeling and simulating the dynamics of mechanical multibody systems. The computation capabilities of MapleTM are used to create concise and efficient sets of system equations in symbolic form, which facilitate visualization, physical insight, and information sharing. These tools simplify the process of design, optimization, simulation, and control of complex engineering system models.