Design And Simulation Analysis Of An Active Seat Belt Pretensioner

Seat belts are an important part of the occupant restraint system. Using seat beltscorrectly can effectively reduce occupant injury in a traffic accident. In order toensure that the occupant do not be bounded on the seat too tightly, usually there is aslack of seat belt about80-120mm. However, researches indicate that the webbingslack will reduce the protective effect of the seat belt. To deal with this problem, thetraditional pretensioners have been proposed and they are widely used in the currentrestraint system. The traditional pretensioners tighten the seat belt before the relativemovement between the occupant and vehicle, to prevent the occupant from jerkingforward in the crash, and thus provide a better protection for the occupant. However,accident statistics indicate that most drivers trigger emergency braking system beforethe accident, which makes the occupant lean forward before the collision. In this case,the traditional pretensioner seat belt cannot restrain the occupant very well and willdo harm to the occupant.For these reasons, a new kind of active seat belt pretensioner was presented inthis paper. In order to study the protective effects to the occupant of the active seat beltpretensioner in the frontal collision and study its advantages comparing with the traditionalone, based on MADYMO simulation method, a simulation model based on the brakingprocess had been built with a validated frontal impact model. The study analyzed thedynamic response of the occupant of active pretensioner and traditional pretensionerat the braking and crashing process. The simulation results indicate that the activeseat belt pretensioner can restrain the occupant more effectively and reduce thedamage parameters that the occupant suffers in the frontal collision.The active pretensioner developed in this thesis uses the acceleration sensor tocollect acceleration signals in real time. When emergency braking happens, ECU(Electronic Control Unit) can judge this action accurately and then trigger thepretensioner, which can pretension the seat belt ahead of the accident so as to reducerisks of second collision of the occupant. Structural design of the active seat beltpretensioner was provided in this thesis. A specimen of the active pretensioner wasmade and the performance of the specimen of the pretensioner was tested by statictest.Based on the emergency brake action of driver, the control system of theactive seat belt pretensioner controlled by braking acceleration signal was developed by the moving window quadrature algorithm. The circuit and C-Program of thi ssystem was presented. Real vehicle tests showed that the emergency brake actioncan be identified by this system and this system can control the motor to achievethe intended purposes.The research results had reference value on the promotion of the study of activepretensioner seat belt at home and on the study of adaptive occupant restraint systemdevelopment.