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Using MADYMO to develop new restraint system components


in order to reduce the possible injury to the front row out of position passengers after the airbag is triggered, and to improve the protection of the front row passengers' head and chest by the existing restraint system, this paper proposes a new restraint device. That is, on the basis of the existing restraint system that can meet the expected performance requirements of medical device companies, a collapsible small inflatable air cushion is added to the safety belt body. In case of a frontal collision, this air cushion will form an additional buffer and energy absorption effect between the human body and the airbag. The protective effect of airbag on human body can be produced in the shortest time of collision. It can also reduce the triggering speed and energy of the airbag and reduce the possible injury to the out of position passengers. This paper uses MADYMO software to carry out the dynamic simulation calculation of occupant restraint system, and shows the effect of occupant collision protection before and after the installation of this device


the widespread popularity of seat belts and airbags in passenger cars has greatly reduced the casualties of passengers in traffic accidents and the injury index of passengers. However, in the out of position (OOP) condition, the deployment of airbag may often cause harm to passengers, especially children and small women. Due to its narrow body and small contact area with the human body, the safety belt is very easy to cause body surface bruises and even sternum fractures without a force limiting device. This paper proposes an inflatable air cushion, which can be sewn on the shoulder belt of the safety belt after folding. When the collision occurs, the air cushion inflates and deploys, forming additional protection between the airbag and the safety belt: 1. Because the air cushion has a certain thickness after inflation, it can be in contact with the deployed airbag in the early stage after the collision, which directly plays a role of cushioning and energy absorption to the passenger's body. 2. After the air cushion is deployed, it can almost cover the entire upper body of the passenger, so that the local load of the original seat belt body on the passenger is dispersed to the entire upper body of the passenger. 3. It can reduce the triggering energy of the airbag and reduce the injury to the out of position passengers. This paper studies two cases of a minibus and a car, in which the minibus is not equipped with an airbag, and the car is equipped with an airbag. The dynamic simulation models of the occupant restraint system of the two cars are established by using MADYMO software, and have been verified by the test run crash test. On this basis, this paper discusses the protective effect of the new restraint device on the above two cars respectively

1. Establishment of simulation model

1.1 structural description of new restraint components

the webbing material of safety belt is polyester filament, with a width of about 50mm and a thickness of 1.1 ~ 1.2mm. The air cushion is sewn up by two pieces of square fabric with 340mm side length and sewed with the belt of the safety belt. The four corners of the square fabric should be rounded to avoid scratching the human body when unfolding. During sewing, the diagonal of the square air cushion coincides with the long side of the safety belt, and the inflatable air cushion is not equipped with a vent hole or a tension strap

1.2 establishment of new restraint component model

according to the prototype design and referring to the geometric data of the safety belt of two models, the CAD model of this component is established, and then the lattice is divided in the finite element software. The body of the safety belt and the air cushion are integrated models, all of which are divided by triangular elements, with a total of 1208 nodes and 3212 triangular elements. (see Figure 1)

Figure 1

fold the air cushion after the finite element lattice is built, and then input the node coordinates and element composition of the element in the format of MADYMO file, and use a pre simulation program to determine the coordinates of the nodes of the safety belt and the folded air cushion in the front impact occupant restraint system. Replace the calculated coordinates of each node of the finite element model at the last moment back to the original model for calculation, and observe whether the finite element lattice is stable in the calculation. If it is unstable, the coordinates of each node of the safety belt finite element model at other times should be selected and then substituted into the calculation until the lattice is stable. In Figure 2, the corrected occupant restraint system model of a minibus is shown on the left, and the model with new restraint system components is shown on the right. The purple part is the folded inflatable air cushion

figure 2

using the same method, the inflatable air cushion is also added to the occupant restraint system model of a car. Figure 3 shows the situation after the air cushion is deployed (70ms time). For convenience of observation, the deployed airbag is hidden in the figure

figure 3

2 Improvement of restraint efficiency

2.1 comparison of simulation results of minibus restraint system

minibus has become an automobile product especially suitable for China's national conditions at present because of its low manufacturing and use cost. However, due to the structure and cost of the car body, the protection of passengers is very limited. The general economical minibus rarely matches the airbag, and due to the large installation angle of the steering system and less energy absorption structure in the front of the body, once a collision occurs, the driver's head and chest are likely to directly collide with the steering wheel rim, wheel hub and body interior trim, causing fatal injury

the basic model used in this paper is the 48km/h frontal impact occupant restraint system model of a minibus, and the dummy model used is the 50th percentile male dummy extracted from the MADYMO dummy library. On this basis, an inflatable air cushion was added. The synthetic acceleration curves and injury indexes of the head and chest of the two models were compared as follows: (Figure 4, figure 5, and table 1)

because the minibus was not equipped with an airbag, the dummy's chest contacted the steering wheel rim during the collision, and the head hit the steering wheel hub, resulting in excessive peak acceleration curves of the head and chest. The model with air cushion obviously avoids the above problems and greatly protects the safety of passengers

2.2 comparison of simulation results of car restraint system

the car restraint system model is equipped with an airbag, which cooperates with the safety belt to provide better protection for the dummy. On the basis of this model, after adding an inflatable air cushion and reducing the value of the airbag mass flow rate curve to the original 80%, the synthetic acceleration curves and injury indexes of the head and chest of the two models are compared as follows (Fig. 6, FIG. 7, and table 2)

through the comparison of the synthetic acceleration curves of the dummy's chest, it can be seen that due to the role of the inflatable air cushion, the dummy is subjected to additional restraint loads in about 20ms, Therefore, the synthetic acceleration is higher than the result of the original model. From the perspective of absorbing energy, the early absorption of energy can reduce the peak acceleration in the later stage, and because the contact area between the air cushion and the passenger's body is much larger than the safety belt, the passenger's body will be injured due to large local load without replacing new hydraulic oil

at present, there have been reports abroad about the inflatable belt for aircraft. As long as the sensor detects a deceleration of more than 9g, the inflatable belt will be inflated. The inflatable air cushion described in this paper can use the same impact sensor as the airbag, and ignite at the earliest time after the ECU determines that a collision occurs. The gas generator can be placed in the B-pillar and connected to the air cushion with a soft nylon fabric conduit

3. Conclusion

from the simulation results, this inflatable air cushion can provide additional protection for passengers, and can reduce the triggering energy of the airbag by installing this component, so as to achieve the purpose of protecting the out of position passengers. Introduction to the software function of the liquid crystal rubber tensile tester of Jinan new era gold testing Instrument Co., Ltd.:. For the minibus without airbag, it can greatly protect the safety of passengers. However, some problems of this component are also found in the simulation results, that is, compared with the original simulation model, the dummy chest compression index is not significantly improved, which may be related to the loading time of the air cushion on the chest. Using MADYMO software and simulation methods, the next step can continue to explore the impact of different inflatable air cushion shapes and different fabric air release rates on occupant injury indicators. To study the influence of inflatable air cushion on different percentile dummies and female dummies. Study whether the device can be extended to front and rear passengers


1 “Airbags for Aviation” Instrument Pilot,May 2004

2. “MADYMO THEORY MANUAL” Version 6.1.

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