Utoliv’s goal is to introduce breakthrough safety innovation methods, expand its special safety equipment and continuously improve the protection ability of passengers. In order to evaluate the performance of airbag and safety belt systems and reduce the noise generated by them, Autoliv uses LMS test system to measure the noise level, which is usually faced by the test model in the collision simulation test. The LMS test system will also be used to evaluate individual safety products, such as seat belts, seat frames and driving rod devices. LMS test.lab ensures the reliability of measurement to the greatest extent and greatly shortens the time required for the test.

Maximize the safety of passengers

Autoliv’s latest products in automotive safety include anti whip seats, airbags to protect the chest from side impact and expansion curtains to prevent side impact and protect the head. At present, Autoliv is at the forefront of the development of rollover protection, night vision and pedestrian protection systems.

In the process of collision accident, there are usually a series of pre-set measures to protect passengers. Thomas Norberg, the laboratory manager of Autoliv in Sweden, described the situation at the time of the collision as follows: “A small load signal will activate the safety belt tightening device, which can tighten the safety belt and fix the passenger as soon as possible. After this step, the load limiter can determine that the load on the passenger’s chest will not become too large. In this way, the fully expanded front airbag can absorb too much energy more evenly.” The main function of airbag is to prevent the head and chest from hitting the hard surfaces in the front of the vehicle, such as steering wheel, instrument panel and windshield. Safety belt and airbag can greatly reduce the risk of serious injury and death of passengers in front collision (see Figure 1) In order to avoid injuries to drivers and passengers in side impact accidents, Autoliv also launched special airbags for head, pelvis and chest integrated in the vehicle interior.

Figure 1 safety belts and fully inflated front airbags play a vital role in effectively protecting the safety of drivers and passengers

Strive to reduce intolerable airbag inflation noise

As part of the development of new safety products, Autoliv invests in research and development to reduce the noise generated by the signal initiation mechanism. It is necessary to reduce this explosive noise level, because it may increase the risk of hearing impairment. In addition to the sound pressure level, the human ear is also very sensitive to the timing of the start-up of safety equipment. Usually, for example, the sound from the seat belt signal tightening device will stimulate the stapidus reflection of the passenger’s ear. The ear reflex is a self-protection response, which will temporarily hinder the auditory function after about 10ms. This means that during this stage, passengers may hear less airbag collision noise.

Autoliv engineers use special acoustic test equipment to measure noise in the vehicle (see Figure 2). The vehicle is equipped with a series of fully integrated safety belts and airbags, as well as up to five human models for crash tests. The special excitation unit accurately controls the preset excitation program to start the safety belt tensioner and airbag expansion. Microphones are placed in the ears of these human models, which can capture the noise generated by constantly triggering the starting mechanism, and transmit the captured noise to the front end of LMS SCADAS III data acquisition. The engineer uses LMS test.lab and LMS Cada-X test software to manage the communication with the trigger unit and process the required data. The complete sequence of these experiments is often photographed with special cameras.

Using LMS test system to improve airbag inflation noise

Figure 2 human model used by Autoliv for noise measurement in the car: a microphone is placed in the ear of the human model to capture and transmit noise

Thomas Norberg explained that the recorded noise time signal forms the basis of special frequency analysis, so that the most important components of maximum amplitude and generation frequency can be known. “The main purpose of these studies is to test the noise performance of different types of expansive materials and adjust the mechanism of airbag starting design to the best state in the later stage of development. Engineers have developed a special algorithm to convert the test data required for each microphone into a single value, which can truly reflect the risk of hearing impairment. Using this algorithm can improve The efficiency and consistency of the noise measurement evaluation process, which can quickly explain the noise performance of the new design modification scheme and compare it with the previous results. “

Eliminate noise from safety equipment

In Autoliv’s noise laboratory, engineers also pay attention to how to eliminate the noise generated by other relevant safety equipment during normal operation, including seat belts and seat frames. Even the slightest noise generated by these systems will affect the comfort of drivers and passengers. In order to reduce noise interference, engineers are measuring the environmental noise of special safety equipment. For example, when the unidirectional vibration exciter system mechanically excites the newly developed safety belt device or the folding driving lever with integrated airbag, the noise obtained shall be measured and analyzed. These environmental tests are very cruel because the exciter system can excite a weight of 0.5T with an acceleration of up to 60g; In addition, the change of site ambient temperature is – 50 ℃ ~ 110 ℃. The purpose of these tests is to conduct safety system calibration tests and further carry out R & D and innovation activities. Engineers will edit the vibration applied to the product to be tested, which is based on accelerometer measurements on the same or similar safety equipment during the study of the tested vehicle on the road and test bench. They used LMS test.lab for random power spectral density (PSD) calculation to accurately convert the required vibration measurement into a representative and effective exciter table control spectrum (see Figure 3). In order to further improve the test capacity and the turnover capacity of its noise test equipment, Autoliv company uses LMS test.lab to expand its existing LMS Cada-X installation system.

Figure 3 in LMS test.lab, engineers accurately convert the required vibration measurement into a representative and effective vibration exciter workbench control spectrum

Referring to the help of the extended system to the test work, Thomas Norberg concluded: “For many years, we have used LMS test system to meet our special test needs. By using LMS test.lab, the time required for the test is greatly shortened. The improvement of work efficiency is mainly due to the high flexibility and efficiency standards of the software, which help speed up the test setting and post-processing stage. The process oriented application Workbook of LMS test.lab also speeds up the repeatability calibration The test work has greatly improved the consistency of relevant data. Autoliv engineers take the high accuracy of data acquisition, the flexibility of user calculation and the reliability of external communication as the core to further accelerate the test efficiency, strengthen their work and achieve the best passenger protection. “

Responsible editor: GT

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