J. Strittmatter, P. Gümpel, HTWG Konstanz University of Applied Sciences, Konstanz, Germany
In automotive applications, especially in safety systems, a lot of electromagnetically driven actuators are integrated to run comfort and control these systems in modern passenger cars. Using shape memory alloys (SMA) the existing systems could be simplified, performing the same function through new mechanisms with reduced size, weight and costs. A drawback for the use of SMA in safety systems is the lack of materials knowledge concerning the durability of the switching function (long-time stability of the shape memory effect).Pedestrian safety systems play a significant role to reduce injuries and fatal casualties caused by accidents. One automotive safety system for pedestrian protection is the bonnet lifting system. Based upon such an application this paper gives an introduction to existing bonnet lifting systems for pedestrian protection, describes the use of quick changing SM actuators and the results of the study concerning the long-time stability of the tested NiTi-wires. These wires were trained, exposed up to four years at elevated temperatures (up to 140°C) and tested regarding their phase change temperatures, times and strokes. For example it was found that Ap-temperature is shifted towards higher temperatures with longer exposing periods and higher temperatures. However, in the functional testing plant a delay in the switching time could not be detected.
This paper gives some answers concerning the long-time stability of NiTi-wires that were missing till now. With this knowledge the number of future automotive applications using SMA can be increased. It can be concluded, that the use of quick changing SM actuators in safety systems could simplify the mechanism, reduce maintenance and manufacturing costs and should be insertable also for other automotive applications.
Summary: Pedestrian safety systems play a significant role to reduce injuries and fatal casualties caused by accidents. One automotive safety system for pedestrian protection is the bonnet lifting system. Based upon such an application this paper gives an introduction to existing bonnet lifting systems for pedestrian protection, describes the use of quick changing shape memory actuators and the results of the study concerning the long-time stability of the tested NiTi-wires that were exposed up to four years at low-range temperatures up to 140°C.
This paper gives some answers concerning the long-time stability of NiTi-wires that were missing till now. With this knowledge the number of future automotive applications using SMA can be increased. It can be concluded, that the use of quick changing shape memory actuators in safety systems could simplify the mechanism, reduce maintenance and manufacturing costs and should be insertable also for other automotive applications.
