Abstract
In modern automobiles a lot of actuators are used to run safety systems. Nowadays these are mechanical, electromechanical, pneumatic, pyrotechnic or electromagnetic actuators. For releasing them electrical or mechanical energy is used. This paper presents a new class of actuators in safety systems using shape memory wires. They are able to replace the conventional actuators. The goal for this research work is to use shape memory elements in a clamping system of a steering column as well in safety as in comfort area. The shape memory elements control the opening and closing function that presses with maximum 5,000 N against the steering jacket. For the first prototype, called drum type, shape memory wires are used to open the system and disc springs are used for closing. The second prototype is a so-called lateral actuator, where shape memory elements are used for the opening and closing function. Tests with the drum prototype are carried out with up to 16 wires up to date. Each wire is preloaded with 50 N that corresponds to a compression of the disc springs of 800 N. When the wires are electrically activated they contract the disc springs until 1,200 N over a stroke of 1 mm. In this configuration an electrical power of 16 V and 56 A is used. The second prototype is designed with four wires of 0.5 mm diameter for closing and two wires for opening the clamping system. To open the clamping system in less than one second an electrical power of 7 A and 12 V is necessary, while 14 A and 12 V is needed to close it within 1.5 s. At the moment the application of the first prototype is restrained through an energy limitation, because the battery of modern automobiles would not be sufficiently adequate. Anyway, in the near future more electrical cars will be on the market and therefore this prototype can successfully be implemented. One of the advantages using shape memory alloys in the design of a steering column is its lightweight. Moreover it is possible to control the energy in any time because of the electrical activation and the control of the electrical resistance of the shape memory actuators. Thereby this actuator can be activated and the steering column can even be released in special crash situations in order to create enough space for the airbag and to avoid a possible touch of the body of the driver with the steering wheel.
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