Controllability and Acceptance of an Unforeseeable High Power MSB Pre-Tensioning

In comparison to today’s series’ retractors, the reversible High Power Motorized Seatbelt (HPMSB) allows to position a passenger with higher tensioning forces. This applies both for lateral accelerations as resulting from evasive maneuvers and for Out-of-Position (OOP) situations when preceding an accident. Despite forces impacting on the upper torso can be adapted variably, their magnitude exceeds conventional retractors and might thus result in unwanted leg or arm movements. These might in turn affect pedal and steering wheel operation and could in the worst case result in an accident. Following ISO 26262 (Road Vehicles – Functional Safety) this would require an ASIL (Automotive Safety Integrity Level) rating, especially concerning the criteria Controllability. To assess the effect on controllability of an unwanted tensioning via HP-MSB an experimental study with predominantly external participants (30 out of 36) was conducted in a three channel static driving simulator. Besides a valid driving license, the absence of potentially relevant illnesses or operations especially on the upper body were a prerequisite for the participation. Both during recruiting and before the experiment all participants were informed about the nature of the study and potential risks. Due to the general increasing injury risk with age participants older than 54 years were excluded. With 16 female and 21 males the gender distribution was almost balanced. The driven road consisted of 12km of rural road and 15km of motorway. Their order was balanced between participants. At the beginning of each road category the participants experienced a slack-reduction. Near the end of each road category participants were exposed to the unforeseeable HP-MSB pre-tensioning. Pre-tensioning forces were 600N with a maximum ramp up time of 200ms. Following each slack reduction and each pre-tensioning the participants were asked for their subjective ratings. Due to its relevance for controllability, driving data was in the focus of the analyses. The analyses comprised absolute values after pre-tensioning, the statistical analyses of differences before and after pre-tensioning and between pre-tensioning sections and comparable, nontensioning sections with similar road geometry. While, not surprisingly, participants’ acceptance of the unforeseeable pre-tensioning was small, the data still exhibited a relatively high subjective controllability that was situated around the medium range of the scale. Driving data showed clear effects of the pre-tensioning both in the comparison between before and after pre-tensioning, as well as between comparison sections without pre-tensioning and pre-tensioning sections. The relevance of the results regarding the ASIL factor Controllability is discussed in the publication. © 2022, VDI Verlag GMBH. All rights reserved.