Developing dynamic driver head envelope for passenger cars considering real-time road conditions 2024-01-2493

Ergonomics plays an important role in automobile design to achieve optimal compatibility between occupants and vehicle components. The overall goal is to ensure that the vehicle design accommodates the target customer group, who come in varied sizes, preferences and tastes. Headroom is one such metric that not only influences accommodation rate but also conveys a visual perception on how spacious the vehicle is. An adequate headroom is necessary for a good seating comfort and a relaxed driving experience. Headroom is intensely discussed in magazine tests and one of the key deciding factors in purchasing a car. SAE J1100 defines a set of measurements and standard procedures for motor vehicle dimensions. H61, W27, W35, H35 and W38 are some of the standard dimensions that relate to headroom and head clearances. While developing the vehicle architecture in the early design phase, it is customary to specify targets for various ergonomic attributes and arrive at the above-mentioned dimensions. In general, specifications that relate to headroom are only a consequence of static assessments carried out inside a laboratory and not on real-time driving condition. The static assessment can be as simple as positioning a digital manikin in CAD environment and then specifying how high or low the interior trim of the headliner be to achieve a certain head clearance. In actual driving scenario, the vehicle would experience rough terrain. In such cases, the road undulations can displace the occupant from their normal seated position in effect reducing the head clearance. Therefore, it is important to understand this dynamic variance of head clearance on actual driving condition. Undertaking a volunteer test to study this variance comes with risk of endangering the participant and has other measurement related complexities. Hence, we adopt a simulation-based approach for the same using Human Body Models (HBMs) of different anthropometry, which are proven having high bio-fidelity. The aim of this study is to validate this hypothesis and develop a head envelope for drivers considering dynamic road conditions, thus enabling vehicle manufactures digitally evaluate head clearance during early development phase. A typical driving scenario with various vehicle speeds on different stochastic roads and braking conditions are simulated using MBS vehicle models and the acceleration signatures from the simulations are used to estimate the vertical lift of driver over the seat. The resulting displaced posture is compared with the normal driving posture and various head clearances are analyzed. The outcome of this work will help in validating and (or) updating the static head envelope and use it for specifying the headroom target for driver in the early phase of the vehicle design.