User perception of upper interior space in the rear seat of a car: A human centric approach to assess head roominess

Abstract

The upper interior space in a car is an important aspect to consider in the design process for creating overall riding comfort. During the development of sufficient roominess a population’s anthropometrics together with ergonomic dimensions and measuring standards are utilized. The interest underlying this thesis study is that head roominess evaluation is considered as a physically measured entity, when it is substantially a combination of physical measurement (objective) and perceived roominess which is subjective to the user. Investigative studies were done at Volvo Cars and recommendations were generated based on the results from the study. The master thesis study started with literature study followed by three research phases which included qualitative and quantitative studies; Awareness, Identification and Investigation phase. The initial phase (Awareness) was focused in obtaining wider knowledge, and in the final phase (Investigation) involving specific investigation to attain in-depth knowledge. During the second phase (Identification), a qualitative study was applied, and six parameters of the category Vision and Spatial distances were identified as critical for the perceived roominess. The parameters were analyzed in the Investigation phase, the third and last phase, using a quantitative user study with 34 test persons, divided into two groups based on their sitting height; Short and Tall. The rear-outer seat was studied (behind the driver seat on the left side) in a XC90 car. The rear seat and the driver seat were set in design position (SgRP), the car had light interior trim with a covered panorama roof and the test was performed with the Swedish population. In total thirteen manipulations were randomly performed and a Visual Analogue Scale (VAS) was utilized to assess test person’s perceived upper interior space for every manipulation. Nine manipulations were intended for the Vision parameters; Cant rail height, Belt line height and C-pillar forward/rearward position, one change in the Spatial distance (vertical height) and four VAS rating were obtained when the car was in a nominal state. This data together with additionally retained angles and eye points were then statistically analyzed to find trends, tendencies and correlations for all the studied parameters. For the Vision parameters, the change in Belt line had the highest (negative) influence on the VAS rating irrespective of the Short and Tall group. A high correlation was established between VAS rating and retained angle for the Cant rail. Moreover, C-pillar had the same influence on the Short and Tall group and a common borderline was acknowledge. However, for the Spatial distances, the Tall group had a stronger correlation with these distances than the Short group, who did not establish any correlation with the VAS rating. As recommendations, the acceptable angles for all the parameters have been translated into a definite designed colour range guidance of what would be acceptable, critical or poor for the Vision parameters when perceiving the interior space.