Front seat passengers’ experience of ride comfort and NVH in modern cars

Licentiate thesis, 2022

Due to the refinements in combustion-engine and electric cars, ride comfort has become a prominent attribute when it comes to developing cars in the future. A variety of factors, such as seat, seatbelt, sound and vibration, have been shown to influence perceived overall ride comfort in passenger cars. Numerous studies have investigated human responses to sound and vibration. However, few studies have investigated passengers’ experiences of sound and vibration in real passenger cars, in different real-world driving scenarios.

The purpose of this licentiate thesis is to identify human experiences of sound and vibration in modern passenger cars. An approach has been developed to investigate how sound and vibration influence overall perceived ride comfort in combustion-engine cars (CVs) and electric cars (EVs). The first research question relates to the definition of ride comfort, from the passenger’s perspective, and the methodology used to specify the factors that influence overall ride comfort. The second research question deals with specifying how ride comfort is influenced by sound and vibration.

The research includes literature reviews of human responses to sound and vibration and a user study using a mixed-method research approach that focused on subjective judgements and objective measurements of overall ride comfort.

The literature reviews found that several laboratory studies have covered the level and frequency ranges of interest for vibration and sound found in passenger cars. Other studies have employed realistic ride postures with populations of various ages, gender and anthropometric measures to investigate the influence of vibration on ride comfort. Studies of sound in passenger car have explored approaches to identify sound sources, assess sound quality and design product sound. The overall conclusion from the literature reviews was that there is a lack of studies that consider all the different parameters influencing the overall ride comfort experience of automotive vehicle passengers. Also, further studies are specifically needed to investigate the influence of sound and vibration on passengers’ experience of overall ride comfort.

The user study comprised eight typical driving scenarios (initial comfort, start/stop, acceleration and deceleration, constant speed, speed bumps, long bumps and cornering, bridge joints and rough roads) with ten participants in a CV and an EV. The overall results indicated that the two cars were similar in terms of the prominent effects of ingress, room for the body, seat adjustment and seat support on initial comfort, but varied in terms of dynamic discomfort. Induced body movements dominated dynamic discomfort in the CV, while annoying sound dominated in the EV. Sound annoyance in the CV was primarily triggered by tyre noise at lower speeds and wind noise at higher speeds. In the EV it was the high-frequency tonal sound from electrical components that produced the most annoyance. In both cars, vibration discomfort was linked most strongly to induced body movement. Sound annoyance was judged lower when passengers perceived pronounced induced body movement or when participants experienced vibrations coherent to the sound. Nevertheless, the overall influence of sound accumulated over time, making it difficult for passengers to relax. In contrast, the instantaneous judgement of vibration discomfort was not affected noticeably by the simultaneous sound.

The main conclusion of this licentiate thesis is that from the passenger’s perspective, ride comfort encompasses static comfort and dynamic discomfort. Static comfort is associated with ingress, room for the body, seat support and seat adjustment. While dynamic discomfort is attributed to the annoying sound, induced body movement, as well as discordance between sound and vibration. The influence of sound and vibration on perceived ride comfort varies depending on the type of driving scenario (e.g., road profile and speed) and on the type of cars (e.g., CV or EV). Moreover, dynamic discomfort could be controlled by controlling sound and vibration.