Small Parts Make Big Difference in Driving Comfort

Is your daily commute a breeze? Getting to work for that 9 a.m. meeting or returning home in time for a family dinner are journeys often associated with stress and subject to many circumstances outside of our control – and the entire experience can even negatively impact your health.

However, small details contributing to comfortable seating and a noise-free interior can make a huge difference to those commuting by car.

Making sure the driver and passengers are as comfortable as possible has been high on the agenda for both vehicle owners and automotive manufacturers, with two important improvements being the soundscape and the ease of use of the interior systems.

Interior systems such as seating play a part in providing comfort during travel, and so even the smallest parts need to be designed with their impact on the driving experience in mind. Without this consideration, issues such as rattle, wear and excessive torque during adjustment will provide annoyances that make for an even more stressful commute – despite being more easily prevented than, say, rush-hour traffic.

Roadworks, honking horns, loud engines – roads usually are not the quietest places during a typical commute. Fortunately, however, cabin noise has been greatly reduced over the years as engines have been designed to be quieter. This trend is especially true for the emerging electric-vehicle market where powertrain noise has been virtually eliminated.

The downside: Noises that once were too quiet to be heard over the engine – such as squeaks and rattles – now are much more obvious and have become a source of annoyance for both drivers and passengers on quiet stretches of road.

A comfortable interior means a calm and peaceful soundscape, so the little rattles that add to commuter stress need to be addressed to provide the best driving experience.

One cause of annoying rattle noise is clearance between seat bushings and the shafts that incorporate the seat-adjustment mechanism. Clearance means the shaft and bushing move against each other and, as the car vibrates, the shaft can rattle around inside the bushing.

Plastic bushings, for example, have to be designed with a clearance or one-for-one fit so rattle noise cannot always be eliminated. The less compliant the material used, such as injection-molded plastics, the more noise in a rattle situation results. Softer materials such as PTFE-coated bushings offer a degree of damping which can reduce the rattle noise level.

Tests have shown the right choice of bushing can offer up to a 10-dB(A) noise reduction over a plastic bushing in this situation – that’s similar to having to talk over the sound of a busy restaurant with background music instead of having the same conversation at home in a quiet suburb.

When you get into your car in the morning to start the commute, you might find it necessary to adjust the seat mechanism – maybe because you share your car with your partner or kids or use a car-sharing service. However, if you find the mechanism too tight or too loose, this will get your journey off to a bad start before you even turn on the engine.

Seat height adjustment and seat recliner (pictured above, left) mechanisms can have a trade-off in this respect. One system could require little effort to adjust but exhibit free play and, therefore, feel loose or cause rattle. Another system might have no rattle noise but have high adjustment forces. Here, small changes can make a big difference.

One solution is to ensure the sliding layer of the bushing is compliant enough to absorb mating component tolerances. PTFE, as mentioned before, allows for compensation of a wider range of tolerances throughout, which it performs with more consistent torque than alternative plastic solutions.

While seat-bushing solutions might be considered minor parts, especially as the impact of that choice of component on end-user comfort may not be obvious, this seemingly small decision can lead to poor quality performance and ultimately can lead to more stress for the car owner. If car owners feel the car’s quality doesn’t live up to expectations over the mid- to long term, this can have an impact on future car choice.

The design of the bushing, therefore, should be considered as much as the design of the seat frame to avoid unnecessary reduction to comfort levels during the driving experience. With this combination, entire seating systems, not just bushings, can be studied and understood to ensure overall system quality is achieved consistently.

Alfred Lethbridge, Ph.D., (above, left) is a content marketing executive at Saint-Gobain Performance Plastics. He is based in Bristol, U.K.