Page 36 - ATZ11 November 2019 Professional

COVER STORY INTERIOR

FIGURE 1 A car seating structure (left), a recliner system (center) and a folding seat mechanism (right), all showing where PTFE bushings are used in red for
NVH and comfort optimization (© Saint-Gobain)

the agenda for both car users and manu- hybrid vehicles and have become a nism before driving off, maybe because
facturers to ensuring that the stay in the source of annoyance for both drivers you share your car or use a car sharing
car is as comfortable as possible for all and passengers on quiet stretches of service. If one finds the mechanism too
occupants. road. This is a particularly important tight or too loose, this can become a
issue in new vehicles. source of annoyance even before turning
Looking further ahead to autonomous on the engine. From the engineer’s view,
REDUCING RATTLE AND NOISE
driving becoming more popular, even the seat height adjustment and seat
FOR A MORE TRANQUIL DRIVE
more adjustment mechanisms are being recliner mechanisms can have a trade-
Cabin noise has greatly reduced over the introduced as the interior becomes more off in this respect. One system could
years as combustion engines have been flexible. The possibilities of car interior require low effort to adjust but exhibit
designed to be quieter and quieter. Ad - design will shift and expand from the clearance and, therefore, feel loose or
ditionally, electric motors make little to current front-facing interior to swivel cause rattle noise. Another system might
almost no noise. This means that also seats that might allow all passengers to have no rattle due to an interference fit
the interior soundscape and usability of face each other or seats that allow a sin- but have high adjustment forces.
interior design need to be improved con- gle passenger to lie down. The only lim- Here, small changes can make a big
siderably. Interior systems such as first itation here lies in the interior designers’ difference. One tribological solution is
and second row seating play an import- creativity. Nevertheless, interior mecha- to ensure that the sliding layer of the
ant part in providing comfort during nisms need to be designed to be less bushing is compliant enough to absorb
travel. This also includes the mechanics noisy. mating component clearances and toler-
and the design of the bearings, FIGURE 1. These increased requirements of ances. The plastic PTFE as sliding layer
That is why even the smallest parts, smooth adjustment that lasts and low allows for compensation of a wider range
such as PTFE bushings, need to be de - noise lead to a dilemma for interior engi- of clearances throughout, which it per-
signed with their impact on the comfort neers. Bearings are often a key compo- forms with more consistent torque than
and driving experience in mind. Without nent in interior systems which can expe- alternative plastic solutions. This can
this consideration, issues such as dis- rience a variation in friction due to man- be seen in FIGURE 2 where the torque
turbing rattle, wear and excessive torque ufacturing tolerances of the mating required to turn a shaft within two dif-
during adjustment will provide annoy- components. Here, larger bearing clear- ferent bushings was examined for sev-
ances that make for an even more stress- ance can ensure low friction but it also eral different shaft diameters. Testing
ful commute, despite being more easily increases the risk of rattle noise. There’s of the plastic bushing made from Poly-
prevented than, say, rush hour traffic. need for a solution that allows consis- oxymethylene (POM) of a competitor
Fortunately, however, cabin noise has tently low adjustment forces without was stopped at -0.06 mm of clearance as
greatly reduced over the years as com- clearance, so that rattle can be reduced the flange broke during assembly due to
bustion engines have been designed to or eliminated altogether. increasing assembly forces.
be quieter and quieter [4]. Step by step,
the noise limit has been reduced from
MORE TOLERANCE THANKS TO DESIGNING TIPS FOR
82 dB(A) in 1978 to 74 dB(A) which were
PTFE SLIDING LAYERS MINIMAL RATTLE
established in 2016. The downside to this
is that the noises that were once too There’s an added dimension when look- One cause of annoying rattle noise is the
quiet to be heard over the engine – the ing at the comfort topic using the vehicle clearance between the bushings and the
squeaks and rattles – are now much from the driver’s point of view: It might shafts that incorporate the seat adjust-
more obvious due to quiet electric and be necessary to adjust the seat mecha- ment mechanism. This clearance means
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