Page 37 - ATZ11 November 2019 Professional

the shaft and bushing move relative to While it sounds simple in hindsight, the innovative PTFE and spring steel
each other and, as the car vibrates, the developing this PTFE coated tolerance solution shows greatly reduced push/
shaft can repeatedly rattle around inside ring SprinGlide, but this material com- pull forces that are consistent across the
the bushing. Plastic bushings and other bination has to be studied at great tolerance range. Additionally, compared
bushings that offer little compliance length to prove the concept. Tests per- to the injection molded plastic system
have to be designed with a clearance or formed by Saint-Gobain in the USA which often has a low quality feel, PTFE
one-for-one fit. Therefore, avoiding rattle show the force required operating an and spring steel combined significantly
noise is not always a possibility with interior sliding system at the minimum, reduces the stick-slip friction effect, or
these solutions. nominal and maximum clearance con- breakaway force, allowing for a higher
This issue is worsened because less ditions expected from a typical manu- quality feel.
compliant materials, such as injection facturing tolerance range, FIGURE 4. Further tests have shown that when
molded plastics, create more noise than Whereas the currently often used injec- the SprinGlide sliding system was
softer materials such as PTFE. The PTFE tion molded plastic possibility has vibrated front-back and left-right, there
layer in bushings, if not too thin, offer a higher forces that are less consistent, was a decrease in rattle noise of about
degree of damping which, if rattle were to
occur, reduces the noise level. This rattle
damping effect is shown in FIGURE 3.
Here, different bushings were deliber- 25
ately placed into 2-mm clearance con- Plastic bushing, competitor
ditions to be able to measure the result- Norglide T050CG
20
ing noise generation. The right choice
of bushing can offer up to a 10 dB(A)
noise reduction over a conventional 15
plastic bushing in this situation.
In this partic ular test, the Norglide Torque [Nm]
M075GG PTFE bushing improved the 10
most, with 53 dB(A) in comparison
to the conventional plastic bushing’s
63 dB(A). 5

NO CLEARANCE THANKS TO
0
TOLERANCE RING AND PTFE
0.02 0.00 -0.02 -0.04 -0.06 -0.08 -0.10 -0.12
There are several optimization options
for design engineers. One way to ensure
Clearance [mm]
clearance-free properties with consis-
FIGURE 2 The Norglide PTFE bushings perform consistently over a wide range of dimensions when com-
tently low forces is the use of a spring
pared to competing solutions; their sliding layer compensates for manufacturing tolerances of the mating
steel. This material is used in tolerance components, ensuring a consistently smooth adjustment feel when adjusting the seat (© Saint-Gobain)
rings, where the spring-like properties
are used to compensate manufacturing
65
tolerances so the radial forces remain
constant. However, this tolerance ring is
not low friction in nature and is gener-
60
ally employed as a radial fastener, fixing
the mating components together.
There is a simple but genius solution 55
to this issue: Adding a PTFE sliding layer
to one side of the spring steel will pro- Rattle noise [dB(A)]
vide the low friction surface that design 50
engineers need. The PTFE layer on the
tolerance ring has the added bonus of
eliminating the need for lubrication
45
and ensures that the part will last for
the life of the vehicle. This combination,
developed by Saint-Gobain as Sprin-
40
Glide, brings together consistent force
Norglide Norglide Norglide Plastic
throughout the mating component toler-
SM075E M075GG X2T100CG bushing
ance ranges and a low coefficient of fric-
FIGURE 3 Reduction of rattling noise when using different materials – three Norglide PTFE bushings and
tion to ensure smooth and easy adjust- a conventional plastic bushing were tested; the bar shows the rattle noise generated at 2 mm clearance,
ment without rattle noise. with a 20-Hz excitation frequency at 40 m/s² acceleration (© Saint-Gobain)
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