Eco-friendly Product Development at SNR Roulements - NTN

NTN TECHNICAL REVIEW No.772009
3.2 Low torque ball bearings
To reduce friction-induced torque loss on an
automotive transmission, use of a ball bearing rather
than a tapered roller bearing is advantageous.
However, since load carrying capacity of a ball bearing
is smaller compared with a tapered roller bearing, the
size of ball bearing tends to be larger so that the
bearing can satisfy targeted life. Incidentally, the
ordinary fracture mode of transmission bearing is
surface damage starting from a dent mark on the
raceway owing to lubricant contaminated with foreign
matter, rather than fatigue failure of bearing material.
Therefore, to prevent ingress of foreign matter into a
bearing to ensure longer bearing life, a bearing having
filter seals shown in Fig. 12 is used. Filter seals need
to be optimally designed so that they not only provide
good filtering performance but also allow lubricating oil
to be introduced into the bearing to lubricate and cool
down the bearing.
Many bearings with filter seals feature an increased
bearing width dimension to accommodate an additional
elastomer filter seal; however, this configuration leads
to increased frictional torque on bearing. A novel
design developed by SNR, as shown in Fig. 13 has a
clipped double polyamide cage that has filtering
function. The advantages of this design are as follows:
(1) Compact and light-weight design is possible.
(2) Labyrinth clearance between the cage and
raceway can be controlled at higher precision.
(3) Provision of two oil inlets helps increase
lubricating oil flow into the bearing.
(4) Reduced cost
The result of comparison between our newly
developed double seal design and a conventional seal
design is described below.
Fig. 14 illustrates results of measurement of oil flow
through a bearing under oil bath lubrication
environment. The data mapped along the vertical axis
represent filtering effect and oil flow that passes a filter
and contribute to lubrication. Compared with a
conventional filter seal, our newly developed double
filter seals boast better lubrication efficiency as more
oil flows through the bearing though the filtering effect
is roughly same.
Fig. 15 illustrates a result of comparing running
torque of our newly developed bearing with double
filter seals to that of conventional bearing. Torque
occurring inside the bearing including rolling resistance
is virtually the same with both bearing types;
notwithstanding, the total torque on our new bearing
design has been reduced by 65% because the torques
occurring on the seals has been greatly reduced. Also,
heat buildup in our bearing is mitigated; consequently,
our bearing boasts improved seizure resistance.
Furthermore, filtering function of our bearing is virtually
equivalent to that of conventional bearing design, and
the width of our bearing can be smaller. Our bearing
design can be applied to produce compact, light-weight
transmission bearing products.
Oil flow
Filtering effect and oil flow
Running torque Nm
0.350
0.300
0.250
0.200
0.150
0.100
0.050
0.000
Fig. 12 Bearing with filter seals
15.5
Filter seal
(conventional
design)
Double
filter seals
(new design)
Fig. 14 Efficiency against pollution
Conventional
design
Fig. 15 Torque test results
Clipped double
polyamide cage
Fig. 13 Bearing with double filter seals into a clipped
double polyamid cage
Filtering effect
Oil flow
Bearing interior
Seal
65%
reduction
New design
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