Drawn Cup Needle Roller Bearings for Throttle Bodies - NTN

NTN TECHNICAL REVIEW No.732005
New Product
Drawn Cup Needle Roller Bearings for Throttle Bodies
Hideki AKAMATSU
Drawn cup needle roller bearings have an outer ring that is precisely drawn from a thin steel plate.
Of all bearings with outer rings, drawn cup needle roller bearings have the smallest cross sectional
height, which enables both space and cost savings.
This chapter introduces the features as well as the performance of sealed, low friction, low air leak
drawn cup needle roller bearings for use in throttle bodies.
1. Introduction
A throttle valve is a device that controls the amount
of air fed into an engine. To cope with recent growing
needs for better fuel efficiency and lower emissions,
electronically controlled throttle valves that are
capable of fine adjustment of an air/fuel ratio are being
used increasingly.
As a result of the employment of electronic control,
the means for driving throttle valves has changed from
wires to motors. Rolling contact bearings, which
feature decreased friction, are also being used
increasingly to enable both a compact lightweight
design and an improved response with the motor used
for this purpose.
Rolling contact bearings are being used in the
systems that control the airflow into automotive
engines as well. The support for the throttle blade
must not allow air to leak, therefore rolling contact
bearings must have good sealing performance.
To address these needs, we have developed drawn
cup needle roller bearings for throttle bodies that have
seals with lower friction and less air leakage. This
paper introduces the features and performance of
these drawn cup needle roller bearings.
2. Structure and features
The rolling bearings used for electronically controlled
throttle valves can be categorized as deep grooved ball
bearings (hereafter, referred to as "ball bearings") and
drawn cup needle roller bearings (hereafter, referred
to as "drawn cup bearings") (Fig. 1).
Compared with ball bearings, drawn cup bearings
have smaller outside diameters, and as a result, the
radial space of the housing can be smaller and the
housing can be lighter. Ball bearings are narrower
than drawn cup bearings, but their built-in seals alone
cannot completely prevent air leakage so additional
seals must be incorporated, which leads to the need
for additional space and expense.
Our newly developed drawn cup bearing assembly
consists of a drawn cup bearing fabricated by the prebent
technique* and a seal that does not have a core
metal. This bearing does not need additional sealing,
and it can contribute to environmental protection
through cost reduction, space conservation and
reduced weight.
*Pre-bent technique: a technique in which a cage and rollers are
fit into a drawn cup outer ring, and then the assembly is
subjected to heat treatment.
Automotive Sales Headquarters
Needle Roller Bearings Engineering Dept.
-76-

Drawn Cup Needle Roller Bearings for Throttle Bodies
Throttle blade
Return spring
Throttle blade
Return spring
Separate seal
Motor
Motor
Drawn cup bearing
(w/ built-in seal)
Control gearing
Deep groove
ball bearing
Control gearing
Drawn cup bearing application example
Deep groove ball bearing application example
Fig. 1 Structure of electronic throttle bodies
Table 1 Specification of drawn cup needle roller bearings
for throttle bodies
Fig. 2 Structure of drawn cup needle roller bearings
for throttle bodies
Development
target Specifications
Dimensions
Outer ring
Cage
Rollers
Seal
Rated load
Others
Friction
Air leakage
Inscribed circle dia. 10outside dia. 14width 14 mm
Chromium molybdenum steel
V-type welded cage
Crowned
Fluorine rubber, no core metal
Dynamic rated load Cr4500 N
Static rated load C0r5100 N
High performance grease applied
1.1 N-cm max.
0.8cm 3 /min. max.
3. Friction Performance
The friction performance of the bearings that
support the throttle blade is a critical factor in adopting
a compact design and achieving quick response with
the motor.
A friction measurement value is obtained by
inserting a torque gauge with a shaft of a specified
diameter into a drawn cup bearing that is press-fitted
into a standard ring, and turning the gauge 90
degrees. The friction value of these bearings is
approximately 0.8 N-cm, which is sufficiently lower
than the development target of 1.1 N-cm (Table 2)
Table 2 Test result of friction
Development target 1.1 N-cm max.
Number of samples (n) 30 pcs.
Mean value
0.78 N-cm
Max. value
0.85 N-cm
Min. value
0.70 N-cm
Standard deviation 0.054 N-cm
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NTN TECHNICAL REVIEW No.732005
4. Air Leakage Prevention Performance
Because the throttle valve regulates the amount of
air fed into the engine, the amount of air leakage from
the supports of the throttle blade must be strictly
controlled.
The measuring method and resultant
measurements of the air leakage on drawn cup
bearings are summarized below.
Before starting the air leakage measurements, each
drawn cup bearing was press-fit into a ring of specified
dimensions, and the shaft was inserted into the
bearing of a specified diameter. This set was then
mounted to a sufficiently rigid measuring head. The
other measuring head was shut with a lid, and was
used as a standard control. These heads were
connected to an air leakage tester, the open space in
each head was adjusted to a negative pressure, and
then air leakage was measured. Photo 1 shows the
air leakage tester, and Fig. 3 illustrates the
measurement heads.
The amount of air leakage with our drawn cup
bearing was 0.01 cm 3 /min. or lower, which is
sufficiently lower than the development target of 0.8
cm 3 /min (Table 3).
Suction
Suction
Bearing
No.
No.1
No.2
No.3
No.4
Negative
pressure
Fig. 3 Measurement part
Table 3 Test result of air leakage
Diameter of shaft
inserted (mm)
9.975
5. Conclusion
Standard control
Test bearing
Atmospheric
pressure
Air leakage
Development target: 0.8 cm 3 /min. max.
0.01cm 3 /min. max.
0.01cm 3 /min. max.
0.01cm 3 /min. max.
0.01cm 3 /min. max.
This paper has introduced our unique drawn cup
bearing assembly for a throttle valve. This assembly
incorporates a compact, less expensive drawn cup
bearing and a seal that features lower friction and air
leakage prevention capabilities. Use of this bearing
helps reduce the size of the throttle valve and improve
the response speed. We believe that this bearing will
offer better control of air-fuel ratios for automotive
engines, helping realize better fuel efficiency and
lower emissions and thus contributing to global
environmental protection.
Photo 1 Air leakage tester
Photos of author
Hideki AKAMATSU
Automotive Sales Headquraters
Needle Roller Bearings
Engineering Dept.
-78-