NTN TECHNICAL REVIEW No.77（2009）
[ New Product ]
Low-torque Roller Lifter Unit
Masashi NISHIMURA*
The demand for improved fuel consumption and exhaust emissions
control in cars has increased on a global basis in recent years. Automobile
companies are working to develop gasoline direct-injection engines as one
means to achieve new fuel efficiency targets. Other demands include
increasing the fuel pressure and reducing the friction in the fuel
compression process in the high-pressure fuel pumps used for directinjection engines. NTN has developed a low-torque roller lifter unit that responds to these demands.
This report introduces the features of this NTN low-torque roller lifter unit.
better compared with the FY2004 level 2).
To address this situation, automakers have been
committed to development of hybrid electric vehicles
and electric vehicles; as well as fuel economy
improvement through techniques including variable
valve system and idling stop. Direct-injection gasoline
engine also appears to be a particularly promising
means.
Direct-injection engines are characterized by the
fact that air alone is drawn into cylinders and
compressed. Fuel is compressed by a fuel pump is
directly injected into the cylinders where the fuel is
fired. In contrast with conventional engines that draw
air-fuel mixture generated in an intake pipe into the
cylinders (port injection), direct-injection engines are
said to develop better fuel economy owing to
operation of the following reasons 3), 4).
1. Introduction
EU has decided to enact in 2012 its CO2 emissions
regulation according to average CO2 emission per
passenger car of 130 g/km or lower, which means
20% reduction relative to the present emissions level.
Also, USA has established targets for improved fuel
economy which include average 40% improvement in
fuel economy by fiscal year 2020 in terms of the
amount of gasoline consumed by passenger cars or
compact trucks 1). Thus, NTN believes that the need
for more fuel-efficient cars will increase and more
stringent emissions standards will be introduced.
In Japan, a new fuel economy standard (see Table
1) has been legislated whose deadline is set at fiscal
year 2015: accordingly, the fuel economy of
passenger cars in Japan in FY2015 will be 23.5%
(1) Improved anti-knock properties to allow for a
higher compression ratio (greater engine power).
(2) Accurate control of the air/fuel ratio
(3) Reduced pumping loss at a lower load range
Table 1 2015 year fuel-efficient target
(Improvement rate compare with 2004) 2)
Car type
Actual value Estimated value
for FY2004
for FY2015
Improvement in fuel
economy over
FY2004 level
Passenger car 13.6
（km/R） 16.8
（km/R）
23.5%
8.3
（km/R） 8.9（km/R）
7.2%
（km/R） 15.2
（km/R）
Compact truck 13.5
12.6%
Compact bus
*Needle Roller Bearing Engineering Dept. Automotive Sales Headquarters
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Low-torque Roller Lifter Unit
high as 20 MPa 5) in order to improve combustion
efficiency. It appears that much higher injection
pressure will be increasingly adopted.
A higher fuel injection pressure means a greater
load exerted onto the lifter. A conventional lifter, in
particular, whose contact surface to the cam is a
sliding surface can experience deterioration in fuel
economy owing to greater friction with the cam.
At the same time, to be able to adopt higher fuel
pressure, it will be necessary to increase a number of
cam-operated compression cycles (increased cam
cyclic rate and increased number of high points on
cam) as well as a cam lift. To cope with these
changes, the outer circumference length of cam needs
to be longer if the base circle dimension of cam
remains unchanged. Consequently, the bearing used
in this type of application needs to be capable of
higher running speeds.
2. Peripheral structure around directinjection engine and typical
applications of roller lifter unit
Fig. 1 shows an appearance of a roller lifter unit
while Fig. 2 illustrates a structure around a fuel pump
on a direct injection engine. Fig. 3 provides a view of
typical application of a roller lifter unit.
In combination with a cam, a roller lifter unit situated
in a fuel pump drive on a direct injection engine
transmits rotary motion of the engine shaft to a
reciprocating plunger.
Previously, most commonly used roller lifter units
had a sliding surface in contact with a cam. Now,
certain automakers are adopting rolling type roller lifter
units in order to reduce friction loss from contact with
a cam and to allow a cam to be able to run at a higher
speed.
Usually, on a direct injection engine, the fuel is
injected with a pressure of 4 to 13 MPa. On certain
direct injection engines, the injection pressure is as
Fuel pump
Fig. 1 Appearance of roller lifter unit
Fig. 2 Direct injection engine, fuel pump
Roller lift unit
Fuel pump
Mating guide hole
Intake camshaft
Fuel pump driving cam
Fig. 3 Application of roller lifter unit
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NTN TECHNICAL REVIEW No.77（2009）
complement roller type bearing.
Furthermore, NTN has optimized wall thicknesses
of various areas of the casing of its roller lifter unit so
that the casing features lighter weight while
maintaining necessary mechanical strength. Thus,
NTN has reduced the inertial force occurring on its
roller lifter unit in reciprocating motion so that its roller
lifter unit can more accurately follow the motion of cam
running at higher speed.
Fig. 4 shows the specification for NTN low-torque
roller lifter unit.
3. Structure and advantages of NTN
Low Torque Roller Lift Unit
As mentioned above, more common roller lifter units
previously used have sliding contact surface that is in
contact with a cam: certain automakers are using
roller lifter units incorporating rolling bearings in order
to mitigate friction loss. The rolling bearings used for
this purpose are full complement roller bearings
because of their excellent load bearing performance
and longer life*1. However, full complement roller
bearings can pose problems such as heat buildup and
increased running torque. Intermittent loading by the
cam as well as inclination occurring from the gap
between the roller lifter unit and mating guide hole will
lead to skew on the rollers. This skew will cause the
bearing to develop lateral runout , which triggers the
above-mentioned problems.
In order to mitigate lateral runout on the bearing for
roller lifter unit, NTN has adopted a caged roller
bearing to inhibit skew occurrence on the rollers,
reduce running torque on the bearing, and improve
high-speed durability of the roller lifter unit. Also, NTN
has adopted FA treatment which is NTN’s propriety
heat treatment technique to improve bearing life,
thereby NTN has achieved a calculated bearing life
that is equivalent to or better than that of full
4. Evaluation by performance
Higher fuel temperature means a greater load
applied to the lifter. In particular, on conventional
lifters whose contact surface to the cam is a sliding
surface. The friction on the contact surface will be
greater and can cause deterioration in fuel economy.
Furthermore, to help achieve higher fuel pressure, the
lifter needs to be more durable at higher speed.
In order to evaluate the performance of our roller
lifter unit, NTN measured torques and temperature
increases on the bearing. The section below presents
some portion of information about our tests for
evaluating our roller lifter unit.
[Outer ring]
[Rollers]
FA treatment
30
[Cage]
[Detent pin]*2
[Shaft]
Special induction
heat-treated
Hollow shaft
[light-weight design]
φ26
[Casing]
Bearing size: ID 8 ×OD 16×W18 (in mm)
Fig. 4 Specification of NTN low-torque roller lifter unit
*1: “Full complement roller bearing” means a roller bearing type not having a cage. Though this bearing type boasts greater load rating
because of a greater number of rollers for a given bearing size, but can develop problems such as skew proneness of rollers because
the rollers are not guided by a cage.
*2: The detent pin slides in the groove formed in the mating guide hole to prevent the roller lifter from rotating in the circumferential
direction on the casing.
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Low-torque Roller Lifter Unit
4.1 Torque measuring operation
4.1.2 Result of torque measurement
NTN measured torques on bearings in lifter units to
determine the reduction of friction loss using NTN low
torque caged roller lifter compared to conventional
sliding type lifters and full complement roller type lifter
units.
Fig. 6 Graphically plots the resultant torque
measurements.
From Fig. 6, our findings are apparent; in
comparison with a sliding type lifter, NTN’s standard
torque roller lifter unit (caged type) boasts an 85%
reduction in starting torque and 73 to 86% reduction in
running torque. Also, in comparison with a full
complement roller type, NTN’s standard torque roller
lifter unit exhibits 8 to 29% torque reductions in
various measuring conditions.
4.1.1 Torque measuring conditions
Table 2 summarizes the conditions for our torque
measuring test and Fig. 5 schematically illustrates the
test rig used.
Table 2 Rotational torque measurement conditions
Loading
conditions
500 N, 1,000 N (Measurement was performed
with starting torque set at 500 N.)
Bearing
speed*4
1000min-1，3000min-1，6000min-1，9000min-1 The starting toque at start-up phase, where
acceleration from 0 to 3,000 min-1 takes place,
was measured (with outer ring rotated*5).
Lubrication
Lubricating oil: engine oil with dynamic viscosity
of 0W-20
Lubricating temperature: ordinary temperature
Lubricating system: splash lubrication (oil level:
centerline of drive roll)
Running torque
(full complement roller type)
Torque ratio
(relative to full complement roller type)
Running torque (caged type)
Running torque
(relative to sliding type lifter)
Torque ratio (relative to sliding type lifter)
1.4
1
1.2
0.8
1
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
1000
3000
6000
Bearing speed
Running torque
(full complement roller type)
Torque ratio
(relative to full complement roller type)
Running torque (caged type)
Running torque
(relative to sliding type lifter)
Torque ratio (relative to sliding type lifter)
1
Running torque N・m
1.4
1.2
0.8
1
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
1000
3000
6000
Bearing speed
Load
Running torque
Torque meter
Temperature measuring point
(end face of shaft)
9000
0
min-1
Caged type
Full complement roller type
Relative to sliding type lifter
Starting torque N・m
Electric motor
0
min-1
Running torque (at load 1000 N)
*3 Because the contact surface of sliding type lifter in contact with the
cam is a flat face of cylindrical tappet, the diameter and height of
the tappet are given here.
*4 Means running speed of outer ring of rolling bearings (caged type,
full complement roller type). Measurement on sliding type lifter was
taken while allowing the drive roll to run at a running speed
equivalent to that for measuring bearing speed of rolling bearing.
*5 A test method where the drive roll is brought into contact with the
outer circumference of outer ring to allow the outer ring to turn in
response to the rotary motion of the drive roll. (The outer ring is
allowed to rotate on the roller lifter unit installed on an actual
automotive fuel pump.)
Samples being tested
9000
Relative torque ratios
of caged type
Samples
being tested
• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)
• Rolling bearing (full complement roller type)
Size: ID 7.67×OD 16×W16 (in mm)
• Sliding type lifter
Size: D 30×H 25 (in mm)*3
Running torque (at load 500 N)
Drive roll
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Fig. 5 Diagrammatic illustration of test machine
Fig. 6 Result of rotational torque measurement
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Relative torque ratios
of caged type
Torque tester (outer ring rotation tester complete
with a torque meter)
Running torque N・m
Test
equipment
NTN TECHNICAL REVIEW No.77（2009）
4.2 Temperature-rise test
Temperature rise tests for bearings on roller lifter
units have been performed to verify the excellent high
speed durability of NTN’s caged low torque unit
compared to complement roller type lifter units.
4.2.1 Temperature-rise test conditions
Table 3 summarizes the test conditions adopted.
Table 3 Temperature-rise test condition
Tester
Outer ring rotation tester (See Fig. 5.)
Samples
being tested
• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)
• Rolling bearing (full complement roller type)
Size: ID 7.67×OD 16×W16 (in mm)
Loading
conditions
P/C=0.22
*Relative to rolling bearing (caged type)
Bearing
speed
Eight incremental steps: 4,500, 9,000, 13,500,
18,000, 22,500, 27,000, 31,500 and 36,000 min-1
(with outer ring rotated)
Lubrication
Lubricating oil: engine oil with dynamic viscosity
of 0W-20
Lubricating temperature: ordinary temperature,
lubricating oil flow rate: 150 ml/min
Lubricating system: circulating lubrication
Fig. 8 Appearance of test sample
(Full complement roller type)
4.3 Bearing life test
The bearing of the NTN’s low torque roller lifter unit
is a caged type. Accordingly, the number of rollers in
this type is unavoidably smaller compared with the full
complement roller type causing its load bearing
capacity to be lower and expected service life is to be
shorter. In order to address a problem of shorter
bearing life on the NTN’s low torque roller lifter unit,
NTN is subjecting the rollers to our unique FA
treatment and the shaft to special induction heating
treatment as previously described in Sec. 3. NTN has
performed a life test on the bearing section in question
in order to verify the effectiveness of these life
extending measures.
4.2.2 Results of temperature-rise test
Fig. 7 graphically plots comparison of temperature
rise on the samples tested and Fig. 8 shows a view of
seizure on a rolling bearing (full complement roller
type) having undergone the test.
The full complement roller type has developed
seizure as a result of lateral runout of its bearing at
18,000min-1. In contrast, the NTN’s standard low
torque roller lifter unit (caged type) has not developed
seizure up to 36,000 min-1. Thus, we have verified that
the high speed durability, in terms of maximum
allowable running speed, of the caged type is more
than twice as much as that of the full complement
roller type.
4.3.1 Test conditions for bearing life test
Table 4 summarizes the test conditions applied for
the life test.
Table 4 Life test conditions
Test
equipment
Outer ring rotation tester (See Fig. 5.)
Samples
being tested
• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)
Loading
conditions
Bearing
speed
Full complement roller type has
developed seizure at 18,000 min-1.
Temperature rise ˚C
60
50
Lubrication
Calculated
life per JIS
97h
(Information) Calculated life for full complement
roller type is 203 hours.
40
30
20
10
0
4,500
9,000
13,500
18,000 22,500 27,000
31,500 36,000
Bearing speed min-1
Fig. 7 Comparison of temperature-rise
(Full complement roller type)
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28000min-1 (with outer ring rotated)
Lubricating oil: engine oil with dynamic viscosity
of 0W-20
Lubricating temperature: ordinary temperature,
lubricating oil flow rate: 150 ml/min
Lubricating system: circulating lubrication
Caged type
Full complement roller type
P/C=0.22
Low-torque Roller Lifter Unit
4.3.2 Result of bearing life test
5. Conclusion
Fig. 9 shows graphical plotting of the result of our
bearing life test.
NTN has have subjected the rollers to FA treatment
and the shaft to a unique induction heat treatment
process. The results have verified that the standard
rating life of our bearing stands at 1,370 hours, which
is 14 times as long of a life value calculated according
to a JIS method (97 hours).
When assuming that the average engine speed is
3,000 min-1 (equivalent to average running speed of
7,500 min-1 at the bearing of roller lifter unit*6), the
average load acting on the bearing is 1,000 N*7, and
the above-mentioned life value calculated per a JIS
standard is multiplied by 14, then the resultant bearing
life for our roller lifter unit stands at 5×104 hours and
this life coincides with a life of 27 years*8. Assuming
that the useful life of an average passenger car is 15
years, the NTN’s bearing well satisfies this useful life
requirement.
This paper has presented information about NTN’s
low torque roller lifter unit and associated technology.
The size of market will further expand for direct
injection engines as one of potential measures for
improving fuel economy for automobiles. To address
this trend, NTN will further market its low torque roller
lifter products as well as enhance their functionality.
References
1) Website of Japan Automobile Manufacturers
Association, Inc. (JAMA)
2) Website of Ministry of Land, Infrastructure, Transport
and Tourism
3) H. Ando: Technical Prospects of Gasoline Direct
Injection Engines, Engine Technology Review Vol. 1,
No. 1 April 2009, 18-23
4) T. Sena and Y. Katsuragi, Introduction to Engine
Science, first edition, Grand Prix Publishing, (1997)
173–183 (Japanese)
5) Direct Injection, Car Mechanism Encyclopedia Engine
Volume, August 2009 special issue 111–115
(Japanese)
Cumulative failure probability %
*6 Assumptions: This speed is equivalent to cam running speed
of 1,500 min-1, and the cam outside circumference length is
five times as long as the bearing outside circumference
length.
*7 Assumptions: The fuel pressure is set at 13 MPa, and the
pump plunger diameter measures 10 mm.
*8 Assumption: The average daily use time for an average
passenger car is 5 hours.
95
90
80
70
60
50
40
30
20
10
5
8
9
1
103
1.5
Life
2
103
2.5
3
h
Fig. 9 Life test result
Photo of author
Masashi NISHIMURA
Needle Roller Bearing
Engineering Dept.
Automotive Sales Headquarters
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