U.S. patent application number 10/811728 was filed with the patent office on 2004-11-25 for valve train for internal combustion engine.
Invention is credited to Takamura, Hiroyuki.
Application Number | 20040231622 10/811728 |
Document ID | / |
Family ID | 33458980 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040231622 |
Kind Code |
A1 |
Takamura, Hiroyuki |
November 25, 2004 |
Valve train for internal combustion engine
Abstract
The present invention provides a valve train for an internal
combustion engine, capable of preventing the minute slippage
between the cam lobe and the roller follower, and thereby reducing
the friction loss in the valve train system. At least one of the
following measures is applied to the valve train. Measure 1: A cam
lobe made of an iron sintered material is used, and the surface
roughness Ra of the outer circumferential surface thereof is made
to be in a range of 0.4 to 2.2 .mu.m. Measure 2: The surface
roughness Ra of the outer circumferential surface of the roller of
the roller follower is made to be in a range of 0.4 to 2.2
.mu.m.
Inventors: |
Takamura, Hiroyuki;
(Tochigi-ken, JP) |
Correspondence
Address: |
Richard J. Streit
Ladas & Parry
Suite 1200
224 South Michigan Avenue
Chicago
IL
60604
US
|
Family ID: |
33458980 |
Appl. No.: |
10/811728 |
Filed: |
March 29, 2004 |
Current U.S.
Class: |
123/90.6 |
Current CPC
Class: |
F01L 2820/01 20130101;
F01L 2301/00 20200501; F01L 2305/00 20200501; F01L 1/053 20130101;
F01L 1/181 20130101 |
Class at
Publication: |
123/090.6 |
International
Class: |
F01L 001/34; F01L
001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2003 |
JP |
2003-095649 |
Mar 31, 2003 |
JP |
2003-097478 |
Apr 24, 2003 |
JP |
2003-120256 |
Feb 26, 2004 |
JP |
2004-052364 |
Claims
What is claimed is:
1. A valve train for an internal combustion engine comprising a cam
lobe fixed on a cam shaft and a roller follower provided with a
roller to come in rotation-contact with the cam lobe, wherein the
cam lobe is made of an iron based sintered material, and the
surface roughness Ra of the outer circumferential surface thereof
is 0.4 to 2.2 .mu.m.
2. The valve train according to claim 1, wherein the surface
roughness Ra of the outer circumferential surface of the roller is
0.4 to 2.2 .mu.m.
3. A valve train for an internal combustion engine comprising a cam
lobe fixed on a cam shaft and a roller follower provided with a
roller to come in rotation-contact with the cam lobe, wherein the
surface roughness Ra of the outer circumferential surface of the
roller is 0.4 to 2.2 .mu.m.
4. The valve train according to claim 3, wherein the surface
roughness Ra of the outer circumferential surface of the cam lobe
is 0.4 to 2.2 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a valve train for an
internal combustion engine, comprising a cam lobe fixed on a cam
shaft, and a roller follower provided with a roller to be contacted
with the cam lobe while rotating.
[0003] 2. Description of the Related Art
[0004] Recently, from the viewpoint of the environment protection,
low fuel consumption is highly requested. As to the internal
combustion engine, the friction reduction more than the
conventional ones is required for reducing the energy transmission
loss in order to realize the low fuel consumption. According to a
valve train comprising a cam follower for converting the rotating
motion of the cam shaft to the reciprocal motion of the valve, a
cam lobe fixed on the cam shaft is contacted with the cam follower
while sliding or rotating. The friction loss between the cam lobe
and the cam follower is one of the major factors of the friction
loss in the entire internal combustion engine, and thus it is
desired to reduce the same as much as possible. Therefore, various
methods have been taken for the purpose of the friction reduction
in the valve train.
[0005] For example, Japanese Patent Application Laid Open No.
2002-70507 discloses a method for reducing the resistance due to
the friction, in which the slide-contacting type cam follower is
allowed to have a surface layer with a lowered coefficient of
dynamic friction by forming at least the area of the surface layer
sliding against the cam lobe is formed with a diamond and making
the surface roughness Ra of this area be 0.3 .mu.m or less.
[0006] On the other hand, the low friction has been achieved by
changing from the can follower of the type of slide-contacting with
the cam lobe (ex., flat tappet, or the like) to the roller follower
of the type of rotation-contacting, such as a roller rocker arm and
a roller tappet. Japanese Patent Application Laid Open No. 3-78507
discloses that a minute ruggedness of Ra in the range of 0.08 to
0.25 .mu.m is formed on an outer circumferential surface of the
rotation-contacting part (roller rim) of the roller follower with
respect to the cam lobe which is a part coming in rotation-contact
with the cam lobe to improve a performance of retaining a lubricant
oil on such outer circumferential surface, thus preventing the
abnormal wear.
[0007] Furthermore, Japanese Patent Application Laid Open No.
2001-329807 discloses that a surface roughness Ra of an outer
circumferential surface of the cam lobe in the valve train is made
0.5 .mu.m or less, and a surface roughness Ra of an outer
circumferential surface of the rotation-contacting part (roller
rim) of the roller on the roller rocker arm with respect to the cam
lobe is made 0.1 .mu.m or less to achieve prevention of pitching in
the outer circumferential surface of the cam lobe and prevention of
peeling from the outer circumferential surface of the roller as
well as reduction of wear on the outer circumferential surface of
the cam lobe, and it also discloses that a surface roughness Ra of
an outer circumferential surface of the cam lobe is made 0.5 .mu.m
or less to achieve reduction of aggressiveness (attacking) with
respect to the outer circumferential surface of the rotation
contacting part (roller rim) of the roller of the roller rocker arm
with respect to the cam lobe.
SUMMARY OF THE INVENTION
[0008] However, the inventor of the present invention found the
following fact. That is, in a rotation-contacting type combination
of the cam lobe and the roller follower, the cam lobe and the
roller follower are both abrasion products and accordingly low in
the dynamic friction coefficient so that minute slippage is caused
between the cam lobe and the roller follower and accordingly the
efficient rotation is obstructed, thus leading a problem that the
friction loss is caused.
[0009] In view of the above-mentioned circumstances, the present
invention has been achieved, and an object thereof is to provide a
valve train for an internal combustion engine, capable of
eliminating the minute slippage between the cam lobe and the roller
follower, and reducing the friction loss in the valve train
system.
[0010] The present inventor has found out that the friction loss in
the valve train system having a combination of a cam lobe and a
roller follower can be reduced by increasing the dynamic friction
coefficient between the cam lobe and the roller follower so as to
eliminate the minute slippage at the time of rotation-contact.
[0011] A first aspect of the present invention provides a valve
train for an internal combustion engine, which comprises a cam lobe
fixed on a cam shaft, and a roller follower provided with a roller
to come in rotation-contact with the cam lobe, wherein the cam lobe
is made of an iron based sintered material, and the surface
roughness Ra of the outer circumferential surface thereof is in a
range of 0.4 to 2.2 .mu.m.
[0012] According to the valve train of the above-mentioned first
aspect, it is preferable that the surface roughness Ra of the outer
circumferential surface of the roller is in a range of 0.4 to 2.2
.mu.m.
[0013] A second aspect of the present invention provides a valve
train for an internal combustion engine, which comprises a cam lobe
fixed on a cam shaft, and a roller follower provided with a roller
to come in rotation-contact with the cam lobe, wherein the surface
roughness Ra of the outer circumferential surface of the roller is
in a range of 0.4 to 2.2 .mu.m.
[0014] According to the valve train of the above-mentioned second
aspect, it is preferable that the surface roughness Ra of the outer
circumferential surface of the cam lobe is in a range of 0.4 to 2.2
.mu.m.
[0015] Since the valve train of the present invention allows smooth
rotation of the roller follower, the minute slippage between the
cam lobe and the roller follower can be eliminated, thus reducing
the friction loss in the valve train system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the accompanying drawings:
[0017] FIG. 1 is a view showing a configuration example of a valve
train for an internal combustion engine according to the present
invention;
[0018] FIG. 2 is a view showing an example of a cam lobe.
[0019] FIG. 3 is an enlarged front view of an example of a contact
part of a rocker arm with respect to a cam lobe;
[0020] FIG. 4 is a graph showing the transition of the friction
characteristic (1,500 rpm) according to the combination between the
cam lobe outer circumferential surface roughness and the roller
outer circumferential surface roughness;
[0021] FIG. 5 is a graph showing the transition of the friction
characteristic (2,000 rpm) according to the combination between the
cam lobe outer circumferential surface roughness and the roller
outer circumferential surface roughness:
[0022] FIG. 6 is a graph showing the transition of the friction
characteristic (2,500 rpm) according to the combination between the
cam lobe outer circumferential surface roughness and the roller
outer circumferential surface roughness;
[0023] FIG. 7 is a graph showing the transition of the pitching
characteristic according to the combination between the cam lobe
outer circumferential surface roughness and the roller outer
circumferential surface roughness;
[0024] FIG. 8 is a view showing the configuration of a friction
torque measuring device; and,
[0025] FIG. 9 is a view showing the configuration of a roller on
roller rolling-and sliding wear tester device for measuring the
number of pitching.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] A valve train for an internal combustion engine according to
the present invention comprises a cam lobe fixed on a cam shaft to
be rotated synchronously with a crank shaft of an engine, and a
roller follower provided with a roller to come in rotation-contact
with the cam lobe. Herein, a term "rotation-contact" means that the
roller is in contact with the cam shaft while the roller is
rotating. The roller follower is a member provided with a roller to
be in rotation-contact with a cam lobe at its part contacting with
the cam lobe for converting the rotating motion of the cam shaft to
the valve reciprocal motion, and it can be designed in a suitable
form according to the structure of the valve operating mechanism.
Examples of the roller follower include, a rocker arm (roller
rocker arm) or a tappet (roller tappet) both of which are of the
type provided with a roller at its contacting part with respect to
the cam lobe, or another type in which a roller to be in
rotation-contact with the cam lobe is directly mounted on the top
end at the base part of the valve member, or the like.
[0027] FIG. 1 shows an embodiment of a valve train according to the
present invention. The valve train of this embodiment is composed
of a cam lobe 2 fixed on a cam shaft 1, and a rocker arm 3 provided
with a roller 4 to be in rotation-contact with the cam lobe. The
rocker arm 3 has a rocker arm main body 5, at one end part of which
it supports the roller 4 rotatably by a pin 6, and the rocker arm 3
itself is supported swayably at a middle part of the main body 5 by
a rocker shaft 7, and furthermore, an adjusting screw 8 which is
screwed on the other end part of the rocker arm 3 butts against an
end face of a base part of a valve body 9 by its top end part. A
compression spring 10 applies an elastic force to the valve body 9
in the direction of closing an intake port or an exhaust port.
[0028] FIG. 2 includes a front view (2A) and a side view (2B)
respectively showing an example of the shape of the cam lobe 2.
FIG. 3 is an enlarged front view of an example of the contact part
of the rocker arm 3 at which it comes in contact with the cam lobe
2. The rocker arm 3 supports the roller 4 rotatably in the
following manner: a pair of supporting wall parts 5a each having a
bearing hole 5b and positioning with an interval therebetween is
formed on one end part of the rocker arm main body 5, at which the
rocker arm main body 5 comes into contact with the cam lobe 2, the
roller 4 having a bearing hole 4a is disposed between the pair of
the supporting wall parts 5a, and the pin 6 is inserting through
one bearing hole 5b of the supporting wall parts, the bearing hole
4a of the roller 4, and then the other bearing hole 5b of the
supporting wall parts. Moreover, it is preferable to put a bearing
between the pin 6 and the bearing hole 4a and/or the bearing hole
5b for alleviating the friction loss. Although the material of the
roller 4 is not particularly limited, and for example, a bearing
steel such as the bearing steel SUJ2, or the like is
preferable.
[0029] According to the present invention, at least one of the
measures described below is applied to the valve train in order to
rotate the roller smoothly without causing the minute slippage at
the time of bringing the cam lobe 2 of the cam shaft into
rotation-contact with the roller 4 of the roller follower.
[0030] Measure 1: A cam lobe made of an iron sintered material is
used, and the surface roughness Ra of the outer circumferential
surface thereof is made to be in a range of 0.4 to 2.2 .mu.m,
preferably 0.4 to 1.2 .mu.m, and particularly preferably 0.85 to
1.2 .mu.m.
[0031] Measure 2: The surface roughness Ra of the outer
circumferential surface of the roller of the roller follower (the
contacting surface with respect to the cam lobe) is made to be in a
range of 0.4 to 2.2 .mu.m, and preferably 0.4 to 1.2 .mu.m
[0032] In the case of taking the above-mentioned measure 1, the
dynamic friction coefficient of the contact surface between the cam
lobe and the roller is increased by using an iron based sintered
material for forming the cam lobe and further setting the surface
roughness Ra of the outer circumferential surface to 0.4 .mu.m or
more. Such increase of the dynamic friction coefficient can prevent
the minute slippage therebetween, thus alleviating the friction
loss of the valve train system. In addition to such intention of
obtaining the appropriate dynamic friction coefficient for
preventing the minute slippage in the rotation-contacting surface,
in order to restrain the pitching wear by preventing the
deterioration of the pitching resistance due to a large surface
pressure loaded on a localized portion in the rotation-contacting
surface, the surface roughness Ra of the outer circumferential
surface on the cam lobe is set to 2.2 .mu.m or less.
[0033] As the sintered cam lobe for the first measure, one made of
any iron based sintered alloy such as a Mo--Ni--Fe based ones and a
Mo--Ni--Cr--Fe based one can be used. Moreover, as the iron based
sintered alloy, those having a porosity about 2 to 10% can be used
from the view point of the strength, the wear resistance or the
like of the cam lobe. In the case when the surface roughness Ra of
the outer circumferential surface (the contacting surface with the
cam lobe) of the roller 4 is also set within a range of 0.4 to 2.2
.mu.m, in particular 0.4 to 1.2 .mu.m in addition to control of
that of the outer circumferential surface on the cam lobe, the
friction loss can further be alleviated while restraining the
increase of the pitching wear, and thereby the minute slippage
between the cam lobe and the roller can further be restrained to
the lower degree, thus being preferable. Although the material of
the roller 4 is not particularly limited, for example, a bearing
steel, such as the bearing steel SUJ2 is preferable.
[0034] On the other hand, in the case of taking the above-mentioned
measure 2, the dynamic friction coefficient of the contact surface
between the cam lobe and the roller is increased by setting the
surface roughness Ra of the outer circumferential surface on the
roller to 0.4 .mu.m or more. Such increase of the dynamic friction
coefficient can prevent the minute slippage therebetween, thus
alleviating the friction loss of the valve train system. In
addition to such intention of obtaining the appropriate dynamic
friction coefficient for preventing the minute slippage in the
rotation-contacting surface, in order to restrain the pitching wear
by preventing a large surface pressure from being loaded on a
localized portion in the rotation-contacting surface, the surface
roughness Ra of the outer circumferential surface on the roller is
set to 2.2 .mu.m or less.
[0035] For the second measure, although the material of the cam
lobe 2 is not particularly limited, any material known for the
conventional cam lobe may be used, and examples thereof include an
iron based sintered alloy, a carbon steel S50C (it may be subjected
to high frequency quenching), or the like. In the case when the
surface roughness Ra of the outer circumferential surface (the
contacting surface with the roller) on the cam lobe 2 is also set
within a range of 0.4 to 2.2 .mu.m, in particular, 0. 4 to 1.2
.mu.m, in addition to control of that of the outer circumferential
surface of the roller, the friction loss can further be alleviated
while restraining the increase of the pitching wear, and thereby
the minute slippage between the cam lobe and the roller can further
be restrained to the lower degree, thus being preferable.
[0036] It is preferable to execute the above-mentioned measures 1
and 2 in combination with each other since the effect of reducing
the friction loss can further be improved.
[0037] The method for controlling the surface roughness of each
contact surface on the roller and the cam lobe in the
above-mentioned range is not particularly limited, and various
surface works can be applied, for example, the grinding work such
as cross hatching, and blasting work such as shot blasting which is
a method of blowing the hard particles such as the metal particles
and the ceramic particles at the high speed and high pressure. In
the case of applying the blast work, shot blasting is suitable, and
particularly suitable condition for the shot blasting is to jet the
steel grids having a 44 .mu.m average particle size by 0.44 to 0.55
MPa.
[0038] Moreover, the cam lobe after sintering process may be
subjected to a refining process as needed, and the cam lobe
subjected to such process may be used as it is without applying the
blast work.
[0039] As heretofore explained, according to the valve train of the
present invention, since the roller of the roller follower can be
rotated smoothly, the minute slippage between the cam lobe and the
roller follower is eliminated so that the friction loss in the
valve train system can be reduced.
EXAMPLES
[0040] The transitions of the friction characteristic and the
pitching characteristic according to the various combination of the
iron based sintered material cam lobes having different surface
roughnesses Ra of the outer circumferential surface and the SUJ2
quenched steel rollers having different surface roughnesses Ra of
the outer circumferential surface were examined.
[0041] <Production Method>
[0042] The sintering powder were prepared such that the element
composition after secondary sintering was adjusted to C: 0.8% by
mass, Mo: 0.5% by mass, Ni: 2.5% by mass, and Fe: remainder.
Furthermore, as the lubricating agent, a zinc stearate was added
and mixed.
[0043] Next, a temporary sintered compact was obtained by executing
first press molding (primary molding) the prepared sintering
particles by a 500 to 800 Mpa (5 to 8 ton/cm.sup.2) surface
pressure so as to form a green compact, and by executing temporary
sintering (primary sintering) the green compact at 600.degree. C.
to 900.degree. C. in a vacuum sintering furnace. Then, a secondary
sintered compact was obtained by executing second press molding
(secondary molding) the temporary sintered compact by a 700 to 1200
Mpa (7to 12ton/cm.sup.2) surface pressure, and by executing main
sintering (secondary sintering) the secondary compact at
1,100.degree. C. to 1,200.degree. C. in a vacuum sintering furnace.
This secondary sintered compact was further subjected to the quench
and temper process, and then grinding finish process of the outer
circumferential surface, thereby obtaining a cam lobe made of an
iron based sintered material which had an outer circumferential
hardness at 52 HRC, a density at 7.46 Ngm.sup.-3, and a surface
roughness Ra of the outer circumferential surface in the range of
0.2 to 2.2 .mu.m.
[0044] On the other hand, a bearing steel SUJ2 shaped in a roller
was subjected to the quench and temper process, and then grinding
finish process of the outer circumferential surface, thereby
obtaining a roller having an outer circumferential hardness at 61
HRC, and a surface roughness Ra of the outer circumferential
surface in the range of 0.2 to 2.2 .mu.m.
[0045] <Measurement of the Friction Torque>
[0046] The friction torque was measured for the cam lobes and the
rollers obtained by the above-mentioned production method in the
combinations shown in the Tables 1 to 3 by the following method and
condition. The combinations shown in the Tables 1 to 3 are encoded
as shown in the Tables 4 to 6.
[0047] Using the apparatus having the configuration shown in FIG.
8, the force Fz in the horizontal direction (the direction
perpendicular to the cam shaft) of the roller circumference, the
friction force Fy with respect to the guide part 12, and the force
Fx in the cam shaft direction were measured by a three component
force sensor 13, and the load Fp of the push rod 11 was measured by
a force sensor 14. The friction torque Ff was calculated from the
measurement results and the contact angle .alpha. and the contact
load Fc between the cam lobe and the roller, and using the
below-mentioned formula.
Fc sin .alpha.+Ff cos .alpha.=Fz
Fc cos .alpha.-Ff sin .alpha.=Fy+Fp+Fx
[0048] The results are shown in the Table 1 and FIG. 4, the Table 2
and FIG. 5, and the Table 3 and FIG. 6.
[0049] (Measurement Condition)
[0050] Roller size: the contact part with the cam lobe of the
roller rocker arm having a 34 mm cylinder size provided with the
roller part having a 28 mm outer diameter and a 17 mm width
[0051] Cam lobe size: basic circle radius 23 mm, lifting amount 7.9
mm
[0052] Lubricant oil: SAE10W-30
[0053] oil temperature: 90.degree. C.
[0054] oil pressure: 0.3 MPa
[0055] Cam rotation speed: 1,500 rpm, 2,000 rpm, 2,500 rpm
[0056] <Measurement of Cycle Times Leading to Occurrence of
Pitching>
[0057] The cycle times leading to the occurrence of pitching was
measured for the combinations of the cam lobe materials and the
roller materials shown in the Table 7 by means of a roller on
roller rolling-and sliding wear tester machine shown in FIG. 9,
using the cam lobe material having a surface roughness Ra of the
outer circumferential surface of 0.2 to 2.2 .mu.m, and the roller
material having a surface roughness Ra of the outer circumferential
surface of 0.2 to 2.2 .mu.m produced in the same manner as the
above-mentioned production method.
[0058] With the cam lobe material and the roller material installed
in the testing machine, the cycle times of the rotation at which
the pitching was caused was measured in the following manner: the
outer circumferential surface on the cam lobe iron based sintered
material (test piece 15) of the cam shaft and that on the roller
(counterpart cylindrical test piece 16) of the roller rocker arm
were brought into contact with each other under 3,000 N of the
applied lord (load 18); the rotation of the cam lobe iron based
sintered material (test piece 15) was started at a constant
rotation frequency (rotation speed) while a lubricant oil 17 was
dropped to the contact surface between the test pieces; and then
the cycle times of rotation was counted till occurrence of the
pitching. The results are shown in the Table 7 and FIG. 7. The
combinations shown in the Table 7 are encoded as shown in the Table
8.
[0059] (Measurement Condition)
[0060] Test machine: roller on roller rolling-and sliding wear
tester
[0061] Rotation speed; 1,500 rpm
[0062] Lubricant oil: SAE10W-30
[0063] Oil temperature: 100.degree. C.
[0064] Amount of lubricant oil supplied: 2.times.10.sup.-4
m.sup.3/min
[0065] Load: 3,000 N
[0066] Slipping ratio: 0%
[0067] Judgment method: The occurrence of cracks due to the
pitching was detected by the AE (acoustic emission), and the cycle
times when the occurrence of cracks was detected was defined as the
cycle time leading to the pitching.
[0068] <Test results>
[0069] As shown in the Tables 1 to 3 and FIGS. 4 to 6, the friction
torque was smaller in the combination having a larger surface
roughness Ra of the cam lobe and the roller.
[0070] Specifically, the friction torque (Ff (0.2/0.2)) of the
combination with the surface roughness Ra of the outer
circumferential surface of the cam lobe of 0.2 .mu.m and the
surface roughness Ra of the outer circumferential surface of the
roller of 0.2 .mu.m, that is, the combination with the surface
roughness Ra of the outer circumferential surface of the cam lobe
of less than 0.4 .mu.m and the surface roughness Ra of the outer
circumferential surface of the roller of less than 0.4 .mu.m was
0.28 N.multidot.m, 0.19 N.multidot.m, and 0.15 N.multidot.m,
respectively at the 1,500 rpm, 2,000 rpm and 2,500 rpm. Although
the friction torque in this case tends to be reduced with the rise
of the rotational frequency, since the surface roughness Ra of the
outer circumferential surface of the cam lobe and the surface
roughness Ra of the outer circumferential surface of the roller are
both small, the minute slippage accompanied by the decline of the
dynamic friction coefficient in the contact surface between the cam
lobe and the roller was caused so that the friction torque as a
whole was high, and thus the friction loss was not reduced
sufficiently.
[0071] In contrast, the friction torque (Ff (2.2/2.2)) of the
combination with the surface roughness Ra of the outer
circumferential surface of the cam lobe of 2.2 .mu.m and the
surface roughness Ra of the outer circumferential surface of the
roller of 2.2 .mu.m was 0.12 N.multidot.m, 0.08 N.multidot.m, and
0.07 N.multidot.m, respectively at the 1,500 rpm, 2,000 rpm and
2,500 rpm. The friction torque in this case tends to be reduced
with the rise of the rotational frequency. Since this case has a
combination with the surface roughness Ra of the outer
circumferential surface of the cam lobe and the surface roughness
Ra of the outer circumferential surface of the roller are both
large, the dynamic friction coefficient in the contact surface
between the cam lobe and the roller is high so that the friction
torque was small as a whole. The improvement ratio
(Ff(2.2/2.2)/Ff(0.2/0.2)) of the friction torque (Ff (2.2/2.2)) in
the combination of the surface roughnesses Ra of the cam lobe and
the outer circumferential surface of the roller of both 2.2 .mu.m
with respect to the friction torque (Ff (0.2/0.2)) in the
combination of the surface roughnesses Ra of the cam lobe and the
outer circumferential surface of the roller of both 0.2 .mu.m was
each about 4.3/10, 4.2/10 and 4.7/10, respectively at the 1,500
rpm, 2,000 rpm and 2,500 rpm. By increasing the surface roughness
Ra of the outer circumferential surfaces of the cam lobe and the
roller, reduction of the friction loss was achieved.
[0072] As mentioned above, by increasing the surface roughness Ra
of the outer circumferential surfaces of the cam lobe and the
roller so as to control them at 0.4 or more, the friction torque
can be reduced to the extremely small degree.
1TABLE 1 Transition of Friction torque (Cam rotation speed: 1,500
rpm) Outer circumferential surface roughness Ra of Roller part of
Roller follower (.mu.m) Friction torque Material: quenched SUJ2
(Nm) 0.2 0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 0.28 0.28 0.27 0.27 0.26
0.25 0.25 circumferential 0.4 0.25 0.25 0.24 0.24 0.23 0.23 0.23
surface 0.8 0.20 0.18 0.17 0.16 0.15 0.15 0.14 roughness Ra of 1.0
0.18 0.17 0.16 0.15 0.15 0.14 0.13 Cam lobe (.mu.m) 1.4 0.17 0.17
0.16 0.15 0.14 0.13 0.13 Material: iron 1.8 0.16 0.16 0.15 0.14
0.14 0.13 0.13 based sintered 2.0 0.16 0.16 0.15 0.14 0.13 0.13
0.12 material 2.2 0.15 0.15 0.15 0.14 0.13 0.13 0.12
[0073]
2TABLE 2 Transition of Friction torque (Cam rotation speed: 2,000
rpm) Outer circumferential surface roughness Ra of Roller part of
Roller follower (.mu.m) Friction torque Material: quenched SUJ2
(Nm) 0.2 0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 0.19 0.18 0.18 0.17 0.16
0.16 0.15 circumferential 0.4 0.17 0.15 0.15 0.14 0.13 0.13 0.12
surface 0.8 0.14 0.14 0.13 0.13 0.11 0.10 0.10 roughness Ra of 1.0
0.13 0.13 0.12 0.12 0.11 0.10 0.09 Cam lobe (.mu.m) 1.4 0.11 0.11
0.10 0.10 0.09 0.09 0.09 Material: iron 1.8 0.11 0.11 0.10 0.10
0.09 0.09 0.09 based sintered 2.0 0.11 0.10 0.10 0.09 0.09 0.09
0.09 material 2.2 0.10 0.10 0.09 0.09 0.09 0.09 0.08
[0074]
3TABLE 3 Transition of Friction torque (Cam rotation speed: 2,500
rpm) Outer circumferential surface roughness Ra of Roller part of
Roller follower (.mu.m) Friction torque Material: quenched SUJ2
(Nm) 0.2 0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 0.15 0.15 0.15 0.14 0.13
0.13 0.13 circumferential 0.4 0.14 0.13 0.12 0.12 0.12 0.12 0.11
surface 0.8 0.11 0.10 0.10 0.10 0.10 0.10 0.10 roughness Ra of 1.0
0.11 0.10 0.10 0.10 0.10 0.10 0.10 Cam lobe (.mu.M) 1.4 0.10 0.10
0.10 0.10 0.09 0.09 0.09 Material: iron 1.8 0.09 0.09 0.09 0.09
0.09 0.09 0.08 based sintered 2.0 0.09 0.09 0.09 0.08 0.08 0.08
0.08 material 2.2 0.08 0.08 0.08 0.08 0.08 0.07 0.07
[0075]
4TABLE 4 Combination in the Table 1 (Cam rotation speed: 1,500 rpm)
Outer circumferential surface roughness Ra of Roller part of Roller
follower (.mu.m) Friction torque Material: quenched SUJ2 (Nm) 0.2
0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 A1 B1 C1 D1 E1 F1 G1
circumferential 0.4 A2 B2 C2 D2 E2 F2 G2 surface 0.8 A3 B3 C3 D3 E3
F3 G3 roughness Ra of 1.0 A4 B4 C4 D4 E4 F4 G4 Cam lobe (.mu.m) 1.4
A5 B5 C5 D5 E5 F5 G5 Material: iron 1.8 A6 B6 C6 D6 E6 F6 G6 based
sintered 2.0 A7 B7 C7 D7 E7 F7 G7 material 2.2 A8 B8 C8 D8 E8 F8
G8
[0076]
5TABLE 5 Combination in the Table 2 (Cam rotation speed: 2,000 rpm)
Outer circumferential surface roughness Ra of Roller part of Roller
follower (.mu.m) Friction torque Material: quenched SUJ2 (Nm) 0.2
0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 H1 I1 J1 K1 L1 M1 N1
circumferential 0.4 H2 I2 J2 K2 L2 M2 N2 surface 0.8 H3 I3 J3 K3 L3
M3 N3 roughness Ra of 1.0 H4 I4 J4 K4 L4 M4 N4 Cam lobe (.mu.m) 1.4
H5 I5 J5 K5 L5 M5 N5 Material: iron 1.8 H6 I6 J6 K6 L6 M6 N6 based
sintered 2.0 H7 I7 J7 K7 L7 M7 N7 material 2.2 H8 I8 J8 K8 L8 M8
N8
[0077]
6TABLE 6 Combination in the Table 3 (Cam rotation speed: 2,500 rpm)
Outer circumferential surface roughness Ra of Roller part of Roller
follower (.mu.m) Friction torque Material: quenched SUJ2 (Nm) 0.2
0.4 0.8 1.2 1.6 2.0 2.2 Outer 0.2 O1 P1 Q1 R1 S1 T1 U1
circumferential 0.4 O2 P2 Q2 R2 S2 T2 U2 surface 0.8 O3 P3 Q3 R3 S3
T3 U3 roughness Ra of 1.0 O4 P4 Q4 R4 S4 T4 U4 Cam lobe (.mu.m) 1.4
O5 P5 Q5 R5 S5 T5 U5 Material: iron 1.8 O6 P6 Q6 R6 S6 T6 U6 based
sintered 2.0 O7 P7 Q7 R7 S7 T7 U7 material 2.2 O8 P8 Q8 R8 S8 T8
U8
[0078] As shown in the Table 7 and FIG. 7, the cycle times leading
to the occurrence of pitching (number of pitching occurrence) was
smaller in the combination with a larger surface roughness Ra of
the outer circumferential surface of the cam lobe and the roller so
that the pitching resistance was lowered.
[0079] Specifically, in the combination of the surface roughness Ra
of the outer circumferential surface of the cam lobe of 2.2 .mu.m
and the surface roughness Ra of the outer circumferential surface
of the roller of 2.2 .mu.m, the number of pitching occurrence was
5.0.times.10.sup.5, and it was smallest.
[0080] In contrast, according to a past experience of the present
inventor, when the conventional chilled cast iron cam shaft is used
in combination with the roller follower, the number of the pitching
occurrence is about 1.3.times.10.sup.5 under 3,000 N in the test
condition, so that the excellent pitching characteristic cannot be
obtained, the durability is insufficient, and thus it is not suited
for the long term use.
[0081] That is, even in the case of the combination of the surface
roughness Ra of the outer circumferential surface of the iron based
sintered material cam lobe of 2.2 .mu.m and the surface roughness
Ra of the outer circumferential surface of the roller of 2.2 .mu.m,
which has the smallest number of pitching occurrence among the
combinations shown in the Table 7, the number of the pitching
occurrence can be improved by about 4 times compared with the case
of using the chilled cast iron cam shaft in combination with the
roller follower. Furthermore, according to the combination of
having the surface roughness Ra of the outer circumferential
surface of the iron based sintered material cam lobe and the roller
of less than 2.2 .mu.m, the number of the pitching occurrence is
improved over 4 times.
[0082] That is, by controlling the outer circumferential surface Ra
on the outer circumferential surface of the cam lobe and the roller
at 2.2 .mu.m or less, the high friction characteristic can be
provided and at the same time the excellent pitching resistance can
be obtained.
[0083] In contrast, according to the combination of the surface
roughness Ra of the outer circumferential surface of the cam lobe
of 0.2 .mu.m and the surface roughness Ra of the outer
circumferential surface of the roller of 0.2 .mu.m, that is, the
combination of the surface roughness Ra of the outer
circumferential surface of the cam lobe of less than 0.4 .mu.m, and
the surface roughness Ra of the outer circumferential surface of
the roller of less than 0.4 .mu.m, the number of the pitching
occurrence was 2.0.times.10.sup.7, so that the excellent pitching
resistance can be demonstrated. However, in the above-mentioned
measurement of the friction torque, the friction torque was high in
this combination.
7TABLE 7 Transition of Number of Pitching Occurrence (Contact load:
3,000 N) Outer circumferential surface roughness Ra of Roller part
of Roller follower (.mu.m) Number of pitching Material: quenched
SUJ2 occurrence 0.2 1.0 1.8 2.0 2.2 Outer circumferential 0.2 2.0
.times. 10.sup.7 8.8 .times. 10.sup.6 5.0 .times. 10.sup.6 4.2
.times. 10.sup.6 3.6 .times. 10.sup.6 surface roughness Ra of 1.0
9.1 .times. 10.sup.6 6.2 .times. 10.sup.6 4.1 .times. 10.sup.6 3.3
.times. 10.sup.6 2.1 .times. 10.sup.6 Cam lobe (.mu.m) 1.8 5.5
.times. 10.sup.6 4.7 .times. 10.sup.6 3.1 .times. 10.sup.6 2.1
.times. 10.sup.6 1.2 .times. 10.sup.6 Material: iron based 2.0 5.0
.times. 10.sup.6 4.1 .times. 10.sup.6 1.2 .times. 10.sup.6 9.2
.times. 10.sup.5 8.0 .times. 10.sup.5 sintered material 2.2 3.8
.times. 10.sup.6 3.2 .times. 10.sup.6 9.5 .times. 10.sup.5 7.0
.times. 10.sup.5 5.0 .times. 10.sup.5
[0084]
8TABLE 8 Combination in the Table 7 Outer circumferential surface
roughness Ra of Roller part of Roller follower (.mu.m) Number of
Pitching Material: quenched SUJ2 Occurrence 0.2 1.0 1.8 2.0 2.2
Outer 0.2 V1 W1 X1 Y1 Z1 circumferential 1.0 V2 W2 X2 Y2 Z2 surface
1.8 V3 W3 X3 Y3 Z3 roughness Ra of 2.0 V4 W4 X4 Y4 Z4 Cam lobe
(.mu.m) 2.2 V5 W5 X5 Y5 Z5 Material: iron based sintered
material
[0085] From the results of the Tables 1 to 3, and FIGS. 4 to 7, it
was learned that the combination with the larger surface roughness
Ra of the outer circumferential surfaces of the cam lobe and the
roller was advantageous for improving the effect of reducing the
friction loss, however, in contrast, the pitching characteristic
was deteriorated in the combination with the larger surface
roughness Ra of the outer circumferential surfaces of the cam lobe
and the roller part. The balance of the friction characteristic and
the pitching characteristic was particularly preferable when both
of the surface roughness Ra on the outer circumferential surface of
the cam lobe and the roller were in a range of 0.4 to 2.2
.mu.m.
* * * * *