U.S. patent application number 10/558624 was filed with the patent office on 2007-01-11 for cam lobe material, camshaft using the same and method for producing cam lobe member.
This patent application is currently assigned to Nippon Piston Ring Co., Ltd. Invention is credited to Hiroyuki Takamura, Shunsuke Takeguchi.
Application Number | 20070006828 10/558624 |
Document ID | / |
Family ID | 34100623 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070006828 |
Kind Code |
A1 |
Takamura; Hiroyuki ; et
al. |
January 11, 2007 |
Cam lobe material, camshaft using the same and method for producing
cam lobe member
Abstract
The present invention provides a cam lobe material that is
excellent in sliding characteristics, such as wear resistance,
scuffing resistance and pitting resistance, and can be
advantageously used in engines to which high loads are applied, and
a method of manufacturing the cam lobe material. The
above-described task is fulfilled by providing a cam lobe material
that is formed from an iron-based sintered alloy that contains 0.3
to 5.0 mass % Ni, 0.5 to 1.2 mass % C, 0.02 to 0.3 mass % of at
least either of B and P, and incidental impurities as the balance,
and has a hardness of a peripheral surface of not less than HRC 50
and a density of not less than 7.5 g/cm.sup.3. The iron-based
sintered alloy can further contain not more than 2.5 mass % Mo. The
above-described task can also be fulfilled by a method of
manufacturing the cam lobe material, that a compression molding
step and a sintering step are repeated at least twice, the
compression molding step involving compression molding iron-based
alloy powders prepared so as to provide the composition of the
ferrous sintered alloy in a prescribed cam lobe shape, and the
sintering step involving sintering the compression molded compact
body, and that the sintered body is subjected to quench and
tempering treatment.
Inventors: |
Takamura; Hiroyuki;
(Shimotsuga-gun, Tochigi, JP) ; Takeguchi; Shunsuke;
(Tochigi, JP) |
Correspondence
Address: |
STEPTOE & JOHNSON LLP
1330 CONNECTICUT AVENUE, N.W.
WASHINGTON
DC
20036
US
|
Assignee: |
Nippon Piston Ring Co., Ltd
12-10, Nonmachi-higashi 5-chome, Chuo-ku
Saitama-shi
JP
338-8503
|
Family ID: |
34100623 |
Appl. No.: |
10/558624 |
Filed: |
July 28, 2004 |
PCT Filed: |
July 28, 2004 |
PCT NO: |
PCT/JP04/10736 |
371 Date: |
November 28, 2005 |
Current U.S.
Class: |
123/90.6 |
Current CPC
Class: |
F01L 1/04 20130101; F01L
2301/00 20200501; F01L 2303/00 20200501; C22C 38/12 20130101; F01L
1/047 20130101; C22C 38/08 20130101; F16H 53/025 20130101 |
Class at
Publication: |
123/090.6 |
International
Class: |
F01L 1/04 20060101
F01L001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 2003 |
JP |
2003203133 |
Claims
1. A cam lobe material, characterized in that the cam lobe material
is formed from an iron-based sintered alloy that contains 0.3 to
5.0 mass % Ni, 0.5 to 1.2 mass % C, 0.02 to 0.3 mass % of at least
either of B and P, and incidental impurities as the balance, and
has a hardness of a peripheral surface of not less than HRC 50 and
a density of not less than 7.5 g/cm.sup.3.
2. The cam lobe material according to claim 1, characterized in
that the iron-based sintered alloy further contains not more than
2.5 mass % Mo.
3. The cam lobe material according to claim 1, characterized in
that the cam lobe material uses a roller follower as a mating
member.
4. A cam shaft, characterized in that the cam shaft is provided
with a cam lobe formed from the cam lobe material according to
claim 1.
5. A method of manufacturing the cam lobe material according to
claim 1, characterized in that a compression molding step and a
sintering step are repeated at least twice, the compression molding
step involving compression molding iron-based alloy powders
prepared so as to provide the composition of the ferrous sintered
alloy in a prescribed cam lobe shape, and the sintering step
involving sintering the compression molded compact body, and that
the sintered body is subjected to quench and tempering
treatment.
6. The method of manufacturing the cam lobe material according to
claim 5, characterized in that the peripheral surface of the cam
lobe material is shot blasted.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cam lobe material used in
an internal combustion engine, a cam shaft that uses the cam lobe
material, and a method of manufacturing the cam lobe material.
BACKGROUND ART
[0002] As a cam shaft of a valve train used in an internal
combustion engine, there has been known an assembly type cam shaft
provided with a cam lobe in a shaft. The cam lobe to be provided in
the cam shaft is divided into a type in which a cam follower that
makes rolling contact (a roller follower) is used as a mating
member and a type in which a cam follower that makes sliding
contact (slide contact) (a slipper follower) is used as a mating
member (refer to Patent Document 1, for example).
[0003] In such an internal combustion engine, parts such as cam
shaft and rocker arm slide at high speeds during operation and
hence they are required to have sliding characteristics.
Particularly, in the above-described cam lobe that uses a roller
follower making roller contact as a mating member, the area of
contact with the roller follower is small and hence this cam lobe
is required in its peripheral surface to be excellent in all of the
sliding characteristics of wear resistance, pitting resistance and
scuffing resistance.
[0004] For this reason, there has hitherto been used a cam shaft
that is provided with a chilled cam in which a cam nose part is
rapidly cooled and caused to solidify during casting by using a
chiller in this part, whereby a hard white cast iron structure is
formed in the surface part of the cam nose. This chilled cam shaft,
which has a hard chilled structure on its peripheral surface, has
excellent wear resistance and scuffing resistance.
[0005] On the other hand, in an assembly type cam shaft, there have
been known techniques that involve improving the density of a cam
piece by warm forming the cam piece thereby to solve the problem
that a cam piece is broken during the diameter expanding of a shaft
(refer to, Patent Document 2, for example). Patent Document 1:
Japanese Patent Laid-Open No. 2001-240948 Patent Document 2:
Japanese Patent Laid-Open No. 2003-14085
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0006] However, chilled cam shafts had the problem that they are
inferior in pitting resistance. For this reason, chilled cam shafts
had the problem that it is difficult to use them in engines to
which high loads are applied.
[0007] Furthermore, there is a limit to an improvement in the
density of cam pieces by warm forming, and as with chilled cam
shafts, cam pieces had the problem that it is difficult to use them
in engines to which high loads are applied.
[0008] Therefore, by solving these problems, the present invention
has as its object the provision of a cam lobe material that is
excellent in sliding characteristics, such as wear resistance,
pitting resistance and scuffing resistance, and can be
advantageously used in engines to which high loads are applied, a
cam shaft using this cam lobe material, and a method of
manufacturing the cam lobe material
MEANS FOR SOLVING THE PROBLEM
[0009] A cam lobe material of a present invention for solving the
above-mentioned problem is the cam lobe material formed from an
iron-based sintered alloy that contains 0.3 to 5.0 mass % Ni, 0.5
to 1.2 mass % C, 0.02 to 0.3 mass % of at least either of B and P,
and incidental impurities as the balance, and has a hardness of a
peripheral surface of not less than HRC 50 and a density of not
less than 7.5 g/cm.sup.3.
[0010] According to the invention, because a cam lobe material is
fabricated from an iron-based alloy having a specific chemical
composition, it is possible to provide a high-hardness,
high-density cam lobe material. Particularly, because at least
either of B and P is contained, the density of a manufactured cam
lobe material can be increased by causing a liquid phase to be
formed during sintering. As a result, a cam lobe material of the
invention is excellent in sliding characteristics such as wear
resistance, scuffing resistance and pitting resistance. For this
reason, it is possible to provide a cam lobe that can be
advantageously used even in engines to which high loads are
applied, for example, an engine to which a compressive load that is
about twice the compression load in usual engines is applied.
[0011] In the cam lobe material of the present invention mentioned
above, the iron-based sintered alloy further contains not more than
2.5 mass % Mo. According to the present invention, in addition to
the above advantage, it is possible to obtain a cam lobe material
in which the solid solution effect of the iron-based alloy matrix
is enhanced by increasing the hardenability of the cam lobe
material after sintering.
[0012] In the cam lobe material of the present invention mentioned
above, the cam lobe material uses a roller follower as a mating
member. According to the present invention, owing to its toughness
and hardness a cam lobe material is improved in its repeated
contact fatigue strength and, therefore, this cam lobe can be
advantageously used as a mating member of a roller follower that is
required to have contact fatigue strength represented by pitting
resistance.
[0013] A cam shaft of a present invention for solving the
above-mentioned problem is the cam shaft provided with a cam lobe
formed from the cam lobe material according to the present
invention mentioned above. According to the present invention, it
is possible to provide a cam shaft that is excellent in sliding
characteristics such as wear resistance, scuffing resistance and
pitting resistance and can be advantageously used even in engines
to which high loads are applied.
[0014] A method of manufacturing the cam lobe material of a present
invention for solving the above-mentioned problem is the method of
manufacturing the cam lobe material according to the present
invention mentioned above, a compression molding step and a
sintering step are repeated at least twice, the compression molding
step involving compression molding iron-based alloy powders
prepared so as to provide the composition of the ferrous sintered
alloy in a prescribed cam lobe shape, and the sintering step
involving sintering the compression molded compact body, and that
the sintered body is subjected to quench and tempering
treatment.
[0015] According to the present invention, the dimensional accuracy
before and after the final sintering step is high and cutting after
the manufacture of a cam lobe is unnecessary or the amount of
cutting is small. For this reason, the labor and cost necessary for
the manufacture of a cam lobe can be reduced. Furthermore, it is
possible to obtain a hardness of a peripheral surface of not less
than HRC 50 and a density of not less than 7.5 g/cm.sup.3. For this
reason, high hardness and high density can be ensured in a cam lobe
material after manufacture and it is possible to obtain a cam lobe
material excellent in sliding characteristics such as wear
resistance, scuffing resistance and pitting resistance. Therefore,
it is possible to provide a cam lobe that can be advantageously
used even in engines to which high loads are applied, for example,
an engine to which a compressive load that is about twice the
compressive load in usual engines is applied.
[0016] In the method of manufacturing the cam lobe material of the
present invention mentioned above, the peripheral surface of the
cam lobe material is shot blasted. According to the present
invention, the pitting resistance of a cam lobe material can be
improved by performing shot blasting.
EFFECT OF THE INVENTION
[0017] As described above, a cam lobe material of the invention is
made of an iron-based alloy of a specific chemical composition and,
therefore, it is possible to provide a high-hardness, high-density
cam lobe material. Particularly, because at least either of B and P
is contained, the density of a manufactured cam lobe material can
be increased by causing a liquid phase to be formed during
sintering. As a result, a cam lobe material of the invention is
excellent in sliding characteristics such as wear resistance,
scuffing resistance and pitting resistance. For this reason, it is
possible to provide a cam lobe that can be advantageously used even
in engines to which high loads are applied, for example, an engine
to which a compressive load that is about twice the compressive
load in usual engines is applied. And a cam lobe material of the
invention can be advantageously used as a mating member of a roller
type cam follower.
[0018] Also, according to a method of manufacturing a cam lobe
material of the present invention, the dimensional accuracy before
and after the final sintering step is high and cutting after the
manufacture of a cam lobe is unnecessary or the amount of cutting
is small. For this reason, the labor and cost necessary for the
manufacture of a cam lobe can be reduced. Furthermore, it is
possible to obtain a hardness of a peripheral surface of not less
than HRC 50 and a density of not less than 7.5 g/cm.sup.3. For this
reason, high hardness and high density can be ensured in a cam lobe
material after manufacture and it is possible to obtain a cam lobe
material excellent in sliding characteristics such as wear
resistance, scuffing resistance and pitting resistance. Therefore,
it is possible to provide a cam lobe that can be advantageously
used even in engines to which high loads are applied, for example,
an engine to which a compressive load that is about twice the
compressive load in usual engines is applied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIGS. 1A and 1B are respectively a perspective view of an
aspect of a valve train of an internal combustion engine provided
with a cam lobe material of the invention and a plan view of a cam
shaft of the invention;
[0020] FIG. 2 is a schematic diagram of a double cylinder contact
testing machine used in the evaluation of embodiments of the
invention;
[0021] FIG. 3 is a graph that shows the relationship between the
density of a cam lobe material and the Ni (nickel) content in
embodiments of the invention;
[0022] FIG. 4 is a graph that shows the relationship between the
hardness of a cam lobe material and the Ni content in embodiments
of the invention;
[0023] FIG. 5 is a graph that shows the relationship between the
frequency of occurrence of pitting of a cam lobe material and the
Ni content in embodiments of the invention;
[0024] FIG. 6 is a graph that shows the relationship between the
rate of dimensional change of a cam lobe material and the Ni
content in embodiments of the invention;
[0025] FIG. 7 is a graph that shows the relationship between cam
lift errors of a cam lobe material and the Ni content in
embodiments of the invention;
[0026] FIG. 8 is a graph that shows the relationship between the
density of a cam lobe material and the C (carbon) content in
embodiments of the invention;
[0027] FIG. 9 is a graph that shows the relationship between the
hardness of a cam lobe material and the C content in the
embodiments of the invention;
[0028] FIG. 10 is a graph that shows the relationship between the
density of a cam lobe material and the P (phosphorus) content in
embodiments of the invention;
[0029] FIG. 11 is a graph that shows the relationship between the
hardness of a cam lobe material and the P content in embodiments of
the invention;
[0030] FIG. 12 is a graph that shows the relationship between the
frequency of occurrence of pitting of a cam lobe material and the P
content in embodiments of the invention;
[0031] FIG. 13 is a graph that shows the relationship between the
density of a cam lobe material and the B (boron) content in
embodiments of the invention;
[0032] FIG. 14 is a graph that shows the relationship between the
hardness of a cam lobe material and the B content in embodiments of
the invention;
[0033] FIG. 15 is a graph that shows the relationship between the
density of a cam lobe material and the Mo (molybdenum) content in
embodiments of the invention; and
[0034] FIG. 16 is a graph that shows the relationship between the
hardness of a cam lobe material and the Mo content in embodiments
of the invention.
EXPLANATION OF SYMBOLS
[0035] 1 Cam lobe material (a rolling contact type) [0036] 2 Cam
shaft [0037] 3 Roller follower (a rolling contact type cam flower)
[0038] 4 Valve train of an internal combustion engine [0039] 5 Cam
lobe material (a sliding contact type) [0040] 6 Slipper follower (a
sliding contact type cam follower) [0041] 7 Shaft [0042] 8 Test
piece of cam lobe material [0043] 9 Cylindrical test piece of
mating material [0044] 10 Lubricating oil [0045] 11 Load
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] A cam lobe material, a cam shaft and a method of
manufacturing the cam lobe material of the invention will be
described below.
[0047] A cam lobe material of the invention is formed from an
iron-based sintered alloy that contains 0.3 to 5.0 mass % Ni, 0.5
to 1.2 mass % C, 0.02 to 0.3 mass % of at least either of B and P,
and incidental impurities as the balance, and has a hardness of a
peripheral surface of not less than HRC 50 and a density of not
less than 7.5 g/cm.sup.3. The iron-based sintered alloy can further
contain not more than 2.5 mass % Mo.
[0048] First, the iron-based sintered alloy is described.
[0049] Ni (Nickel) has the action of increasing strength and
toughness. The specified Ni content is 0.3 to 5.0 mass %. If the Ni
content is less than 0.3 mass %, sufficient strength and toughness
cannot be obtained. On the other hand, if the Ni content exceeds
5.0 mass %, the amount of dimensional change during sintering
increases, thereby worsening accuracy. It is preferred that Ni be
contained in an amount of 1.0 to 3.0 mass %.
[0050] C (carbon) has the action of capable of obtaining the
hardness of a cam peripheral surface that satisfies wear
resistance. The specified C content is 0.5 to 1.2 mass %. If the C
content is less than 0.5 mass %, it is difficult to obtain a
desired hardness of a peripheral surface of a cam after quench and
tempering treatment and the peripheral surface of a cam is inferior
in wear resistance. On the other hand, if the C content exceeds 1.2
mass %, compressibility decreases greatly and density does not
increase. It is preferred that C be contained in an amount of 0.8
to 1.0 mass %.
[0051] B (boron) and P (phosphorus) have the action of promoting
sintering by forming a low-melting-point ternary eutectic liquid
phase with Fe (iron) and C. At least either of B and P is contained
in an iron-based sintered alloy of a cam lobe material of the
invention. The content of at least either of B and P is 0.02 to 0.3
mass %. If the content of at least either of B and P is less than
0.02 mass %, the above-described action is weak and the density and
hardness that will be described later may not sometimes be
obtained. On the other hand, if the content of at least either of B
and P exceeds 0.3 mass %, the amount of shrinkage during sintering
increases and the dimensional accuracy of a cam lobe material
worsens. It is preferred that at least either of B and P be
contained in an amount of 0.05 to 0.20 mass %. Incidentally, when
both B and P are to be contained, usually the ratio of content of B
and P should be B:P=2:1 to 1:2 or so although this ratio is not
especially limited.
[0052] Mo (molybdenum) that is arbitrarily added has the action of
increasing hardenability and promoting the solid solution effect of
the iron-based alloy matrix. The specified Mo content is not more
than 2.5 mass %. Although the effect of Mo is obtained little by
little from a content of 0.05 mass % or so, compressibility worsens
greatly and density does not increase if the Mo content exceeds 2.5
mass %. It is preferred that Mo be contained in an amount of 0.2 to
1.5 mass % or so.
[0053] Incidentally, incidental impurities as the balance include
residues of lubricants such as zinc stearate added to sintering
powders and of components of other additives in addition to trace
amounts of impurities that mix into raw material powders.
[0054] Subsequently, a description will be given of the physical
properties of a cam lobe material formed from the above-described
iron-based sintered alloy.
[0055] The hardness of the peripheral surface of a cam lobe
material should be not less than HRC 50. If this hardness is less
than HRC 50, wear resistance cannot be satisfied. An upper limit to
the hardness of the peripheral surface of a cam lobe material is
usually HRC 60 or so although this upper limit is not especially
limited. It is preferred that the hardness of the peripheral
surface be HRC 50 to 55. The peripheral surface of a cam lobe
material is the surface that slides with a cam follower when the
cam lobe material is used in a cam shaft as a cam lobe.
[0056] The density of a cam lobe material should be not less than
7.5 g/cm.sup.3. If the density is less than 7.5 g/cm.sup.3,
strength decreases due to the porosities of a cam lobe material and
pitting resistance worsens. Therefore, the cam lobe material cannot
be used in engines to which high loads are applied. Incidentally,
an upper limit to the density of a cam lobe material is usually 7.7
g/cm.sup.3 or so although this upper limited is not especially
limited. It is preferred that the density be 7.5 to 7.6
g/cm.sup.3.
[0057] Because as described above a cam lobe material of the
invention has high density and high hardness, the cam lobe material
has high pitting resistance in the contact with a cam follower. For
this reason, a cam lobe fabricated from a cam lobe material of the
invention can be advantageously used in engines to which high loads
are applied. Furthermore, a cam lobe material of the invention is
also excellent in wear resistance and scuffing resistance and in
sliding characteristics as well.
[0058] A cam lobe material of the invention is advantageously used
as a mating member of a roller type cam follower (a roller
follower). FIG. 1A is a perspective view of a valve train 4 of an
internal combustion engine to show how a cam shaft 2 provided with
a cam lobe 1 formed from a cam lobe material of the invention is in
contact with a roller follower (rolling contact type cam flower) 3.
Incidentally, on the forward side of FIG. 1A are shown a cam lobe 5
provided on a cam shaft 2 and a slipper follower (a sliding contact
type cam follower) 6.
[0059] A roller tappet, a roller rocker arm, etc. can be enumerated
as this roller follower 3. Such a roller follower 3 and the cam
lobe material 1 that is a mating member of this roller follower are
required to have repeated contact fatigue strength represented by
pitting resistance. In the invention, a liquid phase is formed by
the component of B or/and P during the sintering of a cam lobe
material and the cam lobe material is densified to increase its
density. The toughness and hardness of a cam lobe material are
improved in this manner and the repeated contact fatigue strength
is improved. For this reason, a cam lobe material of the invention
can be advantageously used as a mating member of a roller
follower.
[0060] Incidentally, by using the above-described cam lobe material
of the invention it is possible to provide a cam shaft 2 as
described in FIGS. 1A and 1B. Aspects and manufacturing method of
this cam shaft 2 will be described later.
[0061] Subsequently, a method of manufacturing a cam lobe material
of the invention will be described. This manufacturing method
applies to only the above-described cam lobe material of the
invention.
[0062] A method of manufacturing a cam lobe material of the
invention involves using iron-based alloy powders blended and
prepared to obtain an iron-based sintered alloy of the
above-described composition, repeating a compression molding step
and a sintering step at least twice and performing quench and
tempering treatment. Furthermore, the peripheral surface of the cam
lobe material can be shot blasted.
[0063] The components, blending ratios, actions, etc. of elements
to be added to the iron-based alloy powders are the same as in the
description of the above cam lobe material. The iron-based alloy
powders are blended and prepared so as to obtain component ratios
within the above-described ranges after sintering.
[0064] A description will be given of the compression molding step
that involves mixing such iron-based alloy powders in such a manner
as to ensure that each component is uniformly mixed and compression
molding the iron-based alloy powders to a prescribed shape. This
compression molding step is performed at least twice. Incidentally,
the second and later compression molding steps are performed after
the sintering step.
[0065] This compression molding step is performed by use of a
hitherto publicly known compression molding device, and usually
press forming is performed by use of a mechanical press etc. The
compressive load during compression molding is usually 5 to 7
tons/cm.sup.2 or so in the compression molding step (temporary
molding) except the final compression molding. In the final
compression molding step, the compressive load is higher than in
temporary molding and usually 7 to 12 tons/cm.sup.2 or so.
Incidentally, the temperature in the compression molding step is
the same as usually and 20 to 40.degree. C. or so.
[0066] A description will be given of the sintering step in which
after the compression molding of the iron-based alloy powders in
this manner, a compact body is sintered. This sintering step is
performed at least twice.
[0067] This sintering step can be performed by use of a hitherto
publicly known sintering device, and usually it is performed by use
of a vacuum sintering furnace etc. The temperature in the sintering
step is usually 650 to 850.degree. C. or so in the sintering step
(temporary sintering) except the final sintering step. In the final
sintering step, the sintering temperature is higher than in
temporary sintering and usually 1100 to 1200.degree. C. or so,
preferably 1130 to 1180.degree. C. or so. The atmosphere
surrounding a compact body in the sintering step is the same as the
atmosphere during usual sintering and is not especially limited.
Sintering is performed in an atmosphere of Ax gas, Rx gas, vacuum,
etc. The time required by the sintering of a compact body of a cam
lobe material is the same as usual sintering time and is not
especially limited. This sintering time is 30 to 90 minutes or
so.
[0068] Next, the sintered body of the cam lobe material obtained in
the final sintering step is subjected to quench and tempering
treatment. The quenching treatment is performed by holding the
sintered body at 800 to 950.degree. C. for 30 to 150 minutes or so
usually in a heat treatment furnace etc. and then quenching the
sintered body to 30 to 100.degree. C. or so by use of oil, water,
etc. The tempering treatment is performed usually at 120 to
200.degree. C. for 30 to 150 minutes or so after the
above-described quenching treatment and then performing cooling to
10 to 40.degree. C. or so at a rate of 2 to 10.degree. C./minute or
so. The quench and tempering treatment enables the wear resistance
of a cam lobe to be improved by increasing the hardness of the
peripheral surface of the cam.
[0069] It is preferred that the peripheral surface of a sintered
body of a cam lobe material be further shot blasted. Residual
compressive stresses are caused to be generated on the peripheral
surface of the cam lobe material by performing shot blasting,
thereby to improve pitting resistance. Usually shot blasting is
performed by rotating the cam lobe material, adjusting a nozzle so
as to be able to shot the peripheral surface, and causing grits of
steel, glass beads, etc. to strike against the peripheral surface
of the cam lobe material at a pressure of 5 kg/cm.sup.2 or so.
[0070] Incidentally, in a cam lobe material manufactured by a
method of manufacturing a cam lobe material of the invention, the
rate of dimensional change before and after the final sintering
step becomes +- (.+-.)0 to 0.5% or so. This rate of dimensional
change is obtained by measuring the peripheral shapes of a compact
body before the final sintering step and of a sintered body after
the final sintering step at a minimum of one point per degree over
360 degrees by use of a three-dimensional measuring machine,
determining the rate of dimensional change at each measuring point
by superposing the two shapes that are traced from the measuring
points, and finding a maximum value among the dimensional changes
at the measuring points.
[0071] Thus, according to a method of manufacturing a cam lobe
material of the invention, because a cam lobe material undergoes
the compression molding step and the sintering step at least twice,
the dimensional accuracy before and after the final sintering step
is high and cutting after the manufacture of a cam lobe material is
unnecessary or the amount of cutting is small. For this reason, the
labor and cost necessary for the manufacture of a cam lobe can be
reduced. Furthermore, it is possible to obtain a hardness of a
peripheral surface of not less than HRC 50 and a density of not
less than 7.5 g/cm.sup.3. For this reason, high hardness and high
density can be ensured in a cam lobe material after manufacture and
it is possible to obtain a cam lobe material excellent in sliding
characteristics such as wear resistance, scuffing resistance and
pitting resistance. Therefore, it is possible to provide a cam lobe
material that can be advantageously used even in engines to which
high loads are applied, for example, an engine to which a
compressive load that is about twice the compressive load in usual
engines is applied.
[0072] Incidentally, by assembling a cam lobe material thus
manufactured on a shaft and fixing the cam lobe material, an
assembly type cam shaft 2 as shown in FIG. 1B is obtained. This cam
shaft 2 is obtained by assembling a cam lobe material by shrinkage
fit or cooling fit in a prescribed position of the shaft 7 that is
formed, for example, from a material such as S45C at a prescribed
angle and fixing the cam lobe material. As a method of assembling a
cam lobe material on a shaft and fixing the cam lobe material, the
above-described shrinkage fit and cooling fit are desirable from
the standpoint of assembling accuracy and inexpensive equipment
cost. However, it is also possible to adopt other methods such as
press fit and diffusion bonding. Also, this cam shaft 2 may be
provided with only the cam lobe 1 formed from a cam lobe material
of the invention or as shown in FIG. 1A, the cam shaft 2 may be
provided with both the cam lobe 1 according to the invention and a
cam lobe 5 having sliding characteristics suitable for a sliding
type cam follower 6. The camshaft thus manufactured does not
require cutting the cam lobe at all or requires only a very little
amount of cutting even if cutting is necessary. Thus, it is
possible to provide a cam shaft that is excellent in sliding
characteristics such as wear resistance, scuffing resistance and
pitting resistance and can be advantageously used in engines to
which high loads are applied.
EMBODIMENTS
[0073] The present invention will be described more concretely
below with reference to embodiments and comparative examples.
Embodiments 1 to 30
[0074] Sintering powders were prepared by adding each element to an
iron powder so as to obtain the final component compositions shown
in Table 1, and the sintering powders were compression molded in
cam lobe shape at a compressive load of 6 tons/cm.sup.2 and then
sintered at 700.degree. C. for 90 minutes. Furthermore, this
sintered body was compression molded in cam lobe shape at a
compressive load of 10 tons/cm.sup.2 and then sintered at
1140.degree. C. for 60 minutes. Subsequently, this sintered body
was heated at 900.degree. C. for 100 minutes and after that,
quenching treatment was performed by oil quenching. Furthermore,
this sintered body was heated at 150.degree. C. for 60 minutes and
after that, tempering treatment was performed by air cooling. After
that, shot blasting was performed and the cam lobe materials of
Embodiments 1 to 30 were obtained.
COMPARATIVE EXAMPLE 1
[0075] Each element was caused to melt so as to obtain the final
component composition shown in Table 1, the melt was poured into a
mold having a chiller and rapidly cooled, and chilled cast iron was
obtained by causing the melt to solidify. The cam lobe material of
Comparative Example 1 was fabricated by polishing the chilled cast
iron.
COMPARATIVE EXAMPLES 2 TO 5
[0076] Sintering powders were prepared by adding each element to an
iron powder so as to obtain the final compositions shown in Table
1, and the sintering powders were compression molded in cam lobe
shape at a compressive load of 5 tons/cm.sup.2 and then sintered at
1100.degree. C. for 60 minutes, whereby the cam lobe materials of
Comparative Examples 2 to 5 were obtained. TABLE-US-00001 TABLE 1
Final composition/mass % C Ni Cu B P Mo Si Mn Cr Fe Embodiment1 0.8
0.5 -- -- 0.1 -- -- -- -- Balance Embodiment2 0.8 1.0 -- -- 0.1 --
-- -- -- Balance Embodiment3 0.8 2.0 -- -- 0.1 -- -- -- -- Balance
Embodiment4 0.8 2.5 -- -- 0.1 -- -- -- -- Balance Embodiment5 0.8
3.0 -- -- 0.1 -- -- -- -- Balance Embodiment6 0.8 3.5 -- -- 0.1 --
-- -- -- Balance Embodiment7 0.8 4.5 -- -- 0.1 -- -- -- -- Balance
Embodiment8 0.8 5.0 -- -- 0.1 -- -- -- -- Balance Embodiment9 0.5
3.5 -- 0.05 -- -- -- -- -- Balance Embodiment10 0.8 3.5 -- 0.05 --
-- -- -- -- Balance Embodiment11 1.0 3.5 -- 0.05 -- -- -- -- --
Balance Embodiment12 1.2 3.5 -- 0.05 -- -- -- -- -- Balance
Embodiment13 0.8 0.5 -- -- 0.05 -- -- -- -- Balance Embodiment14
0.8 0.5 -- -- 0.2 -- -- -- -- Balance Embodiment15 0.8 0.5 -- --
0.3 -- -- -- -- Balance Embodiment16 0.8 3.5 -- -- 0.2 -- -- -- --
Balance Embodiment17 0.8 3.5 -- 0.02 -- -- -- -- -- Balance
Embodiment18 0.8 3.5 -- 0.1 -- -- -- -- -- Balance Embodiment19 0.8
3.5 -- 0.3 -- -- -- -- -- Balance Embodiment20 0.8 3.5 -- -- 0.1
0.3 -- -- -- Balance Embodiment21 0.8 3.5 -- -- 0.1 1.0 -- -- --
Balance Embodiment22 0.8 3.5 -- -- 0.1 2.0 -- -- -- Balance
Embodiment23 0.8 3.5 -- -- 0.1 2.5 -- -- -- Balance Embodiment24
1.0 3.5 -- 0.05 -- 0.3 -- -- -- Balance Embodiment25 1.0 3.5 --
0.05 -- 1.0 -- -- -- Balance Embodiment26 1.0 3.5 -- 0.2 -- 2.0 --
-- -- Balance Embodiment27 1.0 2.0 -- 0.1 -- 0.3 -- -- -- Balance
Embodiment28 1.0 3.0 -- 0.2 -- 1.0 -- -- -- Balance Embodiment29
1.0 1.0 -- 0.2 -- 2.0 -- -- -- Balance Embodiment30 1.0 1.0 -- 0.2
0.2 2.0 -- -- -- Balance Comparative 3.4 (Ni + Cu)2.0 -- -- 2.0 2.0
0.7 0.8 Balance example1 Comparative 0.8 2.0 -- -- -- -- -- -- --
Balance example2 Comparative 0.8 -- -- -- 0.05 -- -- -- -- Balance
example3 Comparative 0.3 0.2 -- -- 0.01 -- -- -- -- Balance
example4 Comparative 1.5 6.0 -- -- 0.4 -- -- -- -- Balance
example5
(Evaluation Method and Results)
[0077] For the cam lobes obtained in each embodiment and each
comparative example, (1) density, (2) Rockwell hardness HRC of
peripheral surface, (3) frequency of occurrence of pitting and wear
losses, (4) rate of dimensional change, and (5) cam lift errors
were measured. Measuring methods of each item will be described
below and the results of the measurements of each item are shown in
Table 2.
(1) Density
[0078] Test pieces from the obtained cam lobe materials were sealed
with paraffin and density was measured by the Archimedes'
method.
(2) Rockwell Hardness of Peripheral Surface
[0079] The periphery of a cam nose of a test piece of each of the
obtained cam lobe materials was measured at five points on the C
scale by use of a Rockwell hardness meter, and an average value of
measurements was calculated as the Rockwell hardness of a
peripheral surface.
(3) Frequency of Occurrence of Pitting and Wear Losses
[0080] The frequency of occurrence of pitting and wear loss were
measured as follows. By use of a double cylinder contact testing
machine shown in FIG. 2, rotary surfaces of each test piece 8 of
the cam lobe material rotating at a constant speed and a
cylindrical test piece 9 of the mating member were brought into
contact with each other and caused to rotate by applying a
prescribed load 11 while a lubricating oil 10 was caused to drop
onto the contact surfaces of the two test pieces, and the number of
revolutions until the occurrence of pitting was measured as the
frequency of occurrence of pitting. Also, by rotating each test
piece 8, the amount of sinking due to wear (.mu.m) for a given
number of revolutions (1.times.10.sup.5 times) was measured as wear
loss.
(Measuring Conditions)
Measuring device: Double cylinder contact testing machine
Number of revolutions: 1500 rpm
Lubricating oil: Engine oil 10W30
Oil temperature: 100.degree. C.
Oil volume: 2.times.10.sup.-4 m.sup.3/min
Load: 3000 N
Slip ratio: 0%
Mating member: SUJ2
[0081] Judgment method: A crack of the occurrence of pitting was
detected from AE (acoustic emission), an S-N curve was prepared by
using the frequency of contact at that time as the frequency of
occurrence of pitting, and a comparison with each test piece was
made.
(4) Rate of Dimensional Change
[0082] The peripheral shapes of a secondary compact body and a
secondary sintered body were measured at a minimum of one point per
degree over 360 degrees by use of a three-dimensional measuring
machine, the rate of dimensional change at each measuring point was
determined by superposing the two shapes that are traced from the
measuring points, and a maximum value among the dimensional changes
at the measuring points was found as the rate of dimensional change
of the secondary sintered body relative to the secondary compact
body. Incidentally, for Comparative Examples 2 to 5, for which
compression molding and sintering were performed only once, the
rate of dimensional change was measured for the peripheral shapes
of a primary compact body and a primary sintered body.
(5) Cam Lift Errors
[0083] Cam lift errors were measured for test pieces obtained by
shot blasting secondary sintered bodies that had been subjected to
quench and tempering treatment. Cam profiles were measured by use
of an adcall for a cam profile measuring program and compared with
a target profile, and errors were detected as lift errors.
Incidentally, for Comparative Examples 2 to 5, for which
compression molding and sintering were performed only once, cam
lift errors were measured for test pieces after quench and
tempering treatment of primary sintered bodies. TABLE-US-00002
TABLE 2 Rate of Frequency of Wear loss dimensional Cam lift errors
Density Hardness occurrence .mu.m/ change % mm(absolute g/cm.sup.3
HRC of pitting 1 .times. 10.sup.5 times (absolute value) value)
Embodiment1 7.52 52.5 1.2 .times. 10.sup.6 0.22 -0.1 0.02
Embodiment2 7.53 53.0 1.6 .times. 10.sup.6 0.19 -0.1 0.02
Embodiment3 7.55 53.0 1.5 .times. 10.sup.6 0.21 -0.3 0.04
Embodiment4 7.55 53.5 5.0 .times. 10.sup.6 0.23 -0.3 0.03
Embodiment5 7.55 54.0 4.3 .times. 10.sup.6 0.20 -0.4 0.04
Embodiment6 7.56 55.0 4.0 .times. 10.sup.6 0.22 -0.4 0.04
Embodiment7 7.58 55.0 4.5 .times. 10.sup.6 0.21 -0.5 0.05
Embodiment8 7.58 55.5 6.0 .times. 10.sup.6 0.21 -0.5 0.04
Embodiment9 7.55 51.5 1.5 .times. 10.sup.6 0.25 -0.1 0.02
Embodiment10 7.52 53.5 2.5 .times. 10.sup.6 0.21 -0.3 0.03
Embodiment11 7.52 53.5 2.0 .times. 10.sup.6 0.18 -0.3 0.02
Embodiment12 7.51 55.5 2.2 .times. 10.sup.6 0.19 -0.3 0.03
Embodiment13 7.51 52.0 8.5 .times. 10.sup.5 0.23 -0.1 0.03
Embodiment14 7.52 53.5 1.1 .times. 10.sup.6 0.20 -0.2 0.03
Embodiment15 7.54 54.0 1.5 .times. 10.sup.6 0.21 -0.2 0.03
Embodiment16 7.56 54.5 3.9 .times. 10.sup.6 0.23 -0.3 0.02
Embodiment17 7.51 53.5 2.0 .times. 10.sup.6 0.21 -0.2 0.03
Embodiment18 7.53 54.0 3.2 .times. 10.sup.6 0.22 -0.2 0.02
Embodiment19 7.52 53.0 2.8 .times. 10.sup.6 0.24 -0.4 0.04
Embodiment20 7.53 55.5 2.5 .times. 10.sup.6 0.20 -0.1 0.03
Embodiment21 7.51 56.0 2.2 .times. 10.sup.6 0.20 -0.1 0.03
Embodiment22 7.50 56.5 2.0 .times. 10.sup.6 0.21 0 0.03
Embodiment23 7.50 56.5 2.0 .times. 10.sup.6 0.19 -0.2 0.04
Embodiment24 7.51 55.5 3.1 .times. 10.sup.6 0.16 -0.3 0.01
Embodiment25 7.51 56.0 3.5 .times. 10.sup.6 0.21 -0.4 0.03
Embodiment26 7.50 56.5 2.0 .times. 10.sup.6 0.17 0 0.03
Embodiment27 7.54 55.5 2.1 .times. 10.sup.6 0.18 -0.3 0.04
Embodiment28 7.52 56.0 2.0 .times. 10.sup.6 0.21 -0.2 0.04
Embodiment29 7.50 56.0 2.1 .times. 10.sup.6 0.16 -0.2 0.02
Embodiment30 7.51 56.0 1.8 .times. 10.sup.6 0.20 -0.1 0.03
Comparative 7.10 49.5 1.3 .times. 10.sup.5 1.2 -- -- example1
Comparative 7.45 52.0 3.0 .times. 10.sup.5 0.6 -0.8 0.08 example2
Comparative 7.35 47.0 4.0 .times. 10.sup.5 1.1 -0.6 0.06 example3
Comparative 7.40 41.0 8.0 .times. 10.sup.4 2.3 -0.1 0.05 example4
Comparative 7.46 48.0 3.0 .times. 10.sup.5 1.5 -2.5 0.15
example5
(Consideration of Measurement Results) (a) Effect of Ni (Nickel)
Content (Embodiments 1 to 8, 16)
[0084] Embodiments 1 to 8 and 16 show test results of the density,
hardness, frequency of occurrence of pitting, wear losses, rate of
dimensional change and cam lift errors of alloys having Ni contents
that are different from each other.
[0085] At the Ni contents of 0.5% to 5.0% the density, hardness and
frequency of occurrence of pitting all tend to increase with
increasing Ni content. As shown in FIG. 3, the density tends to
increase little by little from 7.52 to 7.58 g/cm.sup.3. As shown in
FIG. 4, in the same manner as the density, the hardness also tends
to increase little by little from 52.5 to 55.5 HRC. As shown in
FIG. 5, the frequency of occurrence of pitting also tends to
increase from 1.2.times.10.sup.6 to 6.0.times.10.sup.6.
[0086] At the Ni contents of 0.5% to 5.0% wear losses, which are
0.19 to 0.23 .mu.m/1.times.10.sup.5 times, show relatively small
changes and are stable.
[0087] As shown in FIG. 6, at the Ni contents of 0.5% to 5.0% the
rate of dimensional change, which is -0.1 to -0.5%, tends to
increase little by little. As shown in FIG. 7, at the Ni contents
of 0.5% to 5.0% cam lift errors, which are 0.02 to 0.05 mm, tend to
increase little by little.
(b) Effect of C (Carbon) (Embodiments 9 to 12, 24, 25)
[0088] Embodiments 9 to 12, 24 and 25 show test results of the
density, hardness, frequency of occurrence of pitting, wear losses,
rate of dimensional change and cam lift errors of alloys having C
contents that are different from each other.
[0089] As shown in FIG. 8, at a low C content of 0.5% the density
is 7.55 g/cm.sup.3 and somewhat high, the density tends to decrease
with increasing C content, and at a high C content of 1.2% the
density is 7.51 g/cm.sup.3 and somewhat low. As shown in FIG. 9, in
contrast to the density, at the C contents of 0.5% to 1.2% the
hardness, which is 51.5 to 56.0 HRC, tends to increase.
[0090] At the C contents of 0.5% to 1.2% the frequency of
occurrence of pitting, which 1.5.times.10.sup.6 to
3.5.times.10.sup.6, show relatively small changes and is stable. As
with the frequency of occurrence of pitting, at the C contents of
0.5% to 1.2% wear losses, which are 0.16 to 0.25
.mu.m/1.times.10.sup.5 times, show relatively small changes and are
stable. At the C contents of 0.5% to 1.2% the rate of dimensional
change, which is -0.1 to -0.4%, tends to increase a little. At the
C contents of 0.5% to 1.2% cam lift errors, which are 0.01 to 0.03
mm, show relatively small changes and are stable.
(c) Effect of P (Phosphorus) (Embodiments 1, 13 to 15)
[0091] Embodiments 1, 13 to 15 show test results of the density,
hardness, frequency of occurrence of pitting, wear losses, rate of
dimensional change and cam lift errors of alloys having P contents
that are different from each other.
[0092] The relationships between the P content and the density,
hardness and frequency of occurrence of pitting show the same
tendency as in the case of Ni. As shown in FIG. 10, at the P
contents of 0.05% to 0.3% the density, which is 7.51 to 7.54
g/cm.sup.3, tends to increase little by little. As shown in FIG.
11, at the P contents of 0.05% to 0.3% also the hardness, which is
52.0 to 54.0 HRC, tends to increase little by little in the same
manner as the density. Also, as shown in FIG. 12, at the P contents
of 0.05% to 0.3% the frequency of occurrence of pitting, which is
8.5.times.10.sup.5 to 1.5.times.10.sup.6, tends to increase.
[0093] At the P contents of 0.05% to 0.3% wear losses, which are
0.20 to 0.23 .mu.m/1.times.10.sup.5 times, show relatively small
changes and are stable. As with wear losses, at the P contents of
0.05% to 0.3% the rate of dimensional change, which is -0.1 to
-0.2%, shows relatively small changes and are stable. At the P
contents of 0.05% to 0.3% cam lift errors, which are 0.02 to 0.03
mm, show relatively small changes and are stable.
(d) Effect of B (Boron) (Embodiments 10, 17 to 19)
[0094] Embodiments 10, 17 to 19 show test results of the density,
hardness, frequency of occurrence of pitting, wear losses, rate of
dimensional change and cam lift errors of alloys having B contents
that are different from each other.
[0095] As shown in FIG. 13, at the B contents of 0.02% to 0.3% the
density, which is 7.51 to 7.53 g/cm.sup.3, shows small changes and
is stable. As shown in FIG. 14, at the B contents of 0.02% to 0.3%
the hardness, which is 53.0 to 54.0 HRC, shows small changes and is
stable as with the density.
[0096] At the B contents of 0.02% to 0.3% the frequency of
occurrence of pitting, which is 2.0.times.10.sup.6 to
3.2.times.10.sup.6, shows relatively small changes and is stable.
At the B contents of 0.02% to 0.3% wear losses, which are 0.21 to
0.24 .mu.m/1.times.10.sup.5 times, show relatively small changes
and are stable. As with wear losses, at the B contents of 0.02% to
0.3% the rate of dimensional change, which is -0.2 to -0.4%, shows
relatively small changes and are stable. At the B contents of 0.02%
to 0.3% cam lift errors, which are 0.02 to 0.04 mm, show relatively
small changes and are stable.
(e) Effect of Mo (Molybdenum) (Embodiments 6, 20 to 23, 26 to
30)
[0097] Embodiments 6, 20 to 23, 26 to 30 show test results of the
density, hardness, frequency of occurrence of pitting, wear losses,
rate of dimensional change and cam lift errors of alloys having Mo
contents that are different from each other.
[0098] As shown in FIG. 15, at a low Mo content of 0.3% the density
is 7.54 g/cm.sup.3 and somewhat high, the density tends to decrease
with increasing Mo content, and at a high Mo content of 2.5% the
density is 7.50 g/cm.sup.3 and somewhat low because compressibility
worsens greatly. As shown in FIG. 16, at the Mo contents of 0.3% to
2.5% the hardness, which is 55.5 to 56.5 HRC, is somewhat high
because of increased hardenability, shows small changes and is
stable.
[0099] At the Mo contents of 0.3% to 2.5% the frequency of
occurrence of pitting, which is 1.8.times.10.sup.6 to
2.5.times.10.sup.6, show relatively small changes and is stable. At
the Mo contents of 0.3% to 2.5% wear losses, which are 0.16 to 0.21
.mu.m/1.times.10.sup.5 times, are somewhat low, show relatively
small changes and are stable. At the Mo contents of 0.3% to 2.5%
the rate of dimensional change, which is 0 to -0.3%, shows
relatively small changes and is stable. At the Mo contents of 0.3%
to 2.5% cam lift errors, which are 0.02 to 0.04 mm, show relatively
small changes and are stable.
(f) Various Combinations of Ni, B and Mo (Embodiments 24 to 29)
[0100] Embodiments 24 to 29 show test results of the density,
hardness, frequency of occurrence of pitting, wear losses, rate of
dimensional change and cam lift errors of alloys having Ni, B and
Mo contents that are different from each other.
[0101] Consideration will be given to results of various tests
conducted in combinations of Ni contents of 1.0% to 3.5%, B
contents of 0.05 to 0.2% and Mo contents of 0.3% to 2.0%.
[0102] Because density is affected by Mo, there is scarcely any
effect even if the Ni and B contents are changed and the density
develops at relatively low and medium levels of 7.50 to 7.54
g/cm.sup.3. Because the C content is somewhat high and hardness is
affected by Mo, the hardness develops at relatively high levels of
55.5 to 56.5 HCR.
[0103] Because density is affected by Mo and also due to the effect
of Ni, the frequency of occurrence of pitting develops in a wide
range of 1.8.times.10.sup.6 to 3.5.times.10.sup.6. The C content is
somewhat high and the hardness is somewhat high because hardness is
affected by the synergistic effect of C and Mo. Therefore, wear
losses develop at relatively low levels of 0.16 to 0.21
.mu.m/1.times.10.sup.5 times.
[0104] The rate of dimensional change, which is affected by Ni,
develops in a wide range of 0 to -0.4%. Cam lift errors, which are
affected by Ni as with the rate of dimensional change, develop in a
wide range of 0.01 to 0.04 mm.
(g) Combination of B and P (Embodiment 30)
[0105] Embodiment 30 of Table 2 shows test results of the density,
hardness, frequency of occurrence of pitting, wear losses, rate of
dimensional change and cam lift errors of an alloy in which a
combination of B and P is used.
[0106] Because the C and Mo contents are somewhat high, the density
is somewhat low and conversely, the hardness is somewhat high.
Therefore, the frequency of occurrence of pitting and wear losses
develop at intermediate levels of the ranges of the above-described
embodiments, the rate of dimensional change is somewhat low, and
cam lift errors are somewhat high. Thus, even a combination of B
and P is used, the density and hardness in the ranges of the
invention were obtained and good results were obtained also in
other items.
(h) Comparative Examples
[0107] Embodiments 1 to 30 were superior to all of Comparative
Examples 1 to 5.
[0108] Comparative Example 2 is not included in the present
invention in that neither B nor P is contained. As a result of
this, Comparative Example 2 had lower density and frequency of
occurrence of pitting than in each embodiment and was inferior in
pitting resistance. Also, Comparative Example 2 had a larger wear
loss than in each embodiment and was inferior in wear resistance.
Because Comparative Example 2 was produced by performing
compression once and sintering once (this method is hereinafter
called 1P1S), the rate of dimensional change was higher than in
each embodiment and cam lift errors were also somewhat higher than
in each embodiment. Thus, Comparative Example 2 was inferior in
both the rate of dimensional change and cam lift errors.
[0109] Comparative Example 3 is not included in the present
invention in that Ni is not contained. As a result of this,
Comparative Example 3 had lower density and frequency of occurrence
of pitting than in each embodiment and was inferior in pitting
resistance. Also, because Comparative Example 3 had lower density
and hardness than in each embodiment, it had a larger wear loss
than in each embodiment and was inferior in wear resistance.
Because Comparative Example 3 was produced by 1P1S, it had a rate
of dimensional change somewhat higher than in each embodiment and
also a cam lift error somewhat higher than in each embodiment.
Thus, Comparative Example 3 was inferior in both the rate of
dimensional change and cam lift errors.
[0110] Comparative Example 4 is not included in the present
invention because its C, Ni and P contents are lower than the
respective contents specified in the invention. As a result of
this, Comparative Example 4 had lower density and frequency of
occurrence of pitting than in each embodiment and was still
inferior to Comparative Examples 2 and 3 described above in pitting
resistance. Also, because Comparative Example 4 had lower density
and hardness than in each embodiment, it had a larger wear loss
than in each embodiment and Comparative Examples 2 and 3 described
above and was very inferior in wear resistance.
[0111] Comparative Example 5 is not included in the present
invention because its C, Ni and P contents are higher than the
respective contents specified in the invention. As a result of
this, as with Comparative Examples 2 and 3, Comparative Examples 5
had lower density and frequency of occurrence of pitting than in
each embodiment and was inferior in pitting resistance. Also,
because of lower density and hardness than in each embodiment,
Comparative Example 5 had a larger wear loss than in each
embodiment and was inferior in wear resistance. Furthermore,
because Comparative Example 5 was produced by 1P1S, it had a rate
of dimensional change very higher than in each embodiment and also
a cam lift error very higher than in each embodiment. Thus,
Comparative Example 5 was inferior in both the rate of dimensional
change and cam lift errors.
* * * * *