U.S. patent application number 13/429934 was filed with the patent office on 2012-10-04 for piston ring.
This patent application is currently assigned to TPR CO., LTD.. Invention is credited to Takatsugu IWASHITA, Tomoyuki SATO.
Application Number | 20120248711 13/429934 |
Document ID | / |
Family ID | 45811322 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120248711 |
Kind Code |
A1 |
IWASHITA; Takatsugu ; et
al. |
October 4, 2012 |
PISTON RING
Abstract
A piston ring which is provided with a carbon-based coating
which has a low friction property and wear resistance, that is, a
piston ring which has a carbon-based coating formed over its
sliding surface, in which piston ring, the coating is a multilayer
coating comprised of two types of layers having different
hardnesses laminated in at least two layers, a hardness difference
between the two types of layers is 500 to 1700 HV, a high hardness
layer has the same or greater thickness than a low hardness layer,
and the coating as a whole has a thickness of 5.0 .mu.m or more.
The high hardness layer has a thickness of 5 to 90 nm. The surface
on which the coating is formed has a base material roughness of 1.0
.mu.mRz or less.
Inventors: |
IWASHITA; Takatsugu;
(Chiyoda-ku, JP) ; SATO; Tomoyuki; (Chiyoda-ku,
JP) |
Assignee: |
TPR CO., LTD.
Chiyoda-ku
JP
|
Family ID: |
45811322 |
Appl. No.: |
13/429934 |
Filed: |
March 26, 2012 |
Current U.S.
Class: |
277/444 ;
277/440 |
Current CPC
Class: |
C23C 28/044 20130101;
C23C 28/44 20130101; F16J 9/26 20130101; C23C 14/16 20130101; C23C
14/0605 20130101 |
Class at
Publication: |
277/444 ;
277/440 |
International
Class: |
F16J 9/26 20060101
F16J009/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2011 |
JP |
2011-069676 |
Claims
1. A piston ring which has a carbon-based coating formed over its
sliding surface, in which piston ring, said coating is a multilayer
coating comprised of two types of layers having different
hardnesses laminated in at least two layers, a hardness difference
between said two types of layers is 500 to 1700 HV, a high hardness
layer has the same or greater thickness than a low hardness layer,
and the coating as a whole has a thickness of 5.0 .mu.m or
more.
2. A piston ring as set forth in claim 1, wherein said high
hardness layer has a thickness of 5 to 90 nm.
3. A piston ring as set forth in claim 1, wherein the surface on
which said coating is formed has a base material roughness of 1.0
.mu.mRz or less.
4. A piston ring as set forth in claim 1, wherein a surface-most
layer of said coating is a high hardness layer.
5. A piston ring as set forth in claim 1, wherein a low hardness
layer of said coating contains carbon alone or carbon and also Cr
or Ti.
Description
[0001] This application claims benefit of Serial No. 2011-069676,
filed 28 Mar. 2011 in Japan and which application is incorporated
herein by reference. To the extent appropriate, a claim of priority
is made to the above disclosed application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a piston ring for an
internal combustion engine.
[0004] 2. Description of the Related Art
[0005] A carbon-based coating is known as a coating which has a low
coefficient of friction, but the coating stress is high and self
fracture occurs, so increasing the thickness is difficult. Japanese
Patent Publication (A) No. 2006-008853 proposes a carbon-based
coating with a low coefficient of friction which is made a
multilayer structure with a surface-most layer comprised of a soft
layer and with soft layers and hard layers alternately laminated
and which enables a smooth surface to be easily obtained.
[0006] See the above Japanese Patent Publication (A) No.
2006-008853 for the related art.
[0007] Japanese Patent Publication (A) No. 2006-008853 does not
define the hardness difference between the hard layer and the soft
layer. However, in Japanese Patent Publication (A) No. 2006-008853,
the soft layer is meant as a fitting layer, while the hard layer is
meant as a wear resistance layer, so the hardnesses are, in Example
1, soft layer: 18 GPa and hard layer: 42 GPa and, in Example 2,
soft layer: 20 GPa and hard layer: 41 GPa. The hardness difference
between the soft layer and hard layer was large.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a piston
ring which is provided with a carbon-based coating which has a low
friction property and excellent wear resistance.
[0009] The present invention provides a piston ring which has a
carbon-based coating formed over its sliding surface, in which
piston ring, the coating is a multilayer coating comprised of two
types of layers having different hardnesses laminated in at least
two layers each, a hardness difference between the two types of
layers is 500 to 1700 HV, a high hardness layer has the same or
greater thickness than a low hardness layer, and the coating as a
whole has a thickness of 5.0 .mu.m or more.
[0010] Preferably, the high hardness layer has a thickness of 5 to
90 nm.
[0011] Preferably, the surface on which the coating is formed has a
base material roughness of 1.0 .mu.mRz or less.
[0012] Preferably, a surface-most layer of the coating is a high
hardness layer.
[0013] Preferably, a low hardness layer of the coating contains
carbon alone or carbon and also Cr or Ti.
[0014] Summarizing the advantageous effects of the invention,
according to the piston ring of the present invention, by making
the carbon-based coating a multilayer coating of two types of
layers which have a hardness difference of 500 to 1700 HV,
increasing the thickness becomes possible and both a low friction
property and excellent wear resistance are given. If the hardness
difference is less than 500 HV, coating cracks cause the sliding
surface to become rough, the coefficient of friction to become
larger, and the wear of the opposing material to become greater as
well. If the hardness difference becomes larger than 1700 HV,
sliding causes the low hardness layer to become worn, stress
concentrates at the surface relief parts of the high hardness layer
(see FIG. 1B), the coating chips, the coefficient of friction
becomes larger, and wear at the opposing material also becomes
greater. If the overall thickness of the coating is less than 5.0
.mu.m, the wear resistance becomes insufficient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the attached
drawings, wherein
[0016] FIGS. 1A to 1C show an embodiment of the present invention,
wherein
[0017] FIG. 1A is a longitudinal cross-sectional view which shows
one part of a piston ring,
[0018] FIG. 1B is an enlarged cross-sectional view of a coating
part, and
[0019] FIG. 1C is a view which shows one part of a coating surface
after sliding, and
[0020] FIG. 2 is a schematic view of a reciprocating wear
tester.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] Below, a preferred embodiment of the present invention will
be explained while referring to the drawings.
[0022] A piston ring 1 has a carbon-based coating 2 formed on its
outer circumference. The carbon-based coating 2 is a DLC
(diamond-like carbon) coating comprised of a multilayer coating of
two types of layers A and B with different hardnesses laminated in
at least two layers each. In FIGS. 1A to 1C, the two types of
layers A and B are laminated in six layers each. The surface-most
layer is a layer A with a high hardness. The hardness difference
between the two types of layers A and B is 500 to 1700 HV. The
layer A with the high hardness (hereinafter referred to as the
"high hardness layer A") has a thickness of 5 to 90 nm, while the
layer B with a low hardness (hereinafter referred to as the "low
hardness layer B") has the same or greater thickness. The overall
thickness of the carbon-based coating 2 is 5.0 .mu.m or more. The
base material roughness of the outer circumference is 1.0 .mu.mRz
or less. The low hardness layer B may contain Cr or Ti. If Cr or Ti
is contained, the adhesion with the high hardness layer A is
improved more.
[0023] If the thickness of the high hardness layer A is smaller
than 5 nm, the required widths of the high hardness layer A and the
low hardness layer B which are exposed at the outer circumference
after sliding (see FIG. 1C) cannot be sufficiently secured, the oil
retention property falls, and the low friction effect becomes
insufficient. If the thickness becomes larger than 90 nm, the
widths of the high hardness layer A and the low hardness layer B
which are exposed at the outer circumference after sliding become
too great, coating cracks occur, the coefficient of friction
becomes greater, and the wear of the opposing material also becomes
greater. If the base material roughness of the outer circumference
is larger than 1.0 .mu.mRz, sliding causes the low hardness layer B
to wear, stress to concentrate at surface relief parts of the high
hardness layer A (see FIG. 1B), the coating to chip, the
coefficient of friction to become greater, and the wear of the
opposing material to also become greater. If the surface-most layer
is a high hardness layer A, the surface of the opposing material
can be quickly smoothened.
[0024] The above carbon-based coating 2 is formed using the PVD
method by alternate sputtering (forming low hardness layer B) and
ion plating (forming high hardness layer A). The thicknesses of the
layers are adjusted by changing the formation times, while the
hardnesses are adjusted by changing the bias voltage.
[0025] Below, the results of use of a reciprocating wear tester to
measure the self wear amount, opposing wear amount, and coefficient
of friction will be explained.
[0026] FIG. 2 shows an outline of a reciprocating wear tester which
is used for the test. A pin-shaped top test piece 10 is held by a
holding block 11. From above, a hydraulic cylinder 12 is used to
apply a downward load whereby a bottom test piece 13 is pressed
against. On the other hand, a flat disk shaped bottom test piece 13
is held by a movable block 14 and is made to move back and forth by
a crank mechanism 15. Reference numeral 16 indicates a load
cell.
[0027] The test conditions were as follow: [0028] Load: 100 N
[0029] Speed: 600 cpm/min [0030] Lubrication oil: 5 W-20 [0031]
Time: 1 hour
[0032] Top test piece: pin-shaped test piece for piston ring given
DLC coating [0033] Bottom test piece: flake shaped graphite cast
iron material for cylinder liner
TABLE-US-00001 [0033] TABLE 1 Elements A, B layer of B Base A layer
B layer hardness layer material A layer hardness hardness
difference other roughness thickness Self Opposing Coefficient HV
HV HV than C .mu.mRz nm wear .mu.m wear .mu.m of friction Ex. 1
2000 300 1700 -- 0.2 5 0.5 1 0.04 Ex. 2 1900 1400 500 -- 0.3 20 0.5
1 0.04 Ex. 3 2700 1000 1700 -- 0.2 30 0.5 1 0.04 Ex. 4 1700 400
1300 -- 0.2 90 0.5 1 0.04 Ex. 5 2500 1000 1500 Cr 0.3 80 0.5 1 0.04
Ex. 6 1700 400 1300 -- 0.5 10 0.5 1 0.04 Ex. 7 1700 400 1300 -- 1.0
10 0.5 1 0.04 Comp. Ex. 1 1800 1400 400 -- 0.2 90 Coating 5 0.09
breaks Comp. Ex. 2 2800 1000 1800 -- 0.3 90 2.0 4 0.07 Comp. Ex. 3
1900 1400 500 -- 0.3 3 0.5 1 0.06 Comp. Ex. 4 1700 300 1400 -- 0.2
110 2.0 5 0.09 Comp. Ex. 5 2000 300 1700 -- 0.2 3 0.5 1 0.07 Comp.
Ex. 6 1700 400 1300 -- 1.2 10 1.5 2 0.07
[0034] While the invention has been described with reference to
specific embodiments chosen for purpose of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
* * * * *