U.S. patent application number 12/977805 was filed with the patent office on 2011-06-30 for engine valves.
This patent application is currently assigned to AISAN KOGYO KABUSHIKI KAISHA. Invention is credited to Mineo FUJINO, Tadayoshi TOMINAGA, Shigeki YAMADA.
Application Number | 20110155088 12/977805 |
Document ID | / |
Family ID | 44173157 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110155088 |
Kind Code |
A1 |
TOMINAGA; Tadayoshi ; et
al. |
June 30, 2011 |
ENGINE VALVES
Abstract
An engine valve according to the present teaching has a
hot-forged head portion having an oxidized surface layer at a
radially outer peripheral surface. The oxidized surface layer is
formed during hot-forging of the head portion.
Inventors: |
TOMINAGA; Tadayoshi;
(Aichi-ken, JP) ; FUJINO; Mineo; (Obu-shi, JP)
; YAMADA; Shigeki; (Nagoya-shi, JP) |
Assignee: |
AISAN KOGYO KABUSHIKI
KAISHA
Obu-shi
JP
|
Family ID: |
44173157 |
Appl. No.: |
12/977805 |
Filed: |
December 23, 2010 |
Current U.S.
Class: |
123/188.3 ;
29/888.4 |
Current CPC
Class: |
F01L 2303/00 20200501;
F01L 3/04 20130101; F01L 2301/02 20200501; F01L 3/02 20130101; Y10T
29/49298 20150115; F01L 2301/00 20200501 |
Class at
Publication: |
123/188.3 ;
29/888.4 |
International
Class: |
F01L 3/02 20060101
F01L003/02; B21K 1/22 20060101 B21K001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2009 |
JP |
2009-292502 |
Claims
1. An engine valve comprising: a shaft portion and a head portion
each made of heat resistant alloy; wherein the head portion is
disposed at one end of the shaft portion in continuity therewith
and hot-forged without forming any burr at a radially outer
peripheral surface of the head portion; wherein the radially outer
peripheral surface of the head portion is not machined so that the
radially outer peripheral surface of the head portion has an
oxidized surface layer formed by oxidization of the heat-resistant
alloy.
2. The engine valve as in claim 1, wherein the radially outer
peripheral surface of the head portion has a curved
configuration.
3. The engine valve as in claim 1, wherein the heat-resistant alloy
is heat-resistant steel.
4. The engine valve as in claim 1, wherein the heat-resistant alloy
is titanium alloy.
5. The engine valve as in claim 1, wherein a surface of the engine
valve includes a flat head surface, a valve face formed in
continuity with the head surface via the radially outer peripheral
surface, and a neck surface having a diameter decreasing toward the
shaft portion.
6. A method of manufacturing an engine valve, comprising: preparing
a rod made of heat resistant alloy; forming the rod into an
intermediate product having a shaft portion and a head portion
primary body; and hot-forging the head portion primary body into a
head portion, so that an oxidized surface layer is formed on a
surface of the head portion without producing any burr at a
radially outer peripheral surface of the head portion.
7. The method as in claim 6, wherein the step of forming the rod
into the intermediate product comprises forging a portion of the
rod into the head portion primary body.
Description
[0001] This application claims priority to Japanese patent
application serial number 2009-292502, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present teaching relates to engine valves made of
heat-resistant alloy and having a valve head portion that is
hot-forged in continuity with one end of a shaft portion.
[0004] 2. Description of the Related Art
[0005] A process of manufacturing this kind of poppet-type engine
valve is hereinafter described. As shown in FIG. 3 (a), one end of
a bar member is cold-forged to form a valve intermediate body 106
having a shaft portion 102 and a head portion primary body 105
having a block-like shape and formed in series at one end of the
shaft portion 102. The valve intermediate body 106 is then inserted
into a casting mold 110 and heat-forged in a manner that a punch
111 presses against the head portion primary body 105. In this way,
the head portion primary body 105 is cast into a head portion 103
that fits to the shape of the casting mold 110. Conventionally, in
order to ensure that the head original body 105 becomes a net shape
fitting accurately to the shape of the mold 110, the forging
process is made in such a manner that a burr 107 is formed around
the outer peripheral edge of the head portion 103. More
specifically, the volume of the head portion primary body 105 is
determined to be slightly larger than the volume defined by a head
portion mold surface 110a of the casting mold 110 and a bottom
surface of the punch 111. Therefore, the burr 107 is inevitably
formed at the outer peripheral edge of the head portion 103 after
the hot-forging process. The burr 107 is then removed by a
machining operation such as a grinding or cutting operation.
Examples of engine valves manufactured in this way are disclosed in
Japanese Laid-Open Patent Publication Nos. 3-86457 and 4-8402.
[0006] When the heat resistant alloy is hot-forged, the base
material is oxidized to form an oxidized layer on a surface layer
portion of the valve intermediate body. The oxidized layer has a
favorable heat insulation property. Therefore, in the case of an
engine valve that is exposed to a high temperature environment and
receives a high thermal load, it is preferable that the oxidized
layer is left without being removed. Due to the heat insulation
property of the oxidized layer formed in the surface layer portion,
the amount of heat transmitted into the engine valve is reduced and
increase of temperature of the engine valve is suppressed.
Especially, the heat insulation effect in the head portion is
significant because the head portion is easily heated to have a
high temperature as it is directly opposed to a combustion chamber
of the engine.
[0007] However, in the case of Japanese Laid-Open Patent
Publication Nos. 3-86457 and 4-8402, the burr produced around the
outer peripheral edge of the head portion is removed by a machining
operation. Therefore, even if an oxidized layer 101b is formed at
the surface layer of the base material 101a by the heat-forging
process, it may be removed at an outer peripheral surface 103d of
the head portion 103 by the machining operation as shown in FIG. 4.
Under the circumstance where the oxidized layer 101b is removed,
the outer peripheral surface 103d of the head portion 103 is easily
heated. Accordingly, the possibility of occurrence of "pre-ignition
phenomenon" may be increased. Here, the term "pre-ignition
phenomenon" is used to mean a phenomenon in which timing of
combustion is advanced prior to controlled ignition by a sparking
plug because air-fuel mixture in the combustion chamber may be
combusted by the highly heated engine valve.
[0008] In order to avoid the pre-ignition, an oxidized layer may be
formed again on the outer periphery surface (machined surface)
after the burr has been removed from the head portion of the engine
valve as disclosed in Japanese Laid-Open Patent Publication Nos.
3-86457 and 4-8402. However, the re-forming process is troublesome
and leads to increase of the cost.
[0009] Therefore, there is a need in the art for an engine valve
that is difficult to be heated due to a high heat insulation
property of an oxidized layer formed on an outer peripheral surface
of a head portion.
SUMMARY OF INVENTION
[0010] An engine valve according to the present teaching has a
hot-forged head portion having an oxidized surface layer at a
radially outer peripheral surface. The oxidized surface layer is
formed during hot-forging of the head portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a sectional view of an engine valve according to
an example;
[0012] FIGS. 2(a) and 2(b) are views showing manufacturing steps of
the engine valve;
[0013] FIGS. 3(a) and 3(b) are views showing manufacturing steps of
a known engine valve; and
[0014] FIG. 4 is a sectional view of the known engine valve.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Each of the additional features and teachings disclosed
above and below may be utilized separately or in conjunction with
other features and teachings to provide improved engine valves.
Representative examples of the present invention, which examples
utilize many of these additional features and teachings both
separately and in conjunction with one another, will now be
described in detail with reference to the attached drawings. This
detailed description is merely intended to teach a person of skill
in the art further details for practicing preferred aspects of the
present teachings and is not intended to limit the scope of the
invention. Only the claims define the scope of the claimed
invention. Therefore, combinations of features and steps disclosed
in the following detailed description may not be necessary to
practice the invention in the broadest sense, and are instead
taught merely to particularly describe representative examples of
the invention. Moreover, various features of the representative
examples and the dependent claims may be combined in ways that are
not specifically enumerated in order to provide additional useful
embodiments of the present teachings.
[0016] In one example, an engine valve includes a shaft portion and
a head portion each made of heat resistant alloy. The head portion
is disposed at one end of the shaft portion in continuity therewith
and hot-forged without forming any burr at a radially outer
peripheral surface (marginal surface) of the head portion. The
outer peripheral surface of the head portion is not machined so
that the outer peripheral surface of the head portion has an
oxidized surface layer formed by oxidization of the heat-resistant
alloy. The valve face of the head portion contacting the valve seat
may be ground for removing the oxidized surface layer if necessary
or desired. The radially outer peripheral surface of the head
portion is a surface extending between the flat head surface for
facing to) a combustion chamber and the valve face for contacting
the valve seat.
[0017] If no burr is formed when the head portion is forged, the
machining operation such as a cutting or grinding operation to
remove the burr is not required. Therefore, the radially outer
peripheral surface of the head portion is remained as it is forged.
More specifically, the oxidized layer formed by oxidization of the
surface layer of the base material during the hot-forging process
is not necessary to be removed by the machining operation. In this
way, the oxidized layer may be maintained on the outer periphery
surface of the head portion. Because the oxidized layer having high
heat insulation property is remained also at the outer peripheral
surface of the head portion, increase of temperature of the head
portion, which is easily heated to a high temperature, can be
prevented. Accordingly, it is possible to lower the temperature of
the engine valve (especially the head portion) during operation of
the engine compared to the known techniques as disclosed in
Japanese Laid-Open Patent Publication Nos. 3-86457 and 4-8402. In
this way, a critical region for occurrence of pre-ignition is
improved. If the critical region for occurrence of pre-ignition is
improved, combustion of the fuel mixture within the engine is
stabilized. Accordingly, an engine output and fuel consumption can
also be improved by increasing the compression ratio of the fuel
mixture. Further, because the oxidized layer formed during the
hot-forging process is simply maintained, it is not necessary to
form the oxidized layer again after the machining operation or it
is not necessary to form a heat insulation layer separately.
Accordingly, the engine valve can be manufactured efficiently and
at a lower cost.
[0018] Preferably, the outer peripheral surface of the head portion
has a curved configuration. Because a high heat insulation property
is ensured, it may be possible that the outer peripheral surface is
pointed. However, if the surface is curved, occurrence of the
pre-ignition of the air-fuel mixture may be more effectively
prevented compared to the pointed surface As a heat-resistant
alloy, a heat-resistant steel may be used.
[0019] An example of an engine valve of the present teaching is
explained below with reference to the drawings.
[0020] As shown in FIG. 1, a poppet-type engine valve 1 has a
bar-shaped shaft portion 2 and a head portion 3 having a
configuration enlarged in a direction away from the shaft portion
2. The head portion 3 is formed in continuity with on one end of
the shaft portion 2. The engine valve 1 may be used for introducing
air into a combustion chamber of an internal combustion engine
(hereinafter simply called "engine") or for discharging exhaust gas
from the combustion chamber. Thus, the engine valve 1 may be used
as an intake valve for introducing air-fuel mixture into the
combustion chamber or as an exhaust valve for discharging exhaust
gas produced after combustion of the mixture in the combustion
chamber. Although not shown in the drawings, when the engine valve
1 is mounted on the engine, the other end of the shaft portion 2
may be pressed by a cam, a pivot, and a locker arm, etc., so that
the engine valve 1 moves away from a valve seat to open an intake
port or an exhaust port of the combustion chamber.
[0021] The engine valve 1 is made of heat-resistant alloy. For
example, heat-resistant alloy may be heat-resistant steel, such as
SUH3, SUH11 or SUH35 (in JIS classification). Alternatively,
titanium alloy may be used as the heat-resistant alloy. The head
portion 3 includes a flat head surface 3a, a valve face 3b and a
neck portion 3c. The flat head surface 3a may face to the
combustion chamber. The valve face 3b can contact the valve seat in
order to close the intake port or the exhaust port of the
combustion chamber. The neck portion 3c is formed in series from
the face surface 3b to a shaft portion 2. The diameter of the neck
portion 3c is gradually reduced towards the shaft portion 2. The
head surface 3a and the face surface 3b are connected to each other
via a radially outer peripheral surface 3d of the head portion 3.
The outer peripheral surface 3d of the head portion 3 is configured
as a curved surface as it is not machined. The engine valve 1 has
an oxidized surface layer 1b formed throughout on its outer
surface. The oxidized surface layer 1b is formed due to oxidization
of a base material 1a of the engine valve 1. In particular, the
outer peripheral surface 3d of the head portion 3 is covered with
the oxidized layer 1b.
[0022] A manufacturing process of the engine valve 1 will be
explained below with reference to FIGS. 2(a) and 2(b). First, a rod
made of the heat-resistant alloy is cold-forged or hot-forged, for
example, by drawing the rod with a four-side high-speed forging
apparatus or is upset-forged by an electric upset-forging apparatus
(i.e. an electric upsetter), so that a valve intermediate body 6
(intermediate product) is formed as shown in FIG. 2(a). As shown in
FIG. 2(a), the valve intermediate body 6 includes a massive head
portion primary body 5 formed in continuity with one end of the
shaft portion 2. The valve intermediate body 6 is inserted into a
forging die 10 as shown in FIG. 2(a). The volume of the head
portion primary body 5 is set to be slightly smaller than a volume
of a head portion to be forged (hereinafter called "head portion
volume"), which is defined between a mold surface 10a of the
forging die 10 and a bottom surface of a punch 11 when the punch 11
is positioned at its lowermost position. Then, the head portion
primary body 5 is hot-forged by being punched several times from
above by the punch 11 that reciprocates between its uppermost
position and lowermost position by a predetermined stroke. In this
way, the head portion primary body 5 is plastically deformed.
Accordingly, the head portion primary body 5 is forged into the
head portion 3 having a configuration corresponding to the shape of
the head portion volume of the forging die 10. Because the volume
of the head portion primary body 5 is slightly smaller than the
head portion volume defined by the forging die 10, no burr is
formed at the radially outer peripheral surface 3d of the head
portion 3, and therefore, the radially outer peripheral surface 3d
maintains a curved configuration given as a result of plastic
deformation. When the punch 11 is at the lowermost position, the
punch 11 does not contact the forging die 10 and thus, there is a
slight clearance between the punch 11 and the forging die 10.
[0023] The hot-forging process of the head portion primary body 5
may be made at a temperature of 800.degree. C. or more. The heat
may only be applied to the head portion primary body 5 to be
plastically deformed. Due to the hot-forging of the head portion
primary body 5, the oxidized layer 1b is formed on the surface of
the engine valve 1 as a result of oxidization of the base material
1a (e.g., heat resistant steel). In the present teaching, the burr
is not formed at the radially outer peripheral surface 3d of the
head portion 3 after the hot-forging process. Accordingly, it is
not necessary to remove the burr from the outer peripheral surface
3d of the head portion 3 by a machining operation, such as grinding
or cutting. In this way, the engine valve 1 having the oxidized
layer 1b formed by the hot-forging process also at the outer
peripheral surface 3d of the head portion 3 may be obtained.
Because the oxidized layer 1b having a high heat insulation
property is formed at the outer peripheral surface 3d of the head
portion 3, any heat that may be applied to the outer peripheral
surface 3d of the head portion 3 during the operation of the engine
can be effectively insulated. Therefore, increase in temperature of
the head portion 3 is also well prevented compared to the known
engine valve. Accordingly, it is possible to improve a critical
region for occurrence of pre-ignition.
[0024] The valve face 3b may be ground if necessary or desired. In
addition to the oxidized layer 1b, another kind of heat insulation
layer (a heat insulation film) may be formed on the surface of the
engine valve 1. A nitriding treatment such as a soft-nitriding
treatment in a salt bath and a gas soft-nitriding treatment may
also be applied to the surface of the engine valve 1. As a material
of an additional heat insulation layer, ceramic series oxide, such
as alumina, cordierite, zirconia, zircon, oxidized titanium and
magnesia; ceramic series carbide, such as silicon carbide; and
ceramic series nitride, such as silicon nitride may be used. In
addition to these materials, ceramic series materials having high
heat resistance and heat insulation property, such as aluminum
silicate, oxidized chrome, WC/Co alloy, WC/Ni/W/Cr3C2 alloy, and
Cr3C2/Ni--Cr alloy are also appropriate to be used for the heat
insulation layer. The heat insulation layer could be used as a
single layer or a plurality of heat insulation layers made of
different materials maybe layered. The heat insulation layer may be
formed by using a suitable technique, such as gas flaring, arc
spraying, plasma spraying, blast spraying, sputtering and ion
plating techniques. Furthermore, it may be desirable to anneal the
heat insulation layer at a low temperature, for instance,
approximately at 400.degree. C. for removing residual stress
generated during the forging process.
* * * * *