U.S. patent application number 12/568726 was filed with the patent office on 2010-04-01 for engine valves.
This patent application is currently assigned to AISAN KOGYO KABUSHIKI KAISHA. Invention is credited to Shigeki YAMADA.
Application Number | 20100077983 12/568726 |
Document ID | / |
Family ID | 41795280 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077983 |
Kind Code |
A1 |
YAMADA; Shigeki |
April 1, 2010 |
ENGINE VALVES
Abstract
The present invention includes an engine valve including a stem
portion and a head portion disposed at one end of the stem portion.
A heat insulation layer is formed on a surface of the head portion.
A heat conductive layer is formed on a surface of the stem
portion.
Inventors: |
YAMADA; Shigeki;
(Nagoya-shi, JP) |
Correspondence
Address: |
DENNISON, SCHULTZ & MACDONALD
1727 KING STREET, SUITE 105
ALEXANDRIA
VA
22314
US
|
Assignee: |
AISAN KOGYO KABUSHIKI
KAISHA
Obu-shi, Aichi-ken
JP
|
Family ID: |
41795280 |
Appl. No.: |
12/568726 |
Filed: |
September 29, 2009 |
Current U.S.
Class: |
123/188.9 |
Current CPC
Class: |
F01L 3/04 20130101 |
Class at
Publication: |
123/188.9 |
International
Class: |
F01L 3/04 20060101
F01L003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2008 |
JP |
2008-256275 |
Claims
1. An engine valve comprising: a stem portion; a head portion
disposed at one end of the stem portion; a heat insulation layer
formed on a surface of the head portion; and a heat conductive
layer formed on a surface on the stem portion.
2. The engine valve as in claim 1, wherein the heat conductive
layer is made of at least one of aluminum nitride and chrome
nitride.
3. The engine valve as in claim 1, wherein the engine valve is a
solid exhaust valve.
4. The engine valve as in claim 3, wherein the heat insulation
layer is formed on at least a back side surface of the head
portion.
5. The engine valve as in claim 1, wherein the heat insulation
layer is formed on at least a front side surface of the head
portion.
6. The engine valve as in claim 4, wherein the heat insulation
layer is formed on at least a front side surface of the head
portion.
7. The engine valve as in claim 1, wherein the heat insulation
layer is made of ceramic-based material.
8. The engine valve as in claim 2, wherein the heat insulation
layer is made of ceramic-based material.
9. The engine valve as in claim 7, wherein the heat insulation
layer is made of at least one of oxide ceramic and nitride
ceramic.
10. An engine valve for mounting to a cylinder head of an engine,
comprising: a body having a stem portion and a head portion
disposed at one end of the stem portion; a heat insulation layer
formed on a surface of the head portion and having a heat
conductivity lower than a heat conductivity of the body; and a heat
conductive layer formed on a surface on the stem portion and having
a heat conductivity higher than the heat conductivity of the
body.
11. The engine valve as in claim 10, wherein: the heat insulation
layer is formed on the surface of the head portion that is not in
contact with the cylinder head.
12. The engine valve as in claim 10, wherein the heat conductive
layer is formed on at least a part of the surface of the stem
portion that can contact with the cylinder head.
13. The engine valve as in claim 11, wherein the heat conductive
layer is formed on at least a part of the surface of the stem
portion that can contact with the cylinder head.
14. The engine valve as in claim 10, wherein the heat conductive
layer is made of at least one of aluminum nitride and chrome
nitride.
15. The engine valve as in claim 10, wherein the heat insulation
layer is made of at least one of oxide ceramic and nitride ceramic.
Description
[0001] This application claims priority to Japanese patent
application serial number 2008-256275, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to engine valves.
[0004] 2. Description of the Related Art
[0005] In recent years, automobile engines have been increasingly
altered by consumers to performance. However, as the engines are
souped-up, combustion temperature of the engines becomes higher,
which can cause potential damage or earlier deterioration of engine
components. Therefore, it has been proposed to set the air-fuel
ratio of a fuel mixture to be rich in fuel in order to lower the
combustion temperature. However, when the fuel mixture that is rich
in fuel is combusted, an HC component contained in an exhaust gas
may increase to cause potential deviation from emission
regulations. In particular, in recent years, emission regulations
tend to become stricter from a viewpoint of environmental concerns.
Therefore, it is desired to achieve souping-up of engines while a
fuel mixture having a theoretical air-fuel ratio is combusted to
meet emission regulations. However, if souping-up of engines is
achieved with combustion of a fuel mixture having a theoretical
air-fuel ratio, increase in combustion temperature is inevitable.
Hence, improvements of engine components are necessary to be
made.
[0006] Engine valves for controlling intake of a fuel mixture into
a combustion chamber of an engine and for controlling discharge of
an exhaust gas from the combustion chamber are examples of engine
components that need the above improvements. The engine valves
generally have a stem portion and a mushroom-like head portion
disposed at one end of the stem portion. The heat may be
transmitted to the engine valve from a front side of the head
portion, which faces to the combustion chamber, and the heat may be
dissipated from a face part contacting with a valve seat. The stem
portion slidably contacts a valve guide. In the case of an intake
valve, the heat may be also dissipated from a back side of the head
portion by the intake air. However, in the case of an exhaust
valve, the heat may be transmitted from the exhaust gas to a back
side of the head portion, and therefore, the temperature of the
exhaust valve tends to become higher than the temperature of the
intake valve.
[0007] The balance between transmission and dissipation of heat
described above governs the temperature of the engine valve during
the operation of the engine valve. In the case of the exhaust
valve, it is likely that the amount of dissipation of heat is
smaller than the amount of transmission of heat to the valve.
Therefore, depending on the operation condition of the engine, the
head portion may have a high temperature and a heat load to the
valve increases. For this reason and in view of the durability,
martensitic or austenitic heat resisting steel having a good
high-temperature property has been used in some known engine
valves. According to the other examples, nickel alloy, aluminum
alloy, magnesium alloy or titanium alloy is used for achieving
lightweight construction. However, in general, heat resisting
steels are relatively expensive and aluminum alloy or the like has
a problem in heat resisting strength. For instance, the head
portion of the engine valve may be heated to be more than
900.degree. C. in some cases. Although nickel alloy may keep a good
heat resistance strength until 850.degree. C., it does not have a
good heat resistance strength when the temperature is increased to
900.degree. C. or more.
[0008] For the above reason, there has been proposed to reduce the
temperature load to the engine valve by improving the structure of
the engine valve itself. For example, Japanese Laid-Open Patent
Publication No. 2007-32465 has proposed to construct the engine
valve to have a hollow structure in order to mainly improve the
dissipation of heat from the stem portion. Japanese Laid-Open
Patent Publication Nos. 2003-307105 and 4-311611 have proposed to
form a ceramic-type heat insulation layer on a surface of the head
portion in order to reduce transmission of heat to the valve.
[0009] However, the manufacturing cost of the engine valve may be
increased if the engine valve is constructed to have a hollow
structure. In particular, in the case that this structure is
applied to an exhaust valve, it may be necessary to fill a
refrigerant, such as sodium, into the hollow space, and therefore,
the material cost may be increased. In addition, if the amount of
transmission of heat to the valve via the head portion is large,
dissipation of heat may soon reach a limit. In the case that the
heat insulation layer is formed on the surface of the head portion,
it may be possible to reduce transmission of heat to the valve to
some extent. However, the effect of reduction of transmission of
heat is limited and it is not possible to improve dissipation of
heat from the stem portion.
[0010] Therefore, there is a need in the art for engine valves that
can reduce a heat load applied thereto without accompanying
substantial increase in cost.
SUMMARY OF THE INVENTION
[0011] One aspect according to the present invention includes an
engine valve having a stem portion and a head portion disposed at
one end of the stem portion. A heat insulation layer is formed on a
surface of the head portion. A heat conductive layer is formed on a
surface of the stem portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a vertical sectional view of an engine valve
according to an embodiment of the present invention;
[0013] FIG. 2 is a schematic structural view of a valve operating
mechanism incorporating the engine valve shown in FIG. 1; and
[0014] FIG. 3 is an enlarged view of a part of FIG. 2 and showing
the state where an exhaust port is opened by the 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.
[0016] 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.
[0017] In one embodiment, an engine valve includes a stem portion
and a head portion disposed at one end of the stem portion. A heat
insulation layer formed on a surface of the head portion. A heat
conductive layer formed on a surface on the stem portion. The stem
portion may have a rod-like configuration and may slidably contact
a valve guide of a cylinder head of an engine. The head potion may
have a face part that can contact a valve seat of the cylinder
head. The head portion may also have a front side surface and a
back side surface. The back side surface extends from the face part
toward the stem portion and may be called as a neck part.
[0018] With this construction, transmission of heat to the head
portion can be inhibited by the heat insulation layer. In addition,
because the heat conductive layer is formed on the surface of the
stem portion, the heat can be effectively dissipated from the stem
portion. Therefore, a potential heat load applied to the engine
valve can be effectively reduced. As a result, a broader choice of
materials for the valve body is possible, and there is no need to
configure the valve body to have a hollow construction.
[0019] Preferably, the heat conductive layer is made of aluminum
nitride or chrome nitride. Aluminum nitride or chrome nitride is
suitable as the material of the heat conductive layer, because
these materials have a good heat resisting property in addition to
a good heat conductivity.
[0020] Although the present invention can be applied to an engine
valve having a hollow structure, the present invention is
advantageously applied to an exhaust valve having a sold valve body
in order to maximize the advantage of the present invention. Thus,
the manufacturing cost and the material cost of a solid valve body
is lower than a hollow valve body. In addition, a large heat load
reduction effect can be achieved, because an exhaust valve may be
heated to a higher temperature than an intake valve.
[0021] The heat insulation layer may be formed on one or both of a
front side surface and a back side surface of the head portion. In
the case that the engine valve is an exhaust valve, an exhaust gas
flows along the back side surface of the engine valve when the
exhaust gas is discharged from a combustion chamber of the engine
into an exhaust port. Because a cross sectional area across the
back side surface is smaller than a cross sectional area across the
front side surface, a heat capacity at the back side surface is
smaller than a heat capacity at the front side surface. In other
words, a potential heat load at the back side surface is larger
than that at the front side surface, because a heat capacity at the
back side surface is smaller than that at the front side surface.
Therefore, if the heat insulation layer is formed on one of the
back side surface and the front side surface, it is preferable that
the back side surface is preferentially selected. Although it is
most preferable that the heat insulation layer is formed on both of
the front side surface and the back side surface, it is still
possible to achieve a sufficient heat insulation effect by forming
the heat insulation layer only on the front side surface of the
head portion. Thus, it is possible to inhibit transmission of heat
directly from the combustion chamber of the engine by the heat
insulation layer on the front side surface of the head portion.
[0022] Preferably, the heat insulation layer is made of
ceramic-based material, so that it is possible to reliably inhibit
transmission of heat to the engine valve.
[0023] An embodiment of the present invention will now be described
with reference to FIGS. 1 to 3. Referring to FIG. 1, an engine
valve 1 includes a rod-like stem portion 2 and a mushroom-like head
portion 3 disposed at one end of the stem portion 2. The head
portion 3 has a diameter that increases in a direction away from
the stem portion 2. The head portion 3 has a face part 3a for
contacting with a valve seat 19 that will be explained later. In
this embodiment, the engine valve 1 has a solid body although the
engine valve 1 may have a hollow body. In addition, the engine
valve 1 of this embodiment is suitably used for an exhaust valve
that may be heated to a higher temperature than an intake valve,
although it is possible to use the engine valve 1 as an intake
valve.
[0024] Heat insulation layers 4 made of material having a good heat
insulation property are formed on a front side surface 3b of the
head portion 3 facing a combustion chamber (not shown) of an engine
10 (see FIG. 2) and on a back side surface (neck surface) 3c of the
head portion 3 facing to an exhaust port 18 of the engine 10,
respectively. No heat insulation layer is formed on a surface of
the face portion 3a. A heat conductive layer 5 made of material
having a good heat conductivity is formed on a surface of the stem
portion 2.
[0025] Various ceramic materials, each having a good heat
resistance and a good heat insulation property, can be used as the
material of the heat insulation layers 4. For example, oxide
ceramics including alumina, cordierite, zirconia, zircon, titanium
oxide and magnesia, carbide ceramics including silicon carbide, and
nitride ceramics including silicon nitride can be used. It is also
possible to use aluminum silicate, chrome oxide, WC--Co alloy,
WC--Ni--W--Cr.sub.3C.sub.2 alloy and Cr.sub.3C.sub.2--Ni--Cr alloy.
The thickness of the heat insulation layers 4 may be determined by
taking into account a heat insulation effect and reduction in
weight and may preferably be about 0.1 to 2 mm. A single layer or a
plurality of stacked or laminated layers may constitute each of the
heat insulation layers 4.
[0026] As the material of the heat conductive layer 5, aluminum
nitride or chrome nitride each having a good heat conductivity and
a good heat resisting property may preferably used. The thickness
of the heat conductive layer 5 may be determined by taking into
account of necessary heat dissipation property and reduction in
weight and may preferably be about 1 to 100 .mu.m.
[0027] There is no limitation to the material of the body of the
engine valve 1 and any materials used in known engine valves can be
used as the material of the body. However, if a natural oxide layer
is formed on the surface of the body, such an oxide layer may
interfere with the heat conductivity. Therefore, it may be
preferable to remove such an oxide layer from the surface of the
engine valve body before forming the heat conductive layer 5.
Although it is possible to form the heat conductive layer 5 on the
entire surface of the stem portion 2, the heat conductive layer 5
may be formed on at least a part of the surface of the stem portion
2, which slidably contacts with a valve guide 12 of the engine 10
(see FIG. 2). It is preferable to form the heat conductive layer 5
only on the part of the surface of the stem portion 2, which
slidably contacts with the valve guide 12, from a viewpoint of
reduction of material cost.
[0028] The heat insulation layers 4 and the heat conductive layer 5
may be formed using various techniques, such as gas burning, arc
spraying, plasma spraying, explosion spraying, spattering and
ion-plating techniques, etc.
[0029] A valve operating mechanism for the engine valve 1 will be
generally described prior to explanation of the operation of the
engine valve 1. It should be understood that the valve operating
mechanism explained below is only an example and that the engine
valve 1 can be applied to any other valve operating mechanisms
having different configurations form that explained below.
[0030] Referring to FIG. 2, the stem portion 2 of the engine valve
1 (exhaust valve in this embodiment) is axially (vertically in FIG.
2) slidably inserted into the valve guide 12 that is fixedly
attached to a cylinder head 11 of the engine 10. A spring retainer
15 is mounted to an upper end 2a (an end opposite to the head
portion 3) via a cotter 14 that is in engagement with a cotter
receiving groove 13 formed in the upper end 2a. A compression coil
spring 16 is interposed between a spring seat 11a and the spring
retainer 15. The spring seat 11a is formed on the upper surface of
the cylinder head 11 in such a way that the spring seat 11 a
surrounds the valve guide 12. A valve seat 19 is fixedly attached
to the inner circumference of an opening of the exhaust port 18 on
the side of the combustion chamber. The engine valve 1 is normally
biased upwardly by the coil spring 16, so that the face portion 3a
of the head portion 3 contacts the valve seat 19 for closing the
opening of the exhaust port 18. A cam 21 is mounted to a camshaft
20 that is rotatably driven by a crankshaft (not shown). A rocker
arm 23 is swingably mounted to a rocker shaft 22 that extends
parallel to the camshaft 20.
[0031] When a mixture of the fuel (e.g., gasoline) and the air is
combusted within the combustion chamber, the camshaft 20 rotates
for discharging an exhaust gas produced after combustion of the
mixture. Then, the rocker arm 23 swings as the cam 21 rotates, so
that the engine valve 1 is pressed downward against the biasing
force of the coil spring 16. Therefore, the head portion 3 of the
engine valve 1 moves to be separated from the valve seat 19, so
that the exhaust port 18 is opened. As the rocker arm 23 returns to
its original position, the engine valve 1 moves upward by the
biasing force of the coil spring 16. Hence, the face part 3a of the
head portion 3 contacts the valve seat 19 to again close the
exhaust port 19.
[0032] The operation of the engine valve (exhaust valve) 1 will be
described in relation to the valve operating mechanism described
above. When the mixture of the fuel and the air is combusted within
the combustion chamber, heat is produced by combustion and is
transmitted to the engine valve 1 via the front side surface 3b of
the head portion 3. However, because the heat insulation layer 4 is
formed on the front side surface 3b, transmission of heat from the
combustion chamber to the engine valve 1 via the front side surface
3b can be reduced. When the engine valve 1 moves to be separated
from the valve seat 19 in order to discharge the exhaust gas from
the combustion chamber to the exhaust port 18, the exhaust gas that
has a high temperature is discharged into the exhaust port 18 in
such a way that the exhaust gas flows along the back side surface
3c. Therefore, the heat may be transmitted from the exhaust gas to
the engine valve 1 also via the back side surface 3c. However,
because the heat insulation layer 4 is also formed on the back side
surface 3c, it is possible to reduce transmission of heat to the
engine valve 1 via the back side surface 3c. In this way, because
transmission of heat to the head portion 3 can be reduced at both
of the front side surface 3b and the back side surface 3c, the heat
load applied to the head portion 3 including the back side surface
3c at the neck portion having a small heat capacity can be
reduced.
[0033] However, the transmission of heat to the head portion 3 is
not completely stopped, therefore the head portion 3 temperature
may further increase. As a result, the heat transmitted to the head
portion 3 is conducted to the stem portion 2 and is thereafter
dissipated to the valve guide 12 that slidably contacts the stem
portion 2. Because the heat conductive layer 5 is formed on the
surface of the stem portion 2, conduction of heat from the stem
portion 2 to the valve guide 12 can be effectively performed. In
other words, the heat conductive layer 5 improves the ability of
heat to dissipate from the stem portion 2 to the valve guide
12.
[0034] Therefore, the heat load to the head portion 3 can be
further reduced. When the engine valve 1 is closed to cause the
face part 3a to contact with the valve seat 19, the heat can be
also dissipated from the face part 3a to the valve seat 19. Because
no heat insulation layer is formed on the face part 3a, the heat
dissipation ability is not lowered at this part.
[0035] Preferably, the valve guide 12 may be made of copper alloy
that has a good heat conductively, so that the dissipation of heat
from the stem portion 2 can be further improved. In general, the
valve seat 19 is constructed as a separate member from the cylinder
heat 11. In many cases, a joint surface between the cylinder head
11 and the valve seat 19 is not always a flat surface but has a
roughness in micron units. Therefore, a clearance may be formed due
the roughness to inhibit the heat conductive ability and to
eventually lower the ability of dissipating heat from the engine
valve 1. For this reason, the valve seat 19 is preferably
configured as a clad seat that is formed integrally with the
cylinder head 11 by building up the cylinder head 11.
* * * * *