U.S. patent application number 10/536682 was filed with the patent office on 2006-07-27 for valve seat and method for producing a valve seat.
Invention is credited to Reiner Heigl.
Application Number | 20060162686 10/536682 |
Document ID | / |
Family ID | 32335805 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060162686 |
Kind Code |
A1 |
Heigl; Reiner |
July 27, 2006 |
Valve seat and method for producing a valve seat
Abstract
A valve seat for a cylinder head of an internal combustion
engine includes an additional material fused to the base material
of the cylinder head. The additional material includes at least two
layers above one another, the inner layer, facing the cylinder
head, having good joining properties with respect to the base
material of the cylinder head, and the outer layer, remote from the
cylinder head, having good strength and wear properties.
Inventors: |
Heigl; Reiner; (Remseck,
DE) |
Correspondence
Address: |
AKERMAN SENTERFITT
P.O. BOX 3188
WEST PALM BEACH
FL
33402-3188
US
|
Family ID: |
32335805 |
Appl. No.: |
10/536682 |
Filed: |
October 21, 2003 |
PCT Filed: |
October 21, 2003 |
PCT NO: |
PCT/EP03/11615 |
371 Date: |
November 10, 2005 |
Current U.S.
Class: |
123/188.8 ;
29/888.44 |
Current CPC
Class: |
Y10T 29/49306 20150115;
F01L 3/04 20130101 |
Class at
Publication: |
123/188.8 ;
029/888.44 |
International
Class: |
F01L 3/22 20060101
F01L003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2002 |
DE |
102 55 447.1 |
Claims
1-15. (canceled)
16. A valve seat for a cylinder head of an internal combustion
engine, which includes an additional material fused to the base
material of the cylinder head, which additional material includes
at least an inner layer (6) facing the cylinder head (1) and an
adjacent outer layer (7) more remote from the cylinder head (1),
the inner layer (6) including copper or a copper alloy and having
good joining properties with respect to the base material of the
cylinder head (1), and the outer layer (7) including an alloy
comprising nickel, iron and/or cobalt as its main constituent.
17. The valve seat as claimed in claim 16, characterized in that
the inner layer (6) has good heat conduction properties.
18. The valve seat as claimed in claim 16, characterized in that
the copper alloy of the inner layer (6) includes aluminum as an
alloying constituent.
19. The valve seat as claimed in claim 16, wherein the copper alloy
of the inner layer (6) includes iron as an alloying
constituent.
20. The valve seat as claimed in claim 16, wherein the nickel, iron
and/or cobalt alloy of the outer layer (7) includes chromium as an
alloying constituent.
21. The valve seat as claimed in claim 16, wherein the nickel, iron
and/or cobalt alloy of the outer layer (7) includes silicon as an
alloying constituent.
22. The valve seat as claimed in claim 16, wherein the nickel, iron
and/or cobalt alloy of the outer layer (7) includes molybdenum as
an alloying constituent.
23. A process for producing a valve seat for a cylinder head of an
internal combustion engine which includes an additional material
fused to the base material of the cylinder head, which additional
material includes at least an inner layer (6) facing the cylinder
head (1) and an adjacent outer layer (7) more remote from the
cylinder head (1), the inner layer (6) including copper or a copper
alloy and having good joining properties with respect to the base
material of the cylinder head (1), and the outer layer (7)
including an alloy comprising nickel, iron and/or cobalt as its
main constituent, the process comprising fusing the inner layer to
the cylinder head at the location at which the valve seat is to be
formed by the introduction of energy, after the inner layer has
been fused to the base material of the cylinder head, fusing the
outer layer to the inner layer by the introduction of energy,
wherein the inner layer (6) is placed onto the cylinder head (1) in
the form of a solid ring, and wherein the outer layer (7) is
applied to the inner layer (6) in powder form.
24. The process as claimed in claim 23, wherein the additional
material is fused to the cylinder head (1) by means of a laser beam
(9, 9').
25. The process as claimed in claim 23, wherein the additional
material is fused to the cylinder head (1) by means of an electron
beam.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a valve seat for a cylinder head of
an internal combustion engine of the type defined in more detail in
the preamble of claim 1. Furthermore, the invention relates to a
process for producing a valve seat for a cylinder head of an
internal combustion engine of the type defined in more detail in
the preamble of claim 10.
[0003] 2. Related Art of the Invention
[0004] DE 199 12 889 A1 describes a valve seat of the generic type
and a process of the generic type for producing it. In this case,
an additional material, namely an alloy or a mixture of an
aluminum-silicon alloy and nickel, is fused to the base material of
the cylinder head by a laser beam.
[0005] DE 35 17 077 C1 has disclosed a process for reinforcing the
valve seat surface of a gas exchange valve in which reinforcing
plating material preferably consisting of a nickel- or cobalt-based
superalloy is introduced into an encircling recess on the valve
plate.
[0006] A process for coating the surface of metallic workpieces
with an additional material in powder or wire form is described by
DE 199 12 894 A1.
[0007] A further process of this type is known from EP 0 092 683
B1. In this case, the base material of the cylinder head
substantially comprises aluminum, and either iron or nickel or an
alloy comprising one of these two metals is used as the main
constituent of the additional material for forming the valve
seat.
[0008] One drawback in this case is that iron and nickel have a
significantly higher melting point than the cylinder head, which
consists of aluminum. This can lead to the cylinder head already
being in molten form under the action of a laser beam when the
additional material is only just starting to melt. Moreover, it may
be the case that the previously liquid iron has already solidified
while the aluminum is still in molten form. This leads to the
formation of intermetallic phases in the interfacial region between
iron and aluminum material, which can lead to a very brittle
microstructure. Consequently, it is difficult to achieve a
homogeneous join between the valve seat to be created and the base
material of the cylinder head; the different surface tensions of
the materials also play a major role in this context.
[0009] EP 0 228 282 B1 describes a cylinder head consisting of an
aluminum alloy. The valve seats of this cylinder head are formed
from a plated-on copper alloy layer.
[0010] If copper is used as material for valve seats, however, the
drawback arises, in particular in the case of diesel internal
combustion engines, that the sulfur contained in the diesel fuel
attacks the copper, which causes problems with regard to the
exhaust gases produced and corrosion. The use of copper for valve
seats is therefore only appropriate for spark-ignition internal
combustion engines, which means that this solution cannot be
employed economically.
[0011] DE 196 39 480 A1 has described a process for the internal
coating of cylinder liners by means of pulverulent additional
materials which are alloyed on by laser radiation.
[0012] DE 22 00 003 A1 reveals a process for the surface treatment
of light metal components, in particular of light metal pistons of
internal combustion engines, having an additional material which
increases the strength and/or is resistant to wear.
[0013] Moreover, for further prior art relating to valve seats for
internal combustion engines and processes for producing them,
reference is made to the following documents: U.S. Pat. No.
4,059,876, JP 05256190 A, JP 07284970 A, JP 08047787 A, JP 08224680
A, JP 08224681 A, JP 08224682 A, JP 08224683 A, JP 10141132 A, JP
10176511 A, JP 11002154 A, EP 0 209 366 A1, U.S. Pat. No.
4,723,518, JP 02196117 A, JP 04123885 A, JP 06042320 A and JP
08174245 A.
[0014] If the valve seat is to be fused as additional material to
the base material of the cylinder head, the problem tends to arise
that this additional material has to ensure both bonding to the
base material of the cylinder head and the strength properties for
absorbing the forces introduced by the gas exchange valve as well
as the tribological properties required to minimize the wear at the
surface of the valve seat. This imposes very complex boundary
conditions for the choice of materials, which is reflected in the
prior art by the very wide range of proposals which have been made
as to the use of certain materials. Hitherto, however, no solution
has been so convincing that it has been able to replace the process
of pressing the valve seat rings into place, which has long been
used in practice.
SUMMARY OF THE INVENTION
[0015] Therefore, it is an object of the present invention to
provide a valve seat for a cylinder head of an internal combustion
engine and a process for producing it which has both good bonding
to the base material of the cylinder head and good strength and
wear properties.
[0016] According to the invention, this object is achieved by the
features listed in claim 1.
[0017] The two layers above one another according to the invention
advantageously allow the very different roles which the valve seat
has to perform to be split. For example, according to the
invention, the inner layer, facing the cylinder head, can perform
the role of joining the valve seat to the base material of the
cylinder head and the outer layer, remote from the cylinder head,
can be designed in such a way that it has good strength and wear
properties for the valve seat.
[0018] This advantageously improves the bonding of the valve seat
to the cylinder head, which prevents the whole of the valve seat
from becoming detached from the cylinder head. Nevertheless,
relatively high loads can be imposed on the valve seat according to
the invention with relatively low wear rates, on account of the
configuration of the outer layer. The overall result achieved in
this way is a considerably widened range of materials, in
particular also with regard to the different demands imposed by
spark-ignition and diesel internal combustion engines.
[0019] If, in an advantageous configuration of the invention, the
inner layer has good heat conduction properties, the dissipation of
heat from the valve seat surface into the cylinder head is
advantageously improved since the melt-metallurgy bonding avoids
the air gap between the valve seat and the cylinder head.
[0020] In particular, in the case of cylinder heads made from
aluminum, it has proven advantageous for the inner layer to include
copper or a copper alloy, since in particular a material of this
type can be successfully bonded to the aluminum material of the
cylinder head. In this context, the outer layer prevents the copper
material of the inner layer from combining with sulfur-containing
fuel or exhaust-gas constituents, thereby having an adverse effect
on the emission levels.
[0021] Furthermore, it is possible to provide for the outer layer
to include nickel, iron and/or cobalt or an alloy comprising at
least one of these materials. These materials have proven
particularly hard and wear-resistant and have a very high strength.
A further advantage of these materials is their good ability to
bond to the copper material which may have been used for the inner
layer.
[0022] A process solution is given by the features of claim 10.
[0023] This sequential process allows the at least two layers
according to the invention to be bonded to the base material of the
cylinder head in a particularly simple and reliable way, in terms
of process engineering, while retaining the advantageous properties
of the valve seat explained above.
[0024] A process which is particularly economical in terms of
manufacturing technology results if the inner layer is placed onto
the cylinder head in the form of a solid ring, and the outer layer
is applied to the inner layer in powder form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Further advantageous configurations and refinements of the
invention will emerge from the remaining subclaims and from the
exemplary embodiments outlined below with reference to the drawing,
in which:
[0026] FIG. 1 shows a section through a valve seat according to the
invention for a cylinder head of an internal combustion engine;
[0027] FIG. 2 shows an embodiment for carrying out the process
according to the invention;
[0028] FIG. 3 shows a further embodiment for carrying out the
process according to the invention; and
[0029] FIG. 4 shows a further embodiment of the process according
to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIG. 1 shows part of a cylinder head 1 of an internal
combustion engine, which is not illustrated in its entirety. The
cylinder head 1, in a manner which is known per se, has an intake
port 2 which can be closed and opened by a gas exchange valve 3.
When the gas exchange valve 3 is opened, a fuel/air mix can enter a
combustion chamber 4 located beneath the cylinder head 1 from the
intake port 2 in a manner which is known per se. Furthermore, the
cylinder head 1 has a valve seat 5, against which the gas exchange
valve 3 bears in its closed position, in this way separating the
intake port 2 from the combustion chamber 4.
[0031] As can also be seen from FIG. 1, the valve seat 5 has two
layers 6 and 7 formed from respective additional materials, namely
a lower or inner layer 6, facing the cylinder head 1, and an upper
or outer layer 7, which is remote from the cylinder head 1 and
faces the gas exchange valve 3. The inner layer 6 is used to join
the valve seat 5 to the cylinder head 1 and therefore has good
joining properties with respect to the base material of the
cylinder head 1. The outer layer 7, by contrast, has good strength
and wear properties in order to be able to absorb the forces acting
on the valve seat 5 from the gas exchange valve 3.
[0032] Since in the present case the cylinder head 1 consists of a
light metal, in particular of aluminum, copper or a copper alloy is
used for the inner layer 6, since this material has a particularly
good affinity for aluminum. In this case, in particular when using
the alloy CuAl.sub.10, i.e. a copper alloy containing 10 percent by
weight of aluminum, the inner layer 6 is securely bonded to the
material of the cylinder head 1. Moreover, iron has also proven to
be a suitable further alloying constituent for the inner layer.
However, it is also possible for pure copper to be used for the
inner layer 6.
[0033] In addition to the good joining properties with respect to
the base material of the cylinder head 1, the inner layer 6 also
has good heat conduction properties in order to improve the
dissipation of heat from the surface of the valve seat 5 into the
cylinder head 1. This is because the air gap between the valve seat
5 and the cylinder head 1 is avoided by the melt-metallurgy
bonding. In this context, the thermal conductivity of copper at
20.degree. C. is approx. 350-400 W/mK, that of aluminum at
20.degree. C. is approx. 200-250 W/mK and that of the alloy used
for the inner layer 6 at 20.degree. C. is approx. 200-400 W/mK.
[0034] To achieve the required strength, wear or hardness
properties of the outer layer 7, it is preferable for nickel, iron
and/or cobalt or an alloy comprising at least one of the materials
to be used for this outer layer. Although a material of this type
would tend to form intermetallic phases under certain circumstances
when joined to the aluminum of the cylinder head 1, which could
lead to the formation of cracks, the presence of the inner layer 6
means that the outer layer 7 is not joined to the cylinder head 1,
and consequently intermetallic phases of this type do not
arise.
[0035] In particular, chromium, silicon and molybdenum have proven
particularly suitable as further alloying constituents for the
material of the outer layer 7. A few alloys which can be used for
the outer layer 7 are listed below by way of example; in addition
to the three elements mentioned above, it is also possible for
other elements to be used as further alloying constituents:
Co25Cr10Ni7W0.5C, Co28Mo8Cr2Si, Co28 Mo17Cr3Si, Ni17Cr6A10.5Y,
Ni22Cr10A11.0Y, Ni25Cr6A10.4Y, Ni31Cr11A10.6Y,
Ni23Co20Cr8.5Al4Ta0.6Y, Ni15Cr4Si3FeB0.75C, Ni21.5Cr8.5Mo3Fe0.5Co,
Ni19Cr18Fe3 Mo1Co1Ti or Ni8.5Cr7Al5Mo2Si2B2Fe3TiO2. Of course, this
list makes no pretence to be complete, and it is possible to employ
materials used in commercially available valve seat rings. The
choice of materials also depends, inter alia, on whether the
cylinder head 1 is used in a spark-ignition or diesel internal
combustion engine.
[0036] If other materials are used for the cylinder head 1, it is,
of course, also possible for the two layers 6 and 7 to consist of
other materials which ensure that the inner layer 6 has good
bonding properties with respect to the base material of the
cylinder head 1 and the outer layer 7 has good strength and wear
properties.
[0037] FIG. 2 and FIG. 3 show two different processes used to
produce the valve seat 5 by fusing the additional materials
mentioned above to the cylinder head 1; only the application of the
inner layer 6 to the cylinder head 1 is illustrated.
[0038] In the embodiment shown in FIG. 2, a nozzle 8 which
discharges the additional material for forming the inner layer 6
toward the cylinder head 1 is arranged in the region of the valve
seat 5 that is to be formed. As soon as the additional material
comes into contact with the cylinder head 1 or enters a groove
formed therein, it is simultaneously fused to the outer layer of
the base material of the cylinder head 1 by a laser beam 9, in
order to produce a molten material 10 at the cylinder head 1.
During production of the groove, the machining operation is matched
to the coating process. As an alternative to the laser beam 9
described, it is also possible for an electron beam (not shown) or
a suitable device for producing the molten material 10 from the
additional material 7 by the application or introduction of energy,
to be used as the energy source. The additional material 7 is in
this case applied in powder form; it can also be applied in the
form of a strip.
[0039] To achieve a continuous process, the nozzle 8 and the laser
beam 9 are advanced continuously along a circular path
corresponding to the contour of the valve seat 5. When the laser
beam 9 has moved away from the molten material 10, in the direction
of advance corresponding to arrow A, the molten material solidifies
to form the inner layer 6. This is what is known as a single-stage
process.
[0040] FIG. 3 shows an alternative process for producing the valve
seat 5, in which the additional material is placed into a groove in
the cylinder head 1 or placed onto the cylinder head 1, for example
in the form of a paste, a wire, a sintered body or a powder
preform, preferably in the shape of a ring, and is then fused to
form the molten material 10 by the laser beam 9 or an electron
beam. In this case, too, the inner layer 6 of the valve seat 5 is
formed from the molten material 10 after the removal of the laser
beam 9 in arrow direction A. This process is known as a two-stage
process.
[0041] The outer layer 7 can be applied in a very similar way in
both processes, although it is, of course, being fused not to the
cylinder head 1, but rather to the inner layer 6. A combination of
these two processes, in which, for example, the inner layer 6 can
be placed onto the cylinder head 1 in the form of a ring and then
the outer layer 7 can be joined to the inner layer 6 in powder
form, is also possible.
[0042] FIG. 4 provides a highly diagrammatic representation of a
further possible way of carrying out the process for producing the
valve seat 5. In this case, there are two laser or electron beams 9
and 9', of which the first laser beam 9 is responsible for joining
the inner layer 6 to the cylinder head 1, and the second laser beam
9' is responsible for joining the outer layer 7 to the inner layer
6. Since the molten material 10 of the inner layer 6 has solidified
as soon as the laser beam 9 has moved just a few millimeters away
in the direction of arrow A, the second laser beam 9' can track the
first laser beam 9 at a relatively short distance, so that the
entire process for producing the valve seat 5 takes up only
slightly more time than if the valve seat 5 were to consist of just
one layer. This process can be carried out in an advantageous way
if the outer layer 7 is applied in powder form, it being possible
for the material for the inner layer 6 to be applied in a manner as
described above.
* * * * *