Note: Descriptions are shown in the official language in which they were submitted.
CA 02302348 2000-02-25
Exhaust valve for internal combustion engines
The invention concerns an exhaust valve for internal combustion engines,
comprising a cylindrical valve stem with a longitudinal cooling duct with an
internal wall surface, and a circular, substantially disc-shaped head securely
connected to the valve stem, the head (3) having at least one cooling duct
which extends from the bottom of the valve stem's cooling duct to an outlet
on the head's surface, in order to conduct coolant through the valve stem,
through the head to exhaust gases from the engine.
In Norwegian patent application no. 972301 a valve of this kind is described,
where there extends through the valve stem and the valve head a passage
which leads into a valve surface portion which communicates with the
downstream side of the valve.
In order to achieve high efficiency in an engine the valve must be capable of
withstanding high temperatures, thus entailing the choice of a valve material
which can withstand high temperatures. In addition, it is advantageous to
cool the valve. With the above-mentioned valve, satisfactory cooling of the
valve head is obtained, but the cooling of the valve stem is not satisfactory.
DE-A-32 23 920 describes an exhaust valve for internal combustion engines
comprising a cylindrical valve stem with a longitudinal cooling duct. The
valve comprises a circular, substantially disc-shaped head securely connected
to the valve stem. Cooling ducts extend from the bottom of the valve stem's
cooling duct to an outlet on the head's surface in order to conduct coolant
through the valve stem, through the head to exhaust gases from the engine. In
the valve stem's cooling duct there is inserted a cross section reducing
insert.
An object of the invention is to provide a valve of the type mentioned in the
introduction where the cooling of the valve stem is better than in the case of
known valves.
The object is achieved with a valve of the type mentioned in the introduction,
characterized by the features which are indicated in the claims.
The valve will now be described in more detail with reference to the drawing,
in which:
fig. 1 is a longitudinal section through a valve according to the invention.
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Fig. 2 is a cross section along the intersecting line II-II in fig. 1.
Fig. 3 is an enlarged cross section of a valve insert for use in a valve
according to the invention.
Fig. 4 is an enlarged longitudinal section through a valve head for a valve
according to the invention.
The same reference numerals are used for corresponding parts or portions of
the different figures.
Fig. 1 illustrates an exhaust valve for internal combustion engines,
comprising a cylindrical valve stem 1, and a circular, substantially disc-
shaped head 3 securely connected to the valve stem. When the valve is used
in a combustion engine, the head 3 will be brought into alternating contact
with a not shown valve seat, and heated by passing exhaust gases. Depending
on the engine's design, the same exhaust gases will also heat the valve stem
to a greater or lesser degree.
The valve stem 1 has a longitudinal cooling duct 2, which is connected at its
bottom 5 to cooling ducts 4 in the head 3. The cooling ducts 4 lead to an
outlet 6 on the head's surface 7. When the engine is running, coolant,
generally air, is passed through the cooling ducts in the valve stem 1 and the
head 3 to the outlets 6, where the coolant is mixed with the engine's exhaust
gases. By this means both the valve stem and the head are cooled.
According to the invention there is inserted in the valve stem's cooling duct
2
a cross section-reducing insert 8. The insert causes the coolant to flow at a
higher rate along the insert, which results in better heat transfer from the
valve stem 1 to the coolant in the area in which the insert is located. This
improved heat transfer is assumed to be due to the fact that by flowing at a
high rate the coolant breaks down a greater portion of the boundary layer
along the cooling duct's wall surface 12 than it does at a low rate.
It is obvious per se that a high rate of flow in the coolant can also be
obtained by increasing the amount of coolant supplied, but this will entail
increasing the dimensions of the coolant's supply pipe and the device,
generally a compressor, which supplies the coolant. An increase in the
amount of coolant would also necessitate an increase in the dimensions of the
engine's outlet pipe. Such an size increase is undesirable. It is, of course,
also
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possible to obtain an increase in the rate of flow of the coolant by reducing
the cross sectional area of the valve stem's cooling duct 2, but this will
simultaneously reduce the area of the cooling duct's wall surface 12, thus
reducing the heat transfer from the valve stem 1 to the coolant.
Consequently, it is desirable to have a cooling duct with a large cross
sectional area.
In a preferred embodiment, see fig. 1, the insert 8 is located in such a
manner
that it extends from or approximately from the bottom 5 of the valve stem's
cooling duct and along the valve stem 1 for a length 11 which corresponds to
at least half of the valve stem's length 12. Improved cooling of the valve
stem
1 is thereby achieved in an area where it is most exposed to the hot exhaust
gases.
In a further preferred embodiment the insert 8 is located in such a manner
that it extends from or approximately from the bottom 5 of the valve stem's
cooling duct and along the valve stem 1 for substantially the entire length 12
of the valve stem. Improved cooling of the whole valve stem 1 is thereby
achieved. _
Fig. 2, which is a cross section through the cooling duct 2 and the insert 8,
illustrates a further preferred embodiment where the insert 8 is composed of
a longitudinally centrally located, solid central section 9 with longitudinal,
outwardly projecting ribs 10 along the circumference, thus providing
between the outwardly projecting ribs 10 longitudinal grooves 11 for the
coolant. This causes the coolant to be passed along the cooling duct's wall
surface 12, resulting in a high degree of heat transfer from the valve stem 1
to the coolant.
In a further preferred embodiment, see fig. 2, the valve stem's cooling duct 2
has a circular or polygonal cross section, while at the same time the insert's
central section 9 has a circular or polygonal cross section, and is located in
the middle of the cooling duct 2. The outwardly projecting ribs 10 extend
radially from the central section 9 to the cooling duct's wall surface 12. A
uniform distribution is thereby obtained of the grooves 11 along the cooling
duct's wall surface 12, resulting in a uniform heat transfer from the valve
stem 1 to the coolant.
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Fig. 3 illustrates a further preferred embodiment where the number of
outwardly projecting ribs 10 amounts to at least 6. A uniform distribution is
thereby obtained of coolant along the cooling duct's wall surface 12, thus
ensuring a uniform heat transfer from the valve stem 1 to the coolant.
In a further preferred embodiment, see fig. 3, the outwardly projecting ribs
have a constant thickness t from the central section 9 to the cooling duct's
wall surface 12, i.e. over its entire area, indicated by rl. This gives the
insert
adequate strength, while at the same time the grooves 11 obtain a trapezoidal
cross section with the largest side of the trapeze located against the cooling
10 duct's wall surface 12, thus ensuring satisfactory heat transfer from the
valve
stem 1 to the coolant.
In a further preferred embodiment, see fig. 3,, the outwardly projecting ribs
10 have a radial extension rl which is approximately equal to the radius r2 of
the central section 9. The result of this is that the grooves' 11 trapezoidal
cross section obtains a shape which provides a reasonable compromise
between the desire for high rate of flow for the coolant, low flow resistance
in the cooling duct 2 and good heat transf~,r from the valve stem 1 to the
coolant.
Fig. 4; which is an enlarged longitudinal section through the valve head,
illustrates a further preferred embodiment where the insert 8 is passed right
down to the bottom 5 of the valve stem's cooling duct 2, and a portion 13 of
the insert which is located at the bottom 5 of the valve stem's cooling duct
is
tapered or graduated in order to permit passage of coolant to the cooling
ducts 4 in the valve head 3. This provides an advantageous attachment of the
insert 8 in the cooling duct 2, since the insert can be passed right down to
the
bottom of the cooling duct, to abut against it. The other end of the insert
may
be attached to the valve stem's upper portion in various ways, for example by
welding or insertion of an internal plug in the cooling duct 2. Such means of
attachment are prior art and will not be discussed further.
In a further preferred embodiment the insert 8 is inserted into the valve
stem's cooling duct 2 with a light force fit. A simple installation of the
insert
is thereby achieved, while at the same time providing a valve stem in which
the insert is at rest in the cooling duct and follows its movement without any
play, which could cause undesirable wear on the insert and the cooling duct
and flow problems for the coolant.
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The invention has been described above with reference to a specific
embodiment. It is obvious, however, that variants of the invention may be
designed within the scope of the claims, for example associated with the
number of ribs, since it will be possible to replace the illustrated number of
ribs with a larger or smaller number, which will lead to slight alterations in
the cooling and flow conditions, thus enabling the invention to be adapted to
the engine concerned.
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