AN ARRANGEMENT OF COATINGS FOR A TWO-STROKE ENGINE PISTON

UN ARRANGEMENT DE REVETEMENTS DESTINE A UN PISTON DE MOTEUR A DEUX TEMPS

English Abstract

A piston for a two-stroke internal combustion engine, comprising at least a
piston crown and a skirt,
whereas one or more arrangements of coatings is applied on the piston crown,
whereas for each
arrangement of coatings, a thermal barrier coating (1BC) is applied on a
metallic coating, whereas
the metallic coating is larger than the TBC, whereas the TBC could be made
with one or more
layers, where each layer could be or not of the same material, whereas the
metallic coating could be
made with one or more layers, where each layer could be or not of the same
material, whereas many
different areas could be possible for each layer of each coating, including
the method of fabrication
and the use thereof.

French Abstract

Un piston pour un moteur à combustion interne à deux temps comprend au moins une tête et une jupe de piston, une ou plusieurs configurations de revêtements étant appliquées sur la tête de piston. Pour chaque configuration de revêtements, un revêtement de barrière thermique (TBC) est appliqué sur un revêtement métallique, lequel est plus grand que le TBC, qui peut être composé dune ou plusieurs couches, chaque couche pouvant être faite du même matériau ou non. Le revêtement métallique peut être fait dune ou plusieurs couches, chaque couche pouvant être faite du même matériau ou non. De nombreuses zones différentes peuvent être possibles pour chaque couche du revêtement.

Claims

What is claimed is
1. A piston for a two-stroke internal combustion engine, comprising at least a
piston crown and
a skirt, whereas
one or more arrangements of coatings is applied on the piston crown, whereas
for
each arrangement of coatings
a thermal barrier coating (TBC) is applied on a metallic coating,
whereas the metallic coating is larger than the TBC,
whereas the TBC could be made with one or more layers, where each layer could
be
or not of the same material,
whereas the metallic coating could be made with one or more layers, where each
layer could be or not of the same material,
whereas many different areas could be possible for each layer of each coating.
2. The piston of claim 1, whereas said thermal barrier coating is made of one
or a combination
of the following materials: oxide ceramics, ceramic abradables, mullite.
3. The piston of claim 1, whereas said metallic coating is made of one or a
combination of the
following materials: NiCr, NiAl, NiCrAl, NiCrAlY, NiCrAlMo.
4. The piston of claim 1, whereas said thermal barrier coating is made of
zirconia-yttria.
5. The piston of claim 1, whereas said thermal barrier coating is made of
zirconia-magnesia.
6. The piston of claim 1, whereas the skirt of the piston is coated by a
molybdenum coating.
7. A method for fabricating a piston for a two-stroke internal combustion
engine, said piston
comprising at least a piston crown and a skirt, whereas
one or more arrangements of coatings is applied on the piston crown, whereas
for
each arrangement of coatings
a thermal banier coating (TBC) is applied on a metallic coating,
whereas the metallic coating is larger than the TBC,
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Date Recue/Date Received 2024-04-15

whereas the TBC could be made with one or more layers, where each layer could
be
or not of the same material,
whereas the metallic coating could be made with one or more layers, where each
layer could be or not of the same material,
whereas many different areas could be possible for each layer of each coating,
whereas said thermal barrier coating is deposited by a process chosen from a
group
comprising plasma spray, High Velocity Oxy-Fuel (H.V.O.F.), High Velocity Air
Fuel (H.V.A.F.) and flame spray;
said metallic coating is deposited by a process chosen from a group comprising
plasma spray, High Velocity Oxy-Fuel (H.V.O.F.), High Velocity Air Fuel
(H.V.A.F.), electric arc spray, flame spray and electroplating.
8. The use of a piston in an internal combustion engine, said piston
comprising at least a piston
crown and a skirt, whereas
one or more arrangements of coatings is applied on the piston crown, whereas
for
each arrangement of coatings
a thellnal barrier coating (TBC) is applied on a metallic coating,
whereas the metallic coating is larger than the TBC,
whereas the TBC could be made with one or more layers, where each layer could
be
or not of the same material,
whereas the metallic coating could be made with one or more layers, where each
layer could be or not of the same material,
whereas many different areas could be possible for each layer of each coating.
9. The use of a piston of claim 8, whereas said thermal banier coating is made
of one or a
combination of the following materials: oxide ceramics, ceramic abradables,
mullite.
10. The use of a piston of claim 8, whereas said metallic coating is made of
one or a combination
of the following materials: NiCr, NiAl, NiCrAl, NiCrAlY, NiCrAlMo.
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Date Recue/Date Received 2024-04-15

11. The use of a piston of claim 8, whereas said thermal banier coating is
made of zirconia-
yttlia.
12. The use of a piston of claim 8, whereas said thermal banier coating is
made of zirconia-
magnesia.
13. The use of a piston of claim 8, whereas the skirt of the piston is coated
by a molybdenum
coating.
14. The use of a piston of claim 8 where the piston has been fabricated by the
following steps
one or more arrangements of coatings is applied on the piston crown, whereas
for
each arrangement of coatings
a thermal barrier coating (TBC) is applied on a metallic coating,
whereas the metallic coating is larger than the TBC,
whereas the '1BC could be made with one or more layers, where each layer could
be
or not of the same material,
whereas the metallic coating could be made with one or more layers, where each
layer could be or not of the same material,
whereas many different areas could be possible for each layer of each coating,
whereas said thermal barrier coating is deposited by a process chosen from a
group
comprising plasma spray, High Velocity Oxy-Fuel (H.V.O.F.), High Velocity Air
Fuel (H.V.A.F.) and flame spray;
said metallic coating is deposited by a process chosen from a group comprising
plasma spray, High Velocity Oxy-Fuel (H.V.O.F.), High Velocity Air Fuel
(H.V.A.F.), electric arc spray, flame spray and electroplating.
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Date Recue/Date Received 2024-04-15

Description

Title
An arrangement of coatings for a two-stroke engine piston
Field
[0001] Herein is described an arrangement of coatings to alter the properties
of the surface of a two-
stroke piston crown. This relates to a method to obtain a two-stroke piston
which has the capacity to
operate within a two-stroke engine's combustion chamber whereas conditions are
created to reduce
emissions, and further relates to these pistons themselves and their use.
Background
[0002] In a two-stroke engine such as may be commonly found in snowmobiles,
chain saws, off-
road motorcycles, or other machines which use two-stroke engines, the piston
is submitted to an
intense heat. The piston is sliding in a cylinder which has many holes and/or
ports which reduce the
area in contact with the piston. These areas which are not in contact with the
piston cannot
contribute to give a thermal conductivity between the piston and the cylinder.
The piston is also
exposed to a combustion process for each crankshaft rotation. A rich air/fuel
mixture contributes to
avoid the risk of overheating of the piston but it is a handicap to produce
low emissions.
[0003] The risk of overheating for a two-stroke piston operating within an
engine's combustion
chamber is influenced by the air-fuel ratio. The air-fuel ratio is the given
quantity of fuel mixed in a
given quantity of air, which results the air-fuel mixture. In a two-stroke
engine, a too lean air/fuel
mixture could results in internal engine's parts destruction. In such
conditions, what we frequently
see is piston seizure. The temperature of the piston influences its thermal
expansion and the piston's
metal also has a melting point. If the piston becomes too hot, it could melt
and/or the piston to
cylinder clearances could become too tight, which may results in a piston
seizure.
[0004] The stoichiometric ratio is the perfect air-fuel ratio to obtain a more
complete combustion,
but also a very hot combustion. The emissions are influenced in part by the
air/fuel ratio. Modifying
a piston to improve its capacity to resist against heat will help it to accept
hotter combustion. This
obtain piston could give an ideal breeding ground for a cleaner air-fuel
mixture.
[0005] It is known that a piston crown could be coated with a thermal barrier
to offer a good
resistance against heat. It is also known that a thermal barrier could alter
exhaust emissions.
Furthermore, if less heat is removed by the internal surfaces, more heat will
stay trapped in the
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combustion chamber and produce more expanded gases, which results in more
energy to push the
piston during the power stroke.
[0006] There is therefore a need to overcome the above-mentioned shortcomings
of existing two-
stroke engine pistons, and more specifically to obtain a piston crown with
crown surface
characteristics which contribute to create an environment to reduce emissions.
Summary
[0007] Herein is described a piston for a two-stroke internal combustion
engine, comprising at least
a piston crown and a skirt, whereas a metallic coating covers a first portion
of the piston crown's
surface, a thermal barrier coating covers a second portion of the piston
crown's surface, whereas
said second portion of the piston crown's surface has a smaller area than said
first portion of the
piston crown's surface, whereas said thermal barrier coating partially covers
said metallic coating,
said second portion overlapping completely over said first portion.
[0008] In some examples, said thermal barrier coating is made of one or a
combination of the
following materials: oxide ceramics, ceramic abradables, mullite. In some
examples, said metallic
coating is made of one or a combination of the following materials: NiCr,
NiAl, NiCrAl, NiCrAlY,
NiCrAlMo. In some examples, said thermal barrier coating is made of zirconia-
yttria. In some
examples, said thermal barrier coating is made of zirconia-magnesia. In some
examples, the skirt of
the piston is coated by a molybdenum coating.
[0009] This also relates to methods for fabricating such a piston for a two-
stroke internal
combustion engine, said piston comprising at least a piston crown and a skirt,
whereas a metallic
coating covers a first portion of the piston crown's surface, a thermal
barrier coating covers a second
portion of the piston crown's surface, whereas said second portion of the
piston crown's surface has
a smaller area than said first portion of the piston crown's surface, whereas
said thermal barrier
coating partially covers said metallic coating, said second portion
overlapping completely over said
first portion. In some examples, said first portion of the piston whereas said
thermal barrier coating
is deposited by a process chosen from a group comprising plasma spray, High
Velocity Oxy-Fuel
(H.V.O.F.), High Velocity Air Fuel (H.V.A.F.), electric arc spray and flame
spray. In some
examples, said metallic coating is deposited by a process chosen from a group
comprising plasma
spray, High Velocity Oxy-Fuel (H.V.O.F.), High Velocity Air Fuel (H.V.A.F.),
electric arc spray,
flame spray and electroplating.
[0010] This also relates to the use of such a piston in a piston internal
combustion engine.
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[0011] Other and further aspects and advantages of the present arrangement of
coatings for a two-
stroke engine piston will be obvious upon an understanding of the illustrative
embodiments about to
be described or will be indicated in the appended claims, and various
advantages not referred to
herein will occur to one skilled in the art upon employment of the arrangement
of coatings for a
two-stroke engine piston in practice.
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Brief Description of the Drawings
[0012] The above and other aspects, features and advantages of the arrangement
of coatings for a
two-stroke engine piston will become more readily apparent from the following
description,
= reference being made to the accompanying drawings in which:
[0013] Figure 1 is the illustration of a top view of a piston top (crown) and
a sectional view of a
part of the same piston top end, incorporating an arrangement of coatings in
accordance to one
example of the technology described herein and in accordance to one example of
a piston.
Detailed Description
[0014] In one example, there is provided a novel arrangement of coatings for a
two-stroke engine
piston as described hereinafter. Although the arrangement of coatings for a
two-stroke engine piston
is described in terms of specific illustrative embodiments, it is to be
understood that the
embodiments described herein are by way of example only and that the scope of
the arrangement of
coatings for a two-stroke engine piston is not intended to be limited thereby.
[0015] Figure 1 is the illustration of a top view of a piston top (crown) and
a sectional view of a part
of the same piston top end, incorporating an arrangement of coatings in
accordance to one example
of the technology described herein and in accordance to one example of a
piston. The broken line on
the sectional view shows that only the upper end is shown. An arrangement of
coatings is shown,
whereas the surface areas of each coating could vary. Number 101 shows a
thermal barrier coating
(TBC). Number 102 shows a metallic coating underneath the TBC which overshoots
around the
TBC, therefore covering a larger portion of the piston crown. Number 103 shows
a non-coated
surface of the piston crown. It is understood that if there is several layers
which overshoot
underneath the layer applied over it, it is possible to get more than only one
layer which overshoot,
whereas each layer could be or not of the same metal or material. The TBC
could also be made with
= multiple overshooting layers of different materials, so it is understood
that many different areas
could be possible.
[0016] A thermal barrier coating (TBC) ¨number 101 of figure 1- is applied on
a metallic coating ¨
number 102 of figure 1-. The TBC could be made with one or more layers and
materials. The TBC
could be, or not, in a recess. The area and thickness of the TBC could vary,
but its area covers only a
portion of the piston crown. Varying the thickness and the area of the TBC
influence the surface's
thermal conductivity and/or the protection against heat, so for a given
cooling, it may influence the
piston temperature. All heat unabsorbed by the TBC may remain totally or in
part in the combustion
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chamber, it may be considered in part to set the temperature range within the
combustion chamber.
Number 102 of figure 1 shows the metallic coating. This metallic coating has a
lower
thermal conductivity than the piston's metal. The area of this metallic
coating could vary and it
could be recessed, or not, in the piston's crown. The premier function of this
metallic coating could
be to create a bond coat for the TBC, but this metallic coating also
overshoots the TBC. The TBC ¨
number 101 of figure 1- is illustrated as a circle or a disc, and the metallic
coating ¨number 102 of
figure 1- appears as a ring or a band or a loop, but it is possible to change
the geometrical forms of
each coating. It could also be possible to have more than one arrangement on
the same piston to
accommodate engines which have more than one spark plug. Number 103 of figure
1 shows the area
preferably left uncoated. This area varies depending on where the metallic
coating ends. The goal of
this area preferably left uncoated is to keep the original surface's
characteristics and behaviour in
this region.
[0017] Using a coating on a piston crown may alter the crown surface behaviour
while protects this
said piston. The surface behaviour may play a role in evaporation of the fuel,
which may alter the
hydrocarbon emission level. This behaviour is influenced by areas created by
the coatings whereas
the coating areas and coatings are chosen to reach a more complete combustion.
A lower
hydrocarbon emission level may indicate that the efficiency of the engine is
higher. A higher
efficiency could result in a better fuel economy and/or more power.
[0018] An optional coating could be applied on the said piston skirt. A recess
could be made in the
said piston skirt, which will be filled by the coating. This optional coating
could be pure
molybdenum, which is known to provide a good skirt bearing properties. It's
also known that
molybdenum coatings provide a tough and hard surface with excellent sliding
properties. It is
understood that the thermal conductivity of molybdenum could be lower than the
piston's metal, so
its effect on heat exchange has to be considered if applied.
[0019] The said thermal barrier is made of one or a combination of the
following materials: oxide
ceramics, ceramic abradables, mullite.
[0020] The metallic coating is made of one or a combination of the following
materials: NiCr, NiAl,
NiCrAl, NiCrAlY, NiCrAlMo, whereas Al is aluminum, Cr is chromium, Mo is
molybdenum, Ni is
nickel and Y is yttrium.
[0021] The best method to carry the arrangement of coatings related hereby is
done by the
application of coatings with a thermal spray process, which could be one a
combination of the
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following processes: plasma spray, High Velocity Oxy-Fuel (H.V.O.F.), High
Velocity Air-Fuel
(H.V.A.F.), electric arc spray, flame spray or electroplating.
[0022] Hereby, the arrangement of coatings could be done with existing
coatings and coatings
processes. There is not a coating process apparatus or unique coating process
demonstration; the
described coatings and coating processes cited hereby are only to illustrate a
method to obtain
coatings.
[0023] While illustrative and presently preferred embodiments of the
arrangement of coatings for a
two-stroke engine piston have been described in detail hereinabove, it is to
be understood that the
inventive concepts may be otherwise variously embodied and employed and that
the appended
claims are intended to be construed to include such variations except insofar
as limited by the prior
art.
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