PISTON FOR AN ALCO SERIES 251 DIESEL ENGINE

PISTON POUR MOTEUR DIESEL ALCO, DE SERIE 251

English Abstract

IMPROVED PISTON FOR AN ALCO? SERIES 251
DIESEL ENGINE
ABSTRACT OF THE DISCLOSURE
A piston cap for a medium size diesel engine is described
wherein a "bowl" shaped recess is formed in the top surface thereof.
The design is energy efficient in that considerable saving in fuel is
accomplished by the new bowl shape.

Claims

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The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A piston cap for a composite piston of a medium size
internal combustion diesel engine, said piston being of the shape of
a shallow cylinder, having a diameter of about 9 inches and a
sidewall depth of about 3.5 inches, said piston cap having a top
surface composed a bowl shaped depression located symmetrically
with the centre of the piston cap surrounded by a narrow, flat annual
outer surface extending from said depression to the sidewall of said
piston cap, a recess formed in the bottom surface of the piston cap
extending upwardly toward the top surface so that said piston cap is
essentially hollow, the upper surface of said recess which is located
somewhat below said top surface and having a pair of circular
concentric grooves formed therein, an outer groove having a
complex shape and rising to a distance of about 2.8 inches above
the bottom surface of said cap and an inner groove spaced from the
outer groove by a narrow annular shaped flat land, said inner groove
rising about 2.7 inches above the bottom surface of said cap and a
shaft formed integrally in the upper surface of the centre of said
recess which extends downwardly a predetermined distance from
said upper surface.
2. A piston cap as claimed in claim 1 wherein said
piston is composed of steel, and has three piston ring grooves in the
lower portion of the sidewall, said bowl having a maximum diameter
of about 7.75 inches and extends to a maximum depth of 0.9 inches
below the narrow flat annular outer surface, said narrow flat surface
having four valve pocket recesses in spaced relationship located
therein.
3. A steel piston cap for a medium size diesel engine,
said piston cap having a crown and skirt integrally formed into the
shape of a shallow hollow closed cylinder having nominal
dimensions of about 9.0 inches in diameter, and about 3.5 inches in

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height, the crown having a continuous closed surface which has a
bowl shaped recess extending substantially across a major portion of
the top surface of said crown, and being surrounded by a narrow flat
annular surface at the exterior thereof, said bowl having a surface
which extends downwardly at a shallow angle to a maximum depth of
about 0.9 inches below the surface of said flat annular outer surface
with the surface rising toward the centre to a point just below the
height of said outer annular surface, the outer annular surface
having of at least two valve pockets formed therein equidistantly
spaced in a symmetrical fashion, the skirt of said cap having three
grooves formed therein for receiving suitable piston rings, the interior
of piston cap skirt being formed into a cavity of a predetermined
complex shape by surfaces of revolution, and having a central shaft
integrally formed in the top surface of said cavity and extending
downwardly a predetermined distance below the lower surface of
said skirt.
4. The piston cap of claim 1, wherein the diameter of
said bowl is about 7.75 inches and the upper surface of said cavity
comprises a first and second spaced apart annular shaped
concentric grooves, the first groove being at the exterior of said
upper surface and having a complex predetermined shape and being
separated from the second interior groove by a first narrow flat land,
a second land formed on the inside of said second groove, said
central shaft being surrounded by said second land.
5. The piston cap of claim 4 wherein the first and
second grooves rise about 2.8" and about 2.7" respectively above
the lower surface of said skirt.
6. For use in an internal combustion diesel engine, a
steel piston cap which forms part of a composite piston assembly for
reciprocation in said engine, said piston cap comprising:
a shallow, substantially hollow cylinder of diameter of
about 9 inches and a height of about 3.5 inches having a top

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surface, and a lower surface, and three piston ring grooves in the
cylindraceous side wall near said lower surface, said top surface
having a narrow flat annular surface at the exterior thereof, and a
shallow bowl extending inwardly and downwardly to a maximum
depth of about 0.9 inches below said flat annular surface and rising
slightly into a peak at the center of said top surface, a recess
extending upwardly from said lower surface such that the lower
portion of said cap is hollow, said recess extending upwardly a
predetermined distance toward said top surface, and being formed of
surfaces of revolution so that said recess is essentially
cylindraceous in nature, such that the upper surface of said recess is
formed by a pair of spaced apart concentric annular grooves, the
outer groove having a complex shape such that the groove extends
outwardly and upwardly toward the top surface of said piston cap
said second groove being spaced inwardly of said first groove, and
separated by a first flat annular shaped land, said second groove
extending inwardly and upwardly toward the top surface of said
piston cap, the inward wall of said second groove being adjacent a
second annular shaped land, the surface of which is slightly above
said first land, said second land surrounding a shaft which extends
downwardly from the center of the recess to a point a predetermined
distance below the lower surface of said piston cap.
7. A piston cap as claimed in claim 6 wherein the
diameter of the bowl is about 7.75 inches and the outer groove and
second groove rise upwardly from the lower surface of said cap to a
maximum distance of about 2.8 and 2.7 inches respectively from the
lower surface.
8. A piston cap as claimed in claim 9 wherein the top
annular flat surface is interrupted by at least two valve pockets,
symmetrically spaced therein.
9. A piston cap for a composite piston of a medium size
diesel internal combustion engine, said piston cap being essentially

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of a hollow nature having a nominal diameter of 9 inches and a
depth of about 3.5 inches between said top surface and the bottom
of said piston cap, said cap having an integral skirt formed in the
lower portion of said cap, said skirt having three piston ring receiving
grooves formed therein, the cap having a cavity formed of surfaces
of revolution such that a mating surface of a predetermined shape is
formed at the top of the cavity, said mating surface being suitable for
mating with a suitable piston body said mating surface having a pair
of concentric grooves formed therein, an outer groove having a
complex shape and rising to a distance of about 2.8 inches above
the lower surface of the skirt, a second groove spaced inwardly of
said first groove having a diameter substantially less than said outer
groove and rising above the lower surface of said skirt by about 2.7
inches and a shaft formed integrally in the center of said lower
surface, said shaft extending slightly below the lower surface of said
skirt, and having a threaded portion formed thereon,
the top surface of said piston cap having an outer flat
surface of approximately about 0.6 inches, width said surface being
interrupted by at least two valve pockets formed therein,
said top surface having a shallow bowl formed in a
concave manner extending downwardly from said outer flat surface
at a shallow angle to a depth of about 0.9 inches below said top
surface and then sloping upwardly to form an apex at the centre of
said top surface to form a shallow apex therein, said apex rising to a
height slightly below said outer flat top surface.
10. A piston cap as claimed in claim 9 wherein said
grooves in said mating surface are separated by a flat annular land.
11. A piston cap as claimed in claim 10 in which the
diameter of said bowl is about 7.75 inches.

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12. For use in an internal combustion diesel engine, a
steel piston cap which is part of a composite piston assembly for
reciprocating movement in the engine, said piston cap comprising:
a shallow cylinder having a central axis and having a
diameter of about 9 inches and a depth of about 3.5 inches, said
piston cap having a top surface comprising a shallow bowl shaped
depression which is concentric with said axis, said depression
extending downwardly and inwardly from a narrow flat annular
surface which extends from the periphery of the top surface of said
piston cap to said depression, said annular surface having at least
two valve pockets formed therein in a spaced symmetrical manner,
the lower surface having a recess formed therein, said recess being
formed from surfaces of revolution such that said recess extends
upwardly a predetermined distance below said top surface such that
the lower portion of the cap is hollow, said lower surface having a
shaft extending downwardly therefrom for fastening said cap into
said piston body
13. A piston cap as claimed in claim 12 in which said
flat annular surface has a width of about 0.6 inches and said surface
of revolution comprise a pair of spaced apart grooves concentric with
said central axis, and a pair of annular shaped flat lands in
juxtaposition with the grooves and spaced inwardly therefrom.

Description

20861 33
GECAN31 02
IMPROVED PISTON FOR AN ALCo~9 SERIES 251
DIESEL ENGINE
This invention is directed to the cap or crown of a
piston for a medium size diesel engine. ~;
The diesel engine is characterized by the fact that the
fuel air mixture is ignited by heat produced during the compression
of the air in the cylinder. The air of the cylinder is compressed to a
predetermined pressure to ensure that the required temperature for
fuel ignition is reached before the piston has reached top dead
centre so that when the fuel is begun to be injected into the hot air
combustion will take place. Combustion begins before the piston
reaches top dead centre and the pressure in the cylinder continues
to increase until the piston reaches top dead centre where upon the
combustion continues for a predetermined period of time with the
maximum cylinder pressure occurring shortly after top dead centre. ~ - ;
The piston is driven to the bottom of the cylinder (where the exhaust
stroke begins) and it is only during the power stroke that useful work
is accomplished by the burning fuel.
In the past, this particular diesel cycle type of operation
has been employed in en~ines all over the world that are
characterized by long life in which the operation tends to be more
efflcient than the gasoline powered internal combustion engine.

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Recently, environmental considerations have been
responsible for careful study of the modern diesel operation in order
reduce the amount of fuel consumed in the engine as well as to
reduce the harmful emissions of exhaust gases which are delivered
to the atmosphere. The design of the engine and in particular, the
design of the piston for a modern diesel can be extremely critical.
The designer must be careful to ensure that the piston will withstand
the maximum cylinder pressures which will be encountered by the
piston and caution must be taken to ensure that the fuel air mixture
is burned in the most efficient manner possible to decrease the
amount of pollutants which are produced during the combustion
process and subsequently delivered to the atmosphere. At the same
time, the peak pressures in the cylinder imposes load on the piston .
which can place a severe burden on the lubricating medium and in
the long term damage both piston and bearings associated
therewith.
Thus the piston in a modern diesel must be as light as
possible in order to reduce the mass of material which is
reciprocated for each stroke of the engine. The piston must also
have sufficient strength to withstand the severe loads placed upon it
during combustion and the piston must also maintain a temperature
profile which will give the "best" combustion of the fuel air mixture for
reasons of efficiency and environmental considerations. It is to this
end that the piston of the present invention has been developed.
Improved engine efficiency has been a primary goal for
diesel engine designers and while the task presents a significant
challenge to the designer of a "new" engine, the task has proven to
be extremely difficult in instances where the design parameters are
largely already defined, such as would be the case of older, proven
engines where it is desired to "rebuild the engine" with components
that increase engine efficiency, reduce exhaust pollutants and do not
jeopardize engine life.
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GECAN31 02
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It is with this object in view that this invention relates.
One such application is the design of a replacement piston for an
engine which is fairly large, and which engine has a proven service
record, and the specific engine to which this relates is the ALCO
Model 251 Series '~'-type diesel engine previously manufactured
under license by Bombardier Inc. in Quebec, Canada and now
manufactured by General Electric Canada Inc. in Quebec, Canada.
The constraints on the designer of the piston are such that the same
components be used in associa~ion with the redesigned piston, ie ~ ~:
the block, crankshaft and connecting rods and bearings used
previous to the "new" piston design may be successfully utilized in
the modified ALCO 251 engine, and yet be able to realize the
desired improvement in operation.
SUMMARY OF THE INVENTION
According to this invention, there is provided a
replacement piston the ALCO Model 251 diesel engine which will be
of a two piece construction. A crown or cap (which is the subject of
this invention) is attached to a body such that the two parts form an :
integral piston which will provide more efficient engine operation
than the piston of the prior art ALCO 251 diesel engines.
A BRIEF DESCRIPTION OF THE DRAWINGS ~:
The following is a more detailed description of some of
the embodiments of the invention by way of example.
Reference is made to the accompanying drawings in
which:
Figure 1 is a view of the composite piston assembly.
Figure 2 is a sectional view of the piston cap of the prior
art, showing the body sleeve in phantom;
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GECAN31 02
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Figure 3 is a top perspective view of the cap of the
piston which is the subject of this invention.
Figure 4 is a sectional view piston cap of this invention.
Figure 1 is shown to illustrate the general nature of the
composite piston assembly to which this invention relates.
Figure 2 illustrates a piston cap or crown of the prior
design for the ALCO 251 V16 engine. It will be appreciated that the
piston cap shown is the upper part of the piston assembly shown in
Figure 1 which acts as a seal in the cylinder, however the lower part
of the piston assembly, ie the cylindraceous sleeve or body which
houses a connecting rod pin will not be shown further or described in
detail herein as it forms no part of this invention. The piston cap
shown in Figures 2 and 3 has a nominal diameter of about 9" and a
height from the bottom surface to the top of the crown of about 3
1/2". The piston cap shown is composed of a steel alloy and is
provided with three grooves and adjacent lands for receiving piston
rings in the lower part of the skirt. These grooves are designated as
12, 14, and 16. The top of piston 10 has a flat annular surface 18
which is provided with four valve pockets 20, 22, 24 and 26.
The piston cap is provided with a depression or bowl 28
which is curved sharply downwardly at the surface 30 near the
exterior of the piston cap 10 to a point of maximum depression at 32
and the bowl rises at a shallow angle to a high point 34 at the center
of the bowl and cap. The point of maximum depression in this
instance will be about 1.1" below surface 18. The lower surface of
the crown is a complex shape formed by surfaces of revolution so
that it is essentially hollow. Near the exterior at the top of the lower
surface of the piston cap is a circular groove 36 which rises deeply
into the piston cap 10 at ever increasing diameter but at substantially
constant width. A second concentric groove 38 spaced somewhat
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GECAN3102
inwardly from groove 36 is formed at the lower surface of the piston
cap 10. Between grooves 36 and 38 is a first flat land 40 which will
be used to bear on the lower part of the piston assembly, such as
that shown in Figure 1. A second flat land 42 is also shown on a
lower surface of the piston cap 10 for support of the centre of the
piston bowl. Finally the lower surface of the piston cap is produced
into a single shaft 46 which is provided with a threaded end 48 so
that the piston cap 10 may be rotatably secured to the lower body of
the piston assembly.
The ALCO Model 251 piston cap 10 of the prior art has -
functioned satisfactorily in the transportation industry for many years I
in circumstances wherein the compression ratio to be withstood by
the piston 10 would be in the order of 11.5 to 1.
Referring now to Figures 3 and 4 a piston cap110 of the
present invention is shown having a nominal diameter of 9" and a
depth of about 3.5". Piston cap 110 has grooves 112, 114, and 116
for receiving piston rings at the lower part of the skirt. The top of
piston cap 110 has an annular flat surface 118 which is interrupted
by four valve pockets 120, 122, 124 and 126 formed therein. The
central top portion of the top surface has been provided with a
shallow bowl 128 which is shaped such that the bowl surface 130
slopes downwardly and inwardly in a shallow angle to reach its
maximum depth at 132, which is about 0.9" below surface 118. The
surface rises in a shallow angle to a shallow apex 134 at the centre
of the top surface of bowl 128. Apex 134 rises almost to the height
of annular surface 118.
The lower surface of the piston cap 110 is essentially
hollow and provided with an exterior groove 136 which rises in a
complex shape at an increasing diameter and variable width.
Concentrically located in the lower surface is a second groove 138
somewhat spaced from groove 136 and between which is a flat
annular shaped land 140 which is provided for support of the lower

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GECAN31 02
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surface on the lower body assembly of the composite piston (which
is not shown).
A second flat annular land 142 is formed in the interior
of the lower surface of the piston cap 110 adjacent to which is
developed a shaft 144, which projects downwardly from the centre of
the lower surface of the piston cap 110. Threaded portion 146 of
shaft 144 corresponds to threaded section 48 of piston cap 10 of
Figure 1.
The piston cap shown in Figures 3 and 4 is formed of a
steel alloy and has the same nominal outer diameter as the piston
cap shown in Figures 2 and 3. However, it will become immediately
apparent to the reader that the top surface of the piston cap 110 is
substantially different from the piston cap shown in Figure 1. The
bowl of 128 of ~he piston cap 110 is of a much shallower nature than
the bowl 28 of the piston cap 10. Both piston caps are intended for
operation in cylinders of the same nominal diameter and piston cap
110 provides an overall improvement in fuel efficiency of
approximately one and half percent (1.5%). In an engine which may
use as many as 12 or 16 cylinders of a nominal diameter of about 9"
this improvement is substantial over its operating life.
It is not entirely understood why the improvement
results, however, it is believed that the piston cap 110 leads to a
more complete combustion of the fuel-air mixture than does piston
cap 10.
The operation of a diesel engine is concerned with high
internal pressures in a combustion chamber during the compression
stroke, and a minimum amount of diesel fuel is injected into the hot
compressed air usually beginning just before top dead centre. In
most diesel engines, the fuel-air mixture is quite lean (in comparison
to a gasoline burning engine) and the reasons for incomplete
combustion of the burning fuel in a diesel are not well understood.

208613~
GECAN31 02
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The surface temperature of the parts of the piston and surrounding
cylinder walls will certainly have a bearing on the combustion
process within the cylinder. It will be seen that the bowl of the piston
cap 110 is much shallower than the bowl of piston cap 10 of the prior
art. The propagation of the flame front from the point of injection to
the piston as it moves away from top dead centre will no doubt be
substantially different for pistons caps 10 and 110.
The heat transfer of the surrounding cylinder is
expected to remain a constant regardless of whether the piston cap
110 or piston cap 10 is employed, however, the piston cap 10 will
have considerably different heat transfer properties through the head
of the piston than piston cap 11 0.
It is noted that the improvement in performance has
resulted largely from a deviation from the previous shape of the prior
art piston cap design. It is to be noted that there has been no
change in material from which the piston cap is fabricated and there
has been no attempt to alter the heat transmissibility of the piston
cap by the use of exotic coatings. Indeed, the piston cap has been
the only change that results in the improvement of engine fuel
efficiency. Note that the compression ratio has not been altered by
the new piston cap design.
.,
While the piston cap described in this invention has
been precisely described, minor changes will become apparent to
those skilled in the art.
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Representative Drawing