Note: Descriptions are shown in the official language in which they were submitted.
:~';7 56~
ENGINE VALVING AND PORTING
INCLUDING PISTON PORTING
The present invention has the general objective
of improvlng the performance, power output, flexibility,
repsonse and fuel economy of internal combustion engines,
especially two-cycle, variable speed, crankcase compression
engines as used, for example, on motorcyc:Les.
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A. Summary of the Invention : :
In considering some of the major general objectives
of the invention it is first noted that performance character-
istics of engines and especially of two-cycle engines are
determined in large part by the fuel intake capabilities,
which are in turn governed by the total cross-sectional area
of the intake passages, the duration of the intake, the :
portion of the cycle during which intake occurs, and the
~ responsiveness of the action of the intake valves. With
- these features in mind the present invention provides novel
arrangements and interrelationships of intake porting and
reed valves which mutually contribute to an increase in
the cross-sectional intake flow area for the fuel, to an ex-
tension of the portion of the cycle during which intake of
fuel occurs, and to increased responsiveness or sensitivity
of the intake valves.
According to one aspect o~ the present invention
there is provided a fuel intake system for a variable speed
~;l two cycle crankcase compression internal combustion engine
having a piston working in a cylinder with transfer porting :~
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extended between the compression and the intake sides of
the piston and with an intake port adaptec7 to communicate
with the cylinder at the intake s.ide of the piston when the
piston is positioned to block the transfer porting, and
having a fuel intake chamber for receiving fuel from a supply
source and for delivering the fuel to the intake port, a
:~ ported valve seat presented downstream of the fuel flow through
the intake chamber, a primary reed valve coverina said seat
and the valve port therein, said primary reed being supported
throughout substantially its entire periphery by said seat
and being sufficiently flexible to open the port under the
influence of decrease in pressure in the intake chamber incident
to high speed engine operation but being sufficiently rigid
to remain closed under the influence of decrease in pressure
in the intake chamber incident to low speed engine opexation, . .
said primary reed having a.secondary valve port therethrough
of smaller size than the por-t through the valve~seat, and
a secondary reed valve covering the secondary port and being
sufficiently flexible to open the secondary port under the
influence of decrease in pressure in the intake chamber incident
to engine operation either at said high speed or at said
low speed.
According to another aspect of the invention; a
variable speed two-cycle crankcase compression internal com-
25 bustion engine comprises a cylinder, a piston working inthe cylinder, a crankcase having a crank space below the
cylinder, a combustion chamber above the piston and a fuel :~
flow space immediately below the piston but above the crank
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space even in bottom dead center position of the piston,
fuel intake porting and passage means for supplying fuèl
to the engine and including fuel intake porting in the cy-
linder wall confronting the bottom dead center position of
the piston and being of sufficient exial climension to supply
fuel to said fuel space immediately below the piston through-
out at least a substantial part of the upward stroke of the
piston and further including a fuel tract approaching the
cylinder in the region of said intake porting above said
fuel space, a fuel transfer system having transfer porting
through the cy].inder wall above the piston in bottom dead
center position and comprising passage means provid.ing uninter-
rupted intercommunication between said transfer porting and
said tract, a passage providing uninterrupted intercommunica-
tion between said fuel flow space and said fuel tract through-
out the cycle of the engine, and reed valve means in said
fuel tract for controlling the fuel supply to the engine.
In another aspect such a variable speed, two-cycle,
crankcase compression, internal combustion engine comprises
a cylinder having a combustion chamber, a piston working
in the cylinder, a crankcase, port means in the cylinder
including intake porting providing communication with the .
crankcase, an intake tract in fluid communication with the .
j intake porting, valve means disposed in the intake tract ..
: 25 for controlling the flow of fluid therethrough, the port ~:~
means further including transfer porting communisating with
; the combustion chamber, and a transfer passage, one end of
which commun}cates with tbe transfer portiny and. the other
end of which communicates with the crankcase, below tlhe pis~on~ I
30 for conveying fluid from the crankcase to the transfer porting, ~ ~:
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the communication of the intake porting with the crankcase
being independent of the transfer passage, and a region of
the transfer passage intermediate its ends being in communica-
tion with the intake tract downstream of the valve means
and providing for flow of fluid from the intake tract directly
into the transfer passage.
'
In still another aspect there is provided a variable
speed, two-cycle, crankcase compression internal combustion
engine comprising a cylinder, a piston working in the cylinder,
a crankcase having a crank space below the cylinder, a combustion
chamber above the piston and a fuel flow space immediately
below the piston but above the crank space even in bottom
dead center position of the piston, fuel intake porting and
passage means for supplying fuel to the engine and including
fuel intake porting in the cylinder wall confronting the
bottom dead center position of the piston and being of sufficient
axial dimension to supply fuel to said fuel space immediately
below the piston throughout at least a substantial part of
the upward stroke of the piston and Eurther including a fuel
tract approaching the cylinder in the region of said intake
porting above said fuel space, ~ fuel transfer system having
transfer porting through the cylinder wall above the piston
in bottom dead center position and comprising passage means
providing uninterrupted in~ercommunication between ~aid trans
fer porting and said uel space, a fuel supply passage commu-
nicating with said transfer passage means independently of
said fuel space, and reed valve means controlling the flow
through said supply passage.
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Various of the features of the present invention
which contribute to the foregoing general objectives will
be exp].ained more specifically hereinafter, followlng a
brief description of the prior art in this field.
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t the Prior Art
In two-stroke engines of the crankcase compression
type9 the moving piston is utili~ed to effect ~he intake
of a charge of combustible fluid into the cylinder of the
en~ine and to effect the exhaust of burned gases from the
cylinder of the engine. Basically~ this is accomplished
by using the piston ~o uncover and cover three types of ports -
an inlet port, an exhaust port, and a transfer port - formed
in the walls of the cylinder~ On the up stroke of the piston,
combustible fluid is drawn into the crankcase by the ascending
piston and is compressed therein on the down stroke of the
piston and is then transmitted by a transfer port to the
oombustlon chamber of the engine. The piston uncovers both
the transfer port and the exhaust port thereby effecting
the intake of combustible gases and exhaust of spent gases.
At the outset, problems were encountered in the
two-s~roke design because of the mixing of the incoming combus-
tible charge with the out~oing exhaus~ gases, with a resulting
decrease in power output and fuel economy. Efforts to solve
this problem have included deflector - top pistons wherein
a deflecting surface on the top of the piston directs the
incoming combustible charge toward the cylinder head of the
,
engine to prevent the charge from being drawn out through
~; the open exhaust portO This solu~ion was displaced by later
techniques of cylinder sca~enging where~n the velocity and
direction of the charge issuing from the transfer ports is
con~rolled and resonances or pressure pulses in the exhaust
and inlet tracks are harnessed for precise control of gas
flow, These techniques are dlsadvantageous from the standpoint
that the resonance points ar pressure pulses are a function
of engine speed and optimal conditions occur only over a
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very narrow speed range. Thus9 these efforts resulted in
engines which are not flexible in terms of producing power
output over a varying range of engine speeds.
Some measure of control over the above noted problems
has been achieved by the use of reed valves for delivering
in timed fashion, the charge of combustible fluid to the
inlet port of the engine. However, such designs have utili~ed
a single reed petal or flap, formed of a piece of this spring
steel or a val~e assembly having a plurality of such flaps.
These single stage designs place opposing requirements on
the reed petal structure which must be compromised with the
result that engine response and power, particularly in the
low speed range is reduced. A brief consideration of the
design illustrates the problem involved. At low engine speeds,
vacuum on the downstream side of the ~alve is low and to
provide a valve which will operate under these conditions
to time the flow of the incoming charge, it would be necessary
to utilize a relatively yieldable reed pe~al, i.e. one having
a low spring constant. However, such a reed petal does not
provi de optimal performance a~ middle and high engine speeds
because at higher engine speeds, ~he vacuum developed in
the crankcase becomes greater resulting in a grester pressure
differentiaL across the reed and at such press~re differentials,
~he reed petal tends to flex ~pen to or near the position
of ~reatest openi~gO In addit~on, as the engine speed is
increased the rate at which the crankcase is placed alternately
under pressure or vacuum by the rapidly moving piston is
increased. Under these conditions, the frequency of response
of the reed petal tthe time required by the reed petal to
Qpen and close) is exceeded and the reed petal therefore
fails to provide positive control of the timing and stre~gth
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~7S~g
of the incoming cha~ge and allows the spit back of portions
of the incoming charge into the carburetor. Further when
the alternations in the crankcase from vacuum to positive
pressure occur at intervalls which are less in time tnan
the response tlme of the reed petals, the reed petal, as
it is in an open position, is sub~ected to the high positive
pressure developed by the descending piston. As a consequence
of this, reed petal life is substantially dlminished because
of the uncontrolled flexure of the reed petal as it opens
and whipping of the reed petal as it closes. Reed stops
have been employed to li~it 1exure of the reed petal~ but
such stops limit the opening of the reed petal, thereby restrict-
ing the flow of charge through the valve. Conversely ~hen
a less yieldable reed petal is utilized~ i.e.~ one having
a higher spring constant, low speed performance of the engine
is adversely affected because the low vacuum existing on ~-
the downstream side of the valve is insufficient to open
the reed petal for a duratioD long enough to ins~re an adequate
incoming charge. Present designs of this type are engineered
to provide a compromise between low speed and hi8h speed
performance so that at the mid range of speed, power o~tput
is maximized but power output in the lo~ speed and high speed
ranges is less than optimal.
One known attempt to solve the problems referred
to hereinabove is shown in U~S. Pat. No. 2,689,552 to E~
C. KeikhaeferO In that design, a single reed petal is utili7ed
to open and close an inlet port to the crankcase of a two-
cycle engine~ An additional, shorter spring flap is placed
; over a port~on of the reed petal 90 that, at l~w engine RPM9
the free end of the reed petal flexes to admit an incoming
charge, and at high RPM the entire reed petal flexes against
.
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the actlon of ~he overlying spring to provide the timed delivery
of combustible mixture to the crankcase.
In addition, engines having t~ansfer ports extending
from the intake tract to the combustion side of the piston
have been proposed, as in U.S. Pat. NOr 3,687,118 to K. Nomura.
As ~ill be noted, the aforementioned patent discloses the
use of a reed valve assembly employing single reed petals.
In this design, the crankcase is cut off from the inlPt tract
for a significant portion of the cycle~ about 90~ Thus,
while advantage is taken of the additional transfer capabilities
of this design arising by reason of the fact that negative
pressure pulses in the exhaust port draw combustible gas
to the combustion side of the piston, there is, however,
a restriction in the total capability of this design because
the intake tract is cut off from the crankcase during this
critical portion of the engine cycle, when certain phenomena
could be utilized to impro~e scavenging and performance.
Also, engines of this basic design having pistons with ports
in the skirt thereof have been proposed. In these designs,
such ports have been placed in the lower portion of the skirt
of the piston and thus the plston still acts ~o close off
the intake tract from the crankcase for a significan~ portion
of the cycle. Such designs have contemplated positioning
the piston ports so that communication between the inlet
tract and the crankcase is cut off until almost 45 to 50
after bot~om dead center position of the piston. In such
designs, when the piston ports uncover the intake port9 ~eed
val~es pGsitioned in the intake tract snap open. This results
in a discontinuous flo~ of combustible fluid to the engine
and in the intake of lesser volumes of combustion fluid in
comparison to engines utlli~ing aspects of the invention
disclosed herein.
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In addition to the general objectives hereinabove
referred to the invention also has other objectives including
the following:
Thus~ it is another ob~ect of this invention to
provide improved reed valves for the control of combustible
fluids to internal combustion engines and particularly to
engines of the two-stroke design.
It is an additional object of this invention to
provide a valve asse~bly having lncreased life.
Further~ it is an object of this invention to provide
~wo-stroke engines having increased power output, a broader
power band, and improved power characteristlcs.
.
It is also an object of this invention to provide
a method and means for obtaining a supercharging effec~ to
increase the volume of the charge of combustible fluid intro-
duced into the combustion cha~ber of an internal combustion
en8ine.
It is still another object of the inventlon to
provide greatly increased intake por~ing for a t~70-cycle
engine and ~o provide for an increase in ~he portion of th~
cycle during which the in~ake porting is open,
It is a urther objec~ of the invention to pro~7ide
a port in the pistoD skirt, for delivery of fuel into the
; 25 crankc~se for co~pression therein~ w~ich skirt port is so
~ :
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~756~
located in the piston skirt as to remain open ~hen the transfer
ports are open and which is so located as to provide for
communicaeion between the intake chamber and the crankcase
when the pist~n is positioned to block the intake porting
so that there is constant communication between the intake
chamber and the crankcase throughout the entire cycle of
the operation of the engine.
The invention has as a further object the employment
of special intake ports, herein referred to as injector ports,
interconnecting the intake passage at a point ~ust downstream
of the intake valve with the transfer ports, thereby providing
still another channel through which intake of fuel may occur
whenever the transfer ports are open. In this aspect of
the invention, one e~bodiment i9 featured by the provision
of injector port means which can be made in the simplest
possible manner, taking the form of a cavity provided in
the cylinder in position to confront an outer side portion
of the piston.
How the foregoing and other ob~ects and advantages
are obtained will be clear from the following description
referring to the accompanying drawings in which:
Figure 1 is a sectional ViPw of a two-~ycle internal
conbustion engine ha~ing intake valves and intake porting
conforming with the present invention;
Figure 2 is a section of certain of the valve ports
shown in Figure 17
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Figure 2G is a graph showing co~parative curves
representing the power output in relation to speed for conven-
tlonal two-cycle engines and for engines utili~ing certain
features of the invention as disclosed in F:igures 1 and 2;
~ 5 Figure 3 is a view similar ~o Figure 1 but illustra-
ting a modified ~alve arrangement;
Figure 4 is a view of a cylinder showlng certain
improved inlet ports and showing also an arrangement of val~es
positioned as in Figure 3;
Figure 5 is an elevational view of a piston adapted
for use in an arrangement according to the present invention
and incorporating extended porting~ as described hereinafter;
Figures 6A, 6B, 6C~ 6D and 6E are schematic illustra-
tions showing the operating sequence of an engine employing
porting arrangements according to the present invention;
-
Figure 7 is a graph showing the portion of the
cycle during which the intake valves are open in the arrangements
illustrated in Figures 1 and 3 to 6E;
Figure 8 is a graph showing comparative power curves
of a prlor art arrangement in comparison with an arrangemen~
conforming with Figures 3 to 6E, and still further with curve
number 3 of graph 2G;
Figures 9 and 10 are views similar to Figues 3
and 4 but illustrating the provlsion of injector ports, as
hereinafter explained;
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Figure 11, on the same sheet as Figures 7 and
8, is a graph showing the power curves for two engines con-
structed according to the present invention, in one of which
the injector ports are utilized and the other of which the
in]ector ports are not utilized; and
Figures 12 and 13 are views similar to Figures
9 and 10, respectively, but illustrating the provision of
a modified form of injector portsO
Turning now to the drawings, reference is first
made to the embodiment illustrated in Figures 1, 2 and 2G.
Referring to Figure 1, there is shown therein
a schematic representation of a two-cycle piston engine
having a cylinder 12 and a piston 14.
~, , .
The cylinder 12 includes main transfer ports 16
for delivering a combustible gas from the crankcase (not
shown) to the combustion side of the piston 14. As is con-
ventional, combustible gases pressurized by the descending
piston, flow from the crankcase through suitable conduits ~ - :
(not shown) to the main transfer ports 16.
The cylinder 12 also includes an inlet port 18
which communicates with a valve housing 20 which may be
mounted on or formed integrally with the barrel of cylinder
12, and which housing defines, at least in part, the above~
mentioned intake passage or tractO
. 25 A valve assembly 27 is received in the housing
20 and may be secured therein by a readily removable cover
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plate 24 ~hat extends over the flanges 22 of the valve assembly
and which preferably includes an intake passage extension
26 for receiving a carburetor ~not shown) thereon~
Referring to Figures 1 and 2, a preferred embodiment
of a type of valve is shown therein in greater detail. The
valve assembly 27 can include a valve body 29 having two
convergent surfaces 30 and 32 joined in an apex by a transver~e
member 35. The surfaces 30 and 32 include at least one opening
34 and 36 extending through each of the surfaces 30 and 32.
While the openlng 34 and 36 could be made in the form of
one continuous opening, it is preferred that at least two
openings be formed in the surfaces 30 and 32 for reasons
as will be hereinafter explained. It should be noted that
in Figure 2 the reed petals 38 and 42 at the top are shown
lS closed, but those at the bottom ase shown open~ It will
be ~nd~rstood that in actual use the flexing of both sets
of reed petals on both sides of the ~alve will always be
substantially the same, depending upon the opera~ion condition.
As the reed petal assemblies to be hereinafter
d~scribed are the same on surface 30 as on surface 32, héreinafter
reference will be made only to ~he reeds disposed on surface
30, it bei~g understood that the comments so made are Pqually
applicable to the assemblies on surface 32. Disposed over
the opening 34 is a primary reed 38. The size and shape
o the primary reed is such that peripheral surfaces thereo~
extend beyond side edges of the openings 34 so that the flow
of fluid through opening 34 is substantially precluded when
the reed 38 i5 urged by i~s own resilience against the surface
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The primary reed 38 has a vent or opening 40 for~ed
therethrough. A secondary reed 42 of a size and shape suffi-
cient to o~erlay vent 40 is mounted over the vent 40 by,
for instance, a machine screw 44 that secures both the secondary
reed 42 and the pri~ary reed 38 to the valve body 29.
The primary and secondary reeds 38 and 42 respecti~ely
are both formed of a yieldable, resilient material. However,
it is important that the secondary reed 42 be more yieldable
than the primary reed 38 beca~se secondary reed 42 must ope~l
at lower intake port pressures than primary reed 38, as will
hereinafter be described. It should be understood that any
thin, resilient matPrlal can be used to form the primary
and secondary reeds~ A preferred material that has been
used with good result is a woven glass fiber and epo~y laminate
commonly identified as G~10, or example as marketed by the
Formica Company. Reed assemblies of ~his material wherein
; the thickness of ~he primary reed is abou~ 0.022~ to about
00026" and wherein the thickness of the secondary reed is
about 0.014" to about 0.016" have been found satisfactory.
. . :
An arrange~ent similar ~o that described abo~e `ii
is illustrated in Figure 3, which lattPr Figure is more fully
described hereinafter, but with reference to which it should
be no~ed that it is preferred in all of the arrangements
according to the invention that the primary reeds 38 should
overlie the entire opening 34, (shown in broken lines in ~ -
~igure 3~, and further that the primary reeds 38 are wider
and longer than the secondary reeds 420 This has the ad~antage
of greatly reducin~ the mass of each secondary reed 42 making
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it more responsive to lower pressure differentials across
the val~e assembly and more able eo work independently of
the operation of primary reed 38.
In addition~ it should be noted that the vent 40
is positioned closer to the end of reed 38 ~hich is secured
to the valve body 29. This allows the length of the secondary
reed 42 to be kept to a minimum9 thereby resulting in a decrease
in the mass of the secondary reed as heretofore noted.
Also the provision of the vent 40 reduces the mass
of the primary reed 38 thereby further decreasing ine~ial
effects on that reed, The decrease in mass of the prim~ry
and secondary reeds, it is believed, results in lncreased
reed life as it reduces overflexing and eliminates the need
for reed stops. Furthermore~ when both primary and secondary
reeds are open, a larger volume of char~e passes through
the ~alve, in comprarison to single reed valves9 because
the impedance of the pri~ary reed to flow is reduced as portions
of the charge c~n flow through the vent which is opened by
the more yieldable secondary reed.
By providing a plurality of openings 34 and 36
and concomitantly a plurality of primary reeds and secondary
reeds~ the mass of each of the reeds ls maintained at a minimum.
This in turn reduces inertial effects on the pri~ary and
secondary reeds and increases the freque~cy of response of
the reeds thereby making ~he englne more responsive to changes
in thro~tle settings~
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As can be seen in Figures 1 and 2 the valve body
29 includes a transverse apex ~orming member 35 formed a-t
the point of convergence of surfaces 30 and 32. The member
35 has formed -thereon an aerodynamic sur~ace 37 which gives
the member 35 an air foil or tear drop cross section. Thus
formed, the member 35 offers minimum resistance to passage
of incoming gas. In single stage reed designs as heretofore
discussed the corresponding surface 37 of the apex member
35 is flat or poin-ted and presents a non-aerodynamic sub-
sonic barrier to the passage of gases thereover. The flator pointed surface is required ln certain single reed designs
to lift the reeds from the surfaces of the valve body -to
which they were mounted, by means of the shock and turbulence
created at the apex member, which, it is felt, interfers
with -the timed, uniform delivery of the charge into the intake
port.
Referring to Figures 1 and 2, the valve assembly
as heretofore disclosed operates in the following manner.
- At very low engine speeds, the secondary reed 42 opens each
time the piston 14 moves upwardly in the cylinder 12 -to uncover
the inlet port 18, as the force generated by the pressure
of -the combustible gas, ~or instance, air-fuel mixture from
a carburetor (not shown) on the upstream side of the secondary
reed 42 is sufficient to overcome the resistive force gen-
, 25 erated by the relatively yieldable secondary reed. Thisallows the passage of a quantity of air-fuel mixture into
, the inlet port at each stroke of the piston and provides
; a timed supply of the air-fuel mixture to the cylinder 12
a-t very low engine speed. As the engine speed increases
to mid range, the pressure differential across the valve
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assembly becomes great enough to cause the primary reed 38
to begin to operate, alternately opening and closing wi-th
the stroke of piston 14 to deliver a timed charge of the
air-fuel mixture through the opening 30 to the inlet port
S 18. In the high speed range, because of -the high vacuum
conditions existing at the inlet port 18 and the increased
frequency at which the crankcase changes from a condition
of positive pressure to a condition of vacuum, secondary
reed 42 remains open, varying in posi~ion in accordance wi-th
the crankshaft ro-tation, while the less yieldable primary
reed 38 continues to provide a timed charge in the manner
heretofore described. Thus, the system described provides
valve timing throughou-t the en-tire speed range of the engine.
The blow back of the air-fuel mixture -through the opened
vents 40 at high RPM is preven-ted by the restricted area
o~` these vents and by the mom~ntum of the entering high veloci-
- ty intake charge.
Referring again to Figure 1, the more efficient -
porting involves an increase in the charge delivered to the
combustion side of the piston 14, by reason of a supercharging
effect at low RPM occurring through main transfer ports 16
and auxiliary transfer port 46. This supercharging effect
at lvw ~PM ranges results from the low pressure wake occurring
in the crankcase as the compressed charge suddenly exits
from the crankcase through the main transfer ports 16 and
`~ auxiliary transfer port 46. The low pressure in the crankcase
is communica-ted via a port 58 in the piston (more fully described
hereinafter) to the intake port 18. This in turn causes
secondary reed ~2 to open early, about 45 before BDC at
Iow engine speeds, delivering a charge to the auxiliary
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transfer por-t 46, immediately downstream from the valve assem-
bly and to the inle-t port 18 and thence through the crankcase
to -the -transfer ports 16. This increased charge is in turn
delivered -to the compression side of -the piston, thereby
improving scavenging of the exhaust gases and charging of
the cylinder, which results in an increase in -the overall
compression ratio of -the engine and thus an increase in the
power output.
An advantage of the sys-tem herein described is
that at high RPM, the flow of the air-fuel mixture into the
intake port 18 is significantly more constant because the
secondary reeds ~2 remain open. In sys-tems using single
reeds, the flow of the air-fuel mixture is stopped and started
by the opening and closing of the single reed thereby reducing
the speed and uniformity of the flow of the air-fuel mixture
into the intake port 18.
:~,
Ano-ther advantage of the valve assembly herein
disclosed is -that the secondary reeds, which opera-te at low
engine pressure differentials and which have faster response
times allow a more efficient porting of the cylinder and
piston. Single reed petal designs require greater vacuum
in the inlet port to open the reed petals and require -the
plston -to close off the intake system from the crankcase
so tha-t the necessary vacuum can be achieved. The foregoing
?5 is a problem occurring most frequently in larger displacement
engines, for instance engines having a displacement exceeding
100 cc. As the valve assembly herein disclosed does not
require the buildup of a high vacuum to operate the secondary
reeds, the intake system of the engine may be ported directly
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~756al9
-to the crankcase at all times to yield better flow of the
air fuel mixture at low engine speeds for larger displacement
~ engines.
:~
Another advantage realized by the vented reed sys- ~
tem herein disclosed is increased responsiveness of the en- "
gine. This aIises from the situa-tion that when the throttle
plate of the carburetor (not sho~n) is closed, the vacuum
upstream from the valve assembly 27 is the sarne as the crank~
case vacuum and both reeds remain closed. But immediately
upon the opening of the throttle plate in the carburetor
(not shown), the vacuum upstream of the valve assembly 27
drops while the vacuum in the crankcase rearnins. The vented
reeds snap open earlier and more quickly, in comparison to
single reed designs, because the vented valves are respon-
sive to lower pressure differentials occurring across the
valve assembly and provide more area for the flow of gases
with less flexing, as earlier described.
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~ nother advantage to -the design herein disclosed
is vastly increased life of the reeds. In single stage reed
designs fatigue failures of the reeds being oecurring within
twenty hours of service. Attempts to eliminate this situation
include the use of spring steel reed elements. While these
reed elements exhibit a longer life, failure of these ele-
' ments results in destruction of the engine if the steel
.
reeds are drawn into the cylinder. Dual reed assemblies ofthe type herein disclosed, on the contrary, have exhibited
a normal service life in excess of one year.
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Referring to ~igure 2G, there is shown therein a
graph indicating the power input in relation to engine speed
for an engine modified as heretofore described. The graph
shows the result of tests performed on a 25 cc. two-cycle
engine utilizing, in stock form, piston controlled inlet
ports and exhaust expansion chambers for exhaust extraction.
.~ :
The line identified by the numeral "1" represents
the results of dynamometer testing for the above engine not
utilizing reed valves of the type herein disclosed and em-
ploying carburetor jetting suitable for normal use at varyingspeeds and loads. As can be seen from the graph, peak power
of about 22 horsepower is developed a-t a speed of about 6600
RPM and power output falls off rapidly beyond -the peak power
speed.
~.
Line 2 shows the result of testing the engine as
equipped in test l with the exception that the carburetor jet-
- ting was chosen to obtain maximum dynamometer power. A maxi-
mum power of about 28 horsepower was achieved at a speed of ~ ;
I approximately 6600 ~PM. Again, as with test l, there was ex-
20 perienced a rapid fall off in power after the peak power
point, and maximum RPM safely achievable was indicated to be
about 8500 RPM. It should be pointed out that the engine as
set up in test 2 was not suitable for use in application re- -
quiring varying speeds as the mixture became unduly rich each
time the throttle plate was closed thereby loading the cylin-
der with unburned fuel.
In test 3, an engine of the type used in tests l and
.! 2 but further including reed valves of the type herein
.,
~7~ 9
disclosed plus auxiliary transfer por-ting of the type herein
disclosed was tested. As can be seen from -the graph of test
3, power output below 5000 RPM is significantly increased,
somewhere in the order of` S0% and peak power of about 29
5 horsepower was achieved at a speed of about 7300 RPM. More-
over, power output beyond peak power speed ~alls off more
gradually than that for the number 1 and number 2 tests.
Further, maximum engine speeds of almost ll,000 RPM were
achieved.
In test 4, an engine with the same modifications
as -that in number 3 and further including a carburetor with
a larger venturi diameter, auxiliary transfer porting, modi-
fied exhaust porting, and a modified exhaust expansion chamber
was used. Peak power on this engine rose to 3~ horsepower at
a speed of about 9200 RPM. Maximum engine speed was found to
be in excess of 12,500 RPM.
::
It should be understood in connection with the vent-
ed reed valve arrangements heretofore discussed that valve
assemblies having more than two reeds are contemplated accord-
ing to the invention. For example, triple reed valve arrange-
ments may be employed, in which even-t the secondary reeds
~; will be apertured or vented, so that the third or tertiary
reeds serve to open and close the vent in the secondary reeds.
In this case, the tertiary reeds are desirably smaller and
more flexible than the secondary reeds.
With further reference to Figure 3, it is pointed
out tha-t the arrangement of Figure 3 is similar to that des-
cribed above and that all of the parts descrlbed above are
.
-18- ~
1~7~
also employed, bu-t the reed valve assembly is differently
positioned in the valve housing 20. In effect, the reed
valve assembly in Figure 3 is merely rotated 90 in the valve
housing, as compared with i-ts' position in Figures 1 and 2. ;
Because of -the angular position of the valve assembly in
Figure 3, the reed valves themselves occupy a different posi-
tion in relation to -the porting and to the axis of the cylinder.
This is oE advantage because it allows a more predictable flow
; , pattern of combustion fluid through the system, especially
during high speed engine operation. The flow is more evenly
divided between the sets of reeds disposed on each side of
the valve body 29 and is directed in a manner which conforms
to the natural directions of the fluid flow through the engine,
i.e., curved toward the sides of the crankcase where the trans-
fer passages are open to the crankcase, by reason of the fluidflowing through the valve port which acts as an orifice having
a fixed side and a yieldable side defined by the reeds which
cause the flow to curve. By reason of the orientation of the
valve assembly as shown in Figure 3, the reeds are placed
closer to the par-t 46 and the flow into port 46 is smoother
because the fluid does not have to flow upwardly from the reeds
as in the Figure 1 embodimen-t.
.
This orientation of the reed valves is also desirable
because it improves cold starting of the engine, which is
particularly advantageous with engines requiring manual starting.
The reason for this is that when the engine is at rest, there
is no vacuum in the crankcase to operate -the reeds. Thus, at
start up, the engine must be cranked to develop sufficient
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19
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~75~9
vacuum in the crankcase to cause -the reeds to open and allow
the passage of the combus-tion fluid into -the engines. When
the valves are positioned as shown in Figure l, the combustion
fluid passing through -the bottom se-t of reeds must flow up-
wardly as it enters -the valve assembly 27 so that it can exit
through the vent in the primary reed 38. These factors re-
quire a greater vacuum -to be developed in the crankcase in
order to draw the combustion fluid through the valve assembly
and this necessitates higher cranking speed at start-up. When
the arrangement shown in Figure 3 is used, the only forces
which must be overcome in order to draw combustion fluid through
the valve assembly are the resistive forces developed by the
secondary reeds. This reduces the vacuum required to draw the
combustion fluid through the valve and correspondingly decreases
the cranking speed or starting effort required. In some engines
this difference is so great as to make it practical to manually
start the engine if the valve arrangement of the invention is
; used, whereas manual starting would not be practical without
the valve arrangements of the invention.
In connection with the orientation with the reed
valves as shown in Figure 3, it should be kept in mind that
in many installa-tions such as motorcycles and snowmobiles, the
intake passage and also the engine itself is somewhat inclined
in a direction so that liquid fuel would tend to flow from the
carburetor through the intake passage and intake port into the
cylinder. This inclination is shown in Figure 3. With the
vaives oriented as in Figure 3, some liquid fuel may readily
leak past the valves or may accumulate immediately upstream
o~ the valves, which is in contrast with the condition when
'~ :
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-20=
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the orientation of the valves is as shown in Figures 1 and 2.
The arrangement of ~igure 3, par-ticularly where the intake
passage and engine is inclined, is therefore of special advan-
tage where easy s-tar-ting is an important factor.
:':
I-t shoulcl be noted that the foregoing benefits are
achieved from orien-tation of the valve assemblies as shown ln
Figure 3 with vented reeds as heretofore disclosed, and also
with single reed designs. Single reed designs benefit because
the single reeds are less yieldable than the vented reeds and
therefore do not open as easily.
Turning now to Figures 4, 5 and 6A to 6E, a-ttention
is directed to the porting employed in accordance with the
present invention.
Figure 4 shows a cross-section, taken along line
4-4 of Figure 3, of a typical cylinder showing the preferred
manner of mounting the valve assemblies 27 in relation to the
cylinder. In this embodiment, two valve assemblies 27, are
positioned vertically as discussed above with respect to
Figure 3 in a housing 20 which is attached to the cylinder C.
The valve assemblies 27 are positioned so that each valve
assembly is aligned with one of the intake ports 18. The use -
of the two valve assemblies 27 is advantageous because it causes
the flow of combustion fluid to agree with the natural flow pat-
tern of the engine, and this results in a smoother, more direc
2S tional flow of combustion fluid through the engine. The com-
bustion fluid flows through each of the valves 27 into an
aligned inlet port lB and into -the crankcase of the engine and
` from there into the transfer passages 53 and is introduced to the ~
.' ' :.
., ~, ,.
.:
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,
~CI 7~609
combustion side of the piston through the transfer ports 16.
It should be noted that this is particular:Ly important in
the preferred embodiment of cylinder arrangements as shown in
Figures 3 and 4 because in such designs, the axes o~ the trans-
fer ports 16 are angularly displaced f`rom the axis of the in-
take tract by about 90 , as is shown in Figure 4. These designs
require that the combustion fluid make an abrupt change in
direction once inside the engine, i.e., a direction change of
to either side of the engine to enter the transfer pas-
sages 53, and without the arrangements as shown in Figures 3and 4, the charge has little inherent directional tendency to
flow toward either side of the crankcase, and in fact does not
do so until after the charge has been compressed and flow
starts through the transfer passages. ~t high operating
speeds, -the time during which the change in direction can occur
is short and therefore -the change must occur quite rapidly.
When using the double valve assembly arrangement shown, the
valve assemblies give direction to the combustion fluid streams
before the streams enter the engine. This predetermining
results in the combus-tion fluid stream undergoing the direction
change more efficiently, rapidly, and smoothly, thereby ultima-te-
ly resulting in the delivery of a larger volume charge to
the combustion side of the piston.
It should be noted -that the axis of the entire inlet
tract of the engine shown in Figure 4, including the valve
assemblies 27 and -the intake ports 18, is positioned so that
it is aligned along a radius enamating from the center of the
cylinder bore and is angularly offset from the axes of the
transfer ports.
There is shown in Figure 5 a pis-ton which is usable
in conjunction with a cylinder such as shown in Figure 4. The
-22-
7SÇ;~9
piston 56 includes two spaced pis-ton ports 58, each of which
is positioned to be aligned with one of the in-talce ports 18
of cylinder C. An important aspect of the pis-ton shown in
Figure 5 is that the height of the ports 58 is grea-tly in-
creased over that of prior designs. As will be hereinaftermore fully explained, this resul-ts in allowing the inlet ports
18 (and thus the inlet trac-t including -the reed valves) -to
communicate with the crankcase at all times during the engine
cycle. The height of -the ports 58 can be increased in designs
as shown in Figures 3 and 4 both with single reed valves and
with ven-ted valves as hereto~ore disclosed. This is so because
the improved fluid flow resulting from the vertical placement
; causes the engine to start more easily and does not require the
intake ports to be closed off from the crankcase in order -that
sufficient vacuum be developed -to operate the reeds--the mode
of operation,necessary in designs having horizontally orien~ted
reeds. The increased heigh-t of the piston ports, and the
concomitant increase in port area allows a longer induction
period and thus greater charge of fuel to be inducted into
-the engine and this results in higher engine outputs.
There is shown in Figures 6A-E a schematic representa-
tion of the operating cycle of an engine employing vented reed
valved of the type heretofore described and employing a ported
piston as shown in Figure 5.
.: .
., ' :.
, 25 Figure 6A shown the position of the piston 56 just
.!
slightly before it reaches bottom dead center. The combustion
fluid charge compressed by the~descending piston 56 has exited -
from the crankcase 60 and is in-troduced via the transfer ports
;~ 16 and somewhat through auxiliary port ~6 to the combustion
: -
-23-
. .
~s~
side of the piston. As described above, the rapid exi-ting
of the compressed combustion fluid from the crankcase 60
causes a vacuum to be created in its wake in -the crankcase
60. This vacuum is -transmitted via the pis-ton por-t 58 to the
reed valves which open allowing the introcluction of additional
charge of combustion fluid through the auxiliary -transfer
port 46 to the combustion side of the piston and also into
the crankcase 60 through the piston port 58, resulting in
extended delivery of charge through ports 16 (as shOwn by
the arrows). This creates what is known as a supercharging
effect in the lower RPM ranges, and results in higher engine
outputs.
I`here is also a supercharging effect which occurs
at high RPM. At high RPM, it will be recalled, the second-
ary reeds remain open, by reason of the fact that the in- -
coming charge of the air-fuel mixture is travelling at high
velocity and has significant momentum, and therefore, the -
charge continues to flow through the open vent in the pri-
mary reed and allows the system to maintain a higher delivery
rate. Also, at piston bottom dead center, typical exhaust ex-
pansion chambers are supplying suction to the cylinder. At this
posi:tion, the auxiliary transfer por-t 46 is open to the combus-
-tion side of the piston, and because of the high monentum of
the incoming charge which maintains secondary reeds open at
high RPM, a portion of the air-fuel mixture flows directly from
the intake tract, through the port 46. Thus, this portion of
the charge bypasses the crankcase at high RPM -to fill the
cylinder thorougly. Any of the charge tending to escape
through the exhuast port as the piston moves upwardly is now
held in the cylinder by a positive reflective wave generated
by a typical exhuast expansion chamber. Also, because the
~.
-24-
'
;6;~
secondary reeds remain open a-t high RPM ranges, there is an
increase in the amount of charge drawn into the crankcase
through the skir-t port 58 and a correspondingly increased
flow of gases through the crankcase and to the transfer ports.
Figure 6B shows the piston as it has just closed
off the transfer port 16 and auxiliary port 46. The piston
is ascending, thereby creating a vacuum in the crankcase which
is communicated to the reed valves via the piston port 58,
thereby causing the reed valves to open further. Combustion
fluid flow from the inlet port 56 and also from the auxiliary
; transfer port 46 when the piston 56 hasmoved high enough,
through the piston port 58 to the crankcase. At this point,
the skirt of the pis-ton has not ye-t begun opening -the intake
port 18.
.
In ~igure 6C, the bottom edge of the skirt of the
piston 56 has cleared the intake port. Under these conditions,
the reed petals are open, combustion fluid flows beneath the ~
bottom of the piston and also through the piston part 58 in-to -
the crankcase. It should be noted that combustion fluid flow-
ing through auxiliary transfer port 46 is directed upwardly
through the pis-ton port 58 toward the underside of -the top of
piston 56. This latter flow cools the top portion of the
piston. ~-
. . .
j As shown in Figure 6D, the piston 56 is approaching
the -top of its stroke, the bottom edge of the skirt has com-
pletely opened the intake port l~, thereby allowing a great
volume of combus-tion fluid to be drawn into the crankcase
through the open reed valves.
~7~6~9
Figure 6E shows the piston 56 descending and clos-
ing off the intake port 18. The piston is of course compress-
ing the volume of combustion fluid drawn into the crankcase
during the previous up stroke of the piston. A-t this time,
the pressure of the fluid in the crankcase is greater than the
pressure on the upstream side of the valve assembly and blow-
back of the pressurized charge is prevented by the closed
reeds in the lower RPM ranges and by the restricted area of
the vents and the monentum of the incoming charge entering
through the vents at high RPM ranges. It should be noted that -
at all times through the cycle the crankcase is in communi-
cation with the intake tract, either via the piston port 58,
the inlet port 18, or a combination of both. This provides
for the induction of larger qu~antities of combustion fluid into
the engine and results in higher power and higher torque
outputs.
Figure 7 is a graph based upon the type of valve and
port arrangemen-ts shown in Figures 1, 3, 4, 5 and 6A to 6E,
including the vertically extending porting 58 provided in the
piston skirt as shown in Figure 5. In Figure 7, the graph there
shown plots two curves, curve 1 represen-ting typical operating
behavior of the reed petals at low intake ~velocities, i.e.,
engine speeds below the power peak, and curve 2 representing
typlcal operating behavior o~ the reed pe-tals a-t high intake
veloci-ties, i.e., engine speeds above the power peak. As has
been seen, at high intake air velocities, the intake is open to
at least some extend throughout the entire cycle of operation
of the engine. As plotted in the graph of Figure 7, 180 re-
presents the bottom dead cen-ter posi-tion of the engine cranlc,
and 360 represents the top dead center position of the engine
crank.
-26-
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:~7~i609
It will be noted that the vertical scale of the
graph of Figure 7 represents the degree of reed valve opening,
graduated at quarterly intervals from zero opening to full
opening, and the lowermost quarter of th:is scale comprehends
the extend of opening provided by ~he secondary reeds, it
being assumed that at the one-quarter position on the graph
the secondary reeds are fully open.
The graph of Figure 7, also shows that even a~ low
intake air velocity, the duration of reed or valve opening is
extended throughout approximately 240 of the cycle of opera-
tion. This aids in maintaining relatively high output and
performance at low engine RPM, un~er which condition both the
primary and secondary reeds c~cle, as has been described.
~' "'
The duration o~ reed opening as described above in ~`
relation to Figure 7 is greater than prior arrangements both at
low as well as at high int~ke air velocity, and these condi-
tions can only be achieved when the skirt porting 58 is high
enough to be open whenever the piston skirt would block com-
munication from the intake passage to the crankcase. In
prior arrangements, where the skirt port is closed during a
portion of the cycle, the commencement of opening of the valve
is delayed bo ~x beyond the 180 position, i.e., bottom dead
canter. Such prior arrangements ad~ersely af~ect the torque
at both high and low engine RPM.
.`
It should be noted that the graphs shown in Figure 7
are representative of engines emplo~ing standard transfer port
timing, i.e.~ usually not in excess of 120 duration. It has
- `
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~5~
been found that when using vented reed valves as herein dis-
closed, especially in conjunction with piston porting as
heretofore described, that the height of the transfer ports
16, as shown in Figures 1, 3 and 6A-E, 9 and 10, can be
raised to give greater transfer duration. Engines having
transfer port durations of about 148 have been found to have
power curves as depicted by line 4 of Figure 2G. It will be
note~ that greatly increased power results at high RP~q. In
addition, the height of the exhaust port can be raised t result-
ing in increased scavenging time and concomitant higher engineoutputs.
Turning now to the graph of Figure 8, the graph
indicated by the numeral 1 represents a prior known sinyle
reed valve engine and is characterized b~ rapid drop-off of
horsepower after the power peak is passed. The curve identi-
fied by the numeral 2 is similar to curve 3 of Fi~ure 2G, and
illustrates one arrangement or embodiment of the present inven-
tion incorpoxating a vented reed valve assembly. This curve
shows much less tendency for the horsepower to drop off after
the pea]c is reached. In another embodiment conforming with
the present invention of the kind shown in Figures 3 and 4,
in which multiple pairs of reed valves are arranged and in
which a pair of spacecl intake ports 18 are provided, a horse-
power curve as shown by numeral 3 in Figure 8 is secured. Here
it will be seen that the peak horsepower is still higher and
further, that the horsepower at the higher RPM levels off,
instead of dropping sharply, as in the case of curve 1
'. :.
Turning now to Figures ~ and 10, there is here shown
still ano~her feature as applied to arrangements similar to
'
~8- -
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:~75~
those illustrated in Figures 3 an~ 4. Similar parts are
again iden~ified b~ the same re~erence numerals. In these
Figures however, additional ports, hereiil referred to as "in-
jector" ports, are provided. Two injector ports are illus-
trated at 62,62. Each of these ports int:erconnects one of
the intake passages 18 with one of the transfer passages 53,
as is shown in Figures 9 and 10. These i.njector ports are
open at all times, and serve to increase intake of fuel at
the higher ~PM's, especially above 6000 or 7000 RPM.
It will be noted from Figure 9 that the longitudinal ::
axis o~ the injector ports 62 is arranged at substantially a
90 angle to the axis of the transfer passage 53. When the
charge contained in the crankcase is pressurized by khe des-
cendiny piston, the charge i5 caused to flow upwarclly through
the transfer passages 53 to the transfer por-~s 16 at high
velocity. In accordance with Bernoulli's Principle, the
rapidly moving charge in the passage 53 moving past the open-
ing of injector port 62 causes an eductor effect in the injec-
tor por~ 62 which causes a low pressure to exist in the port
62, which low pressure is communicated to the intake tract just
downstream of the reed assemblies. In this manner, a quantity
of charge is drawn rom the intake tract downstream rom the
valve assembly, through the port 62 and into the transfer pas-
sage 53. This results in a higher density charge passing
through the portion of the transfer port between the injector
~ port 6? and the transfer port 16. It is believed that injec-
: tor ports can be used with beneficial results in two-cycle
: engine designs having valving in the inlet tracts, for example, .-
:; rotary in~ake valves. As will be noted below, in connection
::~ -2~
~s~
with discussion of Figure 11, especially ~ood results are
achieved when injector ports are used in engines having reed
valves, especially vented reed valves of the type disclosed
herein.
It is also preferred, as shown in Figures 9 and 10,
to provide a partition or wall 64 between the two intake chan-
nels 18 and the two pairs of reed valvesl thereby aiding in
dixecting the intake flow through the channels 18 and into the
crankcase through the porting provided in the piston skirt.
~ .
Comparative analysis of a given engine of somewhat ~
higher horsepower than that employed as the basis for the graphs
of Figures 2G and ~, both with and without the in~ector ports
gives horse~ower curves such ~s shown in Figure 11. Here curve
1 is a curve of an engine conforming with the arrangements of
Figures 9 and 10 except for the omission of the injector ports,
and curve 2 represents the same engine altered merely by add- :
ing the injector ports. It will be seen that the peak horse-
power has been raised, and further, that the drop-off of horse-
power after the peak is further reduced, which is important at
high RPM.
', :
Figures 12 and 13 illustrate a modified form of in~
jectox port means which achieves the operational features con~
sidered above with reference to the injector ports of Figures
9 and 10, but which is additionally advantageous because of its :
simplicity in manufacture and consequent cost advantage. The
-~ embodiment of Figures 12 and 13 also presents minimal flow
obstruction and, consequently, maximizes the induction of in- .` ;
take fluid, and therefore affords still greater efficiency even
' ~ .
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... . .. . .. - ~ : .. ~
7~9
as compared with the arrangement of Figures 9 and 10. Por-
tions of this modified apparatus, which correspond to the
similarly functioning injector ports of Figures 9 and 10, are
identified b~ similar reference numerals r but include the
subscript a.
.
As is the case with the embodiment of Figures 9 and
10, two port areas which serve an injector function are provid-
ed in the modified embodiment. These are shown at 62a, 62a,
and each is arranged at a substantially 90~ angle to the axis
of the adjacent transfer passage 53, which terminates in the
transfer port 16a. As will be apreciated, the transfer port
16a is that portion of the transfer passage which lies above
the upper surface of the piston P, when the latter, as shown
fragmentarily in Figure 12, occupies its bottom d~ad eenter
position.
In the embodiment of Figures 12 and 13 each of the
injector port means 62a takes the form of a cavity recessed
in the cylinder wall in a position in which its open side con~
fronts an outer side wall portion of the piston P. This cavi-
ty is simpler to provide than the injector ports 62, of Figures9 and 10, which are passages completely enclosed by the metal
of the cylinder and its liner. This construction facilitates
casting of the cylinder. The outer side wall of piston P
provides the inner wall limit (considered radially of the
cylinder) of each injector port 62a, as appears in Figure 13.
Each of the resultant enclosed cavities 62a provides one of
the injector ports, and each interconnects one of the intake
passa~es 18 (in the zone 62b~ with on~ of the transfer pas-
~' sag~s, as (at 62c).
. . .
~ -31-
7~
As described above, with reference to the earlier
embodiment, the rapidly moving charge in the passa~e 5 3 f low~
ing past the open end 62c o~ in~ector port 62a causes low pres-
sure to exist throughout the injector means 62a. This low
pressure is communicated to the intake tract through the open
passage existing in the region 62h, all with results and
horsepower advantayes similar to those already d~scribed with
respect to Figures 9, lQ and 11.
With the fore~oing embodiments in mind, it is here
desired to point out certain additional advantages and desirable
operating characteris~ics secured when employing not only the
multiple reed valves herein disclosed, but also when employing
various of the porting features described.
The employment of reed valves also makes possible
extensive increase in the total cross-sectional area of the
intake portin~, as is disclosed herein, and still further
makes possible considerable increase in the total time in the
; cycle during which the valves are open, both at ~ow speed and
at high speed. The employment of reed valves further makes ~ -
possible extending the porting 58 in the piston skirt to the
point where the intake tract is open to the crankcase when
the transfer ports are open. The use of reed valves also en-
ables the vertical extension of the piston skirt porting to a
point such that the intake tract is constantly open to the
crankcase ~hroughout the entire cycle of operation of the
engine.
-:
It should be noted that many manufacturers of two-
cycle engines have been reluctant to adopt reed valves as a ~
-32- ;
. :
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~756~
means o controlling the flow of the cha:rge to the sylinder.
This is believed to be because prior reed valve designs have
added to the complexity of the enqine design compared with
piston port intake systems and have exhibited unsatisfactory
service life, yet have yielded onl~ modest benefits in terms of
somewhat higher power output at low ~PM. Applicant's vented
reed design, alone and in combination with the porting
arrangements herein disclosed, has on the other hand achieved
very significant increases in power output, torque output, and
power band width. It is believed that these impxovem~nts
make the adoption of reed valves by engine manufacturers much
more likely.
~'
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