U.S. patent number 3,703,937 [Application Number 05/145,746] was granted by the patent office on 1972-11-28 for multiple rpm range tuned exhaust pipe and silencer for two-cycle engine.
Invention is credited to William L. Tenney.
United States Patent |
3,703,937 |
Tenney |
November 28, 1972 |
MULTIPLE RPM RANGE TUNED EXHAUST PIPE AND SILENCER FOR TWO-CYCLE
ENGINE
Abstract
An expansion chamber exhaust system operative to obtain high
power output from two-cycle engines at more than one engine rpm
range. The exhaust system includes automatic or manual means to
change the effective range of engine rpm at which it is providing
power increase. At least one valve member is provided, which is
open in a low speed position, to permit substantially unrestricted
passage of the exhaust gases and exhaust gas pressure waves past
the valve member, and which closes at higher engine rpm to provide
a pressure wave reflecting surface so positioned to reflect a
positive pressure wave to arrive at the exhaust port of the
two-cycle engine just before the port closes, at the desired higher
rpm range of the engine. The exhaust systems can be made with a
fixed positive wave reflecting surface downstream from the valve
member, or they may open directly to atmosphere downstream from the
valve member, and they may include a silencing muffler, is
desired.
Inventors: |
Tenney; William L. (Crystal
Bay, MN) |
Family
ID: |
22514349 |
Appl.
No.: |
05/145,746 |
Filed: |
May 21, 1971 |
Current U.S.
Class: |
181/226; 60/314;
181/277 |
Current CPC
Class: |
F01N
13/08 (20130101); F02B 27/06 (20130101); F01N
1/165 (20130101); F01N 1/166 (20130101); F01N
2590/04 (20130101); Y02T 10/12 (20130101); Y02T
10/146 (20130101); F02B 2075/025 (20130101) |
Current International
Class: |
F01N
1/16 (20060101); F01N 7/08 (20060101); F02B
27/00 (20060101); F02B 27/06 (20060101); F02B
75/02 (20060101); F01n 001/08 (); F01n 001/20 ();
F01n 003/00 () |
Field of
Search: |
;181/35R,33R,33D,36R,36D,47A,64R,64B,65 ;60/312,314,322 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
656,983 |
|
Jan 1929 |
|
FR |
|
278,857 |
|
Oct 1927 |
|
GB |
|
301,556 |
|
Dec 1928 |
|
GB |
|
Primary Examiner: Ward, Jr.; Robert S.
Claims
What is claimed is:
1. An exhaust system for two-cycle engines including an exhaust
port, a tubular exhaust duct member including a portion generally
expanding in cross sectional area in direction of exhaust gas flow
from said exhaust port and in communication therewith, and having
an exhaust gas outlet, valve means positioned in said tubular
exhaust duct member, means to move the valve means between a first
position wherein said valve means does not substantially influence
exhaust gas flow through said tubular member, and a second position
where it forms a pressure wave reflecting surface so positioned
with respect to said exhaust port as to reflect a positive pressure
wave timed to arrive back at the exhaust port of said engine
immediately prior to closing of said exhaust port when said engine
is operating in a preselected speed range.
2. The combination as specified in claim 1 wherein said valve means
comprises a blade member pivotally mounted about an axis positioned
in a preselected relationship with respect to exhaust gas flow in
said exhaust system.
3. The combination as specified in claim 2 wherein said means for
moving said valve means toward its first position comprises bias
means acting to create a moment about the axis of pivot of said
blade member.
4. The combination as specified in claim 3 wherein said bias means
comprises a weight member.
5. The combination as specified in claim 3 wherein said bias means
comprises a spring.
6. The combination as specified in claim 3 wherein said blade
member is positioned at a preselected angle of attack with respect
to direction of normal exhaust gas flow through said exhaust
system, means mounting said blade member so that said exhaust gas
flowing across said blade member creates a lift on a portion of
said blade member to move said blade toward said second position
when the exhaust gas flow across said blade member has
substantially reached a preselected velocity.
7. The combination of claim 4 wherein said weight member is mounted
directly on said blade member adjacent the leading edge thereof
with respect to the direction of flow of exhaust gas.
8. The combination as specified in claim 2 wherein the axis of
mounting of said blade member is offset with respect to a
transverse bisecting line of said blade member and the major
portion of said blade member is upstream from the axis.
9. The exhaust system of claim 1 further characterized in that
means forming an engine noise silencing device is mounted
downstream from said valve means.
10. The exhaust system of claim 9 wherein said noise silencing
device forms a fixed wave reflecting surface located farther
downstream from said valve means.
11. The combination as specified in claim 1 and a chamber wall
forming a fixed positive pressure wave reflecting surface spaced in
downstream direction away from said valve means with respect to the
direction of exhaust gas flow.
12. The combination as specified in claim 1 and manually operable
means to operate the valve means between its first and second
positions.
13. The combination as specified in claim 2 wherein said blade is
mounted onto a shaft, said shaft being pivotally mounted in said
tubular duct member, a lever on said shaft, bias means acting
through said lever and arranged to bias said blade member toward
its open position.
14. The combination as specified in claim 13 and means to permit
adjustment of said bias means with respect to the axis of rotation
of said shaft to change the effective moment of said bias means on
said shaft.
15. The combination as specified in claim 2 and stop means to stop
said blade member in its first position at a preselected angle with
respect to the direction of exhaust gas flow and permit said blade
member to move to its second position.
16. The combination as specified in claim 2 and stop means to stop
said blade member when said blade member moves to its second
position.
17. The combination as specified in claim 2 and separate bias means
urging said blade member from its second position toward its first
position during at least initial portions of blade travel from its
second position.
18. The combination as specified in claim 1 and at least one second
valve means located in said tubular member a different distance
from the exhaust port than said first valve means, said second
valve means being movable from a first position wherein it does not
substantially influence flow of gases through the exhaust system,
to a second position where it forms a pressure wave reflecting
surface so positioned with respect to said exhaust port as to
reflect a positive pressure wave timed to arrive back at the
exhaust port of said engine immediately prior to closing of said
exhaust port when said engine reaches a second preselected speed of
operation.
19. The combination as specified in claim 1 and power means to
operate said valve means, an engine speed sensor means to actuate
said power means at a preselected engine speed to selectively move
said first valve means to its first and second positions.
20. The combination as specified in claim 19 wherein said power
means comprises a solenoid.
21. The combination as specified in claim 19 wherein said power
means comprises a fluid pressure actuated cylinder.
22. The combination of claim 1 wherein said valve means comprises a
blade member, and guide means to support said blade member for
sliding movement between said first and second positions.
23. The combination of claim 1 and rim members positioned around
the inner periphery of said tubular exhaust member, said valve
means comprising a pivoting blade member, said blade member at
least partially engaging said rim members when said blade member
pivots to its second position.
24. The combination of claim 1 and an outlet pipe positioned in
said tubular member, said valve member comprising a blade having a
U-shaped opening that fits over said pipe when said valve member
moves to its second position whereby exhaust gases will be
discharged from said pipe when the valve member is in its second
position.
25. The combination of claim 1 wherein said tubular exhaust duct
member has a central flow axis that changes direction, and muffler
means positioned generally within the space defined by the tubular
duct member.
26. The combination of claim 25 wherein said tubular duct member
bends into a generally "U" shape, and said muffler means is
positioned between the legs of the "U."
27. The combination as specified in claim 25 wherein said muffler
means and curved tubular exhaust duct member are formed with
divider walls inside a common housing.
28. The combination as specified in claim 2 and dashpot means
coupled to said pivoting blade member to dampen movement of said
blade member.
29. The combination of claim 1 and bias means to exert a force
urging said valve means toward its first position when the valve
means has substantially reached said second position.
30. The combination as specified in claim 1 wherein said valve
means comprises a pair of blade members, each pivotally mounted in
said exhaust duct member, means operating said blade members
together for coordinated movement whereby in said first position of
said valve means the blade members are substantially parallel to
the flow of exhaust gases and in said second position cooperate to
form a surface means converging in the direction of exhaust gas
flow.
31. An exhaust system for two-cycle engines having an exhaust port,
an exhaust pipe open to said exhaust port and having an exhaust gas
outlet, and blade valve means positioned within said exhaust pipe,
means to hold the blade means in a first predetermined position
wherein it does not substantially influence exhaust gas flow
through said tubular member, and means to move said blade means to
a second position wherein it forms a pressure wave reflecting
surface so positioned with respect to said exhaust port as to
reflect a positive pressure wave timed to arrive back at the
exhaust port of said engine shortly prior to closing of said
exhaust port when said engine is operating in a speed range
preselected to be a higher speed range than when said blade means
is in its first position.
32. The exhaust system as specified in claim 31 wherein said blade
means is pivotally mounted about an axis substantially transverse
to the direction of exhaust gas flow through said exhaust pipe, and
stop means to support said blade means in its first position at a
preselected angle of attack with respect to exhaust gas flow
whereby when exhaust gas flow reaches a predetermined velocity said
blade means will be moved to its second position by action of
aerodynamic forces.
33. The exhaust system as specified in claim 32 wherein said means
for holding said blade means in its first position comprises bias
means to create a moment about the axis of pivot of said blade
means.
34. The combination of claim 27 and bias means to exert a force
urging said blade means toward its first position when the blade
means has substantially reached said second position.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to expansion chamber exhaust systems
for two-cycle engines.
2. Prior Art
The advantages in the use of expansion chamber exhaust systems with
two-cycle engines are well known in the art, including the use of
positive wave reflecting surfaces downstream from the expanding
section to increase the power output of the engines. It has also
been recognized that the useful rpm range of operation of such a
resonant exhaust system is relatively narrow. For example, my U.S.
Pat. No. 3,367,311 discloses two or more exhaust systems with valve
means to direct the exhaust gases from the two-cycle engine to one
or the other of the systems in order to provide improved power
output at two or more engine speeds or rpm ranges.
Further, it has been recognized that one method of changing the
useful rpm range of an expansion chamber exhaust system is that of
changing the distance of the positive pressure wave reflecting
surface from the engine exhaust port by the "slide trombone" or
telescoping pipe method. A type of "slide trombone" or extensible
telescoping pipe exhaust is shown in the patent to Kopper, U.S.
Pat. No. 3,254,484. It can be understood that complex, expensive
and difficult structure is necessary for "tromboning" because of
the necessary telescoping members with attendant heat, sliding,
sealing and control problems.
Another trombone type exhaust is shown in U.S. Pat. No. 3,434,280
to Burkhardt, but this does not appear intended for other than a
"fixed" type of adjustment.
Mufflers which utilize internal valves that open when the gas
pressure from the exhaust system exceeds a preselected amount have
been used, but not for providing a positive pressure wave
reflecting surface in order to increase the power output of
two-cycle engines. Prior art valved muffler construction is used
for the purpose of relieving the back pressure caused by the
muffler during periods of high engine output. This mode of
operation is opposite from that desired for power increase in
two-cycle engines when exhaust pressure wave charging of the
cylinder is utilized. The patent to Kopper, U.S. Pat. No.
1,483,354, illustrates a typical muffler configuration utilizing a
flapper valve that opens when the speed of the engine increases.
Another device of this type which operates as a foot controlled
motorcycle engine "cutout" is shown in Austrian Pat. No. 117,331.
Another type of "cutout" is shown in U.S. Pat. No. 3,346,071.
These devices all fail to suggest the desired result of obtaining a
multiple operating rpm range power increasing, resonance exhaust
system for two-cycle engines via extremely simple mechanical
devices which can be readily adapted to automatic operation.
SUMMARY OF THE INVENTION
The present invention relates to a power increasing exhaust system
for two-cycle engines. The system includes an exhaust expansion
section in combination with means which may be operated as desired
to provide a positive pressure wave reflecting surface so located
as to increase the power output of the engine at some desired rpm
range, but that may also be set to a relatively neutral or
non-reflective position which does not interfere with lower speed
operation. The device therefore provides for selection of ranges of
engine rpm at which the maximum power increasing effect of the
expansion chamber exhaust system is available. A single expansion
chamber pipe is utilized, but the power increasing effects are
similar to those which may be obtained by use of alternate pipes
attached to a selector valve. The invention comprises the
utilization of a valve member which in a first position is open and
does not materially restrict exhaust gas flow and in a second or
closed position reflects a positive gas pressure wave to the
cylinder exhaust port in order to cause a supercharging effect at
the engine cylinder at some desired engine rpm range. The valve
member is in its closed or positive pressure wave reflecting
position at a higher engine rpm than the rpm when the valve is in
its open position. When multiple valves are used in series, the
position of the valves located downstream from whichever valve is
in use as the positive wave reflector, is relatively
unimportant.
In exhaust systems where there is a single fixed positive wave
reflecting surface positioned for engine performance improvement
over a given rpm range, lower rpm performance of the engine is
affected adversely when the positive reflected pressure wave
arrives at the cylinder early and the scavenging port is still
open. The reflected positive pressure wave then inhibits cylinder
scavenging, charging and engine performance by interfering with
entrance of the scavenging and charging medium through the
scavenging port. A device made according to the present invention
does not develop this inhibiting effect at low engine rpm, and in
preferred forms it provides a positive reflected pressure wave
properly timed for low engine rpm. When the valve means is closed,
a reflected positive pressure wave properly timed for higher engine
rpm is provided.
The invention also includes the use of more than one valve so that
increased power output may be achieved at several different engine
rpm ranges. In addition, silencing mufflers can be added to or made
part of the exhaust system for cutting down the exhaust noise, or
the exhaust pipe can be open ended. In the preferred form, there is
provided a fixed reflecting surface downstream from the valve, to
provide a reflected positive pressure wave timed for lower engine
rpm range operation.
The invention further involves the concept of the use of a biasing
member for holding the valve in its open, relatively non-reflecting
position, wherein the valve is so designed as to close
automatically at such time as the engine speed reaches a desired
level.
In the forms of the invention shown, a flapper type valve having a
blade rotatable through an arc is utilized. Operation of the valve
may be either manual or automatic. For the simplest type of
automatic actuation, the valve is biased open with weights or
springs and is designed so that exhaust gases flowing over the
valve blade tend to cause it to close against the bias force.
Weights can be mounted directly on the valve blade or attached to a
control lever, and the weights can be adjustably mounted. The
adjustable weight permits changing the engine speed at which the
valve will close in order to provide the positive pressure wave
reflecting surface. The flow of exhaust gases over the valve blade
creates a pressure differential which causes the valve to close
after the gas flow reaches a given velocity.
The full throttle engine rpm at which the valve closes can also be
adjusted by varying the angle of attack of the valve blade to the
gas flow, with the valve in the open position. The angle of attack
setting may be easily varied by means of an adjusting screw.
The valve is not sealed in the closed position because of the need
for providing for the relatively spent exhaust gases to escape
without undue back pressure. Thus the blade may be provided with an
outlet opening or openings, or merely made with suitable clearance
inside the exhaust pipe to allow the gases to escape.
In one form of the invention, the low rpm range fixed reflecting
surface comprises a muffler. The surface incorporates outlets of a
type that will tend to interfere with the sound waves and thus
provide a silencing effect. A muffler of the ordinary "can" type
can be utilized to provide a low engine speed positive wave
reflecting surface, for example. Multiple exhaust tube mufflers,
multiple chamber mufflers, etc., can also be used.
The valve may be manually controlled directly via a hand or foot
lever, or indirectly via control cable, push-pull rods or the like.
Solenoid or hydraulic or pneumatic cylinder operation in response
to either manual selection or to engine speed sensors, such as a
flyball governor, an electronic engine speed sensor, or an intake
or exhaust airflow sensor, can be utilized if desired.
A form of the invention shown includes a housing having a curved
exhaust chamber with a fixed positive wave reflecting surface, and
a muffler portion mounted in the space defined by the curved
exhaust chamber. The valve in this form may be automatically or
manually actuated as desired.
The valves are acted upon by stop means to properly position the
valves in their open position. Stop means may also be provided in
the closed position in order to prevent jamming in this position,
in order to regulate the escape of gases, or for other desired
purposes.
In the simplest automatic forms, instead of a weight, a spring may
be used for urging the valve member in the exhaust system to the
normally open position. The weight or spring may be connected to
the valve so that the force on the valve acts through a different
lever arm leverage ratio when the valve is in the closed position,
to help compensate for exhaust gas pressure against the valve blade
which tends to hold it quite tightly once it has closed. In some
instances the valve will not open until the engine rpm has dropped
considerably lower than the rpm at which it closed, due to exhaust
gas pressure on the blade tending to hold it closed, once it has
closed. In order to overcome this differential in actuating speed,
it is in most instances only necessary to momentarily close or
"blip" the engine throttle to get opening of the valve. Springs can
also be utilized for overcoming this effect of differential in
engine speed between valve operation on the "upshift" during
increasing speed and on the "downshift" during decreasing speed. As
shown, a small spring force exerted on a stop member for the valve
blade tends to compensate for the exhaust gas pressure buildup on
the blade when the blade approaches and reaches its closed
position.
It is thus an object of the present invention to provide an exhaust
system for a two-cycle engine utilizing an expansion chamber, plus
valve means to provide for a positive pressure wave reflecting
surface at desired engine rpm which can be moved to position
wherein it does not adversely affect engine operation at lower
engine rpm. It is a further object of the present invention to
present different means for actuating such valve means. It is a
still further object of the invention to provide high power output
per cubic inch of engine displacement across a wide range of engine
speeds.
It is another object of the present invention to present resonant
exhaust systems that are useful through several different engine
speed ranges, and which may thus utilize more than one valve
located in series in the exhaust system.
It is a still further object of the present invention to provide
such exhaust systems which incorporate muffler elements for sound
level reduction.
Other objects are apparent from the foregoing summary and in the
following description of preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a motorcycle having a
resonating exhaust system made according to the present invention
installed thereon;
FIG. 2 is a fragmentary vertical sectional view of the valve
portion and a section of the muffler utilized with the device of
FIG. 1;
FIG. 3 is a sectional view taken as on line 3--3 in FIG. 2;
FIG. 4 is a fragmentary side elevational view of a snowmobile
showing an exhaust system made according to the present invention
installed thereon;
FIG. 5 is a side elevational view of the exhaust system of FIG.
4;
FIG. 6 is a fragmentary side view of a valve portion of the exhaust
system of the invention as viewed from an opposite side from FIG.
5;
FIG. 7 is a vertical sectional view showing the internal details of
a valve in the exhaust system of FIG. 5;
FIG. 8 is a sectional view taken as on line 8--8 in FIG. 7;
FIG. 9 is a side elevational view of a modification of the device
shown in FIG. 5 utilizing a spring for valve control force;
FIG. 10 is a side elevational view of a further modification of the
present invention showing a muffler attachment and a dashpot on a
control lever;
FIG. 11 illustrates a modification of the present invention showing
the utilization of a dual range valve in a resonant exhaust system
with the exhaust chamber ending just downstream from the valve;
FIG. 12 illustrates a modified form of the device showing a manual
operation device for the valve utilized with the exhaust system of
the present invention;
FIG. 13 illustrates a modification of the present invention showing
a solenoid operated valve operated in response to an engine rpm
sensor;
FIG. 14 illustrates a further modification of the present invention
utilizing two internal valves positioned in series within the
exhaust system made according to the present invention to obtain
resonance at three engine rpm ranges;
FIG. 15 illustrates further modification of the present invention
showing a pair of valves that cooperate to form a double tapered
positive wave reflecting surface at high engine speed;
FIG. 16 illustrates a further modified form of the present
invention showing a muffler wall installed at the end of an exhaust
chamber and forming a positive wave reflecting surface for low
speed engine operation;
FIG. 17 illustrates a further modified form of the present
invention showing a rim around the interior of the exhaust chamber
for seating the valve of the present invention;
FIG. 18 is a sectional view taken as on line 18--18 of FIG. 17;
FIG. 19 illustrates a further modified form of the invention
showing a sliding valve used for dual range resonance in the
exhaust system of the present invention;
FIG. 20 is a sectional view taken as on line 20--20 in FIG. 19;
FIG. 21 is a view of a resonant chamber exhaust-muffler combination
having the resonant chamber curved into a U shape with the muffler
between the legs of the U shaped chamber and taken as on line
21--21 in FIG. 22; and
FIG. 22 is a view from the side of the device of FIG. 21 showing it
with the cover removed to show the internal construction
thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First, in a preferred embodiment shown in FIGS. 1, 2 and 3, the
exhaust system of the present invention is installed on a two-cycle
engine that is used on a motorcycle illustrated generally at 10. As
shown, the motorcycle has a frame 11, a front wheel 12 that is the
steering wheel operated through handlebars 13, and a rear power
driven wheel 14. The motorcycle is powered by a two-cycle engine
illustrated at 15, of any desired construction. For example, a
single cylinder two-cycle engine is shown having a cylinder 16, a
piston 17 mounted for movement vertically in the cylinder, and an
exhaust port 18. The engine is shown as being typical of motorcycle
type two-cycle engines. The engine can be of the general type shown
in my U.S. Pat. No. 3,367,311 or any desired type of two-cycle
engine wherein the exhaust port 18 is used for discharging exhaust
gases and is opened and closed by actuation of the piston 17 in the
cylinder. It can also be of the two-cycle engine type wherein the
exhaust port is opened or closed by a valve such as a sleeve valve,
rotary valve, or poppet valve. In the engine of illustrated type,
transfer ports and transfer passages leading from the crankcase are
used for introducing a fresh charge of combustible gases into the
cylinder in the usual manner, and it is to be specifically
understood that the type of two-cycle engine utilized is not a
limitation of the invention, but is merely for illustrative
purposes since any of the usual forms of two-cycle engine
constructions will benefit by the utilization of the exhaust system
of the present invention.
The engine 15 drives through the usual gear shift type transmission
controlled by foot and/or handlebar controls on the motorcycle, or
an automatic transmission may be used. The chain 21 is used for
driving the rear wheel. An operator seat 22 is provided as is the
usual fuel tank 23.
The improved exhaust system member is illustrated generally at 25.
As shown, the exhaust system has a lead-in exhaust pipe section 26
connected with a flange 26A to a mating face on the engine, and
open to the exhaust port 18. The exhaust pipe section 26 is bent in
a suitable configuration to clear the engine so that the exhaust
system can be placed alongside the frame of the motorcycle. The
pipe section 26 is joined to a generally expanding cross sectional
area exhaust pipe which includes sections 27, 27A and 27B. The pipe
as shown, curves to cooperate with the particular configuration of
the motorcycle, and expands from the junction with the exhaust pipe
26 in direction away from the exhaust port 18. The pipe comprising
sections 27, 27A and 27B of generally expanding cross section aids
in reflection of a suitable suction or negative pressure wave to
arrive at the exhaust port at a suitable time to aid in exhausting
the spent charge from the cylinder and drawing in the fresh charge,
as is well known. The cross section of the chamber formed by pipe
sections 27, 27A and 27B increases in area until it reaches a
constant cross sectional area tubular pipe forming a chamber 28
which is downstream from the expanding pipe. The chamber 28 may be
made of other than constant cross sectional area, if desired, as is
well known in the art. It is also well known in the art that the
pipe 26 need not be of strictly constant cross sectional area.
At the downstream end of the uniform cross sectional area chamber
28, there is, as shown, first a reducing cross sectional area pipe
forming a chamber 30 which has an interior surface 31 that forms a
positive pressure wave reflecting surface for the exhaust, in order
to, at a particular engine speed or rpm range, provide for a
positive reflected exhaust pressure wave arriving at the exhaust
port 18 just prior to the closing of the exhaust port by the piston
17 (substantially in the position shown in FIG. 1) to in effect
prevent escape of fresh charge gases that have entered the cylinder
16 through the transfer ports and also force back into the cylinder
fresh charge gases that may have passed from the cylinder into the
exhaust pipe. The power output of the engine is markedly increased
thereby and at the same time the specific fuel consumption is
decreased.
The overall length of the exhaust pipe from the exhaust port 18 to
the reflecting surface 31, including the exhaust pipe section 26,
the pipe sections of expanding cross sectional area 27, 27A and
27B, and the constant cross sectional pipe forming chamber 28
determines the engine speed range at which the positive pressure
wave will be reflected back to the exhaust port. This is designed
to occur at an advantageous time, so as to increase engine power
output as described above, and is herein referred to as the
"resonant speed" of the exhaust system 25. With the long pipe
shown, the surface 31 will cause properly timed positive pressure
wave reflection at a relatively low engine speed. The expanding
pipe sections 27, 27A and 27B are also of major importance in such
resonant exhaust systems, as is well known in the art.
If the positive pressure wave reflecting surface 31 is positioned
so as to provide for arrival of the positive pressure reflected
wave at the exhaust port at the proper time for a given engine rpm
range, then it will work to the detriment of engine operation at a
lower engine rpm range. At such lower engine rpm range the
reflected positive pressure wave arrives too early, while the
scavenging or transfer ports are too far open, and interferes with
the transfer of fresh charge gases into the cylinder. The present
invention eliminates this problem.
As is well known in the art the positive pressure wave which is
first reflected back to the exhaust port as a negative pressure
wave due to passing through the expanding cross sectional area pipe
section, and is then reflected back to the exhaust port as a
positive pressure wave due to passing through the reducing cross
sectional area pipe section, is generated at the outset by rapid
opening of the exhaust port and consequent explosive release of
high pressure exhaust gases from the engine cylinder into the
exhaust pipe.
If desired, a silencing muffler 34 can be mounted at the outlet of
the exhaust system 25. As shown, this is of a conventional type
having an outer casing 35, that is sealed onto a pipe 36 leading
from the reducing cross section chamber 30, and which pipe has a
plurality of apertures 37 in the side wall thereof. The end of the
pipe 36 is closed off, so that the gases coming from the reducing
cross section chamber 30 have to pass through the apertures and
thus reduce exhaust noise. An outlet pipe 38 is also sealed with
respect to an end wall of the outer casing 35, and has a closed
inner end. This pipe 38 has inlet apertures 39 to further attenuate
the sound waves so that the sound level is reduced substantially.
The silencing muffler is an optional feature, and a straight outlet
pipe 36 with an open end can be used. An open pipe does reduce the
weight, size and cost of the exhaust assembly and thus where noise
is not objectionable, the muffler can be omitted.
It also can be seen that a second pipe 41 leads from the constant
cross section chamber 28 through the side wall of the reducing
cross section chamber 30, and is sealed with respect thereto. Pipe
41 also is sealed with respect to the end wall of the casing 35 of
the muffler section, and has a blocked off end with apertures 42
inside the muffler for noise reduction.
A suitable strap or bracket 43 can be used between the muffler
casing 35 and the frame 11 of the motorcycle for supporting the
unit and also, support bracket 44 can be used along the exhaust
system.
Whereas the muffler 34 is shown as a dual muffler which serves both
outlet pipe 36 and outlet pipe 41, it is of course understood that
a separate muffler of usual configuration may be utilized for each
of these two outlet pipes.
It is well known that the engine rpm range across which such
resonating exhaust systems or pipes are favorably operative, is
relatively narrow. Particularly, for maximum power output, a
positive pressure wave reflecting surface which is effective at the
top rpm range of the engine is desired. If the exhaust system is
thus "tuned" for high speed output, the positive wave reflecting
surface is closer to the exhaust port than is desirable for lower
speed operation. This results because at higher speeds a shorter
effective distance between the positive wave reflecting surface and
the exhaust port is necessary in order to provide for the positive
pressure reflected wave to arrive at the exhaust port 18 at the
proper time.
In the present invention, as stated previously, the overall length
of the exhaust system 25 is such that the positive pressure wave
reflecting surface 31 is positioned from the exhaust port 18 a
sufficient distance so that the arrival of the positive pressure
wave at the exhaust port will be properly timed for lower or medium
engine rpm range operation. This will not be satisfactory for high
engine output at high engine rpm operation, since the reflected
positive pressure wave will then arrive too late to be effective,
after the exhaust port has been closed by piston 17.
In order to provide improved engine performance at a high engine
rpm range, a movable valve member is placed in the chamber 28. When
closed, the valve provides a positive pressure wave reflecting
surface properly positioned for high engine speed operation, and
when moved to open position it does not reduce engine performance
during lower speed operation. This effectively broadens the rpm
range where peak engine performance is obtained.
In the embodiment shown in FIGS. 1-3, this is accomplished by
mounting a valve assembly 45 in the interior of the pipe section
forming chamber 28. As shown, the assembly includes a cross shaft
46 pivotally mounted in the side walls 47, 47 forming the chamber
28 and a valve blade member 48 which is fixed to the shaft 46 and
movable therewith about the axis thereof. As shown, the cross
section of the chamber 28 is defined by parallel side walls 47 and
rounded top and bottom walls 49 and 50. The shape of valve blade 48
is matched to the configuration of the chamber 28, and the blade
has side edges that fit between and adjacent the side walls 47, and
ends that are curved and beveled to fit up against the top and
bottom walls 49 and 50, respectively. The blade member is not
centered on shaft 46, but has a longer portion extending upstream
from the shaft than that extending downstream, when referenced in
the direction of normal exhaust gas flow.
In solid line position, valve blade 48 rests in its open position
against a stop screw 53 whereby it is not substantially inhibiting
gas flow through the chamber 28 in direction as indicated by the
arrow 52. Stop screw 53, as shown is threadably mounted through a
reinforcement 54 and is restrained from turning by a lock nut 55.
The stop screw prevents the upstream end of valve blade 48 from
dropping downwardly past a position wherein the blade is at the
desired angle of attack with respect to the normal exhaust gas flow
which is approximately parallel to the longitudinal axis of the
chamber 28. A weight member 56 is attached to the leading end
portion of the valve blade 48, and this weight 56 is oriented so
that it will urge the blade 48 to its open position under the force
of gravity. As shown, the weight 56 is made with an approximately
streamlined or airfoil shaped cross section having a rounded
forward end, and a tapered rearward upper surface so that as gas
flows past the weight 56 in direction as indicated by the arrow 52
there will be a lifting action created on the weight and on the
entire valve blade because of its angle of attack to the exhaust
gas flow. The weight is selected as to size and mass such that when
the gas flow over the valve blade reaches a certain velocity, the
leading end of the blade 48 lifts upwardly due to the aerodynamic
forces acting on it and the valve will shift to its dotted line
position shown in FIG. 2, wherein the bottom surface of the blade,
indicated at 48A, will present a pressure wave reflecting surface
to exhaust gas pressure waves impinging on this surface. The
upstream portion of chamber 28 surrounding the valve blade of
course also acts in cooperation with the blade as a wave reflecting
surface. The blade 48 when in closed position thus cooperates with
the walls of chamber 28 to provide a reducing cross sectional area
outlet for the exhaust system at this location. The reducing outlet
commences along the leading edge of the valve blade in its dotted
line position as indicated by the numeral 60. An adjustable stop
screw 59 may be used to stop the blade 48 in its closed position.
The screw 59 is threadably adjusted so the weight 56 on the blade
48 strikes the end of the screw when the blade reaches the desired
position. This prevents jamming of the blade in the closed
position.
Because the valve blade 48 fits quite closely along the inner
surface of the upper wall 49, and along the walls 47, 47 it is
necessary that an outlet be provided for the exhaust gases. The
pipe 41 extends forwardly into the chamber 28 so that when the
valve blade 48 is in its dotted line position (high speed positive
pressure wave reflecting position) the forward end of the pipe 41
extends just past the lower portion of the blade 48. Blade 48 is
provided with a generally U-shaped recess 61 that fits over the
sides of the pipe 41 so that the exhaust gases will be permitted to
escape into the inlet end of the pipe 41, out through the apertures
42 and into the muffler 34. If a muffler is not used the pipe 41
can be open ended and discharge the exhaust gases directly into the
atmosphere.
As shown, the effective moment arm of control weight 56 about the
axis of shaft 46 decreases slightly as the valve blade 48 moves to
its closed position. When the exhaust gas velocity is reduced to a
point where the weight exerted moment overcomes the gas forces
holding the valve closed, the forward end of blade 48 will drop
down to its solid line position against the stop 53. The surface 31
will again be effective as the positive wave reflecting surface at
the lower engine rpm range corresponding to the lower gas
velocity.
The unit is simple, neat, low in cost and reliable. The weight 56
is attached directly to the valve blade 48, and the only external
parts are the adjustable stops 53 and 59, and the ends of shaft 46
which may be covered or sealed off, if desired. Automatic operation
is achieved for a two speed range resonant pipe, in a simple, low
cost, neat and reliable manner.
A modified form of the invention is shown in FIGS. 4-8. Here, the
exhaust system is installed on a snowmobile 70 that has a drive
track 71 and skis 72 in the usual form. The snowmobile, as shown,
is powered with a two-cycle engine 73. The engine has a cylinder
74, a piston 75 that moves up and down in the cylinder in the usual
manner, and an exhaust port 76. The exhaust port 76 is again valved
by the piston, and opens to an exhaust pipe section 77. It will be
understood that an exhaust port valved by other means can also be
utilized. The exhaust pipe section 77 leads into an expanding cross
sectional area pipe 78A forming an expanding chamber 78 of the
exhaust system 79. The expanding cross sectional area chamber 78
leads into a tubular pipe section 82A forming a substantially
constant cross sectional area chamber 82. Again, it will be
understood that chamber 82 may be made somewhat varying in cross
sectional area without departing from the teachings of the
invention. The constant cross sectional area chamber 82 extends
into a reducing cross sectional area tubular pipe 83A section
forming a chamber 83 of the exhaust system. This reducing cross
sectional area chamber has an interior surface 84 forming a
positive wave reflecting surface (see FIG. 7). The outer end of the
reducing cross section chamber 83 may terminate in pipe 85 with no
further sound suppression, or, if desired, a suitable muffler can
be attached to or made integral with the pipe 85 in order to reduce
the noise level of the machine. A suitable muffler can also take
the place of pipe 85, or pipe 85 can be omitted completely.
In order to provide for favorable resonance of the exhaust system
at two different speeds, it is provided with a valve blade which
operates in much the same way as the blade 48 shown in connection
with FIGS. 1-3. Referring to FIGS. 7 and 8, it can be seen that a
cross shaft 86 is rotatably mounted through spaced apart side walls
87 of the constant cross sectional area chamber 82 and also the
shaft extends into a framework 88 formed around the pipe. The shaft
and valve can also be placed in the expanding cross sectional area
chamber or reducing cross sectional area chamber, if desired, in
accordance with the demands of the particular exhaust system
design.
A valve blade 90 is fixed to the shaft 86 and is located in the
interior of the constant cross sectional area chamber 82. The shaft
86, as shown, extends through the walls of chamber 82 on both sides
thereof, and a lever 91 is fixedly attached to one outer end of the
shaft on one side. A weight 92 is slidably mounted on the lever 91
and a set screw 93 is used for adjustably fixing the weight in
position along the lever to change the moment arm of the weight. It
should be noted that the lever 91 is positioned so that the weight
will normally act to hold the valve blade 90 in open position.
The blade 90 is shaped to fit closely within the periphery of the
chamber 82, and there is a longer section of the blade extending
forwardly from the shaft 86 with respect to the direction of
exhaust gas flow, than extends rearwardly. The opposite end of the
shaft 86 from lever 91 has a stop lever 94 attached thereto, and
the stop lever 94 is positioned to align with a first stop screw 95
threaded into the frame 88 which engages the lever 94 to prevent
the blade 90 from rotating in counterclockwise direction (as
indicated by the arrow 96) beyond its solid line position shown in
FIG. 7. A spring loaded stop 97 is provided to engage the lever 94
and to prevent the ends of blade 90 from jamming against the walls
of the chamber 82, when the blade is in closed position.
The position and mass of the weight 92 on the lever 91 in relation
to the angle of attack of the blade will be selected so that when
the engine speed has reached the desired level, the exhaust gas
velocity in direction as indicated by the arrow 98 will be
sufficiently great to create an unbalanced force on the forward
portion of the blade which will rotate the blade to its closed
position.
The valve blade 90 has a U-shaped opening 99 at the lower portion
thereof to permit exhaust gases to escape from the exhaust system
out through the tailpipe 85 when the blade 90 is in closed
position. When the blade 90 is in its closed position, the
forwardly downwardly facing surface of the blade cooperates with
the surrounding portions of chamber 82 to form a positive pressure
wave reflecting surface effective to reflect a pressure wave back
to the exhaust port 76 just before the port closes, during high rpm
range operation of the engine. Thus the positive pressure wave
reflecting surface is moved from interior surface 84 closer to the
exhaust port automatically when the speed of the engine increases
and causes the exhaust gas velocity in the chamber 82 to increase
and thus flip the blade 90 to its closed position.
When the blade 90 is in its closed position, the weight 92 acts
through a greater effective leverage ratio than in its open
position. This can be seen by referring to FIG. 5, wherein the
dotted line position of the valve control lever 91 is shown. The
effective moment arm about the shaft 86 increases. Even with weight
92 thus exerting additional valve opening force through increased
leverage, the exhaust gas pressure tending to hold the blade 90 in
its closed position may make the engine speed at which the blade
returns to its open position lower than that at which is shifts
from open to closed. This means that there may be a speed range on
deceleration where full power is not being developed because the
valve would be closed, providing a positive wave reflecting surface
that causes the reflected pressure wave to arrive at the exhaust
port 76 too soon. In order to overcome this tendency, a small
spring load acting in a direction tending to open blade 90 when it
is in its closed position, may be provided so that there is a force
tending to counteract whatever excess gas pressure forces may be
holding the blade closed against its seat on the walls of chamber
82. For example, a small spring 102 can be positioned between the
head of stop 97 and a bracket 103 fixed to the exhaust pipe. The
stop 97 is slidably mounted in the bracket 103 and lock nuts 103A
mounted on the stop 97 will determine the position where the head
of the stop contacts lever 94. When the blade 90 moves to its
closed position, the lever 94 contacts stop 97 and compresses the
spring 102 upwardly. This spring load then will tend to urge the
blade 90 toward open position to resist the excess exhaust gas
pressure forces and help make the shifting of the blade at both
increasing speed and decreasing speed occur at substantially the
same engine rpm range. This can be of assistance in an instance
such as hill climbing on a motorcycle because there may come a time
when the engine is decreasing in rpm even though the throttle is
held wide open, and if the shifting of the blade 90 does not take
place, the positive reflected exhaust pressure wave will arrive at
the exhaust port too early, with resultant loss of engine output
torque. If the shifting of the blade 90 takes place at the proper
time, the beneficial torque increasing effects of the positive
reflected pressure wave will be available at the desired lower
engine range.
The use of the stop 97 also can aid by preventing the blade from
closing too tightly and tending to stick or jam against the walls
of chamber 82. Additionally, the blade edges may be beveled as
illustrated so that these edge surfaces mate with the interior
surfaces of chamber 82 when the valve is in the closed
position.
In FIG. 9, a modification of the control of the device shown in
FIGS. 4-8 is illustrated. Here, the shaft 86 has blade 90 mounted
thereon, and in place of using the weight for control force, a
lever 105 is mounted onto the shaft 86, and a spring 106 is
attached to the outer end of the lever and is attached to a clip
107 that is attached to the outer wall of the exhaust pipe. A
series of adjustment holes may be provided in the lever to permit
changing the spring force, or the spring force may otherwise be
rendered adjustable in a desired manner such as by movement of clip
107. In this modification, when blade 90 is moved to its closed
position, it will move in direction as indicated by the arrow 108,
and will stretch the spring 106. It should also be noted here that
the effective lever arm ratio of the lever 105 will increase as the
blade 90 moves to its closed position so that the spring force from
spring 106 will exert greater leverage, and this will aid in
getting proper opening of the valve as the speed of the engine
decreases. Additionally the spring itself will exert more force as
it is stretched further, in accordance with the known physical laws
governing spring rates. Another feature of this modification using
the spring as shown is that the control force is less subject to
disturbance due to inertial effects during acceleration or
deceleration, bouncing, etc.
This exhaust system is attached to an engine as previously
explained, and likewise has an expansion section in the exhaust
system ahead of the valve. The expansion section increases in cross
sectional area in downstream direction of the exhaust gas flow.
An adjustable stop screw 109 is also provided which is similar to
and performs the same function as the adjustable stop screw 95, in
FIG. 6. Automatic operation is achieved by selecting the angle of
attack of the blade 90 (by means of adjustable stop screw 109) with
respect to the direction of exhaust gas flow which is indicated by
arrow 110, so that the valve will be moved to its closed position
when the velocity of the gases increases a sufficient amount to
lift the upstream portion of the blade.
FIG. 10 shows a further modified form of the present invention. The
exhaust system includes a pipe section forming an expansion section
115 which increases in cross sectional area in downstream direction
with respect to the exhaust gas flow. The expansion section is open
at one end to the exhaust port of an engine, and corresponds to the
expansion section 78 in FIG. 7. The exhaust system also has a
tubular pipe section 116 in which a valve blade member is pivotally
mounted for movement between an open position and a closed position
as shown in dotted lines. A pivot shaft 118 is used for mounting
the valve blade member 117. A lever 119 is attached to the shaft
118 and as can be seen in dotted lines, a weight 120 is used to
urge the blade 117 to its open position. The lever 119 is attached
to an output shaft 122 of a dashpot 123 of conventional design. The
base of the dashpot is pivotally attached to a bracket 124 mounted
on the exhaust pipe. The dashpot dampens any tendency toward
fluttering of the valve during transient periods or fluttering
caused by inertia forces, and smooths the actuation in both the
closing and opening directions. This modification can be used in
any of the forms of the invention merely by extending the pivoting
valve shaft and adding a lever and dashpot. In the case shown in
FIGS. 4-8, the dashpot may be attached to the lever on which the
weight is mounted.
Also shown in FIG. 10 is an exemplification of a muffler 128 that
can be fabricated as part of the single outlet pipe 85 shown in
FIG. 4. An outer casing 129 is sealed onto an outlet pipe 130
leading out of the exhaust system. The pipe 130 is blocked by a
transverse wall 131. The pipe 130 is provided with apertures in its
side wall inside the casing 129. The transverse wall 131 inside
pipe 130 divides the pipe into two sections so the exhaust gases
must pass through the apertures in the side wall of pipe 130, into
the interior of casing 129, and back through the apertures of the
downstream section of pipe 130 before being exhausted to the
atmosphere through the open outer end of the pipe outside the
casing 129. This causes a desirable reduction in the exhaust sound
level. It is understood that the muffler 128 may be of other known
design and construction. If desired, the muffler could be designed
to open directly to the valve chamber of the exhaust pipe, and the
muffler itself would then provide surfaces for obtaining a positive
pressure reflected wave at low engine speeds.
FIG. 11 shows a modification of the present invention wherein there
is no positive pressure wave reflecting wall surface for lower
engine speeds, but a valve is provided for positive pressure wave
reflection at high speeds where peak power is required. Such an
arrangement is very noisy when operating in the low engine rpm
range, with the valve in open position, since it then acts
substantially as a megaphone type exhaust. A wide, useful low rpm
power band is provided with this arrangement and it has the
advantage, especially for racing use where the noise is not
objectionable, of being more compact, shorter and lighter than the
previously described and illustrated embodiments.
As shown, the exhaust pipe member 135 has a tapering expansion
section 136 leading from the exhaust port of an engine, for
example, in the same manner as the expansion section 78. The
chamber 136A expands all the way to the valve in the illustrated
form. A shaft 138 is rotatably mounted in the walls of the section
136, and a blade 139 is mounted on the shaft. A control lever 140
corresponding to control lever 91 and having a weight 140A is
mounted on the outer end of the shaft 138. The weight 140A holds
the blade 139 in its open position as shown against an adjustable
stop screw 137. The blade 139 is fastened at its lower edge to the
shaft 138, and is spaced upwardly from the bottom of the chamber
136A to permit exhaust gases to escape through an opening 142 when
the valve is closed.
In this instance, the exhaust pipe 135 is trimmed off along a plane
141 that is parallel to the plane of the valve blade 139 when the
blade is in its dotted line or closed position. There is no
positive pressure wave reflecting surface provided for low speed
operation, and there is no silencing muffler. The exhaust system
merely opens into the atmosphere along this plane when the blade
139 is open. As the speed of the engine increases, the blade 139
will be lifted to its closed position because of the angle of
attack of the blade and a positive pressure wave reflecting surface
is formed by the undersurface of the blade 139 in cooperation with
the surrounding chamber walls, for high speed operation. The
exhaust system will be selected in length so that the reflected
positive pressure wave will arrive at the exhaust port at the
correct time for high speed operation.
The cross section of exhaust chamber 136A surrounding the blade may
be square or rectangular, or of any other cross sectional shape
which permits the valve blade to move freely from the open to the
closed position and vice versa.
In the device of FIG. 11, one of the important features is the fact
that the blade opens and moves out of the way of the exhaust gases
so that it does not detract from the normal engine power at lower
speeds. The expanding chamber is still present in the exhaust
system to provide improved scavenging and with the high speed
positive pressure wave reflecting surface out of the way, the
engine operation will not be adversely affected at these low
speeds.
FIG. 12 shows a further modified form of the present invention
wherein the exhaust system has a tubular pipe section forming an
expanding chamber 145, another portion forming a chamber 146 which
may be of constant or varying cross sectional area, and a trailing
tubular pipe section forming a positive pressure wave reflecting
surface chamber 147 that has an outlet pipe 148. The outlet pipe
may be omitted and the exhaust gases may escape simply through an
orifice or orifices, if desired. In this embodiment the chamber
surrounding the valve blade may be circular in cross section, if
desired.
In FIG. 12 a valve blade 149 is mounted on a shaft 150 that is
rotatably mounted in the pipe, but in this instance the valve blade
can be centered on the shaft and the axis of the shaft can
intersect the longitudinal axis of the pipe chamber. The shaft 150
has a control lever 151 attached thereto on an outer end thereof. A
push-pull control wire 152 is attached to the outer end of the
lever 151, and the control wire slides inside a housing 153. The
housing 153 may be attached to a panel or similar mounting 154 for
example on the snowmobile shown at 70 in FIG. 4, and the control
button 155 attached to the control wire 152 is used for actuating
the blade 149 when desired. Manual valve actuation is thus provided
for. When the control knob is pulled outwardly, away from panel
154, the blade is moved to high speed operating position. By being
able to recognize the speed of the engine, the operator can obtain
satisfactory dual range resonance. The positive wave reflecting
surface formed by the reducing cross sectional area chamber 147 is
effective at low speeds, and the surface of the blade 149 provides
the positive pressure wave reflecting surface for higher speeds.
The blade 149 of course will have an opening therethrough for
escape of exhaust gases as previously shown or may have openings of
other suitable design.
Referring now to FIG. 13, a further modified automatic control
system is shown. In this instance, a valve is shown mounted in an
exhaust system 160 which corresponds to the exhaust system 79 in
FIG. 4. The exhaust system has an expanding cross sectional area
chamber 161, a valve chamber 162, and if desired has a reducing
cross sectional area chamber 163. Of course, the control means
shown and about to be described can be used with any of the
previous forms of the invention, even that shown in FIG. 11, and
can be used in place of the manual control means in FIG. 12. In
FIG. 13, a blade 164 corresponding to the blade 90 in FIG. 7 is
mounted onto a shaft 165 that is rotatably mounted in the valve
chamber 162 and a control lever 166 is mounted on the outer end of
the shaft. The cross sectional shape of the valve chamber 162 can
be made of desired contour which will cooperate with the shape of
blade 164.
The blade 164 is automatically controlled in response to engine
speed, but in this embodiment a separate engine speed sensor 167
actuates a switch (not shown) for controlling a circuit from a
battery 168 to a solenoid 169. The solenoid is attached to the
lever 166 and to a bracket 170 that is attached to the exhaust
system. The solenoid 169 can be of any desired form and is shown
merely schematically in the present device.
The engine speed sensor 167, likewise, is shown schematically
because many different types of engine speed sensors can be
utilized interchangeably. There are solid state electronic engine
speed sensors presently available which are extremely accurate; fly
ball devices can be utilized; inlet gas flow sensors to determine
the mass rate flow of inlet gas can be used, and different types of
engine speed sensors that operate from the exhaust gases can also
be utilized. For example, in my U.S. Pat. No. 3,367,311 there is a
showing of several different types of engine speed sensors that
could be utilized with this present invention as well.
As explained above, the engine speed sensor 167 in turn controls
suitable contacts to control the circuit to solenoid 169 when the
proper engine speed has been reached for shifting the blade 164 to
its closed position and thus introducing a high speed positive
pressure wave reflective surface. The solenoid 169 may be power
actuated to either open or close the valve at the proper engine
rpm. The solenoid may be spring loaded to the open or closed valve
position if desired, and then for high or low speed operation, when
the correct engine rpm has been reached, the solenoid only has to
be relaxed. The valve can also be spring loaded by an "over center"
type spring and lever arrangement, whereby the valve is retained in
both its open and closed positions by spring pressure.
The solenoid can be replaced with a fluid pressure cylinder
actuated from a source of fluid pressure through a valve controlled
by speed sensor 167, if desired.
Referring now to FIG. 14, a modified form of the invention which
will provide for at least three resonant engine speeds is shown. In
this form of the invention, an exhaust system 175 includes an
expanding cross sectional area pipe forming a chamber 176 leading
from an engine exhaust port into a valve chamber 177. The cross
sectional shape of the chamber 177 can be of any desired
configuration, but for purposes of explanation may be assumed to be
the same as that shown in FIG. 8. It can, as in any of the previous
forms, be rectangular, square, elliptical or of any other desired
cross section, which will cooperate properly with the particular
shape of the blade utilized.
In this exhaust system, a reducing cross sectional area chamber 178
is shown and forms a positive pressure wave reflecting surface 179
suitable for low engine speed operation.
The device shown in FIG. 14 is made for operation as a tuned pipe
at three separate engine speeds or ranges of speeds. There are, as
shown, two blades, 180 and 182. Blade 180 is mounted on a shaft 181
that is rotatably mounted between the side walls of the valve
chamber 177, and blade 182 is mounted onto a shaft 183 also
extending between the side walls of the chamber 177. The blade 180
is positioned for power increase at medium speeds, and is the blade
that is farthest downstream with respect to the direction of gas
flow, which is indicated by the arrow 184. Shaft 181 has a lever
185 attached thereto, with a weight 186 mounted thereon and
operating as the lever 91 and weight 92 of FIG. 5. The weight 186
will retain the blade 180 in its open (solid line) position under
slow speed conditions. As shown, the weight 186 is also adjustable
along the lever 185. The blade 180 will be stopped in open position
with a suitable adjustable stop screw 187, and when the velocity of
the exhaust gas reaches a preselected level, the leading portion of
blade 180 will be lifted up by gas flow action because of its angle
of attack with respect to the gas stream, and moved to its closed
position shown in dotted lines. The lower surface of valve blade
180 will then form a positive pressure wave reflecting surface in
cooperation with the surrounding walls of valve chamber 177, and
will be properly positioned for improving engine operation at a
higher rpm range than the reflecting surface 179. The valve blade
180 of course will have an outlet opening provided therethrough, or
at least will have a loose enough fit inside the exhaust pipe
chamber 177 so that a sufficient flow of the exhaust gases can
escape past the blade 180.
The shaft 183 for the blade 182 has a lever 190 attached thereto,
and a weight 191 mounted on the lever to urge the blade 182
normally to its open position, shown in FIG. 14, resting against an
adjustable stop screw 192. The weight 191 may be of greater mass
than weight 186 or may act through a greater effective leverage
ratio so that the valve blade 182 is held open until the engine rpm
is higher than that at which valve blade 180 closes. Thus valve
blade 182 is the one that, when closed, provides a positive
pressure wave reflecting surface for top engine speed operation.
When the flow of exhaust gases past valve blade 182 becomes
sufficient to move the blade to its closed position shown in dotted
lines, then it provides a positive wave reflecting surface in
cooperation with the surrounding valve chamber walls, and because
it is positioned closer to the exhaust port than the other valve
blade 180, the rpm at which the positive pressure reflected wave
from blade 182 is properly timed is higher than the proper rpm for
the blade 180. Openings through or in cooperation with the valve
blade 182 will permit the exhaust gases to escape when the blade is
in the closed position.
It is apparent of course that separate engine rpm sensors could be
used for operating these series valve blades 180 and 182 if
desired, or that manual control also could be used. With an engine
rpm sensor, the valve blade 180 would be actuated to close at
medium rpm, and at a higher engine speed the valve blade 182 would
be actuated to close.
In FIG. 15 a modified form of the invention is utilized wherein two
separate valves are positioned to form a double tapering positive
pressure wave reflecting surface in cooperation with the
surrounding tubular chamber. The exhaust pipe system 195 includes
the pipe section forming an exhaust expanding chamber 196 that
extends from the exhaust port of a two-cycle engine, and a pipe
section forming a valve chamber 197. It also can include, if
desired, the reducing cross sectional area chamber 198 which
provides the positive pressure wave reflecting surface for low
speed operation. In this instance, the cross sectional shape of the
chambers 196, 197 and 198 can be rectangular or can be such as that
shown in FIG. 8.
In the valve chamber 197, a pair of valve blades 201 and 202 are
mounted. The valve blade 201 is mounted onto a shaft 203 that is
rotatably mounted in the walls of chamber 197 of the exhaust system
and the valve blade 202 is mounted onto a shaft 204 which is also
rotatably mounted in the chamber 197. The shafts 203 and 204 in
turn have gears mounted thereon. The shaft 203 has a gear 205
mounted thereon and this gear meshes with a gear 206 that is
mounted on the shaft 204. A lever 207 is also mounted on the shaft
204 and is actuated by means of a hydraulic cylinder 208. The
hydraulic cylinder controls movement of the lever 207 about the
axis of the shaft 204. The cylinder 208 can be controlled by means
of an engine rpm sensor and suitable valving. The sensor and
valving are shown only schematically as a control system box
209.
When the cylinder 208 is actuated it moves lever 207. Lever 207
drives valve blade 202 and gear 206 drives gear 205 and valve blade
201, so the valve blades move to their dotted line positions. The
two valve blades 201 and 202 then provide a V-shaped positive
pressure wave reflecting surface in cooperation with the
surrounding chamber wall. The control system 209 actuates the
cylinder 208 to return the valve blades to their open positions
when the engine speed drops below a preselected level. The cylinder
shifts the valve blades to their dotted line or closed positions
for high speed operation. The valve blades 201 and 202 provide for
exhaust gas escape where their ends mate as shown in dotted lines,
or the valve blades can have separate openings through which the
exhaust gases can escape.
The cylinder 208 could be pneumatically actuated, or it could be
replaced with an electric actuator. Control system 209 could then
be modified to suit the type of power actuator being utilized.
In FIG. 16, a further modified form of the invention is shown. An
exhaust system 215 has an expanding chamber 216 leading from the
exhaust port of a two-cycle engine, into a valve chamber 217.
Downstream from the valve chamber is a perforated baffle wall 218
which has openings 219 provided therein. This perforated wall
provides an exhaust silencing effect, and at the same time provides
a low speed positive pressure wave reflecting surface. There could
also be perforated pipes provided, each opening through a separate
aperture in a wall similar to 218. If desired, the wall 218 could
be planar and normal to the axis of the exhaust pipe, or could be
tapered, or in any other desired configuration. Any configuration
desired may be placed downstream of wall 218, such as additional
muffler baffles, perforated tubes or simple outlet pipes. The
exhaust pipe could also terminate at wall 218, if desired. For high
speed operation, a valve blade 220 is mounted onto a shaft 221 that
is rotatably mounted in the walls forming the chamber 217, and can
be actuated as explained before and held in its open position as
before with suitable weights or springs or with a power actuator or
manual control. The valve is shown merely for illustrative purposes
to demonstrate that it will cooperate with the perforated end wall
218 fixed in place as a muffler wall or as part of a silencing
system. The valve blade 220 is designed and actuated so that it
will move to its dotted line position when the engine rpm
increases, forming a positive pressure wave reflecting surface for
high rpm operation. The valve blade 220 includes an opening 222 for
exhaust gases to escape when the valve is closed. The wall 218 will
provide an exhaust silencing effect whether the valve 220 is open
or closed.
In FIGS. 17 and 18 there is shown a further modified form of the
invention. In this form, the exhaust pipe 225 is of the expansion
chamber type as before, and has a tubular pipe section forming an
expanding chamber 226 and a pipe section forming a chamber 227. A
reducing cross sectional area chamber 228 may be provided for a low
speed positive pressure wave reflecting surface. In this instance,
a valve blade 230 is mounted onto a cross shaft 231 and is
controlled with a suitable weight or spring system holding the
blade in open position as before, and there is also provided a stop
member 236 for stopping it in proper open position. The valve blade
230 extends across the cross sectional area of the chamber, and
moves from an open position shown in solid lines in FIG. 17, to a
closed position shown in dotted lines. In this particular form of
the invention, the valve blade 230 rests against a projecting rim
arrangement 232 and 233 when in closed position. A first rim member
232 is provided adjacent the upper portions of the chamber 227 and
the upper edges of the upstream part of the valve blade 230 will
rest against this rim member when the valve is in closed position.
A separate rim member 233 is provided along the lower portions of
the chamber 227 and the lower edges of the downstream portion of
the valve blade will rest against this rim member. Thus the rim
members will contact the edge surfaces of the valve blade 230 when
the valve closes so as to give positive sealing around the
peripheral edges of the valve blade and also to support the blade
when it is closed and thus prevent it from jamming or sticking
against the interior surfaces of the chamber 227, while at the same
time maintaining a positive gas seal. The rim members are in offset
planes, as shown, so that they will seal on opposite sides of the
valve blade when it pivots to its closed position.
The valve blade 230 provides, in combination with the surrounding
tube walls, the positive pressure wave reflecting surface for high
speed operation and may automatically be shifted to its closed
position, or can be manually controlled if desired. The shaft 231
can have a lever 234 (FIG. 18) thereon and a weight 235 on the
lever for urging the valve to open position in the same manner as
shown in FIGS. 4-8. In this particular instance, the valve chamber
can be rectilinear in cross section as shown. This does not affect
the operation of the valve or exhaust, because the cross sectional
shape can be varied as desired to cooperate with the particular
valve blade outline and pivot location. A gas outlet opening 237 is
provided in blade 230.
In FIGS. 19 and 20 a further modified form of the present invention
is shown wherein an exhaust pipe 240 has expansion section 241
leading from the exhaust port of a two-cycle engine, and a valve
chamber 242. The chamber 242 can be open at its downstream end, or
can have a reducing cross sectional area chamber, or a muffler or
any desired configuration downstream of the valve blade 244. Guide
tracks 243 in which a sliding valve blade 244 can be mounted are
positioned along the sides of chamber 242. The slide valve blade
244 can be manually operated (as shown) or can be controlled
through a suitable linkage so that the blade can be moved to a
position wherein it substantially blocks the chamber 242, or can be
slid outwardly as shown in solid lines to where it substantially
clears the interior of the chamber 242 so that there is a straight
through flow of exhaust gases. The slide valve passes through a
slit in one wall of the exhaust pipe, and can have an insulated
handle as shown.
When the sliding blade valve 244 is in open position, the engine
will operate with the benefits of the expansion section exhaust
available and whatever exhaust arrangements may be located further
downstream, and when the blade 244 is in the closed position it
provides, in cooperation with the surrounding duct walls, a
positive pressure wave reflecting surface that is inclined with
respect to the longitudinal axis of the exhaust chamber so as to
provide positive pressure wave reflection suitable for high speed
operation of the engine. As shown, an opening 245 can be provided
in the sliding blade 244 to permit exhaust gases to escape when the
blade is in closed position. If desired, the sliding blade 244
could instead have a plurality of perforations in it to help in
muffling the engine noise rather than a single opening 245. Also,
the sliding blade can otherwise be designed so as not to close the
the chamber completely, when in closed position, thus permitting
the escape of exhaust gases.
The slide member here is shown in a valve chamber having a
substantially square cross section. The guide tracks 243 for the
valve blade can be of any desired configuration and as shown,
extend on the outside of the exhaust pipe to support the slide
valve blade when it is open. The handle for the valve passes
between the guides. The friction of the guide members holds the
valve in its open or closed position or other suitable arrangements
can be provided for this purpose.
A further modified form of the present invention in a different
type of exhaust system is shown in FIGS. 21 and 22. FIG. 21 is an
edge view of an expansion chamber muffler assembly as viewed along
line 21--21 in FIG. 22. FIG. 22 is a side view showing the unit as
it would be placed along the side of the motorcycle in FIG. 1 or
the snowmobile in FIG. 4. The muffler assembly shown in FIGS. 21
and 22 is disclosed in its general form in my copending
application, Ser. No. 9,507, filed Feb. 9, 1970 and entitled
"IMPROVEMENTS IN TWO-CYCLE ENGINE RESONANCE EXHAUST SYSTEMS." The
description in this application will therefore be abbreviated.
First, the exhaust system 250 comprises a relatively flat housing
252 that encloses a complete resonant exhaust system and muffler
combination by curving or bending the central axis of the tubular
resonant system at least once, preferably at least 90.degree.,
between its inlet and outlet and positioning a muffler in the space
defined by the curved tubular member. As shown, the tubular
resonant chamber member is bent or curved into a "U" and the
muffler is located between the legs of the U. Also as shown, the
entire tubular exhaust channel and muffler are in a single housing,
but they could be separate. As shown in FIG. 22, the cover 275 of
the exhaust system is removed. An exhaust or header pipe 251 leads
from an exhaust port of a two-cycle engine such as the exhaust or
header pipe 26 in FIG. 1 or pipe 77 in FIG. 4. The pipe 251 opens
into a chamber 253 that is expanding in cross sectional area in
direction of exhaust gas flow indicated by the arrow 254. This
chamber is defined between an outer wall 255 of the unit, and a
divider wall 156. These walls extend to a constant cross sectional
area chamber 257 of the unit defined between a curved portion 258
of the outer wall 255 and a curved inner wall 259 that joins wall
256. It should be noted that the expanding chamber extends
partially around the curved walls.
The curved wall 259 merges into a wall 260 that extends
substantially parallel to an outer wall section 261 for a short
distance, and then extends at an angle toward the outer wall
section 261 to form a positive pressure wave reflecting area near
the outlet of the resonant exhaust chamber. The reflecting area is
sufficiently far from the exhaust port of the engine with which the
exhaust system 250 is used so that it will provide for a positive
pressure reflected wave to arrive back at the engine exhaust port
at the proper time for aiding engine power output during lower
speed operation of the engine.
The wall 260 terminates spaced from the wall section 261 so that
there is an outlet opening 263 provided from the curved tubular
exhaust channels formed in this housing. This outlet opening 263
leads into a channel 264 that is defined between the wall 260 and
another wall 265. There are a plurality of apertures shown in
dotted lines at 266 opening through the wall 265 into a second
chamber 267. A partition wall 268 also is provided with a plurality
of apertures shown in dotted lines at 269 that lead from chamber
267 into an outlet chamber 270. The apertures 266 and 269 through
the walls tend to break up the exhaust sound waves as the gases
flow from the outlet opening 263 to the outlet chamber 270. The
exhaust gases then pass through apertures 271 of an exhaust outlet
pipe 272. This causes further muffling of the engine noise. The
exhaust outlet pipe 272 passes out through the end wall of the
housing 252.
As shown in FIG. 21, the housing 252 has a cover member 275 mounted
thereon to close off the open side of the chambers. In FIG. 22 the
cover member is removed, and this cover member can be held in place
with suitable cap screws or other fasteners 276. The interior walls
extend from a fixed outside wall to the cover to form the necessary
chambers.
Adjacent the downstream end of the exhaust chambers which curve
from the header pipe 251 to the outlet 263, there is a planar valve
blade 280 positioned in constant cross sectional area chamber 257.
Valve blade 280 is mounted onto a shaft 281 that is in turn
rotatably mounted in the cover 275, and also is rotatably mounted
through the fixed side wall of the housing 252 with a boss 282. The
shaft 281 is free to pivot about its axis, and as shown, the valve
blade 280 includes an airfoil shaped or streamlined weight 283
adjacent the leading end thereof, when viewed with reference to
direction of exhaust gas movement past the valve. The weight 283 is
positioned with respect to the shaft 281 so that when the housing
252 is properly positioned, the weight will bias or urge the blade
280 to its open position shown in solid lines in FIG. 22. A stop
screw 284 is threaded through a boss 285 provided on the housing
252 and this stop can be locked in place with a suitable lock nut
to support the blade in its desired open position at the selected
angle of attack. When the exhaust gas velocity and pressure coming
from the exhaust pipe 251 through the chamber 257 reaches a
preselected level, the blade will be lifted up to its dotted line
position, and the surface of the blade facing the exhaust pipe 251
will provide a positive pressure wave reflecting surface, in
cooperation with the surrounding chamber walls, so located that the
system will resonate at a higher rate than the resonating rate with
the reflecting area adjacent outlet opening 263. An opening 286 is
provided in the blade 280 so that exhaust gases can escape. The
exhaust gases then go out the outlet opening 263 into the muffler
section through the apertures 266, 269 and 271 and out the pipe
272.
When the engine rpm drops so that the pressure of the gas against
the valve blade 280 drops sufficiently, the blade will drop to the
open position, and the area adjacent outlet opening 263 will again
be operative as the positive pressure wave reflecting area. Thus
the concept of having a plural range of resonant speeds in one
single exhaust system is carried out in this muffler-resonant pipe
combination structure.
In all instances, the cross sectional shape of the exhaust chambers
can be varied as desired or as necessary to cooperate usefully with
the shape of the valve blade, and in FIGS. 21 and 22, of course,
the device is rectilinear in cross section.
Also, the spacing between the valve means and the fixed reflecting
surface or area provided for lower engine speed operation can be
varied to meet design objectives for different usages. The valve
means and fixed reflecting surface or area thus need not be as
close together as shown in the drawings.
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