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BACKGROUND OF THE INVENTION
This invention relates to a motorcycle and more particularly to an improved
induction system for a motorcycle that permits a compact arrangement with
a highly effective intake system.
As is well known, motorcycles offer considerable design problems because of
their relatively small size and compact nature. That is, the components of
the motorcycle must be designed so as to achieve their intended purpose in
a facile manner while at the same time avoiding intrusion with the other
components of the motorcycle and their function.
As a specific example, it has been proposed to employ a suspension for the
rear wheel of the motorcycle in which a single suspension element
(normally a combined spring, tubular shock absorber) is employed. In order
to employ such a single suspension element for the rear suspension, it is
desirable if not necessary to place this suspension element on or near a
plane passing through the longitudinal center of the motorcycle. As a
result, the suspension element must be positioned at least in part beneath
the motorcycle seat. However, the engine is also located in this area and
frequently the engine induction system including the carburetor extends to
the rear of the engine and in proximity to the suspension element. As a
result, the induction system must clear the suspension element and these
two components should not interfere with the operation of the other.
One way of avoiding such interference would be to position the engine at a
lower than desired level in the motorcycle. Such lowering of the engine,
however, has the effect of reducing the ground clearance of the
motorcycle. Alternatively, interference between the induction system and
specifically the carburetor and the suspension element may be avoided by
shortening the overall height of the engine. This also gives rise to
problems, particularly if it is desirable to use an engine of large
displacement. Such large displacement engines, particularly if of the
single cylinder four-cycle type, occupy considerable space and their
induction system may well interfere with a suspension element of the type
wherein a single suspension element is employed for the rear wheel of the
motorcycle.
In addition to the aforenoted problems, it is the common practice to employ
a carburetor for motorcycle engines of the sliding piston throttle valve
type. With a large displacement engine, the carburetor itself also has a
large displacement and large bore and hence the sliding piston throttle
valve requires additional clearance. This, of course, further aggrevates
the problem of positioning all of the components in such a location that
they can operate efficiently and without interference from the others.
In addition to the problem of providing clearance between the various
components and optimum operation, the arrangements as aforedescribed can
cause the carburetor of the engine to be positioned in a location wherein
servicing is extremely difficult. That is, if the engine is raised to such
a level as to provide the desired ground clearance and if the carburetor
is positioned so as to clear the suspension element, the carburetor itself
may be positioned in a relatively inexcessible location with prior art
type of induction systems.
It is, therefore, a principal object of this invention to provide an
improved motorcycle configuration wherein maximum power can be achieved
and the components will not interfere with each other.
It is another object of the invention to provide an improved induction
system for a motorcycle having a rear suspension that embodies a single
suspension element without sacrificing ground clearance or engine
performance.
It is another object of this invention to provide a compact, high
efficiency induction system for a motorcycle.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in a motorcycle having a rear
wheel, a suspension for supporting the rear wheel for relative movement
that includes a single suspension element extending generally in the
longitudinal center plane of the motorcycle, a seat supported at least in
part above the suspension element and an engine disposed forwardly of the
rear wheel and having a combustion chamber. In accordance with the
invention, the engine has a pair of induction passages each serving the
combustion chamber. The induction passages lie in side-by-side
relationship and extend rearwardly from the engine toward the rear wheel.
Charge forming means are provided for delivering a charge to each of the
induction passages.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a motorcycle constructed in accordance
with a first embodiment of the invention, with portions broken away and
with other portions shown in phantom.
FIG. 2 is a partially schematic, top plan view on an enlarged scale of the
engine and induction system of the embodiment of FIG. 1.
FIG. 3 is an enlarged view, with portions shown in cross section, through
the primary barrel of the carburetor of the embodiment of FIG. 1.
FIG. 4 is a cross-sectional view taken through the secondary barrel of the
carburetor of the embodiment of FIG. 1.
FIG. 5 is a side elevational view showing the throttle linkage system of
the carburetor.
FIG. 6 is a partially schematic top plan view, in part similar to FIG. 2,
showing another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1 and 2, a motorcycle constructed in accordance
with the first embodiment of this invention is identified generally by the
reference numeral 11. The motorcycle 11 includes a frame consisting of a
down tube 12, a pair of spaced right and left back tubes 13 and 14 and a
pair of spaced seat rail tubes 15 (only one of which appears in the
drawings). The seat rail tubes 15 are each affixed as by welding to the
upper ends of the back tubes 13 and 14 in a known manner. In addition, a
bracket 16 is affixed to the forward end of the down tube 12 via a head
pipe 17. The forward ends of the seat rail tube 15 are fixed, as by
welding, to the bracket 16. The remaining components of the frame will not
be described in any detail and it is to be understood that the
construction of the frame generally may take any of the known forms in
this art.
An engine, indicated generally by the reference numeral 20, is supported
within the frame and in the illustrated embodiment the engine 20 has a
crankcase 18 that is affixed to the down tube 12 and the back tubes 13 and
14 so as to form a structural part of the frame assembly.
A front wheel, shown in phantom and indicated generally by the reference
numeral 19, is supported by means of a suspension system (not shown) on a
front fork 21 which, in turn, is rotatably journalled for steerning
movement by the head pipe 17. A handlebar 22 is affixed to the front fork
21 in a known manner and carry handle grips 23 at their outer ends, one of
which may constitute an accelerator grip.
A rear wheel 24 is journalled by means of a pair of triangular frame
assemblies, indicated generally by the reference numeral 25, positioned at
each side of the wheel 24. Each frame assembly includes a generally
horizontally extending member 26 and an inclined member 27 with the frame
assemblies at each side being interconnected by means including a briding
member 28. Each frame assembly 25 is pivotally supported at its forward
end by means of a pivot pin 29 that is carried by a bracket 31 that is
affixed to the crankcase 18.
The pivotal movement of the wheel 24 and frame assemblies 25 relative to
the motorcycle frame is controlled by means of a single suspension
element, indicated generally by the reference numeral 32 that is
positioned generally on the longitudinal center plane of the motorcycle
11. The suspension element 32 may, in a preferred form of the invention,
take the form of a combined tubular shock absorber and surrounding coil
spring assembly. One end of the suspension element 32 is pivotally
connected to the frame assemblies 25 by means of a suitable connection to
the interconnecting part 33 of the angular members 27 of the frames 25 on
each side of the wheel 24. The forward end of the suspension element 32 is
pivotally connected to the bracket 16 at its trailing end in a known
manner.
A seat 34 is carried by the seat rails 15 and overlies at least in part the
rearward portion of the suspension element 32. A fuel tank 35 of generally
saddle shape is carried by the bracket 16 in front of the seat 34 and in
partial overlying relationship to the suspension element 32. It should be
noted that the suspension element 32 extends generally above the engine
20.
The engine 20, in the illustrated embodiment, is of the reciprocating,
single cylinder type and has a combustion chamber 36 that is served by a
pair of intake ports 37 and 38 and cooperating intake valves 39 and 41.
Also serving the chamber 36 are a pair of exhaust ports 42 and 43 and
cooperating exhaust valves 44 and 45. The intake valves 39 and 41 and the
exhaust valves 44 and 45 are all operated by means of a single overhead
camshaft 46 via rocker arms in a known manner.
A pair of spark plugs 47 are positioned on diametrically opposite sides of
the combustion chamber 36 between the intake valve 39 and exhaust valve 44
and the intake valve 41 and the exhaust valve 45, respectively.
The cylinder head exhaust ports 42 and 43 merge into cylinder head exhaust
passages 48 and 49 which, in turn, feed a common exhaust pipe 51 for
discharge of the exhaust gases to the atmosphere.
The induction system for the engine 20 includes a pair of intake pipes 52
and 53 that serve the cylinder head intake passages that terminate at the
intake ports 38 and 39. A two-stage carburetor, indicated generally by the
reference numeral 54, serves the intake pipes 52 and 53. The carburetor 54
has a primary barrel 55 which serves an intake passage 56 of the pipe 52
and a secondary barrel 57 that serves a secondary intake passage 58 of the
pipe 53.
Referring now additionally to FIG. 3, the primary barrel 55 includes an
intake passage 59 in which a venturi section is formed by means of a
sliding piston type of throttle valve 61. The position of the throttle
valve 61 is controlled by a link 62 that is pivotally connected at one of
its ends to the throttle valve 61 and at its opposite end to an actuating
lever 63. The lever 63 is, in turn, affixed to a throttle valve shaft 64
which is rotated in a manner to be described. The piston 61 carries a
metering rod 65 that cooperates with a main metering jet 66 to control the
flow of fuel from a fuel bowl 67 into the induction passage 59 at an
amount determined by the position of the throttle valve 61. In addition,
an idle or slow speed fuel discharge port 68 is positioned in the intake
passage 59 downstream of the throttle valve 61.
Referring now additionally to FIG. 4, the secondary barrel 57 includes an
induction passage 69 in which a sliding piston 71 is supported. In this
barrel, the sliding piston 71 is controlled automatically to maintain a
constant pressure drop across the piston 71. For this purpose, the upper
side of the piston 71 is provided with an enlarged piston portion 72 that
is received in a housing 73 and which divides the housing into an upper
chamber 74 and a lower chamber 75. The upper chamber 74 is exposed to
pressure on the downstream side of the piston 71 by means of a pressure
sensing port 76 that extends through the lower face of the piston portion
71. The chamber 75 is, on the other hand, exposed to atmospheric pressure
or the pressure upstream of the piston 71 through a suitable port (not
shown). A spring 77 is contained within the housing 73 and normally urges
the piston 71 downwardly to its idle position.
The piston 71 carries a metering rod 78 that cooperates with a main
metering jet 79. The main metering jet 79 is positioned at the mouth of a
fuel well 81 that is served from the fuel bowl 67 of the primary barrel
55. In this way, it is unnecessary to provide two fuel bowls for the
carburetor 54 and, therefore, the carburetor 54 may be made more compact
than with prior art type of arrangements.
A manually operated butterfly type throttle valve 82 is positioned in the
induction passage 69 downstream of the piston type valve 71. The throttle
valve 82 is affixed to a throttle valve shaft 83 and is operated by means
of a lost motion connection so that the throttle valve 82 will open at
some point after a predetermined opening of the primary throttle valve 61
by means of a linkage system now to be described.
A linkage system 84, shown in most detail in FIG. 5, is interposed between
the carburetor barrels 55 and 57. The linkage system 84 includes a bell
crank 85 that is affixed against rotation to the primary throttle valve
shaft 64. A pair of control wires 86 and 87 are affixed to opposite arms
of the bell crank 85 and are connected to the accelerator grip 23 for
rotation of the throttle valve shaft 64 for manual positioning of the
primary throttle piston 61.
The bell crank 85 defines a generally U-shaped recess 88 into which a tang
89 formed at one end of a control lever 91 ends. The control lever 91 is
journalled on the primary throttle valve shaft 64. On the rear side of the
tang 89, the bell crank 85 is formed with a generally parallelly extending
tang 92. A screw 93 is threaded through the bell crank tang 92 and is
locked in place by a lock nut 94. The screw 93 is adapted to engage the
rear side of the tang 89 and rotate the control lever 91 in a manner to be
described.
A guide pin 95 extends from the opposite side of the bell crank gap 88 and
is surrounded by a coil compression spring 96 which engages the opposite
side of the control lever tang 89 so as to maintain the tang 89 in
engagement with the screw 93.
The opposite end of the control lever 91 carries a pin 97 that is adapted
to coact with a tang 98 formed on a control lever 99 that is fixed to the
secondary throttle valve shaft 83. A torsional spring (not shown) normally
biases the control lever 99 in a counterclockwise direction as viewed in
FIG. 5 so that the secondary throttle valve 82 will be maintained normally
in a fully closed position. The throttle valve 82 is closely fitted to the
induction passage 69 (FIG. 4) so as to substantially preclude any flow
when it is closed. The pin 97 is normally spaced from the control lever
tank 98 in the idle position so as to provide some lost motion in the
opening of the throttle valves 61 and 82, as will be described. The amount
of this lost motion is determined by the adjustment of the screw 93.
Air cleaners 101 are provided for each of the carburetor barrels 55 and 57
on opposite sides of the suspension element 32 (FIG. 1). The air cleaners
101 supply filtered and, if desired, silenced air to the carburetor 54 and
specifically to its barrels 55 and 57.
The operation of this embodiment will now be described by reference to all
figures. The figures show the engine as it appears when it is in its
idling condition. In this position, the manually operated throttle valve
61 is at its idle position and, as has been noted, the manually operated
secondary throttle valve 82 is fully closed. Thus, during this running
condition, only the primary carburetor barrel 55 will supply fuel air
mixture to the cylinder head intake ports 38 and 37. Both the intake
valves 39 and 41 will continue to open and close and to provide some
cooling for the secondary intake valve 39, a small transfer passage 102
extends from the primary barrel 55 to the secondary barrel 57 downstream
of the respective throttle valves 61 and 82. Thus, a small amount of
fuel/air mixture will be delivered to the intake port 37 through this
transfer passage 102.
As the accelerator grip 23 is rotated in an opening direction, the bell
crank 85 will also be rotated in a counterclockwise direction as viewed in
FIG. 5 and the primary throttle piston 61 will begin to open. The metering
rod 65 will increase the fuel flow as the air flow is increased due to
opening of the primary throttle valve 61. Until the pin 97 contacts the
control lever tang 98, however, the secondary throttle valve 82 will be
held closed. As has been previously noted, the amount of lost motion or
delay before opening of the secondary throttle valve 82 is adjusted by the
screw 93. During this continued opening of the primary throttle valve 61,
a small amount of fuel/air mixture will continue to be delivered to the
secondary cylinder head intake port 37 by the transfer passage 102.
Once the pin 97 contacts the control lever tang 98, continued opening of
the primary throttle piston 61 will cause opening of the secondary
throttle valve 82. When this occurs, the piston 71 will seek a position to
maintain a constant pressure drop across the induction passage 69 and the
metering rod 78 will appropriately control the fuel discharge. Thus,
additional fuel/air mixture will be delivered to the engine chamber 36
through both of the intake ports 38 and 37.
It should be readily apparent that this embodiment of the invention
provides good maximum power output by providing sufficient fuel/air flow
while at the same time permits the use of smaller intake passages and
smaller carburetors barrels for each intake passage. Therefore, the
carburetor barrels 55 and 57 may be conveniently positioned without
interference from the adjacent suspension element 32. Also, it is possible
to use piston type throttle valves without interference with the
suspension element 32 or the lower portion of the seat 34. In addition,
because of the use of the staged throttle valves, a high velocity of the
intake charge may be achieved even at low engine speeds so as to insure
good fuel economy and efficient control of unwanted exhaust gases. In
addition, the use of the transfer passage 102 insures against any damage
to the intake valve 39 and against the accumulation of carbon deposits
even under low speed running. The compact construction also permits the
carburetor 54 to be positioned so that it can be serviced and adjusted
easily and without removal of other components of the motorcycle. This
compactness is further achieved through the use of a single fuel bowl 67
for both barrels 55 and 57.
In the embodiment of FIGS. 1 through 5, the plural intake passages were
used in conjunction with an engine of the type having two intake valves
for each cylinder. Of course, the invention may be used in conjunction
with an engine in which only a single intake valve is used for each
cylinder. Such an embodiment is shown in FIG. 6 wherein the engine
induction system is only illustrated. It is believed that only this
portion of this embodiment need be illustrated since the application of it
to the complete motorcycle is believed to be readily apparent to those
skilled in the art.
The engine constructed in accordance with this embodiment of the invention
is identified generally by the reference numeral 151. The engine 151 is of
the single cylinder type and has a combustion chamber 152 in which a
single intake port 153 and single exhaust port 154 are provided.
Respective intake and exhaust valves 155 and 156 control the flow through
the ports. The exhaust port 156 serves a cylinder head exhaust passage 157
which as in the preceding embodiment discharges into an exhaust pipe.
In this embodiment, a pair of cylinder head intake passages 158 and 159
serve the single intake port 156. The passages 158 and 159 are served by
intake pipes 52 and 53 as in the preceding embodiment. The remaining
components including the carburetor are the same as the embodiment of
FIGS. 1 through 5 and for that reason these components have been
identified by the same reference numeral and will not be described again.
In addition, the operation of this embodiment also will not be described
because it is believed to be readily apparent to those skilled in the art
and is the same as the previously described embodiment.
In the embodiments described and illustrated, a two-barrel staged
carburetor was employed. It is to be understood that the invention may be
used in conjunction with two single barrel type carburetors that are
operated in staged sequence. Alternatively, each intake passage may be
served by a respective two-barrel carburetor.
In the embodiments described, only a single cylinder engine has been
illustrated. It is to be readily understood that the invention may be used
with engines having two or more cylinders by employing plural intake
passages with separate carburetor barrels for each of these intake
passages. Also, although the invention has been described in conjunction
with two intake passages for each chamber, it is to be readily understood
that it may be used in conjunction with engines having more than two
intake passages per chamber.
In all embodiments, the arrangement permits a very compact arrangement by
permitting individual carburetors to be smaller than those previously
employed and also permits the use of piston type throttle valves without
interference with the remaining components of the engine and without
compromises in design. Furthermore, the staging of the carburetors permits
good performance throughout the entire engine speed and load ranges.
Various other changes and modifications than those specifically described
and illustrated may be made without departing from the spirit and scope of
the invention, as defined by the appended claims.
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