Note: Descriptions are shown in the official language in which they were submitted.
2~8d497
OVERHEAD CAM ENGINE WITH DRY
SUMP LUBRICATION SYSTEM
The present invention pertains to a portable
engine, and, in particular, to a single cylinder
internal combustion engine of the size and type
adapted for use in power equipment such as that
used in lawn and garden, general utility and snow
removal operations. Such equipment includes but
is not limited to lawnmowers, snow throwers,
generators, string trimmers, leaf blowers, ice
augers, earth movers, etc.
A variety of portable engines which are
relatively lightweight have been employed with
outdoor or lawn and garden power equipment such as
lawnmowers, string trimmers and the like. While
both four cycle and two cycle engine designs have
previously been utilized, four cycle engines have
generally emerged as the preferred design from the
standpoint of reducing exhaust and noise
emissions. In particular, recent legislation has
reduced allowable exhaust emission levels to a
point where the engine must be carefully designed
to comply with promulgated emission levels, and
four cycle engines typically burn cleaner than two
cycle engines.
One shortcoming of some commercially
available four cycle engines that undesirably
leads to higher emissions relates to their
propensity to distort in shape. As the engine
heats up during usage, the thermal expansion of
the engine cylinder block components may produce
bore distortions which allow leakage, such as
lubricating oil, to pass the piston rings and
pollute the engine exhaust. In particular, due to
weight and space restrictions inherent in the
utilization of these portable engines, and in
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2
order to accommodate other mechanical workings of
the engines such as drive components for an
overhead camshaft, the cylinder bore wall
thickness may vary markedly around the bore
perimeter. In addition, the walls may be less
rigid than optimal because a thin inner wall must
be provided to separate multiple internal
chambers. In addition, reinforcing ribbing may be
withheld due to spacing requirements. These wall
thickness variations and lack of rigidity may
result in a non-uniform expansion or distorting of
the cylinder bore during combustion pressure and
thermal cycling, and consequently an unclean
engine combustion may occur. A further
consequence of such distortion producing leakage
is to form oil-based deposits in the combustion
chamber. It is well known that these deposits are
an important source of the emission of volatile
organic compounds, a critical constituent in the
control of exhaust emissions. Build-up of these
deposits over time is the main contributor to the
deterioration of the control of exhaust emissions
over the useful life of an engine.
Another potential source of cylinder bore
distortion stems from the use of a separate head
and cylinder. When a cylinder head is fastened to
the cylinder block, the point loading around the
cylinder bore which occurs with head bolt torquing
may create sufficient bore distortion to
compromise the seal with the piston. The head
gasket normally introduced between the cylinder
and head creates additional bore distortion
concerns. For example, because the head gasket
serves as a heat transfer barrier and thereby does
not uniformly distribute the heat energy over the
cooling surfaces of the engine, distortion
~~8049~
3
potential of the cylinder bore associated with
thermal expansion may be exacerbated.
Another shortcoming of some existing single
cylinder engines relates to their lubrication
system. Many engines depend on a continual
splashing of the lubricant collected in the sump
to lubricate the moving engine components. This
splashing technique is not entirely satisfactory
as it tends to be less reliable in thoroughness
than pressurized lubrication. Further, because
splash-type lubrication demands that the engine
remain in a designed-for orientation to ensure the
oil splashers extend into the collected lubricant,
the orientations at which the engine can operate
may be limited, thereby hindering engine
applications. In other systems, a pump immersed
in the lubricant collected in the crankcase sump
distributes that lubricant around the engine. In
addition to having a limited range of engine
orientations at which a given pump will function,
this configuration has several disadvantages. For
example, a separate pump is required which may
increase the engine weight, engine cost and be
inconvenient to access for servicing. In
addition, the amount of oil is limited by the
crankcase volume. Still other engines which use a
dry sump lubrication system require an additional
pump mechanism to pump the sump contents to a
reservoir, and this additional pump adds
undesirable weight and cost.
The need for flywheels introduces other
problems in portable engines. Due to space
constraints, flywheels are typically mounted on
the crankshaft at a position external of the
engine housing and in a cantilevered fashion. To
support this cantilevered flywheel mass without
21~~497
4
failure, the crankshaft must be formed with a
stronger shaft than would be required without an
external flywheel. Regardless of whether this
stronger shaft is obtained by using a stronger
material or by providing a larger diameter shaft,
the overall weight of the engine is likely to be
increased, and the ease of portability of the
engine is thereby diminished. In addition,
flywheels are frequently formed separately from
the crankshaft and then rotatably fixed together
via keying. Unfortunately, during aggressive or
emergency stopping which can occur by accident or
by use of braking devices, the inertia of the
flywheel can lead to breakage of the key between
the crankshaft and the flywheel, which renders the
engine nonoperational.
Thus, it is desirable to provide a small
internal combustion engine which overcomes these
and other disadvantages of prior art engines.
The present invention provides a single
cylinder, four cycle overhead cam engine designed
to satisfy existing emission standards while still
providing a lightweight construction convenient
for applications such as lawnmowers and handheld
devices. The uniform wall thickness and
reinforcing ribs incorporated into the engine
cylinder block reduces bore distortions which
precipitate an unclean operation. The dry sump
lubrication system employed eliminates the need
for an extra pump, which would undesirably add
weight to the engine, to lift oil used to
lubricate the engine parts back to a reservoir for
recirculation. This unique means of providing
"free" lift pumps saves both weight and cost. By
mounting the engine flywheels internally of the
engine housing and introducing a lightweight fan
21~~~~~
on the crankshaft externally of the housing, the
inventive engine can be formed with a lighter
crankshaft but still be provided with a cooling
air flow over the engine housing.
5 The invention, in one form thereof, is a
single cylinder, four stroke cycle, overhead cam
engine having an engine block that includes an
integrally formed cylinder and cylinder head and
having a crankshaft cavity and a crankcase cavity,
an interconnected crankshaft, connecting rod and
piston disposed in the crankcase cavity, and a
camshaft and belt assembly disposed in said
camshaft cavity.
A pair of valve stem bores extend through the
block between the camshaft and crankcase cavities,
the valve assembly including valve stems disposed
in the stem bores. There are no further internal
passages in the block extending between the
camshaft and crankcase cavities. Along the axial
segment of the cylinder wall in which the piston
reciprocates, the wall has a substantially uniform
thickness around substantially all of the wall
circumference.
In accordance with another form of the
invention, the engine comprises an engine housing
including a cylinder and a cylinder head wherein
the cylinder defines an internal bore. A
crankshaft is disposed within the housing and
extends externally thereof and a piston is
operably connected to the crankshaft and mounted
for reciprication within the bore. A camshaft is
disposed within the housing and is operably
connected to the crankshaft, and a valve assembly
is operably connected with the camshaft for
regulating inlet to and exhaust from the cylinder
bore. A lubricant reservoir is located external
CA 02180497 1999-OS-17
6
to the engine housing and lubricant is supplied from the
reservoir to 'the camshaft by means of a pump that
includes a mechanism for returning lubricant used to
lubricate the camshaft within the engine back to the
external reservoir by means of a pumping action produced
by shifting o~F said valve assembly to force lubricant
through a conduit to the reservoir.
According to one aspect of the present invention
there is prov_Lded a single cylinder, four stoke cycle,
overhead cam ~:nternal combustion engine comprising:
an engine housing including an integrally formed
cylinder and cylinder head, said cylinder including a
cylinder wall having an inner radial periphery portion
defining an internal bore;
a crankshaft disposed within said engine housing and
extending externally thereof;
a piston operably connected to said crankshaft and
mounted for reciprocation within said cylinder internal
bore, said piston cooperating with said cylinder head and
said cylinder to define a combustion chamber within said
bore, wherein said piston reciprocates during operation
along an axial segment of said cylinder;
wherein along said axial segment said cylinder wall
includes an outer radial periphery portion ringing said
internal bore and externally exposed to permit cooling by
a passing air flow, wherein said cylinder wall defined by
said inner radial periphery portion and said outer radial
periphery portion comprises a generally ring-shaped
configuration with a substantially uniform wall thickness
around substantially all of the wall circumference;
CA 02180497 1999-OS-17
6a
at least one cooling fin circumscribing said outer
radial periphery portion and radially projecting
therefrom;
an overhead camshaft disposed within said engine
housing and o~perably connected to said crankshaft; and
a valve assembly operably connected with said
camshaft for :regulating inlet to and exhaust from said
cylinder internal bore.
According to another aspect of the present invention
there is provided an internal combustion engine
comprising:
an engine housing including a cylinder head and a
cylinder, said cylinder including an internal bore, said
cylinder head including at least one valve assembly
cavity having a lubricant outlet;
a crankshaft rotatably supported on at least first
and second crankshaft bearings within said engine
housing;
a camshaft rotatably supported on at least first and
second camshaft bearings within said engine housing and
operably connected to said crankshaft, said camshaft
including at least one cam;
a reciprocating piston slidable within said internal
bore and opera.bly connected to said crankshaft;
a lubricant reservoir;
at least one supply passage providing lubricant flow
communication between said lubricant reservoir and said
camshaft bearings, wherein lubricant introduced at said
camshaft bearings passes to said valve assembly cavity
during camshaft lubrication;
CA 02180497 1999-OS-17
6b
at least one return passage providing lubricant flow
communication between said valve assembly cavity
lubricant outlet and said lubricant reservoir; and
a valve assembly in communication with said cylinder
internal bore and operable by said at least one cam, said
valve assembly including a pumping element movable within
said valve assembly cavity during shifting of said at
least one valve assembly, said pumping element structured
and arranged ;such that movement of said pumping element
within said valve assembly cavity in a first direction
reduces a volume within said valve assembly cavity
between said :Lubricant outlet and said pumping element to
create a high pressure within said valve assembly cavity,
wherein said high pressure propels lubricant within said
valve assembler cavity out of said cavity through said
lubricant outT_et .
According to yet another aspect of the present
invention there is provided an internal combustion engine
comprising:
an engine' housing including a cylinder and cylinder
head, said cylinder defining an internal bore;
a crankshaft disposed within said engine housing and
extending externally thereof;
a piston operably connected to said crankshaft and
mounted for reciprocation within said cylinder internal
bore;
a camshaft disposed within said engine housing and
operably connected to said crankshaft;
a least one valve assembly operably connected with
said camshaft for regulating inlet to and exhaust from
said cylinder internal bore;
CA 02180497 1999-OS-17
6c
a lubricant reservoir located external of said
engine housinc3;
means fo:r supplying lubricant from said reservoir to
said camshaft,, said lubricant supplying means comprising
a pump; and
means for returning lubricant used to lubricate said
camshaft from within said engine housing back to said
external reservoir, wherein said lubricant returning
means comprises a pumping action produced by shifting of
said at least one valve assembly within said engine
housing to force said lubricant through a conduit to said
reservoir.
According to still yet another aspect of the present
invention there is provided an internal combustion engine
comprising:
an engine: housing including a cylinder and cylinder
head, said cylinder defining an internal bore;
a crankshaft disposed within said engine housing and
extending externally thereof;
a piston connected to said crankshaft and mounted
for reciprocation within said cylinder internal bore;
a camshaft disposed within said engine housing and
operably connected to said crankshaft;
at least one shiftable valve assembly operably
connected with said camshaft for regulating inlet to and
exhaust from said cylinder internal bore;
a lubricant reservoir located external of said
engine housing;
a pump supplying lubricant from said reservoir to at
least one of s,~id camshaft and crankshaft;
CA 02180497 1999-OS-17
6d
said pump disposed externally from said cylinder
internal bore; and at least one lubricant passageway
connected between said camshaft and said crankshaft; and
means for returning lubricant used to lubricate said
crankshaft from within said engine housing back to said
external reservoir, wherein said lubricant returning
means comprises a pumping action produced by movement of
said piston within said cylinder internal bore to force
said lubricant through a conduit to said reservoir.
Accordin~3 to still yet another aspect of the present
invention there is provided for use with a four cycle,
single cylinder internal combustion engine including an
engine housing with camshaft bearings, a crankshaft with
a drive sprocket, a reciprocating piston within a
cylinder bore,, an endless loop drive member connectable
to the drive ;sprocket, first and second valve assemblies
for regulating inlet to and exhaust from the cylinder
bore, and a ge~rotor pump for engine lubricant
pressurization, a camshaft comprising:
a cam sprocket connectable to the endless loop drive
member;
a gerotor inner rotor for the gerotor pump;
first and second bearing journals rotatably
supported by the housing camshaft bearings;
first and second cams for biasing said first and
second valve assemblies respectively; and
wherein said cam sprocket, said gerotor inner rotor,
said first and. second bearing journals, and said first
and second cams are integrally constructed in a one-piece
molding of one of a thermoplastic material or a thermoset
material.
CA 02180497 1999-OS-17
6e
According to still yet another aspect of the present
invention there is provided a single cylinder, four
stroke cycle, overhead cam internal combustion engine
comprising:
an engine block including integrally formed cylinder
and cylinder :head and having a camshaft cavity and a
crankcase cavity;
an inter~~onnected crankshaft, connecting rod and
piston assemb:Ly disposed in said crankshaft cavity;
an overhead camshaft and valve assembly disposed in
said camshaft cavity;
a pair o~E valve stem bores extending through said
block between said camshaft cavity and said crankcase
cavity, said ~ralve assembly including valve stems
disposed in said stem bores;
said cylinder being substantially symmetric about
the axis of the piston stroke; and
a lubricant reservoir disposed externally of said
engine block.
According to still yet another aspect of the present
invention theme is provided a single cylinder overhead
cam internal combustion engine comprising:
an engines housing including an integrally formed
cylinder and cylinder head, said cylinder comprising an
internal bore;
a crankshaft rotatably mounted within said engine
housing, said crankshaft driving a drive sprocket located
externally of said engine housing;
a piston operably connected to said crankshaft and
mounted for reciprocation within said cylinder internal
bore;
CA 02180497 1999-OS-17
6f
an overhead camshaft rotatably mounted within said
engine housing and extending externally thereof, said
camshaft comprising a camshaft sprocket located external
of said engine housing;
a valve ~~ssembly in communication with said cylinder
internal bore and operably connected with said camshaft;
and
an endless loop drive member interconnecting said
drive sprockets and said camshaft sprocket for
transmitting rotational motion therebetween, said drive
member being external to said cylinder.
One advantage of the engine of the present invention
is that the substantially uniform wall thickness of the
cylinder reduces the possibility of bore distortion
likely to cau~ie undesirable emissions.
Another advantage of the present invention is that
cooling fins completely encircling the cylinder increase
the rigidity c>f the cylinder and thereby reduce the
possibility of~ bore distortion.
Another advantage of the present invention is that
the integral cylinder and cylinder head eliminates the
need for a head gasket as well as elimination of
distortion producing fasteners between the cylinder head
and cylinder block.
Another advantage of the present invention is that a
pressurized lubricating system provides a reliable
lubrication at a variety of engine orientations.
Another advantage of the present invention is that a
dry sump lubrication system is provided which does not
require an additional pump to convey oil from the sump to
an external reservoir. In addition, the dry sump
CA 02180497 1999-OS-17
6g
lubrication system provides increased flexibility of
engine orientation.
Another advantage of the present invention is that
the camshaft can be conveniently molded in one-piece from
a non-metallic material which
~18Q497
generates less noise during operation than many
metal camshafts. In addition, this camshaft
design is much lighter in weight than metallic
camshafts, and requires no machining after
molding.
Another advantage of the present invention is
that the one-piece molded camshaft can be provided
with an inner rotor of a gerotor pump mechanism to
reduce the number of component pieces of the
engine.
Still another advantage of the present
invention is that the flywheel is located within
the crankcase and not cantilevered externally of
the crankcase, thereby allowing the use of less
strong crankshafts and smaller bearings, thus
reducing weight and friction.
Still another advantage of the present
invention is that the flywheel may be formed
integrally with the crankshaft, thereby allowing
for design of a lighter crankshaft from less
costly materials. This allows weight and cost
savings as well as allowing for drastic braking of
the crankshaft without risk of the flywheel
breaking free from the crankshaft.
Still another advantage of the present
invention is that a plastic fan mounted on the
crankshaft can be used to effectively cool the
engine without adding excessive weight.
Still another advantage of the present
invention is that the overhead valve seat can be
cast in place during cylinder block casting,
thereby eliminating the need to machine the
cylinder head for receipt of the valve seat. This
reduces cost as well as eliminating a common
reliability problem caused by pressed-in seats
falling out during operation.
'w X180497
8
The above mentioned and other advantages and
objects of this invention, and the manner of
attaining them, will become more apparent and the
invention itself will be better understood by
reference to the following description of
embodiments of the invention taken in conjunction
with the accompanying drawings, wherein:
Fig. 1 is a diagrammatic vertical view in
partial cross-section of an internal combustion
engine configured according to the principles of
the present invention;
Fig. 2 is a diagrammatic plan view of the
engine of Fig. 1, wherein portions have been
removed to better illustrate the interconnection
of the camshaft and crankshaft externally of the
cylinder block via the timing belt;
Fig. 3 is an exploded view of selected
portions of the engine of Fig. 1, namely the cam
cover, cylinder block, crankcase cover, camshaft,
crankshaft, and timing belt;
Fig. 4 is a cross-sectional view, taken along
line 4-4 of Fig. 1, showing the generally uniform
wall thickness of the cylinder;
Fig. 5 is a perspective view of the one-piece
camshaft of the engine of Fig. 1;
Fig. 6 is an abstract perspective view of one
embodiment of a crankshaft in a disassembled
condition;
Fig. 7 is a perspective view of the
crankshaft mounted fan of the engine of Fig. 1;
Fig. 8 is an enlarged view of that portion of
the lubrication system shown in Fig. 1 utilized to
lubricate the camshaft region of the engine;
Fig. 9 is an enlarged view of that portion of
the lubrication system shown in Fig. 1 utilized to
lubricate the crankshaft region of the engine;
9
Fig, 10 is a diagrammatic view of the overall
configuration and operation of one embodiment of
the dry sump, pressurized lubrication system of
the present invention; and
Figs, 11A and 11B are enlarged diagrammatic
views of the valve assemblies and the driving
camshaft at two sequential stages of operation
during which the alternating reciprocating motion
of the valve assemblies pumps the oil introduced
around the valve assemblies back to the external
oil reservoir.
Corresponding reference characters indicate
corresponding parts throughout the several views.
Although the drawings represent embodiments of the
invention, the drawings are not necessarily to
scale and certain features may be exaggerated in
order to better illustrate and explain the present
invention.
The embodiments disclosed below are not
intended to be exhaustive or limit the invention
to the precise forms disclosed in the following
detailed description.
Referring to Fig. 1, there is
diagrammatically shown a vertical crankshaft type
internal combustion engine, generally
designated 20, configured in accordance with the
present invention. While the shown vertical
crankshaft orientation finds beneficial
application in a variety of devices including
lawnmowers, engine 20 could be otherwise arranged
and oriented, for example with a horizontally
oriented crankshaft or any angle inbetween, within
the scope of the invention.
As shown in Fig. 1, and with additional
reference to the perspective view of fig. 3, the
housing of engine 20 is formed in part by a
~~804~'~
i0
cylinder block including a central cylinder 22
integrally formed with both cylinder head 24 and
an upper crankcase skirt 26. The cylinder block
is a one-piece die casting which is cast from a
lightweight material, such as aluminum, and then
machined to a final shape. The engine housing
also includes die cast cam cover 28 and crankcase
cover 30 respectively secured to cylinder head 24
and crankcase skirt 26 with suitable fasteners
such as bolts (not shown). Cylinder head 24 and
cam cover 28 include cooperating journal bearings
32, 33, 34 and 35 upon which an overhead camshaft,
generally designated 40, is rotatably supported.
At their interface, crankcase skirt 26 and
crankcase cover 30 similarly include cooperating
journal bearings 36, 37 and 38, 39 for the
crankshaft, generally designated 42. Journal
bearings 32-39 may be integrally formed with their
respective engine housings as shown, or could be
otherwise provided within the scope of the
invention.
Cylinder 22 is provided with a cylindrical
axial bore 44 in which a die cast elliptical
barrel-faced piston 46 with associated rings
translates in a reciprocating fashion during
operation. The volume within bore 44 between
piston 46 and cylinder head 24 serves as a
combustion chamber for engine 20. Along at least
the axial segment of the cylinder bore 44 in which
piston 46 slides during reciprocating strokes,
cylinder 22 is substantially symmetrical about the
axis of the piston stroke. This symmetry
advantageously results in a more uniform thermal
expansion of cylinder 22 in the radial direction
during use that reduces cylinder bore distortion.
For example, as shown in Fig. 4, which is a
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11
transverse cross-section taken along line 4-4 of
Fig. 1, cylinder 22 is formed of a single,
generally ring-shaped wall 48 having an inner
radial periphery 50 defining bore 44. The outer
radial periphery 52 of wall 48 is exposed to allow
passing air to draw off heat generated during
combustion within bore 44. Except for two
radially projecting bosses 54, 55 spaced 180
apart and through which pass symmetrical axially-
extending lubrication conduits 56, 57 drilled
therethrough, wall 48 is exactly ring-shaped.
Wall 48 has a substantially uniform thickness in
the range of 0.180" to 0.250", and preferably a
thickness of about 0.180". As best shown in
Fig. 4, circumscribing cylinder 22 and radially
projecting therefrom are a series of axially
spaced, annular cooling fins 59. Fins 59 are
uniformly shaped along the length of cylinder 22.
In addition to providing an increased surface area
for dissipating heat, cooling fins 59 act as
stiffening ribs for cylinder 22 that add rigidity
which further hinders bore distortion.
With direction in reference to the stroke of
piston 46 relative to crankshaft 42, at the top of
cylinder bore 44 is a one-piece valve seat 61
provided within cylinder head 24. Valve seat 61
seats the valve heads 64, 65 of exhaust and inlet
poppet valve assemblies 67, 68. Valve seat 61 is
a net shape insert, preferably preformed from a
powdered metal composition such as Zenith sintered
product no. F0008-30, which is cast in cylinder
head 24. In particular, after valve seat 61 is
inserted into the cylinder block die, the die is
closed and the casting of the block occurs.
Raised plateau sections 62 that laterally and
upwardly project from opposite side edges of valve
~~$~49~
12
seat 61 permit the molten aluminum injected into
the closed die to mold around the raised
sections 62 to maintain valve seat 61 in position.
It will be recognized that no machining is
required to insert valve seat 61 into the cylinder
block with this cast-in insertion technique.
Alternately shaped and arranged modules, including
recesses provided within valve seat 61, that
provide similar securing functions as raised
plateau sections 62 could naturally be substituted
within the scope of the invention.
Valve assemblies 67, 68, which control flow
communication between the combustion chamber 44
and the inlet port 70 (See Fig. 3) and the exhaust
port (not shown) in the cylinder block, or vice
versa, may be of traditional design and are
selectively engaged during the four stroke engine
cycle by overhead camshaft 40. Suitable seals
(not shown) prevent lubricant introduced within
the camshaft cavity region from reaching bore 44.
As further shown in Fig. 5, camshaft 40 includes a
cam sprocket 72 such as a notched pulley at one
axial end, a gerotor pump inner rotor 74 with
pilot 75 at the opposite axial end, intermediate
journal sections 76, 77 that rotate within
bearings 32-35, and cam lobes 79, 80 that directly
actuate separate valve assemblies 67, 68.
Camshaft 40 is preferably formed in one-piece from
a lightweight thermoset or thermoplastic material,
such as Fiberite FM-4017 F. This plastic material
tends to produce less noise during engagement with
valve assemblies 67, 68 and bearings 32-35 than do
standard metal materials. This material further
allows ready provision of precisely designed
shapes requiring little or no machining while
achieving a low weight. Alternative camshaft
X180497
13
constructions, including an assembly of component
parts made from various materials, may also be
employed.
Aligned parallel to camshaft 40 is
crankshaft 42, which is diagrammatically shown in
Fig. 1. Crankshaft 42 is formed from cast ferrous
material such as ductile iron and includes a lower
shaft portion including a journal section 83 and a
stub shaft 84 which outwardly extends from the
engine housing for power take off to drive, for
example, a lawnmower blade. The upper shaft
portion of crankshaft 42 includes journal
section 86, a shaft segment 87, and an upper stub
shaft 88 (see Fig. 3). A sintered metal drive
sprocket 90 such as a pulley with a notched outer
periphery is axially inserted over shaft
segment 87 and is attached for rotation therewith
via a tapered key (not shown). Between bearing
journals 83, 86 and housed within the crankcase
cavity 91 defined by crankcase cover 30 and
crankcase skirt 26, crankshaft 42 includes a pair
of counterweight/flywheel members 94, 95.
Members 94, 95 are preferably integrally formed
with journal sections 83, 86, respectively, and
are interconnected by a spanning crank pin 93. A
two-piece extruded or cast connecting rod 92 is
pivotally attached to piston 46 with a wrist pin
(not shown) and is rotatably supported on crank
pin 93. In an alternative embodiment the
connecting rod may be of one piece construction.
The wrist pin can be secured with conventional
retainers or alternatively with plastic inserts at
either end of the axially floating wrist pin which
engage the cylinder bore wall and the opposite
ends of the wrist pin.
z~~o4o7
14
As best shown in Fig. 3,
counterweight/flywheel members 94, 95 include
disc-shaped flywheel portions 97, 98 axially
centered on crankshaft 42. Flywheel portions 97,
98 function as a conventional flywheel to provide
all the rotational inertia to crankshaft 42
necessary to even out crankshaft rotation during
the four cycle operation and to maintain
crankshaft rotation during the piston strokes
other than the power stroke.
Counterweight/flywheel members 94, 95 further
include counterweight portions 99, 100 at the same
axial locations along crankshaft 42 as flywheel
portions 97, 98. While in the shown configuration
part of the flywheel portions 97, 98 and
counterweight portions 99, 100 are merged
together, the portions could have an alternative
arrangement, such as an axially stacked
arrangement within cavity 91. The placement of
flywheel portions 97, 98 within cavity 91 and in
close proximity to the journal bearings 36-39
avoids the use of a large cantilevered mass
outside the engine housing which cannot be
perfectly balanced and thus creates unwanted
torsional forces on the crankshaft. In addition,
bending and shear stresses are also imparted to
the crankshaft.
As represented in the abstract perspective
view of Fig. 6, crankshaft 42 can be fashioned by
forming counterweight/flywheel members 94, 95
integral with the upper and lower shaft portions
respectively. Crankshaft 42 is completed by
providing a crank pin 93 having cylindrical plugs
93a, 93b insertable into cooperatively shaped
recesses 101, 102 provided in members 94, 95. An
~..- 218 ~ 4 9'~
alternative to the shown configuration of a
stepped crank pin would be a straight pin.
Referring again to Fig. 1, drive sprocket 90
and cam sprocket 72 are preferably interconnected
5 by an endless loop driver, such as a chain or
timing belt, mounted externally of the engine
housing. Timing belt 105 shown effects the
transmission of rotational motion from
crankshaft 42 to camshaft 40 and achieves the
10 timed relation therebetween necessary for proper
engine operation. Flexible timing belt 105, which
includes notches on its inner or outer surface
oriented perpendicular to the direction of belt
travel, also passes over idler pulley 106, which
15 is abstractly shown in Fig. 2. Idler pulley 106
is a non-spring loaded, adjustable sealed ball
bearing mounted on an eccentric, but may also be
of other conventional constructions, including
spring loaded for automatic adjustment. A
governor (not shown) of a suitable construction
may be axially mounted on idler pulley 106 or cam
sprocket 72 to regulate the engine speed. By
mounting a governor at such a location, the
governor can be positioned in close proximity to
the carburetor, and also need not be associated
with leak-prone sealed rods projecting from the
crankcase. The governor may also be of a commonly
known air vane type.
Mounted to upper stub shaft 88 is a
lightweight centrifugal-type fan 108 utilized to
force cooling air over the housing of engine 20.
Fan 108 may be constructed with minimal mass as it
is not intended to provide the rotational inertia
already provided by flywheel portions 97, 98. As
a result, the moment produced on the crankshaft is
relatively minor. As further shown in the
~~80497
16
perspective view of Fig. 7, fan 108 includes a
disc-shaped body 109 molded from thermoset or W
modified thermoplastic with blades 111 for air
circulation. Body 109 includes a raised spoke 113
having an outer radial periphery into which
ignition magnets 115, 116 are molded.
Magnets 115, 116 cooperate with engine ignition
system 128 mounted to the engine housing 22 to
generate sparking within the combustion chamber
that initiates internal combustion. Fan body 109
further includes counterweight 118 which balances
the weight of magnets 115, 116 and spoke 113, and
counterweight 118 may include a metal insert
molded therein. Molded into the center of
body 109 is a relatively sturdy, multi-lobed
aluminum insert 120 which functions in the shown
embodiment as both a mounting hub for fan 108 and
a starter cup. In particular, mounting
hub/starter cup insert 120 includes axial bore 121
which receives stub shaft 88 and is attached for
rotation therewith via a tapered key (not shown).
In outer surface 123, mounting hub/starter cup 120
includes recesses 124 structured for engagement
with the pawls (not shown) of recoil starter 129
which descend when starter 129 is utilized.
Radial lobes 125, 126 shown in Fig. 7 define
angular gaps therebetween filled with molded
plastic to prevent insert 120 from separating from
fan body 109 during starting. As the precise
construction of ignition system 128 and recoil
starter 129 are not material to the present
invention and can be one of a variety of well
known types, further explanation is not provided
herein. In situations where an electric starter
sccompanies or replaces recoil starter 129, a
grooved ring (not shown) preferably integrally
,.,. ~ 18 ~ 4 ~'~
17
formed in the bottom surface of fan body 109 may
be utilized for engaging a starter pinion.
Although plastic is preferred from a weight
standpoint, other materials including aluminum may
be used to form fan body 109. In an alternative
embodiment (not shown) using commonly known
alternative ignition means, the fan 108 may be of
a simpler construction with additional cooling
blades replacing spoke 113, magnets 115, 116 and
counterweight 118. This simpler, lighter, more
efficient fan would be fastened to a stub shaft
(not shown) with simpler fasteners, such as
intregrally molded clips or simple rivets. In
this alternative the recoil starter hub may be
separately attached or integrally molded to the
fan.
Referring again to Fig. 1, engine 20 is
preferably kept lubricated with a dry sump
pressurized lubrication system that allows for
multi-positional operation. The system includes
an oil reservoir 135 mounted externally of and to
the engine housing. Although shown at an
elevation below the engine housing, reservoir 135
could be positioned above the balance of engine 20
without compromising the lubrication system
operation. Oil reservoir 135 may be formed of a
durable transparent plastic material such as nylon
6.6 thermoplastic, and with appropriate indicia to
allow a visual determination of oil level. A
first oil return conduit 138 formed of flexible
tubing with a 0.125" - 0.500" internal diameter
extends between a crankcase outlet 140, namely a
housing bore opening into crankcase cavity 91, and
a reservoir inlet 141 opening into oil
reservoir 135 above the collected lubricant. A
second similarly constructed oil return
~~$~J497
18
conduit 143 with a 0.125" - 0.500" internal
diameter communicates with an outlet 145 and
reservoir inlet 147. Outlet 145 is a bore,
drilled through cylinder head 24, which opens into
the head cavity 180, shown in Fig. 8, in which the
biasing components of valve assembly 67 are
housed. Return conduits 138 and 143 circulate the
oil delivered to crankshaft 42 and overhead
camshaft 40 respectively as described further
below.
An abstractly shown breather/filler cap 150
securely fits over an inlet 152 through which
replacement oil can be poured into reservoir 135.
Breather 150 is a conventional filter-type
assembly that includes check valve 149 allows one-
way air flow out of reservoir 135, while
preventing oil passage. Breather 150 includes an
air exhaust port 151 which may be connected in
flow communication with air intake port 70 on the
carburetor air filter (not shown) or with the
carburetor (not shown). The particular
construction of breather 150 is not material to
the invention and may be one of many suitable
designs known in the art. Rather than being
formed into the inlet cap, breather 150 could
instead be integrated into a wall of reservoir 135
removed from inlet 152. Oil pick-up 155 includes
an oil filter submerged within the volume of oil
maintained in reservoir 135 and connects to a
0.125" - 0.500" internal diameter supply
conduit 159 leading to the lubrication system pump
mechanism used to pressurize the oil introduced
into engine 20. Oil pick-up 155 may be
constructed of flexible tubing with a weighted
inlet end to cause it to remain submerged within
the reservoir fluid when the engine is tilted from
.. . ~18~497
19
a standard orientation. Check valve 157 is of a
standard construction and is located within
conduit 159 to permit one way flow of oil from
reservoir 135. Oil reservoir 135 may also be
mounted directly to oil pump 161 in certain
orientations (not shown) which precludes the need
for supply conduit 159 and check valve 157
The configuration of the pressurized
lubrication system will be further explained with
reference to Figs. 8 and 9, which respectively
show enlarged views of the engine parts used to
lubricate camshaft 40 and crankshaft 42. The
preferred pump mechanism fed by supply conduit 159
is a gerotor type pump which operates in a known
manner. In the shown embodiment, the pump is
generally designated 161 and utilizes the rotation
of camshaft 40 to perform the pumping operations.
Alternate types of pumps, including those which
are separate from the remaining working components
of engine 20, may be used to drive the lubrication
system within the scope of the invention. The
pump 161 includes a thermoset plastic cover
plate 162, attached to the engine housing with
bolts and an 0-ring seal (not shown). A pressed
metal or plastic outer rotor 165, which is
retained by plate 162 and cooperatively shaped
with inner rotor 74 of camshaft 40 to effect fluid
pressurization is also included. Camshaft hub 75
is provided with bearing surfaces 166 in cover
plate 162. Pump inlet port 163 communicates with
the downstream end of oil supply conduit 159.
Pressurized oil that is outlet at port 164 is
forced into bore 167 within cam cover 28. A
pressure relief valve 168 returns high pressure
oil from port 164 to inlet port 163 to prevent
excessive pressure. Cross bores 169, 170
X180497
distribute oil within bore 167 to annular
grooves 172, 173 which are provided in bearings
32, 34 and 33, 35 respectively and which ring
journals 76, 77. At their upstream ends, oil
5 conduits 56, 57 open into grooves 172, 173 to
allow oil communication therebetween. Conduits
56, 57 extend through cylinder head 24 and
cylinder 22 toward crankshaft 42. Conduits 56, 57
are shown being parallel to bore 44, and
10 consequently bosses 54, 55 radially project a
uniform distance along the axial length of
cylinder 22.
Referring now to Fig. 9, at its downstream
end, oil conduit 56 terminates at bearing
15 surface 36 to effect lubrication of crankshaft
journal 83. For the vertical type crankshaft
arrangement shown, journal 83 is further
lubricated by the quantity of oil which falls to
the bottom of cavity 91. Oil conduit 57
20 terminates at annular groove 175 formed in journal
bearings 37, 39. Lubrication bore 177 drilled
through counterweight/flywheel member 95 and
journal 86 extends between annular groove 175 and
the bearing surface between connecting rod 92 and
crank pin 93. Annular groove 175 continuously
communicates with bore 177 during crankshaft 42
rotation to provide uninterrupted pressurized
lubrication for the bearing surface of connecting
rod 92 throughout operation. Although not shown,
an axial bore extending between the connecting rod
bearing surface and the wrist pin for piston 46
may be provided to provide pressure lubrication
for the wrist pin.
The structure of the lubrication system of
the present invention will be further understood
in view of the following general explanation of
2180497
21
its operation. This explanation refers to
Fig. 10, which schematically shows an alternate
orientation of the invention shown in Fig. 1 in
that the crankshaft is horizontally disposed. It
will be appreciated that still further
modifications to the lubrication system can be
performed within the scope of the invention.
Lubricant 136 such as oil within external
reservoir 135 is drawn through supply conduit 159
by pump 161 and introduced at high pressure into
camshaft 40. Cross bores in camshaft 40 direct
the oil to the journal bearings, such as
bearings 32, 33 shown. The high oil pressure
causes an overflow portion of the oil from both
journal bearings to migrate axially inwardly and
thereby lubricate the camshaft lobes 79, 80. Due
to camshaft 40 rotation, the lubricating oil is
also slung off camshaft 40 to splash lubricate the
remainder of the surfaces and components within
the cavity between cam cover 28 and cylinder
head 24, including the portions of the valve
assemblies represented at 67, 68 exposed within
cavities 180, 181.
The remainder of the oil introduced at the
journal bearings within grooves 172, 173 (See
Fig. 8) is forced under positive pressure axially
through conduits 56, 57 toward crankshaft 42. The
oil is maintained cool during this travel time by
the transfer of heat to the bosses 54, 55 which
are exposed to passing cooling air. At its
downstream end, conduit 56 includes an opening
through which the conveyed oil is outlet to
pressure lubricate shaft journal 83. Oil from
conduit 57 outlets to lubricate shaft journal 86
as well as to fill annular groove 175 (See
Fig. 9), and lubrication bore 177 routes
2~ga49~
22
pressurized oil from groove 175 to lubricate the
connecting rod bearing surfaces. The overflow oil
displaced from the pressure lubricated bearing
surfaces by the arrival of additional oil is slung
off crankshaft 42 to splash lubricate the moving
components within crankcase cavity 91, such as
piston 46, the piston rings, the wrist pin, the
wrist pin bearings and the cylinder wall.
The circulation of the oil within engine 20
back to the external reservoir 135 is effected by
positive displaement and/or pressure fluctuations
caused by the reciprocating motion of the valve
assemblies and piston. With additional reference
to Figs. 11A and 11B, which are enlarged, abstract
views of the valve assemblies and the camshaft at
sequential stages of engine operation, the oil
which lubricates camshaft 40 and its associated
valve assemblies 67, 68 accumulates in cavities
180, 181 provided in cylinder head 24. The
spring-biased cam followers 183, 184, which in the
shown embodiment are bucket-shaped tappets but
could be otherwise configured, as well as the top
of their associated valve stems 186, 187 reside
within cavities 180. 181. Cam followers 183, 184
are tightly toleranced to the dimensions of
cavities 180, 181 to act as pistons to facilitate
the following pumping operations. As camshaft 40
rotates, as shown in Fig. 11A, cam lobe 80 drives
bucket tappet 184 downwardly, thereby reducing the
effective volume of cavity 181 and creating a high
positive pressure therein. This positive pressure
forces the oil accumulated within cavity 181 to
pass through slot 189 formed in valve head 24
between cavities 181, 180. Rather than an open-
ended slot proximate camshaft 40, a bore or
aperture could be substituted within the portion
~18U49~
23
of cylinder head 24 between the cavities. As
shown in Fig. 11B, as camshaft 40 continues to
rotate cam follower 184 returns to its unengaged
position and cam lobe 79 subsequently drives cam
follower 183 downward to pressurize cavity 180.
Outlet bore 145 in cylinder head 24 is provided
with a larger cross-sectional area than slot 189
such that the path of least resistance for the oil
accumulated within pressurized cavity 180 is
through bore 145. Consequently, the positive
pressure created within valve cavity 180 by the
piston-like pumping action of valve assembly 67
forces the oil toward return conduit 143.
The oil in return conduit 143 is propelled in
a step-wise fashion therethrough to oil
reservoir 135. In particular, when a quantity of
oil and air within valve assembly cavity 180 is
forced into supply conduit 143, oil and air within
the segment of conduit tubing adjacent inlet 147
is displaced and empties in a spurt into oil
reservoir 135. The oil pumped into return
conduit 143 for a particular valve assembly
pumping stroke empties into oil reservoir 135 only
after multiple additional pumping strokes have
occurred, and the multiple is dependent in part
upon the length of return conduit 143.
Breather 150 allows air to be exhausted from
within reservoir 135 such that a high pressure
does not build up within reservoir 135 which would
prevent oil pumping. Oil does not return into
cavity 180 on the upstroke of valve assembly 67
because inlet 147 is above the oil level thus
allowing only air to be drawn back out of
reservoir 135. Thus, step-wise return of the oil
to the oil return conduit and thus to the oil
reservoir is effected by the positive pressure
2~.8049'~
24
created by the pumping action of the valve
assemblies.
Oil is returned from crankcase cavity 91 by
exploiting the pumping action of piston 46. As
piston 46 is driven downwardly within cylinder
bore 44, the pressure in crankcase cavity 91
increases. This positive pressure forces a
quantity of the lubricating oil and entrapped air
within cavity 91 completely through oil return
conduit 138 and into oil reservoir 135.
Breather 150 achieves air venting of the volume of
air which is blown through tubing 138 to prevent a
pressure build-up. As piston 46 is driven
upwardly within bore 44 to create a vacuum within
crankcase cavity 91, air flows through
breather 150, through the oil return conduit 138,
and into crankcase cavity 91. Because port 141 is
above the fluid level, the only oil reintroduced
through conduit 138 into cavity 91 during the
piston upstroke is any small quantity of oil in
conduit 138 which failed to reach reservoir 135
during the piston downstroke.
While this invention has been described as
having a preferred design, the present invention
may be further modified within the spirit and
scope of this disclosure. This application is
therefore intended to cover any variations, uses,
or adaptations of the invention using its general
principles. Further, this application is intended
to cover such departures from the present
disclosure as come within known or customary
practice in the art to which this invention
pertains.
