U.S. patent application number 10/896598 was filed with the patent office on 2004-12-23 for four-stroke internal combustion engine.
Invention is credited to Bartelt, Ronald Lee, Braun, Michael Paul, Hirsch, Nicholas Robert, Hotz, Peter, Hubbard, Brian, Schaefer, Mark Donald, Wiatrowski, Darrell Albert.
Application Number | 20040255895 10/896598 |
Document ID | / |
Family ID | 33302458 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040255895 |
Kind Code |
A1 |
Hirsch, Nicholas Robert ; et
al. |
December 23, 2004 |
Four-stroke internal combustion engine
Abstract
A four-stroke internal combustion engine is provided that is
capable of use in many power tools, including those power tools
subjected to tippable applications. There is provided within an
engine housing, an oil reservoir and a valve chamber which
independently communicate with a crank chamber. A system of
strategically placed dividers and passageways within the engine
housing appropriately directs lubricant within the engine housing
so that the internal cavity of the engine is lubricated during use
in any operational attitude, and so that the lubricant flows to and
is held in the proper chambers during storage. There is also
provided a breather arrangement for an internal combustion engine
which includes a camshaft having a hollow passageway in
communication with a crank chamber.
Inventors: |
Hirsch, Nicholas Robert;
(Pewaukee, WI) ; Schaefer, Mark Donald; (Waukesha,
WI) ; Braun, Michael Paul; (Wauwatosa, WI) ;
Hotz, Peter; (Whitefish Bay, WI) ; Wiatrowski,
Darrell Albert; (Beach Park, IL) ; Bartelt, Ronald
Lee; (Muskego, WI) ; Hubbard, Brian; (West
Bend, WI) |
Correspondence
Address: |
Casimir F. Laska
Michael Best & Friedrich LLP
100 East Wisconsin Avenue
Milwaukee
WI
53202-4108
US
|
Family ID: |
33302458 |
Appl. No.: |
10/896598 |
Filed: |
July 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10896598 |
Jul 21, 2004 |
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09600096 |
Jun 7, 2001 |
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6810849 |
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09600096 |
Jun 7, 2001 |
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PCT/US00/00841 |
Jan 13, 2000 |
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60117215 |
Jan 25, 1999 |
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Current U.S.
Class: |
123/196R ;
123/197.4 |
Current CPC
Class: |
F02B 2075/027 20130101;
F01M 11/06 20130101; F02B 2275/30 20130101; F02B 63/02 20130101;
F02B 69/00 20130101; F05C 2201/021 20130101; F01M 9/10 20130101;
F01M 2011/0041 20130101; F01M 11/067 20130101; F01M 3/00 20130101;
F02B 1/04 20130101; F01M 11/065 20130101; F02F 1/305 20130101; F02B
75/16 20130101; F02B 2275/22 20130101; F01M 11/064 20130101; F01M
2013/0422 20130101; F01M 1/04 20130101; F01M 13/022 20130101; F01M
11/0004 20130101; F16H 57/043 20130101 |
Class at
Publication: |
123/196.00R ;
123/197.4 |
International
Class: |
F01M 001/00; F02B
075/32 |
Claims
What is claimed is:
1. A four-stroke internal combustion engine, comprising: an engine
housing including a crankcase and a cylinder; a crank chamber
disposed within said crankcase; a crankshaft supported for rotation
within said crank chamber; a piston operably interconnected with
said crankshaft for reciprocation within said cylinder in response
to rotation of said crankshaft; an oil reservoir disposed within
said crankcase, and in fluid flow communication with said crank
chamber; an arcuate divider at least partially separating said
crank chamber from said oil reservoir; and a depending wall
extending at least partially into said crank chamber to define a
lubricant receiving space between said divider and said depending
wall.
2. An engine as set forth in claim 1, wherein said divider includes
an opening, such that said crank chamber and said oil reservoir are
in fluid flow communication through said opening.
3. An engine as set forth in claim 2, wherein said divider further
includes a second opening and a third opening, said second opening
positioned substantially across from said third opening, said crank
chamber and said oil reservoir being in fluid flow communication
through said second and third openings.
4. An engine as set forth in claim 1, wherein said depending wall
is a cylinder side wall.
5. An engine as set forth in claim 1, further comprising an intake
valve and an exhaust valve disposed within the engine housing to
the side of the cylinder, wherein said engine housing further
includes a valve chamber in which said intake valve and said
exhaust valve are disposed, said valve chamber being in fluid flow
communication with said crank chamber.
6. An engine according to claim 1, further comprising: a cam shaft
rotatably driven by said crankshaft and oriented substantially
normal with respect to said crankshaft.
7. An engine according to claim 6, further comprising first and
second valve tappets associated with a respective valve and
operatively engaging said cam shaft, wherein said valves are
disposed substantially normal to said crankshaft.
8. An engine according to claim 6, wherein said cam shaft has an
axial passageway and a radial aperture communicating between said
crank chamber and said passageway, said engine further comprising a
breather tube having one end communicating with said passageway of
said cam shaft and another end communicating with an air intake
system of said engine.
9. An engine according to claim 1, wherein said crankshaft is
cantilevered, said crankcase includes an access hole, said piston
includes an aperture, said access hole and aperture being alignable
during assembly of said engine; and wherein said engine further
comprises: a connecting rod having one end pivotally attached to
said crankshaft and the other end pivotally connected to said
piston; and a wrist pin insertable through said access hole and
into said aperture in said piston to pivotally connect said
connecting rod to said piston.
10. An engine according to claim 1, wherein said crank chamber
includes at least two bearing pockets, one pocket having a larger
diameter than the other and both pockets being disposed on the same
side of said depending wall.
11. An engine according to claim 1, further comprising a shroud at
least partially surrounding said engine housing and including a
pair of opposed channels, and a fuel tank having opposed
outwardly-extending shoulders, such that said shoulders of said
fuel tank are received by said respective channels of said
shroud.
12. An engine according to claim 1, wherein said engine housing
further includes a back plate which is adjacent to a flywheel, and
wherein said crankcase, cylinder, and back plate are cast as a
single component.
13. An engine according to claim 1, wherein said cylinder includes
elliptical intake and exhaust ports on opposite sides of said
engine housing, and intake and exhaust valves in communication with
said intake and exhaust ports, respectively.
14. An engine as set forth in claim 1, wherein the divider is
substantially U-shaped.
15. An engine as set forth in claim 14, wherein one side of the
divider is exposed to the oil reservoir and an opposite side of the
divider is exposed to the crank chamber.
16. The engine of claim 1, wherein said cylinder defines a bore
having a bore axis, and wherein said depending wall extends into
said crank chamber generally parallel to said bore axis.
17. The engine of claim 1, wherein said cylinder defines a bore,
and wherein said depending wall defines an extension of said
cylinder bore into said crank chamber.
18. The engine of claim 17, wherein said bore extension and said
cylinder bore have substantially the same diameter.
19. The engine of claim 18, wherein said bore extension and said
cylinder bore are substantially coaxial with each other.
20. The engine of claim 1, further comprising a cylinder head
mounted to said engine housing over said cylinder to at least
partially define a combustion chamber in said cylinder, and intake
and exhaust valves disposed within said engine housing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a continuation of U.S. application Ser.
No. 09/600,096, filed Jun. 7, 2001, which is a .sctn.371 filing of
International Application No. PCT/US00/00841, filed Jan. 13, 2000
and claiming priority to U.S. Provisional Application No.
60/117,215, filed Jan. 25, 1999. The entire contents of these prior
applications are hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates, generally, to four-stroke
internal combustion engines and, more particularly, to four-stroke
internal combustion engines used in trimmers, blowers, vacuums,
chain saws, other hand-held power tools, snowblowers, generators,
vegetation cutting devices such as lawn mowers, or other outdoor
power equipment.
BACKGROUND OF THE INVENTION
[0003] Many hand-held power tools or other outdoor power equipment
are powered by electric motors or two-stroke internal combustion
engines. Electric motors are limited to certain applications due to
the available power for products utilizing a cord, and battery
longevity for cordless products. Conventional two-stroke engines
include a lubricating means in which the lubricant is mixed with
fuel which allows the engines to operate in any given position such
as upright, inclined, sideways or upside down. For example, when
using a chain saw, the chain saw is typically capable of use in
either an upright, sideways or upside down condition. Over the past
few years, there has been a requirement by various governing bodies
to reduce the emissions associated with all small gas engines,
particularly, conventional two-stroke engines. Thus, because
four-stroke engines do not require the mixing of lubricant and
fuel, it is desirable to use four-stroke engines in place of
conventional two-stroke engines, since four-stroke engines normally
release fewer undesirable emissions as compared to the amount of
undesirable emissions released by conventional two-stroke
engines.
[0004] However, previously, it was widely viewed that four-stroke
internal combustion engines could only be used for limited
applications, such as lawn mowers, snowblowers, generators, or
other portable products having wheels. It was thought that these
prior four-stroke engines were too heavy and cumbersome to be used
in operator-carried power tools. Moreover, since it is generally
necessary to store oil separate from the gas so that the oil can be
used for lubrication, traditional low-cost four-stroke engines were
not designed to operate in any position other than a substantially
upright position because if the engine was significantly tipped or
tilted, the lubricant would foul the engine. Only very recently has
it been contemplated that a four-stroke engine may be used in a
hand-held power tool or in other applications where the engine may
operate in a tipped or tilted condition.
SUMMARY OF THE INVENTION
[0005] Accordingly, there is a need for a four-stroke internal
combustion engine that is capable of use in various power tools,
and yet is also capable of having low emissions and being
sufficiently light to be carried by an operator when desired. What
is also needed is a four-stroke internal combustion engine that is
capable of operating in many different attitudes of the engine.
What is also needed is a four-stroke engine that eliminates the
need for an elaborate lubrication system. What is needed is a
four-stroke internal combustion engine which accomplishes these
features and other features and which is also economical to
manufacture.
[0006] In one embodiment of the present invention, there is
provided a four-stroke internal combustion engine, preferably a
side valve or "L" head engine, having an engine housing which
includes a crankcase and a cylinder. A cylinder head which at least
partially defines a combustion chamber is positioned adjacent to
the cylinder. An intake valve and an exhaust valve are disposed
within the engine housing. A crank chamber and an oil reservoir are
disposed within the crankcase in such a way that the oil reservoir
is in fluid flow communication with the crank chamber. A
strategically placed agitator, located at least partially within
the crank chamber, moves lubricant within the engine housing during
operation of the engine to lubricate the necessary components of
the engine.
[0007] A divider is disposed within the crankcase to at least
partially divide the crank chamber and the oil reservoir. The
divider assists in directing the lubricant during operation and
storage of the engine in order to prevent a substantial amount of
lubricant from undesirably migrating into the combustion chamber
when the engine is operated or stored in an upright or tilted
position. In one aspect of the present invention, the divider
defines a path which extends about the divider. The path allows
lubricant in the oil reservoir to flow around a substantial portion
of the divider to further enhance the lubricating and storage
features of the engine according to the principles of the present
invention.
[0008] The engine is constructed of light weight material and
appropriately sized so that the engine is sufficiently light enough
to be usable in hand-held power tools. Thus, the four-stroke
internal combustion engine according to the present invention may
be utilized in those applications which are traditionally limited
to the use of two-stroke internal combustion engines.
[0009] In one aspect of the present invention, the divider includes
at least one opening such that the crank chamber and the oil
reservoir are in fluid flow communication through the opening. The
opening helps ensure that the crank chamber is substantially
continuously lubricated during operation of the engine, even if the
engine is operated under a tilted condition. The opening in the
divider is positioned such that at least some of the lubricant
found in the crank chamber after operation of the engine may flow
back into the oil reservoir even if the engine is stored in a
tilted state. Preferably, the divider includes a plurality of
openings.
[0010] In another aspect of the present invention, the engine
housing further includes a cylinder side wall which at least
partially extends into the crank chamber to define a lubricant
receiving space between the divider and the cylinder side wall.
Preferably, the cylinder side wall at least partially defines a
piston bore. During operation, as the agitator mixes and slings
lubricant around the inside cavity of the engine as a result of the
rotating action of the agitator, the lubricant is more likely to be
slung into the open area between the divider and the cylinder side
wall rather than into the piston bore. Moreover, during storage,
the open area or lubricant receiving space provides additional
space for the lubricant to be held if the engine is stored in a
sideways or upside down position to also prevent a substantial
amount of the lubricant from flowing into the piston bore. As
previously noted, migration of the lubricant into the combustion
chamber leads to an unwanted condition. A function of the lubricant
receiving space is to inhibit lubricant from reaching the piston
bore, thereby preventing a substantial amount of lubricant from
reaching the combustion chamber.
[0011] In another aspect of the present invention, the engine
housing further includes a valve chamber. The intake valve and
exhaust valve are disposed within the valve chamber and the valve
chamber is in fluid flow communication with the crank chamber. The
operation of the agitator, the pressure pulses created within the
engine during operation of the engine, the communication of the oil
reservoir with the crank chamber, and the communication of the
crank chamber with the valve chamber together allow the working
components found within the valve chamber to be lubricated, even if
the engine is operated in a tilted manner. Preferably, the valve
chamber is also in fluid flow communication with the cylinder side
wall to further enhance the lubrication of the working components
located within the valve chamber. The strategic positioning of the
fluid flow openings into the valve chamber will prevent the valve
chamber from receiving too large of a quantity of lubricant when
the engine is being operated or being stored.
[0012] In another embodiment of the present invention, the engine
includes a cantilevered crankshaft which has opposite ends and
which is substantially located within the crank chamber. The
agitator includes a counterweight which is interconnected to the
cantilevered end of the crankshaft. The counterweight is adapted to
reduce windage resistance on the crankshaft and to sling lubricant
about the crank chamber as the crankshaft rotates during operation
of the engine. Further, the counterweight throws the lubricant away
from the main bearings of the crankshaft, thereby substantially
preventing the main bearings from being flooded by the lubricant
during operation of the engine. The divider may be provided with a
scraper which is used to limit the amount of lubricant which comes
into contact with the agitator or the counterweight. The scraper
preferably at least partially extends into the crank chamber, so
that as the agitator rotates past the scraper during operation of
the engine, the scraper meters the amount of lubricant which comes
into contact with the agitator.
[0013] In another aspect of the present invention, a cam shaft
disposed substantially normal to the crankshaft is rotatably driven
by the crankshaft. The substantially normal arrangement of the cam
shaft and crankshaft enables the engine to be longer in a direction
parallel to a power take off, as compared to a conventional engine
in which the cam shaft is parallel with the crankshaft. Such an
engine is desirable in certain hand-held power tool applications,
such as power trimmers, in order to provide an overall better
balance of the power tool for the convenience of the user. The
substantially normal arrangement of the shafts also allows for an
intake port and an exhaust port disposed in the cylinder to be
significantly spaced apart. Segregating the ports will reduce heat
migration from the exhaust port to the intake port which could
result in hot restart (e.g., vapor lock) problems.
[0014] Preferably, the intake and exhaust ports are elliptical in
shape. The elliptical configuration of the ports enables the
overall profile or height of the engine housing to be reduced,
thereby reducing the amount of material needed for the overall
engine housing. This helps reduce the overall weight of the engine
housing. The port walls are provided with sufficient surface area
and strength to support the portion of the engine housing and
cylinder head disposed above the ports. The substantially normal
relationship between the crankshaft and the cam shaft also allows
the valves to be disposed substantially normal to the crankshaft. A
first valve tappet associated with the intake valve and a second
valve tappet associated with the exhaust valve operatively engage
the cam shaft to provide for the proper operation of the valves
with respect to a four-stroke internal combustion engine. Such a
compact arrangement further limits the overall weight of the
engine.
[0015] In another embodiment of the present invention, a breather
arrangement for the four-stroke internal combustion engine is
provided. The cam shaft is provided with an axial passageway and
several radial apertures. The radial apertures communicate with the
crank chamber and the passageway. A breather tube communicates with
the passageway and an air intake system of the engine. A
check-valve is positioned between the end of the cam shaft and the
air intake system to maintain the negative pressure created within
the engine. Blow-by gas inside the engine is admitted into the
radial aperture of the cam shaft and is sent through the axial
passageway of the cam shaft and into the breather tube, so that the
blow-by gas is recirculated within the engine. The pressure pulses
created within the engine cause the blow-by gas to enter the cam
shaft and be recirculated as described. However, the centrifugal
action of the cam shaft counters the action created by the pressure
pulses, thereby substantially preventing the heavier lubricant, as
compared to the blow-by gas, from entering the radial apertures in
the cam shaft. As a result, the lubricant will substantially remain
within the cavity of the engine and will not travel through the
breather tube to the air intake system of the engine.
[0016] In another aspect of the present invention, the engine
housing is designed to cooperate with a piston found within the
piston bore such that a connecting rod can be conveniently attached
to the piston and the crankshaft. The crankcase and the piston each
include an access hole. A connecting rod is operatively attached to
the crankshaft and the piston in the following manner. The access
hole in the crankcase and the access hole or aperture in the piston
are aligned during installation of a wrist pin. The wrist pin is
inserted into the piston aperture and through an end of the
connecting rod to connect the connecting rod to the piston. A star
washer is used to hold the wrist pin in place after
installation.
[0017] The compact size of the engine according to the present
invention and the cantilevered crankshaft make it difficult to
assemble the internal components of the engine, such as the
piston-connecting rod-crankshaft assembly. The cooperation of the
access holes in the crankcase and the piston allow for easy
assembly of the piston-connecting rod-crankshaft assembly.
Preferably, it is desirable to use the same engine housing casting
for engines having different horsepower ratings, simply by changing
the connecting rod and thus, the length of the piston throw. To
facilitate assembly and to permit the same engine housing casting
to be used for different sized engines, an elliptical, or the like,
wrist pin boss is formed in the crankcase of the engine housing.
The wrist pin boss can be machined at its upper end to provide an
access hole in the crankcase for a first horsepower rating or
piston throw, and the wrist pin boss can be machined at its lower
end to provide an access hole in the crankcase for a second
horsepower rating or piston throw. After the wrist pin boss is
properly machined, the wrist pin-which connects the piston to the
connecting rod-is inserted through the crankcase aperture and into
the piston aperture as previously explained. In this way, the same
engine housing casting can be used for different sized engines.
[0018] In another aspect of the present invention, the crank
chamber includes at least two bearing pockets. One of the pockets
has a larger diameter than the other. Both of the bearing pockets
are disposed on the same side of the internal cylinder side wall.
The cantilevered crankshaft is supported by two main bearings
located in the respective bearing pockets. The bearing pocket
nearest the cantilevered (input) end of the crankshaft is the
larger diameter bearing pocket so that the bearing pockets can be
machined in the crank chamber from the same side with a single tool
thereby eliminating unnecessary tooling requirements. This provides
a significant savings in capital costs and manufacturing expenses.
Preferably, before assembling the crankshaft in the crank chamber,
the outer bearing and then the agitator or counterweight are
properly positioned around the cantilevered end of the crankshaft.
The counterweight is provided with an access aperture in order to
allow a tool to appropriately contact the adjacent bearing and the
crankshaft. In this way, as the crankshaft is placed into the crank
chamber, the bearing is not damaged and the crankshaft is properly
positioned.
[0019] In another aspect of the present invention, the combustion
chamber is adapted to enhance swirl of the air/fuel mixture to
increase efficiency of the engine. Preferably, a spark plug is
positioned closer to the exhaust valve than the intake valve to
also improve engine efficiency, and reduce the likelihood of
self-ignition within the engine.
[0020] In another aspect of the present invention, the engine
housing is designed in such a way so as to permit two engine
housings to be produced using only one die tool and one die casting
machine. This also reduces capital costs and manufacturing
expenses.
[0021] In another aspect of the present invention, a starter
assembly is attached to the rear of the engine and is designed to
utilize a crankshaft pin which is integral with the crankshaft. The
crankshaft pin is the contact point for the internal rotation of
the crankshaft in order to start the engine.
[0022] In another aspect of the present invention, the blower
housing has an inwardly extending hub. The hub fits over the
crankshaft. The starter assembly slides onto the hub. A star washer
or the like is placed over the hub so as to prevent the axial
movement of the starter assembly, particularly the pulley. This
arrangement eliminates the need for separate mounting bosses and
fasteners which are normally needed to attach the starter assembly
to the blower housing and which typically block the cooling air
flow by the fan.
[0023] In another aspect of the present invention, a shroud is
provided to at least partially surround the engine housing. The
shroud is provided with a pair of opposed channels. A fuel tank
having opposed, outwardly extending shoulders is held by the shroud
as the shoulders are received by the respective channels.
Preferably, a filler material is positioned between each of the
channels and respective shoulders so as to provide a more snug fit
between the shroud and the fuel tank.
[0024] In a preferred embodiment, a fuel line includes a fuel
filter attached to the end of the fuel line disposed within the
fuel tank. The fuel filter acts as a weight. During operation of
the engine, as the engine is tipped in different orientations, the
weighted fuel line swings to the bottom of the fuel tank so that
fuel is always picked up by the fuel line regardless of the
orientation of the engine.
[0025] In one aspect of the present invention, the shroud includes
an opening around the intake port. An intake isolator is provided
having an air/fuel passageway extending therethrough. The intake
isolator is mounted to the engine housing so that the air/fuel
passageway of the intake isolator is aligned with the intake port.
Further, the intake isolator is positioned within the opening of
the shroud to substantially ensure that cooling air passing between
the engine housing and the shroud cannot escape through the opening
in the shroud. The intake isolator is also used to insulate the
intake air/fuel mixture from the surrounding environment to the
extent feasible to ensure that the air/fuel ratio remains
substantially correctly calibrated. In one embodiment of the
present invention, a carburetor is interconnected with the intake
isolator.
[0026] In one aspect of the present invention, the shroud includes
a plurality of raised portions on one side thereof. If desired, the
engine can be placed on the ground to rest on the raised portions.
This could be useful, for example, on a trimmer when the user
desires to change the cutting line located on the end of the shaft
which is spaced a significant distance from the engine.
[0027] In another aspect of the present invention, the engine
housing includes a back plate which is adjacent to a flywheel.
Preferably, the crankcase, the cylinder and the back plate are cast
as a single component, thereby reducing manufacturing and assembly
costs, and thereby limiting the overall size of the engine housing.
In a preferred embodiment, the engine housing further includes at
least one fin integrally formed thereto. The fin extends from the
back plate and beneath the crankcase to increase the stability
between the back plate and the crankcase. The fin also is adapted
to help cool the engine housing, particularly, the crankcase.
[0028] In another aspect of the present invention, a muffler is
connected to the engine housing. The muffler includes a boss which
extends into the exhaust port. In one embodiment, the engine
housing includes an angled, stepped sealing surface located in the
exhaust port. The end of the muffler boss mates against the exhaust
port sealing surface to substantially prevent the exhaust from
undesirably escaping into the surrounding atmosphere. Preferably, a
sealing gasket is positioned between the end of the boss and the
exhaust port sealing surface to even better prevent the exhaust
from undesirably escaping into the atmosphere. In another
embodiment, the muffler boss is surrounded by a portion of the
exhaust port to define a clearance between the outside liner of the
boss and the adjacent surface of the exhaust port. A gasket is
positioned between the muffler and the engine housing to seal the
clearance space between the muffler and the engine housing so as to
prevent exhaust from undesirably escaping into the atmosphere. In a
preferred embodiment, the gasket is an enlarged gasket which also
serves as a heat shield between the engine housing and the
user.
[0029] In one aspect of the present invention, the muffler includes
a pair of outer shells having a pair of mounting bolt holes
extending therethrough for receiving a pair of mounting bolts. A
pair of bolt receiving bores are located on opposite sides of the
exhaust port in the engine housing. This arrangement ensures that
the muffler will be securely attached to the engine housing in a
stable manner. In a preferred embodiment, the muffler includes an
inner shell sandwiched between the outer shells. The inner shell is
a baffle plate adapted to reduce the amount of exhaust admitted
into the atmosphere. The inner shell also includes a pair of
mounting bolt holes to receive the mounting bolts. In yet another
preferred embodiment, one of the outer shells includes a shoulder
extending around an edge of the outer shell. The other outer shell
includes a hook-shaped flange extending around an edge of the outer
shell. The hook-shaped flange of the one outer shell receives the
shoulder of the other outer shell upon assembly of the muffler. The
assembly is such that if exhaust leaks out of the muffler, the
exhaust will leak away from the engine housing so as not to
substantially heat the engine housing.
[0030] In one aspect of the present invention, the four-stroke
internal combustion engine includes an engine housing having an
integrally formed crankcase, cylinder and flywheel back plate. The
flywheel back plate includes at least one mounting boss on one side
and at least one other mounting boss on an opposite side. An
assembly fixture is utilized to hold the engine housing during
assembly of the engine. Each mounting boss on the flywheel back
plate receives a separate pin of the assembly fixture to secure the
engine housing to the assembly fixture. A shroud is provided to at
least partially surround the engine housing. The shroud includes at
least two slots such that the slots surround the pins of the
assembly fixture when the shroud is positioned around the engine.
The shroud can then be firmly attached to the engine. After the
shroud is attached to the engine, the pins can be removed from the
mounting bosses. In this manner, the engine can be substantially
completely assembled while the engine is mounted to the assembly
fixture.
[0031] Accordingly, it is a principal feature of the present
invention to provide a four-stroke internal combustion engine which
includes a simple and inexpensive lubricating system which enables
the engine to be functional in various operational attitudes.
[0032] It is a feature of the present invention to provide a
four-stroke engine incorporating the foregoing features and yet
also simple and easy to manufacture and assemble.
[0033] Other features and advantages of the invention will become
apparent to those skilled in the art upon review of the following
detailed description, claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is an exploded perspective view of a four-stroke
internal combustion engine according to the present invention.
[0035] FIG. 1A is a perspective view of the four-stroke engine of
FIG. 1 illustrating the engine as assembled for use with, e.g., a
power trimmer.
[0036] FIG. 2 is a cross-sectional end view and a partial schematic
view of the engine of FIG. 1 taken along line 2-2 of FIG. 3.
[0037] FIG. 3 is a cross-sectional side view of the assembled
engine of FIG. 1.
[0038] FIG. 4 is an enlarged view of a portion of the engine shown
in FIG. 3 illustrating the rotational relationship between a cam
gear and a crank gear, a portion of a lubricant flow path, and a
portion of a breather system for the engine shown in FIG. 1.
[0039] FIG. 5 is an enlarged view of a portion of the engine shown
in FIG. 3 illustrating a piston in its bottom dead center
position.
[0040] FIG. 6 is a schematic representation illustrating another
aspect of the present invention which concerns the attachment of a
connecting rod to a piston and a crankshaft.
[0041] FIG. 7 is a perspective front view taken along line 7-7 of
FIG. 9 illustrating a counterweight positioned adjacent to a main
bearing of the crankshaft.
[0042] FIG. 7A is a side view of the counterweight of FIG. 7.
[0043] FIG. 7B is another perspective view of the counterweight of
FIG. 7.
[0044] FIG. 8 is a perspective view illustrating an agitator
cooperating with a scraper found on a wall within the engine cavity
in order to regulate the amount of lubricant which comes into
contact with the agitator.
[0045] FIG. 8A shows the rotational movement of the agitator of
FIG. 8 and how the scraper controls the lubricant which comes into
contact with the agitator.
[0046] FIG. 9 is a schematic representation of another aspect of
the present invention illustrating the positioning of a crankshaft
within a crank chamber disposed in an engine housing.
[0047] FIG. 10 is a partial schematic view of a top portion of the
engine housing taken along line 10-10 of FIG. 3 illustrating the
spatial relationship between a combustion chamber, a piston bore,
an intake valve and an exhaust valve.
[0048] FIG. 11 is a partial schematic view of a cylinder head taken
along line 11-11 of FIG. 3 illustrating the spatial relationship
between the combustion chamber, the piston bore, the intake valve,
the exhaust valve and portions of a spark plug.
[0049] FIG. 12 is a schematic view illustrating the path of an
air/fuel mixture through an intake system to the combustion chamber
and the path of the exhaust out of the combustion chamber through
an exhaust system in an engine according to the present
invention.
[0050] FIG. 13 is a cross-sectional partial schematic view of an
engine according to the present invention showing the state of the
lubricant in the crank chamber and an oil reservoir when the engine
is in an upside down state.
[0051] FIG. 14 is a cross-sectional view of another embodiment of
the present invention showing a starter assembly attached to the
rear of a four-stroke internal combustion engine.
[0052] FIGS. 15-18 are schematic representations of two engine
housings which are capable of being produced using one die tool and
one die casting machine.
[0053] FIG. 19 is a schematic view of a power trimmer in which
another four-stroke internal combustion engine according to the
present invention is employed.
[0054] FIG. 20 is a perspective view of a shroud which at least
partially surrounds an engine, wherein the shroud is adapted to
enhance overall assembly operations of the engine.
[0055] FIG. 21 is an exploded partial perspective view of the
four-stroke engine of FIG. 19.
[0056] FIG. 22 is another exploded partial perspective view of the
four-stroke engine of FIG. 19.
[0057] FIG. 23 is a perspective view of an engine housing with a
muffler attached thereto.
[0058] FIG. 24 is an exploded perspective view of FIG. 23.
[0059] FIG. 25 is a perspective view illustrating the flywheel end
of the engine housing of FIG. 23.
[0060] FIG. 26 is an enlarged partial cross-sectional view taken
along line 26-26 of FIG. 23 illustrating a connection between the
engine housing and muffler of FIG. 23.
[0061] FIG. 27 is an alternative connection between the engine
housing and muffler of FIG. 26.
[0062] FIG. 28 is a perspective view of the engine housing of FIG.
23 without the muffler.
[0063] FIG. 29 is a front view of an intake isolator as shown in
FIG. 22 and FIG. 20.
[0064] FIG. 30 is a cross-sectional view of the intake isolator of
FIG. 29.
[0065] FIG. 31 is a partial cross-sectional side view of the
assembled engine of FIGS. 21 and 22.
[0066] FIG. 32 is an enlarged view of a portion of the engine shown
in FIG. 31 illustrating a piston in its bottom dead center
position.
[0067] FIG. 33 is an enlarged view of the relationship between the
shroud and starter assembly in terms of retaining the starter
assembly on the shroud.
[0068] FIGS. 34-38 illustrate various views of the starter pulley
shown in FIG. 33.
[0069] FIGS. 39-40 are schematic representations of two engine
housings which are capable of being produced using one die tool and
one die casting machine.
[0070] Before the embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangements
of components set forth in the following description or illustrated
in the drawings. The invention is capable of other embodiments and
of being practiced or of being carried out in various ways. Also,
it is to be understood that the phraseology and terminology used
herein is for the purpose of description and should not be regarded
as limiting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Illustrated in FIG. 1A of the drawings is a four-stroke
internal combustion engine 20 according to the present invention.
The engine 20 drives a conventional shaft typically housed in a
shaft tube 22 which in turn drives an implement having a rotary
head, cutting filament or blade, rotary impeller, or the like,
depending on the type of power tool in use (see, e.g., FIG. 19).
The shaft arrangement shown in FIG. 1A (and FIG. 19), typically
used in conjunction with a hand-held power trimmer, is used for
illustrative purposes only and it should be understood that other
power tools such as those mentioned previously herein are capable
of utilizing the four-stroke engine of the present invention. In
other words, generally, the engine according to the present
invention is preferably used in an orientation where the implement
or working tool has an axis which is substantially parallel with a
crankshaft axis. The engine according to the present invention may
also be orientated with the crankshaft being horizontal or
vertical. The engine according to the present invention is
particularly well suited for those applications in which high RPMs,
e.g., 3,000 RPMs up to 7,000-8,000 RPMs or more, may be required
and in which an output of less than 1 to over 6 horsepower may be
supplied. Importantly, whichever type of power tool is used in
combination with the four-stroke engine according to the present
invention, the engine is capable of working, at least temporarily,
in substantially any operational position of the power tool.
[0072] Illustrated in FIG. 1 of the drawings is an exploded
perspective view showing various components of the four-stroke
internal combustion engine 20 according to the present invention.
Shown in FIG. 1 is a side valve or "L" head engine in which the
various features of the present invention are employed. Side valve
engines are sometimes referred to as "L" head engines because of
the positional relationship of an intake valve and an exhaust valve
with respect to a combustion chamber. As will be apparent below,
the "L" is in reference to the path taken by an air/fuel mixture
and the exhaust through respective valves and ports found in the
engine body. Also, importantly, in an "L" head engine, the intake
valve port and the exhaust valve port are located in the engine
housing, not in the cylinder head which is generally common to
overhead valve or overhead cam engines.
[0073] Before describing in detail the various features of the
present invention, the components shown in FIG. 1 are identified
for the sake of clarity. Shown are an ignition coil screw 24 used
to attach an ignition coil (not shown) to the engine 20; shroud
screws 27 attach shroud 26 to an engine housing 28; cover screws 30
attach sump cover 32 and sump cover gasket 34 to the engine housing
28 in order to seal one end of the engine housing 28; cylinder head
screws 36 attach cylinder head 38 and cylinder head gasket 40 to
the engine housing 28 thereby at least partially defining a
combustion chamber 39 (FIG. 2); carburetor 42 and muffler 44 are
appropriately connected to the engine 20; carburetor 42 cooperates
with intake port 41 and air cleaner or filter 43 (FIG. 2); muffler
44 cooperates with exhaust port 45; flywheel 46 which includes an
integral fan (not shown) is positioned between the shroud 26 and
engine housing 28 with the help of a flywheel key (not shown) in
order to cool the engine 20 during operation; piston 48 is received
by piston bore 50 within engine housing 28; intake valve 52 and
exhaust valve 54 are positioned adjacent piston bore 50 within
engine housing 28; intake valve seat 56 and exhaust valve seat 58
are placed within engine housing 28 to cooperate with the
respective heads of valves 52 and 54; valve springs 60 are placed
in a valve spring chamber and held within the valve spring chamber
by valve spring keepers 62; the valve spring chamber is sealed by
valve cover 64 and valve cover gasket 66; crankshaft bearing 68,
crankshaft bearing 70, worm-helical or spiral gear 74,
counterweight 76, crank pin 78 and crankshaft 80 are part of
crankshaft assembly 82; counterweight 76 includes an aperture 77;
connecting rod 84 includes connecting rod bearings 86 and 88; one
end of connecting rod 84 fits over crank pin 78 and a wrist pin 90
connects the other end of connecting rod 84 to piston 48 by sliding
in aperture 92 of piston 48; wrist pin 90 cooperates with access
hole 93 of engine housing 28 when attaching the connecting rod 84
to the piston 48; cam shaft bushing 94, cam shaft bushing 96, cam
shaft 98, cam lobes 100 and 102 (FIG. 2), and worm-helical or
spiral gear 104 are part of cam shaft assembly 106; cam cap 108 and
cam cap gasket 110 are attached to engine housing 28 by cam cap
screws 111 in order to seal cam shaft assembly 106; tappets 112 are
properly positioned within the engine 20 to cooperate with valves
52 and 54; spark plug 114 is positioned in a spark plug hole within
cylinder head 38; divider 116 having slots 118, 120 and 122 is
disposed within engine housing 28 and at least partially defines a
crank chamber 124 and a lubricant or oil reservoir 126; and the
piston bore 50 includes an extension 128 which at least partially
extends into crank chamber 124.
[0074] Other components and features not clearly shown in FIG. 1
will be described below according to the features of the present
invention.
[0075] FIG. 1 shows the carburetor 42 and the exhaust muffler 44
mounted on opposite sides of the engine housing 28. The carburetor
42 may be of any type of carburetor that is tippable such as a
standard variable venturi diaphragm carburetor found in small gas
engines, but a rotary valve carburetor available from, e.g.,
Walbro, is particularly well suited for use in an engine according
to the present invention. The air cleaner or filter 43
(schematically shown in FIG. 2) is mounted in or near an inlet of
an intake passage in the carburetor 42. A fuel tank (not shown in
FIG. 1) is mounted typically to a lower surface of the engine
housing 28 and cooperates with the carburetor 42 so that fuel and
air can be supplied to the intake port 41 (FIG. 2) in the engine
housing.
[0076] The engine housing 28 is typically made of a lightweight
aluminum alloy casting having a cylindrical bore or piston bore 50
formed therein. As noted, the piston bore 50 is configured to
partially extend into the crank chamber 124 disposed within the
engine housing 28. The area or space 136 (FIG. 13) between the
extended piston bore 50 and divider 116 accepts volumes of the
lubricant or oil during operation and storage to prevent too much
lubricant or oil from entering the piston bore 50 or valve chamber
156 (FIG. 2). The piston 48 is preferably coated, such as with an
iron coating, or chrome plated so as to eliminate the need for a
sleeve such as an iron sleeve within the piston bore 50.
Alternatively, piston bore 50 may include an iron cylinder
sleeve.
[0077] The divider preferably includes bottom slot 118 which is
located directly below the piston bore 50. Optional side slots 120
and 122 of the divider 116 may be located substantially directly
across from one another at a predetermined distance from the bottom
of the piston bore 50. The slots 118, 120 and 122 may be replaced
with one or more holes or other apertures. As noted, the present
invention is, of course, not limited to a particularly sized
engine, but may be used with any internal combustion engine. The
design considerations to determine the size and location of the
slots or holes will be apparent below. The slots or holes should be
configured for different sized engines taking into consideration
the various features of the present invention.
[0078] FIGS. 8 and 8A show another aspect of the divider 116. In
operation, as shown, the counterweight 76 is caused to rotate in
one direction, usually, a clockwise direction. The bottom slot 118
includes opposing sides 130 and 132. The second side 132, with
respect to the direction of travel of the counterweight 76, has a
scraper 134 adjacent thereto. Preferably, the scraper 134 is
positioned within 0.020 to 0.060 inches of the counterweight 76
when the counterweight 76 is located closest to the scraper 134.
The scraper 134 limits or meters the amount of lubricant or oil
(shown in broken dotted lines) which comes into direct contact with
the counterweight 76. The scraper 134 helps to limit the amount of
lubricant or oil which may be slung into the piston bore 50 during
operation and reduces the wind resistance caused by excessive
lubricant on counterweight 76. It should be noted that the scraper
134 could be configured in other ways. For example, bottom slot 118
in the divider 116 could be a diagonal slot such that the second
side of the diagonal slot acts as the scraper 134 but the scraper
is not a raised scraper as shown in FIGS. 8 and 8A. Alternatively,
the bottom slot 118 in the divider 116 could be a straight slot
without the use of a scraper.
[0079] As noted, FIG. 1 shows the oil reservoir 126 disposed within
the engine housing 28 defined by the divider 116 and the engine
housing 28. The oil reservoir 126 is in fluid flow communication
with the crank chamber 124, preferably through slots 118, 120 and
122. As shown, the oil reservoir 126 and the divider 116 are
substantially curved or U-shaped. The divider 116 is preferably
curved to direct lubricant away from the piston bore 50 when the
engine is tipped or inverted. The communication between the two
chambers 124 and 126 allows for the crank chamber 124 to be
properly lubricated during use as the lubricant is allowed to flow
between the two chambers 124 and 126 during use, and for the
lubricant to flow back into the oil reservoir 126 during storage so
that an excessive amount of lubricant does not adversely flow into
the piston bore 50.
[0080] Referring to FIGS. 1 and 3, crankshaft 80 is mounted within
the crank chamber 124. The crankshaft worm-helical or spiral gear
74 drives the cam shaft assembly 106. Worm-helical or spiral gears
are commonly known in the art and readily available from any number
of gear manufacturers and suppliers. The crankshaft 80 and gear 74
may be manufactured in any number of known ways. However, injection
molding the gear around a trim metal piece representing the
crankshaft would work well according to the principles of the
subject invention. The injection mold material may be a
thermoplastic material or nylon material known to those skilled in
the art. Another alternative is to provide a metal crankshaft with
an enlarged cylindrical piece of metal on the crank where a
worm-helical or spiral gear is intended to be located. The
crankshaft then is subjected to a hobbing procedure in which the
gear is machined on the crankshaft.
[0081] Still referring to FIGS. 1 and 3, bearings 68 and 70 are
positioned around the crankshaft 80 in order to support the
cantilevered crankshaft 80 when it is placed within the crank
chamber 124. The bearings 68 and 70 are placed on opposite sides of
the worm-helical or spiral gear 74 and on the same side of the
piston bore 50. The inner bearing 68 is smaller in diameter than
the outer bearing 70. The bearings 68 and 70 are dimensioned in
this manner such that the bearing pockets found in the crank
chamber 124 are machined from one side of the engine housing 28
using only one tool. As can be appreciated by those skilled in the
art, machining bearing pockets from one direction reduces
equipment, time and expense usually associated with having to
machine bearing pockets from different directions.
[0082] As shown in FIG. 1, counterweight 76 is mounted on one end
of the crankshaft 80. FIGS. 7, 7A and 7B show in greater detail the
shape and contours of the counterweight 76. As generally
understood, the forces resulting from the operation of the piston
48, the connecting rod 84 and the associated components, are
balanced by the counterweight 76. Depending on the size of the
engine, more than one counterweight may be necessary. The
counterweight 76 includes wing-tipped aerodynamic sides 138 and
140. Each wing-tipped side includes a back 142 that is positioned
adjacent the main bearing 70 and a front 144 opposite the back 142.
The wing-tipped sides 138 and 140 have contoured surfaces that
extend from the back 140 to the front 142 of the counterweight 76.
In this way, as will be more evident below, the aerodynamic shape
of the counterweight 76 assists in reducing air resistance on the
counterweight 76, generating the proper turbulence of air and
lubricant within the internal cavity of the engine 20 and directing
the lubricant within the internal cavity of the engine 20.
[0083] The tool access hole or aperture 77 of counterweight 76
(FIG. 7) is used for positioning the crankshaft 80 within the crank
chamber 124. FIGS. 7 and 9 schematically show a tool 146 which is
used to position the outer bearing 70, counterweight 76 and the
crankshaft 80 within the crank chamber 124. Bearing 68 is press
fitted into the crank chamber 124 and is adapted to receive one end
of the crankshaft 80. Once the crankshaft 80 has been manufactured,
the bearing 70 is press fitted onto the crankshaft 80. The
counterweight 76 is then fixed to the crankshaft 80. FIG. 7A
illustrates a step 141 which provides a clearance of approximately
0.050 of an inch between the counterweight 76 and bearing 70. As
shown in FIG. 7, only portions 69 of the outside race of the main
bearing 70 are exposed after the counterweight 76 is placed on the
crankshaft 80. The access aperture 77 allows the tool 146 (FIG. 9)
to contact the outside race of the main bearing 70 in three spots
when assembling the crankshaft 80 and associated components of the
crankshaft assembly 82 into the crank chamber 124. A fourth leg of
the tool (FIG. 9) contacts the cantilevered end of the crankshaft
80. This assembly helps ensure that the main bearing 70 will not be
damaged upon assembly and the crankshaft 80 will be properly seated
when inserted into the crank chamber 124.
[0084] FIG. 6 schematically illustrates how the connecting rod 84
is attached to the crankshaft 80 and piston 48. A custom shoulder
bolt (not shown) may be utilized to affix the connecting rod 84 to
the crank pin 78. The entire crankshaft assembly 82 (FIG. 1) is
mounted within the crank chamber 124 (FIG. 3). The piston 48 is
slid into the piston bore 50 from the top of the engine housing 28.
The aperture 92 in the piston 48 is lined up with the access
aperture 93 in the engine housing 28. The connecting rod 84 is
attached to the crankshaft assembly 82 by virtue of crank pin 78
and positioned within a cut out portion 148 of the piston 48. The
wrist pin 90 is inserted through the access hole 93 of the engine
housing 28 into the access hole 92 of the piston 48 and through the
bearing 86 of the connecting rod 84. Since the aperture 92 of the
piston 48 is not drilled all the way through the piston 48, one end
of the wrist pin 90 abuts an inner portion 150 of the piston 48.
The wrist pin 90 can be held in place within the piston 48 by a
star washer 151 inserted in the open end of the aperture 92 (see
also FIG. 5). Preferably, the wrist pin 90 and the crank pin 78 are
hollow so as to reduce the overall weight of the reciprocating mass
which in turn means a smaller counterweight with less weight is
needed to balance the forces generated by the reciprocating mass.
Reducing the overall weight of the reciprocating components
improves vibration and makes the engine lighter for ease of
operation.
[0085] The cam shaft 98, the eccentric style cam lobes 100 and 102
and the cam gear 104 are shown as separate parts in FIG. 2. It
should be noted that these parts can be injected molded as a single
component using, for example, a thermoplastic or nylon material.
Alternatively, certain components may be injected molded around a
piece of trim metal to create the final assembly in similar manner
to that contemplated for the crankshaft 80 and worm-helical or
spiral gear 74.
[0086] FIG. 2 illustrates that the cam shaft 98 includes a
passageway 152. FIGS. 2, 3 and 4 show that a portion of the cam
shaft assembly 106 (FIG. 1) adjacent the worm-helical or spiral
gear 104 includes at least one radial aperture 154 exposed to the
passageway 152 and crank chamber 124. The passageway 152 and
aperture 154 may be drilled into the proper portions of the cam
shaft assembly 106 or molded therein. Essentially, the passageway
152 and the aperture 154 and cam shaft assembly 106 cooperate to
provide a breather arrangement for the internal combustion engine
which will be fully outlined below. Further, the radial aperture
154 may be found in a radial disc (not shown) attached to the cam
shaft assembly 106 in close proximity to the gear 104 so as to be
in communication with the passageway 152 and crank chamber 124.
[0087] As shown, the cam shaft 98 is located normal to the
crankshaft 80. As can be appreciated by those skilled in the art,
generally, in typical small gas engines, the cam shaft and the
crankshaft are parallel to one another, not normal as shown
according to the present invention. A parallel arrangement leads to
a wider engine whereas the normal arrangement according to the
present invention leads to a longer engine design with the
crankshaft axis being substantially parallel to the longitudinal
axis of the tool. A longer unit is particularly desirable for those
hand-held applications such as power trimmers which require better
balance for ease of operation. A wider engine may tend to cause the
unit to want to rotate in the operator's hands during use.
[0088] FIG. 2 shows that cam shaft 98 sits in bushings 94 and 96
which rest in respective pockets within the crank chamber 124 in
engine housing 28. The worm-helical or spiral gears 74 and 104
(FIGS. 2 and 3) are preferably designed such that when cam shaft 98
is placed generally normal to crankshaft 80, the gears 74 and 104
mesh so that the rotational relationship between the crankshaft 80
to cam shaft 98 is 2 to 1.
[0089] The tappets 112 and the intake valve 52 and the exhaust
valve 54 cooperate with cam shaft 98 (FIG. 2). Intake valve 52 and
exhaust valve 54 are positioned within engine housing 28 adjacent
to piston 48 and piston bore 50. The valves 52 and 54 are
positioned such that the valve heads are closer to the centerline
of the bore 50 as compared to the lower portions of the valves
(FIG. 3). Preferably, the valves 52 and 54 are set at an angle of
approximately between zero and eight degrees from a line parallel
with the centerline of the bore. The intake valve seat 56 and the
exhaust valve seat 58 are placed within engine housing 28 and
cooperate with the heads of the respective valves 52 and 54 to
alternately create a seal or an opening into the combustion chamber
39 with respect to the ports 41 and 45. The valve spring keepers 62
and valve compression springs 60 are positioned within the valve
chamber 156 (FIG. 2). Each tappet 112 includes a respective head
158 which is in operational contact with respective cam lobes 100
and 102. As the cam shaft 98 rotates by virtue of drive gear 74,
cam lobes 100 and 102 properly engage tappets 112 such that valves
52 and 54 move up and down as is commonly understood by those
skilled in the art.
[0090] With reference to FIGS. 2, 3 and 4, the crank chamber 124 is
in communication with the valve chamber 156 via access passageway
or aperture 160. Additionally, the valve chamber 156 is in
communication with the piston bore 50 via access passageway or
aperture 162. The passageways 160 and 162 allow valve chamber 156
and the components therein to receive lubricant during operation of
the engine 20 in substantially any attitude. Additionally, during
storage, with the aid of divider 116, the extended piston bore 50,
and the slots 118, 120 and 122, a significant amount of lubricant
will not remain or flow into the valve chamber 156.
[0091] Referring to FIGS. 1, 2 and 3, cylinder head gasket 40 is
positioned between the cylinder head 38 and the engine housing 28
so as to provide a proper seal between the two. Spark plug 114
projects into the enclosed combustion chamber 39. Spark plug 114
fires in combination with the ignition coil and magneto (not shown)
to provide the necessary charge or high voltage signal to ignite
the air/fuel mixture in the combustion chamber 39 when the engine
20 is in operational mode.
[0092] FIGS. 10 and 11 schematically show, at least in part, the
combustion chamber 39 with respect to the intake valve 52, exhaust
valve 54 and piston bore 50. As shown, the combustion chamber 39
only partially extends over the piston bore 50. The orientation of
the combustion chamber 39 and shape of the combustion chamber 39
enhances swirl in the mixing chamber 39 so as to provide a better
air/fuel mixture to enhance ignition of the mixture. Also, the
spark plug 114 is positioned closer to the exhaust valve 54 than it
is to the intake valve 52. The electrode 164 is properly oriented
to provide a firing spark. Placing the spark plug 114 nearer the
exhaust valve 54 allows the hotter air/fuel mixture to be burned
sooner by the spark ignited flame front. This will reduce the
self-ignition tendency of the hotter air/fuel mixture at the
exhaust side of the combustion chamber 39. If the spark plug 114 is
positioned closer to the intake valve 52, there is a risk of having
two combustions, resulting in a loss of power.
[0093] As shown in FIG. 2, the intake port 41 and the exhaust port
45 are located 180 degrees apart from each other. The position of
the valves 52 and 54 is a result of the substantially normal
arrangement of the cam shaft 98 and crankshaft 80 and allows the
ports 41 and 45 to be positioned on opposite sides of the engine
housing 28. This provides an additional feature of operator safety.
For example, when using a power trimmer, the exhaust port 45 and
muffler 44 (FIG. 1) are positioned farther away from the operator
during use. Another advantage of placing the ports 41 and 45 as far
apart as possible is to reduce heat migration from the exhaust port
45 to the intake port 41 which, if did occur, could result in hot
restart vapor lock issues, or difficulty in calibrating the
air/fuel ratio.
[0094] FIG. 12, with reference to FIGS. 2 and 10 as needed, shows a
schematic representation of the path traveled by the air/fuel
mixture and exhaust through the engine 20. The air/fuel mixture
enters the intake port 41, travels past the intake valve 52, and
into the combustion chamber 39. The engine 20 combusts the air/fuel
mixture in order to generate power, and the remaining exhaust
travels past the exhaust valve 54 and out the exhaust port 45. The
arrangement of the cam shaft 98 and the crankshaft 80 is also shown
to illustrate how such an arrangement contributes to the overall
scheme associated with the air/fuel and exhaust paths through the
engine 20.
[0095] An important feature of the present invention is that the
four-stroke engine according to the present invention is capable of
use in substantially any position. A problem with prior
conventional four-stroke engines is that if the engine is
substantially tilted, the lubricant will run into undesirable
locations, such as the carburetor, thereby causing the engine to
malfunction or cease working altogether. The four-stroke engine
according to the present invention is designed to solve this
problem and other problems typically associated with conventional
four-stroke engines.
[0096] The oil or lubricant reservoir 126, the crank chamber 124,
the piston bore 50, and the valve chamber 156 include strategically
placed slots, passageways, or apertures so as to enable various
working components within the engine to be lubricated at virtually
all times during operation. Additionally, in cooperation with the
divider 116, the counterweight 76 has been designed such that only
a proper amount of lubricant comes into contact with the
counterweight 76. The design of the counterweight 76 also allows
the counterweight to meter the amount of lubricant that finds its
way to the main bearing 70 so as not to flood that part of the
crank chamber 124 encapsulating the gears 74 and 104. This also
will help prevent too much lubricant from entering the valve
chamber 156 through passageway 160 and 162. Moreover, the piston
bore 50 and divider 116 have been designed to ensure that the
lubricant has a place to go regardless of whether the engine is
operating or being stored, so as not to foul the internal
components of the engine.
[0097] The piston bore 50, connecting rod 84, the crankshaft
assembly 82, the cam shaft assembly 106, and the valve chamber 156
and the components therein all require some lubrication. It is a
feature of the present invention to use a minimal amount of
lubricant or oil to lubricate the engine. This is accomplished in a
number of ways. First, the highest part that needs lubrication,
considering when the engine is in an upright (spark plug up)
condition, is the valve chamber 156. Second, the roller bearings 86
and 88 for the connecting rod 84 require less lubrication versus a
solid shaft with aluminum bushings. Third, since the lubricant will
follow the path of least resistance, the divider 116, the
counterweight 76 and the various slots, apertures and passageways
previously mentioned help direct the lubricant to particular areas
of the engine depending on the attitude of the engine.
[0098] In an upright non-operating position, lubricant or oil is
stored within the oil or lubricant reservoir 126. In this position
and in this state, the level of the lubricant is preferably below
the bottom slot 118 in the divider 116. During operation, the
reciprocating movement of the piston 48 creates pressure pulses
within the internal cavity of the engine 20. The lubricant moves in
response to the movement of the piston 48. The counterweight 76
agitates the lubricant or oil and blow-by gas within the inside
cavity of the engine 20. As the piston 48 travels in its downward
direction during the intake and power strokes, the lubricant is
forced through the main bearing 70 to lubricate the bearings 70 and
68, the worm-helical or spiral gears 74 and 104, the crankshaft 80,
the cam shaft 98 and the bushings 94 and 96 due to increased
pressure in the engine cavity. The action of the cam gear 104 will
cause some lubricant to enter aperture 160 and migrate to the valve
chamber 156. Moreover, any oil found in piston bore 50 could be
pushed into aperture 162 to also lubricate the valve chamber 156.
On the upward strokes, i.e., the compression and exhaust strokes,
the lubricant will be drawn back over the just mentioned areas to
further lubricate the components due to a partial vacuum in the
engine cavity. The reciprocating movement of the piston 48 moves
the lubricant back and forth within the internal cavity of the
engine 20. The invention does not require a control valve to
control movement of the lubricant.
[0099] There are at least a couple of aspects to consider when
discussing lubricating the engine 20. First, there is resistance or
energy lost as the counterweight 76 agitates the lubricant and
blow-by gas. Second, it is undesirable to supply too much lubricant
to the piston bore 50 and the valve chamber 156 which, if did
occur, could result in damage to the engine 20.
[0100] As noted, since the static oil level is preferably below the
bottom slot 118 in an upright condition, the counterweight 76
preferably does not dip directly into the lubricant, although
direct dipping could be used. The more direct contact made with the
lubrication, the more energy that is lost from the engine 20. The
least amount of lubricant resistance is desired. As mentioned, the
counterweight 76 is designed to throw the lubricant away from the
main bearing 70 and towards the sump cover 32. The design of the
counterweight 76 also limits the amount of lubricant slung into the
piston bore 50. In this way, only a limited amount of oil will find
its way to the valve chamber 156. The counterweight 76 is designed
to reduce the amount of drag that the counterweight 76 has when it
is rotating through and churning up the lubricant. In addition, the
counterweight 76 design reduces windage which creates a more
efficient engine. It should be noted that although the
counterweight 76 is shown and described as the device which
agitates the lubricant and blow-by gas within the internal cavity,
a separate agitator may be provided to accomplish the same results.
Such an agitator may be a splasher or mixer attached to the
rotating crankshaft or connecting rod, or caused to rotate in any
number of other ways.
[0101] In an upside down (spark plug down) position such as that
shown in FIG. 13, the extended piston bore 50, the divider 116, the
slots 118, 120 and 122, and the passageways 160 and 162 (FIGS. 2
and 3) ensure that the engine will continue to function properly,
for at least a limited amount of time, or be capable of storage in
this position without fouling the engine. During operation, the
changing pressure pulses, the blow-by gas and the agitator 76 will
cause the lubricant to be mixed and moved inside the cavity of the
engine 20. Although some oil will be flung into the piston bore 50,
not a significant amount will go there. Also, it should be noted
that the access passageway 162 is located such that the oil ring
166 in the piston 48 does not travel over or past the passageway
162 as the piston 48 reciprocates within the piston bore 50
(FIG.5). Otherwise, it would be possible for lubricant found within
the valve chamber 156 to find its way into the combustion chamber
39, thereby burning off the lubricant and creating excess
emissions.
[0102] The crank chamber 124 includes the area or space 136 between
the extended piston bore 50 and divider 116 for receiving oil or
lubricant when the engine is tilted or inverted as representatively
shown in FIG. 13. During storage, the slots 118, 120 and 122 will
allow most of the oil to remain in the oil reservoir 126, and the
area 136 between the divider 116 and the piston bore 50 will hold
most of the remaining lubricant. Any oil left in the valve spring
chamber 156 during use is thought to be negligible and will not
significantly affect the operation of the motor. Importantly,
because of the positioning of the slots 120 and 122 above the oil
in the inverted position, the valve chamber 156 will not be able to
receive any significant amount of oil.
[0103] To further explain certain features of the present
invention, the oil reservoir 126 should be in communication with
the crank chamber 124 so as to allow for proper lubrication of the
engine 20 in substantially any operational position. The various
described slots, passageways, holes and apertures perform at least
two functions. First, if the engine 20 is operating in a sideways
condition, the slot 120 or 122 in the divider wall 116 facing down
towards the ground allows oil to travel into the crank chamber 124
with the pressure pulsations in a manner similar to when the engine
is in an upright state during which lubricant moves through the
bottom slot 118. Second, if for whatever reason, a significant
amount of lubricant finds its way to the crank chamber 124 during
operation and the engine 20 is turned off and turned upside down or
sideways for storage, the side slots 120 and 122 allow oil to
migrate from the crank chamber 124 to the oil reservoir 126 so as
to prevent the piston bore 50 and valve chamber 126 from
undesirably receiving a significant amount of lubricant.
[0104] Another important feature of the present invention is to be
able to vent blow-by gas from the crank chamber 124 by separating
the blow-by gas from the lubricant/blow-by gas mixture. As
described, the cam shaft 98 is provided with a hollow passageway
152 and properly positioned radial passages 154. With reference to
FIG. 2, one end of the cam shaft cover 108 includes a nipple 168
which is attached to a flexible hose 170 (schematically shown).
Although not shown, there may be an oil seal placed between the cam
cover 108 and engine housing 28. As the pressure pulse forces the
lubricant/blow-by gas mixture through the main bearing 70, the
blow-by gas is driven into the radial holes 154 and passageway 152
while the oil is prevented from passing through the holes 154 as a
result of the centrifugal action of the operating cam shaft 98. The
blow-by gas travels through the cam cover 108 and nipple 168
affixed to cam cover 108, through the flexible hose 170 and back
into the intake of the carburetor 42. A check valve may be
positioned between the end of the cam shaft 98 and the air intake
system to maintain the negative pressure created within the
engine.
[0105] FIG. 14 shows a cross-sectional view of the four-stroke
engine according to the present invention with a starter mechanism
172 attached to the sump cover plate 32 with screws 30. A
crankshaft adapter 174 is connected to crank pin 78. A clutch
bearing 176 is press fitted around the crankshaft adapter 174. A
starter shaft 178 is positioned around the clutch bearing 176 and
is keyed or molded to the starter 180. An oil seal or O-ring 181 is
placed around the starter shaft 178 to provide a seal between the
starter mechanism 172 and the sump cover 32. A thrust washer or
bearing 182 is placed on each side of the starter 180. Starter 180
is preferably a rewind starter having a pull cord 184. Locating the
starter mechanism 172 or the sump cover 32 on the back of the
engine 20 enables the operator to have easy access to the pull
cord. Further, integrally connecting the starter to the piston 48
through connecting rod 84 and the crankshaft 80 through the crank
pin 78 reduces the rope pull force needed to start the engine 20.
Alternatively, other starter assemblies may be utilized.
[0106] FIGS. 15-18 depict a layout for the dies used to manufacture
an engine housing according to the present invention. The engine
housing is designed to permit two engine housings to be produced
using one die tool and one die casting machine. The engine housing
is designed to include walls which allow for the needed draft
angles given different orientations for each engine housing within
the die tool. The draft angles enable the engine housing to readily
separate from the die. The engine housing is designed to permit
slide tooling access (i.e., the piston and cam shaft bores) when
two engine housings are fabricated from one tool. In FIGS. 15-18,
the dies 188 and 190 are formed so that the centerlines of the
engine cylinder bores (which are parallel to direction C) are
parallel to each other. Boxes 194 and 196 represent the edges of
the tool. By positioning the dies in this manner, the inserts used
to form the dies are inserted only along a few directions, i.e., in
directions A, B and C. This die configuration reduces the overall
space required to make the engine housings, while still enabling
two engine housings to be made at the same time. The two die halves
188 and 190 are parted along parting line 192. It should be noted
that the back wall of the engine housing is not shown and is
separately formed and then fastened to the engine housing with
bolts or other suitable fasteners. It is, however, possible that
the back wall could be formed integral with the engine housing
according to the principles set forth above. It should also be
noted that the parting line 192 could be moved to another location.
The draft angles of the engine housing outer walls would change
accordingly so as to accommodate the new location of the parting
line.
[0107] FIGS. 39-40 depict another embodiment of a layout for the
die 529 used to manufacture an engine housing according to the
present invention. In this embodiment, it is still possible to
permit two engine housings to be produced using one die tool and
one die casting machine. The die 529 is laid out in such a manner
that the centerlines of the piston bores are parallel but in
opposite directions. Further, both cavities are oriented such that
the stationary bodies of material compose the internal features of
the oil reservoir, the barrier wall and the inner crank chamber.
The engine housing is designed to include walls of which are needed
for draft angles parting line jumps, and slide shut-offs for the
given orientation within the die layout. By orienting the die in
such a prescribed manner, the inserts for the die pieces are
inserted only along a few directions, i.e., in directions D, E, F
and G. This embodiment of the die layout also serves to minimize
the overall space necessary to manufacture the two-engine housings
out of a single die.
[0108] With such a die layout, the datum targets or reference
features for both cavities are created by the same piece of
stationary material. By having these references on the same piece
of stationary material, there is less variance to accommodate
between the casting in the machining of the finished engine
housing. This further translates into less variance in the
finished-machined engine housing even though the casting is being
derived from two separate cavities.
[0109] As shown, this embodiment also integrally creates the
flywheel back-plate into the engine housing casting. It is further
desirable to gate 531 the casting into the deck of the cylinder and
route the gates parallel to directions F and G into the
cavities.
[0110] The engine 20 shown in FIG. 1 has been described in such a
manner to identify the various aspects of the present invention.
However, the features of the present invention described above may
be incorporated into other four-stroke internal combustion engine
configurations. Moreover, the features identified above may be
slightly modified to accommodate different engine designs. As such,
FIGS. 19-40 illustrate another four-stroke internal combustion
engine in which the features previously described may be employed
and which incorporates additional inventive features not yet
previously described. It should be noted that the features
specifically described in relation to FIGS. 19-40 may be
incorporated into the engine described in FIGS. 1-18, or other
engines.
[0111] FIG. 19 illustrates a four-stroke internal combustion engine
300 according to the present invention. The engine 300 is shown as
used in a power trimmer but may be used in other devices as
described for the engine of FIG. 1.
[0112] Again, before describing in detail the various features of
the present invention, the components shown in FIGS. 21 and 22 are
identified for the sake of clarity. Many of the components are
assembled in the same or similar manner as described in reference
to FIG. 1 or as generally understood by those skilled in the art.
Accordingly, the manner of assembly is not described in great
detail below except if the manner of assembly pertains to specific
features of the present invention. Greater detail of such features
will be provided in reference to the drawings to follow when
needed. Shown in FIG. 21 are spark plug 302; cylinder head screws
304; cylinder 306; cylinder head gasket 308; compression rings 310
and 312 and oil ring 313 which are appropriately positioned in
annular slots located in piston 314; connecting rod 316 and
connecting rod bearings, preferably needle roller bearings, 318 and
320; exhaust valve 322, intake valve 324, valve springs 326 and
valve spring keepers 328; engine housing 330; valve cover 332 and
associated screws 334; flywheel 336, crankshaft adapter 338,
ignition coil 340, wiring assemblies 342 and 346, and screws 344
all of which are part of a starter assembly; muffler mounting bolts
350; muffler 352; and blower housing 348 which is part of an
overall shroud further described below.
[0113] Shown in FIG. 22 are sealing O-ring 366 and oil gauge 367;
intake gasket 368, intake isolator 369 and screws 370; carburetor
gasket 372, carburetor 374 and O-ring 376; air filter assembly 378,
screws 380 and air filter cover 382; wrist pin 384 and star washer
wrist pin retainer 386; oil sealing ring 388, roller bearing 390,
crankshaft 392 and counterweight 393; sump cover 394 and screws
396; muffler housing 398 which is part of an overall shroud further
described below and mounting screws 400; tappets 402, cam shaft
404, cam shaft cover 406; screws 408 and breather tube 410; check
valve 411; fuel tank 412 having fuel line 414, opposing shoulders
416; and filter material 418 which is placed around shoulders 416
as further described below.
[0114] Other components and features not clearly shown in FIGS. 21
and 22 will be described below. Moreover, the significance of any
of the components shown in FIGS. 21 and 22 or their interaction,
will be described below in conjunction with the principles of the
present invention.
[0115] FIG. 23 more clearly shows the engine housing 330 with the
muffler 352 attached thereto by mounting bolts 350. The engine
housing 330 includes a crankcase 420 and a cylinder 422. The
cylinder head 306 (FIG. 21), which at least partially defines a
combustion chamber, is disposed adjacent to the cylinder 422. A
crank chamber 426 is disposed within the crankcase 420. An oil
reservoir 428 is also disposed within the crankcase 420 and is in
fluid flow communication with the crank chamber 426, preferably,
through slot 430 and opposing holes 432 (only one being shown)
disposed in a divider 433. The divider 433 is disposed within the
crankcase 420 and at least partially divides the crank chamber 426
and the oil reservoir 428. A plurality of holes 434 are provided in
the engine housing 330 so that the sump cover 394 and sump cover
gasket can be attached thereto. The engine housing 330 also
includes an oversized wrist pin boss 436. The wrist pin boss 436
may be integrally formed with the divider 433. The function of the
wrist pin boss 436 will be further described below. The engine
housing 330 also includes a flywheel back plate 438 with at least
one mounting boss 440, the function of which will be described
below.
[0116] FIG. 24 is an exploded perspective view of FIG. 23 showing
how the muffler 352 is connected to the engine housing 330. The
cylinder 422 includes an exhaust port 442 and an intake port 444
(FIG. 25). Preferably, the intake port 444 and exhaust port 442 are
elliptical in shape thereby enabling the overall height of the
engine housing 330 to be reduced. This will naturally reduce the
overall weight of the engine housing, which is an especially
important factor for hand-held power tools. The walls of the ports
442 and 444 are provided with sufficient material so as to be able
to support the weight of the engine housing 330 and cylinder head
306 disposed thereabove.
[0117] The muffler 352 includes a boss 446 which is preferably
elliptical. The boss 446 extends into the exhaust port 442.
Mounting bolts 350 extend through holes 448 in the muffler 352 and
into holes 450 formed in the cylinder 422. Preferably, the holes
448 are spaced apart and positioned on opposite sides of the
exhaust port 442 to maximize the stability of the muffler 352 with
respect to its connection to the cylinder 422.
[0118] FIGS. 26 and 27 are enlarged partial cross-sectional views
taken along line 26-26 of FIG. 23 showing preferred alternative
mounting connections between the muffler 352 and cylinder 422. FIG.
26 shows the engine housing 330 having an angled, step sealing
surface 452 located in the exhaust port 442 of cylinder 422. The
end 454 of boss 446 can mate against the exhaust port sealing
surface 452 to substantially prevent exhaust from undesirably
escaping into the environment. Preferably, a sealing gasket 456 is
positioned between the end 454 of the boss 446 and the sealing
surface 452 to even better prevent the exhaust from escaping.
[0119] FIG. 27 shows the outside liner of the boss 446 of the
muffler 352 surrounded by the surface 458 of the exhaust port 442,
thereby defining a clearance space 460 therebetween. Although
surface 458 is shown as an angled surface, it may take on other
configurations so long as clearance space is provided between the
muffler 352 and the exhaust port 442. A gasket 462 is positioned
between the muffler 352 and cylinder 422 or engine housing 330 to
seal the clearance space 460, thereby preventing exhaust from
escaping into the atmosphere. Preferably, the gasket 462 is an
enlarged gasket which also serves as a heat shield between the
engine housing 330 and the muffler 352.
[0120] The muffler 352 (FIG. 24) preferably includes a pair of
outer shells 464 and 466 having respective mounting bolt holes 448
for the mounting bolts 350. An inner shell or baffle plate (not
shown) is preferably located between the outer shells 464 and 466.
The inner shell also is adapted to allow the mounting bolts 350 to
pass therethrough. The baffle plate is designed to reduce noise.
Outer shell 464 includes a shoulder 470 which extends around an
edge of the outer shell 464. Outer shell 466 includes a flange (not
shown) which extends around an edge of the outer shell 466. Upon
assembly, the shoulder 470 receives the flange such that if exhaust
does leak out of muffler 352, the exhaust will leak away from the
engine. Although not shown, a deflector may be placed over the
exhaust holes 372 (FIG. 23) of the muffler 352 to protect the
operator from receiving a direct blast of exhaust.
[0121] Given the nature of the four-stroke engine according to the
principles of the present invention, it is desirable to provide an
economical engine with features which allow the engine to be easily
assembled. One feature is to use the same engine housing 330 for
engines having different horsepower ratings, simply by changing the
connecting rod 316 (FIG. 21) and thus, the length of the piston
throw. To accomplish this feature, the oversized wrist pin boss 436
(FIG. 23) is provided. The wrist pin boss 436 can be machined at
its upper end 474 to provide an access hole (not shown) in the
crankcase 420 for a first piston throw, and the wrist pin boss 436
can be machined at its lower end 476 to provide an access hole (not
shown) in the crankcase 420 for a second piston throw. After the
wrist pin boss 436 is properly machined, the wrist pin 384 (FIG.
22) is inserted through the crankcase access hole and into the
piston access hole to connect the piston 314 (FIG. 21) to the
connecting rod 316 (FIG. 21). Accordingly, the same engine housing
330 can be used for different sized engines. FIG. 31 shows a
completed assembly on such engine. FIG. 32 shows the piston 314 in
its bottom most dead center position so that the wrist pin 384 can
be appropriately positioned within the engine.
[0122] FIG. 28 is an enlarged view of the engine housing 330 of
FIG. 24 without the muffler 352. As shown, the divider 433 defines
a path 478 which extends substantially about the divider 433 and
over the wrist pin boss 436. The path 478 allows lubricant found in
the oil reservoir 428 to flow around a substantial portion of the
divider 433 to further enhance the lubricating and storage features
according to the principles of the present invention. The path 478
allows the amount of lubricant found on both sides of the divider
433 to equalize when the engine 300 is turned upside down. This
further inhibits a substantial amount of the lubricant from
migrating into the crank chamber 426.
[0123] Another feature which reduces assembly costs of the engine
thereby reducing the overall cost of the engine relates to the
manner of assembling a shroud to the engine housing. As noted with
reference to FIG. 23, the flywheel back plate 438 is provided with
at least one mounting boss 440. FIG. 25 is a perspective view of
the engine housing 330 of FIG. 23 only from a different
perspective. As shown, the opposite side of the flywheel back plate
438 also includes at least one mounting boss 480. Upon assembling
the engine 300, an assembly fixture (not shown) is adapted to hold
the engine 300. Each mounting boss 440 and 480 receives a separate
pin (not shown) of the assembly fixture to secure the engine
housing 330 to the assembly fixture. A shroud 482 (FIG. 20) is
provided to at least partially surround the engine housing 330.
Preferably, the shroud comprises the blower housing 348 (see also
FIG. 21) and muffler housing 398 (see also FIG. 22). Shroud 482
includes at least one slot 484. Each slot 484 is designed to
surround a respective pin of the assembly fixture extending out of
the mounting bosses 440 and 480 when the shroud 482 is positioned
around the engine housing 330. The shroud 482 can be attached to
the engine housing 330 by threading screws 486 (FIG. 20) into
respective holes such as hole 488 (FIG. 25) of the engine housing
330. Thus, the entire engine 300 can be substantially assembled
while remaining attached to a single assembly fixture.
[0124] Another feature of the shroud 482 is that the muffler
housing 398 preferably includes a plurality of raised portions 490
(FIG. 31). Thus, if desired, the engine 300 may be placed on the
ground to rest on the raised portions 490. It should be noted that
the blower housing 492' of FIG. 31 is slightly different from the
blower housing shown in FIG. 20. The purpose of this is to show
that various suitable configurations of the shroud 482 are possible
without affecting the scope of the present invention.
[0125] As shown in FIG. 20, the shroud 482 is provided with an
opening 494 which surrounds the intake port 444 (FIG. 25). An
intake isolator 369 (FIG. 22) having an air/fuel passageway 496
(FIGS. 29 and 30) extending therethrough is provided. The intake
isolator 369 is mounted to the engine housing 330 so that the
air/fuel passageway 496 is aligned with the intake port 444. The
intake isolator 496 is positioned within the opening 494 of the
shroud 482 to substantially ensure that cooling air passing between
the engine housing 330 and the shroud 482 cannot escape through the
opening 494 in the shroud 482. Preferably, the intake isolator 369
includes an integrally formed back wall 498 and a side wall 500
(FIG. 22) to accomplish this feature.
[0126] To further reduce manufacturing costs, the crankcase 420,
the cylinder 422 and the back plate 438 are cast as a single
component. In a preferred embodiment, the engine housing 330
further includes at least one fin 502 integrally formed thereto
(FIG. 28). The fin 502 extends from the back plate 438 and beneath
the crankcase 420 for stability and cooling purposes.
[0127] Although the shroud 482 may be of many different designs
consistent with the principles of the present invention, the shroud
482 is designed to hold the fuel tank 412. As best shown in FIG.
31, the shroud 482 is provided with a pair of opposed channels 504
(only one is shown). The outwardly extending shoulders 416 (see
also FIG. 22) are received by the respective channels 504 so that
the fuel tank 412 is held by the shroud 482. The filler material
418 (see also FIG. 22), preferably a polyethylene, high-density,
closed cell, high-temperature and gasoline-resistant foam material,
is positioned between each channel 504 and the respective shoulder
416 to provide a tight fit between the shroud 482 and the fuel tank
412. The fuel line 414 (FIG. 22) includes a fuel filter 506
attached to the end of the fuel line 414 disposed within the fuel
tank 412. It should be noted that the extra line shown in FIG. 22
is a purge line. The fuel filter 506 acts as a weight such that
during operation of the engine, if the engine is tipped, the
weighted fuel line 414 swings to the bottom of the fuel tank 412 to
ensure that fuel is picked up by the fuel line 414.
[0128] Another aspect of the present invention concerns the starter
assembly 507 shown in FIG. 33. The blower housing 348 is provided
with a hub 508 having an inwardly facing extension 510. The hub 508
is adapted to fit over the crankshaft 392 (FIG. 22) or crankshaft
adapter 338 (FIG. 21). The starter assembly 507 which includes the
pulley 516, rope 518 and spring 520 is positioned onto the hub 508.
A star washer 514 is placed over the hub extension 510 so as to dig
into the extension material. The star washer 514 holds the starter
assembly 507 in place with respect to the blower housing 348. This
arrangement eliminates the need for separate mounting bosses and
fasteners typically needed to hold the starter assembly in place.
Such mounting bosses and fasteners generally block the cooling air
flow by a fan.
[0129] FIGS. 34-38 show various views of the pulley 516. The spring
520 (FIG. 33) is positioned on one side 522 of the pulley 516
having an appropriately shaped annular recess 524. The opposite
side 526 of the pulley 516 includes a plurality of spokes 528 for
engagement with a flywheel such as flywheel 336 shown in FIG. 21.
The rope 518 includes a knot 530 on one end thereof which is held
in a chamber 532 formed in a hub 534 of the pulley 516 beneath the
pulley rope portion 536. The rope 518 extends through a hole 538 in
the pulley rope portion 536 and is wrapped around the pulley 516.
The other end of the rope 518 is attached to a starter handle 540
(FIG. 20).
[0130] The foregoing description of the present invention has been
presented for purposes of illustration and description.
Furthermore, the description is not intended to limit the invention
in the form disclosed herein. Consequently, variations and
modifications commensurate with the above teachings in skill or
knowledge of the relevant art, are within the scope of the present
invention. The embodiments described herein are further intended to
explain the best modes known for practicing the invention and to
enable others skilled in the art to utilize the invention as such,
or other embodiments and with various modifications required by the
particular applications or uses of the present invention. It is
intended that the appended claims are to be construed to include
alternative embodiments to the extent permitted by the prior
art.
[0131] Various features of the invention are set forth in the
following claims.
* * * * *