Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 2 ~
-- 1 --
Field and Background of the Invention
This invention relates to an internal combus-
tion (IC) engine, and more particularly to an IC ~-~
engine particularly suited for use in hand-held
(portable) tools.
Relatively small size IC engines are well known
and are commonly used to power tools such as chain
saws, blowers, line trimmers, etc. Since such tools
are normally carried and used by a single person,
the engine must be light weight and capable of oper-
ation in different orientations (sideways or
straight up, for example).
At the present time, most engines for this
purpose are two-stroke air-cooled engines because
they have a good power vs. weight and size ratios,
do not have a complex construction, and they are all
position or orientation engines. The latter feature
is made possible because such engines utilize a
diaphragm-type carburetor and engine lubrication is
accomplished by adding lubrication oil to the fuel
(typically a 40:1 fuel-to-oil mixture).
While two-stroke engines of this type work
well, they have certain drawbacks. The fuel con-
sumption rate is relatively high and the operating
-
~ ~2~
noise level is also high. A very important disad-
vantage is that the emissions levels of such engines
are quite high because the exhaust includes a siz-
able amount of fresh fuel. The State of California
regulations soon to become effective limit the
amounts of hydrocarbons and carbon monoxide that may
be produced, and most or all two-stroke engines
presently in use will not be able to meet the
California standardsO It is expected that those
standards will also be adopted by other states and
countriesO
Four-stroke IC engines are, of course, also
well known and they generally have lower hydrocarbon
and carbon monoxide emissions than two-stroke en-
gines. This is true because four-stroke engines
exchange the exhaust and fresh fuel/air mixture in a
more positive ~nn~r with the use of valves. Four-
stroke engines also in general have lower noise lev-
els.
Relatively small four-stroke engines are avail-
able and have been used in, for example, model or
hobby aircraft. While such engines are sufficiently
small to be used in portable tools, they would not
be satisfactory because they have a relatively com-
plex and light duty construction. Four-stroke en-
gines normally have an oil sump in a crankcase at
the bottom of the engine and an oil pump for moving
the oil to the moving parts such as the overhead
valves and the valve actuating ~chAni sms. This
type of lubricating system is not satisfactory for
all-position use.
- ~
- 3 -
In addition, the Y. Imagawa et al. U.S. patents
No. 5,176,116, dated January 5, 1993, and No.
5,213,074, dated May 25, 1993 describe a lubrication
system for a portable four-stroke engine, wherein
some of the engine parts are lubricated by oil in a
crankcase and other parts by grease which is packed
around moving parts. It is questionable whether
grease will provide satisfactory lubrication for
engine parts that become very hot during use. In
any event it is doubtful that grease is satisfactory
for long-term use in an engine in field and garden
use because the grease should be periodically
cleaned out and repacked. This is not practical in
engines used, for example, in home gardening tools.
The R. G. Everts U.S. patent No. 5,241,932
dated September 7, 1993, and the Y. Imagawa et al.
U.S. patent No. S,267,536 dated Dec h~r 7, 1993,
describe engines generally similar to the engine de-
scribed in No. 5,213,074. Both patents describe
lubrication systems for a four-stroke engine, in-
cluding oil in a cr~nkc~e sump and a splasher.
Patent No. 5,241,932 also states that "mist ladened
air" moves from the crankcase through the valve
guide tubes to the valve cover, to lubricate the
valves and the rocker arms.
The D. E. Stinebaugh U.S. patent No. 4,708,107,
dated November 24, 1987, describes a four-stroke
engine including a cr~nkc~e-compression arrange-
ment. A carburetor supplies a "combustible working
fluid such as an air-gasoline mixture" to the crank~
case, and the mixture is pumped through a "boost -
plenum or reservoir", through a throttle valve, to
the cylinder intake valve. A cam shaft and cam
-~ 2~2~
followers for the intake and exhaust valves are
mounted in the boost plenum.
It is therefore a general object of the present
invention to provide an improved four-stroke engine.
Summarv of the Invention
An engine constructed in accordance with this
invention comprises an engine frame including a
block portion and a head portion, the block portion
forming at least one cylindrical cylinder and a
crankcase. A piston is mounted for reciprocation in
the cylinder, and a crank and connecting rod are
mounted in the crankcase and connected to the pis-
ton. The head portion forms one end of the cylinder
and the piston forms the other end, and the intake
air and the exhaust flow through intake and exhaust
passages formed in the head portion. The crankcase
includes a fuel inlet port and an outlet port, and a ' -
duct connects the outlet port to the intake passage
in the head portion. The inlet port is connected to
a supply of a combustible mixture comprising fuel,
lubricating oil and air.
During engine operation, the mixture flows
through the cranXcase from the fuel inlet port to
the outlet port, the piston functioning as a pump to
move the mixture. The oil in the mixture lubricates
the engine parts in the cr~nkcA~e. From the outlet
port, the mixture, including the lubricating oil,
moves along a flow path through the duct to the
intake passage in the head portion. The valves and
the valve actuating ~chAni are located such that
they are lubricated by the combustible mixture.
~i~P'~ v~ 33
Thus the moving parts of the engine are lubricated
by the oil in the mixture which is continuously re-
plenished and flows around the moving parts during
engine operation.
Valves may be provided at the fuel inlet and
outlet ports of the crankcase to achieve crAnkcA~e
compression of the mixture, and the duct may form a
plenum or reservoir of the mixture under pressure.
The engine may include more than one cylinder and
piston, such as a two-cylinder engine (or an engine
having multiples of two cylinders) having two pis-
tons which simultaneously move toward the crankcase
or the cylinder heads.
The valves and the valve actuating mechanisms
are located in the mixture flow path to be
lubricated by the mixture. The actuating ?ch~ni sm
may be located in the head portion of the engine or
they may be located in the crankcase.
~.,
Brief Description of the Drawings -
-,
This invention may be better understood from ~
the following detailed description taken in conjunc- - -
tion with the accompanying figures of the drawings
wherein:
Figs. lA through lD are schematic views illus- ~'
trating the four operating strokes of an engine
incorporating the present invention;
: ,
Figs. 2A through 2D are views similar to Figs.
lA through lD but illustrate an alternative cons-
truction of the engine;
- Figs. 3A and 3B are similar to Figs. lC and lD
but illustrate still another alternative construc-
tion of the invention;
Figs. 4A and 4B are similar to Figs. 3A and 3B
but illustrate still another alternative construc-
tion of the invention;
Fig. 5A further illustrates an engine con-
structed in accordance with the invention;
Fig. 5B shows the engine of Fig. 5A but with
some parts broken away to show underlying parts.
Fig. 6A is a view, partially in section, of
another engine constructed in accordance with the
invention; and
Figs. 6B and 6C are additional views of the
engine shown in Fig. 6A.
Detailed Description of the Drawings
Figs. lA through lD illustrate a four-stroke
overhead valve internal combustion engine 110,
wherein Fig. lA shows the compression stroke, Fig.
20 lB shows the expansion or power stroke, Fig. lC -
shows the exhaust stroke, and Fig. lD shows the
intake stroke. The engine includes a frame includ-
ing a block portion 111, a crankcase portion 112,
and a head portion 113. The block portion 111 forms
a cylinder 114 and a piston 116 is reciprocally
mounted in the cylinder 114. A crank shaft 117 is
rotatably mounted in the block portion 111 and a
connecting rod 118 connects the piston 116 to the
2 ~ ~ ~
shaft 117. Mounted on the head portion 113 are an
intake valve 119 and an exhaust valve 120 which are
enclosed by a valve cover 122. An exhaust duct 123
surLou~lds the exhaust valve 120-and conveys exhaust
5 from the cylinder 114 to a muffler (not illustrat-
ed). Also mounted on the head portion 113 is a
spark plug 124 which has its points 125 ext~n~li ng
into a combustion chamber 126 formed between the
crown of the piston 116, the side walls of the cyl-
10 inder 114 and the head portion 113.
A fuel inlet port 128 is formed in the sidewall of the crankcase 112 and, during engine opera-
tion, receives a combustible mixture from a carbure-
tor indicated by the reference numeral 129. The
15 carburetor 129 iS preferably an all-position type
such as a diaphragm carburetor. A one-way or check
valve 130 is connected across the inlet port 128 and
allows the mixture to flow only in the direction
from the carburetor 129 to the interior chamber 115
20 of the crankcase 112. The intake side of the carbu-
retor 129 iS connected to a supply tank 127 of a
fuel-oil mixture such as a 40-1 mix of gasoline and
oil. The oil may be the type commonly used with
small two-stroke engines. ~rhe gas-oil mixture is
25 further mixed with air in the carburetor 129 to form
the previously mentioned combustible mixture that
flows from the carburetor 129 into the cr~nkcA~:e
Ch;~. h~r 115.
The crAnkc~ce 112 also has an outlet port 131
30 formed therein, and a duct 132 has one end thereof
connected to the outlet port 131 of the crankcase
112 and its other end 134 connected to an enclosure
136 formed in the head portion 113 and the cover
~1~2~
- 8 -
122. The duct 132 thus conveys the mixture from the
Ch~ h~r 115 of the crankcase 112 to the enclosure
136 within the cover 122. Also included in the
engine but not illustrated in Figs. lA to lD are
valve operating or actuating mechanisms, located
within the flow of the mixture such that the mecha-
nisms are lubricated. For example, the valves and
the valve actuating ~ch~n; ~ms of all of the
embodiments disclosed herein may include a cam and
push rod arrangement for driving rocker arms that
operate the valves, the cam and push rods being
located in the ch~ h~r 115 and/or in the duct 132,
and the rocker arms being located in the enclosure
136. Alternativelyl a timing belt may be connected
between the crankshaft 117 and a cam ?ch~ni ~
mounted in the enclosure 136 as illustrated in Figs.
5A and 5B~ Still another arrangement is shown in ~;
Fig. 6 wherein the cam shaft, push rods and valves
are mounted in a ch~ h~r formed in the block
portion, in flow c~ ication with the crankcase.
The valves and valve actuating ?ch~ni - of the
engines shown in Figs. 2A to 2D, Figs. 3A to 3B and
Figs. 4A to 4B may also be one of the foregoing
types.
Considering the operation of the engine, during
the cc _ession stroke illustrated in Fig. lA, the
two valves 119 and 120 are closed and the piston 116
moves toward the head portion 113, thereby compress-
ing the mixture within the combustion chamber 126.
As the piston 116 moves upwardly, it increases the
interior space or volume of the cr~nkc~e chamber
115 formed by the crankcase 112 and the underside of
the piston 116, thereby drawing the combustible
- 9 -
mixture through the inlet port 128 from the carbu-
retor 129. The check valve 130, of course, opens as
illustrated in Fig. lA to allow flow in this direc-
tion. Near the end of the compression stroke, the
spark plug 124 fires and ignites the combustible
mixture in the chamber 126, thereby driving the
piston 116 in the downward direction as seen in Fig.
lB, the two valves 119 and 120 being closed. Since
the piston 116 moves downwardly, it reduces the
volume of the Ch~ hPr 115 within the crankcase 112,
thereby increasing the pressure of the mixture with-
in the ÇhA hPr 115. This action closes the valve
130 and compresses the combustible mixture within
- the chamber 115, the duct 132 and the enclosure 136.
At the end of the power stroke shown in Fig.
lB, the piston 116 moves upwardly again in the ex- ~
haust stroke as illustrated in Fig. lC, and at this ~ -
time the valve actuating ~ch~n; opens the exhaust
valve 120. Cylinder exhaust gases from the previous
power stroke are purged from the combustion chamber
126 by the upward movement of the piston 116 which
pushes them out of the combustion chamber 126
through the open exhaust valve 120 and the exhaust
duct 123.
At the end of the exhaust stroke, the piston
- 116 again moves downwardly in the fuel intake stroke
as shown in Fig. lD. The exhaust valve 120 is
closed and the intake valve 119 is opened by the
valve actuating mech~ni~m. The downward movement of
the piston 116 sucks the mixture into the combustion
chamber 126 and pushes the mixture from ths crank-
case chamber 115 through the duct 132, through the
2 5 2 2 '~
-- 10 --
open intake valve 119 and into the combustion cham-
ber 126. The intake valve 119 closes at the end of
the intake stroke of the piston 116, and the piston
then starts upwardly again in the next compression
stroke (Fig. lA), thereby completing one operating
cycle of the engine.
.
It will be apparent from the foregoing that the
combustible mixture from the carburetor 129 flows
through the crankcase 112 and through the valve
cover 122, and the ~ixture contacts all of the mov-
ing parts requiring lubrication. The mixture forms
an oil mist in the crankcase Ch~ h~r 115 and in the
cover 122 which is continuously replenished as the
mixture flows around the parts to the intake valve,
the parts being in the flow path. The enclosure 136
around the valves and the valve actuating mech~ni
and the cr~nkc~se contain a quantity of an oily mist
which lubricates the parts. Some of the oil in the
mist settles on the moving parts and clings thereto,
thereby providing continuous lubrication for these
parts.
The engine 210 illustrated in Figs. 2A through
2D is generally similar to the engine shown in Figs.
lA through lD, and the same reference numerals for
corresponding parts are employed except that in
Figs. 2A through 2D the numerals are in a 200 series
rather than in the 100 series of Figs. lA to lD.
The engine 210 shown in Figs. 2A to 2D includes
a duct 232 connecting the crankcase 212 with the
valve cover 222. The duct 232 includes an enlarged
portion 240, whereby the duct 232 forms a storage
2 ~
plenum or surge tank. The engine 210 further in-
cludes a one-way or check valve 241 exten~; ng across
the outlet port 231 of the crankcase 212. As illus-
trated, the valve 241 permits flow of the combusti-
ble mixture only in the direction from the crankcasec-h~ hPr 115 to the plenum 240.
The engine 210 operates similarly to the previ-
ously described engine, with the exception that the
volume of the mixture in the plenum 240 will have a
higher pressure than that of the mixture in the duct
132. This is true because, with reference to Figs.
2A and 2B, as the piston 216 moves upwardly in the
compression stroke, the mixture is drawn into the ~-
crankcase ch~ h~r 115 from the carburetor and the
check valve 241 is closed. During the power stroke
shown in Fig. 2B, the piston 216 moves downwardly
and the inlet valve 230 closes, and consequently the
piston forces the mixture into the plenum 240 and it
is compressed. The mixture is trapped by the closed
valves 119 and 241 in the plenum ch~ h~r during the
exhaust stroke shown in Fig. 2C and during the next
subsequent intake stroke when the piston moves down-
wardly again as shown in Fig. 2D, additional mixture
is pumped into the plenum and the valve 219 opens.
The pressure in the plenum at the end of the intake
stroke is increased and is a function of the crank-
case chamber 115 volume, the volume of the plenum
240 and the displacement of the piston 216, and it
may be approximately 8 to 15% above ambient pres-
sure, for example. This increased pressure or su-
percharging, of course, i ,L~ves the volumetric
efficiency of the engine and allows the engine to
produce greater power for a given size than would
otherwise be the case.
2~
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In addition, the increased pressure creates a
denser or more concentrated mixture, resulting in an
increased amount of lubricant flowing past and sur-
rounding the parts, thereby increasing the efficien-
cy of lubrication.
.
Figs. 3A and 3B illustrate an engine 310 having
a pair of cylinders, but otherwise constructed simi- ~ ;
larly to the engine illustrated in Figs. lA through
lD. The two cylinders have pistons which recipro- -
cate in synchronism such that they simultaneously
move toward the cr~nkc~ce or toward the cylinder
head. In the present specific example, one pair of
cylinders is shown although multiple pairs may be
provided. While opposed cylinders are illustrated
and described herein, the cylinders could instead be
parallel or in a V configuration, for example. The
engine 310 includes a crankcase 312 having an inlet
port 328 covered by a check valve 330, the port 328
connecting the cr~nkc~ce ~h. h~r 315 with a carbure-
tor 329. The crAnkc~e further has two outlet ports333a and 333b connected with two ducts 332a and
332b. ~
':
The engine further includes two opposed cylin-
ders 311a and 311b, and pistons 316a and 316b mount-
ed for reciprocation with the cylinders. The twopistons are connected by connecting rods 318a and
318b to a crank~h~ft 317, the connections being
arranged such that the two pistons simultaneously
move toward each other and then away from each other
in the operating cycles of the engine. The firing
order of the two pistons is, however, reversed so
that when the piston 316a is moving outwardly in the
exhaust stroke (Fig. 3A) the piston 316b is moving
7 ~J ~
- 13 -
outwardly in the compression stroke, and when the
piston 316a is moving inwardly in the intake stroke
(Fig. 3B), the other piston 316b is moving inwardly
in the power or expansion stroke. Each cylinder '~
further includes intake and exhaust valves, a valve
operating ?~h~ni~ (not shown), such as one of the
previously discussed types, and a spark plug mounted
in a head portion of the engine frame, the construc-
tion and operation of these parts being generally
the same as that of the engine shown in Figs. lA to
lD. Simultaneous outward movement of the pistons as
shown in Fig. 3A causes the mixture to be drawn from
the carburetor 329 and into the crankcase chamber
315, and simultaneous inward mov~ -nt of the two
pistons causes the mixture to be pumped from the
chamber 315 through one of the two ducts 332a and
332b and one of the intake valves 319a and 319b.
Figs. 4A and 4B illustrate an engine 410 having
two opposed cylinders 411a and 411b and two pistons
416a and 416b, similar to the engine 310. The en-
gine 410 further includes a plenum 440 and an outlet
check valve 441 which are common to the two cylin-
ders and feed the mixture received from the crank-
case chamber 415 to the two ducts 432a and 432b.
Thus the engines 310 and 410 operate similarly ex-
cept that the supercharged pressure in the intake
ducts (as described in connection with the engine
2A) will be higher, giving the engine 410 higher
efficiency. ~he supercharged pressure in the plenum ~;
440 will, however, be higher than that in the plenum
240 because the total volume swept by the two pis-
tons is twice the displacement of one cylinder while
the volume to be filled (one combustion chamber) for
, k
-- 1 4 --
each revolution equals the displacement of one cyl-
inder. The pressure at the end of the intake stroke
may be about 16-25% above ambient pressure in a two-
cylinder engine without a plenum (sr surge tank) as
shown in Figs. 3~ and 3B, and may be about 21-45~
above ambient in an engine with a plenum as shown in
Figs. 4A and 4B.
Figs. 5A and 5B illustrate another engine 510
constructed according to the invention, and again
the same reference numerals used in Figs. lA to lD
are used for corresponding parts, but in the 500
series. With particular reference to Fig. 5B, the
engine frame includes a block 511, a crankcase 512
and a head 513 which also forms a valve cover 522.
~5 In this specific example, the engine is air-cooled,
and cooling fins 540 are formed on the outside of
the block 511 and the head 513.
A piston 516 is mounted for reciprocation in
the cylinder 514, and the piston is connected by a
connecting rod 518 to the cr~nk~h~ft 517 in the
customary manner. A crank arm 541 is mounted on the
cr~nk~haft 517 and connects to the rod 518, and the
arm 541 includes a counterbalance portion 542. As
shown in Fig. 5B, the ch~ hPr 515 of the crankcase
512 is relatively small and closely confines the
cr~nk~h~ft 517 and the crank arm 541, this being
made possible because the case 512 is not also re-
quired to form a sump for a lubricating oil. The
block 511 and the cr~nkc~e 512 are tightly connect-
ed together and form the interior ch; hPr 515 whichis sealed except for inlet and outlet ports 528 and
531 to be described.
~2~
- 15 -
A combustion chamber 526 is formed between the
crown of the piston 516, the wall of the cylinder
514 and the inside of the head 513. A head gasket
543 between the block 511 and the head 513 seals the
connection between them. The inside of tha head 513
forms a wall 544 across the upper (as seen in Fig.
5B, although the engine could have other orienta- -
tions) side of the cylinder 514. Formed in the wall
54~ are an intake port, an exhaust port lnot shown)
and an opening for the spark plug 524. An intake
valve 519 and an exhaust valve (not shown) are moun-
ted to open and close the respective ports in the
conventional manner for a four-stroke engine. Each
valve includes a valve stem 547 that is slidably
mounted in a valve guide 548, and a valve spring 549
urges the valve upwardly toward the closed position.
The engine further includes a valve actuating
or driving ?ch~nism including a rocker arm 55~ -
pivotably mounted on a rocker shaft 552. One end of
each arm 551 engages the outer end of a valve, and
the other end engages a valve cam 553 secured to a
cam shaft 554. This arrangement forms a conven-
tional overhead-valve, overhead-cam arrangement
which is contained in the enclosure 536 formed by
the valve cover portion 522 of the head.
With reference to Fig. 5A, a cogged timing belt
558 is provided to rotate the cam shaft 554, and is
driven by a drive sprocket (not shown) mounted on
the cr~nkRh~ft 517. The cr~nkRh~ft 517 is supported
by at least one bearing 559 (Fig. 5B) on the block
511 and the cr~nkcase 512. In the specific example
of the engine shown in Figs. 5A and 5B, both ends of
the shaft 517 extend out of the block, and the end ~-
, ',
- 16 -
not shown in the drawings is shaped to be attached
to a tool or implement to be driven. The other end,
shown in ~ig. 5A, is secured by a nut 561 to a wheel
562 that forms a flywheel and a fan. Fins or vanes
563 are provided on the wheel 562 and cause cooling
air to circulate around the fins 540. The above-
mentioned drive sprocket is also driven by the shaft
517 and may form part of the wheel 562. The belt
558 also ?ehes with a driven sprocket 564 which is
secured to one end of the cam shaft 554. The sproc-
ket ratio is such that the cam shaft 554 makes one
revolution for two revolutions (one operating cycle)
of the crank shaft 517. The cam shaft 554 is rotat-
ably supported by bearings (not shown) on the head
513. Both the bearings for the c~ -hAft and the
bearings for the cr~nk~h~ft are accessible from
within the enclosure 536 and the chr h~r 515 for
lubrication purposes, as will be described more
fully hereinafter.
As previously mentioned, an inlet port 528 and
an outlet port 531 are formed in the block 511. The
inlet port 528 is located in the sidewall of the
cylinder 514 at the location when the port is open
when the piston 516 is at the top-dead-center (TDC)
position, which is illustrated in Fig. 5B. As the
piston 516 moves toward the bottom-dead-center (BDC)
position (not illustrated), the skirt 566 of the
piston gradually covers and then closes the port 528
twice in each operating cycle.
The carburetor 529 is connected to the inlet
port 528 by a tube 567 and it is supported by a
brace 568 that is fastened to the block. The air
intake of the carburetor 529 is connected to an air ~ ~
:. ~.~.
- 17 - :
cleaner 569, and the fuel intake is connected to the
fuel supply tank 527 by a tube 571. The carburetor
529 may be a conventional diaphragm type, and the
tank 527 and the air cleaner 569 may also be conven- ~:
tional. A passage 572 connects the crankcase cham-
ber 515 to the carburetor 529 for pumping fuel to
the carburetor, in a conventional -nnPr.
The outlet port 531 is connected to the duct
532 by a tube 533 and a one-way valve 541. In the
present example, the valve 541 is a reed valve type
which allows flow only in the direction toward the
duct 532.
The duct 532 may be made, for example, of plas-
tic or other flexible material, and it has one end
connected to the valve 541 outlet and its other end
connected to a port 573 formed on the valve cover
522. The duct 532 is generally U-shaped and extends ~
clear of and separate from the block 511. As shown :-.
in Fig. 5B, the port 573 communicates directly with
20 the valve cover enclosure 536 and with the valve ~ : :
port in the head 513 for the intake valve 519.
The port in the head 513 for the exhaust valve
(not shown in Figs. 5A and 5B) is similar to the
corresponding parts of the engines 110, 210, 310 and
410, where it will be noted that the exhaust duct
123, for example, is closed off from the enclosure
136. Consequently the exhaust does not enter the
enclosure 536 but instead flows through the exhaust
duct to a muffler 574. The valve guides 548 and the
valve springs 549 of both the intake and exhaust
valves are open or accessible to the flow of the
2~,fV~
- 18 -
air-gas-oil mixture in the enclosure 536 for lubri-
cation purposes.
Considering the operation of the engine S10,
the operator pours a quantity 576 of fuel-oil (such
as a 40:1 mix of gasoline and oil commonly used for
two-stroke engines) into the tank 527. The mix is
drawn into the carburetor 529 through the tube 571,
and mixed with air to form a combustible mixture.
The gasoline vaporizes and the oil forms a very fine
mist.
When the piston 516 moves toward TDC, the vol-
ume of the crankcase chamber 515 increases, causing
the pressure in the enclosure 515 to drop, and the
piston skirt 566 moves to the illustrated position
and the inlet port 528 is opened. The mixture is
drawn into the ch; h~r 515 from the carburetor 529
and the reduced pressure in the enclosure 515 closes
the outlet valve 541. This occurs during both the
compression and exhaust strokes.
When the piston 516 moves from TDC toward BDC,
the piston skirt closes the inlet port 528 and the
moving piston reduces the volume of the cr~nkc~Re
Ch; h~r 515. The resulting compression of the mix-
ture in the ch~ h~r 515 opens the valve 541 and
forces the mixture into the duct 532. In the power
stroke, the mixture in the duct 532 is compressed
because the intake valve 51g is closed, and the
increased pressure in the duct is held or retained
when the reed valve 541 closes at the time the pis-
ton moves up again. In the intake stroke, the com-
pressed mixture is drawn into the cylinder and
-- 19 --
additional mixture is forced into the duct by the
piston. Thus the cr~nkc~e compression acts as a
supercharger and makes possible an increase in power
ou~u~ for a given size engine. The compression
also increases the density of the oil mist and im-
proves the lubrication of the parts.
As previously mentioned, a gasoline-oil-air
mixture flows through the crankcase ~h~ h~r 515, the
duct 532 and the enclosure 536 of the valve cover
522. The mixture forms an oil mist in the chamber
515 and the enclosure 536 which flows past and sur-
rounds and lubricates all of the parts requiring
lubrication. Since there are four strokes in each
operating cycle, and since the mixture leaves the
enclosure 536 in only one stroke (the air intake
stroke), the oil mist is relatively stationary in
the chamber 515 and the enclosure 536. The chamber
515 and the enclosure 536 contain a sizeable
quantity of the oil mist which ~Loul,ds and col-
lects on the moving parts, thereby lubricating theparts without the use of an oil sump or grease
packed around the parts.
The engine 510 is further advantageous in that
the relatively large internal volume of the duct 532
functions similarly to a plenum or surge tank. The
large volume of the duct is due to the U-shaped bend
of the duct. The location of the port 528 and the
piston 516 which closes and opens the port is also
advantageous because it avoids the need for a sepa-
rate check valve, and this arran~ - -nt also allows
for an advantageous placement and location of the
carburetor. This is particularly important in en-
gines for small hand-held implements such as chain
.
:':
2 ~
- 20 -
saws. Any blow-by gas past the piston flows into
the crankcase chamber 515 and is LeLuLI.ed to the
combustion chamber.
Figs. 6A, 6B and 6c illustrate an engine which
is generally similar to the engine shown in Figs. 5A
and 5B but which has a different head construction
and a different valve and valve actuating ~ch~n; ~m.
The engine frame includes a block 611, a crank-
case or pan 612, and a head 613. In this instance,
the head 613 has an "L" head (or flat head) design,
and a gasket 643 is between the head and the block.
Both the head 613 and the block 611 have air cooling
fins 640 on the outside. The block 611 is fastened
to a mounting flange 680 which is provided for
mounting the engine on a portable tool or implement.
A piston 616 is mounted in a cylinder 614, and
a connecting rod 618 connects the piston 616 to a
cr~nkQh~ft 617. A counterbalance 642 is also con-
nected to the cr~nkch~ft, and these parts rotate in
the crankcase chamber 615. A sparkplug 624 is
mounted in a hole 625 in the head 613.
The engine further includes a conventional ~ ~-
carburetor 629 which preferably is an all-position
type such as a diaphragm carburetor as illustrated
in Fig. 6A. The carburetor includes a manually
adjustable throttle 681 for controlling engine
speed, and it receives air through a conventional
air cleaner 669. A fuel (such as gasoline) supply
tank (not illustrated) similar to the tank 527 is ~
30 provided, and it forms a source of a fuel-oil ;
mixture as previously described. ~-
- 21 -
The carburetor 629 forms a combustible mixture
of air-fuel-lubricating oil, the oil being in the
form of a fine mist or droplets. As in the
previously described embodiments, the mixture flows
through the cr~nkc~e and a plenum ~h~ hPr or surge
tank to the combustion çhr- h~r, and the mixture
effectively lubricates the engine parts requiring
lubrication.
The mixture flows from the carburetor 629 and
into the crankcase chamber 615 through an inlet port
628 formed in the sidewall of the cylinder. The
port 628 is at a lower part of the cylinder wall and
is covered by the skirt of the piston 616 except
when the piston is near top-dead-center, as
described in connection with the engine shown in
Fig. SB.
The mixture is p, ,~~ and compressed by the
movement of the piston and it flows through a cham-
ber 682 formed in the block to a plenum chamber or
surge tank 683. The chamber 683 has one side 684
formed by the block 611 and an outer side formed by ;'
a cover 686 which is secured to a side of the block
(see Figs. 6A and 6C). A port 687 and a check valve
688 allow flow only in the direction from the
ch~ h~r 682 to the chr her 683. The plenum chamber
683 includes a portion 689 formed in the block, the
portion 689 leading to a port 691 of an air intake
valve 692. The upper side (as seen in Fig. 6A) of
the valve port 691 leads to a cavity 693 formed in
the underside of the head 613, the cavity 693
forming part of the combustion çh~ her.
, .: ~ , ,. ,, , , :
- 22 -
Mounted in the chA h~r 682 is an actuating
me~-h~n;sm 694 for the valve 692. The -~h~ni ! 694
in,cludes a cam shaft 696 rotatably mounted on the
block 611 and having a gear connection (not illus-
5 trated) with the cr~nkch~ft 617. The cam shaft 696
includes a cam 697 that engages one end of a fol-
lower and push rod 698. The other end of the push
rod 698 engages the lower end (as seen in Fig. 6A)
of the stem 699 of the valve 692. The push rod 698
and the stem 699 are slideably mounted in bearings
700 mounted on the block. A compression return
spring 701 positioned between a ledge 702 of the
block and a clip 703 on the valve 699, and the
spring 701 holds the rod 698 against the cam 697 and
urges the valve 692 to the closed position.
The engine shown in Figs. 6A to 6C further
includes an exhaust valve 706 (Figs. 6B and 6C) '~
movably mounted in an exhaust port 707 formed in the
block adjacent the cylinder 614 and the intake port -
20 691. The exhaust valve 706 is operated by a valve ,~
actuating mec-h~nism (not illustrated) constructed
and located similarly to the actuating mer,h~n;c for
the intake valve 692. The cam shaft 696 supports a ,
second cam (not shown) similar to but angularly ~'
offset from the cam 697, of the actuating mechanism
for the valve 706, and the stem of the valve 706 is ,
movably mounted on the block 611. When the valve ' ,~
706 is open, exhaust gases flow from tha cylinder
614 and the head cavity 693, through the open
exhaust port 707, through an exhaust flow passage
708 formed in the block 708, and to a muffler 709
mounted on the side of the block.
2''~
- 23 -
The engine design shown in Figs. 6A to 6C is
especially advantageous because all of the engine
parts requiring lubrication are located in the
~rankcase c-h~ hprs 615 and 682. The rotating parts
attached to the crAnk~h~ft and the movement sf the
piston cause turbulence of the fuel-oil-air mixture
in the crankcase chambers, and the turbulence
ensures that there is adequate flow of the mixture
around the parts requiring lubrication. Thus the
parts are more effectively lubricated than would be
the case if some of the parts were in the plenum or
in the head. Further, the engine shown in Figs. 6A
and 6B has a compact design.
In a single cylinder engine having a storage
plenum or surge tank, as illustrated in Figs. 2A-2D,
Fig. 5A and Fig. 5B and Figs. 6A to 6C, for example,
the volume of the surge tank and the volume of the
crankcase have a considerable effect on the gas
pressure in the cylinder at the start of the com-
pression stroke. For a single cylinder engine,assuming that the gas transformation is isothermal,
then:
Pc = Po (V + Vc) -- -- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ (1)
Vc
Pt = Pc ~ Vc + Pa ~ Vt - - - - - - - - - - - - (2)
Vt + Vc
Pa = Pt ~ Vt + Pc ~ Yc - (3)
Vt + Vc + V + Vcc V + Vc + Vt + Vcc
where:
Po is the ambient pressure.
'', " , '
-
23.22
- 24 -
Pa is the pressure in the cylinder at the
bottom dead center before the
compression stroke.
Pt is the maximum pressure in the surge
5tank at the bottom dead center.
Pc is the -~i theoretical pressure in
the crankcase at the bottom dead
center.
V is the total engine displacement.
10Vc is the crankcase clearance volume.
Vt is the surge tank volume.
Vcc is the cylinder clearance volume.
For a two cylinder engine having a surge tank
(such as shown in Figs. 4A and 4B), again assuming
an isothermal gas transformation, then~
Pc = Po (V + Vc) - - - - - - - - - - - - - - - - (4)
Vc
Pt = Pc ~ Vc + Pa ~ Vt - - - - - - - - - - - - - ~5)
Vt + Vc
Pa = Pt ~ Vt + Pc ~ Vc -- (6)
Vt + Vc + V/2 + Vcc V/2 + Vc + Vt + Vcc
The pressure Pa stabilizes after a few revolu-
tions of the engine.
It will be apparent from the foregoing that an
improved four-stroke engine is described. The mov-
ing parts of the engine are lubricated by the fuel- -~
';
- 25 -
oil-air mixture, which arrangement avoids the need
for a separate lubrication system. The mixture is
supercharged without the need for a separate super- -~
charger. Since it is a four-stroke engine, the
emissions are relatively clean despite the presence
of the oil in the mixture.
