Field and Background of the Invention
[0001] This invention relates to an internal combustion (IC) engine, and more particularly
to an IC engine particularly suited for use in hand-held (portable) tools.
[0002] 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 operation
in different orientations (sideways or straight up, for example).
[0003] 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).
[0004] While two-stroke engines of this type work well, they have certain drawbacks. The
fuel consumption rate is relatively high and the operating noise level is also high.
A very important disadvantage is that the emissions levels of such engines are quite
high because the exhaust includes a sizable 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 standards. It is expected that those standards
will also be adopted by other states and countries.
[0005] Four-stroke IC engines are, of course, also well known and they generally have lower
hydrocarbon and carbon monoxide emissions than two-stroke engines. This is true because
four-stroke engines exchange the exhaust and fresh fuel/air mixture in a more positive
manner with the use of valves. Four-stroke engines also in general have lower noise
levels.
[0006] Relatively small four-stroke engines are available 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 complex and light
duty construction. Four-stroke engines 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 mechanisms. This type of lubricating
system is not satisfactory for all-position use.
[0007] 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.
[0008] 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. 5,267,536 dated December 7, 1993, describe engines generally
similar to the engine described in No. 5,213,074. Both patents describe lubrication
systems for a four-stroke engine, including oil in a crankcase 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.
[0009] The D. E. Stinebaugh U.S. patent No. 4,708,107, dated November 24, 1987, describes
a four-stroke engine including a crankcase-compression arrangement. A carburetor supplies
a "combustible working fluid such as an air-gasoline mixture" to the crankcase, 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 followers for the intake and exhaust
valves are mounted in the boost plenum.
[0010] It is therefore a general object of the present invention to provide an improved
four-stroke engine.
Summary of the Invention
[0011] 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 piston. 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.
[0012] During engine operation, the mixture flows through the crankcase 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 crankcase. 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 mechanism
are located such that they are lubricated by the combustible mixture. Thus the moving
parts of the engine are lubricated by the oil in the mixture which is continuously
replenished and flows around the moving parts during engine operation.
[0013] Valves may be provided at the fuel inlet and outlet ports of the crankcase to achieve
crankcase 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 pistons which simultaneously move toward the crankcase or the cylinder heads.
[0014] The valves and the valve actuating mechanisms are located in the mixture flow path
to be lubricated by the mixture. The actuating mechanism may be located in the head
portion of the engine or they may be located in the crankcase.
Brief Description of the Drawings
[0015] This invention may be better understood from the following detailed description taken
in conjunction with the accompanying figures of the drawings wherein:
Figs. 1A through 1D are schematic views illustrating the four operating strokes of
an engine incorporating the present invention;
Figs. 2A through 2D are views similar to Figs. 1A through 1D but illustrate an alternative
construction of the engine;
Figs. 3A and 3B are similar to Figs. 1C and 1D but illustrate still another alternative
construction of the invention;
Figs. 4A and 4B are similar to Figs. 3A and 3B but illustrate still another alternative
construction of the invention;
Fig. 5A further illustrates an engine constructed 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
[0016] Figs. 1A through 1D illustrate a four-stroke overhead valve internal combustion engine
110, wherein Fig. 1A shows the compression stroke, Fig. 1B shows the expansion or
power stroke, Fig. 1C shows the exhaust stroke, and Fig. 1D shows the intake stroke.
The engine includes a frame including 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 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 surrounds the exhaust
valve 120 and conveys exhaust from the cylinder 114 to a muffler (not illustrated).
Also mounted on the head portion 113 is a spark plug 124 which has its points 125
extending into a combustion chamber 126 formed between the crown of the piston 116,
the side walls of the cylinder 114 and the head portion 113.
[0017] A fuel inlet port 128 is formed in the side wall of the crankcase 112 and, during
engine operation, receives a combustible mixture from a carburetor indicated by the
reference numeral 129. The 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 of the crankcase 112. The intake side of the carburetor
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.
The gas-oil mixture is further mixed with air in the carburetor 129 to form the previously
mentioned combustible mixture that flows from the carburetor 129 into the crankcase
chamber 115.
[0018] The crankcase 112 also has an outlet port 131 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
122. The duct 132 thus conveys the mixture from the chamber 115 of the crankcase 112
to the enclosure 136 within the cover 122. Also included in the engine but not illustrated
in Figs. 1A to 1D are valve operating or actuating mechanisms, located within the
flow of the mixture such that the mechanisms are lubricated. For example, the valves
and the valve actuating mechanisms 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 chamber 115 and/or in the duct 132, and
the rocker arms being located in the enclosure 136. Alternatively, a timing belt may
be connected between the crankshaft 117 and a cam mechanism 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 chamber formed in the
block portion, in flow communication with the crankcase. The valves and valve actuating
mechanisms 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.
[0019] Considering the operation of the engine, during the compression stroke illustrated
in Fig. 1A, the two valves 119 and 120 are closed and the piston 116 moves toward
the head portion 113, thereby compressing the mixture within the combustion chamber
126. As the piston 116 moves upwardly, it increases the interior space or volume of
the crankcase chamber 115 formed by the crankcase 112 and the underside of the piston
116, thereby drawing the combustible mixture through the inlet port 128 from the carburetor
129. The check valve 130, of course, opens as illustrated in Fig. 1A to allow flow
in this direction. 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. 1B, the two valves 119 and 120 being
closed. Since the piston 116 moves downwardly, it reduces the volume of the chamber
115 within the crankcase 112, thereby increasing the pressure of the mixture within
the chamber 115. This action closes the valve 130 and compresses the combustible mixture
within the chamber 115, the duct 132 and the enclosure 136.
[0020] At the end of the power stroke shown in Fig. 1B, the piston 116 moves upwardly again
in the exhaust stroke as illustrated in Fig. 1C, and at this time the valve actuating
mechanism 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.
[0021] At the end of the exhaust stroke, the piston 116 again moves downwardly in the fuel
intake stroke as shown in Fig. 1D. The exhaust valve 120 is closed and the intake
valve 119 is opened by the valve actuating mechanism. The downward movement of the
piston 116 sucks the mixture into the combustion chamber 126 and pushes the mixture
from the crankcase chamber 115 through the duct 132, through the open intake valve
119 and into the combustion chamber 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. 1A), thereby completing one operating cycle of the
engine.
[0022] 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 mixture
contacts all of the moving parts requiring lubrication. The mixture forms an oil mist
in the crankcase chamber 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 mechanism and
the crankcase 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.
[0023] The engine 210 illustrated in Figs. 2A through 2D is generally similar to the engine
shown in Figs. 1A through 1D, 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. 1A to 1D.
[0024] 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 plenum or surge tank. The engine 210 further includes
a one-way or check valve 241 extending across the outlet port 231 of the crankcase
212. As illustrated, the valve 241 permits flow of the combustible mixture only in
the direction from the crankcase chamber 115 to the plenum 240.
[0025] The engine 210 operates similarly to the previously 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 chamber 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 chamber during the exhaust stroke shown in Fig. 2C and during
the next subsequent intake stroke when the piston moves downwardly 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 crankcase 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 pressure, for
example. This increased pressure or supercharging, of course, improves the volumetric
efficiency of the engine and allows the engine to produce greater power for a given
size than would otherwise be the case.
[0026] In addition, the increased pressure creates a denser or more concentrated mixture,
resulting in an increased amount of lubricant flowing past and surrounding the parts,
thereby increasing the efficiency of lubrication.
[0027] Figs. 3A and 3B illustrate an engine 310 having a pair of cylinders, but otherwise
constructed similarly to the engine illustrated in Figs. 1A through 1D. The two cylinders
have pistons which reciprocate in synchronism such that they simultaneously move toward
the crankcase 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 crankcase
chamber 315 with a carburetor 329. The crankcase further has two outlet ports 333a
and 333b connected with two ducts 332a and 332b.
[0028] The engine further includes two opposed cylinders 311a and 311b, and pistons 316a
and 316b mounted for reciprocation with the cylinders. The two pistons are connected
by connecting rods 318a and 318b to a crankshaft 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 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 mechanism (not shown), such
as one of the previously discussed types, and a spark plug mounted in a head portion
of the engine frame, the construction and operation of these parts being generally
the same as that of the engine shown in Figs. 1A to 1D. 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 movement 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.
[0029] 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 engine 410 further includes
a plenum 440 and an outlet check valve 441 which are common to the two cylinders and
feed the mixture received from the crankcase chamber 415 to the two ducts 432a and
432b. Thus the engines 310 and 410 operate similarly except 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. The supercharged pressure in the
plenum 440 will, however, be higher than that in the plenum 240 because the total
volume swept by the two pistons is twice the displacement of one cylinder while the
volume to be filled (one combustion chamber) for each revolution equals the displacement
of one cylinder. 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 (or surge tank) as
shown in Figs. 3A and 3B, and may be about 21-45% above ambient in an engine with
a plenum as shown in Figs. 4A and 4B.
[0030] Figs. 5A and 5B illustrate another engine 510 constructed according to the invention,
and again the same reference numerals used in Figs. 1A to 1D 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. 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.
[0031] A piston 516 is mounted for reciprocation in the cylinder 514, and the piston is
connected by a connecting rod 518 to the crankshaft 517 in the customary manner. A
crank arm 541 is mounted on the crankshaft 517 and connects to the rod 518, and the
arm 541 includes a counterbalance portion 542. As shown in Fig. 5B, the chamber 515
of the crankcase 512 is relatively small and closely confines the crankshaft 517 and
the crank arm 541, this being made possible because the case 512 is not also required
to form a sump for a lubricating oil. The block 511 and the crankcase 512 are tightly
connected together and form the interior chamber 515 which is sealed except for inlet
and outlet ports 528 and 531 to be described.
[0032] 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 the head
513 forms a wall 544 across the upper (as seen in Fig. 5B, although the engine could
have other orientations) side of the cylinder 514. Formed in the wall 544 are an intake
port, an exhaust port (not shown) and an opening for the spark plug 524. An intake
valve 519 and an exhaust valve (not shown) are mounted 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.
[0033] The engine further includes a valve actuating or driving mechanism including a rocker
arm 551 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 conventional overhead-valve, overhead-cam arrangement
which is contained in the enclosure 536 formed by the valve cover portion 522 of the
head.
[0034] 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 crankshaft
517. The crankshaft 517 is supported by at least one bearing 559 (Fig. 5B) on the
block 511 and the crankcase 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 not shown
in the drawings is shaped to be attached to a tool or implement to be driven. The
other end, shown in Fig. 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 meshes with a
driven sprocket 564 which is secured to one end of the cam shaft 554. The sprocket
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 rotatably supported
by bearings (not shown) on the head 513. Both the bearings for the camshaft and the
bearings for the crankshaft are accessible from within the enclosure 536 and the chamber
515 for lubrication purposes, as will be described more fully hereinafter.
[0035] 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.
[0036] 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 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 conventional. A passage 572 connects
the crankcase chamber 515 to the carburetor 529 for pumping fuel to the carburetor,
in a conventional manner.
[0037] 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.
[0038] The duct 532 may be made, for example, of plastic 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 the valve cover enclosure 536 and with the valve port in the head 513
for the intake valve 519.
[0039] 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 air-gas-oil
mixture in the enclosure 536 for lubrication purposes.
[0040] Considering the operation of the engine 510, 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.
[0041] When the piston 516 moves toward TDC, the volume 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 chamber 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.
[0042] 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 crankcase chamber 515. The
resulting compression of the mixture in the chamber 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 519 is closed, and the increased pressure in the
duct is held or retained when the reed valve 541 closes at the time the piston moves
up again. In the intake stroke, the compressed mixture is drawn into the cylinder
and additional mixture is forced into the duct by the piston. Thus the crankcase compression
acts as a supercharger and makes possible an increase in power output for a given
size engine. The compression also increases the density of the oil mist and improves
the lubrication of the parts.
[0043] As previously mentioned, a gasoline-oil-air mixture flows through the crankcase chamber
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 surrounds
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 surrounds and collects on the moving parts, thereby
lubricating the parts without the use of an oil sump or grease packed around the parts.
[0044] 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 separate check valve, and this arrangement also allows for an advantageous
placement and location of the carburetor. This is particularly important in engines
for small hand-held implements such as chain saws. Any blow-by gas past the piston
flows into the crankcase chamber 515 and is returned to the combustion chamber.
[0045] 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 mechanism.
[0046] The engine frame includes a block 611, a crankcase 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.
[0047] A piston 616 is mounted in a cylinder 614, and a connecting rod 618 connects the
piston 616 to a crankshaft 617. A counterbalance 642 is also connected to the crankshaft,
and these parts rotate in the crankcase chamber 615. A sparkplug 624 is mounted in
a hole 625 in the head 613.
[0048] 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 provided, and it forms a source of a
fuel-oil mixture as previously described.
[0049] 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 crankcase and a plenum chamber or surge tank to the
combustion chamber, and the mixture effectively lubricates the engine parts requiring
lubrication.
[0050] 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. 5B.
[0051] The mixture is pumped and compressed by the movement of the piston and it flows through
a chamber 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 chamber 682 to the chamber 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 chamber.
[0052] Mounted in the chamber 682 is an actuating mechanism 694 for the valve 692. The mechanism
694 includes a cam shaft 696 rotatably mounted on the block 611 and having a gear
connection (not illustrated) with the crankshaft 617. The cam shaft 696 includes a
cam 697 that engages one end of a follower 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.
[0053] 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 691. The exhaust valve 706 is operated by a valve actuating
mechanism (not illustrated) constructed and located similarly to the actuating mechanism
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 the 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.
[0054] The engine design shown in Figs. 6A to 6C is especially advantageous because all
of the engine parts requiring lubrication are located in the crankcase chambers 615
and 682. The rotating parts attached to the crankshaft and the movement of 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.
[0055] 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 compression stroke. For a single cylinder
engine, assuming that the gas transformation is isothermal, then:
![](https://data.epo.org/publication-server/image?imagePath=1994/52/DOC/EPNWA1/EP94106092NWA1/imgb0001)
where:
Po is the ambient pressure.
- Pa is the
- pressure in the cylinder at the bottom dead center before the compression stroke.
- Pt is the
- maximum pressure in the surge tank at the bottom dead center.
- Pc is the
- maximum theoretical pressure in the crankcase at the bottom dead center.
- V is the
- total engine displacement.
- Vc is the
- crankcase clearance volume.
- Vt is the
- surge tank volume.
- Vcc is the
- cylinder clearance volume.
[0056] For a two cylinder engine having a surge tank (such as shown in Figs. 4A and 4B),
again assuming an isothermal gas transformation, then:
![](https://data.epo.org/publication-server/image?imagePath=1994/52/DOC/EPNWA1/EP94106092NWA1/imgb0002)
The pressure Pa stabilizes after a few revolutions of the engine.
[0057] It will be apparent from the foregoing that an improved four-stroke engine is described.
The moving parts of the engine are lubricated by the fuel-oil-air mixture, which arrangement
avoids the need for a separate lubrication system. The mixture is supercharged without
the need for a separate supercharger. Since it is a four-stroke engine, the emissions
are relatively clean despite the presence of the oil in the mixture.
1. A four-stroke internal-combustion engine for operation with a combustible mixture
of air, fuel and lubricating oil, comprising:
a) an engine frame comprising a block portion and a head portion forming a cylinder
and a crankcase chamber;
b) a crankshaft rotatably mounted in said crankcase chamber, and a piston mounted
for reciprocation in said cylinder, a rod connecting said piston with said crankshaft,
said cylinder, said head portion and said piston forming a combustion chamber;
c) said engine further including an intake valve, an exhaust valve, and an actuating
mechanism for said valves, said actuating mechanism operating in synchronism with
said piston and opening said intake valve during an intake stroke of said piston and
opening said exhaust valve during an exhaust stroke of said piston;
(d) a carburetor for creating a combustible mixture of fuel, air and an oil mist;
(e) a duct connecting said crankcase chamber with said intake valve; and
(f) said carburetor, said crankcase chamber, said duct, and said intake valve forming
a flow path for said mixture from said carburetor to said combustion chamber, said
crankshaft, said rod, and said actuating mechanism being located in said flow path
and being lubricated by said oil mist.
2. An engine as set forth in Claim 1, and further including a first one-way valve between
said carburetor and said crankcase and enabling flow of said mixture in the direction
of said crankcase.
3. An engine as set forth in Claim 2, and further including a second one-way valve between
said crankcase and said duct and enabling flow of said mixture only in the direction
of said duct.
4. An engine as set forth in any one of Claims 1, 2 or 3, wherein said valves and said
actuating mechanism are mounted in said crankcase chamber.
5. An engine as set forth in any one of Claims 1, 2 or 3, wherein said head portion has
a cavity formed therein and said flow path includes said cavity, and said valves and
said actuating mechanism are mounted in said cavity.
6. An engine as set forth in any one of Claims 1, 2 or 3, wherein said carburetor is
an all-position type, and said engine is relatively small, lightweight and portable.
7. An engine as set forth in Claim 3, wherein said duct forms a surge tank.
8. An engine as set forth in Claim 4, wherein said actuating mechanism comprises a cam
shaft rotatably mounted in said crankcase, and further including gears connecting
said cam shaft with said crankshaft.
9. An engine as set forth in Claim 5, wherein said actuating mechanism comprises a cam
shaft rotatably mounted in said head, and further including a belt connecting said
cam shaft with said crankshaft.
10. An engine as set forth in Claim 7, wherein said duct has one side thereof formed by
a side of said block portion and another side thereof formed by a cover fastened to
said side of said block portion.
11. An engine as set forth in Claim 7, wherein said duct is U-shaped and is spaced from
said block portion.
12. An engine as set forth in Claim 1, and further including a second engine frame, a
second piston connected to said crankshaft, and second intake and exhaust valves and
valve actuating mechanism, said carburetor, said crankcase and said duct being common
to both of said engines.
13. An engine as set forth in Claim 2, wherein said first one-way valve comprises a port
in said cylinder and a skirt portion of said piston, said skirt portion opening and
closing said port.
14. An engine as set forth in Claim 2, wherein said first one-way valve comprises a port
in said engine frame between said carburetor and said crankcase chamber, and a one-way
flow valve in said port.
15. A multiple cylinder four-stroke engine fueled by a combustible mixture of fuel, oil
and air, said engine comprising:
a) an engine frame forming a crankcase chamber and first and second cylinders;
b) first and second pistons mounted for reciprocation in said first and second cylinders
respectively and forming with said frame first and second combustion chambers, said
first and second pistons moving simultaneously toward or away from said crankcase
chamber whereby said crankcase chamber has a volume which alternately increases and
decreases with said reciprocation of said pistons;
c) said frame further forming first and second valve enclosures adjacent said first
and second combustion chambers, and said engine further including first and second
valve mechanisms mounted in said first and second valve enclosures, respectively;
d) each of said valve mechanisms comprising a fuel intake valve and an exhaust valve
and a valve actuating mechanism;
e) said frame further including at least one inlet port leading to said crankcase
chamber and at least one outlet port leading out of said crankcase chamber, said at
least one inlet port being connectable to receive said mixture; and
f) duct means connecting said at least one outlet port with said first and second
valve enclosures and with said fuel intake valves, said mixture flowing through said
crankcase chamber and said valve enclosures and lubricating the parts therein during
engine operation.
16. An engine as set forth in Claim 15, and further including a first one-way valve in
said inlet port for permitting flow into said crankcase chamber.
17. An engine as set forth in Claim 15, wherein said duct means forms a surge tank.
18. An engine as set forth in Claim 17, and further including a second one-way valve in
said outlet port for permitting flow out of said crankcase chamber.
19. An engine as set forth in Claim 15, wherein said engine further comprises a crankshaft
in said crankcase chamber and rotatably mounted on said frame, said first and second
pistons being connected to said crankshaft, said engine having an operating cycle
formed by two revolutions of said crankshaft, and said pistons having power strokes
in alternate revolutions.
20. An engine as set forth in Claim 19, wherein said cylinders are mounted in opposed
relation and said pistons reciprocate toward and away from each other.
21. An engine as set forth in Claim 15, wherein said crankcase chamber and said valve
enclosures are shaped to flow sufficient quantities of said mixture around engine
parts therein to lubricate said engine parts.
22. An engine as set forth in Claim 15, wherein said duct means is U-shaped and has ends
connected to said crankcase chamber and to said valve enclosure and a central portion
which is separate and spaced from said frame.