U.S. patent application number 13/239803 was filed with the patent office on 2013-03-28 for engine lubrication method.
This patent application is currently assigned to ETG Limited. The applicant listed for this patent is Katsumi Kurihara, Shigeo Yamamoto. Invention is credited to Katsumi Kurihara, Shigeo Yamamoto.
Application Number | 20130074792 13/239803 |
Document ID | / |
Family ID | 47909841 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130074792 |
Kind Code |
A1 |
Kurihara; Katsumi ; et
al. |
March 28, 2013 |
Engine Lubrication Method
Abstract
A four-cycle engine has a lightweight aluminum alloy engine
block having a cylindrical bore and an enclosed oil reservoir
formed therein. A crankshaft is rotatably mounted in the engine
block for rotation about a crankshaft axis. A piston reciprocates
within the bore and is connected to the crankshaft by a connecting
rod. An oil pump driven by the cam gear, which mates with crank
gear that is driven by crank shaft, inhales the oil from the oil
reservoir and the valve chamber to splash lubricate into the
cylinder bore. The engine is provided with a cylinder head assembly
defining a compact combustion chamber having a pair of overhead
intake and exhaust ports and cooperating intake and exhaust
valves.
Inventors: |
Kurihara; Katsumi; (Aichi,
JP) ; Yamamoto; Shigeo; (Hiroshima, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kurihara; Katsumi
Yamamoto; Shigeo |
Aichi
Hiroshima |
|
JP
JP |
|
|
Assignee: |
ETG Limited
Hong Kong
CN
|
Family ID: |
47909841 |
Appl. No.: |
13/239803 |
Filed: |
September 22, 2011 |
Current U.S.
Class: |
123/90.17 |
Current CPC
Class: |
F01L 1/18 20130101; F01L
1/20 20130101; F01L 2810/02 20130101; F01L 1/181 20130101; F01M
2001/0261 20130101; F01L 1/026 20130101; F01L 1/146 20130101 |
Class at
Publication: |
123/90.17 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Claims
1. A single-cylinder, four-stroke cycle, spark ignition internal
combustion engine for mounting on a power tool comprising: a
cylinder block having a cylinder, a cylinder head, a piston mounted
for reciprocation in said cylinder, said cylinder head defining an
air-fuel combustion chamber; a lower case mating with said cylinder
block by a plane perpendicular to the cylinder bore axis; a
crankshaft chamber formed by said cylinder block and said lower
case; an air-fuel mixture intake port and an exhaust gas port in
said cylinder head; a valve cover on said cylinder head defining a
valve chamber; an intake valve and an exhaust valve mounted in said
intake and exhaust port, respectively, for reciprocation between
port-open and port-closed positions; a valve-actuating valve train
in a valve chamber, said valve train including at least one rocker
arm and at least one valve train push rod assembly extending
therefrom within said valve chamber and engaging said rocker arm; a
crankshaft rotatably mounted in said crankshaft chamber, wherein
said crankshaft includes a crank portion and at least one
counterweight web and has an axis which is on the mating plane of
said cylinder block and said lower case; a connecting rod having
articulated connections at one end thereof to said piston and at an
opposite end thereof to said crank portion, thereby forming a
piston-connecting rod crankshaft assembly; a cam chamber having at
least one earn being drivably connected to said crankshaft, said at
least one cam having a cam gear and being driven at one-half
crankshaft speed, the opposite end of said push rod assembly being
drivably connected to said cam whereby said push rod assembly is
actuated with a reciprocating motion upon rotation of said at least
one cam, said cam chamber having communication means to the
crankshaft chamber; a lubrication oil reservoir formed below the
lower case; and an oil pump connected drivably to said cam gear-cam
assembly, wherein said pump inhales lubrication oil from said oil
reservoir and valve chamber and splashes the oil in parallel into
the cylinder and into the cam chamber to lubricate the engine parts
inside the cylinder and the cam chamber and the valve chamber.
2. The engine set forth in claim 1 further comprising an air
cleaner box connected to said valve chamber via a first passage
through which breathing oil mist gas flows, a second passage
connecting the air cleaner box to the crankshaft chamber or
cylinder block, and a valve being provided at the entrance of said
passage into the crankshaft chamber, wherein the opening of the
valve is controlled by reciprocating motion of said piston, and
wherein said valve opens when pressure in the crankshaft chamber is
negative and closes when the pressure in the crankshaft chamber is
positive, thereby the oil mist flow control valve structure
establishing a lubrication oil mist flow circuit from said valve
chamber to said crankshaft chamber or said cylinder block through
said air cleaner box.
3. The engine set forth in claim 1, wherein said oil pump is
integrally attached with the cam or the cam gear.
4. The engine set forth in claim 1, wherein said oil pump is a
trochoid pump.
5. The engine set forth in claim 1, wherein said oil pump has two
separated inlet cavities.
6. The engine set forth in claim 1, wherein said oil pump has at
least one relief passage which communicates between outlet cavity
of the pump and the oil reservoir.
7. The engine set forth in claim 1, wherein said lower case has a
circular arc wall to separate said oil reservoir from said
crankshaft chamber, said circular arc wall at least partially
surrounding said web at a slight distance therefrom, and said
circular arc wall having a drain hole and slits to communicate
between said crankshaft chamber and oil reservoir.
8. The engine set forth in claim 1, wherein said circular arc wall
is shaped to be a 20 to 45 degree to said drain hole.
9. A hand-held, transportable, or stationary power tool driven by
the engine set forth in claim 1, wherein said power tool is driven
by a horizontal or vertical or inclined power shaft.
10. The engine set forth in claim 1, wherein said cylinder block
has at least one oil recess to store oil when the engine is
oriented to incline and to prevent oil in the crankshaft chamber
from flowing into combustion chamber.
11. The engine set forth in claim 1, wherein said lower case has at
least one oil recess to store oil when the engine is oriented to
incline and to prevent oil in the oil reservoir from flowing into
said combustion chamber.
12. The engine set forth in claim 1, wherein said lower case has at
least one long pipe to prevent oil in the oil reservoir from
flowing into said cam chamber or said valve chamber.
13. The engine set forth in claim 1, wherein said intake and
exhaust valves are inclined with respect to each other.
14. The engine set forth in claim 1, wherein said cylinder block
has at least one oil passage located near the intake valve to
communicate between said valve chamber and said oil reservoir.
15. The engine set forth in claim 1, wherein said cylinder block
has at least one oil passage located near the intake valve to
communicate between said valve chamber and said oil recess in the
cylinder block.
16. The engine set forth in claim 15, wherein said cylinder block
has at least one long pipe to prevent oil in the oil recess from
flowing into said valve chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an engine, and more particularly,
an engine construction and lubrication method for a small
four-cycle internal combustion engine which is particularly
suitable for the use with portable or transportable power
tools.
[0003] 2. Description of the Related Art
[0004] U.S. Pat. No. 7,287,508 to Kurihara and U.S. Pat. No.
7,624,714 to Kurihara et al., which are incorporated herein by
reference, disclose a light weight and compact prior art small
four-cycle engine construction.
[0005] Portable power tools such as line trimmers, blower/vacuums,
chain saws are mostly powered by two-cycle internal combustion
engines or electric motors. Some transportable power tools such as
tiller/cultivators, generators are currently powered by two-cycle
or four-cycle internal combustion engines. With the growing concern
regarding air pollution, there is increasing pressure to reduce the
emissions of both portable and transportable power equipment.
Electric motors unfortunately have limited applications due to
power availability for corded products, and battery life and power
availability for cordless devices. In instances where weight is not
an overriding factor such as lawn mowers, emissions can be
dramatically reduced by utilizing heavier four-cycle engines. When
it comes to power tools such as line trimmers, chain saws and
blower/vacuums, four-cycle engines pose a very difficult problem.
Four-cycle engines tend to be too heavy for a given horsepower
output and lubrication becomes a very serious problem since
portable or transportable power tools must be able to run in a very
wide range of orientations except generators or tiller/cultivators.
For some tiller/cultivators powered by four-cycle engines with
vertical power shafts, lubrication also becomes a serious problem
since it is difficult to use the same lubrication system as engines
with horizontal power shafts.
[0006] Therefore, it is an object of the present invention to
provide a small four-cycle internal combustion engine having low
emissions that is sufficiently light weight to be carried and/or
transported by an operator, which is especially suitable for a
hand-held or transportable power tool.
[0007] It is a further object of the present invention to provide a
small four-cycle internal combustion engine having an internal
lubrication system enabling the engine to be run at a wide variety
of orientations typically encountered during normal operation,
which is especially suitable for a portable or transportable power
tool.
[0008] It is a further object of the present invention to provide a
small lightweight four-cycle engine having an engine block, an
overhead valve train and a lubrication system to splash oil mist to
lubricate the crankshaft chamber throughout the normal range of
operating positions, which is especially suitable for a portable or
transportable power tool.
[0009] It is a further object of the invention to provide a
lubricant return system to return lubrication oil into oil
reservoir after lubricating parts in the crankshaft chamber and the
overhead valve chamber.
[0010] In the prior art previously referred, circular and
scroll-type walls play important roles in the inventions. However,
the construction to make these walls are not so cost effective and
not so compact. Thus, it is a further object of the present
invention to provide a more cost effective and more compact
construction.
[0011] These and other objects, features, and advantages of the
present invention will become apparent upon further review of the
remainder of the specification and the accompanying drawings.
SUMMARY OF THE INVENTION
[0012] In order to achieve the above objects, a four-cycle,
internal combustion engine is provided which is suitable for use
with portable or transportable power tools. The four-cycle engine
is provided with an engine block having at least one cylindrical
bore oriented in a normally upright orientation having an enclosed
combustion chamber.
[0013] A lower case is attached to the said cylinder block with a
horizontal mating plane. The cylinder block and said lower case
form a crankshaft chamber. A crankshaft is pivotably mounted within
the crankshaft chamber. An enclosed oil reservoir is located below
the crankshaft chamber separated from the crankshaft chamber by a
substantially circular wall.
[0014] A pump is connected drivably to cam gear-cam assembly, and
said pump inhales lubrication oil from the oil reservoir to splash
oil into the cylinder.
[0015] When lubrication oil is properly filled, the engine is able
to rotate or to be stored without oil flowing into combustion
chamber at any inclination posture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-sectional side elevation view of the
engine taken along the rotating axis of the crankshaft and axis of
cylinder bore taken along line I-I in FIG. 2.
[0017] FIG. 2 is a cross-sectional side elevation view of the
engine taken along line II-II in FIG. 1;
[0018] FIG. 3 is an enlarged schematic illustration of the camshaft
and the follower mechanism;
[0019] FIG. 4 is a cross-sectional side elevation view of the
engine of FIG. 2 when it is oriented to be upside down.
[0020] FIG. 5 is a cross-sectional side elevation view of the
engine of FIG. 1 when it is oriented to be upside down.
[0021] FIG. 6 is a section view of the oil pump cover that shows
the detail construction of inlet and outlet cavities of the pump
taken along line VI-VI in FIG. 11.
[0022] FIG. 7 is a section view of the cylinder block and the lower
case taken along line III-III in FIG. 1.
[0023] FIG. 8 is an elevation view of the cylinder block viewing
from A in FIG. 7.
[0024] FIG. 9 is a cross-sectional side elevation view of the
engine of FIG. 1 when it is oriented with the power take off end
down.
[0025] FIG. 10 is a cross-sectional side elevation view of the
engine of FIG. 1 when it is oriented with the power take off end
up.
[0026] FIG. 11 is an enlarged view of the pump shown in FIG. 1.
[0027] FIG. 12 is a cross-sectional side elevation view of the
engine according to another embodiment of the present
invention.
[0028] FIG. 13 is a cross-sectional side elevation view of the
engine of FIG. 12 when it is oriented to be upside down.
DESCRIPTION OF THE EMBODIMENTS
[0029] FIGS. 1 and FIG. 2 illustrate a cross-sectional side
elevation view of a four-cycle engine. The four-cycle engine is
made up of a lightweight aluminum housing including a cylinder
block 1 having a cylindrical bore 2 formed therein.
[0030] A lower case 3 and said cylinder block 1 mate with each
other at the horizontal interface and form a crankshaft chamber
5.
[0031] A crankshaft 4 is pivotably mounted within the crankshaft
chamber 5 in a conventional manner. The axis of said crankshaft 4
is contained at the horizontal interface to mate cylinder block 1
and lower case 3.
[0032] A piston 6 slides within the cylindrical bore 2 and is
connected to the crankshaft 4 by a connecting rod 7. A cylinder
head 8 is integrated to the engine block 1 to define an enclosed
combustion chamber 9.
[0033] The cylinder head 8 is provided with an intake port 10
coupled to an insulator 11 and a carburetor 100 and selectively
connected to the combustion chamber 9 by an intake valve 12. A
filter element of air cleaner 101 eliminates dust from the intake
air into the engine. The cylinder head 8 is also provided with an
exhaust port 13 connected to a muffler 14 and selectively connected
to the combustion chamber 9 by an exhaust valve 15.
[0034] As illustrated in FIGS. 1 and 2, the cylinder axis 16 of
four-cycle engine is generally upright when in normal use.
[0035] The lower case 3 is connected to a bottom cover 17 that
provides an enclosed oil reservoir 18.
[0036] The crankshaft 4 is provided with an axial shaft member 19
having an output end 20 adapted to be coupled to a flywheel 21
which has an implement input member 22. An input end 23 of axial
shaft member 19 is coupled to a counterweight web 24. A crankpin 25
is affixed to counterweight webs 24, 26 and is parallel to and
radially offset from the axial shaft 19. The crankpin 25 pivotally
cooperates with a roller bearing 27 (FIG. 2) mounted in connecting
rod 7.
[0037] The axial shafts 19 and 28 of crankshaft 4 are pivotably
attached to between the cylinder block 1 and the lower case 3 by a
pair of bearings 29 and 30. At the side of bearing 30, a crank gear
31 is mounted on the crankshaft 4 in a cam chamber 53.
[0038] A camshaft drive and valve lifter mechanism is best
illustrated in FIGS. 1 and 3. The crank gear 31 mounted on the
crankshaft 4 in turn drives a cam gear 32 with twice the number of
teeth as the crank gear 31, resulting in the camshaft 33 rotating
in one-half engine speed. The cam gear 32 is affixed to a camshaft
33 which is journaled to the cylinder block 1 and includes a rotary
cam lobe 34. In the embodiment illustrated, a single cam lobe is
utilized for driving both the intake and exhaust valves. Followers
35 and 36 are pivotably connected to the cylinder block 1 by a
pivot pin 37.
[0039] Push rods 38 and 39 extend between camshaft followers 35 and
36 and rocker arms 40 and 41 located within the cylinder head 8.
The cam 34, push rods 38, 39 and rocker arms 40, 41 are part of a
valve train assembly. Affixed to the cylinder head 8 is a valve
cover 42 which defines therebetween an enclosed valve chamber
43.
[0040] A wall 44 surrounds the intake and exhaust push rods 38 and
39 in a conventional manner in order to prevent the entry of dirt
into the engine.
[0041] The cam chamber 53 and the valve chamber 43 are in
communication with each other.
[0042] In order to lubricate the engine, a pump 45 such as a
trochoid pump is placed at the side of cam gear 32. As illustrated
in FIG. 1, FIG. 6 and FIG. 11, the pump 45 is formed of a
stationary pump cover 120 comprising an inner portion 121 mounted
on the camshaft 33 and a stationary pump body 122 comprising an
annular outer portion 123 coaxially disposed around the inner
portion 121 with a certain distance from the inner portion 121, an
inner rotor 46 formed on the outer surface of the camshaft 33 and
an outer rotor 47 formed on the inner surface of the outer portion
of the pump body. In other embodiments of the present application,
a gear pump or plunger pump may be used.
[0043] The inner rotor 46 formed on the outer surface of the
camshaft 33 is driven by the cam gear 32, and the outer rotor 47
formed on the inner surface of the outer portion 123 is rotated
following the rotation of the inner rotor 46. Lubrication oil is
inhaled from the passage 48. One end of the passage 48 leads to an
oil entrance of the pump. The other end of passage 48 is connected
to one end of a flexible tube 49. The other end of flexible tube 49
is connected to a filter with weight 50. By means of the weight 50,
an entrance of the flexible tube 49 is dipped in the oil in the oil
reservoir 18 at any orientation of the engine.
[0044] The oil pushed out by the pump 45 is lead in parallel to a
hole 52 formed in the cylinder wall and a hole 125 formed in the
outer wall of the cam shaft 33 through an inner through hole 51 of
the cam shaft as illustrated in FIG. 1. Accordingly, the engine
parts inside the crankshaft chamber 5 and the cam chamber 53 are
mist lubricated by the oil splashed by means of the rotation of
and/or the centrifugal force generated by the rotating parts such
as web 24, 26.
[0045] As illustrated in FIGS. 1 and 2, a circular arc wall 55
surrounding the counterweight web 24,26 of the crankshaft 4
separates crankshaft chamber 5 from the oil reservoir 18. The arc
wall 55 is substantially co-axial with the axis of the
counterweight web 24 or 26 and is located with a certain distance
from the webs 24 and 26.
[0046] At the bottom of circular arc wall 55, a drain hole 56 is
provided. As illustrated in FIG. 1, in the section of circular arc
wall 55 by planes which are parallel to a plane including
crankshaft axis and cylinder axis 16, circular arc wall 55 is 20-45
degrees inclined to the mating surface of cylinder block 1 and
lower case 3 to make a funnel as cylinder axis 14 is a mirror axis.
Slit 57 and 58 are provided at the bottom of circular arc wall 55
to communicate with the crankshaft chamber 5 and the oil reservoir
18.
[0047] At the side of the cylinder block 1, a drilled oil passage
104 is provided. One end of the passage 104 leads to the oil
entrance of the pump together with the passage 48. The other end of
passage 104 leads to upper portion in the valve chamber 43 as
illustrated in FIG. 1.
[0048] A small hole 109 is opened from the valve chamber to the
passage 104 near the bottom surface of the valve chamber.
[0049] In other embodiments of the present application, a flexible
tube may be used to provide passage 104. An oil inlet 107 is
provided at said other end of the passage 104.
[0050] As best illustrated in FIG. 6 and FIG. 11, the pump 45 has a
first inlet cavity 200 which inhales oil from the oil reservoir 18
through the passage 48 and a second inlet cavity 201 which inhales
oil from the valve chamber 43 through the passage 104.
[0051] Between the first inlet cavity 200 and the second inlet
cavity 201, a wall 202 is provided to separate the cavities 200 and
201. An outlet cavity 203 provides a passage for oil to the
cylinder bore through the inner hole 51. A relief oil passage is
formed in the outer portion 123 of the pump body 122. One end of
the relief oil passage 204 opens to the outlet cavity 203. The
other end of the relief oil passage 204 opens to the oil reservoir
18 through a drilled hole (not shown).
[0052] In the valve chamber 43, a breather pipe 61 is opened
through the valve cover 42. One end of the breather pipe 61 is
connected to an air cleaner case 62 through a breather tube 63. At
said one end of breather pipe 61, a check valve 60 is installed.
The valve chamber 43 opens when the pressure in the valve chamber
43 is higher than the pressure in the breather tube 63, and the
valve chamber 43 closes when the pressure in the valve chamber is
lower than the pressure in the breather tube 63. In the air cleaner
case 62, an oil separating deflector 102 is provided. The breathing
oil mist provided through the breather tube 63 is separated into
oil-lean gas and oil-rich gas by the deflector 102.
[0053] A return tube 64 interconnects the air cleaner case 62 and a
return hole 65 formed in the cylinder wall. The return hole 65
opens and closes with a reciprocating motion of the piston 6 and
the oil-rich mist returns into the crankshaft chamber 5 only when
the pressure in the crankcase is negative. The oil-lean mist is
inhaled to the carburetor 100 through the filter element 101.
[0054] As illustrated in FIG. 2, around the outside wall of
cylinder bore in the crankshaft chamber 5, oil recess 75 and 76 are
provided.
[0055] FIG. 7 is a section view of the cylinder block 1 and lower
case 3 at the portion where the bearing 29 or 30 is supported. FIG.
8 is an elevation view of the cylinder block 1 seen from A
illustrated in FIG. 7.
[0056] As illustrated in FIG. 1, another oil recess 77 is provided
at the outside of the bearing 29. The oil recess 77 and the oil
recesses 75, 76 of the crankshaft chamber 5 are communicated by
slits 78 and 79 as illustrated in FIGS. 7 and 8.
[0057] By the same way, in the boss to support bearing 30, slits 80
and 81 are provided to communicate between the crankshaft chamber 5
and cam chamber 53.
[0058] By the reciprocating motion of the piston 6, pressure in the
crankshaft chamber 5 changes up and down and oil mist in the
crankshaft chamber 5 is pushed out to the cam chamber 53 and
lubricate the valve actuating parts in the cam chamber 53.
[0059] As illustrated in FIG. 1, at the bottom of the cam chamber
53, a pipe 54 is provided. One end of the pipe opens to the cam
chamber 53 and the other end of the pipe 54 opens to oil reservoir
18 with a small distance from the wall of the bottom cover 17.
[0060] The axes of intake valve 12 and exhaust valve 15 are
inclined to each other. Therefore, a corner 82 of a deck 84 of the
cylinder head 8 near the inlet valve spring 83 in the valve chamber
43 is lower than the top of the deck 84. So, in the normal
operation posture of the engine in which the cylinder head 8 is
upright, lubricating oil in the valve chamber 43 flows easily to
the corner 82 of the deck 84 after lubricating the parts in the
valve chamber.
[0061] A passage 85 is provided between the corner 82 of the deck
84 and the oil reservoir 18. At one end of the passage 85, a pipe
86 is provided in the oil reservoir 18 with a small distance from
the wall of the bottom cover 17. Since intake and exhaust valves
12, 15 are inclined to each other, cooling performance of the
engine in accordance with the present invention is better than that
of the prior art because a cooling air passage 124 between valves
is wide.
[0062] Other parts not specifically referenced in the foregoing
relate to conventional four-cycle engines. As illustrated in FIG.
1, a spark plug 66 is installed in a spark plug hole formed in the
cylinder head 8. A coil 67 is an ignition coil. A re-coil starter
68 having a re-winding rope 69 is provided at a side of crankshaft
4. At the lower corner of the lower case 3, a cooling air entrance
70 is provided which inhales cooling air for the engine generated
by rotation of blade 71 on the flywheel 21.
[0063] A fuel tank 72 is provided below the oil reservoir 18,
adequately spaced apart therefrom. As illustrated in FIG. 2, in the
fuel tank 72, a fuel filter 73 and a fuel pipe 74 are provided to
inhale fuel into the carburetor 100 therethrough.
[0064] In order to achieve high power output and relatively low
exhaust emissions, the four-cycle engine in accordance with the
present invention is provided with a very compact combustion
chamber 9. When the engine is started by pulling the winding rope
69 illustrated in FIG. 1, lubricating oil is immediately inhaled to
the oil pump 45 by rotation of the rotors 46, 47 through flexible
tube 49. Lubricating oil is splashed into the cylinder bore through
the holes 51 and 52 and into the cam chamber 53 through the slits
80 and 81. By means of the weight 50 supported by and connected to
the flexible tube 49, oil is inhaled at any position of the engine.
The oil mist in the cam chamber 53, in which the valve actuating
parts are installed, lubricates the valve train and then flows into
the air cleaner box through the passages 61 and 63 as shown in FIG.
2. When the pressure in the cylinder bore is negative, a port 65
formed in the wall of cylinder bore opens and the mist returns from
the air cleaner case 62 into the cylinder bore through passage
64.
[0065] The excess oil after lubricating parts in the valve chamber
43 returns into oil reservoir 18 through the passage 85 shown in
FIG. 2.
[0066] As illustrated in FIGS. 1 and 2, the circular arc wall 55
surrounds the counterweight webs 24, 26 at a slight distance from
the web. The crankshaft webs 24 and 26 splash the oil to mist
lubricate the internal engine parts.
[0067] After lubricating the engine parts, as the webs 24, 26
rotate, the oil returns into the oil reservoir 18 through the drain
hole 56.
[0068] The excess oil in the cam chamber 53 returns into the oil
reservoir 18 through the pipe 54.
[0069] Portable or transportable power tools are operated with
various orientations. For instance, a typical brush cutter, which
installs an engine at an upper end of the boom and a cutter at the
lower opposite end of the boom, is usually operated with 25-40
degrees inclination of the boom relative to the ground.
[0070] In the present invention, the circular arc wall 55 is funnel
shaped with a 20-45 degree conical angle. Therefore, lubricating
oil is not agitated excessively by rotation of web 24 and drops
into the oil reservoir 18 when a brush cutter is operated in normal
operation posture.
[0071] As illustrated in FIGS. 4 and 5, even when the engine is
positioned upside down, lubrication oil in the oil reservoir 18 is
kept in it helped by the circular arc wall 55 and oil is prevented
from flowing into the cylinder head part. Further, oil in the
crankshaft chamber 5 is kept in the oil recesses 75, 76 (FIGS. 4)
and 77 (FIG. 5) and oil is prevented from flowing into combustion
chamber 9.
[0072] As illustrated in FIGS. 4 and 5, the pipe 54 (FIG. 5)
prevents oil from flowing into cam chamber 53 and the pipe 86 (FIG.
4) prevents oil from flowing into valve chamber 43 when the engine
is oriented upside down.
[0073] As illustrated in FIG. 1, when the engine is in a normal
orientation, the lubricating oil is inhaled from the oil reservoir
18 through the small hole 109 into the valve chamber 43. Further,
as illustrated in FIG. 5, when the engine is positioned upside
down, the oil, after lubricating various parts in the valve chamber
43, is inhaled by pump 45 from the oil inlet 107 and sent to the
oil pump 45 through the passage 104. Accordingly, excess oil does
not remain in the valve chamber 43.
[0074] It is necessary to be sure that portable or transportable
power tools are safely stored. For instance, even if a brush cutter
is stored with a posture with the vertical boom side up and the
engine side down, lubrication oil should not flow into the
combustion chamber 9. On the contrary, even if the same brush
cutter is stored with a posture with the vertical boom side down
and the engine side up, lubrication oil should not flow into the
combustion chamber 9 also.
[0075] FIG. 9 illustrates storage of the engine when the output
side of the engine is orientated to be down. Oil A is kept in the
oil reservoir 18 and does not flow into crankshaft chamber 5. Oil B
is kept in the recess 77 in the cylinder block 1 and does not flow
into the crankshaft chamber 5.
[0076] FIG. 10 illustrates storage of the engine when the output
side of engine is oriented to be up. Oil is kept in the cam chamber
53 and does not flow into crankshaft chamber 5.
[0077] 5
[0078] The function of the relief passage 204 the pump 45 is as
follows: Assuming that the sectional area of oil passage of the
hole to splash oil into cylinder bore is S.sub.1, the sectional
area of relief passage is s.sub.2, and the discharge volume by pump
is Q. Then, the discharge volume in to the cylinder bore is
Q*S.sub.1/(S.sub.1+S.sub.2). Return volume of oil to the oil
reservoir is Q*S.sub.2/(S.sub.1+S.sub.2). So, by adequate design,
in accordance with the present invention, some part of the oil
discharged by the pump 45 always returns into the oil reservoir 18.
In the prior arts, on the other hand, because there is provided no
relief passage, in some operation condition, all of the oil in the
oil reservoir 18 is sucked and sent into the cylinder bore, and no
oil returns into the oil reservoir 18. This means that there may be
a rare instance where the crankshaft chamber 5 is filled by a lot
of oil. The present invention solves this problem.
[0079] FIGS. 12 and 13 show another embodiment of the present
invention, wherein a passage 85 is provided between the corner 82
of the deck 84 and the oil recess 76 in the cylinder block. At one
end of the passage 85, a pipe is provided in the oil recess with a
similar height with the upper wall 127 of the crankshaft chamber 5.
As illustrated in FIG. 13, the pipe 125 prevents oil from flowing
into the valve chamber 43 when the engine is oriented to be upside
down.
[0080] It is believed that small light weight four cycle engines
made in accordance with the present invention will be particularly
suitable for the use with hand-held or transportable power tools
having low emissions and will be sufficiently light to be carried
and/or transported by an operator. In the prior art, effective
lubricating methods for hand-held or transportable power tools have
been presented. However, they require complicated arc and scroll
shaped wall to control flow of lubricating oil in the engines and
to prevent oil from flowing into cylinder head when engine is
positioned upside down or vertical.
[0081] In the present invention, however, more simple and economic
construction is provided to solve the problem in the prior
arts.
[0082] Further, construction such as the pump in the prior art is
basically followed, so that specific feature and advantage of the
prior art are maintained in the present invention.
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