U.S. patent application number 15/009299 was filed with the patent office on 2016-08-11 for lubricating device for engine.
This patent application is currently assigned to MAKITA CORPORATION. The applicant listed for this patent is MAKITA CORPORATION. Invention is credited to Tomoyuki KUTSUNA, Hiroki SUGIYAMA.
Application Number | 20160230621 15/009299 |
Document ID | / |
Family ID | 55411145 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160230621 |
Kind Code |
A1 |
KUTSUNA; Tomoyuki ; et
al. |
August 11, 2016 |
LUBRICATING DEVICE FOR ENGINE
Abstract
A lubricating device for an engine is provided. A first opening
part penetrates a first partition wall separating a crank chamber
and an oil sump chamber. A second opening part penetrates a second
partition wall separating the crank chamber and a valve drive
chamber. In a lubricating device for an engine, when the pressure
in the crank chamber is positive, gas in the crank chamber is
injected into the oil sump chamber through the first opening part
and impacts oil, thus generating mist oil in the oil sump chamber,
and mist oil in the crank chamber passes through the second opening
part and is supplied to the valve drive chamber, whereas when the
pressure in the crank chamber is negative, mist oil in the oil sump
chamber passes through the first opening part and is supplied to
the crank chamber.
Inventors: |
KUTSUNA; Tomoyuki;
(Anjo-shi, JP) ; SUGIYAMA; Hiroki; (Anjo-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MAKITA CORPORATION |
Anjo-shi |
|
JP |
|
|
Assignee: |
MAKITA CORPORATION
Anjo-shi
JP
|
Family ID: |
55411145 |
Appl. No.: |
15/009299 |
Filed: |
January 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01M 1/04 20130101; F01M
9/10 20130101 |
International
Class: |
F01M 1/04 20060101
F01M001/04; F01M 9/10 20060101 F01M009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2015 |
JP |
2015-020886 |
Claims
1. A lubricating device for an engine, comprising: a crank chamber,
a pressure in which varies as a piston moves up and down; an oil
sump chamber which is disposed below the crank chamber and that
stores a lubricating oil; a valve drive chamber which is disposed
on a side of the crank chamber and that accommodates drive
components of each valve mechanism for intake and exhaust; a first
partition wall that separates the crank chamber and the oil sump
chamber; a second partition wall that separates the crank chamber
and the valve drive chamber; a first opening part that penetrates
the first partition wall and provides communication between the
crank chamber and the oil sump chamber; and a second opening part
that penetrates the second partition wall and provides
communication between the crank chamber and the valve drive
chamber, wherein, in the case in which a pressure in the crank
chamber is a positive pressure, a gas in the crank chamber is
injected into the oil sump chamber through the first opening part
and impacts an oil in the oil sump chamber thereby to generate a
mist oil in the oil sump chamber, and a mist oil in the crank
chamber passes through the second opening part and is supplied to
the valve drive chamber, and in the case in which the pressure in
the crank chamber is a negative pressure, the mist oil in the oil
sump chamber passes through the first opening part, and is supplied
to the crank chamber.
2. The lubricating device for an engine according to claim 1,
wherein the first opening part is positioned in a projection plane
of the piston in the first partition wall.
3. The lubricating device for an engine according to claim 1,
wherein an opening area of the first opening part is within a range
of from 3% up to 40% of a cross-sectional area of the piston.
4. The lubricating device for an engine according to claim 1,
wherein a flow velocity of the gas injected through the first
opening part into the oil sump chamber and blown onto an oil
surface in the oil sump chamber is within a range of from 1,000
cm/s up to 10,000 cm/s.
5. The lubricating device for an engine according to claim 1,
wherein the first partition wall has a tubular section that
projects downward from a lower surface of the first partition wall
such that the tubular section surrounds the first opening part.
6. The lubricating device for an engine according to claim 1,
wherein a bearing that rotatably supports a crank shaft is provided
in the second opening part, and the bearing is an open ball bearing
that allows passage of the mist oil.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The application claims priority to Japanese Patent
Application No. 2015-020886, filed on Feb. 5, 2015, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a lubricating device for an
engine (internal combustion engine) that can be installed in a
portable work machine or the like.
[0004] 2. Description of Related Art
[0005] An engine installed in a portable work machine, such as a
brush/weed cutter, may include a crank chamber, the pressure in
which varies as a piston moves up and down, and an oil sump chamber
which is disposed beneath the crank chamber and that stores a
lubricating oil. Such an engine is disclosed in Japanese Patent
Application Laid-open Publication No. 2004-293448. According to the
Japanese Patent Application Laid-open Publication No. 2004-293448,
a crank chamber and an oil sump chamber are in communication
through an opening part, and the mist oil generated in the oil sump
chamber is supplied to the crank chamber through the opening
part.
[0006] However, according to the Japanese Patent Application
Laid-open Publication No. 2004-293448, the opening area of the
opening part, which provides the communication between the crank
chamber and the oil sump chamber, is relatively large. Hence, a gas
in the crank chamber is supplied extensively in the oil sump
chamber through the opening part when the pressure in the crank
chamber is a positive pressure, so that a force (pressure) of the
gas impacting the surface of the oil is relatively low. Therefore,
according to the Japanese Patent Application Laid-open Publication
No. 2004-293448, it has been difficult to generate sufficient mist
oil in the oil sump chamber.
[0007] In view of such circumstances, an object of the present
invention is to efficiently generate mist oil in an oil sump
chamber.
SUMMARY OF THE INVENTION
[0008] According to one aspect of the present invention, a
lubricating device for an engine is provided. The lubricating
device for an engine includes: a crank chamber, a pressure in which
varies as a piston moves up and down; an oil sump chamber which is
disposed beneath the crank chamber and that stores a lubricating
oil; a valve drive chamber which is disposed on a side of the crank
chamber and that accommodates drive components of each valve
mechanism for intake and exhaust; a first partition wall that
separates the crank chamber and the oil sump chamber; a second
partition wall that separates the crank chamber and the valve drive
chamber; a first opening part that penetrates the first partition
wall and provides communication between the crank chamber and the
oil sump chamber; and a second opening part that penetrates the
second partition wall and provides communication between the crank
chamber and the valve drive chamber. In the lubrication device for
an engine, when the pressure in the crank chamber is a positive
pressure, a gas in the crank chamber is injected into the oil sump
chamber through the first opening part and impacts an oil in the
oil sump chamber thereby to generate a mist oil in the oil sump
chamber, and a mist oil in the crank chamber passes through the
second opening part and is supplied to the valve drive chamber. In
the lubricating device for an engine, when the pressure in the
crank chamber is a negative pressure, the mist oil in the oil sump
chamber passes through the first opening part and is supplied to
the crank chamber.
[0009] Other objects and features of aspects of the present
invention will be understood from the following description with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of an engine according to an
embodiment of the present invention;
[0011] FIG. 2 is a plan view of the engine according to the
embodiment;
[0012] FIG. 3 is a sectional view taken at line I-I in FIG. 2;
[0013] FIG. 4 is a partial perspective view of a crank case of the
engine according to the embodiment when the crank case is observed
from the oil sump chamber side;
[0014] FIG. 5 is a view illustrating a bearing that rotatably
supports a crank shaft of the engine according to the embodiment;
and
[0015] FIG. 6 is a schematic explanatory diagram of a lubricating
device of the engine according to the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The following will describe an embodiment of the present
invention with reference to the accompanying drawings.
[0017] FIG. 1 and FIG. 2 are a perspective view and a plan view,
respectively, of an engine according to an embodiment of the
present invention. FIG. 3 is a sectional view taken at line I-I in
FIG. 2. FIG. 3 illustrates the engine when a piston is positioned
near a top dead center. Furthermore, as used in the present
embodiment, "upper side" approximately coincides with a vertical
upper side in a state in which the engine is used over a longest
period of time (erect state).
[0018] An engine 1 is an overhead valve (OHV) 4-stroke, air-cooled
engine. The engine 1 has a cylinder block 2, a crank case 4, and a
cylinder head 6. The crank case 4 is disposed on one end (the lower
end) in the longitudinal direction of the cylinder block 2 and
constitutes a crank chamber 3. The cylinder head 6 is disposed on
the other end (the upper end) in the longitudinal direction of the
cylinder block 2 and constitutes, together with the cylinder block
2, a combustion chamber 5.
[0019] In the present embodiment, the cylinder block 2, the crank
case 4, and the cylinder head 6, which are all provided separately,
are connected by bolts. An oil case 7 for storing a lubricating oil
is connected to the lower end of the crank case 4.
[0020] The crank case 4 is provided at the lower end of the
cylinder block 2. The cylinder block 2 and the crank case 4
rotatably support a crank shaft 9. More specifically, both ends of
the crank shaft 9 are disposed so that the ends project out of the
crank chamber 3 formed inside the crank case 4. In the present
embodiment, both ends of the crank shaft 9 projecting out of the
crank chamber 3 are held between the cylinder block 2 and the crank
case 4, and are rotatably supported thereby. Furthermore, in the
present embodiment, one end of the crank shaft 9 (namely, the end
adjacent to a valve drive chamber 30, which will be described
below) is rotatably supported by the cylinder block 2 and the crank
case 4 via a bearing 40, which will be described below. This will
be described below in more detail with reference to FIG. 5.
[0021] A cylinder 10 having a columnar space is provided in the
cylinder block 2. A piston 11 is inserted in the cylinder 10 such
that the piston 11 can reciprocate in the vertical direction. The
piston 11 is connected to the crank shaft 9 of the crank chamber 3
via a crank web 12 and a connecting rod 13. Thus, the reciprocating
motion of the piston 11 is converted into the rotational motion of
the crank shaft 9. Furthermore, the reciprocation of the piston 11
also changes the pressure (air pressure) in the crank chamber
3.
[0022] The cylinder head 6 is provided with an intake port 15 and
an exhaust port 16. The intake port 15 is in communication with a
carburetor (not illustrated). The exhaust port 16 is in
communication with a muffler 17. Furthermore, the cylinder head 6
is provided with an intake valve 18, which opens and closes the
intake port 15, and an exhaust valve 19, which opens and closes the
exhaust port 16.
[0023] Furthermore, the cylinder head 6 includes a valve system
chamber 20, which accommodates the intake valve 18 and the exhaust
valve 19. The valve system chamber 20 is formed of the cylinder
head 6 and a valve system chamber cover 21.
[0024] The intake valve 18 and the exhaust valve 19 are provided
with a valve mechanism 25 (refer to FIG. 6) for driving the intake
valve 18 and the exhaust valve 19. The valve mechanism 25 includes
a valve drive gear 26, a cam gear 27, a cam 28, a pair of cam
followers (not illustrated), a pair of pushrods (not illustrated),
and valve springs (not illustrated). The valve drive gear 26 is
fixed to the crank shaft 9. The cam gear 27 is driven by the valve
drive gear 26. The cam 28 is provided on one end of the cam gear
27. The pair of cam followers is swung by the cam 28 and rotatably
supported by the cylinder block 2. The pair of pushrods is
supported by a rocker shaft (not illustrated) provided on the head
of the cylinder block 2, one ends thereof being in contact with the
valve heads of the intake valve 18 and the exhaust valve 19. The
valve springs urge the intake valve 18 and the exhaust valve 19 in
a valve closing direction.
[0025] Among the sections constituting the valve mechanism 25, the
valve drive gear 26, the cam gear 27, and the cam 28 are
accommodated in the valve drive chamber 30. The valve drive chamber
30 is disposed on a side of the crank chamber 3. The valve drive
chamber 30 is composed of the cylinder block 2, the crank case 4,
and a valve drive chamber cover (not illustrated). Among the
sections constituting the valve mechanism 25, the pushrods and the
valve springs are accommodated in the valve system chamber 20. The
valve system chamber 20 is disposed above the combustion chamber
5.
[0026] The valve mechanism 25 corresponds to "each valve mechanism
for intake and exhaust" in the present invention. Furthermore, the
valve drive gear 26, the cam gear 27, and the cam 28 correspond to
"the drive components of each valve mechanism for intake and
exhaust" in the present invention.
[0027] The oil case 7 is formed of a casing surrounding all sides
and the bottom. By attaching the oil case 7 to the crank case 4, an
oil sump chamber 32 is formed by the cases 4 and 7. A lubricating
oil is stored in the oil sump chamber 32. A semi-cylindrical part
of the crank case 4 rotatably accommodates the crank shaft 9, and
the semi-cylindrical part provides a first partition wall 33, which
separates the crank chamber 3 and the oil sump chamber 32.
[0028] FIG. 4 is a partial perspective view of the crank case 4 of
the engine 1 according to the present embodiment when the crank
case 4 is observed from the oil sump chamber 32 side.
[0029] As illustrated in FIG. 3 and FIG. 4, the crank chamber 3 and
the oil sump chamber 32 are separated by the first partition wall
33. The first partition wall 33 has a semi-cylindrical shape. More
specifically, the first partition wall 33 functions to rotatably
accommodate the crank web 12, which is accommodated in the crank
chamber 3, on the crank chamber 3 side, thus providing a curved
surface part bulging toward the oil sump chamber 32. A central
portion 34 of the curved surface part bulges most toward the oil
sump chamber 32.
[0030] A first opening part 35, which provides communication
between the crank chamber 3 and the oil sump chamber 32 is
penetratingly formed in the central portion 34 of the
semi-cylindrical first partition wall 33. The first opening part 35
is positioned within a projection plane of the piston 11 in the
first partition wall 33. In other words, the first opening part 35
is penetratingly formed in an area hidden by the piston 11 when the
first partition wall 33 is observed from the combustion chamber 5
side.
[0031] The first opening part 35 is preferably positioned right
below the central portion of the piston 11. In other words, the
central axis of the first opening part 35 and the central axis of
the piston 11 are preferably positioned on the same axial line.
[0032] The opening area of the first opening part 35 is preferably
within a range of from 3% up to 40% of the cross-sectional area of
the piston 11, and more preferably within a range of from 5% up to
35% of the cross-sectional area of the piston 11. The
cross-sectional area of the piston 11 refers to the cross-sectional
area of the piston 11 in a plane that is orthogonal to the
direction of the reciprocation of the piston 11 (i.e., the central
axis of the piston 11).
[0033] Although the shape of the cross-section of the first opening
part 35 is rectangular in the present embodiment, the shape of the
cross-section of the first opening part 35 is not limited thereto,
and may be, for example, circular. Furthermore, the first opening
part 35 in the present embodiment is composed of the single through
hole; however, the first opening part 35 may alternatively be
composed of two or more through holes. If the first opening part 35
is composed of two or more through holes, then the total sum of the
opening areas of the two or more through holes, i.e. the total
opening area, is preferably within a range of from 3% up to 40% of
the cross-sectional area of the piston 11, and more preferably
within a range of from 5% up to 35% of the cross-sectional area of
the piston 11.
[0034] A tubular section 36 is provided, surrounding the first
opening part 35, at the lower surface of the semi-cylindrical first
partition wall 33. The tubular section 36 projects downward from
the lower surface of the first partition wall 33. In the present
embodiment, the tubular section 36 has a rectangular
cross-sectional shape. Alternatively, however, the cross-section of
the tubular section 36 is not limited to the rectangular shape, and
may be, for example, a circular shape.
[0035] FIG. 5 illustrates the bearing 40 that rotatably supports
the crank shaft 9 of the engine 1 according to the present
embodiment. The crank chamber 3 and the valve drive chamber 30 are
separated by a second partition wall 42. The second partition wall
42 is composed of the cylinder block 2 and the crank case 4.
[0036] In the second partition wall 42, an upper opening part 43
having a semicircular cross-section is formed in the lower end of
the cylinder block 2. In the second partition wall 42, a lower
opening part 44 having a semicircular cross-section is formed in
the upper end of the crank case 4.
[0037] A second opening part 45 is composed of the semicircular
upper opening part 43 and the semicircular lower opening part 44
and has a circular cross-sectional shape. The second opening part
45 penetrates the second partition wall 42, providing communication
between the crank chamber 3 and the valve drive chamber 30.
[0038] The bearing 40 is inserted in the second opening part 45 of
the second partition wall 42. In other words, the bearing 40 is
provided in the second opening part 45 of the second partition wall
42. The bearing 40 is an open ball bearing, which has a gap between
the inner ring and the outer ring thereof and has gaps among a
plurality of balls thereof. Thus, the bearing 40 allows the passage
of a mist oil, which is a mist-like oil.
[0039] The bearing 40 has one end of the crank shaft 9 (the end on
the valve drive chamber 30 side) inserted in the inner ring thereof
to rotatably support the crank shaft 9. Hence, the one end of the
crank shaft 9 (the end on the valve drive chamber 30 side) is
rotatably supported by the cylinder block 2 and the crank case 4
via the bearing 40. A valve drive gear 26 is fixed to a portion of
the one end of the crank shaft 9 that is positioned in the valve
drive chamber 30. FIG. 5 does not illustrate the cam gear 27 driven
by the valve drive gear 26.
[0040] Referring now to FIG. 6, a description will be given of a
lubricating device 50 of the engine 1 according to the present
embodiment. FIG. 6 is a schematic explanatory diagram of the
lubricating device 50 of the engine 1 according to the present
embodiment. The lubricating device 50 of the engine 1 utilizes the
changes in the pressure in the crank chamber 3 caused by the
reciprocation of the piston 11 to circulate the oil stored in the
oil sump chamber 32, thereby lubricating each section of the engine
1.
[0041] A circulation path 61 for circulating the oil is provided
between the oil sump chamber 32 and the valve system chamber 20.
The circulation path 61 includes the first opening part 35, the
second opening part 45, the valve drive chamber 30, the valve
system chamber 20, an oil feed passage 62, and the crank chamber
3.
[0042] If the piston 11 moves toward the top dead center, causing
the pressure in the crank chamber 3 to become a negative pressure,
then the mist oil in the oil sump chamber 32 passes through the
first opening part 35 and is supplied to the crank chamber 3.
Thereafter, if the piston 11 moves toward a bottom dead center,
causing the pressure in the crank chamber 3 to become a positive
pressure, then the mist oil in the crank chamber 3 passes through
the second opening part 45 and is supplied to the valve drive
chamber 30 and the valve system chamber 20.
[0043] The bearing 40 is provided in the second opening part 45
(refer to FIG. 5). With this arrangement, mist oil droplets having
relatively large diameters among the mist oil droplets in the crank
chamber 3 are blocked by the bearing 40, thus restricting their
passage to the valve drive chamber 30 from the crank chamber 3.
Meanwhile, among the mist oil droplets in the crank chamber 3, mist
oil droplets having relatively small diameters pass through the gap
between the inner ring and the outer ring of the bearing 40 and
through the gaps among the plurality of balls of the bearing 40,
and are supplied to the valve drive chamber 30. Thus, the valve
drive gear 26, the cam gear 27, the cam 28, the pushrods, and the
valve springs constituting the valve mechanism 25 are lubricated by
the mist oil flowing through the circulation path 61.
[0044] A suction passage 64 through which the oil in the valve
system chamber 20 is drawn in is provided inside the valve system
chamber 20. The oil feed passage 62 is provided between the suction
passage 64 and the crank chamber 3. The oil feed passage 62 has the
open end on one side thereof connected to the suction passage 64
and the open end on the other side thereof connected to the crank
chamber 3. The open end on the other side of the oil feed passage
62 is positioned such that the open end is fully opened when the
piston 11 reaches the top dead center.
[0045] When the pressure in the crank chamber 3 becomes a negative
pressure due to the movement of the piston 11 to the top dead
center, the mist oil in the valve system chamber 20 is drawn in
through the opening of the oil feed passage 62 and fed into the
crank chamber 3 through the suction passage 64 and the oil feed
passage 62. The oil fed into the crank chamber 3 is returned into
the oil sump chamber 32 through the first opening part 35.
[0046] A discharge passage 65 for discharging the blow-by gas in
the oil circulation path to the combustion chamber 5 is provided
inside the valve system chamber 20. One end 66 of the discharge
passage 65 is provided in the valve system chamber 20, while the
other end thereof is connected to an air cleaner 67. The air
cleaner 67 is provided on the upstream side of the above-mentioned
carburetor and functions to remove dust and the like in the
air.
[0047] The blow-by gas containing oil, which has been sent to the
air cleaner 67, is subjected to the gas-liquid separation to be
separated to the blow-by gas and oil by an oil separator 68
provided in the air cleaner 67. The separated oil passes through a
reflux passage 70, which provides communication between the air
cleaner 67 and the crank chamber 3, to be sent to the crank chamber
3. The open end of the reflux passage 70 on the crank chamber 3
side is positioned such that the open end is fully opened when the
piston 11 reaches the top dead center. Hence, when the pressure in
the crank chamber 3 becomes a negative pressure due to the movement
of the piston 11 to the top dead center, the oil separated by the
oil separator 68 is drawn through the reflux passage 70 and fed
into the crank chamber 3. Meanwhile, the blow-by gas separated by
the oil separator 68 is burnt in the combustion chamber 5 and then
discharged to the outside through the muffler 17.
[0048] When the pressure in the crank chamber 3 becomes a positive
pressure due to the movement of the piston 11 to the bottom dead
center, a high-pressure gas in the crank chamber 3 is injected into
the oil sump chamber 32 through the first opening part 35. In other
words, the gas in the crank chamber 3 that is pushed out as the
piston 11 moves to the bottom dead center is injected into the oil
sump chamber 32 through the first opening part 35. The injected gas
impacts the oil in the oil sump chamber 32. The high-pressure gas
from the crank chamber 3 blown onto the oil surface in the oil sump
chamber 32 in the manner described above expedites the misting of
the oil in the oil sump chamber 32, thus efficiently generating a
mist oil in the oil sump chamber 32.
[0049] If the opening area of the first opening part 35 is unduly
large, then it becomes difficult to cause the gas in the crank
chamber 3 to vigorously impact the surface of the oil in the oil
sump chamber 32 through the first opening part 35. This may lead to
unsuccessful generation of a mist oil. Meanwhile, if the opening
area of the first opening part 35 is unduly small, then the crank
chamber 3 functions like a pump, and the output of the engine 1 may
be reduced. Thus, the upper limit value of the opening area of the
first opening part 35 can be set, considering the efficiency of the
generation of the mist oil in the oil sump chamber 32. Furthermore,
the lower limit value of the opening area of the first opening part
35 can be set, considering the output required of the engine 1.
Taking these into account, the opening area of the first opening
part 35 is preferably within a range of from 3% up to 40% of the
cross-sectional area of the piston 11, and more preferably within a
range of from 5% up to 35% of the cross-sectional area of the
piston 11.
[0050] According to the present embodiment, the lubricating device
50 of the engine 1 includes: the crank chamber 3, the pressure
inside which varies as the piston 11 moves up and down; the oil
sump chamber 32 which is disposed below the crank chamber 3 and
that stores a lubricating oil; the valve drive chamber 30 which is
disposed on the side of the crank chamber 3 and that accommodates
the drive components of each valve mechanism for the intake and the
exhaust; the first partition wall 33 that separates the crank
chamber 3 and the oil sump chamber 32; the second partition wall 42
that separates the crank chamber 3 and the valve drive chamber 30;
the first opening part 35 that penetrates the first partition wall
33 and provides communication between the crank chamber 3 and the
oil sump chamber 32; and the second opening part 45 that penetrates
the second partition wall 42 and provides communication between the
crank chamber 3 and the valve drive chamber 30. In the lubricating
device 50 of the engine 1, when the pressure in the crank chamber 3
is a positive pressure, the gas in the crank chamber 3 is injected
through the first opening part 35 into the oil sump chamber 32 and
impacts the oil in the oil sump chamber 32 thereby to generate the
mist oil in the oil sump chamber 32, and the mist oil in the crank
chamber 3 passes through the second opening part 45 and is supplied
to the valve drive chamber 30. In the lubricating device 50 of the
engine 1, when the pressure in the crank chamber 3 is a negative
pressure, the mist oil in the oil sump chamber 32 passes through
the first opening part 35 and is supplied to the crank chamber 3.
Thus, the high-pressure gas from the crank chamber 3 is blown onto
the oil surface in the oil sump chamber 32 so as to disturb the oil
surface. This makes it possible to expedite the misting of the oil
in the oil sump chamber 32, thus efficiently generating a mist oil
in the oil sump chamber 32.
[0051] Furthermore, according to the present embodiment, the first
opening part 35 is positioned in the projection plane of the piston
11 in the first partition wall 33. Therefore, the high-pressure gas
generated in the crank chamber 3 by the reciprocation of the piston
11 can be vigorously blown, through the first opening part 35, onto
the oil surface in the oil sump chamber 32 to disturb the oil
surface, thus permitting more efficient generation of the mist oil
in the oil sump chamber 32.
[0052] Furthermore, according to the present embodiment, the
opening area of the first opening part 35 is within a range of from
3% up to 40% of the cross-sectional area of the piston 11. This
allows the mist oil to be efficiently generated in the oil sump
chamber 32 and also allows the output required of the engine 1 to
be ensured.
[0053] Furthermore, according to the present embodiment, the first
partition wall 33 has the tubular section 36, which projects
downward from the lower surface of the first partition wall 33 and
which surrounds the first opening part 35. This makes it possible
to restrain the oil in the oil sump chamber 32 from excessively
flowing into the crank chamber 3 through the first opening part 35
during, for example, an inverted operation of the engine 1.
[0054] Furthermore, according to the present embodiment, the
bearing 40 rotatably supporting the crank shaft 9 is provided in
the second opening part 45. The bearing 40 is an open ball bearing,
which permits the passage of the mist oil. Hence, mist oil droplets
having relatively small diameters among the mist oil droplets in
the crank chamber 3 pass through the gap between the inner ring and
the outer ring of the bearing 40 and through the gaps among the
plurality of balls of the bearing 40, and are supplied to the valve
drive chamber 30, thus making it possible to restrain oversupply of
the oil to the valve drive chamber 30 and the valve system chamber
20.
[0055] In the present embodiment, the dimensions, the opening area,
the shape and the like of the first opening part 35 may be set
based on the volume of the stroke of the vertical movement of the
piston 11 in the cylinder 10 (cylinder capacity) of the engine
1.
[0056] Furthermore, in the present embodiment, the flow velocity of
the gas injected through the first opening part 35 into the oil
sump chamber 32 and blown onto the surface of the oil in the oil
sump chamber 32 (i.e. the blowoff velocity of the gas at the first
opening part 35) is preferably within a range of from 1,000 cm/s up
to 10,000 cm/s, and more preferably within a range of from 1,500
cm/s up to 8,000 cm/s. Setting the blowoff velocity of the gas at
the first opening part 35 to the ranges mentioned above permits
efficient generation of the mist oil in the oil sump chamber
32.
[0057] Furthermore, the engine 1 in the present embodiment can be
installed, as a drive source, in a portable work machine, such as a
brush/weed cutter, a hole digging machine, or a concrete cutter.
Furthermore, the engine 1 can be installed, as a drive source, in a
backpack work machine, such as a backpack blower, a sprayer, a
duster, or a backpack brush/weed cutter.
[0058] In the lubricating device for an engine according to the
present invention, the mist oil is generated in the oil sump
chamber by a gas in the crank chamber being injected into the oil
sump chamber through the first opening part and impacting the oil
in the oil sump chamber when the pressure in the crank chamber is a
positive pressure. This makes it possible to expedite the
generation of the mist oil (misting) in the oil sump chamber by
blowing the high-pressure gas from the crank chamber onto the
surface of the oil in the oil sump chamber, so that the mist oil
can be efficiently generated in the oil sump chamber.
[0059] Although the embodiment of the present invention has been
described, the present invention is not limited to the foregoing
embodiment, and it is obvious that more modifications, changes and
the like can be made on the basis of the technical idea of the
present invention.
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