U.S. patent application number 09/790605 was filed with the patent office on 2001-12-13 for motorcycle.
This patent application is currently assigned to SUZUKI KABUSHIKI KAISHA. Invention is credited to Yamada, Shinichi, Yoshida, Koji.
Application Number | 20010050193 09/790605 |
Document ID | / |
Family ID | 18572021 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050193 |
Kind Code |
A1 |
Yoshida, Koji ; et
al. |
December 13, 2001 |
Motorcycle
Abstract
An engine of a motorcycle includes a cylinder block and a
cylinder head inclined forward on an upper front portion of a
crankcase of the engine in an engine installed state. The crankcase
comprises a plurality of vertical case sections comprising an upper
case section, a middle case section and a lower case section, and
the crankshaft is pivotally supported at a mating portion between
the upper case section and the middle case section and a
transmission shaft is pivotally supported at a mating portion
between the middle case section and the lower case section. The
upper case section is integrally formed with a lower portion of the
cylinder block, and a breather cover manufactured independently is
provided in a forward inclined manner so as to cover an upper
surface of the middle case section at the rear portion of the upper
case section so as to define a breather chamber inside the breather
cover and a breather hose extends substantially perpendicularly
upward from a rear upper portion of the breather cover and is
connected to the air cleaner at a bottom portion thereof.
Inventors: |
Yoshida, Koji;
(Hamamatsu-Shi, JP) ; Yamada, Shinichi;
(Hamakita-Shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
SUZUKI KABUSHIKI KAISHA
300, Takatsuka-Cho, Shizuoka-Ken
Hamamatsu-Shi
JP
|
Family ID: |
18572021 |
Appl. No.: |
09/790605 |
Filed: |
February 23, 2001 |
Current U.S.
Class: |
180/219 |
Current CPC
Class: |
F02M 25/06 20130101;
F02B 75/20 20130101; F01P 5/10 20130101; F01M 13/04 20130101; F02B
61/02 20130101; F02B 2275/18 20130101; Y02T 10/121 20130101; F02F
2001/245 20130101; F02B 2075/1816 20130101; Y02T 10/12
20130101 |
Class at
Publication: |
180/219 |
International
Class: |
B62K 011/00; B62M
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2000 |
JP |
P2000-50207 |
Claims
What is claimed is:
1. A motorcycle comprising: a motorcycle body provided with a body
frame extending in a longitudinal direction thereof; a steering
member supporting a front wheel to be rotatable and connected to
the body frame; a swing arm unit mounted to the body frame and
connected to a rear wheel to be rotatable; an engine disposed
substantially central portion of the motorcycle body and including
a crankcase, a cylinder block and a cylinder head in a forward
inclined manner in a standing state of the motorcycle, said
crankcase being separated into a plurality of vertical case
sections comprising an upper case section, a middle case section
and a lower case section so that a crankshaft is pivotally
supported to a mating portion between the upper and middle case
sections; a transmission shaft pivotally supported to a mating
portion between the middle and lower case sections; a fuel tank
disposed above the engine; a seat member disposed to a rear portion
of the fuel tank; a fuel supply unit disposed at a rear upper
portion of the engine; and an air cleaner disposed above the fuel
supply unit, wherein said upper case section is secured to a lower
portion of the cylinder block, and a breather cover is provided in
a forward inclined manner so as to cover an upper surface of the
middle case section at the rear portion of the upper case so as to
define an interior of the breather cover as a breather chamber and
a breather hose extends upward from a rear upper portion of the
breather cover and is connected to the air cleaner at a bottom
portion thereof.
2. A motorcycle according to claim 1, wherein said breather cover
is provided at an intermediate position in a width direction of a
motorcycle frame, a starter motor for the engine is mounted on one
side of the breather case and a water hose for a
liquid-cooled-engine is arranged on the other side thereof.
3. A motorcycle according to claim 1, wherein said breather hose
extends between a fuel pump disposed so as to protrude downward
from a rear lower surface of the fuel tank and a fuel feed pipe of
the fuel supply unit located in front of the fuel pump and is
connected to the air cleaner.
4. A motorcycle according to claim 1, wherein a mating portion
between the middle case section and the breather cover is provided
with a recess portion recessed downward so as to form a breather
recess with a bottom surface inclined forward.
5. A motorcycle according to claim 4, wherein a breather hole is
formed in a vicinity of an intermediate portion in the front and
rear direction of a side wall of the breather recess so as to form
an oil return path in a vicinity of the front end on the bottom
surface, so that the breather hole and the oil return path are
respectively communicated with an interior of the crankcase.
6. A motorcycle according to claim 4, wherein a gasket is
interposed between the breather recess and the breather cover, the
interior of the breather cover is divided by partition walls into a
plurality of compartments which lie in a row in the front and rear
direction of the engine and communicate with each other, the gasket
is formed with an opening so that the frontmost compartment is
communicated with the front end portion of the breather recess, and
an extension of the breather hose is communicated with the rearmost
compartment.
7. A motorcycle according to claim 1, wherein the mating portion
between the middle case section and the breather cover is formed in
parallel with the mating portion between the middle case section
and the upper case section so as to provide same height level.
8. A motorcycle in which an engine is mounted below a fuel tank and
an air cleaner, the engine includes a cylinder block and a cylinder
head inclined forward on an upper front portion of a crankcase of
the engine in an engine installed state, the crankcase is separated
into a plurality of vertical case sections comprising an upper case
section, a middle case section and a lower case section, the
crankshaft is pivotally supported on a mating portion between the
upper case section and the middle case section and a transmission
shaft is pivotally supported on a mating portion between the middle
case section and the lower case section, wherein said upper case
section is integrally formed with a lower portion of the cylinder
block, and a breather cover manufactured independently is provided
in a forward inclined manner so as to cover an upper surface of the
middle case section at the rear portion of the upper case so as to
define a breather chamber inside the breather cover and a breather
hose extends substantially perpendicularly upwards from a rear
upper portion of the breather cover and is connected to the air
cleaner at a bottom portion thereof.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a motorcycle mounted with
an engine in which a breather chamber is disposed on an upper
surface portion of a crankcase of an engine.
[0002] Many of straddle type motorcycles have such a structure that
a fuel tank is installed on a front half upper portion of a
motorcycle frame, a seat is provided at the rear portion thereof,
and the engine is mounted below the fuel tank.
[0003] In a case where the engine is an in-line multi-cylinder
type, as disclosed in Japanese Patent Laid-open Publication No. HEI
8-86223, the motorcycle often has a layout in which a cylinder
block and a cylinder head are mounted on a front portion of an
upper surface of a crankcase of the engine, and a crankshaft and a
transmission shaft extending in the frame width direction are
pivotally supported inside of the crankcase.
[0004] The engine disclosed in this publication has a structure
that a cylinder block and a cylinder head are provided in a forward
inclined manner on the front portion of the upper surface of the
crankcase which is vertically oplitable into three sections,
comprising an upper case section, a middle case section and a lower
case section, a crankshaft is pivotally supported on a mating
surface portion (joint portion) between the upper case section and
the middle case section, and two transmission shafts are pivotally
supported on a mating surface (joint portion) between the middle
case section and the lower case section. In this manner, the
crankshaft and the transmission shafts are pivotally supported in a
stepped arrangement from each other, and a distance between axes of
the crankshaft and the front transmission shaft is reduced, thus
making small a size of the crankcase (i.e. engine) in the front and
rear direction (longitudinal direction of the motorcycle body).
[0005] With such an in-line multi-cylinder structure engine, a
breather chamber is integrally provided on the rear portion of the
upper surface of the upper case section of the crankcase. The
breather chamber acts as an oil separation chamber having a
labyrinth structure with a predetermined capacity and is adapted to
alleviate a pressure change in the crankcase occurring with a
reciprocal motion of a piston of a piston-cylinder assembly of the
engine and leakage of a blowby gas without jetting externally the
oil stored in the crankcase outside. As the capacity of the
breather chamber increases, vapor-liquid separability of the blowby
gas and the oil becomes better, thus making the operation of the
engine smooth.
[0006] However, main components of the engine, such as crankcase,
cylinder block and cylinder head, are generally formed of aluminum
castings, and the outer wall of the breather chamber integrally
provided on the upper case section of the crankcase is also formed
of an aluminum casting. Therefore, as the capacity of the breather
chamber increases, the weight of the engine also increases, and as
a result, it becomes hence difficult to make increase the capacity
of the breather chamber.
[0007] Moreover, even if there is adopted a structure in which the
capacity of the breather chamber is increased, no enough space will
exist in the vicinity of the crankcase, because supplementary
equipments or members such as starter motor and water pump are
installed in the vicinity of the crankcase. Thus, it is considered
as only one option to increase the height dimension or the breather
chamber. However, if the height of the breather chamber is made
high over the mating surface portion between the upper case section
of the crankcase and the cylinder block of the engine, it becomes
difficult to work or assemble the upper case section of the
crankcase, which will involve an increase of the production cost of
the engine.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to substantially
eliminate inconveniences or difficulties encountered in the prior
art mentioned above and to provide a motorcycle capable of reducing
a production cost of the engine and improving a layout of
supplementary machinery around the engine, while improving the
breather performance and light weight of the engine.
[0009] This and other objects can be achieved according to the
present invention by providing, in one aspect, a motorcycle in
which an engine is mounted below a fuel tank and an air cleaner,
the engine includes a cylinder block and a cylinder head inclined
forward on an upper front portion of a crankcase of the engine in
an engine installed state, the crankcase comprising a plurality of
vertical case sections including an upper case section, a middle
case section and a lower case section, the crankshaft is pivotally
supported at a mating portion between the upper case section and
the middle case section and a transmission shaft is pivotally
supported on a mating portion between the middle case section and
the lower case section,
[0010] wherein the upper case section is integrally formed with a
lower portion of the cylinder block, and a breather cover
manufactured independently is provided in a forward inclined manner
so as to cover an upper surface of the middle case section at the
rear portion of the upper case so as to define an interior of the
breather cover as a breather chamber and a breather hose extends
substantially perpendicularly upwards from a rear upper portion of
the breather cover and is connected to the air cleaner at a bottom
portion thereof.
[0011] In preferred examples of the above aspect, the breather
cover is provided substantially at an intermediate position in a
width direction of a motorcycle frame extending in the longitudinal
direction of the motorcycle body, a starter motor for the engine is
mounted on one side of the breather cover and a water hose for a
liquid-cooled-engine extending from a water pump is arranged on the
other side thereof.
[0012] A breather hose extending from the rear upper portion of the
breather cover extends between a fuel pump disposed to protrude
downward from a rear lower surface of the fuel tank and a fuel feed
pipe of a fuel supply system located in front of the fuel pump and
is connected to the air cleaner.
[0013] A portion in a mating portion between the middle case
section and the breather cover is recessed downward so as to form a
breather recess with a bottom surface inclined forward, a breather
hole is formed in the vicinity of an intermediate portion in the
front and rear direction of a side wall of the breather recess so
as to form an oil return path in the vicinity of the front end on
the bottom surface, so that the breather hole and the oil return
path are respectively communicated with an interior of the
crankcase, a gasket is interposed between the breather recess and
the breather cover, the interior of the breather cover is divided
by partition walls so as to form a plurality of compartments which
lie in a row along the front and rear direction of the engine and
communicate with each other, an opening is formed to the gasket so
that the frontmost compartment is communicated with the front end
portion of the breather recess, and an extension of the breather
hose is communicated with the rearmost compartment.
[0014] The mating portion between the middle case section and the
breather cover is formed in parallel with the mating portion
between the middle case section and the upper case section so as to
provide same height level.
[0015] In a modified aspect, there in provided a motorcycle
comprising:
[0016] a motorcycle body provided with a body frame extending in a
longitudinal direction thereof;
[0017] a steering member supporting a front wheel to be rotatable
and connected to the body frame;
[0018] a swing arm unit mounted to the body frame and connected to
a rear wheel to be rotatable;
[0019] an engine disposed substantially central portion of the
motorcycle body and including a crankcase, a cylinder block and a
cylinder head in a forward inclined manner in a standing state of
the motorcycle, the crankcase being separated into a plurality of
vertical case sections comprising an upper case section, a middle
case section and a lower case section so that a crankshaft is
pivotally supported to a mating portion between the upper and
middle case sections;
[0020] a transmission shaft pivotally supported to a mating portion
between the middle and lower case sections;
[0021] a fuel tank disposed above the engine;
[0022] a seat member disposed to a rear portion of the fuel
tank;
[0023] a fuel supply unit disposed at a rear upper portion of the
engine; and
[0024] an air cleaner disposed above the fuel supply unit,
[0025] wherein the upper case section is secured to a lower portion
of the cylinder block, and a breather cover is provided in a
forward inclined manner so as to cover an upper surface of the
middle case section at the rear portion of the upper case so as to
define a breather chamber in the breather cover and a breather hose
extends upward from a rear upper portion of the breather cover and
is connected to the air cleaner at a bottom portion thereof.
[0026] According to the structures and subject features of the
present invention mentioned above, since the breather cover is
provided independently from the upper case section, the breather
cover can be formed of a material lighter than that of the upper
case section formed of an aluminum casting. Moreover, since the
height dimension of the breather cover can be increased, regardless
of the shape of the upper case, the capacity of the breather can be
increased.
[0027] The improvement in the breather performance and light weight
of the engine can be both contemplated. The breather chamber having
a large capacity can be provided without impairing the layout of
the supplementary machinery around the engine.
[0028] Moreover, according to the preferred examples of the present
invention, since the breather hose is arranged substantially in the
perpendicular direction, vapor-liquid separability of the blowby
gas and the oil becomes excellent to thereby improve the breather
performance.
[0029] Furthermore, the Interior of a large-capacity breather
chamber composed of the breather cover and the breather recess is
divided by the gasket and the partition walls and formed like a
labyrinth. Moreover, the extension of the breather hose and the oil
return path are located on the uppermost portion and the lowermost
portion of the breather chamber, respectively. Accordingly, the
vapor-liquid separability of the blowby gas and the oil can be
improved in the crankcase, thereby improving the breather
performance.
[0030] Furthermore, the mating portion with the upper case section
and the mating portion with the breather cover in the middle case
section of the crankcase can be made flat at the same time, and
hence, the middle case section can be easily manufactured, thus
reducing the production cost of the engine.
[0031] The nature and further characteristic features of the
present invention will be made more clear from the following
descriptions made with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In the accompanying drawings:
[0033] FIG. 1 is a left side view showing one embodiment of a
motorcycle according to the present invention;
[0034] FIG. 2 is an enlarged sectional view of an engine, a fuel
injection system, an air cleaner, a fuel pump and the like of the
motorcycle of FIG. 1 of the present invention; and
[0035] FIG. 3 is an illustration viewed from a rear side of the
engine in a direction of an arrow III in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] One embodiment of the present invention will be described
hereunder with reference to the accompanying drawings.
[0037] With reference to FIG. 1 showing a motorcycle 1 of the
present invention, the motorcycle 1 is provided with a motorcycle
frame 2 supporting, at a front end thereof, a steering member
including a front fork 4 for supporting a front wheel 3 to be
pivotal or turn in lateral direction with respect to the
longitudinal direction of the motorcycle 1 together with a handle
cover 5 and also provided with a swing arm 8 for supporting a rear
wheel 7 to be pivotal on a pivot shaft 6 supported in the width
(lateral) direction of the frame of the motorcycle body at its
central lower portion to be vertically movable.
[0038] The front half upper portion of the motorcycle frame 2 is
comprised of a pair of left and right thick main pipes 10, and a
fuel tank 11 is installed on the main pipes with a seat 12 being
disposed at the rear portion of the fuel tank 11. For example, an
in-line four-cylinder four-stroke-cycle DOHC (double-over-head-cam)
type water cooled engine 13 is mounted below the fuel tank 11. As
shown in FIG. 2 and FIG. 3, a fuel supply unit as an fuel injection
system 14 including transverse four fuel injectors is connected to
the rear upper portion of the engine 13, and an air cleaner 15
having a box shape is installed on the fuel injection system
14.
[0039] The air cleaner 15 is housed in a recessed portion (recess)
11a formed to the lower surface of the fuel tank 11, and the
interior of the air cleaner 15 is divided by an air filter 16 into
a dirty side 16a and a clean side 16b with the dirty side 16a being
provided with an air inlet 17 leading to the outside thereof and
the clean side 16b being connected with the upper portion of the
fuel injection system 14. A fuel pump 18 is located in the fuel
tank 11 at the rear portion of the air cleaner 15 and the fuel
injection system 14 so that the lower portion of the fuel pump 18
protrudes downward from the rear lower surface of the fuel tank
11.
[0040] FIG. 2 is an enlarged sectional view showing the arrangement
of the engine 13, the fuel injection system 14, the air cleaner 15,
the fuel pump 18 and the like showing one embodiment of the present
invention, and FIG. 3 is a back-side view of the engine 13 as
viewed in the direction of the arrow III in FIG. 2.
[0041] The engine 13 has a cylinder block 22, a cylinder head 23,
and a head cover 24 formed through aluminum casting so as to be
inclined forward and installed on the upper surface front portion
of a crankcase 21 also formed through the aluminum casting. The
crankcase 21 is vertically divided into three sections, in an
engine installed state to a motorcycle, comprising an upper case
section 25, a middle case section 26 and a lower case section 27,
and an oil pan 28 is mounted to the lower portion of the lower case
section 27.
[0042] Further, these upper, middle and lower case sections 25, 26
and 27 will be referred to hereunder as merely upper, middle and
lower case 25, 26 and 27 for the convenience sake.
[0043] The upper case 25 of the crankcase 21 is integrally formed
with the lower portion of the cylinder block 22, and a crankshaft
30 disposed in the engine crankcase is pivotally supported on a
mating portion (joint surface) A between the upper case 25 and the
middle case 26 in a shape along the width direction of the
motorcycle frame, and two front and rear transmission shafts 31 and
32 are pivotally supported at the rear portion of the crankshaft 30
at a mating portion (joint surface) B between the middle case 26
and the lower case 27.
[0044] The mating portion A between the upper case 25 (cylinder
block 22) and the middle case 26 is in parallel with the mating
portion B between the middle case 26 and the lower case 27 and with
a mating portion (joint surface) C between the cylinder block 22
and the cylinder head 23, thus, all these mating portions A, B and
C being inclined forward as shown in the side view. However, since
a mating portion (joint surface) D between the lower case 27 and
the oil pan 28 is made horizontal, the side portion of the lower
case 27 has substantially a wedge shape which becomes narrower
toward the front side.
[0045] On the other hand, four cylinder bores 34 are formed
transversely parallelly in the cylinder block 22, and four
combustion chambers 35 are formed on the bottom face of the
cylinder head 23 so as to align with the cylinder bores 34,
respectively, and a piston 36 (piston pin 37) inserted into the
cylinder bore 34 to be slidable and a crank pin 38 disposed
eccentrically with the axis of the crankshaft 30 are connected by
means of a connection rod 39.
[0046] Moreover, an inlet port 41 and an exhaust port 42
communicated with the combustion chamber 35 from the outside
thereof are formed in the cylinder head 23, and an inlet valve 43
disposed in the inlet port 41 and an exhaust valve 44 disposed in
the exhaust port 42 are controlled to be opened and closed at a
predetermined timing by an inlet cam shaft 45 and an exhaust cam
shaft 46 pivotally supported in the cylinder head 23,
respectively.
[0047] The reciprocal motion of the piston 36 in the cylinder bore
34 is converted into the rotational motion of the crankshaft 30
through a connection rod 39, and the rotation speed of the
crankshaft 30 is changed by a transmission, not shown, mounted
rotatably on two transmission shafts 31 and 32, is taken out as an
output of the engine 13 and is then transmitted to the rear wheel 7
through a chain 47 (see FIG. 1).
[0048] A water pump 50 for circulating a cooling water is installed
on the left side of the crankcase 21 (lower case 27), and an outlet
union 51 and an inlet union 52 disposed on the rear surface of the
cylinder block 22 are connected through a water hose 53 to supply
the cooling water discharged from the water pump 50 to a water
jacket 54 in the cylinder block 22 and the cylinder head 23 so as
to perform a cooling function. Moreover, the oil, not shown,
collected in the oil pan 28 is supplied to each section of the
engine 13 through an operation of the oil pump, thus performing the
lubrication.
[0049] To the inlet port 41 is connected the lower portion of the
above-described fuel injection system 14, and to the outlet port 42
is connected an exhaust pipe 56 (see FIG. 1). The exhaust pipe 56
extends from the exhaust port 42, passes around the front surface
and the lower surface of the engine 13, extends rearward and is
then connected to an exhaust muffler 57. The front half upper
portion of the frame body of the motorcycle 1 is covered by a
streamlined cowling 58 to thereby cover the engine 13, the fuel
injection system 14, the air cleaner 15, the exhaust pipe 56, etc.
from the outside.
[0050] Here, a breather cover 60 formed independently is provided
so as to be inclined forward on the upper surface portion of the
middle case 26 and at the rear position of the upper case 25. This
breather cover 60 is provided substantially in an intermediate
position in the width direction of the motorcycle, as shown in FIG.
3, and a starter motor 61 for engine starting is installed on one
side (for example, the right aide) of the breather cover 60, and
the water hose 53 is arranged in a prescribed location on the other
side thereof (for example, the left side).
[0051] The mating portion (joint surface) E between the breather
cover 60 and the middle case 26 is formed in parallel with the
mating portion A between the middle case 26 and the upper case 25
(cylinder block 22) in the same height level. A breather recess
(recessed portion) 62 is formed on the portion of the mating
portion E so as to be recessed downward, and the breather recess 62
and the inner space of the breather cover 60 are joined together to
thereby partition and define a breather chamber 63.
[0052] The bottom surface of the breather recess 62 has a forward
inclination, and an oil return path 64 is formed in the vicinity of
the front end thereof, while a breather hole 65 is formed in the,
vicinity or the intermediate portion in the front and rear
direction (longitudinal direction of the motorcycle) of the side
wall of the breather recess 62. The oil return path 64 and the
breather hole 65 are respectively communicated with the interior of
the crankcase 21. On the other hand, the inner space of the
breather cover 60 is divided by two front and rear partition walls
66 and 67 so as to form three compartments 68, 69 and 70 which lie
in a row along the front and rear direction and communicate with
each other like a labyrinth.
[0053] A plate-like gasket 71 is interposed between the breather
recess 62 and the breather cover 60 (mating surface E), so that the
frontmost compartment 68 in the breather cover 60 is communicated
with the front end portion of the breather recess 62 through an
opening 72 formed to the front portion of the gasket 71. Moreover,
the rearmost compartment 70 is communicated with the outside
portion through a union 73 disposed at the rear upper portion of
the breather cover 60.
[0054] The one end of a breather hose 74 is connected to the union
73 and the other end thereof is connected to a union 75 disposed on
the bottom portion, on the clean side 16b, of the air cleaner 15
from the lower side thereof. This breather hose 74 passes between
the fuel pump 18 disposed in the fuel tank 11 and a fuel feeding
pipe 76 of the fuel injection system 14 located in front of the
fuel pump 18 so as to be arranged substantially
perpendicularly.
[0055] In the motorcycle 1 of the structure as mentioned above, at
the time of operation of the engine 13, the pressure in the
crankcase 21 continually changes due to the reciprocal motion of
the piston 36 in the cylinder bore 34 and the blowby gas leaking
from the combustion chamber 35 to the crankcase 21. This pressure
change is alleviated by the breather chamber 63.
[0056] That is to say, at the time of the pressure Increase in the
crankcase 21, as shown by a solid arrow in FIG. 2, the blowby gas
passes from the crankcase 21 through the breather hole 65 into the
breather recess 62 and further through the opening 72 of the gasket
71 into the frontmost compartment 68 in the breather cover 60, and
thereafter, the pulsation of the blowby gas is alleviated, while
moving sequentially towards the rear compartments 69 and 70. Then,
the blowby gas flows through the breather hose 74 through the union
73 of the breather cover 60, finally to the clean side 16b of the
air cleaner 15, and is then drawn into the engine 13 together with
the fresh air (shown by a broken line arrow) taken into the air
cleaner 15.
[0057] Accordingly, unburnt components (HC, CO etc.) harmful to the
environment, which is included in the blowby gas, is not discharged
outside and burnt again in the combustion chamber 35, thus avoiding
the air pollution. When the interior of the crankcase 21 becomes
negative pressure, the fresh air taken into the air cleaner 15
flows backward along the route mentioned above and then flows into
the crankcase 21.
[0058] At the time of the flow-back of the blowby gas in the
crankcase 21 to the air cleaner 15, as described above, the oil
component contained in a large amount in the blowby gas in form of
mist flows down from the oil return path 64 and returns to the oil
pan 28, while being mostly vapor-liquid separated in the breather
chamber 63 (breather recess 62 and compartments 68, 69 and 70). The
vapor-liquid separation effect will be increased, as the capacity
of the breather chamber 63 increases.
[0059] Since the bottom surface of the breather recess 62 is
inclined forward to form the oil return path 64 in the vicinity or
the front end thereof, the oil component flowing down to the bottom
surface of the breather recess 62 returns to the oil pan 28 quickly
without staying in the breather chamber 63. Accordingly, the oil
component hardly flows into the breather hose 74, and even if the
oil component flows into the breather hose 74, since the breather
hose 74 is arranged substantially perpendicularly, the oil
component is separated during the upward movement in the breather
hose 74 and then flows downward along the inner wall of the
breather hose 74. As a result, there is no possibility that the oil
component flows into the air cleaner 15.
[0060] In the engine 13 of the structure mentioned above, the
breather cover 60 is arranged independently from the upper case 25
of the crankcase, so that the breather cover 60 is formed of a
light material such as resin, magnesium or the like, which is
particularly lighter than the aluminum material forming the upper
case 25, and the height dimension H (see FIG. 3) of the breather
cover 60 can be increased, regardless of the shape of the upper
case 25, thus ensuring sufficiently large capacity of the breather
chamber 63. If the breather cover 60 becomes light, even if the
breather cover 60 is made large, the engine 13 can be made light,
and hence improvement in the breather performance and light weight
of the engine 13 can be both contemplated.
[0061] Moreover, since the breather cover 60 is provided
substantially in the intermediate position in the width direction
on the middle case 26, the starter motor 61 is installed on the one
side thereof, and the water hose 53 is arranged on the other side
thereof, the breather chamber 63 having a large capacity can be
provided without impairing the layout of the supplementary
machinery around the engine 13.
[0062] In addition, since the breather chamber 63 has a structure
in which the breather cover 60 is disposed on the breather recess
disposed through the gasket 71 on the side of the middle case 26,
and the interior of the breather cover 60 is divided by the
partition walls 66 and 67 so as to form a plurality of compartments
68, 69 and 70, the interior of the breather chamber 63 is formed as
a complicated labyrinth. Moreover, since the extension of the
breather hose 74 (union 73) and the oil return path 64 are located
in the uppermost portion and the lowermost portion of the breather
chamber 63, respectively, the vapor-liquid separability of the oil
component from the blowby gas in the crankcase 21 becomes
excellent, thus achieving an improved breather performance in these
viewpoints.
[0063] Furthermore, since the breather hose 74 extending from the
rear upper portion of the breather cover 60 passes between the fuel
pump 18 and a fuel feed pipe 76 of the fuel injection system 14
located in front or the fuel pump 18 so as to be connected to the
air cleaner 15, the breather hose 74 is arranged substantially
perpendicularly, thus improving the vapor-liquid separability of
the oil component from the blowby gas in the breather hose 74 and
achieving the improved breather performance.
[0064] On the other hand, since the mating portion E between the
middle case 26 and the breather cover 60 is formed to be parallel
to the mating Portion A between the middle case 26 and the upper
case 25 so as to provide the same height level, both the mating
portions A and E can be made flat at the same time of producing the
middle case 26. Accordingly, the middle case 26 can be easily
produced, contributing to reduction in the production cost of the
engine 13.
[0065] It is to be noted that the present invention is not limited
to the described embodiment and many other changes and
modifications may be made without departing from the scopes of the
appended claims.
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