Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: Valve System for Engine
FIELD OF THE INVENTION
The present invention relates to a valve system
for an engine, in which a valve stem for an engine valve
is slidably fitted in a guide cylinder provided in a
cylinder head, and a rocker arm rockable in interlocking
with rotation of a cam shaft is interlocked with the
valve stem.
BACKGROUND OF THE INVENTION
Valve systems of this type have been known, for
example, from Japanese Patent Laid-.open No. Sho 56-27009
and Japanese Patent Publication No. Hei 1-20290.
In the above-described related art valve
system, an upper end of a valve stem is pressed down by a
threaded tappet screwed in a rocker arm with the
forward/backward position of the tappet screw adjustable.
With this structure, since the threaded tappet is moved
along an circular-arc centered at the fulcrum of the
rocker arm, a bending load is applied to the valve stem,
with a result that there occur local wear, galling, and
the like in the guide cylinder provided in the cylinder
head in such a manner as to guide the valve stem.
In view of the foregoing, the present invention
has been made, and an object of the present invention is
to provide a valve system for an engine, which is capable
of preventing occurrence of local wear, galling, and the
like of a guide cylinder, thereby enhancing the
reliability.
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SUMMARY OF THE INVENTION
To achieve the above object, according to an
invention, there is provided a valve system for an
engine, in which a valve stem for an engine valve is
slidably fitted in a guide cylinder provided in a
cylinder head and a rocker arm rockable in interlocking
with rotation of a cam shaft is interlocked with the
valve stem, characterized in that a lifter is interposed
between the rocker arm and the valve stem, the lifter
being formed into a cylindrical shape with its bottom
closed and having a diameter larger than an outside
diameter of the valve stem; the lifter is fitted in a
lifter housing in such a manner as to be slidable in the
axial direction of the valve stem; and the lifter housing
is fixed to the cylinder head.
With this configuration, since a drive force
from the rocker arm is applied to the valve stem for an
engine valve via the lifter having a cylindrical shape
with its bottom closed, a bending load is not applied to
the valve stem having a relatively small diameter, so
that it is possible to prevent the occurrence of local
wear, galling, and the like in the guide cylinder.
Further, since the lifter has a relatively large
diameter, even if a bending load is applied from the
rocker arm to the lifter, it is possible to minimize the
occurrence of local wear, galling, and the like between
the lifter housing and the lifter, and hence to improve
the reliability.
According to an invention, in addition to the
configuration of the invention, the lifter housing is
formed into such a cylindrical shape as to allow the
lifter to be slidably fitted therein; and the lifter
housing has an oiling hole opened in an inner surface of
the lifter housing. With this configuration, since the
lifter can be more smoothly slid in the lifter housing,
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it is possible to more certainly prevent the occurrence
of local wear, galling, and the like between the lifter
housing and the lifter.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are
shown in the drawings, wherein:
FIG. 1 is a vertical sectional rear view of an
engine.
FIG. 2 is an enlarged sectional view taken on
line 2-2 of FIG. 1.
FIG. 3 is an enlarged sectional view taken on
line 3-3 of FIG. 2.
FIG. 4 is an enlarged sectional view taken on
line 4-4 of FIG. 2.
FIG. 5 is a sectional view taken on line 5-5 of
FIG. 1 showing a cylinder head.
FIG. 6 is a sectional view taken on line 6-6 of
FIG. 5 showing the cylinder head in a state in which a
head cover is removed.
FIG. 7 is a view seen along an arrow 7 of FIG.
6.
FIG. 8 is a sectional view taken on line 8-8 of
FIG. 7.
FIG. 9 is a sectional view taken on line 9-9 of
FIG. 1.
FIG. 10 is an exploded perspective view of a
structure for connecting a pull rod to a cam follower.
FIG. 11 is an exploded perspective view,
corresponding to FIG. 10, showing another embodiment of
the present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present
invention will be described with reference to the
accompanying drawings.
FIGS. 1 to 10 show one embodiment in which the
present invention is applied to a four-cycle horizontal
opposed type two-cylinder engine, wherein FIG. 1 is a
vertical sectional rear view of the engine; FIG. 2 is an
enlarged sectional view taken on line 2-2 of FIG. 1; FIG.
3 is an enlarged sectional view taken on line 3-3 of FIG.
2; FIG. 4 is an enlarged sectional view taken on line 4-4
of FIG. 2; FIG. 5 is a sectional view taken on line 5-5
of FIG. 1 showing a cylinder head; FIG. 6 is a sectional
view taken on line 6-6 of FIG. 5 showing the cylinder
head in a state in which a head cover is removed; FIG. 7
is a view seen along an arrow 7 of FIG. 6; FIG. 8 is a
sectional view taken on line 8-8 of FIG. 7; FIG. 9 is a
sectional view taken on line 9-9 of FIG. 1; and FIG. 10
is an exploded perspective view of a structure for
connecting a pull rod to a cam follower.
Referring first to FIG. 1, there is shown a
four-cycle horizontal opposed type engine E to be mounted
on automobiles, motorcycles, aircraft, and the like. A
main body 11 of the engine E includes a left engine block
12L disposed on the left side as seen from the rear side
of the engine E and a right engine block 12R disposed on
the right side as seen from the rear side of the engine
E.
The left engine block 12L includes a left
cylinder block 13L, a left crank case 14L formed
integrally with the left cylinder block 13L, and a left
cylinder head 15L connected to the side, opposite to the
left crank case 14L, of the left cylinder block 13L.
Similarly, the right engine block 12R includes a right
cylinder block 13R, a right crank case 14R formed
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integrally with the right cylinder block 13R, and a right
cylinder head 15R connected to the side, opposite to the
right crank case 14R, of the right cylinder block 13R.
The cylinder block 13L (or 13R) has a cylinder
bore 16L (or 16R). A piston 18L (or 18R) is slidably
fitted in the cylinder bore 16L (or 16R) in such a manner
as to form a combustion chamber 17L (or 17R) between the
cylinder bore 16L (or 16R) and the cylinder head 15L (or
15R).
Both the engine blocks 12L and 12R are
oppositely disposed with axial lines of the cylinder
bores 16L and 16R kept substantially in the horizontal
direction. The left and right crank cases 14L and 14R
are fastened to each other to form a crank case 19 in
cooperation with each other. A crank shaft 21 connected
to the pistons 18L and 18R via connecting rods 20L and
20R is rotatably supported between the left and right
crank cases 14L and 14R.
Referring to FIG. 2, the crank case 19 is
provided with a front journal wall 22F, an intermediate
journal wall 22M, and a rear journal wall 22R, which are
spaced from each other in the longitudinal direction.
Three portions, spaced from each other in the axial
direction, of the crank shaft 21 are rotatably supported
by these journal walls 22F, 22M and 22R. The crank shaft
21 is housed in a crank chamber 24 formed in the crank
case 19, and a partition wall 25 defining the bottom of
the crank chamber 24 is provided on the inner wall of the
crank case 19.
A rear end portion (left end portion in FIG. 2)
of the crank shaft 21 projects rearwardly from the rear
journal wall 22R. A rotor 27 of a generator 26 is
coaxially connected to the rear end portion of the crank
shaft 21, and a stator 28 of the generator 26 is disposed
behind the rear journal wall 22R and is fixedly supported
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by a supporting plate 29 fixed to the crank case 19. A
cover 30 for covering the generator 26 is fastened to a
rear portion of the crank case 19.
A drive gear 31 is fixed to the crank shaft 21
at a position between the rear journal wall 22R and the
supporting plate 29. A rotating shaft 33, to which a
first intermediate gear 32 meshing with the drive gear
31, is rotatably supported by the rear journal wall 22R
and the supporting plate 29. A second intermediate gear
34, which is integrally provided on the rotating shaft
33, meshes with a gear 35 provided on a cam shaft 36.
The cam shaft 36 having an axial line parallel to the
crank shaft 21 is rotatably supported by the crank case
19 at a position under the partition wall 25.
In this way, a power is transmitted from the
crank shaft 21 to the cam shaft 36, at a reduction ratio
of 1/2, via the drive gear 31, first intermediate gear
32, second intermediate gear 34, and gear 35.
A water pump 37 is mounted to the cover 30. A
pump shaft 38 of the water pump 37 is coaxially connected
to the rotating shaft 33 in such a manner as not to be
rotated relative to the rotating shaft 33, whereby a
rotational power is transmitted from the crank shaft 21
to the water pump 37.
Referring to FIGS. 3 and 4, an oil pan 42 is
connected to a lower portion of the crank case 19 in such
a manner as to form an oil reservoir chamber 43 under the
cam shaft 36. An oil pump 44 configured as a trochoide
pump is housed in the oil pan 42.
A pump housing 45 of the oil pump 44 is formed
by connecting a pair of housing halves 46 and 47 to each
other. A drive shaft 48 having an axial line parallel to
the crank shaft 21 and the cam shaft 36 is rotatably
supported by the housing half 46. The drive shaft 48 is
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connected to a rotor 49 disposed between both the housing
halves 46 and 47.
A partition wall 46a is integrally provided on
the housing half 46, whereby a power transmission chamber
50 partitioned from the oil reservoir chamber 43 formed
in the oil pan 42 is formed between the partition wall
46a and a side wall of the oil pan 42. A gear 51 meshing
with the gear 35 of the cam shaft 36 rotated by a power
transmitted from the crank shaft 21 is fixed to an end
portion, on the power transmission chamber 50 side, of
the drive shaft 48. In this way, a rotational power is
transmitted from the crank shaft 21 to the oil pump 44.
The partition wall 46a has an approximately U-
shaped transverse cross-section opened upwardly. The
upper end of the partition wall 46a is located at a
position higher than an oil level L of oil reserved in
the oil reservoir chamber 43, so that oil does not flow
from the oil reservoir chamber 43 side to the power
transmission chamber 50 side. On the other hand,
although oil flows from the crank chamber 24 side into
the power transmission chamber 50 via a gear train
disposed in the power transmission route from the crank
shaft 21 to the gear 51, the oil in the power
transmission chamber 50 is splashed to the oil reservoir
chamber 43 side across the upper end of the partition
wall 46a by rotation of the gear 51.
A pair of boss-like mounting portions 52 are
integrally provided on a portion, corresponding to the
housing half 46, of the bottom of the oil pan 42 in such
a manner as to project therefrom. The housing half 46 is
removably mounted on the mounting portions 52 with bolts
53. Similarly, a pair of boss-like mounting portions 52
are integrally provided on a portion, corresponding to
the housing half 47, of the bottom of the oil pan 42 in
such a manner as to project therefrom. The housing half
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47 is removably mounted on the mounting portions 52 with
bolts 53. That is to say, the pump housing 45 is
removably mounted on the mounting portions 52 provided on
the bottom of the oil pan 42.
An inlet 54 is provided in the housing half 46
of the pump housing 45, and an oil strainer 55 connected
to the inlet 54 is fixedly held between the housing half
46 and the oil pan 42. To be more specific, an upper
portion of the oil strainer 55 is inserted from below in
a lower portion of the housing half 46 in such a manner
as to be continuous to the inlet 54, and a lower
peripheral edge of the oil strainer 55 is received on a
receiving portion 56 provided on the bottom of the oil
pan 42.
An outlet 57 is provided in the housing half 47
of the pump housing 45, and a relief valve 58 connected
to the outlet 57 is fixedly held between the housing half
47 and the oil pan 42 while being kept in a posture
parallel to that of the oil strainer 55. To be more
specific, an upper portion of the relief valve 58 is
inserted from below in a lower portion of the housing
half 47 in such a manner as to be continuous to the
outlet 57, and a lower end of the relief valve 58 is
received by a raised portion 59 provided on the bottom of
the oil pan 42.
An oil passage 61 communicated to the outlet 57
is provided in the housing half 47. An oil passage 62
communicated to the oil passage 61 is provided in the
lower portion of the oil pan 42 when the pump housing 45
is mounted to the oil pan 42. An oil filter 63 connected
to the oil passage 62 is removably mounted to an outer
surface of a side wall of the oil pan 42. An oil passage
64 for leading oil cleaned through the oil filter 63 is
provided in both the oil pan 42 and the crank case 19,
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which passage is communicated to a main gallery 65
provided in the crank case 19.
A front portion of the crank shaft 21 is formed
into a cylindrical hollow shape for reducing the weight
of the crank shaft 21. A cylindrical spacer 66, having
an annular chamber 67 formed between the inner surface of
the crank shaft 21 and the outer surface of the spacer
66, is fitted in the cylindrical hollow portion of the
crank shaft 21. The annular chamber 67 extends at least
between portions corresponding to the front and
intermediate journal walls 22F and 22M of the crank case
19. Both axial ends of the annular chamber 67 are fluid-
tightly sealed by mounting seal members to both ends of
the spacer 66 or press-fitting both the ends of the
spacer 66 in the crank shaft 21.
An oil passage 68 for supplying oil to a
portion to be lubricated between the intermediate journal
wall 22M and the crank shaft 21 is provided in the crank
case 19 in such a manner as to be communicated to the
main gallery 65. The crank shaft 21 has a passage hole
69 for leading the oil from the portion to be lubricated
between the intermediate journal wall 22M and the crank
shaft 21 to the annular chamber 67, and a passage hole 70
for leading oil from the annular chamber 67 to a portion
to be lubricated between the front journal wall 22F and
the crank shaft 21.
The crank shaft 21 integrally includes a crank
pin 21L connected to the connecting rod 20L on the left
engine block 12L side and a crank pin 21R connected to
the connecting rod 20R on the right engine block 12R
side. An oil passage 71 for leading the oil from the
annular chamber 67 to a portion to be lubricated between
the connecting rod 20L and the crank pin 21L is provided
in the crank shaft 21. Oil is supplied from the main
gallery 65 to a portion to be lubricated between the rear
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journal wall 22R and the crank shaft 21. An oil passage
72 for leading the oil from the portion to be lubricated
between the rear journal wall 22R and the crank shaft 21
to a portion to be lubricated between the connecting rod
20R and the crank pin 21R is provided in the crank shaft
21.
By the way, in order to lead oil to the portion
to be lubricated between the connecting rod 20L and the
crank pin 21L, the entire cylindrical hollow portion of
the crank shaft 21 can be used as an oil passage;
however, in this case, since the volume of the oil
passage becomes excessively large, there may occur
inconveniences that a hydraulic pressure rising time upon
start-up of the engine E be retarded and a residual
amount of oil upon oil exchange be increased. From this
viewpoint, according to this embodiment, since the
annular chamber 67 formed between the cylindrical hollow
portion of the crank shaft 21 and the spacer 66 is, as
described above, used as the oil passage, the passage
volume can be set to a suitable value, to prevent the
retardation of the hydraulic pressure rising time and to
prevent the increase in residual amount of oil upon oil
exchange. Also, since the inside diameter of the
cylindrical hollow portion of the crank shaft 21 can be
set to a relatively large value without increasing the
passage volume, it is not required to increase the
accuracies of penetrating depths of the passage holes 69
and 70. Further, by making the spacer 66 from a material
lighter in weight than that of the crank shaft 21, the
entire crank shaft 21 can be made lighter in weight.
The oil, which has lubricated the portion to be
lubricated between the connecting rod 20L and the crank
pin 21L and the portion to be lubricated between the
connecting rod 20R and the crank pin 21R, is dropped in
the crank chamber 24 and is once accumulated on the
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partition wall 25. Oil through-holes 73 for leading the
oil accumulated on the partition wall 25 to portions of
the crank case 19 for supporting both ends of the cam
shaft 36 are provided in the partition wall 25. As a
result, the oil is supplied even to portions to be
lubricated between the cam shaft 36 and the crank case
19.
Referring to FIGS. 5 and 6, a pair of intake
valve ports 76 and a pair of exhaust valve ports 77 are
provided in the cylinder head 15R of the right engine
block 12R in such a manner as to be positioned on both
sides of a first virtual plane 78 containing the axial
line of the cylinder bore 16R and passing through the
center of the combustion chamber 17R, and to face to the
combustion chamber 17R. The first virtual plane 78
crosses an axial line C of the crank shaft 21 at an angle
a on the projection plane perpendicular to the axial line
of the cylinder bore 16R (parallel to the paper plane of
FIG. 5).
Referring to FIGS. 7 and 8, a pair of ignition
plugs 80 are mounted in the cylinder head 15R in such a
manner that the end portions thereof project in the
combustion chamber 17R, and that the axial lines thereof
pass through the center of the combustion chamber 17R and
are disposed on the first virtual plane 78.
Both the ignition plugs 80 are disposed
symmetrically with respect to the second virtual plane 79
perpendicular to the first virtual plane 78, and are
mounted in the cylinder head 15R in such a manner as to
be tilted with a distance therebetween becoming smaller
toward the combustion chamber 17R. The end portions,
projecting in the combustion chamber 17R, of both the
ignition plugs 80 are disposed in a region surrounded by
both the intake valve ports 76 and both the exhaust valve
ports 77.
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Both the ignition plugs 80 are connected to an
ignition circuit (not shown) and are usually operated in
synchronization with each other by the ignition circuit.
Inner ends of plug insertion cylinders 81 in
which the ignition plugs 80 are to be inserted are
fixedly fitted in the cylinder head 15R, and outer ends
of the plug insertion cylinders 81 are located in opening
portions 83 formed in a head cover 82R fastened to the
cylinder head 15R. Spaces between the outer ends of the
plug insertion cylinders 81 and the head cover 82R are
sealed.
A single intake port 84 commonly communicated
to both the intake valve ports 76 and having its axial
line disposed on the second virtual plane 79 is provided
in the cylinder head 15R in such a manner as to be opened
in an upper side surface of the cylinder head 15R. A
single exhaust port 85 commonly communicated to both the
exhaust valve ports 77 and having its axial line disposed
on the second virtual plane 79 is provided in the
cylinder head 15R in such a manner as to be opened in a
lower side surface of the cylinder head 15R.
An intake pipe 74 is connected to the upper
side surface of the cylinder head 15R in such a manner as
to be communicated to the intake port 84, and a fuel
injection valve 75R is additionally provided in the
intake pipe 74R.
Each of the intake valve ports 76 is
openable/closable by an intake valve VI as an engine
valve. A valve stem 86 of the intake valve VI is
slidably fitted in a guide cylinder 87 provided in the
cylinder head 15R. The intake valve VI is elastically
biased in the valve closing direction by a valve spring
89 provided between the cylinder head 15R and a retainer
88 fixed to an end, projecting from the guide cylinder
87, of the valve stem 86.
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Each of the exhaust valve ports 77 is
openable/closable by an exhaust valve VE as an engine
valve. A valve stem 90 of the exhaust valve VE is
slidably fitted in a guide cylinder 91 provided in the
cylinder head 15R. The exhaust valve VE is elastically
biased in the valve closing direction by a valve spring
93 provided between the cylinder head 15R and a retainer
92 fixed to an end, projecting from the guide cylinder
91, of the valve stem 90.
Like the right cylinder head 15R, the left
cylinder head 15L on the left engine block 12L side is
provided with a pair of intake valves VI and a pair of
exhaust valves VE, and also provided with a pair of
ignition plugs. A head cover 82L is fastened to the
cylinder head 15L, and an intake pipe 74L additionally
provided with a fuel injection valve 75L is connected to
an upper side surface of the cylinder head 15L.
The pair of the intake valves VI and the pair
of the exhaust valves VE disposed in the right cylinder
head 15R are opened/closed by a valve system 94R, and the
pair of the intake valves VI and the pair of the exhaust
valves VE disposed in the left cylinder head 15L are
opened/closed by a valve system 94L. The configuration
of the valve system 94R is the same as that of the valve
system 94L, and therefore, only the configuration of the
valve system 94R on the right cylinder head 15R side will
be hereinafter described.
The valve system 94R includes a holder 97 which
integrally includes cylindrical lifter housings 95
coaxial with valve stems 86 of both the intake valves VI
and cylindrical lifter housings 96 coaxial with valve
stems 90 of both the exhaust valves VE and which is
fastened to the cylinder head 15R; an intake side rocker
shaft 98 and an exhaust side rocker shaft 99, which have
axial lines parallel to each other and which are fixedly
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supported by the holder 97; an intake side rocker arm 100
rockably supported by the intake side rocker shaft 98 and
an exhaust side rocker arm 101 rockably supported by the
exhaust side rocker shaft 99; lifters 102 slidably fitted
in the lifter housings 96 in such a manner as to be
interposed between the intake rocker arm 100 and both the
intake valves VI and lifters 103 slidably fitted in the
lifter housings 97 in such a manner as to be interposed
between the exhaust side rocker arm 101 and both the
exhaust valves VE; the cam shaft 36 interlocked with the
crank shaft 21 at a reduction ratio of 1/2; and a push
rod 104 for imparting a valve opening force to the intake
side rocker arm 100 according to the rotation of the cam
shaft 36, and a pull rod 105 for imparting a valve
opening force to the exhaust side rocker arm 101
according to the rotation of the cam shaft 36.
The intake side and exhaust side rocker shafts
98 and 99 are mounted to the cylinder head 15 in such a
manner as to be disposed on both sides of the pair of
ignition plugs 80. To be more specific, the intake side
rocker shaft 98 is disposed between the pair of the
intake valves VI, that is, the lifter housings 95 and
both the ignition plugs 80, and the exhaust side rocker
shaft 99 is disposed between the pair of exhaust valves
VE, that is, the lifter housings 96 and both the ignition
plugs 80. On the projection plane perpendicular to the
axial line of the cylinder bore 16R (parallel to the
paper plane of FIG. 7), postures of both the rocker
shafts 98 and 99 are set such that axial lines thereof
extend in parallel to the first virtual planes 78 on both
sides of the first virtual plane 78 while crossing the
axial line C of the crank shaft 21.
The lifter 102 (or 103) is formed into a
cylindrical shape with its bottom closed, which has. a
diameter larger than an outside diameter of the valve
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stem 86 of the intake valve VI (or the valve stem 90 of
the exhaust valve VE). The lifter 102 (or 103) is
slidably fitted in the lifter housing 95 (or 96) with the
closed end thereof directed to the rocker arm 101 (or
102) side. The closed end of the lifter 102 (or 103) has
a plurality of through-holes 106 (or 107) arranged along
a circular line for reducing the weight of the lifter 102
(or 103).
A pair of drive arms 100a and 100b extending to
the lifters 102 are integrally provided on the intake
side rocker arm 100. The leading ends of the drive arms
100a and 100b are in contact with the outer surfaces of
the closed ends of the lifters 102 in order to impart
drive forces for pressing the intake valves VI in the
valve opening direction to the valve stems 86 of the
intake valves VI via the lifters 102.
A pair of drive arms 100a and 100b extending to
the lifters 103 are integrally provided on the exhaust
side rocker arm 101. The leading ends of the drive arms
101a and 101b are in contact with the outer surfaces of
the closed ends of the lifters 103 in order to impart
drive forces for pressing the exhaust valves VE in the
valve opening direction to the valve stems 90 of the
exhaust valves VE via the lifters 103.
By the way, according to this embodiment, to
adjust a tappet clearance, as shown in FIG. 6, a shim 121
is held between the valve stem 86 and the lifter 102 and
a shim 122 is held between the valve stem 90 and the
lifter 103. In place of the shim 121 (or 122), a tappet
screw screwed in the leading end of the drive arm 100a
(or 100b, 101a, or 101b) in such a manner as to be
adjustable in its forward or backward movement position
may be brought into contact with the lifter 102 (or 103).
An oil passage 108 to which the oil is lead
from the oil pump 44 is provided in both the cylinder
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head 15R and the holder 97 connected to the cylinder head
15R. An oiling hole 109, which is communicated to the
oil passage 108 and to annular recesses 110 and 111
provided in inner surfaces of the lifter housings 95 and
96, is provided in the holder 97 and in the lifter
housings 95 and 96.
Referring to FIG. 9, the cam shaft 36 disposed
under the crank shaft 21 is provided with an intake side
cam 112R corresponding to the intake valves VI on the
right engine block 12R side, an intake side cam 112L
corresponding to the intake valves VI on the left engine
block 12L side, an exhaust side cam 113R corresponding to
the exhaust valves VE on the right engine block 12R side,
and an exhaust side cam 113L corresponding to the exhaust
valves VE on the left engine block 12L side.
Cam followers 114R and 114L following the
intake side cams 112R and 112L and cam followers 115R and
115L following the exhaust side cams 113R and 113L are
rockably supported by the crank case 19. The cam
followers 114R and 115L are disposed on the right engine
block 12R side with respect to the cam shaft 36, and are
rockably supported by a common supporting shaft 118
mounted to the crank case 19. The cam followers 114L and
115R are disposed on the left engine block 12L side with
respect to the cam shaft 36 and are rockably supported by
a common supporting shaft 119 mounted to the crank case
19.
Referring to FIG. 7, input arms 100c and 101c
extending, on the projection plane perpendicular to the
axial line of the cylinder bore 16R, from the intake side
rocker arm 100 and the exhaust side rocker arm 101 to the
cam shaft 36 side (lower side of FIG. 7), are provided on
the rocker arms 100 and 101, respectively. The input arm
100c of the intake side rocker arm 100 is connected to
the cam follower 114R by means of a push rod 104, and the
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input arm 101c of the exhaust side rocker arm 101 is
connected to the cam follower 115R by means of the pull
rod 105. The push rod 104 acts, upon movement thereof in
the direction opposite to the cam shaft 36, to push up
the input arm 100c for rocking the intake side rocker arm
100 in the valve opening direction. The pull rod 105
acts, upon movement thereof on the cam shaft 36 side, to
pull the input arm 101c for rocking the exhaust side
rocker arm 101 in the valve opening direction.
A rod chamber 120 extending from the crank case
19 to both the cylinder heads 15R and 15L is formed under
the engine main body 11. The push rod 104 and the pull
rod 105 are contained and disposed in the rod chamber
120. In addition, since the tensile strength of a
material for forming both the rods 104 and 105 is higher
than the compression strength thereof, the diameter of
the pull rod 105 is set to be smaller than that of the
push rod 104.
Spherical portions 104a and 104b are provided
on both ends of the push rod 104. The spherical portion
104a at one end of the push rod 104 is swingably received
on the cam follower 114R, and the spherical portion 104b
at the other end of the push rod 104 is swingably
received on the leading end of the input arm 100c
provided on the intake side rocker arm 100.
As shown in FIG. 10, an approximately U-shaped
fork 116 opened to the side opposite to the cam shaft 36
is integrally provided on the cam follower 115R, and a
pin 123 fixed in one end of the pull rod 105 by press-
fitting or the like is engaged with the fork 116.
Further, an approximately U-shaped fork 117 opened on the
side opposite to the cam shaft 36 is integrally provided
on the leading end of the input arm 101c provided on the
exhaust side rocker arm 101, and a pin 124 fixed in the
other end of the pull rod 105 is engaged with the fork
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117. With this configuration, since both the ends of the
pull rod 105 can be connected to the input arm 101c
provided on the exhaust side rocker arm 101 and the cam
follower 115R only by engaging both the ends of the pull
rod 105 with the forks 116 and 117, one end of the pull
rod 105 can be connected to the cam follower 115R from
the cylinder head 15R side without disassembly of the oil
pan 42, with a result that the workability upon
maintenance work can be improved.
The function of this embodiment will be
described below. Since the pump housing 45 of the oil
pump 44 for supplying lubricating oil to various portions
of the engine E is removably mounted on the mounting
portions 52 provided on the bottom of the oil pan 42
connected to the lower portion of the crank case 19, it
is possible to set the oil pump 44 at a relatively low
position in the engine E, and hence to lower the center
of gravity of the engine E and to improve the suction
efficiency and maintenance performance of the oil pump
44.
Since the oil strainer 55 connected to the
inlet 54 of the oil pump 44 is fixedly held between the
oil pan 42 and the pump housing 45, it is possible to fix
the oil strainer 55 between the oil pan 42 and the pump
housing 45 without use of parts specialized for fixture
thereof such as bolts, and hence to reduce the number of
parts and the number of assembling steps. Further, since
an oil suction passage between the inlet 54 of the oil
pump 44 and the oil strainer 55 can be shortened, the
pumping loss of the oil pump 44 can be reduced.
Since the relief valve 58 connected to the
outlet 57 of the oil pump 44 is fixedly held between the
oil pan 42 and the pump housing 45 while being kept in a
posture parallel to that of the oil strainer 55, the
relief valve 58 can be disposed by making effective use
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of a space which is formed on a side of the oil strainer
55 by holding the oil strainer 55 between the pump
housing 45 and the oil pan 42. Also, since the relief
valve is directly connected to the pump housing 45 of the
oil pump 44, it is possible to shorten and simplify the
oil discharge passage composed of the oil passages 61 and
62 extending from the oil filter 63 mounted on the outer
surface of the side wall of the oil pan 42 to the oil
pump 44. Further, since a relief port of the relief
valve 58 can be easily set in oil in the oil pan 42, it
is possible to prevent the oil from being bubbled.
By the way, the partition wall 46a forming the
power transmission chamber 50, which is partitioned from
the oil reservoir chamber 43 formed in the oil pan 42,
between the side wall of the oil pan 42 and the partition
wall 46a, is formed on the housing half 46 constituting
part of the pump housing 45, and the gear 51 rotated by a
power transmitted from the crank shaft 21 is fixed to the
end portion, on the power transmission chamber 50 side,
of the drive shaft 48 rotatably supported by the pump
housing 45. Accordingly, since the gear 51 rotated for
transmitting a power from the crank shaft 21 to the drive
shaft 48 does not agitate the oil reserved in the oil
reservoir chamber 43 in the oil pan 42, it is possible to
prevent the occurrence of friction loss and oil mist due
to agitation of the oil.
The lifter 102 (or 103) formed into a
cylindrical shape with its bottom closed, which has a
diameter larger than that of the valve stem 86 (or 90) is
interposed between the valve stem 86 of the intake valve
VI (or the valve stem 90 of the exhaust valve VE) and the
intake side rocker arm 100 (or exhaust side rocker arm
101) rocked in interlocking with the rotation of the cam
shaft 36; and the lifter 102 (or 103) is slidably fitted
in the cylindrical lifter housing 95 (or 96) which is
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integrally provided on the holder 97 fixed to the
cylinder heads 15R and 15L and which is coaxial with the
valve stem 86 (or 90).
With this configuration, a drive force from the
intake side rocker arm 100 (or the exhaust side rocker
arm 101) is applied to the valve stem 86 of the intake
valve VI (or the valve stem 90 of the exhaust valve VE)
via the lifter 102 (or 103), so that a bending load is
not applied to the valve stem 86 (or 90) having a
relatively small diameter. As a result, it is possible
to prevent the occurrence of partial wear, galling, and
the like in the guide cylinder 87 (or 91). Further,
since the lifter 102 (or 103) has a relatively large
diameter, even if a bending load is applied from the
intake side rocker arm 100 (or exhaust side rocker arm
101), it is possible to minimize the occurrence of
partial wear, galling, and the like between the lifter
housing 95 (or 96) and the lifter 102 (or 103), and hence
to improve the reliability of the valve systems 94R and
94L.
Since the oiling hole 109 opened in the inner
surfaces of the lifter housings 95 and 96 are provided in
the holder 97 and in the lifter housings 95 and 96, it is
possible to make the sliding motion of the lifter 102 (or
103) in the lifter housing 95 (or 96) smoother, and hence
to more certainly prevent the occurrence of partial wear,
galling, and the like between the lifter housing 95 (or
96) and the lifter 102 (or 103).
In this case, if a point of the lifter 102 (or
103), to which a drive force is applied from the intake
side rocker arm 100 (or 101), is offset from the center
of the lifter 102 (or 103), the lifter 102 (or 103) can
be rotated around its axial line and correspondingly the
intake valve VI (or exhaust valve VE) can be rotated, to
thereby prevent the occurrence of seize on one side of
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the intake valve VI (or exhaust valve VE). From this
viewpoint, according to this embodiment, the intake valve
VI (or exhaust valve VE) can be easily rotated by
smoothly sliding the lifter 102 (or 103) in the lifter
housing 95 (or 96).
The pair of the intake valve ports 76 and the
pair of the exhaust valve ports 77 are provided in the
cylinder head 15R (or 15L) in such a manner as to be
located on both the sides of the first virtual plane 78
containing the axial line of the cylinder bore 16R (or
16L) and passing through an approximately center of the
combustion chamber 17R (17L) and to face to the
combustion chamber 17R (17L); and the pair of the
ignition plugs 80 are mounted in the cylinder head 15R
(or 15L). Both the ignition plugs 80, which are
approximately symmetrical with respect to the second
virtual plane 79 passing through the center of the
combustion chamber 17R (or 17L) and being perpendicular
to the first virtual plane 78, are disposed in the
cylinder head 15R (or 15L) in such a manner that the
axial lines thereof extend substantially along the first
virtual plane 78 and that they are tilted with a distance
therebetween becoming smaller toward the combustion
chamber 17R (or 17L). The ends, projecting in the
combustion chamber 17R (or 17L), of the ignition plugs 80
are disposed in the region surrounded by both the intake
valve ports 76 and both the exhaust valve ports 77.
With this configuration, since the ends,
projecting in the combustion chamber 17R (or 17L), of the
pair of ignition plugs 80 are disposed in proximity to an
approximately central portion in the combustion chamber
17R (or 17L), it is possible to ideally propagate flame
in the combustion chamber 17R (or 17L), and further, even
if there occurs accidental fire in either of both the
ignition plugs 80, since the other ignition plug 80 is
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located at the approximately central portion of the
combustion chamber 17R (or 17L), it is possible to
minimize the deterioration of the flame propagation
condition.
Since both the ignition plugs 80 are disposed,
as seen from the direction perpendicular to the first
virtual plane 78, in an approximately V-shape opened in
the direction opposite to the combustion chamber 17R (or
17L), both the ignition plugs 80 can be easily mounted in
the cylinder head 15R (or 15L) with the ends, projecting
in the combustion chamber 17R (or 17L), of the ignition
plugs 80 allowed to be disposed in proximity to an
approximately central portion of the combustion chamber
17R (or 17L).
Since both the ignition plugs 80 are
collectively disposed in the vicinity of the central
portion of the combustion chamber 17R (or 17L), it is
possible to enhance the degree of freedom of the shape of
a water jacket on the cylinder head 15R (or 15L) side and
the degree of freedom of disposition of fastening bolts
for fastening the cylinder head 15R (or 15L) to the
cylinder block 13R (or 13L), and hence to improve the
sealing performance between the cylinder head 15R (or
15L) and the cylinder block 13R (or 13L) as well as
improve the cooling performance.
The intake side and exhaust side rocker arms
100 and 101 are rockably supported by the intake side and
exhaust side rocker shafts 98 and 99 having the axial
lines extending along the first virtual plane 78, which
plane contains the axial line of the cylinder bore 16R
and passes through the center of the combustion chamber
17R, and which plane crosses the axial line of the crank
shaft 21 at the angle a on the projection plane
perpendicular to the axial line of the cylinder bore 16R;
and the intake side and exhaust side rocker shafts 98 and
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99 are mounted to the cylinder head 15R (or 15L) in such
a manner as to be disposed on both the sides of both the
ignition plugs 80. With this configuration, it is
possible to set the width of the cylinder head 15R (or
15L) at a relatively small value in the direction along
the second virtual plane 79, and hence to contribute to
compactness of the engine E.
The input arm 101c extending, on the projection
plane perpendicular to the axial line of the cylinder
bore 16R (or 16L), from the rocker arm 101 to the cam
shaft 36 side is provided on the exhaust side rocker arm
101, and the pull rod 105 reciprocating in the axial
direction according to the rotation of the cam shaft 36
is connected to the input arm 101c in order to rock the
exhaust side rocker arm 101 in the valve opening
direction when the pull rod 105 is moved to the cam shaft
36 side. With this configuration, it is not required to
enlarge the width of the cylinder head 15R (15L) in the
direction along the axial line of the crank shaft 21 for
disposing the pull rod 105, and hence to reduce the size
and weight of the engine E in the direction along the
axial line of the crank shaft 21.
The input arm 100c extending, on the projection
plane perpendicular to the axial line of the cylinder
bore 16R (or 16L), from the rocker arm 101 to the cam
shaft 36 side is provided on the intake side rocker arm
100, and the push rod 104 reciprocating in the axial
direction according to the rotation of the cam shaft 36
is connected to the input arm 100c in order to rock the
intake side rocker arm 100 in the valve opening direction
when the push rod 104 is moved to the cam shaft 36 side.
According to the configuration in which the
intake and exhaust side rocker shafts 98 and 99 and the
intake side and exhaust side rocker arms 100 and 101 are
disposed as described above and also an opening/closing
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force is imparted to the intake side rocker arm 100 by
the pull rod 105 and an opening/closing force is imparted
to the exhaust side rocker arm 101 by the push rod 104,
the space in the simulator 15R (or 15L), which space is
necessary for disposing the rocker shafts 98 and 99 and
the rocker arms 100 and 101 constituting parts of the
valve system 94R (or 94L) can be made small in the
direction along the axial line of the crank shaft 21.
Further, it is not required to enlarge the
width of the cylinder head 15R (or 15L) in the direction
along the axial line of the crank shaft 21 for disposing
the pull rod 105 and the push rod 104, so that a drive
system between the cam shaft 36 and both the rocker arms
100 and 101 can be disposed in good balance. This makes
it possible to reduce the size and weight of the engine E
in the direction along the axial line of the crank shaft
21.
Since the pair of the intake valves VI and the
pair of the exhaust valves VE are disposed in the
cylinder head 15R (or 15L) in such a manner as to face
the combustion chamber 17R (or 17L), it is possible to
improve the suction efficiency and thereby increase the
output torque in a low speed rotational range of the
engine E.
FIG. 11 shows another embodiment of the present
invention. A spherical portion 105a is provided at one
end of a pull rod 105, and an engagement portion 126
formed into a bowl shape having a slit 127 allowing the
insertion of the pull rod 105 is provided on a cam
follower 115R to be connected to the one end of the pull
rod 105. The one end of the pull rod 105 is connected to
the cam follower 115R by engaging the spherical portion
105a with the engagement portion 126.
Even in this embodiment, since the one end of
the pull rod 105 can be connected to the cam follower
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115R from the cylinder head 15R side without disassembly of
the oil pan 42, it is possible to improve the workability
upon maintenance work.
While the preferred embodiments have been
described as described above, the present invention is not
limited thereto, and it is to be understood that various
changes in design may be made without departing from the
scope of the claims.
For example, the present invention can be widely
applied to engines other than the horizontal opposed type
two-cylinder engine.
As described above, according to the invention, it
is possible to prevent the occurrence of local wear,
galling, and the like in the guide cylinder, and also to
minimize the occurrence of local wear, galling, and the like
between the lifter housing and the lifter and hence to
improve the reliability.
According to the preferred embodiment where the
lifter housing has a cylindrical shape and slidably receives
the lifter in the housing, it is possible to reduce the
occurrence of local wear, galling, and the like between the
lifter housing and the lifter.
Although various preferred embodiments of the
present invention have been described herein in detail, it
will be appreciated by those skilled in the art, that
variations may be made thereto without departing from the
spirit of the invention or the scope of the appended claims.
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