Title: Internal combustion engine
Abstract: A multicylinder internal combustion engine has a valve chamber containing a valve train for opening and closing intake valves and exhaust valves, and decompression mechanisms. First, second and third cylinders are arranged in a row parallel to an axial direction parallel to the axis of a camshaft. An exhaust cam for opening and closing the exhaust valve, which is opened and closed by the decompression mechanism, for the second cylinder is not coincident with respect to the axial direction with an abutment end of the exhaust valve with which a rocker arm driven by the exhaust cam comes into contact, and is coincident with respect to the axial direction with the decompression mechanism. Thus, a space for placing the decompression mechanism is secured while suppressing increase in the length of the camshaft and in the longitudinal size of the valve chamber. Consequently, the internal combustion engine can be formed in compact construction. Interference between the pump cam and the decompression mechanism can be avoided and increase in the length of the camshaft can be suppressed by disposing the centrifugal weight of the decompression mechanism for the third cylinder at a specific position on the side of the cam lobe of the pump cam as viewed in the axial direction.
Patent Number: 6,868,835 Issued on 03/22/2005 to Tsubouchi
| Inventors:
|
Tsubouchi; Masanori (Wako, JP)
|
| Assignee:
|
Honda Motor Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
702719 |
| Filed:
|
November 6, 2003 |
Foreign Application Priority Data
| Jan 17, 2003[JP] | 2003-010417 |
| Jan 17, 2003[JP] | 2003-010419 |
| Current U.S. Class: |
123/508; 123/182.1; 123/90.6 |
| Intern'l Class: |
F01L 013//08; F01L 001//18; F02F 001//38; F02M 037//04 |
| Field of Search: |
123/508,182.1,196 W,90.31,90.6
|
References Cited [Referenced By]
U.S. Patent Documents
| 2054928 | Sep., 1936 | Church.
| |
| 5816208 | Oct., 1998 | Kimura | 123/182.
|
| 5829414 | Nov., 1998 | Tsunoda et al. | 123/508.
|
| 6082336 | Jul., 2000 | Takahashi et al. | 123/508.
|
| 6374792 | Apr., 2002 | Suzuki et al. | 123/182.
|
| 6386168 | May., 2002 | Suzuki et al. | 123/182.
|
| 6513504 | Feb., 2003 | Ikuma | 123/509.
|
| Foreign Patent Documents |
| 03-003904 | Jan., 1991 | JP.
| |
| 03172513 | Jul., 1991 | JP.
| |
| 06280530 | Oct., 1994 | JP.
| |
| 2000-227064 | Aug., 2000 | JP.
| |
Primary Examiner: Lo; Weilun
Attorney, Agent or Firm: Carrier, Blackman & Associates, P.C., Carrier; Joseph P., Blackman; William D.
Claims
What is claimed is:
1. An internal combustion engine comprising:
three or more cylinders arranged in parallel;
a crankshaft driven for rotation by pistons that reciprocate in the
cylinders;
a camshaft supported for rotation, interlocked with the crankshaft and
extending across all the cylinders;
a valve chamber forming member forming a valve chamber to contain the
camshaft;
a valve train disposed in the valve chamber to open and close intake valves
and exhaust valves; and
decompression mechanisms, respectively for the cylinders, arranged in the
valve chamber to open the intake valves or the exhaust valves during a
compression stroke;
wherein the valve train includes the camshaft, and valve cams formed on the
camshaft for the cylinders to open and close the intake valves and the
exhaust valves through valve-operating members,
a specific one, corresponding to a specific one of the cylinders, among the
valve cams is located at a position not coincident with respect to an
axial direction parallel to the axis of the camshaft with a position where
an abutment portion, in contact with the valve-operating member, of the
intake valve or the exhaust valve is located, and the decompression
mechanism for the specific cylinder is located at a position coincident
with respect to the axial direction with the position of the abutment
portion of the intake valve or the exhaust valve.
2. The internal combustion engine according to claim 1, wherein the
specific cylinder is an intermediate one of the cylinders.
3. The internal combustion engine according to claim 1, wherein the
specific valve cam is offset toward the cylinder adjacent to the specific
cylinder relative to the abutment portion of the intake valve or the
exhaust valve, and a part of the camshaft, extending between the specific
valve cam or the decompression mechanism for the specific cylinder, and
the valve cam or the decompression mechanism for the cylinder adjacent to
the specific cylinder, lacks any bearing for supporting said part of the
camshaft.
4. The internal combustion engine according to claim 1, wherein the
specific cylinder is an intermediate one of the cylinders, a part of the
camshaft, extending between the specific valve cam or the decompression
mechanism for the specific cylinder, and the valve cam or the
decompression mechanism for one of the two cylinders on the opposite sides
of the specific cylinder, lacks a bearing for supporting said part of the
camshaft, and another part of the camshaft, extending between the specific
valve cam or the decompression mechanism for the specific cylinder, and
the valve cam or the decompression mechanism for the other one of the two
cylinders on the opposite sides of the specific cylinder, is supported for
rotation in a camshaft bearing.
5. The internal combustion engine according to claim 1, wherein the valve
cam or the decompression mechanism for the specific cylinder is disposed
adjacently to the valve cam or the decompression mechanism for cylinder
adjacent to the specific cylinder.
6. An internal combustion engine comprising:
cylinders;
a crankshaft driven for rotation by pistons that reciprocate in the
cylinders;
a camshaft supported for rotation, and interlocked with the crankshaft;
a valve chamber forming member forming a valve chamber to contain the
camshaft;
a valve train disposed in the valve chamber to open and close intake valves
and exhaust valves;
decompression mechanisms, respectively for the cylinders, arranged in the
valve chamber to open the intake valves or the exhaust valves during a
compression stroke; and
a fuel pump attached to the valve chamber forming member forming the valve
chamber;
wherein the camshaft is provided with a pump cam having a cam surface with
which a pump-operating member for driving the fuel pump comes into contact
to drive the fuel pump, and one of the decompression mechanisms is
provided with a centrifugal weight supported on the camshaft for turning
and disposed adjacent to the pump cam with respect to an axial direction
parallel to the axis of the camshaft, the centrifugal weight is on a side
of a cam lobe defined by the cam surface of the pump cam as viewed in the
axial direction, and the centrifugal weight turns toward the axis of the
camshaft so as to approach a tip part of the cam lobe of the pump cam as
the rotational speed of the camshaft increases.
7. An internal combustion engine comprising:
cylinders;
a crankshaft driven for rotation by pistons that reciprocate in the
cylinders;
a camshaft supported for rotation, and interlocked with the crankshaft;
a valve chamber forming member forming a valve chamber to contain the
camshaft;
a valve train disposed in the valve chamber to open and close intake valves
and exhaust valves;
decompression mechanisms, respectively for the cylinders, arranged in the
valve chamber to open the intake valves or the exhaust valves during a
compression stroke; and
a fuel pump attached to the valve chamber forming member forming the valve
chamber;
wherein the camshaft is provided with a pump cam having a cam surface with
which a pump-operating member for driving the fuel pump comes into contact
to drive the fuel pump, and one of the decompression mechanisms is
provided with a centrifugal weight supported on the camshaft for radial
movement and positioned adjacent to the pump cam with respect to an axial
direction parallel to the axis of the camshaft, and the centrifugal weight
moves in a range corresponding to the cam surface of the pump cam as
viewed in the axial direction.
8. The internal combustion engine according to claim 1, further including:
a fuel pump attached to the valve chamber forming member forming the valve
chamber;
wherein the camshaft is provided with a pump cam having a cam surface with
which a pump-operating member for driving the fuel pump comes into contact
to drive the fuel pump, and one of the decompression mechanisms is
provided with a centrifugal weight supported on the camshaft for turning
and disposed adjacent to the pump cam with respect to an axial direction
parallel to the axis of the camshaft, the centrifugal weight is on a side
of a cam lobe defined by the cam surface of the pump cam as viewed in the
axial direction, and the centrifugal weight turns toward the axis of the
camshaft so as to approach a tip part of the cam lobe of the pump cam as
the rotational speed of the camshaft increases.
9. The internal combustion engine according to claim 1, further including:
a fuel pump attached to the valve chamber forming member forming the valve
chamber;
wherein the camshaft is provided with a pump cam having a cam surface with
which a pump-operating member for driving the fuel pump comes into contact
to drive the fuel pump, and one of the decompression mechanisms is
provided with a centrifugal weight supported on the camshaft for turning
and disposed adjacent to the pump cam with respect to an axial direction
parallel to the axis of the camshaft, and the centrifugal weight moves in
a range corresponding to the cam surface of the pump cam as viewed in the
axial direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal combustion engine provided
with a decompression mechanism incorporated into a camshaft included in a
valve train and disposed in a valve chamber. The internal combustion is
intended for use as, for example, an outboard engine.
2. Description of the Related Art
A multicylinder internal combustion engine intended for use as an outboard
engine disclosed in, for example, JP2000-227064A (FIGS. 4 and 5) is a
two-cylinder internal engine provided with a decompression mechanism to
facilitate an engine starting operation. This two-cylinder internal
combustion engine is provided with a camshaft disposed in a cam chamber
defined by a cylinder head and a cylinder head cover, intake and exhaust
cams formed on the camshaft to operate intake valves and exhaust valves,
rocker arms driven for a rocking motion by the intake and exhaust cams, a
decompression lever mounted on the camshaft so as to be turnable in a
vertical plane under the exhaust cams, and a fuel pump. In this internal
combustion engine, the exhaust cam in contact with the contact part of the
rocker arm, and the end of the stem of an exhaust valve in contact with
the pushing part of the rocker arm are at the same position with respect
to a direction parallel to the axis of the camshaft, and hence the rocker
arm extends perpendicularly to the axis of the camshaft. The decompression
lever has an upper part provided with a decompression cam, and a lower
part provided on its opposite sides with weights. The weights are moved
radially outward by centrifugal force as the engine speed increases.
A multicylinder internal combustion engine, intended for use as an outboard
engine, disclosed in JP3-3904A is a three-cylinder internal combustion
engine provided with a camshaft supported in four camshaft bearings on a
cylinder head forming a valve chamber, and cams formed on the camshaft to
rock rocker arms (hereinafter referred to as "valve cams"). In this
multicylinder internal combustion engine, the valve cam in contact with
the contact part of the rocker arm, and the end of the stem of an intake
or exhaust valve in contact with the pushing part of the rocker arm are at
the same position with respect to a direction parallel to the axis of the
camshaft, and hence the rocker arm extends perpendicularly to the axis of
the camshaft. This known three-cylinder internal combustion engine has the
camshaft, the valve cams, and a fuel pump driven by a driven rod driven
for axial movement by an eccentric cam formed on the camshaft. The fuel
pump is attached to a side surface of the cylinder head.
It is difficult to secure an axial space for mounting a decompression lever
mentioned in JP3-3904A on the camshaft extending across the three
cylinders of the internal combustion engine disclosed in JP3-3904A.
Consequently, the length of the camshaft needs to be increased and thereby
the axial length of the valve chamber needs to be increased accordingly.
As mentioned in JP3-3904A, the driven rod serving as a pump-operating
member in contact with the eccentric cam, i.e., a pump drive cam, is used
to transmit the driving force of the eccentric cam to the fuel pump. When
the decompression lever mentioned in JP2000-227064A is disposed
contiguously with the pump drive cam, the decompression lever and the pump
drive cam must be arranged so that the swinging decompression lever may
not interfere with the pump-operating member. Consequently, the length of
the camshaft needs to be increased and thereby the axial length of the
valve chamber needs to be increased accordingly.
The present invention has been made in view of such circumstances and it is
therefore an object of the present invention to secure a space for placing
a decompression mechanism in an internal combustion engine without
increasing the length of a camshaft extending across three or more
cylinders and the axial size of a valve chamber, and to form a
multicylinder internal combustion engine in compact construction. Another
object of the present invention is to ensure stable operation of a valve
train included in a multicylinder internal combustion engine during the
operation of the multicylinder internal combustion engine at high engine
speeds.
A further object of the present invention is to avoid interference between
a pump drive cam and a decompression mechanism, suppressing increase in
the length of a camshaft extended in a valve chamber and provided with a
pump drive cam and decompression mechanisms and in the axial size of the
valve chamber, and to form a multicylinder internal combustion engine in
compact construction.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an internal combustion
engine comprises: three or more cylinders arranged in parallel; a
crankshaft driven for rotation by pistons that reciprocate in the
cylinders; a camshaft supported for rotation, and interlocked with the
crankshaft and extending across all the cylinders: a valve chamber forming
member forming a valve chamber to contain the camshaft; a valve train
disposed in the valve chamber to open and close intake valves and exhaust
valves; and decompression mechanisms, respectively for the cylinders,
arranged in the valve chamber to open the intake valves or the exhaust
valves during a compression stroke; wherein the valve train includes the
camshaft, and valve cams formed on the camshaft for the cylinders to open
and close the intake valves and the exhaust valves through valve-operating
members, a specific one corresponding to a specific one of the cylinders
among the valve cams is located at a position not coincident with respect
to an axial direction parallel to the axis of the camshaft with a position
where an abutment portion, in contact with the valve-operating member, of
the intake or the exhaust valve is located, and the decompression
mechanism for the specific cylinder is located at a position coincident
with respect to the axial direction with the position of the abutment
portion of the intake or the exhaust valve.
Since the specific valve cam for the specific cylinder among the cylinders
arranged in a row can be disposed at a position not coincident with
respect to the axial direction with the abutment portion, in contact with
the valve-operating member, of the intake or the exhaust valve regardless
of the axial position of the abutment portion of the intake or the exhaust
valve, a space formed by spacing the specific valve cam with respect to
the axial direction from the abutment portion of the intake or the exhaust
valve is available for disposing the decompression mechanism so as to be
coincident with respect to the axial direction with the abutment portion
of the intake or the exhaust valve.
Consequently, the present invention has the following effects. Since the
valve train includes the valve cams formed on the camshaft to open and
close the intake and the exhaust valves for the cylinders through the
valve-operating members, the specific valve cam for opening and closing
the intake or the exhaust valve to be opened and closed by the
decompression mechanism for the specific cylinder is not coincident with
respect to the axial direction with the abutment portion, in contact with
the valve-operating member, of the intake or the exhaust valve, and the
decompression mechanism is coincident with respect to the axial direction
with the abutment portion of the intake or the exhaust valve, and the
space formed by spacing the specific valve cam with respect to the axial
direction from the abutment portion is available for disposing the
decompression mechanism so as to be coincident with respect to the axial
direction with the abutment portion of the intake or the exhaust valve, a
sufficient space is available for disposing the decompression mechanism,
increase in the length of the camshaft extending across the three or more
cylinders and in the longitudinal size of the valve chamber can be
suppressed, and the multicylinder internal combustion engine can be formed
in compact construction.
Typically, the specific cylinder is an intermediate one of the cylinders.
According to the present invention, the specific valve cam may be offset
toward the cylinder adjacent to the specific cylinder relative to the
abutment portion of the intake or the exhaust valve, and a part of the
camshaft, extending between the specific valve cam or the decompression
mechanism for the specific cylinder, and the valve cam or the
decompression mechanism for the cylinder adjacent to the specific
cylinder, may be not supported in any camshaft bearing.
Thus, a space available for disposing the specific valve cam at the
position offset relative to the abutment portion of the intake or the
exhaust valve can be formed around the abutment portion, not supported in
any camshaft bearing, of the camshaft.
Consequently, increase in the length of the camshaft and in the
longitudinal size of the valve chamber can further effectively be
suppressed, and the multicylinder internal combustion engine can be formed
in further compact construction.
Typically, the specific cylinder may be an intermediate one of the
cylinders, a part of the camshaft, extending between the specific valve
cam or the decompression mechanism for the specific cylinder, and the
valve cam or the decompression mechanism for one of the two cylinders on
the opposite sides of the specific cylinder, may be not supported in a
camshaft bearing, and another part of the camshaft, extending between the
specific valve cam or the decompression mechanism for the specific
cylinder, and the valve cam or the decompression mechanism for the other
one of the two cylinders on the opposite sides of the specific cylinder,
may be supported for rotation in a camshaft bearing.
Omission of a camshaft bearing for supporting the part of the camshaft
between the middle cylinder and one of the adjacent cylinders provides an
effect similar to the aforesaid effect, and the support of the part of the
camshaft between the middle cylinder and the other adjacent cylinder in
the camshaft bearing further effectively prevents the deformation of the
camshaft under a load placed on the valve cams even during the high-speed
operation of the camshaft.
Consequently, the present invention has the following effects. Omission of
a camshaft bearing for supporting the part of the camshaft between the
valve cam or the decompression mechanism for the middle cylinder and the
valve cam or the decompression mechanism for one of the adjacent cylinders
provides an effect similar to the aforesaid effect, the support of the
part of the camshaft between the middle cylinder and the other adjacent
cylinder in the camshaft bearing further effectively prevents the
deformation of the camshaft under a load placed on the valve cams to
ensure the stable operation of the valve train even during the high-speed
operation of the multicylinder internal combustion engine.
Preferably, the valve cam or the decompression mechanism for the specific
cylinder is disposed adjacently to the valve cam or the decompression
mechanism for a cylinder adjacent to the specific cylinder.
When the valve cam or the decompression mechanism for the specific cylinder
is thus disposed, any structure, such as a journal, that obstructs the
close arrangement of the valve cams or the decompression mechanisms for
the specific and the adjacent cylinder is not formed in the part of the
camshaft between the valve cam or the decompression mechanism for the
specific cylinder, and the valve cam or the decompression mechanism for
the adjacent cylinder, and hence a sufficient space is available for the
decompression mechanism.
Consequently, the following effects are obtained. Since the camshaft is
provided with the valve cam or the decompression mechanism for the
specific cylinder adjacently to the valve cam or the decompression
mechanism for the adjacent cylinder, a sufficient space is available for
placing the decompression mechanism. Therefore, increase in the length of
the camshaft and the size of the valve chamber can be further effectively
suppressed, and the multicylinder internal combustion engine can be formed
in a further compact construction.
According to the present invention, the multicylinder internal combustion
engine further comprises a fuel pump attached to the valve chamber forming
member forming the valve chamber, the camshaft is provided with a specific
one of the decompression mechanisms, and a pump cam having a cam surface
with which a pump-operating member for driving the fuel pump comes into
contact to drive the fuel pump, the specific decompression mechanism is
provided with a centrifugal weight supported on the camshaft for turning
and positioned adjacent to the pump cam with respect to the axial
direction parallel to the axis of the camshaft, the centrifugal weight is
on the side of the cam surface of the pump cam as viewed in the axial
direction, and the centrifugal weight turns toward the axis of the
camshaft so as to approach a tip part of a cam lobe defined by the cam
surface of the pump cam as the rotational speed of the camshaft increases.
When the engine speed increases after the multicylinder internal combustion
engine has been started, the centrifugal weight disposed on the side of
the cam lobe turns toward the tip part, remotest from the axis of the
camshaft, of the cam lobe of the pump cam. Therefore, a turning range in
which the centrifugal weight turns to a position where the centrifugal
weight overlaps the cam lobe as viewed in the axial direction is wider
than a turning range in which the centrifugal weight would turn radially
if the centrifugal weight were disposed at a position other than that on
the side of the cam lobe.
Consequently, the following effects are obtained. Since the centrifugal
weight turns in a wide range to the position where the centrifugal weight
overlaps the cam lobe as viewed in the axial direction, the pump cam and
the decompression mechanism can be disposed close to each other without
causing interference between the centrifugal weight and the pump-operating
member for driving the fuel pump. Therefore, increase in the length of the
camshaft and in the longitudinal size of the valve chamber can be
suppressed, and the multicylinder internal combustion engine can be formed
in compact construction.
According to the present invention, the multicylinder internal combustion
engine further comprises a fuel pump attached to the valve chamber forming
member forming the valve chamber, the camshaft is provided with a specific
one of the decompression mechanisms, and a pump cam having a cam surface
with which a pump-operating member for driving the fuel pump comes into
contact to drive the fuel pump, the specific decompression mechanism is
provided with a centrifugal weight supported on the camshaft for radial
movement at a position near the pump cam with respect to the axial
direction parallel to the axis of the camshaft, the centrifugal weight
moves in a range corresponding to a cam lobe defined by the cam surface of
the pump cam as viewed in the axial direction.
When viewed in the axial direction, the centrifugal weight does not jut
outside the cam surface with which the valve-operating member comes into
contact.
Consequently, the following effects are obtained. Since the centrifugal
weight does not jut outside the cam surface as viewed in the axial
direction, the pump cam and the decompression mechanism can be disposed
close to each other without causing interference between the centrifugal
weight and the pump-operating member for driving the fuel pump in the set
turning range of the centrifugal weight. Therefore, increase in the length
of the camshaft and in the longitudinal size of the valve chamber can be
suppressed, and the multicylinder internal combustion engine can be formed
in compact construction.
In this specification, unless otherwise specified, "axial direction"
signifies a direction parallel to the axis of the camshaft.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic, right-hand side elevation of an outboard engine
including an internal combustion engine in a preferred embodiment of the
present invention;
FIG. 2 is a sectional view taken on the line II--II in FIG. 3;
FIG. 3 is a rear view of a cylinder head included in the internal
combustion engine shown in FIG. 1 with a head cover removed;
FIG. 4 is a sectional view generally taken on the line IVa--IVa in FIG. 3,
including a sectional view of a part around the free end of an exhaust
rocker arm near an exhaust valve taken on the line IVb--IVb in FIG. 3, and
a sectional view of a part around the free end of an exhaust rocker arm
near an exhaust valve taken on the IVc--IVc in FIG. 3;
FIG. 5 is a fragmentary sectional view of a cylinder head and a fuel pump
generally taken on the line Va--Va in FIG. 3 including a sectional view of
a camshaft and a swing arm taken on the line Vb--Vb in FIG. 3;
FIG. 6 is a sectional view taken on the line VI--VI in FIG. 3, of
assistance in explaining the arrangement of a decompression mechanism with
respect to the rotating direction of the camshaft;
FIG. 7A is a fragmentary side elevation taken in the direction of the arrow
VII in FIG. 6, in which the decompression mechanism is in an operative
state;
FIG. 7B is a fragmentary side elevation taken in the direction of the arrow
VII in FIG. 6, in which the decompression mechanism is in an inoperative
state;
FIG. 8 is a cross-sectional view taken on the line VIII--VIII in FIG. 7A;
FIG. 9 is a cross-sectional view taken on the line IX--IX in FIG. 7A;
FIG. 10A is a side elevation of a decompressing member included in the
decompression mechanism;
FIG. 10B is a view taken in the direction of the arrow B in FIG. 10A;
FIG. 10C is a view taken in the direction of the arrow C in FIG. 10A; and
FIG. 10D is a view taken in the direction of the arrow D in FIG. 10A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described with
reference to FIGS. 1 to 10.
Referring to FIG. 1 showing the right side of an outboard engine 1
employing an internal combustion engine E in a preferred embodiment of the
present invention in a schematic side elevation, the internal combustion
engine E is a vertical internal combustion engine having a crankshaft
extending with its axis L1 in a vertical position. More specifically, the
internal combustion engine E is a three-cylinder in line overhead-camshaft
water-cooled four-stroke cycle vertical internal combustion engine.
The internal combustion engine E has a cylinder block 2 provided with a
first cylinder C1, a second cylinder C2 and a third cylinder C3, a
crankcase 3 fasted to the front end of the cylinder block 2 with a
plurality of bolts, a cylinder head 4 fastened to the rear end of the
cylinder block 2 with a plurality of bolts B1 (FIGS. 3 and 4), and a head
cover 5 fastened to the sealing surface 4g (FIG. 3) of the rear end of the
cylinder head 4 with an annular sealing member 6 (FIG. 2) held between the
rear end of the cylinder head 4 and the head cover 5 in close contact with
the sealing surface 4g by screwing a plurality of bolts in threaded holes
4h (FIG. 3).
In this embodiment, words including up, upward, down, downward, front,
forward, rear, rearward, right, rightward, left, leftward and such are
used to express positions, sides, directions and such in connection with
the front end, the rear end, the right side, the left side and such of a
ship on which the outboard engine 1 is mounted. Thus, an upward direction
is one of opposite axial directions A1 parallel to the axis L2 of a
camshaft 31, a downward direction is the other of the opposite axial
directions A1, a forward direction is one of the opposite directions A2
parallel to the axes L3 (FIG. 2) of the cylinders C1 to C3, and a rearward
direction is the other of the opposite directions A2. A side, on which
intake valves 43 are arranged, on one side of a reference plane including
the axes L3 of the cylinders and parallel to the camshaft 31 or the axis
L1 of the crankshaft 9 is called an intake side, and a side, on which
exhaust valves 44 are arranged, on the other side of the reference plane
is called an exhaust side.
Pistons 7 fitted for reciprocation in the cylinders C1 to C3 are connected
to the crankshaft 9 by connecting rods 8. The crankshaft 9 is disposed in
a crank chamber 10 defined by a front part of the cylinder block 2 and the
crankcase 3 and is supported for rotation by main bearings on the cylinder
block 2 and the crankcase 3. A crankshaft pulley 11, a flywheel 12 serving
also as a flywheel magnet, and a recoil starter 13 provided with a starter
knob 13a and serving as a starting device are mounted and arranged on an
upper end part 9a of the crankshaft 9 projecting upward from the crank
chamber 10 in that order upward.
A lower engine case 14 has a mount case 14a and an under case 14b, which
are formed integrally. The cylinder block 2 is joined to the mount case
14a. The upper end of an extension case 15 is joined to the lower end of
the lower engine case 14. A gear case 16 is joined to the lower end of the
extension case 15. The under case 14b of the lower engine case 14 covers a
lower part of the internal combustion engine E and the mount case 14a. An
upper engine cover 17 is joined to the upper end of the lower engine case
14 with a sealing member held between the upper engine cover 17 and the
upper end of the lower engine case 14. The upper engine cover 17 covers an
upper part of the internal combustion engine E. Thus, the internal
combustion engine E is contained in an engine compartment formed by the
under case 14b and the upper engine cover 17. The mount case 14a and the
under case 14b may be separately formed and may be joined together to form
the lower engine case 14.
A drive shaft 18 is connected to the lower end of the crankshaft 9 and
extends through the lower engine case 14. The drive shaft 18 is
interlocked with a propeller shaft 20 by a forward/reverse change gear 19
consisting of a bevel gear mechanism and a clutch mechanism and contained
in the gear case 16. The power of the internal combustion engine E is
transmitted from the crankshaft 9, through the drive shaft 18, the
forward/reverse change gear 19 and the propeller shaft 20 to a propeller
21 to drive the propeller 21 for rotation.
A swivel case 24 is supported for turning in a vertical plane by a tilt
shaft 23 on a transom clamp 22 for detachably mounting the outboard engine
1 on the ship. A swivel shaft 25 is fitted in a tubular support part 24a
of the swivel case 24 so as to be turnable. The swivel shaft 25 has an
upper end connected to the lower engine case 14 by a rubber mount, and a
lower end connected to the extension case 15 by a rubber mount. A steering
handle, not shown, connected to the swivel shaft 25 is turned in a
horizontal plane to turn the outboard engine 1 on the swivel shaft 25 in a
horizontal plane for steering.
Referring to FIGS. 1 and 2, a valve chamber 30 is formed by the cylinder
head 4 and the cylinder head cover 5. Arranged in the valve chamber 30 are
a valve train V for opening and closing intake valves 43 and exhaust
valves 44 (FIG. 4), and decompression mechanisms D1 to D3 for relieving
compression pressures in the cylinders C1 to C3 during compression strokes
at the start of the internal combustion engine E. The valve train V
includes a camshaft 31. The cylinder head 4 and the head cover 5 are valve
chamber forming members for forming the valve chamber 30.
The camshaft 31 is supported for rotation on the cylinder head 4 in the
valve chamber 30 with its axis L2 extended parallel to the axis L1 (FIG.
1) of the crankshaft 9. As shown in FIG. 2, the camshaft 31 penetrates the
upper wall 4a of the cylinder head 4, i.e., an end wall at one end of the
cylinder head 4 with respect to the axial direction A1. An oil seal 32
seals the gap between the camshaft 31 and the upper wall 4a. A pulse
generator 33 for detecting the angular position of the camshaft 31, and a
camshaft pulley 34 are mounted and arranged on an upper end part 31a of
the camshaft 31 projecting upward from the valve chamber 30 in that order
upward. The power of the crankshaft 9 is transmitted to the camshaft 31 by
a power transmitting mechanism including the crankshaft pulley 11, the
camshaft pulley 34 and a timing belt 35 extended between the crankshaft
pulley 11 and the camshaft pulley 34 to drive the camshaft 31 at half the
rotating speed of the crankshaft 9 in a direction A0 (FIGS. 4 and 6).
The pulse generator 33 includes one magnetic member 33a (FIG. 3) attached
to the inner surface of the camshaft pulley 34, and a coil unit 33b
attached to the upper wall 4a and surrounding the upper end part 31a. The
coil unit 33b includes three pickup coils arranged at equal
circumferential intervals. The magnetic member 33a passes the three pickup
coils successively as the camshaft 31 rotates. Ignition for the cylinders
C1 to C3 is timed on the basis of the output signals of the pickup coils.
A trochoid oil pump 37 has a pump body 37b and a pump cover 37c. The oil
pump 37 is fastened to the lower wall 4b, i.e., the other end wall with
respect to the axial direction A1, of the cylinder head 4 with a plurality
bolts B2 passed through the pump body 37b and the pump cover 37c. The oil
pump 37 has a shaft 37a connected to the lower end of the camshaft 31 by a
connecting member 36. The camshaft 31 drives the shaft 37a. The oil pump
37 sucks lubricating oil contained in an oil pan 38 (FIG. 1) attached to
the lower end of the lower engine case 14 through a suction pipe 39b
provided with an oil strainer 39a, and suction passages formed in the
cylinder block 2 and the cylinder head 4. The lubricating oil discharged
from the oil pump 37 flows through discharge passages formed in the
cylinder head 4 and the cylinder block 2, and an oil filter into a main
oil gallery. The lubricating oil is distributed from the main oil gallery
to the main bearings and to moving parts to be lubricated.
The internal combustion engine E will be described with reference FIGS. 2
and 3.
The first cylinder C1, the second cylinder C2 and the third cylinder C3 are
arranged in a row along the axial direction A1. The second cylinder C2 is
the middle cylinder. The first cylinder C1 and the third cylinder C3 are
on the opposite sides, respectively, of the second cylinder C2.
Referring to FIG. 4, the cylinder head 4 is provided with a combustion
chamber 40, an intake port 41 through which intake gas supplied from an
intake device, not shown, attached to the right wall 4c of the cylinder
head 4, i.e., a side wall on the intake side, is supplied into the
combustion chamber 40, and an exhaust port through which the combustion
gas is discharged from the combustion chamber 40 into an exhaust passage,
not shown, for each of the cylinders C1 to C3. The intake device includes
carburetors, i.e., fuel supply devices for producing air-fuel mixture by
introducing fuel into intake air, respectively for the cylinders C1 to C3,
and an intake manifold for distributing the air-fuel mixture to the intake
ports 41.
An intake valve 43 for opening and closing the intake port and an exhaust
valve 44 for opening and closing the exhaust port are slidably inserted in
valve guides on the cylinder head 4 for each of the cylinders C1 to C3.
Valve springs 46 force by their resilience the intake valve 43 and the
exhaust valve 44 for each of the cylinders C1 to C3 back up onto their
valve seats.
In the suction stroke, in which the intake valve 43 is opened and the
piston 7 moves toward the bottom dead center, the air-fuel mixture is
sucked through the intake port 41 into the combustion chamber 40. In the
compression stroke, the air-fuel mixture is compressed by the piston 7
moving toward the top dead center, ignited by an ignition plug 45 attached
to a part of the cylinder head 4 on the exhaust side above the exhaust
valve 44 and burns. In the expansion stroke, the piston 7 is moved toward
the bottom dead center by the pressure of a combustion gas, driving the
crankshaft 9 through the connecting rod 8 for rotation. In the exhaust
stroke, in which the piston moves toward the top dead center, the
combustion gas is discharged as an exhaust gas from the combustion chamber
40 through the exhaust port 42 into the exhaust passage. The exhaust gas
is discharged through an exhaust pipe from the outboard engine 1.
The valve train V includes the camshaft 31 extended in the valve chamber
across the cylinders C1 to C3 and provided with intake cams 47, 49 and 51,
and exhaust cams 48, 50 and 52 for the cylinders C1 to C3, a pair of
rocker-arm shafts supported on the cylinder head 4 nearer to the head
cover 5 than the camshaft 31, i.e., an intake rocker-arm shaft 53 and an
exhaust rocker-arm shaft 54, intake rocker arms 55, 57 and 59, and exhaust
rocker arms 56, 58 and 60 supported for rocking motion on the intake
rocker-arm shaft 53 and the exhaust rocker-arm shaft 54, respectively
(FIG. 3). The intake rocker arms 55, 57 and 59, and the exhaust rocker
arms 56, 58 and 60 are cam followers driven by the intake cams 47, 49 and
51, and the exhaust cams 48, 50 and 52, respectively. Those component
parts of the valve train V are arranged in the valve chamber 30.
The camshaft 31 has journals 61, 62 and 63 supported by bearings 64, 65 and
66, respectively, in the valve chamber 30. The journals 61 to 63 of the
camshaft 31 are a first end journal 61 formed on the camshaft 31 at a
position in the upper end part of the valve chamber 30 near the upper end
part 31a, a second end journal 63 formed on the lower end part 31b of the
camshaft 31 coinciding with the connecting member 36 with respect to the
axial direction A1 in the lower end part of the valve chamber 30, and a
middle journal 62 formed in a middle part of the camshaft 31 between the
first end journal 61 and the second end journal 63. The diameter of the
middle journal 62 is greater than those of the end journals 61 and 63. The
bearings 64 to 66 are a first end bearing 64 formed integrally with the
upper wall 4a to support the first end journal 61, a second end bearing 66
formed in the lower wall 4b to support the second end journal 63, and a
middle bearing 65 positioned between the end bearings 64 and 66 to support
the middle journal 62.
The first end bearing 64 and the middle bearing 65 are formed integrally
with the cylinder head 4 and protrude toward the head cover 5. The second
end bearing 66 coinciding with the connecting member 36 with respect to
the axial direction A1 is a tubular projection 37d formed integrally with
the pump body 37b and projecting through a through hole 4e formed in the
lower wall 4b into the valve chamber 30. The bearings 64 to 66 are
provided with bearing holes 64b, 65b and 66b for slidably receiving the
journals 61 to 63 respectively.
The camshaft 31 is integrally provided with a flange 67 having a contact
surface 67a in contact with an end surface 64a, facing the valve chamber,
of the first end bearing 64, and a plate-shaped pump cam 68, i.e., an
eccentric cam, having a contact surface 68a in contact with an end surface
66a, facing the valve chamber, of the second end bearing 66. The pump cam
68 is adjacent to the second end bearing 66, i.e., a specific bearing. The
flange 67 and the pump cam 68 are in contact with the end bearings 64 and
66, respectively to serve as thrust bearing members for restraining the
camshaft 31 from movement in the axial directions A1. More concretely, the
flange 67 in contact with the end surface 64a restrains the camshaft 31
from upward movement, and the pump cam 68 in contact with the end surface
66a restrains the camshaft 31 from downward movement.
The camshaft 31 is integrally provided with the intake cam 47 and the
exhaust cam 48 for the first cylinder C1, i.e., the upper end cylinder,
the intake cam 51 and the exhaust cam 52 for the third cylinder C3, i.e.,
the lower end cylinder, and intake cam 49 and the exhaust cam 50 for the
second cylinder C2 in parts thereof between the flange 67 and the pump cam
68.
As best shown in FIG. 4, the intake cams 47, 49 and 51, and the exhaust
cams 48, 50 and 52 have round base parts Mi and Me for closing the
corresponding intake valves 43 and exhaust valves 44 pushed in the closing
direction by the valve springs 46, respectively, and cam lobes Ni and Ne
for timing the opening and closing operations and lifts of the
corresponding intake valves 43 and exhaust valves 44, respectively.
In the cylinders C1 to C3, the exhaust cams 48, 50 and 52 are below the
intake cams 47, 49 and 51, respectively. Decompression mechanisms D1 to D3
are disposed below the exhaust cams 48, 50 and 52, respectively. The
decompression mechanisms D1 to D3 opens and close the exhaust valves 44
during the compression stroke in starting the internal combustion engine E
by means of the recoil starter 13. The decompression mechanisms D1 to D3
open the exhaust valves 44 by a small decompression lift to enable the
air-fuel mixture compressed in the cylinders C1 to C3 to escape through
the slightly opened exhaust ports 42 to relieve compression pressure for a
decompressing operation.
The intake cams 47 and 49, the exhaust cams 48 and 50, and the
decompression mechanisms D1 and D2 respectively associated with the first
cylinder C1 and the second cylinder C2 are arranged between the middle
journal 62 and the first end journal 61. The intake cam 51, the exhaust
cam 52 and the decompression mechanism D3 associated with the third
cylinder C3 are arranged between the middle journal 62 and the second end
journal 63. Views of parts, around the decompression mechanisms D1 to D3,
of the camshaft shown in FIGS. 1 to 3 are those taken from an angular
direction different from an angular direction from which the rest of the
parts of the camshaft 31 are viewed. Actually, the decompression
mechanisms D1 to D3 are arranged at equal angular intervals with respect
to the rotating direction A0 of the camshaft 31.
A cylindrical part 31c of the camshaft 31 extends between the intake cam 49
for the second cylinder C2 nearer to the first cylinder C1 than the
exhaust cam 50 and the decompression mechanism D2, and the decompression
mechanism D1 associated with the first cylinder C1, is nearer to the
second cylinder C2 than the intake cam 47 and the exhaust cam 48 for the
first cylinder, and is not supported by any bearing and not provided with
any journal.
The intake cam 49 among the intake cam 49, the exhaust cam 50 and the
decompression mechanism D2 associated with the second cylinder C2 is
adjacent to the decompression mechanism D1 among the intake cam 47, the
exhaust cam 48 and the decompression mechanism D1 associated with the
first cylinder C1. Therefore, a part, adjacent to the decompression
mechanism D1 associated with the first cylinder C1 with respect to the
axial direction A1, of the camshaft 31 is the intake cam 49 for the second
cylinder C2. Thus, a centrifugal weight 91 included in the decompression
mechanism D1 and the intake cam 49 are adjacent to each other.
The middle journal 62 is formed in a cylindrical part 31d, extending
between the decompression mechanism D2 nearer to the third cylinder C3
than the intake cam 49 and the exhaust cam 50 for the second cylinder, and
the intake cam 51 nearer to the second cylinder C2 than the exhaust cam 52
and the decompression mechanism D3 associated with the third cylinder C3,
of the camshaft 31. The middle journal 62 is supported by the middle
bearing 65.
The intake cam 51, the exhaust cam 52 and the decompression mechanism D3
associated with the third cylinder C3 are arranged between the second end
bearing 66 and the middle bearing 65 adjacent to the second bearing 66
with respect to the axial direction A1. The decompression mechanism D3
among the intake cam 51, the exhaust cam 52 and the decompression
mechanism D3 is disposed near the pump cam 68 with respect to the axial
direction A1 opposite the second bearing 66 with respect to the pump cam
68.
The intake cam 49 for the second cylinder C2 is at a short distance toward
the intake cam 47 for the first cylinder C1 from a position dividing the
interval with respect to the axial direction A1 between the intake cams 47
and 51 respectively for the first cylinder C1 and the third cylinder C3
into two equal parts. Similarly, the exhaust cam 50 for the second
cylinder C2 is at a short distance toward the exhaust cam 48 for the first
cylinder C1 from a position dividing the interval with respect to the
axial direction A1 between the exhaust cams 48 and 52 respectively for the
first cylinder C1 and the third cylinder C3 into two equal parts. The
decompression mechanism D2 for the second cylinder C2 is disposed in a
space extending in the axial direction A1 and formed by disposing the
intake cam 49 and the exhaust cam 50 of the second cylinder C2 nearer to
the first cylinder C1.
The camshaft 31 is mounted on the cylinder head 4 in the following manner.
The camshaft 31 provided with the decompression mechanisms D1 to D3 is
passed upward through the through hole 4e of a diameter greater than that
of the middle journal 62, a through hole 69a of a diameter greater than
that of the middle journal 62 formed in a shaft support 69, the bearing
hole 65b of the middle bearing 65, and the bearing hole 64b of the first
end bearing 64. Then, the oil pump 37 is joined to the lower wall 4b such
that the contact surface 67a of the flange 67 is in contact with the first
bearing 64 and the second end journal 63 is fitted in the bearing hole 66b
of the second end bearing 66.
Referring to FIGS. 2 to 5, the rocker-arm shafts 53 and 54 are inserted in
through holes 4f and 4g formed in the lower wall 4b. The rocker-arm shafts
53 and 54 are passed through a pair of through holes 69f (FIG. 3) and 69g
(FIG. 5) formed in a rocker support 69 formed integrally with the cylinder
head 4 at a position between the lower wall 4b and the middle bearing 65
so as to protrude toward the head cover 5. The rocker-arm shafts 53 and 54
are extended upward through the through holes 4f and 4g formed in the
lower wall 4b, a pair of through holes 65f and 65g formed in the middle
bearing 65 and a pair of through holes 64f and 64g formed in the first end
bearing 64, respectively. As shown in FIG. 4, bolts B3 are screwed through
cuts 53a and 54a formed in parts, in the middle bearing 65, of the
rocker-arm shafts 53 and 54 in threaded holes formed in the middle bearing
65 to restrain the rocker-arm shaft 53 and 54 from rotation and to hold
the same in place.
Referring to FIGS. 2 to 4, the intake rocker arms 55, 57 and 59 have ends
provided with adjusting screws 55a, 57a and 59a, respectively. The tips of
the adjusting screws 55a, 57a and 59a (only the tip 57a1 of the adjusting
screw 57 is shown in FIG. 4) are in contact with the ends 43a of the valve
stems of the intake valves 43 (the end 43a of the valve stem in contact
with the tip 57a1 of the adjusting screw 57a attached to the intake rocker
arm 57 is denoted by 43A for convenience' sake). The intake rocker arms
55, 57 and 59 have the other ends provided with slippers 55b, 57b and 59b,
i.e., contact parts, in contact with the intake cams 47, 49 and 51,
respectively. Fulcrums 55c, 57c and 59c provided with through holes are
formed in middle parts, between the adjusting screws 55a, 57a and 59a, and
the slippers 55b, 57b and 59b, of the intake rocker arms 55, 57 and 59,
respectively. The intake rocker-arm shat 53 is extended through the
through holes of the fulcrums 55c, 57c and 59c.
The exhaust rocker arms 56, 58 and 60 have ends provided with adjusting
screws 56a, 58a and 60a, respectively. The tips of the adjusting screws
56a, 58a and 60a (only the tip 58a1 of the adjusting screw 58 is shown in
FIG. 4) are in contact with the ends 44a of the valve stems of the exhaust
valves 44 (the end 44a of the valve stem in contact with the tip 58a1 of
the adjusting screw 58a attached to the exhaust rocker arm 58 is denoted
by 44A for convenience' sake). The exhaust rocker arms 56, 58 and 60 have
the other ends provided with slippers 56b, 58b and 60b, i.e., contact
parts, in contact with the exhaust cams 48, 50 and 52, respectively.
Fulcrums 56c, 58c and 60c provided with through holes are formed in middle
parts, between the adjusting screws 56a, 58a and 60a, and the slippers
56b, 58b and 60b, of the exhaust rocker arms 56, 58 and 60, respectively.
The exhaust rocker-arm shat 54 is extended through the through holes of
the fulcrums 56c, 58c and 60c.
Positioning collars 70 and positioning springs 71 are mounted on the intake
rocker-arm shaft 53 and the exhaust rocker-arm shaft 54 to position the
intake rocker arms 55, 57 and 59, and the exhaust rocker arms 56, 58 and
60 respectively for the cylinders C1 to C3 with respect to the axial
direction A1.
The intake rocker arm 57 and the exhaust rocker arm 58 for the second
cylinder C2 are specific rocker arms. The tips of the adjusting screws 57a
and 58a of the intake rocker arm 57 and the exhaust rocker arm 58 are
offset toward the decompression mechanism D2, i.e., downward, with respect
to the axial direction A1 relative to the corresponding slippers 57b and
58b. The tip of the adjusting screw 58a of the exhaust rocker arm 58
coincides with the decompression mechanism D2 with respect to the axial
direction A1. The tip 57a1 of the adjusting screw 57a of the intake rocker
arm 57, the end of 43A of the valve stem of the intake valve 43, and the
exhaust cam 50 coincide with each other with respect to the axial
direction A1. Consequently, a straight line connecting the slipper 57b and
the tip of the adjusting screw 57a of the intake rocker arm 57 , and a
straight line connecting the slipper 58b and the tip of the adjusting
screw 58a of the exhaust rocker arm 58 extend obliquely relative to the
intake rocker-arm shaft 53 and the exhaust rocker-arm shaft 54,
respectively.
The exhaust cam 50 is a specific valve cam for operating the exhaust rocker
arm 58 to operate the exhaust cam 44, operated by the decompression
mechanism D2, for the second cylinder C2. The exhaust cam 50 does not
coincide with and is positioned above the end 44A of the valve stem of the
exhaust valve 44 for the second cylinder C2 with respect to the axial
direction A1. The decompression mechanism D2 coincides with the end 44A of
the valve stem of the exhaust valve 44 with respect to the axial direction
A1. The second cylinder C2 is a specific cylinder.
The intake cams 47, 49 and 51 and the exhaust cams 48, 50 and 52 rotating
together with the camshaft 31 rocks the intake rocker arms 55, 57 and 59
and the exhaust rocker arms 56, 58 and 60 to open and close the intake
valves 43 and the exhaust valves 44 for the cylinders C1 to C3 at
predetermined crank angles, respectively.
Referring to FIGS. 2 and 3, part of the lubricating oil sent into the main
oil gallery flows through an annular oil passage K1 formed between a bolt
hole formed in a top boss S1 formed in a part of the cylinder head 4 on
the exhaust side and a head bolt B1 inserted in the bolt hole of the top
boss S1, and an oil passage K2 formed in the cylinder head 4 into a small
oil chamber K3 sealed by a cover 72. Then, the lubricating oil flows from
the oil chamber K3 through oil passages K4 and K5 (FIG. 5) formed in the
hollow rocker-arm shafts 53 and 54, and radial oil holes formed in the
rocker-arm shafts 53 and 54 to the sliding parts of the intake rocker arms
55, 57 and 59, the exhaust rocker arms 56, 58 and 60, the intake
rocker-arm shaft 53 and the exhaust rocker-arm shaft 54, flows through an
oil passage K6 formed in the first end bearing 64 and opening into the
bearing hole 64b to the sliding parts of the first end bearing 64 and the
first end journal 61, flows through the oil passage K4, and holes formed
in the intake rocker-arm shaft 53 and the middle bearing 65 to the sliding
parts of the middle bearing 65 and the middle journal 62. A through hole
4g into which the lower ends of the oil passages K4 and K5 open is covered
with the pump body 37b of the oil pump 37.
The lubricating oil flowed through the small holes and lubricated the
sliding parts drips into the valve chamber 30, and lubricates the sliding
parts of the intake cams 47, 49 and 51, the exhaust cams 48, 50 and 52,
the intake rocker arms 55, 57 and 59, the exhaust rocker arms 56, 58 and
60, the sliding parts of the decompression mechanisms D1 to d3, and the
sliding parts of the second end bearing 66 and the second end journal 63,
and then collects on the bottom wall, formed by the lower wall 4b and the
lower wall of the head cover 5, of the valve chamber 30. Then, the
lubricating oil collected on the bottom wall flows through oil passages K7
and K8 (FIG. 2) formed in the cylinder block 2, and an oil pipe 73
connected to the head cover 5 into an oil passage K9 formed in the lower
engine case 14, and returns through a return pipe to the oil pan 38.
Referring to FIGS. 2, 3 and 5, a fuel pump 74 for pressurizing the fuel to
the carburetor is a displacement pump driven for a pumping action by the
pump cam 68. The fuel pump 74 is fastened to a pump mount formed on the
outer surface of the right wall 4c of the cylinder head 4 with bolts B4.
The pump cam 68 formed in the camshaft 31 is adjacent to the upper side of
the second end journal 63 in the bottom part of the valve chamber 30. The
decompression mechanism D3 is disposed above and close to the pump cam 68,
and the exhaust cam 52 is above the decompression mechanism D3. As shown
in FIGS. 5 and 6, the pump cam 68 is a circular eccentric cam of a radius
R having its center F displaced by a predetermined eccentricity toward the
intake side from the axis L2 of rotation. The circumference of the pump
cam 68 serves as a cam surface 68b. A section, in which the distance
between the axis L2 of rotation and the cam surface 68b is greater than
the radius R, of the cam surface 68b defines a cam lobe Np.
Referring to FIG. 5, the fuel pump 74 has a housing 75 defining a pump
chamber 76, a diaphragm 77, and an actuating rod 78 connected to the
diaphragm 77.
The housing 75 is formed by stacking up three members 75a, 75b and 75c. The
member 75a nearest to the cylinder head 4 has a flange 75a1 (FIG. 3)
fastened to the pump mount with bolts B4, and a tubular projection 75a2
projecting through a through hole 4e into the valve chamber 30.
The actuating rod 78 is formed by combining a first rod 78a connected to
the diaphragm 77, and a second rod 78b provided with a bottomed hole for
receiving the first rod 78a, and connected to the first rod 78a with a pin
78c. The second rod 78b is fitted slidably in a guide hole 75a3 formed in
the tubular projection 75a2 so that its end part 78b1 projects from the
inner open end of the tubular projection 75a2 into the valve chamber 30. A
swing arm 79, i.e., a pump-operating member, is in contact with the tip of
the end part 78b1. The actuating rod 78 is pushed by a pushing spring 78e
toward the valve chamber 30 so that an end part 78b1 projects from the
tubular projection 75a2, and the tip of the end part 78b1 is pressed
against the swing arm 79.
The tubular projection 75a2 and the actuating rod 78 are disposed above the
second end journal 63, the pump cam 68, and the lowermost head bolt B1b or
the lowermost boss S2 provided with a bolt hole for receiving the head
bolt B1b, or nearer to the exhaust cam 52 with respect to the axial
direc
