Structure of overhead-valve internal combustion engine and...

Details Structure of overhead-valve internal combustion engine and... Structure of overhead-valve internal combustion engine and...

2000-09-20

2001-06-12

Lo, Wellun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Lubrication

C123S193500, C123S1960CP, C184S006900

Reexamination Certificate

active

06244231

ABSTRACT:

FIELD OF THE INVENTION
This invention concerns a structure of an overhead-valve internal combustion engine and the manufacturing method for it. More specifically, it concerns the configuration of the valve operating mechanism which operates the valves in an overhead-valve type internal combustion engine with an intake valve and an exhaust valve, and the lubrication device in the valve operating mechanism of the same kind of engine.
BACKGROUND OF THE INVENTION
It is relatively simple to assemble the valve-operating mechanism in an engine with the aforesaid bathtub-type combustion chamber. However, the combustion efficiency of this chamber is inferior to that of the aforesaid pent roof-type. In recent years, this has led to greater use of pent roof chambers.
FIGS. 18 and 19
show an example of an air-cooled single-cylinder overhead-valve four-cycle internal combustion engine with the aforesaid pent roof combustion chamber which belongs to the prior art.
FIG. 18
is a cross section of the engine which includes the cylinder and the push rods.
FIG. 19
is a cross section taken along line Z—Z in FIG.
18
.
In
FIGS. 18 and 19
,
1
is the combustion chamber;
2
is the air-cooled cylinder;
5
is the crankshaft;
6
is the connecting rod;
7
is the piston;
8
is the cylinder head;
14
a
is the intake valve; and
14
b
is the exhaust valve (Hereafter, the aforesaid intake valve
14
a
and exhaust valve
14
b
will be referred to in common as induction/exhaust valves
14
.)
17
is the camshaft, which is engaged with the aforesaid crankshaft
5
through a gear train;
17
a
is the cam on the said camshaft
17
;
16
is the tappet;
15
is the push rod;
13
is the rocker arm shaft, which is fixed to and supported on rocker arm supporting base
22
, which is itself fixed to the top of the aforesaid cylinder head
8
.
11
is the rocker arm, which engages with the said rocker arm shaft
13
in such a way that it is free to swing.
18
is the valve spring.
19
is the valve spring bearing.
9
Is the head cover, which is mounted on top surface
8
b
on top of cylinder head
8
and which covers the mechanism which operates the valves. When this engine operates, induction/exhaust valves
14
open and close according to a timing determined by cam
17
a
, whose rotating speed is reduced to half that of crankshaft
5
by a timing gear (not pictured).
In
FIG. 18
, the rotation of camshaft
17
a
forces push rods
15
upward, and rocker arms
11
swing around shaft
13
. Intake valve
14
a
or exhaust valve
14
b
is pushed upward against the elastic force of valve spring
18
, and the valve opens.
In an OHV engine like this, to insure that the action of cam
17
a
is transmitted reliably to induction/exhaust valve
14
through push rods
15
, the aforesaid valve spring
18
must have a relatively large spring constant, meaning that a strong spring must be used; and rocker arm shaft
13
must have a relatively large diameter.
To insure that the contacting surfaces of the valve operating mechanism do not experience excessive force when the engine is running and the cylinder head gets hot, an adjustment screw (not pictured) is provided to adjust the clearance between the contacting portions of rocker arms
11
and push rods
15
.
In the aforesaid cylinder head
8
, the aforesaid head cover
9
is hermetically sealed to top surface
8
b
, the upper surface of peripheral wall
8
c
, which surrounds the head. The aforesaid rocker arm supporting base
22
for the rocker arms is bolted to an area in the center of upper surface
8
a
which is lower than the said top surface
8
b
by a fixed amount.
In the four-cycle overhead valve internal combustion engine from the prior art which is pictured in
FIGS. 18 and 19
, there are two surfaces at the top of cylinder head
8
,
8
b
and
8
a
.
8
b
is the top surface onto which head cover
9
is fixed;
8
a
is the mounting surface on which rocker arm supporting base
22
, which supports the rocker arms, is fixed. These two surfaces must be finished by a machining process so that they are relatively smooth.
However, in the prior art cylinder head
8
, top surface
8
b
, on which cover
9
is mounted, and mounting surface
8
a
, on which rocker arm supporting base
22
is mounted, are at different heights. This means that they must be machined in a two-stage process or that the machinist must change tools in mid-process. This increases the number of processes required and incurs an extra cost for set-up.
Designs for overhead valve engines with a hemispherical combustion chamber and the intake and exhaust valves arranged so that they radiate from the center have been proposed in Japanese Patent Publications (Kokai) Hei5-133205. In this prior art, one intake valve, one exhaust valve, and one spark plug are arranged so that the angles of these center lines (L
1
), (L
2
), (L
3
) against the center line of cylinder are same as each other, and they are located at a same distance from the center of the cylinder in order to manufacture the cylinder easily.
Another prior art is proposed in Japanese Patent Publications (Kokai) Hei5-133205. In both of these, however, the structure which supports the valve operating mechanism in the cylinder head is three-dimensional. It is difficult to achieve the high level of precision required by the processing, and the structural components of the valve operating mechanism experience torsion force when the valves are driven, which shortens their service life.
For a structure of a lubrication device for an OHV engine, there is a breather passage between the crankcase and the valve operating mechanism chamber which contains the valve operating mechanism. Oil which is taken up by a dipper, splashed about and suspended in the crankcase is conveyed via this breather passage into the aforesaid valve operating mechanism chamber with the movement of air caused by the downward stroke of the piston. In this way the said valve operating mechanism chamber is lubricated.
An example of an existing lubrication device for the valve operating mechanism in a small multipurpose OHV engine can be found in Japanese Utility Model Publication (Kokoku) 63-15530. The details of this device are shown in
FIGS. 20 through 22
.
These drawings show an OHV engine whose cylinder is canted upward from the horizontal. Breather passage
131
, which connects crankcase
101
and valve operating mechanism chamber
102
, is formed within the walls of cylinder barrel
116
and cylinder head
118
.
The end portion
131
a
of the said breather passage
131
in valve operating mechanism chamber
102
faces from above intake valve
151
toward the point where valve stem
152
a
of exhaust valve
152
and rocker arm
162
come in contact. Branching passage
131
b
faces to the point where valve stem
151
a
of intake valve
151
and rocker arm
161
come in contact.
Because this OHV engine is configured in this prior art, the air which is moved by the downward stroke of piston
107
forces the oil picked up by dipper
115
and suspended in crankcase
101
into the aforesaid breather passage
131
. The greater part of this suspended oil goes in a straight line through portion
131
a
and is splashed upon the operating mechanism for exhaust valve
152
in the vicinity of the point where valve stem
152
a
and rocker arm
162
come in contact. This is how most of the suspended oil is supplied.
The remainder of the suspended oil goes through branching passage
131
b
and is splashed upon the operating mechanism for intake valve
151
in the vicinity of the point where valve stem
151
a
and rocker arm
161
come in contact.
When the air forced into the aforesaid valve operating mechanism chamber
102
goes through breather valve
108
, the lubricating oil is separated out. The air enters breather chamber
109
, travels through breather tube
132
and is returned to carburetor
111
. The oil flows down the interior surface of valve operating mechanism chamber
102
. It goes through the space around push rod
122
and tappet
121
and is recovered in crankcase
101
.
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