Four stroke engine for outboard motor

Details Four stroke engine for outboard motor Four stroke engine for outboard motor

2002-11-06

2004-07-20

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Camshaft drive means

C123S090270

Reexamination Certificate

active

06763792

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a four stroke engine and more particularly to a camshaft drive arrangement most suitable to an outboard motor that has a protective cowling for the engine.
2. Description of Related Art
As is well known, a number of outboard motors, which are expected to produce a large horsepower, are provided with engines having V-shaped banks, each bank involving multiple cylinders. The cylinders are vertically spaced relative to each other and extend generally horizontally. Such a V-shaped configuration is quite suitable to outboard motors because power head of these motors can be small versus their engine powers. In addition to this, conventional outboard motors are mostly powered by two stroke engines. Since the two stroke engines are compact in nature, a power head accommodating this two stroke engine in the V-shaped configuration can be formed as small as possible.
Recently, however, some outboard motors incline to utilize four stroke engines. One reason for this tendency is that emissions of the four stroke engines are clean rather than that of two stroke engines. Generally, however, the four stroke engines have relatively complicated structures as compared with the two stroke engines. Particularly, if the engine is a DOHC (Double Over Head Camshaft drive) engine, it is provided with a relatively large size camshaft drive for activating intake valves and exhaust valves at its cylinder head assembly. This arrangement, thus, gives rise to making the cylinder head assembly be bulky. In addition, camshafts must rotate at a speed half as slow as that of the crankshaft in connection with activating timings of intake and exhaust valves. This means that the diameters of driven wheels such as pulleys or chain sprockets on the camshafts should be twice as large as the diameter of the crankshaft. Accordingly, the cylinder head assembly is likely to be more bulky.
In the meantime, usually a protective cowling encircles the engine in an outboard motor. Thus, the engine is desirable to be as small as possible for contributing to compactness of the outboard motor per se. However, the large driven wheels prevent this desire and the protective cowling tends to be large.
The aforedescribed situations will be described below with reference to a conventional, exemplary four stoke engine shown in FIG.
1
.
FIG. 1
illustrates a plan view of the engine
10
and specifically a camshaft drive
12
. This engine
10
has V-shaped cylinder banks
14
a,b
each having a few cylinders spaced vertically to each other. Each cylinder bank
14
a,b
has two overhead camshafts
16
a,b
(
16
c,d
) disposed vertically for activating intake valves and exhaust valves. Thus, the engine
10
is a DOHC engine. At the bank
14
a
, which is located on the starboard (the left-hand side in the figure), the camshaft
16
b
positioned on the inside has a driven wheel
18
such as a pulley or a chain sprocket at its uppermost end. The camshaft
16
b
also has a driving wheel under the driven wheel
18
, although it is not seen. Another camshaft
16
a
has a driven wheel
20
and an endless transmitter
22
such as a cog belt or a chain is wounded around the unseen driving wheel and the driven wheel
20
. Meanwhile, the bank
14
b
located on the port side (the right-hand side in the figure) has a similar structure except that the camshaft
16
d
positioned on the outer side has a driven wheel
24
.
Further, the engine
10
has a single crankshaft
26
extending vertically in the engine
10
and having a driving wheel
28
at its almost top end. An endless transmitter
30
, like the transmitter
22
, is wounded around the driving wheel
28
and the respective driven wheels
18
,
24
of the camshafts
16
b,d
. With the rotation of the crankshaft
26
, thus, the camshafts
16
b,d
are rotated and then the camshafts
16
a,c
are also rotated.
The driven wheels
18
,
24
have the diameters twice as large as the diameter of the driving wheel
28
. Because the camshafts
16
a,b,c,d
must rotate at a speed that is half as slow as that of the crankshaft in connection with activating timings of the intake and exhaust valves as described above.
On the other hand, although not shown, a protective cowling, which is generally tapered upwardly, encircles the engine
10
. The large driven wheels
18
,
24
, particularly the wheel
24
positioned on the outer side, tend to make the protective cowling be large.
It is, therefore, a principal object of this invention to provide an improved DOHC engine contributing to compactness of an outboard motor accommodating the engine.
It is another object of this invention to provide a DOHC engine for an outboard motor, whereby a camshaft drive does not prevent a protective cowling encircling the engine from being formed compact.
Also, in order to minimize an outboard motor, an arrangement of an air induction system for a DOHC engine is quite important.
It is, therefore, a further object of this invention to provide a DOHC engine wherein an air induction system is arranged properly in view of the minimization of an outboard engine.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in a four stroke internal combustion engine for an outboard motor having a protective cowling encircling the engine.
In accordance with one aspect of this invention, at least two cylinders forming V-shaped banks are provided. Each cylinder includes a combustion chamber for burning intake charge. An intake valve is also included for admitting the intake charge into the combustion chamber. A first camshaft is further included for activating the intake valve. An exhaust valve is still further included for allowing the burnt charge being discharged from the combustion chamber. A second camshaft is yet further included for activating the exhaust valve. The first and second camshafts are disposed transversely relative to each other and generally vertically. A mechanism is also included for driving one of the first and second camshafts by another one of the first and second camshafts. A piston is reciprocally moved in the cylinder by burning of the intake charge in the combustion chamber. A single crankshaft rotated by the movement of the pistons is provided. The crankshaft is disposed generally vertically and apart from the respective camshafts. The crankshaft has a driving wheel. One of the first and second camshaft positioned on the inside relative to another one of the first and second camshafts in each of the banks has a driven wheel which diameter is larger than a diameter of the driving wheel. An endless transmitter is wound around the driving wheel and the driven wheels so that the driven wheels are driven by the driving wheel when the crankshaft is rotated by the movement of the pistons.
In accordance with another aspect of this invention, at least two cylinders forming V-shaped banks are provided. Each cylinder includes a combustion chamber for burning intake charge. An intake valve is also included for admitting the intake charge into the combustion chamber. A first camshaft is further included for activating the intake valve. An exhaust valve is still further included for allowing the burnt charge being discharged from the combustion chamber. A second camshaft is yet further included for activating the exhaust valve. The first and second camshafts are disposed transversely relative to each other and generally vertically. A mechanism is also included for driving the first and second camshafts. A piston is reciprocally moved in the cylinder by burning of the intake charge in the combustion chamber. At least one intermediate shaft is provided for activating the mechanism. A single crankshaft rotated by the movement of the pistons is provided. The crankshaft is disposed generally vertically and apart from the respective camshafts. The crankshaft has a driving wheel. The intermediate shaft has a driven wheel which diameter is larger than a diameter of the driving wheel. An endless transmitter is wound around the driving wheel and the drive

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