Marine propulsion – Means for accomodating or moving engine fluids – Means for handling exhaust gas
Reexamination Certificate
1999-06-21
2001-03-06
Stormer, Russell D. (Department: 3612)
Marine propulsion
Means for accomodating or moving engine fluids
Means for handling exhaust gas
C440S075000, C440S077000
Reexamination Certificate
active
06196888
ABSTRACT:
TECHNICAL FIELD
The present invention relates to outboard motors (or outboard marine engines) which comprises an internal combustion engine used as a power source for a watercraft. More particularly, the present invention relates to a relatively small outboard motor in that an exhaust pipe outlet is submerged under water in an operable state of the outboard motor and a driving force from the engine is prevented from being transmitted to the propeller during engine start.
BACKGROUND OF THE INVENTION
Outboard motors are often used as a power source for a watercraft such as a boat. In many small-power outboard motors, an exhaust pipe connected to an exhaust port of an internal combustion engine in the outboard motor extends downwardly to such an extent that the outlet opening of the exhaust pipe is submerged beneath the water level in an operable state of the outboard motor. Such configuration can reduce the exhaust noise and/or prevent overheating of the extension case into which the hot exhaust gas is discharged. Although it may be conceived to use an additional pump for lifting up water to cool the exhaust gas, this is often impractical in small-power outboard motors in which power loss resulting from operating the additional pump may be significant and/or there may be little spare room for mounting the pump.
It has been also known in small-power outboard motors to connect the output shaft (or crankshaft) of the internal combustion engine and the propeller via a centrifugal clutch system so that the driving force from the engine is prevented from being transmitted to the propeller when the crankshaft rotation speed is lower than a prescribed value. (See for example Japanese Utility Model Publication (kokoku) No. 60-24714.) This can reduce the necessary starting torque produced from a recoil starter and thereby facilitate the starting of the engine. In such outboard motors, however, a so-called “reverse rotation” of the engine (or crankshaft) tends to take place in the event of failure to successfully start the engine. The reverse rotation lowers the pressure inside the cylinder (or combustion chamber) of the engine, generating a negative exhaust pressure.
Thus, if a reverse rotation of the engine takes place in an outboard motor with the exhaust pipe outlet submerged under water, the engine will work as a suction pump and lift up water. Since the number of reciprocating movements of the piston in a single reverse rotation can be estimated to be fewer than five, if the volume inside the exhaust pipe between the water level and the engine exhaust valve (or exhaust port) is greater than five times of the displacement volume of piston, intrusion of water into the combustion chamber can be prevented. However, it is very difficult to achieve such an exhaust pipe having a sufficient volume in a small outboard motor which has little space to spare.
BRIEF SUMMARY OF THE INVENTION
In view of the above, a primary object of the present invention is to provide an improved outboard motor in that a driving force from the engine is prevented from being transmitted to the propeller during engine start and an exhaust pipe outlet is submerged under water in an operable state of the outboard motor, in which it is ensured that intrusion of water into the engine cylinder is prevented if a reverse rotation takes place as a result of unsuccessful engine start.
A second object of the present invention is to provide such an outboard motor in a simple and cost-effective manner.
According to the present invention, these and other objects can be accomplished by providing an outboard motor for a watercraft, comprising: an internal combustion engine having a crankshaft; a drive shaft extending generally vertically; a propeller shaft extending generally horizontally and carrying a propeller at its one end, the propeller shaft operatively connected to a lower end of the drive shaft; clutch means disposed between the crankshaft and the drive shaft for drivingly connecting the crankshaft to the drive shaft only when crankshaft rotation speed is higher than a prescribed rotation speed; an exhaust pipe having one end connected to an exhaust port of the internal combustion engine and extending generally vertically so that the other end thereof is submerged under water in an operable state of the outboard motor, the exhaust pipe provided with an exhaust vent which is positioned above a water level in an operable state of the outboard motor so that atmospheric air can enter the exhaust pipe through the exhaust vent when a pressure in the exhaust pipe becomes negative. Thus, when a reverse rotation takes place in the event of failure in starting the engine, the atmospheric air flowing into the exhaust pipe through the exhaust vent prevents the internal combustion engine from working as a suction pump, to thereby prevent intrusion of water into the engine cylinder.
In order to ensure that the exhaust vent is positioned above water when starting the engine, it is preferable that the outboard motor further comprises a stern bracket to attach the outboard motor to a transom of the watercraft and the exhaust vent is positioned above a surface of the stern bracket contacting an upper end of the watercraft transom in a state that the outboard motor is attached to the watercraft transom.
Further preferably, the outboard motor comprises an engine cowling for covering the internal combustion engine and the exhaust vent is positioned inside the engine cowling. This can minimize the water entrained with the air and entering the exhaust system through the exhaust vent.
When the engine is operating at low speeds or idling, it is often desirable that an exhaust gas from the internal combustion engine is allowed to be discharged through the exhaust vent to thereby reduce the back pressure of the exhaust gas. In such a case, it will be advantageous, for the purpose of preventing the exhaust gas discharged through the exhaust vent from adversely affecting the engine cowling or the like, if the outboard motor further comprises a cooling fan for cooling the internal combustion engine in such a manner that the exhaust gas discharged from the exhaust vent is carried by an air flow caused by the cooling fan to the outside of the engine cowling.
In a preferred embodiment of the invention, during normal speed operation of the outboard motor the exhaust gas flowing through the exhaust pipe drags outside air into the exhaust pipe through the exhaust vent in accordance with an “ejector effect.” Without any additional valve or the like, this can prevent a relatively large amount of exhaust gas generated during normal speed operation of the outboard motor from being discharged through the above-water exhaust vent and causing discomfort to the user on the watercraft. This will be particularly beneficial in such an outboard motor in that the exhaust vent is positioned inside the engine cowling in view of preventing the hot exhaust gas from being discharged into and adversely affecting the engine cowling if utilized.
The present invention will be particularly advantageous in the outboard motors where the clutch means consists of a centrifugal clutch system which can automatically prevent the driving force of the engine from being transmitted to the propeller when the crankshaft rotation speed is lower than a prescribed value such as when starting the engine.
According to a preferred embodiment of the present invention, the outboard motor comprises a subsidiary exhaust pipe connected to the exhaust pipe, the subsidiary exhaust pipe having a first opening aligned with an opening provided to the exhaust pipe and a second opening which is positioned above the water level in an operable state of the outboard motor so as to serve as the exhaust vent. Such configuration can facilitate the adjustment of the orientation and/or size of the exhaust vent. Moreover, the subsidiary exhaust pipe may comprise a plate member having a plurality of holes and disposed transversely in the subsidiary exhaust pipe so that the subsidiary exhaust pipe functions as a muffle
Aihara Takao
Kawamura Hiroshi
Tanaka Mitsuharu
Honda Giken Kogyo Kabushiki Kaisha
MacPherson Alan H.
Michelson Greg J.
Skjerven Morrill & MacPherson LLP
Stormer Russell D.
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