Marine propulsion – Means for accomodating or moving engine fluids – Cooling for engine
Reexamination Certificate
2002-02-13
2003-03-04
Swinehart, Ed (Department: 3617)
Marine propulsion
Means for accomodating or moving engine fluids
Cooling for engine
Reexamination Certificate
active
06527604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an outboard engine mounted to a boat's stern with a mounting device having a tilt shaft, and more particularly, to a structure related to a return oil path for returning lubricant oil to an oil pan after lubricating portions of an engine to be lubricated.
2. Description of the Related Art
Heretofore, lubricant oil discharged from an oil pan in an outboard engine has been returned to the oil pan located at a lower portion of an engine body through a return oil path after lubricating some portions of the engine to be lubricated. Regarding such a return oil path, in an outboard engine disclosed in Japanese Patent Laid-Open Publication No. hei 7-149290, for example, an opening is provided in an occlusive plate forming the bottom wall of the engine block of the engine having a vertically extending crankshaft, such that return oil flowing from the crank chamber onto the occlusive plate can drop into the oil pan through the opening through an oil communication path formed in an engine mount case. Below the occlusive plate, a flywheel is disposed, which is fixed to a lower end portion of the crankshaft extending through the occlusive plate, covered by the occlusive plate thereabove, and surrounded by the circumferential wall of an engine mount case and an encircling wall. The oil communication path is formed between the encircling wall that is one of the circumferential wall and the encircling wall located behind and another circumferential wall located behind the encircling wall with a distance, and the opening is formed at a rear portion of the occlusive plate opposite from the flywheel located forward with respect to the encircling wall.
In the conventional outboard engine, the opening defining the return oil path for returning the lubricant oil accumulating in the crank chamber to the oil pan is located at a rear portion of the crank chamber located above the flywheel. Therefore, if the outboard engine is driven in a tilt-up condition during cruising in shallow water, part of the lubricant oil on the occlusive plate stays in a front portion within the crank chamber. As a result, the quantity of the lubricant oil returning to the oil pan decreases as much as the retained quantity. Thus, in order to prevent shortage of the supply amount of lubricant oil to portions to be lubricated, the conventional outboard engine has the need of using a large quantity of lubricant oil beforehand, and this forces to use a bulky oil pan and hence causes the outboard engine to be bulky and heavy. Furthermore, in a configuration where the crankshaft stirs the lubricant oil staying in the crank chamber, it invites an increase of the output loss of the engine. In addition, since a relatively large quantity of retained lubricant oil rushes to the opening immediately after the tilt-up is released during operation of the outboard engine, for the purpose of ensuring smooth outflow of lubricant oil from the crank chamber, the opening must be large, the occlusive plate inevitably becomes large, and these have encumbered realization of a compact, lightweight outboard engine.
The present invention has been made cognizing those problems in the background, and its main object is to provide a compact, lightweight outboard engine and prevent its output loss by substantially eliminating or minimizing the possibility of lubricant oil staying in the crank chamber during operation of the outboard engine in the tilt-up condition. Another object of the invention is to enable an inflow opening of the return oil path to be located in an optimum location.
SUMMARY OF THE INVENTION
According to the invention, there is provided an outboard engine having an engine body, an engine including a flywheel positioned at a lower end portion of a crankshaft extending vertically in the engine body and an oil pan positioned below the flywheel, a supply oil path for supplying lubricant oil released from an oil pump to a portion of the engine to be lubricated, and a return oil path for returning lubricant oil supplied to the portion to be lubricated back to the oil pan, and mounted to a boat stern with a mount device having a tilt shaft, characterized in that an upper wall of a flywheel chamber accommodating the flywheel is made up of a bottom wall of a crank chamber of the engine, the bottom wall having a front return oil path at a location forward of an inner circumferential surface of a circumferential wall of the flywheel chamber, the front return oil path being an oil path forming the return oil path to return lubricant oil from the crank chamber.
According to the invention, lubricant oil present in the crank chamber after lubricating portions of the engine to be lubricated flows down or drops onto the bottom wall of the crank chamber, then flows along the upper surface of the bottom wall forming the upper wall of the flywheel chamber, and flows into the return oil path, exiting from the crank chamber, until finally returning back to the oil pan
5
. When the outboard engine is driven under a tilt-up condition, such as during cruising in shallow water, lubricant oil flowing on the bottom wall, then inclining down forward, flows into the front return oil path positioned forward of the inner circumferential wall surface of the circumferential wall of the flywheel chamber. Therefore, during operation under a tilt-up condition, it is possible to substantially prevent or minimize lubricant oil staying on the bottom wall. Also, immediately after the tilt-up condition is released, since substantially no lubricant oil or only an extremely small amount of lubricant oil stays in the cranks chamber, lubricant oil smoothly flows out from the crank chamber through the front return oil path.
As a result, the following effects are obtained. That is, when the outboard engine is in a tilt-up condition, since almost all of lubricant oil present on the bottom wall of the crankcase in the crank chamber flows into the front return oil path and finally returns back to the oil pan without staying on the bottom wall, it is possible to substantially prevent or minimize lubricant oil staying on the bottom wall. Therefore, unlike the conventional techniques, there is no need of increasing the quantity of lubricant oil retained in the oil pan, which will be required to be larger in capacity, taking account of the quantity of lubricant oil that will stay in the crank chamber. Accordingly, the oil pan can be decreased in size and weight, and the outboard engine can be decreased in size and weight as well.
Further, since it is substantially prevented that the crankshaft stirs lubricant oil staying in the crank chamber, output loss by agitation of lubricant oil can be prevented. Furthermore, since substantially no or only an extremely small amount of lubricant oil stays in the crank chamber, the front return oil path need not be increased in diameter for the purpose of ensuring smooth outflow of lubricant oil from the crank chamber including the lubricant oil having stayed there, immediately after the tilt-up condition is canceled, the front return oil path can be decreased in diameter in comparison to those of the conventional techniques, and the outboard engine can be made compact and lightweight so much.
Preferably, the circumferential wall is made up of double-wall portions and single-wall portions, a left wall portion and a right wall portion of the circumferential wall are made up of the single-wall portions, a front wall portion of the circumferential wall is made up of the double-wall portion having an inner wall and an outer wall, and the inner wall and the outer wall of the front wall portion define a space therebetween, in which the return oil path is formed.
According to this configuration, since the left wall portion and the right wall portion forming a part of the circumferential wall of the flywheel chamber are made up of single-wall portions, i.e. single-layered walls in the radial direction of the flywheel, the outer diameter of the flywheel chamber decreases in th
Kuroda Tatsuya
Tsubouchi Masanori
Tsunoda Masaki
Tsusaka Haruo
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Honda Giken Kogyo Kabushiki Kaisha
Swinehart Ed
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