Crankcase arrangement for engine

Details Crankcase arrangement for engine Crankcase arrangement for engine

2000-07-31

2001-12-04

McMahon, Marguerite (Department: 3747)

Internal-combustion engines

Frame construction

Horizontal cylinder

C123S1950HC, C123S1960CP

Reexamination Certificate

active

06325037

ABSTRACT:

PRIORITY INFORMATION
This invention is based on and claims priority to Japanese Patent Applications No. Hei 11-216563, filed Jul. 30, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a crankcase arrangement for an engine, and more particularly relates to a crankshaft bearing structure suitable for a vertically oriented engine.
2. Description of Related Art
A typical outboard motor employs an internal combustion engine disposed within a power head of the motor. The engine includes a crankshaft that extends generally vertically. The crankshaft is confined in a crankcase cavity defined by a cylinder body and a crankcase member, and is rotatably journaled by a bearing structure formed between the cylinder body and the crankcase member. The bearing structure thus extends generally transversely across an axis of the crankshaft in the crankcase cavity.
The engine normally includes a lubrication system to lubricate various moving portions of the engine. The crankshaft bearing structure is one of such portions that need lubrication. Lubricant (e.g., oil) often is supplied to the crankshaft bearing structure from a lubricant reservoir by a lubricant pump through one or more lubricant passages formed within the cylinder body. The lubricant reservoir is normally disposed in a driveshaft housing of the outboard motor, which depends from a power head, and the crankshaft usually drives the lubricant pump.
The oil lubricates the crankshaft bearing structure and then is spattered toward an internal side wall of the crankcase member by the centrifugal force produced with rotation of the crankshaft. The majority of the lubricant first adheres on the wall and then cascades down to the bottom of the crankcase cavity so as to return to the lubricant reservoir under gravity.
The flow direction of the lubricant, however, is across the transversely extending crankshaft bearing structure. This construction of the bearing structures, which protrudes from the sidewall of the crankcase member, blocks the lubricant from flowing downwardly to the lubricant reservoir.
In one prior arrangement, such as that disclosed by Japanese Laid-Open Patent Publication No. Hei 09-273406, through-holes are provided in the respective bearing sections adjacent to the sidewall of the crankcase member so as to permit the lubricant to fall more freely towards the bottom of the crankcase. Japanese Laid-Open Patent Publication No. Hei 09-273407 discloses another arrangement to address the foregoing problem. In this arrangement, a bearing cap is provided separately from a crankcase member and a lubricant return passage is defined between the bearing cap and the crankcase member. Both constructions, however, suffer from other disadvantages.
If, in the arrangement of the former publication, the through-holes were large enough to produce a generally free flow of the lubricant, the rigidity of the bearing sections would be significantly reduced and the bearing structure would be weakened. Such Large holes in the slender section of the bearing section would weaken these structures. Conversely, smaller holes would not permit the lubricant to return quickly to the lubricant reservoir. The quick return of the lubricant to a lubricant reservoir is required because the lubricant must be recycled through the engine.
In the latter arrangement, the uppermost and lowermost bearing sections are slender. While this construction affords some clearance between the bearing cap and the crankcase member without increasing the height of the engine, it also weakens the bearing upper and lower bearing structure.
A need therefore exists for an improved crankshaft bearing structure for an engine that can allow the lubricant to return quickly to the lubricant reservoir from the crankcase even though the engine has a compact structure.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body, a crankcase member, a crankshaft and a bearing cap. The crankcase member defines a crankcase chamber with the cylinder body. The crankshaft extends within the crankcase chamber. The cylinder body includes at least a first bearing portion, an intermediate bearing portion and a second bearing portion. The crankcase member includes a first bearing section and a second bearing section. The cylinder body and the crankcase member rotatably journal the crankshaft between the upper bearing portion and the upper bearing section and also between the lower bearing portion and the lower bearing section. The bearing cap cooperates with the intermediate bearing portion to further rotatably journal the crankshaft within the crankcase. The bearing cap can be attached to the cylinder body apart from the crankcase member.
In accordance with another aspect of the present invention, a crankshaft bearing arrangement is provided for an internal combustion engine. The engine has a cylinder body and a crankcase member. The crankshaft bearing arrangement comprises a bearing cap and a plurality of fasteners. The cylinder body, the crankcase member and some of the fasteners form a first bearing unit. The cylinder body, the bearing cap and the rest of the fasteners form a second bearing unit.
In accordance with a further aspect of the present invention, a method is provided for supporting a crankshaft in an internal combustion engine. The method comprises affixing a bearing cap to a cylinder body so as to rotatably journal a crankshaft between the cylinder body and the bearing cap. The method further comprises affixing the crankcase member to the cylinder body so as to further rotatably journal the crankshaft between the cylinder body and the crankcase member.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment that follows.


REFERENCES:
patent: 4616610 (1986-10-01), Ishida
patent: 5009205 (1991-04-01), Abe et al.
patent: 5461940 (1995-10-01), Morita
patent: 5572959 (1996-11-01), Hedelin
patent: 5687686 (1997-11-01), Takahashi
patent: 5752866 (1998-05-01), Takahashi et al.
patent: 5778847 (1998-07-01), Takahashi et al.
patent: 5890461 (1999-04-01), Iikura
patent: 5904604 (1999-05-01), Suzuki et al.
patent: 5941205 (1999-08-01), Hiraoka et al.
patent: 9-273406 (1997-10-01), None
patent: 9-273407 (1997-10-01), None

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