1. Field of the Invention
The present invention is generally related to a shaft of an engine having a counterweight and a housing structure disposed at least partially around the counterweight and, more particularly, to a balance shaft support structure of which portions are formed integrally with housing structures of the crankcase and/or oil pan.
2. Description of the Related Art
Many different products are known in which a shaft of some type is provided with an overmolded structure which encapsulates the shaft.
U.S. Pat. No. 4,508,069, which issued to Dobler et al. on Apr. 2, 1985, describes an internal combustion engine balance shaft bearing arrangement at a crankcase. The arrangement for the balance shafts for balancing second order inertia forces on an internal combustion engine is described. The shafts run parallel to the crankshaft on both longitudinal walls of a crankcase and have the ends carrying the balance weights supported by means of journal bearings within the crankcase and having driven ends supported by means of roller bearings outside the crankcase in the region of a crankcase end wall.
U.S. Pat. No. 5,401,199, which issued to Shibata on Mar. 28, 1995, describes an outboard motor engine. Two embodiments of balancer arrangements for internal combustion engines particularly adapted for use in outboard motors are described. In each embodiment, the balancer shaft is journaled within the crankcase chamber of the engine and is driven from the crankcase from a point between its ends. Single and twin balancer shaft arrangements are disclosed.
U.S. Pat. No. 5,850,764, which issued to Bostelmann et al. on Dec. 22, 1998, describes a crankshaft drive for an internal combustion engine. It comprises at least one cylinder having a cylinder head, and a crankcase housing a crankshaft rotating at a predetermined direction and at a predetermined speed and a balance shaft extending parallel to the crankshaft and rotating at the predetermined speed of the crankshaft in a direction opposite to the predetermined rotating direction of the crankshaft. The crankshaft and the balance shaft carry balance weight means for balancing a mass of first order. An auxiliary shaft extends parallel to the crankshaft and rotates at the predetermined speed of the crankshaft in the predetermined rotating direction of the crankshaft. The auxiliary shaft carries a counterweight for balancing a residual moment resulting from the rotating balance shaft with respect to the rotating crank shaft.
U.S. Pat. No. 5,893,346, which issued to Hosoya on Apr. 13, 1999, describes an engine balance shaft. A mounting arrangement for a balance shaft of a four cycle overhead cam shaft internal combustion engine is described wherein the balance shaft is driven from the crankshaft and is disposed within the crankcase chamber and is disposed below the axis of rotation of the crankshaft. The balance shaft is driven from an end of the crankshaft and is journalled at least in part by a detachable crankshaft journaling member.
U.S. Pat. No. 6,186,111, which issued to Hilbig et al. on Feb. 13, 2001, describes a support arrangement for the crankcase of a reciprocating piston internal combustion engine. The support arrangement for the open area of a crankcase facing an oil pan in an internal combustion engine has a plate-like component which is attached to the crankcase walls by lugs, thereby reinforcing the housing, and contains integral bearings rotatably supporting a balance shaft.
U.S. Pat. No. 6,189,499, which issued to Iwata et al. on Feb. 20, 2001, describes a balancing device for a reciprocating engine. There is provided a balancing device for a reciprocating engine comprising two balance shafts gear connected to each other, a chain/sprocket mechanism for coupling at least one of the balance shafts with a crankshaft in an interlocking fashion, a chain tensioner for automatically adjusting the tension of the chain and a pump receiving portion integrally provided in a balance shaft holder for supporting the balance shafts for receiving a rotor of a lubricating oil pump.
U.S. Pat. No. 6,601,557, which issued to Hayman et al. on Aug. 5, 2003, describes an engine oil pump and balance shaft module. It includes a housing supporting a rotatable balance shaft carrying at opposite ends balance weights for offsetting unbalanced forces of the engine. The balance weights are enclosed in open top enclosures from which oil is pumped by veins on the weights and an associated gear, driven by the engine crankshaft.
U.S. Pat. No. 6,708,663, which issued to Stuckler on Mar. 23, 2004, describes a device for balancing out mass forces in internal combustion engines. The device compensates the inertia forces in reciprocating piston machines and consists of a balance shaft housing and balance weights mounted in the latter in friction bearings and having compensating weights. The balance shaft housing is fastened in one part and to the engine block.
U.S. Pat. No. 7,201,622, which issued to Hoi on Apr. 10, 2007, describes an internal combustion engine including improved balance shaft structure. An internal combustion engine is provided for a personal watercraft. A portion of the engine is enlarged to accommodate a balance shaft and is minimized in size, whereby the internal combustion engine is made compact. Balance shafts for preventing secondary vibration are arranged together with a crankshaft on a dividing plane between a crankcase and a cylinder block of an internal combustion engine.
U.S. Pat. No. 7,341,039, which issued to Jaszewski et al. on Mar. 11, 2008, discloses a lubrication system for a marine propulsion system with a tilted in-line engine. The lubrication system for an in-line engine which has a piston symmetry plane that is tilted relative to the vertical plane is provided with an oil pan and windage tray that facilitates the transfer of oil from a rotating crankshaft to the oil pan without excessive aeration. In addition, it facilitates the removal of entrained air from liquid oil as it passes from the crankshaft to a pool of oil collected in an oil pan. A windage tray is provided with a louver structure and a louver opening structure that assists this passage of oil droplets without undue aeration being caused.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It would be significantly beneficial if balance shafts could be effectively supported with a minimal amount of hardware required. It would also be beneficial if the balance shafts could be efficiently enclosed within a housing structure below or adjacent to an engine. A significant improvement could be provided if the weight of the overall engine structure, with its balance shaft support components, could be reduced. Additionally, it would be beneficial if the overall number of components could be reduced so that assembly costs are minimized.