Internal-combustion engines – Poppet valve operating mechanism – Camshaft drive means
Reexamination Certificate
2000-10-30
2002-12-31
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
Camshaft drive means
C123S090270, C123S090440, C123S090600
Reexamination Certificate
active
06499453
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates to overhead valve engines for use in a variety of applications, such as walk behind lawnmowers, lawn and garden implements, or in small utility vehicles such as riding lawnmowers, lawn tractors, and the like.
2. Description of the Related Art
Prior known engines having drive trains of an overhead valve design are well known in the art. For example, in one known arrangement, a crankshaft drives a camshaft, located in the crankcase, through a gear set. The camshaft includes one or more lobes which actuate a pair of cam followers mounted for rotation on a cam follower shaft. The cam followers in turn actuate push rods extending from the crankcase to the cylinder head for rotating a pair of rocker arms mounted in the cylinder head to open and close the intake and exhaust valves.
In another known arrangement, a camshaft located within the cylinder head is driven from the crankshaft by means of a belt, chain, or the like. The camshaft includes one or more lobes that actuate the intake and exhaust valves either directly, or through a pair of rocker arms rotatably mounted in the cylinder head.
A disadvantage with the first arrangement is that the several components of the valve train, including the camshaft, cam lobes, cam follower shaft, cam followers, push rods, and rocker arms tend both to increase the inertial forces of the valve train and increase the overall size of the engine. The several components also increase the cost and complexity of the engine, the difficulty of assembly thereof, and the likelihood of failure of one of the components.
A disadvantage of the second arrangement is that locating the camshaft in the cylinder head does not allow for a compact engine design. Specifically, such an arrangement increases the width of the cylinder head due to the lateral space between cam lobes and/or between a cam lobe and the pulley or sprocket which is mounted on the camshaft and driven from the crankshaft. The location of the camshaft directly above the valves, when the camshaft actuates the valves directly, also increases the height of the cylinder head. In addition, the height of the cylinder head is further increased to accommodate the relatively large pulley or sprocket mounted on the camshaft which is necessary for speed reduction. Further, the belt, chain or the like which drives the camshaft in the crankshaft is prone to wearing or breakage.
Often, such engines include a pressure lubrication system to bring oil into contact with moving the parts in the engine crankcase. Alternatively, a splasher or other agitator driven from the crankshaft splashes oil in the oil sump to create an oil mist in the crankshaft of the engine. Pressure and turbulence in the crankcase caused by the reciprocating piston bring the oil mist into contact with the crank flywheel bearing, the coupling between the connecting rod and the crankshaft, and other components which require lubrication yet are not in contact with the oil sump. Also, splashed oil may contact such components in a random fashion to lubricate same. However, such a lubrication arrangement does not allow for the continuous and direct lubrication by liquid oil of the engine components which are not in contact with the oil sump, especially components which are located substantially above the oil sump. Problematically, such components are substantially unlubricated during the time immediately following engine startup, before an adequate oil mist can be generated in the crankcase and brought into contact with such components, or before sufficient time has elapsed for oil splash to lubricate such components. Also, in engines which include plunger oil pumps, it is desired to supply a greater amount of pressurized oil to components therein which require lubrication than the amount supplied by the plunger oil pumps in such engines.
In known engine designs, exhaust blow-by gases from the engine crankcase are either discharged through a breather into the atmosphere, or communicated to an air cleaner through a hose connecting the breather to the air cleaner, and communicated to the carburetor through a second hose connected to the air cleaner and the carburetor. Disadvantageously, this arrangement requires a hose, hose fittings located on each of the breather cover of the breather, the air cleaner, and the carburetor, as well as a number of hose clamps for securing the hoses to the fittings.
What is needed is a drive train for an engine which is compact, such that the drive train may allow a smaller engine height and width, and an overall reduced engine profile.
A further need is for a drive train for an engine, where the drive train is simplified, and includes a minimum number of components.
An additional need is for a method of more effectively directly and continuously lubricating by liquid oil moving parts in the crankcase which are located externally of the oil sump, to ensure direct and effective lubrication of such parts as soon as possible after engine startup, and during the running of the engine.
A further need is for a simplified air cleaner assembly which reduces the number of necessary components, as well as the difficulty of assembly, associated with attaching the air cleaner assembly to the breather cover and to the carburetor.
SUMMARY OF THE INVENTION
The present invention provides a drive train for an overhead valve engine, including a cam gear driven by the crankshaft, the cam gear supported for rotation in the cylinder block externally of the cylinder head and having a cam lobe mounted thereon for actuating a pair of rocker arms mounted for rocking motion in the cylinder head, which in turn actuate intake and exhaust valves in the cylinder head. The cam gear may be supported for rotation within a gear pocket located externally of the cylinder head, the gear pocket integral with the cylinder block and located radially adjacent the cylinder bore.
Advantageously, mounting the cam gear externally of the cylinder head allows the cam gear to be located within the gear pocket adjacent the cylinder bore and externally of the cylinder head, resulting in a reduced overall engine profile and a more compact engine design. The rocker arms include cam follower arms which extend into the gear pocket to engage the cam lobe at respective locations thereof which are located within the gear pocket and spaced opposite the crankshaft.
Additionally, a combination oil pump and governor assembly is driven from the crankshaft, and pumps oil through a first lubrication passageway provided in the crankcase of the engine to communicate oil to an oil seal around the upper crankshaft bearing. A second lubrication passageway provided in the crankshaft communicates oil from the oil seal around the upper crankshaft bearing to the coupling between the crankshaft and the connecting rod.
The combination oil pump and governor assembly supplies pumped oil directly to the moving parts within the crankcase, and advantageously, incorporates both the oil pump and governor into a single assembly, thereby reducing the number of engine components and also obviating the need for further engine space to accommodate separate oil pump and governor assemblies.
An air cleaner body is provided, having an integral fitting extending therefrom which fits within an opening in the breather cover to directly communicate the breather chamber with the air cleaner. Advantageuosly, the air cleaner body may be mounted to the cylinder block in an easy, one-step operation in which the fitting is inserted in to the breather cover opening and the air cleaner body is fastened directly to a mounting flange of the carburetor, thereby facilitating easier assembly and obviating the need for additional components such as hoses, hose fittings on each of the breather cover, air cleaner, and carburetor, and hose clamps.
In one form thereof, an internal combustion engine is provided, including a crankshaft, connecting rod, piston assembly, the piston reciprocating within a cylinder bore in a cylinder b
Adams Gar M.
Immel Thomas A.
Baker & Daniels
Dahbour Fadi H.
Tecumseh Products Company
Walberg Teresa
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