Internal-combustion engines – Poppet valve operating mechanism
Reexamination Certificate
2000-03-17
2001-08-28
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
Reexamination Certificate
active
06279522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates to overhead valve engines, such as overhead cam 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. In particular, the invention relates a drive train for such engines in which the crankshaft drives an internally profiled cam gear which in turn actuates a pair of rocker arms having cam followers in engagement with the cam profile to open and close intake and exhaust valves in the cylinder head.
2. Description of the Related Art
Prior known engines containing 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 near 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, and the push rods rotate 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 in 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 drive train, including the camshaft, camshaft lobes, cam follower shaft, cam followers, push rods, and rocker arms tends to increase the overall size of the engine. The multiple components also increase the cost and complexity of the engine, the difficulty of assembly, 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 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 length of the cylinder head. In addition, the length 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 from the crankshaft is prone to wearing or breakage.
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.
A further need is for a drive train for an engine where the drive train is simplified and includes a minimum of components.
SUMMARY OF THE INVENTION
The present invention provides a drive train for an overhead cam engine, including a cam gear driven by the crankshaft through drive linkage, the cam gear having an internal cam profile surface, and a pair of cam followers extending from a pair of rocker arms mounted in the cylinder head, which engage the cam profile surface and actuate the rocker arms to open and close the intake and exhaust valves.
The internally profiled cam gear is mounted on a camshaft located in the side of the cylinder head, rather than axially above the cylinder bore as in previous arrangements, such that the cam gear is shifted toward the crankshaft and mounted in the side of the cylinder head closely adjacent the rocker arms and valves. The internally profiled cam gear is driven by the crankshaft at half speed through drive linkage, such as an intermediate gear driven by a drive gear mounted on the crankshaft. The intermediate gear and cam gear are located in a gear pocket integral with the cylinder block.
In one embodiment, the cam follower arms are rigidly connected to the rocker arms, and extend perpendicular to the cam gear and terminate in rollers which engage the internal cam profile of the cam gear.
Alternatively, in another embodiment, the rocker arms include cam follower arms that overlap each other in a crosswise arrangement and terminate in ends which each engage the internal cam profile of the cam gear.
In one form thereof, an overhead cam engine is provided, including a crankshaft, connecting rod, and piston assembly, the piston reciprocating within a cylinder block adjacent the cylinder head. A cam gear is driven by the crankshaft and rotatably supported in the cylinder head, the cam gear having gear teeth around an outer periphery thereof, and a cam profile surface disposed around an inner periphery thereof. Drive linkage is disposed between the crankshaft and the cam gear, and a pair of rocker arms are rotatably mounted in a cylinder block for actuating a pair of valves, each rocker arm including a cam follower in engagement with the cam profile surface.
An advantage of this arrangement is that it allows the size of the engine to be minimized. First, the cam gear is mounted laterally in the side of the cylinder head closely adjacent the rocker arms and valves. Also, the internal cam profile of the cam gear obviates the need for an external lobe mounted on the camshaft which would necessitate a larger cylinder head. Additionally, the cam follower arms engage the internal cam profile near an outer edge of the cam gear such that the outer edge of the cam gear does not extend substantially past the top of the valve stems, which further conserves space in the cylinder head.
A further advantage is that the diameter of the intermediate gear may be varied, and the intermediate gear may be disposed in a lateral offset relationship with the drive gear and the cam gear to accommodate differing shapes and sizes of engine housings. Also, the intermediate gear may be used to drive an auxiliary device such as a combination oil pump and governor, for example.
A further advantage is that the intake and exhaust valves are oriented in a plane parallel to the piston axis, such that cooling air from the flywheel is directed by the blower housing into contact with the cylinder head equally around the intake and exhaust valves. Additionally, air passages extending through the cylinder head above the intake and exhaust ports allow cooling air to flow through the cylinder head.
A further advantage is that oil pumped to the cylinder head may drain under gravity back into the oil sump through the gear pocket, and therefore does not need to be pumped back to the oil sump.
A still further advantage is that the drive train includes a simple gear set having a minimal number of durable components.
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Adams Gar M.
Balzar Rodney J.
Immel Thomas A.
Kubista Kyle I.
Baker & Daniels
Patel Vinod D
Tecumseh Products Company
Walberg Teresa
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