Internal-combustion engines – Poppet valve operating mechanism – Overhead camshaft
Reexamination Certificate
2000-03-29
2001-08-21
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Overhead camshaft
C123S090390, C123S090440, C123S090600
Reexamination Certificate
active
06276324
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 lawnmowers, other lawn and garden implements, or in small utility vehicles such as riding lawnmowers, lawn tractors, and the like. In particular, the invention relates to a drive train for such engines where the intake and exhaust valves are actuated by rocker arms which are rotated by a cam ring, the cam ring driven by a timing shaft with gears at each end to connect the cam ring to the crankshaft.
2. Description of the Related Art
Prior known engines that contain drive trains of an overhead valve design are well known in the art. In one arrangement, the crankshaft supplies rotary mechanical motion to a camshaft by means of a belt, chain, or the like through a pulley or sprocket mounted on the camshaft. The camshaft includes one or more lobes that actuate the intake and exhaust valves in the cylinder head either directly, or indirectly through the use of rocker arms, push rods, or other similar means.
In another arrangement, the 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 reciprocate a pair of push rods extending therefrom to the cylinder head, which in turn rotate a pair of rocker arms mounted in the cylinder head to open and close intake and exhaust valves.
A disadvantage with the first arrangement is that the location of the camshaft in the cylinder head increases the width of the cylinder head due to the lateral space between cam lobes and between a cam lobe and the pulley or sprocket which is driven from the crankshaft. In addition, the location of the camshaft directly above the valves, and the relatively large size of the pulley or sprocket necessary for speed reduction from the crankshaft increase the length of the cylinder head. Further, the belt or chain which drives the camshaft from the crankshaft is prone to wearing or breakage.
A disadvantage with the second arrangement is that the several components of the drive train, including the camshaft, camshaft lobes, cam followers, cam follower shafts, push rods, and rocker arms tend to increase the size, complexity, and cost of the engine, as well as the difficulty of assembly and likelihood of failure of one of the components. The relatively large number of reciprocating parts additionally increases engine noise.
An additional disadvantage of each of the above arrangements is that they permit little variation in the location, size, and arrangement of the components thereof, and therefore restrict design freedom.
What is needed is an engine having a drive train which is compact, to allow a smaller cylinder head, shorter engine length, and an overall reduced engine silhouette.
Another need is for an engine having a drive train including a minimum number of durable components and a minimum number of reciprocating components.
A further need is for an engine in which the location and size of the drive train components may be varied to allow a large degree of design freedom.
SUMMARY OF THE INVENTION
The present invention provides a drive train for an overhead cam engine where the cylinder head valves are actuated by rocker arms having cam follower portions which engage cam lobes on an upper surface of a cam ring which rotates on an axis coincident with the axis on which the piston reciprocates, and is driven by the crankshaft through the drive linkage.
The drive linkage may be a gear train arrangement including a drive gear mounted to the crankshaft which drives a timing shaft having gears at each end thereof, which in turn drives the cam ring. The valve sequence, kinematics and timing are controlled by the lobe placement on the cam ring. In one embodiment, the cam ring includes gear teeth about an outer periphery thereof, which are in engagement with a gear mounted on the timing shaft. In a second embodiment, the cam ring rotates with a gear ring attached to the underside of the cam ring. The cam ring or gear ring may be carried on a plane bearing on a top surface of the cylinder head, such that the cam ring rotates around the valve stems, and valve stems extend through the center of the cam ring.
In one form thereof, an overhead cam engine is provided, including a crankshaft, connecting rod and piston assembly, the piston reciprocating within a cylinder bore in a cylinder block along an axis, the cylinder block connected to a cylinder head; a cam ring supported in the cylinder head above the cylinder bore for rotation about the axis, the cam ring including an upper surface with at least one cam lobe protruding therefrom; drive linkage connected between the crankshaft and the cam ring; and a pair of rocker arms rotatably mounted in the cylinder head, the rocker arms engaging the at least one cam lobe to actuate a pair of valves in the cylinder head.
In another form thereof, the cam ring has gear teeth around an outer periphery thereof, and is supported for rotation on the cylinder head about the piston axis.
In a further form thereof, an overhead cam engine is provided including a crankshaft, connecting rod and piston assembly, the piston reciprocating within a cylinder bore and a cylinder block along an axis, the cylinder block connected to a cylinder head; a gear ring rotatably supported on the cylinder head above the cylinder bore; a cam ring attached to the gear ring and rotatable therewith about an axis parallel to the piston axis, the cam ring including an upper surface and at least one cam lobe protruding from the upper surface; drive linkage connected between the crankshaft and the gear ring; and a pair of rocker arms rotatably mounted in the cylinder head, the rocker arms engaging the at least one cam lobe to actuate a pair of valves in the cylinder head.
An advantage of this arrangement is that the cam ring design permits the valves to be disposed in a plane which may be oriented at an infinite number of rotational angles relative to the crankshaft. Therefore, the intake an exhaust ports, muffler and carburetor may be disposed at a variety of locations on the engine block. Additionally, the valves may be oriented in a plane which allows maximum access to cooling air directed thereto from the flywheel.
An additional advantage is that the cam ring obviates the need for a camshaft, and the location of the cam ring may be shifted either toward or away from the crankshaft along the piston axis, where the length of the timing shaft is easily varied to accommodate various locations of the cam ring. This allows the engine dimension from the crankshaft to the extreme edge of the rocker box cover, and the engine silhouette, to be reduced as compared to a typical overhead camshaft engine.
Additionally, the number and location of the lobes on the cam ring may be varied such that the cam ring may actuate two or four valves. Also, the number of reciprocating components in the drive train is minimized, resulting in quieter operation of the engine.
The timing shaft is located in a timing shaft pocket integral with the cylinder block, and is disposed underneath the cylinder block parallel with the cylinder bore in a vertical crankshaft orientation, or oriented vertically adjacent the cylinder bore in a horizontal crankshaft configuration. In either configuration, the timing shaft pocket provides a passage for returning lubricating oil to the crankcase from the rocker box located above the cylinder head.
In addition, the engine includes a crankcase which is split along a plane disposed at an angle acute to the crankshaft to define a cylinder casing and a mounting flange casing, allowing both of the crankshaft journals to be carried in fill bearings. The cylinder block, cylinder head, and flywheel bearing are integral with the cylinder casing. The main bearing is located within the mounting flange casing. Splitting the cylinder and mounting flange casings i
Adams Gar M.
Immel Thomas A.
Baker & Daniels
Corrigan Jaime
Denion Thomas
Tecumseh Products Company
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