Over the past several decades, substantial effort has been invested in the design and development of improved internal combustion engines. Design efforts have been, directed toward the creation of smaller, lighter engines with improved fuel efficiency and power. Engines have been characterized by their method of combustion, e.g., compression (diesel) or spark-ignited (gasoline). Further, engines are described and identified by the orientation and/or number of their pistons and cylinders, e.g., V-8, in-line 6, radial, Wankel rotary, horizontal and horizontally-opposed.
Internal combustion engines with horizontally-oriented pistons and cylinders have been the subject of much research over the past several decades. Their inherent low profile offers an opportunity to reduce engine size while maintaining fuel efficiency and power. Various countries have introduced several variations of both four cylinder and six cylinder horizontally-oriented engines.
A typical horizontally-oriented engine configuration includes multiple pairs of horizontal cylinders with a separate piston slidably disposed in each separate cylinder. The top or "crown" of each piston, in combination with the cylinder walls and a separate cylinder head, forms a unique, single combustion chamber. Each cylinder head, also provides a separate surface for intake and exhaust valve assemblies. In the case of spark-ignited engines, each cylinder head also provides a port for installation of some means for igniting the combustible mixture, usually a spark plug. For a typical horizontally oriented engine, each piston is connected to a common crankshaft.
During operation, a mixture of air and fuel is introduced into each combustion chamber. The mixture is then combusted, by either compression (diesel engines) or a spark (gasoline engines). When combusted, the energy generated by the exothermic expansion of the combustible mixture serves to drive the piston away from the cylinder head. In so doing, the piston's linear kinetic energy is delivered to the engine's crankshaft by a connecting rod rotatably attached to the piston. The crankshaft then delivers rotational power to the power train.
Several patents have offered modifications to the typical horizontally-oriented piston and cylinder configuration. Most notably, and of relevance to the present invention, is that prior art which teaches horizontally-oriented engine configurations with one combustion chamber shared between two or more pistons/cylinders. Generally, these types of engines are known as horizontally-opposed engines.
For example, Henry (U.S. Pat. No. 1,533,004) teaches an internal combustion engine with a combustion chamber shared between two cylinders. The shared combustion chamber is formed by the walls of two interconnected cylinders, the crowns of two opposing pistons which slidably reciprocate within the cylinders, and a single cylinder head. In addition to acting as a wall of the shared combustion chamber, the cylinder head provides a surface for intake and exhaust ports as well as spark plug access. In Henry, the pistons simultaneously converge toward each other and then simultaneously diverge away from each other during the various engine cycles.
Other patents, including most notably Feeback (U.S. Pat. No. 3,485,221), Rassey (U.S. Pat. No. 4,244,338), Johnson (U.S. Pat. No. 4,554,894) and Honkanen (U.S. Pat. No. 5,133,306) have proposed variations on the horizontally-opposed engine configuration. Each of the above include intake and exhaust valve assemblies which are located to the side of each cylinder pair. Consequently, as with Henry discussed above, these engines all require at least one separate cylinder head per cylinder pair.
Other relevant prior art teaches internal combustion engines with shared combustion chambers, but whose converging pistons are not horizontally-oriented. For example, Ascari (U.S. Pat. No. 5,447,818) teaches an engine with at least four cylinders that form two separate shared combustion chambers. Two cylinders and pistons are oriented at angles of approximately ninety degrees to each other, with the crown of each piston oriented toward a shared plane of symmetry. Ascari likens his engine to a "superimposed twin V." Again, the shared combustion chamber is formed by the cylinder wall, two piston crowns and a single cylinder head.
The prior art clearly evidences that the ability to reduce the overall size and weight of opposed piston engines with shared combustion chambers has been hampered by the need to include a suitable surface, i.e. a cylinder head, to accommodate the shared intake and exhaust valve assemblies. As previously indicated, in engines without shared combustion chambers, each cylinder has a cylinder head which provides a surface for the valve assemblies. Engines with shared combustion chambers have generally provided for the placement of the shared intake and exhaust valve assemblies in a separate "cylinder head-like" element that is separately bolted to the side of the cylinder blocks.
The present invention advances the prior art by eliminating the need for a separate cylinder head. Although the prior art teaches reduction in the number of required cylinder heads for dual piston/cylinder engine configurations from two to one, it still struggles with valve design and placement. The intake and exhaust valve assemblies are typically located between the ends of the dual cylinders to serve a common or shared combustion chamber. Consequently, this additional space requirement frequently limited the ability to bring the ends of the cylinders, and hence, the crowns of the pistons, closely together.
The patent to Rassey specifically teaches that "previous attempts to adapt poppet valves [in horizontally-opposed engines] have proven largely unsuccessful since the poppet valves cannot be positioned above the piston head as in the more conventional internal combustion engines."
Accordingly, a need exists for a cylinder/piston configuration of simple and reliable design which includes a combustion chamber shared between two horizontally-opposed cylinder/piston assemblies, yet allows the use of poppet valve assemblies to service the shared combustion chamber, while eliminating the need for a separate cylinder head to house the valve assemblies, thereby minimizing the size, weight and vertical profile of the engine for equivalent power requirements and providing for smoother, more efficient and less polluting operation.