The present invention is directed to internal combustion engines and more particularly to internal combustion engines having oblong cylinders.
Internal combustion engines have been developed which employ engine cylinders which are not circular in cross-section. These cylinders have been elliptical in the true mathematical sense, oblong and broadly elliptical or oval. In describing such cylinders, the term "oval" will be used to cover rounded cross-sections which are other than circular and which may be truly elliptical or broadly elliptical, e.g. having rounded ends and straight sides. In most cases, engines employing these piston and cylinder configurations were developed as a means for effecting a reduced external dimension of the engine in question without reducing its overall displacement. A variety of configurations have been developed with the long dimension of the engine cylinders both parallel and perpendicular to the crankshaft and one such design has employed two connecting rods associated with the piston for coupling with the crankshaft (British Patent No. 142,516).
The present invention is associated with the development of an oval piston internal combustion engine which is designed for relatively high speed operation. The engine employs a valve configuration which, for volumetric and fluid dynamic reasons (see co-pending application Ser. No. 91,837 filed Nov. 6, 1979 now U.S. Pat. No. 4,256,068), enables productive speeds on the order of 19,000 RPM. With speeds approaching 20,000 RPM, a variety of special conditions must be considered. Among these, friction and inertial forces become increasingly important factors in realizing efficient and reliable engine operation. The large inertial effects on the pistons, connecting rods and crankshaft associated with such high speed operation can cause detrimental vibrational effects, particularly in the crankshaft. Principal load requirements on the crankshaft also become more and more imposing with increased engine RPM. The piston may also take on unusual motions at higher RPM's.
The normal practice responsive to increased forces is to simply strengthen the components. To this end, a larger crankshaft diameter would normally be warranted. The same is true of the connecting rod associated with the piston. However, these normal practices find disadvantage in the increased inertia and the increased friction resulting from the increase in engine speed.
The friction of a rotating bearing increases roughly as a power of 1 to 1-1/2 of the diameter of the bearing. As greater inertial loads are placed on the crankshaft and connecting rods, greater diameters would normally be employed to resist direct and vibrational loadings. With the increases in crankshaft diameter, friction is rapidly increased. The added inertia also results in greater structural requirements throughout the engine if reliability is to be maintained. Thus, designs employing a substantially strengthened crankshaft and connecting rods have proved to negate some of the power advantages achieved by the unusual engine design.