Patent ID: 8783218

Claim:
An internal combustion engine, comprising: a cylinder wall; a first piston disposed in the cylinder; a second piston disposed in the cylinder in an opposed relationship with respect to the first piston; a crankshaft having first and second eccentric journals; a first connecting rod coupling the first piston to the first eccentric journal; and a second connecting rod coupling the second piston to the second eccentric journal, wherein: the pistons reciprocate within the cylinder upon rotation of the crankshaft; there is a particular angle of rotation of the crankshaft at which the pistons are closest to each other; the piston top of the first piston has three regions: a center, an outer ring near the periphery of the piston, and an inner ring, all of which have a center that is substantially coincident with a central axis of the cylinder; the piston top of the second piston has three regions: a center, an outer ring near the periphery of the piston, and an inner ring, all of which have a center that is substantially coincident with the central axis of the cylinder; a face of the first piston and a face of the second piston are a predetermined distance apart in their respective center regions and the same predetermined distance apart in their respective outer rings when the crankshaft is at the particular angle, the predetermined distance is taken in a direction parallel to the central axis of the cylinder; and a volume between the first and second pistons proximate the inner ring substantially forms a toroidal volume when the crankshaft is at the particular angle.