Reduction of ring clipping in two-stroke cycle engines

A ported cylinder for an engine constructed for two stroke-cycle operation, in which:

• the cylinder includes a bore surface, a sidewall, and spaced-apart exhaust and intake ports;
• the exhaust port includes at least one generally circumferential array of port openings near an end of the cylinder, and each port opening extends from the bore through the sidewall;
• and,
• the port openings have a port opening shape in the bore surface defined by opposing top and bottom edges joined by side edges, and each of the top and bottom edges is characterized by rounded corner transitions to the side edges, a rounded peak, and inclined ramp portions extending from the rounded corner transitions to the rounded peak, in which the rounded peak is disposed between the rounded corners and is offset outwardly of a port opening, in a top center direction of a piston controlling the port.

An opposed piston engine;

• comprising:
• at least one cylinder with a bore surface and longitudinally-spaced exhaust and intake ports, and a pair of opposed pistons disposed in the cylinder for sliding movement along the bore surface;
• and,
• the exhaust port including at least one generally circumferential array of port openings near an end of the cylinder, and each port opening extending from the bore through the sidewall;
• in which,
• the port openings have a port opening shape in the bore surface defined by opposing top and bottom edges joined by side edges, and each of the top and bottom edges is characterized by rounded corner transitions to the side edges, a rounded peak, and inclined ramp portions extending from the rounded corner transitions to the rounded pea, in which the rounded peak is disposed between the rounded corners and is offset outwardly of a port opening, in a top center direction of a piston controlling the port.