Port sealing in a rotary valve

A rotary valve assembly for an internal combustion engine comprising:

• a valve having a cylindrical center portion,
• an inlet port and an exhaust port terminating respectively as an inlet opening and an exhaust opening in the periphery of said center portion,
• a cylinder head having a bore in which said valve rotates about an axis with a predetermined clearance between said bore and said center portion, said center portion having a bridge spanning between said inlet opening and said exhaust opening,
• a window in said bore communicating with a combustion chamber, said inlet opening and said exhaust opening periodically communicating with said window as said valve rotates about said axis,
• first and second floating elongate axial seals substantially parallel with said axis and adjacent opposite sides of said window, each located in a slot in said bore and biased against said center portion, and
• at least one floating elongate axial masking seal is located in a blind ended slot in said bore and biased against said center portion, said masking seal being disposed substantially parallel to said axis, circumferentially outside said window and circumferentially remote from each of said first and second axial seals, the axial extremities of said inlet and exhaust openings being axially between the ends of said masking seal,
• wherein said masking seal is in contact with said bridge during at least one portion of a cycle where a pressure gradient across said bridge is high and a resulting leakage across said bridge significantly adversely affects performance of said internal combustion engine.