Methods and devices for controlling the compression ratio of an opposed piston engine

An opposed piston engine comprising:

• a rotatable collar slidably positioned coaxially and centrally around a fixed cylinder, wherein the collar is configured at a position between a portion of the fixed cylinder and a portion of a fixed sealing bearing, the collar comprising an opening for receiving intake fuel as the opening rotatably aligns with an intake opening in the cylinder and an intake opening in the bearing and for expelling exhaust from the cylinder as the opening separately, rotatably aligns with an exhaust opening in the cylinder and exhaust opening in the bearing as the engine cycles through its respective combustion cycle;
• driving means for rotating the collar and the opening in the collar;
• and
• a controller for controlling the voltage and current supplied to the driving means to control the rotation of the collar and the collar opening such that the collar opening aligns with the cylinder and bearing openings at the appropriate times to allow fuel to be appropriately fed to the engine's combustion chamber or allow combusted gases to be appropriately expelled from the combustion chamber, wherein the controller is further operable to control one or more rotational speeds of the collar and its respective opening, wherein one of the rotational speeds of the collar and the collar opening is half the speed of an average crankshaft speed.