Two-stroke internal combustion engine with variable compression ratio and an exhaust port shutter

A two-stroke internal combustion engine comprising:

• at least one piston reciprocable within a cylinder;
• an exhaust port allowing communication of the cylinder with an exhaust passage, which port is opened and closed by the piston during the reciprocal motion thereof;
• moveable shutter means for varying the effective area of the exhaust port, which shutter means varies the effective area cyclically in a timed relationship to the reciprocal motion of the piston within the cylinder;
• a compression ratio variation mechanism additional to and separate from the moveable shutter means for varying a compression ratio of the cylinder;
• sensor means for measuring one or more operating characteristics of the engine and for generating signals corresponding thereto;
• and
• a control unit which processes the signals generated by the sensor means and controls the motion of the shutter means accordingly to control the effective area of the exhaust port and controls the compression ratio variation mechanism to vary the compression ratio of the cylinder;
• wherein:
• the engine uses gasoline as fuel and is capable of operating with both homogeneous charge compression ignition and spark ignition;
• the control unit at low speeds and/or loads of the engine controls the compression ratio variation mechanism to apply a first compression ratio in the cylinder and varies operation of the shutter means to reduce the effective area of the exhaust port during exhausting of combustion gases to trap combusted gases in the cylinder for mixing with subsequently introduced charge air and fuel to create a mixture suitable for homogeneous charge compression ignition;
• the control unit at high speeds and/or loads of the engine controls the compression ratio variation mechanism to apply a second lower compression ratio in the cylinder and varies operation of the shutter means to increase the effective area of the exhaust port during exhausting of combusted gases to facilitate spark ignition without undesired pre-ignition;
• the shutter means comprises a shutter and a transmission mechanism for oscillating the shutter between a first position in which the exhaust port has a first effective area and a second position in which the exhaust port has a second smaller effective area, the transmission mechanism being connected to a crankshaft connected to the piston of the engine and comprising a plurality of interconnected links;
• the control unit varies the first position of the shutter with change in sensed operating characteristics to advance or retard the opening of the exhaust passage;
• the shutter is in or close to the first position when the piston passes the shutter when moving from a top dead centre position thereof to a bottom dead centre position thereof;
• the control unit varies the first position of the shutter by varying the amplitude of oscillation of shutter travel between the first and second positions thereof, the control unit decreasing the shutter movement to retard opening of the exhaust passage;
• the second position of the shutter is constant for all engine operating conditions;
• an electro-mechanical device is connected to one of the interconnected links, the electro-mechanical device being controlled by the control unit to alter the configuration of the interconnected links to vary the cyclical motion of the shutter;
• and
• the motion of the shutter during the period between the uncovering of the inlet ports by the piston and the piston reaching the bottom dead centre position thereof is motion towards the second position of the shutter, whereby the effective area of the exhaust port is reduced to reduce loss of fresh charge from the cylinder.