The invention discloses a double-
crankshaft-contained variable-compression-ratio Atkinson-cycle internal-
combustion engine mechanism, which is an internal-
combustion engine technology and is used for improving the
usability of an Atkinson-cycle internal-
combustion engine and improving the
thermal efficiency of the internal-combustion engine to enable the
thermal efficiency to be approximate to the highest theoretical efficiency of a
Carnot cycle. The mechanism comprises a rocking arm, a second
crankshaft, a connecting rod of the second
crankshaft, a driving chain, a phase
regulator and a derived three-crankshaft Atkinson internal-combustion engine mechanism, wherein the rocking arm is used for connecting a
piston connecting rod and a connecting rod of a first crankshaft; the second crankshaft and the connecting rod of the second crankshaft are used for driving the rocking arm to make periodic motion; the driving chain is used for connecting gears on the first crankshaft and the second crankshaft; the
gear ratio of the gear for the first crankshaft to the gear for the second crankshaft is 1:2; and the phase
regulator is used for regulating the rotary
phase relation between the first crankshaft and the second crankshaft. Through the double-crankshaft-contained variable-compression-ratio Atkinson-cycle internal-combustion engine mechanism, the
fuel efficiency of a naturally-aspirated internal-combustion engine can be effectively improved, and meanwhile, the double-crankshaft-contained variable-compression-ratio Atkinson-cycle internal-combustion engine mechanism has the actions of additionally regulating the
compression ratio and changing the discharging quantity within a
small range.