The long-term constraint on the design structure principle of an
internal combustion engine transmission conversion mechanism is broken through, two sets of pistons, gears and racks are symmetrically arranged to form linkage assemblies, the two linkage assemblies form a
coupling relation with the 90-degree
phase difference, and the two
coupling assemblies alternately do work and are overlapped for shift connection. The racks which are disengaged during operation of the mechanism are thoroughly separated from a load, and the racks are clamped at the corresponding positions of
piston stop points under the cooperation of the gears and lock a re-entering tooth
entry point; and the disengaged gears are driven by the
coupling assemblies, rotate to the
entry point along a set restriction track of the racks, and are integrated to be engaged again. Through locking of the racks, constant-volume
combustion, constant-volume interval computer tracking and timely ignition are created, and coupling meshing with synchronous rack speed is achieved. According to an improved
internal combustion engine, the alternating side pressure of a
crankshaft dead point and the pistons on the
pipe wall is eliminated, loss is reduced, vibration is reduced, the conversion efficiency of working medium gas is improved,
combustion is thorough,
pollution is reduced, the environment is protected, and power and performance are greatly improved.