Combuistion engine with variable compression ratio

The crankshaft has an eccentric sleeve (4) rotatably mounted on the crankpin (3) and engaging with a drive gear so that it rotates only with activation of the drive gear relative to the crankpin. The drive gear is formed by a motor (7) with a worm (6), whereby the worm meshes with teeth (5) on the sleeve. The gearing consisting of the teeth on the sleeve and on the worm is self-locking. The drive gear may be hydraulically or electrically actuated. The drive gear is connected to the crankshaft bearing's oil supply via a piloted valve.