Variable compression-ratio mechanism and working method thereof

The invention provides a variable compression-ratio mechanism. The variable compression-ratio mechanism comprises a connecting rod and an eccentric member; two ends of the connecting rod are separately a first end and a second end; the first end of the connecting rod is used for being connected with a piston, and a circular cavity is formed in the first end; the eccentric member is disposed in thecavity in the first end of the connecting rod and capable of rotating circumferentially; the eccentric member and the first end of the connecting rod are jointly connected with the piston through a piston pin; the length of the center of the piston pin to the center of the second end of the connecting rod is changed through the rotation of the eccentric member, and therefore the position of a topdead center of the piston is changed so as to achieve the purpose of changing the compression ratio; a first hydraulic chamber and a second hydraulic chamber are disposed in the first end of the connecting rod; the first hydr