It is an application of the 4-bar linkage with only revolution joints. The seat plays role of a connection rod. Green parts are used as buffers when unfolding.
Lift the front side of the seat to fold.

The list of all videos in channel thang010146 (uploaded till 31 Oct. 2017) including pictures, brief descriptions and YouTube links (2700 Animated Mechanical Mechanisms) now is available.The list consists of 4 parts:
Part 1: Transmission of continuous rotation
Part 2: Other kinds of motion transmission
Part 3: Mechanisms of specific purposes
Part 4: Mechanisms for various industries