Abstract: Overrunning Speed Clutch is one of the key pats in impulse Stepless Speed Regulators, and working capability depends on the control factor of its mechanism efficiency, twist moment and life-span. Aiming at the characteristic of poor dynamic-power, additional dynamic load and speed fluctuation of the
higher pair Overrunning Speed Clutch, we put forward a new lower-pair Differential and Double Brake-block Overrun-ning Speed Clutch, and introducing the process of its evolution.The internal contact between the natural increment coefficient and brake blocks was studied, the natural increment coefficient is an important gist, which scales and distinguishes whether Differential and Double Brake-block Overrunning Speed
Clutch can realize normal work or not. According to analyze the company coupler mechanism of Differential and Double Brake-block Overrunning Speed Clutch, we consider this kind of Overrunning Speed Clutch possesses the character functions that can pressurize through internal force. It can automatically adapt to the slight size change of output shaft in the direction of X ax-is and Y axis. So the working ability is improved.

Key words: overrunning speed clutch, evolution, company coupler mechanism, automatic adaptability