Clutch fill control is the key enabler for a smooth clutch-to-clutch shift, which is critical for the performance and fuel economy of both automatic and hybrid transmissions. While a precise and robust clutch fill is crucial, its control is very challenging as the traditional approach is still in the open-loop fashion due to the lack of a feedback sensor. To address this challenge, a new clutch actuation mechanism is proposed, which realizes an internal feedback structure without any sensor measurement. The proposed mechanism is novel as it embeds all the control elements in the orifice area regulation, which successfully solves the precise and robust control of the hydraulic system with nonlinear dynamics. In this paper, we first present the working principle of the new clutch actuation mechanism. Then, the mechanical system design is shown and the system dynamic model is built. To this end, the proposed internal feedback control mechanism is fabricated and validated in a transmission testing fixture. The new mechanism performance is finally presented through a series of simulation and experimental results. © 2012 IEEE.