Patent ID: 8561443

Claim:
A clutch for an electronic door lock, comprising: a rotatable first shaft having a camming surface; a second shaft with an aperture therein, the second shaft is axially co-aligned with and rotatably disposed adjacent the first shaft; a spring disposed in the aperture; a rheological fluid held within the aperture, the fluid capable of changing from a first state in which the fluid has a first viscosity to a second state in which the fluid has a second viscosity in response to the application of an electrical current across the fluid; a plunger biased by the spring into selective coupling engagement with the first shaft and capable of selective motion into the aperture in response to contact by the camming surface due to relative rotation of the first shaft with respect to the second shaft; and a restriction disposed within the aperture and having an orifice that extends from a first side of the restriction to a second side of the restriction, the orifice allowing communication of rheological fluid therethrough; wherein when the rheological fluid is in the second viscosity state and the plunger is contacted by the camming surface the fluid exerts a hydraulic blocking force which impedes the motion of the plunger into the aperture and maintains coupling engagement between the plunger and the first shaft.