Semi-active electrorheological fluid clutch for electronic door lock

An electronic door lock, comprising:

• a rotatable door handle;
• a handle shaft operably connected to the door handle and capable of being rotationally actuated thereby, the handle shaft having an inner camming surface;
• a lock shaft with an aperture therein, the lock shaft axially co-aligned with and rotatably mounted adjacent the handle shaft and rotatably connected to a latch mechanism;
• a bellow spring disposed in the aperture;
• a rheological fluid held within the bellow spring, the fluid having a first state in which the fluid has a first viscosity and a second state in which the fluid has a second viscosity;
• a plunger biased by the bellow spring into selective coupling engagement with the handle shaft and capable of selective linear motion into the aperture in response to contact with the inner camming surface due to relative rotation of the handle shaft with respect to the lock shaft;
• and
• a restriction disposed within the bellow spring 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 the restriction is capable of being selectively electrically activated to change the rheological fluid adjacent the orifice from the first viscosity to the second viscosity, in the second viscosity state the rheological fluid exerts a hydraulic blocking force sufficient to impede the linear motion of the plunger into the aperture, and
• wherein the hydraulic blocking force maintains coupling engagement between the plunger and the handle shaft when the plunger is rotationally contacted by the inner camming surface thereby coupling the lock shaft with the handle shaft to unlock the latch mechanism.

A method of coupling an outer door handle shaft with an inner door handle shaft in an electronic door lock, comprising:

• applying an electrical current to a rheological fluid housed internally within the inner door handle shaft, wherein the application of the electrical current changes the rheological fluid from a first viscosity state to a second viscosity state, and wherein the second viscosity state exerts a hydraulic blocking force sufficient to impede linear motion of a plunger into the inner door handle shaft;
• and
• rotating the outer door handle shaft relative to the inner door handle shaft to contact a camming surface of the outer door handle shaft with the plunger thereby allowing for coupling rotation of the inner door handle shaft with the outer door handle shaft,
• wherein the rheological fluid is housed within a first chamber and a second chamber which are divided by a restriction, and
• the restriction comprises an orifice that allows a portion of the rheological fluid to flow between the first chamber and the second chamber through when the rheological fluid is in the first viscosity state.