Torque transfer device having an electric motor/brake actuator and friction clutch

A transfer case for use in a four-wheel drive vehicle having a powertrain and first and second drivelines, comprising:

• a differential having an input driven by the powertrain and first and second outputs driving the first and second drivelines;
• a friction clutch assembly operably disposed between any two of said input and said first and second outputs of said differential;
• a clutch actuator for generating a clutch engagement force to be applied to said friction clutch assembly, said clutch actuator including a ball screw operator rotatably driven by one of said first and second outputs and having a first component in threaded engagement with a second component, said first component being axially moveable in response to relative rotation between said first and second components, said first component adapted to exert a clutch engagement force on said friction clutch assembly the magnitude of which corresponds to the axial position of said first component relative to said second component, and an electric motor having a rotor fixed for rotation with said second component of said ball screw operator, said motor is operable in a motor mode wherein said rotor is driven to cause relative rotation between said first and second components, and said motor is operable in a brake mode wherein said rotor is braked to cause relative rotation between said first and second components;
• and
• a controller for actuating said motor so as to control the direction and amount of rotation of said rotor which, in turn, controls the direction and amount of axial travel of said first component of said ball screw operator for varying the clutch engagement force exerted on said friction clutch assembly, said controller further operable for switching from said motor mode to said brake mode when the rotary speed of one of said first and second outputs exceeds a redetermined threshold value.

A power transmission device, comprising:

• a first rotary member;
• a second rotary member;
• a torque transfer mechanism for transferring drive torque from said first rotary member to said second rotary member, said torque transfer mechanism including a friction clutch assembly operably disposed between said first and second rotary members and a clutch actuator assembly for applying a clutch engagement force on said friction clutch assembly, said clutch actuator assembly including an electric motor having a rotor, and a torque/force conversion mechanism rotatively driven by one of said first and second rotary members and having a first component fixed for rotation with said rotor and a second component supported for movement between a first position and a second position in response to relative rotation between said first and second components, said second component operable to exert a minimum clutch engagement force on said friction clutch assembly when located in its first position and a maximum clutch engagement force when located in its second position, said motor being operable in a motor mode wherein said rotor is driven to cause relative rotation between said first and second components and a in brake mode wherein said rotor is braked to cause such relative rotation;
• and
• a controller for switching said electric motor from said motor mode into said brake mode when the rotary speed of one of said first and second rotary members exceeds a predetermined rotary speed value.