Torque transfer device with double ball screw clutch actuator

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 having a first threaded component driven by said first output, a second threaded component in threaded engagement with said first threaded component, and a third threaded component in threaded engagement with said second threaded component, said third component being axially moveable relative to said second component in response to relative rotation between said first and second components, said third component adapted to exert a clutch engagement force on said friction clutch assembly the magnitude of which corresponds to the axial position of said third 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 third 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 predetermined 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 having a first component fixed for rotation with said first rotary member, a second component fixed for rotation with said rotor, and a third component supported for movement between a first position and a second position in response to relative rotation between said first and second components, said third 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 in a 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.