Full-time transfer case with synchronized range shift mechanism and on-demand differentiation control

A power transfer system for a four-wheel drive motor vehicle having a power source and front and rear drivelines, comprising:

• a transfer case including a housing;
• an input shaft rotatably supported in said housing and driven by the power source;
• a front output shaft rotatably supported in said housing and coupled to the front driveline;
• a rear output shaft rotatably supported in said housing and coupled to the rear driveline;
• a quill shaft supported on said rear output shaft for rotation relative thereto;
• a gear reduction unit operable for defining a high-range drive mode whereat said quill shaft is driven at a direct speed ratio relative to said input shaft and a low-range drive mode whereat said quill shaft is driven at a reduced speed ratio relative to said input shaft, said gear reduction unit including a layshaft rotatably supported in said housing and having first and second gears secured thereto, a high-range gear secured to said input shaft that is meshed with said first gear on said layshaft, and a low-range gear rotatably supported on said quill shaft that is meshed with and rotatably driven by said second gear on said layshaft;
• a clutch apparatus including a range sleeve supported for rotation with said quill shaft and movement between a first range position whereat said range sleeve couples said input shaft to said quill shaft for establishing said high-range drive mode, a second range position whereat said range sleeve couples said low-range gear to said quill shaft for establishing said low-range drive mode, and a third range position whereat said range sleeve uncouples said quill shaft from said input shaft and said low-range gear for establishing a non-driven mode, and synchronizer means for causing speed synchronization between said input shaft and said quill shaft in response to movement of said range sleeve to said first range position, said synchronizer means further operable for causing speed synchronization between said quill shaft and said low-range gear in response to movement of said range sleeve to said second range position;
• a range actuator for moving said range sleeve;
• an interaxle differential interconnecting said quill shaft to said front and rear output shafts for permitting speed differentiation therebetween, said interaxle differential including a first sun gear fixed for rotation with said rear output shaft, a second sun gear rotatably supported on said rear output shaft and operably coupled to said front output shaft for rotation therewith, and a carrier assembly fixed for rotation with said quill shaft, said carrier assembly having a first pinion gear journally supported thereon that is meshed with said first sun gear and a second pinion gear journally supported thereon that is meshed with said second sun gear and said first pinion gear;
• a transfer clutch operable for controlling speed differentiation between said front and rear output shafts, said transfer clutch including a set of first clutch plates supported for rotation with said front output shaft, a set of second clutch plates supported for rotation with said rear output shaft and which are alternately interleaved with said first clutch plates, a thrust mechanism movable between a first mode position whereat a minimum clutch engagement force is exerted on said clutch plates for permitting unrestricted speed differentiation between said front and rear output shafts and a second mode position whereat a maximum clutch engagement force is exerted on said clutch plates for inhibiting speed differentiation, and a biasing mechanism for normally biasing said thrust mechanism toward said first mode position;
• and a mode actuator for selectively moving said thrust mechanism;
• sensor means for detecting dynamic and operational characteristics of the motor vehicle and generating sensor input signals indicative thereof;
• a mode select mechanism for enabling a vehicle operator to select one of a full-time four-wheel high-range drive mode, a part-time four-wheel low-range drive mode and a neutral mode, said mode select mechanism further operable for generating a mode signal indicative of the particular mode selected;
• and
• a controller for controlling actuation of said range and mode actuators in response to said mode signal and said sensor input signals, said controller causing said range actuator to move said range sleeve to said first range position and said mode actuator to move said thrust mechanism between said first and second mode positions as a function of said sensor input signals for automatically controlling speed differentiation between said front and rear output shafts when said mode signal indicates selection of said full-time four-wheel high-range drive mode, said controller causing said range actuator to move said range sleeve to said second range position and said mode actuator to move said thrust mechanism to said second mode position when said mode signal indicates selection of said part-time four-wheel low-range drive mode, and said controller causing said range actuator to move said range sleeve to said third range position and said mode actuator to move said thrust mechanism to said first mode position when said mode signal indicates selection of said neutral mode.