Full-time transfer case with synchronized range shift arrangement

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 planetary gear reduction unit operable for establishing a high-range drive mode in which said quill shaft is driven at a direct speed ratio relative to said input shaft and a low-range drive mode in which said quill shaft is driven at a reduced speed ratio relative to said input shaft, said planetary gear reduction unit having a first sun gear driven by said input shaft, a second sun gear, and a carrier assembly driving said quill shaft and having planet gears journally supported thereon intermeshed with said first and second sun gears;
• a first clutch apparatus including a first range sleeve supported for rotation with said input shaft and movement between a neutral position uncoupled from said carrier assembly and a high-range position coupling said input shaft to said carrier assembly, and first synchronizer means for causing speed synchronization between said input shaft and said carrier assembly in response to movement of said first range sleeve from its neutral position to its high-range position;
• a second clutch apparatus including a second range sleeve supported for rotation with said second sun gear of said dual-planetary gear reduction unit and movement between a neutral position uncoupled from said housing and a low-range position coupling said second sun gear to said housing, and second synchronizer means for causing speed synchronization between said second sun gear and said housing in response to movement of said second range sleeve from its neutral position to its low-range position;
• a drive mechanism interconnected to said first and second range sleeves for controlling coordinated movement thereof, said drive mechanism being movable between a first range position whereat said first range sleeve is located in its high-range position and said second range sleeve is located in its neutral position, a second range position whereat said first and second range sleeves are each located in its neutral position, and a third range position whereat said first range sleeve is located in its neutral position and said second range sleeve is located in its low-range position;
• a range actuator for moving said drive mechanism between said various range positions;
• an interaxle differential interconnecting said quill shaft to said front and rear output shafts for permitting speed differentiation therebetween, said interaxle differential including a third sun gear fixed for rotation with said rear output shaft, a fourth sun gear fixed for rotation with said front output shaft, and a second carrier assembly fixed for rotation with said quill shaft and having planet gears journally supported thereon that are meshed with said third and fourth sun gears;
• 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 secured to a first drum member that is secured for rotation with said front output shaft, a set of second clutch plates secured to a second drum member that is secured for rotation with said rear output shaft, said second clutch plates being alternately interleaved with said first clutch plates, a piston defining an oil chamber with one of said first and second drum members and being 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 piston toward said first mode position;
• and a mode actuator for selectively moving said piston, said mode actuator including a source of pressurized fluid and a control valve operable for regulating the supply of pressurized fluid to said oil chamber for moving said piston between said first and second mode positions;
• 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 neutral mode, and a part-time four-wheel low-range drive 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 drive mechanism to said first range position and actuate said control valve for modulating the position of said piston between said first and second mode positions as a function of said sensor input signals when said mode signal indicates selection of said full-time four-wheel high-range drive mode, wherein said controller causes said range actuator to move said drive mechanism to said second range position and actuate said control valve for moving said piston to said first mode position when said mode signal indicates selection of said neutral mode, and wherein said controller causes said range actuator to move said drive mechanism to said third range position and actuate said control valve for moving said piston to said second mode position when said mode signal indicates selection of said part-time four-wheel low-range drive mode.