Powershift transfer case

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 range clutch operable in an actuated mode for coupling said carrier assembly for common rotation with said input shaft and in a non-actuated mode for releasing said carrier assembly from coupled engagement with said input shaft;
• a second range clutch operable in an actuated mode for coupling said second sun gear to said housing to brake rotation thereof and in a non-actuated mode for releasing said second sun gear from coupled engagement with said housing;
• 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 pinion gears journally supported thereon that are meshed with said third and fourth sun gears;
• a mode clutch operable for controlling speed differentiation between said front and rear output shafts, said mode 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 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 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 position;
• 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 each of said first and second range clutches and said mode clutch in response to said mode signal and said sensor input signals, said controller causing said first range clutch to be shifted into its actuated mode and said second range clutch to be shifted into its non-actuated mode and thereafter modulate the position of said thrust mechanism between said first and second 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 first and second range clutches to be shifted into their respective non-actuated modes and move said thrust mechanism to said first position when said mode signal indicates selection of said neutral mode, and wherein said controller causes said first range clutch to be shifted into its non-actuated mode and said second range clutch to be shifted into its actuated mode and move said thrust mechanism to said second position when said mode signal indicates selection of said part-time four-wheel low-range drive mode.