Torque modulated transfer case

A power transfer system for a motor vehicle having an engine and first and second sets of wheels, said power transfer system comprising:

• a transfer case having an input shaft rotatably driven by the engine, a first output shaft interconnected to the first set of wheels, a second output shaft interconnected to the second set of wheels, a shift mechanism movable between an engaged position for coupling said first output shaft to said input shaft for establishing a drive mode and a released position for uncoupling said first output shaft from said input shaft for establishing a non-driven mode, a transfer clutch for selectively transmitting drive torque from said first output shaft to said second output shaft, said transfer clutch being operable for varying the drive torque transmitted therethrough in relation to a corresponding variation in a clutch engagement force, a drive mechanism for generating said clutch engagement force, said drive mechanism movable between a first position whereat a minimum clutch engagement force is generated and a second position whereat a maximum clutch engagement force is generated, a movement coordinating apparatus for coordinating movement of said shift mechanism and said drive mechanism, and an actuator for selectively moving said movement coordinating apparatus between a two-wheel drive position whereat said shift mechanism is in said engaged position and said drive mechanism is in said first position, a four-wheel drive position whereat said shift mechanism is in said engaged position and said drive mechanism is in said second position, and a neutral position whereat said shift mechanism is in said released position and said drive mechanism is in said first position;
• sensor means for sensing an operational characteristic of the vehicle and generating an input signal indicative thereof;
• mode select means for enabling a vehicle operator to select one of a Part-Time Four-Wheel drive mode, an On-Demand drive mode and a Neutral mode and generate a mode signal indicative of the particular mode selected;
• and
• controller means for controlling actuation of said actuator in accordance with said input signal and said mode signal, and wherein said controller means is operable for causing said actuator to move said movement coordinating apparatus to said four-wheel drive position when said mode signal indicates selection of said Part-Time Four-Wheel drive mode, said controller means causing said actuator to modulate the position of said movement coordinating apparatus between said two-wheel drive and four-wheel drive positions as a function of the magnitude of said input signal for varying the torque transmitted through said transfer clutch when said On-Demand drive mode is selected, and said controller means operable for causing said actuator to move said movement coordinating apparatus to said neutral position when said Neutral mode is selected.

A power transfer system for a motor vehicle having an engine and first and second sets of wheels, said power transfer system comprising:

• a transfer case having an input shaft rotatably driven by the engine, a first output shaft interconnected to the first set of wheels, a second output shaft interconnected to the second set of wheels, a shift mechanism movable between an engaged position for coupling said first output shaft to said input shaft for establishing a drive mode and a released position for uncoupling said first output shaft from said input shaft for establishing a non-driven mode, a transfer clutch for selectively transmitting drive torque from said first output shaft to said second output shaft, said transfer clutch being operable for varying the drive torque transmitted therethrough in relation to a corresponding variation in a clutch engagement force, a drive mechanism for generating said clutch engagement force, said drive mechanism movable between a first position whereat a minimum clutch engagement force is generated and a second position whereat a maximum clutch engagement force is generated, a movement coordinating apparatus for coordinating movement of said shift mechanism and said drive mechanism, and an actuator for selectively moving said movement coordinating apparatus between a two-wheel drive position whereat said shift mechanism is in said engaged position and said drive mechanism is in said first position, a four-wheel drive position whereat said shift mechanism is in said engaged position and said drive mechanism is in said second position, and a neutral position whereat said shift mechanism is in said released position and said drive mechanism is in said first position;
• sensor means for sensing the rotational speed of the first and second set of wheels and respectively generating first and second speed signals indicative thereof;
• mode select means for enabling a vehicle operator to select one of a Two-Wheel drive mode, a Part-Time Four-Wheel drive mode, an On-Demand drive mode and a Neutral mode and generate a mode signal indicative of the particular mode selected;
• and
• controller means for receiving said first and second signals and generating a speed differential signal that is indicative of a speed differential between the first and second set of wheels, said controller means operable for controlling actuation of said actuator in accordance with said speed differential signal and said mode signal, said controller means causing said actuator to move said movement coordinating apparatus to said two-wheel drive position when said mode signal indicates selection of said Two-Wheel drive mode, said controller means causing said actuator to move said movement coordinating apparatus to said four-wheel drive position when said mode signal indicates selection of said Part-Time Four-Wheel drive mode, said controller means causing said actuator to modulate the position of said movement coordinating apparatus between said two-wheel drive and four-wheel drive positions as a function of said speed differential signal for varying the torque transmitted through said transfer clutch when said On-Demand drive mode is selected, and said controller means operable for causing said actuator to move said movement coordinating apparatus to said neutral position when said Neutral mode is selected.