On demand vehicle drive system

In an adaptive vehicle drive system including a primary drive shaft coupled to a primary differential having an output coupled to a primary pair of driven wheels, a secondary drive shaft coupled to a secondary differential having an output coupled to a secondary pair of driven wheels, the improvement comprising,

• a transfer case having a driven input shaft, a planetary gear speed reducing assembly coupled to said input shaft and having an output member, a primary output shaft coupled to said primary drive shaft, clutch means for selectively coupling said primary output shaft to one of said input shaft and said output member, a secondary output shaft coupled to said secondary drive shaft, modulating clutch means for selectively coupling said primary output shaft to said secondary output shaft and substantially decoupling said primary output shaft from said secondary output shaft,
• means for sensing the rotational speed of said primary output shaft,
• means for sensing the rotational speed of said secondary output shaft, and
• a microcontroller including means for comparing the speed of said primary output shaft and said secondary output shaft and incrementally engaging said modulating clutch when the difference between said speeds exceeds a predetermined value.

A torque distributing system for a vehicle comprising, in combination,

• a first drive shaft coupled to a first differential having an output coupled to a first pair of drive wheels,
• a second drive shaft coupled to a second differential having an output coupled to a second pair of drive wheels,
• a transfer case having a first output shaft coupled to said first drive shaft, a second output shaft coupled to said second drive shaft, clutch means for selectively transferring torque from said first output shaft to said second output shaft and substantially inhibiting torque transfer from said first output shaft to said second output shaft,
• means for sensing the rotational speed of said first output shaft and providing a first speed signal,
• means for sensing the rotational speed of said second output shaft and providing a second speed signal, and
• a microcontroller including first means for determining the speed of such vehicle from said first signal, second means for computing the difference between said first and said second speed signals, third means for generating a clutch incrementing signal when said speed difference exceeds a predetermined value related to said vehicle speed and fourth means for generating a clutch decrementing signal when said speed difference no longer exceeds said predetermined value.

An adaptive four-wheel vehicle drive system comprising, in combination,

• a primary drive shaft coupled to a primary differential having an output coupled to a primary pair of drive wheels,
• a secondary drive shaft coupled to a secondary differential having an output coupled to a secondary pair of drive wheels,
• a transfer case having a primary output shaft coupled to said primary drive shaft, a secondary output shaft coupled to said secondary drive shaft, modulating electromagnetic clutch means for selectively transferring torque from said primary output shaft to said secondary output shaft and substantially inhibiting torque transfer from said primary output shaft to said secondary output shaft,
• sensor means for determining vehicle conditions, and
• control means for providing a predetermined minimum current to said electromagnetic clutch means to maintain said clutch means, said secondary drive shaft and said secondary differential in a staged condition.

An adaptive four-wheel vehicle drive system comprising, in combination,

• a primary drive shaft coupled to a primary differential having an output coupled to a primary pair of driven wheels,
• a secondary drive shaft coupled to a secondary differential having an output coupled to a secondary pair of driven wheels through an axle engaging and disengaging means,
• a transfer case having a primary output shaft coupled to said primary drive shaft, a secondary output shaft coupled to said secondary drive shaft, modulating clutch means for selectively transferring torque from said primary output shaft to said secondary output shaft and substantially inhibiting torque transfer from said primary output shaft to said secondary output shaft,
• sensor means for determining vehicle conditions, and
• microcontroller means for applying a minimum level of current to said modulating clutch, engaging said secondary axle engaging and disengaging means and inhibiting incrementing of said modulating clutch for a predetermined time period.

An adaptive four-wheel drive system including a transfer case component for four-wheel drive operation having a primary output shaft and a secondary output shaft, an adjustable clutch, and means for controlling operation of said clutch in response to a demand for increased torque, said means for controlling clutch operation comprising:

• means for providing a measure of primary output shaft speed,
• means for providing a measure of secondary output shaft speed,
• means for determining a desired speed difference between said primary output shaft speed and said secondary output shaft speed,
• means for determining a measure of the speed difference between said primary output shaft speed and said secondary output shaft speed,
• means for comparing said desired speed difference and said measured actual speed difference to provide an error signal representative of the difference between said desired speed difference and said measured actual speed difference,
• means responsive to said error signal for providing an output signal representative of a required clutch engagement rate to allow said clutch to engage at a required controlled amount to facilitate a coupling of said primary output shaft and said secondary output shaft and a required clutch disengagement rate to allow said clutch to disengage at a required controlled amount to facilitate substantial decoupling of said primary output shaft and said secondary output shaft.

In an adaptive four-wheel drive system including a torque distributing system for four-wheel drive operation having a primary drive and a secondary drive line, clutch means associated with said secondary drive line, and means for controlling operation of said clutch means in response to predetermined conditions, a method for controlling clutch operation comprising:

• determining primary drive line speed,
• determining secondary drive line speed,
• determining the speed difference between said primary drive line speed and said secondary drive line speed,
• comparing a desired speed difference and said determined speed difference to provide a signal representative of the difference between said desired speed difference and said determined speed difference,
• engaging said clutch at a predetermined rate to transfer torque from said primary drive line to said secondary drive line, and
• disengaging said clutch at a predetermined rate to substantially inhibit torque transfer from said primary drive line to said secondary drive line.

An adaptive four-wheel vehicle drive system comprising, in combination,

• a primary drive line having primary drive wheels,
• a secondary drive line having secondary drive wheels,
• a transfer means having a primary output shaft adapted to drive said primary drive line, a secondary output shaft adapted to drive said secondary drive line,
• modulating clutch means for selectively transferring torque from said primary drive line to said secondary drive line and substantially isolating said primary drive line from said secondary drive line,
• means for sensing the rotational speed of said primary drive line,
• means for sensing the rotational speed of said secondary drive line, and
• microcontroller means for comparing the speed of said primary drive line with the speed of said secondary drive line and incrementally engaging said modulating clutch means when the difference between said speeds is greater than a predetermined value.

A method of controlling torque delivery in a four-wheel vehicle drive system comprising the steps of:

• sensing the speed of a primary drive line having a primary drive shaft and primary drive wheels and providing a primary speed signal,
• sensing the speed of a secondary drive line having a secondary drive shaft and secondary drive wheels and providing a secondary speed signal,
• comparing said primary speed signal and said secondary speed signal to determine a difference value, and
• incrementally engaging a clutch to transfer torque from said primary drive line to said secondary drive line when said difference value exceeds a predetermined value dependent upon vehicle speed and incrementally disengaging said clutch to isolate said primary drive line from said secondary drive line when said difference value is less than said predetermined value.

A transfer case for use in a four-wheel drive vehicle comprising, in combination,

• an input shaft,
• a primary output shaft,
• a secondary output shaft,
• a speed reducing assembly coupled to said input shaft and having an output member, clutch means for selectively coupling said primary output shaft to either said input shaft or said output member of said speed reducing assembly, electric drive means for positioning said clutch means and encoder means for providing data indicating said clutch means position,
• modulating clutch means operably disposed between said primary output shaft and said secondary output shaft for selectively substantially inhibiting torque transfer between said primary output shaft and said secondary output shaft and providing incremental levels of torque transfer between said primary output shaft and said secondary output shaft, said modulating clutch means including a disc pack clutch operably disposed between said primary output shaft and said secondary output shaft, and means for incrementally engaging said disc pack clutch.