On demand vehicle drive system

An adaptive four-wheel vehicle drive system (10;10') comprising, in combination,

• a primary drive line (32,36,38;12',14',24') including a primary drive shaft (38;24) and primary drive wheels (34;22'),
• a secondary drive line (12,14,24;32',36',37) including a secondary drive shaft (24;37) and secondary wheels (22;34'), a transfer means (28,25) having a primary output shaft (40) adapted to drive said primary drive wheels (34;22'), a secondary output shaft (26;37) adapted to drive said secondary drive wheels (22;34'), modulating clutch means having a primary, cone clutch (125) and a secondary disc pack clutch (150) (124;124') for selectively transferring torque from said primary output shaft (40) to said secondary output shaft (26;37),
• means (170;170') for sensing the rotational speed of said primary drive line (32,36,38;12',14',24'),
• means (176;176') for sensing the rotational speed of said secondary drive line (12,14,24;32',36',37),
• and microcontroller means (200) for comparing the long-term speed of said primary drive line (32,36,38;12',14',24') with the speed of said secondary drive line (12,14,24;32',36',37) and determining an average speed difference, comparing the speed of said primary drive line (32,36,38;12',14',24') with the speed of said secondary drive line (12,14,24;32',36',37) and determining a short-term speed difference and engaging said modulating clutch means (124;124') when the short-term difference between said speeds is greater than a predetermined value adjusted by said average speed difference and incrementally disengaging said modulating clutch means (124;124') when said difference is less than said predetermined value adjusted by said average speed difference.

A method of controlling torque delivery in a four-wheel vehicle drive system (10;10') comprising the steps of:

• sensing the speed of a primary drive line (32,36,38;12',14',24') having a drive shaft and drive wheels and providing a primary speed signal,
• sensing the speed of a secondary drive line (12,14,24;32',36',37) having a drive shaft and drive wheels and providing a secondary speed signal,
• comparing said primary speed signal and said secondary speed signal to determine a first transient difference value and a second non-transient difference value, and
• engaging a clutch (124;124') to transfer torque from said primary drive line (32,36,38;12',14',24') to said secondary drive line (12,14,24;32',36',37) when said transient difference value exceeds a predetermined value adjusted by said non-transient difference value and disengaging said clutch when said transient difference value is less than said predetermined value adjusted by said non-transient difference value.