Driving-torque control system for four-wheel-drive vehicle

A driving-torque control system for a four-wheel drive vehicle with main drive wheels and auxiliary drive wheels, said control system comprising:

• a transfer clutch for variably adjusting a driving-torque distribution ratio between said main drive wheels and said auxiliary drive wheels by varying an engaging force of said transfer clutch;
• speed difference detection means for detecting a speed difference between said main drive wheels and said auxiliary drive wheels;
• calculation means for deriving a command value of said engaging force of said transfer clutch from said speed difference;
• load-condition detection means for detecting an input load condition of said transfer clutch, on the basis of said speed difference and said command value of said engaging force;
• means for comparing said input load condition detected by said load-condition detection means with a predetermined threshold;
• engaging-force compensation means for compensating said engaging force of said transfer clutch so that said engaging force is held at a maximum for a predetermined holding time duration when said input load condition detected by said load-condition detection means exceeds said predetermined threshold;
• and
• holding-time-duration compensation means for monitoring a state of operation of said engaging-force compensation means, and for compensating said predetermined holding time duration in response to the state of operation of said engaging-force compensation means.

A driving-torque control system for a four-wheel-drive vehicle, said control system comprising:

• a transfer clutch employed in a transfer of the four-wheel-drive vehicle for varying a distribution ratio of driving torque between front and rear road wheels depending on a front-and-rear wheel revolution-speed difference;
• a calculation unit configured to derive a command value of an engaging force of said transfer clutch from said front-and-rear wheel revolution-speed difference;
• a load-condition detection unit coupled to said transfer clutch and said calculation unit, said load-condition detection unit configured to detect an input load condition of said transfer clutch, on the basis of said front-and-rear wheel revolution-speed difference and said command value of said engaging force;
• a comparing unit coupled to said load-condition detection unit and configured to compare said input load condition detected by said load-condition detection unit with a predetermined threshold;
• and
• a compensation unit coupled to said comparing unit and configured to compensate said engaging force of said transfer clutch so that said transfer clutch is held in a completely engaged state for a predetermined holding time duration, when the input load condition exceeds said predetermined threshold.