Torque distribution control system for four wheel drive vehicle

A vehicle comprising:

• a power unit comprising an engine;
• a wheel system comprising left and right front wheels and left and right rear wheels;
• a drive system for transmitting a driving torque from said power unit to said front and rear wheels, said drive system comprising an input member for receiving the driving torque from said power unit, a first output member for driving said rear wheels, a second output member for driving said front wheels, and a torque distributing clutch through which said second output member is drivingly connected with said input member;
• a sensor group comprising rotation sensors for sensing an actual wheel speed of each of said front and rear wheels, and a sensor for sensing a turning motion of the vehicle;
• an actuator for varying a clutch engagement force of said torque distributing clutch in accordance with a control signal;
• and
• a controller for receiving signals from said sensors, determining an actual front wheel speed of said front wheels, an actual rear wheel speed of said rear wheels, an actual front and rear wheel speed difference which is a difference resulting from subtraction of said front wheel speed from said rear wheel speed, an actual lateral acceleration of the vehicle, a dead band which increases with increase in said lateral acceleration, a corrected front and rear wheel speed difference which is a difference resulting from subtraction of said dead band from said actual front and rear wheel speed difference, and a desired control magnitude which increases with increase in said corrected wheel speed difference, and producing said control signal representing said desired control magnitude.

A vehicle comprising:

• a power unit comprising an engine and a transmission;
• a wheel system comprising left and right front wheels and left and right rear wheels;
• a drive system comprising a transfer, a front drive line comprising a front differential connected between said left and right front wheels and a front propeller shaft drivingly connecting said front differential with said transfer, and a rear drive line comprising a rear differential connected between said left and right rear wheels and a rear propeller shaft driving connecting said rear differential with said transfer, said transfer comprising an input member connected with said transmission, a first output member which is always connected with said input member of said transfer and which is further connected with said rear propeller shaft, a second output member which is drivingly connected with said front propeller shaft, and a multiple disk transfer clutch for continuously varying a driving torque transmitted to said left and right front wheels, said second output member being connected through said transfer clutch with said input member;
• a hydraulic system comprising a solenoid valve for producing said control oil pressure in accordance with an electric control signal;
• a sensor group for sensing a wheel speed of each of said wheels, and a lateral acceleration of the vehicle;
• and
• a controller for determining an actual front wheel speed which is an arithmetic mean of the wheel speeds of said left and right wheels, an actual rear wheel speed which is an arithmetic mean of the wheel speeds of said left and right wheels, an actual front and rear wheel speed difference which is a difference resulting from subtraction of said actual front wheel speed from said actual rear wheel speed, a dead band which is a quantity continuously increasing as said lateral acceleration increases, a corrected front and rear wheel speed difference which is a difference resulting from subtraction of said dead band from said actual front and rear wheel speed difference, a control gain which is inversely proportional to said lateral acceleration, and a desired clutch engagement force which is a product resulting from multiplication of said corrected front and rear wheel speed difference by said control gain, and for producing said control signal representing said desired clutch engagement force.