Patent ID: 6871125

Claim:
A method of operating an electric vehicle having a left front, a right front, a left rear and a right rear wheel, and a plurality of drive motors, comprising the steps of: preparing a plurality of different steering modes, comprising an M 1 steering mode wherein the travel paths of the right and left rear wheels follow the travel paths of the right and left front wheels, respectively; an M 2 steering mode wherein the travel paths of the front and rear wheels lie parallel to each other; an M 3 steering mode wherein the rear wheel turning path relative to the wheel turning path is an inside wheel difference path; an M 4 steering mode wherein the vehicle turns to the right with the right rear wheel as the center of rotation of the turn, and turns to the left with the left rear wheel as the center of rotation of the turn; and, an M 5 steering mode wherein the vehicle turns to the right with the right front wheel as the center of rotation of the turn, and turns to the left with the left front wheel as the center of rotation of the turn; selecting one of the steering modes based on a particular driving condition, and giving a vehicle speed/direction command; and, controlling the steering angle and rotation of speed of each wheel separately, in accordance with a condition equation for performing steering/drive operations according to the selected steering mode and vehicle speed/direction command, thereby effecting steering/drive control separately for each wheel, wherein the condition equations required to perform steering/drive operations according to the steering mode M 1 can be expressed as the condition equations α 1 = - α 3 = tan - 1 ⁢ ( L R - W ) α 2 = - α 4 = tan - 1 ⁢ ( L R + W ) n 1 :n 2 :n 3 :n 4 =√{square root over (( R−W ) 2 +L 2 )}:√{square root over (( R+W ) 2 +L 2 )}:√{square root over (( R−W ) 2 +L 2 )}:√{square root over (( R+W ) 2 +L 2 )} where α 1 , α 2 , α 3 , and α 4 are the steering angles for the right front, left front, right rear, and left rear wheels, respectively; n 1 , n 2 , n 3 , and n 4 are the wheel rotation speeds for the right front, left front, right rear, and left rear wheels, respectively; L is the distance between each wheel and a center line X between the front wheels and rear wheels; W is the distance between each wheel and a center line Y between the right wheels and the left wheels; and, R, for the case in which the turning paths of the wheels inscribe concentric arcs, is the distance between the center of the concentric arcs and a point central to the locations of the four wheels.