Apparatus for determining linearity of tire characteristic

A program for determining linearity of tire characteristic, which causes a computer to execute a process to determine whether tires of a traveling vehicle stand in a linear region or in a non-linear region of the tire characteristic, the process comprising the steps of:

• receiving at least one of an operation amount of an operation unit with which a driver of the traveling vehicle performs a steering operation and an actually steered amount of steerable wheels of the traveling vehicle, which are detected by an operation amount detector and a steered amount detector, respectively;
• calculating a standard vehicle behavior indicator based upon the at least one of the operation amount of the operation unit and the actually steered amount of the steerable wheels;
• receiving an actual vehicle behavior indicator detected by a vehicle behavior detector;
• calculating a vehicle behavior deviation by subtracting the actual vehicle behavior indicator from the standard vehicle behavior indicator;
• calculating a rate of change of the vehicle behavior deviation;
• determining a first sign of one of the vehicle behavior deviation and the rate of change of the vehicle behavior deviation, and a second sign of the actual vehicle behavior indicator;
• if the first and second signs are both positive and the rate of change of the vehicle behavior deviation is greater than a first prescribed value, determining that the tires of the traveling vehicle stand in the non-linear region of the tire characteristic;
• and
• if the first and second signs are both negative and the rate of change of the vehicle behavior deviation is less than a second prescribed value, determining that the tires of the traveling vehicle stand in the non-linear region of the tire characteristic.

A steering control method for a steer-by-wire vehicle having a steer-by-wire system which includes an operation unit with which a driver performs a steering operation, a steering motor that drives steerable wheels to be steered, and a reaction force motor that gives a reaction force against operation of the operation unit, to perform a steering operation through electric connections, the method comprising:

• calculating a standard vehicle behavior indicator based upon at least one of an operation amount of the operation unit and an actually steered amount of the steerable wheels;
• comparing an actual vehicle behavior indicator obtained by detection with the standard vehicle behavior indicator, to determine whether tires of the vehicle during traveling stand in a linear region or in a non-linear region of tire characteristic;
• and
• if it is determined that the tires of the traveling vehicle stand in the non-linear region of the tire characteristic, controlling at least one of the reaction force motor and the steering motor to steer the steerable wheels toward such a direction as to reduce the steering amount thereof.