Electric control apparatus for four-wheel steering system

An electric control apparatus for a four-wheel steering system in an automotive vehicle having a set of dirigible front road wheels and a set of dirigible rear road wheels, comprising:

• mode selection means for selecting any one of a plurality of rear wheel steering modes;
• memory means for memorizing a plurality of control rules respectively corresponding with the rear wheel steering modes;
• calculation means for calculating a steering angle of the rear road wheels on a basis of the memorized control rule corresponding with the selected rear wheel steering mode;
• and
• an electrically operated rear wheel steering mechanism for steering the rear road wheels at the calculated steering angle;
• wherein the electric control apparatus further comprises first means for calculating a difference between new and old steering angles respectively calculated by said calculation means when the selected rear wheel steering mode has been changed to another one of the rear wheel steering modes and immediately before change of the selected rear wheel steering mode;
• second means for gradually decreasing an absolute value of the calculated difference at a predetermined time interval;
• and third means for correcting the new steering angle in accordance with the absolute value of the calculated difference until the absolute value becomes zero after change of the selected rear wheel steering mode and for controlling an actual steering angle of the rear road wheels in accordance with the corrected new steering angle.