Patent ID: 7604089
Filing Date: 2009-10-20
Classification: B62D

Abstract:
1. A vehicle steering system comprising: a transmission ratio variable mechanism that is placed between a steering wheel and steerable vehicle wheels in a vehicle and includes an electric actuator, which is rotated to change a transmission ratio between a steering angle of the steering wheel and a turning angle of the steerable vehicle wheels, wherein the transmission ratio variable mechanism makes a change in the turning angle of the steerable vehicle wheels in a generally linear relationship with a sum of the steering angle of the steering wheel and a rotational angle of the electric actuator; a rotatable member that is rotated synchronously with the electric actuator; a lock means for locking and unlocking the transmission ratio variable mechanism, wherein the lock means locks the transmission ratio variable mechanism by holding the rotatable member and unlocks the transmission ratio variable mechanism by releasing the rotatable member; a control means for controlling the electric actuator and for checking whether the unlocking of the transmission ratio variable mechanism succeeds by rotating the rotatable member through rotation of the electric actuator in a stopped state of the vehicle; a storage means for storing an initial sum, which is obtained by summing the steering angle of the steering wheel and the rotational angle of the electric actuator before the checking of the unlocking of the transmission ratio variable mechanism by the control means; and a sensing means for sensing an abnormality of the storage means, wherein the sensing means determines that the storage means is abnormal when a sum, which is obtained by summing the steering angle of the steering wheel and the rotational angle of the electric actuator after the checking of the unlocking of the transmission ratio variable mechanism by the control means, differs from the initial sum, which is retrieved from the storage means.