Patent ID: 8897968

Claim:
An electric power steering system comprising: a steering force assist device configured to give an assist force to a steering system based on a magnetomotive force generated by dual-system motor coils, the dual-system motor coils being provided independently; and a controller configured to control an operation of the steering force assist device through an electric power supplied to the dual-system motor coils, the controller including: an assist control section being configured to generate a basic command for supplying the three-phase electric power to the dual-system motor coils in order to generate a motor torque corresponding to the assist force, a control signal output section being configured to output independent dual-system control signals based on the basic command, independent dual-system driver circuits being configured to supply the three-phase electric power to the dual-system motor coils based on the independent-dual system control signals; and an anomaly detection section configured to detect, for each phase of the three-phase electric power, an occurrence of an energization failure in respective power supply paths of a first system and a second system of the dual-system motor coils, wherein: when the occurrence of the energization failure is detected in the first system, the control signal output section gives a higher priority to a control signal output to the second system, when the occurrence of the energization failure is detected in the second system, the control signal output section gives the higher priority to a control signal output to the first system, and when the occurrence of the energization failure is detected in an energization failure occurring phase that is only one phase of the three-phase electric power and a value of the basic command exceeds an upper limit, the control signal output section gives the higher priority to a control signal output to the dual-system driver circuits in order to supply electric power, corresponding to an excess of the upper limit, by the two phases of the three-phase electric power other than the energization failure occurring phase, and the upper limit being set to a normal system that gives high priority to the output of the control signal.