To provide an electric power steering system in which a rack subjected to transmission of torque of an electric motor is a variable ratio rack and which can achieve proper steering assistance corresponding to steering situations.
A q-axis current indication value-generating unit obtains an assist-side rack gain Ga in the present rack shaft position. Next, the q-axis current indication value-generating unit obtains a reference q-axis current indication value Iqo* corresponding to steering torque T, by using a map storing the relationship between the steering torque and a q-axis current indication value (reference q-axis current indication value Iqo*) when the assist-side rack gain Ga is a rack gain reference value Gao. Subsequently, the q-axis current indication value-generating unit converts the reference q-axis current indication value Iqo* to a q-axis current indication value Iq* corresponding to the assist-side rack gain Ga.
MAEDA NAOKI
Mio Kawasaki
Hideyuki Kayama