Patent ID: 8825301

Claim:
An electric power steering apparatus comprising: a steering mechanism; a motor for providing a steering force to said steering mechanism; and a friction compensator, wherein: a current command value is calculated based on at least a steering torque, and the motor is controlled by a current control value calculated based on said current command value to provide a steering assist force to said steering mechanism, the friction compensator calculates, in advance, a friction compensation value for compensating a friction to said steering mechanism on a basis of said steering torque, said friction compensator sets a steering torque target value range which has a predetermined range having an upper target limit and an lower target limit based on said steering torque, and is configured to calculate said friction compensation value in accordance with a difference between said steering torque and an intermediate value measured within the upper target limit and the lower target limit of said steering torque target value range, said steering torque target value range is composed of a first range and a second range, said first range has an equal width to said intermediate value aid and is set within a range that said friction compensation value does not vary, said second range has a larger width than said first range to said intermediate value and is set within a range without any uncomfortable steering feeling, and said intermediate value is included within said first range and said first range is included within said second range, said friction compensator sets said friction compensation value to be zero when said steering torque is within said first range, calculates said friction compensation value in accordance with a difference between said steering torque and said intermediate value of said steering torque target value range when said steering torque is outside said first range but within said second range, updates said intermediate value for a lead side and sets said steering torque target value range again when said steering torque is outside said first range and said second range so that said steering torque becomes within said steering torque target value range, and said current command value is corrected by said friction compensation value, and wherein an operation that said first range and said second range and said second range are newly set to an updated steering torque target value range, is repeated.