1. Field of the Invention
The present invention relates to an electric power steering control apparatus for controlling an electric motor device that generates assist torque for assisting steering torque of an automobile driver.
2. Description of the Related Art
Among conventional electric power steering control apparatus is one disclosed in JP-A-2001-239951 in which one or more stages of first-order low-pass filters are formed to estimate road surface reaction torque and the time constants of the low-pass filters are arranged in accordance with the steering speed. JP-A-2001-122146 discloses an electric power steering control apparatus in which the time constant of a low-pass filter is arranged in accordance with the vehicle speed.
However, the conventional technique of arranging the time constants of the low-pass filters in accordance with only the steering speed has a problem that the accuracy of estimation of road surface reaction torque is lowered as the vehicle speed increases. The technique of arranging the time constant of the low-pass filter in accordance with only the vehicle speed has a problem that the accuracy of estimation of road surface reaction torque is lowered as the steering speed increases. No technique has been proposed that determines the time constant of a low-pass filter in accordance with both of the vehicle speed and the steering speed or the rotation speed of the electric motor device that generates assist torque.