Electric power steering system

摘要

When a steering speed reaches a steering speed determination threshold, a steering speed gain is set to “0”. As a result, a final basic assist controlled variable becomes “0”, and application of an assist force to a steering system is stopped. Therefore, repetition of so-called reverse assist that is a cause of occurrence of an unintended steering behavior, such as self-excited vibration, is stopped. Accordingly, the steering behavior is improved.

主权项

1. An electric power steering system comprising:
a steering effort assist device that includes a motor as a drive source and applies an assist force to a steering system of a vehicle; a torque sensor that generates a sensor signal according to a steering torque that acts on a steering shaft; a control device that calculates an assist controlled variable that is a control component according to the assist force to be applied to the steering system, based on the steering torque obtained from the sensor signal and based on a multiplication factor of a steering speed gain calculated on the basis of a vehicle speed and a steering speed, and controls the motor according to the assist controlled variable, wherein the control device makes the assist controlled variable zero when an absolute value of a steering speed is equal to or higher than a threshold set based on a possibility that an unintended steering behavior occurs, the assist control variable being calculated using a vehicle-speed-adaptive three-dimensional map, the map set so that a value of a steering speed gain is set to 1 until the absolute value of the steering speed reaches a first threshold, and once the absolute value of the steering speed reaches the first threshold, the value of the steering speed gain is set to gradually decrease and is set to zero once the steering speed reaches a second threshold higher than the first threshold, and wherein the unintended steering behavior is a self-excited vibration caused when reverse gain failure occurs in the torque sensor.