CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from and the benefit of Korean Patent Application No. 10-2017-0178877, filed on Dec. 22, 2017, which is hereby incorporated by reference for all purposes as if set forth herein.

BACKGROUND

Field

Exemplary embodiments relate to a torque compensation apparatus and method for a Motor Driven Power Steering (“MDPS”) system, and more particularly, to a torque compensation apparatus and method for an MDPS system, which can compensate for assist torque of the MDPS system during sudden steering.

Discussion of the Background

The MDPS system refers to a system that enables a driver to easily perform a steering operation by providing a part of steering torque which the driver needs to apply to a steering wheel when steering a vehicle, using an assist power source.

The MDPS system determines driving conditions of the vehicle through a column torque sensor to measure a driver's column torque inputted to the steering wheel, a steering angle sensor to measure a steering angle or steering angular velocity of the steering wheel, and a vehicle velocity sensor to measure a vehicle velocity, and provides assist torque through an electric motor based on a column torque applied to a steering shaft when the driver operates the steering wheel.

Unlike the existing hydraulic steering system, the MDPS system generates torque through current control on the motor by a control unit such as an ECU (Electronic Control Unit), and thus includes various control logics for controlling the motor. Such control logics may include a logic for implementing a steering feel desired by a driver, a logic aiming to improve the stability of a vehicle, and a logic for improving system stability, and outputs of the respective logics are decided according to preset tuning parameter values.

The MDPS motor has output torque which decreases according to the increase of an operating speed, and assist torque outputted from the MDPS system relies on the tuning parameters of the respective logics. Therefore, when the tuning parameters of the respective logic circuits are improperly tuned, a driver may have a heavy steering feel during sudden steering. Furthermore, since a damping logic and returning logic, which are included in the MDPS system so as to perform damping and returning functions, strengthen self-alignment torque of the vehicle, the response to sudden steering may be degraded.

The related art of the present invention is disclosed in Korean Patent Publication No. 2013-0066835 published on Jun. 21, 2013.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and, therefore, it may contain information that does not constitute prior art.

SUMMARY

Exemplary embodiments of the present invention are directed to a torque compensation apparatus and method for an MDPS system, which can secure the degree of freedom in tuning, and solve a problem that a driver has a heavy steering feel during sudden steering which occurs when outputs of logics included in the conventional MDPS system rely on tuning parameters.

In one embodiment, a torque compensation apparatus for an MDPS system may include: a column torque sensor configured to detect a column torque applied to a steering shaft; a steering angle sensor configured to detect a steering angle of a steering wheel; and a controller configured to calculate a compensation ratio by sudden steering, based on one or more of the column torque detected by the column torque sensor and a steering angular velocity calculated from the steering angle detected by the steering angle sensor, and compensate for basic assist torque outputted from the MDPS system according to the compensation ratio.

The torque compensation apparatus may further include a vehicle velocity sensor configured to detect a vehicle velocity, wherein the controller calculates the compensation ratio by further considering the vehicle velocity detected by the vehicle velocity sensor.

The controller may calculate the compensation ratio, based on a column torque compensation gain which is calculated as a larger value as the column torque increases in a preset torque compensation section, a steering angular velocity compensation gain which is calculated as a larger value as the steering angular velocity increases in a preset angular velocity compensation section, and a vehicle velocity compensation gain which is calculated as a larger value as the vehicle velocity increases in a preset vehicle velocity compensation section.

When the compensation ratio has a value between 0 and 1, the controller may compensate for the basic assist torque by adding sudden steering compensation torque to the basic assist torque, the sudden steering compensation torque being calculated as the product of the basic assist torque and the compensation ratio.

The controller may not compensate for the basic assist torque when the compensation ratio has a value of 0, but compensate for the basic assist torque using preset maximum assist torque when the compensation ratio has a value of 1.

In another embodiment, a torque compensation method for an MDPS system may include: determining, by a controller, whether a steering state of a vehicle is a sudden steering state, based on one or more of a column torque and a steering angular velocity; calculating, by the controller, a compensation ratio by sudden steering based on one or more of the column torque and the steering angular velocity, when the steering state of the vehicle is a sudden steering state; and differently compensating for, by the controller, basic assist torque outputted from the MDPS system according to the compensation ratio.

In the calculating of the compensation ratio, the controller may calculate the compensation ratio by further considering a vehicle velocity.

In the calculating of the compensation ratio, the controller may calculate the compensation ratio, based on a column torque compensation gain which is calculated as a larger value as the column torque increases in a preset torque compensation section, a steering angular velocity compensation gain which is calculated as a larger value as the steering angular velocity increases in a preset angular velocity compensation section, and a vehicle velocity compensation gain which is calculated as a larger value as the vehicle velocity increases in a preset vehicle velocity compensation section.

In the compensating for the basic assist torque, when the compensation ratio has a value between 0 and 1, the controller may compensate for the basic assist torque by adding sudden steering compensation torque to the basic assist torque, the sudden steering compensation torque being calculated as the product of the basic assist torque and the compensation ratio.

In the compensating for the basic assist torque, when the compensation ratio has a value of 1, the controller may compensate for the basic assist torque using preset maximum assist torque.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

