Driver torque estimation apparatus and steering system including the same
An electric power steering system includes a second shaft coupled to a first shaft via a torsion bar, a basic driver torque estimation unit (extended state observer) configured to estimate a basic driver torque by using a disturbance observer based on a torsion bar torque and a rotation angle of the second shaft, a gravity torque calculation unit configured to calculate, by using a rotation angle of a steering wheel, a gravity torque applied to the first shaft by gravity acting on the center of gravity of the steering wheel, and a driver torque estimation unit configured to estimate a driver torque by using the basic driver torque estimated by the basic driver torque estimation unit and the gravity torque calculated by the gravity torque calculation unit.
1. A driver torque estimation apparatus, comprising:
a first shaft to which a steering wheel to be used for steering a vehicle is coupled;
a second shaft coupled to the first shaft via a torsion bar;
a torque sensor configured to detect a torsion bar torque applied to the torsion bar;
a rotation angle sensor configured to acquire a rotation angle of the second shaft; and
an electronic control unit configured to:
estimate a basic driver torque by using a disturbance observer based on the torsion bar torque and the rotation angle of the second shaft;
calculate, by using a rotation angle of the steering wheel, a gravity torque applied to the first shaft by gravity acting on a center of gravity of the steering wheel;
calculate a Coulomb friction torque acting on the steering wheel and the first shaft by using an angular velocity of the steering wheel;
estimate a driver torque by using the estimated basic driver torque, the calculated gravity torque and the calculated Coulomb friction torque; and
control a position of the steering wheel based on an application of the estimated driver torque.
2. The driver torque estimation apparatus according to claim 1 , wherein the electronic control unit is further configured to:
estimate the basic driver torque, and also estimate the rotation angle of the steering wheel, and
calculate the gravity torque by using the estimated rotation angle of the steering wheel.
3. The driver torque estimation apparatus according to claim 1 , wherein the electronic control unit is further configured to:
estimate the basic driver torque, and also estimate the rotation angle of the steering wheel and the angular velocity of the steering wheel,
calculate the gravity torque by using the estimated rotation angle of the steering wheel; and
calculate the Coulomb friction torque by using the estimated angular velocity of the steering wheel.
4. The driver torque estimation apparatus according to claim 1 , wherein
when an angle formed by a vertical line passing through a center-of-rotation position of the steering wheel with respect to a rotational plane of the steering wheel is defined as a steering wheel inclination angle, and an angle determined based on a rotation amount and a rotation direction of the steering wheel from a neutral position that is a position of the steering wheel at which a direction of the vehicle is a straightforward direction is defined as a steering wheel rotation angle,
the electronic control unit is configured to calculate, as the gravity torque, a product of a distance between a center-of-gravity position and the center-of-rotation position of the steering wheel, a mass of the steering wheel, a sine value of the steering wheel rotation angle, and a cosine value of the steering wheel inclination angle.