Power steering controller with compensation for tire deformation and caster
In a steering control device, a road surface reaction force torque calculation module ( 52 ) uses a vehicle speed, steering angle, and vehicle model to calculate a caster-trail-caused torque, a self-aligning torque, and a road surface reaction force torque. A reaction force command current calculation module ( 53 ) uses the road surface reaction force torque and the vehicle speed to calculate a reaction force command current.
1. A steering control device for controlling drive of a motor for imparting a power to a steering system of a vehicle, the steering control device comprising a steering control device main unit for calculating a self-aligning torque from a steering angle signal received from a steering angle detector for generating a steering angle signal corresponding to a steering angle of the steering system, by using a vehicle model containing a predetermined frequency characteristic representing a rotational rate of a steered wheel of the steering system from the steering angle to the self-aligning torque, and setting a drive torque of the motor based on a result obtained by multiplying the calculated self-aligning torque by a predetermined gain which varies based on a speed of the vehicle.
2. A steering control device according to claim 1 , wherein the vehicle model includes a characteristic of a twist torque of a tire of the steered wheel, the twist torque being a torque which is generated by the tire itself twisted by an elastic deformation and acts on the steering system.
3. A steering control device according to claim 2 , wherein the steering control device main unit calculates a caster-trail-caused torque from the steering angle signal by using a caster-trail-caused torque calculation model containing a predetermined frequency characteristic representing a vehicle characteristic from the steering angle to the caster-trail-caused torque, the caster-trail-caused torque being a torque which is generated by a caster trail and a tire lateral force and acts on the steering system, and corrects the drive torque based on the calculated caster-trail-caused torque.
4. A steering control device according to claim 3 , wherein the steering control device main unit corrects the drive torque based on results obtained by multiplying the calculated self-aligning torque and the caster-trail-caused torque by the predetermined gain, respectively.
5. A steering control device according to claim 2 , wherein the steering control device main unit is configured to:
calculate a basic assist torque based on a steering torque signal from a steering torque detector for generating the steering torque signal corresponding to a steering torque applied to the steering system by a driver; and
correct the drive torque using the calculated basic assist torque.
6. A steering control device according to claim 2 , wherein the steering control device main unit corrects the set drive torque depending on a change in at least any one of:
the speed of the vehicle;
a steering torque detected by a steering torque detector for detecting a steering torque applied to the steering system by a driver;
the steering angle detected by the steering angle detector;
a vehicle weight obtained by vehicle weight acquisition circuitry for detecting or estimating a vehicle weight;
a road surface friction coefficient obtained by road surface friction coefficient acquisition circuitry for detecting or estimating a road surface friction coefficient;
a steering speed based on the steering angle; and
a steering direction based on any one of the steering angle and the steering torque.
7. A steering control device according to claim 2 , wherein the vehicle model changes depending on a change in at least any one of:
the speed of the vehicle;
a vehicle weight acquired by a vehicle weight acquisition circuitry which detects or estimates the vehicle weight; and
a road surface friction coefficient acquired by road surface friction coefficient acquisition circuitry which detects or estimates the road surface friction coefficient.
8. A steering control device according to claim 1 , wherein the steering control device main unit calculates a caster-trail-caused torque from the steering angle signal by using a caster-trail-caused torque calculation model containing a predetermined frequency characteristic representing a vehicle characteristic from the steering angle to the caster-trail-caused torque, the caster-trail-caused torque being a torque which is generated by a caster trail and a tire lateral force and acts on the steering system, and corrects the drive torque based on the calculated caster-trail-caused torque.
9. A steering control device according to claim 8 , wherein the steering control device main unit
corrects the drive torque based on results obtained by multiplying the calculated self-aligning torque and the caster-trail-caused torque by the predetermined gain, respectively.
10. A steering control device according to claim 1 , wherein the steering control device main unit is configured to:
calculate a basic assist torque based on a steering torque signal from a steering torque detector for generating the steering torque signal corresponding to a steering torque applied to the steering system by a driver; and
correct the drive torque using the calculated basic assist torque.
11. A steering control device according to claim 1 , wherein the steering control device main unit corrects the set drive torque depending on a change in at least any one of:
the speed of the vehicle;
a steering torque detected by a steering torque detector for detecting a steering torque applied to the steering system by a driver;
the steering angle detected by the steering angle detector;
a vehicle weight obtained by vehicle weight acquisition circuitry for detecting or estimating a vehicle weight;
a road surface friction coefficient obtained by road surface friction coefficient acquisition circuitry for detecting or estimating a road surface friction coefficient;
a steering speed based on the steering angle; and
a steering direction based on any one of the steering angle and the steering torque.
12. A steering control device according to claim 1 , wherein the vehicle model changes depending on a change in at least any one of:
the speed of the vehicle;
a vehicle weight acquired by a vehicle weight acquisition circuitry which detects or estimates a vehicle weight; and
a road surface friction coefficient acquired by road surface friction coefficient acquisition circuitry which detects or estimates a road surface friction coefficient.