Steering control method and apparatus of motor-driven power steering system
View Patent ↗A steering control method and apparatus of a motor-driven power steering system, ma include setting, by a controller, a virtual steering model including a reaction force apparatus provided between a steering wheel and a rack gear; inducing, by the controller, a state equation for the virtual steering model, the state equation representing momentum of the steering wheel, the reaction force apparatus, and the rack gear as state variables of the state equation; determining, by the controller, target steering torque acting in the reaction force apparatus through numerical integration of the state equation; and feedback-controlling, by the controller, a steering motor control amount to the motor-driven power steering system to bring a steering torque of the motor-driven power steering system into agreement with the target steering torque.
1. A steering control method of a motor-driven power steering system, the steering control method comprising:
setting, by a controller, a virtual steering model including a reaction force apparatus provided between a steering wheel and a rack gear;
inducing, by the controller, a state equation for the virtual steering model, the state equation representing momentum of the steering wheel, the reaction force apparatus, and the rack gear as state variables of the state equation;
determining, by the controller, a target steering torque acting in the reaction force apparatus through numerical integration of the state equation; and
feedback-controlling, by the controller, a steering motor control amount of the motor-driven power steering system to bring a steering torque of the motor-driven power steering system into agreement with the target steering torque,
wherein, in the virtual steering model,
a steering angle speed and a rack force are applied as input variables of the virtual steering model;
inertia of a steering wheel, rigidity of the reaction force apparatus, a damping constant of the reaction force apparatus, a column friction of the reaction force apparatus, a pinion radius, and weight of the rack gear are applied as system characteristic parameters of the virtual steering model; and
the target steering torque determined by relations of the input variables of the virtual steering model with the system characteristic parameters of the virtual steering model to form the state equation, is applied as an output variable of the virtual steering model,
wherein the reaction force apparatus is a torsion bar, the damping constant of the reaction force apparatus is a damping constant of the torsion bar, and the column friction of the reaction force apparatus is a column friction of the torsion bar, and
wherein the target steering torque is determined by an equation of
T q_ref =K t ×q 5 +B t ×{dot over (q)} 5
Tq_ref: Target steering torque
Kt: Rigidity of torsion bar
q5: Twisting displacement of torsion bar
Bt: damping constant of torsion bar damper
{dot over (q)} 5 : Differential value of twisting displacement of torsion bar.
2. The steering control method of claim 1 , wherein the state equation for the virtual steering model is induced by use of a bond graph.
3. The steering control method of claim 1 , wherein the state equation is induced by setting twisting displacement of the torsion bar, rack gear momentum, steering wheel momentum, and rack gear displacement as the state variables of the state equation.
4. A steering control method of a motor-driven power steering system, the steering control method comprising:
setting, by a controller, a virtual steering model including a reaction force apparatus provided between a steering wheel and a rack gear;
inducing, by the controller, a state equation for the virtual steering model, the state equation representing momentum of the steering wheel, the reaction force apparatus, and the rack gear as state variables of the state equation;
determining, by the controller, a target steering torque acting in the reaction force apparatus through numerical integration of the state equation; and
feedback-controlling, by the controller, a steering motor control amount of the motor-driven power steering system to bring a steering torque of the motor-driven power steering system into agreement with the target steering torque,
wherein, in the virtual steering model,
a steering angle speed and a rack force are applied as input variables of the virtual steering model;
inertia of a steering wheel, rigidity of the reaction force apparatus, a damping constant of the reaction force apparatus, a column friction of the reaction force apparatus, a pinion radius, and weight of the rack gear are applied as system characteristic parameters of the virtual steering model to form the state equation; and
the target steering torque determined by relations of the input variables of the virtual steering model with the system characteristic parameters of the virtual steering model is applied as an output variable of the virtual steering model,
wherein the reaction force apparatus is a torsion bar, the damping constant of the reaction force apparatus is a damping constant of the torsion bar, and the column friction of the reaction force apparatus is a column friction of the torsion bar, and
wherein the target steering torque is determined by an equation of
T q_ref =K a ×( K t ×q 5 +B t ×{dot over (q)} 5 )
Tq_ref: Target steering torque
Ka: Assist gain
Kt: Rigidity of torsion bar
q5: Twisting displacement of torsion bar
Bt: Damping constant of Torsion bar damper
{dot over (q)} 5 : Differential value of twisting displacement of torsion bar.
5. The steering control method of claim 4 , wherein the target steering torque (Tq_ref) is changeable according to the assist gain which is greater than zero and less than or equal to 1.
6. The steering control method of claim 1 , wherein the target steering torque is changeable by changing at least one of the system characteristic parameters of the virtual steering model.
7. A steering control apparatus of a motor-driven power steering system, the steering control apparatus comprising:
a setting portion setting a virtual steering model including a reaction force apparatus provided between a steering wheel and a rack gear;
a determining portion determining a target steering torque acting in the reaction force apparatus through numerical integration of a state equation after inducing the state equation for the virtual steering model, the state equation representing momentum of the steering wheel, the reaction force apparatus, and the rack gear as state variables of the state equation; and
a feedback controller feedback-controlling a steering motor control amount to the motor-driven power steering system to bring a steering torque of the motor-driven power steering system into agreement with the target steering torque,
wherein in the virtual steering model,
a steering angle speed and a rack force are applied as input variables of the virtual steering model;
inertia of a steering wheel, rigidity of the reaction force apparatus, a damping constant of the reaction force apparatus, a column friction of the reaction force apparatus, a pinion radius, and weight of the rack gear are applied as system characteristic parameters of the virtual steering model to form the state equation; and
the target steering torque determined by relations of the input variables of the virtual steering model with the system characteristic parameters of the virtual steering model is applied as an output variable of the virtual steering model,
wherein the reaction force apparatus is a torsion bar, the damping constant of the reaction force apparatus is a damping constant of the torsion bar, and the column friction of the reaction force apparatus is a column friction of the torsion bar, and
wherein the target steering torque (Tq_ref) is determined by an equation of
T q_ref =K t ×q 5 +B t ×{dot over (q)} 5 ,
Tq_ref: Target steering torque
Kt: Rigidity of torsion bar
q5: Twisting displacement of torsion bar
Bt: Damping constant of Torsion bar damper
{dot over (q)} 5 : Differential value of twisting displacement of torsion bar.
8. The steering control apparatus of claim 7 , wherein the state equation for the virtual steering model is induced by use of a bond graph.
9. The steering control apparatus of claim 7 , wherein the state equation is induced by setting twisting displacement of the torsion bar, rack gear momentum, steering wheel momentum, and rack gear displacement as the state variables of the state equation.
10. A steering control apparatus of a motor-driven power steering system, the steering control apparatus comprising:
a setting portion setting a virtual steering model including a reaction force apparatus provided between a steering wheel and a rack gear;
a determining portion determining a target steering torque acting in the reaction force apparatus through numerical integration of a state equation after inducing the state equation for the virtual steering model, the state equation representing momentum of the steering wheel, the reaction force apparatus, and the rack gear as state variables of the state equation; and
a feedback controller feedback-controlling a steering motor control amount to the motor-driven power steering system to bring a steering torque of the motor-driven power steering system into agreement with the target steering torque,
wherein in the virtual steering model,
a steering angle speed and a rack force are applied as input variables of the virtual steering model;
inertia of a steering wheel, rigidity of the reaction force apparatus, a damping constant of the reaction force apparatus, a column friction of the reaction force apparatus, a pinion radius, and weight of the rack gear are applied as system characteristic parameters of the virtual steering model to form the state equation; and
the target steering torque determined by relations of the input variables of the virtual steering model with the system characteristic parameters of the virtual steering model is applied as an output variable of the virtual steering model,
wherein the reaction force apparatus is a torsion bar, the damping constant of the reaction force apparatus is a damping constant of the torsion bar, and the column friction of the reaction force apparatus is a column friction of the torsion bar, and
wherein the target steering torque is determined by an equation of
T q_ref =K a ×( K t ×q 5 +B t ×{dot over (q)} 5 ),
Tq_ref: Target steering torque
Ka: Assist gain
Kt: Rigidity of torsion bar
q5: Twisting displacement of torsion bar
Bt: damping constant of torsion bar damper
{dot over (q)} 5 : Differential value of twisting displacement of torsion bar.
11. The steering control apparatus of claim 10 , wherein the target steering torque (Tq_ref) is changeable according to the assist gain which is greater than zero and less than or equal to 1.
12. The steering control apparatus of claim 7 , wherein the target steering torque is changeable by changing at least one of the system characteristic parameters of the virtual steering model.
13. The steering control method of claim 1 , wherein the state equation is determined by an equation of:
d
dt
[
q
5
P
10
P
2
q
13
]
=
[
0
-
1
R
p
M
r
1
J
sw
0
K
t
R
p
B
t
R
p
2
M
r
B
t
R
p
J
sw
0
-
K
t
B
t
R
p
M
r
-
B
t
J
sw
0
0
1
M
r
0
0
]
[
q
5
P
10
P
2
q
13
]
+
[
0
0
1
0
]
T
in
+
[
0
1
0
0
]
F
rack
+
[
0
-
1
R
p
0
0
]
T
fric
_
c
+
[
0
0
-
1
0
]
T
fric
_
sw
wherein q 5 is the twisting displacement of the torsion bar, P 10 is rack gear momentum, P 2 is steering wheel momentum, and q 13 is rack gear displacement, J sw is the inertia of a steering wheel, K t is rigidity of torsion bar, B t is the damping constant of torsion bar damper, T fric_c is column friction of a lower part of the torsion bar, R p is the pinion radius, M r is the weight of rack gear, T in is a driver steering torque, T fric_sw is a column friction of an upper portion of the torsion bar, and F rack is rack force.