US 8,818,636 B2Granted

Electric power steering apparatus, control method thereof and computer readable medium

AssigneeShowa Corporation

InventorHideyuki Murakami

Life of this patent

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Abstract

The electric power steering apparatus is provided with: a steering torque detector that detects steering torque of a steering wheel; an electric motor that applies steering assist force to the steering wheel; a current detector that detects an actual current actually supplied to the electric motor; a target current setting unit that sets a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector; a feedback controller that performs feedback control so that the target current and the actual current coincide with each other; and a feedforward controller that performs feedforward control for increasing the actual current detected by the current detector if the target current increases, the feedforward controller including a frequency compensator that provides a smaller amount of increase in the actual current as a frequency of a variation in the target current is lower.

Claims11

Dependent claims

An electric power steering apparatus, comprising:

a first rotary shaft connected to a steering wheel;
a rack shaft configured to effect turning of a wheel to be turned, by a rectilinear motion;
a second rotary shaft configured to effect the rectilinear motion of the rack shaft;
a torsion bar configured to provide a connection between the first rotary shaft and the second rotary shaft, and configured to be twisted by operation of the steering wheel;
an electric motor configured to apply assist force for the operation of the steering wheel;
a steering torque detector configured to detect steering torque of the steering wheel;
and
a target current setting unit configured to set a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector,
a feedback controller configured to perform feedback control on the target current set by the target current setting unit,
the target current setting unit comprising:
a target current determination unit configured to determine the target current;
and
a resonance compensator provided on an output side of the steering torque detector that is also an input side of the target, current determination unit, the resonance compensator being configured to suppress a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, and
the target current setting unit being further configured to set the target current in accordance with the steering torque subjected to the suppression of the resonance frequency component by the resonance compensator,
wherein a transfer function H(s) of the resonance compensator is defined as:
H(s)=a·((2πfc1)·(2πfc2))/((s+2πfc1)·(s+2πfc2));
wherein:
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
J
1
+
4
⁢
⁢
π
2
·
J
2
+
m
·
γ
2
2
)
·
s
2
+
4
⁢
⁢
π
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
,
⁢
or
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
J
1
+
4
⁢
⁢
π
2
·
γ
1
2
·
J
2
+
m
·
γ
1
2
·
γ
2
2
)
·
s
2
+
4
⁢
⁢
π
2
·
γ
1
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
·
γ
2
;
⁢
and
wherein:
s donates an operator for the Laplace transform,
fc12 and fc2 represent cut-off frequencies of low-pass filters,
γ1=θ1/θ2, where θ1 represents an angle of rotation of the electric motor, and θ2 represents an angle of rotation of the second rotary shaft,
γ2=2·π·r, where r represents a radius of rotation of the second rotary shaft,
J1 represents inertia of a motor shaft of the electric motor,
J2 represents inertia of the second rotary shaft,
m represents mass of the rack shaft, and
ktb represents a spring constant of the torsion bar.

146 more elements

An electric power steering apparatus, comprising:

a first rotary shaft connected to a steering wheel;
a rack shaft configured to effect turning of a wheel to be turned, by a rectilinear motion;
a second rotary shaft configured to effect the rectilinear motion of the rack shaft;
a torsion bar configured to provide a connection between the first rotary shaft and the second rotary shaft, and configured to be twisted by operation of the steering wheel;
an electric motor configured to apply assist three for the operation of the steering wheel;
a steering torque detector configured to detect steering torque of the steering wheel;
and
a target current setting unit configured to set a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector,
a feedback controller configured to perform feedback control on the target current set by the target current setting unit,
the target current setting unit comprising:
a target current determination unit configured to determine the target current;
and
a resonance compensator provided on an output side of the steering torque detector that is also an input side of the target current determination unit, the resonance compensator being configured to suppress a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, and
the target current setting unit being further configured to set the target current in accordance with the steering torque subjected to the suppression of the resonance frequency component by the resonance compensator,
wherein:
the second rotary shaft comprises a first pinion shaft;
the apparatus further comprises a second pinion shaft that is connected to the electric motor and is configured to transmit torque produced by the electric motor to the rack shaft;
the resonance compensator is further configured to suppress the resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the first pinion shaft, the second pinion shaft, and the rack shaft as inertial elements, and
a transfer function H(s) of the resonance compensator is defined as:
H(s)=a·((2πfc1)·(2πfc2))/((s+2πfc1)·(s+2πfc2));
wherein:
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
γ
3
2
·
J
1
+
4
⁢
⁢
π
2
·
γ
3
2
·
J
2
+
γ
2
2
·
γ
3
2
·
m
+
4
⁢
⁢
π
2
·
γ
2
2
·
J
3
)
·
s
2
+
4
⁢
⁢
π
2
·
γ
2
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
·
γ
2
·
γ
3
and
wherein:
s donates an operator for the Laplace transform,
fc1 and fc2 represent cut-off frequencies of low-pass filters,
γ1=θ1/θ2, where θ1 represents an angle of rotation of the electric motor, and θ2 represents an angle of rotation of the second pinion shaft,
γ2=2·π·r1, where r1 represents a radius of rotation of the second pinion shaft,
γ3=2·π·r2, where r2 represents a radius of rotation of the first pinion shaft,
J1 represents inertia of a motor shaft of the electric motor,
J2 represents inertia of the second pinion shaft,
J3 represents inertia of the first pinion shaft,
m represents mass of the rack shaft, and
ktb represents a spring constant of the torsion bar.

116 more elements

A control method of an electric power steering apparatus including a first rotary shaft connected to a steering wheel;

a rack shaft that effects turning of a wheel to be turned, by a rectilinear motion;
a second rotary shaft that effects the rectilinear motion of the rack shaft;
a torsion bar that provides a connection between the first rotary shaft and the second rotary shaft and is twisted by operation of the steering wheel;
an electric motor that applies assist force for the operation of the steering wheel, the control method thereof comprising:
detecting steering torque of the steering wheel;
suppressing a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, before setting a target current to be supplied to the electric motor;
setting a target current to be supplied to the electric motor in accordance with the steering torque subjected to the suppression of the resonance frequency component;
and
defining a transfer function H(s) of a resonance compensator as:
H(s)=a·((2πfc1)·(2πfc2))/((s+2πfc1)·(s+2πfc2));
wherein:
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
J
1
+
4
⁢
⁢
π
2
·
J
2
+
m
·
γ
2
2
)
·
s
2
+
4
⁢
⁢
π
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
;
⁢
or
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
J
1
+
4
⁢
⁢
π
2
·
γ
1
2
·
J
2
+
m
·
γ
1
2
·
γ
2
2
)
·
s
2
+
4
⁢
⁢
π
2
·
γ
1
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
·
γ
2
;
⁢
and
wherein:
s donates an operator for the Laplace transform,
fc1 and fc2 represent cut-off frequencies of low-pass filters,
γ1=θ1/θ2, where θ1 represents an angle of rotation of the electric motor, and θ2 represents an angle of rotation of the second rotary shaft,
γ2=2·π·r, where r represents a radius of rotation of the second rotary shaft,
J1 represents inertia of a motor shaft of the electric motor,
J2 represents inertia of the second rotary shaft,
m represents mass of the rack shaft, and
ktb represents a spring constant of the torsion bar.

140 more elements

A control method of an electric power steering apparatus including a first rotary shaft connected to a steering wheel;

a rack shaft that effects turning of a wheel to be turned, by a rectilinear motion;
a second rotary shaft that effects the rectilinear motion of the rack shaft;
a torsion bar that provides a connection between the first rotary shaft and the second rotary shaft and is twisted by operation of the steering wheel;
an electric motor that applies assist force for the operation of the steering wheel, the control method thereof comprising:
detecting steering torque of the steering wheel;
suppressing a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, before setting a target current to be supplied to the electric motor;
and
setting a target current to be supplied to the electric motor in accordance with the steering torque subjected to the suppression of the resonance frequency component,
wherein the second rotary shaft of the electric power steering apparatus comprises a first pinion shaft and the electric power steering apparatus further comprising a second pinion shaft that is connected to the electric motor to transmit torque produced by the electric motor to the rack shaft, the control method suppressing the resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the pinion shaft, the second pinion shaft, and the rack shaft as inertial elements;
defining a transfer function H(s) of a resonance compensator as:
H(s)=a·((2πfc1)·(2πfc2))/((s+2πfc1)·(s+2πfc2));
wherein:
a
=
(
4
⁢
⁢
π
2
·
γ
1
2
·
γ
3
2
·
J
1
+
4
⁢
⁢
π
2
·
γ
3
2
·
J
2
+
γ
2
2
·
γ
3
2
·
m
+
4
⁢
⁢
π
2
·
γ
2
2
·
J
3
)
·
s
2
+
4
⁢
⁢
π
2
·
γ
2
2
·
k
tb
4
⁢
⁢
π
2
·
γ
1
·
γ
2
·
γ
3
;
and
wherein:
s donates an operator for the Laplace transform,
fc1 and fc2 represent cut-off frequencies of low-pass filters,
γ1=θ1/θ2, where θ1 represents an angle of rotation of the electric motor, and θ2 represents an angle of rotation of the second pinion shaft,
γ2=2·π·r1, where r1 represents a radius of rotation of the second pinion shaft,
γ3=2·π·r2, where r2 represents a radius of rotation of the first pinion shaft,
J1 represents inertia of a motor shaft of the electric motor,
J2 represents inertia of the second pinion shaft,
J3 represents inertia of the first pinion shaft,
m represents mass of the rack shaft, and
ktb represents a spring constant of the torsion bar.

108 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/561,239Filed 30 Jul 2012 · division
Priority: JP 2009-03975423 Feb 2009
Published: US 2012/0290174 A115 Nov 2012
Granted: 26 Aug 2014
Term ends: Not estimatedThe source records don’t support an estimate.

Classification3 codes

B62D 5/0472
Controlling the motor: for damping vibrations
B62D 5/0463
Controlling the motor: calculating assisting torque from the motor based on driver input
B62D
Motor vehicles

Family

Application12/565,271Parent of this division · filed 23 Sep 2009
US 2012/0290174 A1Pre-grant publication · published 15 Nov 2012
US 8,260,500 B2Parent of this division
US 2010/0217487 A1Published application
US 8,818,636 B2This patent

From the US filing history. Foreign family members aren’t listed.