Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-03-23
2003-07-15
Arthur, Gertrude (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S446000
Reexamination Certificate
active
06594568
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus for detecting a steering torque applied to a steering wheel and controlling driving of a steering assist motor according to the detected steering torque.
An electric power steering apparatus, which controls driving of a steering assist motor based on a result of detection of steering torque applied to a steering wheel and assists power required for steering an automobile by the torque of the motor so as to give a comfortable steering feel to a driver, has spread.
FIG. 1
is a block diagram showing an example of the constitution of “a power steering apparatus” proposed by the assignee of the present application in Japanese Patent No. 2694213.
In this power steering apparatus as an electric power steering apparatus, an output signal of a torque sensor
6
is inputted to a control unit
7
. The control unit
7
supplies a drive signal to a steering assist motor
8
based on this output signal. The steering assist motor
8
transmits its torque to the lower shaft of a steering shaft.
The torque sensor
6
detects, as the steering torque applied to a steering wheel, a relative displacement in a circumferential direction which is generated between the upper and lower shafts of the steering shaft turning about the axis of the steering wheel according to turn of the steering wheel with twist of a torsion bar interposed between the upper and lower shafts.
A rotation detector
17
for detecting a rotational position of the motor
8
is attached to the rotation shaft of the motor
8
.
The control unit
7
is supplied with a rotation detection signal of the rotation detector
17
and an output signal of a vehicle speed detector
18
for detecting a vehicle speed as well as the above-mentioned output signal of the torque sensor
6
, and outputs a drive signal for driving the motor
8
and an electromagnetic clutch
16
.
A torque detection signal outputted by the torque sensor
6
is supplied to each of a phase compensating unit
71
a
for stabilizing a system by advancing the phase of the torque detection signal, an angular acceleration calculating unit
71
b
for calculating an angular acceleration &ohgr;′ of turn of the steering wheel, a middle point determining unit
71
c
for determining the middle point of the steering wheel of a vehicle traveling in a straight direction, and a lock detecting unit
71
f
for detecting whether the motor
8
is locked.
Moreover, a vehicle speed detection signal outputted by the vehicle speed detector
18
is supplied to each of the lock detecting unit
71
f
, middle point determining unit
71
c
, directing current function unit
73
a
, correction current function unit
73
b
and change current function unit
73
c.
The directing current function unit
73
a
is supplied with an output signal of the phase compensating unit
71
a
and a later-described change current Ia, determines a directing current I for the motor
8
based on the steering torque, change current Ia and vehicle speed detection signal, and outputs the determined directing current I.
The correction current function unit
73
b
is supplied with the angular acceleration &ohgr;′ of the steering wheel outputted by the angular acceleration calculating unit
71
b
, determines a correction current Ic for correcting the force of inertia of the motor
8
during acceleration and deceleration and the force of inertia of the traveling system of the vehicle based on the angular acceleration &ohgr;′ and vehicle speed detection signal, and outputs the determined correction current Ic.
The change current function unit
73
c
is supplied with a steering angle &thgr; outputted from a later-described steering angle determining unit
71
d
, determines a change current Ia for changing the characteristic of the directing current I based on the steering angle &thgr; and vehicle speed detection signal, and outputs the determined change current Ia.
The rotation detection signal of the rotation detector
17
is supplied to the lock detecting unit
7
If, middle point determining unit
71
c
, angular acceleration calculating unit
71
b
and steering angle determining unit
71
d.
The steering angle determining unit
71
d
determines a steering angle &thgr; based on the rotation detection signal and the middle point determined by the middle point determining unit
71
c
, and outputs the determined steering angle &thgr;.
The lock detecting unit
71
f
detects whether the motor
8
is locked, based on the rotation detection signal, when the supplied torque detection signal and vehicle speed detection signal are larger than their predetermined values, respectively. When the lock detecting unit
71
f
detects that the motor
8
is locked, a driving circuit
72
b
disconnects the electromagnetic clutch
16
.
The output signal of the directing current function unit
73
a
and the output signal of the correction current function unit
73
b
are added together by an adder
74
a
, and the result of addition is supplied to an error amplifier
74
b
. The error amplifier
74
b
calculates the difference between the result of addition and a feedback signal from a current detecting circuit
71
e
for detecting a current flowing in the motor
8
, and a voltage corresponding to the calculation result is supplied to the motor
8
by a PWM (Pulse Width Modulation) driving circuit
72
a.
The following description will explain an operation of an electric power steering apparatus having such structures.
The directing current function unit
73
a
determines a directing current I for the motor
8
based on the torque detection signal whose phase has been compensated by the phase compensating unit
71
a
, the change current Ia outputted by the change current function unit
73
c
and the vehicle speed detection signal outputted by the vehicle speed detector
18
, and outputs the determined directing current I.
Meanwhile, the change current function unit
73
c
determines a change current Ia for changing the characteristic of the directing current I, based on the steering angle &thgr; given by the steering angle determining unit
71
d
and the vehicle speed detection signal outputted by the vehicle speed detector
18
, and outputs the determined change current Ia.
The angular acceleration calculating unit
71
b
reads a torque detection signal T supplied from the torque sensor
6
and a motor rotational speed &ohgr;
m
of the motor
8
supplied from the rotation detector
17
, and calculates the angular acceleration &ohgr;′ of the steering wheel according to the following equation.
&ohgr;′=
T″/K+&ohgr;
m
′
(1)
Here, equation (1) can be given by the following equations.
T=K
(&thgr;
i
−&thgr;
o
)
where
&thgr;
i
: a steering angle of the upper shaft of the steering shaft,
&thgr;
o
: a steering angle of the lower shaft of the steering shaft,
K: a spring constant of the torsion bar.
&thgr;
i
−&thgr;
o
=T/K
&thgr;
i
″−&thgr;
o
″T″/K
&thgr;
i
″=T″K+&thgr;
o
″ (2)
Meanwhile,
&thgr;
o
′=&ohgr;
m
&thgr;
o
″=&ohgr;
m
′
(n: the deceleration ratio of the motor rotation shaft to the lower shaft)
∴ According to equation (2),
&thgr;
i
″=&ohgr;′=T″/K+&ohgr;
m
′
(1)
The correction current function unit
73
b
calculates a correction current Ic for correcting the effects of the force of inertia of the motor
8
and the force of inertia of the traveling system of the vehicle, based on the angular acceleration &ohgr;′ calculated by the angular acceleration calculating unit
71
b
and a vehicle speed detection signal V outputted by the vehicle speed detector
18
.
The adder
74
a
adds the correction current Ic calculated by the correction current function unit
73
b
to the directing current I calculated by the directing current function unit
73
a
, and outputs the resultant current. Hence, it i
Darby & Darby
Koyo Seiko Co. Ltd.
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