Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
1997-12-30
2001-07-17
Martin, David S. (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S433000, C318S282000, C180S443000, C180S446000
Reexamination Certificate
active
06262547
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a motor-driven power steering apparatus, and more particularly to an improvement of a driver's steering feeling.
A motor-driven power steering apparatus has been disclosed, for instance, by Postexamined Japanese Patent Publication 3-42235/(1991). Its arrangement is as shown in FIG.
6
.
In
FIG. 6
, reference numeral
1
designates an assist direction motor current indicating section. The assist direction motor current indicating section
1
comprises: a torque sensor
11
which detects the torsion torque of a steering shaft, and outputs a torque signal in proportion to the torsion torque as shown in
FIG. 7
; and an output torque value instruction function section
12
which, in response to the torque signal of the torque sensor
11
, provides an assist direction motor current instruction value i according to a function as shown in FIG.
8
.
Further in
FIG. 6
, reference numeral
2
designates a phase compensation section which outputs a signal proportional to the differential value of the torque signal of the torque sensor
11
, the output signal of the section being added to the aforementioned torque signal; and
21
, a phase compensation instruction function section which outputs a phase compensation current instruction value ip which, as shown in
FIG. 9
, changes continuously when the signal of the phase compensation section
2
is lower than a predetermined value, and is constant when the output signal of the phase compensation section is higher than the predetermined value. The phase compensation current instruction value ip is added to the assist direction motor current instruction value i of the output torque value indicating function section
21
to obtain an addition value. The addition value thus obtained is applied to a control circuit
3
, to drive an electric motor
4
, to power-assist a steering mechanism
5
.
The aforementioned control circuit
3
comprises: a positive or negative discriminating section
31
which determines whether the addition value of the assist direction motor current instruction value i and the phase compensation current instruction value ip is positive or whether the addition value is negative; an absolute value conversion section
33
which obtains the absolute value |i+ip| of the above-described addition value; a motor drive section
32
which determines the direction of rotation of the motor
4
according to the output signal of the positive or negative value discriminating section
31
and drives the motor
4
in response to the current instruction value provided by the absolution value conversion section
33
; and a duty control section
34
which compares a motor armature current detected by an armature current detecting section
35
with the current instruction value of the absolute value conversion section
33
, to perform duty control.
The conventional motor-driven power steering apparatus operates as follows:
The phase compensation section
2
obtains a signal proportional to the differential value of the torque signal of the steering shaft. The assist direction motor current instruction value based on the addition signal of the aforementioned signal and the torque signal is added to the phase compensation current instruction signal which changes continuously when the output signal of the phase compensation section
2
is lower than the predetermined value, and is constant when it is higher than the predetermined value, to obtain the addition value. The addition value thus obtained is utilized to control the control section
3
. This improves the motor power assistance follow-up characteristic (responsibility), and prevents the occurrence of self-oscillation at the time of rest steering, and absorbs the effect of the motor's inertial force when the vehicle is traveling at high speed, thus eliminating a sense of incongruity during steering.
In the above-described conventional motor-driven power steering apparatus, the motor
4
is driven according to the output of the torque sensor. Therefore, when the torsion torque is not applied, the motor
4
is not driven. Thereafter, when a steering operation is started, a torque loss occurs which attributes to the static friction of the motor and a steering mechanism, and therefore a great steering torque is necessary for the steering operation; that is, the driver feels unpleasant about the steering operation. In addition, when the steering wheel is released after the steering operation, the return of the steering wheel is obstructed by the friction of the motor and the steering mechanism; that is, it is rather difficult for the steering wheel to return to the neutral position (the straight movement of the vehicle).
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to eliminate the above-described difficulties accompanying a conventional motor-driven power steering apparatus.
More specifically, an object of the invention is to provide a motor-driven power steering apparatus in which the effect of the friction, particularly static friction, of the motor and the steering mechanism is eliminated, so that the driver may feel comfortable about the steering operation.
The foregoing object and other objects of the invention have been achieved by the provision of a motor-driven power steering apparatus which, according to the invention, comprises: a torque sensor for detecting a steering torque; assist indicating means for outputting an indication signal which indicates the direction and magnitude of an output torque of a motor power-assisting a steering mechanism; dither signal generating means for outputting a high-frequency dither signal; and control means for controlling a current supplied to the motor according to the indication signal provided by the assist indicating means and the dither signal provided by the dither signal generating means.
In the motor-driven power steering apparatus, the amplitude of the dither signal outputted by the dither signal generating means is so set that the output torque of the motor which is produced by the dither signal is equal to or smaller than a torque loss attributing to the friction of the steering mechanism.
A half period of the dither signal outputted by the dither signal generating means is equal to or longer than electrical response delay of the control means and shorter than mechanical response delay of the steering mechanism.
In a predetermined operating condition, the generation of the dither signal by the dither signal generating means is inhibited.
Furthermore, in the motor-driven power steering apparatus, when a vehicle speed is equal to or lower than a predetermined value, the generation of the dither signal is inhibited.
Moreover, in the apparatus, when the number of revolutions per minute of an engine is equal to or smaller than a predetermined value, the generation of the dither signal is inhibited.
In addition, when the number of revolutions per minute of the motor is equal to or larger than a predetermined value, the generation of the dither signal is inhibited.
When the armature current of the motor is equal to or larger than a predetermined value, the generation of the dither signal is inhibited.
When the output of the torque sensor is equal to or larger than a predetermined value, the generation of the dither signal is inhibited.
In the apparatus, the amplitude of the dither signal generated by the dither signal generating means is varied according to a vehicle operating condition.
Furthermore, in the apparatus, the amplitude of the dither signal may be varied according to the number of revolutions per minute of the motor.
Moreover, in the apparatus, the amplitude of the dither signal may be varied according to the armature current of the motor.
In addition, in the apparatus, the amplitude of the dither signal may be varied according to the output of the torque sensor.
In the apparatus, the dither signal generated by the dither signal generating means is a signal whose higher harmonic components have been attenuated.
The nature, u
Kifuku Takayuki
Wada Shunichi
Martin David S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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