U.S. patent application number 16/638607 was filed with the patent office on 2021-04-22 for vehicle steering apparatus.
This patent application is currently assigned to NSK LTD.. The applicant listed for this patent is NSK LTD.. Invention is credited to Hiroyasu KUMAGAI, Takahiro TSUBAKI.
Application Number | 20210114653 16/638607 |
Document ID | / |
Family ID | 1000005327015 |
Filed Date | 2021-04-22 |
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United States Patent
Application |
20210114653 |
Kind Code |
A1 |
TSUBAKI; Takahiro ; et
al. |
April 22, 2021 |
VEHICLE STEERING APPARATUS
Abstract
A vehicle steering apparatus that obtains the appropriate
steering torque to the steering angle without being affected by
road surface state and changes of mechanical characteristics of the
steering system due to aging. The steering apparatus includes a
target steering torque generating section to generate a target
steering torque, a converting section to convert the target
steering torque into a target torsional angle, and a torsional
angle control section to calculate a motor current command value so
as to follow-up a torsional angle to the target torsional angle.
The target steering torque generating section includes an offset
correcting section to obtain the first torque signal from a
characteristic depending on the set steering angle based on an
offset value of the steering torque and outputs the first torque
signal as a target steering torque. The steering apparatus drives
and controls the motor based on the motor current command
value.
Inventors: |
TSUBAKI; Takahiro;
(Maebashi-Shi, JP) ; KUMAGAI; Hiroyasu;
(Fujisawa-Shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NSK LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
NSK LTD.
Tokyo
JP
|
Family ID: |
1000005327015 |
Appl. No.: |
16/638607 |
Filed: |
February 19, 2019 |
PCT Filed: |
February 19, 2019 |
PCT NO: |
PCT/JP2019/006041 |
371 Date: |
February 12, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B62D 5/0409 20130101;
B62D 15/022 20130101; B62D 6/008 20130101; B62D 5/0481
20130101 |
International
Class: |
B62D 6/00 20060101
B62D006/00; B62D 5/04 20060101 B62D005/04; B62D 15/02 20060101
B62D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2018 |
JP |
2018-133056 |
Claims
1-8. (canceled)
9. A vehicle steering apparatus that comprises, at least, a torsion
bar having any spring constant and a sensor to detect a torsional
angle of said torsion bar, and assist-controls a steering system by
driving and controlling a motor, comprising: a target steering
torque generating section to generate a target steering torque; a
converting section to convert said target steering torque into a
target torsional angle; and a torsional angle control section to
calculate a motor current command value so as to follow-up said
torsional angle to said target torsional angle, wherein said target
steering torque generating section comprises an offset correcting
section to obtain a first torque signal from a characteristic
depending on a steering angle which is set based on an offset value
of a steering torque and outputs said first torque signal as said
target steering torque, wherein said offset correcting section
comprises an offset correction calculating section to calculate a
basic torque signal depending on a steering state and said steering
angle and outputs said basic torque signal which has a hysteresis
characteristic whose absolute value is saturated to an absolute
value of a hysteresis width which is larger than an absolute value
of said offset value of said steering torque when said steering
angle is within a predetermined angle range, as said first torque
signal, and wherein said vehicle steering apparatus drives and
controls said motor based on said motor current command value.
10. The vehicle steering apparatus according to claim 9, wherein,
in a case that said steering angle varies from -.theta.h2 to
+.theta.h2 in a right-turning steering and varies from +.theta.h2
to -.theta.h2 in a left-turning steering, said predetermined angle
range of said steering angle is in a range from -.theta.h1 to
+.theta.h2 (.theta.h2>.theta.h1>0) in said right-turning
steering and is in a range from +.theta.h1 to -.theta.h2 in said
left-turning steering.
11. The vehicle steering apparatus according to claim 9, wherein
said offset correcting section further comprises a vehicle speed
sensitive gain section to calculate said first torque signal by
multiplying said basic torque signal by a vehicle speed sensitive
gain.
12. The vehicle steering apparatus according to claim 11, wherein
said vehicle speed sensitive gain has a characteristic that a value
of said vehicle speed sensitive gain becomes smaller when a vehicle
speed is higher.
13. The vehicle steering apparatus according to claim 9, wherein
said target steering torque generating section further comprises: a
basic map section to obtain a second torque signal from said
steering angle and said vehicle speed using a basic map; and a
damper calculating section to calculate a third torque signal based
on an angular velocity information using a damper gain map which is
sensitive to said vehicle speed, and wherein said target steering
torque generating section calculates said target steering torque
from at least one of said second torque signal and said third
torque signal and said first torque signal.
14. The vehicle steering apparatus according to claim 13, wherein
said basic map is sensitive to said vehicle speed and has a
characteristic that said second torque signal is zero when said
vehicle speed is zero.
15. The vehicle steering apparatus according to claim 13, wherein
said target steering torque generating section further comprises a
phase compensating section which is disposed at a previous stage or
a subsequent stage of said basic map section and performs a phase
compensation, and obtains said second torque signal from said
steering angle and said vehicle speed via said basic map section
and said phase compensating section.
16. The vehicle steering apparatus according to claim 14, wherein
said target steering torque generating section further comprises a
phase compensating section which is disposed at a previous stage or
a subsequent stage of said basic map section and performs a phase
compensation, and obtains said second torque signal from said
steering angle and said vehicle speed via said basic map section
and said phase compensating section.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-performance vehicle
steering apparatus that obtains a desired steering torque based on
a torsional angle of a torsion bar and so on, and maintains the
desired steering torque without being affected by a road surface
state and changes of mechanical system characteristics due to
aging.
BACKGROUND ART
[0002] An electric power steering apparatus (EPS) which is one of
vehicle steering apparatuses provides a steering system of a
vehicle with an assist torque (a steering assist torque) by means
of a rotational torque of a motor, and applies a driving force of
the motor which is controlled by using an electric power supplied
from an inverter as the assist torque to a steering shaft or a rack
shaft by means of a transmission mechanism including a reduction
mechanism. In order to accurately generate the assist torque, such
a conventional electric power steering apparatus performs a
feed-back control of a motor current. The feed-back control adjusts
a voltage supplied to the motor so that a difference between a
steering assist command value (a current command value) and a
detected motor current value becomes small, and the adjustment of
the voltage supplied to the motor is generally performed by an
adjustment of a duty ratio of a pulse width modulation (PWM)
control.
[0003] A general configuration of the conventional electric power
steering apparatus will be described with reference to FIG. 1. As
shown in FIG. 1, a column shaft (a steering shaft or a handle
shaft) 2 connected to a handle (a steering wheel) 1 is connected to
steered wheels 8L and 8R through a reduction mechanism 3, universal
joints 4a and 4b, a rack-and-pinion mechanism 5, and tie rods 6a
and 6b, further via hub units 7a and 7b. In addition, a torque
sensor 10 for detecting a steering torque Ts of the handle 1 and a
steering angle sensor 14 for detecting a steering angle .theta.h
are provided in the column shaft 2 having a torsion bar, and a
motor 20 for assisting a steering force of the handle 1 is
connected to the column shaft 2 through the reduction mechanism 3.
The electric power is supplied to a control unit (ECU) 30 for
controlling the electric power steering apparatus from a battery
13, and an ignition key signal is inputted into the control unit 30
through an ignition key 11. The control unit 30 calculates a
current command value of an assist command (a steering assist
command) based on the steering torque Ts detected by the torque
sensor 10 and a vehicle speed Vs detected by a vehicle speed sensor
12, and controls a current supplied to the motor 20 for the
electric power steering apparatus (EPS) by means of a voltage
control command value Vref obtained by performing compensation or
the like to the current command value.
[0004] A controller area network (CAN) 40 exchanging various
information of a vehicle is connected to the control unit 30, and
it is possible to receive the vehicle speed Vs from the CAN 40.
Further, it is also possible to connect a non-CAN 41 exchanging a
communication, analog/digital signals, a radio wave or the like
except for the CAN 40 to the control unit 30.
[0005] The control unit 30 mainly comprises a central processing
unit (CPU) (including a micro controller unit (MCU), a micro
processor unit (MPU) and so on), and general functions performed by
programs within the CPU are shown in FIG. 2.
[0006] Functions and operations of the control unit 30 will be
described with reference to FIG. 2. As shown in FIG. 2, the
steering torque Ts detected by the torque sensor 10 and the vehicle
speed Vs detected by the vehicle speed sensor 12 (or from the CAN
40) are inputted into a current command value calculating section
31. The current command value calculating section 31 calculates the
current command value Iref1 that is a control target value of a
current supplied to the motor 20 based on the inputted steering
torque Ts and vehicle speed Vs and by using an assist map or the
like. The current command value Iref1 is inputted into a current
limiting section 33 through an adding section 32A. A current
command value Irefm whose maximum current is limited is inputted
into a subtracting section 32B, and a deviation I (=Irefm-Im)
between the current command value Irefm and a motor current Im
being fed-back is calculated. The deviation I is inputted into a
proportional integral (PI)-control section 35 for improving a
characteristic of the steering operation. The voltage control
command value Vref whose characteristic is improved by the
PI-control section 35 is inputted into a PWM-control section 36.
Furthermore, the motor 20 is PWM-driven through an inverter 37. The
motor current Im of the motor 20 is detected by a motor current
detector 38 and is fed-back to the subtracting section 32B.
[0007] A compensation signal CM from a compensation signal
generating section 34 is added to the adding section 32A, and a
characteristic compensation of the steering system is performed by
the addition of the compensation signal CM so as to improve a
convergence, an inertia characteristic and so on. The compensation
signal generating section 34 adds a self-aligning torque (SAT) 343
and an inertia 342 at an adding section 344, further adds the added
result at the adding section 344 with a convergence 341 at an
adding section 345, and then outputs the added result at the adding
section 345 as the compensation signal CM.
[0008] In such a conventional assist control of the electric power
steering apparatus, the steering torque applied by the manual input
of the driver is detected as the torsional torque of the torsion
bar by the torque sensor, and the motor current is controlled as
the assist current depending on mainly the detected steering
torque. However, in this method, different steering torques are
generated depending on the steering angle due to the difference of
the road surface state (for example, a tilt of the road surface).
Moreover, even variations of the motor output characteristic due to
the long-term use of the motor are affected to the steering
torque.
[0009] In order to resolve the above problems, the electric power
steering apparatus disclosed in, for example, Japanese Patent No.
5208894 (Patent Document 1) is proposed. The electric power
steering apparatus of Patent Document 1 sets the target value of
the steering torque based on a relationship (a steering reaction
force characteristic map) between the steering angle and the
steering torque which is determined based on a relationship between
the steering angle or the steering torque and a tactile amount in
order to apply the appropriate steering torque based on the tactile
characteristic of the driver.
THE LIST OF PRIOR ART DOCUMENTS
Patent Documents
[0010] Patent Document 1: Japanese Patent No. 5208894 B2
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0011] However, in the electric power steering apparatus of Patent
Document 1, it is required that the steering reaction force
characteristic map is preliminarily obtained. Since the control is
performed based on the deviation between the target value of the
steering torque and the detected steering torque, the affection to
the steering torque will still be remained.
[0012] The present invention has been developed in view of the
above-described circumstances, and an object of the present
invention is to provide a vehicle steering apparatus that easily
obtains equivalent steering torques to the steering angle and so on
without being affected by a road surface state and changes of
mechanical characteristics of a steering system due to aging.
Means for Solving the Problems
[0013] The present invention relates to a vehicle steering
apparatus that comprises a torsion bar having any spring constant
and a sensor to detect a torsional angle of the torsion bar, and
assist-controls a steering system by driving and controlling a
motor, the above-described object of the present invention is
achieved by that: comprising a target steering torque generating
section to generate a target steering torque, a converting section
to convert the target steering torque into a target torsional
angle, and a torsional angle control section to calculate a motor
current command value so as to follow-up the torsional angle to the
target torsional angle, wherein the target steering torque
generating section comprises an offset correcting section to obtain
a first torque signal from a characteristic depending on a steering
angle which is set based on an offset value of a steering torque
and outputs the first torque signal as the target steering torque,
and wherein the vehicle steering apparatus drives and controls the
motor based on the motor current command value.
[0014] The above-described object of the present invention is
efficiently achieved by that: wherein the offset correcting section
comprises an offset correction calculating section to calculate a
basic torque signal depending on a steering state and the steering
angle and outputs the basic torque signal which has a hysteresis
characteristic whose value is saturated to a setting value in a
right-turning steering and a setting value in a left-turning
steering, as the first torque signal; or wherein the offset
correction calculating section has a hysteresis characteristic
whose width is larger than the offset value; or wherein the offset
correcting section further comprises a vehicle speed sensitive gain
section to calculate the first torque signal by multiplying the
basic torque signal by a vehicle speed sensitive gain; or wherein
the vehicle speed sensitive gain has a characteristic that a value
of the vehicle speed sensitive gain becomes smaller when a vehicle
speed is higher; or wherein the target steering torque generating
section further comprises a basic map section to obtain a second
torque signal from the steering angle and the vehicle speed using a
basic map, and a damper calculating section to calculate a third
torque signal based on angular velocity information using a damper
gain map which is sensitive to the vehicle speed, and calculates
the target steering torque from the first torque signal and at
least one of the second torque signal and the third torque signal;
or wherein the basic map is sensitive to the vehicle speed and has
a characteristic that the second torque signal is zero when the
vehicle speed is zero; or wherein the target steering torque
generating section further comprises a phase compensating section
which is disposed at a previous stage or a subsequent stage of the
basic map section and performs a phase compensation, and obtains
the second torque signal from the steering angle and the vehicle
speed via the basic map section and the phase compensating
section.
Effects of the Invention
[0015] According to the vehicle steering apparatus of the present
invention, by performing a control to the target torsional angle
obtained based on the target steering torque which is generated at
the target steering generating section, the torsional angle can be
operated so as to follow-up the target torsional angle and the
desired steering torque based on the steering feeling of the driver
can be obtained.
[0016] Further, by the operation of the offset correcting section,
the occurrence of the unintended assist of the driver due to the
offset value of the steering torque can be suppressed and the
steering operation can be stabilized when the characteristic of the
basic map section is not changed depending on the steering angle,
for example in a static steering (the vehicle speed is 0 [km/h])
state as shown in FIG. 6.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the accompanying drawings:
[0018] FIG. 1 is a configuration diagram illustrating a general
outline of a conventional electric power steering apparatus
(EPS);
[0019] FIG. 2 is a block diagram showing a configuration example of
a control unit (ECU) of the electric power steering apparatus;
[0020] FIG. 3 is a structural diagram showing an installation
example of an EPS steering system and various sensors;
[0021] FIG. 4 is a block diagram showing a configuration example of
the present invention (the first embodiment);
[0022] FIG. 5 is a block diagram showing a configuration example of
a target steering torque generating section (the first
embodiment);
[0023] FIGS. 6A and 6B are a diagram showing a characteristic
example of a basic map;
[0024] FIG. 7 is a diagram showing a characteristic example of a
damper gain map;
[0025] FIG. 8 is a block diagram showing a configuration example of
an offset correcting section;
[0026] FIG. 9 is a diagram showing a characteristic example of the
offset correcting section;
[0027] FIG. 10 is a diagram showing a characteristic example of a
vehicle speed sensitive gain;
[0028] FIG. 11 is a block diagram showing a configuration example
of a torsional angle control section;
[0029] FIG. 12 is a diagram showing a setting example of upper and
lower limit values at an output limiting section;
[0030] FIG. 13 is a flowchart showing an operation example of the
present invention (the first embodiment);
[0031] FIG. 14 is a flowchart showing an operation example of the
target steering torque generating section (the first
embodiment);
[0032] FIG. 15 is a flowchart showing an operation example of the
torsional angle control section;
[0033] FIGS. 16A and 16B are a graph showing an example of time
response of a steering angle and a steering torque when the
correction by the offset correcting section is not performed in a
simulation showing an effect of the offset correcting section;
[0034] FIGS. 17A and 17B are a graph showing an example of time
response of the steering angle and the steering torque when the
correction by the offset correcting section is performed in the
simulation showing an effect of the offset correcting section;
[0035] FIG. 18 is a flowchart showing an operation example of the
target steering torque generating section (the second
embodiment);
[0036] FIG. 19 is a block diagram showing a configuration example
of the present invention (the third embodiment);
[0037] FIGS. 20A and 20B are a block diagram showing an insertion
example of a phase compensating section;
[0038] FIG. 21 is a configuration diagram illustrating a general
outline of a steer-by-wire system (SBW system);
[0039] FIG. 22 is a block diagram showing a configuration example
of the present invention (the fourth embodiment);
[0040] FIG. 23 is a block diagram showing a configuration example
of a target steering angle generating section;
[0041] FIG. 24 is a block diagram showing a configuration example
of a steering angle control section; and
[0042] FIG. 25 is a flowchart showing an operation example of the
present invention (the fourth embodiment).
MODE FOR CARRYING OUT THE INVENTION
[0043] The present invention is a vehicle steering apparatus to
obtain an appropriate steering torque to a steering angle and so on
without being affected by a road surface state, and obtains a
desired steering torque by performing a control so as to follow-up
a torsional angle of a torsion bar or the like to a value depending
on the steering angle and so on.
[0044] Embodiments of the present invention will be described with
reference to the accompanying drawings.
[0045] First, an installation example of various sensors which
detect information related to an electric power steering apparatus
(EPS) which is one of the vehicle steering apparatuses according to
the present invention will be described. FIG. 3 is a diagram
showing an EPS steering system and an installation example of the
various sensors, and the torsion bar 2A is provided in the column
shaft 2. A road surface reaction force Fr and a road surface
information p are operated to the steered wheels 8L and 8R. An
upper-side angle sensor is disposed at a handle side of the column
shaft 2 above the torsion bar 2A, and a lower-side angle sensor is
disposed at a steered wheel side of the column shaft 2 below the
torsion bar 2A. The upper-side angle sensor detects a handle angle
.theta..sub.1 and the lower-side angle sensor detects a column
angle .theta..sub.2. The steering angle .theta.h is detected by a
steering angle sensor disposed at an upper portion of the column
shaft 2. The torsion bar torsional angle .DELTA..theta. and the
torsion bar torque Tt can be calculated by following Expressions 1
and 2 from a deviation between the handle angle .theta..sub.1 and
the column angle .theta..sub.2. In the Expression 2, "Kt" is a
spring constant of the torsion bar 2A.
.theta..sub.2-.theta..sub.1=.DELTA..theta. [Expression 1]
-Kt.DELTA..theta.=Tt [Expression 2]
[0046] The torsion bar torque Tt can be detected by using the
torque sensor disclosed in, for example, Japanese Unexamined Patent
Publication No. 2008-216172 A. In the present embodiment, the
torsion bar torque Tt is also treated as the steering torque
Ts.
[0047] Next, the configuration example of the present invention
will be described.
[0048] FIG. 4 is a block diagram showing a configuration example of
the present invention (the first embodiment), and the handle
steering of the driver is assist-controlled by the motor in an EPS
steering system/vehicle system 100. The steering angle .theta.h,
the vehicle speed Vs and a steering state STs which indicates a
right-turning or a left-turning and is outputted from a
right-turning/left-turning judging section 500 are inputted into a
target steering torque generating section 200 which outputs a
target steering torque Tref. The target steering torque Tref is
converted into a target torsional angle .DELTA..theta.ref at a
converting section 400. The target torsional angle
.DELTA..theta.ref, the torsional angle .DELTA..theta. of the
torsion bar 2A and the motor angular velocity .omega.m are inputted
into a torsional angle control section 300. The torsional angle
control section 300 calculates a motor current command value Imc so
as to follow-up the torsional angle .DELTA..theta. to the target
torsional angle .DELTA..theta.ref and the motor of the EPS is
driven by the motor current command value Imc.
[0049] The right-turning/left-turning judging section 500 judges
whether the steering is the right-turning or the left-turning based
on the motor angular velocity .omega.m, and outputs the judged
result as the steering state STs. That is, in a case that the motor
angular velocity .omega.m is a positive value, the
right-turning/left-turning judging section 500 judges
"right-turning", and in a case that the motor angular velocity
.omega.m is a negative value, the right-turning/left-turning
judging section 500 judges "left-turning". Instead of the motor
angular velocity .omega.m, the velocity calculation to the steering
angle .theta.h, the handle angle .theta..sub.1 or the column angle
.theta..sub.2 is performed, and the calculated angular velocity may
be used.
[0050] FIG. 5 shows a configuration example of the target steering
torque generating section 200 and the target steering torque
generating section 200 comprises a basic map section 210, a
differential section 220, a damper gain section 230, an offset
correcting section 240, a multiplying section 250 and adding
sections 251 and 252. The steering angle .theta.h is inputted into
the basic map section 210, the differential section 220 and the
offset correcting section 240. The vehicle speed Vs is inputted
into the basic map section 210, the damper gain section 230 and the
offset correcting section 240. The steering state STs outputted
from the right-turning/left-turning judging section 500 is inputted
into the offset correcting section 240.
[0051] The basic map section 210 has a basic map and outputs a
torque signal (the second torque signal) Tref_a whose parameter is
the vehicle speed Vs using the basic map. The basic map is adjusted
by a tuning. For example, as shown in FIG. 6A, the torque signal
Tref_a increases when the magnitude (the absolute value) |.theta.h|
of the steering angle .theta.h increases, is zero when the vehicle
speed Vs is 0 [km/h] and increases when the vehicle speed Vs
increases. In FIG. 6A, the sign section 211 outputs the sign ("+1"
or "-1") of the steering angle .theta.h to the multiplying section
212, the magnitude of the torque signal Tref_a is obtained by the
basic map from the magnitude of the steering angle .theta.h, and
the torque signal Tref_a is calculated by multiplying the magnitude
of the torque signal Tref_a by the sign of the steering angle
.theta.h. As shown in FIG. 6B, the basic map may change the
behavior in a case that the steering angle .theta.h is a positive
value or a negative value. The basic map shown in FIGS. 6A and 6B
is sensitive to the vehicle speed. However, the basic map may not
be sensitive to the vehicle speed. When the vehicle speed Vs is
zero, the torque signal Tref_a may not be zero and have an
infinitesimal value.
[0052] The differential section 220 differentiates the steering
angle .theta.h and calculates a steering angular velocity .omega.h,
and the steering angular velocity .omega.h is inputted into the
multiplying section 250.
[0053] The damper gain section 230 outputs a damper gain D.sub.G
which is multiplied by the steering angular velocity .omega.h. The
steering angular velocity .omega.h which is multiplied by the
damper gain D.sub.G at the multiplying section 250 is inputted into
the adding section 252 as the torque signal (the third torque
signal) Tref_b. The damper gain D.sub.G is obtained by using a
vehicle speed sensitive-type damper gain map that the damper gain
section 230 has, depending on the vehicle speed Vs. For example, as
shown in FIG. 7, the damper gain map has a characteristic that a
value becomes larger when the vehicle speed Vs is higher. The
damper gain map may be variable depending on the steering angle
.theta.h. The damper calculating section comprises the damper gain
section 230 and the multiplying section 250.
[0054] The offset correcting section 240 calculates the torque
signal (the first torque signal) Tref_c to suppress the occurrence
of the assist due to the offset value of the steering torque in the
static steering state (the steering when the vehicle speed is 0
[km/h]). In a case that the driver does not grip the handle and the
offset value is included in the detected steering torque, when the
target steering torque is set to 0 [Nm] in the static steering
state, there can be the occurrence of the assist because the offset
value is existed. The characteristic depending on the steering
angle .theta.h is set based on this offset value (hereinafter,
referred to as "an offset countermeasure characteristic"). The
torque signal Tref_c is calculated by using the offset
countermeasure characteristic. FIG. 8 shows a configuration example
of the offset correcting section 240, and the offset correcting
section 240 comprises an offset correction calculating section 241
and a vehicle speed sensitive gain section 242.
[0055] The offset correction calculating section 241 defines the
offset countermeasure characteristic as a hysteresis characteristic
shown in FIG. 9, and calculates the torque signal (the basic torque
signal) Tref_s based on the steering angle .theta.h and the
steering state STs. In FIG. 9, a horizontal axis is the steering
angle .theta.h [deg], a vertical axis is the torque signal Tref_s
[Nm], "A.sub.hys" is a hysteresis width, the solid line shows the
characteristic in a case of the right-turning steering, and the
broken line shows the characteristic in a case of the left-turning
steering. FIG. 9 shows an example that the steering direction is
changed from the right-turning steering to the left-turning
steering at the steering angle (+.theta.h2) and the steering
direction is changed from the left-turning steering to the
right-turning steering at the steering angle (-.theta.h2). As shown
in FIG. 9, in a case of the right-turning steering, the torque
signal Tref_s has a constant value A.sub.hys when the steering
angle is between "-.theta.h1" and ".theta.h2" and changes with a
constant rate whose gradient "a"=2A.sub.hys/(.theta.h2-.theta.h1)
when the steering angle is between "-.theta.h2" and "-.theta.h1".
In a case of the left-turning steering, the torque signal Tref_s
has a constant value -A.sub.hys which is a negative value of the
hysteresis width A.sub.hys when the steering angle is between
".theta.h1" and "-.theta.h2" and changes with the gradient "a" when
the steering angle is between ".theta.h2" and ".theta.h1". In order
to suppress the occurrence of the assist due to the offset value of
the steering torque, the value of the hysteresis width A.sub.sys is
set to be larger than the offset value. The offset countermeasure
characteristic may have a hysteresis characteristic which is
changed not in a linear manner shown in FIG. 9 but in a curved
manner (a nonlinear manner). In FIG. 9, the symmetric hysteresis
characteristic is formed between the right-turning steering and the
left-turning steering. A non-symmetric hysteresis characteristic
may be used. For example, in a case that the offset value of the
right-turning steering is different from that of the left-turning
steering, the non-symmetric hysteresis characteristic is
adopted.
[0056] The vehicle speed sensitive gain section 242 outputs the
torque signal Tref_c by multiplying the torque signal Tref_s by the
vehicle speed sensitive gain. The vehicle speed sensitive gain is
set to become smaller when the vehicle speed Vs becomes higher. For
example, as shown in FIG. 10, the vehicle speed sensitive gain is
set to "1.0" when the vehicle speed is 0 [km/h] (the vehicle is in
a stop state). The vehicle speed sensitive gain becomes smaller
with a constant rate when the vehicle speed Vs becomes higher. When
the vehicle speed Vs becomes Vs1 (for example, 2 [km/h]), the
decrease rate of the vehicle speed sensitive gain is set to a
smaller value. When the vehicle speed Vs becomes Vs2 (for example,
6 [km/h]), the vehicle speed sensitive gain is set to zero. The
value of the vehicle speed sensitive gain when the vehicle speed Vs
is 0 [km/h] may be a value other than "1.0", the number of the
portions where the decrease rate of the vehicle speed sensitive
gain is changed may be plural, and the vehicle speed sensitive gain
may be changed not in a linear manner but in a curved manner (a
nonlinear manner).
[0057] Thus, the offset countermeasure characteristic has a
hysteresis characteristic by the offset correction calculating
section 241 and is sensitive to the vehicle speed due to the
vehicle sensitive gain section 242. Thereby, the torque signal
Tref_c which reduces the affection due to the offset value is
generated and the occurrence of the assist due to the offset value
of the steering torque can be suppressed by the torque signal
Tref_c. Instead of using the vehicle speed sensitive gain section
242, the hysteresis width A.sub.hys may be variable depending on
the vehicle speed Vs and then the offset countermeasure
characteristic may be sensitive to the vehicle speed. In this case,
the vehicle speed sensitive gain section 242 is not needed. The
characteristic other than the hysteresis characteristic may be used
as the offset countermeasure characteristic.
[0058] The torque signals Tref_c and Tref_b are added at the adding
section 252, the added torque signal and the torque signal Tref_a
are added at the adding section 251 and the added result is
outputted as the target steering torque Tref.
[0059] The steering angular velocity .omega.h is calculated by
differentiating the steering angle .theta.h and the appropriate low
pass filter (LPF) process is performed to the steering angular
velocity .omega.h for reducing the affection of the noise in the
high frequency region. The processes of the high pass filter (HPF)
and the gain may use in place of those of the differential
calculation and the LPF. Further, the steering angular velocity
.omega.h may be calculated by differentiating not the steering
angle .theta.h but the handle angle .theta..sub.1 which is detected
by the upper-side angle sensor or the column angle .theta..sub.2
which is detected by the lower-side angle sensor and performing the
LPF process to the differentiation result. The motor angular
velocity .omega.m may be used as the angular velocity information
instead of the steering angle .omega.h. In this case, the
differential section 220 is not needed.
[0060] The converting section 400 has a characteristic of"-1/Kt"
which is sign-inverted with respect to a reciprocal of the spring
constant Kt of the torsion bar 2A, and converts the target steering
torque Tref into the target torsional angle .DELTA..theta.ref.
[0061] The torsional angle control section 300 calculates the motor
current command value Imc based on the target torsional angle
.DELTA..theta.ref, the torsional angle .DELTA..theta. and the motor
angular velocity .omega.m. FIG. 11 is a block diagram showing a
configuration example of the torsional angle control section 300,
and the torsional angle control section 300 comprises a torsional
angle feed-back (FB) compensating section 310, a torsional angular
velocity calculating section 320, a velocity control section 330, a
stabilization compensating section 340, an output limiting section
350, a subtracting section 361 and an adding section 362. The
target torsional angle .DELTA..theta.ref outputted from the
converting section 400 is addition-inputted into the subtracting
section 361, the torsional angle .DELTA..theta. is
subtraction-inputted into the subtracting section 361 and is
inputted into the torsional angular velocity calculating section
320, and the motor angular velocity .omega.m is inputted into the
stabilization compensating section 340.
[0062] A deviation .DELTA..theta..sub.0 between the target
torsional angle .DELTA..theta.ref and the torsional angle
.DELTA..theta. is calculated at a subtracting section 361. The
torsional angle FB compensating section 310 multiplies the
deviation .DELTA..theta..sub.0 by a compensation value CFB (a
transfer function)/and outputs a target torsional angular velocity
.omega.ref so as to follow-up the torsional angle .DELTA..theta. to
the target torsional angle .DELTA..theta.ref. The compensation
value CFB may be a simple gain Kpp or a compensation value which is
generally used, such as a PI-control compensation value. The target
torsional angular velocity .omega.ref is inputted into the velocity
control section 330. It is possible to follow-up the torsional
angle .DELTA..theta. to the target torsional angle
.DELTA..theta.ref and obtain the desired steering torque by the
torsional angle FB compensating section 310 and the velocity
control section 330.
[0063] The torsional angular velocity calculating section 320
calculates the torsional angular velocity .omega.t by
differentiating the torsional angle .DELTA..theta., and the
torsional angular velocity .omega.t is inputted into the velocity
control section 330. A pseudo differential which uses the HPF and
the gain may be used as the differential operation. The torsional
angular velocity .omega.t may be calculated from other schemes
using the torsional angle .DELTA..theta. or the schemes not using
the torsional angle .DELTA..theta. and then may be inputted into
the velocity control section 330.
[0064] The velocity control section 330 calculates the motor
current command values Imca1 so as to follow-up the torsional
angular velocity .omega.t to the target torsional angular velocity
.omega.ref by a proportional preceding-type PI-control (I-P
control). A difference (.omega.ref-.omega.t) between the target
torsional angular velocity .omega.ref and the torsional angular
velocity .omega.t is calculated at the subtracting section 333. The
difference is integrated at the integral section 331 having the
gain Kvi, and the integral result is addition-inputted into the
subtracting section 334. The torsional angular velocity .omega.t is
also inputted into the proportional section 332, the proportional
process using the gain Kvp is performed to the torsional angular
velocity .omega.t, and the proportional-calculated result is
subtraction-inputted into the subtracting section 334. As well, the
subtracted result at the subtracting section 334 is outputted as
the motor current command value Imca1. The velocity control section
330 may calculate the motor current command value Imca1 by not
using the I-P control but using the generally used control method
such as the PI-control, a proportional (P) control, a proportional
integral derivative (PID) control, a derivative preceding-type PID
control (a PI-D control), a model matching control or a model
reference control.
[0065] The stabilization compensating section 340 has the
compensation value Cs (the transfer function) and calculates the
motor current command value Imca2 from the motor angular velocity
.omega.m. In order to improve the followability and the external
disturbance characteristic, when the gains of the torsional angle
FB compensating section 310 and the velocity control section 330
increase, the oscillation phenomenon due to the control in the high
frequency region is occurred. As this countermeasure, the transfer
function (Cs) to the motor angular velocity .omega.m, which is
required for the stabilization, is disposed in the stabilization
compensating section 340. Thereby, the stabilization of the overall
EPS control system can be realized. The primary filter which is set
by the gain and the pseudo differential whose structure is, for
example, the primary HPF, is represented by the following
Expression 3 and is used as the transfer function (Cs) of the
stabilization compensating section 340.
C s = K s t a 1 2 .pi. f c s 1 2 .pi. f c s + 1 [ Expression 3 ]
##EQU00001##
[0066] Here, "K.sub.sta" is a gain, "fc" is a cutoff frequency and
"s" is a Laplace operator. For example, the cutoff frequency fc is
set to 150 [Hz]. The secondary filter, the fourth order filter or
the like may be used as the transfer function.
[0067] The motor current command value Imca1 from the velocity
control section 330 and the motor current command value Imca2 from
the stabilization compensating section 340 are added at the adding
section 362, and the added result is outputted as the motor current
command value Imcb.
[0068] The output limiting section 350 limits the upper and lower
limit values of the motor current command value Imcb and outputs
the motor current command value Imc. As shown in FIG. 12, the upper
limit value and the lower limit value to the motor current command
value are preliminarily set. The output limiting section 350
outputs the upper limit value when the inputted motor current
command value Imcb is equal to or larger than the upper limit
value, the lower limit value when the inputted motor current
command value Imcb is equal to or smaller than the lower limit
value and the motor current command value Imcb when the inputted
motor current command value Imcb is smaller than the upper limit
value and is larger than the lower limit value, as the motor
current command value Imc.
[0069] In such a configuration, the operation example of the
present embodiment will be described with reference to flowcharts
of FIG. 13 to FIG. 15.
[0070] When the operation is started, the motor angular velocity
.omega.m is inputted into the right-turning/left-turning judging
section 500, and the right-turning/left-turning judging section 500
judges whether the steering is the right-turning or the
left-turning based on the sign of the motor angular velocity
.omega.m, and outputs the judged result as the steering state STs
to the target steering torque generating section 200 (Step
S10).
[0071] The target steering torque generating section 200 inputs the
steering state STs, the steering angle .theta.h and the vehicle
speed Vs, and generates the target steering torque Tref (Step S20).
The operation example of the target steering torque generating
section 200 will be described with reference to the flowchart of
FIG. 14.
[0072] The steering angle .theta.h inputted into the target
steering torque generating section 200 is inputted into the basic
map section 210, the differential section 220 and the offset
correcting section 240. The steering state STs is inputted into the
offset correcting section 240. The vehicle speed Vs is inputted
into the basic map section 210, the damper gain section 230 and the
offset correcting section 240 (Step S21).
[0073] The basic map section 210 generates the torque signal Tref_a
depending on the steering angle .theta.h and the vehicle speed Vs
by using the basic map as shown in FIG. 6A or FIG. 6B, and outputs
the torque signal Tref_a to the adding section 251 (Step S22).
[0074] The differential section 220 differentiates the steering
angle .theta.h and outputs the steering angular velocity .omega.h
(Step S23). The damper gain section 230 outputs the damper gain
D.sub.G depending on the vehicle speed Vs by using the damper gain
map as shown in FIG. 7 (Step S24). The multiplying section 250
calculates the torque signal Tref_b by multiplying the steering
angular velocity .omega.h by the damper gain D.sub.G, and outputs
the torque signal Tref_b to the adding section 252 (Step S25).
[0075] In the offset correcting section 240, the steering angle
.theta.h and the steering state STs are inputted into the offset
correction calculating section 241, and the vehicle speed Vs is
inputted into the vehicle speed sensitive gain section 242. The
offset correction calculating section 241 performs the hysteresis
correction to the steering angle .theta.h depending on the steering
state STs by using the offset countermeasure characteristic as
shown in FIG. 9 (Step S26), generates the torque signal Tref_s and
outputs the torque signal Tref_s to the vehicle speed sensitive
gain section 242. The vehicle speed sensitive gain section 242
determines the vehicle speed sensitive gain depending on the
vehicle speed Vs by using the characteristic as shown in FIG. 10,
multiplies the torque signal Tref_s by the vehicle speed sensitive
gain and outputs the multiplication result as the torque signal
Tref_c to the adding section 252 (Step S27). The offset
countermeasure characteristic at the offset correction calculating
section 241 may define by using the hysteresis width A.sub.hys, and
the steering angles .theta.h1 and .theta.h2, or may define by using
the hysteresis width A.sub.hys and the gradient "a" instead of the
steering angles .theta.h1 and .theta.h2.
[0076] The torque signals Tref_b and Tref_c are added at the adding
section 252, the added result and the torque signal Tref_a are
added at the adding section 251, and the target steering torque
Tref is calculated (Step S28).
[0077] The target steering torque Tref which is generated at the
target steering torque generating section 200 is inputted into the
converting section 400, and is converted into the target torsional
angle .DELTA..theta.ref at the converting section 400 (Step S30).
The target torsional angle .DELTA..theta.ref is inputted into the
torsional angle control section 300.
[0078] The torsional angle control section 300 inputs the target
torsional angle .DELTA..theta.ref, the torsional angle
.DELTA..theta. and the motor angular velocity .omega.m, and
calculates the motor current command value Imc (Step S40). The
operation example of the torsional angle control section 300 will
be described with reference to the flowchart of FIG. 15.
[0079] The target torsional angle .DELTA..theta.ref which is
inputted into the torsional angle control section 300 is inputted
into the subtracting section 361, the torsional angle
.DELTA..theta. is inputted into the subtracting section 361 and the
torsional angular velocity calculating section 320, and the motor
angular velocity .omega.m is inputted into the stabilization
compensating section 340 (Step S41).
[0080] In the subtracting section 361, the deviation
.DELTA..theta..sub.0 is calculated by subtracting the torsional
angle .DELTA..theta. from the target torsional angle
.DELTA..theta.ref (Step S42). The deviation .DELTA..theta..sub.0 is
inputted into the torsional angle FB compensating section 310, and
the torsional angle FB compensating section 310 compensates the
deviation .DELTA..theta..sub.0 by multiplying the deviation
.DELTA..theta..sub.0 by the compensation value CFB (Step S43), and
outputs the target torsional angular velocity .omega.ref to the
velocity control section 330.
[0081] The torsional angular velocity calculating 320 inputs the
torsional angle .DELTA..theta., calculates the torsional angular
velocity .omega.t by differentiating the torsional angle
.DELTA..theta. (Step S44), and outputs the torsional angular
velocity .omega.t to the velocity control section 330.
[0082] In the velocity control section 330, the difference between
the target torsional angular velocity .omega.ref and the torsional
angular velocity .omega.t is calculated at the subtracting section
333 and is integrated (Kvi/s) at the integral section 331, and the
integral result is addition-inputted into the subtracting section
334 (Step S45). Further, a proportional process (Kvp) is performed
to the torsional angular velocity .omega.t at the proportional
section 332, and the proportional result is subtraction-inputted
into the subtracting section 334 (Step S45). The motor current
command value Imca1 which is the subtracted result of the
subtracting section 334 is outputted from the subtracting section
334, and is inputted into the adding section 362.
[0083] The stabilization compensating section 340 performs the
stabilization compensation to the inputted motor angular velocity
.omega.m by using the transfer function Cs which is represented by
the Expression 3 (Step S46), and the motor current command value
Imca2 from the stabilization compensating section 340 is inputted
into the adding section 362.
[0084] The motor current command values Imca1 and Imca2 are added
at the adding section 362 (Step S47). The motor current command
value Imcb which is the added result is inputted into the output
limiting section 350. The output limiting section 350 limits the
upper and lower limit values of the motor current command value
Imcb by using the preliminarily set upper limit value and the lower
limit value (Step S48) and outputs the limited value as the current
command value Imc (Step S49).
[0085] The motor is driven based on the motor current command value
Imc outputted from the torsional angle control section 300, and the
current control is performed (Step S50).
[0086] In FIG. 13 to FIG. 15, the orders of inputting the data, the
calculation and so on are appropriately changeable.
[0087] The effects of the offset correcting section of the present
embodiment will be described based on the simulation results.
[0088] In the simulations, it is assumed that the offset with 0.05
[Nm] is generated to the steering torque detected at the torsion
bar. Further, assuming that the steering is the static steering,
the basic map that the vehicle speed Vs is 0 [km/h] is used.
Therefore, the value of the torque signal Tref_a outputted from the
basic map section 210 is 0 [Nm]. The differential section 220
performs the pseudo differential using the HPF and the gain as the
differential operation.
[0089] First, in a case of "without the correction by the offset
correcting section", the simulation results of the time responses
of the steering angle and the steering torque will be
described.
[0090] The simulation results are shown in FIGS. 16A and 16B. In
FIGS. 16A and 16B, the horizontal axis denotes a time [sec]. The
vertical axis denotes the steering angle [deg] in FIG. 16A and the
steering torque [Nm] in FIG. 16B. FIG. 16A shows the time response
of the steering angle whose initial value is 0 [deg]. FIG. 16B
shows the time response of the target steering torque by a thin
line and the time response of the detected steering torque by a
bold line. The target steering torque is started from 0 [Nm] and
the steering torque is started from -0.05 [Nm]. Since the steering
torque whose magnitude of the offset is 0.05 [Nm] is adjusted so as
to follow-up the target steering torque 0 [Nm] by the torsional
angle control at the torsional angle control section 300, the time
response is shown in FIG. 16B. As a result, the assist due to the
offset value of the steering torque is occurred and the steering
angle is varied as shown in FIG. 16A. That is, the steering torque
does not become 0.0 [Nm] in a no-grip state because of existing the
offset value, and the torsional angle control serves so as to
follow-up the torsional angle to the target torsional angle.
Thereby, it is estimated that the variation of the steering angle
is occurred due to the offset value of the steering torque.
[0091] Next, in a case of "with the correction by the offset
correcting section", the simulation results of the time responses
of the steering angle and the steering torque will be described. In
this simulation, the gradient "a" in this offset countermeasure
characteristic is set to 0.1 [Nm/deg].
[0092] The simulation results are shown in FIGS. 17A and 17B. The
settings of the axes and so on in FIGS. 17A and 17B are the same as
those in FIGS. 16A and 16B. From FIG. 17A, the steering angle is
slightly varied in the initial stage by performing the correction
at the offset correcting section. Then, it is understood that the
steering angle balances at 0.5 [deg] obtained by dividing the
offset value 0.05 [Nm] by the gradient "a" (=0.1 [Nm/deg]) and the
handle is in the holding state. That is, the occurrence of the
assist due to the offset value of the steering torque is suppressed
by the correction at the offset correcting section.
[0093] Although the target steering torque generating section 200
according to the first embodiment comprises the basic map section
210, the damper calculating section (including the damper gain
section 230 and the multiplying section 250) and the offset
correcting section 240, the target steering torque generating
section 200 may treat only the suppression of the assist occurrence
due to the offset value of the steering torque, and may comprise
only the offset correcting section 240. The configuration example
of the target steering torque generating section in the above case
(the second embodiment) is shown in FIG. 18. In the target steering
torque generating section 600, the torque signal Tref_c outputted
from the offset correcting section 240 is outputted as the target
steering torque Tref. Moreover, the target steering torque
generating section may comprise the basic map section 210 and the
offset correcting section 240 or may comprise the damper
calculating section and the offset correcting section 240.
[0094] The current command value which is calculated based on the
steering torque in the conventional EPS (hereinafter, referred to
as "an assist current command value") may be added to the motor
current command value Imc outputted from the torsional angle
control section according to the first and second embodiments. For
example, the current command value Iref1 outputted from the current
command value calculating section 31 shown in FIG. 2, the current
command value Iref2 in which the compensation signal CM is added to
the current command value Iref1, or the like may be added to the
motor current command value Imc.
[0095] In contrast with the first embodiment, the configuration
example in which the above function is included (the third
embodiment) is shown in FIG. 19. The assist control section 700
comprises the current command value calculating section 31, or
comprises the current command value calculating section 31, the
compensation signal generating section 34 and the adding section
32A. The assist current command value lac outputted from the assist
control section 700 (corresponding to the current command value
Iref1 or Iref2 in FIG. 2) and the motor current command value Imc
outputted from the torsional angle control section 300 are added at
an adding section 710 and the current command value Ic which is the
added result is inputted into the current limiting section 720. The
motor is driven based on the current command value Icm whose
maximum current is limited and the current control is
performed.
[0096] In the first to the third embodiments, the phase
compensating section 260 may be provided at the previous stage of
the basic map section 210 or the subsequent stage of the basic map
section 210 in the target steering torque generating section 200
including the basic map section 210. That is, the configuration of
the region R surrounded by the broken line in FIG. 5 may be changed
to the configuration shown in FIG. 20A or FIG. 20B. The phase
compensation at the phase compensating section 260 is set as the
phase lead compensation. For example, in a case that the phase lead
compensation using the primary filter in which the cutoff frequency
of the numerator is set to 1.0 [Hz] and the cutoff frequency of the
denominator is set to 1.3 [Hz] is performed, the comfortable
steering feeling can be realized. If the target steering torque
generating section has the configuration based on the steering
angle, its configuration is not limited to the above
configuration.
[0097] Further, in a case that the EPS control system is stable,
the stabilization compensating section may be omitted. The output
limiting section can also be omitted.
[0098] In FIG. 1 and FIG. 3, although the present invention is
applied to the column type EPS, the present invention is not
limited to an upstream-type EPS such as the column type EPS, and
can also be applied to a downstream-type EPS such as a rack and
pinion type EPS. Further, from a viewpoint of performing the
feed-back control based on the target torsional angle, the present
invention can be applied to a steer-by-wire (SBW) reaction force
unit which comprises at least the torsion bar having any spring
constant and the sensor to detect the torsional angle. The
embodiment (the fourth embodiment) in which the present invention
is applied to the SBW reaction force unit including the torsion bar
will be described.
[0099] First, the overall SBW system including the SBW reaction
force unit will be described. FIG. 21 shows a configuration example
of the SBW system, corresponding to the general configuration of
the electric power steering apparatus shown in FIG. 1. The same
reference numerals designate the same components, and the detail
explanation is omitted.
[0100] The SBW system does not have an intermediate shaft which is
mechanically connected to the column shaft 2 at the universal joint
4a and is a system that the operation of the handle 1 is
transmitted to the turning mechanism comprising the steered wheels
8L and 8R and so on by the electric signal. As shown in FIG. 21,
the SBW system comprises the reaction force unit 60 and the driving
unit 70, and the control unit (ECU) 50 controls the reaction force
unit 60 and the driving unit 70. The reaction force unit 60 detects
the steering angle .theta.h by the steering angle sensor 14, and
transmits the motion state of the vehicle transmitted from the
steered wheels 8L and 8R as the reaction force torque to the
driver. The reaction force torque is generated by the reaction
force motor 61. Although the SBW system which does not comprise the
torsion bar in the reaction force unit is existed, the SBW system
which is applied to the present invention comprises the torsion bar
and the steering torque Ts is detected by the torque sensor 10. The
angle sensor 74 detects the motor angle .theta.m of the reaction
force motor 61. The driving unit 70 drives the driving motor 71 in
harmony with the steering of the handle 1 by the driver. The
driving force is applied to the pinion and rack mechanism 5 via the
gears 72 and turns the steered wheels 8L and 8R via the tie rods 6a
and 6b. The angle sensor 73 is disposed in the vicinity of the
pinion and rack mechanism 5 and detects the turning angle .theta.t
of the steered wheels 8L and 8R. In order to cooperative-control
the reaction force unit 60 and the driving unit 70, the ECU 50
generates the voltage control command value Vref1 to drive and
control the reaction force motor 61 and the voltage control command
value Vref2 to drive and control the driving motor 71 based on the
information of the steering angle .theta.h, the turning angle
.theta.t and so on outputted from the reaction force unit 60 and
the driving unit 70, the vehicle speed Vs detected at the vehicle
speed sensor 12 or the like.
[0101] The configuration of the fourth embodiment that the present
invention is applied to such an SBW system will be described.
[0102] FIG. 22 is a block diagram showing the configuration of the
fourth embodiment. In the fourth embodiment, the control to the
torsional angle .DELTA..theta. (hereinafter, referred to as "the
torsional angle control") and the control to the turning angle
.theta.t (hereinafter, referred to as "the turning angle control")
are performed. The reaction force unit is controlled by the
torsional angle control and the driving unit is controlled by the
turning angle control. The driving unit may be controlled by
another control method.
[0103] In the torsional angle control, the configuration similar to
that of the first embodiment is used and the operation similar to
that of the first embodiment is performed. The control which
follows-up the torsional angle .DELTA..theta. to the target
torsional angle .DELTA..theta.ref which is calculated through the
target steering torque generating section 200 and the converting
section 400 by using the steering angle .theta.h and so on, is
performed. The motor angle .theta.m is detected by the angle sensor
74, and the motor angular velocity .omega.m is calculated by
differentiating the motor angle .theta.m at the angular velocity
calculating section 951. The turning angle .theta.t is detected by
the angle sensor 73. Although the detail explanation of the process
in the EPS steering system/vehicle system 100 is not described in
the first embodiment, the current control section 130 has the
configuration similar to the combined configuration with the
subtracting section 32B, the PI-control section 35, the PWM-control
section 36 and the inverter 37 shown in FIG. 2, performs the
operation similar to that of the above combined sections, drives
the reaction force motor 61 based on the motor current command
value Imc outputted from the torsional angle control section 300
and the current value Imr of the reaction force motor 61 detected
by the motor current detector 140, and performs the current
control.
[0104] In the turning angle control, the target turning angle
.theta.tref is generated based on the steering angle .theta.h at
the target turning angle generating section 910, the target turning
angle .theta.tref and the turning angle .theta.t are inputted into
the turning angle control section 920, and the turning angle
control section 920 calculates the motor current command value Imct
so as to follow-up the turning angle .theta.t to the target turning
angle .theta.tref. The current control section 930 has the
configuration similar to that of the current control section 130,
performs the operation similar to that of the current control
section 130, drives the driving motor 71 based on the motor current
command value Imct and the current value Imd of the driving motor
71 detected by the motor current detector 940, and performs the
current control.
[0105] The configuration example of the target turning angle
generating section 910 is shown in FIG. 23. The target turning
angle generating section 910 comprises a limiting section 931, a
rate limiting section 932 and a correcting section 933.
[0106] The limiting section 931 limits the upper and lower limit
values of the steering angle .theta.h and outputs the steering
angle .theta.h1. As well as the output limiting section 350 in the
torsional control section 300, the upper limit value and the lower
limit value to the steering angle .theta.h are preliminarily set,
and the steering angle .theta.h is limited.
[0107] In order to avoid the sharp change of the steering angle,
the rate limiting section 932 sets the limit value to the change
amount of the steering angle .theta.h1, limits the change amount of
the steering angle .theta.h1 and outputs the steering angle
.theta.h2. For example, the difference between the present steering
angle .theta.h1 and the steering angle .theta.h1 prior to one
sampling is set as the change amount. In a case that the absolute
value of the change amount is larger than a predetermined value
(the limit value), the addition operation or the subtraction
operation is performed to the steering angle .theta.h1 so that the
absolute value of the change amount becomes the limit value, and
the limited value is outputted as the steering angle .theta.h2. In
a case that the absolute value of the change amount is equal to or
smaller than the limit value, the steering angle .theta.h1 is
outputted as the steering angle .theta.h2. Instead of setting the
limit value to the absolute value of the change amount, the change
amount may be limited by setting the upper limit value and the
lower limit value to the change amount. Instead of limiting the
change amount, the limitation to the change rate or the difference
rate may be performed.
[0108] The correcting section 933 corrects the steering angle
.theta.h2 and outputs the target turning angle .theta.tref. For
example, similar to the basic map section 210 in the target
steering torque generating section 200, the target turning angle
.theta.tref is obtained by the steering angle .theta.h2 using the
map that defines the characteristic of the target turning angle
.theta.tref to the absolute value |.theta.h2| of the steering angle
.theta.h2. Alternatively, the target steering angle .theta.tref may
simply be calculated by multiplying the steering angle .theta.h2 by
a predetermined gain.
[0109] A configuration example of the turning angle control section
920 is shown in FIG. 24. The turning angle control section 920 has
a configuration similar to the configuration example of the
torsional angle control section 300 shown in FIG. 11 excluding the
stabilization compensating section 340 and the adding section 362.
Instead of the target torsional angle .DELTA..theta.ref and the
torsional angle .DELTA..theta., the target turning angle
.theta.tref and the turning angle .theta.t are inputted into the
turning angle control section 920. A turning steering angle
feed-back (FB) compensating section 921, a turning angular velocity
calculating section 922, the velocity control section 923, the
output limiting section 926 and the subtracting section 927 have
the configuration similar to and are performed the operation
similar to those of the torsional angle FB compensating section
310, the torsional angular velocity calculating section 320, the
velocity control section 330, the output limiting section 350 and
the subtracting section 361, respectively.
[0110] In such a configuration, the operation example of the fourth
embodiment will be described with reference to the flowchart of
FIG. 25.
[0111] When the operation is started, the angle sensor 73 detects
the turning angle .theta.t and the angle sensor 74 detects the
motor angle .theta.m (Step S110). The turning angle .theta.t is
inputted into the turning angle control section 920 and the motor
angle .theta.m is inputted into the angular velocity calculating
section 951.
[0112] The angular velocity calculating section 951 calculates the
motor angular velocity .omega.m by differentiating the motor angle
.theta.m and outputs the motor angular velocity .omega.m to the
right-turning/left-turning judging section 300 (Step S120).
[0113] Then, the similar operations from the Step S10 to the Step
S50 shown in FIG. 13 are performed, the reaction force motor 61 is
driven, and the current control is performed (Steps S130 to
S170).
[0114] In the turning angle control, the target turning angle
generating section 910 inputs the steering angle .theta.h and the
steering angle .theta.h is also inputted into the limiting section
931. The limiting section 931 limits the upper and lower limit
values of the steering angle .theta.h by using the preliminarily
set upper and lower limit values (Step S180), and outputs the
limited value as the steering angle .theta.h1 to the rate limiting
section 932. The rate limiting section 932 limits the change amount
of the steering angle .theta.h1 by using a preliminarily set limit
value (Step S190), and outputs the limited value as the steering
angle .theta.h2 to the correcting section 933. The correcting
section 933 corrects the steering angle .theta.h2, obtains the
target turning angle .theta.tref (Step S200) and outputs the target
turning angle .theta.tref to the turning angle control section
920.
[0115] The turning angle control section 920 inputs the turning
angle .theta.t and the target turning angle .theta.tref and
calculates a deviation .DELTA..theta.t.sub.0 by subtracting the
turning angle .theta.t from the target turning angle .theta.tref at
the subtracting section 927 (Step S210). The deviation
.DELTA..theta.t.sub.0 is inputted into the turning angle FB
compensating section 921, and the turning angle FB compensating
section 921 compensates the deviation .DELTA..theta.t.sub.0 by
multiplying the deviation .DELTA..theta.t.sub.0 by the compensation
value (Step S220) and outputs the target turning angular velocity
.omega.tref to the velocity control section 923. The turning
angular velocity calculating section 922 inputs the turning angle
.theta.t, calculates the turning angular velocity .omega.tt by
differentiating the turning angle .theta.t (Step S230) and outputs
the turning angular velocity .omega.tt to the velocity control
section 923. The velocity control section 923 calculates the motor
current command value Imcta by using the I-P control as well as the
operations of the velocity control section 330 (Step S240) and
outputs the motor current command value Imcta to the output
limiting section 926. The output limiting section 926 limits the
upper and lower limit values of the motor current command value
Imcta by using the preliminarily set upper and lower limit values
(Step S250) and outputs the limited value as the motor current
command value Imct (Step S260).
[0116] The motor current command value Imct is inputted into the
current control section 930, and the current control section 930
drives the driving motor 71 based on the motor current command
value Imct and the current value Imd of the driving motor 71 which
is detected by the motor current detector 940, and performs the
current control (Step S270).
[0117] The orders of inputting the data, the calculation and so on
in FIG. 25 are appropriately changeable. As well as the velocity
control section 330 in the torsional angle control section, the
velocity control section 923 in the turning angle control section
920 may use not the I-P control but the realizable control
including at least one of the P-control, the I-control and the
D-control such as the PI-control, the P-control, the PID control or
the PI-D control. Further, the following-up control in the turning
angle control section 920 and the torsional angle control section
300 may be performed by the generally used control configuration.
With respect to the turning angle control section 920, if the
control configuration that the actual angle (the turning angle
.theta.t in this case) follows-up the target angle (the target
turning angle .theta.tref in this case) is employed, the control
configuration is not limited to that of the apparatus for the
vehicle. For example, the control configuration which is used in an
industrial positioning apparatus, an industrial robot and so on may
also be applied.
[0118] In the fourth embodiment, as shown in FIG. 21, one ECU 50
controls the reaction force unit 60 and the driving unit 70. The
ECU for the reaction force unit 60 and the ECU for the driving unit
70 may independently be provided. In this case, respective ECUs
transmit and receive the data by the communication. The SBW system
shown in FIG. 21 does not have a mechanical connection between the
reaction force unit 60 and the driving unit 70. The present
invention is also applicable to the SBW system including the
mechanical torque transmission mechanism in which the column shaft
2 mechanically connects to the turning mechanism via the clutch
when the abnormality occurs in the system. In such an SBW system,
when the system operates in a normal state, the clutch is off
(disengaged) and the mechanical torque transmission is set to an
open state. When the abnormality occurs in the system, the clutch
is on (engaged) and the mechanical torque transmission is set to a
usable state.
[0119] The torsional angle control section 300 in the first to the
fourth embodiments and the assist control section 700 in the third
embodiment directly calculate the motor current command value Imc
and the assist current command value Iac. Alternatively, before
calculating the motor current command value Imc and the assist
current command value Iac, the expected motor torque (the target
torque) is calculated and then the motor current command value and
the assist current command value may be calculated. In this case,
to obtain the motor current command value and the assist current
command value, the generally used relationship between the motor
current and the motor torque is utilized.
[0120] The drawings which are used in the explanation are a
conceptual diagram for qualitatively explaining the present
invention, but the present invention is not limited to the above
drawings. While the above-described embodiments are examples of a
preferable embodiment of the present invention, the present
invention is not limited thereto and various modifications can be
made without departing from the scope of the present invention. The
mechanism which is disposed between the handle and the motor or
between the handle and the reaction force motor and has any spring
constant, may be used. The above mechanism may not be limited to
the torsion bar.
[0121] The main object of the present invention is to achieve the
unit to obtain the target steering torque for resolving the concern
about the assist occurrence due to the offset value of the steering
torque. The unit to follow-up the steering torque to the target
steering torque may not be limited to the above-described unit
including the converting section and the torsional angle control
section.
EXPLANATION OF REFERENCE NUMERALS
[0122] 1 handle [0123] 2 column shaft (steering shaft, handle
shaft) [0124] 2A torsion bar [0125] 3 reduction mechanism [0126] 10
torque sensor [0127] 12 vehicle speed sensor [0128] 14 steering
angle sensor [0129] 20 motor [0130] 30, 50 control unit (ECU)
[0131] 31 current command value calculating section [0132] 33, 720
current limiting section [0133] 34 compensation signal generating
section [0134] 38, 140, 940 motor current detector [0135] 60
reaction force unit [0136] 61 reaction force motor [0137] 70
driving unit [0138] 71 driving motor [0139] 72 gears [0140] 73, 74
angle sensor [0141] 100 EPS steering system/vehicle system [0142]
130, 930 current control section [0143] 200, 600 target steering
torque generating section [0144] 210 basic map section [0145] 230
damper gain section [0146] 240 offset correcting section [0147] 241
offset correction calculating section [0148] 242 vehicle speed
sensitive gain section [0149] 260 phase compensating section [0150]
300 torsional angle control section [0151] 310 torsional angle
feed-back (FB) compensating section [0152] 320 torsional angular
velocity calculating section [0153] 330, 923 velocity control
section [0154] 340 stabilization compensating section [0155] 350,
926 output limiting section [0156] 400 converting section [0157]
500 right-turning/left-turning judging section [0158] 700 assist
control section [0159] 910 target turning angle generating section
[0160] 920 turning angle control section [0161] 921 turning angle
feed-back (FB) compensating section [0162] 922 turning angular
velocity calculating section [0163] 931 limiting section [0164] 932
rate limiting section [0165] 933 correcting section [0166] 951
angular velocity calculating section
* * * * *