1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
VEHICLE STEERING SYSTEM
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING
UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME,
CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND
THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Technical Field
5 [0001]
The present disclosure relates to a vehicle steering system.
Background Art
[0002]
10 A vehicle steering system in which a motor is controlled so as
to change a steering angle in accordance with the target route of
a vehicle is well known. In a vehicle steering system of this type,
distortion in a vehicle steering mechanism may cause a hysteresis
between a steering angle, as a rotation angle of a steering shaft,
15 and a turning angle, as a rotation angle of a vehicle turning wheel.
[0003]
To date, there has been a vehicle steering system in which an
element angle calculation means for correcting a hysteresis between
a steering angle and a turning angle is provided and in which in the
20 case where it is determined that a hysteresis has occurred between
the steering angle and the turning angle, the element angle
calculation means provides the hysteresis to a target steering angle
so that the hysteresis is corrected (e.g., refer to Patent Document
1).
25 [0004]
3
In addition, to date, there has been an electric power steering
apparatus in which a steering component is removed from a dynamic
state quantity such as a rotation speed signal by use of a
small-amplitude filtration filter for filtering small-amplitude
components, and then only a vibration component, which 5 is a component
whose amplitude is smaller than the steering component, is accurately
extracted so that the vibration component is reduced (e.g., refer
to Patent Document 2).
[Prior Art Reference]
10 [Patent Literature]
[0005]
[Patent Document 1] Japanese Patent Application Laid-Open No.
2016-135676
[Patent Document 2] International Publication No.
15 WO2009/078074
Disclosure of the Invention
Problems to be Solved by the Invention
[0006]
20 In the conventional vehicle steering system disclosed in Patent
Document 1, a hysteresis included in the output of a steering angle
sensor is not taken into consideration. Accordingly, in the case
where a hysteresis behind a change in a steering angle exists in a
detected steering angle to be outputted from a steering angle sensor,
25 the detected steering angle does not change in a hysteresis section,
4
even when the steering angle changes. In particular, because in the
case of turn-back steering, a phenomenon that even when a steering
angle changes, the detected steering angle does not change in a
hysteresis section conspicuously occurs, the detected steering angle
suddenly changes at a timing when the steering angle 5 becomes out of
the hysteresis section; therefore, feeling of discontinuity occurs
during the steering. Moreover, because the steering angle becomes
larger than an intended target steering angle by a hysteresis amount,
the traveling route of a vehicle may largely deviate from a target
10 route. Moreover, although provided with a technique for decreasing
vibration components in an electric signal, the conventional electric
power steering apparatus disclosed in Patent Document 2 has no
technology for correcting the deviation of a detected steering angle.
[0007]
15 The present disclosure discloses a technology for solving the
foregoing problems in conventional apparatuses; the objective thereof
is to provide a vehicle steering system that reduces the effect of
a hysteresis included in the output of a vehicle sensor so that
accurate and smooth steering can be performed.
20
Means for Solving the Problems
[0008]
A vehicle steering system disclosed in the present disclosure
is characterized by including
25 a steering mechanism that drives a vehicle,
5
a motor that makes the steering mechanism rotate,
a steering angle sensor that detects a steering angle,
which is a rotation angle of the steering mechanism, and outputs a
detected steering angle having a hysteresis with respect to the
5 steering angle,
a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the steering
angle and the detected steering angle, and
a control unit that controls the motor in such a way as
10 to be equal to a difference between the steering angle and a target
steering angle, which is a target value of the steering angle, based
on the target steering angle, the detected steering angle, and the
hysteresis estimation value.
[0009]
15 A vehicle steering system disclosed in the present disclosure
is characterized by including
a steering mechanism that drives a vehicle,
a motor that makes the steering mechanism rotate,
a yaw-rate sensor that detects a yaw rate of the vehicle
20 and outputs a detected yaw rate having a hysteresis with respect to
the yaw rate,
a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the yaw rate
and the detected yaw rate, and
25 a control unit that controls the motor in such a way as
6
to be equal to a difference between the yaw rate and a target yaw
rate, which is a target value of the yaw rate, based on the target
yaw rate, the detected yaw rate, and the hysteresis estimation value.
Advantage 5 of the Invention
[0010]
A vehicle steering system disclosed in the present disclosure
includes
a steering mechanism that drives a vehicle,
10 a motor that makes the steering mechanism rotate,
a steering angle sensor that detects a steering angle,
which is a rotation angle of the steering mechanism, and outputs a
detected steering angle having a hysteresis with respect to the
steering angle,
15 a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the steering
angle and the detected steering angle, and
a control unit that controls the motor in such a way as
to be equal to a difference between the steering angle and a target
20 steering angle, which is a target value of the steering angle, based
on the target steering angle, the detected steering angle, and the
hysteresis estimation value. Therefore, there can be obtained a
vehicle steering system that reduces the effect of a hysteresis
included in the output of a vehicle sensor so that accurate and smooth
25 steering can be performed.
7
[0011]
A vehicle steering system disclosed in the present disclosure
includes
a steering mechanism that drives a vehicle,
a motor that makes the steering 5 mechanism rotate,
a yaw-rate sensor that detects a yaw rate of the vehicle
and outputs a detected yaw rate having a hysteresis with respect to
the yaw rate,
a hysteresis estimation unit that estimates a hysteresis
10 estimation value corresponding to a difference between the yaw rate
and the detected yaw rate, and
a control unit that controls the motor in such a way as
to be equal to a difference between the yaw rate and a target yaw
rate, which is a target value of the yaw rate, based on the target
15 yaw rate, the detected yaw rate, and the hysteresis estimation value.
Therefore, there can be obtained a vehicle steering system that
reduces the effect of a hysteresis included in the output of a vehicle
sensor so that accurate and smooth steering can be performed.
20 Brief Description of the Drawings
[0012]
FIG. 1 is an overall configuration diagram of a vehicle steering
system according to each of Embodiments 1 and 2;
FIG. 2A is a characteristic chart representing the relationship
25 between a real steering angle and a detected steering angle obtained
8
by a steering angle sensor;
FIG. 2B is a characteristic chart representing the relationship
between a real steering angle and a detected steering angle obtained
by a steering angle sensor;
FIG. 2C is a characteristic chart representing 5 the relationship
between a real steering angle and a detected steering angle obtained
by a steering angle sensor;
FIG. 3 is a configuration diagram of a steering-angle controller
in the vehicle steering system according to each of Embodiments 1
10 and 2;
FIG. 4 is a configuration diagram of a hysteresis estimation
unit in the vehicle steering system according to each of Embodiments
1 and 2;
FIG. 5 is a configuration diagram of a small-amplitude
15 filtration filter in the vehicle steering system according to each
of Embodiments 1 and 2 and in a vehicle steering system according
to each of Embodiments 3 and 4;
FIG. 6 is a configuration diagram of a control unit in the vehicle
steering system according to each of Embodiments 1 and 2;
20 FIG. 7 is a set of explanatory diagrams representing various
kinds of configuration examples in each of which a control deviation
is created by use of a hysteresis estimation value, in the vehicle
steering system according to each of Embodiments 1 and 2;
FIG. 8 is an overall configuration diagram of the vehicle
25 steering system according to each of Embodiments 3 and 4;
9
FIG. 9 is a configuration diagram of a yaw-rate controller in
the vehicle steering system according to each of Embodiments 3 and
4;
FIG. 10 is a configuration diagram of a hysteresis estimation
unit in the vehicle steering system according to each 5 of Embodiments
3 and 4;
FIG. 11 is a configuration diagram of a control unit in the
vehicle steering system according to each of Embodiments 3 and 4;
FIG. 12 is explanatory diagrams representing various kinds of
10 configuration examples in each of which a control deviation is created
by use of a hysteresis estimation value, in the vehicle steering system
according to each of Embodiments 3 and 4; and
FIG. 13 is a block diagram representing the hardware
configuration of each of the steering-angle controller according to
15 Embodiment 1 and the yaw-rate controller according to Embodiment 2.
Detailed Description of the Embodiments
[0013]
Embodiment 1.
20 FIG. 1 is an overall configuration diagram of a vehicle steering
system according to each of Embodiments 1 and 2. In FIG. 1, a vehicle
steering system 100 is provided with a steering mechanism 1 for
steering a vehicle, a motor 2 that makes the steering mechanism 1
rotate through the intermediary of a motor-speed reduction gear 3,
25 a steering angle sensor 4 that detects a steering angle, which is
10
a rotation angle of the steering mechanism 1, and then outputs a
detected steering angle S1, and a steering-angle controller 5. The
steering-angle controller 5 is provided with a hysteresis estimation
unit 6 that outputs an after-mentioned hysteresis estimation value
H1 corresponding to a deviation between the detected 5 steering angle
S1 and a real steering angle, which is an actual steering angle, and
a control unit 7 that creates a current command value Ic, based on
a target steering angle S0 to be outputted from a higher-hierarchy
controller 8, the detected steering angle S1, and the hysteresis
10 estimation value H1. The current command value Ic outputted from the
control unit 7 is transferred to a motor control apparatus
(unillustrated) for controlling the motor 2. Based on the current
command value Ic, the motor control apparatus controls an inverter
apparatus configured with, for example, semiconductor switching
15 devices in such a way that a motor current follows the current command
value Ic. The motor control apparatus including the inverter
apparatus may be incorporated in the control unit 7.
[0014]
The control unit 7 provides the current command value Ic, created
20 based on a deviation between the target steering angle S0 and the
detected steering angle S1, to the motor control apparatus so as to
control a motor current Im, and drives the motor 2 in such a way that
the steering angle follows the target steering angle S0, so that the
steering mechanism 1 rotates. The detected steering angle S1 to be
25 outputted from the steering angle sensor 4 includes a hysteresis
11
behind a change in a real steering angle.
[0015]
The steering mechanism 1 includes a steering wheel 11 to be
operated by a vehicle driver, a steering shaft 12 coupled with the
steering wheel 11, a rack-and-pinion gear 13 to 5 be driven by the
steering shaft 12, and a rack 14 that is driven by the rack-and-pinion
gear 13 so as to turn a pair of turning wheels 10. The foregoing
steering angle sensor 4 measures a real steering angle, which is a
rotation amount of the steering shaft 12, outputs the detected
10 steering angle S1 corresponding to the real steering angle, and then
inputs the detected steering angle S1 to the steering-angle controller
5. The higher-hierarchy controller 8 calculates a target route of
the vehicle, outputs the target steering angle S0 for making the
traveling route of the vehicle follow the calculated target route,
15 and then inputs the target steering angle S0 to the steering-angle
controller 5.
[0016]
Based on the detected steering angle S1 obtained from the
steering angle sensor 4 and the target steering angle S0, the
20 steering-angle controller 5 calculates the current command value Ic
and then provides the current command value Ic to the motor control
apparatus for controlling the motor 2. The motor current Im is
controlled by the motor control apparatus so as to follow the current
command value Ic and is supplied to the motor 2. The motor 2 generates
25 torque corresponding to the supplied motor current Im. The torque
12
generated by the motor 2 is transferred to the steering shaft 12
through the intermediary of the motor-speed reduction gear 3 and is
further transferred to the rack 14 through the intermediary of the
rack-and-pinion gear 13. The rack 14 is driven in the axial direction
thereof by the rack-and-pinion gear 13 so as to turn 5 the pair of the
turning wheels 10.
[0017]
FIG. 2A is a characteristic chart representing the relationship
between the real steering angle and the detected steering angle
10 obtained by the steering angle sensor; a case where a hysteresis is
included in the detected steering angle is represented. In FIG. 2A,
the abscissa denotes the real steering angle [deg], and the ordinate
denotes the detected steering angle [deg].
[0018]
15 As represented in FIG. 2A, the detected steering angle includes
a hysteresis of a dead-zone width 2B behind a change in the real
steering angle. Therefore, when the rotation direction of the real
steering angle starts to be reversed, the change in the detected
steering angle is delayed due to the hysteresis. In the case where
20 in steering-angle control, it is tried to make the target steering
angle S0 and the detected steering angle S1 coincide with each other,
the deviation between the target steering angle S0 and the detected
steering angle S1 increases during the hysteresis section, because
the detected steering angle S1 does not change; when the real steering
25 angle falls out of the hysteresis section, the motor is driven based
13
on the increased deviation and hence the real steering angle may
suddenly change. Moreover, in a steady state, because the detected
steering angle S1 has an error of the hysteresis width 2B with respect
to the real steering angle, there may be a probability that the
traveling route of the vehicle deviates from 5 the target route.
However, in the vehicle steering system according to Embodiment 1,
as described later, the steering angle does not suddenly change; thus,
the traveling route of the vehicle does not deviate from the target
route.
10 [0019]
FIG. 3 is a configuration diagram of a steering-angle controller
in the vehicle steering system according to each of Embodiments 1
and 2; the configuration of the steering-angle controller 5 in which
hysteresis compensation is introduced is represented. In FIG. 3, the
15 steering-angle controller 5 has the hysteresis estimation unit 6,
an addition unit 21, a deviation calculation unit 22, and the control
unit 7. Based on an input value X1 to be inputted, the hysteresis
estimation unit 6 calculates and outputs the hysteresis estimation
value H1. The addition unit 21 adds the detected steering angle S1
20 detected by the steering angle sensor 4 and the hysteresis estimation
value H1, and then outputs the addition value, as a compensation
detected steering angle S2.
[0020]
The deviation calculation unit 22 subtracts the compensation
25 detected steering angle S2 from the target steering angle S0 inputted
14
from the higher-hierarchy controller 8 and then outputs a control
deviation ΔS. Based on the inputted control deviation ΔS, the target
steering angle S0, and the compensation detected steering angle S2,
the control unit 7 calculates the current command value Ic and then
inputs the current command value Ic to the motor 5 control apparatus
for controlling the motor 2. The motor current Im flowing in the motor
2 is controlled by the motor control apparatus so as to follow the
current command value Ic.
[0021]
10 FIG. 4 is a configuration diagram of a hysteresis estimation
unit in the vehicle steering system according to each of Embodiments
1 and 2. In FIG. 4, the hysteresis estimation unit 6 has a
steering-angle estimation unit 31 and an after-mentioned
small-amplitude filtration filter 32. The steering-angle estimation
15 unit 31 inputs a steering-angle estimation value S3, calculated based
on the input value X1, to the small-amplitude filtration filter 32.
The small-amplitude filtration filter 32 outputs the hysteresis
estimation value H1, based on the steering-angle estimation value
S3 inputted from the steering-angle estimation unit 31.
20 [0022]
Because having a frequency responsiveness for making the input
value X1 approach the real steering angle, the steering-angle
estimation unit 31 raises the accuracy of hysteresis estimation by
the hysteresis estimation unit 6. In Embodiment 1, as the input value
25 X1 to be inputted to the hysteresis estimation unit 6, the target
15
steering angle S0 is utilized. The reason therefor is that in the
case where the responsiveness of the steering-angle control is high,
it can be assumed that the target steering angle S0 and the real
steering angle almost approximate each other. In practice, because
the real steering angle follows the target steering 5 angle S0 in a
delayed manner, the steering-angle estimation unit 31 makes an
approximation of the follow-up delay.
[0023]
Specifically, with regard to the real vehicle, the frequency
10 responsiveness of the steering-angle controller 5 is measured so as
to obtain the inherent frequency of the steering-angle controller
5; then, the target steering angle S0, as the input value X1, is
processed through a lowpass filter having the inherent frequency,
so that there is created the steering-angle estimation value S3 having
15 a waveform approximate to the waveform of the real steering angle.
Through the result of measurement in the real vehicle, the applicant
ascertained that the delay of the steering-angle control is
approximately from 0.5 [Hz] to 2.0 [Hz]. Thus, the steering control
apparatus according to Embodiment 1 is configured in such a way that
20 the steering angle is estimated by use of a lowpass filter having
an inherent frequency of approximately from 0.5 [Hz] to 2.0 [Hz],
as the steering-angle estimation unit 31. The steering-angle
estimation value S3 to be outputted from the steering-angle estimation
unit 31 is for estimating nothing but the hysteresis of the sensor;
25 therefore, it is not required that the steering-angle estimation value
16
S3 is created with a high estimation accuracy to the extent that the
steering-angle estimation value S3 completely coincide with the real
steering angle.
[0024]
Next, the small-amplitude filtration filter 32 will 5 be explained.
FIG. 5 is a configuration diagram of a small-amplitude filtration
filter in the vehicle steering system according to each of Embodiments
1 and 2 and in a vehicle steering system according to each of
Embodiments 3 and 4. A small-amplitude filtration filter is utilized
10 also in foregoing Patent Document 2; however, the application thereof
is to extract vibration components in control of an electric power
steering apparatus. In Embodiment 1 according to the present
disclosure, the small-amplitude filtration filter 32 is utilized for
extracting a hysteresis-related signal from a detected steering angle
15 detected by the steering angle sensor in the steering-angle control.
[0025]
In FIG. 5, the small-amplitude filtration filter 32 includes
a hysteresis filter 41 for performing hysteresis-function processing
and a subtractor 42. The hysteresis filter 41 applies
20 hysteresis-function processing to an input value X2 and then outputs
the processed value, as an output value Z. The hysteresis for applying
the hysteresis-function processing to the input value X2 is set in
such a way as to have a sensor hysteresis characteristic including
a width and a history that are preliminarily measured in the real
25 vehicle.
17
[0026]
In Embodiment 1, it is assumed that the hysteresis of the vehicle
has the hysteresis characteristic represented in foregoing FIG. 2A;
therefore, it is desirable that a hysteresis characteristic the same
as that in FIG. 2A is provided also to the hysteresis 5 function of
the hysteresis filter 41. The subtractor 42 outputs, as the
hysteresis estimation value H1, a value obtained by subtracting the
output value Z of the hysteresis filter 41 from the input value X2
of the hysteresis filter 41. In Embodiment 1, as the input value X2
10 to be inputted to the small-amplitude filtration filter 32, the
steering-angle estimation value S3 outputted from the steering-angle
estimation unit 31 is utilized.
[0027]
Next, the control unit 7 will be explained. FIG. 6 is a
15 configuration diagram of a control unit in the vehicle steering system
according to each of Embodiments 1 and 2. In FIG. 6, the control unit
7 includes a first pseudo-differentiation device 51, a second
pseudo-differentiation device 52, a first gain 53, a second gain 54,
a third gain 55, a phase compensator 56, an addition unit 57, and
20 a subtraction unit 58. The control unit 7 represented in FIG. 6
basically performs feedback control in such a way as to suppress the
foregoing control deviation ΔS.
[0028]
A target steering angle speed R0 is created from the target
25 steering angle S0 by means of the first pseudo-differentiation device
18
51; a value obtained by multiplying the target steering angle speed
R0 by the first gain 53 is inputted to the addition unit 57. A
steering-angle-speed command value Rc is created from the control
deviation ΔS through processing by the second gain 54 and the phase
compensator 56; then, the steering-angle-speed command 5 value Rc is
inputted to the subtraction unit 58. The second gain 54 and the phase
compensator 56 are designed in such a way as to create the
steering-angle-speed command value Rc in which desired stability and
trackability to the control deviation ΔS are secured. A detected
10 steering angle speed R1 is created from the compensation detected
steering angle S2 through the second pseudo-differentiation device
52; then, the detected steering angle speed R1 is inputted to the
subtraction unit 58.
[0029]
15 The detected steering angle speed R1 is subtracted from the
steering-angle-speed command value Rc by the subtraction unit 58;
a value calculated by multiplying the value obtained through the
subtraction by the third gain 55 is inputted to the addition unit
57. The addition unit 57 adds a value obtained by multiplying the
20 foregoing target steering angle speed R0 by the first gain 53 and
a value obtained by multiplying a value, obtained by subtracting the
detected steering angle speed R1 from the steering-angle-speed
command value Rc, by the third gain 55, and then outputs the added
value, as the current command value Ic.
25 [0030]
19
In order to raise the stability, the control unit 7 represented
in FIG. 6 includes a major loop of feedback control utilizing the
target steering angle speed R0 obtained from the target steering angle
S0 and the steering-angle-speed command value Rc obtained from the
control deviation ΔS and a minor loop of feedback 5 control utilizing
the detected steering angle speed R1 obtained from the compensation
detected steering angle S2 and the steering-angle-speed command value
Rc obtained from the control deviation ΔS. In addition, in the control
unit 7, there is configured cascade control in which the feedback
10 control utilizing the foregoing minor loop is added to the feedback
control utilizing the foregoing major loop.
[0031]
Because in the control unit 7 represented in FIG. 6, not the
detected steering angle S1 but the compensation detected steering
15 angle S2 to which hysteresis compensation has been provided is
utilized, the effect of a hysteresis included in the detected steering
angle S1 from the steering angle sensor 4 is reduced and hence the
steering control can more accurately be performed. Moreover, in
order to raise the responsiveness, feed-forward control of the target
20 yaw rate speed YR0 is added.
[0032]
As described above, Embodiment 1 makes it possible that in
steering-angle control in a vehicle steering system, the hysteresis
in a steering angle sensor is estimated and compensated; thus, smooth
25 steering in which the effect of the hysteresis is reduced can be
20
performed.
[0033]
In foregoing Embodiment 1, in the steering-angle controller 5,
as explained in FIG. 3, the hysteresis estimation unit 6 creates the
hysteresis estimation value H1; the addition unit 21 5 adds the detected
steering angle S1 and the hysteresis estimation value H1 so as to
create the compensation detected steering angle S2; then, the
deviation calculation unit 22 subtracts the compensation detected
steering angle S2 from the target steering angle S0 so as to create
10 the control deviation ΔS. However, as the configuration in which the
control deviation ΔS is created by use of the hysteresis estimation
value H1, there exist configurations other than the one represented
in FIG. 3.
[0034]
15 FIG. 7 is a set of explanatory diagrams representing various
kinds of configuration examples in each of which a control deviation
is created by use of a hysteresis estimation value, in the vehicle
steering system according to each of Embodiments 1 and 2. The
configuration represented in (a) of FIG. 7 corresponds to the
20 configuration represented in FIG. 3; the hysteresis estimation value
H1 is added to the detected steering angle S1 so that the compensation
detected steering angle S2 is created; then, the compensation detected
steering angle S2 is subtracted from the target steering angle S0
so that the control deviation ΔS is created. The reference numeral
25 23 denotes a subtractor.
21
[0035]
It may be allowed that as the configuration represented in (b)
of FIG. 7, which replaces the configuration represented in (a) of
FIG. 7, the control deviation ΔS is created by subtracting the
hysteresis estimation value H1 from a value obtained 5 by subtracting
the detected steering angle S1 from the target steering angle S0;
alternatively, it may be allowed that as the configuration represented
in (c) of FIG. 7, the hysteresis estimation value H1 is subtracted
from the target steering angle S0 so that a compensation target
10 steering angle S4 is created and then the detected steering angle
S1 is subtracted from the compensation target steering angle S4 so
that the control deviation ΔS is obtained. The configuration
represented in each of (a), (b), and (c) of FIG. 7 provides the same
effect.
15 [0036]
Moreover, in Embodiment 1, the steering-angle estimation unit
31 obtains the steering-angle estimation value S3 by use of a transfer
function; however, it may be allowed that in order to reduce the
calculation load, the steering-angle estimation value S3 is obtained
20 by use of a mere gain. Furthermore, it may be allowed that in order
to raise the estimation accuracy of the steering-angle estimation
unit 31, nonlinear processing such as saturation processing or
dead-zone processing is performed.
[0037]
25 Still moreover, as the hysteresis filter 41 in the
22
small-amplitude filtration filter 32, a filter having an ideal
hysteresis characteristic represented in FIG. 2A is utilized; it is
important to make the characteristic of the hysteresis filter 41
coincide with the hysteresis characteristic of the steering angle
sensor. For example, in the case where as represented 5 in FIG. 2B,
the hysteresis characteristic of the steering angle sensor has a shape
in which in comparison with the hysteresis characteristic in FIG.
2A, the lower-right and upper-left corner portions of the hysteresis
loop are suppressed, a hysteresis filter having a hysteresis
10 characteristic coinciding with that particular hysteresis
characteristic is utilized. In addition, in the case where as
represented in FIG. 2C, the hysteresis characteristic of the steering
angle sensor has a dead zone in the vicinity of the origin, a hysteresis
filter having a characteristic coinciding with that particular
15 characteristic is utilized. As described above, the accuracy of the
hysteresis estimation value H1 can be raised by making the hysteresis
characteristic of the hysteresis filter 41 coincide with the
hysteresis characteristic of the steering angle sensor.
[0038]
20 In the above explanation, it is assumed that a hysteresis exists
in the relationship between the steering angle and the detected
steering angle; however, the generating factor of the hysteresis is
not particularly limited. For example, even when the generation of
the hysteresis is caused by the characteristic of the steering angle
25 sensor itself, by a mechanical backlash of the steering mechanism
23
for making the steering angle sensor rotate, or further by both thereof,
the vehicle steering system according to Embodiment 1 can be utilized
and the same effect can be demonstrated.
[0039]
5 Embodiment 2.
Next, a vehicle steering system according to Embodiment 2 will
be explained. In Embodiment 1, as described above, as the input value
X1 to be inputted to the hysteresis estimation unit 6, the target
steering angle S0 is utilized. However, in the case where the control
10 responsiveness is low or under the environment in which disturbance
such as friction exists, the difference between the target steering
angle S0 and the steering angle becomes large; therefore, in the
configuration according to Embodiment 1, estimation of the hysteresis
may become inaccurate. In Embodiment 2, the vehicle steering system
15 is configured in such a way that estimation of a hysteresis is
performed by inputting an input value other than a target steering
angle to the hysteresis estimation unit 6. Hereinafter, the vehicle
steering system according to Embodiment 2 will be explained mainly
with regard to the difference from the vehicle steering system
20 according to Embodiment 1. FIGS. 1, 3, 4, 5, 6, and 7 are applied
also to the vehicle steering system according to Embodiment 2.
[0040]
The hysteresis estimation unit 6 according to Embodiment 2 is
configured in such a way that the hysteresis estimation value H1 is
25 calculated by use of the detected steering angle S1, as the input
24
value X1 represented in FIG. 4. With this configuration, estimation
of the hysteresis cannot be performed in a hysteresis section where
the detected steering angle S1 does not move; however, in the section
out of the hysteresis section, the detected steering angle S1 moves.
Accordingly, in the situation where the fluctuation 5 of the steering
angle is sufficiently larger than the hysteresis width, the hysteresis
can be estimated and hence the hysteresis estimation value H1 can
be obtained.
[0041]
10 As a variant example of Embodiment 2, the hysteresis estimation
unit 6 is configured in such a way that the hysteresis estimation
value H1 is calculated by use of an input value based on the yaw rate
of a vehicle. Because when a vehicle pivots, a yaw rate occurs, it
can be determined that steering has been started, based on the
15 occurrence of the yaw rate. In addition, because the yaw rate is
substantially proportional to each of the steering angle and the
vehicle speed, the steering angle can be estimated based on the yaw
rate and the vehicle speed.
[0042]
20 In this case, as the input value X1, an input value based on
a value detected by a yaw-rate sensor may be utilized; alternatively,
the yaw rate and the hysteresis estimation value H1 may be calculated
by use of an input value based on a vehicle condition such as the
acceleration, the vehicle speed, or the rotational difference between
25 the right and left wheels.
25
[0043]
As an additional variant example of Embodiment 2, the hysteresis
estimation value H1 may be calculated by use of a value based on the
motor current Im, as the input value X1 to be inputted to the hysteresis
estimation unit. In the case where there exists 5 static friction
between a road surface and a set of the steering mechanism and the
turning wheels and the motor current Im is within a specific value,
the static friction is large and hence the steering angle does not
move; however, when the motor current Im exceeds the specific value,
10 the steering angle overcomes the static friction and then starts to
move. Because it is made possible to determine the occurrence of
steering by use of the value of this motor current, as a current
threshold value, the estimation of the hysteresis can more accurately
be performed.
15 [0044]
As described above, the vehicle steering system according to
Embodiment 2 demonstrates an effect that even in the case where the
difference between the target steering angle and the steering angle
is large, it is made possible to estimate the hysteresis. In addition,
20 as the input values, either a single kind of signal or two or more
signals including a target steering angle may be utilized so as to
estimate the hysteresis.
[0045]
Each of foregoing Embodiments 1 and 2 is obtained by converting
25 the vehicle steering system, described in one of the items (1) through
26
(10) below, into a tangible form.
(1) A vehicle steering system comprising:
a steering mechanism that drives a vehicle;
a motor that makes the steering mechanism rotate;
a steering angle sensor that detects a steering 5 angle, which
is a rotation angle of the steering mechanism, and outputs a detected
steering angle having a hysteresis with respect to the steering angle;
a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the steering
10 angle and the detected steering angle; and
a control unit that controls the motor in such a way as to be
equal to a difference between the steering angle and a target steering
angle, which is a target value of the steering angle, based on the
target steering angle, the detected steering angle, and the hysteresis
15 estimation value.
In the vehicle steering system configured in such a manner as
described above, compensation is made so as to cancel the hysteresis
of the steering angle sensor; thus, steering can smoothly be performed.
Moreover, the deviation between the traveling route and the target
20 route of a vehicle can be suppressed.
[0046]
(2) The vehicle steering system according to (1),
wherein the hysteresis estimation unit is configured in such
a way as to estimate the hysteresis estimation value corresponding
25 to a difference obtained by subtracting the detected steering angle
27
from the steering angle, and
wherein the control unit is configured in such a way as to control
the motor, based on a value obtained by subtracting the detected
steering angle and the hysteresis estimation value from the target
5 steering angle.
In the vehicle steering system configured in such a manner as
described above, addition and subtraction according to the foregoing
signs are applied to the target steering angle, the detected steering
angle, and the hysteresis estimation value, so that the control
10 deviation becomes a value equal to the difference between the target
steering angle and the steering angle; thus, there is demonstrated
an effect that steering-angle control utilizing a desirable deviation
input can be performed.
[0047]
15 (3) The vehicle steering system according to any one of (1) and (2),
wherein the hysteresis estimation unit is configured in such a way
as to calculate the hysteresis estimation value, based on the target
steering angle.
In the vehicle steering system configured in such a manner as
20 described above, there is demonstrated an effect that even in a section
where as at a start of steering or as at a turnback of steering, the
detected steering angle does not move, it is made possible to estimate
the hysteresis.
[0048]
25 (4) The vehicle steering system according to any one of (1) through
28
(3), wherein the hysteresis estimation unit has a steering-angle
estimation unit for estimating a response of the steering angle to
an input value to the hysteresis estimation unit and is configured
in such a way as to calculate the hysteresis estimation value, based
on a steering-angle estimation value to be 5 outputted from the
steering-angle estimation unit.
In the vehicle steering system configured in such a manner as
described above, the input value is converted into a signal
corresponding to the steering angle, so that the accuracy of
10 hysteresis estimation can be raised.
[0049]
(5) The vehicle steering system according to any one of (1) through
(4), wherein the hysteresis estimation unit has a steering-angle
estimation unit for outputting a steering-angle estimation value
15 whose high-frequency phase is delayed with respect to the target
steering angle, and is configured in such a way as to calculate the
hysteresis estimation value, based on the steering-angle estimation
value.
In the vehicle steering system configured in such a manner as
20 described above, a frequency response for making the target steering
angle approach the steering angle is added, so that the accuracy of
hysteresis estimation can be raised.
[0050]
(6) The vehicle steering system according to any one of (1) through
25 (5),
29
wherein the hysteresis estimation unit has a small-amplitude
filtration filter, and
wherein the small-amplitude filtration filter includes a
hysteresis filter for performing hysteresis-function processing
having a hysteresis width corresponding to the 5 hysteresis and a
subtractor that subtracts an output signal of the hysteresis filter
from an input signal of the hysteresis filter.
In the vehicle steering system configured in such a manner as
described above, there is demonstrated an effect that a simple logic
10 makes it possible to extract a sensor hysteresis.
[0051]
(7) The vehicle steering system according to any one of (1) through
(6), wherein the hysteresis estimation unit is configured in such
a way as to compensate a hysteresis of the steering angle sensor
15 itself.
In the vehicle steering system configured in such a manner as
described above, the hysteresis of the steering angle sensor itself
can be compensated.
[0052]
20 (8) The vehicle steering system according to any one of (1) and (2),
wherein the hysteresis estimation unit is configured in such a way
as to calculate the hysteresis estimation value, based on the detected
steering angle.
In the vehicle steering system configured in such a manner as
25 described above, there is demonstrated an effect that even in a
30
situation where the target steering angle and the detected steering
angle do not approximate each other, it is made possible to estimate
the hysteresis.
[0053]
(9) The vehicle steering system according to any one 5 of (1) and (2),
wherein the hysteresis estimation unit is configured in such a way
as to calculate the hysteresis estimation value, based on a current
in the motor.
In the vehicle steering system configured in such a manner as
10 described above, there is demonstrated an effect that even in a
situation where the target steering angle and the detected steering
angle do not approximate each other and a friction disturbance is
included, it is made possible to estimate the hysteresis.
[0054]
15 (10) The vehicle steering system according to any one of (1) and (2),
wherein the hysteresis estimation unit is configured in such a way
as to calculate the hysteresis estimation value, based on a yaw rate
of the vehicle.
In the vehicle steering system configured in such a manner as
20 described above, there is demonstrated an effect that even in a
situation where the target steering angle and the detected steering
angle do not approximate each other and the detected steering angle
does not move, it is made possible to estimate the hysteresis.
[0055]
25 Embodiment 3.
31
In each of Embodiments 1 and 2, the hysteresis of the detected
steering angle S1 in steering-angle control is compensated. In
contrast, in Embodiment 3, the hysteresis of a yaw rate in yaw-rate
control is compensated. FIG. 8 is an overall configuration diagram
of a vehicle steering system according 5 to Embodiment 3.
[0056]
In FIG. 8, the vehicle steering system according to Embodiment
3 performs yaw-rate control, instead of the steering-angle control
in the vehicle steering system according to Embodiment 1; based on
10 a detected yaw rate Y1 obtained from a yaw-rate sensor 9 and a target
yaw rate Y0 created by the higher-hierarchy controller 8, the current
command value Ic is created; then, the motor control apparatus is
controlled based on this current command value Ic, so that the motor
2 is controlled.
15 [0057]
In the case where the detected yaw rate Y1 includes a hysteresis,
with respect to a yaw rate, that has a characteristic similar to the
hysteresis characteristic represented in foregoing FIG. 2A, FIG. 2B,
or FIG. 2C, a dead zone due to the hysteresis causes a delay in the
20 detected yaw rate, when the yaw rate of the vehicle changes. In the
case where in yaw-rate control, it is tried to make the target yaw
rate Y0 and the detected yaw rate Y1 coincide with each other, the
deviation between the target yaw rate Y0 and the detected yaw rate
Y1 increases during the hysteresis section, because the detected yaw
25 rate Y1 does not change; when the yaw rate falls out of the hysteresis
32
section, the detected yaw rate Y1 is caused to suddenly change.
Moreover, in a steady state, because the detected yaw rate Y1 has
an error of a width B with respect to the yaw rate, required yaw-rate
control cannot be performed. In the vehicle steering system
according to Embodiment 3, as described later, the 5 yaw rate does not
suddenly change; thus, the traveling route of the vehicle does not
deviate from the target route.
[0058]
In FIG. 8, a vehicle steering system 200 is provided with the
10 steering mechanism 1 for steering a vehicle, the motor 2 that makes
the steering mechanism 1 rotate through the intermediary of the
motor-speed reduction gear 3, the yaw-rate sensor 9 that detects a
yaw rate and then outputs the detected yaw rate Y1, and a yaw rate
controller 61. The yaw rate controller 61 is provided with a
15 hysteresis estimation unit 62 that outputs an after-mentioned
hysteresis estimation value H2 corresponding to a deviation between
the detected yaw rate Y1 and a real yaw rate, which is an actual yaw
rate, and a control unit 63 that creates the current command value
Ic, based on the target yaw rate Y0 to be outputted from the
20 higher-hierarchy controller 8, the detected yaw rate Y1, and the
hysteresis estimation value H2. The current command value Ic
outputted from the control unit 63 is transferred to a motor control
apparatus (unillustrated) for controlling the motor 2. Based on the
current command value Ic, the motor control apparatus controls an
25 inverter apparatus configured with, for example, semiconductor
33
switching devices in such a way that a motor current follows the
current command value Ic. The motor control apparatus including the
inverter apparatus may be incorporated in the control unit 63.
[0059]
The control unit 63 provides the current 5 command value Ic,
created based on a deviation between the target yaw rate Y0 and the
detected yaw rate Y1, to the motor control apparatus so as to control
the motor current Im, and drives the motor 2 in such a way that the
yaw rate follows the target yaw rate Y0, so that the steering mechanism
10 1 rotates. The detected yaw rate Y1 to be outputted from the yaw-rate
sensor 9 includes a hysteresis with respect to a real yaw rate.
[0060]
The steering mechanism 1 includes the steering wheel 11 to be
operated by a vehicle driver, the steering shaft 12 coupled with the
15 steering wheel 11, the rack-and-pinion gear 13 to be driven by the
steering shaft 12, and the rack 14 that is driven by the
rack-and-pinion gear 13 so as to turn a pair of turning wheels 10.
The yaw-rate sensor 9 measures a real yaw rate of the vehicle, outputs
the detected yaw rate Y1 corresponding to the real yaw rate, and inputs
20 the detected yaw rate Y1 to the yaw rate controller 61. The
higher-hierarchy controller 8 calculates a target route of the vehicle,
outputs the target yaw rate Y0 for making the traveling route of the
vehicle follow the calculated target route, and then inputs the target
yaw rate Y0 to the yaw rate controller 61.
25 [0061]
34
Based on the detected yaw rate Y1 obtained from the yaw-rate
sensor 9 and the target yaw rate Y0 from the higher-hierarchy
controller 8, the yaw rate controller 61 calculates the current
command value Ic and then provides the current command value Ic to
the motor control apparatus (unillustrated) for controlling 5 the motor
2. The motor current Im is controlled by the motor control apparatus
so as to follow the current command value Ic and is supplied to the
motor 2. The motor 2 generates torque corresponding to the supplied
motor current Im. The torque generated by the motor 2 is transferred
10 to the steering shaft 12 through the intermediary of the motor-speed
reduction gear 3 and is further transferred to the rack 14 through
the intermediary of the rack-and-pinion gear 13. The rack 14 is driven
in the axial direction thereof by the rack-and-pinion gear 13 so as
to turn the pair of the turning wheels 10.
15 [0062]
FIG. 9 is a configuration diagram of a yaw-rate controller in
the vehicle steering system according to Embodiment 3; the
configuration of the yaw rate controller 61 in which hysteresis
compensation is introduced is represented. In FIG. 9, the yaw rate
20 controller 61 has the hysteresis estimation unit 62, the addition
unit 21, the deviation calculation unit 22, and the control unit 63.
Based on an input value X3 to be inputted, the hysteresis estimation
unit 62 calculates and outputs the hysteresis estimation value H2.
The addition unit 21 adds the detected yaw rate Y1 and the hysteresis
25 estimation value H2, and then outputs the addition value, as a
35
compensation detected yaw rate Y2.
[0063]
The deviation calculation unit 22 subtracts the compensation
detected yaw rate Y2 from the target yaw rate Y0 and then outputs
a control deviation ΔS. Based on the inputted control 5 deviation ΔS,
the target yaw rate Y0, and the compensation detected yaw rate Y2,
the control unit 63 calculates the current command value Ic and then
inputs the current command value Ic to the motor control apparatus
for controlling the motor 2. The motor current Im flowing in the motor
10 2 is controlled by the motor control apparatus so as to follow the
current command value Ic.
[0064]
FIG. 10 is a configuration diagram of the hysteresis estimation
unit in the vehicle steering system according to Embodiment 3. In
15 FIG. 10, the hysteresis estimation unit 62 has a yaw-rate estimation
unit 71 and a small-amplitude filtration filter 72. The yaw-rate
estimation unit 71 inputs a yaw-rate estimation value Y3, calculated
based on the input value X3, to the small-amplitude filtration filter
72. The small-amplitude filtration filter 72 outputs the hysteresis
20 estimation value H2, based on the yaw-rate estimation value Y3
inputted from the yaw-rate estimation unit 71.
[0065]
Because having a frequency responsiveness for making the input
value X3 approach the real yaw rate, the yaw-rate estimation unit
25 71 raises the accuracy of hysteresis estimation by the hysteresis
36
estimation unit 62. In Embodiment 3, as the input value X3 to be
inputted to the hysteresis estimation unit 62, the target yaw rate
Y0 is utilized. The reason therefor is that in the case where the
responsiveness of the yaw-rate control is high, it can be assumed
that the target yaw rate Y0 and the real yaw rate 5 almost approximate
to each other. In practice, because the real yaw rate follows the
target yaw rate Y0 in a delayed manner, the yaw-rate estimation unit
71 makes an approximation of the follow-up delay.
[0066]
10 Specifically, with regard to the real vehicle, the frequency
responsiveness of the yaw rate controller 61 is measured so as to
obtain the inherent frequency of the yaw rate controller 61; then,
the target yaw rate Y0, as the input value X3, is processed through
a lowpass filter having the inherent frequency, so that there is
15 created the yaw-rate estimation value Y3 having a waveform approximate
to the waveform of the real yaw rate. The yaw-rate estimation value
Y3 to be outputted from the yaw-rate estimation unit 71 is for
estimating nothing but the hysteresis of the sensor; therefore, it
is not required that the yaw-rate estimation value Y3 is created with
20 a high estimation accuracy to the extent that the yaw-rate estimation
value Y3 completely coincide with the real yaw rate. As another
example of the input value X3, the detected yaw rate Y1 from the
yaw-rate sensor 9 may be utilized; alternatively, it may be allowed
that the yaw rate is calculated based on a vehicle condition such
25 as the acceleration, the vehicle speed, or the rotational difference
37
between the right and left wheels and then is utilized as the input
value.
[0067]
Next, the control unit 63 will be explained. FIG. 11 is a
configuration diagram of a control unit in the vehicle 5 steering system
according to each of Embodiments 3 and 4.
[0068]
FIG. 11 is a configuration diagram of a control unit in the
vehicle steering system according to each of Embodiments 3 and 4.
10 In FIG. 11, the control unit 63 includes the first
pseudo-differentiation device 51, the second pseudo-differentiation
device 52, the first gain 53, the second gain 54, the third gain 55,
the phase compensator 56, the addition unit 57, and the subtraction
unit 58. The control unit 63 represented in FIG. 11 basically performs
15 feedback control in such a way as to suppress the foregoing control
deviation ΔS.
[0069]
A target yaw rate speed YR0 is created from the target yaw rate
Y0 by means of the first pseudo-differentiation device 51; a value
20 obtained by multiplying the target yaw rate speed YR0 by the first
gain 53 is inputted to the addition unit 57. A yaw-rate-speed command
value YRc is created from the control deviation ΔS through processing
by the second gain 54 and the phase compensator 56; then, the
yaw-rate-speed command value YRc is inputted to the subtraction unit
25 58. The second gain 54 and the phase compensator 56 are designed in
38
such a way as to create the yaw-rate-speed command value YRc in which
desired stability and trackability to the control deviation ΔS are
secured. A detected yaw rate speed YR1 is created from the
compensation detected yaw rate Y2 through the second
pseudo-differentiation device 52; then, the detected 5 yaw rate speed
YR1 is inputted to the subtraction unit 58.
[0070]
The detected yaw rate speed YR1 is subtracted from the
yaw-rate-speed command value YRc by the subtraction unit 58; a value
10 calculated by multiplying the value, obtained through the subtraction,
by the third gain 55 is inputted to the addition unit 57. The addition
unit 57 adds a value obtained by multiplying the foregoing target
yaw rate speed YR0 by the first gain 53 and a value obtained by
multiplying a value, obtained by subtracting the detected yaw rate
15 speed YR1 from the yaw-rate-speed command value YRc, by the third
gain 55, and then outputs the added value, as the current command
value Ic.
[0071]
In order to raise the stability, the control unit 63 represented
20 in FIG. 11 includes a major loop of feedback control utilizing the
target yaw rate speed YR0 obtained from the target yaw rate Y0 and
the yaw-rate-speed command value YRc obtained from the control
deviation ΔS and a minor loop of feedback control utilizing the
detected yaw rate speed YR1 obtained from the compensation detected
25 yaw rate Y2 and the yaw-rate-speed command value YRc obtained from
39
the control deviation ΔS. In addition, in the control unit 63, there
is configured cascade control in which the feedback control utilizing
the foregoing minor loop is added to the feedback control utilizing
the foregoing major loop.
5 [0072]
Because in the control unit 63 represented in FIG. 11, not the
detected yaw rate Y1 but the compensation detected yaw rate Y2 to
which hysteresis compensation has been provided is utilized, the
effect of a hysteresis included in the detected yaw rate Y1 from the
10 yaw-rate sensor 9 is reduced and hence the steering control can more
accurately be performed. Moreover, in order to raise the
responsiveness, feed-forward control of the target yaw rate speed
YR0 is added.
[0073]
15 As described above, Embodiment 3 makes it possible that in
yaw-rate control in a vehicle steering system, the hysteresis in a
yaw-rate sensor is estimated and compensated; thus, smooth steering
in which the effect of the hysteresis is reduced can be performed.
[0074]
20 In Embodiment 3, in the yaw rate controller 61, as explained
in FIG. 9, the hysteresis estimation unit 62 creates the hysteresis
estimation value H2; the addition unit 21 adds the detected yaw rate
Y1 and the hysteresis estimation value H2 so as to create the
compensation detected yaw rate Y2; then, the deviation calculation
25 unit 22 subtracts the compensation detected yaw rate Y2 from the target
40
yaw rate Y0 so as to create the control deviation ΔS. However, as
the configuration in which the control deviation ΔS is created by
use of the hysteresis estimation value H2, there exist configurations
other than the one represented in FIG. 9.
5 [0075]
FIG. 12 is explanatory diagrams representing various kinds of
configuration examples in each of which a control deviation is created
by use of a hysteresis estimation value, in the vehicle steering system
according to each of Embodiments 3 and 4. The configuration
10 represented in (a) of FIG. 12 corresponds to the configuration
represented in FIG. 9; the hysteresis estimation value H2 is added
to the detected yaw rate Y1 so that the compensation detected yaw
rate Y2 is created; then, the compensation detected yaw rate Y2 is
subtracted from the target yaw rate Y0 so that the control deviation
15 ΔS is created.
[0076]
It may be allowed that as the configuration represented in (b)
of FIG. 12, which replaces the configuration represented in (a) of
FIG. 12, the control deviation ΔS is created by subtracting the
20 hysteresis estimation value H2 from a value obtained by subtracting
the detected yaw rate Y1 from the target yaw rate Y0; alternatively,
it may be allowed that as the configuration represented in (c) of
FIG. 12, the hysteresis estimation value H2 is subtracted from the
target yaw rate Y0 so that a compensation target yaw rate Y4 is created
25 and then the detected yaw rate Y1 is subtracted from the compensation
41
target yaw rate Y4 so that the control deviation ΔS is obtained. The
configuration represented in each of (a), (b), and (c) of FIG. 12
provides the same effect.
[0077]
Moreover, in Embodiment 3, the yaw-rate 5 estimation unit 71
obtains the yaw-rate estimation value Y3 by use of a transfer function;
however, it may be allowed that in order to reduce the calculation
load, the yaw-rate estimation value Y3 is obtained by use of a mere
gain. Furthermore, it may be allowed that in order to raise the
10 estimation accuracy of the yaw-rate estimation unit 71, nonlinear
processing such as saturation processing or dead-zone processing is
performed.
[0078]
Still moreover, as the hysteresis filter 41 in the
15 small-amplitude filtration filter 72, a filter having an ideal
hysteresis characteristic represented in FIG. 2A is utilized; it is
important to make the characteristic of the hysteresis filter 41
coincide with the hysteresis characteristic of the steering angle
sensor. For example, in the case where as represented in FIG. 2B,
20 the hysteresis characteristic of the steering angle sensor has a shape
in which in comparison with the hysteresis characteristic in FIG.
2A, the lower-right and upper-left corner portions of the hysteresis
loop are suppressed, a hysteresis filter having a hysteresis
characteristic coinciding with that particular hysteresis
25 characteristic is utilized.
42
[0079]
In addition, in the case where as represented in FIG. 2C, the
hysteresis characteristic of the yaw-rate sensor has a dead zone in
the vicinity of the origin, a hysteresis filter having a
characteristic coinciding with that particular 5 characteristic is
utilized. As described above, the accuracy of the hysteresis
estimation value H2 can be raised by making the hysteresis
characteristic of the hysteresis filter 41 coincide with the
hysteresis characteristic of the yaw-rate sensor.
10 [0080]
In the above explanation, it is assumed that a hysteresis exists
in the relationship between the yaw rate and the detected yaw rate;
however, the generating factor of the hysteresis is not particularly
limited. For example, even when the generation of the hysteresis is
15 caused by the characteristic of the yaw-rate sensor itself, by a
mechanical backlash of the steering mechanism for making the yaw-rate
sensor rotate, or further by both thereof, the vehicle steering system
according to Embodiment 3 can be utilized and the same effect can
be demonstrated.
20 [0081]
As described above, the vehicle steering system according to
Embodiment 3 makes it possible that in yaw-rate control, the
hysteresis in a yaw-rate sensor is estimated and compensated; thus,
smooth steering in which the effect of the hysteresis is reduced can
25 be performed.
43
[0082]
Embodiment 4.
Next, a vehicle steering system according to Embodiment 4 will
be explained. In Embodiment 3, as described above, as the input value
X3 to be inputted to the hysteresis estimation 5 unit 6, the target
yaw rate Y0 is utilized. However, in the case where the control
responsiveness is low or under the environment in which disturbance
such as friction exists, the difference between the target yaw rate
Y0 and the yaw rate becomes large; therefore, in the configuration
10 according to Embodiment 3, estimation of the hysteresis may become
inaccurate. In Embodiment 4, the vehicle steering system is
configured in such a way that estimation of a hysteresis is performed
by inputting an input value other than a target yaw rate to the
hysteresis estimation unit 62. Hereinafter, the vehicle steering
15 system according to Embodiment 4 will be explained mainly with regard
to the difference from the vehicle steering system according to
Embodiment 3. FIGS. 8, 9, 10, 11, and 12 are applied also to the
vehicle steering system according to Embodiment 4.
[0083]
20 The hysteresis estimation unit 62 according to Embodiment 4 is
configured in such a way that the hysteresis estimation value H2 is
calculated by use of the detected yaw rate Y1, as the input value
X3 represented in FIG. 10. With this configuration, estimation of
the hysteresis cannot be performed in a hysteresis section where the
25 detected yaw rate Y1 does not move; however, in the section out of
44
the hysteresis section, the detected yaw rate Y1 moves. Accordingly,
in the situation where the fluctuation of the steering angle is
sufficiently larger than the hysteresis width, the hysteresis can
be estimated and hence the hysteresis estimation value H2 can be
5 obtained.
[0084]
As a variant example of Embodiment 4, the hysteresis estimation
value H2 may be calculated by use of a value based on the motor current
Im, as the input value X3 to be inputted to the hysteresis estimation
10 unit 62. In the case where there exists static friction between a
road surface and a set of the steering mechanism and the turning wheels
and the motor current Im is within a specific value, the static
friction is large and hence the steering angle does not move; however,
when the motor current Im exceeds the specific value, the steering
15 angle overcomes the static friction and then starts to move. Because
it is made possible to determine the occurrence of steering by use
of the value of this motor current, as a current threshold value,
the estimation of the hysteresis can more accurately be performed.
[0085]
20 As described above, the vehicle steering system according to
Embodiment 4 demonstrated an effect that even in the case where the
difference between the target yaw rate and the yaw rate is large,
it is made possible to estimate the hysteresis. In addition, as the
input values, either a single kind of signal or two or more signals
25 including a target yaw rate may be utilized so as to estimate the
45
hysteresis.
[0086]
Each of foregoing Embodiments 3 and 4 is obtained by converting
the vehicle steering system, described in one of the items (11) through
(14) below, into 5 a tangible form.
(11) A vehicle steering system comprising:
a steering mechanism that drives a vehicle;
a motor that makes the steering mechanism rotate;
a yaw-rate sensor that detects a yaw rate of the vehicle and
10 outputs a detected yaw rate having a hysteresis with respect to the
yaw rate;
a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the yaw rate
and the detected yaw rate; and
15 a control unit that controls the motor in such a way as to be
equal to a difference between the yaw rate and a target yaw rate,
which is a target value of the yaw rate, based on the target yaw rate,
the detected yaw rate, and the hysteresis estimation value.
In the vehicle steering system configured in such a manner as
20 described above, compensation is made so as to cancel the hysteresis
of the yaw-rate sensor; thus, yaw-rate control can smoothly be
performed.
[0087]
(12) The vehicle steering system according to (11),
25 wherein the hysteresis estimation unit estimates the hysteresis
46
estimation value corresponding to a difference obtained by
subtracting the detected yaw rate from the yaw rate, and
wherein the control unit is configured in such a way as to control
the motor, based on a value obtained by subtracting the detected yaw
rate and the hysteresis estimation value from the 5 target yaw rate.
In the vehicle steering system configured in such a manner as
described above, addition and subtraction according to the foregoing
signs are applied to the target yaw rate, the detected yaw rate, and
the hysteresis estimation value, so that the control deviation becomes
10 a value equal to the difference between the target yaw rate and the
yaw rate; thus, there is demonstrated an effect that yaw-rate control
utilizing a desirable deviation input can be performed.
[0088]
(13) The vehicle steering system according to any one of (11) and
15 (12), wherein the hysteresis estimation unit has a yaw-rate estimation
unit for estimating a response of the yaw rate to an input value to
the hysteresis estimation unit and is configured in such a way as
to calculate the hysteresis estimation value, based on a yaw-rate
estimation value to be outputted from the yaw-rate estimation unit.
20 In the vehicle steering system configured in such a manner as
described above, the input value is converted into a signal
corresponding to the yaw rate, so that the accuracy of hysteresis
estimation can be raised.
[0089]
25 (14) The vehicle steering system according to any one of (11) and
47
(12), wherein the hysteresis estimation unit has a yaw-rate estimation
unit for outputting a yaw-rate estimation value whose high-frequency
phase is delayed with respect to the target yaw rate, and is configured
in such a way as to calculate the hysteresis estimation value, based
on the yaw-rate 5 estimation value.
In the vehicle steering system configured in such a manner as
described above, a frequency response for making the target yaw rate
approach the yaw rate is added, so that the accuracy of hysteresis
estimation can be raised.
10 [0090]
Although the present application is described above in terms
of various exemplary embodiments and implementations, it should be
understood that the various features, aspects and functions described
in one or more of the individual embodiments are not limited in their
15 applicability to the particular embodiment with which they are
described, but instead can be applied, alone or in various
combinations to one or more of the embodiments. Therefore, an
infinite number of unexemplified variant examples are conceivable
within the range of the technology disclosed in the present
20 application. For example, there are included the case where at least
one constituent element is modified, added, or omitted and the case
where at least one constituent element is extracted and then combined
with constituent elements of other embodiments.
[0091]
25 FIG. 13 is a block diagram representing the hardware
48
configuration of each of the steering-angle controller according to
Embodiment 1 and the yaw-rate controller according to Embodiment 2.
As illustrated in FIG. 13, each of the steering-angle controller 5
according to Embodiment 1 and the yaw-rate controller 61 according
to Embodiment 2 includes a processor 1000 and a 5 storage apparatus
1001. Although not illustrated, the storage apparatus 1001 has a
volatile storage device such as a random access memory and a
nonvolatile auxiliary storage device such as a flash memory.
Additionally, instead of the flash memory, a hard disk may be included
10 as the auxiliary storage device. The processor 1000 implements a
program inputted from the storage device 1001. In this case, the
program is inputted from the auxiliary storage device to the processor
1000 by way of the volatile storage device. Moreover, the processor
1000 may output data such as a calculation result either to the
15 volatile storage device of the storage device 1001 or to the auxiliary
storage device by way of the volatile storage device. In addition,
it may be allowed that in the steering-angle controller 5 according
to Embodiment 1, only each of the hysteresis estimation unit 6 and
the control unit 7 has the hardware configuration illustrated in FIG.
20 13 and/or that in the yaw-rate controller 61 according to Embodiment
2, only each of the hysteresis estimation unit 62 and the control
unit 63 has the hardware configuration illustrated in FIG. 13.
Description of Reference Numerals
25 [0092]
49
100, 200: vehicle steering system
1: steering mechanism
2: motor
3: motor-speed reduction gear
4: steering 5 angle sensor
5: steering-angle controller
6, 62: hysteresis estimation unit
7, 63: control unit
8: higher-hierarchy controller
10 9: yaw-rate sensor
10: turning wheel
11: steering wheel
12: steering shaft
13: rack-and-pinion gear
15 14: rack
21, 57: addition unit
22: deviation calculation unit
31: steering-angle estimation unit
32, 72: small-amplitude filtration filter
20 41: hysteresis filter
23, 42: subtractor
51: first pseudo-differentiation device
52: second pseudo-differentiation device
53: first gain
25 54: second gain
50
55: third gain
56: phase compensator
58: subtraction unit
61: yaw rate controller
71: yaw-rate 5 estimation unit
1000: processor
1001: storage apparatus
51
We Claim :
1. A vehicle steering system comprising:
a steering mechanism that drives a vehicle;
a motor that makes the steering mechanism rotate;
a steering angle sensor that detects a steering 5 angle, which
is a rotation angle of the steering mechanism, and outputs a detected
steering angle having a hysteresis with respect to the steering angle;
a hysteresis estimation unit that estimates a hysteresis
estimation value corresponding to a difference between the steering
10 angle and the detected steering angle; and
a control unit that controls the motor in such a way as to be
equal to a difference between the steering angle and a target steering
angle, which is a target value of the steering angle, based on the
target steering angle, the detected steering angle, and the hysteresis
15 estimation value.
2. The vehicle steering system according to claim 1,
wherein the hysteresis estimation unit is configured in such
a way as to estimate the hysteresis estimation value corresponding
20 to a difference obtained by subtracting the detected steering angle
from the steering angle, and
wherein the control unit is configured in such a way as to control
the motor, based on a value obtained by subtracting the detected
steering angle and the hysteresis estimation value from the target
25 steering angle.
52
3. The vehicle steering system according to any one of claims 1 and
2, wherein the hysteresis estimation unit is configured in such a
way as to calculate the hysteresis estimation value, based on the
target 5 steering angle.
4. The vehicle steering system according to any one of claims 1 and
2, wherein the hysteresis estimation unit is configured in such a
way as to calculate the hysteresis estimation value, based on the
10 detected steering angle.
5. The vehicle steering system according to any one of claims 1 and
2, wherein the hysteresis estimation unit is configured in such a
way as to calculate the hysteresis estimation value, based on a current
15 in the motor.
6. The vehicle steering system according to any one of claims 1 and
2, wherein the hysteresis estimation unit is configured in such a
way as to calculate the hysteresis estimation value, based on a yaw
20 rate of the vehicle.
7. The vehicle steering system according to any one of claims 1 through
6, wherein the hysteresis estimation unit has a steering-angle
estimation unit for estimating a response of the steering angle to
25 an input value to the hysteresis estimation unit and is configured
53
in such a way as to calculate the hysteresis estimation value, based
on a steering-angle estimation value to be outputted from the
steering-angle estimation unit.
8. The vehicle steering system according to any one of 5 claims 1 through
6, wherein the hysteresis estimation unit has a steering-angle
estimation unit for outputting a steering-angle estimation value
whose high-frequency phase is delayed with respect to the target
steering angle, and is configured in such a way as to calculate the
10 hysteresis estimation value, based on the steering-angle estimation
value.
9. The vehicle steering system according to any one of claims 1 through
8,
15 wherein the hysteresis estimation unit has a small-amplitude
filtration filter, and
wherein the small-amplitude filtration filter includes a
hysteresis filter for performing hysteresis-function processing
having a hysteresis width corresponding to the hysteresis and a
20 subtractor that subtracts an output signal of the hysteresis filter
from an input signal of the hysteresis filter.
10. The vehicle steering system according to any one of claims 1
through 9, wherein the hysteresis estimation unit is configured in
25 such a way as to compensate a hysteresis of the steering angle sensor
54
itself.
11. A vehicle steering system comprising:
a steering mechanism that drives a vehicle;
a motor that makes the steering 5 mechanism rotate;
a yaw-rate sensor that detects a yaw rate of the vehicle and
outputs a detected yaw rate having a hysteresis with respect to the
yaw rate;
a hysteresis estimation unit that estimates a hysteresis
10 estimation value corresponding to a difference between the yaw rate
and the detected yaw rate; and
a control unit that controls the motor in such a way as to be
equal to a difference between the yaw rate and a target yaw rate,
which is a target value of the yaw rate, based on the target yaw rate,
15 the detected yaw rate, and the hysteresis estimation value.
12. The vehicle steering system according to claim 11,
wherein the hysteresis estimation unit estimates the hysteresis
estimation value corresponding to a difference obtained by
20 subtracting the detected yaw rate from the yaw rate, and
wherein the control unit is configured in such a way as to control
the motor, based on a value obtained by subtracting the detected yaw
rate and the hysteresis estimation value from the target yaw rate.
25 13. The vehicle steering system according to any one of claims 11
55
and 12, wherein the hysteresis estimation unit has a yaw-rate
estimation unit for estimating a response of the yaw rate to an input
value to the hysteresis estimation unit and is configured in such
a way as to calculate the hysteresis estimation value, based on a
yaw-rate estimation value to be outputted from the yaw-5 rate estimation
unit.
14. The vehicle steering system according to any one of claims 11
and 12, wherein the hysteresis estimation unit has a yaw-rate
10 estimation unit for outputting a yaw-rate estimation value whose
high-frequency phase is delayed with respect to the target yaw rate,
and is configured in such a way as to calculate the hysteresis
estimation value, based on the yaw-rate estimation value.