U.S. patent application number 09/911617 was filed with the patent office on 2002-03-14 for suspension control system.
Invention is credited to Ichimaru, Nobuyuki, Kobayashi, Takahide, Uchino, Toru, Uchiyama, Masaaki.
Application Number | 20020032508 09/911617 |
Document ID | / |
Family ID | 26597086 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020032508 |
Kind Code |
A1 |
Uchino, Toru ; et
al. |
March 14, 2002 |
Suspension control system
Abstract
By passing the vertical acceleration through a phase adjusting
filter and a gain adjusting filter, the phase of the vertical
acceleration is advanced by 49 degrees so that the phase difference
with respect to the actual relative velocity becomes 180 degrees in
the neighborhood of the vehicle body resonance point, thereby
making the phase of the vertical acceleration, in effect,
coincident with the phase of the relative velocity. In the
neighborhood of the vehicle body resonance point (1 Hz), the gain
of the estimated relative velocity takes a small value. In
frequency regions other than the neighborhood of the vehicle body
resonance point, the gain of the estimated relative velocity is
increased. Consequently, the controlled variable in the
neighborhood of the vehicle body resonance point increases, and the
controlled variable in higher frequency regions decreases. Damping
force is adjusted in correspondence to the controlled variable.
Thus, it is possible to improve ride quality in the neighborhood of
the vehicle body resonance point (1 Hz).
Inventors: |
Uchino, Toru; (Kanagawa-ken,
JP) ; Ichimaru, Nobuyuki; (Kanagawa-ken, JP) ;
Uchiyama, Masaaki; (Tokyo, JP) ; Kobayashi,
Takahide; (Saitama-ken, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
26597086 |
Appl. No.: |
09/911617 |
Filed: |
July 25, 2001 |
Current U.S.
Class: |
701/37 ;
280/5.515 |
Current CPC
Class: |
B60G 2400/40 20130101;
Y10S 180/902 20130101; B60G 2500/10 20130101; B60G 2400/10
20130101; B60G 2202/40 20130101; B60G 17/01933 20130101; B60G
2400/61 20130101 |
Class at
Publication: |
701/37 ;
280/5.515 |
International
Class: |
B60G 017/015 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2000 |
JP |
232131/2000 |
Apr 27, 2001 |
JP |
133447/2000 |
Claims
What is claimed is:
1. A suspension control system comprising: a shock absorber having
adjustable damping characteristics, said shock absorber being
interposed between a sprung member and an unsprung member of a
vehicle; a sprung mass vibration detecting device for detecting
vibration of the sprung member of the vehicle; a sprung mass
absolute velocity detecting device for obtaining an absolute
velocity of the vibration of the sprung member from a detected
signal obtained from said sprung mass vibration detecting device; a
relative velocity estimation device for adjusting a phase of the
detected signal obtained from said sprung mass vibration detecting
device to use said detected signal as an estimated relative
velocity between said sprung member and said unsprung member; and a
control unit for generating a control signal for controlling the
damping characteristics of said shock absorber on a basis of the
absolute velocity obtained from said sprung mass absolute velocity
detecting device and the estimated relative velocity obtained from
said relative velocity estimation device and for outputting said
control signal to said shock absorber; wherein said relative
velocity estimation device adjusts the phase of said detected
signal so that a phase difference of said detected signal with
respect to an actual relative velocity is minimized in a sprung
mass resonance frequency band.
2. A suspension control system according to claim 1, wherein
adjustment of the phase of said detected signal is made on a basis
of adjusting parameters for said detected signal, and
characteristics of said adjusting parameters are changed according
to a condition of the vehicle.
3. A suspension control system according to claim 1, wherein said
control unit judges a road surface condition on a basis of the
detected signal obtained from said sprung mass vibration detecting
device, and adjustment of the phase of said detected signal is made
on a basis of adjusting parameters for said detected signal, and
further characteristics of said adjusting parameters are changed
according to a result of judgment on said road surface
condition.
4. A suspension control system according to claim 1, wherein said
control unit converts the relative velocity obtained from said
relative velocity estimation device into a signal for generating
said control signal on a basis of predetermined conversion
characteristics and changes said conversion characteristics
according to a condition of the vehicle and/or a road surface
condition.
5. A suspension control system according to claim 2, wherein said
condition of the vehicle is a vehicle condition related to a weight
of said vehicle.
6. A suspension control system according to claim 2, wherein said
condition of the vehicle is a vehicle condition related to a speed
of said vehicle.
7. A suspension control system according to claim 2, wherein said
condition of the vehicle is a vehicle condition related to a change
in attitude of said vehicle.
8. A suspension control system according to claim 4, wherein said
condition of the vehicle is a vehicle condition related to a weight
of said vehicle.
9. A suspension control system according to claim 4, wherein said
condition of the vehicle is a vehicle condition related to a speed
of said vehicle.
10. A suspension control system according to claim 4, wherein said
condition of the vehicle is a vehicle condition related to a change
in attitude of said vehicle.
11. A suspension control system according to claim 1, wherein said
sprung mass vibration detecting device is an acceleration sensor,
and said relative velocity estimation device uses an acceleration
detected with said acceleration sensor as an estimated relative
velocity between said sprung member and said unsprung member.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a suspension control system
for use in a vehicle.
[0002] One example of conventional suspension control systems is
disclosed in U.S. Pat. No. 5,533,597. A system according to the
second embodiment shown in the patent publication includes a shock
absorber of the variable damping coefficient type interposed
between the body of a vehicle and an axle. The system further
includes an actuator for adjusting the damping coefficient of the
shock absorber. An acceleration sensor is attached to the vehicle
body to detect a vertical acceleration acting on the vehicle body.
An integrator circuit integrates the acceleration detected with the
acceleration sensor to obtain the vertical velocity (absolute
velocity, not relative velocity) of the vehicle body. Then, the
absolute value of the vertical acceleration of the vehicle body is
obtained, and the vertical velocity of the vehicle body obtained by
the integration is divided by the absolute value of the vertical
acceleration. The actuator is instructed to adjust the damping
coefficient of the shock absorber on the basis of the value
obtained by the division, thereby effecting vibration damping
control for the vehicle body.
[0003] The above-described conventional suspension control system
effects control resembling a control method based on the sky-hook
damper theory.
[0004] According to the sky-hook damper theory, the damping
coefficient C1 of the shock absorber (damper) provided between the
vehicle body and the axle is obtained as follows.
[0005] Assuming that:
1 V: the vertical absolute velocity of the vehicle body (sprung
mass); X: the vertical absolute velocity of the axle (unsprung
mass); CZ: the damping coefficient of an imaginary shock absorber
(damper) as provided between the vehicle body and a point in an
absolute coordinate system;
[0006] if the following condition is satisfied;
V(V-X)>0
[0007] the damping coefficient C1 is determined as follows:
C1=CZ V/(V-X)
[0008] If the following condition is satisfied;
V(V-X)<0
[0009] the damping coefficient C1 is determined as follows:
C1=0. (2)
[0010] In the above-described conventional suspension control
system, a vertical acceleration acting on the sprung mass is
detected with only the vertical acceleration sensor provided on the
vehicle body without using a stroke sensor, and the damping
coefficient C1 is determined on the basis of the detected vertical
acceleration as stated below. More specifically, because the
vertical acceleration signal changes in a manner similar to that of
the actual relative velocity (V-X), the vertical acceleration
signal M is used as an estimated relative velocity according to the
following control rules in place of the actual relative velocity
(V-X) between the sprung mass and the unsprung mass in the above
Equation (1). That is, the conventional suspension control system
obtains the damping coefficient C1 on the basis of the sky-hook
damper theory as follows:
[0011] If V(V-X)>0,
C1=K V/M (1a)
[0012] If V(V-X)<0,
C1=Cmin (2a)
[0013] In the above Equations (1a) and (2a), K is a constant and
Cmin.noteq.0.
[0014] With the acceleration sensor used in the above-described
conventional suspension control system, the stroke of the shock
absorber (damper) set out in FIG. 38 cannot be determined.
Therefore, the suspension control system uses the above-described
shock absorber of the variable damping coefficient type, in which
when the damping coefficient for the extension stroke changes, the
damping coefficient for the compression stroke becomes constant at
a small value (Cmin), whereas when the compression-side damping
coefficient changes, the extension-side damping coefficient becomes
constant at a small value (Cmin).
[0015] Thus, the sign (positive or negative) of (V-X) in FIG. 38
(i.e., the stroke of the shock absorber) is not judged, but instead
when V>0, a combination of C1 for extension and Cmin for
compression is selected, and damping force for extension is
controlled on the basis of C1. When V<0, a combination of Cmin
for extension and C1 for compression is selected, and damping force
for compression is controlled on the basis of C1.
[0016] The system may be arranged so that when C1 is positive, the
damping coefficient for extension is controlled, whereas when C1 is
negative, the damping coefficient for compression is controlled. In
such a case, if it is possible to detect the vertical absolute
velocity V of the vehicle body and the absolute value of the
vertical acceleration signal M, it is possible to perform control
approximate to the sky-hook damper theory by outputting C1 obtained
by using the following Equation (1b):
C1=KV/.vertline.M.vertline. (1b)
[0017] Incidentally, the above-described prior art uses the vehicle
body vertical acceleration signal M as data that can be regarded as
approximation to the actual relative velocity (V-X). In actuality,
however, there is a phase difference between the vehicle body
vertical acceleration signal 71 and the actual relative velocity
72, as shown in FIG. 39, under the influence of spring force and so
forth [FIG. 39 shows an example of measurement of the vertical
acceleration and relative velocity of the body of an automobile of
a certain type when the vehicle body vibrates at 1 Hz, in which the
phase of the vehicle body vertical acceleration signal 71 leads
that of the actual relative velocity 72 by 131 degrees].
[0018] Because there is a phase difference between the vehicle body
vertical acceleration signal 71 and the actual relative velocity
72, ideal damping characteristics such as those obtained on the
basis of the sky-hook damper theory cannot be obtained with the
conventional suspension control system that uses the vehicle body
vertical acceleration signal 71 as an estimated relative velocity
in place of the relative velocity 72 corresponding to the relative
velocity (V-X) in the sky-hook damper theory. Accordingly, ride
quality is not always good, particularly in a sprung resonance
frequency band at relatively low frequencies (i.e. a frequency band
in which vibration of the vehicle body influences ride quality to a
considerable extent).
SUMMARY OF THE INVENTION
[0019] The present invention was made in view of the
above-described circumstances.
[0020] Accordingly, an object of the present invention is to
provide a suspension control system capable of obtaining damping
characteristics closer to those obtained on the basis of the
sky-hook damper theory by improving controllability in the sprung
resonance frequency band, in particular, in consideration of the
above-described phase difference due to spring force and so
forth.
[0021] The present invention provides a suspension control system
including a shock absorber having adjustable damping
characteristics that is interposed between sprung and unsprung
members of a vehicle. A sprung mass vibration detecting device
detects vibration of the sprung member of the vehicle. A sprung
mass absolute velocity detecting device obtains the absolute
velocity of the vibration of the sprung member from the detected
signal obtained from the sprung mass vibration detecting device. A
relative velocity estimation unit adjusts the phase of the detected
signal obtained from the sprung mass vibration detecting device to
use the detected signal as an estimated relative velocity between
the sprung and unsprung members. A control unit generates a control
signal for controlling the damping characteristics of the shock
absorber on the basis of the absolute velocity obtained from the
sprung mass absolute velocity detecting device and the estimated
relative velocity obtained from the relative velocity estimation
unit and outputs the control signal to the shock absorber. The
relative velocity estimation unit adjusts the phase of the detected
signal so that the phase difference of the detected signal with
respect to the actual relative velocity is minimized in the sprung
mass resonance frequency band.
[0022] Preferably, the phase adjustment for the detected signal is
made on the basis of adjusting parameters for the detected signal,
and the characteristics of the adjusting parameters are changed
according to the condition of the vehicle.
[0023] Preferably, the control device judges the road surface
condition on the basis of the detected signal obtained from the
sprung mass vibration detecting device, and the phase adjustment
for the detected signal is made on the basis of adjusting
parameters for the detected signal. Further, the characteristics of
the adjusting parameters are changed according to the result of the
judgment on the road surface condition.
[0024] Preferably, the control device converts the relative
velocity obtained from the relative velocity estimation unit into a
signal for generating the control signal on the basis of
predetermined conversion characteristics and changes the conversion
characteristics according to the condition of the vehicle or/and
the road surface condition.
[0025] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the preferred embodiments thereof, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagram schematically showing a suspension
control system according to a first embodiment of the present
invention.
[0027] FIG. 2 is a diagram showing damping force characteristics of
a shock absorber used in the suspension control system shown in
FIG. 1.
[0028] FIG. 3 is a block diagram schematically showing the
arrangement of a controller used in the suspension control system
shown in FIG. 1.
[0029] FIG. 4 is a diagram showing frequency-phase characteristics
of a phase adjusting filter of the controller shown in FIG. 3.
[0030] FIG. 5 is a diagram showing frequency-gain characteristics
of a gain adjusting filter of the controller shown in FIG. 3.
[0031] FIG. 6 is a diagram showing damping force characteristics
obtained with the suspension control system shown in FIG. 1 in
comparison with a conventional system and a theoretical value.
[0032] FIG. 7 is a diagram schematically showing a railway vehicle
to which the suspension control system according to the present
invention is applied in place of an automobile.
[0033] FIG. 8 is a diagram schematically showing a suspension
control system according to a second embodiment of the present
invention.
[0034] FIG. 9 is a block diagram schematically showing the
arrangement of a controller used in the suspension control system
shown in FIG. 8.
[0035] FIG. 10 is a flowchart showing a main routine executed by
the controller used in the suspension control system shown in FIG.
8.
[0036] FIG. 11 is a flowchart showing a time constant determination
subroutine in FIG. 10.
[0037] FIG. 12 is a diagram concerning frequency-phase
characteristics of a relative velocity estimation unit in FIG. 9,
comparatively showing the difference in frequency-phase
characteristics when correction is made by a time constant
determination unit and when it is not.
[0038] FIG. 13 is a diagram concerning frequency-gain
characteristics of the relative velocity estimation unit in FIG. 9,
comparatively showing the difference in frequency-gain
characteristics when corrected is made by the time constant
determination unit and when it is not.
[0039] FIG. 14 is a diagram schematically showing a suspension
control system according to a third embodiment of the present
invention.
[0040] FIG. 15 is a block diagram schematically showing the
arrangement of a controller used in the suspension control system
shown in FIG. 14.
[0041] FIG. 16 is a flowchart showing a time constant determination
subroutine executed by the controller shown in FIG. 15.
[0042] FIG. 17 is a diagram concerning frequency-phase
characteristics of a relative velocity estimation unit in FIG. 15,
comparatively showing the difference in frequency-phase
characteristics when correction is made by a time constant
determination unit and when it is not.
[0043] FIG. 18 is a diagram concerning frequency-gain
characteristics of the relative velocity estimation unit in FIG.
15, comparatively showing the difference in frequency-gain
characteristics when corrected is made by the time constant
determination unit and when it is not.
[0044] FIG. 19 is a block diagram schematically showing the
arrangement of a controller used in a suspension control system
according to a fourth embodiment of the present invention.
[0045] FIG. 20 is a flowchart showing a main routine executed by
the controller shown in FIG. 19.
[0046] FIG. 21 is a flowchart showing a time constant determination
subroutine in FIG. 20.
[0047] FIG. 22 is a diagram showing frequency-gain characteristics
varying in accordance with the change in frequency in a relative
velocity estimation unit of the controller shown in FIG. 19.
[0048] FIG. 23 is a diagram showing frequency-gain characteristics
varying in accordance with the change in frequency in a relative
velocity estimation unit in a fifth embodiment of the present
invention.
[0049] FIG. 24 is a diagram schematically showing a suspension
control system according to a sixth embodiment of the present
invention.
[0050] FIG. 25 is a block diagram schematically showing the
arrangement of a controller used in the suspension control system
shown in FIG. 24.
[0051] FIG. 26 is a flowchart showing a main routine executed by
the controller used in the suspension control system shown in FIG.
24.
[0052] FIG. 27 is a flowchart showing a time constant determination
subroutine in FIG. 26.
[0053] FIG. 28 is a diagram showing frequency-gain characteristics
varying in accordance with the change in frequency at a relative
velocity estimation unit of the controller shown in FIG. 25.
[0054] FIG. 29 is a diagram showing frequency-gain characteristics
varying in accordance with the change in frequency at a relative
velocity estimation unit in a seventh embodiment of the present
invention.
[0055] FIG. 30 is a block diagram showing a controller used in a
suspension control system according to a sixteenth embodiment of
the present invention.
[0056] FIG. 31 is a flowchart showing a main routine executed by
the controller shown in FIG. 30.
[0057] FIG. 32 is a flowchart showing a map selection subroutine in
FIG. 31.
[0058] FIG. 33 is a diagram showing the relationship between each
element of a segment for conversion used in the control operation
of the controller shown in FIG. 30 and the controlled variable as
Table 1.
[0059] FIG. 34 is a diagram showing the relationship between the
conversion segment, map first segment and map second segment used
in the control operation of the controller shown in FIG. 30 and the
controlled variable as Table 2.
[0060] FIG. 35 is a diagram showing an example of maps used in the
controller shown in FIG. 30.
[0061] FIG. 36 is a diagram showing another example of maps used in
the controller shown in FIG. 30.
[0062] FIG. 37 is a diagram showing frequency-gain characteristics
corresponding to various vehicle weights.
[0063] FIG. 38 is a diagram showing the relationship between the
direction of motion of the sprung mass and the shock absorber
stroke in the form of a table.
[0064] FIG. 39 is a waveform chart showing the phase difference
between the vertical acceleration and vertical relative velocity of
the vehicle body in the prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0065] A suspension control system according to a first embodiment
of the present invention will be described below with reference to
FIGS. 1 to 4. In FIG. 1, a spring 3 and a shock absorber 4 having
adjustable damping characteristics are interposed in parallel
between a vehicle body 1 (sprung mass) and each of four wheels 2
(unsprung mass; only one of them is shown in the figure), which
constitute an automobile (vehicle). The spring 3 and the shock
absorber 4 support the vehicle body 1.
[0066] It should be noted that in the first embodiment and second
to sixteenth embodiments (described later), the suspension control
system according to the present invention is applied to an
automobile of the type having such characteristics that, as shown
in FIG. 39, the phase of the vehicle body vertical acceleration
signal 71 leads that of the actual relative velocity 72 by 131
degrees, by way of example.
[0067] The shock absorber 4 is of the extension/compression
inverting type in which, as shown in FIG. 2, when the
compression-side damping force has a small value ("soft" damping
characteristics), the extension-side damping force is varied
between a small value ("soft" damping characteristics) and a large
value ("hard" damping characteristics), whereas when the
extension-side damping force has a small value, the
compression-side damping force is varied between a small value and
a large value. The shock absorber 4 is provided with an actuator 5
for adjusting the damping force (damping coefficient) of the shock
absorber 4 by actuating a damping force adjusting mechanism (not
shown) provided in the shock absorber 4.
[0068] An acceleration sensor 6 (sprung vibration detecting device)
is mounted on the vehicle body 1 to detect the vertical
acceleration (sprung acceleration) M of the vehicle body 1 relative
to the absolute coordinate system. The acceleration M (detected
signal) detected with the acceleration sensor 6 is supplied to a
controller 7 (control device). It should be noted that a total of
four combinations of springs 3, shock absorbers 4 and so forth as
shown in FIG. 1 are provided to correspond to the four wheels 2;
however, only one combination is shown in the figure for the sake
of convenience.
[0069] As shown in FIG. 3, the controller 7 has an integrator
circuit 8 (sprung mass absolute velocity detecting device) for
obtaining the vertical velocity (absolute velocity) V by
integrating the acceleration M. A divider circuit 9 divides the
absolute velocity V by a signal D (described later) to obtain a
corrected signal E. An amplifier circuit 10 multiplies the
corrected signal E by a control gain K of a predetermined magnitude
to obtain a signal F. A command signal output unit 11 (control
signal output unit) obtains a command current I with a magnitude
corresponding to the signal F obtained from the amplifier circuit
10 and supplies the command current I (control signal) to the
actuator 5 to adjust the damping force of the shock absorber 4.
With this arrangement, the controller 7 effects vibration damping
control for the automobile (vehicle) to ensure favorable ride
quality and steering stability. It should be noted that although
the controller 7 is provided for each wheel in the foregoing
arrangement, the suspension control system may be arranged to
control the four wheels with a single controller. In such a case,
it is desirable that the contents of the control operation shown in
FIG. 3 should be calculated independently for each wheel.
[0070] Further, although FIG. 3 shows only the basic control for
controlling the vertical vibration of each wheel, the signals M, V,
D, E and F may be corrected according to vehicle body attitude
change conditions, e.g. rolling and pitching, road surface
condition, and various running conditions, e.g. vehicle speed. The
correction of the signals M, V, D, E and F may be made by various
methods, for example, by multiplying each signal by a gain, or
adding a value to each signal, or providing a dead zone and
adjusting the width of the dead zone.
[0071] The controller 7 further has a phase adjusting filter 13
supplied with the acceleration M from the acceleration sensor 6 as
an input to adjust the acceleration M to the same phase as that of
the actual relative velocity in the vicinity of the sprung mass
resonance frequency band. A gain adjusting filter 14 processes the
phase-adjusted signal B through a low-pass filter 14a and a
high-pass filter 14b to generate a signal C. An absolute value
computing unit 15 obtains the absolute value of the signal C [a
signal obtained from the absolute value computing unit 15 will
hereinafter be referred to as "signal D", and the magnitude of the
signal D is defined as "gain D"]. The phase adjusting filter 13 and
the gain adjusting filter 14 constitute in combination a relative
velocity estimation unit 16.
[0072] The phase adjusting filter 13 has a transfer function G1(s)
shown by the following Equation (3), which contains a phase-lead
element:
G1(s)=(1+T2s)/(1+T1s) (3)
[0073] where T1 and T2 are time constants.
[0074] The phase adjusting filter 13 advances the phase of the
vertical acceleration M, which leads the phase of the actual
relative velocity by a predetermined angle as shown in FIG. 39, by
a predetermined angle so that the phase difference becomes 0
degree, for example. Thus, the vertical acceleration M is adjusted
so as to be in phase with the relative velocity. The phase-adjusted
vertical acceleration M is outputted as an estimated relative
velocity (signal B).
[0075] In this embodiment, the phase of the vertical acceleration M
leads that of the actual relative velocity by 131 degrees. By
passing the vertical acceleration M through the phase adjusting
filter 13, the phase of the vertical acceleration M is advanced by
49 degrees when the road surface input is in the neighborhood of 1
Hz (hereinafter referred to as "the neighborhood of vehicle body
resonance point") 20 corresponding to the vehicle body resonance
point [sprung mass resonance frequency; 1 Hz] as shown in FIG. 4,
so that the phase difference with respect to the actual relative
velocity becomes 180 degrees. Because the signal outputted from the
phase adjusting filter 13 becomes the absolute value through the
absolute value computing unit 15, the phase of the vertical
acceleration M is made, in effect, coincident with that of the
actual relative velocity by providing a phase difference of 180
degrees therebetween.
[0076] The phase adjusting filter 13 outputs the vertical
acceleration B (estimated relative velocity) adjusted so as to be
in phase with the actual relative velocity to the gain adjusting
filter 14.
[0077] In this embodiment, the time constants T1 and T2 are
determined as follows. For the time constant T1=1/(2.pi.f1), f1 is
set equal to 50 Hz. For the time constant T2=1/(2.pi.f2), f2 is set
equal to 0.85 Hz.
[0078] The gain adjusting filter 14 comprises a low-pass filter 14a
and a high-pass filter 14b connected in parallel to the output
terminal of the phase adjusting filter 13. The gain adjusting
filter 14 adds together the outputs from the low-pass filter 14a
and the high-pass filter 14b to obtain a band-pass signal C and
outputs the band-pass signal C to the absolute value computing unit
15.
[0079] The low-pass filter 14a and the high-pass filter 14b have
transfer functions G2(s) and G3(s) shown by the following Equations
(4) and (5), respectively, and consequently, the gain adjusting
filter 14 has a transfer function G4(s) shown by the following
Equation (6):
G2(s)=1/(1+T3s) (4)
[0080] where T3 is a time constant.
G3(s)=T4s/(1+T4s) (5)
[0081] where T4 is a time constant.
G4(s)=1/(1+T3s)+T4s/(1+T4s) (6)
[0082] The gain adjusting filter 14 adjusts the gain of the
estimated relative velocity to generate the signal C (and thus the
signal D), in a manner as shown in FIG. 5. That is, in the
neighborhood of vehicle body resonance point 20, the gain adjusting
filter 14 reduces the gain of the estimated relative velocity. In
frequency regions other than the neighborhood of vehicle body
resonance point 20, the gain adjusting filter 14 increases the gain
of the estimated relative velocity.
[0083] In this embodiment, the time constants T3 and T4 are
determined as follows. For the time constant T3=1/(2.pi.f3), f3 is
set equal to 0.5 Hz. For the time constant T4=1/(2.pi.f4), f4 is
set equal to 2.0 Hz.
[0084] For the time constants T1, T2, T3 and T4, optimum values
should be set in accordance with the weight of the vehicle, the
spring constant of the spring provided between the sprung and
unsprung members, etc. (i.e. the type of vehicle).
[0085] In this embodiment, the damping coefficient C2 is obtained
as follows:
[0086] If V(V-X)>0,
C2=K V/D (1c)
[0087] If V(V-X)<0,
C2=Cmin (2c)
[0088] In the suspension control system arranged as stated above,
the phase adjusting filter 13 and the gain adjusting filter 14 are
arranged to act on the acceleration M from the acceleration sensor
6. That is, the phase adjusting filter 13 advances the vertical
acceleration M by 49 degrees in the neighborhood of vehicle body
resonance point 20 so that the vertical acceleration M has a phase
difference of 180 degrees with respect to the actual relative
velocity, thereby making the phase of the vertical acceleration M
coincident, in effect, with the phase of the relative velocity in
the neighborhood of vehicle body resonance point 20. Further, the
gain adjusting filter 14 adjusts the gain of the estimated relative
velocity to generate the signal C in such a manner that in the
neighborhood of vehicle body resonance point 20, the gain adjusting
filter 14 reduces the gain of the estimated relative velocity,
whereas in frequency regions other than the neighborhood of vehicle
body resonance point 20, the gain adjusting filter 14 increases the
gain of the estimated relative velocity. Thus, when the divider
circuit 9 performs the calculation of (V/D), a coefficient E
(corrected signal E) having a large value is obtained in the
neighborhood of vehicle body resonance point 20. Consequently, the
controlled variable in the neighborhood of vehicle body resonance
point 20 increases, and the controlled variable in higher frequency
regions decreases. Damping force is adjusted in correspondence to
the controlled variable. Thus, it is possible to improve ride
quality in the neighborhood of vehicle body resonance point (1
Hz).
[0089] When damping force 40 expected to be obtained by this
embodiment (i.e. damping force generated according to the new
control rules) was determined by computation, the data as shown in
FIG. 6 was obtained. The damping force 40 generated according to
the new control rules is equal in peak to the damping force 41
according to the sky-hook damper theory (i.e. theoretical damping
force). In comparison with damping force 42 generated by the
above-described prior art, the damping force 40 is closer to the
theoretical damping force 41. Thus, it was confirmed that this
embodiment allows an improved control.
[0090] Further, the suspension control system according to this
embodiment uses a damping coefficient varying type shock absorber 4
having invertible damping characteristics. Accordingly, it is not
required to sense the stroke (direction) of the shock absorber 4
(damper). Thus, vibration damping control for an automobile
(vehicle) can be effected to ensure favorable ride quality of
steering stability by using the acceleration sensor 6, which is
relatively inexpensive, in place of a costly sensor such as a
stroke sensor. Therefore, costs can be reduced correspondingly. It
should be noted that the shock absorber 4 is not necessarily
limited to the above-described damping coefficient varying type
shock absorber having invertible damping characteristics. As a
matter of course, a sensor, such as a stroke sensor which is
capable of determining the stroke of a shock absorber (damper), may
be used. In such a case, a shock absorber of non-invertible damping
characteristics (with the damping characteristics varying in
similar ways in both extension and compression strokes) can be
used.
[0091] In the foregoing embodiment, the suspension control system
is used in an automobile, by way of example. The suspension control
system is also usable in a railway vehicle 30, as shown in FIG. 7,
by replacing the vertical acceleration of the vehicle body 1 with
the horizontal acceleration of the body 31 of the railway vehicle
30 and replacing the vertical absolute velocity of the vehicle body
1 with the horizontal absolute velocity of the vehicle body 31 and
further replacing the axle with the truck 32. The fact that the
suspension control system according to the present invention is
applicable to a railway vehicle in place of an automobile holds
true for the following second to sixteenth embodiments.
[0092] In the foregoing embodiment, the magnitude of extension-side
and compression-side damping force of the shock absorber 4 is
varied according to the magnitude of electric current corresponding
to the command signal from the command signal output unit 11 (see
FIG. 2), by way of example. However, the arrangement may be such
that damping characteristic positions H/S, S/S and S/H are
selectably provided for the shock absorber 4 to allow setting of a
desired combination of damping force characteristics for the
extension and compression sides, i.e. a combination of "hard"
damping characteristics for the extension side and "soft" damping
characteristics for the compression side, or a combination of
"soft" for the extension side and "soft" for the compression side,
or a combination of "soft" for the extension side and "hard" for
the compression side. In this case, the command signal outputted
from the command signal output unit 11 is arranged to select one of
the damping characteristic positions H/S, S/S and S/H. It should be
noted that this holds true for the following second to sixteenth
embodiments.
[0093] Although in the foregoing embodiment the phase adjusting
filter 13 contains a phase-lead element for advancing the phase,
the present invention is not necessarily limited thereto. The phase
adjusting filter 13 may contain a phase-lag element for adjusting
the phase by retarding it. In other words, the phase adjusting
filter 13 may contain any phase adjusting element capable of phase
adjustment so that points at which each signal intersects the
horizontally extending time axis are coincident with each other. It
should be noted that this holds true for the following second to
sixteenth embodiments.
[0094] Next, a second embodiment of the present invention will be
described with reference to FIGS. 8 to 13. It should be noted that
illustration and description of members or portions equivalent to
those in the first embodiment (FIGS. 1 to 7) are omitted according
to circumstances.
[0095] The second embodiment differs from the first embodiment
mainly in the following points (a) to (c):
[0096] (a) As shown in FIGS. 8 and 9, a sprung mass sensor 17 is
provided to detect the weight P1 of the vehicle (sprung mass).
[0097] (b) The time constants T1, T2, T3 and T4 of the relative
velocity estimation unit 16 and hence filter constants (gain and
phase) [adjusting parameters for the acceleration M] are variable.
Moreover, the controller 7 is provided with a time constant
determination unit 18.
[0098] (c) The controller 7 adjusts the phase of the acceleration M
(detected signal) from the acceleration sensor 6 on the basis of
the filter constants (gain and phase) [adjusting parameters for the
acceleration M] of the relative velocity estimation unit 16, and
changes the filter constants (gain and phase) by determining the
values of the time constants T1, T2, T3 and T4 according to the
result of detection by the sprung mass sensor 17.
[0099] The controller 7 has a vehicle weight reference value P0
stored therein to make a comparison with the vehicle weight P1
detected by the sprung mass sensor 17. The controller 7 performs a
comparative operation using the vehicle weight reference value P0
as described later. The contents of arithmetic control performed by
the controller 7 will be described below with reference to FIGS. 10
and 11.
[0100] In FIG. 10, the controller 7 starts execution of control
software as the power supply is turned on (step S1). First, the
controller 7 executes initialization (step S2).
[0101] Next, the controller 7 judges whether or not a predetermined
control cycle has elapsed (step S3). If it is judged at step S3
that the predetermined control cycle has not yet elapsed, the
controller 7 returns upstream to judge again whether or not the
predetermined control cycle has elapsed.
[0102] If it is judged at step S3 that the predetermined control
cycle has elapsed, the controller 7 outputs the contents of the
operation executed in the previous control cycle (i.e. the command
current I having a magnitude corresponding to the signal F obtained
by the amplifier circuit 10, etc.) to the actuator 5 to adjust the
damping force of the shock absorber 4 (step S4).
[0103] Subsequently to step S4, sensor information is read from the
acceleration sensor 6, the sprung mass sensor 17 and various
sensors not illustrated (step S5). At step S5, the controller 7
outputs a signal to each port (not shown). Next, the controller 7
judges the condition of the vehicle and performs necessary
computation such as computation of damping force (step S6).
Subsequently to step S6, the controller 7 executes a time constant
determination subroutine (step S7) and then returns to step S3.
[0104] At step S6, the controller 7 also performs computation to
calculate the sprung mass resonance frequency and the phase
difference between the sprung mass acceleration and the actual
relative velocity in the neighborhood of the resonance point on the
basis of the vehicle weight P1 (sprung mass) from the sprung mass
sensor 17 and so forth. On the basis of the result of the
computation, the controller 7 determines the values of the time
constants T1, T2, T3 and T4 in the time constant determination
subroutine at step S7 as stated below, thereby adjusting the gain
D, the phase, etc.
[0105] In the time constant determination subroutine, as shown in
FIG. 11, the controller 7 judges whether or not the vehicle weight
P1 exceeds the vehicle weight reference value P0 (step S10). If it
is judged at step S10 that the vehicle weight P1 exceeds the
vehicle weight reference value P0 (YES), the controller 7 executes
the operation at step S11. At step S11, the controller 7 determines
the values of the time constants T1, T2, T3 and T4 so that the
following condition will be obtained, and then returns to the main
routine shown in FIG. 10. That is, the values of the time constants
T1, T2, T3 and T4 are determined so that, as shown by the curve
"After Correction" in FIG. 13, the gain D of the signal C and thus
the signal D (corresponding to the estimated relative velocity)
becomes smaller than in the case of "Before Correction" in FIG. 13
as a whole [particularly smaller in the neighborhood of vehicle
body resonance point 20 (i.e. in the neighborhood of sprung mass
resonance frequency)], and, as shown by the curve "After
Correction" in FIG. 12, the phase of the vertical acceleration M
becomes larger (advanced) than in the case of "Before Correction"
in FIG. 12 in the neighborhood of vehicle body resonance point 20
and in frequency regions higher than the resonance point 20.
[0106] If it is judged at step S10 that the vehicle weight P1 is
not in excess of the vehicle weight reference value P0 (NO), the
controller 7 determines the values of the time constants T1, T2, T3
and T4 so that the gain D of the signal D (corresponding to the
estimated relative velocity) in the neighborhood of the sprung mass
resonance frequency becomes large (step S12), and then returns to
the main routine shown in FIG. 10.
[0107] In the second embodiment arranged as stated above, if the
vehicle weight P1 exceeds the vehicle weight reference value P0 (if
YES is the answer at step S10), the values of the time constants
T1, T2, T3 and T4 are determined by processing at step S11,
whereby, as shown by the curve "After Correction) in FIG. 13, the
gain D of the signal D (corresponding to the estimated relative
velocity) in the neighborhood of the sprung mass resonance
frequency becomes smaller than in the case of "Before Correction",
and, as shown by the curve "After Correction" in FIG. 12, the phase
of the vertical acceleration M becomes larger (advanced) than in
the case of "Before Correction".
[0108] As has been stated above, when the vehicle weight P1 exceeds
the vehicle weight reference value P0, the gain D of the
applicable, estimated relative velocity (signal D) decreases, and
the phase of the vertical acceleration M increases (advances) in
the high frequency regions. Consequently, the corrected signal E
obtained in the divider circuit 9 using the signal D as a
denominator, i.e. the command current I (i.e. a signal directly
influencing the final desired damping force) increases in value,
and the phase of the vertical acceleration M is made, in effect,
coincident with the phase of the absolute velocity and hence
possible to achieve an improvement in ride quality.
[0109] Further, because the command current I (i.e. a signal
directly influencing the final desired damping force) is increased
when the vehicle weight P1 exceeds the vehicle weight reference
value P0, it is possible to rapidly cope with a deficiency in
damping force due to a change in weight to thereby improve ride
quality.
[0110] Further, the time constants T1, T2, T3 and T4 of the
relative velocity estimation unit 16 and hence the filter constants
(gain and phase) [adjusting parameters for the acceleration M] are
variable. Therefore, the controlled variable (command current I)
can be changed by varying the time constants T1, T2, T3 and T4.
Thus, it is possible to ensure damping characteristic control of
high accuracy. It should be noted that this holds true for the
following third to fifteenth embodiments.
[0111] Further, in the neighborhood of vehicle body resonance point
20, the gain D of the applicable, estimated relative velocity
(signal D) decreases, whereas in frequency regions other than the
neighborhood of vehicle body resonance point 20, the gain D of the
estimated relative velocity (signal D) increases, as in the case of
the first embodiment. Accordingly, the controlled variable in the
neighborhood of vehicle body resonance point 20 increases. Thus, it
is possible to improve ride quality in the neighborhood of vehicle
body resonance point (1 Hz).
[0112] In the second embodiment, the vehicle weight P1 detected
with the sprung mass sensor 17 is judged (step S10) by using a
single vehicle weight reference value P0. However, the arrangement
may be such that the judgment is made by using a plurality of
different vehicle weight reference values, and the determination of
time constants [hence the change of the gain and phase (adjusting
parameters)] is made so that the time constants assume different
values according to the result of the judgment. With this
arrangement, control characteristics of high accuracy can be
attained.
[0113] The arrangement may also be such that a variable vehicle
weight reference value is used in place of a single vehicle weight
reference value P0 as stated above, and the vehicle weight
reference value is varied by a manual operation or automatically
according to circumstances, for example, whether or not a little
child is included among the occupants of the vehicle, or according
to the surface condition of the road on which the vehicle is about
to run.
[0114] In this embodiment, the frequency-gain characteristics of
the relative velocity estimation unit 16 are determined according
to the vehicle weight as follows:
[0115] (1) When the vehicle weight is standard (the number of
occupants is two), the time constants are determined so that the
frequency-gain characteristics are as shown by the segment T16 in
FIG. 37. In this case, for the time constant T3=1/(2.pi.f3), f3 is
set equal to 0.5 Hz, and for the time constant T4=1/(2.pi.f4), f4
is set equal to 2.0 Hz.
[0116] (2) When the vehicle weight is equivalent to that in a case
where the number of occupants is four, the time constants are
determined so that the frequency-gain characteristics are as shown
by the segment T15 in FIG. 37. In this case, for the time constant
T3=1/(2.pi.f3), f3 is set equal to 0.4 Hz, and for the time
constant T4=1/(2.pi.f4), f4 is set equal to 1.5 Hz.
[0117] (3) When the vehicle weight is equivalent to the sum of the
total weight of four occupants and the weight of baggage, the time
constants are determined so that the frequency-gain characteristics
are as shown by the segment T14 in FIG. 37. In this case, for the
time constant T3=1/(2.pi.f3), f3 is set equal to 0.3 Hz, and for
the time constant T4=1/(2.pi.f4), f4 is set equal to 0.9 Hz.
[0118] In the second embodiment, the sprung mass sensor 17 is
provided to detect the vehicle weight P1 (sprung mass), and the
vehicle weight P1 is used for the judgment (step S10) to determine
the time constants [and hence change the gain and phase (adjusting
parameters)]. However, the arrangement may be such that the rate of
change in the vehicle weight P1 (vehicle weight change rate) is
obtained, and the vehicle weight change rate is compared with a
predetermined vehicle weight change rate reference value to make a
judgment to determine the time constants [and hence change the gain
and phase (adjusting parameters)].
[0119] With the above-described arrangement, it is possible to
rapidly cope with a deficiency in damping force due to a change in
the sprung mass to thereby improve ride quality.
[0120] In the second embodiment, the vehicle weight P1 (sprung
mass) detected with the sprung mass sensor 17 is used, by way of
example. However, the suspension control system may be arranged to
use, in place of the vehicle weight P1, information detected with a
seat switch (a change in vehicle weight of approximately 50 to 60
kg can be judged from the on-off switching operation of a seat
switch), the pressure in an air suspension system, the pressure in
the cylinder of a shock absorber, the measured value of a gasoline
gauge, or information as to whether or not an occupant fastens a
seat belt (a change in vehicle weight of approximately 50 to 60 kg
can be judged from fastening or unfastening of a seat belt).
[0121] Next, a third embodiment of the present invention will be
described with reference to FIGS. 14 to 18. It should be noted that
illustration and description of members or portions equivalent to
those in the first and second embodiments (FIGS. 1 to 13) are
omitted according to circumstances.
[0122] The third embodiment differs from the second embodiment
mainly in the following points. As shown in FIGS. 14 and 15, a
vehicle speed sensor 17A for detecting the vehicle speed R1 by
obtaining the rotational speed of the wheel is provided in place of
the sprung mass sensor 17. In addition, a time constant
determination subroutine (step S7A) shown in FIG. 16 is provided in
place of the time constant determination subroutine (step S7) shown
in FIGS. 10 and 11. Thus, the vehicle speed R1 is used to determine
the time constants in place of the vehicle weight P1. It should be
noted that a vehicle speed reference value to be compared with the
vehicle speed R1 has previously been stored in the controller
7.
[0123] At step S7A (time constant determination subroutine), as
shown in FIG. 16, the controller 7 judges whether or not the
vehicle speed R1 exceeds the vehicle speed reference value R0 (step
S10A). If it is judged at step S10A that the vehicle speed R1
exceeds the vehicle speed reference value R0 (YES), the controller
7 executes the operation at step S11A. At step S11A, the controller
7 determines the values of the time constants T1, T2, T3 and T4 so
that the following condition will be obtained, and then returns to
the main routine shown in FIG. 10. That is, the values of the time
constants T1, T2, T3 and T4 are determined so that, as shown by the
curve "After Correction" in FIG. 18, the gain D of the signal C and
thus the signal D (corresponding to the estimated relative
velocity) becomes smaller than in the case of "Before Correction"
in FIG. 18 as a whole and particularly smaller in the neighborhood
of vehicle body resonance point 20 (i.e. in the neighborhood of
sprung mass resonance frequency), and, as shown by the curve "After
Correction" in FIG. 17, the phase of the vertical acceleration M
becomes larger (advanced) than in the case of "Before Correction"
in FIG. 17 in the neighborhood of vehicle body resonance point 20
and in frequency regions higher than the resonance point 20.
[0124] If it is judged at step S10A that the vehicle speed R1 is
not in excess of the vehicle speed reference value R0 (NO), the
controller 7 determines the values of the time constants T1, T2, T3
and T4 so that the gain D of the signal D (corresponding to the
estimated relative velocity) in the neighborhood of the sprung
resonance frequency becomes large (step S12A), and then returns to
the main routine shown in FIG. 10.
[0125] In the third embodiment arranged as stated above, if the
vehicle speed R1 exceeds the vehicle speed reference value R0 (if
YES is the answer at step S10A), the values of the time constants
T1, T2, T3 and T4 are determined by processing at step S11A,
whereby, as shown by the curve "After Correction) in FIG. 18, the
gain D of the signal D (corresponding to the estimated relative
velocity) in the neighborhood of the sprung mass resonance
frequency becomes smaller than in the case of "Before Correction",
and, as shown by the curve "After Correction" in FIG. 17, the phase
of the vertical acceleration M becomes larger (advanced) than in
the case of "Before Correction".
[0126] As has been stated above, when the vehicle speed R1 exceeds
the vehicle speed reference value R0, the gain D of the applicable,
estimated relative velocity (signal D) decreases, and the phase of
the vertical acceleration M increases (advances) in the high
frequency regions. Consequently, the corrected signal E obtained in
the divider circuit 9 using the signal D as a denominator, i.e. the
command current I (i.e. a signal directly influencing the final
desired damping force) increases in value, and the phase of the
vertical acceleration M is made, in effect, coincident with the
phase of the absolute velocity and hence possible to achieve an
improvement in ride quality.
[0127] Further, because the command current I (i.e. a signal
directly influencing the final desired damping force) is increased
when vehicle speed R1 exceeds the vehicle speed reference value R0,
it is possible to rapidly cope with a deficiency in damping force
due to a change in vehicle speed to thereby improve ride
quality.
[0128] Further, in the neighborhood of vehicle body resonance point
20, the gain D of the applicable estimated relative velocity
(signal D) decreases, whereas in frequency regions other than the
neighborhood of vehicle body resonance point 20, the gain D of the
estimated relative velocity (signal D) increases, as in the case of
the first embodiment. Accordingly, the controlled variable in the
neighborhood of vehicle body resonance point 20 increases. Thus, it
is possible to improve ride quality in the neighborhood of vehicle
body resonance point (1 Hz).
[0129] In the third embodiment, the vehicle speed R1 detected with
the vehicle speed sensor 17A is judged (step S10A) by using a
single vehicle speed reference value R0. However, the arrangement
may be such that the judgment is made by using a plurality of
different vehicle speed reference values, and the determination of
time constants [hence the change of the gain and phase (adjusting
parameters)] is made so that the time constants assume different
values according to the result of the judgment. With this
arrangement, control characteristics of high accuracy can be
attained. An example of this arrangement, in which two reference
values are used, will be described below. In this example, the
frequency-gain characteristics of the relative velocity estimation
unit 16 are determined according to the vehicle speed as
follows:
[0130] (1) When the vehicle speed is standard (50 to 80 km/h), the
time constants are determined so that the frequency-gain
characteristics are as shown by the segment T1 in FIG. 22. In this
embodiment, for the time constant T3=1/(2.pi.f3), f3 is set equal
to 0.5 Hz, and for the time constant T4=1/(2.pi.f4), f4 is set
equal to 2.0 Hz.
[0131] (2) When the vehicle speed is high (higher than 80 km/h),
the time constants are determined so that the frequency-gain
characteristics are as shown by the segment T2 in FIG. 22. In this
embodiment, for the time constant T3=1/(2.pi.f3), f3 is set equal
to 0.3 Hz, and for the time constant T4=1/(2.pi.f4), f4 is set
equal to 3.0 Hz.
[0132] (3) When the vehicle speed is low (lower than 50 km/h), the
time constants are determined so that the frequency-gain
characteristics are as shown by the segment T3 in FIG. 22. In this
case, the time constants may be determined so that the
frequency-gain characteristics are as shown by the segment T1 in
FIG. 22. When the time constants are determined so that the
frequency-gain characteristics are as shown by the segment T3, in
this embodiment, for the time constant T3=1/(2.pi.f3), f3 is set
equal to 0.6 Hz, and for the time constant T4=1/(2.pi.f4), f4 is
set equal to 1.5 Hz.
[0133] In the third embodiment, the vehicle speed sensor 17A is
provided to detect the vehicle speed R1, and the vehicle speed R1
is used for the judgment (step S10A) to determine the time
constants [and hence change the gain and phase (adjusting
parameters)]. However, the arrangement may be such that the rate of
change in the vehicle speed R1 (vehicle speed change rate)
[acceleration] is obtained, and the vehicle speed change rate
[acceleration] is compared with a predetermined vehicle speed
change rate reference value to make a judgment to determine the
time constants [and hence change the gain and phase (adjusting
parameters)].
[0134] With the above-described arrangement, it is possible to
rapidly cope with a deficiency in damping force when the vehicle is
running at high speed to thereby improve ride quality.
[0135] In the third embodiment, the vehicle speed sensor 17A
detects the vehicle speed by obtaining the rotational speed of the
wheel, by way of example. However, the vehicle speed sensor 17A may
be replaced with a device for detecting the vehicle speed by using
information obtained from GPS or combined information consisting of
the engine speed and the gear position (1st gear, 2nd, etc.).
[0136] As has been stated above, when the vehicle speed R1 exceeds
the vehicle speed reference value R0, the gain D of the applicable
estimated relative velocity (signal D) decreases, and the phase of
the vertical acceleration M increases (advances) in the high
frequency regions. Consequently, the corrected signal E obtained in
the divider circuit 9 using the signal D as a denominator, i.e. the
command current I (i.e. a signal directly influencing the final
desired damping force) increases in value, and the phase of the
vertical acceleration M is made, in effect, coincident with the
phase of the absolute velocity and hence possible to achieve an
improvement in ride quality.
[0137] Further, because the command current I (i.e. a signal
directly influencing the final desired damping force) is increased
when the vehicle speed R1 exceeds the vehicle speed reference value
R0, it is possible to rapidly cope with a deficiency in damping
force due to a change in vehicle speed to thereby improve ride
quality.
[0138] Next, a fourth embodiment of the present invention will be
described with reference to FIGS. 19 to 22. It should be noted that
illustration and description of members or portions equivalent to
those in the first to third embodiments (FIGS. 1 to 18) are omitted
according to circumstances.
[0139] The fourth embodiment differs from the second embodiment
mainly in the following points (a) to (d):
[0140] (a) As shown in FIG. 19, the sprung mass sensor 17 is not
used.
[0141] (b) The time constant determination unit 18 provided in the
controller 7 is supplied as an input with the acceleration M
(detected signal) from the acceleration sensor 6 (sprung mass
vibration detecting device) and judges the road surface condition
as stated later.
[0142] (c) The controller 7 adjusts the phase of the acceleration M
from the acceleration sensor 6 on the basis of the filter constants
(gain and phase) [adjusting parameters for the acceleration M] of
the relative velocity estimation unit 16 and changes the filter
constants (gain and phase) by determining the values of the time
constants T1, T2, T3 and T4 according to the result of the judgment
on the road surface condition.
[0143] (d) A time constant determination subroutine (step S7B)
shown in FIGS. 20 and 21 is provided in place of the time constant
determination subroutine (step S7) shown in FIGS. 10 and 11.
[0144] The controller 7 has an ordinary road reference value and a
rough road reference value stored therein in advance for comparison
with the acceleration M detected with the acceleration sensor 6
(sprung mass vibration detecting device). The controller 7 executes
a comparative operation using the ordinary road reference value and
the rough road reference value as stated later to judge the road
surface condition to be "ordinary road" or "rough road" according
to the acceleration M. The judgment on the road surface condition
is made by using the amplitude and vibration period (frequency) of
the acceleration M.
[0145] At step S7B (time constant determination subroutine), as
shown in FIG. 21, the controller 7 executes an operation (step S21)
for judging the road surface condition, such as extraction of the
amplitude and vibration period of the acceleration M, and judges
whether or not the road surface condition is "ordinary road" (step
S22) on the basis of the information (acceleration M) obtained at
step S21.
[0146] If it is judged at step S22 that the road surface condition
is "ordinary road" (YES), the controller 7 executes the operation
at step S23 and then returns to the main routine shown in FIG.
20.
[0147] If it is judged at step S22 that the road surface condition
is not "ordinary road" (NO), the controller 7 judges whether or not
the road surface condition is "rough road" (step S24).
[0148] If the road surface condition is judged to be "rough road"
(i.e. the low-frequency component of the acceleration M is
large)(YES) at step S24, the controller 7 executes the operation at
step S25 and then returns to the main routine shown in FIG. 20.
[0149] If it is judged at step S24 that the road surface condition
is not "rough road" (NO), the controller 7 executes the operation
at step S26 and then returns to the main routine shown in FIG.
20.
[0150] At step S23, the filter constants (gain and phase) of the
relative velocity estimation unit 16 (i.e. the phase adjusting
filter 13 and the gain adjusting filter 14) are set to an ordinary
road filter state by changing the time constants.
[0151] At step S25, the filter constants of the relative velocity
estimation unit 16 are similarly set to a rough road filter state
by changing the time constants.
[0152] At step S26, the filter constants of the relative velocity
estimation unit 16 are similarly set to an undulating road filter
state by changing the time constants.
[0153] The setting of the ordinary road filter state at step S23 is
effected by determining the values of the time constants T1, T2, T3
and T4 so that the gain D of the signal C and thus the signal D
(corresponding to the estimated relative velocity) becomes small in
the neighborhood of vehicle body resonance point 20 (i.e. in the
neighborhood of sprung mass resonance frequency) as shown by the
segment T1 in FIG. 22. In this case, for the time constant
T3=1/(2.pi.f3), f3 is set equal to 0.5 Hz, and for the time
constant T4=1/(2.pi.f4), f4 is set equal to 2.0 Hz.
[0154] The setting of the rough road filter state at step S25 is
effected by determining the values of the time constants T1, T2, T3
and T4 so that the gain D of the signal C and thus the signal D
(corresponding to the estimated relative velocity) becomes larger
than the segment T1 (ordinary road filter state) in all the
frequency regions, including the neighborhood of vehicle body
resonance point 20 (i.e. the neighborhood of sprung mass resonance
frequency) as shown by the segment T3 in FIG. 22. In this case, for
the time constant T3=1/(2.pi.f3), f3 is set equal to 0.6 Hz, and
for the time constant T4=1/(2.pi.f4), f4 is set equal to 1.5
Hz.
[0155] The setting of the undulating road filter state at step S26
is effected by determining the values of the time constants T1, T2,
T3 and T4 so that the gain D of the signal C and thus the signal D
(corresponding to the estimated relative velocity) becomes smaller
than the segment T1 (ordinary road filter state) in all the
frequency regions, including the neighborhood of vehicle body
resonance point 20 (i.e. the neighborhood of sprung mass resonance
frequency) as shown by the segment T2 in FIG. 22. In this case, for
the time constant T3=1/(2.pi.f3), f3 is set equal to 0.3 Hz, and
for the time constant T4=1/(2.pi.f4), f4 is set equal to 3.0
Hz.
[0156] In the fourth embodiment arranged as stated above, when the
road surface condition is judged to be "rough road", the setting of
the rough road filter state is executed (step S25), and the values
of the time constants T1, T2, T3 and T4 are determined [and hence
the magnitudes of the gain and phase (adjusting parameters) are
adjusted] as stated above. Consequently, the gain D of the signal C
and thus the signal D (corresponding to the estimated relative
velocity) becomes larger than the segment T1 (ordinary road filter
state) as shown by the segment T3 in FIG. 22. Accordingly, the
corrected signal E obtained in the divider circuit 9 using the
signal D as a denominator, i.e. the command current I (i.e. a
signal directly influencing the final desired damping force)
decreases in value, and it becomes possible to achieve an
improvement in ride quality.
[0157] When the road surface condition is judged to be "undulating
road", the setting of the undulating road filter state is executed
(step S26), and the values of the time constants T1, T2, T3 and T4
are determined [and hence the magnitudes of the gain and phase
(adjusting parameters) are adjusted] as stated above. Consequently,
the gain D of the signal D (corresponding to the estimated relative
velocity) becomes smaller than the segment T1 (ordinary road filter
state) as shown by the segment T2 in FIG. 22. Accordingly, the
corrected signal E obtained in the divider circuit 9 using the
signal D as a denominator, i.e. the command current I (i.e. a
signal directly influencing the final desired damping force)
increases in value, and it becomes possible to achieve an
improvement in ride quality.
[0158] As has been stated above, the ordinary road filter state,
the rough road filter state or the undulating road filter state is
set according to the road surface condition (step S23 or step S26),
and the values of the time constants T1, T2, T3 and T4 are
determined [and hence the magnitudes of the gain and phase
(adjusting parameters) are adjusted] as stated above. Therefore,
the gain D of the signal D (corresponding to the estimated relative
velocity) is adjusted according to the road surface condition.
Accordingly, the command current I (i.e. a signal directly
influencing the final desired damping force) is generated according
to the result of the adjustment. Thus, suspension control is
effected according to various road surface conditions, and it
becomes possible to achieve an improvement in ride quality.
[0159] In the foregoing fourth embodiment, the acceleration M
detected with the acceleration sensor 6 is used for judgment on the
road surface condition, by way of example. However, the arrangement
may be such that a vehicle height sensor or a non-contact road
surface sensor is provided and information detected with such a
sensor is used for the road surface condition judgment instead of
using the acceleration M as in the foregoing embodiment.
[0160] In the fourth embodiment, a judgment is made to distinguish
between an ordinary road and a rough road, and the road surface
condition is classified into one of "ordinary road", "rough road"
and "undulating road", according to the result of the judgment.
However, the road surface condition may be classified even more
finely according to the result of the judgment to further improve
the control accuracy.
[0161] In the fourth embodiment, the road surface condition is
judged on the basis of the acceleration M detected with the
acceleration sensor 6, and the values of the time constants T1, T2,
T3 and T4 [and hence the filter constants (gain and phase)] are
adjusted according to the result of the judgment, by way of
example. However, the arrangement may be such that an acceleration
sensor (not shown) is provided in addition to the acceleration
sensor 6 to detect the condition of change in the attitude of the
vehicle, i.e. pitching, bouncing and rolling of the vehicle, and
information detected with the acceleration sensor 6 and another
accelerations sensor (not shown) is divided into a plurality of
modes. Thus, the values of the time constants T1, T2, T3 and T4
[and hence the filter constants (gain and phase)] are adjusted
according to the detected mode.
[0162] An example (a fifth embodiment of the present invention) in
which the suspension control system is arranged as stated above
will be described below with reference to FIG. 23. It should be
noted that illustration and description of members or portions
equivalent to those in the first to fourth embodiments (FIGS. 1 to
22) are omitted according to circumstances.
[0163] In the fifth embodiment, information detected with the
acceleration sensor 6 and the other acceleration sensor (not shown)
is classified into one of three modes, i.e. pitching, bouncing and
rolling.
[0164] For the bouncing, pitching and rolling modes, the values of
the time constants T1, T2, T3 and T4 are determined so as to
provide frequency-gain characteristics represented by the segment
T4, T5 or T6 in FIG. 23, i.e. so that, in each mode, the gain takes
smallest value at the resonance frequency.
[0165] In this case, the resonance frequencies of the bouncing,
pitching and rolling modes become higher in the order mentioned. In
the bouncing mode (segment T4), the values of the time constants
T1, T2, T3 and T4 are determined so that in frequency regions lower
than the resonance frequency, the gain is smaller than in the other
modes, whereas in frequency regions higher than the resonance
frequency, the gain is larger than in the other modes.
[0166] In the pitching mode (segment T5), the values of the time
constants T1, T2, T3 and T4 are determined so that in frequency
regions lower than the resonance frequency, the gain characteristic
curve lies between those of the other modes, and also in frequency
regions higher than the resonance frequency, the gain
characteristic curve lies between those of the other modes.
[0167] In the fifth embodiment arranged as stated above,
information detected with the acceleration sensor 6 and another
acceleration sensor (not shown) is classified into one of the
bouncing, pitching and rolling modes, and the values of the time
constants T1, T2, T3 and T4 are determined according to the
detected mode, i.e. one of the bouncing, pitching and rolling modes
so that the gain in the neighborhood of the resonance frequency is
made small.
[0168] Accordingly, when the bouncing, pitching or rolling mode is
detected, the values of the time constants T1, T2, T3 and T4 are
determined [and hence the magnitudes of the gain and phase
(adjusting parameters) are adjusted] so as to provide
frequency-gain characteristics represented by the segment T4, T5 or
T6 in FIG. 23, i.e. so that the gain at the resonance frequency of
the bouncing, pitching or rolling mode becomes small. As a result,
the corrected signal E obtained in the divider circuit 9 using the
signal D as a denominator, i.e. the command current I (i.e. a
signal directly influencing the final desired damping force)
increases in value. Thus, it is possible to achieve an improvement
in ride quality.
[0169] In the foregoing fifth embodiment, the values of the time
constants T1, T2, T3 and T4 are fixed for each of the bouncing,
pitching and rolling modes. However, the time constants may be
varied in magnitude according to the vehicle speed or weight.
[0170] Next, a sixth embodiment of the present invention will be
described with reference to FIGS. 24 to 28. It should be noted that
illustration and description of members or portions equivalent to
those in the first to fifth embodiments (FIGS. 1 to 23) are omitted
according to circumstances.
[0171] The sixth embodiment differs from the second embodiment
mainly in the following points (a) to (c):
[0172] (a) As shown in FIGS. 24 and 25, a steering speed sensor 17B
is provided in place of the sprung mass sensor 17 to detect the
steering speed R11.
[0173] (b) The controller 7 adjusts the phase of the acceleration M
(detected signal) from the acceleration sensor 6 on the basis of
the filter constants (gain and phase) [adjusting parameters for the
acceleration M] of the relative velocity estimation unit 16 and
changes the filter constants (gain and phase) by determining the
values of the time constants T1, T2, T3 and T4 according to the
steering speed R11.
[0174] (c) A time constant determination subroutine (step S7C)
shown in FIGS. 26 and 27 is provided in place of the time constant
determination subroutine (step S7) shown in FIGS. 10 and 11.
[0175] The controller 7 has a steering speed reference value R10
stored therein in advance for comparison with the steering speed
R11 detected with the steering speed sensor 17B, and executes a
comparative operation using the steering speed reference value R10
as stated later. The contents of arithmetic control performed by
the controller 7 will be described below with reference to FIGS. 26
and 27.
[0176] In FIG. 26, the controller 7 starts execution of control
software as the power supply is turned on (step S1). First, the
controller 7 executes initialization (step S2).
[0177] At step S7C (time constant determination subroutine), as
shown in FIG. 27, the controller 7 judges whether or not the
steering speed R11 is less than the steering speed reference value
R10 (step S10C). If it is judged at step S10C that the steering
speed R11 is less than the steering speed reference value R10
(YES), the controller 7 executes the operation at step S11C to
effect steering speed "low" setting (segment T10), and then returns
to the main routine shown in FIG. 26. If it is judged at step S10C
that the steering speed R11 is not less than the steering speed
reference value R10 (NO), the controller 7 executes the operation
at step S12C to effect steering speed "high" setting (segment T11),
and then returns to the main routine shown in FIG. 26.
[0178] In the steering speed "low" setting operation (segment T10)
at step S11C, the values of the time constants T1, T2, T3 and T4
are determined [and hence the magnitudes of the gain and phase
(adjusting parameters) are adjusted] so that the gain D of the
signal C and thus the signal D (corresponding to the estimated
relative velocity) has a small value in the neighborhood of vehicle
body resonance point 20 (i.e. in the neighborhood of sprung mass
resonance frequency) as shown by the segment T10 in FIG. 28. In
this case, for the time constant T3=1/(2.pi.f3), f3 is set equal to
0.5 Hz, and for the time constant T4=1/(2.pi.f4), f4 is set equal
to 2.0 Hz.
[0179] In the steering speed "high" setting operation (segment T11)
at step S12C, the values of the time constants T1, T2, T3 and T4
are determined [and hence the magnitudes of the gain and phase
(adjusting parameters) are adjusted] so that the gain D of the
signal C and thus the signal D (corresponding to the estimated
relative velocity) has a small value in the neighborhood of vehicle
body resonance point 20 (i.e. in the neighborhood of sprung
resonance frequency) as shown by the segment T11 in FIG. 28. In the
steering speed "high" setting operation (segment T11) at step S12C,
the values of the time constants T1, T2, T3 and T4 are so
determined that the gain is smaller than in the case of the
steering speed "low" setting operation (segment T10) in the entire
range at step S11C. In this case, for the time constant
T3=1/(2.pi.f3), f3 is set equal to 0.3 Hz, and for the time
constant T4=1/(2.pi.f4), f4 is set equal to 3.0 Hz.
[0180] In the sixth embodiment, when the steering speed R11 is less
than the steering speed reference value R10, the filter first
setting operation (segment T10) at step S11C is executed to
determine the values of the time constants T1, T2, T3 and T4 [and
hence adjust the magnitudes of the gain and phase (adjusting
parameters)]. Accordingly, the gain D of the signal D
(corresponding to the estimated relative velocity) becomes larger
than the segment T11 in the neighborhood of vehicle body resonance
point 20 (i.e. in the neighborhood of sprung mass resonance
frequency). Thus, it is possible to achieve an improvement in ride
quality.
[0181] When the steering speed R11 is not less than the steering
speed reference value R10, the filter second setting operation
(segment T11) at step S12C is executed. As a result, the gain D of
the signal D becomes smaller than in the case of the
above-described step S11C in all the frequency regions.
Accordingly, the controlled variable can be increased, and it is
possible to improve steering stability and ride quality.
[0182] In the sixth embodiment, the filter constants of the
relative velocity estimation unit 16 are changed in two steps, i.e.
filter first setting and filter second setting. However, the
present invention is not necessarily limited to the described
arrangement. The filter constants may be changed in three or more
steps or continuously. This holds true for the following
embodiments.
[0183] In the sixth embodiment, when the steering speed R11 is not
less than the steering speed reference value R10, the values of the
time constants T1, T2, T3 and T4 are determined [and hence the
magnitudes of the gain and phase (adjusting parameters) are
adjusted] so that the gain D of the signal D becomes smaller in all
the frequency regions than in the case of the above-described step
S11C (i.e. the steering speed R11 is less than the steering speed
reference value R10), by way of example. However, the arrangement
may be as shown in FIG. 29 (a seventh embodiment of the present
invention).
[0184] In the seventh embodiment, when the steering speed R11 is
judged to be less than the steering speed reference value R10 (i.e.
YES is the answer at step S10C), the filter first setting operation
determines the values of the time constants T1, T2, T3 and T4 [and
hence adjusts the magnitudes of the gain and phase (adjusting
parameters)] so as to provide gain characteristics represented by
the segment T12 in FIG. 29. When the steering speed R11 is judged
to be not less than the steering speed reference value R10 (i.e. NO
is the answer at step S10C), the filter second setting operation
determines the values of the time constants T1, T2, T3 and T4 [and
hence adjusts the magnitudes of the gain and phase (adjusting
parameters)] so as to provide gain characteristics represented by
the segment T13 in FIG. 29.
[0185] Regarding the filter first setting operation (segment T12)
and the filter second setting operation (segment T13), the gain D
of the signal D is adjusted to the same magnitude in frequency
regions above a frequency slightly higher than the neighborhood of
vehicle body resonance point 20 (i.e. the vicinity of the sprung
mass resonance frequency).
[0186] Regarding the segment T12 (filter first setting operation),
for the time constant T3=1/(2.pi.f3), f3 is set equal to 0.5 Hz.
For the time constant T4=1/(2.pi.f4), f4 is set equal to 2.0 Hz.
Regarding the segment T13 (filter second setting operation), for
the time constant T3=1/(2.pi.f3), f3 is set equal to 0.3 Hz. For
the time constant T4=1/(2.pi.f4), f4 is set equal to 2.0 Hz.
[0187] In the seventh embodiment, when the steering speed R11 is
not less than the steering speed reference value R10, the gain in
high frequency regions is increased. Accordingly, the controlled
variable is not increased in the high frequency regions. In low
frequency regions, on the other hand, a sufficiently large
controlled variable can be ensured. Therefore, it becomes possible
to minimize vibrations that give an unfavorable floating
feeling.
[0188] In the seventh embodiment, the filter constants are changed
on the basis of the steering speed detected with the steering speed
sensor 17B. However, it is also possible to use a steering angle in
place of the steering speed. Alternatively, the horizontal
acceleration or the rate of change in the horizontal acceleration
may be used to change the filter constants.
[0189] The arrangement may also be such that a brake switch is
provided in place of the steering speed sensor 17B, and the filter
constants of the relative velocity estimation unit 16 are changed
on the basis of brake information obtained from the brake switch
(an eighth embodiment of the present invention). In the eighth
embodiment, for example, when the brake is not activated, the
values of the time constants T1, T2, T3 and T4 are determined [and
hence the magnitudes of the gain and phase (adjusting parameters)
are adjusted] so as to provide gain characteristics represented by
the segment T10 in FIG. 28. When the brake is activated, the values
of the time constants T1, T2, T3 and T4 are determined [and hence
the magnitudes of the gain and phase (adjusting parameters) are
adjusted] so as to provide gain characteristics represented by the
segment T11 in FIG. 28.
[0190] In the eighth embodiment, when the brake is activated, a
sufficiently large controlled variable can be ensured in
low-frequency regions without increasing the controlled variable in
high frequency regions, as in the case of the seventh embodiment.
Accordingly, it becomes possible to minimize vibrations that give
an unfavorable floating feeling.
[0191] It should be noted that the filter constants of the relative
velocity estimation unit 16 may be changed on the basis of (1)
information concerning deceleration of the vehicle, (2) a
combination of the deceleration information and the brake
information, (3) longitudinal acceleration, or (4) the rate of
change in longitudinal acceleration, instead of using the brake
information as in the eighth embodiment.
[0192] The filter constants of the relative velocity estimation
unit 16 may be changed by using inter-road/vehicle information or
inter-vehicle information (a ninth embodiment of the present
invention) in place of the steering speed used in the sixth
embodiment. In the ninth embodiment, when inter-road/vehicle
information or inter-vehicle information indicates that the
distance between two vehicles is short or indicates that the
vehicle is in danger (danger information), for example, the values
of the time constants T1, T2, T3 and T4 are determined [and hence
the magnitudes of the gain and phase (adjusting parameters) are
adjusted] so that the gain characteristic curve changes from the
segment T10 to the segment T11 in FIG. 28.
[0193] In the ninth embodiment, when the distance between two
vehicles is shorter than a reference value or when danger
information is given, the controller 7 determines the values of the
time constants T1, T2, T3 and T4 so as to provide gain
characteristics represented by the segment T11 in FIG. 28.
Therefore, it is possible to reduce sprung vibrations generated
when the brake is activated and hence possible to improve steering
stability. In this case, if the values of the time constants T1,
T2, T3 and T4 are determined [and hence the magnitudes of the gain
and phase (adjusting parameters) are adjusted] so as to provide
gain characteristics represented by the segment T13 in FIG. 29, a
sufficiently large controlled variable can be ensured in
low-frequency regions without increasing the controlled variable in
high frequency regions. Therefore, it becomes possible to minimize
vibrations that give an unfavorable floating feeling.
[0194] The filter constants of the relative velocity estimation
unit 16 may be changed on the basis of information (user option
information) obtained from a vehicle characteristic selecting
switch for selecting a sports mode, a regular mode, etc. (a tenth
embodiment of the present invention) instead of using the steering
speed as in the sixth embodiment. In the tenth embodiment, for
example, when the regular mode is selected, the values of the time
constants T1, T2, T3 and T4 are determined so that gain
characteristic represented by the segment T10 in FIG. 28 are
obtained. When the sports mode is selected, the values of the time
constants T1, T2, T3 and T4 are determined so as to provide gain
characteristics represented by the segment T11 in FIG. 28.
[0195] The arrangement may be such that the filter constants of the
relative velocity estimation unit 16 are changed on the basis of
throttle opening information indicating the degree of opening of
the throttle (an eleventh embodiment of the present invention),
instead of using the steering speed as in the sixth embodiment. In
the eleventh embodiment, for example, when the throttle opening is
small, the values of the time constants T1, T2, T3 and T4 are
determined so as to provide gain characteristics represented by the
segment T10 in FIG. 28. When the throttle opening is large, the
values of the time constants T1, T2, T3 and T4 are determined so as
to provide gain characteristics represented by the segment T11 in
FIG. 28. It should be noted that the filter constants of the
relative velocity estimation unit 16 may be changed on the basis of
(1) throttle opening speed information, (2) the rate of change in
vehicle speed, or (3) the combination of the vehicle speed change
rate and the throttle opening information, instead of using the
throttle opening information as in the eleventh embodiment.
[0196] The arrangement may be such that the filter constants of the
relative velocity estimation unit 16 are changed on the basis of
headlight information indicating ON/OFF of the headlight (a twelfth
embodiment of the present invention), instead of using the steering
speed as in the sixth embodiment. In the twelfth embodiment, for
example, when the headlight is off, the values of the time
constants T1, T2, T3 and T4 are determined so as to provide gain
characteristics represented by the segment T10 in FIG. 28. When the
headlight is on, the values of the time constants T1, T2, T3 and T4
are determined so as to provide gain characteristics represented by
the segment T11 in FIG. 28.
[0197] When the vehicle is running at night (i.e. when the
headlight is on), light from the headlight oscillates in response
to vibrations of the vehicle body. Accordingly, the driver is
visually sensitive to vibrations. Further, at night, the amount of
information is smaller than in the daytime. Therefore, it may be
necessary to cope with a situation in which the driver has to brake
suddenly or turn the steering wheel suddenly. For these reasons,
the filter constants are set as stated above.
[0198] In the twelfth embodiment, when the headlight is on, the
values of the time constants T1, T2, T3 and T4 are determined so as
to provide gain characteristics represented by the segment T11 in
FIG. 28. Accordingly, the controlled variable can be increased in
all the frequency regions. Thus, it is possible to suppress
vibrations during running at night.
[0199] It should be noted that the headlight information may be
replaced by (1) clock information, (2) a combination of clock
information (time) and calendar IC information (date), or (3)
detected information from a sensor for detecting the amount of
light (sunshine information).
[0200] The arrangement may also be such that the filter constants
of the relative velocity estimation unit 16 are changed on the
basis of detected information (friction coefficient information)
from a sensor for detecting the coefficient of friction of a tire
with respect to the road surface (a thirteenth embodiment of the
present invention). In the thirteenth embodiment, for example, when
the friction coefficient is small, the values of the time constants
T1, T2, T3 and T4 are determined so as to provide gain
characteristics represented by the segment T10 in FIG. 28. When the
friction coefficient is large, the values of the time constants T1,
T2, T3 and T4 are determined so as to provide gain characteristics
represented by the segment T11 in FIG. 28.
[0201] When the friction coefficient of the tire is small owing to
the weather or the road surface condition, if the controlled
variable is increased easily, the vehicle is likely to become
unstable owing to variations in ground contact force of the tire.
Therefore, when the friction coefficient is small, the gain is
increased (i.e. the gain characteristics are adjusted to those
represented by the segment T10 in FIG. 28) so that the suspension
characteristics (controlled variable) weaken.
[0202] It should be noted that the friction coefficient information
may be replaced by (1) the rate of change in wheel speed, (2) wiper
operation information, or (3) detected information from a raindrop
sensor.
[0203] The arrangement may also be such that the filter constants
of the relative velocity estimation unit 16 are changed on the
basis of vehicle dive detection information (a fourteenth
embodiment of the present invention), instead of using the steering
speed as in the sixth embodiment. In the fourteenth embodiment, for
example, when no dive is detected, the values of the time constants
T1, T2, T3 and T4 are determined so as to provide gain
characteristics represented by the segment T10 in FIG. 28. When
dive is detected, the values of the time constants T1, T2, T3 and
T4 are determined so as to provide gain characteristics represented
by the segment T11 in FIG. 28.
[0204] The arrangement may also be such that the filter constants
of the relative velocity estimation unit 16 are changed on the
basis of vehicle squat information (a fifteenth embodiment of the
present invention), instead of using the steering speed as in the
sixth embodiment. In the fifteenth embodiment, for example, when no
squat is detected, the values of the time constants T1, T2, T3 and
T4 are determined so as to provide gain characteristics represented
by the segment T10 in FIG. 28. When squat is detected, the values
of the time constants T1, T2, T3 and T4 are determined so as to
provide gain characteristics represented by the segment T11 in FIG.
28.
[0205] Next, a sixteenth embodiment of the present invention will
be described with reference to FIGS. 30 to 36. It should be noted
that illustration and description of members or portions equivalent
to those in the first and seventh embodiments (FIGS. 1 to 29) are
omitted according to circumstances.
[0206] The sixteenth embodiment differs from the sixth embodiment
mainly in the following points (a) to (c):
[0207] (a) As shown in FIG. 30, the controller 7 is provided with a
map selecting unit 18A.
[0208] (b) The controller 7 changes elements (dead zone height H1,
dead zone width W, limit value H2, etc.) of the conversion segment
60 of a map (FIG. 35) in the absolute value computing unit 15,
whereas the controller 7 in the sixth embodiment varies the values
of the time constants T1, T2, T3 and T4 [and hence changes the
filter constants (gain and phase) of the relative velocity
estimation unit 16].
[0209] (c) A map selection subroutine (step S7D) shown in FIGS. 31
and 32 is provided in place of the time constant determination
subroutine (step S7C) shown in FIGS. 26 and 27.
[0210] The absolute value computing unit 15 has the conversion
segment 60 stored therein in a map form in which the signal C is
plotted along the abscissa axis, and the gain D along the ordinate
axis. The conversion segment 60 has elements (dead zone height H1,
dead zone width W, limit value H2, and inclination angle .beta.)
arranged to be changeable. The change of the elements is effected
by the map selecting unit 18A. As shown in the frame indicating the
absolute value computing unit 15 in FIG. 30 and also shown in FIG.
35, the conversion segment 60 keeps the gain D at a constant level
when the signal C assumes a value in the neighborhood of "0"
(including "0"). For the sake of convenience, the region where the
gain D is kept at a constant level will hereinafter be referred to
as "dead zone", and the gain D at a constant level in the dead zone
will be referred to as "dead zone height H1". Further, the width of
the signal C from the minimum value (left-hand side) to the maximum
value (right-hand side) in the dead zone will be referred to as
"dead zone width W [conversion characteristics].
[0211] The conversion segment 60 has a predetermined angle of
inclination (rate of change) .beta. [conversion characteristics] in
a +(plus)-side region in which the signal C exceeds the dead zone
(the right-hand region in FIG. 35) and also in a -(minus)-side
region in which the signal C is below the dead zone (the left-hand
region in FIG. 35). Further, when the signal C becomes larger a
predetermined magnitude in the plus-side region or becomes smaller
than a predetermined magnitude in the minus-side region, the gain D
is kept at a constant level (hereinafter referred to as "limit
value H2") [conversion characteristics].
[0212] At step S7D (map selection subroutine), as shown in FIG. 32,
the controller 7 judges whether or not the steering speed R11 is
less than the steering speed reference value R10 (step SLOD). If it
is judged at step SLOD that the steering speed R11 is less than the
steering speed reference value R10 (YES), the controller 7 executes
an operation for setting a map first segment 60a (see Table 2 in
FIG. 34) at step S11D, and then returns to the main routine. If it
is judged at step S10D that the steering speed R11 is not less than
the steering speed reference value R10 (NO), the controller 7
executes an operation for setting a map second segment 60b (Table 2
in FIG. 34), and then returns to the main routine.
[0213] The elements (dead zone height H1, dead zone width W, limit
value H2, and inclination angle .beta.)[conversion characteristics]
of the conversion segment 60 (the map first segment 60a and the map
second segment 60b) are arranged to be changeable so that the
magnitude of the controlled variable (command current I) changes
according to the magnitude of the value of each element, as shown
in Table 1 of FIG. 33. In this embodiment, the size of each element
is set as shown in Table 2 of FIG. 34, so that when the map first
segment 60a is set, the controlled variable becomes small, whereas
when the map second segment 60b is set, the controlled variable
becomes large.
[0214] In the sixteenth embodiment arranged as stated above, when
the steering speed R11 is not less than the steering speed
reference value R10, the map second segment 60b (Table 2 in FIG.
34) is set (step S12D). Consequently, the controlled variable
(command current I) becomes large. Accordingly, it is possible to
improve steering stability and ride quality.
[0215] In addition, the elements (dead zone height H1, dead zone
width W, limit value H2, and inclination angle .beta.) [conversion
characteristics] of the conversion segment 60 (the map first
segment 60a and the map second segment 60b) are changeable. Thus,
the controlled variable (command current I) is changed according to
the size of the value of each element. This makes it possible to
ensure damping characteristic control of high accuracy.
[0216] In the sixteenth embodiment, all the elements (dead zone
height H1, dead zone width W, limit value H2, and inclination angle
.beta.) of the conversion segment 60 (the map first segment 60a and
the map second segment 60b) are changed, by way of example.
However, the arrangement may be such that one, two or three of the
elements (dead zone height H1, dead zone width W, limit value H2,
and inclination angle .beta.) are changed to change the controlled
variable (command current I).
[0217] For example, the arrangement may be such that for a map
first segment 60a shown by the solid line in FIG. 35 and by the
dotted line in FIG. 36, only the dead zone height H1 and the dead
zone width W are changed to set a map second segment 60b shown by
the solid line in FIG. 36. For the map first segment 60a and the
map second segment 60b, the limit value H2 and the inclination
angle .beta. are set equally. In terms of the dead zone height Hi
or the dead zone width W, the map second segment 60b is shorter
than the map first segment 60a.
[0218] By changing the dead zone as shown in FIG. 36, it is
possible to change the controlled variable only for vibrations that
give a low estimated relative velocity without changing the damping
characteristics for vibrations that give a high estimated relative
velocity. Thus, it becomes possible to suppress slight
vibrations.
[0219] In the sixteenth embodiment, the change of each element of
the conversion segment 60 (the map first segment 60a and the map
second segment 60b) is made on the basis of the steering speed.
However, the steering angle may be used in place of the steering
speed.
[0220] Further, the change of each element of the conversion
segment 60 (the map first segment 60a and the map second segment
60b) may be made by using information as shown below.
[0221] (1) Brake information (detected signal from the brake
switch, deceleration, a combination of deceleration and brake
switch information, longitudinal acceleration, or the rate of
change in longitudinal acceleration).
[0222] (2) Inter-road/vehicle information, or inter-vehicle
information.
[0223] (3) Information (user option information) obtained from a
vehicle characteristic selecting switch for selecting a sports
mode, a regular mode, etc.
[0224] (4) Throttle information (throttle opening information,
throttle opening speed, the rate of change in vehicle speed, or a
combination of the vehicle speed change rate and throttle opening
information).
[0225] (5) Time information (headlight information, clock
information, a combination of clock information and calendar IC
information, or detected information from a light-intensity
detecting sensor).
[0226] (6) Coefficient of friction of tire with respect to the road
surface (the rate of change in wheel speed, wiper operation
information, or detected information from a raindrop sensor).
[0227] (7) Road surface condition information (acceleration,
detected information from a vehicle height sensor, or detected
information from a non-contact road surface sensor).
[0228] (8) Vehicle mode (bouncing, pitching, or rolling)
[0229] (9) Vehicle speed information (vehicle speed, wheel speed, a
combination of gear position information and engine speed
information, or information from GPS).
[0230] (10) Vehicle weight information (seat switch information,
air suspension pressure information, shock absorber cylinder
pressure information, gasoline gauge information, seat belt ON/OFF
signal, or light optical-axis adjustment information).
[0231] As has been detailed above, the suspension control system
according to the present invention eliminates the phase difference
of the acceleration of vibration data with respect to the estimated
piston speed in the sprung mass resonance frequency band.
Accordingly, it is possible to generate damping force closer in
magnitude to damping force expected in control based on the
sky-hook damper theory. Thus, it is possible to achieve an
improvement in controllability.
[0232] Further, in high-frequency regions, the controlled variable
can be reduced positively. Thus, it is possible to minimize
degradation of ride quality caused by a delay in control and hence
possible to ensure favorable ride quality.
[0233] In addition, the use of a damping characteristic inverting
type shock absorber dispenses with a vehicle height sensor and
hence makes it possible to attain high performance at reduced
costs.
[0234] Further, according to the present invention, the phase
adjustment for the detected signal is made on the basis of
adjusting parameters for the detected signal, and the
characteristics of the adjusting parameters are changed. Therefore,
it becomes possible to adjust the controlled variable (control
signal) by changing the characteristics of the adjusting
parameters. Thus, it is possible to ensure damping characteristic
control of high accuracy.
[0235] Further, according to the present invention, the relative
velocity obtained from the relative velocity estimation unit is
converted into a signal for generating the control signal on the
basis of predetermined conversion characteristics, and the
conversion characteristics are changed according to the condition
of the vehicle or/and the road surface condition. Therefore, it is
possible to change the controlled variable (control signal)
according to the condition of the vehicle or/and the road surface
condition and hence possible to effect damping characteristic
control with correspondingly high accuracy.
[0236] Further, according to one aspect of the invention, the
aforesaid adjusting parameters are varied based on a vehicle
condition related to a weight of the vehicle. Thus, it is possible
to ensure damping characteristic control of high accuracy even when
the vehicle weight varies due, to change in the number of
passengers and luggage load, for instance.
[0237] Further, according to another aspect of the invention, the
aforesaid adjusting parameters are varied based on a vehicle
condition related to a speed of the vehicle. Thus, it is possible
to ensure damping characteristic control of high accuracy even when
the vehicle speed varies, due to a road condition, for
instance.
[0238] Further, according to another aspect of the invention, the
aforesaid adjusting parameters are varied based on a vehicle
condition related to a change in attitude of the vehicle. Thus, it
is possible to ensure damping characteristic control of high
accuracy even when the vehicle's attitude varies, as it turns,
accelerates or decelerates, for instance.
[0239] Further, according to another aspect of the invention, the
aforesaid conversion characteristics are varied based on a vehicle
condition related to a change in a weight of the vehicle. Thus,
even when the weight of the vehicle varies, due to change in the
number of passengers and luggage load, for instance, it is possible
to change a value of control (control signal) depending on the
change in the vehicle weight. Therefore, it is possible to ensure
damping characteristic control of high accuracy.
[0240] Further, according to another aspect of the invention, the
aforesaid conversion characteristics are varied based on a vehicle
condition related to a speed of the vehicle. Thus, even when the
speed of the vehicle varies, due to a change in road condition, for
instance, it is possible to vary an amount of control (control
signal) depending on the change in the vehicle speed. Therefore, it
is possible to ensure damping characteristic control of high
accuracy.
[0241] Further, according to another aspect of the invention, the
aforesaid conversion characteristics are varied based on a vehicle
condition related to a change in attitude of the vehicle. Thus,
even when the vehicle's attitude varies, as it turns, accelerates
or decelerates, for instance, it is possible to vary an amount of
control (control signal) depending on the change I the vehicle's
attitude. Therefore, it is possible to ensure damping
characteristic control of high accuracy.
[0242] Further, according to another aspect of the invention, an
acceleration sensor is used as a sprung mass vibration detecting
device and a relative velocity estimation device uses an
acceleration detected with the acceleration sensor as an estimated
relative velocity between the sprung member and unsprung member.
Thus, reduction in cost for producing a suspension control system
is realized with a cheap acceleration sensor.
[0243] It should be noted that the present invention is not
necessarily limited to the foregoing embodiments but can be
modified in a variety of ways without departing from the gist of
the present invention.
* * * * *