Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-07-25
2002-08-13
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S038000, C280S005514, C280S005515, C180S902000
Reexamination Certificate
active
06434460
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a suspension control system for use in a vehicle.
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.
The above-described conventional suspension control system effects control resembling a control method based on the sky-hook damper theory.
According to the sky-hook damper theory, the damping coefficient C
1
of the shock absorber (damper) provided between the vehicle body and the axle is obtained as follows.
Assuming that:
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;
if the following condition is satisfied;
V
(
V−X
)>0
the damping coefficient C
1
is determined as follows:
C
1
=
CZV/
(
V−X
) (1)
If the following condition is satisfied;
V
(
V−X
)<0
the damping coefficient C
1
is determined as follows:
C
1
=0 (2)
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 C
1
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 C
1
on the basis of the sky-hook damper theory as follows:
If V(V−X)>0,
C
1
=
KV/M
(1a)
If V(V−X)<0,
C
1
=Cmin (2a)
In the above Equations (1a) and (2a), K is a constant and Cmin≠0.
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).
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 C
1
for extension and Cmin for compression is selected, and damping force for extension is controlled on the basis of C
1
. When V<0, a combination of Cmin for extension and C
1
for compression is selected, and damping force for compression is controlled on the basis of C
1
.
The system may be arranged so that when C
1
is positive, the damping coefficient for extension is controlled, whereas when C
1
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 C
1
obtained by using the following Equation (1b):
C
1
=
KV/|M|
(1b)
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].
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
The present invention was made in view of the above-described circumstances.
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.
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.
Preferably, the phase adjustmen
Ichimaru Nobuyuki
Kobayashi Takahide
Uchino Toru
Uchiyama Masaaki
Nguyen Tan
Tokico Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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