Page 350 - Mechatronics for Safety, Security and Dependability in a New Era

Ch68-I044963.fm Page 334 Tuesday, August 1, 2006 8:30 PM
Ch68-I044963.fm
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334 Page 334 Tuesday, August 1, 2006 8:30 PM
that the on/off valve has a simple configuration and, furthermore, can be a logical interface between a
computer and hydraulic systems. Hence, a low cost and highly reliable system may be developed,
under the recent condition that the systems are equipped with computers.
In the present study, we propose an active control hydro-pneumatic suspension system composed of
high speed on/off solenoid valves which are driven in a PWM (Pulse Width Modulation) digital mode.
In order to realize a robust control system even when measurement errors exist, we adopted a preview
control method equipped with an ADF (adaptive digital filter). The experiment was performed by
using a bench system which physically simulates induced vibrations from the road and also simulates
the body mass of an automobile. The results obtained from the system using preview control with an
ADF were compared with those obtained from a system using a conventional sky-hook control.

CONSTITUTION OF THE ACTIVE SUSPENSION SYSTEM

p p
s s
M M b b
Mb
Valve-1
Va l v e - 1 x b x b
at
Ac
Actuator
or
t
u
p g p g
x g x g
p p a1 p p a2
a2
a1
rin
p
G Gas spring g
a
s s
M M w w x x
Mw
Valve-2
V al ve- 2 w w
K t K t
x x r r
Figure 1: The outline of the system used for the experiment
The configuration of the new system proposed in this study is shown in Figure 1. The pressure
control valve, which is used in a conventional active suspension system, is replaced by two on/off
valves (valves 1 and 2). The valves are of a high-speed solenoid type. In this system, the supply flow
rate to the cylinder is controlled by either valve 1 or valve 2 according to the PWM-signal. The
constitution of the on/off valve is illustrated in Figure 2.
o pump or reservoir
To pump or reservoir
Poppet valve
Poppet valve
u u
a
a
o
e t
g
V
na
g
l
v
o
Si Signal voltage to Valve1 e 1
t
lv
l
a
V
lv
o
na
l
v
Linear Spring Si Signal voltage to Valve2 e 2
Spring
g
a
g
e t
o
l
t
solenoid To cylinder
cylinder
Figure 2: Structure of a high-speed ON/OFF valve Figure 3: PWM (Pulse-Width-Modulation )
The poppet in the valve is actuated by the on/off input voltage applied to the solenoid and thus the
flow rate through the valve is controlled in digital mode in accordance to a duty signal. Tn the
following, the principle of the PWM method adopted in this study is demonstrated based on the
experimental results shown in Figure 3.
In Figure 3, the signal u denotes the control input (=Duty) and the triangle waves are carrier waves.
The input signal voltage to valves 1 and 2 is generated by comparing the control input u with the
triangle carrier waves as shown in the figure.