Note: Descriptions are shown in the official language in which they were submitted.
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A SOLENOID VALVE CONTROL DEVICE
FIELD OF THE INVENTION
The present invention relates, in general, to a solenoid
valve control device and, more particularly, this invention
relates to a solenoid valve control device that controls the
switching of a three-position solenoid valve, which has
supply, overlapping and exhaust positions, with a command
current value, and which may be applied to a brake device for
a railway vehicle.
BACKGROUND OF T~E lNV~N'l'ION
Pneumatic devices have hitherto been applied to brake
devices for railroad cars. This type of device is configured
so as to output an output pressure using a solenoid valve,
amplify the volume of this output pressure into a brake
pressure with a relay valve, and actuate the brake cylinder
with this brake pressure.
A three-position solenoid valve, which has a first port
connected to the atmosphere, a second port connected to the
air supply reservoir, and a third port connected to the relay
valve, may, for example, be applied as the solenoid valve for
producing the output pressure. That is, this three-position
solenoid valve can adopt an exhaust position for exhausting
the air in the relay valve by connecting the first port with
the third port, a supply position for supplying compressed air
from the air supply reservoir to the relay valve by connecting
the second port with the third port, and an overlapping
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("lap") position for holding the output pressure by closing
off all of the first, second and third ports.
Details of the configuration of such a three-position
solenoid valve can be found in, "~x~;ned Japanese Utility
Model Publication" (JP-B-U) No. H 7-31020 (1995).
By operating a brake controller provided on the driver's
seat of the railroad car, it is possible to output a brake
command with a total of 8 levels from level 0 to level 7.
Based on this brake command, the solenoid valve control device
produces a three-level excitation current for controlling the
position of the three-position solenoid valve to the~exhaust
position, supply position or overlapping position. When there
is a difference between the excitation currents needed to move
from the exhaust position to the overlapping position and from
the supply position to the overlapping position, the
excitation current corresponding to the overlapping position
may also be set at two levels. In this case, an excitation
current with a total of four levels may be input to the three-
position solenoid valve.
However, with this configuration wherein the three-
position solenoid valve is controlled with a three-level or
four-level excitation current, it has not been possible to
avoid the occurrence of overshoot or undershoot.
Consequently, it takes some time for the pressure output from
the three-position solenoid valve to converge on the brake
command pressure, and as a result there has been the problem
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that the responsivity, until the desired brake pressure is
obtained, is unavoidably poor.
Also, if overshoot or undershoot occurs, the position of
the three-position solenoid valve must be repeatedly switched
over until the output pressure converges on the brake command
pressure, so that the Iifetime of the three-position solenoid
valve is reduced and there is a danger of the control becoming
unstable.
If the above-mentioned overshoot and undershoot problems
can be overcome, one can thus expect to achieve an improvement
in the damping characteristics of the railroad car, together
with increased lifetime of the brake device.
SUMM~RY OF THE INVENTION
In a presently preferred embodiment of the present
invention there is provided a solenoid valve control device,
which is a control device for a three-position solenoid valve
that is controlled by receiving a command current value
corresponding to a pressure command signal, whereby it
switches between a supply position which increases the output
pressure, an exhaust position which decreases the output
pressure, and an overlapping position which holds the output
pressure. The solenoid valve control device is characterized
in that it has an output pressure detecting means that will
detect the output pressure of the three-position solenoid
valve and a command current value calculating means that
compares the output pressure signal from this output pressure
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detecting means with the pressure command signal and, based on
the difference, calculates and outputs the cn~m~n~ current
value so as to make the output pressure signal match the
pressure command signal. Further the command current value
calculating means calculates and outputs the command current
value, based on the difference between the output pressure
signal and pressure command signal, as a current value ranging
freely between the current value at which the solenoid valve
adopts the supply position and the current value at which it
adopts the exhaust position.
OBJECT~ OF THE lNVh'N'l'l ON
It is, therefore, one of primary objects of the present
invention to provide a solenoid valve control device that can
ameliorate the response characteristics by improving the way
in which the three-position solenoid valve is controlled to
output the output pressure.
Another object of the present invention is to provide a
solenoid valve control device with enhanced longevity and
reliability.
Still another object of the present invention is to
provide a solenoid control device wherein the desired brake
pressure can be reliably produced irrespective of the
hysteresis characteristics of the driving resistance force.
Yet another object of the present invention is to provide
a solenoid control device wherein it is possible to calculate
the command current value so that overshoot and undershoot do
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not occur.
An additional object of the present invention is to
provide a solenoid control device wherein it is possible to
use fuzzy control means to calculate the command current value
by using the membership functions of fuzzy sets corresponding
respectively to "much larger", "somewhat larger", "roughly
equal", "somewhat smaller", and "much smaller".
A further object of the present invention is to provide a
solenoid control device wherein a time variation rate of the
output signal is included in the input to the fuzzy reasoning
in order to suppress or prevent overshoot and undershoot even
more effectively.
Still yet another object of the present invention is to
provide a solenoid control device wherein, it is preferabie
that the output pressure signal from the output pressure
detecting means is compared with the pressure co~-n~ signal,
and the fuzzy control means calculates the command current
value by using the membership functions of fuzzy sets
corresponding respectively to "much larger", "somewhat
larger", "roughly equal", "somewhat smaller", and "much
smaller", and by using the membership function of a fuzzy set
corresponding respectively to whether the time variation rate
of the output pressure signal from the output pressure
detecting means is "large and positive", "roughly zero", or
"negative with a large absolute value".
It is also an object of the present invention to provide
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a solenoid control device wherein it is possible to implement
accurate control of the output pressure by eliminating the
hysteresis characteristics relating to the driving resistance
force of the three-position solenoid valve.
In addition to the objects and advantages of the present
invention which has been described in detail above, various
other objects and advantages will become readily apparent to
those persons skilled in solenoid valves from the following
more detailed description of such invention, particularly,
when such description is taken in conjunction with the
attached drawing Figures and with the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram showing the schematic
configuration of a solenoid valve device according to one
embodiment of the present invention.
Figure 2 is a block diagram showing the configuration of
a brake pressure output device.
Figure 3 is a chart showing the membership functions of
the condition part and conclusion part of the fuzzy rules,
wherein (a) shows the membership functions corresponding to
the pressure difference between the output pressure and the
command pressure, (b) shows the membership functions
corresponding to the gradient of the output pressure, and (c)
shows the membership functions corresponding to the command
current value.
Figure 4 is a chart for explaining one example of the
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fuzzy reasoning wherein MIN-MAX is applied for use in the
evaluation of the fuzzy rules and the center-of-gravity method
is applied for de-fuzzification.
Figure 5 is a chart for describing another example of
fuzzy reasoning.
BRIEF DESCRIPTION OF T~E PRESENTLY
PREFERRED AND VARIOUS ALTERNATIVE
EMBODIMENTS OF THE PRESENT lNV~NlION
Prior to proceeding to the more detailed description of
the various embodiments of the invention, it should be noted
that, for both the sake of clarity and understanding of the
three position solenoid valve according to the present
invention, identical components which have identical functions
have been identified with identical reference numerals
throughout the several views which have been illustrated in
the attached drawing Figures.
An embodiment of a solenoid valve control device
according to this invention is described in detail below.
Figure 1 is a block diagram showing the schematic
configuration of a railway vehicle brake control device to
which one embodiment of this invention has been applied,
wherein the configuration for a single car is shown.
In this embodiment, a car (not shown) is equipped with
two trucks 1 and 2. The trucks 1 and 2 are each equipped with
a pair of axles 11, 12 and 21, 22, respectively, and wheels
(not shown) are fixed to the two ends of each axle.
Pneumatically-operated brake cylinders BCll, BC12 and BC21,
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BC22 are installed in relation to each axle. The pair of
brake cylinders provided on one truck are made so that their
respective brake pressures are applied from brake pressure
output devices 15, 25, 35 and 45.
The brake pressures output by such brake pressure output
devices 15, 25, 35 and 45 are controlled based on a normal
brake command or an emergency brake command depending on the
operation of a brake controller provided for the engineer of
the train, rotation rate signals for each axle, which are
detected by speed sensors (not shown), and the output signal
of a load-responding instr.ument 51 which detects either the
load on the car or the load on the trucks 1 and 2.
More specifically, the normal brake command and emergency
brake command are input to the brake pattern unit 52 of a
brake control unit 50 along with the output signal of load-
responding instrument 51. Based on the input signals, brake
pattern unit 52 calculates the pressure command signals for
each wheel in order to perform normal brake control and
emergency brake control, and outputs individual command
signals to brake pressure output devices 15, 25, 35 and 45.
Also, the speed signals from the speed sensors are input
to a slip control unit 53 for preventing the wheels from
slipping on the rails. This slip control unit 53 calculates
pressure command signals for performing slip control and
outputs signals to each brake pressure output device 15, 25,
35 and 45.
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Brake pressure output devices 15, 25, 35 and 45 supply
appropriate brake pressures to brake cylinders BC11, BC12 and
BC21, BC22, respectively, based on the pressure command
signals from brake control unit 50.
Figure 2 is a block diagram illustrating, in simplified
form, the configuration of the brake pressure output device 15
that corresponds to axle 11. It should be noted that the
remaining brake pressure output devices 25, 35 and 45 have a
similar configuration.
Brake pressure output device 15 comprises a relay valve
60 for supplying a brake pressure to the brake cylinder BC11,
a three-position solenoid valve 61 that supplies the output
pressure to relay valve 60, a constant-current control
amplifier 62 that outputs a driving current for driving three-
position solenoid valve 61, and a fuzzy control unit 65 that
uses fuzzy reasoning to calculate and output a command current
value for determining the current to be output by this
constant-current control amplifier 62.
The pressure command signal from brake control unit 50 is
input to fuzzy control unit 65. Furthermore, there is an
output pressure sensor 64 for detecting the output pressure
output by three-position solenoid valve 61 installed in
relation to this three-position solenoid valve 61. The output
pressure signal from this output pressure sensor 64 is
amplified by amplifier 67 and fed back to fuzzy control unit
65. Fuzzy control unit 65 regularly samples the output signal
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from such output pressure sensor 64 in specific sampling
periods (e.g. 5 milliseconds).
Three-position solenoid valve 61 uses technology known
hitherto, and has a configuration such as that disclosed in,
for example, "Examined Japanese Utility Model Publication"
(JP-B-U) No. H7-31020 (1995). That is, three-position
solenoid valve 61 has a first port P1 connected to the
atmosphere, a second port P2
connected to air supply reservoir 70, and a third port P3
connected to pressure chamber 60a of relay valve 60. As
mentioned earlier, the air pressure output from third port P3
is the output pressure, and this output pressure is monitored
by output pressure sensor 64.
Three-position solenoid valve 61 is driven by a current
supplied ~rom constant-current control amplifier 62, and can
selectively adopt any of three positions: an exhaust position,
a supply position, and an overlapping (lap) position. In the
exhaust position, first port P1 is connected with third port
P3, and the output pressure decreases. In the supply
position, second port P2 is connected with third port P3, and
the output pressure increases. In the overlapping position,
first, second and third ports P1, P2 and P3 are all closed
off, and the output pressure is held.
Based on the pressure command signal output by brake
control unit 50 and the output pressure signal from output
pressure sensor 64, fuzzy control unit 65 uses fuzzy reasoning
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to calculate and output the command current value as a current
value ranging freely between the current at which solenoid
valve 61 adopts the supply position and the current at which
it adopts the exhaust position. When a current of this
command current value is output from constant-current control
unit 62, the position of three-position solenoid valve 61 is
controlled to the exhaust position, the supply position or the
overlapping position.
In this embodiment, the command current value output by
fuzzy control unit 65 can adopt an essentially continuous
value. Three-position solenoid valve 61 can thus adopt
positions that restrict the flow rate, such as an intermediate
position between the exhaust position and overlapping
position, or an intermediate position between the supply
position and overlapping position. For example, at an
intermediate position between the exhaust position and the
overlapping position, first port P1 and third port P3 are
incompletely blocked off and consequently the output pressure
gradually decreases. Similarly, at an intermediate position
between the supply position and the overlapping position,
second port P2 and third port P3 are incompletely blocked off
and consequently the output pressure gradually increases.
The volume of the pressure output by three-position
solenoid valve 61 is amplified by relay solenoid valve 60 and
converted into a brake pressure. This brake pressure is
supplied to brake cylinders BCll and BC12.
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Next, the fuzzy reasoning of fuzzy control unit 65 is
described. In this embodiment, the fuzzy input is taken to be
the difference between the output pressure signal from output
pressure sensor 64 and the pressure command signal, or in
other words the difference between the output pressure
detected by output pressure sensor 64 and the command pressure
(brake command pressure) which is the target pressure (this
dif~erence in pressure is referred to as the "pressure
difference" hereinbelow). Furthermore, the time variation
rate of the output signal from output pressure sensor 64, or
in other words the time variation rate of the output pressure
(referred to as the "output pressure gradient" hereinbelow) is
also taken as the fuzzy input. Table 1 below shows one
example of the fuzzy rules.
TABLE 1
Rule ~ p~rt
nO. Output ~ . of output C~ - ~~ purt
mueh lurger ~PL~ ; ~L~
2 ~ t Isrger ~PM~ otrongl~ I ~ .e ~PL~ ~L~
3 ~ o~ rger ~PM~ gentle ~zn~ - ~L~
4 ~ P - l~rger ~PM~ ~trongl~ - f ''.~ ~L~ lup ~ZR~
roughtl~ equ~ZR~ Inp ~Zl~
G r- ~ om~ller ~M~ drongl~ I - .e ~PL~ y ~ZR~
7 _ .A omdler ~gentle ~ZR~ ouppl~ ~YL~
om~ller ~M~ otrongl~ ~L~ ouppl~ ~PL~
g mueh om~-llerINL~ ouppl~ ~PL~
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Rules No. 1, 5 and 9 should be self-explanatory. Rules
No. 2, 3 and 4 correspond to the case where the output
pressure is somewhat larger than the command pressure. In
this case, the gradient of the output pressure is brought into
consideration. That is, "exhaust NL" is the fuzzy set of the
conclusion part corresponding to the cases where the gradient
is strongly positive and where it is gentle, and "lap ZR",
which corresponds to the overlapping position, is the fuzzy
set of the conclusion part corresponding to the case where the
gradient is strongly negative. When the output pressure is
larger than the command pressure, it is necessary to reduce
the pressure by exhaust. However, when the gradient of the
output pressure is strongly negative at the point where the
output pressure approaches the command pressure, there is a
danger that the output pressure will drop below the command
pressure due to the sharp drop in pressure, giving rise to
undershoot. Rule No. 4 alleviates this sort of undershoot.
Rules No. 6, 7 and 8 act in a similar fashion. That is,
when the output pressure is lower than the command pressure,
it is necessary to increase the pressure by supply, but when
the gradient of the output pressure is strongly positive at
the point where the output pressure approaches the command
pressure, there is a danger that an overshoot will occur.
Rule No. 6 alleviates this overshoot, and the fuzzy set of
this conclusion part is "lap ZR".
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Figure 3 shows the membership functions of the condition
part and conclusion part. Figure 3 (a) shows the membership
functions corresponding to the pressure difference, Figure 3
(b) shows the membership functions corresponding to the
gradient of the output pressure, and Figure 3 (c) shows the
membership functions of the conclusion part corresponding to
the command current value.
The membership functions shown in Figure 3 (a)
respectively correspond to the fuzzy set "PL", which
corresponds to the output pressure being much larger than the
command pressure, fuzzy set "PM", which corresponds to the
output pressure being somewhat larger then the command
pressure, fuzzy set "ZR", which corresponds to the output
pressure being roughly equal to the command pressure, fuzzy
set "NM", which corresponds to the output pressure being
somewhat smaller then the command pressure, and fuzzy set
"NL", which corresponds to the output pressure being much
smaller than the command pressure.
The membership function corresponding to fuzzy set "PL"
rises up gently from the region of a 1 kgf/cm2 pressure
difference, and its grade reaches 1.0 near a pressure
difference of over 3 kgf/cm2. Also, the membership function
corresponding to fuzzy set "PM" rises up steeply in the region
of a O kgf/cm2 pressure difference, its grade will become less
than 1.0 from near a 0.5 kgf/cm2 pressure difference, and the
grade decreases gently in the region up to a 3.0 kgf/cm2
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pressure difference. The membership function corresponding to
fuzzy set ZR rises up fairly steeply from near a -0.6 kgf/cm2
pressure difference, has a grade of 1.0 in the region of
pressure differences from -0.2 kgf/cm2 to near O kgf/cm2,
drops off steeply at a pressure difference of O kgf/cm2, and
then extends up to the region of 3 kgf/cm2 without changing
its gradient. The membership function corresponding to fuzzy
set "NM" rises up gently from near a pressure difference of -
3kgf/cm2, its grade peaks at 0.5 near a pressure difference of
-0.1 kgf/cm2, and thereafter it drops off steeply toward a
pressure difference of O kgf/cm2. The membership function
corresponding to fuzzy set "NL" has a grade of 1.0 in the
region below a pressure difference of about -3.5 kgf/cm2, the
grade gently decreasing in the region of greater pressure
difference, and becoming zero near a pressure difference of -
1.5 kgf/cm2.
When the case of a zero pressure difference is taken as a
base point, it can be seen that the membership functions are
asymmetric between positive and negative pressure differences.
This results from giving consideration to the hysteresis
characteristics of three-position solenoid valve 61. That is,
when the spool for driving the valve body disposed within such
three-position solenoid valve 61 is driven in one direction,
the resistance force due to the springs pressing on the valve
body and on the mechanical friction of the seal members and
the like differs from when it is driven in the other
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direction. Consequently, when the brake pressure is to be
increased or decreased, the driving current applied to three-
position solenoid valve 62 must be changed. By using the
asymmetric membership functions, it is possible to eliminate
the hysteresis effects and to control three-position solenoid
valve 62 satisfactorily.
When determining the membership functions of Figure 3 (a)
corresponding to the pressure difference between the output
pressure and the command pressure, it is preferable to
evaluate some or all of the following: step braking, step
releasing, stepping, single-step braking, analog increase, and
analog decrease. Step braking is a way of applying the brakes
so that the brake pressure is increased by specific increments
in a stepwise fashion. Also, step releasing is a way of
releasing the brakes so that the brake pressure is decreased
by specific increments in a stepwise fashion. Furthermore,
stepping is varying the brake pressure by two or more steps at
a time.
Single-step braking is the application of brake pressure
from the zero state to the fourth or higher step in one go.
Also, analog increase and analog decrease are the continuous
monotonic increase and decrease of brake pressure. Items that
can be evaluated when the brake pressure is changed are the
size of the overshoot or undershoot, and the size of the
difference between the output pressure and command pressure.
16
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Figure 3 (b) shows the membership functions respectively
corresponding to fuzzy set "NL", which corresponds to a sudden
negative change in the output pressure, fuzzy set "ZR", which
corresponds to a gentle change in the output pressure, and
fuzzy set "PL", which corresponds to a sudden positive change
in the output pressure. The membership function corresponding
to fuzzy set "NL" has a grade of 1.0 in the region where the
gradient of the output pressure is less than about -0.017
kgf/cm2 per sampling period, the grade then falls off
gradually at higher gradients, and the grade ~ecomes zero at a
gradient of generaally about -0.005 kgf/cm2 per sampling
period. Also, the membership function corresponding to fuzzy
set "ZR" rises up from near a gradient of -0.0017 kgf/cm2 per
sampling period, reaches a grade of 1.0 at a gradient of 0
kgf/cm2 per sampling period, then gradually falls away again
so that the grade becomes zero near a gradient of 0.017
kgf/cmZ per sampling period. Furthermore, the membership
function corresponding to fuzzy set "PL" rises up near a
gradient of 0.005 kgf/cm2 per sampling period, and the grade
becomes 1.0 above a gradient of about 0.017 kgf/cm2 per
sampling period.
As can be seen from Figure 3 (b), the membership
functions relating to the gradient of the output pressure have
a shape that is symmetrical about the negative region and
positive region, taking zero as a base point. The membership
functions of the conclusion part shown in Figure 3 (c) are
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simple. That is, the command current values corresponding to
the exhaust, overlapping and supply positions are triangular
functions centered on H mA (milliamps), L mA and K mA
respectively.
Figure 4 explains the fuzzy reasoning process when MIN-
MAX is applied for the evaluation of the fuzzy rule and when a
center-of-gravity method is applied for de-fuzzification. An
example of the input to the fuzzy reasoning is as follows:
~ pressure difference between output pressure and
command pressure: 0.07 kgf/cmZ
~ gradient of output pressure: 0 kgf/cm2 per
sampling period
The membership functions corresponding to the fuzzy sets
"PM" and "ZR" have meaningful grades with respect to the
pressure difference of this input example. That is, the grade
for fuzzy set "PM" is 0.9, and the grade for fuzzy set "ZR" is
0.6. Also, the membership function for fuzzy set "ZR", whose
grade is 1.0, has a meaningful grade with respect to the
gradient of the abovementioned input example. It can thus be
seen that of the fuzzy rules in the abovementioned Table 1,
the applicable rules are rule No. 3 and rule No. 5.
In the MIN method, the smaller value of the outputs
corresponding to two conditions is taken as the final output,
so that the output for rule No. 3 is 0.9. The conclusion part
is thus the fuzzy set "NL" of grade 0.9. Also, the output for
rule No. 5 is 0.6, and the fuzzy set "ZR" of grade 0.6 is
18
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obtained as the conclusion part.
The fuzzy sets of the conclusion part obtained in this
way are synthesized with the MAX method, and furthermore, the
command current value is obtained by finding the center of
gravity. In this case, the center of gravity (the command
current value) may be found based on the surface areas of the
membership functions of the fuzzy sets "NL" and "ZR" after
synthesis, and the command current value may be determined by
the following formula.
H ~ 0.9 + L 0.6
(command current value) =
0.9 + 0.6
Figure 5 shows an example of the reasoning for another
input example. The input example is as follows:
~ pressure difference between output pressure and
command pressure: 1.5 kgf/cm2
~ gradient of output pressure: 0.01 kgf/cm2 per
sampling period
For a pressure difference of 1.5 kgf/cm2, the membership
functions of fuzzy sets "PL" and "PM" each have meaningful
values. Also, for an output pressure gradient of 1.5 kgf/cm2
per sampling period, fuzzy sets "PL" "ZR" have meaningful
values. Thus of the fuzzy rules in Table 1, rules No. 1, No.
2, No. 3 and No. 5 are applicable. Therefore, when the
condition part is evaluated by applying the MIN method to each
19
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rule for, fuzzy set "NL" of grade 0.6 is obtained for rule No.
1, fuzzy set "LN" of grade 0.4 is obtained for rule No. 2,
fuzzy set "ZR" of grade 0.4 is obtained for rule No. 3, and
fuzzy set "ZR" of grade 0.3 is obtained for rule No. 5.
A synthesized membership function is therefore obtained
by applying the MAX method to synthesize the fuzzy sets of the
conclusion parts obtained corresponding to each rule,
including fuzzy set "NR" of grade 0.6 and fuzzy set "ZR" of
grade 0.4. The command current value is obtained by de-
fuzzifying this synthesized membership function by applying
the center-of-gravity method.
With this embodiment, a command current value
corresponding to the current to be applied to three-position
solenoid valve 61 is thus calculated by fuzzy reasoning and
output, taking the gradient of the output pressure and the
difference between the command pressure and the output
pressure detected by output pressure sensor 64 as the fuzzy
input 65. In this way, a current of a suitable value
according to the relationship between the output pressure and
command pressure and the behavior of the output pressure is
input into three-position solenoid valve 61. Feedback control
is thus performed based on the detected output pressure, so
that three-position solenoid valve 61 can be suitably
controlled.
Also, in this embodiment, the current value input to such
three-position solenoid valve 61 can take an essentially
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continuous value, so that it can be controlled smoothly
compared with the prior art in which the three-position
solenoid valve is controlled with a three-level or four-level
discrete current. More specifically, since it is possible to
control three-position solenoid valve 61 in gentle exhaust
states and gentle supply states, it is possible to prevent
sudden decreases or increases in pressure in the stage where
the output pressure has approached the command pressure. In
this way, it is possible to suppress or prevent overshoot and
undershoot, and it is thus possible for the output pressure to
approach the command pressure rapidly. Since this means that
the brake pressure that acts during braking rapidly approaches
the target pressure, the damping characteristics of the
railroad car are thereby improved.
Also, by avoiding overshoot and undershoot, three-
position solenoid valve 61 is not controlled by frequently
switching it a large number of times, and the lifetime of
three-position solenoid valve 61 is thereby increased. In
this way, the longevity and reliability of the railway vehicle
brake device can be increased.
Embodiments of this invention are not limited to the one
described above. For example, although fuzzy reasoning is used
in the embodiment mentioned above, the output of output
pressure sensor 64 and the pressure command signal can be
input to a differential amplifier circuit, and the output of
this differential amplifier circuit can be input to constant-
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. ~ ,
current amplifier 62 as the command signal. Since the output
current of constant-current amplifier 62 can also take a
continuous value in this configuration, three-position
solenoid valve 61 can adopt an overlapping position close to
the exhaust or air intake position. Consequently, overshoot
and undershoot can be effectively prevented.
Also, in this embodiment, the command current value
output by fuzzy control unit 65 was assumed to be capable of
adopting a continuous value, but it could alternatively be
capable of adopting only discrete values as long as there are
a sufficient number of them.
Furthermore, the membership functions in the description
are only one example of such, and needless to say the
membership functions can be tuned according to the preferred
and/or required degree of precision.
Also, the fuzzy reasoning method, in the above
description, is just one example of such, and there are other
rule evaluation and de-fuzzification methods that can also be
applied, such as, for example, the maximum/algebraic product
method or the alpha IDM method.
Furthermore, in the above embodiment, the example was
described where the brake pressure was controlled for each
axle, but the brake pressure may also be controlled for each
truck instead.
The solenoid valve control device of this invention can,
of course, be applied to the control of other three-position
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solenoid valves besides the three-position ~olenoid valves
that are used for the brake pressure control, and can be
altered in various ways without departing from the scope of
the technology described in the appended claims.
As described above, with an invention according to a
first embodiment the detected value of the output pressure
output by the three-position solenoid valve is fed back, and
the command current value is calculated based on the
difference between the output signal corresponding to this
output pressure and the pressure command signal, such that the
output pressure signal approaches the pressure command signal.
Consequently, it is possible to control the three-
position solenoid valve more appropriately than in the prior
art, where the command current value could only adopt either
three-level or four-level fixed values, and it is thus
possible to suppress or prevent overshoot and undershoot and
to make the output pressure converge rapidly on the command
pressure. In this way, it is possible to improve the
responsivity of the solenoid valve. Furthermore, since it is
possible to prevent the three-position solenoid valve from
being frequently switched over, it is possible to improve the
longevity and reliability of the three-position solenoid
valve.
With an invention, according to a second embodiment, the
command current value is calculated by factoring in the
temporal rate of change of the output pressure signal when the
CA 02212308 1997-08-01
output pressure signal has approached the pressure command
signal. In this way, since the output pressure approaches the
command pressure gently near the pressure command signal,
overshoot and undershoot can be suppressed. In this way,
since the output pressure can be made to converge on the
command pressure even more rapidly, the damping
characteristics of the solenoid valve device can be
ameliorated.
With an invention according to another embodiment, the
driving force applied to the three-position solenoid valve
differs when increasing and decreasing the output pressure in
order to approach the command pressure. In this way, it is
possible to cancel the effects of the hysteresis
characteristics of the driving resistance force of the three-
position solenoid valve, and the three-position solenoid valve
can be satisfactorily controlled. As a result, the co~n~
pressure can be accurately controlled.
With an invention according to still other embodiments,
the command current value may be calculated by fuzzy
reasoning, so that the command current value can be calculated
by a relatively simple software process so that overshoot and
undershoot do not occur.
With an invention according to still other embodiments,
the time variation rate of the output pressure signal is
included in the input to the fuzzy reasoning, so that the same
effect can be achieved by a simple software process.
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CA 02212308 1997-08-01
In the invention according to still another embodiment,
by the application of fuzzy reasoning, it is possible to
obtain the same effect as another embodiment of the invention
by a simple software process.
It can be seen from the above description that with a
solenoid valve control device of the present invention, the
output pressure that is output from the three-position
solenoid valve is detected by an output pressure detecting
means. The detection result of this output pressure detecting
means is fed back to the command current value calculating
means, which calculates a command current value used for
controlling the three-position solenoid valve.
The command current value calculating means compares the
output pressure signal from the output pressure detecting
means with the pressure c~ n~ signal, and calculates the
command current value based on the difference between the two.
This command current value is a value that can be utilized to
control the three-position solenoid valve so that the output
pressure signal is made to match the pressure command signal.
The command current value calculated by the command
current value calculating means is set to a current value
ranging freely between the current value at which the three-
position solenoid valve adopts the supply position and the
current at which it adopts the exhaust position, but this
command current value is preferably made capable of taking an
essentially continuous value~
CA 02212308 1997-08-01
In this way, it is possible to set the three-position
solenoid valve at intermediate positions between the exhaust
position and overlapping position, and at intermediate
positions between the supply position and overlapping
position. At these intermediate positions, it can be made to
perform gentle exhaust or supply. It is thus able to suppress
or prevent undershoot and overshoot due to sudden exhaust or
supply.
Another embodiment of the invention is characterized in
that, in the solenoid valve control device described above,
the co~-n~ current value calculating means calculates the
command current value by factoring in the time variation rate
of the output pressure signal from the output pressure
detecting means when the difference between the output
pressure signal from the output pressure detecting means and
the pressure command signal has a value within a specific
range.
With this configuration, the time variation rate of the
output pressure signal is factored into the calculation of the
command current value when the output pressure signal is close
to the pressure command signal. For example, when the output
pressure is only slightly higher than the command pressure
corresponding to the pressure command signal and the time
variation rate of the output pressure is negative with a large
absolute value, it is preferable to calculate a command
current value that can set the three-position solenoid valve
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into a gentle exhaust state. In this way, when the output
pressure has suddenly approached the command pressure while
the output pressure is falling due to the exhaust, the exhaust
rate is reduced near the command pressure. It is thus
possible to make the output pressure converge rapidly on the
command pressure by effectively suppressing or preventing
undershoot.
In the same way, when the output pressure is slightly
lower than the co n-n~ pressure and the time variation rate of
the output pressure is large and positive, it is preferable to
calculate a command current value that can set the three-
position solenoid valve into a gentle supply state. In this
way, the rate of pressure increase is reduced near the command
pressure when the supply pressure suddenly approaches the
command pressure due to the supply. Consequently, it is
possible to effectively suppress or prevent overshoot, and the
output pressure can thus be made to converge rapidly on the
command pressure.
Another embodiment of the invention is characterized in
that, in the solenoid valve control device when the difference
between the output pressure signal quantity from the output
pressure detecting means and the pressure command signal
quantity is either positive or negative, the above-mentioned
command current value calculating means calculates the command
current value so that the ratio of the variation of the
command current value differs with respect to the difference.
CA 02212308 1997-08-01
With this configuration, when the difference between the
output pressure signal quantity and the pressure command
signal quantity is positive or negative, the ratio of the
variation of the command current value differs with respect to
the difference. In other words, the driving force applied to
the three-position solenoid valve differs according to whether
the output pressure is increasing or decreasing in order to
approach the command pressure.
In this way, even when the three-position solenoid valve
exhibits so-called hysteresis characteristics whereby the
driving resistance force ~f the three-position solenoid valve
differs between going from the exhaust position to the
overlapping position and going from the supply position to the
overlapping position, this effect can be eliminated. That is,
by controlling the three-position solenoid valve properly, the
desired brake pressure can be reliably produced irrespective
of the hysteresis characteristics of the driving resistance
force.
A further embodiment of the invention, as described
above, is characterized in that, in the solenoid valve control
device, the command current value calculating means is a fuzzy
control means that calculates the command current value by
fuzzy reasoning, taking the difference between the output
pressure signal from the output pressure detecting means and
the pressure command signal as its input.
In this configuration, fuzzy reasoning is applied and, by
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CA 02212308 1997-08-01
means of simple software processing, it is thereby possible to
calculate the command current value so that overshoot and
undershoot do not occur.
In still another embodiment, of the present invention, it
is preferable that the output pressure signal from the output
pressure detecting means is compared with the pressure command
signal, and the above-mentioned fuzzy control means calculates
the command current value by using the membership functions of
fuzzy sets corresponding respectively to "much larger",
"somewhat larger", "roughly equal", "somewhat smaller", and
"much smaller'.
Yet another embodiment is characterized in that, in a
solenoid valve control device the command current value
calculating means is a fuzzy control means that obtains the
command current value by fuzzy reasoning, taking the
difference between the output pressure signal from the output
pressure detecting means and the pressure command signal, and
the time variation rate of the output pressure signal from the
output pressure detecting means as its input.
Clearly, fuzzy reasoning is also applied in this
configuration. The difference in this embodiment is that the
time variation rate of the output signal is included in the
input to the fuzzy reasoning. Since a suitable command
current value is thereby calculated according to the direction
and rate of change of the pressure, overshoot and undershoot
can be suppressed or prevented even more effectively.
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CA 02212308 1997-08-01
In a further embodiment, it is preferable that the output
pressure signal from the output pressure detecting means is
compared with the pressure command signal, and the fuzzy
control means calculates the command current value by using
the membership functions of fuzzy sets corresponding
respectively to ~-much larger", "somewhat larger", "roughly
equal", "somewhat smaller", and "much smaller", and by using
the membership function of a fuzzy set corresponding
respectively to whether the time variation rate of the output
pressure signal from the output pressure detecting means is
'-large and positive", "roughly zero", or "negative with a
large absolute value".
Still another embodiment of the invention is
characterized in that, in a solenoid valve control device the
output pressure signal from the output pressure detecting
means is compared with the pressure command signal, and the
membership functions of the fuzzy sets respectively
corresponding to "much larger", "somewhat larger", "roughly
equal", "somewhat smaller", and "much smaller" are set so as
to be asymmetric about the point where the difference between
the output pressure signal and pressure command signal is
zero.
With this configuration, fuzzy reasoning is still applied
and the effect mentioned in a previous embodiment can be
achieved. That is, it is possible to implement accurate
control of the output pressure by eliminating the hysteresis
CA 02212308 1997-08-01
characteristics relating to the driving resistance force of
the three-position solenoid valve.
While a presently preferred and a number of alternative
embodiments of the present invention have been described in
detail above, it should be understood that various other
adaptations and/or modifications of the three-position
solenoid may be envisioned by those persons who are skilled in
the relevant art without departing from either the spirit of
the invention or the scope of the appended claims.
