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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to fluid control apparatus, and more particularly to
devices that employ microminiature valves, sensors and other components
for controlling pressure responsive valves in fluid passages.
Fluid valves typically employ flexible membranes or other pressure
responsive elements in governing fluid flow. A typical valve includes a
housing with inlet and outlet ports, and a valve seat along the main
passage between the ports. A flexible membrane or diaphragm near the valve
seat forms a partition between the passage and a pressure chamber. An
intake passage to the pressure chamber communicates with the inlet port,
whereby fluid can enter the chamber. An outlet passage from the chamber to
the outlet port provides pressure relief. An electromagnetic servo valve
or pilot valve is provided in the outlet passage.
When the pilot valve is closed, fluid enters the pressure chamber via the
intake passage and increases pressure in the chamber, flexing the
diaphragm against the valve seat to prevent fluid flow through the main
passage. Opening of the servo valve permits fluid flow out of the chamber
through the outlet passage, and the diaphragm is removed from the valve
seat in response to the diminishing fluid pressure in the pressure
chamber, thus opening the main valve. An exemplary valve of this type is a
hydraulic valve disclosed in Holzer U.S. Pat. No. 4,418,886.
Odajima et al U.S. Pat. No. 4,898,200 and Odajima et al U.S. Pat. No.
4,722,360 disclose fluid control devices in which a nozzle back pressure
is selectively varied to control a valve positioned between a supply port
and an output port. The control mechanism includes side-by-side
piezoelectric ceramic members movable between open nozzle and closed
nozzle positions. When the nozzle is open, back pressure, atmospheric
pressure and supply pressure reach an equilibrium that keeps the main
valve closed.
Sparrow U.S. Pat. No. 3,414,010 discloses a modulating valve in which
current to an electromagnet flexes a magnetostrictive bimetal member, in
turn flexing a modulating valve diaphragm to restrict fluid flow. The
resulting increased pressure in a pressure chamber flexes a diaphragm
along one side of the pressure chamber, to open a main valve.
While these devices perform satisfactorily, they have inherent difficulties
as well, including their large size and weight, the required level of
volts and watts to operate the pilot valves, their relatively high
fabrication cost, and their lack of direct compatibility with digital data
storage and handling apparatus. This final disadvantage is substantial in
view of the continuing trend to increasingly employ microprocessors in
controlling valves and other devices. A further disadvantage is the lack
of ability to modulate these pilot valve structures, i.e. to effectively
adjust the pilot valve to a position intermediate fully open and fully
closed.
Therefore, it is an object of the present invention to provide a fluid
valve in which the servo valve is compatible with transistor-transistor
logic (TTL), to facilitate microprocessor control including modulation of
the pilot valve.
Another object is to provide a fluid valve in which a fixed orifice, a
variable servo orifice and a fluid flow sensing device are provided in a
monolithic semiconductor chip.
A further object of the invention is to provide a gas valve in which a
normally open servo valve maintains the main valve closed while providing
an acceptably low flow of gas.
Yet another object is to provide a low cost and reliable fluid valve
operable at low voltages.
SUMMARY OF THE INVENTION
To achieve these and other objects, there is provided a fluid valve. The
valve has a housing with an inlet port, an exit port, a main passage
between the inlet port and the exit port, and a servo passage between the
inlet and exit ports. A control chamber is provided within the housing, in
fluid communication with the servo passage. A main valve means in the
housing includes a valve seat in the main passage, and a main valve
membrane or closure mounted near the valve seat. The main valve closure is
movable against the valve seat to close the main valve means responsive to
an increase in pressure within the control chamber. The main valve closure
further is movable away from the valve seat to open the main valve
responsive to decreases in pressure in the control chamber. A fixed
orifice in the servo passage allows fluid to flow from the control chamber
to the exit port. The fixed orifice has a profile with a size selected to
restrict the flow of fluid from the control chamber to a predetermined
maximum amount, in response to an expected maximum pressure differential
across the fixed orifice. A servo valve in the servo passage includes a
servo orifice for allowing fluid to flow from the inlet port into the
control chamber. A servo closure, mounted near the servo valve orifice,
moves between a closed position against the servo valve orifice to prevent
the flow of fluid therethrough, and an open position for allowing fluid to
flow from the inlet port into the control chamber.
Preferably the servo valve closure is an elastically deformable tab or
flap, normally disposed in the open position and movable into the closure
position responsive to an applied electrostatic force. The preferred main
valve closure is a flexible diaphragm forming a partition between the main
passage and the control chamber.
According to another aspect of the invention, a monolithic semiconductor
chip is mounted in the fluid valve housing. The fixed orifice is formed
through the chip, and allows fluid to flow between the control chamber and
a selected one of the inlet and outlet ports. A servo valve means includes
a servo valve orifice formed through the semiconductor chip and disposed
in the servo passage. The servo valve orifice allows fluid flow between
the control chamber and the other one of the inlet and outlet ports. The
servo valve further includes a servo closure mounted proximate the servo
orifice for movement between a closed position against the servo orifice
to prevent fluid flow therethrough, and an open position for allowing
fluid flow through the servo orifice.
A sensing means preferably is mounted on the semiconductor chip and
disposed along the main passage, for detecting the rate of fluid flow.
The preferred servo valve closure means is a flap movable toward and away
from the servo valve orifice. The flap is formed as part of a dielectric
layer applied to the semiconductor chip, and includes an embedded
electrode. A potential applied to the electrode provides an electrostatic
force for positionally adjusting the flap to open or close the servo valve
orifice.
An advantage of the invention arises from providing a fixed orifice with a
substantially reduced profile, e.g. circular with a diameter of 2-10 mils
or square with sides of 2-10 mils, and locating the fixed orifice between
the control chamber and the exit port. In this configuration, the servo
valve is positioned between the inlet port and the control chamber, and is
kept open to maintain the main valve closed.
The normally open servo valve results in a continuous fluid flow (leak)
through the servo passage. Due to its small profile, however, the fixed
orifice restricts this leak to a minute, acceptable level, e.g. fifty
cubic centimeters per hour, based upon a maximum expected pressure
differential across the fixed orifice of about 0.5 pounds per square inch.
The main valve remains closed unless a potential is applied to
electrostatically close the servo valve. An interruption in power to the
servo valve causes it to open, which closes the main valve, thus insuring
fail-safe operation of the main valve.
The size of the control chamber and servo orifice can be selected with
reference to the fixed orifice, to further enhance operation of the valve.
More particularly, the control chamber volume when sufficiently large,
provides a "soft start" of the main valve in response to closure of the
servo valve. More particularly, the reduced profile fixed orifice causes a
gradual release of fluid from the control chamber, and a correspondingly
gradual diaphragm movement away from the valve seat. In practice, it has
been found feasible to provide main valve starting times in the range of
from 1 to 10 seconds.
Conversely, main valve closure should occur more rapidly, preferably in
less than one second. To this end, the control chamber volume can be kept
to less than an acceptable maximum, and the servo valve orifice profile
can be substantially larger than the profile of the fixed orifice, e.g. in
the range of from 3 to 10 times as large.
Another feature of the invention arises from the electrostatically
controlled flap or closure in the servo valve, in that the potential
applied to the electrodes can be controlled in order to provide for a
partial closure of the servo valve. Alternatively, a pulse modulated
voltage can be applied to the electrode. In either case, modulation of the
servo valve results in a corresponding modulation of the main valve,
substantially increasing the degree of control over fluid flow through the
valve. The servo valve can be operated under low voltage, e.g.
substantially less than 50 volts, is actuated, e.g. closed with extremely
low energy levels in the range of about a microjoule, and maintained
closed with very low power levels, e.g. in the range of microwatts.
Thus, in accordance with the present invention a small, low cost valve
configuration operates in a fail-safe manner under low power requirements,
and affords a soft start and a sufficiently rapid closure of a servo
controlled main valve.
IN THE DRAWINGS
For a further understanding of the above and other features and advantages,
reference is made to the following detailed description and to the
drawings, in which:
FIG. 1 is a top view of a gas valve constructed in accordance with the
present invention;
FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1;
FIG. 3 is a sectional view taken along the line 3--3 in FIG. 2;
FIG. 4 is an enlarged view of a portion of FIG. 2;
FIG. 5 is a further enlarged view of a portion of FIG. 4;
FIG. 6 is a top view of a flow sensor of the valve, taken along the line
6--6 in FIG. 4;
FIG. 7 is a top view of a gas valve according to a second embodiment of the
invention;
FIG. 8 is a sectional view taken along the line 8--8 in FIG. 7;
FIG. 9 is a top view of a normally closed microvalve employed in accordance
with a third embodiment of the invention;
FIG. 10 is a sectional view taken along the line 10--10 in FIG. 9, showing
the microvalve closed;
FIG. 11 is a view similar to that in FIG. 10, showing the microvalve open;
FIG. 12 is a side sectional view of a normally closed microvalve used
according to a fourth embodiment;
FIG. 13 is a side sectional view of a microvalve according to a fifth
embodiment of the invention; and
FIG. 14 is a side sectional view of a microvalve according to a sixth
embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings, there is shown in FIGS. 1-3 a gas flow
regulating device 16 having a rigid, rectangular housing (typically
aluminum) including a top wall 18, a bottom wall 20, opposed side walls 22
and 24 and opposite end walls 26 and 28. A conduit 30 with external
threads 32 extends from end wall 26, while a similar conduit 34 with
external threads 36 fixed ends from the opposite end wall. Conduits 30 and
34 provide for fluid communication between regulating device 16 and a
supply or source of gas (not shown), and between the device and household
appliances using gas.
Conduit 30 can be connected to the supply and conduit 34 connected to an
appliance, to provide for gas flow from left to right as viewed in FIG. 2.
Thus, conduit 30 provides an inlet or supply port, while conduit 34
provides an exit or outlet port. Alternatively, conduit 34 can be
connected to provide the inlet port, with conduit 30 providing the exit
port. In this latter (and preferred) arrangement, the servo valve remains
open in order to maintain the main valve closed, which is advantageous in
combination with a properly sized fixed orifice.
As perhaps best seen in FIG. 2, wall sections within the housing define a
main fluid passage 38 and a control flow passage or servo passage 40, both
of which are in fluid communication with conduits 30 and 34. An annular
wall section forms a valve seat 42 along the main flow passage. Valve seat
42 is part of a main valve 44 which also includes a thin, circular and
flexible membrane or diaphragm 46 constructed of rubber. Membrane 46 is
planar, except for an annular prominence 48 formed near the periphery to
stiffen the membrane. The membrane is shown in solid lines engaged with
valve seat 42, which closes the main valve to prevent passage of gas
through the main flow of passage. When membrane 46 is deflected away from
the valve seat, as shown in broken lines at 46a, gas flows through the
main flow of passage as indicated by the arrows in FIG. 2, with conduit 34
providing the inlet port.
Membrane 46 forms a partition between main flow passage 38 and a valve
control chamber 50 below the membrane. The main valve is governed by the
pressure differential across membrane 46. More particularly, when fluid
pressure in chamber 50 is equal to or greater than fluid pressure above
the membrane, the membrane remains against valve seat 42 as shown in FIG.
2 in solid lines. When control chamber pressure is less than pressure
above the membrane, the differential provides a force to deflect the
membrane downwardly to open the main valve. As seen in FIGS. 2 and 3,
servo passage 40 is formed by a control flow tube 52 with a relatively
narrow, horizontal section 54 and a somewhat wider vertical section 56.
A semiconductor chip 58 is supported on a plate 60 immediately below
section 56 of the control flow tube. A fixed orifice 62 is etched through
semiconductor chip 58, and an opening 64 is formed through plate 60
immediately below the fixed orifice. A servo valve orifice 66 forms part
of a microvalve 67. Orifice 66 is etched through the chip above a large
opening through plate 60, occupied by a filter 68. Thus, servo passage 40
is in fluid communication with valve control chamber 50. Fluid in passage
40 flows downward through servo valve orifice 66 and filter 68 into the
control chamber, then upwardly through opening 64 and fixed orifice 62, to
the exit port.
A filter 70 is mounted between semiconductor chip 58 and a shelf 72 above
servo valve orifice 66. Filter 70 cooperates with filter 68 to protect
microvalve 67 against particulate contamination.
Immediately upstream of filter 70 (i.e. to the right of the filter as
viewed in FIG. 2), main flow passage 38 and servo passage 40 merge and
communicate with conduit 34, which in this configuration provides the
inlet port. A microbridge flow sensor 74 is formed in the semiconductor
chip along the region of merger, and detects the rate of gas flow toward
the passages. A connector 76 is electrically coupled to electrical
circuitry formed on semiconductor chip 58 for electrostatically
controlling microvalve 67 in a manner explained below.
Semiconductor chip 58 preferably is formed of silicon. Substantial portions
of semiconductor chip are removed by etching or otherwise, to form
pedestals 78 that contact plate 60, fixed orifice 62, servo valve orifice
66, and microbridge flow sensor 74 on a comparatively thin bridge 84.
Fixed orifice 62 consists of two circular apertures 86 and 88 through chip
58, although the apertures could be rectangular as well. These apertures
are sized to provide a combined profile (i.e. open area in the direction
normal to fluid flow) equivalent to the profile of a single opening having
a diameter in the range of from 2-10 mils, i.e. from about
2.times.10.sup.-3 mm.sup.2 to about 5.times.10.sup.-2 mm.sup.2. It is to
be appreciated that the term "orifice profile" as used herein refers to
the profile of the aperture in the case of a single aperture orifice, or
the combined or composite profile of a plurality of apertures forming a
single orifice, whether or not such apertures are circular. The fixed
aperture profile thus is substantially less than a typical profile of
conventional fixed apertures in this type of valve (e.g. at least 0.02
inches in diameter).
Microvalve 67 includes six apertures 90 forming the servo valve orifice.
Each of apertures 90 has an associated closure plate or tab 92, fixed at
one end in cantilever fashion with respect to semiconductor chip 58. Each
tab is flexible whereby it is movable between an open position as
illustrated in FIGS. 2 and 4, and a closed position in which the tabs
collectively prevent fluid flow through the servo valve orifice.
FIG. 5 illustrates one of apertures 90 forming the servo valve orifice, and
its associated one of tabs 92. The tabs are formed, first by depositing a
dielectric layer 94, for example silica (SiO.sub.2) or silicon nitride
(Si.sub.3 N.sub.4) onto the upper surface of chip 58. Tab 92 is formed of
the dielectric material as part of layer 94. A gap 96 between the tab and
remainder of the layer is formed by depositing a sacrificial layer of
aluminum, and subsequently etching away the aluminum. Two electrodes are
encapsulated in the dielectric layer near aperture 90, including a fixed
electrode 98 integral with the semiconductor chip, and a movable electrode
100 in tab 92. Electrodes 98 and 100 preferably are constructed of chrome,
platinum, gold, or nickel iron. Conductors 102 and 104 electrically couple
their associated electrodes to connector 76.
Normally, i.e. when not subject to an external stress, each tab 92 is in
the open position as in FIG. 4. Microvalve 67 is closed by bringing tabs
92 into engagement with the dielectric layer immediate their respective
apertures 90, to prevent fluid flow through these apertures. In connection
with tab 92 in FIG. 5, power is supplied to conductors 102 and 104 to
provide potentials of opposite polarity in electrodes 98 and 100. This
tends to draw the electrodes toward one another, eventually moving tab 92
into a complete closure. When equal potential is applied to the conductive
film electrodes, or when conductors 102 and 104 are shorted, tab 92
returns to the open position under an internal, elastic restoring force.
Given the size of tabs 92 and electrodes 98 and 100 (e.g. in the 50-500
micron range), a minute power requirement in the range of 10.sup.-6 joules
is sufficient to maintain the tabs in their closure positions. In the
normally open valve, the pressure differential on opposite sides of
microvalve 67 tends to move tabs 92 into the closed position, and tends to
keep the tabs closed. Accordingly, tabs 92 are formed with a restoring
force sufficient to open them against the force of the pressure
differential in the absence of the electrostatic closure force. For
further information on microvalves of this type, reference is made to U.S.
Pat. No. 5,082,242, issued Jan. 21, 1992, entitled "Electronic Microvalve
Apparatus and Fabrication", by U. Bonne et al. and assigned to the
assignee of this application.
As an alternative to the arrangement shown in FIGS. 2 and 4, tabs 92 could
be positioned along the bottom of semiconductor chip 78 rather than the
top, which of course necessitates a slight repositioning of filter 68 to
provide clearance for the tabs to open. This alternative arrangement would
be fail safe, in that the pressure differential on opposite sides of
microvalve 67 would tend to open tabs 92, rather than close them, thus
tending to close the main valve. This alternative, however, would be more
difficult to fabricate, either requiring multilayer processing on both
sides of a single semi-conductor chip, or requiring at least two chips.
As previously mentioned, fixed orifice 62 has a profile substantially less
than that of a typical orifice in conventional valves of this type. One
reason for the substantially reduced profile is the normally open
condition of microvalve 67. With the microvalve open as shown in FIG. 2,
gas from the supply flows through conduit 34 and servo valve orifice 66
into valve control chamber 50. Further, gas from the control chamber flows
through fixed orifice 62 and out of the valve through conduit 30,
resulting in a continuous flow or leak through regulating device 16.
However, in view of the fixed orifice profile and a maximum expected
pressure differential across the fixed orifice of about 0.5 pounds per
square inch, the continuous flow is less than 50 cubic centimeters per
hour, well below the limit of 200 cubic centimeters per hour required for
AGA acceptance.
A further advantage arises from the manner in which the profile of servo
valve orifice 66 and the volume of control chamber 50 can be selected in
view of the fixed orifice profile, to provide a valve with a reasonably
short time (under one second) to close the main valve, and a "soft"
start-up of more than one second. More particularly, servo valve orifice
66 is formed with a profile ranging from three to ten times the fixed
orifice profile. Accordingly, so long as microvalve 67 is open, gas tends
to flow into control chamber 50 more rapidly than it flows out of the
chamber through the fixed orifice, until an equilibrium is reached of
relatively high pressure in the control chamber, thus maintaining membrane
46 against valve seat 42. Of course, the largest flow differential occurs
when microvalve 67 is first opened, having been maintained closed to keep
main valve 44 open. As the servo valve orifice profile is increased
relative to a given fixed orifice profile and valve control chamber
volume, the time for closing main valve 44 decreases. Start-up time, by
contrast, is largely a function of the fixed orifice profile and volume of
valve control chamber 50.
In one example, the fixed orifice was given a profile to insure a maximum
leak of 50 cubic centimeters per hour, and the microvalve was designed for
a range of flow rates, from closed to open, of from 5 to 500 cubic
centimeters per hour. The variance in control chamber volume over nominal
chamber volume (dV/Vmax) is assumed equal to the deviation in pressure
over nominal pressure (dP/P) which, assuming atmospheric pressure of 14.7
pounds per square inch and a differential of 0.5 pound per square inch
across device 16, is:
0.5 psi/14.7 psi=0.034
Using this factor, the nominal (maximum) volume for control chamber 50, to
achieve a starting or valve opening time of less than or equal to ten
seconds, is calculated as follows:
##EQU1##
The closing time, assuming a maximum flow rate of 500 cm.sup.3 /h (i.e.
0.14 cm.sup.3 /s), is calculated as follows:
##EQU2##
The control chamber volume of 3.7 cm.sup.3, is substantially less than
corresponding chamber volumes in conventional valves, which typically are
well over 100 cm.sup.3. From the above example it is seen that closing
time can be reduced by reducing the control chamber volume, or by
enlarging servo valve orifice 66 to increase the maximum flow rate through
an open microvalve 67. Further, enlarging the servo valve orifice
facilitates reducing closing time with negligible impact upon start-up
time.
An advantage of microvalve 67 arises from the ability to modulate this
valve, i.e. maintain each tab 92 in a partially open position as
illustrated in FIG. 5. Each tab is maintained partially open by providing
potentials of opposite polarity to electrodes 98 and 100, but at levels
insufficient for complete closure. The actual levels applied can be
reduced. Alternatively, applied levels are effectively reduced by pulse
modulation of the level normally applied to close the tabs.
A controller 120 (FIG. 4) determines the level of power provided to
microvalve 67 over conductors 102 and 104 via connector 76, to open and
close tabs 92, or to modulate the tabs in setting their position
intermediate fully closed and fully opened. Controller 120 governs
microvalve 67 based on selected inputs, for example a temperature control
setting for an appliance over a line 122, or input from microbridge flow
sensor 74 over a line 124. The operation of devices such as controller 120
is known in the art, not particularly germane to the present invention,
and thus not further discussed herein.
FIG. 6 illustrates the portion of bridge 84 including microbridge flow
sensor 74. Semiconductor chip 58 forms the body or base that supports the
flow sensor. Sensor 74 includes two substantially identical thin film
resistor grids 106 and 108 that function as heat sensors. A thin film
heater resistor grid 110, centrally positioned between resistor grids 106
and 108, generates heat sensed by the resistor grids. The heater and
resistor grids preferably are fabricated of nickel-iron or platinum, and
encapsulated in a thin film of a dielectric such as silicon nitride.
An air space or gap 112 (FIG. 4) is formed in the chip just below bridge
84. As a result, heater 110 and resistor grids 106 and 108 are
substantially surrounded by air. Openings are formed through dielectric
layer 94 on opposite sides of the heater and sensing resistor grids, as
indicated at 114 and 116, to promote the flow of gas below bridge 84 as
well as above it. Consequently, heat received by resistor grids 106 and
108, as a result of heat generated by heater grid 110, is due to
convective transfer and to a lesser extent radiation, as opposed to
conduction through the silicon nitride dielectric layer.
Given the specific heat capacity of the gas, and ambient temperature as
sensed by a thin film reference sensor grid 118 upstream of the heater and
sensing grids, the rate of fluid flow is determined with accuracy, based
upon the temperature difference between the upstream and downstream
temperatures sensed at resistor grids 108 and 106, respectively. For
further information concerning this type of flow sensor, reference is made
to Higashi et al U.S. Pat. No. 4,501,144.
FIGS. 7 and 8 show an alternative embodiment flow regulating device 130
constructed in accordance with the present invention. Device 130 includes
a rectangular housing 132 having top and bottom walls 134 and 136,
opposite side walls 138 and 140, and opposite end walls 142 and 144. A
conduit 146 having external threads extends from end wall 142 and provides
an exit port. A similar conduit 148 provides an inlet or supply port.
A main flow passage 150 tends from conduit 146 to conduit 148. Along the
main passage, an annular wall section forms a valve seat 152. A membrane
154 is mounted inside of housing 132 and can engage the valve seat as
shown in FIG. 8 to close the main valve. As indicated in broken lines at
154a, membrane 154 is movable away from the valve seat to open the valve
for fluid flow along the main passage. Interior wall sections 156 and 158
support membrane 154 at is periphery. The membrane is flexible and planar,
with the exception of an annular prominence 160.
A servo valve orifice 162 is formed through wall section 158, to permit
fluid flow from inlet port conduit 148 into a control chamber 164. The
control chamber forms part of a servo (contro | | |
