U.S. patent application number 09/858831 was filed with the patent office on 2001-10-25 for extended range proportional valve.
Invention is credited to Freisinger, Paul W., Haller, John J., Holborow, Peter A..
Application Number | 20010032947 09/858831 |
Document ID | / |
Family ID | 22391826 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032947 |
Kind Code |
A1 |
Freisinger, Paul W. ; et
al. |
October 25, 2001 |
Extended range proportional valve
Abstract
An extended range proportional valve which can control rates of
mass flow over continuous low, intermediate and high ranges has a
pilot member mounted on an armature of a solenoid which can be
dithered onto and off of a pilot opening in a main valve member
which seals a main valve opening to control mass flow rates over
the low range by varying the duty cycle and/or frequency of a pulse
width modulated current in the solenoid coil. Intermediate and high
flow rates are achieved by dithering the pilot valve member with a
duty cycle and/or frequency sufficient to raise the main valve
member relatively short and relatively long respective distances
from the main valve seat.
Inventors: |
Freisinger, Paul W.;
(Stockholm, NJ) ; Haller, John J.; (Boonton,
NJ) ; Holborow, Peter A.; (Califon, NJ) |
Correspondence
Address: |
LEVINE & MANDELBAUM
350 FIFTH AVENUE SUITE 7814
EMPIRE STATE BUILDING
NEW YORK
NY
10118
US
|
Family ID: |
22391826 |
Appl. No.: |
09/858831 |
Filed: |
May 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09858831 |
May 17, 2001 |
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09505820 |
Feb 17, 2000 |
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60120673 |
Feb 19, 1999 |
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Current U.S.
Class: |
251/30.03 ;
251/129.08 |
Current CPC
Class: |
F16K 31/404 20130101;
G05D 16/2095 20190101 |
Class at
Publication: |
251/30.03 ;
251/129.08 |
International
Class: |
F16K 031/06; F16K
031/34 |
Claims
What is claimed is:
1. A proportional flow valve for selectively controlling the rate
of flow of fluid over an intermediate range of mass flow rates
between a contiguous low range of mass flow rates and a contiguous
high range of mass flow rates, comprising: a valve body including
an inlet port, an outlet port, and a main valve seat mounted in
said body and having an inlet side exposed to said inlet port and
an outlet side exposed to said outlet port, a main valve member
movably mounted within said valve body into and out of engagement
with the main valve seat to close and open the valve, said main
valve unit having a pilot opening extending therethrough and a
pilot seat surrounding said pilot opening, a pilot valve member
movably mounted within said valve body into engagement with the
pilot seat for sealing the pilot opening thereby preventing fluid
flow from said inlet port to said outlet port through said pilot
opening and out of engagement with the pilot seat for exposing the
pilot opening thereby permitting fluid flow from said inlet port to
said outlet port through said pilot opening, a solenoid actuator
having an armature on which said pilot valve member is mounted for
movement therewith, and a coil for producing a flux as a function
of an electrical current flowing therein, said armature being
movable in response to said flux, and alternating current
electrical energizer means operatively connected to said coil for
selectively inducing therein an alternating current having a
characteristic with a magnitude selectable from a range of
magnitudes for disengaging said pilot valve member from said pilot
valve seat for a time long enough to cause sufficient flow of said
fluid through said pilot opening for creating a differential
pressure across said main valve member sufficient to disengage said
main valve member from said main valve seat by a distance equal to
a fraction of a diameter of said main valve opening for causing
flow of said fluid through said pilot opening at a mass flow rate
in said intermediate range of flow rates.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a valve of the proportional flow
type operated by an electrical solenoid. More particularly, this
invention relates to a valve having a high turn down ratio, i.e.,
one which can control flow rates ranging from very low, through
intermediate, to very high magnitudes.
[0002] Proportional flow valves find utility in performing mixing
and measurement functions. For example, proportional flow valves
are used to accurately blend gasolines to achieve desired
characteristics, such as particular octane ratings, to mix hot and
cold water to obtain a desired temperature, and to dispense
compressible and noncompressible fluids, including liquids such as
gasoline, and gases such as air and natural gas. Depending on the
application for which a proportional flow valve is to be used, it
may be necessary to maintain constant flow rates of a very low
magnitude as well as constant flow rates of a very high magnitude,
and constant flow rates of an intermediate magnitude between said
high an low magnitudes.
[0003] In some prior art proportional valves, a main valve member
is lifted off of and lowered onto a main valve seat to open and
close the valve. The main valve member can be mounted at the center
of a diaphragm. Such a valve is shown in U.S. Pat. No. 5,676,342.
This valve permits a rate of fluid flow through the valve
proportional to the amount of electric current flowing through the
coil of the solenoid actuator controlling the valve. In this type
of arrangement, the actuator behaves in a linear matter, i.e., the
force produced by the solenoid armature is linearly proportional to
the current applied to the solenoid. As a result, the solenoid
armature works in a linear manner against a closing spring which
constantly urges the valve member toward the valve seat. In this
way, the distance which the valve member is moved away from the
valve seat is proportional to the amount of current applied to the
solenoid.
[0004] Atop the main valve member is a pilot valve seat which
surrounds a pilot opening through the center of the main valve
member. The plunger of a solenoid above the main valve member
carries a pilot valve member which is lowered to seal the pilot
valve opening in the main valve member and raised to open the pilot
valve opening in the main valve member.
[0005] There is also a bleed opening in the housing or diaphragm,
or through another channel, through which fluid can flow between a
reservoir chamber above the diaphragm and an inlet chamber below
the diaphragm. This bleed opening is smaller than the pilot
opening. When the pilot opening is sealed by the plunger, fluid
from the inlet port enters the inlet chamber below the diaphragm
and passes through the bleed opening in the diaphragm to the
reservoir above the diaphragm. The fluid above the diaphragm urges
the diaphragm downwardly toward the main valve seat thereby sealing
a main valve opening surrounded by the main valve seat, and closing
the valve. When the solenoid is actuated to lift the plunger off of
the pilot opening, fluid above the diaphragm is drained through the
pilot opening faster than it can enter through the smaller bleed
opening thereby lessening the pressure above the diaphragm and
causing fluid pressure from the inlet below the diaphragm to force
the diaphragm upward thereby lifting the main valve member off of
the main valve seat for opening the valve.
[0006] The valve of the above mentioned U.S. Pat. No. 5,676,342 has
been found to admirably perform its function. However when very low
flow rates are to be maintained, the plunger is moved to a position
which enables the diaphragm to lift the main valve member just
slightly off of the main valve opening. At this time, the pressure
differential between the areas above and below the diaphragm is so
great that the main valve member tends to jump when lifted off of
the main valve seat thereby preventing attainment of very low flow
rates. This occurrence denotes the bottom end of the flow vs.
current characteristic. That is, in a valve where flow rate is
uniformly diminished by decreasing the current applied to the
solenoid coil, flow is abruptly shut off when the solenoid coil
current is reduced to a level whereat the main valve member is
forced onto the main valve seat.
[0007] Conversely, while the main valve member is in engagement
with the main valve seat and the current induced in the coil of a
proportional solenoid valve is gradually increased, a level is
reached whereat the main valve member jumps off of the main valve
seat to a position whereat the lowest possible flow rate for that
valve is achieved. Although this minimum flow rate can be optimized
through careful selection of design parameters for the valve's
components, it can not be improved sufficiently in cases where
precise low flow rates are required.
[0008] It is also known in the art to operate a solenoid valve at a
constant high flow rate by applying to the valve solenoid a full
wave AC current for displacing the main valve member from the main
valve seat, and at a constant low flow rate by rectifying the AC
current to obtain a half-wave AC signal which, when applied to the
solenoid coil, enables fluid to pass through the pilot opening but
does not provide sufficient lifting force to enable the main valve
member to be lifted off of the main valve seat. Such a valve is the
subject of U.S. Pat. No. 4,503,887 to Johnson et al.
[0009] It is further known in the art to vary the degree of
displacement of a pilot valve member from a pilot valve seat in a
proportional valve by applying power to the valve's solenoid coil
in the form of a periodically pulsed DC current, the amount of
current varying with the length of "on" and "off" times of the
pulses, sometimes referred to as pulse width modulation. Pulse
width modulation for this purpose is disclosed in U.S. Pat. No.
5,294,089 to LaMarca and U.S. Pat. No. 5,676,342 to Otto et al.
[0010] None of the foregoing approaches has provided a solution to
the problem of making a proportional solenoid valve with a high
turn-down ration, i.e., one which enables continuous variation of
flow rate from very high and intermediate levels during which the
main valve member is displaced from the main valve seat, to low
levels during which the main valve member remains seated for
sealing the main valve opening, and fluid flow is limited to
passage through the pilot opening.
SUMMARY OF THE INVENTION
[0011] According to the invention, low flow rates are achieved over
a continuous range, without lifting the main valve member off of
the main valve seat, through pulse width and/or frequency
modulation of the current applied to the coil of a proportional
solenoid valve. For low flow rates, e.g., gas flowing at a rate of
0.5 standard cubic feet per minute (scfm) to 5.0 scfm, the solenoid
armature or plunger is oscillated or dithered onto and off of the
pilot valve seat on the main valve member with a duty cycle during
which the pilot opening is exposed to inlet fluid under pressure
for a portion of the cycle, and the pilot opening is closed for the
balance of the cycle thereby maintaining the main valve member on
the main valve seat and limiting fluid flow to a path through the
pilot opening. For increasingly greater flow rates, the duty cycle
of the solenoid armature is adjusted to increase the proportion of
the cycle during which the pilot opening is exposed to the fluid,
and thereby increase the rate of fluid flow through the pilot
opening.
[0012] As the rate of fluid flow approaches a level that can allow
control of the displacement of the main valve member from the main
valve seat without the problem of jumping which is encountered at
lower flow rates, the duty cycle of the solenoid current is further
adjusted to enable the pilot valve to remain open long enough to
raise the main valve member from the main valve seat a distance
corresponding to a desired intermediate rate of flow whereat the
rate of flow through the pilot opening is supplemented by limited
flow through the main valve opening. Flow at intermediate mass flow
rates is permitted as the main valve member is lifted to a position
a short distance from the main valve seat. Higher flow rates, to
which the contribution of flow through the pilot opening becomes
insignificant, are achieved as the main valve member is lifted
further away from the main valve seat.
[0013] It is therefore an object of the invention to provide a
single proportional flow valve which can provide continuous
variation of flow rates over a range heretofore unrealizable.
[0014] Another object of the invention is to provide a proportional
flow valve with a solenoid actuator which can be energized by a
current having a variable duty cycle for dithering a pilot valve
member onto and off of a pilot seat on a main valve member for
enabling a continuous range of low flow rates through a pilot
opening in the valve without raising the main valve member from the
main valve seat.
[0015] Still another object of this invention is to provide
apparatus for modulating flow through the pilot opening in the
seated main valve member without reaching the critical flow rate at
which open the main valve member is lifted of off the main valve
seat.
[0016] A further object of the invention is to provide a valve of
the type described above wherein the duty cycle and/or frequency of
the pulse width modulated solenoid current can be adjusted to
enable the pilot valve to remain open long enough to raise the main
valve member from the main valve seat in degrees corresponding to a
desired rate of intermediate or high volume fluid flow.
[0017] Still another object of the invention is to maintain
continuity between low flow, intermediate flow, and high flow rates
in a proportional solenoid valve as a transition takes place from a
range of low flow rates only through the pilot opening (main valve
closed) through intermediate flow rates having significant
components passing through both the pilot and main valve openings,
to high flow rates which occur principally through the main valve
opening.
[0018] Other and further objects of the invention will be apparent
from the following drawings and description of a preferred
embodiment of the invention in which like reference numerals are
used to indicate like parts in the various views.
DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross sectional view of a proportional flow
valve in accordance with the preferred embodiment of the invention,
the solenoid actuator being deenergized and the valve closed.
[0020] FIG. 2 is a view similar to FIG. 1, but showing the valve
while permitting a low range of mass flow rates.
[0021] FIG. 3 is a view similar to FIG. 1, but showing the valve
while permitting an intermediate range of mass flow rates.
[0022] FIG. 4 is a view similar to FIG. 1 but showing the valve
while permitting a high range of mass flow rates.
[0023] FIG. 5 is a schematic block diagram depicting the power
supply for the solenoid of FIGS. 1-4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Referring to FIGS. 1-4 of the drawings, a proportional flow
valve 10 chosen to illustrate the present invention includes a
valve body 12 having a fluid inlet port 14, a fluid outlet port 16,
and main valve seat 18 surrounding a main orifice 20. The outlet
port 16 resides within a hollow elbow having a right angular bend
24 which joins a horizontal section 22 and an a vertical section
28, the latter terminating at the main valve seat 18.
[0025] A main valve unit 30 includes a main valve member 32
slidably mounted within vertical section 28 of outlet port 16 for
reciprocal axial movement. The main valve member 32 has a generally
circular cross section and axially extending circumferentially
spaced parallel vanes 34, two of which can be seen in the drawings.
The outer circumference of the main valve member 32 is profiled to
accept an upper diaphragm support washer 36 having a planar lower
annular surface and a diaphragm retaining ring 38 having a planar
upper annular surface. Sandwiched between the lower annular surface
of upper diaphragm support washer 36 and upper annular surface of
diaphragm retaining ring 38 for movement with the main valve member
32 is the central area of an annular flexible diaphragm 17 which
serves as a pressure member for the valve 10.
[0026] A bonnet plate 40 is secured to the top of the valve body 12
by suitable fasteners 42. Disposed between the bonnet plate 40 and
a raised circumferential ridge 44 on the top of the valve body 12
is the outer circumference of diaphragm 17 which is fixedly held on
its top side by the bonnet plate 40, and on its bottom side by the
raised circumferential ridge 44 of the valve body 12 and a seal 46
inside and concentric with the ridge 44. Seal 46 cushions the
underside of the diaphragm 17 and prevents leakage of fluid at the
interfaces between the bonnet plate 40, valve body 12, and
diaphragm 17.
[0027] An annular retaining clip 48 captured in a groove
circumscribing the main valve member 32 urges the upper diaphragm
support washer 36 toward the central region of diaphragm 17 to
secure diaphragm 17 against diaphragm retaining ring 38. The vanes
34 are notched to received an annular main valve seal 50 below
retaining ring 38. Main valve seal 50 is preferably fabricated from
an elastomeric material.
[0028] The main valve unit 30 includes main valve member 32, upper
diaphragm support washer 36, diaphragm retaining ring 38, diaphragm
17, retaining clip 48, and main valve seal 50, all of which move
toward and away from the main valve seat 18 as a unit. During such
movement, an intermediate annular portion 54 of diaphragm 17 is
free to flex and stretch while the periphery of diaphragm 17 is
held fixedly in place. Axial movement of the main valve unit 30
takes place with the vanes 34 of main valve member 32 guided within
a vertical cylindrical wall of the outlet port 16 leading from the
main valve seat 18.
[0029] Within the main valve member 32, running along its central
axis, is a pilot passageway in the form of a circular bore 56
surrounded at its upper end by a pilot valve seat 58 and opening at
its lower end into the outlet port 16. The pilot passageway 56 is
selectively opened and closed by a pilot valve sealing member
68.
[0030] A main valve spring 60 is compressed between a shoulder 62
formed with the bonnet plate 40 and the top surface of the upper
diaphragm support washer 36 thereby urging the main valve unit 30
downwardly into engagement with the main valve seat 18.
[0031] The fluid inlet port 14 is bounded by the underside of the
main valve unit 30 (including diaphragm 17) and the exterior
surface of vertical section 28 of outlet port 16. A reservoir 64
occupies the open volume above the main valve unit 30.
[0032] The diaphragm 17 is impermeable to the fluid to be
controlled by the proportional flow valve 10. A bleed passageway 66
in the bonnet 40 and valve body 12 enables fluid communication
between the reservoir 64 and inlet port 14 so that fluid from the
inlet port 14 can enter the reservoir 64 above the main valve unit
30. The bleed passageway 66 has a smaller cross section than the
smallest cross section of pilot passageway 56 so that fluid can
flow through the pilot passageway 56 faster than through the bleed
passageway 66 when the pilot passageway 56 is open.
[0033] When the pilot valve is closed, as shown in FIG. 1, i.e.,
when pilot valve sealing member 68 engages pilot valve seat 58, and
when the main valve is closed, i.e., when main valve seal 50
engages main valve seat 18, fluid cannot flow from the fluid inlet
port 14 to the fluid outlet port 16. When the pilot valve is open,
i.e., when pilot valve sealing member 68 is not in engagement with
pilot valve seat 58, and the main valve is closed, as shown in FIG.
2, a fluid can flow from the fluid inlet port 14 to the fluid
outlet port 16 only through the bleed hole passageway 66 into the
reservoir 64, and then from reservoir 64 through pilot passageway
56. Such fluid flow is therefore limited to a low range of mass
fluid flow rates, the actual rate of flow being dependent on the
relative time during which the pilot valve is open versus the time
during which the pilot valve is closed.
[0034] When main valve seal 50 is out of engagement with main valve
seat 18, fluid flow can occur through the space between the vanes
34 of main valve member 32. The exposed area of the openings
between the vanes 34 increases as the main valve unit 30 rises
thereby correspondingly increasing the rate of flow from the fluid
inlet port 14 to the fluid outlet port 16.
[0035] Initially, for example when the main valve member is removed
from the main valve seat by a distance equal to or less than 25% of
the diameter of the main valve opening, flow through the main valve
opening is restricted and the rate of flow through the pilot
opening constitutes makes a significant contribution to the total
rate of flow through the valve, i.e., the sum of the mass flow
rates through both the main valve opening and pilot valve opening.
Under the above-described condition where the main valve member is
removed from the main valve seat by a distance equal to or less
than 25% of the diameter of the main valve opening, mass flow
through the valve can occur over an intermediate range of rates,
greater than the low range to which the valve is restricted when
flow is limited to the pilot opening.
[0036] Once the main valve member is removed from the main valve
seat by a distance greater than 25% of the diameter of the main
valve opening, a high range of mass flow rates is achievable. Flow
at high rates occurs principally through the main valve opening,
and the amount of flow through the pilot opening becomes
negligible.
[0037] In order to achieve low flow rates solely through the pilot
opening of the valve, i.e., while the valve is in the state shown
in FIG. 2, the pilot valve member is dithered onto and off of the
pilot valve seat by a current having a frequency and duty cycle
which rapidly permits and interrupts the flow of fluid through the
pilot opening so as to maintain sufficient pressure in the
reservoir 64 to prevent the inlet pressure beneath the diaphragm
from lifting the main valve member off of the main valve seat.
[0038] The rate of flow through the pilot opening need not be
limited to a single magnitude. By varying the frequency and/or duty
cycle of the pulse width modulated solenoid current, the relative
time during which the pilot valve opening is exposed to fluid
within the reservoir 64, versus the time the pilot opening is
sealed by the pilot valve member, can be varied to continuously
increase or decrease the rate of fluid flow through the pilot
opening while preventing the pressure in the reservoir 64 from
decreasing enough to permit the diaphragm be raised from the main
valve seat.
[0039] Depending on the frequency and pulse width of the solenoid
current, the valve will alternate between the off state shown in
FIG. 1 and the on state shown in FIG. 2 to permit low rates of
fluid flow without opening the main valve, that is, without lifting
the main valve member from the main valve seat.
[0040] Surmounting the bonnet plate 40 is a solenoid actuator 70.
The solenoid actuator 70 includes a coil 72 of electrically
conductive wire wound around a spool 74 made of non-electrically
and non-magnetically conductive material. Suitable terminals are
provided for connection to a source of electric current for
energizing the solenoid coil 72. A housing 76 of magnetic material,
surrounds the solenoid coil 72.
[0041] A stationary armature or plugnut 78 is located within the
upper portion of the spool 74. A core tube 80 extends downwardly
from the plugnut 78 and through the remainder of the spool 74.
Surrounding the lower portion of the core tube 80 is a collar 82
which is, in turn, fastened to the upper portion of the bonnet
plate 40. Fastening between the core tube 80 and collar 82, and
between the collar 82 and bonnet plate 40 can be by press fit,
welding, crimping, threading or in any other conventional manner of
forming a sturdy and fluid tight connection as will be known to
those skilled in the art.
[0042] Slidably axially disposed within the core tube 80 is a
movable armature 84 of magnetic material. Mounted on the movable
armature 84 near its lower end is a circumferential flange 86. A
pilot valve spring 88 surrounding the movable armature 84 is
compressed between circumferential flange 86 and the bottom surface
of collar 82 and urges the movable armature 84 downwardly away from
plugnut 78. The upper face of the movable armature 84 and lower
face of the plugnut 78 are correspondingly profiled so that the two
faces mesh as the movable armature 84 moves toward the plugnut 78.
At its lower end, the movable armature 84 carries the pilot valve
sealing member 68 formed of resilient material.
[0043] When solenoid coil 72 is deenergized (FIG. 1) and the fluid
inlet port 14 of proportional flow valve 10 is connected to a
source of pressurized fluid, e.g. a gasoline pump, the fluid is
forced through the bleed channel 66 into the reservoir 64 above the
main valve unit 30. The area of the top of the main valve unit 30
exposed to the fluid is greater than the area of the bottom of the
main valve unit 30 exposed to the fluid. Hence, the force of the
fluid on the top of main valve unit 30, combined with the force of
the spring 60, holds main valve seal 50 against main valve seat 18
to close the proportional flow valve 10. When solenoid coil 72 is
first energized by an electric current (FIG. 2), movable armature
84 is attracted to plugnut 78, and hence begins to move upwardly
against the force of spring 88. As movable armature 84 rises, it
moves pilot valve sealing member 68 away from pilot valve seat 58,
thereby permitting inlet fluid to flow through passageway 56 into
outlet port 16 which is at the lower outlet pressure. Because the
effective flow rate through the pilot passageway 56 is greater than
the effective flow rate through the bleed channel 66, the pressure
above the main valve unit 30 and diaphragm 17 begins to decrease.
Although the pilot opening in the illustrated preferred embodiment
of the invention is of larger diameter than the bleed opening, it
is possible to have a greater effective flow rate through the pilot
opening than through the bleed opening even if the pilot opening
has the smaller diameter when the flow channels are such that
turbulence retards the rate of flow through the bleed channel
relative to the rate of flow through the pilot opening.
[0044] If the frequency and pulse width of the solenoid current are
sufficient to raise the pilot valve sealing member 68 from the
pilot valve seat 58 for a large enough proportion of time, the
upward force of the fluid inlet pressure on the main valve unit 30
begins to exceed the downward force of the fluid pressure on the
main valve unit 30, the main valve unit 30 begins to rise (FIG. 3),
and main valve unit 30 moves away from main valve seat 18. Main
valve seal 50 disengages main valve seat 18 and communication
between fluid inlet port 14 and fluid outlet port 16 through the
spaces between vanes 34 of main valve member 32 is enabled, thereby
initially permitting intermediate range fluid flow from inlet port
14 to outlet port 16.
[0045] The main valve unit 30 continues to rise until pilot valve
seat 58 engages pilot valve sealing member 68, i.e., the pilot
valve is closed. As a result, high pressure fluid cannot escape
from the reservoir 64. As fluid entering the reservoir 64 builds
up, the downward force on the main valve unit 30 increases until
it, in combination with the downward force of the spring 60, again
exceeds the upward force of the inlet fluid against the bottom of
main valve unit 30. The result is downward movement of the main
valve unit 30. However, as soon as the main valve unit 30 begins to
move downwardly, pilot valve 68 opens, once again permitting high
pressure fluid above the main valve unit 30 to escape through
passageway 56 to the fluid outlet port 16. An equilibrium position
(FIG. 4) is quickly established in which main valve unit 30
constantly oscillates a very short distance as pilot valve 68 is
repeatedly opened and closed.
[0046] The location of the main valve unit 30 as it oscillates is
determined by the position of movable armature 84 and, hence, pilot
valve sealing member 68. This position also determines the spacing
between main valve member 32 and main valve seat 18, and hence
determines the rate of flow through the main valve opening.
[0047] Whether intermediate or high mass flow rates are obtained is
determined by the extent to which the main valve member is raised
from the main valve seat, which is in turn set according to the
position of movable armature 84 is a function of the duty cycle
and/or frequency of the pulse width modulated current applied to
solenoid coil 72, the preferred method of current control on
solenoid activated proportional flow control valves being by pulse
width modulation (PWM).
[0048] With pulse width modulation, as employed in prior art
proportional solenoid valves, a fixed frequency variable duty cycle
square wave is applied to the coil of the solenoid in order to vary
the current in the coil in a linear fashion, thereby varying the
force exerted by the solenoid on the valve actuating mechanism, and
thus changing the flow through the valve. The use of a square wave
signal has two distinct advantages over the use of a linear
amplifier to control of the solenoid current. First, the switching
type of controller has much greater efficiency than a linear
amplifier. Second, the proper choice of the fixed switching
frequency of the square wave can provide a small variation in
solenoid current that translates into a mechanical dither of the
raised solenoid armature which, in turn, reduces the effects of
static friction and mechanical hysteresis in the valve. By
carefully controlling the mechanical dither via pulse width
modulation and/or frequency modulation, selection of a desired rate
of mass flow through the pilot opening is possible over a range of
flow rates without opening the main valve. This range is herein
referred to as a low range of mass flow rates.
[0049] Intermediate and high flow rates are achieved by increasing
the duty cycle of the pulse width modulated solenoid current so
that the magnitude of flow through the pilot opening is great
enough to relieve the pressure in the reservoir above the main
valve member thereby permitting the main valve member to rise off
of the main valve seat.
[0050] If the pulse width modulation voltage has a 50% duty cycle,
the current flowing through the solenoid coil 72 will be 50% of
maximum. As a result, the movable armature 84 will rise though one
half its maximum stroke between its position when the main valve is
closed (FIG. 1) and its position when the valve is fully open (FIG.
4), i.e., when its upper face engages the lower face of the plugnut
78. Consequently, the main valve unit 30 will be permitted to rise
through just 50% of its maximum rise, and hence main valve unit 30
will be spaced from main valve seat 18 about 1/2 of the maximum
spacing. Thus, approximately 1/2 of the rate of maximum flow
through the valve will be permitted between fluid inlet port 14 and
fluid outlet port 16.
[0051] If the voltage is on 75% of the time and off 25%, i.e.,
there is a 75% duty cycle, movable armature 84 will rise through
3/4 of its maximum stroke, and as a result approximately 3/4 of the
rate of maximum flow through the valve will be permitted between
fluid inlet port 14 and fluid outlet port 16. It will be
appreciated, therefore, that the rate of high volume flow through
the main valve is proportional to the amount of current supplied to
the solenoid coil 72.
[0052] Intermediate and high mass flow rates can be achieved
depending on the maximum stroke of the solenoid armature and the
diameter of the main valve opening. For example if the pulse width
modulation voltage has a 25% duty cycle, the current flowing
through the solenoid coil 72 will be 25% of maximum. As a result,
the movable armature 84 will rise though one quarter its maximum
stroke. Consequently, the main valve unit 30 will be permitted to
rise through just 25% of its maximum rise and main valve unit 30
will be spaced from main valve seat 18 about 1/4 of the maximum
spacing. If the diameter of main valve opening is greater than 25%
of the maximum stroke of the movable armature 84, flow will be in
the intermediate range.
[0053] When operated at high flow rates, i.e., whereat fluid flow
is primarily across the main valve seat, the valve of the instant
invention behaves like the valve of U.S. Pat. No. 5,294,089. That
valve is a fluid assisted design, which by the control of a small
pilot orifice, allows the solenoid to effectively position the
diaphragm which, in turn controls the flow through a much larger
orifice. This type of valve typically has a turn down ratio of
about 10 to 1 in flow over its control range. As in the case of the
aforementioned prior art valve, control of armature position is
most precise when a pulsed DC source is applied to the solenoid
coil 72, as compared to simply varying the amplitude of a
continuous DC current.
[0054] Prior art valves are operable only in the intermediate and
high ranges. Pulsing the current in such valves imparts a dither to
the movable armature 84 with an amplitude that is very small in
comparison with the displacement of the main valve member from the
main valve seat. Hence the dithering has negligible effect on flow
rate which is determined by the exposed area of the openings
between the vanes 34, and which increases as the main valve unit 30
rises.
[0055] In the valve of the present invention, low rates of flow
occur solely through the pilot opening. To achieve low flow rates
over a continuous range, the pulse width and frequency of the
dithered pilot valve sealing member are varied to determine the
rate of fluid flow through the valve. It has been found that
pulsing the pilot solenoid over a carefully controlled range of
pulse durations will allow precise control of flow through the
pilot flow opening in the valve without causing the diaphragm to
open the main valve by raising the main valve member from the main
valve seat. By simultaneous variation of the pulse width and
frequency of the wave form applied to the solenoid coil, a close
approximation of a linear correspondence between current and flow
rate in the low flow range can be obtained, as it has heretofore
been done in the intermediate and high flow ranges. Moreover, the
transition from low flow range to the intermediate flow range can
be made transparent with no abrupt discontinuity in the current vs.
flow characteristic, as can be done in the transition from the
intermediate flow range to the high flow range.
[0056] For low flow rates, the on time of the pulse must be within
a range that allows the solenoid to lift the pilot valve member
from the pilot seat but does not allow the pilot valve member to
expose the pilot opening sufficiently to cause the diaphragm to
lift the main valve member from the main valve seat. Also, the
frequency of the current applied to the solenoid coil must be
limited to a range over which the armature of the pilot solenoid
will continue to operate in a pulsing mode.
[0057] Balancing of three mechanical parameters enables achievement
of a continuous range of low flow rates, each of which can be
selected by controlling the frequency and pulse wave duty cycle of
the solenoid coil current. These mechanical parameters are pilot
orifice area, effective bleed channel area and diaphragm hold down
spring constant and spring force.
[0058] The area of the pilot orifice is a major controlling factor
in achieving a wide range of low flow rates. As the cross sectional
area of the pilot opening increases, so too does the range of
available low flow rates or turn down ration of the low flow region
of the current vs. flow rate characteristic.
[0059] The bleed channel of a proportional solenoid valve balances
the pressures and forces above and below the diaphragm. The cross
sectional area of the bleed channel is typically smaller than the
cross sectional area of the pilot opening through the main valve
member. Exposure of the pilot opening by lifting of the pilot valve
member from the pilot valve seat causes a pressure imbalance across
the diaphragm which urges the valve main member away from the main
valve seat. Conversely, sealing of the pilot opening balances the
pressures on both sides of the diaphragm thereby allowing it to be
closed in response to a mechanical force, e.g., from a spring. The
size of the bleed channel is somewhat critical. If the bleed area
is too small, pressure in the reservoir will decrease so rapidly
during the opening phase of the pulse cycle as to cause the
diaphragm to lift the main valve member prematurely, thus limiting
the high end of the low flow range. A bleed area which is too
large, while potentially extending the flow range obtained by
dithering the pilot valve member onto and off of the pilot seat,
would interfere with the needed unbalancing of the pressures on
either side of the diaphragm need for displacing the main valve
member from the main valve seat for transition to the high flow
range, i.e., across the main valve seat.
[0060] It has been found that by placing on top of the diaphragm, a
spring having an appropriate spring constant and spring force, it
is possible to keep the main valve member in a closed position,
i.e., sealing the main valve opening, thereby allowing operation at
higher duty cycles and frequencies, thus maximizing the low flow
range.
[0061] By balancing solenoid duty cycle and frequency, pilot
opening area, bleed channel area, and diaphragm spring constant and
spring force, high turn-down ratios, i.e., wide ranging flow rates,
can be achieved by a single proportional solenoid valve.
EXAMPLE 1
[0062] In a proportional solenoid valve having a circular pilot
opening 0.078 inches in diameter, a bleed channel 0.073 inches in
diameter, and a diaphragm hold-down spring with a spring force of
1.5 lbs. a low flow range of 0.5-5.0 scfm was obtainable by varying
the pulse width duty cycle and frequency of the solenoid coil
current from 8% and 20 Hz to 50% and 25 Hz, respectively. Depending
on the size and design of the valve, frequencies as high as 40 Hz
or more, when combined with appropriate duty cycles, can be
effective in obtaining low flow rates over a substantial range.
[0063] Referring now to FIG. 5 of the drawings, a square-wave
generator 101 applies current in the form of pulsed DC signals to
the coil 72 of the proportional valve solenoid 70. The duty cycle,
i.e., the percentage of on-time vs. off-time for a single cycle of
the square wave signal is controlled by a pulse width modulator 103
the construction of which will be known to those skilled in the
art. A frequency setting circuit 105 is also provided for setting
the number of cycles per second of the pulsed DC signal produced by
the generator 101. The construction of the frequency setting
circuit will also be known to those skilled in the art.
[0064] A manual control device, e.g., the control lever on the
handle of a gasoline pump, can be mechanically linked to a
transducer for sending signals to a digital microcontroller 107
which is connected to the pulse width modulator circuit 103 and
frequency adjusting circuit 105 for simultaneously adjusting the
frequency and duty cycle of the DC pulses applied to the solenoid
coil by the generator 101. The microcontroller 107, pulse width
modulator circuit 103, and frequency setting circuit 105, may be
designed and/or programmed so that narrow pulses are applied, i.e.,
the pulsed waveform has a low duty cycle, for enabling low flow
rates at which time the solenoid armature is dithered for allowing
flow only through the pilot opening of the proportional valve while
preventing lift off of the main valve member from the main valve
seat. Moreover, the duty cycle and frequency of the solenoid coil
current may be adjusted to increase the rate of flow through the
pilot opening while still preventing main valve member lift-off.
Flow rate is still further increased by enlarging the duty cycle of
the solenoid coil current beyond a percentage whereat lift-off of
the main valve member from the main valve seat occurs.
[0065] It has been found that by employing an extended range
proportional valve in accordance with the invention, a
substantially linear relationship between flow rate and pump handle
position may be achieved over a range from very low flow rates to
very high flow rates, thereby enabling linear flow control over a
turn-down ratio of as much as 100 to 1 or more.
[0066] In designing an extended range proportional valve in
accordance with the invention, it is preferable to model the
operation of the valve by examining the response of the valve to a
PWM (pulse width modulated) control voltage that is applied to the
coil of the solenoid operator. This voltage waveform causes a
variation in the position of the armature of the solenoid. The
motion of the armature of the solenoid, in turn, causes a variation
in rate of mass flow through the valve.
[0067] The motion of the armature can be described by a standard
second order differential derived from a free body diagram of the
armature and all relevant forces acting on it, including gravity,
return spring force, and the magnetic force of attraction.
Md.sup.2x/dt.sup.2+Bdx/dt+Kx=F-F.sub.0
[0068] where
[0069] x=Displacement of the armature from its initial position in
meters
[0070] F=The magnetic attraction force on the armature in
newtons
[0071] t=time in seconds
[0072] M=Mass of armature in kilograms
[0073] B=Friction force on the armature in newton/meter/sec
[0074] K=Spring constant of armature spring in newton/meter
[0075] F.sub.0=The initial force on the armature that must be
overcome to start motion, in newtons
[0076] The dynamics of the electric circuit of the solenoid coil,
which is driven by the PWM excitation voltage, are described by the
following relationships.
[0077] During the `ON` period of the PWM signal
E=N d.phi./dt+IR
[0078] During the `OFF` period of the PWM signal
Nd.phi.dt+IR=0
[0079] Where
[0080] .PHI.=Total flux in webers, which links the turns of the
solenoid coil
[0081] I=Coil current in solenoid
[0082] R=Resistance of solenoid coil
[0083] E=Voltage on solenoid coil when during on period of PWM
signal
[0084] N=Number of turns in the solenoid coil
[0085] The coil current in the solenoid and the magnetic attraction
force on the armature in newtons are both functions of the total
flux which links the turns of the solenoid coil, and the
displacement of the armature from its initial position, i.e.,
I=f(.PHI.,x) and F=f(.PHI.,x)
[0086] Both of the above relationships are non-linear functions,
that are dependent upon the geometry of the solenoid operator and
the materials from which the valve components are constructed.
Solutions to the foregoing equations may be obtained by modelling
the mechanical and electrical elements of the valve on a digital
computer by use of circuit solver software, such as the
commercially available SPICE program. In such a model, the
electrical driver circuitry is directly modeled by electrical
elements, and the mechanical components are represented by
corresponding electrical analogs.
[0087] The magnetic coupling of back emf (Nd.phi./dt), core
position, current, and solenoid force can be modeled with the use
of an element that accepts tabular data about the solenoid's
parameters. This tabular data can be extracted from a magnetic
finite element analysis of the solenoid over a range of operating
conditions with solutions obtained for various values of core
position and coil excitation. An example of a commercially
available software solver capable of performing this analysis on a
digital computer is EMSS by Ansoft of Pittsburgh Pa. This solver
integrates magnetic finite element analysis programs with a version
of the SPICE program. By modeling this problem in such a solver, a
solution in the form of a time variant waveform that represents the
displacement x, i.e., the displacement of the armature from its
initial position, can be obtained.
[0088] In the range of low mass flow rates, the total mass flow
through the valve is equal to pilot flow only. That is, the main
valve member remains seated on the main valve seat thereby
preventing flow through the main valve opening. Using the
displacement, x, as determined by the solver, the mass flow of a
gas or liquid through the pilot opening of the main valve member
can be calculated from the following relationships.
[0089] Where the fluid passed through the valve is a gas:
M.sub.pilot(gas)=(K P.sub.1 C.sub.d .pi. x D.sub.1
N.sub.12)/(T.sup.1/2),
[0090] where
[0091] .gamma.=gas constant
[0092] M=Mass flow per unit of time
[0093] Ro=degrees Rankine
[0094] x=Displacement of the armature from its initial position in
inches
[0095] K=Constant (Ro.sup.1/2)/unit
temp.=[(.gamma.-1)/2.gamma./((P.sub.1/-
P.sub.2).sup.(.gamma.-1)/.gamma.-1)]-(1.gamma.)
[0096] P.sub.1=Inlet pressure in psia
[0097] P.sub.2=Pressure downstream of main valve seat
[0098] C.sub.d=Discharge coefficient
[0099] D.sub.1=Pilot sealing surface diameter
[0100] N.sub.12=Ratio of actual flow to sonic flow per unit area at
given values of total temperature and pressure
[(P.sub.2/P.sub.1).sup.2/.gamma.-(P.sub.2/P.sub.1).sup.((.gamma.+1)/.gamma-
./(.gamma.-1)/2(2/.gamma.+1)).sup.(.gamma.+1)/(.gamma.-1))].sup.1/2
[0101] T Inlet temperature in Ro
[0102] Where the fluid passed through the valve is a gas:
M.sub.pilot (liquid)=C.sub.d.times.D.sub.1 (2g.sub.cp
(P.sub.1-P.sub.2)).sup.1/2,
[0103] where
[0104] g.sub.c=gravitational constant (386
in-lbm/lbf-sec.sup.2)
[0105] p=density (lbm/in.sup.3)
[0106] The total mass flow through the valve equals mass pilot flow
until the displacement of the main valve member from the main valve
seat, i.e., diaphragm stroke, X.sub.d>0
[0107] In order to determine when the main valve member is lifted
from the main valve seat, thereby unsealing the main valve opening
for increasing the mass flow rate through the valve, the
relationship between the changes in pressure, temperature and
volume occurring within the valve can be considered as follows.
[0108] The Ideal Gas Equation is known to be
M=PV/RT
[0109] where
[0110] P=pressure in diaphragm chamber
[0111] V=volume in diaphragm chamber
[0112] R=perfect gas constant
[0113] M=mass of gas in diaphragm chamber
[0114] Taking the derivative of the Ideal Gas Equation:
m/M=p/P+v/V+t/T=0
[0115] Where
[0116] m=change in mass M
[0117] v=change in volume V
[0118] p=change in pressure P
[0119] t=change in temperature T
[0120] Assuming a polytropic process, the relationship of pressure
change to volume change is calculated from the following:
P=nPA.sub.dX.sub.d/V,
[0121] where
[0122] A.sub.d=diaphragm area
[0123] X.sub.d=diaphragm movement
[0124] n=number between 1 (for constant temperature) and .gamma.
(for constant entropy)
[0125] .gamma.=ratio of specific heats
[0126] Solving for X.sub.d gives the diaphragm displacement:
X.sub.d=pV/nPA.sub.d
[0127] By varying the duty cycle of the pulse width modulated
current in the solenoid coil, and/or the frequency of the current,
to dither the pilot valve member onto and off of the pilot valve
seat, mass flow rates can be achieved over a continuous low range.
When the rate of pilot mass flow is increased to a magnitude
whereat the differential pressure across the main valve member
causes it to be initially raised from the main valve seat, mass
flow through the pilot opening in the main valve member is
supplemented by limited mass flow through the main valve opening
which is partially blocked by the main valve member being in close
proximity to the main valve opening. While the main valve member is
displaced from the main valve seat a distance equal to or less than
25% of the diameter of the main valve opening, mass flow rates over
an intermediate range can be achieved. Once the main valve member
is raised from the main valve opening by a distance position
greater than 25% of the diameter of the main valve opening, mass
flow rates over a high range can be achieved
[0128] Once the main valve opening is unsealed, the mass flow rate
throughout the intermediate range of flow rates can be calculated
as follows.
[0129] M.sub.total=mass flow rate through the extended range
proportional valve
M.sub.total@Xd>0.25 D2=M.sub.diaphragm+M.sub.pilot
[0130] where
[0131] D.sub.2=diameter of the main value opening
[0132] M.sub.diaphragm=mass flow rate through the main valve
opening
[0133] M.sub.pilot=mass flow rate through the main valve
opening
[0134] As main valve member displacement increases and the main
valve member is no longer in close proximity to the main valve
opening, the rate of mass flow through the pilot opening in the
main valve member becomes insignificant relative to the rate of
mass flow through the main valve opening and can be ignored. Hence,
the mass flow rate throughout the high range of flow rates can be
calculated as follows.
M.sub.total@Xd>0.25D2=M.sub.diaphragm
M.sub.diaphragm (gas)=(K P.sub.1 A.sub.1 N.sub.12)/(T.sup.1/2)
M.sub.diaphragm (liquid)=A.sub.1 (2g.sub.c p
(P.sub.1-P.sub.2)).sup.1/2,
[0135] where
[0136] A.sub.1=X.sub.dC.sub.dD.sub.1.pi.=effective area of main
valve opening
[0137] The effective area of the main valve opening when the main
valve member is displaced from the main valve seat by less than 25%
of the diameter of the main valve opening is equal to the area of
the main valve opening across which an equal pressure drop occurs
under similar conditions when the main valve member is sufficiently
displaced from the main valve seat so as not to affect mass flow
rate through the main valve opening.
EXAMPLE 2
[0138] In an extended range proportional valve that was constructed
in accordance with the preferred embodiment of the invention for
controlling the flow of natural gas (methane gas constant used),
the following parameter values applied.
[0139] K=Gas constant (Ro.sup.1/2)/unit temp.=[((ratio of specific
heats, .gamma.-1)/2.gamma.) ((P1/P2)
(.gamma.-1)/.gamma.-1)]-(1/.gamma.)=23.14
[0140] P.sub.1=Inlet pressure in=79.7 psia
[0141] C.sub.d=Discharge coefficient 0.35 (takes into account loss
due to inlet restriction)
[0142] D.sub.1=Pilot sealing surface diameter=0.056"
[0143] N.sub.12=Ratio of actual flow to sonic flow per unit area at
given values of total temperature, and
[0144] pressure=P.sub.2=0.95P.sub.1=75.72 psia
[0145] Therefore
N.sub.12=0.4507
[(P.sub.2/P.sub.1).sup.2/y-(P.sub.2/P.sub.1).sup.(y+1)/y/(- (y-1)/2
(2/(y+1)).sup.(y+1)/(y-1))].sup.1/2
[0146] T=Inlet temperature in degrees Rankine (Ro)=527
[0147] C.sub.dD.sub.1=main orifice=0.328"-(0.1652 to 0.326)
[0148] M=Mass of armature in kilograms=0.0277
[0149] B=Friction force on the armature in
newton/meter/second=9.0
[0150] K=Spring constant in newton/meter=2185
[0151] F.sub.o=Initial force on the armature that must be overcome
to start motion, in newtons=1.338
[0152] R=Resistance of solenoid coil=6.5 ohms
[0153] N=Number of turns in the solenoid coil=850
[0154] It is to be appreciated that the foregoing is a description
of a preferred embodiment of the invention to which variations and
modifications may be made without departing from the spirit and
scope of the invention. For example, this invention could also be
applied to a pilot operated proportional solenoid valve design
wherein pressure on a rigid piston, instead of a flexible
diaphragm, is used to lift the main valve member.
* * * * *