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Patent Abstract
The solenoid valve comprises a duct having an inlet opening and
an outlet opening through which the fluid can pass substantially
without changing direction, a valve seat within the duct, a closure
member movable between a closure position and a fully-open position,
and electromagnetic means for acting on the closure member in order
to move it to any position between the closure position and the
open position in dependence on an electrical control quantity. The
electromagnet means comprise a core of ferromagnetic material, fixed
firmly to the closure member and movable substantially along the
same axis as the fluid, and a solenoid for generating a force on
the ferromagnetic core along the same axis. A second closure member,
movable along the same axis, may be provided in order to provide
a solenoid valve with a double seal. The solenoid valve described
is less bulky and expensive than known solenoid valves because it
does not require a metal housing body.
Patent Claims
We claim:
1. A solenoid valve for delivering a fluid at a variable flow-rate,
comprising: a duct having an inlet opening and an outlet opening
through which the fluid can pass substantially without changing
direction, a valve seat within the duct, between the inlet opening
and the outlet opening, a closure member movable between a closure
position and a fully-open position, electromagnetic means for acting
on the closure member in order to move it to any position between
the closure position and the open position, in dependence on an
electrical control quantity, the electromagnetic means comprising
a core of ferromagnetic material, fixed firmly to the closure member
and movable substantially along the same axis as the fluid, and
a solenoid for generating a force on the ferromagnetic core along
the same axis.
2. A solenoid valve according to claim 1, comprising: an inlet
element which defines a first portion of the duct adjacent the inlet
opening and is made at least partially of ferromagnetic material,
an outlet element which defines a second portion of the duct adjacent
the outlet opening and comprises the valve seat, and a sheath of
non-ferromagnetic material which joins the inlet element to the
outlet element and defines between these elements a chamber in which
the core with the closure member is housed in a slidable manner.
3. A solenoid valve according to claim 2, comprising resilient
means for urging the core, with the closure member, to the closure
position.
4. A solenoid valve according to claim 2 in which the core divides
the chamber defined by the sheath into a first compartment which
is in communication with the first portion of the duct, and a second
compartment which is in communication with the second portion of
the duct when the closure member is not in the closure position,
the core comprising ducting means which put the two compartments
of the chamber into communication with one another.
5. A solenoid valve according to claim 1 in which the closure member
and the valve seat have respective substantially complementary conical
surfaces.
6. A solenoid valve according to claim 1 in which the inlet element
and the core have respective substantially complementary conical
surfaces.
7. A solenoid valve according to claim 2, having a support structure
comprising two discs of ferromagnetic material with central openings
through which the end portions of the inlet element and of the outlet
element extend, and fixing means which interconnect the two discs.
8. A solenoid valve according to claim 1, comprising a further
valve seat, a further core of ferromagnetic material, a further
closure member fixed firmly to the further core, and further resilient
means having dimensions such that, when the solenoid is not energized,
the further closure member is urged against the further valve seat
in order to block the passageway for the fluid and, when the solenoid
is energized, the further closure member is removed from the valve
seat to allow the fluid to pass through.
9. A valve system comprising a solenoid valve according to claim
8, means for detecting the flow-rate of the fluid output from the
solenoid valve and regulating means for varying the electrical quantity
(I) controlling the solenoid in a manner such as to keep the flow-rate
of the fluid output at a predetermined value.
10. A valve system according to claim 9 in which the detecting
means comprise a turbine disposed in the path of the fluid output,
at least one permanent magnet movable with the turbine, and a Hall-effect
sensor, and in which the regulating means comprise an electronic
unit for controlling the electrical control quantity in dependence
on the difference between a signal generated by the Hall-effect
sensor and a signal corresponding to the predetermined flow-rate
value.
11. A valve system according to claim 9 in which the detecting
means comprise a pressure sensor disposed in the path of the fluid
output, and in which the regulating means comprise an electronic
unit for controlling the electrical control quantity in dependence
on the difference between a signal generated by the pressure sensor
and a predetermined pressure signal corresponding to the predetermined
flow-rate value.
Patent Description
FIELD OF THE INVENTION
[0001] The present invention relates to solenoid valves and, more
particularly, to a solenoid valve for delivering a fluid at a variable
flow-rate, of the type.
BACKGROUND OF THE INVENTION
[0002] Solenoid valves of this type are used widely in gas burner
supply systems, for regulating the input gas-flow and thus modulating
the production of heat by the burner. A typical known solenoid valve
comprises a hollow metal body with an inlet connector and an outlet
connector with a valve seat, and a closure member movable along
an axis perpendicular to the flow of the fluid. The closure member
is connected or otherwise mechanically coupled to a ferromagnetic
core which forms part of a magnetic circuit activated by a solenoid
mounted on the body. The valve seat and the closure member are shaped
in a manner as to define between them an aperture the size of which
is variable continuously from zero, that is, from a position in
which the flow of fluid is blocked, to a maximum value, that is,
to a position in which the fluid has the maximum flow-rate, in dependence
on an electrical control quantity, usually the current passing through
the solenoid. Flow-rate regulating means may also be provided to
ensure stable positioning of the closure member at all points of
its travel and gradual movement of the closure member, without hysteresis.
The hollow body is generally made of a ferrous alloy, by pressing
or die-casting, and has structural and dimensional characteristics
such as to ensure the necessary torsional and bending strength.
It is generally quite heavy and bulky and constitutes a fairly expensive
part of the solenoid valve. The adjustment means also constitute
a critical part of the solenoid valve since they are often quite
complex, requiring particular care and tight manufacturing tolerances,
particularly when they comprise hydraulic position-control systems.
SUMMARY OF THE INVENTION
[0003] An object of the present invention is to provide a solenoid
valve which does not have a conventional body such as that described
above and which is therefore less bulky and expensive than known
solenoid valves. This object is achieved, according to the invention,
by a solenoid valve for delivering a fluid at a variable flowrate,
comprising a duct having an inlet opening and an outlet opening
through which the fluid can pass substantially without changing
direction, a valve seat within the duct, between the inlet opening
and the outlet opening, a closure member movable between a closure
position and a fully-open position, electromagnetic means for acting
on the closure member in order to move it to any position, in dependence
on an electrical control quantity, the electromagnetic means comprising
a core of ferromagnetic material, fixed firmly to the closure member
and movable substantially along the same axis as the fluid, and
a solenoid for generating a force on the ferromagnetic core along
the same axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The invention will be understood better from the following
detailed description of three non-limiting embodiments thereof,
given with reference to the appended drawings, in which:
[0005] FIG. 1 shows, in axial section, a gas-delivery solenoid
valve according to a first embodiment of the invention, more particularly,
a normally-closed solenoid valve with a single closure member for
modulating the output flowrate,
[0006] FIG. 2 is a graph showing the output pressure of the solenoid
valve of FIG. 1 as a function of the electrical control current,
[0007] FIG. 3 shows, in axial section, a second embodiment of the
solenoid valve according to the invention, more particularly, a
normally-closed solenoid valve such as that of FIG. 1, but with
an additional closure member,
[0008] FIG. 4 shows a valve system with a solenoid valve such as
that of FIG. 3 with stabilization of the fluid output flow-rate,
and
[0009] FIG. 5 shows a valve system similar to that of FIG. 4 in
which the flow-rate of the fluid is stabilized with the use of a
Hall-effect sensor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] As shown in FIG. 1, the valve according to the invention
comprises two cylindrical elements 20 and 21, fitted in a leaktight
manner in a sheath 22 of non-ferromagnetic material, and a ferromagnetic
core 23 slidable in the sheath between the two elements 20 and 21.
The elements 20 and 21 have coaxial through-holes 24 and 25 which
are enlarged outwardly to form the inlet opening 26 and the outlet
opening 27 of the valve, respectively. The element 20 with the inlet
opening or, briefly, the inlet element 20, is made of ferromagnetic
material and the element 25 with the outlet opening or, briefly,
the outlet element 25, may equally well be made of non-ferromagnetic
material, for example, brass, or of ferromagnetic material.
[0011] A solenoid 28 surrounds the sheath 22 and parts of the elements
20 and 21 and a cylindrical shell 29 surrounds the solenoid 28.
The parts of the valve described above are held together by a support
structure which, in this embodiment, comprises two discs 30, 31
and two bolts 34, 35. The two discs 30 and 31, which are made of
ferromagnetic material and have central holes through which the
end portions of the two elements 20 and 21 extend, are in contact
with respective annular abutments 32, 33 of the two elements 20
and 21. The two bolts 34 and 35 are inserted in holes provided in
opposed radial projections of the discs 30 and 31 and hold the various
structural parts of the valve together, ensuring the necessary torsional
and bending strength.
[0012] The core 23 is formed as a piston which is movable in the
cylindrical chamber defined by the sheath 22 and divides this chamber
into two compartments 36, and 37. The two compartments 36 and 37
communicate with one another through holes in the core 23, that
is, in this embodiment, an axial hole 38 and radial holes 39. A
closure member 40 which, in this embodiment, is made of rubber or
other elastomeric material, has a frustoconical end and is fixed
firmly to the core 23. The axial hole 25 in the element 21 is flared
towards the inside of the compartment 37 and forms a valve seat
41 having a conical surface which mates with the conical surface
of the closure member 40 when the latter is in the valve-closure
position. The portion of the core 23 remote from the closure member
40 has a cavity, also with a frustoconical surface, which mates
with a corresponding surface of the inner end 42 of the inlet element
20 when the core 23 is in the position in which the valve is fully
open. A spring 43, housed in a cavity in the inner end 42 of the
inlet element 20, bears on the facing surface of the core 23 so
as to keep the closure member in the closure position, in the absence
of other forces.
[0013] If a current is passed through the solenoid 28 so as to
induce in the core 23 a force in a direction and of an intensity
sufficient to overcome the resilient force of the spring 43, the
closure member 40 moves away from the valve seat 41. If the inlet
element 20 is connected to a gas-supply pipe, the gas can pass through
the axial hole 24 of the inlet element 20, the compartment 36, the
holes in the core, the compartment 37 and the aperture formed between
the closure member 40 and the valve seat 41 by virtue of the displacement
of the core 23, to reach the valve-outlet opening 27. The size of
the aperture is determined by the current flowing through the solenoid
and, more precisely, by the current for which the axial component
of the force induced in the core 23 is in equilibrium with the resilient
force of the spring 43.
[0014] By virtue of the complementary frustoconical surfaces of
the core 23 and of the inlet element 20, the axial component of
the force induced increases gradually and substantially in proportion
to the electrical control quantity.
[0015] FIG. 2 is a graph which shows, by way of example, how the
pressure Pout, and hence the flow-rate, of the gas output varies
as a function of the current I flowing through the solenoid. The
curve indicated A relates to an opening operation and the curve
indicated B relates to a closure operation.
[0016] As can be seen, the configuration of the valve with the
closure member movable along the same axis as the flow of fluid
(gas in the embodiment described) makes it possible to do without
a conventional valve body and thus to save the production costs
thereof. The saving is even more appreciable by virtue of the fact
that the main parts of the valve can easily be produced by inexpensive
turning operations. As already mentioned, the necessary torsional
and flexural stiffness are ensured by the support and fixing structure
composed of the two opposed discs and of the two bolts.
[0017] FIG. 3, in which parts identical or equivalent to those
of FIG. 1 are indicated by the same reference numerals, shows a
solenoid valve with two closure members which is usable advantageously
as a regulation and safety valve for the supply of a gas installation
in which a so-called double gas seal is required, for example, a
domestic water-heater.
[0018] In comparison with the solenoid valve of FIG. 1, the inlet
element is divided into two portions: a first portion, which is
made of non-ferromagnetic material and indicated 20', and which
basically has the function of an inlet connector, and a second portion,
which is made of ferromagnetic material and indicated 20" and
is separated from the first portion by a cylindrical chamber 50.
A second closure member, housed slidably in the chamber 50, is constituted
by a sealing member which, in this embodiment, is a rubber disc
52, fixed to one end of a core 51 of ferromagnetic material with
radial grooves or axial holes (not visible in the drawing). A spring
53 inside the chamber 50 urges the core 51 towards the portion 20"
so that, in the absence of other forces, the rubber disc 52 closes
the valve seat 54 defined by the end of the axial hole in the portion
20" of the inlet element. When the solenoid 28 is energized,
the core 51 moves, overcoming the resilient force of the spring
53 and opening the passageway for the gas towards the axial hole
in the portion 20". The spring 53 selected is such that the
core 51 moves to the open position, that is, to the position in
which the disc 52 is removed from the valve seat 54, at the latest,
at the moment at which the regulation valve with the movable core
23 starts to open. The second seal ensured by the second closure
member 52 constitutes a safety measure, should the closure member
40 stick in the open position for any reason.
[0019] If the precision of the regulation of the flow-rate by the
solenoid valve of FIG. 1 or of FIG. 3 is not considered sufficient,
it is possible to provide, in known manner and as shown schematically
in FIG. 4, a pressure sensor 63 downstream of the solenoid valve
and an electronic control unit 64 which regulates the current I
in the solenoid in dependence on the sensor signal in order to keep
the pressure, and hence the flow-rate of fluid output, constant
at a predetermined value Pref.
[0020] A particularly advantageous method of regulating the flow-rate
of a solenoid valve according to the invention is shown in FIG.
5. As can be seen, a small turbine 60 is mounted at the output of
the solenoid valve and rotates at a speed variable with the output
gas flowrate. At least one magnet is encapsulated in the turbine.
A Hall-effect sensor 61 generates an electrical signal proportional
to the speed of the turbine. An electronic control unit 62 compares
the information coming from the sensor 61 with a reference quantity
Qref corresponding to a predetermined flow-rate and causes the supply
current I of the solenoid to vary so as to keep the output gas-flow
stable at the predetermined flowrate.
[0021] A solenoid valve with flow-rate stabilizer in a single very
compact, simple and at the same time, reliable structure, is thus
obtained.
[0022] Although only three embodiments of the invention have been
described and illustrated, clearly many variations and modifications
are possible within the scope of the same inventive concept. |