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Patent Abstract
A solenoid valve is provided which may be used to inject fuel into
an internal combustion engine for automotive vehicles. The solenoid
valve is designed to keep an air gap between a stator and an armature
at a constant interval required to ensure a normal operation of
the solenoid valve. The solenoid valve includes a spacer which is
provided between the stator and the armature to keep the air gap
without any hit of the armature on the stator. In one embodiment,
the spacer is installed on a peripheral portion of the stator or
the armature.
Patent Claims
What is claimed is:
1. A solenoid valve comprising: a housing in which a valve hole
is formed for blocking and establishing fluid communication between
an upstream and a downstream portion of a fluid passage; a valve
member disposed in said housing slidably to close and open the valve
hole selectively; an armature connected to said valve member to
be movable along with said valve member; a stator disposed within
said housing, said stator working to attract said armature in a
direction to open said valve hole; a coil producing a magnetic attractive
force through said stator when energized; and a spacer provided
between said stator and said armature to keep a given air gap therebetween
without any hit of said armature on said stator, said spacer being
provided on a peripheral portion of one of said stator and said
armature.
2. A solenoid valve as set forth in claim 1, wherein said spacer
is made of the same material as that of at least a portion of said
armature and formed integrally with said armature in an annular
form.
3. A solenoid valve as set forth in claim 1, wherein said spacer
is made of a solid film harder than said armature and fixed on the
peripheral portion of said armature.
4. A solenoid valve as set forth in claim 2, wherein said spacer
is made up of a plurality of discrete members disposed on the peripheral
portion of said armature.
5. A solenoid valve as set forth in claim 1, wherein said spacer
is made of the same material as that of at least a portion of said
stator and formed integrally with said stator in an annular form.
6. A solenoid valve as set forth in claim 1, wherein said spacer
is made of a solid film harder than said stator and fixed on the
peripheral portion of said stator.
7. A solenoid valve as set forth in claim 5, wherein said spacer
is made up of a plurality of discrete members disposed on the peripheral
portion of said stator.
8. A solenoid valve as set forth in claim 1, further comprising
a bearing member which supports said valve member slidably.
9. A fuel injector comprising: a nozzle valve working to open and
close a spray hole selectively; a nozzle body supporting said nozzle
valve slidably; a pressure chamber producing therein a fuel pressure
working to urge said nozzle valve in a spray hole-closing direction;
and a solenoid valve working to control the fuel pressure in said
pressure chamber, said solenoid valve including (a) a housing in
which a valve hole is formed for blocking and establishing fluid
communication between an upstream and a downstream portion of a
fluid passage; (b) a valve member disposed in said housing slidably
to close and open the valve hole selectively; (c) an armature connected
to said valve member to be movable along with said valve member;
(d) a stator disposed within said housing, said stator working to
attract said armature in a direction to open said valve hole; (e)
a coil producing a magnetic attractive force through said stator
when energized; and (f) a spacer provided between said stator and
said armature to keep a given air gap therebetween without any hit
of said armature on said stator, said spacer being provided on a
peripheral portion of one of said stator and said armature.
Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates generally to a solenoid valve
and a fuel injector which may be used to inject fuel into an internal
combustion engine for automotive vehicles, and more particularly
to a simple and compact structure of a solenoid valve designed to
keep an air gap between a stator and an armature at a constant interval
required to ensure a normal operation of the solenoid valve and
a fuel injector using the same.
[0003] 2. Background Art
[0004] In general, a solenoid valve is used in fuel injectors for
internal combustion engines. In order to avoid a failure in operation
of the solenoid valve caused by residual magnetism or remanence
after the supply of current to a coil is cut off, an air gap is
provided between a stator and an armature. In the following discussion,
a clearance remaining between a stator and an armature after a valve
member is lifted up fully will be referred to as an air gap.
[0005] U.S. Pat. No. 6,027,037, issued on Feb. 22, 2000, assigned
to the same assignee as that of this application discloses a solenoid
valve used in an accumulator fuel injection apparatus for diesel
engines which is schematically illustrated in FIG. 7.
[0006] An armature disk 104 has a protrusion 103 projecting from
the center thereof to a stator 101 to form an air gap H between
the armature disk 104 and the stator 101. A needle valve 107 which
is lifted up and down along with the armature disk 104 is supported
by a radial bearing 105 installed in a housing 106.
[0007] The above structure, however, needs to minimize the play
of the needle valve 107 in order to ensure the air gap H required
to avoid the failure in operation of the solenoid valve due to the
remanence by designing the bearing 105 to be long and machining
the bearing 105 and the needle valve 107 accurately so that the
clearance therebetween will fall within a range of 5 to 10 .mu.m.
The increase in length of the bearing 105 will result in an increase
in overall size of the solenoid valve. The accurate machining of
the bearing 105 and the needle valve 107 will increase manufacturing
costs of the solenoid valve.
[0008] Moreover, because of a small height of the protrusion 103,
a shift in reciprocating path of the needle valve 107 and the armature
104 may cause an outer edge of the armature 104 to hit on the bottom
of the stator 101 when the armature 104 is attracted by the stator
101, thereby resulting in a variation in air gap H in the circumferential
direction of the armature 104, which will contribute to a failure
in operation of the solenoid 102.
SUMMARY OF THE INVENTION
[0009] It is therefore a principal object of the invention to avoid
the disadvantages of the prior art.
[0010] It is another object of the invention to provide a small-sized
solenoid valve designed to ensure the air gap between an armature
and a stator with simple arrangements and a fuel injecting apparatus
using the same.
[0011] According to one aspect of the invention, there is provided
a solenoid valve which may be used in a fuel injector for automotive
vehicles. The solenoid valve comprises: (a) a housing in which a
valve hole is formed for blocking and establishing fluid communication
between an upstream and a downstream portion of a fluid passage;
(b) a valve member disposed in the housing slidably to close and
open the valve hole selectively; (c) an armature connected to the
valve member to be movable along with the valve member; (d) a stator
disposed within the housing, the stator working to attract the armature
in a direction to open the valve hole; (e) a coil producing a magnetic
attractive force through the stator when energized; and (f) a spacer
provided between the stator and the armature to keep a given air
gap therebetween without any hit of the armature on the stator,
the spacer being provided on a peripheral portion of one of the
stator and the armature.
[0012] In the preferred mode of the invention, the spacer is made
of the same material as that of at least a portion of the armature
and formed integrally with the armature in an annular form.
[0013] The spacer may also be made of a solid film harder than
the armature and fixed on the peripheral portion of the armature.
[0014] The spacer may alternatively be made up of a plurality of
discrete members disposed on the peripheral portion of the armature.
[0015] The spacer may alternatively be made of the same material
as that of at least a portion of the stator and formed integrally
with the stator in an annular form.
[0016] The spacer may alternatively be made of a solid film harder
than the stator and fixed on the peripheral portion of the stator.
[0017] The spacer may alternatively be made up of a plurality of
discrete members disposed on the peripheral portion of the stator.
[0018] A bearing member may further be provided which supports
the valve member slidably.
[0019] According to another aspect of the invention, there is provided
a fuel injector which may be used to inject fuel into an internal
combustion engine for automotive vehicles. The fuel injector comprises:
(a) a nozzle valve working to open and close a spray hole selectively;
(b) a nozzle body supporting the nozzle valve slidably; (c) a pressure
chamber producing therein a fuel pressure working to urge the nozzle
valve in a spray hole-closing direction; and (d) a solenoid valve
working to control the fuel pressure in the pressure chamber. The
solenoid valve comprises a housing in which a valve hole is formed
for blocking and establishing fluid communication between an upstream
and a downstream portion of a fluid passage, a valve member disposed
in the housing slidably to close and open the valve hole selectively,
an armature connected to the valve member to be movable along with
the valve member, a stator disposed within the housing, working
to attract the armature in a direction to open the valve hole, a
coil producing a magnetic attractive force through the stator when
energized, and a spacer provided between the stator and the armature
to keep a given air gap therebetween without any hit of the armature
on the stator. The spacer is provided on a peripheral portion of
one of the stator and the armature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be understood more fully from
the detailed description given hereinbelow and from the accompanying
drawings of the preferred embodiments of the invention, which, however,
should not be taken to limit the invention to the specific embodiments
but are for the purpose of explanation and understanding only.
[0021] In the drawings:
[0022] FIG. 1 is a vertical sectional view which shows a fuel injector
equipped with a solenoid valve according to the first embodiment
of the invention;
[0023] FIG. 2 is a partial sectional view which shows an internal
structure of the solenoid valve installed in the fuel injector of
FIG. 1;
[0024] FIG. 3(a) is a partial sectional view which shows a spacer
working to keep an air gap between an armature and a stator;
[0025] FIG. 3(b) is a partial sectional view which shows a modification
of the spacer of FIG. 3(a);
[0026] FIGS. 4(a) and 4(b) show modified forms of a spacer as shown
in FIG. 2;
[0027] FIG. 4(c) shows a comparative example of a spacer;
[0028] FIGS. 5(a), 5(b), 5(c), and 5(d) show modified forms of
a spacer as shown in FIG. 2;
[0029] FIG. 6 is a partial sectional view which shows an internal
structure of a solenoid valve according to the second embodiment
of the invention; and
[0030] FIG. 7 is a vertical sectional view which shows a conventional
solenoid valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Referring to the drawings, wherein like reference numbers
refer to like parts in several views, particularly to FIGS. 1 and
2, there is shown a fuel injector 1 according to the invention.
[0032] The fuel injector 1 is installed in a head of an internal
combustion engine (not shown) and inject fuel directly into one
of cylinders of the engine.
[0033] The fuel injector 1 includes a housing 11 (i.e., an injector
body) and a nozzle body 12 which are joined by a retaining nut 14.
[0034] The housing 11 has a needle chamber 11d formed therein.
Similarly, the nozzle body 12 has a needle chamber 12e formed therein.
A nozzle valve 20 is disposed within the needle chambers 11d and
12e.
[0035] The housing 11 has an inlet 11f which works as a connector
to a fuel pump (not shown) The inlet 11f has a fuel inlet passage
11a formed therein. A bar filter 13 is installed in the fuel inlet
passage 11a. The fuel inlet passage 11a communicates with a fuel
passage 12d formed in the nozzle body 12 through a fuel passage
11b. The fuel passage 12d communicates with the needle chamber 12e
through a fuel sump 12c. The needle chamber 12e communicates with
spray holes 12b formed in a head of the nozzle body 12. The fuel
supplied from the fuel pump to the inlet 11f flows through the bar
filter 13 to the fuel inlet passage 11a, the fuel passages 11b and
12d, the fuel sump 12c, and the needle chamber 12e and is injected
from the spray holes 12b into a cylinder of the engine. The housing
11 also has a leak passage 11c leading to the needle chamber 11d.
[0036] The nozzle valve 20 consists of a needle 20c, a rod 20b,
and a control piston 20a. The needle 20c is made up of a seating
portion (i.e., a valve head), a small-diameter portion, a tapered
portion, and a large-diameter portion. The large-diameter portion
is disposed hermetically within the needle chamber 12e to be movable
in a lengthwise direction of the nozzle valve 20. The tapered portion
is urged upward, as viewed in FIG. 1, by the fuel pressure in the
fuel sump 12c. An annular gap is formed between an outer wall of
the small-diameter portion and an inner wall of the needle chamber
12e. The seating portion is of a conical shape and rests on a valve
seat 12a to close the spray holes 12b. The rod 20b abuts at one
end on the needle 20c and at the other end on the control piston
20a. A coil spring 15 is disposed around the rod 20b and urges the
needle 20c through the rod 20b into constant engagement with the
valve seat 12a. The control piston 20a is disposed slidably within
the needle chamber 11d hermetically to be movable in the lengthwise
direction thereof.
[0037] A first annular plate 16, as shown in FIG. 2, is disposed
within a cylindrical end chamber which is formed in an end portion
of the housing 11 in communication with an upper end of the needle
chamber lid. The first plate 16 has formed therein an outlet orifice
16a leading to the needle chamber 11d and an inlet orifice 16b communicating
between the outlet orifice 16a and the fuel inlet passage 11a through
a fuel passage 11g. A pressure chamber 16c is defined by the end
of the control piston 20a, the inner wall of the needle chamber
11d, and an inner wall of the outlet orifice 16a.
[0038] A second annular plate 18 and a third annular plate 17 are
laid on the first plate 16 to overlap each other. The third plate
17 is screwed into the end chamber of the housing 11 to hold the
first plate 16 and the second plate 18 therewithin. The third plate
17 has through holes 17a and 17b formed therein. The through hole
17a defines a valve chamber. The second plate 18 has formed therein
a valve hole 18a which establishes communication between the pressure
chamber 16c and the through hole 17a. A clearance 11e is, as clearly
shown in FIG. 1, formed in a circumferential direction between side
walls of the first and second plates 16 and 18 and the inner wall
of the end chamber of the housing 11. The clearance 11e leads to
the leak passage 11c and to the holes 17a and 17b through a recess
17c formed in a surface of the third plate 17 facing the second
plate 18.
[0039] The fuel injector 1 also has a solenoid valve 2. The solenoid
valve 2 has a stator 31 disposed within a hollow cylindrical casing
33. The casing 33 has a flange 33a which is held between an inner
step of a retaining nut 52 and the end of the housing 11 through
an annular member 19 to join the casing 33 to the housing 11. The
casing 33 has an upper opening closed by an end body 53. The end
body 53 is joined at an end surface thereof to an end surface of
the stator 31 firmly by bending an upper edge of the casing 33 inwardly,
thereby holding the stator 31 within the casing 33. In the stator
31, a bobbin 34 and a coil 32 wound around the bobbin 34 are fixed
through resin. The coil 32 leads electrically to a terminal 51 extending
into a connector 50.
[0040] A control valve 20 is disposed slidably within the stator
31 and the third plate 17. The control valve 20 consists of a spherical
member 40a, a stem 40b, and a spring seat 40c. The spherical member
40a, the stem 40b, and the spring seat 40c may be connected together
in press-fits or formed by machining a single member. The spherical
member 40a has a flat surface which works to close the valve hole
18a. The stem 40b is press fit at a base thereof within a central
hole formed in an armature 41 and extends into the hole 17a of the
third plate 17.
[0041] A second coil spring 38 is disposed in a central bore 31a
formed in the stator 31 between an end of a spring pressure-adjusting
pipe 37 forced into the end body 53 and the spring seat 40c to urge
the spherical member 40a into constant engagement with the second
plate 18 through the stem 40b to close the valve hole 18a.
[0042] The armature 41 is made of a magnetic disk and disposed
slidably between the third plate 17 and the stator 31. A ring-shaped
spacer 42 is disposed between an edge portion of the surface of
the armature 41 facing the stator 31. The spacer 42 is made of,
for example, a hard chrome film or a hard nickel-phosphate film
and may be, as shown in FIG. 3(a), formed on the surface of the
armature 41 using wet plating techniques or dry plating techniques
such as evaporation or adhered to the surface of the armature 41
after being machined. The spacer 42 may alternatively be formed,
as shown in FIG. 3(b), by machining the surface of the armature
41.
[0043] The spacer 42 is, as described above, made of a ring-shaped
member which has an inner diameter substantially identical with
that of the casing 33 and an outer diameter substantially identical
with that of the armature 41, however, not limited in shape and
size to the one shown in FIGS. 3(a) and 3(b) as long as it can keep
the air gap between the armature 41 and the stator 31 constant.
FIGS. 4(a) and 4(b) show modifications of the spacer 42. Reference
number 300 indicates a body of the stator 31. In FIG. 4(a), the
spacer 42 has an outer diameter slightly smaller than that of the
armature 41. In FIG. 4(b), the spacer 42 is made up of rectangular
parallelopiped members arrayed in a circle along the periphery of
the armature 41. Each of the rectangular parallelopiped members
may alternatively be arranged at any location on the armature 41
where it is in contact with the body of the stator 31. Specifically,
if the stator 31 is made of a relatively friable material, the spacer
42, as shown in FIG. 3(a) or 3(b), which is so formed as to be in
contact with the casing 31 is useful in terms of the rigidity. Conversely,
if the stator 31 is made of an impact-resistive material, the spacer
42, as shown in FIG. 4(a) or 4(b), which is so formed as to be in
contact with the body 300 of the stator 31 is useful. Each of the
rectangular parallelopiped members of the spacer 42 of FIG. 4(b)
is so determined in width, length, and interval from the center
of the armature 41 that the periphery of the armature 41 does not
hit on the stator 31 directly between adjacent two of the rectangular
parallelopiped members.
[0044] FIG. 4(c) shows a comparative example in which the spacer
42 is unsuitable in location and shape for establishing a desired
air gap between the armature 41 and the body 300 of the stator 31.
Specifically, the spacer 42 is too small in outer diameter to avoid
a hit of the periphery of the armature 41 against the body 300 of
the stator 31 when the armature 41 is attracted to the body 300
of the stator 31.
[0045] FIGS. 5(a) to 5(d) show modifications of the spacer 42.
[0046] In FIG. 5(a), the annular spacer 42 is attached to the bottom
of the casing 33. In FIG. 5(b), the bottom of the casing 33 projects
from the end surface of the stator 31 to define the spacer 42. In
FIG. 5(c), the spacer 42 whose outer diameter is smaller than that
of the armature 41 is attached to the end surface of the stator
31. In FIG. 5(d), the spacer 42 is formed by machining the end surface
of the stator 31 to form an annular protrusion projecting from the
bottom of the casing 33.
[0047] A fuel injection operation of the fuel injector 1 will be
discussed below.
[0048] When it is required to inject the fuel into the internal
combustion engine, an ECU (electronic control unit), not shown,
actuates a fuel injection pump and delivers the fuel to an accumulator
pipe. The fuel is stored in the accumulator pipe at a constant high
pressure level and supplied to the fuel injector 1 through a supply
pipe connected to the inlet 11f.
[0049] The ECU produces a control valve-actuating current as a
function of an operating condition of the engine and outputs it
to the coil 32 of the stator 31 in the form of a pulse signal. When
the coil 32 is energized, it will cause the stator 31 to produce
an attractive force. When the sum of the attractive force and the
fuel pressure within the pressure chamber 16c acting on the control
valve 40 exceeds the spring pressure of the second spring 38, the
armature 41 is attracted to the stator 31, thereby causing the control
valve 40 to be lifted upward, as viewed in FIGS. 1 and 2, so that
the spherical member 40a of the control valve 40 leaves the valve
hole 18a to open the outlet orifice 16a. When the outlet orifice
16a is opened, it establishes the fluid communication between the
pressure chamber 16c and a low-pressure chamber (i.e., the through
hole 17a), thereby causing the fuel to flow from the pressure chamber
16c to the low-pressure chamber. The fuel entering the low-pressure
chamber is drained to a fuel tank through the through holes 17a,
17b, and 31a, and the inside of the adjusting screw 37.
[0050] When the pressure chamber 16c communicates with the low-pressure
chamber, it will cause the fuel flowing out of the pressure chamber
16c through the valve hole 18a to be greater than that flowing into
the pressure chamber 16c from the inlet orifice 16b, so that the
fuel pressure within the pressure chamber 16c drops. When the fuel
pressure in the pressure chamber 16c decreases, and the sum of the
spring pressure of the first spring 15 and the fuel pressure in
the pressure chamber 16c urging the needle 20c in the spray hole-closing
direction overcomes the fuel pressure in the fuel sump 12c urging
the needle 20c in the spray hole-opening direction, it will cause
the needle 20c to be moved away from the valve seat 12a to open
the spray holes 12b, thereby producing a fuel jet.
[0051] When it is required to stop the fuel injection, the ECU
deenergizes the coil. 32. When the coil 32 is deenergized, it will
cause the attractive force to disappear from the stator 31, so that
the spring pressure of the second spring 38 overcomes the fuel pressure
in the pressure chamber 16c to move the control valve 40 downward,
thereby closing the valve hole 18a through the spherical member
40a. The fuel continues flowing into the pressure chamber 16c through
the inlet orifice 16b, so that the fuel pressure in the pressure
chamber 16c is elevated. When the sum of the spring pressure of
the first spring 15 and the fuel pressure in the pressure chamber
16c acting on the needle 20c in the spray hole-closing direction
overcomes the fuel pressure in the fuel sump 12c in the spray hole-opening
direction, it will cause the needle 20c to move downward, as viewed
in FIG. 1, so that the needle 20c rests on the valve seat 12a to
close the spray holes 12b, thereby stopping the fuel injection.
[0052] When the control valve 40 is attracted by the stator 31,
the spacer 42 hits on the casing 33 and stops the movement of the
control valve 40. The spacer 42 is, as described above, located
away from the center of the armature 41 in a radius direction thereof,
so that the armature 41 is kept separated from the stator 31 without
hitting on the casing 33 as well as the stator 31, thereby ensuring
the desired air gap between the armature 0 and the stator 31.
[0053] The clearance between the through hole 17a of the third
plate 17 and the stem 40b of the control valve 40 is relatively
great.
[0054] Specifically, the third plate 17 does not support the stem
40b directly, thus allowing tolerances of the through hole 17a and
the stem 40b to be increased, which provides for ease of machining
of the through hole 17a and the stem 40b. The spacer 42 does not
hit on the stator 31 directly, thus allowing the stator 31 to be
made of a relatively friable material. The reciprocating motion
of the control valve 40 is supported by the armature 41, thus allowing
the third plate 17 to be decreased in thickness or omitted for decreasing
the overall length of the fuel injector 1.
[0055] FIG. 6 shows the solenoid valve 2 according to the second
embodiment of the invention which is different from that in the
first embodiment only in that a bush 60 is provided which serves
as a bearing for the control valve 40. Other arrangements are identical,
and explanation thereof in detail will be omitted here.
[0056] The bush 60 is formed by a thin-walled hollow cylindrical
member made having a relatively high hardness and press fit in the
through hole 17a of the third plate 17. The clearance between the
bush 60and the stem 40b is approximately 100 .mu.m.
[0057] The use of the bush 60 results in a decrease in wear of
parts supporting the control valve 40, thereby increasing the overall
service life of the fuel injector 1 and also improves the resistance
to heavy use of the fuel injector 1 allowing the amount of lift
of the control valve 40 to be increased and/or the current energizing
the coil 32 to be increased. The spacer 42, like the first embodiment,
works by itself to keep the desired air gap between the stator 31
and the armature 41 constant, thus allowing the clearance between
the bush 60 and the stem 40b to be increased, which provides for
ease of machining of the bush 60.
[0058] While the present invention has been disclosed in terms
of the preferred embodiments in order to facilitate better understanding
thereof, it should be appreciated that the invention can be embodied
in various ways without departing from the principle of the invention.
Therefore, the invention should be understood to include all possible
embodiments and modifications to the shown embodiments witch can
be embodied without departing from the principle of the invention
as set forth in the appended claims.
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