U.S. patent application number 13/306264 was filed with the patent office on 2012-03-22 for precision ground armature assembly for solenoid actuator and fuel injector using same.
This patent application is currently assigned to CATERPILLAR INC.. Invention is credited to Daniel R. Ibrahim, Shriprasad G. Lakhapati, Stephen R. Lewis, Avinash R. Manubolu.
Application Number | 20120067981 13/306264 |
Document ID | / |
Family ID | 41503810 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120067981 |
Kind Code |
A1 |
Manubolu; Avinash R. ; et
al. |
March 22, 2012 |
Precision Ground Armature Assembly For Solenoid Actuator And Fuel
Injector Using Same
Abstract
A solenoid actuator includes a hard guide piece and a soft flux
piece. The hard guide piece has a stop surface ground to create a
final air gap distance between the soft flux piece and a stator
assembly when the stop surface on the guide piece is in contact
with the stator assembly. The final air gap is set by grinding the
stop surface on the guide piece so that the distance between the
stop surface on the guide piece and a top surface on the soft flux
piece along an axis of the guide bore is equal to the final air
gap. The step of grinding the armature assembly may be done after
attaching the guide piece and the flux piece together. In an
exemplary embodiment, the step of grinding the stop surface and
associated guide surface(s) are performed in a single chucking.
Inventors: |
Manubolu; Avinash R.;
(Edwards, IL) ; Lakhapati; Shriprasad G.; (Peoria,
IL) ; Lewis; Stephen R.; (Chillicothe, IL) ;
Ibrahim; Daniel R.; (Metamora, IL) |
Assignee: |
CATERPILLAR INC.
Peoria
IL
|
Family ID: |
41503810 |
Appl. No.: |
13/306264 |
Filed: |
November 29, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12217622 |
Jul 8, 2008 |
8083206 |
|
|
13306264 |
|
|
|
|
Current U.S.
Class: |
239/585.1 |
Current CPC
Class: |
F02M 63/0024 20130101;
F02M 61/12 20130101; F02M 2200/8069 20130101; Y10T 29/49009
20150115; F02M 47/027 20130101; H01F 7/1623 20130101; H02K 33/02
20130101; F02M 51/0642 20130101 |
Class at
Publication: |
239/585.1 |
International
Class: |
F02M 51/06 20060101
F02M051/06 |
Claims
1. A fuel injector comprising: an armature assembly including a
flux piece attached to a guide piece which includes a stop surface;
the guide piece being slidably movable from a first position where
the guide piece is out of contact with a valve member and the stop
surface on the guide piece is in contact with a stator assembly,
and a second position where the guide piece is in contact with the
valve member and the stop surface on the guide piece is out of
contact with the stator assembly.
2. The fuel injector of claim 1 wherein: the valve member moves a
valve travel distance between a first stop and a second stop; the
armature assembly moves an armature travel distance between the
first position and the second position; the armature travel
distance being greater than the valve travel distance.
3. The fuel injector of claim 1 further including: a first spring
operatively positioned to bias the armature assembly towards the
second position; a second spring operatively positioned to bias the
valve member towards the second stop.
4. The fuel injector of claim 3 wherein: the first spring has a
first preload; the second spring has a second preload; the first
preload being greater than the second preload.
5. The fuel injector of claim 3 wherein energizing the stator
assembly pulls the armature assembly towards the first position
against the bias of the first spring.
6. The fuel injector of claim 1 wherein energizing the stator
assembly operatively moves the armature assembly and the valve
member.
7. The fuel injector of claim 1 wherein: the armature assembly
being guided via an interaction between the guide piece and a guide
sleeve of the stator assembly; the guide piece having a first guide
surface separated from a second guide surface by a reduced diameter
section; and an air gap being defined by a distance between a
surface on the flux piece and the stop surface along an axis of a
guide bore defined by the guide sleeve.
8. A fuel injector comprising: solenoid actuator assembly, which
includes an armature assembly and a stator assembly, mounted in an
injector body; the armature assembly including a flux piece
attached to a guide piece; the stator assembly includes an inner
pole piece with an inner wall in contact with a guide sleeve
defining a guide bore; the guide piece being slidably received in
the guide bore, and having a stop surface movable between a first
position in contact with the stator assembly and a second position
out of contact with the stator assembly; and an air gap being
defined between a bottom surface on the stator assembly and a top
surface on the flux piece when the guide piece is in the first
position.
9. The fuel injector of claim 8 wherein a distance between the top
surface on the flux piece and the stop surface along an axis of the
guide bore equals the air gap.
10. The fuel injector of claim 8 wherein the flux piece is welded
to the guide piece.
11. The fuel injector of claim 8 wherein the flux piece is press
fitted onto the guide piece.
12. The fuel injector of claim 8 wherein the air gap is about 0.05
mm.
13. The fuel injector of claim 8 wherein the armature assembly is
guided via an interaction between the guide piece and the guide
sleeve of the stator assembly.
14. The fuel injector of claim 13 wherein the guide piece includes
a first guide surface separated from a second guide surface by a
reduced diameter section; and a valve member unattached to, but in
contact with, the guide piece.
15. The fuel injector of claim 8 wherein the bottom surface, which
is partially defined by the guide sleeve and the inner pole piece,
is planar.
16. The fuel injector of claim 8 including a first spring that
biases the armature assembly away from the stator assembly; and a
second spring that biases the armature assembly toward the stator
assembly.
17. The fuel injector of claim 8 wherein the stator assembly
includes a coil positioned in a cavity defined by the inner pole
piece and an outer pole piece.
18. The fuel injector of claim 8 including a valve member out of
contact with armature assembly at the first position, but the valve
member being in contact with the armature assembly at the second
position.
19. The fuel injector of claim 8 including a valve member that
moves a valve travel distance between a first stop and a second
stop; the armature assembly moves an armature travel distance
between the first position and the second position; and the
armature travel distance is greater than the valve travel
distance.
20. A fuel injector comprising: solenoid actuator assembly, which
includes an armature assembly and a stator assembly, mounted in an
injector body; the armature assembly including a flux piece
attached to a guide piece; the stator assembly having a planar
bottom surface; the guide piece having a stop surface movable
between a first position in contact with planar bottom surface of
the stator assembly and a second position out of contact with the
stator assembly; the flux piece being out of contact with the
stator assembly at both the first position and the second position,
the flux piece being separated from the planar bottom surface of
the stator assembly by an air gap at the first position; and a
distance between a top surface on the flux piece and the stop
surface of the guide piece along an axis of the guide piece equals
the air gap.
Description
RELATION TO OTHER PATENT APPLICATION
[0001] This application is a divisional of co-pending patent
application Ser. No. 12/217,622 filed Jul. 8, 2008 with the same
title.
TECHNICAL FIELD
[0002] The present disclosure relates to the field of solenoid
actuators, and more particularly, to the field of solenoid air gap
features in electronically controlled fuel injectors.
BACKGROUND
[0003] People skilled in the art recognize the goal to mass produce
a solenoid actuator having smaller initial and final air gaps with
improved parallelism between a stator assembly and an armature in a
cost efficient manner. Even though it may be possible to produce a
solenoid actuator assembly having a very small air gap and where
the armature is parallel to the stator assembly, those in the art
recognize there are significant costs involved in mass producing
such assemblies.
[0004] Typical solenoid actuated fuel injectors include an armature
connected to a valve member that controls the flow of fuel and/or
pressure through the fuel injector. By having the armature
connected to the valve member, the movement of the armature within
the stator assembly may be compromised. By moving the armature with
the valve member coupled thereto, the armature might travel at
reduced speeds due to the increased mass, and any attempts to
improve parallelism with the stator assembly were also hindered due
to the tolerance stack ups that invariably increase during
production with more connected parts. Moreover, in the past, some
armature assemblies included a hard guide piece that was part of,
or drove a fuel injection valve member, and a soft armature piece
that served to enhance the magnetic forces acting on the armature.
In order to improve parallelism and maintain a predetermined
initial and final air gap, manufacturers used various category
parts that took into account the inaccuracies that existed in the
dimensions of the solenoid actuator assembly despite establishing
very tight tolerances during mass production.
[0005] When the coil of the solenoid is energized, the armature
moves towards the stator assembly, moving the valve member, and
thereby controlling the fluid flow and/or pressure in the fuel
injector. When the coil ceases to be energized, a mechanical spring
or other bias forces the armature away from the stator assembly,
causing the valve member to return to its original position and
thereby controlling the fluid flow and/or pressure in the fuel
injector again. It is known in the art that the time taken for the
solenoid actuator, and hence the control valve of a fuel injector,
to move from a first position to a second position and back again
is a function of the highest possible forces acting on the armature
over the shortest possible travel distance. It is desired by those
in the art to reduce the time taken for the armature to travel from
the initial air gap position to the final air gap position and back
to the initial air gap position.
[0006] The magnetic forces acting on the armature are functions of
the electromagnetic properties of the armature, the initial and
final air gap between the armature and the stator assembly and the
parallel orientation of the armature with reference to the stator
assembly, including others. It is well known in the art that a
magnetic field in a solenoid has the greatest force when the
armature is parallel to the stator assembly and the air gap between
them is as small as possible. Having a larger initial air gap will
translate to the armature having a lower initial attraction force
and maybe a larger travel distance, hence increasing the time taken
to travel from the initial air gap position to the final air gap
position. Having a smaller final air gap will allow for a smaller
initial air gap and also allow a stronger magnetic force to act on
the armature, hence increasing the speed at which the armature
travels from the final air gap position to the initial air gap
position and back. A lack of parallelism can create side forces
leading to imbalance and increased wear at guide interfaces.
[0007] There has been an ongoing effort to improve parallelism in
prior references, while striving to achieve the smallest final air
gap. One prior art reference, U.S. Patent Application
US2006/0138374 A1 teaches the use of an adjustable spacer coupled
between the armature housing and the stator. The spacer is adjusted
depending on the tolerance variation of the assembled parts. U.S.
Pat. No. 6,550,699 teaches the use of plating a hard film layer on
the armature as a spacer. The prior art, although geared towards
achieving some of the goals this disclosure aims to achieve, have
been met with limited success.
[0008] The present disclosure is directed to one or more of the
problems set forth above.
SUMMARY
[0009] In one aspect, a method for assembling a solenoid actuator
includes the steps of attaching a soft flux piece to a hard guide
piece. A stop surface is ground on the guide piece relative to the
top surface on the flux piece so that a final air gap is at a
predetermined distance when the stop surface is in contact with a
stator assembly.
[0010] In another aspect, a solenoid actuator assembly includes an
armature assembly and a stator assembly. The armature assembly
comprises a soft flux piece attached to a hard guide piece, which
has a stop surface ground on it. The stator assembly defines a
guide bore through which the guide piece is slidably received. The
guide piece moves between a first position where the stop surface
on the guide piece is in contact with the stator assembly, and the
second position where the stop surface is out of contact with the
stator assembly. Also, a final air gap is defined between a bottom
surface on the stator assembly and a surface on the flux piece when
the guide piece is in the first position.
[0011] In yet another aspect, a fuel injector assembly comprises an
armature assembly. The armature assembly is made of a soft flux
piece attached to a hard guide piece, which includes a stop
surface. The guide piece moves between a first position where the
stop surface on the guide piece is in contact with the stator
assembly, but the guide piece is out of contact with a valve
member. When moved to a second position, the stop surface is out of
contact with the stator assembly, but the guide piece is in contact
with the valve member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a sectioned front view of a fuel injector
according to the present disclosure;
[0013] FIG. 2 is an enlarged sectioned front view of the control
valve portion of the fuel injector shown in FIG. 1;
[0014] FIG. 3 is an enlarged sectioned front view of the fuel
injector shown in FIG. 1; and
[0015] FIG. 4 is a sectioned front view of an enlarged armature
assembly of the fuel injector shown in FIG. 1.
DETAILED DESCRIPTION
[0016] Referring to FIG. 1, a fuel injector 10 includes an
electronically controlled valve assembly 60 and a valve nozzle 92
that is opened and closed by a valve needle 90. The electronically
controlled valve assembly 60 includes a solenoid actuator assembly
20, a valve member 61, a first spring 56 having a first pre-load
and a second spring 58 having a second pre-load. The solenoid
actuator assembly 20 includes a stator assembly 21 and an armature
assembly 40. The stator assembly 21 and armature assembly 40 are
both made from various assembled parts. Valve needle 90 includes a
closing hydraulic surface 66 exposed to fluid pressure in a needle
control chamber 67. Energizing and de-energizing solenoid actuator
assembly 20 moves valve member 61 to change pressure in needle
control chamber 67 (via fluid connections not shown) to allow valve
needle 90 to open and close valve nozzle 92 in a conventional
manner.
[0017] Referring now to FIGS. 2 and 3, the stator assembly 21
includes an outer pole piece 25 attached to an inner pole piece 24,
such as via welding them together at the weld joint 30. In other
embodiments, other attachment mechanisms and locations may be used
to attach the inner pole piece 24 to the outer pole piece 25. The
pole pieces 24 and 25 may have co-planar bottom surfaces. As the
pole pieces 24 and 25 are attached to each other, in this
embodiment they share the same bottom surface, which is referred to
as the planar bottom surface 26. In one embodiment, a coil 29 is
carried on a bobbin 28 inside a cavity formed within the pole
pieces 24 and 25. The remainder of the space between the pole
pieces may be filled with plastic filler 27. Inner walls of the
inner pole piece 24 form a pole bore 23 through which a guide
sleeve 31 is attached. In one embodiment, the guide sleeve 31 may
be press fitted through the pole bore 23 so that it fits snugly
along the inner walls of the inner pole piece 24. Other embodiments
may contemplate other ways of attaching the guide sleeve 31 to the
inner walls of the inner pole piece 24, such as a weak press fit
accompanied by a weld. The guide sleeve 31 has an inner diameter
surface 32, which defines a guide bore 33. The guide bore 33 has a
longitudinal axis 35 that is perpendicular to the planar bottom
surface on the pole piece 26. The guide sleeve 31 has a stop
surface 77, which is the bottom surface on the guide sleeve 31 and
in one embodiment, it may be flush with, or be considered part of
the bottom surface 26. In one embodiment of the disclosure, the
bottom surface 26 on the entire stator assembly 21 is machined to
form a planar bottom surface on the entire stator assembly 21.
Those skilled in the art will recognize that guide sleeve 31 and
pole pieces 24 and 25 may be made from the same or different
materials. For instance, pole pieces 24 and 25 may be chosen for
their magnetic flux channeling capacities, but the guide sleeve
material may be chosen more for wear characteristics in guide bore
33 and stop surface 77.
[0018] Referring now to FIG. 4, the armature assembly 40 includes a
guide piece 43 made of a hard material which exhibits impact
resistant properties and a flux piece 45 made of a soft material
which exhibits high magnetic properties. The flux piece 45 may be
attached to the guide piece 43 at a weld joint 53. In many
embodiments, the pieces may be attached by welding the pieces
together, press fitting them or using a combination of a light
press fit and a weld, among other attachment strategies. The guide
piece 43 includes at least one guide surface 36 and 37, an enlarged
diameter portion 44 and a stop surface 75 located on the portion
44. In the embodiment shown in FIG. 4, the guide piece 43 has a
first guide surface 36, a second section or guide surface 37 and a
reduced diameter section 38. By reducing the diameter on the guide
piece 43 in section 38, the armature assembly 40 has a lower mass
and therefore, requires a smaller force to displace the armature
assembly 40. In one embodiment, the outer surface on the guide
piece, including the first guide surface 36 and second guide
surface 37, may be ground after attaching the guide piece 43 to the
flux piece 45 in such a manner that when the guide piece 43 is
received in the guide bore 33, the guide clearance along the inner
diameter surface 32 on the guide sleeve 31, and hence the guide
sleeve 31 itself, is so small resulting in a much improved
parallelism between the top surface 50 on the flux piece 45 and the
planar bottom surface 26. Thus, armature assembly 40 may be guided
through the guide bore 33 via an interaction between the guide
piece 43 and the guide sleeve 31. Furthermore, the stop surface 75
on the guide piece 43 will not be planarly flush with a top surface
50 on the flux piece 45 in an exemplary embodiment. The distance
between the stop surface 75 on the guide piece 43 and the top
surface 50 on the flux piece 45 along the axis 35 of the guide bore
33 is a predetermined final air gap 70. In one embodiment of the
disclosure, a final air gap of about 0.05 mm can be achieved on a
consistent basis while maintaining efficient operating costs. The
term "about" means that when the number is rounded to a like number
of significant digits, the numbers are equal. Thus, both 0.045 and
0.054 are about 0.05.
[0019] One other aspect of the disclosure teaches the step of
grinding the stop surface 75 on the guide piece 43 to be performed
after the flux piece 45 is attached to the guide piece 43.
Conventional wisdom in the art focuses on producing pieces with
ever increasing tightened tolerances so that after attachment, the
tolerance stack-ups would not amount to substantial variations.
This disclosure resolves the problems faced by others in the art by
allowing parts to be manufactured under less stringent tolerances,
attaching the pieces together and then grinding the surfaces on the
pieces in a single chucking. This produces an armature assembly 40
that compensates for the tolerance variations in the geometric
dimensions of each individual piece while producing a much more
accurate orientation between the guide piece 43 and the guide
sleeve 31. The grinding step may be performed by grinding a stop
surface 75 on the shoulder of the guide piece 43, such that the
stop surface 75 is parallel to the flux piece 45 of the armature
assembly 40 and is at a distance equivalent to the final air gap
70. Also, the grinding step can include grinding the guide surfaces
36 and 37 of the guide piece 43 and grinding the stop surface 75 on
the guide piece 43 in a single chucking. This will allow a more
improved orientation of the guide piece 43 into the guide bore 33
and also allow the guide piece 43 to have an orientation that is
perpendicular to the flux piece 45, improving the parallelism
between the flux piece 45 and the bottom planar surface 26.
[0020] In FIGS. 1, 2 and 3, the armature assembly 20 is shown in a
first position. In the first position, the coil 29 is energized
causing the solenoid actuator 20 to apply a pulling force on the
armature assembly 40 bringing stop surface 75 of the armature
assembly 40 in contact with the stop surface 77, which is part of
the planar bottom surface 26 of the stator assembly 21. The
armature assembly 40 may have a larger travel distance than the
valve member 61 in order to be decoupled from the valve member 61.
In this position, armature assembly 40 is out of contact with the
valve member 61, resulting in a gap 71 between the armature
assembly 40 and valve member 61. The stop surface 75 on the guide
piece 43, however, comes into contact with the stop surface 77 on
the guide sleeve 31. A final air gap 70 is formed between the
planar bottom surface 26 and the top planar surface 50 on the flux
piece 45. Furthermore, the first spring 56 remains in contact with
the guide piece 43 and exerts a first pre-load bias force on the
guide piece 43 in a direction away from stator assembly 21. The
second spring 58 exerts a second pre-load bias on the valve member
61 forcing the valve member 61 to move from the lower valve seat 64
toward upper valve seat 65 in a conventional manner.
[0021] The armature assembly 40 moves toward a second position when
the coil 29 is de-energized. The stop surface 75 on the guide piece
43 moves out of contact with the stop surface 77 on the guide
sleeve 31. The guide piece 43, however, is in contact with valve
member 61 and valve member 61 moves into contact with lower seat 64
under the action of first spring 56. Furthermore, the first spring
56 now has a greater pre-load than the pre-load of the second
spring 58 so that valve member 61 will move to its lower seat when
coil 29 is de-energized. The distance between the planar bottom
surface 26 and the top planar surface 50 on the flux piece 45 along
the longitudinal axis 35 of the guide bore 33 is equivalent to an
initial air gap.
[0022] By decoupling the action of solenoid assembly 20 from valve
member 61 slight misalignments between an axis of valve member 61
and guide axis 35 can be tolerated with altering performance. In
addition, the speed of the valve member 61 moving between seats 64
and 65 are determined primarily by respective pre-loads on springs
56 and 58, which may be set precisely with respective spacers 80
and 81. Seats 64 and 65 may be considered as first and second stops
for valve member 61. The decoupled solenoid assembly 20 can now
function with greater precision and may allow for a smaller initial
and final air gap 69 and 70. Furthermore, by decoupling the
armature assembly 40 and the valve member 61, the armature assembly
40 will function independently of the valve member 61 as long as
the armature assembly 40 travels faster than the valve member 61.
This also desensitizes the valve member 61 from any misalignments
that may occur due to construction tolerance variances and any
lateral shifting in the armature assembly 40 in order to improve
parallelism between the armature assembly 40 and the stator
assembly 21.
INDUSTRIAL APPLICABILITY
[0023] The present disclosure finds potential application in any
solenoid assembly in any machine. Although this particular
embodiment of the disclosure is directed towards an electronically
controlled valve assembly for use in a common rail fuel injector,
the disclosure is not limited to fuel injectors and could find
applicability in a much broader array of industries that use
solenoid actuators. The present disclosure finds particular
application to fuel injectors used in compression ignition engines.
Other fuel injector applications include, but are not limited to,
cam and/or hydraulically actuated fuel injectors. Electronically
controlled valve assemblies may be used to control the flow of
fluids and/or pressure through a fuel injector. In the present
disclosure, the valve assembly performs repeated cycles of movement
at an extremely high rate over many millions of cycles.
[0024] The solenoid actuator 20 has two states. An off or
de-energized state, which corresponds to the second position of the
armature assembly 40 and an on or energized state, which
corresponds to the first position of the armature assembly 40. In
the off state, the solenoid actuator 20 is switched off and no
current is passing through the coil 29 of the solenoid actuator 20.
As there is no current passing through the coil 29, there are no
magnetic forces produced within the stator assembly 21. The first
spring 56 exerts a force on the armature assembly 40 and the valve
member 61 causing them to be pushed away from the stator assembly
21 to stop when valve member 61 contacts lower seat 64. The second
spring 58 exerts an opposite force on the valve member 61 and the
armature assembly 40 towards the stator assembly 21 but the force
is not great enough to overcome the force exerted by the first
spring 56. Therefore, the net resulting force from the two springs
56 and 58 causes the valve member 61 to assume a second stop
position in contact with the valve seat 64 that corresponds to
either an open or a closed position which in turn controls the flow
of fluid and/or pressure through the fuel injector 10 depending on
the configuration of the valve assembly 60. The armature assembly
40 is positioned away from the planar bottom surface 26 and the
distance from the planar surface 50 of the flux piece 45 to the
planar bottom surface 26 of the stator assembly 21 along the
longitudinal axis 35 of the guide bore 33 is the initial air
gap.
[0025] As the solenoid actuator 20 is switched to its on state, the
armature assembly 40 moves from its second position to its first
position. Switching the solenoid actuator 20 on energizes the coil
29. The coil 29 produces a magnetic field around the stator
assembly 21 and creates a magnetic force in the surrounding region.
The force of the magnetic field is strong enough to pull the
armature assembly 40 towards the stator assembly 21. This force is
greater than the force of the spring 56 hence causing the armature
assembly 40 to move towards the stator assembly 21. In addition,
when the armature assembly 40 is pulled towards the stator assembly
21, the armature assembly 40 may be pulled faster than the valve
member 61 is pushed upward by the second spring 58. This allows the
armature assembly 40 to lose contact with the valve member 61. The
valve member 61 moves from the second stop position to a first stop
position that corresponds to either an open or a closed position
which in turn controls the flow of fluid and/or pressure through
the fuel injector 10 depending on the fluid configuration of the
valve assembly 60. The guide piece 43 moves up the guide bore 33 of
the stator assembly 21 maintaining a guide clearance with the guide
sleeve 31. The guide piece 43 stops moving when the stop surface 75
on the guide piece 43 comes in contact with the stop surface 77 on
the guide sleeve 31. A top surface 49 on the guide piece 43 remains
in contact with the first spring 56. The distance between the
planar bottom surface 26 of stator assembly 21 and the top surface
50 on the flux piece 45 is at its smallest distance, corresponding
to the final air gap 70, and may be equal to the distance between
the stop surface 75 on the guide piece 43 and the top surface 50 on
the flux piece 45. When the armature assembly 40 is in the first
position, the first spring 56 exerts a bias force on the guide
piece 43. However, as long as the coil 29 is energized, the
magnetic force is exerted on the armature assembly 40 and the
armature assembly 40 remains in the first position. Depending on
the fluid connections, fuel injection events may be initiated and
ended by energizing and de-energizing solenoid actuator 20 in a
known manner.
[0026] Finally, the solenoid actuator 20 is turned off again and
the coil 29 is de-energized. The coil 29 no longer provides a
magnetic force therefore allowing the net resulting force of the
springs 56 and 58 to force the armature assembly 40 to move from
the first position to the second position again. The first spring
56 exerts a force on the top surface 49 on the guide piece 43. The
stop surface 75 on the guide piece 43 loses contact with the stop
surface 77 on the guide sleeve 31, while the bottom impact surface
48 on the guide piece 43 comes back in contact with the valve
member 61 pushing the valve member 61 back to its original
position, and thereby allowing the valve member 61 to control the
fluid flow and/or pressure through the fuel injector 10 again. The
armature assembly 40 finally stops when it reaches the second
position, wherein the distance between the flux piece 45 and the
planar bottom surface 26 is equal to the initial air gap 69.
[0027] The armature assembly 40 continues to move from the second
position to the first position and back as long as the solenoid
actuator 20 is turned on and turned off. This continuous process
demonstrates why it may be important for the impact surfaces of the
guide piece 43 to be made of a hard, impact resistant material. The
continuous pounding of the bottom surface 48 and the stop surface
75 of the guide piece 43 with member 61 and the guide sleeve 31,
respectively, cause wear and tear on the surfaces on the guide
piece 43 possibly requiring the impact surfaces of guide piece 43
to be made of a material able to withstand these impacts over
extended periods of use. It is known to those in the art that the
flux piece 45 should be made of a soft material possessing superior
magnetic properties in order to move between the first and second
position with less force than might otherwise be needed. With the
structure shown, the travel distance of valve member 61 will
inherently be smaller than the travel distance of armature assembly
40.
[0028] This disclosure provides numerous ways to reduce the initial
and final air gap of solenoid actuators and improve parallelism
between the top surface 50 on the flux piece 45 and the bottom
surface 26 on the stator assembly 21. Grinding the stop surface 75
on the guide piece 43, after attaching the armature assembly 40,
may permit smaller geometric variations than in the past. Grinding
the surface 75 after the attaching step eliminates the need to
develop parts with ever increasingly tightened geometric tolerances
because the grinding step after attachment allows parts with larger
geometric variations to be ground to the same predetermined
dimensions. Furthermore, when the armature assembly 40 is ground
(guide surfaces 36, 37 and stop surface 75) in a single chucking,
the guide piece 43 and the flux piece 45 are oriented more
accurately than if ground in more than a single chucking. This
produces an improved, more geometrically aligned stop surface 75 on
the guide piece 43 and better parallelism between the top surface
50 on the flux piece 45 and the planar bottom surface 26 of the
stator assembly 21.
[0029] It should be understood that the above description is
intended for illustrative purposes only, and is not intended to
limit the scope of the present disclosure in any way. Thus, those
skilled in the art will appreciate that other aspects of the
disclosure can be obtained from a study of the drawings, the
disclosure and the appended claims.
* * * * *