GB2572946A

GB2572946A - Electro actuator of a fuel injector with plated pole piece or armature

Info

Publication number: GB2572946A
Application number: GB1805463.5A
Authority: GB
Inventors: Breedijk Cas
Original assignee: Delphi Automotive Systems Luxembourg SA
Current assignee: BorgWarner Luxembourg Automotive Systems SA
Priority date: 2018-04-03
Filing date: 2018-04-03
Publication date: 2019-10-23
Also published as: GB201805463D0

Abstract

A method to manufacture a fuel, eg gasoline, injector actuator defining an airgap G between the circular face 20 of a magnetic pole piece 16 and the circular face 22 of a magnetic armature 18, the method comprising plating 24 locally one of the faces 20, 22 with non-magnetic deposit material M, eg chromium, to prevent magnetic sticking and to provide a durable interface. The other face may be hardened. The plating 24 may be an annular deposit near the periphery of the flat, planar surface of the pole piece 16 or armature 18. Alternatively, the plated deposit may be several concentric annuli, a continuous deposit, or a plurality of separate spots or straight lines. The plated deposit may have a thickness T24 of 10-30µm ±2 µm. The plating may be done with masking by tooling, or by lithography, masking being done by protective layers and etching, or by micro-cladding.

Description

The present invention relates to a fuel injector actuator and particularly to a method for improving the part-to-part variation and manufacturing of a magnetic pole piece of the actuator.

BACKGROUND OF THE INVENTION

A gasoline injector comprises an electromagnetic actuator wherein a magnetic armature is fixed to a valve member so that, when the actuator is energized, the armature moves toward a pole piece and said valve member opens a fuel injection passage.

To control damping, avoid magnetic sticking and to create a durable interface of the armature onto the pole piece, either the armature or the pole piece is provided with a step to limit the contact area. This step is machined and then chrome plated. The chrome plating adds additional dimensional and form tolerances especially on the edge of the faces where the chrome plating forms a “ bone effect ” with an extra thickness. Further attention and manufacturing operations are required to keep the tolerances small and keep homogeneity in the part-to-part manufacturing.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a method to manufacture a fuel injector actuator, defining an airgap, between a circular face, of a magnetic pole piece, and a circular face, of a magnetic armature, so that, when the actuator is energized the armature moves toward the pole piece and closes said airgap and, when energization is ended the armatures moves and re-opens said airgap, the method comprising the following steps:

A) manufacturing said faces, of the pole piece and of the armature;

B) plating, locally one of said faces with non-magnetic deposit material.

The manufacturing step A may comprise the following sub-step:

al) manufacture said face so that the part of the face that is in use, the closest to the face, of the armature is a flat and planar area.

The plating step B may comprise following sub-step:

bl) plating is localized on said flat and planar area.

The sub-step al may specify with the following sub-step:

a2) said flat and planar area comprises at least the outer peripheral area of said face and wherein, the sub-step bl may comprise the following sub-step:

b2) plating thickness T, may be between 10pm and 30pm the thickness tolerance being of +/- 2pm.

The sub-step a2 may be specified with the following sub-step:

a3) said flat and planar area covers the entire face, and wherein, the plating step B, may be specified with the following sub-step:

b3) plating material is chromium.

Method, as claimed in claim wherein the sub-step b3 may be specified with the following sub-step:

b41) the plated area defines an annulus close to the peripheral edge.

The method may further comprise the step C) hardening the other face that faces the face plated locally at step B).

The invention further extends to a pole piece of an actuator of a fuel injector, said pole piece having a face, adapted to be in regards of a face, of a magnetic armature so that an airgap, is defined between said faces, said face of the pole piece being locally plated as per a method as described above.

Alternatively, the invention extends to an armature of an actuator of a fuel injector, said armature having a face adapted to be in regards of a face of a pole piece so that an airgap is defined between said faces, said face of the armature being locally plated as per a method described above.

The invention further extends to a fuel injector comprising a body housing an electro-actuator wherein a pole piece at least partially plated as mentioned above cooperates with a magnetic armature.

Alternatively, the invention extends to a fuel injector comprising a body housing an electro-actuator wherein a pole piece cooperates with a magnetic armature which face is at least partially plated as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section of a fuel injector.

Figure 2 is a magnified zone of figure 1.

Figure 3 is a bottom view of the pole piece of the injector of figures 1 or 2.

Figure 4 is a manufacturing drawing presenting the detail of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures is described a gasoline fuel injector 10 having an elongated shape extending along a main axis X. The injector 10 comprises a body housing an electro-actuator 12 cooperating with a needle valve member 14 to enable or prevent fuel injection.

Said actuator 12 comprises an annular solenoid, a magnetic pole piece 16 and a magnetic armature 18 to which is attached said needle 14. An airgap G is defined between an under face 20 of the pole piece 16 and an upper face 22 of the armature. Said under face 20 of the pole piece and upper face 22 of the armature are both circular, flats, parallel to one another, both being transverse to the main axis X. Said faces 20, 22 are entirely flat and, for reasons not discussed here, they may be provided with central recesses, the flat areas wherein is defined said airgap G being the largest annular peripheral area of the faces.

In use, when the solenoid is energized, it generates a magnetic field that loops around the solenoids and circulates in the pole piece 16 and in the armature 18 which is then attracted and moves toward the pole piece, closing the airgap G and pulling the needle to an open position lifted to enable fuel spray through fuel injection holes.

To avoid magnetic sticking of the pole piece and the armature, said parallel faces are kept separate by a thin non-magnetic member interposed between said faces, the thickness T24 of said interposed member 24 defining the minimum value of the airgap.

In the embodiment presented, said interposed member 24 is a plating deposit of chromium provided on the under face 20 of the pole piece, said deposit defining an annulus following the peripheral edge 26 of said under face 20. Alternatively to chromium, another non-magnetic material M may be chosen. Said plating deposit 24 has a typical width W24 of about 0.15mm +/- 0.05mm, the annulus running along the outer edge of the face at a distance D of about 1 mm and, the thickness T24 of the plating is comprised between 10 pm and 30pm. Said annulus is the functional area 24F of the plated member 24, the plating operation may outwardly extend to and over the edge 26 of the pole piece, said extension area 24E thinning relative to said functional area 24F.

To avoid deformation and damage of the upper face 22 of the armature, said upper face is hard. This can be achieved by hardening said face via a hardening treatment of by covering said face with a hard plating, such as a chromium plating or any other surface treatment such as any deposition or thermal chemical treatment.

In alternatives not represented, the plated member 24 may comprise several concentric annulus or may have another shape then an annulus, defining a continuous member or a plurality of separate areas such as spots or straight lines, each having the same thickness.

Moreover, in yet another and symmetrical alternative, said plated member 24 may be provided on the upper face 22 of the armature. In such symmetrical construction, the under face 20 of the pole piece is harden as previously described.

The method 100 for the plating operation may be done with traditional chrome plating and masking by tooling, or with lithography, masking being done by protective layers and etching to clear protective layer in some areas to deposit chromium or, by micro cladding where chromium powder is locally transformed to chrome plating.

A major advantage of said process is the repeatability and precision of the plating process enabling a tight control of the thickness within a narrow tolerance +/- 2 pm so improving by reducing the part-to-part variation.

LIST OF REFERENCES

	X	axis
	G	airgap
	T24	thickness
5	W24	width
	D	distance
	M	material
	10	injector
10	12	electro-actuator
	14	needle valve member
	16	pole piece
	18	magnetic armature
	20	under face of the pole piece
15	22	upper face of the armature
	24	interposed member - plated member
	24F	functional area
	24E	extension area
	26	peripheral edge of the pole piece under face

Claims

1. Method (100) to manufacture a fuel injector actuator (12) defining an airgap (G) between a circular face (20) of a magnetic pole piece (16) and a circular face (22) of a magnetic armature (18) so that, when the actuator is energized the armature moves toward the pole piece and closes said airgap and, when energization is ended the armatures moves and re-opens said airgap, the method comprising the following steps:

A) manufacturing said faces (20, 22) of the pole piece and of the armature;

B) plating (24) locally one of said faces with non-magnetic deposit material (M).

2. Method (100) as claimed in the preceding claim wherein, the manufacturing step A) comprises the following sub-step:

al) manufacture said face (20, 22) so that the part of the face that is in use, closest to the opposite face (22, 20) is a flat and planar area and wherein, the plating step B) comprises following sub-step:

bl) plating is localized on said flat and planar area.

3. Method (100) as claimed in claim 2 wherein, the sub-step al) is specified with the following sub-step:

a2) said flat and planar area comprises at least the outer peripheral area of said face and wherein, the sub-step bl) comprises the following sub-step:

b2) plating thickness (T24) may be between 10pm and 30pm the thickness tolerance being of +/- 2pm.

4. Method (100) as claimed in claim 3 wherein, the sub-step a2) is specified with the following sub-step:

a3) said flat and planar area covers the entire face (20) and wherein, the plating step B) is specified with the following sub-step:

b3) plating material (M) is chromium.

5. Method (100) as claimed in claim 4 wherein the sub-step b3) is specified with the following sub-step:

b41) the plated area defines an annulus close to the peripheral edge (26).

6. Method (100) as claimed in any one of the preceding claims further comprising the step:

C) hardening the other face (20, 22) that faces the face plated locally (24) at step B).

7. Pole piece (16) of an actuator of a fuel injector, said pole piece having a face (20) adapted to be in regards of a face (22) of a magnetic armature so that an airgap (G) is defined between said faces, said face of the pole piece being locally plated as per a method (100) as claimed in any one of the preceding claims.

8. Magnetic armature (18) of an actuator of a fuel injector, said armature having a face (22) adapted to be in regards of a face (20) of a pole piece so that an airgap (G) is defined between said faces, said face (22) of the armature being locally plated as per a method (100) as claimed in any one of the claims 1 to 6.

9. Fuel injector (10) comprising a body housing an electro-actuator (12) wherein a pole piece as claimed as in claim 7 cooperates with a magnetic armature (18).

10. Fuel injector (10) comprising a body housing an electro-actuator (12) wherein a pole piece cooperates with a magnetic armature (18) as claimed in claim 8.