EP0301620A2

EP0301620A2 - Electromagnetically controlled fuel injector for feeding fuel to internal combustion engines

Info

Publication number: EP0301620A2
Application number: EP88201411A
Authority: EP
Inventors: Roberto De Concini; Luciano Ramacciotti
Original assignee: Weber SRL
Current assignee: Weber SRL
Priority date: 1987-07-27
Filing date: 1988-07-06
Publication date: 1989-02-01
Also published as: IT8721450A0; EP0301620A3; IT1222137B

Abstract

The electroinjector is equipped with a central magnetic core (10) from which a guide tube (19) protrudes, which acts as a guide for an anchor (12) of ferromagnetic material, which bears the injector shutter (17). In a form of practical embodiment, the anchor (12), in its opening movement, comes to stop against a shoulder element (24) made from an amagnetic material fastened on the core (10) in such a protruding position, as to define an air gap (T) and prevent the core (10) and the anchor (12) from magnetically sticking to each other. The shoulder element (24) is provided with a fastening cylindrical portion (30), and an adjacent portion (31) with a prevailingly radial development, which acts as the stop portion. The element, which can also be fastened onto the anchor (10), can be obtained from a rolled sheet or by drawing a thin tube.

Description

The present invention relates to an improved electroinjector for feeding fuel to internal combustion engines, of the type comprising a housing body, inside which a central core of ferromagnetic material is installed, and is at least partially surrounded by a coil, a movable anchor of a ferromagnetic material, having a substantially hollow cylindrical shape, and bearing at an end a shutter element capable of interrupting the fuel flow through an injection nozzle under the action of a return spring, which returns said anchor to a position, and a substantially annular shoulder element, made from an impact-resistant material and at least partially amagnetic, capable of acting as a stop for said anchor in another position of said anchor, in which position the shutter element leaves open the passage through which the fuel flows through the injection nozzle, with the anchor being guided by a tube integrally inserted in the central core, and protruding from it.
In an electroinjector of such a type, the annular shoulder element, coaxially slid on the outer wall or on the inner wall of the central core, and fixed, e.g., by diametrical interference, axially protrudes from the core end, in such a way that in the position of lifting stroke end of the anchor, when said anchor is in contact with the annular element, a small air gap remains between the anchor and the core. This air air gap, together with the amagnetic nature of the annular element, prevents any possible occurrences of phenomena of magnetic sticking between the anchor and the core, improving the anchor closure transients.
The annular shoulder element should have such a thickness as to provide, at its stop end, an annular surface having a large enough surface area for withstanding the repeated impacts by the anchor.
If the annular shoulder element is installed externally of the core, the anchor, which normally has an outer diameter equal to the outer diameter of the core, should be enlarged up to reach the outer diameter of the shoulder element, thus increasing in weight and consequently the dynamic characteristics of the electroinjector becoming worse.
This drawback can be obviated by reducing the outer diameter of the core in the shoulder element fastening portion, thus creating on the core a stop shoulder for the shoulder element, but in this way the surface area of the core end, through which the anchor attraction action is performed, is decreased, and the dynamic characteristics of the electroinjector are also worsened.
The same happens if the annular shoulder element is slid inside the core, inside a purposely provided housing for it, which necessarily reduces the end core surface area.
The placing of the annular shoulder element in such a position as to define the exact air gap involves furthermore serious tolerance problems. The tolerance limits to be realized and maintained are generally smaller than 20 µ for the air gap, which involves extremely small values of tolerance for the annular shoulder element and the possible stop shoulder on the core, values which are difficult to maintain with reduced costs and in a series production.
A purpose of the present invention is to provide an electoinjector of the initially specified type, wherein the position of installation of the annular shoulder element enables the initial shape of the core and/or of the anchor to be preserved, or, at maximum, to be only slightly modified, so as not to reduce or, at worse, to only slightly reduce the surface area of the core attraction surface, so as to possibly fully exploit the initial surface area existing between both elements, advantageously from the standpoint of the dynamic answer of the electroinjector.
Still a purpose of the invention is to provide an electroinjector as above specified, which can be obtained by a series manufacturing process, with reduced prices and does not cause tolerance problems.
A not least purpose of the present invention is to provide an electroinjector wherein the arrangement of the shoulder element does not considerably alter the conditions of passage of fuel, as compared to the above reminded electroinjector type known as above specified.
In order to achieve these purposes, according to the present invention an electroinjector of the type specified in the introduction is proposed, wherein the shoulder element has a fastening portion of substantially cylindrical shape, and an adjacent portion of radial development, suitable for acting as a stop portion.
Advantageously, the shoulder element with the cylindrical portion and the radial portion can be obtained by means of a single process step, e.g. by pressing from a rolled sheet, or by drawing of a thin-wall tube.
The shoulder element can be fastened either on the core, or on the anchor.
In an electroinjector of such a type, the measure of the air gap is defined by the thickness of the radial portion of the shoulder element, a thickness which can be obtained by means of the above mentioned processes at low cost, with very narrow tolerances. Therefore, providing ar inner or outer stop shoulder on the core (or on the anchor) with precise tolerance values is no longer required, and not even the cylindrical portion of the shoulder element has any longer to be formed with narrow tolerances.
The radial portion can extend towards the inside or towards the outside of the cylindrical portion, according to whether the stop element has to be installed externally or internally of the core or of the anchor.
Owing to the reduced thickness of the cylindrical portion, generally equal to the value of the air gap, even if the shoulder element is fastened inside the core or the anchor, it only involves a very small reduction in the surface area of core/anchor attraction surface. When it is mounted externally of the core or of the anchor, the shoulder element does not involve a reduction in such a surface area, or an increase in respectively anchor or core size, in that the stop area is defined by the radial portion of the element, and not even does it involve a perceivable reduction in the surface area of the fuel passage opening.
Further details and advantages of the present invention will be clearer from the following disclosure of some preferred and non-limitative forms of practical embodiment of the same invention, depicted, for exemplifying purposes, in the hereto attached drawings, wherein:

Figure 1 shows an axial sectional view of an electroinjector according to the present invention;
Figure 2 shows an axial sectional view on an enlarged scale of the end portion of a first form of practical embodiment of an electroinjector according to the present invention;
Figure 3 shows a sectional view similar to that of Figure 2, but depicting another form of practical embodiment;
Figure 4 shows a sectional view similar to those of Figures 2 and 3, but depicting a further possible form of practical embodiment;
Figure 5 shows a plan view of the shoulder element of Figure 2;
Figure 6 shows a plan view of the shoulder element of Figure 3;
Figures 7 and 8 show two forms of practical embodiment, wherein the shoulder element in installed on on the anchor and not on the core.

Referring first to Figure 1, an electroinjector of the type according to the present invention comprises a central cylindrical core 10 of a ferromagnetic material, housed inside a housing body 11, also of a ferromagnetic material, and extending outside the body 11 to form a fitting 10a in order to connect the injector with the fuel feed.
With the core 10 a movable anchor 12 of a ferromagnetic material is coaxially associated, which, together with the core 10 and the body 11, forms a magnetic circuit.
The core 10 is at least partially surrounded by a coil 13 wound on a bobbin 14, which is fed with electrical power, in a per se known way, with intermittent drive, by means of leads 15 partially embedded in a plastic cap 16.
The movable anchor 12, of a substantially hollow cylindrical shape, bears a shutter element 17 with the interposition of a washer 18, and is guided by a guide tube 19 slid inside the core 10, but protruding from it. A spring 20 keeps the shutter element 17 normally pressed against a shoulder portion of an injection nozzle 21, fitted, in a per se known way, with a calibrated bore for fuel outlet. The spring 20 reacts against a grub screw 22 screwed down, with interference, inside the core 10, and provided with a central channel, in order to allow the fuel to flow through.
Between the nozzle 21 and the body 11, an annular shim 23 is interposed, which substantially defines the stroke of the anchor 12, which, on core 10 side, comes to stop against an annular shoulder element 24 made from an impact-resistant material, and at least partially amagnetic, installed on the core 10 in such a way as to axially protrude from the end of the core 10, leaving a small air gap "T", Figure 2, between the anchor 12 and the core 10 in the anchor position of lifting strole end, when the shutter element 17 leaves open the passage through the nozzle 21. The annular shoulder element 24 secures that phenomena of magnetic sticking do not occur, which are dangerous in that would prevent a fast injector shutting action.
The tightness to liquids is ensured by seal rings 25, 26 and 29. The fuel, fed through the grub screw 22, comes, in a per se known way, to the external portion of the nozzle 21, flowing through the bores 27 of the core 10 and the bores 28 of the anchor 12.
One can easily understand that when the coil 13 is deenergized, the anchor 12, under the action by the spring 20, is in its lower position, wherein the shutter element 17 shuts the passage for fuel flow through the nozzle 21, whilst, when the coil 13 is energized, the anchor 12 is in its lifted position, into contact with the annular shoulder element 24 and the shutter element 17 leaves open the passage for fuel flow through the injection nozzle 21.
As Figures 2 to 8 clearly show, the shoulder element 24 is formed by a fastening portion of a substantially cylindrical shape 30, and an adjacent portion 31 with a substantially radial development, which forms, relatively to the cylindrical portion, an angle of substantially 90°, and is suitable for acting as a stop portion. Advantageously, both portions 30 and 31 have a same thickness.
The thickness of the radial portion 31 defines the "T" air gap when the anchor 24 is in its position of attraction stroke end, and by "C" the stroke of anchor 12 is indicated.
In the form of practical embodiment depicted in Figure 2, the radial-development portion 31 extends towards the interior of the shoulder element 24, and the cylindical portion 30 is slid on the core, externally to it, and is fixed, e.g., by interference. The portion 31 engages the core end potion 10.
Due to the very small thickness of the shoulder element 24, the outer diameter of the cylindrical portion 30 results to be only slightly larger than the outer diameter of the core 10, so that neither overall dimension problems inside the coil 14, nor considerable reductions in fuel passage cross section surface area arise.
One should remark that although the annular element 24 is assembled on the outer surface of the core, neither the thickness of the anchor 12 has to be increased, nor the core 10-anchor 12 attraction surface area has to be decreaed.
The size of the radial portion 31 is so selected, as to have a high enough shoulder surface area as to withstand the repeated impacts by the anchor 12 during operation.
In the form of practical embodiment depicted in Figures 3 and 4, the shoulder element 24 has its radial portion 31 directed outwards. The cylindrical portion 30 can be fixed by interference inside the core 10 inside a seat 32 provided on it (Figure 3), or by interference on the guide tube 19 for the anchor 12 (Figure 4). This tube 19 has a very precise diameter and an extremely good surface finish as well as a high hardness, which makes it easier the shoulder element 24 to be applied to the same tube.
One should observe that the housing seat 32 must no longer define a stop shoulder with a narrow tolerance, as it occurredd in case of the injector known from the prior art, but can result even considerably longer that the height of the cylindrical portion 30, inasmuch as the stop shoulder is realized by resting against the flat end surface of the core 10. One should furthermore observe that the small thickness of the cylindrical portion 30, substantially equal to the width of the air gap "T", does not cause a considerable decrease in the surface area of core 10-anchor 12 attraction surface. The radial size of the radial portion 31 is obviously selected in such a way as to have a large enough shoulder surface area for withstanding the repeated anchor impacts.
Instead on core 10, the shoulder element 24 could be fixed, in an equivalent way, on the anchor, as shown in Figures 7 and 8.
Advantageously, the shoulder element 24 according to the present invention can be manufactured by pressing from a rolled sheet, or by drawing of a thin-wall tube.
When the element 24 is manufactured from a rolled sheet, a thickness with very narrow tolerances (±0.05 mm) and a very good surface finish is obtained at a low cost. The rolling process usually causes also an increase in material hardness, which could render non-necessary a surface hardening treatment of the shoulder element, such as, e.g., the application of a titanium nitride layer, as provided for the shoulder element of the injector known from the prior art, with the manufacturing costs being hence further reduced.
In case the air gap must be very small, e.g., of 0.030 mm of thickness, the shoulder element 24 could be manufactured as well by a drawing process, but starting from a larger-thickness sheet, e.g., of 0.20 mm, and subsequently processing the element on its outer portion, in order to achieve the desired thickness. The element could be then hardened before being assembled on the core or on the anchor.
The shoulder element 24, integrally obtained by pressing or by drawing, with or without a finishing processing, could be also assembled on the core, on the anchor or on the guide tube with a precise free coupling, and then fastened by spot-welding.
A shoulder element 24 has been herein disclosed and illustrated, which has a portion 31 of annulus shape, but not necessarily should the portion 31 be continuous, in that it can also be provided with radial interruptions or slots, in particular in case of an inwards-developing radial portion 31, in order to prevent a closed chamber from being formed inside the portion 31 when the anchor 12 is in its attracted position, which would negatively affect the anchor detachment, owing to a depressure action caused by the fuel inside said chamber.
The portion 31 could also be positioned at a not perfectly square angle with the cylindrical portion 30, or could have a not entirely flat development. Many other modifications and changes are of course possible, without departing from the scope of the inventive concept ot the present finding.

Claims

1. Improved electroinjector for feeding fuel to internal combustion engines, of the type comprising a housing body, inside which a central core of ferromagnetic material is installed, and is at least partially surrounded by a coil, a movable anchor of a ferromagnetic material, having a substantially hollow cylindrical shape, and bearing at an end a shutter element capable of interrupting the fuel flow through an injection nozzle under the action of a return spring, which returns said anchor to a position, and a substantially annular shoulder element, made from an impact-resistant material and at least partially amagnetic, capable of acting as a stop for said anchor in another position of said anchor, in which position the shutter element leaves open the passage through which the fuel flows through the injection nozzle, with the anchor being guided by a tube integrally inserted in the central core, and protruding from it, characterized in that the shoulder element has a fastening portion of a substantially cylindrical shape, and an adjacent portion with a radial development, suitable for acting as a stop portion.

2. Electroinjector according to claim 1, characterized in that said radial-development portion extends towards the interior of the shoulder element, and the substantially cylindrical portion is fastened inside the core, with the radial-development portion engaging the core end surface.

3. Electroinjector according to claim 1, characterized in that the radial-development portion extends towards the outside of the shoulder element, and the substantially cylindrical portion is fastened inside the core, with the radial-development portion engaging the core end surface.

4. Electroinjector according to claim 3, characterized in that the substantially cylindrical portion is fastened inside a seat provided inside the core.

5. Electroinjector according to claim 1, characterized in that the radial-development portion extends towards the outside of the shoulder element, and the substantially cylindrical portion is fastened to the anchor guide tube.

6. Electroinjector according to claim 1, characterized in that the radial-development portion extends towards the inside of the shoulder element, and the substantially cylindrical portion is fastened to the outer surface of the anchor, with the radial-development portion engaging the anchor end portion.

7. Electroinjector according to claim 1, characterized in that the radial-development portion extends towards the outside of the shoulder element, and the substantially cylindrical portion is fastened to the inner surface of the anchor, with the radial-development portion engaging the anchor end portion.

8. Electroinjector according to one of the preceding claims, characterized in that both portions are portions of a single element.

9. Electroinjector according to one of the preceding claims, characterized in that the radial-development portion and the substantially cylindrical portion have a same thickness.

10. Electroinjector according to one of claims from 1 to 8, characterized in that the radial-development portion has a thickness smaller than of the cylindrical portion.

11. Electroinjector according to one of the preceding claims, characterized in that the shoulder element is hardened.

12. Electroinjector according to one of the preceding claims, characterized in that the shoulder element is manufactured from a rolled sheet.

13. Electroinjector according to one of claims from 1 to 11, characterized in that the shoulder element is manufactured by drawing a tube.

14. Electroinjector according to one of the preceding claims, characterized in that the shoulder element is fastened to the core or to the guide tube by means of spot welding.

15. Electroinjector according to one of the preceding claims, characterized in that the radial-development portion is provided with radial interruptions or slots in its wider surface.