EP0172591B1

EP0172591B1 - Improved electroinjector for feeding fuel to an internal combustion engine

Info

Publication number: EP0172591B1
Application number: EP85201124A
Authority: EP
Inventors: Luciano Ramacciotti
Original assignee: Weber SRL
Current assignee: Weber SRL
Priority date: 1984-07-12
Filing date: 1985-07-09
Publication date: 1989-03-08
Also published as: DE3568610D1; IT8421869A0; IT8421869A1; EP0172591A1; IT1175561B

Description

The present invention relates to an electroinjector of the general type defined in the preamble of claim 1.
An electroinjector of this type is known from FR-A-2 241 008.
Electroinjectors must be designed in such a way as to make the armature opening and closing transients quick and repetitive, and for this purpose the armature must be of reduced mass, the friction coefficients between the armature and its respective guide means must be low, the gaps must be dimensioned in order to optimise the efficiency both in the opening stage and in the closing stage of the armature.
As it is known to those skilled in the art, the time duration of the closing transient of the armature acting as a shutter of the injector can be influenced by the effects of the so-called "hydraulic and magnetic sticking" which is experienced when a direct stroke end engagement between the armature and the central core exists, due to the relative wear which takes place between the contacting surfaces.
The repeated knocks between the armature and the core tend to annul the micro-unevennesses of the respective surfaces, until the surfaces become perfectly smooth and coplanar, so that the effective contact area between the surfaces of the armature and of the central core increases with time and a remarkable increase happens of the adhesion forces, of both magnetic and hydraulic characters.
This increase of the effective contact area between the armature and the core involves an increase both of the remanence force, and of the resistance against separation due to the adhesion, also called as attraction force between contacting smooth surfaces.
As a consequence of these phenomenons, the drift appears of electroinjectors, in that their response time at closure increases.
In view of what has been previously exposed, it is necessary that the magnetic and hydraulic sticking effect is eliminated between the contacting surfaces of the armature and of the core.
It has been suggested in DE-A-2123 145 and DE-A-3 015 192 to place a shoulder element of a magnetic and hard material in an intermediate position between the armature and the core, in such a way as to leave a gap which prevents the magnetic sticking, and to reduce to the minimum the contact area between the armature and the shoulder element, so as to reduce the adhesion force, and at the same time to maintain unchanged with time the effective contact area.
The arrangement of such a shoulder element in a projecting position such as to act as a stop element for the attracted armature in an electroinjector allows to solve the problems connected with magnetic sticking but it may create problems as to hydraulic sticking because depending on the construction and arrangement of the elements of the injector with respect to fuel passages the projecting shoulder element could create closed zones where fuel under pressure could remain confined when the attracted armature contacts the shoulder element. This would increase the hydraulic sticking owing to a depressurizing effect which would arise when the armature initiates its backwards movement into the fuel closing position.
Therefore, closure transients would not become faster although there would not be any notable magnetic sticking.
In known electroinjectors the construction is further rather complex and the armature is rather massive and this represents a handicap insomuch as massive armatures involve longer transients in the opening and the closing stage.
The present invention intends to solve the problem of providing an electroinjector having a simple construction and quick and repetitive transients whereby not only magnetic sticking but also hydraulic sticking which could be created by a projecting shoulder element acting as a stop for the attracted armature are avoided.
This problem is solved according to the invention by an electroinjector of the type specified in the preamble of claim 1, characterized in that the guide for the armature is a guide tube projecting from inside the central core and the armature is an annular armature slidable on said guide tube, and in that the shoulder element is made of effectively non magnetic material and projects from said end of the core, and said annular end surface of the armature is notched to define at least one radial passage therein.
The structural and functional characteristics of the invention and its advantages in comparison to the prior art will appear still more evident from the following disclosure, referred to the schematic drawings attached, which show examples of embodiments of the invention itself.
In the drawings:
Figure 1 is a longitudinal section view showing an electroinjector designed according to the invention; and
Figures from 2 to 9 are enlarged details illustrating components and alternatives of the invention itself.
Referring first to Figure 1 of the drawings, an electroinjector structurally comprises a core 10 of ferromagnetic material, an outside shell 11, it too consisting of ferromagnetic material, and an armature 12, which form altogether a magnetic loop.
By 13 a coil is indicated, wound on a bobbin 14, which surrounds the central core 10 and can be electrically powered with intermittent power by means of connectors 15 housed within a casing of plastics 16.
The armature 12, which is coupled with a sealing insert 17 of suitable material, with the interplacing of a washer 18, is guided by a small tube 19 inserted with interference in the central core 10, and is pressed by a spring 20 against the shoulder of a nozzle 21 equipped with a gauged bore for the outlet of fuel.
The spring 20 interacts with an insert 22 inserted with interference inside the central core 10.
A packing 23 defines the value of the stroke "H" of armature 12, which ends its stroke against a second annular element 24 assembled on core 10 in such a way as to protrude outward by the same value of desired gap "T" (Figure 2).
Rings 25, 26 and 36 guarantee the hydraulic tightness, whilstthe crimping of the shell 11 on the core 10 and on the nozzle 21 render monolithic the electroinjector.
An electroinjector provided as above described operates as follows.
Fuel is fed through the outer tubular wall of core 10, passes through the central bore of insert 22, then through bores 27 in the core and bores 28 in the armature, it arrives externally to nozzle 21.
Until the electroinjector is not electrically powered, the spring 20 holds the armature 12 with its sealing insert 17 pressed against the sealing flat surface of the nozzle, which is thus closed.
When, by means of the electrical connectors 15, electrical current is fed to the coil 13, a flux is generated in the magnetic loop, which draws back armature 12 from its sealing position to its position of stroke end, defined by contact on the annular element 24 of non magnetic hardened material. This lifting of armature 12, which takes place within a very short time (opening transient) allows the fuel to flow out of the nozzle in a quantity which, at each cycle, for a given gauging of the nozzle, is a function of fuel pressure, and of electrical excitation of the coil.
When the electrical powering is turned off, the armature returns to its contacting position on the sealing seat of the nozzle, pushed by spring 20 within a time which characterizes the closure transient.
The armature 12 may be manufactured with a harder material than pure iron, such as for instance Permenorm 5000H3. The annular element 24 (Figures 2 and 3) can be made from AISI 310 or bronze.
The inserted annular element 24 can be assembled in such a way as to rest against a flat surface 29 of central core 10 (Figures 1, 5, 6, 7 and 8), or it can be pushed so as to define the desired value of gap "T" (Figures 2 and 3), fixing the reached position by dimensional interference, or by other known means, such as by soldering or by glueing means. Another way of fixing the position of element 24 is to provide a longitudinal slot, such as in 30 (Figure 4) in it, or as in 31 (Figure 5), along its whole length, or along a part of it, then slidingly forcing it on to the central body, exploiting its elasticity within the limits of a given dimensional intereference.
Moreover, to the purpose of reducing still more the wear effect of the annular element 24 by the stroke end shoulder surface of the armature 12, a surface layer can be placed of very reduced thickness, of hard material, on the shoulder surface 32 of armature (Figure 9), said material could be e.g. titanium nitride.
In addition, by ensuring the hardening of the shoulder surfaces of element 24, as well as of armature 12, the said surfaces can be provided in such a way as to be positioned, instead of parallel, so as to form a given a angle between each other (Figure 7), of e.g. 1°, or the shoulder surface of the same element 24 can be made rounded, as in 33 (Figure 6).
By both these solutions, the contact surface between the two components of the shoulder is as reduced as possible.
The annular element 24, which defines the gap "T" and the end of the stroke "H" of armature, eliminates the magnetic sticking effect, while the hydraulic sticking effect is reduced by the reduced thickness of the wall of element 24 itself and by the hardness of contact surfaces, being it possible to increase such hardness as previously explained.
Moreover, by increasing the hardness of the shoulder surfaces, it becomes possible to reduce the contact geometry of said surfaces, by varying the shape of either or of both the surfaces said.
In order to avoid pumping effect of the liquid present inside the annular chamber 34 (Figure 2), which, during the initial stage of downward motion of armature would give rise to a delay of closure transient, a notch 35 is provided in the upper end surface of armature itself defining at least one radial passage therein. Therefore, hydraulic sticking is surely avoided.

Claims

1. Electroinjector for intermittently feeding quantities of fuel to an internal combustion engine, comprising a core (10) of ferromagnetic material, a coil (13) surrounding the core (10), an injection nozzle (21), a movable armature (12) positioned axially between the core (10) and the injection nozzle (21) and coaxial with both, a return spring (20) for pushing the armature (12) towards the injection nozzle (21), a guide (19) for the armature (12), a delivery duct of the fuel to the injection nozzle (21), an external shell (11) which closes the magnetic loop with the core (10) and the armature (12), a shoulder element (24) of essentially annular shape, at least partly consisting of shock-resistant material, mounted on the end of the core (10) and having a substantially annular end surface fitted to come in contact, at least partly, with a substantially annular end surface of said armature (12), characterized in that the guide forthe armature (12) is a guide tube (19) projecting from inside the central core (10) and the armature (12) is an annular armature slidable on said guide tube (19), and in that said shoulder element (24) is made of effectively non magnetic material and projects from said end of the core (10), and said annular end surface of the armature (12) is notched (notch 35) to define at least one radial passage therein.

2. Electroinjector as claimed in claim 1, characterized in that the said annular end surface of the armature (12) is coated by means of applied hard material, preferably titanium nitride.

3. Electroinjector as claimed in claim 1, characterized in that said substantially annular end surface of said shoulder element (24) is coated by means of an applied hard material, preferably titanium nitride.

4. Electroinjector as claimed in claim 1, characterized in that one of said annular end surfaces has a curved profile in cross section.

5. Electroinjector as claimed in claim 1, characterized in that at least one of said annular end surfaces is inclined through a certain angle with respect to a surface perpendicular to the longitudinal axis of the electroinjector.