Electromagnetic Fuel Injectors For Internal Combustion Engines

Abstract

An electromagnetically controlled injector for internal combustion engines adapted to cut out the effects on uniformity of feed of all parasitic phenomena such as the rebounds of the needle and modifications in the pressure prevailing in the feed pipes. To this end, the liquid fuel is protected against the formation of waves by a throttling of the incoming liquid in a channel extending laterally of the stationary armature or else axially through the latter directly into the needle. Thus it is possible to obtain for the curve of injected fuel amounts vs. time a straight line between the desired minimum and maximum amount values.

Description

BACKGROUND OF THE INVENTION

The present invention relates to improvements in electromagnetic fuel injectors for internal combustion engines. It is a well known fact that it is possible to measure the amount of fuel injected by means of electromagnetic injectors adapted to receive for the execution of each injection an electric signal of a predetermined duration, which duration depends on the operative conditions of the internal combustion engine. The injectors should operate at considerable speeds ; by way of example, it should be remarked that the durations of injection range between 0 and 2 ms for Diesel engines and from 0.8 to 4 ms. for gasoline-operated engines, the amounts of injected fuel ranging between 7 and 40 cubic mm.

The injectors resorted to are of the type provided with a needle cooperating with a port defining the throughput. The needle is rigid with the movable electromagnet armature constituted by the lamellatted plate of the electromagnet. The movable armature registers with the stationary armature.

The needle rises by amounts of a magnitude of 0.1 mm. and,with injectors of such a type operating at such speeds to,it is necessary to cut out all parasitic phenomena which may have an influence on the amount of fuel injected in conformity with the duration of the electric signals.

In fact, the speedy upward and downward movements of the injector needle lead to rebounds and to large modifications in pressure in the pipes,which are ascribable to the high instantaneous outputs and wave effects.

Consequently, the amount of fuel injected with reference to time does not follow a linear law and it depends on the following characteristics: wave effects are produced by the reflection of waves inside the pipe system ; there is a threshold below which it is no longer possible to foresee to a sufficient extent the actual amount of injected fuel. The slope of the curve corresponding to the amount of fuel injected as a function of time is very high at such a point by reason of the elastic properties of the liquid inside the injector. The shape of the curve always shows a speedy rise at the beginning, a relative maximum, and a relative minimum produced by the rebounds of the needle on its abutments. It is only beyond the minimum that the curve shows its useful section which should be substantially linear. It should be remarked that the pressure waves in the different injectors act mutually on one another.

By reason of the influences and interactions mentioned hereinabove, an injector, operating at an injection pressure selected to provide the maximum amount of fuel to be injected during a predetermined period, may not permit the amount of fuel injected to drop below a minimum amount of fuel which is higher than the minimum amount required for a proper operation of the engine. Conversely, if the injection pressure is selected and the injector is designed so as to provide the minimum amount of fuel required for the engine, it is not possible to obtain the necessary maximum amount of fuel.

The present invention has for its object to solve such a problem by causing the non-linear section of the curve defining the injected amount of fuel vs. the time elapsed to assume a lower level in order to obtain the minimum amount of fuel required at the beginning of the linear section of the curve while the fuel injection pressure is slightly increased so as to allow the maximum fuel output to be obtained for a predetermined duration of injection.

SUMMARY OF THE INVENTION

According to the present invention, the injector is designed so that it has a minimum idle volume filled with gasoline and communicating with the injection port so as to completely cut out the effects of the elasticity of the liquid in the fuel injector. Further, at least a portion of the channel between the seat of the injector valve and the supply of compressed fuel has a cross-section which retards the speed of progression of the liquid by submitting it to a sufficient inertia so that it is possible to obtain a comparatively slow fuel flow through the injector which lasts substantially during the rebounds of the injector needle.

As a development of this general principle, no idle volume is provided between the stationary electromagnet armature and the body of the injector. The armature is provided with a central bore having a diameter of about 2 mm. The bore provides fuel from the supply to a central bore in the needle of the injector through a central bore in the movable armature.

According to another embodiment of the invention, a tube having a diameter of about 2 mm. is provided to supply fuel to the injector port. The tube is bent so as to pass round the stationary armature of the injector, thus presenting no idle volume within the injector body, and opens into the space enclosing the movable armature of the injector. This space in turn communicates with the injector port when the injection valve is open.

A further object of the invention consists of producing an injector body which has little sensitivity to thermic expansion. A nozzle of case hardened steel is spaced with reference to the magnetic circuit by a bronze ring. The ring is provided for locking the nozzle on the body of the injector and for permanent positioning of the magnetic circuit by its bearing against the lower section of the latter. The magnetic circuit is adherently secured to the injector body only along the lateral outer surface of its lower section.

An embodiment of the invention is illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of an injector extending through line I--I of FIG. 2;

FIG. 2 is a partial sectional view of the same injector as seen through line II--II of FIG. 1;

FIG. 3 is a sectional view of a further embodiment of the injector; and

FIG. 4 is a diagrammatic illustration of the curve showing the amounts of fuel injected as functions of the duration of the control signal.

BRIEF DESCRIPTION OF THE INVENTION

As illustrated FIGS. 1 and 2, the body 1 of the injector has at its upper end terminals 2 and 3 feeding the inducing winding 4 of the armature constituted by the magnetic circuit 5. The needle carrying part 11 of the injector, which is held spaced from the central section of the magnetic circuit by a washer 6, is guided inwardly of the body 1 by a projection 8 on the magnetic circuit. The projection is subjected to the pressure of the spring 12. The needle carrying part 11 slides in the axial bore of the nozzle 9. Both the movable part 11 and the nozzle 9 are made of case hardened steel. A bronze ring 7 serves as a mechanical spacer between the nozzle 9 and a shoulder on the injector body 1. The ring 7 is made of an amagnetic material to prevent the magnetic flux from closing over the movable needle and subjecting the latter to friction-producing lateral strains.

The ring 7 projects inwardly of the shoulder and ensures the permanent positioning of the magnetic circuit bearing along its lower part.

The magnetic circuit does not adhere to the body of the injector throughout its lateral surface,but only through the outer surface of the enlarged lower end of the circuit. The outer surface engages the upper surface of the ring 7. Thus, the longitudinal expansions of the injector body and of the magnetic circuit are practically independent. The reference points of the expansions of the body and the circuit lies near the gap.

The recess in which the plate carrying the movable part and needle 11 and the recess formed in the vicinity of the injection port are connected by a bore 14 formed in the nozzle 9. The injector is fed with fuel through a pipe 13 of a small diameter allowing speeds of progression which are generally above 1 m/ sec. The length and diameter of the pipe 13 are selected so that upon opening of the injector 1 and as a consequence of the phenomena of inertia of the liquid and of the propagation of the wave inside the pipe, the liquid reaches its speed corresponding to a continuous output only at the end of the period during which the movable part or needle rises and rebounds.

In the embodiment illustrated in FIG. 3,the pipe 13 is replaced by an axial bore 13a extending through the stationary armature 5 and communicating with the inside of the needle 11 through a bore 5b formed in the projection 5a on the armature. The cross-section of the bore 13a is substantiallyt the same as that of the pipe 13 so that it is possible to obtain substantially the same effect of inertia. However, the idle volume of the embodiment of FIG. 3 is still more reduced since the recess in the plate 11a is no longer in communication with the opening in the nozzle 9.

During the opening of the injector, the pressure in the injector drops rapidly to a substantial extent so that the output is then lower,if the amount of liquid stored elastically inside the injector is small.

The throughput increases with time and the nominal output is reached only at the end of the ballistic period during which the movable section rises.

The output threshold is thus considerably lowered and the effects of rebound are reduced to a minimum.

If the feed pressure varies speedily,for instance, by reason of modifications in pressure ascribable to the action of the other injectors, the mass of liquid carried in the pipe acts through its inertia and limits the modifications in throughput produced by the parasitic modulations in pressure.

In FIG. 4,there is illustrated the curve of fuel amounts injected as a function of time. The solid line curve corresponds to the case of an injector providing a maximum amount of fuel q for a duration of the control signal of a predetermined value T2, but also providing a minimum amount q which is too large for the engine considered. By resorting to an injector according to the present invention,it is possible to lower the curve as a whole so as to obtain a minimum amount q min for a signal of a duration T1, although in such a case only a lesser maximum amount q max is obtained. With a slight increase in the injection pressure, it is possible to increase the slope of the curve so as to obtain again the desired maximum amount. It should be remarked that in all cases the non-linear section of the curve between TO and T1 is entirely unfit for use.

Claims

What I claim is:

1. An electromagnetic fuel injector for an internal combustion engine comprising an elongated body having a fuel input port and a fuel output port disposed adjacent the opposite ends thereof, a stationary armature mounted in the body, an electromagnetic winding for inducing flux in the stationary armature, a movable armature slidably mounted within the body for longitudinal movement to and from a closing position, the movable armature having a needle at one end thereof for closing the output port when the movable armature moves to the closing position, a fuel chamber surrounding the needle of the movable armature adjacent to the output port and being in communication with the fuel output port when the movable armature is moved from the closing position, the fuel chamber having a reduced volume, and an elongated fuel passage in the body extending from the fuel input port to the fuel chamber, the fuel passage having a small bore, the small bore of the fuel passage restricting the flow of fuel from the fuel output port when the movable armature initially moves from the closing position, thus reducing the amount of fuel per unit of time initially discharged from the fuel output port during the transient fuel flow period when the needle is initially moved from the fuel output port.

2. An electromagnetic injector in accordance with claim 1 in which the fuel passage has an approximately uniform cross-section.

3. An electromagnetic fuel injector in accordance with claim 2 in which the fuel passage has a circular cross-section, the ratio of the length of the fuel passage to the diameter thereof being equal to or greater than about 10.

4. An electromagnetic fuel injector in accordance with claim 3 in which the diameter of the fuel passage is approximately 2 millimeters.

5. An electromagnetic fuel injector in accordance with claim 2 in which at least a substantial portion of the fuel passage extends along the longitudinal axis of the stationary and movable armatures, the movable armature having a port therein adjacent the needle for communicatively connecting the longitudinally extending fuel passage with the fuel chamber.

6. An electromagnetic fuel injector in accordance with claim 2 in which the body further comprises a space surrounding the movable armature, a first portion of the fuel passage communicatively connecting the fuel input port and the space, the first portion of the fuel passageway extending laterally around the electromagnetic winding, and a second portion of the fuel passage communicatively connecting the space and the fuel chamber.

7. An electromagnetic fuel injector in accordance with claim 1 wherein the body comprises an upper portion and a nozzle portion, the upper portion for mounting the stationary armature therein with a portion of the stationary armature adjacent one end thereof, the one end of the upper portion being adapted to engage the nozzle portion, the nozzle portion for mounting the movable armature for longitudinal movement therein, the nozzle portion engaging the upper portion for positioning the movable armature adjacent to but spaced apart from the stationary armature, the movable armature being biased against the nozzle portion, the nozzle portion being constructed of a material having a low thermal expansion coefficient, and a ring constructed of an amagnetic material being disposed between the upper portion and the nozzle portion and abutting a portion of the upper portion and another portion of the nozzle portion for spacing the nozzle portion with respect to the upper portion, the ring thus establishing the spaced apart relationship of the stationary armature and the movable armature, the combination of the amagnetic ring and the nozzle portion constructed of a material having a low thermal expansion coefficient for reducing the sensitivity of the fuel injector to expansion caused by magnetic field generated by the electromagnetic winding.

8. An electromagnetic fuel injector in accordance with claim 1 wherein the stationary armature has three parallel core members, the middle core member being surrounded by the electromagnetic winding, the stationary armature being laminated, the movable armature comprising a laminated plate having an upper surface adjacent to but spaced apart from the lower surface of the stationary armature.