Method for obtaining a fuel injector for an internal-combustion engine, and an injector made according to said method

A fuel injector for an internal-combustion engine comprises an injector body and an injection-control valve, which in turn comprises: an open/close element; an elastic thrust element for pushing the open/close element; and a solenoid actuator, which can be actuated for exerting an action countering the thrust exerted by the elastic element. The solenoid actuator is formed by a monolithic assembly obtained in a mould, in which there is injected, on a core and a coil coupled to one another, a plastic material, which defines, once it has solidified, a body for insulation of the core from the injector body and which forms, once it has solidified, a monolithic assembly with the core and the coil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for obtaining a fuel injector for an internal-combustion engine. In particular, the present invention relates to a method for obtaining a fuel injector comprising a hollow injector body and an injection-control valve. The valve in turn comprises: a valve body of a tubular shape inserted into the injector body; an open/close element pressed against a head surface of the valve body by an elastic thrust element; and a solenoid actuator which can be actuated to exert an action countering the one exerted by the elastic element and to enable the open/close element to recede from the aforesaid head surface.

2. Description of the Related Art

In the known solutions, the solenoid actuator comprises: a core; a coil housed in the core and provided with a pair of rod-shaped contacts traversing the core for the connection of the coil to a control unit for controlling injection; and a set of parts to be assembled so as to form, once they have been assembled, a block of non-magnetic material such as to guarantee magnetic insulation of the core from the injector body and electrical insulation of the rod-shaped contacts. The block of non-magnetic material is normally made of non-magnetic steel or brass.

Even though known injectors of the type described above are employed, they entail relatively high production costs and relatively long times for assembly. This may basically be put down to the fact that the block of non-magnetic material is relatively complex from a production standpoint since it has to be coupled at least partially to the rods and to the core, ensuring, at the same time, the necessary electrical and magnetic insulation and correct positioning of the electromagnet in the injector. Each part that constitutes the non-magnetic block requires specific machining operations on almost dedicated machine tools, with particularly long production times. Furthermore, the assembly operation, which involves also the core and the coil, proves particularly complex and such as to require dedicated machines and specific equipment and/or the use of specialized manpower, thus increasing the production times and costs.

BRIEF SUMMARY OF THE INVENTION

One purpose of the present invention is to provide a method for making a fuel injector, which provides a simple and economically advantageous way of construction.

According to the present invention, a method is provided for making a fuel injector for an internal-combustion engine and comprising an injector body, and an injection-control valve, which, in turn, comprises an open/close element. The fuel injection also includes an elastic thrust element for pushing said open/close element; and a solenoid actuator which can be actuated for exerting an action countering the one exerted by the elastic element. The solenoid actuator comprises: a coil, a core, and a body made of non-magnetic and insulating material for carrying the core and the coil and insulating them from said injector body. The method is characterized in that the core and the coil are inserted into a mould having a cavity delimited by a surface substantially complementary to the one delimiting said body made of insulating material, the core and the coil are positioned inside said mould, and a plastic material is injected in said cavity for englobing at least partially said core and forming with the core and said coil a monolithic assembly.

Preferably, in the method defined above, the core and the coil are coupled to one another prior to their introduction into said mould.

The present invention also relates to a fuel injector for an internal-combustion engine.

According to the present invention, a fuel injector for an internal-combustion engine is provided, which comprises an injector body and an injection-control valve, which in turn comprises an open/close element, an elastic thrust element for pushing the open/close element, and a solenoid actuator, which can be actuated for exerting an action countering the thrust exerted by the elastic element. Said solenoid actuator comprises a core, a coil, and a body made of non-magnetic and insulating material for carrying the core and the coil and insulating them from said injector body. Said fuel injector is characterized in that said body made of insulating material is made of plastic material molded directly onto said core to form with said core and said coil a monolithic block.

Preferably, in the injector defined above, said coil carries two rod-shaped electrical contacts; at least one intermediate portion of said electrical contacts being embedded in said body made of plastic material.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, the reference number1designates, as a whole, a fuel injector for an internal-combustion engine (not illustrated).

The injector1comprises an injector body2of a tubular shape having an axis3and comprising, starting from the free top end4, two tubular stretches, designated by5and6, which have internal diameters decreasing starting once again from the aforesaid free top end4. The stretches5and6are adapted to one another by an internal shoulder8orthogonal to the axis3, and house an injection-control valve12secured via a ring-nut16. The valve12further comprises an open/close element18, which is pushed against a contrast surface19by a helical compression spring20, and is retracted from the surface19itself by the countering action exerted by a solenoid actuator21forming part of the valve12and partially housed in the stretch5.

Once again with reference toFIG. 1, the solenoid actuator21comprises a hollow core23, a coil24, in itself known, housed in the core23and provided with a pair of rod contacts25, which are parallel to the axis3and are set at a distance from one another in the transverse direction, and which project in cantilever fashion beyond the stretch5(FIG. 1). The solenoid actuator21further comprises a body28made of plastic material, preferably polyamide with fiber-glass fillers, for example “Zytel” or “Stanyl”, in which there are embedded part of the core23, part of the coil24, and part of the intermediate stretches25aof the electrical contacts25, the top terminal stretches25bof which project axially in cantilever fashion beyond the body28. In the specific case, the body28has two portions integral with one another, designated by30and31, of which the portion30has outer dimensions approximating (albeit smaller than) the internal dimensions of the tubular stretch5, to which the portion30itself is coupled via the interposition of a seal gasket32. The portion31, which projects on the outside of the end stretch5, has an outer diameter decidedly smaller than that of the portion30, and is adapted to the portion30itself via an annular intermediate axial shoulder33orthogonal to the axis3. The shoulder33is set at a distance from a top end edge34of the stretch5by a pre-set amount and defines a resting surface for a compression spring35, conveniently of the Belleville type or crinkle-washer type, forced against the shoulder33by a ring-nut36shaped like a cup set upside down, one side wall37of which is screwed on an outer threading of the stretch5, and one annular end wall38of which surrounds, with radial play, the stretch31of the body28, is set so that it bears upon the top edge34of the stretch5, and defines an axial contrast for the Belleville spring or crinkle washer35.

In the variant illustrated inFIG. 3, the ring-nut36and the spring35are replaced with an elastic body40for gripping, which is, for example, of the type described in the European patent EP-B-1 219 823, filed in the name of the present applicant and, in any case, comprises a collar41, which is fitted, with play, on the stretch31and comprises an axial projection41aco-operating with the shoulder33by bearing upon it. The collar41carries coupled thereto one or more elastically deformable stays42(two of which are the ones illustrated inFIG. 3), which are, conveniently, integral with the collar41, extend downwards, and terminate with two engagement portions43for engaging via snap action in respective retention seats44of the injector body2. Alternatively, according to a variant (not illustrated), the retention seats44are obtained on an auxiliary body carried by the injector body.

Once again with reference toFIG. 1, the terminal stretches25bof the rods25are electrically connected, in a known way, to respective terminals45, carried by a terminal block46housed in an electrical-insulation cap47. Again with reference toFIG. 1, for each rod25provided between the terminal block46and the body28is a respective seal gasket48, which surrounds the corresponding rod25and is housed in a blind axial cavity49of the body28. According to a variant (not illustrated), the valve is without the gaskets48and tightness is ensured by the coupling between the rods and the body made of plastic material.

The injector1described is obtained according to the following procedure. First, the coil24provided with the rods25and the core23are inserted and positioned in a mould50, partially illustrated inFIG. 2, which has a cavity51delimited by an internal surface substantially complementary to the external lateral surface of the body28. Preferably, the coil24and the core23are coupled to one another prior to being inserted into the mould50. In any case, once they have been positioned in the mould50, the latter is closed and, inside the cavity51, there is injected the plastic material that is to form the body28, embedding in the plastic material itself part of the core23and of the coil24beyond the intermediate portion25aof the rods25. Once solidification has occurred, the core23, the coil24, the rods25, and the body28are locked in fixed relative positions and consequently constitute different parts of a stable block or monolithic assembly53, which is electrically and magnetically insulated and which can no longer be disassembled. Following upon extraction of the monolithic assembly from the mould50, the gasket32is housed in its own seat, after which the valve12is inserted into the injector body2and secured via the ring-nut16. Then the assembly53is inserted into the stretch5of the injector body2until the core23is brought up against a spacer ring55(FIG. 1), which is preferably made of a non-magnetic and insulating material and is set so that it bears upon the shoulder8. Alternatively, the ring55could be an ordinary spacer ring. At this point, the spring35is set so that it bears upon the shoulder33, and the ring-nut36shaped like a cup set upside down is fitted on the body28and screwed onto the stretch5until its end wall38sets itself bearing upon the terminal edge34of the stretch5. Following upon fitting-on of the ring-nut36, the terminal block46couples to the rods25and to the cap47in a known way. Alternatively, the terminal block and the cap are assembled on the monolithic assembly prior to their installation in the injector body.

From the foregoing description it appears clearly evident that, as compared to known solutions, molding of the body28made of plastic material directly on the core23and on the coil24enables, on the one hand, a perfect electrical and magnetic insulation between the various parts to be guaranteed and, on the other, a reduction in the times and costs of production and assembly. In fact, in a single molding operation the body28is obtained, with the core23and the coil24fixed simultaneously to one another and to the body28itself. In addition, on account of the molding operation, also the rods25are embedded in the plastic material, and consequently the required fluid tightness is ensured, so that the gaskets48in this case perform only a safety function and in some cases can even be omitted.

The use of the ring-nut36screwed on the injector body2so that it couples with the elastic element35enables the monolithic assembly53to be gripped and blocked elastically inside the injector body2and, in particular, makes it possible to separate the gripping load of the monolithic assembly53from the gripping torque of the ring-nut36, since the travel of the ring-nut36is limited by the contrast of its annular wall38against the edge34of the injector body2. The gripping load is instead determined only by the stiffness and working length of the elastic element. The aforesaid length is equal to the distance between the two contrast surfaces33and34and can be defined in the design stage so that the required load is provided exactly. Furthermore, if the stiffness of the elastic element is sized in an appropriate way, the aforesaid load remains practically invariant both in normal operating conditions and in the case where the body28presents geometrical or dimensional variations, for example because it is subjected to high thermal gradients.

The use of fast-action clamps instead of the ring-nut36and springs35, as illustrated inFIG. 3, enables a further reduction in the times required for assembly and for maintenance and repair.

From the foregoing description it is clear that modifications and variations can be made to the injector1described herein, without departing from the sphere of protection of the present invention. In particular, the body28could be made with a material different from the one described herein by way of example, and the monolithic assembly53obtained in the mould could have shapes and dimensions different from the ones indicated and could be coupled to the injector body2in a way different from the one described herein by way of example.