Field of the Invention

This invention relates generally to solenoid-operated fuel injectors, and specifically to a method for reducing certain audible operating noise from such a fuel injector.

Background and Summary of the Invention

Certain fuel-injected automobile engines operate sufficiently quietly that certain audible noise from the operating fuel injectors may be distinguished by some persons in the vicinity. The detection of such noise may be deemed objectionable by the manufacturer, and/or it may be mistakenly perceived by the customer as a defect in the product despite the fact it is operating entirely properly.

The present invention relates to a method for attenuating certain audible noise emissions from an operating fuel injector which achieves meaningful noise reduction in an inexpensive manner. Analysis of an operating fuel injector before the present invention has revealed resonances in the range of about 8 kHz to about 12 kHz for the injector housing and inlet connector. The application of the present invention to that fuel injector has shifted the resonances to higher frequencies and has dampened the amplitude with the result that the measured A-weighted noise level has been reduced from about 60 dB to about 56 dB.

Briefly, the invention comprises injection molding a suitable material, such as nylon, into unoccupied space between the solenoid and the injector housing contemporaneously with injection molding like material onto the exterior of the housing and inlet connector in surrounding relation to the joint between them to form an axial end cap for the housing through which the inlet connector protrudes and which also contains a formation that cooperates with electrical terminals that protrude from the solenoid coil through the housing to form an electrical connector plug that is adapted to be connected to a mating connector plug from electric circuitry for operating the fuel injector. The material that has been

injection-molded into the unoccupied space on the interior of the housing enclosure cures to create in combination with the fuel injector a structure that operates more quietly than its predecessor. Principles of the invention are of course potentially applicable to forms of fuel injectors other than the one specifically herein illustrated and described.

A fuel injector of the type to which principles of the present invention have been successfully employed is depicted in commonly assigned US Patent 4,610,080. Fig. 3 of that patent shows the housing and inlet connector after the solenoid assembly has been inserted into the interior of the housing and after the non-metallic end cap has been applied, but before the housing is joined to the valve body assembly that forms the lower portion of the fuel injector. That Fig. shows that a portion of the bobbin which contains the electrical terminals protrudes through a hole in an end wall of the housing so as to make the terminals available for external electrical connection to mating terminals from a wiring harness that connect to the fuel injector. That Fig. shows the non-metallic end cap fitting over the protruding terminal-containing portion of the bobbin, but itself not extending through the hole into the interior of the housing. A drawing accompanies the present disclosure and illustrates a presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.

Brief Description of the Drawings Fig. 1 is an elevational view, partly in cross section, through a fuel injector embodying the present invention.

Fig. 2 is a view of a portion of Fig. 1 at an earlier stage of the fabrication process.

Fig. 3 is a top end view of one of the individual parts of the fuel injector by itself, the part being the housing.

Fig. 4 is a cross sectional view in the direction of arrows 4-4 in Fig. 3.

Description of the Preferred Embodiment

Fig. 1 shows the fuel injector 10 to comprise: a housing 12 of magnetically permeable material; an inlet connector 14 in the form of a tube also of magnetically permeable material; an adjusting tube 16; a helical coil spring 18; an armature 20; a solenoid coil assembly 22; a non-metallic end cap 24; and a valve body assembly 26. The relative organization and arrangement of these various parts are essentially the same as in the fuel injector of the aforementioned commonly assigned US Patent 4,610,080. The injector is of the type which is commonly referred to as a top-feed type wherein fuel is introduced through inlet connector 14 and emitted as injections from the axially opposite nozzle, or tip, end.

The differences essentially relate to the inventive features of the present disclosure. When solenoid coil assembly 22 is disposed within the interior enclosure of housing 12 during the fabrication process as illustrated by Fig. 2, there is unoccupied space 28 between the solenoid assembly and the housing wall. Space 28 extends completely around solenoid coil assembly 22 in the circumferential sense and almost the full length of solenoid coil assembly 22 in the axial sense. Solenoid coil assembly 22 comprises a solenoid coil 30 that is disposed on a plastic bobbin 32 between axial end flanges 34, 36 of the bobbin. The lower bobbin flange 36 has a close fit to the housing sidewall while the upper bobbin flange 34 is spaced radially inwardly of the housing sidewall. Solenoid coil assembly 22 is assembled into housing 12 by insertion through the housing's open lower end as viewed in Fig. 2. The solenoid coil assembly includes a pair of electrical terminals which are initially straight and parallel with the solenoid coil's axis so that they will pass through an aperture means in housing 12, namely through respective through-holes 38, 40 that are closely spaced apart in the axial end wall 42 of housing 12. Only one of the terminals appears in the drawing Figs. It is designated by the numeral 44 and passes through hole 38. The reader should understand that the other terminal passes through hole 40 in analogous manner. Corresponding portions of the bobbin material surround the two terminals as they pass through their respective holes 38, 40. The straight terminals are subsequently bent at an angle to create the shape that is shown in Figs. 1 and 2.

in addition to through-holes 38, 40, end wall 42 contains three circular through-holes 46, 48, 50, at the six, nine, and twelve o'clock positions respectively as shown in Fig. 3. These holes provide communication between space 28 and the exterior of housing 12. After the assembly of solenoid coil assembly 22 into housing 12 and the bending of the two electrical terminals, the sub-assembly is placed in an injection molding cavity of an injection mold 52, as shown in Fig. 2. Suitable injection molding material, nylon for example, is introduced into the cavity to form end cap 24 to the illustrated shape covering the joint between housing end wall 42 and inlet connector 14 and also forming a shell 54 that laterally bounds the two electrical terminals so as to form therewith a connector for connection with a mating connector on a wiring harness (not shown) that leads to circuitry for delivery of operating current to the fuel injector. While holes 38 and 40 are essentially plugged by the electrical terminals and surrounding bobbin material passing through them, holes 46, 48, and 50 are open. Consequently, some of the injected molding material flows through the latter three holes and into space 28.

The process continues until space 28 is essentially completely filled. The uncured injected molding material 56 is allowed to cure into solid form with the finished result being depicted by Fig. 1 where it can be seen that the cured material is axially coextensive with substantially the full length of solenoid coil assembly 22 except for lower flange 36. During the injection molding process a plugging portion of the mold is inserted into the open lower end of the housing to close off the risk of any material exuding past flange 36.

The result of the application of the invention to the fuel injector is that its operating noise is reduced in the manner described earlier. As the reader will have recognized, the noise-attenuating structure is created concurrent with the process of creating the end cap, and only a small amount of additional material is required for introduction into space 28. The invention may therefore be practiced with efficiency and economy.

Generic principles are applicable to other embodiments: for example, partial fills may be suitable in some cases, hole patterns and sizes may be varied, different materials may be used, different injectors

may be involved. Holes 38 and 40 could be enlarged so that some of the injected molding material could pass through them.