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 effective manner that does not require major revisions to component parts of existing fuel injectors. Analysis of an operating fuel injector before the present invention has revealed certain noise in the range of about 4 kHz to about 10 kHz. The application of the present invention to that fuel injector has significantly attenuated that noise 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 the implementation of certain constructional features into the fuel injector in the vicinity of the armature/stator interface. 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.

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 one form of the present invention. Fig. 2 is a fragmentary view like that of Fig. 1 , but of a modified form.

Fig. 3 is a cross sectional view in the direction of arrows 3-3 in Fig. 2.

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, including electrical terminals extending therefrom via which the fuel injector is connected with an electrical operating circuit for selectively energizing the solenoid coil; 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. Inlet connector tube 14 is disposed within solenoid coil assembly 22, and in addition to conveying pressurized liquid fuel into the interior of the fuel injector, it functions as a stator of the magnetic circuit that operates armature 20. The lower end of tube 14 and the upper end of armature 20 cooperatively define a working gap 28. Because the axial dimension of the working gap is small, it appears in the drawing Fig. simply as a line thickness. When the solenoid coil assembly is not energized, spring 18 pushes armature 20 away from tube 14 to cause valve body assembly 26 to be operated closed and thereby stop injection of liquid fuel from the fuel injector. When the solenoid coil assembly is

energized, it pulls armature 20 toward tube 14 to cause valve body assembly 26 to be operated open and thereby inject liquid fuel from the fuel injector. The motion of armature 20 toward tube 14 is arrested by their mutual end-to-end abutment. This abutment creates impact forces which can give rise to the emission of audible noise from the fuel injector. Such noise is successfully attenuated by the inclusion of a circumferential groove, or slot, 30 extending completely around the outside of tube 14 just a short distance from the end that is abutted by armature 20. By way of example in an injector of the type disclosed here, such a slot has an axial dimension of about 1.00 mm., a radial dimension of about 1.25 mm., and is spaced about 0.85 mm. from the end surface that is impacted by the armature. This construction creates a circular flange 32 of about 0.85 mm. axial dimension at the end of the tube. It is believed that this flange absorbs some of the impact by bending, and in that way attenuates the impact forces, and hence the emitted audible noise. The thickness of the wall of tube 14 is about 1.80 mm.

Fig. 2 illustrates a modified form in which slot 30 is filled with a material 34 that is different from the material of tube 14. Typically the material of tube 14 is steel which has good impact resistance. Material 34 is a dimagnetic material that imposes a force on armature 20 which opposes the electromagnetic force that is imposed on the armature when the solenoid coil assembly is energized to displace the armature toward tube 14. This opposing dimagnetic force is effective in reducing impact. Known dimagnetic materials are sodium, antimony, and. bismuth. Principles of the invention are susceptible to being implemented in other forms of solenoid-operated valves.