Method for fabricating a wear-resistant magnet-containing component and resulting article

Abstract: A piece (28) to be magnetized and a covering cap (20) are brazed together to a member (18), such as a spring seat for a diesel engine injector needle lift sensor. The entire assembly is then subjected to a vacuum ion treatment to case-harden at least the cap (20) and the wear surface of the member (18). Either before or after the member (18) is case-hardened, the assembly is subjected to an electromagnetic field to magnetize the piece (28) through the cap (20).

Description: The invention relates to a method for fabricating a wear-resistant magnet-containing component and resulting article, and in particular to a method for fabricating a magnetic spring seat attachment for diesel engine fuel injectors. In U.S. Patent 5,069,064, there is disclosed a construction for a magnetic spring seat attachment useful with injection sensor for diesel engines. It is the object of the invention to provide a simplified method in the field of internal combustion engines for fabricating sensors useful in maximizing the efficiency of engine operation. This object is achieved with the method according to the present invention, wherein a piece to be magnetized is brazed to a member which may comprise a spring seat for a diesel engine injector needle lift sensor. At the same time, a cap is brazed over the piece and to the member. The entire assembly is then subjected to a vacuum ion treatment to case-harden at least the cap and a wear surface of the member. Either before or after the member is subjected to the case-hardening vacuum ion process to case-harden the wear surface of the member, the assembly is subjected to an electromagnetic field to magnetize the piece through the covering cap fixed over the piece to the member. The term "ion nitriding" refers to a thermal-chemical process for case-hardening iron containing metal surfaces. The invention is further discussed by the attached drawings. Fig. 1 is a side view, partially in cross section, of a diesel engine fuel injector sensor and associated hardware. Fig. 2 is a cross section of a spring seat assembly which forms a part of the construction of Fig. 1. Fig. 3 is a flow chart illustrating the processing steps according to the method of the present invention. In Fig. 1, there is illustrated a portion 10 of a fuel injector sensor assembly, including a sensor element 12 and associated lead 14 which is dimensioned to extend through the injector spring 16 into proximity with the injector spring seat assembly 18. The spring seat assembly 18 includes an upper cap 20 that extends upwardly through the spring 16 and, as shown in Fig. 2, the cap 20 covers a piece 28 in form of a magnet or consisting of a magnetizable material. In operation, the motion of the piece 28 in form of a magnet or in form of magnetized material upwardly with the spring 16 is sensed by element 12 to provide precise fuel injection information, to thereby maximize the efficiency of engine operation and reduce unwanted exhaust emissions. Referring to Fig. 2, the spring seat assembly 18 comprises a spring seat body 22 preferably formed from a nickel chromium steel. The body 22 includes a recess 24 into which a fuel injector needle (not shown) extends during engine operation. The recess includes a wear surface 26 which specifically engages an extension of the needle. As shown in the upper portion of Fig. 2, the piece 28 is attached to the upper surface 30 of the spring seat body 22 by a brazing joint 32. The cap 20 is fabricated of a non-magnetic, deep-drawn steel material, and is brazed along surface 30 at joints 34 and around the piece 28, preferably at the same time that the piece 28 is brazed to the surface 30. The specific details of the method of the present invention will now be described with reference to Fig. 2 and the flow chart of Fig. 3. The cap 20, the spring seat 22 und the piece 28 which is or is to become a magnet are brazed together at joints 32, 33 and 34 according to steps 42 and 44 of Fig. 3. Preferably, the brazing step is carried out at a temperature in the order of slightly over 1,000 °C, using silver braze. The piece 28 is then magnetized after it has been brazed to the upper surface 30, either before or after a vacuum ion treatment. The entire combination of the piece 28, cap 20 and spring seat body 22 including wear surface 26 are subjected to a vacuum ion treatment at the necessary elevated temperature in order to case-harden at least the wear surface 26 und the cap 20 (Step 46 in Fig. 3). However, all of the exposed surface of the combination will become case-hardened in the treatment. Typically, the ion nitriding process is carried out at a temperature in the order of 320 °C, and therefore does not adversely affect the braze joints 32, 34. There are a number of known vacuum ion treatments, including ion nitriding, ion carbonizing, ion boronizing, ion plating and ion sputtering. In an ion nitriding process, the spring seat assembly 18 (with piece 28 and cap 20 already brazed in place) is placed inside a furnace, and a vacuum is drawn within the furnace to less than 6,6 Pa (50 µm of mercury). An inner gas, such as hydrogen, is then injected into the furnace and the assembly is heated. When the temperature reaches a point where the hydrogen gas begins to discharge a positive ion, the spring seat assembly is subjected to a high adhesive voltage, creating a positively charge potential resulting in a bombardement of the positive hydrogen ions across the surface of the assembly. Nitrogen gas is then injected into the furnace, and also ionized and bombards the assembly. As a result, ferrous nitride layers are developed along any exposed surface having an iron-containing composition, such as the wear surface 26 and the surface of the cap 20, thereby achieving the desired case-hardening. After the assembly 18 is cooled, the magnetizable piece 28 is then subjected to an electromagnetic field of sufficient strength to magnetise the piece 28 through the cap 20 (Step 48 in Fig. 3). As noted previously, the magnetizing step may be carried out before the ion nitriding step or a magnet can be used as piece 28.

Claims: A method for fabricating a wear-resistant, magnet-containing component, comprising the following steps in succession: providing a piece (28) of magnet or to be magnetized; brazing the piece (28) to a member (18) having a wear surface and brazing a cap (20) over the piece (28) to the member (18); subjecting the member (18) and the cap (20) to case-hardening by vacuum ion treatment at a temperature substantially below the temperature of the brazing step; and magnetizing the piece (28), if necessary. The method recited in Claim 1 wherein for the vacuum ion treatment an ion nitriding process, an ion carbonizing process, an ion boronizing process, an ion plating process, or an ion sputtering process is used. The method recited in Claim 1 or 2 wherein the brazing step is carried out at a temperature in the order of 1,000°C or above. The method recited in one of the preceding Claims wherein the member (18) is a spring seat (18) having a wear surface (26) dimensioned to engage a diesel engine injector needle under high wear conditions and a mounting surface (30) on which the piece (28) is to be brazed.

Inventors: WOLFF GEORGE D, WOLFF, GEORGE D.
Applicants: WOLFF CONTROLS CORP, WOLFF CONTROLS CORPORATION
Application year: 1993
Main classification: F02M65
IPC codes: F02M51, F02M65, F02M61, B23K1, H01F41, G01M15, F02B3, C23C14, H01F7