Electromagnetic fuel injection valve and method for manufacturing same

An electromagnetic fuel injection valve wherein it is possible to prevent undesired adhesion between the respective abutting surfaces of an armature and a stationary core as well as to ensure the required wear resistance for the abutting surfaces and wherein the amount of lift of the valving element is unlikely to change is provided. After rough surfaces like satin-finished surfaces have been farmed on the abutting surfaces by shot peening, the rough surfaces are flattened by spotting. Therefore, the abutting surfaces can easily separate from each other without likelihood of adhering so closely that is difficult for them to separate from each other. Also, the amount of lift of the valving element is unlikely to change. Accordingly, the amount of fuel injected by the fuel injection valve is unlikely to change with passage of time. Thus, stable fuel supply can be performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic fuel injection valve for use in an internal-combustion engine. More particularly, the present invention relates to an electromagnetic fuel injection valve wherein it is possible to prevent undesired adhesion between the respective abutting surfaces of an armature and a stationary core as well as to improve wear resistance of the two abutting surfaces.

2. Discussion of Related Art

A typical electromagnetic fuel injection valve has an electromagnetic coil and a valving element secured to an armature. In operation, the electromagnetic coil is excited to lift the armature. When the armature thus lifted abuts against a stationary core, a gap is created between the valving element and the associated valve seat, thereby allowing fuel to be injected through the gap. Accordingly, it is necessary to ensure wear resistance for the respective abutting surfaces of the armature and the stationary core and to eliminate or minimize residual magnetism between the abutting surfaces. It has already been known that at least one of the two abutting surfaces is plated with chromium or nickel to ensure the required wear resistance and to eliminate or minimize the residual magnetism (for example, see Published Japanese Translation of PCT International Publication No. Hei 8-506876).

SUMMARY OF THE INVENTION

However, a complicated operation is needed to plate the abutting surface of the armature or the stationary core as stated above. In addition, an extra number of man-hours is needed for the plating operation. Hence, costs increase unavoidably. If the plated abutting surfaces are mirror finished surfaces, they may adhere, when abutting, so closely that it is difficult for them to separate from each other. This causes a delay in the valve closing operation of the valving element. Under these circumstances, a technique wherein the abutting surfaces are previously formed into rough surfaces like satin-finished surfaces by shot peening has already been disclosed as a method for solving the above-described problems [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 11-247739]. With this technique, however, the abutting surfaces abut against each other at the tips of asperities of the rough surfaces. Therefore, the tips of the asperities may be worn away in a short period of time by repeated contact, resulting in an increase in the amount of lift of the valving element. This may cause the fuel injection quantity to increase undesirably.

Accordingly, an object of the present invention is to provide an electromagnetic fuel injection valve wherein it is possible to prevent undesired adhesion between the abutting surfaces as well as to ensure the required wear resistance for the abutting surfaces and wherein the amount of lift of the valving element is unlikely to change.

To attain the above-described object, the present invention is applied to an electromagnetic fuel injection valve wherein an armature having a valving element secured thereto is lifted by excitation of a coil so that an abutting surface of the armature abuts against an abutting surface of a stationary core, thereby allowing fuel to be injected through an injection port provided downstream of a valve seat. The abutting surface of the armature and the abutting surface of the stationary core have respective rough surfaces like satin-finished surfaces formed by shot peening. According to the present invention, the rough surfaces are flattened by spotting.

Thus, according to the present invention, after rough surfaces like satin-finished surfaces have been formed on the respective abutting surfaces of the armature and the stationary core by shot peening, the rough surfaces are flattened by spotting. Therefore, the abutting surfaces can easily separate from each other without likelihood of adhering so closely that it is difficult for them to separate from each other. In addition, because the tips of asperities of the rough surfaces are flattened by spotting, the tips of the asperities will not easily be worn away by repeated contact, and the amount of lift of the valving element is unlikely to change.

The present invention offers the following advantageous effects. According to the present invention, after rough surfaces like satin-finished surfaces have been formed on the respective abutting surfaces of the armature and the stationary core by shot peening, the rough surfaces are flattened by spotting. Therefore, the abutting surfaces can easily separate from each other without likelihood of adhering so closely that it is difficult for them to separate from each other. In addition, because the tips of asperities of the rough surfaces are flattened by spotting, the tips of the asperities will not easily be worn away by repeated contact, and the amount of lift of the valving element is unlikely to change. Accordingly, the amount of fuel injected by the fuel injection valve is unlikely to change with passage of time. Thus, stable fuel supply can be performed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. InFIG. 1, a fuel injection valve1includes a stationary core2. The stationary core2has a fuel passage2aprovided in the center thereof. An armature (moving core)3is slidably disposed in the fuel passage2a. A fuel passage3ais provided in the center of the armature3to pass fuel. A ball valve (valving element)4is secured to the distal end of the armature3, for example, by welding to constitute a moving valve5. A communicating hole3bis provided in the armature3near the ball valve4to allow fuel to flow to the outside from the fuel passage3a. A nozzle7is secured to the lower opening of the stationary core2by press fitting or welding. The nozzle7has a valve seat6and an injection port7a. The moving valve5is arranged to move between the valve seat6and an abutting surface2bof the stationary core2with an appropriate lift (gap). A cylindrical sleeve8is press-fit into the rear end portion of the fuel passage2a. The forward end of the sleeve8retains the rear end of a spring9for pressing the moving valve5against the valve seat6.

A filter10is press-fit into the upper opening of the stationary core2. A coil subassembly13is fitted on the outer periphery of the stationary core2. The coil subassembly13comprises a bobbin11and a coil12wound around the bobbin11. The coil subassembly13is integrally resin-molded with a synthetic resin housing15with a yoke14provided therebetween. One end of the coil12is connected to a terminal16. The other end of the coil12is grounded. Thus, an electric signal is input through the terminal16. The upper end portion of the fuel injection valve1is connected to a delivery pipe through an O-ring17. The lower end portion of the fuel injection valve1is connected to an intake manifold through an O-ring18. Fuel flowing into the fuel injection valve1through the filter10is injected through the injection port7awhen the moving valve5is pushed up in response to the energization of the coil12. The abutting surface2bof the stationary core2and the abutting surface3cof the armature3have been formed with plateau surfaces, respectively. That is, the abutting surfaces2band3care subjected to shot peening process to form rough surfaces like satin-finished surfaces. Thereafter, the peaks of the rough surfaces are flattened by spotting.

Next, the formation of the abutting surface of the stationary core according to this embodiment will be described with reference to the drawings. InFIG. 2, the stationary core2is held in a direction in which the abutting surface2bfaces upward. An injection nozzle19for shot peening is inserted into the stationary core2from above. The tip of the injection nozzle19is positioned so that a shot19awill be applied to the whole abutting surface2bin view of the relationship between the divergence angle of the shot19aand the position of the injection nozzle tip. By the shot peening process, the hardness of the abutting surface2bbecomes HV 300 to 400, and a rough surface like a satin-finished surface with a surface roughness of about 6 μm (Rz) is formed thereon. It should be noted that the surface roughness of the body material before the shot peening process is about 2 μm (Rz), and the hardness thereof is approximately HV 150.

Next, the abutting surface2bformed into a rough surface like a satin-finished surface is subjected to spotting by flattening process. InFIG. 3, the stationary core2is held in a direction in which the abutting surface2bfaces upward. A punch20for flattening is inserted into the stationary core2from above. Flattening is carried out with a pressure of about 2 kN. The surface roughness after the flattening process is about 3 μm (Rz). It should be noted that shot peening and spotting for the abutting surface3cof the armature3are carried out by the same methods as the above. Therefore, a description thereof is omitted.

A dynamic flow change rate measuring test was performed on three samples, i.e. a conventional hard chrome-plated product (sample A), a product subjected to only the shot peening treatment (sample B), and a product of the present invention subjected to both the shot peening treatment and spotting (sample C). The results of the measurement 80 hours after the initiation of the test were as follows.

SampleRate of change of flowSample Anot more than +4%Sample Bnot less than +10%Sample Cnot more than +4%

Thus, the product of the present invention (sample C) shows a favorable result.

It should be noted that the present invention is not necessarily limited to the foregoing embodiment but can be modified in a variety of ways without departing from the gist of the present invention.