Method for manufacturing a solid housing

Abstract

A method for manufacturing a solid housing, in particular a valve housing for an electromagnetically operable valve, includes the following operations or steps: a) providing a base element made of a magnetic or magnetizable material, b) carburizing and/or nitride-hardening of at least one subarea of the base element by diffusion of carbon and/or nitrogen under thermal treatment for forming a non-magnetizable structure in the area of the diffusion zone, and c) finishing the base element so created until an intended geometry of the housing is achieved. The housing is suitable in particular for use in fuel injectors in fuel injector systems of mixture-compressing spark-ignition internal combustion engines.

Description

FIELD OF THE INVENTION

The present invention is directed to a method for manufacturing a solid housing.

BACKGROUND INFORMATION

FIG. 1 shows a fuel injector from the related art having a traditional three-part design of an inner metal flow guidance part and housing component at the same time. This inner valve tube is formed by an inlet connection piece forming an internal pole, a nonmagnetic intermediate part and a valve seat carrier holding the valve seat, as explained in greater detail in the description of FIG. 1.

German patent document DE 35 02 287 A1 discusses a method for manufacturing a hollow cylindrical metal housing having two magnetizable housing parts including a nonmagnetic housing zone between them, forming a magnetic isolation between the housing parts. This metal housing is premachined in one piece from a magnetizable blank down to an excess outside diameter, a ring groove being cut in the inside wall of the housing in the width of the desired middle housing zone. In the case of a rotating housing, a nonmagnetizable filler material is filled into the ring groove, while the ring groove area is heated up, and rotation of the housing is continued until the filling material solidifies. The housing is then turned on the outside down to the final dimension of the outside diameter, so that there is no longer a connection between the magnetizable housing parts. A valve housing manufactured in this way may be used, e.g., in solenoid valves for antilock brake systems (ABS) in motor vehicles.

In addition, methods for manufacturing a solid core for fuel injectors for internal combustion engines are known from DE 42 37 405 C2 (FIG. 5 of the document). These methods are characterized in that a one-piece sleeve-shaped magnetic martensitic workpiece which is provided directly or via prior transformation processes undergoes a local heat treatment in a middle section of the magnetic martensitic workpiece to convert this middle section into a nonmagnetic, austenitic middle section. Elements forming austenite and/or ferrite molten by laser during the local heat treatment are alternatively added at the site of the heat treatment to form a nonmagnetic, austenitic middle section of the solid core.

SUMMARY OF THE INVENTION

The method according to the present invention for manufacturing a solid housing having the characterizing features of the main claim has the advantage that housings having a magnetic isolation may be reliably mass produced in a particularly simple and inexpensive method.

Due to the simplicity of the individual components, the complexity and expenditure in terms of special tools are reduced in comparison with the known manufacturing methods.

It is also an advantage that it is possible to design the geometry of the housing itself with great flexibility, in terms of length, external diameter and shoulders, for example.

Advantageous refinements of and improvements on the method characterized in the main claim are possible through the measures characterized in the subclaims.

It is particularly advantageous to let the carburizing and/or nitride-hardening of the at least one subarea of the base element take place in a C- and/or N-containing environment, the appropriate thermal treatment being carried out at high temperatures or being plasma-induced in order to enable diffusion of the carbon or nitrogen molecules into the edge layer of the base element.

Exemplary embodiments of the present invention are shown in simplified form in the drawing and explained in greater detail in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fuel injector according to the related art having a three-part inner metal valve tube as a housing.

FIG. 2 schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 3 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 4 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 5 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 6 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 7 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 8 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 9 also schematically shows method steps of a method according to the present invention for manufacturing a solid housing.

FIG. 10 shows a schematic section from an injector having a housing manufactured according to the present invention.

DETAILED DESCRIPTION

Before describing the method steps of the method for manufacturing a solid housing according to the exemplary embodiments and/or examplary methods of the present invention with reference to FIGS. 2 through 9, a fuel injector according to the related art will be explained in greater detail below with reference to FIG. 1 as a possible insert product for a housing manufactured according to the exemplary embodiments and/or examplary methods of the present invention.

The electromagnetically operable valve as shown in FIG. 1, for example, in the form of a fuel injector for fuel injection systems of internal combustion engines operating by spark ignition of a compressed fuel-air mixture has a tubular core 2 surrounded by a magnet coil 1, functioning as the fuel inlet connection piece and internal pole. The tubular core has a constant outside diameter over its entire length, for example. A coil body 3 having steps in the radial direction receives a winding of magnet coil 1 and, in combination with core 2 permits a compact design of the fuel injector in the area of magnet coil 1.

A tubular nonmagnetic metallic intermediate part 12 is joined tightly by welding to a lower core end 9 of core 2 concentrically with a longitudinal valve axis 10 and surrounds core end 9 axially in part. A tubular valve seat carrier 16 is fixedly joined to intermediate part 12 and extends downstream from coil body 3 and intermediate part 12. An axially movable valve needle 18 is situated in valve seat carrier 16. A spherical valve closing body 24 provided on downstream end 23 of valve needle 18 has, for example, five flat areas 25 on its circumference to allow fuel to flow past it.

The fuel injector is operated electromagnetically by the known method. The electromagnetic circuit having magnet coil 1, core 2 and an armature 27 is used to produce the axial movement of valve needle 18 and thus to open the valve against the spring force of a restoring spring 26 and/or for closing the fuel injector. Tubular armature 27 is fixedly joined, e.g., by a weld to one end of valve needle 18 facing away from valve closing body 24 and is aligned with core 2. A cylindrical valve seat body 29 having a fixed valve seat 30 is tightly mounted by welding into the downstream end of valve seat carrier 16 facing away from core 2.

Spherical valve closing body 24 of valve needle 18 cooperates with valve seat 30 of valve seat body 29 tapering in the form of a truncated cone in the direction of flow. On its lower end face, valve seat body 29 is fixedly and tightly joined to an spray orifice disk 34 designed in the form of a pot, for example, the joint being formed by a weld created using a laser, for example. At least one, e.g., four spray orifices 39 shaped by erosion or punching are provided in spray orifice disk 34.

To direct the magnetic flux to armature 27 for optimum operation of armature 27 when current is applied to magnet coil 1 and thus for secure and accurate opening and closing of the valve, magnet coil 1 is surrounded by at least one, for example, bow-shaped guide element 45 and functions as a ferromagnetic element, at least partially surrounding magnet coil 1 in the circumferential direction and is in contact with core 2 at one end and with valve seat carrier 16 at its other end and is joinable to them by welding, soldering and/or gluing, for example. Core 2, nonmagnetic intermediate part 12 and valve seat carrier 16, which are fixedly joined together and extend as a whole over the entire length of the fuel injector, form an inner metal valve tube as the basic structure and thus also the housing of the fuel injector. All other function groups of the valve are situated inside or around the valve tube. This arrangement of the valve tube is a classic three-part design of a housing for an electromagnetically operable unit such as a valve having two ferromagnetic, i.e., magnetizable housing areas which are isolated magnetically from one another by a nonmagnetic intermediate part 12 for effective conduction of the magnetic circuit lines in the area of armature 27 or are at least joined together by a magnetic restriction.

The fuel injector is mostly surrounded by a plastic sheathing 51 which extends starting from core 2 axially over magnet coil 1 and the at least one conducting element 45 to valve seat carrier 16, at least one conducting element 45 being completely covered axially and circumferentially. An integrally molded electric plug 52, for example, is part of this plastic sheathing 51.

Using the method steps of the method for manufacturing a solid housing according to the present invention as schematically indicated in FIGS. 2 through 9, it is possible in an advantageous manner to manufacture housings 66 having thin walls for a variety of purposes, which may be for electromagnetically operable valves that may replace a three-part valve tube as described above and to do so in a particularly simple and inexpensive manner.

In a first method step (FIG. 2), for example, a cylindrical base element 55 is provided, from which housing 66 is to be manufactured, and which is made of a magnetic or magnetizable material and is, for example, ferromagnetic or has a ferritic or a martensitic material structure. Base element 55 may initially be solid and may be obtained from long bar material for a particularly effective manufacture of a plurality of housings 66, for example. For obtaining local magnetic properties, a thermal treatment is carried out in a subarea of base element 55 in which carbon and/or nitrogen is/are individually or in combination diffused into the material of base element 55. In order to achieve a change in the magnetic properties in only a small selected area, the remaining area of base element 55 is provided with a two-part pot-shaped cover 57. Cover 57 protects base element 55 from diffusion of carbon and/or nitrogen outside diffusion zone 58 to be treated. Carburizing or nitride-hardening of base element 55 in the area of diffusion zone 58 takes place by placing base element 55 in C- and/or N-containing environment 59 until a non-magnetizable, in particular austenitic, structure is formed in diffusion zone 58. Carbon and/or nitrogen molecules diffuse at high temperatures or by induced plasma into the edge layer of the magnetic material.

Covering 57 of the areas of base element 55 not to be affected may, as shown in FIG. 2, be carried out via a mechanical protective cover or also via a coating, e.g., using a thermal protection paste or the material of base element 55 itself which is suitably contoured for this purpose (FIGS. 7 through 9).

For example, diffusion zone 58, which is formed in the middle area of base element 55, ultimately represents the area of the magnetic isolation, as FIG. 3 shows.

Due to the diffusion of carbon and/or nitrogen into base element 55, three lengthwise zones are created which each directly successively have different magnetic properties due to the thermal treatment in connection with the addition of carbon and/or nitrogen. Both outer zones of base element 55 have the same magnetic properties while the middle diffusion zone 58 assumes a non-magnetizable or poorly magnetizable, in particular austenitic or partially austenitic, material structure having no or only very low saturation magnetization and is isolated from both outer zones (FIGS. 4 and 6).

While an inner longitudinal opening 60 for forming a tubular housing 66 (FIGS. 3 and 4) is made into solid base element 55, for example, only subsequently to the thermal treatment with local carburizing and/or nitride-hardening, it is also conceivable to use an already tubular base element 55 having an inner longitudinal opening 60 as the starting blank and provide it locally with a diffusion zone 58 at an intended spot (FIGS. 5 and 6). A base element 55 which is already tubular prior to the thermal treatment has the advantage that a diffusion of the austenite-stabilizing elements C and/or N is possible from the outer wall and the inner wall of base element 55.

As mentioned above, cover 57 may be formed by the material itself of base element 55 which must be suitably contoured for this purpose. Based on FIGS. 7 through 9 it is explained what such a contour of base element 55 may look like. For example, a circumferential recess 62, similar to a groove or a cut-in, is provided in the area of the later intended diffusion zone 58, base element 55 having a larger external diameter than housing 66 which is subsequently made from it. Edge zone 63 of base element 55 is now consecutively magnetically influenced in C- and/or N-containing environment 59. Base element 55 is reworked subsequently to the thermal treatment by removing edge zone 63 largely down to recess 62. This may be carried out, for example, by using known mechanical or non-mechanical methods for removal, such as milling, grinding, thermal removal via electrical discharge machining, electron beam or laser beam, electrochemical machining (ECM, etching) or chemical removal. As FIG. 9 shows, removal of edge zone 63 is carried out until there is a housing 66 which has diffusion zone 58 exclusively in an intended area having changed material properties. The material thicknesses are not shown to scale.

Here also, an inner longitudinal opening 60 for forming a tubular housing 66 may be made into solid base element 55 either prior or subsequently to the thermal treatment via local nitride-hardening and/or carburizing.

Prior to installation of housing 66 in a valve or other assemblies, housing 66 is subjected to a finishing operation to have solid housing 66 in an intended geometry. In the event of using a housing manufactured according to the exemplary embodiments and/or examplary methods of the present invention in a fuel injector, it may be an advantage to specifically form housing 66 using technical manufacturing measures such as ironing, tumbling, swaging, flanging and/or flaring. Housing 66 represents a component which, in a known fuel injector according to FIG. 1, may completely take on the functions of the valve tube made up of core 2, intermediate part 12, and valve seat carrier 16 and may thus extend over the entire length of a fuel injector.

FIG. 10 shows a schematic section from a fuel injector having housing 66 manufactured according to the exemplary embodiments and/or examplary methods of the present invention which is installed as a thin-walled sleeve in the valve and surrounds core 2 and armature 27 radially and in the circumferential direction and is itself surrounded by magnet coil 1. It becomes clear that the area of diffusion zone 58 of housing 66, which has changed magnetic properties and is, for example, austenitic, is located in the axial extension area of a working air gap 70 between core 2 and armature 27 in order to guide the magnetic circuit lines optimally and effectively in the magnetic circuit. Instead of clamp-shaped guide element 45, shown in FIG. 1, the outer magnetic circuit component is designed as magnet pot 46, the magnetic circuit between magnet pot 46 and housing 66 being closed via a cover element 47. The method according to the present invention makes it also possible to change housings 66 having greater wall thicknesses locally in their magnetic properties so that a higher internal pressure resistance is ensured despite a minimized magnetically active area in favor of the magnetic force.

The exemplary embodiments and/or examplary methods of the present invention is by no means limited to use in fuel injectors or solenoid valves for antilock brake systems but instead it also pertains to all electromagnetically operable valves of different areas of application and in general all solid housings in units in which zones of differing magnetism are necessary in succession. Thus not only housing 66 having three successive zones may be manufactured by the method according to the exemplary embodiments and/or examplary methods of the present invention but also housings 66 having more than three zones.

Claims

1-11. (canceled)

12. A method for manufacturing a solid valve housing for an electromagnetically operable valve, the method comprising:

a) providing a base element made of a magnetic material or a magnetizable material;

b) at least one of carburizing and nitride-hardening at least one subarea of the base element by diffusing at least one of carbon and nitrogen under thermal treatment for forming a non-magnetizable structure; and

c) finishing the resulting base element until an intended geometry of the housing is achieved;

wherein the housing includes at least three zones and two directly adjacent zones have different magnetic properties.

13. The method of claim 12, wherein the base element is ferromagnetic, has a ferritic material structure or has a martensitic material structure.

14. The method of claim 12, wherein the base element is provided in cylindrical form.

15. The method of claim 14, wherein the base element is provided prior to the thermal treatment and a change of magnetic properties of a solid cylindrical form or a hollow cylindrical form having an inner longitudinal opening.

16. The method of claim 12, wherein at least one subarea of the base element is at least one of carburized and nitride-hardened in at least one of a C-containing and an N-containing environment.

17. The method of claim 12, wherein a diffusion zone, which forms the non-magnetizable zone, is created by diffusing at least one of C and N thereinto.

18. The method of claim 17, wherein the base element is provided with a cover outside the diffusion zone.

19. The method of claim 18, wherein the cover is one of a mechanical protective cover and a coating which is applied using a thermal protection paste.

20. The method of claim 12, wherein the base element is contoured so that the base element is at least one of carburized and nitride-hardened throughout, so as to create an entirely magnetically influenced edge zone.

21. The method of claim 20, wherein a groove-like recess is provided on the base element in whose place a local diffusion zone solely remains after removal of the edge zone.

22. The method of claim 12, wherein finishing of the base element is done via at least one of ironing, tumbling, swaging, flanging, and flaring.