Abstract:
The method for manufacturing a solid housing, in particular a valve housing for an electromagnetically operable valve, is characterized in that the following method steps are used: a) providing a sheet metal strip made of a magnetic or magnetizable material, b) introducing an additive into a middle area of the sheet metal strip and fusing there for forming a non-magnetizable structure, c) cutting the sheet metal strip into a sheet metal piece of desired width, d) deforming the sheet metal piece into a sleeve shape, e) mutual fastening of the cut edges now facing each other and running in the longitudinal direction of the sleeve for forming a sleeve blank, f) final machining of the sleeve blank until a desired 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:
BACKGROUND INFORMATION 
     The present invention is directed to a method for manufacturing a solid housing. 
     BACKGROUND INFORMATION 
       FIG. 1  shows a conventional fuel injector 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 Published Patent Application No. 35 02 287 describes 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 described in German Published Patent Application No. 42 37 405 (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 
     The method according to example embodiments of the present invention for manufacturing a solid housing 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 conventional manufacturing methods. Band material, which is easily manufacturable by rolling, may be used as the starting material for the necessary sheet metal strips. Further processing of the sheet metal pieces cut to length may also be carried out via very inexpensive sheet metal shaping processes. 
     If continuous sheet metal bands are used as sheet metal strips, then the manufacturing process may be configured to be inexpensive and have reduced cycle time. 
     It is also advantageous that great flexibility is possible in the design of the geometry of the housing itself, e.g., in the length, outside diameter and gradations. 
     Due to the industrial mass manufacture of the housing, the welds which are critical in the usual manufacturing technology may be optimized here for process reliability due to the good accessibility and optimizable parameters. 
     Advantageous refinements of and improvements on the method are possible through the measures described below. 
     Exemplary embodiments of the present invention are shown in simplified form in the drawings and explained in greater detail in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a conventional fuel injector having a three-part inner metal valve tube as a housing, 
         FIGS. 2 through 9  schematically show the method steps of a method according to example embodiments of the present invention for manufacturing a solid housing, 
         FIG. 10  shows a schematic section from an injector having a housing manufactured according to example embodiments of the present invention, and 
         FIG. 11  shows section XI in  FIG. 10  in an enlarged representation. 
     
    
    
     DETAILED DESCRIPTION 
     Before describing the method steps of the method for manufacturing a solid housing according to example embodiments of the present invention with reference to  FIGS. 2 through 9 , a conventional fuel injector will be explained in greater detail below with reference to  FIG. 1  as a possible insert product for a housing manufactured according to example embodiments 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, e.g., a conventional 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 example embodiments of 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, preferably 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 ), a flat sheet metal strip  60  is provided, sheet metal strip  60  being made of a ferromagnetic and/or soft-magnetic or magnetizable material and has, for example, a ferritic or a martensitic material structure. This sheet metal strip  60  to be provided is a sheet metal section rolled flat, exactly machined, and tailor-made which is referred to as a “tailored blank.” Material 1.4418 or material 1.4016, for example, may be used as the rolled base material. For a particularly effective manufacture of housing  66 , sheet metal strip  60  may be provided as a flat continuous band. While sheet metal strip  60  is moved in the longitudinal direction of the band according to arrow  55 , alloying of nickel, manganese, carbon, or nitrogen individually or in combination is carried out into a middle area of sheet metal strip  60  using an additional wire  61  or a powder in such quantity that a non-magnetizable structure is created. Weld-fusing of additional wire  61  or the powder for alloying the nickel or another additive is carried out by using a welding unit  62 . Laser welding, electron-beam welding, plasma welding or the like may be used as methods for fusing. Instead of an additional wire  61  or an additional powder, the intended additives may be applied to sheet metal strip  60  already prior to fusing via partial coating or rolling-on. An alloy zone  63 , created in the middle area of sheet metal strip  60 , ultimately represents the area of magnetic separation. A longitudinal groove  64  may optionally be provided in sheet metal strip  60  in the area of alloy zone  63  so that the additive minimizes the material buildup. For example, longitudinal groove  64  may be introduced into sheet metal strip  60  prior to alloying using a profiled roller. Boundary edges  65  of sheet metal strip  60  are provided with a bevel in order to optimize subsequent welding of boundary edges  65  facing each other ( FIG. 8 ). 
     Due to alloying nickel into the middle area of sheet metal strip  60 , three lengthwise zones are created which each directly sequentially have different magnetic properties based on the fused materials. The two outer zones of sheet metal strip  60  have the same magnetic properties, while the middle alloy zone  63  assumes a non-magnetizable, in particular austenitic, material structure and is magnetically isolated from the two outer zones. 
     The continuous sheet metal strip  60  is subsequently cut to the desired length, thereby creating a sheet metal piece  60 ′ whose width b ultimately corresponds to the circumference of subsequent housing  66 .  FIG. 3  shows a flat sheet metal piece  60 ′ having a defined width b which, in addition to boundary edges  65 , is delimited by two cut edges  72  facing each other.  FIG. 4  shows a view corresponding to viewing direction IV in  FIG. 3  onto a cut edge  72  of sheet metal piece  60 ′, which makes it apparent that alloy zone  63 , including the added material nickel, does not extend over the entire thickness of sheet metal piece  60 ′, for example, but only over a partial area, over ⅔ of the thickness, for example. 
     Alternatively, alloy zone  63  may also extend over the entire thickness of sheet metal piece  60 ′. By milling or rolling a longitudinal groove  64  into sheet metal strip  60 , the material buildup beyond the sheet metal thickness may also be minimized, for example. 
     In a further processing step, sheet metal piece  60 ′, being present in this manner, is brought into a sleeve shape by rolling or tumbling or bending namely up to a state in which the two cut edges  72 , which extend over all three zones of sheet metal piece  60 ′, are close opposite one another or are in contact. Roll-bending of sheet metal pieces  60 ′ may take place in multiple steps. For example, an arbor-like tool is used here ( FIG. 5 ).  FIG. 6  shows a side view of sheet metal piece  60 ′ at boundary edge  65 . Similar to boundary edges  65  of sheet metal strip  60 , cut edges  72  are each provided with a bevel, for example, which are applied prior to roll-bending and which are used for improved positioning of cut edges  72  opposite one another for mutual fastening. 
     Following this method step, a sleeve blank  68  is present whose two opposite, lengthwise cut edges  72  form abutting edges at which mutual fastening takes place ( FIG. 7 ). This joining together of cut edges  72  of the rolled or bended sheet metal piece  60 ′ may be carried out via laser welding using a welding unit  62 . In this way, sleeve blank  68  is welded longitudinally at the opposite cut edges  72  to form a closed sleeve ( FIG. 8 ).  FIG. 9  shows a housing  66  closed in the circumferential direction having three magnetic zones subsequently to rolling or bending and welding of cut edges  72  by applying a weld  69  running longitudinally. 
     Prior to installation of housing  66  in a valve or other assemblies, housing  66  is subjected to a finishing operation to have fixed housing  66  in a desired geometry. In the event of using a housing manufactured according to example embodiments 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 conventional 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 example embodiments 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 .  FIG. 11  shows section XI in  FIG. 10  in an enlarged representation. It is apparent here that the middle area of alloy zone  63  of housing  66 , modified in its magnetic properties and being austenitic, for example, is situated in the axial extension area of working air gap  70  between core  2  and armature  27  in order to guide the circuit magnetic lines optimally and effectively in the magnetic circuit. 
     The present invention is not 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 example embodiments of the present invention but also housings  66  having more than three zones.