BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method for aligning an elongated component that is to be fitted, with at least two component segments, into two coaxial installation points spaced apart from one another. 
         [0003]    2. Description of Related Art 
         [0004]    Fuel injection systems for multi-cylinder internal combustion engines have fuel injection valves, one of which is allocated to each combustion cylinder of the internal combustion engine, and a fuel distributor connected to the fuel injection valves, through which fuel is delivered at high pressure to the fuel injection valves. The fuel injection valves are usually fitted into bores in the cylinder head and protrude, with a valve neck formed by the valve seat carrier, into a combustion chamber of a combustion cylinder of the internal combustion engine. Oppositely therefrom, elongated tubular fuel connector fittings of the fuel injection valves project out of the cylinder head bores and are fitted into tubular fittings of the fuel distributor. The axes of the tubular fittings are aligned coaxially with the axes of the cylinder head bores. It is therefore absolutely necessary, for installation of the fuel injection valves, that the segment of the fuel injection valve received in the cylinder head bore, and the segment of the fuel injection valve to be inserted into the tubular fitting, be aligned exactly coaxially, so that upon automated assembly, the fuel distributor can be placed with its tubular fitting onto the connector fittings of the fuel injection valves secured in the cylinder head bores. 
         [0005]    Because of the extreme length-to-diameter ratio of the fuel injection valves, the tubular valve seat carrier and the tubular connector fitting are usually fabricated from two separate sleeves that are intermaterially connected to one another. The intermaterial connection is preferably achieved by welding, by producing a circumferential weld seam at the abutting point of the two sleeves. The two sleeves become distorted in the context of welding, however, so that coaxiality between the two valve segments, retained on the one hand in the cylinder head bore and on the other hand in the tubular fitting of the fuel distributor (so-called “concentricity”), no longer exists with the required accuracy. 
         [0006]    In the context of a known method for welding together two cylindrical elements, for example a valve element and a magnet armature of a fuel injection valve (published German patent application DE 102 07 146 A1), in order to avoid deformation of the cylindrical elements as a result of welding, the two hollow cylindrical elements that are inserted in positively fitting fashion into one another are rotated about their center axis during welding, and welding is performed using two energy sources offset 90° from one another on the circumference. The cylindrical elements are thereby, in segments, melted and welded a first time by the first energy source, and melted and welded a second time by the second energy source. 
       SUMMARY OF THE INVENTION 
       [0007]    The method according to the present invention for aligning an elongated component has the advantage that a non-coaxiality present in the component between the installation regions on the component that are provided for installation, which non-coaxiality occurs e.g. in the context of joining two component parts and welding them together, can be eliminated in a manner that is simple in terms of production engineering. In this context, a concentricity accuracy, i.e. coaxiality, that is referred to the length of the component is achieved between the axes of the two installation regions of the component. In fuel injection valves, for example, in which the tubular component assembled from a valve seat carrier and connector fitting has at least one installation segment provided on the valve seat carrier and one close to the free end of the connector fitting, a concentricity accuracy from 50 to 150 μm, for a spacing of approx. 100 mm between the installation segments on the component, is achievable with the method according to the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0008]    The invention is explained further in the description below with reference to exemplifying embodiments depicted in the drawings, in which: 
           [0009]      FIG. 1  is a longitudinal section through a fuel injection valve for internal combustion engines, having an elongated component assembled from a hollow-cylindrical connector fitting and a hollow-cylindrical valve seat carrier. 
           [0010]      FIG. 2  is a longitudinal section through the component in  FIG. 1 , with the connector fitting and valve seat carrier in the joined position. 
           [0011]      FIG. 3  is the same depiction as in  FIG. 2 , after intermaterial connection of the connector fitting and valve seat carrier. 
           [0012]      FIG. 4  is the same depiction as in  FIG. 3 , after alignment of the component. 
           [0013]      FIG. 5  is the same depiction as in  FIG. 2 , with modified joining of the connector fitting and valve seat carrier. 
           [0014]      FIG. 6  is a side view of a component assembled from a connector fitting and valve seat carrier and having an electromagnet, locally surrounding the valve seat carrier, of a fuel injection valve, according to a further exemplifying embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The electromagnetically actuated fuel injection valve depicted in longitudinal section in  FIG. 1  has a hollow-cylindrical connector fitting  11  and, placed against the end face thereof, a hollow-cylindrical valve seat carrier  12 , which are assembled in intermaterially connected fashion to yield an elongated tubular component  13 . In the exemplifying embodiment described, the intermaterial connection is created by a circumferential weld seam  31  at the abutting point of connector fitting  11  and valve seat carrier  12 . Tubular component  13  is surrounded, in the region of the abutting point, by an electromagnet  14  that has a solenoid  15 , an armature  16 , and a magnet cup  18 . Armature  16  is guided axially displaceably in valve seat carrier  12 , and is fixedly connected to a valve needle  17 . A working air gap of electromagnet  14  is present between armature  16  and the end of connector fitting  11  disposed axially opposite it. Magnet cup  18 , which closes the electromagnetic circuit through armature  16 , is fastened externally on the connector fitting and on valve seat carrier  12 . Connector fitting  11 , electromagnet  14 , and (in part) valve seat carrier  12  are encapsulated by a plastic housing  10  into which an electrical plug connector  20  for solenoid  15  is integrated. The fuel injection valve is inserted into a cylinder head bore of an internal combustion engine which is embodied as a stepped bore; plastic housing  10  rests against the bore wall of the larger-diameter bore segment in the region of electromagnet  14 , and a sealing ring  22 , disposed in the region of valve seat carrier  12  on plastic housing  10 , seals the fuel injection valve with respect to the bore wall of the smaller-diameter bore segment. Valve seat carrier  12 , projecting partly into the combustion chamber of a combustion cylinder of the internal combustion engine, carries in its free end a valve body  23  into which are recessed a valve opening  24  and a valve seat  25  surrounding valve opening  24 . Valve body  23  is welded together with a perforated spray disk  28  on valve seat carrier  12 . Welded to the end of valve needle  17  facing away from armature  16  is a spherical closure element  26 , coacting with valve seat  25 , that is pressed via valve needle  17  onto valve seat  25  by a valve closure spring  27  that is braced in connector fitting  11 . The fuel volume sprayed out of valve opening  24  as closure element  26  lifts off from valve seat  25  is widened by perforated spray disk  28  into a fan-like stream of fuel. 
         [0016]    The fuel injection valve is inserted, with its free end toward the connector fitting, into a tubular fitting of a fuel distributor (not depicted here) and is sealed against the tubular wall of the tubular fitting by way of a sealing ring  21  that braces against the end face of plastic housing  19 . For proper fitting of the injection valve into the cylinder head bore on the one hand and into the tubular fitting of the fuel distributor on the other, it is necessary that the retaining regions of the fuel injection valve in the cylinder head bore and in the tubular fitting be oriented coaxially. In order to ensure this coaxiality, axes  111 ,  121  of connector fitting  11  and of valve seat carrier  12  must be in line with one another, but at least those regions of component  13  assembled from connector fitting  11  and valve seat carrier  12  that are fastened in the tubular fitting and cylinder head bore must be lined up coaxially. Because a distortion usually occurs when connector fitting  11  and valve seat carrier  12  are welded together to form component  13 , this coaxiality (called “concentricity”) is not guaranteed, and is produced by alignment of the component subsequent to welding. The procedure for this is as follows: 
         [0017]    Valve seat carrier  12  is retained in clamping jaws  30  of a holding apparatus ( FIG. 2 ). Connector fitting  11  and valve seat carrier  12  are then joined, by abutting the end of connector fitting  11  onto the retained valve seat carrier  12 . Connector fitting  11  and valve seat carrier  12  are welded to one another at their interface along the circumference, using a welding apparatus, e.g. a welding laser. The circumferential weld seam resulting in that context is labeled  31  in  FIGS. 3 and 4 . Connector fitting  11  usually becomes distorted upon welding, and an offset or deflection a of axis  111  of connector fitting  11  is produced with respect to alignment line  23  coaxial with axis  121  of valve seat carrier  12  ( FIG. 3 ). Once the welding point has cooled, the magnitude and direction of deflection a are measured. In a surface region, diametrical with respect to the direction of deflection a, of component  13  made up of connector fitting  11  and valve seat carrier  12 , between the component segments that serve for fastening in the tubular fitting of the fuel distributor and in the cylinder head bore, a material fusion area  32 , limited radially and in the circumferential direction, is generated at a magnitude such that the axial shrinkage occurring upon cooling of material fusion area  32  annuls the measured deflection a, so that the component segments serving for fitting into the tubular fitting of the fuel distributor and the cylinder head bore are once again mutually coaxial within tolerable limits. In the exemplifying embodiment shown in  FIGS. 3 and 4 , material fusion area  32  is generated in the surface region of connector fitting  11  close to weld seam  31 , so that once the material fusion area has cooled, axes  111  and  121  of connector fitting  11  and of valve seat carrier  12  once again line up with one another, as depicted in  FIG. 4 . The partial material fusion area  32  is preferably generated using a laser. The location of the material fusion area, the melting depth, and the length (viewed in a circumferential direction) of material fusion area  32  are taken from a characteristics diagram in which these values are stored in correlation with the direction and magnitude of deflection a. The characteristics diagram has been ascertained empirically. If a first material fusion area  32 , implemented as described, does not yet yield the desired result, then at least one further material fusion area is carried out at a short distance (viewed in a circumferential direction) from the first material fusion area  32 . 
         [0018]    In the case of the exemplifying embodiment of component  13 , depicted in longitudinal section in  FIG. 5 , that once again is assembled from connector fitting  11  and valve seat carrier  12 , the manner in which they are joined prior to intermaterial connection is modified. Connector fitting  11  and valve seat carrier  12  no longer rest in abutment against one another; instead, connector fitting  11  penetrates, with a reduced-diameter end segment  112 , in positively engaged fashion into valve seat carrier  12 . Intermaterial connection (once again welding in this case) is accomplished in the overlap region between connector fitting  11  and valve seat carrier  12 . A distortion of component  13  occurring after welding is compensated for in the manner described above. 
         [0019]      FIG. 6  is a side view depicting a further exemplifying embodiment of an oriented, elongated component  13 . The component is once again assembled from a tubular connector fitting  11  and a tubular valve seat carrier  12 , which are intermaterially connected to one another in the region of weld seam  31 . Valve seat carrier  12  is enclosed locally by electromagnet  14 , whose magnet housing  18  is welded onto valve seat carrier  12 . When it is later used as a fuel injection valve, component  13  is fastened in the cylinder head bore at the points identified in  FIG. 6  as A and B, or A and B 1 , with the result that axis  121  of valve seat carrier  12  is aligned coaxially with the bore axis. Component  13  is furthermore fastened in the tubular fitting of the fuel distributor in the component segment labeled C, and has for that purpose an external thread segment  33 , embodied at the end of connector fitting  11 , for threading into the tubular fitting (equipped with an internal thread) of the fuel distributor. An example of such a fuel distributor is found in EP 1 359 317 A1. Because the component distorts when connector fitting  11  is welded onto valve seat carrier  12 , it is necessary to align component  13  so that component segment C is aligned coaxially with the component segment between retention points A and B or A and B 1 , i.e. substantially coaxially with axis  121  of valve seat carrier  12 . This is achieved once again with material fusion area  32  generated with a laser in the surface region of component  13 , which area has been introduced in the region between component segment C and component segment B/A or B 1 /A. The concentricity of component  13  is measured at point C 1  in  FIG. 6 . 
         [0020]    The alignment method described above is not limited to the welding together of a connector fitting and a valve seat carrier for a fuel injection valve. Instead, any tubes or sleeve or other elongated elements can be intermaterially connected to one another and then aligned in the manner described. In the same fashion, one-piece elongated components that exhibit a distortion over their length can also be aligned in the manner described.
A method for aligning an elongated component that is to be fitted, with at least two component segments, into two coaxial installation points (A/B; C) spaced apart from one another. In this context, the coaxiality of the component segments is checked and any existing deviation from coaxiality is measured. At least one material fusion area, limited radially and in a circumferential direction, is generated in a surface region of the component located between the component segments, at a magnitude such that as a result of the axial shrinkage ensuing upon cooling of the material fusion area, coaxiality of the component segments is produced at least within tolerable limits.