Method for producing a valve-seat body for a fuel injection valve, and corresponding fuel injection valve

Abstract
Besides the conventional process steps of manufacturing a valve-seat body, forming a through opening inside the valve-seat body, forming a valve-seat as a frustoconical section of the through opening, and forming a guide area, the proposed method for manufacturing a valve seat for a fuel injector includes the simultaneous fine-machining of all guide sections in the guide area and the valve-seat area using a master ball.
Description




BACKGROUND INFORMATION




1. Field of the Invention




The present invention is based on a method for manufacturing a valve-seat body having a valve seat for a fuel injector and for manufacturing a fuel injector.




2. Background Information




German Application No. 40 37 952 already describes a fuel injector having a valve-seat body which, inter alia, has a guide bore and a valve seat. The guide bore serves for guiding an axially movable valve needle which is provided with a valve-closure member designed as a ball. This ball co-operates with the valve seat which tapers frustoconically in the downstream direction, forming a sealing-seat valve with it. In the guide bore located upstream of the valve seat, guide sections and fuel ducts alternate over the circumference of the guide bore. In the case of a conventional valve-seat body of this kind, both the guide sections and the valve seat are reworked upon reforming (massive forming, turning). In this context, the guide sections are machined separately from the machining of the valve seat in terms of time and tools by relatively inaccurate internal cylindrical grinding. In internal cylindrical grinding, an abrasive pencil is introduced into the guide bore and used for machining the guide sections in a rotational movement. The valve seat is also fine-machined by grinding, additional reworking by honing being necessary depending on the requirements. To achieve a high rotational accuracy combined with an optimum sealing behavior, several machining tools and sequential fine-machining steps are necessary.




Known from, for example, German Application No. 196 02 068, is a method for manufacturing rotationally symmetric valve-seat faces having a high surface finish at valves, in which method the valve seat is reworked as described above using a spherical tool body. In this context, the spherical tool body is designed with a diameter which is smaller than the cross-section of the guide opening in the valve-seat body to be machined so that only the immediate valve-seat face is fine-machined. The clearance of the guide opening must inevitably be greater than the diameter of the spherical tool since the tool could otherwise not immerse through the, in an axial direction, relatively long guide opening up the valve-seat face in the valve-seat body at all. Furthermore, there is such a great cutting volume for fine-machining in such a cylindrical guide opening that it is impossible to use a spherical tool body for the guide area.




Furthermore, German Patent Application No. 195 37 382 already describes a fuel injector which has a valve-seat body as well as a disk-shaped guide body lying upstream thereof. In this context, the guide body has an at least partially dome-shaped internal guide opening for a spherical valve member. The valve-seat body and the guide body are fine-machined, in each case, separately of each other at their internal openings to be made accurately. This is also carried out using different machining tools in different chucks.




SUMMARY OF THE INVENTION




The method according to the present invention for manufacturing a valve-seat body having a valve seat for a fuel injector has the advantage that, both guide sections and a valve-seat area in a valve-seat body are fine-machined most accurately in a simple fashion requiring little outlay of material, time, and tools. In this context, it is particularly advantageous that only one single machining tool, namely a very accurately formed “master ball”, is required for the fine-machining of the different areas, which, besides, is carried out simultaneously in an ideal manner.




It is particularly advantageous to fine-machine the guide sections and the valve seat by ball honing, or ball precision grinding or ball lapping. Using these processes, it is possible to remove minimal quantities of material at the desired locations in the valve-seat body so that, compared to known grinding methods, there are only very small cutting volumes resulting from the, in terms of the surface area, very small guide sections.




Using this machining technology, desired minimal curvatures are produced at the guide sections which have a radius which corresponds to the radius of the master ball. The guide sections, from the start, are advantageously formed narrow in the axial direction and in the circumferential direction, and have therefore a small surface area so that they can be accurately machined in an optimum fashion using the master ball. Thus, rotational accuracies are achieved in an advantageous fashion, which cannot be achieved in the case of conventional ball/conical sealing-seat arrangements with a comparably small outlay.




The fuel injector according to the present invention has the advantage that a valve-seat body having a valve-seat area and a guide area can be fine-machined in a particular simple and cost-effective manner, and, moreover, in an extremely high quality with regard to rotational accuracy and tightness. For that, the guide sections, from the start, are advantageously formed narrow in the axial direction and in the circumferential direction, and have therefore a small surface area so that they can be accurately machined in an optimum fashion using the master ball as machining tool.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

shows a fuel injector having a specially formed valve seat which is manufactured according to the present invention.





FIG. 2

shows the valve-seat body including a “master ball”.





FIG. 3

shows a top view of the valve-seat body including a spherical valve-closure member which is located inside and cooperates with the valve seat.





FIG. 4

shows a top view of only the valve-seat body in which the contact spots of the valve-closure member in the valve-seat body are identified not to scale.











DETAILED DESCRIPTION




As an exemplary embodiment, an electromagnetically operated valve in the form of a fuel injector for fuel-injection systems of mixture-compressing internal combustion engines with externally supplied ignition is partially depicted in FIG.


1


. The valve has a tubular valve-seat body


1


, in which a longitudinal borehole


3


is formed concentrically to a longitudinal valve axis


2


. An axially movable valve needle


6


is arranged in longitudinal borehole


3


.




The electromagnetic operation of the valve is carried out in a conventional manner. For axially moving valve needle


6


and, consequently, opening the valve against the spring resistance of a return spring


8


, and respectively, closing the valve, an only partially shown electromagnetic circuit including a magnetic coil


10


, a core


11


, and an armature


12


is used. Valve needle


6


is formed of armature


12


, a spherical valve-closure member


13


, and a connecting part


14


connecting these two component parts, connecting part


14


having a tubular design. Return spring


8


supports itself against the upper end face of connecting part


14


with its bottom end. Armature


12


is connected to the end of connecting part


14


facing away from valve-closure member


13


via a welded seam


15


, and aligned with core


11


. On the other hand, valve-closure member


13


too is firmly connected to the end of connecting part


14


facing away from armature


12


, for example, via a welded seam


16


. Magnetic coil


10


surrounds core


11


which represents the end, enclosed by magnetic coil


10


, of a fuel inlet connection which is not further identified, and which serves for supplying the medium to be metered in by the valve, here fuel.




Concentrically to longitudinal valve axis


2


, a tubular metal intermediate piece


19


is joined to the bottom end of core


11


and to valve-seat support


1


, e.g., by welding, in a sealing fashion. In the downstream end of valve-seat support


1


facing away from core


11


, a cylindrical valve-seat body


25


is mounted by welding in a sealing manner in longitudinal borehole


3


, which runs concentrically to longitudinal valve axis


2


. The valve-seat body


25


designed according to the present invention has a fixed valve-seat area


26


facing core


11


.




Magnetic coil


10


is, at least partially surrounded in the circumferential direction by at least one conductive element


30


used as a ferromagnetic element which is designed, for example, as a bracket, and which engages on core


11


with its one end, and on valve-seat support


1


with its other end, and is connected to these by welding, soldering or bonding.




A guide area


31


of a through opening


32


of valve-seat body


25


serves for guiding valve-closure member


13


during the axial movement. Valve-seat area


26


also represents an area of through opening


32


which, for example, immediately adjoins guide area


31


in the downstream direction. At its one bottom end face


33


facing away from valve-closure member


13


, valve-seat body


25


is concentrically and firmly connected to a spray-orifice plate


34


having, for example, a pot-shaped design. The connection between valve-seat body


25


and spray-orifice plate


34


is made, for example, by a continuous and tight welded seam


45


which is made, for example, using a laser. By this method of assembly, the risk of an unwanted deformation of spray-orifice plate


34


in the area of its at least one, for example, four spray orifices


46


produced by erosive machining or punching is prevented. In an advantageous manner, spray-orifice plate


34


should be fixed to valve-seat body


25


prior to the fine-machining of valve-seat body


25


which will still be described in more detail in the following.




The insertion depth of the valve-seat part composed of valve-seat body


25


and spray-orifice plate


34


into longitudinal borehole


3


determines, inter alia, the adjustment of the stroke of valve needle


6


since the one end position of valve needle


6


is determined by the engagement of valve-closure member


13


on valve-seat area


26


when magnetic coil


10


is deenergized. The other end position of valve needle


6


is determined, for example, by the engagement of a top end face


22


of armature


12


on a bottom end face


35


of core


11


when the magnetic coil


10


is energized. The travel between these two end positions of valve needle


6


represents the stroke.




The spherical valve-closure member


13


co-operates with the, in the downstream direction, frustoconically tapering surface of valve-seat area


26


of valve-seat body


25


. The immediate valve seat can also be formed by a narrow annular seat area


26


′ which is slightly raised compared to the frustoconically formed surface. In such a case, annular seat area


26


′ projects from valve-seat area


26


by approximately 50 to 100 μm. Guide area


31


has a plurality of flow passages


27


allowing the medium to flow in a direction towards valve seat


26


,


26


′ of valve-seat body


25


.





FIG. 2

shows seat body


25


as individual component part together with a “master ball”


130


which is used as a machining tool for fine-machining in the practical application of the manufacturing process according to the present invention. In this context, master ball


130


is attached to, for example, a bar-shaped, rotating tool-holding body


129


which, in a comparable form, is known, for example, from German Application No. 196 02 068. Through opening


32


in valve-seat body


25


has a plurality of differently formed sections or areas which axially adjoin each other. In this context, the essential areas of through opening


32


are an inlet area


47


which tapers in the downstream direction, a middle opening area


48


which has a greater inside diameter than the diameter of spherical valve-closure member


13


or master ball


130


respectively, guide area


31


, valve-seat area


26


or annular seat area


26


′ respectively, as well as an outlet area


49


. While areas


47


,


48


,


26


or


26


′, and


49


have a uniform design over their circumference, guide area


31


is characterized by a sequence of web-type guide sections


51


and duct-type flow passages


27


alternating over its circumference. This above described contour of the inner through opening


32


as well as the otherwise substantially cylindrical outside contour are produced in known manner by appropriate creative forming and massive forming (e.g., cold working, cold pressing; optionally hardening).




According to the present invention, the final fine-machining of valve-seat area


26


and guide sections


51


in guide area


31


is carried out simultaneously using master ball


130


. In this context, the very hard master ball


130


, which can be produced very accurately and has an ideal spherical shape, has a slightly greater diameter than valve-closure member


13


which cooperates later with valve seat


26


,


26


′. The fine-machining of valve-seat body


25


using master ball


130


is a honing (ball honing), or precision grinding, or lapping in which finest-grained honing oils, lapping pastes or grinding pastes are used, making it possible to remove minimal quantities of material at the desired locations in valve-seat body


25


. Using this machining technology, desired minimal curvatures are produced at guide sections


51


which have a radius which corresponds to the radius of master ball


130


. Guide sections


51


, from the start, are advantageously formed very short and narrow in the axial direction and in the circumferential direction, so that they can be accurately machined in an optimum fashion using master ball


130


.




In this context, guide sections


51


, as viewed in an axial direction, are located in an ideal fashion in the area of ball equator


52


,


52


′ of master ball


130


, or respectively, of valve-closure member


13


which will later be arranged there, the guide sections


51


beginning minimally before ball equator


52


,


52


′ following opening area


48


as viewed, for example, in the downstream direction. Ball equator


52


′ of valve-closure member


13


is indicated in FIG.


1


. Guide sections


51


, while facing away from valve-seat area


26


,


26


′, extend axially to the extent that they project beyond ball equator


52


′ of valve-closure member


13


maximally by only 150 μm when valve-closure member


13


engages on valve-seat area


26


,


26


′. Flow passages


27


which, in each case, have a radially outer passage bottom


54


having, for example, the radius of opening area


48


as an extension thereof, extend between the individual guide sections


51


. As elucidated in

FIGS. 3 and 4

which are top views of valve-seat body


25


, it is useful to provide five guide sections


51


and five flow passages


27


in guide area


31


in an alternating fashion over the circumference. However, designs using different numbers are also conceivable but at least three guide sections


51


should exist at all events. The top view of valve-seat body


25


shown in

FIG. 4

is primarily intended to elucidate the places of contact of valve-closure member


13


, which is not shown here, in the area of valve seat


26


,


26


′, and at guide sections


51


in valve-seat body


25


respectively, the used blackenings not representing a true-to-scale marking.




Thus, areas


26


,


26


′,


51


of valve-seat body


25


which perform sealing and guiding functions are simultaneously fine-machined with the assistance of the very exactly formed master ball


130


. In the application of the ball honing, or precision grinding, or lapping using master ball


130


, the immediate sealing surface, which, in the exemplary embodiment shown in

FIG. 2

, is the slightly raised annular seat area


26


′, as well as guide sections


51


are exactly adapted to the form of master ball


130


, or the minimally smaller valve-closure member


13


respectively. In the process, master ball


130


transfers its curvature to the axially very short guide sections


51


, the end result being slightly curved guide sections


51


at the end of guide area


31


facing away from valve-seat area


26


. Using the above described machining technology, rotational accuracies are achieved in an advantageous fashion, which cannot be achieved in the case of known ball/conical sealing-seat arrangements with a comparably small outlay. This manufacturing process guarantees nearly ideal roundnesses in valve-seat area


26


, having deviations (circularity tolerances) of only 0.5 μm or less.



Claims
  • 1. A fuel injector having a longitudinal valve axis, comprising:a valve needle including at least a spherical valve-closure member and a valve-seat body which has a through opening, the through opening having at least a guide area, a valve-seat area situated in a downstream direction, and at least one of an inlet area and an opening area, the valve-closure member cooperating with the valve-seat area, the guide area having a plurality of guide sections which are interrupted in a circumferential direction by flow passages, the plurality of guide sections, while facing away from the valve-seat area, extending axially to project beyond a ball equator of the valve-closure member by a maximum distance of 150 μm when the valve-closure member engages on the valve-seat area; and an actuator axially moving the valve needle.
  • 2. The fuel injector according to claim 1, wherein the plurality of guide sections have a slight curvature with a first radius, the first radius substantially corresponding to a second radius of the valve-closure member.
  • 3. A method for manufacturing a valve-seat body, comprising the steps of:manufacturing the valve-seat body having a cylindrical outside contour, the valve-seat body including a valve seat for a fuel injector; forming a through opening inside the valve-seat body, the through opening including a guide area, a valve-seat area and at least one of an inlet area and an opening area; forming the valve-seat area as a frustoconical section of the through opening; forming the guide area to include web-type guide sections and duct-type flow passages which are arranged in an alternating manner over a circumference of the guide area; and simultaneously fine-machining all of the web-type guide sections and the valve-seat area using a master ball, the master ball functioning as a machining tool.
  • 4. The method according to claim 3, wherein the fine-machining step is performed using a ball honing procedure.
  • 5. The method according to claim 3, wherein the fine-machining step is performed using a precision grinding procedure.
  • 6. The method according to claim 3, wherein the fine-machining step is performed using a lapping procedure.
  • 7. The method according to claim 3, wherein a first diameter of the master ball is slightly greater than a second diameter of a spherical valve-closure member, the spherical valve-closure member cooperating with the valve seat.
  • 8. The method according to claim 3, further comprising the step of:premolding a raised annular seat area on the frustoconical valve-seat area.
  • 9. The method according to claim 8, wherein a raised portion of the annular seat area is located at a distance of approximately between 50 μm and 100 μm from the valve-seat area.
  • 10. The method according to claim 3, further comprising the step of:transferring a curvature of the master ball to the guide sections to form slightly curved guide sections at an end portion of the guide area, the end portion facing away from the valve-seat area.
Priority Claims (1)
Number Date Country Kind
197 57 117 Dec 1997 DE
PCT Information
Filing Document Filing Date Country Kind 102e Date 371c Date
PCT/DE98/02928 WO 00 8/19/1999 8/19/1999
Publishing Document Publishing Date Country Kind
WO99/32259 7/1/1999 WO A
US Referenced Citations (3)
Number Name Date Kind
3191277 Glasgow Jun 1965
5285968 Greiner et al. Feb 1994
5785254 Zimmerman et al. Jul 1998
Foreign Referenced Citations (5)
Number Date Country
40 37 952 Jun 1992 DE
44 18 228 Sep 1995 DE
195 37 382 Apr 1997 DE
196 02 068 Jul 1997 DE
9-068134 Mar 1997 JP