Abstract:
A valve needle for use in an electromagnetically operable injection valve of a fuel injection system in an internal combustion engine includes a connecting part that is made of a plastic bar and that is connected to an armature and a valve closing element. In order to achieve a tight connection of the valve needle components, the connecting part enters into a form-fitting connection with the armature and with the valve closing element. The form-fitting connection between the connecting part and the valve closing element includes corresponding areas of larger and smaller diameters engaging with one another.

Description:
BACKGROUND INFORMATION 
     The present invention relates to a valve needle for an injection valve. German Published Unexamined Application No. DE-OS 40 08 675 describes a valve needle for an electromagnetically operable valve comprising an armature, a valve closing element and a sleeve-like connecting tube joining the armature to the valve closing element, which may be spherical, for example. The individual sections are individual parts manufactured separately and joined together by a joining method such as laser welding. The armature completely encompasses the connecting tube radially and at least partially axially, because the connecting tube is secured in a longitudinal through-bore in the armature. The connecting tube itself also has a longitudinal inside through-hole in which fuel can flow in the direction of the valve closing element and then come out close to the valve closing element through radial cross-holes provided in the wall of the connecting tube. Fuel thus flows first inside the valve needle, leaving the valve needle positioned only toward the valve seat. 
     In addition, U.S. Pat. No. 4,610,080 describes a valve needle in a fuel injection valve which is designed in two parts. A pot-shaped armature is fixedly connected to an elongated metal rod-shaped connecting part on whose downstream end is shaped directly a valve closing body in the form of a spherical section. A connecting sleeve having an internal opening extends out of the bottom part of the pot-shaped armature. The inside opening is provided with several grooves following one another at a distance axially, resulting in successive areas of larger and smaller diameters in the opening. The connecting part projects with its end opposite the valve closing body, which is also grooved and is opposite the valve closing section, into the opening in the connecting sleeve, so the two metal parts are joined together in a form-fitting manner. 
     German Published Unexamined Application No. DE-OS 195 03 224 describes a three-part valve needle for electromagnetically operable injection valves formed by a tubular armature, a sleeve connector part and a spherical valve closing body. The connecting part made of plastic engages with catch elements on the outer periphery of the armature to provide a secure connection of the armature and the connecting part. The downstream end of the connecting part has a cup-shaped recess in which the spherical valve closing body is snapped or clipped. The bottom part of the recess is so elastic that it widens when the valve closing body is pressed into it, then encircles the valve closing body tightly. 
     SUMMARY OF THE INVENTION 
     The valve needle according to the present invention can be manufactured especially easily and inexpensively. Each individual part of the valve needle, namely an armature, a valve closing element and a connecting part that connects the armature to the valve closing element, can be manufactured and machined especially inexpensively because of their very simple contours. The connecting part made of a plastic ensures a lower weight of the valve needle in comparison with metal valve needles. Especially with injection valves having a delivery point that is shifted especially far forward, where relatively elongated valve needles are used, very good dynamic valve properties can be achieved through such a design of the connecting part. The damping properties of the plastic also ensure reduced noise generation. In an advantageous manner, the valve closing element and the connecting part designed according to the present invention have a small outside diameter, so that an injection valve with such a valve needle can be designed to be very slender. The form-fitting connection of the valve closing element and the connecting part designed according to the present invention can be achieved in an especially simple manner and is nevertheless very secure. The possibility of detachment during the axial movement of the valve needle inside the injection valve is completely ruled out with this connection method. 
     It is especially advantageous that inexpensive bar stock is used for the connecting part, which can be adjusted very easily to an exact length for use on the valve needle in accordance with a desired valve length. In this way, valve needles for injection valves having a delivery point shifted far forward can be designed very easily. The connecting part, which is made of solid plastic, has the advantages of a small outside diameter because no internal flow orifices are provided, and therefore it also has a low mass. The valve needle, which is designed to be very slender, permits an especially narrow design of the injection valve, in particular a reduction in the size of the valve seat body in comparison with known injection valves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an injection valve with a valve needle according to the present invention. 
     FIG. 1 a  shows an enlarged detail of the area within the hatched circle in FIG.  1 . 
     FIG. 2 shows the valve needle of FIG. 1 from the perspective of a different scale. 
    
    
     DETAILED DESCRIPTION 
     The valve shown in FIG. 1 is in the form of an electromagnetically operable injection valve for fuel injection systems used in mixture-compression, externally ignited internal combustion engines. This valve has a tubular core  2  as an internal pole which serves as the fuel inlet connection and is surrounded by magnet coil  1 . A coil body  3  accommodates a winding of magnet coil  1  and together with core  2  it permits an especially compact design of the injection valve in the area of magnet coil  1 . 
     A tubular metal connecting part  12  is connected tightly, e.g., by welding, to a lower end  9  of core  2  concentrically with a longitudinal axis  10  of the valve and partially surrounds core end  9  axially. An elongated, thin-walled, sleeve-shaped valve seat carrier  16  running from the lower end of connecting part  12  is connected tightly and fixedly to connecting part  12  and has a definitely forward delivery point due to its relatively large axial length. Close to core end  9 , connecting part  12  has a magnetic choke point  13  characterized by a much smaller wall thickness than that of the other sections of connecting part  12 . Nonmagnetic intermediate parts used in the conventional manner can thus be omitted. 
     A longitudinal orifice  17  which is concentric with the longitudinal axis  10  of the valve is provided in valve seat carrier  16 , which is a thin-walled sleeve and also serves as a connecting part, and an optional sleeve-shaped insulation element  18  which is also elongated is in close contact with the wall of the longitudinal orifice  17 . Insulation element  18  made of plastic extends over most of the axial length of connecting part  12  and valve seat carrier  16  between a pot-shaped armature  20  and a valve seat body  21 . Insulation element  18 , which serves mainly for thermal insulation, is fixedly inserted into valve seat carrier  16  by means of a press fit. An inside longitudinal orifice  19  running concentrically with longitudinal axis  10  of the valve is in turn provided in sleeve-shaped insulation element  18 . A solid valve needle  22  designed according to the present invention and provided in longitudinal orifice  19  has a cylindrical valve closing element  23 , for example, on its downstream end. The entire valve needle  22  is formed by armature  20 , valve closing element  23  and an elongated bar-shaped connecting part  24  which joins armature  20  and valve closing element  23 . 
     Valve seat carrier  16 , which is made of nonmagnetic steel, for example, but may also be made of a magnetic ferritic material, surrounds not only the lower end of connecting part  12  but also valve seat body  21  on its opposite end and a spray hole disk  25  attached to it. With the elongated design of valve seat carrier  16 , the delivery point of the injection valve is shifted forward to a great extent. With the conventional design positions of injection valves in internal combustion engines, this means that the injection valve with its downstream end and thus with its metering and delivery area definitely extends into the intake tube. This makes it possible to largely avoid wetting of the wall of the intake tube through delivery of spray onto one or more inlet valves, and consequently the exhaust gas emission by the combustion engine can be reduced. 
     The injection valve is operated in a known way, namely electromagnetically in the case of the injection valve shown in FIG.  1 . The electromagnetic circuit with magnet coil  1 ; core  2  and armature  20  serves to provide axial movement of valve needle  22  and thus opening against the spring force of a restoring spring  26  or closing of the injection valve. Armature  20 , which is pot-shaped for example, is aligned with core  2  and is fixedly connected to end  28  of connecting part  24  which faces away from valve closing element  23 . Valve seat body  21 , which may be cylindrical, for example, and has a fixed valve seat  31 , is mounted tightly by welding in longitudinal orifice  17  of the downstream end of valve seat carrier  16  which faces away from core  2 . 
     A guide disk  33 , which is attached, for example, to an upper end face  32  of valve a seat body  21  and which faces away from spray hole disk  25 , serves to guide valve closing element  23  during the axial movement of valve needle  22  along longitudinal axis  10  of the valve. Armature  20  is guided especially in the area of magnetic choke point  13  during its axial movement in correcting part  12 . A specially designed guide face may be provided for this purpose on the outer circumference of armature  20 . Valve closing element  23 , which is largely cylindrical and has the contour of a spherical section facing valve seat  31 , works together with valve seat  31  of valve seat body  21 , which tapers in the form of a truncated cone in the direction of flow. On its end face which faces away from guide disk  33 , valve seat body  21  is fixedly connected to spray hole disk  25 , which may be pot-shaped, for example. Spray hole disk  25  has at least one spray delivery orifice, e.g., four such orifices, which may be formed by punching, etching or eroding. A holding edge of spray hole disk  25  is bent conically outward, so that it is in contact with the inside wall, which is defined by longitudinal orifice  17 , of valve seat carrier  16 , which results in a radial pressure. Spray hole disk  25  is tightly joined, e.g., by welding, to the wall of valve seat carrier  16 . 
     The depth of insertion of valve seat body  21  determines the length of the stroke of valve needle  22 . The one end position of valve needle  22  when magnet coil  1  is not energized is determined by the contact of valve closing element  23  with valve seat  31 , while the other end position of valve needle  22  when magnet coil  1  is energized is obtained by the contact of armature  20  with core end  9 . Magnet coil  1  is surrounded by at least one control element  38 , which is designed as a strap, for example, and serves as the ferromagnetic element, surrounding magnet coil  1  at least partially in the circumferential direction. Outside of valve seat carrier  16 , the injection valve is also largely surrounded by a plastic sheathing  40  with an integrally molded electric plug connector  41 . 
     FIG. 1 a  shows an enlarged detail of the injection valve shown in FIG. 1 in the area of guide disk  33 . Guide disk  33  serves to provide radial guidance of valve needle  22  during its axial movement in longitudinal orifice  17  or  19  to prevent excessive wear on valve seat  31  and asymmetrical flow conditions between valve seat  31  and the spray delivery orifices in spray hole disk  25 . A central through-hole  43  provided in circular guide disk  33  has a slightly larger diameter than the outside diameter of valve closing element  23  of valve needle  22 . These differences in dimensions result in a minimal clearance of approximately 10 μm. Outside of through-hole  43 , multiple passages  44  are provided in guide disk  33 , guaranteeing unhindered flow to valve seat  31 . Passages  44  may also be so small (e.g., &lt;60 μm) that they also perform a filter function. 
     FIG. 2 shows, on a different scale, valve needle  22 , which is composed of armature  20 , connecting part  24  and valve closing element  23 , as a single part. Pot-shaped armature  20  has a peripheral jacket part  46  running axially and a flat bottom part  47  perpendicular to longitudinal axis  2  of the valve. In bottom part  47  of armature  20  there is at least one passage, e.g., three or four passages  48  through which fuel flows in the direction of valve seat  31 . The fluid, in particular a fuel, flows downstream from passages  48  along the outer periphery of connecting part  24  in longitudinal orifice  19 . In addition, in bottom part  47  there is provided a central orifice  49  through which connecting part  24  extends with its end  28 . Armature  20 , which is made of a magnetically soft material, has a wear-resistant surface treatment, e.g., chrome plating, on the outside periphery of jacket part  46  or its upper end face  50 , which faces away from valve closing element  23  and serves as a stop. 
     Connecting part  24  has a peripheral ring groove  52 , for example, on its upper end  28  which is connected to armature  20 . The base of ring groove  52  has a smaller outside diameter than the areas of bar-shaped connecting part  24  which follow directly upstream and downstream from ring groove  52 . Ring groove  52  has an axial length which corresponds approximately to the thickness of bottom part  47  of armature  20 , because bottom part  47  engages in ring groove  52  in a form-fitting manner, so that the diameter of the base of ring groove  52  and the diameter of orifice  49  of armature  20  are the same. End  28  of connecting part  24  is designed so that it projects a short distance into the interior of armature  20 . End  28  of valve connecting part  24  projects into restoring spring  26  which rests on an inside end face  53  of bottom part  47  outside central orifice  49 , thereby ensuring that restoring spring  26  will be centered. End  28  of connecting part  24 , partially surrounded by restoring spring  26 , has a peripheral chamfer  54 , for example, on its end. Connecting part  24  is made of plastic, e.g., by injection molding. Connecting part  24  is inserted into orifice  49  of armature  20  by pressing or crimping or, by a hot-riveting method. 
     On its lower end  56  facing away from armature  20 , connecting part  24  has an inside orifice  57 , which has a bottom and is like a blind hole, running concentric with longitudinal valve axis  10  or the longitudinal axis of valve needle  22 , and bolt-like valve closing element  23  fits into the orifice  57 . A firm and form-fitting connection of connecting part  24  and valve closing element  23  is achieved due to the fact that valve closing element  23  is pressed into orifice  57 . Orifice  57  has multiple successive, peripheral grooves  58  spaced a distance apart over its axial extent. Thus, orifice  57  is designed alternately with multiple axially successive areas of larger and smaller diameters. Since valve closing element  23  is designed with a negative structure with respect to orifice  57  on its upper section  59 , which engages in connecting part  24 , i.e., it also has areas of larger and smaller diameters in alternation, this guarantees a secure, precise form-fitting engagement of valve closing element  23  in orifice  57 . 
     Section  59  of valve closing element  23 , which is embedded in connecting part  24  in a form-fitting manner, ends facing away from armature  20  on a lower shoulder  60  starting shoulder  60 , downstream valve closing element  23  is designed with a larger diameter than that of section  59  and is in contact with lower end face  61  of connecting part  24 . The high-precision-manufactured area of valve closing element  23 , which may be made of hardened stainless steel, for example, and is downstream from shoulder  60 , is guided in through-hole  43  of guide disk  33 , as mentioned previously. In this area downstream from shoulder  60 , valve closing element  23  has a smaller outside diameter than connecting part  24  over most of its axial length, for example. 
     The form-fitting connection of valve closing element  23  and connecting part  24  is achieved, for example, by pressing or crimping valve closing element  23  into orifice  57 . However, valve closing element  23  may also be sheathed directly during the plastic injection molding process for manufacturing connecting part  24  as an insertion part. In addition, snap engagement of valve closing element  23  is also conceivable, in which the areas of a smaller diameter of orifice  57  are chamfered, for example. This results in multiple sawtooth-like sections in succession in orifice  57 . Another possibility of introducing valve closing element  23  consists of heating and sinking valve closing element  23  into orifice  57 . Furthermore, valve closing element  23  may be treated with ultrasound so that heating occurs and the plastic of connecting part  24  close to orifice  57  is partially fused when valve closing element  23  is inserted. After cooling, this yields a form-fitting joint.