Abstract:
An injection needle comprising a needle tip, elastically connected to a needle shaft by means of a connector piece. A damping of the force with which the needle tip hits the corresponding sealing seat is possible by means of the elastic connection. The load on the sealing seat is thus reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of co-pending International Application No. PCT/DE01/04102 filed Oct. 30, 2001 which designates the United States, and claims priority to German application number DE10054183.6 filed Nov. 2, 2000. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The invention relates to an injection needle and an injection valve with such an injection needle.  
         BACKGROUND OF THE INVENTION  
         [0003]    Injection needles have an enormous variety of forms, in particular in the region of the needle tip, with a resulting impact on the flow of fuel. A sealing surface is also configured at the needle tip, which is assigned to a sealing seat of a nozzle body. The sealing seat is subject to high levels of dynamic and static loading when the injection valve opens and closes. Small differences in the adjustment of the injection needle in the injection valve result in a higher level of wear at the sealing seat. Wear causes an increase in the lift of the injection needle and/or leakage at the sealing seat. It is already known how to configure expensive geometries at the sealing seat or at the injection needle to keep sealing seat wear within limits.  
         SUMMARY OF THE INVENTION  
         [0004]    It is therefore the object of the invention to provide a simply structured injection needle with which the sealing seat is subject to a lower level of wear.  
           [0005]    The object of the invention is achieved by means of an injection needle for an injection valve, said needle comprising the following features: a needle body comprising a needle shaft and a needle tip, and a sealing surface configured on the needle tip, said surface being configured to rest on a sealing seat of the nozzle body, wherein the needle tip is connected via an impetus-damping element to the needle shaft.  
           [0006]    A significant advantage of the invention is that the needle tips are connected to the needle shaft by means of a flexible element. The flexible element damps the impetus with which the injection needle hits a sealing seat with the needle tip, so the sealing seat is subject to a lower level of loading.  
           [0007]    A preferred embodiment of the flexible element involves configuring a connector piece disposed with central symmetry between the needle shaft and the needle tip. The needle tip, connector piece and needle shaft are configured as a single part. This results in a particularly simple embodiment of the invention.  
           [0008]    The connector piece is preferably configured in such a way that a ring-shaped circumferential groove is incorporated into the injection needle, defining the connector piece.  
           [0009]    A preferred embodiment of the invention involves configuring the connector piece with a diameter of 0.5 to 1.5 mm.  
           [0010]    Good flexible properties of the needle tip are achieved if the groove is at a distance in the range of 0 to 1 mm from a sealing edge of the needle tip.  
           [0011]    In a preferred embodiment, the groove has a U-shaped cross section. A U-shaped groove is simple to incorporate, so the injection needle can be manufactured at low cost. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention is described in more detail below using the figures:  
         [0013]    [0013]FIG. 1 a diagrammatic structure of an injection valve; and  
         [0014]    [0014]FIG. 2 a needle tip with a needle shaft. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 1 shows an injection valve  1 , which has a nozzle body  2 . An injection needle  10  is guided in a movable manner in the nozzle body  2 . The injection needle  10  has a needle tip  11  with a sealing surface  6 . When the injection valve  1  is in the closed position, the sealing surface  6  lies with one sealing edge  22  on a sealing seat  5 , which is configured above injection holes  4  on the inner wall of the nozzle body  2 . An injection chamber  3  is configured between the injection needle  10  and the nozzle body  2 , said chamber being connected to an intake hole  8 . The injection chamber  3  is supplied with fuel via the intake hole  8 . In a preferred embodiment, the intake hole  8  is connected to a fuel store, which supplies fuel at a predetermined pressure.  
         [0016]    In the injection valve  1 , an actuator  7  is disposed above the injection needle  10  with electrical connections  9 . The actuator  7  is actively connected to the injection needle  10  and determines the position of the injection needle  10  on the basis of activation via the connections  9 . If injection is to take place, the actuator  7  is activated accordingly and the injection needle  10  is lifted off the sealing seat  5  by the actuator  7 . This results in a hydraulic connection between the injection chamber  3  and the injection holes  4 . Fuel is supplied via the injection holes  4  as a result.  
         [0017]    If injection is to be terminated, activation of the actuator  7  is interrupted and the actuator  7  moves the injection needle back with the sealing surface  6  onto the sealing seat  5 , so that the hydraulic connection between the injection chamber  3  and the injection holes  4  is broken.  
         [0018]    [0018]FIG. 2 shows a partial section of the front area of the injection needle  10  and the nozzle body  2 . The injection needle  10  is subdivided into a needle shaft  12  and a needle tip  11 , with the needle tip  11  being connected by means of a connector piece  13  to the needle shaft  12 . The needle tip  11  comprises a tapered sealing surface  6 , which is configured with rotational symmetry in respect of an axis of symmetry  14 . The sealing surface  6  is assigned a tapered sealing seat  5 , which is also configured with rotational symmetry in respect of the axis of symmetry  14  on the inner wall of the nozzle body  2 . A differential angle A is configured between the sealing surface  6  and the sealing seat  5  so that a reliable seal is ensured between the sealing seat  5  and the sealing surface  6 . In the closed position, the sealing surface  6  lies above the injection holes  4  with the sealing edge  22  on the sealing seat  5  in a circumferential ring surface.  
         [0019]    The needle shaft  12  changes from a first cylindrical section  15  to a second tapered section  16 . A third section  17  is connected to the second section  16  and is also configured as cylindrical but has a smaller cross-section than the first section  15 . The third section  17  in turn tapers over a circumferential ring-shaped groove  18  in a fourth section  19 , which represents the connector piece  13 . The cross-section then expands starting from the fourth section  19  in a fifth section  20 . The fifth section  20  represents the upper part of the needle tip  11 . The needle tip  11  tapers in the shape of the sealing surface  6  up to an end surface  21 , which completes the needle tip  11 .  
         [0020]    The fifth section  20  and the third section  17  preferably have the same cross-section. The groove  18  preferably has a U-shaped cross-section. Other shapes of groove  18  are however possible.  
         [0021]    The connector piece  13  is preferably disposed with central symmetry in respect of the axis of symmetry  14  and preferably has a diameter D of 0.5 to 1.8 mm. A preferred size for the diameter of the connector piece  13  is in the range from 1.1 to 1.3 mm.  
         [0022]    The width B of the groove  18  viewed parallel to the axis of symmetry  14  preferably has a value of 0.1 to 1 mm. Particularly good properties have been achieved with a groove width of 0.25 to 0.35 mm.  
         [0023]    The groove  18  comprises a lower edge  23 , at which the needle tip  11  tapers to the connector piece  13 . The distance between the sealing edge  22  and the lower edge  23  is of particular significance, as the distance essentially determines the flexible properties of the connection of the needle tip to the injection needle and therefore the damping properties of the injection needle. Good damping properties are achieved with a distance Z of the lower edge  23  from the sealing edge  22 , which is in the range of 0.1 to 1 mm.  
         [0024]    The lower edge  23  preferably runs perpendicular to the longitudinal axis of the injection needle after a curve. An important function of the groove  18  is to achieve a reduction of the cross-section of the connector piece  13 .  
         [0025]    Tests have shown that a configuration of the connector piece  13  with a short distance to the sealing edge  22  facilitates particularly damping properties. However it is advantageous for reasons of manufacturing accuracy and possible wear to maintain a specified distance from the sealing edge  22 .  
         [0026]    The damping action of the connector piece  13  means that the maximum yield stress, exercised by the needle tip  11  on the nozzle body  2 , can be reduced by up to 50%.  
         [0027]    Preferred values for a combination of the diameter D and the distance Z are 1-1.3 mm for the diameter D and 0.1 to 1 mm for the distance Z.  
         [0028]    The injection needle  10  in FIG. 2 is configured as a single part comprising the needle shaft  12 , the connector piece  13  and the needle tip  11 . For example the injection needle  10  is manufactured from working steel S  652  or the material  100  chrome  6 .  
         [0029]    The invention is however not limited to the single part configuration form but the needle shaft  12 , the connector piece  13  and the needle tip  11  can also be made from different materials, with the connector piece  13  being connected to the needle shaft  12  and the needle tip  11  by means of appropriate connecting surfaces or connecting means. For example the connector piece  13  can be screwed into the needle shaft  12  and the needle tip  11  or be welded to the needle shaft  12  and the needle tip  11 .  
         [0030]    In this embodiment the connector piece  13  is preferably made from a material which has more damping properties than the material of the needle shaft  12  and/or the material of the needle tip  11 .  
         [0031]    [0031]FIG. 3 shows a further embodiment of the injection needle, in which the lower edge  23  is taken up to a diameter D of the connector piece  13 . The lower edge  23  changes to a radius of curvature R, which is in the range of 0.15 to 0.4 mm. A truncated cone-shaped transition surface  24  connects tangentially to the radius of curvature forming an angle of 40° to 75° with the central axis of the injection needle. The diameter of the injection needle increases again constantly up to the diameter of the needle shaft  12  starting from the radius of curvature R.  
         [0032]    Good damping properties are achieved with this embodiment too. Tests show that the size of the span of the connector piece  13  parallel to the longitudinal axis of the injection needle has little impact on the damping properties of the connection with the needle tip  11 . The distance Z and diameter D of the constriction of the injection needle between the needle tip and the needle shaft are significant.  
         [0033]    The values for the distance Z and the diameter D are adapted by a person skilled in the art in conjunction with the flexible properties of the material from which the injection needle is manufactured.