Abstract:
A fuel injector for fuel injection systems of internal combustion engines, having a valve needle which works together with a valve seat face to form a sealing seat, has an armature acting on the valve needle. The armature is movably guided on the valve needle and is damped by an elastomer ring made of an elastomer. The armature has at least one fuel channel for supplying fuel to the sealing seat. A flat supporting ring which axially supports the elastomer ring in the area of the outlet end of the fuel channel is arranged between the elastomer ring and the armature.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injector. 
     BACKGROUND INFORMATION 
     U.S. Pat. No. 4,766,405 describes a fuel injector having a valve closing body connected to a valve needle and working together with a valve seat face designed on a valve seat body to form a sealing seat. For electromagnetic operation of the fuel injector, a solenoid works together with an armature connected in a friction-locked manner to the valve needle. An additional mass is provided in the form of a cylinder around the armature and the valve needle and is connected to the armature by an elastomer layer. One disadvantage is the complicated design featuring an additional component. The large-area elastomer ring is also a disadvantage for the variation of the magnetic field and makes it difficult for the field lines to close and thus interferes with achieving high attraction forces in the opening movement of the fuel injector. 
     U.S. Pat. No. 4,766,405 also describes an embodiment of a fuel injector; a cylindrical mass which is movably held and secured in position by two elastomer rings is provided around the armature and the valve needle for damping and reducing rebound. When the valve needle strikes the valve seat, this second mass can move relative to the armature and the valve needle and prevent rebounding of the valve needle. One disadvantage of the embodiment described there is the additional complexity and space required. The armature itself is not isolated and its momentum thus increases the tendency of the valve needle to rebound. 
     U.S. Pat. No. 5,299,776 describes a fuel injector having a valve needle and an armature which is movably guided on the valve needle and whose movement is limited by a first stop in the stroke direction of the valve needle and by a second stop against the stroke direction. Within certain limits, the axial movement play of the armature defined by the two stops results in isolation of the inert mass of the valve needle from the inert mass of the armature. This counteracts within certain limits the rebound of the valve needle from the valve seat face in closing of the fuel injector. However, since the axial position of the armature with respect to the valve needle is completely undefined due to the free mobility of the armature with respect to the valve needle, rebound pulses are prevented only to a limited extent. In particular, the design of the fuel injector known from U.S. Pat. No. 5,299,776 does not prevent the armature from striking the stop facing the valve closing body in the closing movement of the fuel injector and transmitting its momentum abruptly to the valve needle. This abrupt transfer of momentum can cause additional rebound pulses of the valve closing body. 
     It is also known from practice that the armature guided on the valve needle can be movably secured in its position by an elastomer ring. To do so, the armature is held between two stops, with an elastomer ring located between the armature and the bottom stop. However, then the problem arises that a bore through the armature is necessary to supply fuel to the valve seat face. The bore through the armature is provided close to the valve needle, and the valve seat side end of the bore is partially covered by the elastomer ring. This results in irregular pressure on the elastomer ring and finally the bore edges result in the destruction of the elastomer ring due to edge pressure. Furthermore, the vibrations are induced in the unsupported elastomer ring, which also contributes to destruction by the bore edges. This occurs especially at low temperatures, when the elastomer enters a rigid vitreous state. 
     SUMMARY OF THE INVENTION 
     The fuel injector according to the present invention has the advantage over the related art that the elastomer ring is supported axially over its full surface. Thus, there cannot be any edge pressure on the elastomer ring. This improves the long-term stability of the elastomer ring. 
     This is achieved in that the fuel injector has a flat supporting ring between the elastomer ring and the armature, supporting the elastomer ring axially over its entire surface and thus also in the area of the fuel channel. 
     This is achieved in that the longitudinal axis of the fuel channel is inclined to the longitudinal axis of the armnature so that the fuel channel opens radially outside the elastomer ring. In this way, the elastomer ring is also supported over its entire surface on an end face of the armature. In this embodiment, no vibration is induced in the elastomer ring by fuel flowing past it. 
     The supporting ring may advantageously have an integrally molded shoulder. Therefore, the elastomer ring is also supported radially and is protected from vibration induced by the fuel flowing past it. Accordingly, the end face of the armature may have a projection which provides radial protection. 
     A conventional inexpensive O ring may be used to advantage as the elastomer ring. 
     The elastomer ring may be made of an elastomer having a high internal damping and a great low-temperature elasticity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an axial section through a generic fuel injector. 
     FIG. 2 shows a detail of a first embodiment of a fuel injector according to the present invention. 
     FIG. 3 shows a detail of a second embodiment of a fuel injector according to the present invention in a partially cutaway diagram. 
     FIG. 4 shows a detail IV from FIG. 2 on an enlarged scale. 
     FIG. 5 shows a detail V from FIG. 2 on an enlarged scale in a modified form. 
     FIG. 6 shows a detail VI from FIG. 3 on an enlarged scale. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a detail of a generic fuel injector  1  in a sectional diagram to better explain the present invention. Fuel injector  1  injects fuel into an internal combustion engine having fuel mixture compression and spark ignition. The embodiment illustrated here is a high pressure fuel injector opening inward for direct injection of fuel into the combustion chamber of the internal combustion engine. 
     Fuel injector  1  has a valve closing body  3  which is connected in one piece to a valve needle  2  in this embodiment and works together with a valve seat face designed on a valve seat body  4  to form a sealing seat. Valve seat body  4  is connected to a tubular valve seat carrier  5  which can be inserted into a receiving bore of a cylinder head of the internal combustion engine and is sealed with respect to the receiving bore by a gasket  6 . On its inlet end  7 , valve seat carrier  5  is inserted into a longitudinal bore  8  of a housing body  9  and is sealed with respect to the housing body  9  by a sealing ring  10 . Inlet end  7  of valve seat carrier  5  is under pre-tension by a threaded ring  11 , with a lift adjusting disk  14  clamped between a step  12  of housing body  9  and an end face  13  of inlet end  7  of valve seat carrier  5 . 
     A solenoid  15  wound onto a coil frame  16  is used for electromagnetic actuation of fuel injector  1 . When solenoid  15  is electrically energized, an armature  17  is pulled upward until its end face  19  on the inlet end is in contact with a step  18  of housing body  9 . The gap width between the upstream end face  19  of armature  17  and step  18  of housing body  9  determines the valve lift of fuel injector  1 . In its stroke movement, armature  17  entrains valve needle  2  which is connected to first stop body  20  and valve closing body  3  which is connected to valve needle  2  because of the contact of its upstream end face  19  with a first stop  21  provided on a first stop body  20 . Valve needle  2  is welded to first stop body  20  by a weld  22 . Valve needle  2  moves against a restoring spring  23  which is secured between an adjusting sleeve  24  and first stop body  20 . 
     Fuel flows through an axial bore  30  of housing body  9  and at least one fuel channel  31 , which is provided in armature  17  and is designed here as an axial bore, as well as through axial bores  33  provided in a guide disk  32 , into an axial bore  34  of valve seat carrier  5  and from there to the sealing seat (not shown) of fuel injector  1 . 
     Armature  17  is movable between first stop  21  of first stop body  20  and a second stop  26  designed on a second stop body  25 , with armature  17  in this embodiment being held in contact with first stop  21  by a bearing spring  27  in the resting position, so that a gap is formed between armature  17  and second stop  26 , thus permitting a certain movement play of armature  17 . Second stop body  25  is secured on valve needle  2  by a weld  28 . 
     Due to the movement play of armature  17  between stops  21  and  26 , isolation between the inert masses of armature  17  and valve needle  2  with valve closing body  3  is achieved. Therefore, in the closing movement of fuel injector  1 , only the inert mass of valve closing body  3  and valve needle  2  strikes against the valve seat face, in which case armature  17  is not decelerated abruptly when valve closing body  3  strikes the valve seat face, but instead it moves further in the direction of second stop  26 . The isolation of armature  17  from valve needle  2  improves the dynamics of fuel injector  1 . However, end face  29  of armature  17  on the spray end striking second stop  26  does not cause any valve rebound. This is achieved through an elastomer ring  35  shown in FIG. 2 between second stop body  25  and armature  17 . Bearing spring  27  may optionally also be eliminated because of the damping by elastomer ring  35 . 
     FIG. 2 shows a detail of armature  17  with valve needle  2  of a fuel injector according to the present invention; elements that have already been described are shown with the same reference numbers to facilitate a correlation. 
     The drawing shows armature  17  of fuel injector  1  according to the present invention having fuel channel  31 , valve needle  2 , second stop body  25  welded onto valve needle  2  by weld  28  and second stop  26 , as well as end face  29  opposite second stop  26 . Valve needle  2  is welded to first stop body  20  by weld  22 . 
     FIG. 4 shows an embodiment according to the present invention as illustrated in detail IV from FIG. 2 on an enlarged scale. Between end face  19  of armature  17  and second stop  26  there is an elastomer ring  35 , a flat supporting ring  36  between elastomer ring  35  and armature  17  supporting elastomer ring  35  over its entire area, i.e., in particular also in the area of fuel channel  31 , and thus preventing edge pressure at the edge of fuel channel  31 . 
     FIG. 5 shows an alternative embodiment according to the present invention as illustrated in detail V from FIG. 2 on an enlarged scale. Between end face  19  of armature  17  and second stop  26  there is an elastomer ring  35 , designed as an O ring  37  in this embodiment. This O ring  37  is supported by flat supporting ring  36  over its entire area, i.e., also in the area of fuel channel  31  in particular, flat supporting ring  36  also supporting O ring  37  radially by an integrally molded, axially angled shoulder  39 . Thus a commercially available component such as O ring  37  can be inexpensively used. Inducement of vibration in O ring  37  by fuel passing by it is prevented by the larger coverage of O ring  37 , which also extends laterally. This counteracts destruction of elastomer ring  35  due to the edge pressure on fuel channel  31  and due to inducement of vibration. 
     In particular due to the radial support of O ring  37 , use of an elastomer with a greater internal damping is possible. High damping by an elastomer is usually also associated with a low elasticity modulus. Since O ring  37  is protected against the forces mentioned above which shorten the lifetime of an O ring  37 , such an elastomer may be used for O ring  37  without having a negative effect on the service life of O ring  37 . 
     A low elasticity modulus of an elastomer at low temperatures usually results in an even greater sensitivity to edge pressure and inducement of vibration at the operating temperature. Therefore, in the embodiment described here as an example, it is also possible to achieve a great low-temperature elasticity of O ring  37  and thus favorable operating performance of fuel injector  1  at low temperatures, e.g., after a cold start of the engine. 
     FIG. 3 shows an enlarged detail of armature  17  and valve needle  2  of a fuel injector  1  according to another embodiment of the present invention. 
     FIG. 3 shows armature  17  of fuel injector  1  according to the present invention, valve needle  2 , second stop body  25  welded by weld  28  onto valve needle  2  and having a second stop  26 , and end face  29  of armature  17  opposite second stop  26 . Valve needle  2  is welded by weld  22  to first stop body  20 . The at least one fuel channel  31  opens radially outside of elastomer ring  35  because it is inclined with respect to the axis of valve needle  2 . 
     Elastomer ring  35  which is designed as O ring  37  is shown in FIG. 6 with its area facing the environment according to detail VI from FIG. 3 in an enlarged view. In the embodiment illustrated here, fuel channel  31  opens into a tangential groove  36  which accommodates bearing spring  27 . This embodiment is especially advantageous because there is no inducement of vibration of O ring  37  by fuel flowing past it, and no enlargement of the diameter of armature  17  is necessary due to the inclination of fuel channel  31  to the axis of valve needle  2 . 
     In the embodiment illustrated in FIG. 6, end face  29  of armature  17  has a projection  40 . Due to the fact that O ring  37  is also covered laterally, it is possible to use an elastomer having a high internal damping and therefore a relatively low elastic modulus without any negative effect on its service life. The fact that O ring  37  is also supported radially prevents it from swelling forward and thus prevents the destruction of O ring  37  by compressive forces. 
     It is thus also possible to achieve a great low-temperature elasticity of O ring  37  without causing a shortened service life at the operating temperature of fuel injector  1 .