Abstract:
A solenoid valve is described, its armature having a part that is slidingly displaceable on the foundation bolt and is movable between two stops of the foundation bolt against the tension force of a restoring spring. When the armature strikes the valve seat of the solenoid valve, the slidingly displaceable part moves further under the influence of its inertial mass on the foundation bolt in the closing direction against the tension force of the restoring spring, until it strikes the second stop of the foundation bolt. The resulting transfer of momentum to the foundation bolt reduces impact of the armature on the valve seat and causes the armature to more quickly reach a defined rest position in which the solenoid valve is closed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a solenoid valve for controlling a fuel injector for an internal combustion engine. 
     BACKGROUND INFORMATION 
     A solenoid valve is discussed in German Published Patent Application No. 196 50 865 which is used to control the fuel pressure in the control pressure space of a fuel injector, e.g., an injector of a common rail injection system, where the fuel pressure in the control pressure space in turn controls the movement of a valve member, so that an injection opening of the injector may be opened or closed. This solenoid valve has an electromagnet situated in a housing part and having a coil and a magnetic core, a movable armature and a control valve element that is moved with the armature and is acted upon by a closing spring in the closing direction. This control valve element cooperates with a valve seat of the solenoid valve and thus controls the flow of fuel out of the control pressure space. In the case of the solenoid valve discussed in German Published Patent Application No. 196 50 865, the armature is designed in two parts having a foundation bolt and an anchor plate in a slidingly displaceable mount on the foundation bolt. In addition, however, there are solenoid valves for controlling injectors in which the foundation bolt is fixedly connected to the anchor plate. 
     One disadvantage of the known solenoid valves is armature rebound. When the magnet is shut down, the control valve element, which is secured to the armature, is accelerated suddenly toward the valve seat by the closing spring to close a fuel outflow channel out of the control pressure space. The impact of the control valve element on the valve seat may result in vibration and/or rebound of the control valve element, which is a disadvantage and has a negative impact on the injection operation. In the case of the solenoid valve having a two-part armature, which is discussed in German Published Patent Application No. 196 50 865, rebound is prevented by the fact that the anchor plate is displaceable on the foundation bolt and is moved further against the tension force of a restoring spring in impact of the control valve element on the valve seat. The effectively braked mass thus becomes smaller. However, then it is necessary to prevent post-pulse oscillation of the anchor plate on the foundation bolt, which would be a disadvantage. This is achieved by a hydraulic damping space formed between a sliding sleeve secured on the anchor plate and a sliding piece situated in a stationary mount on the housing part of the solenoid valve, damping any post-pulse oscillation of the anchor plate. In the case of a very strong deflection of the anchor plate in the direction of closing of the control valve element, the anchor plate strikes against the sliding piece situated in a stationary mount in the housing part. Any residual pulse is transferred to the stationary sliding piece and from there to the housing part. 
     SUMMARY OF THE INVENTION 
     The solenoid valve according to an exemplary embodiment of the present invention may be situated on a slidingly displaceable part on the foundation bolt, the part being displaceable between two stops, both of which may be fixedly situated on the foundation bolt. On impact of the control valve element with the valve seat, the slidingly displaceable part may move in the direction of closing of the control valve element against the tension force of the restoring spring, like the anchor plate in the case of the solenoid valve from the related art. The mass of the slidingly displaceable part and the tension force of the restoring spring may be designed so that the slidingly displaceable part may strike against the second stop of the foundation bolt. Since this second stop is not fixedly mounted on the housing, but instead may be movable with the armature and may be secured on it, rebound of the armature from the valve seat may be reduced by the transfer of momentum of the slidingly displaceable part to the foundation bolt. This may be possible because the momentum of the armature rebounding on the valve seat and the momentum of the lagging, displaceable part on the foundation bolt may be directed in opposing directions. The present invention may also be used to advantage with such solenoid valves in which the anchor plate may be designed in one piece with the foundation bolt, thus preventing post-pulse oscillation of the anchor plate. By reducing the rebound and post-pulse oscillation of the control valve element on the valve seat, it may advantageously be possible to set shorter intervals between preinjection and the main injection, because the armature may take less time to assume a defined rest position. 
     The second stop formed on the foundation bolt may be formed to advantage by a ring surface, facing the slidingly displaceable part, of a hollow cylindrical sleeve fixedly connected to and displaced on the foundation bolt. In assembly, the displaceable part may be pushed onto the foundation bolt first and then the sleeve may be pushed onto it. 
     The first stop opposite the second stop for the displaceable part may be formed in a simple manner by a ring shoulder on the foundation bolt between the anchor plate and the second stop. 
     The slidingly displaceable part may advantageously include a sleeve-shaped base body pushed onto the foundation bolt and having on its end facing the first stop a flange on which the restoring spring is supported. 
     The mass of the slidingly displaceable part may correspond approximately to the mass of the armature formed by the anchor plate and the foundation bolt and this may result in the momentum of the displaceable part being approximately the same as that of the armature rebounding on the valve seat. 
     The present invention may be applied with solenoid valves using a one-part armature having an anchor plate secured on the foundation bolt or using a two-part armature having an anchor plate displaceable relative to the foundation bolt. In the latter case, the anchor plate may then be provided as the slidingly displaceable part which strikes against the second stop of the foundation bolt in the closed position of the solenoid valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section through the top part of a fuel injector and having a solenoid valve. 
     FIG. 2 shows a partial cross section through an exemplary embodiment of the solenoid valve according to the present invention having an electromagnet, an armature, a control valve element and a valve seat. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the top part of a fuel injector  1  intended for use in a fuel injection system equipped with a high-pressure fuel reservoir which may be supplied continuously with high-pressure fuel through a high-pressure delivery pump. Fuel injector  1  may have a valve housing  4  having a longitudinal bore  5  in which may be situated a valve piston  6  which works with its one end on a valve needle  42  situated in a nozzle body. The valve needle  42  may be situated in a pressure space which may be supplied with fuel under high pressure through a pressure bore  8 . In an opening lifting movement of valve piston  6 , the valve needle  42  may be lifted against the closing force of a spring by the high-pressure fuel acting constantly on a pressure shoulder of the valve needle  42  in the pressure space. Then the fuel may be injected into the combustion chamber of the engine through an injection opening connected to the pressure space. By lowering valve piston  6 , the valve needle  42  may be pushed in the closing direction into the valve seat of the fuel injector, and the injection operation may be concluded. 
     As shown in FIG. 1, on its end facing away from the valve needle  42 , valve piston  6  may be guided in a cylinder bore  11  which may be provided in a valve piece  12  which may be inserted into valve housing  4 . In cylinder bore  11 , end face  13  of valve piston  6  may close a control pressure space  14  which may be connected by an inlet channel to a high-pressure fuel connection. The inlet channel may be designed in essentially three parts. A bore passing radially through the wall of valve piece  12 , its inside walls forming an inlet throttle on a portion of their length, may be constantly connected to an annular space  16  surrounding the valve piece, this annular space may in turn be constantly connected, through a fuel filter inserted into the inlet channel, to the high-pressure fuel connection of a connector  9  that may be screwed into valve housing  4 . Annular space may be sealed by a ring gasket  39  with respect to longitudinal bore  5 . Control pressure space  14  may be exposed to the high fuel pressure prevailing in the high-pressure fuel reservoir via inlet throttle  15 . Coaxially with valve piston  6 , a bore running in valve piece  12  may branch off out of control pressure space  14 , forming a fuel outflow channel  17  which may be provided with an outflow throttle  18  and may open into a relief space  19 , which may be connected to a low-pressure fuel connection  10 , which in turn may be connected to a fuel return of injector  1 . The outlet of fuel outflow channel  17  out of valve piece  12  may be in the area of a conically countersunk part  21  of the exterior end face of valve piece  12 . Valve piece  12  may be fixedly braced via a screw element  23  with valve housing  4  in a flange area  22 . 
     A valve seat  24  with which a control valve element  25  of a solenoid valve  30  controlling the fuel injector cooperates may be provided in conical part  21 . Control valve element  25  may be linked to a two-part armature in the form of a foundation bolt  27  and an anchor plate  28 , the armature cooperating with an electromagnet  29  of solenoid valve  30 . Solenoid valve  30  may also include a housing part  60  which may hold the electromagnet and may be fixedly connected to valve housing  4  via screwable connecting means  7 . With the solenoid valve, anchor plate  28  may be mounted so that it may be dynamically displaceable on foundation bolt  27  under the influence of its inertia against the prestressing force of a restoring spring  35 , and it may be pressed by this restoring spring in the rest state against a stop ring  26  secured on the foundation bolt. At its other end, restoring spring  35  may be supported fixedly on the housing on a flange  32  of a sliding piece  34  guiding foundation bolt  27 , the sliding piece  34  may be fixedly clamped with this flange between a spacer disk  38  placed on valve piece  12  and screw element  23  in the valve housing. Foundation bolt  27 , and with it armature disk  28  and control valve element  25  which may be connected to the foundation bolt, may be constantly acted upon in the closing direction by a closing spring  31  supported fixedly on the housing, so that control valve element  25  may normally be in contact with valve seat  24  in the closed position. On energization of the electromagnet, anchor plate  28  may be pulled by the electromagnet, and in doing so, outflow channel  17  may be opened toward relief space  19 . Between control valve element  25  and anchor plate  28  there may be a ring shoulder  33  on foundation bolt  27 , this ring shoulder may stop on flange  32  when the electromagnet is energized and thus may limit the opening lift of control valve element  25 . Spacer disk  38  may be used to adjust the opening lift between flange  32  and valve piece  12 . 
     The opening and closing of the injector may be controlled by the solenoid valve. Foundation bolt  27  may be acted upon constantly by closing spring  31  in the closing direction, so that control valve element  25  may be in contact with valve seat  24  in the closed position and control pressure space  14  may be closed toward relief space  19 , so that a high pressure may very rapidly be built up there through the inlet channel and may also be applied in the high-pressure fuel reservoir. Over the area of end face  13 , the pressure in control pressure space  14  may generate a closing force on valve piston  6  and the valve needle  42  which may be connected to it, this closing force may be greater than the forces acting in the opening direction as a result of the applied high pressure. If control pressure space  14  is opened by opening the solenoid valve toward relief side  19 , the pressure in the small volume of control pressure space  14  may drop very rapidly, because the latter may be uncoupled from the high pressure side via inlet throttle  15 . Consequently, the force acting on the valve needle  42  in the opening direction from the fuel high pressure prevailing at the valve needle  42  may be predominant, so that it may move upward and the at least one injection opening may be opened for the injection. However, if solenoid valve  30  closes fuel outflow channel  17 , the pressure in control pressure space  14  may be built up again by additional fuel flowing through inlet throttle  15 , so that the original closing force may be applied and the valve needle  42  of the fuel injector may close. 
     In closing the solenoid valve, closing spring  31  may press foundation bolt  27  with control valve element  25  suddenly against valve seat  24 . Rebound or post-pulse oscillation of the control valve element, which would have a negative effect, may occur due to the fact that the impact of the foundation bolt on the valve seat may produce an elastic deformation of the same. This elastic deformation may act as an energy storage mechanism, a portion of the energy in turn being transferred to the control valve element, which may then rebound away from valve seat  24  together with the foundation bolt. The known solenoid valve, which is shown in FIG. 1, therefore may use a two-part armature having an anchor plate  28  uncoupled from foundation bolt  27 . Although in this way it may be possible to reduce the total mass striking the valve seat, a post-pulse oscillation of the anchor plate, which would be a disadvantage, may need to be reduced by a hydraulic damping device between anchor plate  28  and sliding piece  34 . 
     FIG. 2 shows an exemplary embodiment of the solenoid valve according to the present invention. The same parts are labeled with the same reference numbers. The solenoid valve illustrated in FIG. 2 may have a one-part armature in which anchor plate  28  may be designed in one piece with foundation bolt  27 . A guide journal  37  which may project away from anchor plate  28  may be slidingly displaceable in a recess in electromagnet  29 . A projection  36  on the anchor plate may guarantee a minimum distance between the electromagnet and anchor plate  28  on contacting electromagnet  29 . Furthermore, an additional part  50  may be provided, including a sleeve-shaped base body made of metal on whose one end a flange  52  may be formed. Part  50  may be situated in a slidingly displaceable manner on foundation bolt  27  of the armature, the movement of slidingly displaceable part  50  on foundation bolt  27  being limited by a first stop  43  and a second stop  41 . The inside diameter of an opening  51  formed in the slidingly displaceable part may be slightly larger than the outside diameter of middle section  55  of foundation bolt  27 . First stop  43  may be formed by a ring shoulder or step of foundation bolt  27 . Second stop  41  may be formed by a ring-shaped surface piece of a hollow cylindrical metal sleeve  40  pushed onto the foundation bolt. End section  53  of foundation bolt  27  facing valve seat  24  may have a smaller diameter than center section  55  of foundation bolt  27  carrying slidingly displaceable part  50 , so that the two sections form one step  54 . In the manufacture of the armature, first slidingly displaceable part  50  may be pushed onto center section  55  of the foundation bolt and then sleeve  40  may be pushed onto end section  53 . When sleeve  40  is pushed onto the foundation bolt, the sleeve may come to rest against step  54  and may be secured in this position on the foundation bolt, which may be accomplished by welding, caulking or some other suitable method. As also shown in FIG. 2, a guide disk  45  having an opening  56  may be also provided. Guide disk  45  and a spacer  57  are clamped between a screw element  23  and valve piece  12  in the valve housing. End section  53  of foundation bolt  27  may be provided with control valve element  25  and may be slidingly displaceably mounted in opening  56  in guide disk  45 . A restoring spring  35  may be supported at one end on flange  52  of slidingly displaceable part  50  and at its other end it may be supported on guide disk  45  fixedly on the housing. 
     In a position in which the armature may be in contact with electromagnet  29 , restoring spring  35  may press slidingly displaceable part  50  with flange  52  against first stop  43 . When the electromagnet is shut down, the armature together with the anchor plate and the foundation bolt may be accelerated by closing spring  31  toward valve seat  24 . The greater tension force of closing spring  31  may counteract the smaller tension force of restoring spring  35 . As soon as control valve element  25  strikes the valve seat, slidingly displaceable part  50  may move in the closing direction because of its inertial mass, so the additional mass of part  50  may not increase the total mass to be decelerated by the valve seat. Slidingly displaceable part  50  may move on foundation bolt  27  against the tension force of restoring spring  35 . Shortly after the moment when foundation bolt  27  strikes valve seat  24 , lagging, slidingly displaceable part  50  may strike stop  41  of foundation bolt  27 . In doing so, the momentum of slidingly displaceable part  50  may be transferred to the foundation bolt, so that the momentum of the rebounding armature directed in the opposite direction may be reduced by the transfer of momentum. The mass of the slidingly displaceable part may be advantageously designed so that the absolute value of both momentums is the same. Slidingly displaceable part  50  may make it possible to achieve the result that the rebounding movement of the armature may be prevented or at least diminished, and the solenoid valve may be closed more reliably. Part  50  may thus actively counteract rebound and/or post-pulse oscillation of the armature. This may shorten the time required to move control valve element  25  into a defined rest position, thus permitting a smaller interval between preinjection and main injection. Then slidingly displaceable part  50  may be pushed back by restoring spring  35  into its starting position at first stop  43 . 
     In deviation from the exemplary embodiment illustrated here, the armature may also be designed in two parts, having an anchor plate slidingly displaceably mounted on the foundation bolt. In this case, the anchor plate may be regarded as the slidingly displaceable part which transfers its kinetic energy to the foundation bolt through its impact on the second stop of the foundation bolt and thus may actively prevent rebound of the armature.