Abstract:
A solenoid valve is proposed for controlling an injection valve of an internal combustion engine, including a housing part, an electromagnet having a magnetic coil and a magnetic core, an armature acted upon by a valve spring and axially movable between the electromagnet and a valve seat, and a control valve member moved by the armature and cooperating with the valve seat for opening and closing a fuel passage, in which the armature is situated in the housing part movable in the radial direction free from mechanical guiding means. A further development provides that, when a current is applied to the electromagnet, the armature may be aligned in the radial direction, by magnetic reluctance forces then acting upon the armature, into a centrical position with reference to the centerline of the electromagnet.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a solenoid valve for controlling an injection valve of an internal combustion engine.  
         BACKGROUND INFORMATION  
         [0002]    German Published Patent No. 196 50 865 discusses a solenoid valve used for controlling the fuel pressure in the control pressure chamber of an injection valve, such as an injector of a common rail injection system. In such injection valves, the fuel pressure in the control pressure chamber controls the movement of a valve plunger with which the injection opening of the injection valve is opened or closed. The known solenoid valve has an electromagnet situated in a housing part, an axially movable armature guided in a sliding piece and acted upon by a closing spring, and a control valve member moved by the armature which cooperates with the valve seat of the solenoid valve and thereby controls the fuel discharge from the control pressure chamber. The armature has an armature plate, and an armature bolt which is supported in a slidingly movable manner in the mechanical guideway formed as a bore in the sliding piece.  
           [0003]    In the known solenoid valves the sliding piece has to be manufactured with great precision in order to guarantee optimal functionality of the solenoid valve. The mechanical armature guideway through the sliding piece gives rise to frictional losses, which have to be considered when designing the overall system. In addition to that, fitting the sliding piece into the housing part of the solenoid valve requires a mechanically costly overall construction.  
         SUMMARY OF THE INVENTION  
         [0004]    The advantages of the present invention arise by saving the sliding piece which has been used up to the present time, and discontinuing of the production and work steps connected with the sliding piece. Because of the discontinuation of the sliding piece guiding the armature, frictional losses caused by the mechanical armature guideway during opening and closing the solenoid valve are avoided. Because of the discontinuation of the sliding piece, the construction of the armature can advantageously be greatly simplified and optimized from a functional point of view. On account of the simplified construction, the deviation of the dynamic behavior of the solenoid valve is further advantageously reduced, so that the reliability of the overall system is increased. Beyond that, a substantial advantage comes about from the considerable cost reduction during production of the solenoid valve. Thus, not only is the sliding piece omitted, but the armature can also be designed to be less costly, and can be made, for example, as a simple stamped part.  
           [0005]    A particularly flat construction method of the armature is achieved by designing the armature as a disk-shaped armature plate, which acts directly upon the control valve member with its side facing away from the electromagnet. Advantageously, in the closed position of the solenoid valve, tilting moments transmitted by the closing spring to the armature are greatly reduced.  
           [0006]    Advantageously, armature plate and control valve member are produced as separate components, so that the radially movable armature plate can shift relatively to the control valve member, without the control valve member necessarily being shifted from its centrical position relative to the valve seat. A lateral impact of the control valve member next to the valve seat and a sliding into the valve seat connected with frictional losses are hereby largely avoided.  
           [0007]    Especially advantageous is an exemplary embodiment in which, when a current is applied to the electromagnet, the armature may be aligned in the radial direction, by magnetic reluctance forces acting upon the armature, into a centrical position with reference to the centerline of the electromagnet. This can advantageously be achieved if the armature and the magnetic core have geometrical structures situated concentrically about their respective centerline at their mutually facing pole faces, which structures cooperate, when current is applied to the electromagnet, in such a way that the armature is aligned in the centrical position.  
           [0008]    Because in the centrical position of the armature its center axis is situated concentrically with the fuel passage, tilting moments acting upon the armature may be further reduced. During the closing of the solenoid valve, the armature meets the control valve member centrically from its centrical position, so that in the closed state of the solenoid valve the control valve member lies centrically on the valve seat for fuel passage, and tilting moments are reduced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a section of the upper part of a fuel injector in an exemplary embodiment of the solenoid valve according to the present invention.  
         [0010]    [0010]FIG. 2 shows a section from the upper part of a fuel injector in another exemplary embodiment of the solenoid valve according to the present invention.  
         [0011]    [0011]FIG. 3 shows an enlarged detailed view as in another exemplary embodiment having the geometrical structures centering the armature.  
         [0012]    [0012]FIG. 4 shows an enlarged detailed view of another exemplary embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 shows the upper part of a fuel injector which is intended for use in a fuel injection system, particularly a common rail system for diesel fuel, which is equipped with a fuel high-pressure reservoir that is continually supplied with high-pressure fuel by a high-pressure fuel booster pump. The fuel injector has a valve housing  4  having a longitudinal bore  5 , in which a valve plunger  6  is positioned, which acts with its one end upon a valve needle positioned in a nozzle body. The valve needle is situated in a pressure chamber which is supplied with fuel under high pressure via a pressure bore. When there is an opening lift movement of valve plunger  6 , the valve needle is lifted by the high fuel pressure, applied steadily to a pressure shoulder of the valve needle, in the pressure chamber counter to the closing force of a spring. The injection of the fuel into the combustion chamber of the internal combustion engine takes place through an injection orifice then connected to the pressure chamber. By lowering of valve plunger  6 , the valve needle is pressed in the closing direction into the valve seat of the injection valve, and the injection process is ended. Valve plunger  6  is guided in a cylindrical bore  11 , at its end facing away from the valve needle, which has been inserted into valve piece  12  which is set into valve housing  4 . In cylindrical bore  11 , the end face of valve plunger  6  closes in a control-pressure chamber  14 , which is connected to a fuel high-pressure connection via a supply channel. The supply channel is essentially designed in three parts. A bore going radially through the wall of valve piece  12 , whose inner walls form a supply throttle  15  along part of their length, is constantly connected to an annular space  16  surrounding valve piece  12  on its outer circumference, which annular space, in turn, is in constant connection to the fuel high-pressure connection. Control pressure chamber  14  is subjected via supply throttle  15  to the high fuel pressure prevailing in the high-pressure reservoir. A bore running through valve piece  12  branches out from control pressure chamber  14  coaxially with valve plunger  6 , and it forms a fuel discharge channel  17 , furnished with a discharge throttle  18 , which opens out into a discharge chamber  19 , which is connected to a fuel low-pressure connection. The outlet of fuel discharge channel  17  from valve piece  12  lies in the region of a cone-shaped, countersunk part  21  of the end face of valve piece  12 . In the exemplary embodiment shown here, valve piece  12  is held in valve housing  4 , with the aid of a clamping element  23  having two alternate clamping shoulders, together with housing part  39  of the solenoid valve via a screw member  7 . For this purpose, valve piece  12  has a circumferential flange  13  which lies on an annular shoulder  47  of valve housing  4 . Flange  13  is clamped between clamping element  23  and valve housing  4 . An adjustment disk  48  lies against the other shoulder of clamping element  23 , facing away from valve housing  4 . The circumferential edge section of housing part  39  of the solenoid valve lies up against adjustment disk  48 . The clamping shoulder of screw member  7  lies against solenoid valve housing  39 , and is screwed to valve housing  4 . In this exemplary embodiment, using only one screw member  7 , solenoid valve housing  39  is fixed to valve housing  4  and valve piece  12  is clamped at the same time.  
         [0014]    In conical part  21  a valve seat  24  is formed, with which a control valve member  22 ,  25  of a solenoid valve controlling the injection valve cooperates. Control valve member  22 ,  25  is formed in two parts, having one valve ball  25  and a socket part  22  accommodating valve ball  25  and coupled to an armature  27  which acts together with an electromagnet  29  of the solenoid valve. Although it is conceivable to form the armature and control valve member  22 ,  25  in one piece, it is provided in the exemplary embodiment shown here that armature  27  and control valve member  22 ,  25  shall be formed as separate parts. The side of socket part  22  facing away from valve ball  25  is formed as a flat contact surface for armature  27 . Armature  27  is made in one piece, and is formed essentially as a circular disk-shaped armature plate. The armature plate has a pole face  37  facing electromagnet  29  and a flat surface  36  facing away from it which acts directly upon socket  22  of the control valve member. A peg  35  projects perpendicularly from pole face  37  of armature  27 , which penetrates a recess  10  of electromagnet  29 , in which a closing spring  31  is also situated which is supported on peg  35 . Armature  27  and control valve member  22 ,  25  coupled to the armature are constantly acted upon by a housing-mounted supported closing spring  31  in the closing direction, so that control valve member  22 ,  25  normally lies adjacent to valve seat  24  in the closing position. When the electromagnet is activated, armature  27  is drawn away from valve seat  24  in the axial direction, and discharge channel  17  is opened towards discharge chamber  19 .  
         [0015]    As can also be seen in FIG. 1, electromagnet  20  includes a solenoid coil  32  and a magnetic core  33 . Magnetic core  33  at its pole face  38  has an annular recess  41 , in which solenoid coil  32  is situated. Connections  34  of the solenoid coil run to the outside through magnetic core  33 . Recess  41  subdivides pole face  38  of the magnetic core into an inner annular pole face section  45  and an outer annular pole face section  44 , which both face pole face  37  of the armature plate, as can be seen best in FIG. 3. When a current acts upon the electromagnet, a closed magnetic circuit forms over the gap between pole face section  44  and pole face  37  of the armature and the gap between pole face  37  of the armature and pole face section  45  of the magnetic core. Between the pole face of magnetic core  33  and pole face  38  of the armature plate a minimum distance may be allowed, in order to prevent a so-called magnetic adhesion of the armature to magnetic core  33 . As shown in FIG. 3, this can be achieved, for example, by a layer  26  made of a magnetic, non-conductive material on pole face  37  of the armature plate. Layer  26  can be made, for instance, of chromium or teflon. The layer may be connected to the armature by soldering, welding, adhesion, or in another suitable way. It is also possible to insert one or more distance washers between pole face  38  of armature  27  and magnetic core  33 . A further possibility for seeing that the minimum distance between the armature plate and the magnetic core is kept, is to provide the armature with structures proceeding from pole face  37  (such as studs), which are supported on the electromagnet or on a sleeve mounted in the electromagnet. Furthermore, for example, the armature plate may be made to lie against a sleeve mounted in the electromagnet and proceeding from pole face  38  of magnetic core  33 .  
         [0016]    The opening and closing of the injection valve is controlled by solenoid valve  30 , as described below. As described before, armature bolt  27  is constantly acted upon by closing spring  31  in the closing direction, so that control valve member  25  lies against valve seat  24  in the closing position when the electromagnet is not activated, and control pressure chamber  14  is closed towards discharge side  19 , so that high pressure very rapidly builds up there, via the supply channel, which is also present in the fuel high-pressure reservoir. The pressure in control pressure chamber  14  generates a closing force on valve plunger  6 , and thus on the valve needle connected with it, which is greater than the forces acting, on the other hand, in the opening direction as a result of the high pressure present. If control pressure chamber  14  is opened toward discharge side  19  by opening the solenoid valve, the pressure in the low volume of control pressure chamber  14  goes down very fast, since it is decoupled from the high-pressure side via supply throttle  15 . As a result, the force acting on the valve needle in the opening direction outbalances the high fuel pressure present at the valve needle, so that the latter moves upwards, and with that the at least one injection orifice is opened for injection. However, if solenoid valve  30  closes fuel discharge channel  17 , the pressure in control pressure chamber  14  may be built up again by fuel that continues to flow via supply channel  15 , so that the original closing force is present, and the valve needle of the fuel injector closes.  
         [0017]    As shown in FIG. 1, armature  27  of the solenoid valve according to an exemplary embodiment of the present invention may be moved in housing part  39  of the solenoid valve in the radial direction without interference by a mechanical guideway. During a radial movement of armature  27 , surface  36  of the armature plate may glide along on socket part  22 . During closing of the solenoid valve, closing spring  31  presses armature  27  and control valve member  22 ,  25  against valve seat  24 , it being possible that the mechanically unguided armature plate may tilt a little if it hits socket part  22  in an off-center fashion. However, even in the case of a slight deflection of the armature plate in the radial direction, control valve member  25  is always reliably pressed into valve seat  24 . Because of the flat design of armature  27  as a disk-shaped armature plate, the tilting moments are greatly reduced in comparison with the case of a T-shaped armature having armature bolts proceeding from the armature plate.  
         [0018]    [0018]FIG. 2 shows a further exemplary embodiment of the present invention. The basic design of the solenoid valve shown in FIG. 2 is similar to that in FIG. 1. The same parts have the same reference numerals. As may be seen, in contrast to FIG. 1, plate-shaped armature  27  here has a centrical recess  40  on its side facing the electromagnet, into which closing spring  31  penetrates. Here the point of contact of closing spring  31  lies particularly close to ball  25  of the control valve member, so that tilting moments acting upon the armature when the solenoid valve is closed are even further reduced. Furthermore, valve piece  12  is clamped into valve housing  4  using a separate, screwable clamping member  23 . Solenoid valve housing  39  is fastened by screw member  7  directly to valve housing  4  via adjustment disk  48 . In order to have sufficient room for clamping member  23 , in spite of the flat armature, end face  12  of the valve piece which faces the electromagnet is provided with a truncated-cone-shaped section  20 , which is surrounded by a flange  13 . Valve seat  24  is mounted centrically into truncated-cone-shaped section  20 . As may be seen, the space surrounding truncated-cone-shaped section  20  forms an accommodation for adjusting nut  23 , which lies adjacent to flange  13  of valve piece  12 . The minimum distance between armature  27  and electromagnet  29  is attained by putting a coating of nonmagnetic material on the armature.  
         [0019]    A further exemplary embodiment of the present invention is especially advantageous, in which the armature plate is centered using magnetic reluctance forces, in order to avoid off-centering of the armature plate and the resulting tilting of the armature plate when it hits the control valve member. This may be attained by providing armature  27  and magnetic core  33  of electromagnet  29  with geometrical structures which cooperate, when a current is applied to electromagnet  29 , in such a way that armature  27  is aligned to a centrical position, in which its centerline  45  runs coaxially with centerline  30  of the electromagnet (centerline  45  and centerline  30  lie on a straight line). This has the advantage that the armature plate is constantly centered when the solenoid valve is opened, and, at switching off of the electromagnet when the solenoid valve is closed, it hits the control valve member from this centrical position. The geometrical structures may be provided both for the solenoid valve shown in FIG. 1 and the one shown in FIG. 2. In FIG. 2 the geometrical structures are indicated by reference numerals  41  and  42 . An enlarged detailed view is found in FIG. 3.  
         [0020]    As may be seen in FIG. 3, electromagnet  29  has a magnetic core  33  and a coil  32 . Magnetic core  33  is furnished with groove-shaped recess  41  running concentrically with its centerline  30 , in which coil  32  is mounted. Pole face  38  of magnetic core  33  is subdivided into an outer annular pole face section  44  and an inner pole face section  45  by recess  41 . The special feature of this exemplary embodiment is the recess  42 , which is inserted in pole face  37  of armature  27  concentrically with centerline  45  of the armature, and facing magnetic core  33 . This likewise annular recess  42  in the form of a circumferential groove has approximately the same outer diameter and inner diameter, and thus it has the same width d as recess  41  of magnetic core  33 . Recesses  41  and  42 , allocated to each other, cooperate magnetically in such a way that, when a current is applied to the electromagnet, centerline  45  of armature  27  runs coaxially with centerline  30  of the electromagnet. The magnetically centering effect is explained by magnetic reluctance forces which appear when there is a radial deflection of the armature plate. If recesses  41  and  42  are not situated over one another in a covering manner, the magnetic field lines at the edges of the two recesses  41 ,  42  are distorted. The reluctance forces resulting from this pull the armature plate back again until recesses  41 ,  42  lie above one another in a covering manner, and centerline  45  of the armature runs coaxially with centerline  30  of electromagnet  29 . For this, recess  42  does not necessarily have to be mounted circumferentially in armature  27 . It is also possible to use segments situated concentrically with centerline  45  or other suitable designs.  
         [0021]    An additional exemplary embodiment is represented in FIG. 4. In this exemplary embodiment pole face  37  of armature  27  is designed without a recess, but it has an external diameter which is a little greater than the internal diameter of outer pole face section  44  of the magnetic core. Preferably, the external diameter of pole face  37  of the armature is designed to be about one millimeter larger than the internal diameter of outer pole face section  44  of magnetic core  33 . When a current is applied to the electromagnet, the magnetic field in the overlapping region e of pole face  37  and of outer pole face section  44  is strengthened, since there the magnetic field lines have to run more densely. The strengthening is the greater, the smaller the overlapping region e. In the case of a radial deflection of the armature plate, strong reluctance forces act in this region, which drive the armature plate back into the centrical position, in which centerlines  30 ,  45  lie coaxially (i.e. lie on a straight line).