Abstract:
In a device for operating a gas exchange valve of an internal combustion engine having an electromagnetic actuator including a valve opening magnet and a valve closing magnet, between which there is arranged an armature which, together with an opening spring, engages a valve stem against the force of a closing spring, and a hydraulic play-compensating element is arranged in the valve operating force transmission structure, the hydraulic play-compensating element is installed in the transmission structure together with a mechanical adjusting element providing for minimal valve play when the engine is shut down.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for operating a gas exchange valve of an internal combustion engine with an electromagnetic actuator which includes an opening magnet and a closing magnet and an armature movably disposed between the opening and closing magnets for operating a valve shaft against the force of a closing spring. 
     Electromagnetic actuators for actuating gas exchange valves usually have two operating magnets, a valve opening magnet and a valve closing magnet, with opposite pole faces between which an armature is arranged. The armature acts directly or indirectly on a valve stem of the gas exchange valve. Actuators operating in accordance with the principle of mass-oscillation include a spring mechanism, wherein two springs act on the armature in opposite directions. Usually, two pre-stressed compression springs are used as the spring mechanism, of which one is a valve opening spring which biases the gas exchange valve in the valve opening direction and the other is a valve closing spring, which biases the gas exchange valve in the valve closing direction. When the magnets are not excited, the armature is retained by the valve springs in a position of equilibrium between the two magnets. This position corresponds to a center position, that is an equilibrium position of energy, between the two springs. 
     DE 35 13 107 C2 discloses a gas exchange valve with an actuator in which the armature, together with an opening spring, acts on the valve stem, via an armature tappet, against the force of a closing spring, which acts on the valve stem of the gas exchange valve. 
     DE 39 20 931 A1 discloses an electromagnetic actuator for gas exchange valves of displacement engines, in particular of internal combustion engines, which operates one or more gas exchange valves via a lever mechanism. The lever mechanism provides for a variable motion transmission between the actuator and the gas exchange valve. A play-compensating element compensates for the play, which is caused by the transmission system or which develops therein. The play-compensating element may be arranged in various positions in the transmission system either on the side of the gas exchange valve or on the side of the magnet, e.g. between the support structure of the lever system or between the closing magnet and the housing. The play compensation arrangement also includes a structure common to the gas exchange valve, or individual adjustment devices for changing the transmission ratios and to adapt the position of equilibrium of the oscillating system to the new spring forces by changing the position of one or more spring support points. 
     DE 39 20 976 A1 discloses a similar adjusting device in which a hydraulic play-compensating element is supported in the armature and engages the valve stem of the gas exchange valve. The play-compensating element may be supplied with oil under pressure via the armature. Also provided is a setting screw which is inserted in a top cover and acts on one support point of an opening spring which, with its other support point, engages the armature. By virtue of the setting screw, the position of equilibrium of the armature is adjustable such that the armature rests in the center between the operating magnets when the magnets are de-energized. 
     When the internal combustion engine is at a standstill, the hydraulic play-compensating element empties whereby the pre-determined position of equilibrium is changed in the direction toward the opening magnet. When the internal combustion engine is then started up again, the closing magnet has to generate a relatively high force. This causes a high mechanical, electrical and thermal load. Furthermore, in the closed position of the armature, there is a relatively large gap between the play-compensating element and the valve stem, which results in an annoying noise. In many cases, oscillation excitation of the system is not possible. 
     It is the object of the invention, to improve the start-up capabilities of an internal combustion engine controlled via electromagnetic actuators. 
     SUMMARY OF THE INVENTION 
     In a device for operating a gas exchange valve of an internal combustion engine having an electromagnetic actuator including an opening magnet and a closing magnet, between which there is arranged an armature which, together with an opening spring, engages a valve stem against the force of a closing spring, and a hydraulic play-compensating element arranged in the valve operating force transmission structure, the play-compensating element is installed in the transmission structure together with a mechanical adjusting element providing for minimal valve play when the engine is shut down. 
     The mechanical play compensating element compensates for all deviations or tolerances resulting from the manufacture so that the hydraulic play-compensating element need only compensate for the changes in length resulting from the operation of the internal combustion engine. As a result, any gap between the play-compensating element and the adjacent component is minimal when the engine is started up again after stand-still, with the result that no significant noise or excessive mechanical, electrical or thermal loading is generated. Operation of the internal combustion engine is possible however also with a defective mechanical play-compensating element. 
     The adjusting element may simply comprise an adjusting disc, an eccentric shaft or a setting screw. It may be arranged at various locations of the device, so that there is a high level of design freedom. 
     Further embodiments and advantages of the invention will become apparent from the following description of the invention on the basis of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows, schematically, a device according to the invention having a hydraulic play-compensating structure shown in a position as it is during operation of the internal combustion engine or shortly after the engine has come to a standstill, 
     FIG. 2 shows a device according to FIG. 1 while the internal combustion engine is at a standstill and the oil has drained from the hydraulic play-compensating structure, 
     FIG. 3 shows a device according to FIG. 1 of the internal combustion engine immediately after start-up before the hydraulic play compensation structure has been readjusted, 
     FIG. 4 shows an enlarged detail area as indicated by the circle IV in FIG. 1, and 
     FIG. 5 shows, in detail, another embodiment of the invention, that is, a variant from the arrangement of FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the arrangement  1  of the invention as shown in FIG. 1, an electromagnetic actuator  11  operates a gas exchange valve  2  in the cylinder head  33  (FIG. 5) of an internal combustion engine. The actuator  11  has a top closing magnet  15  and a bottom opening magnet  16  as well as an armature  12 , which is arranged axially movably between the magnets  15  and  16 . The armature  12  acts on a valve stem  4  of the gas exchange valve  2  via an armature tappet  13  and a play-compensating element  10 . Located at the free end of the valve stem  4  is a valve disc  3 , which interacts with a valve seat ring  6  positioned in the cylinder head  33 . A valve guide  5  guides the valve stem  4  in the cylinder head  33 . For the sake of clarity, the cylinder head  33  has not been illustrated in FIGS. 1-4. 
     A pre-stressed spring system, comprising a valve closing spring  7  and a valve opening spring  17 , retains the armature  12  in a position of equilibrium when the magnets  15 ,  16  are de-energized. The position of equilibrium corresponds generally to a center position  19  with regard to the energy of the two springs  7  and  17 . The closing spring  7  is supported at one end, on the cylinder head  33  via a spring support structure  8  and, at the other end, on the valve stem  4  via a closing spring support plate  9 . The opening spring  17  is supported, at one end, on the actuator  11  and, at its other end, on the armature tappet  13  via an opening spring plate  18 . 
     FIG. 1 shows the armature  12  during engine operation in the center position  19  between the two magnets  15  and  16 . During engine operation the play-compensating element  10  is activated and ensures that the gas exchange valve  2  closes in a play-free manner. Then in the closed position  21 , that is, with the gas exchange valve  2  closed, the armature  12  butts against the closing magnet  15 . The closing spring  7 , which is pre-stressed, engages the gas exchange valve  2  with a predetermined closing force. 
     The play-compensating element  10  includes a cylinder  24  which butts against the valve stem  4  and in which a piston  25  is arranged in an axially movable manner. Together with the cylinder  24 , the piston  25  forms a pressure space  26 . Located in the latter is a spring  30  which biases the piston  25  against the armature tappet  13 , which is disposed in a recess  31  at the free end side of the piston  25 . The pressure space  26  is connected to an oil supply via a connection bore  14  in the armature tappet  13  and a connecting bore  27  in the piston  25 . A ball  28 , which is biased into a bore closing position by a spring  29  forms a check valve opening in the direction of the pressure space  26 . It controls fluid flow from the connecting bore  27  out of the pressure space  26  valve. If the pressure prevailing in the pressure space  26  is lower than in the connecting bore  27 , because, for example, the valve disc  3  butts against the valve seat ring  6  before the armature  12  reaches the closing magnet  15 , the ball  28  is unseated against the force of the spring  29  and oil flows into the pressure space  26 . In this way, the piston  25  is adjusted axially until the armature  12  engages the closing magnet  15  when the gas exchange valve  2  is closed. 
     When the internal combustion engine is at a standstill, the valve closing spring  7  and the valve opening spring  17  subject the play-compensating element  10  to a loading, whereby the oil escapes from the pressure space  26  via throttle gaps provided (but not illustrated specifically). As a result, the play-compensating element  10  is compressed to the fullest extent. Accordingly, the position of equilibrium  20  of the armature  12  is changed in the direction toward the opening magnet  16  (FIG.  2 ). This means that, when the internal combustion engine is started up again, a gap  22  is formed between the play-compensating element  10  and the valve stem  4  when the armature  12  is located in a closed position  21  (FIG. 3) and the armature engages the closing magnet  15 . The gap  22  makes correct functioning of the gas exchange valve  2  more difficult or disrupts operation completely. According to the invention, minimal valve play is therefore set during the installation by an adjusting element in the form of an adjusting disc  23 ,  32 ,  37 ,  39  or in the form of a setting screw  35 . For this purpose, the distance between the parts adjacent to the play-compensating element  10 , e. g. the distance between the valve stem  4  and the armature tappet  13 , is measured when the valve  2  is closed and the armature  12  engages the closing magnet  15 . The fully compressed length of the play-compensating element  10  is subtracted from this measurement. The remainder gives the desired thickness of the adjusting discs  23 ,  32 ,  37 ,  39  plus a minimal valve play. The setting screw  35  is to be turned accordingly. Instead of the adjusting disc  23 ,  32 ,  37 ,  39  or the setting screw  35 , it is also possible to use other mechanical adjusting elements, e.g. an eccentric shaft (not illustrated specifically) or the like. The adjusting elements  23 ,  32 ,  37 ,  39  may be arranged in any desired position in the force transmission path of the play-compensating element  10 . 
     In the embodiments according to FIGS. 1 to  3 , an adjusting disc  23  is provided beneath the opening magnet  16 . It is alternatively possible to arrange an adjusting disc  32  in the opening  31  of the piston  25  of the play-compensating element  10  (FIG.  4 ). In the exemplary embodiment according to FIG. 5, three alternatives are illustrated. The first alternative consists of an adjusting disc  37 , which is installed between a securing means in the form of a cover  36  and the cylinder head  33 . Further, the actuator  11 , which is arranged in a floating manner in the cylinder head  33 , may be supported on the cover  36  via the play-compensating element  10 . As an alternative to the adjusting disc  37 , it is possible to provide a setting screw  35  in the cover  36 , the play-compensating element  10  being supported on the setting screw  35 . As a third alternative, an adjusting disc  39  may be positioned between the actuator  11  and the play-compensating element  10  may be supported thereon. Hydraulic fluid is fed to the play-compensating element  10  via a supply line  34 . 
     With a proper selection of the adjusting elements  23 ,  32 ,  37 ,  39 , the internal combustion engine can be started up again with a minimal gap  22  so that the loading of the components and development of noise are minimized.