Abstract:
An electromagnetic actuator for operating a cylinder valve in an internal combustion engine includes first and second housings secured to one another. Each housing has a cavity and a through bore extending therefrom. First and second electromagnets are disposed in the cavity of the respective housings. Each electromagnet has a yoke, a coil and a pole face. The pole faces are oriented toward and spaced from one another, and a reciprocating armature is disposed between the pole faces. A spring which urges the armature away from the first electromagnet has an end oriented away from the armature. A support cap is axially insertable in the through bore of the first electromagnet and includes a cap base having an inner face supporting the spring end. A locking arrangement secures the support cap to the housing and has a component axially insertable in the through bore with the support cap.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of German Application No. 100 18 739.0 filed Apr. 15, 2000, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     An electromagnetic actuator for operating a cylinder valve of a piston-type internal-combustion engine has to be mass produced in large numbers in an economical manner. Such an electromagnetic actuator includes opening and closing electromagnets having spaced, facing pole faces, an armature reciprocated between the pole faces and coupled to the cylinder valve to move the latter into open and closed positions, as well as opening and closing (resetting) springs opposing the armature motion. 
     German Offenlegungsschrift (application published without examination) 198 25 728 discloses an electromagnetic actuator of the above-outlined type. The electromagnets are each provided with a respective, separate housing for receiving the magnet yoke which supports a coil. Such housings make possible a mass produced assembly of complete electromagnetic actuators. The housings are expediently made of a non-magnetic metal, for example, aluminum or an aluminum alloy so that they may be mass produced with a suitable casting process (such as die casting) in large numbers in an economical manner and adapted to individual requirements. On its side oriented away from the pole face of the inserted yoke body, the housing is provided with a tubular passage for receiving one end of a resetting spring. Thus, each housing may be used either for the part serving the opening function or the part serving the closing function. 
     In the housing oriented towards the cylinder valve the closing spring extends through the housing passage and is supported at its ends by the engine block and, respectively, by a spring seat disk affixed to the cylinder valve stem. 
     In the housing oriented away from the cylinder valve the opening spring passes through the housing passage and is supported on a threaded sleeve, by means of which the mid position of the armature between the pole faces of the two electromagnets may be adjusted. Such a threaded sleeve involves not only high manufacturing and assembly costs but also has disadvantages as concerns the reproducibility of an optimal setting and its handling during maintenance work. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved electromagnetic actuator of the above-outlined type from which the discussed disadvantages are eliminated. 
     This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the electromagnetic actuator for operating a cylinder valve in an internal combustion engine includes first and second housings secured to one another. Each housing has a cavity and a through bore extending therefrom. First and second electromagnets are disposed in the cavity of the respective housings. Each electromagnet has a yoke, a coil and a pole face. The pole faces are oriented toward and spaced from one another, and a reciprocating armature is disposed between the pole faces. A spring which urges the armature away from the first electromagnet has an end oriented away from the armature. A support cap is axially insertable in the through bore of the first electromagnet and includes a cap base having an inner face supporting the spring end. A locking arrangement secures the support cap to the housing and has a component axially insertable in the through bore with the support cap. 
     By eliminating the conventional, disadvantageous threaded sleeve, both actuator housings may be made from identical blanks without major finishing costs. By using an axially insertable support cap including a plug-in lock, cutting threads into the housing for a threaded adjusting sleeve cooperating with the opening spring is no longer needed. Merely geometrical elements for a plug-in lock are needed which may be readily formed in the housing blank. The presence of such housing configuration is harmless for the other, cap-less housing (accommodating the opening magnet) because, as concerns the opening magnet, only the closing spring is received in the housing passage and therefore any particular housing shape required for the support cap does not cause disturbance during service. Plug-in support bodies may be installed in a simple manner and further have the advantage that they may be made in large numbers of shaped steel sheet. Making the support cap from steel sheet also has the advantage that the cap, although exposed to high tension forces, may be relatively thin-walled. A further advantage compared to a conventional thread provided in the actuator housing resides in the fact that the securing and locking means can be made as large-area members so that the securing means of the steel supporting cap and the housing (such as an aluminum casting) may engage one another with a low surface pressure. 
     According to a preferred embodiment of the invention, in the region of the through bore the support cap and the housing together form the support cap lock which immobilizes the support cap in the actuator housing. This is achieved by configuring the lock as a bayonet lock composed of at least one radial projection and a receiving element for accommodating the projection, provided, for example, on the outer surface of the support cap and the housing, respectively. Upon assembly, the support cap may be plugged into the housing passage (through bore) and is thereafter rotated about its axis to lock it in place. 
     According to a particularly advantageous feature of the invention the projection and/or the projection receiving element is configured as a helical ramp in relation to the longitudinal actuator axis. As a result, by rotating the support cap relative to the housing, the bias of the opening spring may be changed and thus the mid position of the armature between the two pole faces may be adjusted. According to the invention, securing means are provided for fixing the support cap in the housing in a predeterminable position of installation. 
     According to a further advantageous feature of the invention, the outer surface of the cap base whose inner bottom surface is engaged by the opening spring is provided with at least one element for receiving a mounting tool. Such an element may be a rectangular opening provided in the cap base or two openings radially spaced from the central axis of the supporting cap to receive, respectively, a quadrilateral wrench or a hook wrench. After inserting the supporting cap into the housing bore while compressing the opening spring, the support cap may be turned into its locked position by the wrench inserted into the receiving element. 
     In accordance with a further advantageous feature of the invention, at least the base of the support cap made of steel sheet is tempered (hardened). The opening spring engages at one end a spring seat disk which is made of a wear resistant material and which is affixed to an armature guide bar. The other end of the opening spring engages the inner surface of the cap base. Since at that location substantial spring forces have to be taken up and the support of the springs in operation is exposed to a fluctuating pressing load, a hardened cap base prevents the spring end from working itself into the cap material. 
     Instead of providing a helical ramp for the projection and/or the projection-receiving element of the bayonet lock for the support cap, according to another feature of the invention at least one adjusting washer is positioned on the inner face of the cap base for engaging the opening spring. By inserting adjusting washers of different thicknesses or as a stack, it is possible to adjust, within the required accuracy, the mid position of the armature between the two pole faces. By virtue of this measure the structure of the lock between the support cap and the housing is simplified since the support cap needs only to be inserted into the housing bore and then locked to the housing by rotation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial sectional view of an electromagnetic cylinder valve actuator incorporating the invention. 
     FIG. 2 is a perspective view of a housing for the closing magnet of the actuator, provided with a support cap for the opening spring according to a preferred embodiment of the invention. 
     FIG. 3 shows the magnet housing of FIG. 2 without the support cap. 
     FIG. 4 is a sectional view taken along line IV—IV of FIG.  3 . 
     FIG. 5 is a perspective view of the support cap shown in FIG.  2 . 
     FIG. 6 is a sectional view taken along line VI—VI of FIG.  5 . 
     FIG. 7 is a sectional elevational view of a support cap according to a variant of the FIG. 6 structure. 
     FIG. 8 is a perspective view of another preferred embodiment of the invention. 
     FIG. 9 is a sectional view taken along line IX—IX of FIG.  8 . 
     FIG. 10 is a perspective view of a support cap according to the embodiment shown in FIG.  8 . 
     FIG. 11 is a perspective view of another preferred embodiment of the support cap for use in a housing shown in FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The electromagnetic actuator illustrated in FIG. 1 includes a closing electromagnet  1  and an opening electromagnet  2 . The magnets  1 ,  2  which are separated from one another by spacer members  3 . 1  and  3 . 2  have respective pole faces  4  oriented toward one another. In the space between the two pole faces  4  an armature  5  is movable from one pole face to the other and is attached to a guide bar  6  passing through the electromagnet  2 . In the illustrated embodiment the armature  5  has a rectangular outline. 
     A further guide bar  7  passes through the electromagnet  1  in aligned contact with the guide bar  6 . At its upper end  7 ′ the guide bar  7  is connected with a resetting spring  8  which serves as an opening spring. The lower free end  9  of the guide bar  6  engages the upper free end  10  of the valve stem  11  of a valve which is guided in an only symbolically shown cylinder head  12  of an internal combustion engine. By means of a resetting spring  13  which serves as a closing spring, the cylinder valve is urged in the closing direction. The closing spring  13  and the opening spring  8  exert their spring force in facing, opposite directions whereby in the de-energized state of the electromagnets  1  and  2  the armature  5  assumes its position of rest in the mid region between the two pole faces  4  of the electromagnets  1  and  2 , as illustrated in FIG.  1 . 
     In case the two electromagnets  1  and  2  are alternatingly energized, the armature  5  alternatingly arrives at the respective pole face  4  of the two electromagnets  1  and  2  and, accordingly, the cylinder valve is, for the duration of the energization, maintained in the open position (engagement of the armature  5  with the pole face  4  of the electromagnet  2 ) against the force of the closing spring  13  or in the closed position (engagement of the armature  5  with the pole face  4  of the electromagnet  1 ) against the force of the opening spring  8 . 
     The electromagnetic actuator illustrated in FIG. 1 is a structural unit composed of practically identical modular elements. The two electromagnets are preferably of identical construction and are each composed essentially of a separate housing  14  which has a cavity  15  oriented towards the armature  5  for receiving a yoke body  16  carrying a coil  17 . The housing  14  further has a through bore  18  through which the respective opening spring  8  or closing spring  13  may partially pass. 
     As indicated by the flatness of the actuator housing  14  shown in FIG. 2, the electromagnetic actuator is of very narrow construction allowing a close, side-by-side installation of such actuators in the limited space of the engine. The yoke body  16  is, together with the coil  17 , inserted into the cavity  15  of the housing  14  and is fixed and held therein by means of a suitable cast mass. 
     The housing  14  further has an additional lateral opening  20  which permits access to the terminals  21  of the coil  17 . By virtue of such an arrangement the two electromagnets  1 ,  2  may be connected to the actuator control by a coded, one-piece plug  22  (shown in dash-dot lines) in a non-interchangeable manner. The plug  22  is positioned and protected in the lateral flanks of the lateral opening  20 . 
     Reverting to FIG. 1, the two housings  14  made, for example, of an aluminum alloy by means of die casting, have aligned passages  23  which extend parallel to the axis of the guide bars  6  and  7  and cooperate with similar apertures provided in spacers  3 . 1  and  3 . 2  positioned between the two housings  14 . The two housings  14  may thus be firmly bolted to one another and/or to the engine block  12  with the interposition of the spacers  3 . 1  and  3 . 2 . 
     The opening spring  8  is supported by a support cap  25  serving as a spring-force setting element. By turning the support cap  25  or by inserting adjusting washers, the mid position of the armature  5  between the two pole faces  4  may be altered. 
     As may be seen in FIG.  1  and particularly in FIG. 2, the through bore  18  is surrounded by a flange  19  at its end oriented away from the yoke body  16 . Also referring to FIG. 3, on the inside the through bore  18  is, on diametrically opposite sides, provided with groove-like recesses  26  cooperating with respective, radially outwardly oriented projections  27  provided on the support cap  25 , as also shown in FIGS. 5,  6  and  7 . By virtue of this structure the support cap  25  may be inserted axially into the through bore  18  and then rotated to be immobilized in the housing  14  by a bayonet-type lock. Upon insertion of the support cap  25 , the opening spring  8 , previously positioned on a spring seat disk  7 ″ affixed to the upper end  7 ′ of the guide bar  7 , is compressed. By virtue of the bias of the opening spring  8  the support cap  25  is held in its position even when the armature  5  is in engagement with the pole face  4  of the opening magnet  2 . 
     The base  28  of the support cap  25  is provided with a polygonal (for example, rectangular, as shown in FIG. 2) aperture  29  for receiving a non-illustrated turning tool to rotate the support cap  25  after it has been inserted into the through bore  18 . 
     In actuator constructions in which the upper end of the guide rod  7  passes through the opening spring  8  and through the base  28  of the support cap  25  and is provided with sensor elements, the through aperture  29  is circular. In such a case, as illustrated in FIG. 5, as tool receptors spaced bore holes  29 . 1  are provided into which a suitable hook wrench may be inserted for turning the support cap  25 . 
     The embodiment illustrated in FIG. 2 is shown in detail in FIGS. 4 and 5 and will be further described as the specification progresses. 
     As may observed in FIG. 4, adjacent the groove like recesses  26  the lower edge  30  of the through bore  18  has an undercut which is configured as a helical ramp  31  provided with a plurality of consecutive depressions. 
     Correspondingly, as seen in FIG. 5, the projections  27  have nose-like elevations  32  which may be brought into engagement with the depressions on the ramp  31  by rotating the support cap  25  in the through bore  18 . By virtue of the slope of the ramp  31  the distance of the cap base  28  changes relative to the pole face  4  of the closing magnet  1  in the shortening direction if, after insertion of the support cap  25  the latter is turned clockwise. As a result, the bias of the opening spring  8  is increased and, accordingly, the armature  5  is shifted in the direction of the pole face  4  of the opening magnet  2 , simultaneously compressing the closing spring  13 . By virtue of the engagement of the nose-shaped elevations  32  into the depressions on the ramp  31 , the support cap  25  is immobilized in the housing  14  and thus securely prevented from rotating. 
     Instead of depressions on the helical ramp  31  and corresponding nose-like elevations  32  on the support cap  25 , it is feasible to configure the ramp  31  as well as the projection  27  to have a smooth surface as shown in FIG.  7 . The angular immobilization of the support cap  25  after adjustment of the mid position of the armature  5  may be effected by a plug-in pin which passes through radial bores  33  in the support cap and corresponding, non-illustrated radial holding bores in the housing flange  19 . It is also feasible, however, to provide the edge  27 . 1  of the projections  27  with a series of tooth-like recesses associated with at least one holding bore passing axially parallel through the flange  19 . Thus, after setting the mid position of the armature by turning the support cap  25  in the appropriate angular position, the support cap  25  may be angularly immobilized by a pin passing through the holding bore in the flange  19  and a corresponding, axially parallel bore in the edge  27 . 1  of the projection  27 . 
     FIG. 8 is a perspective view of an embodiment in which the housing is provided with partial collar-like elevations  19 . 1  on its side oriented away from the housing cavity for the yoke body. As shown in FIG. 9, radial holding pins  34  pass through the elevations  19 . 1  and project into corresponding recesses  35  provided in the circumferential wall of the support cap  25 . The recesses  35  may be through openings as shown in FIG.  10 . For loosening the support cap the pins  34  are removed. 
     As shown in the variant illustrated in FIG. 11, it is also feasible to provide, in the circumferential wall of the support cap  25 , a slit-like recess  36  having an approximately L-shaped course and terminating in a detent  37 . Such a support cap may be inserted on the pins  34  affixed to the collar-like insert  19 . 1  and may be immobilized by rotation. Here too, the support cap  25  is held in its position by the bias of the opening spring  8 . 
     In the embodiment according to FIGS. 9,  10  and  11  but also in all the previously described embodiments when suitably modified, the adjustment of the mid position of the armature  5  is effected by inserting and positioning on the base  28  of the support cap  25  one or more washers  38  of predetermined thickness before attaching the support cap  25  to the housing  14 . 
     The adjusting washers  38  may also be used when for the adjustment of the mid position of the armature  5  only an insufficient setting path is available for the projection  27  on the helical ramp  31 . 
     The wall thicknesses available for the housing  14  are sufficient to take up fluctuating stresses even if made of aluminum or aluminum die cast. The support cap  25  which should be thin-walled, is expediently made of steel sheet; for increasing the wear resistance, at least the base  28  is tempered to prevent the end of the opening spring from working itself into the base  28  during operation. Despite the thinness of the walls, the fluctuating spring forces acting between the housing  14  and the support cap  25  may be taken up as tension stresses via the steel plate material of the support cap  25 . 
     The drawings readily show that the arrangement of projections and projection-receiving elements may be interchanged, that is, the through bore  18 , instead of the groove-like receiving elements  26 , may be provided with the radial projections  27  and, likewise, the support cap  25 , instead of the projections, may be provided with the groove-like receptors. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.