Abstract:
The invention provides an electromagnetic actuator comprising at least two coils ( 5, 6 ) associated with ferromagnetic cores ( 11 ) and disposed facing each other, and a moving element ( 1 ) extending between the coils ( 5, 6 ) and associated with an actuator rod ( 2 ), the coils ( 5, 6 ) comprising conductors ( 7 ) with ends ( 16 ) extending transversely to an axis ( 100 ) of the coils ( 5, 6 ) and fixed directly to pins ( 21 ) carried by a connection plate ( 18 ) fixed on one side ( 7 ) of the coils ( 5, 6 ) and including a connection circuit ( 24 ) providing connections with a connector ( 25 ) also carried by the connection plate ( 18 ).

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This application is a National Stage of Application PCT/FR02/00074, filed Jan. 10, 2002, incoporated herein by reference in its entirety. 

   BACKROUND 
   The invention relates to an electromagnetic actuator. 
   In reciprocating engines presently under study, it is envisaged that the admission and exhaust valves will be actuated by electromagnetic actuators. 
   In general, an electromagnetic actuator comprises at least two coils associated with ferromagnetic cores and disposed facing each other, and a moving element that extends between the coils and is associated with an actuator rod. The actuator rod co-operates with the end of the stem of a valve in order to actuate it. 
   When assembling such actuators, the coils are not secured to each other. They must therefore be placed one by one in the actuator housing, which increases assembly time. Flexible cables are then fixed to the coils in order to connect them to a power supply connector. Such connection is made difficult by the fact that the coils are already in the actuator housing, so the ends of the conductors constituting the coils are difficult to access. 
   Alternatively, if assembly is begun by connecting the coils to the connector, then it becomes awkward to take the set of coils and place them in the actuator housing. 
   SUMMARY 
   In the invention, the coils comprise conductors having ends extending transversely to a coil axis and directly fixed to pins carried by a plate fixed on one side of the coils and including a connection circuit providing a connection with a connector also carried by the plate. 
   Thus, the plate serves both to provide electrical connection between the coils and the connector, and mechanical fastening of the coils relative to one another. This disposition makes it possible to assemble the card to the coils away from the actuator housing, and then take the assembly as built up in this way to the housing. This simplifies assembly of the actuator considerably. 
   Advantageously, each end of a conductor extends through a hole in the plate and opens out adjacent to a pin on a face of the plate opposite from the coils. 
   Thus, the end of the conductor is automatically positioned facing a pin while it is being inserted in the corresponding hole, and can thus be soldered to the pin by a hot clamp whose movements are not impeded by the coils. 
   Advantageously, the coils are covered in insulating material having external projections to which the connection plate is fixed. The coils also have spacers that bear against one another to maintain spacing between the coils. The spacers are preferably integral with the insulating material, and are formed by the external projections. 
   In an embodiment in which the actuator comprises four coils associated in two adjacent pairs, the coils in corresponding positions in each pair have ferromagnetic cores carried by a common ferromagnetic support. Putting the coils into place on the common support thus begins the process of mechanically securing the two pairs of coils. 
   In another aspect of the invention, the ferromagnetic cores project from the coils beside the moving element. These ferromagnetic cores thus form an abutment for the moving element, which prevents the coils being damaged. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention appear more clearly in the light of the following description of a particular non-limiting embodiment of the invention described with reference to the figures, in which: 
       FIG. 1  is an exploded perspective view of a portion of an actuator of the invention; 
       FIG. 2  is a section view of the actuator on II-I of  FIG. 1 ; 
       FIG. 3  is a front view of the actuator of  FIGS. 1 and 2  after assembly; and 
       FIG. 4  is an enlarged perspective view of a connection pin at one end of a conductor. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The actuator described herein is suitable for controlling the opening and closing of two valves (not shown) having parallel axes. The actuator is substantially symmetrical about a plane P defining a boundary between actuator components associated with controlling different valves. 
   The actuator comprises two moving elements  1  each mounted on the actuator to slide along a respective axis  100 . Each of these moving elements  1  comprises an actuator rod or plunger  2  having one end  3  projecting from the actuator to co-operate with the end of the stem of a valve. 
   The other end of the plunger  2  is secured to an armature  4  extending perpendicularly to the axis  100  and constrained to move between two coils  5  and  6  faced facing each other along the axis  100 . 
   Each coil comprises a conductor  7  embedded by molding in an insulating material  8  forming a substantially rectangular block, the conductor  7  being wound in such a manner as to leave a central hole  9  through the coil. 
   The two coils  5  are engaged as a force-fit on a common support  10  made of laminations of ferromagnetic material stacked on one another. The support  10  has cores  11  extending in the central holes  9  of the coils  5 . The cores  11  are pierced to allow the plungers  2  to pass through. The support  10  also comprises a central web  12  and two end webs  13  on either side of the coils  5 . 
   The two coils  6  are engaged as a force-fit on a support  14  entirely similar to the support  10 , with the exception of the cores of the coils  6  which are not pierced. 
   The cores  11  and the webs  12 ,  13  of the supports  10  and  14  project from the facing faces of the coils  5  and  6  so as to form abutments for the armatures  4  when they move. 
   Projections  15  are molded out of the insulating material  8  so as to project from the facing faces of the coils  5  and  6 . The projections  15  of one coil form spacers which co-operate with the projections  15  of the facing coil so as to maintain a determined spacing between the coils. 
   On each coil, the ends  16  of the conductor  7  project by extending perpendicularly from a side face  17  of the coil. 
   The side faces  17  of the four coils form a support plane for a printed circuit  18  which is fixed to each coil by means of screws  19  each screwed into a respective projection of a coil. 
   Each conductor end  16  extends into a hole  20  of the printed circuit  18  and comes out in the vicinity of a pin  21  on a face of the printed circuit card remote from the coils. 
   Each pin  21  has a portion  22  which is parallel to the conductor end  16  and which is soldered thereto. This portion  22  is connected in stable manner to the printed circuit  18  by means of a tripod  23 . 
   The ends of the tripod  23  pass through the printed circuit  18  to be electrically connected with conductor tracks  24  made on the face of the printed circuit facing the coils. The conductor tracks  24  form a connection circuit connecting the conductor ends  16  to a connector  25  carried by the printed circuit  18 . 
   The procedure for assembling the actuator is as follows:
         the coils  5  are fitted on the support  10 , and then the coils  6  are fitted on the support  14 ;   the moving elements  1  are threaded through the holes in the support  10 , and then the two coil assemblies as built up in this way are presented to each other so as to cause the projections  15  of each coil to co-operate with the projections  15  of the facing coil of the other assembly;   the printed circuit  18  is presented and screwed to the side faces  17  of the coils disposed in this way; and   each conductor end  16  is soldered to the adjacent pin  21 , e.g. by means of a hot clamp that delivers solder. This operation is made easier by the fact that the pins  21  are on a face of the printed circuit  18  that is easily accessible, and by the fact that the pins  21  are far enough apart from one another to make it easy to engage such a clamp.       

   All of the ends  16  are thus directly wired to the connector  25  without there being any need to extend any of them by means of a flexible cable. In addition, the four coils are secured mechanically to one another by means of the printed circuit  18  and can thus be transported as a block for placing in a housing (not shown) of the actuator. 
   Furthermore, all of the components (pins, connector) of the printed circuit  18  are situated on the same face thereof and can therefore be flow-soldered to the printed circuit  18  prior to the printed circuit being assembled to the coils. 
   The invention is not limited to the particular embodiment described above, but on the contrary covers any variant coming within the scope of the invention as defined by the claims. 
   In particular, although the actuator is described as having a printed circuit  18 , it is possible to use a plate of synthetic material having conductors embedded therein, which conductors are made by stamping a metal sheet in order to form the connection circuit. 
   Although the actuator is described with a support common to two coils, it is possible to replace such a support by two independent ferromagnetic cores, and to join together the two coils fitted with these cores by connection means on their facing faces. 
   Although the external projections of the coils are used in this case as coil spacers, it is possible to make provision for using spacers that are fittings separate from the external projections. 
   Although the printed circuit described is screwed to the coils, other fasteners could be used, for example it could be snap-fastened or bonded by adhesive. 
   It is also possible to provide an additional structural member between the coils, for example straps fixed to the coils on their side face remote from the connection circuit. 
   Although the printed circuit  18  is described as carrying only the connector  25  and the pins  21 , it could also carry electronic components for managing the supply of power to the conductors of the coils. It is also possible for it to carry connections to a sensor associated with the moving elements  1 .