Abstract:
The present invention pertains to an electromechanical actuator controlling a valve of an internal combustion engine by means of a first magnetic field, generated in a variable manner by an electromagnet, and a second magnetic field, generated by at least one magnet associated with the electromagnet. According to the present invention, the actuator is characterized in that it comprises at least one connecting part forming a magnetic circuit facilitating the passage of the flux generated by the electromagnet for part of the field generated by the magnet, the connecting part being magnetically saturated by the partial field of the magnet.

Description:
This application claims priority under 35 U.S.C. §119(a) to French Patent Application No. 04 50092, filed on Jan. 15, 2004. 
   FIELD OF THE INVENTION 
   The present invention pertains to an electromagnetic actuator for controlling a valve for an internal combustion engine and to an internal combustion engine equipped with such an actuator. 
   BACKGROUND 
   An electromagnetic actuator  100  ( FIG. 1 ) for a valve  110  comprises mechanical means, such as springs  102  and  104 , and electromagnetic means, such as electromagnets  106  and  108 , for controlling the position of the valve  110  by means of electric signals. 
   The stem of the valve  110  is applied for this purpose against the rod  112  of a magnetic plate  114  located between the two electromagnets  106  and  108 . 
   When a current is flowing in the coil  109  of the electromagnet  108 , the latter is activated and generates a magnetic field attracting the plate  114 , which will come into contact with it. 
   The simultaneous displacement of the rod  112  permits the spring  102  to bring the valve  110  into the closed position, the head of the valve  110  coming against its seat  111  and preventing the exchanges of gas between the interior and the exterior of the cylinder  117 . 
   Analogously (not shown), when a current is flowing in the coil  107  of the electromagnet  106 , the electromagnet  108  being deactivated, it will be activated and attracts the plate  114 , which will come into contact with it and displace the rod  112  by means of the spring  104  such that the rod  112  acts on the valve  110  and brings the latter into the open position, the head of the valve being moved away from its seat  111  to permit, for example, the admission or the injection of gas into the cylinder  117 . 
   Thus, the valve  110  alternates between the open and closed positions, the so-called commuted positions, with transient displacements between these two positions. The state of an open or closed valve will hereinafter be called the “commuted state.” 
   The actuator  100  may also be equipped with a magnet  118  located in the electromagnet  108  and with a magnet  116  located in the electromagnet  106 , which said magnets are intended to reduce the energy needed to maintain the plate  114  in a commuted position. 
   Each magnet is located for this purpose between two subunits of the electromagnet with which it is associated in such a way that its magnetic field, possibly combined with the field generated by the electromagnet, reinforces the maintenance of the valve  110  in the open or closed position. For example, the magnet  116  is located between two subunits  106   a  and  106   b . 
   Due to the action of the magnet on the magnetic plate, such an electromagnet  106  or  108 , called an electromagnet with a magnet or a polarized electromagnet, requires considerably less energy to control a valve, the maintenance of a valve in a commuted position representing a considerable energy consumption for the actuator. 
   SUMMARY OF THE INVENTION 
   The present invention results from the observation that in such a prior-art polarized actuator, the magnetic flux of the electromagnet passes through the magnet (or magnets) that is associated with it, which causes an increase in the equivalent air gap considered by the electromagnet during its action on the plate. As a consequence of this, a higher current and hence a higher consumption is necessary for the actuator to control the valve. 
   The present invention aims at accomplishing this object. It pertains to an electromagnetic actuator controlling a valve of an internal combustion engine by means of a first magnetic field, generated in a variable manner by an electromagnet, and a second magnetic field, generated by at least one magnet associated with the electromagnet, characterized in that the actuator comprises at least one connecting part forming a magnetic circuit facilitating the passage of the flux generated by the coil for part of the field generated by the magnet, the connecting part being magnetically saturated by this partial field of the magnet. 
   In such an actuator, the magnetic field of the electromagnet circulates via the connecting part of the actuator when the plate is attracted or maintained by the actuator such that the efficiency of the action of the electromagnet on the plate is not diminished by the presence of a magnet. 
   Consequently, the magnetic field of the electromagnet passes only partially through the magnet that is associated with it during this operation of the actuator (attraction and maintenance of the plate) such that there is no risk of the magnet being demagnetized. 
   Also, if a defluxing field intended to compensate the field of the magnet is used by the actuator during the separation from the plate, this field passes through the air gap in the direction opposite that generated by the magnet and thus reduces the force of attraction of the plate. 
   In addition, an actuator according to the present invention has a fixed magnetic circuit at the level of the electromagnet, which is formed by a single piece, which leads to good mechanical rigidity and increased ease of assembly of the actuator. 
   In one embodiment, with the electromagnet having the shape of an E, at least one magnet is located in one of the branches of this electromagnet, for example, one of the two end branches. 
   In one embodiment, at least one magnet is located in each of the branches of the actuator. 
   In one embodiment, the axis merged with the cross section of the magnet is inclined in relation to the axis of the E-shaped electromagnet. 
   According to one embodiment, the end branches have a cross section that is twice that of the central branch. 
   In one embodiment, when the electromagnet generates a magnetic field intended to move away a mobile magnetic plate in relation to the actuator, this field partially demagnetizes the associated magnet. 
   According to one embodiment, when the electromagnet generates a magnetic field intended to attract and/or maintain a mobile magnetic plate in relation to the actuator, the connecting part forms a magnetic circuit for this field of the electromagnet. 
   In one embodiment, the actuator comprises a plurality of magnets arranged symmetrically in the actuator, for example, above the coil of the electromagnet. 
   According to one embodiment, the actuator comprises a plurality of connecting parts. 
   In one embodiment, the actuator comprises at least one connecting part between the coil of the electromagnet and each magnet. 
   The present invention also pertains to an engine equipped with an electromagnetic actuator controlling a valve of an internal combustion engine by means of a first magnetic field, generated in a variable manner by an electromagnet, and a second magnetic field, generated by a magnet associated with the electromagnet, characterized in that the actuator, comprising an connecting part such that it forms a magnetic circuit for a part of the field generated by the magnet, the connecting part being magnetically saturated by this partial field of the magnet, corresponds to one of the embodiments described above. 
   Finally, the present invention pertains to a vehicle equipped with an electromechanical actuator controlling a valve of an internal combustion engine by means of a first magnetic field, generated in a variable manner by an electromagnet, and a second magnetic field, generated by a magnet associated with the electromagnet, characterized in that the actuator, comprising an connecting part such that it forms a magnetic circuit for part of the field generated by the magnet, the connecting part being magnetically saturated by the partial field of the magnet, corresponds to one of the embodiments described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the present invention will appear from the description given below as an illustrative and nonlimiting description of preferred embodiments of the present invention based on the attached figures, in which: 
       FIG. 1 , already described, shows a prior-art polarized actuator, 
       FIGS. 2   a ,  2   b ,  3   a ,  3   b  and  4  show actuators according to the present invention, which are provided with an connecting part for each magnet comprised in these actuators, 
       FIG. 5  shows the differences in efficiency between an actuator according to the present invention and an actuator according to the prior art, 
       FIGS. 6   a ,  6   b  and  7  show actuators according to the present invention, provided with two connecting parts per magnet comprised in these actuators, and 
       FIGS. 8   a ,  8   b  and  8   c  show actuators according to the present invention having a magnetic flux concentration of each magnet. 
   

   DETAILED DESCRIPTION 
     FIG. 2   a  shows an E-shaped actuator  200  equipped with magnets  202  generating a magnetic field H mag , and an electromagnet  204  generating a magnetic field H ele  for attracting and possibly maintaining the plate  206  against the actuator  200 . 
   According to the present invention, the actuator comprises an connecting part  201  forming a magnetic circuit for a part of the field H mag  generated by a magnet  202 , this connecting part being magnetically saturated by this partial field of the magnet when the actuator is not generating any flux. 
   However, when the plate  206  is attracted by the actuator  200 , the field H ele  generated by the electromagnet  200  has a direction opposite the sense of the field of the magnet in this connecting part. 
   In other words, the action of the fields of the magnets  202  and of the electromagnet  204  is combined at the level of the plate  206 , ensuring an intense action on the latter, whereas these fields have opposite senses at the level of the connecting part  201  in which the flux of the magnet H ele  of the electromagnet is flowing. 
   Therefore, as was indicated above, this flux of the field H ele  passes through the magnet  202  only partially, so that there is no risk of this electromagnet becoming demagnetized. 
   When the plate  206  is released by an actuator  250  ( FIG. 2   b ) according to the present invention, the electromagnet  204  generates a field H ele  of a direction opposite the direction of the field H ele  used to attract or maintain the plate  206 . 
   In this case, the field H ele  of the electromagnet  204  is opposite the field H mag  of the magnets  202  at the level of the plate  206 , the action of the electromagnet opposing the action of the magnet in relation to the plate  206 . 
   At the level of the connecting part  201 , the fields H ele  of the electromagnet  204  and H mag  of the magnets are of the same direction, such that, the connecting part  201  being saturated, the field H ele  of the electromagnet  204  passes partially through the magnets  202 . 
   As will be described in detail below, such a situation offers the advantage of diminishing the magnetic field generated by the magnet and thus facilitating the release of the plate. 
   It appears that at a given magnet cross section Sa, the height x of such an connecting part  201  results from a compromise between the obtaining of the magnetic flux of the magnet required in the plate, for example, to ensure the maintenance of the latter in the commuted position, which requires low values of the height x of the connecting part, and the improvement of the mechanical rigidity of the electromagnet, as well as the improvement of the action of the electromagnet on the plate, which said improvements are facilitated by high values of the height x of the connecting part. 
   Finally, it should be noted that the actuator  200  described in connection with  FIG. 2   a  differs from the actuator  250  described in connection with  FIG. 2   b  in that the coil of the electromagnet  204  is located below ( FIG. 2   a ) or above ( FIG. 2   b ) the magnets  202 . 
   Experiments have shown that the configuration in which the magnets are arranged above the coil was preferable in terms of energy consumption to the configuration in which the magnets are arranged below the coil. 
   Analogously,  FIGS. 3   a  and  3   b  show actuators  300  and  350  which differ from one another only in the arrangement of the coils of the electromagnet  304  being considered below and above the magnets  302  associated with that electromagnet. 
   These embodiments also differ from the embodiments described in connection with  FIGS. 2   a  and  2   b  in that the magnets  302  used have reduced thicknesses e a  compared to the coil of the electromagnet  304 , contrary to the embodiments described in connection with  FIGS. 2   a  and  2   b , in which the magnets  202  and the coil had equal thickness. 
   These reduced thicknesses e a  offer the advantage of permitting the use of low-cost magnets  302  and of permitting a higher rigidity for the ferromagnetic circuits. Measurements have shown that magnet thicknesses between 2 mm and 8 mm were satisfactory. 
   Independently from the thickness of the magnets, connecting parts  301  of a height on the order of magnitude of 2 mm led to satisfactory results. 
   Finally, it should be stressed that for reasons of clarity, the field generated by the electromagnet  304  is not present in  FIGS. 3   a  and  3   b.    
     FIG. 4  shows another embodiment of the present invention in which an connecting part  401  is associated with each magnet  402  of the actuator  400 , as was described above in  FIGS. 2   a ,  2   b ,  3   a  and  3   b.    
   However, the actuator  400  has the connecting parts  401  between the coil of the electromagnet  404  and the magnets  402  of the actuator. 
     FIG. 5  shows a diagram comparing the forces exerted by the polarized actuators either provided with an connecting part (curve C ist ) according to the present invention or not provided with an connecting part (curve C pa ) according to the prior art. 
   This diagram has an ordinate  500  indicating the force (in Newtons) exerted by an actuator being considered as a function of the current flowing in the coils of the electromagnets of these actuators, indicated on the abscissa  502  in A/turn. 
   It is thus seen that when a positive current flows in these coils and the actuator attracts the plate, the actuator according to the present invention (curve C ist ) exerts a stronger force on the actuator according to the prior art (curve C pa ). 
   In fact, the presence of an connecting part (connecting parts) in the actuator enables the latter to have a more effective electromagnet to reinforce the magnetic flux of the magnets given the absence of an equivalent air gap formed by the magnet in relation to the magnetic flux of the electromagnet, which flux flows in the connecting part. 
   When a negative current is flowing in the coil, i.e., when the plate is moving away from the actuator, the force exerted by the actuator comprising an connecting part decreases more rapidly than the force exerted by an actuator without an connecting part, which reduces the energy consumption necessary for the moving away of the plate. 
     FIGS. 6   a  and  6   b  show other actuators  600  and  650  according to the present invention, in which two connecting parts  601  and  603  are located above the magnets  602  and between these magnets  602  and the coil of the electromagnet  604  being considered, respectively, this embodiment having the advantage of confining the magnets and facilitating the mechanical rigidity of the actuator. 
   In this embodiment, the connecting parts have a height x/2 that is half the height x of the connecting parts in the above embodiments, in which a single connecting part is associated with each magnet. 
     FIG. 6   b  shows an advantageous embodiment of an actuator  650  with two connecting parts per magnet, using magnets  652  of a small thickness e a , and especially of a thickness e a  smaller than the thickness of the coil of the electromagnet  654 . 
   In addition, the ratios of the cross section Sa of the magnet and the thicknesses (e and 2e) of the branches of the ferromagnetic circuit are such that they concentrate the flux of the magnetic field at the level of the plate in order to increase its action. 
   According to other considerations optimizing the operation of the actuator, the thickness epp of the magnetic plate  656  is equivalent to the thickness e of the end branches of the actuator, whereas the height x/2 of the connecting parts is equal to half the height x of the connecting parts when a single connecting part is associated with one magnet. 
     FIG. 7  shows an actuator  700  comprising four magnets  702  arranged in the actuator in such a way that they form three connecting parts  701 ,  703  and  705 . Such a configuration has the advantage of having increased mechanical stability. 
   It should be noted at this point that the above-described embodiments use magnets whose edges are arranged in parallel to the edges of the coils of the actuator. 
   Now, it is possible to use magnets  802  ( FIG. 8   a ,  8   b  or  8   c ) inclined in relation to the associated electromagnets in order to increase the cross section S a  of the magnet at a fixed actuator height H a , as will be described in detail below. 
   In a first embodiment ( FIG. 8   a ), the actuator  800  comprises a magnetic circuit of a constant cross section by means of the magnetic plate  806 , of a cross section epp practically equal to the cross section ep of the end branches of the E-shaped actuator and to half the cross section ep/2 of the central branch of this actuator, which leads to a concentration of the magnetic flux and consequently to an increase in the force exerted by the electromagnet  804  on the plate  806 . 
   Thanks to such an arrangement, the cross section Sa of the magnets  802  can be larger than the height Ha available for accommodating the magnets in the electromagnet, this height Ha being equal to the height H of the electromagnet reduced by the height Hb of the coils of the electromagnet  804 . 
   Permitting the cross section Sa of the magnet to be increased, this embodiment makes it possible to increase at the same time the action of the magnet on the plate and consequently to reduce the current consumption necessary for the electromagnet to act on the latter. 
     FIGS. 8   b  and  8   c  show other variants of actuators  850  and  875 , whose magnets  802  are likewise inclined in relation to the respective electromagnets. 
   However, the magnets are located in the end branches of the electromagnets in these variants in such a way that these magnets  802  have a height H equal to the height of the electromagnet to be able to be accommodated in the latter. 
   In other words, the height of the coils of the electromagnet  804  is not limiting in relation to the cross section Sa of the magnets. 
   Conversely, the presence of magnets  802  does not represent any additional constraints in terms of the possible height of the coil of the electromagnets  804 . 
   It should be noted that depending on the arrangement of the magnets in relation to the coils of the electromagnet  804 , the electromagnet  850  or  875  has different properties. 
   Thus, such an arrangement ( FIG. 8   b ) of the magnets  802  that the end  803  of the magnets  802  that is close to the plate  806  is also the end of this magnet  802 , which end is moved away from the coil  804 , has the advantage of using a plate of shorter dimensions than when ( FIG. 8   c ) the end  803  of the magnets  802 , which is close to the plate  806 , is also the closest end of the coil  804 . 
   However, it should be noted that when ( FIG. 8   c ) the end  803  of the magnets  802  is also the closest end of the coil  804 , the actuator has the advantage of permitting the use of magnets ( 802 ) of larger cross sections. 
   The embodiments described in connection with  FIGS. 8   a ,  8   b  and  8   c  have the advantage of ensuring good maintenance of the magnets  802  because the latter are arranged inside the actuator.