Abstract:
A high voltage resonator-amplifier for a radiofrequency ignition system that can be used in an internal combustion engine, the resonator-amplifier including at least two electrodes, a coil arranged in alignment with the electrodes along a longitudinal axis, and a linking mechanism retaining the coil and the electrodes in a relatively fixed position. The coil is wound around a closed bend which in turn wraps around the longitudinal axis.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates, generally, to plasma generation techniques. 
     More precisely, the invention relates to a high-voltage resonator-amplifier for radiofrequency ignition system usable in an internal combustion engine, this resonator-amplifier comprising at least two electrodes, a coil arranged in forward alignment relative to the electrodes in relation to a longitudinal axis, and linking means holding the coil and the electrodes in a fixed relative position. 
     A resonator-amplifier of this type, generally dubbed “spark plug coil”, is in particular known to the person skilled in the art through patent FR 2 859 869. 
     In so far as spark plug coils are mounted in the cylinder head of the engine, their structure is heavily conditioned by the structure of this cylinder head. 
     The shape of the cylinder head as well as the free spaces made available therein are therefore crucial parameters to be taken into account in the design of these spark plug coils. 
     Now, not only are today&#39;s cylinder heads divided into two types, depending on whether they do or do not comprise an access well for the ignition spark plug, but also the diameter of the access wells is tending to decrease for cylinder heads of the second type. 
     Hence, the adaptation to these new conditions of use of spark plug coils of tubular shape as described and illustrated in the above-mentioned patent is becoming increasingly tricky. 
     SUMMARY OF THE INVENTION 
     In this context, the aim of the present invention is to propose a high-voltage resonator-amplifier or “spark plug coil” whose structure addresses this requirement for development. 
     To this end, the resonator-amplifier of the invention, moreover in accordance with the generic definition thereof given by the above preamble, is essentially characterized in that the coil is wound around a closed curve which itself surrounds the longitudinal axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will emerge clearly from the description thereof given hereinafter, by way of wholly nonlimiting indication, with reference to the appended drawings, in which: 
         FIG. 1  is a sectional schematic view of a known example of a resonator-amplifier with tubular coil; 
         FIG. 2  is a sectional schematic view of a resonator-amplifier in accordance with a first possible embodiment of the invention; 
         FIG. 3  is a sectional schematic view of a resonator-amplifier in accordance with a second possible embodiment of the invention; 
         FIG. 4A  is a schematic view from above of a coil of a first type, usable for the implementation of the invention; 
         FIG. 4B  is a schematic view from above of a variant of the coil illustrated in  FIG. 4A , optimized for the implementation of the invention; 
         FIG. 5A  is a schematic view from above of a coil of a second type, usable for the implementation of the invention; 
         FIG. 5B  is a schematic view from above of a variant of the coil illustrated in  FIG. 5A , optimized for the implementation of the invention; 
         FIG. 6A  is a schematic view from above of a coil of a third type, usable for the implementation of the invention; and 
         FIG. 6B  is a schematic view from above of a variant of the coil illustrated in  FIG. 6A , optimized for the implementation of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As declared previously, the invention relates to a high-voltage resonator-amplifier intended to be fitted to a radiofrequency ignition system for an internal combustion engine. 
     A known resonator-amplifier is illustrated in  FIG. 1  and comprises two electrodes  11  and  12 , a coil  2  arranged in forward alignment relative to the electrodes in relation to a longitudinal axis Z, and linking means  3  whose function is at least to hold the coil  2  and the electrodes  11  and  12  in a fixed relative position. 
     The ground electrode  12 , which surrounds the central electrode  11 , bears a threading which makes it possible to screw it into the cylinder head Q of the engine. 
     As shown by  FIG. 1 , known resonator-amplifiers exhibit a structure adapted to engines whose cylinder head Q exhibits an access well P intended to receive them. 
     In the resonator-amplifier of the invention, which is adaptable to cylinder heads of all geometries, the coil  2  is wound around a closed curve K which itself surrounds the longitudinal axis Z ( FIGS. 2 and 3 ). 
     In the case where the cylinder head Q does not exhibit any access well, the linking means can thus be restricted to a minimal structure, as shown by  FIG. 2 . 
     In the case where the cylinder head Q exhibits an access well P ( FIG. 3 ), the linking means comprise a body  3  which is elongate in relation to the longitudinal axis Z. 
     The lower end  31  of the body  3  then carries the functional ends of the electrodes  11  and  12 , while the coil  2  is carried by the upper end  32  of this body  3 . 
     As shown by  FIGS. 4A to 6B , the coil  2  comprises two conducting wire connection leads,  201  and  202 , intended to allow the connection of this coil  2  to an electrical energy source (not represented), and a set of windings such as  21 A to  24 B, mounted in series between the connection leads  201  and  202 . 
     In the most advantageous embodiments, which are illustrated in  FIGS. 4B ,  5 B and  6 B and which are presented hereinafter, the set of windings of the coil  2  is formed of a first subset of windings such as  21 A and  22 A, comprising at most two thirds of the windings of the coil, and of a second subset of windings such as  22 B,  23 B and  24 B, comprising at least one third of the windings of this coil. 
     Preferably, if the total number of windings of the coil  2  is even, the two subsets comprise the same number of windings, and if the total number of windings of the coil  2  is odd, the two subsets comprise the same number of windings to within a unit. 
     Each winding is coiled on a part of the closed curve K, the windings of the first subset, namely  21 A and  22 A, and the windings of the second subset, namely  22 B,  23 B, and  24 B, being coiled in opposite directions, at one and the same time along the curve K and around this curve. 
     Thus, in the case where the windings  21 A and  22 A are coiled in the direction of traversal S 1  of the curve K, the windings  22 B,  23 B, and  24 B are coiled in the direction of traversal S 2  of this curve K, and vice versa. 
     Likewise, if the windings  21 A and  22 A are coiled around the curve K in a levogyratory direction of winding, the windings  22 B,  23 B, and  24 B are coiled around this curve K in a dextrogyratory direction of winding, and vice versa. 
     This layout, which allows the various windings to contribute in the same manner to the construction of the magnetic field of the coil  2  without, however, having to be coiled in the same direction, allows the leads  201  and  202  to be spaced apart and the potential difference between the leads  201  and  202  to be divided by a factor of two or around two. 
     The windings  21 A and  22 A of the first subset can for example be contiguous, that is to say arranged on the closed curve K in succession to one another, the windings  22 B,  23 B, and  24 B of the second subset therefore being themselves arranged on the curve K in succession to one another. 
     In practice, the windings  21 A and  22 A of the first subset are preferably arranged on the closed curve K in succession to one another in the same direction of traversal as these windings themselves, and therefore advantageously follow one another in the direction S 1  if these windings  21 A and  22 A are individually coiled in the direction S 1 , or in the direction S 2  if these windings  21 A and  22 A are individually coiled in the direction S 2 . 
     Likewise, the windings  22 B,  23 B, and  24 B of the second subset are preferably arranged on the closed curve K in succession to one another in the same direction of traversal as these windings themselves, and therefore advantageously follow one another in the direction S 1  if these windings  22 B,  23 B, and  24 B are individually coiled in the direction S 1 , or in the direction S 2  if these windings  22 B,  23 B, and  24 B are individually coiled in the direction S 2 . 
     Finally, it may be judicious, in particular in the case where the total number of windings of the coil  2  is small, to equip this coil with a core  4  of ferromagnetic material which closes up on itself along the closed curve K, and on which each of these windings is coiled.