Abstract:
A fluid injection device including a protruding needle. One end of the needle forms a valve and can be moved between a closed position, in which the valve seals the fluid-release opening, and an open position, in which the valve is positioned at a controlled distance from the opening. Movement of the valve between the closed position and the open position is produced by the controlled intrinsic extension of the protruding needle.

Description:
The present invention relates to a fluid-injection device. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention can be applied particularly advantageously in the automotive field, especially as regards the injection of fuel into a combustion chamber. 
   2. Description of Related Art 
   From the prior art there is known a first type of injection devices designated as recessed needles. In this traditional configuration, each injector is provided with a jet needle that is capable of being displaced axially. This mobility exists between a closed position, in which the distal end of the jet needle blocks an aperture intended for ejection of the fluid, and an open position, in which the said distal end is positioned at a distance from this same aperture. 
   It must also be noted that it is immaterial whether the aperture comprises a single orifice or a plurality of holes arranged downstream from the seat, which is intended to cooperate sealingly with the distal end of the jet needle. This latter configuration proves particularly adapted to the injection of liquid, since the presence of orifices in large numbers is of such nature as to perturb the ejection of the liquid and consequently to multiply the droplets. 
   Be that as it may, this type of recessed-needle injector suffers from the disadvantage that it functions almost by the all-or-nothing principle. In other words, the needle tip either allows a maximum quantity of pressurized fluid to pass, or it prevents it from escaping via the aperture. Thus the parameters for adjustment of such a system are essentially limited to the fluid pressure and to the discharge cross section of the aperture. 
   In actual practice, and especially in the case in which the fluid is a liquid, a recessed-needle injector almost always functions at constant pressure. Thus it is the diameter of the holes that will determine the size of the droplets. Since the dimensions of the holes in question are fixed by design, however, it appears to be particularly difficult to modify the droplet size at all. Even if the recessed needle is opened and closed very rapidly, the perturbation then created will be very largely insufficient to generate a mist of small diffuse droplets effectively. 
   Thus, with an injection device of the recessed-needle type, it is certainly possible to control the quantity of fluid injected, but from all evidence it is not conceivable that the size and diffusion of droplets can be controlled precisely. As is well known, this constitutes a major drawback in terms of efficiency. 
   Another important parameter to be controlled concerns the minimum quantity that it is possible to inject. As it happens, in a large proportion of recessed-needle injectors, the fluid overpressure is used to move the jet needle from its closed position to its open position. The response time of the system then depends on the magnitude of the pressure in question. In practice, it is necessary to raise the fluid pressure if it is desired to shorten the opening time of the recessed needle, but then the minimum quantities injected are increased. This constitutes a further disadvantage for this type of system. 
   A second type of prior art injection devices, designated as protruding needles, makes it possible to alleviate these difficulties. Here, each injector is provided with a kind of valve composed of a stem, one end of which forms a poppet and is capable of cooperating by leaktight contact with a seat defining a fluid-ejection aperture. As in the preceding case, the poppet stem formed in this way is mounted to be mobile by axial displacement between a closed position, in which the poppet blocks the aperture, and an open position, in which the said poppet is positioned at a distance from the said aperture. 
   The mobility of such a poppet stem is generally achieved by using either a piezoelectric actuator or a magnetostrictive actuator. Specifically, this consists in coupling the poppet stem of the injector with an appended element advantageously composed of a material known as active, meaning capable of changing shape, and especially of growing longer, when either an electric current or a magnetic field respectively is passed through it. Since the corresponding physical principles and the modes of operation of such actuators are fully known, they will not be further described here. It will be recalled simply that the assembly is generally arranged in such a way that excitation of the active material, electrical or magnetic respectively, causes elongation of the appended element and consequently a displacement of the poppet stem in its entirety. The distal end of the poppet stem is then no longer in contact with its seat, so that the fluid under pressure can then escape via the aperture. 
   Compared with their recessed-needle homologs, the protruding-needle injectors have the advantage of being able to have a variable lift at the poppet level. At constant pressure, therefore, it is possible to have a discharge cross section that is variable in time. For example, in the case of a piezoelectric actuator, a given elongation of the active material will be obtained as a function of the voltage applied to the appended element. The corresponding elongation of the appended element then causes a proportional displacement of the poppet stem, and consequently an equally proportional lift of the poppet. 
   Nevertheless, the injection devices of the protruding-needle type suffer from disadvantages that are peculiar to them. 
   With an appended element of piezoelectric material, it is possible to achieve deformations on the order of one thousandth, or in other words approximately 10 μm of displacement per 10 mm of piezoelectric stack. That means that the appended element must be extremely long if it is wished to obtain a poppet displacement of traditionally 50 μm. That then implies the need to charge very large capacitances, on the order of 3 to 3.5 μF, for a 30-mm stack, for example. Consequently, electronics of considerable power are needed if it is wished to shorten the switching time. 
   In addition, during operation of the protruding-needle injector, the great length of the appended element then constitutes a disadvantage in terms of weight. The assembly composed of the poppet stem, of the appended element and of other means for elastic return, then constitutes a relatively large mobile mass. The resulting significant inertia will then retard the responsiveness of the piezoelectric material even more. 
   Thus, by reason essentially of the large capacitances to be charged and of the large mass to be displaced, the injection devices having protruding needles and piezoelectric actuators prove to be intrinsically limited in terms of response time. 
   With an appended element of magnetostrictive material, it is essentially the problem of system inertia that constitutes the main handicap. After all, it must not be forgotten that the mobile mass being displaced is very large with prior art injection devices, since it corresponds to the combined masses of the stem, which is often long, and of the associated poppet. 
   BRIEF SUMMARY OF THE INVENTION 
   The technical problem to be solved by the object of the present invention is therefore to provide a fluid-injection device having a protruding needle, one end of which forms a poppet and is capable of being displaced in controlled manner at any instant between a closed position, in which the poppet blocks an aperture intended for ejection of the fluid, and an open position, in which the said poppet is positioned at a chosen distance from the said aperture, which injection device could make it possible to avoid the problems of the prior art by offering in particular substantially improved response times, or in other words substantially shorter opening and closing times of the poppet, as well as a variable opening capacity. 
   According to the present invention, the solution to the technical problem posed consists in the fact that the displacement of the poppet between its closed position and its open position is generated by an intrinsic elongation of the protruding needle. 
   In contrast to the prior art injection devices, what takes place here is not the displacement of the protruding needle in its entirety but the longitudinal deformation thereof in such a way as to generate a consequent displacement of its free end, or in other words the one carrying the poppet. The assembly is arranged in such a way that the mobility of the poppet exists between the previously defined closed position and open position, the mobility being controlled at every instant. 
   The invention defined in this way has the advantage of permitting a considerable reduction of the mobile mass and therefore a proportional decrease of the system inertia. Consequently, the response times of this type of injection devices are significantly improved. 
   The present invention also relates to the characteristics that will become apparent during the description hereinafter and that will have to be considered individually or in all of their possible technical combinations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This description, given by way of non-limitative example, will provide a better understanding of how the invention can be implemented, with reference to the attached drawings, wherein: 
       FIG. 1  illustrates a fluid-injection device according to a first embodiment of the invention. 
       FIG. 2  constitutes an alternative version of the first embodiment of  FIG. 1 . 
       FIG. 3  represents a fluid-injection device according to a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   For reasons of clarity, like elements have been designated by identical references. Similarly, only those elements essential for understanding the invention have been illustrated, albeit not to scale and in schematic manner. 
     FIG. 1  illustrates an injection device  1  intended to distribute a liquid fuel into a combustion chamber of a motor-vehicle engine. 
   In this particular embodiment, chosen solely by way of example, injection device  1  is composed mainly of three parts. Firstly there is distinguished a first casing  10 , in which there is axially arranged a first bore  11 . Then there is noted the existence of a second casing  20 , which itself is provided with a second bore  21 . These two casings  1 o,  20  are sealingly interlocked by the intermediary of a coupling nut  30 , whose operation is reversible. The assembly is arranged in such a way that first bore  11  and second bore  21  are in communication. The combination of the two casings  10 ,  20  then forms the body of injection device  1 . Finally there is noted the presence of a protruding needle  40 , which is disposed in the continuous space defined by bores  11 ,  21 . 
   According to this  FIG. 1 , the distal end of protruding needle  40  is conformed in such a way that it is able to cooperate with a traversing hole  12  that is arranged in the lower part of first casing  10  and that defines an aperture  13  intended for ejection of the liquid. The distal end of protruding needle  40 , forming a poppet  41 , is more precisely capable of cooperating on the one hand, by sliding contact with a guide surface  14  arranged at the internal end of traversing hole  12  and, on the other hand, by sealing contact with a seat  15 , which in turn is arranged at the external end of the said traversing hole  12 . Be that as it may, poppet  41  is capable of being displaced between a closed position in which it blocks aperture  13 , and an open position in which it is positioned at a distance from the said aperture  13 . 
   It is also noted in  FIG. 1  that the upper part of second bore  21  cooperates with an inserted and abutting closure cover  50 , which is provided with a recirculation duct  51  for the liquid under pressure. 
   In addition, there is noted the presence of a supply system  60  for liquid under high pressure. This is provided with a main duct  61 , which is arranged longitudinally in the thickness of second casing  20  and which communicates with an intermediate duct  62  extending at right angles to the axis of injection device  1 , at the interface of second casing  20  and first casing  10 . The annular form and the positioning of intermediate duct  62  make it possible to distribute the liquid under pressure into a plurality of secondary ducts  63   a ,  63   b , which are regularly distributed in the thickness of first casing  10  and which connect into an annular cavity  64 . This annular cavity  64 , traditionally arranged between poppet  41  and traversing hole  12 , has a shape, layout and function that are fully known and that therefore will not be further described here. It will be stipulated simply that the assembly is conformed in such a manner that it can generate and regulate, in traditional manner, a continuous circulation of liquid toward internal bores  11 ,  21  of injection device  1 . 
   According to the object of the present invention, the displacement of poppet  41  between its closed position and its open position is advantageously generated here by an intrinsic elongation of protruding needle  40 . 
   According to a particular feature of the invention, the intrinsic elongation of protruding needle  40  takes place up to the direct vicinity of poppet  41 , or in other words at the level in particular of that part of the said protruding needle  40  which is situated directly in proximity to the said poppet  41 . 
   It is in fact particularly advantageous that the deformation takes place as close as possible to the poppet, in order to minimize as well as possible the mobile mass to be displaced, which ideally should be limited to that of poppet  41 . With such a configuration, the opening and closing times are consequently shortened in considerable proportions. 
   According to another particular feature of the invention, protruding needle  40  is provided with a hollow stem  42  having a solid end  43  that forms a poppet  41 , as well as with an internal bar  44  composed of an active element  45  integral with a rear element  46 , forming an inertial mass. Furthermore, this internal bar  44  is mounted to be mobile axially inside hollow stem  42 , in the sense that it is interlocked only at the level of solid end  43 , via active element  45 . Thus active element  45  is mobile by means of axial elongation, while the rear element in turn is mobile by means of axial displacement. The junction zone between active element  45  and rear element  46  has the form of an interface  47 . 
   It is to be noted that, throughout this text, the notion of active element  45  denotes essentially a piezoelectric element or a magnetostrictive element. Nevertheless, it is quite obviously possible for any other material whose dimensions could be modulated under the effect of variation of a physical variable to be adopted. 
   In particularly advantageous manner, hollow stem  42  has mechanical elasticity such that its longitudinal deformation can take place in reversible manner. 
   The mechanical elasticity involved can be derived from the intrinsically elastic nature of the material of which hollow stem  42  is composed, and/or from a particular structure, such as an open-worked structure, of the said hollow stem  42 . This characteristic permits hollow stem  42  to offer a minimum of resistance to deformation during the phase of opening of poppet  41 , while favoring return to the initial state during the closing phase, as soon as active element  45  is no longer energized. The fact that the elastic energy transmitted during deformation is restored on return makes it advantageously possible to dispense with specific restoring means, as is the case with the prior art injection devices. 
   According to another particular feature of the invention, rear element  46  has a density and rigidity much greater than those of the other elements of which protruding needle  40  is composed. 
   That means that rear element  46  is made of a particularly dense and hard material, so that, respectively, on the one hand it can constitute a true inertial mass and on the other hand not be deformed under the action of elongation of active element  45 . 
   Thus, as can also be seen in  FIG. 1 , injection device  1  is additionally equipped with prestressing means  70 , which are capable of permanently compressing internal bar  44  against solid end  43  of hollow stem  42 . 
   The purpose is quite obviously to impose compression indirectly on active element  45 , in order to optimize its capacities, especially in terms of elongation and responsiveness. Regardless of whether such an active element  45  is composed of a piezoelectric or magnetostrictive material, it is known that it is imperative that it be prestressed in order that it can be used effectively. In fact, materials of this type have greater difficulty in withstanding elongations than compressions, and so, to ensure that they are not in this state at any moment, it is indispensable to provide means capable of permanently exerting a compressive force on active element  45 , even when the latter is in an elongation phase. This characteristic also makes it possible to preserve material whose resistance to expansion is relatively low, substantially by a factor of ten compared with its compression resistance. 
   In the example of  FIG. 1 , prestressing means  70  comprise a compression spring  71 , which acts axially on the apparent cross section  48  of internal bar  44 . 
   According to another particular feature of the invention, injection device  1  is equipped with interlocking means  80 , which have two functions. The first consists in permitting immobilization of protruding needle  40  relative to the body of injection device  1  when the said protruding needle  40  is subjected to a force whose intensity is below a given threshold. This first characteristic advantageously makes it possible to neutralize low-intensity and/or point forces, such as vibrations. 
   The second function of interlocking means  80  is to permit protruding needle  40  nevertheless to move translationally relative to the body of injection device  1 , as soon as the intensity of an applied force exceeds the threshold alluded to in the foregoing. This second characteristic makes it possible to absorb more intense and/or continuous forces, such as those resulting from thermal expansions of internal components of injection device  1 , and especially of protruding needle  41 . 
   In the particular embodiment of  FIG. 1 , interlocking means  80  first comprise three external grooves  82 , which are arranged parallel to one another on the surface of a tubular element  81 , forming a shoulder. This tubular element  81  is itself interlocked rigidly around protruding needle  40 , but in removable manner, by the intermediary of a reversible mounting means composed in the present case of a traditional cooperation between two complementary screw threads. In addition, each external groove  82  extends in a plane orthogonal to the axis of protruding needle  40 . Interlocking means  80  are additionally provided with a helicoidal groove  83 , which is arranged in the interior of the body of injection device  1 . Finally, interlocking means  80  are provided with a ball  84  for each external groove  82 . In addition, the assembly is arranged in such a way that each ball  84  is able to cooperate, by partial insertion, with the corresponding external groove  82 , into which substantially one half fits, and with helicoidal groove  83 , into which substantially the other half fits. Specifically, balls  84  are positioned at the points of intersection between helicoidal groove  83  and external grooves  82 . 
   It is particularly advantageous for the three balls  84  to be distributed in equidistant manner, at 120° from one another in the present case. In this way, they can fully perform the function of centering means for tubular element  81  and consequently for protruding stem  40 . 
   According to one characteristic of this particular embodiment, the depth of each external groove  82  is substantially greater than the radius of the corresponding ball  84 , whereas that of helicoidal groove  83  corresponds substantially to the radius of each ball  84 . In addition, each external groove  82  is provided with a compression means  85  capable of pushing corresponding ball  84  to the bottom of helicoidal groove  83 . 
   Thus each ball  84  is positioned with one half in helicoidal groove  83  on the one hand, and with the other half in corresponding external groove  82  on the other hand. This characteristic allows the mechanical stresses at the level of each connection point manifested by each assembly comprising ball  84 , external groove  82  and helicoidal groove  83  to be distributed equitably. 
   Be that as it may, when an external force of sufficient intensity is applied to protruding needle  40 , the resulting displacement remains relatively limited. In fact, since on the one hand the only mobility permitted is the combination of a rotation and an axial translation, and since on the other hand the pitch of helicoidal groove  83  is relatively small, the system can respond only with low amplitudes and a very long time constant. This advantageous characteristic permits in particular tension-applying means  90 , which will be described hereinafter, to fully exert their function and also to compensate for the variations in length due to thermal expansions. 
   As  FIG. 1  shows, it is to be noted that in this practical example the upper part of tubular element  81  is integral with a disk  87 , which advantageously constitutes a stop for compression spring  71  of prestressing means  70 . 
   According to another particular feature of the invention, injection device  1  is provided with tension-applying means  90 , which are capable of maintaining poppet  41  of protruding needle  40  braced against its seat  15 . 
   In this practical example, tension-applying means  90  are provided with a compression spring  91 , which is disposed axially around protruding needle  40 . Positioned in this way, compression spring  91  is capable of cooperating by contact with a part  86 , forming a shoulder, of tubular element  81  on the one hand, and with a part  22 , forming a stop, of the body of the injection device on the other hand. 
     FIG. 2  illustrates an alternative version of the first embodiment described in the foregoing, which differs solely by the nature of the prestressing means  70   a  employed. In this case these means use pressurized liquid  72 , which acts axially on the apparent cross section of internal bar  44 , as well as a regulating poppet  73 , which is capable of limiting the internal pressure of liquid  72  to a specified value. 
   In this particular embodiment, regulating poppet  73  is traditionally composed of a ball  74  which, under the action of a compression spring  75 , and via an intermediate washer  76 , is braced against a seat  77  defining an escape duct  78 . In addition, there is to be noted the presence of an elastic ring at the interface between intermediate washer  76  and the body of regulating poppet  73 . 
   Since the functioning of such a system is fully known, it will not be described further here. It will be stipulated simply that the purpose of regulating poppet  73  is to control the overpressure of the liquid present in the interior of injection device  1 , and more precisely to fix the said pressure at a predefined value corresponding to the level of prestress that it is desired to apply to active material  45 . 
   It will also be specified that the presence of pressurized liquid  72  in the interior of injection device  1  results in this case directly from the recirculation phenomenon established to cool the internal components. But of course an independent high-pressure liquid system could very well be adopted as an alternative. 
   In the first embodiment of  FIGS. 1 and 2 , protruding needle  40  includes a piezoelectric active element  45 , whose length can be increased under the effect of an electric field. In addition, the elongation of piezoelectric active element  45  is capable of longitudinally deforming that external part of protruding needle  40  which surrounds the said piezoelectric active element  45 . 
   However, and according to the second embodiment illustrated in  FIG. 3 , an injection device  100  can be equipped with a protruding needle  140  that includes a magnetostrictive active element  145 , whose length can be increased under the effect of, in this case, a magnetic field. The assembly here is again arranged in such a way that the elongation of magnetostrictive active element  145  is of such nature as to longitudinally deform that external part of protruding needle  140  which surrounds the said magnetostrictive active element  145 . 
   In practice, and as can be seen in  FIG. 3 , it is then appropriate to provide, as is traditional, the presence of a solenoid  200  and of a tube  201  of magnetic material disposed axially inside injection device  100 . Specifically, magnetic tube  201  is positioned concentrically around solenoid  200 , which is itself positioned concentrically around magnetostrictive element  145 . 
   According to a particular feature of this second embodiment, when active element  145  is magnetostrictive, it is advantageous to choose an amagnetic material for rear element  146 . Protruding needle  140  is then provided in addition with two intermediate elements  147 ,  149 , which are positioned respectively between rear element  146  and active element  145  on the one hand, and between active element  145  and solid end  143  of hollow stem  142  on the other hand. In addition, each intermediate element  147 ,  149  is made of a magnetic material capable of causing the lines of the magnetic field used to excite active element  145  to form a closed loop. 
   It is to be noted that, by analogy with these intermediate elements  147 ,  149 , the function of magnetic tube  201  is also to cause the lines of the magnetic field generated to bring about elongation of active element  145  to form a closed loop. 
   Prestressing means  170  of this second embodiment are identical to those of the first embodiment, as described in connection with  FIG. 1 . However, the alternative version of the first embodiment, or in other words the one using pressurized fluid, quite obviously could be easily adapted to injection device  100  of this second embodiment. 
   Of course, the invention also relates to any motor vehicle equipped with at least one injection means such as described hereinabove.